There are two parts in CNC system, one is NC and the other is PLC, which have different functions in CNC machine tools. \r\n 1。 Realize the digital control of the geometric motion law of the tool relative to each coordinate axis of the workpiece. This task is completed by NC; \r\n2。 The control of machine tool auxiliary equipment is completed by PLC. During the operation of CNC machine tools, it controls the operation of tool magazine, tool changing mechanism and coolant according to the internal signs of CNC machine tools, the states of control switches, detection elements and running parts of the machine tools and the control logic set by the program. \ r \ Compared with PLC, machine tools and NC are external. Signals from NC to PLC and signals from PLC to NC are used for information exchange between PLC and NC. \ r \ nThe information exchange between programmable controller (PLC) and numerical control system (NC) and numerical control machine tool (MT) has the following signals: \ r \ nCompared with PLC, machine tool and NC are external. The information exchange between PLC and machine tools and numerical control system is very important to the function of PLC. The information exchange between PLC and the outside world usually consists of four parts: \r\n( 1), the switch signal from machine tool side to PLC: the switch signal from machine tool side is input to PLC through I/O unit interface. Except for a few signals, the meaning of most signals and the input address of configuration can be defined by PLC programmers or program users themselves. The manufacturer of CNC machine tools can modify the PLC program and address allocation conveniently according to the function and configuration of machine tools. \r\n(2), PLC to machine tool: The control signal of PLC is sent to the machine tool through the output interface of PLC, and the meaning and output address of all output signals are also defined by PLC programmers or users themselves. \r\n(3), NC to PLC:CNC to PLC: The information sent by CNC to PLC can be directly sent to the register of PLC by CNC. The meaning and address (switch address or register address) of all signals sent by CNC to PLC are determined by CNC manufacturer, and PLC programmers can only use immutability and add or delete. Such as M, S and T functions of NC instructions, are decoded by CNC and sent directly to the corresponding registers of PLC. \r\n(4) PLC to CNC: PLC information sent by PLC to CNC is also completed by switch signals or registers. The addresses and meanings of all signals sent by PLC to CNC are determined by CNC manufacturers and can only be used by PLC programmers, and cannot be changed, added or deleted. \ r \ Control function of NPLC in CNC machine tools: \r\n( 1), control of operation panel. The operation panel is divided into system operation panel and machine tool operation panel. The control signal of the system operation panel first enters NC, and then is sent to PLC by NC to control the operation of CNC machine tools. The control signal of the machine tool operation panel directly enters the PLC to control the machine tool operation. \r\n(2) Input signal of external switch of machine tool. Input the switch signal of the machine tool side into the feed PLC for logical operation. These switch signals include many detection element signals (such as travel switch, proximity switch, mode selection switch, etc. ) \r\n(3), output signal control: PLC output signal is output to the controlled object through relays, contactors, solenoid valves, etc. In the peripheral control circuit. \r\n(4), t function realization. The system sends a T instruction to PLC, and after decoding, it looks up the tool number specified by the T code in the data table and compares it with the tool number of the spindle. If not, issue a tool change instruction and change the tool. After the tool change is completed, the system will send out a completion signal. \r\n(5), m function realization. The system sends M instructions to PLC, and outputs control signals after decoding to control the forward and reverse rotation, start and stop of the spindle. M instruction is completed, and the system sends out a completion signal.