Dept. of Mech. Eng., Zhejiang Univ., Hangzhou 310027, People's Republic of China
A study on active control of vibration isolation of a magnetic levitation platform used for the calibration of precision inertia instruments is presented in this paper. Nonlinear and linearized dynamic models of the system in state-space were deduced by using the theory of an electromagnetic field. The stability of both the open- and closed-loop system was investigated in the cases of different configuration of the current coils. A LQG optimal control strategy was employed in the control syntheses of the magnetic levitation system, since the system input perturbance is a stochastic excition acting on the fixed base from the ground. The transfer functions from the exciting current or the control current or the base displacement to the vibratory displacement of the levitation platform were verified experimentally. Open- and closed-loop vibration responses were calculated. The results show that compared to the base displacement, the vibration of the magnetic levitation platform can be attenuated more than 20 dB by using active control, over frequencies ranging from 0.1 to 10 Hz, which cover the main peaks of the ground perturbance.