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Servo Pattern for Helical Tape Drive System With Drift Compensation

IP.com Disclosure Number: IPCOM000081369D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Wong, KY: AUTHOR

Abstract

A tape servo system has strips of magnetic parallelogram patterns 12 recorded parallel to the tape edges. Parallelogram strips S1 and S2 and drift compensation strip C1 are located near one side of the tape edge; these three strips together form a 'hand' of servo information. Servo strips S3 and S4 and drift compensation strip C2 are located near the opposite side of the tape edge.

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Servo Pattern for Helical Tape Drive System With Drift Compensation

A tape servo system has strips of magnetic parallelogram patterns 12 recorded parallel to the tape edges. Parallelogram strips S1 and S2 and drift compensation strip C1 are located near one side of the tape edge; these three strips together form a 'hand' of servo information. Servo strips S3 and S4 and drift compensation strip C2 are located near the opposite side of the tape edge.

The rotating head entrance angle to the tape is theta and the servo write heads are inclined at an angle normal to the rotating head path. The width of the servo write head is H and the length of the parallelogram in the longitudinal tape direction is H/sin theta. The parallelograms are equally spaced at a distance of H/sin theta, as shown in the figure. The servo strips S1 and S2 are separated by a distance of H/2, measured in the track direction, with the drift compensation strip C1 in the center. Strip C1 has the same width W as the rotary read head and is usually much smaller than the servo write head width H.

As the rotating head scans across the tape, it will sense magnetic flux changes as it goes over the parallelograms 12. The number of pulses from the rotary read head increases as it changes in track position, towards the diagonal of a parallelogram from the vertex. Hence, the pulse count from the read head is an indication of its position relative to the prerecorded parallelograms 12 in the tape.

When a track...