Browse Prior Art Database

Null Servo Pattern

IP.com Disclosure Number: IPCOM000084894D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Betts, AJ: AUTHOR

Abstract

Information for controlling the position of a servo head in a disk file is derived from alternate adjacent tracks written with time coincident transitions of opposite polarity. Two such adjacent servo tracks 1 and 2 are shown with this servo encoded information occurring in the section of the tracks marked FIELD 2. Thus when in the ""on-track'' position, as illustrated by servo head 3, the read gap of the servo head experiences two transitions of equal amplitude and opposite polarity with a net result of zero as shown in waveform (b).

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Null Servo Pattern

Information for controlling the position of a servo head in a disk file is derived from alternate adjacent tracks written with time coincident transitions of opposite polarity. Two such adjacent servo tracks 1 and 2 are shown with this servo encoded information occurring in the section of the tracks marked FIELD 2. Thus when in the ""on-track'' position, as illustrated by servo head 3, the read gap of the servo head experiences two transitions of equal amplitude and opposite polarity with a net result of zero as shown in waveform (b).

If the head is displaced to lie entirely over track 1, as illustrated by servo head 4, then the output is as shown in waveform (a). If the head is displaced to lie entirely over track 2 as illustrated by servo head 5, then the output is shown in waveform (c). From the waveforms (a) and (c) it is seen that the output signals from each written track are of opposite polarity. Hence to produce a position error signal, alternate portions of the head signal in FIELD 2 are inverted using the negative level of the timing signal shown as waveform (d).

The resulting switched output from the head 4 in track position 1 is shown as waveform (e), that for the head 3 in the on-track position as waveform (f), and that for the head 5 in track position 2 as waveform (g). The switched signal for the on-track position, shown as waveform (f), has small disturbances such as would result in practice from the transitions on the two writt...