JPS6472792A - Thread detector in sewing machine - Google Patents

Abstract

PURPOSE: To detect the existence of a thread without forcing it to be mechanically burdened by grasping presence or absence of the fluctuation of an electric charge which occurs in a detection electrode owing to the horizontal shake of the thread as against a needle location hole. CONSTITUTION: The detection electrode 22 is circularly formed along the peripheral edge of a thread carrying through hole 21 and a timing signal generating means 5 generates a timing signal by synchronization with the vertical movement of a needle 3 in case the thread to be detected exists inside the detection electrode 22 in a sensor 4. When a body 32 to be detected is rotated by the rotation of a main shaft 31 in the sewing machine, a proximity detecting signal is given to a timing signal generating circuit 34 whenever the body 32 approaches an proximity sensor 33 and the timing signal is outputted. Then a judging means 6 judges the existence of the fluctuation of a voltage signal by receiving the voltage signal from the sensor 4 and the timing signal from the timing signal creating means 5 and outputs a thread absence judging signal in case of no fluctuation in it. The judging means 6 is constituted of an amplifier part 35, a timing circuit 36 and a comparing circuit 37 and a stop control means 7 stops a motor for driving the main shaft of the sewing machine when it receives the thread absence judging signal (thread breakage signal) from the judging means 6.