Gripping arrangement for picking up, transporting and placing a layer of product

Abstract

The invention relates to a gripping arrangement for picking up, transporting and placing a product layer, comprising a gripper with a support structure to which at least one gripping element is attached to hold the product layer on the gripper in a gripping plane, wherein the gripper has a first measuring section, wherein a first corner contour of the product layer is exposed on the first measuring section in a direction transverse to the gripping plane, and wherein the gripper has a first reference element in the region of the first measuring section, and a measuring system for measuring positions in the gripping plane relative to a reference coordinate system, which is configured to measure a position of the first corner contour with respect to the reference coordinate system, as well as to measure a position of the first reference element with respect to the reference coordinate system in order to determine a relative position of the product layer with respect to the gripper.

Description

SCOPE OF APPLICATION AND STATE OF THE ART

[0001] The invention relates to a gripping arrangement for picking up, transporting, and placing a product layer. The invention particularly relates to a gripping arrangement suitable for picking up, transporting, and placing product layers, such as a gas diffusion layer (GDL) or a membrane electrode assembly (MEA) of a fuel cell.

[0002] Product layers are individual layers, for example, product layers within a stack. A product layer needs to be picked up for processing and placed at a destination. Particularly with thin product layers, it is not possible to grip them using a form-fitting gripper. Therefore, it is known to use vacuum grippers to suction the product layer using negative pressure, hold it, and place it at the destination.

[0003] High precision is often required when placing product layers at their destination. Particularly in fuel cell manufacturing, the individual product layers of the fuel cell components must be positioned with an accuracy of tenths of a millimeter. Similar requirements apply to grippers that position product layers for electrolyzers (perforated plates, sealing layers, gas diffusion layers, membrane electrode assemblies), redox flow batteries, battery electrodes and battery separators, as well as membrane humidifiers. Even during the initial pick-up of a product layer, deviations from the ideal position within the gripper occur. These deviations are especially pronounced when the product layer is picked up at its destination. Further deviations can occur when repositioning the picked-up product layer. These deviations primarily involve position control deviations in the drives for transporting and rotating the gripper.The accumulated positional deviations make it difficult to meet the accuracy requirements when placing the product in the correct position. TASK AND SOLUTION

[0004] One object of the invention is to create a gripping arrangement that enables the placement of a product layer at a target location with high positioning accuracy.

[0005] This problem is solved by the gripping arrangement with the features of claim 1. Advantageous embodiments are set out in the dependent claims.

[0006] According to the invention, a gripping arrangement for picking up, transporting, and placing a product layer is provided. The gripping arrangement comprises a gripper with a support structure to which at least one gripping element is attached to hold the product layer on the gripper in a gripping plane, wherein the gripper has a first measuring section, wherein a first corner contour of the product layer is exposed on the first measuring section in a direction transverse to the gripping plane, and wherein the gripper has a first reference element in the region of the first measuring section, and a measuring system for measuring positions in the gripping plane relative to a reference coordinate system, which is configured to measure a position of the first corner contour with respect to the reference coordinate system and to measure a position of the first reference element with respect to the reference coordinate system in order to determine a relative position of the product layer with respect to the gripper.

[0007] The expressions “ein”, “eine” or “einer” are used only as indefinite articles and not as counters.

[0008] The gripping arrangement is designed to pick up a single layer of product at a receiving location, transport it from the receiving location to a destination location while held by the gripping elements, and deposit it there. For this purpose, the gripping arrangement has transport drives configured to move the gripper in space. The product layer should be deposited at the destination location according to a target position. Deviations from an expected or calculated position of the product layer when held by the gripper lead to positional inaccuracies at the destination. Therefore, these positional deviations should be minimized. Position refers to the combination of location and orientation. The destination location typically already defines the plane in which the product layer is to be deposited. This results in the requirements for depositing the product layer, particularly regarding its two-dimensional position and orientation within the target plane.In other words, the accuracy requirements arise particularly with regard to deviations in the X-direction, Y-direction and in the direction of rotation relative to the normal of the target plane.

[0009] The gripping arrangement according to the invention enables the position of the product to be measured after it has been picked up and while the product is held by the gripper. Any positional deviations that arose before or during the picking process are thereby eliminated. Because the position of the product is measured relative to the gripper, the gripper can take this relative position into account and compensate for it when placing the product. The result is a gripping arrangement with a gripper that can place the product at the target location with high accuracy.

