JP3742664B2 - Differential magnetic head - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a differential magnetic head.
[0002]
[Prior art]
Magnetic recording is to write information by magnetizing a recording medium, or to read information by detecting the magnetization state of the recording medium, and is applied to various fields such as storage devices, magnetic cards, and bill identification. A magnetic head used for magnetic recording typically includes a ring core in which two U-shaped cores are fixed to each other with a non-magnetic spacer sandwiched between both gap butting surfaces, and the ring core. A coil that is wound, information is written by applying a current to the coil, and information is read by detecting an induced voltage generated in the coil.
[0003]
Further, a differential magnetic head with improved sensitivity in detecting magnetic information is known. This magnetic head is formed by, for example, joining a pair of E-type cores, and one core is wound with an exciting coil. The two detection coils wound around the other core are connected in series so that the induced electromotive forces in the two detection coils cancel each other. This differential magnetic head is time-consuming to assemble because it is necessary to join the E-type cores at three joint surfaces when assembling.
[0004]
Japanese Patent Publication No. 62-36540 proposes a differential magnetic head having a magnetic core composed of two C-shaped leg portions and one rod-like portion (see FIG. 1). The magnetic core according to this proposal is such that both end faces of each of the C-shaped leg portions 11 and 12 are fixed to the rod-like portion 13, and there are two joining points at the time of assembling the core, so that the assembly is easy. is there. In FIG. 1, reference numeral 14 indicates an exciting coil wound around the rod-shaped portion 13 and excited by an AC power source, and 15 and 16 indicate detection coils wound around the leg portions 11 and 12. Both detection coils 15 and 16 are differentially connected to each other. Reference numerals 17 and 18 indicate gaps, and reference numerals 19 and 20 indicate joints.
[0005]
[Problems to be solved by the invention]
The differential magnetic head according to the above proposal has good detection sensitivity and is easy to assemble. There is a problem that sliding noise occurs when sliding. One of the causes of the occurrence of sliding noise in the proposed apparatus is understood to be that the joint portion 19 between the C-shaped leg portion 12 and the rod-like portion 13 exists on the sliding side.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a differential magnetic head that can reduce sliding noise by providing a core joint on the anti-sliding side.
[0007]
[Means for Solving the Problems]
The second and third cores are arranged on both sides of the first core around which the first coil is wound, and the second and third coils wound around the second and third cores are respectively arranged. In a differential magnetic head that is differentially connected, the present invention provides a first gap between the first core and the second core on the sliding side, and the first core and the third core. A second gap is provided between the first core and the second core, and each of the second and third cores is joined to the first core on the anti-sliding side, and the second gap is formed in the axial direction of the first core. It is characterized in that it is positioned on the anti-sliding side with respect to the first gap.
[0008]
Preferably, a nonmagnetic material having a shape corresponding to the sliding side portion of the second core is arranged on the sliding side of the third core.
[0009]
[Action]
When the differential magnetic head of the present invention is used, for example, to detect magnetic information from a recording medium, the recording medium is slid with respect to the magnetic head while an AC bias current is passed through the first coil. The magnetic flux generated by applying the bias current passes through the second and third cores, and the same induced voltage is generated in the second and third coils in accordance with the change of the magnetic flux. The outputs of both differentially connected coils cancel each other, and therefore the differential outputs of the second and third coils are small.
[0010]
If the sliding portion of the recording medium is not magnetized, the external magnetic flux leaking from the recording medium due to magnetic information is not introduced into the magnetic head via the first and second gaps. On the other hand, if the sliding portion of the recording medium is magnetized, an external magnetic flux is introduced through the first gap close to the recording medium, and a little external magnetic flux is introduced through the second gap spaced from the recording medium. Is done. As a result, when passing through the magnetized region, a large induced voltage is generated in the second coil, a small induced voltage is generated in the third coil, and a large differential output is transmitted from the second and third coils. The Therefore, magnetic information is detected with high sensitivity.
[0011]
The joint between each of the second and third cores and the first core exists on the anti-sliding side, and therefore no sliding noise is generated due to the core joint on the sliding side. Further, when electrical disturbance noise is generated, the disturbance noise is introduced through the first and second gaps, and an induced voltage is generated in the second and third coils. However, both coils are differentially connected. Therefore, the induced voltage corresponding to noise is canceled out, and noise is reduced.
[0012]
According to the aspect in which the nonmagnetic material is arranged on the sliding side of the third core, the recording medium is guided by the first core and the nonmagnetic material, and the sliding motion is appropriately performed.
