EP3133337B1 - Laser headlamp with reduced colour error - Google Patents

Description

The present invention relates to a laser headlight with a laser light source, a lamp and a light deflecting device, which is set up to illuminate different partial areas of the phosphor with laser light at different times, the lamp having the property of preferably scattering incident laser light into a first solid angle area , which is smaller than a second solid angle range in which the illuminant emits fluorescent light and in which the first solid angle range is completely contained, and with a projection lens which is arranged so that its light entry surface intersects the first solid angle range transversely to the direction of propagation of the scattered laser light.

Such a headlight is assumed by the inventors to be known per se. In the known laser headlights, the light source, which contains phosphorus, for example, is stimulated to fluorescence with a laser emitting blue laser light. The fluorescent light emanating from the illuminant has frequencies from the yellow-red spectral range. Together with the blue laser light scattered in the lamp, white mixed light results.

If a focused laser beam is directed with a scanning device, for example with a controllably movable micromirror, to scan different areas of the illuminant, the resulting light distribution can be varied in a targeted manner. This allows an adaptive headlight to be provided that allows the light distribution to be dynamically adapted to the driving situation, in which, for example, areas of the light distribution in which other road users could be dazzled are not illuminated, and in which other areas in which such There is no risk of dazzling, particularly bright and extensive or bright and wide lighting. The traffic situation is recorded by an on-board camera, for example, and subjected to image processing in order to generate control signals for the micromirror.

Such a laser headlight is for example from the DE 10 2007 055 480 B3 known. In the known object, a focused laser beam of a laser that emits blue light is moved with the help of a scanner over a fluorescent material (e.g. a phosphor), which converts the blue light of the laser into white mixed light by mixing it with yellow or yellow-red fluorescent light. The white light is directed onto the roadway via optics. Any desired light distributions can be generated by moving the light spot of the focused laser beam on the illuminant and simultaneously modulating the laser power.

From the EP 0 291 475 A2 a headlight is known which has an angularly movable reflector which deflects a narrow beam very quickly in different spatial directions. As a result, small areas are sequentially illuminated in time with the changes in direction of the beam and thus scanned and thus scanned with light. The total area, which results from the union of the sequentially illuminated small areas, presents itself to the human sense of sight with sufficiently fast scanning and periodically sufficiently quickly repeated scanning sequence as a coherent, bright area and thus as a coherent light distribution. Sufficiently fast scanning results for example, when the sampling sequence is repeated at a frequency greater than 100 Hz.

For the practical implementation of such a headlight, projection optics are required which project an internal light distribution generated within the headlight by the scanning illumination of individual areas of the lamp with sufficient imaging quality onto the road, so that the road and its surroundings are illuminated as brightly as possible. In order to avoid glare, such light distributions are generated with light-dark borders, which demarcate darkened areas from light areas of the light distributions. The darkening is done with the aim of avoiding dazzling other road users and / or one's own dazzling from highly reflective signs.

When using individual lenses, as is well known, because of the dependence of the refractive index of the lens on the wavelength of the light, also known as dispersion, chromatic aberration occurs, that is, color errors which are disruptive and run along the light-dark boundary Show color fringes. From the DE 10 2013 215 976 A1 a headlamp arrangement is known which uses two light sources that generate light with different spectra to generate mixed light distributions of variable color. From the WO 2015/111649 A1 or the US 2015 176778 A1 a laser headlight with a laser light source, a lamp, a light deflecting device and a projection lens is known.

In order to generate light distributions with sharp light-dark boundaries on the road, high-quality imaging optics consisting of several lenses are generally required, the lenses being made of material with different refractive indices from lens to lens.

The known projection optics which correct such color errors with a plurality of lenses are expensive.

Against this background, the object of the invention is to provide a headlight of the type mentioned at the outset, the light distributions of which have no color fringes or only clearly less pronounced color fringes.

This object is achieved with the features of claim 1. The present invention differs from the prior art mentioned at the beginning in that the lens in the central area is designed in such a way that it is of a Fluorescent light emanating from the point of the illuminant and illuminating the edge zone of the light entry surface is focused in the same image point as fluorescent light which emanates from the same point of the illuminant and which illuminates the central area of the light entry surface. These characteristics achieve the following effects:
The light propagating in the first solid angle range is composed of a portion of scattered laser light and a portion of fluorescent light. The rays running in the first solid angle range are rays running comparatively close to the optical axis. For these rays, the chromatic aberration in particular is much smaller than a chromatic aberration of rays which pass through the edge region of the light entry surface.

