Problem
A tandem fixture assembly machine with 3 pneumatic cylinders was guarded by a finger-detection light curtain. Breaking the curtain triggered a safety exhaust valve that dumped all air from the machine. That met the safety requirement, but every trip meant re-priming and a soft start, and the lost time made the cycle-time target unworkable.
Replacing the cylinders with electric actuators would have meant a redesign and a cost the project couldn't carry.
Approach
The required performance level was confirmed as PLd, and the hazards were reviewed axis by axis:
- Operator access is reach-in at the guard boundary only, with no full-body entry.
- The 2 horizontal cylinders carry no load. Their safety function is to stop and prevent motion when the curtain is broken.
- The vertical cylinder carries a gravity load and only needs to hold at end of stroke.
The safe stop was changed from a full air dump to stop-and-hold: closed-center 5/3 valves to stop motion, pilot-operated check valves to trap air in place, and a spring-applied rod lock with engagement monitoring on the vertical axis.
Result
In progress. Results will be added here when the conversion is validated.