Kinematics And Restraining Stiffness Analysis Of A3-PRRU Parallel Robot

With the development of parallel mechanism technology, the lower-mobility parallel robots which has less than six degrees of freedom arise people’s concerns. Because lower-mobility parallel robots have advantages of simple structure, lower cost in design manufacturing and maintenance, it is widely used in a number of place where do not need six degrees of freedom. The [PP]S parallel can undergo two rotational DOFs and one translational DOF that has great value in industry application. Thus, it has received extensively attention from international industrial and academic circles.This paper focuses on stiffness analysis of a3-PRRU PR. And the main contributions are as follows.According to the relationship of the twist screw system and the wrench screw system, the Matlab GUI interface to solve the wrench screw system was developed.Based on the screw theory, the DOFs was worked out by using the general analytical method in the base coordinate frame. And the wrench screw system of moving platform was solved through respectively establishing the twist screw system of the three branches. The wrench screw system was analysed, which not only confirmed the DOF of mechanism, but also illustrated the attribute of the DOF. At last the number of the DOFs was verified again by Kutzbach Grubler formula.The forward and inverse position of the3-PRRU parallel robots were analysed, and then the3-PRRU parallel robot capability of orientation was proposed, which was helpful in gaining workspace of tool extremity. Finally, the influence of structure parameters on the working space was concluded.Based on the concept of sub-space in the moving coordinate frame, the Generalized jacobian matrix of the institutions was established so as to propose institution static stiffness matrix and define the elements of the matrix. And finally through the theoretical simulation, the maps of different directions static stiffness were obtained, as well as the minimum stiffness matrix pattern.The3D virtual prototype of3-PRRU parallel robot was established in SolidWorks, and the stiffness of three positions of the institutions were obtained by COSMOS works. At last the results were compared with the theoretical analysis. Modal analysis of the typical position of3-PRRU was studied in order to draw fifth-order natural vibration frequency of the system, as well as vibration mode maps.The achievements stated in this thesis lay a solid theory foundation for the realization of structural optimization design and trajectory planning.