Research On Measuring Method Of Multi-dimensional Force For Surgical Robot Instrument Based On Fiber Bragg Grating

Robotic surgery can reduce doctor fatigue,alleviate the suffering of the patient,and help to shorten the rehabilitation time.Therefore,it has a wide application in helping the surgeon to conduct surgical operations.However,existing robotic surgical system still lacks of force feedback.For the surgeon,the absence of the interaction force between the surgical instruments and patient's tissues makes it difficult to accurately control the operation.Therefore,force sensing technology for robotic surgical system has become the hotspot and frontier in this field.However,the exsting researches still encounter some drawbacks,such as insufficient measurement dimensions,inapplicable measurement range or accuracy,severe interdimensional coupling and poor compatibility with surgical instruments.The above shortcomings restrict the development of robotic surgical systems.FBG(fiber Bragg grating)is particularly attractive for force detection of robotic surgical system,due to its inherent advantages,such as immunity to electromagnetic interference,small profiles,light weights,no zero drift,high precision,and good biocompatibility.Considering the existing problems in force sensing for robotic surgical system,we focus our research on FBG-based multi-dimensional force sensing technology and some related technical issues,such as encapsulation,temperature compensation.The specific contents of this dissertation are listed as follow:(1)We have analyzed the measurement error of the multi-dimensional force measurement system,and have obtained the important factors affecting the measurement error.The temperature compensation of FBGs encapsulated with different methods have been investigated in consideration of the application environment of surgical instruments.We have simulated the abrupt temperature environments that the surgical instruments may encounter.A series temperature experiments have been conducted to recearched the relatedness between the temperature compensation errors and multi factors.Moreover,we have also established the strain transfer and thermal transfer models to provide theoretical support.The research could serve as important references for the FBG encapsulation and temperature compensation in force sensing for robotic surgical system.(2)We have proposed a 3-axis force sensing technology with optimized FBG layout and differential measurement principle for wrist joint in robotic surgical system.The classical Maltese-cross beam with multiplexed FBGs has been designed for threedimensional force sensing.Strain distribution characteristics and dynamic performance of the Maltese-cross elastomer have been investigated.Comprehensive performance test has been carried out,and the experimental results demonstrate that the sensor can measure the 3-axis force by use only 5 FBGs.Moreover,it also possesses good linearity,weak coupling,and creep resistance.(3)A low coupling 6-axis force/torque sensing technology with multi-layer mode has been developed for some complex surgical procedures.Becaused of interdimensional decoupling,the sensor is designed based on a new concept of multilayer measurement in which the elastic structure is divided into four layers.The force and torque transmission characteristics have been investigated by the established mechanical model,which has verified the decoulpling function of the multilayer structure.Calibration experiments demonstrate high resolutions and sensitivities.Frequency response characteristics has been investigated through an impact test.Dynamic performances of the designed sensor have been evaluated in comparison with a commercial force/torque sensor.(4)We have researched force sensing technology for probe-like surgical instruments.The stiffness characteristic of the probe-like instrument has been researched,it is revealed that the axial stiffness of probe instruments is too large,which is not conducive to axial force detection.To slove this problem,we have developed a cylindrical coil spring structure with rectangular section,which is sensitive to all three dimensional force components.Measurment matrix is derived through measurement principle analysis and calibration tests.Moreover,for good biocompatibility,a layer of titanium coating has been plated on the adhesive surface through magnetron sputtering,and the applicability in high pressure steam sterilization environment have also been investigated.(5)The developed sensors and instruments have been experimentally evaluated in surgical robot development platform.The blunt dissection experiments and simulated lens implantation experiment have demonstrated that it is feasible to apply the researched prototype in robotic surgical system for force sensing and force feedback.