DE102010060958A1 - Laser processing apparatus comprises processing laser for generating processing laser beam to structural change, scan laser for generating scan laser beam, light detector, and reference structure for calibrating unit of control device - Google Patents

Abstract

The laser processing apparatus comprises: a processing laser (3) for generating a processing laser beam (5) to a structural change modifying a workpiece incorporated into the laser processing apparatus, where the laser beam is movably guided in a laser-coordinate system associated by a processing beam-guiding device; a scan laser for generating a scan laser beam, which is movably guided by a scan beam-guiding device to the laser coordinate system; and a control device (25), which is connected with the processing beam-guiding device and the scan beam-guiding device. The laser processing apparatus comprises: a processing laser (3) for generating a processing laser beam (5) to a structural change modifying a workpiece (27) incorporated into the laser processing apparatus, where the laser beam is movably guided in a laser-coordinate system associated by a processing beam-guiding device; a scan laser for generating a scan laser beam, which is movably guided by a scan beam-guiding device to the laser-coordinate system; a control device (25), which is connected with the processing beam-guiding device and the scan beam-guiding device such that the scan laser beam is feasible by the scan beam-guiding device of the laser-coordinate system assigned to a transverse position over an outer peripheral edge of the workpiece incorporated into the laser processing apparatus; and a light detector (31), which is connected with the control device and arranged and adapted such that a brightness change of a secondary light in form of reflected and/or transmitted scan laser beam light is caused by passing the outer peripheral edge of the workpiece through the scan laser beam, and/or an edge scan-brightness profile encompassing the brightness change is detectable. The control device is further arranged such that it is based on the edge scan-brightness profile, which is detected by the light detector for passing over the position on the outer peripheral edge of the workpiece, where the positioning of the workpiece relative to the laser coordinate system is determinable. The associated position of the outer peripheral edge with respect to the laser coordinate system based on a transition between two constant brightness levels is determined. The control device is further arranged such that: the scan laser beam is guided to the position in both transverse directions passing over the outer peripheral edge of the workpiece and bidirectionally guided over the surface of the workpiece; and the transition between two constant brightness levels is recognized as a structure boundary into a surface scan-brightness profile. The processing laser and the scan laser are identical. The light detector is arranged such that: it forms on a scan laser beam-incident side of the workpiece incorporated into the laser processing apparatus, where the workpiece is turned away by the scan laser beam-incident side of the workpiece; and the brightness change of the secondary light is detected in form of the transmitted scan laser beam light. The light detector comprises a light-diffusing plate that is arranged such that it receives/diffuses the secondary light, and light sensors (35), which are arranged such that it detects an intensity of the secondary light received by the light-diffusing plate. The laser processing apparatus further comprises a reference structure for calibrating a unit of the control device and the positioning of the scan-laser beam achieved by the scan beam-guiding device. The control device is arranged such that a unit of the scan beam-guiding device of the scan laser beam is guided over the reference structure. The light detector is arranged such that the brightness change of the secondary light is reflected in form of the reference structure and/or is transmitted by the reference structure to the scan-laser beam-light, which is generated during the reference structure with the scan-laser beam, and/or a calibration-brightness profile encompassing the brightness change is detectable. The control device is further arranged such that it is calibrated by a unit of the calibration-brightness profile through the control device and the scan beam-guiding device obtaining the positioning of the scan-laser beam. Independent claims are included for: (1) a position-determining device for determining the positioning of a workpiece incorporated into a laser processing apparatus; and (2) a structure determining device for determining the structure of a surface of a workpiece incorporated into the laser processing apparatus.

Description

The invention relates to a position detecting device, for. B. for use in determining the positioning of a recorded in a laser processing device workpiece, a structure determination device, for. For use in determining the surface structure of a workpiece received in a laser processing apparatus, and a laser processing apparatus, for example, for use in structurally changing laser processing of workpieces. The work leading to this invention has been funded under the Grant Agreement No 219050 under the Seventh Framework Program of the European Community (FP7 / 2007-2013).

Machining devices for machining a workpiece by means of a tool -. As a milling head, a drill, a laser beam or a welding device (such as a welding electrode or a welding torch head) - require a precise positioning of the workpiece.

For example, in laser processing devices, e.g. As laser scanners, for processing a workpiece with a laser beam usually first the workpiece positioned below a Laserscankopfs and then processed by means of a laser beam, wherein certain positions are approached on the workpiece with a laser beam to z. B. remove material at these positions by means of the laser light or to connect parts of the workpiece by laser welding together or separate from each other.

Therefore, such a laser processing apparatus typically requires precise mechanical feeds, such as carriage tables or turntables, by means of which the workpiece can be positioned below the scan head.

The invention provides a position-determining device, a structure-determining device and a laser processing device which provide precise machining, e.g. As laser machining, allow a workpiece to work stably and at the same time are simple and inexpensive to produce.

According to one aspect of the invention, a position detecting device is provided for determining the positioning of a workpiece received in a laser processing device, the laser processing device having a scanning laser for generating a scanning laser beam, wherein the scanning laser beam is guided in a laser coordinate system by means of a scanning beam guiding device is provided with a control device which is connected to the scanning beam guiding device and is arranged such that from it the scanning laser beam by means of the scanning beam guiding means associated with the laser coordinate system at at least one position across the outer peripheral edge of the in the Laserscanvorrichtung taken workpiece is feasible; a light detector, which is connected to the control device and is arranged and arranged such that a change in brightness of a secondary light in the form of reflected and / or transmitted scanning laser beam light by the sweeping of the outer peripheral edge of the workpiece by the scanning laser beam is caused, as well as a brightness change comprehensive Kantenscan brightness curve is detected; wherein the control device is further arranged such that it can determine the positioning of the workpiece with respect to the laser coordinate system based on the edge scan brightness course, which is detected by the light detector for sweeping the at least one position on the outer peripheral edge of the workpiece.

For example, the position detecting device may be part of a processing device that is provided for machining the workpiece by means of a tool, wherein z. B. the determined by means of the determination device positioning of the workpiece from the processing device for positioning or guiding the tool with respect to the workpiece can be used. For example, the position detecting device may be provided for detecting the positioning of a workpiece in a laser processing apparatus.

