JPH0816703B2 - Mixed metal detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field of the Present Invention> The present invention relates to a mixed metal detector for detecting the presence or absence of metal mixed in an object to be inspected by a static magnetic field generated by a permanent magnet.

<Prior Art> In a food product such as sausage or ice cream, a minute metal, for example, a metal fragment such as a needle tip or a cutting edge may be erroneously mixed in the manufacturing process.
There is a need to detect metals in such products.

If the product is packaged in a non-ferrous metal bag such as aluminum foil, it is necessary to detect the metal in the product by a static magnetic field in order to reduce the influence of the metal bag. Known to be good, traditionally
It has been proposed to use a permanent magnet instead of supplying a direct current to the coil so as to generate a strong static magnetic field (Shokai 59-155571).

That is, as shown in FIGS. 7 (a), (b) and (c),
In the detection head 1 of the conventional metal detector using the static magnetic field of the permanent magnet, two receiving coils of the same shape that are wound back in a longitudinal shape are provided below the hollow portion 1a through which the conveyor belt 4 passes.
2a and 2b are arranged side by side in the conveyance direction of the object W to be inspected side by side and symmetrically arranged, and a plurality of them are arranged above the hollow portion 1a so as to be located above the boundary line between the two receiving coils 2a and 2b. The permanent magnets 3, 3, ... Are installed. The permanent magnets 3, 3, ... All have the N pole and the S pole on the same side, and the magnetic flux has two receiving coils 2a, 2b symmetrically arranged as shown in FIG. 7 (b). It is arranged so as to cross the same number.

When the product W wrapped with the aluminum package A is passed by the conveyor belt 4 in the direction in which the two receiving coils 2a and 2b are arranged side by side, when metal is present in the product W, the permanent magnets 2, 2, ... .. changes in the static magnetic field, which changes the number of magnetic fluxes that traverse the receiving coils 2a and 2b, causing induced voltages in the receiving coils 2a and 2b, respectively, and a difference in induced voltage between the two. The difference voltage detects the presence of metal in the product W.

<Problems to be Solved by the Present Invention> However, in the detection head 1 of this metal detector,
As shown in FIG. 7 (b), since the magnetic flux leaking to the outside of the detecting head 1 is large, the magnetic flux changes due to the influence of noise from the devices (conveyor, motor, solenoid) around the detecting head 1, For this reason, a malfunction is likely to occur in the detection of the metal in the inspection object.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such problems and to provide a mixed metal detector in which leakage magnetic flux is reduced to prevent malfunction due to noise from peripheral devices.

<Means for Solving the Problems> In order to solve the problems, the mixed metal detector of the present invention is a frame of a frame body in which a hollow portion for passing an inspection object is provided in the center, Each of them is formed in an air-core flat shape, and is arranged closely along the passage direction of the object to be inspected with the flat surface facing the hollow portion inside the frame, and arranged symmetrically with respect to the boundary line. And two receiving coils that output a signal corresponding to a change in the magnetic flux passing through the inside, and two magnetic poles of different polarities, which are provided inside the frame and are opposed to each other by a permanent magnet and a yoke. With one magnetic pole having its magnetic pole center aligned with a line that passes through the boundary line between the two receiving coils and is substantially orthogonal to the passing direction of the object to be inspected, the boundary line between the two receiving coils and the hollow portion are placed between them. It is arranged so as to sandwich it, Of the two magnetic poles, one of the magnetic poles located on the opposite side of the hollow portion across the boundary line has a width along the inspected body passing direction of 2
A magnetic circuit formed to be narrower than a width of one of the receiving coils along the passing direction of the object to be inspected, and an outer surface of the frame excluding the hollow portion, to magnetically shield the two receiving coils and the magnetic circuit from the outside. A magnetic shield, a conveyor for passing the inspection object through a position near the two receiving coils in the hollow portion of the frame, and the two receptions when the inspection object passes through the hollow portion of the frame by the conveyor And a detection circuit for detecting the metal mixed in the object to be inspected based on the difference between the signals of the coils.

<Operation> Because of this, the mixed metal detector of the present invention
The magnetic flux between the two magnetic poles of the magnetic circuit is formed such that its width is narrower than the width of the two receiving coils, and the magnetic pole center passing through the boundary line between the two receiving coils is offset from the boundary line between the two receiving coils by the other magnetic pole. You will pass through intensively. As a result, leakage to the outside is significantly reduced. For this reason, changes in magnetic flux due to the effects of noise from surrounding equipment are reduced,
Malfunctions in metal detection are reduced. Further, since the magnetic flux concentrates near the boundary line between the two receiving coils and the object to be inspected passes through the positions near the two receiving coils, the metal mixed in the object to be inspected moves toward the boundary line of one receiving coil. When passing, the magnetic flux crossing the other receiving coil changes greatly near this boundary line, the difference between the magnetic fluxes crossing the two receiving coils becomes significant, and the sensitivity of metal detection is also improved.

