Metal detector and method for detecting metal in an object to be transported - Patent application

Abstract

The metal detector includes a support structure defining a passageway for the transported object, the passageway extending from an entrance to an exit of the transported object in a longitudinal direction of the support structure, the longitudinal direction being alignable parallel to the transport direction. A coil system is also provided, the coils being disposed on the support structure and defining a detection zone between the entrance and the exit. The coils include a transmitter coil and a receiver coil. The first transmitter coil device is operable to generate a first excitation field with a first field direction oriented transverse to the longitudinal direction, and the first transmitter coil device includes first transmitter coils that can be excited in phase and disposed on both sides outside the passageway and have coil axes oriented transverse to the longitudinal direction.

Description

[Technical Field]

[0001] The present invention relates to a metal detector for detecting electromagnetically detectable components in an object to be transported, the object comprising components made of materials with different electromagnetic properties passing through the detection zone of the metal detector in the conveying direction along a conveying section. [Background technology]

[0002] Metal detectors of the type considered in this application operate according to electromagnetism principles, so that materials or fragments can be recognized or detected based on their electrical and / or magnetic conductivity (permeability), and also to distinguish different components from one another if there is a sufficiently large difference between these electromagnetic properties. The term "metal detector" relates to its suitability for the detection of metal (as a typical representative of materials with relatively high electrical conductivity) in the object to be conveyed, which may include materials with lower electrical conductivity or no conductivity at all.

[0003] Possible fields of use for metal detectors are found, for example, in the food industry, pharmaceutical industry, plastics industry or more broadly in the chemical or packaging industry. The purpose of using metal detectors in these application fields is to quickly and reliably detect the presence of unwanted metal particles in objects to be transported, which usually consist mainly or exclusively of electrically non-conductive or only weakly electrically conductive material. The objects to be transported may be individual items, i.e. items that can be transported individually "in one piece", or in some cases bulk items. Such metal detectors are widespread in the industrial sector and are often integrated into production or packaging lines.

[0004] A non-limiting application example is food monitoring on conveyor belts, specifically the detection of very small metal particles that cause contamination during food processing and / or packaging.

[0005] Another field of use is that of material sorting, in particular metal sorting, which may involve separating fractions made of highly electrically conductive non-ferrous metals, such as copper, aluminum or their alloys, from mixtures containing components made of metallic and / or non-metallic materials with low electrical conductivity, for example as part of a recycling process.

[0006] So-called tunnel metal detectors are frequently used as standards today. In addition to their simple design, traditional tunnel detectors are particularly sensitive and robust, which is why they have been considered the standard for food monitoring for many years. However, traditional tunnel detectors also have various drawbacks, including the need for a relatively large space on the belt due to the extensive metal-free zone (MFZ), which in turn requires product rectification during detection. The MFZ is the area upstream and downstream of the end of the tunnel that must be kept free of metal fragments to avoid disturbances in the detection zone. Moving metal fragments are particularly critical.

[0007] European Patent No. 2 729 831 discloses a conventional tunnel-type metal detector, comprising a metal housing with a rectangular entrance opening and a rectangular exit opening. Inside the housing is a coil system comprising at least one transmitter coil, which can be excited by an alternating current, at least one first receiver coil, and at least one second receiver coil. These coils extend between the entrance and exit openings and define a detection zone along which the object to be examined moves. The transmitter and receiver coils extend between the entrance and exit openings and surround a "tunnel" through which the object to be transported passes. In one embodiment, cancellation devices are located at the entrance and exit openings to cancel the primary electromagnetic field generated by the transmitter coil. This allows for a reduction in the size of the "metal-free zone" (MFZ).

[0008] German Patent No. 44 24 058 discloses a device constructed in the form of a tunnel detector and intended to generate a recognition signal in the presence of metallically conductive fragments in an at least substantially non-conductive transport flow, in which an AC generator generates an alternating electromagnetic field by means of a transmitter coil in a monitored section of the transport flow, and the amplitude and phase variations of the alternating electromagnetic field are captured by a coil system that feeds an evaluation circuit in order to derive the recognition signal. The coil system comprises at least two individual systems, each with a transmitter coil and a receiver coil, one of which is arranged, based on the transport flow, such that the magnetic field of its transmitter coil extends mainly in the direction of the transport flow, and at least one of which is arranged such that the magnetic field of its transmitter coil extends mainly transversely to the direction of the transport flow. Each individual system is provided with an evaluation circuit, the signal output of which is connected to an evaluation logic circuit that is designed to perform an object-specific evaluation based on the signal supplied to the evaluation logic circuit. The device is intended to be particularly sensitive to small, elongated fragments, such as short pieces of wire or wire nails. Summary of the Invention [Problem to be solved by 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, has compact dimensions and only a small metal-free zone, takes up very little installation space for integration into the conveying section, and requires no or only moderate commutation of the product for reliable detection.

