WO2016146904A1

WO2016146904A1 - Head-up display device, particularly for a motor vehicle

Info

Publication number: WO2016146904A1
Application number: PCT/FR2016/000050
Authority: WO
Inventors: Pierre Mermillod
Original assignee: Valeo Comfort And Driving Assistance
Priority date: 2015-03-17
Filing date: 2016-03-17
Publication date: 2016-09-22
Also published as: FR3033904A1; FR3033904B1

Abstract

The invention relates to a head-up display device, particularly for a motor vehicle, comprising at least one laser source (4, 5, 6) producing a light beam (10), means for forming an image in an intermediate image plane (111), and a semi-reflective element (126) forming a virtual image (130) of said image in the intermediate plane (111), characterised in that the head-up display device also comprises diffraction means (140) which are arranged in the intermediate image plane (111) and diffract the beam (10) into a plurality of zero-order (40) and higher-order (30) diffraction beams.

Description

Head-up display device, in particular for a motor vehicle

The present invention relates to a head-up display device and in particular to the image-forming means.

The invention will find applications, for example, in motor vehicles to inform users of the vehicle, especially its driver. Head-up display systems are known in vehicles. These systems make it possible to inform the driver, by displaying in his field of vision, information related to the state of the vehicle such as speed, information related to the route. This system allows the driver to visualize a form of augmented reality in his field of vision.

Such systems are provided with a light source, for example comprising one or more laser sources, which are combined to form a collimated beam. After passing through scanning means, the light beam is imaged on a diffuser screen. This screen makes it possible to broadcast the collimated beam. Such a diffuser generally comprises a rough face, causing the dispersion of the light beam. A semi-reflective device then makes it possible to create a virtual image of the screen in the driver's field of vision comprising the information to be displayed. However, when a coherent source, such as a laser, is projected on the diffuser screen, random spots will appear on the virtual image, these tasks coming from constructive interference (high intensity tasks) and destructive (tasks darker) between different components of the scattered light. These random tasks are called scabs or "speckle" in English. The driver may be dazzled by the lighter tasks, and when he changes his position, these tasks will appear darker, causing a gene to the driver when changing position.

The invention proposes a head-up display device comprising at least one laser source producing a light beam, means for forming an image in an intermediate image plane, a semi-reflective element forming a virtual image of said image in the image. intermediate plane, characterized in that the head-up display device further comprises: diffraction means placed in the intermediate image plane and diffracting the beam into a plurality of zero order and higher order diffraction beams.

By introducing diffraction means into the intermediate image plane, the latter make it possible to control the interference occurring within the light beam. These interferences, which are at the origin of scab, can thus be reduced or even eliminated and thus avoid the appearance of scab, or "speckle" in the virtual image viewed by the user. Preferably, means for masking the zero order of the diffracted beam are arranged between the intermediate image plane and the semi-reflective element.

Since the virtual image generated with the zero order is not homogeneous, it is preferable to hide the zero order and to use at least one higher order to generate the virtual image. On the other hand, the luminous intensity of the zero order may be too strong for the user, and may even dazzle him, see generate damage to the eyes of the user. Advantageously, the masking means are configured to selectively transmit to the semi-reflecting element at least one of the higher orders of diffraction. Advantageously, the masking means includes an appropriate optical alignment between the diffractive means and the semi-reflecting element so that the zero order is not transmitted to the semi-reflective element.

Preferably, the higher order of diffraction transmitted to the semi-reflecting element is the first order.

Advantageously, the device further comprises a light trap configured to capture the zero-order beam. Advantageously, the diffraction means further comprise diffusion means.

Preferably, the diffusion means are configured so that the diffusion of one of the higher orders of the diffracted beam is optimized.

Preferably, the diffusion means are configured so that the diffusion of the order 1 of the diffracted beam is optimized.

Advantageously, the diffraction means comprise a diffractive optical element traversed by the beam and having at least two different levels of thickness in the direction of propagation of the beam.

Advantageously, the diffractive optical element is used in transmission. Preferably, the diffractive optical element is binary, and the optical path difference between the two thickness levels is substantially equal to half of the average wavelength, the average wavelength being the average of the wavelengths. wave of at least one laser source.

