Dynamical Modelling And Analysis Of Vibration-driven Capsule Robots In The Inner Wall Of A Small Intestine With Folds

Self-propelled capsule robots have a wide range of promising applications in gastrointestinal testing,particularly in the case of gastric examinations,capsule endoscopes that can enter the stomach instead of a gastroscope are now available on the market.However,unlike the bulge in the stomach,the abundant circular folds in the small intestine are permanent and do not disappear during peristaltic movement of the bowel.There is no doubt that such folds provide a significant portion of resistance to capsule movement and are a major obstacle to self-propelled capsule travel in the small intestine.However,this issue has not been taken into account in many relevant studies.For this reason,the thesis proposes and validates a new resistance model that is applicable throughout the capsule's climbing over the fold.The model is able to calculate the resistance encountered by the capsule at different sizes of folds.The results show that the resistance reaches a maximum immediately after the capsule first hits the fold and decreases gradually during the tumbling process.In addition to this,the effects of single parameter variables and the variation of the maximum resistance are discussed.The thesis then investigates the kinetics of vibration to drive the capsule over the intestinal tissue,with both square-wave and sinusoidal driving.Under square wave drive,it was found,based on numerical simulations and bifurcation analysis,that the capsule's movement is always period-one when the driving force is small;whereas overturning the fold requires a larger excitation amplitude,especially when the duty cycle is small.In contrast,the drive period has little effect on capsule overturning.However,the internal mass,the capsule mass,the coefficient of friction and the height of the fold have a significant influence on the driving force required for capsule overturning.Also,the Young's modulus of the tissue is a key determinant of the bifurcation pattern of the non-linear capsule dynamics,with stiffer tissues leading to the coexistence of three different attractors.The length of the capsule and the stiffness of the spring,on the other hand,have little effect.Whereas,after changing the driving method to sinusoidal excitation,a polynomial approximation was used instead of a complex drag integral in order to speed up the computational efficiency.Similar to the square wave excitation,simulations and bifurcation analysis of the capsule under three frequencies of driving force were also done.In the results it is found that the frequency and amplitude of the driving force play a crucial role in the response and motion of the capsule.Due to the nature of the sinusoidal signal itself,a capsule excited by it will move in more diverse ways,including: backing away from the fold,advancing and being blocked by the fold,advancing over the fold and continuing on,and advancing over the fold and then moving backwards and being blocked by it,for a total of four types.It is worth noting that the geometry of the fold has no important effect on the bifurcation pattern,but the presence or absence of a fold significantly alters the movement of the capsule.Overall,this paper presents and validates a resistance model applicable to the entire process of capsule overturning folds for the scenario of a self-propelled capsule robot travelling through the small intestine.The model is also used to investigate the kinetic mechanisms of the vibrating capsule moving over the intestinal tissue,including both square wave and sinusoidal driving methods,and a series of results are obtained through simulation and analysis.In practical applications,the optimal driving method should be an organic combination of the two.