Camera system for optically inspecting the surface of an element of an energy cell, and associated inspection method

Abstract

The invention relates to a camera system (10) for optically inspecting the surface (11) of an element (12) of an energy cell, in particular a battery, said camera system comprising at least one image capture device (13) which is designed to capture a surface portion (14) of an element (12) conveyed relative to the image capture device (13). At least two light sources (15, 16, 17) are provided, the light of which is incident on the surface portion (14) of the conveyed element (12) from different illumination directions (18, 19, 20). The surface portion (14) can be captured by the at least one image capture device (13) with at least two different images (21, 22) which are associated with different illumination directions (18, 19, 20). A data-processing unit (24) is provided which is designed to process the captured, different images (21, 22) to produce a combination image (23). The invention also relates to a corresponding inspection method.

Description

[0001] CAMERA SYSTEM FOR OPTICAL INSPECTION OF THE SURFACE OF AN ELEMENT OF AN ENERGY CELL AND

[0002] ASSOCIATED INSPECTION PROCEDURE

[0003] 5 The present invention relates to a camera system for optically inspecting the surface of an element of an energy cell, in particular a battery, according to the preamble of claim 1 and to a corresponding inspection method for optically inspecting the surface of an element of an energy cell, in particular a battery, using such a camera system according to the preamble of claim 10.

[0004] Energy cells or energy storage devices within the meaning of the invention are used, for example, in motor vehicles, other land vehicles, ships, aircraft, or even in stationary storage systems in the form of battery cells or fuel cells, where very large amounts of energy must be stored over extended periods of time. Providing a sufficient quantity of energy cells, especially battery cells, requires mass-market manufacturing technologies with high production speeds. The high production speeds and the use of continuous production processes, together with high quality requirements, pose a challenge for inline inspection of intermediate products of energy cells.To ensure high quality of the final product, it is advantageous, among other things, to inspect the surfaces of an intermediate product, for example an anode or cathode sheet, for defects before stacking, folding, or rolling into an energy cell, especially a battery cell. Such surface defects can be particles or cracks. Furthermore, such defects can affect the general edge quality, particularly in the case of an active material in an energy cell or battery, i.e., in the case of anode or cathode material on a conductor foil. The undesired particles on the surface of an intermediate product or element of an energy cell can primarily be particles of the same material as the surface, which prevents the particles from being distinguished from the surface based on color. Furthermore, typical anode and cathode materials, e.g.NMC, LFP, or graphite, exhibit very dark colors, resulting in only a low brightness contrast between the particles on the surface. Inspecting the surface for particles larger than 50 pm, usually with a resolution of 10 pm to 15 pm, combined with high conveying speeds and the optical properties of the materials, places very high demands on a camera system for optically inspecting the surface of an energy cell element, especially a Li-ion battery.

[0005] Against this background, the object of the invention is to provide a camera system for the optical inspection of the surface of an element of an energy cell, in particular a battery, and a corresponding inspection method which can meet the aforementioned requirements.

[0006] The invention solves this problem with the features of the independent claims. Further preferred embodiments of the invention can be found in the subclaims and the associated descriptions and drawings.

[0007] To achieve this objective, a camera system for optically inspecting the surface of an element of an energy cell, in particular a battery, is proposed, comprising at least one image capture device configured to capture a surface section of an element conveyed relative to the image capture device. At least two light sources are provided, the light of which impinges on the surface section of the conveyed element from different illumination directions. The surface section can be captured by the at least one image capture device using at least two different images, each of which is assigned to different illumination directions, preferably each to one of the illumination directions. A data processing unit is provided, configured to process the captured, different images into a combined image and preferably to output the combined image.

[0008] With such a camera system, a type of three-dimensional information about surface defects, in particular particles on the surface to be inspected, can be captured in the combined image. In particular, sensitivity can be achieved with respect to parts of the particle surface that are at a favorable reflection angle, for example, the slope, of the respective light source to the image capture device. By combining multiple images of the same surface section and thus preferably also of the surface defects, for example, the same particles on this surface section, with different exposure directions, such defects or particles can be identified in the combined image and their size can be estimated.Therefore, the particles are not always fully reproduced in the combined image; rather, they may represent several partial areas of the particles, which nevertheless allow sufficient particle detection. Thus, particles on typically extremely dark materials can be detected in the combined image with the short possible exposure time due to the high conveying speeds. In advantageous embodiments, detection can be achieved through automated image analysis of the combined image.