[0010] The gripping element or elements are typically designed as vacuum gripping elements or Venturi gripping elements. Alternatively, the gripping elements can be designed as needle gripping elements. A combination of two or more different types of gripping elements is also possible.

[0011] The corner contour is representative of the product's position. The corner contour is formed by at least one edge of the product with a distinct profile. In preferred embodiments, the corner contour is formed by two edges that meet at a corner. In alternative embodiments, the corner contour is formed by one or more edges with virtually any profile. For example, the corner contour can be formed by a curved edge, by several edges connected by corners, or it can have a protrusion or a recess.

[0012] The product layer has a rectangular base shape. Accordingly, such a product layer has four corner contours. A corner contour refers to the outline of the product layer's edge in the area of ​​a corner. However, instead of a rectangular base shape, the product layer can also have any other arbitrary base shape, for example, the shape of a parallelogram, a trapezoid, or generally a quadrilateral, or a triangle, pentagon, or any other polygon. The base shape of the product layer, as well as its target dimensions, i.e., the lengths of the edges and the angles between adjacent edges, are known.

[0013] By measuring the position and orientation of a corner of the product layer, it is possible, given the basic shape and dimensions of the product layer, to determine the positions of all corner contours, as well as the center of gravity and the orientation of the product layer. Using a rectangular product layer as an example, the lengths of the edges in the longitudinal and transverse directions are known, as well as the fact that the edges meet at right angles.

[0014] The position of a corner contour is known if the directions of its edges and the position of the corner where the edges meet are known. To measure the position of the corner contour, the measuring system can measure the position of the corner and / or one or more points along one or both edges. For example, to determine the position of the corner contour, it is sufficient to know the position of the corner and another point along one of the two edges. Alternatively, it is sufficient to know the positions of two points along a first edge and the position of one point along a second edge. A prerequisite may be that the angle at which the edges meet at the corner is known. However, preferably, the positions of many points along the two edges are measured to minimize measurement errors.

[0015] To enable the measuring system to measure the position of the corner contour, the corner contour is exposed within the measuring section. "Exposed" means that the corner contour is accessible to the measuring system for position measurement. The measuring section is exposed on at least one side with respect to the gripping plane, preferably on both sides. The gripper positions the picked-up product position within a measuring area of ​​the measuring system to measure the relative position of the product before placing it at the target location. Therefore, after picking up the product position, the gripper first moves into the measuring area and, after measuring the position, moves to the target location to place the product position.

[0016] The reference element is part of the supporting structure or connected to it in such a way that the position of the reference element relative to the other components of the gripper, and in particular to the supporting structure, is fixed. The position of the reference element is thus representative of the position of the gripper. The reference element is arranged at least approximately in the same plane as the product position. In particular, the reference element is optically or tactilely detectable. In a simple example, the reference element is designed as an optically detectable reference mark.

[0017] In certain embodiments, the gripper has a second measuring section, wherein a second corner contour of the product position is exposed at the second measuring section in a direction transverse to the gripping plane, and the gripper has a second reference element in the area of ​​the second measuring section. The measuring system is configured to measure the position of the second corner contour and the second reference element with respect to the reference coordinate system in order to determine the relative position of the product position with respect to the gripper. The positions of the first and second corner contours with respect to the gripper position are measured independently of each other. Therefore, by fusing this measurement information, the overall measurement error for the position of the product position with respect to the gripper can be reduced.Furthermore, this allows for the detection of errors in the dimensions of the product layer that can occur during its manufacture and cause the actual dimensions of the product layer to deviate from the target dimensions. Preferably, the first measuring section and the second measuring section are arranged diagonally opposite each other with respect to the product layer.

[0018] A diagonal connects corners of a polygon that are not adjacent. This means that the measurement of the positions of the two corner contours is based on information about four edges of the product layer. As a result, the relative position of the product layer can be measured even more precisely than would be possible if the first and second corner contours were adjacent. Preferably, the product layer has a mirror-symmetrical shape. To measure the positions of the first and second corner contours, the first and second measuring sections are arranged sequentially within the measuring area of ​​the measuring system.

[0019] In various embodiments, the gripper has a number of measuring sections, with each measuring section exposing further corner contours of the product position. The gripper also includes an additional reference element in the area of ​​each measuring section. The measuring system is configured to measure the position of these additional corner contours and the reference elements relative to the reference coordinate system in order to determine the relative position of the product position with respect to the gripper. The greater the number of corner contours whose positions are measured, the greater the accuracy with which the relative position of the product position with respect to the gripper can be determined. In particular, the gripper has as many measuring sections as the product position has corner contours. This gripping arrangement thus enables the measurement of the position of each corner contour.

