In this study, the longitudinal shrinkage behavior of knitted fabrics during drying has been studied. In this context, a model is presented to predict the longitudinal shrinkage of plain knitted fabric during drying process. In order to model the shrinkage behavior, a 1DOF model consists of a mass, a linear spring and a linear damper have been used. In presented model the time-varying mass is considered due to fabric drying process. Nonlinear Equation of motion derived from the model have been solved using Three-order Straight Forward Expansion method. The results of the model were compared with the experimental results for five samples with different courses densities. The results shown that in high courses densities the presented model is capable enough to predict the longitudinal shrinkage of plain knitted fabric mass center during drying process. Error rate is 11.3 percent for the samples with high density. But with decrease in density, the error rate increases to 18 percent. Then the genetic algorithm is used to optimize the model. Using optimized model the simulated error rate fell into 5.7 percent for samples with high density and the rate fell to 6.1 percent with decrease in density. تفاصيل المقالة

Sewing is one of the most commonly used manufacturing processes in the world. In the textile industry, development of sewing machines with optimal mechanical performance is very important. Obviously, the quality of sewing, the increase of the needle transmission force and the optimal mechanical advantage are greatly dependent on the design criteria of the needle driving mechanism. Unfortunately, despite the importance of this topic, very limited number of researches has been carried out in this regard. Therefore, in this paper, first a newly developed needle driving mechanism of a sewing machine is introduced. Then, the concepts of transmission angle and mechanical advantage are described. Next, the multiobjective constrained optimization process of this mechanism using the genetic algorithm is explained. For this purpose, some objective functions are presented to reduce the needle generated heat by minimizing the needle velocity in the penetration zone, to reduce undesirable vibrations by minimizing the needle jerk, and to increase the mechanical performance by maximizing the mechanical advantage and minimizing deviations of the transmission angle from its ideal value. Results confirm improvement of the required design criteria of the newly developed mechanism in this study تفاصيل المقالة