Optical inspection of objects in a material flow, such as bulk material.

Description

[0001] The invention relates to a device for optically examining objects in a material stream, and a corresponding method.

[0002] When optically examining objects in a material stream, objects with different spectral reflectances are distinguished, and in particular, the different components and materials of the respective objects are identified. One method is classical line spectroscopy, in which light is decomposed into its wavelength components using dispersive optical elements within the image plane. Disadvantages of this method include the high manufacturing precision required and the one-dimensional object resolution. There are also multispectral cameras that either have time-varying filters, consist of a camera array with pre-installed filters, or, instead of the usual red-green-blue (RGB) filter arrays, incorporate additional sensors or other filter arrays.

[0003] All of these solutions suffer from insufficient spectral resolution and, consequently, low flexibility. Cameras with time-varying filters are also susceptible to failure due to their mechanical components. Camera arrays generate high data streams by multiplying sensor data, which is also disadvantageous. Alternative methods utilize time-varying illumination with different predefined light spectra to reconstruct parts of the spectral reflectance. A disadvantage here is the need for constant, high-speed switching of the illumination, which on the one hand limits the choice of available light sources and thus the possible light spectra, and on the other hand limits the lifespan of the illumination or the speed of the measurement.

[0004] DE 297 24 853 U1 describes a device for identifying and sorting belt-fed objects, in which a measuring point is moved in a scanning motion over the objects on the conveyor belt. Optical detection of the objects ensures that different object materials are identified only where an object is located. Similar systems are known from quality assurance in tablet production, in which tablets are arranged in rows and columns on a synchronized conveyor belt, and the individual tablets are scanned with a measuring probe during the respective pauses in movement within a detection area. US 9,785,851 B1 describes a system and a method for sorting scrap particles, which includes imaging a moving conveyor containing scrap particles using an image processing system to generate an image.To classify scrap particles, a portion of the material is vaporized by irradiation with laser pulses. The resulting emission radiation is then analyzed spectroscopically. German patent DE 44 26 475 A1 describes an arrangement and a method for using lasers in laser plasma spectroscopy for material identification of moving parts that follow a statistical sequence. EP 0 696 236 B1 describes a method and a device for sorting material parts.

[0005] Furthermore, the usual illumination of a relatively large area has the disadvantage that an unfavorable signal-to-noise ratio makes evaluation more difficult.

[0006] The task is to overcome the disadvantages described above of known devices for the optical examination of objects in a material stream.

[0007] This problem is solved by the subject matter of the independent patent claims.

[0008] Advantageous embodiments are shown in the dependent claims, the description and the figure.

[0009] One aspect concerns a device for the optical inspection of objects in a material stream, in particular for the optical spectroscopy of objects in a material stream. The objects can be belt-fed items such as bulk material. The device comprises a light source, a tracking device, a deflection device, and a sensor device with an optical sensor.

[0010] The light source device is designed to generate examination light suitable for the optical inspection of objects in the material stream. Within the scope of this disclosure, optical inspection includes examination in the visible region of the spectrum, as well as examination in the infrared, ultraviolet, or X-ray ranges. Accordingly, the examination light can be electromagnetic radiation in the infrared range, particularly in the near-infrared range, in the visible range, in the ultraviolet range, or in the X-ray range. Preferably, the spectral distribution of the examination light lies in an infrared range and / or in a visible range and / or in an ultraviolet range. The infrared range can extend from 2200 nm to 640 nm, the visible range from 640 nm to 380 nm, and the ultraviolet range from 380 nm to 190 nm.These spectral distributions are particularly advantageous for classifying objects, especially bulk material objects.

[0011] In principle, the solution described below can also be applied to an unloaded acoustic investigation, in which the light source device is replaced by a suitable sound source device, which accordingly generates an investigation sound, for example in the form of a directed sound cone.

[0012] The tracking device is designed to track at least one object, i.e., one or more objects, within the material flow and to output corresponding location information for the tracked object. The output of the location information preferably occurs repeatedly, particularly continuously, with a corresponding temporal resolution, which can also be adjustable. Tracking can be carried out using conventional object tracking methods, for example, as described in patents EP 3 122 479 B1 or US 2020 388 042 A1.

