metal detector

Abstract

To provide a metal detector that solves or partially solves an issue that a mixture or a metal foreign metal which is smaller than a predetermined size cannot be detected.SOLUTION: The metal detector includes at least one transmission coil and at least one reception coil. The transmission coil and the reception coil are each arranged in one flat surface having a normal vector perpendicular to the flat surface. The transmission coil and the reception coil are connected to a measurement device. A product is carried through the metal detector along a rate vector. The rate vector and at least one of the normal vector of the transmission coil and the normal vector of the reception coil forms an angle α larger than 0°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] A metal detector comprising at least one transmitting coil and at least one receiving coil, the transmitting coil and the receiving coil each arranged in a plane, each plane having a normal vector orthogonal to the plane, the transmitting coil and the receiving coil connected to a measurement device, and a product being conveyed past the metal detector along the velocity vector. [Background technology]

[0002] Metal detectors of the type considered here are used in particular for product control, for example in food production, to check individual products or more or less continuous product flows for metal contaminants, such as metal chips or particles, wires, screws or nuts, tools or other foreign objects.

[0003] In a metal detector, a magnetic field is generated which is disturbed by metal particles and this disturbance, a convergence or suppression of the magnetic field lines depending on the material of the contaminant, can be detected and evaluated.

[0004] In a typical application, products are transported on a conveyor belt or similar conveying device past a metal detector, which includes three or more coils that surround the conveyor belt and the products being transported thereon.

[0005] A high-frequency alternating current is applied to one of the coils, causing it to generate a magnetic field at the location of the product flow and thus functioning as a transmitting coil. The other two coils are used as receiving coils; that is, a current is induced in them in response to the generated magnetic field. In this case, the receiving coils are connected in series in opposite directions relative to the winding direction, so that when the magnetic field is not disturbed, the resultant voltage is zero. If the magnetic field is disturbed, especially by a metal foreign object, a non-zero output voltage is generated. For example, German Patent Specification No. 195 30 987 (C1) discloses a corresponding metal detector.

[0006] A drawback of the known prior art is that if contaminants or metallic foreign bodies are below a certain size, they can no longer be detected. Summary of the Invention

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a metal detector which overcomes or at least alleviates the disadvantages known from the prior art.

[0008] This object is achieved in the metal detector described above by ensuring that the angle between the velocity vector and at least one of the normal vectors of the transmitter coil and / or the receiver coil is greater than 0°. This allows for the detection of metallic foreign objects in the product with a diameter of less than 1 mm. In metal detectors known from the prior art, the transmitter coil and receiver coil are arranged perpendicular to the conveyor belt, so only metallic foreign objects with a diameter of at least 1 mm can be detected. Relatively small metallic foreign objects cannot be found in the product. Furthermore, metallic foreign objects, particularly wires, for example, wires with a length of 1 meter and a diameter of 0.8 mm, cannot be detected by metal detectors known from the prior art if they are arranged in the product in the direction of conveyance or the velocity vector.

[0009] The metal detector according to the present invention can detect spherical or cylindrical metallic foreign objects less than 1 mm in size because the transmitter coil and / or receiver coil are disposed at an angle to the conveyor belt, or because the angle formed between the velocity vector and at least one of the normal vectors of the transmitter coil and / or the receiver coil and the normal vector of the receiver coil is greater than 0°. This is achieved by the magnification caused by the angle formed between the normal vector of the transmitter coil and / or the normal vector of the receiver coil and the velocity vector of the cross section of the metallic foreign object.

[0010] In one alternative configuration, the housing has a cavity through which the product is conveyed on a conveyor belt past the cavity in the metal detector, and the housing is positioned perpendicular to the conveyor belt.

