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JP-7856732-B2 - Continuous waveform driving in multicolor electrophoresis displays

JP7856732B2JP 7856732 B2JP7856732 B2JP 7856732B2JP-7856732-B2

Inventors

  • アミット デリワラ
  • スニル クリシュナ サイニス

Assignees

  • イー インク コーポレイション

Dates

Publication Date
20260511
Application Date
20241204
Priority Date
20210209

Claims (14)

  1. A method for driving an electrophoretic medium comprising at least four types of particles, wherein each particle has different optical properties from one another, and each type of particle has different combinations of charge polarity and charge magnitude from one another. The method includes providing a continuous drive waveform for at least 500 ms, The continuous drive waveform has at least 16 distinct voltage levels during the 500 ms period, the continuous drive waveform has a measurable rate of change in V/ms, and the time-dependent change of the rate of change is from -1 V/ ms² to 1 V/ ms² . A method for driving the electrophoretic medium from one optical state to a desired optical state, wherein the continuous drive waveform is determined by minimizing a cost function based on a differentiable surrogate model of the electrophoretic medium.
  2. The method according to claim 1, wherein the continuous drive waveform includes at least 32 unique voltage levels during the 500 ms.
  3. The method according to claim 1, wherein the at least four types of particles include two particles of a first polarity and two particles of a second polarity.
  4. The method according to claim 1, wherein the at least four types of particles include three particles of a first polarity and one particle of a second polarity.
  5. The method according to claim 1, wherein the optical property is a color, and the color is selected from the group consisting of white, red, magenta, orange, yellow, green, cyan, blue, purple, and black.
  6. The method according to claim 1, wherein at least two types of particles comprise a surface polymer, and each of the two types of particles has a different type of surface polymer.
  7. A method for driving an electrophoretic medium comprising at least four types of particles, wherein each particle has different optical properties from one another, and each type of particle has different combinations of charge polarity and charge magnitude from one another. The method includes providing a continuous drive waveform for at least 500 ms, The continuous drive waveform as a function of time is, throughout the entire continuous drive waveform, The method is in which V(t) is a waveform voltage as a function of time, x is a value representing time, the continuous drive waveform includes at least three voltage levels, and the continuous drive waveform for driving the electrophoretic medium from one optical state to a desired optical state is determined while minimizing a cost function based on a differentiable surrogate model of the electrophoretic medium.
  8. The method according to claim 7, wherein the continuous drive waveform lasts for at least one second.
  9. A display system, wherein the display system is A first light-transmitting electrode and An electrophoretic medium comprising at least four types of particles, wherein each particle has different optical properties, and each type of particle has different combinations of charge polarity and charge magnitude, A second electrode, wherein the electrophoretic medium is positioned between the first light-transmitting electrode and the second electrode, Controller and A power source operably connected to the first light-transmitting electrode and the second electrode, wherein the power source is configured to provide at least 16 distinct voltage levels, The controller provides at least three of the unique voltage levels between the first light-transmitting electrode and the second electrode when the electrophoretic medium is changed from a first display state to a second display state. A display system in which the controller is configured to determine a continuous drive waveform for driving the electrophoretic medium from one optical state to a desired optical state, while minimizing a cost function based on a differentiable surrogate model of the electrophoretic medium.
  10. The display system according to claim 9, wherein the power source is configured to provide at least 32 distinct voltage levels.
  11. The display system according to claim 9, wherein the power source provides at least two voltage levels that differ by a voltage greater than 20 volts.
  12. The display system according to claim 9, wherein the at least four types of particles include two particles of a first polarity and two particles of a second polarity.
  13. The display system according to claim 9, wherein the at least four types of particles include three particles of a first polarity and one particle of a second polarity.
  14. The display system according to claim 9, wherein the optical property is color, and the color is selected from the group consisting of white, red, magenta, orange, yellow, green, cyan, blue, purple, and black.

Description

(Related applications) This application claims priority to U.S. Provisional Patent Application No. 63/147,465, filed on 9 February 2021. All patents and published documents disclosed herein are incorporated together by reference. Electrophoretic displays (EPDs) change color by modifying the position of charged colored particles on a light-transmitting viewing surface. Such electrophoretic displays are typically referred to as "electronic paper" or "e-paper" because the resulting display has high contrast, much like ink on paper, and is readable in sunlight. Electrophoretic displays are widely used in e-book readers such as Amazon Kindle® because they offer a book-like reading experience, consume less power, and allow users to carry libraries of hundreds of books in a lightweight, handheld device. For many years, electrophoretic displays contained only two types of charged colored particles: black and white (to be clear, "color" as used herein includes both black and white). White particles are often light-scattering, such as titanium dioxide, while black particles are absorbent across the visible spectrum and may consist of carbon black or other absorbent metal oxides such as copper chromite. In its simplest sense, a monochrome electrophoretic display requires only a light-transmitting electrode on the viewing surface, a back electrode, and an electrophoretic medium containing conversely charged white and black particles. When a voltage of one polarity is applied, white particles move to the viewing surface; when a voltage of the opposite polarity is applied, black particles move to the viewing surface. If the back electrode contains controllable regions (pixels) (segmented electrodes controlled by transistors, or active matrices of pixel electrodes), a pattern can be fabricated to appear electronically on the viewing surface. This pattern could be, for example, the text of a book. In recent years, a variety of color options, including three-color displays (black, white, red; black, white, yellow) and four-color displays (black, white, red, yellow), are becoming commercially available for electrophoretic displays. Similar to the operation of a monochrome electrophoretic display, an electrophoretic display with three or four reflective pigments operates similarly to a simple monochrome display, as the desired color particles are driven relative to the viewing surface. While the driving scheme is far more complex than that of black and white alone, the optical function of the particles remains the same. Furthermore, it is noteworthy that such displays can show only a single color at a time (i.e., only one set of colors of particles driven relative to the viewing surface). Advanced color electronic paper (ACEP ™ ) also contains four particles, but the cyan, yellow, and magenta particles are not reflective but rather subtractive, thereby enabling thousands of colors to be produced in each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and inkjet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the case of ACeP, the relative positions of the cyan, yellow, magenta, and white particles to the viewing surface will determine the color in each pixel. While this type of electrophoretic display enables thousands of colors in each pixel, it is crucial to carefully control the position of each pigment (50-500 nanometers in size) within a working space of approximately 10-20 microns in thickness. Obviously, variations in the position of the pigments will result in the display of the wrong color in a given pixel. Therefore, precise voltage control is required for such systems. Further details of the system are available in the following U.S. Patents, namely U.S. Patent No. 9,361,836 (Patent Document 1), No. 9,921,451, No. 10,276,109, No. 10,353,266, No. 10,467,984, and No. 10,593,272 (all of which are incorporated as a whole by reference). For the most part, electrophoretic media, such as those described above, are designed to be driven using low-voltage square waves, such as those produced by driver circuits from thin-film transistor backplanes. Such driver circuits are closely related to the driver networks and fabrication methods used to create liquid crystal display panels, such as those found in smartphones, laptop monitors, and televisions, and can therefore be mass-produced inexpensively. Conventionally, even when electrophoretic media are driven directly by insulating electrodes (e.g., segmented electrodes), the driving pulse is delivered as a square wave having a certain amplitude and a certain time width. See, for example, U.S. Patent No. 7,012,600 (Patent Document 2) (which is incorporated as a whole by reference). In this form of driving, the electrical impulse, i.e., the amount of time the charged particles are exposed to a field of a given size, determines