[0020] The reference element is configured either as a contour section of the support frame or as a contour part attached to the support frame. In the first case, the reference element is integrally formed with the support frame. In the second case, the reference element is provided separately from the support frame but is firmly connected to it. This ensures, in a simple manner, that the reference element maintains its position relative to the support frame. In particular, the contour section or contour part is designed to at least partially surround the corner contour with respect to the gripping plane. This configuration has two advantages. Firstly, the contour section or contour part extends over a specific length and in both the X and Y directions with respect to the gripping plane. Secondly, the distance between the contour section or contour part and the corner contour along its longitudinal extent is comparatively small.Both contribute to an accurate measurement of the positions of the corner contour and the gripper relative to each other.

[0021] The measuring system is implemented as an optical measuring system that measures the positions of the corner contour and the reference element relative to the reference coordinate system using an optical imaging method. This enables non-contact measurement of the positions.

[0022] Non-contact measurement prevents the product's position from being altered during the measurement process, as could happen with tactile measurement methods. Furthermore, optical measurement systems offer high accuracy and allow for rapid measurements.

[0023] The measuring system incorporates telecentric optics in various configurations, enabling it to measure the positions of the corner contour and the reference element relative to the reference coordinate system. The telecentric optics ensure that the image of the measuring section and the product position remains sharp over a comparatively large range of object distances. Consequently, the distance between the reference element and the product position and the measuring system, particularly to a transmitter or receiver, or deviations from an ideal distance, have little or no impact on the measurement accuracy. This results in low accuracy requirements for the gripper during positioning within the measuring area.

[0024] The measuring system comprises a light source and a light detector, arranged on different sides relative to the gripping plane. The system measures the positions of the corner contour and the reference element using a backlight imaging method. The measuring section can be positioned at various distances from the light source and the light detector while maintaining largely consistent measurement accuracy. From the light detector's perspective, the reference element and the corner contour appear in high contrast against the background of the light source. This high contrast makes the contours of the reference element and the corner contour clearly visible, thus enabling high measurement accuracy.

[0025] In alternative configurations, the light source and the light detector are arranged on one side relative to the gripping plane, and the measuring system includes a contrast element arranged on the other side relative to the gripping plane. The measuring system measures the positions of the corner contour and the reference element against the background of the contrast element using reflected light imaging. The measuring section can be positioned at various distances from the light source and the light detector on the one hand, and the contrast element on the other, while maintaining largely consistent measurement accuracy. A high contrast with the reference element can be achieved by appropriately selecting the contrast element, and in particular its color. The contrast element can be specifically tailored to the product position and the reference element.The contrast element can be positioned within the measuring system's field of view, behind the corner contour and reference element, particularly for the duration of the measurement, and removed again afterward. This, along with the fact that the light source and light detector are located on the same side relative to the gripping plane, allows the measuring system to be particularly space-saving.

[0026] In some configurations, the gripping arrangement includes a storage unit in which reference values ​​for the gripper's positioning parameters and corresponding reference or correction values ​​for the gripper's position, detectable via the measuring system, can be stored. When the gripper is positioned according to actual values ​​for the positioning parameters, its actual position can be determined by interpolating the corresponding reference or correction values. The gripper's position in the various approached positions can be measured via the reference element. This enables high accuracy in controlling and positioning the gripper. Specifically, the reference or correction values ​​for the gripper's position are measured against the reference values ​​for the positioning parameters in a preparatory phase before the actual operation of the gripping arrangement for picking up, transporting, and placing the product layers.

[0027] In certain configurations, the measuring system comprises a first and a second measuring station to simultaneously measure the position of the first and second corner contours, as well as the first and second reference elements, using a single measuring station. This saves time when measuring the positions of the reference elements and corner contours. In particular, the multiple measurement sections do not need to be moved sequentially into the measuring area of ​​the system. The measuring system also includes a third and further measuring stations, depending on the number of corner contours in the product position or the number of measurement sections in the gripper. This allows the position of all corner contours and their associated reference elements to be measured at once. Preferably, the distance between the measuring stations relative to the gripping plane is adjustable to the distance between the corner contours or the measurement sections. Depending on the distance between the corner contours, the distance between the measuring stations is increased or decreased.The measuring stations are preferably mounted on one or more support rails so that they can be moved. This allows the measuring stations to be used for product layers with different dimensions and basic shapes.

