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 has been studied extensively in the past decade because of its research challenges as a piecewise-smooth dynamical system and broad applications in engineering and healthcare technologies. This paper reports our team’s first attempt to scale down the prototype of the vibro-impact capsule to millimetre size, which is 26 mm in length and 11 mm in diameter, aiming for small-bowel endoscopy. Firstly, an existing mathematical model of the prototype and its mathematical formulation as a piecewise-smooth dynamical system are reviewed in order to carry out numerical optimisation for the prototype by means of path-following techniques. Our numerical analysis shows that the prototype can achieve a high progression speed up to 14.4 mm/s while avoiding the collision between the inner mass and the capsule which could lead to less propulsive force on the capsule so causing less discomfort on the patient. Secondly, the experimental rig and procedure for testing the prototype are introduced, and some preliminary experimental results are presented. Finally, experimental results are compared with the numerical results to validate the optimisation as well as the feasibility of the vibro-impact technique for the potential of a controllable endoscopic procedure.

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This paper aims to study a realistic finite element (FE) model to depict the nonlinear dynamics of a vibro-impact capsule moving on the small intestine for active capsule endoscopy. The FE model takes both the nonlinear vibro-impact mechanism and the viscoelastic deformation of the small intestine into account. FE results are compared with the simulation results obtained using non-smooth differential equations and experimental results. It is found that the FE model can provide a more realistic prediction of the system in the complex intestinal environment in terms of capsule's tilted motion and asymmetric distribution of capsule-intestine contact pressure. In particular, the capsule's dynamics is very sensitive to the surface condition of the intestine, so a comprehensive bifurcation analysis is needed for fully understanding its dynamics under intestinal peristalsis.

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