Mario Liuzza | Chris Loughnane | Ashley Pierce | Dan Spangler Bionic Ankle

Background and need 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 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. Background and Need Background & Need ” “ -

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

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 Capacity: 300lb College Park Trustep Marketplace

What is missing?

Leg Member High Ankle Actuator Experiences loads of up to 700 N High Ankle Member 20º of dorsiflexion | 45º of plantar flexion Subtalar Axis Located 42° from the XZ plane and 23° from the XY plane. Subtalar Actuator Leaf Spring Subtalar Member 25-30° of inversion and 5-15° of eversion. Foot Design X Y Z

Considerations Weight, in lbf, of a 95 th percentile male 250 Safety factor 1.5x Maximum ground reaction force factor 1.5x Effective force, in lbf 562.5

High Ankle Axis Subtalar Axis Moment Analysis

High Ankle Kinetics RyRy W RxRx FxFx FyFy COM COP

Subtalar Kinetics

Max = 315 MPa FEA: Stress

Max = 315 MPa Max = % FEA: Strain

Material Selection Foot Body – Delrin Leaf Spring – Spring Steel Subtalar Member – 6061 Aluminum Leg Member – 6061 Aluminum High Ankle – 6061 Aluminum

Control System Sensing Actuation Control

Layout Options Strain Gauge Measures the unbalance in foot member Economical ($10-$100) Half Wheatstone bridge Configuration 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

LabVIEW Sensor RelationshipsActuator Reaction LabVIEW Block Diagram Retract Extend Subtalar High Ankle

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 25 psi) – Subtalar: 9/16” Ø (25lbs 25 psi)

Test Fixture 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 KowalskiBrian Weinberg Pat and the Northeast Automation CrewJeff Doughty Kevin McCueJohn Doughty