There is a Spring and Pneumatics on some machines pushing the pin out.

You'll have to verify that this action is happening.

Is the Stopper binding?
(IMG 2) Is there air pressure holding the pin from extending when there shouldn't be?
- If there is pressure on the cylinder on the wrong side, holding it back from moving your solenoid may be bad.
- If there is correct pressure to extend but the cylinder can't extend, you may have an issue with the cylinder being bound.
With the air pressure off, the spring on the stopper should extend the cylinder. However, if that motion is delayed because of mechanical binding, and the Z axis starts to fall, the Stopper may not be able to stop the fall.
(IMG 3) Are the Relay and Solenoid functioning correctly in your Schematic drawings?
- The next tab will help diagnose wiring for the solenoid and Relay.

Explanation