Reflective display device

Abstract

The invention relates to a reflective display device comprising a matrix array of pixels (60), each pixel being defined by a fixed volume extending over the surface of the pixel between a plate (67) that is transparent in at least part of the visible spectrum and a carrier (66). Each pixel comprises at least one impermeable inert flexible membrane (62) that is transparent in at least part of the visible spectrum, extending over this surface of the pixel and separating a chamber (68) on the side of its face oriented towards the transparent plate and a chamber (63) on the side of its face oriented towards the carrier, the volume of the pixel thus consisting of a number of chambers equal to the number of membranes plus one. Each chamber is fluidly connected to a store of liquid, via a means for moving this liquid from the store to the chamber or from the chamber to the store.

Description

[0001] DESCRIPTION

[0002] REFLECTIVE DISPLAY DEVICE

[0003] Technical field of the invention

[0004] The present invention relates to a reflective display device. It applies, in particular, to the display of texts or still or animated images, in natural light, without backlighting.

[0005] State of the art

[0006] Video walls, large-scale displays, currently use light-emitting diodes (or LEDs, better known as "light emitting diodes") that emit visible light at each point of the image (or "pixel"). As a result, their electricity consumption is high, because even if part of their use consists of displaying text or fixed images, each pixel is refreshed several thousand times per second.

[0007] The display and visual communication sector makes massive use of this type of so-called emissive screen, covering increasingly large surfaces, which emit light and therefore constitute a source of light pollution, constantly consume energy and which, to be visible, must generate all the more light (and therefore consume all the more energy) as the ambient environment is bright.

[0008] On the other hand, ferroelectric liquid crystal displays have very low power consumption, but their dimensions are limited. Their diagonal is less than 75 centimeters.

[0009] Document WO 2016 / 197023 is known, which describes an optical shutter comprising chambers of constant volume, in each of which a liquid moves according to the deformation of the membrane separating these chambers. Such a shutter allows the quantity of light passing through it to be varied. It therefore does not allow the construction of a reflective display system, nor of a passive pixel because a power consumption is constantly necessary to maintain its open state and therefore the level of light which can pass through it.

[0010] Summary of the invention

[0011] The invention is part of a logic of reducing energy waste and limiting light pollution by proposing a technical solution for producing reflective information devices that do not emit light but use and reflect ambient light. They are therefore not visible at night unless additional external lighting is integrated.

[0012] The reflective display device of the invention is based on microfluidic techniques and the circulation of liquids of different colors in micro-channels and chambers that will form the basis of the screen. The invention is based on a set of chambers, membranes and actuators for setting colored liquids in motion and recycling them. This system for circulating colored liquids allows the color of each pixel to be modulated, and is sized to be able to refresh the entire surface of the screen at a frequency compatible with video animations. If the image to be displayed is static, there is no movement of liquid, and the information can remain visible indefinitely without any energy consumption since no actuator is powered.

[0013] Characteristics of certain embodiments of the reflective display device which is the subject of the invention are given below:

[0014] - the device is designed in a modular way in order to be able to create theoretically infinite display surfaces,

[0015] - each module is formed from a matrix of pixels, the shape and sizes of which can depend on the intended application,

[0016] - each pixel is formed of a cavity of fixed volume V, divided by at least one transparent flexible membrane into at least two superimposed chambers,

[0017] - each chamber of each pixel is accessible from the back of the module in order to be able to inject independently into each of them and for each pixel a colored liquid,

[0018] - the membranes defining the chambers prevent liquids of different colors from mixing, so that they can be recycled, i.e. returned to liquid reservoirs common to the different pixels,

[0019] - the number of chambers is directly linked to the number of primary colors required to obtain the desired colorimetric rendering. An additional chamber to the chambers receiving the primary colors allows the pixel to be completely emptied of colored liquid, by filling this chamber with a transparent liquid (thus revealing the background color of the support) or a liquid corresponding to the background color. Thus, for a monochrome display, each pixel is divided into two chambers by a membrane. For a color display using the “CMY” trichromy (Cyan, Magenta, Yellow), each pixel is divided into four chambers by three membranes,

[0020] - the coloring of the pixels is done by injecting a more or less significant volume of colored liquid into the chambers of the pixel in question, and the final color is obtained by the superposition by transparency of the primary colors of the liquids injected into the different chambers of the pixel concerned,

[0021] - each pixel operates at a fixed total volume corresponding to the volume V of the cavity. If the volume of each chamber is variable depending on the volume of liquid injected into it, the sum of the volumes of the chambers permanently corresponds to the volume V of the pixel cavity,

[0022] - the modification of the color of the pixel is done only by injecting the quantity of liquid of a color to be intensified, which expels an identical quantity of liquid of color to be attenuated or of transparent liquid or of the background color,

[0023] - the background color is injected through an orifice located in the middle of the pixel area, which corresponds to the deepest point of the cavity, if the pixel has such a point, - the colored liquids are injected through orifices positioned outside the visible surface of the pixel so as not to interfere with its color rendering,

[0024] - the injection points for the background color are interconnected by line,

[0025] - the injection points for the other colors are connected by columns,

[0026] - the whole forms a micro-fluidic network in columns and lines,

[0027] - injection points for several neighboring pixels can be shared in order to limit their number. The pixel concerned by the injection is then selected by validating which of the chambers neighboring the injection point is authorized to empty to make room for the liquid to be injected,

[0028] - the injection is carried out via a pump which draws the colored liquid from a reservoir to send it into the display's fluid network,

[0029] - emptying is carried out by opening a valve connected to the display's fluid network and which allows the colored liquid to return to the tank,

[0030] - pump and valve connected to a single pixel chamber can be combined to require only one actuator to reduce the number of actuators,