[0009] In the combined image, the at least two different images, each associated with one of the illumination directions, are preferably combined with one another, more preferably with pixel-accurate combinations. Pixel-accurate combinations or processing can be achieved, in particular, with a camera system that captures the at least two different images, each with one of the illumination directions of the same surface section, using the same sensor or sensor chip.

[0010] In possible embodiments, the illumination directions may be a combination of several directions and / or sources, as long as different illumination scenarios, each with different illumination directions, are achieved overall, which can be assigned to different images of the same surface section.

[0011] The element of an energy cell, in particular a battery cell, is preferably a flat precursor or intermediate product of such a cell. The element can be, for example, a conductor foil coated with anode material, e.g. graphite, a conductor foil coated with cathode material, e.g. NMC (lithium nickel manganese cobalt oxide), or a separator foil. Furthermore, the element can be a web, for example an electrode web, in particular an anode or cathode web, or a separator web. Preferably, the element is a continuous web. Alternatively, the element can be, for example, an individual electrode sheet which is not conveyed as a web. The element is preferably conveyed continuously.

[0012] Furthermore, the camera system is preferably configured for inspecting a surface section on one side of a planar element. In possible embodiments, the camera system is configured for double-sided inspection, so that surface sections on both sides of the planar element of an energy or battery cell can be inspected.

[0013] The camera system is designed to inspect preferably the entire surface of an active material of an element.

[0014] Therefore, a plurality of surface sections can be inspected or checked in a temporal sequence corresponding to the, in particular continuous, conveyance of the element relative to the camera system and the image capture device. The detected surface sections preferably adjoin one another, so that optimal efficiency of the camera system can be achieved. In possible alternative embodiments, the detected surface sections overlap.

[0015] An image with an associated illumination direction can also correspond to a partial image of a partial area of ​​a sensor or a partial image of an image recording (frame).

[0016] According to a further development, it is proposed that the at least two light sources each have different light colors. Different light colors of the respective light sources, which project light onto the surface section with different illumination directions, enable a technically simple assignment of an image to a corresponding illumination direction. Different light colors result from different emission spectra of the light sources. A light source with one illumination direction can, for example, also consist of an arrangement of several light-emitting diodes. Such an assignment can be achieved, for example, via the spectral sensitivity of the image capture device or parts thereof.A corresponding spectral sensitivity, which enables the detection and assignment of only one illumination direction from a light source, can be achieved, for example, via color filters and a corresponding design of a sensor in the image capture device.

[0017] According to a further development, it is proposed that the at least two different images of the surface section can be captured at different measuring positions relative to the camera system.

[0018] The different measuring positions can result, for example, from the conveyance of the element relative to the camera system, so that, for example, two images assigned to two different illumination directions are recorded of the same surface section at different times. The resulting time difference preferably corresponds to the distance between the measuring positions due to the relative conveyance speed of the element. In possible embodiments, the acquisition of these two or more different images by the camera system can be carried out using an image recording device, wherein the respective surface section can, for example, be positioned at a different position in the image recording. Accordingly, two or more images of different surface sections can be created in one image recording of an image recording device.In this case, preferably several surface sections, for example two or more, can be captured in parallel using an image capture device in one image recording. The parts of the image recording that show a respective surface section can thus form an image of a surface section with an associated illumination direction. In another possible embodiment, the two or more different images can be captured using two or more different image capture devices.

[0019] In an advantageous embodiment, the light sources are switched alternately. This ensures that only one light source with one illumination direction is incident on a surface section of an element at a time. This allows images to be clearly assigned to a particular illumination direction.

[0020] In alternative embodiments, the light sources can be arranged spatially separated, so that a clear assignment of illumination directions to images is possible, preferably with the corresponding number of image capture devices.

[0021] According to a further development, it is proposed that the image capture device comprise a color line-scan time-delay and integration line-scan camera (multi-field TDI line-scan camera). A time-delay and integration line-scan camera, also known as a TDI line-scan camera (where TDI stands for Time Delay and Integration), comprises a sensor having multiple illumination levels. The illumination levels each preferably capture the same section corresponding to the movement of the conveyed element or surface section, with the charges preferably being shifted or copied from illumination level to illumination level, thus achieving integration across the corresponding number of illumination levels used.

