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					                   Bionic Ankle
                 Bionic Ankle




Mario Liuzza | Chris Loughnane | Ashley Pierce | Dan Spangler
             BackgrounddandNNeed
              B a c k g r o u n and & e e d
                      Background    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
                         No control system
                         Anatomically incorrect second axis of rotation
                         Weight: 1.43 lb
College Park Trustep     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                • Located 42° from the XZ plane and
           • 25-30° of inversion and 5-15° of eversion.              23° from the XY plane.



                                           Leaf Spring
                                                                                 Y
                                                                                            Z


                                                         Foot

                                                                                            X
Considerations
                  Moment Analysis




High Ankle Axis

                                    Subtalar Axis
                             High Ankle Kinetics

                                   W

                       Ry

                             Rx
                                                                              F     X        RX  FX  max


                         COM
                                                                              F     Y        RY  Wb  FY  maY

                                                                              M              I
                                   COP
                                                        Fx                               o
                                        Fy

                                                    Force Vector High Ankle

            800



            700



            600



            500
Force (N)




            400



            300



            200



            100



             0
                  0   0.05        0.1        0.15            0.2              0.25            0.3     0.35     0.4   0.45
                                                                   Time (s)
                                                                                                        Subtalar Kinetics



                                                                                               Optimized ST Moment Arm of Normal Force

                                                      3.5
                                                                  After Initial Optimization
                                                                  Current Prototype
                                                        3
Moment arm of normal force about Subtalar Axis (in)




                                                      2.5


                                                        2


                                                      1.5


                                                        1


                                                      0.5


                                                        0
                                                             0%     10%            20%          30%       40%         50%          60%         70%   80%   90%   100%

                                                      -0.5


                                                       -1


                                                      -1.5
                                                                                                      Length of foot (0% = Heel, 100% = Toe)
                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

                                    Subtalar
                        Retract                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

				
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posted:7/23/2011
language:English
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