Modeling of Velocity-dependent Frictional Resistance of a Capsule Robot Inside an Intestine

A model is first built for predicting the velocity-dependent frictional resistance of a capsule robot that moves inside the intestine in the paper. The capsule robot plays a more and more important role in checking diseases in the intestine. This study aims to optimize the locomotion mechanism and the control strategy of the capsule robot. The model consists of three parts: environmental resistance, viscous friction, and Coulomb friction. Environmental resistance is induced by the stress due to the viscoelastic deformation of the intestinal wall. Viscous friction is analyzed according to the apparent viscosity of intestinal mucus. Coulomb friction is a product of the local contact pressure and the Coulomb friction coefficient. In order to analyze the effects of the intestinal deformation, a five-element model is used to describe the stress relaxation of the intestinal material. Experimental investigation is used to identify the model parameters with homemade physical simulation measurement system and fixtures. Finally, the model's validity is verified by experimental results. It is shown that the model predicting results can fit the experimental results well when the moving velocity of the capsule is lower than 20 mm/s. The R (2) of these two sets of data is 0.8769. But at a higher velocity, there are significant differences between the two results and the R (2) declines to 0.1666. The friction model is expected to be useful in the development of the medical equipment in the intestine and the study of biomechanics of the intestine.