Projection device comprising a coherent light source and a textured projection surface

Abstract

A 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 light module (10) including at least one light source (11) configured to emit a beam of coherent light, and a projection surface (20). The light module (10) is 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). The projection surface (20) has a texture configured to limit the speckel contrast of said at least one image. Figure 1

Description

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

[0001] The present invention relates to a lighting device for a motor vehicle, comprising in particular a coherent light source. Prior art

[0002] Lighting devices are fitted to motor vehicles, particularly the vehicle interior. 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 context, the use of laser sources offers advantages because laser sources emit a directional beam. This characteristic allows for high luminous efficiency of the device, compared to light sources such as Lambertian emission light-emitting diodes (LEDs), even in compact devices.Indeed, most of the light from a laser source can be easily used, whereas the light emission from a Lambertian source extends over a half-space, so a significant portion of the light rays emitted in a direction at a large angle to the general direction of emission cannot be easily recovered and is therefore generally lost.

[0003] 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 luminous image. This phenomenon is well known to those skilled in the art under the English term "speckle," and in French as "laser granularity." Speckel corresponds to random interference that generates luminous spots in certain areas and in certain directions of observation, which are also random. This creates a speckled image, an unpleasant flickering effect when observing the surface with the projected image on it, particularly when moving relative to that surface. Furthermore, with a multicolored light beam, chromatic aberration effects appear, because each wavelength generates its own speckel, and these speckel are offset from one another.

[0004] 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. Summary of the invention

[0005] The object of the invention is to address at least in part the problems mentioned above, and in particular to resolve, or at least limit, the scintillation effect due to speckel.

[0006] In this respect, the object 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 beam of light; • 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.

[0007] Coherent light is understood to mean light whose coherence length is greater than 250 times the wavelength, in particular about 500 times the wavelength. For example, for a peak wavelength of 520 nm, and a spectrum having a full width at half maximum (FWHM) of µm, the coherence length is about 250 pm.

[0008] Advantageously the light source comprises a laser or a laser diode.

[0009] The expression "limit speckel contrast" means 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. Speckel contrast corresponds to the standard deviation of luminance divided by the average luminance over the entire surface illuminated by coherent light.

[0010] The image is a luminous image, intended to be seen by an observer, particularly one present in the passenger compartment of the vehicle. The projected image or images may be static, that is to say, the image obtained on the projection surface is fixed, or dynamic, the image obtained on the projection surface then evolving over time.

[0011] Advantageously, the lighting device has one or more of the following characteristics, taken alone or in combination.

[0012] The light module comprises several light sources, each configured to emit a coherent beam of light.

[0013] Coherent light beams have the same color.

[0014] Coherent light beams exhibit different colors from one another others.

[0015] The light module comprises three light sources emitting respectively a coherent beam of light of red, green and blue color.

[0016] The light module includes at least one projection device configured to receive at least a part 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.

[0017] The projection device includes a system for scanning the beam emitted by the light source.

[0018] The scanning system includes a microelectromechanical system (MEMS, for "microelectromechanical systems" in English).

[0019] The microelectromechanical system includes a micro-mirror. The micro-mirror receives at least a portion of the beam emitted by at least one light source.

[0020] The projection device comprises a micro-mirror array. The micro-mirror array receives at least a portion of the beam emitted by at least one light source.

[0021] The light module includes a micro-mirror and / or micro-mirror matrix control circuit, 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.

[0022] The projection device includes a static optical element. The static optical element receives at least a portion of the beam emitted by at least one light source.

[0023] The static optical element comprises one or more reflectors.

[0024] The static optical element comprises one or more lenses.

[0025] The static optical element comprises a combination of one or more reflectors and one or more lenses.

[0026] Several light sources are associated with the same projection device.

[0027] Each light source is associated respectively with a projection device which is unique to him.

[0028] Some light sources are associated with the same projection device, and other light sources are each associated with their own projection device.

[0029] The light beam emitted by a light source is divided into several branches, for example by using a semi-reflective mirror, or several semi-reflective mirrors in cascade.

