Study On Active Control Of Stewart Platform For Vibration Isolation

Vibration isolation must be concerned in using the high-precision instruments as itwill affect their performance in the practical application. People continue to pursue anisolator with superior performance, especially for those in aerospace. Currently, passivevibration isolation cannot meet the targets under the complex environment andrequirements. The active vibration isolation with precision, fast response and excellentisolation effect attracts considerable attentions. Stewart platform is a6DOF parallelmechanism which has the advantages of high precision, high stiffness and well capacity.It has been investigated by many scholars in kinematic and dynamic performance,structure, optimization and control. The Stewart platform applied with active controlcan achieve wonderful goals in vibration isolation. Up to now, few papers studied thelow-frequency isolation with Stewart platform.In this thesis, the low-frequency micro isolation for high-precision equipment onsatellites is studied. We derivate the dynamic equation of Stewart platform, study itsdynamic properties and design an active controller for low-frequency region. Details areas follows.First, we investigate the kinematics and dynamics of the legs and obtain thedynamic equations of Stewart platform with Newton-Euler Method in task space andjoint space. Then transform them into state space with micro-gravity andmicro-perturbation.Second, linearize the equation and investigate the properties on natural frequency,transfer function, coupling, anisotropy, etc. Then, the effects of some nonlinear factors,like amplitudes of excitation and spring stiffness, on the platform are analyzed bynumerical calculation. And some limits are set on working conditions to guarantee thelinear equation replace the original one.Finally, considering the constant parameter uncertainty, noise and sensor error forlinear system, we devise robust controller with H∞Optimal Control Theory andGeneralized μ Analysis, respectively. Also, the simulation is presented to compare andverify the effects of the two methods.