Swivel bending machine for determining the deformation of a measuring jaw

Abstract

The present invention relates to a pivot bending machine (1) for determining the deformation of a measuring jaw (15) during a bending process. The pivot bending machine (1) comprises a lower jaw (3) and a movable upper jaw (4), between which a sheet metal part (12) can be clamped for bending during the bending process, a pivotable or rotatable bending jaw (5) for bending the clamped sheet metal part (12), a camera-laser system (6), and a control device (7). The camera-laser system (6) comprises a laser unit (20) suitable for emitting a laser beam (22), and a camera unit (21) with a camera sensor (23) suitable for receiving the laser beam (22) and for outputting images of the laser beam (22) received by the camera sensor (23) during the bending process. The control device (7) is operatively connected to the camera unit (21) and is suitable for determining the deformation of the measuring cheek (15).The upper jaw (4) or the bending jaw (5) is designed as the measuring jaw (15), which deforms during the bending process. The laser unit (20) and the camera unit (21) are mounted on the measuring jaw (15) at a distance from each other along its length and are aligned such that the laser beam (22) of the laser unit (20) can be projected onto the camera sensor (23). The control device (7) is suitable for receiving the images (B1, B2) output by the camera unit (21) during the bending process, determining a position of a laser center of gravity (P1, P2) in each image (B1, B2) based on the images (B1, B2), and determining the deformation (Δwx, Δwz) of the measuring cheek (15) based on deviations between the determined positions of the laser centers of gravity (P1, P2) in the images (B1, B2) output during the bending process.

Description

The present invention relates to a swivel bending machine for bending a sheet metal part, as well as an associated method and computer program product. A swing bending machine is a forming machine for producing bent parts from sheet metal. It comprises a lower jaw on which the sheet metal to be processed is placed on a support surface, an upper jaw with which the sheet metal is clamped and fixed against the lower jaw during the bending process, and a bending jaw which is pivotally or rotatably mounted about a horizontal bending axis. To perform a bending operation, the sheet metal is first positioned between the upper and lower dies and clamped (fixed) between them by lowering the upper die. The bending die is then rotated or pivoted relative to the lower die, bending the free protruding portion of the sheet metal (bend leg) at a bending angle relative to the rest of the sheet metal. During the bending process, due to the large forces acting, a deformation (deflection) of the upper jaw and the bending jaw typically occurs, which can result in an undesirable deviation of the actual bending angle of the sheet from a desired target bending angle or in a varying leg length of the bent component (along the bending axis). To determine the actual bending angle of a sheet metal part and thus also any undesirable deviations from a target bending angle, a variety of solutions have been proposed in the prior art. For example, DE 20 2006 020 110 U1 describes a swivel bending machine in which the sheet metal is measured at several measuring points after bending using a probe in order to determine the actual bending angle and to initiate any necessary corrective measures. Methods like these, which rely on measuring the workpiece (i.e., the bent sheet metal), are quite time-consuming because no bending force should be applied to the workpiece by the bending die during the measurement process to avoid distorting the measurement. Therefore, the bending die must be moved away from the workpiece before it is measured. Furthermore, while such methods capture the effect of unwanted deformation of the upper and bending dies, they do not capture the deformation of the upper and bending dies themselves. Therefore, conclusions about the actual geometric conditions of the upper and bending dies during the bending process can only be drawn to a very limited extent. The present invention is based on the objective of providing a swivel bending machine of the type described above, which is characterized by improved practicality, in particular with regard to more detailed monitoring of the bending process during the ongoing bending process (in real time). This problem is solved by the swivel bending machine according to claim 1, the method for determining the deformation of a measuring cheek of a swivel bending machine according to claim 8 and the computer program product according to claim 15. The swivel bending machine according to the invention for determining the deformation of a measuring jaw during a bending process comprises: a lower jaw and an upper jaw movable relative to the lower jaw, between which a sheet metal can be clamped for bending during the bending process; a pivotable or rotatable bending jaw for bending the sheet metal clamped between the lower jaw and the upper jaw; a camera-laser system comprising a laser unit suitable for emitting a laser beam and a camera unit with a camera sensor suitable for receiving the laser beam on the camera sensor and suitable for outputting images of the laser beam received on the camera sensor during the bending process (which in particular each comprise pixels and associated pixel values ​​that depict the intensity of the received laser beam); and a control device (functionally connected to the camera unit) for determining the deformation of the measuring jaw.wherein - the upper jaw or the bending jaw is designed as the measuring jaw which deforms during the bending process, - the laser unit and the camera unit are mounted on the measuring jaw at a distance from each other in the longitudinal direction of the measuring jaw and are aligned such that the laser beam of the laser unit can be projected onto the camera sensor, and - the control device is suitable (configured) to receive the images output by the camera unit during the bending process, to determine a position of a laser center of gravity in each image based on the images (in particular based on the pixel values ​​of the images), and to determine the deformation of the measuring jaw based on deviations between the determined positions of the laser centers of gravity in the images output during the bending process. The invention is based on the understanding that a swivel bending machine can be realized through the synergistic combination of the features according to the invention, in which the deformation of the measuring jaw, i.e., the upper jaw or the bending jaw, can be determined in a simple and precise manner during the ongoing bending process. The term measuring jaw is based on the idea that the deformation of this measuring jaw is determined, i.e., the measuring jaw is, in a sense, "measured". The invention thus enables simple and precise measurement of the measuring cheek during the bending process. This allows the actual cause of undesirable deviations between the real bending process and the ideal bending process (e.g., deviation of the actual bending angle from the target bending angle, undesirable changes in the leg length along the bend line, bulging of the bend line) to be directly identified and determined. Based on this, the bending process can be monitored more precisely and / or corrective measures can be initiated. Measuring the bent sheet metal (workpiece) after bending is therefore unnecessary, thus accelerating and simplifying the production process. During the bending process, the upper jaw and the bending jaw each bend to a certain extent due to the acting bending forces. The resulting deformation of the jaw is typically not uniform along its length, but rather increases steadily from the edges of the jaw to its center (inner area). This can be explained by the fact that the upper jaw and the bending jaw are typically supported or attached to the rest of the bending machine at their two edges along their length, and it is there that the forces for clamping the upper jaw against the lower jaw or for twisting / pivoting the bending jaw are applied. If, according to the invention, the laser unit and the camera unit are arranged at a distance from each other in the longitudinal direction of the measuring cheek, the two units displace to different degrees when the measuring