The Research On Measurement Techniques For Rotating Objects Based On Digital Image Correlation

Digital Image Correlation (DIC) is a non-contact method which has been widelyapplied in engineering. Although it possesses advantages such as the good adaptability forthe environment, simple experimental procedures, high precision and large range ofmeasurement, DIC is difficult to be applied to the measurement of objects with largerotations. Based on this consideration, a modified DIC has been proposed which isspecifically suitable for rotating objects.Firstly, a modified Newton-Raphson iteration has been proposed which can detectlarge rotations in the subset. In detail, Newton-Raphson iteration is first conducted whichallows rotating the subset and considers only the rigid-body rotation and translation tocalculate the approximate rotation angle and displacement components. These numbers aretaken as the initial values for the further Newton-Raphson iteration which considers thesubset as a deformable body. The results in the adjacent subset are to be taken as the initialvalues of Newton-Raphson iteration for the next subset. The simulation showed that thisalgorithm is robust to identify the movement of the object if the rotation angle is less than16degrees between the adjacent images. The subpixel precision is equivalent to theconventional Newton-Raphson algorithm.Secondly, based on a pair of high-speed cameras and Zhang’ calibration method, a3Dmeasurement system has been developed, which is effective for rotation inspection. Thetranslation experiment indicated that the precision of3D system was accurate. The systemhas been applied to the measurement of the wind turbine blade model, the three-dimensionalmotion data of seven points along the blade during rotation was calculated, then theinformation of one point in the frequency domain was obtained through fast fouriertransform analysis. This experiment proved that the method can be used to measure thethree-dimensional motion of a rotating object successfully.