Research On Servo Control Techniques For Ultra-precision Machine

Ultra-precision machining is very important in the current development of machining technology. With the high surface machine quality and low cost, diamond turning becomes one of the major development directions. In the aspheric surface ultra-precision machining, contouring accuracy of the cutting tool decides the machine's aspheric surface machining accuracy. And it is very difficult to control the tool contouring with nanometer lever accuracy. With the aim of aspheric surface ultra-precision machining, this article's research major in the servo control and contour tracking control of the machine's feeding system based on the self-constructed ultra-precision turning machine. The main content of this article include the research of motion characteristics of feeding mechanism, the research of servo control and tracking control techniques of feeding systems, and contour error control techniques of multi-axis motion.1. The motion characteristics of feeding mechanism are the foundation of its control strategy research. And decide the motion accuracy of feeding mechanism. Ball screw mechanism is common used in ultra-precision machine. The factors, which influence the motion accuracy of ball screw mechanism, are researched, such as friction, contact stiffness, backlash, etc. The micro movement characteristics of ball screw mechanism are researched, and a proper micro dynamic model is proposed.2. The transfer function of feeding system is developed based on the combined method of experiment and theoretical derivation. A control method named gain self-adapt control based on motion error is proposed. The method is used for machine control. The motion resolution of the machine tools is achieved to be 0.01 (am.3. A multi-axis motion control board used for ultra-precision machine is developed. Besides the basic functions of commonly used motion controller, the controller integrates a control algorithm suitable for ultra-precision machine. A direct interpolator based on universally optical equation is also integrated in this control board. And the controller is already used for machine control.4. Robust ability is a basic requirement to the servo system of ultra-precision machine. Quantitative Feedback Theory is used for the machine's robust controller design. Because the requirements of a machine controller are various, a multi-controller combined tracking controller design ideal is adopted in the machine controller design. And a QFT tracking controller combined with velocity feed-forward control and reset control is proposed. Simulated result displays that the controller can achieve nanometer lever tracking accuracy.5. The factors that influence contour accuracy of the machine are analyzed. The equation of contour error due to feeding axis's dynamics is derived by circular contour motion of the machine, and a model of contour error is proposed. Based on this model, Cross-Coupling Control and Synchronizing Control strategy are researched. A new contour control strategy that is thecombination of sub-interpolation and cross-coupling control is put forward. This method can make the CCC control algorithm easer for use, and can greatly decrease the high frequency oscillation motion in the machine produced by interpolation instructions.