Design And Research Of A Small-diameter Industrial Endoscopic Imaging System

In modern industrial fields,accurately recognizing the defects of small-sized components in complex environments has becomes increasingly important.As a significant branch of non-destructive testing technique,endoscopic detection is capable of detecting areas that cannot be directly observed by human eyes in harsh environments.Till date,endoscopic diagnose has been widely used in diverse applications such as construction,car overhaul,mechanical overhaul and many more.In this dissertation,I have proposed and demonstrated a newly-designed optical endoscope modality,which aims at detecting the defects in the inner wall of small-aperture industrial pipe parts.The main works of this dissertation are shown as following:1.Analysis on the development of massive representative endoscopes is reported and presented.I propose a small-diameter endoscopic modality with a rigid tube,which employs CMOS image sensor instead of conventional eyepieces to enhance the quality of imaging and facilitate its operation.The achievable detection angle of the inner wall is 360~oby rotating the whole industrial component.2.The proposed endoscopic arrangement is mainly composed of an objective lens group,a rotation lens group and a rear objective lens group,which are individually designed and then reasonably combined.The objective lens group is designed as Telecentric structure,and further gluing the steering prism and subsequent lens is able to mitigate the assembly error.According to the actual volume of the tested component,I choose the appropriate working distance of the endoscope through adding the rotation lenses.In the procedure for designing the rear objective lens group,its size should firstly match the active area of used commercial CMOS device.Placing one protection glass on the last position of the rear objective lens group is utilized to prevent air dust affection for clearly imaging.The specific features of the proposed endoscopic modality includes objective distance of 2 mm,diameter of3 mm,field of view of±30°,viewing angle of 90°and working distance of 50 mm,which is operated in visible band.3.On the basis of the accomplished optical system,I in turn design the mechanical structure of the endoscope,and simulate the assembly procedure in 3D software to ensure the perfect match between various optical lenses.The endoscopic modality is manufactured and assembled,and further experimentally tested its characteristics and performance.The attainable spatial resolution is greater than 50lp/mm at the fixed objective distance of 2 mm,which completely satisfies the requirement for practical utilization.4.To overcome the limited depth of field(DOF)of the proposed endoscope,wavefront coding technique is employed to largely extend the initial depth of field.I analyze the inherent reasons that cause the limitation of DOF,and report the wavefront encoding and decoding techniques in detail.One designed and optimized phase mask is placed at the pupil aperture of the system,which has the capability to remarkably improve the original DOF.The presented and simulated endoscopic system with extended DOF is expected to be valuable for a variety of industrial applications.