Active-passive hybrid actuators for tracking and focusing motions in optical pickup devices

This paper is aimed to propose a piezo-based optical pickup device with passive damping to enhance the capabilities of precision positioning and shock resistance in optical disk drives (ODDs). The proposed piezo-based pickup device can be combined with a first stage large stroke actuator such as existing sled motor or voice coil motor to form a novel dual-stage servo system for the next generation high resolution ODDs. This active-passive hybrid actuator possesses two piezoelectric actuators cooperated together to move a lever beam that bears an objective lens for tracking motion or to contract or extend the lever beam to lift the objective lens upwards and downwards for focusing motion. Moreover, the viscoelastic damping layer is sandwiched between the constraining layer and the piezoelectric bimorph actuator to act a cushioning function to reduce the transmission of shock to the pickup device and dissipate vibration energies from the device. In the paper, piezo-based pickup devices with and without passive damping are fabricated, tested and compared to verify the design of pickup unit. Experiments are carried out to investigate their damping abilities and transmissibilities. Several parameters are studied to evaluate their effects on the characteristics of the piezo-based pickup device. Finally, the closed-loop performances of the piezo-based pickup device are compared with the current voice coil motor optical pickup using the internal model controller.