This paper deals with the sensitivity analysis and optimization of system parameters for a classical slider-crank mechanism as a multibody system which includes a clearance between the joints of coupler and slider. Due to the nonlinearity involved in the dynamics of clearance joints, the base reaction force, exerted on the base from the crank, changes roughly and does not vary as smooth as the case of the mechanism with ideal joint. Variation of the base reaction force can be a measure of the undesired vibrations induced due to the effect of clearance joint. After deriving the equations of motion and modeling the clearance, the direct differentiation method is used to conduct a local sensitivity analysis to assess the sensitivity measure of the base reaction force on some kinematic and contact parameters. The results show that the reaction force is more sensitive to the variation of link lengths and link masses compared to the variation of contact surface characteristics such as Young’s modulus, restitution coefficient and contact generalized stiffness in most parts of the motion cycle. On the other hand, the sensitivity of the base reaction force to the clearance size is very higher than its sensitivity to the above-mentioned kinematic and contact properties. Finally, based on the results of the sensitivity analysis, an optimization procedure is used to reduce the amount of the maximum base reaction force by choosing the optimized link lengths. Manuscript profile

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 Manuscript profile