Tech Briefs Magazine - May 2024 - 32

A Bioinspired Multimaterial Soft Robotic Hand
The work demonstrates finite element analysis can serve as a valuable tool to support the
design and control of the hand's fingers.
University of Coimbra, Portugal
A
research paper by scientists at the
University of Coimbra proposed a
soft robotic hand comprising soft actuator
cores and an exoskeleton, featuring
a multimaterial design aided by finite element
analysis to define the hand geometry
and promote finger's bendability.
The new research paper, published on
August 8 in the journal Cyborg and Bionic
Systems, presented the development,
fabrication, and control of a bioinspired
soft robotic hand and demonstrated finite
element analysis can serve as a valuable
tool to support the design and control
of the hand's fingers.
" Recent research led to impactful
achievements in functional designs, modeling,
fabrication, and control of soft robots.
Nevertheless, the full realization of
life-like movements is still challenging to
achieve, often based on trial-and-error
considerations from design to fabrication,
consuming time and resources. Using finite
element analysis to support the design
process, saving time and resources, " said
study author Pedro Neto, a Professor at the
University of Coimbra.
The finite element analysis comprising
(a) hyperelastic behavior of the soft
materials, (b) finite rotation and large
strain of the exoskeleton and actuators,
and (c) frictional contact between exoskeleton
and actuators.
" This integrated solution will make
soft robotic hands more available to
people, at a reduced cost, avoiding the
time-consuming design-fabrication trial-and-error
processes, " the authors said.
Thus, they proposed a soft robotic hand
composed of soft actuator cores and an
exoskeleton, featuring a multimaterial
design aided by finite element analysis to
define the hand geometry and promote
finger's bendability.
Soft robots can be fabricated by using
multiple materials and using different
manufacturing processes, ranging from
silicone molding to 3D printing. 3D-printing
methods bring significant benefits in
design and fabrication, making it easy to
introduce complex geometries within soft
32
A
B
C
Not actuated
Actuated
B
A
A
B
Actuators
SECTION AA
External elastometer layer
PET reinforcement
SECTION BB
D
Internal elastometer layer
Air chamber
Platinum-catalyzed silicone
(Ecoflex 00-05)
Polyethylene terephthalate
PET
Polylactic acid
PLA
Thermoplastic
polyurethane TPU
(Ninjaflex)
Air tubes
(A) Multimaterial finger's soft actuator composed of two silicone layers and internal PET reinforcement.
(B) Exoskeleton geometry of a single finger designed to bend in three joints (distal, middle,
and proximal). (C) Operation principle where the pneumatic actuator inside a stiffer exoskeleton
shell promotes the bending of the finger. (D) Attached to a robot manipulator, the soft robotic hand
is capable of grasping and manipulating objects of various shapes, weights, and sizes. (Image:
Samuel Alves, University of Coimbra, CEMMPRE, ARISE, Department of Mechanical Engineering)
robots, accelerating/automating the fabrication
process, and reducing its cost.
The team showed that the multimaterial
soft actuators are designed and fabricated
at a reduced cost and time effort,
using standard fabrication processes such
as molding and single-step 3D printing.
The ON-OFF controller, while simple,
keeps the set fingers bending angles stable,
even in the presence of leaks. The robotic
hand demonstrated dexterity and capability
to grasp objects with different shapes,
weights, and sizes.
" The reinforcement in a circumferential
direction guarantees the actuator's
elongation and consequently the fingers
bent when inside the exoskeleton, " said
author Samuel Alves. " The robotic hand
achieved an interesting dexterity level,
being able to grasp objects of different
shapes and sizes. Nevertheless, it strugwww.techbriefs.com
gles
to grasp heavier objects featuring
slippery surfaces, showing a concentrated
deformation at the base of the fingers
while the thumb motion is constrained.
" In addition, depending on the grasping
surface and geometry, there exists
mechanical interference between the
fingers. Since the soft hand is highly
nonlinear, with most variables of interest
being coupled between themselves,
future work will be dedicated to an indepth
analysis of the grasping phenomena
together with further standardization
of testing benchmarks, " said Alves.
This soft robotic hand is accessible and
can be built at a reduced cost, avoiding
the time-consuming design-fabrication trial-and-error
processes, and inspiring innovation
around it.
For more information, contact Ning
Xu at xuning1907@foxmail.com.
Tech Briefs, May 2024
PET
reinforcement
Proximal joint
Distal joint
Middle joint

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