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Design and Applied Technology (Secondary 4

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1. Ly Sal 3 2 Normally Close NC manual x 2 5 2 directional valve air pilot x 1 IV Hints Double acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration Design and Applied Technology Secondary 4 6 QUESTION 8 RELEVANT TOPIC ELECTRO PNEUMATICS PROGRAMMABLE LOGIC CONTROLLER When the push button is pressed two motor M1 and M2 outputs must run After 4 minutes Motor 1 stops Motor 2 keeps running for another 2 minutes and stops At this moment a lamp is switched on After a further 90 seconds the lamp will go off and the cycle restarts If the stop switch is pressed at any time the motor will continue until the completion of this cycle then stop On Motor 1 On Time minutes On Motor 2 Of Time minutes On Lamp Off Time minutes Figure A 9 Timing diagram for the operation sequence 1 Construct a ladder diagram and program it to PLC to make it work 2 Draw an electro pneumatic circuit diagram Design and Applied Technology Secondary 4 6 SS QUESTION 9 RELEVANT TOPIC PROGRAMMABLE LOGIC CONTROLLER Components pass along a pair of photo sensors along the conveyor belt When the components pass the sensors the light beam is interrupted and the signal will go low Off After 6 components have been counted by the sensors an eject operation will be actuated and used to remove the batch out of the c
2. 8 Repair air leaks immediately 9 Wear safety glasses when working with pneumatic cylinders 10 Protect equipment and patrons with a good safety envelope II Advantages of Pneumatics 1 High efficiency A relatively small compressor can fill a large storage tank to meet intermittent high demands for compressed air 2 Unlike hydraulic systems no return lines are required The used compressed air can be released through the exhausted ports to atmosphere without harm High reliability because of fewer moving parts Low cost easy installation and maintenance Availability of components of wide range of standard sizes and ratings Ao er Air devices create no sparks in explosive atmospheres They can also be used under wet conditions with no electrical shock hazard 7 The design problems involved are usually not too difficult to solve and equipment selection procedures are relatively simple and straightforward Installation is relatively simple because of relatively low power and light duty IID Limitations of Pneumatics 1 Difficult to perform speed control in pneumatics cylinders Load line and return exhaust line will be required in this case as flow restriction devices are installed Usually no return line is needed in pneumatics circuits as compressed exhaust air can release into working environment with no harm and damage 2 Additional drying and filtering systems are needed as dust and moisture needed to be removed befor
3. settee J eh atone sre 5 oh oe i Figure 1 2 Sprinkler head left Alarm gong mid Break glass right Design and Applied Technology Secondary 4 6 Traditionally the fire alarm system is triggered by the break glass manually to alert people inside the building in the event of fire The red alarm gong will be triggered to alert the residents inside the building and the pedestrians outside the building The fire is extinguished by the sprinkler system that is triggered locally by the heat of fire The pre pressurized water inside the pipes of sprinkle system will be sprayed through the nozzle of each sprinkler head until the pressure head along the pipeline drops to zero 2 Automatic Fire Alarm AFA or Intelligent Fire Alarm IFA system Cluster 2 Cluster 1 Digital Video Recorder DVR Detection Algorithms Security Alarm Surveillance Operator s Server Console on duty Figure 1 3 Block diagram of Intelligent Fire Alarm system For the Intelligent Fire Alarm System the fire is detected by intelligent sensors which verify the flame by the heat and smoke of the location The signal will be transmitted to the Control Panel that is usually housed in the security room and monitored by the on duty operator The control panel is basically comprised of a CPU and a number of interfacing cards and networking cards Once the flame is verified by the intelligent system the signal will be sent
4. 3 updating output status CHECK INPUT STATUS EXECUTE PROGRAM Y Scan Time UPDATE OUTPUT STATUS Figure 3 4 Scan cycle of PLC Design and Applied Technology Secondary 4 6 g amp wy Step 1 Check Input Status Firstly the input signals to the PLC through the input module are sampled by the processor The contents are stored in the input memory Step 2 Execute Program The control program is executed by the processor The input values stored in the input memory are used in the control logic operation to determine the values of outputs Step 3 Update Output Status Finally the PLC updates the status of the outputs which is based on the input values and the results of executing the control program Scan and Scan time A scan is referred to the cycle of reading the inputs executing the control program and updating the outputs A scan time is referred to the time taken to complete one scan The time vary from 1 to 100ms It depends on the number and complexity of control functions to be performed for each scan cycle This means it depends on the number of rungs in the ladder diagram and the complexity of the logic operation to be carried out on each rung What will happen if the value of input changes immediately after it has been sampled during a scan cycle IV Advantages of Programmable Logic Controller Programming the PLC is easier than wiring the relay control pa
5. 4 1 4 2 4 3 4 4 4 5 Definition of Robots Mechanical Structure of Industrial Robotic Arms Robot Anatomy Robot Control Systems Applications of Robots These topics include learning materials that facilitate you to Identify different mechanical structure of industrial robots Identify different robot anatomy Understand different robot control methods Understand various applications of robots Design and Applied Technology Secondary 4 6 aero s i i T Bo Te pas Pe 4 1 Definition of Robots Robot is officially defined by the Robot Institute of America as A re programmable multi functional manipulator designed to move materials parts tools or special devices through variable programmed motions for the performance of a variety of tasks Figure 4 1 Typical industrial robotic arm Variations of robots are available for use in industrial applications They are used to carry out repeated actions with high accuracy and without any variation Robots require a control program to govern its velocity direction acceleration deceleration and the distance of movement at any time An Industrial Robot IR which is usually referring to a robotic arm consists of several links connected in series by linear revolute or prismatic joints At one end the robot is fixed to a supporting base while the other end is equipped with a tool and manipulated into position to perform tasks However the definition of rob
6. HG for Heard Road Green HY for Heard Road Yellow eS Design and Applied Technology Secondary 4 6 Converting the traffic lights situations into a light sequence condition for analysis State Oi Kwan Road Light Heard Road Light Sme Red Red aR AR Red Red Table 2 1 Light and state conditions The light sequence can be represented by the state diagram and timing chart for better understanding Figure 2 2 State diagram for the traffic lights intersection II Learning tasks Part A 1 Equipment A PLC with a handheld programmer or a computer LEDs Red Yellow and Green for 2 sets x Ik resistors Connecting wires Design and Applied Technology Secondary 4 6 2 Tasks A Construct the timing diagram B Construct the ladder diagram C Setup the PLC control and demonstrate to teacher Part B Figure 2 3 Traffic light on a motorway for pedestrian Students can conduct a simple field study at the zebra crossing point and observe the traffic light operation in a real scenario They can record the sequence of light cycle The traffic light should have a button interrupt for the pedestrian to adjust the traffic light to cross the road 1 Equipment A PLC with a handheld programmer or a computer LEDs Red Yellow and Green for 1 set A push button x Ik resistors Connecting wires 2 Tasks A Construct the timing diagram B Construct the ladder diagram C Setup the P
7. Metal Strip Solenoid Valve Feeding device Working air line Figure 2 60 Punching Machine Accessory Function For a conventional metalworking punching machine a continuous supply of compressed air is needed to blow the finished work pieces off the way It will cause wastage of compressed air if it is supplied continuously during the punching action To improve this situation a 2 way solenoid valve and an opt electrical switch will work together The control valve will actuate only when the dies are open the compressed air will then blow out of the nozzle to push the finished parts out of the way for collection That will save 50 volume of compressed air One of the advantages of pneumatic system is theoretically of no cost at all as the supply of air is free in the atmosphere Therefore in the above case why engineers need to design an automatic system to reduce the wastage of compressed air I Safety Consideration of Pneumatic systems 1 Contaminants of solid particles may come from damaged pump and valve sealing Liquid contamination may come from oil water or cleaning solvents wo A loose fitting or damaged hose allowing contaminants into the system by passing the filter Worn out misused or incorrectly routed hoses Use the right voltage for solenoid valve Calculate the correct air pressure to activate your device T a Use pressure relief valves Design and Applied Technology Secondary 4 6
8. in this PTP control only the final location of an individual joint is controlled The path taken for the joint to move from the initial location to the final location is not of concern c Continuous Path control The movement of the arm and wrist is controlled during the motion Servo control is used to maintain the continuous path control over the position and speed of the robotic arm Its advantage is to provide a smooth continuous path for the robot d Intelligent Robot With the advancement in microprocessor and Artificial Intelligence AI technology robots can be equipped with advanced sensory systems such as vision sensors and face recognition technology that process information and function like a human brain AI allows a robot to perceive conditions and make decision based on the perceived condition An intelligent robot can make decisions when things go wrong during the work cycle communicate with human beings and make computation and correction during the motion cycle Design and Applied Technology Secondary 4 6 c Figure 4 34 Intelligent robot with machine vision and face recognition technology HI Programming a robot a Teach Pendant Method A teach pendant handheld programmer is used to control and program the robot Operator can teach the robot by driving individual robotic joints independently The operator can use either the world coordination system WCS which is located at the robot base or Tool coordinate
9. is the number of independent movements the arm can make referring to the point of view of the end effector e g a grasping hand Figure 4 15 Total 12 Degree of Freedom of an object Each joint enables the robot with a certain number of Degree of Freedom DOF of motion Each joint can provide more than one DOF For an industrial robot there are commonly less than or equal to 3 DOF in the body arm assembly and up to 3 in the wrist assembly but it is possible have any number of DOM Another DOF may come from the end effector such as open and close of gripper DOF of an arm can be a combination of vertical radial and translational movements Vertical ability to move up and down z axis motion Radial extension and retraction in and out or y axis motion Rotational rotation about the vertical axis x axis motion or swivel about the vertical axis at the base Design and Applied Technology Secondary 4 6 Radial A Figure 4 16 Combination of vertical radial and translational movements It is important to identify the number of DOF of a robot because the most important specifications and criteria of selecting robots is to state the number of degree of freedom that the robot possesses To establish the orientation of the object the wrist assembly may have the following 3 typical DOF configurations Pitch type R joint for up and down motion of the object Yaw type R joint for right to left rotat
10. light bulb and solenoid An LED can be driven directly from any output The 330k resistor serves the functions of protecting the input pin from the risk of short circuit in the event of LED blows and prevents the LED from blowing out by the over current SS vo Design and Applied Technology Secondary 4 6 k e r a Le ee ee Pin 1 Pin 18 Pin 10 REAN Pin 9 OV Figure 3 22 Output circuitry for LED 7 segment displays can display the number from 0 to 9 by outputting logic 1 or high signal to the display segment in correct sequence Figure 3 23 Output circuitry for 7 segment display A Piezo speaker can be directly connected to the output pin to produce a range of sounds because of its high internal resistance The sounds are produced by the output signals that are in form of pulses and at a variety of frequencies The frequencies can be generated by the programmed instructions see D gt Design and Applied Technology Secondary 4 6 k E EE ee e ee a a a a a ES Rr rr OV Figure 3 24 Output circuitry for Piezo speaker Higher current devices cannot be driven directly by the output signal from PIC which is usually as low as 6V DC It requires a simple transistor to transistor pair switching circuit the Darlington driver to amplify the current rating It is significant when the PIC is required to control electrical actuators in industrial application the power rating is usually higher sa
11. motion gis LE V rkpiece N Lower Limit Switch Figure 3 13 Schematic diagram of automatic drilling system Limiti srar woi o Limit2 l Motor2 Down Motor2 3 Up Figure 3 14 Timing diagram for sequential control of automatic drilling system Exercise 2 Control of traffic light Pushbutton S1 is pressed momentarily to start a traffic light cycle The Red signal will be ON for 5s Then followed by the Yellow signal for 2s Final the Green will be ON for 8s The cycle will be reset and wait until the start button is pressed again Design and Applied Technology Secondary 4 6 Time 71 5s Time T2 2s Time T3 8s Figure 3 15 Traffic light control IV Entry of ladder logic diagram into the PLC The ladder logic diagram is directly entered into the PLC memory It requires PC based application software or a handheld programmer with limited graphics user interface to display the symbols in the ladder diagram The ladder diagram is inputted to the PLC memory rung by rung Below is an example of ladder logic program entry by a handheld programmer to a typical PLC Figure 3 16 Handheld Programmer for PLCs Design and Applied Technology Secondary 4 6 Ladder Diagram Programmer Address Instruction o fst xo ststowet ST XI STSTLWRT CE E 2 ANST2WRT OT YI OT AN 1 WRT Table 3 4 Example of inputting ladder diagram into PLC Remarks Command button ST is START
12. s rotating speed within a selected range During the tumble wash phase the motor works at low speed and high torque Although power consumption during the tumble wash phase is comparatively low this phase lasts much longer than the spin dry phase Therefore driving the drum motor efficiently during the tumble wash phase can reduce the total power consumption Balancing the load before fast spinning is very important because it reduces power consumption during acceleration In order to achieve a rapid power saving spin dry phase maximum drum speed is required Why A C motor not D C motor is used to drive the washing machine State your reasons Design and Applied Technology Secondary 4 6 D Timing diagram for the Washing Drying operation Drum Speed RPM Time min Tumble wash Spin dry Figure 1 9 Timing diagram for washing processes During the spin dry phase the washer drum rotates at high speed typically 400rpm for brief intervals as shown in the Time phase diagram in Figure 1 9 Between these high speed intervals the drum rotates at low speed for longer intervals Regarding the diagram the drum rotates for 1 min at 400 rpm and then rotates at low speed for about 3 minutes in both directions Then there is a second 400 rpm spin 1 min long followed by another low speed spin for 3 minutes in both directions Finally there is a high speed spin for 1 minute followed by a low speed spin for another
13. 1 minute in a single direction ID Timing diagram for Tumble wash phase Drum Speed RPM Time min Counter Clockwise Figure 1 10 The timing phase diagram for tumble wash phase The tumble wash phase is typically three to four times longer than the spin dry phase When the scale of the time phase diagram is enlarged as in Figure 1 9 It can be found that during the tumble wash phase the drum rotates slowly typically at 40 rpm first turns clockwise Design and Applied Technology Secondary 4 6 C CW and stops then turns counter clockwise CCW and stops and so on Rotation time interval varies and depends on the nature of laundry such as delicate light heavy or mixed according to the manufacturer s specifications The diagram shows that there is a 90 percent rotation time in a 100 sec interval Why the tumble wash cycle is not 100 percent continuous rotating and needs to be stopped for a while 10 percent time before reversing in direction ID Flow diagram analysis of washing machine operation Flow diagrams are widely used to explain decision making processes in a logical manner They are particularly useful for converting sequential events into a series of Yes or No operations to each decision to be made Flow diagram is also used for understanding a process to be controlled before producing a ladder diagram in PLC programming Here are some major symbols used in flow diagrams Functi
14. 3 Operate and explain to teacher ENW O Sees Tye ear Ls Design and Applied Technology Secondary 4 6 IV Hints 3 2 Normally closed NC air pilot x 1 3 2 Normally closed NC manual x 1 Flow speed control valve x 1 Single acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration Design and Applied Technology Secondary 4 6 SN QUESTION 7 RELEVANT TOPIC PNEUMATICS I Situation A furnace outlet has a single conveyor that can transport iron bars to two different loading docks In order to shift the out feed of the conveyor to the alternate loading dock the operator must push a button As a safety precaution the conveyor will always be held in the last shifted position until the reception of next signal Figure A 8 Furnace and a conveyor belt ID Control Task To be able to design and assemble a Memory circuit to actuate a double acting cylinder IID Circuit Problem Using the given components and layout design a schematic circuit that requires the operator to push one of two buttons that in turn shifts a retented two position four way valve The valve is air piloted in both directions to operate a double acting cylinder 1 Design and draw schematic diagram 2 Connect components in according to the schematic diagram 3 Operate and explain to teacher Design and Applied Technology Secondary 4 6 E
