METHOD FOR DETERMINING THE PLACING ACCURACY OF A MULTIPLE OF ELECTRODE SHEETS IN A STACK

Description

[0001] The invention relates to a method for determining the placement accuracy of a plurality of electrode sheets in a stack. The electrode sheets extend in mutually parallel planes and are stacked on top of each other to form a stack. The placement accuracy describes the relative positions of the edges of all electrode sheets within the stack.

[0002] Batteries, especially lithium-ion batteries, are increasingly used to power motor vehicles. Batteries are typically composed of cells, each cell comprising a stack of anode, cathode, and, if applicable, separator sheets or separator material. These anode, cathode, and, if applicable, separator sheets are referred to below as electrode sheets.

[0003] The electrode sheets are usually manufactured by punching or cutting, e.g. laser cutting.

[0004] The positioning accuracy of individual electrode sheets within a stack significantly impacts safety-relevant quality criteria and performance of lithium-ion battery cells. Therefore, the positioning accuracy, i.e., the deviation in the positions of the individual electrode sheets from one another, must be maintained within tight limits. Computed tomography (CT) is an established method for determining positioning accuracy. This involves generating a three-dimensional image of a stack through a lengthy measurement process. However, this method is very expensive and therefore only suitable for limited use in a production line.

[0005] Unlike computed tomography, there are also measuring devices that enable a two-dimensional image of the stack or the test object using X-rays. These are significantly less expensive than computed tomography and are also capable of performing measurements faster. However, a direct measurement of the position of the electrode sheets relative to each other is not possible with this method.

[0006] A conveying device for a battery cell is known from KR 10 2020 0088 222 A. This conveying device comprises X-ray sources that scan the edges of the individual layers of the battery cell. The X-ray sources are aligned so that the X-rays are parallel to the scanning edge of the layers.

[0007] From WO 2016 / 114257 A1, it is known to use X-rays to detect the edges of the coated areas of an electrode foil. The X-ray sources are aligned so that the X-rays are parallel to the edge of the layers being detected.

[0008] From DE 10 2020 112 814 A1, a device for inspecting battery cells using radiography is known. In this device, the battery cell can be moved relative to the X-ray source. The X-ray sources are aligned so that the X-rays are parallel to the edge of the layers being inspected.

[0009] KR 102 236 815 B1 relates to a method for identifying defects in a stack of electrode sheets. The stack is exposed to X-rays from two positions.

[0010] The EP 3 826 090 A1 and the JP 2011 039014 A are each directed towards a system for detecting positional deviations of electrode sheets. In this system, the edges of a stack of electrode sheets are irradiated with an X-ray source.

[0011] The object of the present invention is to at least partially solve the aforementioned problems. In particular, a method for determining the placement accuracy of a plurality of electrode sheets in a stack is to be proposed. Specifically, the position of each individual electrode sheet should be identifiable, so that a deviation can be attributed to a specific electrode sheet within the stack.

[0012] A method with the features according to claim 1 contributes to solving these problems. Advantageous further developments are the subject of the dependent claims. The features listed individually in the claims can be combined in a technologically meaningful way and can be supplemented by explanatory facts from the description and / or details from the figures, thereby showing further embodiments of the invention.

[0013] A method for determining the placement accuracy of a plurality of electrode sheets is proposed. The electrode sheets extend in mutually parallel planes, are stacked on top of each other, and form a stack. The placement accuracy describes the relative positions of the edges of all electrode sheets within the stack, or the exactness of the overlap of the electrode sheet edges. The method is performed with a measuring device comprising a two-dimensionally resolved X-ray system with at least one X-ray source and a detector. The method includes at least the following steps: a) Providing the stack and arranging the stack in the measuring device between the at least one beam source and the detector; b) Irradiating the stack with the at least one beam source from a first spatial coordinate, wherein the beam direction is at least transverse to the planes and towards the detector, wherein a beam from the beam source detects the stacked edges of the electrode sheets and projects a two-dimensional first contour of the edges of the stack onto the detector; c) Irradiating the stack with the at least one beam source from at least one second spatial coordinate differing from the first spatial coordinate, wherein the beam detects the stacked edges of the electrode sheets and projects a two-dimensional second contour of the edges of the stack onto the detector; d) Detecting the first contour with the detector; e) Detecting the at least one second contour with the detector;f) Evaluating the different contours and determining the positions of the edges of the electrode sheets.

[0014] The above (non-exhaustive) classification of the procedural steps into a) to f) is primarily intended for differentiation purposes and does not impose any sequence or dependency. The frequency of the procedural steps, e.g., during the execution of the procedure, can also vary. It is also possible that procedural steps may overlap, at least partially. Most preferably, procedural step a) occurs before steps b) to f). In particular, steps b) and c) occur sequentially. Specifically, step d) occurs concurrently with step b), and step e) occurs concurrently with step c). In particular, steps c) and e) can be performed multiple times, with each subsequent spatial coordinate differing from the previous ones. Specifically, steps a) to f) are performed in the following order: step a), step b), step d), step c), step e), step f).

