Magnetic Levitation for Soft-Tethered Capsule Colonoscopy Actuated With a Single Permanent Magnet: A Dynamic Control Approach

Abstract

The present letter investigates a novel control approach for magnetically driven soft-tethered capsules for colonoscopy-a potentially painless approach for colon inspection. The focus of this work is on a class of devices composed of a magnetic capsule endoscope actuated by a single external permanent magnet. Actuation is achieved by manipulating the external magnet with a serial manipulator, which in turn produces forces and torques on the internal magnetic capsule. We propose a control strategy which, counteracting gravity, achieves levitation of the capsule. This technique, based on a nonlinear backstepping approach, is able to limit contact with the colon walls, reducing friction, avoiding contact with internal folds, and facilitating the inspection of nonplanar cavities. The approach is validated on an experimental setup, which embodies a general scenario faced in colonoscopy. The experiments show that we can attain 19.5% of contact with the colon wall, compared to the almost 100% of previously proposed approaches. Moreover, we show that the control can be used to navigate the capsule through a more realistic environment-a colon phantom-with reasonable completion time.

Keywords: Medical robots and systems; force control; motion control.

Fig. 1

Schematic representation of the platform.

Fig. 2

Control scheme.

Fig. 3

3D tracking. The IPM (solid line) and EPM (dashed line) trajectories for all trials performed.

Fig. 4

Evaluation of levitating performance.

Fig. 5

Experimental setup: Colon simulator.

Fig. 6

Trials on the colon simulator.