An Integrated Feedforward Robust Repetitive Control Design for Tracking near Periodic Time Varying Signals

This paper addresses the tracking of near periodic time varying signals by proposing an integrated approach for simultaneously designing previewed feedforward, feedback, and repetitive control in a unified framework. The design problem is formulated as a μ-synthesis problem, in which the distance between a specified reference model and the achievable tracking performance with feedforward compensation is minimized in terms of the structure singular value. Desired upper bounds of disturbance rejection as well as tracking performance are conveniently incorporated in the proposed controller design. The reference signal is assumed to be previewed with a certain length and is near periodic. This structural knowledge about the reference signal characteristics is reflected in a μ-synthesis framework as a feedforward block and a periodic signal generator. The periodic signal generator enables the control system to track the periodic component of the reference while the previewed feedforward action compensates for the slow changes in magnitude and phase of the periodic signal. Such type of reference signals has applications in turning of non-circular profiles with tapers and twists, and camless engine valve actuators for variable valve timing operations. The proposed design is applied to an electrohydraulic actuator to generate a cam-shape profile that varies in both the angular θdirection and the axial x-direction. Experimental results demonstrate its effectiveness.