Sensor arrangement for optical elements in laser material processing heads

Abstract

The present disclosure provides a sensor arrangement for reflecting scattered light from a laser beam, comprising a first optical element; a cone of a housing which is arranged behind the first optical element in the direction of the beam path of a laser beam, wherein the cone of the housing comprises a conical step-shaped reflector whose shape corresponds to the shape of the cone of the housing and wherein the conical step-shaped reflector is formed from a plurality of annular elements, each annular element having reflector surfaces on its inner side facing the beam path of the laser beam; and an element for receiving the light reflected from the respective reflector surfaces of the plurality of annular elements, which is arranged on the side of the optical element opposite the cone of the housing.Another object of the present disclosure is a laser material processing head comprising an opening for coupling in a laser beam; and a sensor arrangement according to any one of claims 1 to 7. Another object of the present disclosure relates to a device for laser material processing comprising a laser material processing head according to claim 8 or 9 and a device for moving the laser material processing head.

Description

Territory of Revelation

[0001] The present disclosure relates generally to a sensor arrangement for monitoring optical elements in laser material processing heads and to a method using the sensor arrangement. Brief description of the state of the art

[0002] COHERENT ® The company develops and manufactures lasers, laser processing heads and systems, components and accessories, as well as laser measuring instruments. The laser processing heads and systems are designed for processing materials, including welding, soldering, and cutting.

[0003] Laser processing heads and systems comprise a variety of optical elements. For beam shaping, laser processing systems use lenses, for example, which collimate or focus the laser beam. The optical elements are usually arranged in groups along the optical axis and are assembled in so-called tubes. Often, entire groups of optical elements can be replaced as needed, eliminating the need to replace numerous individual elements.

[0004] Welding and cutting of workpieces generates emissions that can accumulate in the vicinity of the processing point. These deposits can impair the function of laser optics by forming deposits on the optical surfaces. These deposits not only reduce the performance of the optical systems but can also damage or even destroy the laser optics.

[0005] The surface of an optical element, e.g., a protective glass or a lens, must therefore be monitored with regard to the deposition of contaminants or emissions.

[0006] Since the signal ratio after emission through the optical element is significantly higher in the optical direction than in the opposite direction, between the desired beam path and scattered radiation resulting from contamination or deposits, it would be advantageous to position a sensor behind the optical element. For example, a sensor for monitoring the protective glass of a cutting optic would then have to be located within the pressure or flow chamber for the cutting gas to benefit from this advantageous arrangement. Firstly, the effort required to place this sensor there in a pressure-tight manner and connect it electrically to the outside is very high, and secondly, this arrangement can disrupt the rotational symmetry of the cutting gas flow. Therefore, positioning the sensor in this way is disadvantageous.

[0007] Solutions are known in the art for measuring the scattered light signal at the cylindrical surface of an optical element. The disadvantage of such a solution is that the signal is highly dependent on the surface's properties, and the ratio of clean to dirty signal perpendicular to the optical propagation direction is low.

[0008] Furthermore, an arrangement is known in the prior art in which the optical sensor is arranged opposite to the optical propagation direction and in the direction of the optical propagation direction, and also achieves only a low signal ratio.

[0009] An arrangement is also known from the prior art in which the sensor is arranged in the optical direction of propagation and thus achieves a high signal ratio, but must also be spatially arranged against the direction of propagation.

[0010] Another arrangement is known in which the signal from a transmitting diode is reflected at the optical surface. A disadvantage of this arrangement is that both elements must be located in the optical direction of propagation, and only heavy contamination can cause interference.

[0011] The surface temperature of optical elements can also be measured with a pyrometer. However, these operate at wavelengths of 2–14 µm, for which quartz glass is hardly transparent, and are therefore only of limited use in transmitted light applications.

