Patent GB-1031790-A (GB)
Title: Improvements in or relating to optical telemetry
IPC: G01C3/08
Filed: 1964-10-12
Abstract: 1,031,790. Photo-electric distance measuring. SUD - AVIATION SOC. NATIONALE DE CONSTRUCTIONS AERONAUTIQUES. Oct. 12, 1964 [Oct. 18, 1963], No. 41793/64. Heading H4D. In an optical telemeter, wherein a periodically occulted light source S, Fig. 1 (not shown), illuminates, via lens L 1 , the object T, the distance h of which is to be measured, and said illumination is detected by two photo-cells S 1  and S 2  via lens L 2 , the differential output from the photocells is synchronously detected by a periodic signal in phase with the illumination of the object to produce a signal which is used to laterally move the photo-cell until they are equally illuminated such that the incidence angle α and h=d tan α, may be formed, d being the distances between the lenses. The means R occulting the light source S may be a rotating cylinder. Fig. 3 (not shown), surrounding the light source and having alternate equal apertures and obscuring portions, on a toothed rotating disc. Fig. 2 (not shown). The image A 1 O 1 B 1  of aperture AOB is thus periodically projected on to the object T and lens L 2  forms a second image A 2 O 2 B 2  of said image. If the occulting means is moving in the direction f, the image A 2 O 2 B 2  will be formed first at A 2  and end at B 2 . Seven possible positions of the cells S 1  and S 2  relative to the image A 2 O 2 B 2  are shown in Fig. 4 (not shown) and the outputs E 1  and Eg of the two cells, together with the fundamental components V 1  and V 2  of these outputs, are shown in Fig. 5 (not shown) for the seven positions, the X co-ordinate being time or the position of the aperture in means R. If the components V 1  and V 2  are subtracted from one another, the amplitude of the resultant signal varies as the cells move through the seven positions as shown in Fig. 6 (not shown). In the arrangement of Fig. 13 the cells S 1  and S 2  are moved along and threaded drive 8 under the control of motor 9. The cell outputs are subtracted by means of the subtractively seriesconnected secondaries of transformers 10 and 11, which feed the resultant signal to one input of a synchronous detector 13, via passband amplifier 12. The synchronous detector 13 is such that when a periodic signal E(t) of period T is detected by a reference signal of identical period but phase-shifted by a valve #, it produces a signal given by:- The reference signal is in phase with the illumination of the object T, and may be obtained from a photo-cell S 3  arranged to receive the occulted light from source S, Fig. 12 (not shown), or from an alternator having its rotor keyed to a shaft rotating the occulting cylinder of Fig. 12 and having a number of polepairs equal to the number of apertures in the cylinder. The reference signal is applied to the second input of synchronous detector 13, to produce an output signal which varies as shown in Fig. 7 (not shown) with the position of the two cells S 1  and S 2 . A null output occurs at position IV where the centre point between the cells is in line with the centre of the image A 2 O 2 B 2 . The output is applied to one contact a of a relay 17 having its moving contact P connected to a motor 9 which moves the cells. Since the output of detector 13 will only cause the motors to move the cells into position IV when the cells are between positions III and V, relay coil 17 is only energized to bring contact P into contact with contact a, when the cells position is within said range. The coil is energized by the output of a second synchronous detector 14, detecting the output of amplifier 12 using a reference signal produced by phase-shifting that used for detector 13 by #/2. The variation of the output signal with the cells position is as shown in Fig. 8 (not shown), the relay being sensitive to positive signals only. When the cells are outside the servo-controlled range, contact P is in contact with contact b such that a fixed voltage from source 18 causes the motor to move the cells in one direction until the servo-controlled range is reached. If it is not considered necessary to limit the servo control of the cells position to the range of positions III to V, the relay 17 and detector 14 may be dispensed with and detector 13 and source 18 connected to the motor 9 by means of a change-over switch. To retain relay 17 and detector 14, and still allow servo-control over the entire range of positions I to VII, the energizing signal of relay 17 may be obtained by adding the rectified outputs of the two detectors (see Figs. 9, 10 and 11, not shown, and Fig. 19, not shown). Noise may be removed from the outputs of the detectors by means of low-pass filters, Fig. 14 (not shown), or by means of capacitors connected across the relay coil and/or the motor, Figs. 16 and 17 (not shown). The value of h may be read off a calibrated meter, connected via a selsyn-drive to a reduction gear coupled to the threaded drive of the two photo-cells.