System Design And Structural Optimization For AC Active Magnetic Bearings Using In High Speed Electric Spindle

Magnetic bearings is a new high performance bearing which with magnetic force makes rotor suspend in the space and whitout any mechanicical contact with stator. It will have huge potential application value in the NC machine tools and other machining due to the advantages of no friction, in-gage, high-speed, high-precision, long service life, and so on. Because of the emphases research of magnetic bearing at home and abroad is DC active magnetic bearings (AMBs) at present, and the cost of DC power amplifiers is much higher than AC power converters. Our team have researched a new kind of three-phase AC active magnetic bearing (AMB) and an innovated radial-axial active magnetic bearing with sharing biased current, which combine radial and axial active magnetic bearings in a unit. The volume and consumption of power amplifier is decreased, and the cost is deduced, and the last magnetic bearing's radial suspension forces were improved which the baised magnetic flux of the radial direction and axial direction were produced by axial current coil. On this basis, the 5-DOF electric spindle was designed; the digital control system of 5-DOF AMB was designed. The detail contents of this dissertationare as follows:Firstly, an AC active magnetic bearing and a radial-axial active magnetic bearing with sharing biased current were designed which were used in high speed electric spindle's suspension, respectively. The flux path of these magnetic bearings were calculated by using equivalent magnetic circuit, and the mathematical models of suspension forces were deduced respectively. Then based on the mathematics models, the relatively design parameters were given. Nonlinearities of suspension forces and cross coupling between different degrees of freedom were analyzed by using simulation software MATLAB, and the mechanical structures and magnetic circuit configurations of these novel magnetic bearings were calculated and analyzed by using finite element analysis software ANSOFT. The control strategy of these active magnetic bearings were also proposed, respectively.Secondly, the control system simulation mode of the radial-axial active magnetic bearing with sharing biased current is constructed under MATLAB/SIMULINK simulation environment and simulation research is done. The simulation results have shown that the whole control system has good dynamic and static performance.Lastly, to use the chip TMS320F2812 DSP of TI company as the digital controller of 5-DOF AMBs system. The hardware and software flow chart of the digital controller is designed. The results of theory research and test have shown that the configurations design are reasonable, parameters design are accurate, and control performance of digital control system is also accurate for high-speed machine tool electric spindle supported by 5-DOF AMBs.