Reflective image projection device using electrochromic materials

Abstract

One aspect of the present invention is - a light source (6) for emitting a light beam; - The light rays from the light source are reflected beams (F R an image forming module (Im) including a reflecting assembly (10) capable of reflecting as a - the reflected beam (F R a projection optical system (8) arranged in the path of the light source (1) and capable of projecting an image formed by the image forming module; The present invention relates to an image projection device (5) comprising: The reflector assembly comprises a multilayer structure (S) comprising a substrate (2), a metal layer (3) and a layer (4) of electrochromic material containing at least one cell, the at least one cell being sealed in an electrolyte layer and connected to a pair of electrodes; The image projection device further comprises an electrical control circuit capable of varying a voltage applied to the pair of electrodes to change the color of the at least one cell.

Description

[Technical Field]

[0001] The technical field of the invention is that of image projection devices, in particular devices that can be fitted to motor vehicles to project images onto the ground. [Background technology]

[0002] Currently, such devices (sometimes called "dynamic carpet projectors") exist that can project images onto the ground when a door is opened or unlocked, when a door is approached, or when a driver brings a key or fob to open the vehicle's door closer.

[0003] Such devices include a light source (typically a light-emitting diode) that produces an illuminating light beam. The light beam is shaped by an illumination or collimating lens located downstream of the light source (between the light source and the image to be projected). The image to be projected transmits or reflects the illuminating light beam (depending on the technology used) towards projection optics, which then projects the image onto the ground.

[0004] The image to be projected can be created using various technologies. For example, an array of micromirrors (i.e., DMD, which stands for Digital Micromirror Device) can be used. This technology has the drawback of creating hot spots inside the device and is therefore not thermally robust. Arrays of microLEDs can also be used, but they also face the problem of heat dissipation. A third technology is laser-scanned microelectromechanical systems ("laser-scanned MEMS"). This last technology is emerging and is not robust against mechanical vibrations. Summary of the Invention

[0005] The present invention provides a solution to the problems mentioned above by proposing an alternative technique for producing the image to be projected.

[0006] A first aspect of the present invention is a light source for emitting a beam of light; an imaging module including a reflecting assembly capable of reflecting light rays from a light source as a reflected beam; a projection optical system arranged in the path of the reflected beam and capable of projecting the image formed by the image forming module; The present invention relates to an image projection device including the above.

[0007] The reflective assembly comprises a multi-layer structure including a substrate, a metal layer, and a layer of electrochromic material including at least one cell, the cell being sealed within an electrolyte layer and connected to a pair of electrodes; The image projection device further comprises an electrical control circuit capable of varying a voltage applied to the pair of electrodes to change the color of the at least one cell.

[0008] Thus, thanks to the present invention it is possible to project an image onto the ground without any hot spots or heat dissipation problems and without any robustness problems.

[0009] According to a first embodiment, the layer of electrochromic material may comprise a single cell, and the image forming module may further comprise at least one mask positioned between the reflection assembly and the projection optical system, the mask being capable of creating a pattern of the image formed by the image forming module.

[0010] Thus, by controlling the voltage applied to a single cell it is possible to change the color of the projected pattern, the pattern being determined by the mask, thus making it possible to create dynamic projections, at least by changing the color, without any hot spots, heat dissipation or robustness issues.

[0011] The image forming module may also include a set of multiple masks, and the electrical control circuit may be capable of selecting one of the masks in the set to create the pattern of the image formed by the image forming module.

[0012] It is thus possible to vary the projected image both in terms of its colour and in terms of the projection pattern, thus making it possible to project varying images and to create lighting animations.

[0013] Alternatively, according to the second and third embodiments, the reflective assembly may comprise a plurality of pixels, each pixel formed by at least one cell and connected to at least one pair of electrodes, and the electrical control circuitry may independently vary the voltage applied to the at least one pair of electrodes for each pixel.

[0014] It is thus possible to project pixelated images by reflection using a layer of electrochromic material, which has the advantage that it does not pose heat dissipation problems, allows for a high degree of robustness and is less bulky than prior art solutions.

