Intermittent Axis 4 Position Errors on R-50 Robot Following Encoder Cable Replacement with NXB-SNS-ENC521-005

Description

We are experiencing intermittent but recurring position tracking faults on Axis 4 of our R-50 robot, which is used in a critical press tending application. The issue began last week, immediately after we replaced a damaged encoder cable with a new NexBot Robotics ENC521-005. The robot will run normally for several hours, then suddenly halt with an E-4114 'Axis Position Tracking Fault' error. During operation, we've also observed slight hesitation or jitter on Axis 4 during fast, sweeping motions, which was not present before the cable swap. Our maintenance team has double-checked the M12 and D-sub connectors at both the motor and controller ends, and they are secure. We have also verified the 24VDC supply is stable. The cable itself shows no visible signs of damage. The frequent stops are causing significant production delays, as we have to manually clear the fault and re-home the robot each time. We suspect an issue with the new cable or a potential compatibility mismatch, despite it being the recommended part for the R-50 series.

Symptoms

• Intermittent position tracking alarms on a single axis
• Robot hesitates or jitters during high-speed movements
• Fault appears randomly after hours of normal operation
• Error clears after a system reset but eventually returns

Resolution

The root cause was determined to be electromagnetic interference (EMI) affecting the PROFINET signal in the new NXB-SNS-ENC521-005 encoder cable. The customer's maintenance team had routed the new 5-meter signal cable in the same cable tray and zip-tied it directly alongside the high-power servo motor cable for Axis 4. This routing introduced significant electrical noise, corrupting the sensitive encoder data and causing the controller to lose track of the precise motor position. By physically separating the encoder cable from the motor power cable, the signal integrity was restored, and the position tracking faults were eliminated.

Resolution Steps

1. Power down the robot and controller following standard lockout/tagout procedures.
2. Inspect the physical installation path of the NXB-SNS-ENC521-005 cable from the Axis 4 motor to the main controller cabinet.
3. Identify sections where the encoder cable runs parallel to and in close proximity (less than 15cm) with high-power motor or VFD cables.
4. Carefully re-route the encoder cable into a separate, dedicated channel or conduit for low-voltage signal wires.
5. If a separate channel is not available, ensure a minimum physical separation of 20cm is maintained between the encoder cable and any power cables.
6. Verify that the encoder cable's shielding is properly terminated to the chassis ground at the controller end of the connection only.
7. Power up the system, clear any residual faults from the controller log, and re-home the robot.
8. Execute a test program that cycles Axis 4 through its full range of motion at maximum velocity and acceleration for 30 minutes to confirm stability.