Lebanese University Faculty of Engineering II Final year project Submitted in fulfillment of the requirements for the Electrical Engineering Degree by Hady Zeinoun Antoine Zeidan Cut to length line Project supervisor: Dr. Georges Eid 2012
List of contents Dedication -------------------------------------------------------------------------p.3 Introduction--------------------------------------------------------------------------p.4 Chap 1: Description of the line---------------------------------------------------p.5 Chap 2: First machine in the line: 2.1) Electrical system--------------------------------------------p.9 2.2) PLC-----------------------------------------------------------p.12 2.3) Hydraulic System-------------------------------------------p15 2.4) Automatic mode + Synchronization----------------------p.20 Chap 3: Second machine in the line 3.1) Electrical and pneumatic system---------------------------p.26 3.2) Programming a new PLC------------------------------------p.31 3.3) Wiring----------------------------------------------------------p.36 3.4) Load cell-------------------------------------------------------p.38 Conclusion--------------------------------------------------------------------------p.40 Appendix A A.1) Electrical catalogue-------------------------------------------p.41 A.2) Hydraulic catalogue------------------------------------------p.49 Appendix B B.1) The program of the PLC -------------------------------------p.61 B.2) HMI -------------------------------------------------------------p.82 2
Dedication There are a number of people without whom this project might not have been accomplished and written, and to whom we are greatly indebted. To our parents who supported us all the way since the beginning of our studies. To Dr. Georges eid who has been the ideal project supervisor. His sage advice and patient encouragement aided the success of our project in innumerable ways. He was our main source of information and not once he stopped supporting us, and giving us from his time to help us find solutions to our problems. To Mr. Hussein suffi who gave us the chance to complete our project in his factory and giving us all the needed support and comfort during our work. To the operators of the line, who helped us during this project in many ways. 3
Introduction The main difficulty in our project is that most of the hardware was missing and no wiring or drawings were present, so we had to use common engineering logic, invent and fill the gaps. The line is called cut to length line. As the name means, the line take a coil of iron which weighs 8 to15 tons, straightens the iron and then cuts it into plates according to the length entered by the operator into the PLC. And then the plates enter another machine so they can be arranged above each other. Once the number of plates is equal to the number wanted by the operator, they are moved by a conveyor to a weighing machine. In total, the line is divided into 2 machines: 1) The first machine itself is divided into 3 major parts: a) the decoiler b) the leveler c) the cutting part 2) The second machine is also divided into 2 parts: a) accumulation part b) weighing machine The project is located at Ras-Maska, in Tripoli, and the company who benefits from it is named Anwar steel. The line is bought from a company in Italy, but this company did not accomplished the contract made with Anwar steel and left the line without making the electrical wiring, nor accomplishing the hydraulic system and even without delivering the electrical drawing and all the parts necessary for the complete work of the line, that's when Mr. Hussein suffy contacted Dr Georges eid, and the project was given to us as our final project. 4
Chap 1: Description of the machine First of all, a large roll of iron is deposited on a trolley which advance and stops above a vertical piston. This hydraulic piston holds the roll and raises it so the decoiler can hold it. Once held, the decoiler turns and the roll will unwind and will be stretched by the aid of a plate. Once stretched, the iron will be directed to the leveler and will be flattened. The leveler is constituted of a set of tight cylinders, from above and under, for high accuracy. Two asynchronous motors are above the leveler which determines the height between the fix and mobile part of the leveler, and a DC motor for rotating the cylinders. 5
All mechanical movements described above are controlled by a PLC which controls the solenoid valves (110V) and the contactors. The control of the machine and the PLC is via push buttons, which are connected to inputs of the PLC or relays or contactors. After being straightened, the iron must be cut into plates of length specified by the operator from a screen connected to the PLC. The number of plates is also specified by the operator. Before being cut, and to know the length of material that entered under the cutting part, a circular absolute encoder is used. Once the length desired passes, a DC motor make the blades rotate, cutting the iron in synchronization with the speed of the line. That's how we get the iron plates. After cutting a sheet of iron, a conveyor takes the plate beneath a sensor that detects its presence. Once the board passes, two iron frames are opened and the board falls on a new conveyor which is at rest at this time. 6
So on until the number of accumulated boards on the second conveyor is equal the number specified by the operator and then the conveyor will turn until the boards arrive over a load cell so they could be weighed. 7
Chap2: First machine in the line 2.1) Electrical system 2.2) PLC 2.3) Hydraulic System 2.4) Automatic mode + Synchronization 8