[0010] To this end, the invention provides a metal detector having the features of claim 1 and a method having the features of claim 13. Advantageous developments are specified in the dependent claims, the language of all claims being incorporated into the content of this description by reference. [Means for solving the problem]

[0011] According to one aspect, the present invention relates to a metal detector for detecting electromagnetically detectable components in an object to be conveyed, the object comprising components made of materials with different electromagnetic properties passing through a detection zone of the metal detector in the conveying direction along a conveying section. In some applications, the object to be conveyed consists primarily of electrically non-conductive or only weakly electrically conductive material, and the fragments to be detected are pieces of metal having a relatively high electrical conductivity compared to the material, which represent undesirable foreign matter in the object to be conveyed.

[0012] The conveying section preferably extends substantially horizontally. The conveyor belt can be guided through a detection zone, for example, so that objects to be conveyed placed on the upper side of the conveyor belt are conveyed through the detection zone of a metal detector. Other conveying directions in space are also possible.

[0013] The metal detector comprises a support structure defining a passageway for the objects to be transported, the passageway extending in the longitudinal direction of the support structure from an entrance to an exit for the objects to be transported, and the metal detector is typically arranged such that the longitudinal direction of the support structure is oriented parallel or substantially parallel to the direction of transport.

[0014] The lateral direction of the support structure is oriented perpendicular to the longitudinal direction. The height direction of the support structure is perpendicular to the plane spanned by the longitudinal and lateral directions. In most applications, the longitudinal and lateral directions lie in a horizontal plane, and the (vertical) height direction of the support structure extends perpendicular to the horizontal plane. Other orientations in space are possible.

[0015] The lateral usable width of the passage is adapted to the width of the transport device so that each conveyed item passes through the detection zone. The height of the passage is usually less than the width of the passage and can be adapted to the maximum height of the conveyed objects to be conveyed that need to pass through the passage. The passage often has a flat rectangular cross section, the (lateral) width of the cross section being significantly greater than the height of the cross section, for example at least twice or at least five times greater. However, there can be variations from this.

[0016] Metal detectors use the generation and detection of eddy currents in electrically conductive materials, such as metals, to detect conductive fragments according to the transmitter-receiver principle. For this purpose, the metal detector comprises a coil system with multiple coils arranged on a support structure and defining a detection zone between an entrance and an exit. The coils include a transmitter coil and a receiver coil.

[0017] The essential function of the support structure is to ensure that the coils of the coil system mounted on the support structure have a fixed spatial allocation. The support structure may therefore be a mechanically stable assembly that can be transported as a whole and installed at the site of use with the coils mounted on the support structure. However, the components of the support structure need not be directly connected to each other. It is also possible for the support components of the support structure to be attached to the walls, ceiling, or floor of a room and be held in a fixed spatial relationship to each other only through the structural components of the building containing the room. For example, one portion of the support structure may be suspended from the ceiling, while another portion rests on the floor.

[0018] According to one embodiment of the present invention, the coil system comprises a first transmitter coil device and a second transmitter coil device, the first transmitter coil device being configured to generate a first excitation field during operation with a first field direction oriented transversely, specifically perpendicularly, to the longitudinal direction, and for this purpose comprising two first transmitter coils that can be excited in phase and are arranged outside the passageway, on either side, and have coil axes oriented transversely, specifically perpendicularly, to the longitudinal direction.

[0019] Furthermore, there is (at least) a second transmitter coil device that generates a second excitation field in a second field direction oriented transversely, specifically perpendicular to the longitudinal direction, and the second transmitter coil device can be excited in phase and comprises two second transmitter coils arranged on either side outside the passageway and with coil axes oriented transversely, specifically perpendicular to the longitudinal direction. The second transmitter coil device is arranged offset longitudinally with respect to the first transmitter coil device. The second field direction is opposite to the first field direction.

[0020] During operation, the transmitter coil is preferably connected to an AC voltage source to generate a persistent alternating electromagnetic field, the main field component of which is oriented transversely, specifically perpendicular to the longitudinal direction of the passageway. The alternating electromagnetic field induces a voltage in the receiver coil, which is evaluated using a connected evaluation device. As soon as an electrically conductive part, specifically a metal piece, enters the detection zone, eddy currents are generated in that part by the transmitter coil's AC electromagnetic field and act on the receiver coil by mutual induction. This means that the incoming metal fragments cause disturbances in the AC field that are detected by the receiver coil. The evaluation device processes the corresponding signal, evaluates it, and reports the presence or absence of electrically conductive, specifically metallic, contamination in the transported object under precisely definable conditions.

