Image-projection device with reflection using electrochromic material

Abstract

One aspect of the invention relates to an image-projection device (5) comprising: - a light source (6) for the emission of light rays, - an image-forming module (Im) comprising a reflection assembly (10) which is able to reflect the light rays originating from the light source as a reflected beam (FR), - an optical projection system (8) placed in the path of the reflected beam (FR) and able to project an image formed by the image-forming module, wherein the reflection assembly comprises a multilayer structure comprising a substrate, a metal layer, and a layer of electrochromic material comprising at least one cell, at least one cell being encapsulated in an electrolyte layer and connected to a pair of electrodes. The image-projection device further comprises an electrical control circuit which is able to vary an electric voltage applied to the pair of electrodes so as to vary a colour of the at least one cell.

Description

Image projection device with reflection by electrochromic material TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of image projection devices and more particularly those equipping motor vehicles and allowing the projection of images onto the ground. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Today, there are such devices, sometimes called "dynamic carpet projectors" in English (modular ground projectors), which allow images to be projected onto the ground when a door is opened or unlocked, or when approaching it, when the driver brings a key or an opening badge close to the vehicle.

[0003] Such a device comprises a light source, generally a light-emitting diode, which produces an illuminating light beam, shaped by an illumination or collimating lens placed downstream of the source, between the source and the image to be projected. The image to be projected transmits or reflects, depending on the technology used, the illuminating light beam towards an optical projection system, which projects the image onto the ground.

[0004] The image to be projected can be produced by different technologies. For example, a micromirror array (or DMD for "digital micromirror device") can be used. This technology has the disadvantage of creating hot spots inside the device and is therefore not thermally robust. Alternatively, a microLED array can be used, but heat dissipation problems are also encountered. A third technology is that using laser-scanned microelectromechanical systems ("laser-scanned MEMS"). This last technology is emerging and is not robust to mechanical vibrations.

[0005] The invention offers a solution to the problems mentioned above, by proposing an alternative technology for the production of the image to be projected.

[0006] A first aspect of the invention relates to an image projection device comprising:- a light source for emitting light rays,- an image formation module comprising a reflection assembly capable of reflecting light rays from the light source into a reflected beam,- an optical projection system placed in the path of the reflected beam and capable of projecting an image formed by the image formation module.The reflection assembly comprises a multilayer structure comprising a substrate, a metal layer, and a layer of electrochromic material comprising at least one cell encapsulated in a layer of electrolyte and connected to a pair of electrodes,the image projection device further comprising an electrical control circuit capable of varying an electrical voltage applied to the pair of electrodes so as to vary a color of said at least one cell.

[0007] Thus, thanks to the invention, it is possible to project an image on the ground without any hot spot or heat dissipation problems and without any robustness problems.

[0008] According to a first embodiment, the layer of electrochromic material may comprise a single cell and the image formation module may further comprise at least one mask positioned between the reflection assembly and the optical projection system, said mask being capable of producing a pattern of the image formed by the image formation module.

[0009] Thus, it is possible to vary the color of the projected pattern by controlling the electrical voltage applied to the single cell, the pattern being determined by the mask. It is thus possible to achieve dynamic projection, at least by varying the color, without problems of hot spots, heat dissipation or robustness.

[0010] Additionally, the image formation module may comprise a set of several masks, and the electrical control circuit may be capable of selecting one of the masks from the set for producing the pattern of the image formed by the image formation module.

[0011] This makes it possible to vary the projected image, both in terms of its color and the projected pattern. This makes it possible to project varied images or create light animations.

[0012] Alternatively, according to second and third embodiments, the reflection assembly may comprise a plurality of pixels, each pixel being formed by at least one cell and being connected to at least one pair of electrodes, the electrical control circuit being capable of independently varying the electrical voltage applied to said at least one pair of electrodes of each pixel.

[0013] It is thus made possible to project pixelated images by reflection with a layer of electrochromic material, which has the advantages of not posing any heat dissipation problems, allowing high robustness and less bulk compared to prior art solutions.

