Image projection apparatus using electrochromic material for reflection

Abstract

One aspect of the invention relates to an image projection device (5) comprising:-a light emitting source (6) for emitting light rays,-an image forming module (lm) comprising a reflective assembly (10) capable of reflecting the light rays from the light emitting source into a reflected light beam (FR),-an optical projection system (8), and an optical projection system placed in the path of the reflected light beam (FR) and capable of projecting an image formed by the image forming module, in which the reflective assembly comprises a multilayer structure comprising a substrate, a metal layer, and an electrochromic material layer comprising at least one cell, the image projection apparatus includes at least one cell encapsulated in an electrolyte layer and connected to a pair of electrodes, the image projection apparatus further including an electrical control circuit capable of changing a voltage applied to the pair of electrodes in order to change a color of the at least one cell.

Description

Technical Field

[0001] The technical field of the invention is that of image projection devices, more specifically image projection devices which equip a motor vehicle and allow an image to be projected onto the ground. Background Art

[0002] Such devices currently exist, sometimes called "dynamic carpet projectors" (adjustable floor projectors), which allow an image to be projected onto the floor when a door is opened or unlocked, or when approaching a door, as the driver approaches with a key or key fob used to open the vehicle.

[0003] This device comprises a light source, usually a light emitting diode, which generates an illumination beam which is shaped by an illumination or collimating lens placed downstream of the light source and between the light source and the image to be projected. Depending on the technology used, the image to be projected transmits or reflects the illumination beam towards an optical projection system which projects the image onto the ground.

[0004] Various techniques can be used to generate the image to be projected. For example, an array of micromirrors (or DMD, which stands for digital micromirror device) can be used. This technique has the disadvantage of creating hot spots within the device and is therefore not robust from a thermal point of view. Alternatively, an array of micro-LEDs can be used, but also faces heat dissipation issues. A third technique is to use laser scanning microelectromechanical systems ("laser scanning MEMS"). The latter technique is an emerging technology and is not robust to mechanical vibrations. Summary of the invention

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

[0006] A first aspect of the present invention relates to an image projection device, the image projection device comprising:

[0007] - a light source for emitting light,

[0008] - an image forming module, the image forming module comprising a reflective component capable of reflecting light from a light source into a reflected light beam,

[0009] - an optical projection system placed in the path of the reflected light beam and capable of projecting the image formed by the image forming module.

[0010] The reflective assembly includes a multilayer structure including a substrate, a metal layer and an electrochromic material layer, the electrochromic material layer including at least one unit, the at least one unit is encapsulated in an electrolyte layer and connected to a pair of electrodes,

[0011] The image projection device also includes an electrical control circuit capable of varying the voltage applied to the pair of electrodes in order to vary the color of the at least one cell.

[0012] Thus, by means of the present invention, an image can be projected onto the ground without any hot spots or heat dissipation problems and without any robustness issues.

[0013] According to a first embodiment, the layer of electrochromic material may comprise a single unit, and the image forming module may further comprise at least one mask positioned between the reflective assembly and the optical projection system, the mask being capable of producing a pattern of an image formed by the image forming module.

[0014] Thus, the color of the projected pattern can be changed by controlling the voltage applied to the individual cells, the pattern being determined by the mask. Thus, dynamic projections can be produced, at least by changing the color, without any hot spots, heat dissipation or robustness issues.

[0015] Additionally, the image forming module may include a set of a plurality of masks, and the electrical control circuit may be capable of selecting one of the masks in the set for use in producing the pattern of the image formed by the image forming module.

[0016] Therefore, the projected image can be changed in terms of its color and in terms of its projection pattern. Therefore, a changing image can be projected or a luminous animation can be generated.

[0017] Alternatively, according to the second and third embodiments, the reflective assembly may include a plurality of pixels, each pixel being formed of at least one unit and connected to at least one pair of electrodes, and the electrical control circuit is capable of independently varying a voltage applied to the at least one pair of electrodes of each pixel.

