DE102020122449A1 - Apparatus and method for generating images of a light source array - Google Patents

Abstract

A device 1 for generating images 2 of a light source array 3 on a projection surface 4 is specified. The device has a light source array 3, a projection surface 4 and at least one projection objective 6 arranged in a beam path 5 between the light source array 3 and the projection surface 4, with an imaging scale m deviating from +1 in at least one spatial direction, the at least one projection objective 6 being lateral with respect to of the light source array 3 and/or with respect to the projection surface 4. In addition, a method 100 for generating images 2, a control unit 9 and a computer program for controlling a device 1 for generating images 2 of a light source array 3 on a projection surface 4 and a non-volatile computer-readable storage medium with instructions stored thereon for controlling a device 1 for generating images 2 of a light source array 3 on a projection surface 4 specified.

Description

The invention relates to a device and a method for generating images of a light source array on a projection surface, as well as a control unit, a computer program and a non-transitory computer-readable storage medium with instructions for controlling such a device.

Selective laser melting (SLM) is the most common process in the additive manufacturing of workpieces. Here, a powder bed of powder particles with a typical layer thickness of 20 μm to 100 μm is applied to a substrate. At the points where a solid layer of material is to be built up, the powder is melted using a laser beam, so that the resulting melt bonds with the substrate surface underneath, which is also melted, and thus forms a solidified new layer of material.

The movement of the laser beam over the powder bed, together with the melting and solidification process, is also referred to as "writing". When a layer is completely written, a new layer of powder is applied to the previously written layer and the process is repeated. In this way, very complicated structured workpieces such. B. with cavities, are built up in layers over a large number of layers.

Such workpieces can only be produced with great difficulty or not at all using conventional machining. Typical workpieces that are already manufactured using an SLM process are e.g. B. workpieces with complicated channels for fluids, such as workpieces with integrated cooling channels, filigree lightweight structures with a variety of thin-walled support elements or in the field of medical technology joints and dental prostheses. The SLM process is also increasingly finding its way into prototype construction and small series.

Other additive manufacturing processes are closely related to selective laser melting, e.g. B. selective laser sintering (SLS, engl. selective laser sintering), which differs from the SLM process only in that the powder particles are not completely melted, but instead sintered. Depending on the specific process conditions, workpieces made of metal, plastic, ceramics and other materials that can be melted or sintered by the laser beam used can be produced from the corresponding powders using SLM and SLS processes. Additive manufacturing processes that use a laser beam as the energy source are summarized below under the term LAM process (LAM for laser additive manufacturing).

Classic LAM devices are roughly the size of a milling machine for a comparable workpiece size and work with a laser beam that is directed to the positions to be described on the prepared powder bed by means of a galvanometer scanner unit placed above the workpiece. The process times for a workpiece are relatively long, since all areas to be melted on each of the many layers have to be completely scanned with a laser beam with a relatively narrow focus diameter of typically 50 µm, whereby the scanning speeds for good process results are usually less than 2 m/s. The workpieces manufactured using this process are correspondingly expensive, which is why they are primarily used in the area of capital goods or in medical technology, but not in the end consumer area. For workpieces with a volume of a few liters, prices in the five-digit euro range are asked, depending on the degree of volume filling and the complexity of the structures to be written.

In order to be able to reduce the process times, several manufacturers of LAM devices offer devices with up to four laser scanning units. The process times can be reduced significantly, but not by the order of magnitude that would be necessary to make the process attractive for a broader range of applications, e.g. B. the production of spare parts on demand (English spare parts on demand) instead of z. T. years of storage.

A substantial reduction in the LAM process times could be achieved by parallelizing the writing process to a high degree, so that ideally a complete layer is written in one pass by linearly guiding a ruler with controllable laser light points over the powder bed.

Such an approach is known in principle from US 2017/0 021 454 A1. The method described in US 2017/0 021 454 A1 provides a distance between the melting or sintering areas generated by the laser beam, in that the laser light points are spaced apart accordingly. On the device side, a laser beam source array and an optical head are provided, which are coupled to one another by means of optical fibers. To carry out the writing process, there is a movement unit for moving the optical head relative to the powder bed so that the laser beams can be directed to the desired positions in the Powder bed can be performed. The individual laser beam sources of the laser beam source array are controlled as required by means of a control unit.

In contrast, US 2017/0 021 454 A1 does not explain exactly how the multiplicity of fiber light sources are to be imaged in the powder bed. Only an abstract optics unit with one or more lenses is described, which is used to focus the individual laser beams emerging from the fibers, so that the desired distance between the melting and sintering areas can be achieved.

The beam path shown in US 2017/0 021 454 A1 suggests individual imaging optics for each fiber, which requires a relatively large distance between the individual fiber ends despite a relatively small distance between the optics unit and the powder bed. This distance is proportional to the exit-side numerical aperture of the optics unit and proportional to the working distance of the optics unit to the powder bed. In addition, there is the lateral installation space for the optical mount technology.

A numerical example should illustrate the problem. Assuming a numerical aperture of 0.08 on the exit side and a working distance between the optics unit and the powder bed of 200 mm, this results in a beam diameter on the exit side of 2 x 0.08 x 200 mm = 32 mm. Taking into account the space required for the mounting technology, this results in a diameter of around 50 mm for an optical channel. This means that only about ten light sources can be arranged next to each other over an assumed workpiece width of 500 mm.

However, if a pixel pitch of 50 µm is aimed for in order to be able to write finer structures in the range of 0.1 mm with sufficient resolution, the pixel array would have to be 10 x 1,000 = 10,000 elements, which means that the estimated dimensions of an optical channel of 50 mm the fiber array of the optical head would extend to 50 mm x 1 000 = 50 m in the second direction. Although this seems theoretically conceivable, it is practically impossible to realize and would require a very large LAM device.

The dimensions of the optics unit and the fiber array could be reduced by forming arrays from subarrays, with the light points of a subarray each sharing a common objective of the optics unit. But here, too, there is the problem that the distance between the individual lenses is given by the image distance, the numerical aperture on the output side and the mounting space.

In addition, with outputs of 100 W - 1 kW per light point, a maximum total optical output of 1 MW - 10 MW should be assumed. Even if the losses in the optics unit are minimized to around 1%, this results in power losses of 10 kW to 100 kW in the optics unit, which are dissipated as heat. The dissipation of such heat output in the cramped space that remains inside the optics unit represents a great to unsolvable challenge.

In addition, the necessary small distance to the powder bed poses a major problem, since the optics unit is directly exposed to the ejection of glowing particles and smoke from the melting zone and, without active countermeasures, would very quickly become dirty and thus become unusable. Furthermore, the proximity of the optics unit to the powder bed causes a significant limitation in the design of the devices for preparing the powder bed and for cooling it.

Furthermore, the device with a movable optical head known from US 2017/0 021 454 A1 requires a fiber bundle of optical fibers that has to be carried along when the optical head is moved. The usual fiber cables for high-power lasers in the medium power class (approx. 100 W to approx. 1,500 W) have a diameter of around 10 mm due to the necessary mechanical robustness and armouring, but are still sufficiently flexible so that they can also be used to carry out lateral movements in the range of up to several meters would be suitable.

An extension to a few parallel fiber cables seems quite conceivable. Realizing a flexible cable bridge for several hundred to several thousand fiber cables, which can also be moved over the workpiece area in two axial directions, requires a very expensive to impractical cable trail.

A movement of the powder bed instead of the optics head, as also described in US 2017/0 021 454 A1, seems conceivable in principle, but with high accelerations (> approx. 2 m/s ² ) the flattened powder bed is destroyed and possibly also the built-up workpiece embedded in it depends on its design and construction status. Thus, the maximum accelerations of the powder bed and workpiece represent an inherent limitation in the trajectory planning of the writing process, which generally results in a significant throughput limitation.

Against this background, it is the object of the invention to specify a device and a method with which at least some of the disadvantages explained above can be reduced or even completely avoided. A further object is to specify a control unit, a computer program and a non-transitory computer-readable storage medium with instructions for controlling such a device.