[0014] Additionally, each pixel of the plurality of pixels may have a length and width of between 50 and 500 micrometers, in particular between 70 and 150 micrometers.

[0015] This makes it possible to project a high resolution image with a smaller footprint of the image projection device.

[0016] According to the second embodiment, each pixel can be formed by a single cell and is connected to a single pair of electrodes.

[0017] Thus, the color control of each pixel is determined directly by the electrical voltage applied to the corresponding cell, which simplifies the control of the projected image.

[0018] According to the third embodiment, each pixel may be formed by a plurality of cells and, for each pixel, the plurality of cells may comprise at least a first set of at least one cell and a second set of at least one cell, the first set being connected to a first pair of electrodes and the second set being connected to a second pair of electrodes, and the electrical control circuit may be capable of varying the color of each pixel by varying a first electrical voltage of the first pair of electrodes and a second electrical voltage of the second pair of electrodes.

[0019] Thus, the color of a pixel is obtained by synthesizing the colors of cells that make up the pixel. This makes it possible to project color images with a wide range of colors.

[0020] Additionally, for each pixel, the first set can include several cells and the second set can include several cells.

[0021] This simplifies the control of the color of each pixel compared to cell-by-cell control. In particular, it is possible to create smaller cells and therefore reduce the size associated with the image projection device.

[0022] According to embodiments, the electrochromic material can be selected from PEDOT, PMMA or polycarbonate.

[0023] Such materials are electrochromic, are robust and have lower costs compared to prior art solutions.

[0024] A second aspect of the invention relates to a method for controlling an image projection device according to the first aspect of the invention, the image projection device comprising the following steps: - reception of an instruction by the electrical control circuit; - determination of an electrical voltage to be applied to each pair of electrodes as a function of said instruction; - application, for each pair of electrodes, of said electrical voltage by the electrical control circuit.

[0025] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0026] The figures are presented for information purposes only and in no way limit the invention: - L schematically represents a vehicle equipped with an image projection device according to embodiments of the invention, seen from the side; - L schematically represents an image projection device according to embodiments of the invention; - L schematically represents a reflection assembly comprising a multilayer structure according to embodiments of the invention; - L represents a reflection assembly of an image projection device according to embodiments of the invention; - L illustrates the dependence of the wavelength reflected by a layer of electrochromic material illuminated by a broadband spectrum beam as a function of the thickness of this layer; - L illustrates a front view of a reflection assembly of an image projection device, according to a first embodiment of the invention;- illustrates a front view of a reflection assembly of an image projection device, according to a second embodiment of the invention; - illustrates a front view of a reflection assembly of an image projection device, according to a third embodiment of the invention.; DETAILED DESCRIPTION

[0027] The figures are presented for information purposes only and in no way limit the invention. Unless otherwise specified, the same element appearing in different figures has a single reference.

[0028] The represents a motor vehicle 1 equipped with an image projection device 5, allowing the projection of an image 103 onto the ground. The device 5 can be controlled by the opening of a front or rear door 100, or another opening such as the trunk 101.

[0029] The device 5 is placed at the bottom of the body, where the height is limited and the environment is aggressive (water splashes, risk of impact with elements on the road, etc.). It is therefore protected by a housing, of limited size (since the device is 20 cm to 30 cm from the ground), for example 4 to 10 cm on each side. The housing is more compact than the housings of the prior art due to the technology used in the present invention. Alternatively, the device 5 can be placed in a rearview mirror.

[0030] Diagrammatically represents the image projection device 5 according to the invention.

[0031] The image projection device 5 comprises a light source 6 for emitting a source beam F s . Advantageously, as will be seen later, the source beam F s has a broadband emission spectrum. Typically, the source beam F sis a beam of white light. The light source 6 is, for example, a light-emitting diode. In another example, the light source 6 is a laser source.

[0032] The device 5 also includes an optional illumination optical system 7, and an image formation module Im.

