Patent ID: 7513203

Claim:
A sewing machine, comprising: a needle which is supplied with an upper thread; a drive element which drives the needle to perform a reciprocating movement in order to carry the upper thread through a sewing material which is advanced between the upper thread and the lower thread, so that the upper thread forms a loop beneath the sewing material; a shuttle which houses a lower bobbin for the lower thread; a shuttle arm on the shuttle which catches in the loop of the upper thread and carries the upper thread around the lower bobbin, so that a stitch is executed on the sewing material; and a thread tensioning and take-up lever which on each stitch draws tight a knot that is formed in the sewing material by interaction of the upper thread and the lower thread; a thread feeder for feeding the upper thread to the needle; a control element which controls the advance of the thread from the thread feeder, so that the thread feeder on each stitch: advances a predetermined length of upper thread, including an excess thread at the beginning of a stitch and corrects the length of the upper thread on completion of the stitch in order that the thread tensioning and take-up lever will receive the correct length of the upper thread when the knot in the stitch is drawn tight, in that the thread feeder either retracts the excess upper thread, or advances the further upper thread required.