It would be desirable to be able to image a densely packed array of light sources on the surface of a flat powder bed. The distance between the optics unit and the powder bed should preferably be large enough. In addition, the number of optical interfaces should be as small as possible, the optical interfaces should be able to be realized with very low optical losses and dissipated heat should be easily dissipated. Furthermore, the image of the light source array should be able to be moved over the surface of the powder bed without having to move the light source array itself or the powder bed.

This problem is solved by the subject matter of the independent claims. The dependent claims relate to design variants of these solutions according to the invention.

A first aspect of the invention relates to a device for generating images of a light source array on a projection surface. The device has a light source array, a projection surface and at least one projection lens. The at least one projection objective is arranged in the beam path between the light source array and the projection surface and has an imaging scale m that deviates from +1 in at least one spatial direction. The at least one projection lens can be displaced laterally with respect to the light source array and/or with respect to the projection surface.

A light source array can be a one-, two- or three-dimensional arrangement of one or preferably several light sources, e.g. B. between 100 and 100,000 light sources are understood. In a one-dimensional arrangement z. B. all light sources arranged in a row, in a two-dimensional arrangement, the light sources are distributed over a surface, z. B. in the form of several rows and columns. The distances between the light sources can be the same or different. All light sources can be arranged in one plane. Depending on requirements, however, the light sources can also be arranged on a curved surface.

The light sources of the light source array can preferably be arranged on the object surface of the projection lens. If the object surface is flat, the light source array can consequently also be flat. If the object surface is curved, the light source array can consequently also have a curvature. For example, the light sources can be arranged on part of a rotationally symmetrical surface centered around the axis of symmetry of the optics. This rotationally symmetrical surface can be, for example, a spherical or aspherical surface, e.g. B. be a parabolic surface.

The light source array can consist of direct light sources, e.g. B. laser light sources, for example in the form of laser light diodes, or it can be light-conductingly connected to direct light sources, so that light generated by the direct light sources is guided to the light source array and emitted by it into the environment. For example, there is the possibility of emitting light from direct light sources, which can also be arranged in the form of an array, to the environment via light guides, the ends of which form the light source array. Possible light guides are e.g. B. optical waveguides or optical fibers, with different fiber types, z. B. single mode fibers, multimode fibers, z. B. step index fibers or gradient index fibers, "photonic crystal" fibers, "hollow core" fibers, etc., can be used. In other words, the term light source array also includes an array formed from the ends of light guides.

Within the scope of the invention, the light source array can preferably be designed as a laser beam source array, i. H. laser radiation can be used as light. The wavelength of the laser radiation can be adjusted as required, e.g. B. depending on the desired material interaction, be selected and z. B. in the range between 100 nm and 3 microns, but also in the wavelength range of X-rays or other electromagnetic radiation.

More preferably, the light sources of the light source array are designed in such a way that the light they emit can melt or sinter a material. In other words, the device can be set up and designed for additive manufacturing.

The light source array can be designed in such a way that the light sources of the light source array can be controlled together, ie all light sources are activated and deactivated together. In addition, it can be provided that light sources of the light source array can be controlled individually or in groups, so that individual light sources or groups of light sources are activated and can be disabled. This enables the generation of different images and consequently a different energy input into the projection surface, e.g. B. the surface of the powder bed. The execution of an LAM method with the device can be carried out more precisely as a result.

In the present case, the term “projection surface” refers to a surface, preferably a plane, onto which the image of the light source array is projected. The projection surface consequently lies at least partially in the image plane of the projection objective. As will be explained in more detail below, the projection z. B. be the surface of a powder bed, the z. B. is used in an additive manufacturing process. In other words, the projection surface can be made of a meltable or sinterable material, e.g. B. a meltable or sinterable powder material, such as a metal powder.

The projection lens is arranged in the beam path between the light source array and the projection surface, so that optical elements of the projection lens interact with the light beams emitted by the light source array and project them onto the projection surface or generate an image of the light source array on the projection surface.

The device can also have a number of projection lenses in order to be able to cover, for example, a workpiece width or a correspondingly large projection area with a number of projection lenses. This can be advantageous in order to select a smaller projection lens size for a given workpiece size and thus to reduce the production costs of a projection lens. With a given projection objective size, however, larger workpieces can also be manufactured by arranging a plurality of projection objectives next to one another.

In this way, configurable machine and workpiece sizes can be made possible, in which the number of variants of projection lenses can be drastically reduced and, at best, down to a single variant. In other words, the number of variants of the projection lenses can be significantly reduced by specifying a minimum size and using a plurality of projection lenses next to one another in the case of larger workpieces or machines.

The position of the image on the projection surface can be changed by lateral displacement of the projection lens with respect to the light source array, with respect to the projection surface or with respect to both the light source array and the projection surface, i. H. the lateral displacement of the projection objective causes a corresponding displacement of the beam path. In other words, the projection lens itself can be moved in a plane essentially parallel to the light source array and parallel to the projection surface while maintaining the distance between the projection lens and the light source array and between the projection lens and the projection surface.

For the lateral displacement of the projection lens, the device can have a displacement unit, which is designed for the lateral displacement of the projection lens. Such a traversing unit can i.a. Have drives and guides.

However, the position of at least the light source array or the projection surface, preferably both the light source array and the projection surface, can be unchangeable, i. H. the light source array and/or the projection surface can be arranged in a stationary manner, in particular in a stationary manner in the x-direction and y-direction. This has the advantage that no devices for changing the position of the light source array or the projection, such. B. a traversing device, a controller, a flexible cable bridge, etc., are required.

However, a lateral displacement of the projection surface in relation to the projection objective can also be provided optionally, for example in order to implement larger changes in position.

The projection lens has a magnification m that differs from +1 in at least one spatial direction. In other words, the imaging scale m is not +1 in at least one spatial direction. The image scale is defined as the ratio between the image size of the image of the light source array and the real size of the light source array.

The projection lens can preferably have a negative imaging scale m in at least one spatial direction, i. H. a magnification m<0. More preferably, the magnification m in at least one spatial direction can be in the range -10≦m≦-0.1, more preferably in the range -10≦m≦-1 and particularly preferably in the range -2≦m≦- 1, lying. The imaging scale m can be -1 in at least one spatial direction, for example. A negative magnification means that the image of the light source array is reversed compared to the light source array.

eines idealen Gauß-Strahls ausschließlich von der Wellenlänge λ abhängt und dieses auch nicht unterschritten werden kann. Hierbei stehen wo für den Strahlradius in der Strahltaille und θ₀ für den halben Strahldivergenzwinkel im Fernfeld. Für einen Gauß-Strahl mit einem für SLM-Anwendungen typischen Strahlradius von wo = 25 µm ergibt sich beispielsweise bei einer Wellenlänge von λ = 1,0 µm ein Fernfeld-Divergenzwinkel von θ₀ = 12,7 mrad. Möchte man nun mit einem Objektiv mit einem Abbildungsmaßstab von m = 10 ausgangsseitig einen Strahlradius von wo = 25 µm erhalten, müsste der Strahlradius eingangsseitig um den Abbildungsmaßstab reduziert werden. Dies impliziert wiederum, dass der Divergenzwinkel des eingangsseitigen Strahls um den Abbildungsmaßstab anwächst, in diesem Fall also auf θ₀ = 127 mrad. Damit das Objektiv die Ausläufer des Gauß-Strahls nicht zu eng abscheidet, müsste die eingangsseitige numerische Apertur des Objektivs auf den 1,5- bis 2-fachen Divergenzwinkel ausgelegt werden, also eine numerische Apertur von etwa 0,2 bis 0,25. Ab einer numerischen Apertur von etwa 0,2 bis 0,3 wächst die Designkomplexität eines Projektionsobjektives jedoch im Allgemeinen dramatisch an.A magnification m, for which |m| > 10 is also possible. However, as the amount of magnification increases, either the light source array shown with its light points is so large that only rough structures can be written, or the light source array must be correspondingly reduced on the object side, which is limited by the packing density of the light sources and the minimum practicable size of the light sources. Furthermore, a reduction in the size of the light sources means that the divergence angle of the light beams increases in accordance with the reduction factor and thus also the necessary input-side numerical aperture of the projection lens. This is because the beam parameter product θ ₀ w ₀ $${\theta }_0{w}_0=\frac{\mathrm{\lambda }}{\mathrm{\pi }}$$

of an ideal Gaussian beam depends exclusively on the wavelength λ and cannot be fallen below. Where where stands for the beam radius in the beam waist and θ ₀ for half the beam divergence angle in the far field. For example, a Gaussian beam with a beam radius of wo=25 μm, which is typical for SLM applications, results in a far-field divergence angle of θ ₀ =12.7 mrad at a wavelength of λ=1.0 μm. If one now wants to obtain a beam radius of wo = 25 µm on the output side with a lens with a magnification of m = 10, the beam radius on the input side would have to be reduced by the magnification. This in turn implies that the divergence angle of the input-side beam increases by the magnification, in this case to θ ₀ = 127 mrad. To ensure that the lens does not separate the extensions of the Gaussian beam too closely, the numerical aperture of the lens on the input side would have to be designed for 1.5 to 2 times the divergence angle, i.e. a numerical aperture of around 0.2 to 0.25. From a numerical aperture of about 0.2 to 0.3, however, the design complexity of a projection lens generally increases dramatically.

