Servo control system operable on digital basis with limit cycle suppressed

摘要

In a digital servo control system (31) for a carriage of a serial printer or a like movable element, a control signal (125) digitally represents a reference angular velocity for a motor (26) until an instant at which a displacement from a current position of the element to a commanded position decreases to a predetermined value, a positional error during a preselected interval following the instant, and an integrated value (52) of a position error between the current and the commanded positions to suppress limit cycle after the interval. A PWM signal (56-57) is derived from the control signal and position pulses (62 or 63) representative of a variation in the current position. Preferably, small- amplitude limit cycle is forced to occur during the interval with the positional error indicated by a modified signal (182) derived by adding unity to positive and zero position errors.