Patent Application
20160170225
The present patent application claims the priority benefit of French patent application FR13/56950 which is herein incorporated by reference.
The present application relates to a transmissive diffuser screen, for example, for a rear projection display device.
Rear projection display devices are advantageously compatible with different rear projection supports, also called screens. They are in particular compatible with rear projection supports having curved or complex shapes. Such devices are thus particularly capable of providing information in passenger compartments of vehicles, for example cars. Indeed, rear projection display devices may for example be integrated in the central console of the passenger compartment of a car, or also above this central console.
However, devices integrated in vehicle passenger compartments are subject to significant constraints: such devices should in particular be relatively compact and sufficiently directional to avoid projections towards reflective elements such as the windshield or lateral windows. Further, such devices should ensure the generation of an output light flow sufficient to avoid problems of readability when the vehicle is placed under an illumination of high luminosity, for example, from the sun.
To limit readability problems, a cap is generally provided above the display screens in vehicle passenger compartments. However, this solution is not adapted to the integration of a screen on a significant surface area, for example, in the central console of the vehicle.
An object of an embodiment is to provide a transmissive diffuser screen capable of being integrated in a rear projection display device overcoming all or part of the disadvantages of known devices.
Thus, an embodiment provides a transmissive diffuser screen comprising a transparent support, a first side of the support being covered with a first diffusive microstructure, and a second side of the support being covered with an optical focusing structure having its surface covered with a second diffusive microstructure.
According to an embodiment, the optical focusing structure is a Fresnel lens.
According to an embodiment, the second diffusive microstructure is defined on the surface of each of the convex portions of the Fresnel lens.
According to an embodiment, the focusing structure is placed on the support by means of glue.
According to an embodiment, the support, the optical focusing structure, the first diffusive microstructure, and the second diffusive microstructure are defined in a single block.
According to an embodiment, the first diffusive microstructure and the second diffusive microstructure are formed of films placed at the surface, respectively, of the first side of the support and of the optical focusing structure.
According to an embodiment, the optical focusing structure has a focal distance in the range from 200 to 400 mm.
Another embodiment provides a rear projection device, comprising a screen of the above-mentioned type.
Another embodiment provides a central console of a vehicle, comprising a rear projection device of the above-mentioned type.
The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which:
For clarity, the same elements have been designated with the same reference numerals in the different drawings and, further, as usual in the representation of optical systems, the various drawings are not to scale.
The transmissive diffuser screen which is provided herein is particularly capable of being used in a rear projection display device to replace the selection of screen 14 or of the screens placed at the level of sections 12 of central console 10, or to replace the assembly of sections of the central console, without using a cap, the device being provided to be sufficiently directional to avoid projecting information towards the windshield or the lateral windows and being further sufficiently bright to be readable when the screen is reached by parasitic ambient light rays, for example, from the sun.
Further, the transmissive diffuser screen provided herein may have a curved shape and thus be integrated in the passenger compartment, and particularly in the central console, “seamlessly”, that is, in a single block at the front of the central console.
The device comprises a package 20 having projection elements of the rear projection display device integrated therein. In the shown example, package 20 is defined by two substantially parallel first walls 22 and 24, two second walls 26 and 28 substantially parallel to each other, and a third wall 29. Walls 26 and 28 form a non-right angle with walls 22 and 24 and, more specifically, the angle between wall 26 and wall 22 is an obtuse angle and the angle between wall 22 and wall 28 is an acute angle. Wall 29 is perpendicular to walls 22 and 24 and is positioned between walls 24 and 26. Wall 24 is slightly shorter than wall 22 and wall 26 is slightly shorter than wall 28 in the plane of
Package 20 comprises an output opening in wall 22 having a transmissive diffuser screen 30, for example, a holographic diffuser screen, positioned therein. Screen 30 allows the transmission of the rays reaching it on the inner side of package 20 to the outside of package 20 with a slight diffusion of these rays.
Two planar reflective mirrors 32 and 34 respectively positioned along wall 28 and wall 26 are provided inside of the package. A laser projector 36, for example, a pico projector forming an image by scanning of a laser beam, is substantially positioned at the angle between walls 24 and 29. In projector 36, the scanning is for example obtained via a rotating mirror, for example, according to a technology called DLP, for “Digital Light Processing”, in the art. Laser source 36 is positioned to illuminate mirror 34, so that the beam reflected by mirror 34 reaches mirror 32, and that the beam reflected by mirror 32 reaches transmissive holographic diffuser 30. As shown in the example of
The positioning of mirror 32 relative to transmissive holographic diffuser 30, according to an acute angle, enables to provide a projection with no deformation (a square gives a square). This constraint imposes for mirror 32 to be placed relatively opposite the transmissive holographic diffuser.
