US20220228852A1

US20220228852A1 - Apparatus and method for edge detection when machining workpieces

Info

Publication number: US20220228852A1
Application number: US17/658,050
Authority: US
Inventors: Mathias Cornelißen
Original assignee: II VI Delaware Inc
Current assignee: II VI Delaware Inc
Priority date: 2019-12-10
Filing date: 2022-04-05
Publication date: 2022-07-21
Also published as: US20210172724A1; DE102019133695B4; DE102019133695A1; US11320258B2

Abstract

An apparatus and method for detecting edges or for seam tracking when machining workpieces by means of a laser beam, e.g. joining or cutting. The present invention provides an apparatus for seam tracking of the process in the laser material processing, comprising at least two separate illumination elements, each emitting differently polarized light and a polarization camera.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is continuation of U.S. patent application Ser. No. 16/710,700 filed Dec. 11, 2019, which claims the benefit of German Application No. DE 10 2019 133 695.3 filed Dec. 10, 2019, both of which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for detection of edges or seam tracking when machining workpieces by means of a laser beam, e.g. joining or cutting. The machining can be a laser material processing of workpieces in three-dimensional space.

2. BRIEF DESCRIPTION OF THE RELATED ART

During laser material processing of workpieces, seam tracking is used for process monitoring, regulation or control and for quality management. For this purpose, mostly image processing systems are used.
Edge detection is an essential step in seam tracking. From the prior art methods and systems are known in which the camera image of an optical camera is evaluated by means of special algorithms. The evaluation is based on a monochrome image, from which the in-tensity of the light reflected into the camera is utilized as image information. With optically difficult materials, which have only a small or very diffuse reflection, there are difficulties in the evaluation, since often only very poor and low-contrast images are available. Such materials may have, for example, matte or dark surfaces.
Remote laser welding is a special variant of laser beam welding. In this method, welding can be performed in any direction in three-dimensional space, and the direction may also change during the welding operation. This is a difference in comparison to other welding processes, which usually only weld in one direction. In such devices, detectors or guide elements are used, which run ahead of the joining process.
Furthermore, in the methods known from the prior art several recordings with different optical filters of the machining process of the workpieces are needed to allow reliable control. For this purpose, the required information is calculated by means of special algorithms.
Furthermore, in methods known from the prior art, it is usually also necessary to use a plurality of cameras in order to obtain the required image data.
There is a need for an apparatus and a method which allow even with optically difficult materials to ensure reliable seam tracking.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a novel apparatus and a novel method for seam tracking.
The present invention provides an apparatus for seam tracking of the process in laser material processing, comprising at least two separate illumination elements, each emitting differently polarized light, and a polarization camera.
In a further aspect of the invention, it is provided that the at least two separate illumination elements each emit light having polarization rotated by 90°.
Furthermore, an embodiment is provided, comprising four separate illumination elements.
In a further aspect of the invention, an apparatus may also comprise an even multiple number of illumination elements.
If more than two illumination elements are used, it is provided that in each case two of the separate illumination elements emit identically polarized light.
Furthermore, it is provided that then the at least two separate illumination elements, which emit identically polarized light, are arranged opposite to each other.
In a further aspect of the invention it is provided that the polarization camera is arranged coaxially to a laser beam for material processing.
Another object of the present invention is a method for seam tracking in laser material processing, comprising the steps:
a. Use at least two separate illumination elements to illuminate the area of interest with polarized light;
b. Capturing at least one image of the illuminated area of interest with a polarization camera;
c. Transferring the at least one image to an evaluation unit;
d. Evaluation of the at least one image.
In the method according to the invention, the two separate illumination elements may emit light having polarization rotated by 90°.
In a further aspect of the invention, it is provided for the method that the evaluation unit is a device for data processing.
The method according to the invention can also be designed such that four separate illumination elements are used.
Furthermore, in each case two of the four illumination elements can emit identically polarized light when carrying out the method.
The method may, in another aspect of the present invention, comprise the arrangement of the illumination elements with identically polarized light opposite each other.
Another object of the present invention relates to a laser material processing head comprising an apparatus for seam tracking in laser material processing as described above.
A method of using an apparatus as described above for seam tracing in a remote laser welding process is a further object of the present invention.
Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a preferable embodiments and implementations. The present invention is also capable of other and different embodiments and its several details can be modified in various obvious respects, all without de-parting from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described on the basis of figures. It will be understood that the embodiments and aspects of the invention described in the figures are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects of other embodiments of the invention, in which:

FIGS. 1 and 2 show an optic of a remote laser welding head from below with different polarization directions of the illumination elements.

FIG. 3 shows an optic of a remote laser welding head from below with an alternative arrangement of the illumination elements.

