Analysis And Research On Static Error Of 3-UPU Parallel Mechanism

In recent years,the study on the positioning error of parallel mechanisms has received extensive attention from researchers at home and abroad.The research of positioning error mainly includes error analysis,error modeling and kinematic calibration.Kinematic calibration is divided into four steps: calibration modeling,pose measurement,parameter identification and error compensation.This paper is based on the 3-UPU parallel mechanism to compensate the positioning error.Kinematic analysis of 3-UPU parallel mechanism.First,establish a coordinate system according to the structural of the mechanism to obtain the position coordinates of key components.Then,based on the closed-loop vector method,the forward and reverse position solutions of the mechanism are solved.The spiral theory is used to calculate the degrees of freedom.Finally,the coordinate transformation is used to study the Jacobian matrix and singularity.Error modeling and analysis of 3-UPU parallel mechanism.According to the structure and assembly of the mechanism,the main sources of positioning errors affecting the parallel mechanism are analyzed.An error model is established based on the vector differential theory,and it is simulated and analyzed using Matlab software.Obtain the influence of the rod length error and the circumscribed circle radius error of the moving and fixed platforms on the end position error,and draw the curve.The kinematics calibration method is used to study the positioning error of the 3-UPU parallel mechanism.Establish a calibration model with error compensation based on the positive position solution.Using laser interferometer to measure the actual movement displacement of the mechanism,and then the structural error compensation is identified by the least squares optimization algorithm.Finally,the optimized structural error compensation parameters are substituted into the CNC system.Based on the particle swarm optimization algorithm,the parameter identification ofthe 3-UPU parallel mechanism is carried out.Optimize the initial rod length error and the moving and fixed platform radius errors of the parallel mechanism.Then,the optimization results are compared with the results of parameter identification using the least square method.