DE102022102298A1 - Guidance system for a laser beam - Google Patents

Abstract

The invention relates to a steering system for a laser beam for laser material processing, which has at least one deflection device, by which the laser beam can be deflected, at least one feed line, through which the laser beam can be fed to the deflection device, and at least one fiber array with a plurality of optical fibers, which is arranged in this way that the laser beam is deflected by the deflection device onto a coupling surface of the fiber array, the deflection device having at least one non-mechanical deflection element.

Description

The invention relates to a steering system for a laser beam for laser material processing.

Today, lasers are used as an established tool in many areas of production and manufacturing. Laser beam sources, which are referred to as lasers for short, are used, for example, for automated cutting, welding, additive manufacturing, surface functionalization and general processing of various materials, such as glass, metal and polymers through to composite materials. Laser beams enable materials to be processed with very high precision and are now a tool with almost no alternative for many industrial manufacturing applications. So-called laser scanners are often used, which move the laser beam in one or more spatial directions relative to a workpiece to be processed. The limited relative speed between the laser beam and the workpiece is problematic in many applications. The consequences of this limitation are limited machining speeds and thermally induced stresses due to uneven heat input in the workpiece to be machined.

Commercially available galvanometer scanners enable scanning speeds of up to 50 m/s for two-dimensional processing with a laser power of more than 1 kW. This means that the light spot caused by the laser beam hitting the workpiece moves over the surface of the workpiece at this maximum speed. Alternative technologies, such as polygon scanners, achieve significantly higher speeds of up to one km/s, but only allow one-dimensional processing with a constant speed of the light spot on the workpiece. No solution is available in the prior art for multidimensional high-speed machining of several thousand m/s using galvanometer scanners and polygon scanners. Beam deflection systems that do not have accelerated mass-afflicted components achieve very high beam deflection speeds of several km/s. However, the processing field is limited to a few mm ² with parameters that are common for laser material processing.

In the context of the present invention, a laser is a device that emits coherent electromagnetic radiation, the so-called laser radiation. The laser beam is the light beam emitted by the laser, i.e. the electromagnetic radiation propagating in a straight line. If the laser beam is moved, the direction in which the electromagnetic radiation propagates changes. This means that the path along which electromagnetic radiation travels changes and shifts over time.

The invention is therefore based on the object of proposing a steering system for a laser beam for laser material, with which a higher deflection speed of the laser beam can be achieved. In addition, the processing field should be as large as possible and preferably designed to be freely formable, for example as a line.

The invention achieves the stated object with a steering system for a laser beam for laser material processing, which has at least one deflection device, by which the laser beam can be deflected, at least one feed line, through which the laser beam can be fed to the deflection device, and at least one fiber array with a plurality of optical fibers , which is arranged such that the laser beam is deflected by the deflection device onto a coupling surface of the fiber array, the deflection device having at least one non-mechanical deflection element.

In the case of the invention, a deflection device, with which a laser beam can be deflected for laser material processing, is consequently combined with at least one fiber array, which can also be referred to as a fiber bundle. Such a fiber bundle has a plurality of optical fibers into which the laser light can be coupled. For this purpose, the fiber array has a coupling surface, which is preferably formed from the coupling surfaces of the individual optical fibers of the fiber array. The steering system is based on fiber pixel-based control, with each optical fiber of the fiber array representing a pixel, and has significantly fewer radiation sources, i.e. lasers, than controllable fiber channels. Each optical fiber of the fiber array forms an individual fiber channel.

The in-coupling surface of the fiber array can be designed as a single in-coupling surface or be made up of a plurality of in-coupling sub-areas. In this case, each optical fiber preferably has its own partial coupling-in area, which in a simple configuration corresponds to the end face of the respective optical fiber.

At the end opposite the coupling-in surface, the individual optical fibers have at least one coupling-out surface from which laser beams coupled into the optical fiber are coupled out. This radiation can be guided through the optical fiber to the required location, so that the necessary deflection of the laser beam is no longer caused by the deflection device itself, but rather by the path that the optical fiber takes walked, formed and achieved. The decoupling surface is preferably formed from a plurality of partial decoupling surfaces. The end faces of the individual optical fibers are preferably the decoupling sub-areas. Alternatively, a substrate can be attached to individual, some or all of these end faces of the optical fibers, the surface of which opposite the end faces then forms the decoupling surface or the partial decoupling surface for the optical fibers attached to the substrate.

