Research On Three-dimensional Large Displacement Measurement Of A Vane Based On Digital Image Processing

The large displacement of a vane resulting from the high-speed motion is very important original data for its structural analysis and performance evaluation. It is a difficult issue in structure detection and a focus in engineering research. To measure the large displacement, it is necessary to develop a measurement system with simple measurement principles and easy-to-use instruments. It is also important to establish a real-time system that can process image and deal with a series of date automatically. Therefore, this paper explores the measurement system for 3D large displacement based on digital image processing, and thus to meet the demand for measuring large dynamic displacement.This paper studies the basic theory of 3D large displacement measurement based on digital image processing, proposes the mathematical formulas for measuring large displacements and the magnitudes of the uncertainty in measurement, examines the construction of the test system, describes methods of analyzing and processing images by software MATLAB, and illuminates the visualization of the measurement data. This measurement system provides an effective way to achieve precise, intelligent, and real-time measurement for large dynamic displacement.This paper is composed of the following parts:1. Studying on the basic theory and establishing the mathematical formula for measuring large displacement and identifying the uncertainty. This paper deduces the formula of image coordinates, spatial coordinates and displacement of every measurement spot, solves the key problem of correctly confirming the coordinates of measuring point on the image, and analyzes the magnitude of the uncertainty of each value under influence of comprehensive error. It provides the basic theory for measuring large dynamic displacement of an object resulting from high-speed motion.2. Examining the construction of the test system and solving four key problems of the measurement system. To ensure measurement effectiveness, this paper presents two sets of cursor system----additional cursor system and self-loading cursor system, explores the adjustment way----"method of reference coordinate and assistant screen"to keep parallel the laser beams rapidly, and solves the key problem of inaccurate measurement caused by the laser transmission and lens aberration.3. Researching into the analysis and processing of images. To improve the measurement accuracy, this paper studies the ways to analyze and process images with software MATLAB, including noise filtering, edge detection, measurement area identification, displacement information capture, and giving the exact result of the center of the measurement spot. These ways are necessary to realize intelligent measurement system.4.Researching into experiments of measuring the large displacement. The experiments cover the displacement of 2D, 3D and dynamic state. By applying MATLAB, this paper processes the images, calculates the magnitudes of the uncertainty and gives the visualization of the data of the measurement. The experiment testifies the necessity of the correction of the image coordinates and justifies the uncertainty theory, and provides the solution of increasing the measurement resolution and accuracy.