[0030] Each branch is associated respectively with its own projection device.

[0031] The projection surface has a first portion and a second portion disjoint from each other.

[0032] The projection surface has a texture formed of patterns, said patterns comprising peaks and hollows following one another randomly.

[0033] The texture has an arithmetic mean roughness of between 4pm and 25pm inclusive, and advantageously between 9pm and 18pm inclusive.

[0034] The texture exhibits an extreme gap between peaks and troughs, between 25pm and 150pm, advantageously between 50pm and 120pm, particularly between 60pm and 100pm.

[0035] The texture has an average pattern width of between 150 µm and 500 µm, and advantageously between 225 µm and 375 µm.

[0036] 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.

[0037] Which projection surface comprises a fabric.

[0038] The fabric comprises natural fibers. By natural fiber is understood to mean a vegetable or animal fiber, for example cotton, wool, hemp, linen, jute or silk

[0039] The fabric comprises artificial or synthetic fibers. An artificial fiber is understood to be a fiber obtained from plant pulp. A synthetic fiber is understood to be a fiber obtained by the synthesis of chemical compounds. Artificial or synthetic fibers are, for example, based on polyamide, such as nylon, viscose, polyolefin, vinyl polyether siloxane, polyester, or acrylic.

[0040] The fabric comprises a mixture of two or more fibers.

[0041] The fabric is a textile, comprising a warp and a weft, a velvet or a felt.

[0042] The projection surface constitutes part or all of a dashboard, a seat, a door, or a pillar such as those bordering the windshield of the vehicle. See figures for details.

[0043] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and the illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0044] [Fig-1] shows a general view of a lighting device according to the invention;

[0045] [Fig.2] shows a detailed schematic view of the light module, according the invention;

[0046] [Fig.3] shows a detailed schematic view of a projection surface according to the invention;

[0047] [Fig.4] shows a curve of a roughness profile of a projection surface according to the invention. Detailed description

[0048] It should first be noted that while the figures illustrate the invention in detail for its implementation, these figures can of course also serve to further define the invention, if necessary. It should also be noted that these figures only show examples of embodiments of the invention.

[0049] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0050] In the figures, the elements common to several figures retain the same reference.

[0051] 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 illustrated example, the projection surface 20 has a first portion 20a and a second portion 20b that are separate from each other. However, the projection surface can also be a continuous surface, or it can have more than two separate portions. This allows it to adapt to the internal configuration of the vehicle's passenger compartment.

[0052] The light module 10 emits light towards the projection surface 20. This allows an image to be generated on said projection surface 20. This light is schematically represented by light rays R2. The light emitted by the light module 10 is coherent.

[0053] 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 significant speckeling, leading to an unpleasant flickering effect when viewing the projection surface 20 illuminated by the light module 10. The texture of the projection surface 20 according to the invention reduces this flickering effect, and thus improves the perception of said image.

[0054] 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.

[0055] According to a non-limiting embodiment, the projection surface 20 has a unique texture over its entirety, regardless of whether it consists of a continuous surface or one comprising several disjoint 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, portion 20a may have a first texture and portion 20b may have a second texture, the first and second textures being different from each other.In addition, the first portion 20a may have several zones, each zone having a different texture from the other zones and / or the second portion 20b may have several zones, each zone having a different texture from the other zones, and all textures being configured to limit the speckel contrast value, as indicated above.

[0056] 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 a pillar such as those bordering the windshield.

[0057] The image generated on the projection surface 20 can, for example, be information for the vehicle's occupants, such as the vehicle's speed or the presence of nearby obstacles, information from a navigation system, or from media such as a radio or music player. It can also be a welcome message when an occupant enters the vehicle, or a farewell message when they leave the vehicle.

