Research On Friction Collision And Dynamic Jamming Of Linear Elastic And Nonlinear Material Two-link System

In modern life,multi-legged robots have a wide range of applications,such as climbing floors and exploring complex terrain.The collision with friction between this kind of robot and the ground usually produce a huge impact in the process of motion,which has a negative effect on the balance control and gait planning.In addition,the occurrence of dynamic jamming in the system will also have an impact,which tests the stability of the whole system.The leg of flexible and soft robots can be replaced by two-link systems of linear elastic and nonlinear materials,respectively.At present,there are many researches on collision with friction,but there is not enough research on dynamic jamming,these two kinds of problems both involve contact and friction.Therefore,this paper studies the frictional contact mechanism of linear elastic and nonlinear material two-link robotic system,the specific research contents are as follows:(1)Combining the two-link system model using nonlinear rubber material with the local compliant contact model and the corresponding event driven method,a hybrid computational model(HCM)are proposed to calculate the contact force and motion response of the twolink system.The model of two-link system is discretized by absolute nodal coordinate method(ANCF),the local compliant contact model uses tangential and normal flexible elements to obtain the contact force,and the solution method of system dynamic equations is generalized ? method.(2)The change of energy and stress,the influence of friction coefficient on contact state and contact force are analyzed during collision with friction,when linear elastic material and nonlinear rubber material are used in the two-link system.Compared with linear elastic material,the collision process of nonlinear rubber material is very long,the energy consumption of deformation is very small.In both cases,axial stress wave(P-wave)and bending stress wave(S-wave)have obvious propagation phenomenon.P-wave has faster velocity generally.And the increase of friction coefficient will lead to the decrease of normal contact force,the increase of tangential contact force,the rod tip is more likely to stick.(3)The theoretical model of dynamic jamming of rigid two-link rod is introduced,and HCM is applied to study the dynamic jamming of linear elastic material two-link rod.The results of HCM algorithm and experiment are compared,and the dynamic jamming influence factors of linear elastic material two-link rod system are discussed.In comparison with the experiment,it is found that the dynamic jamming of the system is accompanied by obvious contact bounce phenomenon,and the tiny gap between the rod tip and the platform has no effect on the dynamic jamming.The initial configuration and friction coefficient of the system will affect the occurrence of dynamic jamming,but the plate speed will not.(4)The HCM is tentatively applied to study the dynamic jamming of nonlinear rubber two-link rod.Then,the influence of material on the dynamic jamming of the system is analyzed from the critical friction coefficient and two-link rod energy by using FEM software.The current contact model still needs to be improved in dealing with the dynamic jamming,especially the setting of contact parameters.When the material stiffness of the two-link rod is small,the system is more prone to dynamic jamming,but the bounce phenomenon is not obvious,deformation is more obvious instead.