2.1)Electrical system Not having any catalogues or drawings forced us to start our work by identifying all the electrical parts, so we started our project by localizing each motor that exist on the machine. Since our work was to make the machine run, and even before connecting it to the electricity, and using our engineering logic, we predicted the job of each motor, and what's its role in the whole system. And even more, we didn't know the program of the PLC, so it was very important to predict the logical sequence of the line. In total we have 13 asynchronous three-phase motors, and 5 DC motors each one controlled by a different drive, in the first machine of the line and 6 electrical cabinets. When the machine was imported from Italy, some of the electrical cables were tagged accordingly to the numbers of the junctions in the electrical cabinet. But before connecting them, we traced the cables at both ends, and to secure that no problems will occur when running the machine, we made sure that each cable is in a good condition and that it is electrically continuous. To ensure the good conditions of a cable, we measure the resistance between both ends of the cable, it should be too low in a way that the voltmeter must beep because no resistance or load is connected since the resistance of the cable itself is low. This step of the work took some time because of the big number of cables, and it made us know more about the wiring inside the electrical cabinet. Once we knew that all the cables are in good conditions, now it was the time to know if the motors are working and are connected in the correct way to ensure that the rotor will turn in the right direction so the machine can perform correctly. In this stage of our project, it was the first time we put electricity on the first electrical cabinet that contains the main PLC. 9
The PLC is a General Electric (GE) PLC. As seen in the figure above, in the left side of the cabinet, two colors of cables are connected to the PLC : -Blue cables are for input -Red cables are for output The inputs (24 Volts) come from sensors that are installed on the machine, from push buttons The outputs (110 Volts) are connected to electro valves, to contactors or to relays On the upper right side of the cabinet, the thermal circuit breaker are installed, this type of circuit breaker trips when excessive current passes through it and creates Joule heating of the bimetal and its deformation. This bimetal mechanically triggers a contact, which breaks the circuit protected. The electromechanical system is fairly simple and robust but not very precise and its reaction time is relatively slow. It is mostly used to avoid the direct trip of the circuit breaker when a motor is starting. 01
And below the thermal circuit breaker, we have 34 contactors, 26 of them control 13 synchronous motors (for forward and backward rotation) and the other are used to let the outputs of the PLC passes when the program requires it. So we started by pressing manually the contactors that control these motors to be sure that they are not defected. Now, and in the first machine of the line, we still have 5 DC motors that are controlled each one by a drive. One is for the first stage of the straightening, the second is for the leveler, the third for the cutting part, and the fourth and fifth for two conveyors after the cutting. Each drive has his own cabinet. We connected each cabinet to electricity, but some problems occurred. In the first one, the drive didn't work. After checking all the components (contactors, relays, filter, fuses) we found out that one fuse is defected, and when we changed it the motor worked as needed in the JOG mode. In the third cabinet, the motor turned in a unusual way, at a high speed but not in a regular way: it turn normally, for a certain time, and then suddenly the speed rises sharply. That's why the first thing we checked was the encoder since it is the device that is connected to the drive and according to it the speed change. So we disconnected it from the motor, and dismantled it. We discovered that the disk that is the main part of the encoder was scratched. So we took the necessary information from it (2500 pulses and dimensions) and we ordered a new one and installed it, in this way the problem was resolved and the motor turned normally. In the other drives we didn't face any problem. 00
2.2) PLC The heart of the line, and the main component, is the PLC. A programmable logic controller (PLC) is a digital computer used for automation of electromechanical processes. Since in this machine the PLC was already installed by the Italian company, we started by listing all the inputs and outputs and, tracking them. The sensors used in this line are: a) Inductive sensor, it is and electronic proximity sensor, which detects metallic objects without touching them. They are used in our line to take notice that the metal is present in the particular part where it is installed. It is used in the first straightening part, and before and after the cutting. If these sensors didn't return 24 volts it means the metal isn't present and the machine will no longer continue working waiting for the presence of the material, or it is used for the homing of the knife, (the zero position of the knife is detected when a metallic plate, welded to the axe of the motor, passes in the middle of the sensor as shown in the picture, in that moment the zero position is achieved). b) Limit switch, it is operated by the motion of a machine part or presence of an object. It marks the end of the movement of any object. It can cause the stop of the motor, or gives a signal (24 volts) to the PLC 02
to stop feeding the electro valves or the contactor to stop the movement. It ensure the safety of the people and the line itself. There two kinds of push buttons, normally open and normally close buttons. The normally close push buttons are used usually as emergency buttons. In case we push them they would be opened and it will stop feeding the input of the PLC, that's how the PLC will stop the line according to the program to ensure the safety and avoid any damage especially on humans. The normally open push buttons are connected to the PLC, only when they are pushed they will feed the PLC with 24 volts at the input, and according to the program an output will be on. 03
