FR3094098A1 - Head-up display with curved screen - Google Patents

Abstract

The invention relates to a head-up display (1) comprising: - a screen (22) adapted to generate a light beam via an output face (22B), and, - an image return device (30) adapted to receive the light beam generated by the backlit screen and send it towards a partially transparent slide (80). According to the invention, the exit face of the screen has a non-zero radius of curvature. Abstract figure: Figure 1

Description

Head-up display with curved screen

Technical field to which the invention relates

The present invention generally relates to the field of head-up displays.

It relates more particularly to a head-up display comprising:

- a screen adapted to generate a light beam via an exit face, and,

- an image transmission device adapted to receive the light beam generated by the backlit screen and to send it in the direction of a partially transparent blade.

The invention finds a particularly advantageous application as a head-up display in a motor vehicle.

Technology background

For the driver of a motor vehicle, it is particularly comfortable to view information relating to the operation of the vehicle, the state of the traffic, or the like, without having to look away from the road facing the vehicle.

It is known for this purpose to equip a motor vehicle with a so-called “head-up display” display such as that described in the introduction.

In such a head-up display, the backlit screen generates a light beam representing a virtual image comprising the information to be displayed and the image-returning device returns the light beam generated in the direction of the partially transparent strip, located in front of the driver, in order to visually superimpose the virtual image represented by the light beam on the environment facing the vehicle.

For the comfort of the driver, the virtual images thus created in front of him should be of good quality, and in particular should have as few defects as possible.

To do this, it is known to anticipate the defects of the virtual image seen by the driver, such as deformations or aliasing, and to digitally compensate for these defects by calculating contrary defects and by generating at the level of the screen a light beam creating a virtual image with opposite defects.

It is known in particular that the virtual image seen by the driver is deformed by the curvature of the partially transparent strip onto which it is sent by the image-returning device. This phenomenon is better known as “warping” in the English language. To avoid this phenomenon, the final distortion is anticipated and digitally corrected during the generation of the image by the screen, so that the screen initially generates a light beam forming an inversely distorted image.

It is also known that the virtual image seen by the driver has aliasing, i.e. the driver sees the virtual image as pixelated. To avoid this phenomenon, also known as "aliasing" in English, it is known to digitally erase the pixelation, for example by imposing greater lighting on the pixels of the screen that are fully lit, and by darkening the pixels of the screen partially illuminated only.

These two known digital corrections require heavy calculations for the head-up display. In addition, they do not make it possible to correct the sharpness of the virtual image seen by the driver.

However, the virtual image seen by the driver is generally blurred on the edges, because, to prevent the parasitic rays illuminating an output face of the screen from being reflected in the direction of the partially transparent blade and being superimposed on the virtual image, the screen is preferably not positioned in a plane perpendicular to the optical axis of the image-reflecting device.

Object of the invention

In order to remedy the aforementioned drawback of the state of the art, the present invention proposes a head-up display which improves the sharpness of the virtual image seen by the driver.

More particularly, according to the invention, a display is proposed as defined in the introduction, in which the output face of the screen has a non-zero radius of curvature.

Thus, the screen corrects and physically compensates for blurring issues associated with screen tilt and/or curvature of other optical elements of the head-up display.

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

- the screen is backlit, on an entry face, by a light source;

- the concavity of the exit face of the screen is turned towards the image-returning device;

- the concavity of the exit face of the screen faces away from the image-reflecting device, i.e. towards the light source;

- the exit face of said screen has a first radius of curvature along a first main direction of the screen, and a second radius of curvature along a second main direction of the screen, perpendicular to said first main direction;

- the exit face of said screen has a first radius of curvature in any direction with respect to a first main direction of the screen, and a second radius of curvature in any second direction with respect to a second main direction of the screen, the two directions of curvature being able to present any cone angle between them comprised for example between -45° and +45°;

- the radius of curvature of the exit face of the screen is determined according to the radius of curvature of at least one of the optical elements of the image-reflecting device and/or the radius of curvature of the partially transparent blade;

- the radius of curvature of the output face of the screen is such that each point of said output face is equidistant from an object focal plane associated with said screen;

- the radius of curvature of the exit face of the screen is between 10 cm and 50 cm;

- a plane tangent to the exit face of the screen, at the level of the intersection between said screen and an optical axis associated with the image-returning device, is inclined at a non-zero angle with respect to a perpendicular plane to said optical axis;

- the screen comprises a plurality of pixels, all the pixels of the screen having an identical size;

- provision is made for the image-returning device to include at least one curved magnifying mirror;

- the absolute value of the ratio between the radius of curvature of the exit face of the screen and the radius of curvature of the magnifying mirror is between 0.5 and 2;

- the magnifying mirror is interposed between the screen and the partially transparent blade on the path of the light beam;

- The partially transparent blade is formed by a separate blade located between a windshield of the vehicle fitted with said head-up display and the eyes of the driver of this vehicle;

- The partially transparent blade is formed by a windshield of the vehicle fitted with said head-up display.

