Multiple color writing tablet
First Claim
1. A multicolor writing tablet comprising:
- electrically conductive layers;
at least two active layers stacked over each other, each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material;
an outer layer of flexible transparent material forming a writing surface;
a light absorbing back layer adapted to absorb light passing through said active layers;
wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions;
electronic circuitry for applying erasing and writing voltages to said electrically conductive layers for each of said active layers;
wherein said erasing voltage is a voltage that enables said liquid crystal material of said active layers to be placed in a planar texture reflecting light of a predetermined color or a different erasing voltage that enables said liquid crystal material of said active layers to be placed in an essentially transparent focal conic texture; and
wherein said writing voltage enables writing on said tablet in a color selected from any of said active layers by applying said writing voltage to said electrically conductive layers for a non-selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said non-selected active layer to be in said essentially transparent focal conic texture and by not applying said writing voltage to said electrically conductive layers for a selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said selected active layer to be in said planar texture reflecting light of a predetermined color.
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Accused Products
Abstract
One aspect of the invention is a bistable cholesteric writing tablet on which an image is formed by applying a suitable voltage while applying writing pressure, which results in a focal conic texture in a reduced gap region of the active layer while not changing the texture of the unreduced gap region of the active layer (e.g., a written portion being in a focal conic texture on a background in the planar texture). Another aspect of the invention is a multi-color stacked writing tablet in which a color of an image is selected by applying a suitable voltage while applying writing pressure using an instrument such as an untethered stylus on the surface of the tablet. The writing tablet includes at least two or three stacked layers of bistable cholesteric liquid crystal material. Selected colors can be additively mixed to achieve intermediate colors as desired. The image can be erased and new images written on the tablet. Gray scale achieved by varying the applied voltage during writing or the writing pressure in some cases, enables the writing tablet to produce a broad range of colors. The writing device is suitable for many applications such as a toy, sketch pad, erasable signage, tags or a large writing board without the mess of chalk or ink.
89 Citations
35 Claims
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1. A multicolor writing tablet comprising:
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electrically conductive layers; at least two active layers stacked over each other, each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material; an outer layer of flexible transparent material forming a writing surface; a light absorbing back layer adapted to absorb light passing through said active layers; wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions; electronic circuitry for applying erasing and writing voltages to said electrically conductive layers for each of said active layers; wherein said erasing voltage is a voltage that enables said liquid crystal material of said active layers to be placed in a planar texture reflecting light of a predetermined color or a different erasing voltage that enables said liquid crystal material of said active layers to be placed in an essentially transparent focal conic texture; and wherein said writing voltage enables writing on said tablet in a color selected from any of said active layers by applying said writing voltage to said electrically conductive layers for a non-selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said non-selected active layer to be in said essentially transparent focal conic texture and by not applying said writing voltage to said electrically conductive layers for a selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said selected active layer to be in said planar texture reflecting light of a predetermined color. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 18, 19, 20)
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12. A method of forming a multicolor image on a writing tablet, comprising:
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providing a writing tablet including electrically conductive layers, at least two active layers stacked over each other each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material, an outer layer of flexible transparent material forming a writing surface and a light absorbing back layer adapted to absorb light passing through said active layers, said back layer being a back color or black, wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions; selecting initial states by applying an erasing voltage to said electrically conductive layers effective to place each said active layer in a planar texture reflecting light of a predetermined color or by applying a different erasing voltage to said electrically conductive layers effective to place said active layer in an essentially transparent focal conic texture; and
thenwriting at a selected color by applying said writing pressure to said writing surface while applying a writing voltage to said conductive layers for a non-selected active layer enabling said reduced gap region of said non-selected active layer to be in said essentially transparent focal conic texture and by not applying said writing voltage to said conductive layers for a selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said selected active layer to be in said planar texture reflecting light of a predetermined color. - View Dependent Claims (13, 14, 15, 16, 17, 21, 22, 23, 24, 25)
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26. A method of forming a multicolor image on a writing tablet comprising:
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providing a writing tablet including electrically conductive layers, at least two active layers stacked over each other each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material, an outer layer of flexible transparent material forming a writing surface and a light absorbing back layer adapted to absorb light passing through said active layers, said back layer being a back color or black, wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions; selecting initial states by applying an erasing voltage to said electrically conductive layers effective to place said active layer in a planar texture reflecting light of a predetermined color or by applying a different erasing voltage to said electrically conductive layers effective to place said active layer in a transparent focal conic texture; and
thenwriting at a selected color by applying said writing pressure to said writing surface while applying a writing voltage to said electrically conductive layers for a non-selected active layer enabling said reduced gap region of said non-selected active layer to be at a gray scale level of reflectivity between a minimum level of reflectivity of said focal conic texture and a maximum level of reflectivity of said planar texture and by not applying said writing voltage to said electrically conductive layers for a selected active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said selected active layer to be in said planar texture reflecting light of a predetermined color.
