Standard Grade Technological Studies

AND control

AND control

• Pneumatic systems tend to be very safe.

• But, moving parts such as pistons can be potentially dangerous.

• It is important to take safety precautions.

• AND control circuits can be used to create safety features.

AND control

• AND control can detect if a guard is in place before a machine is turned on.

• These type of circuits can be used to stop a machine being switched on accidentally or stop operators placing their hands in the machine when it is running.

SLIDINGDOOR

VALVEPOSITION

AND control

• AND control utilises two 3/2 valves connected in series.

• The output from the first valve becomes the input to the other.

• The single acting cylinder will only outstroke when both valve A and B are pressed at the same time. Valve A Valve B

AND control

The operation of an AND control circuit can be summarised in a truth table.

OFF OFF INSTROKE

ON OFF INSTROKE

Valve A Valve B Cylinder

OFF ON INSTROKE

ON ON OUTSTROKE

Assignment 9

1. A company logo is to be stamped onto boxes using a single-acting cylinder.

To prevent accidents, the machine will only work when the operator has both hands on the two start buttons.

If either button is released the machine will stop.

BOX BOX BOX BOX

STAMP

Assignment 9

• Design a circuit that will solve the problem.• Using a computer simulation, build and test your

solution.• Construct your circuit using pneumatic components.• Explain how the circuit works.

Assignment

2. Sometimes the operator manages to jam the buttons so that he can move some of the boxes on the conveyor belt.

This is very dangerous and the manager wants the machine guarded.

It should now only work when the guard is in position and the operator has both hands on the start buttons.

Assignment 4

• Redesign your circuit to overcome this new problem.• Using a computer simulation, build and test your

solution.• Construct your circuit using pneumatic components.• Explain how the circuit works.• Draw a truth table to summarise the operation of the

new circuit.