Application of PLC for Elevator Control System
Contents
1. International Symposium on Devices MEMS Intelligent Systems amp Communication ISDMISC 2011 Proceedings published by International Journal of Computer Applications IJCA Application of PLC for Elevator Control System Saurabh Sharma T Y Ladakhi A P Tiwary Dr B B Pradhan R Phipon Assistant Professor Assistant Associate Professor Associate lI Professor ll Professor Mech Engg Dept Professor Mech Engg Dept Mech Engg Dept Mech Engg SMIT Majitar Mech Engg SMIT Majitar SMIT Majitar Dept SMIT Majitar SMIT Majitar forms the interface by which field devices are connected to the ABSTRACT controller The purpose of this interface is to condition the In this research paper an attempt has been made to integrate the programmable logic controller PLC with elevator for developing its control system Thus this paper describes the application of programmable logic controller for elevator control system The PLC used for this project is GE FANUC with six inputs and four outputs The programming language used is ladder diagram Keywords Programmable logic controller PLC Elevator 1 INTRODUCTION With the overall rapid development taking place in all spheres the living standard of human being particularly in urban areas has tremendously increased as such the high rise buildings are constructed for malls and housing purposes Thus the installation of elevators in these high rise buildings becomes an integral part of t2. ensing devices executes the stored user program from memory and sends appropriate output command to control devices The I O system various signals received from or sent to external field devices The programming device or terminal is used to enter the desired program into the memory of the processor This program is entered using relay ladder logic The program determines the sequence of operation and ultimate control of equipment or machinery 1 Fig 1 Block diagram representing the different parts of PLC 2 APPLICATION OF PLC FOR CONTROL SYSTEM The working principle of PLC for elevator control system functions in the similar manner as that the elevator we use in our daily life The motion of the elevator that people normally use is controlled by a stepper motor It consists of a pulley which helps in upward and downward movement of the lift The position feedback is provided by the limit switches The principle of this set up is whenever the cabinet is called to any level the motor either runs in forward or reverse direction and then stops at the level indicated The indication of the level or the position of the cabinet is given by the limit switches which act as a sensor and gives the signal indicating that the cabinet has reached the required position 3 DEVELOPMENT OF HARDWARE AND SOFTWARE FOR INTERFACING PLC WITH ELEVATOR PLCs may need to interact with people for the purpose of configuration alarm reporting or ev
3. eryday control A Human Machine Interface HMI is employed for this purpose HMIs are also referred to as MMIs Man Machine Interface and GUIs Graphical User Interface A simple system may use buttons and lights to interact with the user Text displays are available as International Symposium on Devices MEMS Intelligent Systems amp Communication ISDMISC 2011 Proceedings published by International Journal of Computer Applications IJCA well as graphical touch screens More complex systems use programming and monitoring software installed on a computer with the PLC connected via a communication interface 6 3 1 Hardware The different devices used for the development of this set up consist of a GE Fanuc Nano PLC Stepper motor voltage supply push buttons switches and connecting wires The details of each of the elements mentioned above are given below 3 1 1 GE FANUC PLC General Electric Fanuc PLCs offer the perfect solution for smaller packaging machines dispensing machines and relay replacement applications with 6 inputs and 4 outputs In spite of its small size this versatile controller provides powerful programming features such as built in high speed counter functionality support for floating point function blocks and subroutines ability to assign passwords and privilege levels override capability etc It operates on 24V DC nominal input power and accept inputs from 6 positive or negative logic inputs Table 1 S
4. evice with large step angles of either 45 or 90 degrees Its simple construction and low cost make it an ideal choice for non industrial applications such as a line printer print wheel positioner Fig 3 a Internal arrangement of Permanent Magnet Motor Unlike the other stepping motors the PM motor rotor has no teeth and is designed to be magnetized at a right angle to its axis Figure 3 a shows a simple 90 degree PM motor with four phases A D and fig 3 b shows the photographic views of PMM Applying current to each phase in sequence will cause the rotor to rotate by adjusting to the changing magnetic fields Although it operates at fairly low speed the PM motor has a ar T a 4 E relatively high torque characteristic 2 Fig 3 b Permanent Magnet Motor 3 2 Software The software used for the development of the set up is the Versapro 2 02 The programming language used in this software is ladder diagram The ladder diagram language is basically a symbolic set of instructions used to create the International Symposium on Devices MEMS Intelligent Systems amp Communication ISDMISC 2011 Proceedings published by International Journal of Computer Applications IJCA controller program These ladder instructions are arranged to obtain the desired control logic that is to be entered into the memory of the PLC 1 3 3 Interfacing of PLC with Elevator PLC used in this set up is GE FANUC with si