[0021] The term "coil axis" in this application refers to a direction perpendicular or substantially perpendicular to the winding plane defined by the path of the coil's windings. In the case of a flat coil with windings extending helically within a common winding plane, the coil axis is oriented perpendicular to the winding plane. In the case of a coil with windings extending in a spiral, the coil axis is provided by the longitudinal axis of the spiral and, depending on the inclination of the spiral, may extend only 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 is directed. The transmitting coil may also be referred to as a "field coil" or an "excitation coil." The alternating electromagnetic field generated by the transmitting coil is also referred to herein as the excitation field, or the transmit field or primary field.

[0023] Preferably, there are exactly two transmitter coil devices arranged one after the other in the longitudinal direction, but if necessary, one or more further transmitter coil devices may also be provided, i.e., for example, three or four transmitter coil devices in total.

[0024] Compared to conventional tunnel-type metal detectors, there are significant structural and functional differences, manifested in particular in the type of coil orientation and placement, which provide certain technical advantages.

[0025] Conventional tunnel metal detectors have at least one transmitter coil that completely surrounds the passageway of the object to be transported and accordingly extends in the longitudinal direction of the passageway, i.e. has a coil axis that is substantially parallel to the direction of transport of the object to be transported. In contrast, metal detectors of the type described herein preferably do not have a transmitter coil that surrounds the passageway and has a longitudinally oriented coil axis.

[0026] In contrast to the transmitter coils surrounding the passageway, the first and second transmitter coils therefore have an orientation rotated by 90°, so that a focus is created, as it were, transversely, specifically perpendicularly, to the transport direction, the term "focus" in this case referring to the direction in which the main excitation field is directed (direction of the first and second fields).

[0027] This orientation can be used to ensure that only those metal objects substantially within the detection zone, i.e., between the entrance and the exit, trigger a detection signal. On the other hand, if a moving metal object is outside the detection zone, even if it is near the entrance or exit, it will hardly generate a detection signal. Therefore, the so-called metal-free zone (MFZ), i.e., the area upstream or downstream of the end of the passageway that must be kept free of metal fragments to avoid interfering with detection in the detection zone, can be significantly shorter or smaller than conventional metal detectors and, if necessary, can be omitted entirely. Consequently, moving metal fragments can be mounted a short distance immediately upstream of the entrance or immediately downstream of the exit, in some cases. This means that when such a metal detector is integrated axially into a production or conveyor line, only a small "metal-free" installation space is required, which facilitates integration into the line.

[0028] Another major advantage is that the arrangement of two transmitter coil devices connected in series in the conveying direction ensures that only elements within the detection zone provide significant evaluation results, thus enabling shorter longitudinal product distances. The term "product distance" in this case refers to the distance between products that must be maintained so that the metal detector can unambiguously assign a signal to one of the products. If the products are too close to each other in the axial direction, it is impossible to infer from the detection signal which of the products contains the contamination that triggers the signal. This provides a significant advantage in terms of the product distance required for reliable detection in the conveying direction or axial direction, allowing more products to be reliably examined per unit time without changing the conveying speed.

[0029] The first and second transmitter coil devices can be differentially connected or operated. In other words, the first and second excitation fields are phase-shifted by 180° relative to each other. This can be achieved, for example, by the fact that two transmitter coils (first transmitter coil and second transmitter coil) located on the same side of the passageway are electrically connected in series but have opposite winding orientations, so that an excitation current flowing through both transmitter coils generates opposing fields in the two coils. It would also be possible to design the windings of the first and second transmitter coils on one side to be in the same orientation and ensure the required 180° phase shift by operating using an AC power supply.

[0030] This configuration allows for the generation of two excitation fields in the detection zone that are connected in series in the transport direction and have opposite field directions that are substantially uniform across the width and height of the passageway. Figuratively speaking, the object to be transported passes through two excitation field curtains with opposite field directions in immediate temporal succession.

[0031] The differential circuitry allows for increased sensitivity, making it possible to detect even the smallest particles. In addition, the detection signal generated when passing through the detection zone also provides information about the position of the object being transported in the transport direction, thus creating spatial resolution in the transport direction.

[0032] For this purpose, a symmetrical structure is advantageous. According to one development, the first transmitter coil arrangement and the second coil arrangement are designed to be substantially axially symmetrical with respect to an axis of symmetry extending between the coil arrangements perpendicularly to the field direction of the coil arrangements.

[0033] While it is possible to use only a single receiver coil covering the entire width of the detection zone, a preferred embodiment is characterized in that the receiver coil comprises a first receiver coil and at least one second receiver coil arranged side by side on one (outer) side of the passageway, offset relative to each other in a transverse direction oriented perpendicular to the longitudinal direction, the receiver coils having coil axes oriented transversely, in particular perpendicularly, to the longitudinal direction.