[0033] The light source 6 is positioned so as to illuminate the optical lighting system 7. The optical lighting system 7 here comprises a collimator 71 and a condenser 72. The optical lighting system 7 makes it possible to shape the source beam F s , in particular transform it into a beam hereinafter called homogeneous beam F H. The optical illumination system 7 is placed downstream of the light source 6, between the light source 6 and the image formation module. The image formation module Im, which will be described later, comprises at least one image formation assembly 10 which is capable of reflecting the homogeneous beam F H in a reflected beam F R .

[0034] The image forming assembly 10 according to the invention comprises at least one cell having a multi-layer structure described with reference to the.

[0035] The device 5 also comprises an optical projection system 8 arranged to project onto the ground, from the motor vehicle 1, the image to be projected formed by the image formation module Im. The optical projection system 8 is located on the path of the reflected beam F R, downstream of the image formation module to be projected Im. Typically, the optical projection system 8 comprises one or more lenses. Preferably, the image formed by the image formation module Im is positioned in the object focal plane of the optical projection system 8.

[0036] The optical projection system 8 forms on the ground an image 103 of the image to be projected, with a very high magnification, and, in general, an expansion effect. Indeed, the image 103 formed on the ground has at least 0.5 m on each side, and can even occupy an area 1 m long by 1 m wide or more, and the ground is illuminated grazingly by the image projection device.

[0037] One of the particularities of the invention lies in the reflection assembly 10 which comprises a multilayer structure S, shown schematically in the, composed of the stack of a substrate 2, which may be flexible, of a metallic layer 3, and of a layer of electrochromic material 4.

[0038] For example, the flexible substrate 2 is an organic material made of silicone, polycarbonate or PMMA. The substrate 2 has, for example, a thickness of the order of 500 microns.

[0039] The metal layer 3 is delimited by a first face F1 and a second face F2. The first face F1 is in contact with a face F0 of the flexible substrate 2. For example, the metal layer 3 may be made of aluminum, chromium or gold. The metal layer 3 has, for example, a thickness of between 70 and 100 nm.

[0040] The electrochromic organic material layer 4 is delimited by a third face F3 and a fourth face F4. By electrochromic is meant a material that changes color when an electric voltage is applied to it for a short time. The material retains the new color after the voltage is applied, but can return to its original state after applying a voltage of opposite sign. The third face F3 is in contact with the second face F2. For example, the electrochromic organic material is PEDOT (poly(3,4-ethylenedioxythiophene)). Other examples of electrochromic material that can be used are 2-alkylthieno[3,4-b]thiophene (T34bT), PMMA or polycarbonate. The electrochromic material layer 4 has for example a thickness between 75 and 300 nm.

[0041] The layer of electrochromic material 4 can here be structured into N cells or elements, N being an integer greater than or equal to 1.

[0042] When N is greater than or equal to 2, the reflection set 10 may comprise several pixels, each pixel being formed by at least one of the N cells. The reflection set 10 then comprises N pixels or less than N pixels.

[0043] A portion of the multilayer structure with N cells C1, C2, C3,… and CN, is shown in the, with N equal to 4. For example, the electrochromic material layer 4 is structured into a matrix of N cells.

[0044] Each cell among the N cells may be encapsulated in an electrolyte solution or gel, to which is connected a pair of electrodes provided for voltage biasing the corresponding cell. Alternatively, when each pixel comprises several cells according to the third embodiment described in the following, a set of several cells may be encapsulated in an electrolyte solution or gel, so as to be connected to the same pair of electrodes.

[0045] The size of each cell depends on the embodiment considered, three embodiments being described in the following.

[0046] The encapsulation and arrangement of the N cells and the arrangement of the corresponding electrode pairs on each cell or set of cells are carried out similarly to those of a liquid crystal plate.

[0047] All pairs of electrodes are connected to a low voltage battery and connected to an electrical control circuit 15 connected to the vehicle's electrical network.

[0048] The following describes how the color of a cell among the N cells of the layer of electrochromic organic material 4 is controlled. Such a cell acts as a Fabry-Pérot cavity formed by the portion of the third face F3 and the portion of the fourth face F4 corresponding to each other. This cavity produces, from the light it receives, interferences of a determined wavelength. These interferences result in multiple reflections of colored rays propagating in the opposite direction to the rays received from the light source 6. Thus, it is by a phenomenon of interference, and not of absorption as when pigments or dyes are used, that the cell produces, for an observer, a colored rendering.

