Metal detector and method for detecting metal in conveyed material

Abstract

The invention relates to a metal detector for detecting electromagnetically detectable components in a conveyed material having components made of materials of different electromagnetic properties and running in a conveying direction along a conveying path through a detection region of the metal detector, comprising: a support structure, the load bearing structure defines a passage for conveying material. The passage extends from an inlet for conveying the material to an outlet in a longitudinal direction of the support structure that can be oriented parallel to the conveying direction. Furthermore, a coil system having a plurality of coils is provided, which coils are arranged on the carrier structure and define a detection zone between the inlet and the outlet. The coil comprises a transmitting coil and a receiving coil. The first transmitting coil arrangement is used for generating a first excitation field in a first field direction which is oriented transversely to the longitudinal direction, and the first transmitting coil arrangement is provided with a first transmitting coil which can be excited in phase; the first transmitting coil is arranged at opposite sides outside the passage and has a coil axis oriented transversely to the longitudinal direction. The second transmitting coil arrangement is used for generating a second excitation field in a second field direction which is oriented transversely to the longitudinal direction, and the second transmitting coil arrangement is provided with a second transmitting coil which can be excited in phase; the second transmitting coil is arranged at an opposite side outside the passage and has a coil axis oriented transversely to the longitudinal direction. The second transmitting coil arrangement is offset in the longitudinal direction with respect to the first transmitting coil arrangement. The second field direction is directed opposite the first field direction.

Description

Technical Field

[0001] The invention relates to a metal detector for detecting electromagnetically detectable components in a conveyed material, which has components made of materials with different electromagnetic properties and passes through a detection zone of the metal detector along a conveying path in a conveying direction. Background Art

[0002] Metal detectors of the type considered in this application operate according to the electromagnetic principle and are therefore able to identify or detect materials or objects based on their electrical conductivity and / or magnetic permeability (permeability) and, if the differences in the electromagnetic properties are sufficiently large, also to distinguish different components from one another. In this context, the term "metal detector" refers to the ability to detect metals (as a typical representative of materials with relatively high electrical conductivity) in conveyed materials, which may contain materials with poor electrical conductivity or even no electrical conductivity at all.

[0003] Possible areas of application for metal detectors are, for example, the food industry, the pharmaceutical industry, the plastics industry or more generally the chemical industry or the packaging industry. The purpose of using metal detectors in these application areas is to quickly and reliably detect the presence of unwanted metal parts in conveyed materials, which otherwise consist mainly or only of non-conductive or only weakly conductive materials. The conveyed material can be individual pieces, i.e. items that are transported individually "by piece", but also bulk materials. Such metal detectors are widely used in the industrial sector and are often integrated in production lines or packaging lines.

[0004] A non-limiting example of application is food monitoring at a water flow belt. This is particularly related to the detection of the smallest metal particles that cause contamination within the scope of food processing and / or food packaging.

[0005] Another field of application is that of material sorting, in particular of metal sorting, where, for example in the context of recycling, it may be necessary to separate objects made of non-ferrous metals with good electrical conductivity (such as copper, aluminum or their alloys) from mixtures with components made of metals and / or non-metals with poor electrical conductivity.

[0006] As a standard, so-called tunnel metal detectors are often used today. In addition to their simple construction, conventional tunnel metal detectors offer high sensitivity and stability in particular and have therefore been considered the standard in food monitoring for many years. However, they also have a number of disadvantages, in particular the relatively large space requirement on the belt due to the large metal-free zone (MFZ) and the necessary product balancing during detection. The MFZ is the area in front of and behind the ends of the tunnel that must be kept free of metal objects in order not to interfere with the detection in the detection zone. Moving metal objects are particularly critical here.

[0007] Document EP 2 729 831 B1 discloses a conventional tunnel metal detector having a metal housing with a rectangular input opening and a rectangular exit opening. There is a coil system in the housing, which has at least one transmitting coil that can be excited by an alternating current, at least one first receiving coil and at least one second receiving coil. These coils limit the detection zone in the direction of travel, which extends between the input opening and the exit opening, and the items to be inspected move through the detection zone. The transmitting coil and the receiving coil surround a "tunnel" extending between the input opening and the exit opening, through which the conveyed material passes. In one embodiment, an elimination device is arranged at the input opening and the output opening to eliminate the primary electromagnetic field generated by the transmitting coil. As a result, the extension of the "metal-free zone" (MFZ) can be reduced.

[0008] Document DE 44 24 058 C1 discloses a device designed in the manner of a tunnel detector for generating an identification signal when a metallic conductive object is present in an at least substantially non-conductive conveying flow, wherein an alternating electromagnetic field is generated by an alternating current generator via a transmitting coil in a section of the conveying flow to be monitored, the amplitude and phase changes of which are detected by means of a coil system supplied to an evaluation circuit in order to derive the identification signal. The coil system consists of at least two individual systems, each comprising a transmitting coil and a receiving coil, one of which is arranged relative to the conveying flow in such a way that the magnetic field of its transmitting coil extends predominantly in the direction of the conveying flow, and at least one other is arranged in such a way that the magnetic field of its transmitting coil extends predominantly transversely to the direction of the conveying flow. Each of the individual systems is provided with an evaluation circuit, and the signal output of the evaluation circuit is connected to an evaluation logic circuit, which is designed in such a way that it performs an object-specific evaluation as a function of the signal supplied to it. The device should be particularly sensitive to small and elongated objects, such as short wires or thread pins. Summary of the invention

[0009] Against this background, the object of the present invention is to provide a metal detector and a method for detecting metal which, compared to the prior art, require only less structural space for integration in a conveyor section with compact dimensions and only a small metal-free zone and require no or only moderate product balancing for reliable detection.

