Browse Prior Art Database

Non-Destructive Disk Flatness Measurement Method

IP.com Disclosure Number: IPCOM000099482D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Aoyagi, A: AUTHOR [+3]

Abstract

Disclosed is a method to measure radial flatness of a hard disk without destruction, using a single disk tester.

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This is the abbreviated version, containing approximately 56% of the total text.

Non-Destructive Disk Flatness Measurement Method

       Disclosed is a method to measure radial flatness of a hard
disk without destruction, using a single disk tester.

      The principle of this method is based on Wallace's longitudinal
sinusoidal magnetic recording equation (*).

                            (Image Omitted)

      V =  mo .a .N .W .{m/(m+1)} .v .Mr .T(g) .S(g) .G(g) where
    V    :Read-back signal amplitude
    mo   :Permeability of a vacuum
    a    :Read-back efficiency
    N    :Number of turns
    W    :Track width
    m    :Permeability of core
    v    :Relative velocity
    Mr   :Peak remanence of the medium
    T(g) :Thickness factor   = 1-exp (-2 .f .t/g)
    S(g) :Separation factor  = exp(-2 .f .d/g)
    G(g) :Gap Length factor  = sin(f .g/g)/(f .g/g)
    t    :Medium thichness
    g    :Wavelength of the sinusoidal recording
    d    :Head-to-medium spacing (fly height)
    g    :Gap length
    If fly height changes from d to d+w, read-back signal amplitude
will change from V to V'. V'/V is described as follows.

      V'/V = S'(g)/S(g) = {exp(-2 .f .(d+w)/g)}/{exp(-2 .f .d/g)}
    = exp(-2 .f .w/g)
    (1)
    The head used for this measurement is the tri-rail
mini-monolithic 3370 type head.  This head flies on a disk at a
distance of 0.3 mm by air pressure which is produced between the
smooth surfaces c...