DC Servo Motor NXB-SRV-DC112-001 on C-10 Joint 4 showing excessive vibration and position errors

Description

We are experiencing a critical issue with a NexBot Robotics DC Servo Motor (SKU: NXB-SRV-DC112-001) installed on the J4 axis of our C-10 series robot. For the past 48 hours, the motor has been exhibiting significant vibration, especially during low-speed positioning moves. This is accompanied by a distinct, high-pitched humming noise that was not present before. The robot controller is frequently throwing a position deviation alarm (E-4511), causing production halts. We have verified the 48VDC power supply is stable and within spec. We also inspected the PROFINET and encoder cabling between the motor and the drive controller, and all connections are secure with no visible damage. Manually rotating the joint with the brakes released feels notchy and rough, suggesting a mechanical issue within the motor itself rather than a drive or configuration problem. We need guidance on further diagnostics or if an RMA is required.

Symptoms

• Excessive vibration at low speeds
• Audible high-pitched humming noise
• Frequent position deviation alarms
• Rough, notchy feeling when rotating joint manually

Resolution

The root cause was determined to be a premature failure of the primary drive-end bearing within the NXB-SRV-DC112-001 motor. Diagnostic checks confirmed that the motor windings had correct resistance values and the encoder was functioning, but physical inspection and manual rotation pointed to a mechanical fault. The excessive vibration and positioning errors were caused by shaft play resulting from the failing bearing. The issue was resolved by replacing the faulty servo motor with a new unit. After installation, the axis was re-homed and a test cycle was run for 2 hours under load with no further alarms or abnormal vibration.

Resolution Steps

1. Perform a Lockout/Tagout (LOTO) procedure on the robot controller and associated machinery.
2. Disconnect the power and encoder cables from the faulty J4 servo motor.
3. Unbolt the NXB-SRV-DC112-001 motor from the J4 gearbox mounting plate and carefully remove it.
4. Install the new NXB-SRV-DC112-001 motor, ensuring the mounting bolts are torqued to the manufacturer's specification.
5. Reconnect the power and encoder cables to the new motor.
6. Remove LOTO and power on the robot controller.
7. Clear all active alarms from the teach pendant.
8. Perform the axis homing procedure for J4, followed by a full robot mastering/calibration check.
9. Run the robot through a 20-minute motion test program at varying speeds to confirm smooth operation and monitor for any new alarms.