[0013] The deflection device is designed to direct the examination light onto the tracked object and / or to direct a portion of the examination light reflected from the tracked object onto the sensor device with the optical sensor. In both cases, the deflection is carried out according to the output location information. Thus, the examination light can be used to selectively illuminate the tracked object, and then the reflected portion of the examination light can be detected across the entire area, i.e., not location-specifically. Conversely, the material flow containing the object(s) can be illuminated across the entire area, i.e., not location-specifically, and only the portion of the examination light reflected from the tracked object(s) can be selectively directed onto a sensor device with an optical sensor.Accordingly, in these cases the light source device and deflection device can be spatially separated from the sensor device, or the deflection device and sensor device can be spatially separated from the light source device, i.e., in particular, each with its own housing.

[0014] Alternatively, the deflection device can also be designed to simultaneously direct the examination light onto the tracked object and, in particular, only the portion of the examination light emanating from the tracked object onto the sensor device with the optical sensor. This can be achieved, for example, by ensuring that the respective beam paths overlap at least partially, as can be realized with appropriate beam splitters. Such combined beam paths are known, for example, from the quality control systems for tablets described above; in this case, only the portion of the reflected light that propagates precisely along the scanning light beam back to a corresponding beam splitter and from there to the sensor device is evaluated.

[0015] This has the advantage that the spectral information of measurement points or areas on moving objects can be selectively acquired without requiring area-wide coverage. This significantly reduces the amount of data generated. By tracking the measuring beam in the shape of the inspected light or the reflected portion of the inspected light transmitted to the sensor, it is also possible to variably define the achievable measurement time, even different lengths for different measurement points or areas. This also results in an improved signal-to-noise ratio of the sensor data supplied by the sensor compared to conventional methods, as there are fewer scattering losses.This enables the evaluation of signals acquired by the sensor device using methods that, due to their comparatively poor efficiency, are not typically employed in combination with known devices for the optical inspection of objects within a material stream. Such methods include, for example, Raman spectroscopy, fluorescence spectroscopy, fluorescence lifetime analysis, laser-induced plasma spectroscopy, and / or object inspection based on highly accurate polarization detection.

[0016] According to the invention, the light source device comprises one or more point light sources, in particular laser point light sources, by means of which a respective measuring area, in particular a respective measuring point, on the object(s) can be illuminated with the examination light.

[0017] The measurement area or point is, in particular, smaller than or equal to the size of the object, for example, at most half the size of the object itself. The examination light is thus directed onto a portion of the object's surface, the corresponding measurement area or point. The respective point light sources can be assigned one or more different spectral distributions, i.e., wavelengths or wavelength distributions. This has the advantage of enabling particularly precise measurements.

[0018] According to the invention, the deflection device is designed to consecutively direct the examination light to at least two, i.e., two or more than two, different measuring areas or measuring points on the tracked object. This has the advantage that the objects in the material flow can be examined particularly precisely and flexibly.

[0019] It can further be provided that the deflection device is designed to direct the examination light for an individually configurable measurement time onto at least two different measurement areas or points on the object(s) being tracked. In particular, the respective measurement times can differ from one another. Preferably, the measurement times are more than one millisecond, more preferably more than three milliseconds, and most preferably more than five milliseconds. This contributes to a further increase in the accuracy of the optical examination. For example, such an examination scenario is conceivable in which several different measurement areas are first briefly illuminated with the examination light, and then a subset of the briefly illuminated measurement areas can be illuminated again for a longer period for a more precise examination.For the different measurement ranges or even the different measurements in the same measurement ranges, different wavelengths of the examination light can be used, as described below, which further allows for a more precise examination of the object(s).

[0020] In a further advantageous embodiment, the examination light can exhibit at least three different wavelengths, i.e., different wavelength peaks, and in particular at least eight different wavelengths or wavelength peaks. The spectral distribution of the examination light can therefore have at least three different peaks or maxima, or at least eight different peaks or maxima, which are referred to simply as different wavelengths. The examination light can thus be, or be described as, a multispectral or hyperspectral examination light. This allows for a more precise examination of objects within the material stream.