[0049] In the present invention, the light received by the N cells can come from the homogeneous beam F H or can come directly from the light source 6 .

[0050] Typically, electrochromic material reflects between 60% and 90% of the light it receives. For example, the light source, when it is a white light-emitting diode, has a flux of 400 lumens, the material thus reflecting between 240 lumens and 360 lumens.

[0051] As previously stated, the source beam F s emitted by the light source 6 preferably has a broadband emission spectrum. Thus, the range of wavelengths, in other words the range of colors, which can be reflected by the electrochromic material is wider.

[0052] The thickness of the layer of electrochromic organic material 4 has an influence on the color perceived by an observer. For example, as shown in the, a PEDOT layer of thickness e1 equal to 800 nm, when it receives a light of broadband light spectrum S(λ), produces by reflection a red color of wavelength λ1, a PEDOT layer, when it receives a light of broadband light spectrum S(λ) of thickness e2 equal to 600 nm produces by reflection a green color of wavelength λ2, a PEDOT layer of thickness e3 equal to 500 nm, when it receives a light of broadband light spectrum S(λ), produces by reflection a blue color of wavelength λ3.

[0053] For example, the N cells of the electrochromic organic material layer 4 can have different thicknesses so as to adjust their color when no voltage is applied to them.

[0054] Alternatively, all cells have the same thickness and control of the color they return is enabled by the voltage that is applied to each of the cells or each set of cells.

[0055] The electrical control circuit 15 makes it possible to control the voltage across the N cells of the layer of electrochromic organic material 4. A correspondence table between the desired color and the voltage to be applied across a pair of electrodes makes it possible to voltage control the color change of a cell or a set of cells. The correspondence table depends on the electrochromic organic material used. For example, the voltage across a pair of electrodes varies between a minimum voltage of -10 Volts and a maximum voltage of +10 Volts.

[0056] A single pair of electrodes connected to the control circuit 15 has been shown in the figure, for the sake of simplification.

[0057] Thus, the electrical control circuit 15, by receiving an instruction, makes it possible to control the voltage at the terminals of each pair of electrodes in order to control the color of the corresponding cell or of the corresponding set of cells.

[0058] The image to be projected is thus formed from at least the set of N pixels whose color is controlled by the application of a voltage, in the second and third embodiments described below. In a first embodiment with a single cell, only the color of the image to be projected is controlled by the reflection assembly 10, a pattern of the image being formed by means of the mask 9 placed between the reflection assembly 10 and the optical projection system 8.

[0059] The image to be projected is thus customizable.

[0060] This is a front view of a reflection assembly 10 of a device 5 according to a first embodiment of the invention.

[0061] According to the first embodiment, the layer of electrochromic material 4 comprises a single cell C. The electrical control circuit 15 is capable of controlling the electrical voltage of the single cell C in order to vary the color of the light reflected by the single cell C.

[0062] In the first embodiment, the reflection assembly 10 with a single cell is advantageously combined with the mask 9 so as to form the image formation module Im. The pattern of the image to be projected is thus produced by means of the mask 9 placed in interception in the reflected beam FR, between the reflection assembly 10 and the optical projection system 8, while the color of the image to be projected is determined by the electrical voltage applied by the electrical control circuit 15 to the single cell C.

[0063] Note that the mask 9 may be a single mask, or a set of masks. The electrical control circuit 15 may in particular select, by a control signal, the mask from the set of masks which is placed in interception between the reflection assembly 10 and the optical projection system 8. It is thus made possible to vary the pattern and the color of the image to be projected. The masks of the set may be distributed in a circular manner, and the application of a given rotation to the set may allow the electrical control circuit 15 to select one of the masks of the set.

[0064] No restrictions are attached to the dimensions of the single cell C, in particular to the width and length of the cell C, i.e. to the dimensions shown in the front view of the.

