JP3266587B2 - Magnetic detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic detector for detecting that a magnetic substance such as a needle is mixed in an article.

[0002]

2. Description of the Related Art Needles, nails, stapler needles, and the like are mixed into products during the manufacturing process, transportation, and over-the-counter sales of products such as foods, and there are many cases in which consumers see very dangerous eyes. . For this reason, the manufacturer / distributor checks the presence or absence of magnetic material such as needles by passing the product through a tunnel-type magnetic detector, and sends only products that have been confirmed to be free to consumers. providing.

Conventionally, as a tunnel type magnetic detector,
JP-A-10-88469 and JP-A-10-121
No. 370 is known. They are,
As shown in FIG. 14, two magnetic pole surfaces 2 and 3 having different polarities are opposed to each other across a passage 1 of an article, and a magnetic pole surface generated when an article containing a magnetic material enters the passage 1. The increase of the magnetic flux is detected by the search coil 4 arranged on one of the magnetic pole surfaces. In order to prevent the magnetic flux from leaking to the outside, the ferromagnetic rectangular frame 5 surrounds the passage.

In addition, as another method for detecting a magnetic material, a pulse current is applied to a sensor coil facing a magnetic metal, and this current is cut off by an eddy current flowing in the magnetic metal. Detecting the presence or absence of the presence of the reflected waveform by utilizing the change in the transient response characteristic of the reflected waveform (Japanese Patent Laid-Open No. Hei 5-232245); For detecting rotation by detecting the tooth tip with a magnetic detector (JP-A-8-320327)
There is.

[0005]

The above-mentioned structure in which the two magnetic pole surfaces 2 and 3 having different polarities are opposed to each other to form a passage for an article cannot be used unless the distance between the magnetic pole surfaces 2 and 3 is reduced. was there. This is because, as shown in FIG. 15, when the magnetic body 6 is located near the magnetic pole surfaces 2 and 3, the magnetic body 6 is strongly magnetized, and the magnetic flux flowing therethrough increases. While a sufficiently large change in magnetic flux can be detected, as shown in FIG. 16, when the magnetic body 6 is at a position away from the magnetic pole surfaces 2 and 3, the magnetic flux flowing through this magnetic body is small, and the search coil 4 This is because the ratio of the magnetic flux detected by the above to the total amount becomes extremely small, making detection difficult.

Accordingly, the height of the passage of the article is reduced, and the article can be used for inspection of articles having a small height such as sewing products, but cannot be used for inspection of articles having a large height such as bread. Was.

It is conceivable to increase the interval between the magnetic pole faces 2 and 3 by increasing the amplification degree of the search coil output to increase the detection sensitivity. In addition to extreme differences in detection sensitivity, it also responds to changes in magnetic flux and geomagnetism leaking slightly from the magnetic detector, and the magnetic material near the magnetic detector The movement of watches, coins, etc. carried by staff members will cause malfunctions,
Stable operation is not possible.

Further, even if the distance between the magnetic pole faces is reduced, as shown in FIG. 17, when a thin magnetic body 6 such as a needle passes in a posture parallel to the magnetic pole faces 2 and 3, the length in the magnetic field direction becomes longer. However, there is also a problem that the amount of change in magnetic flux is so small that detection becomes difficult.

[0009] The above-described sensor for detecting magnetic metal by passing a pulse-like current through the sensor coil can be used only for a narrow detection area, and a permanent magnet and a magnetic detector are combined to form a gear. Since rotation detection uses the condition that the magnetic material is at a close distance,
These cannot be applied to a magnetic detector of a tunnel type in which the height and width of the passage of the article are large.

In view of the above circumstances, the present invention can stably detect a magnetic substance mixed in a large article without increasing the degree of amplification of the detector output, regardless of the position of the small magnetic substance. An object of the present invention is to provide a tunnel-type magnetic detector.

