WO2016162632A1

WO2016162632A1 - System for displaying a floating image

Info

Publication number: WO2016162632A1
Application number: PCT/FR2016/050779
Authority: WO
Inventors: Christophe Martinez
Original assignee: Commissariat à l'énergie atomique et aux énergies alternatives
Priority date: 2015-04-09
Filing date: 2016-04-06
Publication date: 2016-10-13
Also published as: FR3034878A1

Abstract

The invention pertains to a system (10) for displaying a floating image comprising: - at least one image source (210); - a semi-reflecting structure (300); - a partially transparent display screen (100); - at least one projection optic (220) adapted for projecting onto the display screen by way of the semi-reflecting structure the image provided by said image source; - the display screen (100) being partially transparent and partially retro-reflecting, and comprising retro-reflecting portions (140) with wedge-shaped structurations (120; 121, 121').

Description

SYSTEM FOR DISPLAYING A FLOATING IMAGE

TECHNICAL AREA

The field of the invention is that of the display systems of a so-called floating image, that is to say a superimposed image of a scene, the image can appear three-dimensional or quasi-three-dimensional.

STATE OF THE PRIOR ART

Floating image display systems exist in the field of entertainment since the nineteenth century and are currently developed to address the particular field of advertising and event communication. They are based on an optical illusion effect, said Pepper's ghost, whose principle is recalled with reference to Figure 1 which illustrates a display system described in US2009 / 0009862.

In this example, the display system 1 comprises an image source 2, for example an emissive screen, adapted to supply a plurality of source images at its emission face 3, and a semi-reflecting structure 4 in the form of a pyramid with polygonal base positioned inversely vis-à-vis the screen 2, that is to say that its apex A is located opposite the emitting face 3 of the screen 2. Thus, the semi-reflective outer faces of the pyramid are oriented towards the screen and towards the environment of the display system. The screen 2 provides a plurality of source images each positioned facing a semi-reflecting face 5 of the pyramid. Thus, the light beams of each source image provided by the screen 2 are reflected in part by the corresponding face 5 of the pyramid towards the environment. An observer placed in front of one of the faces 5 of the pyramid then sees a virtual image of the image provided by the emissive screen 2, this virtual image being positioned in a virtual plane located inside the pyramid. The semi-transparency of the pyramidal structure 4 superimposes the image displayed with the scene, which gives the observer the impression of observing a floating image. Moreover, in this example, an observer who would turn around the display system would see different virtual images located inside the pyramid, which would give the impression of observing a three-dimensional floating image.

A disadvantage of this type of display system is that the semi-reflecting structure 4 is necessarily oriented so that the semi-reflecting faces 5 are oriented towards the image source 2 and the environment of the display system. As a result, the field of view is limited by the emission face 3 of the screen on the one hand and by the base 6 of the semi-reflecting structure on the other hand.

In addition, the reverse orientation of the pyramid vis-à-vis the emissive screen requires to provide the pyramid holding elements when it is located above the screen, or maintenance of the emissive screen when it is positioned above the pyramid. In the latter case, one of the holding elements must also include an electrical circuit for the power supply of the screen. The presence of these holding elements adds an unsightly effect to the system and reduces the comfort of vision of the observer.

STATEMENT OF THE INVENTION

The object of the invention is to remedy at least in part the drawbacks of the prior art, and more particularly to propose a system for displaying a floating image offering improved vision comfort. To this end, the invention proposes a system for displaying a floating image, comprising at least one image source adapted to provide an image to be displayed, and a semi-reflecting structure adapted to reflect light beams originating from the source. image.

According to the invention, it further comprises a partially transparent display screen comprising at least one display face, the screen being adapted to display an image projected on its display face via the semi-structured structure. reflective, and partially transmitting an incident light on its opposite side to the display face; and at least one projection optics adapted to project on the display screen via the semi-reflecting structure the image provided by said image source. Furthermore, the display screen is partially transparent and partially retro-reflective at its display face, and has retro-reflective portions and transparent portions distributed over all or part of its area, each retro-reflective portion reflective being separated from neighboring retro-reflective portions by a transparent portion. The retro-reflective portions include cube corner structures.

The image displayed by the display screen advantageously corresponds to the real image of the image supplied by said image source.

The semi-reflecting structure advantageously has, optionally in association with the display screen, a pyramid shape whose base is located opposite an elementary projector formed of said image source and said projection optical system.

Thus, the screen may comprise a plate of a transparent material having a first smooth face, and a second face opposite to the first and structured in the form of cube corner protuberances at the retro-reflective portions and smooth at the portions. transparent.

The display screen may be partially transparent and partially retro-reflective on its two opposite sides to each other, each forming a display face.

Thus, the display screen may comprise at least one plate of a transparent material whose two faces opposite to each other are smooth so as to form display faces, and comprises transparent portions and portions retroreflective reflectors distributed over all or part of its extent, each retro-reflective portion being separated from neighboring retro-reflective portions by a transparent portion, each retro-reflective portion comprising at least two wedge-shaped notches arranged opposite each other; one of the other according to the thickness of the screen and oriented so that the base of the cube corner of each is opposite the corresponding display face.

The display system may comprise at least one first linear polarizer having a first transmission axis disposed between the projection optics and the semi-reflective structure, and at least one second linear polarizer having a second axis of orthogonal transmission to the first axis and disposed on one side of the semi-reflecting structure opposite the display screen and the projection optics, for example at a face thereof opposite the oriented face to the screen.

The display system may further comprise a third linear polarizer having a third transmission axis coplanar with the second axis and orthogonal to the first axis, the third polarizer being on one side of the display screen opposite to the second polarizer. This third polarizer may be located at a face opposite to the display face of the screen. Alternatively, the semi-reflective structure comprising two semi-reflective blades disposed on either side of the display screen, the second and third polarizers being each disposed on the side of a blade opposite to the screen.

The internal lateral faces of the wedge-shaped notches are advantageously covered with a metal layer.

