Optical Signalling

Abstract

Visual display devices containing a matrix of areas which can be selectively illuminated to display a predetermined legend or symbol. In place of individual lamps used hitherto, the proposed visual display devices utilise bundles of optical fibres coupled to a reduced number of light sources, thus simplifying the assocated control circuitry.

Description

BACKGROUND OF THE INVENTION

This invention relates to a visual display device for use in conveying information to the occupants of moving transport. The main application of the invention is for use in displaying information to drivers and passengers of motor vehicles travelling on motorways.

In known U.K. motorway visual display devices, a rectangular display area is defined by a matrix of usually 139 electric light bulbs and to provide a display such as numerals for speed limits, direction arrows, warning words etc. selected bulbs are illuminated. These devices are adapted to display any one of 13 meaningful signs and this is done by routing 13 electrical conductor wires and a return wire to the device. By transmitting a signal down the appropriate wire, the appropriate meaningful sign is displayed as the signal is routed through a matrix of diodes which switch on the light bulbs which make up the sign. Each bulb is contained at one end of a cylindrical housing with a part parabolic mirror behind the bulb. The other end of the housing is placed against a transparent pin spot screen which also encloses the openings of all the other light bulb housings forming the front of the matrix.

As will be appreciated, the electrical wiring and switching system of a known display device as described above is complicated and therefore expensive. It has another disadvantage in that it does not indicate to the controllers desk, which bulbs are not functioning; it would be possible to monitor each bulb individually, but the increase in cost and complexities of the device would make this impractical. A further disadvantage of the known arrangement is that the mirrors behind the bulbs tend to cause "ghost images."

SUMMARY OF THE INVENTION

An object of this invention is to provide a visual display device, particularly but not exclusively for motorways which at least in its preferred form, obviates or mitigates the abovementioned disadvantages.

According to the present invention there is provided a visual display device comprising a display area made up of a matrix of regions, a plurality of bundles of optical fibres with each bundle having the individual ends of the fibres grouped together at one end of the bundle to define an input and the other individual fibre ends splayed apart and connected to regions of the display area which make up a meaningful sign, so that illumination of any input results in the display of a meaningful sign, and each of said regions being defined by an optical cell which provides a collimated beam of light upon the illumination of any of said inputs having an optical fibre leading to such cell.

Preferably, there is an illumination means comprising an electric light bulb for each input. Each electric light bulb is preferably a tungsten halogen bulb with a reflector assembly.

Each of said regions is preferably constituted by an optical unit including a length of clad optical rod against one end of which butts the end of the optical fibre or ends of the optical fibres terminating at the region, and a converging lens positioned on the axis of the rod so that light issuing from the rod is eventually directed into a beam with a divergent angle of approximately 5.degree..

Upon illumination of an input therefore, the regions connected optically to the splayed ends of the individual fibres are illuminated and the appropriate meaningful sign is displayed.

The optical fibres therefore disperse the light from a single source and produce a meaningful sign thereby.

It will be appreciated that various regions may be common to two or more meaningful signs and because of this such regions will be illuminated if either or any one of such meaningful signs is displayed. In this connection the optical rod of the optical unit of each regions acts as a light integrating chambers to channel the light from any of the optical fibres leading thereto onto the same axis as the lens. This is a distinct advantage because off-axis fibres would cause projection of the light beam from the lens in an off axis direction with a divergent half angle of approximately 5.degree..

A display device according to a preferred feature of the invention and adapted for U.K. motorways requires only 13 bulbs as compared with 139 bulbs in the known device. If, as preferred, tungsten halogen bulbs are used, the power rating of each is 70 watts, which is much higher than the wattage of each of the bulbs in the conventional display device. However, in the conventional device the sign with the maximum number of bulbs lit at any one time, requires 49 bulbs to be illuminated and this would require a power of 140 watts, so the device of the invention can present a saving in power.

Moreover, much of the complicated electrical circuitry can be removed because in actual fact the switching is replaced by the optical fibres. It is estimated that in the known device 500 diodes are required in the switching circuit, all of which are eliminated by the present invention.

The device is preferably in two parts, one part comprising the optical fibres and display area (which would be almost maintenance free) and the other part comprising the illumination means and associated circuitry, which could be replaced in its entirety if a fault developed, would require a power of approximately 120 watts.

