U.S. patent application number 13/697435 was filed with the patent office on 2013-05-30 for sensor sleeve for health monitoring an article.
The applicant listed for this patent is Peter V. Buca, Jay Lee, Mark Schulz, Vesselin Shanov, Surya Sundaramurthy, Xiangdong Zhu. Invention is credited to Peter V. Buca, Jay Lee, Mark Schulz, Vesselin Shanov, Surya Sundaramurthy, Xiangdong Zhu.
Application Number | 20130134992 13/697435 |
Document ID | / |
Family ID | 44259601 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130134992 |
Kind Code |
A1 |
Zhu; Xiangdong ; et
al. |
May 30, 2013 |
SENSOR SLEEVE FOR HEALTH MONITORING AN ARTICLE
Abstract
A sensor sleeve (10) for use in detecting a failure in an
article (18) (e.g., a hydraulic hose), the sensor sleeve includes
an insulator layer (12) that separates two electrode layers (14,
16). As such, the electrode layers deform to contact each other,
which changes the impedance as measured across the electrode
layers. The sensor sleeve is designed to change electrical
impedance (resistance) due to fluid pressure initiating a hole
through the sensor itself. The sensor sleeve will detect the fluid
leak when the hole penetrates the sensor and brings the two elastic
electrodes in contact with each other and/or the fluid, which when
the fluid is conductive fluid, creates a signal path between the
first electrode layer and the second electrode layer, which also
changes the impedance as measured across the electrode layers.
Inventors: |
Zhu; Xiangdong; (Dublin,
OH) ; Buca; Peter V.; (Sandusky, OH) ; Lee;
Jay; (Mason, OH) ; Schulz; Mark; (West
Chester, OH) ; Sundaramurthy; Surya; (Cincinnati,
OH) ; Shanov; Vesselin; (Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zhu; Xiangdong
Buca; Peter V.
Lee; Jay
Schulz; Mark
Sundaramurthy; Surya
Shanov; Vesselin |
Dublin
Sandusky
Mason
West Chester
Cincinnati
Cincinnati |
OH
OH
OH
OH
OH
OH |
US
US
US
US
US
US |
|
|
Family ID: |
44259601 |
Appl. No.: |
13/697435 |
Filed: |
May 12, 2011 |
PCT Filed: |
May 12, 2011 |
PCT NO: |
PCT/US11/36190 |
371 Date: |
February 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61333828 |
May 12, 2010 |
|
|
|
Current U.S.
Class: |
324/658 ;
324/649; 73/753 |
Current CPC
Class: |
G01M 3/182 20130101;
G01N 27/24 20130101; G01N 27/20 20130101; G01L 9/003 20130101; G01M
3/18 20130101; G01R 27/2605 20130101 |
Class at
Publication: |
324/658 ;
324/649; 73/753 |
International
Class: |
G01R 27/26 20060101
G01R027/26; G01L 9/00 20060101 G01L009/00 |
Claims
1. A sensor sleeve for detecting damage to a surface of an article,
the sensor sleeve comprising: a first electrode layer covering at
least a portion of a surface of an article; a dielectric layer
covering a least a portion of the first electrode layer; and a
second electrode layer covering at least a portion of the
dielectric layer, wherein damage to the surface of the article
covered by the first electrode layer, the dielectric layer and the
second dielectric layer causes the first electrode layer to contact
the second electrode layer, thereby decreasing the impedance
between the first electrode layer and the second electrode
layer.
2. The sensor sleeve of claim 1, wherein the first electrode layer
includes one or more contacts, wherein the contacts are configured
to puncture through the dielectric layer and make contact with the
second electrode layer.
3. The sensor sleeve of claim 1, wherein the article is a
pressurized hose having at least one hose layer operable to
transfer fluids from one place to another, wherein the hose layer
has a circumferential surface; and the first electrode layer covers
at least a portion of the circumferential surface of the hose
layer.
4. The sensor sleeve of claim 1, wherein at least one of the first
electrode layer and the second electrode layer are flexible.
5. The sensor sleeve of claim 1, wherein the dielectric layer is
discontinuous.
6. The sensor sleeve of claim 1, wherein the dielectric layer
contains one or more voids formed between the first electrode layer
and the second electrode layer.
