Method and control unit for setting a focal position

Abstract

The present invention relates to a method for setting a focal position of a laser beam (100) of a laser system (110), wherein the laser system (110) has a machining head (120) which has laser optics and is provided to orient the laser beam (100) onto a workpiece (130), said method having the following steps: a. setting a predefined focal position; b. orienting the laser beam with the set focal position onto a location on the workpiece such that a track is intersected; c. reference-setting a reference focal position and orienting the laser beam with the reference focal position onto the location from step b.; d. detecting whether, during orienting onto the location, the laser beam with the reference focus position interacts with the workpiece [what does that mean] or lies completely within the track; and e. transferring the result of the detection, in particular to a control unit. The invention also relates to a control unit for a laser system, the control unit being designed and intended to carry out the method.

Description

[0001] Method and control unit for setting a focus position

[0002] Technical area

[0003] The present invention relates to a method for adjusting a focus position of a laser beam of a laser system and a control unit configured and provided to carry out the method.

[0004] State of the art

[0005] Laser systems, especially multi-axis laser systems, have become an indispensable technology in many industries in recent years. They offer high precision and flexibility and enable materials to be processed efficiently, for example, by cutting, welding, and / or coating. Laser systems feature a processing head with laser optics that directs a high-intensity laser beam onto a workpiece. The laser beam has a focal position, also called the beam waist, in which the diameter of the laser beam, also called the spot diameter, is minimal. The specific focal position of a laser beam depends on the respective laser system. The theoretical focal position, which is known in advance, is subject to a tolerance of up to 2 mm. The actual focal position is therefore unknown.The tolerance is due, for example, to mechanical deficiencies within the laser optics, such as minimal deviations in manufacturing, and / or deviations in the production of optical components and / or contamination of the lenses involved.

[0006] For optimal machining of the workpiece, depending on the machining process, it is desirable for the laser beam to hit the workpiece at least in the area of ​​the focus position, because this is where the laser energy density is greatest. Due to the tolerances mentioned, the actual focus position is unknown for the respective laser system, which is why the focus position of the laser beam must be adjusted individually. Japanese laid-open patent application JP 2016 002580 A discloses a method in which a laser is moved orthogonally to a plane containing an opening that is minimally larger than the laser diameter at an ideal focus position. International publication WO 2017 220682 A1 discloses a method for determining a reference focus position, wherein a relative movement trajectory is intersected.

[0007] Description of the invention

[0008] Based on the known prior art, it is an object of the present invention to provide an improved method for adjusting a focus position of a laser beam of a laser system, as well as a control unit for a laser system. The invention aims in particular to enable efficient, reproducible adjustment of the focus position that compensates for deviations between the actual focus position and the theoretical focus position. Furthermore, the invention particularly aims at adjusting the focus position in which components existing in a laser system can be used for adjustment without resorting to specific adjustment tools that are used exclusively for adjusting the focus position. The invention can also aim to integrate the adjustment of the focus position into a processing sequence in a time- and material-saving manner.

[0009] The object is achieved by a method for adjusting the focus position of a laser beam of a laser system and a control unit for a laser system according to the features of the independent claims. Advantageous further developments emerge from the subclaims, the description, and the figures.

[0010] Accordingly, a method for adjusting a focus position of a laser beam of a laser system is proposed, wherein the laser system has a processing head with laser optics designed to align a laser beam onto a workpiece. The focus position, also called the beam waist, is the position at which the diameter of the laser beam, also called the spot diameter, is minimal. This focus position can be desired because the highest energy density of the laser beam prevails at the smallest diameter. The focus position, which is determined, among other things, by the laser optics, can be adjusted such that a deviation of an actual focus position from a theoretical focus position is compensated. The theoretical focus position can be the focus position that the respective laser system is intended to have. The actual focus position can be the focus position that the respective laser system has.The actual focus position may deviate from the theoretical focus position due to tolerances. The tolerances can be due to mechanical deficiencies within the laser optics, for example due to minimal deviations in manufacturing, and / or deviations in the production of optical components and / or contamination of the lenses involved. The set focus position can ensure that the laser beam is aligned under optimal conditions. The laser system can be a system for laser cutting, laser welding and / or laser cladding. In a system for laser cutting and / or laser welding, the focus position can be set so that it hits the workpiece in the focus position. In a system for laser cladding, the focus position can be set so that it hits the workpiece on or above the workpiece surface.The workpiece can be a calibration workpiece used solely for determining the focus position. Alternatively, the workpiece can be a scrap part, i.e., a scrap part that remains after machining a good part.

