Optical coherence tomography apparatus for laser processing system and laser processing system having the same

Abstract

The invention relates to an optical coherence tomography device for measuring the distance from an object in a predetermined distance region in a laser processing system, comprising: a measuring arm for aligning a measuring beam to the object; a reference arm for guiding a reference beam, the reference arm having a plurality of reference segments, the reference segments having different measurement regions; and a controllable switching element for switching between the reference segments of the reference arms. The measurement area of each reference road section comprises a negative active measurement area and a positive active measurement area, and the dead zone is located between the negative active measurement area and the positive active measurement area. A dead zone of one of the reference segments overlaps a negative or positive active measurement region of at least one individual reference segment. The positive and negative active measurement regions of the reference section together cover a predetermined distance region.

Description

Technical Field

[0001] The present disclosure relates to an optical coherence tomography device for a laser processing system, wherein the optical coherence tomography device is used for measuring a distance between an object and a workpiece, and a laser processing system having the optical coherence tomography device. Background Art

[0002] In systems for material processing with the aid of lasers, i.e. in laser processing systems, a laser beam emitted by a laser light source or the end of a laser-conducting fiber is focused or bundled onto the workpiece to be processed by means of beam guidance optics or focusing optics. Laser processing heads with collimator optics and focusing optics are typically used, with the laser light being supplied via an optical fiber. In laser material processing, optical coherence tomography (OCT) devices can be used in order to measure various process parameters, such as the distance to the workpiece, the edge position in upstream processes, and the weld penetration depth during welding processes or the surface topography in downstream processes. In this case, the measuring beam is directed to the desired position on the workpiece by means of a scanner device.

[0003] Optical coherence tomography (OCT) uses interference effects to determine the distance difference relative to a reference section. The predefined reference section of the OCT device determines the absolute distance to the object to be measured. At this distance, the measurement can be carried out in the measurement area. The measurement area of ​​the OCT is determined by the characteristics of the measurement light source (e.g. superluminescent diode) and the detector used. Typically, the size of the measurement area is in the range of a few millimeters <20 mm. In other words, the OCT device measures the difference between the optical path length of the measuring arm and the optical path length of the reference arm in order to determine the distance.

[0004] In so-called scanner laser processing systems, the laser beam (i.e., the processing laser beam) can be directed to different positions on the workpiece with the aid of a scanner device. Typically, the scanner device includes at least one scanning element, such as at least one scanning mirror, which can pivot around one or two axes to deflect the laser beam. Therefore, in a scanner laser processing system, the optical path length (OWL) changes with the deflection of the mirror. In order to be able to perform the same measurement in the entire working area or scanning area, the OWL change needs to be taken into account during the measurement and thereby reduce the OCT measurement area that can be effectively used. In many cases, the increase in the optical path length is greater than the measurement area of ​​the OCT. Then, especially at the edge of the scanning area, it is no longer possible to perform spacing measurements. For this reason, it is necessary to use multiple reference sections with different lengths or different measurement areas or to use reference sections that can be changed in length so that measurements can be performed in the entire scanning area.

[0005] Known methods for increasing the measuring range of an OCT measuring system, such as those described in DE 10 2013 008 269 A1, are based on a synchronous adaptation of the optical path length in the reference arm. The adaptation is carried out by mechanically changing the optical path length of the reference arm, for example by changing the position of an end mirror or a prism on a linear axis. The disadvantage of these methods is the very complex control of the described mechanical device. EP 3 830 515 B1 describes an OCT measuring system in which the reflected measuring light is simultaneously guided into a plurality of reference paths of the reference arm.

[0006] These known methods utilize a unilateral measurement region of the OCT measurement system, i.e. a positive measurement region or a negative measurement region (i.e. a positive or negative solution of the Fourier transform of the output distance signal). In this case, it is determined, for example, by pre-calibration, which part of the measurement region is used in order to achieve a clear uniqueness of the measurement and to avoid singularities at the zero point. Thus, the number of reference sections that should cover the distance region ΔM is generated: N=ΔM / Δm, wherein Δm is the maximum possible measurement region under the reference arm setting, i.e. the reference arm setting for the reference section. Here, the maximum possible measurement region refers to a unilateral measurement region in which a recognizable measurement signal can be detected. For example, in the case of a scanner laser processing system, the pre-determination of a large ΔM leads to the need to construct a large number of reference sections. Therefore, for use in a scanner laser processing system, a very high number of reference sections is required or other expensive components need to be used, which leads to high manufacturing costs, a large space requirement and high calibration costs. Summary of the invention

[0007] The object of the present invention is to propose an optical coherence tomography device for a laser processing system, wherein the optical coherence tomography device is used for measuring the distance to an object or a workpiece, wherein the optical coherence tomography device comprises an extended measuring area or enables better use of the measuring area, and to propose a laser processing system having the optical coherence tomography device.

[0008] The object of the present invention is to propose a cost-effective and compact optical coherence tomography device for a laser processing system, the optical coherence tomography device being used for measuring the distance to an object or a workpiece, the optical coherence tomography device in particular having as large a measuring area as possible and as small a number of reference sections in the reference arm structure as possible, and to propose a laser processing system having the optical coherence tomography device.

[0009] The object of the present invention is to provide a cost-effective and compact optical coherence tomography device for a laser processing system, the optical coherence tomography device being used for measuring the distance to an object or to a workpiece, the optical coherence tomography device having in particular a large measuring area and a compact reference arm structure, and to provide a laser processing system having the optical coherence tomography device.

[0010] The object of the present invention is to propose an optical coherence tomography device for a scanner laser processing system, the optical coherence tomography device being used for measuring the distance to an object or a workpiece, the optical coherence tomography device being suitable for measuring large surfaces on which components or workpieces having different heights (due to assembly and production tolerances) are placed, and to propose a laser processing system having the optical coherence tomography device.

[0011] The object of the present invention is to provide an optical coherence tomography device for a scanner laser processing system, which is used for measuring the distance to an object or a workpiece, and which has a compact and passive reference arm structure so that components can be measured at different positions despite relatively large height fluctuations due to mechanical tolerances, and to provide a laser processing system having this optical coherence tomography device.

[0012] At least one of these tasks is achieved by the optical coherence tomography apparatus according to the present invention and a laser processing system having the optical coherence tomography apparatus.

[0013] The invention is based on the idea of ​​using a reference arm with a plurality of reference sections in an optical coherence tomography device for distance measurement in laser processing, wherein the number of required reference sections is reduced in that a switching element or an element that can be controlled (e.g. a motor or, in particular, a MEMS-based fiber optic switch) ensures the change between the individual reference sections and utilizes both the positive and the negative measuring range of the reference section. The sensor principle used here is optical short-coherence interferometry for distance measurement. In this disclosure, "distance" may also be referred to as "relative distance".

[0014] As indicated at the beginning, conventionally, when measuring the distance, it is not distinguished which of the two arms has the longer optical path length, because only the length difference or the magnitude of the length difference is measured. That is, since it is not possible to distinguish between positive and negative measuring regions in which the optical path length of the measuring arm or the optical path length of the reference arm is longer, generally only one of the two regions is applicable (for example, when the optical path length of the reference arm is shorter than the optical path length of the measuring arm). Therefore, half of the measuring region that is theoretically available, that is, the measuring region that can physically realize the distance measurement, is not used. According to the present invention, not only the positive measuring region of the reference section but also the negative measuring region of the reference section is used for the distance measurement, in which the positive or negative measuring region of one reference section is switched or replaced in a targeted manner with the help of a switching element to the positive or negative measuring region of the other reference section of the reference arm. In the case of using a single-sided measuring region in a conventional reference arm structure, when the distance (i.e., the measuring distance or the distance to be measured) becomes larger, it is always necessary to switch to a longer reference section in order to compensate for the distance change. According to the invention, when the measuring distance becomes longer, it is obviously possible and advantageous to switch to a shorter reference section, that is, to switch from the negative active measuring range of the longer reference section to the positive active measuring range of the shorter reference section. This can significantly reduce the number of required reference sections.

