Sewing machine, fabric and thread dynamics
In recent years, sewing technology has witnessed dramatic increases in machines speeds, new types of materials, new sewing threads and evaluation methods – but the principal type of sewing machine remains the lockstitch type and this is likely to remain the most common and versatile for the foreseeable future, particularly for sewing woven fabrics. Sewing machine speed increases lead to a loss of control of the sewing process due largely to an increase of the dynamic forces and consequently to problems such as seam pucker. In this research computer-based instrumentation and high-speed digital image and signal acquisition systems were developed to study the dynamic effects of the sewing machine, fabric and thread on seam pucker. Needle thread tension, needle bar pressure/tension, presser-foot pressure and displacement signals were acquired simultaneously by 4 strain-gage/piezo-quartz sensors mounted on a Pfaff-563 machine and results were related to pucker measured by a CCO colour-video camera system integrated with the sewing machine. A series of experiments conducted on various types of fabrics provided illustrative examples of the characteristics of each signal acquired (distinctive shape, amplitudes-peaks valleys locations, duration etc), and also enabled their characteristics to be compared and the interactions among the signals to be studied. For example it was found that the increases in magnitude of the dynamic forces in relation to sewing machine speed increases from 200rpm to 5500rpm were lower than expected (needle thread tension 2.6 fold, presser-foot 1.2 fold and needle penetration force 3.2 fold). A comparison of the needle thread tension for standard woven fabrics and micro-fibre fabrics showed a significant difference in the signal shape, location and amplitudes. The instrumentation developed is located at the Institute of Textiles and Clothing of the Hong Kong Polytechnic University in Hong Kong.