GB759868A - Improvements in and relating to automatic curve-following apparatus - Google Patents

Abstract

759,868. Automatic curve following ap paratus. ENGLISH ELECTRIC CO., Ltd. March 11, 1955 [March 12, 1954], No. 7259/54. Class 40(1) [Also in Group XL(b)] The invention relates to automatic curve following apparatus of the type described in Specification, 690,426 wherein a cyclical scanning device 1 scans a curve 2, which may be a line, as in Fig. 1, or the edge of an area, as in Fig. 2 so that photoelectric detection apparatus causes electric pulses to be produced when the line or edge 2 is crossed, the spacing of such pulses being used to operate circuits controlling servo mechanism, which guides the scanner device along the line. In such apparatus, the follower is arranged to follow a curve in response to a resolved component along a reference axis x or y of an instantaneous error distance between the actual position of said follower and a required position on said curve, and is characterized according to the invention, in that said resolved component is obtained automatically from information contained in a wave form of an electrical signal derived from a cyclically operating scanning device by computer means which are arranged to respond to the phase displacements between a reference position in the wave form and two characteristics in the wave form which indicate the two interceptions per cycle between the scanning path of said scanning device and the curve, said scanning device and the curve, said computer means serving to produce two signals respectively proportional to the cosines of said two phase displacements and serving to add these two signals to produce an output which is a measure' of the resolved component of said error distance 'along said reference axis, which is an axis related to said reference position. The apparatus operates on the principle that the error distance e may be resolved into parts # Sin # and # Cos # and introduces corrective components #dx/t# = Vcos#-g # Sm# and #y/#t = VSin#+ ge Cos# into the drive of the scanning head (V being the speed of the scanning head and "g" a suitable conetant). Figs. 1-3 represent diagramatically the scanning device which produces pulses when the edge 2 is crossed at the points A and B as indicated in Fig. 4. Such pulses are fed to a control circuit as shown in Fig. 7, wherein the function of the first part, above the dotted line, is to separate the pulses corresponding to intersection A from those corresponding to intersection B and the function of the other part, below the dotted line, is to convert the wave form of the separated pulses into some form which will be appropriate to give a control as indicated above, the wave forms marked being converted by electronic gate and clamp units 6.