[0015] This process is used particularly in the manufacturing of battery cells. Electrode sheets, i.e., anode sheets, cathode sheets, and, if applicable, separator sheets, cut to the appropriate shape, are arranged in a predetermined sequence and aligned with each other. The individual electrode sheets in the resulting stack should be arranged as close as possible to each other (edge-to-edge).

[0016] The electrode sheets extend in mutually parallel planes and, when stacked on top of each other, form a stack. The stack comprises at least two electrode sheets, i.e., at least one anode sheet and one cathode sheet. A separator material is arranged between each anode sheet and a cathode sheet. This can be, for example, a coating on one of the anode and cathode sheets or a separate separator sheet.

[0017] The electrode sheets are generally rectangular in shape. Potentially, conductive tabs extend beyond this rectangular shape. These tabs are generally uncoated, meaning they are not coated with the active material, and serve to electrically connect the respective electrode sheet, i.e., the anode or cathode sheet.

[0018] The placement accuracy describes, in particular, the relative positions of the edges of all electrode sheets within the stack. Specifically, the electrode sheets should be arranged in a predetermined orientation relative to each other. Since the size of the anode sheets and cathode sheets, as well as any separator sheets present, can differ, the placement accuracy is determined primarily at the edges of the electrode sheets that are aligned with each other along a first direction extending transversely to the planes.

[0019] In particular, the placement accuracy of the electrode sheets is determined only at one edge of each electrode sheet.

[0020] The method is carried out, in particular, with a measuring device comprising a two-dimensionally resolved X-ray system with at least one X-ray source and a detector. Several fixed or movable beam sources may be provided. Several fixed or movable detectors may also be provided.

[0021] A radiation source emits X-rays along a specific beam direction. A detector captures the X-rays to create an X-ray image.

[0022] The detector enables, in particular, the display of a two-dimensional image of the X-ray radiation. The proposed method is intended to allow for precise placement of the electrode sheets based on these two-dimensional images from the detector.

[0023] According to step a), the stack is provided and arranged in the measuring device between the at least one radiation source and the detector. It is possible for the stack to be formed separately and then arranged as a whole in the measuring device. However, it is also possible for the stack to be (partially) formed and thus arranged simultaneously within the measuring device itself.

[0024] According to step b), the stack is irradiated with the at least one beam source from a first spatial coordinate, with the beam direction extending at least transversely to the planes and towards the detector. A beam from the beam source detects the stacked edges of the electrode sheets and projects a two-dimensional first contour of the stack edges onto the detector. In particular, the beam source is positioned precisely above the edges, i.e., without any lateral offset from the edges.

[0025] For the arrangement of the stack, it is assumed that the edges of the electrodes are in a predetermined target position. The actual position of the edges, if deviating from this, is determined as part of the procedure.

[0026] According to step d), the first contour is detected by the detector.

[0027] According to step c), the stack is irradiated with the at least one beam source from at least one second spatial coordinate that differs from the first spatial coordinate, whereby the beam detects the superimposed edges of the electrode sheets and projects a two-dimensional second contour of the edges of the stack onto the detector.

[0028] According to step e), at least one second contour is detected with the detector;

[0029] According to step f), the various contours are evaluated and the positions of the electrode blade edges are determined. This evaluation can be performed, in particular, by a data processing system.

[0030] In particular, the measuring device comprises a data processing system that includes means suitable for carrying out the procedure, such as a processor, a memory in which instructions to be executed by the processor are stored, and data lines or transmission devices that enable the transmission of instructions, measured values, data, or the like between the aforementioned elements.

[0031] A contour detected by the detector comprises a two-dimensional image in which the edges of the electrode sheets can be identified based on the transitions between color intensities. Assigning the edges present in the contour to individual electrode sheets is not readily possible. The following proposes a method for achieving this assignment.

[0032] In this process, several contours of a single stack are generated by the radiation source and detected by the detector. Due to the varying arrangement of the radiation source relative to the stack and its edges, different contours are generated. These contours are evaluated, in particular, using linear equations. That is, based on the known arrangement of the radiation source and detector and the linear, i.e., straight, path of the beam generated by the radiation source, the position of each edge within the stack can be determined from its position within the respective contour. Specifically, as many different contours are generated as necessary to determine the edge position for each of the electrode sheets present in the stack.

[0033] In particular, two different versions of the procedure are possible, which can be combined if necessary.

[0034] In a first embodiment, the beam source is moved parallel to the planes towards the second spatial coordinate between steps b) and d). In a second embodiment, the beam source is moved perpendicular to the planes towards the second spatial coordinate between steps b) and d). The resulting different contours allow for the unambiguous determination of the edge of each electrode sheet.

[0035] In particular, the first spatial coordinate and the at least one second spatial coordinate differ by their distance from the stack. This distance extends along a first direction perpendicular to the planes. Alternatively or additionally, the first spatial coordinate and the at least one second spatial coordinate differ by their distance to the edges, with this distance extending along a second direction parallel to the planes and perpendicular to the edges.

