Transcript Distal Muscle Plug

Active Ankle-Foot Orthotic
Air Muscle Tethered
Team P13001
Nathan Couper, ME
Bob Day, ME
Patrick Renahan, IE
Patrick Streeter, ME
This material is based upon work supported by the National Science Foundation under Award No. BES-0527358.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and
do not necessarily reflect the views of the National Science Foundation.
Agenda
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•
•
•
•
Assumptions
Customer Needs
Engineering Specifications
Test Plan
Mechanical Analysis
– Proximal Attachment
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•
Static Analysis
Fatigue Analysis
– Distal Attachment
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•
Static Analysis
Fatigue Analysis
• Air Muscle Testing
– Transient Flow
– Muscle Contractions
• Risk Assessment
• Proposed Schedule
• Questions and Criticism
Assumptions and Project Scope
• Patient maintains zero muscle control over dorsi-flexion, plantar-flexion,
and toe extension
• This product is designed to be used on a treadmill in a clinical setting; but
can be incorporated into an aquatic setting
– Tethered System
• The elastomer can be adjusted on a patient basis so that when the
patient’s full weight is applied on the AFO, the foot rests at angle slightly
above 90 degrees with respect to the patient’s lower limb
• Designed patient has the ability to use a dorsi-flex assist AFO without
receiving tone-lock spasms
• For calculations:
– Anthropometric Data is from the ANSUR (military) Database
• Based on the 50th percentile man
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–
–
–
2D system
no resistive forces/friction associated with the joints
a normal gait cycle time of 1.2 to 1.5 steps per second is assumed
Isotropic, Elastic Materials
Customer Needs
Objective
Number
Customer Objective
Description
S1
follow safety guidelines
and standards
Comment/Status
energy stored safely
Air source designed for
specified pressure
no sharp protrusions
Attachments designed to be
flush inside AFO
allergy conscious
No new materials to be in
contact with user
FT1
support regular gait
cycle
System designed for
responsiveness necessary for
normal gait
FT2
hold foot up when
stepping forward
Dorsi-assist AFO design has
been proven successful
S3
S4
S5
range of motion to allow full
dorsiflexion and plantar
flexion
Tamarac joint allows flexion of joint. Hard
stops of AFO prevent over flexion
resist foot slap
Dorsi-assist AFO design has been proven
successful
FT5
operate smoothly/simulate
normal muscle behavior
Regulation of air muscles will allow for
adjustment on patient by patient
basis
FT6
allow for extended use without
straining leg from weight
FT2
FT4
non-invasive
Designed to not interfere with normal fit
of AFO
secure foot in orthotic
Existing orthotic attachment is
unchanged
non-abrasive
No new materials to be in contact with
user
CF6
allow normal cooling of leg
This is a challenge with existing orthotics:
vent holes will be drilled into orthotic
CF7
allow bending of knee
Orthotic will stop below the knee
allow toes to flex up
Toe flexion will not be hampered by air
muscle device
CF2
CF3
CF4
CF8
allow natural movement down
stairs and ramps
Air muscle system will provide proper
plantar flexion during gait cycle
adapt to different terrains
Terrain sensing system will be compatible
with air muscle control
ST3
fast system response between
sensing and doing
Low computative demands on system.
Concern is with actuation speed.
Intial testing suggests system has
responsiveness required
ST4
correctly interprets sensor
information
Sensor integration with team 13002 is
pending
support foot drop over obstacles
Dorsi-assist AFO design has been proven
successful
ST1b
ST2
ST5
Engineering Specs
Engineering
Specification
Number
Engineering
Specification
Description
Units
Nominal
Value*
Ideal Value
**
Method of
Validation
Comments
s1
Torque on Foot
N-m
≥±1.5
Fmuscle =
53.10 N
Test
Force represents requirement for 50th
percentile male
s2
Air muscle fill time
Ms
<150
<200
Test
Based on descending stairs gait analysis
s3
predicts step up
yes/
no
yes
x
-
No terrain sensing
s4
predicts step down
yes/
no
yes
x
-
No terrain sensing
s5
predict flat
yes/
no
yes
x
-
No terrain sensing
s6
predicts ramp up
yes/
no
yes
x
-
No terrain sensing
s7
predicts ramp down
yes/
no
yes
x
-
No terrain sensing
s8
predicts speed of person
m/s
±0.1
x
-
No terrain sensing
s9
measure angle of foot
Degrees
±5
x
-
Not necessary for system operation
*Nominal value represents the initial target value for specifications.
