Kinematics Analysis And Trajectory Planning Of A Serial-parallel Robot

Compared with serial mechanism,a well-designed parallel mechanism has some advantages,such as high stiffness and satisfactory precision,but since it possesses the characteristics of closed-loop structure,there are some problems about the relatively small workspace of the mechanism and a small posture angle of end-effector affecting the machining properties of the mechanism.Nowadays,serial-parallel mechanism which consists of limited-DOF parallel mechanism and serial mechanism moving in other directions has become the hot issue in the field of robot research.Based on Delta robot widely used for industry and considering the advantages of the serial mechanism,a five-DOF serial-parallel robot is analyzed in this dissertation.Not only does the serial-parallel robot expand the workspace of purely parallel mechanism to a great extent,but also makes up for low stiffness of purely serial mechanism.Firstly,kinematic character of the parallel part of the serial-parallel robot is analyzed via screw theory,and kinematic DOF of the robot is found by using K-G correction formula;D-H parameters of the robot are presented,and the inverse kinematic is performed via D-H method;the direct kinematic is deduced by using analytical method;the algorithm error of the direct and inverse kinematics is analyzed by using MATLAB,and the algorithm turns out to be effective and to have the satisfactory computation precision.Secondly,based on the inverse kinematic of the parallel part of the serial-parallel robot,graphical method is proposed to analyze the workspace of the parallel part,which is compared with that of finding through Monte Carlo method,and there is feasibility for analyzing the workspace of its parallel part via graphical method;the workspace of the serial part of the robot is found by using graphical method;the figures of the workspace of the serial-parallel robot is presented in MATLAB.Thirdly,the fundamental conception and correlation theory of trajectory planning are briefly introduced;cubic polynomial algorithm is compared with quintic polynomial algorithm in joint space;according to trajectory planning algorithms,the direct and inverse kinematic algorithms are used to plot all kinematic curves of five joint chains in MATLAB;the trajectory of the robot is planned by using linear and arc interpolation algorithm in Cartesian coordinate space.Finally,the DOF of the serial-parallel robot added kinematic pairs is verified in ADAMS/View,and the result indicates that there is a five-DOF of the serial-parallel robot;STEP5 function is used for driving function to the simulations of the serial-parallel robot model,and all kinematic curves of end-effector and five joint chains are plotted in ADAMS/View;the result indicates that there are all smooth curves,which verifies feasibility of the kinematic algorithms;it also verifies that using quintic polynomial algorithm could ensure that the serial-parallel robot runs smoothly in a simulation process,which enables motors to use longer and provides a theoretical basis for the following research about trajectory control further.