Machine control using Programmable Logic Controller (PLC) 1 Nidhi Ponnamma M.A, 2 E. Elavarasi M.Tech, IV Semester, DEC, Asst. Professor Dept. of ECE, AMCEC Email: 1 nidhi9253@gmail.com, 2 elu_ye@yahoo.co.in Abstract: PLC and ladder logic are the workhorses of factory automation. Earlier automated systems used hundreds or thousands of electromechanical relays; which used to consume lot of time in wiring. A single PLC can be programmed as an efficient replacement. This paper speaks of programming the PLC and designing HMI screens used in the design & development of an induction hardening machine. Induction hardening is a form of heat treatment in which a metal part is heated by induction heating and then quenched. PLC is a digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequencing, timing, counting and arithmetic, to control various types of machines or process through digital or analog input/output. HMI is the part of the machine that handles the Human-machine interaction. This helps in communicating with the machine. HMI screen is also referred as the operator interface terminal, it allows to: view faults, operate machine and control manual functions. Keywords: PLC, Ladder logic, Simatic Manager, Induction hardening, Quenching, Quenchant, WinCC Flexible Advance and HMI. I. INTRODUCTION TO PLC Programmable Logic Controller (PLC) is a specialized industrial computers used for controlling and operating the manufacturing process and machinery. It uses a programmable memory to store instructions and execute functions including on/off control, timing, counting, sequencing, arithmetic, and data handling. The PLC accepts inputs from switches and sensors, evaluates them based on a program (logic), and changes the state of outputs to control a machine or process. Programmable Logic Controllers (PLC s) are used in every aspect of industry to expand and enhance production. Where older automated systems would use hundreds or thousands of electromechanical relays, a single PLC can be programmed as an efficient replacement. Programming is carried out using LADDER LOGIC. II. INDUCTION HARDENING Heat treatment is usually carried out to provide metal with desirable properties. Induction hardening is a thermal hardening process in which the material is austenitized through inductive heating followed by quenching, which causes the austenitized volume to transform to martensite. It is an energy effective method; only the volume to be hardened is heated. This method provides the desired hardness profile at a reasonable cost. Hardening is carried out to improve the final properties of the metal such as, tensile strength, fatigue strength, elasticity and wear resistance. Quenching is the rapid cooling of a work piece to obtain certain material properties. It must be rapid enough to transform austenite to matensite. Commonly used water based polymer quenchants are: Polyalkylene Glycols (PAG) and acrylates (PA). III. DESCRIPTION OF CPU 315-2 PN/DP Fig.1. PG to PLC interface 32
1. Status and Error display: It is used to display internal CPU fault or fault in module. 2. Bay for Simatic Micro card: It is the slot provided for a memory card. Programs are saved in memory card. 3. Mode selector: It allows us to select the mode of PLC; Run mode or Stop mode. 4. Industrial Ethernet twisted pair cable for connecting to additional PROFINET devices: It is used to interface PLC and Human Machine Interface. 5. Industrial Ethernet twisted pair cable for interconnecting PN interface X2: It is used to interface PLC and computer/pg. 6. Programming device (PG) with STEP 7 software: It is referred to the computer/laptop in which the software is installed. Step 7 or Simatic Manager is the software used for programming. 7. Mounting rail: It is used to mount the CPU/ PLC. 8. Power supply ON/OFF: It is used to indicate the supply given to the PLC. IV. HARDENING MACHINE OPERATION Below figure.2 represents the block diagram of hardening machine. It consists of Chiller unit 1 and 2, Control panel, Air blower, Quench water, Quench tank, Power source, Loading conveyor, Unloading conveyor and heating station. A. Heating station Component/ Parts are heated at the heating station. In this station metal is heated to hardening temperature (austenitizing). B. Cooling station or Quench water Component/ Parts are cooled using continuously showering quench water. It is carried out to transform austenite to martensite. Hardening is followed by quenching in a suitable quenchant. Quenching should be fast enough, but not so fast that it causes problems such as cracking or unnecessary distortion. The most used quenchant is a polymer solution in water and the next most used is pure water. The heating zone can be quenched in different ways, but the spray quenching method is the most common. C. Chiller unit It is used to remove heat from liquid via a vaporcompression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. D. Source Power source used is CAMI 100kw, with low frequency. E. Control unit CPU, S7 315-2 PN/DP is present on the control unit. Programs are downloaded onto the CPU, S7 315-2 PN/DP using MPI. Fig.2. Block diagram of Hardening machine The overall system operation is controlled using PLC and the programming is carried out using ladder. This machine is used for hardening different sized component/part/work piece. Component size selection and power percentage selection is made on Human Machine Interface (HMI). Hardening machine consists of 14 meters long conveyor. Left side of the machine is referred as loading conveyor and the right side is referred as unloading conveyor. Seven proximity sensors are placed on the conveyor. Each sensor performs different functions. First sensor senses, when the component is loaded to the conveyor (loading side). When second sensor is high, the component is heated; Pyrometer is used to monitor component temperature, and programming is done in such a way that the pyrometer value is read on the HMI screen. Air blower starts when third sensor gets activated. If third and fourth sensors are low, then blower should be switched OFF. When proximity sensor 5 gets enabled unload the component at unloading side. Last two sensors are used to indicate conveyor chain cut (both loading and unloading). These functions are digitally operated using PLC. PLC used is S7300 with CPU 315-2PN/DP. Three modes of operation are: Manual mode, Semi Auto mode and Auto mode. 33
