Method, computing unit, laser cutting machine and computer program product for calculating a contour deviation for controlling a laser cutting machine

Abstract

On the one hand, the present invention relates to the calculation of a contour deviation (ka) for controlling a laser cutting machine (L) using control instructions (sa). The contour deviation (ka) is calculated based on a displacement vector (vv), which is determined based on an image comparison between an image captured by an imaging device (K) and a virtual reconstructed image (v). The virtual reconstructed image (v) is determined based on a reference texture (RT) applied to a workpiece (W) and a control value (sw).

Description

Technical Field

[0001] The present invention belongs to the technical field of laser cutting, and in particular relates to a method, a computing unit, and a computer program for controlling a laser cutting machine and for calculating a contour deviation. Background Art

[0002] The demand for laser cutting machines in terms of productivity and precision is constantly increasing. The aim is to be able to cut workpieces / components as quickly and precisely as possible. However, these two goals are limited, or the goals of "as fast as possible" and "as precise as possible" are even contradictory. For example, the faster one wants to cut around a corner, the lower the geometric precision of the cut corner will be, because due to the overshoot of the inertia and elasticity (mass inertia) of the machine, the axes, the cutting bridge, and the cutting head, the actual cutting contour will deviate from the target contour. Since the internal encoder measurement system on the drive shaft measures only indirectly (usually optically) and cannot take into account the above-mentioned inertia torques and / or elasticity, the exact position of the machining laser beam usually cannot be measured either.

[0003] Other reasons for the deviation between the actual cutting contour and the target cutting contour are vibrations of the gantry system or the robot to which the machining head is attached, or vibrations of the workpiece or the workpiece support, which cause overshoot when cutting along the cutting contour. Other reasons for path deviations can also be friction, static friction, recoil, incorrect compensation values, etc.

[0004] In order to be able to cut the part to be cut within the desired tolerance (path deviation / contour error), the dynamic limitations of the machine (especially in the area of small radii and corners) are usually subject to a blanket restriction, which leads to a reduction in productivity or quality.

[0005] In addition, there are different structural designs of laser cutting systems with bridges (gantries), axes, etc. of different sizes, and each laser cutting system has different mass inertia and / or elasticity. Therefore, a blanket reduction in dynamics is not feasible. For example, smaller systems require less dynamic reduction, while very large moving masses require greater dynamic reduction.

[0006] Therefore, it is desirable to be able to determine the correct path deviation of the machine (with components such as gantries, axes, bridges, cutting heads, etc.).

[0007] Various methods are known from the prior art in order to be able to determine path accuracy. These methods are partly based on optical methods.

[0008] DE 10 2018 217 940 A1 proposes a method for improving contour accuracy by using a camera device and a reflection pattern. The camera device moves along a target path of a component contour, the camera device captures the reflection pattern of the workpiece surface in overlapping sub-areas in a spatially resolved manner, and uses the reflection pattern to measure the deviation in the path traveled relative to the target path. In particular, the position increment along the component contour is determined by the optimum value of a similarity function, which is also described in DE 10 2005 022095 A1.

[0009] Starting from this prior art, the object of the present invention is to determine the contour deviation from a specified target path and thus to determine the contour fidelity of a cutting task. In particular, where applicable, the determination of the contour deviation for correction or compensation should have occurred before cutting in order to reduce the number of incorrectly cut components. In summary, the quality of the cutting result will be improved. In addition, it should be possible to calibrate the cutting system or a cutting machine having its structural components (such as a gantry, machine axes, cutting bridge, cutting head, etc.). In other words, the contour deviation should be determined for the cutting system in order to be able to specifically adjust the dynamics at specific positions on the target path. This is intended to improve the quality and productivity of the component to be cut.

[0010] This object is achieved by the appended claims, in particular by a computer-implemented method, a computing unit and a computer program. Summary of the Invention

[0011] According to a first aspect, this object is achieved by a computer-implemented method for calculating a contour deviation for controlling a laser cutting machine, which contour deviation can occur when cutting a workpiece using the processing laser beam of the laser cutting machine, the method comprising the following method steps:

[0012] a) Reading a cutting plan that specifies a target path for the cutting head of the laser cutting machine;

[0013] b) Defining a reference texture or reading a reference texture from the cutting plan;

[0014] c) An application run of the laser cutting head to apply the reference texture to the workpiece at least at selected positions along the target path;

[0015] d) Performing an image capture run of the laser cutting head to capture at least one image at at least one selected position along the target path, in which at least a part of the applied reference texture is imaged by means of an optical capture device arranged on the laser cutting head;

[0016] e) Reconstructing at least one virtual reconstructed image based on control values calculated from the target path and based on the defined reference texture;

[0017] f) Using an image processing device to compare the at least one captured image and the reconstructed virtual reconstructed image to determine the displacement vector between the associated pixels in each case;

[0018] g) Outputting the contour deviation calculated based on the determined displacement vector.

[0019] The calculated and output contour deviation is preferably used to calibrate a laser cutting machine. Thus, the "calibration" of the laser cutting machine is based on the calculated contour deviation. The calibration can include creating a compensation model for the laser cutting machine. Preferably, the calculated contour deviation is captured and stored with its different correlations, that is, in particular, captured and stored according to acceleration, advancement, change in direction, position on the workbench, etc. The calibration is used to avoid or minimize contour deviations in production cutting. In particular, the output contour deviation can be used to specifically reduce the dynamics at selected positions on the target path, in particular, specifically reduce the dynamics at selected positions on the target path according to the specific contour deviation caused by the mass inertia and / or elasticity of the moving parts of the laser cutting system. Instead of reducing the dynamics, according to the present invention, the position values of the control values (X, Y) are shifted by the contour deviation (a few micrometers). The pair of values (shifted position values) determined in this way is used as a control instruction for the control axis. The calculated control instruction includes a correction instruction and is determined based on the calculated contour deviation.

[0020] The reduction of the dynamics at certain positions is a measure to reduce the contour deviation. Alternatively or additionally and preferably, the control values (X, Y) should be shifted by the displacement vector. This has the technical advantage that the contour error caused by the dynamics can be offset. Instead of reducing the dynamics, the position values of the control values (X, Y) are shifted by the contour deviation (a few micrometers).

[0021] The solution described here has many advantages. The reference texture is used as a simple but precisely definable signature. The method can be performed before production cutting; there is no need to perform a test cutting process (no micro joints). The method is fast and provides calibration of the laser cutting machine, especially before production cutting. The method works precisely and without waste. Using this process, the machine can be calibrated without "unnecessarily" cutting parts (since it is only used for calibration). The metal sheet only needs to be provided with a reference texture; it does not need to be cut.

[0022] The terms used in this application are explained in more detail below.

[0023] The laser processing machine is preferably a laser cutting machine, and in particular, a laser cutting machine in a flat cutting system. This laser cutting machine is specifically designed to cut flat workpieces, and the flat workpieces are supplied to the laser cutting machine for this purpose.