[0021] In a further advantageous embodiment, the deflection device comprises a mirror galvanometer and / or a beam splitter. This allows the examination light to be directed particularly quickly and precisely to the respective measuring areas. The combination with a beam splitter allows the examination light and the reflected portion of the examination light, which is directed to the optical sensor, to be guided in the same beam path as described above, thus enabling a particularly compact design.

[0022] In another advantageous embodiment, the deflection device includes an aperture unit configured to direct only the portion of the examination light reflected from the tracked object onto the sensor device, i.e., to allow only that portion to pass through which it is reflected from the specified measurement area(s) on the object. The aperture unit thus acts as a dynamic filter for the reflected portion of the examination light. This has the advantage that the light source can also utilize a surface light source that illuminates not only the respective measurement area but also the object and, if necessary, even its surroundings within the light stream, while still achieving the aforementioned advantages.

[0023] In a further advantageous embodiment, the tracking device is configured to track the object(s) based on a motion model, in particular a learned motion model, especially even outside a detection range of the tracking device that is valid for the respective tracked object. The tracking device can therefore be configured to predict the movement of an object outside a detection range based on the detected movement of that object and to output corresponding location information relating to a location outside the detection range. The tracking, in particular the motion model, can use a predefined or adjustable conveying speed of a (particularly belt) conveyor as a parameter.This has the advantage of particularly precise tracking, as well as the flexible arrangement of the tracking device relative to the light source device and deflection device.

[0024] In a further advantageous embodiment, the tracked object(s) are moving objects that are in motion during the tracking process and the direction of the examination light onto the respective object and / or the direction of the reflected portion of the examination light onto the sensor devices. This has the advantage that the movement of the objects does not need to be interrupted for optical inspection, meaning the material flow does not need to be interrupted.

[0025] In a further advantageous embodiment, the device includes a (in particular belt) conveyor for transporting and thus moving the objects illuminated by the examination light. The device can also include an analysis device for analyzing an electrical or electronic signal generated by the optical sensor as a function of the reflected portion of the examination light detected by the optical sensor.

[0026] Another aspect concerns a method for optically examining a material stream of objects, in particular for optical spectroscopy of a material stream of objects, with the following process steps: Generating an examination light suitable for optically inspecting the objects of the material flow with a light source device comprising one or more point light sources, in particular laser point light sources, by means of which a respective measuring area, in particular measuring point, on the object is illuminated with the examination light; tracking at least one object; outputting location information of the tracked object; directing the examination light onto the tracked object or directing a portion of the examination light reflected from the tracked object onto a sensor device with an optical sensor, by means of a deflection device (5), according to the output location information.

[0027] According to the invention, the examination light is directed consecutively by means of the deflection device onto at least two different measuring areas, in particular measuring points, on the tracked object.

[0028] Advantages and advantageous embodiments of the method correspond here to advantages and advantageous embodiments of the device and vice versa.

[0029] Optical analysis can include Raman spectroscopy, fluorescence spectroscopy, fluorescence lifetime analysis, and / or laser-induced plasma spectroscopy of the material stream. This is particularly advantageous due to the improved signal-to-noise ratio that can be achieved.

[0030] The schematic drawing shown in the following figure is intended to explain the subject matter of the invention in more detail, without limiting it to the specific embodiments shown here.

[0031] This shows Fig. 1 An exemplary embodiment of a device for the optical examination of a material flow of objects.

[0032] The device 1 for optically inspecting objects 2 in a material stream comprises, in the example shown, a light source device 3, a tracking device 4, a deflection device 5, a sensor device 6, and, by way of example, a conveyor device 7, which is implemented as a belt conveyor. The light source device 3 serves to generate an inspection light 8 suitable for optically inspecting the objects 2 in the material stream. The tracking device 4 serves to track at least one object 2 and output corresponding location information of the tracked object 2 to the deflection device 5, in particular to a control unit associated with the deflection device 5.The deflection device 5 is designed here to direct the examination light 8 onto the corresponding tracked object 2, and in the present example also to direct a portion 8' of the examination portion 8 reflected by the tracked object 2 onto the sensor device 6. For this purpose, the deflection device 5 here comprises a correspondingly controlled mirror galvanometer and a beam splitter.

