| There has been an increasing number of diseases related to gastrointestinal tract,which are gradually threatening people’s health and even their lives.Currently,there are two main diagnostic methods in clinical application:traditional electronic insertion endoscope and capsule endoscope,which have limitations and deficiencies in the aspects of safety,accuracy and comprehensiveness.And as the most potential alternative to the existing main diagnostic methods,the micro-robot providing non-invasive gastrointestinal diagnosis has become the focus of domestic and foreign research.Under the support of National Natural Science Foundation Project（No.61673271,No.81971767）,Shanghai Scientific Research Project（No.19441910600,No.19441913800,No.19142203800）and Medical Robot Research Institute Project of Shanghai Jiaotong University（No.IMR2018KY05）,this paper studied the key technologies of the micro-robot system for non-invasive gastrointestinal diagnosis,including the robot-intestinal mechanical properties,the design of motion mechanism,the analysis and optimization of mechanism elastic dynamics and the design of wireless power transmission system.In terms of the research of robot-intestinal mechanical properties:in order to accurately describe the mechanical relationship between the robot and intestine,this paper comprehensively analyzed and compared several different mechanical equations describing the strain-stress relationship in the human intestine by studying the biological structure and mechanical properties of the gastrointestinal tract,and used Constitutive Equation of 3D Ogden Incompressible Hyperelastic Model to express the stress-strain model of gastrointestinal tissue.According to Laplace theorem,a robot-intestinal dilation mechanical model was established to describe the relationship between intestinal dilation pressure and elongation.Through the analysis of the residence of the robot in the intestine,the robot-intestinal residence mechanical model that describes the relationship between the robot retention force and the intestinal elongation was established by the use of the robot-intestinal dilation mechanical model and the principle of virtual work.The establishment of the two mechanical models could provide a theoretical basis for the design of the expansion and residence mechanism of the gastrointestinal micro-robot,which has important guiding significance.In terms of the design of the micro-robot motion mechanism:the motion mechanism,which is mainly composed of radial expansion mechanism and axial contraction mechanism,is the key to micro-robot system for non-invasive gastrointestinal diagnosis,and is the carrier of each internal module.The new radial expansion mechanism designed in this paper adopted a double-layer staggered expansion arm structure.The variable diameter ratio could reach 3.3.The large variable diameter ratio greatly improved the adaptability of the robot in the intestine.The power unit adopted the combination of a DC hollow cup motor and a five-layer planetary gear reducer with a reduction ratio of 1024.The theoretical expansion force,vertex speed and acceleration were obtained through the analysis of the mechanics and kinematics of the expansion arm.Combined with mechanical model of the expansion mechanism and resident mechanism,small intestine of a pig with a radius of9mm was selected as the research object.After detailed analysis,it could be known that the expansion mechanism theory had a theoretical maximum expansion radius of 14.7 mm,and the theoretical expansion force was F（14.7）=2.39 N,the theoretical residence force in this pig’s small intestine was 3.28N.The axial contraction mechanism of micro-robot utilized a screw-nut device to realize the axial movement.The thrust of the robot’s axial motion mechanism was 13.696N obtained by theoretical analysis,and was about10.271N measured by experiment.Detecting whether the motor was locked to obtain the motion state of the robot would result in serious heat generation,short life of the motor and greatly reduced the reliability and stability of the mechanism and circuit.In order to solve this problem,this paper added a limit protection device on the basis of Hall sensor to the robot system.Its working principle was based on the design of A1172 Hall sensor and corresponding radial and axial limit mechanism.The device was simple in structure,small in size and easy to install,and the stability and reliability of its work were verified through experiments.In terms of the analysis and optimization of mechanism elastic dynamics:the expansion arm is the key component of the robot,which directly contacts and interacts with the gastrointestinal tract.Its performance is directly related to the stability and reliability of the entire system,the intestinal safety,and the efficiency of movement.For the expansion arm structure,its elastic dynamic model was established,and its movement in the actual working condition in the intestine was simulated.The finite element simulation software was used for elastic dynamics analysis to obtain the stress magnitude,distribution,velocity and acceleration during the movement,and to check the strength.Considered the finite element analysis,the structure of the expansion arm was optimized with the stress safety strength as the boundary condition,the thickness and shape of the expansion arm as the optimization variables,and the minimum weight of the expansion arm as the optimization objective.After the optimization,the stress distribution of the expansion arm was more uniform,the overall thickness was reduced by 0.4mm,and the weight was reduced by 31%under the requirements of strength and safety.In terms of the design of wireless power transmission system:the energy supply of storage battery cannot provide enough energy for the micro-robot system,and the cable-power supply makes the micro-robot unable to penetrate into the intestine,so the wireless power transmission is one of the most promising methods for energy supply for the gastrointestinal micro-robot.In this paper,a wireless power transmission system for micro-robot was designed,analyzed and built.First,five typical transmitting coil structures,namely solenoid,solenoid pair,double-layer solenoid pair,split solenoid and Helmholtz coil,were compared to analyze their respective advantages and disadvantages.And the double-layer solenoid pair was selected as the wireless energy transmitting coil structure of the system.In view of the relevant safety regulations of ICNRP for specific absorption rate（SAR）of human tissues and current density J,this paper analyzed the relevant parameters of the transmitting coil of the double-layer solenoid adopted in the system,and obtained the excitation current with an upper limit of 1.98 A.Based on the coil structure and electromagnetic safety,the relevant driving circuit was developed.The contour map of magnetic induction intensity inside the transmitting coil was obtained through experiments.And the magnetic induction intensity was measured to be in the range of（0.95～1）×10-4 T in the200 mm×200 mm region of the central area of the transmitting coil,indicating that the double-layer solenoid pair can produce uniform magnetic field.Finally,an interleaved hollow cylindrical three-dimensional receiving coil was wound,and its output power under different postures was measured through experiments.It was concluded that the minimum power received by the coil could meet the energy requirements of the robot under normal working conditions.In this paper,a robot-intestinal expansion and resident mechanical model was established,a new type of micro-robot motion mechanism was designed,and the mechanism was optimized according to elastic dynamics analysis.Also,a wireless power transmission system for micro-robot energy supply was built.The studies mentioned above provide theoretical basis and experience for the development of micro-robot system for non-invasive gastrointestinal diagnosis and have important guiding significance. |
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