[0015] Also, each pixel of the plurality of pixels may have a length and width between 50 and 500 micrometers, particularly between 70 and 150 micrometers.

[0016] Thus, it becomes possible to project high resolution images with a smaller bulk image projection device.

[0017] According to a second embodiment, each pixel may be formed by a single cell, connected to a single pair of electrodes.

[0018] Thus, the color control of each pixel is directly determined by the voltage applied to the corresponding cell, thereby simplifying the control of the projected image.

[0019] According to a third embodiment, each pixel may be formed by a plurality of cells, and for each pixel, the plurality of cells may include 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 able to change the color of each pixel by changing the first voltage of the first pair of electrodes and the second voltage of the second pair of electrodes.

[0020] Thus, the color of a pixel is obtained by combining the colors of the cells that make up that pixel, making it possible to project color images in a wide range of colors.

[0021] Also, for each pixel, the first set may include multiple cells and the second set may include multiple cells.

[0022] Thus, control of the color of each pixel is simplified compared to control on a cell-by-cell basis. In particular, there is the potential to create smaller cells and therefore reduce the bulk associated with the image projection device.

[0023] According to embodiments, the electrochromic material may be selected from PEDOT, PMMA, or polycarbonate.

[0024] Materials such as these are electrochromic, robust and low cost compared to prior art solutions.

[0025] A second aspect of the present invention provides a method for controlling an image projection apparatus according to the first aspect of the present invention, the image projection apparatus comprising: - receiving a set value by an electrical control circuit; - determining a voltage to be applied to each electrode pair based on the setpoint; - applying said voltages to each pair of electrodes by an electrical control circuit; The present invention relates to a method comprising:

[0026] The invention and its various applications will be better understood from a reading of the following description and from a study of the accompanying drawings, in which:

[0027] The figures are provided for information purposes only and are not intended to limit the invention in any way. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a side view schematically showing a vehicle equipped with an image projection device according to various embodiments of the present invention; [Figure 2] 1 is a diagram illustrating an image projection device according to embodiments of the present invention; [Figure 3] 1A and 1B are schematic diagrams illustrating a reflective assembly with a multi-layer structure according to embodiments of the present invention; [Figure 4] 1 illustrates a reflector assembly of an image projection device according to embodiments of the present invention. [Figure 5] FIG. 1 illustrates the dependence of the wavelength reflected by a layer of electrochromic material illuminated by a broadband beam on the thickness of this layer. [Figure 6a] 1 is a front view of a reflection assembly of an image projection device according to a first embodiment of the present invention; [Figure 6b] FIG. 10 is a front view of a reflecting assembly of an image projection device according to a second embodiment of the present invention. [Figure 6c] FIG. 10 is a front view of a reflection assembly of an image projection device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Each figure is presented as a non-limiting representation of the invention. Unless otherwise specified, identical elements appearing in different figures are given a single reference number.

[0030] 1 shows a motor vehicle 1 equipped with an image projection device 5 for projecting an image 103 onto the ground. The device 5 can be controlled by opening a front or rear door 100 or another hatch such as a trunk 101.

[0031] The device 5 is installed at the bottom of the vehicle body, where the height is limited and the environment is aggressive (splash, risk of collision with road elements, etc.). The device is therefore protected by a small housing, for example 4 to 10 cm on each side (since the device is 20 to 30 cm from the ground). Thanks to the technology used in the present invention, the housing is more compact in size than prior art housings. Alternatively, the device 5 can be installed in the rearview mirror.

[0032] FIG. 2 shows a schematic representation of an image projection device 5 according to the invention.

[0033] The image projection device 5 projects a light source beam F S As will be seen hereinafter, the source beam F S Advantageously, the source beam F has a broadband emission spectrum. S is typically a beam of white light. The light source 6 is, for example, a light emitting diode. Alternatively, the light source 6 is a laser light source.

[0034] The device 5 also comprises optional illumination optics 7 and an image forming module Im.