[0010] To achieve this object, the invention provides a metal detector having the features of claim 1 and a method having the features of claim 13. Advantageous developments are described in the dependent claims. The wording of all claims is incorporated into the content of the description by reference.

[0011] According to one embodiment, the invention relates to a metal detector for detecting electromagnetically detectable components in a conveyed material, the conveyed material having components made of materials with different electromagnetic properties and passing through a detection zone of the metal detector along a conveying section in a conveying direction. In some application cases, the conveyed material consists mainly of non-conductive or only weakly conductive materials, and the objects to be detected are metal parts with a relatively high conductivity in comparison thereto, which constitute undesired foreign bodies in the conveyed material.

[0012] Preferably, the conveying section extends more or less horizontally. For example, the conveyor belt can be guided through the detection zone in such a way that the conveyed material located on the upper side of the conveyor belt is conveyed through the detection zone of the metal detector. Other conveying directions in space are possible.

[0013] The metal detector has a supporting structure which defines a through passage for conveying material. The through passage extends in the longitudinal direction of the supporting structure from an inlet to an outlet for conveying material. Normally, the metal detector is arranged with respect to the conveying direction such that the longitudinal direction of the supporting structure is oriented parallel or substantially parallel to the conveying direction.

[0014] The transverse direction of the load-bearing structure is oriented perpendicularly to the longitudinal direction. The height direction of the load-bearing structure is perpendicular to the plane spanned by the longitudinal direction and the transverse direction. In most applications, the longitudinal direction and the transverse direction lie in a horizontal plane, and the (vertical) height direction of the load-bearing structure runs perpendicularly to this horizontal plane. Other orientations in space are possible.

[0015] The available width of the passage in the transverse direction is adapted to the width of the conveying device in such a way that each conveyed object passes through the detection zone. The height of the passage is usually smaller than its width and can correspond to the maximum height of the conveyed material that is to pass through the passage. The passage often has a flat rectangular cross section, whose width (in the transverse direction) is significantly greater than its height, for example at least twice or at least five times. However, situations different from this are possible.

[0016] Metal detectors detect conductive objects based on the transmitter-receiver principle by generating and detecting eddy currents in conductive materials (e.g. metals). To this end, the metal detector comprises a coil system with a plurality of coils, which are arranged at a supporting structure and define a detection zone between an inlet and an outlet. The coils comprise a transmitting coil and a receiving coil.

[0017] The significant function of the support structure is to ensure a fixed spatial relationship between the coils of the coil system that are installed thereon. The support structure can be a component of a corresponding mechanically stable construction, which can be transported as a whole if necessary and is set up together with the coils installed thereon at the place of use. However, the components of the support structure do not have to be directly connected to each other. It is also possible that the support parts of the support structure are mounted on a room wall, a room ceiling or a floor and are only kept in a fixed spatial relationship with each other via structural components of the building containing the room. For example, one part of the support structure can be mounted in a manner suspended from the ceiling of a room, while another part is located on the floor.

[0018] According to one embodiment of the invention, the coil system comprises a first transmitting coil arrangement and a second transmitting coil arrangement. The first transmitting coil arrangement is configured such that, during operation, the first transmitting coil arrangement can generate a first excitation field in a first field direction oriented transversely, in particular perpendicularly, to the longitudinal direction. For this purpose, the first transmitting coil arrangement has two first transmitting coils that can be excited in phase, which are arranged on opposite sides outside the passage and have a coil axis oriented transversely, in particular perpendicularly, to the longitudinal direction.

[0019] Furthermore, there is (at least one) second transmitting coil arrangement for generating a second excitation field in a second field direction oriented transversely, in particular perpendicularly, to the longitudinal direction, wherein the second transmitting coil arrangement has two second transmitting coils that can be excited in phase, which are arranged on opposite sides outside the passage and have coil axes oriented transversely, in particular perpendicularly, to the longitudinal direction. The second transmitting coil arrangement is arranged offset in the longitudinal direction relative to the first transmitting coil arrangement. The second field direction points opposite to the first field direction.

[0020] During operation, the transmitting coil is connected to an alternating voltage source and generates a preferably continuous alternating electromagnetic field, the main field component of which is directed transversely, in particular perpendicularly, to the longitudinal direction of the passage. The alternating electromagnetic field induces a voltage in the receiving coil, which is evaluated by means of a connected evaluation device. As soon as an electrically conductive object, in particular a metal object, enters the detection zone, eddy currents are generated in the object by the alternating electromagnetic field of the transmitting coil, which act on the receiving coil by mutual induction. Therefore, the alternating field is disturbed by the entering metal object, which is detected by the receiving coil. The evaluation device processes the corresponding signal, evaluates the signal and reports the presence of electrically conductive, in particular metallic contaminants in the conveyed material under precisely definable conditions.

