1. Field of Invention
The invention relates to the field of visual displays. More particularly, the invention relates to a gyricon or twisting ball visual display having a controlled response to triboelectric charge effects.
2. Description of Related Art
Paper has traditionally been a preferred medium for the presentation and display of text and images. Paper has several characteristics that make it a desirable display medium, including the fact that it is lightweight, thin, portable, flexible, foldable, high-contrast, low-cost, relatively permanent, and readily configured into a myriad of shapes. It can maintain its displayed images without using any electricity. Paper can also be read in ambient light and can be written or marked upon with a pen, pencil, paintbrush, or any number of other implements, including a computer printer.
Unfortunately, paper is not well suited for real-time display purposes. Real-time imagery from computer, video, or other sources cannot be displayed directly with paper, but must be displayed by other means, such as by a cathode-ray tube (CRT) display or a liquid-crystal display (LCD). However, Teal-time display media lack many of the desirable qualities of paper, such as physical flexibility and stable retention of the displayed image in the absence of an electric power source.
Electric paper combines the desirable qualities of paper with those of real-time display media. Like ordinary paper, electric paper can be written and erased, can be read in ambient light and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper can be made in the form of a light-weight, flexible, durable sheet that can be folded or rolled into a tubular form about any axis and placed into a shirt or coat pocket, and then later retrieved, re-straightened, and read without loss of information. Yet unlike ordinary paper, electric paper can be used to display fall-motion and other real-time imagery as well as still images and text. Thus, electric paper can be used in a computer system display screen or a television.
The gyricon, also called the twisting-ball display, rotary ball display, particle display, dipolar particle light valve, etc., provides a technology for making electric paper. A gyricon display is a display that can be altered or addressed. A gyricon display is made up of a multiplicity of optically anisotropic balls which can be selectively rotated to present a desired surface to an observer.
The optical anisotropy of the gyricon balls is provided by dividing the surface of each gyricon ball into two or more portions. One portion of the surface of each gyricon ball has a first light reflectance or color. At least one other portion of the surface of the gyricon ball has a different color or a different light reflectance. For example, a gyricon ball can have two distinct hemispheres, one black and the other white. Additionally, each hemisphere can have a distinct electrical characteristic, e.g., a zeta potential with respect to a dielectric fluid. Accordingly, the gyricon balls are electrically as well as optically anisotropic. It is conventionally known that when particles are dispersed in a dielectric liquid, the particles acquire an electric charge related to the zeta potential of their surface coating.
The black-and-white gyricon balls are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of spheroidal cavities. Each of the spheroidal cavities is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accommodate the gyricon balls, one gyricon ball per cavity, to prevent the balls from migrating within the sheet. Each cavity is slightly larger than the size of the gyricon ball so that each gyricon ball can rotate or move slightly within its cavity.
A gyricon ball can be selectively rotated within its respective fluid-filled cavity by applying an electric field, so that either the black or white hemisphere of the gyricon ball is exposed to an observer viewing the surface of the sheet. By applying an electric field in two dimensions, for example, using a matrix addressing scheme, the black and white sides of the balls can be caused to appear as the image elements, e.g., pixels or subpixels, of a displayed image.
Gyricon displays are described further in U.S. Pat. No. 5,389,945 to Sheridon, incorporated herein by reference in its entirety. The 945 patent discloses that gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, that are not found in CRTs, LCDs, or other conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays.