GB2174276A - Image enlarger for a cathode ray tube - Google Patents

Abstract

An image enlarger for a cathode ray tube has a curved concave face 3 on one side to fit against the face- plate 5 of the CRT and a display face 4 on the opposite side. The enlarger comprises an assembly of light guides in the form of adjoining elongate cells 2 with open ends and internally reflective walls, extending radially with respect to the concave face 3 of the enlarger so that the display face 4 is larger than the concave face. Each cell tapers towards the concave face so that the image element transferred through the cell to the display face is enlarged. The cells may be formed by tapered tubes of bright-anodised aluminium or chromium-plated plastic 14 glued together and preferably having a hexagonal cross-section to give the enlarger a honeycomb structure. A number of these enlargers (7) can be arranged one in front of each CRT of a composite display screen composed of a matrix of CRTs (8) mounted next to one another, the enlargers abutting one another at the edges of their display faces (4) so as to bridge the gaps between the images on the CRTs. <IMAGE>

Description

SPECIFICATION Image enlarger for a cathode ray tube The invention relates to an image enlarger for a cathode ray tube having a spherically curved face-plate, the enlarger being constructed to be arranged on the face-plate and having a display face on one side and a spherically curved concave face on the opposite side with substantially the same radius of curvature as the outer surface of the face-plate, and comprising an assembly of light guides arranged side-by-side and each of which extends radially with respect to the concave face of the enlarger from this face to the display face.

In use, an image enlarger of this kind is arranged with its concave rear face in contact with the face-plate of the cathode ray tube.

The rear face of the enlarger is defined by the rear ends of the assembled light guides and has a boundary which corresponds in shape and size to the boundary of the display area of the face-plate of the cathode ray tube, which is the area within which an image can be formed on the face-plate. Since the light guides extend radially with respect to the rear face of the enlarger they are distributed over a larger area at the front face, i.e., the display face, of the enlarger than at the rear face, resulting in an enlarged display area at the front face, which face is defined by the front ends of the assembled light guides.

Such image enlargers can be used on a multi-tube composite display screen to obliterate the gaps between the images on adjacent tubes in the screen. Such a display screen is composed of a matrix of cathode ray tubes mounted next to one another on a wall, for example, each tube forming part of a display device such as a TV display monitor and being arranged to display a part of the overall image to be transmitted. Since the image on each tube does not extend right to the periphery of the face-plate of the tube, and also each tube usually has a frame around the face-plate, gaps or "dead regions" exist between the images on adjacent tubes and these gaps mar the overall visual effect of the composite display. By fitting an image enlarger of the above kind on the face-plate of each tube, these gaps can be bridged.The size of each enlarger should be such that the display faces of adjacent enlargers are contiguous, thus giving the impression of one large continuous screen.

An example of this use is described in United States Patent Specification 3,498,864, which discloses an image enlarger of the above kind with fibre-optic light guides. these light guides consist of solid plastics light conductors made by a compression-moulding process. In this process, sheets of a plastics material are produced with a fan-shaped array of light conductors moulded on one side of each sheet. A low-index cladding is provided on the conductors and then several of the sheets are cut to a desired shape and stacked on one another to form a unitary assembly which constitutes the image enlarger. the light conductors may be tapered, but as a result of forming them on sheets they are slightly spaced apart, leaving areas between them through which no light is conducted or transferred.

Also, the sheets add to the weight of the enlarger, which is an important consideration when the enlarger is used on a multi-tube composite display screen. A heavy enlarger is difficult to manipulate when erecting the screen, which may consist of some hundreds of cathode ray tubes and extend to a considerable height above the ground. The process of manufacturing this known enlarger is quite complex and is costly in terms of time and the amount of material used.

United Kingdom Patent Specification 908,754 discloses a fibre-optic image enlarger which comprises an assembly of light conductors in the form of glass rods, which may be tapered and may be of square cross-section, arranged in side-by-side relationship with one another. this image enlarger forms the actual face-plate of a cathode ray tube, however, and therefore cannot be used in the manner described earlier herein on a multi-tube composite display screen. It is also costly to produce and again, consisting as it does of solid glass rods, is heavy.