[0021] In the present application, the term "coil axis" refers to a direction perpendicular or substantially perpendicular to a winding plane defined by the course of the winding wires of the coil. In the case of a flat coil with winding wires extending helically in a common winding plane, the coil axis is oriented perpendicular to the winding plane. If the winding wires extend helically in the coil, the coil axis is given by the longitudinal axis of the helix and, depending on the pitch of the helix, only extends approximately perpendicular to the winding plane.

[0022] The "field direction" is the direction in space in which the main component of the alternating electromagnetic field generated by the transmitting coil arrangement points. The coils may also be referred to as "field coils" or "excitation coils". The alternating electromagnetic field generated by the transmitting coil is also referred to herein as the excitation field or the transmitting field or the primary field.

[0023] Preferably, there are exactly two transmitting coil arrangements arranged one behind the other in the longitudinal direction, but one or more further transmitting coil arrangements may also be provided as required, ie, a total of, for example, three or four transmitting coil arrangements.

[0024] Compared to conventional tunnel metal detectors, there are significant structural and functional differences, which are manifested in particular in the orientation and arrangement of the coils and which bring about particular technical advantages.

[0025] In conventional tunnel metal detectors, there is at least one transmitting coil which completely surrounds the passage for conveying material and accordingly has a coil axis which runs in the longitudinal direction of the passage, i.e. essentially parallel to the conveying direction of the conveyed material. In contrast, metal detectors of the type described here preferably do not have a transmitting coil which surrounds the passage with a coil axis which points in the longitudinal direction.

[0026] Compared to the transmission coils surrounding the passage, the first and second transmission coils therefore have an orientation rotated by 90°, so that a focus is produced, so to speak, transversely, in particular perpendicularly, to the conveying direction. The term "focus" here refers to the direction in which the main excitation field is oriented (first field direction and second field direction).

[0027] This orientation makes it possible to achieve that essentially only such metal objects can trigger a detection signal, which are located in the detection zone, i.e. between the entrance and the exit. If, on the other hand, moving metal objects are outside the detection zone, these objects do not actually generate a detection signal, even if they are near the entrance or the exit. Therefore, compared with conventional metal detectors, the so-called metal-free zone (MFZ) (i.e. such areas in front of and behind the ends of the passage, which must remain free of metal objects in order not to interfere with the detection in the detection zone) is significantly shorter or smaller and can be completely omitted if necessary, so that metal objects that are moved if necessary can also be arranged directly in front of the entrance or directly behind the exit at a small distance. As a result, when such a metal detector is integrated into a production line or a conveyor line, only less "metal-free" structural space is required in the axial direction, which simplifies integration in the assembly line.

[0028] Another significant advantage is that, due to the arrangement of the two transmitting coils connected successively in the conveying direction, only the elements in the detection zone provide a significant evaluation effect, and thus a smaller product spacing in the longitudinal direction is achieved. Here, the term "product spacing" refers to the following spacing between two products, which should be maintained so that the metal detector can clearly associate a possible signal with one or another product. If the products are too close to each other axially, it is not possible to know from the detection signal which of the products contains the impurity that triggers the signal. Therefore, there is a significant advantage in the product spacing required for reliable detection in the conveying direction or axial direction, so that more products can be reliably checked per unit time when the conveying speed remains unchanged.

[0029] The first transmission coil arrangement and the second transmission coil arrangement are connected to each other in a differential manner or can be operated in a differential manner. In other words, the first excitation field and the second excitation field are phase-shifted by 180° relative to each other. This can be achieved, for example, by connecting two transmission coils (the first transmission coil and the second transmission coil) arranged on the same side of the passage electrically in series, but with opposite winding directions, so that the excitation currents through the two transmission coils generate fields of the two coils that point in opposite directions. It is also possible to design the windings of the first transmission coil and the second transmission coil on one side in the same direction and to ensure the required 180° phase shift by controlling them with the aid of an AC current source.

[0030] According to this configuration, two excitation fields can be generated in the detection zone, which are connected successively in the conveying direction and are substantially uniform in the width and height of the passage, and have opposite field directions. Figuratively speaking, the conveyed material passes through two excitation field curtains with opposite field directions directly successively in time.

[0031] By differential switching, the sensitivity can be increased and even the smallest particles can be detected. In addition, the detection signal generated when passing through the detection zone now also gives conclusions about the position of the conveyed material in the conveying direction, thereby creating a position resolution in the conveying direction.

[0032] For this purpose, a symmetrical design is advantageous. According to one development, the first transmitting coil arrangement and the second transmitting coil arrangement are designed substantially axisymmetrically with respect to an axis of symmetry running between the coil arrangements perpendicularly to their field direction.

