Browse Prior Art Database

Dynamic Coarse Track Positioning

IP.com Disclosure Number: IPCOM000042012D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Cooper, ES: AUTHOR

Abstract

A position signal of excellent quality, free from noise, is essential to the operation of a disk file access servomechanism. A noisy position signal will produce a miscount of traversed tracks when accessing at high velocity and a distortion of the servo target track landing, particularly during the last one-half track of positional movement. Short duration voltage spikes with a large time rate of change, that are due to minute imperfections in disk media, sometimes sufficiently degrade the integrity of the position signal such that the servo system is totally inoperable. Described here is a means for providing a measure of immunity from spikes in the position signal during the high velocity portion of accessing. A conventional servo position signal is shown in Fig. 1.

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Dynamic Coarse Track Positioning

A position signal of excellent quality, free from noise, is essential to the operation of a disk file access servomechanism. A noisy position signal will produce a miscount of traversed tracks when accessing at high velocity and a distortion of the servo target track landing, particularly during the last one-half track of positional movement. Short duration voltage spikes with a large time rate of change, that are due to minute imperfections in disk media, sometimes sufficiently degrade the integrity of the position signal such that the servo system is totally inoperable. Described here is a means for providing a measure of immunity from spikes in the position signal during the high velocity portion of accessing. A conventional servo position signal is shown in Fig. 1. Decode of the position signal with positive and negative compare limits, defined as Å coarse track, enables logic decode circuitry to determine incremental track movement as the servo accesses. In order for the servo logic circuitry to establish that a track has been traversed, the absolute value of the position signal must exceed plus or minus coarse track. Failure of the servo to properly access occurs when distortion or noise on the position signal prevents the position signal from achieving coarse track. This problem is particularly acute at higher velocities where the time in which the position signal exceeds coarse track becomes very small. The present circuitry makes coarse track inversly proportional to actuator velocity such that coarse track is made progressively lower at higher velocities. With lower coarse track voltage at high velocity, the physical size and electrical amplitude of the defect is permitted to be larger before fa...