[0033] In Fig. 1For illustrative purposes, object 2 is also referred to as object 2* at a later time, when the object has moved relative to its position at the time of detection by the tracking device 4. Accordingly, the examination light tracked by the deflecting device 5 is designated as examination requirement 8*, and the reflected component is designated as reflected component 8'* at a later time. It should be noted that object 2 is located outside a detection range 9 of the tracking device 4 at a later time, yet it can still be tracked by the tracking device 4 because the chosen tracking method of the tracking device 4, for example, based on a motion model for object 2, also allows for a corresponding prediction of object 2 moving outside the detection range 9.This motion model can depend on the conveying speed s of the conveying device 7.

Claims

1. A device (1) for optically examining objects (2) in a material flow, in particular for the optical spectroscopy of objects (2) in a material flow, comprising - a light source device (3) for generating an examination light suitable for optically examining the objects (2) in the material flow (8, 8*), the light source device (3) comprising one or more point light sources, in particular laser point light sources, by means of which a respective measurement range, in particular a measurement point, on the object (2) can be illuminated with the examination light (8, 8*); - a tracking device (4) for tracking at least one object (2) of the material flow and providing location information of the tracked object (2); - a sensor device (6) with an optical sensor; and - a deflection device (5) for directing the examination light (8, 8*) onto the tracked object (2) in accordance with the provided location information or for directing a portion (8', 8'*) of the examination light (8, 8*) reflected by the tracked object (2) onto the sensor device (6); characterised in that the deflection device (5) is configured to direct the examination light (8, 8*) consecutively onto at least two different measurement ranges, particularly measurement points, on the tracked object (2).

2. The device (1) according to the preceding claim, characterised in that the deflection device (5) is configured to direct the examination light (8, 8*) onto the at least two different measurement ranges or measurement points on the tracked object (2) for a respective individually predefinable measurement time, in particular for measurement times that differ from one another.

3. The device (1) according to any of the preceding claims, characterised in that the examination light (8, 8*) has at least three different wavelengths, in particular at least eight different wavelengths.

4. The device (1) according to any of the preceding claims, characterised in that the deflection device (5) comprises a mirror galvanometer and / or a beam splitter.

5. The device (1) according to any of the preceding claims, characterised in that the deflection device (5) has an aperture unit which is configured to direct only that portion (8', 8'*) of the examination light (8, 8*) reflected by the tracked object (2) onto the sensor device (6) which is reflected from at least one predetermined measurement range on the object (2).

6. The device (1) according to any of the preceding claims, characterised in that the tracking device (4) is configured to track the object or objects (2) based on a motion model, in particular a learned motion model, especially outside a detection range (9) of the tracking device (4) for the respective tracked object (2).

7. The device (1) according to any of the preceding claims, characterised in that the tracked object or objects (2) are moving objects (2) which are in motion during the tracking and the directing of the examination light (8, 8*) onto the respective object (2) and the directing of the reflected portion (8', 8'*) of the examination light (8, 8*) onto the sensor device (6).

8. The device (1) according to any of the preceding claims, characterised by a conveying device (7) for conveying the objects (2) illuminated by the examination light (8, 8*).

9. A method for optically examining a material flow of objects (2), in particular for the optical spectroscopy of a material flow of objects (2), by - generating an examination light (8, 8*) suitable for optically examining the objects (2) of the material flow, using a light source device (3) comprising one or more point light sources, in particular laser point light sources, by means of which a respective measurement range, in particular a measurement point, on the object (2) is illuminated with the examination light (8, 8*); - tracking at least one object (2); - providing location information of the tracked object (2); - directing the examination light (8, 8*) onto the tracked object (2) or directing a portion (8', 8'*) of the examination light (8, 8*) reflected by the tracked object (2) onto a sensor device (6) with an optical sensor, by means of a deflection device (5), corresponding to the provided location information, characterised in that the examination light (8, 8*) is directed by means of the deflection device (5) consecutively onto at least two different measurement ranges, in particular measurement points, on the tracked object (2).

10. The method according to the preceding claim, characterised in that the optical examination is or comprises a Raman spectroscopy and / or a fluorescence spectroscopy and / or a fluorescence lifetime analysis and / or a laser-induced plasma spectroscopy of the material flow.