Electronically controlled prosthetic knee

• US 6,764,520 B2
• Filed: 01/22/2001
• Issued: 07/20/2004
• Est. Priority Date: 01/20/2000
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Herr, Hugh M., Pratt, Gill A., Deffenbaugh, Bruce W., Wittig, Michael B.
• Primary Examiner(s): STEWART, ALVIN J
• Application Number:
  US09/767,367
• Publication Number:
  US 20010029400A1
• Time in Patent Office: 1,275 Days
• Field of Search: 623/24-27, 623/39-45
• US Class Current: 623/24
• CPC Class Codes: A61F 2/5046 for designing or making customized prostheses, e.g. using templates, finite-element analysis or CAD-CAM techniques
• CPC Class Codes: A61F 2/64 Knee joints
• CPC Class Codes: A61F 2/70 electrical
• CPC Class Codes: A61F 2/74 fluid , i.e. hydraulic or pneumatic
• CPC Class Codes: A61F 2/80 Sockets, e.g. of suction type
• CPC Class Codes: A61F 2002/5003 having damping means, e.g. shock absorbers
• CPC Class Codes: A61F 2002/5004 operated by electro- or magnetorheological fluids
• CPC Class Codes: A61F 2002/5016 adjustable
• CPC Class Codes: A61F 2002/5043 with rotation-limiting stops, e.g. projections or recesses
• CPC Class Codes: A61F 2002/607 Lower legs
• CPC Class Codes: A61F 2002/6614 Feet
• CPC Class Codes: A61F 2002/6863 magnetic
• CPC Class Codes: A61F 2002/704 computer-controlled, e.g. robotic control
• CPC Class Codes: A61F 2210/009 magnetic
• CPC Class Codes: A61F 2250/0034 differing in viscosity
• CPC Class Codes: F16F 9/535 Magnetorheological [MR] fluid dampers springs comprising magnetorheological [MR] elastomers F16F1/361

Abstract

The present invention relates to a variable-torque magnetorheologically actuated prosthetic knee which utilizes a plurality of interspersed and alternating rotors and stators to shear magnetorheological fluid in gaps formed therebetween. Advantageously, by operating in the “shear mode” there is substantially no or negligible fluid pressure buildup or change. Moreover, the multiple MR fluid gaps or flux interfaces desirably allow for the production of a large torque at low speed—eliminating the need for a transmission—and also for a wide dynamic torque range. One embodiment of the invention allows the rotors and/or stators to close the gaps therebetween to create a frictional torque component, thereby forming a “hybrid” braking system which provides a total torque or damping which is a combination of viscous torque and frictional torque.

Claims

1. A prosthetic knee, comprising:

a plurality of rotors being rotatable about a longitudinal axis of said prosthetic knee;

a plurality of stators alternatingly interspersed with said rotors to form gaps therebetween;

a fluid adapted to undergo a rheology change in response to an applied magnetic field and residing in said gaps formed between said rotors and said stators;

whereby, controlled variation of said magnetic field varies the fluid rheology and shearing of said fluid caused by relative rotation between said rotors and stators during knee rotation generates a controllable variable knee torque.

2. The prosthetic knee of claim 1, wherein said stators are rotatable about the longitudinal axis of said prosthetic knee.

3. The prosthetic knee of claim 1, wherein least one of said rotors and said stators are laterally displaceable about the longitudinal axis of said prosthetic knee to create mechanical contact between adjacent rotors and stators to provide a frictional component to the torque.

4. The prosthetic knee of claim 1, wherein said rotors and said stators comprise a magnetically soft material.

5. The prosthetic knee of claim 1, wherein said rotors and said stators comprise generally annular disks.

6. The prosthetic knee of claim 5, wherein said rotors and said stators have a thickness of about 0.2 mm (0.008 inches).

7. The prosthetic knee of claim 1, wherein said plurality of rotors comprises hundred or less rotors and said plurality of stators comprises hundred or less stators.