[0033] It is possible to cover the entire width of the detection zone using only a single receiving coil. In contrast, a preferred embodiment is characterized in that the receiving coils have a first receiving coil and at least one second receiving coil, which are arranged side by side offset from one another on one side of the passage (outside) in a transverse direction oriented perpendicularly to the longitudinal direction, wherein the receiving coils have a coil axis oriented transversely, in particular perpendicularly, to the longitudinal direction.

[0034] Therefore, a plurality of receiving coils, namely two, three, four or more receiving coils, are provided, which are arranged on the same side outside the passage. The plurality of receiving coils are arranged offset from each other in the transverse direction. The transmitting coil extends in the transverse direction over the entire width of the passage, so that during operation, the transmitting coil generates its excitation field over the entire width of the detection zone, while each of the receiving coils covers only a portion of the width of the passage in the transverse direction, in particular, at most half of the width, and if necessary, less than 50% of the width, for example, about 33% or about 25% or about 20% or about 12% to 13%. In other words: the receiving coils define two, three, four or more adjacent detection sectors in the transverse direction. Therefore, the coil arrangement becomes sensitive to the transverse direction depending on the position, so that when evaluating the signal of the receiving coil, it can be determined whether the metal object that triggers the signal has basically passed through the area or detection sector monitored by the first receiving coil or the area monitored by the second receiving coil. It is also possible to allow a smaller product spacing in the transverse direction than in the prior art, thereby further improving the detection capability of the metal detector.

[0035] It is possible that the probe arrangement can have a receiving coil only on one side outside the through-channel, for example below the through-channel. Preferably, it is provided that for each receiving coil on one side, the coil system has a further receiving coil on the side of the through-channel opposite to this side. In this case, two receiving coils associated with each other arranged on different sides each form a receiving coil pair (that is to say a pair of two receiving coils associated with each other on opposite sides of the through-channel).

[0036] If more than one receiving coil is provided on one side, namely a first receiving coil and at least one second receiving coil which is offset in a lateral direction relative to the first receiving coil, then a corresponding number of receiving coil pairs is preferably provided.

[0037] Preferably, the first receiving coil and the second receiving coil of the receiving coil pair arranged on opposite sides each have a coaxial coil axis. Thus, when viewed in the transverse direction, there may be, for example, two, three, four or more pairs of receiving coils coaxially arranged opposite each other.

[0038] In addition to the position resolution in the lateral direction, a position resolution in the height direction, i.e., in the direction between two receiving coils, can therefore also be achieved, since it can be determined from the detection signals of the receiving coils of a sector that are arranged opposite one another whether the detected object has passed through the passage closer to one receiving coil or closer to a receiving coil that is arranged, for example, coaxially opposite one of the receiving coils.

[0039] Thus, the traversing channel can be divided into two detection sectors in the direction in which the receiving coil and the associated further receiving coil are coaxially arranged opposite each other. In a transverse direction perpendicular thereto, the number of sectors can correspond to the number of receiving coils arranged side by side. Preferably, four receiving coils are provided in the transverse direction, so that the detection channel can preferably be divided into eight detection sectors (four in the transverse direction multiplied by two in the height direction). A finer division is theoretically possible, but is usually not required.

[0040] However, a coaxial arrangement is not the only possibility. A pair of receiving coils can also be arranged offset from each other laterally (that is, in the transverse direction). Thus, for example, a first receiving coil on one side can be arranged opposite a transition region between two other second receiving coils on opposite sides. Thus, given the number of transversely offset receiving coils on one side, the position resolution in the transverse direction can be finer than in the case of a coaxial arrangement of a pair of receiving coils.

[0041] In order to ensure reliable and gap-free detection of products passing through in the transverse direction, in a preferred embodiment, it is provided that receiving coils that are directly adjacent and arranged offset from each other in the transverse direction directly adjoin each other or partially overlap in the overlapping area. This can prevent a drop in sensitivity in the transverse direction that could constitute a safety risk.

[0042] According to one improvement, it is provided that the receiving coils, in particular each first receiving coil and each second receiving coil, respectively surround a coil surface, which extends in the longitudinal direction over the first coil arrangement and the second coil arrangement in such a way that, in the absence of field disturbances, the first excitation field and the second excitation field induce oppositely identical voltages in the receiving coils. Thus, each receiving coil compensates itself and no voltage is induced therein, as long as the field distribution in the detection zone is not asymmetrically disturbed by metal objects or the like. As a result, the sensitivity of the arrangement can be increased.

[0043] The coil can be present as a coil wound from a wire. According to an improved solution, the components of the coil arrangement are manufactured by a method according to circuit board technology in the form of a printed circuit. In particular, it can be that the coils of the coil arrangement are arranged in the form of rectangular flat coils with spirally extending windings in different coil layers of a multilayer arrangement, wherein insulating layers made of electrically insulating material are respectively arranged between adjacent coil layers of the multilayer arrangement. The coil can have windings in multiple layers in order to achieve a sufficient number of windings in a limited lateral space. Such a coil arrangement allows the metal detector to be constructed compactly, relatively lightly and still stably compared to the prior art. This simplifies the operation in particular.

