CN113168005B - Illumination system for reflective display - Google Patents

Abstract

A display device (30) comprising: a reflective display (38) arranged to provide a first image visible through a viewing surface; and a projection device (31-37) arranged to provide an image in reflection on the viewing surface Visible second image; reflective display (38) and projection means (31-37) mounted on a common frame.

Description

Lighting systems for reflective displays

References to related applications

This application claims Provisional Application Serial No. 61/636,070 filed April 20, 2012, and Provisional Application Serial No. 61/654,405 filed June 1, 2012 and common Interest in pending non-provisional application Serial No. 13/867,633. However, applicant hereby declares that, pursuant to 37 CFR 1.78(a)(6), this application also contains rights to the claimed invention with an effective filing date on or after March 16, 2013.

The foregoing co-pending applications, as well as all patents, co-pending applications and published applications mentioned below, are hereby incorporated by reference in their entirety.

technical field

The invention relates to lighting systems for reflective displays. More specifically, the present invention relates to displays and devices for projecting patterned light onto at least a portion of the display. The invention also relates to a method for directing spatially and spectrally modulated illumination onto a reflective display to improve contrast and colorfulness under ambient lighting conditions. Certain embodiments of the present invention relate to a display that is primarily intended for outdoor use, but which may also have some indoor applications (in terms of use within buildings, tents, and other similar structures); these aspects of the display of the present invention Embodiments utilize a reflective bistable electro-optic display in combination with a light source arranged to illuminate the reflective electro-optic display.

Background technique

The term "electro-optic" as applied to materials or displays is used here in its conventional meaning in the field of imaging to refer to a material having a first and a second display state whose At least one optical property is different, and application of an electric field to said material causes the material to change from its first display state to a second display state. Although an optical property is usually a color perceivable by the human eye, it can be another optical property such as light transmission, reflection, luminescence, or in the case of displays for machine reading, electromagnetic wavelengths outside the visible range False color in the sense of a change in reflectivity.

The term "gray state" is used here in its conventional meaning in the imaging field to refer to a state between, but not necessarily, between two extreme optical states of a pixel transition between black and white. For example, several Ink patents and published applications referenced below describe electrophoretic displays in which the extreme states are white and dark blue such that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the change of optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above . The term "monochrome" may be used below to refer to a drive scheme that drives a pixel to only its two extreme optical states, without an intermediate gray state.

The terms "bistable" and "bistable" are used herein in their conventional meaning in the art to refer to a display that includes a display element having a first and a second display state, the first and second display states being The second display state differs in at least one optical property such that after any given element is driven to assume its first or second display state with an addressing pulse of finite duration, that state will persist after termination of the addressing pulse The time for is at least several times (eg at least 4 times) the minimum duration of the addressing pulse required to change the state of the display element. It is shown in U.S. Patent No. 7,170,670 that some particle-based electrophoretic displays that support gray scale can be stabilized not only in their extreme black and white states, but also in their intermediate gray states, and some other types of electro-optic displays are also in this way. This type of display is properly called "multistable" rather than bistable, but for convenience the term "bistable" may be used here to cover both bistable and multistable display.

Several types of electro-optic displays are known. One type of electro-optic display is the rotary dichroic member type, as described in, for example, U.S. Pat. "rotating dichroic ball" displays, but the term "rotating dichroic member" is preferred to be more precise because in some of the patents mentioned above the rotating member is not spherical). Such displays use many small bodies (usually spherical or cylindrical) comprising two or more parts with different optical properties and internal dipoles. These bodies are suspended within the matrix in liquid-filled vacuoles that are filled with liquid so that the bodies rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the subject into various positions and changing the portion of the subject seen through the viewing surface. Electro-optic media of this type are usually bistable.

Another type of electro-optic display uses an electrochromic medium, for example in the form of a nanochromic film comprising an electrode formed at least in part of a semiconducting metal oxide and a reversible color-changing film attached to the electrode. multiple dye molecules; see eg O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in US Patent Nos. 6,301,038; 6,870,657; and 6,950,220. Media of this type are also usually bistable.

Another type of electro-optic display is the electrowetting display developed by Philips, which is described in Hayes, R.A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). It is shown in US Patent No. 7,420,549 that such an electrowetting display can be made bistable.

One type of electro-optic display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which multiple charged particles move through a fluid under the influence of an electric field. Compared with liquid crystal displays, electrophoretic displays can have the attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays are prone to sedimentation, resulting in insufficient lifetime of these displays.

As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but electrophoretic media can be produced using gaseous fluids; see for example Kitamura, T. et al., "Electronic toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCS 1-1, and Yamaguchi, Y. et al., "Toner display using insulating particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4). See also US Patent Nos. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in a direction that allows particle settling, such as in signage where the medium is arranged in a vertical plane, this gas-based electrophoretic Electrophoretic media are susceptible to the same type of problems. In fact, the problem of particle settling in gas-based electrophoretic media is more severe than in liquid-based electrophoretic media because the lower viscosity of the gaseous suspension fluid allows faster settling of the electrophoretic particles compared to liquids.

Numerous patents and applications assigned to or on behalf of the Massachusetts Institute of Technology (MIT) and Iink Corporation describe various techniques for encapsulating electrophoretic and other electro-optic media. This encapsulated medium comprises a number of vesicles, each vesicle itself comprising an inner phase containing electrophoretically mobile particles in a fluid medium, and a wall surrounding the inner phase. Typically, the capsule itself is held in a polymer binder to form a coherent layer between the two electrodes. Technologies described in these patents and applications include:

(a) Electrophoretic particles, fluids and fluid additives; see, eg, US Patent Nos. 7,002,728 and 7,679,814;

(b) Capsules, adhesives, and encapsulation processes; see, eg, US Patent Nos. 6,922,276 and 7,411,719;

(c) Films and subassemblies comprising electro-optic materials; see, eg, U.S. Patent Nos. 6,982,178 and 7,839,564;

(d) Backplanes, adhesive layers, and other auxiliary layers and methods for use in displays; see, for example, U.S. Patent Nos. D485,294; 6,124,851; 6,130,773; 6,177,921; 6; 6,413,790; 6,422,687; 6,445,374; 6,480,182; 6,498,114; 6,506,438; 6,518,949; 6,521,489; 6,535,197; ,664,944; 6,680,725; 6,683,333; 6,724,519; 6,750,473; 6,816,147; 5,010; 6,967,640; 6,980,196; 7,012,735; 7,030,412; 7,075,703; 7,106,296; 7,110,163; ,190,008; 7,206,119; 7,223,672; 7,230,751; 7,256,766; 7,259,744; 7,280,094; 2,363; 7,388,572; 7,442,587; 7,492,497; 7,535,624; 7,551,346; 7,554,712; 7,583,427; ,672,040; 7,688,497; 7,733,335; 7,785,988; 7,843,626; 7,859,637; 9,947; 8,077,141; 8,089,453; 8,208,193 and 8,373,211; and U.S. Patent Application Publication Nos. 2002/0060321; 2004/0105036; 2005/0122306; 2005/0122563; 489; 2007/0109219; 2007/0211002; 2009/0122389 2009/0315044; 2010/0265239; 2011/0026101; 2011/0140744; 2011/0187683; 1/0292493; 2011/0292494; 2011/0297309; 2011 /0310459; and 2012/0182599; and International Application Publication No. WO 00/38000; European Patent Nos. 1,099,207B1 and 1,145,072B1;

