Winding frame for metal detection device

Abstract

To suppress decrease in sensitivity of a metal detector.SOLUTION: In a metal detector 1 having at least one transmitter coil 7 and at least one receiver coil 8, the transmitter coil and the receiver coil are arranged in a housing 6. The transmitter coil and the receiver coil are wound around a bobbin, and the bobbin forms a search channel 4. A conveyance device 2 conveys a product through the search channel. The bobbin has an external surface oriented in a direction of an inner space of the housing, and a search channel surface oriented in a direction of the conveyance device 2. The transmitter coil and the receiver coil are arranged on the external surface of the bobbin and connected to a measuring device. In the metal detector, the bobbin is formed of a support material, an electrically conductive layer is disposed on the search channel surface of the bobbin, and the electrically conductive layer is interrupted by at least one groove.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] A metal detector having at least one transmitting coil and at least one receiving coil, wherein the transmitting coil and the receiving coil are arranged within a housing, the transmitting coil and the receiving coil are wound around a bobbin, the bobbin forms a search channel, a conveying device conveys a product through the search channel, the bobbin has an outer surface oriented in the direction of the inner space of the housing and a search channel surface oriented in the direction of the conveying device, the transmitting coil and the receiving coil are arranged on the outer surface of the bobbin and are connected to a measuring device.

Background Art

[0002] Metal detectors of the type considered here are used, particularly for product control, for example in food production, to inspect individual products or a more or less continuous product flow for metal contaminants. Such contaminants can be metal pieces 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, depending on the material of the contaminant, the convergence or suppression of the magnetic field lines can be detected and evaluated.

[0004] In a typical application example, a product is conveyed on a conveyor belt or a similar conveying device through a metal detector, which includes three or more coils surrounding the conveyor belt and the product conveyed thereon.

[0005] One of those coils has a high-frequency alternating current applied thereto, whereby that coil generates a magnetic field at the location of the product flow and thus acts as a transmitting coil. The other two coils are utilized as receiving coils. That is, an electric current corresponding to the generated magnetic field is induced in those two coils. In this case, since the receiving coils are connected in series in opposite directions with respect to the winding direction, when the magnetic field is not disturbed, the resulting voltage is zero. In particular, when the magnetic field is disturbed by a foreign metal object, an output voltage different from zero occurs. For example, DE19530987C1 discloses a corresponding metal detector.

[0006] Furthermore, from the prior art, a winding frame made of, for example, cardboard or MDF board is known. The winding frame is arranged to surround the product in a tunnel shape. The side facing the product is coated, for example, with a graphite paint or an alternative paint mixed with conductive particles, and on the side opposite the product, grooves for accommodating the transmitting unit and the receiving unit are formed by milling. The graphite layer is provided over the entire surface. Thereby, it is possible to define auxiliary eddy currents that interact with the product guided over that surface.

[0007] A disadvantage of the known prior art is that the eddy currents generated in the graphite layer enhance the product effect, thereby reducing the sensitivity of the metal detector. The product effect depends on the product to be inspected. In this case, the product itself to be inspected has a signal that, depending on its own conductivity or magnetic properties, may in some cases have a signal with the signal of the product containing contaminants superimposed. In order to reduce false detections due to the product effect, for example, it is conceivable to lower the sensitivity of the metal detector, but thereby, contaminants up to a certain size can no longer be detected. SUMMARY OF THE INVENTION

[0008] Accordingly, an object of the present invention is to provide a winding frame for a metal detector that eliminates or at least mitigates the disadvantages known from the prior art.

[0009] This problem is achieved in the metal detector as described at the beginning, where the winding frame is made of a support material, a conductive layer is arranged on the search channel surface of the winding frame, and the conductive layer is interrupted by at least one groove. The groove has a groove bottom surface and two groove side surfaces, and at least the surface of the groove bottom surface of the groove is made of the support material. In particular, the groove side surfaces can also be made at least partially of the support material. The conductive layer is, in particular, a graphite layer, and this graphite layer is deposited on at least one surface of the support material. The support material consists of a non-conductive material or an insulating material. In particular, the support material is made of cardboard or MDF board. The winding frame is arranged, in particular, in a special steel housing that is grounded. Due to the voltage of the transmitting coil in the range of, for example, 60 V, eddy currents are generated in the conductive layer, and these eddy currents interact with the product to be inspected, thereby reducing the sensitivity to metal inclusions or foreign metal objects depending on the product to be inspected. Since there is at least one groove, the conductive layer is divided, thereby reducing the propagation or generation of eddy currents. The groove is preferably provided by a separation process or a removal process, particularly by a machining process, a laser ablation process or a laser trimming process. Particularly preferably, the groove is formed by milling the support material. In particular, the conductive layer is deposited on the support material before the separation process or the removal process.

