FR3083330A1 - HEAD-UP DISPLAY DEVICE - Google Patents

Abstract

A head-up display device comprises an image generation unit (3) designed to emit at least a first light beam intended to be projected at the output of the head-up display device in the direction of a partially transparent plate, the 'image generation unit (3) comprising a backlight system, a first screen (26) and a second screen (27), the backlight system illuminating the first screen (26) so as to generate the first light beam and the backlighting system illuminating the second screen (27) so as to generate a second light beam. The head-up display device also includes a filter for limiting the angular spread (28) of the first light beam.

Description

Head-up display

Technical field to which the invention relates

The present invention relates generally to head-up display systems, in particular intended to equip vehicles.

It relates more particularly to a head-up display device.

Technological background

A head-up display device installed in a vehicle generally comprises an image generation unit emitting a light beam and at least one optical element intended to project this light beam towards a partially transparent blade. The light beam is then reflected by the partially transparent blade towards the eyes of the driver of the vehicle. The image generation unit generally includes a light source and a screen, the light source providing the backlight for the screen.

The design of future generations of head-up display devices envisages the exploitation of larger viewing angles, with greater projection distances in order in particular to take advantage of the characteristics of augmented reality.

Such head-up display devices require the use of suitable screens and a sufficient light intensity of the transmitted light beam. Using a single light source to backlight a large screen results in too high a light intensity, degrading the image seen by the driver.

A head-up display device has already been proposed comprising two projection units each associated with a light source. The use of two backlighting systems of the two screens then makes it possible to halve the light intensity of the light beams generated.

Each of the two screens diffuses light according to a light cone whose angular spread can be marked. In particular, the light cone from the screen can be analyzed as useful radiation and parasitic radiation. The useful radiation is located near the optical axis (low angular spread). The stray radiation is observed for a large angular spread.

However, the use of two adjacent screens results in the presence of an overlap zone between the useful radiation of one screen and the stray radiation of the other, thus degrading the image seen by the driver.

Object of the invention

In order to remedy the aforementioned drawback of the state of the art, the present invention proposes to improve the design of the head-up display device, in particular to limit the overlap area between the two screens.

More particularly, a head-up display device is proposed according to the invention comprising an image generation unit designed to emit at least a first light beam intended to be projected at the output of the head-up display device in the direction of a partially transparent strip, the image generation unit comprising a backlight system, a first screen and a second screen, the backlight system illuminating the first screen so as to generate the first light beam and the backlight system illuminating the second screen so as to generate a second light beam; the device is characterized in that it also comprises at least one filter for limiting the angular spreading of the first light beam.

Such a filter makes it possible to reduce the angular spread of the light cone formed after the screen with which it is associated. The stray radiation at the output of this screen is reduced. This filter then allows an overlap area limited to the useful radiation from the two screens. This allows the formation of a continuous image from the two generated half-images of the two light beams, limiting the degradations due to the interactions of the two light beams.

Other non-limiting and advantageous characteristics of the head-up display device according to the invention, taken individually or in any technically possible combination, are the following:

- The backlight system includes a first light source and a second light source;

a direction perpendicular to the surface of the first screen and a direction perpendicular to the surface of the second screen are substantially parallel;

- an optical axis of the light emitted by the first light source and an optical axis of the light emitted by the second light source are substantially parallel;

a direction perpendicular to the surface of the first screen and a direction perpendicular to the surface of the second screen form a first non-zero angle, for example less than 30 degrees;

the optical axis of the light emitted by the first light source and the optical axis of the light emitted by the second light source form a second non-zero angle;

- the limiting filter is characterized by a characteristic angle of light transmission;

- the characteristic angle is between 30 degrees and 60 degrees;

- the limitation filter comprises elements designed to absorb rays of the first light beam having angles greater than the characteristic angle;

- The limitation filter is placed at any position on the path of said first light beam between the first screen and the partially transparent blade;

- the limitation filter is located in contact with an output face of the first screen;

- the limitation filter is laminated on the output face of the first screen;

- the limitation filter is placed between the first light source and the first screen;

- the limitation filter is located in contact with an input face of the first screen;

- the limitation filter is laminated on the input face of the first screen;

- the head-up display device comprises a first limitation filter, positioned between the first screen and the partially transparent blade, and a second limitation filter, positioned between the second screen and the partially transparent blade;

Advantageously, the two screens each have a filter for limiting the angular spreading in order to homogenize the brightness of the complete reconstructed image.

