Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Patent
1995-10-17
1997-11-04
Epps, Georgia Y.
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
359631, 359637, G02B 2714
Patent
active
056846347
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to head-up displays.
Head-up displays (HUDs) have been in use for many years, particularly in military aircraft, and present information to the pilot such that it appears focussed a long distance in front of him and superimposed on his forward view of the outside world. HUDs therefore eliminate the dead time that would otherwise be taken for the pilot to change his gaze from the outside world to an instrument panel and back again to the outside world.
Simple HUDs comprise a display tube (usually a CRT) which generates the information to be presented to the pilot, a collimating optic which delivers the information to a partially reflecting combiner which is located in the pilots line of vision. However, these devices are of limited application because the pilots instantaneous field of view is limited according to the size of the collimating optic and the pilots position relative to that optic. That is, the pilot has the impression of looking through a distant porthole and head movement is required to see the edge of the field through the porthole.
Pupil-relay HUDs have been introduced to alleviate the "porthole" problem and these have the effect of locating the porthole in the plane of the pilots eyes and thereby provide for much larger instantaneous fields of view. Pupil-relay HUDs comprise a display tube followed by a relay optic which forms an intermediate image of the display in advance of the combiner which is powered so as to collimate the intermediate image for delivery to the pilot and to re-image the aperture stop formed by the relay lens as an exit pupil at the pilots eye position.
The design of the relay optic of a pupil-relay HUD is difficult if high-quality imagery is to be achieved over a reasonable field of view. For example because it requires to be relatively powerful it is difficult to prevent it introducing chromatic linespread of the display CRT. This can be corrected by increasing the complexity of the relay optic. Further, the complete system of relay optic and powered combiner optic must have an intrinsically low Petzval sum to be capable of providing a flat collimated image from a flat CRT and this complicates the relay optic since the combiner optic has to remain relatively simple to perform its dual purpose task. All of these factors lead to a comparatively large relay optic which in the environment of an aircraft cockpit, whether military or civil, produces packing problems in trying to fit the HUD into the existing aircraft roof-line. Prismatic wedges could be used in association with the relay optic to deviate its optical axis to conform to the aircraft roof-line but this proposal itself extends the axial length of the BUD and adversely affects chromatic linespread.
It is an object of the present invention to provide a new and improved form of head-up display which is comparatively compact and yet provides a comparatively wide instantaneous field of view to the operator.
SUMMARY OF THE INVENTION
According to the present invention there is provided a head-up display comprising a display device for generating information to be presented to an operator in superimposition with his forward view of the outside world, an off-axis reflectively-powered combiner optic for effecting said superimposition and a relay optic between the display device and the combiner optic, said relay optic being arranged to form an intermediate image of the displayed information in advance of the combiner optic and the combiner optic being arranged to collimate the intermediate image for delivery to the operator and to re-image the aperture stop formed by the relay optic as an exit pupil at the operator's eye position, wherein the relay optic comprises a relay lens and an axis deviation arrangement, said arrangement comprising a pair of surfaces which are mutually inclined at an acute angle each surface being both transmissive and reflective according to the angle of incidence of light thereon.
The reflective/transmissive surfaces are preferably in the f
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Abstract of Japan--vol. 11, No. 303 (P-622) and JP,A,62 094 816 (Mitsubishi), May 1, 1987.
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Epps Georgia Y.
Mack Ricky
Pilkington P.E. Limited
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