Head-up display

Details Head-up display Head-up display

1993-09-07

1993-09-07

Lerner, Martin

Optical: systems and elements

Holographic system or element

Head up display

359 16, 359630, G02B 532, G02B 2710, G02B 2742

Patent

active

052434486

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a head-up display arrangement particularly suitable for land or sea vehicles or helicopters. Head-up displays, which present displays of indicia and/or measurement indications superimposed on any external view seen by a pilot, were originally developed for and are now normal equipment in high-speed military aircraft. Their advantage is that they present essential information to a pilot without requiring him to redirect or (if collimated) refocus his vision. This would also be a useful advantage in land and sea vehicles and in helicopters, but for such applications it is preferable that much less expensive head-up display arrangements should be devised.
A major concern in all head-up displays is to provide sufficient contrast between the display and the background, and to minimise unwanted reflections of ambient light from the display unit, which tend to seriously degrade the contrast and visibility of the display indicia. In many designs for use in military aircraft expensive high-brightness display tubes are used to maintain sufficient contrast.
The object of the present invention is to provide a colour head-up display using a comparatively simple and inexpensive arrangement which achieves a considerable reduction in the proportion of ambient light which can be reflected from the display into the observer's field of view.
According to the present invention there is provided a head-up display arrangement for a vehicle, for presenting an optical display of information superimposed on a forward external view seen by an observer in the vehicle, including display means for producing a display of information, an optically transmitting diffractive element placed below the observer's line-of-sight to the external view, light from the display means (when in use) being incident on the diffractive element from a direction below and forward of the diffractive element and being diffracted by the diffractive element onto a partially relecting surface and thence to the observer's eye and characterised in that the diffractive element is inclined towards the rear of the vehicle.
Light is incident on the diffractive element from a direction below and forward of the diffractive element (i.e. nearer the front of the vehicle) rather than below and behind it in order to provide greater rejection of unwanted ambient light.
The partially reflecting surface may be the windscreen of the vehicle of a separate combiner. Such a combiner, which would be placed between the windscreen and the observer, may be adjustable so that the display light reflected off its surface is visible and in a suitable position in the field of view to observers of differing heights. The windscreen or combiner may have a coating comprising a narrow band filter which reflects at the display light wavelength without substantially reducing transmission of the external view and helps to reduce the unwanted effects of stray ambient light. The combiner may be comparatively thin and planar and should be used if curvature of the windscreen would distort the image of the display seen by the observer. Furthermore, it may be mounted at an angle which may be better for viewing and improving rejection of unwanted reflections.
For most installations, the optimum value of the angle of inclination of the diffractive element to the horizontal, .phi., lies between 5.degree. and 30.degree.. This tilting of the diffractive element makes it easier to mask or screen unwanted upward reflections from the observer, without vignetting his view of the display information.
A high value for the diffraction angle, .theta., of the diffractive element is advantageous from the point of view of sunlight reflections. For most installations the optimum value of .theta. lies between 5.degree. and 45.degree.. Preferably, the diffraction angle .theta. is such that the central ray of the head-up display arrangement's field of view enters the diffractive element at an angle parallel to or diverging away from the windscreen. Under such conditions there is a further improve

REFERENCES:
patent: 4613200 (1986-09-01), Hartman
patent: 4818048 (1989-04-01), Moss
patent: 4832427 (1989-05-01), Nanba et al.
patent: 4880287 (1989-11-01), Moss
patent: 4932731 (1990-06-01), Suzuki et al.
patent: 4967191 (1990-10-01), Iino

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