Research On The Key Techniques Of Measuring Helicopter Blade’ Section Stiffness Based On Binocular Stereo Vision

Rotor blade is a key component of helicopter which withstands complex forces in fight. Torsional stiffness, flap stiffness and lag stiffness of each section directly affect the dynamic characteristic of the blade. At present, the accuracy and reliability of the existing method for measuring the helicopter blade’s section stiffness, especially the torsional stiffness, are low. Therefore, the paper integrated the usage of computer vision, image processing, mechanics of materials, and other basic theories, researched a way of measuring blade section stiffness based on binocular stereo vision measurement method. That is, clamp rod or drawing reticle at the section to be detected, keep binocular camera still, and shoot a set of images of blade before and after a known load applied on it. Image processing technology, image matching technology and 3D reconstruction technology were adopted to calculate the relative deformation on both sides of the profile. By this method, the torsional stiffness, flap stiffness and lag stiffness are calculated.The key techniques of the method have been deeply studied in this thesis, The main research contents and innovative points are summarized as follows:① An overall scheme for measuring blade stiffness was designed, which includes clamping scheme, loading scheme and deformation measurement scheme. In-depth analysis of the deformation form and internal structure of the helicopter blade was made. The clamping fixture and loading fixture was designed. As the blade is rigid in the process of deformation, two sets of deformation measurement method were used.② On the basis of deep research of binocular stereo vision theory, the key techniques of abinocular measurement system was realized, including binocular stereo calibration, image matching,3D reconstruction, etc. The algorithms used for circular point center and cross line center recognitionwere also proposed.③ In-depth analysis of helicopter blade’s torsional deformation and wave deformation and shimmy deformation was made. Torsional model and flexural model is put forward, and deduce the calculation method of blade’s section stiffiness.④ On the basis of deep research on the theory of key techniques in this thesis, a prototype stiffness measurement system, namely B IM S -B(Binocular Stereo Measurement System- Blade) was independently designed and realized based on the above key algorithms and techniques. The performance of the system was verified.Experimental results show that the binocular-vision-based method has low repeated accuracy for measuring sectional flap stiffness and lag stiffness of the blade, and therefore can not take place of the strain-gage-based method for measuring blade’s sectional flap and lag stiffness. However, the binocular-vision-based method exhibits relatively high repeated accuracy for measuring sectional torsion stiffness. In addition, the torques applied and the measured torsional angle values satisfy linear relation as expected. So, as a new effective way, the binocular-vision-based method has potential to replace the laser-triangulation-based method for measuring blade’s sectional torque stiffness.