Elastically stretchable fabric force sensor arrays and methods of making

• US 8,161,826 B1
• Filed: 03/05/2009
• Issued: 04/24/2012
• Est. Priority Date: 03/05/2009
• Status: Active Grant

• Current Assignee: PatienTech, LLC
• Original Assignee: Stryker Corporation
• Inventors: Taylor, Geoffrey L.
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): DUNLAP, JONATHAN M
• Application Number:
  US12/380,845
• Time in Patent Office: 1,146 Days
• Field of Search: 73862041-862046
• US Class Current: 73/862.044
• CPC Class Codes: A47C 27/082 with non-manual inflation, e.g. with electric pumps
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/1036 Measuring load distribution, e.g. podologic studies
• CPC Class Codes: A61B 5/6892 Mats
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
• CPC Class Codes: G01L 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G01L 5/228 using tactile array force sensors
• CPC Class Codes: G01N 2203/0623 using piezoelectric gauges
• CPC Class Codes: G01N 3/08 by applying steady tensile or compressive forces G01N3/28 takes precedence
• CPC Class Codes: H01L 29/84 controllable by variation of applied mechanical force, e.g. of pressure

Abstract

Force or pressure transducer arrays have elastically stretchable electrically conductive polymer threads disposed in parallel rows and columns that contact at intersections thereof a piezoresistive material which has an electrical resistivity which varies inversely with pressure or force exerted thereon to form a matrix array of force or pressure sensor elements. The threads are fixed to a single one or pair of flexible elastically stretchable substrate sheets made of thin sheets of an insulating polymer such as PVC, or for greater elasticity and conformability to irregularly-shaped objects such as human body parts, an elastically stretchable fabric such as LYCRA or SPANDEX. Elastic stretchability of the sensor arrays is optionally enhanced by disposing either or both row and column conductive threads in sinuously curved, serpentine paths rather than straight lines.

Claims

1. A force sensing transducer for measuring force exerted thereon, said transducer comprising:

a. an elongated, elastically stretchable, electrically conductive row thread,

b. an elongated, elastically stretchable electrically conductive column thread,

c. the elastic stretchability of at least one of said row and column conductive threads being at least as great as one percent, and

d. a piezoresistive material located between and in electrically conductive contact with said row and column threads.

2. The force sensing transducer of claim 1 wherein said piezoresistive material is further defined as being contained in an elastically deformable coating on at least one of said row and column conductive threads.

3. The force sensing transducer of claim 2 wherein said row and column threads are attached to inner facing sides of a pair of elastically deformable substrate sheets.

4. The force sensing transducer of claim 3 wherein at least one of said substrate sheets is made of a woven fabric.

5. The force sensing transducer of claim 4 wherein at least one of said row and column conductive threads is attached to a substrate sheet by a sewn insulating thread.

6. The force sensing transducer of claim 2 wherein said row and column conductive threads are attached to one side of an insulating elastically deformable substrate sheet.

7. The force sensing transducer of claim 6 wherein at least one of said substrate sheets is made of a woven fabric.

8. The force sensing transducer of claim 7 wherein at least one of said row and column conductive threads is attached to a substrate sheet by a sewn insulating thread.

9. The force sensing transducer of claim 1 wherein said piezoresistive material is further defined as being contained in an elastically deformable piezoresistive substrate sheet containing a piezoresistive substance contacted by said conductive row thread, and contacted by said conductive column thread.

10. The force sensing transducer of claim 9 wherein said piezoresistive substrate sheet is impregnated with said piezoresistive substance.

11. The force sensing transducer of claim 9 wherein said row and column threads are attached to opposite planar surfaces of said piezoresistive substrate sheet.

12. The force sensing transducer of claim 11 wherein at least one of said row and column threads is attached to an elastically deformable substrate sheet.

13. The force sensing transducer of claim 1 wherein at least either of said row and column conductive threads has a polymer core.

14. The force sensing transducer of claim 13 wherein said polymer core is in the form of a thread.

15. The force sensing transducer of claim 13 wherein said polymer core is in the form of a yarn.

16. The force sensing transducer of claim 13 wherein said polymer core has formed thereon an electrically conductive coating.

17. The force sensing transducer of claim 1 wherein the elastic stretchability of at least either of said row and column conductive threads is at least as great as about ten percent.

18. The force sensing transducer of claim 1 wherein the elastic stretchability of at least either of said row and column conductive threads is at least as great as about thirty percent.

19. The force sensing transducer of claim 1 wherein said conductive row thread comprises one of a plurality m of parallel conductive row threads.