According to one aspect of the invention, there is provided a laser processing apparatus comprising a processing laser for generating a processing laser beam for structurally modifying a workpiece received in the laser processing apparatus, the processing laser beam being movably guided in a laser coordinate system associated therewith by means of a processing beam guiding means is; a scanning laser for generating a scanning laser beam, wherein the scanning laser beam is guided guided by a scanning beam guiding device according to the laser coordinate system; a control device, which is connected to the processing beam guiding device and the scanning beam guiding device and is arranged such that from the scanning laser beam by means of the scanning beam guide means associated with the laser coordinate system at at least one position across the outer peripheral edge of a in the laser processing device taken workpiece is feasible; a light detector, which is connected to the control device and is arranged and arranged such that one of them Change in brightness of a secondary light in the form of reflected and / or transmitted scanning laser beam light, which is caused by the sweeping of the outer peripheral edge of the workpiece by the scanning laser beam, as well as an edge scan comprising the brightness change is detectable; wherein the control device is further configured such that it can determine the positioning of the workpiece with respect to the laser coordinate system based on the edge scan brightness course, which is detected by the light detector for sweeping the at least one position on the outer peripheral edge of the workpiece.

By, for. For example, just before a machining step, the positioning of the workpiece using the scanning laser with respect to the laser coordinate system can be determined, the workpiece does not need to be precisely positioned in advance with respect to the laser coordinate system.

The term "structure-modifying modification" here includes, for. For example, any kind of structurally altering machining of a workpiece by energy input by means of a laser beam, such as cutting or cutting (ie, separating two parts of a workpiece by laser action), (ie, joining, eg by soldering or welding, two parts Laser action), material application (eg by sintering or coating, eg by layer deposition by laser beam evaporation), material removal (eg decoating, surface and deep engraving, drilling, or material removal by means of laser ablation), or material conversion (eg, interior engraving of transparent materials, texturing, tempering, doping, curing, foaming, carbonizing, eg, by structural conversion of the laser-irradiated material) and cold ablation by ultrashort pulse lasers. The structure-changing effect can be z. B. on heat input caused by the laser beam or on caused by the laser light, z. As photochemical, reactions based. The term "laser processing" are summarized below all, z. B. understood the above-mentioned, structurally altering types of processing by means of a laser beam. The workpieces can z. B. of metal and / or plastic or any other structurally changeable by a laser material.

The scanning laser and the processing laser can z. B. in each case as a continuous wave laser (CW laser) or as a pulse laser. The scan laser can z. B. be designed such that the scanning laser beam for non-structure-changing (i.e., structure-preserving) scanning (eg., The workpiece) is suitable, wherein z. As the wavelength and / or intensity of the scanning laser beam, z. Example, by means of the control device, can be set such that the scanning laser beam causes no structural change of the workpiece when hitting the workpiece.

When sweeping the outer peripheral edge of the workpiece, which z. B. may be included in a workpiece receiving device of the laser processing device, the reflection behavior and / or the transmission behavior of the (primary) incident scan laser beam may change, with a (secondary) reflected and / or transmitted portion of the light of the scanning laser beam (or scan laser light) can change. For example, a reflected and / or transmitted portion of the scanning laser light may take on different values depending on whether the scanning laser beam impinges on or passes the workpiece (eg, when the optical properties of the workpiece exceed those of the environment of the workpiece differ).

Here, the term "reflected" light z. Also, for example, (eg, on the workpiece or on a workpiece receiving device) diffusely reflected and in the reverse direction (opposite to the direction of incidence on the workpiece, in a direction to the incident scanning beam light back) scattered scanning laser light, while the term "transmitted "Light z. B. also includes (eg on the workpiece) scattered in the forward direction and past the workpiece passed scanning laser light, wherein the wavelengths of the reflected and transmitted light may also be different from the wavelength of the incident scanning laser light.

According to an embodiment of the position detecting device or the laser processing device, the control device is further configured such that from the edge scanning brightness course, which is detected by the light detector for sweeping the at least one position on the outer peripheral edge of the workpiece, the corresponding position of the outer peripheral edge of the laser coordinate system is determined by the transition between two substantially constant brightness levels.

For example, when sweeping the outer peripheral edge of a workpiece from a highly reflective and opaque material (at the wavelength of the laser light used), as the scanning laser beam exits the workpiece, the brightness of the reflected portion of the scanning laser light may change from a higher level Brightness (ie, light intensity) change to a lower brightness level, whereas the brightness of the transmitted portion of the scanning laser light changes from a lower brightness level to a higher brightness level can change, wherein the position of the outer peripheral edge can be given by the transition between the two substantially constant brightness levels.

According to one embodiment of the position-determining device or the laser processing device, the control device is set up in such a way that it guides the scanning laser beam at the at least one position in both transverse directions transversely across the outer peripheral edge of the workpiece.

By this bidirectional scanning can z. For example, a following error or delay error that characterizes a difference between a target position on the workpiece which is controlled by the scan laser beam at a particular time and the actual position of the scan laser beam actually present at this point in the evaluation of the edge scan. Brightness gradients are eliminated, so that a precise determination of the positioning of the workpiece can be done without knowledge of this delay error.

According to a further aspect of the invention, the control device is alternatively and / or additionally configured such that the scan laser beam can be guided by the scanning beam guiding device assigned to the laser coordinate system via a surface of a workpiece received in the laser processing device; wherein the light detector is alternatively and / or additionally arranged and arranged such that from it a change in brightness of a secondary light in the form of reflected on the workpiece and / or transmitted through the workpiece scan laser beam light when sweeping the surface of the workpiece with the Scanning laser beam is generated, as well as the brightness change comprehensive surface scan brightness curve is detected; and wherein the control device is alternatively and / or additionally set up such that the structure of the surface of the workpiece can be determined from the surface scan brightness curve. According to this aspect can thus z. For example, a texture detection apparatus for detecting the surface structure of a workpiece received in a laser processing apparatus can be provided.

The term "structure of the surface" here includes z. For example, a structure formed by a three-dimensional patterning of the surface (eg, by depressions formed in the surface), but also a structure formed by a roughness of the surface and / or different materials. For example, when sweeping the surface of a workpiece in the form of a perforated grid from a (in the laser light used) opaque material with the scanning laser beam, the perforated grid structure of the surface of the workpiece using a corresponding light-dark pattern of the transmitted scanning beam light determined become. Furthermore, z. Example, when sweeping a surface of a workpiece, which consists of different materials, each with known different reflection and absorption coefficients, the material structure of the surface using a corresponding gray scale pattern of the reflected and / or the transmitted scanning beam light are determined, wherein different Grayscale different reflection or transmission coefficients and thus different materials can be assigned. Furthermore, with the material remaining the same, a variation of the reflected and / or the transmitted scanning beam light occurring when passing over an edge (for example at the edge of a depression) can enable the edge position to be determined. The roughness of the surface can z. B. be detected by a reduced by an increased scattering proportion of the directionally reflected and / or transmitted scanning beam light.