[0011]

According to a first aspect of the present invention, there is provided a magnetic detector having a substantially uniform strength by enclosing substantially the entire circumference with magnetic pole surfaces of the same polarity having a width corresponding to the facing distance. A permanent magnet for forming a passage that forms a passage for an article filled with magnetism, and an end face of the permanent magnet facing the opening of the passage with a magnetic pole surface having a polarity opposite to that of the magnetic pole surrounding the passage. are distributed in position, the pole face opposite to the magnetic pole surface of the opposite polarity, the pole faces of the pole face opposite the permanent magnet, a plurality of magnetic flux leakage at the bonded compact magnetic binder ferromagnetic A focusing permanent magnet and a leakage magnetic flux concentrating device, which are arranged near the leakage magnetic flux concentrating permanent magnet and leak from an opening of a passage.
A plurality of magnetic detectors that convert a change in magnetic flux focused on a permanent magnet for use into an electric signal, and a detection circuit that detects a magnetic body by comparing the output of each magnetic detector with a predetermined threshold value. It is characterized by having.

According to a second aspect of the present invention, in the magnetic detector according to the first aspect, in order to prevent magnetic leakage to the outside, a permanent magnet for focusing a leakage magnetic flux is provided on a passage of an article. It is characterized by being arranged at both the entrance and the exit.

According to a third aspect of the present invention, in the magnetic detector according to the first or second aspect, the ferromagnetic magnetic coupling material includes a permanent magnet for forming a passage and a magnetic flux for focusing a leakage magnetic flux. It is characterized in that the permanent magnet is formed in a cylindrical shape surrounding it from the outside, and a magnetic shielding plate made of a ferromagnetic material is arranged on the outer periphery of the magnetic coupling material with a non-magnetic material having a predetermined thickness interposed therebetween. .

According to a fourth aspect of the present invention, there is provided the magnetic detector according to any one of the first to third aspects, wherein the magnetic flux detector includes a permanent magnet for converging the leakage magnetic flux and a magnetic pole having a polarity opposite to that of the permanent magnet. An antenna disposed at a predetermined distance away from the opening, and a ferromagnetic magnetic induction material that extends from the antenna and forms a magnetic gap for disposing a magnetic detector between the magnetic coupling material, The magnetic flux flowing from the path opening through the antenna, the magnetic induction material, and the magnetic gap toward the magnetic coupling material, and the magnetic flux flowing from the permanent magnet for focusing the leakage magnetic flux through the magnetic coupling material, the magnetic gap, and the antenna , The change in magnetic flux due to the magnetic material to be detected flows in the magnetic gap at a large ratio.

[0015]

1 and 2 show an embodiment of a magnetic detector 7 according to the present invention. FIG. 1 is a sectional view taken along the line AA in FIG. In the figure, reference numeral 8 denotes four passageway permanent magnets, which are arranged so that the magnetic pole surfaces of the same polarity N face inward to form a rectangular frame, thereby forming a passageway 9 for articles. Numeral 10 is a small permanent magnet for condensing leakage magnetic flux, and four permanent magnets are arranged at the entrance and the exit at positions facing the center of the opening edge of the passage 9 (the end face of the permanent magnet 8 for forming the passage). Reference numeral 11 denotes a magnetic detector, which is disposed at the exit of the passage 9.
A total of four small magnets are arranged in the vicinity of the small permanent magnets 10 for focusing the leakage magnetic flux. The output of the magnetic detector 11 is compared with a predetermined threshold value by a detection circuit 12 as shown in FIG. Numeral 13 denotes a magnetic coupling material of a ferromagnetic material, which is formed of a ferromagnetic material such as iron in a rectangular frame shape, and on the inner surface thereof, the permanent magnet 8 for forming the passage and the permanent magnet 10 for focusing the leakage magnetic flux are attached. These are magnetically coupled. Numeral 14 denotes a non-magnetic spacer member which is used to attach a rectangular cylindrical magnetic shielding plate 15 to the outside of the rectangular frame-shaped magnetic coupling material 13 at a constant interval.

Next, each component of the magnetic detector 7 and its operation will be described in detail. The four permanent magnets 8 for forming the passage are flat plate-like members that surround the passage 9 of the article from four sides, and are surrounded by magnetic pole surfaces of the same polarity having a width corresponding to the facing distance so that the article can pass therethrough. The inside of the road is filled with magnetism of substantially uniform strength. This means that a space having a substantially uniform magnetic potential in the cross-sectional direction is formed in the passage. The strength of the magnetic field at a position away from the center of the pole face of the permanent magnet in the vertical direction is substantially uniform until the pole is separated by the short side L of the pole face, and when further away, it attenuates in inverse proportion to the square of the distance. There is a property that. Therefore, in order to fill the magnetic poles with substantially uniform strength as described above while maximizing the distance between the opposing magnetic pole faces, the width L of the short side of the permanent magnet 8 is reduced as shown in FIGS. Is set to half of the facing distance 2L between the pole faces.