Since the deflection device has at least one non-mechanical deflection element, only a few masses, but preferably no masses at all, have to be moved in order to deflect the laser beam. Consequently, the deflection device particularly preferably does not have moving parts, such as mirrors, which have to be moved in order to deflect the laser beam.

Due to mass inertia, the feed rate is limited in currently used laser beam steering systems for laser material processing, which have moving parts. The use of non-mechanical deflection elements, which achieve significantly higher deflection speeds, offers the possibility of further increasing the process speed. The consequences of a low speed are the low output (e.g. with roll-to-roll processes) or the distortion of the printed component which is caused by thermal input (e.g. with LPBF (3D printing)).

At least one non-mechanical deflection element preferably has an acousto-optical deflector (AOD) by which the laser beam can be deflected. An acousto-optic deflector, also known as an acousto-optic modulator (AOM), uses the acousto-optic effect. For this purpose, for example, a piezoelectric transducer is attached to a material that is transparent to the wavelength of the laser radiation, such as tellu dioxide or quartz glass. An oscillating electrical signal drives the transducer to vibrate, creating sound waves in the material. These are generated in such a way that standing or moving sound waves form in the material, which locally change the refractive index as density fluctuations. This results in a diffraction grating on which incident electromagnetic radiation, in this case the laser light of the laser beam, is diffracted. If the frequency of the generated sound waves is varied, the diffraction pattern and thus the deflection of the laser beam can be changed.

The deflection device particularly preferably has two acousto-optical deflectors, each of which deflects the incident light in one spatial direction. The first deflector consequently deflects the laser beam in a first spatial direction. The second deflector deflects the laser beam in a second spatial direction.

The first spatial direction and the second spatial direction are preferably perpendicular to one another and consequently enclose a right angle. This is an advantage, but not necessary. It is sufficient if the two spatial directions are linearly independent of one another. The two acousto-optical deflectors then make it possible to carry out a complete two-dimensional adjustment of the deflection of the laser beam.

At least one non-mechanical deflection element preferably has at least one electro-optical deflector, by which the laser beam can be deflected. This exploits the fact that certain materials show an electro-optical effect, i.e. the change in optical properties under the influence of an electric field. The Pockels effect and the Kerr effect are mentioned as examples. In both cases there is a change in the refractive index of the respective material under the influence of the electric field caused by the application of a voltage. A special non-linear electro-optical effect in certain, well-defined cut crystals of selected transparent materials is used to generate a linear refractive index gradient that is proportional to the applied signal voltage. When a laser beam passes perpendicularly to the gradient, it is deflected, with the deflection angle being controllable by the externally applied voltage.

The deflection device particularly preferably has two electro-optical deflectors, each of which deflects the incident light in one spatial direction. The first deflector consequently deflects the laser beam in a first spatial direction. The second deflector deflects the laser beam in a second spatial direction. The first spatial direction and the second spatial direction are preferably perpendicular to one another and consequently enclose a right angle. This is an advantage, but not necessary. It is sufficient if the two spatial directions are linearly independent of one another. The two electro-optical deflectors then make it possible to carry out a complete two-dimensional adjustment of the deflection of the laser beam.

It is also conceivable that the deflection device has an electro-optical deflector and an acousto-optical deflector, each of which deflects the laser beam in one of the two spatial directions.

At least one non-mechanical deflection element preferably has a device for coherent beam combination. In this case, at least one laser beam, which is generated by at least one laser, is divided into different parts, which are then optionally combined and added in a phase-shifted but coherent manner. The optical power of the components can also be increased, if necessary individually. The coherence of the respective components leads to interference, the effect of which depends on the phase shift. This also allows the spatial direction in which the constructive interference is formed, in which the laser beam extends, to be changed. This can also be combined with one or more electro-optical deflectors and/or with one or more acousto-optical deflectors.

In addition to the at least one non-mechanical deflection element, the deflection device preferably has at least one mechanical deflection element. This preferably has at least one galvanometer scanner and/or at least one polygon scanner, by which the laser beam can be deflected. In addition or as an alternative to this, at least one mechanical deflection element has a micro-electro-mechanical system, by which the laser beam can be deflected.

The steering system preferably has a laser beam source.

The optical fibers of the fiber array preferably each have a decoupling surface through which the coupled-in laser beams can be decoupled and which is arranged in such a way that the coupled-out laser beams are fed to at least one laser material processing station. This can have a further deflection element, for example a polygon scanner. It is therefore advantageous if the laser radiation coupled out of the coupling-out surface is fed to a further deflection device.

