HMI Button

Can anyone explain to me the reason for an HMI button that requires the operator to keep his finger on it while raising and lowering a s set of press rolls? I believe for safety.

Yes, you will know where at least one of hands are located. However this is not to be confused with a anti-tie down.

Regards,
Garry
http://www.accautomation.ca

I totally aree jsut looking for a standard or written explanation to bring to them. I see how the two hand rule kind of play into this but not fully.

Well, if you wanted it to stop, how would you do it besides releasing the button?
It sounds like a manual function like jog (slowly) open or closed.
Sure hope the guards still need to be in place while this is going on.

Hi if the hardwired interlocks such as safety gates are closed and reset, the PLC output can be taken via the safety relay so that it breaks the signal to the drive

I am not a fan of using the HMI as a "hand" detector either. It is not a certified safety device at the end of the day

I can imagine that it may be to protect the machine against damage, for example the operator must visually check that there are no collision between parts.

We do not allow this because the HMI screen itself does not have a failsafe. We have had the screen button to stick on several units because of excessive usage.

regards,
james

Reading your other post I, this is my thoughts.
#1 since you are retro fitting the system you should use mechanical pushbuttons and eliminate the potential problem I discussed earlier.
#2 if you are on split levels you cannot do as you suggest, you must have dual controls - line of sight rule. You cannot watch both sections
at the same time.

#3 you must get with engineering, safety, and maintenance and do a risk accessment.
#4 an HMI controlled lift instead of manual controls is just asking for trouble. Check your code books for rules on lifts.