Research Of Six Degrees Of Freedom Maglev Vibration Isolation System And Mechanical Characteristics

In recent years, space technology develops rapidly and the exploration of the universe constantly goes deeper. Scientific activities in micro-gravity environment have gained more attention, such as deep space detection, laser communication, space science experiments. However, the spacecraft suffers various disturbances, which may come from the sun light pressure, atmospheric drag, orbit changing, attitude adjustment and equipment vibration in the spacecraft. Those disturbances are the main factors that influence the imaging precision of high resolution satellite, gravity gradient measurement and scientific experiments in the space station. Whereas, the equipment that used to isolate low frequency micro-vibration in space have not been developed at present. The related research is still at the preliminary stage, and there are many key technologies that need to be solved urgently.The overall design process of six degrees of freedom maglev vibration isolation system was put forward through mechanical system, perception system and control system. Non-contactive active control scheme was chosen. The force constant was taken as checking standard, which meet the current resolution of electrical system. Taking the maximum magnetic flux density and minimum coil mass and heat loss as optimization targets, the sizes of the permanent magnet and the coil were optimized. The structure of an actuator with light quality, low heat loss and good linearity was designed based on the Lorentz force principle. Design of six degrees of freedom maglev vibration isolation platform was carried out and the spatial layout design of multiple actuators was conducted. A model describing the relation among force, moment and current distribution was established for control, which showed the mapping relation between the platform and the actuators. Based on the measurement principle of accelerometers and position sensors, the placements of the accelerometers and position sensors were studied. The measurement models of six degrees of freedom acceleration and relative position and angle were established, which provide theoretical basis for the acquisition of effective information during control.The transimission characteristics of the flexible cable of maglev vibration isolation system were studied. Considering the flexibility and large deformation characteristics of the cable, nonlinear mechanical model of the cable was established on the basis of mechanical model of elastic thin rod. Differential quadrature method was used to solve the disturbing force and disturbing moment of the end of cable under the sinusoidal disturbances. Then the relation among force, moment and disturbance parameters were obtained, and the equivalent dynamics model of cable was built by fitting method. By analyzing the influence of frequency, amplitude and initial configuration on disturbing forces and moments, the applicability of the equivalent dynamic model of the cable was studied. A cable dynamic characteristics test system, including posture adjustment module, excitation module and acquisition module, was designed. The results verified the nonlinear mechanical model and the feasibility to obtain equivalent dynamic model by fitting method.A six degrees of freedom nonlinear dynamic model of the maglev vibration isolation system for control was established by integrating the equivalent dynamic model of the cable and the mechanical-electrical-magnetic model of the actuator. The system has the characteristics of nonlinearity and broad band. Based on the absolute acceleration of the floating platform and the relative position between the floating platform and the base, a double closed-loop control strategy was put forward. The absolute motion controller and the relative motion controller were designed. A six-degrees of freedom control system simulation program was developed in MATLAB/SIMULINK by adopting PID control algorithm and nonlinear sliding mode control algorithm. Through simulation, the system can achieve vibration isolation for different kinds of disturbances and motion tracking in the very-low frequency range. This study provided theoretical guidance for system testing.A principle prototype of maglev vibration isolation platform with six degree of freedom was developed. Six three-axises accelerometers, four position sensitive deteters and multi-channels data acquisition board were used for signal acquisition and processing. Motion controller and actuator drivers were used to achieve active control. Experiments were carried out. The driving characteristics of actuators were tested. The acceleration measurement model, relative position measurement model and system dynamics model were verified. The response test of six degrees of freedom relative position and angle were conducted. The vibration isolation effect of system on the direct and indirect disturbance were evaluated. Functions of the prototype and theoretical analysis were verified by test results.