PLC-control with Electrical Motors
Contents
1. Figure 3 9 Points of design deviations Figure 3 9 illustrates the regions of the changes made The major changes were imple mented because of too high static friction at the point 1 and the point 4 The car riages for respectively X and Y movement The solution was to spread the friction be tween two carriages so an extra carriage was inserted into both rails This caused a slight increase in the weight especially in the vertical movement Y as the carriage uses an aluminium quadratic bar to carry the Z platform The bar became roughly 10 cm longer adding roughly 100 g to the construction For the X movement an extra guiding wheel was mounted The guiding wheel is placed on the bottom of the vertical Y guide point 2 and follows an aluminium plate mounted at the bottom edge of the shelf point 3 For the pictures of the details see Appendix B 3 3 Results and possible improvements The system was tested by a spring scale The spring scale was applied closest possible to the points where the timing belts are mounted to the carr ages The force needed to move the fully loaded carriage was measured by pulling the scale n desired speed The force needed to move in the X direction was measured to be roughly 1 kg while trying to maintain desired constant speed The force in the Y direction was measured to be roughly 2 1 kg and in the Z direction roughly 0 3 kg 26 Estimated2. j i i N j j 1 j i j j j f 11 i a i u amj t f 49 ES 149 19 V j 7 T E 249 299 349 399 442 400 549 500 0 640 699 749 799 Figure 4 14 Performance of the X motor 4 3 2 Test of the Y axis motion The Y axis motion was tested first with a full load but the system would turn off after 20 seconds This 1s caused by the protective function of the servo system which turns of the motor if the torque of the load exceeds the rated torque of the motor with 2046 1n more than 20 seconds The system was tested with 820g This weight showed a stable continues torque If the weight was higher the torque needed to maintain the vertical position would differ from time to time considerably with the same load applied The FigureX X shows the test run with 820g The tests were done by moving 5000 pulses roughly 15 cm and with full processing speed of DC541 2500 pps roughly 7 6 cm s The graph in the Figure 4 15 shows clearly that the vertical movement up caused some vibrations 35 Electrical design 5D Torque Command 96 upu peqpeey peeds 49 300 100 l 79 225 p li pee i ac 140 109 249 230 ll 543 63 d D 348 338 425 ag 248 zu a 749 Eg 645 Figure 4 15 Performance of the Y motor 4 3 3 Improvements The results of the test show that the momentary torque
3. M MC MoveVelocity E amp MZ GearOut MC Gearin Slave f x MC Camin S ave MC GearlnPos Slave UU MC Cam Out MC VelocityPrcfile MC Acceleration Profe MC MoweAbsolute MC Move Relative MC MoveAbsciute MC PositionProfile A MC_TorqueConirol MC_MoveSupermposed MC_Gearln Slawe VC Caninius MC MoveRelative f MC Halt MC GearinPos qu p MC MoveAbsolute MC Mowe Relative MC_AetelesationFrofile Spree if MC MoveAddtiwe MC FositionProfile MG MoveVaipcity MC Posi amp onPrefile MC Halt x A MC VelocitProfile MC Hay fr MC TerqueCaniral MC Anz V elocitd MC Mowe Velocity MC Velocity rofle MC EK zceseratenProfile MC TorqueControl f MC MoveContinucus i MCL Stop MC MoveAbsclute MC MoweRaelabve MC Move ddtive MC MovesSupernmpeose MC PasitionProfile Figure 5 18 PLCopen state diagram 39 Software design 5 2 Implementation To implement the test program the concept of the PLCopen Motion Control Libraries was adopted The program is implemented by two tasks one taking care of communica tion with inputs and outputs and the other carries out the operations of the desired mo tion profile The tasks interfere through the structures that represent the axis The axis can recognise only two states Standstill and Discrete motion 5 2 1 Function Blocks and the AXIS REF structure For the purpose of the test program some simple FBs were developed The
4. Mechanical design Type N17 N27 N40 Width of rail 17 mm 27mm 40 mm Fy 50N 500 N 700N Fz 50 N 500 N 700 N Mx Nm 5 Nm 10 Nm My Mz Nm 3 Nm 6 Nm Table 3 3 Data for DryLin N guides N80 80 mm 1000 N 1000 N 32 Nm 15 Nm Axis bearings are of type Iglide Clip Bearings also a product from Igus See Figure 3 5 a Eee a E 8 S Figure 3 5 Iglide Clip Bearings and DryLin Se guides For transforming the rotational movement to the linear movement a system of timing belts was used The belts and the pulleys were chosen from the Bondy A S catalogue Another frequently used assembly part in the design 1s made of a quadratic aluminium profile This part is mounted at the ends of the Drylin guides and is used either to carry the axes for the pulleys or to carry a motor The size was chosen to satisfy all axis movements as this was the most efficient solution The profiles mounted to carry the pulleys have a long mounting slot so it would be possible to tighten the timing belt Front view Front view Bottom view Figure 3 6 Assembly parts 22 Mechanical design 3 1 2 Concept for Z movement The movement in and out of the shelf the Z movement was designed as illustrated in the Figure 3 7 TOP VIEW amp Z movement IN and OUT of the shelf o Drylin N rail l amp 8 2 sp s c p D D CD CD GD GD CD GCD CD D CD D sooo oo oo
5. 0838 BYTE Output 8 15 CHANNEL Q F iK Senoing ay 4 Target Settings f RUN XAT 960X38 0 BOOL Output 8 CHANNEL 88 T ask configuration f Reset XAT 960X38 1 BOOL Output 9 CHANNE 7 Watch and Recipe Manager f RUN Y AT QX38 2 BOOL Output 10 CHANNE iS R Workspace f Reset Y AT QX38 3 BOOL Output 11 CHANNI RF A amp G G8 X BOOL C Ouput 127 CHANNEL GJ f AT QX38 5 BOOL Output 13 CHANNEL Q f AT 0X38 6 BOOL Output 14 CHANNEL Q f AT 0X38 7 BOOL Output 15 CHANNEL Q Figure C 3 PLC I O configuration The Figure C 3 shows the configuration of the signals in CoDeSys programming soft ware on the PLC side 55 Wiring p Figure C 4 Terminal Blocks 56 D SERVO DRIVER PARAMETERS The Figure D 1 shows the setting for the servo drivers when testing It is a window of the programming software for the Omron servo driver WMON Win The Y axis motion used default settings for the controller parameters The Setup Parameters Cn 01 and Cn 02 were the same for both axes The parameters describe the mode of control as de scribed in the chapter 2 1 2 of the report When testing the setup profile was made to start the servo driver at the power plug in and clearing of the deviation was also auto matic The values for Cn 01 and Cn 02 with the mentioned features were O8ED and 0480 ils WMON Win Untitl
6. Direct http automationnotebook com 3S Smart Software Solutions GmbH 2005 User Manual for PLC Programming with CoDeSys 2 3 4 A MECHANICAL DIMENSIONING Choice of the DriLin N guides The table bellow shows the consideration behind the choice of the guide types Distance j Type and the to the Estimated Torque f Weight Mass M torque direc center of Torque limit tion mass Y movement 140kg 13 72N 8 00 cm 1 098 Nm 6 000Nm DryLin N 40 My X movement 2 00 kg 19 60 N 15 00 cm 2 940 Nm 5 000Nm DryLin N 27 Mx Z movement 1 10 kg 10 78 N 1 00 cm 0 108Nm 2 500Nm DryLin N 27 Mz Table A 1 Calculations for DriLin N The Weight collumn is an estimation of the weight to be mounted on the carriages The last two columns describes the chosen type of the guide and the torque limit for the car riage associated with the guide The directions x y z are not related to the X Y Z plane of the system It is directions used in the manual of the product The fomula is Estimated Torque m Distance to tire canter of mas X Marr esthnated Choice of the pulleys Estimated R Pull Estimated Weight Mass Friction a Max Radius d a limits Radius Torque Y movement 1 50 kg 14 70 N 0 4 not used 0 159 Nm 10 82 mm 9 68mm 0 142 Nm X movement 2 50 kg 24 50N 0 4 0 159 Nm 6 49 mm 14 08 mm 0 138 Nm Zmovement 110kg 10 78 N 0 4 N A N A 6 10 mm 0 026 Nm Table A 2 Pulleys calculations The choice of the pulleys s made to justify the rate
7. Speed Cn 15 Brake Timing 2 Cn 16 These parameters determine the output timing of the brake interlock signal BKIR which controls the electromagnetic brake Brake timing 1 sets the delay time from the time of brake interlock goes OFF until the servo turns off The setting range 1s O to 50 X10 ms and the factory setting is for O x 10 ms The brake command speed is the speed r m used to turn OFF the brake n terlock The setting range is O to 4 500 r m and the factory setting is for 100 r m Brake timing 2 sets the wait time from when the servo goes OFF until the brake inter lock goes OFF The setting range 1s 10 to 100 X10 ms and the factory setting is for 50 X10 ms If the run command turns off a servo error occurs or the main circuit power supply turns off during operation of a Servomotor with a brake the dynamic brake comes on setup parameter Cn Ol bit no 6 0 and Servomotor rotation speed 1s decreased When the speed drops to the level of the value set for the brake command speed Cn 15 the brake interlock output BKIR CN1 7 turns OFF Even if the speed does not drop to the level of the value set for the brake command speed Cn 15 the brake interlock output BKIR CN1 7 turns OFF after the time set for brake timing 2 has elapsed This time setting is made for the purpose of preventing damage to machinery or the Servomotor holding brake e Torque Command Filter Time Constant Cn 17 This sets the low pass
