Abstract
A method for engraving a texture on a physical object by a laser beam emitted by a laser head through a galvanometer integrated in a machine tool, in particular a 5-axis laser machine tool comprises: providing an image representing the texture, wherein the image includes a plurality of pixels; defining a plurality of groups of the pixels in accordance with at least one characteristic of the pixels, assigning to each group of the pixels a set of machining parameters; and emitting the laser beam on the physical object to engrave the texture on the surface of the object, wherein the set of machining parameter is applied to engrave the corresponding group of pixels on the physical object.
Claims
1. A method for engraving a texture on a physical object by a laser beam emitted by a laser head through a galvanometer integrated in a machine tool, in particular a 5-axis laser machine tool, comprising: providing an image representing the texture, wherein the image includes a plurality of pixels; defining a plurality of groups of the pixels in accordance with at least one characteristic of the pixels; assigning to each group of the pixels a set of machining parameters; emitting the laser beam on the physical object to engrave the texture on the surface of the object, wherein the set of machining parameter is applied to engrave the corresponding group of pixels on the physical object.
2. The method according to claim 1, wherein at least two groups of pixels are determined and for each group a set of machining parameters is assigned.
3. The method according to claim 1, wherein the pixel is the color information of the pixel.
4. The method according to claim 1, wherein the image is a grey-level image and the plurality of groups of the pixels are defined in accordance with the grey-level information of the pixels, in particular the pixels having the same range of grey levels are assigned into the same group, preferably the pixels having the same grey-level are assigned into the same group.
5. The method according to claim 1, wherein the image is a RGBA image and the plurality of groups of the pixels are defined in accordance with the color information of the pixel in particular the pixels having the same range of color scale are assigned into the same group, preferably the pixels having the same color scale are assigned into the same group.
6. The method according to claim 1, wherein the characteristic of the image is the positional information of the pixel.
7. The method according to claim 1, wherein the type of the set of machining parameters for at least two groups of the pixels are different and/or the value of the machining parameters included in the set of machining parameters for at least two groups of pixels are different.
8. The method according to claim 1, wherein the laser machining parameter is one or more of the following: laser source, laser impact density, number of impact, laser impact overlapping, hatching distance, laser spot size, laser beam shaping parameters such as top hat and Gaussian, laser beam polarization parameter, laser wavelength, laser power, laser pulse repetition rate, laser pulse duration and laser burst mode parameters.
9. The method according to claim 1, wherein the engraving is conducted in a group-by-group manner, in which all pixels of a first group are machined and then all pixels of a second group are machined, in particular engraving the pixels of at least one group is conducted by repositioning at least once the laser head.
10. The method according to claim 1, wherein the surface of the object can be divided into a plurality of patches and the engraving is conducted in a patch-by-patch manner, in particular at least for one patch the machining parameters must be adapted in accordance to the assigned set of machining parameter to the corresponding groups.
11. The method according to claim 9, wherein the engraving is conducted in a combination of the group-by-group manner and the patch-by-patch manner.
12. A data-processing unit for generating machining data for laser engraving, comprising wherein the data processing unit is configured to: receive an image representing the texture, wherein the image includes a plurality of pixels; define a plurality of groups of the pixels in accordance with at least one characteristic of the pixels; and assign to each group of the pixels a set of machining parameters; and generate machining data including the machining parameters.
13. The data-processing unit according to claim 12, wherein the data processing unit is further configured to conduct the method of according to claim 2.
14. Machine tool for engraving a texture on a physical object by a laser beam emitted by a laser head integrated in the machine tool comprising a control unit configured to receive the generated machining data from the data-processing unit and control the machine tool to emit the laser beam on the physical object to engrave the texture on the surface of the object, wherein the set of machining parameter is applied to engrave the corresponding group of pixels on the physical object.
15. A machine tool according to claim 14, wherein the control unit is further configured to conduct the method according to claim 9.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] A more particular description of the principles briefly described above will be rendered in the following by reference to specific embodiments thereof, which are illustrated in the drawings. These drawings illustrate exemplary embodiments of the disclosure and are not therefore to be considered to limit its scope. The principles of the disclosure are described and explained with details through the use of the accompanying drawings in which:
[0052] FIG. 1: Illustrates a machine tool for laser ablation and a laser head thereof;
[0053] FIG. 2: Illustrates a machine tool for laser ablation and a laser head thereof;
[0054] FIG. 3: illustrates one example of 3-D modeling file;
[0055] FIG. 4: illustrates one example of a plurality of pixels of a grey-level image;
[0056] FIG. 5: illustrate one example of grey-level images and the image mapped on the object;
[0057] FIG. 6: illustrate one example of grey-level images and the image mapped on the object;
[0058] FIG. 7: illustrate another example of grey-level image to be applied on the object and the surface of the machined object; and
[0059] FIG. 8: illustrate another example of grey-level image to be applied on the object and the surface of the machined object.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0060] FIG. 1 illustrates an example of a laser machine tool 100 for laser texturing. The machine tool includes a laser head 3 for emitting and moving the laser beam and a machine table for clamping an object thereon. The laser head 3 may be displaced in the three dimensions X, Y and Z of a Cartesian reference frame. Advantageously, the laser head is also mobile in rotation about rotation axes, not represented to obtain a greater accuracy and a greater flexibility. The laser head comprises a laser source 1 for emitting laser beam, optical devices, and a galvanometer. The laser head 3 and the object are positioned in relation to one another according to five mechanical axes, which makes it possible to orient the direction of the laser beam emitted and to position the focal point of the laser on the surface of the object.
