FR3153047A1 - Projection device comprising a coherent light source and a textured projection surface - Google Patents

Abstract

Projection device comprising a coherent light source and a textured projection surface A lighting device (1) for a motor vehicle, the lighting device comprising a lighting module (10) comprising at least one light source (11) configured to emit a beam of coherent light, and a projection surface (20). The lighting module (10) is configured to project at least a portion of the coherent light emitted by the light source (11) toward the projection surface (20) in order to generate at least one image on said projection surface (20). The projection surface (20) has a texture configured to limit the speckel contrast of said at least one image. Figure 1

Description

Projection device comprising a coherent light source and a textured projection surface Technical field of the invention

The present invention relates to a lighting device for a motor vehicle, comprising in particular a coherent light source.

State of the prior art

Luminous devices are used in motor vehicles, particularly in the interior of vehicles. Increasingly, such devices are used to project images or information onto surfaces inside the passenger compartment, for example the dashboard, seats, doors or pillars such as those bordering the windshield. In this perspective, the use of laser sources has advantages because laser sources emit a directional beam. This characteristic allows for high luminous efficiency of the device, compared to light sources such as light-emitting diodes (LEDs) with Lambertian emission, including in compact devices. Indeed, most of the light from a laser source can be easily used, whereas the light emission of a Lambertian source extends over a half-space, a significant part of the light rays emitted in a direction presenting a large angle with the general direction of emission cannot be easily recovered and, therefore, is generally lost.

However, due to the coherence of the light emitted by a laser source, random spots appear when the beam is projected onto a surface to generate a light image. This phenomenon is well known to those skilled in the art under the English term "speckle", and under the expression "laser granularity" in French. Speckel corresponds to random interferences which generate light spots in certain areas and certain directions of observation which are also random. This creates a speckled image, an unpleasant flickering effect when observing the surface with the image projected on it, in particular when moving relative to this surface. In addition, with a multi-colored light beam, chromatic effects appear, due to the fact that each wavelength generates its own speckel, and that these are offset from each other.

Furthermore, it is also necessary that the surface onto which the light beam is projected has good reflectivity so that the image thus created on said surface has good brightness, and is thus clearly visible to an observer.

The aim of the invention is to respond at least in part to the problems mentioned above, and in particular to resolve, or at least limit the flickering effect due to speckel.

In this respect, the subject of the invention is a lighting device for a motor vehicle, the lighting device comprising:
• a light module comprising at least one light source configured to emit a coherent light beam;
• a projection surface;
the light module being configured to project at least a portion of the coherent light emitted by the light source towards the projection surface in order to generate at least one image on said projection surface;
remarkable in that the projection surface has a texture configured to limit the speckel contrast of said at least one image.

Coherent light is defined as light whose coherence length is greater than 250 times the wavelength, in particular approximately 500 times the wavelength. For example, for a peak wavelength of 520nm, and a spectrum with a full width at half maximum of 1nm, the coherence length is approximately 250µm.

Advantageously, the light source comprises a laser or a laser diode.

By the expression limiting the speckel contrast, we understand that this contrast is less than or equal to 0.25 and advantageously less than or equal to 0.15. A contrast of 0.3 or more is not satisfactory. The speckel contrast corresponds to the standard deviation of luminance divided by the average luminance, over the entire surface illuminated by the coherent light.

The image is a luminous image, intended to be seen by an observer, in particular present in the passenger compartment of the vehicle. The projected image or images can be static, that is to say that the image obtained on the projection surface is fixed, or dynamic, the image obtained on the projection surface then evolving over time.

Advantageously, the lighting device has one or more of the following characteristics, taken alone or in combination.

The light module includes multiple light sources, each configured to emit a coherent beam of light.

Coherent light beams have the same color.

Coherent light beams exhibit different colors from each other.

The light module comprises three light sources emitting respectively a beam of coherent light of red, green and blue color.

The light module comprises at least one projection device configured to receive at least a portion of the beam emitted by the light source and to project it towards the projection surface in order to generate said at least one image on said projection surface.

The projection device includes a system for scanning the beam emitted by the light source.

The scanning system includes a microelectromechanical system (MEMS).

The microelectromechanical system comprises a micromirror. The micromirror receives at least a portion of the beam emitted by the at least one light source.

The projection device comprises a matrix of micro-mirrors. The matrix of micro-mirrors receives at least a portion of the beam emitted by the at least one light source.

The light module comprises a circuit for driving the micro-mirror and/or the micro-mirror matrix, associated with a memory containing the images to be generated, and configured to send instructions to said micro-mirror and/or to said micro-mirror matrix so that the image is generated.

The projection device comprises a static optical element. The static optical element receives at least a portion of the beam emitted by the at least one light source.

The static optical element comprises one or more reflectors.

The static optical element comprises one or more lenses.

