Head-up display for aircraft with a curved windshield

Details Head-up display for aircraft with a curved windshield Head-up display for aircraft with a curved windshield

2002-06-25

2004-11-16

Spector, David N. (Department: 2873)

Optical: systems and elements

Single channel simultaneously to or from plural channels

By partial reflection at beam splitting or combining surface

C359S630000, C359S633000

Reexamination Certificate

active

06819496

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to the field of head-up sights for an aircraft with a curved windshield, that is to say for an aircraft having a windshield with a curved shape. The head-up sight is an optomechanical device which makes it possible to superimpose onto the external scene seen by the pilot of the aircraft, a symbology which is projected at infinity, that is to say far enough away that the pilot does not have to substantially accommodate in order to see said symbology. The symbology comprises, for example, synthetic images and reticules.
(2) Description of the Related Art
Where the windshield of the aircraft is flat, there is no particular difficulty for the head-up sight to superimpose the symbology projected at infinity onto the external scene. On the other hand, where the windshield of the aircraft is curved, although the symbology is projected at infinity, the target appears to the aircraft pilot to be closer than the symbology, which obliges the pilot to accommodate in order to pass from the symbology projected by the sight onto the scene, and vice versa. This phenomenon is called parallax. Specifically, since the shape of the windshield is curved, the windshield is not optically neutral, it is an optical element having a certain optical power, which is generally divergent since the windshield is curved and of constant thickness. It is because of the optical power of the windshield that the target appears to the pilot to be closer than the symbology projected at infinity by the head-up sight. Thus, when the pilot looks at the target, he sees the symbology slightly duplicated, for example, over a few milliradians, while when the pilot looks at the symbology, he sees the target slightly duplicated, for example over a few milliradians. This duplication disrupts the pilot's vision, for example when he has to align a reticule on a target during a firing phase in the case of a military aircraft.
According to a prior art, an example of which is shown in
FIG. 1
, the parallax associated with the curved windshield, more specifically, that is to say with the curved shape of the windshield, is corrected using an additional plate. This additional plate is a plano-cylindrical plate, placed outside the optical combination of the head-up sight, downstream of the last optical element of said optical combination, and mechanically integrated into the head-up sight, that is to say included in the external casing of the head-up sight. This additional plate for compensating the parallax associated with the curved windshield has several drawbacks. The addition of this additional plate comprising a generally opaque mounting constitutes, for the pilot's vision, a supplementary mask, generally of a few degrees, which leads to a reduction in the pilot's visual field, which is a problem for the pilot, and which risks cutting off information from the projected symbology, which is also annoying for the pilot. The inside of the head-up sight is generally also at a higher pressure with respect to the outside of the head-up sight, especially in order to prevent the ambient moisture from penetrating inside the head-up sight; it is therefore necessary, on the one hand, to reconcile the internal overpressure of the head-up sight and the mechanical rigidity of the additional compensation plate in order to eliminate the possibility of the additional compensation plate exploding and, on the other hand, to be able to rinse the supplementary volume due to the presence of the additional compensation plate using a fluid. This overpressure problem requires adaptations of the head-up sight which are sometimes difficult to implement.
FIG. 1
shows schematically the optical combination of a head-up sight according to the prior art for an aircraft with a curved windshield showing the effect of the curved windshield which is external to the sight. The direction of propagation of the light beams is indicated by arrows. Other optical elements are located between the curved windshield and the head-up sight, but are not shown in
FIG. 1
, since they have no optical power; for example, there are partly reflecting mirrors whose function is to superimpose the symbology projected at infinity by the head-up sight onto the external scene seen by the pilot. An additional plate
6
for compensating the parallax associated with the curved windshield
5
is located between the output of the optical combination which comprises optical elements
1
,
2
,
21
,
22
,
23
,
3
,
4
,
41
,
42
, which will be described later in relation to
FIG. 2
, and the curved windshield
5
. The folding mirror
3
is a simple flat mirror enabling the optical combination of the head-up sight to be bent at an angle in order to decrease its overall size.
BRIEF SUMMARY OF THE INVENTION
The invention provides a solution which, on the one hand, does not increase the visual mask of the pilot and which, on the other hand, requires little or no particular adaptation, especially of the external casing of the head-up sight and of the rinsing circuit inside the head-up sight. For this, the head-up sight according to the invention requires no additional compensation plate, since the parallax associated with the curved windshield is corrected by a particular shape of the folding mirror included in each optical combination of a head-up sight. Thus, it is not necessary to add a supplementary optical element, the modification of the shape of an optical element already existing in the optical combination of a head-up sight, that is to say the folding mirror, being enough to correct the parallax associated with the curved windshield, and even to remove this parallax.
According to the invention, provision is made for a head-up sight, for an aircraft with a curved windshield, the windshield being external to the sight, which can project at infinity a symbology intended to be superimposed onto the external scene, comprising a combination of optical elements bent at an angle to a folding mirror, characterized in that the folding mirror has a curved shape adapted to correct the parallax associated with the optical power of the windshield.


REFERENCES:
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patent: 0 631 167 (1994-12-01), None
patent: 0 710 866 (1996-05-01), None
patent: 02/14941 (2002-02-01), None
“Head-up display” The Electronic Engineer, vol. 26, No. 7, p. 29, Jul. 1967.

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