Universal Robots Forum

6th axis position problem under torque load


I’m using a UR10, CB3. We use a tool with some not-so-flexible set of cables. The load on the UR10 toolhead is approx 5kg, so well within the limits. During a lineair move, at speed 250mm/s and acc 1.25m/s^2, we experience a deviation of the tool orientation.

The path taken is indeed lineair and starts / stops correctly and is also taken with the correct speed. We assume the acceleration is fine, too. The robot doesn’t give path deviation errors or a protective stop, or whatever.

Yet, the orientation of the tool is off, approx. 0.2 degrees about the toolflange Z axis, e.g. the 6th axis of the robot. After the use of this tool, we switch to a second tool, but due to the 0.2 degree error, we end up with a 3mm error in the application of the second tool.

The problem is caused by the not-so-flexible cables excerting a torque force about the tool flange Z axis. The tool is solidly mounted and 100% aluminium. It appears as if there is some “play” in the 6th axis. We can see slight movement when we manually apply torque to verify it’s at the robot, not the tool mount / holder.

  • Is there some setting that influences the rigidity of this axis?
  • What can we do to migitate this problem?
  • We believe that the motor / gearbox inside the robot isn’t defective. What is the tolerance the UR10 robot has on this point?