Experimental Evaluation of Triple-Stage-Actuator System with Thermal Actuator for Hard Disk Drives

To improve positioning accuracy in a head-positioning control system for hard disk drives, we have developed a triple-stage-actuator system on a spin-stand tester. In this system, the first stage is a VCM actuator for moving a head-stack assembly, the second stage is a PZT actuator for moving a suspension, and the third stage is a thermal actuator for moving read/write elements. The frequency response of the thermal actuator showed that the thermal actuator system has no mechanical resonant mode. Therefore, this head-positioning system with a thermal actuator can control the head position in high frequency range without negative impact from mechanical resonances. As a result, the servo bandwidth of the proposed triple-stage-actuator system can be higher than that of the conventional dual-stage-actuator system which consists of the VCM and the PZT actuators. This improvement is similar to the improvement from the single-stage-actuator system to the dual-stage-actuator system. Experimental results on the spin-stand tester showed that the proposed control system can dramatically improve the positioning accuracy during a track-following control.