A Study On Meso-scale Part Metrology With Variable Field Of View Using Structured Light Micro Stereo Vision Method

The development of microsystem technology has put forward great demands for the 3D measurement of mesoscale parts within the range from0.1mm to 10 mm. Meso-scale parts are characterized by small size, easily to be integrated, low energy consumption, low cost and so on, and they have been widely used in many areas like national defence, aviation,micro-electronics industry, and biomedicine. Micro testing technologies in the industry are specifically designed for micro parts, and they can’t be directly used for meso-scale parts metrology. A great gap exists between the large demands and the limited metrology ability for meso-scale parts, which limits the development of microsystem technology.Based on large zoom range telecentric projection lens systems and telecentric stereo vision, a structured light micro stereo vision measurement with telecentric lenses is proposed in this dissertation. First of all, a double-sided telecentric zoom lens system with large zoom range is to be designed for mesoscale projection. In thin lens design, the existing design methods are only suitable for small zoom range, and a singular value exists when m=-1. Three-component double-sided telecentric lens system is designed. A detailed ananlysis is performed, and a systematic classification of double-sided telecentric zoom lens system with three components is conducted. For the zooming ability of double-sided telecentric zoom lens system with three components is limited, four-component lens system design with fixed object-to-image distance is proposed. A classification is made for four-component type. There are six types in all, and the math model and the design method for each lens type are given. In aberration design, all thethird-order aberrations are introduced for aberration design of zoom lens system, which is an improvement for aberration design of zoom lens systems.Aberration shift is proposed, which is composed of central Lagrange Invariant shift, central conjugate shift, and central pupil shift, and the forumulas are derived accordingly. Thin lens modules, thick lens modules, and mixed lens modules are proposed for aberration design of zoom lens systems. Based on the above research, a double-sided telecentric zoom lens system is designed.After tolerance analysis, the mechanical components of lens system are designed and manufactured, and then the optical system is assembled and tested. At last, the structured light stereo vision with telecentric lenses is studied. The math model of telecentric imaging is proposed. An improvement is made to the stereo calibration using 2D templates, and we proposed a calibration method using 3D templates. The image rectification algorithm for telecentric stereo vision is also provided, which includes distortion rectification and image rectification. Some meso-scale parts between 0.5mm to 5mm are measured and the point clouds of the measured parts are achieved.Based on those theories and experiment facilities, precision analysis is performed and some experiments are conducted. The accuracy of this configuration can reach several microns, which demonstrates the capability of this method in 3D metrology for meso-scale objects.