Color graphic imager utilizing a liquid crystal display

• US 4,944,578 A
• Filed: 07/21/1988
• Issued: 07/31/1990
• Est. Priority Date: 07/21/1988
• Status: Expired due to Fees

• Current Assignee: Telex Communications Incorporated (Robert Bosch GmbH)
• Original Assignee: Telex Communications Incorporated (Robert Bosch GmbH)
• Inventors: Denison, William W.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/222,164
• Time in Patent Office: 740 Days
• Field of Search: 350/347 E, 350/331 R, 350/333, 350/339 F, 350/341, 350/334, 350/337, 350/332, 353/122, 353/DIG. 3, 353/DIG. 5, 340/765, 340/784
• US Class Current: 349/6
• CPC Class Codes: G03B 21/132 Overhead projectors, i.e. capable of projecting hand-writing or drawing during action epidiascopic projectors G03B21/08
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28
• CPC Class Codes: Y10S 353/05 Transparency holder accessories

Abstract

A display including a liquid crystal cell. The cell includes a liquid crystal material, a plurality of electrodes, and first and second polarizers. The first polarizer is located at a viewing side of the cell such that the vibration direction of light polarized thereby is non-parallel to the optic axis of the liquid crystal material as its front boundary layer. The second polarizer is located on a side of the cell remote from the first polarizer wherein the vibration direrction of light polarized thereby forms an angle with respect to the vibration direction of light polarized by the first polarizer. The liquid crystal is responsive to different magnitudes of the electric field for the display of perceived color differences. The display is interfaced with a computer via circuitry which converts color display information produced by the computer to drive signals for applying the electric field in the different magnitudes across selected ones of the electrodes in order to display the perceived color differences. The display is part of a panel for use with a projector.

Claims

1. A display apparatus comprising:

a liquid crystal cell including

(i) a liquid crystal material having a state of optical retardation variable only within a range between about 0.3 microns and 1.6 microns,

(ii) a plurality of electrodes for applying an electric field across said liquid crystal material,

(iii) a first polarizer at a viewing side of said cell

(iv) a second polarizer on the side of said cell remote from said first polarizer, and

(v) said liquid crystal material in said cell responsive to different magnitudes of the electric field for the display of perceived color differences;

said cell part of a panel positionable on a stage projector, said panel having first and second transparent surfaces to establish a light path therethrough and said cell located therebetween; and

means for interfacing said cell with a computer and for converting color display information produced by said computer to drive signals and means for applying said drive signals to said electrodes wherein different levels of average rms voltage are applied across selected ones of said electrodes to display said perceived color differences.

2. The display apparatus of claim 1 wherein said cell includes a first alignment layer on said viewing side and an axis of polarization of said first polarizer forms an angle of between approximately 25°

and 35°

with respect to a rubbing direction on the first alignment layer.

3. The display apparatus of claim 2 wherein said cell includes a second alignment layer on the side of said liquid crystal material remote from said first alignment layer and an axis of polarization of said second polarizer forms an angle of between approximately -25°

and -35°

with respect to the rubbing direction on the second alignment layer.

4. The display apparatus of claim 1 wherein said liquid crystal material is a supertwisted nematic liquid crystal material that has twist angle of between about 180°

and 270°

.

5. The display apparatus of claim 1 wherein said liquid crystal material is a supertwisted nematic liquid crystal material that has a twist angle of about 240°

.

6. A display apparatus comprising:

a liquid crystal cell including

(i) a supertwisted nematic liquid crystal material having a state of optical retardation variable only within a range between about 0.3 micrometers and 1.6 micrometers,

(ii) a plurality of electrodes for applying an electric field across said liquid crystal material,

(iii) a first polarizer at a viewing side of said cell

(iv) a second polarizer on the side of said cell remote from said first polarizer, and

(v) said liquid crystal material in said cell responding to different magnitudes of the electric field for the display of various perceived colors the majority of which fall outside an envelope defined by the following coordinates connected by straight lines on a 1931 C.I.E. chromaticity diagram;

(x≅

0.25, y≅

0.17), (x≅

0.38, y≅

0.30), (x≅

0.40, y≅

0.38), (x≅

0.34, y≅

0.43), (x≅

0.23, y≅

0.35), and (x≅

0.19, y≅

0.18);

said cell part of a panel positionable on a stage of an overhead projector, said panel having first and second transparent surfaces to establish a light path therethrough and said cell located therebetween; and

means for interfacing said cell with a computer and for converting color display information produced by said computer to drive signals and means for applying said drive signals to said plurality of electrodes wherein different levels of average rms voltage are applied across selected ones of said electrodes to display said perceived color differences.

7. The display apparatus of claim 6 wherein said projector includes means for transmitting a light beam through said cell for forming an enlarged image of the display produced thereby.

8. The display apparatus of claim 6 wherein said electrodes comprise a 640×

200 dot matrix arrangement.

9. A display apparatus comprising:

a liquid crystal cell including

(i) a supertwisted liquid crystal material having a state of optical retardation variable within a range between about 0.3 micrometers and 1.6 micrometers for the display of at least four perceived color differences,

(ii) an array of pixels arranged vertically in columns and horizontally in rows for applying an electric field across said liquid crystal material,

(iii) a first polarizer at a viewing side of said cell,

(iv) a second polarizer on the side of said cell remote from said first polarizer, and

(v) said liquid crystal material in said cell responsive to different magnitudes of the electric field for the display of said perceived color differences;

means for converting color display information produced by a computer and for applying time multiplexed signals to said pixels wherein different levels of average rms voltage are applied across said liquid crystal material by varying an on period relative to a frame period in order to display said perceived color differences; and

said cell part of a panel for use with a projector including means for transmitting a light beam through said cell for forming an enlarged image of a display produced by said cell.

