Noise on Motion Start and Stop

From CPR Wiki

At some robots a distinct noise can be heard when axes start or stop moving. This noise is caused by the current reduction and has no negative effect on the motion. This article explains this observation.

When does it occur?

It can occur when an axis is moving slowly just after or before a full stop or at a far but very slow motion.

There are rare misleading cases where the noise can be heard while an axis is at full speed. Usually this means another axis is moving very slowly. Check your robot program!

Why does it occur?

The motor current is lowered when an axis stops. This is to allow the motor and electronics to cool down and work with a higher current when it actually needs to move. When the current is lowered or raised the torque changes which can be heard.

How to make sure it's not a different issue

  1. Load the parameters off the motor controllers
  2. Open the parameter file in a text editor.
  3. For each axis find the entries CSLoad, CSStart and CSIdle. Note down their values, then set all three to the value of CSLoad
  4. Save the parameters to a new file and write them back to the motor controllers
  5. Restart the robot control
  6. Test the motion and listen whether the noise improved. WARNING: Only do a short test, now the motors can overheat even when not in motion.
  7. Restore the original parameters and restart the robot

How to lower the noise

You can try to increase CSStart and CSIdle but make sure to test the robot for a while and observe the motor temperatures (the temperatures shown in the software are measured at the electronics, not the motors).

But note: As mentioned above the noise does not cause any motion issues and generally you should not change the parameters to fix it. Worst case the motors or electronics get destroyed by heat. Axes with a heavy load may experience a decreased usable motion time since they reach their temperature limits faster.