METHOD FOR DETERMINING A POSITION OF A WORKPIECE FOR A LASER MACHINING PROCESS, AND LASER MACHINING SYSTEM

Abstract

A method for determining a position of a workpiece for a laser machining process includes the steps of: radiating a measurement beam to at least one workpiece and a support device surrounding the workpiece along at least one first and along at least one second measurement path, the first path forming a predetermined angle with the second path; acquiring a portion of the radiated measurement beam, reflected by the support device and the workpiece, along the first and along the second measurement path and generating a corresponding measurement signal, the support device and the workpiece comprising a reflectivity different from each other; and determining a position of the workpiece based on the measurement signal. A method for machining a workpiece by a laser beam includes the method for determining the position of the workpiece. An apparatus for determining a position of a workpiece is configured for conducting the methods.

Claims

1. A method for determining a position of a workpiece for a laser machining process, especially a laser welding process, the method comprising the steps: radiating a measurement beam to at least one workpiece and a support device, which holds said at least one workpiece and at least partly surrounds the same along at least one first measurement path and along at least one second measurement path; acquiring a portion of said radiated measurement beam reflected by said support device and said at least one workpiece along said first measurement path and along said second measurement path by means of at least one photodiode and generating a corresponding measurement signal, said support device and said at least one workpiece being different from each other in reflectivity; and determining a position of said at least one workpiece based on said measurement signal.

2. The method according to claim 1, wherein said radiated measurement beam is a laser beam, a pilot laser beam, or LED light.

3. The method according to claim 1, wherein: a surface of said support device and a surface of said at least one workpiece, to which said measurement beam is radiated, consists of different materials and/or exhibits different surface roughnesses; and/or said surface of said support device is of a metal, especially of aluminum or steel, or comprises the same; and/or said surface of said at least one workpiece being is of a metal, especially of copper, or comprises the same.

4. The method according to claim 1, wherein: said radiated measurement beam exhibits a power of fewer than 300 watts or a power lower than a laser power for said laser machining process and/or is moved along said measurement paths with a speed of at least 0.3 m/s; and/or an energy input by said radiated measurement beam being is adapted such that said measurement beam does not modify and/or melt said at least one workpiece.

5. The method according to claim 1, wherein said first measurement path and/or said second measurement path comprises a first area and a third area on said support device as well as a second area on said at least one workpiece, said second area arranged between said first area and said third area.

6. The method according to claim 1, wherein: said first measurement path and said second measurement path is linear; and/or said predetermined angle is 90°; and/or said first measurement path comprises a plurality of first measurement paths parallel and offset from each other; and/or said second measurement path comprises a plurality of second measurement paths parallel and offset from each other.

7. The method according to claim 1, wherein: said first measurement path is circular; and/or said second measurement path is linear; and/or said first measurement path comprises a plurality of circular concentrically arranged first measurement paths; and/or said second measurement path comprises a plurality of linear and intersecting second measurement paths.

8. The method according to claim 1, wherein radiating said measurement beam along said at least one first measurement path and/or along said at least one second measurement path occurs with constant speed.

9. The method according to claim 1, wherein, for determining said position of said at least one workpiece, said measurement beam is determined to be reflected at a point of said surface of said at least one workpiece, when said measurement signal at said corresponding place is equal to or larger than a predetermined first value.

10. The method according to claim 1, wherein determining said position of said at least one workpiece based on said measurement signal comprises: determining whether said at least one workpiece is present in or at said support device.

11. The method according to claim 1, wherein determining said position of said at least one workpiece occurs taking into account a diameter of said measurement beam on said at least one workpiece.

12. The method according to claim 1, wherein: a first workpiece and a second workpiece are arranged in said support device; and said position of said first workpiece, and/or said position of said second workpiece, and/or a position of said first and second workpieces relative to each other, and/or an interval between said first and second workpieces, and/or a position and/or extension of a gap between said first and second workpieces, and/or a diameter of a machining result, and/or a position of first and second machining results relative to each other, and/or an interval between said first and second machining results are determined.

13. The method according to claim 1, wherein: said at least one workpiece is or comprises an electrode, a bar-shaped electrode, an i-pin, a hairpin, or a winding segment of a stator winding; and/or said support device comprises: a component, and/or a battery, and/or a jig for clamping said at least one workpiece, and/or a jig in which two workpieces to be welded to each other or welded to each other are chucked.

14. A method for machining a workpiece by means of a laser beam, the method comprising: determining a position of said workpiece by means of the method according to claim 1; and radiating a laser beam to said workpiece for machining said workpiece based on said determined position of said workpiece.

15. The method according to claim 1, comprising: machining a plurality of workpieces by radiating a laser beam to two adjacent workpieces, respectively, and welding together said two adjacent workpieces, wherein a plurality of welding domes is generated, wherein determining a position of said workpiece comprises determining at least one interval between two adjacent welding domes.

16. A laser machining system for machining a workpiece by means of a laser beam, comprising: a laser machining apparatus for radiating a measurement beam to said workpiece; a sensor module with at least one photodiode for acquiring reflected measurement radiation; and a control unit, configured to perform the method according to claim 1.

17. The laser machining system according to claim 16, wherein said laser machining apparatus comprises a deflection unit for deflecting said measurement beam along said measurement paths.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Embodiments of the invention are described in detail in the following based on figures.

