Design Of Double Loop Control Based On Finite Time Observer For Servo System

With the development of Aerospace Science and technology,more and more servo mechanisms are applied to spacecraft or satellite,which play an increasingly important role,such as space manipulator,two-dimensional turntable for earth observation and communication.With the increase of spacecraft life and the complexity of space mission,people also put forward the requirement of high precision and long life for space servo structure.The large temperature difference,vacuum and other special environments in space make the friction coefficient of the bearing of the space servo mechanism change significantly.In addition,the inertia coupling problem of the multi degree of freedom servo mechanism makes the model of the space servo mechanism perturbed greatly.In addition,most of the space servo mechanisms work in the condition of small inertia and low speed,the influence of friction dead zone is more serious.How to improve the control method to improve the adaptability of servo mechanism to the model change caused by large temperature difference,grease volatilization and inertia coupling is a practical subject.In order to solve the above problems,this paper proposes a double loop control scheme of speed plus position,which improves the speed signal accuracy by using a finite time observer;designs a speed loop by using self-tuning control to adapt to the changes of model parameters and overcome the effects of friction;designs a composite control to improve the performance of the external loop.The specific work of this paper is as follows:First of all,the theory of finite time stability and the basic principle of finite time observer are analyzed.According to the characteristics of servo system,a finite time speed observer based on the finite time convergence function is selected,and the method of obtaining the observer parameters based on LMI is given.In different simulation conditions,compared with the speed obtained by the position difference method,it is verified that the observed speed has the characteristics of high accuracy and small delay.As the feedback signal of the speed loop,it can effectively improve the performance of the system.Secondly,aiming at the problem that the characteristics of the controlled object of the space servo mechanism will change due to the space environment,a design method of speed inner loop based on the self-tuning control is proposed,that is,the model parameters are identified online by the least square method,and the controller parameters are adjusted by the pole assignment to keep the performance of the closed-loop system constant.Aiming at the slow convergence process and the existence of identification errors,a model verification method is designed to avoid the influence of identification errors on performance.Finally,the effectiveness of the method is verified by simulation.Finally,in order to improve the overall performance of the control system,the external loop controller is designed with the combination of speed acceleration feedforward and lead lag.Then,in the Simulink environment,a complete simulation model including various interference,quantization noise and model perturbation is built,and the low-speed tracking simulation is carried out.By comparing with the two loop control method with differential speed as feedback,the effectiveness and superiority of the proposed method are fully verified.