Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1998-08-28
2001-04-17
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S239000, C209S567000
Reexamination Certificate
active
06218830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for easily and reliably detecting the presence of magnetic substances such as metallic pieces which have been erroneously incorporated in various non-magnetic products such as sewn products, woven and/or knitted products, non-woven fabrics, carpets, tatamis (straw matting), foods, and medical products, particularly broken needles which have been erroneously mingled in sewn products in the sewing process.
2. Description of the Prior Art
The possibility that magnetic substances such as metallic pieces will erroneously enter such various products as mentioned above during or after the course of manufacture is undeniable. When the sewing needles attached to sewing machines are broken or the pins are mislaid, they will possibly enter sewn products after the sewing process. When fasteners are sewn to garments, the possibility exists that the leading ends of sewing needles of sewing machines will break off and disappear in the seems between fasteners and garments. The products holding this possibility, therefore, must be deprived of metallic pieces such as lost needles before they are shipped. Now that the liabilities on the part of producers have been growing particularly since the enforcement of the law concerning the products liability, the problem of the entry of broken needles such as is incurred during the course of sewing fasteners to garments has been gaining in seriousness.
Heretofore, the detection of lost needles such as broken needles has been attained by utilizing the fact that a magnetic field is disturbed when a magnetic substance crosses the magnetic field as disclosed in published Japanese Patent Applications, KOKAI (Early Publication) No. 4-82,958 and No. 56-36,049, for example. To be specific, when a detecting coil is disposed in a magnetic field and a sewn product containing a magnetic substance erroneously incorporated therein is passed through the magnetic field, the magnetic field is disturbed owing to the presence of the magnetic substance and this disturbance of the magnetic field induces a difference in the induced current generated in the detecting coil. Since this difference in the induced current is extremely feeble, it is amplified to a prescribed level to permit the detection of the magnetic substance.
In the case of a method for detecting a magnetic substance by utilizing the disturbance of a magnetic field (a method for detecting a magnetic substance by passing a product under test through a magnetic field) mentioned above, even when a metallic piece which is not a magnetic substance adheres to a sewn product and it happens to have a certain size, this metallic piece never fails to affect the magnetic field and form a cause for mistaken detection. In the case of a fastener to which an aluminum slider or a die-cast zinc slider is attached or a sewn product to which such a fastener is sewn, when the fastener or the sewn product passes through the magnetic field, the slider induces another magnetic field due to an eddy current and disturbs the applied magnetic field. Then, the apparatus for detecting lost needles fails to discern whether the detected disturbance in the magnetic field (induced current) has been caused by a magnetic substance (needle) mingled in the sewn product or by the slider and forms an erroneous judgement that the sewn product contains a magnetic substance (needle) notwithstanding it is not containing one.
The possible effect of an external noise on the detection cannot be ignored because the difference of the induced current which is generated in the detecting coil by the disturbance of the magnetic field is extremely feeble. Since the magnetic substance generates no difference in the induced current flowing through the detecting coil unless this magnetic substance is moved, the apparatus is incapable of discriminating whether or not the magnetic substance (needle) is included in a sewn product under test when the sewn product containing the magnetic substance (needle) is transferred at a low speed or it is kept at a stopped state. Conversely, when sewn products are transferred at a high speed, the apparatus incurs difficulty in selecting only the sewn products that are containing magnetic substances (needles).
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to provide a method and an apparatus for easily, sensitively and reliably detecting the presence of magnetic substances erroneously included in such various non-magnetic products as mentioned above, and even minute magnetic substances such as broken needles contained erroneously in sewn products.
Another object of the present invention is to provide a detecting method and an apparatus for the detection which are capable of detecting the presence of magnetic substances included in the products even when the products have sewn thereto fasteners or other articles made of a non-magnetic metal which affect a magnetic field or they are bulky, and further even when they are being conveyed or being kept at a stopped state.
To accomplish the objects mentioned above, the first aspect of the present invention resides in providing a method for detecting the presence of magnetic substances in non-magnetic products. The first embodiment of this aspect concerns a method for the detection of a magnetic substance included in a non-magnetic product, characterized by applying to the product a magnetic field, preferably the magnetic field of intensity equivalent to or greater than that required for imparting saturated magnetization thereto, then converging a magnetic flux of the residual magnetization of a magnetic substance included in the product to detect the residual magnetization, and judging or determining the presence or absence of the magnetic substance in the product on the basis of the detected residual magnetization.
The second embodiment of the above aspect concerns a method for the detection of a magnetic substance included in a non-magnetic product, characterized by preparatorily applying a magnetic field, preferably the magnetic field of intensity equivalent to or greater than that required for imparting saturated magnetization, to a magnetic substance having the possibility of mingling in the non-magnetic product thereby causing the magnetic substance to assume a state of possessing residual magnetization, then converging a magnetic flux of the residual magnetization of the magnetic substance included in the product to detect the residual magnetization, and judging or determining the presence or absence of the magnetic substance in the product based on the detected residual magnetization.
Preferably, in either of the embodiments mentioned above, a magnetic sensor or magnetometric sensor is disposed at a prescribed position between a pair of opposed soft magnetic members, the non-magnetic product is located or passed through between the pair of soft magnetic members so that a magnetic field caused by external disturbance is absorbed into these soft magnetic members and that a magnetic flux generated by the magnetic substance included in the product is converged to the soft magnetic members, and thus the residual magnetization of the magnetic substance is detected by the magnetic sensor. The detection of the residual magnetization of a magnetic substance such as a metallic piece or a needle which is mingled in a non-magnetic product may be properly attained by arranging a plurality of magnetic sensors as spaced at intervals of a prescribed size in the direction of width of the non-magnetic product and moving the magnetic sensors relative to the non-magnetic product. The relative movement of the non-magnetic product and the magnetic sensors can be accomplished by moving (imparting a scanning motion to) the magnetic sensors. In consideration of the adaptability of the apparatus under discussion to the existing production line and the workability thereof, however, it is desirable that the residual magnetization of the magnetic substance included in the non-ma
Horita Hiromitsu
Kojima Shin-ichi
Yoshida Yasuhiko
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Oda Christine
YKK Corporation
Zaveri Subhash
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