This project won me the first prize at the mini project exhibition held on the eve of Engineers day (September 15 2007). The concept behind the project is the use of a microcontroller to control the actuation of two single acting spring return cylinders. For starters, I am explaining the entire project with the help of circuits that is hand drawn.
I am starting with the explanation of the electronic circuitry involved.
I used a 8051 microcontroller. The power supply circuit and the microcontroller pin diagram is shown in the figure below. I have explained the same using a PIC16F877A. Two pins of the controller were used as the control for the relay actuation sequence.
The pins were connected to the base of a BC547 transistor. Here, the BC547 transistor acts a switch. When the base of the controller is provided a “high” signal from the controller, the circuit closes and the 12V relay is actuated. As soon as the relay is actuated, the “normally closed” contact of the relay “opens” and the “normally open” contact of the relay “closes”. Two 3/2 solenoid operated direction control valves were used in the setup. The terminals of the solenoid which is responsible for extending the cylinder are connected to the normally open ends of the relay. The pneumatic circuit diagram is shown in the figure below: The single acting cylinders could be replaced by two double acting cylinders. An interlocking circuit where one cylinder remains retracted while the other is extended could also be developed easily. This circuit could be controlled for any timing sequence altering the delay between the extension of the cylinders. This is controlled in the program.
Update: The practical application of this circuit could be in a CNC machine. The clamping of a job and the door lock could be interlocked with a simple program using a similar circuit with double acting cylinders.