[0044] In order to further improve the functionality, in some embodiments the metal detector has a field shaping element made of a soft magnetic material, which is arranged outside the coil arrangement at least in the region of the transmitting coil arrangement and is preferably mounted on the support structure. For example, the field shaping element can be formed by a ferrite plate or have a ferrite plate.

[0045] A variety of effects can be achieved by means of field shaping elements. On the one hand, a shielding of the external space with respect to the alternating field generated by the transmitting coil is provided. This shielding also acts in the opposite direction, so that the internal space or the detection zone is also shielded with respect to possible external electromagnetic interference fields. In addition, an inward field concentration effect is achieved, so that the field strength that can be achieved by the transmitting coil in the region of the detection zone is increased compared to variants without field shaping elements.

[0046] If necessary, field shaping elements can be arranged on all sides of the detection channel, which surround the detection channel on all sides beside the passage channel.

[0047] Furthermore, the metal detector can have at least one electric field shield, i.e. a shield which prevents electric fields from penetrating into the detection zone. In variants with a multi-layer arrangement, the electric field shield can be integrated into one layer of the multi-layer structure containing the coil arrangement. This can further increase the sensitivity, since external electric fields cannot or cannot significantly influence the signal generation.

[0048] The concept of the invention as claimed provides technical advantages not only in the field of detection schemes, but also in general operation, especially in the integration of the conveying section. Since the coil system does not need and preferably does not have a transmitting coil or a receiving coil with a coil axis pointing in the longitudinal direction that surrounds the passage, it is very simple to achieve improved lateral accessibility of the conveying section in the area of ​​the metal detector. In some embodiments, the supporting structure has an access opening at least on one side, through which the passage can be accessed laterally. The access opening can be permanently open. It is also possible that, for normal operation, the closing element closes the access opening so as to mechanically stabilize the supporting structure when necessary. The closing element can be easily removed as needed, so that the passage can be accessed from the side. The maintenance work or replacement of the conveyor belt, etc. is thus very simple, because it is no longer necessary to pass the elongated conveying element through the passage closed in the circumferential direction, but it can be simply inserted or removed laterally at a suitable position. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further advantages and aspects of the invention are apparent from the claims and the following description of exemplary embodiments of the invention explained with reference to the drawings.

[0050] Figure 1 An embodiment of a metal detector integrated in a conveying section of a conveying system is shown;

[0051] Figure 2 Only the transmit coil arrangement is shown in an isometric view;

[0052] Figure 3 Only the receiving coil pair is shown in an isometric view;

[0053] Figure 4 shows the spatial arrangement of the coils relative to one another without a supporting structure;

[0054] Figure 5 schematically illustrates the field distribution generated by the transmitting coil in the detection region;

[0055] Figure 6 A metal detector having a magnetically soft field shaping element is shown;

[0056] Figure 7 The effect of the field shaping elements on the field distribution is shown. DETAILED DESCRIPTION

[0057] The important aspects of the novel metal detectors are explained below by way of example using the field of monitoring conveyed materials in the food industry.

[0058] The metal detector generates an electromagnetic field and evaluates the interaction of the electromagnetic field with the conveyed material passing through. As a result, the metal detector can identify or detect materials or objects based on their electrical conductivity and / or magnetic permeability and reliably distinguish different components of the conveyed material from each other if the differences in the electromagnetic properties are large enough.

[0059] Indicative Figure 1 The metal detector 100 integrated in the conveyor section 210 of the conveyor system 200 is shown in an oblique view. The conveyor system has a plurality of conveyor modules connected in succession, which together form a substantially horizontal conveyor section 210, so that a conveyed material 214 in the form of cartons 214 filled with food can be conveyed in a conveying direction 215 at the end of the production line and finally checked. The contents of the cartons should be free of metallic impurities, and the cartons themselves are also made of cardboard, for example, without the use of metallic materials.

[0060] In order to ensure that the cartons entering the market do not contain metallic foreign bodies, which may have been introduced during food processing, for example due to disturbances in operation or at the equipment, the final inspection includes a continuous inspection of all cartons to detect any metallic objects in the conveying material, which ideally consists only of non-conductive materials. The conveyor section can contain further inspection modules, such as downstream weighing units, which are used to determine whether the filling weight of the carton is within the range of a theoretical value.

[0061] The metal detector 100 has a support structure 110, which is essentially composed of a relatively thick plate made of a non-conductive, torsion-resistant plastic, for example a thermosetting plastic material. An upper support plate 112-1 extends horizontally and perpendicularly to the conveying direction 215 in the transverse direction Q of the support structure above the conveying section. A lower support plate 112-2 extends parallel to the upper plate in the transverse direction Q below the conveyor belt. The plates are arranged on a Figure 1 The sides of the middle and rear parts are connected via stable vertical plates 112-3, so that a rectangular U-shape is obtained in the cross section perpendicular to the conveying direction 215. Figure 1 At the front side visible from the front, the support structure is open and thus provides an access opening 114 between the horizontal plates, through which the conveyor section 210 is accessible from this side. In order to stabilize the support structure, the access opening 114 can be closed during operation by one or more closing elements 116 (e.g. vertical plates), which connect the upper plate 112-1 to the lower plate and thus stabilize the essentially rectangular support structure.