cheek is deformed – since the measuring cheek deforms to different degrees along its longitudinal direction. The resulting relative movement between the laser unit and the camera unit allows conclusions to be drawn about the deformation of the measuring cheek. Against this background, the laser unit and the camera unit are preferably spaced apart from each other in the longitudinal direction of the measuring cheek such that one of the two units is located in one (of the two) edge regions of the measuring cheek and the other of the two units is located in an inner region (between the two edge regions) of the measuring cheek, i.e. in the area of ​​the middle of the measuring cheek. The unit positioned at the edge experiences relatively little or no displacement during the bending process because the measuring jaw deforms little or not at all in this area. The unit positioned in the center, however, experiences a relatively large displacement, as the measuring jaw deforms most in its inner area. This positioning of the laser and camera units minimizes measurement errors and ensures that the camera-laser system captures the greatest deformation of the measuring jaw (in the inner area). It is particularly preferred that the camera unit be located in one of the two edge areas and the laser unit be located in the inner area of ​​the measuring cheek, as this further minimizes measurement inaccuracies. During the bending process, the measuring jaw, particularly in its inner area, can twist slightly around its longitudinal axis. If the camera unit is positioned in this twisting inner area, the camera sensor rotates around its longitudinal axis, and with it, the associated image coordinate system relative to the reference coordinate system of the bending machine. This distorts the determination of the deformation of the measuring jaw perpendicular to its longitudinal axis. However, if the camera unit is positioned at the edges of the measuring jaw, this error can be minimized. A measuring cheek has two outer regions and an inner region between them. The measuring cheek extends along its longitudinal direction between its two ends. At these ends, the measuring cheek is connected to and / or supported by the rest of the bending machine. The outer regions of the measuring cheek are located at these ends, while the inner region lies between the two outer regions. The boundary areas are defined here as those sections of the measuring cheek adjacent to the ends of the measuring cheek, which extend on both sides along the outer 20% (in particular 10%) of the longitudinal extent of the measuring cheek. The inner area is defined as the section located between the two edge areas, which extends along the inner 60% (in particular 80%) of the longitudinal extent of the measuring cheek. According to the invention, either the upper jaw or the bending jaw is designed as a measuring jaw, and it is of course also covered by the invention that both the upper jaw and the bending jaw are each equipped with their own camera-laser system to determine the respective deformation. The upper jaw can include not only the upper jaw tool that comes into contact with the sheet metal to be bent, but also those components that are movable relative to the lower jaw together with the upper jaw tool – such as two upper jaw slides that are mounted to move (linearly) relative to the lower jaw and between which the upper jaw tool extends. When determining the longitudinal extent of the upper jaw, the upper jaw slides would therefore also have to be taken into account. A laser unit or camera unit arranged on the upper jaw slides would, according to this definition, be located on the upper jaw. Similarly, the bending jaw can include not only a bending jaw tool that comes into contact with the sheet metal to be bent, but also those components that can be pivoted or rotated together with the bending jaw tool. The following section explains and describes further terms used in connection with the description of the invention: The deformation of the measuring cheek during the bending process refers to the deformation of the measuring cheek that it undergoes during the bending process compared to an undeformed reference state at the beginning of the bending process. This deformation of the measuring cheek occurs particularly perpendicular to its longitudinal direction. The lower beam of the bending machine is typically rigidly connected to the machine bed and includes a horizontal support surface for the sheet metal to be bent. The upper beam can be moved (especially perpendicularly) relative to the support surface of the lower beam by means of a manually or mechanically operated upper beam actuator. The bending beam is pivotable or rotatable relative to the machine bed of the bending machine, can be pivoted or rotated by means of a bending beam actuator, and includes a bending beam slide movably mounted on the machine bed. The bending beam has a bending surface that comes into contact with the sheet metal to be bent during the bending process. The bending surface of the bending beam forms a bending beam angle with the support surface of the lower beam, which changes when the bending beam is pivoted or rotated during the bending process. In the context of the present invention, a camera-laser unit is defined as a measuring system comprising a laser unit capable of emitting a laser beam and a camera unit capable of receiving the laser beam. The measuring system is particularly suitable for detecting a relative displacement (change in position) of the laser unit relative to the camera unit perpendicular to the projection axis of the laser beam. For this purpose, the laser unit and the camera unit are aligned such that the laser beam of the laser unit strikes a camera sensor of the camera unit at its center of gravity. If the position of the center of gravity of the laser on the camera sensor shifts because the laser unit is moved relative to the camera unit (perpendicular to the laser beam) (or vice versa), this change in the position of the center of gravity of the laser can be detected, and the relative displacement (change in position) between the camera unit and the laser unit can be determined. The laser unit and the camera unit are mounted at longitudinal intervals along the measuring jaw, such that their relative positions change when the jaw deforms during bending. This change in position corresponds to the deformation of the measuring jaw between the mounting points (positions) where the laser unit and the camera unit are attached. The laser unit and the camera unit can be attached to the measuring cheek either detachably or permanently. It is also conceivable that the measuring cheek has a cavity into which the laser unit and the camera unit are housed and attached to the cheek there. The laser unit and the camera unit are aligned in such a way that the laser beam of the laser unit is projected onto the camera sensor. The camera unit with its camera sensor is designed to capture optical images and convert them into electronic signals for outputting digital images. The camera sensor comprises a regular arrangement of numerous light-sensitive elements, known as camera sensor pixels, which are capable of detecting light intensities (brightness) and converting them into corresponding signals that are output as pixel values. Each digital image contains (image) pixels corresponding to the camera sensor pixels and associated pixel values ​​that represent the (light) intensity of the received laser beam (for the corresponding pixel). The laser beam can have various cross-sectional shapes, including, in particular, circular, elliptical, linear, or complex patterns, which can be formed by optical elements such as lenses, prisms, or diffractive optical elements (DOEs). The laser beam can be emitted in different wavelength ranges, especially from ultraviolet (UV) through visible light to infrared (IR). A solid-state laser, gas laser, liquid laser, semiconductor laser, and / or fiber laser can be used to generate the laser beam. The laser centroid is the point within a projected laser beam that is defined as the center of the light distribution or intensity. This point serves as a reference for positioning, alignment, and measurement in various optical and laser-based applications. The position of the laser center of gravity in a (digital) image that has pixels and associated pixel values ​​is defined by the image coordinates of the pixel that