Head-up display systems

Details Head-up display systems Head-up display systems

1990-02-09

1991-02-19

Arnold, Bruce Y.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

350 37, 350174, 340705, G02B 2710, G02B 532

Patent

active

049937880

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to head-up display systems.
2. Description of Related Art
More particularly the invention relates to head-up display systems of the kind (hereinafter referred to as "head-up display systems of the kind specified") comprising: an object surface; a holographic combiner which has been constructed using two coherent sources respectively located adjacent to entrance and exit pupils of the combiner so as to deviate an axial ray coming from the object surface through an off-axis angle into an exit pupil of the system and which has a focal surface with axial coma and axial astigmatism; and an optical sub-system along the path of said axial ray between the object surface and the combiner which at least partially compensates said axial coma and said axial astigmatism. Such a system is described in US Pat. No. 3940204.
It will be understood that in such a system the optical sub-system forms at the focal surface of the holographic combiner an aberrated intermediate image of the object surface; and that, by using aberrated wavefronts in the hologram construction, the holographic combiner is formed with aberrations balancing those of the intermediate image, the aberrations thus being at least partially compensatory so that a virtual image of the object surface at infinity is seen by an observer looking through the combiner from the exit pupil, which virtual image is of useful quality.
When such a system is used as a pilot's display system in an aircraft cockpit, to accommodate the system to the spatial constraints of the aircraft cockpit, the optical path between the object surface and the holographic combiner is folded by a reflector means whereby rays from the object surface are redirected at the exit of the optical sub-system to the combiner for reflection thereby to the exit pupil.
In known such arrangements, as are described in the aforementioned US Pat. No. 3940204, the reflector means comprises a prism which is positioned beneath the combiner, in line with the pilot ejection plane of the cockpit, so that there is no room available forward of the ejection plane to accommodate additional display arrangements such as a secondary head-down display arrangement.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a head-up display system of the kind specified whereby this disadvantage may be overcome.
According to the present invention, in a head-up display system of the kind specified including reflector means whereby rays from the object surface are redirected at the exit of the optical sub-system to the combiner said reflector means comprises: a light reflective first optical surface; and a second optical surface possessing both light reflective and light transmissive properties; the two said optical surfaces defining a space tapering in the direction of ray propagation from the object surface, and the arrangement being such that rays from the object surface are first reflected at said first surface to said second surface, are then reflected from said second surface back to said first surface, and are then reflected again at said first surface to said second surface, the rays consequently transmitted by said second surface being incident at the combiner at an angle to which the hologram of the combiner is tuned for reflection.


BRIEF DESCRIPTION OF THE DRAWING

One head-up display system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic representation of a display unit of the system.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figure, the display unit 11 is supported, boresighted, within an aircraft cockpit having a canopy 13, for use by the pilot of the aircraft. The unit 11 includes a housing 15 and a holographic combiner 17 which is upstandingly supported on top of the housing 15 in a rigid frame (not shown).
Within the housing 15 there is an optical sub-system 19 constituted by a multiplicity

REFERENCES:
patent: 3940204 (1976-02-01), Withrington
patent: 4652870 (1987-03-01), Steward

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