JP3534129B2 - Differential magnetic head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential type magnetic head for detecting an object having magnetism. 2. Description of the Related Art Conventionally, as shown in FIGS. 3 and 4, a pair of first and second magnetic cores 10 and 20 each having a substantially E-shape are opposed to a magnetic head of this type. And legs 11, 21, and 1 at both ends of the first and second magnetic cores 10, 20.
A non-magnetic material 30 for forming a gap between
31 are adhered so as to sandwich each. An excitation coil 33 which is excited by an AC bias power supply 32 is wound around the central leg portions 13 and 23 bonded to each other, and the first and second magnetic cores 10 and 23 are wound.
Four detection coils 34 to 37 for generating an induced voltage in accordance with a change in magnetic flux are wound around each of the central portions 14 and 24 of 20. The detection coils 34 to 37 are connected in series and connected to the input terminals of the differential amplifier 38. When the object to be detected (not shown) slides over the gap 30, the detection coils 34, 3
5, a large induced voltage is generated, and a large differential output appears at the output terminal of the differential amplifier 38, thereby detecting the object to be detected. However, in the above-mentioned differential type magnetic head, since four detection coils must be used, the production cost is high, and the cost cannot be reduced. there were. For this reason, conventionally, as shown in Japanese Patent Publication No. 62-36540, there has been a differential magnetic head in which one excitation coil and two detection coils are wound around an S-shaped magnetic core, respectively. In terms of cost reduction, it is understood to be one step. Accordingly, an object of the present invention is to provide a differential type magnetic head capable of reducing the manufacturing cost by providing a minimum required number of detection coils. In order to achieve the above-mentioned object, according to the present invention, there are provided three legs, the shape of which is substantially E-shaped, and an exciting coil attached to a central leg. A first magnetic core on which a certain first coil is wound, a substantially C-shaped shape having two legs, and a second coil serving as a detection coil wound in the center. And a second magnetic core,
There is provided a differential magnetic head having first and second gaps made of a non-magnetic material provided between legs at both ends of the first and second magnetic cores. When an AC bias current flows from the AC bias power supply to the exciting coil, a magnetic flux is generated between the legs at both ends of the first and second magnetic cores sandwiching the first and second gaps. I do. Each magnetic flux generated by the supply of the AC bias current passes through the first and second magnetic cores, and a similar induced voltage is generated in the detection coil according to the change in the magnetic flux. This detection coil is connected differentially,
Therefore, the outputs of the detection coils cancel each other, and the differential output of the detection coils decreases. Next, when an object to be detected made of, for example, a non-magnetic medium approaches the first gap, external magnetic flux leaking from the medium is not introduced into the magnetic head through the first gap. On the other hand, when the magnetic medium approaches, the external magnetic flux leaking from the magnetic medium is introduced into the magnetic head through the first gap, and a large induced voltage corresponding to the external magnetic flux is generated in the detection coil, and the differential of the detection coil The output increases. Therefore, the magnetic information of the medium is detected with high sensitivity. An embodiment of a differential type magnetic head according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram showing one embodiment of a differential magnetic head according to the present invention, and FIG. 2 is a circuit diagram showing electrical connection of coils of the differential magnetic head. In the figure, a differential magnetic head is used in a bill validator (not shown), and has a first magnetic core 40 made of a substantially E-shaped magnetic material,
Second magnetic core 50 made of a substantially C-shaped magnetic body
And first and second gap members 61 and 62 made of a non-magnetic material for forming a gap. The first and second magnetic cores 40 and 50 are made of a magnetic material such as Permalloy or Sendust. First
The magnetic core 40 has a leg 41 on the sliding side of an object to be detected,
Three legs, a leg portion 42 protruding from near the middle of the central portion 44, a leg portion 43 on the non-sliding side of the object to be detected, and a central portion 44.
It is composed of Further, the second magnetic core 50 includes:
It comprises two legs, a leg 51 on the sliding side of the object to be detected, a leg 52 on the side opposite to the sliding side of the object to be detected, and a central portion 53. Further, the leg portions 4 at both ends of the first magnetic core 40 are provided.
1, 43 and the legs 51, 5 at both ends of the second magnetic core 50.
2 are disposed so as to face each other, and the central leg portion 42 of the first magnetic core 40 is disposed so as to project from the central portion 44 toward the central portion 53 of the second magnetic core 50. Have been. An exciting coil 45 is wound around the leg 42 of the first magnetic core 40. The exciting coil 45 is connected to an AC bias power supply 46, and is excited by an AC bias current from the AC bias power supply 46. Have been. A detection coil 54 is wound around the central portion 53 of the second magnetic core 50, and one end of the detection coil 54 is connected to the negative input terminal of the differential amplifier 55, and the other end of the detection coil 54 Is connected to the + input terminal of the differential amplifier 55. First and second gap members 61, 62
Is made of a nonmagnetic material such as beryllium copper or SuS, and is provided between the legs 41 and 51 of the magnetic cores 40 and 50 and between the legs 43 and 52.
It is adhered so as to be sandwiched therebetween to form a gap. The differential amplifier 55 outputs a difference between induced voltages input to each input terminal via an output terminal. That is, the supply of the AC bias current from the AC power supply causes the two legs 41, 51 and 43, of the first and second magnetic cores 40, 50,
