Positioning Inaccuracy and Vibration on Axis 4 of SA011-001 Robot Arm

Description

We have a NexBot Robotics SA011-001 6-Axis Robot Arm (SKU: NXB-ROB-SA011-001) on our primary packaging line that has recently developed a performance issue. The robot is tasked with a high-speed pick-and-place operation, handling components weighing approximately 7.5kg. Over the last week, we've observed inconsistent part placement, causing downstream jams. Upon investigation, the issue appears to be with Axis 4 (wrist rotation). During fast rotational movements, the axis exhibits noticeable vibration and an audible 'chattering' sound. This is causing a positioning error at the tool flange. We are also intermittently receiving an E-4502 error code, which halts the cycle. Slowing the program override down to 60% alleviates the issue, but this is below our required production throughput. We have verified the payload data is correctly configured and the tool center point (TCP) is accurate. We suspect either a mechanical issue in the J4 gearbox or a servo tuning problem. We need assistance in diagnosing and resolving this to restore full production speed.

Symptoms

• Excessive vibration on Axis 4 during high-speed rotation
• Inconsistent part placement in pick-and-place task
• Intermittent 'E-4502 - Axis 4 Following Error' alarms
• Audible chattering noise from the J4 wrist assembly

Resolution

The issue was diagnosed as a servo tuning mismatch for the specific application dynamics. The high-inertia rotational moves of the 7.5kg payload were causing oscillation in the Axis 4 position loop. A remote support session was conducted to analyze the servo performance. A diagnostic trace of Axis 4 confirmed excessive following error and oscillation during high-acceleration moves. The resolution involved adjusting the servo gain parameters for Axis 4. Specifically, the Position Loop Gain was slightly reduced to dampen the system's response and eliminate overshoot, while the Velocity Feedforward Gain was increased to improve tracking of the command signal. After applying and saving the new parameters, the robot was able to run the production cycle at 100% speed without vibration or errors.

Resolution Steps

1. 1. Established a remote connection to the R-10 series controller using the NexBot Maintenance Suite software.
2. 2. Navigated to the Servo Tuning utility and selected Axis 4 (J4).
3. 3. Instructed the customer to run the problematic motion path while a diagnostic trace captured the command position vs. actual position data.
4. 4. Analyzed the trace, which showed a significant following error spike and subsequent oscillation.
5. 5. Decreased the Position Loop Gain for Axis 4 by 15% (from 55 to 47) to reduce system oscillation.
6. 6. Increased the Velocity Feedforward Gain for Axis 4 by 10% (from 100 to 110) to improve responsiveness.
7. 7. Saved the new tuning parameters to the controller and performed a controlled restart of the robot system.
8. 8. Monitored the robot running the full production cycle for 30 minutes, confirming the vibration and E-4502 alarms were eliminated.