(e) Color formation and color adjustment; see, eg, U.S. Patent Nos. 6,017,584; 6,664,944; 6,864,875; 7,075,502; 18; 8,213,076 and 8,363,299; and U.S. Patent Application Publication No. 2004/ 0263947; 2007/0109219; 2007/0223079; 2008/0023332; 2008/0043318; 2008/0048970; 780; 2011/0164307; 2011/0195629; 2011/0310461; 2012/0008188; 2012/0019898; 2012/0075687; 2012/0081779; 2012/0134009; 2012/0182597; 2012/0212462;

(f) methods for driving displays; see, e.g., U.S. Patent Nos. 7,012,600 and 7,453,445;

(g) Display applications; see, eg, U.S. Patent Nos. 6,118,426; 6,473,072; 6,704,133; 6,710,540; 6,738,050; 4; and 8,064,962; and U.S. Patent Application Publication No. 2002/0090980; 2004/0119681; 2007/0285385 and 2010/0201651; and International Application Publication No. WO 00/36560; and

(h) Non-electrophoretic displays, as described in US Patent Nos. 6,241,921; 6,950,220; 7,420,549 and 8,319,759; and US Patent Application Publication No. 2012/0293858.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules can be replaced by a continuous phase in an encapsulated electrophoretic medium in which the electrophoretic medium comprises a plurality of discrete electrophoretic fluids, resulting in a so-called polymer dispersed electrophoretic display The droplets and the continuous phase of the polymer material, and the discrete droplets of the electrophoretic fluid in this polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even if there is no discrete capsule film with Each individual droplet is associated; see, eg, the aforementioned US Patent No. 6,866,760. Accordingly, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

A related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcellular electrophoretic displays, charged particles and fluids are not encapsulated within microcapsules, but are held in multiple cavities formed within a carrier medium, usually a polymer film. See, eg, US Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging Corporation.

Although electrophoretic media are usually opaque (because, for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in reflective mode, many electrophoretic displays can be made in the so-called "shutter mode". ” in which one display state is substantially opaque and one display state is light-transmissive. See, eg, US Patent Nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see US Patent No. 4,418,346. Other types of electro-optic displays are also capable of operating in shutter mode. Electro-optic media that operate in shutter mode can be used in multilayer structures for full-color displays; in this structure, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface. layer.

Encapsulated electrophoretic displays generally do not suffer from the aggregation and settling failure modes of conventional electrophoretic devices and offer additional benefits, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (Use of the word "printing" is intended to include all forms of printing and coating, including but not limited to: pre-metered Roll coating such as knife-on-roller, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing process; electrostatic printing process; thermal printing process; inkjet printing process; electrophoretic deposition (see US Patent No. 7,339,715); and other similar techniques.) Thus, the resulting display can be flexible. Additionally, because the display medium can be printed (using a variety of methods), the display itself can be cheaply manufactured.

Other types of electro-optic media can also be used in the displays of the present invention.

Regardless of the exact technology used to display data on them, electro-optic displays can be functionally divided into two broad categories, emissive displays in which light is emitted from or transmitted through the active layer, and light reflected from the active layer reflective display. Emissive displays communicate through changes in their brightness and can be viewed without ambient light, while reflective displays communicate through changes in their reflectivity and cannot be viewed without ambient light. Emissive displays can contain materials that are electroluminescent in nature (e.g., organic light-emitting diodes, OLEDs), or can be constructed by combining transmissive or reflective light modulators with light sources; for example, liquid crystal displays (LCDs) typically combine non-emissive light The valve layer is combined with the backlight. A digital projector can be thought of as an emissive display that includes a high-intensity light source and light modulator with appropriate lenses to deliver the image to a distant reflective surface. The disadvantage of all emissive displays is that their contrast and apparent color are dependent on the intensity of the ambient light. In very bright environments such as daylight, the emitted light may be swamped and the displayed information difficult to see. The advantage of reflective displays is that their contrast and chromaticity are not affected by the ambient light level, and in fact can even improve in very bright light. However, the reflective display is obviously difficult to see in dim light.

Additional difficulties arise with reflective displays designed to provide color images. For example, as described in US Patent No. 8,054,526, a color filter array may be positioned such that a suitable black and white image is viewed through the color filter array. Although thus providing a color image to the viewer, the color filters necessarily reduce the amount of light reflected from the display in the white state, and the necessary sharing of the available display surface area between the different color primaries limits the apparent chromaticity and color gamut.

Many attempts have been made to construct hybrid emissive/reflective displays that are visible under any ambient light. For example, US Patent No. 7,170,506 describes a hybrid emissive/reflective display in which the intensity of emitted light is adjustable. As mentioned earlier, the legibility of information on an emissive display is compromised in very bright ambient light, so the internal brightness of the display must be increased to counteract the resulting loss of contrast and chromaticity. Conversely, under very low lighting conditions, the legibility of information on a reflective display is compromised, so the illuminance of the display must be increased accordingly to counteract the loss of contrast and chromaticity.

Technical solutions have been developed to increase the contrast ratio of emissive displays so that such displays can display high dynamic range (HDR) still and moving images. Some of these so-called HDR displays combine an LCD color panel with a bright backlight that is modulated with image information, usually in the form of a low-pass filtered luminance channel (this approach is sometimes called "local dimming") ). More generally, HDR display can be achieved by combining two low dynamic range (or low contrast) devices, and generating two low dynamic range images from the HDR image for each display device. Examples of modulated backlights include digital projectors or LED arrays as described in US Patent Application Publication Nos. 2008/0137990 and 2008/0137976. However, no equivalent solution currently exists to increase the contrast and chromaticity of reflective displays.

It is well known that the contrast of a spatially consistent combination of projected and reflected images can exceed the contrast of either projected and reflected image alone. One solution aimed at increasing the contrast of the projected image is described in US Patent No. 6,853,486 (the '486 patent). The patent describes an active projection screen that is registered with the projected image and used to increase the contrast of the projected image under bright ambient light that would reduce the contrast of the same image projected onto a uniformly reflective screen. The main disadvantage of this system is the need to maintain precise registration between the active projection screen and the projector. Without a rigid mechanical coupling of the projector and screen, it is very difficult to achieve and maintain the precise alignment and registration required, and the solution described in the '486 patent, that is, through the "reflection processor" and "display control “transmitter” is the electronic coupling between the projector and the screen, which is expensive.