[0031] - this actuator uses very low consumption technology (piezoelectric type, for example),

[0032] - the components combining pump and valve are distributed by row, by column and by color to limit their number,

[0033] - the “line” components manage the injection and emptying of the liquid representing the background color,

[0034] - multiple "line" components can be used to facilitate the selection of the pixel to be modified; for example, if two neighboring pixels on the same line have a common injection point, a "line" component for even pixels and a "line" component for odd pixels can be used to distinguish them,

[0035] - the “columns” components manage colors other than the background color,

[0036] - an open “line” valve allows all pixels connected to this line to be modified under the action of the “column” pumps,

[0037] - an open “column” valve allows all pixels connected to this column to be modified under the action of the “row” pumps,

[0038] - screen refresh consists of updating the color of each pixel as needed. This need is expressed from the moment when the next image to be displayed (image N+1) is, for the pixel in question, different from the image currently being displayed (image N),

[0039] - the display is refreshed using a multiplexing algorithm for the different actuators, line after line, with all columns being managed simultaneously,

[0040] - to control the quantity of liquid injected into each pixel, this algorithm provides that only one valve per pixel can be opened simultaneously, - to limit the consumption of the actuators, the screen refresh only takes into account the pixels which have undergone a modification between image N and image N+1,

[0041] - if the successive images are identical, the display has zero energy consumption; to maintain the static display, no actuator is used and they are not powered at rest by construction. This is an advantage of the invention which is based on the observation that a large part of visual communication systems display fixed content for a certain time (varying from a few seconds to several days). Unlike a standard display of the prior art (LED or LCD type) which, in all cases, needs to generate light permanently (and therefore consume energy permanently), the display which is the subject of the invention optimizes energy consumption. The energy requirement is limited solely to modifications of the content to be displayed and, where appropriate, to the lighting of the pixels for use in a dark environment.

[0042] Subject of the invention

[0043] The present invention aims to remedy all or part of the drawbacks of the prior art. To this end, the present invention aims at a reflective display device according to claim 1.

[0044] Thanks to these provisions, by moving a first tinted liquid from the reservoir which contains it to the chamber to which this reservoir is connected, the tint of the pixel is enriched by the tint of this first liquid and each other liquid in another chamber of this pixel is expelled towards the reservoir, if the means for moving this other liquid is in a configuration allowing the passage of this liquid towards this reservoir. Thus, a pixel only changes tint if two conditions are met: on the one hand, a means for moving a liquid is activated to inject a liquid into the chamber intended to receive this liquid and, on the other hand, at least one means for moving another liquid allows the evacuation of the liquid present in another chamber.Due to these two conditions, a multiplexing of the pixels of the display device can be achieved, a row of identical pixel chambers of this device being connected to the same displacement means and a column of identical pixel chambers of this device being connected to the same displacement means. Thus, when a means for moving a row is activated to inject a liquid and a means for moving a column is in a configuration allowing the passage of a liquid to a reservoir, only the pixel which is in this row and this column changes color. Of course, the roles of injection or passage authorization of the means for moving the rows and columns set out in the preceding sentence can be reversed and / or the displacement means can have the function of injecting liquid into chambers, or of allowing liquid to pass between the chambers and the reservoir.Similarly, the terms rows and columns may be replaced by inclined lines, for example parallel to diagonals of square subsets of the device having the same number of rows of pixels as columns of pixels. Thanks to the implementation of the present invention, in particular because the display device is reflective, and because the first displacement means does not inject any liquid into a chamber when the control means does not apply any electrical signal to it, the hue of the pixel thus remaining constant in the absence of control by the control means, the energy consumed by the display device is limited to that of the change of state of the pixels. Thus, if the successive images are identical, the display has zero energy consumption: to maintain the static display, no actuator is used and they are not powered at rest.

[0045] Because each chamber is fluidically connected to a liquid reservoir common to a plurality of pixels, the number of such reservoirs is lower than if there were one per primary color and per pixel, the reduction factor being able to reach the ratio between the number of pixels and the sum of the number of rows and the number of columns of the display device.

[0046] In optional embodiments, a row of identical pixel chambers of this device is connected to a first displacement means common to these pixels of the same row and a column of identical pixel chambers of this device are connected to a second displacement means common to these pixels of the same column, each chamber of a pixel thus being connected to a specific pair of liquid displacement means. The multiplexing presented above can thus be implemented by the control means.

[0047] In optional embodiments, the means for controlling the movement means is configured to:

[0048] - determine, between two different images to be displayed successively, the pixels whose hue is different between the two images,

[0049] - determine the rooms of these pixels affected by the variation of tint to be applied,

[0050] - successively control the pairs of liquid displacement means specific to the chambers thus determined.

[0051] Thanks to these provisions, the transition from one image display to another image is faster and consumes less energy, since only the means of movement connected to the chambers whose internal volume is modified are controlled successively.

[0052] In optional embodiments, the support is opaque and has, on the transparent plate side, a uniformly tinted surface defining the background tint. Thanks to these arrangements, when there is only an untinted transparent liquid in the pixel chambers, this pixel takes on the background tint of this surface of the support.

[0053] In optional embodiments, each liquid reservoir is positioned on the side of the support opposite the transparent plate. Thanks to these arrangements, each inert flexible membrane can cover practically the entire surface of the pixel, which improves the contrast between the hues that can be taken by the pixel.

[0054] In optional embodiments, a channel connecting the chamber delimited by the support and the liquid reservoir filling this chamber is positioned in the center of the surface of the pixel. Thanks to these arrangements, the periphery of the surface of the pixel is left free for each other channel connecting another chamber of the pixel to another reservoir.

