Patent GB-840003-A (GB)
Title: Positional control system for scanner
Inventor: FRANTZ WILBERT PATTON
IPC: G01S1/20
Filed: 1957-06-27
Abstract: 840,003. Photo-electric control. SPERRY RAND CORPORATION. June 27, 1957, No. 20404/57. Class 40 (3). [Also in Groups XX and XL (c)] Relates to apparatus for (1) automatically positioning a carriage between two position lines a and b, Fig. 1, marked on a chart 18 such that a point c corresponding to a reference pointer on the carriage is located at a distance x from one line which is a predetermined fraction x/y of the distance y between said lines; or (2) producing a signal proportional to said fraction x/y when the carriage is positioned manually at any arbitrary point between said pair of position lines. The distances x and y are measured in the same direction which may be at any angle to the lines a and b and these lines need not necessarily be straight or parallel. According to the present invention the chart is scanned cyclically by a point element along said direction to produce an electrical output signal A, Fig. 3, comprising two sets of interleaved pulse trains 24, 25 corresponding respectively to the lines a and b and a further set of reference pulses D, Fig. 3, is produced corresponding to the reference point c, means being provided for generating first and second D.C. voltages G and I proportional respectively to the time intervals between an a pulse 24 and the succeeding b and reference pulses. As described the chart is scanned photo-electrically and the line a and b correspond to position lines in a Loran radio navigation system. In the first mode of operation a third D.C. voltage H is derived from the voltage G by means of a potentiometer 31 such that the ratio H/G is equal to said predetermined fraction x/y and the position of the carriage is adjusted automatically by a first servo until the amplitude of the voltage H is equal to that of the voltage I. In the second mode of operation the carriage is located manually at the desired position so that the amplitude of the second voltage I is now proportional to the distance of the carriage from the a line ; the potentiometer 31 is then adjusted automatically by means of a second servo until the amplitude of the third voltage H is equal to that of the second voltage I, the angular position of the potentiometer being then proportional to the required fraction x/y. As shown in Fig. 1 the photo-electric scanner 10 is mounted over the chart 18 on a carriage which may be driven along rails parallel to the scan direction by means of a servomotor 46. An image of the chart 18 is focused by a lens 19 on to the elongated photo-cathode of a photo-tube 11, Fig. 2, the photo-cathode being covered with a mask 14 having a longitudinal slit 15, and the tube 11 with the mask 14 being located within a hollow cylindrical drum 12 having a one-turn helical slit 13 in the wall thereof so that light is admitted to the photo-cathode through the small aperture defined by the intersection of the slits 13 and 15. The drum is driven by a motor 16 so that said aperture scans along a direction parallel to the axis of the drum to produce at the output of the photo-tube the two sets of scan pulses 24, 25, A, Fig. 3, corresponding respectively to the lines a and b. A reference pulse is produced at the centre of each scan by a pick-up coil 21 in co-operation with a magnetic tab 20 attached to the drum 12, the output reference pulses being shaped in a generator 28 to give a corresponding pulse train D, Fig. 3. The scan pulses are amplified at 23 and applied through a delay circuit 60 to trigger a sawtooth generator 26 whose output C, Fig. 3, is sampled (1) in an electronic switch 36 by the reference pulses D to give the D.C. voltage I, and (2) in an electronic switch 61 by pulses F corresponding to the b pulses 25 to give the D.C. voltage G, the F pulses being derived from the trailing edges of pulses E which are initiated in a bi-stable multivibrator 62 by the reference pulses D and terminated by the next succeeding scanning pulses i.e. the b pulses. The voltage H is derived from the voltage G by a potentiometer 31 and an A.C. error voltage K proportional in magnitude and phase to the amplitude difference between voltages H and I is produced by a cyclically operated switch (output J) and filter amplifier 43. In the first mode of operation the switch 44 is in position 1 and the error voltage K is applied together with the A.C. switch-actuating voltage to the first servomotor 46 controlling the position of the carriage; when used in a Loran system, the shaft 33 of the potentiometer 31 may be controlled automatically by the Loran receiver. In the second mode of operation the switch 44 is in position 2 and the error voltage is applied to the second servomotor 49 controlling the potentiometer 31, the position of the carriage being indicated by the pointer 35 on the dial 34. Specifications 840,002 and 840,004 are referred to.