The permanent magnet 10 for focusing the leakage magnetic flux focuses the magnetic flux to be leaked to the outside from the opening of the passage 9 surrounded by the same polarity magnetic pole surfaces of the permanent magnet 8 for forming the passage. As shown in FIG. 5 (a), the light is intensively passed through a space close to the opening, where a strong magnetic field is formed. When the permanent magnet 10 is not provided, as shown in FIG. 5 (b), a large arc is drawn from the opening of the passage 9 to the outside. The permanent magnet 10 for focusing the leakage magnetic flux has two functions in the present invention.

One is that a substantially uniform and high-intensity magnetic field is formed with a short width as a detection area along the entire opening of the passage 9 so that the magnetic material has a large opening area. No. 9 is to strongly magnetize the magnetic material regardless of the position from which the magnetic field is generated, so as to give a large change to the magnetic field. As described above, a substantially uniform magnetic field can be formed along the entire surface of the opening by forming a space having a substantially uniform magnetic potential in the cross-sectional direction in the passage by the passage-forming permanent magnet 8. This is because the magnetic flux flowing out from this is concentrated on the permanent magnet 10 for focusing the leakage magnetic flux. Further, a magnetic field having a high strength can be formed because the magnetic flux is concentrated and flows in a space having a short width.

The other one is that the magnetic flux coming out of the opening of the passage 9 is focused toward the permanent magnet 10 for focusing the leaked magnetic flux, thereby preventing magnetic leakage to the outside and detecting the magnetic substance. In other words, it is possible to eliminate a malfunction caused by a movement of a magnetic material in the vicinity of the device, a wristwatch or coins normally carried by an operator or the like, and to perform a stable operation.

The magnetic detector 11 is disposed near the leakage magnetic flux focusing permanent magnet 10 provided at the exit of the passage, and moved between the opening of the passage 9 and the leakage magnetic flux focusing magnet 10. Detects magnetic field disturbances that occur when an article contains a magnetic material. The permanent magnet 10 for focusing the leakage magnetic flux on the inlet side, which is not provided with the magnetic detector 11, is used only for preventing magnetic leakage to the outside.

This magnetic detector 11 uses, for example, an MR element, and together with a magnet 10 for focusing a leakage magnetic flux, FIG.
It is mounted as shown in FIG. In this figure, 1
3 is the magnetic coupling material, 10 is a magnet for focusing leakage magnetic flux, 1
Reference numeral 6 denotes a ferromagnetic antenna, and reference numeral 17 denotes a rectangular frame-shaped mounting member. The leakage magnetic flux focusing magnet 10 is fixed to the magnetic coupling material 13 with screws. The antenna 16 has a converging portion 16a having substantially the same shape as the magnetic pole surface of the leakage magnetic flux converging magnet 10, and a mounting portion 16b having a reduced width is formed at the tip of the converging portion 16a.

The mounting member 17 is made of a non-magnetic material such as aluminum. As shown in FIG. 7, on the upper surface, a female screw 17a for mounting the antenna and a male screw 18 which is a ferromagnetic magnetic induction material are provided. Female screw 17b for screwing
The lower surface is fixed to the magnetic coupling material 13 with screws. The antenna 16 can be fixed at a predetermined interval above the magnetic flux concentrating magnet 10 by fixing the antenna 16 with a screw on the mounting member 17. By adjusting the insertion amount, the interval of the magnetic gap formed by the tip of the male screw 18 facing the magnetic coupling material 13 can be adjusted.

As shown in FIG. 7, a notch 17c is formed in the lower portion of the side of the mounting member 17, and a magnetic detector M is formed.
The R element 11 is inserted from the notch 17C so as to enter between the magnetic gaps, and is fixed to the magnetic coupling material 13 with an adhesive. Since the MR element is formed by forming a pair of resistance patterns forming two sides of the bridge, the MR element is mounted so that one of the resistance patterns is located between the magnetic gaps. When an MR element is used, an absolute value corresponding to the magnetic field strength can be detected as its output. Therefore, when a search coil is used, it is possible to detect even a slow movement, unlike the case where the output changes depending on the moving speed. In addition, there is an advantage that it is not necessary to consider the relationship with the moving speed of the article when determining the presence or absence of the magnetic body.

