EP-4736154-A1 - ELECTROPHORETIC DEVICE WITH AMBIENT LIGHT SENSOR AND ADAPTIVE WHITENESS RESTORING AND COLOR BALANCING FRONTLIGHT

EP4736154A1EP 4736154 A1EP4736154 A1EP 4736154A1EP-4736154-A1

Abstract

An electrophoretic display apparatus includes an ambient light sensor and a frontlight system for adaptively restoring whiteness and balancing color on the display.

Inventors

HERTEL, DIRK

Assignees

E Ink Corporation

Dates

Publication Date: 20260506
Application Date: 20240603

Claims (20)

CLAIMS 1. An electrophoretic display apparatus, comprising: an electrophoretic device having a viewing surface; a drive system coupled to the electrophoretic device for driving the electrophoretic device among a plurality of optical states; one or more ambient light sensors at the viewing surface of the electrophoretic device for detecting a level of ambient illuminance incident on the viewing surface; a frontlight unit disposed above the viewing surface of the electrophoretic device for illuminating the viewing surface; and a frontlight control system coupled to the one or more ambient light sensors and the frontlight unit, and configured to: (a) receive, from the one or more ambient light sensors, one or more signals indicating a detected level of ambient illuminance incident on the viewing surface of the electrophoretic device; (b) compare the detected level of ambient illuminance to a predetermined threshold level; (c) when the detected level of ambient illuminance is less than or equal to the predetermined threshold level, control frontlight illuminance incident on the viewing surface from the frontlight unit to adaptively maintain a constant viewing surface luminance comprising light reflected by the viewing surface from the frontlight illuminance and the ambient illuminance, irrespective of the detected level of the ambient illuminance; (d) when the detected level of ambient illuminance is greater than the predetermined threshold level, control the frontlight illuminance incident on the viewing surface from the frontlight unit to maintain the viewing surface luminance at generally the same level as a white diffuse reflector under the same detected level of ambient illuminance, wherein the white diffuse reflector comprises a Lambertian reflective surface having a value of L*=100; and (e) repeat steps (a) through (d) a plurality of times.
2. The electrophoretic display apparatus of Claim 1, wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (c) according to: where EFL is the illuminance incident on the viewing surface from the frontlight unit, EAMB is the detected level of ambient illuminance incident on the viewing surface, E AMB , MIN is the predetermined threshold level, and RW is the diffuse reflectance factor of the viewing surface in a white state.
3. The electrophoretic display apparatus of Claim 1, wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (d) according to: where E FL is the illuminance incident on the viewing surface from the frontlight unit, E AMB is the detected level of ambient illuminance incident on the viewing surface, E AMB, MIN is the predetermined threshold level, and RW is the diffuse reflectance factor of the viewing surface in a white state.
4. The electrophoretic display apparatus of Claim 1, wherein the threshold level is between 3 lx and 500 lx.
5. The electrophoretic display apparatus of Claim 1, wherein the threshold level is about 94 lx.
6. The electrophoretic display apparatus of Claim 1, wherein: the one or more ambient light sensors include at least one trichromatic sensor for detecting ambient trichromatic irradiance in red, green, and blue color channels incident on the viewing surface; the frontlight unit includes at least one trichromatic light source comprising independently controllable red, green, and blue color channels; and the frontlight control system is further configured to control the chrominance of illumination from the at least one trichromatic light source to compensate for white states of the electrophoretic device that are off-white.
7. The electrophoretic display apparatus of Claim 1, wherein: the one or more ambient light sensors include at least one trichromatic sensor for detecting ambient trichromatic irradiance in red, green, and blue color channels incident on the viewing surface; the frontlight unit includes at least one trichromatic light source comprising independently controllable red, green, and blue color channels; and the frontlight control system is further configured to (a) receive, from the one or more ambient light sensors, one or more signals indicating a detected level of ambient trichromatic irradiance in the red, green, and blue color channels incident on the viewing surface; (b) compare the detected level of ambient trichromatic irradiance to a predetermined threshold level in each of the red, green, and blue color channels; (c) when the detected level of ambient trichromatic irradiance is less than or equal to the predetermined threshold level in any of the red, green, and blue color channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to adaptively maintain a constant level of trichromatic irradiance comprising the trichromatic irradiance reflected by the viewing surface from the frontlight illuminance and the ambient trichromatic irradiance, irrespective of the detected level of the ambient trichromatic irradiance; (d) when the detected level of ambient trichromatic irradiance is greater than the predetermined threshold level in any of the red, green, and blue color channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to maintain the viewing surface trichromatic irradiance at generally the same level as an ideal Lambertian reflector under the same detected level of ambient trichromatic irradiance; and (e) repeat steps (a) through (d) a plurality of times.
8. The electrophoretic display apparatus of Claim 7, wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (c) according to: where E(R) FL , E(G) FL , and E(B) FL are levels of trichromatic irradiance provided by the frontlight unit in the red, green, and blue channels, respectively; E(R)AMB, E(G)AMB, and E(B)AMB are the detected levels of ambient trichromatic irradiance incident on the viewing surface in the red, green, and blue channels, respectively; E(R) AMB , MIN , E(G) AMB , MIN , and E(B)AMB, MIN are the predetermined threshold levels in the red, green, and blue channels, respectively; and R(R)W, R(G)W, and R(B)W is the diffuse reflectance factor of the viewing surface in a white state in the red, green, and blue channels, respectively.