[0011] The method comprises the step (a.) of setting a predetermined focus position. Even if the actual focus position is unknown, the focus position can nevertheless be set to a predetermined deviation. The predetermined focus position can deviate from the actual focus position such that it lies above the actual focus position. Even if the actual focus position is unknown, its magnitude is known. For example, the predetermined focus position can be set such that it is a certain value, for example 2 mm, above the actual focus position. If, for example, the actual focus position in a first case is 4 mm away from an exit of the laser beam from a light channel of the processing head and in a second case is 3 mm away from the exit of the laser beam, the focus position in the present example can be step (a.) can be set to a distance of 2 mm from the exit in the first case and 1 mm from the exit in the second case. The setting can be made by a control unit. An operator of the laser system can communicate with the control unit via a user interface and specify the predetermined focus position. The predetermined focus position can vary depending on the laser system, the intended processing, and / or the laser source used and its power.

[0012] The method comprises the step (b.) of aligning the laser beam with the adjusted focus position to a position on the workpiece such that a track is cut. A position can also be understood to mean a longitudinally stretched position. For example, the laser beam can be directed along a longitudinally stretched position on the workpiece in order to cut a longitudinally stretched position therein. The cut track can result in a recess in the workpiece. The recess has a width that can be determined by the laser beam. In step (a.), the predetermined focus position can be adjusted such that it lies above the actual focus position. The alignment according to step (b.) thus results in a track whose width is greater than the width that would be present for a track of a laser beam in which the focus position was adjusted such that it compensates for the tolerances and lies close to the actual focus position.

[0013] The method comprises the step (c.) of setting a reference focus position and aligning the laser beam with the reference focus position to the position from step (b.). The reference focus position can be an adjustable focus position. It can remain constant over different adjustment cycles. The alignment according to step (c.) can correspond in terms of its movement to the alignment from step (b.). Alternatively, the laser beam in step (b.) can be aligned to a longitudinally stretched position in order to intersect the track, while the laser beam in step (c.) is aligned to a point-like position that intersects the longitudinally stretched position from step (b.). Step (c.) can be carried out immediately after step (b.). The reference setting can be performed by the control unit. An operator of the laser system can communicate with the control unit via the user interface and specify the reference focus position.The reference focus position may vary depending on the laser system, the intended processing and / or the laser source used and its power.

[0014] The method comprises the step (d.) of detecting whether the laser beam with the reference focus position interacts with the workpiece during alignment to the position or lies completely within the track and therefore does not interact with the workpiece. Interaction with the workpiece can be understood as the laser beam hitting the workpiece. The detection can serve to establish whether the laser beam with the reference focus position, which is directed to the position from step (b.) according to step (c.), is within the track that was cut according to step (b.) and therefore does not interact with the workpiece, or whether the laser beam with the reference focus position has such a width that it cannot lie within the track and therefore interacts with the workpiece. For example, a track can be cut in step (b.) that corresponds to the width of the laser beam set in step (a.).If the laser beam with the reference focus position according to step (c.) now has a width that is greater than the width of the laser set in step (a.), the laser beam with the reference focus position interacts with the workpiece, which is detected accordingly in step (d.). However, if the laser beam with the reference focus position according to step (c.) has a width that is smaller than the width of the laser set in step (a.), the laser beam with the reference focus position lies completely within the track that was cut in step (b.) and therefore does not interact with the workpiece. By detecting whether or not the laser beam with the reference focus position interacts with the workpiece, a statement can be made regarding the width of the respective laser beam with the respective focus position. The method can comprise the step (e.) of transmitting a result of the detection, in particular to a control unit.The result can be transmitted in binary form. A 0 can be transmitted if it was detected in step (d.) that the laser beam with the reference focus position lies completely within the track, and a 1 can be transmitted if it was detected in step (d.) that the laser beam with the reference focus position interacts with the workpiece. Thus, after each cut track and each subsequent alignment of the laser beam with the reference focus position, a control unit can be informed whether an interaction has occurred ("1") or not ("0") in the respective cut track.

