Metal detector and method for detecting metals in objects to be conveyed

Abstract

A metal detector for detecting electromagnetically detectable constituents in objects to be conveyed which comprise components composed of materials having different electromagnetic properties and pass through a detection zone of the metal detector in a conveying direction along a conveying section comprises a support structure that defines a passage channel for the objects to be conveyed. The passage channel extends in a longitudinal direction of the support structure, the longitudinal direction being alignable parallel to the conveying direction, from an entrance to and an exit for objects to be conveyed. Furthermore, a coil system having a plurality of coils is provided, the coils being arranged on the support structure and defining the detection zone between the entrance and the exit. The coils comprise transmitting coils and receiver coils. A first transmitting coil arrangement serves for generating a first excitation field in a first field direction oriented transversely with respect to the longitudinal direction, the first transmitting coil arrangement having first transmitting coils which are excitable in-phase, are arranged on opposite sides outside the passage channel and have coil axes oriented transversely with respect to the longitudinal direction. A second transmitting coil arrangement serves for generating a second excitation field in a second field direction oriented transversely with respect to the longitudinal direction, the second transmitting coil arrangement having second transmitting coils which are excitable in-phase, are arranged on opposite sides outside the passage channel and have coil axes oriented transversely with respect to the longitudinal direction. The second transmitting coil arrangement is arranged offset relative to the first transmitting coil arrangement in the longitudinal direction. The second field direction is opposite to the first field direction.

Description

[0001] Metal detector and method for detecting metals in conveyed material

[0002] FIELD OF APPLICATION AND STATE OF THE ART

[0003] The invention relates to a metal detector for detecting electromagnetically detectable components in conveyed material, which comprises components made of materials with different electromagnetic properties and passes through a detection zone of the metal detector in a conveying direction along a conveying path.

[0004] A metal detector of the type considered in this application operates according to an electromagnetic principle and is therefore capable of recognizing or detecting materials or parts based on their electrical conductivity and / or magnetic conductivity (permeability) and, if these electromagnetic properties differ sufficiently, of distinguishing between the different components. The term "metal detector" refers to the ability to detect metals (typically representing materials with relatively high electrical conductivity) in conveyed material that may contain poorly conductive or even non-conductive materials.

[0005] Possible areas of application for metal detectors include the food industry, the pharmaceutical industry, the plastics industry, or more generally the chemical industry or the packaging industry. One purpose of using metal detectors in these applications is to quickly and reliably detect the presence of unwanted pieces of metal in a conveyed material that otherwise consists predominantly or exclusively of electrically non-conductive or only weakly electrically conductive material. The conveyed material can be piece goods, i.e. objects that can be transported individually "in one piece", but may also be bulk goods. Such metal detectors are widely used in the industrial sector and are often integrated into production or packaging lines.

[0006] A non-limiting application example is food monitoring on the assembly line. This specifically involves the detection of tiny metal particles that lead to contamination during food processing and / or food packaging.

[0007] Another area of ​​application is in the field of material sorting, in particular metal sorting, where, for example, in the context of recycling processes, it may be a matter of separating parts made of electrically highly conductive non-ferrous metals such as copper, aluminum or their alloys from mixtures containing components made of electrically less conductive metals and / or non-metals.

[0008] So-called tunnel metal detectors are widely used today. In addition to their simple design, conventional tunnel detectors offer high sensitivity and robustness, among other things, and have therefore been considered the standard in food inspection for years. However, they also have several disadvantages, including a relatively large space requirement on the conveyor belt due to large metal-free zones (MFZs), which require the product to be strained during detection. An MFZ is the area in front of and behind the ends of the tunnel that must remain free of metallic parts to avoid interfering with detection in the detection zone. Moving metallic parts are particularly critical.

[0009] Document EP 2 729 831 B1 discloses a conventional tunnel metal detector with a metallic housing having a rectangular entrance opening and a rectangular exit opening. Within the housing is a coil system with at least one transmitter coil excitable with alternating current, at least one first receiver coil, and at least one second receiver coil. These coils define a detection zone in the direction of travel, which extends between the entrance opening and the exit opening and through which the objects to be tested move. The transmitter coil and the receiver coils enclose the "tunnel" running between the entrance opening and the exit opening, through which the conveyed material passes. In one embodiment, cancellation devices are arranged at the entrance opening and the exit opening to cancel the electromagnetic primary field generated by the transmitter coil.This can reduce the extent of the “metal-free zone” (MFZ).