The system described in the '486 patent is a large emissive (projection) display, and the patent does not disclose combining the color projection device image and the means for providing the reflected image into the same device so that the two images can be provided in register with each other any device. In one aspect, the present invention seeks to improve the contrast and chromaticity of reflective displays, especially handheld devices, under a wide range of ambient lighting conditions by combining projected and reflected images.

One specific application where bistable electro-optic displays may be useful is outdoor signage, especially traffic control devices. In the past, traffic lights and other traffic control signals have relied on incandescent bulbs to generate light; more recently, light-emitting diodes (LEDs) have begun to be used for this purpose. Incandescent light bulbs and LEDs (and virtually all other emitting light sources) require a continuous power source, usually mains AC power, so any power interruption due to equipment failure, weather conditions, or traffic accidents will result in traffic light failures, traffic accidents, and Major interruption of traffic flow. Conventional traffic signals have other disadvantages, including:

(a) False signals may be produced due to daylight and sun glare; conventional traffic lights must overcome ambient light conditions, including specular reflections from various surfaces of the sign, which may make it difficult to clearly and effectively discern the open and closed states of a particular sign; even Usually the use of light baffles and high-power LEDs or incandescent lamps in the range of 25-100W cannot completely overcome these problems;

(b) Traffic lights are located outdoors and are therefore subject to harsh mechanical and environmental conditions; they must withstand mechanical damage and remain operable even when subjected to vandalism, mechanical shock and impact, extreme temperatures, and exposure to ultraviolet radiation;

(c) The total cost of ownership, and especially the cost of operation, is a very important factor in the use of traffic lights; in New York City alone, there are 11,871 traffic lights, and great efforts have been made to reduce power consumption, including Signal conversion to LED;

(d) There are strict weight restrictions on street lighting to prevent overloading of the signage support structure, therefore, the industrial design and weight distribution of the signage must be carefully managed; and

(e) Requires (in some cases) increased traffic signal size, possibly sacrificing performance in terms of power consumption, weight, and cost.

Accordingly, the present invention seeks to provide a form of information display (which may be in the form of a traffic light or other traffic control device) which overcomes the above-mentioned problems of prior art devices.

A similar problem is encountered when the "traffic control device" is an indicator on a car or other vehicle. Even relatively high-wattage bulbs cannot guarantee adequate visibility. For example, at high speeds, the driver of a car may have to react within a fraction of a second to changes in the brightness of the brake lights of the front car if it is to avoid a collision. The brake lights on most cars have a parabolic reflector to concentrate the light from the bulb. While this parabolic reflector does help concentrate the light from the brake lights into a narrow beam, it also diverts any light incident on the reflector (for example, from the sun or from the headlights of subsequent vehicles) ) gathers through the colored plastic cover and thus creates background reflections that tend to obscure the status of the brake lights. In worst-case scenarios, when the sun is facing the rear of the car, the combination of the specular reflection from the parabolic reflector, the reflection from the glossy paint on the car, and the reflection from the rear windshield significantly reduces the visibility of the brake lights.

In another aspect, the present invention provides a hybrid emissive-reflective display that can improve the visibility of in-vehicle signs under high ambient light conditions, thereby providing an additional safety margin and offering the possibility of reducing power consumption .

Contents of the invention

Accordingly, in one aspect, the invention provides a display device comprising: a reflective display arranged to provide a first image visible through a viewing surface; and a projection device arranged to provide a first image visible in reflection on the viewing surface. Second image of ; reflective display and projection device mounted on a common frame. This display device is hereinafter referred to as the "projection display" of the present invention.

The invention also provides a display device comprising a digital projector and a reflective surface mounted on a common frame, the digital projector comprising a light source, a projection lens and at least one additional optical element adapted to cause a projected image to be formed on the reflective surface An element wherein light passing from the light source through the projection lens is folded more than 180 degrees in a plane containing the principal axis of the projection lens and the plane of symmetry of the at least one additional optical element before being reflected from the reflective surface.

The invention also provides a reflective display arranged to provide a first image visible through a viewing surface; and a projection device comprising a light modulator arranged to provide a second image visible in reflection on the viewing surface; The first image and the second image are overlapping and have approximately the same width and height, the first image has w1 pixels in the width dimension and h1 pixels in the height dimension, where

h1>w1

The second image has w2 pixels in width dimension and h2 pixels in height dimension, where

h2<w2

The invention also provides a display device comprising: a reflective display arranged to provide a first image visible through a viewing surface; and a projection device arranged to provide a second image visible in reflection on the viewing surface; Wherein the frame rate of the reflective display differs by at least 10% from the frame rate of the projection device.

The foregoing display devices may be collectively referred to as a "projection display" of the present invention hereinafter.

The invention also provides a method for providing an image using a reflective display arranged to provide a first image visible through a viewing surface; and a projection device arranged to provide a first image visible in reflection on the viewing surface. the second image of ; the method includes:

(a) dividing the image information into at least two components, a first component comprising at least luminance information and a second component comprising chrominance information; and

(b) Directing the first image using the first component and directing the second image using the second component.

In another aspect, the present invention provides an information display comprising a bistable reflective display having a display surface and at least one light emitter arranged to direct light onto the display surface of the reflective display. In one form of the invention, there are at least two separate reflective displays having display surfaces arranged to display different colors, and independently controllable light indicators arranged to direct light onto the two display surfaces. launcher. This form of the invention may be in the form of a traffic signal having three separate reflective displays with display surfaces arranged to display red, amber and green, respectively, and are three light emitters that direct light onto the three display surfaces. Alternatively, this form of the invention may for example have the form of a crosswalk sign with two separate display surfaces, one forming a red "DON'T WALK" sign and the other forming a white "WALK" sign, and two light emitters arranged to direct light onto the two display surfaces.

