R-50 Robot Joint 4 losing absolute position after power cycle - NXB-SNS-ABS141-010 Encoder

Description

We are experiencing a persistent issue with one of our R-50 robots in a palletizing cell. The Joint 4 axis fails to retain its absolute position after any system power cycle. Every morning, our startup procedure is delayed because we have to manually re-master the joint to get it to the correct home position. The teach pendant is displaying a position tracking fault specific to that axis. We have visually inspected the cabling between the axis motor and the controller, and everything appears to be securely connected with no visible damage. The EtherCAT bus status for all other devices is normal. We suspect the NexBot Robotics ABS141-010 22-Bit Absolute Encoder on that joint is failing internally, as the issue is isolated to this single component and survives a full power-down. This is causing significant downtime and requires an operator intervention at every startup.

Symptoms

• Loss of absolute position on power cycle
• Requires frequent re-mastering of robot joint
• Inaccurate positioning after startup
• Position tracking alarm on controller

Resolution

Troubleshooting confirmed that the 24VDC power supply to the encoder was stable and within specification. EtherCAT network diagnostics showed no packet loss or communication errors with the device. The symptoms pointed to a failure of the encoder's internal non-volatile memory, which is responsible for storing the position data during power-off states. The component was unable to retain its multi-turn count. The faulty encoder was replaced with a new unit. After installation and a one-time re-mastering of the joint, the robot successfully retained its absolute position across multiple power cycles. The E-2103 error has not recurred.

Resolution Steps

1. Perform a full energy lockout/tagout (LOTO) on the robot controller and associated machinery.
2. Carefully remove the protective cover for the Joint 4 motor assembly to gain access to the encoder.
3. Disconnect the EtherCAT and power connectors from the existing NXB-SNS-ABS141-010 encoder.
4. Unbolt the three mounting screws and remove the faulty encoder from the motor's rear shaft.
5. Install the new encoder (SKU: NXB-SNS-ABS141-010), ensuring the shaft key is properly aligned, and tighten the mounting screws to the specified torque.
6. Reconnect the power and EtherCAT cables to the new encoder.
7. Reinstall the motor assembly cover.
8. Remove LOTO, power on the robot controller, and perform the joint mastering procedure for Joint 4 as per the R-50 service manual.