Other non-limiting and advantageous characteristics of the head-up display device according to the invention, taken individually or in any technically possible combination, are the following:

- The first limitation filter is located in contact with an exit face of the first screen and / or the second limitation filter is located in contact with an exit face of the second screen;

the first limitation filter is laminated on the exit face of the first screen and / or the second limitation filter is laminated on the exit face of the second screen.

The invention also relates to a method for controlling an image generation unit comprising a backlight system, a first screen and a second screen, the backlight system illuminating the first screen so as to generate a first light beam and the backlight system illuminating the second screen so as to generate a second light beam, the method comprising a step of controlling the backlight system.

In this method, the first light beam and the second light beam may have an intersection so as to define an overlap zone. At the piloting stage, it can then be provided to carry out at least one processing of an image to be displayed by applying a predetermined coefficient to the luminance of the image to be displayed for at least one pixel of part of the overlap area.

It may also be provided in the piloting step to generate, alternately, on one of the two screens a predefined luminance of the image to be displayed then a luminance complementary to the predefined luminance of the image to be displayed, the another screen being piloted in opposition.

Detailed description of an example of realization

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

In the accompanying drawings:

- Figure 1 schematically shows an example of a head-up display device according to the invention;

- Figure 2 schematically shows a first example of image generation unit included in the head-up display device according to the invention;

- Figure 3 schematically shows a second example of image generation unit included in the head-up display device according to the invention;

- Figure 4 schematically shows an example of limitation filter according to the invention;

- Figure 5 shows a first example of driving an image generation unit according to the invention;

- Figure 6 shows a second example of driving an image generation unit according to the invention;

- Figure 7 shows a third example of driving an image generation unit according to the invention;

- Figure 8 schematically shows a side view of a third example of an image generation unit included in the head-up display device according to the invention; and

- Figure 9 schematically shows a fourth example of an image generation unit included in the head-up display device according to the invention.

FIG. 1 represents an example of a head-up display device 1 fitted to a vehicle, for example a motor vehicle.

The head-up display device 1 comprises a housing 10 and a protective window 12. The housing 10 makes it possible to protect the elements that the device 1 contains from various external deteriorations (dust, liquids, falling objects from the passenger compartment of the vehicle, etc.).

The protective window 12 allows the passage of a light beam coming from the interior of the housing 10 towards the exterior of said housing 10 while protecting the elements contained in the head-up display device 1. The protective window 12 closes an opening of the housing 10.

Alternatively, the protective window 12 is located inside the housing 10, on the path of the light beam.

In another variant, the protective window 12 can be omitted. The opening of the housing 10 is not closed in this case.

The head-up display device 1 comprises, inside the housing 10, an image generation unit 3, an optical conduit 5 and an optical system for projecting the light beam, such as a plane mirror 8.

The light beam which emerges from the image generation unit 3 is intended to be projected outside the head-up display device 1, in the direction of a partially transparent blade 2. The partially transparent blade 2 may correspond for example to the windshield of the vehicle in which said head-up display device 1 is installed. As a variant, the partially transparent blade 2 can be a dedicated blade, retractable or not, sometimes called a combiner. The partially transparent blade 2 is designed to partially reflect the light beam coming from the head-up display device 1 towards a user, often the driver of the vehicle.

The optical conduit 5 connects the image generation unit 3 and the optical system for projecting the light beam on the one hand and said optical projection system and the protective window 12 on the other hand.

The optical conduit 5 is shaped to surround the path of the light beam up to its projection outside the housing 10, in the direction of the partially transparent strip 2. Thus, the image generation unit 3 generates a light beam which is sent through the optical conduit 5 to the projection optical system. The projection optical system returns the light beam generated through the optical conduit 5 towards the partially transparent plate 2.

FIG. 2 schematically represents a first example of the image generation unit 3 included in the head-up display device 1.

The image generation unit 3 comprises a first light source 20, a second light source 21, a first diffuser 22, a second diffuser 23, a first reflector 24, a second reflector 25, a first screen 26, a second screen 27, a first filter for limiting the angular spread 28 and a second filter for limiting the angular spread 29.