[0010] In another configuration, the groove divides the conductive layer into individual conductive strips that are interconnected. Here, the conductive layer is divided into at least two interconnected conductive strips depending on the dimensions of the metal detector and / or the width of the conveying device. In particular, the product has a width and / or height that is at least twice the width of the conductive strip, and preferably, the product has a width that is at least four times the width of the conductive layer. Particularly preferably, the product has a width that is at least six times the width of the conductive strip. This reduces the area of the conductive strip, and as a result, the propagation or generation of eddy currents is at least reduced or completely blocked. Further, the groove extends in a wavy and / or meandering shape. Preferably, the conductive strip and / or the groove has a polygonal, particularly a rectangular, geometry, and the conductive strip and / or the groove do not have to extend linearly between two vertices. Particularly preferably, the conductive strip and / or the groove extend linearly at at least one inflection point and are not in a curved shape.

[0011] In another configuration, the groove consists of at least one longitudinal groove and / or at least one transverse groove. The longitudinal groove extends in the direction of the conveying direction of the product, and the transverse groove extends in a direction transverse to the conveying direction. In particular, the longitudinal groove is longer than the transverse groove. Preferably, the distance between two longitudinal grooves is smaller than the width and / or height of the product. Here, the width and / or height of the product extends perpendicular to the conveying direction. In particular, the area of the groove, particularly the area of the groove bottom surface, is at least 1 / 10 of the area of the conductive layer, preferably the area of the groove, particularly the area of the groove bottom surface, is at least 1 / 5 of the area of the conductive layer, and particularly preferably, the area of the groove, particularly the area of the groove bottom surface, is at most half of the area of the conductive layer. This prevents the milling section of the groove from becoming overly long and enables inexpensive manufacturing.

[0012] Here, the width of one or more products is based on one or more product surfaces that extend perpendicular to the conveying direction. In particular, the width of the product is the average width of the product.

[0013] In another configuration, the winding frame consists of four faces, and the conductive layer is grounded on at least one face of the winding frame. In particular, the conductive layer is provided on all faces of the winding frame, and each face is grounded. For this reason, at least one grounding point of the conductive layer is the receiving coil Facing is arranged. In particular, at least one grounding point of the winding frame is connected to the housing of the metal detector, and this housing is also grounded in the same way.

[0014] In another configuration, the conductive layer has a layer thickness with a surface resistance between 10 ohms and 500 ohms, preferably between 20 ohms and 300 ohms, and particularly preferably between 40 ohms and 200 ohms. To determine the surface resistance of the conductive layer, after the conductive layer is deposited, especially after the conductive layer is completely dried, a plurality of measurement points are positioned at a distance of 30 mm, preferably at a distance of 20 mm, and particularly preferably at a distance of 15 mm, and the surface resistance of the conductive layer is determined between the measurement points.

[0015] In another configuration, the housing of the metal detector is conductive. Thereby, the metal detector is shielded from electromagnetic interference.

[0016] The housing of the metal detector has a detection channel, and the product is conveyed through the detection channel of the metal detector in the conveying device. In particular, the housing is arranged at a right angle to the conveying device. Further, at least one transmitting coil and / or at least one receiving coil are arranged in a direction transverse to the conveying direction of the conveying device. Thereby, all products pass through at least one transmitting coil and at least one receiving coil.

[0017] Furthermore, at least one receiving coil and at least one transmitting coil are wound around a bobbin. In particular, at least two grooves extending in the circumferential direction are arranged on the outer surface of the bobbin, and the transmitting coil and the receiving coil are arranged in these grooves. The transmitting coil and the receiving coil are arranged in the grooves on the outer surface of the bobbin, thereby being maintained in a predetermined position. Furthermore, this eliminates the possibility that the position of the transmitting coil or the receiving coil changes relative to the receiving coil or the transmitting coil during manufacturing or operation. Furthermore, the transmitting coil and the receiving coil are each formed from a winding, among other things. Also, the positions of the transmitting coil and the receiving coil can be maintained by a transport lock.

