Modified LMS feed-forward control for vibration isolation with actuator limits

We propose a modified LMS algorithm for adaptive feedforward control with actuator limits. Unlike the leaky LMS method, which limits the controller effort by introducing an auxiliary cost, in the proposed algorithm we maintain the cost as the performance measurement. We derive the true stochastic gradient of the cost for systems with saturation with respect to the filter coefficients and obtain an adaptation rule very close to that of the filtered-x algorithm, but in the proposed algorithm, the reference filter is a time-varying modification of the secondary channel. In simulations of an active vibration isolation system with actuator limits, the proposed algorithm attains better performance than that attained by the leaky LMS algorithm.