[0011] In another configuration, the metal detector has a housing, and the transmitter coil and receiver coil are arranged within the housing. Therefore, the transmitter coil and / or receiver coil are arranged obliquely within the housing, or the angle between the plane of the transmitter coil and / or receiver coil and the side of the housing is greater than 0°. The dimensions of the metal detector thus correspond to those of conventional or known metal detectors, allowing it to be replaced with existing metal detectors without the need to modify the production line in which the metal detector is installed. Preferably, the angle between the normal vector of the plane of at least one of the transmitter coil and / or receiver coil and the velocity vector is between 3° and 30°, more preferably between 5° and 25°, and particularly preferably between 7° and 20°. This allows the coils to be extended only slightly. However, this is very important, since the length of the transmitter coil and the length of the receiver coil affect the sensitivity of the metal detector.

[0012] To further improve the sensitivity of the metal detector, the angle between the normal vector of the plane of the transmitter coil and the velocity vector is between 3° and 30°, and the normal vector of the plane of the receiver coil and the velocity vector are aligned. This structure improves the sensitivity, since the length of the receiver coils remains unchanged. The sensitivity also depends strongly on the length of the receiver coils. This ensures that at least one transmitter coil is longer than at least one receiver coil.

[0013] In another configuration, the at least one transmitter coil and the at least one receiver coil are arranged in the shape of a rhombohedron. The at least one transmitter coil and the at least one receiver coil each form a parallelogram. Virtually connecting the corners of the transmitter coil and the corners of the receiver coil results in a parallelepiped or rhombohedron. Thus, the at least one transmitter coil and the at least one receiver coil are arranged in planes parallel to each other.

[0014] In one alternative configuration, the at least one transmitter coil and / or the at least one receiver coil are arranged transversely to the conveying direction of the conveyor belt, so that all products pass both the at least one transmitter coil and the at least one receiver coil.

[0015] In another configuration, at least one receiving coil and at least one transmitting coil are wound on a bobbin. In particular, the bobbin has at least two grooves for accommodating at least one transmitting coil and at least one receiving coil. The transmitting coil and the receiving coil are disposed in the grooves of the bobbin and thereby held in position. This further prevents the position of the transmitting coil or the receiving coil from changing relative to the receiving coil or the transmitting coil during manufacturing or operation. Furthermore, the transmitting coil and the receiving coil are each formed, in particular, from a winding.

[0016] In another configuration, the metal detector has at least one second receiver coil, with at least one transmitter coil disposed between the two receiver coils. When two receiver coils are used, the two receiver coils and the transmitter coil can be similarly arranged in a rhombohedron-shaped housing. Alternatively, the normal vectors of the planes of the two receiver coils and the velocity vector can be aligned, with the angle between the normal vector of the plane of the transmitter coil and the velocity vector being between 3° and 30°, preferably between 5° and 25°, and particularly preferably between 7° and 20°.

[0017] In one alternative configuration, two receiver coils are connected in series with opposite winding directions. The transmitter coil generates a magnetic field that can be received by the two receiver coils and induces a voltage in the two receiver coils. Since the receiver coils are connected in series with opposite winding directions, the voltage at the receiver coil's output terminals is zero unless there is an obstruction to the magnetic field, such as a metallic foreign object. If a metallic foreign object affects the magnetic field, the voltage at the receiver coil's output terminals will no longer be zero. [Brief explanation of the drawings]

[0018] Further advantageous aspects will become apparent from the following description of preferred embodiments which refers to the accompanying drawings. [Figure 1] 1 shows a schematic diagram of a metal detector. [Figure 2] 1 shows a plan view of a metal detector. [Figure 3] 1 shows a plan view of another metal detector. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1 shows a metal detector 1 equipped with a conveyor belt 2. An upper transmission belt 3 of the conveyor belt 2 runs through a cavity 4 in the metal detector 1, and a lower transmission belt 5 extends below the metal detector 1. The metal detector 1 has a housing 6 in which at least one transmitting coil 7 and at least one receiving coil 8 are arranged, the transmitting coil 7 and the receiving coils 8, 12, 13 each being arranged in a plane, each plane having a normal vector 15 perpendicular to the plane.

