Device for detecting foreign objects

Abstract

Device for detecting foreign bodies in a conveying stream of bulk material, comprising a detection area (1) through which a material stream flows and at least one camera (4) directed towards the detection area (1), characterized in that the detection area (1) is illuminated by at least three lighting devices (2.1, 2.2, 2.3), one of which is a lighting device (2.3) comprises a planar luminous element which is arranged on or is part of a housing wall of a housing (6) enclosing the at least one camera (4), wherein the planar luminous element has a transparent area designed as a camera window (7) and is bordered by a planar reflective element (3), wherein the at least one camera (4) connected to an image evaluation device (5) is directed towards the reflective element (3) arranged behind the detection area (1), and wherein the image evaluation device (5) is configured to generate a signal when a color and / or a contour differing from the color of the bulk material appears within an image captured by the at least one camera (4).

Description

[0001] The present invention relates to a device for detecting foreign bodies in a bulk material, e.g. food, which is conveyed in a material stream through a detection area.

[0002] In food production, the presence of foreign objects in food products is a significant problem with regard to product quality and consumer protection. Numerous approaches exist to prevent foreign objects in food. Besides preventative measures designed to avoid food contamination, there are methods for targeted sorting, e.g., using filters, centrifuges, compressed air nozzles, or sieves, as well as for the systematic detection of foreign objects in food.

[0003] From DE 10 2018 121 762 A1, it is known to use a metal detector that has a detection range through which foodstuffs are conveyed. In an evaluation unit of the metal detector, foreign bodies are detected as containing metal if the received measurement signal exceeds at least a reference value.

[0004] A disadvantage of metal detector-based methods is their limitation to metallic or metal-containing foreign objects. For example, plastic films are not detected by these methods.

[0005] EP 3 028 031 B1 describes a method for detecting foreign bodies in containers with walls made of an optically transparent material. Optical coherence tomography (OCT) is used to record tomographic data of at least one volume region inside the containers. While this method detects foreign bodies or foreign body particles largely independent of their optical properties, it is only applicable to optically transparent products, such as liquids.

[0006] The packaging device with foreign object detection shown in DE 10 2011 075 607 A1 comprises a metering screw that feeds the product into a package. Two ultra-wideband sensors are arranged on the metering screw, by means of which the density of the product is continuously detected. A density value outside a predefined bandwidth leads to the rejection of the package. However, foreign objects with a density similar to that of the product are not detected by this method.

[0007] German patent DE 10 2017 124 895 B3 describes a foreign object detection device for a multihead weigher that can be emptied into a hopper. The multihead weigher includes a camera for capturing a series of images at the hopper, a lighting unit, and an image processing unit for generating a signal upon foreign object detection in a series of images. Integrating the foreign object detection device into the multihead weigher complicates regular cleaning, which is particularly important in the food industry. Furthermore, clean batches collected in the multihead weigher are first mixed with contaminated batches before being discharged.

[0008] DE 20 2006 016 604 U1 discloses a device for the optical selection of components of at least one fraction from a bulk material stream conveyed along a conveying direction, comprising a camera unit whose viewing direction is directed towards the bulk material stream, an actively luminous background arranged behind the bulk material stream in the camera's viewing direction, the color of which can be adapted to the color of a selected fraction of components of the bulk material stream, an evaluation and control unit connected to the camera unit, in which control commands for a separation unit are generated according to a decision criterion, which, when activated, is able to separate the components to be selected from the bulk material stream.

[0009] EP 1 498 723 A1 discloses a method and a device for detecting foreign bodies in tobacco. In this method, the continuous flow of tobacco on a conveyor belt is illuminated line by a fanned laser beam, and the reflected light is captured by a camera.

[0010] WO 2008 / 046 914 A1 discloses a device for determining particle parameters of a particle stream, comprising a camera-based detection and evaluation device, wherein the device has an integrated NIR spectrometer for determining the material properties of the particles of the particle stream.

[0011] GB 2 534 753 A shows a lighting system for a grain sorting machine, in which the grain kernels fall from a vibrator into a trough and from there through an illuminated detection area. Cameras are directed at the detection area and / or reflective elements located behind it, capturing images of the falling bulk material. The lighting devices illuminate both the bulk material and the reflective elements.

[0012] The invention is based on the objective of avoiding the aforementioned disadvantages, such as the limitation to foreign bodies of a specific material, whereby a method and a device for detecting foreign bodies in a conveying stream of bulk material, e.g. in a filling plant, should be feasible, which enables early (and thus cost-efficient) foreign body detection in the filling process regardless of the material of the foreign bodies, as well as unimpeded cleaning of the filling plant.

[0013] The problem is solved by a device for detecting foreign bodies in a conveyed stream of bulk material, having the characterizing features of claim 1. Advantageous embodiments of the invention are found in the dependent claims. Furthermore, an unclaimed method for detecting foreign bodies in a conveyed stream of bulk material, which solves the problem, is disclosed.

