Broad challenges exist when fundamenta lresearch to study frictional characteristics between medical device and biological tissue is no exception. Capsule robot, which can examine the whole gastrointestinal (GI) tractnon-invasively and actively when performed by doctors who have had special training and are experienced in the endoscopic procedures,is one of the most representative medical devices. The imperfection offriction model between the capsule robot and the intestine has been one of the biggest obstacles of the development of the capsule robot. The capsule robot needs to start and stop frequently when working in the intestine. The frictional resistance increases rapidly from a small value in the robot's starting process. If the driving force of the capsule robot in uniform motion is used in accelerated motion, the capsule robot cannot move smoothly and more energy is wasted.

The researchers aim to figure out the intestinal frictional resistance variation in the starting process of the capsule robot when the capsule robot moves inside the intestine. Some experiments are conducted to measure the actual frictional resistance with a homemade uniaxial experiment platform. The frictional resistance is found to changes with the capsule's velocity, acceleration and original state. Further, curve-fitting is used to deduce the analytical expression of the frictional resistance in the starting process. The validity of the fitting result is verified by experiment result. The achievement of this study is hoped to make certain the intestinal frictional characteristics in the starting process of the capsule robot and optimize the control method of the capsule robot with various driving principle.

This work was supported by the National Natural Science Foundation of China (No. 61105099) and the National Technology R&D Program of China (No. 2012BAI14B03).