The history of linear motors can be traced back to the unsuccessful, rudimentary linear motor made by Wheatstone in 1840. In the following 160 years, linear motors went through three periods: exploration and experimentation, development and application, and commercialization. From 1971 to the present, linear motors have finally entered the period of independent application. The application of various linear motors has been rapidly promoted, and many devices and products with practical value have been made, such as steel pipe conveyors, coal conveyors, various electric doors, electric windows, etc. driven by linear motors. The speed of the magnetic levitation train driven by linear motors has exceeded 500 km/h, which is close to the speed of aviation. The research and application of linear motors in my country began in the early 1970s. The main achievements at present include factory cranes, electromagnetic hammers, and stamping presses. Although my country has also made some progress in the research of linear motors, there is still a big gap in its promotion and application compared with foreign countries. At present, many research units in China have noticed this [1]. Current Status of Linear Motor Applications in CNC Machine Tools In recent years, the use of linear motors in CNC machine tools has become particularly popular internationally. This is because: high-speed and ultra-high-speed machining, aimed at improving production efficiency and part quality, has become a major trend in machine tool development. A responsive, high-speed, and lightweight drive system is needed, with speeds exceeding 40-50 m/min. The traditional "rotary motor + ball screw" transmission method can only achieve a maximum feed rate of 30 m/min and an acceleration of only 3 m/s². Linear motor-driven worktables achieve speeds 30 times faster and accelerations 10 times faster than traditional transmission methods, reaching a maximum of 10g; stiffness is increased by 7 times; linear motor-driven worktables have no reverse dead zone; and due to the low inertia of the motor, linear servo systems can achieve high frequency response. In 1993, the German company ZXCELL-O launched the world's first high-speed machining center with a linear motor-driven worktable, the HSC-240. The maximum spindle speed reached 24,000 r/min, the maximum feed rate was 60 N/min, the acceleration reached 1g, and the contour accuracy reached 0.004 mm when the feed rate was 20 m/min. The American company Ingersoll then launched the HVM-800 high-speed machining center, with a maximum spindle speed of 20,000 r/min and a maximum feed rate of 75.20 m/min. Starting in 1996, Japan successively developed horizontal machining centers, high-speed machine tools, ultra-high-speed small machining centers, ultra-precision mirror machining machines, and high-speed forming machines using linear motors [1]. Zhejiang University in my country developed a stamping machine driven by a linear motor, and the Institute of Production Engineering of Zhejiang University designed a coordinate measuring machine with a parallel mechanism driven by a cylindrical linear motor [2]. In 2001, Nanjing Sikai Company launched its self-developed CNC linear motor lathe using direct linear motor drive. At the 8th China International Machine Tool Exhibition in 2003, Beijing Electric Power Research Institute High-Tech Co., Ltd. showcased a machining center powered by the VS1250 linear motor, with a maximum spindle speed of 15,000 r/min. The Working Principle of a Linear Motor A linear motor is a transmission device that directly converts electrical energy into linear motion mechanical energy without any intermediate conversion mechanism. It can be viewed as a rotary motor radially cut open and unfolded into a plane, as shown in Figure 1. [align=center]Figure 1: Conversion Process of a Linear Motor[/align] The side derived from the stator is called the primary, and the side derived from the rotor is called the secondary. In practical applications, the primary and secondary are manufactured with different lengths to ensure that the coupling between the primary and secondary remains unchanged within the required stroke range. A linear motor can be a short primary and long secondary, or a long primary and short secondary. Considering manufacturing costs and operating expenses, a short primary and long secondary are generally used currently. The working principle of a linear motor is similar to that of a rotary motor. Taking a linear induction motor as an example: when AC power is applied to the primary winding, a traveling wave magnetic field is generated in the air gap. The secondary winding, cut by this traveling wave magnetic field, induces an electromotive force and generates a current. This current interacts with the magnetic field in the air gap to produce an electromagnetic thrust. If the primary winding is fixed, the secondary winding moves linearly under the thrust; conversely, the primary winding moves linearly. Linear Motor Drive Control Technology A linear motor application system not only requires a high-performance linear motor but also a control system capable of meeting technical and economic requirements under safe and reliable conditions. With the development of automatic control technology and microcomputer technology, there are increasingly more control methods for linear motors. Research on linear motor control technology can be basically divided into three aspects: traditional control technology, modern control technology, and intelligent control technology. Traditional control technologies such as PID feedback control and decoupling control are widely used in AC servo systems. Among them, PID control contains past, present, and future information in the dynamic control process, and its configuration is almost optimal, exhibiting strong robustness. It is the most basic control method in AC servo motor drive systems. In order to improve the control effect, decoupling control and vector control technology are often used. Under the conditions that the object model is determined, does not change and is linear, and the operating conditions and operating environment are determined and unchanging, the