The display screen may comprise opaque portions located at least between each notch of the same retro-reflective portion depending on the thickness of the screen.

According to one embodiment:

the display screen comprises at least two faces opposite to each other, called display faces, and is adapted to display a projected image on each of its two display faces, and to partially transmit a incident light on them;

at least two so-called elementary projectors each comprise an image source associated with a projection optical system, and are each adapted to project an image supplied by the image source onto one or other of the display faces of the screen ; and

the semi-reflecting structure is adapted to reflect light beams coming from each elementary projector in the direction of the corresponding display face of the screen.

Advantageously, the elementary projector formed of the image source and the corresponding projection optical system, the semi-reflecting structure and the display screen are arranged mutually so as to dissociate light beams coming from the elementary projector, retro-reflected. by the screen and transmitted by the semi-reflective structure: - light beams from the elementary projector and reflected specularly by the display screen, and / or

- Light beams from the elementary projector and transmitted by the semi-reflective structure. This arrangement may also be adapted so that light beams emitted by the elementary and incident projector on the display face form an angle of incidence (a) relative to the plane of said display face less than 90 °, and preferably between 55 ° and 80 °; or is adapted so that said angle of incidence (a) is greater than 90 ° and preferably between 90 ° and 115 °. The display screen may comprise a plate made of a transparent material, a first surface of which is coated with a layer of a retro-reflective material based on microbeads at the level of the retro-reflective portions, and is smooth at the level of transparent portions.

The display screen may further comprise an active layer adapted to form opaque areas and transparent areas, the opaque areas being located at the level of the displayed image.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, objects, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and with reference to the accompanying drawings. in which, in addition to Figure 1 already described above: Figure 2 is a schematic sectional view of a display system of a floating image according to a first embodiment; Figure 3 is a schematic sectional view of an example of a partially transparent and partially retro-reflective display screen; Figures 4a to 4c are schematic sectional views showing steps of a method of producing the display screen shown in Figure 3; Figures 5a to 5d are schematic sectional views showing steps of a method of making another example of a partially transparent and partially retro-reflective display screen; Figures 6 and 7 are schematic sectional views of two variants of a display system according to a second embodiment, the configuration of which prevents stray light beams are directed towards the observer; Figure 8 is a schematic sectional view of a display system according to a third embodiment, wherein two images are projected on two opposite sides of the same display screen; Figures 9a and 9b are schematic sectional views of two variants of a display screen according to another embodiment, wherein the screen is partially transparent and partially retro-reflective on two opposite display faces; Figure 10 is a schematic sectional view of a display system according to a fourth embodiment, wherein parasitic beams are filtered through linear polarizers.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In the figures and in the remainder of the description, the same references represent identical or similar elements. Figure 2 is a schematic sectional view illustrating a display system 10 of a floating image according to one embodiment.

The display system 10 includes a partially transparent display screen 100 and an image projection device 200 adapted to project at least one image onto the display screen 100 via a semi-transparent structure. The image projection device 200, also called a projector, comprises an image source 210 associated with a projection optical system 220, and, in this example, a reflecting mirror 230. The image source 210 , for example an emissive screen, is adapted to supply the image to be displayed, called the source image, at a transmission face 211. It may be, inter alia, a liquid crystal display (screen LCD), a diode screen electroluminescent (LED), possibly organic (OLED), or even a CRT. The image source will advantageously consist of a matrix of micro mirrors type DMD (for Digital Micromirror Device, in English) associated with an RGB light source. The projection optical system 220 is adapted to project the image provided by the image source 210 onto the display screen 100 through the semi-reflective structure 300, i.e., to form on the display screen 100 a real image of the supplied image. In other words, the projection optical system 220 ensures the conjugation of the emission face of the image source 210 and the display screen 100. It has an optical power function. The projection optical system 220, which may comprise for example one or more lenses, is thus disposed between the image source 210 and the semi-reflecting structure 300. In this example, the projector 200 further comprises a deflection mirror 230 which directs the projection beam towards the semi-reflecting structure 300. The semi-reflecting structure 300 is adapted to partially reflect the light beams from the projector 200 towards the display screen 100, and to transmit the beams from the display screen 100 towards an observer. The structure 300 is formed here of a single semi-reflective plate 310 disposed between the display screen 100 and an observer. It is oriented so as to form an angle of inclination, for example 45 °, with the display screen 100. Thus, the blade 310 has a semi-reflective inner face 311 facing the projector 200 and the screen. 100, and an outer face 312, opposite the inner face, facing the observer. It should be noted that the semi-transparent plate 310 can be replaced by an interference filter performing the same optical function as the semi-transparent plate. Thus, the semi-reflecting structure 300, alone or in combination with the display screen 100, a pyramid shape whose base is located opposite the projector 200.

The screen 100 is a partially transparent display screen, that is to say adapted to reflect and diffuse more or less strongly the incident beams on its display face 110, and to transmit partially without altering the incident beams on its opposite face 111 and coming from the scene. The scene is visible to an observer who would look through the display screen, that is to say that the objects of the scene are distinguishable or clearly visible. Thus, the display screen differs from translucent screens, that is to say screens that transmit light from the scene but by diffusing it in such a way that the objects of the scene are not distinguishable or clearly visible. To form a real image of the image provided by the projector 200, the display screen 100 is disposed in the image plane of the projection optical system 220.

The screen 100 may be formed of a sheet, a plate or a film of a transparent material, whose display faces 110 and its opposite face 111 are preferably substantially planar. The diffusion of the reflected beams at the display face 110 can be obtained by the surface imperfections of this face, or even by means of elements adapted to implement this diffusion function, for example microstructures coating one side of the surface. faces of the screen whose shape is adapted to diffuse only the light reflected by this face without altering the transmitted light. A semi-transparent metal layer may also be provided to promote the reflection of light from the semi-reflective structure. Other transparent reflective diffuser films may be used, for example holographic films, an example of which is given in document US Pat. No. 6,288,885, or even transparent reflective diffusing films of the type marketed by Luminit under the term "Light Shaping Diffuser".