[0015] According to one aspect of the present invention, an optical coherence tomography device for a laser processing system for measuring a distance from an object or a workpiece comprises: a measuring arm for aiming a measuring beam at an object; a reference arm for guiding a reference beam, the reference arm having a plurality of reference sections, the reference sections having different measuring areas or optical path lengths; and a controllable switching element for switching between the reference sections of the reference arm. The measuring area of ​​each reference section comprises a negative active measuring area and a positive active measuring area, and a dead zone is located between the negative active measuring area and the positive active measuring area. The dead zone of one of the reference sections overlaps with the negative or positive active measuring area of ​​at least one other reference section. The positive and negative active measuring areas of the reference section together cover a predetermined distance area. Therefore, not only the positive active measuring area of ​​the reference section but also the negative active measuring area of ​​the reference section are set for distance measurement in a predetermined distance area.

[0016] The controllable switching element can be set up for and / or connected to the reference section in such a way that it can switch back and forth or convert between the positive active measurement range of one of the reference sections and the negative active measurement range of another of the reference sections. In other words, the switching element can be connected to the reference section accordingly so that it can switch to each of the positive and negative active measurement ranges of the reference section.

[0017] The switching element is a switching element that can be controlled, such as a motor-based switching element, an optical switch, a fiber optic switch, and in particular a MEMS-based fiber optic converter. Each reference section can be assigned a position of a switching element. The reference section may include or may be a fiber-bound reference section and / or a free beam reference section. The optical coherence tomography device may include a control device for controlling the switching element. The control device may be set up to switch back and forth between a positive active measurement area of ​​a reference section in the reference section and a negative active measurement area of ​​another reference section in the reference section by means of a switching element. In particular, the control device may be set up to select a reference section with a positive or negative active measurement area corresponding to a predetermined or desired sub-area of ​​the spacing area, and switch to the selected reference section by means of a switching element. To this end, the control device may be set up to receive, for example, a signal with information about a predetermined or desired sub-area of ​​the spacing area from a control device of the laser processing system.

[0018] An optical coherence tomography device can be a device for optical distance measurement during laser material processing, ie, during cutting, welding, ablation, and additive LPBF (Laser Powder Bed Fusion) and LMD (Laser Material Deposition).

[0019] In addition, the optical coherence tomography device may include a measuring light source for generating the measuring light, such as a superluminescent diode or a laser diode. The optical coherence tomography device may include an optical element for dividing the measuring light into a measuring beam and a reference beam. In addition, the optical coherence tomography device may include a detector for detecting an interference signal, i.e., for detecting an interference effect between the measuring arm and the reference arm. The interference signal may be based on interference between a component of the measuring beam reflected from the object and the reference beam or based on an optical path length difference between the measuring arm and the reference arm.

[0020] Each reference section of the reference arm can have a measurement area or an optical path length that is different from other reference sections. In other words, the measurement area of each reference section can correspond to a different range of spacing values (Abstandswertebereich). The measurement areas of the reference sections can be shifted relative to each other by a pre-given amount and / or overlap each other. The measurement areas of the reference sections can be of the same size (but corresponding to different ranges of spacing values). If the reference arm has N reference sections, the n-th reference section can be shorter than the (n + 1)-th reference section (i.e., having a shorter optical path length or including a measurement area with smaller spacing values), where n and N are natural numbers, where 1 < N and 1 ≤ n ≤ N. That is, the first reference section can also be referred to as the shortest reference section, and / or the N-th reference section can be referred to as the longest reference section.

[0021] The measurement area of each reference section, i.e., the measurement area that can theoretically be used, has a negative active measurement area and a positive active measurement area, i.e., a negative area and a positive area, and the negative area and the positive area can be used for spacing measurement. The measurement area of each reference section is separated by a dead zone that contains a singularity around zero and in which no measurement result can be obtained. The dead zone is located between the negative active measurement area and the positive active measurement area and can be directly adjacent to these negative and positive active measurement areas (i.e., in this case there is no tolerance area between them). The spacing value corresponding to the negative active measurement area of the reference section can be smaller than the spacing value corresponding to the positive active measurement area of the same reference section.

[0022] The positive and negative active measurement areas of the reference section together (especially completely or without gaps) cover a pre-given spacing area. That is, the device is set up for making measurements in the entire pre-given spacing range. In other words, the pre-given spacing area refers to the following area: in this area, the device should be set up for making spacing measurements. For this purpose, the dead zone of one of the reference sections overlaps with the negative or positive active measurement area of at least one other reference section.

[0023] The reference section may include at least one reference section as follows: the spacing value corresponding to the negative active measurement area of ​​the reference section is greater than the spacing value corresponding to the negative active measurement area of ​​at least one other reference section, and the spacing value corresponding to the negative active measurement area of ​​the reference section is less than the spacing value corresponding to the positive active measurement area of ​​at least one other reference section. That is, the positive and negative active measurement areas of the reference section may be interlaced with each other. That is to say, the positive or negative active measurement area of ​​another reference section may be arranged between the positive and negative active measurement areas of a reference section. That is, a sub-area of ​​a predetermined spacing area located between the positive and negative active measurement areas of a reference section may be covered by the positive or negative active measurement area of ​​another reference section.

[0024] The positive and negative active measurement areas of the reference section may directly adjoin each other, i.e. preferably, any one of the positive and negative active measurement areas does not overlap with another of the positive and negative active measurement areas. Each of the positive and negative active measurement areas may be assigned to another sub-area of ​​a predetermined spacing area. In particular, each negative active measurement area and each positive active measurement area may be clearly and uniquely assigned to a sub-area of ​​a predetermined spacing area, and / or each sub-area of ​​a predetermined spacing area may be clearly and uniquely assigned to an active measurement area of ​​the positive and negative active measurement areas. Here, the sub-areas of the predetermined spacing area may directly adjoin each other, i.e., they do not overlap with each other. The clear and unique assignment of the active measurement area to the sub-area of ​​the predetermined spacing area enables simple control of the optical coherence tomography device.

[0025] At least one sub-region of the predetermined spacing region can be assigned to a negative active measurement region of one of the reference arms, and another or another sub-region of the predetermined spacing region can be assigned to a positive active measurement region of the same reference arm. In other words, the two active measurement regions of the reference arm are used for spacing measurement in the predetermined spacing region.

[0026] The arrangement of the active measuring regions (in particular the interconnection of the active measuring regions) and / or the assignment of the active measuring regions to sub-regions of a predetermined distance region can be predetermined or preset. The assignment can be stored or saved (for example in a control device of the optical coherence tomography device or in a control device of the laser processing system). The arrangement of the active measuring regions (in particular the interconnection of the active measuring regions) and / or the assignment of the active measuring regions to sub-regions of a predetermined distance region can be referred to as alignment.

[0027] The reference arm may include N reference segments, where N is a natural number greater than 1. The spacing value corresponding to or included in the negative active measurement region of the nth reference segment may be less than the spacing value corresponding to or included in the negative active measurement region of the (n + 1)th reference segment, where N is a natural number greater than 1, and n is a natural number, where 1 ≤ n ≤ N. The spacing value corresponding to or included in the positive active measurement region of the nth reference segment may be less than the spacing value corresponding to or included in the positive active measurement region of the (n + 1)th reference segment, where N is a natural number greater than 1, and n is a natural number, where 1 ≤ n ≤ N.

[0028] The spacing value corresponding to or included in the positive active measurement region of the nth reference segment may be greater than the spacing value corresponding to or included in the negative active measurement region of the (n + 1)th reference segment. The spacing value corresponding to or included in the positive active measurement region of the first (n = 1) reference segment (and / or each positive active measurement region in the positive active measurement region) may be greater than the spacing value corresponding to or included in each negative active measurement region in the negative active measurement regions of the N reference segments.

[0029] The reference segment may include at least one jth reference segment, and the negative active measurement region of the jth reference segment is directly adjacent to the positive active measurement region of the ith reference segment, where i and j are natural numbers, where 1 ≤ i < j ≤ N. That is to say, the reference segment may include at least one jth reference segment, and the negative active measurement region of the jth reference segment corresponds to a sub-region of the spacing region, and this sub-region is directly adjacent to another sub-region of the spacing region, and the positive active measurement region of the ith reference segment corresponds to this another sub-region, where i and j are natural numbers, where 1 ≤ i < j ≤ N. In other words, when the measured spacing becomes longer, it switches from the negative active measurement region of the jth reference segment to the positive active measurement region of the ith reference segment, and conversely, when the measured spacing becomes shorter, it switches from the positive active measurement region of the ith reference segment to the negative active measurement region of the jth reference segment. The jth reference segment may also be referred to as a conversion reference segment, where when the measured spacing becomes longer, it switches to a shorter (i.e., i < j) reference segment. In particular, the Nth reference segment may be a conversion reference segment, that is, j = N. The negative active measurement regions of the first reference segment, the second reference segment,... the jth reference segment, and then the positive active measurement regions of the first reference segment, the second reference segment,... the jth reference segment may correspond to the spacing values of the pre-given spacing region increasing in a given order.