Magnetic flux is generated between the respective 52. The two generated magnetic fluxes pass through the first and second magnetic cores 40 and 50, and the detection coil 54 generates an induced voltage of approximately the same level in accordance with the change of the two magnetic fluxes, and is applied to each input terminal. input. The output terminal of the differential amplifier 55 is connected through a resistor 56 to-
The + input terminal is connected to the input terminal, and the + input terminal is grounded via the resistor 57. In the differential amplifier 55, the resistance value of each resistor is adjusted so that the output voltage is set to a small value in a state where the magnetism of the detection target is not detected. For this reason, in the differential amplifier 55, when the magnetism of the detection target is not detected, the outputs of the detection coils 54 cancel each other, and the differential output of the detection coils 54 decreases. Also,
In the differential amplifier 55, when the magnetism of the object to be detected is detected, an external magnetic flux is introduced into the magnetic flux generated between the legs 41 and 51, and the output of the detection coil 54 accompanying the magnetic flux is changed to the leg 43. , 52, and becomes higher than the output associated with the magnetic flux generated between the coils, and is input to the differential amplifier 55.
The differential output of No. 4 increases, and the object to be detected can be detected. Next, the magnetic detection operation when the differential type magnetic head having such a configuration is used in a bill validator will be described. During the operation of the bill validator, the AC bias power supply 46
, An AC bias current flows to the exciting coil 45, and a bill (not shown) inserted into the bill validator is transported toward the differential magnetic head by a transport roller (not shown) in the above-described apparatus. Is done. A predetermined portion of the bill as the detection target is coated with magnetic ink for bill identification. The bills conveyed by the conveying rollers slide on the differential type magnetic head so as to be orthogonal to the gap. While the banknote portion on which the magnetic ink is not applied passes over the magnetic head, the detection coil 54 is supplied with the leg portions 41 and 51 by the supplied AC bias current.
Only the induced voltage corresponding to the change of the magnetic flux generated between the legs 43 and 52 is generated, and the output (induced voltage) of the detection coil 54 is canceled by the differential amplifier 55 and the difference between the differential amplifier 55 The dynamic output becomes smaller. Next, when the portion of the banknote to which the magnetic ink is applied reaches the magnetic head, the external magnetic flux generated by the magnetic ink becomes the first magnetic flux.
, And a large induced voltage is generated in the detection coil 54 in accordance with a change in the combined magnetic flux of the magnetic flux due to the AC bias current and the external magnetic flux. On the other hand, in the detection coil 54, an induced voltage corresponding to a change in magnetic flux generated between the legs 43 and 52 is generated by the supplied AC bias current. These induced voltages are applied to the differential amplifier 5
5, and as a result, a large differential output appears at the output terminal of the differential amplifier 55. Therefore, in this embodiment, when the object to be detected reaches the differential type magnetic head, an external magnetic flux generated by the object to be detected is introduced through the gap, and the external magnetic flux responds to the change of the external magnetic flux. An induced voltage is generated in the detection coil, and a large differential output appears at the output terminal of the differential amplifier 55.
As a result, in the present embodiment, the magnetized detection target can be detected with high accuracy only by providing the minimum required one detection coil, so that the manufacturing cost can be reduced. The differential output appearing at the output terminal of the differential amplifier 55 is, for example, a determination unit (not shown) of a bill validator.
The differential output pattern is compared with a predetermined pattern by the determination section, and the authenticity of the bill can be determined. Note that the present invention is not limited to the above embodiment,
Various modifications are possible. That is, in the embodiments, the case where the differential magnetic head of the present invention is applied to a bill validator is described.However, the differential magnetic head of the present invention is applicable to various other magnetic recording devices, for example, a coin sorter, The present invention is applicable to an identification device for magnetized securities, a metal material identification device, and the like. As described above, according to the present invention, the present invention has three legs and a substantially E-shape, and the first coil is wound around the center leg. A first magnetic core,
With two legs, the shape is almost C-shaped,
Since the second coil is wound around the center and the second magnetic core is provided, and the first and second gaps are provided between the legs at both ends of the first and second magnetic cores, the detection is performed. The minimum number of coils is provided, and the manufacturing cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing one embodiment of a differential magnetic head according to the present invention. FIG. 2 is a circuit diagram showing electrical connection of coils of the differential type magnetic head shown in FIG. FIG. 3 is a schematic configuration diagram showing a conventional differential magnetic head. FIG. 4 is a circuit diagram showing electrical connection of coils of the differential magnetic head shown in FIG. 3; [Description of Signs] 40, 50 Magnetic cores 41 to 43, 51, 52 Legs 44, 53 Central part 45 Excitation coil 46 AC bias power supply 54 Detection coil 55 Differential amplifier 56, 57 Resistance

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01R 33/02-33/18 G11B 5/127

Claims (1)

(57) Claims 1. A first coil having three legs, a substantially E-shaped configuration, and a first coil wound around a central leg. A magnetic core, having a substantially C-shape having two legs, a second coil wound around a central portion, and the first and second magnetic cores; A differential magnetic head comprising: first and second gaps provided between legs at both ends of a core.