Page 337 - Flexible Robotics in Medicine

328 Chapter 14

CTRs can be further enhanced through the use of sensory information, or, more
specifically, using tactile force sensors to provide haptic feedback and to recognize the
hardness of soft tissue and measure the variation in properties. Additionally, feedback from
the sensors can determine the force being applied and prevent excessive force from
damaging fragile tissue. Experimentation has been carried out on various sensors,
predominantly of the resistive, capacitive, and piezo-electric types [3]. Due to certain
limitations such as size, weight, or electromagnetic interference, many sensors are not
suitable for or easily integrated with sensitive medical equipment. In contrast, fiber Bragg
grating (FBG) sensors have properties that make them well suited to the task. The typical
FBG has a diameter of less than around 250 μm, which is light and resistant to high
magnetic [4] and radiation [5] environments.

A flexible robotic design is proposed that is equipped with concentric tubes to make the
robot viable for minimally invasive endoscopic surgery. A simple kinematic model for the
CTR is then developed along with a multithreaded Python program for control of the robot.
FBG sensors are attached to the distal tip of the CTR to obtain tactile sensor feedback
control of the system. Finally, the FBG sensors are calibrated, and the accuracy of the
model is tested.

14.2 Literature review

14.2.1 Review of concentric tube robot design

Concentric and precurved tubes are able to navigate nonlinear paths via telescoping. As
continuum robots, they are made of precurved pseudoelastic metal tubes, which can be
shaped as necessary for various sections of anatomy [6]. Control of the curved shape of
these devices enables obstacle avoidance in confined and complex spaces. Tubes can be
controlled manually or through motor actuation but with similar principles and actuation
mechanisms. Actuation is used to achieve (1) axial rotation and (2) lateral movement
through the outer tube. Due to the flexible nature of the metal, rotation or extension of the
internal tubes would result in the transformation of the tubes’ original shape based on the
precurved outer tube, which is made of more rigid material.

14.2.1.1 Actuation of concentric tube robots

Most CTRs provide a method for needle insertion and orientation and require trajectory
control precisely steered by their actuation mechanisms [7]. Using motor actuated systems in
CTRs has paved the way for sophisticated robots capable of intracorporeal visualization as
well as teleoperation. The compact two-degree-of-freedom (2-DOF) mechanism can utilize
manual actuation [8]. Utilizing a traction drive, lateral movement of the needle is possible,
with rotation controlled by a gear connected motor. A similar concept in Ref. [9] made use of