JP2003167064A - Metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect foreign matter with high sensitivity without any influence of the material quality, shape and mix-in direction in a tested body. <P>SOLUTION: A coaxial detecting head 1 is provided on the same axis as the conveying direction of a tested body W, and an opposed type detecting head 2 is provided opposite to the conveying direction. When one of the detecting heads 1, 2 is driven at high frequency, the other is time sharing driven at low frequency. The respective detecting heads 1, 2 are respectively capable of detecting with high accuracy without any influence of direction, material quality and shape of metal M mixed in the tested body W because of parallel magnetic field between a transmit coil and a receiving coil and invariable direction of magnetic field intercepting the tested body W even if the tested body W is conveyed and moved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detector for detecting a metal substance mixed in an object to be inspected, and particularly, to detect the foreign substance mixed in the object to be inspected with high sensitivity regardless of the shape, direction and material. The present invention relates to a metal detector that can be detected.

[0002]

2. Description of the Related Art A metal detector determines whether or not a metal is mixed in an object to be inspected by detecting a change in the inspection magnetic field caused by the metal mixed in the object to be inspected. FIG. 8 is a diagram showing the detection principle of the detection head in the metal detector. As shown in FIG. 8, conventionally, a coaxial detection head 50 in which receiving coils 52 and 53 are arranged before and after a central transmitting coil 51 is used.

In the detection head 50, each coil 51,
In the inspection space S that is continuous inside 52 and 53, the induced voltages V1 having opposite phases to the receiving coils 52 and 53 that intersect the magnetic flux due to the alternating magnetic field of the central transmitting coil 51, respectively.
V2 is generated. The receiving coils 52 and 53 are arranged at the same distance with respect to the transmitting coil 51, and in the non-detection state in which the inspection object W is far from the inspection space S, the induced voltages V1 and V2 have the same magnitude and no difference. Becomes

For example, the object W to be inspected containing the metal M is
When it advances in the direction A in FIG. 8 and moves into the front receiving coil 52, the magnetic flux density in the receiving coil 52 increases, and conversely, the magnetic flux density in the receiving coil 53 decreases. Therefore, the induced voltage V1 of the receiving coil 52 becomes larger than the induced voltage V2 of the receiving coil 53. Next, when the inspected object W that has advanced to the inside of the receiving coil 53, the magnetic flux density inside the receiving coil 53 becomes larger than inside the receiving coil 52, so that the induced voltage V2 becomes larger than the induced voltage V1.
In this way, based on the change in the difference between the induced voltages V1 and V2 output from the detection head 50 (fluctuation of the magnetic field), is the metal M mixed in the inspection object W that has passed through the inspection space S? It can be determined whether or not.

In the coaxial detection head 50 used in the above-described conventional metal detector, for example, with respect to the needle-shaped or thin-plate-shaped metal M, the magnetic body which is the metal M of the above-mentioned shape is arranged substantially orthogonal to the magnetic flux. , Or when the non-magnetic material, which is the metal M having the above-mentioned shape, is mixed in the object W to be inspected in an arrangement along the magnetic flux, the induced voltage V1, V
The difference between 2 is small and the detection sensitivity drops. That is, the metal M mixed in the inspection object W may not be detected.

Therefore, there is a configuration shown in FIG.
-80162). A first coil 60 (60a, 60b), which is arranged in parallel with the moving direction of the object W to be inspected and in which two coils having opposite winding directions are connected in series, and an object to be inspected perpendicularly to the first coil 60a, 60b. A second coil 61 arranged so as to surround the movement path of the body W, and a second coil 61
Is placed on the opposite side of the first coil 60 with the first coil,
The second coil 60, 61 and the magnetic field generator 62 for generating a magnetic flux interlinking are provided.

When the object W to be inspected is moved, by combining the output voltages received by the first coil 60 and the second coil 61, a detection signal is detected when a foreign object such as a metal in the object W to be inspected is detected. Can be output. In this metal detector, the second coil 61 produces a magnetic flux in the horizontal direction, and the first coil 60 produces a magnetic flux in the vertical direction. Then, even if the magnetic body, which is the needle-shaped or thin-plate-shaped metal M, is arranged substantially orthogonal to the magnetic flux with respect to the magnetic flux of the second coil 61, the first coil 60 side follows the magnetic flux. Since the arrangement is adopted, the change in magnetic flux is increased and the detection sensitivity is improved.