The listed above sensors and push buttons are connected to the inputs of the PLC. The output of the PLC could be either used to command a contactor which in its turn make a motor work, to command a relay, or to feed an electro valve with 110 volts to it could work. When we finished listing all the inputs and outputs, we connected the PLC to the electricity. A LED light turned on to indicate that the PLC is on. We thought that it was working, but after pushing the push buttons no input was on, so we considered that there was an initial condition that should be on so the PLC could work. We tried to cover the sensors hoping that this action will give the run order to the PLC, but it didn't, so after looking to the not connected inputs, we found that the input number 1 was one of several. So we gave it 24 volts from a transformer and the PLC worked. From that moment we started discovering the program by pushing the push buttons and noticing which output will go on. We tried all the possible combination of inputs to get a more specific view of the concept of the line. As it was predicted the motors worked perfectly but in the manual mode but this time through the PLC command. We still have to work on the hydraulic system. 04
2.3) Hydraulic system Since the heart of the line the PLC worked, the only remaining part of the line that was not working was the hydraulic system. The essential part of the hydraulic system is the hydraulic pumps that supply fluid to the components in the system. Pressure in the system develops in reaction to the load. Hence, a pump rated for 5,100 bar is capable of maintaining flow against a load of 5,100 bar. This pump was not connected to the electricity nor to the hydraulic system. So the first step was to connect it to the electricity to be sure that it works, but since it is a 15 KW pump it is preferable not to connect it directly, but pass it by a soft starter which is a device used with AC electric motors to temporarily reduce the load and torque in the powertrain of the motor during startup. So we installed a soft starter, a contactor and a thermal circuit breaker before the pump. The regulation of the soft starter was made in a way that the motor start with an initial low voltage and a delay time to avoid high current at the startup. 05
Once the pump was tested, the next step was to make a study of the hydraulic system because it was not complete: pipes and control valves were missing. Since the concept of the machine and the mechanical movements were known, we build our study basing on the pre-existing hydraulic system, to be able to accomplish it. So we followed each pipe to where it is connected, and listed the piston as shown in the catalogue. The missing pipes and electro valves are the ones that are related to the decoiler and the coil opening table. Our main sources of information regarding this subject, since 06
we are electrical engineers, were Dr. Eid, the internet and the shops where we visited to take quotations of the valves that we needed to purchase. It was very important to know the mechanical movement of the line so we could complete the missing part of the hydraulic system. Directional control valves or electro valves, route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. The spool slides to different positions in the housing, intersecting grooves and channels route the fluid based on the spool's position. The spool has a central (neutral) position maintained with springs; in this position the supply fluid is blocked, or returned to tank. Sliding the spool to one side routes the hydraulic fluid to an actuator and provides a return path from the actuator to tank. When the spool is moved to the opposite direction the supply and return paths are switched. When the spool is allowed to return to neutral (center) position the actuator fluid paths are blocked, locking it in position. To get a more controllable system we added to the electro valves, pressure regulators that reduce the supply pressure of hydraulic fluids as needed for various circuits. And to maintain a more neutral position and for the piston not to come back to the initial state, we installed check valves which are one-way valves, allowing an accumulator to charge and maintain its pressure after the machine is turned off. In total we bought and installed eight electro valves with its necessary piping. 07
After installing them, we needed to connect the coil of the electro valves to the PLC. There was push buttons and switches in the control panel that are connected to the PLC and when they were pushed, outputs were going on but these outputs weren't connected to any element of the line, and the number of these push buttons and switches were the same as the number of the electro valves, which made us more sure about the wiring that we were doing. After completing the hydraulic system, it was time to test it once we have filled up the reservoir of the pump with the desired fluid. We turned on the pump; the first thing we noticed was leakage in multiple places. A detailed inspection was made on every pipe to make sure that there is no leakage because in case it occurs, the pressure in the hydraulic system will drop enormously which will cause a loss of precision and functionality. The study and purchase of the valves was our responsibility, but their installation was made by the mechanical technicians in the plant. We refilled the reservoir with the fluid and started examining each movement to ensure they work as planned. In some cases were the movement was reversed, we had either to change the connection of the cables that are connected to the coils of the electro valves, or, if installed a one way valve, we replaced the return pipe by the main pipe and vice versa, which are both connected to the same plate, in this method 08
we reversed the movement. At that point, we have a fully tested and working electrical and hydraulic system, but in the manual mode, now we have to try to run the machine in the automatic mode. 09
