Patent GB-1054929-A (GB)
IPC: G06V30/10
Abstract: 1,054,929. Cathode-ray tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 29, 1963 [Dec. 7, 1962], No. 46331/62. Heading H1D. [Also in Division G4] In a character reading apparatus the image of the character is recorded as an electrostatic charge pattern on two or more storage meshes of a storage tube, a uniform electron flood beam is then directed on to the first of the meshes and from there to the second mesh while deflecting the beam direction and the emergent beam from the last of the meshes is directed on to means for generating an output signal. The storage tube comprises an envelope 10 having a photo-cathode 12 at one end and a collector plate 14 at the other. The end wall 11 is of conductive glass or coated with a transparent layer of gold or platinum or provided with a conductive mesh on which the cathode material is deposited. There are four storage mesh groups 15, 16, 17, 18 each consisting of a dielectric mesh 19 between a conductive collector mesh 20 and a field mesh 21. The mesh 20 provides an accelerating field between the cathode 12 and the mesh group, or between mesh groups. The field meshes 21 give a uniform electro-static field between adjacent mesh groups. Between mesh groups are anodes or ring electrodes 22 inside the envelopes and outside the envelopes are deflection coils 23, 24, 25. These each comprise two windings DX, DY for deflections in the X and Y directions. A focusing winding 26 surrounds the whole assembly. The character 28 is illuminated by a lamp 41 and transmitted or reflected light is focused on the photo-cathode 12. A second lamp 29 is provided to flood the photo-cathode 12 as described below. During the various phases of operation different potentials are applied to the electrodes from a source 30. Ganged selector switches 31 are provided for this purpose. Deflection currents are applied from source 33 via further ganged switches 35 and variable resistors 35 controlled by a programme controller 36. The lamps 41 and 29 are also controlled by a ganged switch 38. These switches may be relays, electronic switches or motor-driven commutators. In operation the switches advance from the first to the sixth position. In the first position " b " potentials are applied to the storage mesh groups 15-17 to render them transparent to the tube beam and " a " potential to mesh group 18 to render it capable of receiving a charge. No deflection currents are applied and lamp 41 is lit to image the character on the cathode 12. The electron image passes through mesh groups 15-17 and sets up a charged pattern x. Fig. 3(a) (not shown), on mesh group 18. In the next phase " c " potential is applied to mesh group 18 to hold the image, " a " potential is applied to mesh 17 and " b " potential retained on mesh groups 15 and 16 so that the image is stored on mesh group 17. In the third and fourth positions the pattern is stored on mesh groups 16 and 15 in the same way. In the fifth position the lamp 41 is extinguished and lamp 29 is lit to flood the cathode 12 or a thermal cathode may be used in place of the lamp 29. Also " d " potential is applied to the four mesh groups the effect of which is to allow the flood beam of electrons from cathode 12 to pass through the pattern areas of the other mesh groups. The beam passing through mesh group 15 has the shape of the original character (Fig. 3(a)), and is deflected by windings 23 to strike the next mesh group 16 in a displaced position. Fig. 3(b) (not shown). The overlapping part y 2  is deflected by windings 24 to strike the pattern on mesh group 17. Fig. 3(c) (not shown), the area y 3  passing on to mesh group 18, Fig. 3(d) (not shown). The area y 4  which passes mesh group 18 gives a corresponding output signal from collector 14 which represents the fourpower auto-correlation of the original pattern, for this particular combination of image displacements. The whole process may be repeated a number of times with changing deflection voltages so that a waveform signal is produced characteristic of the original pattern. Electrons which do not pass through a mesh group are collected by the corresponding anodes 22, the outputs of which accordingly represent the non-correlating part of the pattern at each stage. In the last position of the switches the charge patterns are erased by " e " potentials, the cathode 12 being still uniformly illuminated. In a modification the collector 14 is replaced by a phosphor layer 43 so that a light image of the final area y 4  is produced and this is projected by lens 127 on to photocathode 112, Fig. 5(a) (not shown), to be recorded in turn on nine areas of the mesh groups, Fig. 5(b) (not shown), the images on the four mesh groups 115-118 being recorded in turn. Afterwards comparisons are made between the shapes in particular areas of the four mesh groups and the final match pattern is displayed on screen 143 or applied to a photocell. A tube such as ST2 having the extra deflection windings 44 may be used with continuously moving characters, the deflection being adjusted so that the image remains stationary.