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A magnetic material detecting device which detects a magnetic material by applying a magnetic field to the magnetic material and detecting a magnetic field generated from the magnetic material by the applied magnetic field, and which includes a magnetizing coil which emits a magnetic field that excites the magnetic material, and a dummy coil which generates a magnetic field that excites the magnetic material by electromagnetic induction caused by the magnetic field emitted from the magnetizing coil, in which the dummy coil is disposed at a position where the electromagnetic induction is generated.

1. A magnetic material detecting device which detects a magnetic material by applying a magnetic field to the magnetic material and detecting a magnetic field generated from the magnetic material by the applied magnetic field, comprising: a magnetizing coil which emits a magnetic field that excites the magnetic material; and a dummy coil which generates a magnetic field that excites the magnetic material by electromagnetic induction caused by the magnetic field emitted from the magnetizing coil, wherein the dummy coil is disposed at a position where the electromagnetic induction is generated, and the dummy coil has no electrically conductive connection to a driving circuit.

2. The magnetic material detecting device according to claim 1, wherein the magnetizing coil and the dummy coil are wound in the same direction.

3. The magnetic material detecting device according to claim 1, wherein plural magnetizing coils are provided, and the dummy coil is disposed between the plural magnetizing coils.

4. The magnetic material detecting device according to claim 1, wherein the magnetizing coil or the dummy coil is disposed on a cover which covers a medium having the magnetic material.

5. The magnetic material detecting device according to claim 4, wherein a detection control part is provided which detects the magnetic material in association with an opening and closing operation of the cover.

6. The magnetic material detecting device according to claim 1, wherein the magnetizing coil or the dummy coil is disposed below a support which supports a medium having the magnetic material.

7. The magnetic material detecting device according to claim 1, wherein the magnetizing coil or the dummy coil is disposed on a passage through which a medium having the magnetic material moves.

8. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads image information of a medium having the magnetic material, and a control part which controls an image information reading operation according to a result of the detection of the magnetic material.

9. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads and outputs image information of a medium having the magnetic material, and a control part which controls an image information output operation according to a result of the detection of the magnetic material.

10. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads image information of a medium having the magnetic material, an image forming part which forms an image on a medium according to the read image information, and a control part which controls an image forming operation according to a result of the detection of the magnetic material.

11. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads image information of a medium having the magnetic material, wherein: the image information reading part does not read the image information when the magnetic material is detected.

12. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads and outputs image information of a medium having the magnetic material, wherein: the image information reading part does not output the read image information when the magnetic material is detected.

13. The magnetic material detecting device according to claim 1, further comprising: an image information reading part which reads image information of a medium having the magnetic material, and an image forming part which forms an image on a medium according to the read image information, wherein: the image forming part does not form an image when the magnetic material is detected.

14. The magnetic material detecting device according to claim 1, wherein the dummy coil is disposed at a position substantially opposed to the magnetizing coil.

15. The magnetic material detecting device according to claim 14, wherein an induced current which is generated by a magnetic field generated by the magnetizing coil flows in a direction opposite to that of an electric current flowing through the magnetizing coil at a portion opposed to the dummy coil.

16. An image reading device which detects a magnetic material by applying a magnetic field to the magnetic material and detecting a magnetic field generated from the magnetic material by the applied magnetic field, comprising: a magnetizing coil which emits a magnetic field that excites the magnetic material; a dummy coil which generates a magnetic field that excites the magnetic material by electromagnetic induction caused by the magnetic field emitted from the magnetizing coil; and a platen cover, wherein the magnetizing coil or the dummy coil is disposed on the platen cover, the dummy coil is disposed at a position where the electromagnetic induction is generated, and the dummy coil has no electrically conductive connection to a driving circuit.

17. A platen cover of an image reading device which detects a magnetic material by applying a magnetic field to the magnetic material and detecting a magnetic field generated from the magnetic material by the applied magnetic field, comprising: a magnetizing coil which emits a magnetic field that excites the magnetic material; and a dummy coil which generates a magnetic field that excites the magnetic material by electromagnetic induction caused by the magnetic field emitted from the magnetizing coil, the dummy coil is disposed at a position where the electromagnetic induction is generated, and the dummy coil has no electrically conductive connection to a driving circuit.

18. An image reading device which detects a magnetic material by applying a magnetic field to the magnetic material and detecting a magnetic field generated from the magnetic material by the applied magnetic field, comprising; a magnetizing coil which emits a magnetic field that excites the magnetic material; a dummy coil which generates a magnetic field that excites the magnetic material by electromagnetic induction caused by a magnetic field emitted from the magnetizing coil; and a platen glass, wherein the magnetizing coil or the dummy coil is disposed below the platen glass, the dummy coil is disposed at a position where the electromagnetic induction is generated, and the dummy coil has no electrically conductive connection to a driving circuit.

A magnetic material detecting device according to an aspect of the present invention is mounted on an image forming device such as a copy machine, and a magnetic material is applied to printed materials which have, for example, confidential information or the like printed in order to prevent leaks of information, to maintain confidentiality or to manage documents. If such a printed material is attempted to be copied without authorization, the magnetic material detecting device according to the present invention detects the magnetic material applied to the printed material and controls to prevent the copy machine from performing a copying processing operation, thereby capable of preventing confidential information from being copied without authorization and preventing the confidential information from being leaked.

The magnetic material applied to the printed materials has a large Barkhausen effect, or a characteristic of conducting magnetostrictive vibration, and it is also possible to identify a printed material by applying the printed materials with plural magnetic materials having various shapes and sizes in combination.

The magnetic material having the large, Barkhausen effect or the magnetostrictive vibration characteristic causes magnetization reversal or magnetostrictive vibration when it receives a prescribed alternating magnetic field, so that the presence of the magnetic material can be detected in a noncontact manner by detecting a signal of the magnetic pulse or electromagnetic wave emitted at that time.

Accordingly, the magnetic material detecting device of an aspect of the present invention is configured to detect information of the magnetic material by giving a prescribed alternating magnetic field to the magnetic material applied to the printed material and detecting a signal of the magnetic pulse or the electromagnetic wave emitted from the magnetic material.

But, there is a possibility that the magnetic material applied to the printed material is falsely detected without being detected properly depending on the magnetic field strength of the alternating magnetic field given to the magnetic material or the detection output of the magnetic pulse or the electromagnetic wave emitted from the magnetic material, and it is desired that the magnetic material is detected over a large area without fail.

In the following example, a copy machine that can prevent unauthorized copying by preventing false detection of the magnetic material applied to the printed material and detecting information of the magnetic material without fail will be described.