Dynamic analysis of planar four-bar mechanism with clearance in microgravity environment

In the space microgravity environment, joint clearance is an important factor affecting the motion accuracy and stability of the mechanical system. This paper analyzes the dynamics of the four-bar mechanism with clearance in the microgravity environment. The two-state model is employed to describe the revolute joint with clearance. The continuous contact force model and the improved Coulomb friction model are selected to calculate the normal collision force and tangential friction force under the contact state, respectively. On this basis, the dynamic equation of the multibody system is derived, which is verified by both the analog experiments on the ground and simulations. Furthermore, parametric analysis and nonlinear characterization are presented. The results show that the existence of clearance will cause collision impact at the kinematic pair, which reduces the kinematic accuracy and operational stability of the mechanism. The joint clearance destroys the periodicity of the mechanism motion and increases the chaos phenomenon of the system. It could be concluded that properly reducing the clearance size, reducing the rotational speed, and increasing the friction coefficient can reduce the collision impact between the moving components.