Kuka error at safe input , safety swithes

  • Hello,

    I need some of your experience about safety.

    I have made few projects with safety where safety gates are opened quite often(all of them uses X11 with SIBstandart). With some of them I get dual channel safety error quite often, resetting the safety removes error.

    1. Project with custom made gates with troax lock (440K Safety Interlock Switch); KSS8.3; KRC4; KR180 R3200 PA (safety error often)

    2. Project with Satech gates with Troax lock (440K Safety Interlock Switch); KSS8.5; KRC4; KR240 R3200 PA (safety error often)

    3. Project with Satech gates with Satech lock (Schmersal AZ 16-12ZVRK-M16 Switch); KSS8.5; KRC4; KR240 R3200 PA (safety error very very rare)

    Do you have some similar experience with safety switches?

    Maybe it's how Kuka interprets signals or maybe it's my wiring?

    Does anyone has some recommendations about safety switches that work well with Kuka?

    I noticed that on KSS8.5 resert safety error button was added in the menu for easy access, I figured maybe this problem isn't that rare.


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  • such errors are common when switch is mechanical and it is operated manually.

    same goes for EStop buttons, enabling devices etc.

    to reproduce it just move switch very slowly and fault will occur.

    this has to do with fact that for safety switches contacts are operated independently (so in case one fail, other still can work).

    the problem is that the two contacts don't switch at the same time. if switch is operated slowly, that difference is bigger.

    and if it exceeds tolerance of the safety controller then fault is generated.

    this can be minimized by careful design choices, such as:

    choosing devices that do not use mechanical contacts (transponder based),

    considering sensing range and mechanical tolerances of the gate when closed

    considering approach direction so that both switches are activated at the (nearly) same time even if approach is slow etc.

    Consider mastering reference switch for example:

    sensing elements are green circles. which approach direction would result in triggering both of them at the same time?

    certainly not by using Y direction... (Y direction can still be used but approach would need to be sufficiently fast so that time-difference between channels is small enough.)

    Z-approach is not the best either due risk of collision in case of an overshoot. i have seen several of them get damaged by contact.

    for this particular sensor approach in X direction is the best.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • That's odd, I have to admit I almost never run into this issue as long as I'm using safety-rated gate switches, unless I try to deliberately make it happen, as Panic described. In fact, if you have a sufficiently deft touch, you can make it happen on the deadman switches on the SmartPad!

    That said, a single-channel fault occurs when the two channels on a safety interlock have different states for more than a very short time limit -- something on the order of 20-50ms, IIRC. Most safety interlock devices that I've encountered are mechanically designed such that both channels open/close nearly simultaneously.

    So, the easy answer would be, replace all the problematic gate locks with the ones that work better. But, since I suspect that would make the budget people :loudly_crying_face:, the next best thing is to look at the problematic locks and see if you can identify what's going wrong. If key is being pulled or ejected at an odd angle, or the retention chain is too short, that could be an issue. Something as simple as dirt or grime in the works could also contribute.

  • Then I guess I'll use what I know works fine and for now it's just inconvenient, not a system breaking. It might be that this is how you close the gates or it got worn a little(i'll need to investigate this when I'll go there), because during programming this didn't happen.

    Thank you for the replies.

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