Further, even if the needle-shaped or thin plate-shaped metal M, which is a non-magnetic material, is arranged along the magnetic flux with respect to the magnetic flux of the second coil 61, on the side of the first coil 60, Since they are arranged orthogonally to each other, the change in magnetic flux increases and the detection sensitivity becomes good. With such a configuration, when foreign matter such as a needle shape is mixed, it can be detected without being affected by the material and the posture thereof.

The configuration shown in FIG. 10 is provided with two sets of detection heads (Japanese Patent Laid-Open No. 2000-124862). As shown in the figure, a pair of detection heads 70 and 71 are arranged symmetrically with respect to the transport direction of the object W to be inspected at an angle α. With such a configuration, when foreign matter such as a needle shape is mixed, it can be detected without being affected by the material and the posture thereof.

[0010]

However, as shown in FIG.
In any of the ten configurations, when the object W to be inspected is conveyed, the direction of the magnetic field that shields the object W to be inspected fluctuates every moment depending on the conveyance position, so that there is a problem that the detection sensitivity of needle-shaped foreign matter is affected. Occurs. Further, in order to improve the sensitivity, it is necessary that the needle-shaped foreign matter has a relatively large difference (that is, the S / N ratio is large) with respect to the inspection object W when viewed at the reception level (voltage output). As described above, in the conventional configuration in which a plurality of detection heads with different angles are arranged as shown in FIGS. 9 and 10, there are differences in the material of the inspection object W, the shape of the foreign matter, the mixing direction, and the like. It was not possible to deal with this, and highly accurate foreign matter detection could not be performed.

In order to solve the above problems, the present invention provides a metal detector capable of detecting foreign matter with high sensitivity without being affected by the material, shape, direction of mixing of foreign matter into the body to be inspected and the like. It is intended to be provided.

[0012]

In order to achieve the above object, the metal detector according to claim 1 of the present invention is an object to be inspected W.
A transport path of a predetermined length for transporting the test object, a coaxial detection head 30 disposed coaxially with the transport direction of the device under test and having a pair of receiving coils 32 and 33 before and after the central transmission coil 31, and the transport The transmission coil 21 is arranged along the transport direction of the path and is provided on one side of the coaxial detection head.
The receiving coil 42 is provided on the other side of the coaxial detection head.
Opposing detection head 40 having 43 and generating a magnetic flux orthogonal to the magnetic flux of the coaxial detection head, a transmission coil of the coaxial detection head, and a drive signal of a predetermined frequency are respectively supplied to the transmission coil of the opposite detection head. Transmitter 1 to supply
0, 20 and a receiving coil of the coaxial type detecting head and a receiving coil of the facing type detecting head, respectively, for detecting the induced voltage of the receiving coil for each frequency of the drive signal to detect the presence or absence of metal. 31a and 31b, and the coaxial type detection head and the opposed type detection head are driven at high frequency and low frequency, respectively, and a total of four detection outputs are obtained to detect the metal M in the inspected body. .

Further, there is provided control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to the oscillators 10 and 20, and the control means is one of the coaxial type detection head and the opposed type detection head. When one is driven at a high frequency, the other is driven at a low frequency at the same time, and when one is driven at a low frequency, the other is driven at a high frequency at the same time to control the drive frequency in a time division manner.

Further, there is provided control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to the oscillators 10 and 20, and the control means drives the coaxial type detection head at high and low frequencies. At this time, the supply of the drive signal to the opposed detection head is stopped, and when the opposed detection head is driven at high frequency and low frequency, the supply of the drive signal to the coaxial detection head is stopped and driven. The frequency can be controlled by time division.

Further, there is provided control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to the oscillators 10 and 20, the control means performing high-frequency and low-frequency drive for the coaxial type detection head, A high frequency and a low frequency drive for the opposed detection head may be performed at separate timings to control the drive frequency in a time-division manner.

