NexBot Drives DC112-006 Servo Motor on R-20 Robot Joint 4 Overheating and Faulting

Description

We are experiencing a critical failure on one of our R-20 series robots on the main assembly line. The Joint 4 axis motor, a NexBot Drives DC112-006, has begun exhibiting erratic behavior. During the robot's standard pick-and-place cycle, the J4 axis movement became jerky and inconsistent. A maintenance technician inspected the robot and found the motor housing for J4 was extremely hot to the touch, well above its normal operating temperature. The robot controller is now locked out with a persistent motor fault error that we cannot clear. We have attempted a full power cycle of the robot controller and the main cabinet, but the error returns immediately upon trying to enable the drives. This has halted production on this line, and we need to diagnose whether this is a drive parameter issue or a component failure.

Symptoms

• Motor housing is excessively hot.
• Jerky and uncontrolled movement on the affected joint.
• Robot controller displays 'Axis Drive Fault'.
• Audible humming and grinding noise from the motor during attempted operation.

Resolution

Support analysis concluded the symptoms (excessive heat, audible noise, and persistent drive fault) are indicative of an internal failure within the NXB-SRV-DC112-006 DC servo motor, likely due to worn brushes or a seized bearing after prolonged high-cycle operation. The fault code E-4115 corresponds to a motor over-temperature condition combined with a following error, confirming the hardware failure. The motor is not field-serviceable. The resolution was to replace the faulty motor with a new unit.

Resolution Steps

1. Perform a full Lockout/Tagout (LOTO) on the robot cell's main power disconnect.
2. Disconnect the power and PROFINET communication cables from the faulty J4 servo motor.
3. Carefully unbolt and remove the failed NXB-SRV-DC112-006 motor from the J4 axis housing.
4. Mount the new replacement motor (SKU: NXB-SRV-DC112-006) and torque the mounting bolts to the specification listed in the R-20 service manual.
5. Reconnect the power and communication cables to the new motor.
6. Remove LOTO and power up the robot controller.
7. Clear all active faults from the teach pendant.
8. Perform the 'Joint 4 Mastering and Calibration' procedure to ensure correct positioning before returning the robot to service.