Study On Dynamic Of Flexible Mechanism Considering Joint Wear Clearance Numerically And Experimentally

With the rapid development of modern science and technology, mechanical system is developing in high precision, high speed, long life and light weight. The joint clearance and component flexibility will cause obvious influence on dynamic characteristics of mechanism, which will lead to the decrease of precision and reliability of mechanism. Wear is always occurred in clearance joint, which is a very complicated phenomenon and will be influenced by many factors. The accumulation of wear increases the joint clearance, leads to the dynamics response away from the ideal state and makes the precision and reliability decrease even to disability. The clearance joint wear in flexible multibody mechanism with clearance has become a hot issue in the multibidy dynamics. This thesis will study on the joint wear characteristics in flexible and mutibody mechanism considering clearance joint, component flexibility and other factors, which will provide theoretical basis for the optimization design of mechanism with clearance.Firstly, the vector model, mathematical model of joint clearance and the contact force model are established respectively. The flexible component is described using floating coordinate system. The flexible multibody dynamics equations are established based on floating coordinate system and the Lagrange method. Then, the joint clearance model is introduced into flexible multibody dynamics model to establish the flexible multibody dynamics model with joint clearance. The dynamic calculation model of the joint wear in flexible multibody mechanism with clearance is established using the classic Archard wear model method, which proposes the theory foundation for the following study.Then, basing on the dynamic wear calculation model of clearance joint wear, the clearance joint wear characteristics is studied considering the influences of the joint clearance, driving speed, component flexibility, contact stiffness, friction coefficient and so on. Basing on the dynamic wear calculation model of clearance joint, wear process is divided into several calculation periods and it is solved with the thought of finite element to each period. The established model is applied to the crank-slider mechanism and the dynamic equations of the mechanism with clearance and link flexibility are solved. The contact stress and relative slide speed are obtained, which are used as the input parameter of dynamic wear calculation and implanted into dynamic wear calculation process of the clearance joint. The wear characteristics of clearance joint in mechanism are calculated.The irregular clearance after wear is implanted into the mechanism model and the changes of dynamic characteristics after wear are studied. Firstly, the outline of joint element is reconstructed and implanted into the mechanism model. Then the responses of the displacement, velocity, acceleration and the changes of contact force are studied and analyzed. The periodicity of wear is analyzed and the influence between the pre and post period is discussed. The influence of the wear clearance on the response error and reliability of the mechanism are analyzed.Finally, the experiment platform of crank-slider mechanism is built. The dynamic characteristics and wear characteristics of flexible mechanism with joint clearance are studied experimentally. The validity of the previous results is verified. The influence of clearance size and driving speed on the dynamic response and clearance joint wear are studied experimentally. The influences of wear clearance on dynamics of mechanism are obtained.