The first light source 20 and the second light source 21 are placed at one end of the image generation unit 3, respectively upstream of the first screen 26 and the second screen 27. The first light source 20 and the second light source 21 are here constituted by light-emitting diodes (or "LED" for "Light Emitting Diode" according to the acronym commonly used). The first light source 20 and the second light source 21 are included in a backlight system for the first screen 26 and the second screen 27.

Alternatively, a single light source can be placed at the end of the image generation unit 3, upstream of the first screen 26 and the second screen 27.

The first diffuser 22 is placed between the first light source 20 and the first screen 26. The first diffuser 22 is adapted to diffuse the light after the first light source 20 into a light cone, in particular to allow homogeneous lighting of the first screen 26.

The second diffuser 23 is placed between the second light source and the second screen 27. The second diffuser 23 is adapted to diffuse the light after the second light source 21 into a light cone, in order to allow in particular a homogeneous illumination of the second screen 27 .

In practice, the first diffuser 22 and the second diffuser 23 can each be formed of a filter treated on the face opposite an inlet face of the first screen 26 or the second screen 27, said treatment producing a diffusion of the light. As shown in FIG. 2, the first diffuser 22 is glued to the entry face of the first screen 26. As a variant, the first diffuser can be placed at a distance from the entry face of the first screen 26. Similarly, the second diffuser 23 is glued to the entry face of the second screen 27. As a variant, the second diffuser 23 can be placed at a distance from the entry face of the second screen 27.

As shown in FIG. 2, the first reflector 24 constitutes a closed enclosure around the first light source 20, the first diffuser 22 and the entry face of the first screen 26. The first reflector 24 here extends between the first light source 20 and the first screen 26. The internal walls of the first reflector 24 are illuminated by the beam generated by the first light source 20. The surface treatment of the internal walls of the first reflector 24 allows a reflection of the light in direction of the first diffuser 22 and the first screen 26.

The first diffuser 22 and the first reflector 24 make it possible to homogenize the lighting at the entrance face of the first screen 26. The first light source 20, the first diffuser 22 and the first reflector 24 make it possible to backlight the first screen 26 in order to generate a first light beam. As a variant, the first diffuser 22 can be omitted and the diffusion characteristic can be included in the first reflector 24 by adapting the shape thereof.

Similarly, the second reflector 25 constitutes a closed enclosure around the second light source 21, the second diffuser 23 and the entry face of the second screen 27. The second reflector 25 here extends between the second source of light 21 and the second screen 27. The internal walls of the second reflector 25 are illuminated by the beam generated by the second light source 21. The surface treatment of the internal walls of the second reflector 25 allows light to be reflected towards the second diffuser 23 and second screen 27.

The second diffuser 23 and the second reflector 25 make it possible to homogenize the lighting at the level of the entry face of the second screen 27. The second light source 21, the second diffuser 23 and the second reflector 25 make it possible to backlight the second screen 27 in order to generate a second light beam. As a variant, the second diffuser 23 can be omitted and the diffusion characteristic can be included in the second reflector 25 by adapting the shape thereof.

The first screen 26 and the second screen 27 are for example liquid crystal screens (or "LCD" for "Liquid Crystal Display" according to the acronym commonly used).

As shown in FIG. 4, the first screen 26 and the second screen 27 comprises, for example after a layer of liquid crystals (not shown here), a color filter 30 and an output polarizer 35.

The color filter 30 of each screen 26, 27 comprises a color matrix 31, 32, 33 separated by opaque walls. These opaque walls are designed to block light.

The color matrix 31, 32, 33 comprises a plurality of colored elements 31, 32, 33, (here red colored elements 31, green colored elements 32 and blue colored elements 33). Alternatively, the colored elements 31, 32, 33 may have other colors (including the color white, or be undyed) distributed according to predetermined criteria, for example in a pseudo-random manner.

The colored elements 31, 32, 33 are for example conventionally manufactured and according to the well-known technologies of liquid crystal screens from a translucent resin allowing the absorption of only part of the light emitted by each light source 20 , 21.

The colored elements 31, 32, 33 are each adapted to let pass only the light included in a predetermined spectral width of the visible spectrum to generate a given color in the projected image.

Each colored element 31, 32, 33 extends along a first dimension lp. The first dimension l _p is of the order of 0.02 mm, typically between 0.01 mm and 0.05 mm. Alternatively, the first dimension l _p can be specific to each color of the colored element 31, 32, 33.