[0018] Thus, a layer of electrochromic material can be used to project a pixelated image by reflection, which has the advantages of not causing heat dissipation problems, achieving a high level of robustness and a small size compared to prior art solutions.

[0019] Furthermore, each pixel of the plurality of pixels may have a length and a width between 50 micrometers and 500 micrometers, in particular between 70 micrometers and 150 micrometers.

[0020] Therefore, a high-resolution image can be projected using a relatively small-sized image projection device.

[0021] According to a second embodiment, each pixel may be formed of a single unit and connected to a single pair of electrodes.

[0022] Therefore, control of the color of each pixel is directly determined by the voltage applied to the corresponding cell, thereby simplifying control of the projected image.

[0023] According to a third embodiment, each pixel may be formed by a plurality of units, and for each pixel, the plurality of units may include at least at least one unit of a first group and at least one unit of a second group, the first group being connected to a first pair of electrodes and the second group 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 a first voltage of the first pair of electrodes and a second voltage of the second pair of electrodes.

[0024] Therefore, the color of a pixel is obtained by synthesizing the colors of the cells constituting the pixel. Therefore, a color image with a wide color range can be projected.

[0025] Additionally, for each pixel, the first group may include a plurality of cells and the second group may include a plurality of cells.

[0026] Thus, the control of the color of each pixel is simplified compared to a cell-by-cell control. In particular, it is possible to produce cells of smaller size and thus reduce the volume associated with the image projection device.

[0027] According to an embodiment, the electrochromic material may be selected from PEDOT, PMMA or polycarbonate.

[0028] Such materials are electrochromic, robust and have lower costs compared to prior art solutions.

[0029] A second aspect of the present invention relates to a method for controlling an image projection device according to the first aspect of the present invention, the image projection device comprising the following steps:

[0030] - receiving a set point via an electrical control circuit;

[0031] - determining a voltage to be applied to each pair of electrodes based on the set point;

[0032] - said voltage is applied for each pair of electrodes by means of an electrical control circuit.

[0033] The invention and its various applications will be better understood by reading the following description and examining the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] These drawings are presented for reference purposes and in no way limit the invention:

[0035] -[ Figure 1 ] schematically shows a side view of a vehicle equipped with an image projection device according to an embodiment of the present invention;

[0036] -[ Figure 2 ] schematically shows an image projection device according to an embodiment of the present invention;

[0037] -[ Figure 3 ] schematically shows a reflective assembly including a multilayer structure according to an embodiment of the present invention;

[0038] -[ Figure 4 ] shows a reflective component of an image projection device according to an embodiment of the present invention;

[0039] -[ Figure 5 ] demonstrates the dependence of the wavelength reflected by a layer of electrochromic material illuminated by a broad bandwidth light beam on the thickness of this layer;

[0040] -[ Figure 6a ] shows a front view of a reflective assembly of an image projection device according to a first embodiment of the present invention;

[0041] -[ Figure 6b ] shows a front view of a reflective assembly of an image projection device according to a second embodiment of the present invention;

[0042] -[ Figure 6c ] shows a front view of a reflective component of an image projection device according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0043] These drawings are for illustration purposes only and do not limit the scope of the present invention. Unless otherwise specified, the same element appearing in different drawings has a single reference number.

[0044] [ Figure 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 door or a rear door 100 or another hatch, such as a trunk 101.

[0045] The device 5 is placed under the vehicle body, where the height is limited and the environment is aggressive (splashing water, risk of collision with elements on the road, etc.). The device is therefore protected by a small housing (since the device is 20 to 30 cm from the ground), for example 4 to 10 cm on the sides. Thanks to the technology used in the invention, the housing is more compact in size than that of the prior art. Alternatively, the device 5 can be placed in the rearview mirror.

[0046] [ Figure 2 ] schematically shows an image projection device 5 according to the present invention.