The image scale deviating from +1 in at least one spatial direction causes the image to be shifted laterally with respect to the light source array in at least one spatial direction when the projection lens moves laterally. If the imaging scale in a plan view of the device deviates from +1 in a spatial direction, the image can be shifted laterally in one spatial direction. If the imaging scale in a plan view of the device deviates from +1 in both spatial directions, the image can be shifted laterally in both spatial directions. The specifically selected image scale specifies the lateral distance by which the image is shifted when the projection lens is moved laterally. For example, with an imaging scale m=−1, a linear lateral movement of the projection objective results in a displacement of the image in the image plane that is twice as large.

With an imaging scale m=−2, the image is shifted relative to the light source array by three times the distance by which the projection objective was shifted. Consequently, the displacement of the image in relation to the light source array can be defined by the selection of the imaging scale. The displacement of the projection lens results in a scanning of the projection surface, so that the projection lens can also be referred to as a scanning lens.

Depending on the light radiation used, the images produced can bring about further processes. For example, material in the area of the image can be melted or sintered by the input of light. Consequently, the device can be used as part of an additive manufacturing process, with the position of the image defining the locations at which solid layers of material are to be built up by melting or sintering processes. The individual layers, as explained at the outset, can be written by correspondingly scanning the projection surface by means of the described movement of the projection lens.

So that the beam foci can be kept in the projection surface when building up further layers, the projection surface can be displaced in relation to the projection objective to build up further layers, i. H. the powder bed can be designed to be displaceable relative to the projection objective along the principal rays of the optical beams, ie in the z-direction.

• Das gesamte Lichtquellenarray kann abgebildet werden. Die Packungsdichte der Lichtquellen, z. B. der Faserenden von Lichtleitfasern, ist somit nicht durch das abbildende optische System begrenzt, sondern nur durch die Packungsdichte der Lichtquellen selbst, die im Bereich von wenigen Millimetern oder sogar darunter liegen kann. Hierdurch kann ein Lichtquellenarray, z. B. ein Faserarray, derart kompakt realisiert werden, dass dieses in den Feldakzeptanzbereich eines hinsichtlich der Baugröße noch praktikablen Projektionsobjektivs passt.

The device according to the invention enables the imaging of a densely packed light source array onto a planar projection surface, e.g. B. a flat powder bed. By specifically selecting the optical properties of the projection objective, a sufficiently large distance between the projection objective or the optics unit and the powder bed can be ensured. The device according to the invention also offers the following additional advantages:

• The entire light source array can be imaged. The packing density of the light sources, e.g. B. the fiber ends of optical fibers is not limited by the imaging optical system, but only by the packing density of the light sources themselves, which can be in the range of a few millimeters or even less. This allows a light source array, z. B. a fiber array, can be implemented in such a compact way that it fits into the field acceptance range of a projection lens that is still practicable in terms of size.

In addition, the proposed device can be used to implement a scanning principle in which primarily only the projection lens is moved. This means that no bundles of light guides, e.g. B. optical fibers that connect the direct light sources with the light source array, are carried. The powder bed with the workpiece to be formed can also remain at rest while a layer is being written, so that the design and construction condition-dependent limitations of the maximum accelerations for the scanning process described above do not come into play. The mechatronic properties of the moving projection lens, on the other hand, are independent of the workpiece and the powder bed, which is why the parameters of the lens movement are universal. The projection lens itself can be designed according to the necessary mechatronic properties and accelerations.

In addition, the device can also be used to carry out known scanning principles, so that the device can be used very variably.

According to various embodiment variants, the projection lens can be telecentric on one or both sides.

The projection lens can preferably be telecentric, at least on the object side. More preferably, the projection lens can be telecentric on both sides, ie on the object and image side.

Telecentric means that the entrance and exit pupils of the projection lens are at infinity and consequently all main rays in the object or image space run parallel to the optical axis. Consequently, the principal ray angles on the object and image side are 0°. Minor deviations, e.g. B. manufacturing-related deviations from an ideal parallelism are possible. For example, the main beam angles on the object or image side can be less than 5°, preferably less than 2°, more preferably less than 1°.

A telecentric configuration of the projection lens on both sides has the effect that no or at most very small distortion errors are produced. Due to the telecentric design on both sides, shape and position tolerances in the z direction, i.e. in the direction of the optical axis, of the light source array on the one hand and the projection surface on the other hand, only lead to loss of contrast, but not to distortion errors in the optical image. The sensitivity with regard to contrast losses due to defocusing is quite moderate with the relatively small numerical apertures of usually less than 0.1 and is generally easy to control. This means that the radius of a spot increases only moderately when defocused. With a numerical aperture of 0.1, the beam radius increases by 10 µm for every 100 µm shift. If the radius of a beam of z. B. 25 µm are kept stable at 2 µm, the focus position must be controlled to within 20 µm. This is not easy, but still manageable.

The object-side or input-side telecentricity also has the advantage that all light sources, e.g. B. all fiber ends on the fiber array, can be arranged in parallel next to each other, eliminating the need for individual orientation of the light sources, z. B. so the fiber ends can be avoided. This is advantageous with regard to the highest possible packing density of the light sources and simple manufacture of the light source array.

The object-side telecentricity is also particularly advantageous for the light source array during the scanning process. In this way it can be avoided that the individual orientation of each individual light source has to be tracked to the field-dependent orientation of the main ray depending on its current position in the object field. Such tracking would on the one hand lead to a very high complexity of the light source array and on the other hand the space required for active individual beam tracking would greatly reduce the packing density of the light sources in the light source array, i. H. by at least an order of magnitude. In other words, the object-side telecentricity can reduce the complexity of the light source array and save space.

The object-side telecentricity ensures that in every field position the parallel axes of the rotationally symmetrical radiation cones of the light sources coincide with the object-side main beams of the projection lens, which are also parallel due to the telecentricity. The coincidence of the symmetry axes of the emission cones with the object-side main beams of the projection objective means that the aperture of the projection objective given by the object-side pupil can be avoided. A vignetting associated with such an excess and a widening of the point spread function of the image caused by the vignetting and caused by diffraction can be avoided. Furthermore, exceeding the input-side aperture would result in optical losses and stray light generation at the aperture stop of the projection lens, both of which are undesirable and can therefore advantageously be avoided by the object-side telecentricity of the projection lens.

According to various embodiment variants, the projection lens can be a refractive lens.

Refractive objective means that the majority of the optically effective surfaces, preferably all optically effective surfaces, are refracting surfaces or that the number of optically effective refracting surfaces corresponds to the number of optically effective reflecting surfaces. Such a refractive objective has one or more lenses, but no mirrors. For example, two lenses spaced apart from one another in the z-direction can be arranged. Other lenses, e.g. B. to correct field curvature and image errors, z. B. from field position-dependent image errors may be present.

A refractive lens has the advantage of being simple and inexpensive to manufacture. In addition, a refractive lens has the advantage that it can generally be designed to be rotationally symmetrical, which is advantageous for lens manufacture, lens assembly and also for adjustment. Furthermore, refractive optics have the advantage over reflective optics that they are generally much more compact in terms of lateral extension with the same numerical aperture and the same field size, since with reflective optics the rays usually have to be guided past the mirrors.

