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Magnetic Head Position Sensing

IP.com Disclosure Number: IPCOM000079927D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Taylor, NB: AUTHOR

Abstract

This method and apparatus determines the accuracy of a stepper motor 10 (Fig. 5) acting through a lead screw 12, for positioning a magnetic head 14 on a magnetic disk 16.

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Magnetic Head Position Sensing

This method and apparatus determines the accuracy of a stepper motor 10 (Fig. 5) acting through a lead screw 12, for positioning a magnetic head 14 on a magnetic disk 16.

Disk 16 first is magnetically encoded with pulse groups 18 on a plurality of tracks, such as tracks 0, 1, 2, 3 and 4 which are shown in Fig. 1. This may be accurately done by mounting the disk drive unit holding the disk 16 in vertical disposition on a surface plate and measuring, using a height gage, from the surface plate to the magnetic head providing the signal groups 18 on the various disk tracks. Each group 18 includes two sync encodings a and b which are centered with respect to their track, an encoding c having its center located 0.006 inch outwardly of the track center and an encoding d having its center located
0.006 inch inwardly of the track center. Adjacent tracks, such as track 0 and track 1, are recorded on alternate cycles of the encoder so that the pulse groups 18 alternate on the two tracks, as shown in Fig. 1.

Disk 16 is then rotatably mounted on any suitable arbor with its center at 16a (see Fig. 5), with magnetic head 14 being located over a face of disk 16; and disk 16 is then driven. Magnetic encodings a, b, c and d on each of the tracks will produce signals a', b', c', and d' in head 14; and, if head 14 is exactly centered on a track, signals a', b', c' and d' will appear as shown in Fig. 2, with the amplitude of signals c' and d' being equal. If head 14 is low with respect to the track (too far toward the outer periphery of disk 16), signal c' will be greater than signal d' in amplitude as shown in Fig. 3. If head 14 is high with respect to the track, signal d' will be greater in amplitude than signal c' as shown in Fig. 4. If signal c' is equal in amplitude to signals a' and b', as shown in Fig. 3, head 14 is located exactly 0.003 inch low, while, if signal d' is equal in amplitude to signals a' and b', as shown in Fig. 4, head 14 is located exactly 0.003 inch high with respect to the track. The Fig. 5 circuitry which is used for determining the relative magnitudes of signals c' and d' may

In Fig. 5, the output of magnetic head 14 is applied to amplifier 20, and the output of amplifier 20 is applied onto single-shots 22, 24 and 26. The output of single-shot 24 is applied onto single-shot 28, and the...