In this paper a linear bandpass filter is compared to a hybrid integrator-gain based bandpass filter regarding its usefulness in active vibration isolation. Vibration isolation refers to a form of skyhook damping in which a velocity output signal from a system having structural dynamics is fed back to a controller, the latter having bandpass characteristics. At those frequencies where the controller passes the input signal (after gain multiplication) a force proportional to velocity is obtained that can be used to provide active damping to the system, i.e., damping of one (or more) of its structural modes. Outside this frequency band the controller input signal is attenuated, which is often desirable in view of incorrect sensor information at low frequencies and/or to avoid amplification of high-frequency noise. In this context, the use of a hybrid integrator-gain system will be studied regarding its possible phase advantages compared to linear integrators. These advantages stem from the control design itself, in the sense that by design the control output force signal and the input velocity error signal have equal sign. In the context of vibration control, an enhanced transient (closed-loop) response is obtained, i.e., less overshoot and reduced settling times, but at the cost of increased rise times.
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