Design Theory And Application Of Parallel Wind Tunnel Balance Based On Stewart Platform

Balance is a key measurement equipment in the wind tunnel testing. The elementary design method and application are studied in the thesis for the parallel wind tunnel balance based on the Stewart platform, and the main research work is as following: The function, classification ,applicational field and the state-of-art for the wind tunnel balance are summarized systematically,and the advantages and research status of wind tunnel balance based on Stewart platform are also included. Presented a novel conception of 6-SS parallel wind tunnel balance.Firstly, the design theory of the balance is provided by analyzing the forward kinematics and the inverse kinematics of the Stewart platform. According to characteristic of static equilibrium, the relationship between forces and torques applied to the testing model and given six leg forces is derived by using of spatial force transformation, from which obtains the force Jacobian matrix for the balance, and its analytical expression is also obtained based on elementary structural parameters. The condition number of Jacobian matrix of parallel balance is studied by the F-norm based on the force Jacobian matrix, the condition number is used as objective function to design a optimal parallel balance, and the analytical relationship is derived between objective function and the five elementary architectural parameters. According to the minimum Jacobian matrix condition number theory, the minimum of the objective function about intermediate variables is provided by using of numerical method, which is validated by the 2-norm of the force Jacobian matrix, and the derived result is applied to achieve eight optimal architectures for good parallel balance accuracy. The design center of the balance is also provided. The equations of dynamics for the balance are established by Kane's method, from which derives the characteristic equation of natural frequency by means of linearization of dynamic equations, and the six natural frequencies being developed according to the theory of vibration. The law of the six natural frequencies varying with mass of the upper platform and the stiffness of the elastic element are presented,and the Finite Element Method(FEM) is employed to testify the validity of theoretical results. In the end, the range of measurement, the strain sensitive unit, the flexible spherical joint, and the software of data processing and collection are designed based on the design theory and architectural optimal method above. Further more, the model of the parallel balance and the calibration equipment are fabricated. Calibration method of single-component and multi-componet are put to use to work out the calibration matrix, accuracy, precision ,resolution and linearity for the parallel balance. In order to testify the design performance of the balance, standard model is used to compare the experimental data with theoretical data in low speed wind tunnel and the result is satisfactory, which confirms the validity of the thesis.