[0045] FIG. 1 shows a schematic view of a laser machining system for determining a position of a workpiece according to embodiments of the present invention;

[0046] FIG. 2 shows a schematic view of a laser machining system for determining a position of a workpiece according to other embodiments of the present invention;

[0047] FIG. 3 shows a schematic view of workpieces for methods according to embodiments of the present invention;

[0048] FIG. 4 shows a flow diagram of a method for determining a position of a workpiece according to embodiments of the present invention;

[0049] FIG. 5 shows a schematic perspective view of workpieces in a support device;

[0050] FIG. 6 shows the workpieces shown in FIG. 5 and the support device in a schematic top view for illustrating methods for determining a position of a workpiece according to embodiments of the present invention;

[0051] FIG. 7 shows exemplarily the progression of a measurement signal acquired by a method for determining a position of a workpiece according to embodiments of the present invention;

[0052] FIGS. 8 and 9 show cutouts from progression shown in FIG. 7;

[0053] FIG. 10 shows an unprocessed workpiece in the state before a laser machining process and a machined workpiece after a laser machining process;

[0054] FIG. 11 shows a circular and concentrical arrangement of machined workpieces and a measurement path for determining positions of the machined workpieces and/or of intervals between the machined workpieces; and

[0055] FIG. 12 shows a measurement signal progression corresponding to the arrangement shown in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

[0056] In the following, the same reference signs are used for identical and similarly acting elements. In the present disclosure, x, y, and z directions are parallel to axes of an orthogonal or cartesian coordinate system. The z axis here corresponds to a propagation direction of the (non-deflected) measurement or laser beam, respectively, 14 or an optical axis of the laser machining apparatus 12, respectively. A plane spanned by the x direction and the y direction may be denoted as x-y plane. In the present detailed description, embodiments are described, in which the measurement beam 14 is a laser beam. The measurement beam 14 here may stem from a laser source for generating the machining laser beam or from a pilot laser source for generating a pilot laser beam. However, the disclosure is not limited thereto. Readily, the measurement beam 14 may stem from an LED source or a LED light, respectively, coupled into a machining laser beam path of the laser machining apparatus 12.

[0057] FIG. 1 shows a schematic view of a laser machining system configured for determining a position of a workpiece according to embodiments of the present invention.

[0058] The laser machining system 10 for determining a position of a workpiece comprises a laser machining apparatus 12. The laser machining apparatus 12 may, for example, be formed as a laser machining head, especially a laser welding or laser cutting head. The laser machining apparatus 12 is configured to irradiate the measurement beam 14 exiting from one end of an optical fiber 18 or a laser source (not shown) with the help of a beam guiding and focusing optics (not shown) to workpieces to be machined 16a, 16b to thereby perform laser machining, especially laser welding. Especially, the measurement beam 14 may be focused or bundled on the workpieces 16a, 16b to locally heat the workpieces 16a, 16b for laser machining to the melting temperature. As shown in FIG. 1, a sensor module 26 is coupled to the laser machining apparatus 12 for acquiring a reflected portion of the measurement beam. In this example, parts of the beam paths of the laser machining apparatus 12 and of the sensor module 26 extend coaxially. However, the invention is not limited thereto.

[0059] In radiating the measurement beam 14 to the workpieces 16a, 16b, parts of the radiated measurement beam 14 are reflected by the workpieces 16a, 16b. The reflected measurement radiation 20 partly enters the laser machining apparatus 12 again and is there, for example, decoupled from a beam path of the measurement beam 14 by a beam splitter 22 and enters the sensor module 26 mounted to the laser machining apparatus 12. In the sensor module 26, the decoupled radiation 20 impinges on a detector (not shown).

[0060] According to other embodiments not shown, the reflected measurement radiation 20 does not re-enter the laser machining apparatus 12 before entering or being coupled, respectively, into the sensor module 26. In other words, the beam path for the reflected measurement radiation 20 extends fully outside the laser machining apparatus 12. Therefore, the measurement beam 14 is preferably directed to the workpieces 16a, 16b under an angle.

[0061] The detector is configured to detect radiation intensity in a predetermined wavelength range. Especially, the detector may exhibit spectral sensitivity in a wavelength range comprising the wavelength of the measurement beam 14. According to embodiments, the detector exhibits maximum spectral sensitivity at the wavelength of the measurement beam 14. The detector may be or comprise a photodiode or a photodiode array. The detector is also configured to detect an intensity of the reflected measurement radiation 20 and to output a measurement signal based on the detected intensity. The measurement signal may especially be an analog measurement signal, preferably an analog temporally variable voltage signal.

[0062] The laser machining system 10 further comprises a control unit 30. The control unit 30 is configured to receive the measurement signal. The control unit 30 may be configured according to embodiments to convert an analog measurement signal to a digital measurement signal. Therefore, the measurement signal may be acquired by the described sensor module 26. The control unit 30 and/or the sensor module 26 may be configured according to embodiments to record the measurement signal.

[0063] The measurement beam 14 is moved with regard to the workpiece surface. Therefore, the laser machining system 10, especially the laser machining apparatus 12, may comprise a deflection unit for deflecting the measurement beam with regard to the propagation direction of the measurement beam (e.g., scan optics). Alternatively or additionally, the laser machining apparatus 12 may be moved relative to the workpiece surface. In this case, the laser machining apparatus 12 may be a laser machining head with fixed optics. In order to radiate the measurement beam 14 always in a predetermined angle, e.g., substantially perpendicularly, to surfaces of the workpieces 16a, 16b and to always acquire the reflected radiation 20 in a predetermined angle, e.g., substantially in a direction perpendicular to the surfaces of the workpieces 16a, 16b, the laser machining apparatus 12 may be moved by means of a movement apparatus (not shown), e.g., a robot arm, in the three-dimensional space. For example, the laser machining apparatus 12 may be moved along the first direction x, the second direction y, and/or the third direction z. The z direction corresponds to a propagation direction of the measurement beam 14 or an optical axis of the laser machining apparatus 12, respectively, and may be arranged perpendicularly to a to machined surface of the workpieces 16a, 16b.

[0064] FIG. 2 shows a schematic view of a laser machining system for determining a position of a workpiece according to other embodiments of the present invention. FIG. 2 shows a laser machining system 10 with a laser machining apparatus 12 for machining a plurality of workpieces. The laser machining apparatus 12 comprises a deflection unit (not shown), e.g., a scanner unit, also referred to as scan optics, or a galvano mirror, for deflecting the measurement beam 14 and/or a machining laser beam in at least a direction perpendicular to the propagation direction of the measurement beam, to direct the measurement beam to three workpiece pairs P1, P2, and P3. By means of the deflection unit, the measurement beam 14 or the machining laser beam, respectively, may be radiated to the workpieces 16a, 16b of the workpiece pairs P1 to P3, without having to move the laser machining apparatus 12 or the workpiece pairs P1, P2, and P3 relative to each other. Thereby, the measurement beam 14 or the machining laser beam, respectively, may be radiated quickly to a plurality of workpieces 16a, 16b or workpiece pairs P1 to P3, respectively, arranged next to each other. The laser machining apparatus 12 may be stationary in conducting the method according to embodiments of the present invention.

[0065] In this case, the measurement beam is radiated obliquely to the surfaces of the workpieces 16a, 16b or the workpiece pairs P1 to P3, respectively, depending on the distance to the workpiece or the workpiece pair, respectively. For example, the measurement beam may be radiated under an acute angle to the surface normal to the surfaces of the workpieces 16a, 16b or workpiece pairs P1 to P3, respectively, the acute angle lying, for example, between 1° and 20° or between 5° and 10°. The angle may depend on the position of the workpieces 16a, 16b or the workpiece pairs P1 to P3, respectively, and of the laser machining apparatus 12.

[0066] The laser machining system 10 is configured to perform the method for determining a position of a workpiece described in the following and/or the method for machining a workpiece by means of a laser beam. Especially, be the control unit 30 may be configured to control the method for determining a position of a workpiece and/or the method for machining a workpiece. The laser machining system 10 is configured according to embodiments of the present invention to determine the positions of the workpieces 16a, 16b. According to embodiments, the positions of the workpieces 16a, 16b may comprise the positions of the workpieces 16a, 16b in x direction and/or y direction. Further, the positions of the workpieces 16a, 16b may comprise the extension of the workpieces 16a, 16b in the x-y plane, i.e., in the x direction and/or y direction. In addition, the positions of the workpieces 16a, 16b may comprise the orientation of the workpieces 16a, 16b in the x-y plane, especially a rotation of the workpieces 16a, 16b around the z direction. Further, with the method shown, an interval between the workpieces 16a, 16b in the x-y plane may be determined. The interval may be determined as the shortest interval between the workpieces 16a, 16b. According to embodiments, the control unit 30 is configured to control a radiation position and/or a movement speed and/or direction of the measurement beam 14 or the machining laser beam and/or a laser power of the machining laser beam for laser machining based on the determined position of the workpieces 16a, 16b.

[0067] FIG. 3 shows a schematic view of workpieces for methods according to embodiments of the present invention. FIG. 5 shows a schematic view of the workpieces shown in FIG. 3 in a support device.

[0068] The invention is explained in the following by the example of two workpieces formed as bar-shaped electrodes. However, the invention is not limited thereto. The workpieces may also exist in a different number or have another shape.

[0069] The workpieces 16a, 16b are formed as two bar-shaped electrodes in FIG. 3. The bar-shaped electrodes exhibit a cuboid shape and have a rectangular cross section. The ends or end surfaces 17a, 17b, respectively, of the workpieces 16a, 16b are rectangular as well and comprise, according to embodiments, a width (or narrow side) between about 1 mm and about 2 mm and a length (or longitudinal side) between 4 mm and 5 mm. Both workpieces 16a, 16b may be similar and arranged parallel to each other, but the invention is not limited thereto. In FIG. 3, the ends 17a, 17b of the workpieces 16a, 16b are plane surfaces and arranged substantially in an x-y plane, but the invention is not limited thereto.

[0070] According to embodiments, of the invention, the workpieces 16a, 16b are formed as exposed ends 17a, 17b of electric conductors 32a, 32b, e.g., as hairpins or as winding segments of a stator coil for an electric motor. At the ends 17a, 17b of the electric conductors 32a, 32b, a coating or insulation material 33a, 33b has been removed, so that the end 17a, 17b is exposed. For example, the electric conductor 32a, 32b may be freed from coating 33a, 33b over of a length of 10 mm. If the conductors 32a, 32b are arranged next to each other in the support device, due to the insulation material 33a, 33b, a spacing or a gap 36, respectively, may exist between the workpieces 16a, 16b.

[0071] FIG. 4 shows a flow diagram of a method for determining a position of a workpiece according to embodiments of the present invention. With the method shown, for example, the positions of the workpieces 16a, 16b or workpiece pairs P1 to P3, respectively, shown in FIGS. 1 to 3 may be determined. According to embodiments, the positions of the workpieces 16a, 16b may comprise the positions of the workpieces 16a, 16b in x direction and/or y direction, i.e., in at least one direction perpendicular to the beam propagation direction. Further, the positions of the workpieces 16a, 16b may comprise an extension of the workpieces 16a, 16b in the x-y plane, i.e., a width in x direction and/or a length in y direction. In addition, the positions of the workpieces 16a, 16b may comprise the orientation of the workpieces 16a, 16b in the x-y plane, especially a rotation of the workpieces 16a, 16b around the z direction, i.e. the beam propagation direction. Further, with the method shown, the existence of the gap 36 and its size may be determined. The size of the gap 36 may be given as an interval of the workpieces 16a, 16b in the x-y plane. In case the gap 36 does not exist, the interval may be determined to “zero”.

[0072] As illustrated in FIGS. 5 and 6, the method of the invention begins with radiating the measurement beam 14 (S1) to the workpieces 16a, 16b and a support device 38. The measurement beam 14 may be radiated along first measurement paths 40a, 40b, 40c offset parallel to each other and, subsequently, along second measurement paths 42a, 42b offset parallel to each other. The support device 38 surrounds the workpieces 16a, 16b at least partly. Preferably, the ends 17a, 17b or end surfaces, respectively, of the workpieces 16a, 16b may be arranged in a plane. As shown in FIGS. 5 and 6, the support device 38 may be formed as a jig and comprise a through hole 39 for feeding the workpieces 16a, 16b through, but the invention is not limited thereto. Another example can be found in the field of contacting batteries, especially in battery module manufacturing. Thereby, battery cells are connected to each other. The cell connectors lie on the battery cells and are welded onto the poles of the batteries. The position of the cell connectors may be recognized with the invention methods.

