WO2012137544A1

WO2012137544A1 - Magnetic sensor

Info

Publication number: WO2012137544A1
Application number: PCT/JP2012/053746
Authority: WO
Inventors: 濱口大輔
Original assignee: 株式会社村田製作所
Priority date: 2011-04-01
Filing date: 2012-02-17
Publication date: 2012-10-11

Abstract

A plurality of magnetic resistance element mounting sections (13i, 13j, 13k) etc., are formed on the top section of a case (1). Magnet holding sections (14) that house a plurality of magnets (5) are formed in the bottom section of the case (1) and each of the magnets (5) are housed in these magnet holding sections (14). Part of the lower surface of a magnetic resistance element (2j) is joined by an adhesive layer (7) to the magnetic resistance element mounting section (13j) corresponding to the position at a section facing the magnet (5) and the magnet (5). Nearly the entire lower surface of magnetic resistance elements (2i, 2k) are joined by the adhesive layer (7) to the magnetic resistance element mounting sections (13i, 13k) etc., not corresponding to the position at a section facing the magnet (5) and the magnet (5). As a result, a magnetic sensor is configured that is unlikely to generate piezoelectric noise even if the amplitude of bending vibration caused by sympathetic vibration in conjunction with the lengthening of the magnetic sensor increases.

Description

Magnetic sensor

The present invention relates to a long magnetic sensor that detects a magnetic pattern printed on, for example, banknotes.

Patent Document 1 is disclosed as a magnetic sensor for discriminating an object to be detected such as a bill or a security printed with a predetermined pattern with magnetic ink or the like.

Japanese Patent No. 3879777

Depending on the installation environment of the long magnetic sensor, mechanical vibration is applied to the magnetic sensor from the outside. For example, vibrations of a motor provided in the ATM and a mechanism driven by the motor are propagated to the magnetic sensor. The longer the magnetic sensor is, the lower the self-resonant frequency becomes, so the magnetic sensor tends to resonate with vibrations caused by the motor and mechanism. And the vibration amplitude tends to increase with the increase in length.

Since the long magnetic sensor needs to be held in the apparatus without obstructing the conveyance path of bills or the like, both ends of the magnetic sensor are often held by holding parts in the apparatus. At that time, the vibration in the fundamental wave mode is a bending vibration in which both ends of the long magnetic sensor are fixed ends.

Here, the basic configuration of the long magnetic sensor described in Patent Document 1 is shown in FIG. 1 in a partial sectional view. FIG. 1A shows a state in which no bending stress is applied to the long magnetic sensor. A plurality of magnetoresistive elements 2, a plurality of magnets 5 that apply a magnetic field to the magnetic sensing portions of the plurality of magnetoresistive elements 2, and a case 1 that holds the magnetoresistive elements 2 and the magnets 5 are provided. Yes. The plurality of magnets 5 and the plurality of magnets 5 are arranged such that the position of the opposing portion between the magnets 5 of the plurality of magnets 5 is the center position of a certain magnetoresistive element 2 of the plurality of magnetoresistive elements 2. A resistance element 2 is arranged.

FIG. 1B is a partial sectional view exaggeratingly showing a state in which bending stress is applied to the long magnetic sensor. Since the case 1 is a resin molded from a resin mold, the magnetoresistive element 2 and the magnet 5 are softer than the case 1. For this reason, when bending stress is applied to the long magnetic sensor, stress distortion occurs in the magnetoresistive element 2 corresponding to the facing portion (magnet joint position) between the magnet 5 and the magnet 5. The magnetoresistive element 2 is made of an n-InSb material, InAs material, GaAs material, Ge material, or Si material having high electron mobility. Such a magnetoresistive element material has a piezoresistive effect. Therefore, when stress strain occurs in the magnetoresistive element 2, a signal due to the piezoresistive effect is superimposed, and this acts as noise (piezonoise).

If a relatively soft resin material is used for the case 1, the bending stress applied to the magnetoresistive element 2 can be reduced, but not only the distance accuracy between the magnetic sensor and the object to be detected is lowered, but also the amplitude of the bending vibration is increased. End up. Since the detection sensitivity of the magnetic body is affected by the square of the distance between the magnetic sensing portion of each magnetoresistive element of the magnetic sensor and the magnetic body to be detected, a flexible material cannot be used for the case of the magnetic sensor.

