Comparison of a MEMS microactuator and a PZT milliactuator for high-bandwidth HDD servo

A microactuator that moves the slider of a hard disk drive (HDD) was fabricated using MEMS techniques. A suspension-mounted PZT milliactuator was also manufactured. Both actuators were assembled and tested in 10,000 RPM server-class HDDs. The MEMS microactuator has a resonance at 2.2 kHz that can be controlled by feedback, and has virtually no other modes up to 100 kHz. The first mode of the PZT milliactuator is much higher at 8 kHz, but there are many more modes below 100 kHz. Both secondary actuators enable high tracking servo bandwidth, which is necessary to achieve ultra-high track densities. However, the differences in their mechanics require different control strategies, place different limitations on their performance, and have different effects on the use of their limited stroke. Data on assembly, simulations, and drive-level experiments are presented. Challenges that dual-stage actuators will continue to face are also discussed.