Research On Accurate Measurement Method Of Micro-displacement Based On Monocular Vision

With the development of machine vision technology,image processing technology,optoelectronic technology and other technology,visual measurement technology has been rapid development and application.Monocular vision measurement has important applications in the fields of agriculture,industry,transportation,medicine and so on,as a non-contact visual measurement method.In this paper,the measurement of the depth information is obtained by the combination of monocular vision and laser point combination.This method has the advantages of simple system,no need to set the passive marker on the measured object,no need to calibrate the internal and external parameters of the camera.In this paper,the pinhole imaging model and the lens imaging model are introduced firstly.The measurement models based on the combination of aperture imaging and laser spot and the measurement model based on lens imaging and laser spot are analyzed respectively.In order to solve the problem of low precision in the measurement of micro displacement based on the small aperture imaging and laser point composite measurement model,the measurement model based on the combination of lens imaging and laser point combination is proposed.This model uses the lens imaging principle,in the vicinity of neighborhood image distance equal to two times the focal length,when the object has a small change,spot image location on the CCD laser changes significantly.The measuring accuracy can be improved.It is necessary to preprocess the image,including grayscale processing,filtering,threshold segmentation,and obtaining the laser contour when acquiring a laser image with a CCD camera.The central position of the laser spot has an important effect on the measurement accuracy.In this paper,the effects of different objects on the threshold,the different thresholds,boot time,the non-laser spot contours and the edge of the spot contour singular point on the laser center position are studied.The reason of the non-laser spot and the edge of the contour is analyzed.The method of removing the singular point of the non-laser spot and the contour edge is proposed.The feasibility of the proposed method is verified by experiments.According to the position constraint relationship among the various components in the measurement model,a measuring mechanism is designed,such as the selection and design of measurement mechanism of CCD camera,laser,lens,linear motor,physical basis,driver,and other parts of the lens holder respectively.The object-oriented C ++language is chosen as the development language using the VS2010 as the software development platform.According to the principle of interface design and the requirement of the measurement system,the interface between monocular vision and laser point composite measurement is designed by using MFC and OpenCV.Finally,the experimental platform is established,including three coordinate measuring machine,six degree of freedom position and attitude adjusting platform,measuring mechanism,dial gauge etc.The distance between the measured object and the physical basis point is obtained by using the coordinate measuring machine,and the center position of the laser spot is obtained by using the image processing technology.the one-to-one correspondence relationship is established.Then the measured object is moved,the central position of the laser point in the CCD is obtained at each position,and a set of data is obtained.Based on the data,and according to the theoretical model,the fitting function is selected and the least square fitting method is used to get the correction model.After modifying model measurement model were measured and compared with the three coordinate measuring machine measured data,analysis of the reasonability of the modified model.The experimental results show that this method can make high precision micro displacement measurement,the relative error of measurement in the range of 1mm is less than 0.022%.