I am designing a system that normally only has 2 Emergency Stops. We are adding 2 systems that are not related to the standard machine we are supplying and will not be within sight of the main machine that we typically supply (one with 2 estops) My Colleagues have argued that the Emergency Stops for all 3 machines should be all connected and when any of the 3 machines have an E-stop the other 2 processes will shutdown. I don't agree with the approach because it isn't common sense to shutdown the other 2 machines which have a separate process. This is not a manufacturing line that has many machines that are combining efforts to make one product. What type of arguments could one lend to help distinguish when emergency stops should be connected together to form a common emergency stop? all 3 of these machines/systems are in different rooms.

Thanks for any advice, sarcasm, humor, or intelligence you can lend!!

Mike

 

Hi Mike,

I am sorry to hear your problem.

Now, I also requested by production to do interconnecting for 2 emergency stop on 2 machine. But I accept their opinion because those machine is related because problem in one machine will give effect for other.

For your cases, i have opinion:
Basically, emergency stop is installed by consider some matters: machine performance, safety, productivity and cost. So I think interconnecting for 3 machines is futile because:
a. the machines is not have relation with others, so the trouble in one machine will not effect to others.
b. There is no safety improvement if interconnecting will be done.
c. How about production lost if trouble in one machine also can stop other machine.
d. It need additional cost to not useful matter.

I hope it will useful for you.

Best regards from Indonesia
OsaKI

 

Mike,

The best way to resolve this is to check out the NEC on E-Stops and ask a local inspector. This will save you lots of headaches and wasted money.

go to http://www.mikeholt.com,

great resource on NEC code stuff.

MJH

 

My view, based on the regulations here in Europe, is that there should be no ambiguity. A production line, for example, consisting of several machines from separate manufacturers along a common conveyor system, would be considered to be one system, the emergency stop of each machine would be expected to stop the whole line - a machine guard however, would normally stop only the relevant machine. This has been easier to achieve since the availability of safety relays such as PILZ and Preventa. From your description, you have three separate systems. Unless these systems are linked by a common conveyor, or are in full view of each other, then there would be no confusion as to which E-Stop relates to which machine. If you need literature to back up your argument, try these

http://www.pilzsupport.co.uk/downloads_psps.htm
http://www.schneider-electric.com.au/Products/ICandAutomation/Preventa/ESS_Guide_to_Safety.htm

--
Marc Sinclair
http://www.germainesystems.co.uk

 

It should be a pretty straight forward decision. An e-stop is for safety. If an e-stop is pushed, all machinery should stop which would be a possible safety consideration to the person at the e-stop button.

Tell your co-workers that a e-stop is a local condition button, not a plant-wide fire alarm.

 

Mike,

In my opinion, as long as the 3 machines are separate, then their E-stops should not be connected. An E-Stop to me is a "Stop at all costs to protect the operators" type of situation. You should only have to do this to each machine individually. Then, make a circuit so that when any individual machine E-stops the other machines are sent a normal cycle stop command. This way the other 2 machines will stop in a controlled manner.

The important point is "The machines must be separate!"

Good Luck

Gerry

 

In some cases it makes sense to stop (but maybe not e-stop) the previous or next machine in the process. I usually try to send a signal of some sort ahead that no further parts are coming, or to the previous machine that no parts are requested.

often the machine design takes care of this such as by having limit switches to indicate part present at an unload station, or Ok to transfer part signals, etc.

its not common to have to actually estop another machine in such a situation, although potentially you might have to if for instance the machines are using a common guarding system.

Bob Peterson

 

Mike,

From what your saying, I would go with individual E-stops.

1) the machines are separate and stand-alone.
2) the machines are not in view of each other.
3) Check the NEC or applicable code and follow those guidelines.

MJH

 

The concept to shut down other, non-related systems from your machine's E-STOP doesn't seem logical at the first glimpse, however there may be good reasons to do so.
If you have to do this, a new and easy way has recently been approved: ASi fieldbus for the integration of safety systems (including E-STOP) as well as regular controls.
ASi is a simple and effective bit level bus.
See:
http://www.manufacturing.net/ctl/article/CA204924

Ralf

 

It may not be required, but the bottom line is that the customer is always right. Politely express your concerns and then give them what they want; automation accomodation.