overlaps with the laser center of gravity (laser center of gravity pixel). The vertical axis of the image is referred to here as the z-image axis or z-image coordinate, and the horizontal axis as the x-image axis or x-image coordinate. The position of a pixel i in the corresponding image can thus be expressed by its corresponding pixel image coordinates xi, zi. The position of the laser center of mass can be expressed as the xs-zs image coordinate of the laser center of mass pixel. If the position of the laser center of gravity is determined in two different images, the determined positions may differ. By comparing the xz-image coordinates of the laser centers of gravity, the extent of the change in position of the laser center of gravity along the x-axis and along the z-axis can be determined. Given the known size and arrangement of the camera sensor pixels and the known imaging properties of the camera unit, this change in the position of the laser center of gravity can be converted into the corresponding relative displacement (change in position) between the camera unit and the laser unit, and thus into the deformation of the measuring cheek, using methods familiar to a person skilled in the art. The laser center of gravity can be determined in various ways familiar to those skilled in the art. Depending on the method used to determine the laser center of gravity, it is referred to, for example, as the geometric laser center of gravity or the weighted laser center of gravity. In principle, however, the laser center of gravity can be determined within the scope of the present invention by any known method familiar to those skilled in the art. However, it is particularly advantageous if, within the scope of the present invention, the laser center of gravity is determined as a weighted laser center of gravity. The weighted laser center point is determined by a weighted calculation in which the image coordinates of the individual pixels of the digital image are multiplied by their respective light intensities (pixel values). The calculation can be performed using the following steps: The camera sensor detects the intensity of the incident laser light at each pixel xi, zi and stores this as the pixel value ii in the corresponding image (or image file). These intensity values ​​(i.e., the pixel values) are used as weights for the position calculation. The image coordinates of each pixel are multiplied coordinate-wise by the corresponding pixel values ​​(light intensity). These products are then summed coordinate-wise across all pixels. The weighted laser center of gravity is calculated by dividing the weighted sums of the x and z image coordinates by the summed total intensity of all pixels. This yields the image coordinates xs and zs of the laser center of gravity. Mathematically, the weighted laser center of gravity S(xs, zs) can be expressed as follows: The control unit comprises a computer with a processor unit and a memory unit. The computer can be configured as a single-board computer, embedded system, digital terminal, desktop computer, edge device, or server. The processor unit is capable of performing computational operations and can be a CPU, GPU, or similar device with one or more processor cores. The processor unit is specifically designed to receive (digital) images from the camera unit, determine the position of the laser center of gravity in each image based on the images (especially the pixel values), and determine the deformation of the measuring cheek based on deviations between the determined positions of the laser centers of gravity in the images captured during the bending process. The storage unit is suitable for storing data and especially (digital) images and outputting them (to the processor unit) and can be designed as volatile or non-volatile storage. To determine deviations between the specific positions of the laser centers of gravity in the images output during the bending process, at least two images output during the bending process must be compared. According to a further preferred embodiment of the invention, it is provided that: - a bending surface of the bending jaw with a support surface of the lower jaw encloses a bending jaw angle which changes when the bending jaw is pivoted or rotated during the bending process; - the pivoting bending machine has a bending jaw angle sensor which is configured to detect the bending jaw angles associated with the images output by the camera unit during the bending process and to transmit them to the control device; and - the control device is configured to determine the deformation of the measuring jaw as a function of the associated bending jaw angles. In this way, the control device can determine the deformation of the measuring cheek as a function of the respective bending cheek angle and thus a progression of the deformation of the measuring cheek over the bending cheek angle. For example, it can be provided that after a defined bending angle increment or a defined time increment, the camera unit captures and outputs an image, and simultaneously the bending angle sensor captures and transmits the corresponding bending angle, so that the image and the associated bending angle are received by the control device. Based on this image, a deviation of the laser center of gravity position compared to a previous image can then be determined, and the deformation of the measuring beam can be determined as a function of the corresponding bending angle. According to a further preferred embodiment of the invention, the camera-laser system has a density filter, in particular a gray filter, arranged between the laser unit and the camera sensor. A density filter is an optical element used to reduce the intensity of the transmitted (laser) light by absorbing, reflecting, or scattering some of the (laser) light. A special type of density filter is the neutral density filter, also known as a gray filter. A neutral density filter reduces light intensity uniformly across the entire visible spectrum without affecting color rendering. By using a density filter, the intensity of the laser light projected onto the camera sensor can be reduced. This ensures that the maximum light intensity (pixel value) is only registered in small areas or even in no areas of the camera sensor, which can lead to greater accuracy in determining the laser's center of gravity. Furthermore, it can be advantageously provided that the camera-laser system has a beam splitter arranged between the laser unit and the camera sensor, in particular designed as a diffractive optical element (DOE), which divides the laser beam into at least two partial laser beams, and that the laser unit and the camera unit are aligned in such a way that the at least two partial laser beams can be projected onto the camera sensor. In this way, instead of just a single laser beam hitting the camera sensor at a single position, at least two partial laser beams hit the camera sensor at at least two positions. In each image, the position of a partial laser beam's center of gravity can be determined for each partial laser beam. The positions of the partial laser beam centers of gravity in an image can then be averaged, and thus the laser beam center of gravity of the corresponding image can be determined. The inventors recognized that in this way, deviations between the determined positions of the laser centers of gravity in two different images can be determined even more precisely, which improves the accuracy of determining the deformation of the measuring cheek. According to a further advantageous embodiment of the swivel bending machine according to the invention, it is provided that: - the camera-laser system comprises a second camera unit with a second camera sensor, suitable for receiving the laser beam on the second camera sensor and suitable for outputting images of the laser beam received on the second camera sensor during the bending process; - the camera-laser system has a (further) beam splitter, which is arranged between the laser unit and the two camera units and splits the laser beam emitted by the laser unit into two partial laser beams; - the laser unit and the two camera units are mounted on the measuring cheek spaced apart from each other in the longitudinal direction of the measuring cheek and are aligned such that the partial laser beams of the laser unit can each be projected onto one of the two camera sensors; and - the control device is suitable forto receive