2.4) Automatic mode + synchronization In the manual mode, we made sure that the PLC and the hydraulic system are working by feeding the inputs, through the sensors and the push buttons, to get the outputs and then a mechanical movement. But now, to run the machine in the automatic mode, surely in the PLC there are conditions that should be satisfied first. Since the program of the PLC was not available for us, we needed to use our logic as engineers, to predict the way that the program was written by using a trial and error strategy. This work demanded from us the full knowledge about the PLC input, and the concept of the machine. In the automatic mode, all drives should be ready to work in the same time and speed, so the enable signal must be received by the drives at the same time. After checking the connections between the electrical cabinets that contain the drives and the one that contains the main PLC, we found that there is a single cable from each cable that enters the cabinet of the PLC. These cables are connected to different relays, each one is controlled by a different output. Our first reaction was to push the button that is considered to make the machine run in the automatic mode since it is called "Marcia" by the company. So when we pushed it, since it is connected to the PLC, an input is turned on, and at the same time an output, but the machine didn't run. And above that, when the button isn't pushed, the output will turn off, so there is no maintain for the output. So we predicted that there is some conditions that should be fulfilled before it will work automatically. Putting steel in front of sensors, pushing limit switches, all of that didn't work. So we started thinking in a new vision, since we knew the relays that by it passes the enable cables of the drives, we took the output of the PLC that is turned on when "MARCIA" is pushed, and we made a circuit to maintain a relay on when the button is pushed, and off when stop is pushed. The push button stop is a red 21
button located under the "MARCIA" button. This relay controls all the relays responsible of the enable signals. Now we have a button that makes the enable signal pass from the output of the plc to the drives. As any other drives, the speed of the motor is determined by an analogue voltage that feeds an input in the drive, it is called speed reference. In our case, the speed reference of the drive that control the leveler is connected to a potentiometer on the control panel. That same potentiometer feeds the input of the first conveyor directly so it will have the same speed, and it feeds the input of the second conveyor through a resistance to decrease the voltage so the second conveyor will be slower. In the case of the drive that controls the first stage of straightening, it didn't work in the automatic mode, but in the jog mode it worked perfectly, so we started looking in his parameters, nothings was unfamiliar, we looked in its input, the speed reference was missing. In theory, the speed of this motor should be the same as the leveler since it is located just before it and from it the steel enters the leveler. To avoid any damage to the drive, we should know the maximum voltage that the input of the speed reference could tolerate, so we couldn't simply connect the same speed reference as the other drives. So by connecting to the input a variable DC 20
voltage and by observing the speed of the motor, we concluded that the maximum voltage that the speed reference could tolerate is 10 V. So we should take from the other drives a DC output that changes with the speed. We found one by simply changing the speed of the first motor and measuring each voltage of the output of the drive. But this output varies between 0 and 80 V. Connecting this output directly will cause a serious damage to the drive, we needed to decrease that voltage, so we passed the cable through a variable resistance. The main difficulty that confronted us was the synchronization between the motors of the first stage of straightening and the leveler because the steel is pulled by the leveler from the straightening part. This synchronization is determined by the resistance that we added between the two drives. To determine the value of the resistance, we didn't have any choice but to take measurement of the speeds of the two cylinders (since the motor isn't directly connected to the cylinder, but it is connected first to a gearbox than to rotating axes). Our goal was to make the leveler turn in the same speed as the first stage of 22
straightening. But originally the levelers' speed is shown from an analogue display that shows' the speed in meter per minute. And we have taken the speed of the other part in round per minute, by fixing on the cylinder a piece of metal and on the body of the line that is already fix a sensor. We made the motor turn with a specific value of voltage entering the speed reference, and we measured the speed of the cylinder in round per minute (by measuring the time in minute between two consecutive signals of the sensor) and having the radius of the cylinder we get the speed in meter per minute. So we compared the two values with each time changing the value of the resistance until we got the same speed. Then we fixed that value of resistance and started testing if we changed the speed of the leveler, we get the other speed the same. With this method we got the fully synchronization of these two motors. Now we still have the last part of the machine that didn't work in the automatic mode, the cutting part. This part of the machine has its own PLC, HMI and drive. The concept of this part is that the length of the steel needed to be cut is entered into the HMI which in its turn is connected to the PLC. In the PLC, this number compared to another number which is the signal that comes from the encoder. The encoder is also connected to the PLC. So the encoder return to the PLC the length that is entering in that particular moment, when that number is equal to the one entered by the operator, the drive get an enable signal and turn knife so it could cut the steel. The initial condition for that concept to work is that the PLC receives a signal from a sensor installed before the cutting part which indicate the presence of steel. 23
