A new capsule-intestine model for the capsule robot self-propelling in the lower gastrointestinal tract

Abstract

Circular and haustral folds in the lower gastrointestinal tract (small and large intestines) are the major obstructions impeding the locomotion of the capsule robots for endoscopic diagnosis. Understanding the interactions between the capsule and these folds is critical for design and control of these robots to reach the areas of clinical interest. This paper proposes a new mathematical model of capsule-intestine interaction based on our previous work (Yan et al. 2022) by introducing capsule’s rotation during fold crossing. The resisting force of the fold predicted by the new model is more consistent with our finite element and experimental results compared to our previous model. It is found that the obstructive effect of the fold is stronger for a higher and thinner fold with a thinner and stiffer intestine. For the capsule robot, which is actuated by a periodically driven inner mass, a stronger excitation force is required to overcome the fold with a larger resisting force. Moreover, our bifurcation analysis reveals that a small excitation force always incurs a simple period-1 motion for the robot, while a large excitation force may result in various complex dynamics before the fold crossing. The findings of this work may help capsule robotics engineers to evaluate their designs in terms of propulsion and understand the locomotion of their robots in the lower gastrointestinal tract.