Flexible Multibody Dynamics of Sewing Machine with Multi-Clearance Joints

The sewing machine has been widely used in various aspects of life and it is essential to study its kinematic and dynamic characteristics. A dynamic model of flexible multi-link mechanism for sewing machine including joints with clearance is established to analysis its dynamic response in the present work. The configuration of the sewing machine mainly included five subsystems, feeding mechanism, needle bar mechanism, looper mechanism, shearing mechanism and adjusting mechanism. Since the sewing machine mainly consist of linkage mechanisms that are connected by revolute joints and translational joints, the existence of clearances in the joints and the flexibility of crankshafts and linkage are important factors that affect the dynamic performance. Even little clearance can lead to vibration and fatigue phenomena, lack of precision or even make overall behavior as random. The dynamic response of the sewing machine with multi-clearances is discussed and compared between the mechanism with multi-rigid components and with flexible crankshafts and linkages. It is demonstrated that the dynamic response of the mechanism is greatly influenced by the clearance and agrees better with realistic situations when taking the effects of flexibility into consideration. The influence of the clearance size and number of clearance joints on the dynamic response of the mechanism is also investigated.