According to further embodiment variants, the projection lens can be a mirror lens.

Mirror objective means that the majority of the optically effective surfaces, preferably all optically effective surfaces, are reflective surfaces. Plane mirrors, which are only used for the geometric deflection of the light beam path, are not optically effective surfaces.

Mirror lenses advantageously offer the possibility of folding the beam path, so that in comparison to an unfolded beam path, less installation space, particularly in terms of height, is required for the projection lens and for the device as a whole. Due to the folded beam path, a large distance can be realized between the powder bed and the mirrors, so that the mirrors can be arranged out of the reach of particles ejected from the melting zone and escaping dust clouds. In addition, there is sufficient space to take additional measures such. B. to be able to introduce lateral gas curtains to keep the mirrors clean.

In addition, mirrors have a lower weight compared to lenses, which would have to be designed for the proposed projection lens with a large diameter and a large central thickness and would therefore have a high weight, which offers advantages with regard to a movement of the projection lens, since z . B. lower forces act during acceleration. It is also not necessary to limit the acceleration due to the limitation of the maximum forces on the lens mount caused by breaking stresses. Consequently, higher accelerations can be achieved with a mirror lens compared to a refractive lens, so that the scanning process can be carried out at a correspondingly higher speed, ie a higher scan rate.

In addition, a projection lens designed as a mirror lens has the advantage that the number of boundary layers is minimized and optical absorption in the lens material is avoided. In addition, highly reflective, optically effective surfaces can be used, so that very low absorption and scattering losses, e.g. B. losses <0.1% result. In addition, efficient removal of the thermal energy absorbed by the optically effective surfaces is made possible without directly competing for space with the optically effective surfaces and the beam paths.

Compared to a refractive lens, a mirror lens has the further advantage that the mirror lens is inherently achromatic over a wide wavelength range if the coating is chosen accordingly, whereas in lens lenses the wavelength dependency of the refractive index, which is present in all optical glasses, leads to further critical design dependencies . In this case, the light sources would have to be chosen so narrow-band and stable with regard to the wavelength of the emitted light that the chromatic aberrations caused by the lens become sufficiently small over this wavelength band. However, small bandwidths and high laser powers are in conflict and increase the complexity of the light sources. Alternatively, additional lenses for the correction of chromatic aberrations would have to be provided for lenses that are already large. would further increase the weight of the projection lens and result in the acceleration and scan rate limitations discussed above.

The mirror lens can, for example, have two or three reflecting, optically effective surfaces, ie it can be designed as a two-mirror lens or three-mirror lens. The number "two" or "three" in the terms "two-mirror lens" and "three-mirror lens" used below therefore refers to the number of optically effective surfaces in the beam path. Here, several optically effective surfaces on one be arranged optical element. For example, a mirror element can have two reflecting optical surfaces, ie two mirrors.

Since the object and image planes lie in the same plane in telecentric two-mirror lenses on both sides, the projection lens can preferably be designed as an off-axis lens, so that the folded beam path can be guided past the workpiece.

In the case of a two-mirror objective, in order to take into account the curvature of the object field, it can be provided that the light sources of the light source array are also arranged along the curved object field, i. H. the light source array can have a curvature corresponding to the curvature of the object field. For example, the light sources can be arranged on part of a rotationally symmetrical surface centered around the axis of symmetry of the optics. This rotationally symmetrical surface can be, for example, a spherical or aspherical surface, e.g. B. be a parabolic surface.

The device can be designed in such a way that the light source array can track the curved object field during the lateral movement of the projection objective in order to position the image field in the plane of the projection surface, ie z. B. on the surface of the powder bed to keep.

In the case of a two-mirror lens with a magnification of m=−1, mirrors of the same construction can advantageously be used at both mirror positions, as a result of which production costs can be saved and maintenance and servicing can be simplified. The time-averaged optical power density and thus the average thermal power density on the mirror surface are also advantageously approximately the same on both mirrors, so that the mirrors can be cooled in a simple manner. In contrast, the optical power density and the thermal power density in the Offner design described below are significantly higher on the small pupil mirror, generally more than ten times higher, which makes mirror cooling more difficult. Consequently, a two-mirror objective is preferably suitable for high optical power densities.

A three-mirror lens is characterized by the fact that, with a suitable choice of design parameters, it has no field curvature and is free of spherical aberrations, coma, distortion up to the third order and at least free of the lowest order astigmatism. The three-mirror lens can be designed, for example, as a lens that is telecentric on both sides and has three optically effective reflecting surfaces, with the first and third effective surfaces being combined on one mirror element. Such a design, hereinafter referred to as Offner design, goes back to Abe Offner and is in the U.S. 3,748,015 A described, to which reference is made for the explanation of further design parameters, properties and advantages of this design.

A three-mirror lens in the Offner design has the advantage that, with suitable parameter selection, it can be aplanatic up to the third order, i. H. is free from spherical aberrations and coma, is anastigmatic and free from distortion and, moreover, has no curvature of the object and image plane. The first two properties, aplanatic and anastigmatic, are necessary in order to keep the point spread function of the optical image small and thus prevent the light sources to be imaged, e.g. B. the points of light of the fiber ends of the fiber array smear in the image on the projection surface.

The third property, freedom from distortion, is advantageous since no distortion biases need to be taken into account when laterally positioning the light sources in the light source array. The fourth property, the freedom from curvature of the object and image plane, is advantageous because all light sources on the object side, e.g. B. all fiber ends of the optical fibers can be arranged in one plane, which is easier to manufacture than an arrangement on a curved surface. In addition, you can work with a flat projection surface on the image side, e.g. B. a flat powder bed in which flat layers are written.

In addition, there is the advantage that only the projection lens has to perform a linear movement in the X-Y plane during a scanning process. The image plane on which the focus is located agrees with the projection surface without further corrective measures, e.g. B. ie the surface of the powder bed match. In the case of a strongly pronounced field curvature on the object side, on the other hand, the light source array would have to track the curved object field of the moving projection lens in the vertical degrees of freedom in order to keep the image plane in the plane of the projection surface.

In general, the Offner design is very well suited for images with a magnification of approx. m = -1, where the object and image lie in the same plane and where the object-side and image-side numerical apertures are small, i. H. < about 0.1 to 0.2.

Due to the compact design of the Offner design, a corresponding lens frame, which is also suitable for high acceleration, can be designed in a simple manner. Because the The mass of the three-mirror lens in the Offner design is concentrated on the upper large mirror element with the first and third optically effective surface, the small mirror with the second optically effective surface can be carried along on the large mirror. A well-guided linear movement can thus be easily implemented even with high accelerations.

Optionally, in a three-mirror design, the object-side beam path can be folded out together with the light source array using an optically neutral folding mirror. This can advantageously be achieved in that the projection surface can be moved in all directions under the projection lens without colliding with the beam path or the light source array. Consequently, different scanning principles, e.g. B. provide a displacement of only the projection lens, only the light source array, the projection lens and the light source array or only the projection surface can be used.

A further aspect of the invention relates to a method for generating images using one of the devices described above. The method provides for the emission of light beams by means of the light source array and the generation of an image of the light source array on the projection surface by means of the emitted light beams and the projection lens, i. H. the emitted light rays are projected onto the projection surface by means of the projection lens.

The method can be carried out in a computer-implemented manner, i. H. at least one method step, preferably several or all method steps, can be carried out using a computer program with instructions that can be executed on a computer.

Since the method is carried out using one of the devices described above, the above explanations for explaining the device according to the invention also serve to describe the method according to the invention. The advantages mentioned above in relation to the device are correspondingly associated with the method.

Optionally, the method can include melting or sintering of a material forming the projection surface by means of the light beams that generate the image.

Because the position of the image on the projection surface can be fixed by appropriate positioning and adjustment of the projection lens, the melting or sintering can take place selectively, so that workpieces can be selectively machined or manufactured. In other words, the method can be designed as an LAM method. As an alternative to melting or sintering, the projected light beams can also be used in other ways for material processing, e.g. B. for cutting, welding, signing, labeling, engraving etc.