Further, there is provided control means for frequency-controlling the high-frequency and low-frequency drive signals supplied to the oscillators 10 and 20, and the control means is provided for the coaxial type detection head and the opposed type detection head. The drive signals of different high frequencies and different low frequencies can be simultaneously supplied and used.

According to the above construction, by driving the coaxial detection head 1 and the opposed detection head 2 at high and low frequencies, respectively, while the object W to be inspected is being conveyed,
Each detection head has a parallel magnetic field between the transmission coil and the reception coil, so that the influence of the inspection object W can be suppressed and the metal M can be detected with high accuracy. Further, since the coaxial type detection head 1 and the opposed type detection head 2 are driven at a high frequency and a low frequency, respectively, high precision detection can be performed without being influenced by the type of the metal M. The coaxial detection head 1 and the opposed detection head 2 may be time-divisionally controlled so that the same high frequency and low frequency are not used at the same time, or all four frequencies in total may be changed and simultaneously driven. .

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic view showing a detection head of a metal detector of the present invention. As shown in FIG. 1, the metal detector has a coaxial detection head 1 and an opposed detection head 2. The coaxial type detection head 1 is arranged coaxially with the conveyance direction of a conveyance conveyor (inspection W) not shown, and the opposed detection head 2 is arranged along the conveyance direction of the conveyance conveyor (perpendicular to the coaxial detection head 1). Direction)
Is located in.

The coaxial type detection head 1 is provided with coaxially arranged front and rear of the transmission coil 11 at the center thereof and receiving coils 12 and 13 of reverse winding respectively. The coaxial detection head 1 forms a continuous inspection space S inside each coil 11, 12, 13. The coaxial detection head 1 generates a magnetic flux in the front-back direction in the figure by the alternating magnetic field of the transmission coil 11 in the inspection space S by the oscillator 10, so that the phases of the transmission coils 12 and 13 intersecting the magnetic flux are opposite to each other. The induced voltages V1 and V2 are generated. Each receiving coil 12,
13 are arranged at the same distance with respect to the transmission coil 11, and the magnitudes of the induced voltages V1 and V2 are equal and the difference is 0 in the non-detection state.

The opposed detection head 2 has a transmission coil 21 arranged on one side (upper side) of the coaxial detection head 1 and the other side (lower side) of the coaxial detection head 1 facing the transmission coil 21. The receiving coils 22 and 23 are arranged side by side. The opposed detection head 2 forms the inspection space S between the transmission coil 21 and the reception coils 22 and 23. The opposed type detection head 2 generates a magnetic flux in the vertical direction in the figure by the alternating magnetic field of the transmission coil 21 in the inspection space S by the oscillator 20, so that the phases of the transmission coils 22 and 23 intersecting the magnetic flux are reversed. To generate induced voltages V3 and V4. Each of the receiving coils 22 and 23 is
They are arranged at the same distance with respect to the transmission coil 21, and in the non-detection state, the induced voltages V3 and V4 are equal in magnitude and the difference is zero. In the inspection space S, the opposed detection head 2 generates a magnetic flux that is orthogonal to the magnetic flux of the coaxial detection head 1.

The detection heads 1 and 2 are arranged so that a transportation means such as a transportation conveyor (not shown) penetrates through the inspection space S and is housed in a substantially square-shaped housing. The housing is formed of a magnetic shield material such as metal (eg, aluminum alloy or stainless steel). Then, the object W to be inspected is conveyed by the conveyor to pass through the inspection space S.

FIG. 2 is a block diagram showing the detection circuit 31a on one side (coaxial type detection head 1). The other opposed detection head 2 also has a similar detection circuit 31b (see FIG. 1). The outputs of the receiving coils 12 and 13 are differentially connected and input to the detection circuit 31a via the buffer 30 to perform quadrature synchronous detection. The pair of detection units 32 and 33 perform detection in phases orthogonal to each other, and the bandpass filter 3
The magnetizing current Jm and the eddy current rotJ are detected via 4, respectively. FIG. 3 is a magnetization characteristic diagram of the object W to be inspected and the metal M. In the figure, the magnetization current Jm has a value in the X coordinate direction and rotJ has a value in the Y coordinate direction. Based on the difference between the two, the metal M
Can be detected.