[0055] In optional embodiments, at least one channel connecting a chamber and a reservoir of liquid filling this chamber is positioned at the common vertex of the polygonal surfaces of more than two pixels. Thanks to these arrangements, the same channel can connect chambers of several pixels to the same reservoir of a liquid, via the same means of moving this liquid. In addition, this channel thus does not interfere with the chambers to which it is not fluidically connected.

[0056] In optional embodiments, at least one pixel of the device comprises at least two inert flexible membranes. Thanks to these arrangements, this pixel can take on different colors, for example by using liquids tinted with primary colors, for example cyan, magenta, yellow, and a transparent liquid in the visible spectrum (for three membranes and four chambers per pixel).

[0057] In optional embodiments, at least one displacement means comprises a bimetallic actuator. Thanks to these arrangements, the activation of a simple electromechanical component makes it possible to control and / or authorize the movement of a liquid between a reservoir and a pixel chamber or vice versa.

[0058] In optional embodiments, the displacement means is configured so that a deformation of the bimetallic actuator in a deformation interval actuates a pump consisting of a compartment separated from the reservoir by a first non-return valve and separated from at least one chamber of a pixel by a second non-return valve and that a deformation outside this deformation interval authorizes the passage of this liquid from each said chamber and said liquid reservoir. Thanks to these arrangements, the same bimetallic actuator allows, alternatively, the injection into at least one liquid chamber of a pixel, the return of this liquid into the reservoir or the closing of the fluid communication between the chamber and the reservoir.

[0059] In optional embodiments, the device of the invention comprises at least one pixel whose surface is triangular. Thanks to these arrangements, two adjoining pixels are separated by an inclined line, which makes it possible to improve the rendering of images comprising curved or inclined shapes.

[0060] Brief description of the figures

[0061] Other advantages, aims and characteristics of the present invention will emerge from the description which follows, given for explanatory and in no way limiting purposes with regard to the appended drawings, in which:

[0062] [Fig 1] schematically represents an embodiment of the device which is the subject of the invention,

[0063] [Fig 2] represents, schematically, a constitution of the device illustrated in figure 1,

[0064] [Fig 3] schematically represents a diagonal section of a monochromatic round pixel, in a configuration for displaying an average hue, [Fig 4] schematically represents the diagonal section of the pixel illustrated in figure 3, in a configuration for displaying the hue of a tinted liquid present in a lower chamber, [Fig 5] schematically represents the diagonal section of the pixel illustrated in figure 3, in a configuration for displaying the hue of the support of this pixel,

[0065] [Fig 6] represents a nine-pixel matrix of a color display device,

[0066] [Fig 7] schematically represents a section along a cutting line illustrated in figure 6, of a first particular embodiment of pixels,

[0067] [Fig 8] schematically represents a section along the cutting line illustrated in figure 6, of a second particular embodiment of pixels,

[0068] [Fig 9] schematically represents a section along the cutting line illustrated in figure 6, of a third particular embodiment of pixels,

[0069] [Fig 10] schematically represents a particular embodiment of a liquid displacement means, in a closed valve configuration,

[0070] [Fig 11] represents the liquid displacement means illustrated in Figure 10, in an open valve configuration,

[0071] [Fig 12] represents the liquid displacement means illustrated in figures 10 and 11 during a pumping step,

[0072] [Fig 13] represents the liquid displacement means illustrated in figures 10 to 12 during a pumping step,

[0073] [Fig 14] schematically represents means for moving liquids in a monochromatic display device comprising four lines of four pixels each,

[0074] [Fig 15] schematically represents means for moving liquids in a color display device comprising four lines of four pixels each,

[0075] [Fig 16] schematically represents a particular embodiment of a color display device comprising 36 triangular pixels, and

[0076] [Fig 17] represents an image displayed by the display device illustrated in Figure 16.

[0077] Description of particular embodiments of the invention

[0078] Throughout the description, "outer" or "external" refers to that which is close to or oriented towards the face of the display device which displays an image, this being the front face of the screen, and "inner" or "internal" refers to that which is close to or oriented towards the face of the display device opposite the outer face, this being the rear face of the screen, which does not display an image.

[0079] The device that is the subject of the invention is referred to interchangeably as a "display device" or "displayer". Throughout the description, the concept of tint incorporates colored tints (for example red, green and blue), neutral or achromatic tints (white, gray, black) including reflections on an untinted reflective surface.

[0080] Figures 1 and 2 show the outer face of a display device 50. As illustrated in Figure 1, the display device that is the subject of the invention is reflective, that is to say that it is the ambient light, for example sunlight, which is reflected on the pixels 53 of the display 50 and makes their colors visible to an observer represented diagrammatically by an eye in Figure 1. In embodiments (not shown), the display comprises a light source if the ambient brightness is not sufficient, for example lighting of the outer face or backlighting, through the support of the pixels.

[0081] As illustrated in Figure 2, a display 50 which is the subject of the invention may be made up of boxes 51 comprising groups 52 of pixels, for example matrices of four lines of four pixels each. A box is preferably provided with a housing, or casing, framing the groups 52 of pixels. In the remainder of the description, a display device is indifferently a group of pixels 52, a box 51 or all of the boxes of the display 50.

[0082] Thus, the invention is aimed in particular at large-scale displays which are the most energy-hungry due to the illuminated surface. It is therefore based on the principle of juxtaposing modules having a resolution of a certain number of lines and a certain number of columns, these modules being integrated into boxes which mechanically hold these modules. The boxes are, in turn, stacked and juxtaposed in order to construct in a modular manner a theoretically unlimited display surface. Modules and boxes are designed so that the interfaces between modules and between boxes are practically invisible.

