Research And Development Of Soft-PLC In CNC System

Computer Numerical Control is progressing from closed individual construction to open modular architechture, PLC(Programmable Logical Controller) is the key modular to realize the I/O control function of CNC machine tools. Compared to traditional stand-alone PLC, soft-PLC (embedded PLC) is more able to adapt to open CNC system requirements. IEC1131-3 provides the programming language standard and international open criterion for design of soft-PLC. Therefore, it is necessary to research the soft-PLC with independent intellectual property rights, based on open CNC system and IEC1131-3 international criterion.According to the analyzation of the principle and architecture about soft-PLC, referencing to the international criterion, and based on domestic copying digital control system platform, the general research strategy is designed, the overall technical route is laid out, and PLC instruction set applying to open CNC system is established. The soft-PLC is divided to editting modular and compiling modular in the research, in order to meet the function that soft-PLC should have two programming methods of ladder diagram and instruction table.According to control requirements of embedded PLC in NC system and switching characteristics of the machine operation, pagination scanning technology and unit mapping technology are researched. A PLC pagination technology bounded by the NC machine tools' switching intervals is researched to satisfy the real-time requirement of NC system interruption cycle. The memory unit mapping technology of I/O is researched to identify the changing edge state of switch.By using Object-Oriented Programming language C++, the LD editing modular is designed, and the interface is also completed. The editing environment is intuitionistic, convenient and efficient.An algorithm named Based On First Row is put forward. It uses the ladder rung as basic element unit, compiles the following element step by step, transforms the LD into the IL, and formats the PLC execution codes in digital identification.Taking XK5032 NC machine tool control panel and the relay in the control cabinet as basic I/O unit, the soft-PLC system is experimented, and the feasibility and adaptability of the research is testified.