Detailed description of an example of realization

The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

On the attached drawings:

is a schematic representation of a first embodiment of the head-up display according to the invention in a motor vehicle;

is a schematic representation of a second embodiment of the head-up display according to the invention in a motor vehicle; and,

is a schematic representation illustrating the formation of the virtual image by the screen of such a head-up display.

It will also be noted that the identical or similar elements of the different embodiments of the invention shown in the different figures will, as far as possible, be referenced by the same reference signs and will not be described each time.

FIG. 1 schematically represents the main elements of a head-up display 1 intended to equip a vehicle, for example a motor vehicle, a train, a boat such as a barge, a tram, a bus or an air vehicle.

In the remainder of the description, a head-up display 1 fitted to a motor vehicle will be described more particularly.

The head-up display 1 more particularly comprises an image generation unit 20, comprising a backlighting device 21 and a screen 22 illuminated by this backlighting device 21. The screen 22 is for example a liquid crystal screen (or LCD for "Liquid Crystal Display") with thin film transistors (or TFT for "Thin Film Transistor"), backlit by a light source 110 comprising for example LEDs. The screen 22 can then be built on rigid but curved glass plates.

More precisely, the backlighting device 21 is here a light source backlighting the screen 22, that is to say illuminating said screen 22 on an input face 22A of the latter.

The screen 22 comprises a plurality of pixels (arranged in the form of a matrix of pixels), each capable of transmitting more or less the light with which they are backlit. All the pixels of the screen 22 have here an identical size.

As a variant, a technology can be used in which the screen comprises light-emitting pixels, such as in OLED (for " Organic Light-Emitting Diode ") or AMOLED (for " Active-Matrix Organic Light-Emitting Diode ") technology. . This technology is for example based on deposition in the evaporation and encapsulation phase in thin layers. This technology allows the production of curved screens.

The image generation unit 20 is thus adapted to generate, via the output face 22B of the screen 22, a light beam in the direction of an image return device 30 also included in the head-up display 1.

The image deflecting device 30 is adapted to send the light beam generated by the image generation unit 20, in the direction of a partially transparent plate 80 in order, with the partially transparent plate 80, to form a virtual image IMV in a driver's field of vision. The virtual image IMV is thus formed according to the composition of the light beam generated at the level of the image generation unit 20, and more precisely at the level of the screen 22.

It is thus possible to display information in the field of vision of the driver of the vehicle without the driver having to look away from the road.

As shown in Figure 1, the image deflecting device 30 here comprises a plane folding mirror 31 .

As shown in Figures 2 and 3, the image-reflecting device 30 may also comprise, in addition to the plane folding mirror 31, a curved magnifying mirror 32 also called a magnification mirror, for example whose reflecting surface has the form of a polynomial of several degrees. According to a variant not shown, a curved magnifying mirror could replace the plane folding mirror.

Such a magnifying mirror 32 makes it possible to display in the driver's field of vision a virtual image IMV enlarged with respect to that generated by the light beam in the image generating device 20, so that said virtual image IMV is large enough to be clearly visible to the driver at a certain distance. In particular, the greater the magnification mirror 32 has a large radius of curvature, the closer the final IMV virtual image is to the image generated by the screen 22, that is to say it is sharp. closer to the driver.

According to a first variant represented in FIG. 2, it is possible to provide for the image-returning device 30 to comprise a first plane folding mirror 31, followed by a curved magnifying mirror 32, in this order, between the screen 22 and the partially transparent blade 80.

According to a second variant not shown, it is conceivable that the image return device comprises a first curved magnification mirror followed by a second curved magnification mirror, each with their own radius of curvature (thus their own magnification), for return the light beam generated by the screen towards the partially transparent blade.

As a further variant, the image-returning device could comprise other mirrors and/or other optical elements, in addition to or replacing those previously described.

In general, the optical axis X of the image returning device 30 is defined as the axis connecting the center of the light source with the center of the first mirror of the image returning device 30 encountered by the ray optics from said light source. Here, the optical axis X of the image-reflecting device 30 passes through the center of the folding mirror 31 and the center of the light source.

The output face 22B of the screen 22 is arranged in an inclined manner with respect to this optical axis, that is to say that a tangent plane T to the output face 22B of the screen 22, at the level of the intersection between said exit face 22B of screen 22 and the optical axis X associated with the image-reflecting device 30, is inclined by a non-zero angle A with respect to a plane P perpendicular to said optical axis ( see figure 3).