[0030] The reference arm may include K groups of reference sections, where K is a natural number, where 1≤K. The spacing value corresponding to or included in the measurement area of ​​the (j+1)th group may be greater than the spacing value corresponding to or included in the measurement area of ​​the jth group, where j is a natural number, where 1≤j≤K. Each group may include the same number M of reference sections, i.e. K*M=N. Each group of reference sections may include (exactly) one transition reference section. Preferably, the groups complement each other in such a way that the complete spacing range is covered.

[0031] The reference arm may have at least one group of M reference sections, where M is a natural number, where 1≤M≤N. In particular, the reference arm may have multiple groups of reference sections, where the groups include the same number or different numbers of reference sections. For example, the reference arm may include a first reference section or a first group with only one reference section and at least one group with multiple (e.g. two, three, ...) reference sections. Between the negative active measurement area and the positive active measurement area of ​​the mth reference section, the negative active measurement areas of (Mm) individual reference sections of the group and / or the positive active measurement areas of (m-1) individual reference sections of the group may be arranged, where m is a natural number, where 1≤m≤M. That is to say, between the negative active measurement area and the positive active measurement area of ​​the mth reference section, the negative active measurement areas of (Mm) individual reference sections (i.e., the (m+1)th, ... Mth reference sections) and / or the (m-1) positive active measurement areas of the first, ... (m-1)th individual reference sections may be arranged. The spacing value corresponding to or included in the positive active measurement area of ​​the first (m=1) reference section of the group (and / or each positive active measurement area of ​​the M reference sections of the group) may be greater than each negative active measurement area of ​​the negative active measurement areas of the M reference sections of the group. The spacing value corresponding to or included in the positive active measurement area of ​​the mth reference section of the group may be less than the spacing value corresponding to or included in the positive active measurement area of ​​the (m+1)th reference section. Accordingly, the distance value corresponding to or included in the negative active measurement area of ​​the m-th reference section of the group may be smaller than the distance value corresponding to or included in the negative active measurement area of ​​the (m+1)-th reference section. The negative active measurement areas of the first reference section, the second reference section, ... the m-th reference section, the (m+1)-th reference section, ... the n-th reference section, and the positive active measurement areas of the first reference section, the second reference section, ... the m-th reference section, the (m+1)-th reference section, ... the M-th reference section may correspond to the distance values ​​of the predetermined distance areas increasing in the given order.

[0032] The measurement area of ​​each reference section can have a positive tolerance area and / or a negative tolerance area, the positive tolerance area is adjacent to one side or both sides of the positive active measurement area of ​​the reference section, and the negative tolerance area is adjacent to one side or both sides of the negative active measurement area of ​​the reference section. A dead zone can be arranged between the negative and positive tolerance areas. The negative and positive tolerance areas of each reference section can be separated from each other by the dead zone. It can be ensured by the positive and / or negative tolerance areas that, despite the presence of component tolerances or mechanical tolerances, measurement can still be achieved in the corresponding measurement area.

[0033] In other words, the measurement area of ​​each reference road section may include at least one of the following areas: a lower negative tolerance area, which is adjacent to the lower end of the negative active measurement area and has a corresponding spacing value that is smaller than the spacing value corresponding to the negative active measurement area; and / or an upper negative tolerance area, which is adjacent to the upper end of the negative active measurement area and has a corresponding spacing value that is larger than the spacing value corresponding to the negative active measurement area; and / or a lower positive tolerance area, which is adjacent to the lower end of the positive active measurement area and has a corresponding spacing value that is smaller than the spacing value corresponding to the positive active measurement area; and / or an upper positive tolerance area, which is adjacent to the upper end of the positive active measurement area and has a corresponding spacing value that is larger than the spacing value corresponding to the positive active measurement area. A dead zone may be arranged between the upper negative and lower positive tolerance areas. That is to say, the upper negative tolerance area, the dead zone and the lower positive tolerance area can be located between the negative active measurement area and the positive active measurement area of ​​the reference section. The upper negative tolerance area and the lower positive tolerance area can be adjacent to the dead zone, or the dead zone can be arranged between the upper negative tolerance area and the lower positive tolerance area. The negative tolerance area can include the lower negative tolerance area and / or the upper negative tolerance area. The positive tolerance area can include the lower positive tolerance area and / or the upper positive tolerance area.

[0034] The positive and / or negative tolerance region of a reference section can overlap with the negative or positive active measurement region of at least one other reference section. In particular, the entirety of all tolerance regions of all reference sections can be completely overlapped or covered by the active measurement region of the reference section.

[0035] According to one aspect of the present disclosure, a laser processing system comprises a laser processing head, an optical coherence tomography device according to one of the embodiments described herein, and a control device, wherein the optical coherence tomography device is used in the laser processing system for measuring a distance to an object or to a workpiece, and the control device is used to control the laser processing system, in particular the laser processing head and the optical coherence tomography device, in particular the switching element of the optical coherence tomography device. That is, the control device may include a control device of the optical coherence tomography device.

[0036] The control device or the control device of the optical coherence tomography device can be configured to switch to a shorter reference section, i.e., a reference section having a measuring region with a smaller distance value (compared to the measuring region of the previous reference section) when the distance increases. That is, the control device or the control device of the optical coherence tomography device can be configured to switch or change from one reference section to a shorter reference section when the distance to the object or workpiece increases. In other words, the control device or the control device of the optical coherence tomography device can be configured to switch or change from the j-th reference section to the i-th reference section when the distance to the object or workpiece increases, wherein the reference arm has N reference sections, and i, j are natural numbers, wherein 1≤i<j≤N, and the i-th reference section is shorter than the (i+1)-th reference section (i.e., has a shorter optical path length or has a measuring region with a smaller distance value). In particular, the control device or the control device of the optical coherence tomography device can be designed to switch or change from the negative active measuring range of the jth reference section to the positive active measuring range of the i-th reference section as the distance increases.

[0037] The laser processing head may include a scanner device having at least one scanning element for deflecting the laser beam to a plurality of positions on the workpiece. The control device may be configured to control the scanner device. The beam path of the measuring beam of the optical coherence tomography device may be coupled into the beam path of the laser beam in front of the scanner device (i.e. in front of the scanner device in the propagation direction of the laser beam). In other words, the beam path of the measuring beam of the optical coherence tomography device may extend through / via the scanner device.

[0038] The control device or the control device of the optical coherence tomography device can be, for example, a PC or a computing unit. The control device or the control device of the optical coherence tomography device can be configured to switch back and forth between the reference sections by means of a switching element, for example, between a positive active measurement region of one reference section and a negative active measurement region of another reference section.

[0039] The control device or the control device of the optical coherence tomography device can be set up to switch back and forth between the reference sections or select a reference section by means of a switching element, depending on the setting or position of the scanning element. The control device or the control device of the optical coherence tomography device can be set up to select one of the reference sections for distance measurement according to a scanning instruction for setting the scanning element of the scanner device. In one example, the control device can be set up to control the scanner device by means of a scanning instruction or to set the scanning element by means of a scanning instruction, for example, in order to align the laser beam at a certain position on the workpiece. In addition, the control device or the control device of the optical coherence tomography device can be set up to select one of the reference sections or switch to one of the reference sections based on the scanning instruction. However, the scanner device can also be set up or controlled by another unit by means of a scanning instruction. The control device or the control apparatus of the optical coherence tomography device can be designed to switch from a negative measuring range of a longer reference section to a positive measuring range of a further, shorter reference section when the optical path length increases due to a change in the position of the scanning element.

[0040] The laser processing system and / or the optical coherence tomography device may include an analysis device for determining the distance based on the interference between the component of the measuring light beam reflected from the object and the reference beam, in particular based on the interference signal of the detector. The analysis device may be included in a control device of the laser processing system or in a control device of the optical coherence tomography device. In addition, the optical coherence tomography device may include an optical combiner for superimposing the component of the measuring light beam reflected from the object with the reference beam for measuring the distance of the object in an interferometric manner. The optical combiner may also be a beam splitter.

