WO2024041878A1

WO2024041878A1 - Metal detector and method for detecting metals in objects to be conveyed

Info

Publication number: WO2024041878A1
Application number: PCT/EP2023/071836
Authority: WO
Inventors: Michael SPAHLINGER; Lisa Röthlingshöfer; Uri Johannes MÜLLER
Original assignee: Institut Dr. Foerster Gmbh & Co. Kg
Priority date: 2022-08-24
Filing date: 2023-08-07
Publication date: 2024-02-29
Also published as: DE102022208758A1

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

Metal detector and method for detecting metals in conveyed goods

FIELD OF APPLICATION AND STATE OF TECHNOLOGY

The invention relates to a metal detector for detecting electromagnetically detectable components in conveyed goods, which has 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.

A metal detector of the type considered in this application works according to an electromagnetic principle and is therefore able to recognize or detect materials or parts based on their electrical conductivity and / or magnetic conductivity (permeability) and, if there are sufficiently large differences in these electromagnetic properties Different components can also be distinguished from each other. The term “metal detector” refers to the suitability for detecting metals (as typical representatives of materials with relatively high electrical conductivity) in conveyed goods that may contain materials that are less conductive or not conductive at all.

Possible areas of application for metal detectors can be found, for example, in 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 areas of application is to quickly and reliably detect the presence of unwanted metal pieces in a conveyed material which otherwise consists predominantly or exclusively of electrically non-conductive or only weakly electrically conductive material. The conveyed goods can be piece goods, i.e. objects that can be transported individually “in one piece”, but possibly also bulk goods. Such metal detectors are widely used in the industrial sector and are often integrated into production lines or packaging lines.

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

Another area of application is in the area of material sorting, especially metal sorting, where, for example, as part of recycling processes, parts can be made from electrically conductive non-ferrous metals such as copper, aluminum or their alloys To separate mixtures with components made of metals and/or non-metals that are less electrically conductive.

Nowadays, so-called tunnel metal detectors are often used as standard. In addition to their simple structure, conventional tunnel detectors offer, among other things, high sensitivity and robustness and have therefore been considered the standard in food monitoring for years. However, they also have various disadvantages, including a relatively large space requirement on the belt due to large metal-free zones (MFZ) and the resulting necessary product equalization during detection. An MFZ is the area in front of and behind the ends of the tunnel that must remain free of metallic parts in order not to disrupt detection in the detection zone. Moving metallic parts are particularly critical.

Document EP 2 729 831 B1 discloses a conventional tunnel metal detector with a metallic housing that has a rectangular entrance opening and a rectangular exit opening. Inside the housing there is a coil system with at least one transmitter coil that can be excited with alternating current, at least a first receiver coil and at least one second receiver coil. These coils delimit a detection zone in the direction of travel, which extends between the inlet opening and the outlet opening and through which the objects to be tested move. The transmitter coil and the receiver coils enclose the “tunnel” that runs between the inlet opening and the outlet opening and through which the material to be conveyed passes. In one embodiment, canceling devices are arranged at the input opening and at the output opening in order to cancel the primary electromagnetic field generated by the transmitter coil. This allows the extent of the “metal-free zone” (MFZ) to be reduced.

Document DE 44 24 058 C1 discloses a device constructed in the manner of a tunnel detector for generating a detection signal when metallically conductive parts occur in an at least largely non-conductive conveying stream, in which an alternating electromagnetic field is built up by an alternating current generator via a transmitting coil in a section of the conveying stream to be monitored whose amplitude and phase changes are detected by means of 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 transmitter coil and a receiver coil, one of which, based on the flow, is arranged in such a way that the magnetic field of its transmitter coil runs predominantly in the direction of the flow and at least one other is arranged so that the magnetic field of its transmitting coil runs predominantly transversely to the direction of the flow. Each of the individual systems is provided with an evaluation circuit and the signal outputs of the evaluation circuits are connected to an evaluation logic circuit which is designed in such a way that it carries out an object-specific evaluation depending on the signals supplied to it. The device should be particularly sensitive for small and elongated parts, such as short pieces of wire or wire pins.

TASK AND SOLUTION

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 for a Reliable detection requires no or only moderate product equalization.

