抄録
Precision apparatus such as semiconductor equipment is mounted on a table which is isolated by passive isolators to reduce the transmission of vibration from the base. Lower stiffness isolators have the advantage of reducing such vibration, but are sensitive to direct disturbing forces like the reaction force of the stage which is mounted on the table. To reduce the adverse influence of direct disturbing forces, the stiffness of the passive isolator should be high. The passive isolator is thus confronted with conflicting demands. To reduce vibration transmission below the natural frequency of the passive isolators and to minimize the adverse influence of direct disturbing forces, a previous study proposed a way to control the table by means of a position feedback loop; the objective is to keep the table position constant with respect to a reference mass of a one DOF system whose natural frequency is less than the natural frequency of the passive isolators. However, the reference mass tends to be large, and the reference mass of a one DOF system is very sensitive to direct disturbing forces such as aerial current and current noise. To overcome these problems, we decided to apply a two DOF system to the reference mass and develop an active isolation system.