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27. A method of forming an image on a writing tablet, comprising:
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providing a writing tablet including electrically conductive layers, an active layer disposed in a gap between adjacent electrically conductive layers, said active layer including bistable cholesteric liquid crystal material, an outer layer of flexible transparent material forming a writing surface and a light absorbing layer adapted to absorb light passing through said active layer, wherein said active layer is adapted to enable writing pressure applied to said writing surface to reduce a thickness of said gap in a reduced gap region; applying an erasing voltage to place said active layer in an initial texture reflecting light of a color; and applying said writing pressure while applying a writing voltage to said electrically conductive layers effective to place said reduced gap region of said active layer in an essentially transparent focal conic texture while not changing said texture of an unreduced gap region of said active layer. - View Dependent Claims (28, 29)
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30. A method of forming an image on a writing tablet, comprising:
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providing a writing tablet including electrically conductive layers, an active layer disposed in a gap between adjacent electrically conductive layers, said active layer including bistable cholesteric liquid crystal material, an outer layer of flexible transparent material forming a writing surface and a light absorbing layer adapted to absorb light passing through said active layer, wherein said active layer is adapted to enable writing pressure applied to said writing surface to reduce a thickness of said gap in a reduced gap region; applying an erasing voltage to said electrically conductive layers of said active layer, said erasing voltage being a voltage that places said active layer in an initial texture reflecting light of a color or a different erasing voltage that places said active layer in an initial essentially transparent focal conic texture; and applying said writing pressure while applying a writing voltage to said electrically conductive layers effective to place said reduced gap region of said active layer in an essentially transparent focal conic texture while not changing said texture of an unreduced gap region of said active layer; further comprising an additional active layer stacked above or below said active layer in a gap between adjacent electrically conductive layers, comprising placing said additional active layer in said initial texture, wherein while said writing pressure is applied said writing voltage is applied to said electrically conductive layers for said active layer alone or for said active layer and said additional active layer. - View Dependent Claims (31)
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32. A writing tablet comprising:
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electrically conductive layers; at least two active layers stacked over each other each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material having reflective wavelengths that when in a planar texture together reflect white light; an outer layer of flexible transparent material forming a writing surface; a light absorbing black back layer adapted to absorb light passing through said active layers; wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions; electronic circuitry for applying an erasing voltage to said electrically conductive layers for each of said active layers; wherein said erasing voltage enables said liquid crystal material of all of said active layers to be placed in an essentially transparent focal conic texture that displays said black back layer; and wherein said tablet is written in white by applying no writing voltage to any of said electrically conductive layers while applying said writing pressure to said writing surface, enabling said reduced gap region of all of said active layers to be in said planar texture which together reflects white light. - View Dependent Claims (33)
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34. A writing tablet comprising:
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electrically conductive layers; at least two active layers stacked over each other each disposed in a gap between adjacent electrically conductive layers, said active layers including bistable cholesteric liquid crystal material having reflective wavelengths that when in a planar texture together reflect white light; an outer layer of flexible transparent material forming a writing surface; a light absorbing black back layer adapted to absorb light passing through said active layers; wherein said active layers are adapted to enable writing pressure applied to said writing surface to reduce thickness of said gaps to form reduced gap regions; electronic circuitry for applying erasing and writing voltages to said electrically conductive layers for each of said active layers; wherein said erasing voltage enables said liquid crystal material of all of said active layers to be placed in a planar texture so as to together reflect white light; and wherein said writing tablet is written in black by applying said writing voltage to said electrically conductive layers for all of said active layers while applying said writing pressure to said writing surface, enabling said reduced gap region of all of said active layers to be in an essentially transparent focal conic texture thereby displaying said black back layer. - View Dependent Claims (35)
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Specification