8. The prosthetic knee of claim 7, wherein said plurality of rotors comprises forty rotors and said plurality of stators comprises forty one stators.

9. The prosthetic knee of claim 1, wherein said gaps between said rotors and said stators have a size in the range from about 10 microns (μ

m) to about 100 microns (μ

m).

10. The prosthetic knee of claim 9, wherein said gaps between said rotors and said stators have a size of about 40 microns (μ

m).

11. The prosthetic knee of claim 1, wherein said rotors and said stators comprise generally cylindrical tubes.

12. The prosthetic knee of claim 1, wherein said rotors and said stators comprise blue temper steel or silicon steel.

13. The prosthetic knee of claim 1, wherein said fluid comprises a magnetically controllable medium.

14. The prosthetic knee of claim 1, wherein said fluid comprises a magnetorheological fluid adapted to undergo a viscosity change in response to variation in said magnetic field.

15. The prosthetic knee of claim 1, further comprising a magnet to generate said magnetic field which passes through said rotors, said stators and said fluid.

16. The prosthetic knee of claim 1, further comprising a generally central core in mechanical communication with a pair of side plates to form a magnetic return path for said magnetic field.

17. The prosthetic knee of claim 16, wherein said core and said side plates comprise an iron-cobalt (FeCo) high magnetic saturation alloy.

18. The prosthetic knee of claim 16, wherein at least one of said side plates is laterally displaceable about the longitudinal axis of said prosthetic knee.

19. The prosthetic knee of claim 1, further comprising:

a substantially central core and a pair of side plates formed from a magnetically soft material to create a magnetic return path; and

an electromagnet positioned between said core and said rotors and said stators and being responsive to an electrical signal to generate said magnetic field to cause a controlled change in the rheology of said fluid.

20. The prosthetic knee of claim 1, further comprising a rotatable inner spline with said rotors engaged with said inner spline.

21. The prosthetic knee of claim 20, wherein said inner spline comprises a plurality of longitudinal grooves and each of said rotors comprises a plurality of teeth matingly engaged with said longitudinal grooves of said inner spline.

22. The prosthetic knee of claim 20, wherein said inner spline comprises a titanium alloy.

23. The prosthetic knee of claim 20, further comprising a pair of bearings in rotary communication with said inner spline.

24. The prosthetic knee of claim 23, further comprising a pair of rotatable side mounting forks with each in mechanical communication with one of said bearings to facilitate connection of said prosthetic knee to a prosthetic shin.

25. The prosthetic knee of claim 1, further comprising an outer spline with said stators engaged with said outer spline.

26. The prosthetic knee of claim 25, wherein said outer spline comprises a plurality of longitudinal grooves and each of said stators comprises a plurality of teeth matingly engaged with said longitudinal grooves of said outer spline.

27. The prosthetic knee of claim 25, wherein said outer spline comprises an anodized aluminum alloy.

28. The prosthetic knee of claim 25, wherein said outer spline comprises a pyramid stub to facilitate connection of said prosthetic knee to a residual limb socket.

29. The prosthetic knee of claim 1, further comprising a magnetic exterior portion and a pair of mechanically connected magnetic side plates to create a magnetic return path for said magnetic field.

30. The prosthetic knee of claim 1, further comprising a cushioned flexion stop system to control the maximum flexion of said prosthetic knee.

31. The prosthetic knee of claim 1, further comprising a cushioned extension stop system to control the maximum extension of said prosthetic knee.

32. The prosthetic knee of claim 1, further comprising an extension assist device for facilitating in extending said prosthetic knee.

33. The prosthetic knee of claim 1, further comprising a controller to control and monitor the actuations of said prosthetic knee.

34. A prosthetic assembly, comprising:

the prosthetic knee as recited in claim 1;

a stump socket in mechanical communication with said prosthetic knee and adapted to receive the residual limb of an amputee;

a prosthetic shin portion in mechanical communication with said prosthetic knee; and

a prosthetic foot in mechanical communication with said prosthetic shin portion.