Combination of H∞ and PI control for an electromagnetically levitated vibration isolation system

A control system, featuring a combination of H^∞ and PI control methods for control in the vertical direction, of an electromagnetically levitated vibration isolation system was designed. Experiments were carried out to verify this system´s noncontact levitation and microvibration control performance. The main components of this system are a vibration isolation table with built-in acceleration sensors for detecting microvibration, electromagnetic actuators with built-in electromagnets and displacement sensors, and a digital controller with the DSP. An H^∞ controller was designed to be used for an augmented system which included a PI-type controller of relative displacement feedback. This H^∞ controller enabled effective, noncontact stable levitation as well as vibration isolation. Experimental results by a test apparatus revealed that the designed controller yielded a 90% in vibration transmissibility in vertical-direction