Dynamic analysis of a 3-(R) under bar RR parallel mechanism with multiple clearance joints

The existence of joint clearances causes contact and friction between the joint components, leading to important deviations between the expected behavior and real outcome of the mechanism. A 3-(R) under bar RR parallel mechanism with six imperfect joints is analyzed in this paper. The dynamic equations are established by combining Newton-Euler equations with Lankarani-Nikravesh contact force model and improved Coulomb friction force model, the Baumgarte stabilization approach is used to improve the numerical stability. The results show that the joint clearances have considerable effects on the displacement and velocity of the moving platform, and have great influence on the acceleration and driving moments. The mechanism with joint clearances also exhibits nonlinear vibration with high frequencies. In order to better understand the different influence parameters of the mechanism, dynamic responses of the system with different loads, moving velocities and moving trajectories are further studied. It indicates that lighter load, moderate velocity and simpler moving trajectory should be adopted when operating the mechanism to ensure the positioning precision and stability. (C) 2014 Elsevier Ltd. All rights reserved.