The mounting structure described with reference to FIGS. 6 and 7 enables the minute magnetic detector 11 to detect a change in the magnetic field over the entire detection area having a greater extent than the small magnetic detector 11 and to detect the magnetic field change in the magnetic gap. The magnetic flux change caused by the magnetic material is caused to flow at a large ratio, and the magnetic detector 1
1 can be easily detected.

The fact that a small magnetic detector 11 can detect a change in the magnetic field in a detection area having a greater extent than that of the small magnetic detector 11 means that the size of the antenna 16 is substantially equal to the magnetic pole surface of the permanent magnet 10 for focusing the leakage magnetic flux. With the same size, all the magnetic flux flowing from the detection area passes through the antenna 16, and the magnetic potential of the antenna is equalized as a value including a change in magnetic flux due to the magnetic substance in the detection area. The guidance to the magnetic detector 11 means that all changes in magnetic flux due to the magnetic substance in the detection area can be detected.

As shown in FIG. 8, the magnetic flux change caused by the magnetic substance flowing in the magnetic gap at a large ratio is achieved by, as shown in FIG. Since the magnetic flux flowing toward the magnetic coupling material 13 through the magnetic gap and the magnetic flux flowing from the permanent magnet 10 for focusing the leakage magnetic flux through the magnetic coupling material 13, the magnetic gap, and the antenna 16 are in opposite directions,
This means that these steady components are canceled out and the magnetic flux change is made to flow through the magnetic gap at a large ratio. For example,
By adjusting the distance that the antenna 16 takes with respect to the opening of the passage 9 and the distance between the antenna 16 and the permanent magnet 10 for focusing the leakage magnetic flux, when the magnetic material does not enter or exit the opening of the passage 9, The magnetic field in the magnetic gap can be made substantially zero. As a result, it is possible to add only the magnetic field change due to the magnetic substance to be detected to the magnetic detector 11,
The output of the magnetic detector 11 corresponds only to the magnetic change, and signal processing can be easily performed. In particular, M
When an R element is used, its mounting structure is suitable because its output represents the strength of the magnetic field itself. That is, it is possible to eliminate the magnetic saturation of the MR element and to effectively use the detection range.

The magnetic coupling material 13 serves as a support for mounting the permanent magnet 8 for forming the passage and the permanent magnet 10 for converging the leakage magnetic flux, and at the same time functions as a magnetic path for these. A sufficiently thick ferromagnetic material such as iron is used in order to increase the magnetic field strength of the detection area along the surface and reduce magnetic leakage to the surroundings.

The magnetic shielding plate 15 prevents magnetic leakage to the outside,
By further reducing the size of the detector, it is provided to minimize the possibility of malfunction due to passage of a magnetic body near the magnetic body detector or a watch or coins owned by an operator. In the above structure, the magnetic coupling material 13 and the permanent magnet 10 for concentrating the leakage magnetic flux have an effect of preventing the leakage of the magnetic flux to the outside, but this alone cannot completely eliminate the magnetic leakage to the outside. . Therefore, the magnetic shielding plate 15 is provided outside the magnetic coupling material 13 with a length slightly protruding from the opening end of the magnetic coupling material 13 while maintaining a constant interval by sandwiching the non-magnetic spacer member 14. This minimizes magnetic leakage to the outside. by this,
The leakage magnetic flux to the surroundings is drastically reduced, and even if a magnetic substance such as iron moves around, the influence on the internal magnetic field can be almost eliminated.

The detection circuit 12 in FIG. 3 for determining the presence or absence of a magnetic substance from the output of the magnetic detector 11 will be described. The detection circuit 12 individually detects the presence or absence of a magnetic substance by the determination unit 19 for each output of the four magnetic detectors 11 provided on the exit side of the passage 9, and detects any one of the magnetic substances. When the detection is output, a warning sound and lighting are issued for a fixed time thereafter. Since each determination unit 19 has a common circuit configuration, only one of them will be described.

