Research On Performance Analysis And Optimation Of A Family Of 2-Dof Planar Parallel Kinematics Mechanisms

Lower-mobility parallel mechanism, especially the novel parallel mechanism with 2,3 degrees of freedom is the foundation and focus of the innovation and performance evaluation of parallel and hybrid robot mechanisms, and has important potential applications and the development value. In the recent ten years, the large number of 2,3 degrees of freedom parallel mechanism were proposed, however the actual number of parallel mechanism is very poor in the actual application. The reasons of hindering their wide application have two main aspects:(1) difficult to select a suitable mechanism. Since the variety of mechanism type, the comparison of different mechanisms for a given operation task is difficult. (2) Parameter optimization of the mechanism is difficult. The performance index of the parallel mechanism depend on its topological type, the actuated layout and design parameters, so it is difficult to globally optimize in the design. In this dissertation, a class of 2-DOF planar parallel mechanism (PPKM) is constructed, and then a unified method is put forward to solve the problem of their optimization for a specified operating task. The main work is as follows:Firstly, a class of PPKM with PRR branches is built. Mainly jobs include three aspects:(1) Five-bar mechanisms with six different branches are analyzed. The PPKM with PRR branches is chosen for study, which is actuated by P joint fixed on the static platform; (2) According to the number of absolute directions of the two-vector-system, the actuated layout problem of a class of PPKM is analyzed. The coordinate-free description of each kind of actuated layout is given; (3) A unified kinematics model to describe a class of PPKM is proposed, so each mechanism in the family is depicted by means of the type of actuated layout, and the structure parameter. Based on the unified model, the kinematic problems, the Jacobian matrix and isotropic are analyzed. Additional, the kinematics analysis software is designed to avoid analyzing singular mechanism and the vast symbolic computation.Secondly, the performance of three typical actuated layout of PPKM is analyzed, mainly including three aspects:(1) First, according to the geometric constraints condition, the design space models of the three institutions are derived using the normalization principle; (2) The relationship between theoretical workspace, singular trajectory, and dexterous workspace with structural parameters is studied and the distributing regulation in mechanism design space is discussed; (3) The global condition number, the global velocity index, the global stiffness index, and the space utilized rate index of three kinds of PPKM with traditional actuated layout are calculated. The design space is adopted to study the relationship between the full performances and size of mechanisms and to draw the performance diagram. A novel space utilized rate index is defined as the ratio of maximal regular dexterous workspace to the covering area of the whole mechanism, which is more practical. The algorithm of traditional boundary searching is simplified and an efficient numerical algorithm is proposed to determine the reachable workspaces, the dexterous workspaces and the maximal regular dexterous workspaces and their boundaries.Thirdly, for a prescribed operation task, an optimal mechanism is found from three different PPKM. The global velocity index, the global velocity index, the global stiffness index, and the space utilized rate index are considered as optimal criterion. And the optimization is earried out at two levels:(1) Parameters of three different PPKM is optimal designed to produce a regular dexterous workspace close to the prescribed operating space; (2) The optimal mechanism is determined considering the different optimization criteria.Finally, a 5-DOF hybrid high-speed spraying robot is designed and the optimal mechanism is adopted as its main parallel mechanism. The kinematics and dynamic analysis are done, and the mobile trajectory is investigated and simulated with Solidworks software. Meanwhile, both 5-axis hybrid robots with single airbrush and with mult-airbrush for spray painting are developed respectively according to the design method. Furthermore, the performance for the two spray robots with different structures is compared.