8. damaged if the same unit number is used for more than one Unit The setting range 1s from 0 to14 and the factory setting is 0 61 E DC541 MODUL Setting up the module The module installation is illustrated on the Figure E 1 The module should be installed on the right side of CPU Figure E 1 Installing DC541 module The module should be added into PLC configuration with the help of Control Builder CoDeSys Right clicking on Couplers opens the menu as illustrated in the Figure E 2 63 DC541 modul E csoo0 2 wow FJ CPU parameters FI om EE UO Bus FIX El e Interfaces FIX i E COMA Online access SL J COM2 Online access SL 2l FBP none SLOT E Coupl 75 De int i Lar cher A Insert Append Subelement Replace element Calculate addresses Export module Import module External none CM572 External PROFIBUS DP Master CM577 External Ethernet CM578 External CANopen CM575 External DeviceNet DC541 Interrupt counter IO Figure E 2 Adding DC541 to a project When the module is added to the hardware profile it has to be configured as a counter module This is done by right clicking at it and choosing the Counter mode choice When the module is added to the PLC configuration the libraries are automatically added to the project The picture bellow shows the I O configuration for this applica tion Channel 0 and Channel 3 are configur
9. is usually implemented for the systems with negligible distur bances on the process variable Erickson p 769 2005 Obviously this choice ap plication dependent and especially for the position control the closed loop is the first choice Considering that even a system based on switches or discrete sensors is considered to be a closed loop system there 1s undoubtedly very few reasons to im plement an open loop control 2 How to close the loop When considered systems with closed loop control usually the question is how to process the feedback Considering a system that consists of a controller can be CPU or a motion controller a driver and a motor a lot of the systems today offer a de fault configuration examples by closing the loop in the drive This is possible be cause the control itself is usually processed in a so called servo driver The control ler generates the speed or the position command and uses only a conformation sig nal that the command has been carried out Additionally the new servo drivers have also a communication interface which allows the controller to access their data If this is not the case and the motion needs more than just a position conformation the next point has to be addressed 3 System with or without a motion controller Most of the PLC brands today implement high frequency pulse functionality to their systems Usually it is a module capable of reading and writing high frequent digital signals This fun
10. modes e Position Control This mode uses pulse train input signals as a position and speed command Num bers of pulses are used as the position reference and frequency as the speed refer ence e Position Control with Pulse Stop Input Enabled Works with the same principle as the previous mode but implements a signal that prevents the driver from reading the impulse during position control e Internal Speed Control Settings In this mode the speed can be changed to one of the 3 preset values e Internal Speed Control Setting Position Control This mode implements position command and Internal Speed Control The servo driver is programmed from a PC with the WMON Win 1 1 programming software which can be also used for online monitoring Desired configuration 1s created by setting of the parameters in User Parameter window of WMON Win and uploaded to the servo driver There are two 8 bit parameters Cn 01 and Cn 02 that are used for choosing one of the control modes mentioned previously and the rest of the parameters have form of integers and are used as parameters for a control loop of the driver 16 Overview of the design and analyses Position Loop Block Diagram md La En ne bit a D rias 3 Command aulsez Encoder output E Fl ctranic Tgad 2ramrd are Feed honra Biss rotations amount l ge m command wter soeed liz eee X Uf Positioning completion raris Position comt mend
11. of the motors is sufficient for the system but the continuous torque is slightly lower than needed The system has also tendency to vibrate but this could be improved by tuning the controller and finding ideal values for acceleration and deceleration integration constant and position gain 36 9 SOFTWARE DESIGN This chapter describes the software part of the project This includes some standard li braries used for the project as well as the library developed for the control of the motor and a short test program 5 1 Concepts tools and theory 5 1 1 PS501 Control Builder PS501 Control Builder is a standard software package for AC500 programming It in cludes programming software CoDeSys V2 3 as well the tools for configuration of net work and OPC client 5 1 2 DC541 Library DC541 AC 500 VII lib is a function block library that is used to implement the dif ferent modes of DC541 Interrupt and Counter Module The library is installed auto matically after adding the unit into PLC configuration DC541FregOut DC541_FREG_OUT DC541FreqOut_SLOT DC541Freqout CH DC541FreqOut EN VvISLI DC541FreqOut EN E DC541FreqOut START DC541FreqQut STOP DC541Freqout FREQ Do541Freqout PULSE DC541FregOut DONE DC541FreqOut ERR DC541Freqout ERNO DC541FreqOut RDY Figure 5 16 DC541 FREQ OUT Function Block The library contents a number of function blocks used for different configurations of DC541 Figure 5 16 shows the functio
12. oooooononncnccnnonnnnnnnnnnonononnnnnnnnncnnnnnnnos 40 Figure 5 20 Function Block for relative movement oooooonnnnnnnncncnonnnonnnnnnnonononanonncnnnnnnos 41 Figure 5 2E Pest prO a ae ee 41 LISTOF TABLES Table 2 1 Table 2 2 Table 3 3 Table 3 4 Table 3 5 Table 4 6 PN AN PU A TEO E TREND NN 15 Motor data nase T dal ais 18 Data tor Dry Lin NOUS uv ee u 22 Mechanical assembly parts oes Ie a Mr ke 25 Comparison of estimated and measured torque values 27 Comparisoniol DESAL and CE DI 2 32 11 1 INTRODUCTION High resolution position control has been many years the domain of high speed micro processors because of their ability to process high frequency signals from encoders But in the last decade most Programmable Logic Controller producers have introduced new options for motion control by integrating high speed counter units These units are able to sample high frequency signals and generate Pulse Width Modulated signals or a pulse train This feature extends the application field of the PLC technology 1 1 Background The automated warehouse is a project with focus on PLC controlled motion and has been designed to serve the educational purposes The main objective 1s to build a sys tem which would be able to pick a quadratic object of specified weight 1kg from a shelf and unload it at the specified place The size of the object 1s specified to be roughly 20cm x 11cm x 7 cm The model
13. the counter inputs encoders A B Z Table 4 6 Comparison of DC541 and CD522 This means that after each abortion of position command the system will have to per form the origin search This is partly caused also by the library used for DC541 CM The FB that controls output signal does not keep track of the pulses already sent before the stop Without knowing how many pulses have been sent before the abort the only solution is to do homing procedure The system for X and Y axis looks as illustrated in the Figure 4 11 ILILILILILIL 1 L Position M PLC CPU commanc AC Servo Positioning Drive Lu zu completed nN Encoder feedback Figure 4 11 Servo system Interfacing Communication between the PLC and the servo driver is based on a command signal from PLC direction signal and pulse train for position and speed and conformation of successful positioning The signal that confirms successful positioning should be ad justed in PLC code because it goes high every time the motor reaches the referenced position or even 1f the frequency of the command word is too low This might be a problem with higher integration times for the controller settings or with slow motion for homing procedures The extra flag with a delay could be used to solve this The signal is called INP in position Other signals include ALM alarm from the servo driver RESET resets the alarm ECRST resets the deviation cou
