Three-dimensional Microscale Sensing Method Bsaed On Tapered Fourcores Phase-shift Fiber Grating

Design and manufacture of three-dimensional micro structures on the core components become an important trend in fields of high-end equipment manufacturing industries.For example,there is a large number of cooling holes on the complexity surface of a turbine blade in aero-engines.These holes have typical three-dimensional structures,such as forward-expanded type and crescent type.Meanwhile,their diameters are in a range from 300 ?m to 500 ?m.In the fuel injecting system of aero-engines,injecting holes are located on the concentric injecting loops of different angles,and their diameters and depths can reach 200 ?m and 2 mm,respectively.Besides,the thrust performance directly relates to the manufacture accuracy.Research indicates that the maximum thrust could decrease by ~17% when the manufacture errors are over 10%.The first is that the key to accomplish precise manufacture of three-dimensional micro structures begins with solving the three-dimensional microscale sensing problems.However,conventional microscale sensing methods could not satisfy the three-dimensional microscale measurement requirements of high-end equipment manufacturing industries because of the contradiction between the minimum measurable dimension and maximum measurable depth,unrobust three-dimension sensing capacity and complexity measurement chain.Therefore,a direct and precise sensing method is highly demanded to evaluate the manufacture results of the three-dimensional micro structures.Aiming at the problem above,this subject of "Three-dimensional microscale sensing method based on tapered fourcores phase-shift fiber grating" is meant to provide a three-dimensional microscale sensing method of small measurable scale,high measurable depth,short measurement chain and high precision.The measurement principle is built,and a microsacle sensing system is developed and experimentally tested in this thesis.The main research is as follows:A three-dimensional microscale sensing method based on tapered fourcores phase-shift fiber Bragg grating(FBG)is proposed to enhance the minimum measurable dimension and maximum measurable depth.This method employs the deformation of the tapered fourcores phase-shift FBG to achieve the three-dimensional tactile sense and transform tactile displacements into the spectrum shifts of FBGs.To reduce the influences of the spectral signal distortion induced by the tapered stylus on sensing accuracy,a phase-shift point is set in FBG and its fine spectral structure is analyzed to derive the tactile displacements.Finally,the complete model of three-dimensional microscale sensing method based on the tapered fourcores phase-shift FBG is established.The results from analysis indicate that the proposed method has a stable three-dimensional sensing capacity.The phase-shift point can effectively suppress the spectral signal distortion and could significantly reduce the central wavelength error of signal spectrum.Besides,the tapered stylus could extend the minimum measurable dimension at the same time it has a very slight influence on sensitivity.To overcome the barrier of constructing a tapered fourcores phase-shift FBG,a manufacture method of the tapered fourcores FBG probe based on capillary self-assembly technique is proposed.This method is established on the basis of the equilibrium tendency of liquid-solid system achieving its lowest energy state.The complete model is built to futher discuss how to form regular square array of four fibers with an external constraint,and influences of UV-cured adhesive specifications on the velocity of self-assembly process and the sensing performance of the tapered fourcores probe.The fiber length,diameter and UV-cured adhesive specifications are thus optimized.Then,etching method of tapered fibers and self-assembly manufacture method of tapered fourcores probe are studied to achieve tapered fourcores phase-shift FBG probes.This method can be used to manufacturing a 3~8 mm long tapered fourcores phase-shift FBG probe and its spherical tip can be less than 100 ?m in diameter.Structure design of porbes manufactured by this method is no longer limited by commercial fourcores fiber.Besides,SMSR of FBG spectrum is improved from 1~10 dB,reflectivity is increased from 10% to 75%,signal loss is decreased from 1~5 dB to 0.2 dB.Focusing on the influences of complex measurement chain on sensing accuracy,a signal demodulation method based on optoelectronic equivalent narrowband filtering technique is proposed.This method transforms electronic filters into narrowband,rapidly tunable velocity and widely tunable range equivalent optical filters for spectrum analyzing.Thus,sensing signals can be directly derived into the tactile displacements in spectrum domain.Considering influence factors on spectrum power accuracy and resolution,electronic filters and tunable velocity of local external cavity tunable laser are optimized.The results from analysis and experiments demonstrate that spectral resolution of this method is 48 fm and optical power uncertainty is less than 2.1%.A phase-shift FBG is experimentally tested and a fine spectral structure of ~3.4 pm bandwidth can be clearly distinguished.Finally,experiments are conducted to verify the proposed manufacture method based on self-assembly technique and signal demodulation method based on optoelectronic equivalent narrowband filtering technique.Then,a three-dimensional microscale sensing system based on the tapered fourcores phase-shift FBG is designed.Its performances are tested and experimental results indicate that the tapered stylus can reduce the minimum measurable dimension by half and has an influence of less than 13% on sensitivity which is 37% higher than that of a cylinder probe.The phase-shift point can effectively suppress spectral signal distortion and reduce the central wavelength error of signal spectrum from 9 pm to 0.45 pm.Moreover,its resolution is better than 30 nm and positioning repeatability is better than 31 nm.Experiments on measuring a deep micro hole and a micro step height formed by gauge blocks demonstrate that the axial and radial extended measurement uncertainty is inferred to 0.31 ?m(k=2).