In this example, the projector 200 comprises a housing 240 in which are located the image source 210, the projection optical system 220 and the reflecting mirror 230. The housing is here positioned in the lower part of the display system 10 under the screen 100 and the semi-reflecting structure 300, and has an opening 241 through which the projection light beams emerge towards the semi-reflecting structure 300. This arrangement makes it possible to obtain a display system compact with a relatively flat housing whose lateral dimensions can be adapted to further ensure the mechanical maintenance of the display screen and / or semi-reflective structure. In operation, the image source 210 of the projector 200 provides an image to be displayed at its transmission face 211. The light beam emitted by the source 210 is projected by the optical system 220 on the display screen 100, by means of the reflecting mirror 230 which directs the projection beam towards the semi-reflecting structure 300, then of the structure 300 which reflects them partially in the direction of the 100. The screen 100 being placed in the image plane of the projection optical system 220, an actual image of the source image is formed at the display face 110 of the screen 100. incident light beam is then diffusively reflected by the screen 100 in the direction of the semi-reflecting structure 300 which transmits it partially, so that an observer located on the opposite side of the blade 310 displays the image displayed by the 100. In addition, since the display screen 100 and the semi-reflecting structure 300 are partially transparent, the light beams coming from the scene are transmitted by the screen 100 and then by the structure 300 towards the screen. 'observer. The scene thus remains visible by an observer who would look at the display screen 100 through the structure 300, that is to say that the observer can distinguish the objects of the scene. This would not be the case if the display screen was partially translucent instead of being partially transparent.

Thus, the embodiment of the display system 10 described in relation with FIG. 2 has the advantage of projecting a real image at the level of the display screen 100 which can thus be seen by an observer through the semi-reflecting structure 300. Insofar as the screen 100 is partially transparent, the displayed image is superimposed on the scene and then appears as floating in the air. Floating image printing can be enhanced when the displayed image occupies only part of the display surface of the screen 100, the image then being surrounded at least in part and preferably entirely by a the area of transparency of the screen 100 by which the observer sees the scene located behind the display system 10. The observer thus has the impression that the image floats in the air, superimposed on the scene.

Furthermore, the semi-reflecting structure 300, possibly associated with the display screen 100, forms a pyramidal type structure whose base is located opposite the projector 200. The beams projected by the projector 200 towards the structure semi-reflective 300 "enter" into the pyramidal structure by the base thereof. Thus, unlike the example of the prior art mentioned above, the field of view of the observer is not limited or hindered by the base of this pyramidal structure which would be located away from the projector. It is therefore not necessary to provide mechanical support elements of the semi-reflective structure which would be in an inverted position vis-à-vis the projector, which would reduce the viewing comfort of the observer. Figure 3 is a schematic sectional view partially illustrating a variant of a display screen 100 of the display system 10, in which the screen 100 has an additional optical function of retro-reflection. An example of such a partially transparent and partially retro-reflective display screen is described in patent application FR1453404 filed on 16/04/2014. The screen 100 is adapted to retro-reflect the incident light on its display face 110 by diffusing it more or less strongly, and to pass without significant alteration of the incident light on its opposite face 111. The screen thus has a transparency function that allows the observer to see the external scene located on the other side of the screen, ie (unlike the translucent screens) the objects in the scene are distinguishable or clearly visible, and a retro-reflection function allowing an observer looking at the screen through the semi-reflective structure 300 to see the image provided by the projector 200 in superposition of the external scene.

The screen 100 is preferably adapted to diffuse retro-reflected light into a diffusion cone encompassing the observer's pupils so that the observer can see the image projected on the display screen. In addition, the diffusion cone (represented by a dashed circle in FIGS. 6, 7 and 8) may have an angular aperture adapted so that the observer can see, through the semi-reflecting structure, the projected image either in a certain location vis-à-vis the display system, or in a wide range of locations. As such, the angular aperture may be asymmetrical, preferably wide in a horizontal plane, and narrow in a vertical plane. The narrow vertical aperture, for example in the range of 5 ° to 30 °, makes it possible to diffuse the retro-reflective beams essentially in the direction of the observer's face, whereas the wide horizontal aperture, for example included in a range of 30 ° to 120 ° or more, allows the latter to view the image even if it observes the screen at an angle. The screen 100 may thus comprise a reflective diffuser film transparent of the type marketed by Luminit under the term "Light Shaping Diffuser" whose diffusion cone has an asymmetrical angular aperture.

Thus, a first advantage of a display system comprising such a screen is that it has a higher light output than the system of Figure 2. In addition, the realization of such a screen is particularly simple and presents the additional benefits of only retro-reflect the light beams incident on its display side and not the incident beams on the opposite side and transmitted by the screen. Moreover, the retro-reflection function is ensured regardless of the wavelength of the incident beams, unlike holographic films whose retro-reflection optical function is activated for a wavelength or a range of lengths. predetermined wave.

In the example of Figure 3, the screen is formed of a sheet, a plate or a film of a transparent material, a face 110 is substantially smooth and flat and a face 111 opposite to the face plane 110 has substantially identical structures 120 and distributed over the entire surface of the screen. Each structuring 120 is a cube corner protuberance, the bases of the protuberances being here substantially parallel to the plane face 110 of the screen. The screen 100 is intended to be illuminated by its flat face 110. To ensure the partial transparency property of the screen, the protuberances 120 are not adjacent, but are separated from each other by substantially flat and smooth zones 130 this face 111, these areas 130 being substantially parallel to the opposite planar face 110 and form a continuous transparent surface. The term smooth refers to an optical surface quality called "optical polish" through which the optical beams are transmitted or reflected without significant change in their propagation characteristics. As a result, the smooth surface ensures transparency in the sense that an image can be seen without significant distortion. To achieve an optical polish, the roughness of the surface is preferably less than 20 nm RMS and ideally between 2 nm and 15 nm. In this example, each screen portion facing a protuberance 120 of the face 111 corresponds to a retro-reflective portion 140 of the non-transparent screen, and each screen portion facing a smooth zone 130 of the face 111 corresponds to a transparent portion 150 and non-retro-reflective of the screen. The example of FIG. 3 shows several protuberances juxtaposed with each other and each surrounded by smooth zones 130. Thus, viewed from the front, the screen comprises a plurality of essentially identical and juxtaposed elementary regions, covering substantially the entire surface of the screen, each elementary region comprising a retro-reflective portion 140, corresponding to a single protuberance 120 or several juxtaposed protuberances, surrounded by a transparent portion 150 peripheral corresponding to the smooth zone 130 of the face 111. As a for example, the ratio between the area occupied by the protuberance (s) and the total surface area of the elementary region, or occultation ratio by the retro-reflective portions, is advantageously less than or equal to 50% and preferably less than or equal to equal to 20%, so as to allow a good visualization of the scene in transparency through the display screen. Other values are possible depending on the applications.

