Universal Robots Forum

UR3 Wrist 3 reports different number of rotations after Safety Violation

I could not find a specific place to report bugs, so I figured I should post this here.

Specifically, this issue corresponds to tracking the number of revolutions for Wrist 3 on a UR3 after a Safety Violation with a corresponding Protective Stop. In particular, if the robot is reporting 0R and 355 degrees in the ‘Move’ tab and Wrist 3 is rotated quick enough to trigger a “Joint speed limit violated.” error in ‘Freedrive’ mode then upon recovery the ‘Move’ tab will report an arbitrary number of rotations from where the robot stopped.

I understand that this issue should not occur under Normal Operations, but still believe it should be reported and corrective steps applied.

This bug was identified on 3.5.3 and reproducible according to the following steps on a UR3:

  1. Under the “Program Robot” panel “Move” tab, in either ‘Freedrive’ mode or using the move panel jog arrows, rotate Wrist 3 such that it is near the end of one full rotation. As an example, move it to 0R and 355 degrees.

  2. While in ‘Freedrive’ mode, quickly rotate Wrist 3 in the positive direction to reach the next full rotation. The resulting angle in this case should be something like 1R and 15 degrees. This will be shown in the move panel.

  3. If rotated quickly enough, the rotation should result in a Safety Violation. Specifically, “Violation C181A2: Safety system violation: Joint speed limit violated.”

  4. Restart the robot by pressing the “Restart” button on the “Initialize Robot” panel.

  5. Acknowledge the “Safety Message” prompt which states “Protective Stop C153A5: Protective Stop: Position deviates from path: Wrist 3” by pressing “Enable Robot.”

  6. If the controller prompts for confirmation of the robot orientation, ensure that it is correct and proceed as normal.

  7. Start the controller by pressing the “START” button on the “Initialize Robot” panel.

  8. When the robot is fully powered and the brakes are released, go to the “Program Robot” panel.

  9. Under the “Move” tab, observe the reported Wrist 3 angle. When the bug is exposed, the orientation will be some number of whole rotations off from the position reported before the joint speed violation occurs. Sometimes the offset rotation may be positive and in other cases negative. In both cases, an arbitrary number of rotations has been added to the position of Wrist 3.

Hi, I have discovered the same problem, in my case it sometimes appear after a normal restart of the controller - the wrist3 will then start to rotade a full turn when the program starts.
Please let me know of you find a solution to the problem…