[0073] The support device 38 exhibits a reflectivity different from that of the workpieces 16a, 16b. Especially, the support device 38 and the workpieces 16a, 16b exhibit different reflection properties for light of the measurement beam 14. For example, the surfaces of the workpieces 16a, 16b consist of a different material than the surface of the support device 38. According to embodiments, the surfaces of the workpieces 16a, 16b consist of a metal, especially of copper, and the surface of the support device consists of a metal, especially of aluminum or steel. Additionally or alternatively, the surfaces of the support device 38 and the surfaces of the workpieces 16a, 16b may exhibit a roughness different from each other. For example, the surface of the support device 38 may be coarser than the surfaces of the workpieces 16a, 16b. Especially, the surface of the support device 38 may be matted, brushed or sandblasted and the surfaces of the workpieces 16a, 16b may be cut or milled surfaces.

[0074] The support device 38 may comprise a component and/or a component group, in which the at least one workpiece 16a, 16b is integrated or to which the at least one workpiece 16a, 16b is attached. The support device 38 may, for example, be a bottom plate and the workpiece 16a, 16b may be a top plate to be welded to the bottom plate. In another example in the field of battery contacting, the support device is a battery or a battery case, respectively, and the workpiece 16a, 16b is a deflector arranged on it. In the embodiments shown in FIGS. 5 and 6, the support device 38 may comprise a jig for clamping the at least one workpiece 16a, 16b, the other workpiece, the component, and/or the component group. The jig may serve to clamp the workpieces 16a, 16b for later laser machining. The clamping may comprise fixing or positioning the workpieces 16a, 16b in the jig, occurring before radiating the measurement beam for positioning. By clamping forces, a gap 36 between two workpieces 16a, 16b may be kept as small as possible.

[0075] Radiating the measurement beam 14 along the measurement paths occurs in this course with a very low laser power, e. g 240 W or less, and/or with a high speed, e. g 20 m/min or more. The laser power and/or the movement speed may be held constant while radiating the measurement beam 14 along the measurement paths. Therefore, the laser power or the movement speed, respectively, is selected such that the measurement beam 14 does not couple into the material of the workpieces 16a, 16b. In other words, a power density of the measurement beam 14 on of a surface of the workpieces 16a, 16b may be selected to be below a threshold at which the measurement beam 14 couples into the workpieces 16a, 16b or at which the workpieces 16a, 16b melt.

[0076] The intensity of a portion 20 of the radiated measurement beam 14 reflected by the workpieces 16a, 16b and the support device 38 along the respective measurement path 40a, 40b, 40c, 42a, 42b is acquired or recorded, respectively, in step S2 and a corresponding measurement signal is generated. According to embodiments, the measurement signal is a temporally variable voltage signal of a photodiode, as depicted in FIG. 7. According to embodiments, this measurement signal may be preprocessed. Especially, the measurement signal may be converted to a digital voltage signal comprising voltage values associated to points of time. Further, the measurement signal may be smoothed and/or filtered. The measurement signal may, for example, be low-pass filtered or noise filtered.

[0077] In the next step S3, determining a position of the workpieces 16a, 16b occurs based on the measurement signal. To do so, the measurement signal may be evaluated. Determining the positions of the workpieces 16a, 16b is based on the finding that the workpieces 16a, 16b and the support device 38 exhibit different reflection behavior. For example, the measurement beam 14 may be reflected strongly by the workpieces 16a, 16b, so that the measurement signal takes on a relatively higher value, while the measurement beam 14 may be strongly absorbed or scattered by the support device 38, so that the reflected portion 20 of the measurement beam 14 is very low and the measurement signal takes on a relatively smaller value. In a case where the measurement beam 14 along the measurement paths 40a, 40b, 40c, 42a, 42b hits the through hole 39 or the gap 36, respectively, also no reflection may occur, so that no reflected portion 20 be acquired and the measurement signal also takes on a very small value or even the value “zero”. Through the different reflection behavior, for example due to differences in material and surface roughness, the quantity of the back-scattered light is strongly different and clear signal differences result depending on the position of the measurement beam 14. Therefore, by evaluating the measurement signal, it may be determined where along the measurement paths the measurement beam 14 was radiated onto the support device 38, one of the workpieces 16a, 16b, or to the through hole 39 or the gap 36, respectively.

[0078] According to embodiments, a method for machining the workpieces 16a, 16b with a measurement beam may comprise the method for determining the positions of the workpieces 16a, 16b described with regard to FIG. 4, and subsequently radiating the machining laser beam to the workpieces 16a, 16b for machining the workpieces 16a, 16b. For machining the workpieces 16a, 16b, the machining laser beam may have a higher laser power than the measurement beam 14 for determining the positions of the workpieces 16a, 16b. However, the measurement beam 14 and the machining laser beam may be provided by the same laser source (not shown). Alternatively, the measurement beam 14 may also be provided by a pilot laser beam source or a LED source. The laser machining may, for example, comprise laser welding, especially welding together the workpieces 16a, 16b. For example, the laser beam may be radiated to the end surfaces 17a, 17b of the workpieces 16a, 16b such that separate melting baths are formed on it. The separate melting baths subsequently merge to a common melting bath. After solidifying or cooling down, respectively, of the common melting bath, a conductive contact with low resistance exists between both workpieces 16a, 16b. By exact knowledge of the position of the workpieces 16a, 16b or the size of the gap 36 between the workpieces 16a, 16b, respectively, the laser machining may be controlled accordingly. Thereby, the quality of the welding joint between the workpieces 16a, 16b may be increased.

