Laser machining method for machining texture or cavity on workpiece

Abstract

To provide a laser machining method for engraving a texture or a cavity on a workpiece by a machine tool with improved accuracy of the machined part.SOLUTION: The method according to the present invention comprises the steps of: before machining a machining path based on geometry of a workpiece and a texture or a cavity, receiving an initial machining path by a control unit for ablating the workpiece; and ablating the workpiece layer by layer. The machining path defines a sequence of relative positions of a laser head in relation to the workpiece. Calculating the initial machining path includes the steps of: calculating a plurality of machining layers to be machined in succession; and calculating for each layer a plurality of laser tool paths defining positions to be ablated by a laser beam.SELECTED DRAWING: Figure 9c

Description

[Technical Field]

[0001] The present invention relates to a laser processing method for processing a texture or a cavity on a workpiece, and also to a laser machine tool for engraving a texture or a cavity on a workpiece.

[0002] Background technology Laser ablation is widely used to engrave textures onto the surface of physical objects by sublimating material on the surface of the object. The principles used to generate desired structures or textures on the surface of an object are described, for example, in DE 4209933 A1. This process can be considered "inverse stereolithography," i.e., instead of building up a coating to build up, material is sublimated layer by layer by laser processing, and is also described in further publications of EP 1189724 A1.

[0003] Machine tools for processing objects by laser ablation are also well known. European Patent Application No. 2301706 describes, for example, possible technical designs of such devices.

[0004] The complete texturing of an object's surface consists of ablating multiple machining layers, with a set of positions that the machining head must reach for each layer in order to machine a patch for each position of the layer involved. The software always takes into account the actual 3D shape of the object's surface and the texture that is applied to it.

[0005] Therefore, before machining, a machining file containing machining data must be generated based on the geometric shape of the object and the texture or cavity to be machined thereon. The machining file defines the locations where material should be removed, so the machine tool's control unit can read the machining file and control the movement of the laser beam emitted by the laser head. The generated machining file essentially consists of a machining path, which includes a series of positions that the laser machining head must occupy relative to the object and, for each position, a series of ablation operations corresponding to the scans that the laser beam must perform from this position. This directly affects both the machining time and the finish quality of the texture machining.

[0006] Creating a processing file involves modeling the object's geometry and analyzing the image file that defines the texture. The processing file must be generated taking into account the object's texture, image, and geometry. Therefore, the object is typically modeled numerically, usually by triangulation, to generate a 3D modeling file; for example, the object-geometry data is a mesh file. Furthermore, because laser beams can only reach a limited depth, it is not possible to engrave texture or cavities into an object all at once. Therefore, processing is performed layer by layer. During processing file preparation, the object is modeled and the model is divided into multiple so-called processing layers.

[0007] The texture defined by the image file is processed by the software and applied to the mesh file of the object's modeled 3D surface. The gradient image representing the 3D texture is composed of a large number of individual pixels, whereby the depth of a location in the texture is defined as the corresponding gradient of the corresponding pixel. The brighter the pixel, the shallower the texture at that particular point. The darker the pixel, the deeper the texture at that particular location. Preferably, the number of gradients corresponds to the number of layers being applied. The gradient image thus defines, for each layer, whether a particular point needs to be ablated during the processing of each layer. If a pixel in the gradient image is equal to or darker than the gradient of a particular processed layer, the corresponding point needs to be ablated. If a pixel in the gradient image is lighter than the gradient of that particular layer, the corresponding point should not be ablated. Thus, white pixels or regions represent points or regions of the textured surface with no depth. This means that the texture point at that location corresponds to the raw surface and no laser ablation is required. Based on the mapping of the texture on the modeled object, a so-called laser tool path is determined for each processing layer.

[0008] If a cavity needs to be machined, a CAD file can be prepared to model the cavity. The volume to be ablated to form the cavity can be calculated based on the CAD file. Furthermore, the machining layers can be calculated based on the CAD file. In laser machining, the removal rate of the laser parameter must be accurately known to achieve the correct depth of the ablated area. If the removal rate is not accurate enough or the removal is not uniform, the machined bottom cavity will be inaccurate. One problem that often arises in laser machining is inaccuracy of the depth. The machining depth deviates from the target depth. Another problem is the flatness of the machined surface. In particular, because machining is performed layer by layer, inaccuracies already occurring in one machined layer can accumulate in the next layer, causing even more inaccuracies.

[0009] Until now, machining files have been determined before machining and applied throughout the machining process without adjustments during machining, so there is no possibility to compensate during machining for inaccuracies in parts already machined at that location.