According to various embodiment variants, the method can include a lateral displacement of the projection lens with respect to the light source array and/or the projection surface.

It can be provided here that the light source array and the projection surface do not change their position, i. H. they are stationary.

The lateral displacement can be continuous or discontinuous. A continuous shift corresponds to a scanning method in which the projection surface is continuously, e.g. B. line by line or after a predetermined route, departed, d. H. is scanned. An image of the light source array can be generated at definable positions by activating the light sources of the light source array. Depending on requirements, the light sources can be activated and deactivated during the scanning process.

In contrast, in a discontinuous method, a first position on the projection surface is first approached. In this first position, an image of the light source array is generated on the projection surface by light rays being emitted by the light source array. The projection lens is then shifted laterally with respect to the light source array and/or the projection surface in order to move to a further position on the projection surface. An image of the light source array is now generated again on the projection surface in the further position, in that light beams are emitted by means of the light source array. Additional positions on the projection surface can be approached by again lateral displacement of the projection lens.

In addition to the above-described lateral displacement of the projection objective with respect to the light source array and/or the projection surface, images can also be generated at different positions on the projection surface using the principles explained below. A combination of several principles is also possible.

For example, it can be provided that only the light source array is laterally displaced. The projection lens and the projection surface do not change their position, ie they are stationary. Another principle is that Light source array is moved laterally together with the projection lens, whereas the position of the projection surface is not changed. Another principle provides that only the projection area or the powder bed and thus its surface is shifted laterally. The projection lens and the light source array do not change their position. These principles can also be implemented continuously or discontinuously.

The principles described can also be combined with one another. For example, different positions across the width of the projection surface can be achieved by lateral displacement in the transverse direction of only the projection lens. In contrast, different positions of the projection surface over its length can be achieved by laterally displacing the projection surface or the projection lens together with the light source array in the longitudinal direction. In a scanning process, a row can consequently be scanned by lateral displacement of the projection lens. Then, by lateral displacement of the projection surface or of the projection objective together with the light source array, a change is made to the next row, within which a lateral displacement of the projection objective then takes place again.

A further aspect of the invention relates to a control unit for controlling a device for generating images of a light source array on a projection surface. The device has a light source array, a projection surface and at least one projection objective arranged in a beam path between the light source array and the projection surface with an imaging scale m deviating from +1 in at least one spatial direction, the at least one projection objective being positioned laterally with respect to the light source array and/or with respect to the Projection surface is movable. The imaging scale m can preferably be negative in at least one spatial direction, e.g. e.g. -1.

The control unit is designed to generate and output control signals to the device. The control signals cause one or more, preferably all, of the following steps to be carried out: emission of light beams by means of the light source array, generation of an image of the light source array on the projection surface by means of the emitted light beams and the projection lens, and lateral displacement of the projection lens with respect to the light source array and/or the projection surface.

The control signals can cause the light beams to be emitted and projected, preferably in such a way that a material forming the projection surface can be melted or sintered by means of the projected light beams.

The control unit can be used to control one of the devices described above. The control can take place in such a way that such a device executes one of the methods described above.

The above explanations for explaining the device according to the invention and the method according to the invention therefore also serve to describe the control unit according to the invention. The advantages mentioned above in relation to the device and the method are correspondingly associated with the control unit.

The control unit can be realized in terms of hardware and/or software and can be designed physically in one or more parts. The controller generates the control signals based on instructions or code programmed into the controller according to one or more routines. To control the device, the control unit is available with the device or its components, e.g. B. the light source array, in a signaling operative connection, so that the generated control signals can be transmitted to the device or its components and received by them.

The control unit can interact with a traversing unit, which is designed for the lateral displacement of the projection objective, or can be embodied as part of such a traversing unit. Such a traversing unit can i.a. Have drives and guides that can be controlled by the control unit.

A further aspect of the invention relates to a computer program for controlling a device for generating images of a light source array on a projection surface. The device has a light source array, a projection surface and at least one projection objective arranged in a beam path between the light source array and the projection surface with an imaging scale m deviating from +1 in at least one spatial direction, the at least one projection objective being positioned laterally with respect to the light source array and/or with respect to the Projection surface is movable. The imaging scale m can preferably be negative in at least one spatial direction, e.g. B - 1, be.

The computer program has instructions which, when executed on a computer, cause it to generate and output control signals to the device. The control signals cause a or to be executed several, preferably all, of the following steps: emission of light beams by means of the light source array, generation of an image of the light source array on the projection surface by means of the emitted light beams and the projection objective, and lateral displacement of the projection objective with respect to the light source array and/or the projection surface. The control signals can cause the light beams to be emitted and projected, preferably in such a way that a material forming the projection surface can be melted or sintered by means of the projected light beams.

The computer program can be used to control one of the devices described above and can be executed, for example, on the control unit described above. The control can take place in such a way that such a device executes one of the methods described above.

The above explanations for explaining the device according to the invention and the method according to the invention therefore also serve to describe the control unit according to the invention. The advantages mentioned above in relation to the device and the method are correspondingly associated with the control unit.

A computer program can be understood as meaning a program code that can be stored on a suitable medium and/or can be called up via a suitable medium. Any medium suitable for storing software, for example a non-volatile memory installed in a control unit, a DVD, a USB stick, a flash card or the like, can be used to store the program code. The program code can be retrieved, for example, via the Internet or an intranet or via another suitable wireless or wired network.

A further aspect of the invention relates to a non-transitory computer-readable storage medium for controlling a device for generating images of a light source array on a projection surface. The device has a light source array, a projection surface and at least one projection objective arranged in a beam path between the light source array and the projection surface with an imaging scale m deviating from +1 in at least one spatial direction, the at least one projection objective being positioned laterally with respect to the light source array and/or with respect to the Projection surface is movable. The imaging scale m can preferably be negative in at least one spatial direction, e.g. e.g. -1.

The non-transitory computer-readable storage medium includes instructions that, when executed on a computer, cause the computer to generate and output control signals to the device. The control signals cause one or more, preferably all, of the following steps to be carried out: emission of light beams by means of the light source array, generation of an image of the light source array on the projection surface by means of the emitted light beams and the projection lens, and lateral displacement of the projection lens with respect to the light source array and/or the projection surface. The control signals can cause the light beams to be emitted and projected, preferably in such a way that a material forming the projection surface can be melted or sintered by means of the projected light beams.

The instructions stored on the non-volatile computer-readable storage medium can be used to control one of the devices described above and can be executed, for example, on the control unit described above. The control can take place in such a way that such a device executes one of the methods described above.

The above explanations for explaining the device according to the invention and the method according to the invention therefore also serve to describe the non-volatile computer-readable storage medium according to the invention. The advantages mentioned above in relation to the device and the method are correspondingly associated with the non-transitory computer-readable storage medium.

In the following, the invention is explained by way of example with reference to the attached figures using preferred embodiments, with the features presented below being able to represent an aspect of the invention both individually and in various combinations with one another. In the figures, identical or similar elements are provided with identical reference symbols, insofar as this is appropriate. Directional terminology, such as "up", "down", "right", "left", etc., is used with reference to the orientation of the figures being described. directions, such as B. "z-direction", "x-direction" etc. refer to the coordinate systems shown in the figures. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting.