[0041] The zero position of the scanning element, i.e. the position without deflection or the position in which the laser beam extends through the focusing optical system parallel to or coaxially with the optical axis of the focusing optical system, can correspond to the minimum spacing value of a predetermined spacing range or be located in the negative (or positive) active measurement range of the first (shortest) reference section of the reference arm. The correlation between the change in position of the scanning element relative to the zero position and the resulting change in the spacing from the object or workpiece can be saved or stored in a control device or in a control device of the optical coherence tomography device and / or in an evaluation device. Additionally or alternatively, an offset value can be saved or stored in the control device or in a control device of the optical coherence tomography device and / or in an evaluation device for each reference section. This offset value can be taken into account by the evaluation device when determining the time interval.

[0042] The analysis device can be configured to determine the distance based on an adjustment of the scanning element (e.g. a scanning command) or based on scanner data about the position of the laser beam or the measuring beam in the work field and based on an interference signal of the detector or based on the interference between a component of the measuring beam reflected from the object and the reference beam, i.e. based on the superposition of a component of the measuring beam from the measuring arm reflected from the object with a reference beam from a correspondingly selected reference arm (or from a selected or connected reference section of the reference arm).

[0043] The control device can be designed to determine the orientation (in particular the slope and / or the three-dimensional orientation) of the laser processing head relative to the workpiece based on the distance values ​​which are determined by the optical coherence tomography device during the scanning of the measuring beam over the workpiece by means of the scanner device. The scanning can be performed over the entire scanning area of ​​the scanner device, for example as a linear scan or a cross scan or a spiral scan or as a meander scan. For example, if the position of the laser beam or the measuring beam on the workpiece is given in Cartesian coordinates (for example with an origin corresponding to the zero position), then for the scanning the x coordinate can be moved from 0 to a maximum value +x max , or from -x max Move to +x max Additionally or alternatively, for scanning, the y coordinate may be moved from 0 to a maximum value +y max , or from -y max Move to +y max .

[0044] The control device can be configured to assign reference height values ​​recorded, for example, during calibration in a predetermined or desired working plane or reference plane, to the corresponding position in the scanning region or scanning field of the scanner device. The reference height values ​​can also be referred to as calibration data. The control device can be configured to determine the relative distance to the workpiece to be processed (for example with respect to a reference plane, for example a working plane) at a predetermined scanner position by using data from the calibration and from measurements performed on the workpiece at the scanner position. The control device can be configured to determine the actual or absolute distance to the workpiece to be processed at a predetermined scanner position by using data from the calibration (or the difference from the reference plane) and from measurements performed on the workpiece at the scanner position. The measurement can be point-shaped, can be over a path (line, cross, circle, spiral, etc.), or can be a surface scan.

[0045] In one embodiment, in a method for setting up a device in a laser processing system, the following steps can be implemented: a reference plane (e.g., a working plane) of the laser processing system is defined and the optical coherence tomography device is calibrated by assigning reference height values ​​to the corresponding positions in the scanning area. The reference plane or working plane of the laser processing system can be a plane to which the laser processing system is aligned, which plane is, for example, a focal plane of a lens or focusing optics of the laser processing system. During calibration, a reference height value can be assigned to each position on the reference plane in the scanning area in order to determine the difference, i.e., the offset, between the measured value and the actual height value at this position. When measuring on an object or workpiece, the deviation and / or the (relative or absolute) distance from the reference plane can be determined by taking into account the measured values ​​and the calibration data for the corresponding (measured) position in the scanning field.

[0046] The control device can be designed to adapt processing parameters (e.g. welding parameters, in particular collimation of the heat beam, laser power, focus position, etc.) as a function of the measurement performed or as a function of the determined distance, in particular before laser processing at this point or at this scanning position. The control device can be designed to adapt system parameters (focusing of the camera, scaling of the image data, etc.) as a function of the measurement performed or as a function of the determined distance.

[0047] Due to the optical mechanical properties of the scanner system, a deflection of at least one scanning element, for example a scanner mirror, can cause a change in the optical path length relative to the target plane, i.e. a change in the spacing. As a result, a calibration of the measurement signal or the OCT signal or the spacing value may be necessary depending on the deflection (lateral position) or the scanning position. Therefore, the calibration for the laser processing system or for the OCT device of the scanner device can be saved or stored in the control device of the laser processing system and / or in the control device of the optical coherence tomography device. Additionally or alternatively, a model for the laser processing system or for the scanner device for changing the optical path length or the spacing depending on the scanning position can be saved or stored in the control device of the laser processing system and / or in the control device of the optical coherence tomography device. Therefore, the assignment of a reference section to a sub-area in the scanning area or in a predetermined spacing area can be determined. In addition, various parameters of the entire system can be determined.

[0048] In the present disclosure, the following area is referred to as a working area or scanning area: the laser beam or the measuring beam can be directed into this area relative to the laser processing head by means of a scanner device. The predetermined spacing area is the area from the minimum spacing value that can be measured by means of the optical coherence tomography device to the maximum spacing value that can be measured by means of the optical coherence tomography device. Preferably, the position of the scanning element in which the laser beam is not deflected (the so-called zero position of the scanning element) corresponds to the origin of the polar coordinate system. The change in the optical path length due to the change in the position of the scanning element can be displayed as a radial length. The zero position of the scanning element, i.e. the position or setting in which the laser beam is not deflected, can correspond to the shortest optical path length, i.e. the shortest distance to the workpiece or to the object. The control device or the control device of the optical coherence tomography device can be set to set the first or shortest reference path or switch to the first or shortest reference path in the case of the zero position of the scanning element. The predefined distance region can correspond to at least a part of a region of a change in the optical path length which can be achieved by a change in the position of the scanning element.

[0049] Furthermore, the laser processing head can have focusing optics, in particular a flat-field focusing lens, for focusing the laser beam and / or the measuring beam. The focusing optics can be arranged behind the scanner device (with respect to the beam propagation direction of the laser beam).

[0050] The laser processing head may be a laser processing head which is used to carry out a processing operation on a workpiece by means of a laser beam, in particular laser cutting, laser welding, laser soldering, laser drilling or the like.

[0051] The workpiece can be a metal workpiece in particular. The laser processing system or the laser processing head can be configured to process a metal workpiece. The object can be the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Embodiments of the present disclosure are shown in the accompanying drawings and described in more detail below. The accompanying drawings show:

[0053] Figure 1 An optical coherence tomography device according to one embodiment of the present invention is shown;

[0054] Figure 2A Schematically shows a conventionally used measurement area of ​​a reference section, Figure 2B shows a conventional configuration of a reference arm having a plurality of reference sections;

[0055] Figure 3 Schematically shows the measurement area used according to the invention of a reference section;

[0056] Figure 4 The structure of a reference arm having a plurality of reference sections according to one embodiment of the present invention is shown;

[0057] Figure 5 Schematically shows the configuration of a measurement region of a reference section, the measurement region having a negative and a positive tolerance region;

[0058] Fig. 6A and 6B The structures of the reference arms having multiple reference sections according to the embodiments of the present invention are respectively shown;

[0059] Figure 7 A laser processing system having an optical coherence tomography device according to one embodiment of the present invention is shown;

[0060] Fig. 8A and 8B shows the situation when laser processing is performed by a scanner laser processing head;

[0061] Fig. 9 shows the calculation of possible profiles for OCT distance measurement for four reference sections;

[0062] Fig.10 shows complex deviations in the measurement signal with various dependencies, in particular with the scanning position;

[0063] Fig.11 shows the division of the scanning area into the switching states of the switching elements; and

[0064] Fig.12 The figure shows, for example, positioning errors of the calibration plate in the case of an inclined workpiece carrier. DETAILED DESCRIPTION

[0065] Unless otherwise indicated, the same reference numerals are used below for identical and identically functioning elements.