The static optical element comprises a combination of one or more reflectors and one or more lenses.

Several light sources are associated with the same projection device.

Each light source is associated with its own projection device.

Some light sources are associated with the same projection device, and other light sources are each associated with a projection device of its own.

The light beam emitted by a light source is divided into several branches, for example by using a semi-reflecting mirror, or several semi-reflecting mirrors in cascade.

Each branch is associated with its own projection device.

The projection surface has a first portion and a second portion which are separate from each other.

The projection surface has a texture formed of patterns, said patterns comprising peaks and valleys occurring randomly.

The texture has an arithmetic mean roughness between 4µm and 25µm inclusive, and advantageously between 9µm and 18µm inclusive.

The texture has an extreme difference between peaks and valleys, between 25µm and 150µm, advantageously between 50µm and 120µm, particularly between 60µm and 100µm.

The texture has an average pattern width of between 150µm and 500µm, and advantageously between 225µm and 375µm.

The first portion has a first texture and the second portion has a second texture, the first texture and the second texture being different from each other.

Which projection surface has a fabric.

Fabric is made from natural fibers. Natural fibers include plant or animal fibers, such as cotton, wool, hemp, linen, jute, or silk.

The fabric comprises artificial or synthetic fibres. An artificial fibre is a fibre obtained from plant pulp. A synthetic fibre is a fibre obtained by synthesis of chemical compounds. Artificial or synthetic fibres are, for example, based on polyamide, such as nylon, viscose, polyolefin, vinyl polyether siloxane, polyester or acrylic.

The fabric comprises a mixture of two or more fibers.

Fabric is a fabric, comprising a weft and a warp, a velvet or a felt.

The projection surface constitutes part or all of a dashboard, seat, door or pillar such as those bordering the vehicle's windshield.

Presentation of figures

Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiment given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

FIG. 1 shows a general view of a light device according to the invention;

FIG. 2 shows a schematic detailed view of the light module, according to the invention;

FIG. 3 shows a schematic detailed view of a projection surface according to the invention;

FIG. 4 shows a curve of a roughness profile of a projection surface according to the invention.

Detailed description

It should first be noted that while the figures set out the invention in detail for its implementation, these figures can of course be used to better define the invention, where appropriate. It should also be noted that these figures only set out examples of embodiments of the invention.

The features, variants and different embodiments of the invention may be combined with each other in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.

In the figures, elements common to several figures retain the same reference.

There FIG. 1 shows a general view of a lighting device 1 according to the invention. It comprises a light module 10 and a projection surface 20. In the example illustrated, the projection surface 20 comprises a first portion 20a and a second portion 20b separate from one another. However, the projection surface can also consist of a continuous surface, or comprise more than two separate portions. This makes it possible to adapt to the internal configuration of the vehicle's passenger compartment.

The light module 10 emits light towards the projection surface 20. It makes it possible to generate an image on said projection surface 20. This light is represented schematically by light rays R2. The light emitted by the light module 10 is coherent.

The projection surface 20 has a texture configured to limit the speckel contrast of said image. In the absence of said texture, the image exhibits a significant speckel phenomenon, which leads to an unpleasant flickering effect when observing the projection surface 20 illuminated by the light module 10. The texture of the projection surface 20 according to the invention makes it possible to reduce this flickering effect, and thus to improve the perception of said image.

The texture of the projection surface 20 is configured so that the speckel contrast of said image is less than or equal to 0.25 and advantageously less than or equal to 0.15.

According to a non-limiting embodiment, the projection surface 20 has a single texture over its entirety, regardless of whether it consists of a continuous surface or comprises several disjointed portions. According to another non-limiting embodiment, the projection surface 20 has several portions, each portion having a texture different from that of the other portions. Each of the textures is configured so that the speckel contrast of the image generated on the associated area is less than or equal to 0.25 and advantageously less than or equal to 0.15. For example, the portion 20a may have a first texture and the portion 20b may have a second texture, the first texture and the second texture being different from each other. Additionally, the first portion 20a may have several zones, each zone having a texture different from that of the other zones and/or the second portion 20b may have several zones, each zone having a texture different from that of the other zones, and all the textures being configured to limit the value of the speckel contrast, as indicated above.

The projection surface 20 is advantageously an internal surface of the passenger compartment of a motor vehicle, in particular an element of a dashboard, a seat, a door or an upright such as those bordering the windshield.

The image generated on the projection surface 20 may, for example, be information intended for the occupants of the vehicle, such as the speed of the vehicle or the presence of obstacles nearby, information from a navigation system, or from a media such as a radio or music player. It may also be a welcome message when an occupant enters the vehicle, or a goodbye message when the occupant leaves the vehicle.