[0010] EP 3875206 discloses a processing system and a processing method, which includes a housing for accommodating an object, a processing device disposed within the housing for processing the object, a measurement device disposed within the housing for measuring the object processed by the processing device, and a control device for setting processing conditions using the measurement results of the object.

[0011] However, the measurement results of the object are not applied to improve the accuracy of the machining area.

[0012] Summary of the Invention It is an object of the present invention to provide a laser processing method for engraving a texture or cavity on a workpiece by a machine tool that improves the accuracy of the machined part.It is an object of the present invention to provide a laser processing method for engraving a texture or cavity on a workpiece by a machine tool that allows for real-time machining path adjustment.

[0013] According to the invention, these objects are achieved by the features of the independent claims. In addition, further advantageous embodiments emerge from the dependent claims and the description.

[0014] The present invention relates to a laser processing method for engraving a texture or cavity on a workpiece using a machine tool, particularly a five-axis laser machine tool. The laser machine tool includes a machine table for placing the workpiece and a laser head for emitting a laser beam onto the workpiece. The laser beam is guided by a laser galvanometer scanner integrated into the laser head to reach a predetermined position on the workpiece. The machine tool further includes a control unit configured to control the movement of the laser head and the laser galvanometer scanner.

[0015] The method includes receiving an initial machining path by a control unit for ablating the workpiece before machining the machining path based on the geometry and texture or cavities of the workpiece, and ablating the workpiece layer by layer. The machining path defines a sequence of relative positions of a laser head with respect to the workpiece. The step of calculating the initial machining path includes calculating multiple machining layers to be machined in succession and calculating multiple laser tool paths for each layer that define locations to be ablated by the laser beam.

[0016] The method further includes adjusting the machining path after machining at least one layer, the adjusting the machining path including: scanning a defined machining area on a surface of the workpiece with a measuring device to obtain machining depths at multiple positions on the machining area, comparing the measured machining depths with a defined target depth to determine a depth deviation at each measurement position, and at least partially recalculating the machining path based on the determined depth deviation.

[0017] The method further includes applying the recalculated processing path to ablate the remaining layers.

[0018] The present invention can be applied not only to fabricating a texture on a workpiece, but also to fabricating one or more cavities on a workpiece, the dimensions of which can be as small as a few μm. 3 From small cavities with volumes of several cm 3 For most applications, the mechanical cavities need to achieve high precision, for example within a few micrometers.

[0019] Before machining, a machining file is prepared to determine the machining path and the machining parameters to be applied to ablate the workpiece. Typically, the machining file is determined by a processing unit located outside the machine tool and transferred to a control unit of the machine tool. The control unit is configured to control the machine axes and the laser galvanometer scanner to direct the laser beam to ablate the workpiece layer by layer.

[0020] In known methods, the machining path is not adjustable throughout the entire machining process. That is, once a program describing the machining path is loaded into the control unit, the program is executed there. Therefore, there is no possibility of compensating or correcting any inaccuracies or even errors that occur in the workpiece being machined during machining. The object of the present invention is to provide the possibility of monitoring the machining process in real time and reacting accordingly. In particular, the quality of the machined part is monitored during machining, thereby allowing for real-time error correction. This allows for adaptive machining. This has the advantage that certain inaccuracies or errors that occur in earlier machining stages can be compensated or corrected during the remaining machining stages. In particular, geometric inaccuracies or geometric errors in the engraved surface can be detected already in early machining stages and corrected or compensated for in the remaining machining stages. Therefore, the actual machined surface is taken into account during subsequent machining stages, thereby improving the geometric accuracy of the engraved texture or cavity.

[0021] Laser ablation processing is performed in multiple process steps, in which the surface structure is processed layer by layer. The processing path therefore includes multiple processing layers to be processed successively. In each layer, an ablation area is determined. Furthermore, in each layer, multiple laser tool paths are determined, defining the locations where material should be removed. There are different laser processing types, for example, so-called vector laser processing and blasting. In vector laser processing, the ablated laser tool path includes multiple laser vectors. The laser vectors define the locations where the laser beam should be emitted. To ablate the corresponding area, the laser beam is emitted along the laser vectors, vector by vector, from one end of the vector to the other.

[0022] After machining one or more layers, machining path adjustments are made. Preferably, ablation is first stopped before machining path adjustments are made. The partially machined surface of the workpiece is scanned by a measuring device. It is possible to scan the entire surface or a defined area of ​​the surface.

