Abstract: A speed control circuit has a comparator which compares a voltage signal which is indicative of the actual speed of a shaft with a digital reference which is indicative of the desired speed of the shaft. If the actual speed is different than the desired shaft speed, a bi-directional control mechanism is operated in one direction or the other to adjust the actual speed of the shaft. The operation of the bi-directional control mechanism is periodically interrupted to increment the amount the actual shaft speed is changed to prevent overshoot of the desired speed.

Abstract: A tachometer pulse generator is coupled to the shaft of an electric motor. The output of the pulse generator is gated into a pulse counter circuit during a first fixed time interval. During a second fixed time interval which follows the first fixed time interval, the motor is speeded up if the count attained by the counter in the preceeding first time interval is less than a preset number or is slowed down if the count is equal to or greater than the preset number. The first and second time intervals follow each other periodically, thereby alternately measuring the speed of the motor and correcting the same to approach a preset speed which is proportional to the preset number of the counter circuit. Two preset numbers can be employed, one corresponding to a lower speed correction threshold and the other corresponding to an upper speed correction threshold.