Device for monitoring the bobbin thread on double thread lockstitch sewing machines

摘要

A monitor is provided for a bobbin thread on double thread lockstitch sewing machines. This is preferably a sewing machine with a rotating hook with a bobbin housing accommodating the lower thread reserve. The monitor includes a revolution sensor which sends a pulse per revolution of the main shaft of the machine to a microcomputer. An infrared laser light transmitter sends a detection beam directed toward a bobbin. The beam is reflected by the bobbin or by the roll of a residual thread length to a receiver and is sent by the latter to the microcomputer in the form of signals for processing, evaluation and/or forwarding. The microcomputer is adapted to compare the different signal patterns with a detection threshold (DS) to generate signals for controlling the sewing machine. A controllable power source is connected to the microcomputer for the occasional, stepwise reduction of the output of the infrared laser light transmitter. A bobbin can be inserted into the bobbin housing with at least two chambers separated from one another by a radially directed web. One chamber (the residual thread chamber) accommodates a residual thread length and the other chamber (the main chamber) accommodates the main thread length. The front surface of the web faces the infrared laser light transmitter as well as the outer surface of the flange of the bobbin. This outer surface is adjacent to the front surface, reflecting light, wherein the flange has openings for the detection beam.