Reduction in secondary-actuator displacement in dual-stage actuator system by imparting rotational stiffness in hard disk drives

For dual-stage actuator systems in hard disk drives, stroke-saturation of the secondary actuator must be avoided to prevent the servo system from becoming unstable. In this study, a reduction in the secondary-actuator displacement was investigated by imparting a rotational stiffness to a voice coil motor (VCM). It is shown that an increase in the first resonant frequency of the VCM is largely effective for decreasing the secondary-actuator displacement in the general dual-stage actuator system. Then, an actuator, which can impart a rotational stiffness to the VCM, was designed and facilitated. A new control system for dual-stage actuators employing the actuator was also considered. It was confirmed that the proposed servo system reduced the head-positioning errors due to air-flow-induced carriage vibration by more than 35 % compared with a conventional dual-stage actuator system. Furthermore the secondary-actuator displacement was reduced 52 % on average.