Patent ID: 6564733
Filing Date: 2003-05-20
Classification: D05B

Abstract:
A monitor for bobbin thread on double thread lockstitch sewing machines with a rotating hook with a bobbin housing accommodating the lower thread reserve, the monitor comprising:a revolution sensor sending a pulse per revolution of the main shaft of the machine to a microcomputer; an infrared laser light transmitter for sending a detection beam directed toward a bobbin and which is reflected by a bobbin surface or by the roll of a residual thread length; a receiver for detecting reflected light; a microcomputer receiving signals from said receiver in the form of signals for processing, evaluation and/or forwarding, said microcomputer having a comparator for comparing the different signal patterns with a detection threshold to generate signals for controlling the sewing machine; a controllable power source connected to said microcomputer for an occasional stepwise reduction of the output of the infrared laser light transmitter; a bobbin inserted into the bobbin housing and with at least two chambers separated from one another by a radially directed web having a front surface facing the infrared laser light transmitter, wherein a residual thread chamber accommodates a residual thread length and a main chamber accommodates the main thread length, the bobbin surface including an outer surface of a flange of said bobbin, said outer surface being adjacent to a front light reflecting surface wherein said flange has openings for the detection beam.