It should be understood that in any information display of the present invention where the display surface is to display color rather than simply black or white, the necessary chromaticity may be provided by the surface itself or by light emitters. Thus, in a display designed to simulate a conventional traffic signal, it is possible to use three differently colored electro-optic display areas illuminated, if necessary, by white light emitters (using an inherently colored medium or a monochrome medium behind a color filter) , or three regions of monochromatic electro-optic media illuminated by three differently colored light emitters. In general, however, the latter is preferred because it provides higher contrast. The "lit" or colored state of such a monochrome electro-optic media/color light emitter display requires that the electro-optic media be set to its reflective (white) state and the light emitters be turned on so that the colored light from the emitters reflection. In the "unlit" or dark state of such a display, the electro-optic medium is set to its dark, non-reflective state, and the light emitters are turned off, thus producing a very dark display surface and a gap between the two states of the display. high contrast. Although this type of display does require constant use of light emitters, its power requirements can be made relatively modest; for example, the number of LEDs required as light emitters can be reduced compared to conventional LED traffic lights because each Each LED can illuminate the main area of the display surface, in contrast, the entire display surface of conventional LED traffic lights must be covered with LEDs. The LEDs in such displays of the present invention will typically be arranged in a "halo" around the periphery of a circular display surface, and providing LEDs in such a halo may be more compact than providing a compact array on the display surface of a conventional LED traffic signal. A higher number of LEDs is technically simpler. In addition, because the light from the LEDs is spread relatively evenly across the reflective display surface, the appearance of traffic lights tends to be more attractive than that of conventional LED traffic lights, which are less attractive due to the clearly separated LEDs on their display surfaces. Suffers from pixelation.

In another aspect, the present invention provides an electrophoretic display comprising:

at least one front electrode through which a viewer can view the display;

A layer of electrophoretic medium comprising a fluid and two types of charged particles disposed in the fluid and capable of moving through the fluid when an electric field is applied to the fluid, one of the two types of particles being dark and the other ones are reflective and have a different color than the dark particles;

at least one rear electrode disposed on a side of the layer of electrophoretic medium opposite the front electrode, the rear electrode having a plurality of holes extending therethrough; and

a light source arranged on the side of the back electrode opposite the electrophoretic medium layer and arranged to direct light through the electrophoretic medium layer,

The display has a first optical state in which the dark particles are adjacent to the front electrode such that the observer sees a dark color; a second optical state in which the reflective particles are adjacent to the front electrode such that the observer sees the color of the reflective particles; and a third optical state, Where the dark particles are adjacent to the rear electrode, the reflective particle light source generates light, and the color of the reflective particles can be seen by the observer.

The invention extends to a vehicle carrying the electrophoretic display of the invention.

In another aspect, the present invention provides an electrophoretic display utilizing grid electrodes. The grid electrode can be used as the rear electrode of an electrophoretic display. The grid electrode can be used to concentrate the black pigment into relatively small areas corresponding to the grid lines of the grid electrode. Additionally, reflective backings can be used in conjunction with grid electrodes. Accordingly, the backing can reflect a relatively high degree of light, thereby providing an enhanced white state for the electrophoretic display. The enhanced brightness can be obtained by simply modifying the front plane laminate structure of the electrophoretic display, which can be implemented into electrophoretic displays with thin film transistor (TFT) technology as well as segmented electrophoretic displays.

It should be understood that in the electrophoretic display of the present invention, so-called "reflective particles" should not be fully reflective, because in the third optical state, fully reflective particles will not allow any light to pass through the electrophoretic medium. The reflective particles must be sufficiently reflective to reflect most of the light incident on the front electrode when the display is in its second optical state, but still sufficiently transmissive to allow light to pass through when the display is in its third optical state. Pass through reflective particles. As can be seen from the detailed examples below, there is no difficulty in finding commercial pigments that meet these requirements.

The displays of the present invention may utilize any of the types of bistable electro-optic media previously described. Thus, electro-optic media may comprise roto-dichroic members, electrochromic or electrowetting materials. Alternatively, the electro-optic medium may comprise an electrophoretic material comprising a plurality of charged particles arranged in a fluid and capable of moving through the fluid under the influence of an electric field. Charged particles and fluids can be confined within multiple capsules or microunits. Alternatively, the charged particles and fluid may exist as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. Fluids can be liquids or gases.

Description of drawings

1A-1C of the accompanying drawings are schematic diagrams illustrating artifacts associated with glancing angle projection in a projection display of the present invention.

2A-2C are schematic diagrams showing the arrangement of projected images and reflected images in the projection display of the present invention.

3 is a side view of a projection engine used in the projection display of the present invention.

FIG. 4 is a block diagram illustrating a method of controlling the projection display of the present invention.

Figure 5 is a side view of a portion of the information display of the present invention in the form of a traffic signal with a portion of the housing broken away to show the light source.

FIG. 6 is a front view of the same portion of the information display as shown in FIG. 5 .

7 is a three-quarter side view from the front and to one side of the line-of-sight source assembly of the information display shown in FIGS. 5 and 6. FIG.

Fig. 8 is a schematic cross-sectional view through the electrophoretic display of the invention in the form of a brake light for automobiles.

FIG. 9 is a front view of a rear electrode of the electrophoretic display shown in FIG. 8 .

Figure 10 is a graph of L*a*b* values versus time obtained with the electrophoretic display shown in Figures 8 and 9 in certain experiments described below.

FIG. 11 shows an exploded view of an electrophoretic display with rear grid electrodes according to a non-limiting embodiment of the present application.

12A and 12B are photomicrographs showing accumulation of black pigment near grid lines of a grid electrode according to non-limiting embodiments of the present application.

Detailed ways

As stated above, in one aspect, the present invention provides a projection display in which the means for projecting a color image and the means for providing a reflected image are combined into a single unit such that the two images can be superimposed in registration with each other, Composite images with improved color quality visible under a wider range of ambient lighting conditions can be obtained than could be provided using reflective displays or projectors alone. In low light, the projected image is easy to see, and its contrast is enhanced by the reflected image superimposed on it. In bright light, the projected image fades away, but the reflected image will be well lit and have a good edge. In order to save power, it is desirable to adjust the intensity of the projected image (the intensity of which can be measured by means known in the art, such as photodiodes, etc.) according to the ambient lighting. In very bright light, the projector can turn off completely.

The reflective display used in the projection display of the present invention can be any of the types previously described, including but not limited to electrophoretic, electrowetting, electrochromic, roto-dichroic, and reflective liquid crystal; electrophoretic displays can be, for example, magnetophoretic and/or suppresses the total internal reflection subtype. Other types of reflective displays known in the art, such as electronic liquid powder, micromechanical (interferometry), photonic crystals (structural color), electrofluids, and light valves/reflectors may also be employed.

In a preferred form of the invention, the reflective display comprises an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. Charged particles and fluids can be confined within multiple capsules or microunits. Alternatively, the charged particles and fluid may exist in the form of a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. Fluids can be liquids or gases.

The projection device ("engine") used in the projection display of the present invention can use a variety of technologies including light sources, such as colored light emitting diodes (LEDs) and solid-state colored laser sources, in combination with light modulators. The light modulators are, for example, microdisplays made using technologies including liquid crystal on silicon (LCoS), deformable mirror displays (DMD) or scanning mirrors (a type of microelectromechanical system, MEMS). Combinations of light sources, light modulators and associated optical elements such as beam splitters and projection lenses are well known in the art and can be packaged in such small sizes that they are currently referred to as pico-projectors. In a preferred form of the invention, a pico-projector is embedded into a mobile reflective display device such as an Ereader or E-book to form a hybrid display.

