US 5,687,141 A · Method and apparatus for recording information on magnetooptical recording medium while canceling external stray magnetic field · patentgrep

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Abstract

A magnetooptical recording apparatus effects recording of information on a recording medium using an optical head and a magnetic head while cancelling an external stray magnetic field generated from an actuator, a linear motor or the like. The external stray magnetic field is detected by a detection circuit. A magnetic field for cancelling the detected external stray magnetic field is applied to the recording medium using a magnetic member, a coil wound around the magnetic member and a power source for supplying current to the coil. The external stray magnetic field is detected on the basis of a shift amount, caused by the external stray magnetic field, of a B-H curve representing a relationship between a magnetic field H running through the magnetic member and a magnetic flux B generated in the magnetic member.

Claims27

Dependent claims

A magnetooptical recording apparatus comprising:

an optical head for irradiating a light beam to a magnetooptical recording medium;
a magnetic head for applying to the recording medium a magnetic field modulated according to an information signal;
detection means for detecting an external stray magnetic field applied to the recording medium;
and
magnetic field applying means for applying, to the recording medium, a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal outputted from said detection means,
wherein said detection means comprises a detector in which at least one coil is wound around a magnetic member, and a detection circuit connected to the coil, and said detection circuit supplies said coil with a variable bias current so as to saturate a magnetic flux generated in said magnetic member in a predetermined direction and detects a current I.sub.B1 required for saturating the magnetic flux in the predetermined direction and a current I.sub.B2 required for saturating the magnetic flux in the direction opposite to the predetermined direction to output a signal corresponding to a value of 1/2(I.sub.B1 +I.sub.B2) as the detection signal.

3 more elements

A magnetooptical recording apparatus comprising:

an optical head for irradiating a light beam to a magnetooptical recording medium;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to an information signal;
detection means for detecting an external stray magnetic field applied to the recording medium;
and
a drive circuit for supplying said magnetic head with current for generating a magnetic field for cancelling said external stray magnetic field in accordance with a detection signal outputted from said detection means and with a recording current modulated according to the information signal,
wherein said detection means comprises a detector in which at least one coil is wound around a magnetic member and a detection circuit connected to said coil, and said detection circuit supplies said coil with a variable bias current so as to saturate a magnetic flux generated in said magnetic member in a predetermined direction and in a direction opposite to the predetermined direction and detects a current I.sub.B1 required for saturating the magnetic flux in the predetermined direction and a current I.sub.B2 required for saturating the magnetic flux in the direction opposite to the predetermined direction to output a signal corresponding to a value of 1/2(I.sub.B1 +I.sub.B2) as the detection signal.

3 more elements

A magnetooptical recording apparatus comprising:

an optical head for selectively irradiating, to a magnetooptical recording medium, one of a light beam having a constant intensity and a light beam intensity-modulated according to an information signal;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to the information signal when the light beam with the constant intensity is irradiated to the recording medium;
detection means for detecting an external stray magnetic field applied to the recording medium;
and
magnetic field applying means for applying, to the recording medium, a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal outputted from said detection means when the light beam having the constant intensity is irradiated to the recording medium, and for applying, to the recording medium, a recording bias magnetic field in a constant direction when the light beam intensity-modulated according to the information signal is irradiated to the recording medium,
wherein said detection means comprises a detector in which at least one coil is wound around a magnetic member and a detection circuit connected to said coil, and said detection circuit supplies said coil with a variable bias current so as to saturate a magnetic flux generated in said magnetic member in a predetermined direction and in a direction opposite to the predetermined direction and detects a current I.sub.B1 required for saturating the magnetic flux in the predetermined direction and a current I.sub.B2 required for saturating the magnetic flux in the direction opposite to the predetermined direction to output a signal corresponding to a value of 1/2(I.sub.B1 +I.sub.B2) as the detection signal.

3 more elements

A magnetooptical recording apparatus comprising:

an optical head for irradiating a magnetooptical recording medium with a light beam;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to an information signal;
detection means for detecting an external stray magnetic field applied to the recording medium;
magnetic field applying means for applying, to the recording medium, a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal output from said detection means,
wherein said detection means comprises a detector in which a coil is wound around a magnetic member, and a detection circuit connected to the coil, wherein said detection circuit comprises (i) a current detection circuit for detecting current supplied to said coil;
(ii) a low-pass filter for extracting a bias current component from an output of said current detection circuit;
(iii) a first high-pass filter for extracting an AC signal component from the output of said current detection circuit;
(iv) a first amplitude detection circuit for detecting a current amplitude from an output of said first high-pass filter;
(v) a voltage detection circuit for detecting a voltage induced in opposite ends of said coil;
(vi) a second high-pass filter for extracting an AC signal component from an output of said voltage detection circuit;
(vii) a second amplitude detection circuit for detecting a voltage amplitude from an output of said second high-pass filter;
and (viii) a dividing circuit for calculating the impedance of said coil from a ratio of the current amplitude and the voltage amplitude detected by said first and second amplitude detection circuits, respectively, and said detection circuit detects the external stray magnetic field from a relation between a magnetic flux generated inside the magnetic member and a magnetic field extending through the magnetic member, caused by supplying the coil with current;
a current source for supplying said coil with a variable bias current;
and
an oscillator for supplying said coil with an AC signal having a constant frequency, and
wherein said detection circuit detects the external stray magnetic field from a variation in an impedance of said coil with respect to a variation in the bias current.

