GB2202980A - Flight path indicator - Google Patents

Abstract

Colour signals representative of different angular sectors in which an approaching observer is situated, are generated by a plurality of individual light sources 3, beam-forming means 4 for directing light from each of the light sources through a respective colour filter 9 and lens system 5 to produce a plurality of differently coloured diverging light beams and means for directing the beams at different inclinations to define the different sectors. Such an arrangement is capable of producing higher light intensities combined with more satisfactory signal colours and more precisely defined colour sector boundaries than the single optic systems as used hitherto. The filters 9 and output mirrors 1 are adjustable to allow for movement of the assembly due for example to ship's movement. <IMAGE>

Description

Indicator Arrangements This invention relates to indicator arrangements of the kind designed to provide an observer approaching a location with an indication of his position with respect to a particular plane, hereinafter referred to as the approach plane, passing through the location. For example, arrangements of this kind are commonly used to provide pilots of aircraft approaching a landing strip, either on the ground or on an aircraft carrier, with a visual indication of the position of the aircraft relative to an approach plane passing through the landing strip, such arrangements being generally referred to as glide path indicators. However arrangements of this kind can also be used to define a safe channel for ships approaching a harbour, or a preferred track for land vehicles or pedestrians.

Such arrangements usually incorporate projector means for producing a light beam having angular separated portions of different colours which are observable in different positions relatively to the approach plane. The colour boundaries may be inclined at a small angle to the horizontal for use in aircraft guidance on approach and landing, or may be vertical for sea or land guidance.

At present, single lens optical systems are used to project the image of a slide, usually comprising coloured media in two or three different colours, close to the focal plane of the lens, so that an observer looking towards the projector will see a colour signal corresponding to the angular sector in which he is situated.

Several such projectors may be used, these being disposed sufficiently far apart to be resolved as separate lights over the distance at which they are of use. In this case, they may be differently set in vertical or azimuth angle to show different colours in the same angular sector to improve the precision of guidance and give rate of change information.

However, whilst undoubtedly providing useful visual guidance, these single optic systems suffer from a number of disadvantages as follows: (1) Because all the colours are imaged by a single lens, a degree of 'flare' from unwanted colours from adjacent zones appears however well corrected the lens may be. The effect of this is to degrade the saturation of required colour and is of particular importance in the green zone of a red, green, yellow system where the optical transmission of red and yellow transparent media may be greater than that of the green whose colour and transmission characteristics are most critical for visual range and colour recognition.

(2) Using ordinary coloured photographic media it is difficult to obtain adequate resolution without colour confusion at the boundaries in projectors of economic size and useful power.

(3) If separate glass or other transparent materials are used they are usually relatively thick (2-4 mm) in order to have the mechanical strength and density of colour required and are thus more difficult to focus sharply.

(4) Edges of adjacent colour media must be ground flat and parallel with precision without chipping and must remain in contact over the range of service temperatures and vibration conditions encountered.

Since the different coloured media usually have different coefficients of expansion and adsorption of radiant energy this is often difficult to arrange.

(5) A compromise focal position for colours of different dominant wavebands must be found.

(6) The maximum light intensity is limited by the aperture of a single lens which has to embrace the total field coverage of all the coloured zones employed.

(7) If dimming is employed for use at night or in variable visibility conditions it can only be applied without discrimination to all colours whether it be electrical, optical or mechanical.

An object of the invention is to provide an indicator arrangement in which the disadvantages are reduced or avoided.

According to the invention an indicator arrangement of the kind referred to, incorporating at least one projector means designed to provide an observer with colour signals representative of different angular sectors in which he is situated, comprises a plurality of individual light sources, beam-forming means for directing light from each of the light sources through a respective colour filter and lens system, each lens having a respective axis, to produce a plurality of differently coloured diverging light beams, and means for causing the beams to be directed from each projector means at different angles, to define said different angular sectors.

The means for causing the different light beams to be directed at different angles may, for example, comprise a corresponding plurality of opaque boundary-defining elements located in the focal planes of the respective lens systems between the lens systems and the associated light sources, the boundary-defining elements conveniently comprising appropriately positioned knife edge plates.

Such a projector is capable of producing higher light intensities combined with more satisfactory signal colours and more precisely defined colour sector boundaries than single optic systems, as used hitherto.

Moreover physically separating the colour filters and the sector boundary defining elements enables better control of both parameters to be achieved more readily.

The invention has the further advantage in that by associating each colour filter with its own lens the required colour can readily be achieved without regard to matching glass thickness to that of the other colours giving greater design freedom in the choice of material, and by disposing the colour filter in the front of the lens away from the maximum concentration of radiant energy at the focal plane reduces the risk of thermal cracking and the effect of thermochromism which otherwise changes the colour and generally reduces the transmission of some glasses. This therefore gives the possibility of employing lower cost, less temperature resistant colour filter materials. One or both surfaces of each colour filter may be sealed against moisture, the accumulation of dirt and the possibility of abrasion.

The boundary-defining plates are preferably of metal. The knife edges of such plates can readily be formed with precision by normal metal working techniques such as grinding or chemical etching.

The edges of such plates are robust, and as the critical surfaces are not in contact they can be located and adjusted with precision without the need for resilient mounting.

The plates can be re-positioned mechanically to give different colour segment widths and/or positions more readily than glass components in contact which require complete assembly replacement.

The invention has the further advantage that since the colours are separated into individual lenses, more precise focusing for each dominant waveband can be achieved.

Moreover dimming, for various visibility conditions or night operation can be better regulated over a wider range since, if required, the relative level of each colour can be set separately and the differential effect of electrical dimming on different colours compensated for.

By displacing the optical centre lines of each lens appropriately the relevant boundary image can be kept close to the lens centre giving best definition and light intensity at the transition.