[0062] Ideally, the longitudinal direction L of the support structure is oriented parallel to the conveying direction 215, the transverse direction Q perpendicular to the longitudinal direction is oriented horizontally transverse to the conveying direction, and the vertical direction is referred to as the height direction H. A through channel 115 for conveying material is formed between the upper and lower plates of the support structure, which leads in the longitudinal direction L from the inlet 116-1 to the outlet 116-2.

[0063] The metal detector 100 has a coil system 300, which includes a plurality of coils supported by a supporting structure 110. Figure 1 The coils include a transmitting coil for exciting an alternating electromagnetic field in the area traversed by the conveyed material and a receiving coil for detecting metal objects that may interfere with the field distribution. The area in the passage of the metal detector, which should be detected for detection purposes and includes the entire width of the conveyor belt in the transverse direction, is also referred to as the detection zone 120.

[0064] According to the following Figure 1 The coil system 300 includes two transmitting coil arrangements (a first transmitting coil arrangement 310-1, a second transmitting coil arrangement 310-2) connected successively in the longitudinal direction L and four pairs of receiving coils 320-1 to 320-4 arranged side by side and offset from each other in the transverse direction. For better explanation, Figure 2 Only two transmit coil arrangements are shown, Figure 3 Only the receive coil pair is shown, and Figure 4 The spatial arrangement of the coils relative to one another is shown without a supporting structure. Figure 5 The field distribution generated by the transmitting coil in the detection region is schematically illustrated.

[0065] During operation, the first transmitting coil arrangement 310-1, which is closer to the inlet, generates a first excitation field, the field lines of which are oriented in the interior of the detection zone in a first field direction F1, which extends in the vertical direction transversely to, in particular perpendicularly to, the longitudinal direction L. To achieve this, the first transmitting coil arrangement has a pair of first transmitting coils 312-1, 312-2, wherein one of the transmitting coils is arranged above the passage 115 and the other is arranged below the passage 115 (and below the conveying section 210). The two transmitting coils are therefore located on opposite sides outside the passage (that is, above or below). The coil axes of the transmitting coils, which extend perpendicularly to the winding plane, are oriented perpendicularly to the longitudinal direction L, that is, parallel to the height direction H. The first transmitting coils extend in the transverse direction to the left and right beyond the ends of the detection zone 120. During operation, the transmitting coils are operated with in-phase alternating voltages, so that a substantially uniform alternating electromagnetic field in the first field direction F1 is formed between the first transmitting coils.

[0066] The second transmitting coil arrangement 310-2 is arranged offset relative to the first transmitting coil arrangement in the longitudinal direction L and has a similar structure with second transmitting coils above and below the passage 115. The first transmitting coil and the second transmitting coil on one side are electrically connected in succession, but their winding directions are opposite, so that the second excitation field generated by the second transmitting coil arrangement 310-2 has a second field direction F2, which always runs antiparallel to the first field direction F1.

[0067] Figure 5 The simulation results of the field distribution are schematically shown. It can be seen that in the region of the transmitting coils, the field is essentially uniform in each case. As a result, the conveying material first passes through the "curtain" of the alternating electromagnetic field generated by the first transmitting coil arrangement 310-1. After passing through the symmetry plane located between the two transmitting coil arrangements, the conveying material then passes through the second "curtain" of the electromagnetic field with the opposite field direction F2.

[0068] The receiving coils 320 form a total of four pairs of receiving coils that are staggered from each other in the lateral direction. Figure 3 , the receiving coils are isolated from the other coils. Each of the receiving coils extends symmetrically in the longitudinal direction over two successively connected transmitting coil arrangements 310 - 1 , 310 - 2 so that in the absence of metal objects interfering with the magnetic field, the transmitting coil arrangements do not induce voltages in the receiving coils. The first receiving coil 320 - 1 of the first pair has coil axes that are coaxial with one another. A second pair of receiving coils 320 - 1 with a similar structure follows in a staggered manner in the transverse direction Q. Directly adjacent receiving coils overlap slightly (e.g., by a maximum of 10% of their width) in the transverse direction Q so that there are no sensitivity gaps between the respectively covered detection sectors.

[0069] The width in the lateral direction monitored as a whole by the receiving coil 320 determines the width of the detection zone 120. It can be said that the detection zone is divided into four side-by-side detection sectors by the four receiving coil arrangements.

[0070] The metal detector 100 comprises a control unit 150 which comprises an AC voltage source which controls two transmitting coil arrangements 310 - 1 , 310 - 2 and thereby generates an excitation field. The receiving coils 320 - 1 to 320 - 4 are connected to an evaluation unit of the control device 150 .