15. AN is AND OR is OR OT is Output STK is Stack WRT is Write Design and Applied Technology Secondary 4 6 2 amp wy 3 4 Programmable Interface Controller PIC Programmable Logic Controllers are usually used for industrial and electrical application They are rather bulky and expensive for use in school An alternative solution is to introduce a controller based PIC for controlling tasks in student projects 1 Introduction of PIC A Programmable Interface Controller or PIC contains a microprocessor and EEPROM PIC can be provided with 8 18 and 28 pin configurations which provide a variety of outputs and digital analogue inputs The chips use reprogrammable flash memory which can be written and rewritten Constructing a working controller involves connecting the chip to power interfacing input output components and adding a capacitor resonator and a reset switch Flash memory is EEPROM Electrically Erasable Programmable Read Only Memory It means that the PIC is capable of being re programmed over 10 000 times The most commonly used PIC is the 16F84 shown below This is a 18 pin device which has 8 outputs and 5 inputs Pin 1 Pin 18 Pin 9 Pin 10 Figure 3 17 Pin layout diagram of PIC 16F84 Why EEPROM memory is used for PIC II Configuration of PIC 16F84 The 16F84 requires a 6V DC supply This can simply be provided by 4 x AA cells A 4MHz ceramic resonator must also be connected as shown be
16. B Design and Applied Technology Secondary 4 6 When the lever is not activated the spring return actuator in the right side will take control of the valve and the right box will be in operation When the lever is actuated the box next to the lever is then in control of the valve A valve can only be in one Position at a time It should be reminded that there is no external movement occur and only switching of internal connections taking place within the valve housing The number of boxes in a valve symbol indicates the number of positions the valve has Flow direction is indicated by the arrows in each box The number of arrows represents the number of flow paths the valve has when it is in that position The position is depending upon which actuator is taking control of the valve at that time In practice the exhaust port goes directly to atmosphere and no physical port exists The exhaust port is indicated with symbol T IHI Adjustable speed control of air flow A speed control valves consists of a check valve and a variable throttle valve in one housing to restrict the air flow in one direction The air can flow freely from left to right direction to the cylinder but the air has restricted flow for speed regulation in reverse direction to the cylinder lao 38 ee A p 88GI Figure 2 8 Structure and symbol of flow control Valve Would you describe briefly the following two valves to see how much you un
17. Design and draw the schematic circuit diagram 2 Connect components in according to the schematic diagram 3 Operate and explain to teacher hy E TM aby Design and Applied Technology Secondary 4 6 IV Hints 3 2 Normally Close NC x 3 OR Shuttle valve air pilot x 1 single acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration i Design and Applied Technology Secondary 4 6 for EF i T e i Hila QUESTION 6 RELEVANT TOPIC PNEUMATICS 1 Situation A plastic thermo forming machine is capable of heating and forming parts of various thicknesses The parts must be held in their molded positions for curing to its final form The length of time needed to cure the plastic will vary depending on its thickness This requires a forming operation to have a variable time delay function so that the part can be held in place before the part is automatically released Figure A 7 A Forming Machine II Control Task To design and assemble a Time delay off circuit to actuate a single acting spring return cylinder IID Circuit Problem Using the given components and layout design a schematic circuit which will extend a cylinder for an adjustable period of time then automatically retract the cylinder 1 Design and draw the schematic circuit diagram 2 Connect components in according to the schematic diagram
18. Sub systems 7 1 3 Operation of a Washing Machine 9 1 4 Operation of Traffic Lights 13 1 5 Control of Fluid Level in a Tank 17 1 6 Application of Control Systems in a Buggy 20 1 7 Application of Control Systems in Air Conditioner 23 Chapter 2 Pneumatics 25 2 1 Pressure 26 2 2 Pneumatics Components and Symbols 28 2 3 Understanding Pneumatic Components 31 2 4 Pneumatic Circuitry 38 2 5 Electro pneumatic Systems 59 Chapter 3 Programmable Control Systems 64 3 1 What is Programmable Logic Controller PLC 65 3 2 Programming the PLC 71 3 3 Application of Ladder Logic Diagram 76 3 4 Programmable Interface Controller 83 3 5 Stepper Motor and Servomotor 89 Chapter 4 Robotics 95 4 1 Definition of Robots 96 4 2 Mechanical Structure of Industrial Robotic Arms 98 4 3 Robot Anatomy 106 4 4 Robot Control Systems 116 4 5 Applications of Robots 122 ETTET Ter Piet tet ere TT TETTETETT rT eer Tee eee er eer ert et er Theme based Learning Tasks 126 e Practical Design Appreciation Case Study of Intelligent Fire Alarm System 126 e Hands on Activity Controlling an Automated Traffic Lights using Programmable 130 Logic Controller e Design and Make Project Pipe Cleaning Inspection Robot 133 e Mars Exploration Design an Innovative End effector for Mars Lander 136 Assessment Tasks 138 Useful Web Sites 155 References 156 Glossary of Terms 157 Acknowledgements 161 CTION Automation is happening aroun
19. and arm and wrist assembly 2 The physical size of each joints and links 3 The ranges of each joint Cartesian robot has a rectangular work space Polar robot has a partial spherical work envelope and a cylindrical robot has a cylindrical work volume Design and Applied Technology Secondary 4 6 Maximum Envelope WONS Resiicted envelope DE Cpercting mvslope Figure 4 28 Diagrams show the work envelopes of an articulated robot Maximum envelope is the envelope that encompasses the maximum designed movements of all robot parts including the end effector work piece and attachments Restricted envelope is a portion of the maximum envelope which a robot is restricted by some limiting devices Operating envelope is the restricted envelope that is used by the robot while performing its programmed motions STOP AND THINK What is are the use s of knowing the work envelope for a robot Design and Applied Technology Secondary 4 6 e aE _ al z t SSS ig Hi a no a a ee ae 4 4 Robot Control Systems D Drive Systems Usually there are three main classifications of power drive for robots electric pneumatic and hydraulic They are used to drive robots through the use of actuators a Electric For electrical driven robots four major types of electric drive can be used 1 Stepping Motors These are used mainly for simple pick and place mechanisms especially when low cost is the more important c
20. are beginning to work in food factories Figure 4 40 Industrial robot in manufacturing plant V Construction Construction robots aim to improve the efficiency of work at construction sites Robots are used in the applications like inner pipe crawling excavation load transport mining bricklaying earth work foundation prefabrication of reinforcement and pavement work Generally construction robots will replace human workers in dangerous conditions or problem of limited accessibility Figure 4 41 Construction Robot for pavement work Design and Applied Technology Secondary 4 6 e ede i ni es SS ee oe r a VI Space Robots Space robotics is generally divided into two main areas 1 serving the functions of robotic manipulators such as the mechanical arm installed in US space shuttle for maintenance of space station or as a crane for material transfer or construction work 2 Robotic explorer for inspection of hostile environment in planetary surfaces and collection of soil samples for analysis Figure 4 42 MARS lander for US MARS Exploration Program VID Mi ilitary Security Robots They are usually deployed as unmanned remote control vehicles typically of terrace type They are capable of taking surveillance photographs and serve as mine sweepers or bomb disposal to safeguard people from endangering into a hostile environment Figure 4 43 Bomb disposal robot checking suspicious Design and App
21. consisting of a contact and overload It will also contain a communication module used for starting and stopping loads Transistors A solid state electronic switch It is fast switches a small current has a long lifetime and works with DC only Or Silicon Controlled Rectifiers SRCs act as a mediator Design and Applied Technology Secondary 4 6 E between the PLC and the AC output device The triac or SCR functions as a switch that responds to the commands of the PLC logic Design and Applied Technology Secondary 4 6 E ACKNOWLEDGEMENTS The authors wish to thank the following persons organizations for permission to use their photographs and images Under the GNU Free Documentation License Figure 4 2 4 34 P 120 Every effort has been made to trace the copyright for the photographs and images as needed We apologize for any accidental infringement and shall be pleased to come to a suitable arrangement with the rightful owner if such accidental infringement occurs Technology Education Section Curriculum Development Institute Education Bureau The Government of the HKSAR Developed by Institute of Professional Education And Knowledge PEAK Vocational Training Council
22. effect to the pneumatic system Therefore AHU is the primary element in a pneumatic system to provide clean regulated and or lubricated compressed air in all industrial applications The function of an AHU is to prolong the life of pneumatic tools devices and valves and hence reduce the maintenance and downtime costs AHU is also known as Air Preparation Unit APU It is usually composed of Filter Regulator and or Lubricator b Filter A standard filter consists of two units water separator and filter Water separator will collect a considerable quantity of water and the filter will prevent contaminants such as dust and rust particles from entering into the pneumatic system Water collected can be drained off through a manual drain cock or an automatic drain The time required to replace a filter can be alerted by excessive drop of pressure across the filter Air In Filter Element How Drain ei Symbol i Manual Drain Auto Drain Figure 2 3 Typical structure and symbol of a Filter with Drain c Regulator Pressure regulator has a diaphragm to balance the output pressure against an adjustable spring force Design and Applied Technology Secondary 4 6 F futpat Pressure Figure 2 4 Regulator sectional diagram If the consumption required by the pneumatic system increases the output pressure will decrease accordingly This decreases the force acting on the diaphragm and against the spring poppet forc
23. ladder software package Design and Applied Technology Secondary 4 6 E A series of directives or boundaries created to allow a process Logic to be controlled Logic can be programmed via hard wiring as is the case with relay logic or via a PLC Multiple bits can be combined to form bytes or words Network Several devices connected together through electrical means for data acquisition and or control Non retentive All values are resent to zero after powering down the unit Off Delay Timer Will turn an output OFF after X amount of seconds has passed On Delay Timer Will turn an output ON after X amount of seconds has passed Operator Interface O I A device that allows the operator of a machine to monitor and control devices attached to a PLC Register A storage area within the PLC for information Relays An electromechanical switch that can control on off of AC or DC loads Relay Circuits Devices often used in control Can be opened and closed electronically to perform logic circuits Retentive Will store data in memory so that it remains intact after powering down the unit Sensor The basic element that usually changes some physical parameter to an electrical signal Solenoid A type of output device and a specific type of coil Both coils and solenoids utilize voltage to convert electrical energy to mechanical energy via magnetic fields Starter A control device usually
24. of sub systems The sub systems will be brought together again and assembled into larger sub systems Finally they are assembled together into a car a system for test drive The sub systems approach at different intermediate levels is crucial for engineers and any personnel involved in managing a large complex system Through division of sub systems according to their functions engineers can make a detailed design less complex and physical assembly in a manageable scale at a time The sub system approach is also related to the concept of Modularity which is widely adopted in today s civil construction and manufacturing The system approach can be visualized by the Vee model B Design and Applied Technology Secondary 4 6 Performance Test Funtional Finished Requirement Product Feedback Integration validation Integration verification Figure 1 7 Vee Model of System and Sub system approach Design and Applied Technology Secondary 4 6 1 3 Operation of a Washing Machine ___ Power Plug F L Conirol Panel Drain Hose Dispenser Door _ y4 Drain Plug Figure 1 8 Typical structure of a washing machine A washing machine has a rotating drum for holding laundry and water The amount of fabrics and the amount of water in the drum may vary Power is supplied from an inverter to an A C motor which drives the rotating drum A speed control regulates the drum
25. part A tool can be held by collets making the tools changeable and more flexible a Grippers Vacuum or Suction cups Vacuum or suction caps are appropriate when the objects to be handled have a flat smooth un clean surface e g for lifting glass Design and Applied Technology Secondary 4 6 c eee so _ h ei N Figure 4 24 Vacuum gripper Advantages simple in mechanically design ventle force can be applied to lift objects without causing damage reliable light weight can be used on a wide range of materials VI Magnetic Useful only for ferrous materials containing iron Objects of different shapes can be picked up quickly It can pick up parts with holes and irregular surface It 1s inevitable to picks up dirt rubbish or unwanted objects during operation In addition slippage may occur and handling will not very precise Figure 4 25 Articulated robot per permanent magnetic gripper ae Design and Applied Technology Secondary 4 6 It can be powered electromagnetically or use a permanent magnet Dropping an object is easy for an electromagnetic one by simply powering off the gripper However it may be dangerous in the event of power failure For a permanent magnetic one it needs specific mechanism to unload the object from the gripper Other gripper designs may use adhesives hooks scoops etc They are specially designed for picking up parts of particular sh
26. position and pressure releases Figure 2 15 Circuit diagram of Signal inversion c Mono stable circuit A 3 2 manual operated NC valve is used to control a 5 2 valve which actuates a double acting cylinder This circuit has two functions 1 one is for flow amplification 2 Another is the control of double acting cylinder with one 3 2 NC valve Design and Applied Technology Secondary 4 6 Figure 2 16 Switching of two circuits with one manual operated valve d Bi stable Circuit Two normally closed 3 2 valves are used to control a 5 2 directional valve which is used for actuating a double acting cylinder When the left valve is pressed momentarily the cylinder will retract and hold its position until the right 3 2 valve is pressed When the right 3 2 valve is pressed momentarily the cylinder will extend This circuit has two functions 1 flow amplification 2 memory function TH Y 5 Figure 2 17 Switching of two circuits with one manual operated valve e Timing Circuits A 3 2 NC valve is used to control another 3 2 NC valve A flow restriction valve is connected in the pilot line and in a direction that the ON signal is delayed When the valve 1 is pressed the air flow is restricted to the directional valve The cylinder will extend after a certain time delay When the valve 1 is released the exhaust air flows freely The cylinder retracts immediately Design and Applied Technology Secondary 4 6 Fi
27. present to perform a OR logic function Design and Applied Technology Secondary 4 6 CHAPTER 3 PROGRAMMABLE CONTROL SYSTEMS This chapter contains topics on 3 1 What is Programmable Logic Controller PLC 3 2 Programming the PLC 3 3 Application of Ladder Logic Diagram 3 4 Programmable Interface Controller 3 5 Stepper Motor and Servomotor These topics include learning materials that facilitate you to Understand the operation of PLCs Understand the Ladder Logic Function Understand the programming of PLCs Understand the use of PLCs in control Design and Applied Technology Secondary 4 6 ee a 1 in T Wha e 3 1 What is Programmable Logic Controller PLC Figure 3 1 PLCs of different brands A programmable logic controller is defined by the National Electrical Manufacturers Association NEMA as A digitally operating electronic apparatus which uses programmable memory for the internal storage of instructions for implementing specific functions such as logic sequencing timing counting and arithmetic to control through digital or analogue input output modules various types of machines or processes D Why Programmable Logic Controller PLC is needed Basically system automation and process control require at least an on off control in modern commerce and industry application These control systems are no longer built from electromechanical relays switches timers c
28. pumps in machines equipment and industrial production processes 2 Controllers are defined as those used to make the controlled elements to perform their controlling tasks 3 Controlled values are referring to those physical properties that are to be controlled according to the desired value by an automatic control system Commonly they are the temperature speed and displacement 4 References Set points are referring to the values of input signals required by an automatic control system to control the controlled elements 5 Disturbances are referring to those which make the controlled values deviated from the desired value in an automatic control system For those disturbances that are come from the control system itself are called the Internal Disturbance Those come from the surrounding environment are called the External Disturbance 6 Automatic Control System is composed of controlled elements and controllers which work together according to a preset program so that the controlled elements can perform the controlling tasks II Open Loop Control System Open Loop control is the most basic automatic control system and is composed of controller and controlled element It involves the forward function of the control system but without the feedback control The block diagram shows their relationship Disturbance U R C Controller Controlled Hement gt Reference Controlled Value Figure 1 1 Block diagram of Open L
29. still pressed even when valve 2 is tripped at the end of the outstroke 2 Would you suggest any modification to the circuit to improve this situation g Reciprocating strokes Repeating strokes of a double acting cylinder can be designed by two roller actuated 3 2 NC valves They are at both ends of stroke A 3 2 manual operated valve is connected in series with one of the roller operated valve to perform an interlock AND function as a manual switch to start the automatic reciprocating stroke a ez Lt Valve 2 Valve 4 TS INAN ALIS Figure 2 27 Reciprocating stroke of a double acting cylinder Working principle of electromagnetic relay Design and Applied Technology Secondary 4 6 0 4 Coil Com Cail M O N C Figure 2 28 Schematic diagram of electro mechanical relay principle An electromagnetic relay is an electrical switch that can be actuated indirectly by another switch When the coil is energized current flows through the coil and generates an attractive electromagnetic force The armature is pulled down causing the lever arm to close the contacts When the coil is de energized the spring pulls the lever arm down and opens the contacts Electromagnetic relay can be designed with normally open contacts or with normally closed contacts It is a commonly used device in electro pneumatics and PLC applications 1 Functions of Electromagnetic relay It is an electrical switch with a high curr