The judging section 19 comprises a first-stage amplifier 20 for amplifying an output signal of the magnetic detector 11 which is a magnetic-sensitive element, a main amplifier 21 for further amplifying this output to a level capable of signal processing, and a signal direction. And an absolute value detection circuit 22 for detecting any increase or decrease in magnetic flux, and a comparator 23 for outputting a determination signal indicating the presence of a magnetic material when a predetermined threshold value is exceeded. The output of each judging unit is received by the OR circuit 24, and when one or more judging units 19 output with the presence of the magnetic material, the timer circuit 25 holds this for a certain period of time, and displays the display lamp 26 and buzzer 27. To inform.

Next, a specific example of the detection of a magnetic substance in the magnetic substance detector 7 will be described. FIG. 9 shows a state in which the magnetic body 6 in a vertical posture mixed into an article (not shown) exits from the opening of the passage 9. Since the magnetic flux is concentrated and flows in this detection area, the magnetic body 6 is strongly magnetized and a large magnetic flux flows, and the change in the magnetic flux flowing into the permanent magnet 10 for converging the leakage magnetic flux becomes large. 12 and detected with high sensitivity. FIG. 10 shows that the magnetic material 6 mixed into the article (not shown) from the opening of the passageway.
Shows the state when going out in the passing direction,
The magnetic body 6 is strongly magnetized as in FIG.
2 and detected with high sensitivity.

In the detection area, the inside of the passage 9 is maintained at a magnetic potential substantially equal to the magnetic pole surface of the permanent magnet 8 for forming the passage, and the total magnetic flux coming out of the opening of the passage 9 is focused on the leakage magnetic flux. It is formed by concentrating it on the permanent magnet 10 for use, thereby increasing the magnetic flux density in a space with a small width along the opening surface. Therefore, the magnetic body 6 is
The magnetic body 6 can be detected with high sensitivity without causing a variation in the detection output even if it goes out of any of the positions and is strongly magnetized, and even if the vertical and horizontal intervals of the passage 9 are widened. Further, since the sensitivity is high, even when a small magnetic body 6 is detected,
In particular, there is no need to increase the amplification of the detection output, and stable operation is possible.

The width of the detection area in the direction of passage corresponds to the width of the permanent magnet 10 for converging the leakage magnetic flux in the direction of passage. This will be described with reference to FIGS. 11 and 12. As shown in FIG. 11, when the magnetic body 6 in the vertical posture is moved from the opening in the passing direction, when the magnetic body 6 reaches the position s, as shown in FIG.
Output rises sharply, and after that, keeps a constant output, and then falls sharply at the position of e. The output when there is no permanent magnet 10 for focusing the leakage magnetic flux is gentle as shown by the dotted line in FIG. Such output is caused by the action of focusing the magnetic flux on the detection area having a fixed width by the leakage magnetic flux converging permanent magnet 10 and decreasing the magnetic flux density of other portions.

As described above, since a detection area having a clearly defined width is obtained, a switching effect in which a clear signal change appears when entering or exiting this area occurs, and the presence / absence of a magnetic substance can be reliably determined, and the detection accuracy can be improved. Can be improved. This means that the change can be detected even when a search coil whose detection sensitivity is proportional to the moving speed of the magnetic body is used as a magnetic detector, or even when the moving speed of the detected article is slow and slow.

In the present invention, as shown in FIG.
Even when the length in the up-down direction is short because the magnetic body 6 exits the opening while maintaining the horizontal posture orthogonal to the passing direction, the detection sensitivity is high as described above, and the magnetic body 6 When the magnetic detector 11 detects the magnetic field that is strongly magnetized when going in and out and is emitted by the magnetic body itself, the magnetic field can be detected only by lowering the sensitivity. However, in the case of this embodiment, since the permanent magnet 10 for focusing the leakage magnetic flux and the magnetic detector 11 are arranged on both the left and right sides of the passage, the length of the magnetic body 6 is large in that direction. 9 and FIG. 10 are obtained.

The above embodiment shows an example.
Other variations are possible. For example, the permanent magnets 8 for passing over the road form is one permanent magnet having any cross-sectional shape, such as rectangular tube and cylindrical, may be used by magnetizing the inner and outer surfaces in opposite polarity. As the permanent magnet 8, a general magnet such as a ferrite magnet can be used, and it is not necessary to use a particularly strong magnet .

The magnetic detector 11 can use a magnetic sensitive element other than the MR element, and can also use a coil. However, when a coil is used, its output is affected by the moving speed of the magnetic body, so that it is necessary to adjust the detection threshold in relation to the moving speed.