[0058] Figure 2 shows a detailed schematic view of the light module 10, according to a This embodiment comprises at least one light source 11 configured to emit a coherent beam of light, represented by the RI rays, 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 beam of light, the coherent light beams having either the same color or different colors 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 contain almost all visible colors. Advantageously, the wavelengths for red are between 630 and 655nm, particularly between 635 and 645nm, the wavelengths for green are between 510 and 530nm, particularly between 515 and 525nm, and the wavelengths for blue are between 440 and 470nm. particularly between 445 and 455nm. These wavelength ranges, especially the narrower ones, allow us to maximize the number of colors that can be projected.

[0059] According to a non-limiting embodiment, the projection device 12 includes a system for scanning the beam of light emitted by at least one light source 11. This scanning system may, for example, include a microelectromechanical system (MEMS), comprising a micro-mirror receiving at least a part of the beam emitted by at least one light source 11.

[0060] According to a non-limiting embodiment, the projection device 12 comprises a micromirror matrix (DMD, for "digital micromirror device" in English) receiving at least a part of the beam emitted by at least one light source 11.

[0061] 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 at least one light source 11. In a non-limiting example, the static optical element comprises one or more reflectors. In another non-limiting example, the static optical element comprises one or more lenses. In yet another non-limiting example, the static optical element comprises a combination of one or more reflectors and one or more lenses.

[0062] When several light sources 11 are used, they can be connected to the same projection device 12. This reduces the size of the light module. Alternatively, each light source 11 can be connected to its own projection device 12. This configuration allows a different image to be generated on the projection surface 20 for each light source 11. The possible variety of images is thus increased. It is also possible to have some light sources connected to the same projection device in the light module 10, and other light sources each connected to its own projection device. This allows for both a wide variety of images and a controlled size.

[0063] It is also possible to divide the light beam emitted by a light source 11 into several branches, for example by using a semi-reflective mirror, or several semi-reflective mirrors in cascade, and to associate each branch with its own projection device. This makes it possible to generate a wide variety of images with a single light source 11. When the light module 10 has 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.

[0064] The projected image or images can be static, meaning that the image obtained on the projection surface 20 is fixed, or dynamic, meaning that the image obtained on the projection surface 20 evolves over time. The light module includes, for this purpose, a control circuit (not shown) for the micromirror or the micromirror array, associated with a memory (not shown) containing the images to be generated, and configured to send instructions to said micromirror or micromirror array so that the desired image is generated. The static optical element, when used alone, only generates a fixed image.

[0065] Figure 3 shows a detailed view of the projection surface according to the invention. For the sake of clarity, the dimensions of the surface texture patterns have been exaggerated, and these patterns have been represented schematically in a relatively identical manner. In reality, the patterns M constituting the surface texture comprise randomly occurring peaks P and troughs C, with varying heights, depths, and spacing, as can be seen in Figure 4. Thus, the surface has a rough appearance.

[0066] Advantageously, the texture has one or more of the following parameters.

[0067] According to a non-limiting embodiment, the texture has an arithmetic mean roughness, known by the abbreviation Ra, ranging from 4 pm to 25 pm inclusive, and advantageously from 9 pm to 18 pm inclusive. The arithmetic mean roughness is the average of the absolute values ​​of the deviations of the irregularities from the average surface level.

[0068] According to a non-limiting embodiment, the texture has an extreme difference between peaks and troughs, known by the abbreviation Rz, ranging from 25 pm to 150 pm, advantageously from 50 pm to 120 pm, and particularly from 60 pm to 100 pm. 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.

[0069] According to a non-limiting embodiment, the texture has an average pattern width M, known as RSm, of between 150 pm and 500 pm, and advantageously between 225 pm and 375 pm. This value corresponds to the average width of the main patterns. Any peak, or trough, whose height, or depth, is less than 10% of the maximum height, or maximum depth, is considered to be part of a larger pattern and is therefore not taken into account when calculating said average.

[0070] The texture properties exhibit rotational symmetry. In other words, regardless of the direction considered, the surface properties are identical. This simplifies the fabrication of the device because it is not necessary to worry about of the orientation of the fabric surface when cutting out the piece intended to be used to form the projection surface.