[0071] This particular arrangement of the transmitting coils and receiving coils has a number of advantages. The coil axes of all transmitting coils are perpendicular to the travel direction or conveying direction 215, so that the excited field of the detection zone also passes through the detection zone in the vertical direction. As a result, the metal-free zone in front of the inlet 116-1 and behind the outlet 116-2 can be kept relatively narrow. By differentially switching the transmitting coil arrangements 310-1, 310-2 that are switched on successively in the longitudinal direction, the sensitivity of the detection can be increased on the one hand, because the reason why metal objects must be identifiable is that they must generate comparable signals (with opposite signs) when passing through the first field curtain and when subsequently passing through the second field curtain. In addition, a position resolution is obtained in the longitudinal direction L, so that relatively small product spacings between individual products (here: food cartons) can be allowed in the longitudinal direction without having to worry about defective products remaining undetected.

[0072] Furthermore, by providing a plurality of receiving coil pairs, a position resolution is also obtained in the transverse direction Q, since it can be recognized whether a passing product is more likely to pass in the region of a first receiving coil pair or in the region of a second adjacent receiving coil pair, etc. As a result, large product spacings in the transverse direction Q are also not required.

[0073] Finally, there is also position resolution in the height direction H, since by comparing the signal strengths of the upper and lower receiving coils of a pair of receiving coils it is possible to identify whether the product is passing closer to the lower or upper receiving coil.

[0074] Overall, the metal detector 110 of the present exemplary embodiment thus has eight detection sectors which may not be exceeded during the evaluation, so that products passing through in which significant interfering signals are detected can be precisely identified at any time.

[0075] The components of the metal detector to be installed in the area of ​​the conveying section 210 (supporting structure and coils installed therein) exist in a compact structural form, which is easy to operate and easy to integrate in the conveying section due to its light weight. Contributing to this is that the combination of the transmitting coil and the receiving coil that should be arranged on one side of the conveying section (especially above or below) exists as a light structural unit in the form of a flat multilayer arrangement manufactured using the method of circuit board technology. Each coil exists in the form of a rectangular flat coil with a spirally wound winding. The winding of the coil can be located in a single layer, but if necessary, it can also be distributed on two or more adjacent layers separated by an insulating layer. In one embodiment, the multilayer arrangement also includes a functional layer, which is used as an electric field shielding member to prevent the electric field from intruding into the detection area. Here, the functional layer is a comb-shaped shielding element connected to the ground potential during operation.

[0076] Optional further components of the metal detector are explained with reference to the following figures, which components can also improve the function of the metal detector.

[0077] exist Figure 6 In an embodiment of the present invention, a plate-shaped field shaping element 400 made of a soft magnetic material is arranged above the upper coil and below the lower coil and laterally next to the passage. The field shaping element can be, for example, a single plate made of ferrite or a field shaping element composed of multiple plates. When used at a metal detector, such a field shaping element has multiple functions. On the one hand, the excitation field generated by the transmitting coil arrangement is shielded outward. In addition, possible external alternating electromagnetic fields can be shielded from intrusion into the detection zone. As another positive effect, field concentration or field strengthening is generated in the area between the transmitting coils, that is, in the area of ​​the detection zone 120. As a result, under otherwise unchanged conditions, a stronger electromagnetic field can be generated in the detection zone using the transmitting coils than in the case where no field shaping element is present.

[0078] Figure 5 The simulated field distribution of the excitation field without the ferrite plate is schematically shown. The arrows above and below the detection area 120 illustrate the field lines extending outside the metal detector. Figure 7 Schematically, it is shown how the field distribution appears when shielding by a ferrite plate is present, conditions being otherwise the same. Outside the shield formed by the ferrite plate 400, at most a weaker field strength exists, which is symbolically indicated by the absence of arrows. The strength of the shielding effect can be adjusted in particular via the thickness of the shielding element used, which can be in the range of a few millimeters to 1 centimeter or more, for example. The shielding effect and the field concentration effect increase with increasing thickness.

[0079] Other sensors useful in monitoring the conveyed material can also be installed at the metal detector. For example, a distance sensor can be provided, alternatively or additionally, a light barrier can be provided, and alternatively or additionally, at least one temperature sensor can be provided.

[0080] Here, the detection of metal parts in otherwise metal-free conveyed material is explained by way of example. This is a typical application case, for example, in the fields of the food industry, the pharmaceutical industry, the plastics industry or more generally the chemical industry or the packaging industry.

[0081] Metal detectors of the type described can also be used in other ways, for example in the field of metal sorting, where, for example within the scope of recycling processes, it may be necessary to identify objects made of non-ferrous metals with good electrical conductivity (such as copper, aluminum or their alloys) in the conveying flow of shredded objects after the shredding of valuable waste, in order to thereby create the possibility of separating them from components made of metals and / or non-metals with poor electrical conductivity.

