Design and implementation of a hybrid control strategy for an active vibration isolation system

Controller design methodologies based on a single controller are often unable to provide both high performance (i.e., tracking bandwidth) and desired robustness (i.e. retaining stability) in the presence of uncertainty or plant variation. This paper presents a hybrid control strategy to circumvent the basic trade-off between performance and robustness from an individual controller. This hybrid control strategy utilizes a robust controller for guaranteed robustness when the plant model is not well known, and makes an adaptive controller active for high performance after sufficient plant information has been collected on-line. To avoid a degraded transient after controller switching, a bumpless transfer scheme is designed and incorporated into this hybrid control strategy. This bumpless transfer design is a novel extension from a conventional latent tracking bumpless transfer design for a SISO plant with 1 DOF controllers to either a SISO plant with multiple DOF controllers or a MIMO plant. Experimental results implemented on an active vibration isolation testbed demonstrate the effectiveness of the hybrid control strategy including the bumpless transfer design.