[0028] In various embodiments, the gripper has multiple gripping elements that act on the product at different points to hold it in place. The use of multiple gripping elements makes it possible to keep the product as close as possible to the gripping plane. In particular, this prevents the product from sagging, for example, in the area of ​​a corner contour or at its center of gravity. The more closely the shape of the held product corresponds to a plane, the more accurately its position can be determined. Deviations from the plane, on the other hand, lead to measurement inaccuracies. The gripper has, in particular, different types of gripping elements. Preferably, the gripper has several gripping elements distributed along the edge of the product and at least one gripping element located at the product's center of gravity.The number and type of gripping elements are specifically adapted to the properties of the product position, in particular its inherent stiffness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further advantages and aspects of the invention will become apparent from the claims and from the description of an embodiment of the invention, which is explained below with reference to the drawings. These show: Fig. 1 in a top view a gripper of an embodiment of a gripping arrangement, Fig. 2. In a perspective view, the gripping arrangement according to Fig. 1. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES

[0030] Fig. Figure 1 schematically shows a gripper 2 of a gripping arrangement with a product position 1 held on the gripper 2. The gripper 2 has a support structure 20 to which at least one gripping element 21 is attached. Specifically, the gripper 2 has several gripping elements 21 distributed across the support structure 20. The product position 1 is held on the gripper 2 in a gripping plane E by means of the gripping elements 21. The gripping plane E corresponds to the plane of the drawing according to Figure 1. Fig. 1. The held product position 1 extends along an X-axis and a Y-axis in the gripping plane E.

[0031] The gripper 2 has a first measuring section 22-1. A first corner contour K1 of the product position 1 is exposed on the first measuring section 22-1 in a direction transverse to the gripping plane. Accordingly, it is concealed in Fig. Gripper 2 does not grip product layer 1, so that product layer 1 is visible behind gripper 2. Gripper 2 is designed to hold product layer 1 on one side via gripping elements 21. Accordingly, the first corner contour K1 is also on the side facing away from gripper 2 – as shown in the illustration in Fig. 1 in the direction into the drawing plane behind product layer 1 - exposed.

[0032] The supporting structure 20 has a first reference element 23-1 in the area of ​​the first measuring section 22-1. In the embodiment according to Fig. The support structure 20 also has a second measuring section 22-2, at which a second corner contour K2 of the product layer 1 is exposed. The support structure 20 has a second reference element 23-2 in the area of ​​the second measuring section 22-2. The first and second measuring sections 22-1, 22-2 are arranged diagonally opposite each other with respect to the rectangular product layer 1.

[0033] The reference elements 23-1, 23-2 are designed as rectangular, frame-like contour sections attached to the supporting structure 20. The reference elements 23-1, 23-2 comprise three straight edges arranged at right angles to each other and surround the corner contours K1, K2 on three sides. This results in a relatively small distance between each of the three edges and the corner contour K1, K2. The straight edges of the reference elements 23-1, 23-2 are arranged at an angle to the edges of the product layer 1, which form the corner contours K1, K2.

[0034] The in Fig. 1. The rectangle drawn in the middle of gripper 2 is not part of gripper 2.

[0035] Fig. Figure 2 shows the gripper 2 and a measuring system 3. The measuring system 3 is configured to measure positions in the gripping plane E relative to a reference coordinate system. A position can be represented in the form of X and Y coordinates. The measuring system 3 is configured to measure the position of the first corner contour K1 with respect to the reference coordinate system. The measuring system 3 is also configured to measure the position of the first reference element 23-1 with respect to the reference coordinate system. Specifically, the measuring system 3 is configured to measure the respective position by measuring the positions of several points along the first corner contour K1. From the information about the positions of the several points along the two edges that form the first corner contour K1, and, if applicable, the information about the position of the corner of the first corner contour K1, the orientation of the first corner contour K1 with respect to the reference coordinate system can be determined.Measuring system 3 is thus able to measure the position of the first corner contour K1 relative to the reference coordinate system by measuring the positions of several points along the first corner contour K1. Similarly, measuring system 3 measures the position of the first reference element 23-1 relative to the reference coordinate system. From the position of the first corner contour K1 and the position of the first reference element 23-1, the relative position of the product position 1 relative to the gripper 2 can be determined. The relative position can then be expressed as deviations ΔX in the X-direction, ΔY in the Y-direction, and Δα in the direction of rotation with respect to the normal of the gripping plane E.

[0036] In the same way, the measuring system 3 also measures the position of the second corner contour K2 and the position of the second reference element 23-2, each in relation to the reference coordinate system.

