Research And Application Of Key Technology For High Precision Image Measurement System

The technology of precision measurement is the base and the precondition for the industrial development.The developing level of manufacturing as well as the scientific technology depends largely on the accuracy and efficiency of measurement.Image measurement based on machine vision is a modern techonolgy which integrates the discipline of optoelectronics,computer graphics,information processing and automation control.It is becoming a key and promising technology for increasing the inspection efficiency and essuring product quality.Rely on Shanghai key scientific and technological projects "The Research and development of high precision image measurement support Digitized Manufacture"(ID:09DZ 1121600),this paper made a systematic and deep investigation on the key technology of image measurement.An image measurement instrument based on machine vision was developed and many innovation fruits were achieved.The main research contents and innovations of the paper were as follows:(1)In the aspect of digital image acquisition,this paper designed an illumination architecture which includes a back light and three direct ring front light lamp houses.An intelligent illumination control system based on GA was put forward in order to acquire the best quality image of the object.The optimal illumination control parameters aimed at different objects to be measured could be found with the help of intelligent illumination control system.The fuzzy expert system based on the category of objects to measure was built to accelerate the searching process of optimal control parameters.(2)In order to acquire the panorama image of the workpiece which exceeds the field of view(FOV)of the camera,this paper put forth the template matching algorithm based on the mutual information measure.Sub-pixel matching accuracy was obtained using polynomial spline interpolation of cubic polynomial with two unknown according to the similarity compare.The template matching algorithm was optimized through three methods.The first point,we put forward the use of golden cut method to speed up the localization of the matching point.Second,we build up the structure of image pyramid which has different spatial resolution and different scale images in different layers using mean filter,then perform matching in different layers to improve the search efficiency.Third,the closed loop worktable motion control system with feedback of precise grating was utilized to minimize the search area.(3)The optimal template pick-up strategy using run length encoding index was invented and it made a breakthrough in the robustness and speed of template matching algorithm.The optimal template contains image characteristics as much as possible while only the pixels which have edge character and distinct gray value changes participate in the matching operation.Both the precision and speed of template matching algorithm were improved remarkably.(4)For image denoising,to filter the hybrid noise of workpiece image,an adaptive filtering method for hybrid noise is proposed.This method firstly uses specific rule to judge the noise type,then select corresponding distinguished filter to eliminate noise according to noise type.Finally the effectiveness of the filter was tested and verfied by analyzing the improvement factor of signal to noise ratio(SNR).(5)In the aspect of edge detection and localization,we put forward a multi-scale self adaptive LoG algorithm which improved the traditional operator.The filter scale and zero-crossing threshold can be selected flexibly according to the inertia moment of the grey symbiosis matrix in different image areas.Thus the noise can be filtered and the edge can be maintained to the maximum extent.In order to acquire sub-pixel precise edge,this paper improved the traditional Gaussian interpolation based edge localization algorithm.Perform gray value resampling in the edge normal using weighting Lagrange interpolating function,then execute Gaussian interpolation to acquire sub-pixel edge points with higher accuracy.(6)Final,the equipment of image measurement based on machine vision was developed and calibration was performed using improved calibration method.We use standard gauge block and other precise machine parts to test and analyzing the precision of the measuring system.Experiments show the system is stable and could reach the accuracy of micrometer.