To form a real image of the image provided by the projector 200, the display screen 100, more precisely the face 111 comprising the protuberances 120, is disposed substantially in the image plane of the projection optical system 220.

FIGS. 4a to 4c are sectional views which schematically illustrate steps of an exemplary method of producing the screen described with reference to FIG. 3, as described in document FR1453404 filed on 16/04/2014.

FIG. 4a illustrates a first step in which a mold 400 is made of a structured surface 510 of a rigid part 500, this surface including cube-corner-shaped protuberances 511 covering substantially the entire surface of this face. After separation of the rigid part 500 and the mold 400, the latter has protuberances 411 of complementary shape of the protuberances 511 of the rigid part.

FIG. 4b illustrates a step during which the structured face 410 of the mold 400 is partially flattened and polished so that the initially pointed parts of the protuberances 411 become top plates 412 located in the same plane substantially parallel to a base plane of the protuberances.

FIG. 4c illustrates a step during which a retroreflective display screen 100 is produced from the mold 400 obtained during the preceding step, for example by pressing the mold on a part which, once disconnected from the mold , form the screen display. The screen thus obtained in this exemplary embodiment method is illustrated in FIG.

The scattering function of the beams reflected by the display screen 100 can be obtained by the diffraction effects on the edges of the protuberances 120 and / or surface imperfections of the screen. It can also be obtained by elements adapted to implement this broadcast function. As such, according to a first example (not shown in Figure 3), the lateral faces of the protuberances have micro- or nanostructures adapted to diffuse the retro-reflected light by the protuberances. It is advantageous for these micro- or nanostructures to be present only on the lateral faces of the protuberances 120 and not on the smooth zones 130 of the face 111 so as not to alter the transparency of the transparent peripheral portions 150. for example, these micro- or nanostructures can be made from a method as described in US6258443. According to another example, shown in FIG. 3, the screen 100 comprises diffusing elements 160 situated at the level of the plane face 110, facing each protuberance 120. Here also, it is advantageous for these diffusing elements 160 to be located that compared with the protuberances 120 and not facing the smooth areas 130, so as not to affect the transparency of the peripheral transparent portions 150. For example, these diffusing elements may be formed of a layer of a material comprising scattering particles deposited by screen printing, molding, or other deposition technique.

Figures 5a to 5d are sectional views which schematically illustrate steps of making another example of a partially transparent and partially retro-reflective display screen. This screen example differs essentially from the screen described with reference to FIG. 3 in that the cube-corner structures are said to be "buried", that is to say located inside the screen.

FIG. 5a illustrates a first screen portion 170. This portion is typically obtained by using the element 100 of FIG. 4c as a mold, this element being obtained by a method reproducing the steps of FIGS. 4a and 4b. To do this, a metal mold is made by electroplating from the workpiece 400 and serves to replicate the portion 170, this screen portion being a film, a plate or a transparent sheet having a smooth flat first face 171 and a second face 172, opposed to the first, structured so as to have depressions, or notch 121, in the shape of a cube corner. These hollow structures 121 are distributed in a manner similar to the distribution of the protuberances 120 of the screen of FIG. 3, that is to say that the first screen portion 170 comprises, in front view, a a plurality of essentially identical and juxtaposed elementary regions, covering substantially the entire surface of the first screen portion, each elementary region comprising a central retro-reflective portion 141, corresponding to a single notch 121 with a cube corner or with several juxtaposed notches, surrounded by a peripheral transparent portion 151 corresponding to the flat smooth zone 131, in the optical polishing sense mentioned above, of the structured face 172.

FIG. 5b illustrates a step during which a thin metallic layer 173 is deposited, advantageously in a conformal manner, over the entire surface of the structured face 172, so as to extend both inside the indentations 121, that is to say on the lateral faces thereof, and on the flat areas 131 surrounding the notches 121. The thickness of the metal layer 173 is less than the depth of the indentations 121. Typically, a deposit of silver with a thickness of less than 60 nm and greater than 30 nm. The depth of the indentations 121 is typically less than 100 μιη and advantageously less than 60 μιη for a distribution of cube corners distributed over an isosceles triangle mesh 300 μιη side. FIG. 5c illustrates a step during which, for example, by polishing, the metal layer portions 173 present at the flat areas 131 surrounding the indentations 121 are removed. Thus, the metal layer 173 is only present at the the interior of the cube corner notches 121, more precisely at the lateral faces thereof. FIG. 5d illustrates a step during which a second screen portion 175 is assembled to the first screen portion 170 at the structured face 172 of the latter. The second screen portion 175 is formed of a film, a plate or a transparent sheet whose two faces are preferably flat and smooth. The assembly of the two screen portions 170, 175 is here produced by means of an adhesive 161 whose adhesive material is transparent. The two screen portions and the glue may have a substantially equal optical index. Optical adhesives, for example with an index close to 1.5, are commercially available (eg Polytec UV 2137) and fit well with glass or PMMA (index 1.49).