**Ideal value represents the adjusted target value for specifications
based on research and adjusted objectives.
Engineering Specs
s10
allowable range of
motion between foot
And shin
degrees
94.5 to
137.7
72 to 116
with shin as
reference
s11
follow safety standards
yes/no
-
-
s14
fits calf (diameter)
mm
292 to
433
-
Use of custom orthotic
s15
fits foot (length)
mm
212 to
317
-
Use of custom orthotic
s17
force to secure
constraints
N
< 80 N
Test
Only air muscle system considered
s18
force to remove
constraints
N
< 80 N
Test
Only air muscle system considered
s21
monitoring/display of
energy level
yes/no
yes
-
Pressure gauge on air tank
s22
error status
yes/no
yes
-
Test
Equivalent to dorsi assist AFO. Measured
angle between calf of AFO
and bottom of AFO
Engineering Specs
s23
radius of edges/corners
on AFO
mm
0.5mm
-
s25
Harm to user (survey)
scale
-
survey user
s26
Noise Level (at ears of
user)
dB
60
Test
s27
Moving devices and
electronics use standard
dust and water shielding
yes/
no
yes
-
s31a
Minimum life until
failure air muscle
steps
s31b
Minimum life until
failure: Attachment
points
steps
5.5
million
s32
Allowable toe
extension/flexion
Degrees
0-50
>18000
test
Calculated for 95% uptime. Assuming 20
minute replacement, and 44 contractions/min
during use
>15,000
test
100 steps (50 contractions), twice a week
for three years
test
Testing Plan – Required Tests
Engr.
Spec. #
ES26
ES2
ES1
ES31
ES31
ES17,
18
Specification (description)
Noise level (at ears of user)
Unit of
Measure
Marginal
Value
dB
<60
Decibel testing
Sec
<.20
Initial testing indicates good
performance
N-m
>=1.5
Force of air
muscle*moment arm
% uptime
>95%
Time in use versus time
replacing air muscle
Steps
>15,000
Use of air muscles in clinic
must not affect full life of
AFO
N
<80
Velcro straps pre-existing,
and test force to secure
muscle (4)
Nm
.358
Verify clamping force is
sufficient to hold cable
Flow rate – time to inflate
Torque on Foot
Lifetime – Air Muscle
Lifetime – AFO Fixtures
Force to secure/remove constraint
Clamping force: cable to air muscle
Comments/Status
Testing Plan – Required Equipment
Engr.
Spec. #
ES31
Instrumentation or equipment not available (description)
Polymer to simulate AFO for lifetime analysis
Gait Analysis
Stairs: Descending
Percent Gait Cycle
Event
mean
s. d.
Foot Off
15%
3%
Foot Strike
56%
3%
Bovi, et. all
Based on 88 cycles per minute: 0.30 seconds from foot off to foot strike.
