GB872444A - Improvements in or relating to movement-controlling apparatus - Google Patents

Abstract

872,444. Electric copying-machines. LANCASHIRE DYNAMO ELECTRONIC PRODUCTS Ltd. Nov. 5, 1958 [Aug. 16, 1957], No. 25943/57. Class 38 (6). [Also in Group XL (b)] In apparatus for following the outline of a visual pattern a rotating light spot intersects the edge of the pattern the point in the rotation at which the intersection takes place being used to determine the direction of movement of the apparatus. As shown, a spot of light produced by a lens and aperture is directed by fixed mirror C on to mirror D mounted on the end of a motor shaft and inclined to it in such a manner as to produce a ring of light as shown in Fig. 2a. This light may be reflected from a pattern on an opaque background but in the arrangement shown that part of the scanning circle which falls outside the opaque pattern passes through a transparent support and is received by a photo-electric multiplier 10 (Fig. 6). The output of the cell is amplified and produces the square wave pulses shown in Fig. 2b. These pulses are differentiated to produce sampling pulses (Fig. 2b) which pulses are fed to phasesensitive detectors 15, 16 fed with reference sine waves from a source 20 in synchronism with the motor which rotates mirror D. These sine waves are separated in phase by 90 degrees by means of phase-shifter 22. Thus the outputs of the phase-sensitive detectors are two voltages representing respectively the sine and cosine components of the angle (Fig. 2a). These voltages are smoothed at 21 and used to control the output of Ward-Leonard generators G1, G2 feeding motors M1 M2 which each drive the tracing head in one of the co-ordinate directions at speeds V sin # and V cos # so that the tracer follows the outline of the pattern.