Other characteristics, details and advantages of the invention will emerge more clearly on reading the description given below as an indication in relation to drawings in which:

FIG. 1 is a schematic view of an embodiment of a head-up display device according to the invention,

FIG. 2 is a schematic view of an embodiment of an image generator used in the device according to the invention, FIG. 3 is a schematic view of an embodiment of a transmission device used. in the device according to the invention,

FIG. 4 is a schematic view of an embodiment of the

image forming means used in the device according to the invention,

FIG. 5 is a schematic view of another embodiment of the image forming means used in the device according to the invention,

FIG. 6 is a schematic view of the diffusion generated by diffusion means,

FIG. 7a is a schematic view of the diffraction generated by transmission diffraction means,

FIG. 7b is a schematic view of the diffraction generated by reflection diffraction means,

FIG. 8 illustrates the diffraction and diffusion around the zero order of a light beam by a diffractive optical element, in which the diffusion is centered around the order 1, the order 1 and the order zero being well separated,

FIG. 9 is a figure similar to FIG. 8, in which the order 1 and the zero order are partially superimposed.

In these different figures, the same references refer to the same elements.

In addition, it should be noted that the figures disclose the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate.

Figure 1 is a schematic view of a head-up display device according to the invention. As illustrated in FIG. 1, the device comprises an image generator 100, followed by diffraction means 140 placed in an intermediate image plane 111. The image generator 100 produces a beam 30 which, according to one embodiment, is then reflected on a first folding mirror 125. The light beam 30 then passes through a semi-reflective optical element 126, which may be constituted by the windshield of the vehicle or a semi-reflective blade. The combination of the mirror 125 and the semi-reflective plate 126 allows the user to see a virtual image 130 of the image generated by the image generator 100 in the intermediate image plane 111, as if the image were at a distance of about two meters from his eyes and superimposed the road. This image is perceived by the user in an area of the vehicle that is called the eye box 170. The eye box has a dimension of about 5X15 cm ² , and is around the eyes of the driver when driving.

The semi-reflecting blade 126 has a reflectivity of at least 20%, which allows the user to see through the blade the road taken by the vehicle, while enjoying a high contrast to see the virtual image 130.

FIG. 2 illustrates the image generator 100. The latter comprises a transmission device 101 of a light beam 10 and means 102 for forming an image in the plane 111, from said light beam 10.

FIG. 3 is a schematic view of the transmission device 101. Said device comprises one or more sources 4, 5, 6, each emitting a beam 7, 8, 9 of the laser type. These are, for example, laser sources, typically laser diodes, each laser source emitting a monochromatic beam, of wavelength λι, λ ₂ , λ ₃ .

Said device here comprises three sources 4, 5, 6, the device being configured to form the light beam 10 by means of pooling by combining the beams 7, 8, 9 individually emitted by each of the sources 4, 5 , 6. More precisely, it may be sources emitting a beam of a different color from one source to another. Colors are, for example, red, green, or blue (RGB).

The beams 7, 8, 9 emitted by each of the sources are oriented, for example, parallel to each other and reflected in the same direction to form by combination the common light beam 10. The device 101 here comprises semi-transparent optical elements , over a wavelength range, such as dichroic mirrors or combination blades 11, intercepting the beams 7, 8, 9 emitted by each of the sources and combining them according to the direction of the beam 10.

More generally, the device 101 is configured to form the light beam 10 from the laser beam or beams 7, 8, 9, whatever the number of sources 4, 5, 6 involved. In case of a single source, the light beam 10 is composed of the laser beam emitted by the only source used and the resulting image will then be monochrome. In the case of a plurality of sources, typically the three sources 4, 5, 6 mentioned above, the common beam 10 which then forms the light beam will allow the establishment of an image according to a color spectrum whose resolution will correspond to the fineness controlling the supply of sources 4, 5, 6.

As illustrated in FIG. 4, the image-forming means 102 comprise, for example, a scanning generator 110 whose function is to move the light beam 10 horizontally and vertically in order to carry out a scanning according to a frequency, for example equal to 60 Hz.

As shown in FIG. 5, the scanning generator 110 comprises, for example, a scanning mirror 115 with a microelectromechanical system (hereinafter referred to as the MEMS mirror) on which the light beam 10 is reflected in a scanning beam 103. Such a mirror 115 MEMS for example has a diameter of 1 mm ² . The mirror 115 MEMS is able to rotate about two axes of rotation, for example orthogonal, to perform a scan, for example at the refresh rate of 60 Hz, in the intermediate image plane 111 according to a figure composed of successive lines, in the aim of making an image, for example rectangular, alternatively, the mirror 115 MEMS can be replaced by two plane and movable mirrors, whose movements are associated. One of these mirrors can be dedicated to a scan along a horizontal axis while the other mirror can be dedicated to a scan along a vertical axis.