[0010] Document DE 44 24 058 C1 discloses a device constructed in the manner of a tunnel detector for generating a detection signal upon the occurrence of metallically conductive parts in an at least largely non-conductive conveying flow. In this device, 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 a coil system feeding an evaluation circuit to derive the detection 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 with respect to the conveying flow such that the magnetic field of its transmitting coil runs predominantly in the direction of the conveying flow, and at least one other is arranged such that the magnetic field of its transmitting coil runs predominantly transversely to the direction of the conveying flow.Each of the individual systems is equipped with an evaluation circuit, and the signal outputs of the evaluation circuits are connected to an evaluation logic circuit designed to perform an object-specific evaluation depending on the signals supplied to it. The device is intended to be particularly sensitive to small and elongated parts, such as short pieces of wire or wire pins.

[0011] TASK AND SOLUTION

[0012] Against this background, it is an object of the present invention to provide a metal detector and a method for detecting metals which, compared to the prior art, require only little installation space for integration into a conveyor line with compact dimensions and only small metal-free zones and require no or only moderate product attenuation for reliable detection.

[0013] 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 further developments are specified in the dependent claims. The wording of all claims is incorporated into the description by reference.

[0014] According to one formulation, the invention relates to a metal detector for detecting electromagnetically detectable components in conveyed material comprising components made of materials with different electromagnetic properties and passing through a detection zone of the metal detector in a conveying direction along a conveying path. In some applications, the conveyed material consists predominantly of electrically non-conductive or only weakly electrically conductive material, and the parts to be detected are metal pieces with a relatively high electrical conductivity, which represent unwanted foreign bodies in this conveyed material.

[0015] The conveyor line preferably runs more or less horizontally. For example, a conveyor belt can be guided through the detection zone in such a way that the material lying on top of the conveyor belt is conveyed through the detection zone of the metal detector. Other conveying directions in the space are possible.

[0016] The metal detector has a support structure that defines a passageway for the conveyed material. The passageway runs in a longitudinal direction of the support structure from an inlet to an outlet for the conveyed material. The metal detector is typically positioned with respect to the conveying direction such that the longitudinal direction of the support structure is aligned parallel or substantially parallel to the conveying direction.

[0017] The transverse direction of the support structure is oriented perpendicular to the longitudinal direction. The vertical direction of the support structure is perpendicular to the plane spanned by the longitudinal and transverse directions. In most applications, the longitudinal and transverse directions lie in a horizontal plane, to which a (vertical) vertical direction of the support structure runs perpendicular. Other spatial orientations are possible.

[0018] The usable width of the passage channel in the transverse direction is adapted to the width of the conveyor system so that every conveyed object passes through the detection zone. The height of the passage channel is usually less than its width and can be based on the maximum height of the conveyed item that must pass through the passage channel. The passage channel often has a flat, rectangular cross-section whose width (in the transverse direction) is significantly larger than its height, for example, at least twice as large or at least five times as large. Deviations from this are possible, however.

[0019] The metal detector uses the generation and detection of eddy currents in electrically conductive materials, such as metals, to detect the conductive parts according to the transmitter-receiver principle. The metal detector comprises a coil system with a plurality of coils arranged on the support structure and defining the detection zone between the inlet and outlet. The coils include transmitter coils and receiver coils.

[0020] An essential function of the support structure is to ensure a fixed spatial allocation of the coils of the coil system attached to it. The support structure can be a suitably mechanically stable assembly that can, if necessary, be transported as a whole and set up at the place of use together with the coils attached to it. However, the components of the support structure do not have to be directly connected to one another. It is also possible for load-bearing components of the support structure to be mounted on a room wall, a room ceiling or on the floor of a room and to be held in a fixed spatial relationship to one another only by structural components of a building containing the room. For example, one part of the support structure can be mounted suspended from a room ceiling while another part stands on the floor.According to one formulation 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, it can generate a first excitation field in a first field direction oriented transversely, in particular perpendicular to the longitudinal direction. For this purpose, the first transmitting coil arrangement has two in-phase excitable first transmitting coils arranged on opposite sides outside the passage channel and having coil axes oriented transversely, in particular perpendicular, to the longitudinal direction.

[0021] Furthermore, (at least) one second transmitting coil arrangement is provided for generating a second excitation field in a second field direction oriented transversely, in particular perpendicularly, to the longitudinal direction. The second transmitting coil arrangement comprises two second transmitting coils that can be excited in phase and are arranged on opposite sides outside the passage channel and have coil axes that are 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 is directed opposite to the first field direction.

[0022] During operation, the transmitting coils are connected to an alternating voltage source and generate a preferably permanent alternating electromagnetic field, the main field component of which is directed transversely, in particular perpendicularly, to the longitudinal direction of the passageway. The alternating electromagnetic field induces electrical voltages in a receiving coil, which are evaluated by a connected evaluation device. As soon as an electrically conductive part, in particular a piece of metal, enters the detection zone, the alternating electromagnetic field of the transmitting coils generates eddy currents in the part, which act on the receiving coil through mutual induction. Thus, the ingress of metal particles causes a disturbance in the alternating field, which is detected by the receiving coil.The evaluation device processes the corresponding signals, evaluates them and, under precisely defined conditions, reports the presence of electrically conductive, particularly metallic, contamination in the conveyed material.

