| The flexible parallel mechanism is widely used in aerospace,precision machining and measurement due to its advantages of light weight,low energy consumption and high accuracy.However,the flexible components of the parallel mechanism are easy to bend and stretch under the action of driving force or external force,which leads to the decrease of the system motion precision.Meanwhile,elastic deformation will cause large stress resulting in the damage of flexible members.Therefore,to analyze the kinematics and dynamics behavior of flexible parallel mechanism,the establishment of accurate flexible multi-body flexible dynamics model is of great theoretical significance and application value for engineering.In this paper,the flexible planar 3-RRR parallel mechanism is taken as the research object,and the absolute nodal coordinate formulation is adapted to study the modeling method of its dynamic model.According to the basic modeling theory of the absolute nodal formulation method,the dynamic simulations of flexible cantilever beam and flexible space double pendulum are carried out.At the same time,the finite element analysis model is established under the same condition by using the finite element analysis software ANSYS.The accuracy of the absolute nodal coordinate method and the feasibility of using the ANSYS hinge element are verified,respectively.The flexible multi-body dynamic modeling and solving of flexible planar 3-RRR parallel mechanism are completed.The active rod and driven rod described by the absolute nodal coordinate three-dimensional beam elements are all regarded as flexible rods.The direct integration method is used to solve the system dynamic equations and the poses of parallel mechanism at all times are obtained.The results show that due to the bending and stretching deformation of the flexible rods,the output trajectory of the mechanism deviates greatly,the moving platform rotates,the acceleration of the moving platform fluctuates,resulting in that the stability of the system is reduced.The finite element analysis model of planar 3-RRR parallel mechanism is established in ANSYS for further investigation of differences between the results of the two simulation methods It is verified that the absolute nodal coordinate method is superior to ANSYS in dealing with large deformation problems.In order to explore the influence of the parameters of parallel mechanism influence onthe performance of mechanism,two evaluations indexes are set up,which are the standard deviations of the distance from the desired trajectory to the center of mass of the moving platform and the rotating angle of the moving platform.Five parameters that affect the motion performance of the mechanism are analyzed respectively.These parameters are elastic modulus of flexible rod,cross section shape and size of flexible rod,load of mechanism,angular frequency of moving platform and the centroid trajectory of the moving platform.The results show that different values of parameters have different influence on mechanism.The elastic modulus of flexible rods and the cross section shape and size have the most significant influence on the mechanism.The dynamic characteristics of the mechanism can be improved through transforming the parameters of the rod cross section without increasing the mass of the system to actualize the lightweight design of mechanism. |