[0022] A color line-scan time-delay and integration line-scan camera (multi-field TDI line-scan camera), for example, also has three different areas with different spectral sensitivities, so that three different images can be captured with such a camera. In combination with different illumination directions, each with different light colors, each adapted to the three different areas, the camera system can capture at least two, in particular three, corresponding images, which can be processed by the data processing device into a combined image. The combined image is preferably processed from several grayscale images, which can also be performed with color image capture.

[0023] Such an image capture device enables sufficient exposure and a sufficient signal-to-noise ratio, even at high conveyor speeds and with dark materials on the surface of an element to be inspected. Furthermore, the different color lines allow for easy assignment to different illumination directions, provided the different illumination directions each have different light colors. In particular, with a color line camera, time delay and integration, for example, three different images with different illumination directions can be captured and easily processed into a combined image. This is because pixel-precise computation of the different images is possible due to the fact that the images are recorded on a common chip.

[0024] It is further proposed that the light sources be operated in pulsed mode. This, for example, together with the proposed color line time delay and integrated line scan camera, enables a sufficient signal-to-noise ratio. Furthermore, the energy consumption can be minimized compared to continuous operation.

[0025] According to a further development, it is proposed that the image capture device comprise a matrix camera. With a matrix camera, at least two different images with different illumination directions of the same surface section can be captured at different measuring positions and at different times by means of at least two chronologically successive image recordings (frames). Preferably, the illumination direction changes between the image recordings (frames) so that two different images of a surface section, each of which can be a partial image of the image recording, can be captured with different illumination directions. Furthermore, the advantageous possibility exists of using a color matrix camera and different light colors for the different illumination directions to capture correspondingly different images with continuous illumination.

[0026] In an advantageous embodiment, it is proposed that the image capture device comprises a plurality of matrix cameras arranged next to one another and transversely to the conveying direction of the conveyed element. The arrangement of a plurality of matrix cameras next to one another simplifies the scalability of the camera system with respect to the width of the element to be inspected, which is conveyed transversely to the width relative to the camera system. The images from the matrix cameras are preferably evaluated individually, but they can alternatively also be evaluated together in a composite image. An overlap region is preferably provided at the transition between the detection ranges of two matrix cameras. A matrix camera generally has an area sensor; this can, for example, be square or in the format 4:3 or a comparable format, and is therefore different from a line scan camera.

[0027] The camera system is preferably configured to capture a surface section of an element conveyed on a drum relative to the image capture device. A drum enables the continuous conveyance of individual elements of an energy or battery cell, for example, electrode sheets, which can be continuously conveyed on the drum relative to the camera system. A color line-scan camera with time delay and integration can preferably be used as the image capture device for conveyance on a drum, since the depth of field is unproblematic with this image capture device given the typical curvature of the element conveyed on a drum.When using a matrix camera as an image capture device, the recording area on the drum should preferably be limited in the conveying direction of the captured images in order to avoid adverse depth of field blur due to the curvature of the element on the drum.

[0028] Furthermore, to achieve the object, an inspection method for optically inspecting the surface of an element of an energy cell, in particular a battery, with a camera system according to one of claims 1 to 9 is proposed, comprising the following steps:

[0029] - illuminating a surface portion of an element conveyed relative to the image capture device with at least two light sources whose light is incident on the surface portion of the conveyed element from different illumination directions;

[0030] - capturing the surface section with at least one image capturing device with at least two different images, each of which is assigned to different, preferably one of the, illumination directions;

[0031] - Processing the captured, different images into a combined image in a data processing unit;

[0032] - preferably output the combination image.

[0033] The combination image allows detection of surface defects, such as particles larger than 50 pm on the surface, despite very dark surface materials with a very high optical absorption coefficient and very high conveying speed, for example, greater than 60 m / min.

[0034] According to a further development, it is proposed that the processing to create a combined image be carried out by subtracting the at least two images with different illumination directions. Subtracting the different images with different illumination directions of the same surface section is a particularly advantageous method for obtaining a combined image that contains correspondingly advantageous indirect 3D information.

[0035] It is further proposed that the combined image be digitally filtered in the data processing unit before output. Digital filtering of the combined image can, for example, remove noise.

[0036] According to a further development, it is proposed that the combined image be binarized in the data processing unit before output. This allows the contrast between surface defects and intact areas of the surface to be further increased. Binarization of the combined image preferably occurs after digital filtering of a difference image.

[0037] Furthermore, an opening is preferably performed in a digital image processing system before outputting the combined image, especially after binarization. This opening serves to remove very small disturbances or errors, for example, smaller than 50 pm.