[0037] When determining the relative position of the product position 1, the measuring system 3 takes into account both the position of the first corner contour K1 relative to the first reference element 23-1 and the position of the second corner contour K2 relative to the second reference element 23-2.

[0038] In an embodiment not shown, only a single measuring section and a single reference element are provided, and the measuring system measures the position of one corner contour and the position of the single reference element. Based on known dimensions of product layer 1 in the X and Y directions, the position of the entire product layer can be deduced from the position of the single corner contour.

[0039] When positioning gripper 2 to place product layer 1, the relative position of product layer 1 can be taken into account. For this purpose, the position of gripper 2 is corrected by the deviation expressed as ΔX, ΔY, and Δα. This allows product layer 1 to be placed at the target location with relatively high accuracy. Any deviations that occurred during the picking up of product layer 1 or even before this process therefore have no influence on the accuracy of the placement of product layer 1. With this gripping arrangement, accuracies of up to 10 µm can be achieved.

[0040] The measuring system 3 comprises, according to Fig. 2. Two measuring stations 30. Each of the measuring stations 30 is configured to measure positions in the gripping plane E relative to a specific or a common reference coordinate system. By using the two measuring stations 30, it is possible to simultaneously measure the positions of the first and second corner contours K1, K2, as well as the first and second reference elements 23-1, 23-2. The measuring stations 30 are arranged at a distance from each other that corresponds approximately to the length of the diagonal extent of product position 1, i.e., the distance between the corner contours K1, K2.

[0041] Each of the measuring stations 30 comprises a light source 31 and a light detector 32. The light source 31 is arranged on one side of the gripper 2 and the product position 1, the light detector 32 on the other side. According to the illustration of Fig. In section 2, the light source 31 is positioned above the gripping plane E and the light detector 32 is positioned below the gripping plane E. A field of view S of the measuring station 30 extends between the light source 31 and the light detector 32. The field of view S is defined at the first and second measuring sections 22-1 and 22-2 according to... Fig. 2 represented by a cylindrical disk. The field of view S is in Fig. 1 is represented as a circle. The measuring section 22-1, 22-2 and the corner contour K1, K2 are arranged for measuring in the respective field of view S.

[0042] Each of the measuring stations 30 has telecentric optics. Accordingly, the field of view S between the light detector 32 and the light source 31 extends in the form of a cylinder. The telecentric optics make it possible to position the measuring sections 22-1, 22-2 at any point between the light source 31 and the light detector 32 while maintaining measurement accuracy.

[0043] To measure the positions of the corner contours K1, K2 and the reference elements 23-1, 23-2, the light source 31 emits light beams that pass through the field of view S perpendicular to the gripping plane E. When the product position 1 and the reference element 23-1, 23-2 are projected onto a plane of the light detector 32, the light detector 32 receives no light. Where neither the product position 1 nor the reference element 23-1, 23-2 is positioned, the light detector 32 receives light. The path of the corner contour K1, K2 and the reference element 23-1, 23-2 therefore appears as a contrast on the light detector 32. Thus, the measuring station 30 measures according to Fig. 2 using the backlighting principle.

[0044] In an embodiment not shown, the measuring stations 30 are movably mounted and secured on a support rail. Depending on the specific dimensions of the product position, the distance between the measuring stations can be changed by moving one or both measuring stations and adapted to the product position.

[0045] In addition to measuring the relative position of product layer 1 with respect to gripper 2, a lookup table can be created prior to using gripper 2 for picking up, transporting, and placing product layer 1. This table allows for correction of gripper 2 positions. For this purpose, gripper 2 is moved to various positions in space with different rotational orientations by one or more (not shown) transport drives of the gripper assembly, according to positioning parameters. These positioning parameters represent reference values. At the gripper 2's current positions and orientations, the measuring system 3 measures its position and assigns the measured positions as reference or correction values ​​to the reference values ​​for the positioning parameters. The assignment of reference values ​​for positioning parameters and the reference or correction values ​​for gripper 2 positions are stored in a memory of the measuring system 3 as a lookup table.When gripper 2 is subsequently used to pick up, transport, and place the product layers 1, the measured reference or correction values ​​for gripper 2 positions are interpolated from the set actual values ​​for positioning parameters in order to determine the actual position of gripper 2 or the corresponding correction values. This reduces or eliminates inaccuracies in the positioning of gripper 2.

[0046] This is particularly advantageous when setting the rotational positions of the gripper 2. Because with comparatively large dimensions of the product position 1 in the X or Y direction, even small deviations when setting a rotational position of the gripper 2 can lead to large deviations in the position at the edges of the product position 1.

