Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Patent
1998-01-06
1999-11-09
Patidar, Jay
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
324202, 360 7704, G01R 3312, G11B 5596
Patent
active
059821736
ABSTRACT:
A method is disclosed for calibrating a position error signal (PES) to overcome the problem of an amplitude signal that varies as a non-linear function of real displacement when the read transducer is positioned to either side of a null position where the PES equals zero. The amplitude signal and resulting PES is notably nonlinear while reading servo burst information with a Magneto-Resistive (MR) head which has nonlinear magnetic characteristics. The calibration according to this method may be performed at anytime without need for real displacement information from a servo track writer or any sort of special calibration track. The method involves positioning the MR head to a plurality of nominal partial track displacements on either side of the null position, measuring an open loop gain value for a particular frequency at each of the displacements, deriving the coefficients of a 3.sup.rd order polynomial "gain" curve that best fits the data, integrating the "gain" curve using the coefficients to obtain a 4.sup.th order "position" curve, and then correcting subsequent measured displacements. If sufficient memory is available, the x, y values may be stored in a lookup table. The correction is preferably accomplished, however, by "inverting" the 4.sup.th order position curve through a process of establishing a plurality of "x, y" values, swapping the axes of such values, and then fitting a new polynomial to the transposed data.
REFERENCES:
"A Nonlinearity Specification for Constructing the Servo Position Error Signal" by Evert Cooper, Member, IEEE; IEE Transactions on Magnetics, vol. 33, No. 2, Mar. 1997; pp. 1104-1115.
Patidar Jay
Shara, Esq. Milad G.
Western Digital Corporation
Young, Esq. Leo J.
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