**Introduction** Parallel machine tools, also known as virtual axis machine tools or parallel kinematic machines, are a new type of CNC machining equipment based on parallel mechanisms. Essentially, they combine robotics, machine tool structure, and CNC technologies, simultaneously possessing many characteristics of both machine tools and robots. They can be viewed as both robotized machine tools and machine tool-like robots. They offer the flexibility and agility of robots while possessing the rigidity and precision of machine tools, making them a new type of electromechanical equipment integrating multiple functions. **Structure of Parallel Machine Tools** A schematic diagram of the parallel machine tool structure is shown in Figure 1. It consists of a servo (stepper) motor 1, a fixed platform 2, a support 3, a telescopic rod 4, a moving platform 5, a milling head 6, and a worktable 7. The telescopic rod installed between the fixed platform and the moving platform is driven by a servo motor (or stepper motor), which drives the ball screw and nut inside the telescopic rod to move, causing the length of the telescopic rod to change. Because the lengths of each telescopic rod (usually 6 or 3 rods) change, the position of the moving platform changes. Multiple telescopic rods move together, driving the moving platform to achieve movements such as rising, falling, and flipping, and driving the milling head to achieve various movements required for the work. Each telescopic rod is driven by an independent servo drive device. [b]Open Control System Structure[/b] For parallel motion machine tools, the biggest characteristic is that the mechanical structure is very simple, but the control is extremely complex. The control system of parallel motion machine tools must adopt an open structure. Currently, there are three main structural forms of open CNC systems at home and abroad. 1. Dedicated CNC + PC type: This involves embedding the machine into a traditional non-open dedicated CNC system, allowing the entire system to share some computer hardware and software resources. The first type of CNC system performs non-real-time control tasks such as system management, and provides functions such as auxiliary programming, analysis, monitoring, and process scheduling. The second type is responsible for real-time control tasks such as interpolation calculation, servo control, and I/O control. This type of CNC system is only open in the machine part; its specialized CNC part remains closed, and the NC kernel cannot be opened. This type of structure is generally adopted by mainstream CNC system manufacturers. The third type is a PC + motion control card system. This system structure uses a general-purpose microcomputer as the platform and a standard plug-in open motion control card as the control core. The general-purpose PC performs CNC program editing, human-machine interface management, and external communication functions, while the motion control card is responsible for the machine tool's motion control and logic control. It supports secondary development and independent expansion by users, possessing both the openness of a PC and the openness of a dedicated CNC module; it can be said to have both upper and lower-level openness. The fourth type is a pure PC-based CNC system, which is entirely software-based. This system means that all functions are processed by the PC, and servo drives are controlled through a servo interface card installed in the expansion slot. While its software boasts good versatility and flexible programming, it suffers from issues related to operating system real-time performance, standardization, and system stability. Currently, such systems are in the exploratory stage and have not yet become commercial products, but they represent the future direction of CNC systems. If focusing on the design of an economical CNC parallel machine tool control system, an open CNC system using a PC + motion control card is currently the most ideal choice. With a PC and motion control card as the core of the control system, the system platform is directly built upon the PC's hardware and software foundation. The driving element is a stepper motor, and the system is implemented in a Windows environment using VC++. The software design employs an object-oriented approach. The design of a parallel machine tool motion control card based on the PCI bus involves controlling various drive rods of the machine tool to achieve spindle movement. It controls a large number of axes and also needs to obtain the required tool movement trajectory. To achieve high-speed, high-precision trajectory control of the cutting tool, there is a significant amount of data interaction between the motion control card and the PC. Traditionally, this is done using the ISA bus. However, due to the bandwidth limitations of the ISA bus, the data transmission speed is slow, causing the PC to spend considerable time on data transmission, thus reducing processing time in other areas. This system enables communication between the motion control card and the PC, achieving a very high data transmission rate. This significantly enhances the PC's processing power, ensuring the real-time performance of the CNC system and making the development of corresponding platform-based CNC software easier, as well as facilitating interfaces with other supporting software. The hardware composition of the control system is shown in Figure 2. This system uses the company's 32-bit fixed-point DSP chip, TMS320VC33. The DSP chip is responsible for receiving commands and parameters from the PCI local bus, then using motion control algorithms to achieve precise motion control of the stepper motor. Simultaneously, the chip is also responsible for transmitting feedback information to the PCI local bus and controlling the system's peripheral I/O modules. Communication between the DSP and the PC is achieved through the bridge chip CY7C09449PV_1J. The CY7C09449PV uses a high-speed synchronous bus, currently the most widely used and popular type, with a 64-bit bus width, a working frequency of 33 MHz, and a maximum transmission rate of 132 Mb/s. It allows peripherals to be directly connected to the host CPU's local bus and run at CPU speed, significantly improving the operating speed of peripherals. The CY7C09449PV is a fully functional, low-cost dual-port RAM interface chip from Cypress, conforming to the PCI 2-2 bus specification. One port is a PCI interface, suitable for communication with a PC; the other port is a local interface. It provides a master/target interface, allowing connection to any general-purpose microprocessor. It has an on-chip 128 dual-port memory for local processor data sharing with the PCI bus. The connection between the CY7C09449PV and the PCI bus is shown in Figure 3. The dedicated chip CY7C09449PV for PCI bus development uses a single 3.3V power supply, compatible with both 3V and 5V PCI signal environments. Power can be drawn from the PCI slot, which can provide 3.3V, 5V, and 6V. Special attention needs to be paid to two pins, PRSNT1 and 2, in the PCI slot. The four combinations of grounding and floating of these two pins directly determine the power of the PCI card. When using the CY7C09449PV, some pins require pull-down or pull-up resistors with resistance values ​​from 1kfL to 10kfL. Depending on the specific situation, in this design, pull-up resistors are added to the pins of SCI, SDA, AIE, /BE[2], and RDY, and pull-down resistors are added to the pins of TEST-MODE. It is a new generation of floating-point DSP launched by TI. It is a lower-priced version developed on the basis of the original floating-point DSP. The product is characterized by high speed, low power consumption, low cost and easy development. Since it uses internal 1.8V and external 0.3V power supply, the power consumption is reduced by about one order of magnitude compared with the original model. Moreover, it can support a running speed of up to 150 × 10 times/s. It is an ideal DSP device in portable products that require floating-point operations. As the core of the control system, TMS320VC33 mainly completes the real-time interrupt servo control program, including the operation of various underlying hardware. It adopts a 32-bit local bus interface. The clock signal can be a separately provided clock source or any one of the PCI clock signals provided by CY7CO9449PV, PCI KOUT[2O]. Conclusion Parallel machine tools need to control a large number of axes and involve forward and inverse solving operations of parallel mechanisms, which requires a large amount of computation. By adopting a bus-based motion control card, the task of the entire CNC system is jointly undertaken by the PC and the motion control card, which can play an ideal motion control performance in an open CNC system. With the popularization of CNC systems and the improvement of product quality, this motion control card will have a wide range of application prospects. References: Shi Qun, Wang Xiaochun. Design of local bus interface for parallel machine tool position control card. Industrial Instruments and Automation Devices, 2004 (3): 36-39. Cao Guangzhong, Qiu Jian. High-performance floating-point DSP chip TMS320VC33 [-J]. Foreign Electronic Components, 2001 (10): 14-17. Editor: He Shiping