Modelling And Control Method Of Active Hydrostatic Bearing System

Hydrostatic bearing has great prospects in precision and ultra-precision machinery,because it has large bearing capacity,high motion accuracy and vibration suppression.Although traditional hydrostatic bearing has the ability of self-adjustment,it is"passive".This characteristic means that the balance position would change with different loads,and would affect the accuracy and performance.Active hydrostatic bearing system can overcome the shortcomings by actively adjustment.In addition,compared with the traditional hydrostatic bearing,active hydrostatic bearing system has advantages in controlling vibration,modifying bearing dynamic characteristics and improving stability.At present,modelling and control method of active hydrostatic bearing system has not been well solved.Therefore,this thesis has carried out relevant research on these problems.Firstly,the test rig of active hydrostatic bearing system is established and tested.Based on the existing equipment of hydrostatic bearing,the control block is designed,and related program is developed.These works achieve the establishment of active hydrostatic bearing system.Then,static and dynamic characteristics are tested,and the desired orbit is preliminarily realized.Secondly,modelling and parameter identification of active hydrostatic bearing system are carried out.According to the nonlinear and multi-input multi-output characteristics,a piecewise linear model is used to capture the system.Thus,the nonlinear system is transformed to the linear parameter-varying system.Then,the discrete state space equations are obtained by reforming the dynamic equations.The error cost function is calculated by prediction error method.And parameters are solved by particle swarm optimization algorithm.The average fitting percentage of identification model in the horizontal and vertical directions is 92.71%and 83.91%respectively,which shows the effectiveness of identification method.The entire model is described by constant model structure and changing parameters.Then,simulations of decoupling control strategy and error compensation are studied.Firstly,motion error is analyzed.Then,based on the multi-input multi-output characteristics,feedforward decoupling controllers are used to deal with coupling gains.In the Simulink,the trajectory and error compensation under external error are simulated.Under the combined action of feedforward decoupling controllers and proportional integral controllers,this system achieves the desired effect in adjusting the motion error under the influence of external disturbance.Finally,active error compensation experiments under the external disturbance are carried out.Based on the shortcomings of traditional hydrostatic bearing and the potential application of system,system error is analyzed.Through the approximate linearization of identified model,controllable system model is obtained,and then the parameters of controllers are estimated through the simulation model,which is further improved in the experiments.The experimental results show that the compensation time for external error is less than 0.15s,which not only verifies the effectiveness of control strategy,but also shows the good application potential of system.