[0065] Representing a front view, the substrate 2 and the metal layer 3 are only partially visible. Alternatively, the substrate 2 and the metal layer 3 have the same dimensions in length and width as the single cell C, in which case the substrate 2 and the metal layer 3 are not visible in the.

[0066] This presents a reflection assembly 10 of a device 5 according to a second embodiment of the invention.

[0067] In the second embodiment, the layer of electrochromic material 4 of the reflection assembly 10 comprises a matrix of N cells C1 to CN, each cell being individually controlled by a voltage applied to it by the electrical control circuit 15, and each cell thus forming a pixel.

[0068] In the second embodiment, the reflection assembly therefore comprises N individually controllable pixels, and the resolution of the image formed is therefore equal to N.

[0069] Thus, the second embodiment makes it possible to project a pixelated color image from a reflection assembly 10 with a layer of electrochromic material 4.

[0070] No restrictions are attached to the dimensions of each cell C1 to CN, in particular to the width and length of each cell C1 to CN, i.e. to the dimensions represented in the front view of the.

[0071] For example, each cell may have a width and a length of between 50 and 500 micrometers, for example between 50 and 200 micrometers, and in particular between 70 and 150 micrometers. For example, each cell C1 to CN may be square in shape with a side of 100 micrometers.

[0072] Representing a front view, the substrate 2 and the metal layer 3 are only partially visible. Alternatively, the substrate 2 and the metal layer 3 have the same dimensions in length and width as the layer of electrochromic material 4, in which case the substrate 2 and the metal layer 3 are not visible in the.

[0073] Alternatively, cells C1 to CN are separate layers of electrochromic material, arranged on respective substrates 2 and metal layers 3.

[0074] An example with 15 cells is shown in the, for illustrative purposes. However, the reflection set 10 may include more than one hundred cells, or even more than one thousand cells.

[0075] This presents a reflection assembly 10 of a device 5 according to a third embodiment of the invention.

[0076] In the third embodiment, the reflection assembly 10 comprises a matrix of K pixels, K being greater than or equal to 2, each pixel comprising M cells, M being greater than or equal to 2.

[0077] The layer of electrochromic material 4 is thus divided into M*K cells, M cells forming a pixel of a matrix of pixels.

[0078] In the example in, M is equal to 9 and K is equal to 15. Therefore, N, the total number of cells, is equal to 9*15=135.

[0079] In the third embodiment, the color of each of the M pixels is obtained by synthesizing the colors of the K cells that make up the pixel. This allows for greater richness in the colors achievable by each pixel compared to the second embodiment.

[0080] The resolution of the formed image is equal to M, with a large variability of the colors obtained by synthesis of the colors of the K cells of each pixel.

[0081] Each cell in a pixel can be driven individually to reflect a light beam of a given color. Alternatively, multiple sets of cells in a pixel are driven together as a set. For example, each set can be a row or a column of pixels.

[0082] No restrictions are attached to the dimensions of each P1-PK pixel, in particular to the width and length of each P1 to PK cell, i.e. to the dimensions represented in the front view of the.

[0083] For example, each pixel may have a width and a length of between 50 and 500 micrometers, for example between 50 and 200 micrometers, and in particular between 70 and 150 micrometers. For example, each pixel P1 to PK may be square in shape with a side of 100 micrometers.

[0084] There are also no restrictions on the dimensions of the cells in each pixel, including the length and width of each cell. Such dimensions depend on the number of cells per pixel and the dimensions of the pixel. For example, each cell may have a length and width between 20 and 50 micrometers, including between 30 and 40 micrometers.

[0085] An example of the third embodiment is described below, for illustrative purposes only.

[0086] In this example, the nine cells of a given pixel are controllable by column. Thus, each column forms a set of cells whose color can be controlled by the electrical control circuit. Thus, the three columns can be controlled separately, which makes it possible to synthesize a pixel color from the respective colors of the three columns.

[0087] For example, taking the particular example of the fourth pixel P4, the first column includes cells C4,1; C4,4 and C4,7, the second column includes cells C4,2; C4,5 and C4,8 and the third column includes cells C4,3; C4,6 and C4,9.

