Abstract
It is well known that the stitch length increases with increasing operational speed of the singleneedle lockstitch sewing machine. This paper aims to investigate the causes of such increases of stitch length by determining the change of the fabric feed motion. The locus of the point of feed dog during operation were photographically observed for this purpose. The observation has revealed that the feed length of the fabric, increased with increasing operational speed, is dependent on the speed of the feed dog and can almost be predicted both qualitatively and quantitatively.
The presser foot may move up and down at low pressure of the presser foot and high-speed operation. In other words, the presser foot is disconnected from the feed dog. In such case, the fabric cannot be fed normally. Therefore, the higher pressure of the presser foot might be required at high-speed sewing than at low speed.