The technical challenge of combining a pico projector with a mobile reflective display is very difficult. As mobile devices, hybrid displays must be compact. Embedded pico projection systems cannot significantly increase the size and weight of an electronic document reader. The projector must not obstruct the view of the screen and the range of viewing angles from which the user can read the display. To provide compactness and unobstructed viewing, angled projections are required. Such projections are used in "short throw" and "ultra short throw" projectors and are well known in the art; see eg US Patent No. 7,239,360. Some artifacts associated with short-range projections are described in more detail below.

FIG. 1A shows projector 10 configured to provide an image onto reflective screen 12 using angled projection, the term angled projection being used to mean that the central chief ray has an angle of incidence greater than zero with respect to the normal to the display surface (and Preferably, in the present invention at least about 60° or so). A large projection angle is desirable because it allows for more compact packaging and increases the angular range of the viewable display where the projector assembly does not obscure the view. As described in more detail below, folded optics can be used so that the projector can be located below the plane of the reflective screen for maximum compactness. These folded optics are omitted from Figure 1A for clarity.

As shown in Figures 1B and 1C, angled projections introduce image artifacts that increase dramatically with projection angle: such artifacts include keystone distortion (see Figure 1B) and anamorphic distortion (see Figure 1C). Not shown in Figures 1A-1C, but still evident are the visible blurring (when the size of the angled screen exceeds the projector's depth of focus), the drop in light intensity with projection distance (thus the brightness of the projected image is non-uniform ), and other well-known optical aberrations such as chromatic aberration and astigmatism.

In the projection display of the present invention, some of these artifacts can be corrected digitally. For example, keystone and anamorphic distortion and drops in light intensity may be corrected by projecting an image that has been pre-distorted in space and/or brightness, as is known in the art. This digital correction comes at the expense of some other properties of the projected image. For example, spatial correction for keystone and/or anamorphic distortion will reduce the overall resolution of the projected image, while light intensity correction will reduce image brightness. As discussed in more detail below, some artifacts, such as blurring, are not amenable to digital correction but must be corrected by proper optics selection.

The screens of most reflective displays, such as electronic book readers (E-readers), are rectangular. For reading books, screens are typically used in a portrait orientation (ie, the longer dimension is oriented toward and away from the user, while the shorter dimension is oriented horizontally). Most commercially available miniature projection engines are also designed to project rectangular images. However, when such an engine projects at an angle, the most compact package size (i.e., the smallest "throw ratio," which is the ratio of the projector to the screen) is achieved when the projector's landscape orientation projects onto the reflective display's portrait orientation. The distance between divided by the diagonal size of the screen), as shown in Figure 2A-2C.

FIG. 2A shows light source 20 modulated by light modulator 22 to form an image projected onto screen 24 . The modulator is in landscape orientation, but its image is projected onto a portrait-oriented screen.

FIG. 2B shows light source 20 modulated by light modulator 22 to form an image projected onto screen 28 . Both the modulator and the screen are in landscape orientation.

FIG. 2C shows light source 20 modulated by light modulator 26 to form an image projected onto screen 24 . The modulator is in portrait orientation and its image is projected onto a landscape oriented screen.

From Figures 2A-2C it will be clear that when the long axis of the modulator is projected onto the short axis of the screen as shown in Figure 2A, the throw ratio is minimized and thus the compactness of the device comprising the screen and projector is maximized. Therefore, in the projection display of the present invention, it is preferred that the projected image and the reflected image are generally registered and have approximately the same width and height, the reflective display having w1 pixels in the width dimension and w1 pixels in the height dimension h1 pixels, where

h1>w1

The light modulator of the projector has w2 pixels in the width dimension and h2 pixels in the height dimension, where

h2<w2

A disadvantage of the setup of FIG. 2A is that the square pixels in the light modulator 22 become anisotropic in the image projected onto the screen 24, resulting in the size of the projected image pixels and the size of the (square) pixels on the reflective display screen 24 mismatch between. For example, if the reflective screen is 600x 800 pixels (SVGA) and each pixel is a square approximately 150µm wide, and the light modulator of the projection engine is 848x 480 pixels (WVGA), the resolution of the projected image cannot exceed that of the reflective display About half the resolution of the upper image (ie, after the above-mentioned distortion correction, the projected pixels are approximately 300 μm in size and not square).

In the projection display of the present invention, if the achromatic (brightness) information of the combined image is carried by only one of the mixed display components (the projected image or the reflected image), or if the spatial frequency content of one of the achromatic image components is reduced such that the If the effects of alignment are no longer visible, the requirement to map the pixels of the projected image 1:1 onto the pixels of the reflective display can be relaxed. The differential sensitivity of the human visual system to position and motion for achromatic (luminance) and color image components makes possible the reduced visibility of mismatches in resolution. The color acuity of the human visual system is significantly lower than its luminance acuity, such that the perception of sharpness, fineness, and readability of text in displayed images is dominated by achromatic image components.

In preferred embodiments of the projection display of the present invention, the achromatic image components are displayed on a reflective display because the display maintains its contrast ratio over a wide range of ambient light levels, and at very high ambient light levels (e.g. sunlight) In this case, the perceived contrast is even improved. In order to correctly provide luminance and chrominance information using a projection display, the input image is split into achromatic (black and white) and chromatic (color only) components. Examples of color image coding systems that perform such separation into one luma component and two chrominance components include, but are not limited to, YCbCr, YIQ, YCC, CIELab, and oRGB. Using the projection display of the present invention, the following methods can be used to display these achromatic and chromatic components.

An achromatic component can be displayed on a reflected image; a color projector projects a colored component onto this image. The viewer's eyes recombine (blend) the displayed achromatic and color image components into a full-color image. Since the color acuity of the human eye is significantly lower than its achromatic acuity, the perception of clarity, fineness, and readability of text will be dominated by the achromatic component. If the color components projected onto the reflected image are of lower resolution than the displayed achromatic components and/or the chromatic and achromatic components are not in registration, this will not interfere with the clarity, detail and The perception of readability. In addition, the human visual sensitivity is lower to motion of the color components, ensuring that the relative positions of the color and achromatic image components change slightly over time (e.g., if the alignment of the projector to the reflected image is not perfectly rigid, caused by vibration small changes), will not significantly interfere with the perception of detail in the combined image.

In addition to color image information, the projector engine can be provided with spatially filtered achromatic (luminance) image information to improve overall image quality without reintroducing registration requirements. For example, the non-color (brightness) channel can be low-pass filtered (blurred) so that the effects of misalignment and motion (vibration) between the projected and reflected images remain invisible, but is not the same as just projecting the color component to the reflected image Compared to the above image, the contrast of the combined image is increased.

