Performance Analysis And Optimization Design Of (3PUU)+(RPS+SPS+S) Hybrid Mechanism Based On Improved 3PUU

Three translational(3T)parallel mechanism is a classical type of parallel mechanism.Because of its high stiffness,high speed,stability and high accuracy,it is widely used in engineering practice and is the focus of many scholars at home and abroad.For Tsai’s traditional 3PUU parallel mechanism,the arrangement of U pairs of PUU branches of the mechanism is exactly the same,which is difficult to realize in the actual assembly process.Aiming at this problem,this paper proposes an improved 3PUU parallel mechanism by changing the arrangement of U pairs in the branch,and makes the performance analysis and size optimization design of the two parallel mechanisms based on motion / force transmission,and analyzes the constraint performance and stiffness performance of the improved 3PUU parallel mechanism according to the optimized size.Based on the improved 3PUU parallel mechanism,a RPS+SPS+S two rotation parallel mechanism is connected in series,and a series parallel hybrid mechanism model with 3T2 R five degrees of freedom is proposed.The kinematics modeling,solution calculation,transmission performance and constraint performance are analyzed.Firstly,this paper analyzes the problems of traditional 3PUU parallel mechanism,and proposes an improved 3PUU parallel mechanism.Through the inverse kinematics solution of the mechanism,according to the motion / force transfer index,the transfer performance of traditional and improved 3PUU parallel mechanisms is analyzed,and the transfer performance map of the improved 3PUU mechanism is drawn as an example.By improving the constraint relationship of geometric dimensions of 3PUU parallel mechanism,the parameters of the mechanism are optimized,and the dimensions of the mechanism are optimized with global transfer index(GTI),high quality transfer workspace volume(GTWV)and workspace volume as indexes.Based on the optimized dimensions,the constraint performance and stiffness performance of the improved 3PUU parallel mechanism are compared and analyzed,and the kinematic differences between the traditional and improved 3PUU parallel mechanisms are compared and analyzed by experiments.Then,based on the improved 3PUU parallel mechanism,a RPS+SPS+S parallel mechanism is connected in series inside the mechanism,and a new type of 3T2 R five degree of freedom(3PUU)+(RPS+SPS+S)series parallel hybrid mechanism model is proposed.The forward and inverse solutions of its position and velocity are analyzed and solved,and the three-dimensional diagram of the working space of the mechanism is drawn based on Matlab mathematical software.Finally,based on the motion / force transfer index,the transfer performance of(3PUU)+(RPS+SPS+S)hybrid mechanism is analyzed under the translational freedom and rotation freedom.The transfer performance map of the hybrid mechanism is drawn under different degrees of freedom to comprehensively analyze the transmission performance of the hybrid mechanism.By analyzing the dimensions of the internal and external parallel mechanisms of the hybrid mechanism,the optimization map is drawn to optimize the size of the whole hybrid mechanism,Under the optimized size,the output constraint performance of(3PUU)+(RPS+SPS+S)hybrid mechanism under translational and rotational degrees of freedom is analyzed,and the output constraint performance map is drawn to comprehensively analyze the constraint performance of hybrid mechanism.