In the metal detector having the above structure, in the coaxial detection head 1, the object W to be inspected containing the metal M such as metal is mixed.
1 moves in the direction A in FIG. 1 and moves into the front receiving coil 12 by the conveying means, the magnetic flux density in the receiving coil 12 increases, and conversely, the magnetic flux density in the receiving coil 13 decreases. Therefore, the induced voltage V1 of the receiving coil 12 becomes larger than the induced voltage V2 of the receiving coil 13. Then
When the inspected object W which has advanced to the inside of the receiving coil 13, the magnetic flux density inside the receiving coil 13 becomes larger than inside the receiving coil 12, so that the induced voltage V1 is larger than the induced voltage V1.
2 is larger. In this way, the metal M is mixed into the object to be inspected W that has passed through the inspection space S based on the change in the difference between the induced voltages V1 and V2 output from the coaxial detection head 1 (fluctuation of the magnetic field). Can be determined.

Further, in the opposed detection head 2, when the object W to be inspected containing the metal M advances in the direction A in FIG. 1 by the conveying means and moves between the transmitting coil 21 and the receiving coil 22 in front, The magnetic flux density between the transmitter coil 21 and the receiver coil 22 increases, and conversely, the transmitter coil 21 and the receiver coil 2
The magnetic flux density between 3 decreases. Therefore, the receiving coil 22
Is larger than the induced voltage V4 of the receiving coil 23. Next, when the inspected object W that has advanced moves between the transmitting coil 21 and the receiving coil 23, the magnetic flux density between the transmitting coil 21 and the receiving coil 23 becomes larger than that between the transmitting coil 21 and the receiving coil 22. Therefore, the induced voltage V4 becomes larger than the induced voltage V3. In this way, the induced voltage V output from the coaxial detection head 2
Based on the change in the difference between 3 and V4 (fluctuation of magnetic field),
It is possible to determine whether or not the metal M is mixed in the inspection object W that has passed through the inspection space S.

That is, in the metal detector of the present embodiment, when the metal M mixed in the object W to be inspected has a needle shape or a thin plate shape and is a magnetic material such as Fe, the coaxial detection head 1
When the arrangement is substantially orthogonal to the magnetic flux generated in, the arrangement is along the magnetic flux generated in the opposed detection head 2. As a result, in the coaxial type detection head 1, since the change in the magnetic flux is small and the difference between the induced voltages V1 and V2 is small, the detection sensitivity of the metal M is lowered, but in the opposed type detection head 2, the magnetic flux changes a lot and the induced voltages V3 and V4. Since the difference is large, the detection sensitivity of the metal M becomes good.

On the contrary, the needle shape and the thin plate shape are the same, and
When the magnetic metal M is arranged along the magnetic flux generated by the coaxial detection head 1, the magnetic metal M is arranged substantially orthogonal to the magnetic flux generated by the opposed detection head 2. As a result, the opposed detection head 2 has a small change in the magnetic flux and the induced voltages V3 and V.
Since the difference of 4 is small, the detection sensitivity of the metal M is lowered, but in the coaxial type detection head 1, there are many changes in the magnetic flux and the induced voltages V1, V
Since the difference between 2 is large, the detection sensitivity of the metal M becomes good.

Further, in the metal detector of this embodiment,
When the metal M mixed in the object W to be inspected has a needle shape or a thin plate shape and is a non-magnetic material such as stainless steel (SUS), when the metal M is arranged along the magnetic flux generated in the coaxial detection head 1,
The arrangement is substantially orthogonal to the magnetic flux generated by the opposed detection head 2. As a result, in the coaxial type detection head 1, since the change in the magnetic flux is small and the difference between the induced voltages V1 and V2 is small, the detection sensitivity of the metal M is lowered, but in the opposed type detection head 2, the magnetic flux changes a lot and the induced voltages V3 and V4. Since the difference is large, the detection sensitivity of the metal M becomes good.

On the contrary, the needle shape and the thin plate shape are the same, and
When the non-magnetic metal M is arranged substantially orthogonal to the magnetic flux generated in the coaxial type detection head 1, it is arranged along the magnetic flux generated in the opposed type detection head 2. As a result, in the opposed detection head 2, the change in magnetic flux is small and the induced voltage V3 is small.
Since the difference in V4 is small, the detection sensitivity of the metal M is reduced, but in the coaxial type detection head 1, the magnetic flux changes a lot and the induced voltage V1,
Since the difference in V2 is large, the detection sensitivity of the metal M becomes good.

