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EP0272820A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Transient state liquid crystal image bar with contrast enhancement

Assignee: Xerox Corp
•
Filing: 1987-12-02
•
Granted: —
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Expires: 2007-12-02
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Abstract

Abstract A transient state liquid crystal image bar (12) having enhanced contrast with lower required driving voltage. The image bar is of the type having a nematic liquid crystal cell configured as a single array of dot shutters energizable by a single frequency voltage with crossed polarizer (14) and analyzer (15). The polarizing axis of the polarizer is at 45 degrees with the liquid crystal molecules (13) in their rest state. Thus, when all the image bar shutters are energized, it is in the non-transmission condition. For bursts of light to pass, the voltage to selected dot shutters is interrupted and reapplied. In one embodiment, the improvement is achieved by an optical compensator (28) or thin prism placed between the polarizer and the liquid crystal cell. In another embodiment, a quarter-wave plate is placed between the liquid crystal cell and the analyzer, with the analyzer being rotated about the image bar's optical axis a predetermined angle from its initial crossed position with respect to the polarizer, so that there is increased extinction of the light exiting from the liquid crystal cell, when the liquid crystal material is in its normally stable energized state.

Inventors

  • 👤 Gary A. Dir
  • 👤 Alain E. Perregaux

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-10-30 15:00
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/01; G02F1/13; G02F1/137; G02F1/139; G02F1/1393; G02F1/133; G02F1/1333; G02F1/1335; G02F1/13363; G02F1/133528; G02F1/133531; G02F1/133638; G02F2413/00; G02F2413/01

Claims Analysis

Total Claims: 5
Claim 1
Independent Claim 198 words
A transient state liquid crystal image bar (12) for producing latent electrostatic images on a moving, precharged photoconductive member of an electrophotographic printer one line of pixels at a time, the image bar having a nematic liquid crystal cell configured as a single array of dot shutters individually energizable by the selective application (29) of a single frequency driving voltage and having approximately crossed polarizer (14) and analyzer (15), the polarizing axis of the polarizer being at 45 degrees with the liquid crystal molecules (13) in their relaxed state, and substantially perpendicular to the optical axis (10) of the image bar, so that the image bar is non-transmissive when all of the dot shutters are energized, bursts of light for erasing pixels of precharged background area of the photoconductive member being passed by selected dot shutters through the interruption and reapplication of the voltage applied thereto, characterised by: means (26 or 28) for preventing elliptically polarized light generated by the incomplete homeotropic state or tilt of the energized liquid crystal molecules from entering the analyzer, so that the contrast between the transmissive and non-transmissive state of the image bar is increased, and the driving voltage is concurrently reduced.
Claim 2
Dependent Claim 198 words
A transient state liquid crystal image bar (12) for producing latent electrostatic images on a moving, precharged photoconductive member of an electrophotographic printer one line of pixels at a time, the image bar having a nematic liquid crystal cell configured as a single array of dot shutters individually energizable by the selective application (29) of a single frequency driving voltage and having approximately crossed polarizer (14) and analyzer (15), the polarizing axis of the polarizer being at 45 degrees with the liquid crystal molecules (13) in their relaxed state, and substantially perpendicular to the optical axis (10) of the image bar, so that the image bar is non-transmissive when all of the dot shutters are energized, bursts of light for erasing pixels of precharged background area of the photoconductive member being passed by selected dot shutters through the interruption and reapplication of the voltage applied thereto, characterised by: means (26 or 28) for preventing elliptically polarized light generated by the incomplete homeotropic state or tilt of the energized liquid crystal molecules from entering the analyzer, so that the contrast between the transmissive and non-transmissive state of the image bar is increased, and the driving voltage is concurrently reduced.
Claim 3
Dependent Claim 35 words
The image bar of claim 1, wherein the means for preventing elliptically polarized light from entering the analyzer comprises a predetermined optical compensator (28) or retardation plate between the liquid crystal cell and the analyzer.
Claim 4
Dependent Claim 60 words
The image bar of claim 1, wherein the means for preventing elliptically polarized light from entering the analyzer comprises a relatively thin transparent prism (28) between the polarizer and the liquid crystal cell, the deflection angle of light passing through the prism being matched to the deflection angle of light passing through the liquid crystal molecules in their energized state.
Claim 5
Dependent Claim 68 words
The image bar of claim 1, wherein the means for preventing elliptically polarized light from entering the analyzer comprises a quarter-wave plate (26) between the liquid crystal cell and the analyzer to convert the elliptically polarized light exiting from the cell to linearly polarized light; and wherein the polarizing axis of the analyzer is rotated to be coincident with the linearly polarized light exiting from the quarter-wave plate.

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