Yearly Recurrence of Motor Encoder Index Missing Fault on UR5 CB3 Series

Technical Questions
1

I have an UR5 CB3 series robot, acquired in 2019. It began experiencing ‘Motor Encoder Index Missing’ errors in 2023, initially affecting the shoulder joint. In 2024, the same error occurred on the elbow joint, and this year, it has manifested on the base joint. It is financially unsustainable to replace motors every year.

We have submitted the diagnostic logs to our UR Partner. Their consultation with Universal Robots concluded that no errors were found in the robot’s usage, and the issue was attributed to normal wear and tear.

Is this a known issue with the CB3 series, or are there any preventative measures we can take?

*)The URSoftware version I am currently using is 3.12.0.90886

I checked the URSoftware 3.15.3 release notes and saw a bug fix for EMBEDDED: ‘Improved encoder readings.’ Should I upgrade UR Software?

2

The CB3 robots have indeed suffered from weak encoder discs. It should be fixed on new joints, though, and I would recommended sending your robot to UR for a refurbishment.
I do not believe the update will change anything, and it is by far the most common fault we see in the CB3 joints, and there really isn’t anything you can do to prevent it.

A refurbishent should include replacement of all bad encoder discs. The downside to this is of course that the robot and controller must be taken down for a couple of weeks (usually).

Contact your distributor to get an offer and further assistance.

EDIT: Taking into account the robot’s age, I would definitely recommend a refurbishment no matter what.

3

Is this a known issue affecting CB3 Series robots? Does this issue also occur with the eSeries robots?

Furthermore, I’m curious because I have a CB3 Series UR3 robot that is two years older than my UR5, yet it has never experienced an encoder issue. Are fragile encoder discs a problem unique to the UR5? Could it be specific to a certain motor size, perhaps size 3, which I happen to have?

4

It was a specific year or two of manufacturing. As far as I recall it’s 2018 and 2019. I don’t know if it was associated with specific joints, but I’m pretty sure it was all joints from those years.

And it’s only the CB3 series.

5

Is this defect documented in Universal Robots’ release notes?
Could you please share your source for this information?

6

This is not documented, no, and it is mainly based on my experience after replacing many joints during the last 8 years of working for a large UR distributor.

1 Like
7

Thank you for sharing your knowledge and experience. I really appreciate it.