Thus, any stray rays inadvertently illuminating the screen 22 via its exit face 22B are not reflected by the exit face 22B of the screen 22 in the direction of the image-reflecting device 30, so that these do not reach the partially transparent blade 80 and do not deteriorate the quality of the virtual image IMV seen by the driver.

As shown in Figure 1, the partially transparent blade 80 is here formed by a combiner, that is to say a thin plate, partially transparent, arranged between the windshield 2 of the vehicle and the eyes 3 of the driver. The partially transparent blade 80 is therefore a separate blade from the windshield 2.

As a variant, provision can be made, as shown in FIG. 2, for the image-returning device 30 to directly project the light beam generated by the image-generating unit 20 in the direction of the windshield 2 of the vehicle, the aforementioned combiner being then omitted. In this case, the partially transparent blade 80 is formed by the windshield 2 of the vehicle itself.

In addition to being partially transparent, this blade is partially reflective, and thus makes it possible to return towards the driver at least part of the light beam generated by the image generation unit 20, as shown diagrammatically in FIG. 1.

The virtual image IMV, formed in the driver's field of vision by the folding mirror 31, optionally the magnifying mirror 32, and the partially transparent blade 80, is located opposite the driver with respect to the partially transparent blade 80, for example a few meters in front of the partially transparent blade 80, outside the vehicle (see Figures 1 and 2).

Remarkably, the exit face 22B of the screen 22 has, according to the invention, a non-zero radius of curvature. The screen 22 can in particular be concave (see FIGS. 1 or 2) or convex (see FIG. 3), that is to say that the concavity of the screen 22 is turned towards the image-reflecting device 30 ( Figures 1 or 2) or, on the contrary, to the backlight device 21 (Figure 3).

It is possible in particular to provide that all the points of the screen 22, in particular all the pixels, are equidistant from an image focal plane F associated with said screen 22 (see FIG. 3), and this while the exit face 22B of the screen 22 is not positioned orthogonally to the optical axis X associated with the image return device 30.

This makes it possible to prevent the virtual image IMV seen by the driver from being blurred, in particular on the edges of said image. Indeed, as shown in Figure 3, in which the partially transparent blade is omitted, the fact that the output face 22B of the screen 22 is curved allows all the pixels of the screen 22 to be equidistant from the focal plane. image F while allowing said screen 22 to be inclined with respect to the optical axis X. This configuration advantageously straightens the virtual image IMV generated by the screen 22 so that it is entirely contained in a so-called "sharp" zone Z1 and does not overflow into adjacent so-called “fuzzy” zones Z2.

In addition, the curved configuration of the output face 22B of the screen 22 makes it possible to anticipate and compensate for the deformations of the virtual image IMV generated by the curvatures of the other optical elements of the head-up display 1, for example by the partially transparent plate 80 or by the magnifying mirror 32.

Here, as shown in Figure 1, the entry face 22A and the exit face 22B of the screen 22 are both curved.

Advantageously, the radius of curvature of the exit face 22B of the screen 22 is determined as a function of the radius of curvature of at least one of the other optical elements of the head-up display 1, in particular of the radius of curvature of at least one of the optical elements 31 of the image-returning device 30 (magnifying mirror 32 in particular) and/or of the radius of curvature of the partially transparent plate 80 (whether it is a combiner or directly of the windshield).

Provision can be made, for example, for the radius of curvature of the exit face 22B of the screen 22 to be in a ratio comprised in the interval [-2; -0.5] or in the interval [0.5; 2] with respect to the radius of curvature of the magnifying mirror 32, that is to say that the absolute value of the ratio between the radius of curvature of the exit face 22B of the screen 22 and the radius of curvature of the mirror magnification 32 is between 0.5 and 2.

More precisely, the screen 22 extends along two main directions perpendicular to each other. The first main direction is a generally horizontal direction when the head-up display 1 is in place in the vehicle, for example a direction parallel to the ground, while the second main direction is a direction comprising a vertical component when the head-up display 1 is in place in the vehicle, that is to say a direction perpendicular to the ground.

According to a first embodiment of the screen, the output face of the screen is curved along a straight line, called the "axis of greatest deflection", which corresponds to the maximum deformation of the screen with respect to a plane formed by two edges of the screen parallel to this axis of greatest deflection. Thus, when the axis of greatest deflection is vertical, the maximum deformation of the screen is measured with respect to the plane formed by the edges of the screen parallel to the aforementioned second main direction (including the vertical component), while when the axis of greatest deflection is horizontal, the maximum deformation is measured relative to the plane formed by the edges of the screen parallel to the aforementioned first main direction (horizontal). The largest arrow axis is not necessarily a center axis of the screen.

More generally, according to another embodiment of the screen 22, the axis of greatest deflection defining the curvature of the output face of the screen can be oriented along any axis, comprising a component along the first principal direction and a component along the second principal direction.

