I. Introduction Currently, the main host computers used in domestic CNC flame cutting machine systems are single-board computers, microcontrollers, and DOS-based PCs with CPUs below the 386 level. These operating systems suffer from low performance and functionality, making them inconvenient to use. Therefore, it is necessary to develop a high-performance, fully functional, and easy-to-program and operate CNC system. This serves two purposes: firstly, to update the control systems of older CNC flame cutting machines, and secondly, to provide compatibility for new CNC flame cutting machines. With the improvement in performance and the reduction in price of IPCs, the significant advantages of developing CNC systems using IPCs are becoming increasingly apparent. Besides higher reliability and anti-interference capabilities, IPCs, like PCs, offer high operating speeds, abundant hardware resources (CPU, memory, coprocessor, hardware and software drivers, serial/parallel ports, interrupts, timers, bus slots, monitor, keyboard, power supply, etc.), software resources (Windows platform and various available development software, such as AutoCAD, network communication, etc.), and function calls. They also feature an open architecture and a high performance-price ratio. By inserting a self-developed or commercially available drive system servo control card and I/O card into the bus expansion slot, and by fully developing and utilizing the inherent functions of the IPC machine, and by developing the control system software, the IPC machine can be transformed into a powerful CNC system capable of real-time multitasking, with a user-friendly interface. Furthermore, as IPC machines are continuously upgraded, the CNC system developed using them is also easily updated. This article introduces a CNC flame cutting machine CNC system independently developed using an IPC machine as the hardware platform and Windows as the software platform. II. Hardware Composition of the CNC Flame Cutting Machine System The mechanical part of the CNC flame cutting machine mainly consists of a base, a gantry-type moving frame, a flame nozzle, a transmission mechanism, and three stepper motors (figure omitted) to achieve the cutting and processing of flat sheet metal parts. The three stepper motors control the forward and backward movement of the gantry frame (Y motor), the left and right movement of the flame nozzle (X motor), and the up and down movement (Z motor), respectively. The X, Y, and Z axes can achieve coordinated control. The hardware structure of the CNC system is shown in Figure 1. This control system uses an IPC (CPU of 486 or higher, 8MB or more of RAM, 500MB or more of hard disk space) as the host. Besides the IPC's inherent hardware (CPU motherboard, TVGA card, power supply), only a 32-bit optically isolated I/O TIMER (parallel input/output/timer) card is added to the slot. This card's parallel I/O ports control the operation of three stepper motors, the acetylene switch, acetylene ignition, the cutting oxygen switch, and receive limit switch signals and coordinate zero-position signals from the worktable. An 8253 timer on the board serves as the interrupt timer for the stepper motor operation interrupt service routine, with a clock frequency of 2MHz. The control system is operated via the computer keyboard. The pulse equivalent of the three stepper motors in each direction of movement is 0.01mm. Due to the high operating speed of 486 or higher PCs, all work from system program management to machining control can be completed with a single CPU, eliminating the need for a multi-CPU structure with upper and lower computers. Figure 1. CNC System Hardware Structure Diagram III. CNC Flame Cutting Machine CNC System Software Structure 1. Software Composition This CNC system not only includes all the functions of a regular CNC system, but also features functions suitable for its process characteristics, such as automatic ignition before cutting, preheating, oxygen supply, and flameout upon completion of processing, as well as rapid retraction and forward movement of the cutting torch along the processing trajectory during processing. In addition, the system software also has comprehensive functions such as graphical programming, contour programming, direct interpolation of various quadratic curves, dynamic tracking and display of the processing trajectory, dynamic simulation of the processing trajectory, fault diagnosis, and communication transmission of the processing program. Among these functions, the rapid retraction and forward movement of the cutting torch along the processing trajectory is added to accommodate the phenomenon of incomplete cutting of certain parts of the steel plate during processing. When this phenomenon occurs, simply pressing the rapid return key will cause the cutting torch to move rapidly back along the original trajectory. When it reaches the starting point of the incomplete cut, releasing the key will cause the cutting torch to resume cutting along the original trajectory. Figure 2 shows the module structure of this CNC system software. Since the system software was developed under the Windows interface, it has all the advantages of Windows programs: it breaks through the 64kB memory limit, can run multiple applications at the same time (real-time multitasking), and is convenient for keyboard and mouse window operation, etc. Figure 2 Flame cutting machine CNC system software module structure 2. Programming methods The system software provides three programming methods: graphic programming, contour programming, and manual programming. Manual programming is just a functional module in graphic programming and contour programming, that is, full-screen program editing, so it is not listed separately in the software block diagram. 