Three-Stage Control for High Servo Bandwidth and Small Skew Actuation

A three-stage actuation control system is proposed to enable high servo bandwidth track-following and possibly for small skew angle actuation system of hard disk drives. It involves a voice coil motor actuator as a primary actuator and a PZT actuated milliactuator as a secondary actuator. Both of them have the first dominant resonance mode at 5 kHz and the milliactuator has 200 nm stroke. A thermal microactuator having 50 nm stroke is used as a third actuator for a high servo bandwidth. A control strategy with controller design method is proposed to meet the performance requirement of each actuator´s control loop and the overall control system. More than 6 kHz servo bandwidth is achieved and 430 nm external vibration can be covered by the three-stage actuation system. Simulation and experimental results demonstrate the control performance of the three-stage closed-loop system.