Patent GB-1214463-A (GB)
Title: Improvements relating to automatic curve-following apparatus
Inventor: ACKROYD JOHN
IPC: B23Q35/128
Filed: 1967-02-01
Abstract: 1,214,463. Photo-electric line followers. BRITISH AIRCRAFT CORP. Ltd. Feb. 1, 1968 [Feb. 1, 1967], No.5002/67. Heading G1A. The outline of an object or image is traced by a photo-electric follower arrangement comprising scanning means producing a small closed loop scanning pattern, the position of which is adjusted in response to differences in phase between the output signal from a detection means receiving reflected or transmitted light from the object or image and reference signals from the deflection generator circuit of the scanning means. The closed loop scanning pattern itself moves in a closed loop at a lower frequency. In Fig. 1, the scanning pattern is circular and is produced on the screen of cathode ray tube 10 by means of horizontal and vertical deflection amplifiers 14, 15, the output waveforms of which are sinusoidal and of the same frequency, but are phase displaced by 90 degrees and which are produced by connecting the phase-opposed outputs from a 20 KC/S multi-vibrator 16, through frequency dividers 17, 18 (in which the phase displacement is produced) and 10 KC/S filter circuits 19, 20. Light passing through lens 12, aperture 13 and an image under examination, is focused on to a photomultiplier 25 through lens 26. The output of the photo-multiplier is a pulse the length and phase of which are indicative of the position and orientation of the circular scanning pattern with respect to the outline of the image. The output signals are applied to an amplifier 27, and a 10Kc/s filter 31 where output is a sinusoidal waveform at the fundamental 10Kc/s frequency. The phase of this waveform is indicative of the position of the second intersection of the line and the circular scanning pattern. The waveform is compared in two phase sensitive rectifiers 35, 36 with the outputs of divider circuits 18 and 17, respectively, to produce further inputs to the horizontal and vertical deflection amplifiers 14, 15 respectively, which provide corrections to the deflection signals supplied to the cathode ray tube so as to advance the circular scanning pattern along the line keeping as near centred on the line as possible, Fig. 3 (not shown). Phase sensitive rectifiers 35 and 36 each comprise two demodulators (37, 38), Fig. 4 (not shown), both receiving the anti-phase signals from the circuits 17 and 18, and the output of filter 31, for demodulator 37 this filter out signal being inverted. The demodulator outputs are combined in a leaky integrator (40). To provide facility for keeping the pattern centred on the line, further deflection control circuits acting on amplifiers 14 and 15 and a 2Kc/s multi-vibrator circuit, frequency dividers and filters, are provided, to move the 10Kc/s circular scanning pattern in a circle at 1Kc/s. Similar feedback circuitry connected to the output of filter 31 is provided, including an amplitude detector, 1Kc/s filter, and phase sensitive rectifiers. Instead of cartesian co-ordinate deflection, re deflection can be used. In an alternative arrangement, (not shown), the object or image to be scanned is viewed by a television camera arranged to scan an outline such as in the arrangement of Fig. 1, the photo-sensitive screen of the camera providing video signals which are used to control the position of the scanning pattern to follow the curve.