<Examples of the Present Invention> Examples of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) and 1 (b) show a detection head and a conveyer of a mixed metal detector of one embodiment.

In FIGS. 1A and 1B, 10 is a detection head, and 11
Is a square-shaped detection head frame, and a hollow portion 11a through which the transport conveyor 20 passes is provided in the center of the detection head frame.

On the lower side of the hollow portion 11a of the detection head frame 11 (the lower part of the detection head frame 11), two receiving coils 12a, 12b of the same shape that are rewound in the longitudinal direction are arranged next to each other in the transport direction of the transport conveyor 20. They are arranged side by side and symmetrically.

Two receiving coils 12a and 12b are provided above the hollow portion 11a of the detection head frame 11 (upper part of the detection head frame 11).
A plurality of permanent magnets 13, 13, ... Are installed linearly so as to be located above the boundary line of. In these permanent magnets 13, 13, ..., The north pole and the south pole are on the same side, and as shown in FIG. 1 (b), the center line of the magnetic pole facing the lower surface side has two receiving coils. Two receiving coils that match the line passing through the boundary line (direction orthogonal to the paper surface) of 12a and 12b and orthogonal to the passing direction of the DUT, and whose magnetic flux is symmetrically arranged with respect to this boundary line. The permanent magnets 13, 13, ... Are arranged so as to cross the same number of 12a, 12b.

The static magnetic field generated by the permanent magnets 13, 13, ...
A yoke 14 is provided so as to form a magnetic circuit passing through the two receiving coils.

That is, the yoke 14 makes a ring in the detection head frame 11,
The detection head frame 11 has projecting portions 14a and 14b projecting in a direction approaching each other in the upper and lower portions thereof, and the permanent magnets 13, 13, ... Are arranged at the tip of one projecting portion 14a to project the projecting portions 14a and 14b. A magnetic circuit having a gap between the portions 14a and 14b is configured. Note that one magnetic pole of this magnetic circuit is the lower magnetic pole of the permanent magnet 13, and the other magnetic pole is a protruding portion 14b facing the lower magnetic pole of the permanent magnet 13 and having a polarity opposite to this magnetic pole. The center of the protruding portion 14b in the width direction along the inspected object passing direction coincides with the center line of the magnetic pole of the permanent magnet 13, and the width is the width of the two receiving coils 12a, 12b in the inspected object passing direction. Since it is formed to be narrower, the magnetic flux from the permanent magnet 13 intensively passes near the boundary line between the two receiving coils 12a and 12b and collects on the protruding portion 14b.

In FIG. 1, 20 is a detection head for the object to be inspected.
The hollow portion 11a of 10 is conveyed in a direction in which the two receiving coils 12a, 12b are arranged at a position near the two receiving coils 12a, 12b.
It is the same transport conveyor as shown in FIG.
Are rollers of the transport conveyor.

The product W wrapped with the aluminum package A is successively passed by the transport conveyor 20. If metal is present in the product W, the static magnetic field is changed by the permanent magnets 13, 13, ... When passing through the receiving coils 12a, 12b, and thus the number of magnetic fluxes crossing the receiving coils 12a, 12b changes. do it,
An induced voltage is generated in the receiving coils 12a and 12b, and a difference voltage between them is generated. Due to this difference voltage, the presence of metal in the product W is detected by a detection circuit (not shown). In this detection, the yoke 14 causes the two receiving coils 12 to
Since a magnetic circuit having a gap in the hollow portion 11a in which a and 12b are installed is configured, the leakage magnetic flux to the outside of the detection head 10 is significantly reduced, and the influence of the external noise on the magnetic flux is reduced. Therefore, erroneous detection due to external noise is significantly reduced, and since magnetic flux is concentrated near the boundary line between the receiving coils 12a and 12b, when the mixed metal passes along the boundary line between the two receiving coils, this boundary line The difference between the magnetic fluxes intersecting the two receiving coils in the vicinity of becomes noticeable, and as a result, it becomes possible to detect extremely minute metals.

As shown in FIG. 2, if the magnetic shield 15 made of a magnetic material is provided outside the yoke 14, the leakage magnetic flux is further reduced.

