Automated alignment of rotating magnetic field for inducing a continuous spiral motion on a capsule endoscope with a twistable thread mechanism

In order to provide the capsule endoscopes with active mobility in the human digestive system, a new twistable thread module mechanism which forms a neutral, right-handed or left-handed thread based on the rotating direction of the capsule is proposed in this paper. Being installed with disk-type permanent magnets, the capsule endoscope can be put into either a spiral motion or translation motion by an external permanent magnet mounted on a rotational actuator, which can also change the moving direction of the capsule by just leading it in the desired direction. In the in-vitro tests on a straight artificial tract whose properties were made similar to those of a pig’s colon, the thread module could propel the capsule as fast as 400 mm/min when the external magnetic field was rotated at 24 rpm. In order to achieve this speed, 0.6 mm thick arc-shaped wire-type blades with a curvature of 6.25 mm were used to work like helical threads. And it was also necessary that the radial and axial distance of the external magnet from the capsule were maintained at optimum values, while at the same time the rotating axes of the external magnet and the capsule were parallel to each other. To make the latter possible, a control system has been contrived, where a multi-DOF robot was employed to automatically manipulate the position and orientation of the external magnet. Using Hall-effect sensors installed inside the capsule, its position and orientation data were detected to help the manipulator compensate the parallelism and distance errors between the external permanent magnet and the capsule, in repeated cycles. The effectiveness of the control system was verified by in-vitro tests with an arcshaped curved tract, where the capsule speed was kept over 90% of its maximum.