According to an embodiment of the structure determination device or the laser processing device, the control device is further configured such that it detects the transition between two substantially constant brightness levels in the surface scan brightness curve as a structure boundary.

The term "structure delimitation" includes z. B. the contours of the structures listed above or structure transitions. For example, when sweeping such a structure boundary between regions having different optical properties, e.g. B. between areas of different materials and / or different roughness, with the scan laser beam, the position of the structure boundary on the basis of these different optical properties resulting different (but each constant) brightness levels are determined without the optical properties or the nature of the respective areas must be known in detail.

According to a further embodiment of the structure determination device or the laser processing device, the control device is further configured such that the scanning laser beam is guided bidirectionally over the surface of the workpiece for determining the surface scan brightness course.

By this bidirectional scanning can z. As a lag error or delay error in the positioning of the scanning laser beam in the evaluation of the surface scan brightness curve can be eliminated.

According to an embodiment of the laser processing apparatus, the processing laser and the scanning laser are identical. For example, the processing laser can be used simultaneously as a scanning laser, wherein z. B. during scanning to determine the positioning and / or the surface structure of the workpiece of the machining laser with a lower intensity, the z. B. below a (structurally changing) laser processing of the workpiece required intensity (eg, below the material removal threshold of the workpiece to be machined), can be operated as during the laser machining of the workpiece. Thus, according to this embodiment, the laser processing apparatus can have only a single laser, which is both a processing laser and a scanning laser. In this embodiment, the processing beam guiding unit and the scanning beam guiding unit of the laser processing apparatus may be identical, ie, only a single guiding unit may be provided for guiding a laser beam serving as both a machining laser beam and a scanning laser beam.

According to another embodiment of the respective detection device or the laser processing device, the light detector is arranged such that it is located on one side of a workpiece received in the laser processing device, which faces away from a scanning laser beam incidence side of the workpiece, wherein the light detector is arranged such that it detects the change in brightness of the secondary light in the form of transmitted scanning laser beam light.

According to this embodiment, for. B. transmitted from the workpiece scan laser beam light can be detected directly from the light detector, without z. B. on additional deflection devices, such as deflecting mirror to be passed.

According to another embodiment of the respective detection device or the laser processing device, the light detector is arranged such that it is located on a scan laser beam incidence side of a recorded in the laser processing device workpiece, and is arranged such that the brightness change of the secondary light in the form of reflected scan laser beam light is detected.

According to this embodiment, for. B. reflected from the workpiece scan laser beam light can be detected directly from the light detector, without z. B. on additional deflection devices, such as deflecting mirror to be passed.

According to another embodiment of the respective detection apparatus and the laser processing apparatus, the light detector comprises: a light diffusion plate arranged to receive the secondary light and configured to diffuse the secondary light diffusively; and one or more light sensors arranged to detect the intensity of the secondary light received by the light-scattering plate.

This embodiment can enable a large-area, location-independent detection of the secondary light caused by the scanning laser light. The term "light scattering plate" here includes z. B. a plate of a (at the wavelength of the laser light used) translucent material, such as glass or plastic (eg Plexiglas), with a flat and smooth front for receiving the secondary light, wherein the back of the plate with a light-scattering layer is formed. Thus, the secondary light to be detected can impinge on the front of the plate, are diffused at the light-scattering layer, and z. B. by repeated successive total reflection (or reflection) at the front and (diffuse) scattering at the back regardless of the place of impact on the plate evenly over the entire surface of the plate are distributed and z. B. by arranged on the outer circumference of the plate light sensors, z. B. photodiodes, are detected. Thus, z. B. the brightness of the incident on the light scattering plate secondary light are detected substantially independently of the arrangement of the light sensor or the light sensors with respect to the plate.

According to a further embodiment, the respective determining device or the laser processing device further comprises: a reference structure for calibrating the positioning of the scanning laser beam achieved by means of the control device and the scanning beam guiding device; wherein the control device is further arranged such that by means of the scanning beam guide means of the scanning laser beam can be guided via the reference structure; wherein the light detector is arranged such that from it a change in brightness of a secondary light in the form of reflected at the reference structure and / or transmitted through the reference structure scan laser beam light, which is generated when sweeping the reference structure with the scanning laser beam, as well as the Brightness change comprehensive calibration brightness curve is detected; and wherein the control device is further configured such that the position of the scanning laser beam achieved by means of the control device and the scanning beam guiding device can be calibrated by means of the calibration brightness curve.

This embodiment may enable calibration of the laser beam positioning of the laser processing apparatus and the laser coordinate system, respectively. The reference structure may, for. B. as a perforated grid, which serves as a normal, be formed. For example, deviations of the actual positioning of the scanning laser beam from a controlled desired positioning can be determined by the control device during scanning of the reference structure, which can serve as a measurement standard or positioning normal, wherein the control device can be set up such that it can be used the determined deviations are used for correcting the positioning of the scanning laser beam and the machining laser beam, which is e.g. B. can be realized by a corresponding transformation of the laser coordinate system. Also according to this embodiment may be provided the scan laser beam, z. B. to eliminate a following error, bidirectionally over the reference structure.

The invention will be described below with reference to exemplary embodiments, for. B. based on the implementation of the principles of the invention in a laser processing apparatus according to the invention, explained with reference to the accompanying drawings. In the drawings show:

1 a schematic side view of a laser processing apparatus according to an embodiment of the invention,

2 a schematic plan view of a light detector of in 1 shown laser processing apparatus with a workpiece to be machined thereon,

3 one with the in 1 shown laser scanning device detected Kantenscan brightness course when sweeping an outer peripheral edge of a workpiece to be machined with a scanning laser beam,

4 a schematic illustration for explaining a laser processing apparatus according to another embodiment of the invention,

5 a schematic illustration for explaining the use of a calibration brightness curve for calibrating a laser processing apparatus according to an embodiment of the invention.

