Key Technology And Experiment Research On Large Range Flexible Joints Six-axis Force Platform Calibration

As the wide range six-axis force platform is more and more widely used in aircraftlanding gear momentum test, rocket thrust test, spacecraft docking and wind tunnel test,precision requirement for it is getting increasingly higher. However, constrained byserious dimension coupling and decoupling difficulty, calibration accuracy of six-axisforce platform developed in China is low, which restrains the practical application of thelarge-scale six-axis force platform. To solve these problems, based on a wide rangesix-axis force platform with flexible joints developed by ourselves, some key calibrationtechnologies and experimental research of six-axis force platform, such as calibrationdeformation error modeling and nonlinear decoupling, are carried out in this thesis. Themain research contents are as follows:Based on the structural features of flexible joints six-axis force platform, the screwtheory is applied in statics analysis, and its calibration deformation analysis and researchare carried out with FEM method. Meanwhile, a method of calibration deformationdetecting based on the laser interferometer is also given.Based on the continuous stiffness theory of flexible joints parallel mechanism,calibration load platform deformation error modeling problems are researched, variousflexible branching stiffness models and continuous stiffness model of load platform areset up, through solving calibration deformation under continuous stiffness, first orderinfluence coefficient matrix is obtained, and calibration deformation error model is set up.The influences on measurement accuracy of six-axis force platform caused by thestructural deformation under different loadings are also analyzed.A hybrid threshold denoising algorithm based on Donoho and3σ criterition is given,with its correctness verified by simulation experiments. Through further study, anonlinear decoupling model of flexible joints six-axis force platform is established. Basedon advantages of HHGA algorithm in structural parameters optimization, three differentneural networks, i.e., BP, RBF, WNN, are optimized, and three kinds of force platformnonlinear decoupling algorithm based on HHGA-BP, HHGA-RBF, HHGA-WNN areproposed. Based on neural network hybrid modeling technology, through solving knowledge base model with least square method, NNHM-LSM algorithm based on theforce platform hybrid modeling of nonlinear decoupling is given. The above mentionedalgorithm and decoupling process are also designed in detail.To meet the actual demand of flexible joints six-axis force platform calibration test,a function structure model of calibration system is designed. Combined with functionstructure, technical parameters and operating principles of each key hardware systemcomponent, as well as calibration hardware system are designed and put up. Based onvirtual equipment theory, LABView and Matlab techniques, function structure ofcalibration software system is designed, and key function components and correspondingdecoupling algorithms are designed and achieved in detail, thus force platform calibrationsystem is developed.Static calibration process of flexible joints six-axis force platform and six-forceloading scheme based on hydraulic system are designed, and static calibration experimentis carried out. Based on experiment data and various decoupling algorithms, someperformance indexes such asⅠerror, Ⅱ error, linearity and coupling of the platform areobtained. By comprehensive comparison and analysis, the algorithm effectiveness andtechnique rationality mentioned before are verified. The structure deformation of theplatform is detected and analyzed with laser interferometer during the calibration process.Dynamic performance of flexible joints six-axis force platform is studied, its modalanalysis is done with FEM method and its natural frequency and vibration mode areanalyzed. Hammer test method is applied in spectrum analysis test, and dynamicperformance indicators such as natural frequency and damping ratio, are also obtained.This thesis provides a reference for calibration system development andcorresponding experimental studies for other types of large range six-axis force platform,which is significant in developing large range high-precision six-axis force platform.