30. system TCS which is originated at the robot wrist This system is especially useful when the tool 1s near to the work piece This method of programming is very simple to use where simple movements are required However when teaching the robot cannot be run in production this reduces the machine utilization rate Design and Applied Technology Secondary 4 6 Eee EEE Ee ar i meee ee ee i ES a r Wa es fo Figure 4 35 Teach pedant for teach method of robot programming b Leadthrough Programming This programming method is mainly used by spray painting robots The robot is programmed by being physically moved through the task by an operator This is exceedingly difficult where large robots are being used Therefore a smaller version of robot is sometimes used for this purpose Any hesitations or inaccuracies that are introduced into the program cannot be edited easily without reprogramming the whole task The robot controller simply records the joint positions at a fixed time interval during the leadthrough and then plays back the sequences c Off line Programming It is used to program robots from the CAD models of the robots fixtures and accessories The program structure is built up in much the same way as for teaching programming but intelligent programming tools are available which allow the CAD data to be used to generate sequences of location and process information The benefits
31. to the level before the disturbance is interfered IV Sequential Control System Sequential control means one operation or process must be completed before the next one is initiated The execution of next operation or process depends on the execution of the preceding one It will continue in a stepwise order until a termination command is met Sequential control is usually referring to automatic and mostly used in engineering and industry as most of the processes in production line are sequential in nature Take a lift as an example The lift can only move up or down after the door has closed properly and the door will only open when the lift is level with the building floor It implies that automatic sequential control usually work with sensory feedback mechanism We will explore the application of sequential control system by exploring the operation of a washing machine traffic lights and the control systems in a buggy in topics 1 3 1 4 and 1 6 respectively Design and Applied Technology Secondary 4 6 1 2 System and Sub systems Systems are actually everywhere in our daily life from the universe solar system to home entertainment systems from Automatic Teller Machine ATM to missile defense systems In laymen terms people say everything goes smoothly when the system works but disaster comes when the system fails The definition in dictionary for system is that a system is as a whole but with inter related part
32. to the operating motors cylinders relays solenoid valves and any other actuators c Input and output module Input and output modules are the I O connections to the industrial process that is to be controlled d Processor The processor is the Central Processing Unit CPU of the programmable controller It executes various logic and sequencing functions e Memory It consists of input output and flag memory Its storage capacity may ranges from 1K to 48K It contains the program of logic sequencing and other input output operations f Power supply A power supply of 115Vac or 220Vac is typically used to drive the PLC The components of industrial process that are controlled by PLC can have a higher voltage and power rating than the PLC Design and Applied Technology Secondary 4 6 g Programming device The programming device is usually detachable from the PLC cabinet It may be either a hand held programmer similar to those used in robotics or a computer based programming package using PC to input program into the PLC memory Environment Wemor Prograrri Fiag i instruction Memory 2 Instruction Irsirucii ri i Output l Memor Figure 3 3 Functionality of PLC components III How the PLC operate Programmable Logic Controllers PLCs work by continually scanning a program This scan cycle consists of 3 important steps 1 checking input status 2 executing the program and
33. to the pump room to turn on the duty pumps to charge the sprinkle system The fire alarm signal will also be relayed to the Regional Fire Office automatically through the dedicated signaling line The fire engines will then be sent to the fire location through this AFA or IFA Design and Applied Technology Secondary 4 6 Sea r T ie Te T E semi we Huti Logger lt anah tam cfe Smoka GO Fe Oct Actors rich Dirite F F j Aimee j End om 3 oam FOS VIGO 11 SSD AM pipii war 0 F Citas of 1714 2006 1151 58 et Aab 115392 a Summa vee ne Figure 1 4 User Interface of Flame and Smoke detection system Measuring Circuit in Detection Chamber High Current value Radioactive Terminal Reference Source Screw Chamber Radioioactve mater parives Control Unit or Processor Low Current Plastic Cover Smoke attached to particles Alarm Indicator Radioioactve mater parives Detection Detection Chamber Cover Chamber Figure 1 5 A cutaway diagram of intelligent smoke sensor The owner or responsible personnel of this property will also be notified by the messaging function of the control panel through mobile phone The user interface has imported the building floor plan in the initial configuration The floor plan is divided into number of zones according to the arrangement of smoke and heat sensors Once the fire happens the zone concerned
34. will be flashing and alerting sound on the screen to alert the responding personnel to take any pre planned emergency procedure Design and Applied Technology Secondary 4 6 E This intelligent fire alarm system will be integrated with the surveillance system to have a real time monitoring of the fire location as shown in Figure 1 4 Once the flame is notified in one a zone the surveillance system will alert the on duty personnel and indicate the exact location of the building by the pre loaded site drawing or the building floor plan All the intelligent sensors are connected by the twisted pair cables and are communicated through an Ethernet network Each sensor has its own IP address and their distribution over the building are stipulated by the fire regulation IHI Learning Tasks 1 Investigative Questions Students are expected to form groups by conducting information search through Internet and small group discussion to answer the following questions A Explain why the Intelligent Fire Alarm system does not use the pre pressurized sprinkle system but use the dry pipe B Explain why each sensor has its own IP address C Investigate how the intelligent sensors confirm the fire is happening D Investigate what other fire extinguish methods are used besides the sprinkle system 2 Follow up Activities A Form groups and carry out a field study of fire safety measures taken in the school premises Appraise the
35. 6 ee oe E m br a s Eer m TEs Example Estimated force needed is 900 N 25 safety factor included Air pressure to be used is 80 N 80 N x Power Factor 900 N Power Factor 900 N 80 N 11 25 The power factor just above 11 25 is 12 6 Therefore a bore diameter of 4cm cylinder should be used IV Factors affecting the performance of cylinder There are many factors that affect the performance of a cylinder Some of these factors are Quantity and type of fittings leading to the cylinder Hose tube length and capacity Cylinder operating load ee Air pressure V Single Acting Cylinder Figure 2 10 Structure and symbol of Single acting cylinder A single acting cylinder has one air inlet to provide power to the extend stroke The piston rod is returned by an internal spring Single acting cylinders use theoretically one half as much air as double acting cylinders It is operated by a 3 way valve VI Double Acting Cylinder Double acting cylinders have two inlets to provide power to both the extend and retract stroke It requires four ways or five ways directional control valves to control Design and Applied Technology Secondary 4 6 c SeGegaa C A Figure 2 11 Structure and symbol of Double acting cylinder VID Single and Double Rod SINGLE ROD CYLINDER DOUBLE ROD CYLINDER Figure 2 12 Single acting above and Double acting cylinder below Sin
36. Design and Applied Technology Secondary 4 6 x Figure 2 31 Manual operation of a double acting cylinders ii OR control For electro pneumatic system two or more pushbuttons can be used to control the actuation of cylinders through an OR logic control without the problem of air leakage through Switches as in pneumatic system iden r i Po2 T 2 A Figure 2 32 OR operation of double acting cylinders B Design and Applied Technology Secondary 4 6 g amp wh iii Multiple contacts When pressing either the pushbutton of pbl or pb2 the solenoid will be energized and the lamp will be turned on as shown in Figure 2 33 In Figure 2 34 when pb is closed it energizes control relay R1 which will then turn on the lamp and solenoid valve A to extend the cylinder When pressing pb2 only the solenoid A is energized to extend the cylinder but it does not turn on the lamp 2 A Figure 2 33 Control of cylinder and lamp by either pb1 or pb2 Po1 i R1 2 R1 3 Po2 A 4 Figure 2 34 Control of cylinder and lamp by pb1 pb2 for controlling cylinder only 2 Design and Applied Technology Secondary 4 6 c _ Ee p ae E p Ee Sa Ba a iv Control of Slide Unit Double solenoid valve has a bi stable characteristic When Pbl is pressed the slide moves from left to right and is held in that position until Pb2 is pressed Figure 2 35 Control of Slide unit
37. ELEVANT TOPIC PNEUMATICS 1 Situation A part needs to be clamped for a drilling operation An operator needs to activate and deactivate a pneumatic clamp that holds the part in a fixture on a drilling table The clamp must be activated before the drilling cycle begins and deactivated at the end of the drilling cycle Figure A 4 A drilling machine ID Control Task To design and assemble a circuit that extends and retracts a double acting cylinder IID Circuit Problem Using the given components and layout design a schematic circuit which will operate a double acting cylinder with a two position five way valve 1 Design and draw the schematic circuit diagram 2 Connect components in according to the schematic diagram 3 Operate and explain to teacher hy ES oye _ tli Design and Applied Technology Secondary 4 6 IV Hints 3 2 Normally Close NC x 2 5 2 directional valve air pilot x 1 double acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration Design and Applied Technology Secondary 4 6 QUESTION 4 RELEVANT TOPIC PNEUMATICS 1 Situation A large stamping press must have the work piece in place clamps engaged and safety guard in position before the Start button can activate This interlock design is needed for minimizing potential risks Figure A 5 A Stamping machine ID Control Task To design and a
38. II Closed Loop Control System Thermometer Mercury Switch Hgh Sensor circuit Heating Coil Furnance Figure 1 5 Closed Loop control system of furnace Disturbance Reference R e Error signal C Controlled Value K Controller Controlled Hement gt Figure 1 6 Block diagram of Closed Loop control system The main difference between Closed Loop system and Open Loop system is the Feedback function The controlled value is measured and used to compare with the input signal Reference An error signal is then generated by this comparison The error signal is amplified and converted to be used to change the controlled value in an opposing way so as to delete or at least minimize the deviation from the desired value It is called the Feedback control If the feedback signal is used to enhance the controlled value and make it go beyond the desired value it is known as Positive Feedback If the feedback signal is used to reduce the deviation of the controlled value from the desired value it is known as Negative Feedback Most of these control systems are negative feedback so the word negative is usually omitted for simplicity Design and Applied Technology Secondary 4 6 The advantage of Closed Loop control system is that the reference is changed in accordance with the level of disturbance The error signal generated can compensate and oppose the effect of disturbance Therefore the controlled value can go back
39. LC control and demonstrate to teacher D Give any suggestions to improve the road safety for this zebra crossing condition gor Design and Applied Technology Secondary 4 6 Design and Make Project Pipe Cleaning Inspection Robot 1 Introduction In Hong Kong most of the drivers complain that the maintenance and construction work of underground pipe works are so frequent which are blamed for the major cause of traffic jams The repair of underground pipes is mainly due to the leakage caused by prolonged clogging in the old metal pipe and accumulation of rubbish in PVC pipe These pipes cannot be cleaned by routine maintenance Once the leakage happens the only way is to replace them with new ones Therefore it 1s unavoidable to cause a lot of disturbances to the traffic condition If these pipes can be cleaned regularly to reduce the clogging of dirt they can live longer and thus reduce the tremendous maintenance works Figure 3 1 Atypical pipe inspection robot Students are required to apply their knowledge to design and make a Pipe Cleaning Inspection Robot Design and Applied Technology Secondary 4 6 II Project Brief a Consumables 01 Aluminum of wide range of forms and size such numerous as angle flat rod channel and tube etc 02 Acrylics of wide range of forms size and color numerous such as triangle flat rod and tube etc 03 Fasteners i e machine screws washers nuts num
40. O c Rotational Joint type R joint The relative movement between the input link and the output link is rotational with the axes of rotation perpendicular to the axes of the input and output links input link JOutput link Figure 4 12 Axis of rotation is perpendicular to axis of the 2 connecting links Type R d Twisting joint type T joint The relative movement between the input link and the output link is a rotary motion with the axes of rotation parallel to the axes of the input and output links Output link Input link Figure 4 21 Axis of rotation is parallel to the links Type T Design and Applied Technology Secondary 4 6 E III Revolving joint type V joint The axis of output link is perpendicular to the axis of rotation with the axis of rotation of the joint parallel to the axis of input link Output link Input link Figure 4 22 Output link is perpendicular to the input joint but parallel to the axis of rotation Type V IV Joint notation scheme Joint2 Type R Links Link2 Joint3 Type T Joint1 Type R JointO Type T Base Figure 4 23 Joint and link nomination in an Articulated robot For a typical robotic arm it can be divided into 2 main sections a body and arm assembly a wrist assembly Joint notation scheme is that a robotic arm that can be described in terms of the type of joints LOR T V it has which is listed in the order from
41. ON OFF control application is provided below for comparison Stop Motor Power to control relay Motor Start Figure 3 9 Hard wired logic circuit for the same motor ON OFF control ID Use of control relay for alternate switching of motors A relay can be used to control ON OFF actuation of a powered device at remote location A control relay in different rungs of a ladder diagram is used to serve multiple logic function The output load control relay C on one rung in a ladder diagram can be inputs for other rungs When the normally opened contact X is open the relay is not energized The output motor Y1 in the second rung is connected to the power line The motor Y1 turns on When the contact X is closed the normally closed control relay in second rung will open and the normally opened contact in third rung will close The motor Y1 and Y2 will turn off and on respectively B Design and Applied Technology Secondary 4 6 E X C C Y1 C Y2 Figure 3 10 Use of control relay for multiple logic function III Level control in sewage treatment tank Control Relay X1 Hoat Switcch s1 Timer T1 Control 7 Valve C2 Control Relay E 60s Timer T2 sz Control Valve Figure 3 11 Schematic diagram of fluid level control Design and Applied Technology Secondary 4 6 E When the START button X1 is pressed it energizes the control relay C1 C1 in turn energizes the solenoid S1 w
42. ach wheel should reverse Left Weel Adjustable Motor Timer Driver gt Bevel Gears Q gt Right Motor Revel Gears Adjustable Motor Timer Driver Bump Sensor Rght Weel Figure 1 23 The block diagram shows two motors two wheels a bump sensor and two potentiometers for programming the time events The diagram illustrates the sequence of actions when the obstacle avoiding buggy strikes an obstacle The robot is initially moving forward When it strikes the obstacle both motors are switched to reverse and the buggy moves straight backwards How the buggy makes a turn The right motor reverses for a longer time period than the left motor causing the robot to turn to right After a certain period the right motor stops reversing and both motors go forward leading the robot off in a new direction If the robot bumps into obstacle again the process repeats the sequence of actions until the obstacle clears off from its way Design and Applied Technology Secondary 4 6 oy rt wig wl Obstacle avoiding ose lchll ackwar robot moving forward See sion Robot turns right Robot moves forwards again left wneed moves forward Gear of obstacle right wheel moves backward Figure 1 24 The basic operation of the obstacle avoiding buggy Colision detected Signal from bump sensor Time forward Command to right motor Time i Fobot Pobot backing up turning l right backward Robot moving owad Robot mo
43. all three links Good examples of application are flying simulator and 4 D cinema Advantages Increased stability and arm rigidity Faster cycle times than serial linked robots End of arm errors are averaged over parallel link structure Drawbacks Relatively large footprint to work space ratio Small range of motion Design and Applied Technology Secondary 4 6 A ZZ Figure 4 12 Schematics diagram of Parallel Robot VI Articulated Revolute Robots Articulated or Joint Arm Robots are the most versatile robots available It closely simulates the natural form of human arm Articulated robots are mechanical manipulator that looks like an arm with at least three rotary joints One joint is around the base A1 and the others are on the joints A2 and A3 In terms of a human arm these can be compared to the shoulder bicep and forearm A six axis jointed robot includes the axis of the wrist A4 A5 amp A6 known as pitch roll and yaw respectively With these extra axes added this robot can move the end effector to any point at any orientation in the workspace The joint types used are TRR Figure 4 13 Typical Articulated Robots for material handling application Advantages The wrist can reach any position and orientation within the work envelope It can reach areas that are difficult to be reached by other robots Design and Applied Technology Secondary 4 6 It is compact and provides the larges