After cutting the steel, the knife should go to the zero position in his trajectory to avoid any collision when the machine is running in the automatic mode. This phenomenon is called homing. The homing sensor used is described in the first part of the report. And finally, the safety of the people and the line is very essential, so making sure that all the emergency push buttons works is very important, even the operator demanded us to put more emergency push buttons on the machine, so we did by putting them in series with the other buttons that are connected to an input of the PLC. Now we have a system that works automatically by a simple button if all the initial conditions are satisfied. In conclusion, the initial conditions are, we put the length of the metal sheets that we want, no emergency push button are pushed, there are no faults in the drives, the sensor at the beginning of the line should be on for the PLC to acknowledge the presence of metal, and finally the hydraulic and electrical system are in a good condition. 24
Chap 3: Second machine in the line 3.1) Electrical and pneumatic system 3.2) Programming a new PLC 3.3) Wiring 3.4) Load cell 25
3.1) Electrical and pneumatic system The second machine in the line is the one that is responsible of the accumulation of the metal plates after being cut. It is divided into two parts according to the length of the metal plate. If the plate has a length less than 5 meters, only the first part will work, and if the plate is longer, the two parts will work simultaneously. The electrical system of this machine is constituted of one PLC (OMRON), two drives that controls two AC motors for two different conveyors, seven counters located in the control panel and a number of relays and contactors. As the previous part of the line, we don't have the program of the PLC nor the electrical drawings. Since the strategy practiced in the previous part of the line has been successful, we started by identifying all the electrical part in this machine and trying to understand the concept upon which this machine run. Only by the observation of the elements of the machine, we could understand that it works basing on the sensors. What helped us in this case was that on the cable tray, below the contactors, a name that indicate the motor that the contactor control was written by the Italian company, 26
and that let us concentrate more on the sensors and the encoders. By following the cables of each sensor, we indicated the inputs to which they are connected and predicted the role of each one basing on its position in the machine. We made sure that those cables were in good condition. Once the sensors were listed, we started by exploring the electrical cabinet and the control panel. On the control panel seven counters are installed, each one is connected to an encoder that determines the linear displacement of the mechanical part that the motor moves. Now it was the time for checking if anything is missing in the machine. The first thing we noticed is that an encoder was missing, its' cable was connected to the counter and in the other side was hanging in the air. This encoder is located at the end of the machine and to be sure what kind of encoder it was, we dismantled an existing one that is in front of the machine and that in theory should be the same. So we looked in its' characteristics (500 pulses), and we bought a similar one and connected it. When we opened the cabinet, we noticed a capacitor that was connected in parallel with a bridge that gives 24 volts, it was obviously damaged so we changed it. Its' role was to avoid any drop-voltages and maintain a stable voltage. Since the PLC is the heart and mind of the machine, we started by checking all the inputs and outputs. The inputs are connected either to push buttons, or to sensors or to the counters indirectly since the cables are passing by series of relays that are especially related to the counter. Plus, we have a control panel, other than the main one, which is placed on the body of the machine. From this control panel, and since below the buttons are written their names, we traced the cables of each push button and we concluded that they were connected in parallel to other push buttons in the main control panel, and to the PLC. Some of these push buttons were the run button, 27
automatic and manual button The outputs controls the contactors, relays, and pneumatic electro valves. It was time to connect the cabinet to the electricity and see if we could run it without changing the PLC. The next picture shows the state of cabinet when we just opened it. We could see the bad condition and the huge number of cables which made it harder to us to work and to completely explore the wiring. After connecting the panel to the electricity, the PLC and the counters were working in a normal way. So we started testing all the push buttons and taking knowledge of which output will be turned on and which mechanical movement will occur in the machine since the program of the PLC is unknown. In the pneumatic system, many leakages were noticed. This system is installed by the Italian company itself. The reasons of the leakages were mostly of damaged tubes. They were repaired by the technicians of the factory. Once the pneumatic system was complete and running in a normal way, we continued 28
