Patent GB-1138712-A (GB)
Title: Improvements relating to electrical apparatus
Inventor: COWAN CLAUDE ISAAC
IPC: B41B19/01
Filed: 1966-01-21
Abstract: 1,138,712. Phototypesetting apparatus; cathode-ray tube circuits. ELLIOTT BROTHERS (LONDON) Ltd. 13 Jan., 1967 [21 Jan., 1966], No. 2788/66. Headings H4F and H4T. Phototypesetting apparatus comprises four flash tubes 3, Fig. 1 (only two shown), one of which is energized in response to a signal from a digital computer 1 via a buffer store 2 and a switch unit 4 to project opaque characters carried on the mask 15 associated with the energized tube on to the screen of a vidicon camera tube 6. Each character carried by the mask is associated with an opaque base line 17, Fig. 3, parallel to and a fixed distance below a type reference line 18, and of length related to the width of the character. Vidicon 6 scans normal to the base lines 17 the part only of the screen 13 carrying the charge pattern of the character required and its base line (e.g. as with "h" in Fig. 3). The output signal of the vidicon is transmitted to a cathode ray tube 9. The video and raster inputs to the cathode and scan coils 11 of the CRT 9 representing the character (e.g. as with "y" of Fig. 3) are started when the pulse, occurring as the vidicon scan beam crosses the base line 17 on each line of the vidicon raster, reaches the driving amplifier 10, thereby providing an accurate vertical and horizontal positioned register of the character in relation to the start of each scan line forming the input raster. The characters appearing in screen 19 are projected on to a film 21, the characters being accurately positioned by means of a positioning mirror assembly including a mirror 25, Fig. 4, a transparent scale 26, a light sensitive cell 27 and a housing 28. The beam of the CRT 9 is controlled to fall within the portion 24 of the screen 19 so that its image falls after reflection by mirror 25 on to the parallel lines 29, Fig. 5, of scale 26. The beam of the CRT is then deflected in a direction normal to the parallel lines 29 and as the image crosses each of the lines 29 a pulse is produced by cell 27. These pulses are fed to a beam registration circuit (not shown) which is responsive to an output (not shown) of the buffer store to control the scan coils 11 of the CRT to accurately position (horizontally) the image in relation to film 21. The beam is then moved so that the image on scale 26 moves in a direction normal to and toward the base line 30 of scale 26, and as the image reaches the scale base line 30 a pulse is produced to cell 27 which is used to accurately position the image vertically in relation to film 21. Resulting from the accurate horizontal and vertical registration of the beam, the character raster (the start of each line of which is coincident with the position of base line 17) on the screen 19 is formed in portion 23 to produce an accurately positioned image on film 21, the start of each line coinciding with the base line 30 of scale 26. Film 21 remains stationary during the composition of each line of print and is moved only to start a new line. The size of the characters projected to the film may be magnified electronically, and if a single character size on mask 15 is used to produce a number of character sizes on film 21 it is desirable in order to maintain correct positioning of the characters in the film to provide a number of base lines 17 under each character. Alternatively a single base line 17 may be used in conjunction with a scale 26 having a number of base lines 30 each associated with a different degree of magnification.