Magnetic Levitation Electro-spindle System With AC Amplifying Power

Magnetic bearing,in which the rotor can be suspended in the geometric centre of stator by electromagnetic forces,is a new type of high performance bearings with noncontact.Magnetic bearing has a series of advantages such as no friction,no wear,needless lubrication and seal, high-speed,high-precision,long service life,etc.,and creates favorable conditions for improving technology capability of high-speed machine tool spindle system.At present,the main research object of magnetic bearings is still DC active magnetic bearings(AMBs),a radial AMB is ususally driven by two bipolar power amplifiers,which leads to complicated structure,big capacity,high cost of DC active controllable magnetic machine tool spindle,so it is difficult to be used in practice.This dissertation’s work is supported by National Natural Science Foundation of China project(50575099),according to principle of the bearingless motor,a machine tool spindle system which is supported by a kind of new structure AC hybrid magnetic bearings driven by inverter has been designed.The state equations of magnetic machine tool spindle are established,stiffness and damping performance have been analyzed,and digital control technology of the system has been studied.The detail contents are as follows:Firstly,the mathematical models of AC hybrid magnetic bearing and state equations of magnetic machine tool spindle are established.Mechanical structures and working principle of two and three degrees of freedom hybrid magnetic bearings are demonstrated,and the mathematical models are deduced by using equivalent magnetic circuits.On this basis,state equations of machine tool spindle supported by AC-DC five degrees of freedom hybrid magnetic bearings are established.Further,stiffness and damp of AC hybrid magnetic bearings have been defined and studied. On the basis of calculating stiffness and damp,the influence status of stiffness and damp of magnetic bearing affected by control parameters is analyzed,when PD controllers are used in control system of magnetic bearings.In order to study the influence of control strategy on stiffness and damping of magnetic bearings,the generalized stiffness of magnetic bearing is defined.On the basis of defining synthetically dynamic stiffness of magnetic bearings and establishing its’ mathematical models,the influence of eccentricity ratio and bias magnetic field ratio on synthetically dynamic stiffness is simulated by Matlab soft-ware.Finally,the hardware and software digital control system of five degrees of freedom hybrid magnetic bearings are researched.On the basis of designing the whole framework of the system, using the TMS320F2812 DSP chip of TI Company as the digital controller’s CPU,DSP development board is designed,displacement interface circuits and power driver circuits have been developed too.Communication software of slave computer and host computer and DSP control software of the system have also been developed.The results of theory research and experiment have shown that the machine tool spindle system supported by AC hybrid magnetic bearings has reasonable configuration,and digital control system has good performance.