[0020] FIG. 2 shows a plan view of the metal detector 1, showing the receiver coils 8 and transmitter coils 7 arranged below the top surface of the housing. The metal detector 1 has two receiver coils 8 and one transmitter coil 7. The transmitter coil 7 is arranged between the two receiver coils 8. The housing 6 is arranged perpendicular to the conveyor belt 2, and the transmitter coil 7 and the two receiver coils 8 are arranged in a direction transverse to the conveyor belt 2's conveying direction 9 or velocity vector 9. The normal vectors 15 of the transmitter coil 7 and the two receiver coils 8 are arranged at an angle α relative to the velocity vector 9 rather than 0°. Thus, the transmitter coil 7 and the two receiver coils 8 extend obliquely relative to the conveyor belt 2's conveying direction 9 or velocity vector 9. In particular, the angle α is between 3° and 30°, preferably between 5° and 25°, and particularly preferably between 7° and 20°.

[0021] The transmitter coil 7 and the receiver coils 8 are wound around a spool (not shown), which is disposed within the housing 6 of the metal detector 1. The transmitter coil 7 and the two receiver coils 8 are disposed within the housing 6 in the shape of a rhomboid. The transmitter coil 7 and the two receiver coils 8 each form a parallelogram and extend parallel to each other. Connecting the opposing corners of the two receiver coils 8 results in a parallelepiped or rhomboid. Therefore, the transmitter coil 7 and the two receiver coils 8 are disposed on planes parallel to each other. Furthermore, the transmitter coil 7 and the receiver coils 8 extend obliquely to the conveying direction 9 or velocity vector 9, both above and below the conveyor belt 2, and in particular at an angle α with respect to the velocity vector 9 that is greater than 0°. On both side surfaces or vertical sides of the metal detector 1, the transmitter coil 7 and the receiver coils 8 extend parallel to each other in the vertical direction.

[0022] Products 10 on the conveyor belt 2, particularly on the upper transmission belt 3, are conveyed through the gap 4 of the metal detector 1 in the conveying direction 9 or the direction of the velocity vector 9. The products 10 are thus moved past the first receiving coil 12, the transmitting coil 7, and the second receiving coil 13, ensuring reliable detection of metallic foreign objects 11 present in the products 10. To this end, the transmitting coil 7 generates a magnetic field at the location of the products 10 or the product flow. Currents corresponding to the generated magnetic field are induced in the two receiving coils 8, 12, and 13. Since the receiving coils 8, 12, and 13 are connected in series in opposite winding directions, any disturbance of the magnetic field caused by the metallic foreign object 11 is detected by the receiving coils 8, 12, and 13. Once a product 10 containing a metallic foreign object 11 is detected, the product is immediately removed from the product flow. For this purpose, a corresponding device, particularly a pusher or gate, for removing the product 10 can be provided behind the metal detector 1 in the conveying direction 9.

[0023] 3 shows a metal detector 1 equipped with one transmitter coil 7 and two receiver coils 8, 12, and 13, in which the angle α between the normal vector 15 to the plane of the transmitter coil 7 and the velocity vector 9 is 3° to 30°, and the normal vector 15 to the plane of each of the receiver coils 8, 12, and 13 and the velocity vector 9 are aligned. Therefore, the distance from the transmitter coil 7 to the first receiver coil 12 on one vertical side of the metal detector 1 is greater than the distance from the transmitter coil 7 to the opposite vertical side of the metal detector 1, or is greater than the distance from the transmitter coil 7 to the second receiver coil 8 on that vertical side. Therefore, the distance from the transmitter coil 7 to the first receiver coil 12 on the opposite vertical side of the metal detector 1 is less than the distance from the transmitter coil 7 to the opposite vertical side of the metal detector 1, or is less than the distance from the transmitter coil 7 to the second receiver coil 8 on that vertical side.

