Method and apparatus for measuring internal structure of a target magnetic body using inductance
First Claim
1. A method of examining an internal structure of a target magnetic body, said method comprising the steps of:
- (a) applying a magnetostatic field to a target magnetic body to magnetize the target magnetic body;
(b) cutting the magnetostatic field off and subsequently measuring a transient variation in a differential magnetic flux density at a plurality of position in the vicinity of the target magnetic body, the differential magnetic flux density being a differentiation of a magnetic flux density with respect to time;
(c) determining a time constant of the transient variation in the differential magnetic flux density at the plurality of positions; and
(d) determining a specific characteristic value relating to the internal structure of the target magnetic body, based on a distribution of the time constant over the plurality of positions.
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Abstract
The process first applies a magnetostatic field to a target magnetic body to magnetize the target magnetic body. The process then cuts the magnetostatic field off and measures a transient variation in a differential magnetic flux density at a plurality of positions in the vicinity of the target magnetic body. The process subsequently determines a time constant of the transient variation in the differential magnetic flux density at the plurality of positions. The process then determines a specific characteristic value relating to the internal structure of the target magnetic body, based on a distribution of the time constant over the plurality of positions. This arrangement enables a variety of internal structures of the target magnetic body to be examined in a non-destructive manner.
25 Citations
17 Claims
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1. A method of examining an internal structure of a target magnetic body, said method comprising the steps of:
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(a) applying a magnetostatic field to a target magnetic body to magnetize the target magnetic body;
(b) cutting the magnetostatic field off and subsequently measuring a transient variation in a differential magnetic flux density at a plurality of position in the vicinity of the target magnetic body, the differential magnetic flux density being a differentiation of a magnetic flux density with respect to time;
(c) determining a time constant of the transient variation in the differential magnetic flux density at the plurality of positions; and
(d) determining a specific characteristic value relating to the internal structure of the target magnetic body, based on a distribution of the time constant over the plurality of positions. - View Dependent Claims (2, 3, 4, 9, 10)
assuming the transient variation in the differential magnetic flux density to be a combination of a transient variation in a first differential magnetic flux density corresponding to an attenuation of a first magnetic flux density caused by the magnetostatic field and a transient variation in a second differential magnetic flux density corresponding to an attenuation of a second magnetic flux density caused by an eddy current, which is induced by the attenuation of the first magnetic flux density, and determining at least one of a first time constant defining the transient variation in the first differential magnetic flux density and a second time constant defining the transient variation in the second differential magnetic flux density.
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3. A method in accordance with claim 2, wherein the target magnetic body is a plate assembly obtained by joining two metal plates by spot welding, and
wherein said step (d) includes the step of: determining a shape of a nugget portion of a spot welded part, based on a distribution of the first time constant.
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4. A method in accordance with claim 2, wherein the target magnetic body is a plate assembly obtained by joining two metal plates by spot welding, and
wherein said step (d) includes the step of: determining a shape of a joint portion of a spot welded part, based on a distribution of the second time constant.
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9. The method, as recited in claim 1, wherein the cutting the magnetostatic field and subsequently measuring, comprises using a loop coil for the measuring.
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10. The method, as recited in claim 9, wherein the cutting the magnetostatic field and subsequently measuring, further comprises using a hall device electrically connected to the loop coil.
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5. An apparatus for examining an internal structure of a target magnetic body, comprising:
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a magnetostatic field application unit that applies a magnetostatic field to a target magnetic body to magnetize the target magnetic body;
a measurement unit that cuts the magnetostatic field off and subsequently measures a transient variation in a differential magnetic flux density at a plurality of positions in the vicinity of the target magnetic body, the differential magnetic flux density being a differentiation of a magnetic flux density with respect to time;
a time constant determination unit that determines a time constant of the transient variation in the differential magnetic flux density at the plurality of positions; and
a structural characteristic determination unit that determines a specific characteristic value relating to the internal structure of the target magnetic body, based on a distribution of the time constant over the plurality of positions. - View Dependent Claims (6, 7, 8, 11, 12, 13)
wherein said structural characteristic determination unit determines a shape of a nugget portion of a spot welded part, based on a distribution of the first time constant. -
8. An apparatus in accordance with claim 6, wherein the target magnetic body is a plate assembly obtained by joining two metal plates by spot welding, and
wherein said structural characteristic determination unit determines a shape of a joint portion of a spot welded part, based on a distribution of the second time constant. -
11. The apparatus, as recited in claim 5, wherein the measurement unit, comprises a loop coil.
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12. The apparatus, as recited in claim 11, wherein the measurement unit, further comprises a hall device.
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13. The apparatus, as recited in claim 12, wherein the loop coil is electrically connected in series with the hall device.
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14. A method of examining an internal structure of a target magnetic body, said method comprising the steps of:
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(a) applying a first magnetostatic field to a target magnetic body to magnetize the target magnetic body;
(b) cutting the first magnetostatic field;
(c) using a first coil loop to provide a first magnetic flux density measurement at a first location;
(d) determining a first time constant at the first location based on the first magnetic flux density; and
(e) determining a specific characteristic value relating to the internal structure of the target magnetic body is further based on the first time constant at the first location. - View Dependent Claims (15, 16, 17)
(a) applying a second magnetostatic field to the target magnetic body;
(b) cutting the second magnetostatic field;
(c) using a second coil loop to provide a first magnetic flux density measurement at a second location; and
(d) determining a first time constant at the second location based on the first magnetic flux density at the second location, wherein the determining a specific characteristic value relating to the target magnetic body is based on the first time constant at the second location.
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16. The method, as recited in claim 15, further comprising the steps of:
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(a) applying a third magnetostatic field to the target magnetic body;
(b) cutting the third magnetostatic field;
(c) using the first coil loop and a first hall device to provide a second magnetic flux density measurement at the first location;
(d) applying a fourth magnetostatic field to the target magnetic body;
(e) cutting the fourth magnetostatic field; and
(f) using the second coil loop and a second hall device to provide a second magnetic flux density measurement at the second location.
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17. The method, as recited in claim 16, further comprising the steps of:
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(a) determining a second time constant at the first location; and
(b) determining a second time constant at the second location, wherein the determining a specific characteristic value relating to the target magnetic body is further based on the second time constant at the first location and the second time constant at the second location.
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Specification