[0066] Figure 1An optical coherence tomography device 50 according to an embodiment of the present invention is shown, which is also referred to as an OCT device hereinafter. The OCT device 50 is configured to measure the distance to an object in a predetermined distance region O, the object being, for example, a workpiece surface or a component. The OCT device 50 includes a measuring arm 52 and a reference arm 51, the measuring arm being used to project a measuring beam onto the object or guide the measuring light reflected from the object, and the reference arm being used to guide a reference beam, wherein the reference arm 51 includes two or more reference sections 511, which have different optical path lengths, i.e., different measuring regions MB. The OCT device 50 has a detector 57, which is configured to detect interference signals. In addition, a controllable switching element 55 is configured to switch between the reference sections 511 of the reference arm 51. The switching element 55 may include an optical fiber converter, a MEMS-based switching element, a Beckhoff I / O terminal, etc. Based on the switching signal S, the switching element 55 can select a reference section in the reference sections 511, that is, actively switch it for distance measurement or guide the reference beam into the reference section. Optionally, the OCT device 50 may include an OCT processor 58, which can also be referred to as a control device of the OCT device 50. The OCT processor 58 may include an analysis unit. The detector 57 can be connected to the OCT processor 58 or to the analysis unit to provide the interference signal to the analysis unit. The OCT processor 58 can be set up, for example, to output an OCT signal or a measurement signal or a distance value z based on a predetermined offset of the selected reference section 511 and based on the superposition or interference between the component of the measuring light beam from the measuring arm 52 reflected from the object and the reference beam from the reference arm 51. Alternatively or additionally, the OCT processor 58 can be set up to output the switching signal S to the switching element 55 in order to adjust a determined reference section 511. The OCT processor 58 (possibly with an evaluation unit) can be provided separately or integrated into a control device of the laser processing system or of the laser processing head.

[0067] In addition, the OCT processor 50 includes a measuring light source 53 for generating measuring light and an optical element 54 for dividing the measuring light into a reference beam and a measuring beam. The optical element 54 may include or may be at least one beam splitter, a fiber coupler, a prism, and the like.

[0068] Furthermore, the OCT device 50 may include an evaluation unit 59 which is configured to determine the distance based on a superposition of a component of the measuring beam 525 from the measuring arm 52 reflected from the workpiece or component and a reference beam from the measuring arm 51 and based on the switching position or based on the selected reference path 511. Figure 1As shown, the evaluation unit 59 may be integrated into the OCT control device 58, but is not limited thereto. The detector 57 may be connected to the evaluation unit 59 in order to provide the interference signal to the evaluation unit.

[0069] exist Figure 2A The conventionally used measurement area M' of the reference arm or reference section is shown in . Typically, the OCT device measures the distance difference between the optical path length of the measuring arm and the optical path length of the reference arm. The optical path length of the measuring arm can correspond, for example, to the distance from the object or from the component or from the workpiece surface or from the working plane. When the reference arm is longer than the measuring arm, the "negative" measurement area applies, and correspondingly, when the reference arm is shorter than the measuring arm, the "positive" measurement area applies. These parts of the measurement area cannot be distinguished after the Fourier transform generally performed for the analysis and processing of the OCT signal, and cannot be mapped by the OCT processor. That is, the OCT signal or the distance value z can correspond to two possible values: z = |RL-ML|, where RL: the optical path length of the reference arm, ML: the optical path length of the measuring arm (i.e., the distance from the object). In order to ensure a clear and unique measurement, conventionally, only a one-sided (e.g., positive) measurement area is used for the distance measurement, that is, the (e.g., negative) area shown in the shaded part does not exist and the symmetry around the zero point is only schematically mapped. In addition, there is the problem of having a singularity in the signal when the difference is zero, and thus the area around the zero point is not available as a measurement area. This area is also called the dead zone TT and is located between the negative part and the positive part of the measurement area. Therefore, in known OCT devices, the effective or usable measurement area M' is defined as the area in the positive (or negative) measurement area in which a signal or a peak can be detected. The limit of the active measurement area M' is Figure 2A In the min and z max .

[0070] exist Figure 2B A conventional construction of a reference arm with multiple reference sections is shown in . In known OCT devices, the active measurement regions M' of the reference sections are arranged adjacent to each other so as to cover a predetermined spacing region O. As described above, the positive part or the negative part of the measurement region is used as the active measurement region M'.

[0071] Figure 3The measurement area MB of a reference section 511 according to one embodiment of the present invention is shown. The measurement area MB, i.e., the area in which a spacing signal or a peak value can be identified, includes not only a negative active measurement area nMB, but also a positive active measurement area pMB, which together can be referred to as an active measurement area aMB. A dead zone TT is arranged between the negative active measurement area nMB and the positive active measurement area pMB, in which no signal or peak value can be identified. In the embodiment shown here, the negative active measurement area nMB and the positive active measurement area pMB can be directly adjacent to the dead zone TT.

[0072] exist Figure 4 , the structure of the reference arm 51 of the OCT device 50 according to one embodiment of the present invention is shown. The dead zone TT of each reference segment 511 is covered or overlapped by the negative or positive active measurement area nMB or pMB of another reference segment 511. Therefore, gap-free measurement can be achieved in a predetermined spacing area O, that is, from 0 to Omax. The numbering of the reference segments 511 can correspond to the switch state or switching position of the switching element 55. The reference segments 511 are arranged according to their optical lengths, that is, the spacing value contained in the measurement area MB of the reference segment 1 is smaller than the spacing value contained in the measurement area MB of the reference segment 2, the spacing value contained in the measurement area MB of the reference segment 2 is smaller than the spacing value contained in the measurement area MB of the reference segment 3, and the spacing value contained in the measurement area MB of the reference segment 3 is smaller than the spacing value contained in the measurement area MB of the reference segment 4. In other words, the spacing value corresponding to the measurement area MB of reference section 4 is greater than the spacing value corresponding to the measurement area MB of reference section 3, which in turn is greater than the spacing value corresponding to the measurement area MB of reference section 2, which in turn is greater than the spacing value corresponding to the measurement area MB of reference section 1. In particular, the spacing value included in the negative active measurement area nMB of reference section 1 is smaller than the spacing value included in the negative active measurement area nMB of reference section 2, which in turn is smaller than the spacing value included in the negative active measurement area nMB of reference section 3, which in turn is smaller than the spacing value included in the negative active measurement area nMB of reference section 4. Correspondingly, the spacing value contained in the positive active measurement area pMB of reference section 1 is smaller than the spacing value contained in the positive active measurement area pMB of reference section 2, the spacing value contained in the positive active measurement area pMB of reference section 2 is smaller than the spacing value contained in the positive active measurement area pMB of reference section 3, and the spacing value contained in the positive active measurement area pMB of reference section 3 is smaller than the spacing value contained in the positive active measurement area pMB of reference section 4.

[0073] exist Figure 4In the example shown, two groups with two reference sections 1 and 2 or 3 and 4 are shown, wherein the dead zone TT of each reference section of a group overlaps with the negative active measurement area nMB or the positive active measurement area pMB of another reference section 511 of the same group. The measurement areas of the groups are adjacent to each other. In other words, the positive active measurement area pMB of the longest reference section of the first group (reference section 2 in this case) is directly adjacent to the negative active measurement area nMB of the shortest reference section of the second group (reference section 3 in this case). Of course, only one group or more than two groups and / or more than two reference sections per group can also be used to cover the predetermined spacing area O. Here, the negative active measurement areas nMB of the reference sections of a group are arranged directly and continuously, and the positive active measurement areas pMB of the reference sections of a group are arranged directly and continuously. Each group can include at least one reference section, the negative active measurement area nMB of which is directly adjacent to the positive active measurement area pMB of another reference section of the group.

[0074] In the case of an increase in the distance, first a switch is made from reference section 1 to reference section 2 in order to use the negative active measurement range nMB of each of these reference sections. In the case of a further increase in the distance, a switch is made from reference section 2 back to reference section 1 in order to now first use the positive active measurement range pMB of reference section 1 and in the case of a further increase in the distance, the positive active measurement range pMB of reference section 2 is used. Next, a switch is made to reference section 3 of the second group in order to use the negative active measurement range nMB of the same group, and so on. That is, according to the present invention, the switching element 55 is configured to switch to a shorter reference section in order to use the positive active measurement range pMB of the shorter reference section in the case of an increase in the distance.

[0075] As mentioned above, the following problem exists in the OCT measurement principle: when the difference in the optical path length is zero (i.e. when the optical path of the reference arm and the optical path of the measuring arm are identical), a singularity occurs in the signal and the measurement region around zero is therefore not available for measurement ("dead zone"). This region is bridged by switching to another reference path, which enables a consistent measurement within a predetermined spacing range.