our work on the electrical system. So we continued what we were already doing, every push button was tested and taking knowledge of the mechanical movement that it produces. As mentioned above, there were 7 counters; each one is connected to a different encoder related to a motor. The principle of the counter is that we enter a number to the HMI, that number represents the distance that we need it for the motor to move the part that he is related to corresponding to the zero position. When the movable part attend the limit switch, we should make the counter reads zero. So we looked on the internet for the catalogue of the counter named QEM. We looked for the procedure to make a counter reset to zero. We finally discovered it, and made all the necessary calibrations of the machine, and returned all the parts that are moved by the counters to their initial place and zeroed all the counters. The counters controls the motor that moves the parts listed below: 1. Conveyor which receives the plates after being cut. It is moved according to the width of the plates. 2. Straightener in the first part of the machine, left side. It presses the accumulated plates after being dropped from the first conveyor between the two straightening parts from the right and left. It is also moved according to the width of the plates. 3. Straightener in the first part of the machine, right side. 4. Straightener in the second part of the machine, left side. 5. Straightener in the second part of the machine, right side. 6. The part that blocks the way of the metal so they would fall 29
approximately at the same place. One is located in the first part of the machine, and it is moved according to the length of the plates. 7. Blocking part in the second part of the machine. After trying the counters, we checked that all the motors are turning in the right direction, and that all the sensors are returning 24 volts to the input of the PLC. At that moment we were sure that no problems exists in the electrical system, and we should try to run the machine in the automatic mode. The first normal reaction was to push the button that is named automatic, but nothing happened. We predicted that there should be initial condition like any program to run the machine automatically. We tried every scenario, by letting the sensors return 24 volts, even by trying every contactor or relay since in the first machine the automatic mode was discovered through a relay, but still no results. We looked for cables between the two machines, we found one, but it is coming from the drive of the conveyor of the first machine, to the drives of the second machine. It is used as a speed reference so the whole line will work at the same speed. We didn't have anymore hope since we tried everything. So after consulting Dr. Eid, we decided to take a new approach for the project. 31
3.2) Programming of a new PLC Since our goal was to make the machine run automatically, and itwas impossible with the PLC programmed by the Italian company, we decided to make by ourselves a new program for this part of the line since we are familiar to the concept of the machine, and we knew each mechanical movement that the motors and the electro valves do. First we needed to choose which PLC we would work on. And that choice is mostly affected by the price of the PLC, its availability and the decision of the owner. Before determining the mark of the PLC, we needed to determine the number of inputs and outputs that we need. We draw the concept of the machine in the Grafcet mode so we could have a more realistic number of inputs and outputs, and to make the concept of the machine more clear. We didn't take the same number of inputs as the already programmed PLC since each person has a way of thinking even if we have the same machine. So after drawing the Grafcet program, we knew that we want to choose a PLC that could tolerate: 1. 65 inputs distributed between limit switches, sensors and push buttons, 2. 44 outputs, used to control relays, We started looking for a PLC that is not very expensive, heavy duty, and has that much of inputs and outputs. Our first choice was to use an already existing PLC in Dr. Eid company, its mark was LG. But we needed to make sure that it could be extended to support the big number of input and outputs. After a long research in the internet we found out that the PLC available was not extendable. 30
So we purchased a Delta PLC, his type is DVP-EX2, and a human machine interface, DOP-B. The HMI is purchased under the demand of the owner of the factory, he wants to see how much plates are being cut, enter the number of plates to be accumulated, and the number of stacks. First of all, we downloaded the operational manual of the PLC to know all the Ladder logic symbols and the memory map. X represents the external inputs, Y external outputs, M auxiliary relay, T timer, C counter, D data register and K a constant. We started by programming the HMI. Three numerical entries were put in the first page of the HMI, one for the number of plates in one stack, the second for the number of stacks and the third for the length of the plates. When we touch the HMI at the numerical entry, a numerical keypad will appear where a number is entered and saved in a data register in the PLC. In the second page of the HMI, we placed an indicator that shows to the operator the number of plates that entered the machine, and the number of stacks that leaved the machine. Under the indicator, a start and stop push buttons are placed for the operator so he could manage the automatic run of the machine. The start and stop push buttons are considered as inputs in the PLC. Once the HMI is programmed, we started by writing the program. We tried to use all the resources in the machine, which means that we based our program on the push buttons and sensors that are already installed, even some of them we didn't use it at all. At the beginning of the machine, three sensors are already installed in the front, we used two of them to detect the metal, but each one has his own role. The first one (capacitive sensor) is connected to the input of the PLC, and in the program it counts the number of plates that enters the machine. The second one (photoelectric sensor) is 32