the images output by the camera units during the bending process, to determine the position of the laser center of gravity in each image based on the images (especially the pixel values ​​of the images), and to determine the deformation of the measuring cheek for each camera unit based on deviations between the determined positions of the laser centers of gravity in images output during the bending process. The two camera units are positioned at two different attachment points on the measuring jaw. In this way, the deformation of the measuring jaw can be determined for each of the two attachment points of the camera units, resulting in a more detailed and spatially refined measurement. It is also conceivable, and covered by the invention, that the laser camera system comprises three or more camera units in an analogous manner in order to determine the deformation of the measuring cheek in even greater detail. The camera units are distributed particularly evenly in the longitudinal direction of the measuring cheek. The invention is further manifested in a method according to the invention for determining the deformation of a measuring jaw of a bending machine according to the invention (in particular during a bending process) with the following steps: A) optionally clamping (fixing) a sheet to be bent between the lower jaw and the upper jaw and providing the bending jaw at an initial bending jaw angle, B) projecting the laser beam of the laser unit onto the camera sensor and receiving the laser beam on the camera sensor, and C) at a first time point, outputting a first image of the laser beam received on the camera sensor by the camera sensor, D) receiving the first image in the control device and determining a first position of the laser center of gravity in the first image by means of the control device.E) Optional bending of the sheet metal clamped between the lower and upper jaws by pivoting or rotating the bending jaw from the initial bending jaw angle to an end position bending jaw angle; F) At a second time point after the first, output of a second image of the laser beam received by the camera sensor; G) Receiving the second image in the control device and determining a second position of the laser center of gravity in the second image using the control device; and H) Determining the deformation of the measuring jaw using the control device based on the deviation between the first position of the laser center of gravity and the second position of the laser center of gravity. Steps A and E are not strictly necessary for carrying out the method according to the invention. For example, the deformation of the upper jaw can also be determined simply by clamping the sheet metal to be bent between the lower jaw and the upper jaw before the sheet metal is bent by the bending jaw. In this case, at the first point in time, the upper jaw would not yet be in contact with the sheet metal to be bent, but would be lifted from it. At the second point in time, the sheet metal to be bent would then be clamped and fixed between the upper and lower jaws. A preferred embodiment of the method according to the invention further comprises the following steps: I) Detecting the initial position bending cheek angle associated with the first image and the final position bending cheek angle associated with the second image by the bending cheek angle sensor and transmitting the angles to the control device, and J) Receiving the initial position bending cheek angle and the final position bending cheek angle in the control device, wherein the deformation of the measuring cheek is determined as a function of the initial position bending cheek angle and the final position bending cheek angle. The formulation that the deformation of the measuring cheek is determined as a function of the initial position bending cheek angle and the final position bending cheek angle expresses in particular that the deformation of the measuring cheek is related to the respective bending cheek angles and is determined and displayed as a function of the respective bending cheek angle. Preferably, the method according to the invention further comprises the following steps: - during pivoting or rotating the bending beam from the initial position bending beam angle to the end position bending beam angle, outputting intermediate images of the laser beam received by the camera sensor and determining the bending beam angles of the bending beam corresponding to the intermediate images by the bending beam angle sensor, - receiving the intermediate images and the corresponding bending beam angles in the control device, - determining the positions of the laser centers of gravity in the intermediate images by means of the control device, and - determining the progression of the deformation of the measuring beam (between the initial position bending beam angle and the end position bending beam angle) as a function of the bending beam angle using the positions of the laser centers of gravity in the intermediate images and the corresponding bending beam angles by means of the control device. Thus, not only is the deformation of the measuring jaw determined in the initial and final positions of the bending jaw, but also the progression of the measuring jaw's deformation between these two positions as a function of the bending jaw angle. From the curves in such a bending jaw angle-measuring jaw deformation diagram, detailed insights into the geometric relationships of the measuring jaw and the bending behavior of the sheet metal being bent during the bending process can be gained. Such diagrams allow conclusions to be drawn, in particular, about which bend angles the sheet metal to be bent is still ideally elastically deformed and when ideally plastic deformation occurs. Against this background, a further preferred embodiment of the method according to the invention is characterized in that: - the upper jaw is designed as the measuring jaw, - the deformation of the measuring jaw is determined along a (horizontal) x-axis and / or a (vertical) z-axis, and the x-axis runs horizontally and perpendicular to the longitudinal direction of the upper jaw and the z-axis runs vertically and perpendicular to the longitudinal direction of the upper jaw, - the course of the deformation of the upper jaw is determined by the control device along the x-axis and / or the z-axis as a function of the bending jaw angle, and - a yield strength bending angle of the sheet metal is determined from the course of the deformation of the upper jaw along the x-axis and / or the z-axis as a function of the bending jaw angle by the control device. A vertical axis runs parallel to the direction of gravity. A horizontal axis runs within a horizontal plane that is oriented perpendicular to the direction of gravity. The yield point bending angle is defined as the angle at which, during a bending process, the elastic deformation of the material (sheet) to be bent ends and permanent plastic deformation begins, i.e., the yield point of the material (sheet) is exceeded. The deformation of the upper cheek along the horizontal x-axis or the vertical z-axis as a function of the bending cheek angle can be represented, in particular, as a diagram showing the deformation of the upper cheek along its horizontal x-axis or vertical y-axis relative to the bending cheek angle. These diagrams are referred to here as the bending cheek angle-x-upper cheek deformation diagram or the bending cheek angle-z-upper cheek deformation diagram. The inventors realized that the yield strength bending angle of the sheet metal could be easily and precisely derived from these diagrams (or rather, the deformation pattern). Thus, the yield strength bending angle of the sheet metal can be deduced from the deformation of the upper cheek. In a bending cheek angle x-upper cheek deformation diagram, in which the bending cheek angle is represented via the easting axis and the horizontal upper cheek deformation via the northing axis, the yield stress bending angle coincides with the maximum of the curve shown. In a bending cheek angle-z-upper cheek deformation diagram, the yield stress bending angle coincides with the point where the slope of the depicted curve changes (significantly). Using simple tools of curve analysis, the yield stress bending angle of the sheet metal can thus be determined from the course of the deformation of the upper cheek as a function of the bending cheek angle. The yield stress bending angle