[0024] The laser cutting machine includes a laser cutting head. The laser cutting head is moved (along a target path) on the workpiece by an electromechanical drive system. The laser cutting machine can be designed with a portal driver or a gantry driver having a cutting bridge, preferably with two feed motors that move the cutting bridge synchronously on one axis. The laser cutting head is in turn movably arranged on the cutting bridge. Preferably, the laser cutting head can be moved relative to the cutting bridge along three spatial axes.

[0025] Alternatively, the cutting head can also be arranged on a mobile robot. The mobile robot is also moved via an electromechanical drive system which preferably has at least two motors for two spatial axes (the X-axis, Y-axis in the worktable plane). The mobile robot can also be designed to have six degrees of freedom (6DOF).

[0026] The laser processing machine can be designed as a robot control system or a portal system. The laser processing head or in particular the laser cutting head can generally only be directly connected to one axis; for example, directly connected to the Z-axis.

[0027] The drive system is controlled using control values and / or control instructions. The control values are calculated according to the target path. The control instructions include correction instructions to compensate for the calculated contour deviation. The control instructions are used to control the drive system and in particular the individual axes (x_d, y_d).

[0028] The workpiece is in particular a flat workpiece, preferably made of metal. The workpiece is placed on a processing table (such as a cutting grid) for processing by the laser cutting machine. Mechanical components and a controller are used to move the laser cutting head along the target path in order to cut components from the workpiece.

[0029] The path deviation can extend in the X and Y directions relative to the workpiece. The path deviation in the X and Y directions represents the contour deviation (deviation from the target contour), i.e. in particular the deviation between the (expected) target path and the (actually traveled) actual path. This deviation is caused by the inertia of the moving mass and the elasticity between machine components (such as the cutting head, machine axes).

[0030] The target path can be determined according to the cutting plan and used as a specification of the target geometry. Generally, the target path has no time information or no time reference.

[0031] The controller of the laser processing machine (e.g., CNC) uses the cutting plan and the target path to generate control values for controlling the drive axes that move the laser cutting head. The control values have a time reference. Thus, the control values encode the trajectory (= time-dependent path). The control values are used to control the drive system (with at least 2 axes, alternatively 3 axes: X-axis, Y-axis, and Z-axis). The generation of the control values is basically known. According to the present invention, the generated control values are (slightly) adjusted in order to compensate / reduce any contour deviations that may occur. Alternatively, a dynamic radius correction function can also be used (adjust the tool radius in the control cycle (about 1 ms) and adjust the control values accordingly).

[0032] The encoder values of each drive axis can be provided by the measuring system of the drive system (preferably with three drive axes). The encoder values represent the position of the motor of the drive axis that the drive axis actually reaches at a defined time point. However, the position of the laser cutting head and / or the tool center point (TCP) cannot be derived from the encoder values because the mass inertia during movement causes inaccurate positioning. With the help of the axis or drive encoder values, the machine controller precisely knows where the imaging device takes the image A (position A). Therefore, the calculation unit or the machine controller can derive what the expected image (virtually reconstructed image A') at position A should look like.

[0033] Among other things, the mass inertia of the laser cutting head causes contour errors during movement. These contour errors can be determined with the solutions proposed here. According to the determined contour deviations, control instructions for moving the cutting head can be calculated, and using these control instructions, the contour deviations can be reduced or even completely eliminated. In particular, the following calculation can be used:

[0034] Xd: X-axis control value,

[0035] Xt: TCP value in the X direction,

[0036] Xe: X-axis encoder value,

[0037] Kax (contour deviation in the X direction),

[0038] Kax = Xt - Xd,

[0039] Kcomp: Coefficient for compensating contour deviations (1: 100%, 0.8: 80%). It may be advantageous not to compensate for all the differences but only a part of them.

[0040] Xd*: New control value or control instruction for compensating contour deviations (in the X direction):

[0041] Xd* = Xd + Kax, where Kax can be compensated via a dynamic contour deviation interface (e.g., ISG / Beckhoff) or via a dynamic tool radius correction function or by adjusting the dynamics.

[0042] Thus, the control instruction is also a control value, however, it contains a correction instruction for compensating the contour error. The control value represents the value assigned to the motor (X_d, Y_d for the motors of the X-axis and Y-axis). If compensating the contour error, a slightly adjusted control value (X_d*, Y_d*) is used, i.e., the control instruction.

[0043] The control instruction is usually position-specific because the contour deviation is position-dependent. The correction instruction can also be position-specific. For example, the contour deviation can be compensated at a first position (e.g., the first corner) by a factor x and at a second position (e.g., the second corner) by a factor y.

[0044] Preferably, the setpoint should be adjusted. The dynamics do not necessarily have to be reduced. If compensation is desired by reducing the dynamics, a factor of approximately 0.8–0.1 would be meaningful (with a maximum acceleration of 10 m / s^2). However, these factors largely depend on the underlying system and the maximum possible dynamics.

[0045] The control instruction is usually axis-specific.

[0046] The control instruction contains a correction instruction to compensate for certain path deviations caused by the mass inertia or elasticity of the moving parts. The components of the panel machine are selected from the group including:

[0047] · Gantry system (X1-axis and X2-axis),

[0048] · Y-axis,

[0049] · Z-axis,

[0050] · Cutting head,

[0051] · Energy cable and power cable,

[0052] · Signal conduction cable (to the motor / sensor),

[0053] · Cable carrier (guiding the cables in the cable carrier),

[0054] · Machine tool,

[0055] · Cutting grid,

[0056] · Housing and

[0057] · Workpiece.

[0058] The masses of the individual components can vary greatly. For example, the bridge will have a significantly higher mass than the component, with the head of the component being movably mounted on the bridge. By measuring at the TCP with a camera device, the contour deviation can be determined precisely. The causes of the contour deviation are basically minor, but in order to account for the mass differences in the control instructions, a compensation factor (Kcomp) can be calculated as a function of the mass.

[0059] The total mass of the inertial components of the cutting head and the cutting head movement unit can be in the range of 200 kg to 500 kg; the mass of the cutting head can be in the range of 10 kg to 20 kg.

[0060] The main object of the present invention is to detect path deviations, and in particular contour errors that cannot be inferred from the encoder values, such as overshoot of the cutting head at corners. In the prior art, the contour deviation cannot be accurately calculated using the encoder values, which means that precise compensation is not possible. However, with the present invention, such compensation becomes possible.

[0061] In a first embodiment of the present invention, the reference texture is a texture; for example, a texture in the form of a series of numbers and / or letters and / or two-dimensional patterns. In a second embodiment of the present invention, the reference texture is the target path from the cutting plan. In both embodiments, the reference texture is applied to the workpiece.

