Hideaki Ishioka

Compensation for repeatable tracking errors in hard drives using discrete-time repetitive controllers

Presents the repeatable runout (RRO) compensation in hard disk drives (HDDs). To cancel the RRO, we applied repetitive controllers to the tracking system. Through experiments, we obtained a high reduction ratio of from 10 to 45 dB for up to 10th harmonics component of the RRO. Furthermore, by switching filter parameters between the learning state and the steady state, we obtained fast learning of less than two disk rotations.

Head positioning servo and data channel for HDDs with multiple spindle speeds

For hard disk drives (HDDs) having multiple disk rotational speeds, a new data channel and head positioning servo system was developed. Head positioning performance at the low spin-speed was preserved by using a synchronous servo scheme with more servo areas than the conventional scheme. Using a common physical disk format, sufficient servo performance and the same data recording density of 1.3 Gbit/inch/sup 2/ were obtained on two 2.5 inch prototype HDDs with a low spin-speed of 37.5 Hz and a high spin-speed of 75 Hz. Disk interchangeability was also confirmed.

Synchronous servo scheme using maximum-likelihood detectors

For magnetic disk drives, we have developed a scheme for synchronous servo with maximum-likelihood (SSML) detection that is synchronous around the entire circumference of the track and utilizes ML estimation to detect head position, clock mark phase, and track addresses. Compared to the conventional asynchronous sector servo scheme, the SSML scheme has many, much shorter, servo areas-typically several hundred-distributed on the disk. This results in higher servo information rate, which will be needed for future high-track-density disk drives with a wide servo bandwidth. We analyze the performance of the SSML scheme, including the format efficiency. We discuss a limitation of the synchronous servo scheme with respect to the number of servo areas, and we show an appropriate region for its application. Feasibility of the SSML scheme has been demonstrated in prototype 2.5-in hard disk drives.