To solve this problem, the invention provides a metal detector with the features of claim 1 and a method with the features of claim 13. Advantageous further developments are specified in the dependent claims. The wording of all claims is incorporated by reference into the content of the description.

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

The conveyor route 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 the top of the conveyor belt is conveyed through the detection zone of the metal detector. Other funding directions in the room are possible.

The metal detector has a support structure that defines a passage channel for the conveyed goods. The passage channel runs in a longitudinal direction of the support structure Entry to an exit for the conveyed goods. The metal detector is normally arranged 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.

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

The usable width of the passage channel in the transverse direction is adapted to the width of the conveyor device so that every object conveyed runs 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 material that should fit 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. However, deviations from this are possible.

The metal detector uses the generation and detection of eddy currents in electrically conductive materials, e.g. metals, to detect conductive parts according to the transmitter-receiver principle. For this purpose, the metal detector comprises a coil system with a large number of coils which are arranged on the support structure and define the detection zone between the entrance and the exit. The coils include transmitter coils and receiver coils.

An essential function of the support structure is to ensure a fixed spatial assignment of the coils of the coil system attached to it. The support structure can be an appropriately mechanically stable constructed assembly, which can optionally 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 only held in a fixed spatial relationship to one another via structural components of a building containing the room. For example, part of the support structure can be mounted hanging from a ceiling while another part stands on the floor. According to a formulation of the invention, the coil system comprises a first transmission coil arrangement and a second transmission coil arrangement. The first transmitter coil arrangement is configured so 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 transmitter coil arrangement has two first transmitter coils that can be excited in the same phase, which are arranged on opposite sides outside the passage channel and have coil axes that are oriented transversely, in particular perpendicularly, to the longitudinal direction.

Furthermore, there is (at least) a second transmitter coil arrangement for generating a second excitation field in a second field direction oriented transversely, in particular perpendicularly, to the longitudinal direction, the second transmitter coil arrangement having two second transmitter coils which can be excited in the same phase and which are arranged on opposite sides outside the passage channel and have coil axes which are oriented transversely, in particular perpendicular to the longitudinal direction. The second transmitter coil arrangement is arranged offset in the longitudinal direction relative to the first transmitter coil arrangement. The second field direction is opposite to the first field direction.

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 perpendicular to the longitudinal direction of the passage channel. The alternating electromagnetic field induces electrical voltages in a receiver coil, which are evaluated using a connected evaluation device. As soon as an electrically conductive part, in particular a piece of metal, enters the detection zone, eddy currents are generated in the part by the alternating electromagnetic field of the transmitter coils, which act on the receiver coil through counter-induction. Incoming metal parts cause a disturbance in the alternating field, which is detected by the receiver coil. The evaluation device processes the corresponding signals, evaluates them and, under precisely definable conditions, reports the presence of an electrically conductive, in particular metallic, contamination in the conveyed material.

The term “coil axis” in this application refers to a direction that is perpendicular or substantially perpendicular to a winding plane defined by the course of one turn of a coil. In flat coils with turns running spirally 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 through the Longitudinal axis of the helix and, depending on the pitch of the helix, runs only approximately perpendicular to a winding plane.

The “field direction” is the direction in space in which the main component of the alternating electromagnetic fields generated by a transmitter coil arrangement is directed. A transmitter coil can also be referred to as a “field coil” or “excitation coil”. The alternating electromagnetic field generated by the transmitter coil is also referred to here as the exciter field or as the transmitter field or primary field.

Preferably there are exactly two transmitter coil arrangements arranged one behind the other in the longitudinal direction. However, if necessary, one or more further transmission coil arrangements can also be provided, i.e. a total of three or four transmission coil arrangements, for example.

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

In conventional tunnel metal detectors, there is at least one transmitter coil that completely encloses the passage channel for the material to be conveyed and accordingly has a coil axis that runs in the longitudinal direction of the passage channel, i.e. essentially parallel to the conveying direction of the material to be conveyed. In contrast, a metal detector of the type described here preferably does not have a transmitter coil enclosing the passage channel with a coil axis directed in the longitudinal direction.

In contrast to a transmitter coil enclosing the passage channel, the first and second transmitter coils have an orientation rotated by 90°, so that a focus is created transversely, in particular perpendicular to the conveying direction, so to speak. The term “focus” refers to the direction in which the main excitation field is aligned (the first and second field directions).

