An earthworm-like microrobot for colonoscopy.

Miniature robotics for colonoscopy has become a hot research topic with the development of minimally invasive surgery (MIS). In this paper, a novel microrobot for colonoscopy that operates based on a simulation of the squirming motion of the earthworm is described. The robot uses a unique driving unit called a linear electromagnetic driver. The prototype measures 9.5 mm in diameter and 120 mm in length. It is driven by a linear direct current (DC) motor designed and manufactured by the authors. This paper describes the prototype, locomotion principle, and control system in detail. It then describes two models that were built to study the robot's ability to move in the viscoelastic colon environment. A slepe model of motion was developed and some mathematical evaluations of locomotion conditions were conducted. Experiments to test the creeping ability of the prototype on a slope were performed to verify these expressions. From the viscoelastic model relative to acting force between the robot and the colon, a transcendent equation about locomotive efficiency of the critical squirm step was deduced and solved to instruct the design of the robot. Last, in vitro experiments in the fresh colon of a pig were performed. The results show that this kind of microrobot can propel itself freely and reliably in the soft viscoelastic colon. Finally, future areas of research are noted.