There are two main parts of the CNC system, one is the NC, the other is the PLC, which play a different range of roles in the CNC machine.
1, ? Realize the digital control of the geometric movement law of the tool relative to each coordinate axis of the workpiece. This task is accomplished by the NC;
2.? The control of machine tool auxiliary equipment is done by PLC. It is in the CNC machine tool operation process, according to the CNC internal signs and the machine tool of the various control switches, detection elements, the state of the running parts, in accordance with the control logic set by the program such as the tool magazine movement, tool change mechanism, coolant, etc., the operation of the control.
Relative to the PLC, the machine tool and NC are external. The signals from the NC to the PLC and the signals from the PLC to the NC are used to program the PLC program for the exchange of information between the PLC and the NC.
The exchange of information between the programmable logic controller (PLC) and the numerical control (NC) as well as the numerical control machine tool (MT) has the following signals:
Relative to the PLC, the machine tool and the NC are the external. the exchange of information between the PLC and the machine tool as well as the NC is very important for the functioning of the PLC. the exchange of information between the PLC and the external is usually in four parts:
(1), the machine side to the PLC: the machine side of the switching signals through the I / O unit interface input to the PLC, in addition to a very small number of signals, the vast majority of the signals and the meaning of the configuration of the input address can be defined by the PLC programmer or program user. CNC machine tool manufacturers can easily modify the PLC program and address allocation according to the function and configuration of the machine tool.
(2) PLC to machine tool: PLC control signals are sent to the machine tool side through the PLC's output interface, and the meanings and output addresses of all the output signals are also defined by the PLC programmer or user.
(3), NC to PLC: CNC to PLC: CNC to PLC: CNC to PLC information can be sent by the CNC? directly into the PLC registers, all CNC to PLC signal meaning and address (switching address or register address)? All signals and addresses (switching addresses or register addresses) sent from CNC to PLC are determined by the CNC manufacturer, and can only be used by PLC programmers without being changed or added or deleted. Such as CNC instructions M, S, T? function, through the CNC decoding directly into the corresponding registers of the PLC.
(4)?PLC to CNC:?PLC?to CNC?information is also sent by the switching signals or registers to complete all PLC to CNC signal address and meaning of the CNC?manufacturers to determine the PLC?programmers can only be used, can not be altered and added or deleted.
PLC control functions in the CNC machine:
(1), the operator panel control. The operating panel is divided into the system operating panel and machine operating panel. System operating panel control signals first into the NC, and then sent by the NC to the PLC, control the operation of CNC machine tools. Machine operating panel control signals, directly into the PLC, control the operation of the machine.
(2), the machine tool external switch input signal. The switch signals from the machine tool side are input to feed into the PLC for logic operations. These switch signals, including many detection element signals (such as: travel switches, proximity switches, mode selection switches, etc.)
(3), the output signal control: PLC output signals through the peripheral control circuits in the relay, contactors, solenoid valves, etc., output to the control object.
(4), function realization. The system sends out T instruction to PLC, after decoding, searching within the data table, find the knife number specified by T code, and compare with the spindle knife number. If it does not match, the tool change instruction is issued, and the tool is changed, and after the tool change is completed, the system sends out a completion signal.
(5), M function realization. The system sends out M instruction to PLC, after decoding, output control signal, control spindle forward and reverse and start and stop, etc. M instruction is completed, the system sends out the completion signal.
Numerical control system in the PLC control program to realize the auxiliary function of the machine control.
Mainly M function, S function, T function, control.?
The auxiliary functions of the CNC lathe that M (function) S (function) T (function). In the PLC first M, S, T, code decoding. After decoding the M,S,T, code can be used in the PLC program to control the auxiliary functions of the machine. (e.g.? Control spindle forward and reverse, spindle positioning, spindle shift, turret, tool magazine, tailstock, chuck, center frame, chip removal, lubrication, etc.). For example: ? Processing program given M03?, PLC first M03 decoding (assuming that the address of the translated M03 R0,0), then the ladder diagram can be used R0.0? of normally open contacts to connect the spindle positive relay (assuming that Y0,0). The spindle positive relay (assuming Y0,0) can be energized by the open contact of R0.0? Then the Y0.0 output drives the external relay, the external relay drives the contactor, the contactor drives the spindle motor forward.