FLR022-001 Cobot experiencing intermittent position drift on Joint 4 after warm-up

Description

We are experiencing an issue with our NexBot Robotics FLR022-001 Collaborative Robot Arm (SKU: NXB-ROB-FLR022-001) on our assembly line. The robot performs a pick-and-place task for small electronic components. For the first 30-40 minutes of operation, it runs perfectly. After it warms up, we observe a gradual position drift on Joint 4, causing it to misalign with the target fixture by about 1-2mm over the course of an hour. This triggers an E-3114 fault code for position deviation and halts production. We have tried re-homing the robot, which temporarily fixes the issue, but the drift always returns. We've also checked for any physical obstructions or excessive torque on the joint, and everything appears normal. The robot is controlled via EtherNet/IP from our central PLC. The payload is a pneumatic gripper weighing 4.5 kg, well within the 10 kg limit. We need to find a permanent solution as this is impacting our line's efficiency.

Symptoms

• Inconsistent pick-and-place accuracy after 30 minutes of operation
• Visible minor drift on Joint 4 axis
• Periodic E-3114 (Joint Position Deviation Exceeded) faults
• Requires frequent re-teaching of waypoints to maintain accuracy

Resolution

The intermittent position drift on Joint 4 was traced to a thermal expansion effect impacting the joint's absolute encoder zero position. After the robot reached its normal operating temperature, the slight physical change was enough to cause a cumulative positioning error. The issue was resolved by performing a fine calibration routine on Joint 4 after the robot had been running for at least one hour, allowing it to stabilize at its typical operating temperature. This new 'hot' calibration for the zero position now accounts for thermal expansion, eliminating the drift.

Resolution Steps

1. 1. Operate the robot under a typical production load for at least 60 minutes to ensure it reaches a stable operating temperature.
2. 2. Without powering down, switch the controller to Maintenance Mode using the teach pendant.
3. 3. Navigate to the Service menu: System > Calibration > Joint Calibration.
4. 4. Select Joint 4 from the list of axes.
5. 5. Initiate the 'Fine Encoder Zeroing' routine. The robot will slowly move the joint to its mechanical hard stops to find the true zero position.
6. 6. Save the new calibration value when prompted. The system will overwrite the old zero position.
7. 7. Return the controller to Auto Mode and resume the production cycle.
8. 8. Monitor the robot's performance for the next 24 hours to confirm that the position drift has been eliminated.