[0076] Figure 5The measurement area MB of the reference road section 511 according to another embodiment of the present invention is shown. In addition to the negative active measurement area nMB and the positive active measurement area pMB, the measurement area MB includes a negative tolerance area nTB and a positive tolerance area pTB, the negative tolerance area is adjacent to at least one end of the negative active measurement area nMB, and the positive tolerance area is adjacent to at least one end of the positive active measurement area pMB. The negative tolerance area nTB may include a lower negative tolerance area nTB1 and / or an upper negative tolerance range nTB2, the lower negative tolerance area is adjacent to the lower end of the negative active measurement area nMB, the upper negative tolerance range is adjacent to the upper end of the negative active measurement area nMB or the upper negative tolerance range is arranged between the negative active measurement area nMB and the dead zone TT. Similarly, the positive tolerance region pTB may include a lower positive tolerance region pTB1 and / or an upper positive tolerance region pTB2, wherein the lower positive tolerance region is adjacent to the lower end of the positive active measurement region pMB or the lower positive tolerance region is arranged between the dead zone TT and the positive active measurement region pMB, and the upper positive tolerance region is adjacent to the upper end of the positive active measurement region pMB.

[0077] exist Fig. 6A and 6B FIG. 4 shows the structure of a reference arm 51 of an OCT device 50 according to another embodiment of the present invention. Fig. 6A In the embodiment, the reference arm 51 has a plurality of reference sections 511, which have Figure 5 Configuration shown. A plurality of reference sections 511 form a group. Negative and positive active measuring regions nMB or pMB are framed by negative or positive tolerance regions nTB1, nTB2 or pTB1, pTB2, respectively. A dead zone TT is arranged between the upper negative tolerance range nTB2 and the lower positive tolerance range pTB1. In this example, the negative and positive active measuring regions nMB or pMB of the reference section 511 also overlap the measuring region O without gaps. Here, at least the tolerance regions adjoining the dead zone TT of each reference section 511, i.e. the upper negative tolerance range nTB2 and the lower positive tolerance range pTB1, overlap or overlap with the negative or positive active measuring region nMB or pMB of at least one other reference section 511. The absolute length of at least one of these tolerance regions nTB1, nTB2, pTB1, pTB2 can correspond to an expected or predetermined component tolerance or mechanical tolerance Δt. These so-called component tolerances Δt can be, for example, + / - 0.25 mm to + / - 5 mm. Figure 6B , a reference arm 51 having four reference sections 1, ..., 4 (N=4) is also shown. However, Figure 6BThe reference sections in are arranged in two groups (K=2) of reference sections, wherein the first group (K=1) includes three reference sections (M1=3) and the second group (K=2) includes a single reference section (M2=1). In this embodiment, the positive active measurement area pMB of the reference section 4 is not used. Even if the single reference section 4 is arranged corresponding to the end point (Ende) of the measurement area O corresponding to the maximum value, the single reference section can also be arranged additionally or alternatively corresponding to the starting point (Anfang) of the measurement area O corresponding to the minimum value (i.e. as the first reference section of the reference arm).

[0078] If a component of unknown height is to be measured in the vicinity of the dead zone, a further problem can be solved in this way: it is not possible to clearly and uniquely determine which measuring area is exactly located, so it is unclear whether the current measuring section is smaller or larger than the reference section. This problem can be solved by reducing the measuring area: the measuring area for the height measurement of the component can be saved with the help of the tolerance area and the possibility of confusion can be reduced, or at each position (x; y) the clear and unique height position of the component can be determined for a given component tolerance Δt.

[0079] Figure 7 FIG. 1 shows a laser processing system 1000 of an OCT device 50 according to one embodiment of the embodiments described herein. The OCT device 50 may have, for example, a laser processing system 1000 of an OCT device 50 according to one embodiment of the embodiments described herein. Figure 1The structure described. The laser processing system 1000 includes a laser processing head 100, which includes a scanner device 30 with a scanning element (not shown). The scanner device 30 is set up to align the laser beam 10 or the measuring beam 525 of the OCT device 50 at different positions on the workpiece 20. The beam path of the measuring arm 52 can be coupled into the beam path of the laser beam in front of the scanner device 30 in the beam propagation direction, for example, by means of a semi-transparent mirror or a beam splitter. In order to couple the laser beam into the laser processing head 100, a laser port 15, such as a fiber sleeve, can be provided. In addition, the laser processing head 100 can include a focusing optical device 60, such as a flat field focusing lens (F-Theta Object), so as to focus the laser beam 10 or the measuring beam 525. The laser processing system includes a control device 1100, also referred to as a system control device. The OCT control device 58 can be integrated in the control device 1100 or set separately. In each case, the OCT control device 58 is connected to the control device 1100 for unidirectional or bidirectional data exchange. The OCT control device 58 can transmit the measurement signal or the distance value z(t) to the control device 1100. In addition, a scanner control device 35 can be provided separately or integrated in the control device 1100, which is connected to the control device 1100 and / or to the OCT control device 58 for unidirectional or bidirectional data exchange. The scanner control device 35 outputs a scanning command P(x;y) to the scanner device 30 in order to direct the laser beam 10 or the measuring beam 525 to the desired position by means of a scanning element.

[0080] The OCT control device 58 and / or the scanner control device 35 and / or the control device 1100 can be configured to select one of the reference sections 511 for the distance measurement according to a scanning instruction P(x; y) for adjusting the scanning element of the scanner device 30 and to transmit the corresponding scanning instruction P(x; y) to the switching element 55. The zero position P(x=0; y=0) of the scanner device 30 can be defined as the zero point of the polar coordinate system. The zero position can correspond to the minimum optical path length or the minimum value of the predetermined distance range O and can be Figure 46 is marked with 0. The OCT device for distance measurement is set up in a predetermined distance area O, which can correspond to the scanning area of ​​the scanner device 30. The scanning area of ​​the scanner device 30 can be, for example, 400mm x 335mm or 320mm x 320mm or 280mm x 175mm or 185mm x 120mm or 280mm x 175mm or 185mm x 120mm. In other words, the predetermined distance area O can correspond to the possible changes of the optical path due to the deflection by the scanning element. In this way, when laser processing is performed by the scanner laser processing system 1000, a suitable reference section 511 of the reference arm 51 can be selected according to the possible changes of the optical path due to the deflection of the measuring beam 525 by the scanner device 35, so that the distance measurement to the object or component can be achieved at this scanning position.

[0081] Furthermore, the OCT device 50 and / or the laser processing system 1000 may include an evaluation unit 59 which is configured to determine the distance based on a scanning command P(x;y) or based on information about the position (x;y) in the scanning area and based on a superposition of a reflected component of the measuring beam 525 from the measuring arm 52 and a reference beam from a correspondingly selected reference path 511 of the parameter arm 51. The evaluation unit 59 may be integrated in the OCT control device 50 and / or in the control device 1100.

[0082] exist Fig. 8A and 8B , the problem of the change in optical path length as a function of the scanning position P(x; y) is shown. The optical path length changes as the position of the scanning element changes. For example, the surface of the workpiece 20 can be assumed to be flat and defines a working plane for the laser machining process. Deflecting the measuring beam 525 to the position (x; y) results in a length change ΔL relative to the zero position (0; 0). For a scanning area or scanning field of 400 mm x 300 mm, the change in optical path length relative to the zero position can be, for example, 31 mm. In the case of component tolerances or mechanical tolerances of + / - 10 mm, a measurement area to be covered of 51 mm is generated. Therefore, the maximum value of the spacing measurement area O should be at least 51 mm. The optical axis 61 of the focusing optical device 60 is also indicated and coincides with the beam path at the zero position.

[0083] The OCT device 50 may have a Figure 3 or 5 reference road section construction and / or according to Figure 4Or a reference arm design of 6. In order to ensure that the distance to the component 25 arranged on or on the workpiece surface can be measured in the entire predetermined distance range O, it is possible to use Figure 5 A reference arm is constructed in which the negative active measuring area nMB adjoins the upper and / or lower negative tolerance area nTB1, nTB2 and the positive active measuring area pMB adjoins the lower and / or upper positive tolerance area pTB1, pTB2. In this way, it can be ensured that in the case of a switching position selected according to the scanning position or in the case of a reference section selected according to the scanning position, a structure height measurement (at least in the region of the component tolerance Δt) can be achieved. By reducing the active measuring area by the tolerance area, the unambiguous uniqueness of the measurement of the component height in the entire scanning area can be ensured. In other words, the active measuring area aMB (i.e. nMB, pMB) can be used to compensate for path length changes or spacing changes that are related to the scanning position, so that the structure height within the predetermined tolerance limit + / -Δt can be determined subsequently at the scanning position.

