Research On Defect Detection Method For Specular Surface Based On Phase Measurement Deflectometry

The specular object is widespread in modern manufacturing,such as painted automobile body,glass panels and so on,and the defect detection is necessary to ensure the quality.The traditional manual visual method has the disadvantages of high missed detection rate,low efficiency,and high cost.It is urgent to have a more efficient and accurate automatic defect detection method to control the quality of the specular object.The phase deflection method has the advantages of full field,non-contact and high sensitivity,and is considered as the most research value and application prospect of the specular defect detection method.In this paper,the method of specular defect detection based on phase deflection is studied.Considering the demand of detection efficiency and precision in industrial field,the fast and reliable phase extraction is focused on,as well as the defect recognition and localization based on phase information.The main research contents of this paper are summarized as follows:1.The fast and reliable phase extraction method was studied.the phase-shift combined with gray-code method that satisfies both accuracy and efficiency requirements is selected,and the period index correction algorithm is proposed,which can avoid period misalignment without adding images.The experiment proves that the phase-shift combined with gray-code method with the period index correction can obtain high-precision phase extraction results.On the other hand,in order to further determine the true position of the defect,the defect localization method based on the binocular phase deflection system is studied.2.The method of specular defect recognition and localization based on phase information is studied.On the one hand,firstly,the phase image is high-pass filtered by LOG operator to realize the defect area feature enhancement.and then,the algorithm such as threshold segmentation,mathematical morphology,and connected domain extraction is used to obtain the contour,size and center coordinates of the defect on the image.And a method of defect location by using the four vertices of the smallest adjacent rectangle of the defect instead of the center of the defect is proposed,which can solve the problem of location error due to incomplete and inaccurate phase of the defect.The accuracy of the defect identification and localization algorithm is verified by constructing feature defects.3.A binocular phase deflector system was built to detect typical defects on automobile body surface such as dents,bumps and scratches,as well as specular defects on airplane body surface with a size of about 1mm.The results show that the proposed method can accurately identify and locate defects of various types and sizes,and verify the feasibility and effectiveness of the proposed method.