Claims

1. A metal detector (100) for detecting electromagnetically detectable components in a conveyed material (214), the conveyed material having components made of materials with different electromagnetic properties and passing through a detection zone (120) of the metal detector along a conveying section (210) in a conveying direction (215), the metal detector comprising: a support structure (110), the support structure defining a through-channel (115) for the conveyed material, the through-channel extending in a longitudinal direction (L) of the support structure which can be oriented parallel to the conveying direction from an inlet (116-1) to an outlet (116-2) for the conveyed material, A coil system (300) having a plurality of coils, which are arranged on the support structure (110) and define the detection zone (120) between the inlet and the outlet, wherein the coils include a transmitting coil and a receiving coil as follows: a first transmitting coil arrangement (310-1), the first transmitting coil arrangement being used to generate a first excitation field in a first field direction (F1) oriented transversely to the longitudinal direction, wherein the first transmitting coil arrangement has first transmitting coils which can be excited in phase, the first transmitting coils being arranged on opposite sides outside the passage (115) and having a coil axis oriented transversely to the longitudinal direction (L); a second transmitting coil arrangement (310-2), the second transmitting coil arrangement being used to generate a second excitation field in a second field direction (F2) oriented transversely to the longitudinal direction (L), wherein the second transmitting coil arrangement comprises second transmitting coils which can be excited in phase, the second transmitting coils being arranged on opposite sides outside the passage (115) and having a coil axis oriented transversely to the longitudinal direction, The second transmitting coil arrangement (310-2) is arranged offset relative to the first transmitting coil arrangement (310-1) in a longitudinal direction (L), and the second field direction (F2) points opposite to the first field direction (F1).

2. The metal detector according to claim 1, characterized in that: The coil system (300) has no transmitting coil with a coil axis pointing in the longitudinal direction and surrounding the passage (115).

3. The metal detector according to claim 1 or 2, characterized in that: The first transmitting coil arrangement (310-1) and the second transmitting coil arrangement (310-2) are designed substantially axisymmetrically with respect to an axis of symmetry running between the coil arrangements perpendicularly to their field direction.

4. A metal detector according to any one of the preceding claims, characterized in that: The receiving coil has a first receiving coil (320-1) and at least one second receiving coil (320-2), which are arranged side by side and offset from each other on one side outside the passage in a transverse direction (Q) oriented perpendicular to the longitudinal direction (L), wherein the receiving coil has a coil axis oriented transversely to the longitudinal direction.

5. A metal detector according to any one of the preceding claims, characterized in that: The receiving coils each surround a coil surface which extends in a longitudinal direction on the first coil arrangement (310-1) and the second coil arrangement (310-2) such that, without field interference, the first excitation field and the second excitation field induce voltages in the receiving coils which are in opposite directions.

6. A metal detector according to any one of the preceding claims, characterized in that: For each receiving coil (320) on one side, the coil system (300) has a further receiving coil on the side of the passage opposite to the side, wherein two receiving coils associated with each other arranged on different sides each form a receiving coil pair, wherein preferably the receiving coils associated with each other of the receiving coil pair have coil axes that are coaxial with each other.

7. The metal detector according to claim 4, 5 or 6, characterized in that: Directly adjacent reception coils which are arranged offset with respect to one another in a transverse direction (Q) directly adjoin one another or partially overlap in an overlapping region.

8. A metal detector according to any one of the preceding claims, characterized in that: The coil system (300) has, viewed in the lateral direction, two, three, four or more reception coil pairs with reception coils arranged coaxially opposite one another.

9. A metal detector according to any one of the preceding claims, characterized in that: The coils of the coil system (300) are arranged in the form of rectangular flat coils with helically extending windings in different coil layers of a multilayer arrangement, wherein an insulating layer made of an electrically insulating material is arranged between adjacent coil layers of the multilayer arrangement.

10. A metal detector according to any one of the preceding claims, characterized in that The metal detector has a field shaping element (400) made of a soft magnetic material, which is arranged outside the coil arrangement at least in the region of the transmitting coil arrangement, wherein the field shaping element is preferably present in the form of a ferrite plate.

11. A metal detector according to any one of the preceding claims, characterized in that The metal detector (100) has at least one electric field shield which effectively prevents the penetration of electric fields into the detection zone, wherein the electric field shield is preferably integrated into a layer of the multilayer structure containing the coil arrangement.

12. A metal detector according to any one of the preceding claims, characterised in that The support structure (110) has an access opening (114) at least on one side, through which the through-channel (115) is laterally accessible.

13. A method for detecting electromagnetically detectable components in a conveyed material, the conveyed material having components made of materials with different electromagnetic properties and passing in a conveying direction along a conveying section through a detection zone of a metal detector having a transmitting coil and a receiving coil, in, The transmitting coil generates an excitation field in the form of an alternating electromagnetic field, which generates eddy currents in electromagnetically excitable components of the conveyed material, which lead to disturbances in the alternating field, which are detected by the receiving coil and evaluated by an evaluation device. It is characterized in that The conveyed material passes through two excitation field curtains in the detection zone in direct temporal succession, which extend transversely on the conveying section in a transverse direction extending transversely to the conveying direction and have opposite field directions of the excitation fields, respectively extending transversely, in particular perpendicularly, to the conveying direction.

14. The method according to claim 13, characterized in that The receiving coils define two, three, four or more adjacent detection sectors in the transverse direction, and when evaluating the signals of the receiving coils it is determined which detection sector the object triggering the signal has traversed.

Images