Patent GB-1110991-A (GB)
Title: Improvements in or relating photographic reproduction
Inventor: PURDY HAYDN VICTOR
IPC: G06K15/12
Filed: 1964-11-13
Abstract: 1,110,991. Copying by scanning. PURDY & McINTOSH (ELECTRONIC DEVELOPMENTS) Ltd. 15 Nov., 1965 [13 Nov., 1964], No. 46388/64. Heading H4F. In a photo-typesetting system a vertical raster is formed in any one of 16 positions on the face of an index cathode-ray tube and a group of 16 lenses (LA), Fig. 1, not shown, form an image of the whole face of the tube on each of 16 areas of the character matrix (CM), each area of which contains transparent character shapes on an opaque background in groups of 16 characters, and according to the position of the raster on the tube face one character in each of the 16 groups is illuminated by each raster, the output of only one of 16 photomultipliers (PM) positioned behind the matrix (CM), being selected and fed to the reproducing system. A type setter tape is used to select the raster position and photomultiplier. The reproducing and recording system comprises a print-out cathode-ray tube 21, Fig. 2, on the screen of which a flying spot traces invariable horizontal lines in synchronism with the vertical raster lines on the screen of the Index CRT 61, the brightness of the light spot being controlled by the output signals from one of the 16 photomultipliers PM, i.e. modulated according to the form of a particular character. Light from the tube 21 is collimated 5 and passed via mirror 4 and lens 6 on a reciprocating carriage 1, which makes horizontal movements corresponding to the length of a line of a page of characters, to a photographic film 3 which is moved step-by-step for page line spacing at right-angles to the reciprocatory path of the carriage 1. Thus as the carriage moves successive superimposed lines on the face of tube 21 are focused side by side on the film. The line frequency of the raster on index tube 61 and of the successive superimposed lines on printout tube 21 are synchronized and locked to the carriage movement by means of a grating system comprising a fixed grating 8, a movable grating 7 carried by the carriage, and a light source and photo-electric device 9 which produces electrical pulse trains corresponding to the moire-fringe pattern produced. The pulses from the photo-electric equipment 9 pass via amplifier 10, Schmitt trigger circuit 11 and monostable multivibrator 12 to constant current generators 13, 15 and 58, emitter follower 16, 60 and power transistors 50 and 18 to the deflection circuits 51 and 31 of tubes 61 and 21. To provide the highest degree of positioning accuracy of the raster on index tube 61 the character matrix has horizontal and vertical control bars, Fig. 8, not shown, the signals produced by the selected photomultiplier when the scanning beam crosses the control bars being used to activate gates 52 and 55 respectively. The vertical control bars are twice as wide as the horizontal control bars. To reproduce kerning or overhanging type such as certain italic styles, a small proportion of the current in the main sweep coils 31 appropriate to the inclination of the adjacent images, is fed via switch 25 and amplifier 28 into a second set of sweep coils 26 at rightangles to coils 31. To ensure that the characters being kerned are not bodily shifted to the left, power amplifier 56 feeds a bias current to coils 26<SP>1</SP>. In order that the whole width of tube 21 may be used, a continuous bias current is fed into a further set of coils 30 in parallel with the main sweep coils 31. The output of multivibrator 12 is also fed to a counter 208 via a divider 207 if it is desired to count grating lines as a positioning means. In reading out characters from a tape-reader TPR each character code is stored in turn in 34 and applied to character width store 210 which records the widths of the character in counter 208. When the grating pulses applied to divider 207 have counted out the width number recorded in 208, a signal is sent to 34 calling for the next character. The character-in-process store 34 also controls the selection of the photomultiplier activated and also controls the X and Y raster indexing controls 211, 212, by means of which the beam of tube 21 is directed to the desired one of the sixteen raster locations. The spacing of the raster lines of the index tube may be varied in order to produce varying numbers of lines from the same character and so to vary the width of the print-out of such character, the lengths of the traces on the print-out tube being correspondingly adjusted. The position of the linear trace on the print-out tube may be slowly moved to positions parallel to itself to prevent burning of the screen.