[0015] Thus, the effect of a laser beam with varying focus position intersecting a track with a width that varies according to the focus position can be used to adjust the focus position. This enables a time-efficient, resource-saving, and reproducible adjustment of the focus position of a laser system. Tolerances that lead to a deviation between the theoretical focus position and the actual focus position can be compensated for by an appropriately adjusted focus position. Additional steps for measuring individual tracks, for example, through the use of additional tools for determining a focus position, such as a feeler gauge, are no longer necessary. This correspondingly shortens the time required to calibrate the laser system before processing components. The reliability of the laser system is also increased because the process for adjusting the focus position is less error-prone due to the elimination of additional steps.

[0016] In one embodiment, the method comprises the step (f.) of moving the machining head to a changed position on the workpiece. For example, after cutting the track in step (b.), the machining head may be displaced to be able to cut another track parallel to the first track. The angle between the machining head and the workpiece, as well as the distance between these components, may be unaffected by the movement in step (f.). Thus, step (f.) may place the machining head in the basic position to cut another track.

[0017] In one embodiment, the method comprises the step (g.) of setting a focus position that is different from step (a.). The respectively set focus position can determine the width of the track cut by the respective laser beam. Since the width of the track can vary with the respective focus position, a changed focus position can provide further information about the focus position. The changed focus position from step (g.) can differ both from the predetermined focus position and from the reference focus position. It can be varied, for example reduced, by a predefined step width compared to the predetermined focus position. In one embodiment, the method comprises the step (h.) of carrying out steps (b.) to (e.) starting from the changed position with the changed focus position. This means that steps (b.) to (e.) are carried out with the proviso that instead of the position determined in step (a.) set, the focus position changed according to step (g.) is now used and that the position to which the laser beam is aligned according to step (b.) deviates from the position to which it was aligned when steps (a.) to (e.) were carried out for the first time, according to step (f.). When steps (a.) to (e.) are carried out for the first time, a first track with a first width can have been cut. Since the processing head was moved according to step (f.) and the laser beam has a changed focus position according to step (g.), a second track with a second width can be cut when steps (b.) to (e.) are carried out again according to step (h.). Since the width of the track can vary with the respective focus position, a changed focus position can provide further information about the focus position. The reference focus position according to step (c.) can remain unaffected by setting the changed focus position according to step (g.).Precisely because the reference focus position remains constant, a reliable comparison measure for the respective track width and thus the respective focus position can be provided.

[0018] In one embodiment, steps (a.) to (h.) are repeatedly carried out until a plurality of tracks have been cut, each starting from a plurality of changed positions with respectively changed focus positions, wherein the plurality is in particular between 15 and 25, more particularly 21. Thus, between each application of a laser beam with a changed focus position, the processing head can be moved in order to cut a new track in a changed position. Each track can have a varying width due to the respectively changed focus positions. The reference focus position from step (c.) can be constant across the various tracks. In this respect, the laser beam with the reference focus position can serve as a measure for evaluating the respective track width of the various tracks that were cut with each changed focus position.Since the width of the track can vary with the respective focus position, a changed focus position can provide additional information about the focus position.

[0019] In one embodiment, the reference setting according to step (c.) and the subsequent detection according to step (d.) are carried out immediately after the alignment according to step (b.), in particular when a plurality of tracks have been cut. The processing head of the laser system is movable. It can be driven by a gear. A gear has backlash. This is a positioning error caused by a reversal of the direction of travel. The backlash is caused by play between the elements of the gear. The backlash influences the bidirectional repeatability. In this respect, the play caused by the backlash can be prevented from having an influence on the sensitive focus position adjustment, in particular because the detection according to step (d.) has already been carried out before movement according to step (f.).

