Study On Dynamic Characteristics Of Dynamical Model And Control System For Maglev Microgravity Vibration Isolation System

When flying on orbit,the spacecraft will be affected by various disturbances such as solar radiation pressure,atmospheric resistance,attitude and orbit control,and aerospace equipment vibration.It manifests as a state of microgravity that is primarily measured by microgravity acceleration.These low frequency micro-amplitude disturbances can seriously affect the repeatability and credibility of space science experiments.Passive vibration isolation mainly isolates high-frequency vibration and its suppression to low-frequency vibration is not obvious.The active vibration isolation leads the secondary vibration source into the controlled system and adjust the output of secondary vibration source in certain control method,which could not only isolate the vibration of the main vibration source,but also suppress the inertia disturbance of the load itself,thereby realizing the suppression and isolation to low-frequency micro-vibration.Compared with foreign countries,there is no mature and reliable microgravity vibration isolation system in China.The related research is still in its infancy,and there are many key technologies that need to be broken.In order to realize the suppression and isolation of low-frequency micro-vibration for space science experimental loads and ensure their micro-gravity acceleration level,this paper takes maglev microgravity vibration isolation system as the research object to meet the requirements of space science experimental load to micro-gravity acceleration level,and study on the dynamic characteristics of dynamical model and control system of maglev microgravity vibration isolation system.The main contents are as follows.Based on the design principle of high integration and modularity,the structural design scheme of the maglev microgravity vibration isolation system is proposed,which includes platform structure design,actuator design,control scheme design,measurement scheme design and so on.The mechanical structure,magnetic circuit structure and coil structure of maglev actuator are designed based on the Lorentz force principle and self-demagnetization effect.The multi-objective optimization function is used to optimize the structural parameters of the coil to obtain a coil structure with light weight and low power consumption.The static output characteristics and dynamic response characteristics of the actuator are studied by experiments.The spatial distribution state of static output force of the actuator is obtained,and the actuator has a good dynamic response characteristics when the current change frequency is in the range of 100 Hz,which satisfies the requirements of active vibration isolation control.The acceleration measurement model and displacement measurement model of the platform are established based on the principle of rigid body dynamics,respectively,which could provide effective motion information of the platform to the control system.The dynamic model based on Newton's Euler equation of the maglev microgravity vibration isolation platform is established so as to analyze its dynamic response characteristics under different excitations.At the same time,in order to consider the influence of the nonlinearity and hysteresis characteristics of umbilical cord stiffness on the dynamic characteristic of the model,the stiffness characteristic of umbilical cords is studied by experiments.The nonlinear characteristic and change rule of their stiffness changed with displacement are analyzed and obtained by simulation.The dynamic model with nonlinear stiffness characteristic of umbilical cords and the linear dynamic model are established,respectively,by using the S function in the Matlab.The dynamic characteristics of this two model are compared under the same direct or indirect disturbance,respectively.The influence of nonlinear characteristics of the stiffness on the dynamic characteristic of maglev microgravity vibration isolation platform and the output characteristics in various degrees of freedom of the platform are analyzed and obtained,which provides a theoretical basis for the study of active vibration isolation control.In order to realize the suppression and isolation to low-frequency micro-vibration for microgravity vibration isolation system,the theoretical design and simulation analysis of the controller model are carried out by using cascade PID control and mixed H₂/H?control,respectively.On the one hand,the influence law of the control parameters in cascade PID control on the closed-loop transfer function of the system is obtained.On the other hand,the mixed H₂/H?controller model is designed and solved based on the linear matrix inequality?LMI?method.The relationship lines between the nominal performance and robust performance of the closed-loop system is specified,and the influence law of the uncertainty of structural parameters to the closed-loop system?static and dynamic?performance indicators is simulated and analyzed.In order to achieve better vibration isolation performance for the system,pole region constraints and input/output port weight gains are added to optimize mixed H₂/H?controller model.Their effects on the dynamic output characteristics and static performance indexes to the closed-loop system are analyzed by simulation,and the mixed H₂/H?controller model after optimized is finally obtained.The research content provides theoretical guidance for the experimental research of maglev microgravity vibration isolation system.A single-degree-of-freedom active vibration isolation system and a six-degree-of-freedom maglev vibration isolation system prototype are developed,respectively.The vibration control experiment for the single-degree-of-freedom active vibration isolation system is carried out in horizontal direction.The vibration suppression experiment to direct acceleration disturbance on the floater and vibration isolation experiment to indirect acceleration disturbance on the stator are carried out to verify the correctness and validity of the theory and design of our study subject.In this paper,the maglev vibration isolation technology based on Lorentz force principle is applied to the microgravity vibration isolation system and the design method of maglev microgravity vibration isolation system is proposed.The dynamic model with nonlinear stiffness characteristics of umbilical cords is established and the influence of the nonlinear characteristics of structural parameters on the dynamic characteristics to the platform dynamics model is revealed.The design method of the active vibration isolation controller model is also proposed,which lays a theoretical foundation for the design and optimization of the control model for six-degree-of-freedom maglev vibration isolation system.