[0035] The light source 6 is positioned to illuminate an illumination optics 7, which in this case comprises a collimator 71 and a condenser 72. The illumination optics 7 illuminates the source beam F S is shaped (in particular, the uniform beam F H The illumination optics 7 are arranged downstream of the light source 6, between the light source 6 and the imaging module Im. The imaging module Im, which will be described below, converts the uniform beam F H The reflected beam F R The imaging assembly 10 includes at least one imaging assembly 10 capable of reflecting light as a reflection.

[0036] An imaging assembly 10 according to the present invention comprises at least one cell having a multi-layer structure as described with reference to FIG.

[0037] The device 5 also comprises a projection optical system 8 designed to project the image to be projected formed by the image forming module Im from the motor vehicle 1 onto the ground. The projection optical system 8 is configured to direct the reflected beam F downstream of the image forming module Im to form the image to be projected. R The projection optical system 8 is arranged in the path of the light beam. The projection optical system 8 typically comprises one or more lenses. The image formed by the image forming module Im is preferably positioned in the object focal plane of the projection optical system 8.

[0038] The projection optics 8 form an image 103 on the ground of the image to be projected at a very high magnification (typically with a magnifying effect). In practice, each side of the image 103 formed on the ground is at least 0.5 m, but the image can even occupy an area of 1 m long and 1 m wide or more, with the ground illuminated at an oblique angle by the image projection device.

[0039] One particular feature of the present invention is a reflective assembly 10 comprising a multi-layer structure S, shown schematically in Figure 3. The multi-layer structure S is composed of a stack of a possible substrate 2, a metal layer 3 and a layer 4 of electrochromic material.

[0040] For example, the flexible substrate 2 is made of an organic material such as silicone, polycarbonate, or PMMA. The substrate 2 has a thickness of, for example, about 500 microns.

[0041] The metal layer 3 is defined by a first face F1 and a second face F2. The first face F1 is in contact with the 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 a thickness of, for example, 70 to 100 nm.

[0042] The layer 4 of electrochromic organic material is defined by a third surface F3 and a fourth surface F4. Electrochromic refers to a material that changes color when a voltage is applied for a short period of time. The material retains its new color after the voltage is applied, but can return to its original state after a voltage of the opposite sign is applied. The third surface F3 is in contact with the second surface F2. For example, the electrochromic organic material is PEDOT (poly(3,4-ethylenedioxythiophene)). Examples of other electrochromic materials that can be used are 2-alkylthieno[3,4-b]thiophene (T34bT), PMMA, or polycarbonate. The layer 4 of electrochromic material has a thickness of, for example, 75 to 300 nm.

[0043] The layer 4 of electrochromic material can here be organized into N cells or elements, where N is an integer greater than or equal to 1.

[0044] When N is 2 or greater, the reflective assembly 10 may comprise a plurality of pixels, each pixel being formed by at least one of the N cells, in which case the reflective assembly 10 may comprise N pixels or less than N pixels.

[0045] A portion of a multilayer structure with N cells C1, C2, C3,...CN is shown in Figure 4, where N = 4. For example, layer 4 of electrochromic material is organized into an array of N cells.

[0046] Each cell of the N cells is sealed in an electrolyte solution or gel to which a pair of electrodes is connected, the pair of electrodes being designed to bias the corresponding cell with a voltage. Alternatively, if each pixel includes multiple cells according to a third embodiment described below, a set of multiple cells can be sealed in an electrolyte solution or gel so that the sets are connected to identical pairs of electrodes.

[0047] The dimensions of each cell depend on the embodiment considered, three embodiments are described below.

[0048] N cells are sealed and arranged, and a corresponding pair of electrodes is disposed on each cell or set of cells in a manner similar to that of a liquid crystal sheet.

[0049] All of the electrode pairs are connected to a low voltage battery and to an electrical control circuit 15 which is linked to the vehicle's electrical system.