[0038] In an advantageous embodiment, the data processing device evaluates the combined image for surface defects, in particular particles, on the surface section. In alternative embodiments, the evaluation can also be performed outside the camera system. The evaluation can be used, for example, to exclude the corresponding parts of the element, for example, in the case of an electrode track, or the entire element, for example, in the case of an electrode sheet, from further processing.

[0039] According to a further development, it is proposed that successive image recordings are carried out using a matrix camera as the image capture device, each with different illumination directions on the surface section.

[0040] The illumination direction can therefore change between the image recordings (frames), so that two different images of a surface section, each of which can be a partial image of the image recording, can be captured with different illumination directions.

[0041] According to a further development, it is proposed that two consecutive image recordings with a matrix camera as the image capture device capture the same surface section on different sensor areas of the matrix camera. For example, a surface section can be captured in a first image recording in a first half of the lines (e.g., lines 1 to 500) of the image recording (frame) as the sensor area of ​​the matrix camera, and the same surface section can be captured as the sensor area in a second, subsequent image recording in the second half of the lines (e.g., lines 501 to 1000) of the image recording (frame).

[0042] In one possible embodiment, a change in light, ie a different illumination direction, can be carried out within an image recording, so that, for example, the first 500 lines are captured with a first illumination direction and the second 500 lines with a second illumination direction.

[0043] In an advantageous embodiment, a matrix camera as the image capture device has an image capture rate that is matched to the conveying speed of the element being conveyed relative to the image capture device, such that a surface section of the conveyed element covers a maximum of half, preferably half, the sensor range of the matrix camera between two image captures. Thus, the same surface section can be captured with two consecutive image captures (frames) using the same image capture device.

[0044] The invention will be explained below using preferred embodiments with reference to the attached figures.

[0045] Fig. 1 is a schematic representation of a camera system;

[0046] Fig. 2 shows an image of a surface section with a first illumination direction;

[0047] Fig. 3 is an image of a surface section with a second illumination direction;

[0048] Fig. 4 is a combined image of a surface section;

[0049] Fig. 5 a filtered combination image;

[0050] Fig. 6 a binarization of the filtered combination image;

[0051] Fig. 7 shows an opening of the binarized combination image. Figure 1 schematically shows an embodiment of a proposed camera system 10 for optically inspecting the surface 11 of an element 12, for example a cathode track, as a precursor for a battery. The element 12 is conveyed relative to the camera system 10, see symbolic arrow. The camera system 10 has an image capture device 13 which captures a surface section 14 of the element 12. In this embodiment, three light sources 15, 16, 17 are provided, each of which projects light from different illumination directions 18, 19, 20 onto the surface section 14. In this embodiment, the light sources 15, 16, 17 each have a different light color, so that light of different light colors, for example red, green, blue, strikes the surface section 14 from the three illumination directions 18, 19, 20.

[0052] In this embodiment, the image capture device 13 is a color line-scan time-delay and integration camera that captures the three light colors from the different illumination directions separately. Therefore, three images 21, 22 (see also Figures 2 and 3) are recorded, each containing different information about the surface 11 in the surface section 14.

[0053] Figures 2 to 7 show, by way of example, the processing of image data of the surface 11 of an element 12 using the camera system 10. Figures 2 to 7 show the typical dark surface 1 of an electrode material, with Figures 2 to 7 being shown inverted for better illustration. In this advantageous exemplary embodiment, two different images 21, 22 of the same surface section 14 are captured, see Figures 2 and 3. In the data processing unit 24, the images 21, 22 are processed into a combination image 23 by subtraction, see Figure 4. The combination image 23 thus has the combined information with indirect additional 3D information of the surface 11 based on the different illumination directions 18, 19, so that the combination image 23 enables improved inspection of the surface section 14, for example using digital image analysis.In possible embodiments, the resulting combination image 23 can be output by the data processing unit 24 for further data processing, or alternatively evaluated by the data processing unit 24 itself.

[0054] Figure 5 shows the combined image 23 of Figure 4 after digital filtering of the combined image 23 by the data processing unit 24, which can, for example, remove noise in the combined image 23. The combined image 23 can then be binarized so that, preferably, only the colors black and white remain in the image with a correspondingly maximum contrast. Finally, the data processing unit 24 can perform an opening on the binarized combined image 23 so that even the smallest structures of irrelevant sizes can be filtered out.

