GB1015664A - Method and apparatus for automatically following a curve - Google Patents

Abstract

1,015,664. Automatic character reading. GENERAL ELECTRIC CO. Dec. 28, 1961 [Jan. 12, 1961], No. 46459/61. Heading G4R. [Also in Divisions H4 and G1] The character displayed on a transparency 1 has superimposed on it a scanning beam 2 from cathode-ray tube 3. Light passing through the clear parts of the transparency is received by a photo-multiplier 5. The beam is controlled by X and Y voltages applied to the deflection plates through amplifiers 7 and 8 from adders 9, 11. The beam describes a small search circle under the influence of a generator 13 which produces sine waves in quadrature. The position of the centre of the circle is required to trace round the outline of the character in steps equal to the radius of the search circle. The value of the #X and #Y voltages at the output of the circle generator at the instant that the search circle crosses from white to black is repeatedly added at 9 and 11 to the previous X and Y values. For this purpose the photomultiplier output is differentiated and used to set a trigger 23 to produce positive and negative sampling pulses or leads A, B which are applied to diode bridge sampling circuits 15 and 19 to pass the #X and #Y values amplified at 14 and 18 to pulse stretchers which store the values briefly to derive velocity signals X and Y. These pass to Miller-type integrators 17 and 21 to obtain the X and Y voltages which are applied with the #X and #Y signals to the adders 9 and 11 so that the next search circle centred about a point where the previous circle cut the character. The trigger 23 is connected to a scale-of-two circuit 25 and to a switch 24. The switch has three positions; in the first the trigger 23 is connected directly to a self-blanking oscillator 26; in the second it is connected via the scale-of-two circuit 25 and in the third, via circuit 25 and a scale-of-four circuit 27. By adjustment of switch 24 the sampling operation may be made every time the search circle crosses from white to black, every other time or once in four times. The blocking oscillator 26 produces a sharp pulse which is amplified at 28 to give coincident positive and negative sampling pulses for the circuits 15 and 19.