For shipboard mounting, separate means are preferably provided for compensating for pitch and roll. Roll compensation is conveniently achieved by simultaneously rotating the boundary-defining plates approximately about the respective lens axes or by equivalent means, whereas pitch compensation can be achieved by deflecting the whole emergent beam by means of simultaneously movable mirrors disposed in front of the lenses.

Fine tuning of the positions of each coloured beam can then be achieved by differentially setting the appropriate mirrors on a single shaft which can then be driven as a whole assembly to compensate for pitch.

Adjustment of the positions of the boundary-defining plates and the mirrors to provide for roll and pitch compensation can be achieved by gravity or servo techniques. The arrangement requires the movement of relatively lightweight robust components within a housing to achieve precision stabilisation. It is thus potentially suitable for deck mounted shipboard use.

Several projectors could be used in combination to increase light intensity or refine the guidance angle.

Preferably there are at least two light sources.

One indicator arrangement in accordance with the invention in the form of a glide path indicator will now be described by way of example with reference to Figures 1 and 2 of the accompanying schematic drawing, in which Figure 1 represents an external view in diagrammatic form of a projector for use in the arrangement and, Figure 2 illustrates certain internal details of the projector.

Referring to the drawings, the arrangement comprises a projector 1 having, within an outer casing 2, three lamps 3 mounted within respective reflectors 4 designed to concentrate the light from the lamps towards respective colour filters 5 mounted adjacent to associated lenses 6, the light beams passing to separate mirrors 7 which direct the differently coloured beams, in this case yellow, green and red, through a window 8 at the front of the projector casing.

Each lens 6 is focussed upon a respective apertured or knife edge plate of metal or other opaque material, represented at 9, which is located between the associated reflector 4 and the lens, and which, by its position within the focal plane of the lens defines the angular limits of the emergent beam. The positions of the defining apertures or knife edges 9 may be such as to form a sharp or graded boundary between emergent beams of different colours.

The plates 9 are most easily formed with straight apertures or knife edges, but the apertures or knife edges could be given a curvature if necessary to compensate for lens aberrations, for example in a wide angular field projector.

In its simplest form, for airfield, harbour or other land based use, the aperture or knife edge positions may be fixed once the system has been set up. However for shipboard mounted equipment for guiding pilots in the approach and landing of helicopters and other aircraft it is necessary to compensate for ship movement in pitch and roll so that the projected beam boundaries remain relatively constant in spatial position. Compensation in roll may be achieved by synchronously rotating all the apertured or knife edge plates 9 together about the respective beam axes, as indicated by the arrows 11, through the same angle as the detected roll, whereas pitch may be accommodated by tilting the array of mirrors 7 about a transverse axis as at 12 through half the detected angle.Such an arrangement can be gravity stabilised, although it is preferably servo stabilised using signals from local sensors or from the ship's main gyroscope.

The projector 1 is conveniently carried by a frame 13 relative to which it can be adjusted about a nominally vertical axis for setting the azimuthal angle of the beams relative to the supporting structure.

Dimming filter turrets 14 are conveniently disposed between the plates 9 and the lens/colour filter assemblies 5, 6.

A removable panel, as at 15, is conveniently provided at the front of the casing for changing the lamps 3 if necessary, the remainder of the equipment being separately accessible through similar panels at the rear of the casing.

It will be appreciated that a projector similar to that described can be disposed on its side so as to give positional information relative to a vertical approach plane, for example for sea or land guidance.

Moreover although the three beams provided by the projector are shown as being coloured yellow, green and red, other colours can, of course, be employed if desired.

In addition, whereas the equipment illustrated has three optical systems, an indicator arrangement in accordance with the invention can in some cases have two, or four or more such systems depending upon the requirements for any particular case.

Claims (12)

1. An indicator arrangement of the kind referred to, incorporating at least one projector means designed to provide an observer with colour signals representative of different angular sectors in which he is situated, comprises a plurality of individual light sources; beam-forming means for directing light from each of said light sources through a respective colour filter and lens system, each lens having a respective axis, to produce a plurality of differently coloured diverging light beams; and means for causing the beams to be directed from each projector means at different angles, to define said different angular sectors.

2. An indicator arrangement as claimed in Claim 1 wherein said means for causing the beam to be directed at different angles comprises a corresponding plurality of opaque boundary-defining elements located in the focal planes of the respective lens systems between the lens systems and the associated light sources.

3. An indicator arrangement as claimed in Claim 2 wherein said boundary defining-elements comprise straight or curved knife edge plates.

4. An indicator arrangement as claimed in Claim 2 in which the boundary-defining elements have straight or curved apertures.

5. An indicator arrangement as claimed in any preceding claim, mounted on board a ship, including means to compensate for pitch and/or roll of the ship.

6. An indicator arrangement as claimed in Claims 2, 3 or 4 and 5 wherein compensation for roll is achieved by simultaneously rotating the boundary-defining plates approximately about the axes of the respective lenses or by equivalent means.

7. An indicator arrangement as claimed in Claim 5 or 6 wherein compensation for pitch is achieved be deflecting the beams from said filter and lens system by means of simultaneously movable mirrors.

8. An indicator arrangement as claimed in Claim 7 wherein the mirrors are differentially set on a single shaft which is driven as a whole assembly.

9. An indicator arrangement as claimed in Claims 5, 6, 7 or 8 wherein the means to compensate for pitch and/or roll is gravity or servo stabilised.

10. An indicator arrangement as claimed in any of Claims 2 to 9 wherein dimming filters are provided between each boundary-defining plates and each filter and lens systems.

11. An indicator arrangement as claimed in any preceding claim wherein the projector means comprises at least two individual light sources.

12. An indicator arrangement as hereinbefore described and illustrated in the accompanying drawings.