GB2129154A - Display units - Google Patents

Abstract

A display unit for a head-up display system which includes a periscopic arrangement (11a, b) between a combiner (3) and an observer's head position (0). The arrangement is effective to transmit light from a lateral portion of a display which has been reflected by the combiner (3) which otherwise would not be received by the observer without lateral head movement. The periscopic arrangement may be moved to a position out of the line of sight of the observer when it is not needed. <IMAGE>

Description

SPECIFICATION Display units This invention relates to display units for headup display. Such display units comprise a projector for projecting light representing a display onto a combiner for reflection thereby to provide an observer with an image of the display superimposed on his view of the distant scene through the combiner. The projector normally incorporates a collimating system so that the observer is presented with a virtual image of the.

display at infinity.

The rays of light leaving the projector are necessarily confined to an area known as an exit pupil, normally defined by the final lens of the projector optical system. This exit pupil and the observer's eye position with respect to the combiner, and hence the porthole through which the virtual image of the exit pupil produced by the combiner may be viewed determine the instantaneous field of view (I.F.O.V.) available at that eye position. It is generally desirable, however, to increase this field of view.

In our copending U.K. Patent application No.

2,076,1 78A there is disclosed a display unit for a head-up display system which incorporates, adjacent the exit pupil of the projector, a periscopic arrangement comprising a first reflective element and a second element parallel to the first element possessing both light transmissive and light reflective properties, the periscope arrangement being effective by successive reflections at the second and first elements to transmit light from lateral portions of the exit pupil which otherwise would not be received by the observer without lateral head movement.Such a display unit is, however, primarily intended for use in poor visibility conditions when the display unit may be used in conjunction with, for example a forward looking infra red sensor which provides an image of the forward distant scene on the combiner, and is generally redundant in good visibility conditions.

Whilst in the display unit described in our copending U.K. patent application No.

2,076,1 78A it is arranged that the second elements may be moved to a position where the periscope arrangement is inoperative for use in good visibility conditions so that the observer's view on the combiner of the image of the display is not obstructed, this then creates the complication of providing a satisfactory mechanism for their movement.

It is an object of the invention to provide a display unit for a head-up display unit having the capability of an increased l.F.O.V. wherein this difficulty is overcome.

According to the present invention in a display unit for a head-up display system comprising a projector for projecting light representing a display onto a combiner for reflection thereby to provide an observer with an image of the display superimposed on his view of the distant scene through the combiner, and incorporating at least one periscopic arrangement comprising a first reflective element and a second reflective element parallel to the first element, the said periscope arrangement is disposed between the combiner and the observer's head position, said periscopic arrangement being effective by successive reflections at said second element and said first element to transmit to the observer light from a lateral portion of the display which has been reflected by the combiner which otherwise would not be received by the observer without lateral head movement.

Normally two of said periscopic arrangements are provided between the combiner and the observer's head position, effective to transmit to the observer light from the two opposite lateral portions of the display.

In one particular display unit the or each periscopic arrangement constitutes a periscopic unit adapted to be displaceably secured to the display unit. Alternatively such a periscopic unit may be releasibly secured to the display unit. The or each periscopic arrangement may therefore be easily installed or removed as visibility conditions dictate.

Alternatively, the or each periscopic arrangement may constitute a periscopic unit mounted on a helmet worn by the observer. Such a periscopic unit may be releasibly secured to the helmet.

Two display units in accordance with the invention are hereinafter described with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a sectional longitudinal elevation of the first display unit; Figure 2 shows diagrammatically a sectional plan view of the unit of Figure 1; Figure 3 depicts the instantaneous fields of view available using the display unit of Figures 1 and 2 viewed from the observer's eye position, and Figure 4 shows diagrammatically a sectional plan view of the second unit.

Referring firstly to Figure 1 , the first unit to be described includes a projector unit indicated as 1 and a combiner 3. The projector unit includes a collimating lens system for producing a collimated image of a display presented on the screen of a cathode ray tube (not shown). The final lens 5 of the projector unit defines the exit pupil of the projector unit, as indicated by the line E in Figure 1.

The combiner 3 comprises a plane glass sheet with a semi-reflective film 4 on its surface nearer an observer 7. The combiner 3 is angled with respect to the optical axis of light leaving the projector unit 1 so as to reflect display light toward the observer 7, whilst at the same time allowing light from a distant scene to pass through the combiner 3 towards the observer 7. As in conventional display units, a virtual image of the exit pupil of the projector unit is thus formed by the combiner 3. This image constitutes a 'porthole', indicated by P subtending a certain solid-angle with respect to the observer's eye position, through which an image of the display on the screen of the cathode ray tube can be observed.