[0050] The following describes how to control the color of one of the N cells of the layer 4 of electrochromic organic material. Such a cell acts as a Fabry-Pérot cavity formed by corresponding portions of the third face F3 and corresponding portions of the fourth face F4. This cavity produces interference of a given wavelength from the light it receives. This interference results in multiple reflections of colored light rays propagating in the opposite direction to the light rays received from the light source 6. Thus, it is due to the phenomenon of interference that the cell appears colored to the observer, and not due to absorption, as occurs when pigments or dyes are used.

[0051] In the present invention, the light received by the N cells is a uniform beam F H The light may come from the source 6 or directly from the light source 6 .

[0052] Typically, electrochromic materials reflect 60% to 90% of the light that they receive. For example, if the light source is a white light-emitting diode, which has a luminous flux of 400 lumens, the material will reflect 240 to 360 lumens.

[0053] As indicated above, the source beam F emitted by the source 6 S Preferably, the electrochromic material has a broadband emission spectrum, thus providing a wider range of wavelengths, in other words a wider range of colors, that can be reflected by the electrochromic material.

[0054] The thickness of the electrochromic organic material layer 4 has an effect on the color perceived by a viewer. For example, as shown in Figure 5, a PEDOT layer with a thickness e1 of 800 nm reflects red light with a wavelength λ1 when exposed to light with a broadband optical spectrum S(λ), a PEDOT layer with a thickness e2 of 600 nm reflects green light with a wavelength λ2 when exposed to light with a broadband optical spectrum S(λ), and a PEDOT layer with a thickness e3 of 500 nm reflects blue light with a wavelength λ3 when exposed to light with a broadband optical spectrum S(λ).

[0055] For example, the N cells of the layer 4 of electrochromic organic material can have different thicknesses to adjust their color when no voltage is applied.

[0056] Alternatively, all of the cells may have the same thickness, and the color they return may be controlled by the voltage applied to each cell or set of cells.

[0057] An electrical control circuit 15 allows for voltage control across the terminals of each of the N cells of the layer 4 of electrochromic organic material. A correspondence table between the desired color and the voltage to be applied across the terminals of a pair of electrodes allows for voltage control of the color change in a cell or a set of cells. The correspondence table depends on the electrochromic organic material used. For example, the voltage across the terminals of a pair of electrodes can vary between a minimum of -10 volts and a maximum of +10 volts.

[0058] For the sake of simplicity, only one pair of electrodes connected to electrical control circuitry 15 is shown in FIG.

[0059] Thus, the electrical control circuit 15 can be used to control the voltage across the terminals of each electrode pair by receiving a set value to control the color of the corresponding cell or set of cells.

[0060] Thus, in the second and third embodiments described below, the image to be projected is formed from at least a set of N pixels whose color is controlled by the application of voltages. In the first embodiment with a single cell, only the color of the image to be projected is controlled by the reflecting assembly 10, and the pattern of the image is formed by a mask 9 positioned between the reflecting assembly 10 and the projection optics 8.

[0061] The image to be projected is thus personally configurable.

[0062] Figure 6a shows a front view of the reflector assembly 10 in the device 5 according to the first embodiment of the invention.

[0063] According to a first embodiment, the layer 4 of electrochromic material comprises a single cell C. An electrical control circuit 15 is able to control the voltage of the single cell C in order to change the color of the light reflected by said single cell C.

[0064] In the first embodiment, the reflecting assembly 10 in a single cell C is advantageously combined with a mask 9 to form an image forming module Im. The pattern of the image to be projected is thus transmitted between the reflecting assembly 10 and the projection optics 8 as a reflected beam F R The color of the image to be projected is determined by the voltage applied to a single cell C by an electrical control circuit 15.

[0065] It should be noted that the mask 9 may be a single mask or a set of masks. The electrical control circuit 15 may in particular, by means of a control signal, select a mask from a set of masks arranged to interpose between the reflecting assembly 10 and the projection optics 8. In this way, it is possible to vary the pattern and color of the image to be projected. The masks in the set may be assigned in a cyclical manner, and applying a given rotation to the set may enable the electrical control circuit 15 to select one of the masks in the set.

[0066] There is no restriction on the dimensions of a single cell C, in particular the width and length of the cell C (ie the dimensions shown in the front view of FIG. 6a).