[0023] Because the texture or cavity engraved on the workpiece is typically three-dimensional, the surface topology represents the spatial structure of the texture or cavity formed on the workpiece. A target surface topology is specified before machining. The target surface topology is associated with the texture or cavity. The measured surface topology, scanned by a measuring device, represents the intermediate state of the texture or cavity machined on the workpiece. The goal is to have a final machined part with a surface topology corresponding to the specified target surface topology. Therefore, the measured surface topology is compared with the target surface topology to determine whether the remaining machining can be performed by applying the initially determined machining path or whether modifications to the initially determined machining path are necessary for the remaining machining. Deviations between the measured surface topology and the target topology provide information about the geometric inaccuracies of the machined part at this machining stage. Because this is performed before removing the entire material as described, it is still possible to correct this inaccuracy during the remaining machining process by removing more or less material as originally designed. This is achieved by recalculating the machining path and applying the recalculated machining path to the remaining machining process.

[0024] The target surface topology defines target depths at different locations on the surface. The measurement unit is configured to measure the depth of the engraved texture or cavity at different locations on the surface to obtain the surface topology. The scanning allows for the acquisition of machined depth information for all scanned areas. This information may be analyzed to determine whether the machined depth corresponds to the specified target depth at each location on the surface. The measured depth is compared with the target depth at each location to determine a depth deviation. The depth deviation represents machining inaccuracies, particularly material removal at this stage, which provides input for correction.

[0025] In one variant, the step of recalculating the machining path comprises the steps of recalculating at least one machining layer and at least partially recalculating the laser tool path on this layer.

[0026] If the measured depth deviates from the target depth at one position on the machining area, it means that either too much or too little material was removed at this position. Therefore, to correct this error, each machining layer is recalculated so that the error can be compensated for in subsequent machining stages. Adapting a machining layer to the remaining machining is a sufficient way to correct inaccuracies that occurred during the previous machining process. How many layers must be adjusted depends on the depth deviation: the greater the depth deviation, the more layers must be adjusted. Furthermore, these laser tool paths on the machining layers are adjusted.

[0027] In one variation, if the depth deviation indicates underengraving, the machining path is recalculated by adding at least one machining layer to the remaining machining layers and recalculating the laser tool path on this layer. Underengraving occurs when the measured machining depth is smaller than the target depth at a location. Underengraving means that not as much material has been removed from the workpiece as targeted in this machining stage. If the measured surface topology at a location has a shallower depth than the target surface topology, this location is identified as underengraving. To compensate for the underengraving, more material must be removed during the remaining machining stages, and the machining tool path must be adapted accordingly. In particular, the machining layers must be recalculated by adding additional machining layers to the remaining machining layers. For example, a scan is performed after machining N machining layers. The remaining M machining layers are ablated. If underengraving occurs, L additional layers are added to the M machining layers so that material that should have been removed during the machining of the N layers but has not yet been removed can be ablated during the machining of these additional layers L. This means that the recalculated remaining layers will contain a total of M+L layers, rather than the M originally designed.

[0028] Advantageously, machining layers are added only to areas where engraving deficiencies are identified. To optimize machining efficiency, the additional L layers are added only to areas where engraving deficiencies are identified.

[0029] In another variant, if the depth deviation indicates over-engraving, the machining path is recalculated by at least partially removing the laser tool path on at least one machining layer. Over-engraving means that more material has been removed from the workpiece than desired during this machining stage. If the measured machining depth at a location is greater than the target depth, this location is identified as over-engraved. To compensate for the over-engraving, less material must be removed during the remaining machining, and the machining tool path must be adapted accordingly. This is achieved by removing the initially determined laser tool path on subsequent layers. The number of layers to be adapted depends on the depth deviation. In particular, the laser tool path for each machining area on at least one remaining machining layer must be removed. Removing a machining layer for each machining area may require recalculating the machining layers. For example, a scan is performed after machining N machining layers. The remaining M machining layers are ablated. If under-engraving occurs, L additional layers are removed from the M processed layers so that material that should not have been removed during the processing of the M layers but has already been removed is not ablated again during the processing of these additional L layers. This means that the recalculated layers for the over-engraving location will contain a total of M-L layers.

[0030] Preferably, the working layer is removed only from areas where over-engraving is identified.

[0031] In particular, under-engraving and over-engraving can occur in different surface areas, even at the same machining stage. The recalculated machining layers can be different for different surface areas. In under-engraving areas, the recalculated machining layers include M+L layers. In over-engraving areas, the recalculated machining layers include M-L layers. In other areas where no depth deviations are identified, the recalculated machining layers remain the same as before scanning.

[0032] The method allows the program to correct the remaining lines of the defined machining toolpath, taking into account any defects detected during the scan. If not enough material has been ablated, layers are added specifically to the ablation zone. If too much material has been ablated, the remaining machining lines on the already engraved zone are removed. The number of layers removed / added is calculated by the scan and depends on the ablation speed of the laser parameter, which indicates the depth per layer.

