BOBBIN THREAD MONITORING DEVICE OF LOCK STITCH SEWING MACHINE

摘要

PROBLEM TO BE SOLVED: To provide a device for monitoring the three possible operating states of a lock stitch sewing machine which device is manufactured at low cost and is less prone to be contaminated with sewing dust. SOLUTION: The monitoring device is provided with a rotation sensor (19) which sends a pulse to a microcomputer (17) each time a sewing machine arm shaft (20) is rotated by one turn; an infrared laser let-off device (14) which lets off a detection light beam (12) which is directed to a bobbin (2), reflected from the bobbin (2) or the remaining thread on the bobbin toward a photodetector (15), and sent from the photodetector to the microcomputer in the form of consumption signal, evaluation signal, and/or transfer signal; a comparator provided in the microcomputer for comparing variation in various signals with a detection threshold (DS) for generating control signals for controlling the sewing machine; and a power source (16) which is connected with the microcomputer and can be controlled so as to temporally or periodically reduce the power of the infrared laser let-off device.