Fault phenomenon: A CNC grinding machine is equipped with a SIEMENS 810 system. When the machine returns to the reference point, alarms ALM1121 and ALM1681 appear on the Y-axis.
Analysis and processing: The ALM1121 alarm in the SIEMENS 810 system indicates "Y-axis follow-up error is too large (YCLAMPING MONITORING)", while ALM1681 means "service enable signal cancellation (SERVO ENABLE TRAV.AXIS)".
During manual movement of the Y-axis, it was observed that the coordinate value on the CRT display changed, but the actual Y-axis servo motor did not move. When the Y-axis display reached the set following error limit in the machine parameters, the ALM1121 alarm was triggered.
A check of the machine tool's servo unit revealed that the H1/A alarm light on the corresponding servo controller was illuminated during the fault, indicating that the servo motor was overloaded.
Based on the above observations, the fault may be caused by excessive resistance in the moving parts. To locate the issue, the servo motor was disconnected from the mechanical components during maintenance. It was found that the mechanical load was light, as the Y-axis of the machine uses a servo motor with a brake. This led to the initial assumption that the fault was due to a faulty brake.
To confirm the brake's operation, an external power supply was used to test it. Further inspection of the brake's wiring revealed that the power connection was poor, preventing the brake from fully releasing. After re-connecting the wiring, the fault was resolved and the system returned to normal operation.
This case highlights the importance of checking both electrical and mechanical components when troubleshooting CNC systems. Sometimes, a simple connection issue can lead to complex alarm messages, making it essential to systematically isolate and test each part of the system.
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