Each colored element 31, 32, 33 is separated from another colored element 31, 32, 33 by a second dimension e _p . The second dimension e _p is of the order of 0.005 mm, typically between 0.001 mm and 0.005 mm. The sum of the first dimension l _p and the second dimension e _p is called step 10 of the colored elements 31, 32, 33 of each screen 26, 27. The step of the colored elements 31, 32, 33 is of the order of 0.028 mm, typically between 0.01 mm and 0.06 mm.

As shown in Figure 2, the first screen 26 and the second screen 27 are arranged in parallel with each other. In practice, this means that a direction perpendicular to the surface of the first screen 26 is substantially parallel to a direction perpendicular to the surface of the second screen 27. The first screen 26 and the second screen 27 are juxtaposed in the generation unit. picture 3.

In the example described here and presented in FIGS. 2, 3 and 4, the first filter for limiting the angular spreading 28 (or first limiting filter 28 in the following) is placed at the output of the first screen 26. The first limitation filter 28 is positioned at any position between the first screen 26 and the partially transparent blade 2.

Similarly, the second angular spreading limitation filter 29 (or second limiting filter 29 in the following) is placed at the outlet of the second screen 27. The second limiting filter 29 is positioned at any position between the second screen 27 and the partially transparent blade 2

The limitation filters 28, 29 are adapted to reduce the angular spreading 30 of the light beam received by the limitation filters 28, 29 on the one hand the first light beam propagated after the first screen 26 and on the other hand the second beam light propagated after the second screen 27. Each limitation filter comprises elements designed to absorb rays from each light beam.

In practice, each limiting film 28, 29 can be a LCF (“Light Control Films”) type filter manufactured by 3M ™. As shown in FIG. 4, each limitation filter 28, 29 consists of a polycarbonate substrate 37 and a layer for limiting the angular spreading 39 (or limitation layer 39 in the following description).

As can be seen in FIG. 4, the limiting layer 39 is in practice made up of a structure comprising alternating translucent zones 42 and opaque zones 40, for example of the louver type (or "louver" according to the designation of origin Anglo-Saxon). The limiting layer 39 has a height h. The translucent zones 42 are for example composed of acrylic polymerizable resin. The opaque zones 40 are obtained by polymerization by ultraviolet rays (UV) of part of the translucent zones 42. The opaque zones 40 can also comprise black carbon. As a variant, the opaque zones 40 can be produced by screen printing without acrylic resin or by photolithography. In this case, an additional protective layer is necessary on each limitation filter 28, 29.

Each translucent zone 42 extends over a third dimension If, corresponding to the spacing of two opaque zones 40 consecutive.

Each opaque zone 40 extends over a fourth dimension and. The sum of the third dimension If and the fourth dimension ef is called the step of the limiting filter 28, 29. In practice, the step of the limiting filter 28, 29 is a multiple of the step of the colored elements 31, 32, 33 of each screen 26, 27, typically between 0.01 mm and 0.3 mm. This makes it possible, in the direction of the light passing through the first screen 26 and first limiting filter 28 assembly or the second screen 27 and second limiting filter 29 assembly, to match the opaque walls of each screen 26, 27 and the opaque areas 40 of the limiting layer 39 of each limiting filter 28, 29. In this case, the light transmission in a direction orthogonal to the plane of the limiting filter 28, 29 (also called nominal axis) is maximum.

As shown in FIG. 4, the alternation of translucent zones 42 and opaque zones 40 induces the definition of a characteristic angle a of light transmission for each limiting filter 28, 29. The characteristic angle can be defined as the maximum angle for which the incident light is transmitted through the first or second limiting filter 28,

29, up to 50% of the value along the direction orthogonal to the extension plane of the limiting filter 28, 29. In practice, as shown in FIG. 4, the characteristic angle a is determined using the height h of the limitation layer and the third dimension If characterizing the spacing of two consecutive opaque zones.

The presence of the opaque zones 40 on the path of the first and second light beam for large transmission angles makes it possible to control the light passing through the first or the second limitation filter 28, 29. In particular, the presence of the opaque zones 40 for angles greater than the characteristic angle a makes it possible to absorb the incident light, thus limiting the angular spreading of the first and of the second light beam. In practice, the characteristic angle a is conventionally between 30 degrees and 60 degrees, in a vertical or horizontal direction depending on the positioning of each limiting filter 28, 29.

