Study Of Microscale Dimensional Sensing Based On Orthogonal Fiber Micro Focal-length Collimation

With the fast development of modern fabrication and application of micromechanism technology, the demand for complex micro-structure characteristics ofproducts is increasingly urgent. Presently, the measurement of combination of probesensor and coordinate measuring machine is becoming one of the most effective meansin high-precision measurement of microstructures. But those probe sensors cannot solveall the problems in manufacture, aspect ratio, working space, capability of3Dmeasurement, measurement efficiency, etc, which limit the improvement ofmanufacture technique of micro-structures and the development of the related fields.This dissertation is proposed for measurement of micro-structures. Based on thesense theory of micro focal-length collimation, a2D orthogonal path arrangement isproposed. The optical model of micro focal-length collimation is established, thesensing property and related tests are expatiated. The main research works are asfollowings:1. Analysing the performance disadvantages of the measurement of micro-deepcavities based on micro focal-length collimation, and propounding the sensing methodof2D orthogonal path arrangement based on micro focal-length collimation. Areflective objective is used to generate a point light source in this method. This solvesthe problem that the working space is narrow, the displacement transfer ratio is low andonly there is only1D capability of measuring of the probe based on micro focal-lengthcollimation. A fast method of diameter measurement based on perpendicular bisector isproposed, to improve the measurement efficiency of microholes.2. A optical model of micro focal-length collimation based on geometric optics isestablished, and the displacement characteristic is analysed. The field functions of pointlight source (PLS) produced by micro objective and reflective objective lens arecalculated based on Fresnel diffraction and Debye Approximations, and the differencesbetween the circular PLS and annular PLS is analysed. Through FRED simulationbased on ray tracing theory, the change of optical system due to the alter of the PLS isexplored based on wave optics.3. Through FRED, the influence on the displacement sensing property caused bydifferent PLS is expatiated. The transversal and longitudinal displacement sensingproperty curves are obtained. A method of picking up the stripes of the collimationimage is proposed to improve the property in2D sensing. With a fiber stem of125μm indiameter, a theoretical resolution of0.8nm can be achieved using this method. At arange of±3μm, the maximal deviation of transversal displacement sensing property curves due to longitudinal displacement is about±9nm. This method of picking upstripes improves the transversal resolution, and the problem of coupling in2Ddisplacement sensing is solved.4. Fabricating a fiber probe of2D orthogonal path arrangement based on microfocal-length collimation, and its property tests are completed. The experiment resultsindicates that when the diameter of the fiber stem is125μm, and the distance betweenthe fiber and CCD is about125mm, the probe has a resolution of1nm and5nm, ameasurement range of9μm and3μm in1D and2D probing, respectively. And atriggering repeatability of30nm in probing is tested.The research achievements of this paper improve the performance of measurementbased on the sense theory of micro focal-length collimation, and solve its limitations. Itprovides a new method for microscale dimensional measurement.