Characterizing the coefficient of friction between a capsule robot and the colon.

Abstract

A capsule robot (CR) with an onboard active locomotion mechanism, has been developed as a promising alternative to colonoscopy due to its minimally-invasive advantage. Predicting the traction force and locomotion resistance of the CR, which are both the friction force, is significantly important for the CR development and control. However, a comprehensive study concerning the coefficient of friction (COF) in the colon, which is necessary for prediction, is not available in literature. This paper is dedicated to determining a quantitative COF equation in terms of the contact pressure, hoop strain, and sliding velocity. The COFs of three commonly-used materials of the CR (i.e., PDMS, white and transparent ABS plastic), are measured under 144 different friction cases (6 contact pressures×4 hoop strains×6 sliding velocities). By analyzing the measurements, the influence law of the three factors on the COFs of the three materials is revealed, and based on which, a general COF equation involving eight fitted constants is determined. The determination coefficients of the COF equation for the three materials are up to 0.9822, 0.9286, and 0.9696, respectively. The COF equation is used to predict the traction force and locomotion resistance of a crawler CR, and the predicting results fit well with the measured ones. The COF equation can provide a correct COF for friction force prediction. It is promising to enable a better force and locomotion control for the CR in the colon.