Kei Yasuna

Servo bandwidth and positioning accuracy design for high track density disk drives

Possibility of achieving positioning accuracy to meet the areal density of 40 Gb/in/sup 2/ has been studied. Stationary and nonstationary position errors are shown, and the servo design approaches have been proposed. A precise model of head-positioning system has been developed, and the required open loop servo bandwidth is estimated using the model. The experimental results using 2.5-inch HDD show that 750 Hz to 1 kHz servo bandwidth (open loop crossover frequency) is effective to achieve 40 nm positioning accuracy during track-following to meet 60 kTPI for 40 Gb/in/sup 2/.

Influence of pole trimming on track-following accuracy

The correlation between the pole shape of a magnetic write head and the track-following accuracy has been investigated. To evaluate the effect of head properties on head positioning, an analytical model for position signal generation was developed. This model clarified the effect of the erase-band width and the read track-width on the track-following accuracy by revealing the position signal linearity. The investigation demonstrated that pole trimming of the write head improves head-positioning performance.

A technique for evaluating track deviation at nanometer-scale accuracy

A technique for evaluating track deviation in magnetic disk drives has been developed. The technique uses an external position sensor and an error cancellation sequence, and enables measurement of track-to-track spacing. The resolution of track position is less than 2 nm. The repeatability is less than 5 nm. The technique helps reveal track alignment error, which needs to be reduced to achieve over-100-KTPI recording.