If the N pole and the S pole are vertically arranged so as to generate a magnetic flux as shown in FIG. 1, a plurality of small permanent magnets 13, 13, as shown in FIGS. 1A and 1B, .. may be replaced with a single permanent magnet 16 as shown in FIG.

Further, as shown in FIGS. 4 and 5, permanent magnets 13 and 16 may be provided on both upper and lower sides.

Further, as shown in FIG. 6, a permanent magnet 17 is provided on the side of the yoke 14.
May be provided on one side or both sides.

Although the embodiments of the present invention have been described above, it is needless to say that various modifications can be made.

<Effects of the Present Invention> As described above, the mixed metal detector of the present invention has two receiving coils on one side in the passing direction of the object to be inspected with a hollow portion for allowing the object to be inspected to pass through. Are symmetrically arranged with respect to the boundary line, and two magnetic poles of different polarities facing each other in a magnetic circuit composed of a permanent magnet and a yoke pass through the object to be inspected through the magnetic pole center passing through the boundary line of the two receiving coils. The hollow portion and the boundary line between the two receiving coils are arranged so as to sandwich the hollow line and the boundary line between the two receiving coils, and the width of one magnetic pole located on the two receiving coil sides is set to 2 in a state of being aligned with a line substantially orthogonal to the direction.
The receiving coils are formed to be narrower than the width in the passing direction of the object to be inspected, and further, a magnetic shield is provided to cover the outer surface of the frame except the hollow part, and the object to be inspected is positioned by the conveyor so that the positions of the two receiving coils near the hollow part are close. It is configured to pass. For this reason, the leakage magnetic flux is significantly reduced, so that the influence of external noise on the magnetic flux is significantly reduced, erroneous detection is significantly reduced, and the magnetic flux is concentrated near the boundary between the two receiving coils. Since the inspection body passes through the position close to the receiving coil, when the metal mixed in the inspection body passes over the boundary line between the two receiving coils, the difference in the magnetic flux intersecting the two receiving coils becomes remarkable, It becomes possible to detect minute metals.

[Brief description of drawings]

FIGS. 1 to 5 show first to fifth embodiments of the present invention respectively. FIGS. 1 to 5 (a) are longitudinal sectional views, and FIGS. 1 to 5 (b) are respective first to fifth embodiments. It is a central longitudinal cross-sectional view in FIG. FIG. 6 is a vertical sectional view showing a sixth embodiment of the present invention. FIG. 7 (a) is a perspective view showing a detection head of a conventional metal detector, FIG. 7 (b) is a longitudinal sectional view, and FIG. 7 (c) is a central longitudinal sectional view. 10 ... Detection head, 11 ... Detection head frame, 11a ...
… Hollow part, 12a, 12b …… Reception coil, 13 …… Permanent magnet,
14 ... Yoke, 15 ... Magnetic shield, 16,17 ... Permanent magnet, 20 ... Transport conveyor, 20a-20d ... Roller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Shown 59-155571 (JP, U) Shown 55-103585 (JP, U) Shown 61-15580 (JP, U) Shown

Claims (1)

[Claims] 1. A frame of a frame body having a hollow portion at the center for allowing an object to be inspected to pass therethrough, each of which is formed in an air-core flat shape, and the flat surface is formed inside the frame by the hollow portion. Two receiving coils that are arranged close to each other in the passing direction of the inspection object in a state of being directed toward the inspection object and that are arranged symmetrically with respect to the boundary line and that output a signal corresponding to a change in the magnetic flux passing through the inside, Two magnetic poles of different polarities, which are provided inside the frame and are opposed to each other by a permanent magnet and a yoke, are formed.
With one magnetic pole having its magnetic pole center aligned with a line that passes through the boundary line between the two receiving coils and is substantially orthogonal to the passing direction of the object to be inspected, the boundary line between the two receiving coils and the hollow portion are placed between them. Of the two magnetic poles arranged so as to be sandwiched, the width of one of the two magnetic poles located on the opposite side of the hollow portion across the boundary line along the passing direction of the object to be inspected is 2
A magnetic circuit formed to be narrower than a width of one of the receiving coils along a passing direction of the object to be inspected, and an outer surface of the frame excluding the hollow portion,
A magnetic shield that magnetically shields the two receiving coils and the magnetic circuit from the outside, a conveyor that allows the object to be inspected to pass through the hollow portion of the frame near the two receiving coils, and the hollow portion of the frame by the conveyor. And a detection circuit for detecting the metal mixed in the inspected object based on the difference between the signals of the two receiving coils when the inspected object passes through.