Research On Key Technologies Of Optical Biopsy Robot For Gastrointestinal Track

Gastrointestinal cancer is one of the most common diseases in the world.Although conventional histological biopsy is the golden standard for cancer diagnosis,as a traumatic examination,there are many disadvantages such as non-real-time,the risk of infections and slow recovery,etc.Optical biopsy can achieve non-invasive,real-time,cell-level imaging of the diseased area through a miniature probe.However,the imaging probe has a small field of view.There is no force sensing and stability is poor when the physicians perform the scanning manually with a low accuracy to obtain large area mosaicking.It is necessary to combine robotics,microimaging and images stitching and conventional endoscope technologies to achieve large area microscopic panoramic imaging of the gastrointestinal tract tissue.Based on the above technical requirements,this paper has carried out a series of key technologies research.The main and innovative achievements are as follows:To realize the automatic scanning,a novel 2-DOF modular scanning robot(17 mm in outer diameter)and the corresponding design method were proposed.The robot needs to be installed at the end of the endoscope and it is easy and efficient to use.The combination of the rigid and compliant transmission mechanisms realizes the motions decoupling of two degrees of freedom and miniaturization.The actuation unit was equipped on the robot frame that was the distal end of the endoscope and this configuration reduced the motion hysteresis and errors caused by the excessively long transmission chain.Kinematics model of the mechanisms was established and output force was analyzed.The prototype was fabricated and assembled.Combined with the kinematics model,the robot has been controlled to evaluate the motion performances by sensors.These experiments demonstrated that motion accuracy of the two transmission chains were 0.1 mm and 0.23 mm,respectively.The maximum output force was more than 0.2 N.The robot can achieve precise raster trajectory scanning.To further realize the miniaturization of the optical biopsy robot,contact-aided compliant continuum robot based on Nitinol tube and the corresponding design method were proposed.The robot needs to be used through the work channel of the endoscope and actuated by wires to bend in 4 directions with compact structure and high dexterity.The deformation model based on elliptical shape assumption was proposed to predict the maximum strain of the beam with distributed compliance and its reasonability was verified by finite element analysis.The statics model was established to predict the bending behavior of the compliant joint based on Castigliano’s first theorem and the simplified constitutive model of Nitinol.Based on the statistical method,the kinematics model of the continuum robot was established to predict the relationship between the displacement of the actuation wire and the deflection angle of the mechanism.Experimental results demonstrated that the proposed models can predict the motions of the robot.Results of comparison experiments showed that the proposed contact-aided compliant mechanism improved tensile and torsional strength by more than 30%and100%,respectively,compared with the conventional compliant mechanism.Based on the proposed contact-aided compliant mechanism,a flexible scanning robot(2.7 mm in outer diameter and more than 800 mm in length)was designed and realized.Based on the consideration that force sensing can assist imaging and improve the safety of medical operations.A 3-axis force sensing unit with fiber Bragg grating was proposed and packaged.The self-differential method was used for temperature compensation.Utilizing this temperature compensation method,the 3-axis forces were calculated and decoupled by a hybrid force calculation algorithm.The force calibration and the triaxial force random tests have been completed.The tests results showed that the force sensing unit can accurately measure the random spatial force with a high resolution(less than 5 m N).The force sensing unit was combined with the flexible and long continuum scanning robot to achieve functional integration.To realize microscopic imaging acquired and images mosaicking,wide-field fluorescence and confocal laser endomicroscopic systems were built and verified by imaging experiments.The images stitching algorithm was proposed based on normalized correlation coefficient and distance weighting methods.Based on the above research,the modular robot,the flexible continuum robot with force sensing unit and corresponding motion control systems were integrated with the gastroscope system and endomicroscopic imaging systems.Then,the scanning experiments were performed by lens tissue paper and freshly excised porcine gastric tissue stained with acriflavine.The maximum mosaicking covered an area more than18 mm~2 and the 3-axis contact forces were monitored during the scanning process.The results showed that the feasibility of both designs that can be entered into the human gastrointestinal tract to perform scanning and the potential value for large-scale clinical application.