Download Endoskeletons Using Composite Flexure Joint for Biomimetic Meso

2011 IEEE International Conference on Robotics and Automation
Shanghai International Conference Center
May 9-13, 2011, Shanghai, China
Endoskeletons using Composite Flexure Joint
for BioMimetic Meso-scale Robot
Je-Sung Koh, Kyu-Jin Cho, Member, IEEE
Abstract— In this video, composites and a polymer flexure
joint are used to design mechanical elements. This composite
structure can be applied to endoskeleton structures of
biomimetic meso-scale robot. The basic active unit of the
structure is a revolute joint with an SMA spring actuator that
imitates a joint and muscle formation. The conventional
mechanical element is replaced by composite structures design
on 2D pattern. Using these elements, prototypes of a robot are
fabricated to verify feasibility of application of the robot.
A
I. INTRODUCTION
LL THINGS LIVING in
nature have their own skeletons to
maintain their shape and produce locomotion. Mammals
and birds have bones that form an endoskeleton. Insects and
some sea animals have a cuticle shell that form an
exoskeleton. And mollusks and an annelid, like an earthworm,
have an integument that form a hydraulic skeleton. The type
of skeleton determines how an animal moves as a whole
structure. Similarly, a robot has a main frame that produces
motion and forms its body shape.
In the design of a robot, first the main skeleton structure and
its model are established. Although there are several kinds of
skeletons, a model is created using rigid links and joints to
simplify the skeleton structure. The rigid link and joint
modeling is widely used because of simplicity and ease of
control and fabrication. Basically, the rigid link and joint
modeling is an endoskeleton, which becomes the frame of the
robot.
In a small scale below the millimeter range, a novel
fabrication method based on composites and polymer films,
Fig. 1 Replacement of revolute joint in meso-scale
the so called ‘Smart Composite Microstructures (SCM)’, is
introduced [1]. The SMA spring actuator is implemented as
an artificial muscle on the composite structures, and becomes
a basic active joint unit, as shown in Fig. 1. This unit replaces
the conventional small-scale mechanical elements. The robot
frame is composed of many mechanical components such as a
revolute joint, universal joint, rigid link etc. The design area
of the meso-scale robot would be expanded by development
of these components with composites and flexure joints in
small scale.
II. MESO-SCALE MECHANICAL ELEMENTS
Many mechanical elements are used to make a robot.
Composite flexures are used to make these mechanical
elements. In order to produce mechanical elements with
composite flexure, it needs different design based on 2D
pattern.
A. Revolute Joint Unit
An R-joint element performs a simple flexure. As shown in
Fig. 2, the revolute joint is just a composite folding joint at the
flexure. The joint’s stiffness and strength are determined by
Fig. 2 Concept design of basic active unit
Authors are with the School of Mechanical and Aerospace Engineering,
Seoul National University (e-mail:kjs15, [email protected]).
This work was supported by the Basic Science Research Program through
the National Research Foundation of Korea (NRF); the program was funded
by the Ministry of Education, Science, and Technology (Grant No.
2010-0001201, 2010-0015500)
978-1-61284-385-8/11/$26.00 ©2011 IEEE
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Fig. 3 Replacement of multi DOF joint in meso-scale[2][3]
Fig. 4 Foldable joint using SMA torsional spring actuator
Fig. 5 Prototype of foldable structure
the length and thickness of the flexure.
B. Spherical 6-bar Linkage
We employed a special pattern design on a 2D plane,
namely, the spherical 6-bar linkage folding pattern (Fig. 3). It
makes a motion of bending and steering of linkage. The
maximum angle of bending and steering is designed
according to the angle of the flexure joint axis. The spherical
6-bar linkage has 3 degrees of freedom. The stiffness of the
flexure makes it possible to be passive stable joint. The
linkage with this passive joint is controlled by two actuators.
It generates 2DOF motions.
C. Active Foldable Unit
A composite flexure structure is foldable. However,
previous active joint element with linear spring actuator had
difficulty in bending 180 degrees because the artificial
muscle actuator was an obstacle. With the torsional SMA
spring actuator, the link can fold 180 degrees as shown in Fig.
4.
III. MESO-SCALE ROBOTIC APPLICATION
With the mechanical element described in previous chapter,
a small crawling robot inspired by the inchworm and foldable
structures are developed to verify the application feasibility
(a)
of design robot. The rigid links are made of glass fiber
composite and flexure joints are made from a copper
laminated Kapton(Poly-imide) film. The copper laminated
Kapton can be made into a flexible electric circuit after an
etching process. SMA soldered on copper is activated by an
electric current of 0.5~0.2A according to the wire diameter
and material properties.
A. Crawling Robot Inspired by Inchworm: Omegabot
The crawling robot inspired by the inchworm is developed
with a single flexure joint and spherical 6-bar linkage
structures (Fig. 5 (a)). Inchworm crawls with an omega (Ω)
shape bending motion and steering motion. The robot
structures need joints of multi degree of freedom to generate
the inchworm’s motion. The combination of single flexure
and spherical 6-bar linkage enables three or higher DOF.
B. Meso-scale Gripper inspired by prolegs
With a series connection of small scale revolute joints, the
soft tissue of the caterpillar’s prolegs can be replaced. Closed
loop of 6 links can make the gripping motion with the spine?
as shown in Fig. 5 (b). The gripper inspired by prolegs has
1.5cm length and about 5mm thickness. It makes a
mechanical gripping force with spines on a rough surface
such as those of trees, fabric cloth etc.
C. Meso-scale Foldable Structure
The foldable structure converts its body frame from a
compact folded state to a larger functional state. Foldable
structures consist of composite links, flexure joints and SMA
torsional spring actuators. Fig. 6 shows the folding sequence
of the prototype of foldable structures. Four links are folded
by SMA torsional spring actuators.
REFERENCES
[1]
[2]
(b)
Fig. 6 (a) Crawling robot inspired by Inchworm (b)
Meso-scale gripper [2][3]
[3]
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R.J. Wood, S. Avadhanula, R. Sahai, E. Steltz, and R.S. Fearing,
“Microrobot design using fiber reinforced composites,” Journal of
Mechanical Design, vol. 130, 2008, p. 052304.
J. Koh and K. Cho, "Omegabot: Biomimetic Inchworm Robot using
SMA coil actuator and Smart Composite Microstructures(SCM)",
Proceedings of the 2009 IEEE International Conference on Robotics
and Biomimetics(RoBio 2009), 2009, pp.1154-1159.
J. Koh and K. Cho, “Omegabot: Crawling Robot Inspired by Ascotis
Selenaria”, Proceedings of the 2010 IEEE International Conference on
Robotics and Automation, 2010, pp.109-114.