Intermittent E-4115 Position Following Error on R-50 Robot, Joint 3 Servo Drive

Description

We are experiencing intermittent positioning faults with our R-50 robot on the J3 axis, which uses the NexBot Vision SD131-003 servo drive. During high-speed pick-and-place cycles, the drive will suddenly fault out with an E-4115 error, causing the entire line to stop. The operator has to manually clear the fault and re-home the robot, resulting in significant downtime. We have observed the J3 arm slightly overshooting its target position just before the fault occurs. We initially suspected a mechanical binding issue, but the arm moves freely when the brakes are released. We have checked the 480VAC power supply to the drive and it is stable. The EtherCAT communication seems to be stable for all other axes, but we do see occasional lost frame counters for the J3 drive node in the controller logs. The issue has become more frequent over the last two weeks.

Symptoms

• Drive faults with E-4115 (Position Following Error)
• Robot arm (J3) overshoots target position
• Production line stops require manual intervention
• Audible humming from the J3 motor is louder than other axes

Resolution

The root cause was identified as a combination of a loose encoder cable connection and improperly tuned PID loop settings for the new gripper installed last month. The vibration during high-speed moves caused intermittent signal loss from the encoder, leading to the position following error. Reseating the primary encoder connector at the SD131-003 drive and running the auto-tuning procedure via NexBot MotionSuite software resolved the positioning overshoot and eliminated the fault condition. The system has now been running for 48 hours without any recurrence of the E-4115 error.

Resolution Steps

1. 1. Perform a full safety lockout/tagout (LOTO) on the robot cell.
2. 2. Open the control cabinet and inspect the cabling for the J3 servo drive (NXB-SRV-SD131-003).
3. 3. Disconnect and firmly reseat the encoder feedback cable at the X5 terminal on the drive.
4. 4. Remove LOTO and power on the robot controller.
5. 5. Connect to the controller with a laptop running NexBot MotionSuite software.
6. 6. Navigate to the J3 drive parameters and initiate the auto-tuning wizard to compensate for the new payload.
7. 7. Save the new tuning parameters to the drive's non-volatile memory.
8. 8. Run the robot through 20 full-speed production cycles and monitor the 'Position Following Error' value in real-time to confirm it remains within acceptable limits.