GB2109606A - Display device and method of manufacture - Google Patents

Abstract

A display device comprises a surface 3, Fig. 2, from which planar members 2, preferably L-shaped members 10, Fig. 4 extend perpendicularly. The members 2, 10 are arranged along edges 4 of a grid defining cells on the surface 3. In use, when illuminated from a first direction 13, parts 11 of the members 2, 10 cast shadows to form a first image, and when illuminated from a second direction 14, parts 12 of the members 2, 10 cast shadows to form a second image. Illumination from the two directions can be provided by sunlight or artificial light. The device may be made by forming first and second images by polygraphic screening or a half-tone process (Fig. 1), calculating the shaded areas required for each cell on the surface 3 and then constructing the parts 11, 12 of the correct height (h, Fig. 5) to cast shadows to form pictures (Figs. 6 and 7) on the same surface depending on the direction of light. <IMAGE>

Description

SPECIFICATION Display device and method of manufacture This invention relates to a display device and to a method of manufacturing a display device.

Such a display device can be used for, for example, political posters, propaganda, decoration and advertisements.

A display device is known which has geometrical forms disposed on a grid to form an image.

A disadvantage of known display devices is their static nature, complexity of preparation of space geometrical forms and most of all the availability of only a single image on one and the same viewing plane.

It is desirable that a display device should be capable of providing two images on one and the same viewing plane.

According to the present invention, there is provided a display device comprising a surface and a plurality of planar members extending perpendicularly from the surface and arranged along the edges of a grid defining individual cells on the plane surface, the arrangement being such that, in use, each member, when illuminated or viewed from one of first or second directions, respectively casts a shadow to form part of, or includes a face which forms part of, the respective first or second image, but when illuminated from the other of said first and second directions does not substantially effect the second or first image respectively.

Preferably, said members are formed of a rigid non-transparent material and said surface is a plane surface.

The grid can be a square grid, and each cell can have two adjacent sides on which two of said members can be located at right angles to one another.

Advantageously, the planar surface is disposed, or intended to be disposed, vertically, and lines forming the square grid are at an angle of 450 to the horizontal.

Preferably each member is rectangular and dimensioned such that, when illuminated from a respective first or second direction, it casts a substantially square shadow to form part of the respective first or second image.

Preferably, for each cell, two members are integral with one another to form a combined L-shaped member, whose edge is secured to said surface.

The present invention also provides a method of producing a display device as first defined, the method comprising the steps of: (a) forming first and second images by polygraphic screening or a half-tone process from drawings or photographs; (b) calculating the shaded area for each portion of the screen for the first and second images; and (c) arranging planar members on the surface so as to provide the required shaded areas for the first and second images when illuminated from said first and second directions respectively.

In the method of producing a display capable of providing two images on one and the same viewing plane, one must start from two drawings or two photographs, preferably non-colour photographs, which are submitted for screening using a polygraphic screen or which are submitted to a half-tone process. Then one has to calculate separately the areas of the screen calls and set each area equal to the area of a square. The side of the square is used to determine the length of the base of the planar members or platelets, while their heights are obtained analytically dependant on the angle of incidence of the illumination. The platelets of sizes thus determined are provided by combined L-shaped members including an angle of 900 therebetween.For each cell, the area of the shadow projected by the first planar member corresponds to the area of the dots of the first image and the area of the dots of the second image corresponds to the area of the shadow projected by the second planar member, depending on the images to be formed it is possible that a given cell can have one, two or no platelets or planar members.

A display device according to the present invention should have the following properties: (i) it carries a double amount of information on one and the same viewing plane; (ii) the images are kinetic in their nature and are variable and the variation of the images is not accomplished by mechanical or any other devices, but is a result of, for example, the Earth's rotation around its axis (in sunshine) or of the movement of the observer (in conditions of diffuse light). During the evening, the variation of the images can be obtained by means of a lighting installation, which is switched-on periodically at the left and right side of the decorative panel, respectively; (iii) it should be possible to obtain large images, with a high degree of clarity.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a fragment of an image, produced by a polygraphic screen or a half-tone process; Figure 2 shows a fragment of the image of Figure 1 when formed by a display device according to the present invention; Figure 3 shows the direction of orientation of a display device illuminated by the sun; Figure 4 shows a detail of a combined L-shaped member of a display device; Figure 5 shows the analytical solution for the determination of the heights of the members; and Figures 6 and 7 show two views of a display device according to the present invention.

Two black-white drawings or two non-colour photographs are screened using a polygraphic screen or subjected to a half-tone process, in order to produce two images comprising dots of varying sizes, as shown in Figure 1.

A display device comprises a plane surface 3 to which planar members or platelets 2 are attached.

The plane surface 3 is divided by lines 4 into a square grid having square cells 1. The lines 4 are at an angle of 450 to the horizontal. As shown in Figure 4, a combined L-shaped member 10 comprising a planar member 11 and a second planar member 12 is provided for each square cell 1. The first member 11 is intended to form part of an image viewed from a first direction 13, whilst the second member 12 is intended to form part of an image viewed from a second direction 1 4.