[0036] In particular, steps c) and e) are each performed multiple times, wherein the second spatial coordinates of each step c) differ from the respective previous second spatial coordinates of the previous steps c) in the manner described, i.e. according to the first embodiment and / or the second embodiment.

[0037] In particular, in step f) the individual edges in the respective contour are assigned to the respective spatial coordinate using equations of lines.

[0038] The following example describes this relationship. The stack, the steel source, and the detector are considered in a common plane. Therefore, a spatial coordinate z is identical for all components. The first direction, perpendicular to the planes, extends along a y-axis. The second direction, parallel to the planes, extends along an x-axis.

[0039] The first spatial coordinates are, for example, (x q1 | y q1), the second spatial coordinates (x q2 | y q2). The spatial coordinates to be determined for the edge of a specific electrode sheet are denoted as (xe | ye). The positions of the edges of this electrode sheet in the first contour detected by the detector are (x d1 | y d1) for the first spatial coordinates of the radiation source and in the second contour (x d2 | y d2) for the second spatial coordinates of the radiation source.

[0040] The equation of the line representing the first spatial coordinates of the ray source is: m 1 = Δ y 1 Δ x 1 = y d 1 − y q 1 x d 1 − x q 1 y = m 1 ⋅ x − x q 1 + y q 1 y = m 1 x + b 1

[0041] The equation of the line representing the second spatial coordinate of the ray source is: m 2 = Δ y 2 Δ x 2 = y d 2 − y q 2 x d 2 − x q 2 y = m 2 ⋅ x − x q 2 + y q 2 y = m 2 x + b 2

[0042] These equations are set equal to each other, so that: m 1 ⋅ x + b 1 = m 2 ⋅ x + b 2 → m 1 − m 2 ⋅ x = b 2 − b 1 → x e = b 2 − b 1 m 1 − m 2 → y e = m 1 ⋅ b 2 − b 1 m 1 − m 2 + b 1

[0043] In particular, step g) involves an evaluation of the placement accuracy. A limit value is specified for the maximum deviation of the contour from a target position of an edge for the stack. It is assumed that the electrode sheet closest to the detector produces the maximum deviation.

[0044] The maximum deviation is the highest permissible difference between the target position of an edge in the stack and the actual position of the edge. If the maximum deviation is exceeded, a measure is taken, e.g., the stack is marked as defective or the manufacturing process for the stack is adjusted.

[0045] The maximum deviation is determined particularly at the first contour, preferably using the equation of a straight line, i.e. taking into account the first spatial coordinates relative to the target position of the edges.

[0046] For the maximum deviation, it is assumed that the electrode sheet closest to the detector produces the maximum deviation. This electrode sheet is therefore located furthest from the radiation source. Considering the radiation equation, the deviation of an edge's position from its intended position, as seen in the contour, is most pronounced for the electrode sheet closest to the radiation source; thus, the magnitude of the deviation is highest there. Conversely, the deviation of an edge's position, as seen in the contour, is least pronounced for the electrode sheet furthest from the radiation source; thus, the magnitude of the deviation is lowest there.

[0047] The assumption that the maximum deviation is generated by the electrode sheet located furthest from the radiation source ensures, in particular, that no other electrode sheet can exhibit a deviation from a target position exceeding the maximum deviation.

[0048] In particular, to determine the storage accuracy, only steps a), b), d), f) and g) are carried out initially, and steps c) and e) are carried out only if an exceedance of the limit value is detected in step g).

[0049] For example, within the scope of this procedure, each stack is checked for placement accuracy, but the positions of the edges of all electrode sheets in the stack are only determined if the limit value is exceeded. Otherwise, each stack is only checked to see if the limit value has been exceeded.

[0050] In particular, if an exceedance of the limit is detected, steps c) and e) are performed exactly twice with different (second) spatial coordinates, and then steps f) and g) are performed again.

[0051] In particular, the first spatial coordinates are chosen such that the radiation source is positioned exactly above, i.e., aligned in the first direction with, the desired position of the stack's edges. The second two spatial coordinates are then chosen such that the radiation source is offset from the first spatial coordinates in the second direction, specifically one offset towards the stack so that the radiation source is aligned with the stack, and the other offset away from the stack so that the radiation source is laterally adjacent to the stack.

[0052] In particular, if the limit value is repeatedly exceeded in step g), steps c) and e) are performed with a number of repetitions required to uniquely determine the positions of all edges.

[0053] Using this step-by-step method, it is not necessary to fully measure each stack during battery cell production (i.e., to determine the edge positions of all electrode sheets). Based on fewer contours, and thus fewer detector scans, the maximum deviation within the stack can be detected or estimated. If a limit value is exceeded, further measurements can be taken to determine the specific positions of the electrode sheets. Position determination may be performed only for the electrode sheets exceeding the limit value, or only for a specific selection of electrode sheets, such as those with the highest deviation.