This alignment can ensure that essentially only those metallic objects that are within the detection zone, i.e. between the entry and exit, can trigger a detection signal. On the other hand, if there are moving metallic objects outside the detection zone, they generate practically no detection signals, even if they are close to the entrance or exit. The so-called metal-free zone (MFZ), i.e. the area in front of and behind the ends of the The passage channel, which must remain free of metallic parts in order not to disturb the detection in the detection zone, is therefore significantly shorter or smaller in comparison to conventional metal detectors and can, if necessary, be completely eliminated, so that it can also be done immediately before entry or immediately after exit Metal parts that may move at a short distance can be attached. As a result, 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 makes integration into the line easier.

Another significant advantage is that due to the arrangement of the two transmitter coil arrangements connected in series in the conveying direction, only elements within the detection zone provide a significant evaluation effect and thus smaller product distances are possible in the longitudinal direction. The term “product distance” refers to the distance between products that should be maintained so that metal detection can clearly assign any signals to one product or another. If the products are axially too close to one another, it is not possible to determine from a detection signal which of the products contains the impurity that triggers the signal. There are therefore significant advantages in terms of the product distances required for reliable detection in the conveying direction or axial direction, so that more products can be reliably tested per unit of time while the conveying speed remains unchanged.

The first and second transmitter coil arrangements are connected in a difference to one another or can be operated in a difference. In other words, the first excitation field and the second excitation field are 180° out of phase with respect to each other. This can be achieved, for example, in that the two transmitter coils arranged on the same side of the passage channel (a first transmitter coil and a second transmitter coil) are electrically connected in series, but have opposite winding directions, so that the excitation current running through both transmitter coils has oppositely directed fields of the two Coils generated. It would also be possible to design the windings of the first and second transmitter coils on one side in the same direction and to ensure the required 180° phase shift by controlling them using an alternating current source.

According to this configuration, two excitation fields with opposite field directions, which are connected in series in the conveying direction and are essentially homogeneous over the width and height of the passage channel, can be generated in the detection zone. To put it figuratively, the conveyed material passes through two exciter field curtains with opposite field directions in immediate succession. The differential switching can increase the sensitivity and even the smallest particles can be detected. In addition, the detection signals that are generated when passing through the detection zones now also provide information about the position of the material to be conveyed in the conveying direction, so that a spatial resolution in the conveying direction is created.

A symmetrical structure is advantageous for this purpose. According to a further development, the first transmitter coil arrangement and the second coil arrangement are designed essentially axially symmetrical to an axis of symmetry which runs between the coil arrangements perpendicular to their field direction.

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

There are therefore several receiver coils, i.e. two, three, four or more receiver coils, which are arranged on the same side outside the passage channel. The plurality of receiver coils are arranged offset from one another in the transverse direction. While the transmitter coils extend over the entire width of the passage channel in the transverse direction, so that during operation the transmitter coils generate their excitation field over the entire width of the detection zone, each of the receiver coils in the transverse direction only covers a part of the width of the passage channel, in particular at most half of it Width, possibly also less than 50% of the width, for example about 33% or about 25% or about 20% or about 12% to 13%. In other words: the receiver coils define two, three, four or more adjacent detection sectors in the transverse direction. This makes the coil arrangement sensitive to the location depending on 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. It is therefore also possible to allow smaller product distances in the transverse direction than in the prior art, which further increases the detection capacity of the metal detector.

It is possible for the probe arrangement to have receiver coils only on one side outside the through-channel, for example below the through-channel. Preferably is It is provided that the coil system has a further receiver coil on the side of the passage channel opposite this side for each receiver coil that is located on one side. Two mutually assigned receiver coils, which are arranged on different sides, each form a receiver coil pair (ie a pair of two mutually assigned receiver coils on opposite sides of the through-channel).

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

It is preferably provided that the first and second receiver coils of a pair of receiver coils, which are arranged on opposite sides, each have coaxial coil axes. Seen in the transverse direction, there can be, for example, two, three, four or more pairs of receiver coils lying coaxially opposite one another.