9. The electrophoretic display apparatus of Claim 7, wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (d) according to: where E(R)FL, E(G)FL, and E(B)FL are levels of trichromatic irradiance provided by the frontlight unit in the red, green, and blue channels, respectively; E(R)AMB, E(G)AMB, and E(B)AMB are the detected levels of ambient trichromatic irradiance incident on the viewing surface in the red, green, and blue channels, respectively; E(R)AMB, MIN, E(G)AMB, MIN, and E(B) AMB , MIN are the predetermined threshold levels in the red, green, and blue channels, respectively; and R(R)W, R(G)W, and R(B)W is the diffuse reflectance factor of the viewing surface in a white state in the red, green, and blue channels, respectively.
10. The electrophoretic display apparatus of Claim 6, wherein E(R) AMB , MIN , E(G) AMB , MIN , and E(B) AMB , MIN are determined from from E(G) AMB,min .
11. The electrophoretic display apparatus of Claim 1, wherein: the one or more ambient light sensors include at least one multispectral sensor with more than three spectral channels; and the frontlight unit includes at least one multispectral frontlight with more than three independently controlled spectral channels for changing the chrominance of the frontlight illumination.
12. The electrophoretic display apparatus of Claim 11, wherein the frontlight control system is further configured to (a) receive, from the one or more ambient light sensors, one or more signals indicating a detected level of ambient spectral irradiance in the spectral channels incident on the viewing surface; (b) compare the detected level of ambient spectral irradiance to a predetermined threshold level in each of the spectral channels; (c) when the detected level of ambient spectral irradiance is less than or equal to the predetermined threshold level in any of the spectral channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to adaptively maintain a constant level of spectral irradiance comprising the spectral irradiance reflected by the viewing surface from the frontlight illuminance and the ambient spectral irradiance, irrespective of the detected level of the ambient spectral irradiance; (d) when the detected level of ambient spectral irradiance is greater than the predetermined threshold level in any of the spectral channels, control the frontlight illuminance incident on the viewing surface from the frontlight unit in that channel to maintain the viewing surface spectral irradiance at generally the same level as an ideal Lambertian reflector under the same detected level of ambient spectral irradiance; and (e) repeat steps (a) through (d) a plurality of times.
13. The electrophoretic display apparatus of Claim 12, wherein the frontlight illuminance incident on the viewing surface from the frontlight unit is controlled in step (c) according to: where EFL^^^ is the illuminance incident on the viewing surface from the frontlight unit in the spectral channels; E AMB ^^^^are the detected levels of ambient spectral irradiance incident on the viewing surface in the spectral channels; and RW^^^^is the diffuse reflectance factor of the viewing surface in a white state in the spectral channels.
14. The electrophoretic display apparatus of Claim 13, wherein E AMB,min is determined from EAMB,min^^^^XVLQJ^WKH^the photopic luminous efficiency function V^^^^
15. The electrophoretic display apparatus of Claim 13, wherein E AMB,min ^^^^is determined at the ambient illuminance threshold level EAMB,min of about 94lx.
16. The electrophoretic display apparatus of Claim 13, wherein E AMB,min ^^^^is determined at the ambient illuminance threshold level E AMB,min between 3 lx and 500 lx.
17. The electrophoretic display apparatus of Claim 1, wherein the electrophoretic device comprises: a light-transmissive electrode at a viewing surface; a back electrode; and an electrophoretic medium disposed between the light-transmissive electrode and the back electrode comprising: a non-polar fluid; and a multi-pigment particle system dispersed in the non-polar fluid.
18. The electrophoretic display apparatus of Claim 1, wherein the frontlight unit comprises a waveguide, a light source for injecting light into the waveguide, and a frustrator for distributing the light from the waveguide on the viewing surface.
19. A method, comprising: (a) receiving, from one or more ambient light sensors in an electrophoretic display, one or more signals indicating a detected level of ambient illuminance incident on a viewing surface of the electrophoretic display; (b) comparing the detected level of ambient illuminance to a predetermined threshold level; (c) when the detected level of ambient illuminance is less than or equal to the predetermined threshold level, controlling the frontlight illuminance incident on the viewing surface from the frontlight unit to adaptively maintain a constant viewing surface luminance comprising light reflected by the viewing surface from the frontlight illuminance and the ambient illuminance, irrespective of the detected level of the ambient illuminance; (d) when the detected level of ambient illuminance is greater than the predetermined threshold level, controlling the frontlight illuminance incident on the viewing surface from the frontlight unit to maintain the viewing surface luminance at generally the same level as a white diffuse reflector under the same detected level of ambient illuminance wherein the white diffuse reflector comprises a Lambertian reflective surface having a value of L*=100; and (e) repeating steps (a) through (d) a plurality of times.
20. A control system for controlling operation of a frontlight unit of an electrophoretic display, the control system comprising one or more controllers configured to: (a) receive, from one or more ambient light sensors in an electrophoretic display, one or more signals indicating a detected level of ambient illuminance incident on a viewing surface of the electrophoretic display; (b) compare the detected level of ambient illuminance to a predetermined threshold level; (c) when the detected level of ambient illuminance is less than or equal to the predetermined threshold level, control the frontlight illuminance incident on the viewing surface from the frontlight unit to adaptively maintain a constant viewing surface luminance comprising light reflected by the viewing surface from the frontlight illuminance and the ambient illuminance, irrespective of the detected level of the ambient illuminance; (d) when the detected level of ambient illuminance is greater than the predetermined threshold level, control the frontlight illuminance incident on the viewing surface from the frontlight unit to maintain the viewing surface luminance at generally the same level as a white diffuse reflector under the same detected level of ambient illuminance, wherein the white diffuse reflector comprises a Lambertian reflective surface having a value of L*=100; and (e) repeat steps (a) through (d) a plurality of times.

