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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.

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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

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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

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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.

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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.

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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.

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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.

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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

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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.

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