6 and 7 for attaching the magnetic detector 11.
It is not essential to use the antenna 16 and the attachment member 17 as described in the above. For example, the coil is wound with a size surrounding the magnetic pole surface of the permanent magnet 10 for focusing the leakage magnetic flux,
This may be configured to be arranged on the pole face of the permanent magnet 10 or the like. That is, the magnetic detector 11 may be attached as long as it can detect a change in magnetic flux flowing into the permanent magnet 10 for focusing the leakage magnetic flux.

[0039]

According to the invention of claim 1 of the present invention, a permanent magnet for forming a passageway forms a passageway inside which is filled with substantially uniform strength magnetism, and a magnetic flux coming out of the opening is formed. By focusing with a small-sized permanent magnet for converging leakage magnetic flux, which is dispersed and arranged close to the opening edge,
A detection area having a high magnetic flux density is formed in a space having a small width along the opening surface. Then, a magnetic detector arranged near the permanent magnet for converging the leakage magnetic flux is configured to detect a change in magnetic flux in the detection area due to the magnetic material.

For this reason, even if the opening surface is enlarged, the detection sensitivity of the magnetic substance can be kept substantially constant regardless of the position of the magnetic substance coming out of the opening, and even large articles can be inspected. be able to.

Further, by concentrating the magnetic flux in the detection area and strongly magnetizing the magnetic material, the detection sensitivity is extremely increased, and the width of the detection area is controlled by the width in the passing direction of the permanent magnet for focusing the leakage magnetic flux. Since it is clearly sectioned and has a switching effect that a clear signal change appears when entering and exiting this area, the presence / absence determination processing of the magnetic material can be performed reliably and easily. Therefore, even if an amplifier having a particularly high amplification degree is not used, detection of a small magnetic substance can be detected, malfunctions can be reduced, and highly accurate detection can be performed.

According to a second aspect of the present invention, a permanent magnet for converging leakage magnetic flux is disposed at both the entrance and the exit of a passage of an article, thereby detecting a magnetic flux heading outside from an opening of the passage. Enclosed in the area, minimizing magnetic leakage to the outside. As a result, it is possible to reduce malfunctions caused by the magnetic body around the magnetic detector.

According to the invention of claim 3 of the present invention, the magnetic flux is confined inside by a magnetic coupling material provided so as to surround the permanent magnet for forming the passage and the permanent magnet for converging the leakage magnetic flux, and furthermore, to the outside thereof. A magnetic flux to be leaked is surrounded by a magnetic shielding plate with a non-magnetic material having a predetermined thickness interposed therebetween, thereby drastically reducing the magnetic flux leaking to the outside. For this reason, the change in the magnetic field due to the magnetic material passing near the detector can be drastically reduced, and the malfunction can be further reduced, thereby enabling the stable operation.

According to a fourth aspect of the present invention, a minute magnetic detector is provided by an antenna spaced and arranged along a permanent magnet for focusing a leakage magnetic flux and a magnetic induction material extending from the antenna to form a magnetic gap. Therefore, it is possible to detect all magnetic field changes in a detection area having a larger spread than this, and to cause a large ratio of a magnetic flux change due to a magnetic substance to be detected to flow in a magnetic gap where a magnetic detector is arranged. Thus, saturation of the magnetic sensitive element can be prevented, and signal processing can be facilitated.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a magnetic detector according to an embodiment of the present invention.

FIG. 2 is a front view of the magnetic body detector of FIG. 1 as viewed from an opening side.

FIG. 3 is an electric circuit diagram showing a detection circuit of the magnetic detector of FIG. 1;

FIG. 4 is a view for explaining dimensions of a permanent magnet for forming a passage for filling the passage of an article with magnetism having substantially uniform strength in the structure of FIG. 1;

FIG. 5 is a diagram showing a distribution of magnetic flux leaking from an opening of a passageway in the structure of FIG. 1 in a case where a permanent magnet for condensing a leakage magnetic flux is present (a) and a case where it is not (b).

