The high-speed spindle unit technology has developed to a high level in some industrialized countries and has been widely used in the high-speed machine tool industry, which has already produced huge economic benefits. In order to meet the needs of domestic development of high-speed, high-precision CNC machine tools, in the "Ninth Five-Year Plan" period, China has developed a spindle power of 2.5kW ~ 29kW, torque of 4 ~ 86N.m, can be applied to CNC machine tools and machining centers The electric spindle is equipped with some domestic CNC machine tools. However, in general, compared with foreign products, domestically produced electric spindles have large gaps in performance, variety and quality. Therefore, the current domestic high-speed, high-precision CNC machine tools and machining centers are still mainly used. Imported from abroad. The high-speed electric spindle unit technology is the bottleneck restricting China's ultra-high-speed machining technology. In order to catch up with the trend of high-speed processing technology development, China is constantly increasing its research efforts on the key components of ultra-high-speed machining, the electric spindle unit. At present, the National High-efficiency Grinding Engineering Technology Research Center has undertaken the research and development and application of the high-speed spindle unit of the national “Tenth Five-Year Planâ€, and is working hard to improve the technical level of electric spindle units in China.
(4) Linear servo feed technology driven directly by linear motors has matured
The feed drive of high-speed and high-precision machine tools mainly includes two types: the traditional "rotary servo motor + precision high-speed ball screw" and the new "direct drive for linear motor".
Due to the mature technology and wide application, the ball screw not only has high precision (ISO34081), but also has a relatively low cost for high-speed machining, so it is still used in many high-speed machining machines. At present, the high-speed machining machine using ball screw drive has a maximum moving speed of 90m/min and an acceleration of 1.5g. However, the ball screw is mechanical transmission after all. There are a series of mechanical components from the servo motor to the moving parts. There are bound to be elastic deformation, friction and backlash, which will cause motion lag and other nonlinear errors. The current moving speed of the ball screw pair And the acceleration has been increased more, and there is limited room for further improvement. Since 1993, the direct drive of linear motors has been applied to machine tool feed. It is an ideal driving method for high-speed and high-precision machine tools, especially for large-scale machine tools. At present, the high-speed and high-precision machine tools using linear motors have a maximum rapid traverse speed of 208 m/min and an acceleration of 2 g (the level of Mazak's HMCF3-660L machining center), and there is still room for development.
The advantages of direct drive of a linear motor compared to a ball screw drive are:
High stiffness
The linear motor is directly connected to the load, with no gaps and higher dynamic stiffness.
Wider speed range
Modern motor technology makes it easy to achieve wide speed regulation, and the speed variation range is up to 1:10000. For example, the United States Kollmorgen DDL permanent magnet linear motor has a high speed of more than 5m / s and a low speed of 1μm / s.
Good acceleration characteristics, small motion inertia, and higher dynamic response performance.
Smooth operation and high positional accuracy (basically depending on the position feedback detection component).
No travel limit
With modular structure, it can be used to adapt to different travel requirements.
Direct drive with linear motor
All intermediate mechanical transmissions are eliminated, which fundamentally reduces mechanical wear and transmission errors and reduces maintenance work.
The track error is small, and good positioning accuracy can be obtained at high speed. The advantage of direct drive of linear motor just makes up for the shortage of ball screw drive. Compared with ball screw drive, its speed is increased by 30 times, acceleration is increased by 10 times, maximum is 10g, stiffness is increased by 7 times, and the highest response frequency is up to 100Hz.
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