Patent ID: 7225747

Claim:
A sewing machine, comprising: a needle; means for supplying the needle with an upper thread; a loop taker accommodating a bobbin for a bottom thread, wherein the needle during the cyclic movement and in cooperation with the loop taker performs stitches on a sewing material, which is transported between the upper thread and the bottom thread; a drive unit operatively connected to the needle to move the needle in a cyclic movement; a mechanical element operatively connected to the drive unit through coupling members to perform cyclic movements synchronous with the movement of the needle; a take-up lever operative to complete the stitches formed in the sewing material from the upper thread and the bottom thread; a sensor operative to detect a deviation between: a set position of said mechanical element a point of time wherein a predetermined value of a tensile force in the upper thread is reached at the completion of the stitch and an actual position of said mechanical element at a point of time where the predetermined value of the tensile force in the upper thread is reached at the completion of the stitch; and a control operative to control said upper thread supply means to bring the deviation between the set position and the actual position to zero.