Research Of Spectacle Frame Measurement System Based On Structured Light Method

With the improvement of people’s life and emphasis on eye health,the requirements for the quality of glasses have been increasing gradually.Futhermore with the progress of science and technology as well as the rise of smart wearable devices,there is a higher demand on the style,individuation and versatility of glasses.The importance of high-precision and automatic lens processing equipment on the the assembly quality of glasses has been generally realized by glasses manufacturers.Automatic eyeglass lens edging system is now widely used to automatically cut and polish the uncut lens based on the spectacle frame shape data which is obtained from the spectacle frame measuring machine installed on the system.The conventional approach to acquire the frame shape data works in the contact scanning mode with a probe tracing around the groove contour of the spectacle frame which requires a sophisticated mechanical and numerical control system.As a result,the price of the appratus is relatively high and the problems of scratches on the workpiece and abrasion of the probe remain to be solved.In this paper,a novel measuring system is aimed to be developed for measuring the three dimensional(3D)data of the spectacle frame.The main work in this paper is as follows:(1)Different methods of lens processing have been studied and the principle,advantages and disadvantages and application scenarios of various three-dimensional shape detection methods have been researched to supply a good theoretical basis for design of a suitable solution.(2)The measurement scheme based on binary multi-line structured light is proposed and the projection pattern is designed to be projected obliquely in two orthogonal directions to avoid the loss of profile information.The measurement system is simulated in the 3dsMax software and accuracy analysis and structural parameter optimization have been conducted based on the mathematical model of the structured light vision sensor.(3)The problem of high light in three-dimensional shape measurement has been handled.Combined with the Phong illumination model,the cause of high light of specular object is analyzed.A variety of processing methods to the high light problem have been researched,and in the end the techniques of multiple exposuring and high dynamic range imaging are applied to remove high light in the measurement.(4)The image processing of structured light stripes has been conducted after the removal of high light including image contrast enhancement with Gamma transform,ROI extractaction with an auxiliary lighting system of special design,image binarization by otsu algorithm,noise suppression through morphological operation and center extraction of the light stripes.(5)A novel encoding and decoding algorithm for multi-line structured light measurement has been proposed and implemented.The algorithm is designed based on the projection of the iconic stripe and marking of the fringe order.In addition,a retrieval method of point cloud depth information based on look-up table is presented which has been verified by experiment.The experiments have proved that the measuring system based on multi-line structured light for measuring the three dimensional(3D)data of the spectacle frame can perform well.Finaly,the work which has been done in this paper is summarized and the further research issues are proposed.