[0054] In particular, artificial intelligence is used, at least for step f). With the help of artificial intelligence, determining the positions of the edges within the contours can be supported. Furthermore, artificial intelligence can potentially reduce the number of linear equations required to determine the positions of the edges of all electrode sheets.

[0055] In particular, the contours are evaluated using a Convolutional Neural Network (CNN). The Convolutional Neural Network learns from a synthetic, i.e., artificially generated, dataset of a stack with known positions of the edges of the electrode sheets, in order to then determine the position of the edge of each electrode sheet from the contours of this stack acquired according to step d).

[0056] For the application of the CNN and thus the proposed system of equations, it is particularly necessary to take at least as many recordings according to steps b) and c) or to generate and evaluate contours as there are electrode sheets to be measured.

[0057] For training the CNN, a synthetic dataset can be generated that maps a random stack arrangement (electrode sheet number in the stack, orientation in the plane with known edge positions, etc.) to the different contours, the first contour and at least one second contour. The CNN then models the inverse mapping, i.e., the contours onto the stack arrangement.

[0058] Instead of using a Convolutional Neural Network, the evaluation can also be performed using other machine learning or automated learning methods. The following discussion focuses on the Convolutional Neural Network and the processes and terminology used within it.

[0059] The application of such CNNs for the evaluation of images or contours, i.e., images of the detector, is generally known. Here, the use of CNNs for the quality assessment of (cut) edges of electrode sheets is proposed, i.e., in the context of battery component manufacturing.

[0060] In order to implement automated and inline-capable edge evaluation using CNNs, a training dataset, i.e., the synthetic dataset, can first be generated. On each contour, or on each initial image of the detector in this training dataset, the edge path can be manually marked. This manually marked path, i.e., the marked edge path, is then manually exported from the tool. The edge path within the contour, encoded as a pixel matrix, represents the stack geometry or arrangement of the edges for the training dataset, the so-called ground truth.

[0061] Images in this set contain only pixels with the value zero ("0") or one ("1"), for no edge (e.g. value zero) or edge (e.g. value one) at the corresponding location in the contour or of the first image.

[0062] In the following, a CNN is used to learn a mathematical first mapping of the edge depicted in the first image to its corresponding geometry. The CNN trained in this way can then recognize the geometry of previously untrained second images of the detector or contours. Due to the low variance of the first and second images of essentially similar bodies—in this case, edges of stacked electrode sheets with a defined target geometry—and the statistical significance of large datasets, this recognition is more accurate than comparable methods, such as trend edge detection.

[0063] A CNN is known to consist of a series of so-called convolutional layers that discretely convolve a fixed number of filters with image sections. For each of its filters, this layer calculates a feature map. This feature map describes whether a pattern, defined by the filter parameters, was detected at the corresponding location in the respective second image or in the contour. The size of these feature maps is reduced using so-called max-pooling or average-pooling layers to decrease computational complexity. The max-pooling or average-pooling layer overlays an n x n window on the feature map and, in particular, only transfers the maximum value from a given section to the next layer.

[0064] The order and number of convolutional and max-pooling or average-pooling layers, as well as the size of the respective windows and filters, are so-called hyperparameters. The optimization of these hyperparameters is primarily carried out using a validation dataset, which does not influence the optimization of model parameters.

[0065] In the final step, the values ​​of all feature maps are concatenated into a vector, a process known as flattening, and thus serve as input for a feed-forward neural network. This network, in turn, is characterized by a variable number of hidden layers and a variable number of neurons in each hidden layer. These numbers constitute further hyperparameters.

[0066] As an alternative to flattening, the condensed feature maps can first be transformed back to their original size using transposed convolution, and their number can then be reduced back to one using convolutional layers.

[0067] In its output layer, the network attempts to approximate the manually generated edge geometry of the stack's ground truth by assigning each pixel a zero or a one ("1").

[0068] At the start of training, the filter parameters and the parameters of the feed-forward neural network (together forming the CNN) can be randomly initialized, initially leading to inaccurate geometry predictions. During training, all model parameters are adjusted using a gradient descent method to minimize the number of misclassified pixels across all training examples.

[0069] After training, the CNN can be used, for example, in step f) and / or step g), to recognize the path or position of at least one edge in the contour or in the second image of the detector for unknown stacks or newly created contours.

[0070] In particular, in a further step h), at least one process parameter used for the production of the respective stack is determined and changed from the evaluation of the depositing accuracy according to step g), so that a depositing accuracy for further stacks is improved.

[0071] In particular, if, for example, a limit value has been exceeded and / or validated through follow-up measurements, the incorrectly positioned electrode sheet and its deviation from the target position can be determined. Accordingly, the manufacturing process of the electrode sheet can be traced based on this knowledge, and adjustable process parameters can be modified if necessary.

[0072] In particular, a data processing system is proposed which includes means that are appropriately equipped, configured or programmed to carry out the procedure, or that execute the procedure.

