Variable Impedance Mechanical Interface

• US 20130282141A1
• Filed: 03/15/2013
• Published: 10/24/2013
• Est. Priority Date: 03/19/2012
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Herr, Hugh M., Marecki, Andrew, Sengeh, David M.
• Granted Patent: US 10,806,605 B2
• Time in Patent Office: Days
• US Class Current: 623/33
• 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 2/78 Means for protecting prostheses or for attaching them to the body, e.g. bandages, harnesses, straps, or stockings for the limb stump
• CPC Class Codes: A61F 2/80 Sockets, e.g. of suction type
• CPC Class Codes: A61F 2002/5047 using mathematical models A61F2002/505 takes precedence
• CPC Class Codes: A61F 2002/5049 Computer aided shaping, e.g. rapid prototyping
• CPC Class Codes: A61F 2002/505 using CAD-CAM techniques or NC-techniques
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]

Abstract

A mechanical interface connecting a biological body segment, such as a limb, portion of a limb or other body segment, to a wearable device such as a prosthetic, orthotic or exoskeletal device, is fabricated by quantitatively mapping a characterized representation of the body segment to form a digital representation of the mechanical interface shape and mechanical interface impedance. The mechanical interface includes a continuous socket defining a contoured inside surface and a contoured outside surface, and includes a material having an intrinsic impedance that varies through the material, so that the intrinsic impedance varies along the contoured inside surface.

Claims

1. A method for fabricating a mechanical interface for connecting a biological body segment to a wearable device, comprising the steps of:

a) compiling a data set of features corresponding to a biological body segment;

b) processing the compiled data set to thereby form a characterized representation of the body segment;

c) quantitatively mapping the characterized representation of the body segment to form a digital representation of a mechanical interface shape and a mechanical interface impedance; and

d) fabricating a mechanical interface that correlates to the digital representation of the mechanical interface shape and the mechanical interface impedance to thereby form the mechanical interface for connecting a biological segment to the wearable device.

2. The method of claim 1, wherein the data set is compiled by employing at least one method selected from the group consisting of casting, surface scanning, computerized tomography, magnetic resonance imaging, magnetic resonance elastography, ultrasound, photogrammetography and electromechanical measurement tools.

3. The method of claim 1, wherein the compiled data set is processed to generate at least one anatomical and biomechanical model of nodes of data, wherein each node includes a subset of data, the model collectively representing tissue impedance and at least one member of the group consisting of external biological body segment shape, soft tissue depth, tissue distribution, tissue density, tissue viscoelasticity, skin tensile strain, neural muscle activation and sensitivity to externally-applied pressure influenced by underlying anatomy of the body segment.

4. The method of claim 3, wherein the tissue impedance is computed by at least one member of the group consisting of:

orthogonal force;

displacement and speed of displacement of the body segment;

soft tissue depth;

compression strain;

compression damping; and

compression stiffness at each node employed to generate the anatomical and biomechanical model.

5. The method of claim 3, wherein the subset of data of at least a portion of the nodes includes external biological body segment shape and orthogonal impedance of the body segment.

6. The method of claim 5, wherein the subset of data for each node is generated by conducting the steps of:

a) marking a surface of the external biological body segment shape to form a detectable matrix of nodes;

b) quantitatively mapping the nodes; and

c) estimating orthogonal impedance of the body segment at each node.

7. The method of claim 6, wherein the mechanical interface is fabricated to correlate to a distribution of orthogonal impedance of the body segment.

8. The method of claim 7, wherein the orthogonal impedance of the interface surface is inversely proportional to the adjacent orthogonal impedance of the body segment.

9. The method of claim 8, wherein the inversely proportional relationship between interface impedance and body segment impedance is linear.

10. The method of claim 1, wherein the compiled data set is processed to generate at least one anatomical and biomechanical model of nodes of data, wherein each node includes a subset of data, the model collectively representing skin tensile strain and at least one member of the group consisting of external biological body segment shape, tissue orthogonal impedance, soft tissue depth, tissue distribution, tissue density, tissue viscoelasticity, neural muscle activation and sensitivity to externally-applied pressure influenced by underlying anatomy of the body segment.

11. The method of claim 10, wherein the generation of the skin strain model comprises the steps of:

a) marking a surface of the body segment to form a detectable matrix of markings;

b) quantitatively mapping the location of the markings;

c) moving the body segment to thereby cause the markings to redistribute relative to each other; and

d) quantitatively mapping the redistributed markings to thereby generate a three-dimensional image of redistribution of markings that corresponds to skin tensile strain of the body segment caused by the movement of the body segment.

