The Study Of Deformation Measurement Technology Based On Distributed Optical Fiber Sensing

Increasingly harsh requirements are being placed on corresponding structural deformation measurement systems for design optimization,structural health monitoring,and adaptive control of smart,flexible structures.Among the existing deformation measurement technologies,deformation measurement technology based on distributed optical fiber sensing is widely used in aerospace,medical robots and other fields because of its immunity to external electromagnetic fields,small size,light weight and integrated flexibility.However,limited to the imperfect deformation recovery algorithm and strain demodulation method,and low snr sensing signals,the deformation measurement technology still have problems such as low universality,low spatial resolution and low measurement accuracy.To solve the problem mentioned above,a three-dimensional deformation measurement system with high universality,spatial resolution and measurement accuracy is proposed and conducted in this paper.A three-dimensional recovery algorithm based on the rotation-minimizing adapted frame is used to transforms the strain information into deformation information in this system;local spectrum similarity is introduced into the optical frequency domain reflectometer(OFDR)processing algorithm for the realization of millimeter-level spatial resolution of strain measurement in this system;a distributed fiber optical sensor based on multi-lumen tubes is proposed to increase snr.Finally,experiments are conducted for this system.The main research contents of this paper are as follows:(1)The study of three-dimensional deformation measurement: The three-dimensional deformation measurement consists of the principle of strain measurement based on fiber sensing,the mapping model of measuring strain to three-dimensional parameter information and the three-dimensional recovery algorithm.Based on the analysis of the defects of the existing three-dimensional recovery algorithm based on the Frenet frame,this paper introduces a three-dimensional recovery algorithm based on the rotation-minimizing adapted frame to overcome the inflection point failure problem.The algorithm recovers the actual three-dimensional curve by inputting the three-dimensional curve parameter information.For the three-dimensional parameter calculation problem,based on the typical structure of the fiber optical distributed sensor,a mapping model of three-dimensional strain information to three-dimensional parameter information is established.The OFDR processing algorithm is studied to complete the measurement of the strain at each point of the sensing fiber.Finally,a simulation experiment is conducted to analyze and verify the performance of the algorithm.(2)The study of OFDR processing algorithm: In order to further improve the accuracy of deformation measurement,the structure of strain measurement system is designed based on optical frequency domain reflection technology and Rayleigh spectral characteristic principle.Then,the OFDR processing algorithm defects are studied.By introducing the high similarity between the measured spectral segments and the reference spectral segments,an OFDR processing algorithm based on local spectral similarity is proposed to solve the misalignment of the demodulation method under large strain loads.problem.On this basis,the factors affecting the performance of the OFDR processing algorithm are analyzed,and the design of the method parameters is completed.(3)Distributed fiber optical sensor structure and calibration scheme design: Focusing the crosstalk problem and fanout problem for multicore fiber sensor,and the resulting sensor sensitivity degradation,a multi-lumen tube based distributed fiber optical sensor is designed in this paper.The sensor can realize the decoupling of three-dimensional strain by fixing a plurality of sensing fibers in the lumen of the multi-lumen tube to form a multi-core fiber-like sensor structure;at the same time,since the sensor,the optical signal is completely in each strip The fiber propagates alone,so the sensor does not have crosstalk and fanout problems in the multi-core fiber.On this basis,in order to improve the accuracy of deformation measurement,this paper further studies the mechanical model of the sensor and proposes a corresponding calibration scheme.(4)Construction and performance test of three-dimensional deformation measurement system: The three-dimensional deformation measurement system based on fiber distributed sensing is conducted,and performance tests are performed on strain measurement,two-dimensional deformation recovery and three-dimensional deformation recovery.The test results show that the nonlinear error of distributed strain measurement is 10 με,which is 0.33% of the full range of 3000 με.Under the condition of 0.6m sensor length and 3mm spatial resolution,the three-dimensional deformation measurement system based on fiber distributed sensing The plane recovery error is up to 5.47 mm,the maximum 3D recovery error is 5.89 mm,the error is less than 1% of the sensor length,and the recovery cur ve is consistent with the actual curve trend.