[0033] In an advantageous variant, the recalculation of the machining path is performed by modifying at least one machining layer, so that it is not necessary to recalculate all machining layers to complete the machining, which saves computing power and time.

[0034] In particular, if an engraving defect occurs, the step of recalculating the machining path includes the steps of copying at least one machining layer, removing the laser tool path to ablate the area where the engraving defect is not identified, and adding the modified machining layer to the remaining machining layers. By copying and modifying one already determined machining layer, the calculation time and power can be dramatically reduced. Therefore, the calculation can be performed by a processing unit integrated into the machine tool.

[0035] In some embodiments, determining the machining tool path includes defining, for each machining layer, a plurality of patches intended to be machined from a single position of the laser head, and adjusting the machining tool path includes recalculating the patches of at least one machining layer, each patch defining an area that can be ablated by maintaining the laser head in one position, thereby further optimizing machining time and quality of the machined part.

[0036] The frequency of machining path adjustment directly affects the geometric accuracy of the final part. The more frequently the machined surface is scanned and the machining path is adjusted, the higher the accuracy of the final part can be achieved. On the other hand, scanning is preferably performed during machining pauses, which increases the machining time. Therefore, the frequency of adjustment depends on machining priorities, including machining time and accuracy. In one variation, the machining tool path is adjusted after each machining layer is machined. If correction can be performed after each layer is machined, each machining error occurring during the machining of each layer can be immediately corrected, thereby maximizing the accuracy of the machined part.

[0037] In one variant, the adjustments to the machining tool path are made in an irregular manner, with the timing of the adjustments depending on the initial machining path, in particular the number of adjustments during machining of the latter part of a layer being greater than the number of adjustments during machining of the first part of a layer. This is a compromise between machining time and the precision of the machined part. The machining path depends on the shape of the texture or cavity. For example, some parts of the texture or cavity require high precision, while some parts of the texture or cavity require less precision. This method offers the possibility of achieving precision requirements without unnecessarily increasing machining time.

[0038] Preferably, the timing of adjusting the machining tool path is determined based on the geometry of the texture or the geometry of the cavity.

[0039] In particular, the timing of adjusting the machining tool path is determined based on the results of previous scans.

[0040] In a preferred variant, the scan is carried out after the last processing layer has been processed, which measurement allows, on the one hand, the possibility of correcting inaccuracies that occurred during the processing of the last layer, and, on the other hand, the quality of the final processed part.

[0041] Preferably, a scan is performed before machining, which allows obtaining an initial position of the workpiece surface. The workpiece is mounted on a machine table for machining. However, workpieces are not always perfect. The workpiece surface is not perfectly flat. This can lead to inaccurate measurement results from the scan. If the unmachined surface is scanned, these initial position errors can be compensated for later.

[0042] Advantageously, the machining depth is calculated relative to the top surface of the workpiece. For example, the Z position of the surface is measured and the Z position of the machining area is measured. The difference between these two positions gives information on the machined depth. This has the advantage that the measured depth is not affected by the positioning of the workpiece on the machine table or by unevenness of the workpiece surface.

[0043] In particular, the scanning is controlled by the control unit of the machine tool based on the machining path and / or a recalculated machining path, in particular only the area to be machined is scanned.

[0044] In an advantageous variant, cleaning is performed before scanning. To achieve a good scan of the surface, the part must be sufficiently clean. Dust from the ablated material often contaminates the surface or the cavity. The deeper and smaller the cavity, the more difficult it is to clean it from dust.

[0045] In one variant, a dust extraction system is applied for cleaning. Alternatively, a blower system is applied for cleaning. It is also possible to apply a gas or a fluid for cleaning.

[0046] In some embodiments, the laser source parameters are adapted based on the determined depth deviation, which can further optimize the processing. For example, the scan results can indicate which processing process has been performed, including roughing, semi-finishing, or finishing. Depending on the processing process, the laser source parameters can be adapted.

[0047] In one variant, multiple sets of laser source parameters are predefined. After scanning, one of the predefined sets of laser source parameters is selected according to the scanning results. To find ablation parameters that provide interesting results in productivity, many parameters of the laser source need to be adjusted. In many applications, a balance between ablation productivity and ablation quality needs to be achieved. Ablation productivity is defined, for example, by ablation depth per slice, μm / slice. Ablation quality is defined, for example, by surface roughness, S a During the machining process, according to the results of the surface scanning, the program can adapt itself, adapting not only the machining layer and laser tool path, but also the laser ablation parameters between different parameter set groups.