In other words, advantageously, the output face 22B of the screen then has, on the one hand, a first radius of curvature along the first main direction of the screen 22, that is to say that the edges of the exit face 22B of the screen 22 extending mainly along this first main direction as well as all the lines parallel to these edges have the said first radius of curvature, and, on the other hand, a second radius of curvature along the second main direction of the screen 22, that is to say that the edges of the exit face 22B of the screen 22 extending mainly along this second main direction as well as all the lines parallel to these edges present said second radius of curvature. Preferably, the two radii of curvature are different.

More precisely, the first and the second radii of curvature of the output face 22B of the screen are each between 10 cm and 50 cm.

Preferably, the first radius of curvature is greater than the second radius of curvature.

The first radius of curvature along the first direction of the screen 22 (horizontal) makes it possible to mainly compensate for the deformations generated by the radius of curvature of the curved magnifying mirror 32 of the image-reflecting device 30, while the second radius of curvature in the second direction of the screen 22 (including a vertical component) makes it possible to mainly compensate for the blur caused by the inclination of the screen 22 with respect to the optical axis X associated with the image-returning device 30.

According to another possible embodiment, the exit face of the screen has a first radius of curvature in any direction with respect to a first main direction of the screen, and a second radius of curvature in any second direction with respect to to a second main direction of the screen; the two directions of curvature can then have any cone angle between them, for example between -45° and +45°.

According to yet another embodiment of the screen, it is possible for the deformation of the output face of the screen to follow the equation of a sphere, a torus or any Cartesian equation, in order to correct the as finely as possible the aforementioned optical aberrations. In this situation, the output face of the screen has a point of maximum deflection, i.e. the maximum deformation of the output face of the screen, with respect to a plane of the screen passing by two of the parallel edges of said screen, is located at a single point. In the case where the exit face of the screen is curved according to the equation of a sphere, the point of maximum deflection of the screen is located at the intersection of the diagonals connecting two by two the opposite corners of said face. screen output.

Thus, thanks to the curved screen according to the invention, the quality of the virtual image IMV seen by the driver is improved.

Claims (13)

Head-up display (1) comprising:
- a screen (22) adapted to generate a light beam via an exit face (22B), and,
- an image return device (30) adapted to receive the light beam generated by the backlit screen (22) and to send it in the direction of a partially transparent blade (80),
characterized in that the exit face (22B) of the screen (22) has a non-zero radius of curvature. Head-up display (1) according to Claim 1, in which the concavity of the exit face (22B) of the screen (22) faces the image-reflecting device (30). Head-up display (1) according to claim 1, in which the concavity of the exit face (22B) of the screen (22) faces away from the image-reflecting device (30). Head-up display (1) according to one of Claims 1 to 3, in which the exit face (22B) of the said screen (22) has a first radius of curvature along a first main direction of the screen (22), and a second radius of curvature along a second main direction of the screen (22), comprising a component perpendicular to said first main direction. Head-up display (1) according to one of Claims 1 to 4, in which the radius of curvature of the exit face (22B) of the screen (22) is determined as a function of the radius of curvature of at least one optical elements (31) of the image returning device (30) or the radius of curvature of the partially transparent plate (80). Head-up display (1) according to one of Claims 1 to 5, in which the radius of curvature of the exit face (22B) of the screen (22) is such that each point of the said exit face (22B ) is equidistant from an object focal plane associated with said screen (22). Head-up display (1) according to one of Claims 1 to 6, in which the radius of curvature of the exit face (22B) of the screen (22) is between 10 cm and 50 cm. Head-up display (1) according to one of Claims 1 to 7, in which a plane tangent to the exit face (22B) of the screen (22), at the level of the intersection between the said screen (22) and an optical axis (X) associated with the image return device (30) is inclined at a non-zero angle with respect to a plane perpendicular to said optical axis. Head-up display (1) according to one of Claims 1 to 8, in which the screen (22) comprises a plurality of pixels, all the pixels of the screen having the same size. Head-up display (1) according to one of Claims 1 to 9, in which the image-reflecting device (30) comprises at least one curved magnifying mirror. Head-up display (1) according to Claim 10, in which the absolute value of the ratio between the radius of curvature of the exit face (22B) of the screen (22) and the radius of curvature of the magnifying mirror (32) is between 0.5 and 2. Head-up display (1) according to one of Claims 1 to 11, in which the partially transparent blade (80) is formed by a separate blade located between a windscreen of the vehicle equipped with said head-up display and the eyes of the driver of this vehicle . Head-up display (1) according to one of Claims 1 to 11, in which the partially transparent strip (80) is formed by a windscreen (2) of the vehicle equipped with said head-up display (1).