[0018] In another configuration, the metal detector has at least one second receiving coil, and at least one transmitting coil is arranged between the two receiving coils. The two receiving coils are connected in series in opposite directions with respect to the winding direction. Furthermore, at least one transmitting coil and at least one receiving coil are arranged in planes parallel to each other. In particular, the transmitting coil and the receiving coil are symmetrically arranged within the housing. The transmitting coil can be received by the two receiving coils and also generates a magnetic field that induces a voltage in the two receiving coils. For example, as long as there is no obstacle to the magnetic field in the form of a metallic foreign object, since the receiving coils are connected in series in opposite winding directions and are particularly symmetrically arranged within the housing, the voltage generated at the output terminals of the receiving coils is 0. When a metallic foreign object affects the magnetic field, the voltage generated at the output terminals of the receiving coils will no longer be 0.

Brief Description of the Drawings

[0019] Another advantageous aspect will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings.

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0020] FIG. 1 shows a metal detector 1 provided with a conveying device 2. The upper transmission belt 3 of the conveying belt 2 travels through the detection channel 4 of the metal detector 1, and the lower transmission belt 5 extends below the metal detector 1. The metal detector 1 has a housing 6, and at least one transmitting coil 7 and at least one receiving coil 8 are arranged in the housing 6. The transmitting coil 7 and the receiving coil 8 are each arranged in one plane, and each plane extends parallel to each other. The housing 6 is made of, among other things, metal, especially special steel.

[0021] FIG. 2 shows a schematic view of the spool frame 9. The spool frame 9 has at least two grooves 11 on the outer surface 10, and the transmitting coil 7 and the receiving coil 8 extend in these grooves 11. Each groove 11 extends across the entire spool frame 9. The spool frame 9 is made of a support material 12 which is, among other things, cardboard, and a conductive layer 13 which is adhered to at least the detection channel surface 14 of the spool frame 9. The support material 12 is not covered on the outer surface 10 of the spool frame 9, among other things.

[0022] At least one groove 15 is provided on the detection channel surface of the spool frame 9. This groove 15 is formed, among other things, by milling the conductive layer 13, so the conductive layer 13 no longer exists in the region of the groove 15. Here, the depth of the groove follows the layer thickness of the conductive layer 13. The spool frame 9 consists of, among other things, four surfaces 16, 17, 18, 19, and each surface 16, 17, 18, 19 has a conductive layer 13 on the detection channel surface 14, and at least one groove 15 is arranged in each conductive layer 13. The four surfaces 16, 17, 18, 19 consist of, among other things, four individual plates 16, 17, 18, 19, and each plate 16, 17, 18, 19 is adhered to each other, among other things. At least one grounding point 20, especially two grounding points 20, is arranged on each surface 16, 17, 18, 19. The grounding point 20 is the receiving coil 8Facing It is configured, and each grounding point 20 is arranged at the outer edge of the winding frame 9, particularly on each of the surfaces 16, 17, 18, 19. In particular, the grounding point 20 is arranged in the central region of each of the surfaces 16, 17, 18, 19 at the respective outer edges of the winding frame 9. The grounding point 20 is connected to each conductive layer 13. Preferably, the conductive layers of each of the surfaces 16, 17, 18, 19 of the winding frame 13, particularly the conductive layers 13 of the adjacent surfaces 16, 17, 18, 19, are not connected to each other via the conductive layer 13. Therefore, two adjacent surfaces 16, 17, 18, 19 are connected to each other only via the support material 12. The conductive layer 13 is removed in this region, particularly in the corner region.

[0023] Furthermore, the winding frame 9 can have a plurality of reinforcing parts 21, and those reinforcing parts 21 are arranged at each outer edge of the winding frame 9.

