Sign readable at speed

Details Sign readable at speed Sign readable at speed

1990-08-31

1992-11-24

Dorner, Kenneth J.

Card, picture, or sign exhibiting

Display with special effects

40454, 352 58, 352 81, G09F 1912

Patent

active

051651866

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND

The present invention relates to a sign readable at speed and is concerned with such a sign which, for example, is suitable for location by the side of a railway track for presenting information to a viewer of the sign travelling along the track.
U.S. Pat. Specification No. 3,568,346 discloses an optical sign of this type in which the functional assembly of the sign comprises an array of hexagonal or rectangular spherical biconvex lenses of positive power, and a corresponding tessellated array of identical optical objects, each object being disposed in the focal plane of the corresponding lens and being a representation of the information which the sign is to present. However the use of spherical biconvex lenses is disadvantageous due to spheric aberrations.
In order to reduce spheric aberrations British Patent Specification No. 2,149,527 provides an optical sign comprising hexagonal or rectangular lenses which are aspheric and optionally may be of the equivalent fresnel design. The optical object corresponding to each lens is disposed on a hexagonal sheet that conforms to the contour of the focal surface of the lens and is concave with respect to the front of the sign.
However providing the optical object on a surface which conforms to the focal surface of the aspheric lens is difficult.


SUMMARY OF THE INVENTION

Accordingly the present invention provides a sign for presenting information to an observer moving with respect thereto, characterised in that the sign comprises a plurality of elements linearly disposed with respect to one another, each of which elements comprises first and second coaxial lenses and a planar optical object consisting of a representation of the information which the sign is to present and in registry with said first and second lenses, the optical object of each element being substantially identical and said first lens constituting the external surface of the sign, wherein the virtual image of the planar optical object formed by said second lens of each element lies in the focal surface of the first lens of the element such that light rays emanating from any point on the optical object through the second lens emerge in a substantially parallel manner from the first lens.
By "substantially identical" optical objects there is meant identical optical objects or optical objects which differ cinematically from one another so that an animated image is presented to the moving viewer.
In a first embodiment of the invention the first lenses are aspheric and the second lenses are plano-concave lenses wherein the plane surfaces of the plano-concave lenses are most remote from said first lenses and the optical objects lie directly against said plane surfaces of said lenses.
In a second embodiment of the invention the first lenses are aspheric and the second lenses are fresnel lenses of negative power in which the fresnel grooves are formed in the surface nearer to the first lenses, the objects being mounted at a fixed distance from the second lenses, in the direction away from the first lenses.
In a third embodiment of the invention the first lenses are surrounded by an opaque diaphragm, defining apertures which are coaxial with the lenses, such that the functional area of the lens is reduced. Where the first lenses are hexagonal aspheric lenses, the diaphragm may define hexagonal apertures, which apertures may be displaced by 30.degree., with respect to their associated lens, about their common axis. The functional area of the lens may be reduced such that it corresponds with the area of the aperture.
In a fourth embodiment of the invention, the first lenses may comprise fresnel lenses.


BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
FIG. 1 is a partially sectioned front view of one type of known optical sign,
FIG. 2 is a sectional view taken along line 2--2 of the sign of FIG. 1,
FIG. 3 is a perspective vie

REFERENCES:
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patent: 3712727 (1973-01-01), Bonnet
patent: 4117615 (1978-10-01), Gomolak
patent: 4145131 (1979-03-01), Yevick
patent: 4542958 (1985-09-01), Young
patent: 4867514 (1989-09-01), Waldron

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