can be determined not only from the deformation of the upper die along the x-axis and / or the z-axis, but also more generally from the deformation of the upper die (or the bending die). According to a preferred embodiment of the method according to claim 10, the upper die (or the bending die) is configured as the measuring die, and the control device determines the yield stress bending angle of the sheet metal from the deformation of the measuring die as a function of the bending die angle. The control device of the associated swivel bending machine according to the invention is thus, according to a preferred embodiment, configured to determine a yield stress bending angle of the sheet metal from the course of the deformation of the measuring cheek as a function of the bending cheek angle. The inventors also recognized that the flow bending angle allows direct conclusions to be drawn about the springback behavior of the sheet metal. "Springback" refers to the phenomenon that a sheet of metal partially returns to its original shape after a bending process, as soon as the bending force is removed and the sheet is relieved of stress. This elastic re-deformation occurs due to the elastic stresses stored in the material and results in the actual bending angle of the sheet after relief being smaller than the bending angle imposed by the bending die during the forming process. The specified yield bending angle corresponds approximately to the springback angle by which the sheet metal rebounds after being unloaded. This rebound can be (almost) compensated for by moving the bending die further than the target bending angle of the sheet metal by the yield bending angle. For example, if the sheet metal is to be bent by a target angle after being unloaded, it would not only be bent by the target angle during the bending process, but also by the yield bending angle, so that after unloading and rebound, the sheet metal can assume the target bending angle. In the final position of the bending die, the bending die angle would therefore be the sum of the target bending angle and the yield bending angle. The invention enables the simple determination of the yield bending angle and thus an estimation of the sheet metal's springback angle during the bending process. By taking the yield bending angle into account when performing the bending process (or when defining the final bending angle), the sheet metal's springback can be compensated for, allowing the sheet metal to be bent without rework so that it assumes the desired target bending angle after being removed from the bending machine. Previously, estimating the springback angle required relying on experience from previous, comparable bending operations. Often, several test bends were performed with different end-position bending angles to determine the end-position bending angle at which the springback of the sheet metal was (almost completely) compensated. The invention thus makes it possible to determine the end-position bending angle that compensates for the springback of the sheet metal during the ongoing bending process, without having to refer to previous (test) bending operations. In this way, efficiency can be increased and scrap reduced. Against this background, a further preferred embodiment of the method according to the invention comprises the following steps: - Storing a target bending angle for the sheet metal to be bent in the control device, and - Determining the end position bending cheek angle of the bending cheek using the target bending angle and the yield point bending angle, in particular by adding the target bending angle and the yield point bending angle, by means of the control device. The control device of the associated swivel bending machine according to the invention is thus configured according to a preferred embodiment to provide a target bending angle for the sheet metal to be bent, stored in the control device, and to determine an end-position bending cheek angle of the bending cheek using the target bending angle and the yield point bending angle, in particular by adding the target bending angle and the yield point bending angle, wherein the end-position bending cheek angle defines the bending cheek angle at the end of the bending process. Furthermore, it may preferably be provided that the determination of the positions of the laser centers of gravity in the images and / or intermediate images is carried out by means of the control device, by determining the positions of the weighted laser centers of gravity in the respective image by means of the control device. Furthermore, the invention manifests itself in a computer program product according to the invention comprising commands, the execution of which on a control device of a swivel bending machine according to the invention causes the control device to execute steps D, G and H of the method according to the invention. Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Fig. 1 shows a schematic front view of a swing bending machine according to the invention, Figs. 2A & 2B show a section of a schematic side sectional view of a swing bending machine according to the invention at various times during the bending process, Fig. 3A shows a schematic front view of an upper jaw of a swing bending machine according to the invention at various times during the bending process, Fig. 3B shows two superimposed schematic images that were captured by the camera sensor of the swing bending machine according to Fig. 3A at various times during the bending process, Fig. 4 shows a flowchart of a method according to the invention, and Figs. 5A & 5B show a bending jaw angle-z-upper jaw deformation diagram and a bending jaw angle-x-upper jaw deformation diagram. The swivel bending machine 1 according to the invention comprises a machine frame 2 with a lower jaw 3, an upper jaw 4 movable linearly relative to the lower jaw 3, and a bending jaw 5 rotatably mounted relative to the machine frame 2. Furthermore, the swivel bending machine 1 has a camera-laser system 6 arranged on the upper jaw 4, a control device 7, an upper jaw actuator 8, a bending jaw actuator 9, and a bending jaw angle sensor 10. The machine frame 2 (also called machine bed) and the lower cheek 3 form a horizontal support surface 11 on which a sheet metal 12 to be bent can be placed. The upper jaw 4 has an upper jaw tool 13 and two upper jaw slides 14 enclosing it laterally, by means of which the upper jaw 4 is mounted to be linearly movable relative to the machine frame 2 and thus relative to the lower jaw 3. By means of the upper jaw actuator 8, the upper jaw 4 can be moved perpendicular to the support surface 11 and thus to the lower jaw 3 in order to fix and clamp a sheet metal 12 located between the lower jaw 3 and the upper jaw 4. The upper jaw 4 is designed as a measuring jaw 15, as the camera-laser system 6 is arranged on it. The upper jaw 4 extends along its longitudinal direction in a longitudinal extension 16 between two (upper jaw) ends 17, which are formed by the upper jaw slides 14. In the area of ​​the ends 17, the upper jaw 4 is connected to the rest of the swing bending machine 1 via the upper jaw slides 14. The upper cheek 4 is subdivided into different regions 18, 19 along its longitudinal extent 16. The outer regions 18 of the upper cheek 4 extend on both sides along the outermost 20% of the longitudinal extent 16 of the upper cheek 4, while the inner region 19 extends between the two outer regions 18 along the inner 60% of the longitudinal extent 16 of the upper cheek 4. The bending jaw 5 is pivotably mounted on the machine frame 2 and can be pivoted relative to the lower jaw 3 by means of the bending jaw actuator 9 in order to bend the sheet metal 12 fixed between the lower jaw 3 and the upper jaw 4 along a bending edge K. Parallel to the longitudinal direction of the upper cheek 4 (in the undeformed state) runs a y-axis of a reference coordinate system, horizontal and perpendicular to the longitudinal direction of the upper cheek 4 runs an x-axis of the reference coordinate system and vertical and perpendicular to the longitudinal direction of the upper cheek 4 runs a z-axis of the reference coordinate system. The camera-laser system 6 comprises a laser unit 20 and a camera unit 21 operatively connected to the control device 7. The laser unit 20 is capable of emitting a laser beam 22. The camera unit 21 has a camera sensor 23 capable of receiving the laser beam 22 and outputting images 24 