Patent GB-618408-A (GB)
Title: Improvements in and relating to position control and speed control systems
IPC: G05D3/12
Filed: 1944-07-07
Abstract: 618,408. Electric control systems. SPERRY GYROSCOPE CO., Inc. July 7, 1944, No. 13064. Convention date, July 9, 1943. [Class 40 (i)] In a positional control or speed control apparatus, the driving motor has one of its windings supplied cyclically by the control circuit and the back E.M.F. developed during the intervals is used to obtain a current proportional to the speed of the motor, for feeding back into " anti-hunting " circuits and the like. Various networks may be interposed in the feed-back circuit to produce, in a positional control system, an acceleration term or a displacement term, or to eliminate the speed term after a given interval or, in a speed control arrangement, to produce a small surge in the speed of the motor, which dies away to the proper speed by the time the target is reached. This last effect is defined as " aided tracking," in respect of which an alternative network is described for embodiment in the motor input circuit. Current in a coil 6 from source AC#1, Fig. 1, in a conventional selsyn system, produces voltages in coil 8 of magnitude and phase dependent on the relative displacement between an angle-setting device 4 and the driven object 2. This voltage is applied in push-pull to the grids of a double triode 50 with anodes energized from a source in phase with AC#1, so applying current to the field winding 15 of a two-phase driving motor 16 in half-cycle pulses. Another push-pull amplifier 19 has its anodes fed with A.C. 180 degrees out of phase with AC#1, and therefore amplifies the back E.M.F. from coil 15 only when amplifier 50 is not supplying current. D.C. pulses proportional to the motor speed are smoothed by a condenser 23 to provide the required feed-back voltage. Bias provided by a resistance-condenser combination 24 restricts the pulsing period of amplifier 19 to less than a half-cycle to avoid overlap with the driving current pulses due to inductive lag in the magnetic circuits. The D.C. voltage is fed from amplifier 19 back to the valve 50 in opposition to the voltage from coil 8. A differentiating network may be provided by a condenser 32 in series with the feed-back line, in combination with a resistor 32<SP>1</SP> across the line to introduce an acceleration term into the feed-back voltage, or an integrating network may be inserted at C, D, E, F to introduce a displacement term. In Fig. 2 (not shown), the invention is applied to a D.C. or A.C. servomotor. The amplifier 50 is replaced by a vibrating contact which alternately connects the motor armature to the power source and to amplifier 19, the anodes of the latter being fed with D.C. A series condenser and shunt resistance are included in the feed-back path so that the " speed term " is eliminated when the speed attains a steady value. In Fig. 3 (not shown), speed control is effected by manual variation of a D.C. push-pull voltage fed on to the grids of a double triode in a circuit similar to Fig. 1, the feed-back circuit including a resistance and condenser in parallel, which introduces a delay in the feed-back signal, so that a change in speed necessary to follow a target is enhanced momentarily, thus aiding the tracker in catching up with the target without overshooting it. The same effect may be achieved by a differentiating circuit, Fig. 3A (not shown), in the input to double triode 50. Specifications 489,271 and 500,468 are referred to.