Browse Prior Art Database

Digital Slope Pointer for a Linear Track Servo in a Helical Scan Device

IP.com Disclosure Number: IPCOM000087484D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Arter, NK: AUTHOR [+2]

Abstract

The problem of distinguishing good information from bad information is well known in linear track servo systems. In U.S. Patent 3,845,500 a clock counts from event 1 to event 2. This count is designated A. The clock then counts from event 2 to event 3. This second count is identified as B. These two counts, A and B, are then subtracted to obtain offtrack error, i.e., A - B = offtrack error (Fig. 1).

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Digital Slope Pointer for a Linear Track Servo in a Helical Scan Device

The problem of distinguishing good information from bad information is well known in linear track servo systems. In U.S. Patent 3,845,500 a clock counts from event 1 to event 2. This count is designated A. The clock then counts from event 2 to event 3. This second count is identified as B. These two counts, A and B, are then subtracted to obtain offtrack error, i.e., A - B = offtrack error (Fig.
1).

In an article published in the IBM Technical Disclosure Bulletin, Vol. 18, No. 12, May, 1976, p. 3921, a second event station equivalent to points 1 and 3 is positioned on a triangular servo signal. A count analogous to that described above is taken and stored. If either of the counts is incorrect, the system selects the proper count for track following.

The present technique improves on the above-described techniques in that digital pointers are generated from the described servo information and used to point to tracks that are in error. Additionally, the present technique points to a specific slope in error and to a specific part of the slope that is in error. Essentially, this is achieved by generating a count which is proportional to a distance counted from an event on the slope of the servo signal to the peak and then to a second event point on the trailing slope of that servo signal.

Fig. 2 depicts a one track system where three events are selected on each slope. With two or more servo tracks, only two events are required. As is shown in Fig. 2: E + D = F + A

E + C = E + F

A + C = B + D

G = H

I = J

I + H = G + J

Let E + C = B + F = Bad

A + C = B + D = Bad

E + D = F + A = Good.

This implies A, D, E and F are good and B and C are in error. The system has pointed to the bad area, leaving two good numbers which may be used for track following.

Fig. 3 depicts a dual-tr...