Design Of Optical Fiber Force Sensor And Its Signal Analysis For Flexible Ureteroscopy

Ureteroscopic laser lithotripsy is recently becoming an effective treatment method for urinary calculi.However,the ureteroscope currently used has no force sensing at its tip,which may lead to the perforation of urinary tract due to the rush advance of the ureterscope during a lithotripsy treatment.Therefore,it makes sense to design a novel sensor to measure the force applied to the tip of ureteroscope,and to gurantee the ureteroscopy safety.Due to the space limitation at the tip of the ureteroscope,it is a challenge to design a miniature force sensor to meet the requirements of size and accuracy,etc.Meanwhile,it is critical to analyze the contact information from the abrupt force signals during ureteroscopy,to ensure the procedure safety.The main contents of this thesis are as follows:First,a novel sensor structure is designed and simulation analysis has been done.To improve the force sensitivity,a new notched modulation flexture is designed,and two fiber gratings connected in series are used.to achieve temperature compensation.This design makes it easy to integrate into the tip of a ureteroscope.The finite element simulation method is used to analyze the stress distribution and optimiaze the sensor structure parameters,and the simulation results show that the designed sensor meets the requirements of measuring accuracy and range.Second,the force sensor is packaged and calibrated.The position of the adhesive is determined in terms of the result of simulation analysis,which helps to package the sensor.To overcome the limited amount of traditional calibration data,a new force calibration platform is built up,and with the calibration data the demodulation model of axial force is thus established.Then,the performances of the sensor are analyzed through multiple comparison experiments.The designed sensor has a resolution of0.01 N and an accuracy of 0.27 N,and its hysteresis and repeatability are excellent.Third,a temperature compensation scheme is proposed for the devised sensor.Due to the limitation of size,fiber optic sensors rarely uses hardware to achieve temperature compensation.Frequently,it is achieved by the temperature calibration data.Herein,a new temperature compensation scheme is proposed by combining the force decoupled model and hardware compensation.It does not need temperature calibration experiment any more,and only force calibration is needed to get the decoupled force model,therebyavoiding more complicated experiments.The errors data of the decoupled force and the force ground trueth,show that the temperature influence on the devised sensor can be effectively compensated for.Finally,the signal processing method is presented to analyze the force information.During the ureteroscopy,the ureteroscope contacts with various soft tissues and organs of the human urinary system.The abrupt force signal obtained at the tip of the ureteroscope is non-stationary signal that contains important contact information.Therefore,a signal analysis method based on Hilbert Huang transform(HHT)is introduced here.It decomposes the original signal with empirical modes,and the instantaneous amplitude of the intrinsic modes is calculated.The position of the maximum amplitude can be used to determinate the instant of abrupt force.