Pressure distribution characterization system

• US 5,054,323 A
• Filed: 04/04/1989
• Issued: 10/08/1991
• Est. Priority Date: 04/04/1989
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Burke, Shawn E., Hubbard, James E. Jr.
• Primary Examiner(s): Crosland, Donnie L.
• Assistant Examiner(s): SWARTHOUT, BRENT
• Application Number:
  US07/333,108
• Time in Patent Office: 917 Days
• Field of Search: 73/754, 73/753, 73/DIG. 4, 73/708, 73/714, 73/718, 73/724, 310/338, 310/311, 310/330, 310/331, 338/4
• US Class Current: 73/754
• 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: Y10S 73/04 Piezoelectric

Abstract

The present invention is a device for characterizing pressure distributions on a rigid surface with respect to at least one reference (x) axis. The device includes a substrate electrode disposed on the rigid surface for which the pressure distribution is to be characterized. An electrically conductive material may form the substrate electrode, or where the rigid surface itself is electrically conductive, that rigid surface may form the substrate electrode. A piezo film is disposed on and overlying the rigid surface. A sensor electrode is disposed on and overlying at least part of the piezo film. In one form of the invention the sensor electrode of a measurement cell is a composite electrode including at least two electrically isolated portions. One portion has a dimension transverse to the reference axis which varies in proportion to position (x) along the reference axis, and the other portion has a dimension transverse to the reference axis which varies in proportion to one minus position (1-x) along the reference axis.

Claims

1. A device for characterizing pressure distribution on a surface with respect to at least one reference (x) axis, comprising:

A. a substrate defining said surface, said surface being rigid,

B. a substrate electrode disposed on said surface,

C. a piezo film at least partially disposed on and overlying said substrate electrode, said film being characterized by a predetermined strain response transfer function, and

D. a sensor electrode having a portion disposed on and overlying at least part of said piezo film and said substrate electrode, said portion having a predetermined width profile b(x) in the direction transverse to said reference axis, whereby a total charge on said film as a function of time, O(t), is established in said piezo film substantially proportional to;

_o ∫

^L b(x)P(x,t)dx

where L is representative of the maximum dimension of said sensor electrode in said x direction, where t is representative of time, and P(x,t) is representative of said pressure distribution on said surface as a function of x and t,

E. means for generating a signal representative of O(t), said signal being representative of a predetermined characteristic of said pressure distribution on said surface.

2. A device according to claim 1 wherein said sensor electrode is a composite electrode, said composite electrode including at least two electrically isolated and adjacent portions, one of said portions having a dimension transverse to said reference axis which varies in proportion to position along said reference axis from a reference point and defining a first portion, and the other of said portions having a dimension transverse to said reference axis which varies in proportion to one minus position along said reference axis extending from said reference point and defining a second portion.

3. A device according to claim 2 further comprising:

A. means coupled to said first portion for generating a C_m signal representative of the potential difference between said first portion and said substrate electrode,

B. means coupled to said first portion and said second portion for generating a C_l signal representative of the sum of the potential difference between said first portion and said substrate electrode and the potential difference between said second portion and said substrate electrode,

C. means for generating a CP signal representative of the ratio of said C_m signal and said C_l signal.

4. A device according to claim 1 wherein said sensor electrode fully overlies said piezo film.

5. A device according to claim 4 further comprising means for generating a signal representative of the potential difference between said sensor electrode and said substrate electrode.

6. A device according to claim 1 wherein said sensor electrode has a dimension transverse to said reference axis which varies in proportion to position along said reference axis.

7. A device according to claim 6 further comprising means for generating a signal representative of the potential difference between said sensor electrode and said substrate electrode.

8. A device according to claim 1 wherein said sensor electrode has a dimension transverse to said reference axis which varies in proportion to the square of position along said reference axis.

9. A device according to claim 8 further comprising means for generating a signal representative of the potential difference between said sensor electrode and said substrate electrode.