44. ands on experience from these tasks From the application point of view this module will be very challenging to the students who have desires in pursuing innovative design and advanced technology This module will provide students who have interest in logics electronics computer control and system engineering with a lot of opportunities to explore and unlimited space for their innovation Design and Applied Technology Secondary 4 6 CHAPTER 1 BASICS OF CONTROL SYSTEMS This chapter covers topics on 1 1 Open Loop Closed Loop and Sequential Control Systems 1 2 System and Sub systems 1 3 Operation of a Washing Machine 1 4 Operation of Traffic Lights 1 5 Control of Fluid Level in a Tank 1 6 Application of Control Systems in a Buggy 1 7 Application of Control Systems in Air Conditioner These topics include learning materials that facilitate you to Identify Open Loop Closed Loop and Sequential control system Identify input process output state output diagram and time phase diagram Understand some control basics in washing machine traffic lights water level buggy and air conditioner Design and Applied Technology Secondary 4 6 1 1 OPEN LOOP AND CLOSED LOOP CONTROL SYSTEM D Basic terminology of control system 1 Controlled elements are defined as those which are involved in realizing automatic controlling tasks Commonly they are referring to electrical motors pneumatic cylinders and hydraulic
45. apes VII Mechanical gripper Figure 4 26 Mechanical gripper of fingers type It uses fingers jaws usually 2 fingers with 2 positions open and closed making control relatively simple Detachable fingers allow worn fingers to be replaced and is interchangeable between different types of fingers It can have hard fingers which allow precise handling but may damage delicate materials The finger may not be versatile or effective for picking up objects of different shapes The other can be compliant fingers which have some allowance for dealing with some unpredictable shapes Sensors on grippers can provide information to the robot control system that an object has been picked up and allow fingers to apply appropriate force to grasp the object Sensors can be force sensors pressure sensors strain gauges and touch sensors Can you use the Joint Notation Scheme to describe the following robots 1 6 DOF Articulated robot 2 6 SCARA 1 Body and Arm assembly 1 5 2 _ cae Design and Applied Technology Secondary 4 6 11 Wrist assembly 1 2 111 Joint notation scheme 1 2 3 Figure 4 27 a Articulated robot b SCARA robot VIII Work Space Work space is also called Work volume or work envelope It is defined as the space within which the robot can manipulate by the end of its wrist It is determined by the following factors 1 The number and types of joints in the manipulator body
46. ble acting cylinders output A and B ports with common exhaust R 5 2 Switching between Double acting cylinders output A and B ports with separate exhaust R 5 3 Switching between Double acting cylinders output A and B ports with with neutral position for mid position fully sealed stopping all cylinders action Table 2 Symbols ISO of common direction valves Remarks P is inlet port of working air line A is the outlet port of working air line R is the exhaust port II Valve actuator The directional valve can be controlled directly by manual control or automatically by mechanical electrical and air actuation Below are some common actuator symbols Design and Applied Technology Secondary 4 6 Eo OT O Pilot Assist Solenoid Table 2 1 Symbols for common valve actuator Take a typical 5 2 directional valve as an example It shows the method of actuation the number of positions the flow paths and the number of ports Here is a brief illustration of how to read a symbol Left 7 Right Actuator Position amp Flow Boxes Actuator 2 Position Lever Actuated Spring Return valve Figure 2 7 Directional Valve symbol 2 position lever actuated and spring return The left actuator is manually controlled by a lever It is used to shift the valve from right to left when actuated This directional valve has at two positions boxes and each position has three flow paths
47. curacy and stability is usually not high The only way to increase the stability is to make sure that every component used in this system is of high quality and accuracy but it is usually unpredictable This system cannot deal with the disturbance such as frequent opening of the furnace door Design and Applied Technology Secondary 4 6 Thermometer Manual SW override o Heating Coil Furnance Figure 1 3 Human interrupt control of the Open Loop control system Usturbance U Reference R C Controlled Value Figure 1 4 Block diagram of Human override in Open Loop control system The above problem can be solved by the use of manual override to the electromechanical switch A thermometer is used to measure the actual furnace temperature for visual monitoring If the controlled value is deviated from usually lower than the desired value the operator will close the switch in order to give power to the heating coil The furnace temperature can hence be more closely stabilized within the controlled range It is an immediate solution that the controlled value can be used back to control the system however it is by no means an automatic control system If we use some sort of sensor and electrical circuit to measure the temperature and provide the feedback of controlled value to the system the system becomes a Closed Loop Control system Le Design and Applied Technology Secondary 4 6 I
48. d Technology Secondary 4 6 CHAPTER 2 PNEUMATICS This chapter contains topics on 2 Ze 2 3 2 4 25 Pressure Pneumatics Components and Symbols Understanding Pneumatic Components Pneumatic Circuitry Electro pneumatic Systems These topics include learning materials that facilitate you to Understand the characteristics of pressure Identify pneumatics and electro pneumatics components Understand design of pneumatics and electro pneumatics circuits Understand the industrial application of pneumatics Design and Applied Technology Secondary 4 6 2 1 Pressure D Units The atmosphere exerts a pressure on earth surface As a standard pressure is measured at sea level This pressure can be described as a force per unit area The metric unit of pressure is Pascal Pa 1 Pa 1 N m Newton per square meter The force exerted by the atmosphere at sea level is 100 000 Pa 1 standard atmosphere is approximately 14 696 psi or 1 01325 bar or 1 03323 kgf cm2 In English pressure is expressed in psi or pounds per square inch It is also defined as a ratio of force to area 1 MPa 10 bar or 145 psig Physics Pneumatics Vacuum iver pismaiine Techniques Absolute Pressure 500kPa 60 psig 4 bar 400kPa 45 psig 3 bar Atmospheric 100kPa 0 bar Pressure Atmosphere 533 mbar 101325 Pa abs ar Vacuum Figure 2 1 The various systems of pressure notation In the application of pneumatics pressure is usually
49. d us in our daily life from early morning snooze of an alarm clock to boarding the MTR through an automatic door Both of them are examples of industrial automation application and involve different levels of automation An alarm clock is basically a timer The snooze function is in fact a sequential control with preset time variables An automatic door is a typical application of Pneumatic Electro pneumatic systems The duration of door opening is another example of a sequential control with delay function Sometimes the MTR driver performs the Manual Override function for emergency which is to re open the doors when a passenger is clamped between the closing doors Students will be introduced to the basic control systems pneumatics electro pneumatics systems programmable control systems and robotics After completing this module students will have an integrated knowledge in understanding interpreting and appraising basic automation systems such as washing machine traffic lights buggy air conditioner production line automatic door and fire alarm system etc New topics like electro pneumatics micro controller PLCs and robotics will also be introduced in this module For better understanding four thematic learning tasks will be assigned to students With the experience after the tasks students will be technologically competent to solve practical design problems in different scenarios Our students will gain some h
50. derstand at this stage fio ANA b Design and Applied Technology Secondary 4 6 ss a T in Te m h e H G H 1 Cylinder Sizing Calculation The air cylinder size calculation steps are as follow 1 Calculate the area of the cylinder piston Area Pixr 2 Multiply the piston area by the air pressure to be used Area x Pressure Force Output The real force output of a cylinder will be less than the theoretical output because of internal friction and external loading It is best to use a cylinder that will generate from 25 to 50 safety factor more force than theoretically needed 2 Cylinder Bore Size Selection Figure 2 9 Cylinder bore Size Four easy steps 1 Determine the force needed to move the load Add 25 safety factor for friction and to provide enough power for the cylinder rod to move at a reasonable rate of speed 2 Find out how much air pressure will be used and maintained in the system 3 Calculate the power factor by the formula Air pressure x Power factor Cylinder force required 4 Once the power factor is found the bore diameter can be checked from the table below For safety sake the higher approximate value in the table will be chosen for the determination of the bore size Power Factor Table immer a 1 i s 2 fede gt 5 6 rower oa fos ro s aa ao a9 70 83 i2 253 Table 2 2 Power Factor Table 6 Design and Applied Technology Secondary 4
51. e The diaphragm and the poppet will lower until the spring force to be balanced again This will increase the air flow through the orifice until it meets the increased consumption of compressed air If the consumption rate drops output pressure slightly increases This increases the force acting on the diaphragm and valve will then lift until the spring force is equaled again The air flow through the valve will then be reduced until it matches with the reduced consumptions rate The output pressure can be maintained AND THINK Why the output pressure will increase when the consumption flow rate drops and vice versa Can you explain this phenomenon S Design and Applied Technology Secondary 4 6 d Lubricator It is designed to dispense a certain amount of lubrication oil continually to the compressed air Some pneumatic devices need lubrication to run at peak efficiency However some pneumatic applications will omit the lubricator for the following reasons 1 Clean and hygienic environment for food and pharmaceutical application 2 Oil free healthier and safer working environment 3 Reduce cost of additional lubrication equipment lubricating oil and maintenance Adjusting EJ Sight Screw l Venturi Symbol Structure and symbol of a Lubricator In most applications especially for those used in school and vocational training a combined unit or modular design of filter pressure regular and lubricator is comm
52. e entering into the pneumatic systems Dust and moisture will accelerate wearing of pneumatic devices 3 Compressed air will inevitably cause noise pollution It will be a concern if it is used in laboratory or clinical applications 4 Leakage of air is unavoidable in compressed air system Routine maintenance and troubleshooting are required for pneumatic systems 5 The compressed air is compressible The accuracy say the stroke of cylinder will be deteriorating and varied over times Adjustment needs to be done after certain period of servicing 6 The power rating is limited as the compressible nature of air Some critical situation the pneumatics systems will not be applied such as the life saving ladder in a fire engine The power rating and the speed cannot reach the requirement Design and Applied Technology Secondary 4 6 Quizzes chapter 2 What are the limitations of using Pneumatics Why elevator in fire engine cannot be driven by Pneumatics What are the limitations of using a single acting cylinder Suggest methods to detect the leakage of compressed air in a manufacturing plant What are the major reasons of using Electro pneumatics Describe the differences between Solenoid and Electromechanical relay Why some application prefer to use a non lubricated pneumatic system EPA E A Why two 3 2 NC and spring return valve cannot be used to directly control a double acting cylinder 9 Why a shuttle valve must be
53. ed movements Control system simplicity Good accuracy Fast operation Good access to front and sides Structural simplicity offering good reliability Drawbacks Dust contamination around the flexible bellows is hard to avoid for prismatic joint Relatively small workspace compared with Cartesian robot Figure 4 6 Schematics diagram of Cylindrical Robot Cylindrical robot can move up and down and around the column and the arm can be telescopic It has a cylindrical work volume The joint types are usually LTL or TLL Design and Applied Technology Secondary 4 6 III Spherical Polar Robot Figure 4 7 Typical Polar Robot A Polar Robot has one linear axis and two rotary axes It is able to rotate in two different directions along its main axes and the third joint moves in translation forming a hemisphere or polar coordinate system The joint type is usually TRL Advantages Has a large workspace and can reach below its base Easily controlled programmed movements Familiar polar coordinates easily understood Large payload capacity Fast operation Accuracy and repeatability at long reaches Drawbacks Resolution is relatively low and is variable over the workspace The resolution is lower when the end effector is around the base small change in angle produce a large movement Design and Applied Technology Secondary 4 6 lt lt Figure 4 8 Schematics d
54. ed with water via a float operated control valve F A manual globe valve V is on the outlet pipe Both valves are assumed to have same size in term of flow capacity mass flow rate and flow characteristic pressure drop along the pipe The desired water level in the tank is set at the point B This is equivalent to the set desired point of a Closed Loop control system Here the tank is the controlled element The float switch is the measuring device which provides the feedback to the controller The controlled value is the fluid level and the control value is the mass flow rate D When Loading is 50 Half open Control valve in half open position gt Water in p gt Water out Value V Figure 1 19 Valve at 50 open It can be assumed that with valve V half open 50 load the flow rate of water entering via the float operated valve is equal to that leaving the discharge pipe via globe valve V Water level can be maintained in the tank at point B The system can be said to be in equilibrium under control and in a stable condition It means that the flow rate of water entering and leaving the tank is the same and therefore the level is not varying The water level is precisely at the desired water level B and giving the required B outflow Design and Applied Technology Secondary 4 6 _ i i T Tia a When the loading is 0 Fully closed Fully closed
55. ee Design and Applied Technology Secondary 4 6 x i na oe avle Control Systems Robotivs itis ntrol Systems VT SER Design and Applied Technology Secondary 4 6 Elective Module 1 Automation Learning Resource Materials Resource Materials Series In Support of the Design and Applied Technology Curriculum S4 6 Technology Education Section Developed by Curriculum Development Institute Institute of Professional Education Education Bureau And Knowledge PEAK The Government of the HKSAR Vocational Training Council Technology Education Section Curriculum Development Institute Education Bureau The Government of the Hong Kong Special Administrative Region Room W101 1 F West Block Kowloon Tong Education Service Centre 19 Suffolk Road Kowloon Tong Hong Kong Reprinted with minor amendments 2010 Project Advisor Mr Eric Liu Head Department of Multimedia and Internet Technology VE Tsing Y1 Author Mr Li Yu Wai Design and Technology Teacher Project Coordinators Mr Li Yat Chuen Senior Training Consultant PEAK VTC Mr Tsang Siu Wah Training Consultant PEAK VTC The copyright of the materials in this package other than those listed in the Acknowledgments section and the photographs mentioned there belongs to the Education Bureau of the Government of the Hong Kong Special Administrative Region Copyright 2009 Duplication of materials in this package
56. ent rating that is indirectly operated by a low control current It acts as an interface between the low signal levels 5 12V from controllers to high current rating devices It can provide contact points for one to many It can provide contact points from normal close to normal open or vise versa 2 Limitations of Electromagnetic relay It contains moving parts and electrical contacts it has limited operating speed reliability and lifespan It is big in size and requires large mounting racks in application Each relay can only provide a small number of contacts It is very difficult to change the control function of a relay system once it is connected up A complete re wiring may be necessary for changing control tasks Due to limited lifespan the replacement and maintenance involves high cost 3 Latching function of Electromechanical relay It can be connected to an electro pneumatic circuit for the control of solenoid valves and the control function of Programmable Logic Controller PLC an automatic pneumatic system can be realized The latching function of electromagnetic relay can be done by connecting the power line to one of the contact pins Once the coil is energized the contact closes and allows power to Design and Applied Technology Secondary 4 6 the coil When the ON switch is turned off the coil remains energized by the power line An OFF switch is connected to reset the relay Figure 2 29 lef
57. erous rivets pop rivets lock clips studs self locking nuts strap fasteners and spanners etc 04 Conventional workshop hand tools marking out Sufficient tools cutting tools and finishing tools and numbers machinery such as drilling machine sander and buffing machine etc Table 3 1 Consumables needed for making the robots b Test Rig 01 A 300mm internal diameter opaque PVC or l pe transparent acrylic pipe with length of not less than 4 feet 02 A tailor made wooden container with nylon covering for collection of leakage water placed under the test pipe 03 A pair of tailor made wooden stands to support the test pipe and with appropriate fasteners for security and safety Table 3 2 Part list for the test rig Design and Applied Technology Secondary 4 6 c Tasks poke a Figure 3 2 Schematic diagram of Test rig Students are required to design and make a pipe cleaning robot prototype that can demonstrate how to clean a pipe in the test rig The robot can be autonomous with suitable sensory feedback execution of preset program or real time remote control Students have to design an appropriate locomotion that can move effectively along the inner wall of the test pipe An end effector should be a pipe cleaning device It may need to install a camera or appropriate sensors to collect image and information from the pipe being inspected Robots can also be controlled by wireless th
