This paper presents a hybrid vibration isolation system using linearized zero-power control with weight support springs. The isolation system, fundamentally, is developed by linking a mechanical spring in series with a negative stiffness spring realized by zero-power control in order to insulate ground vibration as well as to reject the effect of on-board-generated direct disturbances. In the original system, the table is suspended from the middle table solely by the attractive force produced by the magnets and therefore, the maximum supporting force on the table is limited by the capacity of the permanent magnets used for zero-power control. To meet the growing demand to support heavy payload on the table, the physical model is extended by introducing an additional mechanism-weight support springs, in parallel with the above system. However, the nonlinearity of the zero-power control instigates a nonlinear vibration isolation system, which leads to a deviation from zero compliance to direct disturbance. Therefore, a nonlinear compensator for the zero-power control is employed furthermore to the system to meet the ever-increasing precise disturbance rejection requirements in the hi-technology systems. The fundamental characteristics of the system are explained analytically and the improved control performances are demonstrated experimentally.
Adaptive Control for a Microgravity Vibration Isolation System