Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Patent
1994-08-04
1997-09-02
Sikes, William L.
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
359634, 2502014, G02F 11335
Patent
active
056638175
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector of narrow field moving images.
2. Discussion of Background
In simulators such as air combat simulators, with projection sphere, wide optical field images of the sky and of the ground are projected onto this sphere and images of targets are overlaid onto the former images. The target image projectors can be arranged on either side of the cockpit for piloting the simulator, underneath the pilots' region of visibility, or on a pylon situated behind the cockpit. These projectors have to be as compact as possible so as to avoid mutual occultation.
The targets thus displayed are to be depicted for actual distances from the observer of between 200 and 6000 m approximately. The projectors have therefore to be furnished with an optical and electronic zoom of high ratio (30 for the example cited), and the projected images have to be highly contrasted in order to depict actuality as faithfully as possible.
Known projection devices include liquid-crystal cells illuminated under natural light by complex-optic projectors, and when desiring to have good resolution of the projected targets, cells of large size are necessary as therefore are expensive optics of correspondingly large diameter.
The subject of the present invention is a projector of narrow optical field moving images which are clearly contrasted, the projector employing the cheapest possible optical means.
SUMMARY OF THE INVENTION
The projection device of the invention includes a point light source arranged at the focus of a collimating optic followed by a device for spatially modulating a light beam over its cross section, by a divergent-beam forming optic and by an afocal zoom cooperating with a projection screen.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood on reading the detailed description of several embodiments, given by way of non-limiting examples and illustrated by the attached drawing in which:
FIG. 1 is a diagrammatic view of a first embodiment of the device of the invention using an optical fibre;
FIG. 2 is a diagrammatic view of a second embodiment of the device of the invention with direct coupling of the light source; and
FIG. 3 is a diagrammatic view of a third embodiment of the device of the invention making it possible to obtain colour images.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is described below with reference to a target projector for an air combat simulator, but it is of course understood that it is not limited to such an application, and that it can be employed in other sectors in which there is a need to project images of moving objects with relatively narrow optical field, which objects may vary in size within wide proportions, that is to say whose simulated remoteness with respect to the observer may vary within large proportions (within a ratio of several tens for example).
The projection device depicted in FIG. 1 includes a light source 1 of high luminous intensity, advantageously a laser generator. In the case where a laser is used, it may for example be He-Ne monochrome multimode, or Ar-Kr white multimode. In front of the generator 1 is placed an optic 2 for coupling to the end 3 of an optical fibre 4 for transporting the light ray from this generator. The other end 5 of the fibre 4, which is akin to a point light source, is placed at the focus of an optical collimating device 6, which is a simple convergent lens in the present case. The optical device 6 is followed by a beam modulator 7. In the present example, this modulator is a liquid-crystal cell with matrix addressing, furnished with its usual polarizers. The cell 7 has dimensions corresponding substantially to those of the beam leaving the lens 6. Its resolution may for example be between 250.times.250 pixels and 1000.times.1000 pixels, but may just as well be better. The cell 7 receives a video signal V produced in a manner known per se by a video generator (not depicted). The cell 7 is followed by an optical
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Frapin Pascal
Lacroix Michel
"Thomson-CSF"
Nguyen Tiep H.
Sikes William L.
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