7. The sensor sleeve of claim 1, wherein the dielectric layer
contains an auxetic material and a non-conductive material, wherein
the auxetic material is spaced along the dielectric layer.
8. The sensor sleeve of claim 1, wherein the dielectric layer is
layer of fabric.
9. The sensor sleeve of claim 1, wherein the dielectric layer
includes a wire embedded in a in a conductive material.
10. The sensor sleeve of claim 1, wherein the first electrode
layer, the second electrode layer and the dielectric layer have a
combined mechanical impedance that matches mechanical impedance of
the article.
11. The sensor sleeve of claim 2, wherein the one or more contacts
are spaced apart a uniform distance or a non-uniform distance along
the first electrode layer.
12. The sensor sleeve of claim 2, wherein the contacts are
configured to permanently affix to the second electrode layer when
a damage condition occurs.
13. The sensor sleeve of claim 1, further comprising a coupler
having a first end coupled to first electrode layer and a second
end coupled to the second electrode layer.
14. The sensor sleeve of claim 13, wherein the coupler is
configured to couple an associated measuring device to the sensor
sleeve, wherein the associated measuring device is configured to
measure impedance and/or capacitance across the first electrode
layer and the second electrode layer.
15. The sensor sleeve of claim 1 further comprising a protective
layer that protects at least the second electrode layer from an
environment in which the article is used.
16. The sensor sleeve of claim 1, wherein the sensor sleeve is
integrally formed in the article.
17. The sensor sleeve of claim 1, wherein the sensor sleeve is
extruded over a portion of the article.
18. The sensor sleeve of claim 1, wherein the sensor sleeve is
slipped over the article.
19. The sensor sleeve of claim 1, wherein the sensor sleeve is
embedded in the article.
20. A method for detecting failure of an article, the method
comprising: monitoring impedance of an article, wherein the article
includes a sensor sleeve including a first electrode layer covering
at least a portion of a surface of the article; a dielectric layer
covering a least a portion of the first electrode layer; and a
second electrode layer covering at least a portion of the
dielectric layer, wherein damage to the surface of the article
covered by the first electrode layer, the dielectric layer and the
second electrode layer causes the first electrode layer to contact
the second electrode layer, wherein the impedance is measured
between the first electrode layer and the second electrode layer;
and detecting a failure in the article based at least in part on
the monitored impedance across the first electrode layer and the
second electrode layer.
21. The method of claim 20, further comprising comparing the
impedance measured across the first electrode layer and the second
electrode layer with a database of information including operation
parameters associated with the article.
22. The method of claim 20 further comprising terminating a fluid
input to the article upon detecting the failure of the article.
23. The method of claim 20 further comprising outputting a
notification that the article has failed upon detecting the failure
of the article.
24. The method of any claim 20, wherein the step of detecting
includes determining if one or more contacts in the first electrode
layer is in contact with the second electrode layer.
25-29. (canceled)
30. A sensor sleeve for detecting conductive fluid leakage in an
article, the sensor sleeve comprising: a first electrode layer
covering at least a portion of a surface of the article; a
dielectric layer covering a least a portion of the first electrode
layer, wherein the dielectric layer is a porous and non-absorbent
dielectric layer; and a second electrode layer covering at least a
portion of the dielectric layer, wherein fluid leakage from the
article creates a conductive path through the dielectric layer and
between the first electrode layer and the second electrode
layer.
31. The sensor sleeve of claim 30, wherein the first electrode
layer includes one or more contacts, wherein the contacts are
configured to puncture through the dielectric layer and make
contact with the second electrode layer.
32. The sensor sleeve of any claim 30, wherein the article is a
pressurized hose having at least one hose layer operable to
transfer fluids from one place to another, wherein the hose layer
has a circumferential surface; and the first electrode layer covers
at least a portion of the circumferential surface of the hose
layer.
33. The sensor sleeve of claim 30, wherein at least one of the
first electrode layer and the second electrode layer are
flexible.
34. The sensor sleeve of claim 30, wherein the dielectric layer is
discontinuous.
35. The sensor sleeve of claim 30, wherein the dielectric layer
contains one or more voids formed between the first electrode layer
and the second electrode layer.
36. The sensor sleeve of claim 30, wherein the dielectric layer is
layer of fabric.
