Browse Prior Art Database

Disk Surface Analysis Technique

IP.com Disclosure Number: IPCOM000085113D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 20K

Publishing Venue

IBM

Related People

Eisele, WR: AUTHOR

Abstract

The modulation of information track width by disk surface defects results in peak shift in the read-back signal. Head output is given by F(t) = D(t)I(t), where D is the track width and I is the information signal. Thus peaks will occur where: F(t) = D(t)I(t) + D(t)I(t) = 0 or D(t)/D(t) = -I(t)/I(t).

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Disk Surface Analysis Technique

The modulation of information track width by disk surface defects results in peak shift in the read-back signal. Head output is given by F(t) = D(t)I(t), where D is the track width and I is the information signal. Thus peaks will occur where: F(t) = D(t)I(t) + D(t)I(t) = 0

or D(t)/D(t) = -I(t)/I(t).

In other words, shifted peaks will occur where the instantaneous fractional decay is just balanced by the fractional rate of change of the undisturbed signal.

If a disk to be tested is saturated in one direction along the tracks, the quantity D(t)/D(t) may be determined from the read-back linear signal as follows:

Since head output is given by V(H) = K(H) Phi(H) (t), where K(H) is a head constant and Phi(H) = head flux, and since Phi(H) (t) = Phi(S) D(t), where Phi(S) is the saturation flux, then V(H) = K(H)Phi(S) D(t).

Consequently, D(t) = V(H)/K(H)Phi(S) and D(t) = (integral V(H))/K(H)Phi(S) so that peak shift, D(t)/D(t), is given by V(H)/integral V(H).

In the drawing, a disk pack or module 1 is mounted in a tester drive 2 and saturated unidirectionally. The recorded signal is read back, in a single pass, and the head output V(H) is filtered in amplifier 3 and integrated by integrator 4. The signal is divided by its integral in divider 5 to represent instantaneous peak shift. If the peak shift exceeds a predetermined amount, the disk is defective.

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