Research On A Micro Feed System With High-Precision And Large-Travel

With the development of science and technology, the requirement of machining precision is becoming higher and higher in all kinds of fields, such as national defense industry, navigation technique, biology engineering, micro-electron engineering and nanometer science and technology and so on. The capability and quality, stability and dependability of products can be improved greatly by enhancing fabricate precision. Ultra-precision machine tool is a major tool to ensure machining precision of products. Micro-feed system is the core part of ultra-precision machine tool, whose capability determined directly machining precision. With the development of ultra-precision machining technology, ultra-precision positioning in the range of large displacement needs to be achieved in micro-feed system to machine workpiece with large size and obtain the good machining precision. Traditional feed system can not satisfy requirement of machining precision, which is limited by its characteristic of structure. So a new ultra-precision feed system with high precision and large travel needs to be designed and fabricated, consequently the machining precision of ultra-precision machine tool is improved greatly, which has important significance to improve national economy, shorten the gap of ultra-precision machining and detection between our country and developed countries and accelerate national defense industry modernization construction.A new micro-feed system with large-travel and high-precision based on tribology theory is presented, which is driven by piezoelectric actuators. It provides an economy and reliable method for the realization of nanoposition technique, which has important significant and practicality value on the research and application of ultra-precision positioning system.The micro-feed system consists of driving parts and transmission parts. The friction column is driven by piezoelectric actuator to obtain the output angle displacement in driving parts; Transmission parts consist of ball screw and air static guide, which achieve linear motion. The key parts of system are devised, which consist of adjustable preload mechanisms and air static guide. The static characteristics of preload mechanisms that consist of stiffness, stress and natural frequency are analyzed by finite element analysis method to obtain the physical dimension of flexibility hinges influence on static characteristics. And optimum design is achieved.Physical and mathematic model of micro-feed system are built by modularized method to provide theory basis for devising controller of this system. Dynamics model and equation are built in order to optimize control parameters and reduce influence factors on positioning system during friction drive, such as micro-slip, nonlinear and so on. Simulation and experimental research on dynamic characteristic of system is carried out based on Karnopp"stick-slip"model. The influence rule on dynamical characteristic is obtained which is aroused by normal pressure, friction coefficient and rotary inertia.Inverse Preisach model of driving system is built to describe hysteresis and nonlinear characteristic existing in piezoelectricity. The output displacement is predicted perfectly after a series of random voltage path. And hysteresis nonlinear of displacement is improved availably. The nonlinear error is reduced and control precision is increased.Fuzzy control system with variable speed integrate is designed according to the features of micro-feed mechanism. Two-dimension fuzzy controller is adopted. Non-homogeneous division is adopted to choose membership function of fuzzy variable. Fuzzy subset with low precision is adopted when the error is large. Otherwise fuzzy subset with high precision is done. The disadvantages of quantization, dead zone and bad steady-state behavior which exist in conventional fuzzy controller will be ameliorated, and stability of the system is improved. The simulation of closed-loop control is done by Simulink in Matlab software, which proves that the project is feasible. Experimental research on closed-loop control is carried on. The precision ofthe micro-feed motion is 0.01μm in the travel of 150mm, and positioning precision is up to 0.0347μm. The impact rules of experimental parameters on dynamic characteristic are investigated by experimental method. The result is same to simulation, and optimizing control parameters are obtained.