[0023] In this application, the term "coil axis" refers to a direction that is perpendicular or essentially perpendicular to a winding plane defined by the course of a coil's turn. In flat coils with spiral turns running in a common winding plane, the coil axis is oriented perpendicular to the winding plane. If the turns of a coil are helical, the coil axis is defined by the longitudinal axis of the helix and, depending on the helix's pitch, is only approximately perpendicular to a winding plane.

[0024] The "field direction" is the spatial direction in which the primary component of the alternating electromagnetic fields generated by a transmitting coil arrangement is directed. A transmitting coil can also be referred to as a "field coil" or "excitation coil." The alternating electromagnetic field generated by the transmitting coil is also referred to here as the excitation field or the transmitting field or primary field.

[0025] Preferably, there are exactly two transmitting coil assemblies arranged one behind the other in the longitudinal direction. However, if necessary, one or more additional transmitting coil assemblies can also be provided, i.e., a total of three or four transmitting coil assemblies, for example.

[0026] Compared to conventional tunnel metal detectors, there are significant structural and functional differences, which are expressed, among other things, in the orientation and arrangement of the coils and provide specific technical advantages.

[0027] Conventional tunnel metal detectors have at least one transmitting coil that completely surrounds the passageway for the conveyed material and accordingly has a coil axis that runs in the longitudinal direction of the passageway, i.e., essentially parallel to the conveying direction of the material. In contrast, a metal detector of the type described here preferably does not have a transmitting coil that surrounds the passageway and has a coil axis that runs in the longitudinal direction.

[0028] In contrast to a transmitting coil enclosing the passageway, the first and second transmitting coils are thus rotated by 90°, creating a focus transversely, specifically perpendicular to the conveying direction. The term "focus" refers to the direction in which the main excitation field is oriented (the first and second field directions).

[0029] This alignment ensures that essentially only those metallic objects located within the detection zone, i.e. between the entry and exit, can trigger a detection signal. If, on the other hand, moving metallic objects are located outside the detection zone, they generate practically no detection signals, even if they are close to the entry or exit. The so-called metal-free zone (MFZ), i.e. the area in front of and behind the ends of the passage channel that must remain free of metallic parts in order not to interfere with detection in the detection zone, is therefore significantly shorter or smaller than in conventional metal detectors and can, if necessary, be omitted entirely, so that moving metallic parts can also be installed at a short distance immediately before the entry or immediately after the exit.This means that when integrating such a metal detector into a production line or conveyor line, only a small amount of “metal-free” installation space is required in the axial direction, which facilitates integration into the line.

[0030] A further key advantage is that, due to the series-connected arrangement of the two transmit coil assemblies in the conveying direction, only elements within the detection zone provide a significant evaluation effect, thus enabling smaller product spacing in the longitudinal direction. The term "product spacing" refers to the distance between products that should be maintained so that the metal detection system can clearly assign any signals to one or the other product. If the products are positioned too close together axially, it is not possible to determine from a detection signal which of the products contains the signal-triggering contaminant. There are therefore significant advantages with regard to the product spacing required in the conveying direction or axial direction for reliable detection, meaning that more products can be reliably inspected per unit of time without changing the conveying speed.

[0031] The first and second transmitting coil arrangements are connected in differential mode or can be operated in differential mode. In other words, the first excitation field and the second excitation field are 180° out of phase with each other. This can be achieved, for example, by electrically connecting the two transmitting coils arranged on the same side of the passageway (a first transmitting coil and a second transmitting coil) in series, but winding them in opposite directions, so that the excitation current flowing through both transmitting coils generates oppositely directed fields in the two coils. It would also be possible to design the windings of the first and second transmitting coils on one side in the same direction and to ensure the required 180° phase shift by driving them with an alternating current source.

[0032] According to this configuration, two excitation fields with opposing field directions can be generated in the detection zone, arranged one after the other in the conveying direction and essentially homogeneous across the width and height of the passage channel. Figuratively speaking, the material being conveyed passes through two excitation field curtains with opposing field directions in immediate succession. The differential circuit increases sensitivity, allowing even the smallest particles to be detected. Furthermore, the detection signals generated as the material passes through the detection zones now also provide information about the position of the material in the conveying direction, thus creating spatial resolution in the conveying direction.

[0033] A symmetrical design is advantageous for this purpose. According to a further development, the first transmitting coil arrangement and the second coil arrangement are designed to be substantially axially symmetrical to an axis of symmetry that runs between the coil arrangements perpendicular to their field direction.