According to the 1 and 2 has a laser processing device 1 according to one embodiment, a processing laser 3 for generating a machining laser beam (in short: machining beam) 5 , a scanning laser 7 for generating a scanning laser beam (in short: scanning beam) 9 , and a laser beam guiding device 11 in the form of a scan head 11 on. In the present embodiment, the scan head is used 11 both as a processing beam guiding device and as a scanning beam guiding device. During a scan - z. B. for determining the positioning or the surface structure of a in the laser processing apparatus 1 recorded object - may be the scanning laser 7 (Selective) are activated, whereas in a machining operation for laser machining in the laser processing apparatus 1 recorded object of the machining laser 3 (selectively) can be activated. The scanning beam 9 is - here z. B. by means of a first deflecting mirror 13 and a second, partially transmissive mirror 15 - Guided so that it in a common beam path with the processing beam 5 (ie with the beam path of the processing beam 5 coincident) in the scan head 11 entry. The processing beam 5 happens to the partially transmissive second deflection mirror 13 and then enters the scan head 11 one.

The scan head 11 is set up so that from each of the incident laser beam 5 . 9 in the xy plane of an associated xyz laser coordinate system (see 1 ) can be guided laterally and z. B. the focus of each incident laser beam 5 . 9 in the z-direction of the xyz laser coordinate system can be vertically adjustable. As the beam paths of the machining laser beam 5 and the scanning laser beam 9 when entering the scan head 11 are identical, the leadership or positioning of the two laser beams takes place 5 . 9 by means of the scan head 11 with respect to one and the same laser coordinate system. In the event that the scan head 11 for the processing beam 5 and the scanning beam 9 has different deflection characteristics, the control device 25 Furthermore, be set up such that these different deflection properties of her in the beam positioning taken into account and (by means of a corresponding control of the scan head 11 ) are compensated. Such different deflection properties can, for. B. caused due to different wavelengths of the scanning beam light and the processing beam light.

The lateral deflection of the respective laser beam 5 . 9 in the x-direction and the y-direction of the xyz laser coordinate system, for. B. by means of a deflection of the scan head 11 - Simplified illustrated here by a on a galvanometer drive (not shown) pivotally mounted deflecting mirror 21 - be realized, whereas the vertical focusing of the laser beam 5 . 9 z. B. by means of a focusing optics of the scan head 11 - Simplified here as a focusing lens 23 - can be realized.

The laser processing device 1 further comprises a control device 25 which is set up so that from her the processing laser 3 , the scanning laser 7 and the scan head 11 can be controlled so that z. As the processing laser 3 and the scanning laser 7 can be selectively activated and the processing beam 5 or the scanning beam 9 to one of the control device 25 predetermined position within the xyz laser coordinate system can be focused. The following is under the position of a laser beam 5 . 9 the focus position of the respective laser beam 5 . 9 understood, insofar as not something else results from the context.

The laser processing device 1 Further, a workpiece holder (not shown) for storing a workpiece to be machined by laser machining 27 exhibit. The positioning of the workpiece 27 with respect to the xyz laser coordinate system can, for. B. before editing the workpiece 27 by means of the processing beam 5 , by means of the scanning beam 9 be determined as follows.

The control device 25 is set up so that from her the scanning laser beam 9 by means of the scan head 11 associated with the xyz laser coordinate system (ie, the positioning of the scan beam 9 with respect to the xyz laser coordinate system) at at least one position across the outer peripheral edge 29 of the workpiece 27 can be performed. In the present case, the control device 25 as an example arranged such that the scan beam at three different non-collinear positions P1, P2, P3 (see 2 ) along a respective associated scan line S1, S2, S3 (in 2 drawn as double arrows) across the outer peripheral edge 29 of the workpiece 27 can be performed. For example, the control device 25 be set up so that you first on the basis of predetermined workpiece data, the z. As the shape, dimensions and a target positioning (with respect to the xyz laser coordinate system) of the workpiece to be machined 27 may contain an expected target curve of the outer peripheral edge 29 of the workpiece 27 (represented by the dashed line in FIG 2 ) with respect to the xyz laser coordinate system, the scan laser beam 9 for determining the actual positioning and the actually present actual course of the outer peripheral edge 29 from the control device 25 based on the workpiece data, z. At a constant rate over the outer peripheral edge 29 can be performed. In doing so, the scanning beam 9 by means of the control device 25 , z. B. also based on the given workpiece data on the surface 37 of the workpiece 27 be focused. However, it may also be provided to leave the focus position invariably at a preset value.

The laser processing device 1 also has a light detector 31 on, with the light detector 31 in the execution after the 1 and 2 a light-scattering plate 33 which is arranged substantially parallel to the xy plane of the xyz laser coordinate system, and one or more (here: twelve pieces, see 2 ) along the outer periphery of the light-scattering plate 33 arranged light sensors 35 , here photodiodes, has. The light scattering plate 33 consists of a translucent material, eg. A glass (such as quartz glass) or a plastic (such as Plexiglas), and is at its scan head 11 opposite back with a light scattering layer 39 Mistake. The light-scattering layer 39 can z. B. in the form of a light scattering film, a light scattering coating, or structuring (eg., Roughening) of the back of the light scattering plate 33 be educated. In the configuration after the 1 and 2 is the workpiece 27 directly on the front of the light-scattering plate 33 stored. However, it can be provided, the workpiece 27 externally mounted at a distance from the light-scattering plate 33 to arrange above it.

When sweeping the outer peripheral edge 29 of the workpiece 27 with the scanning beam 9 changes the transmission behavior of the primary light from the scan head 11 incoming scanning beam 9 and thus the intensity of the light scattering plate 33 incident secondary light in the form of the transmitted portion of the scanning beam 9 , When the scanning beam 9 on the surface 37 of the workpiece 27 impinges, z. For example, at least part of the scanning beam light from the workpiece 27 absorbs and / or reflects so that only the portion of the scanning beam light reduced by the reflected and / or absorbed portion is transmitted and on the light-scattering plate 33 hits, whereas when the scanning beam 9 over the workpiece surface 37 out and on the workpiece 27 passes, the scanning beam light unattenuated on the light scattering plate 33 impinges, ie completely to the light-scattering plate 33 is transmitted.

The intensity of the light scattering plate 33 incident, transmitted scanning laser beam light can by means of the photodiodes 35 of the light detector 31 be recorded. Thus, by means of the light detector 31 a change in brightness of the transmitted portion of the scanning laser beam light caused by the sweeping of the outer peripheral edge 29 of the workpiece 27 through the scanning laser beam 9 is caused, and an associated brightness curve when sweeping the outer peripheral edge 29 (in short: edge scan brightness curve) are detected, wherein the light detector 31 z. B. can first capture a brightness-time history.