• 1a schematische Darstellung einer beispielhaften Vorrichtung mit Projektionsobjektiv in Ausgangsposition (Ansicht in y-Richtung);
• 1b schematische Darstellung der Vorrichtung aus 1a mit lateral verschobenem Projektionsobjektiv (Ansicht in y-Richtung);
• 2a schematische Darstellung einer beispielhaften Vorrichtung mit refraktivem Projektionsobjektiv in Ausgangsposition (Ansicht in y-Richtung);
• 2b schematische Darstellung der Vorrichtung aus 2a mit lateral verschobenem Projektionsobjektiv (Ansicht in y-Richtung);
• 2c schematische Darstellung der Vorrichtung aus 2a und 2b (Ansicht in x-Richtung);
• 3a schematische Darstellung einer beispielhaften Vorrichtung mit Zweispiegelobjektiv in Ausgangsposition (Ansicht in y-Richtung);
• 3b schematische Darstellung der Vorrichtung aus 3a mit lateral verschobenem Projektionsobjektiv (Ansicht in y-Richtung);
• 3c schematische Darstellung der Vorrichtung aus 3a und 3b (Ansicht in x-Richtung);
• 4 perspektivische Darstellung der Vorrichtung aus 3;
• 5 Darstellung zur eingangsseitigen Feldkrümmung;
• 6 Darstellung zur Projektion des Lichtquellenarrays in die eingangsseitige Objektschale;
• 7a,b Darstellung zur lateralen Verschiebung des Projektionsobjektivs mit Nachführung des Lichtquellenarrays entlang der objektseitigen Feldkrümmung;
• 8a schematische Darstellung einer beispielhaften Vorrichtung mit Dreispiegelobjektiv in Ausgangsposition (Ansicht in y-Richtung);
• 8b schematische Darstellung der Vorrichtung aus 8a mit lateral verschobenem Projektionsobjektiv (Ansicht in y-Richtung);
• 8c schematische Darstellung der Vorrichtung aus 8a und 8b (Ansicht in x-Richtung);
• 9 perspektivische Darstellung der Vorrichtung aus 8;
• 10a schematische Darstellung einer beispielhaften Vorrichtung mit Dreispiegelobjektiv und Faltspiegel in Vorderansicht;
• 10b schematische Darstellung der Vorrichtung aus 10a in Seitenansicht;
• 10c schematische Darstellung der Vorrichtung aus 10a, b in Draufsicht;
• 10d schematische Darstellung der Vorrichtung aus 10a-c in perspektivischer Darstellung;
• 11a-d schematische Darstellungen verschiedener Prinzipien zur Änderung der Position des Abbilds auf der Projektionsfläche;
• 12a-c schematische Darstellungen zur Anordnung von Projektionsobjektiven über der Projektionsfläche; und
• 13 ein Ablaufschema eines beispielhaften Verfahrens.

It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Features of the various example embodiments described herein may be combined with each other unless specifically stated otherwise. The following description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. Show it:

• 1a schematic representation of an exemplary device with a projection lens in the starting position (view in the y-direction);
• 1b schematic representation of the device 1a with laterally shifted projection lens (view in y-direction);
• 2a schematic representation of an exemplary device with a refractive projection objective in the starting position (view in the y-direction);
• 2 B schematic representation of the device 2a with laterally shifted projection lens (view in y-direction);
• 2c schematic representation of the device 2a and 2 B (view in x-direction);
• 3a schematic representation of an exemplary device with a two-mirror lens in the starting position (view in the y-direction);
• 3b schematic representation of the device 3a with laterally shifted projection lens (view in y-direction);
• 3c schematic representation of the device 3a and 3b (view in x-direction);
• 4 perspective view of the device 3 ;
• 5 Representation of the field curvature on the input side;
• 6 Representation of the projection of the light source array into the input-side object shell;
• 7a,b Representation of the lateral displacement of the projection lens with tracking of the light source array along the object-side field curvature;
• 8a schematic representation of an exemplary device with a three-mirror lens in the starting position (view in the y-direction);
• 8b schematic representation of the device 8a with laterally shifted projection lens (view in y-direction);
• 8c schematic representation of the device 8a and 8b (view in x-direction);
• 9 perspective view of the device 8th ;
• 10a schematic representation of an exemplary device with three-mirror lens and folding mirror in front view;
• 10b schematic representation of the device 10a in side view;
• 10c schematic representation of the device 10a , b in top view;
• 10d schematic representation of the device 10a-c in perspective view;
• 11a-d schematic representations of various principles for changing the position of the image on the projection surface;
• 12a-c schematic representations of the arrangement of projection lenses over the projection surface; and
• 13 a flowchart of an exemplary method.

1 shows an exemplary device 1 for generating images 2 of a light source array 3 on a projection surface 4 in a starting position and an associated control unit 9 in a side view, the viewing direction corresponding to the y-direction.

The device 1 has a light source array 3, which is designed as a laser light source array with a plurality of laser light sources. The laser light can be generated either directly in the light source array 3 or the light source array 3 can be connected to a direct laser light source via optical fibers (not shown), so that the light source array 3 is formed by the ends of the optical fibers. The light source array 3 is stationary, i. H. stationary arranged within the device 1.

The light source array 3 is connected in a signal-transmitting manner to a control unit 9 which is designed to generate a control signal 10a and to output it to the light source array 3 . The control signal 10a causes light beams 8 to be emitted by the light source array 3, with one, several or all light sources of the light source array 3 being able to be caused to emit light beams 8 as required.

The device 1 also has a projection surface 4 on which an image 2 of the light source array 3 is generated. In execution The projection surface 4 is designed as the surface of a powder bed 7 . The powder bed 7 can be a powder material, e.g. B. a metal powder, which can be melted or sintered upon light irradiation by light beams 8 of the light source array 3 . By moving the light beams 8 over the projection surface 4 or the surface of the powder bed 7 in the x-direction (scanning direction), material layers can be formed and workpieces can be additively manufactured, as explained above. The powder bed 7 can be movable in the z-direction in order to enable the projection surface 4 to be correctly positioned after a layer has been written and a new powder layer has been applied. However, a change in the position of the powder bed 7 in the x-direction is not provided.

In the beam path 5 between the light source array 3 and the projection surface 4, a projection objective 6 is arranged with a magnification m that differs from +1. In the exemplary embodiment, the imaging scale is m=−1, with the invention not being restricted to a specific imaging scale m. The projection lens 6 is telecentric on both sides and projects the light beams 8 generated by the light source array 3 onto the projection surface 4.

The projection lens 6 can be displaced laterally with respect to the light source array 3 and with respect to the projection surface 4 in the x-direction. A displaceability in the y-direction can optionally also be provided. By means of this lateral displacement 11, the position of the image 2 on the projection surface 4 can be fixed or the projection surface 4 can be scanned. Since the light source array 3 has a plurality of light sources, the scanning process can take place quickly, resulting in short manufacturing times in additive manufacturing.

To perform the lateral shift 11, which is 1b shown with an arrow, a control signal 10b is generated by the control unit 9 and output to the projection objective 6 . For this purpose, the control unit 9 and the projection lens 6 are likewise connected in a signal-transmitting manner.

1b shows the device 1 of FIG 1a with a laterally shifted projection objective 6, the projection objective 6 being _objectively displaced in the x-direction by the distance Δx. The imaging scale m=−1 causes a corresponding displacement Δx _image of the image 2 on the projection surface 4 by twice the distance Δx _objectively in the x direction. For any imaging scale m, the following applies: $$\Delta {\text{x}}_{\text{image}}=\left(1-\text{m}\right)*\Delta {\text{x}}_{\text{lens}}$$

To improve clarity, the control unit 9 is not shown in the following figures. Nevertheless, a control unit 9, as to 1 described, be present.

In 2a an exemplary device 1 is shown in a schematic representation in a side view, in which the projection lens 6 is designed as a refractive lens. The viewing direction corresponds to the y-direction. The scanning direction, ie the direction of the lateral movement 11 of the projection objective 6, corresponds to the x-direction.

The projection lens 6 is designed as a double-sided telecentric refractive lens with two identical lenses 12a, 12b with a positive focal length. An aperture stop 13 for delimiting the beam path 5 is arranged between the lenses 12a, 12b. 2a shows the projection objective 6 in a starting position (middle position). 2 B shows the projection lens 6 after lateral displacement 11, ie in the deflected position. As in 1b It can also be seen here that with the selected imaging scale m of the projection lens 6 of m=−1, the image 2 of the light source array 3 on the projection surface 4 is also shifted in the x direction, but compared to the projection lens 6 by twice the distance.

2c shows the device 1 viewed in the scanning direction, ie in the x-direction. In this view, the position of the image 2 remains unchanged with a lateral shift 11 .

Optionally, the in 2 The refractive lens shown can also be extended to double-sided telecentric multi-lens systems, in which additional lenses for the correction of field curvature and image errors, in particular also field-position-dependent image errors, are present.

Regarding the other components of the device 1 according to 2 will turn to the remarks 1 referred.