Assumed AFO
Design
• Designs based around
AFO of this structure
• Design is flexible so it
will be able to work on
many different AFO
designs and shapes
• Assumed material =
Proximal Muscle Attachment
• Relatively simple
components
• Low Profile
• Strong
• Removable
Key Components:
• Weld Nut
• Exterior threading
for nut
• Secures device to
AFO
• Screw clamps air inlet
and muscle attachment
to weld nut
• Nozzle screws into block
Weld Nut
• Uses 5/16” Nut to
secure against AFO
• Note external
threads not
shown
• 316 Stainless Steel
• Allows for easy
removal of device
Stress Calculations:
• Treated like a cantilever beam
• 130 N force (Max force air muscle can apply)
• Max Bending Stress: 57.45 Mpa
• Shear Stress: 7.49 MPa
Proximal Anchor and Air Inlet
• Houses weld nut
and exterior nut
• Applies force on
weld nut
• Also clamped on
by ¼-20 screw
• 1/4-inch air inlet
channel
• Threaded hole for
nozzle insertion
• 316 Stainless
Steel
Proximal Anchor and Air Inlet
Element Type: Solid 10node187 (tetrahedral)
Max Stress: 45 MPa
Proximal Anchor and Air Inlet
All displacement is about
0 meters
Nozzle
• Proposed Materials:
Delrin or Stainless Steel
• Threading
• External Threading not
pictured
• Screws into Proximal
Anchor to allow air
supply to muscle
• Air muscle clamps on
to cylinder
• Max Stress: 2.85 Mpa
• Yield Stress:
• 63 MPa (Delrin)
• 290 Mpa (316)
Fatigue Analysis
Fatigue Results: (Using an applied force of 53 N rather than 130N)
• Weld Nut
316 Stainless Steel Properties:
• FOS=15.53
• Endurance Limit (Se): 270 MPa
• Proximal Anchor
• Ultimate Strength (Sut): 579 MPa
• FOS=20.46
• Nozzle (316 Stainless Steel)
Delrin Properties:
• FOS=316.9
• Endurance Limit (Se): 32 MPa
• Nozzle (Delrin)
• Ultimate Strength (Sut): 69 MPa
• FOS=37.6
Distal Muscle Attachment
Assembly
Tendon
Cable
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•
•
•
•
•
Use 1.5 mm diameter cable
Will use bicycle brake cable
Braided Stainless Steel cable
Tension can be easily
adjusted
Preliminary calculations
make us believe this solution
will be more durable than
previous air muscle tendon
materials
Maximum stress = 100.2
MPa; yield stress = 290 Mpa
Factor of Safety = 11.5
Maximum Deformation =
0.233 mm
Distal Muscle
Plug
• Presses against Distal
Muscle Plug Plate with
slot for tendon cable
to rest in
• Plugs distal end of air
muscle
• No air nozzle needed
at the distal end
• Proposed Material =
Delrin
Maximum Stress = 8.5 MPa
Yield Stress = 63 MPa
Distal Muscle
Plug Plate
• Presses against Distal
Muscle Plug
• Creates friction on
tendon cable,
• Allows for tension in
tendon cable to be
easily adjusted
• Proposed Material =
316 Stainless Steel
• Necessary Screw
Clamping Force =
0.358 N-m
Heel Cable Attachment Point
• Attaches distal end of
tendon cable to AFO
heel protrusion
• Held in place by 10-24
screw at distal end,
Heel Cable Attachment
Pin at proximal end
• Allows for:
• full range of
motion of tendon
cable
• ease of cable
changeover
• Proposed Material =
316 Stainless Steel
ANSYS Simulation
Fatigue Analysis
Analyzed with stresses
from 53 N force as opposed
to 130 N
• This will be more
realistic to values
seen during normal
operation
Ultimate Strength = 579 MPa
Endurance Strength = 270 MPa
Factor of Safety = 36.8
Heel Cable
Attachment
Pin
Proposed Material = 316 Stainless Steel
Air Muscle Construction
•
•
•
•
Outer Sleeve
Inner Tube
Clamp
End
Muscle Testing
• Goal of .1 sec inflation time, max of .2 sec,
estimated via gait analysis
– Function of pressure and flow rate
• 4.45cm contraction required for full range of
motion
– Function of muscle construction
Transient testing
• Started by calculating the theoretical flow
– Realized this is questionably accurate and very
complex
• Decided it would be easier and more accurate
to directly measure inflation time
• Took video of the muscle inflating and
counted the number of frames it took to
move.
Transient testing
• 5 video tests
Muscle Contraction
• The muscle was loaded with 53N and inflated
Transient results
Programming Flow Chart
Input from Terrain
Sensing System
Flat terrain
Ascending terrain (up
stairs/up ramp)
Relax air muscle
Release air
Descending terrain
(down stairs/down
ramp)
Ankle angle at foot
strike = -14.65 deg
Ankle angle at foot
strike = -44.96 deg
Gait speed info from
sensors
Gait speed info from
sensors.
Test Plan
See Edge:
https://edge.rit.edu/edge/P13001/public/WorkingDo
cuments/Project%20Management
Updated Risk Assessment
Bill of Materials
Schedule for MSD II
Reference EDGE website for working, detailed
project schedule:
Planning and Execution – Project Plans and
Schedules – “Schedule of Action Items”
http://edge.rit.edu/edge/P13001/public/Planning
%20%26%20Execution
Questions?