It is an object of the present invention to provide an image enlarger of the kind described in the opening paragraph, which is of light weight and is cheap to produce.

According to the invention there is provided an image enlarger for a cathode ray tube having a spherically curved face-plate, the enlarger being constructed to be arranged on the faceplate and having a display face on one side and a spherically curved concave face on the opposite side with substantially the same radius of curvature as the outer surface of the face-plate, and comprising an assembly of light guides arranged side-by-side and each of which extends radially with respect to the concave face of the enlarger from this face to the display face, characterised in that the light guides are formed by elongate cells with internally reflective longitudinal walls and with ends through which light can pass located at the two faces of the enlarger, each cell tapering towards its end which is located at the concave face of the enlarger so that adjacent cells adjoin one another throughout their length.

Provided that the wails of the cells are made sufficiently reflective, the air in the cells will form a satisfactory light-transfer medium.

this results in a very lightweight construction in which the only material required is that needed to form the walls of the cells.

The ends of each cell may simply be left open to permit the necessary passage of light through the ends of the cell.

A preferred embodiment of the invention is characterised in that the cells have a transverse cross-section of regular polygonal shape, and except for the cells at the periphery of the enlarger, each cell is adjoined on all sides by other cells so that there are no interstices between the cells. Discounting the negligible thickness of the walls of the cells, the absence of interstices between the cells means that the whole of the image on the face-plate of the cathode ray tube can be transferred to the display face of the enlarger and that the entire area of this face is available for the display of the enlarged image.

A particularly strong and optically efficient construction is obtained if in the above embodiment the transverse cross-section of the cells is of hexagonal shape so that the enlarger has a honeycomb structure.

An embodiment of particularly simple construction is characterised in that each cell is formed by a tapered tube with an internally reflective wall. The tube may be made of aluminium and be bright anodised on its inner side, or it may be moulded from a plastics material and the wall of the tube be chromium-plated so as to be internally reflective. the tubes may be secured to one another by an adhesive.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a front perspective view of an image enlarger according to the invention arranged on the face-plate of a TV tube, the enlarger having a honeycomb structure with cells which are formed by tapered tubes of hexagonal cross-section; Figure 2 is an enlarged perspective view of one of the tapered tubes which form the cells of the enlarger shown in Figure 1; Figure 3 is a perspective view illustrating a method of assembling the tubes to form the enlarger shown in Figure 1; Figure 4 is a plan view of a portion of a corrugated strip used in an alternative method of constructing an image enlarger according to the invention; Figure 5 is an end view of the corrugated strip shown in Figure 4; Figure 6 is a front edge view of a portion of the strip;; Figure 7 is an edge view of portions of a number of corrugated strips which are secured together to form cells of an image enlarger according to the invention; Figure 8 is a schematic front view of a composite display screen comprising a number of display monitors with image enlargers according to the invention arranged in front of the cathode ray tubes of the monitors, the cells which form the light guides of the enlargers being omitted for the sake of clarity and only the outlines of the enlargers being shown; Figure 9 is a side view of the display screen of Figure 8, drawn to a larger scale; Figure 10 is a rear perspective view of one of the image enlargers of the display screen separated from the associated cathode ray tube.

The image enlarger shown in Figure 1, and designated 1, comprises an assembly of light guides which are formed by open-ended elongate cells 2 with internally reflective walls, each cell extending from the rear face 3 of the enlarger to the display face 4 at the front of the enlarger. The rear face 3, which is defined by the rear ends of the cells 2, is concave with a spherical curvature of substantially the same radius as the spherically curved convex outer surface of the face-plate 5 of the TV tube 6 on which the image enlarger is arranged, so that the rear ends of all the cells bear against the face-plate 5. The means whereby the enlarger is held against the faceplate 5 are not shown in Figure 1 but may be of any convenient form.The boundary of the rear face 3 of the enlarger corresponds in shape and size to the boundary of the display area of the face-plate 5, which is the area within which an image cah be formed on the face-plate. The cells 2 all have the same length and extend radially with respect to the rear face 3 of the enlarger, so that the display face 4, which is defined by the front ends of the cells, has a convex spherical curvature whose centre coincides with the centre of curvature of the rear face 3. Each cell tapers towards its rear end so that adjacent cells adjoin one another throughout their length. In the embodiment shown the cells have a hexagonal transverse cross-section so that the enlarger has a honeycomb structure.The cells may have any other regular polygonal crosssection which will allow each cell, except for the cells at the periphery of the enlarger, to be adjoined on all sides by other cells so that there are no interstices between the cells.

