Preliminary study of a twistable thread module on a capsule endoscope in a spiral motion

In order to provide the capsule endoscopes with active mobility in human digestive system, a twistable thread module mechanism is proposed in this study. The twistable thread module forms a neutral, right-handed or left-handed thread based on the rotational direction of the capsule, which is rotated by the interactions of a revolving external magnet and the disk-type permanent magnets within the capsule. The performance of the twistable thread module mechanism was evaluated by measuring the moving speed of the capsule in an artificial tract, while changing the parameters such as pitch angle, number of thread modules, rotational speed of the external magnetic field and the distance between the external magnet and capsule. It was observed that the capsule moved faster as the pitch angle or the rotation speed of the external magnet was increased. In the double thread modules case, when the pitch angle was at 35A degrees and the external magnet rotated at 24rpm, the capsule could move as fast as 300 mm/min, which is about 60% of the ideal speed of the spiral motion, caused by the threads slip. In the triple thread modules case, although the threads slip decreased, the capsule speed did not increase as expected because of its high friction torque, that hinders the steady rotation of the capsule body. And also, the magnet distance range dropped abruptly. In a living pig's colon, the capsule endoscope propelled by the double thread modules with the pitch angle 35A degrees and external magnet rotating at 18rpm, moved at a speed greater than 200mm/min, which was 83% of the capsule speed as measured in the in-vitro tests.