[0048] The present invention relates to a laser machine tool for engraving a texture or cavity into a workpiece, in particular a five-axis laser machine tool, which includes a machine table for placing the workpiece and a laser head for emitting a laser beam onto the workpiece, the laser beam being directed to reach a predetermined position on the workpiece by a laser galvanometer scanner integrated in the laser head, and the machine tool further includes a processing unit, a control unit, and a measuring device.

[0049] The processing unit is configured to determine a processing path including a series of relative positions of the laser head with respect to the workpiece before processing, calculate a plurality of processing layers intended to be processed successively, and calculate a plurality of laser tool paths for each processing layer defining positions to be ablated by the laser beam. The control unit is configured to apply the defined processing path for ablating the workpiece, and the workpiece is ablated layer by layer. The measuring device is configured to scan a defined area on the surface of the workpiece to obtain processing depths at a plurality of positions on the processing area. The control unit is further configured to compare a target depth with the measured depth to determine a depth deviation and recalculate the processing path based on the depth deviation.

[0050] In one variation, the measurement device is a mechanical sensor such as a contact touch probe. In another variation, the measurement device is an optical sensor such as a 3D camera, structured light sensor, focus variation sensor, laser sensor, interferometer, optical coherence tomography, etc.

[0051] In particular, the measuring device is a distance sensor, a depth sensor, in particular a confocal sensor.

[0052] Advantageously, the measuring device is a dot sensor, a line sensor or a field sensor.

[0053] Preferably, the measuring device is arranged on the machine head and controlled by the control unit, the measuring device is moved by a machine axis of the machine tool, and the machine axis is controlled by the control unit for controlling the movement of the laser beam, so that no additional control unit is required for controlling the measuring device.

[0054] In particular, the measuring device is mounted in the vicinity of an optical scanner used for processing, the measuring device being arranged at a distance between the sensor axis and the laser processing axis.

[0055] Alternatively, the measurement device can be positioned so that it can be aligned with the main beam path of the machine, meaning that movement of the measurement device is achieved by moving the optical laser scanner, thereby reducing scanning times by moving the measurement device with the optical axis rather than the mechanical axis.

[0056] It is possible to provide a dedicated sensor optical scanner that moves the measurement device to scan the surface.

[0057] A more detailed description of the principles briefly described above will now be given with reference to specific embodiments illustrated in the drawings. These drawings illustrate exemplary embodiments of the present disclosure and therefore should not be considered limiting of its scope. The principles of the present disclosure will be described and explained in detail using the accompanying drawings. [Brief explanation of the drawings]

[0058] [Figure 1] FIG. 1 is a diagram showing a laser machine tool. [Figure 2] FIG. 2 is a diagram showing a laser head of a laser machine tool. [Figure 3] FIG. 1 shows an image to be ablated on a workpiece. [Figure 4] FIG. 1 illustrates an ablation region on a processing layer and multiple laser tool paths. [Figure 5] FIG. 10 shows an example of one of the calculated machining layers with the corresponding laser tool path. [Figure 6] FIG. [Figure 7a] 1A and 1B show a theoretical workpiece before and after machining. [Figure 7b] 1A and 1B show a theoretical workpiece before and after machining. [Figure 8a] FIG. 1 illustrates state-of-the-art processing methods. [Figure 8b] FIG. 1 illustrates state-of-the-art processing methods. [Figure 9a]FIG. 10 illustrates how the machining path is adjusted according to the scanning results during machining. [Figure 9b] FIG. 10 illustrates how the machining path is adjusted according to the scanning results during machining. [Figure 9c] FIG. 10 illustrates how the machining path is adjusted according to the scanning results during machining. [Figure 10] FIG. 10 illustrates recalculation of the laser tool path. [Figure 11] FIG. 10 illustrates recalculation of the laser tool path. [Figure 12] FIG. 10 illustrates recalculation of the laser tool path. [Figure 13] FIG. 10 illustrates recalculation of the laser tool path. [Figure 14] FIG. 10 illustrates recalculation of the laser tool path. [Figure 15] FIG. 1 shows a schematic diagram of a machine tool having a measuring device; [Figure 16] FIG. 10 illustrates an example of measured depth of a machine region. [Figure 17] FIG. 1 shows a machine tool with a workpiece placed on the machine table of the machine tool. [Figure 18] FIG. 1 shows a machine tool with a workpiece placed on the machine table of the machine tool.

[0059] FIG. 1 shows a schematic diagram of an example of a laser machine tool 1, including a laser head 2. The laser head and the workpiece to be machined may be positioned relative to one another along three or five machine axes, which allow for the direction of the emitted laser beam and for the laser beam to be focused on the surface of a machined workpiece (not shown) placed in the machine. In the example shown in FIG. 1, the laser head can be displaced in three dimensions X, Y, and Z of a Cartesian reference coordinate system. Advantageously, the head can also be rotated around two rotation axes to further increase precision and flexibility. The laser head includes a device that can rotate around an axis, a laser source, an optical device, and a device commonly referred to as a galvanometer scanner.

