Development Of RTLinux-based Software CNC

The thesis of Development of RTLinux-based Software CNC is the sub item of "Development and Application of Open Architecture Software CNC System ", which is supported by Key Technologies Research and Development Program Fund of Sichuan Province, China (Grant No. 03GG006-013-1) . This thesis dedicates to constructing a prototype of Linux-based CNC system.Along with the fast development of information technology, open CNC system has been entering upon a new phase, which is all-software CNC, software CNC or soft CNC. Software CNC means that all the functions of CNC system, such as interpolation, position control and PLC, are implemented with software modules. The flexibility of software makes it available for CNC systems to achieve higher-level openness."PC-based " is a practical and definite way to actualize the openness of CNC systems at present. The mainstream OS (operating systems) on the PC platform, such as Windows, Linux and so on, are general-purpose OS. The soft real-time characteristic makes them not suitable to be the development platform for software CNC systems. In this thesis, the way to solve this problem is to introduce the RTLinux realtime expansion.Software development is the core of software CNC system development. In this thesis, C language is used as the main development language and Tcl/Tk is used in the development of the graphical user interface. Through analyzing the functional requirements of CNC system and the relationship between the tasks(realtime or nonrealtime), we adopt multilayer structure in the software CNC system. From top to bottom, they are interface layer, management layer and control layer. The one aboveinterface layer is the user, and the one below the control layer is the hardware. Each layer falls into several modules or sub-modules. Through cooperation with each other, the modules of the same layer complete the mission of that layer. The interface layer communicates with the management layer through UNIX signal mechanism and semiduplex pipe. The management layer communicates with the control layer through the kernel real-time pipe, which is provided by RTLinux.The realtime control function of software CNC system is performed by the soft CNC module and the soft PLC module. The soft CNC module comprises four sub-modules, which are pre-interpolation module, interpolation module, position control module and output module. The four sub-modules act as four realtime threads. They work under the pipeline model. The realtime requirement of CNC system is satisfied by the high timer resolution and appropriate buffer management.In this thesis, the hardware platform is general PC or industrial PC. As to the interface between CNC controller and servo system and auxiliary devices, a multifunctional interface card is used. On the one hand, the card transforms the outputting commands of the upper controller into corresponding pulse series, which drive the servo system; on the other hand, it accomplishes the input-output of the switching values.At present, the software CNC system developed in this thesis, has realized basic numerical control functions such as coding, acceleration and deceleration, line and arc interpolation, and so on. It can run stably on the experimental facilities.