The control device 25 is with the light detector 31 connected and arranged such that from there the Kantenscan brightness gradients for the sweeping of the three different, non-collinear positions P1, P2, P3 at the outer peripheral edge 29 of the workpiece 27 with the scanning beam 9 the positioning of the workpiece 27 can be determined in the xy plane of the xyz laser coordinate system.

3 shows as an example a Kantenscan brightness curve 41 when scanning the scanning beam 9 along the x-direction scan line S1, wherein the horizontal axis of the time or the controlled target position x of the scanning beam 9 on the scan line S1, and on the vertical axis, the brightness (intensity I) of the transmitted scanning laser beam light is applied, that of the light detector 31 at that time or at the respective positioning of the scanning beam 9 is detected. The assignment of a respective time to a corresponding positioning of the scanning beam 9 on the scan line can z. B. from the control device 25 respectively.

When the scanning beam 9 from a position next to the workpiece 27 (left side in 3 ) over the outer peripheral edge 29 to a position on the workpiece 27 (right side in 3 ) is moved, the intensity I decreases to the light scattering plate 33 transmitted portion of the scanning beam light from a higher value I1 to a lower value I2, which in 3 through the solid brightness curve 41 is shown (wherein the direction of movement of the scanning beam 9 indicated by the arrow pointing to the right).

The control device 25 may be arranged such that from it the respective position of the outer peripheral edge 29 in the xy plane of the xyz laser coordinate system is determined by the position of the brightness decrease. For example, the intensity of the transmitted light remains at a substantially constant brightness level of intensity I1 as long as the scan beam 9 next to the workpiece 27 is located, and moves at a substantially constant intensity level of intensity I2 as long as the scan beam 9 located on the workpiece. The control device 25 can z. B. be set up so that from her the position of the outer peripheral edge 29 is determined by the transition between these two substantially constant brightness levels I1 and I2. For example, the control device 25 be set up so that from it the position with the largest edge steepness in the edge scan brightness curve 41 as the position of the outer peripheral edge 29 is determined, or that of her the position of the outer peripheral edge 29 is determined by exceeding or falling below a predetermined brightness threshold.

The beam guidance of the laser processing device 1 may have a delay or tracking error, which at a time by the control device 25 controlled target position of the scanning beam 9 (or the processing beam 5 ) of the actually present at this time actual position of the laser beam 5 . 9 differs, the actual position usually runs behind the desired position. The influence of this following error on the determination of the position of the outer peripheral edge 29 from a Kantenscan brightness curve can be eliminated by the scan laser beam 5 extending in both transverse directions over the outer peripheral edge 29 is performed and the associated Kantenscan brightness gradients are evaluated. For this purpose, the control device 25 z. B. be set up so that from her the scanning laser beam 9 at the three positions P1, P2, P3 respectively in both transverse directions extending transversely across the outer peripheral edge 29 of the workpiece 27 is guided (illustrated by the double arrows S1, S2, S3 in 2 ).

In the presence of a following error makes this z. B. thereby noticeable that the detected for the two directions of motion Kantenscan brightness gradients are shifted from each other. The dashed line 42 in 3 illustrates, as an example, an edge scan brightness curve 42 for the method of the scanning beam 9 along the scan line S1 from a position on the workpiece 27 to a position next to the workpiece 27 in the presence of a following error (the direction of movement of the scanning beam 9 indicated by the arrow pointing to the left). To eliminate the following error, the control device 25 z. B. be set up so that from her for the two directions of movement of the scanning beam 9 acquired edge scan brightness gradients 41 . 42 be averaged and the position of the outer peripheral edge 29 is determined from the resulting averaged edge scan brightness curve in one of the ways described above.

By the scanning beam 9 at the three non-collinear positions P1, P2, P3 over the outer peripheral edge 29 of the workpiece is guided, for. Along the in 2 shown scanning lines S1, S2, and S3, and from the associated Kantenscan brightness gradients, the respective positioning of the outer peripheral edge 29 is determined by the control device 25 (eg, using the given workpiece data) the positioning of the workpiece 27 in the xy plane of the xyz laser coordinate system. For example, by sweeping the x-direction scan line S1 with the scan beam 9 the x- Positioning the position P1 of the outer edge 29 can be determined, and by sweeping the two y-direction scan lines S2, S3, the y-positions of the positions P2, P3 can be determined, such that (for example, using the shapes and dimensions of the workpiece contained in the given workpiece data 27 ) the positioning of the workpiece 27 can be determined in the xy plane. For example, the control device 25 be set up so that from her a shift (an offset) and a rotation of the actual positioning of the workpiece 27 with respect to a predetermined target positioning (illustrated by the dashed line in FIG 2 ) can be determined.

In the above-described configuration, the control device is 25 set up so that from her the scanning beam 9 at three different, non-collinear positions P1, P2, P3 over the outer peripheral edge 29 of the workpiece 27 is performed and thus z. B. an offset and a rotation of the actual positioning of the workpiece 27 can be determined with respect to a desired positioning. It can, however, z. B. be provided that the control device 25 is set up so that from her the scanning beam 9 only at a single position over the outer peripheral edge 29 of the workpiece 27 is performed and thus z. B. only an offset of the workpiece 27 can be determined with respect to a corresponding direction, or that of the scan beam 9 at two positions over the outer peripheral edge 29 is performed and thus z. B. only one rotation of the workpiece or an offset of the workpiece with respect to two corresponding directions can be determined. Furthermore, the control device 25 be set up so that from her the scanning beam 9 at more than three (not necessarily non-collinear) positions over the outer peripheral edge 29 is performed, for. B. to the positioning of the workpiece 27 to determine with higher accuracy.

The during scanning by means of the scanning beam 9 determined positioning of the workpiece 27 can z. B. be used to during a subsequent machining operation, the beam guidance of the machining laser beam 5 to correct. For this purpose, the control device 25 z. B. be set up so that from her the machining laser beam 5 using the determined positioning of the workpiece 27 (or the determined deviation of the actual position of the workpiece 27 from the desired position) over the workpiece 27 to be led.

For example, the laser processing apparatus 1 for laser processing, z. B. for laser structuring, may be provided by semiconductor wafers. In this case, the workpiece can 27 z. B. be a semiconductor wafer, wherein initially in a scan by means of the scanning beam 9 the positioning of the wafer can be determined and then during a machining operation by means of the machining beam 5 a precise laser processing of the wafer can take place, wherein z. B. due to the precise determination of the position of the wafer in the xyz laser coordinate system, a maximum material utilization of the wafer can be done.

