This control strategy actually transfers the functional responsibility of the control card to the computer, so the control system is reduced and the cost is reduced. A multi-axis linkage numerical control system based on a computer parallel port is shown. The standard SPP, extended ECP and enhanced EPP. The latter two can realize the bidirectional transmission of data signals, and the transmission rate is also higher than the former one. Parallel port data input and output can be controlled by 8 registers. Different working modes correspond to specific registers. There are three basic registers of the parallel port: data port register, status port register and control port register. The addresses are hexadecimal 0378, 0379 and 037A respectively. As long as the register is accessed by register address, the parallel port output can be controlled. /input signal. It is worth noting that the PIN11 pin is connected to the D7 bit of the status register via the inverter. The D0, D1 and D3 bits of the control register are connected to the PIN1, PIN14 and PIN17 of the interface via the inverter. In other words, the control signal is output. The lower four bits of the signal are 1111 (binary), then the control register setting should be 0010 (binary), and so on. It can be seen from the above analysis that the computer parallel port has a larger number of pins for input/output signals, and can be separately controlled. In the open-loop/semi-closed loop numerical control system, the driver corresponding to each motor basically only needs one pulse signal and one direction signal indicating the position quantity and the speed quantity, and at the same time, if the mechanical body part has feedback signal to be processed, it can be used as The status signal is received by the computer. Therefore, the parallel port of the 25-pin structure can meet the requirements of the two- or three-axis linkage control. Accessing the parallel port under the Windows operating system Generally speaking, the program under the Ring3 ring cannot directly access the operating hardware resources. To perform the underlying operations such as accessing the port, it is necessary to write a driver, a dynamic link library (dll) working on the Ring0 ring, or Use the ActiveX controls included with the program development software. The multi-axis linkage control system based on the parallel port of the computer needs to be able to access the parallel port of the PC in the operating system or the above version to realize the control of the linkage mechanism, and the hardware operation problem needs to be solved. The device driver is called the WDM device model, and its development requires more in-depth system knowledge, and the difficulty increases. Some application development software provides a set of functions for developers to call, to achieve low-level operations such as access ports. The system software function module based on the computer parallel port NC software program can be divided into three levels: the underlying driver and dynamic link library; the middle layer interpolation function; the upper layer human-computer interaction interface and interface. Each functional module of the system can be classified into a certain level. Interpolation function. The multi-dimensional linkage numerical control system based on parallel port design needs to study the linear/circular interpolation algorithm. Excellent interpolation algorithms can improve control accuracy and system stability. In general, the interpolation method has pulse incremental interpolation and numerical incremental interpolation, and each of them is divided into multiple interpolation methods. When determining the interpolation algorithm, it is to find an optimal interpolation method with less calculation and high control precision in the above interpolation method. In addition, closely related to interpolation is the motion acceleration/deceleration control, which causes the machine to move in a trapezoidal or curved mode. Graphic drawing and automatic programming functions. Modern manufacturing companies call for highly intelligent CNC machine tools. For example, medium and high-end CNC engraving machines now have graphical drawing interfaces and automatic programming functions. Even the pattern can be input into the computer via a digital camera or scanner, and processed by software to become a graphic language recognized by the computer for controlling the mechanical body for processing. For the two-dimensional numerical control system, explore the use of AUTOCAD's powerful drawing function to draw user graphics, then access its graphic database and geometric modeling core based on ObjectARX, extract graphic entity information in AutoCAD environment, and process geometric information according to processing technology and requirements. Automatically generate CNC machining instructions. other functions. A complete CNC system requires a number of functional modules to be integrated, such as document management, process parameter library, code input and process simulation modules. Conclusion The multi-axis linkage CNC system can eliminate the control card/box part of the traditional method, and the control operation is flexible and the manufacturing cost is reduced. The key modules such as its interpolation operation are integrated in the computer, so its stability and control rate are largely determined by the host computer. Different configurations of the computer may change the performance indicators of the control system. The solution and improvement of this problem still need to be studied in depth. However, for CNC systems with general accuracy and motion rate requirements, today's mainstream configurations of computers can meet the requirements. 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