CLR032-002 SCARA Robot Z-Axis Following Error after Maintenance

Description

We are experiencing a critical issue with our NexBot Drives CLR032-002 SCARA robot on our semiconductor wafer handling line. After performing the scheduled 6-month preventive maintenance yesterday, the robot is unable to hold its Z-axis position. When the program is running or even when the servos are just enabled, the Z-axis (quill) slowly drifts downwards. After about 5-10 seconds of drift, the controller faults with a following error. We have tried re-homing the robot multiple times, but the issue persists immediately after the homing sequence completes. We've verified the 220VAC single-phase supply is stable and within spec. All EtherCAT communication links are green and show no packet loss. We suspect an issue with the Z-axis brake not engaging properly or a problem with the encoder's absolute position since the maintenance was performed. The robot is currently stopped, halting production on this line.

Symptoms

• Z-axis drifts downward when servo power is enabled but idle.
• Controller displays error code E-4502 (Axis 3 Following Error).
• Homing sequence for Z-axis completes but position is not maintained.
• Audible click of the Z-axis brake engaging sounds weak or delayed.

Resolution

The root cause was determined to be a misaligned Z-axis brake release proximity switch. During the recent maintenance procedure, the switch was inadvertently knocked out of its calibrated position. This prevented the controller from receiving a positive confirmation of brake engagement, causing the servo to fight against gravity and eventually exceed its following error parameter. The resolution involved a physical readjustment of the sensor to the correct gap distance (0.5mm) and performing an encoder reset for Axis 3 to re-establish the absolute position reference.

Resolution Steps

1. Power down the robot controller and engage the main disconnect LOTO (Lockout/Tagout) procedure.
2. Remove the upper Z-axis housing cover (4x M4 screws) to access the brake assembly.
3. Locate the brake release proximity sensor. Loosen its mounting bracket and adjust its position to be within 0.5mm +/- 0.1mm of the metal actuator tab on the brake mechanism.
4. Secure the sensor's mounting bracket and re-install the housing cover.
5. Disengage LOTO and power on the controller. Acknowledge any residual alarms.
6. Navigate to the 'Maintenance' > 'Calibration' screen in the NexBot Teach Pendant software.
7. Execute the 'Axis 3 Encoder Reset' procedure, following the on-screen prompts to manually move the axis to its reference marks.
8. Perform a full system re-homing sequence and verify the robot can hold Z-position under a 2kg test load for 5 minutes without drift.