Robust dual-stage and repetitive control designs for an optical pickup with parallel cantilever beams powered by piezo-actuation

This study proposes a dual-stage lens actuator used for optical disc drives, which includes a piezoceramic parallel-beam as a fine actuator and a voice coil motor (VCM) as the coarse one. The positioning algorithm of the objective lens is comprised of robust H _∞ fine/coarse controllers designed based on μ synthesis and a repetitive controller to further reduce effects of disturbance. To these ends, the dynamic model of the piezoceramic parallel-beam and VCM are first established and then identified by experiments. Based on these identified models, the system dynamics is represented as a standard form, which is ready for μ synthesis to design robust controller. Performing optimization, the desired robust H _∞ controller used for conducting fine/coarse positioning is obtained. In addition to H _∞ control design, the repetitive controller is further forged to reduce the effect of disturbance based on the periodic nature of the disturbance. Simulations and experiments are conducted to validate the performance expected by previously designed controllers. The experiment shows that the fine piezo-actuator bears the responsibilities of compensating in-precision positioning of the coarse VCM actuator and external small level periodic disturbance.