DETAILED DESCRIPTION OF THE INVENTION

The above-mentioned object of the invention is solved by the features of the independent claims. The dependent claims cover further specific embodiments of the invention.
The invention of FIGS. 1-3 provides an apparatus (20) and a method in which an image evaluation is possible even with only slight or diffuse contrasts of the materials or even with highly reflective materials. When reflecting on metallic surfaces, or reflective surfaces in general, there may be a change in the polarization properties of the reflected light compared to the incident light.
The present invention is based on the use of a polarization camera (40). Thus, it is possible in addition to the pure optical image data also additionally to determine the polarization properties of the reflected light. For reflections on differently inclined surfaces, the polarization of the light also changes.
Furthermore, the invention provides that the camera (40) is arranged coaxially to the laser beam, with which a workpiece (not shown) is processed.
Furthermore, it has been found in experiments using a polarization camera (40) that the use of polarized light to illuminate the workpiece is advantageous. In this respect, polarized light sources (21, 22, 23, 24) or the use of polarizing filters (not shown) for the light sources (21, 22, 23, 24) are an essential element of the present invention.
Experiments have shown that the use of at least two different polarized light sources (21, 22, 23, 24) is advantageous. It is furthermore advantageous if the at least two light sources (21, 22, 23, 24) have a polarization direction rotated by 90° with respect to another.
Four light sources (21, 22, 23, 24) can also be used. In this case, two light sources (e.g., 21 and 23, 22 and 24) each have an identical polarization direction and the two pairs (e.g., 21 and 23, 22 and 24) with identical polarization direction are arranged opposite to one another. In principle, an odd number of lighting elements or light sources (21, 22, 23, 24) is within the scope of the invention.
According to the invention polarization cameras (40) will be used, in which only one frame of a recording or captured image (42) is sufficient for evaluation.
The inventive method is advantageous because not only the purely optical properties of the image (42) are taken as a basis, but due to the inclusion of the polarization of the reflected light contrast-sharp images arise, which can then be evaluated by means of a suitable algorithm. The stronger contrast leads to a better recognition.
FIG. 1 shows the optics of a remote laser welding head 10 from below. Four illumination elements 21, 22, 23, 24 are arranged laterally around the outlet opening of the laser processing optics 15. The arrows indicate the polarization direction of the individual illumination elements 21, 22, 23, 24. Opposite illumination elements (i.e., 21 and 23, 22 and 24) each have the same direction of polarization, respectively emitted polarized light. In FIG. 1 is the polarization direction of the lighting elements 21, 22, 23, 24 along their longitudinal direction. The polarization is achieved by polarizing filters (not shown separately) in front of the lighting elements 21, 22, 23, 24.
In FIG. 2 are also four illumination elements 21, 22, 23, 24 arranged around the laser processing optics 15. A polarization camera 40 is arranged coaxially to a laser beam for material processing. Here, the polarization filters (not shown separately) lead to a polarization of the light of the illumination elements 21, 22, 23, 24 transversely or perpendicular to the longitudinal extent of the illumination elements.
FIG. 3 shows an alternative arrangement of the illumination elements 21, 22, 23, 24. These are arranged in the corners of the housing of the laser welding head 10. Opposing illumination elements in the diagonal, i.e. 21, 23 and 22, 24 have an identical polarization direction of the emitted light.
It can be seen from FIGS. 1 to 3 that the polarization direction of the two pairs is in each case rotated by 90° with respect to one another.
In principle, two, four, six, eight or any other even multiple of lighting elements 21, 22, 23, 24 are conceivable. Importantly, the lighting elements 21, 22, 23, 24 are present in pairs, and the lighting elements 21, 22, 23, 24 of a pair face each other, with both lighting elements 21, 22, 23, 24 having the same polarization direction of the emitted light.
The present invention provides an apparatus (20) for seam tracking of the process in laser material processing, comprising at least two separate illumination elements (21, 22, 23, 24), each emitting differently polarized light, and a polarization camera (40).
In a further aspect of the invention, it is provided that the at least two separate illumination elements (21, 22, 23, 24) each emit light having polarization rotated by 90°.
Furthermore, an embodiment is provided, comprising four separate illumination elements (21, 22, 23, 24).
In a further aspect of the invention, an apparatus (20) may also comprise an even multiple number of illumination elements (21, 22, 23, 24).
If more than two illumination elements (21, 22, 23, 24) are used, it is provided that in each case two of the separate illumination elements (e.g., 21 and 23, 22 and 24) emit identically polarized light.
Furthermore, it is provided that then the at least two separate illumination elements (21, 22, 23, 24), which emit identically polarized light, are arranged opposite to each other.
In a further aspect of the invention, it is provided that the polarization camera (40) is arranged coaxially to a laser beam for material processing.
Another object of the present invention is a method for seam tracking in laser material processing, comprising the steps: (a) using at least two separate illumination elements (21, 22, 23, 24) to illuminate the area of interest with polarized light; (b) capturing at least one image (42) of the illuminated area of interest with a polarization camera (40); (c) transferring the at least one image (42) to an evaluation unit (30); and (d) evaluating the at least one image (42).
In the method according to the invention, the two separate illumination elements (21, 22, 23, 24) may emit light having polarization rotated by 90°.
In a further aspect of the invention, it is provided for the method that the evaluation unit (30) is a device for data processing.
The method according to the invention can also be designed such that four separate illumination elements (21, 22, 23, 24) are used.
Furthermore, in each case two of the four illumination elements (e.g., 21 and 23, 22 and 24) can emit identically polarized light when carrying out the method.
The method may, in another aspect of the present invention, comprise the arrangement of the illumination elements (21, 22, 23, 24) with identically polarized light opposite each other.
Another object of the present invention relates to a laser material processing head (10) comprising an apparatus (20) for seam tracking in laser material processing as described above.
A method of using an apparatus (20) as described above for seam tracking in a remote laser welding process is a further object of the present invention.
The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the afore-mentioned documents is incorporated by reference herein.

