Page 20 - Flexible Robotics in Medicine

2 Chapter 1

cavity environments. Thus robots with the ability of flexible motion bring about the interests
of the researchers and developers.

Snake, which goes through 100 million years of evolution, lives in nature almost around the
world with high adaptability, still keeps the long, slim, and limbless body feature. Snake
locomotion has attracted the interests of scientists in bionics and robotics for a long time. Since
Shigeo Hirose in Tokyo Institute of Technology developed the first snake-like robot in the 1970s,
studies on snake-like robots’ locomotion mechanism, mechanical design, gait generation, and
motion control have been continuously published. Among the motion generation theories, gaits
generated based on the curves are the most popular, exceeding the central pattern generator
(CPG) and dynamic model based methods. Chirikjian developed the backbone curve theory, and
Choset studied the discretization of a curve in snake-like robot motion generations. Due to the
hyperredundancy in DOF, snake-like robots can be used as a flexible manipulator to inspect
spaces that are difficult to reach, for example, products by OC Robotics as inspectors. Inspired by
the industrial usages, researchers have been trying to study snake-like robots that can be used for
operational purposes.

Traditional snake-like robots have articulated rigid links. Due to their bulky shape, although
they are found in certain studies that cater to stomach and intestine biopsy applications [1],they
are of low priority in consideration of surgical applications. Continuum robots that take the
form of cable-driven, concentric tube, catheter, steering needle fit the operation environment
better than the snake-like robots of traditional modality. However, continuum robots in a
surgical area have a long and slim shape and move like a snake, so they are often named as
snake-like robots likewise. As has been surveyed previously [2], snake-like robots have been
developed for applications in neurosurgery, otolaryngology, cardiac surgery, vascular surgery,
abdominal surgery, and urological surgery. Take the cable-driven snake-like robot; for example,
the actuation mechanism introduces backlash in the movement [3]. Additionally, the friction
force is hard to be recognized to get an accurate hysteresis model. Besides, when the robots
move inside the human body, it is challenging to build the interaction model. The sensing of
the position, configuration, and force are difficult issues due to their downscaled size. Therefore
accurate control for this type of robot to reach the target and accomplish the operations such as
inspection, biopsy, cutting, and suturing is difficult. This survey discusses snake-like robots in
surgical applications and summarizes the recent progress in mechanical design, modeling,
sensing, and control. Among the contents, the authors will emphasize the motion compensation
techniques, workspace analysis, motion planning, and control of the robots, which have not
been surveyed intensively in previous studies.

1.2 Snake-like robots for surgery

Because of the similarity on shapes, endoscopes can be reckoned as the predecessor of the
snake-like robot for surgical usage. Equipped with cameras and essential transmission