10. The display apparatus of claim 9 wherein said panel has first and second transparent surfaces to establish a light path for the light beam.

11. The display apparatus of claim 10 wherein said array of pixels comprises two 640×

100 dot matrix arrangements.

12. The display apparatus of claim 11 operated in a blue mode and wherein each of said dot matrix arrangements are driven at a 1/100 duty cycle, and said liquid crystal material responsive to said different magnitudes of the electric field to produce a curve on a 1931 C.I.E. chromaticity diagram including points have the following coordinates:

(x≅

0.195, y≅

0.130), (x≅

0.260, y≅

0.140), (x≅

0.425, y≅

0.340), (x≅

0.445, y≅

0.410), (x≅

0.415, y≅

0.430).

13. A display apparatus comprising:

a liquid crystal cell including

(i) a supertwisted nematic liquid crystal material having a state of optical retardation variable only within a range between about 0.3 microns and 1.6 microns,

(ii) an array of pixels arranged vertically in columns and horizontally in rows for applying an electric field across said liquid crystal material,

(iii) a first polarizer at a viewing side of said cell, and

(iv) a second polarizer on the side of said cell remote from said first polarizer, and

(v) said liquid crystal material in said cell responsive to different magnitudes of the electric field for the display of perceived color differences;

means for converting color display information produced by a computer to a plurality of time multiplexed signals; and

means for applying said time multiplexed signals to said array of pixels wherein different levels of average rms voltage are applied across selected ones of said pixels by varying an on period relative to a frame period in order to display said perceived color differences.

14. The display apparatus of claim 13 wherein said cell is part of a panel for use with a projector including means for transmitting a light beam through said cell for forming an enlarged image of the display produced by said cell.

15. The display apparatus of claim 14 wherein said panel may be positioned on a stage of an overhead projector, and said panel has first and second transparent surfaces to establish a light path for the light beam.

16. The display apparatus of claim 13 wherein said means for applying said time multiplexed signal produces at least five levels of average rms voltage.

17. The display apparatus of claim 16 wherein said liquid crystal material is responsive to the different levels of average rms voltage to produce a curve on a 1931 C.I.E. chromaticity diagram including points having the following coordinates:

(x≅

0.195, y≅

0.130), (x≅

0.260, y≅

0.140), (x≅

0.415, y≅

0.340) (x≅

0.445, y≅

0.410), (x≅

0.415, y≅

0.430).

18. The display apparatus of claim 13 wherein the vibration direction of light polarized by said first polarizer is non-parallel to the optic axis of said liquid crystal material at its front boundry layer and the vibration direction of light polarized by said second polarizer forms an angle with respect to the vibration direction of light polarized by said first polarizer.

19. The display apparatus of claim 13 operated in the blue mode.

20. The display apparatus of claim 13 operated in the yellow mode.

21. The display apparatus of claim 13 wherein there are at least four perceived color differences.

24. The display apparatus of claims 13 or 22 wherein said liquid crystal material is responsive to said different levels of average rms voltage to produce various perceived colors the majority of which fall outside an envelope defined by the following coordinates connected by straight lines on a 1931 C.I.E. chromaticity diagram:

(x≅

0.25, y≅

0.17), (x≅

0.38, y≅

0.30), (x≅

0.40, y≅

0.38), (x≅

0.34, y≅

0.43), (x≅

0.23, y≅

0.35), and (x≅

0.19, y≅

0.18).

22. A display apparatus comprising:

a liquid crystal cell including

(i) a birefringent liquid crystal material having a state of optical retardation variable only within a range between about 0.3 μ

m and 1.6 μ

m.

(ii) an array of pixels arranged vertically in columns and horizontally in rows for applying an electric field across said liquid crystal material,

(iii) a first polarizer means at a viewing side of said cell, and

(iv) a second polarizer means on the side of said cell remote from said first polarizer means, and

(v) said liquid crystal material in said cell responsive to different magnitudes of the electric field for the display of perceived color differences;

means for converting color display information produced by a computer to a plurality of signals; and

means for applying said signals to said array of pixels wherein different levels of average rms voltage are applied across selected ones of said pixels in order to display said perceived color differences.

23. The display apparatus of claim 22 wherein said cell is part of a panel for use with a projector including means for transmitting a light beam through said cell for forming an enlarged image of the display produced by said cell.

25. A display apparatus comprising:

a liquid crystal cell including

(i) a liquid crystal material having a state of optical retardation variable within a range between about 0.3 microns and 1.6 microns for the display of at least four perceived color differences,

(ii) a plurality of electrodes for applying an electric field across said liquid crystal material,

(iii) a first polarizer means at a viewing side of said cell,

(iv) a second polarizer means on the side of said cell remote from said first polarizer means, and

(v) said liquid crystal material in said cell responsive to different magnitudes of the electric field of the display of said perceived color differences;

said cell part of a panel positionable on a stage of a projector, said panel having first and second transparent surfaces to establish a light path therethrough and said cell located therebetween; and

means for interfacing said cell with a computer and for converting color display information produced by said computer to drive signals and means for applying said drive signals to said electrodes wherein different levels of average rms voltage are applied across selected ones of said electrodes to display said perceived color differences.