Fault repair showing normal changes and coordinate axis not moving

A CNC drilling and milling machine equipped with SIEMENS 802S shows normal changes during manual operation, but the actual coordinate axis does not move and the system has no alarm display.

Analysis and processing process: After inspection, the driving stepper motor of the machine tool does not rotate, but the machine tool axis enable signal in PLC has been effective, and the system has no alarm; the measurement confirms that the CNC system has issued a feed pulse command.

Since the 802S is a stepper motor open-loop drive system, it has no position detection device. If the “ready” signal of the step driver is not used in the PLC, even if the driver is not working properly, the CNC system can still display and output Command pulse. Therefore, determine the cause of the failure may be caused by the connection between the drive and the CNC or the drive failure.

Upon further inspection, it was found that the input power (85V) of the stepper drive of the machine tool tripped, and the drive was not monitored during the design of the machine tool, which caused the above failure. After closing the main power supply, the machine tool will return to normal.