These methods can be applied if the reflected image is a color image carrying luminance and chrominance information, whereas the projected image carries chrominance information only or chrominance information and luminance information modified as described above.

Figure 3 shows the optical design of a projection display (generally designated 30) for use in the present invention. Projection display 30 includes projector module 31 (which itself includes a light source and a spatial light modulator as described above), and associated optics, such as beam splitters, required to produce modulated images of the three primary colors (red, green and blue). This image is projected onto the viewing surface 38 of the reflective display using the following optics:

(a) Projection lens or lens combination 32 . The lens plane of projection lens 32 intersects the plane of the light modulator (in projector module 31) and the plane of reflective display 38 (corrected for folding of the light path by mirrors 36 and 37) at a common line (i.e., modulator, projection The lens 32 and the reflective display 38 are arranged to satisfy the Scheimpflug condition);

(b) an aspheric achromat lens combination 33 designed to provide additional focusing of the projected image and minimize chromatic aberration (this combination may alternatively be combined with projection lens 32);

(c) An annular lens 34 which minimizes astigmatism caused by the axicon 37 (described below). The lens 34 can be omitted if the mirror 37 has a more complex curvature than a simple cone;

(d) a rotationally asymmetric element 34 which provides variable focusing power with field position;

(e) folding mirror 36, which may be a flat mirror (preferred) or curved (eg conical); and

(f) Axicon 37, which redirects the light beam to the appropriate location on the viewing surface 38 of the display.

The optical elements shown in FIG. 3 are positioned to project an image from projector 31 onto viewing surface 38 . When not in use, they can be folded down to save space, or the entire assembly including elements 31-37 can be detachable from the reflective display. Alternatively, folding mirror 36 may be arranged to be removable from the light path, or replaced by another optical element, so that projector 31 may project an image onto a distant surface instead of viewing surface 38 .

The optical elements shown in Figure 3 can be replaced by diffractive or holographic elements or by elements using nano-optical phase discontinuity technology.

The location of the projection engine may be on the top, bottom or side of the viewing surface 38 when the reader is viewing in portrait mode. If the projection engine is located at the bottom of the viewing surface 38, other elements of the display, such as the keyboard, can be located above the mirror 37 so that the mirror is not visible to the reader. Although viewing surface 38 is shown as planar in FIG. 3, this is not required, as flexible reflective displays are well known in the art, and the curvature of the display surface can be used to simplify or improve the optical design described above. Additional elements such as light baffles may be incorporated to reduce stray light specularly reflected from any surface of the display.

The projection display of the present invention may also include the elements required to drive the projector device and the reflective display. It is not always necessary to drive both displays simultaneously. Thus, for example, it may be desirable to switch a reflective display completely or partially to its white state (or possibly a gray state) and use an embedded projector to project an image onto this white region. This is desirable, for example, if video rate content is to be viewed. At the current state of the art, the switching rates of some reflective display technologies are not as high as those of projection engines.

When video addressing, the frame rate of the reflected image and the frame rate of the projected image do not have to match. For example, a projection engine may run at 60 frames per second, but a reflective display may run at 15 frames per second, with a subset of frames to enhance the contrast of the video.

Figure 4 is a block diagram of one possible controller architecture for the projection display of the present invention. The information to be displayed is loaded onto the controller by the input/output unit 4 and temporarily stored in the memory 44, which also holds the necessary software and firmware. The user interface 41 allows the viewer to control all necessary functions, such as loading, saving, selecting and deleting of information, as well as starting and progressing through viewing information. The image and video signal processing unit 45 conditions the stored information for display and executes image and video processing algorithms, including but not limited to brightness and color correction, split into components for reflective and projective display, and provides display and projector Image, resolution, dithering, geometric predistortion and uniformity correction. The processed image signal is then transferred to the necessary hardware controller. The electrophoretic display controller 48 controls the pixels of the reflective display 51; the microdisplay controller 47 controls the pixels of the image modulator 50 of the projector. The light engine controller 46 operates the light source 49 such that the light source 49 can be adapted to the projected color image or video and the ambient lighting level, and is turned off when not needed to conserve power from the battery 42 , which is provided by the power controller 43 .

The information display of the present invention will now be described in more detail. The display can be used as an outdoor information display, it is suitable for all lighting conditions, spans a wide temperature range, and can be configured to operate without mains power. The information display may comprise an electrophoretic display for daylight conditions, supplemented by LEDs or similar light emitters for low light or other conditions. A light emitter may also be required to assist in dim daylight conditions, or may be used all the time to provide the desired color. Light emitters can be integrated into the front bezel or into the front lighting cavity to best suit the environment.

It is expected that the information display of the present invention requires very low power to operate, and that the display can incorporate solar charging elements for self-sustaining operation without the need for an external power source. Since certain types of electro-optic materials do not function well at low temperatures, it may be necessary to incorporate a layer of front transparent material or rear thermal insulation in the electro-optic portion of the display. Alternatively, the light emitter may be able to generate enough heat to keep the electro-optic material within its operating range. Other forms of electro-optic material heating can be activated as needed to ensure proper switching.

The information displays of the present invention are ideal for replacing existing street signage such as traffic lights and crosswalk signs because they are lighter in weight, lower in power, more visible under sun glare, better in vandal resistance, capable of Advantages of easy deployment in emergency environments, similar bill of materials to prior art signage.

A simple traffic light system can be constructed from three separate electro-optic segmented units, each behind a complementary color filter. Such a system may include multiple light emitters per unit directed towards the electro-optic display in a pattern to maximize color visibility in low light conditions.

Simple crosswalk signs can have a similar design to traffic lights, except instead of a single segmented electro-optic unit, the segmented unit can include multiple segments of icons or messages.

These information displays can be made compatible with the processor and detection system to synchronize the appropriate displayed information with the needs of the situation. Control system options can be provided to manage information using low power wireless, and can incorporate solar charging elements for self-sustaining operation without mains power.

Compared to prior art information displays, the information displays of the present invention provide the following advantages:

reduce system weight;

Improve electricity efficiency;

Improved visibility under sun glare;

Enhanced vandalism;

Easier to deploy in emergency situations;

Multiple improvements with a competitive BOM; and

Ability to scale with minimal design compromises.

Figure 5 of the accompanying drawings is a side view of one unit (generally designated 100) of the three-unit information display of the present invention in the form of a traffic signal; a portion of the figure is exploded to show internal details of the unit. The unit includes a substantially semi-cylindrical visor 102 (best shown in Figure 6) and a lens 104, the visor 102 being in a form similar to that found in prior art traffic lights. A circular monochrome electrophoretic display 106 is arranged at the rear surface of the unit 100 and is provided with a single electrode (not shown) on each of its major surfaces to enable the display to function as a single pixel display. A plurality of light emitting diodes (LEDs) 108 are arranged at uniform intervals around the inner surface of ring 110 (which surrounds display 106) such that light from LEDs 108 is directed onto the surface of display 106. Circle 110 and LED 108 are shown on a larger scale in FIG. 7 . LED 108 has a single color, red, amber or green depending on the particular unit of the traffic signal.

