Design Of Catadioptric Imaging Optical System For Inner Wall Of Pipeline Based On Q-type Surface

With the rapid development of modern manufacturing industry,pipelines are widely used in petrochemical,metallurgical and military fields.However,nowadays,there are many pipelines that have been put into service beyond the time limit,which makes their safety worrying.Therefore,the visual inspection inside the pipeline is particularly important.In order to obtain a panoramic image of the inner wall of the pipeline with a large field of view,this paper studies the development status and application of various panoramic optical systems,and compares and analyzes the above panoramic optical systems.Finally,the catadioptric panoramic optical system is selected to achieve the panoramic imaging of the inner wall of the pipeline.However,most of the traditional catadioptric panoramic optical systems focus on the rear view,which will lead to the instability of the image distance plane of the system and the excessive pressure of the relay system.In addition,for the field of pipeline inner wall imaging,the angle between the main ray of the rear view field and the surface of the pipeline inner wall is too large,which will lead to serious information loss of the pipeline inner wall.However,the catadioptric panoramic imaging system designed in this paper pays more attention to the side view in order to obtain the information of the inner wall of the pipeline,and takes the vertical optical axis as the reference,with the pitch angle of ±25°,that is,the panoramic field of view of 360°×(65°～115°),which avoids the above problems.Based on the imaging principle and characteristics of the catadioptric panoramic optical system,combined with the special requirements of the panoramic imaging of the inner wall of pipeline,the relevant parameters of catadioptric panoramic optical system are formulated,and the basic parameters of mirror unit and relay system are calculated according to the size relationship.Based on the imaging characteristics,the design method of catadioptric panoramic optical system is analyzed,that is,the design method of constructing mirror unit and relay system respectively,field curvature compensation and splicing optimization.The mirror unit of the traditional catadioptric panoramic optical system mainly adopts even aspheric surfaces.However,due to the non-orthogonality between its various coefficients,the mutual interference and even cancellation between the various coefficients,and the seriously small order of magnitude of the coefficients,the problem of low optimization efficiency of the optical system is extremely prominent.By studying the theories of three kinds of Q-type function polynomials in this paper,it can be seen that,compared with even aspheric surface,the base polynomials of Q-type function polynomials are orthogonal to each other,which avoids the problems of redundant interference,precision loss and numerical ill-condition caused by non-orthogonal,and provides more significant figures,improving the optimization design efficiency and machinability of optical system.Combined with the characteristics of Q-type aspheric surface,this paper proposes for the first time to apply Q-type aspheric surface to the mirror unit of the catadioptric panoramic optical system.The catadioptric panoramic optical system based on even aspheric surface and the catadioptric panoramic optical system based on Q-con aspheric surface with the same parameters are designed respectively.The system adopts 1/1.6-inch CMOS image sensor,the field of view angle is 360°×(65°～115°),the focal length is1.05 mm,the F number is 3.3,and the total length is 99.5 mm.And the imaging performance of the system is evaluated and the tolerance analysis is made.Finally,the catadioptric panoramic optical system based on even aspheric surface and the catadioptric panoramic optical system based on Q-con aspheric surface are analyzed and compared.It is concluded that the use of Q-con aspheric surface can improve the design efficiency,machining accuracy and reduce the cost of the system,and at the same time,it can also achieve the design results with smaller distortion,higher image quality.