A servomotor controller of a Phase Locked Loop type, in which a phase control circuit and speed control circuit are composed of digital circuits, makes it possible to set a speed of the servomotor and to change the speed with ease and accuracy. The controller also makes it possible to reduce the assembling...http://www.google.ca/patents/US4599545?utm_source=gb-gplus-sharePatent US4599545 - Servomotor controller
