Abstract: A speed control system for a motor comprising a main motor circuit supplying motor current to the motor from an A.C. power source through a semiconductor element provided with a control electrode, trigger voltage supplying means supplying trigger voltage to the control electrode of the semiconductor element, motor voltage detecting means for detecting voltage induced in the motor, and automatically variable resistance means having its resistance value varied automatically depending on the detected motor voltage. In the system, the trigger voltage supplied by the trigger voltage supplying means is controlled depending on the variation in the resistance value of the automatically variable resistance means, and the firing angle of the semiconductor element is retarded in response to an increase in the detected motor voltage and advanced in response to a decrease in the detected motor voltage.

Abstract: A motor driven sewing machine comprises pulse generator means for generating a first pulse associated with the first predetermined angular position and a second pulse associated with the second predetermined angular position of the main-shaft of the machine, and state-alternating means for alternatively changing its states between first and second states in response to the first and second pulses. The needle position and cloth feed are controlled in accordance with the states of the state-alternating means.

Abstract: A control apparatus for an electrically driven sewing machine with stitch pattern producing means comprises an electric signal generator for generating an electric signal related to at least one predetermined angular position of a main shaft of the sewing machine, set board means capable of setting therein a desired stitch pattern by means of a probe, and pattern detecting means for reading out cloth feed operation information and needle position information of the stitch pattern set at the set board means. The needle bar is set at a predetermined position in dependence upon the needle position information as read out, while cloth feed is effected in dependence upon the cloth feed operation information, whereby sewing operation is performed in the same stitch pattern as the one stored in the set board means.