14. will be build around an ABB PLC unit and Omron servo driver units with servomotors the hardware currently owned by the insti tute 1 2 Problem formulation The assignment consists of a few stages a mechanical design electrical design and in terface and a test program for position control Each of these parts contain a set of prob lems that should be solved with respect to each other as some of the problems are re lated to the mechanical design as well as to the electrical design The problems e designing a model and dimensioning design for the motors available e building a model e interfacing of the PLC units with the servo units e testing the design by a simple program PLC PWM 13 Introduction General requirements are e cost effectiveness e simplicity of manufacturing 1 3 Work by others Most of the manufacturing work for the mechanical part of the project was done by Johnny Andreasen my father in law and the special cables were manufactured by Bertil Morelli from Automation and Control 14 2 OVERVIEW OF THE DESIGN AND ANALYSES This part of the report describes the considerations and the choices in designing the sys tem The model from the hardware point of view consists of two logically distinguish able parts the mechanical and the electrical It is important to look at the limitations of these two parts separately but also in the context of interaction between each other That means that the mecha
15. 0 Factory Setting 200 r min No 3 Internal Speed Setting Cn 21 Factory Setting 300 r min 60 Servo Driver Parameters Make these settings to control speeds by means of internal settings The setting range is 0 to 4 500 r min For details refer to 3 5 3 Setting Internal Speed Control e Electronic Gear Ratio G1 Numerator Cn 24 Electronic Gear Ratio G2 Denominator Cn 25 The motor will be operated by the pulses resulting from the number of command pulses multiplied by the gear ratio G1 G2 The setting range for both G1 and G2 is 65 535 and the settings are restricted as fol lows 1 100 G1 G2 100 The factory setting is Gl 24 G2 1 1 e an electronic gear ratio of 4 1 At the factory setting inputting 2 048 pulses will cause one Servomotor revolution e Position Command Acceleration Deceleration Time Constant Cn 26 This executes smoothing processing on command pulses for Servomotor operation It is valid in the following cases There is no acceleration or deceleration for command pulses The command pulse frequency changes suddenly The electronic gear ratio setting is large G1 G2 _ 10 The setting range is O to 640 X0 1 ms and the factory setting is O X0 1 ms e Feed Forward Command Filter Cn 27 This is the setting for the low pass filter so that the feed forward amount is not added suddenly Using this setting can prevent overshooting in the event of sudden changes in command pulse fre
16. 2 Encoder and PWM module This 1s an expansion module for the PLC dedicated to interfacing with motion servo systems The manual can be found on the CD This module can process RS 422 en coder signals that are used in the Omron servo It has two high frequency outputs with a maximum frequency of 15 kHz DC541 CM Interrupt and Counter Module DC541 is a configurable I O module that can be configured as an interrupt module or a counter module The modes are mutually exclusive The module has 8 channels that can be configured as inputs or outputs When config ured as a high speed counter the module can process 24V input or output signals For the design purposes of this project the functionality of so called Frequency output mode is the most interesting one In this mode all 8 channels can be configured as fre quency outputs at max 2 5 kHz All functions are implemented through the set of Func tion Blocks that are part of the AC500 software library For more details about DC541 see Appendix E While CD522 module would make it possible to track the position of the physical sys tem the module DC541 is only capable to provide the command impulse The table bellow shows the differences in features of the modules that has the biggest impact on the design 3 Electrical design CD522 DC541 CM Number of high fre 2 8 quency outputs Max frequency of the 15 kHz 2 5 kHz outputs Supports RS 422 com patible encoder signals JA two NO for
17. CD amp oo eee owe Motor Y Figure 3 7 Z movement platform The blue painted parts are in a higher plane and consist of the rail and the timing belt for the X movement and the red parts are also in a higher plane but are the rail and the mo tor for Y movement up and down Motor is placed under a little platform supporting a guide rail at the end closer to the shelf The motor will be smaller and lighter than for the other two axes keeping the weight of platform lower The fork is mounted to the carriage and is moved by a timing belt in and out of the shelf For dimensions see chapter 3 1 4 and Appendix A 3 1 3 Concept for X and Y movement Figure 3 8 shows the concept of X and Y axes motion apparatus It 1s a frontal view and the guide rail for X movement is mounted on the top of the shelf Both motions are im plemented with a timing belt pulled by an AC motor For both motions one pulley is mounted directly on the motor axis and the other pulley 1s mounted in the quadratic pro file illustrated on the Figure 3 6 in chapter 3 1 1 The illustration shows clearly placement of the Z motor 23 Mechanical design FRONT VIEW Motor X Figure 3 8 Concept for the X and the Y motion 3 1 4 Dimensioning and choice of components The dimensions of assembly parts were chosen by a qualified guess based on some simplified calculation models Friction coefficient of the guides 1s not listed n the man
18. DC541FreqOut_PULSE DC541FreqOut_DONE DC541FreqOut ERR DC541FreqOut ERNO DC541FreqOut RDY Figure E 4 DC541 FREQ OUT Insane DC541 FREQ OUT Instance name IL o SOT impar BYTE SbtoheDCM Enabling of control via the integrated visualization of block visuDC541 FREQ OUT START Input Output BOOL Start of frequency output STOP Input Output BOOL Termination of frequency output FREQ Input Output LREAL Set value presetting for frequency Hz PULSE Input Output DWORD Set value presetting for pulses 0 infinite gt 0 number of pulses Table E 1 Parameters of DC541 FREQ OUT Table E 1 shows the parameters of the FB The START input triggers the frequency output by rising edge and has to stay high until the block is finished with sending the pulses It is possible to change the values while the FB is active This means that PULSE and FREQ are level sensitive in relation to START 65 67
19. Technical University of Denmark Tomas Andreasen Haviernik PLC control with Electrical Motors Model of an automated warehouse with multidimensional movement Bachelor s Thesis April 2009 DTU Electrical Engineering W Tomas Andreasen Haviernik PLC control with Electrical Mo tors Model of an automated warehouse with multidimensional movement Bachelor s Thesis April 2009 PLC control with Electrical Motors Model of an automated warehouse with mul tidimensional movement The report has been prepared by Tomas Andreasen Haviernik Supervisor s Nils Axel Andersen Ole Ravn DTU Electrical Engineering Automation and Control Technical University of Denmark Elektrovej Building 326 DK 2800 Kgs Lyngby Denmark www elektro dtu dk English research au aspx Tel 45 45 25 35 50 Fax 45 45 88 12 95 Date of publishing 20 april 2009 Classification 1 offentlig Comments This report is part of the requirements to achieve Bachelor of Engineering at Technical University of Denmark The report represents 15 ECTS points Copyrights Tomas Andreasen Haviernik 2009 ABSTRACT The report describes the basic design concepts for the PLC controlled motion systems This is done through the building a model of an automated warehouse The main goal was not to introduce a scalable solution for the industrial use but to build the system that would serve educational purposes The work includes a wide range of p
20. Torque 0 142 Nm 0 138 Nm 0 026 Nm Measured Measured Force 20 58 10 78 2 94 Torque applied on the motor 0 199 Nm 0 152 Nm 0 018 Nm Mechanical design Sugested Radius for Pulley 7 73 mm Table 3 5 Comparison of estimated and measured torque values The Table 3 5 shows that the measured forces are slightly higher than expected This is not as problematic for the horizontal movement as for the vertical The rated torque of the motor is the torque that the system is able to maintain in longer periods The Y mo tor will have to hold the object to be carried n unspecified period of time The me chanical solution to this would be choosing a smaller pulley lighter Z motor and trying to use lighter construction parts For maintaining the speed possible solutions are part of the electrical design 27 Electrical design 4 ELECTRICAL DESIGN Electrical system consists of PLC servo drives and motors This part of the report gives an account on the theory behind the electrical design design itself and the testing of the system 4 1 Technology of PLC controlled motion There are many concepts for controlling the motion with PLC and the choice of the concept 1s very much application dependent Motion control usually means controlling position speed or torque of a motor but most of the systems from logical reasons com bine all three possibilities of control For the purpose of this project