Scattered light and fluorescent light propagate in the first solid angle range. In the part of the second solid angle range that does not belong to the first solid angle range, the fluorescent light dominates, since the scattered light is preferably emitted in the smaller, first solid angle range. The fact that the lens is arranged in such a way that a central area of its light entry surface is illuminated with the light propagating in the first solid angle area and an edge zone of its light entry area surrounding the central area is illuminated with light that is only in the second solid angle area, but not in spreads over the first solid angle area, the area of the lens in which the largest proportion of undesired color fringes occurs in the prior art is illuminated predominantly with fluorescent light and not or only very little scattered laser light. This allows the geometry of the lens there with the aim of being optimized Refraction of the fluorescent light can be designed. An optimized refraction is characterized by the fact that rays running close to the optical axis of the lens and less close to the optical axis of the lens, which emanate from the same point on the illuminant, are refracted into the same point on the optical axis.

The feature that the lens is designed in the central area in such a way that it focuses fluorescent light emanating from a point of the illuminant and illuminating the edge zone of its light entry surface into the same image point as fluorescent light emanating from the same point of the illuminant and which the central area of the light entry surface This means that the edge of the lens is optimized for the wavelengths of the fluorescent light.

Conversely, it follows from this that it is not optimized there for the wavelengths of the scattered laser light. Scattered laser light emanating from a point of the luminous means is therefore not imaged by the edge zone in the same image point as light emanating from the point of the luminous means and refracted through the central region of the lens. This scattered laser light is in particular not mapped into the point in which the fluorescent light emanating from the same point of the illuminant is mapped. This effect, which would again lead to color fringes, is effectively suppressed by restricting the spread of the scattered laser light to a central solid angle in conjunction with optimizing the edge of the lens for the fluorescent light.

The invention enables a relatively high angular resolution to be achieved even with a single, inexpensive plastic lens.

A preferred embodiment is characterized in that the total size of the light entry surface of the lens is four to sixteen times the size of its central area.
It is also preferred that the lighting means contains scattering particles with a diameter between 0.5 micrometers and 10 micrometers.

It is further preferred that the luminous means has a density of scattering particles at which the scattering of the laser light still occurs predominantly in the forward direction, that is to say parallel to the direction of the incident laser light.

It is also preferred that the lighting means has a first layer for scattering the incident laser light and a second layer in which the phosphor is located, which is excited by the incident laser light to emit fluorescent light.

It is further preferred that the scattering layer consists of large microparticles with diameters of more than 500 nm.

A preferred embodiment is characterized in that the scattering layer in the beam path of the incident laser radiation is preferably in front of the layer set up for fluorescence.

Another embodiment is characterized in that the scattering layer is a diffractive element, that is to say, for example, a diffraction grating.

It is also preferred that a non-scattering or only slightly scattering material is used as the material of the second layer becomes.

Further advantages emerge from the dependent claims, the description and the attached figures.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.

Figur 1

eine Anordnung aus einem konventionellem Leuchtmittel und einer Projektionslinse;

Figur 2

die Anordnung aus der Figur 1 mit einem anderen Leuchtmittel, wie es bevorzugt für die Erfindung verwendet wird;

Figur 3

eine Projektionslinse zusammen mit von einem Punkt des Leuchtmittels ausgehenden Strahlen von Fluoreszenzlicht;

Figur 4

die Linse aus der Figur 3 zusammen mit von demselben Punkt ausgehenden Stahlen von Streulicht;

Figur 5

Strahlengänge, wie sie in einem Ausführungsbeispiel der Erfindung auftreten;

Figur 6

ein Ausführungsbeispiel eines erfindungsgemäßen Laserscheinwerfers; und

Figur 7

eine bevorzugte Ausgestaltung eines Leuchtmittels.

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description. The same reference symbols in different figures denote the same or at least comparable elements in terms of their function. They show, each in schematic form:

Figure 1

an arrangement of a conventional illuminant and a projection lens;

Figure 2

the arrangement from the Figure 1 with another illuminant, as it is preferably used for the invention;

Figure 3

a projection lens together with rays of fluorescent light emanating from a point of the illuminant;

Figure 4

the lens from the Figure 3 together with rays of scattered light emanating from the same point;

Figure 5

Beam paths as they occur in one embodiment of the invention;

Figure 6

an embodiment of a laser headlight according to the invention; and

Figure 7

a preferred embodiment of a light source.

In detail, the Figure 1 an arrangement of a conventional illuminant 2 'and a projection lens 6, wherein the illuminant is illuminated with coherent laser light 1 and wherein the illuminant scatters part of the laser light without wavelength conversion, the resulting scattered light 4 having the same wavelength as the incident, coherent laser light, and wherein the illuminant absorbs another part of the incident laser light and converts it into fluorescent light 3 which has a longer wavelength than the laser light 1 and the scattered laser light 4.

A light source generally consists of a mixture of fluorescent substances, for example a phosphor, scattering particles, for example made of titanium dioxide, and a transparent binder or adhesive. Typically, the concentration ratios of these components are chosen so that the scattered laser light emanating from the illuminant and the fluorescent light emanating from the illuminant produce white mixed light.

In known lighting means 2 ', a similar angular distribution of the scattered laser light and the fluorescent light is sought. See for example the DE 10 2012 206 970 A1 . Such a similarity is also found in the subject of Figure 1 insofar as both types of light 3 and 4 each illuminate almost the entire light entry surface of the projection lens 6. This property of illuminating the entire light entry surface of the projection lens is actually always given with the fluorescent light bundle, since the fluorescent light 3 emanating from the illuminant 2 generally has no preferred direction and is emitted almost isotropically, i.e. with an almost hemispherical emission characteristic from the illuminant 2 ' . The projection lens 6 cuts, so to speak, a second solid angle range out of this hemisphere. This second solid angle then results approximately as the quotient of the light entry area of the lens in the numerator and a distance square in the denominator, the distance between an origin point of the hemisphere lying on the illuminant and the light entry area of the projection lens.

In contrast, the scattered light 4 emanates from the illuminant 2 ′ as a rule in a bundle that is centered around a main direction of emission which corresponds to the direction of incidence of the unscattered laser light 1. As a rule, therefore, the prior art already results in a lighting means 2 'which has the property of preferably scattering incident laser light 1 as scattered light 4 in a first solid angle range that is smaller than a second solid angle range into which the lighting means emits fluorescent light 3 , and in which the first solid angle range is completely contained.

In the prior art, attempts are generally made to illuminate the light entry surface of the projection lens 6 as completely as possible not only with the fluorescent light 3 but also with the scattered laser light 4. For this purpose, illuminants 2 'are used, which, by virtue of their composition, are specifically designed to emit laser light in a wide range To scatter solid angle that covers the light entry surface of the lens as much as possible.

The present invention takes a different approach. The Figure 2 shows the arrangement from Figure 1 with another lamp 2, as it is preferably used for the invention. In this respect, the Figure 2 essential elements of a preferred embodiment of the invention. In contrast to the prior art, in this embodiment a light source 2 is used which scatters the laser light 1 into a solid angle area which is so small that only a central area 6a of the projection lens 6 or the light entry surface of the projection lens 6 with the scattered light 4 is targeted is illuminated, while the fluorescent light 3 preferably illuminates the entire light entry surface of the projection lens 6.

The property of scattering laser light only in a relatively small solid angle is preferably realized by one or more of the following modifications of the illuminant 2. A lighting means 2 used in the invention also consists of a mixture of fluorescent substances, for example a phosphor, scattering particles, for example made of titanium dioxide, and a transparent binding agent or adhesive. Here, too, the concentration ratios of these components are selected such that the scattered laser light 4 emanating from the illuminant and the fluorescent light 3 emanating from the illuminant 2 result in white mixed light.

The phosphor particles, which are typically 1 to 10 micrometers in size, scatter predominantly in the forward direction. If the density of the scattering particles is so high that mostly multiple scattering occurs, the scattering distribution becomes isotropic.