In the use of the image enlarger the air in the cells 2 acts as a light-transfer medium which, by virtue of the reflectivity of the walls of the cells, can transfer through each cell from the rear end to the front end thereof an element of the image formed on the face-plate 5 of the TV tube 6. Due to the tapered shape of the cells the image element is enlarged in the transfer. Moreover, since each cell extends radially with respect to the spherically curved faces of the enlarger, the cells are distributed over a larger area at the display face 4 than at the rear face 3 so that the display area provided by the display face of the enlarger is larger than the display area of the face-plate 5 of the TV tube 6.Since there are no interstices between the cells 2, discounting the negligible thickness of the walls of the cells the entire area of the display face of the enlarger is used for the display of the enlarged image.

In the composite display screen shown in Figures 8 and 9, image enlargers 7 of the above construction are arranged one in front of each of the cathode ray tubes 8 of the ríine display monitors which form the screen. The enlargers abut one another at the edges of their display faces 4 to bridge the gaps between adjacent tubes. The contiguous display faces of the enlargers appear as one large screen when viewed from a distance, each face displaying a part of the composite image transmitted by the tubes 8.

In the arrangment shown in Figures 8, 9 and 10, the cathode ray tubes 8 are mounted in separate compartments in a housing 9. The means by which the tubes are supported in the compartments are not shown since they are not relevant to the invention. One method of supporting the enlargers 7 in front of the tubes 8 is shown in Figures 9 and 10 and consists in providing a rectangular wooden or metal frame 10 around each enlarger to fit between the horizontal walls 1 lea and the vertical side walls 11 b of the compartment in which the respective tube 8 is mounted. The frame 10 does not completely enclose the assembly of cells 2 forming the respective enlarger; the front part of the assembly is left free to allow adjacent enlargers to abut one another at their front edges.The front- edge of the frame 10 is in contact with the periphery of the assembly of cells 2 but to the rear of the front edge of the frame there is a gradually widening space between the frame and the assembly of cells, which space is filled with polyurethane foam as shown at 12 in Figure 10. Four tie rods 13 extend rearwardly from the corners of the frame 10 for attachment to the housing 9 to secure the enlarger on the face-plate of the respective cathode ray tube 7.

The cells of the image enlarger 1 in Figure 1 are formed by tapered tubes 14 of hexagonal cross-sectionl, one of which is shown on a very much larger scale in Figure 2. Each tube may have, for example, a length of 75 mm, a wall thickness of 0.3 mm and a transverse dimension, measured between diametrically opposed flat sections of the wall of the tube, of 9.75 mm at the front end of the tube and 8.6 mm at the rear end. The tubes may be made of aluminium and be bright-anodised on their inner sides to give the walls of the tubes the necessary reflectivity, or they may be made of a plastics material and have chromium-plated walls. When made of aluminium each tube is deep-drawn with a press tool in a number of stages, starting with a discshaped blank. When made of plastics the tubes are injection-moulded. Tubes made of plastics may be chromium-plated on their inner or outer sides.In the latter case the tubes would need to be made of a low light-loss clear synthetic resin such as polymethyl methacrylate. If desired, when made of plastics the tubes may each be moulded integrally with a light diffuser at the front end of the tube. In the case of an image enlarger composed of aluminium tubes, a light diffuser in the form of a sheet of plastics material may be arranged over the front ends of the tubes at the display face of the enlarger. The tubes 14, whether made of aluminium or plastics, are glued together.

