Emergency stops

[kazie]

Hey guys. currently running an automation system that includes 60 Panasonic servo drives with STO function. Omron PLC tied into the safety system by the way. The minute i trigger an e stop, is it possible to resume the operation from where the system left off?

 

[kazie]

also STO drives are triggered and all axes stop instantly

 

[Mandel314159]

Usually when guys in charge of me are building E-Stops, it stops a LOT of the processes, and makes sure there's no stored energy in the system. Air systems are bled, electrical systems are just turned off, etc. Usually the reset procedures involve the homing of servo systems on top of resetting the E-stop signals, I'd argue it's probably bad practice to continue motion after pressing an E-stop
There's no reason you can't create a saved tag that saves the positional data of the servo drives when an E-stop is pressed and from there rewrite that tag's information to the target position of the servos from there, right?

 

[mk42]

Every safety standard I've read says that you need a separate start button after the estop condition is removed before anything can happen.

That said, I guess there is no reason it can't pick up where it left off, as long as that makes sense for the process.

 

[James Mcquade]

You cannot resume an automatic cycle when an e-stop is reset.
see nfpa 79 (electrical standard for industrial machinery).
it requires a safety relay first. and other requirements.
james

 

[JesperMP]

The minute i trigger an e stop, is it possible to resume the operation from where the system left off?

This is a bit ambigus.
'Triggering an E-stop' would usually mean pressing the E-stop.
The way the sentence is phrased, it sounds as if you mean 'The moment I reset the E-stop, is it possible to resume the operation from where the system left off ?'.
If that is the question, then no, you have to have an additional start button or switch.

Usually the reset procedures involve the homing of servo systems on top of resetting the E-stop signals, I'd argue it's probably bad practice to continue motion after pressing an E-stop

Why 'bad practice' ? If the application allows for it, and encoder positions are not reset upon the E-stop, IMO it would be totally normal to continue where the process was interrupted.
If you have to reset the process completely, it is not only returning to the home position, but also purging the system of any half-processed material/produce. In large processes that would be a huge problem.

 

[Mandel314159]

Why 'bad practice' ? If the application allows for it, and encoder positions are not reset upon the E-stop, IMO it would be totally normal to continue where the process was interrupted.
If you have to reset the process completely, it is not only returning to the home position, but also purging the system of any half-processed material/produce. In large processes that would be a huge problem.

I'm new enough to where I'm still figuring it out, but in my company, we usually sway to make things return to home position when stuff goes wrong because we're working on robots and stuff that can crush people, so to have it just continue processes or outright stop when and e-stop is hit isn't usually the way to go. That said, I really don't know enough to have a solid opinion on this, so I'm going with the safest answer and saying it depends on the machine/customer

 

[JesperMP]

Well, 'bad practice' are strong words.

 

[Mandel314159]

Well, 'bad practice' are strong words.

note taken

 

[kazie]

This is a bit ambigus.
'Triggering an E-stop' would usually mean pressing the E-stop.
The way the sentence is phrased, it sounds as if you mean 'The moment I reset the E-stop, is it possible to resume the operation from where the system left off ?'.
If that is the question, then no, you have to have an additional start button or switch.


Why 'bad practice' ? If the application allows for it, and encoder positions are not reset upon the E-stop, IMO it would be totally normal to continue where the process was interrupted.
If you have to reset the process completely, it is not only returning to the home position, but also purging the system of any half-processed material/produce. In large processes that would be a huge problem.

So what happens is once the e stop switch is pressed, the drives lose current and absolute encoders are reset to 0. The next best action is to clear the materials and then home the machine and restart the operation from the beginning

 

[kazie]

I'm new enough to where I'm still figuring it out, but in my company, we usually sway to make things return to home position when stuff goes wrong because we're working on robots and stuff that can crush people, so to have it just continue processes or outright stop when and e-stop is hit isn't usually the way to go. That said, I really don't know enough to have a solid opinion on this, so I'm going with the safest answer and saying it depends on the machine/customer

Yes this is presumed as the safest way I would say, to avoid any issues with operators and machines

 

[kazie]

You cannot resume an automatic cycle when an e-stop is reset.
see nfpa 79 (electrical standard for industrial machinery).
it requires a safety relay first. and other requirements.
james

Thanks for the information, i will look it up

 

[kazie]

Every safety standard I've read says that you need a separate start button after the estop condition is removed before anything can happen.

That said, I guess there is no reason it can't pick up where it left off, as long as that makes sense for the process.

Yes we do have a separate start button to restart the operation after the homing of all the stations in the machine

 

[BOWILLY]

Can you restart from the same position as before the e-stop was activated? Yes, BUT it will hinge on what your e-stop has de-energized. Have you lost air pressure? Have you lost positioning data? Have you lost speed data? This data will need to be reloaded before your system is able to restart. As others have mentioned, the proper recovery from an e-stop condition must occur. ie reason for e-stop determined and corrected, safety circuit reset and restart initiated. This usually requires three distinct actions before motion is enabled.

 

[James Mcquade]

let me add this as a safety note.
i do not know your process, but i know what happened at a plant i worked at.
when you reset the estop and get ready to restart the machine
WHERE is each component of the machine process?
1. did any component in the assembly process get dropped by grippers.
2. did any clamped part get released / did any part clamp open?
3. did any component in process when the e-stop was pressed get moved?
4. IS ANY ONE CAUGHT IN THE MACHINE OR INSIDE THE SAFETY FENCE?
these questions must me answered !!!!
it is better to spend time doing an estop at various points in the process to see what happens
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!!
james