Patent GB-975409-A (GB)
Title: Improvements in or relating to guidance systems
Inventor: WILLITS SAMUEL P
IPC: G01S3/789
Filed: 1961-03-13
Abstract: 975,409. Photo-electric scanning. CHICAGO AERIAL INDUSTRIES Inc. March 13, 1961, No. 9179/61. Heading G1A. [Also in Divisions G3 and H4] In a photo-electric target follower signals L<SP>1</SP>, R<SP>1</SP>, C<SP>1</SP> are derived corresponding to overlapping left, right, and centre views of the target, and the steering motor is controlled in accordance with a second space derivative S L<SP>1</SP> + R<SP>1</SP>- 2C<SP>1</SP>. Ambiguities in the sense of the correction, in areas removed from the lock-on position, are resolved by using an L<SP>1</SP>- R<SP>1</SP> signal. Steering may be provided in two dimensions. Target scanner. The target 5 is imaged on photo conductive cell 10 by lens system 6, 9 and a refracting disc 7 with segments oriented to provide left, right and centre'views, Fig. 2, is driven by a motor 11, together with a commutator and slip ring assembly 23 whereby the amplified detector signals corresponding to the three views are separated and fed to averaging circuits 24, 25, 26. Alternative scanners. (i) For two axis operation, the system may be duplicated or a five segment refracting disc may be employed with corresponding commutator segments Fig. 4 (not shown) to provide signals corresponding to "up", "down", "left", "right" and "centre" views Fig. 5 (not shown) (ii) a pair of contra-rotating wedge prisms Fig. 16 (not shown) may be used to provide a rosette scan as in Fig. 17 (not shown). (iii) the Specification suggests the detector 10 or aperture stop member 8 may be oscillated or a pair of relatively rotating reticules may be used. An A.G.C. circuit may be employed before the detector amplifier to maintain linear operation of the subsequent computing circuitry (see Division H4). Derivation of control signal. To obtain the control signal S from L<SP>1</SP>, R<SP>1</SP> and C<SP>1</SP>; L<SP>1</SP> and R<SP>1</SP> are summed by resistors 30, 31 at the input of a modulator, and C<SP>1</SP> subtracted in the modulator, which may be an electro-mechanical chopper charging a capacitor, which provides an input signal to a half-wave demodulator Fig. 14 (not shown). The sense of the correction is determined by obtaining the function L<SP>1</SP>-R<SP>1</SP> from a similar modulator/ demodulator unit. These two signals are fed through power amplifiers to a "logic" switching circuit, comprising a polarity sensitive relay controlled by the L<SP>1</SP>-R<SP>1</SP> signal operating reversing contacts in the S signal path to the steering motor 40, Fig. 15 (not shown). In an alternative computing arrangement, the required negative values are obtained from a phase inversion circuit Fig. 18. As shown the detector amplifier 301 provides two outputs 180 degrees out-of-phase; one output is connected to a commutator 302, having conducting segments arranged to provide an L<SP>1</SP> and R<SP>1</SP> signal, the other output is fed to a second commutator arranged to provide -C<SP>1</SP> and -R<SP>1</SP> signals. After smoothing by "integrator" circuits 308... 311, the signals are summed through resistances at the input of operational amplifiers 317, 318 to provide S and L<SP>1</SP>-R<SP>1</SP> signals to the switching circuit 319. A.G.C. circuit. As described with reference to Fig. 4 (not shown), the five signals representing left, right, centre, up, and down views are fed to a sampling circuit comprising a five stage ring counter, gating clamping circuits (utilising a unilateral semi-conductor) to apply the signals to an A.G.C. amplifier, (not shown in detail). Whenever the output exceeds a reference value, a signal is passed to a commutator 202 having one segment phased to conduct when no view signals are being transmitted Fig. 12 (not shown). The signal from this commutator is passed to the A.G.C. injection amplifier 201, shown in detail Fig. 13 as comprising a pair of shunting diodes 212, 213, biased by the A.G.C. signal which is retained by capacitor 209 in the intervals between the commutator connection. The use of the two shunting diodes prevents spurious signals being injected into the steering system from the A.G.C. input, since the injection points are 180 degrees out of phase with one another in the signal channel.