Further, if the position of the facing portion between the magnet 5 and the magnet 5 is matched with the position of the facing portion between the magnetoresistive element 2 and the magnetoresistive element 2, the stress strain applied to the magnetoresistive element 2 is reduced. However, since the opposing portion of the magnetoresistive element 2 and the magnetoresistive element 2 naturally has no magnetic sensitive part (disconnected), the detection sensitivity of the magnetic material tends to decrease, and the magnet 5 and the magnet 5 Since the opposing part has a tendency that the detection sensitivity of the magnetic material is lowered due to the small magnetic flux density, both sensitivity reduction factors overlap. Therefore, it is difficult to adopt a structure in which the magnet facing portion overlaps the magnetoresistive element facing portion.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a magnetic sensor that solves the above-described piezo noise problem caused by bending vibration accompanying the increase in length of the magnetic sensor.

The magnetic sensor of the present invention includes a plurality of magnetoresistive elements, a plurality of magnets, and a case for holding the plurality of magnetoresistive elements and the plurality of magnets, and the case includes the plurality of magnetoresistive elements in series. And a magnet holding part for holding the plurality of magnets in series so as to apply a magnetic field to the magnetoresistive element placed on the magnetoresistive element placing part. In the magnetic sensor,
The plurality of magnets and the plurality of magnetoresistive elements include a magnet facing portion, which is a facing portion between the magnets of the plurality of magnets, and a magnetoresistive element and a magnetoresistive element of the plurality of magnetoresistive elements. Are arranged so as to correspond to positions other than the opposite part of
The magnetoresistive element is bonded to the case through an adhesive layer at a part of the surface of the magnetoresistive element facing the case.

According to the present invention, a magnetic sensor in which piezo noise associated therewith is reduced even when bending vibration occurs in the magnetic sensor can be configured.

FIG. 1A is a cross-sectional view of a conventional general long type magnetic sensor in a state where no bending stress is applied. FIG. 1B is a partial cross-sectional view in a state where bending stress is applied to the long magnetic sensor. 2A is an external perspective view in the middle of attaching the cover of the long magnetic sensor 201 according to the first embodiment, and FIG. 2B is an external perspective view in a state in which the cover is attached. FIG. 3 is a front view showing a structure in which the magnetic sensor 201 is incorporated into an installation destination device. FIG. 4A is a partial plan view of the magnetic sensor 201 according to the first embodiment with the cover removed. FIG. 4B is a partial view of the central longitudinal cross section of the magnetic sensor 201 in the longitudinal direction. FIG. 5 is a partial perspective view of the case 1 as viewed from the magnet holding portion 14 side. FIG. 6 shows a comparative example of piezo noise generated between the conventional magnetic sensor and the magnetic sensor 201 according to the first embodiment of the present invention. FIG. 7A is a partial plan view of the magnetic sensor 202 of the second embodiment with the cover removed. FIG. 7B is a partial view of the central longitudinal cross section of the magnetic sensor 202 in the longitudinal direction. FIG. 8A is a partial plan view of the magnetic sensor 203 according to the third embodiment with the cover removed. FIG. 8B is a partial view of a central longitudinal section in the longitudinal direction of the magnetic sensor 203.

<< First Embodiment >>
2A is an external perspective view in the middle of attaching the cover of the long magnetic sensor 201 according to the first embodiment, and FIG. 2B is an external perspective view in a state in which the cover is attached. The case 1 made of synthetic resin has

magnetoresistive elements

2a, 2b, 2c, 2d. A terminal pin 6 that conducts to the plurality of

magnetoresistive elements

2a, 2b, 2c, 2d,. Claw engaging grooves 3 are provided on both sides of the case 1 along the longitudinal direction.

The cover 4 made of metal is provided with a cover fixing claw portion that engages with the claw portion engagement groove 3 of the case. As shown, a cover 4 is covered on top of the case 1. The object to be detected 100 is conveyed in a direction substantially perpendicular to the longitudinal direction of the long magnetic sensor 201 as indicated by an arrow in the figure.