[0073] The means include, for example, a processor and a memory in which instructions to be executed by the processor are stored, as well as data lines or transmission devices that enable the transmission of instructions, measurements, data or the like between the aforementioned elements.

[0074] Furthermore, a computer program is proposed, comprising commands which, when the program is executed by a computer, cause it to perform the described procedure or the steps of the described procedure.

[0075] Furthermore, a computer-readable storage medium is proposed, comprising instructions which, when executed by a computer, cause it to perform the described procedure or the steps of the described procedure.

[0076] The explanations regarding the procedure are particularly applicable to the data processing system and / or the computer-implemented procedure (i.e., the computer program and the computer-readable storage medium) and vice versa.

[0077] The use of indefinite articles ("a", "an", "a" and "one"), particularly in the patent claims and the description reproducing them, is to be understood as such and not as a numeral. Accordingly, terms or components introduced by these articles are to be understood as occurring at least once and, in particular, may also occur multiple times.

[0078] It should be noted as a precaution that the numerical terms used here ("first", "second", etc.) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific configuration described. Where a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory.

[0079] The invention and its technical context are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations described in the figures and combine them with other components and findings from the present description. It should be emphasized that the figures, and especially the depicted dimensions, are only schematic. They show: Fig. 1: a first embodiment of the method; Fig. 2: a second embodiment of the method; Fig. 3: step f) of the method according to the first embodiment; Fig. 4: steps b), d) and g) of the method for a first stack; Fig. 5: steps b), d) and g) of the method for a second stack; Fig. 6: steps c) and e) of the method for the first stack; Fig. 7: repeated execution of steps c) and e) of the method for the first stack; Fig. 8: steps c) and e) of the method for the second stack; Fig. 9: repeated execution of steps c) and e) of the method for the second stack.

[0080] The Fig. 1Figure 1 shows a first embodiment of the process. The process is used in a manufacturing process for battery cells. Electrode sheets 1, 2, 3, i.e., anode, cathode, and, if applicable, separator sheets, cut to the appropriate shape, are arranged in a predetermined sequence to form a stack 5 and aligned with each other. The individual electrode sheets 1, 2, 3 in the resulting stack 5 should be arranged in as close alignment as possible with each other.

[0081] The electrode sheets 1, 2, 3 extend in mutually parallel planes 4 and, stacked on top of each other, form a stack 5. The stack 5 comprises a plurality of electrode sheets 1, 2, 3.

[0082] The electrode sheets 1, 2, 3 each have a substantially rectangular shape. Conductor tabs extend beyond this rectangular shape at one edge 9 of the electrode sheets 1, 2, 3.

[0083] The placement accuracy describes the relative positions 6, 7, 8 of the edges 9 of all electrode sheets 1, 2, 3 in the stack 5. The electrode sheets 1, 2, 3 are to be arranged in a predetermined orientation relative to each other. Since the size of the anode sheets and cathode sheets, as well as any separator sheets, can differ, the placement accuracy is determined at the edges 9 of the electrode sheets 1, 2, 3 that are aligned with each other along a first direction 21 extending transversely to the planes 4. The placement accuracy of the electrode sheets 1, 2, 3 is determined only at one edge 9 of each electrode sheet 1, 2, 3.

[0084] The procedure is carried out with a measuring device 10, which includes a two-dimensionally resolving X-ray system 11 with a beam source 12 for X-ray radiation and a detector 13. The beam source 12 serves to emit X-ray radiation along a beam direction 15. A detector 13 serves to capture the X-ray radiation to produce an X-ray image.

[0085] Detector 13 enables the display of a two-dimensional image (hereinafter referred to as contour 17, 19) of the X-ray radiation. The proposed method allows for the precise placement of the electrode sheets 1, 2, 3 from these two-dimensional images of detector 13.

[0086] According to step a), the stack 5 is provided and arranged in the measuring device 10 between the single beam source 12 and the detector 13. According to step b), the stack 5 is irradiated with the beam source 12 from a first spatial coordinate 14, the beam direction 15 being transverse to the planes 4 and extending towards the detector 13 (essentially along a first direction 21). A beam 16 from the beam source 12 detects the superimposed edges 9 of the electrode sheets 1, 2, 3 and projects a two-dimensional first contour 17 of the edges 9 of the stack 5 onto the detector 13. The beam source 12 is positioned precisely above the edges 9, i.e., without any lateral offset from the edges 9.

[0087] For the arrangement of the stack 5, it is assumed that the edges 9 of the electrode sheets 1, 2, 3 are in a predetermined target position. The actual position 6, 7, 8 of the edges 9, which deviates from this, is determined within the framework of the procedure.

[0088] According to step d), the first contour 17 is detected with the detector 13.

[0089] According to step c), the stack 5 is irradiated with the beam source 12 from a second spatial coordinate 18 that differs from the first spatial coordinate 14, whereby the beam 16 detects the superimposed edges 9 of the electrode sheets 1, 2, 3 and projects a two-dimensional second contour 19 of the edges 9 of the stack 5 onto the detector 13.