It is therefore preferred that the luminous means 2 has a density of scattering particles at which the scattering of the laser light still occurs predominantly in the forward direction, that is, parallel to the direction of the incident laser light 1. Small particles of titanium dioxide or silicon dioxide with typical diameters below 500 nm also scatter isotropically. It is therefore also preferred that the illuminant 2, if it has scattering particles made of titanium dioxide and / or silicon dioxide, only have them in a concentration that is sufficiently small so that there is still a sufficiently small solid angle in which the scattered laser radiation 4 occurs spreads.

The reduction in the size of the solid angle filled by the scattered laser light 4 is achieved, based on the lighting means 2 'usually used in laser headlights, by reducing the concentration of scattering particles and / or by using non-scattering phosphor. The spatial distribution of the fluorescent light 3, on the other hand, is only slightly influenced by changes in the parameters mentioned. The isotropy is inherent in the generation of the fluorescent light 3.

As the Figure 2 shows, the reduction of the solid angle into which the scattered light 4 emanating from the illuminant 2 is scattered in connection with the retention of the remaining geometry, in particular the distance f of the light entry surface of the projection lens from the illuminant and the size of the light entry surface of the projection lens transversely to incident light so that only a central area 6a of the light entry surface is illuminated with fluorescent light 3 and scattered light 4 and that an edge zone 6b of the light entry surface is only illuminated with fluorescent light 3. The distance f preferably corresponds to the focal length of the projection lens 6. In the Figures 1 and 2 only light is shown emanating from a point 2 a of the illuminant 2. In the real case, the light also emanates from other points, preferably from the entire surface of the illuminant 2 facing the lens.

The projection lens 6 from the Figures 1 and 2 has in relation to the comparatively small opening angle of the scattered light 4 in Figure 2 a large opening angle on its light entry surface facing the lamp. This large opening angle is advantageous on the one hand in order to be able to use as much fluorescent light as possible for the generation of white mixed light.

Lenses with a large opening angle are particularly prone to chromatic aberrations because the light is refracted comparatively more strongly at the edge of such lenses than at the edge of lenses with a smaller opening angle.

With the arrangement of the projection lens 6 and a light source 2 that bundles the scattered radiation 4 into a comparatively small solid angle, the effect is that the outer edge zone 6b of the lens 6 only refracts fluorescent light 3, i.e. light from a spectral range that does not include the scattered light included and is therefore comparatively narrow. The dispersion effect is correspondingly small, so that color errors are significantly less pronounced than with the subject of Figure 1 . In addition, this edge region 6b can then be optimized for the narrow wavelength range mentioned, so that rays running at different distances from the optical axis 7 and coming from a point of the Illuminants go out, are mapped in a point in the image space.

The Figure 3 shows a projection lens 6 together with from a point 2a of the illuminant Figure 2 outgoing rays of fluorescent light. The lens 6 is made here in such a way that it is designed to be optimized for the fluorescent light 3. The luminous center point 2a is arranged in an object-side focal point of the lens 6 for the fluorescent light 3. The lens 6 collects the fluorescent light 3 emanating from the object-side focal point 2a and focuses this light in its image-side focal point 8 for this light. The fact that this lens 6 is optimized for the fluorescent light 3 means in particular that rays 3.1 emanating from an object point 2a and running near the optical axis 7 are focused in the same image point 8 as marginal rays 3.2 emanating from the same object point 2a. This is preferably achieved by a curvature adapted to the dispersion of the fluorescent light.

The Figure 4 shows the lens from the Figure 3 together with rays of scattered light 4 emanating from the same point 2a. The scattered light 4 has a shorter wavelength than the fluorescent light 3 and is therefore refracted more strongly than the fluorescent light 3, especially in the edge regions of the lens 6 that are far from the optical axis 7 4, which emanates from the same point 2a as fluorescent light 3, is not focused into the same point 8 as fluorescent light 3. Since lens 6 is optimized for fluorescent light 3, it cannot necessarily be optimized for scattered laser light 4 at the same time. This means that edge rays 4.2 of the scattered laser light 4 are refracted more strongly than rays 4.1 of the more central scattered laser light 4.

When the beam paths are superimposed on the Figures 3 and 4 arises in the pixel plane of the Figure 3 a white mixed light point that merges outwards into a ring of scattered light surrounding it. In the prior art, this color error leads to disruptive color fringes in the light distribution.

