Mechanism Dynamics Behavior Analysis And Experimental Study Considering The Clearance Joint Coupling Effect

Clearance is an objective existence between two moving parts,the small amount of clearance has a significant impact on the mechanical system,clearance joint induce mechanical position accuracy degradation,motion instability and unpredictable impact characteristics,which have become important bottlenecks restricting the rapid development of high precision,high controllability,high reliability and long life in major equipment and robotics.In particular,the mechanism's dynamic behavior chaos caused by the clearance and clearance coupling have become a fundamental problem in the dynamic design of mechanical systems.For this reason,this paper takes the general machinery with plane revolute joint and translational joint as research object,and studies the force model of the clearance joint and the nonlinear dynamic behavior of the multi-body dynamic system considering the clearance coupling effect.Through theoretical analysis and experimental verification,the influence of system parameters on the non-linear dynamic behavior of multi-body dynamic systems is explored.It can provide guidance and reference for the prediction of dynamic behavior,the dynamic design,the control and the maintenance of mechanical systems.The main contents of this thesis are as follows:First,the energy dissipation in the non-complete elastic collision process is studied.The dynamic response of the non-elastic collision process is derived based on the simplified elastic oscillator model,the calculation of the dissipated energy in the collision process is realized.A modified continuous Contact collision force model,which can support the calculation of collision force for both full elastic recovery,non-elastic recovery and full inelastic recovery.The effects of different coefficient of restitution and different initial collision velocities on contact force,contact deformation,and energy loss during a collision are analyzed in detail.The hysteretic damping characteristics of the collision process are revealed through the coefficient of restitution.Furthermore,based on the Lu Gre friction model,a tangential friction force model of the clearance joint is given.A normal force and tangential force calculation model during the dynamic contact of the clearance joint was formed,which laid the foundation for the nonlinear dynamics research of the mechanism with clearance.Secondly,the contact state of the clearance joint is analyzed,a continuous contact model of the clearance joint is established,a collision model and a tangential force model are introduced,and algebraic equations of the motion constraints and driving constraints of the clearance joint are constructed.The dynamic equations of multi-body systems with multi-clearance joint or clearance coupling effects are established,that is,second-order differential equations and algebraic constraint equations.By using the Baumgarte constraint stabilization method based on direct integration,combined with the determination of the contact state of the clearance,a general solution strategy for the dynamic equation of a multibody system with multi-clearance joint or clearance coupling effects is given.Then,the nonlinear dynamic behavior of a planar four-bar mechanism with clearance and clearance coupling effects,and the influence of different system parameters on it are analyzed.Poincare maps and phase trajectories were used to analyze the nonlinear dynamic behavior of the mechanism with clearance.The Largest Lyapunov exponent method and bifurcation diagram were used to predict the influence of system parameters on the dynamic behavior of the mechanism with clearance.The simulation results show that with the increase of the clearance size,the restitution coefficient,the crank speed,the system changes from periodic motion to chaotic motion,The static friction plays a role in the hysteresis of the motion of the mechanism,while the dynamic friction plays a role in lag and energy dissipation,in this area(dynamic friction coefficient is from 0.075 to 0.1),the more the dynamic coefficient,the more stable the system is.Multi-clearance coupling dynamics analysis shows that:the clearance coupling effect causes the system's dynamic behavior to be complex and changeable,there are 3~n motion modes(n is the number of clearance joint);at the same time,it is found that:compared with the clearance rotation joint,the dynamic influence of the clearance translational joint on the multi-body clearance mechanical system(collision frequency and amplitude)is much smaller,the clearance rotation joint plays a leading role in the dynamic response of the mechanism with clearance.Finally,in order to study the dynamic response of a multi-body mechanical system with a clearance joint,an experimental test platform of a crank-slider mechanism with a variable clearance hinge was designed to verify the validity and correctness of the proposed prediction model with a clearance joint.The correlation between simulation and experimental results is discussed.The experimental test platform can study the impact of flexible rod and space clearance joint on the system.The research results in this paper can provide theoretical basis for the design,reliability analysis,and stability control of mechanisms with clearances.