Research On Hysteresis Characteristics Of Piezoelectric Actuaors And Control Of A Six Degrees Of Freedom Active Vibration Isolation Platform

With the development of modern science and technology,the resolution of highprecision observation equipment carried by spacecraft is gradually increased,and higher requirements are put forward for the stability of the use environment.However,during the on-orbit operation of spacecraft,the micro-vibration generated by power equipment,such as control moment gyroscope,reaction wheel and momentum wheel,severely damaged the steady-state environment needed by high-precision equipment,resulting in the decline of imaging quality and observation performance,which has become main reasons which limit its application.In order to give full play to the performance of precision equipment,vibration isolation is the most direct technical means.Therefore,this paper takes multi-degree-of-freedom vibration isolation of spacecraft precision equipment as the research background,and conducts in-depth research on six-degree-offreedom vibration isolation platform based on piezoelectric actuators.Piezoelectric actuator is a kind of actuator commonly used in active vibration control.However,due to the inherent hysteresis characteristics of materials,there exists a complex multivalued mapping relationship between the input voltage and output displacement of the actuator,which severely reduces its performance in vibration control system.Aiming at this phenomenon,a mathematical model describing the hysteresis characteristics of actuators is established based on the neuro-fuzzy adaptive reasoning system,and the output accuracy of the model is verified by comparing with experimental data.Two control methods of actuator's hysteresis compensation are put forward.Control performance comparison and effectiveness verification of the two methods are made through simulation.The precise control of actuator hysteresis compensation is achieved,which lays a foundation for its effective application in vibration control.In order to realize the vibration isolation goal based on piezoelectric actuator and study the influence of approximating piezoelectric actuator as linear elements in vibration isolation system,theoretical analysis,simulation and experimental research are carried out.A single-input and single-output vibration isolation system based on piezoelectric actuator is established,and the dynamic model of vibration isolation system with actuator hysteresis displacement as control input is deduced.The vibration control law is designed by using linear quadratic Gaussian / loop transfer function recovery method.Combining with actuator hysteresis compensation control,the actuator's hysteresis compensation control and simplified control comparison simulation and experimental research are carried out.The results show that the vibration isolation system can effectively reduce the vibration of the controlled object.The active control algorithm can improve the vibration isolation performance between frequency range of 5 Hz ~ 200 Hz,and the hysteresis compensation can effectively improve the vibration isolation effect of the vibration isolation system and reduce the energy loss of the system.Aiming at the multi-degree-of-freedom vibration isolation problem of precision equipment with large mass,large size and limited installation space of vibration isolation system,a six-degree-of-freedom vibration isolation platform based on piezoelectric actuators is proposed.An effective vibration isolation unit structure is established,which achieves the design goal of heavy load and large diameter-height ratio.Structural design of observation equipment and reliability verification of vibration isolation platform are completed.Aiming at the influence of the moment of inertia of the legs on the dynamic characteristics of the platform,the friction of the connecting pair and the hysteresis characteristics of the actuator,a complete dynamic model of the vibration isolation platform is established based on Newton-Euler method and the equations of motion with hysteresis of the actuator.System state equations is established with the actuator hysteresis and basic excitation as inputs and the motion variables of the load platform as outputs.Simulation results are highly consistent with results shown in the literature,which verifies the correctness of the model and prepares for the subsequent research of the control system of the vibration isolation platform.Aiming at the coupling characteristics of six-degree-of-freedom vibration isolation platform and the output loop time delay,a general decoupling method of six-degree-offreedom platform is established based on parametric analysis of platform configuration.Decoupling control of the platform is realized by utilizing optimal control algorithm with time delay.The dynamic response of six-degree-of-freedom vibration isolation platform under different signals,directions and control strategies is analyzed by simulation.The effectiveness of decoupling control algorithm is verified,and the effectiveness and necessity to introduce hysteresis variable into vibration control strategy of multi-input multi-output complex dynamic system are verified.Finally,in order to verify the correctness of theoretical analysis and the actual vibration isolation ability of the vibration isolation platform,the vibration isolation performance verification experiments of the vibration isolation platform without control and with different control strategies are carried out.According to the previous design,the mechanical system prototype as well as the measurement and control system for the vibration isolation platform are established and debugged.The vibration isolation performance of the platform is tested under the condition of longitudinal excitation.Experimental results show that vibration isolation can be achieved based on platform decoupling algorithm and optimal control with time delay between 20 Hz ~ 200 Hz,which proves that it is necessary to consider the influence of time delay and modify control method of complex mufti-input multi-output system.The correctness of the research results based on the hysteresis characteristics of piezoelectric actuators and the sixdegree-of-freedom active vibration isolation platform is verified,which provides theoretical research support and practical basis for the application of piezoelectric-actuated six-degree-of-freedom vibration isolation platform to multi-degree-of-freedom micro-vibration isolation of spacecraft precision observation equipment.