[0062] This application can be a physical machining process directly on the workpiece, such as engraving with a laser. Alternatively, another optical or mechanical method can be used. Alternatively, a pattern (such as a hole pattern) can be cut out in the workpiece (such as a metal sheet). The reference texture can also be applied to the workpiece using a printer (such as an inkjet printer arranged outside but permanently connected to the cutting head).

[0063] For example, the reference texture can be applied to the complete target path or only locally at selected positions. For example, when the direction reverses, the reference texture can be applied at corners or in the case of small radii. The reference texture can be particularly applied to positions where contour errors are expected to be dynamically introduced.

[0064] In step e), at least one virtual reconstructed image is reconstructed based on the control values of the defined reference texture.

[0065] In principle, using the solution proposed here, two runs are performed with the laser cutting head before the actual production cutting process. During the actual production cutting process, the laser is activated but not used for cutting, and is at most used to apply a reference texture, for example, by means of an engraving process. The two "preliminary runs" are for different purposes. The first run is an application run for applying the reference texture. The second run is an image capture run, which is used for image capture by means of an optical capture device. The optical capture device is arranged on the laser cutting head, preferably coaxially arranged on the laser cutting head. When the laser cutting head moves, it can take pictures of the workpiece along the path traversed by the laser cutting head. Alternatively, the optical capture device can be arranged eccentrically on the laser cutting head with a corresponding optical deflection element. For example, the optical capture device is a camera device (such as a CCD camera device) or an alternative device for capturing images.

[0066] It should be noted that in the first embodiment (Method 1), image capture occurs on the actual path, while in the second embodiment (Method 2), image capture occurs on the target path.

[0067] The application run is performed along the selected positions and / or directly on the target path. In an exemplary embodiment, the reference texture can be engraved on the complete target path of the contour to be cut. In another exemplary embodiment, the reference texture cannot be engraved on the complete target path, but only on the selected positions of the target path, such as on small radii, corners, and / or when the position of the laser cutting head is reversed, and thus where the mass inertia and / or elasticity of the components of the cutting system have an increased effect.

[0068] The image capture run is performed especially in the case where the reference texture is applied during the previous application run. In an exemplary embodiment, the image capture run can be performed precisely where the application run is also performed. In another exemplary embodiment, the image capture run can only be performed in certain areas of the application run. This is particularly meaningful if the reference texture has been applied to the complete target path during the application run, and image capture is only performed at selected positions, such as only at corners, small radii, and / or when the position is reversed, in order to avoid unnecessary image recording. Therefore, the image capture run does not necessarily have to match the application run.

[0069] In addition, image capture can be configured during the image capture run. The image capture run can be configured with default settings such that image capture occurs during the image capture run according to a preconfigured pattern (e.g., fixed time interval: image recording is performed every 3 ms). Alternatively or additionally, the image capture run can be configured such that image capture occurs at specific locations of the cutting plan, namely especially at the neuralgia location (see above: in the case of a small radius, at a corner, etc.). Image capture does not necessarily have to be performed continuously during the image capture run, but can be triggered intermittently and especially sporadically at the neural location.

[0070] The position can be configured on a (e.g., graphical) user interface (HMI).

[0071] The image processing device can include an algorithm or another evaluation instruction (e.g., heuristic, digital image information extraction method).

[0072] The displacement vector is at least in the plane of the workpiece, i.e., has at least an X-direction value and a Y-direction value in the coordinate system.

[0073] The reference texture is preferably applied directly or overlaid on the target path that the laser cutting head is to traverse or applied or overlaid along the target path (e.g., parallel to the target path). The reference texture must be applied or overlaid in such a way that it can be detected from the field of view (FOV) of the imaging device. The reference texture is preferably applied to the target path in such a way as to create an overlapping area. The reference texture is generally larger than the target path specified as a line or curve. The reference texture can have dimensions, especially a height, in the range between 10 μm and 10 mm, where the dimension or height is defined here as perpendicular to the departure direction of the cutting head. The lateral length or width, i.e., the length or width extending in the traversing direction, is variable and depends on the cutting plan or profile. The reference texture is used for local reference between the virtual reconstruction image and the actual captured image at the same location. The reference texture can preferably be designed as a series of numbers, especially a continuous series of numbers and / or a sequence of letters of the alphabet, especially a continuous sequence of letters, or designed as a non-periodic, non-linear, and non-repeating pattern. For example, the reference texture can be a planar object or a metal sheet having an outer contour corresponding to the target path. The reference texture can be a pattern previously applied (e.g., engraved) onto a metal sheet and / or a natural texture / surface microstructure along the target path (determined when slowly traversing).

[0074] The imaging device can preferably be arranged coaxially or centered relative to the laser beam optical unit and can be used to detect the machining area. Multiple imaging devices can also be configured. The imaging device can be coupled to an illumination source. The imaging device can also be attached offset instead of coaxially; then, the offset must be known and taken into account in the reconstruction of the path actually traversed by the cutting head.

[0075] The target path corresponds to the contour to be cut. The target path can be read from the cutting plan. The target path corresponds to the desired geometry defined in the cutting plan.

[0076] According to a preferred embodiment of the invention, the reference texture can be selected from a set of predefined patterns during the configuration phase. The set of predefined patterns is preferably stored in a memory and / or read via, for example, a human-machine interface, HMI. Preferably, the reference texture is automatically determined and presented as a suggestion on the HMI. The user then has the option to accept or modify the suggestion. Additionally or alternatively, buttons can be provided on the HMI, such that the user can configure the reference texture himself via the buttons. This has the advantage that, for example, the contour fidelity determination method can also be carried out if the data connection to the memory with the stored reference textures is temporarily interrupted.

[0077] In a preferred embodiment of the invention, the reference texture is configurable and can be configured in particular according to the nozzle used (nozzle width), the mechanical actuator, the cutting plan or the contour defined therein and / or the cutting parameters (such as the focus position).

[0078] In another advantageous embodiment of the invention, a command can be provided to trigger the activation or switching on of the illumination source, such that, for example, the illumination source, in particular the illumination laser, is switched on synchronously with the capture of the frame. This is used to optimize the image capture and illumination of the processing area. The illumination source can be located in the camera device or on the camera device or at another location and act directly or indirectly (by reflection) on the processing area.

[0079] The calculation of the contour deviation for the calibration control of the laser cutting machine can be carried out essentially on different selected areas on the workpiece located on the worktable. For example, this enables critical areas for contour error determination to be selected, such as those with many small radii or complex trajectory requirements. For example, this can be carried out by comparing with the material to be cut and / or with the specifications from the cutting plan, for example taking into account the magnitude of the acceleration or curvature. This is primarily because the deviation from the target increment can also occur along a straight line. Although these have a smaller impact on the contour accuracy, they can cause local irregularities during the machining process.