[0020] In one embodiment, the reference setting according to step (c.) and the subsequent detection according to step (d.) are only performed once a plurality of tracks have been cut. In particular, the movement according to step (f.) can take place before the reference setting (c.) and the subsequent detection according to step (d.) are performed. Thus, a plurality of tracks can be cut first before their respective widths are evaluated using the laser beam with the reference focus position. Thus, setting the reference focus position according to step (c.) is only required once, even if a plurality of tracks are cut. The alignment of the laser beam with the reference focus position can, of course, take place for each cut track.

[0021] In one embodiment, process-appropriate laser processing, in particular laser cutting, for producing a good part takes place between the detection according to step (d.) and the movement according to step (f.), so that the laser beam is aligned with the set focus position on a residual skeleton, i.e. a scrap part. In this way, the adjustment of the focus position can be integrated into the laser processing for producing the good part. In this way, the individual tracks within a laser processing step can be distributed over a longer period of time because the sequence of at least two consecutive alignment steps is interrupted by at least one processing cut. For example, only one track is created in the residual skeleton as a good part for each machined workpiece part and checked by reference setting the reference focus position.After the adjustable number of tracks at different positions with each different focus position, for example, after 21 cut parts, the optimal focus position can be precisely determined. The fact that the first few cut parts—in this example, the first 21 cut parts—are at least partially cut with a focus position that deviates from the optimum is accepted in light of the advantage that the determination of the focus position can be integrated into the laser processing.

[0022] In one embodiment, the method comprises the step of evaluating the at least one transmitted result in order to determine a standard focus position that is preset chronologically after the method for adjusting the focus position during the processing of components, and in particular, it comprises the step of storing the standard focus position in a control unit of the laser system. In particular, the evaluation step includes evaluating the plurality of changed focus positions and the tracks cut by them and their widths. Thus, each detection of whether or not there is an interaction between the laser beam with the reference focus position and the workpiece can be stored accordingly in a control unit, and from this, the knowledge can be derived as to how the focus position is to be adjusted in order to obtain an optimal focus position. This knowledge can then be stored in a control unit as a standard focus position.In subsequent processing of components that are processed according to a trajectory stored in the control unit, the standard focus position can be used, particularly to compensate for inaccuracies in the actual focus position. Furthermore, after calibrating the laser beam once with a corresponding focus position, different component series can be processed without the need for further calibration.

[0023] In one embodiment, the evaluation of the at least one transmitted result comprises further steps, namely the step of evaluating the position at which the laser beam interacts with the workpiece and the position at which the laser beam lies completely within the respective track, and setting the standard focus position to a focus position that is in the range of a focus position at which the laser beam interacts with the workpiece, in particular that corresponds to this. For example, the result can be transmitted in binary form. If it was detected in step (d.) that the laser beam lies completely within the track with the reference focus position, a 0 can be transmitted, and if it was detected in step (d.) that the laser beam interacts with the workpiece with the reference focus position, a 1 can be transmitted.In this way, after each cut track and each subsequent alignment of the laser beam with the reference focus position, a control unit can be informed whether an interaction has occurred in the respective cut track (“1”) or not (“0”). The evaluation can then record, for each transmitted 0 and each transmitted 1, at which position a 0 and at which position a 1 was determined. The standard focus position is then set to a focus position that is in the range of at least one focus position for which a 1 was transmitted. This is because transmitting a 1 can mean that the laser beam with the reference focus position is wider than the previously cut track, which is why the changed focus position of the previously cut track has at least a better focus position than the laser beam with the reference focus position.

[0024] In one embodiment, when setting the standard focus position, the focus position is determined as the standard focus position which is an arithmetic mean of those focus positions at which the laser beam has interacted with the workpiece. If, for example, 21 tracks are cut, the laser beam of the respectively changed focus position in the area of ​​the workpiece in tracks 1 to 5 and 17 to 21 can be wider than the laser beam with the reference focus position. In tracks 6 to 16, an interaction can be detected when aligning the laser beam with the reference focus position, which is why the laser beam of the respectively changed focus position in the area of ​​the workpiece in tracks 6 to 16 is narrower than the laser beam with the reference focus position.The arithmetic mean of those focus positions at which the laser beam interacted with the workpiece is therefore "6", as the first interacting focus position, plus "16", as the last interacting focus position, divided by "2" is equal to "11 In this example, the focus position is set to the value that was in the eleventh track. The focus position of the first track can be selected so that it is above the workpiece. It can then be adjusted downwards with each new track. This means that the focus position moves from above the workpiece to below the workpiece. This means that the optimal, because narrowest, focus position moves through the workpiece. This behavior can be used in that the optimal focus position is midway between the last focus position above the workpiece and the first focus position below the workpiece.

