A servo-drive for accurate speed control
D E Caro, J Y Freeman, L U Hibbard · Journal of Scientific Instruments · 1954
A servo-drive system suitable for the accurate control of speed is described. It consists of a high-frequency phonic motor excited by a synchronous signal picked up from the rotor teeth and amplified. The motor torque can be varied rapidly by control of the amplitude and phase of the excitation. A system is described by which the torque is controlled by an applied voltage, the electrical response time being as small as 1 msec. This particularly suits an application in which speed is sampled and corrected impulsively in times of the order of 10 msec. The use of a phonic motor facilitates the development and testing of an accurate closed-loop system as the loop can be broken and accurate steady speeds maintained by oscillator control of the motor excitation. The avoidance of slip rings and commutators simplifies maintenance requirements and reduces electrical interference.