Patent GB-1181152-A (GB)
Title: Electronic Photocopy System
IPC: B41B19/01
Filed: 1967-03-13
Abstract: 1,181,152. Copying by scanning. RCA CORPORATION. 13 March, 1967 [21 March, 1966], No. 11770/67. Heading H4F. An original picture 12, Fig. 1, is scanned by cathode-ray tube flying-spot scanner 16 in conjunction with photo-electric cell 18 and is reproduced by cathode-ray tube 14 as a halftone image formed of dots of variable area produced in response to a spiral scan generator 22, provision being made for operation in first and second modes to obtain respectively positive and negative half-tone elements. The main scanning movements of the tubes are effected under control of clock source 26 and sync. generator 28 with the aid of X and Y counters 36, 38, which respond respectively to dot and line frequency sync. pulses, and digital-toanalogue converters 40 and 46. The tube beams trace out raster lines with step-by-step movements and with blanking between movements so as to create a pattern of dots, Fig. 2 (not shown). A flip-flop 51 slightly displaces the X deflection in alternate lines and the converters 40, 46 are made adjustable, whereby either 45 or 60 degree dot patterns may be produced, Figs. 5a and 5b (not shown). As an alternative to step-by-step movements, continuous movement in conjunction with blanking may produce a similar dot effect. The signals from photoelectric cell 18, Fig. 3e, are converted to duration modulated pulses, Figs. 3f and 3g, with the aid of arrangement 20 which includes an integrator 54. The pulses are then applied to modulate cathode-ray tube 14 via a mixer 68 where dot blanking signals are added as indicated at 63 in Fig. 3g. A switch 66 and inverter 67 are ineluded to allow operation in first and second modes to permit the production of either positive or negative images. Switches 85 and 93 are placed in the lower positions and at each dot position the spot produced in tube 14 is the consequence of spiral scanning as described in Specification 1,181,151 in response to 90 degreephase-displaced sine waves from sine wave generator 70 and phase shifter 74 which are modulated in stages 72, 76 by an exponential signal from an integrator 80 and added to the signals from converters 40, 46 in summing networks 84, 90. In a reciprocal mode of operation switch 65 is placed (as shown) to the left-hand position, whereby the integrator is discharged by blanking signals, Fig. 3b, applied to switch 82. Assuming the original 12 is a negative, operation then proceeds as illustrated in Figs. 3g, 3j and 3k for positive half-tones (i.e. with switch 66 to the left-hand position to provide inverted picture pulse signals), and proceeds as illustrated in Figs. 3g, 3o and 3p for negative half-tones (i.e. with switch 66 to the right-hand position to provide inverted picture pulse signals). The positive half-tone is formed by dots, and the negative half-tones by annuli with the reciprocal size relationship shown in Figs. 6a and 6b. In a residual mode of operation, switch 65 is placed to the right-hand position so that the picture pulse signals also control the discharge of integrator 80. Operation then proceeds as illustrated in Figs. 3g, 3h and 3i for positive half-tones and as illustrated in Figs. 3l, 3m and 3n for negative half-tones. The reproduction in both cases is formed of dots. In a further method of operation, switches 85-93 are placed in their upper positions so that tube 14 is scanned solely by the signals from converters 40 and 46. At each dot position a spot is produced for a period determined by the pulse from mixer 68, the spot assuming a size dependent upon the pulse duration as a consequence of a haze disc formed by electron scattering. Cathode-ray tube 14 may produce a visible image which is photographed on film 132. Alternatively the electron beam may make a direct recording.