[0071] The inventors found that, surprisingly, fabrics were particularly well-suited to solving the speckled problem. Fabrics are understood to mean textile materials. They may include natural fibers, whether plant or animal, such as cotton, wool, hemp, linen, jute, or silk, or artificial or synthetic fibers, such as polyamide-based fibers like nylon, viscose, polyolefin, vinyl polyether siloxane, polyester, or acrylic. They may also include a blend of two or more of these fibers. A fabric may, in particular, be a woven material, comprising a warp and weft, a velvet, or a felt.

[0072] The projection surface 20 is advantageously light-colored to ensure good reflectance. This color can be, for example, white, gray, beige, or any other color, provided 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 for very good image visibility.

[0073] Figure 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 taken on a segment 0.8 mm long taken at random from said projection surface. The height of the surface, represented on the ordinate in a scale of pm, 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.

[0074] The profile exhibits a succession of peaks and troughs of random heights and spacing around an average surface level on this segment, this average level being located vertically at 0. The highest peak PI is at a height of approximately 50 pm. The lowest trough Cl is located at approximately -70 pm. The peaks and troughs can be relatively flared, like peak P3 and trough C2, or rather pointed, like peak P2 and trough C3. Furthermore, it can be seen that the profile of pattern M, between the two dashed lines, is not smooth, but rather exhibits a succession of small secondary peaks PS and secondary troughs CS. Due to their small size, these secondary peaks and troughs do not form patterns in themselves but are included within pattern M. On this profile, the Ra value is approximately 16 pm.

[0075] Thanks to this random profile, the perception of speckel is greatly limited and the image visible on the projection surface has a pleasant appearance.

[0076] The profile shown in [Fig. 4] is a non-limiting example. It is possible, without departing from the scope of the invention, to use other profiles with very diverse parameters, therefore that these parameters allow limiting the value of the speckel contrast of the image generated on the projection surface.

Claims

Demands

1. A lighting device (1) for a motor vehicle, the lighting device comprising: • a lighting module (10) including at least one light source (11) configured to emit a coherent beam of light; • a projection surface (20); the lighting 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, wherein the projection surface (20) comprises a fabric.

2. A light device (1) according to claim 1, wherein the light module (10) comprises several light sources (11), each configured to emit a coherent beam of light, the coherent beams of light having either the same color or different colors from each other, in particular the light module comprises three light sources (11) emitting respectively a coherent beam of light of red color, green color and blue color.

3. Light device (1) according to any one of claims 1 or 2, wherein the light module (10) comprises at least one projection device (12) configured to receive at least a portion 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).

4. Light device (1) according to claim 3, wherein the projection device (12) comprises a beam scanning system for the beam emitted by the light source, and / or a micromirror array, and / or a static optical element.

5. A lighting device (1) according to any one of the preceding claims, wherein the projection surface (20) has a first portion (20a) and a second portion (20b) disjoint from each other.

6. A light device (1) according to any one of the preceding claims, wherein the projection surface has a texture formed of patterns (M), said patterns comprising peaks (P, PI, P2, P3) and hollows (C, Cl, C2, C3) following one another randomly.

7. A light device (1) according to the preceding claim, wherein the texture has an arithmetic mean roughness of between 4pm and 25pm inclusive, and advantageously between 9pm and 18pm inclusive.

8. Light device (1) according to any one of claims 6 or 7, wherein the texture has an extreme gap between the peaks (P, PI, P2, P3) and the troughs (C, Cl, C2, C3), between 25pm and 150pm, advantageously between 50pm and 120pm, in particular between 60pm and 100pm.

9. A lighting device (1) according to any one of claims 6 to 8, wherein the texture has an average pattern width (M) of between 150 pm and 500 pm, and advantageously between 225 pm and 375 pm.

10. A light device (1) according to claim 5, or any 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.

11. A lighting device (1) according to any one of the preceding claims, wherein the projection surface (20) constitutes part or all of a dashboard, a seat, a door or a pillar such as those bordering the windshield of the vehicle.

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