By, for. B. directly before a machining operation, the positioning of the workpiece 27 with respect to the xyz laser coordinate system, the workpiece needs 27 not be precisely positioned in advance. The influence of errors and drift effects (ie the temporal variation of such errors) of the components of the laser processing device 1 - z. As the mechanical structure (eg., Mechanical feeders), the laser 3 . 7 , the scan head 11 or other beam-guiding components - on the positioning accuracy of the laser beam 5 . 9 can be eliminated or at least reduced because these errors and drift effects in determining the position of the workpiece 27 can be completely detected and compensated with respect to the xyz laser coordinate system.

Because both the scanning beam 5 as well as the processing beam 9 by means of the scan head 11 can be guided and focused, can determine the positioning of the workpiece 27 with respect to the xyz laser coordinate system with similar accuracy as the positioning of the machining beam 9 during the laser processing, the accuracy z. B. from the focus size (ie, the diameter of the laser beam 5 . 9 at the focus position), z. B. high accuracy can be achieved with small focus sizes. It can be z. B. the measurement accuracy in determining the positioning of the workpiece 27 by using suitable algorithms in the evaluation of the brightness profiles below the focus size of the scanning beam 9 lie.

In the execution according to 1 are both a machining laser 3 as well as a scan laser 5 intended. However, it may be provided that the machining laser 3 simultaneously as a scanning laser 7 serves, in which case only a single laser can be provided and the deflection mirror 13 . 15 can be dispensable. In this case, z. B. the control device 25 be set up so that from it the intensity of the processing laser 3 can be controlled, wherein the intensity during a scan (eg., To determine the positioning of a workpiece) can be lowered to or below a predetermined threshold, wherein the threshold z. B. can be chosen so that the laser beam intensity is below a necessary for structurally modifying the workpiece material intensity (eg., Below a Material removal threshold or below a melt threshold of the workpiece to be machined), and wherein the intensity during a machining operation for laser machining the workpiece can be increased to a value suitable therefor.

The light detector 31 is located on a scan head 11 opposite side of the workpiece 27 that is on one side of the workpiece 27 , which is the scanning laser beam incidence side of the workpiece 27 (ie the surface 37 of the workpiece 27 ) is turned away, and is arranged such that the brightness or the change in brightness of secondary light in the form of (through the workpiece 27 passing through or past this) transmitted scan laser beam light is detected.

However, it may be provided that the laser processing device 1 alternatively and / or additionally comprises a light detector connected to the control device 25 is connected and arranged and arranged such that a change in brightness in the form of reflected scan laser beam light by the sweeping of the outer peripheral edge 29 of the workpiece 27 through the scanning beam 9 is caused, and an associated Kantenscan brightness curve is detected.

As an example shows 1 one at the level of the focusing lens 23 arranged, surface reflection light detector 43 , wherein the reflection light detector 43 eg one around the scan head 11 or to the focusing lens 23 arranged around, parallel to the xy plane of the xyz laser coordinate system parallel light scattering plate (not shown) and one or more arranged on the outer periphery of the light scattering plate light sensors (not shown), for. B. photodiodes, may have. The reflection light detector 43 is arranged so that it is on the scan head 11 facing side of the workpiece 27 ie on the scan laser beam incidence side of the workpiece 27 , is and is arranged such that the brightness or change in brightness of secondary light in the form of (on the workpiece 27 or at an environment of the workpiece 27 , such as a workpiece holder) reflected scan laser beam light can be detected.

When sweeping the outer peripheral edge 29 of the workpiece 27 with the scanning beam 9 changes the reflection behavior of the primary light on the workpiece surface 37 impinging scan beam 9 and thus also the intensity of the on the reflection light detector 43 incident secondary light in the form of the reflected portion of the scanning beam 9 , Thus, by means of the reflection light detector 43 a change in brightness of the reflected portion of the scanning laser beam light when sweeping the outer peripheral edge 29 with the scanning beam 9 and an associated edge scan brightness trace are detected.

The light detectors 31 . 43 are provided as flat light detectors with a light scattering plate and one or more arranged on the outer periphery of the light scattering plate light sensors, here photodiodes. However, it can be provided in each case to arrange one or more light sensors on the front and / or rear side of the light-scattering plate. As light sensors z. As photodiodes, photoresistors, CCD sensors or any other light sensors can be used. Furthermore, as an alternative and / or in addition to a flat light detector with a light scattering plate z. B. may be provided with a smaller detection area, a plurality of light detectors z. B. each in a position for determining a in the laser processing apparatus 1 recorded object essential scan area of the laser beam 5 . 9 are arranged. Furthermore, z. B. be provided, occurring at different positions in transmission and / or reflection secondary light by means of light-conducting components, eg. As glass fibers, to direct to a single light sensor and thus to capture centrally.

According to a further embodiment, the control device 25 alternatively and / or additionally set up in such a way that from it the scanning laser beam 9 by means of the scan head 11 assigned to the xyz laser coordinate system over the surface 37 of the workpiece 27 can be performed. For example, the focus of the scanning beam 9 by means of the control device 25 in the form of a line screen, z. At a constant speed over the workpiece surface 37 be guided. It can while painting the surface 37 with the scanning beam 9 z. B. from the light detector 31 a brightness change of secondary light in the form of through the workpiece 27 transmitted scanning laser beam light and / or z. B. of the reflection light detector 43 a brightness change of secondary light in the form of on the workpiece 27 reflected scan laser beam light are detected, wherein the respective associated surface scan brightness curve can also be detected. The control device 25 Furthermore, it can be set up such that the structure of the workpiece surface can be derived from such a surface scan brightness curve 37 can be determined.

4 illustrates the operation of the present embodiment schematically using an in transmission of the light detector 31 recorded surface scan brightness curve. According to 4 shows the workpiece 27 z. B. areas of an opaque material (hatched) and areas of a translucent material (not hatched). The surface 37 of the workpiece 27 thus has a structure formed of two different materials.

When stroking the workpiece surface 37 with the scanning beam 9 (For example, along a line in the x-direction) changes the transmission behavior of the scanning laser beam light and thus the intensity of the light scattering plate 33 incident secondary light in the form of the workpiece 27 transmitted scanning laser beam light. When the scanning beam 9 on a region of the translucent material on the workpiece 27 incident, the scanning beam light is almost unattenuated to the light scattering plate 33 transmitted and the light detector 31 detects a high intensity Ia, whereas when the scanning beam 9 incident on a region of the opaque material, the intensity of the transmitted scanning beam light assumes a very low value Ib close to zero.