13 more elements

A magnetooptical recording apparatus comprising:

an optical head for irradiating a magnetooptical recording medium with a light beam;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to an information signal;
detection means for detecting an external stray magnetic field applied to the recording medium;
a drive circuit for supplying said magnetic head with current for generating a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal output from said detection means and a recording current modulated according to the information signal,
wherein said detection means comprises a detector in which a coil is wound around a magnetic member and a detection circuit connected to said coil, wherein said detection circuit comprises (i) a current detection circuit for detecting current supplied to said coil;
(ii) a low-pass filter for extracting a bias current component from an output of said current detection circuit;
(iii) a first high-pass filter for extracting an AC signal component from the output of said current detection circuit;
(iv) a first amplitude detection circuit for detecting a current amplitude from an output of said first high-pass filter;
(v) a voltage detection circuit for detecting a voltage induced in opposite ends of said coil;
(vi) a second high-pass filter for extracting an AC signal component from an output of said voltage detection circuit;
(vii) a second amplitude detection circuit for detecting a voltage amplitude from an output of said second high-pass filter;
and (viii) a dividing circuit for calculating the impedance of said coil from a ratio of the current amplitude and the voltage amplitude detected by said first and second amplitude detection circuits, respectively, and said detection circuit detects the external stray magnetic field from a relation between a magnetic flux generated inside the magnetic member and a magnetic field extending through the magnetic member, caused by supplying said coil with current;
a current source for supplying said coil with a variable current;
and
an oscillator for supplying said coil with an AC signal having a constant frequency, and
wherein said detection circuit detects the external stray magnetic field from a variation in an impedance of said coil with respect to a variation in the bias current.

13 more elements

A magnetooptical recording apparatus comprising:

an optical head for selectively irradiating a magnetooptical recording medium with one of a light beam having a constant intensity and a light beam intensity-modulated according to an information signal;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to an information signal when the recording medium is irradiated with the light beam having the constant intensity;
detection means for detecting an external stray magnetic field applied to the recording medium;
magnetic field applying means for applying, to the recording medium, a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal output from said detection means when the recording medium is irradiated with the light beam having the constant intensity, and for applying, to the recording medium, a recording bias magnetic field with a predetermined direction when the recording medium is irradiated with the light beam intensity-modulated according to the information signal,
wherein said detection means comprises a detector in which a coil is wound around a magnetic member, and a detection circuit connected to the coil, wherein said detection circuit comprises (i) a current detection circuit for detecting current supplied to said coil;
(ii) a low-pass filter for extracting a bias current component from an output of said current detection circuit;
(iii) a first high-pass filter for extracting an AC signal component from the output of said current detection circuit;
(iv) a first amplitude detection circuit for detecting a current amplitude from an output of said first high-pass filter;
(v) a voltage detection circuit for detecting a voltage induced in opposite ends of said coil;
(vi) a second high-pass filter for extracting an AC signal component from an output of said voltage detection circuit;
(vii) a second amplitude detection circuit for detecting a voltage amplitude from an output of said second high-pass filter;
and (viii) a dividing circuit for calculating the impedance of said coil from a ratio of the current amplitude and the voltage amplitude detected by said first and second amplitude detection circuits, respectively, and said detection circuit detects the external stray magnetic field from a relation between a magnetic flux generated inside the magnetic member and a magnetic field extending through the magnetic member, caused by supplying the coil with current;
a current source for supplying said coil with a variable current;
and
an oscillator for supplying said coil with an AC signal having a constant frequency, and
wherein said detection circuit detects the external stray magnetic field from a variation in the impedance of said coil with respect to a variation in the bias current.

13 more elements

A magnetooptical recording apparatus comprising:

an optical head for irradiating a magnetooptical recording medium with a light beam;
a magnetic head for applying, to the recording medium, a magnetic field modulated according to an information signal;
detection means for detecting an external stray magnetic field applied to the recording medium;
magnetic field applying means for applying, to the recording medium, a magnetic field for cancelling the external stray magnetic field in accordance with a detection signal output from said detection means,
wherein said detection means comprises a detector in which first and second coils are wound around a magnetic member, and a detection circuit connected to said coils, and wherein said detection circuit supplies said first coil with the bias current along with supplying said second coil with an AC signal for detecting an impedance so as to detect the external stray magnetic field from a variation in the impedance, said detection circuit comprises (i) a first current detection circuit for detecting current supplied to said first coil;
(ii) a low-pass filter for extracting a bias current component from an output of said first current detection circuit;
(iii) a second current detection circuit for detecting current supplied to said second coil;
(iv) a first high-pass filter for extracting an AC current component from an output of said second current detection circuit;
(v) a first amplitude detection circuit for detecting a current amplitude from an output of said first high-pass filter;
(vi) a voltage detection circuit for detecting a voltage induced in opposite ends of said second coil;
(vii) a second high pass filter for extracting an AC current signal component from an output of said voltage detection circuit;
(viii) a second amplitude detection circuit for detecting a voltage amplitude from an output of said second high-pass filter;
and (ix) a dividing circuit for calculating the impedance of said coil from a ratio of the current amplitude and the voltage amplitude detected by said first and second amplitude detection circuits, respectively, and said detection circuit detects the external stray magnetic field from a relation between a magnetic flux generated inside the magnetic member and a magnetic field extending through the magnetic member, caused by supplying the coil with current.

10 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/320,823Filed 7 Oct 1994 · continuation
Priority: JP 4-14808015 May 1992
Granted: 11 Nov 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification3 codes

G11B 11/10534
Heads: for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
G11B 11/10595
Using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical,…
G11B
Information storage based on relative movement between record carrier and transducer

Family

Serial60,526Parent of this continuation · filed 13 May 1993
US 5,687,141 AThis patent

From the US filing history. Foreign family members aren’t listed.

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