Kinematic Optimization And Error Analysis Of A Novel Two-DoF Rotational Parallel Mechanism

In order to meet the requirements of spatial rotating mechanism in the fields of aerospace and bioengineering,a new type of parallel mechanism with two degrees of rotational freedom,2-RRRR&2-RSR mechanism,is studied in this paper.The research contents include topology analysis,kinematic optimal design,error modeling,and sensitivity analysis.The research results are as follows:1.Based on the structural characteristics of the two-degree-of-freedom rotational parallel mechanism,the geometric conditions of the 2-RRRR&2-RSR mechanism for realizing two-degree-of-freedom rotating motion in its given workspace are studied.For a 2-RRRR&2-RSR mechanism with symmetric structure,the forward and inverse position analysis model and velocity mapping model are developed,and the validity of these theoretical models is verified by software simulation.2.The workspace description of 2-RRRR&2-RSR mechanism is realized based on the motion characteristics of the two-degree-of-freedom rotational parallel mechanism.Considering the practical engineering experience and geometric constraints of the mechanism,the limit boundary search method is used to search the workspace boundary of the mechanism.Faced with the problem that the dimension of Jacobian matrix of rotational parallel mechanism is not uniform,the dimensionless kinematic performance evaluation index is defined based on the relationship between motion screw and constraint screw in screw theory,and the objective function of kinematic optimal design is constructed.Considering the constraint conditions such as the rotation angle of the joint and the interference of the rod,the kinematic optimal design of 2-RRRR&2-RSR mechanism is completed.3.On the basis of the symmetrical structure of 2-RRRR&2-RSR mechanism,the error models of RRRR and RSR limbs are established with the help of screw theory.Unifying these two models into matrix form,the error mapping model of the end pose error of 2-RRRR&2-RSR mechanism with the geometric errors of each limb is established by eliminating repetitive terms and correcting error coefficients.4.According to the error model of 2-RRRR&2-RSR mechanism,the sensitivity analysis index for evaluating the end pose accuracy of the mechanism is proposed based on the Monte Carlo method.Then the influence of geometric parameter error sources on the end pose error of the mechanism is studied,and the error sources which have a greater impact on the end pose error of the mechanism are identified.These results lay a theoretical and technical foundation for the prototype and follow-up research of the two-degree-of-freedom rotational parallel mechanism.