of the laser beam received on the camera sensor 23 during the bending process and transmitting them to the control device 7. The laser unit 20 and the camera unit 21 are attached to the upper jaw 4 in the longitudinal direction of the upper jaw 4, separated from each other, and are aligned such that the laser beam 22 of the laser unit 20 is projected onto the camera sensor 23. The laser unit 20 is arranged in the inner region 19 of the upper jaw 4, and the camera unit 21 in the (left) edge region 18 of the upper jaw 4. According to the schematic figures 1 and 3A, the camera unit 21 is arranged on the upper jaw tool 13. However, an arrangement on one of the two upper jaw slides 14 is also covered by the invention and is conceivable. The images 24 output by the camera sensor 23 each comprise pixels and pixel values ​​that represent the intensity (brightness) of the received laser beam 22 and by means of which the position of the laser center of mass P1, P2 in the respective image 24 can be determined. The position of the pixels within the image 24 can be determined in an image coordinate system; the x- and z-axes of the image coordinate system correspond to the orientation of the associated x- and z-axes of the reference coordinate system. The bending cheek 5 comprises a bending surface 25 which comes into contact with the sheet metal 12 to be bent during bending and encloses a bending cheek angle BW with the support surface 11 of the lower cheek 3. The bending cheek angle sensor 10 is designed to detect the bending cheek angle BW corresponding to the images 24 output by the camera unit 21 during the bending process and to transmit it to the control device 7. The control unit 7 comprises a processor unit and a memory unit and is operatively connected to the camera unit 21, the bending cheek angle sensor 10, the upper cheek actuator 8 and the bending cheek actuator 9 and is configured to receive the images 24 of the camera unit 21 as well as the associated bending cheek angles BW, to determine a position P1, P2 of a laser center of gravity in the respective image 24 based on the pixel values ​​of the images 24 and to determine the deformation of the measuring cheek 15 (upper cheek 4) as a function of the associated bending cheek angle BW based on deviations between the determined positions P1, P2 of the laser centers of gravity in the images 24 output during the bending process. In addition, the control device 7 is designed to control the actuators 8, 9 and thus set them in motion, to determine the yield bending angle FW and to define an end position bending cheek angle EW of the bending cheek 5 using a target bending angle SW stored in the control device 7 and the yield bending angle FW. With reference to Figures 2A to 4, a method 100 according to the invention for determining the deformation of the measuring jaw 15 of the swivel bending machine 1 according to the invention will be explained in more detail below: First, according to step A and Figure 2A, a sheet to be bent is fixed (clamped) between the lower jaw 3 and the upper jaw 4 by moving the upper jaw 4 against the lower jaw 3 by means of the upper jaw actuator 8 – controlled by the control device 7. The bending jaw 5 is located at an initial bending jaw angle AW, in which the bending surface 25 of the bending jaw 5 and the support surface 11 of the lower jaw 3 form an angle of 0°. In this operating situation according to Fig. 2A, before the start of bending the sheet metal 12, at a first time t1, the upper jaw 4 is in a (nearly) undeformed state. This state is also shown in Figs. 2B and 3A by the upper jaw 4 and laser unit 21, respectively, which are depicted with a dashed contour. According to step C, at the first time point, a first image B1 of the laser beam 22 received by the camera sensor 23 is output by the camera sensor 23. The image shows the laser beam striking the camera sensor. Simultaneously, according to step I, the initial bending angle AW corresponding to the first image B1 is detected by the bending angle sensor 10 and transmitted to the control device 7, where it is received according to step J. According to step D, the first image B1 is received in the control unit 7, and a first position P1 of a laser center of gravity of the laser beam is determined by means of the control unit 7. The first position P1 of the laser center of gravity is defined by the image coordinate (xP1zP1) of the corresponding (laser center of gravity) pixel. Subsequently, according to step E, the sheet metal 12, clamped between the upper jaw 4 and the lower jaw 3, is bent along the bending edge K by pivoting and thus moving the bending jaw 5 from the initial bending jaw angle AW to a first end position bending jaw angle EW. For this purpose, the bending jaw actuator 9 is controlled accordingly by the control device 7 to change the bending jaw angle BW. Due to the forces acting on the upper cheek 4 when bending the sheet metal 12, the upper cheek 4 deforms, with the deformation increasing from the edge areas 18 towards the center and reaching its maximum in the inner area 19 of the upper cheek 4. In Fig. 2B and Fig. 3A, the contour of the deformed upper cheek and the laser unit 20 attached to the deformed upper cheek are sketched with a solid line. Since the camera unit 21 is attached to the outer region 18 of the upper cheek 4, while the laser unit 20 is attached to the inner region 19, these two units 20, 21 experience different displacements in the xz-plane of the reference coordinate system due to the deformation of the upper cheek 4. According to Figs. 3A and 3B, the laser unit 20 experiences a displacement of Δwx and Δwzent, respectively, along the x-axis and z-axis of the reference coordinate system. In contrast, the camera unit 21 does not displace at all when the upper cheek 4 is deformed, as shown in Fig. 3A. The resulting relative displacement of the laser unit 20 to the camera unit 21 leads to a displacement of the laser beam 22 relative to the camera unit 21 and thus to a displacement of the laser beam's center of gravity on the camera sensor 23. After the bending jaw 5 has assumed the end position bending jaw angle EW, a second image B2 of the laser beam 22 received by the camera sensor 23 is output by the camera sensor 23 at a second time t2 (which lies after the first time t1) according to step F. Simultaneously, according to step I, the end position bending jaw angle EW corresponding to the second image B2 is detected by the bending jaw angle sensor 10 and transmitted to the control device 7, where it is received according to step J. The output second image B2 is received in control unit 7 according to step G, and a second position of the laser center of mass P2 of the laser beam in the second image B2 is determined by means of control unit 7. The second position of the laser center of mass P2 is defined as the image coordinate (xP2zP2) of the corresponding pixel. Because the deformation of the upper cheek 4 has shifted the laser unit 20 relative to the camera unit 21 and thus also the laser beam center of gravity on the camera sensor 23, the second position of the laser center of gravity P2 (B2 in the second image) deviates from the first position of the laser center of gravity P1 (B1 in the first image). Fig. 3B shows a superposition of the two images B1 and B2 from which the change in position (displacement) of the laser center of gravity from the first position P1 to the second position P2 becomes apparent. Based on the deviation between the first position of the laser center of gravity P1 and the second position of the laser center of gravity P2, the deformation of the upper cheek 4 is determined according to step H. From the displacement of the laser center of mass along the xz-image coordinates from the first position P1 in image B1 to the second position P2 in image B2, the corresponding displacement Δwx, Δwz of the laser unit 20 along the xz-coordinates of the reference coordinate system can be calculated using known methods. The displacement Δwx, Δwz of the laser unit 20 corresponds to the deformation of the measuring cheek 15 (upper cheek 4) between the attachment points where the camera unit 21 and the laser unit 20 are located. In the outlined embodiment of the inventive method 100, the deformation of the measuring cheek 15 is determined not only for the initial position bending cheek angle AW and the final position bending cheek angle EW, but also the course of the deformation of the measuring cheek