Dynamics Analysis Of The 3-CPaR&R₁R₂ Hybrid Mechanism With Joint Clearance

Compared with series and parallel mechanisms,hybrid mechanisms have the advantages both of series and parallel mechanisms,such as large working space,high movement speed,small cumulative error,and strong carrying capacity.They have been widely used in various fields in recent years.With the improvement of industrial technology,the application of hybrid robots is moving towards high speed and high precision.Therefore,more and more requirements are imposed on the structure and dynamic performance of hybrid robots and the control strategy.Based on the above background,this paper studies the dynamic characteristics of a 5-DoF hybrid mechanism with and without joint clearance,besides,the control strategy of the hybrid mechanism is studied in detail.In this paper,a 5-DoF 3-CPaR&R₁R₂ hybrid mechanism is taken as the research object.Firstly,the kinematic constraint equation of the mechanism is established and joint parameters are analyzed based on its position relationship and structural characteristics.Second,the kinetic energy and potential energy of the mechanism is analyzed,then the dynamic model of the mechanism is established by using Lagrange equation.Finally,the dynamic model is analyzed using Maple software,and the generalized driving force curve of each driving joint is obtained with Adams software.The comparison of simulation results of Maple and Adams verified the validity of the dynamic model.In order to study the effect of joint clearance on the dynamic characteristics and chaos of the mechanism,the clearance motion model is established by using the perturbation coordinate method;then,the normal contact force and tangential contact force between clearance joint elements are modeled based on the Flores contact model and the modified Coulomb friction model.Next,the joint contact force is transformed to the generalized driving force,and the non-holonomic system Lagrange equation method is used to complete dynamics modeling of 3-CPaR&R₁R₂ hybrid mechanism with joint clearance;Finally,the effects of different clearance sizes and driving velocities on the dynamic performance and chaos of the mechanism are analyzed in detail through calculations,while the relationship between the stability of the mechanism and the collisions of joint elements are explored.Aiming at the wear characteristics of joints clearance under different physical conditions,this paper take the joint lubrication into consideration and adopt the lubrication model of Sommerfeld lubrication conditions of infinitely long journal-bearing to establish its joint lubrication model.At the same time,a hybrid model proposed by Flores is used to integrate the collision contact force and the lubricating force.Then,the calculation of joint wear is carried based on the Archad's model.Finally,the influence of different clearance sizes and driving velocities on the wear characteristics of clearance joints are analyzed in detail through numerical simulation,and the influence of lubrication factors on the dynamic characteristics and joint wear of the mechanism is further analyzed.In order to design a reasonable and effective hybrid mechanism motion controller,this paper addresses the shortcomings of conventional PID control and combines PID control with fuzzy control strategy,then,a fuzzy PID controller is designed.Finally,MATLAB/Simulink and Adams was used to carry out co-simulation to verify the effectiveness of conventional PID control and fuzzy PID strategy by adding disturbance signals.