1. Design
of
a
Passive
Ankle
Prosthesis
with
Energy
Return
that
Increases
with
Increasing
Walking
Velocity
Alexander
Folz
Advisor:
Dr.
Joseph
Schimmels
Marque<e
University
PROBLEM
An
esFmated
159,000
TransFbial
(below
the
knee)
amputaFons
were
performed
in
the
US
in
19961.
These
individuals
are
oTen
met
with
a
difficult
decision:
selecFon
of
a
prosthesis.
LimitaFons
of
currently
available
prostheses
moFvates
work
on
a
new
soluFon,
the
EaSY
Walk,
a
passive
device
that
mimics
two
key
aspects
of
the
natural
ankle:
non-­‐
linear
rotaFonal
sFffness
through
implementaFon
of
a
sFffening
flexure
mechanism
and
rotaFonal
work
output
that
varies
as
a
funcFon
of
walking
velocity
to
propel
the
user
forward.
INTRODUCTION
MECHANICAL
REALIZATION
§ Fabricate
and
build
prototype
device
§ Robot
and
human
tesFng
Figure
2:
Ankle
profiles
as
a
funcFon
of
Fme,
stance
phase2
FUTURE
WORK
CITATIONS
CONCLUSIONS
Post
opFmizaFon,
the
modeled
prosthesis
averaged
a
return
of
58.57%
of
natural
ankle
work
over
12
trials
for
15
mm
of
deflecFon
while
showing
sFffness
non-­‐lineariFes
akin
to
those
of
the
natural
ankle
were
achieved.
In
addiFon,
as
shown
in
Fig.
10,
the
device
is
capable
of
mapping
addiFonal
work
from
the
translaFonal
space
to
the
rotaFonal
space
as
leg
force
(and
therefore
walking
velocity)
increases.
FUNCTION
THROUGHOUT
GAIT
CYCLE
[1]:
Owings,
M.,
and
Kozak,
L.
J.,
1998.
“Ambulatory
and
inpaFent
procedures
in
the
united
states,
1996”.
Vital
and
Health
StaFsFcs,
Series
13(139),
p.
24.
[2]:
Winter,
David
A.
Biomechanics
and
Motor
Control
of
Human
Mo5on.
New
Jersey:
John
Wiley
&
Sons,
2009
[3]:Palmer,
M.
L.
(2002).
Sagi9al
Plane
Characteriza5on
of
Normal
Human
Ankle
Func5on
Across
a
Range
of
Walking
Gait
Speeds.
Thesis,
Massachuse<s
InsFtute
of
Technology,
Mechanical
Engineering
MODELED
RESULTS
ACKNOWLEDGEMENTS
Work
supported
by
the
Department
of
Health
and
Human
Services/NaFonal
InsFtute
of
Disability
and
RehabilitaFon
Research.
(1):
Heel
Strike
K1
compresses
due
to
increasing
leg
force
(2):
Foot
Flat
Ankle
planarflexes;
K1
conFnues
to
compress
unFl
leg
force
reaches
a
maxima
(3):
Max
Leg
Force
K1
looks
to
decompress;
Sprags
(i.e.,
mech.
diodes)
lock
K1
at
current
deflecFon
(4.1):
Max
Dorsiflexion
1
Jamming
mech.
causes
lower
K1
to
“roll
off”
Body
B
(4.2):
Max
Dorsiflexion
2
FricFon
between
Yellow
Body
and
Body
A
now
constrains
moFon
of
lower
K1
relaFve
to
Body
A
(5):
Powered
Push-­‐off
K1
now
provides
moment
about
the
ankle
joint,
aiding
in
push-­‐off
(6):
Toe
Off
K1
conFnues
to
provide
moment
about
ankle
joint
through
rest
of
stance
cycle
Swing
Phase
Leg
force
now
acts
upwards;
K2
unlocks
sprags
and
lower
K1
KinemaFcally
forced
to
return
to
Body
B
-­‐50
0
50
100
150
200
250
-­‐25
-­‐20
-­‐15
-­‐10
-­‐5
0
5
10
15
20
Ankle
Moment
[Nm]
Ankle
Angle
[Deg]
Prosthesis,
Modeled
Natural
Ankle
The
prosthesis
was
opFmized
for
12
sets
of
data,
11
sets
from
Marque<e
University
data
acquired
from
3
differing
subjects
and
Winters
data.
