Application Analysis of CNC System for EDM Machine
The Windows 9x operating system is widely used for its multi-tasking operation with its rich graphical user interface. Developing a CNC system on the Windows 9x platform can achieve higher efficiency and a more friendly interface than the DOS development platform. However, the Windows operating system is not a real-time system, and Microsoft has adopted a policy of shielding the underlying operations of the system to ensure the security of the system, prohibiting the user program from directly using hardware interrupts, DMA, I/O, and absolute storage access. Whether these difficulties can be overcome is the key to developing an EDM system on Windows9x systems.
The virtual device driver (VxD) is the link between the application and the underlying device. To prevent mutual interference between programs, starting with the 80386, the processor provides a protection mechanism - hierarchical management mechanism, that is, the processor provides four privilege levels: 0 to 3 privilege level, 0 privilege level is the highest. In the Windows 9x operating system, the system service program runs at the 0 privilege level, while the user's application runs at the 3 privilege level. VxD runs at 0 privilege level, so it can manage hardware devices and provide system services. Therefore, the development of a dedicated virtual device driver is the basis for the establishment of the CNC system for the development of Windows9x. The software VtoolsD produced by Vireo encapsulates the DDK package for Windows development drivers, which is convenient for developers to develop. Using the VtoolsD tool, we developed an I/O interface program for reading the interelectrode voltage and a driver for the stepping motor pulse drive circuit. For the user interface, we use the open architecture provided by AutoCAD2000, using ObjectARX technology to carry out secondary development of AutoCAD, and design a beautiful and friendly CNC system interface.
Another key issue in the CNC system of EDM is CAD/CAM integration. Using the DXF file provided by AutoCAD, the automatic programming system of EDM can be conveniently realized. The specific method is: firstly design the two-dimensional parts in the work area, and generate the designed graphics. Dxf file, this file contains the size information of the part. Through an interface program, the size and shape information of the parts are extracted for the CAM and sorted according to processing requirements, and stored in a doubly linked list. After conversion, converting them to pulse numbers provides the stepper motor driver with plane or surface machining. During the processing, it is also necessary to adjust the discharge gap in time according to the discharge state. We use multi-threading technology to achieve gap detection and motor drive synchronization. That is to establish a detection thread responsible for reading the output signal of the measurement section, the pulse equivalent of these output signals. (End)
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