Citation: Kwon, S.; Kim, J.; Moon, Y.;
Kim, K. Hyper-Redundant
Manipulator Capable of Adjusting Its
Non-Uniform Curvature with
Discrete Stiffness Distribution. Appl.
Sci. 2022, 12, 482. https://doi.org/
10.3390/app12010482
Academic Editor: Dario Richiedei
Received: 15 November 2021
Accepted: 29 December 2021
Published: 4 January 2022
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Article
Hyper-Redundant Manipulator Capable of Adjusting Its
Non-Uniform Curvature with Discrete Stiffness Distribution
Seongil Kwon
1,2
, Jeongryul Kim
3,
*, Yonghwan Moon
1,4
and Keri Kim
1,2,
*
1
Augmented Safety System with Intelligence Sensing and Tracking (ASSIST), Korea Institute of Science and
Technology, Seoul 02792, Korea; kstar1@kist.re.kr (S.K.); moonyh1230@kist.re.kr (Y.M.)
2
Division of Bio-Medical Science and Technology, University of Science and Technology, Daejeon 34113, Korea
3
Center for Healthcare Robotics, Korea Institute of Science and Technology, Seoul 02792, Korea
4
School of Mechanical Engineering, Korea University, Seoul 02841, Korea
* Correspondence: jeongkim@kist.re.kr (J.K.); jazzpian@kist.re.kr (K.K.)
Abstract:
Hyper-redundant manipulators are widely used in minimally invasive surgery because
they can navigate through narrow passages in passive compliance with the human body. Although
their stability and dexterity have been significantly improved over the years, we need manipulators
that can bend with appropriate curvatures and adapt to complex environments. This paper proposes
a design principle for a manipulator capable of adjusting its non-uniform curvature and predicting
the bending shape. Rigid segments were serially stacked, and elastic fixtures in the form of flat
springs were arranged between hinged-slide joint segments. A manipulator with a diameter of
4.5 mm and a length of 28 mm had been fabricated. A model was established to predict the bending
shape through minimum potential energy theory, kinematics, and measured stiffnesses of the flat
springs. A comparison of the simulation and experimental results indicated an average position error
of 3.82% of the endpoints when compared to the total length. With this modification, the manipulator
is expected to be widely used in various fields such as small endoscope systems and single-port
robot systems.
Keywords:
flexible robotics; kinematics; mechanism design; hyper-redundant manipulator; non-
uniform curvature
1. Introduction
Minimally invasive surgery (MIS) is common medical practice owing to its conve-
nience for surgeons and reduced patient trauma and recovery time [
1
–
3
]. The internal
structure of the human body is diverse, and there are cases in which a surgical tool may
have to pass through narrow and winding paths. In order to reach the target position
and perform the necessary operations, we require surgical tools with flexible bodies [
4
].
As machines with flexible bodies and high dexterities, a considerable amount of research
focuses on hyper-redundant manipulators [
5
–
8
]. Hyper-redundant manipulators used in
MIS take an underactuated form that transmit power using tendons from the outside. This
is advantageous for miniaturization and entering narrow and winding passages, due to
its flexibility.
On the other hand, owing to the manipulator’s underactuated characteristic, it is
difficult to predict the shape and precisely follow the operator’s intents, and determine
the bending shape according to the situation and environment. Since the joint of the
manipulator is a hyper-redundant structure, and the underactuated method controls all
joints with one tendon, it is difficult to accurately predict the shape of the joint because it
is not possible to control the motion of all joints individually. In addition, it is difficult to
install the actuator for each joint in these manipulators, and since the module that transmits
power is external and transmits power with tendons, it is difficult to perform precise
Appl. Sci. 2022, 12, 482. https://doi.org/10.3390/app12010482 https://www.mdpi.com/journal/applsci