[0034] It is possible to use only a single receiver coil that covers the entire width of the detection zone. Preferred embodiments, however, are characterized in that the receiver coils comprise a first receiver coil and at least one second receiver coil, which are arranged together on one side (outside the) passage channel, offset from one another in the transverse direction oriented perpendicular to the longitudinal direction. These receiver coils have coil axes that are oriented transversely, in particular perpendicular to the longitudinal direction.

[0035] Thus, a plurality of receiver coils, i.e. two, three, four or more receiver coils, are provided, which are arranged on the same side outside the passageway. The plurality of receiver coils are arranged offset from one another in the transverse direction. While the transmitter coils extend across the entire width of the passageway in the transverse direction, so that during operation the transmitter coils generate their excitation field across the entire width of the detection zone, each of the receiver coils covers only a portion of the width of the passageway in the transverse direction, in particular at most half the width, possibly even less than 50% of the width, e.g., approximately 33%, approximately 25%, approximately 20%, or approximately 12% to 13%. In other words, the receiver coils define two, three, four or more adjacent detection sectors in the transverse direction.This makes the coil arrangement location-dependently sensitive in the transverse direction, so that when evaluating the signals from the receiver coils, it can be determined whether the signal-triggering metal part has essentially passed through the area or detection sector monitored by the first receiver coil or the area monitored by the second receiver coil. This also makes it possible to allow smaller product distances in the transverse direction than in the prior art, further increasing the detection capacity of the metal detector.

[0036] It is possible for the probe arrangement to have receiver coils only on one side outside the passage channel, e.g., below the passage channel. Preferably, the coil system includes, for each receiver coil located on one side, another receiver coil on the opposite side of the passage channel. Two associated receiver coils arranged on different sides each form a receiver coil pair (i.e., a pair of two associated receiver coils on opposite sides of the passage channel).

[0037] If more than one receiver coil is provided on one side, i.e. a first and at least one second receiver coil offset in the transverse direction, a corresponding number of receiver coil pairs is preferably provided.

[0038] Preferably, the first and second receiver coils of a receiver coil pair, which are arranged on opposite sides, each have coaxial coil axes. Thus, viewed in the transverse direction, there may be, for example, two, three, four, or more pairs of coaxially opposed receiver coils.

[0039] This allows for spatial resolution in the vertical direction, i.e., the direction between the two receiver coils, in addition to the spatial resolution in the transverse direction. Based on the detection signals from the opposing receiver coils of a sector, it can be determined whether the detected object passes through the passage channel closer to one receiver coil or closer to the receiver coil located coaxially opposite it, for example.

[0040] Thus, the passage channel can be divided into two detection sectors in the direction in which a receiver coil and the associated additional receiver coil are coaxially opposed. In the perpendicular transverse direction, the number of sectors can correspond to the number of adjacent receiver coils. Preferably, four receiver 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 by two in the vertical direction). A finer subdivision is theoretically possible, but usually not necessary.

[0041] However, a coaxial arrangement is not the only possibility. The receiver coils of a pair can also be arranged laterally (i.e., transversely) offset from one another. In this case, for example, a first receiver coil on one side may be opposite a transition region between two second receiver coils on the opposite side. This may result in a finer spatial resolution in the transverse direction for a given number of laterally offset receiver coils on one side than in the case of a coaxial arrangement of the receiver coils of a pair.

[0042] To ensure reliable, seamless detection of products passing through in the transverse direction, preferred embodiments provide for directly adjacent receiver coils that are offset from one another in the transverse direction to be directly adjacent to one another or partially overlap in an overlapping area. This prevents sensitivity drops in the transverse direction that could pose a safety risk.

[0043] According to a further development, a receiver coil, in particular each first and second receiver coil, each encloses a coil surface that extends longitudinally across the first coil arrangement and the second coil arrangement such that, in the absence of field disturbance, the first and second excitation fields induce opposing voltages in a receiver coil. Thus, each receiver coil is internally compensated, and no voltage is induced therein as long as the field distribution in the detection zone is not asymmetrically disturbed by metal parts or the like. This can increase the sensitivity of the arrangement.

[0044] The coils can be in the form of wire-wound coils. According to a further development, the components of the coil arrangement are manufactured using printed circuit board technology methods in the manner of printed circuits. In particular, coils of the coil arrangement can be arranged in the form of rectangular flat coils with spiral windings in different coil layers of a multi-layer arrangement, with an insulating layer of electrically insulating material being arranged between adjacent coil layers of the multi-layer arrangement. A coil can have windings in several layers in order to realize a sufficient number of windings in a limited lateral space. Such coil arrangements make it possible to construct the metal detector in a compact, relatively lightweight, yet stable manner compared to the prior art. This makes handling easier, among other things.