When stroking the workpiece surface 37 according to 4 thus results in the lower part of 4 shown surface scan brightness course 44 , wherein the control device 25 z. B. may be arranged such that of the transition between the two substantially constant brightness levels Ia and Ib in the surface scan brightness curve 44 is recognized as a structural boundary, here as a structural boundary between two different materials. For determining the (two-dimensional) contours of the structure of the workpiece surface 37 can the control device 25 z. B. be set up so that from her from several line scans a (two-dimensional) line image of the structure of the workpiece surface 37 is determined.

The control device 25 can z. B. be set up so that the determined by means of a surface brightness gradient structure of it can be used to identify workpieces, the structures z. B. specially provided identification structures (eg., Barcodes) can be. Furthermore, the control device 25 z. B. be set up so that from it on the basis of the determined structure deformations of a workpiece or z. B. material outbreaks on a workpiece can be determined.

According to a further embodiment, the laser processing device 1 Further, a reference structure for calibrating the means of the control device 25 and the scan head 11 achieved positioning of the scanning beam 9 (or the processing beam 5 ) exhibit. The reference structure may, for. B. reference position markings, their positioning relative to each other (and / or relative to a scan area of the laser beam 5 . 9 ), and thus can serve as a reference standard for detecting and correcting laser beam positioning inaccuracies.

The control device 25 may be arranged such that the scan beam from it 9 can be guided via the reference structure. In this case, when sweeping the reference structure with the scanning beam 9 z. B. from the light detector 31 a brightness change of secondary light in the form of transmitted through the reference structure scan laser beam light and / or z. B. of the reflection light detector 43 a brightness change of secondary light in the form of reflected at the reference structure scan laser beam light are detected, the respective associated calibration brightness curve can also be detected. The control device 25 can also be set up such that deviations of the actual laser beam position achieved from a controlled desired laser beam position are determined by it by means of the calibration brightness curve and used to correct the laser beam positioning.

5 explains the operation of the present embodiment schematically by means of a transmission by means of the light detector 31 recorded calibration brightness curve. According to 5 is the reference structure as a perforated grid 45 from one, here z. B. opaque, plate-shaped substrate 47 (hatched) with through holes formed therein 49 (not hatched) formed, wherein the through holes 49 are arranged periodically at a distance a to each other and can be used as reference position markers.

In the presence of a positionally accurate beam guidance points when sweeping the perforated grid 45 with the scanning beam 9 , here z. B. along a line in the x direction, the associated calibration brightness curve z. B. also the periodicity a of the perforated grid 45 on, in 5 represented by the dashed desired calibration brightness course 51 (where the intensity maxima of the intensity Iα are each the sweeping of a through-hole 49 with the scanning beam 9 whereas the intensity minima of intensity Iβ correspond to the sweep of an opaque substrate region).

The presence of an image field distortion or an error of the scanning beam positioning can be, for. B. make it noticeable that when crossing the perforated grid 45 with the scanning beam 9 from the control device 25 by means of the light detector 31 actually recorded actual calibration brightness curve 53 (represented by the solid brightness curve in FIG 5 ) not the periodicity a of the perforated grid 45 has, wherein z. B. from the control device 25 the location-dependent positioning error of the scanning beam 9 (in 5 illustrated by the arrows 55 . 57 . 59 . 61 ) from the shift of the actual calibration brightness curve 53 against the target calibration brightness course 51 can be determined. The thus determined positioning error can be z. B. from the control device 25 for correcting the positioning of the scanning beam 9 and / or the processing beam 5 be used.

Claims (13)

