Page 351 - Control Theory in Biomedical Engineering

CHAPTER 12

Tunable stiffness using negative

Poisson’s ratio toward load-

bearing continuum tubular

mechanisms in medical robotics

a
a
a
Krishna Ramachandra , Catherine Jiayi Cai , Seenivasan Lalithkumar ,
b
a
Xinchen Cai , Zion Tszho Tse , Hongliang Ren a
a
Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore,
Singapore
b
University of Georgia, Athens, GA, United States
1 Background
While there exists a small number of soft, flexible, and minimally invasive
surgical robotic manipulators for minimally invasive surgery (MIS), the lack
of dynamic load bearing capacity in these instruments has limited their use in
applications requiring exertion of forces. Equipping these MIS devices with
variable stiffness capabilities allows them to be used for isolating and oper-
ating procedures in surgical manipulations that require force applications,
such as tumor isolation, manipulation, and safe extraction, without contam-
inating surrounding tissues. A variable stiffness module adds an element of a
dynamic haptic feedback and additional load-bearing capacity, which makes
the device more intuitive for surgeons. In this work, we take the design-
centric approach and develop a novel method to achieve a tunable stiffness
module aiming to widen the capabilities of MIS devices.
We aimed to create a new actuation mechanism with variable stiffness
(Huan et al., 2016; Li et al., 2016, 2017). A flexible and compliant spring
backbone can navigate tight and narrow spaces (Li et al., 2015b; Wu
et al., 2017). However, in order to be fully implementable as part of a sur-
gical system, our device requires additional fast stiffness tuning features.
While a fully flexible spring body provides the necessary conformability
for safer maneuverability inside the body, it is not well suited for applying
force to the tissue. The lack of rigidity also makes it difficult for the instru-
ments to resist external forces within the body. Ideally, surgical robots and

Control Theory in Biomedical Engineering © 2020 Elsevier Inc.
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