[0045] To further improve functionality, some embodiments of the metal detector include field-shaping elements made of soft magnetic material, which are arranged outside the coil arrangement, at least in the region of the transmitting coil arrangements, and are preferably attached to the support structure. The field-shaping elements can be formed, for example, by ferrite plates or can comprise ferrite plates. Several effects can be achieved by the field-shaping elements. Firstly, the exterior space is shielded against alternating fields generated by the transmitting coils. The shielding also works in the opposite direction, so that the interior space or the detection zone is shielded against possible external electromagnetic interference fields. In addition, an inward field concentration effect is achieved, so that the field strength achievable by the transmitting coils in the detection zone is increased compared to variants without field-shaping elements.

[0046] If necessary, field-forming elements could be attached to all sides of the detection channel, enclosing the detection channel on all sides adjacent to the passage channel.

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

[0048] The concept according to the claimed invention offers not only technical advantages in the area of ​​detection options, but also in general handling, particularly with regard to integration into conveyor lines. Because the coil system does not require, and therefore preferably does not have, a transmitting coil or receiving coil enclosing the passageway with a coil axis oriented in the longitudinal direction, it is very easy to improve the lateral accessibility of the conveyor line in the area of ​​the metal detector. In some embodiments, the support structure has an access opening on at least one side through which the passageway is accessible from the side. The access opening can be permanently open. It is also possible for a closure element to close the access opening for normal operation in order to mechanically stabilize the support structure if necessary.The closure element can be easily removed if necessary, allowing access to the passage channel from the side. This makes maintenance work or the replacement of a conveyor belt or similar device very easy, as the elongated conveyor element no longer needs to be threaded through a circumferentially closed passage channel, but can simply be inserted or removed from the side at a suitable location. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further advantages and aspects of the invention emerge from the claims and from the description of embodiments of the invention, which are explained below with reference to the figures.

[0050] Fig. 1 shows an embodiment of a metal detector integrated into a conveyor line of a conveyor system;

[0051] Fig. 2 shows only the transmitting coil arrangements in an isolated representation;

[0052] Fig. 3 shows only the receiver coil pairs in an isolated representation;

[0053] Fig. 4 shows the relative spatial arrangement of the coils to each other without a support structure;

[0054] Fig. 5 schematically illustrates the field distribution generated by the transmitting coils within the detection zone;

[0055] Fig. 6 shows the metal detector with soft magnetic field forming elements;

[0056] Fig. 7 illustrates the influence of the field shaping elements on the field distribution.

[0057] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] In the following, important aspects of a new type of metal detector are explained using an example from the field of monitoring conveyed goods in the food industry.

[0059] The metal detector generates electromagnetic fields and evaluates their interaction with the conveyed material. The metal detector is thus able to identify or detect materials or parts based on their electrical and / or magnetic conductivity and, if there are sufficiently large differences in these electromagnetic properties, reliably distinguish between the different components of the conveyed material.

[0060] The schematic Fig. 1 shows, in an oblique perspective, a metal detector 100 integrated into a conveyor line 210 of a conveyor system 200. The conveyor system comprises several conveyor modules connected in series, which together form a substantially horizontal conveyor line 210 for conveying goods 214 in the form of cartons 214 filled with food at the end of a production line in a conveying direction 215 and subjecting them to a final inspection. The contents of the cartons should be free of metallic contamination; the cartons themselves are also made without the use of metallic materials, for example, from cardboard.

[0061] To ensure that cartons entering the market are free of any metallic foreign objects that may have entered the cartons during food processing due to operational or equipment malfunctions, for example, the final inspection includes a continuous inspection of all cartons to detect any metal particles in the conveyed material, which ideally consists entirely of electrically non-conductive material. The conveyor line may include additional inspection modules, such as a downstream load cell to determine whether the fill weight of the cartons is within the target range.

[0062] The metal detector 100 has a support structure 110, which is essentially composed of relatively thick plates made of electrically non-conductive, torsion-resistant plastic, e.g., a thermoset material. An upper support plate 112-1 extends above the conveyor line in the transverse direction Q of the support structure horizontally and perpendicular to the conveying direction 215. A lower support plate 112-2 extends below the conveyor belt parallel to the upper plate in the transverse direction Q. The plates are connected at the rear in Fig. 1 via a stable vertical plate 112-3, resulting in a rectangular U-shape in cross-section perpendicular to the conveying direction 215. The front side of the support structure, visible at the front in Fig. 1, is open, thus providing an access opening 114 between the horizontal plates, through which the conveying line 210 is accessible from the side.To stabilize the support structure, the access opening 114 may be closed during operation by one or more closure elements 116, e.g., a vertical plate, which connects the upper plate 112-1 to the lower one and thereby stabilizes the substantially rectangular support structure.

