Dynamics Simulation And Chaotic Phenomena Research On Two Types Of Decoupled Parallel Mechanism With Clearance

The mechanical products increasingly develop towards the goal of high speed, heavy load, precision and high stability, so its requirements to dynamic performance of the mechanism are getting higher and higher. Chaos theory provides new methods for the research of nonlinear phenomena in mechanism, and the motion decoupling of parallel mechanism helps to improve its dynamic performance. In this paper, it is taken as the research object for the decoupled parallel robotic mechanisms, the clearance of kinematic pair is considered, the nonlinear dynamics simulation and chaos phenomena are researched, which help to expand the application scope of the chaos theory and deepen the theory research on the dynamics of the parallel mechanism, and it has important theoretical guiding meanings on the development of high performance parallel robotic equipment. The main contents of this paper are as follows:According to the research achievements at home and abroad, the dynamic modeling methods of mechanism with clearance are organized into four categories by the original three kinds, which are ‘contact-impact-separation’ three-state model, continuous contact model, ‘impact-separation’ two-state model and ‘contact-separation’ two-state model, respectively.The RU-RPR and PU-RCRR-CRRR decoupled parallel robot mechanisms are taken as the research object, the revolute pair clearance is considered, Lankarani-Nikravesh contact force model is used to calculate the normal contact force, and the Coulomb friction force model proposed by Ambrósio is used to calculate the tangential contact force, then the dynamical models are established. The variable step size fourth-order Runge Kutta method is used to solve the dynamic models, moreover the solution procedure is described in detail, and the influences of the clearance on the dynamic response of RU-RPR and PU-RCRR-CRRR mechanism is analyzed.The chaos phenomena in the dynamics of the two kinds of decoupled parallel mechanism are identified by using Poincare mapping and Lyapunov exponents. The influence of different factors on the chaos and impact phenomena in the RU-RPR mechanism are analyzed, and the relationship between the chaos phenomena and the impact phenomena is investigated, further more the influence of friction coefficient on the stability of the RU-RPR mechanism is researched.An additionally spring is used to improve the stability of RU-RPR mechanism with clearance, and the relative parameters of the spring are optimized by using genetic algorithm. Furthermore, a new contact force model is proposed to analyze the dynamics of the mechanism with clearance, and its effectiveness is proved.