12. The method of claim 11, wherein the three-dimensional image is a photogrammetic image.

13. The method of claim 12, wherein additional data are compiled from the body segment by magnetic resonance imaging.

14. The method of claim 13, wherein the body segment is at least a portion of a limb.

15. The method of claim 11, wherein the markings are processed as point clouds and wherein the point clouds are triangulated.

16. The method of claim 15, wherein the triangulated point clouds are processed by a constant strain element analysis.

17. The method of claim 11, wherein the mechanical interface is fabricated to essentially replicate the redistribution of markings that correspond to surface skin strain of the body segment caused by the movement of the body segment, in a manner that reduces skin shear stress across the interface.

18. The method of claim 17, wherein the tensile impedance of the interface surface is inversely proportional to an adjacent change in skin tensile strain caused by the movement of the body segment.

19. The method of claim 18, wherein the surface is defined by a liner, and wherein the wearable device includes the liner and a socket supporting the liner.

20. The method of claim 19, wherein the liner includes a relatively compliant material, proximate to portions of the body segment where relatively large skin tensile strains occur, and a relatively stiff material proximate to portions of the body segment where skin strains are relatively small.

21. The method of claim 20, wherein the liner includes strips of material running orthogonally to the general direction of skin tensile strain of a portion of the body segment most proximate to each individual strip.

22. The method of claim 1, wherein the wearable device is an orthotic device.

23. The method of claim 1, wherein the wearable device is a prosthetic device.

24. The method of claim 1, wherein the wearable device is an exoskeleton.

25. The method of claim 1, wherein the interface includes at least one strut extending from a high impedance interface area to another high impedance interface area.

26. A mechanical interface for connecting a biological body segment to a wearable device, comprising:

a continuous socket defining a contoured inside surface and a contoured outside surface, wherein the socket includes a material having an intrinsic impedance that varies through the material, whereby the intrinsic impedance varies spatially along the contoured inside surface.

27. The mechanical interface of claim 26, further including a relatively rigid open shell mated to the socket, wherein the shell defines an interior surface that supports the socket.

28. The mechanical interface of claim 27, wherein the outside surface of the socket, in combination with the interior surface of the shell, defines, at least in part, at least one gap between the inside surface of the shell and the outside surface of the socket.

29. The mechanical interface of claim 28, wherein the size of at least one gap varies continuously when measured orthogonally to the outside surface of the socket from one end of the gap to another end of the gap.

30. The mechanical interface of claim 28, wherein the maximum size of at least one gap is inversely proportional to the intrinsic impedance of the material of the portion of the socket defining the outside surface of the socket at the gap.

31. The mechanical interface of claim 27, wherein the open shell defines at least one opening along the inside surface of the shell.

32. The mechanical interface of claim 31, wherein the openings of the shell extend about portions of the outside surface of the socket having low orthogonal impedance relative to the orthogonal impedance of adjacent portions of the outside surface of the socket.

33. The mechanical interface of claim 32, wherein the area of the openings defined by the shell are inversely proportional in size to the orthogonal impedance of the socket at the openings of the shell.

34. The mechanical interface of claim 26, wherein the socket further includes at least one strut extending from a high orthogonal impedance socket area to another high orthogonal impedance socket area, whereby the strut and the remainder of the socket define a gap.

35. The mechanical interface of claim 34, wherein the size of the gap is inversely proportional to the intrinsic impedance of the remainder of the socket at the gap.

36. The mechanical interface of claim 35, wherein the strut is rigid relative to the portion of the socket opposite the strut at the gap.

37. The mechanical interface of claim 26, wherein the spatially varying impedance of the socket is an orthogonal impedance.

38. The mechanical interface of claim 37, wherein the orthogonal impedance of the socket is numerically determined from the orthogonal impedance of the most proximate portions of the body segment.

39. The mechanical interface of claim 38, wherein the orthogonal impedance of the socket is inversely proportional to the orthogonal impedance of the most proximate portions of the body segment.

40. The mechanical interface of claim 26, wherein the mechanical interface defines a surface, wherein the surface is defined by a liner, and wherein the wearable device includes the liner and a socket supporting the liner.

41. The mechanical interface of claim 40, wherein the tensile impedance of the liner is numerically determined from the adjacent change in skin tensile strain caused by the movement of the body segment.

42. The mechanical interface of claim 41, wherein the liner has a tensile impedance that includes a relatively compliant material, proximate to portions of the body segment where relatively large skin tensile strains occur, and a relatively stiff material proximate to portions of the body segment where skin tensile strains are relatively small.

43. The mechanical interface of claim 42, wherein the liner includes a plurality of materials.

44. The mechanical interface of claim 43, wherein the liner includes strips of material running transversely to the general direction of skin tensile strain of the portion of the body segment most proximate to each individual strip.