Case Study

4. Case study

In this segment we will see how PLCs are incorporated to control various activities in an industry. In this illustration we have a conveyer belt run with two motors at its ends, three different stations to perform various activities like painting of vehicle body or fitting of any component in chassis etc along with two switches to run conveyer. Figure 3.3.4 shows the photograph of a conveyor belt system. The PLC is of “Bull 1764 Micrologix 1500 LSP Series C” which can be controlled by a Graphical User Interface “ RS Logic 500 Starter”.

Figure 3.3.4 PLC controlled conveyor belt system

To run the conveyer belt with the help of switches

As discussed in earlier sections, PLCs are controlled through Ladder Logic. In input section of the ladder, name of the input device must be mentioned on the top of symbol, followed by primary input port. Secondary input port is mentioned just below symbol. In similar way, output symbol should be mentioned with name and output ports as shown in figure 3.3.5.

Figure 3.3.5 A rung to run the conveyor belt.

To control movement of pneumatic devices in an industry with PLCs

Figure 3.3.6 shows a program code to control the motion of pneumatic cylinder with a switch.

To control the operation of sensors

Figure 3.3.7 Program code to make use of sensors and actuators

In indutrial applications, it is required to use various sensors to control the operations of systems and proceses using PLCs. Figure 3.3.7 shows a typical program to operate an electric motor and a pnematic cylinder with the help of some sensors such pneumatic proximity switch.

To control a mechatronics system we need to combine various mechanical and electrical input and output devices and to operate them in a sequential manner. Consider a prototype of industrial assembly line with 3 stations as shown in Figure 3.3.4.

At first station ST1, the sensor identifies an object (finished product) on the conveyer belt and sends a signal to the controller. Controller processes this information and actuates the electric motor to run the conveyer belt.

Second Station ST2: It is allotted for the inspection of the finished product or object. At ST2, conveyer belt stops. In case any fault diagnosed by the inspection system, the product will be taken away by the pneumatic actuators placed at Station 3, ST3. Following video link will show the demonstration of above system.