Browse Prior Art Database

Disk Edge Detection and Evaluation

IP.com Disclosure Number: IPCOM000083654D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Van Winkle, HE: AUTHOR

Abstract

In apparatus employing an axially movable carriage disposed at the periphery of a stack of commonly rotating circular disks, the axial position of the carriage can be determined by a pair of magnetic sensing heads sensing signals recorded at the outer periphery of the rotating disks.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Disk Edge Detection and Evaluation

In apparatus employing an axially movable carriage disposed at the periphery of a stack of commonly rotating circular disks, the axial position of the carriage can be determined by a pair of magnetic sensing heads sensing signals recorded at the outer periphery of the rotating disks.

In an axially elongated stack of such disks, there may be some axial runout. Accordingly, signals sensed by the heads should enable motion and positioning controls to control the carriage for tracking the axial runout. Each disk has a record track containing a recorded constant frequency for identifying which disk is in a set of disks.

The positioning accuracy of the carriage is such that a set of disks F1 through F4 can be located without reference to the signals on the record tracks. The group size may be increased to 5, 7, or any other number of disks, each disk within a group having its own unique frequency or other code (data pattern).

Assume that it is desired to position the carriage adjacent disks F1 and F2. The voltage-controlled oscillator (VCO) is preset to a frequency such that the heterodyned frequency for filters F1 and F2 is constant. It is desired that the sequence of frequencies can be altered, such that adjacent disks have a maximum frequency separation. For example, in a five-frequency set, the successive disks may have F1, F3, F5, F2, F4, F1....

The detector for detecting which two disks the carriage is immediately adjacent, is driven by a common oscillator VCO which is frequency and phase locked to the rotation of the disks via the tachometer, phase compare, and frequency divider n, which constitutes phase-lock loop PLL. The two demodulators M1 and M2 are a pair of superheterodyne detectors supplying the heterodyned or intermediate frequency to filters F1 and F2.

Signals supplied through the filters drive diode detectors D1 and D2, oppositely poled, with respect to the current summing junction at resistors R1 and R2, such that the signals from the upper and lower heads of the carriage can be disti...