[0084] In the following, it is explained by way of example that an OCT device 50 or a reference arm 51 of the OCT device can be constructed according to one embodiment of the invention. First, a correlation between a deflection or a change in position of a scanning element (e.g. a scanner mirror) and a change in the optical path length (OWL) or a distance from a working plane / reference plane or a (e.g. flat) workpiece surface 20 is determined—either experimentally during calibration or by simulation (see Fig. 8A and 8B ). Next, the resulting change in optical path length associated with the scanning position needs to be divided into the active measurement area of ​​the reference arm 51 of the OCT device. The exact spacing between the individual reference sections 511 is derived from the predetermined component tolerance Δt and from the minimum and maximum measurable values ​​of the OCT device 50, that is, from the spacing area O that can be measured by the OCT device, and the deviation in the height position of the component can be the predetermined component tolerance. Now, the reference section 511 is adjusted in such a way that the generated active measurement areas nMB, pMB complement each other. Therefore, the active measurement areas nMB, pMB of the reference section cover the predetermined spacing area O or the optical path length change in the entire scanning area. The position of the switching element 55 is assigned to each reference section so that it can be switched to one or another reference section according to the scanning position or scanning instruction.

[0085] In the following, examples for such a so-called calibration are described in more detail: That is, first, the reference path is adjusted such that in the case of at least one (or all) of the reference paths 511 in the reference path in the working plane in the scanning area, signals in the negative measurement area nMB can be measured. For example, by means of a conversion module of a switching element 55, for example, and mechanical position adaptation of the end mirror of the corresponding reference path 511 in the reference arm 51, the adjustment of the actual reference path is achieved iteratively. For simplicity, the index of the reference path can correspond to the position of the switching element. For the reference path itself, it should apply that the length of the i-th reference path is less than the length of the (i + 1)-th reference path, i.e., RS_i < RS_i+1. In other words, the spacing value corresponding to the measurement area MB of the i-th reference path is less than the spacing value corresponding to the measurement area MB of the (i + 1)-th reference path.

[0086] Next, the first reference path is adjusted to the position with the shortest optical path length OWL(x; y) or with the shortest spacing such that the measurement signal is in the negative active measurement area nMB, especially on its outer edge (see Figure 4 , 6, and 9). In Fig. 9 , the calculation of the possible variation curves for the spacing measurement from 0 to 200 mm of the scanning position is shown, for example, changing the radial coordinate r from 0 mm to 200 mm. Four curves show four reference paths and correspond to the OWL variation in the case of measuring an idealized flat surface arranged parallel to the scanner plane. The active measurement areas are highlighted on each curve. In addition, the following assumptions are made: The optical scanner system is radially symmetric. That is, in the case of the scanning position (x = 0; y = 0), i.e., in the zero position, the measurement beam is perpendicular to the surface (i.e., the slope is zero). The curves have vertical offsets l_o of 6500, 9500, 12500, and 15500 μm, respectively (in the case of an idealized quadratic variation curve and a curvature k ≈ 0.7). Due to the different vertical offsets l_o, the variation curves of the curves are shifted and enter the (positive or negative) active measurement areas nMB, pMB (i.e., into the "usable measurement area") in the case of the corresponding other scanning positions. In the variation curves of the corresponding curves, the negative and positive active measurement areas can also be identified, which are located on the left and right sides of the inversion point in the case of "length difference = 0". To the left of the inversion point, i.e., in the negative active measurement area nMB, the reference path 511 is longer than the measurement spacing, while to the right of the inversion point, i.e., in the positive active measurement area pMB, the reference path is shorter. Adjacent to the area "length difference = 0", the dead zone TT is marked. The upper length difference area is only shown schematically and is outside the measurement area of the reference path. As Fig. 9As shown, the reference sections are set in such a way that if the measurement signal curve of a reference section leaves the active measurement area of ​​the reference section when the scanning position changes, the measurement signal curve of the adjacent reference section enters the active measurement area of ​​the adjacent reference section. In this way, in the entire scanning area from 0 mm to 200 mm, the surface is always located in the active measurement area of ​​one of the reference sections.

[0087] As described above, the optical path length OWL (x; y) corresponds to the measurement path associated with the scanning position (x; y). Depending on the configuration and the position (x; y), the reference path can be longer or shorter than the measurement path. If the reference path is longer, it can be set in such a way that the signal is set at the larger edge or upper edge of the active measurement area for the first reference path or the shortest reference path at a scanning position of 0, for the second reference path at a scanning position of approximately 60 mm, etc. (see Fig. 9 ). If the reference section is smaller than the measuring section, the smaller edge or the lower edge of the active measuring area can be selected as the starting position. Fig. 9 , it is shown that, in the case of an ideal orientation or arrangement, there is always a region in which the signals of two (or more) reference sections can be detected. If the outer edge of the active measurement region nMB, pMB is reached in the case of a reference section, a switch is made to the next reasonable reference section and the reference section is adjusted until a peak of the reference section can be detected at the corresponding edge of the active measurement region. Other types of adjustment are conceivable.

[0088] The length of the individual reference sections is determined, in particular depending on the specification of the structural tolerances and / or the scanning area and the conditions or configuration of the laser processing system, in particular the OCT detector, the scanner device and the optics. The definition of the length of the reference section can also be derived from the simulation of the system, so that a reference section with a given length can be constructed and only fine adjustment can be performed on the system. Each of the reference sections can then be realized by a combination of a defined fiber length and / or a free beam that can be adjusted.

[0089] Due to the optomechanical properties of the scanner system, a deflection of a scanning element (e.g. a scanner mirror) can lead to a change in the optical path length relative to the target plane, whereby a calibration of the OCT signal or the spacing value becomes necessary depending on the deflection or the scanning position. This also results, for example, from Fig.10 As can be seen in the lower part, complex offsets with various dependencies can occur, in particular with the lengths of the individual reference sections, with the scanning position, with the slope of the laser processing system relative to the working plane or the workpiece surface, with the optical elements used (such as mirrors, lenses), etc.

[0090] Thus, after setting up the reference path or after the alignment has been completed, a reference plane (e.g. a calibration plate) can be scanned over the entire scanning area and the OCT measurement signals can be recorded as a function of the scanning position P (x; y) with the corresponding switching position of the switching element. The measurement signals can be fitted with the aid of at least a quadratic polynomial (e.g. using a RANSAC algorithm). In addition, important related parameters (e.g. for curvature, slope and offset) can be determined. With the aid of these parameters, a model can be created which maps the OWL changes as a function of the x-position and y-position. The parameters are related to different physical parameters:

[0091] The calculated offset of the function for the respective switch position is linked to the length of the reference route.

[0092] The curvature of the function is primarily determined by the properties of the scanner device, such as the arrangement of the scanning elements (eg the scanner mirror arrangement and the scanner mirror spacing), the working distance and / or the properties of the optical elements.

[0093] The slope of the scanner device relative to the workpiece support or relative to the workpiece surface determines the slope of the function.

[0094] The model then provides information for setting the switching element or the information about which switch position is used at a given scanning position. This allows a correct distance measurement to be achieved at each scanning position P(x;y) in the scanning area or scanning zone, which can be decisive for adapting the process parameters. From the properties of the mathematical model for the optical path length as a function of the scanning position OWL(x;y), the following properties of the system can be derived:

[0095] - defining the offset of the measurement signal from the reference plane at the corresponding scanning position P(x;y);

[0096] - assigning the switch position or the switch state to the coordinates of the scanning area;

[0097] - the slope of the workpiece or workpiece support relative to the working plane of the scanner laser processing system;

[0098] -Offset position of each reference section;

[0099] - A global offset of the entire system (ie all reference sections as a whole, relative to the measurement plane).

[0100] exist Fig.11 , an exemplary division of a scanning area with a diameter of approximately 360 mm into the switching positions of the switching element is shown. In this case, each ring corresponds to a switching position or reference path 511 of the reference arm 51. The width of the ring is determined by the Fig. 9Similar active measurement area aMB (nMB, pMB) assignment definition ( Fig. 9 The protruding curve portion corresponds to Fig.11 in the middle).

[0101] exist Fig.12 , the situation for a calibration plate 70 or a workpiece support tilted relative to the laser processing system is shown. The optical axis 61 of the focusing optical device 60 or the undeflected measuring light beam or laser beam is also shown. In the case of a flat-field focusing lens as focusing optical device 60, the focus is located in a flat focal plane 66. In this situation, in which there is a slope between the workpiece or workpiece support and the laser processing system, a virtual working plane 80 can be defined, which extends perpendicularly to the optical axis 61 and / or parallel to the focal plane 66 and through the intersection of the optical axis 61 with the calibration plate 70 or the workpiece support. As described above, during calibration, the tilt angle of the workpiece support or the calibration plate 70 relative to the virtual working plane 80 can be determined.

