GB964991A - Improvements in or relating to apparatus for determining the deviation of a vehicle from a predetermined track - Google Patents

Abstract

964,991. Photo-electric curve-following and information deriving apparatus. DECCA Ltd. July 5, 1962 [July 20, 1961], No. 14375/61. Heading G1A. [Also in Division H4] A device for deriving an error signal indicative of the magnitude and direction of the misalignment between a sensing head and a boundary line on a record includes a sensing element arranged for rotation at a uniform speed about an axis normal to the record and a comparator giving an output or indication dependent on the relative durations of the passage of the sensing element over the parts of the record on either side of the boundary. The detector may be photo-electric and the record boundary defined by the use of areas of different reflectivity of transmissivity. In the embodiment described the boundary defines a course on a chart along which it is desired to navigate a craft. The sensing head is positioned in accordance with the craft position as determined by a radio-navigation system and the error signal applied to a navigational instrument or automatic craft control system. The sensing head 15 is shown movable on screw 16 by motor 17 over chart 10 marked with the course as the boundary between an area of good reflectivity and a darker area 20. The chart is movable in a direction at right angles to the head movement by motor 13 or motor 14. The motors 13,14, and 17 are controlled by the output of radio-navigation system 18 to position head 15 over the chart in accordance with the instantaneous craft position. The head carries a light-guide 23 rotatable by motor 22 so that its face 26 scans round a circular path over the chart. The guide directs light to photo-cell 28. It is preferred to illuminate the chart by light from a lamp 29 interrupted by rotating shutter 30 at a frequency high with respect to the rotational speed of guide 23; the photo-cell output can then be fed to an amplifier 32 tuned to the interruption frequency to give an output independent of any variations in other illumination falling on the chart. The amplified signal is fed to a comparator 33 giving an output dependent on the amount and sense of the deviation of the two output level periods from equality and the output is fed to a centre zero indicator 34 or control system through a reversing switch 35 set in accordance with the direction of travel. Specification 914,185 is referred to.