[0034] Thus, multiple receiver coils, i.e., two, three, four, or more, are provided and positioned outside the passageway on the same side. The receiver coils are laterally offset from one another. While the transmitter coil extends laterally across the entire width of the passageway so that during operation, the transmitter coil generates a transmitter coil excitation field across the entire width of the detection zone, each receiver coil laterally covers only a portion of the passageway width, specifically less than half the width, and in some cases even less than 50% of the width, for example, about 33%, about 25%, about 20%, or about 12% to 13%. In other words, the receiver coils define two, three, four, or more adjacent detection zones laterally. The coil system thus has a location-dependent sensitivity in the lateral direction, so that when evaluating the signal from the receiving coil, it is possible to determine whether the metal part that triggers the signal has substantially passed through the area or detection zone monitored by the first receiving coil or the area monitored by the second receiving coil. It is therefore also possible to admit shorter product distances in the lateral direction than in the prior art, thus further improving the detection capability of the metal detector.

[0035] The coil arrangement can have a receiver coil outside the through-passage, on only one side, for example only below the through-passage. Preferably, the coil system is such that for each receiver coil on one side, a further receiver coil can be provided on the opposite side of the through-passage. Two receiver coils that are assigned to each other and respectively located on different sides form a receiver coil pair (i.e. a pair of two receiver coils that are assigned to each other on both sides of the through-passage).

[0036] When multiple receiving coils are provided on one side, i.e., a first receiving coil and at least one second receiving coil that are offset when placed side by side, it is preferable to provide a corresponding number of receiving coil pairs.

[0037] Preferably, the first and second receiver coils of a pair of receiver coils disposed on opposite sides can have coaxial coil axes, so that there can be, for example, two, three, four, or more pairs of receiver coils that are coaxially opposed to one another when viewed laterally.

[0038] In addition to lateral spatial resolution, spatial resolution in elevation, i.e., in the direction between the two receiver coils, is thus also possible, since the detection signals from opposing receiver coils in the area can be used to determine whether the detection has passed through a path closer to one receiver coil or a path closer to the coaxially opposing receiver coil.

[0039] The passageway can thus be divided into two detection zones in the direction in which the receiver coil and associated further receiver coils are coaxially opposed. In the transverse direction, perpendicular to the coaxially opposed direction, the number of zones can correspond to the number of receiver coils arranged side by side. Preferably, four receiver coils are provided in the transverse direction, so that the detection path can preferably be divided into eight detection zones (four horizontally by two vertically). Finer subdivisions are theoretically possible but are not usually necessary.

[0040] However, a coaxial arrangement is not the only option. Paired receiver coils can also be arranged laterally (i.e., laterally) offset relative to each other. For example, a first receiver coil on one side may face a switching region between two second, further receiver coils on the other side. Thus, if appropriate, if a given number of receiver coils on one side are laterally offset, the lateral spatial resolution can be finer than in the case of a coaxial arrangement of paired receiver coils.

[0041] To ensure reliable and uninterrupted detection of laterally passing products, in preferred embodiments, receiver coils that are immediately adjacent and laterally offset relative to one another are allowed to be immediately adjacent to one another or to partially overlap in an overlap region, thereby preventing any loss of sensitivity in the lateral direction that could pose a safety risk.

[0042] According to one development, the receiving coils, specifically all first and second receiving coils, can surround coil surfaces extending longitudinally across the first and second coil arrangements, respectively, such that in the absence of field disturbances, the first and second excitation fields induce equal and opposite voltages in the receiving coils. Thus, each receiving coil is essentially compensated, and no voltage is induced in each receiving coil unless the field distribution in the detection zone is asymmetrically disturbed by metal fragments or the like. This can improve the sensitivity of the device.

[0043] The coil may be in the form of a wound coil of wire. According to one development, the components of the coil arrangement are produced in the form of a printed circuit using PCB technology methods. In particular, the coils in the coil arrangement may be arranged in the form of rectangular flat coils with spirally extending windings in different coil layers of a multi-layer configuration, with insulating layers made of an electrically insulating material being arranged between adjacent coil layers of the multi-layer configuration. The coil may have windings in several layers in order to achieve a sufficient number of windings in a limited lateral space. With such a coil arrangement, a metal detector can be constructed in a compact, relatively light, and stable manner compared to the state of the art, which makes it easier to handle, among other things.

[0044] To further enhance its functionality, the metal detector in some embodiments comprises a field shaping element made of a soft magnetic material, which is arranged outside the coil device, at least in the area of ​​the transmitting coil device, and preferably attached to a support structure. The field shaping element can for example be formed by or comprise a ferrite plate.

[0045] By means of the field shaping element, several effects can be achieved: on the one hand, the external space is shielded from the alternating current field generated by the transmitter coil; the shielding also acts in the opposite direction, so that the interior or detection zone is shielded from the outside against possible electromagnetic interference fields; in addition, an effect of internal field concentration is achieved, so that the field strength achievable by the transmitter coil in the region of the detection zone is increased compared to a variant without a field shaping element.