[0080] In an advantageous embodiment of the invention, the method comprises or includes the following method steps:

[0081] - Calculate and apply or execute control instructions. These control instructions advantageously include correction instructions for compensating for the contour deviations that have already been output. Thus, the control instructions represent optimized control values for the respective axes (X-axis, Y-axis). The control instructions are transmitted to the drive system for (improved) control. The correction instructions are axis-specific and include the X-axis and Y-axis intercepts. The correction instructions are used to compensate for contour deviations caused by the mass inertia and / or elasticity of all the involved moving parts of the drive system.

[0082] The contour error calculated by the method proposed here can also be used to calibrate the machine model, generalize the machine model (adjusted according to the workspace), and improve the parameterization of the controller.

[0083] In another preferred embodiment of the invention, the reference texture can be engraving. Generally, engraving is carried out with a lower laser power than production cutting. Larger nozzle spacings and different focal positions can be selected for engraving compared to cutting. If desired, the laser is pulsed (pulse frequency and pulse width (duration)). The penetration depth can be variable; it should be chosen to be deep enough (especially in the range of a few micrometers to about 1 mm) so that the engraving in the image can be seen.

[0084] In another preferred embodiment of the invention, the reference texture is applied during the application run with a reduced dynamic value that is lower than the production dynamic value. Applying the reference texture during slow running has the advantage that the reference texture can be applied very precisely. During the image capture run, the production dynamic value is used to traverse the reference texture along the target path with the laser deactivated, and at the same time, the at least one image is captured in step d).

[0085] In a preferred embodiment of the invention, the dynamic value (vector or data set) contains information about speed, acceleration, jerk, and / or other time derivatives thereof. There are two instances of the dynamic value: the production dynamic value applied during the production (cutting) run, and the reduced dynamic value that can be encoded in the calculated control instructions to compensate for the determined path deviation. However, other measures for compensating for contour deviations are also available (such as shifting the control value by a displacement vector).

[0086] Thus, the production speed and / or production acceleration and / or production jerk are, for example, the speed and / or acceleration and / or jerk specified for the workpiece to be machined in the cutting plan or in the parameter file.

[0087] The reduced dynamic value (speed value and / or acceleration value and / or jerk value) is selected such that it is lower than the comparable value used for production machining (such as cutting). Typical low acceleration values are in the range of 0.01 to 0.1 m / s². Typical (high) acceleration values for production machining are in the range of 1 to 100 m / s².

[0088] The acceleration value is mainly used because speed is not the main factor introducing dynamic errors. However, contour errors may also occur at low speeds and high accelerations.

[0089] In order to keep the captured images still clear enough at production speeds, the exposure time of the optical capture device must be set short enough. This setting basically depends on the lighting method and lighting intensity. Using a 2-watt irradiation laser, an exposure time of 30 us is good. An exposure time of 1 to 300 us is useful. The higher the exposure time, the greater the motion blur (image blur). The setting can be made on the HMI. In addition, it has been proven advantageous to set the lighting of the lighting device to a high enough level during image capture. Basically, for selectable settings, the greater the lighting, the lower the exposure can be.

[0090] In another preferred embodiment of the present invention, the reference texture is applied during the application run with production dynamic values corresponding to those used in production machining. During the image capture run, when the laser is deactivated, the target path is traversed with reduced dynamic values. During the image capture run, the at least one image is captured in step d). This corresponds to a second method or embodiment, in which the reference texture is applied with production dynamic values, and in particular with production speed and production acceleration.

[0091] The traversal is performed on or along the target path with the processing laser beam of the processing machine for cutting deactivated. The laser can be activated for engraving and operates at a much lower power than for cutting. During the application run and the image capture run, the laser is deactivated for cutting.

[0092] In another advantageous embodiment of the present invention, the comparison in step f) occurs at the midpoint position of the respective image (the midpoint of the virtual reconstructed image and the midpoint of the at least one captured image).

[0093] In another advantageous embodiment of the present invention, the reference texture can be a texture applied to a carrier object. The carrier object is fixedly arranged in the carrier area of the laser cutting machine for the workpiece and is position-calibrated there.

[0094] In another advantageous embodiment of the present invention, the reference texture is a texture projected onto the workpiece by a projector fixedly connected to the laser cutting machine and position-calibrated.

[0095] In another advantageous embodiment of the present invention, the optical capture device can include at least one camera device arranged in or on the processing head (preferably coaxially arranged in or on the processing head), or arranged on the drive system of the processing head.

[0096] In a further advantageous embodiment of the invention, the actual path, i.e., the path actually traversed by the cutting head, can be extracted from at least one captured image.

[0097] In a further advantageous embodiment of the invention, the method is carried out before or during the production cutting process. The method is preferably carried out before the production cutting. However, the reference texture can also be applied outside the cutting area (but still within the field of view of the imaging device). In this way, for the purpose of obtaining the contour deviation, the images can be compared during the cutting. If the method is used before the production cutting, the laser is deactivated or switched off during the application run and also during the image capture run (except for engraving).

[0098] In a further advantageous embodiment of the invention, the at least one image is captured by activating an illumination device (e.g., an illumination laser). Activating the illumination device generally has at least 50 mW. In principle, there is no upper limit to the wattage. Alternative or additional external light sources can be used. It is important that the reference texture can be easily captured with the cutting head imaging device.

[0099] The problem solution has been described above based on a computer-implemented method. The features, advantages or alternative embodiments mentioned here can also be applied to other claimed subject matters and vice versa. In other words, the claims of the invention (e.g., which relate to a computing unit, a laser cutting machine or a computer program (product)) can also be further developed to have the features described and / or claimed in connection with the method and vice versa. The corresponding functional features of the method are thus formed by the corresponding current modules of the system or product, in particular hardware modules or microprocessor modules, and vice versa. Generally, in computer science, software implementation and the corresponding hardware implementation (e.g., as an embedded system) are equivalent. Thus, for example, the method step for "storing" data can be carried out using a memory unit and the corresponding instructions for writing data to the memory. To avoid redundancy, the device is not explicitly described here, although it can also be used in alternative embodiments described in connection with the method. Therefore, the preferred embodiments of the invention in connection with the method are not explicitly repeated for the device.