[0090] According to step e), the second contour 19 is detected with the detector 13.

[0091] It is shown that steps c) and e) are repeated, the second spatial coordinates 18 of each step c) differing from the previous second spatial coordinates 18 of the preceding steps c). The further spatial coordinates of this repetition of steps c) and e) are referred to as the third spatial coordinates 25 and the contour thereby captured as the third contour 26.

[0092] According to step f), the various contours 17, 19, 26 are evaluated and the positions 6, 7, 8 of the edges 9 of the electrode sheets 1, 2, 3 are determined. The evaluation is carried out by the system 27 for data processing.

[0093] The measuring device 10 comprises a data processing system 27, which includes means that are suitably equipped, configured, or programmed to carry out the procedure, or that execute the procedure. The means include, for example, a processor and a memory in which instructions to be executed by the processor are stored, as well as data lines or transmission devices that enable the transmission of instructions, measured values, data, or the like between the aforementioned elements.

[0094] A contour 17, 19, 26 detected by the detector 13 comprises a two-dimensional image in which the edges 9 of the electrode sheets 1, 2, 3 can be identified based on the transitions between color intensities. Assigning the edges 9 present in the contour 17, 19, 26 to individual electrode sheets 1, 2, 3 is not readily possible. The described method provides a way to achieve this assignment.

[0095] In this process, several contours 17, 19, 26 of a stack 5 are generated by the beam source 12 and detected by the detector 13. Due to the different arrangement of the beam source 12 relative to the stack 5 and the edges 9, different contours 17, 19, 26 are generated. These contours 17, 19, 26 are evaluated using linear equations; that is, from the known arrangement of the beam source 12 and the detector 13 and the linear, i.e., straight, path of the beam 16 generated by the beam source 12, the position 6, 7, 8 of the respective edge 9 in the stack 5 can be deduced from the position of the edges 9 in the respective contour 17, 19, 26.

[0096] The first spatial coordinate 14 and the at least one second spatial coordinate 18, 25 (i.e., the second and the third spatial coordinate) differ by a different distance 22 to the edges 9, the distance 22 extending along a second direction 23 parallel to the planes 4 and perpendicular to the edges 9. A third direction 28 extends parallel to the edges 9, which are measured with the measuring device 10.

[0097] The individual contours 17, 19, 26 are assigned to the respective spatial coordinates 14, 18, 25 by arrows.

[0098] Fig. 2 This shows a second implementation variant of the procedure. See the explanations regarding... Fig. 1 will be referred.

[0099] In contrast to the first embodiment, in which the beam source 12 is moved parallel to the planes 4 towards the second spatial coordinate 18 between steps b) and d), in the second embodiment the beam source 12 is moved perpendicular to the planes 4 towards the second spatial coordinate 18 or the third spatial coordinate 25 between steps b) and d). The different contours 17, 19, 26 thus generated also allow the unambiguous determination of the edge 9 of each electrode sheet 1, 2, 3.

[0100] The first spatial coordinate 14 and the at least one second spatial coordinate 18, 25 (i.e., the second and the third spatial coordinate) differ by a different distance 20 from the stack 5. The distance 20 extends along a first direction 21 extending transversely to the planes 4.

[0101] The individual contours 17, 19, 26 are assigned to the respective spatial coordinates 14, 18, 25 by arrows.

[0102] Fig. 3 This shows step f) of the procedure according to the first implementation variant. See the explanations regarding Fig. 1 will be referred.

[0103] According to step f), the various contours 17, 19, 26 are evaluated and the positions 6, 7, 8 of the edges 9 of the electrode sheets 1, 2, 3 are determined. The evaluation is carried out by the system 27 for data processing.

[0104] The stack 5, the beam source 12, and the detector 13 are considered in a common plane. A spatial coordinate z is therefore identical for all components 1, 2, 3, 5, 12, 13. The first direction 21, i.e., perpendicular to the planes 4, extends along a y-axis (here the vertical axis in the upper diagram of the Fig. 3The second direction 23, i.e. parallel to the planes 4, extends along the x-axis (here the horizontal axis in the upper diagram of the

[0105] Fig. 3 A third direction 28 extends along a z-axis (here the backward-pointing axis in the upper diagram of the Fig. 3 ).

[0106] The first spatial coordinates 14 are (x q1 | y q1 ), the second spatial coordinates 18 are (x q2 | y q2 ). The spatial coordinates to be determined for edge 9 of the first electrode sheet 1 are denoted as (xe | ye ). The positions of edge 9 of this first electrode sheet 1 in the first contour 17 detected by the detector 13 are (x d1 | y d1 ) for the first spatial coordinates 14 of the radiation source 12 and in the second contour 19 (x d2 | y d2 ) for the second spatial coordinates 18 of the radiation source 12.