37. The sensor sleeve of claim 30, wherein the first electrode
layer, the second electrode layer and the dielectric layer have a
combined mechanical impedance that matches mechanical impedance of
the article.
38. The sensor sleeve of claim 30, wherein the one or more contacts
are spaced apart a uniform distance or a non-uniform distance along
the first electrode layer.
39. The sensor sleeve of claim 30, wherein the contacts are
configured to permanently affix to the second electrode layer when
a damage condition occurs.
40. The sensor sleeve of claim 30, further comprising a coupler
having a first end coupled to first electrode layer and a second
end coupled to the second electrode layer.
41-42. (canceled)
43. The sensor sleeve of claim 30, wherein the sensor sleeve is
integrally formed in the article.
44. The sensor sleeve of claim 30, wherein the sensor sleeve is
slipped over the article.
45. The sensor sleeve of claim 30, wherein the sensor sleeve is
embedded in the article.
46. A method for detecting conductive fluid leaking in an article,
the method comprising: monitoring impedance of an article, wherein
the article includes a sensor sleeve including a first electrode
layer covering at least a portion of a surface of the article; a
dielectric layer covering a least a portion of the first electrode
layer, wherein the dielectric layer is porous and non-conductive;
and a second electrode layer covering at least a portion of the
dielectric layer, wherein a leak of conductive fluid creates a
conductive path through the dielectric layer and between the first
electrode layer and the second electrode layer, wherein the
impedance is measured between the first electrode layer and the
second electrode layer; and detecting the leak of conductive fluid
in the article based at least in part on the monitored impedance
across the first electrode layer and the second electrode
layer.
47-49. (canceled)
50. A method for measuring pressure in an article, the sensor
sleeve comprising: mounting a sensor sleeve on at least a portion
of the article, wherein the sensor sleeve includes a first
electrode layer covering at least a portion of a surface of the
article; a dielectric layer covering a least a portion of the first
electrode layer; and a second electrode layer covering at least a
portion of the dielectric layer; monitoring capacitance change
and/or impedance change of the sensor sleeve due to deformation in
the article caused by a change in pressure of fluid passing through
the article, wherein the change in capacitance and/or the change in
impedance is measured between the first electrode layer and the
second electrode layer.
51. The method of claim 50, further including detecting a failure
in the article based at least in part on the monitored capacitance
change and/or impedance change.
52. The method of claim 50, wherein the change in capacitance
and/or impedance is caused by an external force applied to the
article.
53. The method of claim 50, further including calculating an
internal pressure of the article based on the monitored capacitance
and/or impedance.
Description
RELATED APPLICATION DATA
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Patent Application Ser. No. 61/333,828
filed May 12, 2010, which is incorporated herein by reference in
its entirety.
TECHNICAL FIELD
[0002] The present invention relates to a sensor sleeve for
detecting damage to a pressurized article (e.g., a hydraulic
hose).
BACKGROUND
[0003] A hydraulic connector hose is a tube that transfers fluids
under pressure from one place to another. A hydraulic hose is a
composite structure primarily made of rubber or thermoplastic and
steel reinforcement. The steel reinforcement may include wire that
is tightly wound spirally along the length of the hose so as to
form a steel shell or it might be braided across the length of the
hose for higher strength. The outermost covering is usually made of
polymer material that helps protect the inner layers from harsh
environments. Hydraulic hoses operate from a very low pressure to
extremely high pressure depending on the applications. Hydraulic
hoses are used in a variety of industries like heavy-machinery,
household appliances etc and environments. In certain situations,
especially in heavy machinery, the health of a hose is
critical.
[0004] A hydraulic hose has a finite service life and all hoses
eventually fail due to various factors like external damage,
multi-plane bending, operating conditions, etc. The damage to a
hose carrying such high pressures can lead to serious injury or
death of an operator. Hence, monitoring the health of the hose
becomes critical.
[0005] Conventional technology depicted by U.S. Pat. No. 7,555,936
to Purdue Research Foundation and PCT Publication No. WO
2010/004418 to Eaton Corporation generally uses the hydraulic hose
as a sensor. For example, the above listed references use the
principle of capacitance measurement wherein the capacitance of the
hose is measured and used as the health indicator of the hose.
Problems with such methods include: hose metal layers may come in
contact with each other due to crimping, for example; does not
consider a hose with other than two metal layers; and discounts the
damage to the hose caused from a foreign object.
