Research On Dynamic Characterisitcs Of Mechanism With Joint Clearance

As development of the modern high-tech, the requirement of position precision for aerospace and high-precision mechanism is increasing and the operation environment for mechanism is more and more complex. Besides, the manufacture and launch cost of spacecraft is increasing. Thus, more and more researchers have been focus on the issues about high-reliability and long-life of mechanism. Especially, the dynamic characteristics, motion precision, stabilization of mechanical system caused by wear clearance joint for mechanism long time working are the interest point and difficult problem. Friction and wear is one of the chief factors which can cause the reduction, or even failure of the performance and precision of mechanism system. Considering the clearance and wear in joints of mechanical system unavoidance, this work research on the key issues of the dynamic characteristics and wear characteristics of mechanism with clearance joint, which are the theoretical basis of reliability analysis, mechanism design, vibration control, and life forecast of mechanism with clearance joint. The contents are as followings:Considering the mechanism with revolute joint clearance, the clearance vector model of revolute joint clearance is developed and applied to non-regular wear clearance. And the general vector model and mathematical model of revolute joint with clearance are established, which are applicable for both regular assembly clearance and non-regular wear clearance. Then, the dynamics equation of mechanism with clearance is established based on the vector model and mathematical model of revolute joint with clearance. It is the basis of dynamic characteristics and wear characteristics analysis of mechanism with clearance and effect analysis of non-regular clearance on dynamic characteristics of mechanism.The exact description of contact process in joint clearance is necessary for investigating on dynamics characteristics of mechanism with clearance. First, analysis and comparison the conventional contact models are presented. And the nonlinear spring-damp model proposed by Lankarani and Nikravesh is analyzed in detail and then the L-N contact force model is combined with the dynamics equation of mechanism with clearance. Furthermore, the dynamic characteristics of solar panel deployment with clearance, space manipulator with clearance and dual-axis positioning mechanism with clearance are studied and the effects of clearance on dynamics characteristics of space mechanisms are analyzed. Considering the limitation of conventional contact models, a continous hybrid contact model for the revolute joint clearance is proposed based on the improved elastic foundation model. And then the new hybrid contact model is analyzed and compared with the L-N contact model, and the strongpoint of the hybrid contact model is presented. Further, the hybrid contact model is applied to the mechanism with clearance and the correctness and validity of the hybrid contact model for the revolute joint clearance is verified through experiment.Further, the hybrid contact model is applied to analyze the dynamics characteristics of mechanism with clearance. Considering the 4-bar mechanism with clearance, the dynamics model of 4-bar mechanism is established. Then, the dynamic characteristics of mechanism with regular assembly clearance are studied, which is the basis of research on wear characteristics of clearance joint. Hereby, the quantitative analysis method of dynamics characteristics is proposed for mechanism with clearance, and the dynamic characteristics of mechanism are studied quantitatively with cases of different clearance sizes, crank velocities and coefficients of friction.Hereby, the contact loads in joint clearance are obtained. And the wear computational model of revolute joint with clearance is established based on Archard wear model and the dynamic wear calculation frame is presented. For the 4-bar mechanism with clearance presented previously, the wear characteristics of revolute joint with clearance are analyzed and forecasted. As well as the bearing surface profile is reconfiguration after wear. It is indicated that the clearance joint is non-regularly wear and the reasons causing the clearance joint non-regularly wear are presented.Finally, based on the research above, for the non-regular clearance after wear, the nonlinear dynamic variable stiffness coefficient considering the various curvature profiles is introduced to the hybrid contact model. And then, the dynamics and wear integration analysis method is proposed for the mechanism with clearance. Following introducing the wear period, the dynamics characteristics of mechanism with non-regular wear clearance are studied, including research on the effects of non-regular wear clearance on the dynamic characteristics of mechanism are and the wear characteristics of non-regular clearance.