58. f an electrical current flowing through a wire coil to produce magnetic field inside the coil A mechanical spring causes the core to be retracted out of the coil when the electrical current is turned off Design and Applied Technology Secondary 4 6 E What will happen to the above solenoid design in case of power failure during the course of control Would you suggest any modification to alleviate this problem Design and Applied Technology Secondary 4 6 3 2 Programming the PLC PLCs is relatively easy to program The programming language is designed to resemble ladder logic diagram It is designed for an industrial electrician or electrical engineer who is accustomed to reading ladder logic schematics in electromechanical control relay The learning curve becomes short for programming a PLC to perform the same logic control functions D Constructing a Ladder Logic Diagram The power e g 110V AC to the components is provided by two vertical rails The left rail is the power rail and the right rail is the ground bus The horizontal line is the rung It is common to locate inputs and outputs to the left and right of each rung respectively Power flows through a series of normally open or normally closed contacts It powers a coil from left to right and top to bottom over a ladder diagram ID Symbols of components in ladder diagram Normally open contacts are symbolized by two vertical lines along a horiz
59. facing a critical issue of global warming With a view of that an effective control that can improve the cooling efficiency will save the power consumption A simple air conditioning system is shown in Fig 1 26 The only control task in this system is temperature There are two adjustable valves to regulate the temperature Cooling Valve Heating Valve Temperature Sensor Figure 1 26 Block diagram of temperature feedback control system The temperature sensor provides the feedback to the Closed Loop control system If temperature measured Tm is lower than the set point Ts open heating valve Hv fully and close the cooling valve Cv fully to restore the temperature If temperature measured Tm is higher than the set point Ts open cooling valve Cv fully and closes the heating valve Hv fully to restore the temperature In lt T C Low 0 H High 1 ly gt i C High 1 H Low 0 Table 1 1 Relationship of control and controlled valve ID Humidity control In the real world however it is usually not enough to manage an air conditioning system with temperature control only We need to control humidity as well A modified air conditioning system is shown in Fig 1 27 There are two sensors in this system one is to monitor temperature and another is to monitor humidity There are three control elements cooling valve heating valve and humidifying valve water spray nozzle to adjust temperature and o humidity of the ai
60. ffector 1s encouraged to be more innovative not only to the use of 2 or 3 fingers mechanical gripper Figure 4 2 Toys chassis used as a locomotive platform Design and Applied Technology Secondary 4 6 Figure 4 3 Typical 2 fingers gripper design based on linkage and driven by electric motor IHI Follow up Activities A Describe any trade off when designing an innovative end effector B If the answer to the last question is absolute why do we still need to pursue innovation Design and Applied Technology Secondary 4 6 z 1 E i a s Pee ASSESSMENT TASKS QUESTION 1 RELEVANT TOPIC BASICS OF CONTROL SYSTEMS Students are required to study the sequential operations of a washing machine at home BELT ORIVE WASHING MACHINE SHOWN Figure A 1 A cutaway view of a washing machine A Complete the Record Form and study the sequential operations of the washing cycle B Draw a flow chart block diagram to present the sequence of the washing cycle C Draw a timing diagram to represent the washing cycle D List any state variables for the washing cycle WRINKLE FREE gee Figure A 2 Control panels of washing machines Design and Applied Technology Secondary 4 6 E Design and Applied Technology Washing Machine Analysis and Record Form aw ww Student Name Machine Model Capacity if any Tasks Record the sequential actions of the washing cycle Ste
61. float operated control valve to move from fully close to fully open c Level Control Basics The above water level control case illustrates several basic and important concepts such as feedback and proportional control 1 The control valve is triggered in proportion to the error offset in the water level from the set point level A and C 2 The set point can only be achieved at certain load level 50 in this case 3 A stable control state will be achieved between points A and C proportional band Any load disturbance causing a difference in level other than that of B will be the offset Design and Applied Technology Secondary 4 6 1 6 Application of Control Systems in a Buggy The buggy is an obstacle avoiding robot comprised solely of two motors two wheels two contact bump switches and a few discrete electronic components This obstacle avoiding robot is designed to illustrate the basic knowledge of a sequential Open Loop control system This buggy is entirely an analog circuitry without any integrated circuit The block diagram illustrates how the bump sensor is connected to the motor driven wheel actuators Signal will be created when the bump sensor comes into contact with obstacles This signal is sent to the motor driver circuitry the signal amplifier for each wheel signaling the robot to back up An adjustable timer is the RC circuit that is associated with each motor driver to determine how long e
62. gle rod cylinder has a piston rod protruding from only one end of the cylinder Double rod cylinder has a common rod driven by a single piston protruding from both cylinder ends When one end retracts the other end extends Double rod cylinders are excellent for providing an adjustable stroke and additional rigidity Also a double rod with attached cam may be used to trip a limit switch Design and Applied Technology Secondary 4 6 2 4 Pneumatic Circuitry When constructing a pneumatic circuit 1t is drawn from bottom to top and from left to right The circuit layout basically consists of 4 layers The bottom layer is Air Supply Unit the second layer is Signal Level the third level is Control or Logic Level and the top level is Power level Pneumatic circuits are the assemblies of valves and a collection of elementary sub circuits to perform control functions These functions are usually consist of the followings 1 Control output actuators such as single acting double acting cylinders rotary actuator and slide unit 2 Operate another valves such as remote control and safety interlocks 3 Perform logic control functions such as AND OR and NOT D Number notation in pneumatic circuits 10 20 22 al al ga j Eri i F t k 2 1 mat yy Aly TAM s Figure 2 13 Pneumatic circuit with number notation Design and Applied Technology Secondary 4 6 Top level Working 1 01 1 02 2 01 2 02 Mark the auxi
63. gure 2 18 Delayed switching ON circuit A 3 2 NC valve is used to control another 3 2 NC valve A flow restriction valve is connected in the pilot line and is in a direction that the OFF signal is delayed When the valve 1 is pressed the air flow freely to the directional valve However when the valve 1 is released the exhaust flow is restricted Therefore the cylinder retracts after a delay Figure 2 19 Delayed switching OFF circuit Why the air pressure fluctuates within the plants Please list any 4 points 1 2 3 4 Design and Applied Technology Secondary 4 6 f Direct operation and speed control of single acting cylinder A manual operated 3 2 NC valve is used to directly control a single acting cylinder A flow restriction valve is connected in the pilot line The circuit can control the speed of the cylinder outstroke The cylinder is returned by a spring force once the valve is released No flow restriction in the return stroke Figure 2 20 Direct control of a single acting cylinder III Logic Circuits a Logic OR function for a single acting cylinder With a shuttle OR valve connected for the operation of a single acting cylinder the outstroke of the cylinder can be actuated by either of the two 3 2 valve If the shuttle valve is absent in practicality the air from one valve will escape directly through the exhaust port of another valve A flow restriction valve is added to regulate the speed of the outs
64. her O or 1 Boolean expression A general term used to describe logic functions It includes AND OR XOR etc Central Processing Unit The main processor of information in a computer This single CPU chip performs all of the logic and math operations of the PLC Digital signal Any type of input or output signal that has exactly two states on and off An example of a digital device would be a pushbutton which can either be pressed ON or released OFF Design and Applied Technology Secondary 4 6 Amplitude in volts Time in milliseconds DSP Digital Signal is concerned with the representation of the signals by a Processing sequence of numbers and the processing of these signals DSP measures or filters continuous real world analog signals usually to convert the signal from an analog to a digital form Globe Valve is a type of valve used for regulating flow in a pipeline consisting of a movable disk type element and a stationary ring seat in a generally spherical body T O Inputs and Outputs refers to the communication between an information processing system such as a computer Inputs are the signals or data received by the system and outputs are the signals or data sent from it Ladder Diagram The logic of ladder programming used to program and control a PLC The fundamental theories of ladder diagram are consistent among all manufacturers but each PLC manufacturer generally has a proprietary
65. hich is used to actuate a motorized valve allowing sewage flows into the storage tank When the level rises to a certain level the float switch FS will close This will open Cl and in turn de energize S1 to stop the sewage from flowing in FS also energizes other control relay C2 which in turn energizes a timer T1 to provide a 150s time delay for the chemical reaction to take place At the end of time delay C2 powers the solenoid S2 which actuates another motorized valve to drain the tank At the same time C2 also initiates another timer T2 to allow a delay of 90s for the drainage to complete At the end of 60s T2 opens and de energizes C2 and thus de energizes solenoid S2 and stops the out flow X1 FS C C1 C1 S1 FS T2 Co C2 C2 T1 TMR 150s T1 S2 T1 T2 TMR 60s Figure 3 12 Ladder logic diagram for fluid level control Exercise 1 Sequential control of drill automation The upper limit switch L1 normally opened contact is closed at the beginning of the drilling cycle The START normally open contact button is pressed momentarily to start the drilling cycle At the same time the output load motor M1 starts rotating the drill and the other motor Design and Applied Technology Secondary 4 6 M2 starts to descend the drill The drill M1 will stop at the lower limit switch L2 At this time the motor M2 starts to reverse and ascend the drill Upper Limit Switch Drill Motor Vertical Motor for Up and Down
66. iagram of Polar robot IV SCARA Robot Figure 4 9 Typical SCARA Robot SCARA Selective Compliance Assembly Robot Arm is a particular robot design developed in the late 1970 s in Japan It is a version of articulated robot where shoulder and elbow joints rotate about vertical axis and there is a prismatic joint at the shoulder for elevation The basic configuration of a SCARA is a four d of f robot with horizontal positioning much like a shoulder and elbow held perfectly parallel to the ground Advantages Fast cycle times and fast operation Excellent repeatability and high accuracy Relatively high payload capacity due to stiff structure in the vertical direction Extremely good maneuverability Vie within its programmable area Design and Applied Technology Secondary 4 6 o mi T T is i a Foes Drawbacks Difficult to program offline Highly complex arm in mechanical structure Figure 4 10 Work space of polar robot V Parallel Robots Figure 4 11 Delta type left triceps type mid Hexapod type right Parallel Robots Parallel robot uses three parallelograms to build a robot with three translational and one rotational degree of freedom The parallelograms ensure consistent orientation of one end of a link with respect to the other The rotational axis can only be provided by the end effector As the arms are parallel with each other the weight of load is distributed over
67. ing work pieces at an appropriate height The timing of the cylinder displacement must synchronize with the conveyor speed This is achieved after careful calculation and a number of trial runs in the production line The cylinder is fixed to an electro pneumatic slide unit that moves back and forth to serve other conveyor belts For figure 2 44 right it is a CD production line There are two cylinders in this transfer Design and Applied Technology Secondary 4 6 E mechanism One cylinder steadily pushes the CD from the conveyor belt to the material magazine Another cylinder that connects to the magazine needs to vertically move down retract progressively to allow each CD feed to the empty slot every time For the two cases above please suggest with reasons for a what types of cylinder to be used b Should air piloted or solenoid control valves be used in this application b Testing of limit switch Figure 2 45 Testing of limit switches The pneumatic systems above are used for the automatic testing and transfer mechanism The linear drive on the left is used to trip the limit switch for functional or failure test Limit switches are moved along the conveyor belt This action is tedious and requires constant magnitude of force for testing Only automation can do this job at a standard and efficient way Design and Applied Technology Secondary 4 6 c Work piece ejection in punching machine Photo sensor
68. ion of the object Roll type T joint to rotate the object about the arm axis Robot arm Figure 4 17 Atypical wrist would have 3 DOF Design and Applied Technology Secondary 4 6 1 What will be the number of mobility DOM and number of freedom DOF for a telescopic arm which has 4 steps of extension DOM DOF II Joints and links Links are considered to be rigid components of robots There will be two links connected to each joint the input link and output link The purpose of each joint is to provide controlled relative movement between the input and output link There are five types of mechanical joints in industrial robots Two of them provide the linear motion whilst the other three types provide the rotary motion They are listed below a Linear prismatic joint type L joint The relative movement between the input link and the output link is a linear sliding motion with the axes of the two links parallel to each other Input link Output link Figure 4 18 Radial sliding or translational movement Type L b Orthogonal Joint type O joint The relative movement between the input link and the output link is a linear sliding motion with the axes of the two links are perpendicular to each other Design and Applied Technology Secondary 4 6 E Input link lt gt Qutput link T lt _ gt Input link Figure 4 19 Two types of orthogonal joint are also known as Type
69. l at both ends of its stroke In Figure 2 40 the normal open a0 is closed in the initial position When the START button is pressed the timer T1 is energized The timer will in turn energize the solenoid S to extend the cylinder when the preset time is over Design and Applied Technology Secondary 4 6 al a0 Figure 2 40 Double acting cylinder with delay on timer in extend stroke In Figure 2 41 a0 is closed in the initial position as it is triggered in the retract stroke When START button is pressed T1 is energized and cylinder will extend after a certain time of delay When the cylinder rod is fully extended al as a positional switch will be triggered It will energize another delay on timer After a preset period of time the solenoid S will be energized The directional valve will move to the right and the cylinder rod will retract al a0 Figure 2 41 Double acting cylinder with delay on timer in both extend and retract stroke Design and Applied Technology Secondary 4 6 viii Sequential control of electro pneumatic system For simplicity cylinder is omitted in the illustration R1 is a normal close control relay When START button is pressed T1 is energized and the LED is on After the preset period R1 is energized by T1 in line 3 the normal close R1 become open The LED will then be turned off At the same time control relay R1 in line 4 is closed and T2 is energized After the preset duration of T2 T2
70. ler The motor is designed so that it can be held in any fixed position or being rotated bidirectionally Most stepping motors can also be spinned quickly at audio frequencies Both stepping motor and servomotor can be used for precise positioning in industrial application but they are different in working principle Servomotors require analog feedback control systems This usually involves a potentiometer to provide feedback about the rotor position External circuits are needed to drive a current through the motor proportional to the difference between the desired position set point and the actual position Stepping motors can be used in Open Loop control system This is generally adequate for systems that operate at low acceleration with static load Vorktable lt ___ _ _ _ _ es Stepping Motor M eae Cae Leadscrew a Design and Applied Technology Secondary 4 6 Vorktable lt __________ gt Input me Leadscrew Sensor Feedback Signal b Figure 3 29 a Closed loop control of servomotor b Open loop control of stepping motor I Stepping Motor Principle Roter Cup 1 Permanant Magnet Roter Cup 2 Figure 3 30 Exploded view of a typical stepping motor Stepping motor divides a revolution into discrete steps It can be held standstill in a motor position when not rotating and without the need for a positional feedback sensor The steps are created by sequentially energizing the stator electr
71. level of automation for this fire safety measure B Also other groups of students can take a look at the shopping mall nearby Study what fire safety devices and systems are being adopted A comparison can be made with those used in the school campus Prepare a brief verbal report to state the differences and give appropriate reasons C Suggest any improvement plan to upgrade the fire safety system for your school Design and Applied Technology Secondary 4 6 E Hands on Activity Controlling an Automated Traffic Lights using Programmable Logic Controller PLC North ta South Busy highway Oi Kwan Road ee ee ee Heard Road Heard Road East to West East to West E Little used road Oo Yn 2 lt xE 5z Figure 2 1 Traffic light control between Oi Kwan Road and Heard Road D Background A pair of traffic lights is set at the intersection of O1 Kwan Road and Heard Road Oi Kwan Road is the busy highway Heard Road is the little used road One traffic light is used for highway and the other is used for the little used road Three timers are used for the traffic light control 1 First timer is used to provide a short delay of 2 seconds TS_2 2 Second timer is used to provide a medium delay of 5 seconds TM_5 3 Third timer is used to provide a long delay of 10 seconds TL_10 The state variables are as follows OG for O1 Kwan Road Green OY for O1 Kwan Road Yellow AR for both roads Red