[0060] Figure 2 shows a schematic diagram of the operation of a laser galvanometer scanner. A laser source 3 emits a laser beam 9, more specifically a pulsed laser beam. The laser beam 2 is reflected by a mirror 4, which allows the position of the projection point of the laser beam on the surface of the workpiece 5 to be defined according to the X and Y axes of a Cartesian reference coordinate system. An actuator 8 allows the angular position of the mirror 4 to be controlled. The laser beam also passes through a lens 6, commonly called an F-theta lens. This device therefore allows the point of impact of the laser beam with the surface 7 of the workpiece 5 to be defined in a plane located within the focal range under consideration. In existing machines, focal lengths of up to 430 mm are common. EP 2301706 describes other details of the configuration of the laser head 2.

[0061] FIG. 3 shows an example of the texture that needs to be applied by laser ablation to the surface of a workpiece defined by a grayscale image.

[0062] Therefore, a set of machining layers is typically calculated from a 3D modeling file and a gradient texture file representing the workpiece shape. For each machining layer, multiple laser tool paths are calculated to define where the laser beam should be directed to remove material on the corresponding layer.

[0063] To process the workpiece surface, the laser beam constantly moves along a predetermined parallel laser vector 41 over the indicated ablation area 31, jumping to the next position at the boundary of the area, as shown in Figure 4. Figure 4 shows an example where the entire area needs to be ablated.

[0064] Figure 5 shows an example of a calculated machining layer 21 with the corresponding laser tool path 42. The areas 34 covered by the laser vector are ablation areas, i.e. material in these areas must be removed. The white areas are non-ablation areas 32, i.e. no material must be ablated in these areas.

[0065] FIG. 6 illustrates multiple defined machining layers. This is a simplified diagram, and the workpiece is therefore shown as a cube with a rectangular shape and flat surfaces. However, the method of the present invention is not limited to machining workpieces of such simple shapes. It may also be applied to machine tool workpieces of any shape, including curved surfaces. A model of a workpiece 10 is divided into, for example, 30 machining layers L1-L30. Scanning of the machining surface may be performed regularly or irregularly. In a regular method, scanning is performed after machining a set number of machining layers, for example, 10 layers. Machining begins with ablation of the first layer L1 and then continues with ablation of successive layers L2-L10. After machining the first 10 layers, the machined surface is scanned by a measuring device. The machining path is adjusted based on the measured surface shape. Machining then continues until another 10 layers have been machined using the adjusted machining path. A scan of the machined surface is then performed again, and the machining tool path is adjusted again. Irregular scanning: For example, scanning is performed after processing the 5th, 7th, 11th, 20th, and 28th layers.

[0066] 7a and 7b show an example of theoretically machining a cavity 20 on a workpiece 5. FIG. 7a shows the workpiece before machining, and FIG. 7b shows the machined workpiece. According to this specification, the machined surface in the cavity 21 should be flat, as shown in FIG. 7b. However, in reality, the machined surface is not flat due to limitations in machining accuracy.

[0067] Figures 8a and 8b show the state-of-the-art for machining such cavities. The workpiece is machined layer by layer from L1 to Lfinal. During machining, due to the interaction of the laser with the material, not all locations on one machining layer are ablated to the same depth, resulting in an uneven machined surface 22 within the cavity. By applying the method of the present invention, such inaccuracies can be corrected even during machining.

[0068] Figures 9a, 9b, 9c, and 9d show how the machining path is adjusted according to the scanning results during machining. For clarity, the drawings are simplified. For example, the workpiece is shown in a two-dimensional view, and the layers are represented by lines. Each line represents one machining layer.

[0069] FIG. 9a shows the situation before machining. Several machining layers L1 to Lfinal are calculated. Preferably, a surface scan is also calculated when the surface should be scanned, for example after machining the fourth layer L4 and the layer Lx. In particular, a surface scan is performed before machining, as indicated by the symbol Lscan in FIG. 9a. However, it is not necessary to scan the surface before machining.

[0070] Figure 9b shows the situation where the first four layers L1, L2, L3, and L4 are machined, and a scan is performed immediately after machining the fourth layer L4. The fifth layer L5 is the next layer to be machined. Before machining this layer, a surface scan is performed to adjust the machining path. The machining surface of the workpiece being machined is scanned by a measuring device. Curve M is a simplified diagram of the measured surface profile, i.e., the measured machining depth. For each measurement position, the measured depth is compared with the target depth defined before machining. The positions are shown in one dimension, i.e., the ablation depth in the z-direction. However, the scan is a three-dimensional scan. Therefore, the measurement data includes coordinates in all three dimensions, i.e., X, Y, and Z, for each position.

