Patent GB-622991-A (GB)
Title: Improvements in or relating to electrical control systems
IPC: G05D3/14
Filed: 1946-01-11
Abstract: 622,991. Electrical control systems. SPERRY GYROSCOPE CO., Inc. Jan. 11, 1946, No. 24665/47. Convention date, Nov. 17, 1939. Divided out of 622,927. [Class 40 (i)] An electrical control system comprises means for generating a signal responsive amplitude and sign to the magnitude and sense of the deviation of a controlled variable from a controlling variable, the signal being utilised to reduce the deviation to zero, and comprising a low-speed component which passes through one complete cycle of amplitude and sign while a high-speed component passes through a plurality of such cycles; the resultant signal is zero not only for zero deviation, but for a deviation corresponding to half a low-speed cycle on each side of zero deviation; at these secondary zeros the sign of the resultant signal is such as to restore the controlled variable to zero deviation when the low-speed period is an odd multiple of the high-speed period, when the multiple is even the variable is restored to a deviation corresponding to half the low-speed cycle (e.g. 180 degrees deviation when the low-speed cycle is 360 degrees). To avoid this ambiguity when the multiple is even, an electrical bias of the same nature as the signal and of constant amplitude and sign is superimposed on the resultant deviation signal so that the combination becomes zero at one or more deviation values within the low-speed cycle, but that the sign or phase of the combination in the vicinity of such deviation values is such as to restore the deviation to zero, and not to the ambiguous value. When the generated signal is alternating, a particular phase is taken as positive in sign and the antiphase as negative. In Fig. 1, the field windings 8 of high-speed and low-speed selsyn transmitters 3, 4 are driven respectively through 36: 1 gearing and direct by hand wheel 1, the transmitters feeding corresponding receivers 5, 6 whose field windings 8 generate the input signals for the electrical control system described in Specification 622,927, the servomotor 46 of which is coupled back to the field windings through the mechanical follow-up system 13. The signal output of the highspeed receiver is zero when the deviation is zero and that of the low speed receiver is zero when there is a misalignment of 2¢ degrees, as shown in Fig. 2, in which the R.M.S. values of the A.C. signals are plotted against deviation, quantities above the X-axis being 180 degrees out of phase (opposite sign) with those beneath. V<SP>2</SP> in Fig. 2 denotes the low-speed signal, with zero at - 2¢ and 177¢ degrees, which when combined with the bias V<SP>4</SP> becomes the signal V<SP>6</SP> having zero at 0 and 175 degrees. The high-speed signal V<SP>1</SP> has zero values every 5 degrees, but its phase is such that alone it will only synchronize the controlled object at the even zero points, and its peak valve is limited by the rectifier arrangement 31 to a value less than that of the low-speed signal at 5 degrees deviation, as shown by waveform V<SP>3</SP>. The summation of the signal voltages and the bias voltage gives the resultant voltage V6, which operates the servo motor 46 through the electronic means shown in the drawing. This signal has zero points at 0 and 175 degrees. The sign or phase relations of signal values adjacent to 175 degrees are such that the zero point at 175 degrees is unstable, whereas the zero is stable point at 0 degrees. The signal produced by the summation of high speed and low speed signals with zero values at 0 and 180 degrees would produce a combined signal such as to synchronize the controlled object at both 0 and 180 degrees deviation.