[0047] The image projection device 5 comprises a device for emitting a source light beam F s Advantageously, as will be seen below, the source beam F s Typically, the source beam F sis a white light beam. For example, the light source 6 is a light emitting diode. In another example, the light source 6 is a laser source.

[0048] The device 5 also includes an optional optical lighting system 7 and an image forming module Im.

[0049] The light source 6 is positioned to illuminate an optical light system 7. The optical light system 7 here comprises a collimator 71 and a condenser 72. The optical light system 7 allows the source light beam F to be s to shape it, in particular to transform it into what is hereinafter referred to as a uniform beam F H The optical lighting system 7 is placed downstream of the light source 6 and between the light source 6 and the image forming module. The image forming module Im to be described below includes at least one image forming component 10, which is capable of converting a uniform light beam F H Reflection is the reflected beam F R .

[0050] The image forming assembly 10 according to the present invention includes at least one unit having a reference [ Figure 3 ] described multi-layer structure.

[0051] The device 5 also comprises an optical projection system 8 designed to project the image to be projected formed by the image forming module 1 m from the motor vehicle 1 onto the ground. The optical projection system 8 is located between the reflected light beam F R The optical projection system 8 is located in the path of the optical projection system 8 and downstream of the image forming module 1 m for forming the image to be projected. The optical projection system 8 typically comprises one or more lenses. Preferably, the image formed by the image forming module 1 m is positioned in the object focal plane of the optical projection system 8.

[0052] The optical projection system 8 forms an image 103 on the ground where the image is to be projected, at a very high magnification and usually with an extended effect. In practice, the image 103 formed on the ground is at least 0.5 m on a side, and the image may even occupy an area of ​​1 m long x 1 m wide or more, and the ground is illuminated by the image projection device at an oblique angle.

[0053] One of the special features of the present invention is the reflective assembly 10, which comprises [ Figure 3 ] is schematically shown in the multilayer structure S, which is composed of a stack of a substrate 2 (which can be flexible), a metal layer 3 and an electrochromic material layer 4.

[0054] For example, the flexible substrate 2 is an organic material made of silicone, polycarbonate or PMMA. The substrate 2 has a thickness of, for example, about 500 microns.

[0055] The metal layer 3 is delimited 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, for example, between 70 and 100 nm.

[0056] The electrochromic organic material layer 4 is defined by the third face F3 and the fourth face F4. Electrochromic refers to a material that changes color when a voltage is applied thereto for a short period of time. After the voltage is applied, the material retains the new color, but can return to its original state after a voltage of opposite sign is applied. 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 materials that can be used are 2-alkylthiophene [3,4-b] thiophene (T34bT), PMMA (polymethyl methacrylate) or polycarbonate. The electrochromic material layer 4 has a thickness, for example, between 75 and 300 nm.

[0057] The electrochromic material layer 4 may be structured into N units or elements, where N is an integer greater than or equal to 1.

[0058] When N is greater than or equal to 2, the reflective component 10 may include a plurality of pixels, each pixel being formed by at least one of the N units. The reflective component 10 then includes N pixels or less than N pixels.

[0059] [ Figure 4 ] shows a part of a multilayer structure having N units C1, C2, C3, ... and CN, where N is equal to 4. For example, the electrochromic material layer 4 is structured into an array of N units.

[0060] Each of the N cells may be encapsulated in an electrolyte solution or gel to which a pair of electrodes intended to bias the corresponding cell with a voltage are connected. Alternatively, according to a third embodiment described below, when each pixel includes a plurality of cells, a group of a plurality of cells may be encapsulated in an electrolyte solution or gel to be connected to the same pair of electrodes.

[0061] The size of each unit depends on the embodiment under consideration, three embodiments are described below.

[0062] N cells are packaged and arranged, and corresponding pairs of electrodes are arranged on each cell or each group of cells in a manner similar to a liquid crystal cell.