21. accel ration decel ersticn time cons snt Figure 2 1 Concept of the Servo Driver R88D UP Figure 2 1 shows the principle of the control in the driver and some of the parameters For all parameters and wiring see Appendix C 2 1 3 200 VAC Motor with incremental encoder The servomotor is of type R88 U05030VA S1 It is a standard motor for the R88D UP03V servo driver It is a motor without break and with encoder resolution of 2048 pulses 11 Motor 12 Servo Driver R88M U05030H A H88M UO05030VA N miker cm Frequent use Continuous use i000 2000 3000 4000 r min Figure 2 2 Motor torque 17 Overview of the design and analyses Rated output 50W Rated torque 0 159 Nm Rated rota tional speed 3000 r min Momentary maximum 0 48 Nm torque Weight 400 g Default reso 2048 lution of the pulses rotation system Table 2 2 Motor data Figure 2 2 shows the relation between velocity and torque of the motor and Table 2 2 shows the specifications relevant for designing the system 2 2 Design analyses The goal of the project is to build a system that can move an object from a shelf and unload it at specified place For each part of the project there are problems to be solved The following chapters describe the problems to be solved and the basics of the chosen concepts 2 2 1 Mechanical system The objective is to build a mechanical construction that is able to move in three perpen dicular direct
22. ctionality has opened up possibilities to cheaper solutions if the complexity of the movement is lower because most of the servo drivers today re quire these signals as a reference for velocity and position But for the motion that is more complex in the context of synchronising and coordi nation motion controllers are a necessary part of the system 4 1 2 Homing methods with an incremental encoder Homing is a procedure that assigns position to a reference point Because of the incre mental encoders used for the system following chapter describes the most frequent methods for homing or as it is sometimes called the origin search There are three common methods for homing e Absolute switch homing The principle of this method is to search for Off On Off signal from a sensor The method is illustrated on the Figure 4 10 e Limit switch homing 29 Electrical design In this method the search for On signal of a limit switch is performed Direction of the movement 1s dependent on the position of the object e Homing against physical object This method is performed by searching a physical obstacle The method requires torque limits for the motor e Homing with a reference signal Z This method can be combined with an absolute switch or a limit switch It imple ments so called Z signal from the encoder The signal 1s generated once for a rota tion Searching for a switch is performed and when the switch is active movemen
23. d that rates the continues torque to 0 8 Nm The con trol can be implemented with a typical H bridge configuration consisting of two 3Pole Double Throw relays controlled from the PLC An extra pole would be used to avoid activating forward and backward movement at the same time It would turn off the con trol signal for the opposite direction when activated An extra power supply would be required as the supply used for the PLC has no sufficient current rates and using the same power supply for the control signals and the actuators is a bad design practice Figure 4 12 shows the control concept for Z movement Details for wiring of the system are part of Appendix C REV FWD FWD REV Y FWD REV E lt REV FWD Figure 4 12 H bridge 16 3PDT 33 Electrical design 4 3 Results and possible improvements The system was tested by a simple program that with help of a few push buttons moved in the desired direction The functionality of the installation was in this way verified indirectly The performance of the motion functionality was tested by WMON software for the servo driver The software can monitor motor behaviour in the desired period of time and then it generates a graph by spreading the time period over 1000 points The test period in the both illustrated cases was 50 seconds so the graphs have a vertical grid of 2 5 seconds The flow of the test was as follows MOVE WITHOUT A LOAD 2500 pps motion command MAX Fac
24. d torque of the motors used The ated mit formula for the horisontal Y movement is Max Fading 49 Mechanical Dimensioning Aare Hur or the Y and Z movement Max Badius Choice of the timing belts The timing belts for the Z and the Y movement were the standard sizes For the X movement the following formula was used LQ iXatz Xt Where Lg is the length of the belt a is a centre distance z is the number of teeth of the pulley used and t is a distance between the teeth The centre distance for the Y movement is 99 cm so the belt length was chosen to be 210 cm 50 B PICTURES OF THE SYSTEM Figure B 1 Picture of the system Figure B 2 Picture of the modification on the Y axis 51 C WIRING The picture bellow shows the Servor Driver CN1 connector used for interfacing with the PLC Reverse pulse cw y 5202 PI RM ENRIQUE MEM ea ed 7 A WM E BRIA I 1 E gt ml Y mE i Sraxe interlock Forward pulse wig le INP Zn qm I ME Positioning wn uA gt _ completion Klec rmum operating OOW L4 fi Se Ses 2 voltage 30 WDC TGON a e MP Meocirmum output Deviation counter reset gt ae i iaia ig ECAST s 8 _______ 10 detection pow nem amc OGND v sod u Output ground er x gt an 34 ER gt Alarm output ba 72 ALMCOM 27 Do not connect these pins pe 28 E ALD 2g Alarm code output E ALOE Maximum operatin
25. ectronic Gear Ratio G1 Nu Electronic Gear Ratio G2 De P Control Switching Torque C P Control Switching Speed C P Control Switching Accelerz P Control Switching Deviatior 80 Hz 30 1 ms 5 1 s 2 rimin 0 96 100 0 1ms 0 0 1ms 317 317 317 4 0 1ms 100 100 0 ms 0 ms 20 r min 0 10ms 100 r min 50 10ms 3 Command u 1000 Pulses Revc 2048 Pulses Revc EN 200 95 0 r min 0 1 r miny s 10 Command u Servo Status 40 Alarms Commutators and Encoders User Parameters Category Cn No Code Description Value Units Sewo Min Max b R88D LIP Software Ver 5 Unit 0 Com 1 RS 232 Servo On Advanced Figure D 1 Parameters for the X motor 57 Servo Driver Parameters User Parameters from OMNUC U User s Manual e Speed Loop Gain Cn 04 This is the proportional gain for the speed controller The adjustable range is 1 to 2 000Hz the response frequency when equivalent inertia is used As the number is increased the gain is increased The factory setting is for 80 Hz Using the factory setting for the Servomotor alone or with a small load inertia will cause vibration to occur so set the value to a maximum of 20 Hz for operation e Speed Loop Integration Constant Cn 05 This 1s the integration time for the speed controller The adjustable range is 2 to 10 000 ms and it is factory set to 20 ms As the number is increased the gain is decreased The unit can be changed using the
26. ed File View Operations Parameters Help eos 04 MOO LET RIC Speed Feedback Speed Command Pulse Speed Torque Command Pos Deviation Base Block Motor Rotating For Drive Prohibit Rev Drive Prohibit INP TGON T POT T RUN J NOT M ALM 12 18 amp Start 3 5 m CoDeSys testprogram O TEST X fs WMON Win Untitled Switches Switches Gain Gain Gain Gain Gain Gain Gain Torque Torque Torque Torque Torque Torque Sequence Sequence Sequence Sequence Sequence Sequence Sequence Pulse Pulse Pulse Pulse Other Other Other Other MEM1 MEM2 SPDGN SPDTIM POSGN BIASLY FFGN POSFIL FFFIL EMGTRG TLMTF TLMTR TERFEL CLMTF CLMTR SFSACC SFSDEC TGONLY BRKTIM1 BRKSPD BRKTIM2 INPLY PGRAT PULSNO RATG1 RATG2 TROMSW SPDMSW ACCMSVV ERPMSW Setup Parameters 1 Setup Parameters 2 Speed Loop Gain Speed Loop Integration Cons Position Loop Gain Bias Rotational Speed Feed Forward Amount Position Command Accelera Feed Forward Command F ilti Emergency Stop Torque Forward Torque Limit Reverse Torque Limit Torque Command Filter Time Forward Rotation External Cr Reverse Rotation External Ci Soft Start Acceleration Time Soft Start Deceleration Time Rotation Speed For Motor Rc Brake Timing 1 Brake Command Speed Brake Timing 2 Positioning Completion Rang Encoder Divider Rate Number Of Encoder Pulses El
