LA013-007 Axis 4 Drifting Position After Extended Operation

Description

Our NexBot Robotics LA013-007 robot arm (SKU: NXB-ROB-LA013-007) on the main palletizing line is experiencing a positioning issue. After about 3-4 hours of continuous operation, we observe a noticeable position drift on Axis 4 (wrist twist). The drift is minor, about 0.5-1.0 degrees, but it's enough to cause misalignment when placing boxes onto the pallet, leading to unstable stacks. The robot does not throw any error codes on the R-20 controller teach pendant. We have tried re-mastering the axis, which corrects the issue temporarily, but the drift returns after another few hours of runtime. The issue seems to be exacerbated when running at 100% speed. We have confirmed the supply voltage is stable at 415VAC 3-Phase. This is a critical issue as it requires an operator to manually re-stack pallets, causing significant downtime.

Symptoms

• Axis 4 position slowly drifts over several hours of operation.
• No error codes are generated by the controller.
• Re-mastering the robot provides a temporary fix.
• The issue results in misaligned pallet stacks.

Resolution

The root cause was identified as a failing pulse coder on the Axis 4 servo motor. While the motor itself was functioning, the pulse coder was intermittently dropping counts, particularly after reaching operating temperature. This loss of position feedback data resulted in a cumulative position error that was not significant enough to trigger a fault but caused a noticeable physical drift. The resolution was to replace the Axis 4 servo motor, which includes an integrated pulse coder. After replacement and re-mastering the robot, the position held stable over a 24-hour continuous operation test.

Resolution Steps

1. Power down the robot and controller following standard lock-out/tag-out procedures.
2. Disconnect the power and encoder cables from the Axis 4 servo motor.
3. Unbolt and remove the faulty Axis 4 servo motor from the robot arm.
4. Install the new replacement Axis 4 servo motor, ensuring correct alignment and torque on mounting bolts.
5. Reconnect the motor power and encoder cables.
6. Power on the robot and controller.
7. Perform the mastering procedure for the LA013-007, paying special attention to zeroing Axis 4.
8. Run the palletizing program in a continuous loop for 24 hours to validate that the position drift issue is resolved.