20. The force sensing transducer of claim 19 wherein said conductive column thread is angled with respect to said conductive row threads.

21. The force sensing transducer of claim 20 wherein said conductive column thread comprises one of a plurality n of conductive column threads.

22. The force sensing transducer of claim 21 wherein said conductive row threads are located in a first surface.

23. The force sensing transducer of claim 22 wherein said conductive column threads are located in a second surface.

24. The force sensing transducer of claim 23 wherein said first and second surfaces are mutually parallel.

25. The force sensing transducer of claim 1 wherein at least either of said row and column conductive threads is disposed in a path which is sinuously arranged with respect to a line joining first and second ends of said thread.

26. The force sensing transducer of claim 1 wherein at least either of said row and column conductive threads is made from a polymer selected from the group consisting of monofilament thread, woven thread and woven yarn.

27. A force sensing transducer for measuring force exerted thereon, said transducer comprising:

an elongated, elastically stretchable, electrically conductive row thread;

an elongated, elastically stretchable electrically conductive column thread, at least one of said row and column conductive threads having an elastic stretchability at least as great as about one percent, at least one of said row and column conductive threads also having a polymer core on which is formed an electrically conductive coating; and

a piezoresistive material located between and in electrically conductive contact with said row and column threads, said piezoresistive material being defined as a piezoresistive coating formed on said electrically conductive coating.

28. A force sensing transducer for measuring force exerted thereon, said transducer comprising:

an elongated, elastically stretchable, electrically conductive row thread;

an elongated, elastically stretchable electrically conductive column thread, at least one of said row and column conductive threads having an elastic stretchability at least as great as about one percent, at least one of said row and column conductive threads also having a polymer core; and

a piezoresistive material located between and in electrically conductive contact with said row and column threads, said piezoresistive material being defined as a piezoresistive coating formed on said polymer core.

29. A force sensing transducer array for measuring forces exerted on spatially separated parts thereof, said transducer array comprising:

a. a plurality of m elongated elastically stretchable electrically conductive row threads which are spatially separated from one another,

b. plurality n of elongated elastically stretchable electrically conductive column threads which are spatially separated from one another,

c. the elastic stretchability of at least one of said row and column conductive threads being at least as great as one percent, and

d. a piezoresistive material located between and in electrically conductive contact with said row and column conductive threads to thus form at p=m×

n intersections thereof a plurality of p sensor elements.

30. The force sensing transducer array of claim 29 wherein said piezoresistive material is further defined as including a circuit element having a non-bilateral electrical impedance characteristic in series with at least one of said p sensors for reducing cross talk between measurements of electrical impedance of said sensor elements by matrix addressing of selected pairs of row and column conductive threads.

31. The force sensing transducer array of claim 30 wherein said non-bilateral electrical impedance characteristics if further defined as being a diode-like characteristic.

32. The force sensing transducer array of claim 31 wherein said piezoresistive material is further defined as including electrically conductive particles suspended in an elastomeric solid solution.

33. The force sensing transducer array of claim 32 wherein said diode-like characteristic is formed by coating a surface of said piezoresistive material with at least one metallic oxide.

34. The force sensing transducer array of claim 33 wherein said metallic oxide is further defined as including at least one copper oxide.

35. The force sensing transducer array of claim 32 wherein said piezoresistive material is further defined as being contained in an elastically deformable coating on at least one of said row and column conductive threads.

36. The force sensing transducer of claim 32 wherein said piezoresistive material is further defined as being contained in an elastically deformable piezoresistive substrate sheet containing a piezoresistive substrate contacted by said conductive row thread, and contacted by said conductive column thread.

37. A force sensing transducer array for measuring forces exerted on spatially separated parts thereof, said transducer array comprising:

a plurality of elongated elastically stretchable electrically conductive row threads which are spatially separated from one another, said electrically conductive row threads each including a polymer core onto which is formed an electrically conductive coating;

a plurality of elongated elastically stretchable electrically conductive column threads which are spatially separated from one another, said electrically conductive column threads each including a polymer core onto which is formed an electrically conductive coating; and

a piezoresistive material contained in an elastically deformable coating on at least one of the electrically conductive coatings of at least one of the plurality of row and column conductive threads, wherein said plurality of row and column conductive threads define a plurality of sensors at a plurality of intersections of the row and column conductive threads.

38. The force sensing transducer array of claim 37 wherein said electrically conductive row threads and said electrically conductive column threads are attached to an elastically deformable substrate sheet.