[0063] The longitudinal direction L of the support structure is ideally aligned parallel to the conveying direction 215, the transverse direction Q perpendicular thereto in the horizontal direction transverse to the conveying direction, the vertical direction is referred to as the height direction H. Between the upper and lower plates of the support structure, a passage channel 115 for the conveyed material is formed, which leads in the longitudinal direction L from an inlet 116-1 to an outlet 116-2. The metal detector 100 has a coil system 300 that includes numerous coils carried by the support structure 110, which are only shown schematically in Fig. 1. The coils include transmitting coils for exciting an alternating electromagnetic field in the area through which the conveyed material passes, as well as receiving coils for detecting metal parts that could disrupt the field distribution.The area in the passage channel of the metal detector which is to be detected for detection purposes and which covers the entire width of the conveyor belt in the transverse direction is also referred to here as detection zone 120.

[0064] The individual coils, as well as their arrangement and function, are explained below with reference to Fig. 1 and other figures. The coil system 300 comprises two transmitting coil arrangements connected in series in the longitudinal direction L (first transmitting coil arrangement 310-1, second transmitting coil arrangement 310-2) as well as four pairs of receiving coils 320-1 to 320-4, which are arranged offset next to one another in the transverse direction. For better illustration, Fig. 2 shows only the two transmitting coil arrangements, Fig. 3 only the receiver coil pairs, and Fig. 4 shows the relative spatial arrangement of the coils to one another without a support structure. Fig. 5 schematically illustrates the field distribution generated by the transmitting coils within the detection zone.

[0065] The first transmitting coil arrangement 310-1, which is closer to the inlet, generates a first excitation field during operation, the field lines of which are oriented inside the detection zone in a first field direction F1, which runs transversely, in particular perpendicular to the longitudinal direction L in the vertical direction. To achieve this, the first transmitting coil arrangement has a pair of first transmitting coils 312-1, 312-2, one of the transmitting coils being arranged above and the other below the passage channel 115 (and below the conveyor line) 210. These two transmitting coils are therefore located on opposite sides outside (i.e., above or below) the passage channel. Their coil axes, which run perpendicular to the winding plane, are oriented perpendicular to the longitudinal direction L, i.e., parallel to the vertical direction H. The first transmitting coils extend transversely to the left and right beyond the end of the detection zone 120.They are operated with in-phase alternating voltage, so that a largely homogeneous electromagnetic alternating field is formed between the first transmitting coils in a first field direction F1.

[0066] A second transmitting coil arrangement 310-2 is arranged offset in the longitudinal direction L relative to the first transmitting coil arrangement and has an analogous structure with second transmitting coils above and below the passage channel 115, respectively. The first and second transmitting coils of one side are electrically connected in series, but their winding direction is opposite, so that the second excitation field generated by the second transmitting coil arrangement 310-2 has a second field direction F2, which is always counter-parallel to the first field direction F1.

[0067] Fig. 5 schematically shows the result of a simulation of the field distribution. It can be seen that in the area of ​​the transmitting coils, the fields are largely homogeneous. A conveyed item thus first passes through the "curtain" of an alternating electromagnetic field generated by the first transmitting coil arrangement 310-1. After passing through a plane of symmetry lying between the two transmitting coil arrangements, the conveyed item then passes through a second curtain of an electromagnetic field with the opposite field direction F2.

[0068] The receiver coils 320 form a total of four pairs of receiver coils offset from one another in the transverse direction, which can be seen isolated from the other coils in Fig. 3. Each of the receiver coils extends symmetrically in the longitudinal direction over both series-connected transmitter coil assemblies 310-1, 310-2, so that in the absence of metal parts that interfere with the magnetic field, they do not induce any voltage in the receiver coil. The first receiver coils 320-1 of the first pair have coaxial coil axes. Offset in the transverse direction Q is a pair of second receiver coils 320-1 with an analogous structure. The immediately successive receiver coils overlap slightly in the transverse direction Q (e.g., by a maximum of 10% of their width), so that there are no sensitivity gaps between the respectively covered detection sectors.

[0069] The total width in the transverse direction monitored by the receiving coils 320 determines the width of the detection zone 120. This is divided into four adjacent detection sectors by the four receiving coil arrangements.

[0070] The metal detector 100 comprises a control unit 150, which includes an AC voltage source that drives the two transmit coil assemblies 310-2, 310-2, and thus generates the excitation fields. The receiver coils 320-1 to 320-4 are connected to an evaluation unit of the control unit 150.