The image generator 102 may further comprise different mirrors 104, 106, planar or otherwise, arranged on the path of the scanning beam 103. According to the present invention diffractive means are arranged in the intermediate image plane 111, in order to suppress the scabs generated by the diffusion of a coherent laser source on the rough face of the diffuser 140 mentioned above. However, the diffusion means must not be replaced by the diffraction means, but the combination of the two is necessary to generate an image whose pupil is sufficiently large (diffusion means), and without scab (diffraction means), to the user.

Indeed, without the diffusion means, the emission indicator surface does not exist because the incident beams in the intermediate image plane 111 are collimated. The image can only be seen in one direction corresponding to the direction of the incident laser beam. The addition of diffusion means is used to generate an emission indicator surface, thus making it possible to increase the size of the pupil and consequently to improve the comfort of the user. The introduction of diffusion means 150 in the intermediate image plane 111 is illustrated in FIG. 6. The diffusion means 150 may be in one embodiment constituted by a diffusing screen. However, we will see that the diffusion means 150 and the diffraction means can be combined in the same optical element. Advantageously, the diffusion means 150 receive the scanning beam 103 and are arranged to cause a dispersion of this scanning beam 103 according to an angular sector, for example, equal to 30 ° around the direction of propagation of the scanning beam 103. The diffusion means are of the type with enlarged exit pupil, in English "Exit Pupil Expander". The dispersion of the light beam 103 can be illustrated by means of a cone 155.

In the embodiment where the diffusion means comprise a diffuser screen, the latter may be a transparent projection screen for a projection by transparency. This screen comprises in particular on one of its faces, periodic microstructures, whose geometry is complex. He will be able to alternatively be translucent. It is made, for example, of glass, especially frosted, or polycarbonate. One face of the diffuser screen is rough, in that it has asperities which cause the dispersion of the scanning beam 103. The rough face corresponds to that through which the beam leaves, that is to say the face located in the intermediate image plane 111 on which the image is formed.

According to another variant not illustrated, said image forming means do not comprise a scanning generator as described above, but a matrix of micro mirrors (also called Digital micro mirrors system). In this configuration, the image is formed at the level of the mirror array and then projected onto the intermediate image plane 111. In general, a projection optics is placed between the matrix and the intermediate image plane. Each micro mirror corresponds to a pixel of the image. In this embodiment, the image is not formed in the intermediate image plane for the first time, but receives an image previously formed on the mirror array. In this embodiment, the light beam is a fixed beam. In an alternative embodiment, it is possible to use a micro-lens type diffuser ("micro-lens array" in English, or MLA) is used, the image is parasitized by a repetitive structured pattern, called moiré effect. For reasons of manufacturing tolerance, alignment of lasers, etc., the moiré effect and the appearance of scab may also appear simultaneously.

According to the invention, in order to reduce or eliminate scabs and / or the moiré effect, diffraction means 140 are used. Advantageously, the same optical component is used for the diffraction means 140 and the diffusion means 150. the diffraction means 140 and the diffusion means 150 may be provided by two distinct optical elements. In one embodiment of the present invention, the diffraction means 140 comprise a diffractive optical element. The function of this optical element is to decompose the incoming beam into a plurality of output beams propagating in different directions, these different output beams corresponding to different diffraction orders, whose zero order and higher orders (± 1, ± 2, ± 3, etc.). The direction of the outgoing beams depends on the structure responsible for the diffraction that is present on the face of the diffractive optical element 140, and the wavelength of the incident light. Generally, the face of the diffractive optical element comprises a periodic structure, micro-structured, the pitch of which is of the order of the wavelength of the light. For a single dimension, it is a diffraction grating, the pitch of which depends on the wavelength of the light. Preferably, these structures may comprise two thickness levels, in the propagation direction of the light beam: in this case it is a binary diffractive optical element, also called phase shift mask in the literature. Some regions have a smaller thickness, and other regions have a higher thickness, thus inducing an optical path difference and hence a phase shift between different portions of the diffracted beam. Preferably, for the thickness variations of the mask to generate a phase shift in the π beam, the difference in optical path between two regions is λ / 2, where λ corresponds to the wavelength of the incident light. The diffractive optical element is therefore generally optimized for a single wavelength. If the device comprises three laser sources, the diffractive optical element will be optimal for one of the three sources. Preferably, the phase mask is designed for the average wavelength of the different laser sources, the average wavelength being the average of the wavelengths of the laser sources. In another embodiment, the diffractive optical element 140 may comprise a plurality of different thicknesses in the propagation direction of the beam. The multi-level diffracting optical elements are generally designed to make the diffracted beam asymmetrical, for example, to make the order -1 coincide with the order 1. Preferably, the multi-level diffractive optical element is designed for the length of d average wave of different laser sources.

