Patent GB-665541-A (GB)
Title: Electric follow-up systems
IPC: G05D3/14
Filed: 1947-04-01
Abstract: 665,541. Electric follow-up systems. CONTRAVES AKT.-GES. April 1, 1947. [April 1, 1946]. No. 8863/47. Class 40 (i). In an electric follow-up system wherein a control member operates a drive motor through coarse and fine channels comprising transmitters geared to the control member and electrically interconnected with receivers geared to the motor to produce two separate error voltages dependent on the misalignments in the respective transmission systems, the coarse error voltage is connected to the motor control circuit through nonlinear resistance elements whose values are dependent on the current therein while the fine error voltage is connected through ohmic resistance elemencs independent of current, and the current dependent resistance elements are selected in relation to the ohmic elements so that when the coarse error voltage is below a predetermined value only the fine error voltage is effective to control the motor, while when the coarse error voltage is higher than the said value only the latter voltage is effective. Fig. 1 shows a system in which fine and coarse selsyn transmitters have polyphase rotors 1, 4 geared to a control member 9 and connected to the polyphase rotors 2, 5 of corresponding receivers which are geared to a D.C. motor 13 driving the controlled member 12. The transmitter stators are energized from an A.C. line 7 and the receiver stators develop coarse and fine A.C. error voltages, dependent on the magnitude and sense of the positional deviation between the controlling and controlled members, which energize a network C wherein (Fig. 2) a resistance 48 is connected in series with the coarse error signal and two inversely connected dry rectifiers 47 are connected in series with the fine error signal so that when the deviation is small the fine output, and when it is large the coarse output, predominates in the total error signal which is applied to a demodulator D wherein (Fig. 2) a transformer 28 with a double wound secondary combines the error signal in phase and in antiphase with the outputs of a similar transformer 27 energized from the A.C. line. The resultant signals are applied to resistance loaded bridge rectifiers 29, 30 whose outputs are opposed to develop a unidirectional voltage, dependent in magnitude and sign on the positional deviation between the controlling and controlled members, which after amplification excites the field winding 19 of the motor 13 to drive the controlled member into coincidence with the controlling member. An A.C. or D.C. energised potentiometer bridge transmission system may be used instead of that shown, and in the D.C. case the output of the network C may excite the motor directly through a D.C. amplifier. Specification 367,418 is referred to. The Specification, as open to inspection under Sect. 91, describes anti-hunting arrangements wherein the motor is excited through a lowpass filter, D.C. amplifier, and a differentiating circuit introducing a velocity component into the error signal, and wherein the final drive system comprises two D.C. motors energized by permanently excited fields and by fields connected in series with the demodulator output to differentially vary the speeds of the motors, which drive the input members of a first differential gear whose output is geared to one input of a second differential gear and to a worm and nut arrangement controlling a variable speed friction drive connecting a constant speed motor to the other input of the second differential gear, whereby an acceleration component is introduced into the differential output, which drives the controlled member. In a modification, the dual motors are replaced by a variable ratio friction drive operated by an electromagnet excited by the demodulator output, or by a two phase induction motor energised by the A.C. supply and the amplified error - signal from the receiver stators. A degenerative Ward Leonard drive may be used instead of the dual motor and differential gear combination, and the friction drive is replaceable by a Ward Leonard drive, or two motors driving the inputs of a differential gear, excited from a sliding potentiometer contact traversed by the worm and nut arrangement. This subject matter does not appear in the Specification as accepted.