[0079] FIG. 5 shows a schematic perspective view of workpieces 16a, 16b in the support device 38 with an individual measurement path 40b, and FIG. 6 shows a schematic top view of the workpieces 16a, 16b and the support device 38 for illustrating measurement paths 40a, 40b, 40c, 42a, 42c for methods according to embodiments of the present invention. The top view of FIG. 6 is parallel to the x-y plane, in which the workpiece surfaces are arranged in this example. Even though the measurement beam in FIGS. 5 and 6 is shown in z direction, the present invention is not limited thereto. The measurement beam 14 may also impinge on the workpiece surfaces at an acute angle, as illustrated in FIG. 2.

[0080] The measurement beam 14 radiated to the workpieces 16a, 16b, or the support device 38, respectively, generates a patch or a spot on the respective surface. The first measurement paths 40a, 40b, 40c and the second measurement paths 42a, 42b, which are also referred to as “traverses”, may each be defined as a projection of these spots on the x-y plane or, respectively, a plane perpendicular to the optical axis of the laser machining apparatus 12 or the propagation direction of the measurement beam 14, respectively.

[0081] According to embodiments, the measurement paths 40a, 40b, 40c, 42a, 42b are each formed as a straight line, but the invention is not limited thereto. Especially in a plane perpendicular to the beam propagation direction, i.e., in the x-y plane, the measurement paths are preferably linear. The first measurement paths 40a, 40b, 40c are respectively arranged parallel or antiparallel to each other in the x direction and the second measurement paths 42a, 42b are respectively arranged parallel or antiparallel to each other in the y direction, but the invention is not limited thereto. As shown, the first measurement paths 40a, 40b, 40c and the second measurement paths 42a, 42b are arranged in a predetermined angle to each other, the predetermined angle being 90°, but the invention is not limited thereto.

[0082] The first measurement paths 40a, 40b, 40c and the second measurement paths 42a, 42b may be part of a continuous and/or steady movement path of the measurement beam 14 or the spot, respectively, as illustrated in FIG. 6 by the dashed line between the first measurement path 40c and the second measurement path 42a. In other words, the measurement beam 14 musts not be turned off between the individual measurement paths. Accordingly, the measurement signal may be recorded continuously. Accordingly, the measurement signal may comprise the acquired intensity of the reflected measurement radiation 20 for all measurement paths 40a, 40b, 40c, 42a, 42b. However, the invention is not limited thereto. For example, individual measurement signals may be acquired also for each of the measurement paths 40a, 40b, 40c, 42a, 42b. Alternatively, the measurement paths 40a, 40b, 40c may, for example, respectively extend in x direction and the measurement paths 42a, 42b may, for example, respectively extend in y direction. In this case, the measurement beam 14 may be turned off between the individual measurement paths.

[0083] Each measurement path may comprise areas on the support device 38, the through hole 39, the gap 36, and at least one of the workpieces 16a, 16b. In other words, the measurement beam 14 may traverse, along the first measurement paths 40a, 40b, 40c and/or the second measurement paths 42a, 42b, the support device 38, the through hole 39, the gap 36, and at least one of the workpieces 16a, 16b. As shown in FIG. 6, for example, the first measurement paths 40a, 40b, 40c each comprise a first area on the support device 38, a second area on the workpiece 16a, a third area in the gap 36, a fourth area on the workpiece 16b, and a fifth area on the support device 38, the first to fifth areas arranged in this order along the first measurement paths 40a, 40b, 40c. Further, the second measurement paths 42a, 42b each comprise a first area on the support device 38, a second area in the through hole 39, a third area on the workpiece 16a or 16b, respectively, a fourth area in the through hole 39, and a fifth area on the support device 38, the first to fifth areas arranged in this order along the second measurement paths 42a, 42b. In other words, the measurement beam 14 may be radiated along the measurement paths 42a, 42b initially to the support device 38, the through hole 39, then to the workpiece 16a or 16b, respectively, and subsequently to the through hole 39 and the support device 38 again.

[0084] By means of the first measurement paths 40a, 40b, 40c and second measurement paths 42a, 42b shown in FIG. 6, the positions and extensions of the workpieces 16a, 16b and the size of the gap 36 may be comprehensively, unambiguously, and easily determined and quantified, respectively. For an unambiguous determination of the position and extension of the workpieces 16a, 16b and of the size of the gap 36, the measurement path 40c is not required. The measurement path 40c or other measurement paths, respectively, may be used for increasing the accuracy.

[0085] FIG. 7 exemplarily shows the progression of a measurement signal acquired by a method for determining a position of a workpiece according to embodiments of the present invention. FIGS. 8 and 9 show cutouts from the progression shown in FIG. 7. The progression of the measurement signal may also be referred to as a “measurement curve”. As shown in FIGS. 7 to 9, the acquired measurement signal comprises the acquired intensity of the reflected measurement radiation 20 for all measurement paths 40a, 40b, 40c, 42a, 42b.

[0086] According to embodiments, the measurement signal corresponds to a temporally variable voltage signal of a photodiode or the temporally variable output voltage of a photodiode, respectively.

[0087] As shown in FIGS. 7 to 9, every range of the measurement signal corresponds to one of the measurement paths 40a, 40b, 40c, 42a, 42b. In other words, each point along the measurement paths 40a, 40b, 40c 42a, 42b may be associated to a point of time of the progression of the measurement signal shown in FIGS. 7 to 9. Therefore, a value of the measurement signal is associated to each point along the respective measurement path 40a, 40b, 40c, 42a, 42b. Thus, for each point of the respective measurement path 40a, 40b, 40c, 42a, 42b, it is known how large the acquired intensity of the reflected portion 20 of the radiated measurement beam 14 is. This is possible, for example, when the measurement paths 40a, 40b, 40c, 42a, 42b at each point of time, at which the measurement signal is acquired, are known.

