method for forming a knopfloches and knopflochnähmaschine for implementation of the procedure

摘要

A buttonhole sewing machine for automatically forming a buttonhole including right and left parallel side stitching parts, and another stitching part connected to the side stitching parts. The machine has a switch for detecting front and rear ends of each side stitching part, and is capable of sewing the buttonhole in divided parts on opposite sides of a longitudinal centerline thereof so that the two side stitching parts are stitched in the same work feeding direction. The machine comprises a control circuit generating a feed change signal when the number of stitches being formed in one of the side stitching parts has become equal the total number of stitches of the other side stitching part less a predetermined number, and a feed adjusting circuit for reducing a work feeding increment for a time interval between generation of the change signal and a signal from the switch, to avoid a difference in length between the side stitching parts. The machine is also capable of sewing a buttonhole including a circular stitching part contiguous to the side stitching parts, such that one half of the circular stitching parts is sewn immediately after formation of at least one stitch in the other half of the circular stitching part for avoiding a gap between the two halves.