Nano-and Micro-Actuations of Hard Disk’s Head Positioning System: Actuator Design and Evaluation of Performance

High-density magnetic hard disks are key components in information storage. In high-density hard disk drives (HDD), both super fast track seeking and extremely accurate positioning of the read/write head are required. A new multiDOF piezoelectric micro-actuator with nano-transverse and micro-lateral control of the head positioning system for highdensity hard disk drives is proposed. For the track following control of a head positioning system in the HDD, proper modeling of the system including the voice coil motor (VCM), suspension, slider, and gimbal system is very important. Before further comprehensive analysis of the whole assembly, the design concept and the evaluation of the micro-actuator are focused on in this paper. First, design of the new piezoelectric micro-actuator is illustrated. The design of the new micro-actuator is based on the axial deformation of piezoelectric elements for lateral motion control and the bimorph actuation of piezoelectric elements for transverse nm motion control. Next, mathematical models of the micro-actuator system are defined. Lastly, the micro-actuator system is modeled using the commercial finite element package ANSYS. The results from analytical analysis and FE analysis are compared. Static response of the micro-actuator system is evaluated first, followed by analysis of dynamic response analysis. Static actuations of the new actuator system satisfy both lateral (±0.1μm) and transverse (15nm) specifications. Dynamic analysis of the ultra-precision system suggests that the new piezoelectric micro-actuator improves performance of highdensity hard disk drives by increasing servo bandwidth and decreasing flying height.