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Read Write Magnetic Azimuth Adjustment Method

IP.com Disclosure Number: IPCOM000089326D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 61K

Publishing Venue

IBM

Related People

Hart, RG: AUTHOR [+4]

Abstract

The gap 10 in a magnetic core 12 of a magnetic read head 14 may be adjusted so that the gap 10 lies very accurately on a radius R passing through the center C of a disk drive by reading the voltage from the winding 16 of head 14 using a test disk 18 driven about center C. Test disk 18 has sectors 20 and 22 of magnetic transitions that lie alternately at opposite angles Delta with respect to radius R. When the rotative position of head 14 is adjusted so that the voltages 20' and 22' on winding 16 are the same, gap 10 is very accurately located on radius R.

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Read Write Magnetic Azimuth Adjustment Method

The gap 10 in a magnetic core 12 of a magnetic read head 14 may be adjusted so that the gap 10 lies very accurately on a radius R passing through the center C of a disk drive by reading the voltage from the winding 16 of head 14 using a test disk 18 driven about center C. Test disk 18 has sectors 20 and 22 of magnetic transitions that lie alternately at opposite angles Delta with respect to radius R. When the rotative position of head 14 is adjusted so that the voltages 20' and 22' on winding 16 are the same, gap 10 is very accurately located on radius R.

The angle Delta at which the maximum accuracy of adjustment of the rotative position of head 14 may be obtained varies with the width of track T on the magnetic disk, such as that provided by the sectors 20 and 22, and varies also with the bit cell length (the distance between magnetic transitions). For a track T having a width of .007 inch (.1778 mm) and having distances of .000077 inch
(.00195 mm) between transitions, the maximum accuracy for locating gap 10 on the radius R is with the angles Delta equal to 50 minutes. This will be illustrated with reference to the following equations and Fig. 4, showing the relationship of an azimuth angle Alpha of gap 10 with respect to the magnetic transitions in a magnetic track on a recording disk, and with reference to Fig. 3, showing the signal amplitude from winding 16 as a function of azimuth angle Alpha.

The azimuth angle Alpha (Fig. 4) at which a head gap is located with respect to magnetic transitions on a recording disk has two effects on the voltage from winding 16 of magnetic head 14. Firstly, as azimuth angle Alpha increases, the output voltage from winding 16 is reduced, thereby degrading the signal-to-noise ratio. Secondly, the increasing azimuth angle Alpha degrades the resolution and produces more bit shift. The cause of these two effects is that, as the azimuth angle Alpha is increased, the gap begins to read over a greater length than the gap length, as is illustrated in Fig. 4. The greater is the azimuth angle Alpha, the greater is the effective gap length illustrated in Fig. 4. In fact, the gap can actually be reading two transitions at a time if the angle Alpha is sufficiently large. It is therefore the difference between the effective gap length, as shown in Fig. 4, and the ideal gap length that relates to the above problem rather than the azimuth angle Alpha per se.

The voltage output of the winding 16 is described by the following equation:

(Image Omitted)

Where: Alpha = Azimuth angle in radians x(m) = Track width 1(BC) = Bit cell length.

Fig. 3 is a plot of the voltage amplitude from winding 16 as a function of azimuth angle Alpha in minutes for a track width of x(m) of .007 inch (.1778 mm) and a distance 1(BC) between successive magnetic transitions of 77 X 10/-6/ inch (.00195 mm). The parameters of .007 inch (.1778 mm) and 77 X 10/-6/ inch
(.00195 mm) imply that a 5% r...