Research On The Resolving Illumination Problems Of A Video Extensometer

Image measurement is a new measuring technology in this field recently. It bases on optics , together with some modern scientific technology such as opto-electronics,computerization and image processing technology which makes a comprehensive measuring system consisting of optics ,mechanics,computer and calculation . Image measurement is a method using image as a media which measures and transmits information when measuring target object. Its principle is to get geometric parameter of object by processing edge which is the most important in the whole system .With the development of modern science and technology, the applied ranges and kinds of engineering materials have been increased greatly. The serviceability of conventional extensometers for deformation measurements is limited in many facts. For adapting the new lately- develop demand of situation, this text study a kind of technique making use of the video image to measure object, That is to say the technical method of whole image and high precision non-contact strain measurement. Develop a high performance non-contact extensometer with measurement performance.This measure system mainly consists of hardware system and software system. between them, the hardware system includes CCD ,lens, optical lighting system, frame grabbers and PC. The software system is divided into five parts ,including the image capturing part, the image's edge detecting part, the image measuring part, the data processing part and the image storing. The principle diagram of the system as follows: In the non-contact measurement which based on video image, illumination is an important factor that impact input of the system, because it influence the quality of the input data and at least 30% application effect directly. In allusion to the material strain measurement based on video image, this paper studies the lighting problems in the image measurement. The purpose is to find some reasonable accessorial optic fittings and the optimal processing method , solve the lighting problems in the system and improve the image quality. So it lays the foundation for the further research and the development work.The main contents of this text as follows:1.In the lighting part of the video strain measurement system(video- extensometer), we used the LED light designed by ourselves and took the back lighting.Although the choice of light source and lighting fashion for the measurement system is a better configuration,the tested pieces and the environment of lighting are important influencing factors. Through experiments we illuminated powerfully that these factors had important infection in the accurate measurement,and analysed the roots bringing the problem.2.The material property of metal may bring reflex. In practical application, although we give sufficient attention in the design of light system, there is also environmental-impact. It will make some rather strong and some dark in the image because of uneven illumination or some other reasons. Under these circumstances, the edge detection of image can not be achieved to a satisfactory result. It is likely to get error, and lead to the reduction of measurement accuracy ultimately. In order to solve these questions,we use some accessorial optic fittings in the hardware system, and we made theoretic analyse to these accessorial optic fittings. From the images captured in the static experiments and the evaluation of the images'quality, we made a conclusion that it can improve image quality by collocating polarimeter in the hardware system. Following, we made extension strain experiments, and it showed that the veil can reduce the impact of light to some extent, and improve image quality.3. On the other hand, aimming at the questions refered above, we taked measures in the software system by correcting each pixel in the image when processed. We analyzed and compared several methods, and chose LogAbout and reformative Gamma. We did experiments more, the experimental result shows that reformative Gamma has better effect on weaking the impact of light and improving image quality. The reformative Gamma has optimal correction to the reflecting problem on the metal specimens and it can reduce the impact of light to some extent, and improve image quality.4.After designing reasonable light system and choosing The reformative Gamma, we did lots of extension strain experiments, and the experimental result shows that the data curve is close to the theoretic stress- meet an emergency curve. It shows that the measure system completely can measure multifarious material parameter real-time as long as satisfy required precision.5.The text introduced concretely the main issues affecting image accuracy from hardware factors, such as lighting field noise, thermal noise electronic, CCD performance, lens distortion, quantization error, temperature, vibration. The text analyzed the images strain measurement error of the measurement accuracy, gave an effective way to eliminate or reduce errors. Image measurement so as to improve the measurement accuracy is specified in the right direction.The research and analysis shows that now it is very necessary to study the designing of light system and applying of illumination disposal methods in the non-contact measurement system based on video image. It has a direct impact to improve the image quality and the measurement precision of the system. We hope the study in the paper can play a little help to the development and application of image technology domestic.