FIGS. 6A and 6B are a plan view and a side view showing an example of a mounting structure of a magnetic flux detector and a permanent magnet for focusing a leakage magnetic flux used in the structure of FIG. 1;

FIG. 7 is an enlarged perspective view showing a mounting member and a magnetic detector used in the mounting structure of FIG. 6; of

FIG. 8 is a magnetic circuit diagram for explaining the reason why the magnetic field of the magnetic gap can be made zero in the mounting structure of FIG. 6;

FIG. 9 is a side view for explaining a magnetic change when a needle, which is a magnetic substance to be detected, passes in a vertical posture in the structure of FIG. 1;

FIG. 10 is a side view for explaining a magnetic change when the needle, which is a magnetic substance to be detected, passes in a posture parallel to the passing direction in the structure of FIG. 1;

11 is a side view showing a start position s and an end position e of detection when a needle as a magnetic substance to be detected passes in a vertical posture in the structure of FIG. 1;

FIG. 12 is a signal waveform diagram showing an output change of a magnetic detector corresponding to the passage of the magnetic material shown in FIG. 11;

FIG. 13 is a side view showing a case where a needle, which is a magnetic substance to be detected, passes in a horizontal posture orthogonal to a passing direction in the structure of FIG. 1;

FIG. 14 is a front view of a conventional magnetic detector as viewed from an article entrance / exit side.

FIG. 15 is a front view showing a passage position of a magnetic material that can increase detection sensitivity in the magnetic material detector of FIG. 14;

FIG. 16 is a front view showing a passage position of a magnetic material whose detection sensitivity becomes low in the magnetic material detector of FIG. 14;

FIG. 17 is a front view showing a posture of a magnetic body whose detection sensitivity is low in the magnetic body detector of FIG. 14;

[Explanation of symbols]

 7 Magnetic Detector 8 Permanent Magnet for Forming Passageway 9 Passageway of Article 10 Permanent Magnet for Focusing Leakage Magnetic Flux 11 Magnetic Detector 12 Detector Circuit 13 Magnetic Coupling Material of Ferromagnetic Material 14 Nonmagnetic Material (Spacer) 15 Magnet Shielding plate 16 Antenna 18 Magnetic induction material (male screw)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01V 3/10 G01N 27/72 G01V 3/11

Claims (4)

(57) [Claims] A permanent magnet for forming a passage that forms a passage for an article filled with magnetism having substantially uniform strength by surrounding substantially the entire circumference with magnetic pole surfaces of the same polarity having a width corresponding to the facing distance. a magnet, toward the opening of the passage of the pole face opposite polarity pole faces surrounding the passage, are distributed in positions facing the end face of the permanent magnet pole faces opposite the pole face of the opposite polarity A plurality of small permanent magnets for converging leakage magnetic flux , which are coupled to a magnetic pole surface opposite to the magnetic pole surface of the permanent magnet with a magnetic coupling material of a ferromagnetic material; Arranged and passing
Leaks from the opening in the road to form a permanent magnet for focusing the leakage magnetic flux
It is characterized by comprising a plurality of magnetic detectors that convert a change in the magnetic flux to be focused into an electric signal, and a detection circuit that detects a magnetic body by comparing the output of each magnetic detector with a predetermined threshold value. Magnetic detector. 2. The magnetic body detector according to claim 1, wherein permanent magnets for focusing the leakage magnetic flux are arranged at both the entrance and the exit of the passage of the article. 3. A ferromagnetic magnetic coupling material having a cylindrical shape surrounding a permanent magnet for forming a passage and a permanent magnet for focusing a leakage magnetic flux from outside, and further comprising: 3. The magnetic body detector according to claim 1, wherein a magnetic shielding plate made of a ferromagnetic body is arranged so as to sandwich a non-magnetic body having a predetermined thickness. 4. An antenna disposed at a predetermined distance from an opposite polarity magnetic pole surface of a leakage magnetic flux converging permanent magnet toward an opening of a passage, and a magnetic coupling member extending from the antenna. A magnetic induction material of a ferromagnetic material forming a magnetic gap in which a magnetic detector is arranged, and a magnetic flux flowing from the opening of the passage through the antenna, the magnetic induction material, and the magnetic gap toward the magnetic coupling material, By canceling out the magnetic flux flowing through the magnetic coupling material, the magnetic gap, and the antenna from the leaked magnetic flux focusing permanent magnet, a large change in the magnetic flux due to the magnetic substance to be detected flows through the magnetic gap. The magnetic detector according to any one of claims 1 to 3, wherein: