Dual stage actuators for high density rotating memory devices

Maintaining the trend towards higher track densities and data rates in rotating memory devices require track following servo systems of increasing bandwidth for reliable storage and retrieval (R/W) of data. The bandwidth requirements are even more severe in the emerging portable computing applications. Increase in bandwidth under strict constraints on over-sampling is limited by the presence of mechanical resonance modes and other nonlinearities in the voice coil motor (VCM) actuators. One approach to overcoming the problem is by using a dual or a compound actuator. In such a mechanism, a VCM is used as a primary stage while the recording head is mounted on the secondary stage which in turn is mounted on the VCM. The secondary stage provides rapid small-motion and position correction to the recording head. Several dual-stage configurations have been proposed using electrostatic, piezoelectric and electromagnetic secondary actuators. The paper proposes a piezoelectric stack micro-actuator design for a disk drive. It preserves the present suspension and head assembly. A prototype of the actuator is designed, fabricated, and tested. The test results are presented. A dual actuator tracking servo system is proposed. The scheme is a promising alternative for providing high bandwidth actuation for future high performance drives.