[0014] The method according to the disclosure provides for widening and limiting the height of the conveyed flow of bulk material particles transported by a conveying device before a cut-off edge of the conveying device, before the bulk material particles fall through a detection area located directly below the cut-off edge of the conveying flow and illuminated by lighting devices. The bulk material particle flow thus limited falls at the cut-off edge of the conveying device into a filling system, e.g., a multihead weigher, or onto a conveyor belt capable of being driven away.

[0015] At least one camera is directed at the detection area, located directly below the drop edge and illuminated by lighting devices, through which the previously separated bulk material particles fall. Opposite the at least one camera, with respect to the detection area, a planar reflective element is arranged; that is, the bulk material particles fall through the detection area between the reflective element and the at least one camera. At predetermined time intervals, the at least one camera captures an image of each falling bulk material particle, which is then analyzed for color and / or contour of the depicted particles.

[0016] If a color or contour that differs from the color and / or shape of the bulk material is detected in one of the images, a signal is generated, e.g., an alarm and / or stop signal. Additionally, the image in question is stored in an image memory along with other process data, e.g., date and time. A screen can also display the most recent image with foreign object detection for the operator.

[0017] The image acquisition rate is comparatively high; it is at least 40 frames per second, preferably over 50 frames per second. Image acquisition occurs continuously, thus ensuring constant, uninterrupted detection.

[0018] It can be provided that, in the event of a signal, i.e., when the image detection system detects a foreign object, the affected bulk material is sorted out – preferably automatically – before it falls into the filling system. Sorting can be carried out using a retractable conveyor belt, which conveys the contaminated bulk material, for example, against the direction of production into a waste container, or in the direction of production by means of a flipping mechanism into a waste container.

[0019] Advantageously, the method can be used to monitor grated or diced cheese, which may also be treated with an anti-caking agent, e.g. starch, for foreign bodies, e.g. plastic film particles, before weighing and filling into packaging units.

[0020] The device disclosed for detecting foreign bodies in a conveying stream of bulk material comprises a planar reflective element and at least one camera directed at the same, wherein the detection area through which the bulk material falls is located between the reflective element and the at least one camera.

[0021] Furthermore, the device comprises at least three lighting devices for illuminating the detection area and the reflective element. Advantageously, each of the lighting devices illuminates the detection area from a different direction, so that the falling bulk material is illuminated by the lighting devices from at least three different directions.

[0022] In particular, one of the lighting devices is arranged on or forms part of a housing wall of a housing containing at least one camera. The lighting element is planar and includes a transparent area that serves as a window in the housing for the at least one camera. The housing may be slightly tilted forward, meaning that the housing wall containing the lighting device is tilted a few degrees, e.g., 5°, from the vertical.

[0023] The camera(s) are connected to an image evaluation device which is configured to generate a signal when a color and / or a contour that differs from the color of the bulk material and / or from the contour of the bulk material occurs within an image captured by the at least one camera.

[0024] The signal generated in this process can be an (acoustic, electrical and / or optical) alarm signal and / or a control signal directed to a control unit, whereby the control unit, for example, interrupts the flow of the bulk material or controls an ejection device that removes the contaminated part of the flow from the system, e.g., before the bulk material containing foreign objects falls into a filling system with a multi-head weigher.

[0025] The lighting devices emit broadband light in a wavelength range detectable by the at least one camera, preferably in the visible range.

[0026] Preferably, the planar reflective element has a matte surface in a color adapted to the bulk material. The size, i.e., the area, of the reflective element is chosen such that it covers the entire image area captured by the at least one camera.

[0027] All lighting devices can be designed as flat surfaces; preferably they are arranged at the same height with respect to the detection area in such a way that they illuminate the detection area or the bulk material falling through it from different directions.

[0028] It is possible for two of the at least three lighting devices to be arranged opposite each other with respect to the detection range, so that they illuminate each other – even without falling bulk material. The lighting devices can also form a single physical unit, for example, connected by a bridge or designed as a U-shaped component.

[0029] One embodiment provides that the device has at least two cameras. All cameras are directed towards the reflective element, with each camera having a different viewing angle to the reflective element; that is, the viewing angles are arranged at an angle to each other, with each angle being a maximum of 30°, preferably a maximum of 10°. In particular, the image sections captured by the individual cameras overlap, so that improved foreign object detection is enabled by the different viewing angles of the bulk material flow. Preferably, the cameras are arranged on a horizontal line or along a horizontal arc. Additionally, the cameras can be encapsulated in a common housing.

[0030] Furthermore, it can be provided that the device has a singulation device arranged in the conveying direction of the bulk material upstream of the detection area, with which the thickness of the conveying stream can be limited, thereby facilitating the detection of foreign bodies.

[0031] Additionally or alternatively, the device or parts thereof may be movable by means of a sliding mechanism with minimal effort and without the need for tools in at least one degree of freedom, e.g., transversely upwards. In particular, the device may have a dustproof housing enclosing at least one camera, which can be moved by means of a sliding mechanism comprising lever arms and joints, e.g., for cleaning purposes. To reduce the effort required for movement, the sliding mechanism may also include mechanical and / or hydraulic spring elements.