[0046] Field shaping elements may be attached on all sides of the detection path adjacent to the passageway and surrounding the detection path, if desired.

[0047] The metal detector may further comprise at least one electric field shield, i.e. a shield that acts against the penetration of electric fields into the detection zone. In variants using a multilayer configuration, the electric field shield may be integrated into a layer of the multilayer structure including the coil arrangement. This allows for even greater sensitivity, since external electric fields cannot affect, or significantly affect, signal generation.

[0048] The claimed inventive concept offers technical advantages not only in the field of detection possibilities, but also in general handling, specifically with regard to the integration of the conveying section. Due to the fact that the coil system does not require, and therefore preferably does not include, transmitter or receiver coils that surround the passageway and have longitudinally oriented coil axes, it is very easy to improve the lateral accessibility of the conveying section in the area of ​​the metal detector. In some exemplary embodiments, the support structure is provided with an access opening on at least one side, through which the passageway is accessible from the side. The access opening can be permanently open. If necessary, a closure element can close the access opening during normal operation to mechanically stabilize the support structure. If necessary, the closure element can be easily removed so that the passageway is accessible from the side. As a result, maintenance work or replacement of conveyor belts, etc., is very easy, since the elongated conveying element no longer needs to be inserted through a circumferentially closed passageway and can be easily inserted or removed from a suitable side.

[0049] Further advantages and aspects of the present invention will become apparent from the claims and from the following description of exemplary embodiments of the invention, which proceeds with reference to the drawings. [Brief explanation of the drawings]

[0050] [Figure 1] FIG. 1 illustrates an embodiment of a metal detector integrated into a transport section of a conveyor system. [Figure 2] FIG. 1 is a diagram showing only the transmitting coil device separated from the other coil devices. [Figure 3] FIG. 10 is a diagram showing only the receiving coil pair separated from each other. [Figure 4] FIG. 10 shows the relative spatial arrangement of the coils with respect to each other without the support structure. [Figure 5] FIG. 2 shows a schematic diagram of the field distribution generated by the transmitter coil within the detection zone; [Figure 6]FIG. 1 shows a metal detector with a soft magnetic field shaping element. [Figure 7] FIG. 10 illustrates the effect of field shaping elements on the field distribution. DETAILED DESCRIPTION OF THE INVENTION

[0051] Important aspects of the novel metal detector are explained below using as an example the example of the field of monitoring objects to be transported in the food industry.

[0052] Metal detectors generate an electromagnetic field and evaluate its interaction with the object to be transported passing through them. Metal detectors therefore recognize or detect materials or fragments based on their electrical and / or magnetic conductivity and can reliably distinguish different components of the object to be transported from one another if there is a sufficiently large difference in their electromagnetic properties.

[0053] 1 shows a perspective view of a metal detector 100 integrated into a conveying section 210 of a conveyor system 200. The conveyor system comprises a number of conveyor modules connected in series and forming as a whole a substantially horizontal conveying section 210 for transporting objects to be transported 214 in the form of packaging boxes 214 filled with food in a conveying direction 215 to the end of the production line where the objects are subjected to final inspection. The contents of the packaging boxes must be free from metal contaminants and the packaging boxes themselves are produced without metal materials, for example from cardboard.

[0054] To ensure that packaging boxes released to the market do not contain metallic foreign objects that may be introduced into the packaging box during food processing, for example due to operational or equipment malfunctions, final inspection includes in-line testing of all packaging boxes to detect any metallic fragments present in the objects to be conveyed, which ideally consist only of electrically non-conductive materials. The conveying section may also include further testing modules, for example load cells downstream to determine whether the fill weight of the packaging box is within a set range.

[0055] The metal detector 100 comprises a support structure 110, which is substantially composed of a relatively thick plate of electrically non-conductive, twist-resistant plastic, e.g., a thermosetting material. An upper support plate 112-1 extends above the conveying section, horizontally in the transverse direction Q of the support structure 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 side in FIG. 1 via a stable vertical plate 112-3, so that the cross section perpendicular to the conveying direction 215 is rectangular U-shaped. At the front side of the support structure, visible at the front in FIG. 1, the support structure is open, so that there is an access opening 114 between the horizontal plates, through which the conveying section 210 is accessible from this side. To stabilize the support structure, the access opening 114 may be closed by one or more closure elements 116, e.g., vertical plates, that connect the upper plate 112-1 to the lower plate during operation, thereby stabilizing the substantially rectangular support structure.

[0056] The longitudinal direction L of the support structure is ideally 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 called the height direction H. A passage 115 for the objects to be conveyed is formed between the upper and lower plates of the support structure and runs in the longitudinal direction L from an inlet 116-1 to an outlet 116-2.

