Multiple color writing tablet

• US 20090033811A1
• Filed: 05/16/2008
• Published: 02/05/2009
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: Kent Displays Incorporated
• Original Assignee: Kent Displays Incorporated
• Inventors: Schneider, Tod L.
• Granted Patent: US 8,228,301 B2
• Time in Patent Office: Days
• US Class Current: 349/12
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display

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.

Claims

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 said 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 conductive layers for each of said active layers;

wherein said erasing voltage enables said liquid crystal of said active layers to be placed in a planar texture reflecting light of a predetermined color or in a 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 conductive layers for a non-selected said active layer while applying said writing pressure to said writing surface, enabling said reduced gap region of said non-selected said active layer to be in said transparent focal conic texture and said reduced gap region of a selected said active layer to include said planar texture that reflects said predetermined color.

2. The writing tablet of claim 1 comprising an untethered stylus adapted to apply said writing pressure.

3. The writing tablet of claim 1 wherein said conductive layers are patterned or unpatterned.

4. The writing tablet of claim 1 wherein said liquid crystal is dispersed in a polymer matrix.

5. The writing tablet of claim 1 comprising a single flexible substrate or a substrate component between adjacent said active layers, wherein said single substrate includes said conductive layers on both sides thereof while said substrate component includes two flexible transparent substrates having said conductive layers on outside surfaces thereof and index of refraction matching material disposed between said substrates.

6. The writing tablet of claim 1 wherein all of said electrically conductive layers are transparent except for one of said electrically conductive layers closest to said light absorbing layer which is transparent or opaque.

7. A method of forming a multicolor image on a writing tablet, comprising:

providing a writing tablet including electrically conductive layers, at least two active layers stacked over each other each disposed in a gap between adjacent said 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 a voltage to said conductive layers effective to place each said active layer in a planar texture reflecting light of a predetermined color or in a transparent focal conic texture; and

then

writing 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 said active layer enabling said reduced gap region of said non-selected said active layer to be in said transparent focal conic texture and said reduced gap region of a selected active layer to include said planar texture that reflects said predetermined color.

8. The method of claim 7 wherein said conductive layers are patterned or unpatterned.

9. The method of claim 7 wherein said writing voltage is effective to enable 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.

10. The method of claim 7 comprising changing said writing pressure effective to enable said reduced gap region of said 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.

11. The method of claim 7 comprising two of said active layers, said selection of said initial states of said active layers being selected from the group consisting of:

1) both of said active layers in said planar texture,

2) both of said active layers in said focal conic texture, and

3) one of said active layers in said focal conic texture and the other of said active layers in said planar texture.

12. The method of claim 11 wherein a background in unreduced gap regions of said active layers is selected from the group consisting of:

4) black or said back color when said initial states

     2) are selected;

5) a color of said initial planar texture of said active layer when said initial states

     3) are selected;

6) a color that is an additive mixture of colors reflected by said initial planar textures of both of said active layers when said initial states

     1) are selected, and

7) a color that is an additive mixture of said back color and said color

     5) or of said back color and said color

     6).

13. The method of claim 12 whereby said tablet displays a written portion that is i) a color reflected by said selected layer in said reduced gap region thereof or ii) an additive mixture of said color i) and said back color.

14. The method of claim 7 comprising three of said active layers, said selection of said initial states of said active layers being selected from the group consisting of:

1) all three of said active layers in said planar texture,

2) all three of said active layers in said focal conic texture,

3) one of said active layers in said focal conic texture and two of said active layers in said planar texture, and

4) one of said active layers in said planar texture and two of said active layers in said focal conic texture.

15. The method of claim 14 wherein a background in unreduced gap regions of said active layers is selected from the group consisting of:

5) black or said back color when said initial states

     2) are selected;

6) a color of said initial planar texture active layer when said initial states

     4) are selected;

7) a color that is an additive mixture of both of said initial planar texture active layers when said initial states

     3) are selected or is an additive mixture of all three of said initial planar texture active layers when said initial states

     1) are selected, and

8) a color that is an additive mixture of said back color and said color

     7) or

     6).

16. The method of claim 15 comprising selecting said color by applying said writing pressure to said writing surface while applying said writing voltage to said conductive layers enabling said reduced gap region of two of said non-selected said active layers to be in said transparent focal conic texture and said reduced gap region of said selected active layer to include said planar texture, whereby said tablet displays a written portion that is i) a color reflected by said selected layer in said reduced gap region thereof or ii) an additive mixture of said color i) and said back color.

17. The method of claim 15 comprising selecting said color by applying said writing pressure to said writing surface while applying said writing voltage to said conductive layers enabling said reduced gap region of said non-selected said active layer to be in said transparent focal conic texture and said reduced gap region of two of said selected active layers to include said planar texture, whereby said tablet displays a written portion that is i) a color that is an additive mixture of two colors reflected by said planar textures of said two selected active layers or ii) an additive mixture of said color i) and said back color.

18. The method of claim 7 wherein said liquid crystal is dispersed in a polymer matrix.

19. The method of claim 7 wherein said step of writing at a selected color is carried out on said writing tablet that already includes an image.

20. The method of claim 7 wherein all of said electrically conductive layers are transparent except for one of said electrically conductive layers closest to said light absorbing layer which is transparent or opaque.

21. The method of claim 14 wherein pitch lengths of chiral additives of said cholesteric liquid crystal of said active layers are selected such that each of said active layers reflects a different one of red, green and blue in any sequence.

22. A method of forming an image on a writing tablet, comprising:

providing a writing tablet including electrically conductive layers, an active layer disposed in a gap between adjacent said 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;

placing said active layer in an initial planar texture reflecting light of a color or an initial transparent focal conic texture; and

applying said writing pressure while applying a voltage to said electrodes effective to place said reduced gap region of said active layer in said transparent focal conic texture while not changing said texture of said unreduced gap regions of said active layer.

23. The method of claim 22 wherein said initial texture is planar.

24. The method of claim 23 wherein said light absorbing layer is a back color or black, and said writing tablet is said back color or black in said reduced gap region and has a background in said unreduced gap region that is a color reflected by said planar texture of said active layer or an additive mixture of said back color and said color.

25. The method of claim 22 wherein said liquid crystal is dispersed in a polymer matrix.

26. The method of claim 22 further comprising an additional active layer stacked above or below said active layer in a gap between adjacent said 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 conductive layers for said active layer alone or for said active layer and said additional active layer.

27. The method of claim 26 wherein all of said electrically conductive layers are transparent except for one of said electrically conductive layers closest to said light absorbing layer which is transparent or opaque.