Free drive feels as if the robot joints are skidding

We have a UR10 CB3, late 2018. We use the free drive frequently. We’ve noticed that it becomes progressively harder to move the robot with the free drive function. It feels like robot joint 2, is “skidding”, e.g. as if it is hopping over indents, rather then a smooth move. We start to feel the same on joint 3 as well, all though not as bad as joint 2. The effect is most pronounced if the tool head is close to the base and less worse far from it.

During normal operation, e.g. the robot performs a programmed movel(), we notice “bouncing” in the robot motion, but this time when the tool is further out, not close to the base.

The payload is 5kg and the CoG close to the tool mount. Typical moves are only 6 tot 10mm/sec, although sometimes we do have high accelerations ( limited to 2.5m/sec^2). The robot stops frequently, e.g. after every 10mm of moving. It receives new movel() locations after each 10mm move.

Does anyone have a clue what’s going on? What’s causing this behavior?

Any ideas / help / remarks appreciated.

It does sound like worn gears to me. Speed does not wear the gears quite as much as high acceleration/deceleration. 2500mm/s^2 is fairly high imo, and if it has been doing this for 5 years, it could very well have worn some of the gears out.

You should contact your local distributor for a check-up. Even though it might take a while and be costly, it is also possible to have the robot sent to UR themselves, where they will measure all joints and gears through and repair whatever is wrong with the robot. :slight_smile:

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Thanks, was afraid it would be something like that…

first, I think you should try to down accelerations at 1.0m/s2 for a such small linear move (10mm).
do you stop at each waypoint ?