[0083] The heart of the invention lies at the module level, in the operating principles of a pixel, construction of the module and control of the actuators which, together, form a display device which only needs energy to modify the content to be displayed, consumption being zero when the image displayed is static, apart from any possible lighting of the device.

[0084] In Figure 3, we observe a pixel 60, defined by a volume extending over the surface of the pixel 60 between a plate 67 transparent in at least part of the visible spectrum, on the one hand, and a support 66, on the other hand. The pixel 60 comprises a flexible, inert, impermeable membrane 62 transparent in at least part of the visible spectrum, extending over this surface of the pixel 60 and separating an outer chamber 68 on the side of its face oriented towards the transparent plate 67 and an inner chamber 63 on the side of its face oriented towards the support 66, the volume of the pixel thus being made up of a number of chambers equal to the number of membranes plus one.

[0085] Each chamber 63 and 68 is fluidically connected to a liquid reservoir 166 and 167 (see FIG. 14), via a displacement means 140 (see FIGS. 10 to 13) or 164, 165 (see FIG. 14) configured to move this liquid from the reservoir 166 or 167 to the chamber 63 or 68 or to allow the passage of the liquid from the chamber 63 or 68 to the reservoir 166 or 167. Each liquid reservoir, 166 and 167, is common to a plurality of pixels. In the embodiment shown in FIG. 14, each liquid reservoir, 166 and 167, is common to all the pixels of a group of pixels 52 (see FIG. 2).

[0086] At least one liquid in a reservoir connected to the pixel is tinted. For example, the liquid present in the inner chamber 63 is a black liquid, for example a black dye. Preferably, another liquid, that present in the outer chamber 68, is transparent in the visible spectrum. For example, it consists of water. Preferably also, the outer face of the support 66 is of a light color, for example white.

[0087] The device further comprises a control means 220 for each displacement means 140, 164, 165, 169 to 172 and 175 to 178, configured to vary the tint of the pixel 60 by simultaneously controlling a first displacement means so that it injects tinted liquid into the chamber 63 or transparent liquid into the chamber 68, and a second displacement means so that it authorizes the evacuation of another liquid from the chamber, 68 or 63 respectively, to a liquid reservoir. Thus, the total volume of liquid is constant in the pixel 60, the tint of the pixel 60 being a function of the quantity of tinted liquid in its chamber 63.

[0088] Each displacement means, 140, 164, 165, 169 to 172 and 175 to 178, does not inject any liquid into a chamber when the control means 220 does not apply any electrical signal to it. Consequently, the hue of the pixel remains constant in the absence of an injection command issued by the control means 220.

[0089] As illustrated in Figure 4, for a displacement means to inject the tinted liquid from the tinted liquid reservoir into the inner chamber 63, via a channel 65, it is necessary that, simultaneously, another displacement means authorizes the exit of transparent liquid from the outer chamber 68 to a transparent liquid reservoir, through a channel 61. The pixel 60 then takes on an increasingly saturated shade. Conversely, as illustrated in Figure 5, for a displacement means to inject the transparent liquid from the transparent liquid reservoir into the outer chamber 68, via the channel 61, it is necessary that another displacement means authorizes the exit of tinted liquid from the inner chamber 63 to a tinted liquid reservoir. The pixel 60 then gradually takes on the shade of the outer surface of the support 66, the background color, which is preferably light.

[0090] For a monochrome pixel, the screen structure is preferably based on the engraving or molding of cavities on a support having the background color of the pixels and / or on the external transparent plate superimposed at a distance from the support. Each cavity is convex on at least one side, plate side and / or support side. It can therefore be biconvex or plano-convex. In less preferred embodiments, the cavity is flat on the plate side and on the support side. The assembly consisting of the support and the transparent plate defines a fixed volume of the cavity corresponding to the pixel. A transparent flexible membrane divides this volume in two. This impermeable membrane ensures the interface between the liquids of different colors and prevents them from mixing. The color variation of the pixel is done by injecting a predefined volume of colored liquid, an injection which automatically ejects an equivalent volume of the liquid located on the other side of the membrane.The pixel cavity is always full of liquids and it is sufficient to push the liquid tinted with the tint to be enhanced to simultaneously expel the liquid with the tint to be attenuated. Preferably, each liquid reservoir is positioned on the side of the support opposite the transparent plate so that it is not visible to an observer placed in front of the display device and does not cause lateral congestion next to the pixels.

[0091] In Figure 6, we see a matrix 70 of nine pixels 76 of a color display device and a cutting line AA used to make the sections illustrated in Figures 7 to 9. Each pixel is connected to five fluid channels. A central fluid channel 75 connects the lower chamber 91, 111 or 131 (see Figures 7 to 9) to a liquid reservoir (not shown). In this embodiment, the fluid channel 75 is, for example, crossed by a white liquid, or transparent if the upper surface of the support is white. Four fluid channels 71 to 74 are located at the four vertices of each pixel 76. Thus, the fluid channels 71 to 74 are at the common vertex of the polygonal surfaces of four pixels 76.

[0092] For example, the fluid channels 71 are dedicated to a magenta dye, the fluid channels 72 to a cyan dye, the fluid channels 73 to a black dye and the fluid channels 74 to a yellow dye. In order for the four upper chambers of each pixel 76 to be supplied with tinted liquid by these fluid channels 71 to 74, preferably, these form repetitive patterns: on a horizontal line of pixel vertices 76 there are alternately fluid channels 71 and 72 and on the next horizontal line of pixel vertices there are alternately fluid channels 73 and 74.