[0063] All pairs of electrodes are connected to a low voltage battery and to an electrical control circuit 15 which is connected to the electrical system of the vehicle.

[0064] The following describes a method for controlling the color of one of the N units of the electrochromic organic material layer 4. This unit acts as a Fabry-Perot cavity formed by the corresponding portion of the third face F3 and the corresponding portion of the fourth face F4. This cavity produces interference of a given wavelength from the light received by it. This interference causes the colored light to be reflected multiple times and propagate in the opposite direction to the light received from the light source 6. Therefore, for the observer, the unit is colored by the interference phenomenon rather than the absorption phenomenon as when using pigments or dyes.

[0065] In the present invention, the light received by the N units may originate from a uniform light beam F H , or may come directly from the light source 6.

[0066] Typically, an electrochromic material reflects between 60% and 90% of the light it receives. For example, when the light source is a white light emitting diode, the flux of the light source is 400 lumens, so the material reflects a flux of between 240 lumens and 360 lumens.

[0067] As mentioned above, the source light beam F emitted by the light source 6 s It is preferred to have a broadband emission spectrum. Thus, the range of wavelengths (in other words, the range of colors) that can be reflected by the electrochromic material is relatively wide.

[0068] The thickness of the electrochromic organic material layer 4 has an effect on the color perceived by the observer. Figure 5 ], when the PEDOT layer with a thickness of e1 equal to 800 nm receives light with a broadband spectrum S(λ), it generates a wavelength λ through reflection. 1 The red PEDOT layer with a thickness of e2 equal to 600 nm generates a wavelength λ by reflection when receiving light with a broadband spectrum S(λ). 2 When receiving light with a broadband spectrum S(λ), the PEDOT layer with a thickness of 500 nm generates a wavelength λ by reflection. 3 of blue.

[0069] For example, the N units of the electrochromic organic material layer 4 may have different thicknesses so as to adjust their colors without applying a voltage thereto.

[0070] Alternatively, all cells have the same thickness, and control of the color they return is achieved by a voltage applied to each cell or group of cells.

[0071] The electrical control circuit 15 enables the voltage across the terminals of the N cells of the electrochromic organic material layer 4 to be controlled. A table of correspondence between the desired color and the voltage to be applied across the terminals of a pair of electrodes enables voltage control of the color change of a cell or a group of cells. The table of correspondence depends on the electrochromic organic material used. For example, the voltage across the terminals of a pair of electrodes varies between a minimum voltage of -10 volts and a maximum voltage of +10 volts.

[0072] For simplicity, [ Figure 4 ] shows a single pair of electrodes connected to an electrical control circuit 15.

[0073] Thus, by receiving a set point, the electrical control circuit 15 can be used to control the voltage across the terminals of each pair of electrodes in order to control the color of a corresponding cell or a corresponding group of cells.

[0074] Therefore, in the second and third embodiments described below, the image to be projected is formed by at least the group of N pixels, and the colors of these pixels are controlled by applying voltages. In the first embodiment with a single unit, the reflective component 10 controls only the color of the image to be projected, and the pattern of the image is formed by means of a mask 9, which is placed between the reflective component 10 and the optical projection system 8.

[0075] The image to be projected is therefore personalizable.

[0076] [ Figure 6a ] shows a front view of the reflective assembly 10 of the device 5 according to the first embodiment of the present invention.

[0077] According to a first embodiment, the layer of electrochromic material 4 comprises a single cell C. The 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 the single cell C.

[0078] In the first embodiment, the reflective assembly 10 having a single unit is advantageously combined with a mask 9 to form an image forming module Im. Thus, the pattern of the image to be projected is generated by means of the mask 9, which is placed in the reflected light beam FR, between the reflective assembly 10 and the optical projection system 8 for interception, while the color of the image to be projected is determined by the voltage applied to the single unit C by the electrical control circuit 15.

