Patent GB-1169450-A (GB)
Title: Improvements in Methods and Apparatus for Determining the Angular Position of a Shaft.
IPC: G08C19/46
Filed: 1967-03-21
Abstract: 1,169,450. Determining the angular position of a shaft, electrically. SOC. D'APPLICATIONS GENERALES D'ELECTRICITE ET DE MECANIQUE. March 21, 1967 [April 6, 1966], No.13065/65. Heading G1N. In the measurement of the angular position of a shaft by a 2-phase resolver, the rotor of which is coupled thereto, the "main phase difference" between the voltages at a first phase winding of the resolver stator and the first phase winding of its rotor is detected, and this phase difference is corrected by algebraically adding a "complementary phase difference" detected between the voltage across the first or second stator phase winding and the voltage across the second rotor phase winding, the sum of the phase differences giving an indication of said rotor position with reference to the stator. The correction is said to eliminate measurement errors due to non- quadrature phase displacement of the 2-phase input to the stator, and electrical and mechanical defects in the resolver. A mathematical explanation is given. Stator windings S 1 , S 2 , and S 3 , S 4  Fig. 2 are energized by quadrature sinusoidal voltages at frequency # from an oscillator 12 (quartz synchronized multi-vibrator) generating a higher frequency F, via a frequency dividing network 13, squarewave phase shifter 14 and filters 15, 16 which produce sinusoids, and through amplifiers 17, 18. The voltages across stator windings S 1 , S 2 , S 3 , S 4  and rotor windings R 1 , R 2 , R 3 , R 4  are converted to squarewaves Fig. 3 in squaring devices 4, 5, 6, 7 respectively, and fed to a gate system 8 to determine phase differences. The system 8 comprises two gates each constituted by bi-stable trigger circuits. One can be opened only by upward wavefronts of square waveforms C (S 1 S 2 ) Fig. 3, and closed only by upward wavefronts of square waveform C (R 1 R 2 ); thus the "main phase difference" square wave C (R 1 R 2 -S 1 S 2 ) is obtained. The other gate is opened by upward wavefronts of C (S 3 S 4 ) and closed by upward wavefronts C (R 3 R 4 ), thus giving "complementary phase difference" wave C (R 3 R 4 -S 3 S 4 ). The phase difference waveforms are mixed with pulses of frequency F, from the oscillator 12, in a mixer 9 wherein the pulses F, as it were, fill up the positive portions of the phase difference waves as shown at CC in Fig. 3. A counter 10 counts the total number "M" of pulses "F", in a given period ranging from 3 to 5 periods of the stator voltage frequency f, the said total corresponding to the sum of the phase differences to be measured. The angular position of the rotor and shaft with respect to a fixed zero position is equal to:- (M #/F) 180/n where n is the number of pairs of poles phase in the resolver. The total pulses are also stored in a unit 11. An auxiliary resolver may be used to determine which angle sector corresponds to the said angular position. Further, the counting system may be provided with a circuit (not shown) to indicate whether it is necessary to add 360 degrees to the value measured, to give correct angular position. Alternatively, the complementary phase difference used may be that between the voltage across R 3 R 4  and the voltage across S 1 S 2 ; or the corrective phase difference may be taken as one half the complementary phase difference between the voltages at R 3 R 4  and R 1 R 2 .