used to slow the speed of the conveyor when a plate enters the machine by controlling a relay, in the normally close position, 24 Volts is connected to the speed reference of the drives of the conveyors, and when the relay is on, 24 volts passes through a potentiometer to decrease the voltage and then enters the speed reference of the drive.once the plate enters into the machine, the counter in the PLC increases by one. When the whole plate enters the machine, and at the edge down of the sensor, the PLC, through the outputs, gives order to two electro valves, right and left side of the machine, to open the conveyor that holds the plate. On the piston that moves the conveyor, two sensors are installed, one at the beginning and the second at the end. So once the conveyor opens, the sensor at the end of the piston will be on, and return to the PLC 24 volts, at that moment, the PLC orders the electro valves to close until the sensor at the beginning of the piston is on. Meanwhile, the plate will fall into another conveyor. And to ensure the safety of the machine, we installed a sensor that if the height of the accumulated plates attend this sensor, the conveyor will descend for a second. Since the machine is composed of two parts, and if the plates are more than 5 meters, the conveyor of the second part will follow the first one since between the 33
two conveyors there are 3 sensors aligned to determine which way the first conveyor went so the second can follow, and the sensor in the center determine the alignment of the two conveyors. But if the plate is less than 5 meters, the conveyor of the second part will be separated from the system and won't move because the clutch that connects him to the motor will be off. All these options are ordered by the PLC according to the number entered by the operator. With every plate falling from the conveyor, two metal plates along the second conveyor will press the accumulated plates so they would be aligned. This movement is controlled by the PLC outputs that are connected to electro valves on both sides, also according to the length of the plates. This operation will continue until the number of plates that entered into the machine and present on the second conveyor are equal to the number entered by the operator. As an initial condition, the conveyor on which the plates are dropped, if empty, should be at the highest position that is determined by a limit switch since it moves on four vertical axes at the four edges, or if already holding a certain number of plates, it rises until a capacitive sensor turns on which indicate that the plates are present on the conveyor and it could not reach the limit switch. 34
From the moment that all the wanted plates are on the second conveyor, the conveyor start to descend and stops at the limit switch that we determined its position. Than it turns forward so the plates would come out of the machine on the way to the load cell. If the plates are longer than 5 meters, we will have the same scenario as discussed above, but if the plates are less than 5 meters only the first part of the machine will work, which means that the conveyor of the second part will stay at the lowest position, all the time, just it will turn forward when the stack of plates will go out of the machine. To notice that once the number of plates is achieved, and just before the conveyor descend, the first machine in the line will stop to avoid any plate entering the second machine, and it will run again when the stack gets out of the second machine. For the automatic mode, we programmed our PLC according to the concept described above. And in the manual mode, each mechanical movement has its own push button that enters the PLC and an output that controls it. The only things that could limit these movements are the limit switches that are installed to prevent the machine from any damage. A switch connected to the input determines in which mode the machine will run, manual or automatic mode. And to ensure that the whole line will work as a single unit, we made by a simple wiring by connecting the run machine output in parallel with the "Marcia" button, so we could, by the start button in the automatic mode of the second machine, make the whole line work automatically. And the same thing with the stop button. 35
3.3) Wiring Once the program was written, we went to the factory and started dismantling the electrical cabinet. As seen above in the picture of the electrical cabinet, it was in a mess in a way it was difficult to locate a cable. So we started by dismantling the PLC, and before taking of the cables from it, and from the tags on them, we knew if we need this wire or no. If we needed it we will keep it in place, if no we would cut it from the entry of the cabinet and pull it. In this way we clean and rearrange the cabinet so it would be more organized and clean. After finishing this process, we removed the old PLC and installed the new one. To prevent any future problems in the PLC, and to protect the outputs from over current, we installed after each output a relay. This relay is controlled by the PLC and when it is on, it connect 220 volts or 110 volts, to the part that we want to control. Each relay we installed was labeled according to its functionality. So after installing the relays, we started connecting the inputs and outputs that we have in the new program according to a list made by us, and that would help us win some time and be more organized. The next picture shows the big difference between the old and the reorganized cabinet. 36
After finishing the wiring, we connected the cabinet to the electricity and started at first the manual mode. All what we planned for worked properly. Now it was the time for the automatic mode which for us was the biggest challenge. We put the switch into the automatic mode, and we started testing the program. Since we knew the initial conditions, it was easy for us to launch this program. Some modifications were made upon the demand of the operators, even some changes in the positions of sensors were made to ensure the perfect work of the machine. But in total no big changes were done. The result of our program is shown in the picture below. 37