between these two angles. For this purpose, during the pivoting of the bending jaw 5 from the initial bending jaw angle AW to the final bending jaw angle EW, intermediate images of the laser beam received by the camera sensor 23 are output, and the bending jaw angles BW corresponding to these intermediate images are detected by the bending jaw angle sensor 10. The intermediate images and the corresponding bending jaw angles BW are received in the control unit 7. The respective laser centers of gravity in the intermediate images are determined by the control unit 7. The control device 7 is designed to determine the course of the deformation of the upper cheek 4 between the initial position bending cheek angle AW and the final position bending cheek angle EW as a function of the bending cheek angle BW, using the positions of the laser centers of gravity in the intermediate images and the associated bending cheek angles BW, and in particular to output it as a diagram. Figures 5A and 5B show such diagrams, which depict the deformation of the upper cheek 4 along the vertical z-axis and along the horizontal x-axis of the reference coordinate system as a function of the bending cheek angle BW. At the end-position bending angle EW, the deformation of the measuring jaw is Δwx, Δwzentlong along the z- and x-axes of the reference coordinate system. The course of the vertical and horizontal deformations of the upper jaw as a function of the bending angle is shown as curves K1 and K2, respectively. The curve K2 in the bending cheek angle x upper cheek deformation diagram according to Fig. 5B shows a maximum M that marks the transition from elastic to plastic deformation of the sheet 12 and thus defines the yield stress bending angle FW. In the bending angle-z-upper-beam deformation diagram according to Fig. 5A, the yield bending angle coincides with point p, where the slope of the depicted curve K1 flattens significantly. This point p can be determined by approximating the course of curve K1 on both sides of the yield bending angle FW with auxiliary lines h1, h2 and finding the intersection point of both auxiliary lines h1, h2. The control submission 7 is designed to determine the yield stress bending angle FW of the sheet 12 from the course of the deformation of the upper cheek using known methods of curve discussion outlined above as examples. In a further embodiment of the inventive method 100, it is provided that the determined yield limit bending angle FW is used to determine the end position bending cheek angle EW. In the control device 7, a target bending angle for the sheet metal 12 to be bent is first stored. The sheet metal 12 is then bent according to the inventive method 100, and the deformation of the upper jaw 4 is determined as a function of the bending jaw angle BW, and based on this, the yield bending angle FW is determined. The control device 7 then sets the final bending angle EW using the target bending angle and the yield bending angle FW, in particular by adding the target bending angle and the yield bending angle FW. In this way, the springback of the sheet metal 12 can be compensated. Reference symbol list 1 Swivel bending machine 2 Machine frame 3 Lower jaw 4 Upper jaw 5 Bending jaw 6 Camera-laser system 7 Control device 8 Upper jaw actuator 9 Bending jaw actuator 10 Bending jaw angle sensor 11 Support surface 12 Sheet metal 13 Upper jaw tool 14 Upper jaw slide 15 Measuring jaw 16 Longitudinal extent 17 (Upper jaw) ends 18 Edge areas 19 Interior area 20 Laser unit 21 Camera unit 22 Laser beam 23 Camera sensor 24 Images 25 Bending surface BW Bending jaw angle P1, P2 Position of laser centers FW Yield limit bending angle EW End position bending jaw angle 100 Method AW Initial bending jaw angle t1 First time t2 Second time K Bending edge Δwx, Δwz Displacement, deformation K1, K2 Curve M Maximum p Point h1, h2 auxiliary lines

Claims

Swivel bending machine (1) for determining the deformation of a measuring jaw (15) during a bending process, comprising: a lower jaw (3) and an upper jaw (4) movable relative to the lower jaw (3), between which a sheet (12) can be clamped for bending during the bending process; a swiveling or rotatable bending jaw (5) for bending the sheet (12) clamped between the lower jaw (3) and the upper jaw (4); a camera-laser system (6) comprising a laser unit (20) suitable for emitting a laser beam (22), and a camera unit (21) with a camera sensor (23) suitable for receiving the laser beam (22) on the camera sensor (23) and suitable for outputting images (B1, B2) of the laser beam (22) received on the camera sensor (23) during the bending process; and a control device (7) for determining the deformation of the measuring jaw. (15) wherein the upper jaw (4) or the bending jaw (5) is designed as the measuring jaw (15),which deforms during the bending process,- the laser unit (20) and the camera unit (21) are mounted on the measuring cheek (15) at a distance from each other in the longitudinal direction of the measuring cheek (15) and are aligned such that the laser beam (22) of the laser unit (20) can be projected onto the camera sensor (23), and- the control device (7) is suitable for receiving the images (B1, B2) output by the camera unit (21) during the bending process, for determining a position of a laser center of gravity (P1, P2) in each image (B1, B2) based on the images (B1, B2), and for determining the deformation (Δwx, Δwz) of the measuring cheek (15) based on deviations between the determined positions of the laser centers of gravity (P1, P2) in the images (B1, B2) output during the bending process. Swivel bending machine (1) according to claim 1, wherein the laser unit (20) and the camera unit (21) are spaced apart from each other on the measuring cheek (15) in the longitudinal direction of the measuring cheek (15) such that one of the two units (20, 21) is arranged in one of two edge regions (18) of the measuring cheek (15) and the other of the two units (20, 21) is arranged in an inner region (19) of the measuring cheek (15) arranged between the two edge regions (18). Swivel bending machine (1) according to claim 2, wherein the camera unit (21) is arranged in one of the two edge regions (18) and the laser unit (20) is arranged in the inner region (19) of the measuring cheek (15). Swivel bending machine (1) according to one of the preceding claims, wherein - a bending surface (25) of the bending jaw (5) with a support surface (11) of the lower jaw (3) encloses a bending jaw angle (BW) which changes when the bending jaw (15) is swiveled or rotated during the bending process, - the swivel bending machine (1) has a bending jaw angle sensor (10) which is configured to detect the bending jaw angles (BW) associated with the images (B1, B2) output during the bending process and to transmit them to the control device (7), and - the control device (7) is configured to determine the deformation of the measuring jaw (15) as a function of the associated bending jaw angles (BW). Swivel bending machine (1) according to one of the preceding claims, wherein the camera-laser system (6) has a density filter, in particular a gray filter, arranged between the laser unit (20) and the camera sensor (23). Swivel bending machine (1) according to one of the preceding claims, wherein the camera-laser system (6) has a beam splitter arranged between the laser unit (20) and the camera sensor (23), in particular designed as a diffractive optical element (DOE), which divides the laser beam (22) into at least two partial laser beams, and the laser unit (20) and the camera unit (21) are aligned such that the at least two partial laser beams can be projected onto the camera sensor (23). Swivel bending machine (1) according to one of the preceding claims, wherein: - the camera-laser system (6) comprises a second camera unit with a second camera sensor, suitable for receiving the laser beam on the second camera sensor and suitable for outputting images of the laser beam received on the second camera sensor during the bending process; - the camera-laser system (6) has a (further) beam splitter, which is arranged between the laser unit and the two camera units and splits the laser beam emitted by the laser unit into two partial laser beams; - the laser unit (20) and the two camera units are mounted on the measuring cheek (15) spaced apart from each other in the longitudinal direction of the measuring cheek (15) and are aligned such that the partial laser beams of the laser unit (20) can each be projected onto one of the two camera sensors (23); and - the control device (7) is suitable forto receive the images output by the camera units during the bending process, to determine the position of the laser center of gravity in each image based on the images (especially the pixel values ​​of the images), and to determine the deformation of the measuring cheek for each camera unit based on deviations between the determined positions of the laser centers of gravity in images output during the bending process. Method (100) for determining the deformation of a measuring jaw (15) of a swing bending machine (1) according to one of the preceding claims, the swing bending machine (1) comprising: - a lower jaw (3) and an upper jaw (4) movable relative to the lower jaw (3), between which a sheet (12) can be clamped for bending during the bending process, - a pivotable or rotatable bending jaw (5) for bending the sheet (12) clamped between the lower jaw (3) and the upper jaw (4), - a camera-laser system (6) comprising a laser unit (20) suitable for emitting a laser beam (22), and a camera unit (21) with a camera sensor (23) suitable for receiving the laser beam (22) on the camera sensor (23) and suitable for outputting images (B1, B2) of the laser beam (22) received on the camera sensor (23) during the bending process, - a with the camera unit (21) connected control device (7) for determining the deformation of the measuring cheek (15),wherein- the upper jaw (4) or the bending jaw (5) is designed as the measuring jaw (15) which deforms during the bending process,- the laser unit (20) and the camera unit (21) are spaced apart from each other in the longitudinal direction of the measuring jaw (15) and are aligned such that the laser beam (22) of the laser unit (20) can be projected onto the camera sensor (23), and- the control device (7) is suitable for receiving the images (B1, B2) output by the camera unit (21) during the bending process, determining a position of a laser center of gravity (P1, P2) in each image (B1, B2) based on the images (B1, B2), and determining the deformation (Δwx, Δwx) based on deviations between the determined positions of the laser centers of gravity (P1, P2) in the images (B1, B2) output during the bending process.Δwz) of the measuring cheek (15) to determine. with the following steps: A) optionally clamping (fixing) a sheet metal part (12) to be bent between the lower jaw (3) and the upper jaw (4) and positioning the bending jaw (5) at an initial bending jaw angle, B) projecting the laser beam (22) of the laser unit (20) onto the camera sensor (23) and receiving the laser beam (22) on the camera sensor (23), C) at a first time (t1), outputting a first image (B1) of the laser beam (22) received on the camera sensor (23) by the camera sensor (23), D) receiving the first image (B1) in the control device (7) and determining a first position of the laser center of gravity (P1) in the first image (B1) by means of the control device (7), E) optionally bending the sheet metal part (12) clamped between the lower jaw (3) and the upper jaw (4) by pivoting or rotating the bending cheek (5) from the initial bending cheek angle (AW) to an end position bending cheek angle (EW),F) at a second time point (t2) after the first time point (t1), output of a second image (B2) of the laser beam (22) received on the camera sensor (23) by the camera sensor (23), G) receiving the second image (B2) in the control device (7) and determining a second position of the laser center of mass (P2) in the second image (B2) using the control device (7), and H) determining the deformation (Δwx, Δwz) of the measuring cheek (15) using the control device (7) based on the deviation between the first position of the laser center of mass (P1) and the second position of the laser center of mass (P2). Method (100) for determining the deformation of the measuring cheek according to (15) claim 8, wherein: - the swivel bending machine (1) has a bending cheek angle sensor (10) configured to detect the bending cheek angles (BW) associated with the images (B1, B2) output by the camera unit (22) during the bending process and to transmit them to the control device (7), and - the control device (7) is configured to determine the deformation of the measuring cheek (15) as a function of the associated bending cheek angles (BW), comprising the following steps: I) Detection of the initial position bending cheek angle (AW) associated with the first image (B1) and the final position bending cheek angle (EW) associated with the second image (B2) by the bending cheek angle sensor and transmission of the angles (AW, EW) to the control device (7), and J) Receiving the Initial position bending angle (AW) and final position bending angle (EW) in the control device (7),wherein the deformation of the measuring cheek (15) is determined as a function of the initial position bending cheek angle (AW) and the final position bending cheek angle (EW). Method (100) for determining the deformation of the measuring jaw (15) according to claim 9 comprising the following steps: - during pivoting or rotating the bending jaw (5) from the initial bending jaw angle (AW) to the final bending jaw angle (EW), outputting intermediate images of the laser beam (22) received on the camera sensor (23) by the camera sensor (23) and determining the bending jaw angles (BW) of the bending jaw (5) corresponding to the intermediate images by the bending jaw angle sensor (10), - receiving the intermediate images and the corresponding bending jaw angles (BW) in the control device (7), - determining the positions of the laser centers of gravity (P1, P2) in the intermediate images by means of the control device (7), and - determining the progression of the deformation of the measuring jaw (15) as a function of the bending jaw angle (BW) using the positions of the laser centers of gravity (P1, P2) in the Intermediate images and the associated bending cheek angle (BW) by means of the control device (7). Method (100) for determining the deformation of the measuring cheek (15) according to claim 10, wherein: - the upper cheek (4) is designed as the measuring cheek (15), - the deformation of the measuring cheek (15) is determined along an x-axis and / or a z-axis, and the x-axis runs horizontally and perpendicular to the longitudinal direction of the upper cheek (4) and the z-axis runs vertically and perpendicular to the longitudinal direction of the upper cheek (4), - the course of the deformation of the upper cheek (4) is determined by the control device (7) along the x-axis and / or the z-axis as a function of the bending cheek angle (BW), and - from the course of the deformation of the upper cheek (4) along the x-axis and / or the z-axis as a function of the bending cheek angle (BW) a yield stress bending angle (FW) of the sheet (12) is determined by the control device (7). Method (100) for determining the deformation of the measuring cheek (15) according to claim 10, wherein a yield stress bending angle (FW) of the sheet (12) is determined from the course of the deformation of the upper cheek (4) as a function of the bending cheek angle (BW) by the control device (7). Method (100) for determining the deformation of the measuring cheek (15) according to claim 10 or 11, comprising the following steps: - storing a target bending angle for the sheet metal (12) to be bent in the control device (7), and - determining the end position bending cheek angle (EW) of the bending cheek (5) using the target bending angle and the yield bending angle (FW), in particular by adding the target bending angle and the yield bending angle (FW), by means of the control device (7). Method (100) for determining the deformation of the measuring cheek (15) according to one of claims 8 to 13, wherein the determination of the positions of the laser centers of gravity (P1, P2) in the images (B1, B2) and / or intermediate images is carried out by means of the control device (7) by determining the positions of the weighted laser centers of gravity (P1, P2) in the respective image (B1, B2) by means of the control device (7). Computer program product comprising commands, the execution of which on a control device (7) of a swivel bending machine (1) according to one of claims 1 to 7 causes the control device to execute steps D, G and H of the method according to claim 8 and optionally step J of the method according to claim 9.

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