[0079] It should be noted that the mask 9 can be a single mask or a group of masks. The electrical control circuit 15 can in particular select, by control signals, a mask in the group of masks that is placed between the reflective assembly 10 and the optical projection system 8 for interception. Thus, the pattern and color of the image to be projected can be changed. The masks in the group of masks can be distributed in a circular manner, and applying a given rotation to the group can allow the electrical control circuit 15 to select a mask in the group of masks.

[0080] The dimensions of the individual cells C, in particular the width and length of the cells C, that is to say, Figure 6a ] The dimensions shown in the front view are not limited.

[0081] [ Figure 6a ] shows a front view, with the substrate 2 and metal layer 3 only partially visible. Alternatively, the substrate 2 and metal layer 3 have the same length and width dimensions as a single cell C, in which case the substrate 2 and metal layer 3 are in [ Figure 6a ] is not visible in the .

[0082] [ Figure 6b ] shows a reflective component 10 of a device 5 according to a second embodiment of the present invention.

[0083] In the second embodiment, the electrochromic material layer 4 of the reflective assembly 10 comprises an array of N cells C1 to CN, each cell being driven individually by a voltage applied thereto by the electrical control circuit 15 and each cell thus forming a pixel.

[0084] In the second embodiment, the reflective assembly therefore comprises N individually drivable pixels, and the resolution of the formed image is therefore equal to N.

[0085] Thus, the second embodiment may be used to project a pixelated color image from the reflective assembly 10 using the electrochromic material layer 4 .

[0086] The size of each unit C1 to CN, in particular the width and length of each unit C1 to CN, that is, Figure 6b ] The dimensions shown in the front view are not limited.

[0087] For example, each cell may have a width and a length between 50 and 500 microns, such as between 50 and 200 microns, in particular between 70 and 150 microns.For example, each cell C1 to CN may have a square shape with a side of 100 microns.

[0088] [ Figure 6b ] shows a front view, with the substrate 2 and the metal layer 3 only partially visible. Alternatively, the substrate 2 and the metal layer 3 have the same length and width dimensions as the electrochromic material layer 4, in which case the substrate 2 and the metal layer 3 are in [ Figure 6a ] is not visible in the .

[0089] Alternatively again, cells C1 to CN are different layers of electrochromic material arranged on substrate 2 and respective metal layers 3 .

[0090] [ Figure 6b] shows an example with 15 units by way of illustration. However, the reflective assembly 10 may include more than one hundred units, or even more than one thousand units.

[0091] [ Figure 6c ] shows a reflective component 10 of a device 5 according to a third embodiment of the present invention.

[0092] In a third embodiment, the reflective assembly 10 comprises an array of K pixels, K is greater than or equal to 2, and each pixel comprises M units, M is greater than or equal to 2.

[0093] The layer of electrochromic material 4 is thus divided into M*K cells, the M cells forming one pixel in the array of pixels.

[0094] exist[ Figure 6c ], M is equal to 9 and K is equal to 15. Therefore, the total number of cells N is equal to 9*15=135.

[0095] In the third embodiment, the color of each of the M pixels is obtained by synthesizing the colors of the K units constituting the pixel. Therefore, compared with the second embodiment, there can be a greater margin in the color that can be achieved for each pixel.

[0096] The resolution of the resulting image is equal to M, where the colors obtained by synthesizing the colors of K cells per pixel have a large variability.

[0097] Each unit of a pixel may be driven individually so as to reflect a light beam of a given color. Alternatively, groups of units of pixels may be driven group by group. For example, each group may be a row or column of pixels.

[0098] The size of each pixel P1 to PK, in particular the width and length of each unit P1-PK, that is, Figure 6c ] The dimensions shown in the front view are not limited.

[0099] For example, each pixel may have a width and a length between 50 and 500 microns, such as between 50 and 200 microns, in particular between 70 and 150 microns. By way of example, each pixel P1 to PK may have a square shape with a side of 100 microns.

