CONTROL CIRCUIT FOR MOTOR OF SEWING MACHINE

摘要

PURPOSE:To prevent the burning of the motor for the sewing machines beforehand at the time of locking caused by a hevy load, by stopping the circuit which triggers a thyristor when the rotation of the shaft of the main body of the sewing machine is stopped. CONSTITUTION:The sewing-machine motor 7 having a field coil 7a and a rotor 7b is connected to the output terminals of rectifiers 3-6 containing switching elements 3 and 4 with control electrodes, and drives the shaft 13 for driving a sewing- machine needle of the main body of the sewing machine. A trigger circuit 8 which triggers the switching element 3 with the electrodes is controlled by a magnet 12 which is provided on the shaft 13, and by magnetic field detecting switches 11a and 11b for detecting the top dead point and the bottom dead point of the sewing machine needle which is provided so as to oppose said magnet via a timer setting circuit 10 and a timer 9, depending on the rotation of the shaft 13. The operation of the trigger is stopped when the rotation of the shaft 13 is stopped.