This means that, in addition to the spatial resolution in the transverse direction, a spatial resolution in the height direction, i.e. in the direction between the two receiver coils, is also possible. 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 coaxially opposite it, for example.

The passage channel can therefore be divided into two detection sectors in the direction in which a receiver coil and the associated further receiver coil lie coaxially opposite one another. In the transverse direction perpendicular thereto, the number of sectors can correspond to the number of receiver coils arranged next to one another. 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 division is theoretically possible, but usually not necessary.

However, a coaxial arrangement is not the only option. The receiver coils of a pair can also be arranged laterally (ie in the transverse direction) offset from one another. It may then be the case, for example, that a first receiver coil on one side is opposite a transition region between two second further receiver coils on the opposite side. This allows, if necessary, for a given number of lateral If the receiver coils are offset on one side, the spatial resolution in the transverse direction can be finer than in the case of a coaxial arrangement of the receiver coils in a pair.

In order to ensure reliable, gap-free detection of passing products in the transverse direction, preferred embodiments provide that immediately adjacent receiver coils that are offset from one another in the transverse direction connect directly to one another or partially overlap in an overlap area. This can prevent sensitivity drops in the transverse direction, which could pose a safety risk.

According to a further development, it is provided that a receiver coil, in particular each first and second receiver coil, each encloses a coil surface which extends in the longitudinal direction over the first coil arrangement and the second coil arrangement in such a way that in the absence of a field disturbance, the first and the second excitation field in one Receiver coil induce opposite voltages. This means that each receiver coil is internally compensated and no voltage is induced in it as long as the field distribution in the detection zone is not asymmetrically disturbed by metal parts or the like. This allows the sensitivity of the arrangement to be increased.

The coils can be in the form of coils wound from wire. According to a further development, the components of the coil arrangement are manufactured using printed circuit board technology methods. In particular, it can be the case that coils of the coil arrangement are arranged in the form of rectangular flat coils with spiral-shaped turns in different coil layers of a multi-layer arrangement, with an insulating layer made of electrically insulating material being arranged between adjacent coil layers of the multi-layer arrangement. A coil can have turns in multiple layers to realize a sufficient number of turns in a limited lateral space. Such coil arrangements allow the metal detector to be constructed in a compact, relatively light and yet stable manner compared to the prior art. This makes handling easier, among other things.

To further improve the function, in some embodiments the metal detector has field shaping elements made of soft magnetic material, which are arranged outside the coil arrangement at least in the area of the transmitter coil arrangements and are preferably attached to the support structure. The field shaping elements can be formed, for example, by ferrite plates or have ferrite plates. Several effects can be achieved through the field shaping elements. On the one hand, the outside area is shielded against alternating fields generated by the transmission coils. The shielding also works in the opposite direction, so that the interior or the detection zone is shielded against possible electromagnetic interference fields from the outside. In addition, an inward field concentration effect is achieved, so that the field strength that can be achieved by the transmitter coils in the area of the detection zone is increased compared to variants without field-shaping elements.

If necessary, field shaping elements could be attached to all sides of the detection channel, which enclose the detection channel on all sides adjacent to the through-channel.

Furthermore, the metal detector can have at least one E-field shielding, i.e. a shielding that acts against the penetration of electric fields into the detection zone. In variants with multilayer arrangements, the E-field shielding can be integrated into a layer of the multilayer structure containing the coil arrangement. This allows the sensitivity to be further increased since external E-fields cannot or cannot significantly affect signal generation.

The concept according to the claimed invention not only offers technical advantages in the area of detection options, but also in general handling, especially with regard to integration into conveyor lines. Because the coil system does not require and therefore preferably does not have a transmitter coil or receiver coil enclosing the passage channel with a coil axis directed in the longitudinal direction, it is very easy to improve the lateral accessibility of the conveyor path in the area of the metal detector. In some exemplary embodiments, the support structure has an access opening at least on one side, through which the passage channel is laterally accessible. 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. If necessary, the closure element can be easily removed so that the passage channel becomes accessible from the side. This makes maintenance work or replacement of a conveyor belt or the like possible very easily, since the elongated conveyor element no longer has to be threaded through a passage channel closed in the circumferential direction, but can simply be inserted or removed laterally at a suitable point. BRIEF DESCRIPTION OF DRAWINGS

Further advantages and aspects of the invention result from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures.

