Clicking noise on A4 to A6 axis KR6

    I'm wondering if it's normal for the KR6 R700 to have clicking noise when A4 to A6 axis is moved.
    On my robot, the A4 clicking noise is quite noticeable, A5 A6 is more quite.

    When the robot was delivered new from Kuka, it was already clicking, the engineers that did the setup didn't seem bothered by it, the following engineers that come to do repairs and upgrades also never commented on it, so I was under the impression that it's normal.

    Recently I had a visitor to the lab told me that the clicking is abnormal?

    They click whenever their direction changes, regardless of speed, clicking on A4 can be hear when I physically twist that axis (axis doesn't move, but i'll hear the click)
    in term of movement, it seems OK, nothing major enough to cause concerns.

    Attached are two videos of the clicking sound, one when A4 being twisted physically and another when running a program.

    I had this problem with a KR10 which was also as new, like yours, it also clicked on direction change and would often click constantly like a clock at when at rest. There was also an associated problem of a slight delay when the axis was first commanded to move.

    I went through a long slow back and forth with Kuka who tried changing some servo gain settings, but to no avail. In the end they recommended I replace the motors completely at considerable expense. I was reticent to do that since the robot was virtually unused and I couldn't spend that amount anyway.

    Eventually I got sick of the noise and figured out how to remove the motors on A5 and A6. I found they had backlash in the bevel gear attached to the motor. I don't know how much play they are supposed to have, but it did seem to me this could not be helpful. So I machined the gear flanges very slightly to reduce the backlash and now the noise is much diminished.

    Only occasionally now there is a click on direction change, but much less noticeable. A4 still clicks on direction change - I was not able to work out how to get to that one - perhaps leave it for a rainy day... In my view the motors on these axes are probably too small for the job. They work well at high speed but are less stable at very low speed. In fact Kuka made an excuse that the robot is designed for highspeed not for low speed... But I did not see that in the brochure.. :frowning_face:

    Edited once, last by geraldft (April 17, 2022 at 3:07 AM).

    Quote from geraldft

    I went through a long slow back and forth with Kuka who tried changing some servo gain settings

    Could you provide more details on this process?
    I saw on your other post you said :

    Quote

    The gain settings were found in xml files in ROBOTER\Config\User\Common\Mada\NGAxis

    how do I know which value/how much to change?

    Observation from your experience is that changing them is unlikely to fix the problem, but worth a try I guess, I don't exactly have tooling to machine parts, for funding to replace the assemblies.

    Probably best that I reach out to Kuka; even tho their service has always been friendly, but in terms of professionalism it seems somewhat lacking, can't believe they're shipping robots with backlash... not exactly confident in them rn.

    Edited once, last by evo85210 (April 18, 2022 at 5:42 AM).

    Sorry I can't advise on the gain settings specifics. Kuka provided me with a custom program to tweak them, and I'm not supposed to share that - and besides it was for a slightly different model than yours so the actual numbers will be different to start with. But as I mentioned - in the end it didn't help much anyway...

    There may be other reasons they allow a certain amount of "clearance" in the gears, but I'm not privy to that. I can only speculate it might be better for wear at high speed?

    Maybe check yours first and see if you also have any backlash? If you remove the belt from the final drive of A5 or A6, then try turning the output pulleys by hand and feel if they click or not.

    If you are still under warranty then certainly, you should involve Kuka first. Be prepared for a long process. The local guys here didn't know much about it, and it took a lot of explaining and recording of evidence to get it recognised, then I had to wait for enquiries made to Germany. :frowning_face:

    Edited once, last by geraldft (April 18, 2022 at 5:57 AM).

    as with any new purchase, do not wait for product to be out of warranty. contact manufacturer immediately. anything after warranty period has ended will be expensive. in cases like this, one would need to submit for evaluation a good video along with KRCdiag and diagnostic trace as a minimum. KUKA would then determine if this is normal or not and a way to proceed if needed to do something about it.

    note that robots are not silent. they do make some clicking sounds for example when brake is released etc. if there is a backlash, it can be measured and compared with normal values.

    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

    Since Kuka has worked on the machine a few times since it was delivered, I was always under the impression that they'd tell me if something was wrong, that's why I didn't do anything while it was under warranty.

    I'll reach out to Kuka and see what they say; I've also noticed that if I run hours long programs on it, it won't be able to resume if I press pause half way thru...

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