Transcript Bionic Ankle - College of Engineering | Northeastern

Bionic Ankle
Bionic Ankle
Mario Liuzza | Chris Loughnane | Ashley Pierce | Dan Spangler
needN e e d
B a c k gBackground
r o u n dand
&
Background
and
Need
In 2002, more than 110,000 lower extremities were amputated.
That’s more amputations than there are people in Cambridge.
And that’s only in the United States.
“
The challenge for anyone devising a new ankle is to make one that has a good
degree of flexion (i.e. one that makes it easy to walk up and down hills, rotate
etc) whilst at the same time retaining enough support for the person using it to
feel confident in its stability
”-
Amputee Forum Moderator, In response
to a query posed by the Bionic Ankle
Group regarding the biggest complaints
amputees have about their prosthetics
Objective | Scope
Objective
Develop an actively controlled below-knee (BK) prosthetic that minimizes knee
damaging torque by improving upon contemporary standards for stability in varying
terrain.
Scope
To develop the base technology that allows the user to achieve stability on a variety of
terrain. As stability is achieved between heel strike and foot flat, this will be the focus
Marketplace
Ossur Vari-Flex
No Control System
Single Axis of Rotation
Weight: 0.89 lb
Capacity: 365 lb
Ossur ProprioFoot
Actively Controlled
Single Axis of Rotation
Weight: 2.7 lb
Capacity: 250 lb
College Park TruStep
College Park Trustep
No control system
Anatomically incorrect second axis of rotation
Weight: 1.43 lb
Capacity: 300lb
What is missing?
Design
Leg Member
Subtalar Actuator
High Ankle Actuator
• Experiences loads of up to 700 N
High Ankle Member
• 20º of dorsiflexion | 45º of plantar flexion
Subtalar Axis
Subtalar Member
• 25-30° of inversion and 5-15° of eversion.
• Located 42° from the XZ plane and
23° from the XY plane.
Leaf Spring
Y
Z
Foot
X
Considerations
250
• Weight, in lbf, of a 95th
percentile male
1.5x
• Safety factor
1.5x
• Maximum ground reaction
force factor
562.5
• Effective force, in lbf
Moment Analysis
High Ankle Axis
Subtalar Axis
High Ankle Kinetics
W
Ry
F
 RX  FX  max
F
 RY  Wb  FY  maY
X
Rx
Y
COM
M
COP
Fx
o
 I
Fy
Force Vector High Ankle
800
700
600
Force (N)
500
400
300
200
100
0
0
0.05
0.1
0.15
0.2
0.25
Time (s)
0.3
0.35
0.4
0.45
Subtalar Kinetics
Optimized ST Moment Arm of Normal Force
3.5
After Initial Optimization
Current Prototype
Moment arm of normal force about Subtalar Axis (in)
3
2.5
2
1.5
1
0.5
0
0%
10%
20%
30%
40%
50%
60%
-0.5
-1
-1.5
Length of foot (0% = Heel, 100% = Toe)
70%
80%
90%
100%
FEA: Stress
Max = 315 MPa
FEA: Strain
Max = 315 MPa
Max = 0.1059%
Material Selection
Leg Member – 6061 Aluminum
High Ankle – 6061 Aluminum
Subtalar Member – 6061 Aluminum
Leaf Spring – Spring Steel
Foot Body – Delrin
Control System
Sensing
Actuation
Control
Layout Options
Pressure Pad:
•Dynamic force input
•Cost prohibitive ($10,000-$20,000).
Dynamic Force Transducer
•Measures constant pressure output
•Price ($400-$1000)
•Size can limited the array of sensors used
Strain Gauge
•
•
•
Measures the unbalance in foot
member
Economical ($10-$100)
Half Wheatstone bridge Configuration
LabVIEW
LabVIEW Block Diagram
Sensor Relationships
Actuator Reaction
Retract
Subtalar
Extend
High Ankle
Retract
Extend
Electric vs. Pneumatic Actuator
Electric:
-High Force or High Speed: Not Both
-Support System: DC Power Source
Pneumatics:
-High Force and Speed (at high PSI)
-Support System: DC Power Source + Compressed Air
Pneumatics
• Air Regulator
• 3 Position Valves
• Pneumatic Actuators
– High Ankle: 7/8” Ø (60lbs Force @ 25 psi)
– Subtalar: 9/16” Ø (25lbs Force @ 25 psi)
Te s t F i x t u r e
Full Test Fixture
Simplified Design
Range of Motion
Future Improvements
•
•
•
•
•
Install Flow Controls for the Actuators
Implement More Sensors on the Bottom of the Foot
Smooth Out the Control Responses
Optimize Prosthetic Parameters
Consider the option of a PLC Board
Bionic Ankle
Questions?
Specials Thanks To:
Professor Greg Kowalski
Brian Weinberg
Pat and the Northeast Automation Crew
Jeff Doughty
Kevin McCue
John Doughty