Study On Dynamic Modeling And Dynamic Characteristics Of Crank-Slider Mechanism With Translational Joint Clearance

Affected by machining errors,wear and for the need of movement between bodies,the clearance joints exist in various mechanisms,and bring negative effects such as impact,chaos,and precision decline to the mechanical system.The translational joint mainly undertakes the functions of guidance and transmission in the mechanical system,always used in the endeffector.This kind of mechanism requires high stability and accuracy of operation,so the negative impact of translational joint clearance on the system cannot be ignored.This thesis studies the dynamic response of the crank-slider mechanism considering the translational joints clearance,which provides a theoretical basis for the design of the mechanism with translational joints clearance,the prediction of the kinematic characteristics of the system with translational joints clearance,and the improvement of wear.The main contents of this thesis are as follows:The dynamic model of multibody system with translational joint clearance is established based on Newton-Euler method;The motion constraint equations of the system are constructed by vector method,and then the augmented equations of multi-body dynamics are derived;The kinematics model of ideal crank-slider mechanism is also established based on closed-loop vector method.A discrete contact model of translational joint is proposed,which takes into account the nonlinear geometry of clearance contact surface and the complex and changeable contact situation.A suitable model is used to calculate the contact force for different contact conditions.The complex area division is avoided by equating the surface contact force to the joint force of the contact node.Based on MATLAB software,the multi-body dynamics simulation program of crankslider system with moving pair clearance is established,and the simulation is carried out to verify the effectiveness of the model.The influence of clearance size and driving speed on the key dynamic characteristics of the system,such as stability,chaotic degree and contact characteristics,is studied.Aiming at the uneven wear of the translational joint guide,the theory of the local improve of guide is proposed,which is based on the design principle of equal life.According to the distribution rule of contact between the slider and the guide,the contact peak area will replace the wear-resistant material which have lower coefficient of restitution.The system dynamics model after local improved is established.The influence of the position,width and coefficient of restitution of improved region on the motion characteristics of the system is qualitatively analyzed.This study makes innovations in the fields of numerical model of translational joint clearance,dynamic characteristic evaluation of system with clearance and equal life design.The existing theoretical system of motion pair clearance is further improved.The theory of clearance joint is also perfected.The results show that the system with translational joint clearance is highly nonlinear,and the translational joint clearance is an important factor affecting the dynamic response of the system.