[0067] 6a shows a front view, so that the substrate 2 and metal layer 3 are only partially visible, or alternatively, if the substrate 2 and metal layer 3 have the same length and width dimensions as a single cell C, the substrate 2 and metal layer 3 are not visible in FIG.

[0068] Figure 6b shows a reflector assembly 10 of a device 5 according to a second embodiment of the invention.

[0069] In the second embodiment, the layer of electrochromic material 4 of the reflective assembly 10 comprises an array of N cells C1 to CN. Each cell is individually actuated by a voltage applied by the electrical control circuit 15, and thus each cell forms a pixel.

[0070] In the second embodiment, the reflective assembly therefore comprises N individually actuatable pixels and the resolution of the image formed is therefore equal to N.

[0071] Thus, the second embodiment can be used to project pixelated color images from a reflective assembly 10 using a layer 4 of electrochromic material.

[0072] There is no restriction on the dimensions of each of the cells C1 to CN, particularly the width and length of each of the cells C1 to CN (ie, the dimensions shown in the front view of FIG. 6b).

[0073] For example, each cell may have a width and length between 50 and 500 micrometers, e.g., between 50 and 200 micrometers, in particular between 70 and 150 micrometers. By way of example, each cell C1 to CN may have a square shape with each side being 100 micrometers.

[0074] 6b shows a front view, so that the substrate 2 and metal layer 3 are only partially visible, or alternatively, if the substrate 2 and metal layer 3 have the same length and width dimensions as the layer 4 of electrochromic material, the substrate 2 and metal layer 3 are not visible in FIG.

[0075] Alternatively, the cells C1-CN are individual layers of electrochromic material (disposed on a substrate 2 and a respective metal layer 3).

[0076] An example with 15 cells is shown illustratively in Figure 6b, although the reflector assembly 10 may comprise more than 100 cells or even more than 1000 cells.

[0077] Figure 6c shows a reflector assembly 10 of a device 5 according to a third embodiment of the invention.

[0078] In a third embodiment, the reflective assembly 10 comprises an array of K pixels, where K is 2 or greater, and each pixel comprises M cells, where M is 2 or greater.

[0079] The layer 4 of electrochromic material is thus divided into M x K cells, M of which form a pixel in the array of pixels.

[0080] In the example of Figure 6c, M is 9 and K is 15. Therefore, N (total number of cells) is 9 x 15 = 135.

[0081] In the third embodiment, the color of each of the M pixels is obtained by combining the colors of the K cells that make up that pixel, making it possible to obtain a much richer range of colors for each pixel than in the second embodiment.

[0082] The resulting image has a resolution of M, but has excellent variability in color obtained by combining the colors of K cells in each pixel.

[0083] Each cell in a pixel can be individually activated to reflect a light beam of a given color, or multiple sets of cells in a pixel can be activated in sets, for example, each set can be a row or a column of pixels.

[0084] There is no restriction on the dimensions of each of the pixels P1 to PK, particularly the width and length of each of the cells P1 to PK (ie, the dimensions shown in the front view of FIG. 6c).

[0085] For example, each pixel may have a width and length between 50 and 500 micrometers, e.g., between 50 and 200 micrometers, in particular between 70 and 150 micrometers. By way of example, each pixel P1 to PK may have a square shape with each side being 100 micrometers.

[0086] Furthermore, there are no limitations on the dimensions of the cells in each pixel, particularly the width and length of each cell, which are determined by the number of cells per pixel and by the pixel dimensions. For example, each cell can have a width and length between 20 and 50 micrometers, particularly between 30 and 40 micrometers.

[0087] An example of the third embodiment will now be described, by way of example only.

[0088] In this example, the nine cells in a given pixel can be activated column by column, with each column forming a set of cells whose color can be controlled by an electrical control circuit. Thus, three columns can be activated separately, allowing the color of the pixel to be synthesized from the colors of each of the three columns.