[0088] So, when all three columns are red, the pixel is red. When the first column and third columns are blue and the second column is red, the pixel is purple. When the first column and third columns are red, and when the second column is green, the pixel is yellow, and so on.

[0089] A method of controlling the image projection device described above is described below.

[0090] The electrical control circuit 15 can receive an instruction. In the second and third embodiments, on the basis of which the electrical control circuit determines a set of voltages to be applied to the cells or sets of cells of the layer of electrochromic organic material 4. The set of voltages translates the colored pattern forming the image that the user wishes to project. In the first embodiment, the electrical control circuit 15 determines the color of the single cell C, and optionally a mask pattern 9, on the basis of the instruction.

[0091] Once the voltage(s) are applied to the cell(s) of the electrochromic material layer 4, the light source 6 is switched on in order to emit the source beam F S , which is transformed into the homogeneous beam F H by the optical illumination system 7. The multilayer structure S forming the image Im receives the homogeneous beam F Hand reflects it towards the projection optical system 8. The projection optical system 8 projects the image 103 onto the ground.

Claims

Image projection device (5) comprising:- a light source (6) for emitting light rays,- an image formation module comprising a reflection assembly capable of reflecting light rays from the light source into a reflected beam (F R ),- an optical projection system (8) placed on the path of the reflected beam (F R ) and capable of projecting an image formed by the image forming module, wherein the reflection assembly comprises a multilayer structure (S) comprising a substrate (2), a metal layer (3), and a layer of electrochromic material (4) comprising at least one cell encapsulated in an electrolyte layer and connected to a pair of electrodes, the image projection device further comprising an electrical control circuit capable of varying an electrical voltage applied to the pair of electrodes so as to vary a color of said at least one cell. Image projection device (5) according to claim 1, wherein the layer of electrochromic material (4) comprises a single cell (C) and wherein the image formation module (Im) further comprises at least one mask (9) positioned between the reflection assembly and the optical projection system (8), said mask being capable of producing a pattern of the image formed by the image formation module. Image projection device (5) according to claim 2, wherein the image formation module (Im) comprises a set of several masks (9), and wherein the electrical control circuit (15) is capable of selecting one of the masks of the set for producing the pattern of the image formed by the image formation module. Image projection device (5) according to claim 1, wherein the reflection assembly (10) comprises a plurality of pixels, each pixel being formed by at least one cell and being connected to at least one pair of electrodes, the electrical control circuit (15) being capable of independently varying the electrical voltage applied to said at least one pair of electrodes of each pixel. An image projection device (5) according to claim 3, wherein each pixel of the plurality of pixels has a length and a width of between 50 and 500 micrometers, in particular between 70 and 150 micrometers. Image projection device (5) according to claim 3 or 4, wherein each pixel is formed by a single cell (C1-CN) and is connected to a single pair of electrodes. Image projection device (5) according to claim 3 or 4, wherein each pixel (P1-PK) is formed by a plurality of cells (C4,1-C4,9) and wherein, for each pixel, the plurality of cells comprises at least a first set (C4,1; C4,4; C4,7) of at least one cell and a second set (C4,2; C4,5; C4,8) of at least one cell, the first set being connected to a first pair of electrodes and the second set being connected to a second pair of electrodes, and wherein the electrical control circuit (15) is capable of varying the color of each pixel by varying a first electrical voltage of the first pair of electrodes and a second electrical voltage of the second pair of electrodes. Image projection device (5) according to claim 6, wherein, for each pixel (P1-PK), the first set comprises several cells (C4,1; C4,4; C4,7) and the second set comprises several cells (C4,2; C4,5; C4,8). Image projection device (5) according to one of the preceding claims, in which the electrochromic material is chosen from PEDOT, PMMA or polycarbonate. Method for controlling an image projection device (5) according to one of the preceding claims, the image projection device comprising the following steps: - reception of an instruction by the electrical control circuit (15); - determination of an electrical voltage to be applied to each pair of electrodes as a function of said instruction; - application, for each pair of electrodes, of said electrical voltage by the electrical control circuit.

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