27. ed as Frequency output to generate the pulse train for the X and the Y axes respectively The Channels 1 and 4 are the outputs for the direction signals CCW The signal ECRST for resetting the deviation counter was not used but the Channels 2 and 5 were configured as outputs to carry this signal t AT 36922 INT Anal _ i AT WaWa INT E Anal EI Intertaces Fl e E COMA Online access SLOT E COM2 Online access SLOT iur 1 FEF none sLoT ES Ej Couplers FIs ue gy PM x1 ETH Internal Ethernet SLO E Hen Ej 541 Interrupt counter IO PAR Module parameter Index Mame 2 Lhannel Frequency output 3 Channel Output 4 Channel Output A Channel 3 Frequency output b Channel 4 Output P Lhannel5 Output a Channel b Input 3 Channel Input Figure E 3 DC541 configuration 64 DC541 modul DC541 FBs used in the project The manual describing the use of the module includes these FBs for all the application examples TASK INFO reads the cycle of PLC PRG DC541 GET CFG reading the configuration of DC541 DC541 STATE reading writing the static channels of DC541 And DC541 IO this FB is used for writing reading outputs inputs Channel 1 and 4 To use the function of the frequency output FB DC541 FREQ OUT is used DC541FregOut DC541_FREQ_OUT DC541FreqOut SLOT DC541FreqOut CH DC541FreqOut EN VISU DC541FreqOout EN DC541FreqOut START DC541FreqOut STOP DC541FreqOut FREG
28. eee o a ea tei uses sa cceversceeoebesalentesvaddestecsodsewesses 49 B Pictures OF the system 23 iin EEEE 51 OM O ee E EEE 53 D Servo Driver Parameters isssccscsccccesiscescasssosccscseccacssdasssvesessesassabsnbeceusssoacedesssessssesesacs 57 E P GST dicU essen 63 LIST OF FIGURES Figure 2 1 Concept of the Servo Driver R88D UP eene 17 Ligure 2 2 Molortorgue uni ee a Ba adie 17 Figure 2 5 Mechanical CONCE es seed 19 Figure 2 4 Dry Lin N SUIS A a di M deus 21 Figure 3 5 Iglide Clip Bearings and DryLin guides ses 22 Pigeure 5 0 Assembly DAS en aiat e ems e p oU ns 22 Figure 3 7 Z Movement plato anne ae 23 Figure 3 8 Concept for the X and the Y MOti0D oooooooononnccnnnnnononnnnnnnnnnnononnnoncncnnnnnnos 24 Figure 3 9 Points of design ds vias ia 26 Rieure 4 10 HOMNE us we eee ee 30 Figure 2 11 Servo SMA a ss 32 Mitre 412 Thilo nenne 33 Figure 4 13 Test HowCDaEE sso te a ee na 34 Figure 4 14 Performance of the X motor ooccccccccccnnnonconononoonononnnnnnonnnnnonononnnnnanncnanonnss 35 Figure 4 15 Performance of the Y Motor aD 36 Figure 5 16 DC541 FREQ OUT Function Block cccccccnnooncccnnnnnnnnnnnonccnnnnnnnnnnos 37 Figure 5 17 Concept of PLCopen Motion Control Libraries 38 Figure 5 18 PLCopen state diagram uuessssssssssnsnnnnnsnnssssenenneenenennnnnnnnnnnnnnnnnnn 39 Figure 5 19 Function Block for IO comunication
29. filter time constant for the torque command The setting range is 0 to 250 x100 ps and the factory setting is 4 X100 us 59 Servo Driver Parameters The relationship between the filter time constant and the cut off frequency can be found by means of the following formula fc Hz 1 QTrT T Filter time constant If T 400 us fc will be approximately 400 Hz When the characteristic v bration of the machinery is within the response frequency of the servo loop Servomotor vibration will occur In order to prevent this sympathetic vibration based on the characteristic vibration of the machinery set the torque filter time constant to a value that will eliminate the vibration 1 e set it to a high value e Forward Rotation External Current Limit Cn 18 Reverse Rotation External Current Limit Cn 19 These set the Servomotor output torque limits for the forward and reverse directions They are valid when the forward reverse current limits PCL NCL CN1 11 12 are in put This function can t be used if the input command mode is set to internal speed control settings The setting range is O to the maximum torque and the factory setting is for the 100 906 e Position Loop Gain Cn 1A Adjust the position loop gain to the rigidity of themachine Set to between 50 and 70 1 s for general NC machine tools to between 30 and 50 1 s for general and assembly machines and to 10 to 30 1 s for industrial robots Load alarms wi
30. g voltage 30 VDC 24 VDC i Miencmem output current 20 m Run instructian ALOCOM Alarm code output GHO Sain decel eration E r1 TA BERGE Encoder A phase rotation dre J I HE eae mane An Line driver output han u EIA HS422A rotation drive Encoder B phase carizrming prahibit B Load resistance i 200 x mex aa D y P E E r4 B a in n Se 2222 To Z Ka un m G Z Frame ground C Figure C 1 CN1 connector The PLC is connected to the hardware through terminal blocks of two colours orange and grey They are numbered 1 20 Both colours are connected the same way to the Servo Driver controlling the coresponding motor 53 Wiring The Table C 1 shows only the connection for the grey system controlling the axes X luc m e A NN ire DC541 CO 1 0 1 5K resistor in series DC541 C1 1 1 3 _ CCW 1 5K resistor in series E E E en 14_RUN Pull down input RO 0V DER 0 NENNEN 1 8K pull DX522 2 10 1 0 8 INP SINKING output 1 88 pp resistor see 100GND OGND 35 AMMCOM _ALMCOM ant e pe o saw Xm o Lulu oa com Oo w ET 00 m NENNEN Table C 1 Wiring The control signals to servo driver had to be implemented with a resistor in series with the inputs on the terminals 1 3 and 7 The size of the resistors is 1 5 kQ The servo driver outputs INP and Alarm are sinking ou
31. ged to the Standingstill and the output Done goes high AXES_REF is the structure of type VAR_IN_OUT that contains the data representing the axes to be controlled In the design only a few of the structure members were used but the definition was made to satisfy also possible use in the future The structure in this program is used to pass the values for the speed and the distance of travel but also for changing the state and passing the INP signal 5 2 2 Test program The program itself 1s of a very simple structure There are two instances of AXIS_REF Axis representing the X movement and Axis2 representing the Y movement The main task PLC PRG PRG can be seen in the Figure 5 21 A direction hackedir MC MoveRelative MC MoveRelative push Execute 500 Velacity 4000 Distance Axis 4Axis F push Distance Axis m Figure 5 21 Test program It is executed with a period of 5 ms The movement is controlled by push buttons push and push 1 The flow of the program is quite easy to follow from the picture When the button push s activated FBs X direction and Y direction are 17 INP 41 Software design executed when they finnish the execution pushing the button pushl activates backXdir and the Axis returns to the start position The other task COM PRG the one that takes care of the hardware interfacing is executed with a perion of 4 ms and has higher priority than the main
32. his way the FBs can be arranged as a flowchart passing the state of the axis and the needed information through obligatory input AXIS REF AXIS REF is a structure that keeps track of the movement The principle is illustrated in the Figure 5 17 Time or event driven A Figure 5 17 Concept of PLCopen Motion Control Libraries 38 Software design The FBs and AXIS_REF are hardware dependable so the standard gives just some out lines for the functionality The operations are carr ed out sequentially and the standard describes the states of the axis and the transition conditions A change of state 1s re flected immediately when issuing the corresponding motion command Note the response time of immediately is system dependent coupled to the state of the axis or an abstraction layer in the software PLCopen v 1 1 2005 p 13 The behaviour of the system when more blocks are active at the same time s also de scribed in the standard and there 1s given an encounter on the possible configurations The code for these function blocks is not accessible for the user The figure bellow shows the state diagram for the single axis motion libraries with the corresponding FBs The whole series of the publication can be found of the CD MC_Gearln Slave MC CaminiSlave MC Phasing Slave MC MeoyeSupernmposedi slawe MO Gear cene MC Gearln Slave MC_Camini Slave u _ ie _ SearinPas Slave Error m zu
33. in the software part can be 43 Conclusion used as this would make the system flexible to the changes in the motion profiles De veloping a standard library for the hardware configuration would give the students pos sibility to focus more on the structuring of the application and understanding the typical problems the PLC programmers are facing in the working process 44 45 LITERATURE OMRON 1994 User s Manual Omnuc U series Models R88M U AC Servomotors Models R88D UP AC Servo Drivers OMRON 2000 User s Manual Omnuc W series U series Servo Driver Servomotor Computer Monitor Software WMON Win Verl 01 ABB 2007 DC541 Function Block Library AC500 Software Description ABB 2006 System Technology of the DC541 CM Module System Description ABB 2007 AC500 Hardware V2 System Description Erickson K T 2005 Programmable Logic Controllers An emphasis on design and application Dogwood Valley Press Mitsubishi Electric 2000 Programmable Controllers MELSEC F Positioning Con troll Training Manual PLCopen 2005 Technical Specification PLCopen Technical Commitee 2 Task Force Function Blocks for motion control Version 1 1 http www plcopen org PLCopen 2006 Technical Paper PLCopen Technical Commitee 2 Task Force Func tion Blocks for motion control Part 5 Homing Version 0 99 http www plcopen org McDaniel C 2005 Motion Control System Choices Automation Notebook Issue 4 Automation
