Research On Oblique Collision And Painlevé Paradox Of Flexible Robot Manipulator

When design intelligent robot,to find lightening components with much more flexibility gradually become an important research direction.The contact problem with friction is inevi-table when the robot manipulator grasps the target body.The problem can be further divided into two simpler problerms:1)a normal collision problem in which both objects have only nor-mal relative velocity and 2)a tangential friction problem in wlhich both objects have normal and tangential relative velocity.There is a lot of research results on the first one,but there is no enough research on the problem of Painlevé paradox(dynamic self-locking)which may occur in the second problem.These two kinds of problems can all bring high-frequency impact vibra-tion,transient wave propagation and high-amplitude contact force to the flexible structure,which will further lead to the deterioration of the robot's running accuracy and the reduction of the structural strength.Therefore,this paper studies the frictional contact collision mechanism of flexible two-link robot manipulator.The specific research contents are as follows:(1)The modelling methods and numerical integration algorithms for the dynamics of flexible two-link manipulator are studied.The assumed mode method(AMM)and the absolute node coordinate formulation(ANCF)used in the discretization of structural deformation field are emphatically compared.The numerical results show that the computational effi-ciency of AMM is much higher than that of ANCF.But the result of ANCF is much more accurate.It cannot calculate the large deformation problem by AMM.Although the com-putational efficiency of ANCF is low,the calculation results of that is more accurate.And it can calculate the large deformation problem.The propagation mechanism of the transient stress waves excited during the starting and braking phase is analyzed by ANCF.(2)The improved contact model which considers the both of normal and tangential contact compliance is proposed.The relationship between the normal contact force and the pene-tration is obtained when multiple compression-restitution processes occur in a single colli-sion event.The function expression between energy coefficient of restitution and normal elastic-plastic deformation is established,and the application scope of the contact model is further extended.It can not only calculate the elastic contact problem of double hard spheres,but also calculate the elastic-plastic contact problem for multibody with larger flexibility.In this paper,the movement states of the contact points at arbitrary time moment are analyzed,and the propagation of stress waves in flexible two-link manipulator during contact period is studied.It is found that there is the second normal compression for flexible two-link manipulator.The precision of the contact model is verified by comparing the re-sults with experimental data and LS-DYNA solutions.In addition,the effects of energetic coefficients of restitution and frictional coefficients on the dynamics of oblique collision are analyzed.(3)The Painlevé paradox(i.e.dynamic self-locking)problem of the flexible two-link manip-ulator in frictional sliding is analyzed.Based on the absolute node coordinate formulation,the deformation field is discretized,and the improved contact model is introduced to study the influence of friction coefficient on the Painlevé paradox phenomenon.The typical fea-tures for the Painlevé paradox phenomenon are summarized.