As described above, the above-described metal detector uses both the coaxial type detection head 1 and the opposed type detection head 2 whose magnetic fluxes are orthogonal to each other, so that it is difficult to detect with one detection head, such as a needle shape. Also, even the metal M in the direction of mixing into the object W to be inspected is detected by the other detection head, and the metal M mixed into the object W to be inspected is detected without exception. At this time, the transmission coil 11 and the reception coils 12 and 13 of the coaxial detection head 1 and the transmission coil 21 of the opposed detection head 2
There is always a parallel magnetic field between the receiving coil 22 and the receiving coil 23, and the direction of the magnetic field that shields the inspection object W does not change even when the inspection object W is transported and moved, and the S / N N (noise). The component can be made small and the metal M can be detected stably.

FIG. 4 is a diagram for explaining the principle of detection of the metal M by the above detection heads. (A) is a coaxial type,
(B) In each of the opposed detection heads, the metal M is conveyed in the direction A in the figure. In the coaxial detection head 1 of (a), the magnetizing current Jm flows along the outer circumference of the metal M along the winding direction of the coil, and the eddy current ro is generated at the end faces (front and rear ends in the transport direction).
tJ flows. At this time, the magnetizing current Jm is large and the eddy current rotJ is small. In this case, a non-magnetic material such as SUS has a higher detection sensitivity than a magnetic material such as Fe.
In the opposed detection head 2 of (b), the magnetizing current Jm flows to the same metal M along the outer periphery of the metal M along the winding direction of the coil, and the eddy current rotJ flows at the end faces (upper face and lower face). . At this time, the magnetizing current Jm is small and the eddy current ro
tJ is large. In this case, the magnetic substance such as Fe has higher detection sensitivity than the non-magnetic substance such as SUS.

Although the above description has been made only for the metal M, it can be similarly applied to the object W to be inspected. For example, the object W to be inspected containing water such as ham has a predetermined magnetization characteristic like a foreign substance. In order to improve the detection sensitivity of the metal M in the inspection object W, the magnetizing current Jm,
It is necessary that a large amount of the eddy current rotJ flows and that the magnetizing current Jm and the eddy current rotJ do not flow to the object W to be inspected as much as possible. As shown in FIG. 3, the detection accuracy of the metal M can be improved by making the difference in the magnetization characteristics of the metal M serving as the detection component S as large as possible with respect to the magnetization characteristics of the inspection target W serving as the noise component N.

The above principle is an example in which the driving frequency of the sending and receiving coils in the detection head is the same, but a magnetic material such as Fe and a non-magnetic material such as SUS have the highest received level and the detectable frequency. Is different. FIG. 5 is a diagram showing frequency-reception level characteristics for each material. Magnetic Fe
Has a substantially constant reception level from low frequency to high frequency. On the other hand, the nonmagnetic SUS has a high reception level in a relatively high frequency band. As an example of the object W to be inspected, ham has a higher reception level in a high frequency band than SUS. Explaining with an example shown in the figure, the metal M (SUS) in the object W to be inspected
Is detected based on the difference between the reception levels of the two in the high frequency band, and the metal M (Fe) is detected based on the difference between the reception levels of the two in a relatively low frequency band.

FIG. 6 is a diagram showing the detection sensitivity characteristics for each frequency in the configuration of the coaxial-opposed detection head of the present invention.
In the figure, the high frequency is several hundred kHz (range: several tens kHz to several MH)
z), and the low frequency is several tens of kHz (range: direct current to several hundreds of kHz). Generally, the detection sensitivity to SUS is high in the high frequency band, and the sensitivity sensitivity to Fe is high in the low frequency band. Coaxial type detection head 1 shown in (a)
Then, the detection sensitivity for SUS in the vertical direction is high, and the detection sensitivity for Fe in the horizontal direction is high. In the opposed detection head 2 shown in (b), the detection sensitivity for SUS in the horizontal direction is high and the detection sensitivity for Fe in the vertical direction is high. These are characteristics based on the values of the magnetizing current Jm and the eddy current rotJ generated in the metal M depending on the material and the generation direction of the magnetic field. As described above, the use of the coaxial type detection head 1 and the opposed type detection head 2 has the effect of complementing each other's detection sensitivity.

