GB1268979A - Widespan pattern generator - Google Patents

Abstract

1,268,979. Cathode-ray tube circuits. ALPHANUMERIC Inc. 31 March, 1970 [28 March, 1969], No. 15229/70. Heading H4T. In an arrangement in which successive pairs of single lines of alpha-numeric &c. symbols produced sequentially on the screen of a cathode-ray tube CRT (Fig. 1) are recorded, by means of a rotatable mirror RM and two fixed mirrors M1, M2, in abutting end-to-end relationship on a photographic film to produce a succession of lines of symbols having lengths which are twice that of the (optically magnified) trace length on the CRT, precise abutment of the pairs of lines is effected during periodic test modes under the control of a quantity derived from the algebraic difference of two further quantities representative, respectively, of the horizontal distance over which the beam must be deflected from a first known position on the screen until it is sensed by a reference knife edge positioned accurately at the centre of the film utilizing the optical path including mirror M1 and the horizontal distance over which it must be deflected between a second known screen position and the reference knife edge utilizing the optical path including mirror M2. In the operation of the system the symbols are produced by intensity control of vertically scanned lines which are stepped horizontally by unit amounts under the control of the Horizontal Position Generator HPG which stores numbers, supplied sequentially by a computer CP, representative of the horizontal position and as each line is recorded on the film it moves to expose a fresh area of film within the window W (Fig. 2). When a test mode is initiated by the computer the vertical scan is stopped and the unblanked beam is shifted vertically above the level of the window where during horizontal scans it will intersect the slit 14 and so produce a signal via photo-cell PC as it passes the knife edge. The computer then presets a number in HPG which locates the beam slightly to the left of the point 8191 (which is the extreme righthand end of the horizontal scan on the tube) and the beam is incrementally deflected to the right until a signal is received from PC, the left-hand path including mirror M1 being utilized, the number of incremental deflections to effect this being retained in a counter (regard being had to sign). A number is now preset which locates the beam the same number of units to the left of point "0" (the extreme left-hand end of the tube screen and the beam is again incrementally deflected to the right until a signal is received from PC (the right-hand path including mirror M2 being utilized) a count of the number of incremental deflection required being retained in a second counter which also has regard to sign. The difference between the two counts is then deduced and employed to adjust the position of either the right or left-hand scans such that tube screen point 0 falls on film point 8192 during the right-hand scan. The arrangement may be extended to the use of more than two horizontally abutting lines and may be adapted for providing vertical registration.