Journal Club: Bernth et al, 2017

A Novel Robotic Meshworm With Segment-Bending Anchoring for Colonoscopy

Julius E. Bernth | Alberto Arezzo | Hongbin Liu

The authors introduced a novel design worm inspired robotic endoscope with multi degrees of freedom segments, which can move itself forward and backward by anchoring the different segments. The robot comprises of three individual segments which have a flexible and elastic mesh around them and can be driven by tendon antagonistically. The front and rear segments are connected by three motors each which give it three degrees of freedom (DOF) – expansion and contraction about one axis and bending about the other two axes. The middle segment has only one DOF, so it can only accomplish expansion and contraction about one axis. A prototype with one miniature camera of 6mm diameter and LED is prepared in order to evaluate system’s ability to perform as endoscope. The diameter of robot is 31mm when the mesh is uncompressed and 36mm when the mesh is in compressed state. The length of the robot is 500mm when uncompressed.

The locomotion principle is based on the ability of front and end segments to bend in order to lock (anchoring) and unlock (unanchoring) by increasing the frictional force between the robot and colon wall. The forward or backward motion is attained by anchoring one end of the robot. The middle segment then helps the unanchored end to move forward or backward by contracting and expanding itself. With the help of correct sequence of the above process i.e anchoring of one end segment of robot, contraction of the middle segment, unanchoring of the previous end while anchoring of another end segment and extension of middle segments, the locomotion of the robot can be attained. In addition to this locomotion, steering of the robot around turns and orientation of the camera can be controlled by bending each end segment.

In order to accurately control the robot, a hall effect sensory system with PID controller is implemented. Two hall effect sensors are placed around a pulley connected to the motor controlling the tendon. The signal of the hall effect sensors changes with angular position of the pulley. The PID controller processes this signal from the hall sensors to control the length of the tendon which in turns controls the locomotion of the robot. The robot is tested inside 50mm diameter and 1200mm long simulated colon. It produces 1.1N of static frictional force when all the segments are straight and extended while 2N frictional force with bending of end segments. Authors also reported an average speed of 1.21mm/s which is equal to 38% of theoretical maximum.