Browse Prior Art Database

Alignment Disk and Method

IP.com Disclosure Number: IPCOM000060586D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Barr, ER: AUTHOR [+4]

Abstract

This article relates to an improved head-alignment disk, and to a method of using the disk to align the head(s) of a floppy disk drive, as the drive is being manufactured. In such a manufacturing process, the drive's head(s) is adjusted to the correct tangent position, correct radial separation (for a dual head carriage) and correct azimuth angle as the drive's head carriage is being manufactured as a subassembly. However, the carriage's radial position is later adjusted after the head carriage has been mounted on the disk drive. The disk provides a unique quad pattern of four radial-adjust data blocks, as shown in Fig. 1. The first two of these data blocks (10 and 11) comprise a symmetrical set of two blocks which are offset a distance X1 and X2 from track centerline 12 (here X1=X2).

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Alignment Disk and Method

This article relates to an improved head-alignment disk, and to a method of using the disk to align the head(s) of a floppy disk drive, as the drive is being manufactured. In such a manufacturing process, the drive's head(s) is adjusted to the correct tangent position, correct radial separation (for a dual head carriage) and correct azimuth angle as the drive's head carriage is being manufactured as a subassembly. However, the carriage's radial position is later adjusted after the head carriage has been mounted on the disk drive. The disk provides a unique quad pattern of four radial-adjust data blocks, as shown in Fig. 1. The first two of these data blocks (10 and 11) comprise a symmetrical set of two blocks which are offset a distance X1 and X2 from track centerline 12 (here X1=X2). Preferably, this distance is one-half the radial height of the data block. Thus, the base of the data block lies on the track centerline. The second set of these data blocks (13 and 14) is a like symmetrical set. However, this set is offset a distance Y1 and Y2 from the track centerline (here Y1=Y2), where Y is less than
X. Thus, in the preferred embodiment, the base of data blocks 13 and 14 overlaps the track center line. In the method of using the disk, these four patterns have two uses. First, a head carriage to be adjusted is moved radially (by rotating the housing of the carriage's stepping motor) until the sum of the four signals derived from the four data blocks 10, 11, 13, and 14 is zero. This is done by comparing the signals derived from the individual blocks of each set which are offset a similar amount to opposite sides of the track centerline. Fig. 2 shows the formula for comparing these signals, where the voltage derived from pattern 10 is designated V1, pattern 11 is V2, pattern 13 is V3, and pattern 14 is V4. Preferably, the head carriage's four-phase stepping motor is set at a known phase for this adjustment. After this is done, three additional adjacent tracks, having the same quad pattern, are read by the head in its radially adjusted position in order to measure the stepper motor's other phase errors. However, this time the four signals derived from the quad pattern are compared using the algorithm of Fig. 3. This algorithm causes the width of the reading head to be of no consequence to the result, and provides a voltage which is an exact measure, in known length units, of exactly how far off track centerline the center of the reading head is spaced. This measurement can be used to reject the disk drive being adjusted, or it may be possible to intentionally adjust the head slightly off track centerline at the motor's original known ph...