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


Trapped Key Systems

Trapped Key Systems

Trapped Key Systems


My company has used trapped key systems to allow someone to enter a robot cell to touch up which requires valve power on.
We also allow entry into the cell with valve power off, and the robot fence circuit open.

We are eliminating trapped key, but my counterparts would like to have a standard 'just in case'

Do we need a different key for each energy source to be controlled? In other words would we need a key to teach the robot, valve power on, and a separate key to prohibit robot teach, and allow valve power to be on?

Thanks in advance.

RE: Trapped Key Systems

We have multiple robot welding cells and must have the capability of teaching the robots with power to the fixture, robot, and clamping. We also have material handling robots which move weldments from station to station and alternative location capabilities. Teaching robots to complete these different tasks requires a lot of things to be active.
What you lock out tag out requires knowledge of all the activities both known repetitive and unknown out of process activities. Each installation will vary based on these activities and must have safety reviewed by knowledgable people and agreed to by consensus and approved by management.

Eventually safety resides with everybody and is followed by people doing the work.


RE: Trapped Key Systems

And, if you make it too difficult to "follow the rules", then people will begin breaking them "just a little bit" because "you can't get anything done with the power off everywhere" ... which will eventually hurt people.

What about a single supervisor-operated "Kill Everything" switch that must be manned outside the enclosure during the entry?

RE: Trapped Key Systems


I agree with your points, and it is the policy this company follows.
Assuming we are sending someone in for tip force check of a pedestal mounted weld gun. We would want the robot disabled, if not part of the activity. Under these conditions do we need a second key that when activated opens the fence circuit of the robot? So if someone were entering the cell for touch-up, valve power would be on, and the fence circuit would be closed. On the other hand someone entering the cell to change tips, check tip force or other activity that requires one or more valves to energize would not want the robot to move.


Yes safety systems do need to be simple, and our implementation works as follows:
No key on entry, the gate is locked.
One key unlocks the gate, allows robot motion, and valve power.

All, I am trying to verify how many keys we need, one for robot/valves, and a different key for valves only?
I want to remove all traces of trapped key from our specifications, my counterparts want it left in 'just in case'. I am good with leaving it in, but I want to verify our implementation is correct. Or better yet find a specification.

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!


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