In FIG. 5d, the arrows represent the direction of illumination of the display screen making it possible to obtain a retro-reflection effect for a portion of the beams incident on the display face 110. A screen of FIG. display in which the cube-corner notches are protected from the environment by being located inside the screen, and whose angular retro-reflection efficiency is improved by the presence of the portions of the screen. metal layer present only at the indentations.

The degree of occultation by the retro-reflective portions is advantageously less than or equal to 50%, and preferably less than or equal to 20%, so as to allow a good visualization of the scene in transparency through the screen. display.

In order to form a real image of the image supplied by the projector 200, the display screen, more precisely the face 172 comprising the indentations 121, is disposed substantially in the image plane of the projection optical system 220. As mentioned previously, diffusing elements 160 may be provided at the level of the plane display face 110, opposite each cube corner structure 121. It is advantageous for these diffusing elements to be situated only with respect to the structures 121 and not in in view of the planar zones 131 surrounding the structures, so as not to affect the transparency of the peripheral portions 151. FIGS. 6 and 7 are diagrammatic sectional views illustrating different variants of a system for displaying a floating image which differ essentially of the example of FIG. 2 in that the arrangement of the different elements makes it possible to prevent parasitic beams from disturbing the observation of the displayed image. In these examples, the display screen is partially retro-reflective and may be the same or similar to the screens described with reference to FIGS. 3 and 5d.

We note here At the optical axis, said transmission, corresponding to the axis of propagation of light beams from the projector and transmitted by the semi-reflective structure; Arr the optical axis, called retro-reflection, corresponding to the axis of propagation of light beams retro-reflected by the screen and transmitted by the semi-reflective structure; and Ars the optical axis, called specular reflection, corresponding to the axis of propagation of the part of the projection light beams and reflected specularly by the screen, more particularly by the flat and smooth faces of the screen, ie the reflected beams present an angle of reflection substantially equal to the opposite of the angle of incidence of the projection beams. In the description, the so-called specular reflection corresponds to a simple reflection of the beams incident on the screen, in particular at the flat and smooth zones described above, whereas the retro-reflection corresponds to a multiple reflection of the incident beams, in particular in cube corner structures.

The angle of incidence of the projection beams on the display screen is also noted with respect to the main plane of the screen and then retro-reflected; β the angle formed between the retro-reflection optical axis Arr and the transmission optical axis At; and ψ the angle formed by the retro-reflection optical axis Arr and the specular reflection optical axis Ar;

Finally, we note Θ the exit angle of the light beams emitted by the projector in the direction of the semi-reflecting structure with respect to a vertical plane parallel to the main plane of the screen; φ the angle of inclination of the semi-reflecting structure vis-à-vis a horizontal plane orthogonal to the main plane of the screen.

In order to prevent the observer from being obstructed by the specularly reflected projection beams by the display screen 100, the semi-reflecting structure 300 and the projector 200 are arranged with respect to the display screen so as to dissociate the retro-reflection optical axis Arr from the specular reflection optical axis Ars. For this, the output angle Θ of the light beams emitted by the projector 200 is modified in the direction of the semi-reflecting structure 300 (here by the orientation of the reflecting mirror 230), and / or the angle of inclination φ of the blade 310 of the semi-reflecting structure.

In a first example illustrated in FIG. 6, the exit angle Θ and the angle of inclination φ are chosen so that the angle of incidence has projection beams on the display screen 100 being less than at π / 2, which makes the displayed image visible in a dive, that is to say when the observer is above the image. The optical retro-reflection axis Arr is thus dissociated from the specular reflection optical axis Ars. The angle ψ between the Arr and Ars axes is therefore non-zero and its value depends on the angles Θ and cp. In this example, the exit angle Θ is non-zero and the angle of inclination φ is of the order of π / 4. It is furthermore advantageous if this arrangement is optimized to also prevent the observer from being obstructed by the projection beams coming from the projector 200 and transmitted by the semi-reflecting structure 300. Indeed, an angle of incidence that is too low would risk indeed, to bring the retro-reflective optical axis Arr too close to the transmission optical axis At. It is advantageous that the angles Θ and φ are chosen so as to deviate substantially substantially the axis of retro-reflection Arr of the transmission axis At on the one hand, and of the specular reflection axis Ars on the other hand, so that β ~ ψ. In this example, we have β = 2α - π / 2 and ψ = π - 2α, which leads to an angle α of between approximately 55 ° and 80 °, preferably between 60 ° and 75 °, for example 67.5. ° approx. In a second example illustrated in FIG. 7, the exit angle Θ and the tilt angle φ are chosen so that the angle of incidence has projection beams on the display screen 100 being greater than at π / 2, which makes the displayed image visible in a low angle, that is to say when the observer is above the image. The optical axis of retro reflection Arr is here also dissociated from the optical axis of specular reflection Ars. The value of the angle ψ between the Arr and Ars axes depends on the angles Θ and cp, where in this example the exit angle Θ is substantially zero and the inclination angle φ is greater than π / 4. The arrangement of the projector 200 is here modified so that the reflecting mirror 230 is no longer located substantially below the screen as in the example of FIG. 6 but under the semi-reflecting structure 300, thus simplifying the return of the beams of projection towards the blade 310 with an exit angle Θ substantially zero. The angle a can thus be between 90 ° excluded and 115 °, for example between 95 ° and 115 °.

Unlike the previous example, the angle of inclination φ can be large without risk of bringing the retro-reflective optical axis Arr of the transmission optical axis At. Moreover, the semi-reflecting structure 300 , in association with the display screen 100, forms a pyramidal structure whose base has reduced lateral dimensions, which makes it possible to obtain a less bulky display system.

