Intermittent Axis 5 Position Fault on R-50 Robot in Welding Cell

Description

We are experiencing an intermittent but increasingly frequent position fault on our R-50 robot, specifically on the J5 axis (wrist pitch). The robot will stop mid-cycle and the controller logs error E-4115. We can typically clear the fault by power cycling the controller, and the robot will run correctly for another 20-30 cycles before it happens again. The issue seems more common when the robot is performing rapid, complex wrist articulations. We have checked the connections at the base of the robot and at the J5 motor, and they appear secure. We suspect the encoder cable might be failing internally due to the high number of cycles and continuous flexing it undergoes in our application. The robot has been in service for approximately 18,000 hours.

Symptoms

• Robot halts mid-program with a position error.
• Controller displays error code E-4115 (Encoder Communication Fault).
• Fault is intermittent and occurs most frequently during complex J5 movements.
• Problem is temporarily resolved by a power cycle.

Resolution

The symptoms described are highly characteristic of an internal break or fatigue in the encoder signal cable, caused by repeated mechanical stress over many cycles. A visual inspection of the cable harness revealed minor external chafing near the J4/J5 joint housing. A continuity test performed while flexing the cable confirmed an intermittent open circuit on one of the differential signal pairs. The issue was fully resolved by replacing the existing J5 encoder cable with a new unit.

Resolution Steps

1. Perform a full system backup of the robot controller.
2. Follow proper LOTO (Lockout/Tagout) procedures to de-energize the robot and controller.
3. Carefully disconnect the faulty encoder cable from the J5 axis motor and from the corresponding port in the robot's base cabinet.
4. Remove the old cable, noting its exact routing path and any securing clips or ties.
5. Route the new NexBot Drives ENC521-006 Encoder Cable (SKU: NXB-SNS-ENC521-006) along the same path, ensuring it is not pinched or twisted.
6. Securely connect the new cable at both the motor and controller ends.
7. Remove LOTO and power on the system.
8. Perform an axis remastering/calibration procedure for J5 as per the R-50 maintenance manual and test run the production program.