[0024] Figure 3 shows a plan view of the faces 16, 17, 18, 19 of the winding frame 9. The groove 15 divides the conductive layer 13 into individual conductive strips 22 that are interconnected. Here, the conductive layer 13 is divided into at least two interconnected conductive strips 22 depending on the dimensions of the metal detector 1 and / or the width of the conveying device 2. In particular, the product has a width and / or height that is at least twice the width of the conductive strip 22. Further, the groove 15 extends in a wavy and / or meandering shape. The conductive strips 22 have a polygonal, in particular quadrilateral, geometry, in which case the conductive strips 22 do not have to extend linearly between two vertices 23. The groove 15 likewise has a polygonal geometry. Both the groove 15 and the conductive strips 22 can have rounded or chamfered portions in the region of the vertices. Further, the conductive strips 22 and / or the groove 15 extend linearly at at least one inflection point 24 and are not in a curved shape. Also, the groove 15 may extend beyond the edge region of the conductive layer 13, whereby the conductive layer 13 on each of the faces 16, 17, 18, 19 is divided by the groove 15 into at least two conductive layers 13. Thus, each of the faces 16, 17, 18, 19 has two conductive layers 13 that are separated from each other, and those conductive layers 13 are each connected to one ground point 20.

[0025] The groove 15 consists of at least one longitudinal groove 25 and / or at least one transverse groove 26. The longitudinal groove 25 extends in the direction of the product conveyance direction 27, and the transverse groove 26 extends in a direction transverse to the conveyance direction 27 or perpendicular to the conveyance direction 27. The longitudinal groove 25 is longer than the transverse groove 26. Furthermore, the distance between two longitudinal grooves 25 is smaller than the width and / or height of the product. Here, the width and / or height of the product extends perpendicular to the conveyance direction 27. Also, the area of the groove 15, particularly the area of the groove bottom surface, is at least 1 / 10 to at most half of the area of the conductive layer 13. For example, the width BS of the conductive strip 22 may be between 3 mm and 100 mm, preferably between 5 mm and 50 mm, and particularly preferably between 8 mm and 40 mm. Furthermore, for example, the width BN of the groove 15 may be between 1 mm and 50 mm, preferably between 2 mm and 30 mm, and particularly preferably between 4 mm and 20 mm.

[0026] In at least two opposing side regions 28 of each of the plates 16, 17, 18, 19, the groove 15 is longer in this region than the remaining longitudinal grooves 15 and / or the remaining transverse grooves 26. In this case, the groove 15 can extend across the entire width and / or length of each of the plates 16, 17, 18, 19, particularly in at least two opposing side regions 28. Furthermore, the groove 15 in the side region 28 may be wider than the remaining longitudinal grooves 25 and / or the remaining transverse grooves 26.

[0027] Figure 4 shows another arrangement of the grooves 15 on at least one of the surfaces 16, 17, 18, 19 of the winding form 9. Different from the wavy and / or meandering grooves 15 in Figure 3, in Figure 4, a plurality of grooves 15 are arranged parallel to each other, and each groove has a first end 30 and a second end 31. In particular, the second end 31 of the groove 15 extends to the lower edge 29 of the conductive layer 13. However, by leaving a distance from the lower edge 29, the groove 15 does not have to reach the lower edge 29. The same applies to the first end 30 of the groove 15. Therefore, the first end 30 of the groove 15 may reach the upper edge 32, or by leaving a distance from the upper edge 32, the groove 15 does not have to reach the upper edge 32. If at least one of the ends 30, 31 of the groove 15 does not reach the upper edge 32 or the lower edge 29, or if at least one of the ends 30, 31 of the groove 15 terminates at a distance from the upper edge 32 or the lower edge 29, the conductive layer 13 consists of one related conductive layer 13 that is interrupted by the groove 15. In this case, the groove 15 divides the conductive layer 13 into individual conductive strips 22 that are connected to each other. Therefore, only longitudinal grooves 25 extending in the transport direction 27 are arranged in the conductive layer 13. In particular, the conductive layer 13 has a comb-like geometry.

[0028] If the first end 30 of the groove 15 reaches the upper edge 32 and the second end 31 of the groove 15 reaches the lower edge 29, the conductive layer 13 consists of at least two, in particular a plurality of, conductive layers 13 or conductive strips 22 that are not connected to each other or are separated from each other by the groove 15. In this case, each conductive strip 22 can be grounded and / or can have its own ground point 20.

