Preload Design And Active Control Method Of High-speed Precision Spindle

High-speed precision spindle is the key functional component of precision machines.The preload,which plays an important role on the machining accuracy and fatigue life of the spindle,is the bridge of coupling interaction between the thermal and dynamic characteristics of the spindle system.Currently,the preload of the spindle is determined by means of experiments or experience of the manufacturer at home and abroad.This method is inefficient and cannot give full play to spindle performance.Meanwhile,with the development of high-speed,intelligent and multifunctional machining,both heavy cutting at low speed and light cutting at high speed are often performed in a single machine tool spindle.However,the traditional constant pressure preload and fixed position preload cannot meet the requirements.The good dynamic and thermal performance can be ensured only in a certain speed range,not in the whole speed range of the spindle,by utilizing the traditional constant pressure preload method or fixed position preload method.Based on the above problems,this dissertation investigates into the methodologies for preload designing and active controlling of high-speed precision spindle.The main contents are closely related to nonlinear modeling of bearing,designing method for preload,innovative design of variable preload mechanism,active controlling method and model-based controlling strategy for preload.The following contributions have been made.For the nonlinear modeling of the angular contact ball bearing,the nonlinear model of the angular contact ball bearing is established considering the thermal-mechanical coupling effects.The trends of the contact angle,contact load,axial/radial stiffness of the angular contact bearing with preload and speed are analyzed.For preload designing of the spindle-bearing system,the thermal simulation technique of heat-solid coupling FEM and analytical modeling method is adopted to analyze the preloading state of the spindle-bearing system during high-speed.Then,the operational preload modeling method of the spindle-bearing system is constructed by utilizing the nonlinear model of the bearing.On this basis,the preload designing method of the spindle-bearing system is proposed.This method provides theoretical support and technical guidance for the active control and optimization of preload of the spindle-bearing system.For variable preload method and innovative variable preload mechanism of spindle-bearing system,the design principle and control method of the variable preload spindle-bearing system by utilizing piezoelectric actuators is proposed.The preload monitoring and controlling platform for the spindle-bearing system by using the piezoelectric actuators is built,which provides the hardware and software systems to the studies of active preload control strategies of the preload of high-speed precision spindle.For the mechanical modeling of the variable preload spindle-bearing system,the mechanical model of the variable spindle-bearing system considering the external loads and high-speed effects are constructed.Besides,the mechanical model are verified by experiments.Based on the controlling platform,the static and dynamic performance of the variable spindle-bearing system under variable pressure preload and variable position preload is investigated systematically under the external loads as well as the high-speed conditions.For the variable preload control strategy of the spindle-bearing system,the preload control strategy is proposed.The strategy is determined according to the constraint of bearing fatigue life at low speed and the constraint of bearing temperature at high speed.A series of experiments are implemented to verify the validity and superiority of the variable preload control strategy,the running accuary,radial stiffness and temperature of the spindle under active preload control strategy and traditional constant pressure preload strategy are carried out.The experiment results show that the high stiffness at low-speed and low temperature at high speed of the spindle system can be realized by utilizing the proposed preload control strategy.The research work in this dissertation provides theoretical support and technical guidance for the spindle designing,preload controlling and thermal-mechanical characteristic optimizing.It has important theoretical significance and engineering value for the promotion of high-speed precision spindle design level of our country,and has a positive role in promoting for design and development of intelligent electric spindle product,which has the self-regulating function for preload controlling.