72. liary components i e flow components 3 01 3 02 restriction valve Third level ks ode less Mark the components connected to working Control components 1 e 3 2 directional valve to the components single acting cylinder 5 2 directional valve to the double acting cylinder Second level 1 2 1 4 1 6 Mark the signal components responsible for Signal DDD a eos the outstroke of cylinder 1 e 3 2 NC valve Components 1 3 1 5 1 7 Mark the signal components responsible for 23 2 92 the retraction of cylinder 1 e 3 2 NC valve Bottom level 0 1 0 2 0 3 Mark the elementary air supply unit to Air Supply pneumatic circuit 1 e AHUs Components Table 2 3 Numbering notation in pneumatic circuit ID Elementary functions a Flow amplification and remote control A large power rating cylinder is needed for most industrial application Thus a large directional valve with sufficient air capacity is required However it is dangerous to operate a large valve directly or in close proximity by an operator A small manually operated valve is used to control a large pilot operated valve at a remote distance The large capacity valve can be installed close to the cylinder Design and Applied Technology Secondary 4 6 Figure 2 14 Flow amplification and remote control of cylinder b Signal Inversion A 3 2 normally closed valve NC is connected to the 3 2 normally open valve NO When the NC valve is pressed the NC changes
73. lied Technology Secondary 4 6 c ea ni z T a ar i iy Hi Se Tbs Quizzes Chapter 4 1 What is the limitation of Gantry Robot 2 What are the differences of DOM and DOF 3 List the five types of joints used in robots 4 Suggest any specific applications of electric pneumatics and hydraulic drive systems of robots State your reasons 5 What are regarded as Intelligent Robot 6 What will the possible limitations of using surgery robot through Internet be 7 Which of the followings are regarded as robots State your reasons Design and Applied Technology Secondary 4 6 k EE ee 7 e e waar eer i z e e r o m a THEME BASED LEARNING TASK 1 Practical Design Appreciation Case Study of Intelligent Fire Alarm System Figure 1 1 High rise commercial building on fire D Background Most of the Hong Kong people may remember the tragedy of Grade 5 fire in Garley Commercial Building in 1996 The fire had caused a great causality and alerted people to the safety of public premises After this tragedy there is a law stating that all the commercial buildings which were built before 1987 are enforced to install Intelligent Fire Alarm system to safeguard the people from severe causality by early warning and to extinguish the flame automatically and intelligently ID What is Automatic Fire Alarm AFA or Intelligent Fire Alarm system IFA 1 Conventional system
74. low The 16F84 provides an internal clock pulse The resonator is used to regulate the speed of the clock pulse 4MHz Pin 4 reset and must be connected via a 4k7 resistor to V Design and Applied Technology Secondary 4 6 EE mi AN Tmi eelo E S e o II Interfacing Input and Output Devices a Digital input sensors Common input devices are Micro Switches Reed Switches Tilt Switches and Push Switches They can all be directly connected to any input pin of PIC 16F84 Care should be taken to add 10k resistor to prevent short circuit and the 1k resistor to protect the input pin The digital input will trigger from logic O to logic 1 when the switch is pressed Limit switch Reed Switch Tilt Switches Toggle and Push Switches Figure 3 18 Common digital input device to PIC V Figure 3 19 Circuit diagram for connecting input device b Analogue input sensors Although the 16F84 does not have analogue input pins an analogue sensor can also be used by connecting them via a potential divider and a transistor interfacing circuit A phototransistor can be used to switch the input directly Design and Applied Technology Secondary 4 6 c 1014 aie m on Figure 3 20 Interfacing circuit for analogue photo sensors c Output devices Buzzer Light bulb Solenoid Figure 3 21 Common output devices Common output devices are LED 7 segment display Piezo sounder speaker
75. movement Figure 2 36 Slide Unit v Control of rotary actuator The rotary actuator has a built in positional switch at the limit When the START pb1 button is pressed it energizes solenoid S the rotary actuator turns from left to right and is held in that position Once the START button is released the triggered positional switch al energizes the solenoid S immediately and the rotary actuator returns to the left automatically Ls Design and Applied Technology Secondary 4 6 c ae oe ow 1 ii cam Figure 2 37 Automatic return of rotary actuator Figure 2 38 Rotary Actuator vi Reciprocating movement of linear drive Slide actuator usually has positional switches at the ends of movement limit When the START button is pressed and held in this position the side will move back and forth because of the alternate switching of positional switches ao and al ao and al are used for energizing the S and S solenoids for controlling the forward and backward movements respectively Design and Applied Technology Secondary 4 6 Figure 2 39 Reciprocating movement of Linear drive vii Time delay circuit A double acting cylinder can be reciprocating The time of action can be adjusted by delay on timer In case of power failure the cylinder will keep on moving to the end and held in this position until the power resumes The double acting cylinder has two built in positional switches a0 and a
76. nel The PLC can be reprogrammed Conventional controls must be rewired PLCs take less floor space than relay control panel Maintenance of PLC is easier and reliability is greater The PLC can be connected to digital systems more easily than relays Design and Applied Technology Secondary 4 6 aaa z 1 in i a Fo Below is the comparison between Relays logic control and PLC Large complicated systems that take up One PLC can control a large system Takes up less a lot of space floor space than a relay based system Hard wired devices are used to Only the input and output devices are hard wired configure relay ladder The inner configuration of PLC is solid state Difficult to modify or update a program By the programming software it becomes simple to write a new program or modify an existing one and download it into the PLC Limited service of life for mechanical The PLC 1s a solid state device which has the devices characteristic of long service life and little maintenance Require separate hard wired timers and Counters and timers are internal solid state devices counters Table 3 Comparison between Relays and PLCs lt D rection of force when coil is energized Figure 3 5 Working principle of solenoid A solenoid is an electromagnetic actuator that can be used to open and close a valve electrical contact or other mechanical devices The solenoid operates by means o
77. obile Industries In the automobile industry robotic arms are used in diverse manufacturing processes including assembly spot welding arc welding part transfer laser processing cutting grinding polishing deburring testing and painting Robots have been proved to help automakers to be more agile flexible and to reduce production lead times i Figure 4 38 Industrial robot in manufacturing plant 2 g Design and Applied Technology Secondary 4 6 mE a i T k Te a PR IIT Electronics Semi Conductor Application of clean room Robots in semiconductor manufacturing results in the reduction of scraps from broken chips The avoidance of contamination and the Savings in scraps from dropped wafers in machine loading and unloading can be a major savings Typically clean Room robots are used in machine loading unloading and parts transfer in the semiconductor industry Assembly packaging and testing processes are other a Figure 4 39 Industrial robot in manufacturing plant application areas for clean room robots IV Food amp Beverage Food and beverage applications represent a small fraction of industrial robotics application However it is widely recognized as one of the fastest growing segments like automotive industry The vast majority of robots in the Food amp Beverage industry are found in the packaging area High speed material handling robotic arms and vision guided systems
78. of this form of programming are Reduced down time for programming Programming tools make programming off line thus can reduce product lead time Work cell design and allows process optimization Design and Applied Technology Secondary 4 6 However because off line programming is not accurate it requires adjustment interactively on the factory floor until all positions and orientations are correct before the robot can run in the production Figure 4 36 Teach pedant for teach method of robot programming Design and Applied Technology Secondary 4 6 c a oe m E g m T a T Ei C i Tr Tbs 4 5 Applications of Robots Robots offer some obvious advantages in terms of speed accuracy and productivity as they can run 24 7 repeating jobs which would be tedious to operators and without human error Below are some common applications which can provide a robotic solution to increase productivity It may also be possible to integrate more than one application of robots into a system to suit variety of needs ID Medical Robots Robots are used in medical fields because they are highly precision machines By tooling the end effector with surgical instruments they used to perform delicate surgery These machines still require a human surgeon to operate and input instructions Remote control though Internet and voice activation are going to be used to control these surgical robots II Robots in Autom
79. omagnets causing the rotor to line up each time with the resultant magnetic field The shaded area in the diagram indicates the position of the energized magnets and the wedge indicates the angle rotated according to the resultant magnetic field ROTATION OF A STEPPER MOTOR OOo ROTOR STATOR ELECTROMAGNETS Figure 3 31 Alternate Bp for the rotation of rotor lt lt Design and Applied Technology Secondary 4 6 Eee EEE ir i a z ie a Se Se i EE a Stepping Motors can achieve a short and precise movement with quick acceleration No brush maintenance is required This greatly reduces its cost compared with any other brushed motors However the rapid energizing of electromagnets is inefficient at high speed condition Any excessive loads can cause the motor to skip its sequence and stall in the worst case H e H L e H T Control of stepping motor by PIC Unipolar stepping motors have four coils which must be switched on and off in the correct sequence to make the motor turn as shown in previous section The table below shows the correct sequence Table 3 5 The ULN 2003A is a Darlington driver IC used to drive the stepping motor The PIC 6V and stepping motor 12V have different supply voltages but they must be common to ground OV Figure 3 32 Control circuitry for stepping motor by PIC 16F84 n Design and Applied Technology Secondary 4 6 SS II Advantages of Servomotors Fig
80. on Elongated circle Terminator Represent the start or end of a process Connector Rectangles Represent process and action to be taken Input Output Diamond Decision Represent what decisions that must be made Table 1 Main symbols for Flow diagram og Design and Applied Technology Secondary 4 6 Steps of constructing a simple flow diagram 1 Start the flow chart by drawing an elongated circle terminator and label it with Start 2 Draw a rectangle or diamond to represent the first process or action Write the key word of action or question down and then draw an arrow connector from the Start to this shape 3 Represent the actions and decisions of the whole process and in the order of their occurrence Using arrows connectors to indicate the flow of the process 4 Draw a diamond to indicate where a decision needs to be made using arrows leaving out of the diamond to indicate the possible outcomes 5 Use an elongated circle labeled with Finish to indicate the end of the process 6 Review the flow chart from step to step to see if the flow diagram represents the sequence of actions and decisions involved in the process and in a good order i Close Doo Read sensor Door close Read sensor Vater full lt gt i f Figure 1 11 Fead timer s Time up Yes Flow diagram for a classical washing machine The operation of washing machine may vary acco
81. only used Figure 2 6a Structure and symbol of a combined APU What are the advantages of a combined APU Design and Applied Technology Secondary 4 6 2 3 Understanding Pneumatic Components 2 4 Figure 2 6b Position or box details When looking at the box in details the number of ports is determined by the number of end points in a given box and only counted in one box per symbol In this example there is a total of 5 ports In practice the exhaust port sometimes goes directly to atmosphere with no physical port exists It can be noted that the actual ports line will extend beyond the box while the exhaust port is blocked with a symbol T D Directional Control Valves The function of a directional valve is used to determine the direction of compressed air flow through its ports by changing its internal connections The descriptions of directional valves are described by the following parameters l 2 3 4 The number of ports The number of switching positions The normal non operated initial position The method of operation or actuation Switching function Major application 2 2 ON OFF without Pneumatic tools exhaust 3 2 Normally closed NC Single acting cylinders push type Design and Applied Technology Secondary 4 6 Directional Valves symbols Switching function Major application 3 2 Normally open NO Single acting cylinders a pull type 4 2 Switching between Dou
82. onsideration than power or controllability Figure 4 29 Stepping motor i DC Servos For the early electric robots the DC servo drive was used extensively It provides good power output with a high degree of speed and position control 1 AC Servos In recent years the AC servo has taken over from the DC servo as the standard drive These modern motors give higher power output and are almost silent in operation They have no brushes in structure They are very reliable and require almost no maintenance in operation Figure 4 30 AC Servos with controller Design and Applied Technology Secondary 4 6 iv Solenoids Actuator A major advantage of solenoid actuator is their quick operation Also they are much easier to install than pneumatic or hydraulic actuators However solenoid can only have fully open extend or closed retract function They cannot bear much loading IN dicel Fell elie Coli A a Ap Ap a A a a a Sel Mla MIU OP ee ee ee we ee ee ee ee ee ee a Current Induced Field Inside Coil gt ce DAAA AA AA DANAN ay ani SH LELELT LEELA alalatai atata a hk pe ee ee we ee ee 6 Current Figure 4 31 Operation of solenoid actuator b Pneumatic Robots that use compressed air may come in a wide variety of sizes Most of the simple pick and place arms are driven by pneumatics This makes the system low in cost However it has the disadvantage of being diffic
83. ontal rung Normally closed contacts are shown by a diagonal line across a normally open contact Both types of contacts represent ON OFF inputs to the ladder logic These inputs can be limit switches relays photo detectors and any binary contact devices The output loads can be represented by circles in the rung The output loads are motors lights alarms solenoids and any other electrical components The timers and counters are symbolized by squares on the right of a rung When the input signal is received the timer waits the specified delay time before switching on the output signal The timer is reset by turning off the input signal Counters require two inputs The first is a pulse train that is counted by the counter The second is a signal to reset the counter and restart the counting procedure Resetting the counter means zeroing the count for a count up device and resetting the starting value for a count down device The accumulated count can be stored in the flag memory for use if required by the application Design and Applied Technology Secondary 4 6 Normally open contacts switch relay other ON OFF devices Normally closed contacts H switch relay other ON OFF devices Output loads gt motor lamp Solenoid alarm etc o Counter Table 3 1 Symbols of common components in ladder diagram Design and Applied Technology Secondary 4 6 amp K IHI Ladder control logic In
84. onveyor Then the cycle starts again The ejecting device is pushed by a single acting cylinder that is controlled by a solenoid valve Single acting cylinder Ejecting Photo sensor device vY yy On ht ws Figure A 10 Schematic diagram of the system 1 Construct a ladder diagram and program it to PLC to make it work lt lt Design and Applied Technology Secondary 4 6 QUESTION 10 RELEVANT TOPIC PROGRAMMABLE LOGIC CONTROLLER A machine is switched on by pressing either A or B push button A safety guard D is in place with a limit switch D triggered in the closed position In addition there is a proximity switch C to detect if anyone is standing inside the dangerous zone All the switches are normally open contacts and the machine will not start when they remain open ud d LO D j Figure A 11 Schematic diagram of the system 1 Draw a ladder diagram for the system 2 Write a Boolean expression for the system 3 Construct a truth table for all possibilities Design and Applied Technology Secondary 4 6 USEFUL WEB SITES TITLE URL Explanatory Note Traffic light control http home cogeco ca rpaisley4 20step ht 20 sequential circuits circuit ml Traffic Information and http www ics uci edu mghodrat ics151 h Traffic light Lab Sheet Computer Science w prob8 final html Sequential Circuit http www cs swarthmore edu mstone sch Dynamic Traffic Controller De
85. oop control system Taking a furnace temperature control as an example for the Open Loop control system B Design and Applied Technology Secondary 4 6 Heating Coil Furnance Figure 1 2 Open Loop control system of Furnace Temperature Controlled value In this case the controlled element is the furnace or more specifically referring to the heating coil U is the control value that determines the power voltage current to the heating element The furnace temperature c is the controlled value The SW is the switch that is controlled by an electromechanical relay The switch will be turned ON or OFF in a pattern according to the timed sequence The timed sequence is used to maintain the temperature inside the furnace within a controllable range The Disturbance in this case is the frequency at which the furnace door is opened If the door is opened so often the furnace temperature will drop and the controlled value c becomes deviated lower from the desired value However the SW in an Open Loop control system will not be closed to give power to the heating coil to restore the temperature The ON OFF time of this switch has been preset and will not be changed with the furnace temperature in this case In an Open Loop control system the controlled value will not influence the value of input signal Therefore there is no need to measure the furnace temperature controlled value The control system becomes simple but the ac
86. opens and de energize R1 in line 1 R1 in line 1 backs to its NC state and the LED turns on again This sequential operation repeats itself Start Take a game kiosk in an amusement park as an example a pneumatic 2 fingers gripper is installed in a double acting slide The actions are as follow A 2 fingers gripper is open in initial position The gripper is attached to the double acting slide The gripper and the slide are driven by pneumatic but controlled by PLC The slide moves to the right from left when the START button is pressed When it moves to the preset position the gripper will close and try to pick up a toy The slide will move to the initial position with the gripped closed At the end of the return stroke the gripper finger will open and drop the toy Design and Applied Technology Secondary 4 6 uk For simplicity the downward movement of gripper for picking up a toy is omitted a0 al bO and bl are positional switches for slide and gripper respectively bo is closed in its initial state and the gripper is in open position When the START button is pressed A is energized and the slide extends to the left At the end of extend stroke al is triggered and energizes the solenoid B With the energizing of B the 2 fingers gripper closes When b1 is triggered by closing the gripper it in turn energizes A The slide is then retracted After it is fully retracted a0 is closed and in turn energizes B to open the 2 finger