[0029] Furthermore, the distance between the two longitudinal grooves 25 is smaller than the width and / or height of the product, where the width and / or height of the product extends perpendicular to the conveying direction 27. Also, the area of the groove 15, especially the area of the groove bottom surface, is at least 1 / 10 to at most half of the area of the conductive layer 13. For example, the width BS of the conductive strip 22 may be between 3 mm and 100 mm, preferably between 5 mm and 50 mm, and particularly preferably between 8 mm and 40 mm. Further, for example, the width BN of the groove 15 may be between 1 mm and 50 mm, preferably between 2 mm and 30 mm, and particularly preferably between 4 mm and 20 mm.

[0030] In at least two opposing side regions 28 of each of the plates 16, 17, 18, 19, another groove 15 is longer and / or wider in this region than the remaining longitudinal grooves 25, where the groove 15 can extend, in particular in at least two opposing side regions 28, over the entire width and / or length of each of the plates 16, 17, 18, 19.

Explanation of Reference Numerals

[0031] 1 Metal detector 2 Conveying device 3 Upper transmission belt 4 Search channel 5 Lower transmission belt 6 Housing 7 Transmitting coil 8 Receiving coil 9 Winding frame 10 Outer winding frame 11 Groove outer surface 12 Support material 13 Conductive layer 14 Search channel surface 15 Groove search channel surface 16 First surface / plate 17 Second surface / plate 18 Third surface / plate 19 Fourth surface / plate 20 Grounding point 21 Reinforcement part 22 Conductive strip 23 vertices 24 inflection points 25 longitudinal groove 26 transverse groove 27 conveying direction 28 side region 29 lower edge 30 first end groove 31 second end groove 32 upper edge B S width conductive strip B N width groove

Claims

1. A metal detector (1) having at least one transmitting coil (7) and at least one receiving coil (8), wherein the transmitting coil (7) and the receiving coil (8) are arranged within a housing (6), the transmitting coil (7) and the receiving coil (8) are wound around a winding frame (9), the winding frame (9) forms a search channel (4), a conveying device (2) conveys a product through the search channel (4), the winding frame (9) has an outer surface (10) oriented in the direction of the internal space of the housing (6) and a search channel surface (14) oriented in the direction of the conveying device (2), and the transmitting coil (7) and the receiving coil (8) are arranged on the outer surface (10) of the winding frame (9) and are connected to a measuring device, in the metal detector (1). The winding frame (9) is made of a support material (12), a conductive layer (13) is arranged on the search channel surface (14) of the winding frame (9), and the conductive layer (13) is interrupted by at least one groove (15). The groove (15) divides the conductive layer (13) into individual conductive strips (22) that are interconnected, characterized in the metal detector (1).

2. The metal detector (1) according to claim 1, characterized in that the support material (12) is made of a non-conductive material.

3. The metal detector (1) according to claim 1 or 2, characterized in that the surface of the bottom of the groove (15) consists of the support material (12).

4. The metal detector (1) according to any one of claims 1 to 3, characterized in that the groove (15) extends in a wave-like or meandering shape.

5. The metal detector (1) according to claim 4, characterized in that the groove (15) extends linearly at at least one inflection point (24).

6. The metal detector (1) according to any one of claims 1 to 5, characterized in that the area of the groove (15) is at least 1 / 10 to at most half of the area of the conductive layer (13).

7. The metal detector (1) according to any one of claims 1 to 6, characterized in that the groove (15) consists of at least one longitudinal groove (25) extending in the conveying direction (27) of the product and / or a transverse groove (26) extending in a direction transverse to the conveying direction (27).

8. The metal detector (1) according to claim 7, characterized in that the longitudinal groove (25) is longer than the transverse groove (26).

9. The metal detector (1) according to any one of claims 1 to 8, characterized in that the winding frame (9) consists of four surfaces (16, 17, 18, 19), and the conductive layer (13) is grounded on at least one surface (16, 17, 18, 19) of the winding frame (9).

10. The metal detector (1) according to any one of claims 1 to 9, characterized in that at least one grounding point (20) of the conductive layer (13) is arranged facing the receiving coil (8).

11. The metal detector (1) according to any one of claims 1 to 10, characterized in that at least two grooves (11) extending in the circumferential direction are arranged on the outer surface (10) of the winding frame (9), and the transmitting coil (7) and the receiving coil (8) are arranged in the grooves (11).

12. The metal detector (1) according to any one of claims 1 to 11, characterized in that the conductive layer (13) has a layer thickness with a surface resistance between 10 ohms and 500 ohms.

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