SUMMARY
[0006] The present invention is directed to a variety of sensor
sleeves for use in detecting a failure in an article (e.g., a
hydraulic hose). The sensor sleeves generally include an insulator
layer that separates two electrode layers. As such, the electrode
layers deform to contact each other. In general, but not all cases,
the electrode layers are thicker and flexible relative to the
insulator (dielectric) layer.
[0007] The sensor sleeve is designed to change electrical impedance
due to fluid pressure or a foreign object pushing against or
through the sensor itself. The sensor sleeve will detect an oil
leak or foreign object through the hose when a hole is formed by
fluid pressure or foreign object, which deforms and/or penetrates
the sensor and brings the two elastic electrodes in contact with
each other. The flexibility, thickness and geometry of the
electrodes may be designed based on the material the sensor skin is
monitoring. As an example, to monitor a composite material for
impact damage, the sensor skin would have thinner and stiffer
electrodes to match the impedance (stiffness) of the base composite
material. The phrase "composite material" is used herein to
describe elastomeric composite materials (e.g., hoses) and also
fiber reinforced polymer composite materials (e.g., a composite
airplane wing). A composite hose is a combination of rubber
material and steel wire. A fiber reinforced polymer composite is a
combination of strong fibers embedded in a polymer matrix (e.g.,
carbon fibers embedded in epoxy or prepreg carbon fabric layered to
form a panel). Other types of composites are also possible. The
sensor sleeve may include electrodes and a dielectric specifically
designed for the different types of composite materials that can be
monitored.
[0008] Another aspect of the invention relates to a sensor sleeve
designed to change capacitance due to the deformation of itself
caused by fluid leakage or damage caused by a foreign object. In
such, embodiment, the dielectric layer may be thicker then the
electrode layers. Such a sensor should be carefully designed so it
only accounts for critical damages from fluid leakage or foreign
object impact.
[0009] Another aspect of the invention relates to a sensor sleeve
for detecting damage to a surface of an article, the sensor sleeve
including: a first electrode layer covering at least a portion of a
surface of an article; a dielectric layer covering a least a
portion of the first electrode layer; and a second electrode layer
covering at least a portion of the dielectric layer, wherein damage
to the surface of the article covered by the first electrode layer,
the dielectric layer and the second dielectric layer causes the
first electrode layer to contact the second electrode layer,
thereby decreasing the impedance between the first electrode layer
and the second electrode layer.
[0010] Another aspect of the invention relates to a method for
detecting failure of an article, the method including: monitoring
impedance of an article, wherein the article includes a sensor
sleeve including a first electrode layer covering at least a
portion of a surface of the article; a dielectric layer covering a
least a portion of the first electrode layer; and a second
electrode layer covering at least a portion of the dielectric
layer, wherein damage to the surface of the article covered by the
first electrode layer, the dielectric layer and the second
electrode layer causes the first electrode layer to contact the
second electrode layer, wherein the impedance is measured between
the first electrode layer and the second electrode layer; and
detecting a failure in the article based at least in part on the
monitored impedance across the first electrode layer and the second
electrode layer.
[0011] Another aspect of the present invention relates to a method
of manufacturing a sensor sleeve over an article, the method
including: applying a first electrode layer over at least a portion
of an article; applying a dielectric layer over at least a portion
of the first electrode layer; and applying a second electrode layer
at least a portion of the dielectric layer.
[0012] Another aspect of the present invention relates to a sensor
sleeve for detecting conductive fluid leakage in an article, the
sensor sleeve including: a first electrode layer covering at least
a portion of a surface of the article; a dielectric layer covering
a least a portion of the first electrode layer, wherein the
dielectric layer is a porous and non-absorbent dielectric layer;
and a second electrode layer covering at least a portion of the
dielectric layer, wherein fluid leakage from the article creates a
conductive path through the dielectric layer and between the first
electrode layer and the second electrode layer.
