Emergency stops

[mk42]

than to hit the start button and hear parts smashing into each other, parts flying out of the machine, other or someone getting hurt.
i saw the holes in the wall where the parts flew!!

It's amazing how fragile otherwise strong cement block can be compared to a flying hunk of metal, and then we remember that a people is even squishier.....

 

[Mandel314159]

does anyone here have a safety standard to look into for grippers holding parts? We had an issue where a customer wanted to de-energize the process but there was parts being suspended by grippers, causing more issues than fixing them in my point of view

 

[joseph_e2]

does anyone here have a safety standard to look into for grippers holding parts? We had an issue where a customer wanted to de-energize the process but there was parts being suspended by grippers, causing more issues than fixing them in my point of view

This should probably be its own thread....but look at piloted flow controls.

 

[mk42]

does anyone here have a safety standard to look into for grippers holding parts? We had an issue where a customer wanted to de-energize the process but there was parts being suspended by grippers, causing more issues than fixing them in my point of view

I would assume it's covered in the robotics standards, but i don't have a copy of them.

My thought is it's really application dependent. If you're gripping an engine block, dropping it is way worse than continuing to hold. If you gripping a bolt or a box of tissues to pallet it up..... dropping it is fine, and maybe that means someone's finger/arm gets released.

 

[Mandel314159]

This should probably be its own thread....but look at piloted flow controls.

you're correct, I'll go ahead and make one

 

[JLand]

To go back to the original question, how the machine initially runs once its started after a safety event has been reset and the machine commanded to resume production is not a question of safety. Whether or not you want to home the machine is up to you - both technical and procedural questions must be answered, but it is not a matter of safety.

How you allow the machine to resume movement (or any energizing function) is covered under the umbrella of safety. Both IEC 61508 and its derivatives (particularly for your concern would be IEC 62061) and ISO 13849 (and I wager ISO 13850 would be handy too) indicate the following (among other things):

• An estop must be a latching device (i.e. you push in the button and it stays pushed in).
• A safety function must have some sort of resetting action, what the resetting action should be dictated by a risk assessment. Generally, this is a secondary momentary pushbutton (after pulling back out the estop), but technically simply pulling out the estop can be sufficient in lower risk applications.
• Machines cannot re-energize based solely on the resetting of a safety function. A second, non-safety related process start button must be used for this (physical or on a touchscreen is fine).

Homing, resuming immediately - that's up to you. If your company wants you to home the device, that's fine. Not a safety concern. Same goes if they don't want to home the device. If they make that argument in the name of safety, either they are unsure of best safety practice and just playing it safe (even though homing or not homing shouldn't safety) or there are relevant details we were not made aware of.

 

[BOWILLY]

As to retaining a part in a robotic pneumatic gripper after an e-stop is activated .... I've seen this addressed in two different and acceptable ways. First, with piloted air control to lock the air in the system. Second, I have seen power to specific pneumatic solenoid valves run outside the control of the safety system. The implementation of either option will be determined by a risk assessment and engineering approval.

 

[JesperMP]

Regarding weights that are held in place by for example robotic grippers.
I don't have the time to find where it is stated in the standards, but that is a case where the grippers should be excluded from the emergency stop.
Same for example for magnet cranes. The crane may be stopped but the magnet must stay energized.