R-50 Robot A4 Axis Position Fault - Suspected INC142-006 Encoder Failure

Description

We are experiencing a recurring fault on one of our R-50 series robots used for material handling. The robot controller is throwing an E-4502 (Axis Position Tracking Error) specifically on the A4 joint. Before the fault occurs, operators have observed significant jitter and drift in the joint's position, causing the robot to miss its target coordinates. The issue is intermittent but has increased in frequency over the past week, leading to unplanned downtime. Our maintenance team has already checked the motor brake and gearbox for mechanical binding and found no issues. The robot controller's diagnostic logs show inconsistent pulse counts originating from the A4 encoder, which is a NexBot Drives INC142-006. We have verified that the 24VDC power supply to the encoder is stable. We need assistance determining if the encoder itself is failing or if this could be a PROFINET communication or configuration problem.

Symptoms

• Intermittent axis position faults
• Visible joint jitter before faulting
• Inaccurate robot TCP positioning
• Position tracking errors in controller logs

Resolution

The issue was traced to a failing NexBot Drives INC142-006 Incremental Encoder on the A4 axis. Remote diagnostics confirmed that the encoder was intermittently dropping pulse counts under load, leading to the E-4502 position tracking error. Although the 24VDC supply was stable and PROFINET communications were active, internal component degradation within the encoder was the root cause. The customer was instructed to power down the robot, follow lockout/tagout procedures, and replace the faulty unit. A new encoder, part number NXB-SNS-INC142-006, was dispatched and installed. After installation, the axis was re-mastered and the robot passed all positioning and repeatability tests, fully resolving the fault.

Resolution Steps

1. Perform a full system backup of the R-50 robot controller.
2. Execute the site-specific lockout/tagout (LOTO) procedure to de-energize the robot system.
3. Carefully disconnect the PROFINET and power cable from the faulty encoder on the A4 joint motor.
4. Unbolt and remove the existing NXB-SNS-INC142-006 encoder from the motor housing.
5. Install the new NXB-SNS-INC142-006 encoder, ensuring the shaft is properly seated and mounting bolts are torqued to specification.
6. Reconnect the power and PROFINET cables to the new encoder.
7. Remove LOTO devices and power on the robot controller.
8. Perform the axis mastering procedure for the A4 joint and run a repeatability test program to verify correct operation.