The fiber array preferably has at least 5, preferably at least 10, more preferably at least 100, particularly preferably at least 250 optical fibers per square centimeter of cross-sectional area on the coupling-in side and/or on the coupling-out side. The optical fibers are preferably multi-mode fibers, single-mode fibers, polarization-maintaining fibers, hollow core fibers, PCF (photonic crystal fibre), gradient index fibers, step index fibers, leakage channel fibers and/or multi-core fibers. The density of the optical fibers on the coupling-out side of the fiber array is particularly preferably lower than that on the coupling-in side. It is preferably at least 0.2 fibers per square centimeter of cross-sectional area. It is more preferably at least 1, particularly preferably at least 3, optical fibers per square centimeter of cross-sectional area.

The coupled laser beams, which emerge from the decoupling surfaces of different optical fibers, are preferably directed onto a number of workpieces for laser material processing or at a number of points on a workpiece for laser material processing of the workpiece. Due to the high speed and switching rate of the steering system, the various points of one or more workpieces are processed almost simultaneously.

A substrate is preferably mounted, preferably welded or glued, to at least part of the coupling surface, preferably the entire coupling surface, and/or at least part of the coupling-out surfaces, preferably all coupling-out surfaces. A coupling-in surface is also understood to mean a partial coupling-in surface and a coupling-out surface is also understood to mean a partial coupling-out surface.

The substrate is made from a material that is transparent to the laser radiation. The laser beams that are to be coupled into one or more of the optical fibers first enter the substrate. The beams are preferably designed to converge within the substrate. This means that the cross section of the beam decreases on the way through the substrate. This reduces the optical intensity at the air/substrate interface compared to the stress at the air/fiber interface without a substrate. The surface of the substrate opposite the coupling-in surface is preferably provided with a coating, which reduces the reflection of the laser radiation at the coupling-in surface.

The entire coupling surface of the fiber array is preferably attached to the substrate. As an alternative to this, a plurality of substrates are present, which are mounted on different parts of the coupling surface, preferably on different coupling partial surfaces. In one configuration, an end face of each individual optical fiber forms a separate partial coupling area, to which a substrate is attached in each case.

The substrate, which is arranged on the decoupling surface, can preferably have a non-planar exit surface. This exit surface is preferably designed in such a way that the exiting laser beam is collimated or focused. The exit surface of the substrate can in particular be spherical or part-spherical. If several substrates are used, they can be the same or be designed differently. In particular, they can all be spherical.

The fiber array preferably has at least one optical fiber, through the decoupling surface of which laser radiation can be fed to at least one beam trap. A beam trap is a device for absorbing electromagnetic radiation. It is designed, for example, as a black cavity into which the radiation to be absorbed is directed. The beam trap is preferably cooled, for example by water cooling, in order to dissipate the heat introduced by the absorbed electromagnetic radiation.

The fiber array preferably has at least one optical fiber, through the decoupling surface of which laser radiation can be fed to at least one sensor, in particular an intensity sensor and/or a power sensor. This allows the intensity and/or power of the laser radiation to be determined. Such a sensor is, for example, a CCD chip, a diode or a pyrometer. The sensor can also be a corresponding spatially resolved sensor.

At least one cladding of the optical fibers is preferably structured so that laser radiation coupled into the cladding exits at least partially, preferably completely, from the cladding. The cladding can be the cladding of an individual optical fiber. As an alternative or in addition to this, the cladding can also be a cladding surrounding the entire fiber array or part of the fiber array, for example in the form of a glass capillary.

The invention also solves the problem set by a fiber array for a steering system described here.

• 1 - die schematische Darstellung eines Lenksystems gemäß einem ersten Ausführungsbeispiel der vorliegenden Erfindung und
• 2 - die schematische Darstellung eines Lenksystems gemäß einem zweiten Ausführungsbeispiel der vorliegenden Erfindung.

Some exemplary embodiments of the present invention are explained in more detail with the aid of the attached drawing. It shows:

• 1 - The schematic representation of a steering system according to a first embodiment of the present invention and
• 2 - The schematic representation of a steering system according to a second embodiment of the present invention.

