Excessive backlash and audible noise from PLN122-010 gearbox on R-50 Joint 4

Description

We are experiencing a performance issue with one of our R-50 series robots on our assembly line. The robot's fourth axis (J4) is failing to maintain accurate positioning, causing placement errors of up to 5mm. During operation, a distinct, high-pitched whining noise is audible from the J4 assembly, which gets louder under load. We have manually checked the joint with the servo brakes released and can feel significant mechanical play, far exceeding the specified <3 arcmin backlash for the NXB-GBX-PLN122-010 planetary gearbox. The controller is periodically throwing a position deviation alarm. We have already verified the J4 motor encoder is functioning correctly and the motor itself appears to be sound. We suspect premature failure or wear within the gearbox itself. The robot has approximately 8,500 operating hours and this is the first major issue with this axis.

Symptoms

• Audible whining or grinding noise from joint assembly
• Inaccurate positioning at the end-of-arm tooling
• Excessive mechanical play/backlash in the joint
• Position deviation alarms on the robot controller

Resolution

Support analysis confirmed the customer's diagnosis. The symptoms are consistent with advanced wear on the sun and planet gears within the NXB-GBX-PLN122-010 gearbox, leading to increased backlash and operational noise. The root cause was determined to be a seal failure leading to lubrication loss over time. The recommended and completed resolution was the replacement of the entire gearbox assembly on the affected joint. The customer was provided with the procedure for replacement and recalibration of the robot's fourth axis.

Resolution Steps

1. Follow standard Lockout/Tagout (LOTO) procedures to de-energize the robot and controller.
2. Manually maneuver the robot arm to a safe and accessible position for servicing Joint 4.
3. Disconnect the J4 servo motor cables and unbolt the motor from the gearbox input flange.
4. Carefully unbolt the faulty gearbox from the robot arm structure and remove it.
5. Mount the new replacement gearbox (SKU: NXB-GBX-PLN122-010), ensuring the mounting flange is clean and bolts are torqued to the specified value of 85 Nm.
6. Reinstall the servo motor, ensuring the shaft is properly seated in the new gearbox collar.
7. Reconnect all motor cables and remove LOTO.
8. Power on the robot, clear all alarms, and perform the axis mastering procedure for Joint 4 to update its zero position.
9. Run the robot through its programmed motion path at 25% speed to verify smooth operation before returning to full production speed.