| 摘要 |
PURPOSE:To increase the penetrating force of a needle at a low speed, by providing means for supplying electric current intermittently at intervals longer than a response time of a motor for a sewing machine. CONSTITUTION:An intermittent control part 38 for currents is actuated when a motor speed is lower than that of criterion voltage for a low speed. Since this means that the lowest speed command voltage is at the lowest speed command speed, it satisfies two conditions under which a motor 5 for a sewing machine is rotating at a low speed and a load against the motor 5 is excessive. That is to say, a third comparator 56 is used as a low speed-detecting means and is also used as a high load-detecting means, and a second oscillator 57 is used as an intermittently current-applying means. After the penetrating force of a needle is increased and the needle pierces cloth, the motor speed is again raised and the deviation of its rotation is made small, following which a motor current I decreses and low speed rotation at the lowest speed command voltage is continued. |