[0071] The special arrangement of transmit coils and receive coils offers numerous advantages. The coil axes of all transmit coils are perpendicular to the direction of travel or the conveying direction 215, so that the excited fields of the detection zones also penetrate them vertically. This allows the metal-free zones in front of the inlet 116-1 and behind the outlet 116-2 to be kept relatively narrow. The differential connection of the transmit coil arrangements 310-1, 310-2, which are connected in series in the longitudinal direction, can, on the one hand, increase the sensitivity of the detection, since a metal part must be recognizable by the fact that it must generate comparable signals (with opposite signs) both when passing through the first field curtain and when subsequently passing through the second field curtain.Furthermore, a spatial resolution is achieved in the longitudinal direction L, so that a relatively small product distance between the individual products (here: food cartons) can be permitted in the longitudinal direction without having to fear that defective products remain undetected.

[0072] Furthermore, the provision of multiple receiver coil pairs also results in spatial resolution in the transverse direction Q, since it can be detected whether a passing product is more likely to pass through the area of ​​a first receiver coil pair or the area of ​​the adjacent second receiver coil pair, etc. Thus, a large product spacing is also not necessary in the transverse direction Q.

[0073] Finally, a spatial resolution in the height direction H is also provided, since by comparing the signal strengths of the upper receiver coil and the lower receiver coil of a pair of receiver coils, it can be determined whether the product is moving closer to the lower or closer to the upper receiver coil.

[0074] In total, the metal detector 110 of the exemplary embodiment thus has eight detection sectors that can be undershot during the evaluation, whereby the exact product passing through in which a significant interference signal is detected can be identified at any time.

[0075] The metal detector components (support structure and coils attached to it) to be mounted in the area of ​​the conveyor line 210 have a compact design, are easy to handle due to their low weight, and are easy to integrate into a conveyor line. This is contributed to by the combination of transmitting and receiving coils, which are to be arranged on one side (in particular above or below) of the conveyor line, being a lightweight unit in the form of a flat multi-layer arrangement manufactured using printed circuit board technology. The individual coils are each in the form of rectangular flat coils with spirally encircling windings. The windings of a coil can be located in a single layer, but can also be distributed across two or more adjacent layers separated by insulation layers.In one embodiment, the multilayer arrangement also contains functional layers that act as E-field shields against the penetration of electric fields into the detection zone. These are comb-like shielding elements that are connected to ground potential during operation. The following figures illustrate additional optional components of the metal detector that can further improve its functionality.

[0076] In the embodiment of Fig. 6, plate-shaped field-shaping elements 400 made of soft magnetic material are arranged above the upper coils and below the lower coils, as well as laterally next to the through-channel. These can be, for example, individual ferrite plates or field-shaping elements composed of multiple plates. Such field-shaping elements have several functions when used in a metal detector. Firstly, the excitation field generated by the transmitting coil arrangements is shielded from the outside. Furthermore, any external alternating electromagnetic fields can be shielded from penetrating the detection zone. A further positive effect is a field concentration or field amplification in the area between the transmitting coils, i.e., in the area of ​​the detection zone 120.This means that, under otherwise unchanged conditions, stronger electromagnetic fields can be generated with the transmitting coils within the detection zone than in the absence of the field-forming elements.

[0077] Fig. 5 schematically shows the simulated field distribution of the excitation field without the ferrite plates. The arrows above and below the detection zone 120 illustrate field lines that run outside the metal detector. Fig. 7, on the other hand, schematically shows what the field distribution looks like in the presence of shielding by ferrite plates, all other conditions being equal. Outside the shield formed by the ferrite plates 400, at most a weak field strength is present, which is symbolized by the absence of arrows. The strength of the shielding effect can be adjusted, among other things, by the thickness of the shielding elements used; this can, for example, range from several millimeters to 1 cm or more. The shielding effect and the field concentration effect increase with increasing thickness.

[0078] Additional sensors useful for monitoring conveyed material can also be attached to the metal detector. For example, a distance sensor can be provided, alternatively or additionally a light barrier, and alternatively or additionally at least one temperature sensor.

[0079] The example explained here is the detection of metal pieces in otherwise metal-free material. This is a typical application, for example, in the food industry, the pharmaceutical industry, the plastics industry or, more generally, the chemical or packaging industry. A metal detector of the type described can also be used in other ways, for example in metal sorting, where, for example, in recycling processes, after shredding recyclable waste, the aim may be to identify parts made of electrically conductive non-ferrous metals such as copper, aluminum or their alloys in a conveyed stream of shredded parts, in order to create the possibility of separating these from components made of less conductive metals and / or non-metals.