[0032] According to one embodiment, the reflective element can be directly illuminated by a lighting device and / or itself include a lighting element that illuminates the bulk material flow.

[0033] The device for detecting foreign bodies is advantageously used in the food industry for monitoring free-flowing foods, such as grated or diced cheese or legumes, for foreign bodies.

[0034] The invention is explained in more detail below with reference to an exemplary embodiment, wherein identical or similar features are designated with the same reference numerals. The following are shown schematically: Fig. 1: the basic structure of a device for detecting foreign bodies in grated cheese; Fig. 2: a device for detecting foreign bodies in grated cheese according to one embodiment; Fig. 3: a camera housing with integrated lighting device; Fig. 4: a device for detecting foreign bodies in grated cheese according to a further embodiment; and Fig. 5: a device for detecting foreign bodies in a bulk material consisting of peas according to one embodiment.

[0035] According to Fig. The lighting devices 2.1, 2.2 and 2.3, the reflecting element 3 and the cameras 4 are arranged in a plane (the plane of the paper) around the detection area 1, through which the grated cheese (not shown) falls. In this example, the grated cheese falls into the plane of the paper from above. The cameras 4 are connected to the image evaluation unit 5.

[0036] In the design of the device according to Fig. 2. The cameras (not shown) are housed in the dustproof stainless steel housing 6, on the front of which, facing the reflective element 3, the lighting device 2.3 is arranged. The two other lighting devices 2.1 and 2.2 are – analogous to Fig. 1 - arranged to the left and right of detection area 1.

[0037] Fig. Figure 3 shows the housing 6 from its front. The large-area lighting device 2.3 covers the entire front except for a slot-shaped recess, which serves as a camera window 7, so that the two cameras 4 have a clear view of the well-lit bulk flow of grated cheese (not shown). The transparent front of the housing 6 is made of Makrolon.

[0038] The device for detecting foreign bodies in grated cheese according to the embodiment in Fig. 4 includes the discharge conveyor 8, which transports the grated cheese (not shown) falling from the feed conveyor 9 through the detection area 1 into the multihead weigher 10 for packaging the “good” grated cheese or alternatively (by reversing the movement in the opposite direction) into the waste container 11 for sorting out the “contaminated” cheese.

[0039] The device for detecting foreign bodies, for example between peas, according to Fig. Assembly 5 comprises the two discharge conveyors 8.1 and 8.2, with the second discharge conveyor 8.2 being designed to tilt. Upon detection of a foreign object in the peas falling through the detection area (not shown), the second discharge conveyor 8.2 is tilted downwards, so that the "contaminated" peas fall into the waste container 11. List of reference symbols used 1 detection range 2.1 First lighting device 2.2 Second lighting device 2.3 third lighting device 3 reflective elements 4 cameras 5 Image evaluation unit 6 cases 7 camera windows 8 Discharge belt 8.1 Discharge conveyor belt 8.2 Discharge conveyor belt, tiltable 9 Feed conveyor 10 Multihead scales 11 waste containers

Claims

Device for detecting foreign bodies in a conveying stream of bulk material, comprising a detection area (1) through which a material stream flows and at least one camera (4) directed towards the detection area (1), characterized in that the detection area (1) is illuminated by at least three lighting devices (2.1, 2.2, 2.3), one of which is a lighting device (2.3) comprises a planar luminous element which is arranged on or is part of a housing wall of a housing (6) enclosing the at least one camera (4), wherein the planar luminous element has a transparent area designed as a camera window (7) and is bordered by a planar reflective element (3), wherein the at least one camera (4) connected to an image evaluation device (5) is directed towards the reflective element (3) arranged behind the detection area (1), and wherein the image evaluation device (5) is configured to generate a signal when a color and / or a contour differing from the color of the bulk material appears within an image captured by the at least one camera (4). Device for detecting foreign bodies according to claim 1, characterized in that the planar reflective element (3) has a matte surface in the color of the bulk material. Device for detecting foreign bodies according to claim 1, characterized in that a first lighting device (2.1) and a second lighting device (2.2) are arranged opposite each other with respect to the detection area (1). Device for detecting foreign bodies according to claim 1, characterized in that it has at least two cameras (4), wherein an angle between the viewing directions of the cameras (4) on the detection area (1) is a maximum of 30°, wherein the cameras (4) and the reflective element (3) are arranged opposite each other with respect to the detection area (1). Device for detecting foreign bodies according to claim 1, characterized in that it has a singulation device arranged in the conveying direction of the bulk material in front of the detection area (1), with which the thickness of the conveying stream can be limited. Device for detecting foreign bodies according to claim 1, characterized in that the housing (6) enclosing the at least one camera (4) is dustproof, wherein it is displaceable in at least one degree of freedom by means of a displacement device comprising lever arms and joints.

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