Patent GB-1145343-A (GB)
Title: Polypattern generator
IPC: H01J37/302
Filed: 1966-07-15
Abstract: 1,145,343. Electron-beam deflection control. GENERAL ELECTRIC CO. 15 July, 1966 [4 Aug., 1965], No. 31987/66. Heading H4T. In an arrangement for deflecting an electron beam in a desired geometric pattern (e.g. in an electron-beam welding machine), X and Y coordinate voltages representative of the end points of each segment, in the case of straight line patterns, of a particular pattern are selected from a plurality of such voltages, and fed to selected taps on respective X, Y slider potentiometers, the outputs of which, when the latter are rotated, provide the required X and Y beam deflection controls whilst, for circular patterns, the outputs of a sine-cosine potentiometer are utilized. The co-ordinate voltages for certain predetermined patterns, e.g. circle, hexagon, triangle and rectangles having ratios (1: 1, 1: 2, 1:5) of sides are produced by supplying D.C. voltages of -12V and +12V from respective terminals 5a, 5b (see Figs. 2a, 2b, 2c) of a power supply 5 to a voltage divider network 6, the various taps on which supply the X co-ordinate voltages over a cable 200a and the Y coordinate voltages over a cable 100a to certain contacts of twelve decks of a fourteen deck switch 8, the co-ordinate voltages for additional " special " patterns being produced by supplying suitable D.C. voltages to tappings 300-311, and 400-411 in cables 300a, 400a connected to other contacts on the twelve switch decks. Switch 8 is operated to select the co-ordinate voltages appropriate to a desired pattern and the outputs from the various decks are supplied to tappings on X and Y linear resistance potentiometers 9, 10 rotated manually or via a slip clutch driven by motor 16 controlled by speed controller 19 (also Fig. 1, not shown) to produce the actual beam deflection waveforms. The latter are supplied to output terminals 11, 12 via one section 7b of a change-over switch 7 and banks 13 and 14 of switch 8. Section 7b of switch 7 is linked to a section 7a which when operated reverses the polarity of the voltage across the X co-ordinate section of network 6 so that on operation of both sections the pattern is rotated through 90 degrees in a clockwise direction. For the production of circular patterns the output of a sine-cosine potentiometer 14 coupled to the drive shaft of potentiometers 9, 10 and fed via conductors S, V with the voltage across network 6 is supplied to terminals 11, 12, instead of the outputs of the potentiometers, by operation of switch 8 (decks 13 and 14). To increase the effective width of the electron beam a " puddling " (spot-wobble) technique is employed. This is achieved by the circuit of Fig. 2a which provides, at terminals 11a, 12a, two 90 degrees phase-displaced waveforms at the power line frequency (60 c.p.s.) amplitude modulated by a multivibrator 24, the depth of which is controlled by rheostat 25 and the frequency by potentiometer 24b, the circuit being brought into operation by switch 28. The outputs at terminals 11, 12 and 11a, 12a are then supplied to the correspondingly referenced inputs of respective X and Y D.C. amplifiers (Fig. 3, not shown) including negative feedback stabilization, the outputs of which feed the deflection coils for the electron beam. To minimize distoration of the geometric pattern due to non-linearity of the deflection coils, the output circuit of each amplifier includes a photo-resistor influenced by a respective light bulb connected in the output circuit of the other amplifier.