Research On Analysis,Optimization And Trajectory Planning Of 3T1R Parallel Mechanism For Coordinate Assembly

The assembly of vehicles has been realized by industrial robots for years.However,assembly of 3C(Computer,Communication and Consumer Electronics)products still heavily relies on human labor.This is because 3C products are characterized by small size,lightweight and high assembly precision requirements.Increasing price of human labor pushes the automation evolution of 3C product assembly lines.Anyway,current industrial robots are always not capable of satisfying the requirement of high precision,high dexterity and low cost.In view of that,a redundant degree-of-freedom quotient kinematics machine(QKM)is proposed in this thesis which consists of a 4-DOF 3T1R mechanism and a 3-DOF 3R mechanism.In this thesis,an improved 3T1R parallel mechanism,i.e.2PRPaRR-2PRPaR parallel mechanism,is introduced.Most 3T1R mechanisms in the literature,whose rotation degrees of freedom is along the axis perpendicular to the base plane,are designed for pickand-place operations.In contrast,the proposed 3T1R mechanism has a rotation degrees of freedom along the axis parallel to the base plane.Kinematic modeling,forward and backward kinematic solution,singularity analysis,and workspace description is given in this thesis.According to its 3C product assembly application,a dimensional optimization objective function is deduced.The condition number of the dimensionless Jacobian is used as a performance index of the objective function,which is solved by genetic algorithm.A performance comparison between the pre and post optimized mechanism has verified the effectiveness of the optimization approach.Based on the optimization results,3D virtual model design,components selection and prototype development are accomplished.To further study the trajectory planning problem of coordinated assembly,a 3PSS/S is introduced to coordinate with the proposed 3T1R mechanism.A master-slave coordination strategy is developed to assign the 6-DOF demonstrated assembly trajectory to each of the two parallel mechanisms.Afterwards,the cubic B-spline interpolation technique serves to plan the motion trajectories in the joint space for the sake of smoothness of the trajectories.A simulation in V-REP software platform and an experiment with the prototype have demonstrated the usability of the proposed 3T1R mechanism in 3C product assembly in a dual-arm coordination manner.