Abstract This paper introduces the software and hardware structure of a CNC system for a flame cutting machine developed using an industrial personal computer (IPC). In addition to control functions suitable for the characteristics of CNC flame cutting machine processes, this CNC system also features graphical programming, contour programming, machining program screen simulation, and real-time multitasking. The interpolation calculation employs differential interpolation, enabling direct interpolation of all quadratic curves. Keywords : IPC, flame cutting machine, CNC system, graphical programming, dynamic simulation, differential interpolation , multitasking. I. Introduction Currently, domestically produced CNC flame cutting machine systems mainly use 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: updating older CNC flame cutting machine control systems and providing compatibility for new CNC flame cutting machines. With the improvement of IPC performance and the reduction of price, the significant advantages of developing CNC systems using IPCs are becoming increasingly apparent. Besides higher reliability and interference resistance, 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-to-price ratio. By inserting self-developed or commercially available driver system servo control cards and I/O cards into the bus expansion slots, and by fully developing and utilizing the inherent functions of the IPC, and developing control system software, the IPC can be transformed into a powerful CNC system capable of real-time multitasking, with a user-friendly interface. Moreover, as IPCs are continuously upgraded, the CNC systems developed using them are also easily upgraded. This article introduces a CNC flame cutting machine system independently developed using an IPC as the hardware platform and Windows as the software platform. II. Hardware Composition of 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 of the flame nozzle (Z motor), respectively. The X, Y, and Z axes can be linked for control. The hardware structure of the CNC system is shown in Figure 1. This control system uses an IPC (486 or higher CPU, 8MB or more of memory, 500MB or more of hard disk) 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. The parallel I/O ports of this card control the operation of the 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. The 8253 timer on the board serves as the interrupt timer for the stepper motor's interrupt service routine, with a clock frequency of 2MHz. The control system is operated via the computer keyboard. The pulse equivalent of the stepper motors in all three movement directions is 0.01mm. Due to the high operating speed of PCs above the 486, a single CPU can handle all tasks from system program management to machining control, eliminating the need for a multi-CPU structure with upper and lower computers. Figure 1 shows the CNC system hardware structure. III. CNC Flame Cutting Machine CNC System Software Structure 1. Software Composition This CNC system not only includes all the functions of a typical CNC system but also features automatic ignition before cutting, preheating, oxygen supply, and flameout upon completion, as well as rapid torch retraction and advance along the machining trajectory during machining, all tailored to its specific process characteristics. Furthermore, the system software includes comprehensive graphical programming, contour programming, direct interpolation of various quadratic curves, dynamic tracking and display of the machining trajectory, dynamic simulation of the machining trajectory, fault diagnosis, and communication transmission of the machining program. Among these functions, the rapid retraction and forward movement of the cutting torch along the machining trajectory is added to address the occasional incomplete cutting of certain parts of the steel plate during processing. When this occurs, simply pressing the rapid return key will cause the torch to move rapidly back along the original trajectory. Once it reaches the starting point of the incomplete cut, releasing the key will allow the torch to resume cutting along the original trajectory. Figure 2 shows the module structure of this CNC system software. Because this system software is developed under a Windows interface, it possesses all the advantages of Windows programs: overcoming the 64kB memory limit, allowing multiple applications to run simultaneously (real-time multitasking), and facilitating keyboard and mouse window operation. Figure 2: Module Structure of the Flame Cutting Machine CNC System Software. 2. Programming Methods The system software provides three programming methods: graphical programming, contour programming, and manual programming. Manual programming is just one functional module within graphical and contour programming, i.e., full-screen program editing, and therefore is not listed separately in the software block diagram. 1) Graphical Programming The graphical programming module of this system was developed based on 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 machining trajectory (straight line, circle, arc, ellipse, polyline) from the graphic file generated by AutoCAD, optimizes the path (to reduce empty travel) and converts it into the corresponding machining program, and can add empty run instructions between unconnected curves 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 - uses 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 run 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 been transformed into a powerful programmer for the CNC system of the CNC flame cutting machine, making it a major feature of the CNC system. 2) Contour programming For workpieces without dimension annotations but with contour drawings, contour programming can be used to program them. The program compilation process is as follows: (1) Scan the contour drawing with a scanner and form a binary image file. Small contour drawings can be scanned and input at once, while large contour drawings 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 accuracy 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. The machining program's rapid graphical display and dynamic simulation functions serve two purposes: firstly, it previews the machining trajectory, allowing the operator to select the desired program from numerous options; secondly, it displays the size and position of the machining trajectory relative to the worktable, simultaneously showing the two maximum machining dimensions in the X and Y directions, providing the operator with a clear understanding of the machining dimensions and operating range. The rapid graphical display only shows the machining trajectory, excluding the idle travel trajectory. The dynamic simulation function also serves two purposes: firstly, it checks for syntax errors in the machining program; secondly, it verifies the correctness and rationality of the machining path, ensuring it meets the requirements of the machining process. The dynamic simulation displays not only the machining trajectory but also the idle travel trajectory (in different colors), accompanied by 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 machining program's correctness and rationality. If the machining program does not meet the requirements of the machining process, the system software has the function of converting the machining program into an AutoCAD DXF format file, so that it can be re-edited in AutoCAD. When the machining program is converted into an AutoCAD DXF format file, the machining trajectory and the empty running trajectory are processed with different layers and different colors. This function provides extremely favorable conditions for modifying the machining program. 4. Other machining operation control programs adopt a common foreground and background program structure. Among them, the background program is responsible for the initialization of control ports, interpretation and preprocessing of machining programs, control of pausing, continuing, single-segment stopping, ignition, preheating, oxygen supply, and flameout during program operation, speed adjustment, dynamic tracking and display of machining trajectory and dynamic flipping display of coordinate values, and rapid return and forward movement of the cutting torch according to the running trajectory, etc.; the foreground interrupt service program is responsible for modifying the timer interrupt time constant, interpolation calculation, and outputting stepper motor control signals, etc. IV. Conclusion The rapid retraction and forward movement during the machining process makes this control system more suitable for the characteristics of flame cutting. Graphical programming, contour programming, and dynamic simulation functions greatly facilitate the programming and inspection of CNC flame cutting machine machining programs. The user-friendly Chinese character interface increases the system's operability. Real-time multi-tasking 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 domestically produced CNC flame cutting machine control systems. Furthermore, this control system has a certain degree of versatility; besides being used in CNC flame cutting machines, with minor modifications, it can also be used as a control system for machine tools such as waterjet cutting and laser cutting.