1 shows an embodiment of a metal detector that is integrated into a conveyor section of a conveyor system;

Fig. 2 shows only the transmitter coil arrangements in an isolated representation;

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

Fig. 4 shows the relative spatial arrangement of the coils to one another without a support structure;

5 schematically illustrates the field distribution generated by the transmitter coils within the detection zone;

Fig. 6 shows the metal detector with soft magnetic field shaping elements;

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

DETAILED DESCRIPTION OF THE EMBODIMENTS

Below, important aspects of a new type of metal detector are explained using an example from the area of monitoring conveyed goods in the food industry.

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

The schematic Fig. 1 shows a metal detector 100 in an oblique perspective, which is integrated into a conveyor section 210 of a conveyor system 200. The conveyor system has several conveyor modules connected in series, which overall form a substantially horizontal conveyor path 210 in order to convey conveyed goods 214 in the form of boxes 214 filled with food at the end of a production line in a conveying direction 215 and to subject them to a final inspection. The contents of the boxes should be free of metallic contamination; the boxes themselves are also made of cardboard, for example, without the use of metallic materials.

In order to ensure that the cartons coming onto the market do not contain any metallic foreign bodies that could have gotten into them during food processing due to operational or system disruptions, for example, the final inspection includes a continuous test of all cartons to detect any metal parts that may be present in the conveyed goods , which ideally consists exclusively of electrically non-conductive material. The conveyor line can contain further test modules, for example a downstream weighing cell to determine whether the filling weight of the boxes is within the target value range.

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, for example a thermoset material. An upper support plate 112-1 extends horizontally above the conveying path 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 on the in Fig. 1 rear side connected via a stable vertical plate 112-3, so that a rectangular U-shape results in the cross section perpendicular to the conveying direction 215. On the front side of the support structure, which is visible at the front in FIG. To stabilize the support structure, the access opening 114 can be closed during operation by one or more closure elements 116, e.g. a vertical plate, which connect the upper plate 112-1 to the lower one and thereby stabilize the essentially rectangular support structure.

The longitudinal direction L of the support structure is ideally aligned parallel to the conveying direction 215, the transverse direction Q perpendicular thereto is aligned in the horizontal direction transverse to the conveying direction, the vertical direction is referred to as the height direction H. A passage channel 115 for the material to be conveyed is formed between the upper and lower plates of the support structure, 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, which includes numerous coils carried by the support structure 110, which are only shown schematically in FIG. 1. The coils include transmitter coils for exciting an alternating electromagnetic field in the area through which the conveyed material passes, as well as receiver coils for detecting metal parts that can disrupt the field distribution. The area in the passage channel of the metal detector that is to be detected for detection purposes and covers the entire width of the conveyor belt in the transverse direction is also referred to here as detection zone 120.

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 includes two transmitter coil arrangements connected in series in the longitudinal direction L (first transmitter coil arrangement 310-1, second transmitter coil arrangement 310-2) and four pairs of receiver coils 320-1 to 320-4, which are arranged next to one another offset in the transverse direction. For better illustration, Fig. 2 shows only the two transmitter coil arrangements, Fig. 3 shows 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 transmission coils within the detection zone.

The first transmitter coil arrangement 310-1, which is closer to the entrance, generates a first excitation field during operation, the field lines of which are oriented in the interior of the detection zone in a first field direction F1, which runs transversely, in particular perpendicularly, to the longitudinal direction L in the vertical direction. To achieve this, the first transmitter coil arrangement has a pair of first transmitter coils 312-1, 312-2, one of the transmitter coils being arranged above and the other below the passage channel 115 (and below the conveying path) 210. These two transmission coils are located on opposite sides outside (i.e. above or below) of 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 height direction H. The first transmission coils extend in the transverse direction to the left and right beyond the end of the detection zone 120. During operation, they are operated with in-phase alternating voltage, so that a largely homogeneous alternating electromagnetic field is formed between the first transmission coils in a first field direction F1.