The Figure 5 shows ray paths as they occur in an embodiment of the invention. In detail, the Figure 5 a point 2a of a lighting means 2, which has the property of scattering incident laser light as scattered light 4, preferably in a first solid angle area 10, which is smaller than a second solid angle area 12 in which the lighting means 2 emits fluorescent light 3, and in which the first solid angle area 10 is completely included.

A projection lens 6 is arranged such that its light entry surface intersects the first solid angle region 10 transversely to the direction of propagation of the scattered light 4. The lens 6 is arranged in particular in such a way that a central area 6a of its light entry surface is illuminated with the light propagating in the first solid angle area 10 (scattered light 4 and part of the fluorescent light 3) and an edge zone 6b of its light entry area surrounding the central area 6a is illuminated with only in the second solid angle area 12, but not with the light propagating in the first solid angle area 10.

The optical axis of the projection lens 6 is preferably aligned with the emission direction of the light module. The central area 10 is an inner area of the light entry surface of the from, which lies transversely to the optical axis Solid angle 10 is illuminated, or this solid angle is characterized. The larger edge zone, which surrounds the inner area and is illuminated by the solid angle 12 or characterizes this solid angle, preferably extends to the edge of the lens.

The total size of the light entry surface (central area plus edge zone) is preferably four to sixteen times the size of its central area. The lens 6 is designed in the central area 6a in such a way that it focuses the scattered light 4 emanating from the point 2a of the illuminant 2 into an image point 8, and the lens is designed in the edge zone 6b so that it moves from the point 2a of the illuminant 6 outgoing fluorescent light 3 is focused in the same image point 8.

With regard to the rays that run closer to the optical axis 7 than the edge rays, a wavelength-dependent design or optimization of the design plays a much smaller role, since the chromatic aberration is proportional to the radial distance from the optical axis 7 and the rays close to the axis are different Wavelengths can be focused sufficiently well.

The Figure 6 shows an embodiment of a laser headlight 14 according to the invention. The laser headlight 14 has a housing 16 which has a light exit opening. The light exit opening is covered by a transparent cover plate 18. Inside the housing there is a light module which, among other things, is the subject of the Figure 2 having.

The light module has a laser light source 20, a lighting means 2 and a light deflection device 22 which is set up to illuminate different partial areas or points 2a, 2b, 2c, ... of the illuminant 2 temporally separated from one another with laser light 1, the light deflecting device 22 having at least one movable first light deflecting element 22.1 which is set up to detect incident light Directing laser light at different times in different spatial directions, and wherein the light deflection device 22 is set up to direct light directed in a first spatial direction in a first beam path onto a first partial area 2a of the illuminant, and light directed in a second spatial direction in a second beam path to steer to a second sub-area 2b of the illuminant. Such a light deflecting element is also referred to below as a scanner. With such a scanner, for example, headlights can be built that can produce almost any light distribution. This enables a dynamic adaptation of a light distribution generated by the headlight to changing traffic conditions.

For this purpose, for example, a camera 24 installed in the motor vehicle records the traffic situation in front of the vehicle. A control unit 26 analyzes the images and controls the light deflecting element 22 and thus the light distribution so that the road is always optimally illuminated and dazzling oncoming traffic is avoided. A focused laser beam from the laser light source is moved over the lamp with the help of the scanner, which converts the blue light from the laser into white mixed light by mixing it with yellow or yellow-red fluorescent light. The white light is directed onto the roadway via optics. Any light distributions can be generated by moving the light spot of the focused laser beam on the illuminant and simultaneously modulating the laser power will.

As a result of the movement of the light deflecting element 22, the areas 2a, etc. of the illuminant are sequentially illuminated in time with the changes in direction of the beam and thus scanned with light. The total area, which results from the union of the sequentially illuminated small areas, presents itself to the human sense of sight with sufficiently fast scanning and periodically sufficiently quickly repeated scanning sequence as a coherent, bright area and thus as a coherent light distribution. Sufficiently fast scanning results for example, when the sampling sequence is repeated at a frequency greater than 100 Hz.

