Patent ID: 9670608
Date: 2017-06-06
CPC Classifications: D05B,D05D

Claim:
1. A sewing machine comprising: an upper shaft rotatable so as to drive a needle bar; a lower shaft rotatable so as to drive a feed dog; an upper-shaft pulley provided for the upper shaft; a lower-shaft pulley provided for the lower shaft; a belt linking the upper-shaft pulley with the lower-shaft pulley to synchronize respective rotations; a belt adjusting mechanism contacting the belt, and changing a belt length at a tensioned side of the belt where the belt is drawn in and a belt length at a loosened side of the belt where the belt is drawn in; and a tension adjusting idler applying force to the belt in accordance with a change in the belt length, wherein the belt adjusting mechanism comprises: two idlers contacting to the belt at the tensioned side and the loosened side respectively; an arm supporting two idlers; and a motor swinging the arm, wherein when the adjusting mechanism changes the belt length at the tensioned side so as to elongate the belt length, a feeding phase of the lower shaft is advanced relative to a thread take-up lever linked with the upper shaft, and when the adjusting mechanism changes the belt length at the loosened side so as to elongate the belt length, a feeding phase of the lower shaft is retarded relative to a thread take-up lever linked with the upper shaft.