Experimental and numerical studies of intestinal frictions for propulsive force optimisation of a vibro-impact capsule system

Abstract

This paper studies the intestinal frictions acting on a millimetre-scale self-propelled capsule (26 mm in length and 11 mm in diameter) for small bowel endoscopy by considering different capsule-intestine contact conditions under a wide range of capsule's progression speeds. According to the experimental results, intestinal frictions vary from 7 mN to 4.5 N providing us with a guidance for designing the propelling mechanism of the controllable capsule endoscope. Our calculations show that the proposed vibro-impact mechanism can perform as a force magnifier generating a much larger propulsive force on the capsule than its original driving force. Therefore, the self-propelled capsule is capable of moving in the small intestine under a wide range of friction variation.

The vibro-impact capsule system in millimetre scale: numerical optimisation and experimental verification

“…The friction between the capsule and the synthetic small intestine is modelled as a Coulomb friction with the friction coefficient l. It is worth noting that although the intestinal friction when the capsule moved on a flat Fig. 1 (Colour online) a External and b internal views of the prototype [31] cut-open intestine was identified experimentally as a function of capsule's velocity in [31], i.e. 8:778V 0:25 c þ 2:518, the dynamics of the prototype under this friction model was almost the same as the one under the Coulomb friction.…”

“…In the present work, due to the dimension of the current prototype, direct measurement to the inner mass was impossible, so only the displacement of the capsule was recorded by video camera for dynamic analysis. A similar model was also studied in [31] for magnifying the propulsive force of the prototype. However, only a one-sided constraint was considered for the model, and its external excitation was a sinusoidal signal.…”

“…To validate the experimental results, a finite element (FE) model of static testing was also developed in ANSYS WORKBENCH by using the static structural module, where a magnet applied continuous force on a fixed constraint. A detailed description of the FE model can be found from [31]. FE and experimental results of the static testing are presented in Figs.…”

“…The merit of such a capsule is its simplicity in mechanical design and control which does not require any external driving accessories, while allowing independent movements in a complex environment. The study of this method was initiated from mathematical modelling [7,8,26,27], early proof-of-concept investigation [28], multistable dynamics control [15,29], to our recent capsule-intestine contact modelling [30], intestinal friction study [31] and mesoscale demonstration [32,33]. Since the mathematical model of the system belongs to the class of piecewise-smooth dynamical systems, for this type of systems, the state space can be divided into disjoint subregions [34].…”

“…Colour online) a Experimental set-up[31] and force-deflection curves for static testing of b the primary and c the secondary constraints Colour online) Experimental set-up for identification of the friction coefficient l…”