[0057] The metal detector 100 is supported by a support structure 110 and includes a coil system 300, which includes multiple coils, only shown diagrammatically in FIG. 1. The coils include a transmitter coil that excites an alternating electromagnetic field in the area through which the objects to be conveyed pass, and a receiver coil for detecting metal fragments that may interfere with the field distribution. The area within the path of the metal detector that is intended to be captured for detection purposes and that includes the entire lateral width of the conveyor belt is also referred to herein as the detection zone 120.

[0058] The individual coils, as well as their arrangement and function, are described below with reference to FIG. 1 and further figures. The coil system 300 comprises two transmitter coil devices (first transmitter coil device 310-1, second transmitter coil device 310-2) connected in series in the longitudinal direction L, and four pairs of receiver coils 320-1 to 320-4 arranged side by side and offset in the laterally oriented direction. As more illustrative examples, FIG. 2 shows only two transmitter coil devices, FIG. 3 shows only the receiver coil pairs, and FIG. 4 shows the relative spatial arrangement of the coils with respect to each other without any support structure. FIG. 5 shows a schematic representation of the field distribution generated by the transmitter coils within the detection zone.

[0059] The first transmitter coil device 310-1, which is closer to the entrance, generates a first excitation field during operation, and the lines of force of the first excitation field are oriented in a first field direction F1 that extends vertically, transversely, specifically perpendicularly, to the longitudinal direction L inside the detection zone. To achieve this, the first transmitter coil device includes a pair of first transmitter coils 312-1, 312-2, one of which is arranged above the passageway 115 and the other below the passageway (and below the transport section 210). These two transmitter coils are therefore located on either side of (i.e., above or below) the passageway. The coil axes of the transmitter coils, which extend perpendicular to the winding plane, are oriented perpendicular to the longitudinal direction L, i.e., parallel to the height direction H. The first transmitter coil extends laterally to the left and right beyond the ends of the detection zone 120. During operation, the first transmitter coils are operated with in-phase AC voltages, resulting in a substantially uniform alternating electromagnetic field in a first field direction F1 between the first transmitter coils.

[0060] The second transmitter coil device 310-2 is arranged offset in the longitudinal direction L relative to the first transmitter coil device and has a similar structure with second transmitter coils above and below the passageway 115. The first and second transmitter coils on one side are electrically connected in series, but the winding directions of the first and second transmitter coils are opposite, so that the second excitation field generated by the second transmitter coil device 310-2 always has a second field direction F2 that extends anti-parallel to the first field direction F1.

[0061] Figure 5 shows a schematic representation of the simulated field distribution. It can be seen that in the area of ​​the transmitting coils, the fields are approximately uniform. A passing object to be transported thus first passes through a "curtain" of alternating electromagnetic fields generated by the first transmitting coil arrangement 310-1. After passing through the plane of symmetry between the two transmitting coil arrangements, the object to be transported then passes through a curtain of a second electromagnetic field with an opposite field direction F2.

[0062] The receiver coils 320 are offset laterally relative to one another, forming a total of four pairs of receiver coils, which can be seen separated from the other coils in FIG. 3 . Each receiver coil extends longitudinally symmetrically with respect to both of the serially connected transmitter coil systems 310-1, 310-2, so that the transmitter coil systems do not induce voltages in the receiver coils in the absence of metal fragments interfering with the magnetic field. The first pair of receiver coils 320-1 have coaxial coil axes. This is followed by a second pair of receiver coils 320-1, which are offset laterally in the Q direction and have a similar structure. Immediately consecutive receiver coils overlap slightly in the Q direction (e.g., by a maximum of 10% of the receiver coil width), so that there is no sensitivity gap between the detection areas they cover.

[0063] The total lateral width monitored by the receive coil 320 determines the width of the detection zone 120. The detection zone is divided by the four receive coil systems as if it were four adjacent detection areas.

[0064] The metal detector 100 comprises a control unit 150 equipped with an AC voltage source and controlling the two transmitter coil devices 310-1, 310-2 and thereby generating the excitation fields. The receiver coils 320-1 to 320-4 are connected to an evaluation unit of the control device 150.

[0065] The special arrangement of the transmitter and receiver coils offers many advantages. The coil axes of all transmitter coils are perpendicular to the direction of movement, i.e., the conveying direction 215. As a result, the excitation field of the detection zone penetrates the detection zone vertically. This allows the metal-free zones upstream of the inlet 116-1 and downstream of the outlet 116-2 to be kept relatively narrow. The differential circuitry of the longitudinally connected serially connected transmitter coil devices 310-1, 310-2, on the other hand, allows for increased detection sensitivity, since metal fragments should be detectable both when passing through the first field curtain and then when passing through the second field curtain, generating equal (opposite) signals. Furthermore, spatial resolution is achieved in the longitudinal direction L, which allows for relatively short product distances between individual products (here, food packaging boxes) in the longitudinal direction without having to worry about defective products remaining undetected.