In 3a an exemplary device 1 is shown in a schematic representation in a side view, in which the projection lens 6 is designed as a two-mirror lens. The viewing direction corresponds to the y-direction. The scanning direction, ie the direction of the lateral movement 11 of the projection objective 6, corresponds to the x-direction. It is basically the execution of the in 2 shown double-telecentric refractive lens as a two-mirror lens. The representations in 3 are therefore equivalent to those in 2 .

The projection objective 6 is designed as a double-sided telecentric mirror objective with two identical mirrors 14a, 14b, both of which have a positive focal length, ie a converging effect. Out of the light source array 3 Sent light beams 8 are first reflected at the first mirror 14a to the second mirror 14b. After being reflected again on the second mirror 14b, the light beams 8 are projected onto the projection surface 4 and generate the image 2 there.

3a shows the projection objective 6 in a starting position (middle position). 3b shows the projection lens 6 after lateral displacement 11, ie in the deflected position. As in 1 b and 2 B It can also be seen here that with the selected imaging scale m of the projection lens 6 of m=−1, the image 2 of the light source array 3 on the projection surface 4 is also shifted in the x direction, but compared to the projection lens 6 by twice the distance.

3c shows the device 1 viewed in the scanning direction, ie in the x-direction. In this view, the position of the image 2 remains unchanged with a lateral shift 11 .

Since the object and image planes, ie the light source array 3 and the projection surface 4, lie in the same plane in double-sided telecentric mirror lenses with two mirrors 14a, 14b, the projection lens 6 is as in FIG 3c embodied as an off-axis lens, so that the folded beam path 5 is guided past the powder bed 7 . In 4 is a perspective view of the in 3 shown device 1 shown.

Regarding the other components of the device 1 according to 3 and 4 will turn to the remarks 1 referred.

The two-mirror lens has a relatively large field curvature on the input side, i.e. a curvature of the object field 15, as in 5 and 6 shown connected. The reason for this is the curved image field that originally occurs in optical imaging, since the Petzval sum of the inverse mirror radii is not zero due to the use of two mirrors with the same radii. In order to avoid this curved image field, the object field 15 is curved. In other words, the exit-side image field curvature resulting from the lens design is shifted to the entrance-side object field curvature.

In order to take this effect into account, the light source array 3 can preferably be arranged along the curved object field 15 . During the lateral displacement 11 of the projection objective 6, the light source array 3, as in 7a, b shown, are tracked to the curved object field 15 in order to keep the image field, ie the image-side foci, in the plane of the projection surface 4 . The arrow 16 represents the tracking.

In 8a an exemplary device 1 is shown in a schematic representation in a side view, in which the projection lens 6 is designed as a three-mirror lens. The viewing direction corresponds to the y-direction. The scanning direction, ie the direction of the lateral movement 11 of the projection objective 6, corresponds to the x-direction.

The projection lens 6 is designed as a double-sided telecentric mirror lens with three essentially spherical mirrors 14a, 14b, 14c. The first mirror 14a and the third mirror 14c are arranged on a common mirror element and have a collecting effect. The second mirror 14b, on the other hand, has a diverging effect. The centers of the radii of curvature of all mirrors or mirror surfaces coincide and lie in the common object and image plane, the radius of curvature of the second small mirror 14b being half the size of the radii of curvature of the first and third mirrors 14a, 14c.

The light beams 8 emitted by the light source array 3 are initially reflected at the first mirror 14a in such a way that they strike the second mirror 14b and are reflected by it to the third mirror 14c. After being reflected by the third mirror 14c, the light beams 8 hit the projection surface 7 and produce the image 2.

8a shows the projection objective 6 in a starting position (middle position). 8b shows the projection lens 6 after lateral displacement 11, ie in the deflected position. As in 1 b and 2 B It can also be seen here that with the selected imaging scale m of the projection lens 6 of m=−1, the image 2 of the light source array 3 on the projection surface 4 is also shifted in the x direction, but compared to the projection lens 6 by twice the distance. The imaging scale m = -1 results in a plan view for both the x and y directions. If the image scale m is specified along the light path, the result is an image scale m=+1 in the y-direction and an image scale m=−1 in the x-direction, ie the image 2 is a so-called flip image.

8c shows the device 1 viewed in the scanning direction, ie in the x-direction. In this view, the position of the image 2 remains unchanged with a lateral shift 11 .

In 9 is a perspective view of the in 8th shown device 1 shown, wherein for better visibility of the beam path 5, the mirror surface with the mirrors 14a, 14c is only shown in half.

The proposed three-mirror design is distinguished by the fact that, given a suitable choice of design parameters, it has no field curvature, since the Petzval sum, in contrast to the two-mirror objective, is brought to zero by the second mirror 14b. In addition, the three-mirror lens is free of spherical aberrations, coma, astigmatism and distortion up to the third order.

10a until 10d show a design example of a device 1 with a three-mirror lens and a folding mirror 17 in front view, side view and top view as well as in a perspective view. The object-side beam path 5 was folded forward with the light source array 3 by means of an optically neutral folding mirror 17, so that the powder bed 7, from which into the 10a until 10d for improved clarity, only the surface corresponding to the projection surface 4 is shown, can be moved in all directions under the projection lens 6 without colliding with the beam path 5 or the light source array 3 . This allows everyone in 11 outlined scanning principles can be realized.

the 11a until 11d show various principles for changing the position of the image 2 on the projection surface 4, ie ways in which the position of an image 2 of the light source array 3 can be varied on the projection surface 4, in a schematic representation using a three-mirror lens. An initial position of the device 1 is shown on the left in each case, in which the image 2 is imaged in a first position. A further position of the device 1 is shown to the right in each case, in which an image 2 shifted into a second position is generated. The principles can each be implemented continuously or discontinuously.

This in 11a The principle shown corresponds to that referred to above 8th explained principle, in which only the projection lens 6 is moved laterally. The light source array 3 and the projection surface 4 do not change their position, ie they are stationary.

11b shows a principle in which only the light source array 3 is laterally displaced. The projection lens 6 and the projection surface 4 do not change their position, ie they are stationary. Here, the traverse paths that are required for the same position of the shifted image 2 are twice as large as in the case of the in 11a shown principle. Consequently, a twice as large field acceptance window of the projection lens 6 is required in the movement or scanning direction, which is why the mirror surface with the mirrors 14a, 14c is significantly larger in the movement or scanning direction.

11c shows a principle in which the light source array 6 is laterally displaced together with the projection objective 6, whereas the position of the projection surface 7 is not changed. In this case, the dimension of the mirror surface with the mirrors 14a, 14c in the movement or scanning direction can be selected to be significantly smaller than in the case of the 11a and 11b principles shown, since this depends only on the field size, the numerical aperture and the distance of the mirrors 14a, b, c to the light source array 3, but not on the length of the projection surface 4 in the movement or scanning direction.

11d shows a principle in which only the powder bed 7 is laterally displaced together with the projection surface 4. The projection lens 6 and the light source array 3 do not change their position. Here, too, the dimensions of the mirror surface with the mirrors 14a, 14c in the direction of movement or scanning can be chosen to be significantly smaller than in the case of the 11 a and 11 b principles shown.

All four in the 11a until 11d The principles shown can be carried out with the devices 1 described above. The principle according to FIG 11a , which is more preferably carried out continuously, ie as a scanning process, since the advantages of the described devices 1 are particularly evident here. In other words, in addition to known principles, a principle can be implemented in which the image 2 of the light source array 3 is moved over the projection surface 4 or the surface of the powder bed 7 without the light source array 3 itself or the powder bed 7 having to be moved. This enables a very variable use of the proposed device 1.

12a until 12c show three devices 1 with projection lenses 6 and the associated projection surface 4 with a projection lens 6 ( 12a) , four projection lenses 6 ( 12b) and eight projection lenses 6 ( 12c ). In the case of the scanning principles according to 11c and 11d , In which the light source array 3 and the projection lens 6 are not moved to each other, but both are moved together relative to the projection surface 4, multiple projection lenses 6, as in the 12b and 12c shown, are arranged in such a way that the width of the projection surface 4 indicated by the dashed lines is covered by a plurality of projection lenses 6 . This can be beneficial to the lens size given size of the projection area 4 or given surface of the powder bed 4 to be chosen smaller and thus to be able to reduce the production costs. Here, as in 12b shown, projection lenses 6 are arranged laterally offset from one another. Alternatively, as in 12c shown groups of projection lenses 6, z. B. from two or four projection lenses 6, are formed, the projection lenses 6 of a group and / or the groups are offset from one another to each other.