[0093] In the first particular embodiment of pixels 80, illustrated in FIG. 7, the volume of the pixel, between the plate 87 and the support 86 is convex on the side of the plate 87 and flat on the side of the support 86. The plate 87 is thus hollowed out, for example by etching or molding, with cavities corresponding to each of the pixels 80. A chamber 91, delimited by the support 86 and by a membrane 92 is connected, by a central fluidic channel 85 or 185 (see FIG. 15), to a liquid reservoir 195, by means of a liquid displacement means 190. A chamber 93, delimited by the membrane 92 and by a membrane 94 is connected, by a pixel top fluidic channel 82 or 182, to a liquid reservoir 192, by means of a liquid displacement means 197.A chamber 95, delimited by the membrane 94 and by a membrane 96 is connected, by a pixel top fluid channel 81 or 181, to a liquid reservoir 191, via a liquid displacement means 196. A chamber 97, delimited by the membrane 96 and by a membrane 98 is connected, by a pixel top fluid channel 84 or 184, to a liquid reservoir 194, via a liquid displacement means 199. A chamber 99, delimited by the membrane 98 and by the plate 87 is connected, by a pixel top fluid channel 83 or 183, to a liquid reservoir 193, via a liquid displacement means 198.

[0094] Each liquid reservoir, 191 to 195, is common to a plurality of pixels. In the embodiment shown in Figure 15, each liquid reservoir, 191 to 195, is common to all pixels in a pixel group 52 (see Figure 2). In the second particular embodiment of pixels 100, illustrated in FIG. 8, the volume of the pixel, between the plate 107 and the support 106 is flat on the side of the plate 107 and convex on the side of the support 106. The support 106 is thus hollowed out, for example by etching or molding, with cavities corresponding to each of the pixels 100. A chamber 111, delimited by the support 106 and by a membrane 112 is connected, by a central fluidic channel 105 or 185 (see FIG. 15), to a liquid reservoir 195, by means of a liquid displacement means 190.A chamber 113, delimited by the membrane 112 and by a membrane 114 is connected, by a pixel top fluid channel 102 or 182, to a liquid reservoir 192, by means of a liquid displacement means 197. A chamber 115, delimited by the membrane 114 and by a membrane 116 is connected, by a pixel top fluid channel 101 or 181, to a liquid reservoir 191, by means of a liquid displacement means 196. A chamber 117, delimited by the membrane 116 and by a membrane 118 is connected, by a pixel top fluid channel 104 or 184, to a liquid reservoir 194, by means of a liquid displacement means 199. A chamber 119, delimited by the membrane 118 and by the plate 107 is connected, by a pixel top fluid channel 103 or 183, to a liquid reservoir 193, via a liquid displacement means 198.

[0095] In the third particular embodiment of pixels 120, illustrated in FIG. 9, the volume of the pixel, between the plate 127 and the support 126 is convex on the side of the plate 127 and convex on the side of the support 126. The plate 127 and the support 126 are thus hollowed out with cavities corresponding to each of the pixels 120. A chamber 131, delimited by the support 126 and by a membrane 132 is connected, by a central fluidic channel 125 or 185 (see FIG. 15), to a liquid reservoir 195, by means of a liquid displacement means 190. A chamber 133, delimited by the membrane 132 and by a membrane 134 is connected, by a pixel top fluidic channel 122 or 182, to a liquid reservoir 192, by means of a liquid displacement means 197.A chamber 135, delimited by the membrane 134 and by a membrane 136 is connected, by a pixel top fluid channel 121 or 181, to a liquid reservoir 191, via a liquid displacement means 196. A chamber 137, delimited by the membrane 136 and by a membrane 138 is connected, by a pixel top fluid channel 124 or 184, to a liquid reservoir 194, via a liquid displacement means 199. A chamber 139, delimited by the membrane 138 and by the plate 127 is connected, by a pixel top fluid channel 123 or 183, to a liquid reservoir 193, via a liquid displacement means 198.

[0096] As illustrated in Figures 7 to 9, the hue of pixel 80, 100 or 120, respectively, is a function of the volume of each liquid in the different chambers of the pixel. For example, the pixels shown on the right in Figures 7 and 9 are darker than the pixels in the center of these figures because the amount of black liquid in the outer chamber, 99 and 139 respectively, is higher. Similarly, in Figures 7 and 9, the pixels shown on the left are more yellow than the pixels shown on the right in these figures because the amount of yellow liquid is higher. Because the volume of liquid in the pixel is constant, the sum of the volumes of each liquid in the chambers of this pixel is constant.Thus, a pixel only changes color if two conditions are met: on the one hand, a means for moving a liquid is activated to inject a liquid into the chamber intended to receive this liquid and, on the other hand, at least one means for moving another liquid authorizes the evacuation of the liquid present in another chamber. Due to these two conditions, a multiplexing of the pixels of the display device can be carried out, a row of identical pixel chambers of this device being connected to the same displacement means and a column of identical pixel chambers of this device being connected to the same displacement means. Thus, when a means for moving a row is activated to inject a liquid and a means for moving a column is in a configuration authorizing the passage of a liquid towards a reservoir, only the pixel which is in this row and this column changes color.

[0097] Of course, the roles of injection or passage authorization of the means for moving the rows and columns set out in the preceding sentence may be reversed and / or the moving means may have the function of injecting liquid from the reservoir into chambers, or of allowing liquid to pass between the chambers and the reservoir. Similarly, the terms rows and columns may be replaced by inclined lines, for example parallel to diagonals of square subsets of the device having the same number of rows of pixels as columns of pixels.

[0098] Preferably, each liquid reservoir is positioned on the side of the support opposite the transparent plate, so that it is not visible to an observer placed in front of the display device and does not cause lateral clutter next to the pixels.

[0099] Such multiplexing means are described below, with reference to Figures 10 to 15, starting by describing, with reference to Figures 10 to 13, a particular liquid displacement means, which has the advantage of comprising only a single actuator to alternately provide a function of opening or closing a valve allowing liquid to exit from a pixel chamber and a function of pumping liquid from a reservoir to at least one pixel chamber (preferably to a plurality of pixel chambers when multiplexing is implemented).