[0089] For example, taking the particular example of the fourth pixel P4, the first column comprises cells C4,1; C4,4 and C4,7, the second column comprises cells C4,2; C4,5 and C4,8, and the third column comprises cells C4,3; C4,6 and C4,9.

[0090] Thus, when three columns are red, the pixel is red; when columns 1 and 3 are blue and column 2 is red, the pixel is purple; when columns 1 and 3 are red and column 2 is green, the pixel is yellow, etc.

[0091] A method for controlling the image projection device described above is described below.

[0092] The electrical control circuit 15 can receive a set value. In the second and third embodiments, the electrical control circuit determines a set of voltages to be applied to each cell or set of cells in the layer 4 of electrochromic organic material based on the set value. The set of voltages reflects the color pattern that forms the image the user wants to project. In the first embodiment, the electrical control circuit 15 determines the color (and optionally the mask pattern 9) of a single cell C based on the set value.

[0093] When the voltage or voltages are applied to the cell or cells of the electrochromic material layer 4, the light source beam F S The light source 6 is turned on to emit a uniform beam F H The multilayer structure S forming the image Im is transformed into a uniform beam F H and reflects the beam towards the projection optics 8, which projects the image 103 onto the ground.

Claims

1. a light source (6) for emitting a light beam; - the light beam from said light source is a reflected beam (F R an imaging module including a reflective assembly capable of reflecting light as a - the reflected beam (F R a projection optical system (8) arranged in a path of the light source and capable of projecting an image formed by the image forming module; An image projection device (5) comprising: The reflector assembly comprises a multilayer structure (S) comprising a substrate (2), a metal layer (3) and a layer (4) of electrochromic material containing at least one cell, the cell being sealed in an electrolyte layer and connected to a pair of electrodes; The image projection device (5) further comprises an electrical control circuit capable of varying the voltage applied to the pair of electrodes to change the color of the at least one cell.

2. 2. The image projection device (5) of claim 1, wherein the layer (4) of electrochromic material comprises a single cell (C), and the image forming module (Im) further comprises at least one mask (9) positioned between the reflection assembly and the projection optical system (8), the mask being capable of creating a pattern of the image formed by the image forming module.

3. 3. The image projection device (5) of claim 2, wherein the image forming module (Im) comprises a set of a plurality of masks (9), and the electrical control circuit (15) is capable of selecting one of the masks of the set to generate the pattern of the image formed by the image forming module.

4. 2. The image projection device (5) of claim 1, wherein the reflective assembly (10) comprises a plurality of pixels, each pixel formed by at least one cell and connected to at least one pair of electrodes, and the electrical control circuit (15) is capable of independently varying the voltage applied to the at least one pair of electrodes of each pixel.

5. 4. The image projection device (5) according to claim 3, wherein each pixel of said plurality of pixels has a length and a width between 50 and 500 micrometers, in particular between 70 and 150 micrometers.

6. Image projection device (5) according to claim 3 or 4, wherein each pixel is formed by a single cell (C1-CN) and connected to a single pair of electrodes.

7. 5. An image projection device (5) according to claim 3 or 4, wherein each pixel (P1 to PK) is formed by a plurality of cells (C4,1 to C4,9), and for each pixel, the plurality of cells comprises at least a first set of at least one cell (C4,1; C4,4; C4,7) and a second set of at least one cell (C4,2; C4,5; C4,8), 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 able to change the color of each pixel by varying a first voltage on the first pair of electrodes and a second voltage on the second pair of electrodes.

8. 7. The image projection device (5) of claim 6, wherein for each pixel (P1-PK), the first set comprises a plurality of cells (C4,1; C4,4; C4,7) and the second set comprises a plurality of cells (C4,2; C4,5; C4,8).

9. 10. An image projection device (5) according to any one of the preceding claims, wherein the electrochromic material is selected from PEDOT, PMMA or polycarbonate.

10. A method for controlling an image projection device (5) according to any one of the preceding claims, the method comprising: - receiving a set value by said electrical control circuit (15); - determining the voltages to be applied to each electrode pair based on said set values; applying said voltages to each pair of electrodes by said electrical control circuit; A method of providing

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