Shape Condition And Deformation/Strain Measurement Based On Machine Vision

The profile measurement and deformation/strain measurement are essential and important in practical engineering applications. As a kind of modern measurement technology, machine vision has the characteristics of high precision, flexibility, non-contact, real-time online measurement and so on. This paper takes the wheel tread and the blade as the measurement objects to study the condition of object’s shape and deformation/strain measurement based on the machine vision measuring technology.Based on the principle of machine vision measuring technology, the method of using a single camera to acquire surface image and depth information has been studied, as well as the method of measuring three-dimensional deformation and complex strain using binocular vision technology combined with digital image correlation method. The object rotated uniformly and its surface images are captured by a planar array CCD camera with a certain frame rate, and the series of images were stitched to form the complete object surface. At the same time, the depth information could be measured by using optical triangulation method to extract the line structured light line projected on the object surface. Aiming at the strain measurement produced by complex three-dimensional deformation, the length of triangle grids before and after deformation are calculated according to the virtual grids, which overcomes the limit that the initial triangular mesh must have both sides perpendicular in original method. According to the deformation gradient tensor and the Cauchy-Green tensor, as well as the relationship between Lagrange strain and the real strain, the internal strain of grid can be calculated to obtain the regional maximum and minimum principal strain. Finally, strain could be smoothed using the method of weighted mean value. By mean of homography transform to optimize the matching method, difficulties of ranking feature points on the distorted calibration plate image and time-consuming problem have been solved, which reduces the requirements for the image quality in calibration method. Calibration software, three-dimensional deformation measuring and strain calculation software have been developed bymixed programming of C++ and MATLAB.