[0066] Furthermore, by providing multiple receiver coil pairs, it is possible to determine whether a passing product is more likely to be passing through the area of ​​a first receiver coil pair or the area of ​​an adjacent second receiver coil pair, thereby obtaining spatial resolution in the lateral direction Q. Therefore, a long product distance in the lateral direction Q is not required.

[0067] Finally, by comparing the signal strength of the upper receiver coil with the signal strength of the lower receiver coil of a receiver coil pair, it is possible to determine whether the product is flowing closer to the lower receiver coil or the upper receiver coil, thereby providing spatial resolution in the height direction H.

[0068] The metal detector 110 of the exemplary embodiment therefore has a total of eight detection zones that can be distinguished during evaluation, making it possible to identify at any time the exact passing product in which a significant interfering signal is detected.

[0069] The components of the metal detector to be mounted in the area of ​​the transport section 210 (the support structure and the coils attached to it) are compact in design and lightweight, making them easy to handle and integrate into the transport section. This is due to the fact that the transmitter and receiver coil combination to be placed on one side of the transport section (specifically, the upper or lower side) is present as a lightweight structural unit in the form of a flat, multi-layer structure produced using PCB technology. Each individual coil is in the form of a rectangular, flat coil with a helical winding. The coil windings may be located within a single layer, but may also be distributed across two or more adjacent layers separated by an insulating layer. In one exemplary embodiment, the multi-layer structure also includes a functional layer that acts as an electric field shield against the penetration of electric fields into the detection zone. The functional layer is a comb-shaped shielding element that is connected to ground potential during operation.

[0070] The following diagrams are used to describe additional optional components of a metal detector that may also enhance the functionality of the metal detector.

[0071] In the exemplary embodiment of FIG. 6 , plate-like field shaping elements 400 made of a soft magnetic material are arranged above the upper coil and below the lower coil, laterally of the through-passage. The field shaping elements may be, for example, single or multiple plates made of ferrite. When used in a metal detector, such field shaping elements have multiple functions. On the one hand, they shield the excitation field generated by the transmitting coil arrangement from the outside. Furthermore, they can shield the detection zone from external alternating electromagnetic fields. A further beneficial effect is that field concentration or field amplification occurs in the region between the transmitting coils, i.e., in the region of the detection zone 120. This allows the transmitting coils to generate a stronger electromagnetic field in the detection zone under otherwise identical conditions as without the field shaping elements.

[0072] FIG. 5 shows a schematic representation of the simulated field distribution of the excitation field without the ferrite plate. The arrows above and below the detection zone 120 indicate field lines extending outside the metal detector. Meanwhile, FIG. 7 shows a schematic representation of the field distribution under otherwise identical conditions with the shielding provided by the ferrite plate. Outside the shield formed by the ferrite plate 400, only a weak field intensity exists at most, as indicated by the absence of arrows. The magnitude of the shielding effect can be adjusted, inter alia, by the thickness of the shielding element used, which can range, for example, from a few millimeters to over 1 cm. The shielding and field concentration effects increase with increasing thickness.

[0073] Further sensors useful when monitoring the objects to be transported can also be attached to the metal detector, for example a distance sensor may be provided, or alternatively or additionally a light barrier may be provided, and alternatively or additionally at least one temperature sensor may be provided.

[0074] The detection of metal fragments in normally metal-free objects to be conveyed has been described as an example, which is a typical application in the fields of, for example, the food industry, pharmaceutical industry, plastics industry or more broadly the chemical or packaging industry.

[0075] Metal detectors of the type described can also be used in other areas, for example in the field of metal sorting, where, for example as part of a recycling process, after shredding of recyclable materials in a shredder fraction transport stream, it may be necessary to identify fragments made of highly electrically conductive non-ferrous metals such as copper, aluminum or their alloys, thereby making it possible to separate them from components made of less electrically conductive metals and / or non-metals.

