ANALYSIS APPROACH FOR STITCH CONSTRUCTION AND STITCH TIGHTENING OF LOCK STITCH SEWING MACHINE

Conventionally, stitch quality has been evaluated visually. In this study, stitch structures are shown in terms of skeleton stitch models to obtain quantitative analysis of stitch tightness. The analysis results show the following interesting stitch properties: (1) Formation of good stitches largely depends on, besides balanced upper and lower threads tensions, the cloth tightness produced by interlaced upper and lower threads. Accordingly to the analysis results, proper lower thread tension setting is important to get good cloth tightness which has traditionally been undiscussed. A lower tension of the lower thread produces a rectangular stitch model, and a higher tension of the lower thread forms an oval stitch model. (2) In sewing thin, medium, or thick material at a low speed, it has been found that there is a corelation of systematic parabolic regression between the upper and lower thread tensions that lead to formation of well-tensed stitches.