traditional control technology is simple and effective. However, in high-precision micro-feeding high-performance occasions, the changes in object structure and parameters must be considered. Various nonlinear effects, changes in operating environment and environmental disturbances and other time-varying and uncertain factors are necessary to obtain satisfactory control effects. Therefore, modern control technology has attracted great attention in the research of linear servo motor control. Commonly used control methods include: adaptive control, sliding mode variable structure control, robust control and intelligent control. In recent years, intelligent control methods such as fuzzy logic control and neural network control have also been introduced into the control of linear motor drive systems. At present, the main approach is to combine fuzzy logic, neural network and existing mature control methods such as PID and H∞ control to take advantage of their strengths and make up for their weaknesses in order to obtain better control performance [3]. Application examples of linear motors in CNC machine tools Piston turning CNC system The linear motion mechanism using linear motors has the characteristics of fast response and high precision, and has been successfully applied to the CNC turning and grinding of irregular cross-section workpieces. For the non-circular cross-section parts with the largest output, the Non-Circular Cutting Research Center of the National University of Defense Technology developed a high-frequency response large-stroke CNC feed unit based on a linear motor. When used in a CNC piston machine tool, the worktable size is 600mm×320mm, the stroke is 100mm, the maximum thrust is 160n, and the maximum acceleration can reach 13g. Since the linear motor mover and the worktable are fixed together, only closed-loop control can be used. Figure 2 shows a simplified diagram of the control system of this unit. [align=center] Figure 2 Principle block diagram of linear motor position controller[/align] This is a double closed-loop system, the inner loop is the speed loop, and the outer loop is the position loop. A high-precision grating ruler is used as the position detection element. The positioning accuracy depends on the resolution of the grating. The mechanical error of the system can be eliminated by feedback to obtain higher accuracy[4]. Open CNC system using linear motor The CNC system is composed of a PC and an open programmable motion controller. This system uses a general-purpose microcomputer and Windows as the platform, and the motion controller in the form of a standard plug-in on the PC as the control core, realizing the openness of the CNC system. [align=center]Figure 3 Schematic diagram of an open CNC system based on linear motors[/align] The overall design scheme of the open CNC system based on linear motors is shown in Figure 3. This system uses a motion control card inserted into the expansion slot of a PC. The system consists of a PC, motion control card, servo driver, linear motor, CNC worktable, etc. The CNC worktable is driven by a linear motor. Servo control and machine tool logic control are both completed by the motion controller. The motion controller is programmable and interprets and executes CNC programs (G-code, etc., supporting user expansion) in the form of motion subroutines. The motion control card model is PCI-8132. In today's industrial control technology, the PCI bus has gradually replaced the ISA bus and become the mainstream bus form. It has many advantages, such as plug and play and interrupt sharing. The PCI bus adheres to strict standards and specifications, ensuring excellent compatibility and high reliability. It boasts high data transmission rates (132 Mbps or 264 Mbps), is CPU-independent and clock frequency-independent, making it suitable for various platforms and supporting multiprocessors and parallel operation. Furthermore, the PCI bus offers excellent scalability, allowing for multi-level expansion via PCI-PCI bridges. The PCI bus provides significant convenience to users and is currently the most advanced and universal bus on PCs. The PCI-8132 is a 2-axis motion control card with a PCI interface. It can generate high-frequency pulses to drive stepper motors and servo motors, controlling the movement of two axes to achieve linear and circular interpolation. It provides position feedback in CNC machining. The system software is developed on the Windows platform. This software employs a modular programming design, consisting of a user input/output interface and a preprocessing module. The user input/output interface allows users to input CNC codes, issue control commands, configure system parameters, and generate CNC machine tool part machining programs (G-code instructions). After reading the G-code instructions, the preprocessing module compiles and generates a program that can be run by the PCI-8132 motion control card, thereby driving the linear motor to complete linear or circular interpolation. The process of reading the G-code involves first setting the parameters, and then reading the G-code. The program flow is shown in Figure 4. [align=center] Figure 4 Flowchart of G-code reading program[/align] In this system, Parker 406LXR series linear motors are selected. For the two-axis CNC worktable, a 406T07 linear motor with a stroke of 550mm is selected in the x-axis, and a 406T05 linear motor with a stroke of 450mm is selected in the y-axis. Conclusion High-speed machining centers using linear servo motors have become a key technology and product that major international machine tool manufacturers are vying to research and develop. They have already achieved initial application and success in the automotive and aerospace industries. As a new generation of direct-drive servo actuators for high-speed machining centers, linear servo motor technology has also entered the industrial application stage both domestically and internationally. However, domestic research in this area is still in its early stages and there is still a significant gap. This article explores the application of linear motors, and many technical issues still require further efforts in the future.