10. A device according to claim 1 wherein said surface is electrically conductive and said substrate electrode is established by said surface.

11. A device according to claim 1 wherein said strain response transfer function is a function of x, f(x), and is determined by equation:

f(x)=d(x)/t(x),

wherein d(x) is representative of variation in strain response characteristics of said piezo film in a direction transverse to said reference axis as a function of x, and t(x) is representative of said piezo film thickness in a direction transverse to said reference axis as a function of x.

12. A device according to claim 11 wherein said thickness of said piezo film is substantially uniform.

13. A device according to claim 11 wherein said characteristics of the strain response of said piezo film is substantially uniform.

14. A device according to claim 11 wherein said thickness of said piezo film is substantially uniform and said characteristics of the strain response of said piezo film is substantially uniform.

15. A device according to claim 1 wherein said piezo film is piezoelectric film.

16. A device according to claim 12 wherein said piezo film is polymer film.

17. A device according to claim 15 wherein said piezo film is polyvinylidene fluoride.

18. A device according to claim 1 wherein said piezo film is piezoresistive film.

19. A device according to claim 2 wherein said surface is electrically conductive and said substrate electrode is established by said surface.

20. A device according to claim 2 wherein said strain response transfer function f(x) is determined by equation:

f(x)=d(x)/t(x),

wherein d(x) is representative of variation in strain response characteristics of said piezo film in a direction transverse to said reference axis, and t(x) is representative of said piezo film thickness in a direction transverse to said reference axis.

21. A device according to claim 20 wherein said thickness of said piezo film is substantially uniform.

22. A device according to claim 20 wherein said characteristics of the strain response of said piezo film is substantially uniform.

23. A device according to claim 20 wherein said thickness of said piezo film is substantially uniform and said characteristics of the strain response of said piezo film is substantially uniform.

24. A device according to claim 2 wherein said piezo film is polymer film.

25. A device according to claim 24 wherein said piezo film is polyvinylidene fluoride.

26. A device according to claim 2 wherein said piezo film is piezoresistive film.

28. A device according to claim 1 wherein b(x)=b_O, where b_O is a constant, and said signal corresponds to the zeroth moment of said pressure distribution.

29. A device according to claim 1 wherein b(x)=b₁ x, where b₁ is a constant, and said signal corresponds to the first moment of said pressure distribution.

30. A device according to claim 1 wherein b(x)=b₂ x², where b₂ is a constant, and said signal corresponds to the second moment of said pressure distribution.

27. A device for characterizing pressure distribution on a surface with respect to at least one reference (x) axis, comprising:

A. a substrate defining said surface, said surface being rigid,

B. a substrate electrode disposed on said surface,

C. a piezo film at least partially disposed on and overlying said substrate electrode, said film being characterized by a predetermined strain response transfer function,

D. a sensor electrode having a portion disposed on and overlying at least part of said piezo film and said substrate electrode, said portion having a predetermined width profile b(x) in the direction transverse to said reference axis, whereby a total charge on said film as a function of time, Q(t), is established in said piezo film substantially proportional to;

##EQU10## where L is representative of the maximum dimension of said sensor electrode in said x direction, where t is representative of time, and P(x,t) is representative of said pressure distribution on said surface as a function of x and t,

said sensor electrode further being a composite electrode, said composite electrode including at least two electrically isolated and adjacent portions, one of said portions having a dimension transverse to said reference axis from a reference point which varies in proportion to position along said reference axis and defining a first portion, and the other of said portions having a dimension transverse to said reference axis which varies in proportion to one minus position along said reference axis extending from said reference point and defining a second portion,

E. means coupled to said first portion for generating a C_m signal representative of the potential difference between said first portion and said substrate electrode,

F. means coupled to said first portion and said second portion for generating a C_l signal representative of the sum of the potential difference between said first portion and said substrate electrode and the potential difference between said second portion and said substrate electrode, and

G. means for generating a CP signal representative of the ratio of said C_m signal and said C_l signal.