[0012] The purpose of the present disclosure is therefore to provide a sensor arrangement which avoids the disadvantages of the prior art solutions. Summary of Revelation

[0013] The present disclosure provides a sensor arrangement for the reflection of scattered light from a laser beam, comprising a. a first optical element; b. a cone of a housing which is arranged in the direction of the beam path of a laser beam behind the first optical element, wherein the cone of the housing comprises a conical step-shaped reflector whose shape corresponds to the shape of the cone of the housing and wherein the conical step-shaped reflector is formed from a plurality of annular elements, each annular element having reflector surfaces on its inner side facing the beam path of the laser beam; and c. an element for receiving the light reflected from the respective reflector surfaces of the multitude of ring-shaped elements, which is arranged on the side of the optical element opposite the cone of the housing.

[0014] In one embodiment of the sensor arrangement according to 1, the element for receiving the light reflected from the reflector surfaces is a light sensor.

[0015] It is further provided that the element for receiving the light reflected from the reflector surfaces is a deflecting mirror for reflecting the light onto a light sensor, wherein the light sensor in one embodiment is a photodiode.

[0016] In one embodiment of the sensor arrangement according to the present disclosure, the respective reflector surfaces of the plurality of ring-shaped elements each have a different inclination with respect to the first optical element.

[0017] It is further provided that in a sensor arrangement according to the present disclosure, the respective reflector surfaces of the plurality of ring-shaped elements are designed in such a way that they are aligned with the element for receiving the light reflected by the respective reflector surfaces of the plurality of ring-shaped elements.

[0018] In one embodiment of a sensor arrangement, the light sensor is connected to a receiving and evaluation device.

[0019] In one embodiment of the sensor arrangement, the conical, stepped reflector is arranged on the inside of the cone of the housing.

[0020] In one aspect of the sensor arrangement, the conical, stepped reflector is part of the cone of the housing.

[0021] Another subject of the present disclosure is a laser material processing head comprising a. an opening for coupling in a laser beam; b. a sensor arrangement as described above.

[0022] In one embodiment, the cone of the housing of the laser material processing head is a cutting gas cone through which a cutting gas flows.

[0023] Another subject of the present disclosure relates to a device for laser material processing, comprising a laser material processing head as previously described and a device for moving the laser material processing head.

[0024] Another subject of the present disclosure relates to a method for monitoring optical elements for contamination or soiling, comprising the steps a. Guiding a laser beam through a first optical element; b. Reflection of scattered radiation from the first optical element with a conical step-shaped reflector located in a cone of a housing which is arranged behind the first optical element in the direction of the laser beam path, wherein the shape of the conical step-shaped reflector corresponds to the shape of the cone of the housing and wherein the conical step-shaped reflector is formed from a plurality of ring-shaped elements, each ring-shaped element having a reflector surface on its inner side facing the laser beam path; c. Receiving the reflected scattered radiation with an element for receiving the light reflected from the respective reflector surfaces of the multitude of ring-shaped elements, which is arranged on the side of the optical element opposite the cone of the housing.

[0025] In one embodiment of the method according to the present disclosure, the element for receiving the light reflected from the reflector surfaces is a light sensor.

[0026] The method can also be designed such that the element for receiving the light reflected from the reflector surfaces is a deflecting mirror for reflecting the light onto a light sensor.

[0027] Furthermore, the method according to the present disclosure includes a photodiode as a light sensor.

[0028] In one embodiment, it is also provided that the light received by the light sensor is converted into electrical signals, which are processed by a receiving and evaluation device.