[0025] In one embodiment, the laser system adjusts the laser optics according to the determined standard focus position. This adjustment can be performed without further operator interaction or interaction with other tool components. Therefore, the focus position adjustment can be automated because no additional components are required.

[0026] In one embodiment, the predetermined focus position and the reference focus position are set such that they are above the workpiece. Even if the actual focus position is unknown, its magnitude is known. Thus, the laser beam can be adjusted such that the focus position is always above the workpiece. This then enables a gradual lowering of the focus position and, consequently, a shift of the actual focus position from above the workpiece to below it.

[0027] In one embodiment, the predetermined focus position is set such that it lies above the reference focus position. The reference focus position can also be set such that it lies above the workpiece. The predetermined focus position can thus be the focus position at which the focus position is furthest away from the workpiece during the method for adjusting the focus position. This ensures, in particular, that the optimal focus position can actually be detected by gradually reducing the changed focus position.

[0028] In one embodiment, with each adjustment of a further focus position, the focus position is shifted relative to the previous focus position toward the workpiece, and in particular through the workpiece. This ensures, in particular, that the optimal focus position can actually be detected by shifting the focus position through the workpiece. In particular, in combination with the determination of the arithmetic mean, a focus position can thus be efficiently determined and adjusted accordingly.

[0029] In one embodiment, the offset remains the same for each change in the focus position with each repetition. Thus, the number of cut tracks has a linear relationship to the path the focus position has traveled from above the workpiece to below the workpiece. This ensures, in particular, that the optimal focus position can actually be detected and that the determination of the arithmetic mean enables efficient focus position determination. The respective offset can be less than or equal to 0.4 mm. It can also be refined in steps. If the offset is reduced, it can also be increased again to provide an essentially symmetrical step size variation.

[0030] In one embodiment, the generation of process light is detected by a sensor during at least one detection. It is also possible to monitor during each detection whether process light occurs when the laser beam is aligned with the reference focus position, thus the laser beam interacts with the workpiece, or not, thus the laser beam lies completely within the track. This allows for efficient determination of whether a corresponding beam width is present or not.

[0031] In one embodiment, a width of the at least one track corresponds to the width of the respective aligned laser beam. Since the width of the track can vary with the respective focus position, a changed width can provide further information about the focus position.

[0032] In one embodiment, the workpiece is a sheet metal strip, along whose edge the respective tracks are cut like a comb. The workpiece can be a calibration workpiece that is no longer used after the focus position has been adjusted. Once the focus position has been adjusted, the laser system can process corresponding component series at the optimal focus position. This enables laser processing with the highest precision from the first processing step. Alternatively, the workpiece can be a scrap part, i.e. a scrap part that remains after a good part has been processed. This allows the focus position to be adjusted during laser processing, which contributes to process efficiency.

[0033] The disclosure further relates to a control unit for a laser system, which is configured and provided to carry out the method according to the disclosure. The control unit can be part of the laser system. An operator can communicate with the control unit via a user interface. The disclosure further relates to a laser system having a processing head with laser optics, which is provided to direct a laser beam onto a workpiece, wherein the laser system further comprises the control unit according to the disclosure.

[0034] Short description of the characters

[0035] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0036] Figure 1 is a schematic view of a laser system;

[0037] Figure 2 is a schematic view of different laser beams with different focus positions;

[0038] Figure 3 is a schematic view of a workpiece into which focus layers have been cut by different laser beams;

[0039] Figure 4 is a schematic view of a method for adjusting a focus position; and

[0040] Figure 5 shows a workpiece machined by the process.

