UR20 Joint Replacement?

Technical Questions
1

We just got a second hand UR20 and Wrist 1 started acting up today while programming. The robot moves very “jerky” and eventually alarms out. I can provide videos. All other joints move fine. We we get the code “Wrist 1A: C273a9: Cross Monitoring: Disagreement on velocity”

We have tried rebooting the robot and nothing seems to make it work. If I turn the speed down to 10% or so it will work for a bit but as soon as you turn the speed up it alarms out almost immediately.

I also do not have access to the admin or safety passwords. I am trying to obtain that but do not have high hopes. Do I need access to those passwords to replace a joint?

2

I would definitely submit a case to MyUR, but I don’t think you need either password to replace a joint.

As for needing the passwords, see here: Reseting passwords - #8 by terryc for resetting the admin password if it’s lost, and here: In case of lost password - #2 by eric.feldmann for resetting the safety password.

3

Do you have experience with UR robots? To me it sounds like something simple as a wrong payload being active.

Also, which software is installed? You could reset the whole system with a new image, which will also remove the passwords.

Otherwise, I agree with Eric. You should make a case on MyUR and submit a support file with it.

4

Just wanted to update everyone. I opened a case with UR and seent them the tech files from theUR20. We indeed did need a new wrist joint luckily under warranty. We popped that on and everything has worked fine sense. We also updated the software

I also thought it was a payload problem, but I am thinking the joint on its way out was preventing the payload wizard from working correctly causing it to think it had much more weight on it than it did.

5

Hey Zach,
We have to replace elbow joint on our UR20, I know its not the same joint, but was it easy to replace? Just wondering if this is something we can do in house or if we should call a tech. Thanks

6

It wasn’t to bad. We followed the instructions that we found online and it was pretty much plug and play. Not sure how much different the elbow would be but it only took maybe an hour and we were back up and running. Just a set of allen wrenches and a little pick to get the rubber seal moved out of the way was all we needed.

7

FYI, all robots are calibrated from factory. This calibration will not be valid when you replace a joint.
This includes position calibration and friction correction values of all joints.

If the robot is required to perform very precise movements, these will most likely have shifted a bit after replacing a joint. It’s not as bad on the new robot series with clamps compared to the CB-series with bolts.

The friction corrections of the joints allow the joints to move at their max performance. So you might also lose a (tiny) bit of performance (/max speed before going into a protective stop). You should not notice this if the robot is not pushed to its limits, though.

8

Thanks for the response. Did you the instructions on the UR website? Sorry, first time working with a UR.

9

We used this manual. Section 4 starting at page 18 is where it starts.