[0100] On the other hand, the above object is achieved by a computing unit for carrying out the above method. The computing unit is used to control a laser cutting machine and to calculate the contour deviation that may occur when machining a workpiece with the processing laser beam of the laser cutting machine. The computing unit has:

[0101] - a reading interface for reading a cutting plan that specifies a target path for the processing head of the laser processing machine;

[0102] - A reference texture definition module, which is used to define a reference texture or to read a reference texture from a cutting plan; the reference texture definition module can be designed as or include a human-machine interface (HMI) as an input interface, and an input is detected via this human-machine interface to determine the reference texture. Alternatively, a "ready" reference texture can be read, for example, from a memory. The reference texture definition module can alternatively or additionally be designed as a local computing unit, which dynamically and / or specifically calculates a reference texture for a target path (for example, selects a larger reference texture in the case of a large cut width);

[0103] - Wherein, the computing unit is designed to issue a first instruction to cause the application of the laser cutting head to apply the reference texture on the workpiece at least at selected positions along the target path;

[0104] - Wherein, the computing unit is further designed to issue a second instruction to cause the image capture operation of the laser cutting head to capture at least one image at at least one selected position along the target path, in which at least a part of the applied reference texture is imaged by means of an optical capture device arranged on the laser cutting head;

[0105] - Wherein, the computing unit includes a reconstructor, which is designed to reconstruct at least one virtual reconstructed image based on control values calculated from the target path and based on a multi-defined reference texture;

[0106] - Wherein, the computing unit further includes an image processing device, which is designed to compare the at least one captured image with the reconstructed virtual reconstructed image to determine a displacement vector between associated pixels;

[0107] - An output interface, which is designed to output a contour deviation calculated based on the determined displacement vector.

[0108] In another aspect, the present invention relates to a laser cutting machine including such a computing unit.

[0109] In another aspect, the present invention relates to a laser cutting machine for performing the above method.

[0110] In another aspect, the present invention relates to a computer program, wherein the computer program can be loaded into a memory unit of a computer and includes program code portions so that when the computer program is executed in the computer, the computer executes a method for determining a path deviation for controlling a laser cutting machine.

[0111] On the other hand, the present invention relates to a computer program product including the computer program as described above, which is designed to execute the method as described above. The computer program can also be stored on a computer-readable medium.

[0112] In the following detailed description of the drawings, non-limiting exemplary embodiments with their features and other advantages are discussed with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] Figure 1 Various processes of the method according to a preferred embodiment of the present invention are shown on a time axis;

[0114] Figure 2 A schematic diagram showing a drive system for controlling a laser cutting machine and its components is shown;

[0115] Figure 3 A schematic diagram showing the calculation of a control instruction for controlling the drive system based on a determined contour deviation is shown;

[0116] Figure 4 A block diagram of a calculation unit for calculating a contour deviation for controlling a laser cutting machine by means of a control instruction with a correction instruction is shown;

[0117] Figure 5 A flowchart of a method for calculating a contour deviation in different embodiments is shown;

[0118] Figure 6 A schematic representation of a laser cutting head is shown;

[0119] Figure 7 A schematic representation of a target path and an actual path is shown;

[0120] Figure 8a An example of a virtual reconstruction image is shown; and

[0121] Figure 8b An example of an actually captured image at the same position as in Figure 8a is shown;

[0122] Figure 9a An example of a virtual reconstruction image is shown; and

[0123] Figure 9b An example of an actually captured image at the same position as in Figure 9a is shown;

[0124] Figure 10a An example for comparing a captured image and a virtual reconstruction image is shown; and

[0125] Figure 10bYes Figure 10a An enlarged view of the midpoint of the image shown in;

[0126] Figure 11a Shows a schematic representation of a captured image at a corner of a target path;

[0127] Figure 11b Shows at the same position as in Figure 11a A schematic representation of a virtual reconstructed image; and

[0128] Figure 11c Shows a schematic graphical representation of the result of an image processing device (BV) for calculating a displacement vector;

[0129] Figure 12a Shows an example of a reference texture; and

[0130] Figure 12b Shows the reference texture from applied to a workpiece Figure 12a ;

[0131] Figure 13 Shows an exemplary embodiment of a first method; and

[0132] Figure 14 Shows an exemplary embodiment of a second method;

[0133] Figure 15 Shows a front view of a laser cutting machine;

[0134] Figure 16 Shows a representation of a laser cutting system having a cutting table and a cutting head;

[0135] Figure 17 Shows a machine-driven cascade control circuit using an example of the X-axis;

[0136] Figure 18 Shows an overview of the axis system of a laser cutting machine; and

[0137] Figures 19a to 19d Shows a representation of a virtual reconstructed image and an associated image captured by a camera device.

[0138] Detailed description of exemplary embodiments with reference to the accompanying drawings

[0139] The present invention relates to the control of a laser cutting machine L to compensate for a calculated path deviation or profile deviation caused by the inertia and / or elasticity of the moving mass of the components of the laser cutting machine L involved in the cutting process.

[0140] The profile deviation can be determined even before a production cutting process is carried out (i.e., before cutting a profile in a workpiece according to a cutting plan).

[0141] In order to determine a possible path deviation of an actual path (such as traversed by a cutting head) from a target path (according to specifications from a cutting plan), it is proposed to use a cutting head with a camera device and to determine the path deviation (in particular the path deviation in the case of corners) during a calibration process in order to calculate appropriate correction instructions, and then to apply these instructions during the (subsequent) production machining of the component, thereby reducing the path deviation and / or reducing the time per component in the case where the path deviation remains constant.

[0142] In a first embodiment of the invention, the following steps are provided (Method 1, also see Figure 13 ; see below):

[0143] 1. Determine the target path. The geometry located on the reference texture means the target path.

[0144] 2. Application run: Define a reference texture (e.g., a series of numbers) and apply (engrave) it onto the metal sheet along the target path using the processing laser. The machine axes move slowly, so negligible inaccuracies in tool positioning can be expected. No special metal sheet is required. For example, the metal sheet to be machined next can be used directly.

[0145] 3. Image capture run: Traverse the target path at high speed or production speed (without cutting), and use the camera device to record frames (Image A) at points of interest. When doing so, the encoder values are stored at position A during the recording of Image A. In order to optimize the recording by the camera device, the illumination laser can also be switched on synchronously with the image recording.

[0146] 4. Image processing: Comparison (matching) between a virtual target image (Image A') and the recorded actual image (Image A), which virtual target image can be determined using patterns known to the machine controller and precise encoder values.

[0147] 5. Calculate the contour deviation (target - actual), i.e., determine the displacement vector (Dx, Dy) between the virtual reconstructed image (Image A') and the actually recorded actual image (Image A).

[0148] 6. Compensate for the contour deviation by adjusting the target trajectory (or target geometry) using correction instructions.

[0149] 7. Perform production cutting using control instructions that implement the correction instructions.

[0150] In the first method, in step 4 (image comparison), the corresponding image midpoints of the virtual reconstructed image and the corresponding image captured using the camera device are compared.

[0151] In the second embodiment of the present invention, contrary to Method 1 above, engraving is applied at a high (production-related) speed (application run) representing the actual curve. In a second step, the actual curve (image capture run) is photographed at a low speed at the points of interest along the target curve using a cutting head camera device. The comparison of the target curve and the actual curve provides the sought-after displacement vector (Dx, Dy) between the target curve and the actual curve.

[0152] Method 2 (see also Figure 14 ; see below) comprises the following steps:

[0153] 1. Determine the target path, typically having corners or small radii.

