In this paper, we present a semi-active static output feedback variable structure control (VSC) strategy for vibration isolation. The control concept is based on the fact that, for a practical vibration isolation system subject to external disturbances, all state variables are hard to measure on-line and variations of system parameters frequently exist. A bypass electrorheological (ER) damper is designed and manufactured by incorporating a Bingham model of ER fluids. After the voltage-dependent damping characteristics of the ER damper are evaluated, the dynamic model of a two-stage vibration isolation system with one ER damper is derived. Using only the measured information from sensors installed at strategic locations, continuous output feedback VSC controllers are presented, which do not have possible chattering effects. The continuous control law is decoupled from external disturbances by combining controller design under a meeting sliding mode reachable condition with the choice of sliding surface gradient parameters under a guarantee of the Routh-Hurwitz stability of reduced-order sliding mode dynamics. The saturation of the actuator is also incorporated into the controller, showing no adverse effect. The self-adaptability of the vibration isolation system with respect to external disturbances, the robustness of the control method with respect to parameter variations and the effectiveness of vibration isolation are demonstrated by numerical simulation results in the frequency and time domains. It is illustrated that the performance of the presented semi-active static output feedback VSC system is superior to those of optimally passive damping and maximum damping variety even if system parameter uncertainties exist.
Study on mixed H2/H∞ output feedback control of maglev actuator for microgravity vibration isolation system