Description

ELECTROPHORETIC DEVICE WITH AMBIENT LIGHT SENSOR AND ADAPTIVE WHITENESS RESTORING AND COLOR BALANCING FRONTLIGHT CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from U.S. Provisional Patent Application No. 63,523,487 filed on June 27, 2023 entitled ELECTROPHORETIC DEVICE WITH AMBIENT LIGHT SENSOR AND ADAPTIVE WHITENESS RESTORING AND COLOR BALANCING FRONTLIGHT, which is hereby incorporated by reference herein in its entirety. BACKGROUND [0002] An electrophoretic display (EPD) changes color by modifying the position of a charged colored particle with respect to a light-transmissive viewing surface. Such EPDs are typically referred to as “electronic paper” or “ePaper” because the resulting display has high contrast and is sunlight-readable, much like ink on paper. Electrophoretic displays have enjoyed widespread adoption in eReaders, such as the AMAZON KINDLE® because the EPDs provide a book-like reading experience, use little power, and allow a user to carry a library of hundreds of books in a lightweight handheld device. [0003] For many years, EPDs included only two types of charged color particles: black and white. (To be sure, “color” as used herein includes black and white.) The white particles are often of the light scattering type, and comprise, e.g., titanium dioxide, while the black particle are absorptive across the visible spectrum, and may comprise carbon black, or an absorptive metal oxide, such as copper chromite. In the simplest sense, a black and white EPD only requires a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels) – either segmented electrodes or an active matrix of pixel electrodes controlled by transistors – a pattern can be made to appear electronically at the viewing surface. The pattern can be, e.g., the text of a book. [0004] More recently, a variety of color option have become commercially available for EPDs, including three-color displays (black, white, red; black white, yellow), four color displays (black, white, red, yellow), and color filter displays that rely on the black/white particles described above. EPDs with three or four reflective particles operate similar to the conventional black and white displays because the desired color particle is driven to the viewing surface. The driving schemes are far more complicated than only black and white, but in the end, the optical function of the particles is the same, reflecting incoming light back to the viewer in the correct color. [0005] Advanced Color electronic Paper (ACeP™) also included four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thereby allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and ink-jet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the instance of ACeP, the relative positions of the cyan, yellow, magenta and white particles with respect to the viewing surface will determine the color at each pixel. While this type of EPD allows for thousands of colors at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometer-sized) pigments within a working space of about 10 to 20 micrometers in thickness. Obviously, variations in the position of the particles will result in incorrect colors being displayed at a given pixel. Accordingly, exquisite voltage control is required for such a system. More details of this system are available in the following U.S. patents, all of which are incorporated by reference in their entireties: U.S. Patent Nos.9,361,836; 9,921,451; 10,276,109; 10,353,266; 10,467,984; and 10,593,272. [0006] The term gray state is used herein in its conventional meaning in the imaging art to refer to a state intermediate two extreme optical states of a pixel, and does not necessarily imply a black-white transition between these two extreme states. For example, several of the E Ink patents and published applications referred to below describe EPDs in which the extreme states are white and deep blue, so that an intermediate gray state would actually be pale blue. Indeed, as already mentioned, the change in 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 as normally including extreme optical states that are not strictly black and white, e.g., the aforementioned white and dark blue states. [0007] T