[0154] 2. Application run: Define a reference texture, which can also be engraved on the metal sheet at a high axial advance. Most of the time this is simply a (real or virtual) line. Using the processing laser, the reference texture is applied (especially engraved) on the metal sheet along the target path as much as possible. The machine axes move quickly or at production speed or in the case of high dynamic values, so inaccuracies in tool positioning must be expected, especially at the corners. No special metal sheet is required. For example, the metal sheet to be processed next can be used directly.

[0155] 3. Image capture run: Cross the target path at a low speed or remain stationary at the target points of interest, and record a frame (Image A) using a camera device. The encoder value at position A during the recording of Frame A is known. To optimize the camera device recording, the illumination laser can also be switched on synchronously with the image recording.

[0156] 4. Comparison (matching) between the virtual reconstructed image (Image A') and the recorded actual image (Image A), which is known from the exact encoder values.

[0157] 5. Calculate the contour deviation, i.e., determine the displacement vector (Dx, Dy) between the virtual target image (Image A') and the actually recorded actual image (Image A).

[0158] 6. Compensate for the contour deviation by adjusting the target trajectory (or target geometry).

[0159] 7. Production cutting

[0160] Contrary to Method 1, Method 2 cannot compare the midpoints of Image A and Image A' to determine the displacement vector. Because the difference between Image A and Image A' lies only in the path trajectory between the target image and the actual image. Therefore, the displacement vector is not easily determined. It is not very easy to determine which point on the actual path corresponds to the midpoint of Image A'. However, in a first approximation, it can be assumed that the displacement vector can be assumed to be perpendicular to the actual path.

[0161] In a timeline view with a horizontal time axis t, Figure 1 it is shown that several runs are performed using the cutting head SK to determine the contour deviation ka: First, an application run is performed to apply the reference texture RT to the workpiece W; this can be done by engraving the reference texture RT onto the workpiece along the target path. Subsequently, an image capture run is performed for capturing an image b, which depicts the area of the tool center point (TCP) on the workpiece. The optical capture device can be designed in the form of a camera device arranged in the cutting head. Subsequently, control instructions are calculated, which contain correction instructions in order to compensate for the contour deviation determined previously by means of an image comparison between the actual captured image and the virtual reconstructed image during the image capture run. Then, the calculated control instructions can be used and thus the contour error caused by mass inertia and / or elasticity can be compensated, to perform a production run for cutting the part according to the cutting plan. During the application run, the laser can be used for engraving; however, it is deactivated for cutting. The laser is also deactivated during the image capture run.

[0162] Figure 2 A schematic representation of the data sets and intermediate results related to this method is shown. The cutting plan sp is read by an entity via an interface or made available in some other way. The cutting plan sp is transmitted to a controller, in particular a CNC (computer numerical control) controller CNC, which calculates control values sw according to the cutting plan sp. The control values sw are sent to a drive system A of the components for moving the laser cutting head SK. The drive system A typically includes three motors in order to move at least one component of the cutting head SK along three spatial axes (X-axis, Y-axis, and Z-axis). A first control value sw1 for driving a first motor in the X-axis direction can be output, a second control value sw2 for driving a second motor in the Y-axis direction can be output, and a third control value sw3 for driving a third motor in the Z-axis direction can be output. The motors are used for the direct or indirect movement of the cutting head SK. Preferably, an optical capture device, for example in the form of a camera device K, is arranged coaxially on the cutting head SK. The camera device K is used for capturing an image of the workpiece W in the area of the tool center point TCP. The workpiece W can be, for example, another flat workpiece or a metal sheet located on a worktable T.

[0163] Figure 3Shows a data set processed by a computing unit RE according to an advantageous embodiment of the present invention. The cutting plan sp and the control value sw are read. The computing unit RE can determine the contour deviation ka at least based on these values. The determined contour deviation ka can be output on the user interface, in particular before calculating the control instruction sa. The control instruction sa, which includes a correction instruction ki, can be calculated by the computing unit RE in particular according to the determined contour deviation ka. The correction instruction ki is used to compensate for the determined contour deviation ka, which is caused by the elasticity or mass inertia of the moving part. The control instruction sa is sent to the drive system A for control.

[0164] Figure 4 Is a block diagram of the computing unit RE. The computing unit RE includes an input interface ES through which the cutting plan sp can be read. The control value sw can be determined according to the cutting plan sp. This can be done on the controller CNC. The computing unit RE also includes a reference texture definition module RDM. The reference texture definition module RDM is configured to define a reference texture RT (in particular via an input on the human-machine interface / HMI) or read a predefined reference texture RT (for example from an external database). The computing unit RE also includes a reconstructor R. The reconstructor R is configured to generate or reconstruct a virtual reconstructed image v based on the control value sw and the defined reference text RT. The computing unit RE also has an image processing device BV, which can be implemented as, for example, an image processing algorithm and is intended to compare the image b actually captured by the camera device K with the virtual reconstructed image v reconstructed by the reconstructor R. For this purpose, the image processing algorithm includes a reference device so that the actual image b and the virtual image v can be assigned to each other. The reference device can act based on the control value sw. The assignment of the reference texture and the control value is unique. Now, the virtual image can be extracted from the cutting plan for each time point t. See in this regard Figures 19a to 19d . The calculation of the contour deviation (and, correspondingly, the displacement vector) can be carried out in Figure 10a and Figure 10b can be seen.

[0165] In particular, the displacement vector vv is calculated, which represents the contour deviation between the actually traveled path and the expected target path (according to the cutting plan sp). Therefore, the contour deviation ka can be determined or calculated according to the displacement vector vv. The contour deviation ka can be output via the output interface AS.

[0166] As described above, the calculated contour deviation ka can also be used to calculate the control instruction sa, which includes a correction instruction ki, in order to compensate for the contour error. The calculated control instruction sa is used to control the drive system A in a way that corrects for mass inertia.

[0167] The computing unit RE exchanges data with the electronic controller ST for the cutting head SK. The computing unit RE sends a first instruction l1 to the electronic controller ST to trigger the application run of the laser cutting head SK. The computing unit RE sends a second instruction l2 to the electronic controller ST to indicate the image capture run of the laser cutting head SK. In addition, the image b captured by the imaging device K is sent to the computing unit RE via the interface of the electronic controller ST. Optionally, an illumination unit B can be provided for illuminating the processing area. In particular, the captured image b is sent to the image processing device BV, which is then designed to compare the captured image b with the virtual reconstructed image v in order to determine the displacement vector vv.

