Patent GB-631541-A (GB)
Title: Improvements in and relating to servo-motor control systems
IPC: G05F1/00
Filed: 1943-02-18
Abstract: 631,541. Gun-sighting apparatus. SPERRY GYROSCOPE CO., Inc. Feb. 18, 1943, No. 25182. Convention date, July 23, 1941. Divided out of 631,517. [Class 92 (ii)] [Also in Group XXXVIII] A servomotor control system comprises a control member mounted for angular displacement from a normal position whereby it operates a signal generator to produce a signal corresponding in magnitude and sense to the angular displacement of the control member, the controlling devices being such that for any steady value of the control signal the servomotor has an acceleration which corresponds in magnitude and sense with the angular displacement of the control member. The system is particularly adapted for the gun sighting and predictor systems described in Specifications 631,517 and 631,540 respectively, and enables the sighting device to be accelerated to overtake an object and then continue tracking at constant velocity. As described in Specification 631,517, angular deflection of the handle 11 in a vertical plane produces in the pick-up or secondary coils 67, 69 opposing alternating voltages which are rectified in full wave rectifiers 127,129 or other phase-sensitive rectifiers or demodulators, and fed to a D.C. amplifier 131. The output of the D.C. amplifier is connected in opposition to the voltage produced by a D.C. tachometer generator 19<SP>1</SP> on the shaft of the servomotor 17 which drives the sighting device in a vertical plane, the resultant D.C. voltage being applied to a modulator 135 which transforms the D.C. into A.C. voltage of proportional amplitude and of a phase corresponding to the - polarity of the input. This A.C. input is fed to an A.C. amplifier and phase-shifter 81, 83 connected to the field winding 85 of the servomotor 17, the phase-shifter serving to maintain the field 85 in quadrature with the other field 87 connected across the supply lines. The velocity plus acceleration tracking control is effected by an integrating circuit 137 in the input circuit of the modulator 135. This circuit comprises a potentiometer resistance 139 connected across the tachometer generator 191, the movable contact 141 of the potentiometer being connected through a resistance 142 to the fixed contact of a single throw switch 143. The contact arm of this switch is ganged with the contact arms of two other switches 145, 151, the circuit arrangement being such that, with the switch arms in the position shown, the system operates with a straight velocity tracking, and the velocity of the servomotor 17 corresponds to the deflection of the handle 11. With the switch arms all in the alternative position a constant deflection D of the handle 11 provides a constant component of tracking velocity and an acceleration component, so that the tracking speed s may be denoted by s = D + Ddt. If the control handle 11 is released so that it returns to the neutral position the input to the D.C. amplifier drops to zero and there is zero voltage across the output potentiometer 153, whereupon the motor speed falls until the generator output voltage equals the voltage across condenser 147, and the motor will travel at constant velocity. Any change in the motor speed produces charging or discharging current in the circuit comprising the condenser 147 and resistor 149, which has a large time constant. The handle 11 may be deflected to employ straight velocity tracking until an object is sighted, then, by throwing the ganged switches into the position opposite to that shown, and releasing the handle 11, the servomotor automatically continues the same tracking velocity with the control handle 11 at neutral. To stop the motor the control handle is deflected in the direction opposite to its original movement.