Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Safety PLC logic validation

Safety PLC logic validation

Safety PLC logic validation

Simple question ... How?

If you have one robot, and one light curtain, and one gate, and one E-stop button, all the logic pretty much fits on a couple of rungs that will all fit on the screen of your laptop, and it's simple. But that's not what I'm talking about.

Now try a cell with 15 robots and 6 operator stations, with multiple robots going into each operator station (some welding, some material handling), multiple zone rings and/or Fanuc DCS zones (depending on age of robot) to define various safety zones, plus area scanners to detect if someone reaches past the operator station, etc.

We had an operator station pass routine function testing of the safety logic. Break the outer light curtain while the robot was on the zone switches indicating that it was potentially accessing the station and through an area scanner that also detected if the robot was accessing the station, and the robot stopped. All seemed well, until the operator found a particular spot where the robot was accessing the station but wasn't through the area scanner, and the robot jumped while the operator was in there. In retrospect, now that the needle in the haystack had been pinpointed, it was apparent that the two bits (area scanner interrupted, and robot on the zone ring switches) should have been in series rather than parallel. But how do you know where to look for that needle in the haystack before someone else finds it the hard way?

If you ask the system (A-B GuardLogix) to produce a configuration report for the complete system, including all the DCS zones, it takes several hours to generate and it's several thousand pages. Debugging the logic "on paper" is a non-starter.

What are others doing? How do you handle this?

RE: Safety PLC logic validation

Once you have the system installed and in production I would suggest running a trend of safety I/O, and checking it daily for any errors, you might have seen the scanner clear while the ring switches were indicating the robot was in an unsafe position. As far as the base limits and scanner in series, I have had many systems where parallel was the norm, the base limits muting the scanner. While I am talking about base limits we need to be careful how they are configured. Generally speaking the base limits should be actuated while the robot should be muting the scanner, if a wire opens or the switch fall off no muting will occur. I have had equipment arrive on my floor where this was not the case, and the switch bracket was bent, fortunately no injuries.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


eBook - 10 Reasons to Choose CATIA on the Cloud
To compete in today’s fast-paced and competitive market, smaller and newer firms need a powerful platform that will enable them to compete with bigger players, without the heavy investments needed in computer hardware, software and personnel. Download Now
White Paper - Smart Manufacturing for Electronics
This white paper describes a transformative approach to electronics manufacturing made possible by the addition of Mentor Graphics to the Siemens family. It describes a completely digitalized strategy that supports both printed circuit board (PCB) and mechanical design and manufacturing, uniting the entire product lifecycle – from idea and production to customers and back. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close