JC35 Introduction: The development of servo motor control technology has driven the high-speed and high-precision advancement of machining technology. Since the 1980s, CNC systems have gradually adopted servo motors as drive devices. AC servo motors have a brushless structure, require almost no maintenance, and are relatively small in size, which is beneficial for increasing speed and power.
Currently, AC servo systems have largely replaced DC servo systems. In modern CNC systems, the replacement of DC servo systems with AC servo systems and the replacement of hardware control with software control have become the development trend of servo technology. This has led to the development of AC digital drive systems applied to servo feed and spindle devices in CNC machine tools. With the development of microprocessors and fully digital AC servo systems, the calculation speed of CNC systems has greatly increased, and the sampling time has been greatly reduced. The shift from hardware servo control to software servo control has significantly improved the performance of servo systems. For example, the servo control loop of the OSP-U10/U100 network CNC system is a high-performance servo control network. It achieves distributed configuration and network connection of various servo devices and components for autonomous control, further enhancing its control capabilities and communication speed over machine tools. These technological advancements have improved the performance, reliability, ease of debugging, and flexibility of servo systems, greatly promoting the development of high-precision and high-speed machining technology.
Furthermore, the development of advanced sensor detection technology has greatly improved the dynamic response performance and positioning accuracy of AC motor speed control systems. AC servo motor speed control systems typically use brushless rotary transformers, hybrid photoelectric encoders, and absolute encoders as position and speed sensors, with response times of less than 1 μs. Servo motors themselves are also developing towards higher speeds, achieving rapid feeds of 60 m/min or even 100 m/min and accelerations of 1g when combined with the aforementioned high-speed encoders. To ensure smoother motor rotation at high speeds, the motor's magnetic circuit design has been improved, and combined with high-speed digital servo software, this ensures that the motor operates smoothly without creeping, even when rotating at speeds less than 1 μm.
The technology of direct-drive feed using AC linear servo motors has matured. CNC machine tool feed drives come in two types: "rotary servo motor precision high-speed ball screw" and "linear motor direct drive." Traditional ball screw technology is mature, offers high machining accuracy, and has a relatively low cost for achieving high speeds, hence its widespread use. High-speed machine tools using ball screw drives have a maximum travel speed of 90 m/min and an acceleration of 1.5g . However, ball screws are mechanical transmissions, and elastic deformation, friction, and backlash exist between mechanical components, resulting in motion lag and nonlinear errors. Therefore, further increasing the travel speed and acceleration of ball screw pairs is difficult. Since the 1990s, high-speed, high-precision large machine tools have adopted direct-drive feed using linear motors. Compared to ball screw drives, it offers advantages such as higher rigidity, wider speed range, better acceleration characteristics, smaller moment of inertia, better dynamic response performance, smoother operation, and higher positional accuracy. Furthermore, direct-drive linear motors eliminate the need for intermediate mechanical transmissions, reducing mechanical wear and transmission errors, and minimizing maintenance. Compared to ball screw drives, linear motor direct drives offer 30 times the speed, 10 times the acceleration (up to 10g), 7 times the stiffness, and a maximum response frequency of 100Hz, with significant room for further development. Currently, in the field of high-speed, high-precision machine tools, both drive methods will coexist for a considerable period, but the trend indicates that linear motor drives will account for an increasingly larger proportion. All indications suggest that the application of linear motor drives in high-speed, high-precision machine tools has entered a period of accelerated growth.
