E-STOP CIRCUIT

[MIKE31]

HI A machine with push button E-stop and anti tie down palm buttons and light curtain how this machine is wired . thanks

[gravitar]

http://literature.rockwellautomation.com/i...rm001_-en-p.pdf

[Big Country]

I usually try to monitor all my safety circuts through some type of safety relay. EX PILZ PNOZ2.

[gravitar]

Do you know if there's an OSHA requirement for that? We just got a 2-door MIG weld robot cell in from a local integrator, and they are just using prox switches to sense door closure and they're only used as inputs to the PLC, no safety monitoring device. I experienced a very similar problem in years past, at a previous employer on a very similar robot MIG weld cell made by Motoman. This one caused a (thankfully minor) injury to the operator. We described the problem to Motoman and in seemingly the blink of an eye, we had a Motoman tech at our doorstep with safety relays!

[Big Country]

On some of our robot cells we write logic in the robot that if the door limit switch is not made within a certian time it will stop the robot and drop the estop. It more complicated than that but the jest of it is the logic that is wrote in the robot is safer than just the door switch alone. Its just a another redundant way to monitor safety and make me feel more confident about the machine's safety.

[kevinprior]

If you go to www.pilzsupport.co.uk and click on the downloads section, there is an good book which specifies types of circuit, what should be used where etc. As far as I am aware all safety functions must go through via a dedicated relay such as a PNOZ etc. You can use the PLC to monitor the switches in case you want to send a message to a panel view etc, or as big country says in order to provide a little more redundancy. If you leave safety functions down to software through a PLC it is just asking for problems, someone could force the I/O the PLC could fail and so on, and the prox sensors could fail permantly on and you would not know if the guard was open or not. At least with a relay you can be assured that they will fail safe.

[Big Country]

Also another point I forgot is safety relay's are rated in categories and you must evaluate what type of category your machine is in. Wether the operator will get a little scratch in the worse case scenario, this would be a catergory 1 if the operator would receive a fatal injury this would be a catergory 4. Also look at every possible way that the operator could get injured, the reason I say this is just yesterday another eng. friend of mine came in to look at a project that I am working on, I had placed a estop to the left hand of the operator on each opening on the machine. He then asked me what would happen if the operator got their left hand caught on the fight side. They would not be able to reach the estop, after reviewing this with him I also added a pull rope to the machine.

[panic mode]

you need to check the applicable standards, period. if you have robotic cell in USA or Canada, you have to follow RiA and CSA standards such as Z434 (safeguarding of robotic cells) and Z432 (safeguarding of machinery). CSA Z434 is a bit stricter than ANSI/RiA 15.06 which is USA standard. if you use Z434 you are covered in both contries. it is worth noting that ministry of labour will want you as an employer to provide safe working envirment for the workers. user of the equiment (plant) is responsible for safeguarding of machinery (at least in in North America, in Europe it's different).