Servo motor development towards high speed and high precision
The development of servo motor control technology has promoted the high speed and high precision of processing technology. Since the 1980s, CNC systems have gradually applied servo motors as drive devices. The AC servo motor has a brushless structure, requires almost no maintenance, and has a relatively small volume, which is beneficial to the improvement of the rotational speed and power.
At present, the AC servo system has replaced the DC servo system to a large extent. In the contemporary CNC system, AC servo instead of DC servo, software control instead of hardware control has become the development trend of servo technology. This results in an AC digital drive system for servo feed and spindle devices for CNC machine tools. With the development of microprocessors and all-digital AC servo systems, the calculation speed of CNC systems is greatly improved, and the sampling time is greatly reduced. After the hardware servo control becomes software servo control, the performance of the servo system is greatly improved. For example, the servo control loop of the OSP-U10/U100 networked numerical control system is a high-performance servo control network, which realizes the distributed configuration of various servo devices and components for autonomous control, and the network connection further plays its role in the machine tool. Control capabilities and communication speed. The development of these technologies has improved the performance of the servo system, improved reliability, convenient debugging, and enhanced flexibility, which has greatly promoted the development of high-precision and high-speed machining technology.
In addition, the development of advanced sensor detection technology has greatly improved the dynamic response performance and positioning accuracy of the AC motor speed control system. The AC servo motor speed control system generally uses a brushless resolver, a hybrid photoelectric encoder and an absolute encoder as position and speed sensors, and the sensor has a response time of less than 1 μs. The servo motor itself is also developing at a high speed, and with the above-mentioned high-speed encoder, a rapid feed of 60 m/min or even 100 m/min and an acceleration of 1 g are realized. In order to ensure smoother motor rotation at high speed, the magnetic circuit design of the motor is improved, and with the high-speed digital servo software, the motor can be smoothed without creep even when it is rotated less than 1μm.
The direct drive servo technology of AC linear servo motor has matured. The feed drive of CNC machine tools has two types: “rotary servo motor precision high speed ball screw” and “linear motor direct drive”. The traditional ball screw process has high processing precision and the cost of achieving high speed is relatively low, so it is widely used at present. The high-speed machining machine with roller and bead screw drive has a maximum moving speed of 90m/min and an acceleration of 1.5g. However, the ball screw is a mechanical transmission. There are elastic deformation, friction and backlash between the mechanical components, which will cause motion lag and nonlinear error. Therefore, it is more difficult to further improve the moving speed and acceleration of the ball screw. Since the 1990s, linear motors have been used to directly drive feed drives in high-speed, high-precision, large-scale machine tools. It has higher rigidity, wider speed range, better acceleration characteristics, smaller motion inertia, better dynamic response performance, smoother operation and higher positional accuracy than the ball screw drive. And the linear motor is directly driven, no intermediate mechanical transmission is needed, which reduces mechanical wear and transmission error and reduces maintenance work. Compared with the ball screw drive, the direct drive of the linear motor has a speed increase of 30 times, an acceleration of 10 times, a maximum of 10 g, a 7-fold increase in stiffness, and a maximum response frequency of 100 Hz. There is still room for development. At present, in the field of high-speed and high-precision machine tools, the two driving methods will coexist for a long time, but from the development trend, the proportion of linear motor drives will become larger and larger. There are indications that the application of linear motor drives on high-speed, high-precision machine tools has entered an accelerated period of growth.