The invention works particularly well for light distributions that are relatively narrow. An example of a narrow light distribution is what is known as a spot light distribution, which is up to +/- 10 ° wide around a central main radiation direction. In the case of greater lateral scattering, the comparatively narrow bundle of the laser light emanating from the illuminant and bundled by the projection lens, which was previously scattered in the illuminant, is shifted into the edge zone of the projection lens optimized for the fluorescent light. In this case, a further embodiment provides that the laser beam scanning the lamp surface is moved in a controlled manner in such a way that the light beam emanating from the lamp preferably in the forward direction always runs centrally through the projection lens.

The Figure 7 shows a preferred embodiment of a lighting means 6, with which the desired distributions of the scattered laser light (scattered light 4) and the fluorescent light 3 can be achieved. This illuminant has a first layer 60 for scattering the incident laser light and a second layer 62 in which the phosphor is located, which is excited by the incident laser light to emit fluorescent light. The scattering layer 60 preferably consists of large microparticles 64 with diameters of over 500 nm. This layer lies in the beam path of the incident laser radiation 1, preferably in front of the layer 62 set up for fluorescence, and predominantly influences the scattered light 4 that is scattered into the first solid angle. The size of these particles is preferably selected so that the scattering preferably takes place in the forward direction and can thus be optimally adapted to a projection lens 6, or to its central region 6a.

The fluorescent agent used is preferably a non-scattering or only slightly scattering material, as it is, for example, from the publication " Toward scatter-free Phosphors in white Phosphor-converted light-emitting diodes ", Optics Express, Vol. 20, Issue 9, pp. 10218-10228 (2012 ) is known. An only slightly scattering fluorescent agent can be produced, for example, by embedding the phosphor in a matrix material which has the same or at least a similar refractive index as the phosphor particles. It should also be noted that this invention could also be implemented with a non-scanning laser headlight.

Claims (9)

1. Laser headlamp (14) having a laser light source (20), an illuminant (2) and a light deflecting device (22), which is set up to illuminate different partial areas (2a, 2b, ...) of the illuminant with laser light (1) at different times, the illuminant having the property of scattering incident laser light as scattered light (4) preferably in a first solid angle range (10), which is smaller than a second solid angle range (12), into which the illuminant emits fluorescent light (3), and in which the first solid angle range (10) is completely contained, and with a projection lens (6) having a light entry surface, which is arranged such that the light entry surface intersects the first solid angle range (10) transversely to the direction of propagation of the scattered laser light (4), wherein the lens (6) is arranged such that a central region (6a) of its light-entry surface is illuminated with the light propagating in the first solid angle region (10), and an outer zone (6b) of its light-entry surface surrounding the central region (6a) is illuminated with light propagating only in the second solid angle region (12), but not in the first solid angle region (10), and wherein an illuminated part of the light-entry surface is larger than the central region (6a), characterised in that the lens (6) in the central region (6a) is designed so that it focuses fluorescent light (3) emanating from a point (2a) of the illuminant (2) and illuminating the peripheral zone (6b) of the light-entry surface into the same image point (8) as fluorescent light (3.1) which emanates from the same point (2a) of the illuminant and which illuminates the central region (6a) of the light entry surface.
2. Laser headlight (14) according to claim 1, characterized in that a total size of the light entry surface of the lens (6) is four to sixteen times the size of its central region (6a).
3. Laser headlamp according to any of the foregoing claims, characterized in that the light source (2) contains scattering particles having a diameter between 0.5 micrometers and 10 micrometers.
4. Laser headlamp according to claim 3, characterized in that the illuminant has scattering particles in a density at which the scattering of the laser light still occurs predominantly in the forward direction, i.e. parallel to the direction of the incident laser light (1).
5. Laser headlamp (14) according to one of the preceding claims, characterized in that the illuminant (2) has a first layer (60) for scattering the incident laser light and a second layer (62) in which the luminescent substance is located, which is excited by the incident laser light to emit fluorescent light.
6. Laser headlamp (14) according to claim 5, characterized in that the scattering layer (60) consists of large microparticles (64) with diameters of more than 500 nm.
7. Laser headlamp (14) according to claim 5 or 6, characterized in that the scattering layer (60) is preferably located in the beam path of the incident laser radiation (1) in front of the layer (62) set up for fluorescence.
8. Laser headlamp according to claim 6 or 7, characterized in that the scattering layer is a diffractive element.
9. Laser headlamp (14) according to claim 6, characterised in that a non-scattering or only slightly scattering material is used as the material of the second layer.

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