There FIG. 2 shows a schematic detailed view of the light module 10, according to one embodiment. It comprises at least one light source 11 configured to emit a coherent light beam, represented by the rays R1, and a projection device 12 configured to receive at least a portion of the beam emitted by said at least one light source 11, and to project it towards the projection surface 20. Alternatively, the light module 10 may also comprise several light sources 11, each configured to emit a coherent light beam, the coherent light beams having either the same color or different colors from each other so that multicolored light beams are projected. Advantageously, the light module 10 comprises three light sources 11 emitting red (R), green (G) and blue (B) respectively. The combination of these three light sources, forming an RGB light source, allows the projection of light beams that can include almost all visible colors. Advantageously, the wavelengths for red are between 630 and 655nm, in particular between 635 and 645nm, the lengths for green are between 510 and 530nm, in particular between 515 and 525nm, the lengths for blue are between 440 and 470nm, in particular between 445 and 455nm. These wavelength ranges, in particular the most restricted of them, make it possible to maximize the quantity of colors that can be projected.

According to a non-limiting embodiment, the projection device 12 comprises a system for scanning the light beam emitted by the at least one light source 11. This scanning system may for example comprise a microelectromechanical system (MEMS), comprising a micro-mirror receiving at least part of the beam emitted by the at least one light source 11.

According to a non-limiting embodiment, the projection device 12 comprises a micro-mirror matrix (DMD, for “digital micromirror device” in English) receiving at least part of the beam emitted by the at least one light source 11.

According to a non-limiting embodiment, the projection device 12 comprises a static optical element receiving at least a portion of the beam emitted by the at least one light source 11. According to a non-limiting example, the static optical element comprises one or more reflectors. According to another non-limiting example, the static optical element comprises one or more lenses. According to yet another non-limiting example, the static optical element comprises a combination of one or more reflectors and one or more lenses.

When several light sources 11 are used, these can be associated with the same projection device 12. This makes it possible to reduce the size of the light module. Alternatively, each light source 11 is associated respectively with a projection device 12 of its own. This configuration makes it possible to generate on the projection surface 20 a different image for each of the light sources 11. The possible variety for the images is thereby increased. It is also possible to have in the light module 10 certain light sources associated with the same projection device, and other light sources each associated respectively with a projection device of its own. This makes it possible to have both a significant variety of images, and a controlled size.

It is also possible to divide the light beam emitted by a light source 11 into several branches, for example by using a semi-reflecting mirror, or several semi-reflecting mirrors in cascade, and to associate each branch respectively with a projection device specific to it. This makes it possible to generate a wide variety of images with a single light source 11. When the light module 10 comprises several light sources 11, it is possible to divide the light beam emitted by several light sources, or even by all the light sources, into several branches.

The projected image or images may be static, i.e. the image obtained on the projection surface 20 is fixed, or dynamic, the image obtained on the projection surface 20 then evolving over time. The light module comprises for this purpose a control circuit (not shown) for the micro-mirror or the matrix of micro-mirrors, associated with a memory (not shown) containing the images to be generated, and configured to send instructions to said micro-mirror or to said matrix of micro-mirrors so that the desired image is generated. The static optical element, when used alone, makes it possible to generate only a fixed image.

There FIG. 3 shows a detailed view of the projection surface according to the invention. For reasons of readability of this figure the dimensions of the patterns of the surface texture have been exaggerated, and said patterns have been represented very schematically in a relatively identical manner. In reality, the patterns M constituting the surface texture comprise peaks P and troughs C succeeding each other randomly, with variable heights, depths and spacings, as can be seen in the FIG. 4 . Thus the surface has a rough appearance.

Advantageously, the texture has one or more of the following parameters.

According to a non-limiting embodiment, the texture has an arithmetic mean roughness, known by the acronym Ra, between 4 µm and 25 µm inclusive, and advantageously between 9 µm and 18 µm inclusive. The arithmetic mean roughness is the average of the absolute values of the deviations of the irregularities from the average level of the surface.

According to a non-limiting embodiment, the texture has an extreme difference between the peaks and the troughs, known by the acronym Rz, between 25 µm and 150 µm, advantageously between 50 µm and 120 µm, in particular between 60 µm and 100 µm. This is the absolute vertical difference between the maximum height of the peaks and the maximum depth of the troughs, in other words the total height measured between the highest peak and the deepest trough.

According to a non-limiting embodiment, the texture has an average width of the patterns M, known by the acronym RSm, between 150 µm and 500 µm, and advantageously between 225 µm and 375 µm. This value corresponds to the average width of the main patterns. Any peak, respectively any trough, whose height, respectively the depth, is less than 10% of the maximum height, respectively of the maximum depth, is considered as being part of a pattern of greater amplitude, and is therefore not taken into account to calculate said average.

The texture properties are rotationally symmetrical. In other words, the surface properties are identical in all directions. This simplifies the device's manufacturing process because there is no need to worry about the surface orientation of the fabric when cutting out the piece to be used as the projection surface.

