Theoretical And Experimental Research On 3D Size Measurement Of High-temperature Components Based On Infrared Vision

Visible vision technology is a non-contacting method widely used in geometry size measuring, however, the visible imaging result will be greatly affected in harsh environments such as high temperature, high-speed airflow, etc. Infrared thermal imager receives the radiation of target and converted it to electrical signals through photoelectric conversion. It has many advantages in dealing with the challenge in some harsh environments compared with visible camera.Centering on three-dimensional size measuring methods in harsh environments of high temperature, and in combination with the task and demand from a space research institute, a novel method based on infrared vision is proposed to measure 3-D size of high-temperature components, and the related theory and key techniques in this method are researched. The main research contents are as follows:1. The thesis discusses the demand and application of size measuring at high temperature, and it also summarizes the comtemporary state-of-art size measuring methods of high-temperature components and the development of infrared thermal imaging application technology. The research direction and meaning are then determined.2. Based on the Planck blackbody radiation law and CCD's response curve,?factors that affect the vision imaging result in high temperature harsh environment are detailed discussed. The field distribution of high-temperature air is analyzed by means of finite element method.Then the refractive index distribution and the bending extent of light at the selected wavelengthes of 0.38μm, 0.65μm and 14.0μm are both calculated.The bending extent of visible light and infrared light are further verified through some imaging experiments, and results illustrate that the bending extent of visible light is about 10 times compared with far-infrared light at ? and a distance of 1.0 m. 900?C3. A mathematical model of 3D infrared vision measurement systems used for high-temperature component size measurements is established based on the ideal perspective model of infrared thermal imager. Two measurement molds are proposed, which are the simplified high-temperature infrared binocular measurement mold and the measurement mold based on single thermal imager. Both of them are easy to implement. An overall scheme for the infrared vision measurement is presented, and the hardware parameters in the scheme are provides. Some experiment platforms are set up, including the imitation of the actual measured workpiece and the actual high-temperature environment, the comparative experiment system of infrared and visible vision imaging, the simplified high-temperature infrared measurement system, the high-temperature infrared vision measurement system based on single thermal imager and the high-temperature infrared?binocular vision calibration system.4. Non-uniformity correction methods and image enhancement methods of infrared image from high-temperature components are studied. By improving the traditional non-uniformity correction method based on BP neural network, the non-uniformity of infrared image is reduced. In addition, to overcome the lack of sharpness for infrared image from high-temperature component, several measures are developed to heighten the enhancement effect of infrared image, including a novel enhancement algorithm named directionlet transform. In this method, infrared image is decomposed in frequency domain by means of directionlets, which uses some anisotropic and multi-directional filters.5. Calibration methods of internal and external parameters of infrared thermal imagers in high-temperature infrared vision measurement system are researched. A calibration target is designed for infrared high-temperature vision measurement according to the characteristics of infrared thermal imaging. The binocular calibration method based on radial alignment constraint and Zhang Zhengyou algorithm are mainly analyzed. On this basis, the infrared binocular measurement system is calibrated with a method which combines radial alignment constraint and genetic optimization algorithm. The results illustrated that the calibration error of the novel method is less than 0.41mm, and that of traditional methods is less than 0.85mm when the measured workpiece is about 900mm away.6. The methods for edge extraction, binocular feature matching and 3D reconstruction are studied. A sub-pixels method by combining pulse coupled neural network(PCNN) and spatial gray moment is applied to effectively improve the adaptivity and accuracy of edge detection. The approaches to binocular feature initial matching are figured out by using epipolar geometric constraint, and system works efficiently with some other methods which can reduce the possibility of mismatches. Finally, three-dimensional critical sizes measurement and shape reconstruction of high-temperature components are accomplished via data processing of 3D discrete coordinates. The main innovations of this study include:1. For high temperature environment, a solution for 3D size measurement of high-temperature components based on infrared thermal imaging technology was proposed, which can decline the influence of light bending on vision measurement.2. An infrared image enhancement algorithm based on directionlet transform is developed to enhance the feture such as edge and texture of high-temperature component. The results showed that it gets a better enhancement effect compared with some common methods.3. A novel infrared binocular calibration method combining radial alignment constraint with genetic optimization algorithm is researched. Experiments illustrated that it can effectively improve the accuracy of infrared binocular vision system, and thus is more suitable for infrared binocular calibration.4. A sub-pixel level edge detection method based on PCNN (Pulse Coupling Neural Network) and spatial gray moment is proposed, with which the adaptivity and accuracy of infrared edge detection were both improved.