5. he infrastructure for the movement of goods and people So the control system is essential in the smooth and safe operation of the elevator It guides the elevator in what order to stop at floors when to open or close the door etc 1 4 Programmable logic controller PLC is a digital computer used for automation of industrial processes such as control of machinery on factory assembly lines Unlike general purpose computers the PLC is designed for multiple inputs and outputs arrangements extended temperature ranges immunity to electrical noise and resistance to vibration and impact Programs to control machine operation are typically stored in battery backed or non volatile memory A PLC is an example of a real time system since output results must be produced in response to input condition within a given period of time otherwise unintended operation will result PLCs are used in many different machines such as packaging and semiconductor and in various industries for monitoring and controlling PLC has many advantages over other control systems It is known for its flexibility low cost operational speed reliability ease of programming security and it is easy in implementing changes and correcting errors 3 PLC is divided into three parts namely the Central Processing Unit CPU the input output I O selection and the programming device The block diagram of PLC can be seen in fig 1 The CPU reads input data from various s
6. igent Systems amp Communication ISDMISC 2011 Proceedings published by International Journal of Computer Applications IJCA iv It is observed that the PLC based controller for elevator works better than the other control systems the industries and other business establishments will be greatly benefitted from this type of control systems However before pressing this type of control system for commercial use the indepth study experimentation and validation is required 6 REFERENCES 1 Programmable Logic Controller User Manual V I Microsystems Pvt Ltd Advance micro system is available at www ams2000 com Cheded L Al Mulla Ma an Control of a four level elevator system using a programmable logic controller International Journal of Electrical Engineering Education 2002 Yang X Zhu Q 1 Xu H Design and Practice of an Elevator Control System Based on PLC Jack H Programmable Logic Controller
7. pecification of GE Fanuc Nano PLC Description Specification Weight 150 grams Height 80 mm Module Dimensions Depth 47 mm Width 75 mm Typical Scan Rate 1 2 ms K for Boolean logic Inputs Six 24 VDC positive negative logic input circuits Outputs Four transistor outputs Output Power Supplies 5 VDC on pin 7 of Serial Port 100 mA max Maximum number of slave devices per RS 485 8 can be increased with a nee repeater Real time clock accuracy for timer 0 5 functions Fig 2 GE Fanuc Nano PLC 3 1 2 Stepper Motor The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation Advantages of step motors are low cost high reliability high torque at low speeds and a simple rugged construction that operates in almost any environment The main disadvantages in using a stepper motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed There are basically three types of stepping motors variable reluctance permanent magnet and hybrid They differ in terms of construction based on the use of permanent magnets and or iron rotors with laminated steel stators The motor used for the development of the set up is permanent magnet type The permanent magnet motor also referred to as a canstack motor has as the name implies a permanent magnet rotor It is a relatively low speed low torque d
8. the cabinet is already in the required position then the motor won t get actuated Again when push button for the second level is pressed then the motor runs either in forward or reversed condition according to its position till the cabinet reaches its required position and actuates the limit switch which enables the motor to stop and if the cabinet is already in the required position then the motor will not get actuated and subsequently it worked successfully for other levels too Apart from the ladder diagram we can also use the block diagram to control the elevator Switch on the Mains Press button 1 Is cabinet on the desired floor Motor runs in reversed condition Fig 5 Flow Diagram of the whole operation of the PLC based controller for elevator Motor does not run 5 CONCLUSION In this paper the authors have discussed the application of a Programmable Logic Controller for an Elevator Control System The authors successfully designed and developed PLC based control system for elevator The following conclusions have been drawn from this research work 4 Nano PLCs can also be interfaced with an elevator ii Markers can be used as an internal output 111 The generation of adequate pulse by the PLC based control system for developing the required torque in the motor for the movement of the elevator else elevator will not function satisfactorily International Symposium on Devices MEMS Intell
9. x inputs and four outputs The photographic view of interfacing of PLC with elevator is shown in fig 4 The inputs are connected to three limit switches and three push buttons and the four outputs are connected to the stepper motor to generate a pulse PLC consists of an on delay timer which is used to generate a pulse and also resets itself A bit sequencer is also used in the program to generate four pulses continuously in sequence which is also used to change the direction of the motor The program also consists of thirteen markers which are used as an internal output because of the less number of output ports These markers can be used in the program as per the requirements For storing the logic to PLC from the software firstly the PLC is to be selected and connected to the port address that is to be used After this the ladder program has to be created by using the ladder options and then the program can be stored to the PLC after the addressing has been given Fig 4 Interfacing PLC with Elevator 4 RESULTS AND DISCUSSION After the interfacing of PLC with elevator followed by thorough checking for errors the trials of the setup were done and the said setup successfully worked as per the designed and developed control system When push button for the first level is pressed then the motor runs in reversed condition till the cabinet reaches its required position and actuates the limit switch which enables the motor to stop and if
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