FIG. 3 is a front view showing a structure in which the magnetic sensor 201 is incorporated into an installation destination device. The magnetic sensor 201 is mounted on the circuit board 110 via the terminal pins 6. The circuit board 110 is held by a holder 120, and the holder 120 is fixed to a frame or the like of an installation destination device.

FIG. 4A is a partial plan view of the magnetic sensor 201 of the first embodiment. However, it is shown with the cover removed. FIG. 4B is a partial view of the central longitudinal cross section of the magnetic sensor 201 in the longitudinal direction.

FIG. 5 is a partial perspective view of the case 1 as viewed from the magnet holding portion 14 side. The magnet holding part 14 is a recess formed in the lower part of the case 1, and the magnet 5 is accommodated in the magnet holding part 14.

As shown in FIGS. 4 (A) and 4 (B), the case 1 is resin-molded. A plurality of magnetoresistive

element mounting portions

13i, 13j, 13k and the like are formed on the upper portion of the case 1. Magnets 5 are housed in a plurality of magnet holders 14 formed in the lower part of case 1. The magnet 5 is filled with a filler 8 such as an epoxy resin so that the magnet 5 is embedded in the magnet holding portion 14.

The

magnetoresistive elements

2i, 2j, 2k and the like are bonded to the lower surfaces of the magnetoresistive

element mounting portions

13i, 13j, 13k and the like via the adhesive layer 7. A part of the lower surface of the magnetoresistive element 2j is joined by an adhesive layer 7 to the magnetoresistive element mounting portion 13j corresponding to the position of the facing portion between the magnet 5 and the magnet 5. Nearly the entire lower surface of the

magnetoresistive elements

2i, 2k is joined by an adhesive layer 7 to the magnetoresistive

element mounting portions

13i, 13k, etc. that do not correspond to the positions of the opposing portions of the

magnets

5 and 5.

The

magnetoresistive elements

2i, 2j, 2k, etc. are bonded to the magnetoresistive element mounting portion on the opposite side of the magnetosensitive element so that the magnetosensitive part is on the upper surface side. As shown in FIG. 2A, the electrode pad of the magnetoresistive element is joined to the inner lead of the lead frame, and the outer lead of the lead frame is thermocompression bonded to the terminal pin 6, but in FIG. Illustration of these leads is omitted.

The magnetoresistive element that is not at the position of the facing portion between the magnet 5 and the magnet 5 and the height of the magnetosensitive element 2j joined to the magnetoresistive element mounting portion 13j corresponding to the facing portion between the magnet 5 and the magnet 5 The thickness of the adhesive layer 7 is determined so that the heights of the magnetically sensitive portions such as the

magnetoresistive elements

2i and 2k joined to the

placement portions

13i and 13k are uniform. For example, when the adhesive is applied to the magnetoresistive element mounting portion with a dispenser or the like, the viscosity of the adhesive and the coating amount are determined, and the magnetoresistive element is mounted on the magnetoresistive element mounting portion. The spread area of the adhesive on the lower surface of the magnetoresistive element and the thickness of the adhesive layer are determined. Furthermore, the spread amount of the adhesive layer and the thickness of the adhesive layer may be adjusted by the pressing force of the magnetoresistive element on the magnetoresistive element mounting portion.

As described above, the magnetoresistive element 2j joined to the magnetoresistive element mounting portion 13j of the case 1 corresponding to the position of the facing portion between the magnet 5 and the magnet 5 is a part of the lower surface of the magnetoresistive element mounting portion 13j. 1B, even when bending stress as shown in FIG. 1B is applied to the magnetic sensor 201, the bending moment to the magnetoresistive element 2j is reduced. That is, the flat state is maintained with almost no influence of bending at the position of the facing portion between the magnet 5 and the magnet 5 of the case 1. This suppresses the generation of piezo noise.