[0055] The combination image 23 can generally be used to visually inspect the surface 11 of an element 12 of an energy cell, in particular a battery cell, and, if surface defects are detected, e.g., if defined limits for the size and / or number of particles on a surface section 14 are exceeded, to exclude this part from further processing. List of reference symbols

[0056] 10 Camera system

[0057] 11 Surface 12 Element

[0058] 13 Image capture device

[0059] 14 Surface section

[0060] 15, 16, 17 Light source

[0061] 18, 19, 20 Lighting directions 21 , 22 Image

[0062] 23 Combination image

[0063] 24 Data processing unit

Claims

Claims:

1. Camera system (10) for optical inspection of the surface (11) of an element (12) of an energy cell, in particular a battery, - with at least one image acquisition device (13) which is configured to capture a surface section (14) of an element conveyed relative to the image acquisition device (13). (12) to capture, characterized in that - at least two light sources (15, 16, 17) are provided, the light of which falls on the surface section (14) of the conveyed element (12) from different directions of illumination (18, 19, 20), wherein - the surface section (14) with at least two different images (21, 22), each of which is assigned to different lighting directions (18, 19, 20), of which at least one image capture device (13) can be detected, and - a data processing unit (24) is provided which is equipped to - to process the captured, different images (21, 22) into a combined image (23), and - preferably to output the combined image (23).

2. Camera system (10) according to claim 1 , characterized in that - which at least two light sources (15, 16, 17) each have different light colors.

3. Camera system (10) according to claim 1 or 2, characterized in that - that at least two different images (21 , 22) of the surface section (14) can be captured at different measurement positions relative to the camera system (10).

4. Camera system (10) according to one of the preceding claims, characterized in that the light sources (15, 16, 17) are switched alternately.

5. Camera system (10) according to one of the preceding claims, characterized in that the image acquisition device (13) comprises a color line time delay and integration line camera.

6. Camera system (10) according to one of the preceding claims, characterized in that the light sources (15, 16, 17) can be operated in pulsed mode.

7. Camera system (10) according to one of the preceding claims, characterized in that the image acquisition device (13) comprises a matrix camera.

8. Camera system (10) according to claim 7, characterized in that the image acquisition device (13) comprises several matrix cameras which are arranged next to each other and transversely to the conveying direction of the conveyed element (12).

9. Camera system (10) according to one of the preceding claims, characterized in that the camera system (10) is configured to detect a surface section (14) of a surface relative to the image capture device (13) on a drum. to detect promoted element (12). Inspection method for optical inspection of the surface (11) of an element (12) of an energy cell, in particular a battery, with a camera system (10) according to one of claims 1 to 9, characterized by the steps: - Illuminating a surface section (14) of an element (12) conveyed relative to the image acquisition device (13) with at least two light sources (15, 16, 17) whose light falls on the surface section (14) of the conveyed element (12) from different illumination directions (18, 19, 20); - Capturing the surface section (14) with at least one image capture device (13) with at least two different images (21 , 22) which are each assigned to different lighting directions (18, 19, 20); - Processing the captured, different images (21, 22) into a combined image in a data processing unit (24); - preferably outputting the combined image (23). Inspection method according to claim 10, characterized in that the processing to a combined image (23) is carried out by differentiating the at least two images (20, 21) with different illumination directions (18, 19, 20). Inspection method according to claims 10 and 11, characterized in that digital filtering of the combined image (23) is carried out in the data processing unit (24) before output. Inspection method according to any one of claims 10 to 12, characterized in that the combined image (23) is binarized in the data processing unit (24) before output. Inspection method according to any one of claims 10 to 13, characterized in that the data processing unit (24) evaluates the combined image (23) for particles on the surface section (14). Inspection method according to any one of claims 10 to 14, characterized in that successive image acquisitions are performed on the surface section (14) using a matrix camera as the image acquisition device (13), each with different illumination directions (18, 19, 20). Inspection method according to any one of claims 10 to 15, characterized in that two successive image acquisitions are performed using a matrix camera as the image acquisition device (13) to capture the same surface section (14) on different sensor areas of the matrix camera.Inspection method according to one of claims 10 to 16, characterized in that a matrix camera as an image acquisition device (13) has an image acquisition rate adapted to the conveying speed of the element (12) conveyed relative to the image acquisition device (13) such that a surface section (14) of the conveyed element (12) covers a maximum of half, preferably half, the sensor area of ​​the matrix camera between two image acquisitions.

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