[0088] As shown in FIGS. 7 to 9, the workpieces 16a, 16b were traversed a total of five times along the measurement paths 40a, 40b, 40c, 42a, 42b and the reflected measurement radiation 20 was acquired to obtain the shown measurement signal. FIG. 7 shows the acquired raw measurement signal and FIGS. 8 and 9 show cutouts of the acquired raw measurement signal and of the corresponding low-pass filtered measurement signal, wherein in FIG. 8, the measurement signal along a first measurement path 40a is depicted, and in FIG. 9, the measurement signal along a second measurement path 42b is depicted. Alternatively to the raw measurement signal, also the noise of the measurement signal may be evaluated.

[0089] As described before with respect to the method of the invention, the acquired measurement signal corresponds to the acquired intensity of the reflected measurement radiation 20 along the measurement paths 40a, 40b, 40c, 42a, 42b.

[0090] By evaluating the measurement signal, it may be determined, for example, whether the measurement beam 14 at a corresponding point along one of the measurement paths 40a, 40b, 40c, 42a, 42b was directed to one of the workpieces 16a, 16b, the support device 38, the through hole 39 or the gap 36, respectively. The positions of the workpieces 16a, 16b and the size of the gap 36, described before regarding the method of the invention, may also be determined by evaluating the strength of the measurement signal along the measurement paths 40a, 40b, 40c, 42a, 42b.

[0091] The acquired measurement signal may, for example, be evaluated as to whether or how strong, respectively, the measurement beam 14 was reflected along the measurement paths 40a, 40b, 40c, 42a, 42b of the workpieces 16a or 16b, respectively. For example, it may be determined that the measurement beam 14 along the corresponding measurement path 40a, 40b, 40c, 42a, 42b of the surface of one of the workpieces 16a or 16b, respectively, was reflected, when the measurement signal at the corresponding point of time or the corresponding place, respectively, is equal to or larger than a predetermined first value. Therefore, it may be determined that the workpiece 16a, 16b existed the corresponding point along the measurement path 40a, 40b, 40c, 42a, 42b. Similarly, it may be determined that the measurement beam 14 along the corresponding measurement path 40a, 40b, 40c, 42a, 42b was not reflected by the surface of one of the workpieces 16a or 16b, respectively, when the measurement signal at the corresponding point of time or the corresponding place, respectively, is equal to or smaller than a predetermined second value. In this case, no workpiece existed at the corresponding point along the measurement path 40a, 40b, 40c 42a, 42b. In FIGS. 7 to 9, the ranges of the measurement signal, for which the existence of the workpieces 16a, 16b was determined, were highlighted. Since the position, shape, and orientation of the measurement paths 40a, 40b, 40c, 42a, 42c is known, thus, the position and/or orientation of the workpieces 16a, 16b in the x-y plane may be inferred. By evaluating the measurement signal along the measurement paths 40a, 40b, 40c 42a, 42b, the positions of the workpieces 16a, 16b may therefore be determined unambiguously and comprehensively.

[0092] By evaluating the measurement signal along the measurement paths 40a, 40b, 40c, 42a, 42b, the interval 43 between the workpieces 16a, 16b, i.e., the size of the gap 36, may be determined as well. Since the first measurement paths 40a, 40b, 40c are arranged parallel to the x direction, the interval 43 between the workpieces 16a, 16b in the x direction may, for example, be determined based on the interval of the ranges of the measurement signal in FIG. 8 highlighted in gray. According to other embodiments, the interval 43 between the workpieces 16a, 16b may, with knowledge of the position and/or orientation of the workpieces 16a, 16b, be also determined computationally in the x-y plane. As illustrated in FIG. 6, the interval 43 between the workpieces 16a, 16b may be defined as the shortest interval between the workpiece surfaces or as the shortest interval between the workpieces 16a, 16b in the x-y plane, respectively.

[0093] By evaluating the measurement signal, it may be also determined whether the workpiece 16a and/or the workpiece 16b exists at all and/or is mounted or chucked in the support device 38 in a predetermined position or orientation, respectively. For example, it may be determined that the workpieces 16a, 16b do not exist at all, when the measurement signal does not exceed the first value described before. Summarizing, it may be determined that the workpieces 16a, 16b do not exist or do not exist in a predetermined position or orientation, when the measurement comprises signal unplausible or unexpected values. In these cases, according to embodiments, an error may be output.

[0094] In evaluating the measurement signal, for precisely determining the positions of the workpieces 16a, 16b, the diameter of the measurement beam 14 on the workpieces 16a, 16b and/or on the support device 38, also referred to as spot diameter, may be taken into account. In the exemplary course of the measurement signal according to embodiments of the present invention shown in FIGS. 7 to 9, the spot diameter was 340 μm (200 μm fiber diameter×255/150). For example, in FIG. 8, showing the measurement signal for the measurement path 40a, it is considered for the evaluation of the measurement signal and for the determination of the position of the workpieces 16a, 16b that, at the start of a rise of the measurement signal (the rising slope), the spot of the measurement beam 14 still lies to 0% on the workpiece 16a and is only tangent to the workpiece 16a, and that at the start of a drop of the measurement signal (the descending slope) the spot still lies to 100% on the workpiece 16b and is only tangent to the edge of the workpiece 16b. Correspondingly, the measurement signal is classified as workpiece area from the start of the rising slope to the start of the falling slope. Further, it is to be considered that a low-pass filtered measurement signal and/or a measurement signal evaluated with a noise filter is temporally shifted against the raw measurement signal.