[0024] Furthermore, the lengths of the transmitter coil 7 and receiver coil 8 are different, in this case the receiver coil 8 being shorter than the transmitter coil 7 .

[0025] The metal detector 1 does not have to be configured in a parallelepiped shape, but can have a cylindrical shape, particularly a hollow cylindrical shape, and in the case of a hollow cylindrical shape, the metal detector 1 can also be attached to a pipeline. Even in the case of a hollow cylindrical shape, it is conceivable and effective to arrange the normal vector of the plane of the transmitter coil 7 and / or receiver coil 8 so that it forms an angle greater than 0° with respect to the normal vector 9, which points to the pipeline in the conveying direction, in particular. [Explanation of symbols]

[0026] 1. Metal detector 2 conveyor belt 3 Upper transmission belt 4. Vacant Space 5 Lower transmission belt 6. Housing 7 Transmitting Coil 8 receiving coil 9 Conveying direction / speed vector 10 products 11 Metallic foreign bodies 12 First receiving coil 13 Second receiving coil 14 Vertical side 15 Normal Vector

Claims

1. A metal detector (1) comprising at least one transmitting coil (7) and at least one receiving coil (8, 12, 13), a metal detector (1) in which the transmitting coils (7) and the receiving coils (8, 12, 13) are each arranged in a plane, each plane having a normal vector (15) perpendicular to said plane, the transmitting coils (7) and the receiving coils (8, 12, 13) being connected to a measuring device, and a product (10) being conveyed past the metal detector (1) along a velocity vector (9); an angle (α) between the velocity vector (9) and at least one of the normal vector (15) of the transmitting coil (7) and / or the normal vector (15) of the receiving coils (8, 12, 13) is greater than 0°; The metal detector (1) is characterized in that the angle (α) between the normal vector (15) of the plane of the transmitting coil (7) and the velocity vector (9) is 3° to 30°, and the normal vector (15) of the plane of the receiving coils (8, 12, 13) and the velocity vector (9) are located on a straight line.

2. 2. The metal detector (1) according to claim 1, characterized in that the metal detector (1) has a housing (6), and the transmitting coil (7) and the receiving coils (8, 12, 13) are arranged in the housing (6).

3. 3. A metal detector (1) according to claim 2, characterized in that the housing (6) comprises a cavity (4).

4. 4. The metal detector (1) according to claim 3, characterized in that the products (10) are transported through the cavity of the metal detector (1) on a transport belt (2).

5. 5. The metal detector (1) according to claim 4, characterized in that the housing (6) is arranged perpendicular to the conveyor belt (2).

6. 6. Metal detector (1) according to any one of claims 1 to 5, characterized in that the transmitter coil (7) and the receiver coils (8, 12, 13) are arranged in the shape of a rhombohedron.

7. 7. The metal detector (1) according to claim 1, wherein the angle (α) between the normal vector (15) of the plane of at least one of the transmitting coil (7) and / or the receiving coil (8, 12, 13) and the velocity vector (9) is between 3° and 30°.

8. 8. The metal detector (1) according to any one of claims 1 to 7, characterized in that the transmitting coil (7) and the receiving coils (8, 12, 13) are wound on a bobbin.

9. 9. Metal detector (1) according to claim 8, characterized in that the former has at least two grooves for accommodating the transmitting coil (7) and the receiving coil (8, 12, 13).

10. 10. Metal detector (1) according to any one of claims 1 to 9, characterized in that the transmitting coil (7) and the receiving coil (8, 12, 13) each consist of one winding.

11. 11. The metal detector (1) according to any one of claims 1 to 10, characterized in that the metal detector (1) has at least one second receiving coil (8, 13), and the transmitting coil (7) is arranged between two of the receiving coils (8, 12, 13).

12. A metal detector (1) as described in claim 11, characterized in that the two receiving coils (8, 12, 13) are connected in series in opposite directions with respect to the winding direction.

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