Multi-objective Optimization Design Of Two Type Of Three-degree-of-freedoms Parallel Mechanism

Parallel mechanism with Lower-mobility are widely used in engineering and have always been the focus of research by experts and scholars.This paper takes two type of three degree of freedoms parallel mechanism as the research object.Starting from the performance analysis of the two mechanisms,and then to the multi-objective size optimization of the mechanism,the optimal solution of the size of the mechanism that satisfies multiple objective functions is obtained.This paper first takes the SPR+UPR+SPS parallel mechanism with three rotations as the research object,analyzes its inverse solution,and obtains the posture workspace of the mechanism according to the inverse solution and solves its volume.The static analysis of three different types of branch chains in the mechanism is carried out,and the static stiffness model of the mechanism is obtained.The stiffness performance index of the evaluation mechanism is introduced,and the stiffness performance of the mechanism is solved and analyzed.Then,analyze the motion/force transmission performance and constraint performance of the SPR+UPR+SPS mechanism,draw the transmission performance and constraint performance maps of the mechanism,and solve the global transmission index and global constraint index of the mechanism.Taking the organization’s posture work space volume,global stiffness performance index,and the mechanism’s global transfer index and constraint index as the objective function,and the rod length and the rotation angle of the kinematic pair as the constraint conditions,the multi-objective game theory optimization algorithm is used to optimize the size of the mechanism The optimized design was carried out,and the optimized size of the mechanism was obtained,and the performance indexes before and after the optimization of the mechanism were compared.Finally,taking the 2RPU+UPR mechanism as the research object,the closed loop vector method is used to analyze the closed loop of the mechanism,and the precision model of the mechanism is established.Take 2RPU+UPR mechanism’s position and work space volume,motion/force transmission performance,motion/force constraint performance,four global stiffness indexes,and two precision performance indexes as the objective function,and limit the rod length of the mechanism and the rotation angle of the kinematic pair In order to restrict the conditions,a multi-objective optimization mathematical model is established,and the distribution of each objective function in the parameters is analyzed.The optimization algorithm based on multi-objective game theory is used to optimize the size of the mechanism.The advantages and disadvantages of the nine objective functions before and after optimization are compared and analyzed.