[0029] Further aspects, features, and advantages of the present disclosure will readily become apparent from the following detailed description, which simply presents preferred embodiments and implementations. The present disclosure can also be realized in other and different embodiments, and its various details can be modified in various obvious aspects without departing from the teaching and scope of the present disclosure. Accordingly, the drawings and descriptions are to be regarded as illustrative and not as limiting. Additional tasks and advantages of the disclosure are partly set forth in the following description and partly become apparent from the description or can be derived from the execution of the disclosure. Brief description of the characters

[0030] The disclosure is further illustrated below with reference to the figures. It is obvious to the person skilled in the art that these are only possible, exemplary embodiments, without limiting the disclosure to the embodiments shown, wherein: Fig. Figure 1A shows a laser material processing head with a sensor arrangement for direct measurement of reflected scattered light. Fig. Figure 1B shows a laser material processing head with a mirror for deflecting reflected scattered light onto a light sensor. Fig. Figure 2 shows in detail a conical step-shaped reflector in an embodiment with a protective glass as an optical element, which is arranged in a protective glass drawer. Fig. Figure 3 shows the cutting gas inlet at the beginning of the cutting gas cone. Fig. Figure 4 shows the scattered light distribution emanating from the protective glass as an optical element. Fig. Figure 5 shows the distribution of the signal-to-noise ratio starting from the protective glass. Fig. Figure 6 shows the signal ratio of a dirty to a clean protective glass plotted in polar coordinates. Fig. Figure 7 shows the arrangement and inclination of the reflecting inner surfaces of the reflector towards the light sensor. Detailed description of the revelation

[0031] The previously formulated objective of the disclosure is achieved by the features of the independent claims. The dependent claims cover further specific embodiments of the disclosure.

[0032] For the purposes of this disclosure, optical elements shall be understood to mean lenses, protective glasses, mirrors, and beam-shaping elements. The term "fixation" in connection with an optical element encompasses the centering and positioning of the optical element in the beam path.

[0033] The present disclosure provides one or more cylindrically or conically arranged reflectors, which are arranged in the optical direction of propagation, and which reflect the forward scattering through the optical element back through the optical element. This scattered light can then be detected by means of an optical sensor, which is arranged in front of a pressure chamber opposite to the optical direction of propagation. The sensor can, for example, be a photodiode.

[0034] The reflective structure according to the present disclosure can be embedded in the base material of a gas guide cone, which is typically made of aluminum. The reflective structure thus reflects the light scattered forward by the contaminated optical element back through the optical element to the sensor. The light from the cutting process is reflected perpendicular to the beam axis and therefore barely reaches the sensor. The inner contour of the reflective structure follows the conical cutting gas supply and thus does not disrupt the cutting gas flow. This structure can extend over one, several, or the entire conical area of ​​the cutting gas tip.

[0035] Fig. Figure 1A shows a laser material processing head with a sensor arrangement according to the present disclosure. The laser beam 4 is coupled into the housing 1 of the laser material processing head on the left side of the illustrated embodiment. The collimation lens 4 is arranged in front of the focusing lens 3. The focused laser beam 4 passes through the optical element 6, which in the illustrated embodiment is a protective glass in a drawer 5, which in turn separates the interior of the cutting gas cone 9 from the rest of the interior of the housing 1. The cutting gas outlet 10 is also the laser process point onto which the laser beam 4 is focused.

[0036] Conically stepped reflectors 8 are arranged in the cutting gas cone 9. The shape of the reflector 8 follows the conical shape of the cutting gas cone, with the reflector being composed of a multitude of ring-shaped elements, each of which has an inward-facing reflector pointing towards the optical element. Thus, the reflector has a stepped cross-section with differently angled steps. Due to the conical and therefore tapered diameter of the cutting gas cone, the respective ring-shaped elements of the reflector must be angled differently with respect to the surface of the optical element.

[0037] In the direction of the laser beam 4 in front of the optical element 6, the protective glass in Fig. 1, i.e., on the opposite side of the optical element 6 to the reflectors 8, a light sensor 7 is arranged. This sensor is angled with respect to the surface of the optical element 6 in the direction of the annular elements of the reflector 8. Alternatively, a deflecting mirror 14 can be arranged accordingly, which deflects the light reflected from the annular element of the reflector 8 towards a light sensor 7 (see Figure 1). Fig. 1B).

