Six-degree-of-freedom active vibration isolation system with decoupled collocated control

An ultra-precision vibration isolation system for high-resolution equipment is presented in this paper. The system consists of a passive isolation subsystem using a combination of an air spring and a pendulum mechanism, and an active subsystem using collocated actuator-sensor pairs. The six-degree-of-freedom kinematic model of the passive system is derived and then verified by carrying out a set of frequency response experiments. The controller design is based on a combination of decentralized control and modal control. The former is to improve the characteristics of a single passive isolator; the latter is to shape the main vibration modes actively in the frequency domain. The modal decoupling method based on the kinematic model of the system is used to implement the decoupled collocated control. Because of the sensor dynamics and inherent delay of control system, the stability of the vibration control system is affected. The upper boundary of the control gain is obtained through a root locus analysis. The performances of the hybrid system are investigated in the frequency domain and finally validated by comparison with the passive isolation system.