Research On A Miniature Biomimetic Robotic Examination System For Gastrointestinal Tract And Kinematic Compatibility

At the present day, the diagnose and therapy of the diseases of the gastrointestinal tract mainly depend on the means of gastrointestinal endoscopes. Therefore, the research on the gastrointestinal robotic examination system is the fornter and central issue in the international medical apparatus and instruments fields. Based on the micro machining technology, micro actuation technology, microelectrionics technology, wireless communication technology, wireless power transfer technology and clinical medical technology, this study focused on the system design and the locomotion compatibility of a miniature biomimetic robotic examination system for gastrointestinal tract under the support of the National High Technology Development Program.A miniature biomimetic robotic examination system for gastrointestinal tract was developed based on the detailed analysis of the physiological characteristics of human gastrointestinal tract. The first assembled miniature robotic prototype for gastrointestinal examination achieved the characteristics of being wireless. It's outer dimension is 12.1mm in diameter and 165.5mm in length and comprised one head cabin, three driver units and one tail cabin. The robot may execute instructions including forwards, backwards and halt. The images of the inner gastrointestinal tract collected by the video camera module were transmitted to the outside by the wireless communication module. The image streams at rate of 3 frames per second with power consumption of 120mW. The wireless power receiving module supported each part of the robot with energy. The second whole tectorial membrane miniature robotic prototype was developed based on the first robotic prototype, The silicone bellows were laid over the whole robotic prototype. It reduced negative influence of the gastrointestinal viscoelastic behavior and protected the robot at the same time.The wireless transfer systerm was developed using the electromagnetic coupling principle. This power transfer means needed two coils. The launching coil was a solenoid, which was drived by the E class amplifier or switch circuit, and would surround the human trunk. The receiving coil was embedded in the the robot. For a power-efficient realization of an inductive link, the resonance compensation technology was adopted. That is to say, the inductance at the launching and receiving side were commonly cancelled by a parallel-resonant or series-resonant capacitor. The sine exciting current with a certain frequency, which was produced by the resonant lauching coil through adjusting the resonant capacitor, generated a alternating magnetic field. Here, the inductive electromotive force was produced in the receiving coil located in the alternating magnetic field. Through the following commutation and voltage regulation circuit, the inductive electromotive force was transformed to be direct voltage which would support the robot with steady power. At the time of applying the wireless power transfer system to the miniature biomimetic robotic examination system for gastrointestinal tract, the human would exposed to the electromagnetic field. Therefore, the limited close-wound solenoid electromagnetic model was build, the relationships between the electric intensity and the specific absorption rate and current density were deduced and the simulation experiments was done. Experimental results showed that the values of the SAR and the current density related to different tissue catalogs were all very small and not exceed their own limits, respectively, when the supplying power was 480mW and the resonance frequency of operation was 36 kHz.A miniature linear actuator based on the direct current motor was deceloped. It had many advantages such as small volume, light weight, high power-weigth ratio and easy control, etc. Finite element model of the miniature linear actuator was built for optimizing the linear actuator to avoid the sympathetic vibration of system. The mathematics model was also built to the analysis of the dynamics of the miniature linear actuator. The simulation and experimental results showed that the step response of miniature linear actuator was short and the infection of load was small. The driving force of miniature linear actuator could reach to 2.55N and the temperature rise was under 36℃. This research had laid a theory foundation for the motion security and feasibility of the miniature robot in the human intestines lumens.The viscoelastic mechanical behaviors of the gastrointestinal biological tissues were studied and the general three dimension quasi-linear viscoelastic model was introduced. The exponential format of the pseudo-strain energy function was used and the material constants C1 and C2 were determined by using the least-square method to fit the experimental curve. To achieve the lowest order of the strains, the general expression of the viscoelastic bodies was deduced by using the quadratic equation of the exponential format of the pseudo-strain energy function. For a uniaxial extension system, the concrete form of the the general expression of the viscoelastic bodies was deduced and the reduced relaxation function with a continuous spectrum of Fung was cited to reduce the quasi-linear viscoelastic model to be one dimension model. The relationships of the stress-time and the stress–strain of the deforming viscoelastic tissues were solved by using the one dimension quasi-linear viscoelastic model and two deformation functions which simulated the strain of the intestine. The influence by the relaxation function with the different parameters to the model was analyzed. In the analysis of the time-availability, an important conclusion was achieved, that was the stress response had insensitivity with the load rate in a certain range of the strain ratio. The influencing factors, such as the quality of robot, the friction coefficient, the diameter, and the original touching length, to the critical pace were analyzed. The analysis results showed that the locomotion units of the robot should have the lesser weight, the smooth surface, the bigdish diameter and the lesser touching length. Based on these results, a new whole tectorial membrane miniature robot prototype for the gastrointestinal tract examination was developed. According the quasi-linear viscoelastic model, the theoretical critical pace of the new robot was minished from the former 6.45mm to 1.6mm. The bellows could play the role to reduce the adhesion and was fabricated based on the bionic principle. The relationship between the distortion and the force was tested and the maximal elasticity force of the bellows was not exceeding 0.12N which would be conquered by the miniature linear actuator easily. When the miniature linear actutor elongated, the bellows would promote the baffle of the miniature linear actuator depending itself elasticity restoration function.The towing test, the locomotion capability and the in-vitro experimental results were researched and compared. The towing force and locomotion rates of the two robots were measured in the different condictionss, which validated the locomotion model and the driver principle. The in-vitro experiments were done and the results showed that the locomotion efficiency of the whole tectorial membrane miniature robot was promoted obviously.The prototype inegration, the wireless power transfer, the driver technology, the model foundation and the in-vitro experiments were studied thoroughly. All above researches laid the solid foundation to the robot examination system applying in clinic. The power supply and mechanism optimization should be studied in the future.