Sewing machine upper thread guide - is released after thread cutting to prevent stitches missed or jumped on starting a new seam

摘要

Guide for the upper thread in a sewing machine, to maintain thread tension between the lever and the needle or to retain the thread, has an electro-magnet (15) which is operated on cutting the thread at the end of sewing, to start stitching on a new seam. The electro-magnet acts on a swing lever (6) and a drive (27) which rotates in only one direction for a given time span when the lever is pivoted. The rotation of the drive exerts a pull on a Bowden (RTM) cable (44) which acts on the thread guide to release the upper thread. Electro-magnet (15) is activated by a signal from the CPU of a microcomputer integrated into the sewing machine, and it rotates to turn the locking lever (6) anti-clockwise and relase the stop pin of the drive cogwheel (19) from the shoulder of the locking lever (6). Mounting block (23) pivots on an axis (16) through the spring (38) so that the drive wheel (27) is supported by the timing belt. Movement of the mounting block (23) is transferred to the thread guide through the Bowden (RTM) cable (44) to prevent any tension or retention to its start position. Number of stiches which can be made while there is no retention on the upper thread depends on the dia. of the drive wheel (27) and the number of teeth on the drive pinion (20) and drive cogwheel (19). ADVANTAGE - Mechanism opens the thread guide to release the upper thread and prevents stiches being missed or jumped at the start of a new seam after the upper thread has been cut.