34. integration time constant setting unit Cn 02 bit No b HA LA V W Models e Emergency Stop Torque Cn 06 When setup parameterCn 01 bit no 8 1 this sets the braking torque for over travel stopping forward reverse drive prohibit input operation The setting range 1s O to the maximum torque a percentage of the braking torque as 100 of the Servomotor rated torque The factory setting is for the maximum torque e Software Start Acceleration Time Cn 07 Software Start Deceleration Time Cn 23 The Servomotor rotation acceleration time fromO r min to 4 500 r min is set in Cn 07 and the deceleration time from4 500 r min to O r min is set inCn 23 The factory setting is for O ms Set the acceleration and deceleration times to O ms unless using the in ternal speed settings e Forward Torque Control Cn 08 Reverse Torque Control Cn 09 The Servomotor output torque control value for forward rotation is set in Cn 08 and the value for reverse rotation is set inCn 09 The setting range is O to the maximum torque and the factory setting 1s for the maximum torque e Encoder Divider Rate Cn 0A The number of pulses detected A and B pulses per encoder revolution is converted to the number of pulses set for this parameter and output from the Servo Driver The set tng range is 16 to 2 048 pulses revolution and the factory setting is for 1 000 pulses revolution e Rotational Speed for Servomotor Rotation Detection Cn 0b This sets the r
35. ions X Y Z This part of the design is very time demanding in manufac turing so simplicity is crucial for the design That s why the concept should consist of as few parts as possible and they all should be relatively cheap Other things to consider are e weight of the different parts e placement of the parts in relation to the movement e motors have to be able to work with the load e the guides should be able to function with the forces applied on them e size of the pulleys should be related to the speed and the maximum torque of the motors Figure 2 3 shows a concept like that 18 Overview of the design and analyses Figure 2 3 Mechanical concept This concept would allow movement in all directions while the bearing construction would be made of linear guides Other concepts were considered but most of them in cluded one or more parallel mounted linear guides 2 2 2 Electrical system The challenge of the electrical design is in the motor control and interfacing The sim plest solution for movement in XYZ plane is to use 3 independent motors For the me chanical design considered in the previous chapter can be concluded that the movement in the X and the Y direction is dependent on the length of travel to the shelf to be emp tied while the movement in the Z direction is of a fixed distance The Z movement could be carried out by a simple DC motor of smaller size that would react to two mi croswitches as the position se
36. it would be con venient to focus on position control systems Most common methods used in praxis are e Systems with limit switches This method is usually used for the applications that require less precision and can be very cost effective if the number of required position is limited The principle is that switches are used to time the deceleration of the movement and stopping e Step motors Step motors are relatively small so the range of the application is very limited Pre c s on 1s lower in high speed e DC servo systems Because of the brushed DC motors these systems require maintenance changing the brushes They also tend to be less accurate in higher velocities e General purpose inverters Inverters are being used for application where control of torque and speed is more important than position control They are very often used to control blending ma chines in industrial processes e AC servo systems AC servo systems are most common choice for the modern systems that require higher precision for positioning and high power Mitsubishi p 2 4 chapter 1 2000 28 Electrical design 4 1 1 Concepts of PLC motion control There are few possibilities how to configure a motion control system when using PLC The choice is very much dependent on complexity of the movements to be controlled Following are the decisions to be made when designing a motion control system 1 Open loop and closed loop control Open loop control
37. ll be caused by ma chine oscillation if the position loop gain is increased for systems with low rigidity or systems with intrinsically low frequency vibration The setting range is 1 to 500 1 s and the factory setting is 40 1 s e Positioning Completed Range Cn 1b This sets the deviation counter value for outputting the positioning completed output INP When the deviation counter value falls below this setting the positioning com pleted output turns ON The setting range is O to 250 command units and the factory setting 1s 3 command units e Bias Rotational Speed Cn 1C This 1s the setting for position control bias Use this setting according to the load condi tions in order to shorten positioning time The setting range is 1 to 450 r min and the factory setting is O r min e Feed forward Amount Cn 1d This 1s the feed forward compensation for the position controller Positioning time 1s shortened by adding the command pulse differential to the speed command The setting range 1s O to 100 and the factory setting 1s 0 e Deviation Counter Overflow Level Cn 1E This sets the level for detection deviation counter overflow If the deviation counter value exceeds this set value a servo alarm will be generated The setting range is 1 to 32 767 X256 command units and the factory setting is 1 024 X256 command units e No 1 Internal Speed Setting Cn 1F Factory Setting 100 r min No 2 Internal Speed Setting Cn 2
38. me limitation Many parts of the construction are heavier than expected due to the limited choice of material available at the time The electrical design has been implemented with slight changes because of the delivery problems The only part missing 1s implementing the control of the Z movement But the concept has been designed and the motor Z and the microswitches to control it are mounted on the system The biggest challenge of the electrical design was getting to know the hardware and the software used in the project and interfacing sinking outputs and sourcing inputs of the servo driver The system was tested with a small program and the concept for the structure of motion software introduced Testing of the system showed that it 1s capable of handling loads up to 820g 6 2 Further work The Z movement could be implemented as described in the report If the object to be lifted should be more than 820 g the construction of the Z platform could be made from lighter aluminium profiles and the pulley Y can be replaced by a slightly smaller one This would reduce the torque applied on the motor To maintain the speed the electronic gearing can be used It would reduce the precision of the movement but the system can perform with much lower precision and still satisfy the application need With a per spective to implement the full functionality of the system the code should be written to satisfy the application requirements The concept introduced
39. mm 1475 mm width 6 mm 10 mm 10 mm max load 65N 49 N 117 N Pulley type T2 5 T2 5 T2 5 diameter 12 20 mm 28 15 mm 19 35 mm number of teeth 16 36 25 Table 3 4 Mechanical assembly parts Table 3 4 shows the choices for the components For the speed of the movement in Revolutions Per Second applies F m umiar af teeth widti of the taati ADE Considering performance of the electronic system without using electronic gearing the maximum rotational speed for the motors is 1 22 RPS With 2 5 mm teeth this would give 7 6 cm s for the Y movement and 10 8 cm s for the X movement The default reso lution can be calculated by dividing the length of travel per rotation with 2048 The de tailed calculations for the choice of the guides and the pulleys are included in Appendix A 3 2 Implementation The implementation of the concepts introduced in the previous sections was slightly modified The reason for this was that static friction of the carriages was higher than previously expected The maximum moment rates for the carriages seem to characterise the maximum load before the carriage brakes rather than the maximum load for the car 3 RPM 14 RPS 25 Mechanical design riage to fulfil its function allowing the movement of the objects mounted to it When implementing the desired configuration the friction at carriages for the X and the Y movement caused vibrations even at very slow motion 100 00 75 00