[0168] Figure 5 is a flow chart of a method for determining the contour deviation ka, which is used to control the laser cutting head SK in a way that compensates for the contour deviation. After the start of the method, in step a, the cutting plan sp is read, in which the target path is specified. In step b, the reference texture RT is defined. This can be done manually via a man-machine interface or the reference texture RT can be read via an interface from an external data memory. In a first embodiment, the reference texture RT is designed as a graphic pattern, in particular a combination of numbers and / or letters. In a second embodiment, the reference texture RT can be linear and sometimes corresponds to the target path. In a preferred development of the invention, the reference texture RT can be defined as a function of the target path to be cut. For example, the height of the reference texture RT can be adapted to the nozzle width. In step c, an application run is performed to apply the reference texture RT to the workpiece W along the target path and in particular to engrave the reference texture RT into the workpiece W. In step d, an image capture run using the imaging device K is performed. In step e, the virtual reconstructed image v is reconstructed. In step f, the image processing device BV is used to determine the match between the virtual reconstructed image v and the captured image b at the same matching position in order to derive the displacement vector vv therefrom. The reference between the image and the virtual reconstructed image v is via the control value sw. The control value is time-based. At any time t, the control values (x_d(t) and y_d(t)) are known. In order to be able to determine / reconstruct the virtual image, the position on the target path where the image is recorded is required. This enables the calculation of the comparison between the virtual image and the actual recorded image.

[0169] In step g, the contour deviation ka is calculated based on the displacement vector vv and output. Thereafter, the method can end. However, in an advantageous embodiment, step h follows, in which the control instruction sa is calculated based on the calculated contour deviation ka in order to control the drive system A using the correction instruction ki to compensate for the contour deviation ka.

[0170] After these steps are completed, the improved system can be used for production cutting. In this case, the laser system is preferably calibrated relative to the various mechanical components of the laser system.

[0171] Figure 6 The cutting head SK of a laser processing machine is shown, which has an adapted camera device K, which has a field of view (FoV) that ideally observes the process coaxially with respect to the processing laser beam. With this arrangement of the camera device K, the processing area or cutting area is continuously tracked, which makes it possible to detect any contour deviations. To further optimize process monitoring, the coaxial process illumination 3 (with the illumination laser beam shown by a dashed line) is adjusted, which illuminates the process position 8 on the workpiece W. The optical deflection element 5 and / or the lens 7 are arranged in the beam path 12 of the processing laser beam. The laser source 4 can focus the processing laser beam onto the workpiece W through suitable optical elements (such as the optical lens 7).

[0172] To determine possible path deviations, it is proposed to use the above-mentioned cutting head SK during the calibration process to determine path deviations (especially path deviations at corners) in order to calculate the corresponding correction instructions ki, and then apply these instructions to the production processing of the component, and during the production processing of the component, this reduces the path deviations and / or reduces the time for each component in the case where the path deviations remain unchanged.

[0173] As shown schematically in Figure 7 contour deviations occur especially at corners or in the case of small radii. The target path is shown by a dashed line in Figure 7 and the cutting direction is marked by an arrow. Depending on the speed (the advancement of the cutting head), the actually traveled path, i.e., the actual path (shown by a solid line in Figure 7 ) deviates from the target path SB. Especially at high speeds and / or during acceleration, the actual path actually traversed by the cutting head SK will deviate from the target path. At corners, the actual path will usually exceed the target path.

[0174] The desired contour deviations can depend on the dynamics. The higher the selected axis acceleration and / or speed, the greater the expected deviation.

[0175] To avoid this, an automatically calculated adjustment is made based on the calculated correction instructions ki.

[0176] Figure 8a A virtual reconstructed image v as image A' is shown, and Figure 8b an image b (actual) captured using the camera device K (real) as image A is shown. These two images v, b are fed to the image processing device BV for image matching.

[0177] Figure 9a shows the virtual reconstructed image v as the image A', and Figure 9b shows the actually captured image b by the imaging device K as the image A. In the image A'( Figure 9a ), for illustration purposes, the target path (labeled here with reference numeral 21) and the point 23 in the image are shown. In the actual image A( Figure 9b ), the point in the reconstructed image is marked, and the point in the image is marked with reference numeral 24. The target path and the point in the image are not part of the image and are added here only for better understanding.

[0178] The assignment of the reference texture and the control value is unique. Now, the virtual image can be extracted according to the cutting plan for each time point t (see below in this regard Figures 19a to 19d ). The calculation of the contour deviation (and, correspondingly, the calculation of the displacement vector) can be seen in Figure 10a and Figure 10b .

[0179] Figure 10a Shows the matching or image comparison of the two images, in the form of superimposing the real image on the virtual reconstructed image using the corresponding points 23, 24 in the image (see Figure 9). Figure 10b Shows the matching representation from Figure 10a in an enlarged view. Figure 10b The enlarged details around the points 23, 24 shown in Figure 10b show that the points in the image do not completely coincide. The displacement vector vv is labeled with reference numeral 22 in

[0180] Figure 11a Shows a schematic diagram of the image recorded by the imaging device K, where the actual path is shown as a dashed line, and the point in the image is marked as a cross. Figure 11b Shows the virtual reconstructed image of the image A' with the target path 21 and the point in the image, which is also marked as a cross. Figure 11c Schematically shows the superimposed image for the image comparison of the image processing device BV. The displacement vector v is labeled with reference numeral 22 here.

[0181] Figure 12a is an example of a series of digital reference textures RT in the virtual reconstructed image, and Figure 12b shows the corresponding actually captured image, where the applied engraving of the reference texture RT can be seen at the same position.

[0182] Figure 13An example of how Method 1 is executed is shown (first embodiment of the present invention; see above). A tuple of images from a virtual reconstructed image (Image A') and an image captured by a camera device (Image A) is shown on the left - hand side, and an image comparison (mapping) is shown on the right - hand side. In the example above, there is a relatively good fit / match. In the example below, there is a poor match and thus a high contour deviation.

[0183] Figure 14 An example of the application or implementation of Method 2 is shown (second embodiment of the present invention; see above). The reference texture RT is applied precisely along the target path here, and in particular, it is applied precisely on the target path, and is identified by reference numeral 21, and the displacement vector vv is identified by reference numeral 22. The contour deviation is determined based on the displacement vector vv, which is part of a calibration control instruction sa having a correction instruction ki.

[0184] Figure 15 A front view of a laser cutting machine L is shown in a schematic representation. The laser cutting machine L has a cutting grid (only shown), a cutting head SK, a processing laser beam 17, and a tool center point TCP. A workpiece W to be processed is positioned on the cutting grid. Reference numeral 16 represents a bridge (Y - axis), and reference numeral 18 represents the Z - axis.

[0185] Figure 16 It is a representation of a laser cutting machine L, which has a cutting grid 14, a workpiece W, a cutting head SK arranged on a bridge 16, a processing laser beam 17, and a tool center point TCP.

[0186] Figure 17 A cascaded control circuit of a machine driver for an example using the X - axis is schematically shown.

[0187] Figure 18 It is an overview of an axis system.