One
representaFve
set
of
data
from
the
12
(Set
9)
was
selected
and
plo<ed
at
right.
Work
output
percentages,
compared
to
the
natural
ankle,
are
tabulated
in
Table
1.
In
addiFon,
the
primary
impetus
of
this
work
was
to
mimic
energy
return
at
various
walking
velociFes.
It
is
known
that
leg
force
varies
relaFvely
linearly
with
walking
velocity.
As
such,
to
test
this
objecFve,
known
leg
force
data
was
mulFplied
by
several
scalar
values
to
simulate
various
walking
velociFes.
Finally,
work
was
calculated
at
each
of
these
scalar
mulFples
for
all
12
data
sets
and
averaged.
The
results
are
plo<ed
below:
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0.4
0.6
0.8
1
1.2
1.4
1.6
WORK
[J]
SCALAR
MULTIPLIER
OF
LEG
FORCE
MODELED
RESULTS,
CONT.
Figure
1:
Work
flow
diagram
for
2-­‐DOF
Novel
Ankle
Prosthesis
IniFaFve
Figure
3:
Human
Walking
KineFcs
as
a
funcFon
of
Gait
Speed3
Through
3
iteraFons,
the
design
philosophy
for
the
project
has
stayed
idenFcal:
store
translaFon
work
along
the
leg
and
re-­‐
map
it
as
rotaFonal
work
about
the
ankle
joint.
The
3rd
iteraFon
design
differenFates
itself
from
the
previous
two
in
the
following
ways:
A. Early
stance
deflecFon/energy
storage
(Pt.
(3)
in
Fig.
2)
B. Variable
work
output
as
a
funcFon
of
leg
force
Both
of
these
are
accomplished
through
the
use
of
Fming
mechanisms
based
on
maxima/minima
of
ankle
profiles
(i.e.,
dŸ/dt
=
0).
Regarding
B.,
an
increase
in
F(r),
assuming
opFmal
work
mapping,
will
lead
to
a
corresponding
increase
in
rotaFonal
work
output
(See
Fig.
1).
This
falls
inline
with
desirable
ankle
funcFon
at
varying
walking
velociFes
as
shown
in
Fig.
3.
Figure
4:
Device
funcFon
at
criFcal
moments
in
the
gait
cycle;
See
Fig.
2
for
ankle
kineFcs
and
kinemaFcs
at
each
of
these
points
in
the
gait
cycle
Figure
6:
Final
device,
isometric
view
Figure
7:
Final
device,
side
view
Figure
8:
RotaFonal
jamming
mechanism
and
fricFon
block
Figure
5:
TranslaFonal
jamming
mechanism
(sprags
acFng
as
a
mechanical
diode)
Figure
9:
Modeled
prosthesis
performance
compared
to
natural
ankle
of
a
representaFve
Marque<e
University
test
subject
Table
1:
Percent
of
Natural
Ankle
Work
Set
1
Set
2
Set
3
Set
4
Sub
1
61.60
60.51
94.15
47.49
Sub
3
38.40
30.15
28.20
32.25
Sub
4
119.00
86.82
79.94
N/A
Winters
24.00
N/A
N/A
N/A
Average
58.57
Figure
10:
Modeled
work
output
at
various
levels
of
leg
force
0
0.5
1
1.5
2
2.5
-­‐1
0
1
2
3
4
5
6
7
8
-­‐1
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
FORCE
PER
UNIT
MASS
[N/KG]
WORK
PER
UNIT
MASS
[J/KG]
GAIT
SPEED
[M/S]
(Normalized
Ankle
Work)
*10
Normalized
Mean
Ground
ReacFon
Force