[0013]
【Example】
2 and 3, a differential magnetic head according to an embodiment of the present invention is mounted on, for example, a banknote identification device (not shown), and includes a first core 21 having a rectangular bar shape. . A first coil 31 as an exciting coil is wound around the core 21, and the coil 31 is connected to an AC power supply 41. The second and third cores 22 and 23 are disposed on both sides of the first core 21, respectively. The first to third cores 21 to 23 are made of, for example, a high-density ferrite material.
[0014]
On the side on which the recording medium (not shown) slides relative to the magnetic head (hereinafter referred to as the sliding side), the second core 22 has a sliding side end 22 a and a corresponding end 21 a of the first core 21. A first gap is defined between one side and a non-magnetic material 51 made of glass or the like. The second core 22 is joined to one side of the corresponding end 21b of the first core 21 at the anti-sliding side end 22b.
[0015]
Similarly, a second gap filled with the nonmagnetic material 52 is defined between the sliding side end 23a of the third core 23 and the other side of the corresponding end 21a of the first core 21. Further, the anti-sliding side end 23 b of the third core 23 is joined to the other side of the corresponding end 21 b of the first core 21. The second gap is positioned on the anti-sliding side of the first gap in the axial direction of the first core 21. The deviation distance L of the second air gap with respect to the first air gap in the axial direction of the first core 21 is set to a value not less than the size of each air gap, for example, not less than 0.5 mm.
[0016]
The second core 22 and the third core 23 have the same outer dimensions. For this reason, the first core 21 has a length between the second and third cores 22 and 23 and the above-described deviation distance L. It has a length equal to the sum. Reference numeral 53 indicates a nonmagnetic material disposed on the sliding side of the third core 23, and the nonmagnetic material 53 has a shape corresponding to the sliding side portion of the second core 22, preferably, It is formed in a shape that is symmetrical with the sliding side portion of the second core 22 with respect to the axis of the first core 21. As described above, by disposing the nonmagnetic material 53 on the sliding side, the recording medium is guided by the first core 21 and the nonmagnetic material 53, and the sliding movement of the recording medium with respect to the magnetic head can be performed appropriately. I am doing so.
[0017]
Further, a second coil 32 as a detection coil is wound around the second core 22. Similarly, a third coil 33 as a detection coil is wound around the third core 23. Both coils 32 and 33 are connected in series, and one end of the connected coil pair 32 and 33 is connected to the inverting input terminal 42a of the amplifier 42, and the other end of the coil pair 32 and 33 is the non-inverting input of the amplifier 42. It is connected to the terminal 42b. Reference numeral 42 c indicates an output terminal of the amplifier 42, and a differential output between the detection output by the second coil 32 and the detection output by the third coil 33 appears at the output terminal 42 c. That is, the second coil 32 and the third coil 33 are differentially connected to each other. Note that the turn ratio of the coils 32 and 33 is set to, for example, 102: 98. The output terminal 42 c is connected to the inverting input terminal 42 a via the resistor 43, and the non-inverting input terminal 42 b is grounded via the resistor 44.
[0018]
Hereinafter, the operation of the magnetic head having the above-described configuration will be described by taking as an example the case where the magnetic head is mounted on a bill validator (not shown).
During the operation of the bill validator, power is supplied from the AC power source 41 to the first coil 31, an AC bias current flows through the coil 31, and a bill (not shown) inserted into the bill validator is transported by the device. It is conveyed toward the magnetic head by an apparatus (not shown). Magnetic ink for banknote identification is applied to a predetermined portion of the banknote as a recording medium.
[0019]
Since the second and third coils 32 and 33 are connected differentially, the detection output by the second coil 32 and the detection output by the third coil 33 due to application of the AC bias current cancel each other. Is done.
Thereafter, the leading edge of the bill reaches the magnetic head, and the sliding movement of the bill with respect to the magnetic head is started. The banknote is guided by the first core 21 and the non-magnetic body 53, and therefore, the sliding movement of the banknote is properly performed.
[0020]
During this sliding movement, while the bill portion not coated with magnetic ink passes through the magnetic head, the external magnetic flux that is generated by the magnetic ink and leaks from the bill is passed through the first and second gaps. Will not be introduced. Eventually, only the induced current associated with the change in magnetic flux generated by the AC bias current is generated in the second and third coils 32 and 33. For the reasons described above, the second and second coils appearing at the output terminal 42c of the amplifier 42 are generated. The differential outputs of the three coils 32 and 33 are small values.
