| Minimally invasive surgery robots demonstrate significant advantages in terms of high stability,high precision,flexible operation and higher difficulty of fatigue in operation.Therefore,they are important ways to achieve minimally invasive surgery(MIS).However,there is no mature force sensing technology that can be applied in minimally invasive surgical robots.Based on the optical fiber sensing mechanism,FBG was selected as the sensing element for tissue palpation in minimally invasive surgery in this paper.According to the deformation theory of flexible mechanism,a novel flexure has been proposed and the simulation and optimization have been conducted.Combining FBG and the optimized flexure,a miniaturized and high-precision force sensor was developed.The corresponding prototype has been manufactured and verified by experiments.The specific research contents are as follows:Firstly,the advantages and disadvantages of fiber sensing principle based on optical intensity,phase and wavelength modulation were summarized.According to the medical requirements of tissue palpation in MIS and the technical difficulties of minimally invasive surgical robots’ force sensors,FBG was selected as the sensor element,and its sensing principle was deduced theoretically.A two-point pasting method has been utilized that ensures the optical fiber in suspension tension state,which makes FBG produce uniform strain and avoid FBG chirping failure and low repeatability.Then,this paper presents a novel Fiber Bragg Grating(FBG)-based one-dimensional force sensor.The flexure design has been prototyped through the configuration synthesis of Sarrus mechanism by using a rigid-body replacement method to achieve an excellent axial linear force-deformation relationship and a large measurement range.The mounted fiber has been configured at the flexure’s central line with its two ends glued,and its tight suspension configuration can achieve improved resolution and sensitivity compared to the commonly used direct FBG-pasting methods.Finite element method(FEM)-based simulation has been performed to investigate both static and dynamic performance to aid in structural design.Simulation-enabled structural optimization design has also been implemented to further improve the proposed design and the sensor’s sensitivity has been increased.The optimized sensor design has been prototyped and calibrated to demonstrate an excellent linearity with a small linearity error of 0.97% and achieve a high resolution of 2.55 m N within a relatively large measurement range of 0-5 N.Dynamic force stimulation experiments,in-vitro palpation implementation on a silicone phantom embedded with simulated tumors and ex-vivo indentation experiments on a porcine liver have validated the effectiveness of the presented sensor design.Finally,in order to obtain detailed 3D contact force information,an FBG-based three-dimensional force sensor was proposed.An axial flexure with two parallel cross beams and a parallel radial flexible structure which can rotate about two axes of orthogonal hypersurface were proposed via freedom and constraint topology.They are connected in series and combined with FBG to achieve the three-dimensional force sensor design.Simulation analysis and optimization design of this force sensor were conducted by the same research method and a sensor prototype was fabricated.The calibration experiment indicates that the force sensor can achieve a high resolution of the same order magnitude in X,Y and Z directions,which verifies the effectiveness of the proposed sensor. |
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