GB683924A - Improvements relating to servo systems - Google Patents

Abstract

683,924. Electric correspondence-control systems. FERRANTI, Ltd., and McCALLUM. D. M. Sept. 11, 1950 [June 16, 1949], No. 22257/50. Divided out of 683,889. Class 40 (i). An electric correspondence-control system for maintaining positional correspondence between input and output members comprises a first oscillator the frequency of which is controlled by the position of the input member, a second oscillator, whose tuning is controlled by the position of the output member, driven by a signal derived from the first oscillator, so that its output has the same frequency as that of the first oscillator but has a phase relative thereto, which is dependent upon the tuning, and a phase discriminator to which the oscillator outputs are applied to derive a d.c. output error signal having magnitude and sign dependent upon the extent and sense of the departure of the relative phase between the two signals from a datum value, the error signal being applied to a servo-motor coupled to the output member whereby, upon departure of the relative phase from its datum value, the servomotor is so driven that the tuning of the second oscillator is brought into correspondence with that of the first oscillator and simultaneously the output member is moved into positional correspondence with the input member. The position of input shaft 11 controls the frequency of the signal generated by oscillator 10, this signal being applied to amplifier and limiter 12 wherein it is converted to square-wave form and thence applied to phase discriminator 18, preferably comprising a ring modulator. A portion of the square-wave output is also applied via integrator 16, wherein it is converted to symmetrical triangular form, to oscillator 13 to drive it at the same frequency as oscillator 10. The tuning of the oscillator 13 which comprises a multi-vibrator, preferably of the cathode-coupled type, is controlled by the position of the output shaft 14 which is driven by servo-motor 22. The square-wave output from oscillator 13 is applied via amplifier 17 to the phase discriminator 18. When the two oscillators are tuned to the same frequency the outputs therefrom are in quadrature and the discriminator gives zero output. When, however, the shaft 11 is rotated with respect to shaft 14, the two oscillatory outputs cease to be in quadrature so that the discriminator 18 develops a d.c. output which, amplified at 21, so drives the servo-motor 22 that the shaft 14 moves into correspondence with shaft 11 and the two oscillatory signals return to their quadrature relationship.