[0021]
Thereafter, when the magnetic ink application portion of the banknote faces the magnetic head, the external magnetic flux generated by the magnetic ink is introduced through the first gap, and the magnetic flux is slightly introduced through the second gap. Is done. This is because the first gap is close to the banknote and the second gap is spaced from the banknote. Therefore, when passing through the magnetic ink application portion, a large induced voltage is generated in the second coil 32 with a change in the combined magnetic flux of the magnetic flux due to the bias current and the external magnetic flux, and the magnetic flux due to the bias current and a small amount of external magnetic flux are generated. A small induced voltage is generated in the third coil 33 in accordance with the change in the combined magnetic flux. As a result, a large differential output appears at the amplifier output terminal 42c.
[0022]
The differential output is sequentially sent to a determination unit (not shown) of the banknote identification device, and the determination unit compares the differential output pattern with a predetermined pattern to determine the authenticity of the banknote.
The joint between each of the second and third cores 22 and 23 and the first core 21 exists on the anti-sliding side, and therefore there is no core joint on the sliding side. For this reason, during the sliding motion of the bill, sliding noise due to the core joint on the sliding side does not occur, and the sliding noise is greatly reduced.
[0023]
In addition, since both the first and second gaps exist on the sliding side and the second and third coils 32 and 33 are differentially connected, the electrical disturbance noise is the first and second noises. It is introduced through the air gap and is canceled in the second and third coils 32, 33. That is, the amount of noise corresponding to the differential output from the second and third coils 32 and 33 is small, and the magnetic head is excellent in the noise cancellation rate and thus the S / N ratio. Typically, compared with the proposed apparatus shown in FIG. 1, the sliding noise in the magnetic head of this embodiment is 1/10 or less, and the S / N ratio is 3 times or more.
[0024]
The present invention is not limited to the above embodiments, and can be variously modified.
For example, in the embodiments, the case where the magnetic head of the present invention is applied to a bill identifying apparatus has been described. However, the magnetic head of the present invention can be applied to various other magnetic recording apparatuses.
In order to reduce the size of the magnetic head, as shown in FIG. 4, the first core 21 having the same length as the second core 22 is used and the length of the third core 23 is set accordingly. Thus, the first to third cores may be flush with each other on the non-sliding side.
[0025]
【The invention's effect】
As described above, the second and third cores are arranged on both sides of the first core around which the first coil is wound, and the second and third cores are wound around the second and third cores, respectively. In a differential magnetic head in which a third coil is differentially connected, the present invention provides a first air gap between the first core and the second core on the sliding side and the first A second gap is provided between the first core and the third core, each of the second and third cores is joined to the first core on the non-sliding side, and the second gap is Since it is positioned on the anti-sliding side with respect to the first gap in the axial direction of the core, the core joint portion is arranged on the anti-sliding side, and this is caused by the core joint portion on the sliding side. Sliding noise can be removed, and sliding noise can be greatly reduced. In addition, since both the first and second gaps exist on the sliding side, the S / N ratio related to electrical disturbance noise can be improved.
[0026]
Further, in the preferred embodiment, since the non-magnetic material having a shape corresponding to the sliding side portion of the second core is disposed on the sliding side of the third core, the recording medium is appropriately slid with respect to the magnetic head. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic front view illustrating a conventional differential magnetic head.
FIG. 2 is a schematic front view showing a main part of a differential magnetic head according to an embodiment of the present invention.
3 is a schematic block circuit diagram showing a connection between a coil and peripheral elements of the magnetic head shown in FIG. 2; FIG.
4 is a schematic front view showing a modification of the magnetic head shown in FIG. 2. FIG.
[Explanation of symbols]
21 1st core 22 2nd core 23 3rd core 31 1st coil 32 2nd coil 33 3rd coil 41 AC power supply 42 Amplifier 51, 52, 53 Nonmagnetic material

Claims (2)

The second and third coils are wound around the second and third cores, respectively, and the second and third cores are arranged on both sides of the first core around which the first coil is wound. In the differential magnetic head formed by differentially connecting
On the sliding side, a first gap is provided between the first core and the second core, and a second gap is provided between the first core and the third core. Each of the second and third cores is joined to the first core on the moving side, and the second gap is more slid than the first gap in the axial direction of the first core. A differential magnetic head characterized by being positioned on the side. 2. The differential magnetic head according to claim 1, wherein a nonmagnetic material having a shape corresponding to the sliding side portion of the second core is arranged on the sliding side of the third core.

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