CNC equipment external fault can be divided into hard and soft fault fault external hardware damage caused by. Soft failure is due to adjustment of operation,caused by improper handling, this kind of fault occurred in the period of the equipment prophase or the use of equipment adjustment. The CNC system,another trouble spots for servo unit. Due to the movement of each axis is controlled by servo unit servo motor drives the ball screw to realize. Rotary encoder speed feedback, using grating as position feedback. The general trouble spots for driving module rotary encoder and servo unit. There are also individual is due to the power of causes of chaos. Especially for those with computer hard disk data storage system. For example, Germany SIEMENS 840C system.

Example 1: when a NC lathe has just put into use, restart in the system after power failure, must return to reference point. That is, when using the manual mode of each axis is moved to a non interference outside the region, to make each shaft return reference point. Otherwise, likely to crash. So, every day after the operation, the machine tool axis shift best safe position. There won't be aproblem at the re operation or after power failure.

The fault caused by the external hardware operation is the common fault of NCrepair. Is usually   due to a detection switch, hydraulic system, pneumatic system and the electrical actuator, a mechanical device problems. This kind of fault alarm information by reason of some can find fault. There are fault diagnosis function oralarm information of CNC system in general. Maintenance personnel can usethese information means to narrow the diagnosis range. Although there are somefaults and alarm information display, but it can not reflect the real reason of fault.At this point need to analysis according to the alarm information and faultphenomena.