Claims

1. A metal detector (100) for detecting electromagnetically detectable components in an object (214) to be conveyed, said object comprising components made of materials with different electromagnetic properties, passing through a detection zone (120) of said metal detector in a conveying direction (215) along a conveying section (210), said metal detector comprising: a support structure (110) defining a passage (115) for the objects to be conveyed, the objects flowing in a longitudinal direction (L) of the support structure, the support structure being oriented parallel to the conveying direction from an inlet (116-1) to an outlet (116-2) for the objects to be conveyed; a coil system (300) disposed on the support structure (110) and comprising a number of coils defining the detection zone (120) between the entrance and the exit, the coils comprising a transmitting coil and a receiving coil; The transmitter coil and the receiver coil are a first transmitter coil device (310-1) for generating a first excitation field in a first field direction (F1) directed transversely to the longitudinal direction, the first transmitter coil device being capable of being excited in phase and comprising first transmitter coils arranged on either side outside the passageway (115) and having coil axes directed transversely to the longitudinal direction (L); a second transmitter coil device (310-2) for generating a second excitation field in a second field direction (F2) directed transversely to the longitudinal direction (L), the second transmitter coil device being capable of being excited in phase and comprising second transmitter coils arranged on either side outside the passageway (115) and having coil axes directed transversely to the longitudinal direction; Including, the second transmitting coil device (310-2) is arranged offset in the longitudinal direction (L) with respect to the first transmitting coil device (310-1), and the second field direction (F2) is opposite to the first field direction (F1).

2. 2. The metal detector of claim 1, wherein the coil system (300) does not comprise a transmitter coil surrounding the passageway (115) and having a coil axis oriented in the longitudinal direction.

3. 3. The metal detector according to claim 1, wherein the first transmitting coil device (310-1) and the second coil device (310-2) are designed to be substantially axially symmetrical with respect to an axis of symmetry extending perpendicularly to the field direction of the coil devices between the coil devices.

4. 4. The metal detector according to claim 1, wherein the receiver coils comprise a first receiver coil (320-1) and at least one second receiver coil (320-2) arranged side by side on one side of the passageway, offset relative to each other in a transverse direction (Q) oriented perpendicular to the longitudinal direction (L), and the receiver coils have coil axes oriented transverse to the longitudinal direction (L).

5. 5. The metal detector according to claim 1, wherein the receiver coils surround coil surfaces extending in the longitudinal direction across the first coil arrangement (310-1) and the second coil arrangement (310-2), respectively, such that in the absence of field disturbances, the first excitation field and the second excitation field induce equal and opposite voltages in the receiver coils.

6. 6. The metal detector according to claim 1, wherein the coil system (300) comprises, for each receiving coil (320) on one side, a further receiving coil on the side of the passage opposite to said side, and wherein two receiving coils assigned to each other and arranged on different sides each form a receiving coil pair, and the receiving coils of the assigned receiving coil pair preferably have coil axes that are coaxial with each other.

7. 7. A metal detector according to claim 4, 5 or 6, characterized in that the receiver coils which are immediately adjacent and arranged offset relative to one another in the transverse direction (Q) are either immediately adjacent to one another or partially overlap in an overlap region.

8. 8. The metal detector according to claim 1, wherein the coil system (300) comprises two, three, four or more pairs of receiver coils, the receiver coils being coaxially opposed to one another when viewed in the lateral direction.

9. 9. The metal detector according to claim 1, wherein the coils of the coil system (300) are arranged in the form of rectangular flat coils with spirally extending windings in different coil layers of a multi-layer configuration, and wherein insulating layers made of an electrically insulating material are arranged between adjacent coil layers of the multi-layer configuration, respectively.

10. 10. The metal detector according to any one of claims 1 to 9, characterized in that the metal detector comprises a field shaping element (400) made of soft magnetic material and arranged outside the coil arrangement, at least in the area of ​​the transmitting coil arrangement, the field shaping element preferably being in the form of a ferrite plate.

11. 11. The metal detector (100) according to any one of claims 1 to 10, characterized in that the metal detector (100) comprises at least one electric field shield effective against the penetration of electric fields into the detection zone, the electric field shield being preferably integrated into a layer of the multilayer structure including the coil arrangement.

12. 12. The metal detector according to any one of claims 1 to 11, characterized in that the support structure (110) is provided on at least one side with an access opening (114) allowing lateral access to the passage (115).

13. 1. A method for detecting electromagnetically detectable components in an object to be transported, the object comprising components made of materials with different electromagnetic properties, passing in a conveying direction along a conveying section through a detection zone of a metal detector, the metal detector comprising a transmitter coil and a receiver coil; 1. A method, in which a transmitter coil generates an excitation field in the form of an alternating electromagnetic field, said excitation field generating eddy currents in electromagnetically excitable components of the object to be transported, said eddy currents resulting in disturbances of said alternating field being detected by a receiver coil and evaluated by an evaluation device, the object to be transported passes in immediate succession in time in the detection zone through two excitation field curtains, each of which extends laterally across the transport section in a transverse direction extending transversely to the transport direction and has opposite field directions of the excitation fields, each of which extends transversely, in particular perpendicularly, to the transport direction; A method characterized by:

14. 14. The method of claim 13, wherein the receiver coil defines two, three, four, or more adjacent detection areas in the lateral direction, and when evaluating a signal from the receiver coil, it is determined which detection area has passed through which portion triggers a signal.

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