FIG. 8 is a diagrammatic sectional view illustrating another embodiment of a system for displaying a quasi-three-dimensional floating image. The display system here differs from the previously described examples essentially in that two source images are each projected on an opposite side of the same display screen. The projector is here formed of two elementary projectors 201, similar or identical to the projector described with reference to FIGS. 2 and 6. Each elementary projector 201, 201 'thus comprises an image source 210, 210' associated with an optical system. projection 220, 220 ', and in this example a reflecting mirror 230, 230'. The two elementary projectors are arranged here in the same housing 240 having an outlet opening 241 of the beams. The two reflecting mirrors are two reflecting faces of the same optical element located opposite the exit opening.

The semi-reflecting structure 300 comprises two semi-reflecting blades 310, 310 'each adapted to partially reflect the projection beams from the elementary projector 201, 20 opposite which it is located. The beams are reflected towards one of the display faces 110, 110 'of the same screen 100. The semi-reflecting structure 300 thus has a pyramid shape, of which two lateral faces are the reflective strips. As in the examples described above, the base of the pyramid is located opposite the projector 200. The display screen 100 has two faces 110, 110 'opposite to each other, each being adapted to display the image projected by the elementary projector 201, 20 corresponding. The screen is thus adapted to reflect and scatter more or less strongly the incident beams on each of its display faces 110, 110 ', and to partially transmit the incident beams on the opposite face without significantly altering them. To form a real image of the image provided by each elementary projector 201, 20, the screen 100 is located substantially in the image plane of each of the projection optical systems 220, 220 ', the two image planes being approximately merged.

To prevent an observer from being disturbed by the beams transmitted by the screen and coming from the opposite elementary projector, the screen 100 is partially transparent and partially retro-reflective at its two display faces 110, 110 ', and the arrangement of the projectors 201, 20 and semitransparent blades 310, 310 'is provided to dissociate the retro-reflection optical axis Arr, Arr' of the specular reflection optical axis Ars, Ars' and advantageously also of the optical transmission axis At, At '. In addition, it is advantageous that the arrangement of the first elementary projector 201 and the corresponding blade 310 is substantially symmetrical to that of the second projector 20 and the corresponding blade 310 '. Thus, the beams coming from a first elementary projector 201 and transmitted by the screen 100 are substantially superimposed on the beams coming from the second elementary projector 20 and reflected specularly by the screen. The exemplary display system relating to FIG. 8 shows an arrangement of the elements which provides an overhead view, similar to the configuration of FIG. 6. However, an arrangement of the elements providing a low-angle view similar to the The configuration of FIG. 7 is possible, each elementary projector then being preferably oriented so as to place the reflecting mirror under the corresponding blade, the latter being inclined by an angle φ greater than π / 4.

It is furthermore advantageous that the angular diffusion cone of each display face 110, 110 'is asymmetrical, that is to say that the vertical angular aperture is narrow to orient the retro-reflected beams mainly towards the face. of an observer, while the horizontal angular aperture is wide to allow the observer to view the displayed image regardless of its position around the display system. The screen 100 may thus comprise two transparent reflective diffusing films of the type marketed by Luminit under the term "Light Shaping Diffuser", arranged at the display faces and whose diffusion cone has an asymmetrical angular aperture. Thus, when the observer circulates around the display system, he displays the image displayed by a first display face 110 until he displays the image displayed by the second display face 110 '. The displayed images appear not only floating, but also three-dimensional or quasi-three-dimensional.

The semi-reflecting structure 300 thus forms a pyramidal structure within which the display screen 100 is located. The base of the pyramidal structure is located facing projector 200, which can ensure the maintenance of the structure and / or the screen, for example at its housing.

The displayed images may be the same or different. When the two images are different, the image displayed on a first face 110 of the screen can be a front view of an object, and the image displayed on the second face 110 'of the screen can be the view from behind the same object, which reinforces the impression of three-dimensional floating image. When the images to be displayed are identical, it is advantageous to simplify the projector to use only one image source. This is associated with an optical system adapted to project the image on both display faces of the screen. The projector then has an optical beam splitting and return. This receives the beam from the optical system and splits it into two beams, each oriented towards the corresponding semi-reflecting plate. The dissociation and return optics comprise, for example, a cube which receives the incident beam and then reflects a part of the beam towards a first reflecting mirror situated opposite a semi-reflecting plate and reflects a second part of the beam in the direction of a second reflecting mirror located opposite the second semi-reflecting plate. The symmetrical arrangement of the optical elements for one and the other of the parts of the display system thus allows projection on both sides of the screen of the same image orientation. This variant has the advantage of using only one image source and thus reducing the financial cost of the display system. The example of Figure 8 shows a display system with two images displayed, but it can be adapted to display more source images. For this, the display system comprises a number N of elementary projectors each associated with a semireflecting surface of the same semi-reflecting structure so as to reflect the projection beams of each elementary projector towards a d-element. display having a plurality of display faces each located in the image plane of the corresponding optical system.

FIGS. 9a and 9b are diagrammatic sectional views partially illustrating alternative embodiments of a partially transparent and partially retro-reflective screen on its two opposite faces, which can be used in the display system shown in FIG. 8.

In the example of FIG. 9a, two screens as described in the embodiment of FIG. 5d have been assembled to one another, for example by gluing. The screen thus formed comprises two screen portions 180, 180 'fixed back to back. It comprises a plurality of retro-reflective portions 140 surrounded by peripheral transparent portions 150. The retro-reflective portions 140 here comprise structures each formed of a notch 121, 121 ', or cube-shaped hollow patterning, but they can have several adjacent structures. Each retro-reflective portion 140 having at least two wedge-shaped notches 121, 121 'disposed opposite one another according to the thickness of the screen and oriented so that the base of the cube corner each of them facing the corresponding display face. Preferably, the indentations 121, 121 'of the same retro-reflective portion 140 are located vis-à-vis, and in a planar symmetrical with respect to a plane of the screen passing between the two screen portions. The beams incident on a first display face 110 are therefore partially retro-reflected by the indentations 121 of the first screen portion 180 and are partly transmitted by the transparent portions 150 towards the second display face 110. 'and vice versa. Furthermore, diffusing elements 160, 160 'similar to those described with reference to FIG. 5d may be provided on the display faces, preferably only at the level of the retro-reflective portions.