By the way, the coaxial type detection head 1 and the opposed type detection head 2 having the above-mentioned configurations cannot simultaneously measure at the same frequency because the magnetic field generation directions are different in the single inspection space S. Therefore, in the present embodiment, while the coaxial type detection head 1 and the opposed type detection head 2 are simultaneously operated, their detections do not interfere with each other, and the type of metal M and the mixing direction are not affected. The configuration is such that M is detected. Therefore, the coaxial detection head 1 and the opposed detection head 2 are configured to detect the metal M without simultaneously generating the same frequency. Hereinafter, each configuration example will be described.

FIG. 7 is a time chart showing the relationship between the drive frequencies of the coaxial and opposing detection heads. (Structure example 1 ... 2 frequency time division) In the time division control shown in FIG. 7A, when the coaxial detection head 1 is driven at a high frequency, the opposing head 2 is driven at a low frequency at the same time. After that, when the coaxial detection head 1 is driven at a low frequency, the opposing head 2 is simultaneously driven at a high frequency.

(Structure example 2 ... 2 frequency switching) FIG.
The time-division control shown in (b) stops the opposing head 2 when driving only the coaxial detection head 1 side at high and low frequencies. After that, when only the opposed detection head 2 is driven at a high frequency and a low frequency, the coaxial head 1 is stopped.

As described above, when driving each of the high frequency and the low frequency, the oscillators 10 and 20 individually or superimpose these frequencies on the transmission coils 11 and 21, respectively. The drive signal outputs a sin wave, a rectangular wave, or the like by FM, AM modulation, phase modulation, or the like. On the receiving side, the detection circuit 31a shown in FIG.
High-frequency detection units and low-frequency detection units may be provided in parallel for the outputs 2 and 13.

(Structural Example 3 ... Two independent frequencies) FIG. 7 (c)
In the time-division control shown in (1), the high frequency and low frequency of the coaxial detection head 1 are driven, and then the high frequency and low frequency of the opposed detection head 2 are independently driven. In any of the time division control, the drive switching is performed at a predetermined cycle, and this cycle can be executed at a sufficiently high speed as compared with the transport speed of the inspection object W.
The time-division control of the drive signal for the transmission coils 11 and 21 is executed by a control unit (not shown).

(Structure example 4 ... Simultaneous for all frequencies) Although all of the above are structures for performing time division control, the present invention is not limited to time division control. For example, if the high-frequency and low-frequency frequencies of the coaxial detection head 1 and the high-frequency and low-frequency values of the opposed detection head 2 are all different values, they are driven at a total of four different frequencies. be able to. In this case, both high and low frequencies can be put into practical use without mutual interference by only differentiating the frequencies between them by 0.1 kHz.

According to the above construction, both the coaxial type detection head 1 and the opposed type detection head 2 can be driven during the transportation of the object W to be inspected, and each detection head has a transmission coil and a reception coil. Since there is a parallel magnetic field between them, the direction of the magnetic field that shields the object to be inspected W does not change even when the object to be inspected W is transported and moved, so that the direction of the metal M mixed in the object to be inspected W is not affected. This metal M can be detected with high accuracy. In addition, since the coaxial type detection head 1 and the opposed type detection head 2 are driven at high frequency and low frequency, respectively, the type of the metal M (magnetic substance such as Fe, non-magnetic substance such as SUS) and shape are affected. It is possible to detect with high accuracy without receiving it.

In the above-described embodiment, the configuration has been described in which the coaxial type and the facing type detecting heads perform time-division control by using two frequencies of high frequency and low frequency, and frequency control in which all frequencies are different. Not limited to this, 2 depending on the characteristics of the metal M to be detected and the inspection object W.
It is also possible to use three or more frequencies, for example, three frequencies, and perform time division control and frequency control in which all frequencies are different.