Referring now also to Figure 2, between the combiner 3 and the observer's eye position 0 there is also provided a periscopic unit 9 comprising two laterally symmetrical periscopic arrangements 11 a, 11 b. Each arrangement comprises an inner element 1 3a, 1 3b possessing both light reflective, and light transmissive properties, and an outer fully reflective element 1 spa, 1 sub parallel to the inner element 1 3a, 1 3b.

The unit 9 includes a frame (not shown) which supports the elements 1 3a, 1 3b, 1 spa, 1 sub and is itself displaceably and detachably mounted on the rest of the display unit by a manually operable mechanism (not shown) of any suitable construction.

In good light conditions the unit 9 is arranged to be displaced from the observer's line of sight of the combiner 3 either by displacement, or by complete removal. The l.F.O.V. of the observer 3, without any lateral head movement, of the porthole is then limited to the central portion C indicated in Figure 3, the light rays defining the positions P1 and P2 originating from positions inwards of the boundary of the screen of the cathode ray tube.

In poor light conditions the unit 9 is arranged to be in the position depicted in Figures 1 and 2. As indicated in Figure 2, after a double reflection by the elements 1 3a, 1 3b, 1 spa, 1 5b of the periscopic arrangement light rays originating from positions on the screen of the cathode ray tube radially outwards from the positions of the ray defining the positions Pr, P2 will extend the l.F.O.V. of the observer by the side lobes L1, L2 shown in Figure 3. The extreme lateral positions P3, P4 will then correspond to rays coming from positions towards the boundary of the screen of the cathode ray tube, these rays not being viewable by the observer without lateral head movement in the absence of the periscopic unit 9.Thus with the unit 9 in the operable position depicted in Figures 1 and 2, the porthole P subtends a larger solid angle with respect to the observers eye than in the absence of the unit. As the periscopic unit 7 is intended for use primarily in bad visibility conditions, the presence of the elements 1 3a, 1 3b, 1 5a, 1 sub in the observer's forward line of sight is not necessarily a disadvantage as usually a display derived from data produced by an infra-red or low light television sensor would be more use to the observer 7 than his direct view of the distant scene through the combiner. The partially light transmissive properties of the inner elements 1 3a, 1 3D does, however, afford the observer a complete view of the central portion of the porthole.

Referring now also to Figure 4, the second display unit to be described includes a periscopic unit 17 which is mounted on a helmet (not shown) worn by the observer 7, rather than being attached to the rest of the display unit as in the first display unit described herebefore. The principle of operation of the second unit is however the same as the first unit, and thus similar features are correspondingly labelled. The unit 1 7 again comprises two laterally symmetrical periscopic arrangements 1 9a, 1 9b each consisting of two parallel reflective elements 21a, b, 23a, b arranged as shown in the diagram.It will be noted however that the unit 17 is positioned past the point along the optical axis between the observer 7 and the combiner 3 at which the limiting light rays emanating from the normally just visible portions of the screen of the cathode ray tube cross the optical axis, i.e. the position X indicated in Figure 4. Thus light from the extreme lateral positions of the screen will first be reflected by the outer elements 21 a, 23b and then by the inner elements 23a, 23b to reach the observer's eyes.

As the inner elements 23a, 23b are chosen to be small enough not to restrict the observer's forward line of view, these elements can be fully reflective.

The choice of whether the outer elements 21 a, 21 b are fully reflective, or partially light transmissive will, however, depend on their exact position relative to the observer's eyes.

In similar fashion to the first unit the periscopic unit 17 is mounted on the helmet in such a way as to allow the unit to be displaced from the observer's field of view when it is not needed.

Claims (8)

1. A display unit for a head-up display system comprising a projector for projecting light representing a display onto a combiner for reflection thereby to provide an observer with an image of the display superimposed on his view of the distant scene through the combiner, and incorporating at least one periscopic arrangement comprising a first reflective element, and a second reflective element parallel to the first element, wherein said periscope arrangement is disposed between the combiner and the observer's head position, said periscopic arrangement being effective by successive reflections at said second element and said first element to transmit to the observer light from a lateral portion of the display which has been reflected by the cornbiner which otherwise would not be received by the observer without lateral head movement.

2. A display unit according to Claim 1 in which two of said periscopic arrangements are provided between the combiner and the observer's head position, effective to transmit to the observer light from the two opposite lateral portions of the display.

3. A display unit according to either one of the preceding claims in which said second element possesses both light transmissive and light reflective properties.

4. A display unit according to any one of preceding claims in which the or each periscopic arrangements, constitutes a periscopic unit displaceably secured to the display unit.

5. A display unit according to any one of the preceding claims in which the or each periscopic arrangement constitutes a periscopic unit releasibly secured to the display unit.

6. A display unit according to any one of Claims 1 to 3 in which the or each periscopic arrangement constitutes a periscopic unit mounted on a helmet worn by the observer.

7. A display unit according to Claim 6 in which the periscopic unit is releasibly secured to the helmet.

8. A display unit substantially as hereinbefore described with reference to the accompanying drawings.