GB1309326A - Constant speed drive - Google Patents

Abstract

1309326 Automatic speed control INSTRON Ltd 27 Aug 1971 [7 Sept 1970] 42699/70 Heading G3R The speed of a member such as the crosshead of a tensile testing machine is controlled by comparing the phase of reference pulses with the phase of signals derived from the rotor of a synchro coupled to the shaft of a driving motor. In the system shown, the stator windings of a synchro 13 receive 3-phase current from a square wave oscillator 10, a frequency divider 11, and a sinusoidal converter 12. The oscillator 10 also supplies one input of an arithmetic unit 15 which receives a second input from a constant frequency oscillator 20 through an adjustable frequency divider 23. The output from unit 15 is fed to a divider 16 having the same ratio as divider 11. A comparator 17 compares the phases of the signal from the divider 16 and a square wave derived from the synchro rotor through a converter 18. In operation, when the motor is stationary and the unit 15 receives no input from the oscillator 20, the rotor of the synchro 13 is positioned so that the comparator output is zero. The rotor is shifted to this position by the comparator output, through a filter 19 and amplifiers 21, 22, shifting the drive motor 14, the shaft 28 of which is fixed with the synchro rotor. For driving the motor, the divider 23 is set to a required frequency so that pulses are added or subtracted by unit 15 to the signal from oscillator 10. Thus the phase of the signal to the comparator is advanced or retarded, and a signal is transmitted to the motor such that the synchro rotor is driven at the same speed and in the same phase as the reference pulses. The frequency of the oscillator 20 corresponds to the highest required speed of the motor 14, and the divider 23 may have a number of discrete settings corresponding to desired lower speeds.