In the example of FIG. 9b, two screens as described in the embodiment of FIG. 5d have been assembled to one another, for example by gluing. The screen thus formed comprises two screen portions 180, 180 'identical to those described in the example of FIG. 9a. They are fixed back-to-back through a layer 165 having opaque portions 166 located only between each cube-corner indentation. These opaque, non-transparent portions make it possible to limit the effects of transmission diffusion by the indentations.

As a variant, a partially transparent and partially retro-reflective screen on its two opposite faces may be made by assembling two screens to each other as described in the embodiment of FIG. 3, for example leaving a air gap between the two faces which comprise the protuberances. Both screens can be assembled by gluing.

With reference to FIG. 10, a fourth embodiment of an alternative display system is now described with respect to the examples illustrated in FIGS. 6 and 7, in which the optical axes of retro-reflection Arr and of specular reflection Ars are dissociated. by a particular arrangement of the projector and the semi-reflective structure vis-à-vis the display screen. In this fourth embodiment, the parasitic beams are filtered by the use of several linear polarizers, thereby favoring the retro-reflected beams. This variant applies in particular when the retro-reflection of the display screen is provided by non-metallized cube corners (protuberances or indentations), that is to say that it is essentially obtained by total reflection. internally inside the cube corners.

In order to filter the portion of the beams from the specularly reflected projector by the screen, a first linear PI polarizer having a transmission axis μ1 is disposed on the optical path between the projector 200 and the semi-reflective structure 300, for example at the outlet opening 241 of the housing 240. A second linear polarizer P2 having a transmission axis u2 orthogonal to the axis ul is located between the observer and the semi-reflecting structure 300, for example on the outer face 312 thereof. Thus, the portion of the light beams from the projector reflected specularly by the screen 100 is filtered by the polarizer P2 while the retro-reflected part is transmitted towards the observer. Indeed, the beams emitted by the projector and transmitted by the polarizer PI are polarized rectilinearly along the axis ul, then the part reflected specularly by the display screen (which retains the same polarization) is filtered by the polarizer P2 insofar as these reflected beams are polarized linearly along an axis orthogonal to the transmission axis u2. On the other hand, the retro-reflected beams are transmitted by the polarizer P2 insofar as the cube-corner retro-reflection modifies the rectilinear polarization of the incident beams in a different polarization, in particular an elliptical polarization. Thus, the retro-reflected portion of the beams, by its elliptical polarization, is transmitted by the polarizer P2 in a polarized manner along the axis u2.

The polarizer P2 in association with the polarizer PI also filters the portion of the beams coming directly from the projector and transmitted by the semi-reflective structure (Axis beams At described with reference to Figures 6, 7 and 8). Preferably, the polarizer PI has an ul axis oriented so that the polarization at the output of the projector is perpendicular to the plane of incidence on the plate of the structure semi-reflective. This optimizes the reflection of the beams by the semi-reflective structure.

Alternatively or additionally, in order to filter the portion of the beams coming from the projector transmitted by the screen, a third linear polariser P3 of transmission axis u3 coplanar with the axis u2 and orthogonal to the axis ul is located at the face 111 opposed to the display face 110 of the screen 100. Thus, the beams from the projector are transmitted by the polarizer PI and polarized rectilinearly along the axis ul, then the portion transmitted by the screen The display (which retains the same polarization) is filtered by the polarizer P3 insofar as these transmitted beams are linearly polarized along an axis orthogonal to the transmission axis u3.

Moreover, the polarizers P2 and P3 do not disturb the beams coming from the scene and transmitted by the partial transparency of the screen insofar as the transmission axes u2 and u3 are coplanar.

This variant advantageously makes it possible to eliminate the parasitic beams without resorting to the arrangement of the various elements described with reference to FIGS. 6 and 7. Moreover, this variant is all the more advantageous as the screen comprises diffusing elements on the or the display faces.

It is also possible to introduce the polarizers PI and P2 in a display system whose screen has a double display face as shown in Figure 8. In this case, each elementary projector 201 and 20 is provided with of a linear polariser PI, Ρ of axis ul and ul ', and each semi-transparent plate 310 and 310' of a linear polarizer P2, P2 'of axis u2 and u2'. The axes u2 and u2 'are respectively orthogonal to the axes ul and ul', and are coplanar with each other. Thus, it is not necessary that the screen 100 comprises a polarizer P3 located between the two display faces 110 and 110 'insofar as the previously described optical function obtained by the pair of polarizers {P2, P3}, namely the transmission of beams from the scene as well as the filtering of the portion transmitted by the beam screen from the projectors, is provided by the pair of polarizers {P2, P2 '}.

Specific embodiments have just been described. Various variations and modifications will occur to those skilled in the art. As an alternative to the retro-reflective display screen examples described above, the screen may comprise, not protuberances or cube-corner structures providing the retro-reflection function, but areas coated with a layer of a retro-reflective material based on microbeads. The screen then comprises a plurality of substantially identical and juxtaposed elementary regions, disposed over substantially the entire surface of the screen, each of which is formed of a retro-reflective portion surrounded by a peripheral transparent portion. The retro-reflective portions are areas coated with a layer of the microbead-based material and the transparent portions are areas not coated by this layer. This example is thus similar to that of FIG. 3, in which the face comprising the protuberances is here a substantially flat face, some portions of which are covered by the material based on microbeads.

When the screen has a single display face, the retro-reflective portions may be arranged only on one face of the screen, either the face facing the semi-transparent blade or the face opposite to that here, since the microbeads are retro-reflective in all directions of illumination.