[0100] Figure 10 schematically represents a particular embodiment of a liquid displacement means 140, in a closed valve configuration. This displacement means 140 comprises a bimetallic component 141, for example piezoelectric, which deforms according to the voltage applied to it by a voltage source 142. A return valve 143 is closed by a flexible membrane 147 whose center is integral with the free end of the bimetallic component 141. This return valve is connected to a chamber of at least one pixel via a channel 146 and to a liquid reservoir via a channel 148. Thus, depending on the voltage, here negative (figure 11) or zero (figure 10), applied to the bimetallic component 141, the flexible membrane 147 opens, figure 11, or closes, figure 10, the return valve 143 and authorizes or not the return of liquid from each pixel chamber to which the channel 146 is fluidically connected to the liquid reservoir.A rigid housing 153 and 154 contains all the components and channels of the displacement means 140, except for the bimetallic component 141. It is noted that, when the valve 143 is closed, the voltage across the terminals of the bimetallic component 141 is zero. So that maintaining the color of each pixel connected to the control means 220 or 230 in the same state does not cause any electricity consumption.

[0101] In addition to the voltage-controlled return valve function, the displacement means 140 provides a voltage-controlled injector function, as illustrated in FIGS. 12 and 13. For this injector function, the displacement means 140 comprises a compartment 151 separated from the return valve 143 by a flexible membrane 152 and provided with a spring 144 tending to push the return valve 143 towards the bimetallic component 141. The compartment 151 is separated from the channel 146 by a non-return valve 150 which prevents the passage of liquid from the channel 146 to the compartment 151. The compartment 151 is separated from a channel 145 fluidically connected to the liquid reservoir, by a non-return valve 149 which prevents the passage of liquid from the compartment 151 to this reservoir. In variants, channels 145 and 148 are merged into a single channel.

[0102] When the bimetallic component 141 is subjected to a voltage of increasing absolute value, in a predetermined voltage range, here the positive voltages, it deforms towards the compartment 151 and causes the expulsion of liquid from this compartment 151 towards the channel 146 through the valve 150, as illustrated in FIG. 12. The expulsion of liquid from the compartment 151 causes the injection of this liquid into the chamber of each pixel to which this channel 146 is fluidically connected. It is noted that, during this first movement, the valve 143 is closed by the membrane 147. Then, when the bimetallic component 141 is subjected to a voltage of decreasing absolute value in this predetermined voltage range, the spring pushes the valve 143 towards the bimetallic component 141 and causes the suction of liquid from the liquid reservoir towards the compartment 151, via the valve 149.Note that, during this second movement, valve 143 is still closed by membrane 147.

[0103] In other words, the displacement means 140 is the combination of a pump and a valve driven by a single actuator, the bimetallic component 141. The circulation of the liquid in the fluid network resulting from the assembly of the screen is ensured by a system of such low-consumption actuators having three states:

[0104] - an off state shown in Figure 10, in which the actuator 141 is not powered, the valve 143 is closed and the pump is stopped. No circulation of liquid is possible between the reservoir and the pixel chambers to which the displacement means 140 is connected. This corresponds to maintaining the hue for each of these pixel chambers. When all the displacement means 140 are in this state, the image displayed by the display device is frozen. Maintaining the display of a static image by the display device therefore consumes no energy. - an open state of the valve 143 shown in Figure 11, in which the actuator 141 is subjected to a negative voltage. This actuator 141 then bends to release an opening of the valve 143, thus allowing the passage of the liquid through the valve 143 from the chamber of at least one pixel to the reservoir.This state makes it possible to expel liquid from each pixel chamber to which the displacement means 140 is connected, provided that this chamber is pressurized by the injection of liquid into another chamber of this pixel. The quantity of liquid in this chamber can thus reduce as well as the intensity of the shade concerned in this chamber. There is thus no suction, the liquid only returns to the reservoir if a pump connected to a reservoir of liquid of another shade injects a quantity of liquid of this other shade into the corresponding chamber of the same pixel.

[0105] - a pump actuation state shown in Figure 12, in which the actuator 141 is gradually powered by a positive voltage, bends towards the compartment 151, causing a reduction in the volume of this compartment 151, the opening of the outlet non-return valve 150 and the filling of each pixel chamber connected to this pump, provided that a displacement means connected to another chamber of this pixel allows the evacuation of liquid from this other chamber.

[0106] The progressive return to zero of the supply voltage of the actuator 141 shown in Figure 13 brings it back to the stop position, under the effect of the spring 144. The increase in the volume of the compartment 151 causes the outlet non-return valve 150 to close, the inlet non-return valve 149 to open and the compartment 151 to be filled by suction of the liquid into the corresponding reservoir. In embodiments (not shown) the pumping function may be common to several liquid displacement means, these liquid displacement means then being limited to the electrically controlled valve function.

[0107] In Figure 14, we observe liquid displacement means in a monochromatic display device 160 comprising four lines of four pixels 161 each. These displacement means allow multiplexing of the changes in hue of the pixels, thus avoiding the need for each chamber of each pixel to be provided with a liquid displacement means specific to this chamber: no other chamber of this pixel and no chamber of another pixel is associated with this pair of displacement means.

[0108] This display device 160 comprises, for each pixel 161, a central channel 162 corresponding to the channel 65 illustrated in FIGS. 3 to 5. The pixels 161 are distributed into four groups of four pixels each having a common vertex where a vertex channel 173 is located. Two of these vertex channels are connected, via a channel 174 and a displacement means 165 to a liquid reservoir 166. The other two of these vertex channels 173 are connected to the same reservoir 166 via another channel 174 and another displacement means 171.