[0038] Fig. Figure 2 shows in detail an embodiment of a conical, stepped reflector behind an optical element 6, which serves as a protective glass and is arranged in a drawer 5. A cutting gas cone 9 is located behind the optical element 6. The conical, stepped reflector 8 is arranged behind the optical element 6.

[0039] Fig. Figure 3 shows the cutting gas inlet 11 at the beginning of the cutting gas cone 9. Also shown are the optical element 6 in a drawer 5, the reflector 8, light sensor 7, focusing lens 3 and housing 1.

[0040] Fig. Figure 4 shows the scattered light distribution 12 emanating from the optical element 6, which is arranged in a drawer 5. The scattered light 12 is distributed on both sides of the optical element 6. The ring-shaped elements of the conical step-shaped reflector 8 are arranged in the direction of propagation of the scattered light 12. The ring-shaped elements of the conical step-shaped reflector 8 have an inner surface 81 (see Figure 4). Fig. 7) so that the direction of the scattered light strikes the respective inner surface at 90°. The different inclination between the inner surfaces 81 serves to focus the reflection of the scattered light onto the light sensor 7 (see Figure 7). Fig. 7).

[0041] Fig. Figure 5 shows the distribution of the signal-to-noise ratio 13 originating from the optical element 6, which is arranged in a drawer 5. It is clearly evident that the arrangement and extent of the ring-shaped elements of the conical, stepped reflector 8 are based on the distribution of the signal-to-noise ratio originating from the optical element 6.

[0042] Fig. Figure 6 shows, plotted in polar coordinates, the signal ratio 13 of a dirty to a clean protective glass 6. The beam propagation direction in the image runs from left to right along the optical axis 15. A signal ratio of 1:1 means that the scattered light signal of a clean optical element is identical to that of a dirty element, and therefore signal separation is not possible. The highest signal ratio of 1:5 (clean : dirty) is reached in the beam propagation direction 30° from the optical axis. Values ​​below 20° are not shown, as the laser beam propagates at these angles, making measurement impossible.

[0043] Fig.Figure 7 shows the arrangement and inclination of the reflecting inner surfaces 81 of the reflector towards the light sensor 7 with respect to the optical axis 15. The inner surfaces 81 reflect scattered radiation from the contaminated optical element (not shown) onto the sensor 7. The arrangement of the reflector surfaces is perhaps better in the broadest sense. The reflector surfaces are arranged such that a laser beam scattered by a particle from the center of the protective glass, after its reflection by the reflector surfaces, strikes the sensor. However, the refraction of light upon passing through the protective glass must also be taken into account.

[0044] As a technical effect, the features of the present disclosure make it possible to determine the soiling or contamination of an optical element without the need to position a light sensor or other sensors behind the optical element in the direction of the light beam path. Due to the shape and arrangement of the conically shaped, stepped reflector, it is possible to determine soiling of the optical element.

[0045] An advantage of a device according to the present disclosure is that it is sufficient to arrange the reflector behind the optical element, whereby this has no influence on the function of the laser material processing head in the sense of disturbing the cutting gas flow or influencing the laser beam.

[0046] Further aspects, features, and advantages of the present disclosure will readily become apparent from the following detailed description, which simply presents preferred embodiments and implementations. The present disclosure can also be realized in other and different embodiments, and its various details can be modified in various obvious aspects without departing from the teaching and scope of the present disclosure. Accordingly, the drawings and descriptions are to be regarded as illustrative and not as limiting. Additional tasks and advantages of the disclosure are partly set forth in the following description and partly become apparent from the description or can be derived from the execution of the disclosure. Reference sign 1 case 2 Collimation lens 3 Focusing lens 4 Laser beam 5 drawers 6 optical element 7 Light sensor 8 conically arranged reflectors 81 interior surface 9 cutting gas cones 10 Cutting gas outlet - Laser process point 11 Cutting gas inlet 12 Scattered light distribution emanating from the protective glass 13. Distribution of the signal-to-noise ratio starting from the protective glass 14 deflecting mirrors 15 Optical axis