For angles smaller than the characteristic angle a, in practice for angles close to the direction perpendicular to the surface of the first limitation filter 28, respectively of the second limitation filter 29, most of the incident light is transmitted by the first limiting filter 28, respectively the second limiting filter 29.

According to the example of FIGS. 2, 3 and 4, the first limiting filter 28, respectively the second limiting filter 29, is located in contact with an outlet face of the first screen 26, respectively of the second screen 27. The lateral extension of the first light beam is limited to the output of the first screen 26, which makes it possible to limit the area of the first limitation filter 28. Similarly, the extension of the second light beam is limited to the output of the second screen 27, which makes it possible to limit the area of the second limitation filter 29.

The first limiting filter 28, respectively the second limiting filter 29, can for example be laminated on the outlet face of the first screen 26, respectively of the second screen 27. The fixing of the first limiting filter 28, respectively of the second filter limitation 29, by bonding to the output face of the first screen 26, respectively of the second screen 27, allows a better efficiency in the reduction of the angular spreading because each limitation filter 28, 29 is placed directly at the source of image formation. In addition, the fixing of the first limitation filter 28, respectively of the second limitation filter 29, by bonding to the outlet face of the first screen 26, respectively of the second screen 27, makes it possible to be free from the diffusion induced by said first screen 26, respectively said second screen 27, itself.

The presence of the limitation filters 28, 29 makes it possible to reduce the cone of diffusion of the light beam after each screen to the only useful radiation of the light beam. The overlap zone is thus limited to the superposition of the useful radiation of the light beams generated and makes it possible to ensure the continuity of the two half-images projected on the partially transparent plate.

2.

Since the parasitic radiation at the output of each screen 26, 27 is reduced, they no longer cross the surface defined by the optical conduit 5. This solution makes it possible in particular to simplify the design of the optical conduit 5 since surface treatments of the optical conduit 5 in order to capture stray radiation is no longer necessary. Since the angular spread of the light beams is less, this solution also has the advantage of making the design of the optical conduit 5 more compact.

A method for controlling the image generation unit 3 is proposed to limit the overexposure of the overlap area.

The image generation unit 3 comprises a control module (not shown) of the previously introduced backlighting system. The method for controlling the image generation unit 3 includes a step for controlling the backlight system so as to limit the overexposure of the overlap area.

In these different configurations, we want to display a predefined image.

FIG. 5 represents a first example of driving an image generation unit 3. In this example, the driving step consists in driving the pixels of the first screen 26 and of the second screen 27 so as to generate a luminance of the image to be displayed non-uniformly at the level of the first screen 26 and of the second screen 27. This step makes it possible to introduce a lighting transition at the level of the pixels of each screen 26, 27.

In this configuration, the first screen 26 comprises a first part 50 having (for each pixel) a predefined luminance of the image to be displayed and a second part 52 having (for each pixel) a luminance equal to only a fraction of the predefined luminance , here equals half of the preset luminance. Similarly, the second screen 27 comprises a third part 54 presenting (for each pixel) the predefined luminance of the image to be displayed and a fourth part 56 presenting (for each pixel) a luminance equal to only a fraction of the predefined luminance , here equals half of the preset luminance.

In the example of FIG. 5, the second part 52 of the first screen 26 corresponds to the edge of the screen 26 closest to the screen 27 (it is delimited by a dotted line in FIG. 5). This second part 52 is for example illuminated so as to obtain lighting corresponding to half of that expected as explained above. Similarly, the fourth part 56 of the second screen 27 corresponds to the edge of the screen 27 closest to the screen 26 (it is delimited by a dotted line in FIG. 5). This fourth part 56 is lit similarly to the second part 52. The second part 52 of the screen 26 and the fourth part 56 of the screen 27 are therefore directly adjacent. The rest of the two screens 26, 27 is for example fully illuminated. The two half images are generated simultaneously. A transition in the opacity of two half-images makes it possible to limit the overlap area. By principle of superposition of the two generated half-images, the final projected image 100, obtained as the sum of the light beams generated, is therefore continuous and homogeneous.

FIG. 6 represents a second example of control of an image generation unit. In this example, the control is based on the principle of complementarity of the two half-images generated, one of the two screens projects all of the half-image associated with it, the other screen projects the complementary half-image making it possible to get the final picture.

