Adaptive Fuzzy Sliding Mode Control Of Hybrid Magnetic Bearing Based On Disturbance Observer

CNC machine tools are the industrial parent machine for manufacturing.With the development of the manufacturing industry,CNC machine tools are required to meet performance requirements such as high speed and high precision.The core component of CNC machine tools is the electric spindle.The electric spindle connects the motor and the spindle together,eliminating the transmission system in the traditional machine tool.The structure of the CNC machine tool is more compact,the transmission efficiency is higher,and it is easier to achieve high speed and high-precision.The bearing plays a supporting role in the electric spindle,so the spindle bearing needs to meet the speed,temperature and accuracy requirements of the electric spindle.Therefore,the bearings should have the advantages of no need for lubrication or good lubrication effect,low or even frictionless,low heat generation,and good high-speed performance.Magnetic suspension bearings use magnetic force to suspend the rotor in the air without mechanical contact.Therefore,the magnetic bearing has the advantages of no friction,no need for lubrication,less heat generation,little environmental pollution,easy to achieve high speed,no noise,etc.Therefore,this thesis chooses a hybrid magnetic bearing system with active axial control and passive radial control for research.First of all,mathematical modeling and force analysis of the designed hybrid magnetic bearing are carried out.For the radial permanent magnet control part,when the rotor produces relative displacement,the equivalent magnetic charge theory is used to calculate the axial magnetic force generated by the permanent magnet ring.This axial magnetic force generated by the radial permanent magnet becomes the time-varying disturbance of the system.For the force analysis of the axial electromagnetic control part,the relationship between the axial electromagnetic attraction and the displacement and the control current are obtained.It is found that there are serious nonlinearities and open loop instabilities in the axial system.Secondly,based on the nonlinearity and open-loop instability of the axial system again,a closed-loop sliding mode variable structure position controller is designed.Sliding mode variable structure control has the advantages of fast response speed,strong anti-interference ability and simple structure.However,the inherent discontinuous switching characteristics of sliding mode variable structure control will cause system chattering,so adaptive fuzzy control is introduced.An adaptive fuzzy sliding mode variable structure controller is designed,which effectively weakens the chattering effect caused by sliding mode variable structure control.Finally,in view of the time-varying disturbances in the hybrid magnetic bearing system,a slow time-varying disturbance observer is designed for online observation to realize real-time compensation control.When the hybrid magnetic bearing is working at low speed,rated speed,high speed and the instantaneous impact force of the system during tool processing,the simulation is carried out through Matlab to verify the effectiveness of the designed slow timevarying interference observer on the interference signal suppression performance.