[0107] The equation of the line for the first spatial coordinates 14 of the ray source 12 is: m 1 = Δ y 1 Δ x 1 = y d 1 − y q 1 x d 1 − x q 1 y = m 1 ⋅ x − x q 1 + y q 1 y = m 1 x + b 1

[0108] The equation of the line for the second spatial coordinate 18 of the ray source 12 is: m 2 = Δ y 2 Δ x 2 = y d 2 − y q 2 x d 2 − x q 2 y = m 2 ⋅ x − x q 2 + y q 2 y = m 2 x + b 2

[0109] These equations are set equal to each other, so that: m 1 ⋅ x + b 1 = m 2 ⋅ x + b 2 → m 1 − m 2 ⋅ x = b 2 − b 1 → x e = b 2 − b 1 m 1 − m 2 → y e = m 1 ⋅ b 2 − b 1 m 1 − m 2 + b 1

[0110] The spatial coordinates of (xe | ye ) specify the first position 6 of edge 9 of the first electrode sheet 1.

[0111] Fig. 4 shows steps b), d) and g) of the procedure for a first stack 5. Refer to the explanations regarding the Fig. 1 will be referred.

[0112] In the first stack 5, the bottommost electrode sheet 1 exhibits the greatest deviation 24 from a target position. In step g), the placement accuracy is evaluated. For stack 5, a limit value is specified for a maximum deviation 24 of the contour 17, 19, 26 (or the position of edge 9 discernible in the contour) from a target position of an edge 9. For the maximum deviation 24, it is assumed that the electrode sheet 1, 2, 3 closest to detector 13 produces the maximum deviation 24.

[0113] The maximum deviation 24 is the maximum permissible difference between the target position of an edge 9 in the stack 5 and an actual position 6, 7, 8 of the edge 9. The maximum deviation 24 is determined at the first contour 17, taking into account the first spatial coordinates 14 with respect to the target position of the edges 9.

[0114] To determine the placement accuracy, only steps a), b), d), f) and g) are carried out initially, and steps c) and e) (see Figs. 8 and 9 ) only if in step g) (see Fig. 4 ) an exceedance of the limit value is detected.

[0115] For example, each stack 5 is checked for placement accuracy within the framework of the present procedure, but only if the limit value is exceeded is the position of the edges 9 of all electrode sheets 1, 2, 3 of stack 5 determined. Otherwise, for each stack 5, it is only checked whether the limit value has been exceeded.

[0116] If an exceedance of the limit is detected, steps c) and e) are performed exactly twice with different (second) spatial coordinates 18, 25, and then steps f) and g) are performed again (see Figs. 8 and 9 ).

[0117] The first spatial coordinates 14 are chosen such that the radiation source 12 is positioned exactly above, i.e. in the first direction 21 aligned with the target position of the edges 9 of the stack 5 (see Fig. 4 ). The two second spatial coordinates 18, 25 (i.e., second and third spatial coordinates) are then chosen such that the radiation source 12 is arranged offset from the first spatial coordinates 14 in the second direction 23, once offset towards the stack 5 so that the radiation source 12 is aligned with the stack 5, and once offset away from the stack 5 so that the radiation source 12 is arranged laterally adjacent to the stack 5 (see Figs. 8 and 9 ).

[0118] If the limit value is repeatedly exceeded in step g), steps c) and e) are performed with a number of repetitions required to uniquely determine the positions 6, 7, 8 of all edges 9.

[0119] Using this stepwise procedure, it is not necessary to fully measure each stack 5 during production (i.e., to determine the positions 6, 7, 8 of the edges 9 of all electrode sheets 1, 2, 3). Based on fewer contours 17, 19, 26, i.e., fewer detector 13 scans, the maximum deviation 24 in stack 5 can be detected or estimated. If the limit value is exceeded, the respective positions 6, 7, 8 of the electrode sheets 1, 2, 3 can be determined using further measurements.

[0120] Fig. 5 shows steps b), d) and g) of the procedure for a second stack 5. Refer to the explanations regarding the Fig. 4 will be referred.

[0121] In the second stack 5, the uppermost first electrode sheet 1 exhibits the greatest deviation 24 from a target position. In step g), the placement accuracy is evaluated. For stack 5, a limit value is specified for a maximum deviation 24 of the contour 17, 19, 26 (or the position of edge 9 discernible in the contour) from a target position of an edge 9. It is assumed that the electrode sheet 1, 2, 3 closest to detector 13 produces the maximum deviation 24. For the second stack 5 shown, the greatest deviation 24 discernible in the first contour 17 would then be much smaller (i.e., if the first electrode sheet 1 were located at the very bottom of stack 5). In this case, unacceptably large deviations 24 could not be detected.

[0122] If an exceedance of the limit is detected, steps c) and e) are performed exactly twice with different (second) spatial coordinates 18, 25, and then steps f) and g) are performed again (see Figs. 6 and 7 ).