Laser processing device ( 1 ), comprising - a processing laser ( 3 ) for generating a machining laser beam ( 5 ) for structurally modifying a workpiece received in the laser processing device ( 27 ), wherein the processing laser beam in a laser coordinate system (xyz) assigned to it by means of a processing beam guiding device ( 11 ) is movable, - a scanning laser ( 7 ) for generating a scanning laser beam ( 9 ), wherein the scanning laser beam by means of a scanning beam guiding device ( 11 ) is movable according to the laser coordinate system (xyz), - a control device ( 25 ) associated with the machining beam guiding device ( 11 ) and the scanning beam guiding device ( 11 ) and is arranged such that from her the scanning laser beam ( 9 ) associated with the laser coordinate system (xyz) at at least one position (P1, P2, P3) across the outer peripheral edge ( 29 ) of a workpiece received in the laser processing apparatus ( 27 ), - a light detector ( 31 . 43 ) connected to the control device ( 25 ) and arranged and arranged such that a change in brightness of a secondary light in the form of reflected and / or transmitted scanning laser beam light by the sweeping of the outer peripheral edge ( 29 ) of the workpiece ( 27 ) by the scanning laser beam ( 9 ), as well as an edge scan including the brightness change ( 41 ) is detectable, - wherein the control device ( 25 ) is further arranged to be based thereon on the edge scan brightness progression detected by the light detector ( 31 . 43 ) for the sweeping of the at least one position (P1, P2, P3) on the outer peripheral edge ( 29 ) of the workpiece ( 27 ), the positioning of the workpiece with respect to the laser coordinate system (xyz) can be determined. A laser processing apparatus according to claim 1, wherein the control device ( 25 ) is further arranged such that it derives from the edge scan brightness course ( 41 ) detected by the light detector ( 31 . 43 ) for the sweeping of the at least one position (P1, P2, P3) on the outer peripheral edge ( 29 ) of the workpiece ( 27 ), the associated position (P1, P2, P3) of the outer peripheral edge ( 29 ) with respect to the laser coordinate system (xyz) based on the transition between two substantially constant brightness levels (I1, I2). Laser processing apparatus according to claim 1 or 2, wherein the control device ( 25 ) is set up such that the scan laser beam ( 9 ) at the at least one position (P1, P2, P3) extending in both transverse directions transversely across the outer peripheral edge ( 29 ) of the workpiece ( 27 ) to be led. Laser processing device ( 1 ), comprising - a processing laser ( 3 ) for generating a machining laser beam ( 5 ) for structurally modifying a workpiece received in the laser processing device ( 27 ), wherein the processing laser beam in a laser coordinate system (xyz) assigned to it by means of a processing beam guiding device ( 11 ) is movable, - a scanning laser ( 7 ) for generating a scanning laser beam ( 9 ), wherein the scanning laser beam by means of a scanning beam guiding device ( 11 ) is movable according to the laser coordinate system (xyz), - a control device ( 25 ) associated with the machining beam guiding device ( 11 ) and the scanning beam guiding device ( 11 ) and is arranged such that from her the scanning laser beam ( 9 ) by means of the scanning beam guiding device ( 11 ) associated with the laser coordinate system (xyz) via a surface ( 37 ) of a workpiece received in the laser processing apparatus ( 27 ), - a light detector ( 31 . 43 ) connected to the control device ( 25 ) and is arranged and arranged such that from it a brightness change of a secondary light in the form of on the workpiece ( 27 ) reflected and / or transmitted through the workpiece scan laser beam light when passing the surface ( 37 ) of the workpiece ( 27 ) with the scanning laser beam ( 9 ), as well as a surface scan brightness curve comprising the brightness change ( 44 ) is detectable, - wherein the control device ( 25 ) is further configured such that it derives from the surface scan brightness curve ( 44 ) the structure of the surface ( 37 ) of the workpiece ( 27 ) can be determined. A laser processing apparatus according to claim 4, wherein the control device ( 25 ) is further arranged such that the transition between two substantially constant brightness levels (Ia, Ib) in the surface scan brightness course ( 44 ) is recognized as a structural boundary. Laser processing apparatus according to claim 4 or 5, wherein the control device ( 25 ) is set up such that the scan laser beam ( 9 ) bidirectionally over the surface ( 37 ) of the workpiece ( 27 ) to be led. Laser processing apparatus according to one of claims 1 to 6, wherein the processing laser ( 3 ) and the scanning laser ( 7 ) are identical. Laser processing apparatus according to one of claims 1 to 7, wherein the light detector ( 31 ) is arranged so that it is located on one side of one in the laser processing apparatus ( 1 ) received workpiece ( 27 ) facing away from a scanning laser beam incident side of the workpiece, and wherein the light detector ( 31 ) is set up such that it detects the change in brightness of the secondary light in the form of transmitted scanning laser beam light. Laser processing apparatus according to one of claims 1 to 7, wherein the light detector ( 43 ) is arranged so that it is located on a scanning laser beam incidence side of a in the laser processing apparatus ( 1 ) received workpiece ( 27 ), and is arranged to detect the brightness change of the secondary light in the form of reflected scan laser beam light. Laser processing apparatus according to one of claims 1 to 9, wherein the light detector ( 31 ) - a light-scattering plate ( 33 ) arranged to receive the secondary light and adapted to diffuse the secondary light, and - one or more light sensors ( 35 ) arranged to reduce the intensity of the light scattering plate ( 33 ) can detect received secondary light. A laser processing apparatus according to any one of claims 1 to 10, further comprising a reference structure (Fig. 45 ) for calibrating the by means of the control device ( 25 ) and the scanning beam guiding device ( 11 ) achieved positioning of the scanning laser beam ( 9 ), - wherein the control device ( 25 ) is set up so that it can be read by it by means of the scanning beam guiding device ( 11 ) the scanning laser beam ( 9 ) via the reference structure ( 45 ) is feasible, - wherein the light detector ( 31 . 43 ) is set up such that a change in brightness of a secondary light in the form of at the reference structure ( 45 ) reflected and / or transmitted through the reference structure scan laser beam light, which when sweeping the reference structure ( 45 ) with the scanning laser beam ( 9 ) is generated, as well as a brightness brightness change calibration comprehensive calibration curve ( 53 ), and - wherein the control device ( 25 ) is also set up in such a way that it can be read by it by means of the calibration brightness curve ( 53 ) by means of the control device and the scanning beam guiding device ( 11 ) achieved positioning of the scanning laser beam ( 9 ) can be calibrated. Position determining device for determining the positioning of a workpiece received in a laser processing device ( 27 ), which laser processing device is a scanning laser ( 7 ) for generating a scanning laser beam ( 9 ), wherein the scanning laser beam in a laser coordinate system (xyz) by means of a scanning beam guiding device ( 11 ) is movable, comprising: - a control device ( 25 ) connected to the scanning beam guiding device ( 11 ) and is arranged such that from her the scanning laser beam ( 9 ) associated with the laser coordinate system (xyz) at at least one position (P1, P2, P3) across the outer peripheral edge (Fig. 29 ) of the workpiece received in the laser scanning device ( 27 ), - a light detector ( 31 . 43 ) connected to the control device ( 25 ) and arranged and arranged such that a change in brightness of a secondary light in the form of reflected and / or transmitted scanning laser beam light by the sweeping of the outer peripheral edge ( 29 ) of the workpiece ( 27 ) by the scanning laser beam ( 9 ), as well as an edge scan including the brightness change ( 41 ) is detectable, - wherein the control device ( 25 ) is further arranged to be based thereon on the edge scan brightness progression detected by the light detector ( 31 . 43 ) for the sweeping of the at least one position (P1, P2, P3) on the outer peripheral edge ( 29 ) of the workpiece ( 27 ), the positioning of the workpiece with respect to the laser coordinate system (xyz) can be determined. Structure determination device for determining the structure of a surface ( 37 ) of a workpiece received in a laser processing apparatus ( 27 ), which laser processing device is a scanning laser ( 7 ) for generating a scanning laser beam ( 9 ), wherein the scanning laser beam in a laser coordinate system (xyz) by means of a scanning beam guiding device ( 11 ) is movable, comprising: - a control device ( 25 ) connected to the scanning beam guiding device ( 11 ) and is arranged such that from her the scanning laser beam ( 9 ) is assigned to the laser coordinate system (xyz) by means of the scanning beam guiding device via the surface ( 37 ) of the workpiece received in the laser scanning device ( 27 ), - a light detector ( 31 . 43 ) connected to the control device ( 25 ) and is arranged and arranged such that from it a brightness change of a secondary light in the form of on the workpiece ( 27 ) reflected and / or transmitted by the workpiece scan laser beam light, which when passing the surface ( 37 ) of the workpiece ( 27 ) with the scanning laser beam ( 9 ), as well as a surface scan brightness curve comprising the brightness change ( 44 ) is detectable, - wherein the control device ( 25 ) is further configured such that it derives from the surface scan brightness curve ( 44 ) the structure of the surface ( 37 ) of the workpiece ( 27 ) can be determined.

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