Patent GB-1032342-A (GB)
Title: Improvements relating to phase shift comparison circuits
Inventor: WHITE ERIC LAWRENCE CASLING
IPC: B23Q15/00
Filed: 1961-08-15
Abstract: 1,032,342. Automatic speed control. ELECTRIC & MUSICAL INDUSTRIES Ltd. August 2,1962 [Aug 15,1961], No. 29367/61. Heading G3R. [Also in Divisions G1 and H2] An arrangement for indicating the relative angular positions of two shafts, measured on different scales, comprises a resolver coupled to each shaft for phase modulating oscillations of different frequencies applied to the resolvers, a frequency divider for at least one of the modulated signals such that the output signals from the two channels have equal frequencies, and phase sensitive means for comparing the phases of the two output signals. A gear-cutting machine includes a shaft 18 driven by motor 20 and a shaft 21 driven by the same motor through a differential gear 24, and a gear box 23, having a ratio p : 1. Oscillator 1 supplies oscillations which are frequency divided at 2 by b and at 3 by a,and these oscillations are fed to resolvers 4 and 10 on shafts 18 and 21, the output from resolver 4 then being fed to a resolver 6 on shaft 21. Resolvers 4 and 6 give a phase shift of one cycle for one revolution of the rotor, while resolver 10 gives a shift of 180 cycles per revolution. The resolver outputs are filtered and limited, then divided at 9 by a and at 14 by b to equalise the frequencies of the signals, which are then compared in phase at 15. Any phase difference produces a signal which is fed to motor 17, which adjusts the differential 24 to correct the relative settings of the shafts. The division factors a and b are chosen so that a/b = P Œ 1/180, the + or - sign depending on the sense of connection of the stator windings of resolver 6. It is shown that the output of comparator 15 is then proportional to the error in the relative positions of the shafts, i.e. the error in gear-box 23. If desired the system may be used to compensate for a known difference between the gear box ratio and the desired ratio between the shaft speeds. A further division by c may be carried out between resolvers 4 and 6, with compensation in the other channel, to reduce the maximum value of b necessary to adapt the system for any prime number P. The dividers are preferably binary counter chains having feed-back from selected higher order stages to lower order stages so that the full cycle of the counter can be arranged to any desired number. Phase shifting networks 5 and 11 are preferably four-stage ring counters operated by shift pulses of four times the required frequencry,to give outputs separated by 90 degrees whatever the input frequency. Filters 7 and 12 reduce the harmonics, and further filters may be provided in the resolver input lines. At least half of the filters have to be tunable to accommodate different gear ratios. In a modification (Fig.2, not shown) source 1 oscillates at twelve times the frequency of the source in Fig. 1, and after division the resulting square waves are applied to a sine wave generator including a twelve-stage ring counter (see Division H2). This eliminates the lower harmonics, and the higher ones are attenuated by providing amplifiers with feedback capacitors giving 6dB per octave increasing attenuation with increasing frequency. The pulse outputs from dividers 9 and 14 may be applied to a bidirectional circuit which uses a pulse from one channel to split a pulse from the other channel into two parts which are integrated in opposite senses. The pulse being split is arranged to have a constant length of 100Ás. To reduce the range of frequency variation necessary in one or both channels, a common division by a factor d may be provided, preferably included in dividers 2 and 3. For cutting helical gears fractional ratios may be obtained by replacing resolver 4 by a multiple-pole device. An arrangement is also described in which the shafts are driven by separate hydraulic motors, the speed of the motor driving the second shaft being controlled by the output of the phase comparator. A velocity feedback signal may be provided from the second shaft to its driving motor to prevent oscillation.