MA012-004 Robot Arm Overshooting Programmed Path on Joint 4

Description

Our NexBot Robotics MA012-004 robot arm, installed on our assembly line, has started exhibiting inconsistent positioning. Specifically, during a high-speed pick-and-place routine, the end-of-arm tooling is overshooting its target destination by approximately 2-3mm. The deviation seems to be most pronounced when Joint 4 (wrist twist) is making a significant rotation. We have tried re-teaching the points and running a full system calibration, but the issue persists. This is causing misaligned parts and halting our production line. We are intermittently seeing an error code E-4115 on the R-20 controller teach pendant, but it doesn't always appear when the positioning error occurs. The robot is operating well within its 25kg payload limit, and the input voltage is stable at 415VAC.

Symptoms

• Robot arm overshoots target position by 2-3mm
• Inconsistent positioning during high-speed movements
• Visible vibration or 'judder' in Joint 4
• E-4115 (Position Tracking Error) logged intermittently

Resolution

Investigation determined the positioning error was caused by a partially engaging motor brake on Joint 4. The brake was not fully releasing at the start of a motion command, causing excessive drag and leading to a position overshoot when the servo controller attempted to compensate. The issue was not a hardware fault but a timing parameter that needed adjustment for the specific application dynamics. Adjusting the brake release delay parameter in the R-20 controller software provided the brake mechanism with sufficient time to fully disengage before the motor was commanded to move, eliminating the drag and resolving the path deviation.

Resolution Steps

1. 1. Power down the robot and controller following standard lockout/tagout safety procedures.
2. 2. Inspect the wiring harness and connectors for the Joint 4 motor and brake for any signs of damage or loose connections. Reseat the primary connector.
3. 3. Power on the controller and navigate to the advanced motion parameters menu.
4. 4. Locate the parameter group for 'Axis Servo Configuration' and select Axis 4.
5. 5. Find the 'Brake Release Delay (ms)' parameter, which was set to a default of 50ms.
6. 6. Increase the parameter value for Axis 4 to 75ms to allow the brake additional time to fully disengage.
7. 7. Save the new configuration and reboot the robot controller for the changes to take effect.
8. 8. Run the production program at 50% and then 100% speed to verify that the positioning is now accurate and the E-4115 error is no longer present.