Sewing machine with thread-tension control system

Abstract

The tension of the sewing machine's upper thread is varied automatically, in a variety of ways not requiring conscious participation on the part of the user of the machine. When one of a set of selectable stitch-patterns is selected by the user, an appropriate thread-tension value is automatically established, although the user retains the ability to adjust the automatically established tension value if he wishes. When the user swings the presser-foot lever of the machine up, to raise the cloth presser foot up from the cloth, e.g., for basting work, the thread tension is automatically lowered to a predetermined value suitable for basting, although still adjustable by the user if he thinks necessary. Where a stitch-pattern is implemented using an addressable ROM, tension command data for each stitch of the stitch-pattern may be stored in the ROM, for variation of thread tension from constituent stitch of the pattern to the next. Alternatively, the ROM stores no tension control data per se, and instead a calculating circuit calculates, from the mere stitch-control data presented by the ROM, distance-dependent values dependent upon the distances between successive needle-penetration locations of the stitch-pattern, and from those derives appropriate tension command signals.