87. other than those listed in the Acknowledgements section may be used freely for non profit making educational purposes only In all cases proper acknowledgements should be made Otherwise all rights are reserved and no part of these materials may be reproduced stored in a retrieval system or transmitted in any form or by any means without the prior permission of the Education Bureau of the Government of the Hong Kong Special Administrative Region A set of curriculum resource materials is developed by the Technology Education Section of Curriculum Development Institute Education Bureau for the implementation of the Design and Applied Technology Secondary 4 6 curriculum in schools The aim of the resource materials is to provide information on the Compulsory and Elective Part of the DAT Secondary 4 6 to support the implementation of the curriculum The resource materials consist of teacher s guides and student s learning resource materials of each Strand and Module of the DAT Secondary 4 6 arranged in eight folders All comments and suggestions related to the resource materials may be sent to Chief Curriculum Development Officer Technology Education Technology Education Section Curriculum Development Institute Education Bureau Room W101 West Block 19 Suffolk Road Kowloon Tong Hong Kong Introduction Chapter 1 Basics of Control Systems 1 1 1 Open Loop Closed Loop and Sequential Control Systems 2 1 2 System and
88. ots by Robot Institute of America seems to be focused on industrial application robots nowadays are quite popular for leisure and some of them are for innovative purposes such as humanoid and military purpose Design and Applied Technology Secondary 4 6 Figure 4 2 Examples of different types of robotic applications Therefore robot can also be defined as Human made semi or fully autonomous self controlled object or cooperating objects with common objectives with intelligence which is programmable Please state your reasons for the following questions 1 Are movable machines such as cars Robot 2 Are computers Robot Design and Applied Technology Secondary 4 6 SS 4 2 Mechanical Structure of Industrial Robotic Arms Since 80 s of last century there was a rapid growth in the application of robotic arms in industry especially in the car manufacturing and welding process Identifying different types of mechanical robotic structures seem to be an effective and visual way of classifying robots and are a good starting point for learning robotics 1 Cartesian Coordinate Robot Figure 4 3 Typical Cartesian Robot Cartesian robot is formed by 3 prismatic joints which axes are coincident with the X Y and Z planes A Cartesian Coordinate robot with the horizontal member supported at both ends is sometimes called Gantry robot It can be quite large in size Cartesian robot uses 3 perpendicular t
89. ounters and other discrete logic gates to perform sequential control It is because they are all hard wired for specific purpose or controlling specific machines These types of dedicated systems are of no flexibility Therefore digital devices which can be programmed to do a variety of logical functions play an important part in our daily industrial automation The Programmable Logic Controller PLC was invented in 1960s to replace the sequential relay circuits that were commonly used in machine control PLC is a solid state electronic device that controls the operation of a machine It uses logic functions which can be programmed into its built in memory via software This program can be changed or modified when necessary II Basic component of the PLC A typical Programmable Logic Controller contains the following major components Input module Output module Processor Memory Design and Applied Technology Secondary 4 6 Power supply Programming device A schematic diagram is shown below Input module Output module Interface Processor L _ s Handheld Programmer Figure 3 2 Schematic diagram of the basic Programmable Logic Controller a Inputs devices The inputs to the controller are signals from limit switches pushbuttons proximity sensors and any other digital binary or analog continuous devices b Output devices The outputs from the controller are on off signals
90. position Water in A Offset i B Value V Figure 1 20 Valve fully closed With the globe valve V is fully closed the level of water in the tank rises to point A The float operated valve cuts off the water supply The system is still under control and stable but the water level is above level B The difference between level B set point and the actual level A is the proportional band of the control system If globe valve V is half open to give 50 load the water level in the tank will return to the desired level point B b When the loading is 100 Fully open Full open position Water in A B Deviation G Water out Value V Figure 1 21 Valve fully open The globe valve V is fully opened 100 load The float operated valve will be dropped to widely open the inlet valve This allows a higher flow rate of water to meet the increased demand from the discharge pipe When it reaches level C enough water will be entering to meet the discharged needs The water level will be maintained at point C lt lt a Design and Applied Technology Secondary 4 6 Proportional band Xp Figure 1 22 Proportional band The system in this case is still regarded as under control and stable but there is an offset that is the deviation in level between points B and C The difference in levels between points A and C is known as the Proportional Band It is the change in level for the
91. ps No Descriptions N A e g Close the door e g Turn on the power N A e g Turning the control dial to start position e g Water inlet stops e g Drum turn at low speed CW e g Inlet of water automatically 006 Design and Applied Technology Secondary 4 6 QUESTION 2 RELEVANT TOPIC PNEUMATICS D Situation Packs of cut foods are accumulating at the end of conveyor These parts need to be transferred to other conveyor for quality inspection An operator needs to activate a transfer device to remove these accumulated packs This transfer device is powered by a pneumatic cylinder Figure A 3 A conveyor belt ID Control Task To design and assemble a circuit that can extend and retract a single acting spring return cylinder by an operator IID Circuit Problem Using the given components and layout design a schematic circuit which will operate a spring return cylinder with a two position spring return three way valve l Design and draw the schematic circuit diagram 2 Connect components according to the schematic diagram 3 Operate and explain to teacher Hoy AS Design and Applied Technology Secondary 4 6 IV Hints 3 2 Normally Close NC x 1 single acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration Design and Applied Technology Secondary 4 6 a 1 E i Baen oe QUESTION 3 R
92. put contacts can be arranged to conduct logic functions in the ladder diagram X1 AND X2 X1 X1 X2 X1 OR X2 X1 Y En X1 X2 X2 Design and Applied Technology Secondary 4 6 NOT Y C1 X1 X1 AND X2 X1 Y _ aam X1 X2 X2 Design and Applied Technology Secondary 4 6 XI OR X2 X1 X2 Figure 3 6 Ladder logic diagram Design and Applied Technology Secondary 4 6 E 3 3 Application of Ladder Logic Diagram D Starting and stopping an electric motor Stop l a l Figure 3 7 Motor ON OFF control Industrial 3 phase motor Pushbutton is used for starting and stopping an electric motor one for START and the other for STOP When the Start button is pressed momentarily by a human operator power is supplied and maintained for the motor until the STOP button is pressed The operation logic is as follow START STOP MOTOR i e pou fe poe ft e Table 3 3 Truth table of Motor ON OFF control X1 and X2 are input contacts for START and STOP respectively and K1 is the output load to represent MOTOR Y serves as a latch function to maintain the power to motor when the START button is released Design and Applied Technology Secondary 4 6 E Start Stop K1 K1 Figure 3 8 Ladder diagram of motor ON OFF control For a better understanding on the differences between hard wired logic control and programmable control a logic circuit design for the same motor
93. r is in a retracted position when the spring takes the control of that valve Once the valve is pressed momentarily the cylinders will outstroke The speed of both directions can be regulated independently by two flow restriction valve Figure 2 24 Direct control of a double acting cylinder e Bi stable control of a double acting cylinder Two 3 2 NC valves are used for the control of 5 2 valve and in turn control the double acting cylinder When valve 1 is pressed momentarily the cylinder will extend and hold its position Design and Applied Technology Secondary 4 6 even the valve is released The cylinder will retract until the valve 2 is pressed momentarily The speed of both directions can be regulated by two flow restriction valves This circuit is also known as a memory function T IN TS TS Figure 2 25 Memory function of double acting cylinder control f Automatic return of double acting cylinder One of the two manual operated 3 2 NC valves is replaced by a roller actuated valve and is put to the position at the end of the cylinder outstroke When the valve 1 is pressed momentarily the cylinder extends When the cylinder rod trips the valve 2 at the end of outstroke the cylinder will retract automatically a SF Valve 2 fe TN oO LN Figure 2 26 Automatic control of a double acting cylinder Design and Applied Technology Secondary 4 6 1 What will happen in the above circuit if valve 1 is
94. r supply Design and Applied Technology Secondary 4 6 Temperature SENSOY Humidifyine Valve Humidity SENnSor Figure 1 27 Block diagram of temperature and humidity control system The humidity sensor provides the feedback to the Closed Loop control system If humidity measured HUm is lower than the set point HUs open humidifying valve HUV fully to restore the humidity If humidity measured is HUm higher than the set point HUs close humidifying valve HUv fully to reduce the humidity AU lt HU HU High 1 AU gt HU HU Low 0 Table 1 2 Relationship of control and controlled valve 1 Suggest any disadvantage of this type of temperature and humidity control 2 Suggest any method which can improve this control system QUIZZES CHAPTER 1 1 Why automated control systems are so important in industry NO State the differences between Open Loop and Closed Loop control system oS Give one daily example in Open Loop control system and Closed Loop control system Draw the block diagrams for the examples Suggest and name the types of sensors used in a washing machine What is the meaning of set point What is the meaning of proportional band What is the meaning of error signal What is the meaning of offset O WO Nu nu A Describe how an RC circuit functions as a timer 10 What sensors can be used as a bump switch for an obstacle avoiding buggy Design and Applie
95. ranslational slides along the x y z axes and it 1s also called the xyz robot or rectilinear robot It has a rectangular work volume The joint types are obviously LLL Figure 4 4 Schematics diagram of Cartesian robots Design and Applied Technology Secondary 4 6 Advantages The rigid structure can support large robots and heavy payloads Easily controlled programmed movements High accuracy Accuracy speed and payload capacity are constant over entire working range Control system simplicity Familiar X Y Z coordinates can be easily understood Inherently stiff structure Large area coverage Structural simplicity offering good reliability Easy to expand in modular fashion Drawbacks The workspace is limited within the robot size A big robot will require a very large area if it works for a large work piece such as a car Work piece underneath is out of reach by this type of robot Prismatic joints are easily contaminated with dust especially in folds around the flexible bellows ID Cylindrical Robot a Figure 4 5 Typical Cylindrical Robot Cylindrical robot is able to rotate along its main axis forming a cylindrical work space It has two linear axes and one rotary axis around its base Design and Applied Technology Secondary 4 6 E Advantages Base rotation gives high speeds Can reach under objects compared with Cartesian robots Easily controlled programm
96. rding to type price and country of origin Some washing machine controls may be highly sophisticated and use artificial intelligence to improve washing efficiency water consumption acoustic noise electromagnetic interference EMI and the power consumption The example above is the flow diagram for a classical washing machine human operation is included in this case 2 Design and Applied Technology Secondary 4 6 1 4 Operation of Traffic Lights Traffic lights become an integral part of a modernized city The proper operation of traffic lights can smooth the flowing traffic and boost the economic growth Proper operation means precise timing cycling through the states correctly and responding to outside inputs like Walk signals Traffic lights are at least come in pairs and need to be synchronized for proper operation Below is a typical 3 lamp 4 state traffic light signals Se EE Figure 1 12 A typical 3 lamps traffic light sequence When considering the design and implementation of traffic light control at an intersection it is typically between a busy Main road and a less busy Side road Both streets have the ordinary Red Amber Green signal lights The intersection is sometimes fitted with a sensor to detect the vehicle for the side road traffic condition and with a walk request button controlled by pedestrians A single 3 lamp traffic light has three states Red Yellow and Green which are also the ou
97. re is a disturbance in loading servos can make corrections faster Design and Applied Technology Secondary 4 6 2 AY i e Motor speed voltage and current Speed is directly proportional to the amount of voltage applied the more voltage the faster the motor will operate The torque delivered is directly proportional to the current Just like a conventional DC motor the more the current the more the torque to be delivered Both characteristics are very predicable thus servos become easy to apply in any application Can you suggest one application of I servomotor and II stepping motor with an appropriate reason Design and Applied Technology Secondary 4 6 E Quizzes Chapter 3 Name the 6 major components of a typical PLC What are the three main steps of each scan cycle performed by a PLC What are the drawbacks of using electromechanical relays in automated control Give a brief description of what a PLC is Can PLC be regarded as a computer If not why What is the history of PLCs Why PLCs are more commonly used for industrial applications than computers Convert the following logic diagram into a ladder diagram and write a Boolean expression for it et a ee oe a a A B 9 What are the usage of Tilt switch and Reed switch 10 List three advantages for stepping motors and servomotors Design and Applied Technology Secondary 4 6 CHAPTER 4 ROBOTICS This chapter contains topics on
98. referring to gauge pressure GA or psig As the pressure is always above atmospheric pressure it is also regarded as over pressure For gauge pressure in pneumatics application the atmospheric pressure is referenced as zero pressure Design and Applied Technology Secondary 4 6 c Figure 2 2 Gauge Pressure dial In a full vacuum scenario pressure can be expressed as absolute pressure Pa 4gs or psia In vacuum technology a pressure is always below atmospheric and in a state of under pressure The actual atmospheric pressure is 1 013 bars Disregarding the decimals the standard atmospheric temperature is referenced to bar II Pressure and Flow The most important relationship in pneumatics is pressure and flow If there is no flow pressure over the entire system will be the same at every point However once there is a flow from one point to another pressure will be decreasing along the path This difference in pressure is called pressure drop Pressure drop depends on three factors 1 Initial pressure 2 Volume of flow 3 Flow resistance lt lt Design and Applied Technology Secondary 4 6 a 2 2 Pneumatics Components and Symbols I Air Handling Units AHUs a Why needs Air Handling Unit All atmospheric air carries dust and moisture After compression moisture will condense in the air Dust and moisture combine with other contaminants such as pipe scales and worn sealing materials will cause detrimental
99. rough radio frequency or bys wired real time remote control according to the competency of students lt gt Design and Applied Technology Secondary 4 6 ee oe a o _ T F m m a T 1 Tia Mars Exploration Design an Innovative End effector for Mars Lander D Background Figure 4 1 MARS Lander used in sample extraction on Mars surface Though Mars exploration seems to be a far reaching issue to a hassle and financial city like Hong Kong the patented Space Plier that was designed and developed by a group of engineers and scientists from Hong Kong Polytechnics University had been used by Europe NASA in the Mars Exploration Program in 1995 and 2003 respectively The Space Plier is used to pick up soil samples of MARS surface It has a small drilling bit to dig a hole on the surface and has a little pliers like a chopstick to collect the soil sample out of the drilled hole I Task Students are provided with a remote controlled locomotive either wheel driven or terrace type common mechanical toys can be considered The locomotive is a platform on which students are expected to design and make a special end effector to simulate the tasks in MARS Teacher can provide a Mars like field to promote the students motivation The end effector can be driven by whatever the means students can think of maybe powered by water or air syringes elastic bands DC motors or any other means The design of this end e
100. s and emphasizing on internal structure The system approach means in engineering sense integrating analysis and synthesis Let s take automobile as an example When driving a car in a normal situation it works as a whole However when it is tugged to a garage it is obviously a system composed of many inter related subsystems such as transmission ignition steering braking lubricating suspension and more Each of these subsystems is in turn made up of many parts such as the clutch stick shift and gear box for transmission The gear box again in turn consists of many components such as gear shaft and a lot of nuts and bolts In engineering system approach when engineers want to design a car they do not start with a bunch of bolts and nuts They start with a conception of the intended car as a whole with a set of functional requirements Then they decompose the concept car into a number of functional sub systems most importantly with proper interface design for assembly in later stages For example there are sub systems for Power and the subsystem for Transmission Interfacing is the connection of two sub systems to work together Then engineers further analyze the sub systems into their inter related components Finally they come to the specifications of manufacturing a single part in details under the component level After thousands of individual parts are made they will be tested brought together and assembled into a number