[0061] FIG. 2 depicts the operation of the galvanometer laser head. The laser source 1 emits a laser beam 2, or more specifically a pulsed laser beam. The laser beam 2 is reflected by the mirrors 4 and 5, which respectively make it possible to define, according to the axes X and Y of the Cartesian reference frame, the position of the point of projection of the laser beam on the surface of the object 7. Actuators 8 are provided to make it possible to control the angular position of the mirrors 4 and 5. After the deflection by mirrors, the laser beam passes through a lens 6 with a dynamic focusing correction, commonly called F-theta lens. This device is arranged in the laser head to define the point of impact of the laser beam with the surface of the object 7 in a plane situated in the focal range considered. Usually, the systems used with a focal length of for example 430 millimetres make it possible, from a given position of the laser head 3, to machine, using the galvanometer, a planar surface measuring 300×300 mm, called marking field. On the other hand, when the surface of the object 7 to be machined is not planar, the focusing capacity of the lenses limits the marking field in the directions X and Y. If the curvature of the surface of the object is significant, it is then necessary to reduce the dimensions on X and Y of the marking fields for the variation on Z in each marking field. Consequently, this increases the number of different positions occupied by the laser head to carry out a texturing job, namely the number of patches generated must be increased.
[0062] FIG. 3 illustrates one example of modelling 3-dimensional form of the object numerically by a meshing of usually triangular forms 11.1, 11.2 and the calculated patches 10, 10a. The thick black lines present the borderlines of different patches. Each patch consists of a plurality of mesh triangles presented by the thinner black lines. The borderline of patches run along the edge of mesh triangles. Some mesh triangles are positioned at the patch junction such as the mesh triangle numbered as 11.2, some mesh tringles are not at the patch junctions, such as the mesh triangle numbered as 11.1. During the machining of one patch, the laser head stays at one position and laser beam moves within the patch either in a vector-liked manner or in a blasting manner.
[0063] FIG. 4 illustrates a plurality of pixels of a grey-level image. An image is a matrix of pixels, each of which pixel has the defined positional information and the colour-information. This example shows an 8-bit grey-level image, thus the colour information is represented by the grey-scales. The references X and Y represent the position of the pixel in the coordinate system and the number in the bracket represents the grey-level. For example, the pixel 1 is positioned at the a first position (X1, Y1) and has the grey scale of 153, the pixel 2 is positioned at a second position of (X2, Y2) and has the grey scale of 40, the pixel 3 is positioned at the a third position (X3, Y3) and has the lightest grey scale of 1, the pixel 4 is positioned at a fourth position of (X4, Y4) and has the darkest grey scale of 256.
[0064] The texture to be applied respectively engraved on the object surface is typically defined as a grey level image or a colour image. FIG. 5 illustrates one example of a texture represented by a grey-level image 20, which is composed of a multiplicity of pixels. In the present invention, the pixels composed in the grey-level image 20 are divided into a plurality of groups in accordance with the characteristic of the pixels, in particular the grey level of the pixels. FIG. 5 illustrates a simplified example, thus only a reduced number of groups are illustrated. However, the number of groups to be determined is not limited to this number shown in FIG. 5 but dependent on the format of the image. In this example, four groups are shown. The first group 21a, 21b, 21c includes all pixels having a first grey level, the second group 22a, 22b, 22c, 22d includes all pixels having a second grey level, the third group 23a includes all pixels having a third grey level and the fourth group 24a, 24b, 24c, 24d, 24e includes all pixels having a fourth grey level. In the embodiment shown in FIG. 5, the groups are determined based on the grey-level information of the pixel and are independent on the position of the pixel, the pixels belong to the same group are not necessarily located close, respectively neighboured to each other. Therefore, one group can includes several sections, each of which includes a cluster of pixels positioning close to each other.
[0065] It is also possible that one group includes only one section and/or one group or one section of a group includes only a small amount of pixels or even one pixel. The first group includes e.g. a first section 21a, a second section 21b and a third section 21c. The second group includes all pixels having a second grey level. The second group includes e.g. a first section 22a, a second section 22b, a third section 22c and a fourth section 22d. The third group includes all pixels having a third grey level. The third group includes e.g. a first section 23a. The fourth region includes all pixels having a fourth grey level. The fourth group includes e.g. a first section 24a, a second section 24b, a third section 24c and a fourth section 24e. One section of a group can partially surround one section of another group. For example, the first section of the third group 23a surrounds partially the first section of the fourth group 24a, this is determined by the image.