40. n block used for generating a pulse train signal 37 Software design There are few other configuration function blocks that should be added to a program for DC541 to function For the details see Appendix E 5 1 3 PLCopen Motion Control Libraries PLCopen is an independent association for industrial suppliers and users It was founded in 1992 with the main objective to promote usage of the IEC 6113 3 standard The objective later changed from the promotional to supplementary work and through its so called task committees they actively work on creating guidelines for the auto mation standards PLCopen Motion Control Libraries is a programming standard that describes the guidelines for developing libraries for motion control based on IEC 6113 3 function blocks FB definitions The main purpose of this standard 1s to unify the programming interface for motion control and that way to improve compatibility of different systems and shorten time for developing motion control applications This project uses the standard as an inspiration for building the FBs that interface with the previously described hardware The FB s are not compliant with the standard It rather copies the concept of the standard where some simple FBs interfere with hard ware through a structure variable Basic principles of the standard The standard is build around a number of function blocs that each carries on a certain operation on the axes to be controlled T
41. nical part has to take account of limitations of the electrical and vice versa 2 1 Basic components of the design The chapter describes the basic features of the components the design has been build around This is needed to understand the choices made in the further developing of the design 2 1 1 Programmable Logic Controller PLC PM571 Program memory Flash EPROM an ogra e pta OM and 64 kB Data memory integrated 2 sa Ine kB RETAIN SD Memory Card 128 MB Cycle time for 1000 instructions Binary 0 3 ms Word 0 3 ms Floating point 6 0 ms Real time clock with battery back up YES Program execution cyclic YES time controlled YES multitasking YES Table 2 1 PM571 CPU 15 Overview of the design and analyses The PLC used in the project is from the series AC500 from ABB The Central Process ing Unit is of type PM571 and it has three Input Output modules attached to it Two of them are DX522 digital relay IO modules and one analog IO module AX522 The software package for programming includes the CoDeSys v2 3 suite which implements IEC 6113 compliant languages for programming the system These include Instruction List Structured Text Ladder Diagram Function Block Diagram and Sequential Function Chart 2 1 2 Servo Driver R88D UP R88D UP is a programmable servo drive from Omron that uses pulse train input signals for position control and indexing for speed control There are four possible choices for the control
42. nsors for two positions in the shelf and out This con figuration would be also convenient from the mechanical point of view since the Om ron motors are of a considerable weight and the cables used for controlling the motors are also quite thick and heavy The X and the Y movement would be implemented with the Omron system 19 3 MECHANICAL DESIGN This chapter describes the considerations behind the design of mechanical structure of the system It is related to the electrical design mainly through the limitations of the motors 3 1 The design concept and assembly parts The following subchapters describe the assembly of the parts and the concept for the three axis movement 3 1 1 Assembly parts The mechanical construction is build around products from Igus a company producing polymer bearings and guides and timing belts with corresponding pulleys from a sup plier Bondy A S A linear guide series Drylin N is a relatively cheap and solid solution for linear move ment that consists of an aluminium rail and a carriage coated with a special plastic with a low friction coefficient The picture bellow shows Drylin N guide and the limits for the forces to be applied on the guide Table 3 3 shows the data for all 4 versions of the guide using the same plane orientation as Figure 3 4 500N 1 588 mm Te My 5Nm e My 2 5 Nm SOON Mz 2 5 Nm ly 6524 mm Figure 3 4 DryLin N guide 21
43. nter and RUN turns on the servo driver The interface of the servo is based on sourcing inputs and sinking outputs which had to be solved with passing the zero reference by relay outputs to the driver s inputs and by pull up resistors when for the drivers sinking outputs 15 INP 32 Electrical design Homing For the homing procedure the microswitches has been installed They are placed as limit switches on the guide for the X movement and for the Y movement one microswitch was installed at the top end The servo driver has protection for overload so limit switches serve very little purpose Because every abortion of movement would lead to the homing procedure the limits for the movement should be software defined 4 2 2 Z axis control The Z axis control was implemented only on the mechanical level but the concept for electrical implementation was designed For Z axis movement a smaller DC motor should be chosen By choosing a smaller motor for Z axis the weight of the construc tion could be lowered new concept of motion control introduced and the solution would be also more economically efficient Considering that the Z axis needs to recognise only two positions In and Out a control based on limit switches should be sufficient The motor A max 22 from Maxon was mounted on the platform for Z movement to gether with the microswitches but the performance of the motor was not verified It 1s equipped with a planetary gearhea
44. otational speed for detecting whether or not the Servomotor is rotating The setting range is 1 to 4 500 r min When motor rotation detection has been set for the sequence output signal switch Cn 01 bit 4 2 0 the Servomotor rotation detection out 58 Servo Driver Parameters put TGON CNI 9 is turned ON if the Servomotor rotational speed meets or exceeds this set value The factory setting 1s for 20 r min e P Control Switching Torque Command Cn 0C P Control Switching Speed Command Cn 0d P Control Switching Acceleration Command Cn 0E P Control Switching Deviation Pulse Cn OF These set the various points for switching the speed controller from PI control to P con trol 1n order to moderate excessive characteristics when an operation such as accelera tion or deceleration is executed accompanied by output saturation of the controller These selections are made by setting the setup parameter Cn 01 bit nos b d and C e Jog Speed Cn 10 This sets the speed for manual operation The setting range is 0 to 4 500 r min During manual operation operating commands are given from the Parameter Unit The factory setting is for 500 r min e Number of Encoder Pulses Cn 11 This sets the number of pulses per revolution of a connected encoder Do not change this parameter s setting the Servomotor might not operate correctly if it is changed The factory setting 1s for 2 048 pulses revolution e Brake Timing 1 Cn 12 Brake Command
45. quency The setting range is 0 to 640 x 0 1 ms and the factory set ting is O X 0 1 ms e Compensating Gain Cn 28 HA LA V W Models When outputting a large torque during acceleration deceleration etc the speed loop gain is decreased based on this setting Motor vibration can be reduced by increasing this setting also the positioning time can be reduced because the speed loop gain can be set to a higher value If this setting 1s too high follow up delays can occur during acceleration and decelera tion The setting range is O to 100 and the factory setting is O Adjust the compensation gain after adjusting the speed loop gain with Cn 04 and the speed loop integral time constant with Cn 05 The compensation gain may not be 100 due to the speed loop gain and speed loop integral time constant set with Cn 04 and Cn 05 in which case increasing the compensation gain will cause an error Make sure that the set value is O before performing auto tuning Proper gain adjustment may not be possible with auto tuning if the set value is not 0 e Unit Number Setting Cn 29 HA LA V W Models This setting specifies the Servo Driver s unit number when communicating with a per sonal computer Set the unit number to 0 when communicating with a single axis Set the unit number from 1 to 14 when communicating with multiple axes in this case be sure not to use the same unit number for more than one Unit The Servo Driver or per sonal computer might be