[0071] The remaining layers include the fifth layer L5, the sixth layer L6, and all subsequent layers. The machined surface profile, denoted M, is also shown in Figure 9b. Ideally, the surface profile should be flat across the entire surface. However, the scan results show deviations from the ideal profile. The machined depth across the surface is not uniform.

[0072] As shown in Figure 9b, three cases can occur. In zones A and C, the Z position indicated by curve M is higher than the target depth at different positions, which means that the processing depth is smaller than the target depth in these two zones. This indicates under-engraving. For example, the measured position Pm1 in the Z direction is higher than the target position Pt1 because not as much material has been removed as targeted. In zone D, the Z position indicated by curve M is lower than the target depth, which means that the processing depth is greater than the target depth in this zone. This indicates over-engraving. For example, the measured position Pm2 is lower than the target position Pt2 because more material has been removed than targeted. In zone B, neither under-engraving nor over-engraving has occurred.

[0073] Figure 9c shows how to correct the depth error that occurred after machining the first four layers. To compensate for underengraving or overengraving in zones A, C, and D, the machining program is recalculated based on the measurement data obtained by surface scanning. Depending on the scan results, one or several layers must be recalculated. In this example, several layers must be recalculated: the second layer L2', the third layer L3', the fourth layer L4', and the fifth layer L5'. This example shows that not only must the remaining unmachined layer L5 be recalculated, but also the three already machined layers, including the second, third, and fourth layers. For clarity, the recalculated layers are denoted as L2', L3', L4', and L5' in Figure 9c. The remaining layers Lx up to Lfinal are not adjusted. In Figure 9c, the unadjusted laser toolpath calculated before scanning is shown in dotted lines, and the recalculated laser toolpath after scanning is shown in dashed lines.

[0074] In the adjusted layers, the laser toolpaths are adapted with a simple toolpath trimming operation, which means removing the laser toolpaths in areas where correction is not required. In the second layer (L2'), the laser toolpaths are removed so that only the laser toolpaths in Zone A remain, because this area must be ablated again to correct for the underengraving. In the third layer (L3'), the laser toolpaths are removed so that both the laser toolpaths in Zones A and C remain, because these areas must be ablated again to correct for the underengraving. In the fourth layer (L4'), the laser toolpaths for ablating Zone A are removed so that both the laser toolpaths in Zones A and C remain, because these areas must be ablated again to correct for the underengraving. The laser toolpaths for ablating Zone A are included in all three layers, but the size of the ablated area in Zone A may vary from layer to layer. This can also be seen in Figures 10, 11, and 12. In the fifth layer (L5'), the laser toolpaths in Zone D are removed to compensate for the overengraving. The over-engraving in Zone D is too deep, so the sixth layer L6′ must also be corrected by removing the laser tool path in Zone D. However, as shown in FIGS. 13 and 14, the non-ablated area on the sixth layer L6′ is smaller than the non-ablated area on the fifth layer L5′ in Zone D.

[0075] Figure 15 shows the machining area of ​​a machine tool with an integrated measuring device 50. The measuring device is located near the laser head. During scanning, the measuring device moves together with the laser head, particularly in the horizontal direction. Figure 16 shows the measured depth of the machining area. The measured depths are different at positions S1, S2, and S3. The machining depth at S1 is greater than the depth at S3, but less than the depth at S2.

[0076] 17 and 18 illustrate the problem of surface orientation. When an unmachined workpiece is fully prepared, it is perfectly positioned on the machine table 51, as shown in FIG. 17. However, in many cases, the workpiece is not perfectly prepared because the top surface of the workpiece placed on the machine table is tilted, as shown in FIG. 18, for example. To solve this problem, this tilt can be included and taken into account in the measurement data. To compensate for this error, the top surface of the workpiece is first scanned before machining. The measurement value of this initial surface is stored and applied as a reference for calculating the depth deviation. The machining depth is not an absolute value, but a relative value from the scanned top surface of the workpiece.

