Abstract: A motor drive includes an invertor (5) with which a motor (6) is rotated at a variable speed. To suppress noises caused by ripple components contained in currents flowing in phase coils of the motor, the invertor (5) is controlled so as to direct a commuting current flowing from the phase coils to a d.c. power source (1) and at a time when the motor is decelerating to circulate in a path including the phase coils and the switching transistors of the invertor (5). This control is performed when the commuting currents fall below a predetermined level.

Abstract: When a sewing machine is locked during stitching of a thick fabric, the rotational direction of a sewing motor is alternately reversed at a predetermined time interval. A needle operatively coupled to the sewing motor through a mechanical system is moved up and down, whereby the needle sticks into the same stitching point for a desired number of times.

Abstract: In a sewing machine, a judgment is made whether a needle speed is above or below a threshold speed. When the needle speed is above the threshold speed, meaning the machine is sewing normally, a constant power is supplied at a level associated with a foot pedal setting. When the needle speed drops below the threshold, the power is alternated between power on and power off states to drive the needle in a manner similar to a hammer driving a nail. The indication of needle speed may be obtained by measuring the rotating speed of the sewing machine motor, judging the load applied to sewing machine motor, or by detecting the driving current supplied to the sewing machine motor.

Abstract: A control system for a sewing machine includes at least an impulse generating circuit and a counter means connected thereto. A shift register having at least four bits and a mode selecting circuit connected thereto is provided. A circuit for feeding the work material or fabric forwards, a circuit for feeding the work material backwards, and a circuit for resetting these circuits are provided. The system is:(1) capable of selecting, in advance, the number of stitches in a single forward and backward reciprocal non-ravel seaming;(2) capable of doing a desired number of the repeated non-ravel seaming on a certain place (repeated reciprocal non-ravel seaming mode); and(3) capable of free selecting between the conventional non-ravel seaming mode and the above-mentioned repeated non-ravel seaming mode (the free mode selection).

Abstract: An improved speed controlling system for an electric motor, mainly used in a sewing machine includes a motor connected to a power supply, a speed controlling circuit or circuits for operating the motor at variably controlled speeds, and an electrical braking circuit or circuits for braking the motor upon receiving deceleration command from the speed controlling circuit(s) to transfer the motor from a high speed running state to a low speed running one. Electromechanical braking means are provided for acting on the motor, during at least a part of the braking period, the braking means being controlled by the electrical braking circuit(s). A low speed setting circuit is disposed in the speed controlling circuit(s) for maintaining the low speed running state caused by the electromechanical braking means and the electrical braking circuit(s).