[0109] The central channels 162 of each of the eight pixels connected to the displacement means 165 are connected, via channels 179, to eight different displacement means, 164, 169, 170, 172, 175, 176, 177 and 178 connected to a liquid reservoir 167, via channels 168. The same applies to the eight pixels connected to the displacement means 171. Thus, each pixel 161 of the display device 160 is associated with a unique pair of displacement means. As explained above, since two displacement means must be in a state different from the stop state prohibiting the passage of liquid so that a chamber of a pixel 161 receives a liquid while another chamber of this pixel empties of liquid, by actuating the two displacement means associated with a pixel 161, the hue of this pixel 161 is varied without any other pixel 161 changing hue.

[0110] In Figure 14, each means of movement is represented with a valve function towards which two arrows converge, and a pump function, represented by a circle provided with an arrow forming a radius. This representation recalls that, in embodiments (not shown), these two functions of authorization of return of liquid to a reservoir and injection of liquid into a chamber of a pixel are disjoint.

[0111] A control means 220 for the movement means 164, 165, 169 to 172 and 175 to 178 is configured to determine, between two different images to be displayed successively, the pixels 163 whose hue is different between the two images. Then, this control means 220 determines the chambers of these pixels 163 affected by the variation in hue to be applied, that is to say those of these chambers whose volume of liquid must vary to reach the new hue to be displayed and the volumes of liquid to be injected or removed from each of these chambers. Then, the control means 220 successively controls the pairs of movement means 164, 165, 169 to 172 and 175 to 178 of liquid which are specific to only the chambers thus determined to apply to them the variations in volume thus determined. For example, the control means 220 is a microcontroller associated with a memory of a program.

[0112] With respect to a color display device 180 illustrated in Figure 15, a similar multiplexing principle is preferably implemented, by providing a vertex channel at each vertex common to four pixels, as illustrated in Figure 15. Thus, each pixel 186 is connected, by a vertex channel 181 and a displacement means 196, to a liquid reservoir 191. Each pixel 186 is also connected, by a vertex channel 182 and a displacement means 197, to a liquid reservoir 192. Each pixel 186 is also connected, by a vertex channel 183 and a displacement means 198, to a liquid reservoir 193. Each pixel 186 is also connected, by a vertex channel 184 and a displacement means 199, to a liquid reservoir 194. Each pixel 186 is also connected, by a central channel 185 and a displacement means 190, to a liquid reservoir 195.Thus, each chamber of each pixel is associated with a specific pair of a displacement means 190 and a displacement means among the displacement means 196, 197, 198 and 199: no other chamber of this pixel and no chamber of another pixel is associated with this pair. By controlling the states of the two displacement means of such a pair, the hue of the only pixel associated with it is modified. Each displacement means, 190 and 196 to 199, does not inject any liquid into a chamber when the control means 230 does not apply any electrical signal to it. Consequently, the hue of the pixel remains constant in the absence of an injection command issued by the control means 230.

[0113] The principle of controlling the display by multiplexing the filling of the pixels is described below. The display refresh is based on the analysis of the differences between successive images. Only the pixels whose hues change are refreshed in order to minimize the energy required to update the displayed content. The refresh is done line by line in two stages for each line: odd pixels then even pixels.

[0114] All color columns are managed in parallel. The color fluid channels open at the common vertices of the pixels, in the corners of the pixels, so that they do not disturb the color of the visible surface of the pixel. Each vertex fluid channel gives access to the color chamber of the four neighboring pixels having this common vertex. The selection of the chamber, and therefore of the pixel, whose hue is to be modified is done by opening the appropriate valve in the center of each pixel, which explains the management of the lines in two stages: even pixels then odd pixels. The pumps of the liquid displacement means 190 are used to inject white or transparent liquid from the reservoir 195. The valves of the displacement means 190 allow the return of the white or transparent liquid to the reservoir 195 when injecting a liquid of another color (Cyan, Magenta, Yellow or Black).

[0115] The pumps of the displacement means 196 to 199 serve to inject colored liquid from the reservoir 191 to 194, respectively, into the corresponding chambers of the pixels. The valves of the displacement means 196 to 199 allow the return of the colored liquid from the corresponding chambers of the pixels to the reservoirs 191 to 194, respectively.

[0116] A control means 230 for the movement means 190, 196 to 199 is configured to determine, between two different images to be displayed successively, the pixels 186 whose hue is different between the two images. Then, this control means 230 determines the chambers of these pixels 186 affected by the variation in hue to be applied, that is to say those of these chambers whose volume of liquid must vary to reach the new hue to be displayed and the volumes of liquid to be injected or removed from each of these chambers. Then, the control means 230 successively controls the pairs of movement means 190, 196 to 199 of liquid which are specific to only the chambers thus determined to apply to them the variations in volume thus determined. For example, the control means 230 is a microcontroller associated with a memory of a program.

[0117] By default, all pixels are filled with white or transparent liquid, with only the lower chamber being filled. At rest, all actuators are also at rest and not powered. This description is based on square pixels that allow the use of up to four fluid channels in the corners of each pixel. This principle can be applied to pixels of any shape, using a greater or lesser number of fluid channels and therefore primary colors. Figure 16 shows a particular embodiment of a color display device 200 comprising 36 triangular pixels. In this embodiment, four triangular pixels 201, 206, 207 and 208 together form a square.The chambers of each pixel are connected to a central channel 202 connected to a first liquid reservoir, a top channel 203 connected to a second liquid reservoir, a top channel 204 connected to a third liquid reservoir and a top channel 205 connected to a fourth liquid reservoir.