In this configuration, the piloting step of the piloting method consists in driving the pixels of the first screen 26 and of the second screen 27 so as to generate (for each pixel) a luminance corresponding to the image displayed on the first screen 26 and (for each pixel) a non-uniform luminance at the second screen 27. As a variant, a luminance corresponding to the displayed image can be generated (for each pixel) at the second screen 27 and a non-uniform luminance at the first screen 26.

The second screen 27 then comprises a fifth part 66 having (for each pixel) a substantially zero luminance and a sixth part 64 having (for each pixel) a luminance corresponding to the image to be displayed. The fifth part 66 of the second screen 27 is directly adjacent to the first screen 26.

As shown in FIG. 6, the screen 26 is lit so as to observe maximum lighting over the entire screen 26. The screen 27, for its part, has the fifth part 66 delimited by a dotted line in the figure 6, the closest to screen 26, the lighting of which is maintained at zero. The rest of screen 27 has maximum illumination. By complementarity, the projected image is continuous and the overlap area is not overexposed. The configuration of FIG. 6 has the advantage of having maximum illumination of the two half-images on the two screens 26, 27 to display the final image 100.

FIG. 7 represents a third example of control of an image generation unit. The piloting step of the piloting process consists in generating (for each pixel), alternately, on one of the two screens 26, 27 a predefined luminance of the image to be displayed and then a luminance complementary to the predefined luminance. The other screen 26, 27 is piloted in opposition.

For example, this control can be based on the alternation on one of the two screens 26, 27 of a black image and / or the extinction of the associated light source and of the half-image when the lighting is maximum . The period of the alternation between the black image and the half-image is less than 0.1 seconds, so that, thanks to the retinal persistence, the user perceives an image of substantially constant brightness. The other screen 26, 27 is piloted in opposition, that is to say that it projects a complementary image when the other screen does not project an image.

According to another configuration, the first limitation filter 28, respectively the second limitation filter 29, can be positioned between the image generation unit 3 and the plane mirror 8, at a distance from the output face of the first screen 26 , respectively of the second screen 27.

As a variant, the first limitation filter 28 can be placed between the first light source 20 and the first screen 26. In particular, the first limitation filter 28 is then for example positioned between the first diffuser 22 and the inlet face of the first screen 26.

For example, the first limitation filter 28 can be located in contact with the entry face of the first screen 26. In particular, the first limitation filter 28 can be laminated on the entry face of the first screen 26. In this In this case, the first diffuser 22 can be fixed by gluing to the first limitation filter 28, itself fixed by gluing to the inlet face of the first screen 26.

Similarly, the second limitation filter 29 can be placed between the second light source 21 and the second screen 27. In particular, the second limitation filter 29 is then for example positioned between the second diffuser 23 and the face of second screen entry 27.

For example, the second limitation filter 29 can be located in contact with the entry face of the second screen 27. In particular, the second limitation filter 29 can be laminated on the entry face of the second screen 27. In this in this case, the second diffuser 23 can be fixed by gluing to the second limitation filter 29, itself fixed by gluing to the inlet face of the second screen 27.

As a variant, the limitation filters 28, 29 can constitute only one element and can be separated from the screens 26, 27. The assembly of the two limitation filters 28, 29 can for example be in the form of a single cut sheet which can be held opposite the screens 26, 27.

In another variant, the image generation unit 3 can comprise the first light source 20, the second light source 21, the first diffuser 22, the second diffuser 23, the first reflector 24, the second reflector 25, the first screen 26, the second screen 27 and a single filter for limiting the angular spread.

The single angular spread limitation filter can for example be positioned at the output of the first screen 26. The presence of this unique limitation filter on only one of the two screens makes it possible to partially reduce the stray radiation at the output of the unit image generation 3 (by reducing stray radiation from the first screen). The overlap area between the stray radiation from the first screen 26 and the useful radiation from the second screen 27 is thus limited.

In another variant, the single filter for limiting the angular spreading can be positioned at the output of the second screen.

In another variant, a filter of variable opacity can be introduced on one of the two screens or on the two screens in order to reduce the light intensity of the overlap area. The opacity zone is defined so as to present a reconstituted image of homogeneous light intensity.

FIG. 3 schematically represents a second example of the image generation unit 3 included in the head-up display device 1.

The elements common to Figures 2 and 3 bear the same references and will not be described again hereinafter.