Claims

Patent claims 1. Metal detector (100) for detecting electromagnetically detectable components in conveyed material (214), which has components made of materials with different electromagnetic properties and runs in a conveying direction (215) along a conveying path (210) through a detection zone (120) of the metal detector, comprising: a support structure (110) which defines a passage channel (115) for the conveyed material, which passage channel runs in a longitudinal direction (L) of the support structure which can be aligned parallel to the conveying direction from an inlet (116-1) to and an outlet (116-2) for the conveyed material;a coil system (300) having a plurality of coils arranged on the support structure (110) and defining the detection zone (120) between the inlet and the outlet, wherein the coils comprise transmitting coils and receiving coils as follows: a first transmitting coil arrangement (310-1) for generating a first excitation field in a first field direction (F1) oriented transversely to the longitudinal direction, wherein the first transmitting coil arrangement has in-phase excitable first transmitting coils arranged on opposite sides outside the passage channel (115) and having coil axes oriented transversely to the longitudinal direction (L);a second transmitting coil arrangement (310-2) for generating a second excitation field in a second field direction (F2) oriented transversely to the longitudinal direction (L), wherein the second transmitting coil arrangement has second transmitting coils which can be excited in phase and are arranged on opposite sides outside the passage channel (115) and have coil axes which are oriented transversely to the longitudinal direction, wherein the second transmitting coil arrangement (310-2) is arranged offset from the first transmitting coil arrangement (310-1) in the longitudinal direction (L) and the second field direction (F2) is directed opposite to the first field direction (F1); 2. Metal detector according to claim 1, characterized in that the coil system (300) does not have a transmitting coil surrounding the passage channel (115) with a coil axis directed in the longitudinal direction.

3. Metal detector according to claim 1 or 2, characterized in that the first transmitting coil arrangement (310-1) and the second coil arrangement (310-2) are designed substantially axially symmetrically to an axis of symmetry which runs between the coil arrangements perpendicular to their field direction.

4. Metal detector according to one of the preceding claims, characterized in that the receiver coils comprise a first receiver coil (320-1) and at least one second Receiver coils (320-2) which are arranged offset from one another on one side outside the passage channel in a transverse direction (Q) oriented perpendicular to the longitudinal direction (L), said receiver coils having coil axes which are oriented transversely to the longitudinal direction.

5. Metal detector according to one of the preceding claims, characterized in that a receiver coil encloses a coil surface which extends longitudinally over the first coil arrangement (310-1) and the second coil arrangement (310-2) such that, in the absence of a field disturbance, the first and the second excitation fields induce opposite voltages in the receiver coil.

6. Metal detector according to one of the preceding claims, characterized in that the coil system (300) has for each receiver coil (320) of one side a further receiver coil on the side of the passage channel opposite the side, wherein two mutually associated receiver coils arranged on different sides each form a receiver coil pair, wherein preferably mutually associated receiver coils of a receiver coil pair have mutually coaxial coil axes.

7. Metal detector according to claim 4, 5 or 6, characterized in that immediately adjacent receiver coils arranged offset from one another in the transverse direction (Q) are directly connected to one another or partially overlap in an overlapping region.

8. Metal detector according to one of the preceding claims, characterized in that the coil system (300) has, viewed in the transverse direction, two, three, four or more receiver coil pairs with coaxially opposite receiver coils.

9. Metal detector according to 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 spiral windings in different coil layers of a multi-layer arrangement, wherein an insulating layer of electrically insulating material is arranged between adjacent coil layers of the multi-layer arrangement.

10. Metal detector according to one of the preceding claims, characterized in that the metal detector has field forming elements (400) made of soft magnetic material, which are arranged outside the coil arrangements at least in the region of the Transmitting coil arrangements are arranged, wherein field forming elements are preferably in the form of ferrite plates.

11. Metal detector according to one of the preceding claims, characterized in that the metal detector (100) has at least one E-field shield effective against the penetration of electric fields into the detection zone, wherein the E-field shield is preferably integrated into a layer of the multi-layer structure containing the coil arrangement.

12. Metal detector according to one of the preceding claims, characterized in that the support structure (110) has at least on one side an access opening (114) through which the passage channel (115) is laterally accessible.

13. Method for detecting electromagnetically detectable components in conveyed material, which has components made of materials with different electromagnetic properties and runs in a conveying direction along a conveying path through a detection zone of a metal detector which has transmitting coils and receiving coils, wherein a transmitting coil generates an excitation field in the form of an electromagnetic alternating field, which generates eddy currents in electromagnetically excitable components of the conveyed material, which lead to a disturbance of the alternating field, which is detected by a receiving coil and evaluated by an evaluation device, characterized in that the conveyed material in the detection zone passes through two excitation field curtains in immediate succession, which each extend in a transverse direction running transversely to the conveying direction across the conveying path and opposite, each transverse,in particular, have field directions of the excitation field perpendicular to the conveying direction.

14. Method according to claim 13, characterized in that the receiver coils define two, three, four or more adjacent detection sectors in the transverse direction and, upon evaluation of the signals from the receiver coils, it is determined which detection sector a signal-triggering part has passed through.

Images