The other way around, for a given lens size, larger projection surfaces 4 can be selected by arranging a plurality of projection lenses 6 next to one another or offset from one another.

13 shows a flowchart of an exemplary method 100 for generating images 2 of a light source array 3 on a projection surface 4. The method 100 can be carried out, for example, by means of one of the reference to FIG 2 , 3 or 8th devices 1 described are executed.

After the start of the method 100, light beams 8 are emitted by the light source array 3 in a first method step S1. In the exemplary embodiment, these are laser beams. Individual light sources of the light source array 3 can be activated or deactivated as required.

In the following method step S2, an image 2 of the light source array 3 is generated on the projection surface 4 by means of the emitted light beams 8 and the projection lens 6. The projection lens 6 has a magnification m that differs from +1 and can be embodied as a refractive lens, two-mirror lens or three-mirror lens. In this regard, reference is made to the above explanations for the various projection lenses 6 . A first image 2 of the light source array 3 is generated on the projection surface 4 by the emitted light beams 8 being projected onto the projection surface 4 .

In the area of the image 2, the material forming the projection surface 4, e.g. B. a metal powder arranged in the form of a powder bed 7 is melted or sintered by means of the projected light beams 8 .

In method step S4, the projection lens 6 is shifted laterally with respect to the light source array 3 and/or the projection surface 4. This corresponds to the in 11a shown principle. The method steps S1 to S4 are then repeated until all desired images 2 have been generated.

The method 100 can be carried out continuously or discontinuously, a continuous execution in which the projection surface 4 is scanned being preferred. When positions on the projection surface 4 are reached at which an image 2 is to be produced and material is to be melted or sintered, the light sources of the light source array 3 are activated. The light sources of the light source array 3 are deactivated again between positions at which no material is to be melted or sintered. Consequently, method steps S1 to S4 can be carried out with a partial or complete temporal overlap, ie also simultaneously.

For example, by repeating method steps S1 to S4, the projection surface 4 can be scanned and a workpiece can be additively manufactured in layers using an LAM method. New powder material can be added between the writing of the individual layers.

As an alternative to melting or sintering, the projected light beams 8 can be used for other material processing, e.g. B. by cutting, welding, signing, writing, engraving etc. the material forming the projection surface 4 in the area of the image 2 .

Reference List

1

contraption

2

image

3

light source array

4

projection surface

5

beam path

6

projection lens

7

powder bed

8th

rays of light

9

control unit

10a, 10b

control signal

11

lateral displacement

12a, 12b

lens

13

aperture stop

14a, 14b, 14c

mirror

15

object field

16

Tracking of the light source array

17

folding mirror

100

procedure

m

magnification

S1

Emitting light rays by means of the light source array

S2

Generating an image of the light source array on the projection surface by means of the emitted light rays and the projection lens

S3

Melting or sintering of a material forming the projection surface by means of the light beams generating the image

S4

lateral displacement of the projection objective with respect to the light source array and/or the projection surface

Δx lens

Shifting of the projection lens in the x-direction

Δximage

Shifting of the image in the x-direction

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US3748015A [0069]

Claims (18)

Device (1) for generating images (2) of a light source array (3) on a projection surface (4), having: - a light source array (3), - a projection surface (4) and - at least one projection lens (6) arranged in a beam path (5) between the light source array (3) and the projection surface (4) and having an image scale m deviating from +1 in at least one spatial direction, wherein the at least one projection objective (6) can be displaced laterally with respect to the light source array (3) and/or with respect to the projection surface (4). Device (1) after claim 1 , where the magnification m is negative. Device (1) after claim 1 or 2 , wherein the imaging scale m is in the range -10≦m≦-0.1, preferably in the range -2≦m≦-1, more preferably -1. Device (1) according to one of the preceding claims, wherein the light source array (3) and/or the projection surface (4) are arranged in a stationary manner. Device (1) according to one of the preceding claims, wherein the projection lens (6) is telecentric on one or both sides. Device (1) according to one of the preceding claims, wherein the projection lens (6) is a refractive lens. Device (1) according to one of Claims 1 until 5 , wherein the projection lens (6) is a mirror lens. Device (1) after claim 7 , wherein the mirror lens has two reflecting optically effective surfaces. Device (1) after claim 8 , Light sources of the light source array (3) being arranged along a curved object field of the mirror objective having two reflecting optically effective surfaces. Device (1) after claim 7 , wherein the mirror lens has three reflecting optically effective surfaces. Device (1) according to one of the preceding claims, wherein the projection surface (4) is a surface of a powder bed (7). Method (100) for generating images (2) by means of a device according to one of Claims 1 until 11 , comprising: - S1: emission of light beams (8) by means of the light source array (3) and - S2: generation of an image (2) of the light source array (3) on the projection surface (4) by means of the emitted light beams (8) and the projection lens ( 6). Method (100) according to claim 12 , comprising: S3: melting or sintering of a material forming the projection surface (4) by means of the light beams (8) generating the image (2). Method (100) according to claim 12 or 13 , Having: - S4: lateral displacement of the projection lens (6) with respect to the light source array (3) and / or the projection surface (4). procedure after Claim 14 , wherein the lateral displacement of the projection objective (6) takes place continuously or discontinuously. Control unit (9) for controlling a device (1) for generating images (2) of a light source array (3) on a projection surface (4), the device (1) having a light source array (3), a projection surface (4) and at least one Projection lens (6) arranged in a beam path (5) between the light source array (3) and the projection surface (4) with an imaging scale m deviating from +1 in at least one spatial direction, wherein the at least one projection lens (6) is lateral with respect to the light source array (3 ) and/or is displaceable with respect to the projection surface (4), designed to generate and output control signals (10a, 10b) to the device, the control signals (10a, 10b) causing one or more of the following steps to be carried out: - Emission of light beams (8) by means of the light source array (3), - Generating an image (2) of the light source array (3) on the projection surface (4) by means of the emitted light beams (8) and the projection lens (6) and - Lateral displacement of the projection objective (6) with respect to the light source array (3) and/or the projection surface (4). Computer program for controlling a device (1) for generating images (2) of a light source array (3) on a projection surface (4), the device (1) having a light source array (3), a projection surface (4) and at least one in a beam path (5) between the light source array (3) and the projection surface (4) arranged projection lens (6) with a magnification m deviating from +1 in at least one spatial direction, wherein the at least one projection lens (6) can be displaced laterally with respect to the light source array (3) and/or with respect to the projection surface (4), the computer program having instructions , which, when executed on a computer, cause it to generate control signals (10a, 10b) and to output them to the device (1), the control signals (10a, 10b) causing one or more of the following steps to be carried out: - emitting light beams (8) by means of the light source array (3), - generating an image (2) of the light source array (3) on the projection surface (4) by means of the emitted light beams (8) and the projection lens (6) and - lateral displacement of the Projection objective (6) with respect to the light source array (3) and/or the projection surface (4). Non-transitory computer-readable storage medium with instructions stored thereon for controlling a device (1) for generating images (2) of a light source array (3) on a projection surface (4), the device (1) having a light source array (3), a projection surface (4) and at least one projection objective (6) arranged in a beam path (5) between the light source array (3) and the projection surface (4) with an imaging scale m deviating from +1 in at least one spatial direction, wherein the at least one projection objective (6) is lateral with respect to the Light source arrays (3) and / or with respect to the projection surface (4) is displaceable, wherein the instructions, when executed on a computer, cause it to generate control signals (10a, 10b) and output to the device (1), wherein the control signals (10a, 10b) cause one or more of the following steps to be carried out: - Emission of light beams (8) by means of the light source array (3), - Generating an image (2) of the light source array (3) on the projection surface (4) by means of the emitted light beams (8) and the projection lens (6) and - Lateral displacement of the projection objective (6) with respect to the light source array (3) and/or the projection surface (4).

Images