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Head Rotor Control and Maximization of Time Tape Space Utilization

IP.com Disclosure Number: IPCOM000085604D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 5 page(s) / 129K

Publishing Venue

IBM

Related People

Karol, KN: AUTHOR [+3]

Abstract

When a magnetic tape passes over a moving or rotating head as the tape progresses, the data track position relative to the standard position of a data track changes with successive movement of the tape and head. Tape dimensional instability also results in data track position change. Although the changes may be very small and the parallel or angular change in position from a standard or previously recorded data track consequently small, none the less, due to the narrowness of the track (for example --0.006 or less for write and 0.004 or less for read) it becomes paramount that constant correction of the relative position of the tape to the head or the head to the tape occur.

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Head Rotor Control and Maximization of Time Tape Space Utilization

When a magnetic tape passes over a moving or rotating head as the tape progresses, the data track position relative to the standard position of a data track changes with successive movement of the tape and head. Tape dimensional instability also results in data track position change. Although the changes may be very small and the parallel or angular change in position from a standard or previously recorded data track consequently small, none the less, due to the narrowness of the track (for example --0.006 or less for write and
0.004 or less for read) it becomes paramount that constant correction of the relative position of the tape to the head or the head to the tape occur.

To accomplish a rotating head's ability to follow a change in a data track position requires a change in the axis of motion or rotation of the head relative to the tape's axis, there having the angle of rotation conform to the helix's changing lead angle. To insure complete coverage, motion of the axis of rotation in translation achieves the ability to shift with a laterally displaced hexical lead angle. The combination of both motions insures coverage of any rotating head track deviation from an established datum position.

Present rotary heads utilize only about 60% of their available time of travel about their circumference. Data track erasure and rewrite cannot occur without rewind and, therefore, additional space has to be reserved for possible error correction. Rotary head time of travel in a mandrel and tape space use may be maximized by a dual pass of the data tape, each pass using close to 180 degrees of the periphery of the rotating head.

Tape reversal is accomplished through the use of a guide at right angles to the rotating head and mandrel. Control rollers or edges position, angle, tension and nudge the tape relative to the guides. Error correction of the initial data write on the `tape in' pass can occur on the second `tape out' pass -- thereby reducing by 50% the reserve tracks needed for usual error correction which results in increased tape utilization efficiency.

The use of both head rotor control and time/tape space utilization are complimentary, although they may also be used alone. The drawings, individual for sake of simplicity, do not negate their combination.

The changing axis of rotation of the head as its rotor moves is shown in Fig.
1. Skew correction is therefore required, from its main axis of rotation to some "secondary" axis of rotation, in the plane either positively or negatively, and as a function of the angle of skew required. The secondary axis of rotation has as its center of rotation a pivot axis.

As a secondary axis is established through some angle of skew, the main rotor spin plane rotates about the pivot axis by the same angle of skew to a secondary rotor spin plane position. By so doing, the data track position error band is swept through a skew angle e...