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Degree inElectrical and Computer

Engineering

Industrial AutomationPractical Exercices II

Introduction to the GRAFCETmethodology

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Industrial Automation

Degree in Electrical and Computer Engineering

Exercise 1

Write a program, using the GRAFCET methodology, that is able to perform automatic

management of a car parking:

A parking capacity of 10 cars should be considered. The car management should be done with

a counter. Sensor S1 is installed at the entrance of the car parking. When a car is detected C1

is actuated during 4 seconds. When this time is over, sensor S1 switches to OFF state, and a

temporization of 2 seconds is carried out. Then C1 down is actuated during four seconds.During this process the counter is incremented. The procedure is similar to gate 2, with the

exception of the counter, once it must be decremented instead of incremented. When the park

is full, a correspondent light sign is switched on, and the entrance of more cars is not allowed.

A free light sign is turned on, if there are free parking places available.

1. Draw a GRAFCET that solves the problem described previously.2. Write the correspondent program in LADDER language.

Entrance

FULL

Exit

FREE

Light Sign

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Exercise 2

The aim of this problem is to control a railway crossing, for which trains can go in both ways.

The figure represents graphically the problem to be solved.

When sensor S1 to detect the presence of a train, C is actuated (closed) for 4 seconds. When

the train goes through S2, C (open) is actuated and the gates are open.

If the train is coming in the opposite direction, the process is the same.

Note: The train is not completely opaque; this means that there are gaps between carriages

that are detectable by the sensors.


Light Sign

Light Sign

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Exercise 3

The following figure shows a system for container transport and storage of a liquid product:

The process begins with the crane on the left side (sensor S1) and lifted cable (sensor S4). The

cable must goes down using the motor M2 till sensor S5 is turned on. When this happens M2

stops and a delay of ten seconds must be settled, which is the time required to put the

container on the pallet. At this time it is possible to press a button B1, whose purpose is to

keep the process in this state, regardless of the 10 second delay. After this time, or as soon as

B1 switches from ON to OFF, the cable must goes up till sensor S4 is activated. Then motor

M1 (Right) is activated so that the crane moves to the right until it reaches sensor S2. Once in

this state motor M1 stops and the motor M2 (Down) is started, so that the cable goes downuntil the sensor S5 is activated. Here the actuator must be enabled for two seconds, but with

the restriction that there is no container on the conveyor belt. In case there is, the crane should

wait until the ongoing process is complete, and then the container should be placed on the

conveyor. After this action the cable must goes up and returns to starting position to resume

the process.

When in motion, the conveyor belt transports an object until it is detected by sensor S3. Then

the conveyor stops and valve V1 is opened for 5 seconds. After this time the valve closes and

the conveyor starts running again for 2 seconds. At the end of this time, the conveyor is

stopped again for 4 seconds, so that the load is removed. At the end of this time the conveyor

is turned on again. The containers must be counted using the information provided by SensorS3, which detects the containers passing in the conveyor. At the fourth container, valve V2 is

opened for 10 seconds. The process has a button Start / Stop. If the process is stopped (Stop)

by activating this button, when it is turned on (start), the current processes should continue at

exactly the same point where they were when the button was activated.


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Exercise 4

The control system of the process, shown below, follows the following sequence of operation:

When the start button ON is pressed, the system must perform the opening of the gates C1

and C2.

The gate C1 remains open until the weighing-machine shows a L1 reading. When the weighing-machine shows L1, gate C1 is closed and C2 remains open

until L2 reading is checked.

When the weighing-machine shows L2, gate C2 is closed. When the weighing-machine has the required amount of material, a cylinder is

activated till the weighing-machine is empty, and sensor 3 is activated.

If during the whole process, the PE button is pressed, all gates shall be closedand the system must be stopped.

The cycle of operation is automatic, in case the R switch is turned on. A cycle of operation is not affected by turning on the ON button. The cylinders are single acting.


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Exercise 5

The aim of this problem is to control a washing machine with a cold washing program. The

cycle of operation of the machine is as follows:

There is a start button to start the whole process. At the beginning of the cycle,the water drum is filled by turning on valve E until the level sensor is

activated. This level sensor is activated when the drum is filled with water. The washing process is composed of 50 cycles. In each cycle, the motor will

run 30 seconds in one direction (clockwise - motorH) and 30 seconds in the

other direction (counterclockwise - motorA), and it remains stopped for 0.5

seconds between each change of direction.

After the washing process is performed the rinse cycle begins. It consists offour rinses. Each rinse begins by filling the water drum, by actuating valve E

until the level sensor is activated. A rinse consists of 10 cycles. In each cycle,

the motor will run 30 seconds in each direction, stopping 0.5 seconds in each

change of direction.

After each rinse the drum is emptied by activating a drain pump B, until thelevel sensor is switched off. While the drain pump is running, the motor should

rotate counter-clockwise.

Once the rinse process is finished, the spinning process is started. Spinningconsists of motor running at a higher speed (motorC) for 5 minutes. While in

spinning, the drain pump must be activated.


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