Active ankle foot orthosis

• US 8,287,477 B1
• Filed: 02/01/2012
• Issued: 10/16/2012
• Est. Priority Date: 09/25/2003
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Herr, Hugh, Pratt, Gill A., Blaya, Joaquin
• Primary Examiner(s): Brown, Michael A.
• Application Number:
  US13/363,993
• Time in Patent Office: 258 Days
• Field of Search: 602/16, 602/23, 602 26- 27, 128/882, 744/900.1, 744/901
• US Class Current: 602/16
• CPC Class Codes: A61B 5/1038 Measuring plantar pressure during gait
• CPC Class Codes: A61B 5/1071 measuring angles, e.g. using goniometers A61B5/1123 takes precedence
• CPC Class Codes: A61B 5/4519 Muscles A61B5/389, A61B5/224 take precedence
• CPC Class Codes: A61B 5/4523 Tendons
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61F 2/70 electrical
• CPC Class Codes: A61F 2002/701 operated by electrically controlled means, e.g. solenoids or torque motors
• CPC Class Codes: A61F 2005/0155 with actuating means
• CPC Class Codes: A61F 5/0113 Drop-foot appliances
• CPC Class Codes: A61F 5/0127 for the feet A61F5/0111 takes precedence
• CPC Class Codes: A61H 2003/007 secured to the patient, e.g. with belts
• CPC Class Codes: A61H 2201/12 Driving means
• CPC Class Codes: A61H 2205/10 Leg
• CPC Class Codes: A61H 3/00 Appliances for aiding patients or disabled persons to walk about apparatus for helping babies to walk A47D13/04; orthopaedic devices for correcting deformities of, or supporting, limbs A61F5/0102; exercising apparatus for the feet or toes A63B23/10; stairways or ramps E04F11/00

Abstract

An Active Ankle Foot Orthosis (AAFO) is provided where the impedance of an orthotic joint is modulated throughout the walking cycle to treat ankle foot gait pathology, such as drop foot gait. During controlled plantar flexion, a biomimetic torsional spring control is applied where orthotic joint stiffness is actively adjusted to minimize forefoot collisions with the ground. Throughout late stance, joint impedance is minimized so as not to impede powered plantar flexion movements, and during the swing phase, a torsional spring-damper (PD) control lifts the foot to provide toe clearance. To assess the clinical effects of variable-impedance control, kinetic and kinematic gait data were collected on two drop foot participants wearing the AAFO. It has been found that actively adjusting joint impedance reduces the occurrence of slap foot, allows greater powered plantar flexion, and provides for less kinematic difference during swing when compared to normals.

Claims

1. A method for operating an autonomous motorized permanent assistance leg device, the method comprising the steps of:

measuring an amount of time a foot is in contact with ground;

estimating a forward speed based on the ground contact time; and

modulating an impedance of the device based at least in part thereon.

2. The method of claim 1, wherein the measuring step comprises using a sensor comprising at least one of a ground reaction force sensor and a foot sensor, wherein the foot sensor is disposed in at least one of a forefoot region and a heel region.

3. The method of claim 1, wherein the modulating step comprises actuating a series elastic actuator.

4. The method of claim 3, wherein the series elastic actuator comprises a motor in series with a spring.

5. The method of claim 4, wherein actuating the series elastic actuator comprises controlling compression of the spring.

6. The method of claim 1, wherein the impedance modulating step is based at least in part on step-to-step gait variations.

7. The method of claim 1, wherein the impedance modulating step is based at least in part on the forward speed to lift a toe during a swing phase.

8. The method of claim 7, wherein the toe is lifted to provide toe clearance to reduce toe drag during the swing phase.

9. The method of claim 7, wherein the impedance modulating step controls ankle movement during controlled plantar flexion.

10. The method of claim 9, wherein ankle movement is controlled to reduce foot slap during a stance phase.

11. The method of claim 1, wherein the leg device comprises an ankle orthosis comprising an ankle joint, and the method further comprises the step of controlling plantar flexion and dorsiflexion of ankle joint position during at least a stance phase.

12. The method of claim 1, wherein the device comprises an ankle device.

13. The method of claim 12, wherein the modulating step comprises adjusting ankle stiffness.

14. A method for controlling an autonomous motorized permanent assistance ankle device comprising a foot, a leg portion and an actuator, the method comprising the steps of:

monitoring, with at least one sensor, at least one of position and movement of the ankle device throughout at least one gait cycle;

determining at least one characteristic of the gait cycle; and

adjusting the device based on the determined characteristic by controlling the actuator to affect movement of the leg portion relative to the foot.

15. The method of claim 14, wherein the adjusting step comprises using information from the at least one sensor to dorsiflex the foot relative to the leg portion during a swing phase.

16. The method of claim 14, wherein adjusting the ankle comprises dorsiflexing and plantarflexing the ankle.

17. The method of claim 16, wherein during a swing phase of a gait cycle, the ankle is first dorsiflexed then plantarflexed during the swing phase.

18. The method of claim 17, wherein during the swing phase the ankle is first moved to a dorsiflexed position then moved to a plantarflexed position.

19. The method of claim 14, wherein the method is adapted to characterize normal ankle function.

20. The method of claim 19, wherein the ankle in a swing phase follows a substantially second-order mechanical model.

21. The method of claim 20, wherein the ankle in the swing phase follows a substantially underdamped mechanical model.

22. A method for operating an autonomous motorized permanent assistance leg device, the method comprising the steps of:

monitoring, with at least one sensor, a parameter associated with use of the device;

using information from the sensor to determine a phase of a gait cycle; and

using a motor to adjust an ankle angle of the device based on the phase of the gait cycle by dorsiflexing the ankle angle during a swing phase.

23. The method of claim 22, wherein dorsiflexing the ankle angle provides toe clearance.

24. The method of claim 22, wherein the adjustment step is a function of gait speed.