46. roblems starting with mechanical design integrating the electrical design as well as introducing the con cepts of the software design for the PLC motion control TABLE OF CONTENT ADS Cn iaa 3 MUS GN nassen EE TEE TIE I Ud Oeo do PER TEE EINER Load 7 Bist of tables nasse oV Que o Cu dE DUE LE QU SUR RU ON 9 1 nttoducliOIunesetave RL eo be viv ci zug o caua CORPS 13 I Back older 13 LZ Problemi TOP LATOR it A dress 13 Lo A A eed athe a LE 14 2 Overview of the design and analyses sscscccccccssssssssccccccccsssssscscccccccsssssssccsoes 15 2 Basie components of the deste iau oe eo te a u ae a in 15 2 2 ADestotcandly SES ersehen ee 18 3 Mechanical desidi oss icn enana 21 3 1 The design concept and assembly Pas sans 21 32 A ee a ud nei i eS 25 3 3 Results and possible improvements S earen a a nenn 26 A Y PU REED UU m ke 28 4 Technology of PLC controlled motion occcccccnnconnnccnnnnnnnnnnnoncnnnnnnnnnnonannnnnnnnnos 28 4 2 jDesmidandariplemeniadtfOb s uses 31 4 3 Results and possible improvements sse 34 3 SOWAT desion a herren 37 x Concepis tools and The by coss Reo n PEN a e MIRI a 31 Je E Osee derit A ee mn em 40 5 3 Results and possible improvements oocccccncnnncnnnnnnnonnnnnnonnnnnnnnnnnonnnnnnnnonnnonananons 42 6 Conchita 43 Bl AA IO ee 43 9 2 JB rtbet WORK a es ee se 43 Table of content Literaturen seiner 47 A Mechanical DIMENSIONS cosa eve save
47. t continues usually with very low speed until the next Z pulse This method is used for high precision systems as switches might respond with slightly different delay PLCopen Part 5 p 4 8 2006 onf on or AbsSwitch pez MOVING PART gt 4 A PS LimitSwitch on om or on LimitSwitch Possible scenarios Qi orfolor AbsSwitch on or LimitSwitches or on Figure 4 10 Homing The common practice is to perform search first by higher speed and when the switch 1s found the speed s lowered and the search is performed once again This applies of course for the methods that use switches 30 Electrical design 4 2 Design and implementation Design consideration follow three main lines of thought Besides economy and simplic ity as previously mentioned in the requirements the design was also build to demon strate some of the standard solutions for PLC motion control The system consists of two AC servo drivers controlled by PLC that drive the X and Y axis and one smaller motor that could drive Z axis 4 2 1 X and Y axis control For interfacing the servo driver and the PLC the suitable interfacing module had to be found The first design concept was created around the CD522 Encoder and PWM module Unfortunately despite the fact that the product was announced to be in sale al ready in the end of 2008 and was offered by ABB technical support stuff the module will not be available before summer 2009 CD52
48. task It includes two FBs of the type Axes COM that represent the axes X and Y 5 3 Results and possible improvements The program was tested and showed slightly unstable behaviour when two motion FBs were connected the way that the signal Done from the first FB was triggering the Exe cute of the next FB It would than stay in the state Discrete Motion The reason to this 1s the fact that the movement is triggered by the rising edge on the Start input to the DC541 FB If the program leaves the Standstill state very quickly the COM does not restart the Start signal The solution to this could be to increasing the execution period of the main task or introducing a delay to the state machine Decreasing the period time for COM task could cause some problems as it was observed that the tasks maximum period reached 3 3 ms The test program can be found on the CD 42 6 CONCLUSION Working on the project has been a very satisfactory experience It has also brought some challenges Combining concepts of mechanical electrical and software design into one application requires constant considerations of the impacts the change in one con cept would mean for the rest of the system The wide range of the problems to be solved made the work very time consuming but also more interesting 6 1 Results It can be concluded that the most of the goals were achieved with satisfactory results The mechanical design introduced some challenges because of the ti
49. tory settings for the controller ADJUST CONTROLLER PERFORMED ME WELL A YES Y TEST WITH THEFULL LOAD ADJUST CONTROLLER NO YES y END OF TEST Figure 4 13 Test flowchart 4 3 1 Test of the X axis motion When testing the X axis motion the few settings in the servo driver were changed due to performance issues The movement suffers of a high static friction and high acceleration causes strong vibrations in the mechanical system The adjustments of the controller included a higher integration constant using an acceleration and deceleration function ality of the servo driver and using a special bias function that increases the speed when the position deviation 1s too little This helped to suppress the swinging caused by a higher integration constant The detailed settings for controller can be found in the Ap pendix D The Figure 4 14 shows the test with the adjusted settings The graph shows two running of the axis In both cases the travel distance was 5000 pulses which is roughly 22 cm 34 Electrical design The first curve describes the motion with full load The v brations of the system caused by the static friction are clearly recognisable The second curve shows a run was with out the load 100 Torque Command 96 uiu yoeqpes4 peeds i l j 25
50. tputs and are connected follow ing Way 54 Wiring PLC Servo Control 24V 1 8KQ Input Output Gnd Gnd Figure C 2 Pull up resistor For the standard cables see the manual for the servo driver Omron pdf Leg AT ASAIO DOVL VUIpUt iv J e B a Global Variables i ik E i E E MS 8 PM Input and 8 digital Output R Modules at I O b O Global Variables Variable_Configuration VAR CONFIG E library DC541_AC500_V11 Lib 14 2 08 14 57 36 g m C library lecsfc lib 13 4 06 16 51 28 global variables BO C library SysLibMem lib 18 7 05 09 39 56 global varia 2 0 library SysLibTime lib 18 7 05 09 39 56 global vari E library SysT asklnfo lib 18 7 05 09 39 56 global var a library Util lib 1 6 07 10 40 58 global variables 38 Tools PU IN Alarm configuration H H 1 1 L AT IB1 4 BYTE Input 0 7 CHANNEL 1 3 INP X AT 1X1 4 0 BOOL Input 0 CHANNEL 0 y Alm XAT IX14 1 BOOL Input 1 CHANNEL 1 3 CW limit X AT IX14 2 BOOL Input 2 CHANNE 3 CCW limit X AT IX14 3 BOOL Input 3 CHANN y INP_Y AT IX14 4 BOOL Input 4 CHANNEL J eg Alm YAT 9114 5 BOOL Input 5 CHANNEL I y CW limit Y AT 1X14 6 BOOL Input 6 CHANNE eg CCW limit Y AT 1X14 7 BOOL Input 7 CHANN e df Fast counter FIX Digital Output Relais 8 15 FIX I AT
51. ual so relatively high friction coefficient of 0 4 was chosen The weight of the object used in calculations 1s 1 kg Z platform was estimated to be 1 5 kg and the weight of the construction pulled by motor X was estimated to be 2 5 kg 24 e Choice of Drylin N guide dimensions The length was chosen to satisfy the dimensions of the shelf The type of the guide was chosen by calculating the torque that is applied on the carriage by multiplying the estimated center of mass distance with the estimated weight of the object mounted on the carriage e Choice of timing belts Type of the timing belts were chosen in respect to their maximum allowable tensile load The choice was made by estimating the load The length was chosen to satisfy the dimensions of the shelf and the guides e Choice of pulleys The pulleys were chosen with respect to the rated torque of the motors and the maximum torque of the motors while taking to consideration the speed of the linear movement It should be noted here that a change of an electronic component caused Mechanical design lower possible Revolutions Per Minute value for the motors and therefore the choice of the pulleys was based on the limit values of the rated torque of the motors See chapter 2 1 3 for the torque data Axis Z X Y Drylin N type N27 N27 N40 length 330 mm 1000 mm 750 mm width 27mm 27mm 40 mm Timing belt type T2 5 Synchroflex T2 5 BrecoV T2 5 Synchroflex length 6500 mm 2010
52. y were de signed as a possible concept for the further work on the system and can be reused as a library The code is written in ST CO Axes COM BLimit Switch Cuv BLirnit Switch Cow BhyDc541Directian CH BhyDo541ECRST CH Figure 5 19 Function Block for IO comunication Axes COM is the FB that carries out the I O tasks The FB might be a little confusing because some inputs actually interface with the outputs through the DC541 library FBs placed in the Axes Com FB These include the number of slot the number of channel for the pulse train the number of channel for the direction signal and the number of channel for the deviation counter reset The rest of the inputs are the inputs to the sys tem and the outputs are as well outputs to the servo driver The structure Axis 1s a global variable of type AXES REF which passes control signals for the corresponding motor between the instances of the program 40 Software design A direction WC MoveRelative Execute S00 Yelocity 4000 Distance CommandAborted Axis Ads E Active Figure 5 20 Function Block for relative movement The FB MC MovehRelative has a very simple functionality It takes INOUT Axis struc ture as the input With a rising edge of the Execute input new values are passed to the Axes_COM block through the Axis structure and the state of the axes s changed to 99 Discrete Motion When the falling edge of In Position signal is detected the State is chan
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