[0095] The present invention relates to the recognition of a position of workpieces for later laser machining the same based on reflected measurement radiation or based on measurement signals, especially on photodiode signals, respectively. To do so, a measurement beam with very lower power and/or speed is guided over the workpieces, e.g., i-pins or hairpins, and a support device surrounding the workpieces and the back-reflected or back-scattered proportion of the measurement beam is, for example, captured and evaluated with a photodiode. In the area of the hairpins, the measurement radiation is strongly reflected and the back-reflection signal shows pronounced amplitudes. In the area of the support device, the laser power is absorbed and the back-scattered light is very low. By evaluating the measurement signal or the photodiode signal, respectively, it is therefore possible to determine whether the workpieces exist at all, what the position of the workpieces is, and how large a gap between the workpieces is.

[0096] Above, an application of the present invention was described, in which a component position of two workpieces to be machined is detected before the machining process, for example by guiding a pilot laser over the workpieces and evaluating the photodiode signals. Especially, this was explained by the example of two pins to be welded before a welding process.

[0097] However, the present invention may also be applied post-process, i.e., after the machining process, to evaluate the machining result. For example, the method of the invention may be applied after a welding process for welding together pins, to determine intervals between the individual welding domes and/or a size or a diameter, respectively, of a welding dome. In welding together pins of a stator, for example, a minimum creepage distance not to be gone below may be predetermined. Typically, creepage distances between welding domes should be >3 mm. Should these distances be <3 mm, the component is usually scrap.

[0098] FIG. 10 shows in subfigure A two unprocessed individual workpieces 16a and 16b, for example, a pin pair (two pins) in the state before a laser machining process. In subfigure B, the welded pin pair or the generated welding dome 16c, respectively, is illustrated schematically. In welding together both pins 16a, 16b, a welding dome or -seam, respectively, 16c is formed. The welding dome 16c has a circular shape in the schematic depiction. The individual pins 16a, 16b show a substantially elongated shape. However, each different thinkable shape is possible as well, respectively. Thus, subfigure A illustrates the state before the laser machining, that is, the pre-process state, and subfigure B illustrates the state after the laser machining, that is, the post-process state.

[0099] FIG. 11 shows a circular and concentrical arrangement of machined workpieces, e.g., of a plurality of welding domes 16c of a stator, and a measurement path 44, 45 for determining positions of the machined workpieces and/or of intervals d1, d2 between the machined workpieces 16c. Thus, this is a post-processing analysis, especially a quality check of components with welded pins. The machined workpieces presently correspond to welding domes 16c formed between the welded pins 16a, 16b. In a stator, these welding domes 16c may be arranged circularly and concentrically, as shown in FIG. 11. The welding domes 16c in FIG. 11 form, exemplary, two circular arrangements, an inner and an outer circular arrangement with eight welding domes 16c each. However, arrangements with more than two circular arrangements, for example three, four, five, or more, are thinkable as well.

[0100] The distance d1 may be acquired or established substantially along a first measurement path 44. In FIG. 11, first measurement paths are indicated along the circular arrangement of the welding domes 16c, respectively. In other words, a first measurement path 44 extends along a circular arrangement, namely such that it cuts or traverses, respectively, two adjacent welding domes 16c on a circular arrangement. The first measurement path 44 may, for example, lie on an almost perfect or also a only approximately circular track. An approximately circular track may comprise linear track sections, which connect points on a circular path.

[0101] The distance d2 between two adjacent welding domes 16c, which lie on different circular arrangements (on an inner and an outer circle, respectively), may, for example, be acquired along a linear second measurement path 45. In FIG. 11, second measurement paths 45 are indicated, each crossing two adjacent welding domes 16c on an inner and an outer circular arrangement and the respective opposite adjacent welding domes 16c. In other words, the second measurement paths 45 in FIG. 11 each form linear cutting lines leading radially through the circular arrangements of the welding domes 16c, namely through the respective welding domes 16c positioned on the inner and outer circular arrangements.

[0102] In the present example in FIG. 11, two circular paths as well as a linear horizontal track and a linear vertical track are traced or passed through, respectively, by a laser. Further, two linear tracks are traced, each tilted by 45° towards the linear horizontal track and the linear vertical track. The linear tracks, corresponding in FIG. 11 to the second measurement paths 45, extend radial, i.e., through the center of the circular arrangements. Depending on the stator type, such an arrangement may also comprise more than two circular arrangements and/or more or less welding domes 16c. Therefore, correspondingly more or less first measurement paths 44 and correspondingly more or less second measurement paths 45 of the laser may be traced. For example, two, three, four, five, or more first measurement paths 44 may be traced, especially when two, three, four, five, or more circular arrangements exist, respectively.

[0103] Since each circular arrangement in FIG. 11 comprises eight welding domes 16c, four continuous second measurement paths 45 are traced. The welding domes 16c on a circular arrangement lie opposite to each other and, therefore, the second measurement paths 45 of FIG. 11 substantially fully pass the circular arrangements. There may alternatively also exist a circular arrangement, in which the welding domes 16c are arranged not mirror-symmetrically, so that they do not exhibit an opposite neighbor on the circular arrangement. In this case, a second measurement path 45 may pass through the circular arrangement, if only partly, so that one or more welding domes 16 on one side of the respective circular arrangement are intersected along a linear track, wherein the linear track does not extend beyond the center the circular arrangements to the other or opposite, respectively, side of the circular arrangements. Preferably, however, the second measurement paths 45 intersect or pass through, respectively, the circular arrangements substantially fully.

[0104] The first measurement paths and the second measurement paths preferably extend such that the welding domes 16c are intersected or passed through, respectively, substantially centrally by the measurement paths, as for example indicated in FIG. 11. In practice, the relevant measurement paths 44, 45 or tracks, respectively, may be traced by means of a pilot laser.

[0105] The “tracing the tracks” means that e.g., the laser beam of a pilot laser is deflected by mirrors, especially by galvano mirrors, of the scanner optics and the light spot thus carries out or passes through, respectively, tracks on the component. The sensor module, especially a laser welding monitoring sensor (short: LWM sensor) based on photodiodes, registers the back-scattered laser light, and may thus determine or acquire the positions of the welding domes.