[0077] The surface of the workpiece can be selected in particular with reference to the surface to be ablated or with reference to an axis of the machine tool, for example the top surface of the machine table. Figure 17 shows a variant in which the top surface of the workpiece is selected as reference. Figure 18 shows a variant in which the top surface of the machine table is selected as reference. [Explanation of symbols]

[0078] 1 Machine tools 2 laser heads 3 Laser Source 4. Mirror 5 workpieces 6 Lenses 7. Surface of the workpiece 8 Actuators 9 Laser Beam 10 Workpiece model 20 cavities 21 Theoretically machined workpiece surface 22 Machined workpiece surface 32,33 Non-ablation area 34 Ablation area 41,42 Laser toolpath 50 Measuring Devices 51 Machine Table

Claims

1. A laser processing method for engraving a texture or cavity on a workpiece (2) by means of a machine tool (1), the machine tool including a machine table (13) for placing the workpiece and a laser head (2) for emitting a laser beam (9) onto the workpiece, the laser beam being directed to reach a defined position on the workpiece by a laser galvanometer scanner integrated in the laser head, the machine tool further comprising a control unit configured to control the movement of the laser head and the laser galvanometer scanner, a) calculating a machining path based on the workpiece geometry and the texture or the cavity prior to machining, the machining path defining a sequence of relative positions of the laser head with respect to the workpiece, the calculating the machining path including calculating a plurality of machining layers to be machined in succession, and calculating, for each layer, a plurality of laser tool paths that define the locations to be ablated by the laser beam; b. receiving, by the control unit, the machining path for ablating the workpiece; c. ablating the workpiece layer by layer; d. adjusting the processing path after processing at least one layer, i. scanning a defined machining area on the surface of the workpiece with a measuring device (50) to obtain the machining depth at a plurality of locations on the machining area; ii. Comparing the measured processing depth with a defined target depth to determine a depth deviation for each measurement location; iii. recalculating the machining path at least in part based on the determined depth deviation; and e) applying the recalculated machining path to ablate the remaining machining layer.

2. 2. The laser processing method of claim 1, wherein the step of recalculating the processing path includes the steps of recalculating at least one processing layer and at least partially recalculating the laser tool path on that layer.

3. 3. The laser processing method according to claim 1, wherein if the depth deviation indicates insufficient engraving, the processing path is recalculated by adding at least one processing layer to the remaining processing layers and recalculating the laser tool path on this layer, and the insufficient engraving occurs when the measured processing depth is smaller than the target depth at one position.

4. 4. The laser processing method according to claim 3, wherein if the depth deviation indicates the lack of engraving, the step of recalculating the processing path includes the steps of copying at least one processing layer, removing the laser tool path for ablating the area where the lack of engraving is not identified, and adding the corrected processing layer to the remaining processing layers.

5. 5. The laser processing method according to claim 1, wherein if the depth deviation indicates over-engraving, the processing path is recalculated by at least partially removing the laser tool path on at least one processing layer, and the over-engraving occurs when the measured processing depth is greater than the target depth at one position.

6. The laser processing method according to claim 1 , wherein the adjustment of the processing path is performed after processing each processing layer.

7. 7. The laser processing method according to claim 1, wherein the adjustment of the processing path is performed irregularly, the timing of the adjustment depends on the processing path, and in particular, the number of adjustments when processing the second half of the layer is greater than the number of adjustments when processing the first half of the layer.

8. The laser processing method according to claim 1 , wherein the timing of the adjustment depends on the shape of the texture or the shape of the cavity.

9. The laser processing method according to claim 1 , wherein an initial scan is performed before the processing and / or a final scan is performed after the processing.

10. The laser processing method according to any one of claims 1 to 9, wherein the processing area is cleaned before scanning the processing area with the measuring device.

11. The laser processing method according to claim 1 , wherein laser source parameters are adapted based on the determined depth deviation.

12. A laser machine tool, in particular a five-axis laser machine tool, for engraving a texture or a cavity on a workpiece, said machine tool comprising: a machine table for placing said workpiece; and a laser head for emitting a laser beam on said workpiece, said laser beam being directed to reach a predetermined position on said workpiece by a laser galvanometer scanner integrated in said laser head; said machine tool comprising: a processing unit configured to determine, prior to machining, a machining path including a series of relative positions of the laser head with respect to the workpiece, wherein a plurality of machining layers intended to be successively machined are calculated, and for each machining layer, a plurality of laser tool paths defining the locations to be ablated by the laser beam are calculated; b. a control unit configured to apply the defined processing path to ablate the workpiece, wherein the workpiece is ablated layer by layer; the machine tool further comprises a measuring device configured to scan a defined area on the surface of the workpiece to obtain machining depths at a plurality of positions on the machining area, and the control unit is further configured to compare the measured machining depth with a target depth to determine a depth deviation, and recalculate the machining tool path based on the determined depth deviation. Laser machine tools.

13. 13. The laser machine tool according to claim 12, wherein the measuring device is a depth sensor, in particular a confocal sensor.

14. 14. A laser machine tool according to claim 12 or 13, wherein the measuring device is arranged on a machine head and controlled by the control unit.

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