[0100] Furthermore, there is no limit to the size of the cells in each pixel, in particular the length and width of each cell. Such size depends on the number of cells per pixel and the size of the pixel. For example, each cell may have a length and width between 20 microns and 50 microns, in particular between 30 microns and 40 microns.

[0101] An example of the third embodiment is described below by way of illustration only.

[0102] In this example, the nine cells of a given pixel can be driven in columns. Each column thus forms a group of cells whose color can be controlled by an electrical control circuit. Thus, the three columns can be driven independently, thereby allowing the color of the pixel to be synthesized from the corresponding colors of the three columns.

[0103] For example, taking the specific 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.

[0104] So, when those three columns are red, the pixel is red. When the first and third columns are blue and the second column is red, the pixel is purple. When the first and third columns are red and the second column is green, the pixel is yellow, etc.

[0105] A method for controlling the image projection device described above is described below.

[0106] The electrical control circuit 15 may receive a set point. In the second and third embodiments, based on the set point, the electrical control circuit determines a set of voltages to be applied to the cells or groups of cells of the electrochromic organic material layer 4. The set of voltages reflects the color pattern that forms the image that the user wishes to project. In the first embodiment, the electrical control circuit 15 determines the color of a single cell C based on the set point and optionally determines the mask pattern 9.

[0107] Once the voltage or voltages have been applied to the one or more cells of the electrochromic material layer 4, the light source 6 is switched on so as to emit a source light beam F S The source beam is converted into a uniform beam F by the optical lighting system 7. H The multilayer structure S forming the image Im receives the uniform light beam F H , and reflects it toward the optical projection system 8. The optical projection system 8 projects the image 103 onto the ground.

Claims

1. An image projection device (5), comprising: - a light source (6) for emitting light, - an image forming module, the image forming module comprising a reflective component capable of reflecting light from the light source into a reflected light beam (F R ), - an optical projection system (8), which is placed in the reflected light beam (F R ) and capable of projecting an image formed by said image forming module, The reflective component comprises a multilayer structure (S), the multilayer structure comprising a substrate (2), a metal layer (3) and an electrochromic material layer (4), the electrochromic material layer comprising at least one unit, the at least one unit being encapsulated in an electrolyte layer and connected to a pair of electrodes, The image projection device also includes an electrical control circuit capable of varying a voltage applied to the pair of electrodes in order to change a color of the at least one cell.

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

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

4. The image projection device (5) according to claim 1, wherein: The reflective assembly (10) includes a plurality of pixels, each pixel being formed of at least one unit and connected to at least one pair of electrodes, and the electrical control circuit (15) is capable of independently changing the voltage applied to the at least one pair of electrodes of each pixel.

5. The image projection device (5) as claimed in claim 3, wherein: Each pixel of the plurality of pixels has a length and a width between 50 micrometers and 500 micrometers, in particular between 70 micrometers and 150 micrometers.

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

7. The 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 include at least at least one cell of a first group (C4,1; C4,4; C4,7) and at least one cell of a second group (C4,2; C4,5; C4,8), the first group being connected to a first pair of electrodes and the second group being connected to a second pair of electrodes, and wherein the electrical control circuit (15) is capable of changing the color of each pixel by changing a first voltage of the first pair of electrodes and a second voltage of the second pair of electrodes.

8. The image projection device (5) according to claim 6, wherein: For each pixel (P1-PK), the first group includes a plurality of cells (C4,1; C4,4; C4,7), and the second group includes a plurality of cells (C4,2; C4,5; C4,8).

9. The image projection device (5) as claimed in 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) as claimed in one of the preceding claims, the image projection device comprising the following steps: - receiving a set point via said electrical control circuit (15); - determining a voltage to be applied to each pair of electrodes based on the set point; - applying said voltage for each pair of electrodes by said electrical control circuit.

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