NexBot MA012-001 Joint 4 Axis Following Error and Position Drift

Description

We are experiencing a critical issue with our NexBot Robotics MA012-001 robot arm (SKU: NXB-ROB-MA012-001) on our primary assembly line. The robot is programmed for a pick-and-place operation, transferring machined components. For the past 48 hours, the arm has been generating an intermittent E-4103 'Axis 4 Following Error Exceeded' alarm, which now occurs almost constantly, halting production. We've observed that Joint 4 (the first wrist joint) seems to drift from its programmed position during holds, causing the end-of-arm-tooling to be misaligned when it attempts to grip the next part. This has resulted in dropped parts and damage to both the tooling and the components. We have tried power cycling the R-10 controller and re-mastering the robot, but the position drift returns within minutes of resuming operation. The robot is connected via EtherCAT, and all other axes appear to be functioning within their normal parameters. We need urgent assistance to diagnose whether this is a mechanical, electrical, or software issue as this line is now completely down.

Symptoms

• Intermittent E-4103 'Axis 4 Following Error Exceeded' alarm
• Inaccurate Tool Center Point (TCP) positioning
• Visible position drift on Joint 4 when stationary
• Robot fails to complete its programmed path without faulting

Resolution

The issue was traced to a failing encoder within the Joint 4 servo motor assembly. Diagnostic monitoring on the R-10 controller's maintenance screen showed erratic and noisy pulse count signals originating from the Axis 4 encoder, while other axes showed stable signals. The encoder cable and connections at the amplifier and motor were inspected and found to be secure, ruling out a simple connection issue. The conclusion was an internal encoder hardware failure. The entire Joint 4 servo motor assembly (Part # NXB-SM-J4-012A) was replaced. Following the hardware replacement, the robot was remastered and a new zero position was calibrated. The robot has since completed 2000+ cycles with no recurrence of the E-4103 error or observable position drift.

Resolution Steps

1. 1. Performed full Lockout/Tagout procedure on the robot cell and controller.
2. 2. Connected to the R-10 controller and accessed the diagnostic panel to monitor live axis encoder data.
3. 3. Confirmed erratic signal from Axis 4 encoder by commanding small, slow moves and observing the feedback values.
4. 4. Powered down the system and replaced the Joint 4 servo motor assembly.
5. 5. Reconnected all cabling and powered the system back on.
6. 6. Performed the 'Mastering' procedure from the teach pendant to calibrate the new motor's zero position.
7. 7. Executed the 'Path Verification' routine to confirm TCP accuracy and repeatability.
8. 8. Ran the production program in continuous mode for one hour to validate the fix under operational load.