Here, an example of the piezo noise reduction effect according to this embodiment will be shown.
FIG. 6 shows a comparative example of piezo noise generated between the conventional magnetic sensor and the magnetic sensor 201 according to the first embodiment of the present invention. In FIG. 6, Ch.A (before) is piezo noise generated in the channel A of the conventional magnetic sensor, and Ch.B (before) is piezo noise generated in the channel B of the conventional magnetic sensor. Ch.A (after) is piezo noise generated in the channel A of the magnetic sensor 201 of the first embodiment, and Ch.B (after) is piezo noise generated in the channel B of the magnetic sensor 201 of the first embodiment. is there. Here, the channel A corresponds to the sixth magnetoresistive element corresponding to the position of the opposing portion of the magnet 5 among the 18 channels (18 magnetoresistive elements) in total. The channel B corresponds to the eleventh magnetoresistive element corresponding to the position of another facing portion between the magnet 5 and the magnet 5.

In FIG. 6, the horizontal axis represents frequency and the vertical axis represents piezo noise voltage. Both are relative value scales. As shown in FIG. 6, since a mountain shape in which piezo noise rises at a predetermined frequency is drawn, it can be seen that bending vibration is generated at the resonance frequency, and large piezo noise is generated at this resonance frequency. Compared to the magnetic sensor having the conventional structure, the piezo noise can be reduced to about 1/6 or less in the magnetic sensor 201 of the first embodiment.

<< Second Embodiment >>
FIG. 7A is a partial plan view of the magnetic sensor 202 of the second embodiment. However, it is shown with the cover removed. FIG. 7B is a partial view of the central longitudinal cross section of the magnetic sensor 202 in the longitudinal direction.

Case 1 is resin molded. A plurality of magnetoresistive

element mounting portions

13i, 13j, 13k and the like are formed on the upper portion of the case 1. The lower surfaces of these magnetoresistive

element mounting portions

13i, 13j, 13k and the like are magnetoresistive element facing surfaces. In addition, magnet holders 14 that store a plurality of magnets 5 are formed in the lower part of the case 1, and the magnets 5 are stored in these magnet holders 14, respectively. In the magnet holding part 14, the periphery of the magnet 5 is filled with a filler 8 such as an epoxy resin.

What is different from the first embodiment is an adhesive layer 9 for the magnetoresistive element 2j. In this second embodiment, an adhesive in which beads defining the thickness of the adhesive layer are mixed is applied to the magnetoresistive element placement portion 13j of the case 1 corresponding to the position of the facing portion between the magnet 5 and the magnet 5. is doing.

Apply the adhesive so that the

magnetoresistive elements

2i, 2k, etc. joined to the magnetoresistive

element mounting parts

13i, 13k, etc., which are not located at the positions where the

magnets

5 and 5 are opposed to each other, are wetted with the adhesive. Therefore, the control is relatively easy. On the other hand, since the thickness of the adhesive layer that joins the magnetoresistive element 2j to the magnetoresistive element mounting portion 13j is relatively small, the thickness of the adhesive layer can be controlled only with a normal adhesive. May be difficult. As the beads, for example, silica beads having a particle diameter of 150 μm to 200 μm can be used. For example, a mixture of the beads with a Si-based adhesive at a certain ratio is used. As a result, the thickness of the adhesive layer 9 is defined to be approximately equal to the particle size of the beads.

Accordingly, the thickness of the adhesive layer such as the

magnetoresistive elements

2i and 2k on the magnetoresistive

element mounting portions

13i and 13k that are not located at the position where the magnet 5 and the magnet 5 face each other is adjusted by, for example, the amount of adhesive applied. The thickness of the adhesive layer of the magnetoresistive element 2j on the magnetoresistive element mounting portion 13j corresponding to the position of the facing portion between the magnet 5 and the magnet 5 may be adjusted by the particle size of the beads to be mixed.
In this way, the height of the magnetic sensing part of each magnetoresistive element can be made uniform.

Of course, the adhesive applied to the magnetoresistive

element mounting portions

13i, 13k, etc., which is not located at the position where the magnet 5 and the magnet 5 face each other, may be an adhesive mixed with beads defining the thickness of the adhesive layer. Good. Further, the particle size and ratio of the beads to be mixed may be different between the adhesive that limits the application range and the adhesive that is applied to the entire surface.

It is confirmed that the piezo noise reduction effect of the magnetic sensor 202 of the second embodiment is substantially the same as that of the magnetic sensor 201 of the first embodiment.