The device of the invention provides the additional advantage that the controller can learn quickly if one of the bulbs fails, because then no current will be drawn when the controller sets that bulb for illumination, and corrective action can be taken immediately.

Because each sign requires the illumination of only one bulb, it is easy to provide for the display of any of the meaningful signs in any colour, by positioning the appropriate colour filter between the bulb and the associated input. Between each input and its bulb there may be a position adjustable member which carries several different coloured filters, the member being adjustable to position any one of said filters between the source and input so that the colour of the sign displayed can be readily adjustable.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, wherein:

FIG. 1 is a sectional elevation of a display device according to the invention, parts being omitted for clarity; and

FIG. 2 is a sectional elevation to an enlarged scale, of one of the optical units shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 the display device is for motorway use and includes a box, 1, preferably made of lightweight moulded plastic of which the front face 2 is defined by a diffusing screen formed from pin-spot or stippled glass or clear plastic. In an alternative arrangement, a screen of vertical, cylindrical reeded plastic may be used. The light sources, 3 and 4, of which only two of the 13 are shown for clarity, consist of 24 volt 70 watt tungsten halogen bulbs mounted in front of dichroic reflectors 3A, 4A. These reflectors 3A, 4A focus the light from the bulbs on to the common ends of multi-tail fibre optic light guides 7 and 8, and the splayed fibres route the light to various optical units, 5 and 6, of which only two of the 139 are shown for clarity.

Referring to FIG. 2, the optical unit consists of a cylindrical housing 10, made of light metal or plastic and containing at one end a converging lens 12 which can be an aspheric type made from glass or preferably moulded clear plastic. At the other end is a short tube containing a length of fibre optic clad rod 9 which butts on to the end or ends of fibre optic light guides 11 and 13. The front face of the clad rod 9 is placed just at the focal point of the converging lens 12 to provide a collimated beam which is then slightly diverged by the diffusing screen 2 to the required amount according to the specification. The said front face of rod 9 further has a thin slice of image conduit 15 or face plate (shown exaggerated in size for clarity) applied thereto by the transparent adhesive "Crystic," which is a transparent polyester resin manufactured by Scott-Bader. The plate 15 is of slightly larger diameter than rod 9 and is approximately 2 m.m. thick. The function of the plate 15 is to flatten out the polar diagram of the light intensity issuing from the optical cell thereby improving the cosmetic appearance of the display device as a whole when it is operative. The 139 optical units are then held in position by a metal or plastic matrix, not shown.

It should be noted from FIG. 1 that an optical unit, e.g., 5 can be shared by several legends, e.g., bulbs 3 and 4, simply by routing the appropriate light guides, 11 and 13 respectively, to the clad rod face 9. By means of rod 9 off axis cones of light emanating from the off-axis light guides are integrated into an on axis cone of light which is collimated by the lens as shown by the ray diagram in FIG. 2.

Claims

We claim:

1. In a visual display device of the type comprising a display area made up of a matrix of regions, a plurality of bundles of optical fibres with one end of each of a plurality of individual fibres grouped together at one end of the bundle to define an input and the other ends of said individual fibres separately connected to different regions of the display area so that illumination of differing inputs results in the display of differing meaningful signs, a light source for each input, and means for selectively activating the said light sources, the improvement according to which

each of the said regions of the display area is defined by an optical cell comprising a length of clad optical rod against one end of which butts the end of at least one optical fibre terminating at the corresponding region, with a plurality of optical fibres butting said one end of at least some of said rods, and a converging lens positioned on the rod axis to collect light issuing from the other end of said rod and to form said light into a collimated beam, and said display device also comprises

a light diffusing screen covering said optical cells and operative to diverge the collimated beams into beams with a small angle of divergence, whereby to render the whole of any displayed meaningful sign visible from a substantial distance within a relatively narrow angle of view.

2. A device according to claim 1, comprising an illumination means in the form of an electric light bulb for each input, said device being made in two separable parts, one part comprising the optical fibres, cells and screen and the other part comprising the illumination means and associated circuitry.

3. A device according to claim 1, wherein each optical cell has a thin slice of image conduit at the end of the rod from which light issues in order to flatten the polar diagram of the collimated beam issuing from the lens.

4. A visual display device according to claim 1, including a multi-coloured light filter associated with each input of each bundle of fibres, said light filter being capable of position adjustment relative to the input so as to change the colour of the light transmitted through said bundle.