X axis not moving but CNC coordinate is changing

There is Err4 alarm on the X axis AC servo driver, but the CNC controller has no alarm. Err4 means the X axis carriage has gone to the limit of the ball screw, the mechanical part is stuck.

The CNC system has not detected the mechanical stuck so the CNC controller is still running and the coordinate is still changing.

Change the AC servo driver of the X axis, then the CNC controller can detected the driver alarm, then pull back the carriage of X axis from limit, the CNC machine resume.

Conclusion: The CNC controller and AC servo driver’s alarm signals are high level on, when there is high level input to the CNC controller, the CNC will alarm.

As the driver was alarmed also, so it should not be CNC controller problem.

In this case when the AC servo driver alarm, the alarm signal was not converted from low level into high level, so the CNC controller could not detected the alarm signal, this should be AC servo driver alarm signal output problem.