[0123] The first spatial coordinates 14 are chosen such that the radiation source 12 is positioned exactly above, i.e. in the first direction 21 aligned with the target position of the edges 9 of the stack 5 (see Fig. 5 ). The two second spatial coordinates 18, 25 (i.e., second and third spatial coordinates) are then chosen such that the radiation source 12 is arranged offset from the first spatial coordinates 14 in the second direction 23, once offset towards the stack 5 so that the radiation source 12 is aligned with the stack 5, and once offset away from the stack 5 so that the radiation source 12 is arranged laterally adjacent to the stack 5 (see Figs. 6 and 7 ). Reference symbol list

[0124] 1. First electrode sheet 2. Second electrode sheet 3. Third electrode sheet 4. Plane 5. Stack 6. First position 7. Second position 8. Third position 9. Edge 10. Measuring device 11. X-ray system 12. Beam source 13. Detector 14. First spatial coordinate 15. Beam direction 16. Beam 17. First contour 18. Second spatial coordinate 19. Second contour 20. Distance 21. First direction (y-axis) 22. Distance 23. Second direction (z-axis) 24. Deviation 25. Third spatial coordinate 26. Third contour 27. System 28. Third direction (x-axis)

Claims

1. Method for determining the placement accuracy of a plurality of electrode sheets (1, 2, 3), wherein the electrode sheets (1, 2, 3) extend in mutually parallel planes (4) and are arranged in a manner stacked on top of one another and form a stack (5); wherein the placement accuracy describes positions (6, 7, 8) of the edges (9) of all of the electrode sheets (1, 2, 3) relative to one another in the stack (5); wherein the method is carried out using a measuring device (10) having a two-dimensionally resolving X-ray system (11) with at least one beam source (12) for X-ray radiation and a detector (13), and comprises at least the following steps: a) providing the stack (5) and arranging the stack (5) in the measuring device (10) between the at least one beam source (12) and the detector (13); b) irradiating the stack (5) with the at least one beam source (12) from a first spatial coordinate (14), wherein a beam direction (15) extends at least transversely to the planes (4) and towards the detector (13), wherein a beam (16) from the beam source (12) detects the edges (9) of the electrode sheets (1, 2, 3) that are arranged one above the other and project a two-dimensional first contour (17) of the edges (9) of the stack (5) onto the detector (13); c) irradiating the stack (5) with the at least one beam source (12) from at least one second spatial coordinate (18) that differs from the first spatial coordinate (14), wherein the beam (16) detects the edges (9) of the electrode sheets (1) that are arranged one above the other and projects a two-dimensional second contour (19) of the edges (9) of the stack (5) onto the detector (13); d) detecting the first contour (17) using the detector (13); e) detecting the at least one second contour (19) using the detector (13); f) evaluating the different contours (17, 19) and determining the positions (6, 7, 8) of the edges (9) of the electrode sheets (1, 2, 3).

2. Method according to Claim 1, wherein the first spatial coordinate (14) and the at least one second spatial coordinate (18) differ from one another by a mutually different spacing (20) from the stack (5), wherein the spacing (20) extends along a first direction (21) extending transverse to the planes (4), or by a mutually different distance (22) from the edges (9), wherein the distance (22) extends along a second direction (23) extending parallel to the planes (4) and transverse to the edges (9).

3. Method according to either of the preceding claims, wherein, in step f), the individual edges (9) in the respective contour (17, 19) are assigned to the respective spatial coordinates (14, 18) using linear equations.

4. Method according to any one of the preceding claims, wherein, in a step g), the placement accuracy is assessed; wherein a limit value for a maximum deviation (24) of the contour (17, 19) from a target position (25) of an edge (9) is specified for the stack (5); wherein it is assumed for the maximum deviation (24) that the electrode sheet (1, 2, 3) closest to the detector (13) produces the maximum deviation (24).

5. Method according to Claim 4, wherein only steps a), b), d), f), and g) are initially carried out to determine the placement accuracy, and steps c) and e) are carried out only if it is ascertained in step g) that the limit value has been exceeded.

6. Method according to Claim 5, wherein, if it is ascertained that the limit value has been exceeded, steps c) and e) are carried out exactly twice with mutually different spatial coordinates (18, 25) and then steps f) and g) are carried out again.

7. Method according to Claim 6, wherein, if the exceeding of the limit value is repeatedly ascertained in step g), steps c) and e) are carried out with a number of repetitions required for the unambiguous determination of the positions (6, 7, 8) of all of the edges (9).

8. Method according to one of the preceding claims, wherein artificial intelligence is used at least for step f).

9. Method according to Claim 8, wherein the contours (17, 19) are evaluated using a convolutional neural network; wherein the convolutional neural network learns from a synthetic data set for a stack (5) with known positions (6, 7, 8) of the edges (9) of the electrode sheets (1, 2, 3) in order to then determine the position (6, 7, 8) of the edge (9) of each electrode sheet (1, 2, 3) from the contours (17, 19) detected according to step d).

10. Method according to any one of the preceding claims, wherein at least one process parameter used to produce the respective stack (5) is determined from the evaluation of the placement accuracy according to step g) and altered in a further step h), thereby improving the placement accuracy for further stacks (5).