Patent GB-846544-A (GB)
Title: Improvements in or relating to scanning display devices
Inventor: CALDER NIGER DAVID RITCHIE
IPC: H04N3/08
Filed: 1955-11-30
Abstract: 846,544. Television. MULLARD Ltd. Sept. 14, 1956 [Nov. 30, 1955], No. 34362/55. Class 40(3). In a television display, the frame component of scan is produced by an optical arrangement comprising the combination of a rotating carrier carrying a plurality of cylindrical reflectors or lenses and a cylindrical magnifying means, such as a lens or mirror. Fig. 5 shows one embodiment of the invention applied to coloured television. The red, green and blue components of the images are produced separately on parallel bands of phosphor material (extending normally to the plane of the figure) in a cathode-ray tube C scanned in the line direction only and are combined by dichroic mirrors M. The resulting combined line image is then reflected at R to a small rotating drum D which is disposed with its axis of rotation Q parallel to the direction of line scan and is formed on its surface with fine semi-circular concave cylindrical reflectors. The drum is rotated synchronously with the television signals (600 r.p.m. for the British 50 frames per second system) and produces a line image travelling between A 1  and A 1 <SP>1</SP> to form the television raster. The drum is also located with its axis of rotation Q parallel and close to but within the focus F of a parabolic concave cylindrical mirror P so that the image A 1 <SP>1</SP>-A 1  appears to an observer as a magnified image at B - B<SP>1</SP>. To prevent spurious images at the top and bottom of the picture stops L are included, and to prevent loss of focus as the viewers head is moved from side to side, the axial lengths of the cylindrical concave mirrors and the parabolic mirror are made greater than the length of line scan in the cathode-ray tube. The three line images in the cathode-ray tube may be produced by separate electron beams or by a single electron beam deflected transverse the line direction of scan at a high frequency, e.g. 5 mc/s, whilst the colour signals are switched to the beam at the appropriate phase points. The lines are preferably deflected through a small auxiliary scan within the individual phosphor bands at frame frequency to reduce phosphor loading. The drum may conveniently be formed as a plastic moulding with its surfaces silvered to act as the reflectors. Fig. 6 (not shown) illustrates an arrangement generally similar to that in Fig. 5 except that mirror P is given a hyperbolic form. In a modified construction of the rotating drum, Fig. 8 (not shown), each concave reflector is replaced by the combination of a mirror and a converging lens formed by silvering the plane surface of a plane-convex cylindrical lens. In another modification, Fig. 7, the drum is formed of cylindrical convex lenses L and has mounted within it a stationary cylindrical convex mirror M. C denotes the cathode ray tube and SS<SP>1</SP> the travelling line image. In yet a further modification, Fig. 9, the drum D is provided with a plurality of cylindrical convex reflectors in the form of rods H silvered on the surfaces remote from the axis of rotation Q of the drum. The Specification discusses in detail the optical characteristics of the display and gives dimensions for two embodiments.