The diffuser screen comprises a plate 40 having diffusive microstructures 42, ensuring a diffusion of the light beams reaching them, provided on one side thereof. Generally, microstructures 42 are placed on plate 40 of the output side thereof, that is, on its non-illuminated side. A laser beam 44 thus reaches plate 40 on the side opposite to that containing microstructures 42. The laser beam is diffused by microstructures 42, which forms a large number of diffused beams 46 at the plate output.
The right-hand side of
As can be seen in
To limit speckle phenomena, it is known to use mobile diffusers, for example, rotating or mobile in translation. By selecting a motion frequency greater than the persistence of vision, the eye thus averages the speckle patterns. However, the use of mobile parts to drive the screen, in particular in the case of a large screen such as that provided in the above application, implies a significant increase of the cost of the device, while increasing the bulk and decreasing the reliability thereof.
It is thus desired to form transmissive diffuser screens where the coherence, and thus speckle phenomena, are attenuated to obtain an intensity pattern such as that illustrated in dotted lines in curve 53 in
Further, particularly for applications such as those provided in relation with
Thus, to overcome all or part of the disadvantages of conventional diffusion plates, a transmissive diffuser comprising different elements enabling to suppress a great part of speckle phenomena and providing a diffusion in a controlled direction, is here provided.
The screen comprises a transparent plate 50 having diffusive microstructures 52 ensuring a diffusion of rays provided on one side thereof. The side having the microstructures provided thereon is the side intended to be placed on the observer's side, that is, the output side of the transmissive diffuser screen. On the input side of the screen, that is, opposite microstructures 52, is provided an optical focusing structure 54, in the shown example, a Fresnel lens 54. This lens having its primary focal point located at the level of laser source 36 (see
Microstructure 56 thus implies forming a plurality of secondary sources 62 having their beams, after diffusion on microstructure 52, exhibiting an attenuated coherence. Indeed, beams 62 travel different distances in plate 50, which at least largely cancels the spatial coherence of the different beams originating from microstructure 52. Thus, at the device output, the obtained beam substantially has an intensity in the form of that of curve 53 of
In
The cumulated used of the Fresnel lens and of the two microstructures, on the input side and the output side of the diffuser screen, thus provides a good focusing of incident light beams, limits speckle phenomena, while ensuring the main function of the plate, that is, the diffusion of the incident beam.
When the screen of
It should be noted that microstructure 56 is preferably formed of a holographic-type diffuser which enables to control the angles for which light is diffused, these angles corresponding to the width at mid-height of the indicatrix of diffusion. It should also be noted that the diffusion angle of microstructure 56 is selected so that the beam thus diffused by an angle θ generates an image spot on the output side of plate 50 located at a distance e from the input surface of plate 50, compatible with the desired resolution r, that is, satisfying equation: r=2.e.tan(θ/2).
As an example, microstructures 52 and 56 may be formed of holographic films formed at the surface, respectively, of plate 50 and of Fresnel lens 54, topped with a metallization. Such microstructures are particularly known and commercialized by Luminit.
The microstructures may be obtained by molding or by printing. Such microstructures are of pseudo-random nature. As an example, the mold or the printing pattern may be obtained by recording a speckle pattern by a holographic method. The characteristic dimensions of such microstructures are for example an average pitch in the range from 1 to 200 μm, and a depth (or outgrowth height) in the range from 0.5 to 5 μm.
It should be noted that the screen of
Further, the forming of a Fresnel lens 54 at the surface of the plate easily enables to obtain a lens having a focal distance in the range from 200 to 400 mm, for example, in the order of 300 mm, while having a relatively small bulk (for example, with a pitch in the range from 0.2 to 0.3 mm).
Specific embodiments have been described. Various alterations and modifications will occur to those skilled in the art. A diffusion screen where the optical focusing structure is a Fresnel lens has in particular been provided in the drawings. It should be noted that this lens may be replaced with any optical focusing device, microstructure 56 being then defined on the surface of this optical focusing device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1356950 | Jul 2013 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2014/051796 | 7/11/2014 | WO | 00 |