According to the embodiment shown in FIG. 3, the first screen 26 and the second screen 27 are inclined relative to one another. In practice, this means that the direction perpendicular to the surface of the first screen 26 and the direction perpendicular to the surface of the second screen 27 form a normal angle β. In practice, the angle β is less than 30 degrees.

According to this embodiment, the first diffuser 22 and the first limitation filter 28 are inclined at the same angle as the first screen 26. Similarly, the second diffuser 23 and the second limitation filter 29 are inclined at the same angle as the second screen 27.

The embodiment presented in FIG. 3 is particularly advantageous since the useful radiation from the two screens propagates in an adjacent manner, thus limiting the overexposure of the overlap zone.

Alternatively, the first and second light sources 20, 21 may also form an angle between them. For example, the optical axis of the light emitted by the first light source 20 and the optical axis of the light emitted by the second light source 21 form a second non-zero angle β. This allows in particular to enlarge the angle of view while using screens of smaller sizes.

As a further variant, as shown in FIG. 8, each light source 20, 21 can be arranged so that the optical axis defined by the direction perpendicular to the light source 20, 21 is folded back into the associated reflector 24 , 25 in the direction of each screen 26, 27. In this case, the optical axes of the two light sources 20, 21 can therefore form a zero angle between them (while remaining in the same plane).

In another variant, according to the schematic representation of FIG. 9, the reflectors 24 and 25 can be grouped together in a single reflector 60.

Claims (13)

1. Head-up display device (1) comprising an image generation unit (3) designed to emit at least a first light beam intended to be projected at the output of the head-up display device towards a blade partially transparent (2), the image generation unit (3) comprising a backlight system, a first screen (26) and a second screen (27), the backlight system illuminating the first screen (26) generating the first light beam and the backlight system illuminating the second screen (27) so as to generate a second light beam, characterized in that it also comprises at least one filter for limiting the angular spreading (28) of the first light beam. 2. A head-up display device (1) according to claim 1, wherein the backlight system comprises a first light source (20) and a second light source (21). 3. A head-up display device (1) according to claim 1 or 2, in which a direction perpendicular to the surface of the first screen (26) and a direction perpendicular to the surface of the second screen (27) are substantially parallel. 4. Head-up display device (1) according to claim 1 or 2, in which a direction perpendicular to the surface of the first screen (26) and a direction perpendicular to the surface of the second screen (27) form a first non-angle. -null (β). 5. A head-up display device (1) according to any one of claims 1 to 4, in which the limiting filter (28) is characterized by a characteristic angle (a) of light transmission. 6. Head-up display device (1) according to claim 5, wherein the characteristic angle (a) is between 30 degrees and 60 degrees. 7. A head-up display device (1) according to claim 5, in which the limitation filter (28) comprises elements designed to absorb rays of the first light beam having angles greater than the characteristic angle (a). 8. A head-up display device (1) according to any one of claims 1 to 7, comprising a first limitation filter (28), positioned between the first screen (26) and the partially transparent blade (2), and a second limitation filter (29), positioned between the second screen (27) and the partially transparent blade (2). 9. Head-up display device (1) according to claim 8, in which the first limitation filter (28) is located in contact with an outlet face of the first screen (26) and in which the second limitation filter (29) is located in contact with an exit face of the second screen (27). 10. Head-up display device (1) according to claim 8 or 9, in which the first limitation filter (28) is laminated on the outlet face of the first screen (26) and in which the second limitation filter ( 29) is laminated on the exit face of the second screen (27). 11. Method for controlling an image generation unit (3) comprising a backlight system, a first screen (26) and a second screen (27), the backlight system illuminating the first screen (26) so generating a first light beam and the backlight system illuminating the second screen (27) so as to generate a second light beam, said method comprising a step of controlling the backlight system. 12. Method for controlling an image generation unit (3) according to claim 11, in which the first light beam and the second light beam have an intersection so as to define an overlap zone, the piloting step consisting in carrying out at least one processing of an image to be displayed by applying a predetermined coefficient to the luminance of the image to be displayed for at least one pixel of a part of the overlap area. 13. Method for controlling an image generation unit (3) according to the 5 claim 11, wherein the piloting step consists of alternately generating, on one of the two screens (26, 27) a predefined luminance of the image to be displayed then a luminance complementary to the predefined luminance of the image to be displayed, the other screen (26, 27) being driven in opposition.