| Machine vision technology has been widely used in advanced manufacturing, robotics,intelligent equipment, aerospace, military and other fields, but its visual imaging system and visual function is far from being able to achieve the extent of human visual system.Therefore, by imitating the human eye to create a more compact, more flexible and better performance of the optical imaging system, by imitating the human visual system to propose a more complete humanoid machine vision system, will have a wide range of application prospects and important practical value for both optical imaging and machine vision field, and also have great significance to the development of humanoid robot. From the perspective of biological anatomy and neurophysiology of human visual system,combined with theoretical research and experimental verification, on one hand this paper studies the basic principles and the implementation model of humanoid eye structure and optical imaging system focusing on the key problems of miniaturization and intelligent development of optical imaging technology. On the other hand, by imitating the formation mechanism of human monocular stereoscopic vision, it can be regarded as an exploration of humanoid machine vision system with human visual function. This dissertation is divided into seven chapters, each of them is arranged as follows:In chapter ?, the related study background is mainly introduced. By analyzing the limitation of the traditional optical imaging system and the imperfection of the computer vision theory, the significance of this topic is highlighted. The physiological structure,visual formation mechanism and optical characteristics of the human visual system are briefly introduced. According to the current researches of the variable-focus lens and monocular stereo vision technology, the key techniques and current issues of the related research are discussed. Finally, the funding support and research content of this topic are clarified.In chapter ?, the fabrication conditions of PDMS membrane are determined by experiments and the stress-strain characteristics of PDMS samples with different proportions are measured, in view of the widely used PDMS materials for membrane liquid variable-focus lens. Based on the principle model of membrane liquid variable-focus lens,the mechanical model of the PDMS membrane is established. And the equation of deflection curve in the case of small deflection is derived, as well as the differential equation of radial displacement and deflection in the case of large deflection. Through the finite element simulation, the effect of load and membrane dimension on the deformation of PDMS membrane is deeply researched, as well as the effect of liquid gravity on PDMS membrane deformation and surface rotation symmetry. The related studies can serve as the theoretical basis for the following up design and application of variable-focus lens and optical imaging system.In chapter ?, in view of the membrane liquid variable-focus lens, the optical properties, including the relationship between aberrations and focal length, are studied thoroughly according to the varifocal principle. Focusing on the problem of the significant spherical aberrations with dramatic turbulence in the case of small focal length and liquid gravity in membrane liquid variable-focus lens, a doublet solid-liquid mixed variable-focus lens with spherical aberration correction function is proposed by using a PDMA lens with a thick edge and thin central structure. It is proved by experiment that the proposed variable-focus lens has a considerable focal length range,great capability to continuously change focal length, effective spherical aberration correction within the focal length range and also realizes the real time correction of spherical aberration. Meanwhile,the PDMS lens can solve the liquid gravity problem to a certain extent, which provides an effective solution to the problem of unstable image quality and liquid gravity in membrane liquid variable-focus lens when the focal length varies.In chapter ?,aiming at the limitations of the traditional optical zoom system, a novel solid-liquid mixed variable-focus lens which imitates the crystalline lens kernel structure is proposed based on the human eye focusing mechanism and the Gullstrand precision eye model, as well as a novel humanoid imaging system ZJU SY-? based on the proposed solid-liquid mixed variable-focus lens. ZJU SY-? has the advantage of small size, compact structure, simple control, low cost. Based on the design principle of thick edge and thin center structure, a parabolic thick PDMS lens with non-uniform thickness is proposed,which not only can add the degree of freedom of optical system optimization design,improve the image quality and optical performance, but also weaken the liquid gravity influences. The results of imaging experiments show that ZJU SY- has considerable ability to control the focal length and good image quality. Meanwhile, the effect of off-axis aberrations on the imaging quality of ZJU SY-? has been investigated according to the results of the ray tracing simulations.In chapter ?, in order to solve the problem that ZJU SY-? has significant off-axis aberrations in a large field of view, a layered solid-liquid mixed variable-focus lens which imitating the crystal layered distribution structure and the refractive index increased from outside to inside is proposed according to the physiological structure of the human eye, as well as a symmetrical humanoid optical imaging system ZJU SY-? based on the proposed layered solid-liquid mixed variable-focus lens. By increasing the edge thickness of the PDMS lens, the off-axis aberration due to the gravity of the liquid is reduced. Through the imaging experiments and ray tracing simulations, it is verified that ZJU SY-? can greatly improve the imaging quality and optical properties by correcting off-axis aberrations effectively with a larger field of view and higher visual resolution, which is of great research value for the practical application of humanoid eye optical imaging system.In chapter ?, according to the physiological structure and neural control mechanism of human visual system, the formation mechanism of human monocular depth perception depending on the special structure of retina, the human eye focusing mechanism and eye movement is studied thoroughly and a novel humanoid monocular stereo vision technology based on variable-focus lens is proposed, as well as a monocular stereo vision system with two degrees of freedom based on the proposed humanoid optical imaging system ZJU SY-? and a ball-type tracking camera control platform. It is verified by experiments that the proposed stereo vision technology can effectively obtain the 3D geometric information of spatial objects and avoid the problem of stereo matching, and the developed stereo vision system is the same as human eye with exquisite, smart and flexible advantages. The experiments also prove that the developed stereo vision system dose not need the additional light source equipment and can achieve a wide range of spatial scene scanning based on its considerable ability to control the focal length and flexible mobility. It is suitable for the three-dimensional reconstruction of the spatial panorama, which is of great research value for the development of stereo vision technology.In chapter ?, the conclusions of the main research are summarized, the innovations in the dissertation are pointed out, and some subsequent related work are also prospected. |
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