Modeling of industrial sewing machines and the balancing of thread requirement and thread supply

A sewing machine consists of four basic mechanisms: a take-up mechanism, a needle-motion mechanism, a material-feeding mechanism, and a bobbin. Its proper operation requires a delicate balance of these mechanisms. This paper introduces a computer-simulation model that represents these mechanisms and uses the model to predict the kinetic behavior of sewing machines. Based on the simulation, a quantitative understanding of the sewing machine can be achieved that leads to improved sewing-machine design and better sewing-process control. In particular, the balance of thread supply and thread requirement is studied. The thread supply is defined as the amount of thread supplied by the take-up mechanism within one stitch. The thread requirement is defined as the amount of thread required in one stitch and is controlled primarily by the bobbin mechanism. Both properties change instantaneously. From a practical point of view, if the thread requirement were much larger than the thread supply, then there would be skip stitches (when the loop cannot be formed properly) or even thread breakage. On the other hand, if the thread requirement were much less than the thread supply, then there might be poor stitches (with too much thread in the loop) or even needle-jamming. By using the simulation model, the instantaneous balance of the thread supply and the thread requirement is quantitatively studied. It is shown that the balance of thread supply and thread requirement can be changed and optimized by changing the design parameters of the take-up mechanism. The model is validated experimentally by using a Pfaff lockstitch industrial sewing machine.