US 5,963,029 AGranted

Measuring magnetic properties in media by RMS signal processing and incremental erasure

AssigneeSeagate Technology LLC

InventorJason L. Pressesky

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Abstract

A system for magnetically evaluating magnetic data storage media includes a spindle for rotatably supporting magnetic disks, a read/write transducer, and an erasing transducer, both supported for radial movement relative to the disk. The read/write transducer records a sequence of magnetically isolated transitions. When sensing the sequence, the read/write transducer generates a fringing field signal which is low pass filtered and RMS processed to provide a voltage proportional to the remanence-thickness product. The erasing transducer is a ring head transducer having a substantially larger gap and transducer/disk spacing as compared to an aerodynamically supported transducer. Consequently a Hall effect probe is positionable within the gap to directly measure the magnetic intensities of erase fields. Coercivity is determined by applying the erase fields in a sequence of increasing intensities, with each application followed by a measurement of the remanence-thickness product, until the remanence-thickness product has been reduced by one-half. The read/write transducer can be aerodynamically supported to more accurately replicate transitions encountered during normal use, or can be of the ring head type to enable testing of the disk at intermediate fabrication stages.

Claims32

Dependent claims

A system for non-destructively measuring a magnetic property of a magnetic data storage medium, including:

a media support stage maintaining a magnetic data storage medium in a selected orientation, said data storage medium having a magnetizable recording layer;
a transducing arrangement disposed proximate the recording layer and including at least one magnetic transducing head gap of a selected gap length for generating magnetic fields;
a transducing positioning arrangement for selectively positioning the transducing arrangement and the data storage medium relative to one another, to facilitate a use of the transducing arrangement to write magnetic transitions, erase magnetic transitions and sense magnetic fringing fields of the magnetic transitions along a selected segment of the recording layer;
wherein the transducing arrangement, responsive to said sensing of magnetic fringing fields, generates an analog electrical fringing field signal;
a magnetic field sensing element mounted to the transducer arrangement near the transducing head gap, adapted to measure magnetic intensity and to generate an erase field signal indicating a magnetic intensity of a magnetic erase field during said erasing;
and
a controller operatively coupled to the transducing arrangement and to the transducer positioning arrangement, and further coupled to receive the fringing field signal and the erase field signal, said controller adapted to:
(i) cause the transducing arrangement to write a set of magnetically isolated transitions along the selected segment of the recording layer, and to sense a resulting first magnetic fringing field to generate a first fringing field signal with a first amplitude;
and (ii) apply a magnetic erasing field having a target magnetic intensity to said transitions, to form a modified magnetic fringing field that when sensed by the transducing arrangement yields a fringing field signal having a target amplitude substantially equal to a predetermined fraction of said first amplitude;
and
wherein said target magnetic intensity indicates a magnetic property of the magnetic data storage medium along said selected segment.

8 more elements

A device for measuring a magnetic property of a magnetic data storage medium, including:

a media support stage maintaining a magnetic data storage medium in a selected orientation, said data storage medium having a magnetizable recording layer;
a transducing arrangement disposed proximate the recording layer, to write magnetic data transitions in the recording layer, and to sense magnetic fringing fields from the magnetic transitions written in the recording layer and in response generate analog electrical fringing field signals;
a transducer positioning arrangement for selectively positioning the transducing arrangement and the data storage medium relative to one another, to facilitate the writing of transitions and the sensing of the fringing fields along a selected segment of the recording layer;
and
a signal processing circuit coupled to receive the analog electrical fringing field signals, the signal processing circuit including a low pass filtering component for transmitting only low frequency portions of the fringing field signals, and an averaging circuit component coupled to the filtering component to receive the low frequency portions and to generate RMS (root mean square) values based on said low frequency portions, wherein said RMS values indicate a magnetic property of the recording layer along the selected segment.

2 more elements

A system for determining the nature of magnetic properties of a magnetic data storage medium, including:

a media support stage maintaining a magnetic data storage medium in a selected orientation, said data storage medium having a magnetizable recording layer;
a magnetic reading/writing transducer disposed proximate the recording layer, for writing magnetic transitions into the recording layer, sensing magnetic fringing fields resulting from the magnetic transitions written into the recording layer, and in response generating analog electrical fringing field signals;
a magnetic erasing transducer supported in a substantially fixed spaced apart relation to the data storage medium at a spacing of at least about 100 microinches from the recording layer, to generate magnetic erasing fields for erasing the magnetic transitions previously written into the recording layer;
a transducer positioning arrangement for selectively positioning the reading/writing transducer and the erasing transducer for movement relative to the data storage medium, to facilitate said writing, sensing and generating erasing fields along a selected segment of the recording layer;
and
a controller operatively coupled to the erasing transducer and to the transducer positioning arrangement, and further coupled to receive the fringing field signal, to cause the erasing transducer to apply a plurality of magnetic erasing fields to a plurality of magnetically isolated magnetic transitions written into the recording layer along the selected segment, in a sequence of incrementally increasing magnetic intensities, while causing the reading/writing transducer to generate one of the fringe field signals after the application of each erasing field, until a final fringing field signal, generated after the application of a final erasing field of the sequence, has an amplitude at most equal to one-half the amplitude of an initial fringing field signal based on the same magnetic transitions sensed before the application of any erasing field.

3 more elements

A system for non-destructively measuring a magnetic property of a magnetic data storage medium, including:

a media support means for maintaining a magnetic data storage medium in a selected orientation;
a transducing means positionable proximate a recording layer of a data storage medium and including at least one magnetic transducing head gap of a selected gap length for generating magnetic fields;
a positioning means for selectively positioning the transducing means and the data storage medium relative to one another, to facilitate use of the transducing means to write magnetic transitions into the recording layer, apply magnetic erasing fields to the magnetic transitions, and sense magnetic fringing fields of the magnetic transitions to generate analog electrical fringing field signals;
a magnetic field sensing element mounted to the transducing means and disposed near the transducing head gap, for generating erase field signals indicating magnetic erasing field intensity during said application of the magnetic erasing fields;
and
a control means operatively coupled to the transducing means, to the positioning means, and to the sensing element, for (i) causing the transducing means to write a set of magnetically isolated transitions into the recording layer, and generating a first fringing field signal with a first amplitude;
and then (ii) applying a magnetic erasing field having a target magnetic intensity to said transitions, to form a modified magnetic fringing field that when sensed by the transducing means yields a fringing field signal having a target amplitude equal to at most about one-half of the first amplitude;
and
a means for storing a value representing said target magnetic intensity to indicate a magnetic property of the magnetic data storage medium.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/789,303Filed 30 Jan 1997
Granted: 5 Oct 1999
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

G11B 5/012
Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor: recording on, or…
G01R 33/1207
Measuring magnetic properties of articles or specimens of solids or fluids: testing individual magnetic storage devices, e.g. records carriers or…
G11B 27/36
Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel: monitoring, i.e. supervising the progress of recording…
G11B 33/10
Constructional parts, details or accessories not provided for in the other groups of this subclass: indicating arrangements; Warning arrangements