UWE Bristol Engineering showcase 2015

Joshua Ukaegbu
MEng- Mechanical Engineering
Project Supervisor
Dr Appolinaire Etoundi
Design of an Exoskeleton arm to assist upper limb movement
Exoskeleton Simulation
The main aim of the simulation was to determine
the feasibility of the initial exoskeleton design. By
simulating the forces the exoskeleton would be
subject to when holding the weight of a human
arm. The maximum deflection and stresses could
then be analysed, showing important information
like any points of failure on the design.
Deflection Analysis
the forearm support experiences the most
deflection, this is due to the fact it is the part
directly experiencing the force due to the weight
of the users arm. On top of this, the material the
forearm support is constructed from has a large
effect on the amount of displacement present.
When constructed from aluminium the maximum
deflection experienced was 51.18mm, and the
minimum deflection experienced was 1e-30mm.
This was too large of a deflection and failure
occurred.
When Steel was used the simulation showed that
a maximum deflection of 17.06mm was present
when the exoskeleton was constructed from
stainless steel. Considerably less deflection than
when aluminium was used for construction. The
minimum displacement present is 1e-30 mm.
For Titanium the locations of the maximum and
minimum displacements were the same for both
the aluminium and the titanium. However the
maximum displacement had a value of 28.23mm,
which was still considerably less than the
deflection observed for aluminium, but more than
the observed deflection for stainless steel. The
minimum deflection was 1e-30 mm.
Displacement (mm)
60
50
40
30
20
10
0
Displacement across length of forearm support
0 0.2 0.4 0.6 0.8 1
Parametric distance along forearm support (x)
Improvements to the Design
Aluminium
Titanium
Stainless Steel
The inspiration for this hinge joint came from the
Bristol robotics laboratory, where they were
working on a similar sort of joint. The joint has a
range of motion of 170°, which is an improvement
over the 160° range of motion for the forearm
support in the original design. The joint consists of
two independent parts, connected by a advanced
axle. The diagrams below illustrate this, along with
a engineering drawing to show how each part fits
together
This improved mechanical ball and socket joint is
much more robust than the original design. It has
two points of contact, which will make it a much
stronger joint, it should have the capabilities to
uphold the weight of an average human arm.
However the added points of contact do mean it
has a slightly less range of motion than the first
design, it should allow a complete 360° of motion
in the coronal/frontal plane but only around 60° of
motion in the transverse plane.
Project summary
Exoskeletons are robotic suits or mechanical
structures that can be attached to the human body
for a variety of different functions. People with
serious disabilities can now perform movements
and functions that would never have been possible
without the aid of exoskeleton suits. Stroke is a
serious problem in the western world, as it can leave
sufferers with limited motor abilities. This project
focuses on the design of an exoskeleton arm to aid
in the movement and rehabilitation of stroke
sufferers who have partially lost movement in their
arms.
Project Objectives
• The main aim of this project is to design a
mechanical arm exoskeleton that will help patients
affected by strokes regain motion in their arms.
• the second objective of this project is to design an
exoskeleton arm that is aesthetically pleasing; that
attracts potential customers, and encourages them
to enjoy its use.
• So during this project a comfortable and
ergonomic system will be developed for the
attachment of the exoskeleton, to the arm of the
user.
Project Conclusion
• Range of motion is very important, to create a
comfortable exoskeleton with a wide range of motion,
the joints of the exoskeleton should replicate those in
the human body.
• The most common materials used to construct
exoskeletons are steel, aluminium, and titanium.
To create the most efficient exoskeleton, a
combination of these materials should be used.