Patent GB-1086322-A (GB)
Title: A photoelectric line follower
Inventor: DIPROSE KENNETH VICTOR
IPC: B23K7/00
Filed: 1963-07-17
Abstract: 1,086,322. Photo-electric path followers. HANCOCK & CO. (ENGINEERS) Ltd. July 17, 1964 [July 17, 1963], No. 28266/63. Heading G1A. [Also in Division G3] In a photo-electric scanning system a beam of light is projected on to a substrate through a mask, a plurality of shaped apertures being moved with respect to the beam and mask to produce a series consecutive spots of light which travel across an outline on the substrate, outline pulses being produced from a photo-electric device when each spot crosses the outline and the difference in the lapse of time between a timing impulse and the next outline impulse and this impulse and the subsequent timing impulse is used to generate a steering signal causing the outline to be followed. As shown, a lamp 32 is mounted above an optical condenser 34 to provide a beam of light through slots in two discs 35, 36 which overlap. The disc 36 is normally stationary and rotated only to select the slot (42), Fig. 9 (not shown), appropriate to the desired control. The slot (42) is skewed with respect to the outline 52 in order to discriminate between inside and outside corners and so partially compensate for overshoot on a change in direction. The disc 35 has a plurality of slots and is driven by a shaded pole motor 38. The intersection of the slots causes a spot of light to scan the outline 52 and in a preferred arrangement the slots (42) are arranged so that the next spot is formed as a spot is extinguished. The spot of light is focused on the outline through a Dove prism 48 and a lens 50. The reflected light from the spot is received by a photo-transistor device 53 and a signal is derived naving a waveform representative of the position of the outline 52 in the scan. The simultaneous spots due to the preferred overlap of the slots, giving doubled light intensity at the photo-transistor, are used to derive timing pulses, or in an alternative arrangement the timing pulses are derived from a separate photo-transistor receiving a light pulse through a series of holes in the rotating disc. The scan signal from the photo-transistor device 53 and the timing pulses are employed in a transistorized arrangement Fig. 16 (not shown), to derive an error signal representative of the deviation of the following arrangement from the outline, which is applied to a steering motor 69 driving through gearing 71, 72, a steering wheel 70 and a gear 74 rotating the Dove prism 48. Alternatively, the servomotor drives a synchro resolver 73 for a co-ordinate drive system. It is stated that an alternative scanning method comprises a rotatable disc having a number of holes in a circle co-operating with a sheet metal mask having an arcuate aperture, conforming with the circumference of the circle of holes and having a length corresponding to the length of the scanning path; a photo-cell or photo-transistor is arranged near the aperture so that each spot formed by the beam passing through a hole in the disc first strikes the photo-cell to produce a timing pulse and immediately passes through the aperture to form a scanning spot.