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.
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