[0188] Figures 19a to 19d A representation of a virtual reconstructed image and an image captured using a camera device is shown. The reference texture RT is applied on or along the target path. In Figure 19a As an example, the virtual reconstructed image at time t1 is shown in the form of a frame. Figure 19b An image captured by the camera device at this time t1 is shown. Figure 19c and Figure 19d shows Figure 19a and Figure 19b An enlarged view of the images shown in

[0189] Optionally, steps c to g of the above method can be performed at predefined specific locations in the working space and / or for all or selected workpieces and / or parts to be cut, in order to reflect and take into account the position dependence of the profile deviation determination. If the target path and the reference texture RT are in an off-center position in the laser working space (e.g., at one end of the workbench, such that some axes are fully extended), then different profile deviations occur compared to the case where the position is at the center of the working space and in the middle of the working space. Therefore, the application run and the image capture run can be performed at different positions in the working space. Certain positions can be preconfigured automatically for this purpose and displayed on the HMI, and then the user can accept or reject these positions.

[0190] Finally, it should be noted that the description and the exemplary embodiments of the present invention should not be construed as a limitation to a specific physical implementation of the present invention. All features explained and illustrated in connection with the various embodiments of the present invention can be provided in different combinations in the subject matter according to the present invention to achieve its advantageous effects simultaneously.

[0191] The protection scope of the present invention is given by the claims and is not limited by the features shown in the description or in the drawings.

[0192] It is particularly obvious for those skilled in the art that the present invention can be used not only for a laser processing machine with a coaxial camera device, but also for those laser processing machines with different camera device arrangements and adapted to capture the reference texture RT during the image capture run. In addition, the components of the computing unit RE can be implemented or executed in a distributed manner on multiple physical products. For example, the method can be performed entirely on the laser processing machine, or resource-intensive calculations such as the reconstruction of the reconstructed image v can also be outsourced to different hardware entities. For example, the reconstruction in step e and / or the application of the image processing device in step f can be outsourced to a central server that performs the calculations, and then only the calculated displacement vector vv is returned to the laser processing machine.

Claims

1. A method for calculating a contour deviation (ka) for controlling a laser cutting machine (L), which contour deviation can occur when machining a workpiece (W) with a machining laser beam of the laser cutting machine (L), the method having the following method steps: a) Reading a cutting plan (sp), which cutting plan (sp) specifies a target path for a laser cutting head (SK) of the laser cutting machine (L); b) Define a reference texture (RT) or read a reference texture (RT) from the cutting plan (sp), wherein, The reference texture (RT) is an engraving; c) Performing an application run of the laser cutting head (SK) to apply the reference texture (RT) to the workpiece (W) at least at selected positions along the target path; d) Performing an image capture run of the laser cutting head (SK) to capture at least one image (b) at at least one selected position along the target path, in which at least a part of the applied reference texture (RT) is imaged by means of an optical capture device (K) arranged on the laser cutting head (SK); e) Reconstructing at least one virtual reconstructed image (v) based on a control value (sw) calculated from the target path and based on the defined reference texture (RT); f) Using an image processing device (BV) to compare the at least one captured image (b) and the reconstructed virtual reconstructed image (v) to determine a displacement vector (vv) between associated pixels in each case; g) Outputting the contour deviation (ka) calculated based on the determined displacement vector (vv).

2. The method according to claim 1, comprising: h) Calculating and executing a control instruction (sa) with a correction instruction (kl) to compensate for the calculated contour deviation (ka).

3. The method according to claim 1 or 2, wherein The reference texture (RT) is applied with a reduced dynamic value that is lower than the production dynamic value during the application run, and wherein, in the case of laser deactivation, the reference texture (RT) along the target path is traversed with the production dynamic value during the image capture run, and the at least one image (b) is captured during the course of step d).

4. The method according to claim 1 or 2, wherein The reference texture is applied with a production dynamic value corresponding to the production dynamic value used in production machining, and wherein, in the case of laser deactivation, the target path is traversed with a reduced dynamic value during the image capture run, and the at least one image is captured during the course of step d).

5. The method according to claim 1 or 2, wherein The traversal on or along the target path is performed with a machining laser beam of the laser cutting machine (L), which machining laser beam is deactivated for cutting.

6. The method according to claim 1 or 2, wherein The comparison in step f) takes place at the midpoint positions of the respective images (b) and (v).

7. The method according to claim 1 or 2, wherein The reference texture (RT) is a texture applied to a carrier object, wherein the carrier object is fixedly arranged in a carrier area of the laser cutting machine (L) for the workpiece (W) and is position-calibrated there.

8. The method according to claim 1 or 2, wherein The optical capture device includes at least one imaging device (K), which is arranged in the laser cutting head (SK), on the laser cutting head (SK), or on the drive system (A) of the laser cutting head (SK).

9. The method according to claim 1 or 2, wherein The actual path is extracted from the at least one captured image (b).

10. The method according to claim 1 or 2, wherein, The method is performed before or during the production cutting process.

11. The method according to claim 1 or 2, wherein, The at least one image (b) is captured by activating the illumination device (B).

12. A computing unit (RE) for performing the method according to claims 1 to 11, having: - A reading interface (ES) for reading a cutting plan (sp) that specifies a target path for the laser cutting head (SK) of the laser cutting machine (L); - A reference texture definition module (RDM) for defining a reference texture (RT) or for reading the reference texture (RT) from the cutting plan (sp), where the reference texture (RT) is an engraving; - wherein the computing unit (RE) is designed to issue a first instruction (l1) to cause the application of the laser cutting head (SK) to apply the reference texture (RT) on the workpiece (W) at least at selected positions along the target path; - wherein the computing unit (RE) is further designed to issue a second instruction (l2) to cause the image capture operation of the laser cutting head (SK) to capture at least one image (b) at at least one selected position along the target path, in which at least a part of the applied reference texture (RT) is imaged by means of an optical capture device (K) arranged on the laser cutting head (SK); - A reconstructor (R) designed to reconstruct at least one virtual reconstructed image (v) based on control values (sw) calculated from the target path and based on the defined reference texture (RT); - An image processing device (BV) designed to compare the at least one captured image (b) with the reconstructed virtual reconstructed image (v) to determine a displacement vector (vv) between the associated pixels in each case; - An output interface (AS) designed to output a contour deviation (ka) calculated based on the determined displacement vector (vv).

13. A laser cutting machine having the computing unit according to claim 12.

14. The laser cutting machine according to claim 13, further comprising a calibration module configured to calculate and execute a control instruction (sa) with a correction instruction (kl) to compensate for the calculated contour deviation (ka).

15. A computer program product comprising a computer program, wherein, The computer program can be loaded into the memory unit of a computer and contains program code portions to cause the computer to perform the method according to any one of claims 1 to 11 for determining a path deviation for controlling a laser cutting machine (L) when the computer program is executed in the computer.

16. The computer program product according to claim 15, wherein, The computer program can be loaded into the computing unit (RE).

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