[0041] Detailed description of preferred embodiments

[0042] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0043] Figure 1 shows a laser system 110 with a processing head 120 having laser optics. The processing head 120 directs a laser beam 100 with a focus position onto a workpiece 130. The focus position, also called the beam waist, is the position at which the diameter of the laser beam 100, also called the spot diameter, is minimal. This focus position can be desired because the highest energy density of the laser beam prevails at the smallest diameter. The focus position, which is determined, among other things, by the laser optics of the processing head 120, can be adjusted such that a deviation of an actual focus position from a theoretical focus position is compensated. The theoretical focus position can be the focus position that the respective laser system 110 is intended to have. The actual focus position can be the focus position that the respective laser system has. The actual focus position can deviate from the theoretical focus position due to tolerances.The tolerances can be due to mechanical deficiencies within the laser optics, for example due to minimal deviations in manufacturing, and / or deviations in the production of optical components and / or contamination of the lenses involved. The adjusted focus position can cause the laser beam 100 to be aligned under optimal conditions. The laser system 110 can be a system for laser cutting, laser welding and / or laser cladding. In a system for laser cutting and / or laser welding, the focus position can be adjusted such that it strikes the workpiece 130 in the focus position. In a system for laser cladding, the focus position can be adjusted such that it strikes the workpiece 130 on or above the workpiece surface 130.The workpiece 130 may be a rectangular sheet having a dimension of a few centimeters, for example a length between 8 cm and 20 cm and a width between 4 cm and 10 cm.

[0044] Figure 2 shows three laser beams 101, 102, 103. These are each provided by a laser system 100 of identical design. However, the first laser beam 101 has a first focus position F1, the second laser beam 102 a second focus position F2, and the third laser beam 103 a third focus position F3, whereby the three focus positions F1, F2, F3 differ in their position. This differentiation of the focus positions of the individual laser beams of the respective laser systems can be attributed to mechanical deficiencies within the laser optics, for example due to minimal deviations in manufacturing, and / or deviations in the production of optical components and / or contamination of the lenses involved. In order to use the laser system 110 with high quality, the position of the respective focus position of the laser system 110 must be adjusted.This is because the diameter of the laser beam, also called the spot diameter, is minimal at the focal position, which is why the laser beam's energy density is highest there. Accordingly, the laser system can adjust the focal position after determining it so that the workpiece is processed by the laser beam at the focal position. The focal positions F1, F2, and F3, for example, can differ by up to 2 mm.

[0045] Figure 3 shows a method for adjusting the focus position of the laser beam 100 of the laser system 110. In the upper section on the left, a laser beam with a predetermined focus position is first directed onto the workpiece 130. This creates a first track. This has a first width B1, as shown in the middle section on the left. The predetermined focus position is selected such that it lies above the workpiece 130. Thus, the width B1 of the first track is greater than a width at an optimal focus position. After cutting the first track, the laser beam is adjusted to a reference focus position. The reference focus position is selected such that it is above the workpiece 130 and below the predetermined focus position.When the laser beam with the reference focus position is aligned to a position of the first track, as indicated in the left image of the lower section, the laser beam with the reference focus position does not interact with the workpiece 130 and lies entirely within the first track. This is detected by a sensor 140 and passed on to a control unit. For example, a "0" can be stored in the control unit for the first track to store the result of the lack of interaction.

[0046] In the next step, the focus position is changed compared to the predetermined focus position. The middle image in the upper section shows how the laser beam is aligned with the changed focus position on the workpiece 130. The changed focus position is offset towards the workpiece compared to the predetermined focus position. The changed focus position cuts a second track with the width B2 into the workpiece 130, as shown in the middle image in the middle section. To measure the width B2 of the second track, the laser beam with the reference focus position is directed onto the workpiece 130 at the position of the second track. In the present example, the width of the laser beam with the reference focus position is wider than the laser beam with the changed focus position, as shown in the middle image in the lower section.When the laser beam is aligned with the reference focus position on the workpiece 130 at the position of the second track, the sensor 140 detects an interaction between the workpiece 130 and the laser beam with the reference focus position. This is passed on to the control unit. For example, a "1" can be assigned to the control unit for the second track in order to save the result of the detected interaction.

