Patent ID: 8100071

Claim:
A sewing machine, comprising: a needle provided with an upper thread; a gripper housing a horizontally fitted lower bobbin for a lower thread; a feeder for feeding a sewing material being sewn between the upper thread and the lower thread; a drive configured to cause the needle to perform an oscillating movement up and down in order to carry the upper thread through the material so that the upper thread forms a loop under the sewing material; a gripper tip on the gripper hooking the loop of the upper thread and carrying the upper thread round the lower bobbin; a take-up lever tightening inside the material a knot of the upper thread and the lower thread in cooperation so that a stitch is accomplished and forms a seam; means causing, when the needle in a stitch performs a sideways shift relative to a longitudinal direction of the seam, the needle to run along a conical surface which in the plane of the sewing material has the form of an arcuate curve corresponding to an arcuate curve of the periphery of the gripper; a feed motor causing the feeder to advance the sewing material by means of the feeder a length y in the longitudinal direction of the seam, on the basis of a seam setting; and a control comprising an algorithm by which the feed motor is controlled to act upon the feeder in each stitch including a sideways shift of the needle to advance the sewing material a correction length e n in the longitudinal direction of the seam, thereby compensating a corresponding deficiency in the longitudinal shift of the needle relative to the material during the stitch caused by the arcuate sideways movement of the needle.