a) Manual mode: Entire machine operations (from loading the component till unloading) are controlled manually. b) Semi Auto mode: Loading and unloading the component it done manually, remaining operation is carried out automatically. c) Auto mode: Entire machine operation is carried out automatically. Components are loaded with the help of lifter unit and singling unit. Lifter unit is used to lift the work piece, where as singling unit is used to select single component from group of components. Step1: Cycle start Step 2: Turn on the pumps. V. ALGORITHM Step 3: Check for Pre- Condition. If the condition doesn t satisfy, then go to Step 2. Step 4: Press cycle start button. Step 5: Check for Alarms. If there are any active alarms, then go to Step 20. Step 6: Start loading and unloading conveyor motor. Step 7: Check whether the work piece/part is present at loading side. Step 8: Check whether the work piece is present at heating point. Step 9: Switch ON the heat. Step 10: Check whether PS2 and PS 3 is low. Step 11: Switch OFF the heat. Step 12: Wait till PS 3 becomes high. Step 13: Switch ON the Air blower. Step 14: Wait till PS 4 becomes low. Step 15: Switch OFF the Air blower. Step 16: Part/ work piece is cooled at Quench station. Step 17: Wait till PS 5 becomes high. Step 18: Unload the part/work piece. Step 19: Check if Emergency/Cycle stop/reset button is pressed. If yes, then go to step 20. If no, then repeat the steps from step 7. Step 20: Stop. VI. FLOW CHART Figure 3 shows the flow chart of machine operation. Fig.3. Flow chart VII. SIMATIC MANAGER Figure.4 represents the elements present on the Simatic Manager window. Simatic Manager is the tool used to carry out PLC programming. Programmable Logic Controller (PLC) is a specialized industrial computers used for controlling and operating the manufacturing process and machinery. It uses a programmable memory to store instructions and execute functions including turning ON/OFF the control, timing, counting, sequencing, arithmetic, and data handling. The PLC accepts inputs from switches and sensors, evaluates them based on a program (logic), and changes the state of outputs to control a machine or process. Programmable Logic Controllers (PLC s) are used in every aspect of industry to expand and enhance production. 34
Editor Window IX. COMMUNICATION BETWEEN HARDWARE AND SOFTWARE (PLC AND PC/PG): Using the STEP 7 software, S7 program can be created within a project. The S7 programmable controller consists of a power supply unit, a CPU, and input and output modules (I/O modules). MPI is used to communicate between PC and PLC. Through this, the Ladder logic or the programs from PC/PG is downloaded to PLC. Fig.4. PLC editor Window Programs are written on the editor window. On completing the programming part, the programs are compiled ( ), and then the programs are downloaded to the PLC. To download the program, click on download button run mode ( ).. And then the program can be put to VIII. WINCC FLEXIBLE ADVANCE Figure.5 represents the elements present on the WinCC Flexible Advance window. WinCC Flexible Advance is the tool used to carry out HMI screens designing. HMI is the part of the machine that handles the Humanmachine interaction. This helps us to communicate with the machine. Using HMI, we can perform necessary operations like controlling and monitoring the machine operations. HMI screen are also referred as the operator interface terminal, it allows to: view faults, operate machine and control manual functions. In some machines, the viewing screen is touching sensitive. On other machines, a separate keyboard and mouse is used to select and input the data. Fig.6. Communication between PC and PLC X. COMMUNICATION BETWEEN PLC AND HMI: MPI network is used to communicate between the Programmable Logic Controller (PLC) and the Human Machine Interface (HMI) Fig.5. HMI screen editor Window Fig.7. Communication between PLC and HMI XI. CONCLUSION PLC is very versatile and effective tool in industrial automation. It cuts the production costs and increases the quality. Load to load time taken is 90 seconds. Troubleshooting is easy in PLC. Wiring is complicated when electromechanical relays are used, where as wiring 35
is easy when PLC s are used. Hence it is reliable to operate/ control a machine using PLC. REFERENCES [1] R. Filer and L. George Programmable Controllers and Designing Sequential Logic, 1992: Saunders College Pub. [2] L.A. Bryan and E.A. Bryan Programmable Controllers: Theory and Implementation, 1988: Industrial Text. [3] C. D. Simpson Programmable Logic Controllers, 1994: Regents/Prentice-Hall. [4] W. G. Ian Programmable Controllers: Operation and Application, 1988: Prentice-Hall [5] Bing Tian; Chengxiong Mao; Jiming Lu; Dan Wang; Yu He; Yuping Duan; Jun Qiu "400 V/1000 kva Hybrid Automatic Transfer Switch", Industrial Electronics, IEEE Transactions on, On page(s): 5422-5435 Volume: 60, Issue: 12, Dec. 2013 [6] Saracin, C.G.; Saracin, M.; Zdrentu, D. "Experimental study platform of the automatic transfer switch used to power supplies backup", Advanced Topics in Electrical Engineering (ATEE), 2013 8th International Symposium on, On page(s): 1 6 [7] Ashour, Hamdy "Automatic transfer switch (ATS) using programmable logic controller (PLC)", Mechatronics, 2004. ICM '04. Proceedings of the IEEE International Conference on, on page(s): 531 535 [8] Hoge, D.J.; Jensen, J.R. "A comparison of protocol conversion methods for the retrofit of SCADA systems", Petroleum and Chemical Industry Conference, 1988, Record of Conference Papers., Industrial Applications Society 35th Annual, On page(s): 245-248 36