Woo-Sung Kim

Arm Design to Reduce Arm Bending Resonance-Induced Off-Track in a Hard Disk Drive

The paper presents a strategy to reduce the position error signal (PES) induced by arm bending mode in high track density magnetic disk drives. As the track width becomes narrower to increase data storage capacity, off-track due to arm bending mode as well as disk vibration makes a large contribution to track misregistration (TMR). Consequently it is important to reduce arm bending resonance-induced off-track in order to meet TMR budget. A special arm is designed so that head can move back on track to cancel off-track due to asymmetric motion while arm is bending. It is shown that such an arm can reduce TMR due to arm bending mode by allowing the head to move in such a way that will compensate the off-track caused by arm bending mode. Finally, the efficacy of the proposed strategy is verified by measuring PES of actual sample drives with newly designed arm.

Investigation of flow disturbance by disk-shroud configuration of Servo Track Writer

The flow of air in a simplified model of a Off-line Servo Track Writer system has been investigated numerically. The study focused on the space between disks with a fixed shroud. The disk-shroud configuration is especially important in the Servo Track Writer because the flow disturbance by the rotating disks can seriously disrupt accurate electromagnetic data transfer on servo patterning. To improve the reliability and performance of a current Servo Track Writer system while providing a basis for the improved design of future device, it is necessary to advance the understanding the flow pattern by several shrouded disks configuration. The investigation of the flow disturbance by disk shrouded configuration gives advantages and disadvantages for the shroud design.

Optimal arm configuration to reduce arm bending resonance-induced off-track in a hard disk drive

In order to reduce the off-track due to the arm bending mode, whose effect is considerable in a high capacity drive, an arm configuration with maximum arm bending stiffness should be considered. The objective of this work is to find the optimal arm configuration that maximizes the arm bending stiffness subject to the constraint imposed on the moment of inertia of the arm. Herein, the problem of finding the optimal arm configuration maximizing the arm bending stiffness is formulated as a topology optimization for eigenvalue maximization problem. By applying this method, an arm configuration having two balance holes instead of a single balance hole was obtained. Finally, the efficacy of the optimized arm is verified by measuring the position error signal (PES) of actual sample drives; when the optimized arm was used, the PES was reduced by 25%.

Optimal magnet shape design for wideband magnetic bias torque in a hard disk drive

In order to prevent the swing arm parked on the ramp from rotating due to a rotary shock, a wideband magnetic bias torque is generated on a retract pin. This paper presents the optimal magnet shape to generate a wideband magnetic bias torque. To find the optimal magnet shape, the standard shape optimization is employed. The physics behind why the optimized shape of the magnet yielded better performance is briefly explained using numerical simulation. To verify the effectiveness of the optimized magnet, the actual experiment was conducted. Experimental result shows that the optimized magnet shape generates a wideband magnetic bias torque while maintaining the maximum magnetic bias torque compared to a nominal magnet shape.

Design Modification of Micro-Actuator to Improve Shock Resistance of HDD

To realize higher track density of a hard disk drive, increasing servo bandwidth may reduce track-misregistration (TMR). However, the servo bandwidth is limited by the mechanical resonances of the arm, coil of the voice coil motor (VCM) and ball bearing pivot. One approach to overcome the problem is using dual stage actuator system. The dual stage actuator (DSA) consists of an primary actuator driven by VCM and a secondary actuator driven by PZT. VCM actuator is used for coarse control of seek and settling whereas the 2nd actuator is used for fine control of track following. As VCM is turned off during track following in DSA, the VCM resonance does not limit the increase of servo bandwidth any longer. Among the 2nd actuators, the so-called micro actuator locating at the tip of the suspension and driving head slider is advantageous for higher servo bandwidth and collocation of the 2nd actuator and the read/write sensor, whereas it is disadvantageous for shock resistance due to large tip mass. In this study, micro actuator is modified in order to improve shock resistance with simple design parametric study.

Suspension to Reduce Off-track Due to Disk Vibration and Suspension Bending

Design margin of position error signal (PES) is getting smaller as track density of high-capacity disk drives increases. A substantial portion of the PES is caused by disk vibration which makes off-track between head and disk. In this paper, a new HGA design concept is introduced for suppressing the off-track due to disk vibration as well as the off-track due to suspension bending.