3.4) Load cell Once a stack gets out of the second part of the machine, it should pass over a load cell for measuring the weight. A load cell is a transducer that is used to convert a force into electrical signal. The cables of the load cells were not connected, as seen in the picture above. so we connected them to the counter that is specific for this load cell. After looking into the electrical cabinet and taking a good look into the wiring, and since there is no connection between this system and the other machine, we concluded that it is a standalone system. The first step was to connect the cables coming from the machine, sensors and the motors. After connecting the cabinet to the electricity, nothing have worked, even when forced the sensors to be on. We consulted the operators and they decided that they want the system to work only manually. Once the plates get out from the second machine, a switch installed in the control panel makes a conveyor move the stack to another one that is placed above a load 38
cell. This load cell measures the weight which appears on a counter. Than manually and by a switch, the conveyor transport the plates to another conveyor and stay there until the operator takes them away. So the control of the conveyors is manual by switches. And to ensure more safety for the line, we installed an inductive sensor under the first conveyor and connected it to the newly installed PLC. This sensor is used to make sure that when the line is running, there is no stacks waiting at the exit of the line. So when the sensor returns 24 volts, the line should stop waiting for the operator to transport it. The previous picture shows the cabinet before we disconnected all the wiring, and remade it according to the new concept using only contactors, switches and relays. 39
Conclusion This project demanded from us our total concentration and time, our way of thinking as engineers helped to resolve all the problems that came into our way, and to invent and fill the gaps. Not only we made the machine run as we hoped, but we learned so much things from this project with the help of Dr. Georges Eid and the technicians that we worked with in the factory. The trial and error strategy was our strategy in the first machine since we didn't have any electrical drawings and we didn't knew the program of the PLC, but in the second we invented our own concept of the machine and programmed a PLC. Our goal was achieved when we saw the line working and metal plates were cut and accumulated as it should be, and we transformed a metal coil into metallic plates cut according to any length and packed in any number that we want. Before: After: 41
Appendix A A.1) Electrical catalogue Trolley The coil is placed over this trolley and used to transport the coil over a vertical piston. Decoiler(right part) This decoiler is used to unroll the coil.( RIGHT PART). We have in this part 2 electro valves that move the decoiler right or left. 40
Brake for the turning clams part in the decoiler These electro valves installed by us are for these movements: for the up and down of the vertical piston, open and close of the clutch in the decoiler (one for the right decoiler, and another for the right one), turn forward and backward of the decoiler (one for the right decoiler, and another for the right one) 42
Coil opening table This picture shows that when we started our project, these electro valves where not installed, but according to our studies they were purchased and added to the system. Their role is to control the up and down of the table and the two vertical piston. Limit switch: To limit the move of the table to ensure its safety. 43
First stage of straightening These valves are used to move down and up the cylinders to change the pressure on the plate. This sensor is used to detect the metal before getting into the leveler. This motor rotates the cylinder to help the decoiler pull the metal. 44
Leveler The leveler is the part that is mainly responsible of the straightening of the metal. This motor is used for adjusting the pressure of the cylinders on the metal on the right side by changing the slope of the movable part of the leveler. This motor is used for adjusting the pressure of the cylinders on the metal on the left side by changing the slope of the movable part of the leveler. 45
This motor adjusts the pressure of the cylinders on the metal in front and back of the leveler in the right side. This motor adjusts the pressure of the cylinders on the metal in front and back of the leveler in the right side. These valves are used to move down or up each line of cylinders to get more efficiency in the leveling. 46
` These limit switches are used to define the maximum slop that the leveler could achieve. Pinch Roll In this part of the machine is placed the encoder that according to it the PLC knows the length of the metal that entered under the knife. These electro valves controls the pistons in this part that moves up and down the cylinders. 47
This sensors indicate the presence of the metal before it enters the cutting part. Rotary Shear This part of the machine is the cutting part. This sensor is used for the homing of the knife 48
A.2) Hydraulic catalogue Part 1: Decoiler P1: piston 1 ( to move left the coil ). P2:piston 2 ( to move right the coil ). J1: junction 1 L: lift ( to pull up and pull down the coil ). 49
C: clamps (to clamp the coil ). P.C: pressure control H1: hydraulic system 1 E.V: electro valve M: motor T: tank J2 : junction 2 51
1 to 11 : number for each pipe Part2 : Coil opening table ` 50
P1: piston 1 P2:piston 2 J1: junction 1 L: lift J2: junction2 52
Part 3 : straightening 53
P1:piston 1 P2: piston2 P3:piston 3 M: motor E.V: electro valve 54
Part 4 : Leveler 55
Level 1 Level 2 56
Part 5 : Pinch Roll 57
Close view to the junction Piston 1 Piston 2 Motor 58
Part 6 : Rotary Shear 59
P1: piston 1 P2:piston 2 P3: piston 3 P4: piston 4 P5: piston 5 P6:piston 6 Motor Junction going to opposite motor on the other side 61
Appendix B. B.1) The program of the PLC Kindly find the PLC program in the XPS File. 60
B.2) HMI Counters Indicators 62