Claims

[1] Gripping arrangement for picking up, transporting and depositing a product layer (1) comprising a gripper (2) with a support structure (20) to which at least one gripping element (21) is attached to hold the product layer (1) on the gripper (2) in a gripping plane (E), wherein the gripper (2) has a first measuring section (22-1) wherein a first corner contour (K1) of the product layer (1) is exposed on the first measuring section (22-1) in a direction transverse to the gripping plane (E), and wherein the gripper (2) has a first reference element (23-1) in the region of the first measuring section (22-1), and a measuring system (3) for measuring positions in the gripping plane (E) relative to a reference coordinate system, which is configured to measure a position of the first corner contour (K1) with respect to the reference coordinate system, and to measure a position of the first reference element (23-1) with respect to the reference coordinate system. measure,in order to determine the relative position of the product position (1) in relation to the gripper (2). [2] Gripping arrangement according to claim 1, wherein the gripper (2) has a second measuring section (22-2), wherein a second corner contour (K2) of the product position (1) is exposed at the second measuring section (22-2) in a direction transverse to the gripping plane (E), and the gripper (2) has a second reference element (23-2) in the area of ​​the second measuring section (22-2), and wherein the measuring system (22-2) is set up to measure a position of the second corner contour (K2) and the second reference element (23-2) with respect to the reference coordinate system in order to determine the relative position of the product position (1) with respect to the gripper (2), in particular wherein the first measuring section (22-1) and the second measuring section (22-2) are arranged diagonally opposite each other with respect to the product position (1). [3] Gripping arrangement according to claim 2, wherein the gripper (2) has a number of measuring sections, wherein further corner contours of the product position (1) are exposed at each measuring section and the gripper (2) has a further reference element in the area of ​​each measuring section, and wherein the measuring system (3) is set up to measure a position of the further corner contours and the reference elements with respect to the reference coordinate system in order to determine the relative position of the product position (1) with respect to the gripper (2). [4] Gripping arrangement according to claim 1, 2 or 3, wherein the reference element (23-1, 23-2) is designed as a contour section of the support frame (20) or as a contour part attached to the support frame (20), in particular wherein the contour section or contour part is configured to at least partially surround the corner contour (K1, K2). [5] Gripping arrangement according to one of the preceding claims, wherein the measuring system (3) is designed as an optical measuring system which measures the positions of the corner contour (K1, K2) and the reference element (23-1, 23-2) with respect to the reference coordinate system via an optical imaging method. [6] Gripping arrangement according to claim 5, wherein the measuring system (3) comprises a telecentric optic via which the measuring system (3) measures the positions of the corner contour (K1, K2) and the reference element (23-1, 23-2) with respect to the reference coordinate system. [7] Gripping arrangement according to claim 5 or 6, wherein the measuring system (3) comprises a light source (31) and a light detector (32) arranged on different sides with respect to the gripping plane (E), and wherein the measuring system (3) measures the positions of the corner contour (K1, K2) and the reference element (23-1, 23-2) using the backlight principle as an imaging method. [8] Gripping arrangement according to claim 5 or 6, wherein the light source (31) and the light detector (32) are arranged on one side with respect to the gripping plane (E) and wherein the measuring system (3) has a contrast part which is arranged on the other side, and wherein the measuring system (3) measures the positions of the corner contour (K1, K2) and the reference element (23-1, 23-2) against the background of the contrast part using the reflected light principle as an imaging method. [9] Gripping arrangement according to one of the preceding claims, comprising a storage unit in which reference values ​​for positioning parameters of the gripper (2) and associated reference or correction values ​​for positions of the gripper (2) that can be detected via the measuring system (3) can be stored, wherein when the gripper (2) is positioned according to actual values ​​for positioning parameters, the actual position of the gripper (2) can be determined by interpolation of the mutually associated reference or correction values. [10] Gripping arrangement according to one of claims 2 to 9, wherein the measuring system (3) has a first and a second measuring station (30) to measure the position of the first and second corner contour (K1, K2) and of the first and second reference element (23-1, 23-2) simultaneously with a measuring station (30), in particular wherein a distance between the measuring stations (30) with respect to the gripping plane (E) is adaptable to the distance of the corner contours (K1, K2). [11] Gripping arrangement according to one of the preceding claims, wherein the gripper (2) has several gripping elements (21) which act on the product position (1) at different points in order to hold the product position (1).

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