A second transmitter coil arrangement 310-2 is arranged offset from the first transmitter coil arrangement in the longitudinal direction L and has an analog structure with second transmitter coils above and below the passage channel 115. The first and second transmitter coils on one side are electrically connected in series, but their winding direction is opposite, so that the second generated by the second transmitter coil arrangement 310-2 Exciter field has a second field direction F2, which is always counter-parallel to the first field direction F1.

Fig. 5 shows schematically the result of a simulation of the field distribution. It can be seen that the fields in the area of the transmitter coils are largely homogeneous. A conveyed item passing through therefore 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 between the two transmitter coil arrangements, the material to be conveyed then passes through a second curtain of an electromagnetic field with the opposite field direction F2.

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. Each of the receiver coils extends symmetrically in the longitudinal direction over both series-connected transmitter coil arrangements 310-1, 310-2, so that they do not induce any voltage in the receiver coil in the absence of metal parts that disrupt the magnetic field. The first receiver coils 320-1 of the first pair have coil axes that are coaxial with one another. A pair of second receiver coils 320-1 with an analog structure follows, offset in the transverse direction Q. 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 respective covered detection sectors.

The total width monitored by the receiving coils 320 in the transverse direction determines the width of the detection zone 120. This is, so to speak, divided into four adjacent detection sectors by the four receiver coil arrangements.

The metal detector 100 includes a control unit 150, which includes an alternating voltage source that controls the two transmitter coil arrangements 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 device 150.

The special way the transmitter coils and receiver coils are arranged offers numerous advantages. The coil axes of all transmission coils are perpendicular to the direction of travel or to the conveying direction 215, so that the excited fields of the detection zones also pass through them in the vertical direction. This allows the metal-free zones in front of the entry 116-1 and behind the exit 116-2 to be kept relatively narrow. Through the differential connection of the transmitter coil arrangements connected in series in the longitudinal direction 310-1, 310-2, on the one hand, the sensitivity of the detection can be increased, since a metal part must be recognizable by the fact that it emits comparable signals (with opposite signs) both when passing through the first field curtain and when subsequently passing through the second field curtain. must generate. Furthermore, there is a spatial resolution in the longitudinal direction L, so that a relatively small product distance between the individual products (here: food boxes) can be permitted in the longitudinal direction without having to fear that defective products will remain undetected.

Furthermore, the provision of several pairs of receiver coils also results in a spatial resolution in the transverse direction Q, since it can be recognized whether a passing product passes through in the area of a first pair of receiver coils or in the area of the adjacent second pair of receiver coils, etc. This means that no large product distance is necessary in the transverse direction Q either.

Finally, there is also a spatial resolution in the height direction H, since a comparison of the signal strengths of the upper receiver coil and the lower receiver coil of a pair of receiver coils can be used to determine whether the product runs closer to the lower or closer to the upper receiver coil.

Overall, the metal detector 110 of the exemplary embodiment therefore has eight detection sectors that can be undershot during the evaluation, which means that exactly the product passing through in which a significant interference signal is detected can be identified at any time.

The components of the metal detector to be attached to the area of the conveyor line 210 (support structure and coils attached to it) have a compact design, are easy to handle due to their low weight and are easy to integrate into a conveyor line. A contribution to this is made by the fact that the combination of transmitter and receiver coils, which are to be arranged on one side (in particular above or below) of the conveyor path, is present as a lightweight structural unit in the form of a flat multi-layer arrangement produced using circuit board technology. The individual coils are each in the form of rectangular flat coils with spiral-shaped turns. The turns of a coil can lie in a single layer, but may also be distributed over two or more adjacent layers separated by insulation layers. In one embodiment, the multilayer arrangement also contains functional layers that act as E-field shielding 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 explain optional additional components of the metal detector that can further improve its function.

In the exemplary 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 and laterally next to the through channel. It can be, for example, individual plates made of ferrite or field-shaping elements made up of several plates. Such field shaping elements have several functions when used on a metal detector. On the one hand, the excitation field generated by the transmitter coil arrangements is shielded from the outside. Furthermore, any external alternating electromagnetic fields can be shielded against penetration into the detection zone. A further positive effect is a field concentration or field amplification in the area between the transmission coils, i.e. in the area of the detection zone 120. As a result, under otherwise unchanged conditions, stronger electromagnetic fields can be generated with the transmission coils within the detection zone than in the absence of the field shaping elements.