The transition between the polygraphic screen image of Figure 1 and an image produced according to a grid as shown in Figure 2 will now be described. The area of the screen dots of the image shown in Figure 1 is calculated using the equation

where F denotes the area of the dot (in mm2), and d is the mean diameter of the point (in mm). The area F of the dot which can be sealed up or down depending on the size of the display device, is set equal to the area of a square cell 1 with side a, wherefrom the side a of the square is obtained, taking into account the equality of the two areas. In fact, a is the length of the base of one planar member or platelet 2, which is intended to project itself as a shadow having an area adequate for the corresponding dot of the image obtained from the polygraphic screen, as it is shown in Figure 1.In other words, the shadow cast by each planar member 2 in its respective square cell 1- is sized so as to provide a required degree of shading in that cell 1. For illumination incident at an angle P the height of each planar member 2 is determined using the equation h = Tan P, where h denotes the height of the planar member 2 in mm, a the side of the square in mm which is equal to the length of the shadow for illuminating radiation, e.g. sunlight, incident at an angle ,B. With an angle of incidence of the illuminating radiation and determined using a trigonometric dependence, the length of the projected shadow is determined.For example, for a shadow 20 x 20 mm and a planar member with a height of 7 mm, we have: 7 - =0,3500 = Tan P, 20 and therefore: p= 19 19' or, in other words, each screen cell 1 can be a shaded screen cell obtained using a platelet 2 of a width a and height h, which are calculated using the approach given here above.

The display device, for illumination by sunlight, should in the northern hemisphere be located as indicated in Figure 3, i.e. disposed vertically and facing south. With reference to Figure 4, when the sunlight is incident from the direction 14, the planar member 12 casts a shadow to form part of the second image in the respective square cell 1. The first planar member 11 only casts a narrow shadow, whose area is negligible in comparison with the area of the shadow thrown by the planar member 14.

During the afternoon, when the sunlight is incident from the first direction 13, the shadow thrown by the second planar member 12 is in the form of a thin line, which is not visible, while the shadow of the first planar member 11 is of an area necessary for the square cell 1 in the first image.

As can be seen from Figure 1, in polygraphic screening, the images are obtained as dots and their mean diameters can be determined by measurement. On this basis, the analytical dependences are deduced, which enable both the height h and width a (or B) of the planar members 2 which form the images on the plane surface 3 to be determined. For a typical display device the dimensions can be determined according to the following equations:

where h1, B1 are the height and width respectively, of the planar members 2 used for creating the first image, d1 the diameter of the dots from the first image (Figure 1); h2, B2 are the height and width respectively of the planar members 2 used for creating the second image, and d2 the diameter of the dots forming the second image (Figure 1).

Figure 6 shows a view of a display device, when viewed from a first direction so that an image of a lorry is seen. When viewed from a second direction, shown in Figure 7, an image of a bus is seen.

Claims (10)

1. Display device comprising a surface and a plurality of planar members extending perpendicularly from the surface and arranged along edges of a grid defining individual cells on the plane surface, the arrangement being such that, in use, each member, when illuminated or viewed from one of first or second directions, respectively casts a shadow to form part of, or includes a face which forms part of, the respective first or second image, but when illuminated from the other of said first and second directions does not substantially effect the second or first image respectively.

2. A display device as claimed in Claim 1 , where said members are formed of a rigid nontransparent material.

3. A display device as claimed in Claim 1 or 2, wherein said surface is a plane surface.

4. A display device as claimed in Claim 1, 2 or 3, wherein the grid is a square grid, and each cell has two adjacent sides on which two of said members can be located at right angles to one another.

5. A display device as claimed in Claim 4, when appendant to Claim 3, wherein the plane surface is disposed, or intended to be disposed, vertically, and lines forming the square grid are at an angle of 450 to the horizontal.

6. A display device as claimed in Claim 5 or 6, wherein each member is rectangular and dimensioned such that, when illuminated from a respective first or second direction, it casts a substantially square shadow to form part of the respective first or second image.

7. A display device as claimed in Claim 4, 5 or 6, wherein, for each cell, two members are integral with one another to form a combined L-shaped member, whose edge is secured to said surface.

8. A display device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

9. A method of producing a display device as claimed in any preceding claim, the method comprising the steps of: (a) forming first and second images by polygraphic screening or a half-tone process from drawings or photographs; (b) calculating the shaded area for each portion of the screen for the first and second images; and (c) arranging planar members on the surface so as to provide the required shaded areas for the first and second images when illuminated from said first and second directions respectively.

10. A method of producing a display device as claimed in Claim 6 or 7, the method comprising the steps of: (a) forming first and second images by polygraphic screening or a half-tone process from drawings or photographs; (b) calculating the shaded area for each cell for the first and second images; and (c) for each cell, calculating the height and width of a first rectangular planar member for the first image, and a second rectangular planar member for the second image, suitable for casting a respective square shadow in the respective cell when the display device is illuminated from the first direction or from the second direction, respectively; and (d) providing each cell on the plane surface with a combined L-shaped member which comprises a first rectangular planar member and a second rectangular planar member, and which includes an angle of900.