[0102] That is, the parameters obtained from the calibration make it possible to determine the slope between the workpiece support and the working plane 80 of the scanner laser processing system. With the help of this information, it can be indicated to the user whether the tolerance is exceeded or how significant the relative slope is, so that the user can take corrective measures if necessary. In addition, a virtual working plane can be determined, which is parallel to the focal plane of the laser processing system and is ideally identical. The difference with the workpiece support can be taken into account during the measurement, so that the actual distance between the measured point of the surface and the laser processing system is determined. This information can then be used when adjusting the system parameters - in particular when adjusting the collimator of the laser beam to adjust the focal position and / or when adjusting the focus setting of the integrated camera and / or when correcting the height of the working plane.

[0103] According to the invention, the spacing range in which OCT measurements can be made can be expanded by cleverly arranging the reference segments so that, in addition to the positive measurement range of the reference segment, the negative measurement range of the reference segment is also available. By switching to a complementary reference segment, the region around the value 0 ("dead zone") can be bridged. Thus, reliable measurements are ensured without reaching the measurement range limits with errors. The reference segments are set in such a way that they complement each other so that the largest possible optical path length changes can be compensated or the largest possible spacing range O can be covered with the smallest possible number of reference segments.

[0104] Reference numerals list

[0105] 50 Optical Coherence Tomography Equipment

[0106] 51 Reference arm

[0107] 511 Reference Section

[0108] 52 Measuring arm

[0109] 525 Measuring beam

[0110] 53 Measuring light source

[0111] 54 Optical Components

[0112] 55 Switching elements

[0113] 57 Detector

[0114] 58 OCT processor or control device

[0115] 59 Analysis and processing equipment

[0116] O Spacing Area

[0117] MB measurement area

[0118] TT Dead Zone

[0119] nMB Negative Active Measurement Area

[0120] pMB positive active measurement area

[0121] aMB Active measurement area

[0122] nTB Negative tolerance area

[0123] nTB1 Negative tolerance area at the bottom

[0124] nTB2 Upper negative tolerance area

[0125] pTB Positive tolerance area

[0126] pTB1 Positive tolerance area at the bottom

[0127] pTB2 Upper positive tolerance area

[0128] 1000 Laser Processing System

[0129] 1100 System control device or control equipment

[0130] 100 Laser processing head

[0131] 10 Laser beam

[0132] 15 Laser port

[0133] 20 Workpieces

[0134] 25 Components

[0135] 30 Scanner devices

[0136] 35 Scanner Control Device

[0137] 60 Focusing optics

[0138] 61 Optical axis of focusing optics

[0139] 66 Focal plane

[0140] 80 Virtual Plane

Claims

1. An optical coherence tomography device (50) for a laser processing system (1000), the optical coherence tomography device being used for measuring a distance from an object (20, 25) in a predetermined distance range (O), the optical coherence tomography device comprising: A measuring light source (53), the measuring light source being used to generate measuring light; an optical element (54) for dividing the measuring light into a measuring beam (525) and a reference beam; a measuring arm (52) for directing the measuring beam (525) toward the object (20, 25); A reference arm (51), the reference arm being used to guide the reference beam, the reference arm having a plurality of reference sections (511), each of the reference sections having a measurement area (MB); a controllable switching element (55) for switching between reference sections (511) of the reference arm (51); and A detector (57), the detector being used to detect an interference signal between the measuring arm (52) and the reference arm (51); The measurement area (MB) of each reference road section (511) includes a negative active measurement area (nMB) and a positive active measurement area (pMB), and the dead zone (TT) is located between the negative active measurement area and the positive active measurement area; wherein the dead zone (TT) of one of the reference sections (511) overlaps with the negative or positive active measurement area (nMB, pMB) of at least one other reference section (511); and In this case, the positive and negative active measurement ranges (nMB, pMB) of the reference route (511) together cover the predefined distance range (O).

2. The optical coherence tomography apparatus according to claim 1, wherein: The reference arm includes N reference sections, and: The spacing value corresponding to the negative active measurement area of ​​the nth reference section is less than the spacing value corresponding to the negative active measurement area of ​​the (n+1)th reference section, where N is a natural number greater than 1, and n is a natural number, where 1≤n≤N; and / or The spacing value corresponding to the positive active measurement area of ​​the nth reference section is smaller than the spacing value corresponding to the positive active measurement area of ​​the (n+1)th reference section, where N is a natural number greater than 1 and n is a natural number, where 1≤n≤N.

3. The optical coherence tomography apparatus according to claim 1 or 2, wherein: The reference arm includes N reference sections, and the reference sections include at least one j-th reference section, the negative active measurement area of ​​the j-th reference section is directly adjacent to the positive active measurement area of ​​the ith reference section, wherein i and j are natural numbers, wherein 1≤i<j≤N.

4. An optical coherence tomography device according to any one of the preceding claims, in, The reference arm includes a set of M reference sections, where M is a natural number, where 1≤M≤N; and Where, for each group, the following applies: Between the negative active measurement region and the positive active measurement region of the m-th reference section, there are arranged the negative measurement regions of (M - m) other reference sections and / or the positive measurement regions of (m - 1) other reference sections, where m is a natural number, and 1 ≤ m ≤ M.

5. The optical coherence tomography apparatus according to claim 4, wherein: The reference arm includes K groups of reference sections, and the K groups of reference sections include the same number M of reference sections or different numbers M of reference sections. k The reference section; And wherein, the spacing value corresponding to the measurement region of the (k + 1)-th group is greater than the spacing value corresponding to the measurement region of the k-th group, where K is a natural number, 1 < K, and k is a natural number, 1 ≤ k ≤ K.

6. The optical coherence tomography device according to any one of the above claims, in, The measurement region (MB) of each reference section (511) further includes: A positive tolerance region (pTB) that is adjacent to one or both sides of the positive active measurement region (pMB) of the reference section; and / or A negative tolerance region (nTB) that is adjacent to one or both sides of the negative active measurement region (nMB) of the reference section.

7. The optical coherence tomography apparatus according to claim 6, wherein: The negative or positive tolerance region (nTB, pTB) of one reference section overlaps with the negative or positive active measurement region (nMB, pMB) of at least one other reference section.

8. The optical coherence tomography device according to any one of the above claims, the optical coherence tomography device further includes: A control device (58) for controlling the switching element (55) of the optical coherence tomography device; wherein, the control device (58) is configured to select a reference section (511) having a positive or negative active measurement region (nMB, pMB) corresponding to a pre-given sub-region of the spacing region (O), and switch to the selected reference section (511) by means of the switching element (55).

9. The optical coherence tomography apparatus according to claim 8, wherein: The control device (58) is configured to, for spacing measurement in a sub-region with a larger spacing in the pre-given spacing region (O), switch to a shorter reference section (511) by means of the switching element (55).

10. A laser processing system (1000), the laser processing system includes: A laser processing head (100) for injecting a laser beam (10) onto a workpiece (20); The optical coherence tomography device (50) according to any one of the above claims, and A control device (1100) for controlling the laser processing system.

11. The laser processing system according to claim 10, wherein: The laser processing head (100) includes a scanner device (30) having at least one scanning element for deflecting the laser beam (10) to multiple positions on the workpiece (20), and wherein, the control device (1100) is configured to select one reference section from the reference sections (511) according to a scanning instruction for adjusting the scanning element of the scanner device (30) for spacing measurement.

12. The laser processing system according to claim 11, the method further includes: An evaluation device (59) is configured to determine the distance based on the scanning command and based on a superposition of a component of a measuring beam (525) from the measuring arm (52) reflected from the object and a reference beam from the reference arm (51).

13. The laser processing system according to claim 10, 11 or 12, wherein: The control device (1100) is configured to determine an orientation and / or an inclination of the laser processing head (100) relative to a working plane and / or the workpiece (20) based on a distance value determined by the optical coherence tomography device (50) during scanning of the measuring beam (525) over the workpiece (20) by means of the scanner device (30).

14. The laser processing system according to claim 10, 11, 12 or 13, wherein: The control device is designed to assign reference height values ​​to corresponding positions in a scanning range of the scanner device (30) and to determine the distance to a workpiece at a predefined scanner position based on the assignment and measurements at the scanner position.

15. The laser processing system of claim 10, 11, 12, 13 or 14, wherein: The control device is designed to adapt system parameters and / or process parameters based on the determined distance.

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