[0047] In the next step, the focus position is changed again compared to the changed focus position. The right-hand image in the upper section shows how the laser beam is aligned with the again changed focus position on the workpiece 130. The again changed focus position is offset further downwards compared to the previously changed focus position. The again changed focus position cuts a third track with the width B3 into the workpiece 130, as shown in the right-hand image in the middle section. To measure the width B3 of the third track, the laser beam with the reference focus position is directed onto the workpiece 130 at the position of the third track. In the present example, the width of the laser beam with the reference focus position is smaller than the laser beam with the again changed focus position, as shown in the right-hand image in the lower section.When the laser beam is aligned with the reference focus position on the workpiece 130 at the position of the third track, the sensor 140 therefore detects no interaction between the workpiece 130 and the laser beam with the reference focus position. This is again passed on to the control unit. For example, a "0" can be stored in the control unit for the third track to store the result of the lack of interaction.

[0048] The results stored in the control unit can be evaluated. Compared to the predetermined focus position used for the first track, the focus position was shifted downwards twice. In doing so, the focus position moved through the workpiece 130. The control unit stores that no interaction took place between the respective laser beam and the workpiece in the first and third tracks. Furthermore, it stores that interaction did take place in the second track. From this behavior, the control unit can determine that the changed focus position set for the second track resulted in the narrowest width. Of the three set focus positions from the example in Figure 3, the changed focus position of the second track is therefore the one that can be set as the standard focus position.The more tracks are cut and the smaller the respective change in the focus positions, the more precisely the focus position can be adjusted close to the optimal focus position. In particular, 21 tracks can be cut.

[0049] Figure 4 shows five steps of the disclosed method. A plurality of tracks are cut into the workpiece 130, which is formed as a sheet metal in this case. Of the five steps shown, the sensor 140 detects an interaction between the workpiece 130 and the reference laser beam in the middle and second-to-lowest sections of Figure 4 after the respective track has been cut. For example, the middle section of Figure 4 can represent a sixth track, and the second-to-lowest section of Figure 4 can represent a sixteenth track. This would result in the following evaluation table, which is stored in the control unit:

[0050] In the first five tracks, no interaction was detected between the laser beam with the reference focus position and the workpiece 130 after cutting the respective tracks. Accordingly, a "0" is stored in the evaluation table for the respective track. From the sixth track to the sixteenth track, the sensor 140 detected an interaction between the laser beam with the reference focus position and the workpiece 130. Accordingly, a "1" is stored in the evaluation table for these tracks. From the seventeenth to the twenty-first track, no interaction was detected between the laser beam with the reference focus position and the workpiece 130. Accordingly, a "0" is stored in the exhibition table for the respective track.The above evaluation table can be interpreted as follows: since an interaction occurred from the sixth to the sixteenth track, it can be concluded that the optimal focus position lies between the focus position set at the sixth track and the focus position set at the sixteenth track. In particular, if the focus position was shifted downwards between the sixth and the sixteenth track with a constant step size, the average value of 6 and 16 can be used to determine the track where the optimal focus position was achieved. The control unit can then determine that the focus position at the eleventh track will be used as the default focus position when machining subsequent components.

[0051] In another example, the evaluation table can have the following form:

[0052] From this evaluation table, it can be concluded that the optimal focus position was set between the tenth and fifteenth tracks. When determining the standard focus position, the focus position that is the arithmetic mean of the focus positions at which the laser beam interacted with the workpiece can be determined as the standard focus position. In this case, the arithmetic mean is 12.5. Thus, the control unit can determine that the focus position between the focus position at the twelfth track and the focus position at the thirteenth track will be used as the standard focus position when machining subsequent components.

[0053] Figure 5 shows the workpiece 130 from above, similar to a sheet metal view. On the left-hand side, a first track has been cut. In this track, the focus position is well above the workpiece. A second track to the right of the first track has a smaller width. In this track, the focus position is closer to the workpiece. A third, fourth, and fifth track are so narrow that the laser beam interacts with the workpiece at the reference focus position, as indicated by the highlighted stars. In these tracks, the focus position of the respective laser beam is closer to the optimal focus position than the reference focus position. A sixth and seventh track are again wide enough that the laser beam does not interact with the workpiece at the reference focus position. The optimal focus point has therefore moved from above the sheet metal to below the sheet metal. Of the seven tracks cut in Figure 5, the third track was cut.April and fifth, an interaction between the laser beam with the reference focus position and the workpiece is detected. Accordingly, the control unit can determine that the focus position present in the fourth track is used as the standard focus position when machining subsequent components. Where applicable, all individual features presented in the exemplary embodiments can be combined and / or interchanged without departing from the scope of the invention.

