Excessive vibration and positioning errors on 643-001 Linear Rail Track

Description

We have a NexBot R-50 robot mounted on a NXB-GEN-643-001 Linear Rail Track that was installed about 8 months ago. For the past two weeks, we've been experiencing significant issues. The robot is failing to meet its programmed waypoints, with deviations up to 2-3 mm, far exceeding the track's ±0.05 mm repeatability spec. This is causing part-mispicks and collisions with fixtures. The issue is most pronounced when the carriage is moving at speeds over 1000 mm/s or when it's commanded to stop abruptly. We can see the entire carriage assembly visibly shudder during deceleration. There is also an audible, low-frequency grinding or humming sound coming from the carriage drive system that wasn't present before. The robot controller has intermittently faulted with an 'Axis 7 Position Following Error'. We have re-mastered the robot itself and confirmed its TCP is accurate, which leads us to believe the fault lies with the linear track system.

Symptoms

• Inaccurate final positioning of the robot tool center point (TCP).
• Visible shuddering of the track carriage during high-speed moves and deceleration.
• Audible grinding noise from the track's drive motor assembly.
• Intermittent 'E-3115 - Axis 7 Position Following Error' on the main robot controller.

Resolution

The investigation found that the set screw for the pinion gear on the external axis motor shaft had backed out, causing significant mechanical backlash between the motor and the gear rack. This backlash was responsible for the position overshoot, vibration upon stopping, and the position following errors. The issue was resolved by cleaning the threads, applying a thread-locking compound, and re-torquing the pinion gear set screw to the factory specification of 85 Nm. Following the mechanical repair, a servo tuning procedure was performed on Axis 7 to optimize the drive parameters for the restored mechanical stiffness, eliminating any remaining oscillation.

Resolution Steps

1. Perform a full Lock-Out/Tag-Out (LOTO) on the robot cell and linear track power supply (480VAC).
2. Remove the protective steel cover from the linear track carriage drive assembly.
3. Inspect the pinion gear on the motor output shaft. Confirm the set screw has lost torque.
4. Loosen the set screw fully, remove it, and clean both the screw threads and the shaft threads with a degreaser.
5. Apply Loctite 243 (or equivalent medium-strength thread-locker) to the set screw threads.
6. Re-insert and torque the set screw to the 85 Nm specification using a calibrated torque wrench.
7. Reinstall the drive assembly cover and remove LOTO.
8. Power on the system, navigate to the Axis 7 servo tuning menu in the controller, and perform an auto-tune sequence to adjust gain and stability parameters.
9. Execute a repeatability test program, running the track through its full 3m range at various speeds to confirm the issue is resolved.