<< Third Embodiment >>
FIG. 8A is a partial plan view of the magnetic sensor 203 of the third embodiment. However, it is shown with the cover removed. FIG. 8B is a partial view of a central longitudinal section in the longitudinal direction of the magnetic sensor 203. The difference from the first and second embodiments is a configuration for increasing the thickness of the adhesive layer provided on the magnetoresistive element mounting portion 13j of the case 1 corresponding to the position of the facing portion between the magnet 5 and the magnet 5. is there. That is, the engraved portion 12 is formed on almost the entire surface of the magnetoresistive element mounting portion 13j. Therefore, in the state where the thickness of the adhesive layer provided on the magnetoresistive element mounting portion 13j is thicker than the thickness of the adhesive layer provided on the other magnetoresistive

element mounting portions

13i, 13k, etc. The height of can be made constant.

Since the thickness of the adhesive layer 7 provided on the magnetoresistive element mounting portion 13j corresponding to the position of the facing portion between the magnet 5 and the magnet 5 is relatively thick, the bonding strength of the magnetoresistive element 2j with a limited application area Can be maintained sufficiently. In addition, since the elasticity of the adhesive layer 7 acts effectively, stress strain on the magnetoresistive element 2j when bending stress is applied to the magnetic sensor is further reduced.

The adhesive used for joining the magnetoresistive element 2j is the bead mixed adhesive shown in the second embodiment, and the thickness of the adhesive layer 7 provided on the magnetoresistive element mounting portion 13j is defined by the particle size of the beads. You may do it.

It has been confirmed that the piezo noise reduction effect of the magnetic sensor 203 of the third embodiment is substantially the same as that of the magnetic sensor 201 of the first embodiment.

<< Other Embodiments >>
In each embodiment shown above, the example which restrict | limited the application quantity and application | coating range of the adhesive agent with respect to the magnetoresistive element mounting part 13j corresponding to the position of the opposing part of the magnet 5 of the case 1 and the magnet 5 is shown. However, the amount and range of application of the adhesive may be limited for the magnetoresistive

element mounting portions

13i and 13k that are hardly stressed by the bending of the magnetic sensor. For example, the magnetoresistive elements may be joined to all the magnetoresistive element mounting portions only at the central portion thereof via an adhesive layer.

DESCRIPTION OF SYMBOLS 1 ... Case 2 ...

Magnetoresistive element

2a, 2b, 2c, 2d ...

Magnetoresistive element

2i, 2j, 2k ... Magnetoresistive element 3 ... Claw part engaging groove 4 ... Cover 5 ... Magnet 6 ...

Terminal pin

7, 9 ... Adhesion Agent layer 8 ...

Fillers

13i, 13j, 13k ... Magnetoresistive element mounting portion 14 ... Magnet holder 100 ... Object 110 ... Circuit board 120 ... Holders 201-203 ... Magnetic sensor

Claims

A plurality of magnetoresistive elements, a plurality of magnets, and a case for holding the plurality of magnetoresistive elements and the plurality of magnets, wherein the case mounts the plurality of magnetoresistive elements in series. In the magnetic sensor having a magnet holding unit for holding the plurality of magnets in series so as to apply a magnetic field to the mounting unit and the magnetoresistive element mounted on the magnetoresistive element mounting unit,
The plurality of magnets and the plurality of magnetoresistive elements include a magnet facing portion, which is a facing portion between the magnets of the plurality of magnets, and a magnetoresistive element and a magnetoresistive element of the plurality of magnetoresistive elements. Are arranged so as to correspond to positions other than the opposite part of
A magnetic sensor, wherein the magnetoresistive element is joined to the case through an adhesive layer at a part of a surface of the magnetoresistive element facing the case.
2. The magnetic sensor according to claim 1, wherein the adhesive layer is made of an adhesive in which beads defining the thickness of the adhesive layer are mixed.
The thickness of the adhesive layer which joins the said magnetoresistive element with respect to the said magnetoresistive element mounting part corresponding to the position of the said magnet opposing part is thicker than the thickness of the adhesive bond layer of another magnetoresistive element. 2. The magnetic sensor according to 2.
The magnetic sensor according to claim 3, wherein a surface of the magnetoresistive element mounting portion corresponding to a position of the magnet facing portion is lower than a surface of another magnetoresistive element mounting portion.