Claims

[1] A sensor arrangement for reflecting scattered light from a laser beam (4), comprising - a first optical element (6); - a cone of a housing (1) which is arranged in the direction of the beam path of a laser beam (4) behind the first optical element (6), wherein the cone of the housing (1) comprises a conical step-shaped reflector (8) whose shape corresponds to the shape of the cone of the housing (1) and wherein the conical step-shaped reflector (8) is formed from a plurality of annular elements, each annular element having reflector surfaces (81) on its inner side facing the beam path of the laser beam; and - an element for receiving the light reflected from the respective reflector surfaces (81) of the multitude of ring-shaped elements, which is arranged on the side of the optical element (6) opposite the cone of the housing (1). [2] The sensor arrangement according to claim 1, wherein the element for receiving the light reflected from the reflector surfaces (81) is a light sensor (7). [3] The sensor arrangement according to claim 1, wherein the element for receiving the light reflected from the reflector surfaces is a deflecting mirror (14) for reflecting the light onto a light sensor (7). [4] The sensor arrangement according to claim 2 or 3, wherein the light sensor (7) is a photodiode. [5] The sensor arrangement according to one of claims 1 to 4, wherein the respective reflector surfaces (81) of the plurality of ring-shaped elements each have a different inclination with respect to the first optical element (6). [6] The sensor arrangement according to one of claims 1 to 5, wherein the respective reflector surfaces (81) of the plurality of ring-shaped elements are designed such that they are aligned with the element for receiving the light reflected from the respective reflector surfaces (81) of the plurality of ring-shaped elements. [7] The sensor arrangement according to any one of claims 2 to 6, wherein the light sensor (7) is connected to a receiving and evaluation device. [8] The sensor arrangement according to any one of claims 1 to 7, wherein the conical step-shaped reflector (8) is arranged on the inside of the cone of the housing (1). [9] The sensor arrangement according to any one of claims 1 to 7, wherein the conical step-shaped reflector (8) is part of the cone of the housing (1). [10] A laser material processing head comprising - an opening for coupling in a laser beam; - a sensor arrangement according to any one of claims 1 to 7. [11] The laser material processing head according to claim 10, wherein the cone of the housing (1) is a cutting gas cone (9) through which a cutting gas flows. [12] A device for laser material processing, comprising a laser material processing head according to claim 8 or 9 and a device for moving the laser material processing head. [13] A method for monitoring optical elements for contamination or soiling, comprising the steps - Guiding a laser beam (4) through a first optical element (6); - Reflection of scattered radiation from the first optical element (6) with a conical step-shaped reflector (8) located in a cone of a housing (1) which is arranged behind the first optical element (6) in the direction of the beam path of the laser beam (4), wherein the shape of the conical step-shaped reflector (8) corresponds to the shape of the cone of the housing (1) and wherein the conical step-shaped reflector (8) is formed from a plurality of ring-shaped elements, each ring-shaped element having a reflector surface (81) on its inner side facing the beam path of the laser beam; - Receiving the reflected scattered radiation (12) with an element for receiving the light reflected from the respective reflector surfaces (81) of the plurality of ring-shaped elements, which is arranged on the side of the optical element (6) opposite to the cone of the housing (1). [14] The method according to claim 10, wherein the element for receiving the light reflected from the reflector surfaces (81) is a light sensor (7). [15] The method according to claim 10, wherein the element for receiving the light reflected from the reflector surfaces is a deflecting mirror (14) for reflecting the light onto a light sensor (7). [16] The method according to claim 11 or 12, wherein the light sensor (7) is a photodiode. [17] The method according to one of claims 11 to 13, wherein the light received by the light sensor (7) is converted into electrical signals which are processed by a receiving and evaluation device.

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