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

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

The detection of metal pieces in otherwise metal-free conveyed material was explained here as an example. This is a typical application, for example in the food industry, the pharmaceutical industry, the plastics industry or, more generally, the chemical industry or the packaging industry. A metal detector of the type described can also be used in other ways, for example in the area of metal sorting, where, for example, in the context of recycling processes, after shredding recyclable waste, parts made of electrically highly conductive non-ferrous metals such as copper can be found in a conveying stream of shredder parts , aluminum or their alloys in order to create the possibility of separating them 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 material to be conveyed, which extends from an inlet (116-1) to and an outlet (116-2) for the material to be conveyed in a longitudinal direction (L) of the support structure that can be aligned parallel to the conveying direction runs; a coil system (300) with a plurality of coils which are arranged on the support structure (110) and define the detection zone (120) between the entry and the exit, the coils comprising transmitter coils and receiver coils as follows: a first transmitter coil arrangement (310- 1) for generating a first excitation field in a first field direction (F1) oriented transversely to the longitudinal direction, the first transmission coil arrangement having first transmission coils which can be excited in phase and which are arranged on opposite sides outside the passage channel (115) and have coil axes which are transverse to the longitudinal direction ( L) are oriented; a second transmission coil arrangement (310-2) for generating a second excitation field in a second field direction (F2) oriented transversely to the longitudinal direction (L), the second transmission coil arrangement having second transmission coils which can be excited in phase and which are arranged on opposite sides outside the passage channel (115). and have coil axes that are oriented transversely to the longitudinal direction, wherein the second transmitter coil arrangement (310-2) is arranged offset in the longitudinal direction (L) relative to the first transmitter coil arrangement (310-1) and the second field direction (F2) corresponds to the first field direction (F1). is directed opposite.

2. Metal detector according to claim 1, characterized in that the coil system (300) does not have a transmission coil enclosing 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 transmission coil arrangement (310-1) and the second coil arrangement (310-2) are designed essentially axially symmetrical 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 include a first receiver coil (320-1) and at least a second Have receiver coils (320-2), which are arranged together on one side outside the passage channel in a transverse direction (Q) oriented perpendicular to the longitudinal direction (L), offset from one another, these 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 each encloses a coil surface which extends in the longitudinal direction over the first coil arrangement (310-1) and the second coil arrangement (310-2) in such a way that in the absence of a field disturbance the first and 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 a further receiver coil on the side of the passage channel opposite the page for each receiver coil (320) on one side, with two mutually assigned receiver coils which are arranged on different sides are, each form a receiver coil pair, preferably mutually assigned receiver coils of a receiver coil pair having coil axes coaxial with one another.

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

8. Metal detector according to one of the preceding claims, characterized in that the coil system (300), viewed in the transverse direction, has 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-shaped turns in different coil layers of a multi-layer arrangement, with an insulating layer made of electrically insulating material between adjacent coil layers of the multi-layer arrangement Material is arranged.

10. Metal detector according to one of the preceding claims, characterized in that the metal detector has field shaping elements (400) made of soft magnetic material, which are outside the coil arrangements at least in the area of Transmitting coil arrangements are arranged, field shaping elements preferably being 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 shielding which is effective against penetration of electric fields into the detection zone, the E-field shielding preferably being in a layer of the coil arrangement containing multilayer structure is integrated.

12. Metal detector according to one of the preceding claims, characterized in that the support structure (110) has an access opening (114) at least on one side 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 passes in a conveying direction along a conveying route through a detection zone of a metal detector which has transmitting coils and receiver coils, wherein a transmitting coil has an excitation field in the form of an alternating electromagnetic field generated, which generates eddy currents in electromagnetically excitable components of the material to be conveyed, which lead to a disturbance of the alternating field, which are detected by a receiver coil and evaluated by an evaluation device, characterized in that the material to be conveyed in the detection zone passes through two excitation field curtains in immediate succession, which are each extend across the conveying path in a transverse direction running transversely to the conveying direction and have opposite field directions of the exciter field, each running transversely, in particular perpendicular to the conveying direction.

14. The 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 when the signals from the receiver coils are evaluated, it is determined which detection sector a signal-triggering part has passed through.