Requirements -- Dropping Air in machine

You can alos get cylinders with a 'neck lock' which is effectively a clamp that locks the rod so in the event of air loss (E-Stop) the cylinder is basically locked to prevent any movment


As others have said, risk assessment is the way to determine how to determine safety requirements. A combination of more specialist valves and cylinders can be used to trap air, vent air, neck lock or any other outcome as required
 
Ditto to what has already been said.
You need a course in maschine safety, or you must hire a safety consultant.
This is not trivial matter.
If there is an accident with your machine and you havent done everything according to standards you and your company can get into serious trouble.

What I write below is only a generic discussion.

Pneumatically:
What do you do if the cylinders can't drop air without adversely affecting the machine? I imagine you need spring return cylinders, but what if it needs to hold two different positions?
You definitely cannot use spring return cylinders ! In that case a movement would always be started when penumatic pressure is removed.
If this is a situation where an operator must access the area frequently, then you should consider to change the maschine design to remove or minimize the risk. Active measures are difficult to implement.
If on the other hand, this is 'only' for maintenance, then ZES is the way to go. If there are risks because of suspended weights, then additional measures such as jacks and/or locking bolts may be required. I do not like the idea of 'locking' pneumatic cylinders by means of trapping air on one side of the cylinder. What happens when the maintenance guy removes the hose on one side of the cylinder ?

Electrically:
What if I had an area where the operator could load at a given moment, but when something else, like a robot, enters another area and we need to drop control power?
The safety systems of your maschine and the robot would have to be integrated into each other. There would probably have to be some kind of multiple safeties with muting of one safety system while the other takes over. The machine must be safe in all situations.

If you have any diagrams of how it is done electrically or pneumatically, it would really be appreciated! I'm just trying to get a better understanding on how to do these things. Also, if you have any part numbers or examples for air dump valves, I would love to see.
You are far far away from deciding about part numbers.
And I would never post specific advice on how to implement your safety. In the worst case I could be liable.
Even when you pay for advice from experts and manufacturers, you will always only get generic advice, never specific advice. Again because of liability.
 
Careful with the 3 position valves. If you drop air on an E-Stop, and the cylinder loses its pressure (which is what it will eventually do), the rod will not have any back pressure to limit its speed when the cylinder is told to advance.

Our door drop lifter suffered from this, and would launch the doors from about 30 feet up onto unsuspecting workers. But rather than replace the 3 position valve with a 2 position one, the plant chose to put up a massive net to catch the doors as they flew off.
 
In the last year or so, our big car customers are not accepting rod-locks as safety devices (apparently they've experienced some failures). Its been a scramble for the mechanical engineering folks to design in acceptable solutions.
 

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