The inventors found that, surprisingly, fabrics were particularly well-suited to solving the speckel problem. Fabrics are understood to mean textile materials. They may include natural, plant-based or animal fibers, for example, cotton, wool, hemp, linen, jute or silk, or artificial or synthetic fibers, for example, based on polyamide, such as nylon, viscose, polyolefin, vinyl polyether siloxane, polyester or acrylic. They may also include a mixture of two or more of these fibers. The fabric may, in particular, be a woven fabric, comprising a weft and a warp, a velvet or a felt.

The projection surface 20 is advantageously light-colored in order to have good reflectance. This color can be, for example, white, gray, beige, or any other color as long as it is not very saturated. The reflectance, or albedo, of the projection surface 20 has a value greater than or equal to 0.1 to ensure that the image projected onto said surface is visible. A reflectance greater than or equal to 0.25 allows very good visibility of the image.

There FIG. 4 shows a roughness profile of the projection surface 20 according to the invention, characteristic of the texture of said surface. More precisely, it is a measurement carried out on a segment with a length of 0.8 mm taken at random on said projection surface. The height of the surface, represented on the ordinate in a scale in µm, is plotted as a function of the distance along this segment, represented on the abscissa, from 0 at the left end of the curve to 0.8 mm at the right end of the curve.

The profile presents a succession of peaks and troughs, of random heights and spacing, around an average level of the surface on this segment, this average level being located vertically at 0. The highest peak P1 is at a height of approximately 50µm. The lowest trough C1 is located at approximately -70µm. The peaks and troughs can be relatively flared like peak P3 and trough C2, or rather pointed like peak P2 and trough C3. Furthermore, we see that the profile of pattern M, included between the two dotted lines, is not smooth, but that it presents a succession of secondary peaks PS and secondary troughs CS of small dimensions. Because of these small dimensions, said secondary peaks and troughs do not form patterns in themselves but are included in pattern M. On this profile, the Ra value is approximately 16µm.

Thanks to this random profile, the perception of speckel is greatly limited and the image visible on the projection surface has a pleasant appearance.

The profile shown on the FIG. 4 is a non-limiting example. It is possible, without departing from the scope of the invention, to use other very diverse parameter profiles, provided that these parameters make it possible to limit the value of the speckel contrast of the image generated on the projection surface.

Claims (12)

Luminous device (1) for a motor vehicle, the luminous device comprising:

• a light module (10) comprising at least one light source (11) configured to emit a coherent light beam;
• a projection surface (20);

the light module being configured to project at least a portion of the coherent light emitted by the light source (11) towards the projection surface (20) in order to generate at least one image on said projection surface (20);
characterized in that the projection surface (20) has a texture configured to limit the speckel contrast of said at least one image. The light device (1) according to claim 1, wherein the light module (10) comprises several light sources (11), each configured to emit a coherent light beam, the coherent light beams having either the same color or colors different from each other, in particular the light module comprises three light sources (11) respectively emitting a coherent light beam of red color, green color and blue color. Lighting device (1) according to one of claims 1 or 2, wherein the lighting module (10) comprises at least one projection device (12) configured to receive at least part of the beam emitted by the light source (11) and to project it towards the projection surface (20) in order to generate said at least one image on said projection surface (20). Luminous device (1) according to claim 3, in which the projection device (12) comprises a system for scanning the beam emitted by the light source, and/or a matrix of micro-mirrors, and/or a static optical element. Luminous device (1) according to one of the preceding claims, in which the projection surface (20) has a first portion (20a) and a second portion (20b) separate from one another. Luminous device (1) according to one of the preceding claims, in which the projection surface has a texture formed of patterns (M), said patterns comprising peaks (P, P1, P2, P3) and hollows (C, C1, C2, C3) succeeding one another randomly. Luminous device (1) according to the preceding claim, in which the texture has an arithmetic mean roughness of between 4µm and 25µm inclusive, and advantageously between 9µm and 18µm inclusive. Luminous device (1) according to one of claims 6 or 7, in which the texture has an extreme difference between the peaks (P, P1, P2, P3) and the troughs (C, C1, C2, C3), between 25µm and 150µm, advantageously between 50µm and 120µm, in particular between 60µm and 100µm. Luminous device (1) according to one of claims 6 to 8, in which the texture has an average width of the patterns (M), between 150µm and 500µm, and advantageously between 225µm and 375µm. A light device (1) according to claim 5, or one of claims 6 to 9, in combination with claim 5, wherein the first portion (20a) has a first texture and the second portion (20b) has a second texture, the first texture and the second texture being different from each other. Luminous device (1) according to one of the preceding claims, in which the projection surface (20) comprises a fabric. A lighting device (1) according to any preceding claim, wherein the projection surface (20) constitutes part or all of a dashboard, seat, door or pillar such as those bordering the windshield of the vehicle.