[0118] This reflective display device is particularly suitable for displaying shapes comprising curved parts or inclined contours, such as the octagon 210 shown in Figure 17. In other embodiments, the pixels have other polygonal shapes, for example hexagonal, or rounded, for example circles or oval shapes, depending on the needs. The transparent external plate of the display device can be treated anti-reflective, to increase the contrast of the image perceived by the observer, and anti-UV (for ultraviolet) to limit the degradation of colored liquids over time. In addition, a dark mask, for example black, can be added to this transparent external plate, to hide the interstices between the pixels and the injection points in order to increase the contrast of this image and reduce the parasitic color points.

[0119] In the case of a reflective display device without an integrated light source, the transparent superposition of the different layers of colorants (cyan, magenta and yellow, for example) in a chamber of each pixel makes it possible, by precise dosage of the quantity of colorant injected, to produce the color palette in subtractive synthesis if we consider that the support and / or the liquid present in the chamber, a partition of which is formed by the support, is white.

Claims

CLAIMS 1. A reflective display device (50, 160, 180, 200) comprising an array (70, 200) of pixels (53, 161, 186, 201, 206, 207, 208), each pixel being defined by a volume extending over the surface of the pixel between a transparent plate (67, 87, 107, 127) in at least a portion of the visible spectrum and a support (66, 86, 106, 126), each pixel comprising: - at least one flexible, inert, impermeable membrane (62, 92, 94, 96, 98, 112, 114, 116, 118, 132, 134, 136, 138) transparent in at least one part of the visible spectrum, extending over this surface of the pixel and separating a chamber (68, 93, 95, 97, 99, 113, 115, 117, 119, 133, 135, 137, 139) on the side of its face oriented towards the transparent plate and a chamber (63, 91, 93, 95, 97, 111, 113, 115, 117, 131, 133, 135, 137) on the side of its face oriented towards the support, the pixel volume thus being made up of a number of chambers equal to the number of membranes plus one, - each chamber being fluidically connected to a liquid reservoir (166, 167, 191 to 195) common to a plurality of pixels, by means of a means (140, 164, 165, 169 to 172, 175 to 178, 190, 196 to 199) for moving this liquid from the reservoir to the chamber or from the chamber to the reservoir, at least one liquid in a reservoir connected to the pixel being tinted;the device further comprising a control means (220, 230) for controlling each displacement means configured to vary the tint of the pixel by controlling a first displacement means so that it injects tinted liquid into a chamber and a second displacement means so that it allows the passage of another liquid towards a liquid reservoir, in such a way that the total volume of liquid is constant in the pixel, the tint of the pixel thus being a function of the quantity of tinted liquid in each of its chambers, the first displacement means not injecting any liquid into a chamber when the control means does not apply any electrical signal to it.; 2. Device (50, 160, 180, 200) according to claim 1, in which a row of identical pixel chambers (161, 186) are connected to a first displacement means (164, 169, 170, 172, 175 to 178, 190) common to these pixels of the same row and a column of identical pixel chambers (161, 186) of this device are connected to a second displacement means (165, 171, 196 to 199) common to these pixels of the same column, each chamber of a pixel thus being connected to a specific pair of liquid displacement means.

3. Device (50, 160, 180, 200) according to claim 2, wherein the control means (220, 230) of the displacement means is configured to: - determine, between two different images to be displayed successively, the pixels (53, 161, 186, 201, 206, 207, 208) whose hue is different between the two images, - determine the rooms of these pixels affected by the variation of tint to be applied, - successively control the pairs of liquid displacement means specific to the chambers thus determined.

4. Device (50, 160, 180, 200) according to one of claims 1 to 3, in which the support (66, 86, 106, 126) is opaque and has, on the side of the transparent plate (67, 87, 107, 127), a surface of uniform color defining the background color.

5. Device (50, 160, 180, 200) according to one of claims 1 to 4, in which each liquid reservoir (166, 167, 191 to 195) is positioned on the side of the support (66, 86, 106, 126) opposite the transparent plate (67, 87, 107, 127).

6. Device (50, 160, 180, 200) according to one of claims 1 to 5, which comprises a channel (65, 85, 105, 125, 162, 185, 202) connecting the chamber (63, 91, 111, 131) delimited by the support (66, 86, 106, 126) and the liquid reservoir (167, 195) filling this chamber, this channel being positioned at the center of the surface of the pixel (53, 161, 186, 201, 206, 207, 208).

7. Device (50, 160, 180, 200) according to one of claims 1 to 6, which comprises at least one channel (71 to 74, 81 to 84, 101 to 104, 121 to 124, 173, 181 to 184, 203, 204, 205) connecting a chamber (66, 86, 106, 126) and a liquid reservoir filling this chamber, this channel being positioned at the common vertex of the polygonal surfaces of more than two pixels.

8. Device (50, 180, 200) according to one of claims 1 to 7, in which at least one pixel (80, 100, 120) of the device comprises at least two inert flexible membranes (92, 94, 96, 98, 112, 114, 116, 118, 132, 134, 136, 138).

9. Device (50, 160, 180, 200) according to one of claims 1 to 8, in which at least one displacement means (140) comprises a bimetallic actuator (141).

10. Device (50, 160, 180, 200) according to claim 9, wherein the displacement means (140) is configured so that a deformation of the bimetallic actuator (141) in a deformation interval actuates a pump consisting of a compartment (151) separated from the reservoir by a first non-return valve (149) and separated from at least one chamber of one pixel by a second non-return valve (150) and that a deformation outside this deformation interval allows the passage of this liquid from each said chamber and said liquid reservoir.

11. Device (50, 160, 180, 200) according to one of claims 1 to 10, which comprises at least one pixel (201, 206, 207, 208) whose surface is triangular.

Images