The distribution of the light beam emerging from the diffractive optical element 140 depends on the structure of the face of the diffractive optical element. This structure can be computed analytically, by the theory of diffraction gratings or can also be simulated, etc.

Generally, a diffractive optical element 140 also generates scattering. For example, in the case of a binary diffractive optical element, discontinuities in thickness variations generate scattering. The intensity of diffusion also depends on the structure of the diffractive optical element face and can be determined in advance by means of simulations, calculations, etc.

FIGS. 7a and 7b illustrate the diffraction of a monochromatic light beam 70, such as a laser light source, on a diffractive optical element 140. In FIG. 7a, the diffractive optical element 140 transmits the light beam 70. FIG. 7b, the diffractive optical element reflects the light beam 140. After transmission and reflection respectively, the diffractive optical element 140 breaks down the light beam 70 into a plurality of beams corresponding to different diffraction orders in which the orders zero, 1, 2, -1, -2 are represented by the axes of the beams 700, 701, 702, 711, 712 respectively. Diffraction orders are discretely distributed and the angular separation between orders depends on the physical characteristics of the diffractive optical element. In transmission, the zero order 700 is undeviated by the network and in reflection it is reflected according to the laws of geometrical optics. Higher orders, for example orders 1 [701), 2 (702), 3 (not shown), etc. are diffracted according to structure-dependent diffraction angles on the face of the diffractive optical element. The commands -1 (711), -2 (712), -3 (not shown), etc. are the symmetries of orders 1, 2, 3, etc. compared to the zero order 700, as shown in the diagram of FIG. 7.

Generally, the zero order, which is the order whose intensity is dominant relative to the higher orders, is chosen to generate the virtual image 130.

However, the use of the zero order to generate the final virtual image 130 of the device according to the invention poses two major problems. The distribution of light intensity in zero order is not homogeneous: it is concentrated at the center of the image and reduced at the edges. This inhomogeneity of illumination in the field is uncomfortable for the user and causes an image that appears brighter along the direction of the main optical ray and less luminous along the other directions. On the other hand, the luminous intensity of the zero order is strong. This high light intensity can also dazzle the user, even generate damage to the eyes of the user, especially when the light source comprises a laser.

It is possible to design a diffracting optical element structure reducing the intensity of the zero order, however this will only be valid for a single wavelength. Since in the preferred embodiment of the invention, the system comprises three laser sources, this is not a solution.

Preferably, in order to eliminate the zero order, and this for each laser source, means are available for masking the zero order of the diffracted beam disposed between the intermediate image plane 111 and the semi-reflective element 126.

In one embodiment, the masking means are made by adapting the optical alignment between the diffraction means and the semi-reflective element, for example by transmitting to the semi-reflecting element 126 at least one diffracted beam of higher order of the scanned beam 103. To do this, the optical elements placed between the diffractive optical element and the semi-reflective element 126 are oriented such that only one or more higher order beams are transmitted to the element semi-reflective 126, the zero order not being transmitted.

Returning to FIG. 1, which illustrates the propagation of the light beam 30 after diffraction by the diffraction means 140, or more particularly by the diffractive optical element 140.

The light beam 30 corresponds to the order 1 of diffraction of the light beam and the light beam 40 corresponds to the order 0 of the diffraction beam. The folding mirror 125 is positioned such that it receives the order 1 of the diffracted beam.

In one embodiment of the invention, the order 1 is chosen to be transmitted to the following optical elements and form the image 130 of the device according to the invention.

Generally the diffusion is maximum for the zero order, and is along the main axis of the diffractive optical element, the main axis being generally an axis perpendicular to the diffractive optical element. It is possible to optimize the diffusion on one of the higher diffraction orders, that is to say along an axis distinct from the main axis, by using an element diffracting optics for example. The multi-level diffracting optical elements comprise at least two different thicknesses, inducing a plurality of phase shifts of the wave between 0 and 2π, or even 0 and 4π (or any other multiple of 2π). The term optimization initially concerns a spatial optimization of the diffusion. In particular, the diffusion function inscribed on the diffractive optical element is designed to generate a pupil of a certain predetermined size. It is the diffusion cone that will determine this pupil dimension. The term optimization also covers optimization in light intensity. The luminous intensity depends partly on the size of the pupil (or the diffusion cone) but it is also possible to superpose higher orders to increase the luminous intensity. In particular, the light intensity will be determined by the light intensity of the virtual image. The diagram of FIG. 8 illustrates the effect generated by an optimization of the diffusion around the order 1. The incident light 70 and the direction of the zero order 700 coincide. The diffractive optical element 140 is placed in the intermediate image plane 111. The size of the pupil in the plane 111 is identical for the zero order 700 and the order 701. In an output plane 620, the size of the The exit pupil is greater for the order 1 801 than for the zero order 800 thanks to the diffusion 811 generated by the diffractive optical element 140 around the order 1. Thus, the optical alignment of the system is adapted, the Optics will be placed downstream of the exit pupil along the axis 630, perpendicular to the diffractive optical element 140. The zero order 700 is thus masked from the final image, and this for each wavelength. Different parameters can influence the system: the angle between the zero order and the order 1, the angle of the diffusion cone, etc. Preferably, to avoid spurious reflections of the zero order, a light trap 650 is inserted into the device to absorb the zero order light. The light trap can also absorb light from certain higher orders to limit the existence of stray light.

