Systematically measuring friction

Friction must be measured with real drives. Proceed as follows:

INFORMATION

To preserve realistic values for the physics simulation of the drive train, the friction curve should be measured with the robot arm before assembling the drive train.
  1. Activate the comparison calculation in RobotMonitor. See also chapter Settings.
  2. Create a trace with the following variable for all axes:
    • SEW_GVL_Internal.Robot_Axis[i]_PhysicalGearMotor.
      fbMotor.fbDeviationCalculator.stOut.
      lrCalculatedDeviation_Torque
      (Unit: % nominal motor torque in relation to the motor shaft)
  3. Let the drive spin at 100% of the maximum possible speed vmax. The motion can be carried out using an SRL program with two PTP commands in a WHILE loop. For vmax, we recommend using the positive speed application limit in the "Monitoring functions" configuration menu in the "Limit values" submenu of the MOVIKIT® MultiMotion (Parameter 8357.10). The drive must rotate at a constant rotational speed for at least 2-3 seconds after the controller oscillates at the new speed.
  4. Read the mean value of the Mr,100% friction torque during consistent travel from the trace.
  5. Let the drive spin at 10% of the maximum possible speed vmax.
  6. Read the mean value of the Mr,10% friction torque during consistent travel from the trace.
  7. Calculate the following parameters from the read values:
    • Factor of speed-dependent friction: fv = (Mr,100% - Mr,10%)/(0.9 × vmax )
    • Constant friction: oc = Mr,10% - fv × 0.1 × vmax
    • Smoothing factor of friction curve for direction of rotation reversal: vt = 1% × vmax
  8. Configure the calculated parameters in MOVISUITE®.

INFORMATION: To determine even more accurate values for configuration, you can add additional measuring points and add an equalizing line in the torque speed diagram. The Y-axis section is oc. The gradient of the straight sections of factor fv.