1) Graphic programming The graphic programming module of the system was developed on the basis of AutoCAD R12.0. In addition to having all the functions of AutoCAD R12.0, it mainly adds two functions: (1) Automatic programming function - extracts information of the machining trajectory (straight line, circle, arc, ellipse, polyline) generated by AutoCAD, optimizes the path (the purpose is to reduce empty travel) and converts it into the corresponding machining program, and can add empty run instructions between curves that are not connected in the machining trajectory. Here, in order to make the machining path more in line with the requirements of the machining process, the human-computer interaction method can be used to select part or all of the path; (2) Real-time simulation function - use the obtained machining program to perform interpolation calculation and dynamic graphic display. If the machining program is correct, the machining trajectory should be able to gradually cover the graphic drawn by AutoCAD with a thicker line of another color, and the empty running trajectory can also be displayed with a line of a specific color. With this programming, the operator can easily check and judge whether the machining program and machining path are correct and whether they meet the requirements of the machining process, and make timely modifications. AutoCAD has powerful drawing functions. Through the development of AutoCAD, it has become a powerful programmer for the CNC system of CNC flame cutting machine, making it a major feature of the CNC system. 2) Contour programming For workpieces without dimension annotation but with contour drawings, contour programming can be used to program them. The program compilation process is as follows: (1) Scan the contour pattern with a scanner and input it to form a binary image file. Small contour patterns can be scanned and input at once, while large contour patterns can be scanned and input multiple times. Then, they are stitched together in the image editing software; (2) Smooth and reduce noise, and repair broken lines at the same time; (3) Refine the image to obtain the contour line image; (4) Perform vectorization processing according to the given precision and generate a DXF graphic file. After the graphic file is formed, it can be edited and programmed using the graphic programming CAD software developed above. 3. Fast graphic display and dynamic simulation function of machining program The fast graphic display of machining program has two functions: one is to preview the machining trajectory graphic, which allows the operator to find the program to be selected from many machining programs; the other is to display the size and position of the machining trajectory graphic relative to the worktable, and at the same time display the two maximum machining dimensions in the X and Y directions, so that the operator can intuitively understand the machining size and the machining range. The fast graphic display of machining program only displays the machining trajectory and does not display the idle travel trajectory. The dynamic simulation function serves two purposes: checking for syntax errors in the machining program and verifying the correctness, rationality, and compliance with machining process requirements of the machining path. The dynamic simulation displays not only the machining trajectory but also the idle trajectory (in different colors), along with coordinate flipping. During the dynamic simulation, the operator can control the process as if it were actual operation, including pausing, resuming, and single-segment operation. The speed can also be adjusted at any time, providing more comprehensive machining information and allowing for a better assessment of the program's correctness and rationality. If the machining program does not meet the process requirements, the system software can convert it into an AutoCAD DXF file, allowing for re-editing in AutoCAD. When converting the machining program to AutoCAD DXF, the machining trajectory and idle trajectory are displayed on different layers and with different colors. This feature provides extremely favorable conditions for modifying the machining program. 4. Other machining operation control programs employ a common foreground/background program structure. The background program is responsible for initializing the control port, interpreting and preprocessing the machining program, controlling the program's pause, resume, single-segment stop, ignition, preheating, oxygen supply, and extinguishing, adjusting the speed, dynamically tracking and displaying the machining trajectory and dynamically flipping coordinate values, and rapidly returning and advancing the torch along the trajectory. The foreground interrupt service program is responsible for modifying the timer interrupt time constant, interpolation calculations, and outputting stepper motor control signals. IV. Conclusion The rapid retraction and forward movement during machining makes this control system more suitable for the characteristics of flame cutting. Graphical programming, contour programming, and dynamic simulation functions greatly facilitate the compilation and inspection of CNC flame cutting machine machining programs. The human-machine interface with Chinese characters increases the system's operability. The real-time multi-tasking function allows the CNC system to perform other processing tasks while controlling machining. The adoption of a new interpolation method enables the system to directly interpolate quadratic parabolas, ellipses, and hyperbolas, enhancing the system's interpolation calculation capabilities and reducing the difficulty of programming such curves. In summary, the successful development of this system represents a significant step forward in improving the quality of control systems for domestically produced CNC flame cutting machines. Furthermore, this control system possesses a degree of versatility; besides being used in CNC flame cutting machines, it can be adapted for use in control systems for machine tools such as waterjet cutting and laser cutting machines with only minor modifications.