1 shows schematically a steering system according to a first embodiment of the present invention. It has a laser beam source 2 that is set up to emit a laser beam 4 . The laser beam 4 is fed to the actual deflection device 8 via the feed line 6 . This has an acousto-optical deflector, an electro-optical deflector or another non-mechanical deflection element, by which the laser beam 4 is deflected. In the exemplary embodiment shown, the deflection device 8 also has a device for optical beam shaping, which is known from the prior art. After leaving the deflection device 8, the laser beam 4 strikes a coupling surface 10 of a fiber array 12. The laser beam is then guided through the fiber array 12 to the required location, which depends on which optical fiber 14 of the fiber array 12 the laser beam 4 is coupled into. A possible path for the laser beam 4 does not run onto the in-coupling surface 10 of the fiber array 12, but through a further light line 16 to a sensor 18.

2 shows another embodiment of the present invention. The laser beam source 2 generates coherent electromagnetic radiation, which is split into a plurality of individual beams 20 . In the exemplary embodiment shown, five individual beams 20 are shown one below the other. However, this is only schematic and is due to better displayability. The individual beams 20 are phase-shifted by a fixed offset relative to one another via phase elements 22 and then superimposed coherently. This results in interference between the individual beams 20. There is constructive interference in spatial directions that depend on the respective phase shifts of the individual beams 20 that are brought to superposition. The combination of phase elements 22 and the coherent superposition forms in 2 illustrated embodiment, the deflection device 8.

After leaving this deflection device 8, the laser beam 4 hits a beam-shaping device 24 before it hits the coupling-in surface 10 of the fiber array 12.

At the opposite end (not shown) of the individual optical fibers 14 of the fiber array 12 there is a decoupling surface from which the laser radiation is decoupled from the individual optical fibers 14 and fed to a further device.

reference list

2

laser beam source

4

laser beam

6

supply line

8th

deflection device

10

coupling surface

12

fiber array

14

optical fiber

16

light pipe

18

sensor

20

single beam

22

phase element

24

beam shaping device

Claims (18)

Guidance system for a laser beam for laser material processing, the - at least one deflection device by which the laser beam can be deflected, - At least one feed line through which the laser beam can be fed to the deflection device and - Has at least one fiber array with a plurality of optical fibers, which is arranged such that the laser beam is deflected by the deflection device onto a coupling surface of the fiber array, wherein the deflection device has at least one non-mechanical deflection element. steering system claim 1 , characterized in that at least one non-mechanical deflection element has an acousto-optical deflector, by which the laser beam can be deflected. steering system claim 1 or 2 , characterized in that at least one non-mechanical deflection element has at least one electro-optical deflector, by which the laser beam can be deflected. Guidance system according to one of the preceding claims, characterized in that at least one non-mechanical deflection element has a device for coherent beam combination. Steering system according to one of the preceding claims, characterized in that the deflection device additionally has at least one mechanical deflection element. steering system claim 5 , characterized in that at least one mechanical deflection element has a galvanometer scanner, by which the laser beam can be deflected. steering system claim 5 or 6 , characterized in that at least one mechanical deflection element has a micro-electromechanical system, by which the laser beam can be deflected. Guidance system according to one of the preceding claims, characterized in that the guidance system has at least one laser beam source. Guidance system according to one of the preceding claims, characterized in that the optical fibers of the fiber array each have a decoupling surface through which coupled-in laser radiation can be coupled out and which is arranged such that coupled-out laser radiation is fed to at least one laser material processing station. steering system claim 9 , characterized in that laser radiation decoupled from the decoupling surface is fed to a further deflection device. Steering system according to one of the preceding claims, characterized in that the fiber array has at least 10, preferably at least 100, particularly preferably at least 250 optical fibers. Guidance system according to one of the preceding claims, characterized in that the fiber array has at least 10, preferably at least 100, particularly preferably at least 250 optical fibers per square centimeter of cross-sectional area. Steering system according to one of the preceding claims, characterized in that at least one substrate is mounted, preferably welded or glued, to at least part of the coupling surface, preferably the entire coupling surface, and/or at least part of the coupling-out surfaces, preferably all coupling-out surfaces. Guidance system according to one of the preceding claims, characterized in that the fiber array has at least one optical fiber, through the decoupling surface of which laser radiation can be fed to a beam trap. Guidance system according to one of the preceding claims, characterized in that the fiber array has at least one optical fiber through whose decoupling surface laser radiation can be fed to at least one sensor, in particular an intensity sensor and/or a power sensor. steering system claim 15 , characterized in that only part of the laser radiation can be fed to the at least one sensor. Guidance system according to one of the preceding claims, characterized in that at least one cladding of the optical fibers is structured so that laser radiation coupled into the cladding emerges at least partially, preferably completely, from the cladding. A fiber array for a guidance system according to any one of the preceding claims.

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