[0106] If laser light hits a position where no workpiece 16a, 16b, 16c, especially no pin 16a, 16b and no welding dome 16c is arranged, back-scattering at this place is low and, therefore, the signal recorded by the photodiodes is low. If, on the contrary, laser light hits a position at which a workpiece 16a, 16b, 16c, especially a pin 16a, 16b or a welding dome 16c, is arranged, the back-scattering is large, especially compared to the position where no workpiece 16a, 16b, 16c is arranged. At least, the signal is so large that it allows an unambiguous allocation whether a workpiece 16a, 16b, 16c is arranged at this position or not. Substantially, this requires that the signal sufficiently contrasts a noise signal.

[0107] FIG. 12 shows a diagram of an exemplary measurement signal progression corresponding to the arrangement shown in FIG. 11. On the vertical axis, a voltage U (in the unit Volts) is outlined. The voltage U is acquired in the sensor module 26. Especially, the voltage U is proportional to the light intensity acquired by the sensor module 26 of the light reflected at the surface of a component. On the horizontal axis, a time t (in the unit seconds) is outlined in a time interval, in which the voltage U is acquired.

[0108] If the track speed v and the course of the track or the measurement path, respectively, are known, distances between two workpieces 16a, 16b, 16c may be established from the diagram. The diagram corresponds, as already discussed, to plotting the measurement signal, especially a voltage U acquired at the sensor module, against the time t required for tracing the track.

[0109] In the diagram of FIG. 12, three almost box-shaped voltage signals can be recognized. These three voltage signals correspond to the time t, in which the laser respectively traverses one of three welding domes 16c and thus a high proportion of the light is reflected at the welding domes 16c and acquired by the sensor module 26. The time intervals shown between the box-shaped voltage signals in which the acquired voltage is very low, correspond to the moments in which the laser beam impinges on the support device 38 or the substrate, respectively, on which the welding domes 16c are arranged. On the support device 38 itself, only relatively little light of the laser is reflected, so that correspondingly small light intensities are acquired by the sensor module 26 and, therefore, the acquired voltage V is low. Here, this may be a first measurement path 44 or a second measurement path 45.

[0110] Based on the known track speed v and the duration of the traversal of a welding dome 16c to an adjacent welding dome 16c, the distance d1 or d2 or also the diameter or the size, respectively, of the welding dome may be determined. The respective distance d1 or d2 may either correspond to an interval between the opposite edges of the adjacent welding domes 16c, the opposite edges of the adjacent welding domes 16c, or an interval between the central positions, especially the centers of the respective adjacent welding domes 16c. The distance d1 or d2 may be established according to the following equation 1:

d1,d2=v×Δt

[0111] d1, d2 is the distance d1 or d2, v is the track speed, and Δt is the temporal interval or the time difference Δt, respectively, for tracing a track between two adjacent welding domes 16c. Since the temporal interval Δt shown in FIG. 12 for reaching an adjacent welding dome 16c is indicated, this is the determination of the distance d1, d2 between two opposite edges of the adjacent welding domes 16c. In other words, in FIG. 12, the interval from edge to edge of two adjacent welding domes 16c is established.

[0112] So far, a method was presented (method 1) in which the voltage, U, is measured over the time, t. Through knowledge of the speed of the focus point of the pilot laser, according to the above equation, the distance, d, may be calculated. An alternative looks as follows (method 2): as in method 1, sensor signals are captured by a photodiode and the voltage is plotted over the time. As opposed to method 1, this measurement record is now not set in relation to the speed, but the positions of the galvos (=the scanner mirrors) are being read out. By knowledge of the position of the galvos, the position of the focus point of the pilot laser may be inferred. Summary: [0113] 1) A method 1: Photodiode supplies voltage signal over time.fwdarw.through the speed, it is possible to calculate the path. [0114] 2) A method 2: Photodiode supplies voltage signal over time.fwdarw.through the position of the galvos (=scanner mirrors), it is possible to attribute the position on the component.

[0115] In both cases, therefore, the voltage signal may be related to the position on the component and, thus, intervals may be determined.

[0116] The interval d1, d2 between two adjacent welding domes 16c is referred to as creepage distance. The quality evaluation of a component with workpieces after laser machining may be determined by means of the creepage distance or the creepage distances, respectively. For example, a component may not fulfill the quality criteria if the creepage distance goes below a minimum value.

[0117] Therefore, the method of the invention may be applied in the pre-process, but especially also in a post-process. In the post-process, for example, creepage distances d1, d2 between welded pins 16a, 16b, which illustrate welding domes 16c or welding seams, and/or a diameter or a size, respectively, of the welding domes 16c are determined. In the pre-process, for example, intervals between pins 16a, 16b are determined. FIGS. 11 and 12 relate to a post-process analysis. However, the mentioned method features may be analogously transferred to pre-process analyses.

LIST OF REFERENCE SYMBOLS

[0118] 10 laser machining system [0119] 12 laser machining apparatus [0120] 14 measurement beam [0121] 16a, 16b workpieces before a laser welding process [0122] 16c welding joint or dome, respectively, after a laser welding process [0123] 17a, 17b ends [0124] 18 optical fiber [0125] 20 reflected measurement radiation [0126] 22 beam splitter [0127] 26 sensor module [0128] 30 control unit [0129] 32a, 32b conductor [0130] 33a, 33b insulation material [0131] 36 gap [0132] 38 support device [0133] 39 through hole [0134] 40a, 40b, 40c first measurement paths [0135] 42a, 42b second measurement paths [0136] 43 interval between workpieces [0137] 44 first measurement path [0138] 45 second measurement path [0139] A state before the laser machining (pre-process state) [0140] B state after the laser machining (post-process state) [0141] d1, d2 intervals between two adjacent welding joints or domes, respectively [0142] Δt temporal interval between the acquisition of two adjacent welding joints or domes, respectively [0143] t time axis with unit seconds (s) [0144] U axis with unit volts (V)