Intermittent E-4112 Overcurrent Fault on Axis B of MD132-006 Servo Drive

Description

We are experiencing a critical production stoppage on our S-5 robotic welding cell. The robot, which uses a NexBot Drives MD132-006 Dual-Axis Servo Drive (SKU: NXB-SRV-MD132-006) to control Joints 4 and 5, is intermittently faulting. The controller log consistently shows error code E-4112, specifically pointing to an overcurrent condition on Axis B of the drive, which corresponds to our Joint 5 motor. The fault occurs randomly during high-acceleration moves. We have thoroughly inspected the motor power cable for chafing or shorts and found no issues. We also manually articulated the joint with the brakes released and can confirm there is no mechanical binding or unusual resistance. The issue seems to be isolated to the drive itself, as the other axis (Axis A / Joint 4) on the same drive unit is operating without any problems. We have cycled power multiple times, but the fault returns within a few minutes of restarting production.

Symptoms

• Robot halts mid-operation
• Controller displays fault code E-4112
• Red 'FAULT' LED illuminated on the servo drive
• Fault only occurs on one of the two axes controlled by the drive

Resolution

Troubleshooting confirmed the fault was internal to the NXB-SRV-MD132-006 servo drive. By swapping the motor output connections at the drive (connecting the Joint 4 motor to Axis B terminals and Joint 5 motor to Axis A terminals), the E-4112 fault followed the drive's Axis B output, not the motor or cable. This isolated the failure to the drive's internal power stage for that specific axis. The faulty drive was replaced with a new unit, and the parameters from the machine backup were loaded. The robot passed all subsequent diagnostic and production tests without issue.

Resolution Steps

1. Verified error logs to confirm E-4112 was isolated to Axis B of the target drive.
2. Performed a full power-down and lock-out/tag-out of the robot cell.
3. Inspected the motor power and encoder cables for Joint 5, confirming no visible damage or loose connections.
4. Swapped the motor output cables at the X5 and X6 terminals of the drive to isolate the fault. Connected Joint 4 motor to Axis B output and Joint 5 motor to Axis A output.
5. Powered on the system and ran a test cycle. Observed that the E-4112 fault now occurred on the motor connected to the drive's Axis B output, confirming the drive was the point of failure.
6. Replaced the faulty servo drive with a new NXB-SRV-MD132-006 unit.
7. Restored the drive parameters from the most recent controller backup via the EtherCAT master.
8. Cleared all faults and successfully ran the robot through a 1-hour production simulation test.