[0042]

As described above, the metal detector according to the present invention uses two detection heads of the coaxial type and the opposed type, and each of these detection heads produces a magnetic field that shields the inspection object when the inspection object is conveyed. Since the orientation is constant, stable metal detection can be performed. Further, since the coaxial type and the facing type detection heads are driven at high and low frequencies, respectively, highly accurate metal detection can be performed without being affected by the metal material, the mixing direction, the shape, and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a metal detector of the present invention.

FIG. 2 is a circuit diagram showing a detection circuit.

FIG. 3 is a magnetization characteristic diagram of an inspection object W and a metal M.

FIG. 4 is a diagram for explaining detection characteristics of a metal material for each detection head.

FIG. 5 is a diagram showing magnetization characteristics of an object to be inspected and a metal.

FIG. 6 is a diagram for explaining detection characteristics of a metal material and a direction for each detection head.

FIG. 7 is a timing chart showing time division control of frequency for the detection head.

FIG. 8 is a perspective view showing a conventional detection head.

FIG. 9 is a schematic view showing another conventional detection head.

FIG. 10 is a schematic view showing another conventional detection head.

[Explanation of symbols]

1 ... Coaxial detection head, 2 ... Opposed detection head, 11,
21 ... Transmitting coil, 12, 13, 22, 23 ... Receiving coil, 31a, 31b ... Detecting circuit, W ... Inspected object, M ... Metal.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiji Yamagishi             5-10-10 Minamiazabu, Minato-ku, Tokyo Henri             Tsu Co., Ltd. (72) Inventor Shigeru Kuboji             5-10-10 Minamiazabu, Minato-ku, Tokyo Henri             Tsu Co., Ltd. F-term (reference) 2G005 CA03

Claims (5)

[Claims] 1. A transport path of a predetermined length for transporting an object to be inspected (W), and a pair of receiving coils (1) arranged before and after a central transmitting coil (31), which are arranged coaxially with the conveying direction of the object to be inspected. 32,3
3), a coaxial detection head (30), a transmission coil (21) arranged along the transport direction of the transport path, and on one side of the coaxial detection head,
A receiving coil (42, 4) is provided on the other side of the coaxial detection head.
3), the opposed detection head (40) that generates a magnetic flux orthogonal to the magnetic flux of the coaxial detection head, the transmission coil of the coaxial detection head, and the transmission coil of the opposed detection head have predetermined frequencies. An oscillator (10, 20) for supplying a driving signal, a receiving coil of the coaxial type detecting head, and a receiving coil of the facing type detecting head are respectively connected to detect an induced voltage of the receiving coil for each frequency of the driving signal. A detection circuit (31a, 31b) for detecting the presence or absence of metal by driving the coaxial type detection head and the opposed type detection head at high and low frequencies, respectively, and obtain a total of four detection outputs to obtain an object to be inspected. A metal detector characterized by detecting the above metal (M). 2. A control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to said oscillator (10, 20), said control means comprising: said coaxial type detection head and said opposed type detection head. Of these, when driving one at high frequency, at the same time drive the other at low frequency,
The metal detector according to claim 1, wherein when one is driven at a low frequency, the other is simultaneously driven at a high frequency to control the drive frequency in a time-division manner. 3. A control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to the oscillator (10, 20) is provided, wherein the control means controls the coaxial detection head in high-frequency and low-frequency. When driving, the drive signal supply to the opposed type detection head is stopped, and when driving the opposed type detection head at high frequency and low frequency, the supply of the drive signal to the coaxial type detection head is stopped. The metal detector according to claim 1, wherein the driving frequency is controlled by time division. 4. A control means for time-divisionally controlling high-frequency and low-frequency drive signals supplied to the oscillator (10, 20), wherein the control means drives high-frequency and low-frequency with respect to the coaxial type detection head. When,
The metal detector according to claim 1, wherein high-frequency driving and low-frequency driving of the opposed detection head are all performed at separate timings to control the driving frequency in a time-division manner. 5. A control means for frequency-controlling high-frequency and low-frequency drive signals supplied to the oscillator (10, 20) is provided, and the control means controls the coaxial detection head and the opposed detection head. On the other hand, the metal detector according to claim 1, wherein drive signals of different high frequencies and different low frequencies are simultaneously supplied and used.