101. s gripper Start 1 A A RE al B 2 f AS 3 A ONO 4 A al a0 bi b0 Figure 2 43 Sequential controls of pneumatic slide and gripper Design and Applied Technology Secondary 4 6 2 5 Electro pneumatic Systems This section introduces the use of electro pneumatics parts that can be controlled by Programmable Logic Controller PLCs This will also be discussed in Chapter 3 When the electro pneumatic solenoid receives an electrical signal from the electronic controller which can be either PC or PLC Practically the input signal can be accepted in form of 0 20mA DC or 0 10V DC With this input the unit regulates the high pressure air supply to the final control element such as control valve to give a corresponding displacement I Applications of pneumatic electro pneumatic systems Pneumatic and Electro pneumatic control systems are widely adopted in process control and the production line automation in manufacturing industry a Materials Transfer 4 4 a 4 4 4 d 4 4 d 4 Moving downward Accurately to stack up the parts accurately to collect the parts Figure 2 44 Examples of material transfer application In Figure 2 44 left a tailor made container is attached to the end of the cylinder rod to collect the pre cut work pieces that are coming progressively from the conveyor belt As the work pieces fill up the container the cylinder has to move down extend progressively to collect the new com
102. sign ool cs cs24 web lab3 Electrical Training http www tpub com content neets 14187 css Open loop control Series 14187 _92 htm O Reilly Network http www oreillynet com pub a network sy Closed Loop control nd 2003 08 05 closed_loop html http www delphion com details pn10 US Delphion Integrated Washing machine patent article 03264544 LG Washing Machine http www lgwasherdryer com pdf 3431_m_ LG Washing Machine User Manual User Manual anual pdf http www festo didactic com int en learn1 View tL Festo Pneumatics Learning System ng systems equipment sets 562 564 semi ro tary drive size 16 184 htm Application Note air htm Control Review Tool asp http www clippard com downloads genera Introduction to pneumatics and Fluid Power Education Foundation I PDF Documents Intro_to_Pneumatics pdf Pneumatics Circuit problem for FPEF trainer 101 Basic Series http www eatonelectrical com html 101bas Module 24 Programmable Logic Electrical ics Modules Module24 pdtf Controller Introduction to PLC http www idc online com technical_refere programming and nces pdfs instrumentation Intro_to_PLC_20 implementation Pro pdt from Relay logic to PLC logic Pneumatic http www allair com pdf mead_pneumatic Application and handbook pdtf Reference Handbook Loop Technology UK http www looptechnology com index as Industrial Automation Technology Machine Vision System
103. ssemble an AND logic circuit to control a single acting spring return cylinder II Circuit Problem Using the given components and layout design a schematic circuit which will only operate the cylinder when the three valves are all simultaneously operated implying the safety precautions are all in effect 1 Design and draw the schematic circuit diagram 2 Connect components in according to the schematic diagram 3 Operate and explain to teacher Design and Applied Technology Secondary 4 6 IV Hints 3 2 Normally Close NC x 3 AND valve air pilot x 2 Single acting cylinder x 1 Note If there is no pneumatic learning training kit magnetic symbols and white board can be used for demonstration Design and Applied Technology Secondary 4 6 a 7 1 1 ia Te b QUESTION 5 RELEVANT TOPIC PNEUMATICS 1 Situation Semi finished parts are accumulating on a conveyor belt and waiting to be released and transferred to the next stage for wrapping Operators at different points can turn on the gate release mechanism to let the trays moving into the packaging unit Figure A 6 A conveyor for food industry ID Control Task To design and assemble an OR logic circuit to actuate a single acting spring return cylinder IID Circuit Problem Using the given components and layout design a schematic circuit which will operate a spring return cylinder from any one of three identical valves 1
104. t Electrical circuit diagram right Electro pneumatic circuit of latch relay IV Electro pneumatic a Solenoid valve For electro pneumatic applications there are two types of solenoid valve double solenoid and single solenoid For double solenoid valve the cylinder will extend 1f one of the solenoid is energized The extended cylinder will hold its position by either leaving the solenoid in the energized state or un energized state When energizing the opposite solenoid the cylinder will retract For a single solenoid valve the valve will shift back to its original position and the cylinder will retract when power is turned off Figure 2 30 left single solenoid valve right double solenoid valve Design and Applied Technology Secondary 4 6 b Major symbols for Electro pneumatic circuit N O spring return 2 points contact EE N C spring return 2 points contact N O roller operated spring return contact a N C roller operated spring return contact C N O Solenoid controlled proximity contact T 2 me a Table 2 4 ISO symbols of Electro pneumatic circuit c Electro pneumatic circuit i Manual control Manual control push button of a double acting cylinder can be done by using solenoid valves and a 5 2 valve respectively When pressing the pushbutton it energizes the solenoid to extend the cylinder Once the pushbutton is released the cylinder retracts by the spring force
105. t work envelope relative to their size Extremely good working ability Ability to reach over obstructions Easy access to front sides rear and overhead Large reach for small floor area Slim design allowing easy integration into restricted workplace layouts Fast operation due to rotary joints Ability to traverse complex continuous paths Drawbacks Not easy to control The motion of robot from one point to another can be difficult to visualize as the robot will move each joint through the minimum angle required Accuracy is decreased due to the accumulation of joint errors Control of motion is difficult due to the gravitational loading Resolution control varies and has less increment at full reach Figure 4 14 Schematic diagram of Articulated Robots 1 Why Articulated robots are commonly used in welding process in industrial application Please state your reasons 2 What are the limitations of Cartesian robots used in this application Design and Applied Technology Secondary 4 6 4 3 Robot Anatomy Robot Anatomy is to examine matters including types sizes of joints links and any other aspects of a robot I Degree of Mobility Degree of Freedom A joint of an industrial robotic arm especially the articulated robot 1s quite similar to a human arm It provides relative motion or links between two parts of the robot Each link joint pair is known as Degrees of Mobility DOM Degrees of Freedom DOF
106. the base to the end effector 5 joints types can be labeled with L O R T and V for the linear orthogonal rotational twisting and revolving joints respectively They are commonly used in joint notation system to describe a robotic arm Design and Applied Technology Secondary 4 6 We can use TRR as an example to explain the joint notation scheme of TRL A TRR represents a 6 DOF robot where 1 the Body and Arm assembly is made up of 3 joints a twisting joint Type T at the Base rotational joint Type R at Joint 1 and linear joint Type R at Joint 2 2 the Wrist assembly consists of 3 joints a twisting joint Type T for Rolling rotational joint Type R for Pitching and rotational joint Type R for yawing A colon is used to denote the Body and Arm assembly from the Wrist assembly Adopting this joint notation system to identify the 6 configurations of robots is listed below Robot Type Joint Notation Scheme Cartesian Robot LOO Cylindrical Robot TLO Polar Robot TRL SCARA Robot VRO Parallel Robot TRL Articulated Robot TRR Table 4 1 Joint types for different robot configurations V End Effector A device which is attached to the wrist of the robotic arm to perform specific tasks such as grippers for material transfer welding torches for joining and spray guns for surface finishing etc They are mainly divided into two categories by functions Grippers To hold and move objects Tools To perform work on a
107. tputs A single input for the traffic light is values O for no change and 1 for state change This input is connected to the output of a countdown timer which outputs a value of 1 when it counts down to zero Thus for a single light we can draw the state transition diagram as Oy tN 0 N17 Figure 1 13 A State diagram of traffic signal sequence a single light Ls below Design and Applied Technology Secondary 4 6 c ee 7 aaeE u ler i EE z mige a a EE a D Three important parts of Traffic Light Control System Traffic light unit Figure 1 14 A Block Diagram of Typical Traffic Control system The first part is the controller which represents the brain of a traffic system It consists of a computer or a programmable logic controller PLC that controls the selection and timing of traffic lights in accordance to the varying demands of traffic loads The second part is the traffic light unit or signal face Signal faces are used to provide controlling signals to the traffic in a single direction It consists of 3 signal states and operates in synchronization with the sequence of other traffic lights The lamps are conventionally comprised of red amber and green lights The third part is the detector or sensor to indicate the presence of vehicles The detector consists of wire loops placed in the pavement at intersections They are activated by the change of electrical inductance caused by a
108. troke THA pV VV SIMAN IS Figure 2 21 OR Operation of a single acting cylinder Design and Applied Technology Secondary 4 6 b Logic AND function for a single acting cylinder This function is commonly known as an interlock function for safety purpose Two 3 2 NC valves are connected in series Both valves need to be pressed together for the outstroke operation of a single acting cylinder The first valve can be a mechanical plunger operated valve to make sure that the safety door is in place for common machine operation Then the second valve may be the manual switch pressed by the operator The outstroke of single acting cylinder can be made only when both valves are actuated Figure 2 22 Interlock and AND function of a single acting cylinder c Inverse Operation NOT function A 3 2 manual actuated NC valve is used to control a 3 2 NO valve for the inverse operation of single acting cylinder The cylinder is in an outstroke condition as an initial position When the NC valve is pressed momentarily the cylinder will retract at a regulated speed and a flow restriction valve is connected in the exhaust line It may be used for an unlocking function of some mechanical devices Design and Applied Technology Secondary 4 6 Figure 2 23 Signal inversion of a cylinder d Direct control of a double acting cylinder A 5 2 directional valve is used for a basic operation of a double acting cylinder The cylinde
109. ult to control with high accuracy c Hydraulic Robots that use hydraulic are generally performing heavy duty jobs This power type is noisy large and heavier than the other power drive sources Hydraulic drives were used on a large number of early robots as it was more rigid and controllable than pneumatics It could provide more power than the electric drives The problems with hydraulics are that it tends to be fairly slow in operation but the leaks that due to the high pressured oil can be very messy Figure 4 33 Hydraulic actuator un Design and Applied Technology Secondary 4 6 E 1 Why solenoid actuator can only perform duty of light loading 2 Why pneumatic drive system has difficulty of controlling with high accuracy II Types of robot control a Limited sequence robot It is the most elementary control type and can only be used for simple motion cycle such as pick and place application It is designed by arranging the limit switches or mechanical stops at each joints and sequencing the actuation of joints to accomplish the cycle Simple pneumatic driven robot without an electronic controller is the type of limited sequenced robot b Point to Point control The controller has a memory for storing the sequence of motion and the location of each joint in a given work cycle Feedback control is used to assure that an individual joint has achieved the desired location defined in the program However
110. ure 3 33 Servomotor with integrated feedback device Servomotor has the following advantages when compared to other motor technologies fast positioning high peak torques wide speed ranges high controllability In general servomotor is common in positioning applications It provides a wide range of power output that will be suitable for a variety of industrial applications such as packaging material handling laser trimming and automation where high throughput is of concern a High peak torque and High productivity Servomotor of same power rating offers peak torques of 200 400 percent over the continuous duty torque Higher peak torques in practical terms mean that the motor can accelerate and position the load faster b Light weight and Energy savings Servomotors can fit in a tight and compact location Smaller motor size means less weight It is significant in some applications where a load includes the motor itself such as the joint in robotic arm c High controllability Servomotors can offer excellent controllability Servomotors are used with closed loop motion controllers and can position accurately Servos can position up easily to a diameter of one hair d Fast Response and Reliability A measure of controllability is bandwidth This is an indication of response time The higher bandwidth the faster the response Comparing to other motor technologies servos have the highest bandwidth This means that if the
111. us Design and Applied Technology Secondary 4 6 REFERENCES TRE 2007 Ey PETS ERa RREO FE US RTA TRA Sh are Groover M 2000 Automation Production Systems and Computer Integrated manufacturing NJ Prentice Hall Jones J L Flynn A M 1998 Mobile robots inspiration to implementation AK Peters Ltd Mitchell F H 1991 CIM Systems An Introduction to Computer Integrated Manufacturing Englewood Cliffs Prentice Hall Design and Applied Technology Secondary 4 6 E GLOSSARY OF TERMS Algorithms an algorithm is a sequence of instructions often used for calculation and data processing It is formally a type of effective method in which a list of well defined instructions for completing a task will when given an initial state proceed through a well defined series of successive states eventually terminating in an end state The transition from one state to the next is not necessarily deterministic some algorithms known as probabilistic algorithms incorporate randomness Analog signal Any type of input or output that has more than two states on and off An analog signal can vary in magnitude from off to a high end value or between two non zero values An example of an analog device would be a level sensor that returns a voltage somewhere between O and 10 V that can vary over time Ampituda in vols Time in milliseconds A single digit that only has two possible values eit
112. vehicle passing over or standing over the wire loop For a more recent technology it uses the video detection system for the indication of vehicles on the road A small camera is fixed in the traffic light pole to see if any vehicle is present Design and Applied Technology Secondary 4 6 k ee ee EE Ee ur ele i a SEs ee on See 5 i a Figure 1 15 A diagram of Induction loop traffic sensor II A timing diagram to traffic control Figure 1 16 A diagram of a pair of traffic signal unit The sequence of traffic light operation and timing duration can be analyzed or represented by a timing diagram The code O represents an output signal The codes are O 2 00 and O 2 04 for Red O 2 01 and O 2 05 for Amber and O 2 01 and O 2 05 for Red A 1 second delayed period for RED lights on both directions to be illuminated is for road safety reason second delayed period lets drivers from both directions have a brief for readiness and let the vehicles on the junction be cleared off Ls Design and Applied Technology Secondary 4 6 Red O 2 00 Green O 2 02 Amber O 2 01 Green O 2 06 Amber O 2 05 Red O 2 04 Figure 1 17 A diagram of a pair of traffic signal unit Design and Applied Technology Secondary 4 6 1 5 Control of Fluid Level in a Tank uDesired Huid Level C Actual Huid level Controller Tank Figure 1 18 Block diagram of fluid level control system A cold water tank is suppli
113. ving forward forward Command to left motor Time backward Figure 1 25 Timing sequence illustrating the obstacle avoiding buggy s backing up behavior The sequence of actions can be illustrated in timing diagrams Figurel 25 depicts the signal generated by the front bumper sensor Figure 1 26 illustrates the signals sent to the right and left drive motors Initially both motors receive signals to go forward If a collision occurs the bumper sends a o Design and Applied Technology Secondary 4 6 binary signal to the adjustable timers low 0 for no contact high 1 when an obstacle is struck The timers in turn provide a binary signal to the motor drivers high 1 for reverse rotation low 0 for forward rotation Assume that the timers are set for delays of TR seconds and TL seconds for the right and left motors respectively TR gt TL for reversing After encountering an obstacle the buggy will backup for a time TL The left motor turns forward after TL the right motor stays in reverse for a time TR TL It will then resume moving forward Therefore the buggy will move in a different direction and avoid the obstacle The buggy will repeat the sequence until it can totally avoid the obstacle Design and Applied Technology Secondary 4 6 1 7 Application of Control Systems in Air Conditioner I Temperature Control Air conditioning systems are essential in most of our daily lives though we are
114. y 24V DC or more A relay is also a common device used to do this type of switching to drive the output load of different or higher voltage and current rating V Pin 1 Pin 18 10K Pin 9 Pin 10 Figure 3 25 Output circuitry for buzzer D gt Design and Applied Technology Secondary 4 6 k V Pin 1 Pin 18 7 10K Pin 9 Pin 10 Figure 3 26 Output circuitry for Light bulb Pin 18 E 10K OV Pin 10 Figure 3 27 Output circuitry for Solenoid IV Programming PIC The PIC is programmed using a compiler or assembler which is a high level programming language However they are still not easily to be understood by senior secondary students It can be made easier to program this PIC by a program editor which uses flowchart approach The editing software has graphical user interface and adopts drag and drop operation for programming The software will convert the flowchart into BASIC or Assembly language which will be downloaded to the PIC Design and Applied Technology Secondary 4 6 eee e a a i T a B x iho 3 5 Stepper Motor and Servomotor Figure 3 28 Photo of a typical stepping motor Stepping motor is an electric motor without commutators All the windings in the motor are the stator and the rotor is either a permanent magnet or a toothed block of magnetically soft material All commutations are handled externally by a motor control

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