[0054] Reference symbols

[0055] 100 laser beam

[0056] 101 first laser beam

[0057] 102 second laser beam

[0058] 103 third laser beam

[0059] 110 laser system

[0060] 120 machining head

[0061] 130 workpiece

[0062] 140 sensors

[0063] F1 first focus position

[0064] F2 second focus position

[0065] F3 third focus position

[0066] B1 first width

[0067] B2 second width

[0068] B3 third width

Claims

Claims 1. A method for adjusting a focus position of a laser beam (100) of a laser system (110), wherein the laser system (110) has a processing head (120) with laser optics, which is provided for aligning the laser beam (100) onto a workpiece (130), comprising the steps of: a. setting a predetermined focus position; b. aligning the laser beam with the adjusted focus position to a position on the workpiece such that a track is cut; c. setting a reference focus position and aligning the laser beam with the reference focus position to the position from step b.; d. detecting whether the laser beam with the reference focus position interacts with the workpiece during alignment to the position or lies completely within the track; and e. in particular transmitting a result of the detection, in particular to a control unit.

2. The method according to claim 1, comprising the steps: f. moving the machining head to a changed position on the workpiece; g. setting a focus position that is different from step a.; and h. performing steps b. to e. starting from the changed position with the changed focus position.

3. Method according to claim 2, wherein steps a. to h. are carried out repeatedly until a plurality of tracks have been cut, in each case starting from a plurality of changed positions with respectively changed focus positions, wherein the plurality is in particular between 15 and 25, further in particular being 21.

4. Method according to one of the preceding claims, wherein the reference setting according to step c. and the subsequent detection according to step d. are carried out immediately after the alignment according to step b.

5. Method according to one of claims 1 to 3, wherein the reference setting according to step c. and the subsequent detection according to step d. are only carried out when a plurality of tracks have been cut.

6. Method according to one of the preceding claims, wherein between the detection according to step d. and the movement according to step f., a process-appropriate laser processing for producing a good part takes place.

7. Method according to one of the preceding claims, comprising the step Evaluating the at least one transmitted result in order to determine a standard focus position which is preset in time after the method for setting the focus position during the processing of components and in particular storing the standard focus position in a control unit of the laser system, wherein the evaluation of the at least one transmitted result comprises in particular the following steps: Evaluate at which position the laser beam interacts with the workpiece and at which position the laser beam lies completely within the respective track; and Setting the standard focus position to a focus position that is in the range of a focus position at which the laser beam interacts with the workpiece, in particular coincides with this.

8. The method according to claim 7, wherein, in determining the standard focus position, that focus position is determined as the standard focus position which is an arithmetic mean of those focus positions at which the laser beam has interacted with the workpiece, wherein in particular the laser system adjusts the laser optics according to the determined standard focus position.

9. Method according to one of the preceding claims, wherein the predetermined focus position and the reference focus position are adjusted such that they lie above the workpiece.

10. Method according to one of the preceding claims, wherein the predetermined focus position is set such that it lies above the reference focus position. 11 . Method according to one of the preceding claims, wherein with each setting of a further focus position, the focus position is offset relative to the previous focus position towards the workpiece and in particular through the workpiece, wherein furthermore in particular the offset remains the same with each repetition.

12. The method according to any one of the preceding claims, wherein, in the at least one detection step, the generation of process light is detected by means of a sensor (140).

13. The method according to any one of the preceding claims, wherein a width of the at least one track corresponds to the width of the respectively aligned laser beam, wherein, in particular, the workpiece is a sheet metal strip, at the edge of which the respective tracks are cut in the manner of a comb.

14. A control unit for a laser system, configured and intended to carry out the method according to the preceding claims.

15. Laser system (110) for machining a workpiece, comprising a machining head (120) with laser optics, wherein the machining head (120) is provided to direct a laser beam (100) onto a workpiece (130); a control unit according to claim 14.

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