As illustrated in FIG. 9, the light beam corresponding to the zero order 700 may be superimposed at least partially on the light beam corresponding to the scattered order 1701, or the diffusion cone 911 may comprise at least a portion of the light beam corresponding to the zero order 700. In the output plane 620, the exit pupils of the order 1 901 and the zero order 900 are superimposed on the surface 902. The portion 902 of the exit pupil of the order 1 is deleted. Only the light passing through the exit pupil 901 ("Exit Pupil" in English) is exploited by the optical system placed downstream of the plane 620 to form the virtual image 130. The light coming from the zero order 900 and of the order 1 902, confused with the order 0, are not exploited (cut or exploited for other needs). Preferably, to avoid spurious reflections of the zero order, a light trap 650 is inserted into the device to absorb the zero order light.

Preferably, the zero order energy can be monitored by a detector. Any alteration of the diffraction means will result in a zero order power change and this change may therefore be used as a verification of the integrity of the system with respect to the safety associated with the use of a laser. The diffusion effect makes it possible to uniformly illuminate the entire pupil of the optical system and to enlarge the size of the pupil where it will be perceived by the user, that is to say in the box to eye. As shown in Figure 1, the zero order is ignored by the system.

Claims

Head-up display device, especially for a motor vehicle, comprising

at least one laser source (4, 5, 6) producing a light beam (10),

means for forming an image in an intermediate image plane (111),

a semi-reflective element (126) forming a virtual image (130) of said image in the intermediate plane (111),

characterized in that the head-up display device further comprises:

diffractive means (140) placed in the intermediate image plane (111) and diffracting the beam (10) into a plurality of zero order (40) and higher order diffraction beams (30).

The head-up display device according to claim 1, further comprising means for masking the zero-order (40) of the diffracted beam disposed between the intermediate image plane (111) and the semi-reflective element (126). ).

The head-up display device according to claim 2, wherein the masking means is configured to selectively transmit to the semireflective element (126) at least one of the higher diffraction orders.

The head-up display device according to one of claims 2 or 3, wherein the masking means includes an appropriate optical alignment between the diffractive means (140) and the semi-reflective element (126) so that the zero order is not transmitted to the semi-reflective element (126).

A head-up display device according to claims 3 or 4, wherein the higher order of diffraction transmitted to the semi-reflective element [126] is the first order.

The head-up display device according to any one of claims 3 to 5, wherein the device further comprises a light trap configured to capture the zero-order beam (40).

7. A head-up display device according to any one of claims 3 to 6, wherein the device further comprises a light trap configured to capture higher order beams except the first order.

8. A head-up display device according to any one of the preceding claims, wherein the diffraction means (140) further comprises diffusion means (150).

9. A head-up display device according to the preceding claim, wherein the diffusion means (150) are configured so that the diffusion of one of the higher orders of the diffracted beam is optimized.

The head-up display device according to claim 5, wherein the diffusion means (150) is configured so that the diffusion of the order 1 of the diffracted beam is optimized.

Head-up display device according to any one of the preceding claims, in which the diffraction means (140) comprise a diffractive optical element traversed by the beam (10) and having at least two different thickness levels in the beam propagation direction (10).

12. A head-up display device according to any one of the preceding claims, wherein the diffractive optical element is used in transmission.

The head-up display device according to claims 11 and 12, wherein the diffractive optical element is binary, and the optical path difference between the two thickness levels is substantially equal to half the wavelength. mean, the average wavelength being the average of the wavelengths of the at least one laser source (4, 5, 6).

The head-up display device according to any one of the preceding claims, further comprising a scanning generator

(110) for producing a scanning beam (103), the scanning beam (103) being diffracted by the diffraction means (140).

A head-up display device according to any one of claims 1 to 14, wherein the light beam (10) is a fixed beam, the fixed beam being diffracted by the diffraction means (140).