[0066] A first set of machining parameters P1 is assigned to the first group, a second set of machining parameters P2 is assigned to the second group, a third set of machining parameters P3 is assigned to the third group and a fourth set of machining parameters P4 is assigned to the fourth group. Each set of machining parameters includes one or more machining parameters. These four sets of machining parameters are applied for engraving the texture represented by this image, in particular, each set of machining parameter is used to ablate the surface of the object to form the corresponding pixels on the object. The first set of machining parameters P1, the second set of machining parameters P2, the third set of machining parameters P3 and the fourth set of machining parameters P4 are applied to engrave the first group of pixels, the second group of pixels, the third group of pixels and the fourth group of pixels, respectively.
[0067] FIG. 6 shows further one example of mapping the grey-level image shown in the FIG. 5 on the object. The FIG. 6 shows an enlarged view of a small area of the object with the image mapped thereon, thus, the shape of the object cannot be seen in the FIG. 6.
[0068] As explained above, the laser beam can only ablate a small area of the surface at one position of the laser head. Thus, the surface of the object must be divided into a plurality of patches and the machining is conducted normally patch-by-patch to reduce the time for mechanically move the laser head. However, in the known method, the same machining parameters are used for all patches or at least for the same patch, thus, patch-by-patch is an sufficient machining sequence. In the present invention, the machining parameters used to machine different patches can vary. In further, the machining parameters used to machine one patch can vary, since pixels belong to different groups can be located in one patch. The reason is that the groups and the patches are determined independently. As shown in the FIG. 6, within one patch with a boundary drawn in the broken lines, pixels having different grey-levels must be engraved. This means, one patch can contain pixels assigned to different groups. Since different set of machining parameters are assigned to pixels having different grey-levels, the machining parameters must vary during the machining time of one patch. For simplification reasons, only three patches 13, 14 and 15 are shown in this example. Each patch includes at least partially of the different groups of pixels. For example, the second patch 14 includes not only the sections of the first group, 21a, 21b 21c but also the sections of other groups such as the sections of the fourth group 24c, 24d, 24e. In order to optimize the machining sufficiency, different machining sequences can be applied. For example, the third patch 15 includes pixels from two different groups, thus this patch can be machined completely without changing the laser head position. However, during machining this patch the machining parameters must be varied for engraving the pixels from the two different groups. After the machining of this patch, the laser head is moved to another position to machine the next patch. This patch-by-patch sequence is for example also suitable for machining the first patch 13, since the machining parameters must not be changed to many times. The second patch illustrates anther situation. The pixels in this area have more grey-levels than the pixels in the first patch and the second patch. If the pixels in the second patch has to be machined in one go, the machining parameters must be changed many times, which increases the total machining time to much and reduce the machining sufficiency. It is then preferred to machine the pixels in a group-by-group order. This means, all pixels belong to the first group should be machined first and then the pixels belong to the second group should be machined, and so on. During the machining of pixels in one group, the machine head may be repositioned, since the pixels of one group maybe not in one patch. The time required for repositioning the laser head may be increased compared to the patch-by-patch sequence, but the time needed for changing the machining parameters can be reduced, hence the total machining time is still low. Certainly, it depends additionally if the time required to change machining parameters is long compared with the repositioning of the laser head. The pixels of the first group are first machined with the first set of machining parameters. After finishing the engraving of the first group of pixels, the second set machining parameters are set and the pixels of the second group of pixels are then machined with the second set of machining parameters. Logically, during machining the first group or second group the machining head has to be changed several times because the pixels of one group are spread in different patches. It is even considerable to combine the patch-by-patch sequence and the group-by-group sequence to further optimize the machining time.
[0069] FIGS. 7 and 8 illustrate another example. The image representing the texture to be engraved on the object is shown in FIG. 7 and the machined object is shown in FIG. 8. The pixels of this image illustrated in FIG. 7 are divided into three groups. The image shown in FIG. 7 is for example one image representing one texture. The first group includes the pixels having a first grey-level, the second group includes the pixels having a second grey-level and the third group includes the pixels having a third grey level. Three set of machining parameters are assigned to these three groups. Each set of machining parameter includes several machining parameters such as: laser source, laser power, and the laser pulse duration. The same laser source is chosen and the same laser power is set for machining all groups of pixels. However, different laser pulse durations are set for machining the different groups of the pixels. The laser pulse duration of the first set of machining parameter is set to 500 ns, the laser pulse duration of the second set of machining parameter is set to 350 ns, and the laser pulse duration for the third set of machining parameter is set to 120 ns. Therefore, the pixels of the first groups are engraved on the object by using a laser pulse duration of 500 ns, the pixels of the second group are engraved on the object by using a laser pulse duration of 350 ns, and the pixels of the third group are engraved on the object by using a laser pulse duration of 120 ns.
[0070] As shown in FIG. 8, the variation of the laser pulse durations can result in different optical appearance on the machined surface. The first machined surface area 41 where the first group of pixels are engraved has the most sheen. The second machined surface area 42 where the second group of pixels are engraved has less sheen than the first surface area. The third machined surface area 43 where the third group of pixels are engraved has the least sheen.
