Pneumatic cylinders and solenoid valves
Also available in: Català · Castellano
The idea
Pneumatic cylinders make fast, simple movements between two positions (in and out). Solenoid valves receive the PLC’s electrical commands and let air through to one side of the cylinder or the other.
Monostable or bistable
| Monostable | Bistable | |
|---|---|---|
| Signals | One | Two (one per direction) |
| Without a signal | Springs back to rest | Keeps its last position |
| Example in the cell | Piston A (feeder), C (positioner), F (clamp) | Piston D (lifter), rotary arm B, suction cup V1 |
When to choose each: the monostable is simpler and, if the power fails, it returns to a known safe position. The bistable is useful when a position has to be held without keeping the signal on the whole time.
Linear and rotary
- Linear: the rod goes out and in (push, lift, clamp).
- Rotary: the air turns a shaft through a fixed angle between two positions, like arm B, which carries the part from position 1 to position 2.
Confirming the movement
Each cylinder has reed sensors (X_0, X_1) that confirm it has reached the end of its stroke before the program continues.
Interactive demo
Related concepts
Suction cups and the venturi effect
When compressed air is forced through a narrowing, it speeds up and its pressure drops: this creates a vacuum in the suction cup, which holds the part. A vacuum without a pump.
Presence detectors and limit switches
To know whether a part or a piston is in place: contact limit switches, magnetic reed sensors on the cylinders and optical sensors that detect whether the part breaks a light beam.
PLC and GRAFCET
A PLC cyclically reads all its inputs, runs the program and updates the outputs. GRAFCET describes the process as a sequence of steps and transitions: each step waits for a condition before moving to the next.