REFERENCE NUMERALS

- 20 Apparatus
- 21-24 illumination elements
- 30 Camera
- 40 Evaluation Unit
- 15 Beam extraction of the laser processing optics, which also acts as imaging optics for the camera 30
- 10 Housing laser welding head

Claims

1-15. (canceled)

16. An apparatus for tracking a seam during laser material processing with a laser beam, the apparatus comprising:

a plurality of illumination elements being configured to emit polarized light to illuminate an area of interest, one or more first of the illumination elements being configured to emit first of the polarized light to illuminate the area of interest, one or more second of the illumination elements being configured to emit second of the polarized light to illuminate the area of interest, the second polarized light being differently polarized than the first polarized light;

a polarization camera being configured to capture at least one image of the area of interest illuminated with both of the first and second differently polarized light; and

an evaluation unit in operable communication with the polarization camera and being configured to evaluate the at least one image to track the seam.

17. The apparatus of claim 16, wherein the evaluation unit comprises a device for data processing.

18. The apparatus of claim 16, wherein to evaluate the at least one image, the evaluation unit is configured to determine contrast in the at least one image based on polarization properties of reflected light on differently inclined surfaces in the area of interest.

19. The apparatus of claim 16, wherein the plurality of illumination elements comprises polarized light sources, or light sources having polarizing filters.

20. The apparatus of claim 16, wherein the illumination elements are arranged in a longitudinal direction; and wherein the illumination elements are configured to emit the polarized light in a polarization direction along the longitudinal direction.

21. The apparatus of claim 16, wherein the illumination elements are arranged in a longitudinal direction; and wherein the illumination elements are configured to emit the polarized light in a polarization direction perpendicular to the longitudinal direction.

22. The apparatus of claim 16, wherein the one or more first of the illumination elements comprise a first pair of the illumination elements facing one another and having a same first polarization direction; and wherein the one or more second of the illumination elements comprise a second pair of the illumination elements facing one another and having a same second polarization direction different from the first polarization direction.

23. The apparatus of claim 22, wherein the illumination elements of the first pair are arranged opposite to each other, and wherein the illumination elements of the second pair are arranged opposite to each other.

24. The apparatus of claim 16, wherein the one or more first of the illumination elements are configured to emit the first polarized light having polarization rotated by 90° relative to the second polarized light emitted by the one or more second of the illumination elements.

25. The apparatus of claim 16, wherein the plurality of illumination elements comprise an even multiple number of the illumination elements for the first polarized light; and an even multiple number of the illumination elements for the second polarized light.

26. The apparatus of claim 16, wherein the polarization camera is arranged coaxially to the laser beam of the laser material processing.

27. A laser material processing head comprising an apparatus according to claim 16.

28. An apparatus for tracking a seam in laser material processing, the apparatus comprising:

first illumination elements being configured to emit first identically polarized light and being configured to illuminate an area of interest with the first identically polarized light,

second illumination elements being configured to emit second identically polarized light and being configured to illuminate the area of interest with the second identically polarized light, the second identically polarized light being different than the first identically polarized light;

a polarization camera being configured to capture at least one image of the illuminated area of interest; and

an evaluation unit in operable communication with the polarization camera and being configured to evaluate the at least one image for the seam.

29. The apparatus of claim 28, wherein the first illumination elements with the first identically polarized light are arranged in a first pair opposite each other; and wherein the second illumination elements with the second identically polarized light are arranged in a second pair opposite each other.

30. The apparatus of claim 28, wherein to evaluate the at least one image, the evaluation unit is configured to determine contrast in the at least one image based on polarization properties of reflected light on differently inclined surfaces in the area of interest.

31. The apparatus of claim 28, wherein the first and second illumination elements comprise polarized light sources, or light sources having polarizing filters.

32. The apparatus of claim 28, wherein: the first and second illumination elements are arranged in a longitudinal direction, and the first and second illumination elements are configured to emit the first and second identically polarized light in a polarization direction along the longitudinal direction; or wherein: the first and second illumination elements are arranged in a longitudinal direction, and the first and second illumination elements are configured to emit the first and second identically polarized light in a polarization direction perpendicular to the longitudinal direction.

33. The apparatus of claim 28, wherein the first illumination elements are configured to emit the first identically polarized light having polarization rotated by 90° relative to the second identically polarized light emitted by the second illumination elements.

34. The apparatus of claim 28, wherein the polarization camera is arranged coaxially to the laser beam of the laser material processing.

35. A laser material processing head comprising an apparatus according to claim 28.