In normal operation, the LEDs are driven continuously and the phase of the traffic light is controlled by switching the display 106 between its bright and dark states.

The electrophoretic display of the present invention will now be described in more detail. As already mentioned, the third aspect of the invention provides an electrophoretic display comprising: at least one front electrode through which a viewer can view the display; an electrophoretic medium layer comprising a fluid and two electrodes disposed in the fluid. Two types of charged particles, one of the two types of particles is dark, and the other is reflective and its color is different from the color of the dark particles; at least one rear electrode, which is arranged between the electrophoretic medium layer and the on the side opposite the front electrode, the rear electrode having a plurality of holes extending therethrough; and a light source disposed on the side of the rear electrode opposite the electrophoretic medium layer and configured to direct light through the electrophoretic medium layer. The display has a first optical state in which the dark particles are adjacent to the front electrode such that the observer sees a dark color; a second optical state in which the reflective particles are adjacent to the front electrode such that the observer sees the color of the reflective particles; and a third optical state, Where the dark particles are adjacent to the rear electrode, the reflective particle light source generates light, and the color of the reflective particles can be seen by the observer.

This aspect of the invention will be described below primarily in terms of its application as a brake light on a vehicle. However, the electrophoretic display of the present invention is not limited to this application and may be used as any form of vehicle or traffic signage, or in other applications such as warning lights on control panels. Basically, this electrophoretic display is designed to have the normal dark and color states of a conventional two-particle electrophoretic display, and an additional emissive state (especially useful in low-light conditions) in which light from a light source passes through Electrophoretic media and display the color of colored particles.

An electrophoretic display (generally designated 200) of the present invention is shown in Figures 8 and 9 of the accompanying drawings. The display 200 is in the form of a brake light for a vehicle and includes a moisture-resistant film 202 (which is used to protect the remaining components of the display 200 from environmental moisture, including spray when the vehicle is driven in wet conditions), substantially Top transparent front electrode 204, adhesive layer 206 and electrophoretic medium layer (generally designated 208). Electrophoretic medium layer 208 is an encapsulated electrophoretic medium comprising a number of capsules having capsule walls 210 surrounding a dielectric fluid 212 in which are dispersed red particles 214 and black particles 216, red and black The particles are charged with opposite polarity. Behind layer 208 (i.e., to the left as shown in FIG. 8 ) is rear grid electrode 218; as best shown in FIG. Such that the hexagonal hole 222 occupies most of the area of the electrode 218 . Finally, on the side of the electrode 218 opposite the medium 208 is arranged a light source in the form of an incandescent bulb 224 equipped with a parabolic reflector 226 . Although not shown in FIG. 8, an electrophoretic display comprising components 202-218 may be secured to reflector 226 by an optically clear adhesive layer; bulb 224 and reflector 226 may form part of a prior art vehicle brake light .

Display 200 is provided with a voltage source (not shown) for establishing a potential difference between electrodes 204 and 218 . When it is not desired to display brake lights, the potential difference between electrodes 204 and 218 is set to attract black particles 216 adjacent to electrode 204 and red particles 214 adjacent to electrode 218 such that the display assumes a first optical state in which the surface of the brake lights displays a dark color . Note that in this state, it does not matter whether the bulb 224 is lit or not, since no light is emitted from the display 200; however, to conserve power and increase bulb life, the bulb 224 will normally be turned off.

When it is time to turn on the brake lights, the potential difference between electrodes 204 and 218 is reversed so that red particles 214 are adjacent to electrode 204 and black particles 216 are adjacent to electrode 218 . The display thus assumes the second optical state, wherein the red particles 214 reflect light incident on the display, and the brake lights appear red and "on".

Heretofore, descriptions of the operation of display 200 have assumed high ambient lighting conditions. In low light conditions, to turn on the brake lights, the potential difference between the electrodes 204 and 218 is set such that the red particles 214 are adjacent to the electrode 204 and the black particles 216 are adjacent to the electrode 218, and the bulb 224 is lit so that the display exhibits a third optical state, where light from bulb 224 is formed into a narrow beam by parabolic reflector 226, and passes through red particles 214 adjacent electrode 204, thereby causing red light to emanate from the display and the brake light display to illuminate. As a result, display 200 can achieve significantly improved contrast in both low-light and bright-light conditions.

A suitable drive scheme involving voltage or pulse width modulation may be used in the display 200 to produce a defined state of visibility. Such a drive scheme could be synchronized with a clock or a light sensor or temperature sensor to produce the desired level of visibility at any time of day.

In order to provide an experimental test of the electrophoretic display of the present invention, red and black pigment dispersions were prepared comprising Solsperse 17k as charging agent. The red pigment Paliotan Red L 3745 was treated with silane Z6030 and coated with poly(lauryl methacrylate) essentially as described in Example 28 of US Patent No. 8,822,782. An electrophoretic medium containing 50 wt% pigment (10:1 red/black ratio) and 25 mg/gm Solsperse 17k in Isopar E was made and tested in a liquid test cell. As shown in Figure 10, the media achieved a red state of 45a* and a dark state of 10L* (0.01% reflectance).

After replacing the backplate of the test cell with a transparent grid electrode, the black pigment was observed to close the shutter in response to the applied electric field. A movie of the transmission through the test unit was captured on the camera, and the variable transmission through the unit can be clearly seen.

Of course, the electrophoretic medium of the present invention is not limited to the use of red particles. If one of the particles is highly absorbent, the other can be reflective (white), colored, retroreflective or transparent. One or more dyes may also be included in the fluid to obtain a desired color state in the display.

As previously mentioned with respect to FIG. 9, some embodiments of the present invention may include electro-optic displays having grid electrodes. In one embodiment, the electro-optic display may be an electrophoretic display comprising two or more pigments, eg a white pigment and a black pigment respectively comprising electrophoretic particles. The grid electrode can be configured as the rear electrode of the display and can be used in combination with a white or reflective background. An example of a reflective background is a mirror. Conventionally, electrophoretic displays with white and black pigments suffer from a loss of transmitted light in the white state, where the black pigment is located behind the white pigment. According to aspects of the present application, a highly reflective surface can be placed behind an electro-optic layer (eg, an electrophoretic medium), and appropriately configured electrodes manipulated to draw the black pigment into narrow lines, thereby exposing most of the reflective surface. The exposed reflective surface directs transmitted light towards and back through the Lambertian white pigment layer, thereby improving the white state. In at least some embodiments, the electrodes are configured as a grid, although not all embodiments are limited in this manner.

