Intermittent Overcurrent Fault on R-50 Robot Axis 3 - MD132-009 Drive

Description

We are experiencing an intermittent but persistent fault on one of our R-50 robots used in a palletizing cell. The robot will stop mid-cycle and the teach pendant displays an overcurrent fault for Axis 3. This axis, along with Axis 2, is controlled by a NexBot Robotics MD132-009 Multi-Axis Servo Drive. We have inspected the motor power and encoder cables for Axis 3 and found no visible damage, chafing, or loose connections at either the motor or the drive. The fault does not seem to be tied to a specific movement or payload; it can happen during both high and low-speed travel. We have swapped the motor outputs on the drive (Axis 2 to Channel B, Axis 3 to Channel A), and the fault followed the drive channel, now appearing on Axis 2. This leads us to believe the MD132-009 drive itself is the source of the problem. The machine has been in production for approximately 18 months.

Symptoms

• Robot stops unexpectedly during operation
• Teach pendant displays 'E-4115: Drive Overcurrent (A3)'
• Fault follows the drive output channel when motors are swapped
• No visible damage to associated cables or motor

Resolution

Analysis of the drive's fault log confirmed a recurring internal overcurrent condition on Channel A, which is inconsistent with the logged motor command values. This indicates a probable degradation of the IGBT power module for that specific axis channel within the servo drive. The troubleshooting step of swapping the motor outputs effectively isolated the fault to the drive. As the unit was outside of its standard warranty, the customer was advised to purchase a replacement. A new NXB-SRV-MD132-009 was ordered and installed, which resolved the issue.

Resolution Steps

1. Perform a full lock-out/tag-out (LOTO) procedure on the robot controller.
2. Label and disconnect the 480VAC input power, motor cables, and EtherCAT communication cables from the faulty drive.
3. Unscrew the four mounting bolts and remove the NXB-SRV-MD132-009 drive from the cabinet's DIN rail.
4. Mount the new NXB-SRV-MD132-009 drive in its place and secure it.
5. Reconnect all previously disconnected cables to their correct terminals on the new drive.
6. Power on the controller and use the engineering software to download the saved parameter file to the new drive.
7. Clear all active faults from the controller.
8. Run the robot through a series of test cycles to confirm that the overcurrent fault is no longer present.