In the manufacture of the image enlarger 1 the tubes 14 are assembled in a shallow open-topped box 15 (Figure 3) having the desired peripheral shape of the enlarger and the bottom of which has at its inner side 16 a spherical convex curvature identical to that of the outer surface of the face-plate of the TV tube on which the enlarger is to be used and a boundary corresponding to the boundary of the display area of the face-plate. The box 15 is supported in a fairly steeply inclined position, as shown in Figure 3, and a first row of tubes 14a is laid on the side wall of the box which is at the bottom in this position, and which is designated 15a in Figure 3.Adhesive is then applied, for example, by brush, to the upper sides of these tubes and a second row of tubes is laid on the first row, each tube of the second row nesting between the upper sections of two adjacent tubes of the first row. After adhesive has been applied to the upper sides of the tubes of the second row a third row of tubes is laid on the second row, and this process is repeated until the box 15 is filled with tubes. When the adhesive has set the assembly of tubes is removed from the box and the adhesive is allowed to cure.

In an alternative method of constructing an image enlarger according to the invention, corrugated strips of material are used, for example, corrugated strips of aluminium bright-anodised on both sides. A portion of a strip having corrugations which are shaped to form cells of hexagonal cross-section, like the cells 2 of the image enlarger 1 in Figure 1, is shown in Figures 4, 5 and 6. The strip, designated 17, has arcuate edges with the same centre of curvature and of which the concave edge 18 has a radius of curvature equal to that of the face-plate of the cathode ray tube on which the image enlarger is to be used.

The corrugations at each side of the strip have flat crests 19, flat sloping flanks 20 and troughs with flat bottoms 21. The parts 19, 20 and 21 all have the same dimensions and gradually decrease in width towards the concave edge 18 of the strip. The cross-sectional shape of the corrugations is such that when two strips are placed together with the flat crests of the corrugations at one side of one strip in contact with the flat crests of the corrugations at the adjacent side of the other strip, the troughs of the corrugations at the one side of the one strip form with the troughs of the corrugations at the adjacent side of the other strip tapered cells of hexagonal cross-section, as can be seen from Figure 7. An image enlarger can be constructed from a series of these corrugated strips by stacking the strips one upon another in the inclined box 15 and gluing the strips together at the contacting surfaces. The strips would have a width equal to the length of the tubes 14 of the enlarger shown in Figure 1, and the length of each strip at its concave edge 18 would be equal to the width of the bottom 16 of the box 15 at the inner side 16 thereof. If desired, the other edge of each strip may be straight so as to give the enlarger a flat display face.

Claims (9)

1. An image enlarger for a cathode ray tube having a spherically curved face-plate, the enlarger being constructed to be arranged on the face-plate and having a display face on one side and a spherically curved concave face on the opposite side with substantially the same radius of curvature as the other surface of the face-plate, and comprising an assembly of light guides arranged side-by-side and each of which extends radially with respect to the concave face of the enlarger from this face to the display face, characterised in that the light guides are formed by elongate cells with internally reflective longitudinal walls and with ends through which light can pass located at the two faces of the enlarger, each cell tapering towards its end which is located at the concave face of the enlarger so that adjacent cells adjoin one another throughout their length.

2. An image enlarger as claimed in Claim 1, wherein each cell is open at both ends.

3. An image enlarger as claimed in Claim 1 or 2, characterised in that the cells have a transverse cross-section of regular polygonal shape, and except for the cells at the periphery of the enlarger, each cell is adjoined on all sides by other cells so that there are no interstices between the cells.

4. An image enlarger as claimed in Claim 3, characterised in that the transverse cross-section of the cells is of hexagonal shape so that the enlarger has a honeycomb structure.

5. An image enlarger as claimed in Claim 1, 2, 3 or 4, characterised in that each cell is formed by a tapered tube with an internally reflective wall.

6. An image enlarger as claimed in Claim 5, characterised in that the tube is made of aluminium and is bright-anodised on its inner side.

7. An image enlarger as claimed in Claim 5, characterised in that the tube is moulded from a plastics material and the wall of the tube is chromium-plated so as to be internally reflective.

8. An image enlarger as claimed in Claim 5, 6 or 7, characterised in that the tubes are secured to one another by an adhesive.

9. An image enlarger for a cathode ray tube, substantially as herein described with reference to Figures 1, 2 and 10 or Figures 4, 5, 6 and 7 of the accompanying drawings.