Figure 11 shows an embodiment in which the electrophoretic display includes a rear grid electrode. The display 1000 includes a front electrode 1020 , a back electrode 1040 and a backing layer 1060 . The electro-optic layer 1080 is disposed between the front electrode and the back electrode.

The front electrode 1020 may be an indium tin oxide (ITO) layer, and optionally may be on a transparent substrate, such as a polyethylene terephthalate (PET) substrate (not shown separately).

Electro-optic layer 1080 may be an electrophoretic layer comprising a continuous (binder) phase and a discontinuous phase. For ease of illustration, the continuous phase is omitted. The discontinuous phase is shown comprising a plurality of capsules 1100, but may also be encapsulated in polymer dispersed droplets or microunits. The capsules or droplets preferably have an aspect ratio, ie aspect ratio, of about 1:3 to 3:1, more preferably about 1:2 to 2:1. One or more capsules 1100, and in some cases, each capsule 1100 may include black and white pigments formed from suitable electrophoretic particles that may be controlled by front and back electrodes. Five balloons 1100 are shown, but any suitable number may be used.

The rear electrode 1040 may be a wire grid electrode as shown and may be formed from any suitable material, eg, an electroformed mesh of conductive material such as Al, CrMo, NiB, Ag, and CNT, among others. The spacing of the grid and the width of the wires can be adjusted to maximize the open area while maintaining sufficient electric field uniformity for a smooth appearance on the front surface. In some embodiments, the pitch of the gridlines is selected to approximately correspond to the size of the balloon 1100 . To ensure that sufficient light is transmitted through the wire grid electrode to the reflective backing layer, the wire grid electrode preferably has a light transmission of at least 85%. Furthermore, if the electro-optic layer comprises an encapsulating medium, preferably, the area of each open space between the plurality of gridlines forming the back electrode (e.g., one of the squares constituting the grid in Figures 12A and 12B area) is approximately the same as the cross-sectional area of the capsule, microunit or droplet containing electrophoretic particles, preferably, the area of the open space between the grid lines is equal to the cross-sectional area of the capsule, microunit or droplet The ratio between them is about 1:5 to 5:1, more preferably about 1:4 to 4:1.

The backing layer 1060 may be reflective, such as a mirror, or may be a white layer. Although the display 1000 is shown "exploded" for clarity, in actual practice the mirror backplane should be placed as close as possible to the back of the rear electrode 1040.

When the electro-optic layer 1080 is switched to a white state, the front surface of the capsule 1100 will be filled with a uniform layer of white pigment, making the electro-optic layer appear smooth white. As further described below in conjunction with FIGS. 12A and 12B , the black pigment will collect on the gridlines of the back electrode 1040 , exposing a large portion of the backing layer 1060 . Light transmitted through the electro-optic layer in this state will reflect back from exposed portions of the backing layer 1060 and increase the brightness of the white state.

Figures 12A and 12B represent images of an electrophoretic display with grid electrodes and were made using a microscope. The imaged display contains only black pigment. These figures show how the black pigment 2040 inside the capsule 2020 is pulled to the gridline (or wire) 2000 of the rear grid electrode. Therefore, these figures show that the charged black electrophoretic particles aggregate on the microwires of the grid electrode instead of being uniformly distributed in the capsules, thus exposing most of the open area between the microwires. This operation effectively enables shutter mode operation of the display without the need for a conventional shutter mode waveform. As described herein, this behavior serves to attract the black pigment onto a small portion of the capsule's backing surface, exposing the highly reflective backing surface to regain transmitted light. In another embodiment, a single black pigment with a grid takes advantage of the presence of a white backing to create a black and white display. When the black pigment moves to the front of the display (ie disperses), the display is in a dark state. When the black pigment is moved to the grid, the display is in a white state.

It will be apparent to those skilled in the art that many changes and modifications can be made in the specific embodiments of the invention described above without departing from the scope of the invention. Accordingly, the entire foregoing description is to be interpreted in an illustrative rather than a restrictive sense.

Claims (10)

1. An electro-optic display comprising: Light-transmitting front electrode; Electro-optic layer; rear electrode; and flat white or reflective backing, wherein the rear electrode is in the shape of a grid having a plurality of grid lines and is arranged between the planar white or reflective backing and the electro-optic layer, and wherein the electro-optic layer comprises a dispersion comprising a plurality of charged particles in a fluid capable of moving through the fluid upon application of an electric field, wherein the charged particles and the fluid are encapsulated In the plurality of capsules, and wherein, the grid has a plurality of open spaces, and the ratio between the area of the open spaces and the cross-sectional area of the capsule is 1:5 to 5:1. 2. The electro-optic display according to claim 1, wherein the capsule has an aspect ratio of 1:3 to 3:1. 3. An electro-optic display comprising: Light-transmitting front electrode; Electro-optic layer; rear electrode; and flat white or reflective backing, wherein the rear electrode is in the shape of a grid having a plurality of grid lines and is arranged between the planar white or reflective backing and the electro-optic layer, and wherein the electro-optic layer comprises a dispersion comprising a plurality of charged particles in a fluid capable of moving through the fluid upon application of an electric field, wherein the charged particles and the fluid are encapsulated In the plurality of microunits, and wherein, the grid has a plurality of open spaces, and the ratio between the area of the open spaces and the cross-sectional area of the microunits is 1:5 to 5:1. 4. An electro-optic display comprising: Light-transmitting front electrode; Electro-optic layer; rear electrode; and flat white or reflective backing, wherein the rear electrode is in the shape of a grid having a plurality of grid lines and is arranged between the planar white or reflective backing and the electro-optic layer, and wherein the electro-optic layer comprises a dispersion comprising a plurality of charged particles in a fluid capable of moving through the fluid upon application of an electric field, wherein the charged particles and the fluid are encapsulated Within a plurality of discrete droplets, the discrete droplets are surrounded by a continuous phase comprising a polymer material, and wherein the grid has a plurality of open spaces, and the open spaces have an area equal to the lateral width of the droplets. The ratio between the cross-sectional areas is 1:5 to 5:1. 5. The electro-optic display of claim 4, wherein the plurality of droplets have an aspect ratio of 1:3 to 3:1. 6. The electro-optic display of claim 1, wherein the rear electrode has a light transmittance of at least 85%. 7. An electro-optic display according to claim 1, wherein the rear electrode is arranged adjacent to the white or reflective backing. 8. The electro-optic display of claim 1, wherein the plurality of charged particles comprise black particles. 9. The electro-optic display of claim 8, wherein the plurality of charged particles further comprises white particles. 10. The electro-optic display of claim 1, wherein the grid lines comprise micro wires.

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