Research On Three-dimensional Measurement Endoscope System Based On Phase-shifting Structure Light

With the rapid development of three-dimensional measurement technology,three-dimensional reconstruction of the surface of the object has become a hot research direction in the application fields of machine vision.The three-dimensional stereoscopic endoscope can provide the deep image of the body tissue,reconstruct the morphological features of the body tissue,provide guidance for the operation of the doctor,and improve the success rate of the operation.This paper focuses on 3D measurement endoscopy,and the objective is to achieve three-dimensional measurement of objects.The main work includes the design of the three-dimensional measurement endoscope system,the simulation of the factors affecting the measurement accuracy,the design of the phase error compensation algorithm for the object,and the three-dimensional measurement of the actual object.First of all,in view of the miniaturization and real time characteristics of the actual endoscope system,a phase structured light based on optical fiber ordered arrangement is designed.The optical fiber beam has three entrances and one exit.Each fiber beam entrance is illuminated by a LED light source.The required phase structure light is generated by controlling the opening and closing of the LED light source.The light source and fiber are coupled through the lens.We simulate and determine the parameters of the spherical lens,the distance between the lens and the light source and the fiber beam,so as to improve the coupling efficiency of the fiber beam and make a uniform illumination.The camera lens is calibrated,and the distortion of the image is removed according to the calibrated camera parameters to reduce the error of subsequent phase calculation.The coding mode of CMOS drive circuit is designed to realize long-distance transmission of digital image signals.According to the design of the optical fiber module,the light source module and the lens group module,the actual three-dimensional measurement endoscope experiment system is built.We obtain the actual structure light image and analyze the characteristics of the structured light image.The calculation method of phase and depth of the object is introduced,and the mathematical model of phase error is deduced.Because the optical image phase difference is not the standard 120 degrees,the structure light fringe period is not equal,the background light is uneven and there is a large amount of noise,We generate a series of structural light simulation images and calculate the phase error of the structured light simulation image.We explore the relationship between phase difference,the cycle,the background of the structural light stripe,noise and the phase measurement accuracy.In view of the uneven background and the presence of noise in structured light images,Gauss filtering and removing background light are applied to the actual structured light image.Based on the characteristics of structured light,the compensation algorithm for phase error of the object is designed,including the calibration of plane phase error,the calculation of the reference phase of the object,the determination of the corresponding plane by the reference phase and the error compensation of the phase error table.Then,the phase error compensation algorithm is used for plane,inclined plane and curved surface in turn.In the end,the phase and depth of the actual object are measured.The phase and depth of the complex plaster model,the gear shape model,the convex model are calculated,and the phase diagram and the depth map before and after the error compensation are compared.It shows that the phase error compensation algorithm designed in this paper can effectively reduce the calculation error of the phase of the object and improve the accuracy of the experiment.