When the two faces of the screen are display faces, each face has retro-reflective portions surrounded by peripheral transparent portions, each retro-reflective portion of a face being disposed facing a retro-reflective portion of the opposite face and each transparent portion of the same face being disposed opposite a transparent portion of the opposite face. In other words, the arrangement of the retro-reflective portions and the transparent portions is symmetrical from one face to the other with respect to the plane of the screen. It is then advantageous to provide between the two faces of the screen opaque portions located between each pair of retro-reflective portions with microbeads, to limit the diffusion effects in transmission. According to another embodiment of the display screen, the screen may be similar or identical to the screen examples described above and may further comprise an active layer adapted to form, temporarily or permanently, opaque areas and transparent areas on the entire surface of the screen. In the case of a single-sided display screen, this active layer of controlled opacity may be located at the face opposite to the display face (advantageously the plane face 171 of the screen illustrated in FIG. 5d); and in the case of a double-sided display screen, this active layer can be located inside the screen, for example between the two screen portions described with reference to Figures 9a and 9b. This active layer, for example a transparent LCD screen, is connected to control means for activating the opaque areas according to the shape of the displayed image and its position on the screen. Thus, it is advantageous, to improve the contrast of the displayed image, that the location and the extent of the opaque zones correspond substantially to those of the image displayed on the screen.

As an alternative to the previously described display system examples in which the projector is located at the bottom of the display system, an inverted configuration is possible in which the projector is located in the upper part of the display system. and optionally rests on the base of the pyramidal structure formed in part by the semi-reflective structure.

Claims

A display system (10) for a floating image, comprising:

at least one image source (210, 210 ') adapted to provide an image to be displayed; a semi-reflecting structure (300) adapted to reflect light beams from the image source (210, 210 ');

characterized in that it further comprises:

a partially transparent display screen (100) comprising at least one display face (110, 110 '), the screen being adapted:

displaying a projected image on its display face (110, 110 ') via the semi-reflecting structure (300), and o partially transmitting incident light on its opposite side to the display face (110, 110 ');

at least one projection optic (220, 220 ') adapted to project on the display screen (100) via the semi-reflecting structure (300) the image supplied by said image source ( 210, 210 ');

the display screen (100) being partially transparent and partially retroreflective at its display face (110, 110 '), and having retro-reflective portions (140) and transparent portions (150); distributed over all or part of its extent, each retro-reflective portion (140) being separated from neighboring retro-reflective portions by a transparent portion (150), the retro-reflective portions (140) having structure (120; 121, 12 ) in cube corner.

The display system (10) of claim 1, wherein the occultation ratio by the retro-reflective portions (140) is 50% or less.

The display system (10) according to claim 1 or 2, wherein the display screen (100) is partially transparent and partially retroreflective on its two opposite faces (110, 110 '), the other, each forming a display face.

The display system (10) according to claim 3, wherein the display screen (100) comprises at least one plate of transparent material whose two faces (110, 110 ') are smooth to form display faces, and have transparent portions (150) and retro-reflective portions (140) distributed over all or part of its extent, each retro-reflective portion being separated from neighboring retro-reflective portions by a transparent portion, each retro-reflective portion (140) having at least two wedge-shaped notches (121, 12) disposed facing one of the another according to the thickness of the screen and oriented so that the base of the cube corner of each is opposite the corresponding display face (110, 110 ').

The display system (10) of claim 4, wherein the inner side faces of the cube corner indentations (121) are covered with a metal layer.

(173).

The display system (10) according to claim 4 or 5, wherein the display screen has opaque portions (166) located at least between each indentation (121, 121 ') of a same retroreflective portion. reflective (140) depending on the thickness of the screen.

The display system (10) according to any one of claims 3 to 6, wherein:

- The display screen (100) comprises at least two faces (110, 110 ') opposite to each other, said display faces, and is adapted to display a projected image on each of its two faces display, and to partially transmit an incident light thereon;

at least two so-called elementary projectors (201, 20) each comprise an image source (210, 210 ') associated with a projection optical system (220, 220'), and are each adapted to project an image provided by the image source (210, 210 ') on one or the other of the display faces (110, 110') of the screen; and

the semi-reflecting structure (300) is adapted to reflect light beams coming from each elementary projector (201, 20) in the direction of the corresponding display face (110, 110 ') of the screen.

8. Display system (10) according to any one of claims 1 to 3, wherein the screen (100) comprises a plate of a transparent material having a first face (110) smooth, and a second face (111). opposed to the first and structured in the form of cube-corner protuberances (120) at the retro-reflective portions (140) and smooth at the transparent portions (150).

9. Display system (10) according to any one of the preceding claims, wherein the semi-reflecting structure (300) has, optionally in association with the display screen (100), a pyramid shape whose base is located opposite an elementary projector (201, 20) formed of said image source (210, 210 ') and said projection optical system (220, 220').

The display system (10) according to any one of the preceding claims, wherein at least a first linear polarizer (PI) having a first transmission axis (μ1) disposed between the projection optics (220) and the semi-reflective structure (300), and at least one second linear polarizer (P2) having a second transmission axis (u2) orthogonal to the first axis (ul) and disposed on one side of the opposing semi-reflective structure (300) on the display screen (100) and the projection optics (220).

The display system (10) according to any one of the preceding claims, wherein the elementary projector (201, 20) formed of the image source (210, 210 ') and the projection optical system (220, 220 '), the semi-reflecting structure (300) and the display screen (100) are arranged mutually to dissociate light beams from the elementary projector (201, 201'), retro-reflected by the screen (100) and transmitted by the semi-reflecting structure (300):

- light beams from the elementary projector (201, 201 ') and reflected specularly by the display screen (100), and / or

- Light beams from the elementary projector (201, 201 ') and transmitted by the semi-reflective structure (300).

12. Display system (10) according to the preceding claim, wherein said arrangement is adapted so that light beams emitted by the elementary projector (201, 20) and incident on the display face (110, 110 ') form an angle of incidence (a) with respect to the plane of said display face less than 90 °, and preferably between 55 ° and 80 °; or is adapted so that said angle of incidence (a) is greater than 90 ° and preferably between 90 ° and 115 °.

The display system (10) according to any one of the preceding claims, wherein the display screen further comprises an active layer adapted to form opaque areas and transparent areas, the opaque areas being located at the of the displayed image.