Microprocessor Technology in Ankle Prosthetics

Transcription

1 Microprocessor Technology in Ankle Prosthetics Arizona State University Dr. Thomas Sugar Former Students LTC Joseph Hitt, PhD Dr. Kevin Hollander Dr. Matthew Holgate Dr. Jeffrey Ward Mr. Alex Boehler Mr. Ryan Bellman

2 Human Machine Integration Laboratory Design Unique Compliant Actuators Developing Powered Prosthetic Ankles Developing Exoskeletons for Running

3 Robotic Tendon drives a powered AFO Translating a spring back and forth to achieve the desired position and forces

4 Agenda The Robotic Tendon (RT) Designing SPARKy (Spring Ankle with Regenerative Kinetics)

5 Our goal: SPARKy (Spring Ankle with Regenerative Kinetics) Develop a new generation of powered prosthetic devices based on lightweight, energy storing springs that will allow for more functional gait.

6 Microprocessor Controlled Prostheses The Endolite Adaptive Knee and the Otto Bock C-Leg Proprio Foot by Ossur PowerFoot by MIT and iwalk Robotic knee/ankle Goldfarb

7 Human Centric Approach to Wearable Robotics Human Centric Compliant Actuators Continuous Control System Efficiency

8 Robotic Tendon Based Ankle Powered Ankle Prosthetic Walking, Walk on inclines/declines, Walk backwards Ascend/Descend stairs, Jumping, Running

9 Robotic Tendon Based Ankle Powered Ankle Prosthetic Walking, Walk on inclines/declines, Walk backwards Ascend/Descend stairs, Jumping, Running

10 Studying Human Gait A single human walking gait cycle. Ankle angle and normalized moment data. The highlighted region is the push off phase of gait.

11 Passive Systems Passive and untunable. Provides minimal power generation (25% of AB) and ankle motion 15% of AB). No rotation at the ankle. No push-off at the ankle. Sagittal plane ankle angle, moment, and power for a male below the knee amputee using a SACH foot walking at 1.13 sec/step, solid line, versus that of an average able-bodied subject, dashed line.

12 Ankle Gait Analysis Dorsiflexion (Toes Up) Plantarflexion (Toes Down)

13 Ankle Gait Power Assumptions: 80 kg person, walking at 0.8 Hz (1.25 sec/cycle)

14 Robotic Tendon Concept Robot Tendon Concept x x F a K m g o Motor Power: P m F x g gait power F F K spring power

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16 Robotic Tendon Actuator m Robotic Tendon

17 Why use springs? Springs are Powerful Springs are Efficient Springs are Lightweight Springs are Economical Springs are Compliant (308,000 W/kg) (0.999 for spring steel) ( 0.05 kg) (easily mass produced) (safety built-in )

18 Power Decomposition The spring and motor power add to provide the desired output power required for gait. Notice that at 40% of gait, the spring and motor work in opposite direction to store elastic energy and at 50% gait, the spring provides majority of the output power.

19 Ankle Motion The subject walks on a treadmill at 2.2 mph. The ankle has 9 degrees of dorsiflexion and more importantly 23 degrees of plantarflexion. The user has complete control of the ankle motion because the output side of the spring is not controlled. The ankle motion fits the model extremely well.

20 Ankle Moment The ankle moment matches the model very well.

21 Ankle Power The subject walks at 2.2 mph. Measured power out, Po, and power at the nut, Pm, for the test series with a 36KN/m spring and a 9 cm lever at 1 m/s (2.2 mph). The device achieves a very high level of power amplification of 3.7. This is the unique advantage of a Robotic Tendon.

22 Key Accomplishments User has full range of sagittal ankle motion comparable to able-bodied gait. (23 degrees of plantar-flexion, 7 degrees of dorsiflexion.) User has 100% of the required power for gait delivered at the correct time and magnitude. The peak output power is 3-4 times larger than the peak motor power allowing a reduction in motor size and weight. Allows a highly active amputee to regain high functionality and gait symmetry.

23 Design and Build SPARKy 2 Actuation: A Maxon RE40, 150 Watt motor, roller screw and helical spring assembly. Sensors: motor encoder, and ankle encoder, rate gyro FS 3000 Keel from Freedom Innovations. Robotic Tendon FS 3000 Keel Spring Ankle Joint Roller screw Lever arm RE 40 Motor

24 Electronic System Control Platform: Matlab, Simulink, Real Time Workshop Toolbox.

25 Electronic System Design Code using a Graphical Interface in Simulink/Matlab Use Specific Toolboxes for Device Hardware We use the Kerheul Toolbox for Microchip dspic processors Matlab Real Time Workshop generates C-Code automatically Download code using MPLAB

26 Solution A Robotic Tendon stores and releases energy during the gait cycle A tuned spring for a given individual reduces peak motor power and energy as compared to a traditional motor/gearbox system The proximal side of the spring uses robust position control

27 Vision Compliant Actuators: Study the kinematics and kinetics to use springs that are tuned to the body s movement Energy storage Reduce power/energy requirements Microprocessors: Easier to program and develop high-level control Very cost-effective Future BeagleBoards, Rasberry Pi.