Research And Development Of Key Technologies In A PC-Based Multi-Axis Open Architecture Software-CNC System

CNC system experienced the development from special&closed to open& modular feature. Along with the design philosophy of open architecture controller appeared in 80s of the last century and computer technology's fast development, CNC system develops towards the goal of open architecture structure and software realization methodology. With the appearance of software PLC technology and IEC61131-3 international standard, using Software to realize PLC unit in CNC system becomes important in the research of open architecture controller.The realizing method of the software and hardware in the open architecture multi-axis software CNC system is analyzed and confirmed. Based on PC, general Windows OS and RTX real-time extension, SoftSERCANS plug-in card following SERCOS protocol, the system platform of the open architecture CNC system is constructed. High-speed serial communication among the system controller, drivers and IO devices can be realized in the platform to get independency between soft and hardware. Thus the controller becomes application software which entirely runs in the system platform.To attain an open architecture software CNC system following the user's demand, based on the selection of the system interfaces, a series of technologies are adopted to ensure the openness of the system, in which OMAC API is referenced, FSM is adopted, and SERCOS technologies is applied. Object oriented C++ language and modular method are used to develop the system functions in Windows and Visual C++ environment.NC code translator decodes in compiling mode, in which the code information is translated into motion coordinator, speed and PLC switching value to be executed in the interpolation module. Each translated segment's information is input into a deque as a knot. Then it's transferred into the interpolation module through the shared memory to drive the machine tool. Besides C type plane cutter compensation, canned cycle instruction, plane and coordinator selection, rotation, scaling, mirror, subprogram calling functions are all realized in the translator. The instruction system is amplified to make the CNC system useful.According to IEC61131-3, Software PLC's function and realizing method are analyzed and confirmed, and the system is composed of editor and compiling module. Ladder diagram editor, instruction list editor and the transfer function from ladder diagram to instruction list are realized in the editor module. Compiling module is composed of lexical analysis, syntax analysis, semantic analysis and aim code generation parts, and is developed by VC++ associating Lex and Yacc compiling software. The input code is instruction language and the generated aim code is C/C++ language code or binary code which can be run in the PLC running system.Object oriented technology and modular idea is adopted to develop the software PLC running system in the open multi-axis software CNC system and PLC's functions can be well realized by the multi-task regime. Such means as well-organized multi-task system scheduling regime and data encapsulating technology and modular method can make the system works coordinately and reliably.Real time interpolation function is the core of a CNC system. On direct sculptured surface interpolation, a self-defined double NURBS spline interpolation method is realized in the system. The method is presented against the current 5-axis coordinated linear and the 3-axis NURBS interpolation methods, for the proposed method can be used in the machining of curve-level 5-axis sculptured surface.A well designed, function versatile open architecture software multi-axis coordinated CNC system is constructed successfully in the paper. Related experiments proved its function.