Kyo Akagi

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/.

RRO/NRRO characteristics in mobile HDDs

The characteristics of repeatable runout (RRO) and non-repeatable runout (NRRO) of HDDs have to be clarified for higher tracks per inch since the static positional accuracy has almost reached its limit. The most dominant component in NRRO and even in RRO is torque disturbance. We experimentally estimated that the rate of windage - the dominant component of torque disturbance - using a mixture of helium and air.

Servo Signal Quality for Perpendicular Recording in Servo Write Process

In regards to servo-writing with perpendicular recording, we investigated servo-write quality and servo performance, and found that the premagnetization conditions, the magnetic-flux flow mechanism, and head structure strongly affect the servo-write quality. In response to these findings, we clarified that the flux flows through the writer to the reader are one of the root causes of servo-signal deterioration. In addition, we found that the flux amount is related to the magnetization switching ratio (MSR) - a one sided magnetization pole per writer-pole area. On the other hand, the reader can absorb flux even if it is far from the flux source. This means that not only the reader element but also the adjacent structure can absorb flux from the flux source.