[0013] Another aspect of the present invention relates to a method
for detecting conductive fluid leaking in an article, the method
including: monitoring impedance of an article, wherein the article
includes a sensor sleeve including a first electrode layer covering
at least a portion of a surface of the article; a dielectric layer
covering a least a portion of the first electrode layer, wherein
the dielectric layer is porous and non-conductive; and a second
electrode layer covering at least a portion of the dielectric
layer, wherein a leak of conductive fluid creates a conductive path
through the dielectric layer and between the first electrode layer
and the second electrode layer, wherein the impedance is measured
between the first electrode layer and the second electrode layer;
and detecting the leak of conductive fluid in the article based at
least in part on the monitored impedance across the first electrode
layer and the second electrode layer.
[0014] Another aspect of the invention relates to the sensor sleeve
being designed to change capacitance due to the deformation of the
sensor, which may be caused by fluid pressure (e.g., an oil leak)
or damage caused by a foreign object. In such cases, the dielectric
layer may be thicker than the two electrode layers, for example.
Such sensor needs to be carefully designed so it may account for
critical damages caused from fluid pressure and foreign object
impact, for example.
[0015] Another aspect of the present invention relates to placement
of the sensor sleeve. The sensor sleeve may be placed or formed on
the outside of the hose, or anywhere inside the article between the
hose layers. When the sensor sleeve, is formed inside the hose, one
or more hose layers can function as one or more of the sensor
sleeve layers.
[0016] Other systems, devices, methods, features, and advantages of
the present invention will be or become apparent to one having
ordinary skill in the art upon examination of the following
drawings and detailed description. It is intended that all such
additional systems, methods, features, and advantages be included
within this description, be within the scope of the present
invention, and be protected by the accompanying claims.
[0017] It should be emphasized that the term "comprise/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof."
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Embodiments of this invention will now be described in
further detail with reference to the accompanying drawings, in
which:
[0019] FIG. 1 is an exemplary sensor sleeve in accordance with
aspects of the present invention.
[0020] FIG. 2 is a cross-section of the sensor sleeve of FIG. 1
covering an article in accordance with aspects of the present
invention.
[0021] FIGS. 3-9 are exemplary sensor mechanisms in accordance with
aspects of the present invention.
[0022] FIGS. 10A-10B are sensor sleeves for detecting fluid leak in
an article in accordance with aspects of the present invention.
[0023] FIG. 11 is an exemplary system in accordance with aspects of
the present invention.
[0024] FIGS. 12 and 13 are exemplary methods in accordance with
aspects of the present invention.
[0025] FIG. 14 is chart illustrating a change in a resistance in a
sensor sleeve when in a normal condition and a failure
condition.
[0026] FIGS. 15A-15E illustrate development of sensor sleeve in
accordance with aspects of the present invention.
[0027] FIGS. 16A-16B illustrate a sensor sleeve on an outside
surface of an article in accordance with aspects of the present
invention.
[0028] FIGS. 17A-17B illustrate a sensor sleeve on an inner surface
of an article in accordance with aspects of the present
invention.
[0029] FIG. 18 is chart illustrating a change in a resistance in a
sensor sleeve when in a normal condition and a failure
condition.
[0030] FIG. 19 is chart illustrating a change in a resistance in a
sensor sleeve when in a normal condition and a failure condition
for different diameter indenters.
DETAILED DESCRIPTION OF EMBODIMENTS
[0031] Aspects of the present invention are directed to a variety
of sensor sleeves. As used herein, the term "sleeve" includes a
skin, a sheath, an outer cover and a structure formed within a hose
component, for example.
[0032] Referring to FIG. 1, a cross-section of an exemplary sensor
sleeve 10 in accordance with aspects of the present invention is
illustrated. The sensor sleeve 10 generally includes an insulator
layer 12 that separates to a first electrode layer 14 and a second
electrode layer 16. As described below, in general, the electrode
layers 14, 16 deform to contact each other when a fault or failure
condition occurs. Thus, the electrode layers 14, 16 are usually
thicker and flexible relative to the insulator (dielectric) layer
12.
[0033] Referring to FIG. 2, the sensor sleeve 10 is illustrated
covering the surface of an article 18. For example, the article may
be a hose. The article 18 is representative of various types of
hoses that may be used to contain a flowing or static fluid. A
particular example is a hydraulic hose that contains a hydraulic
fluid whose pressure fluctuates. As such, the article 18 may have a
circumferential surface and is operable to transfer fluids from one
place to another. The article 18 has an inner tube 20 that contacts
a fluid flowing through the article 18. The article 18 may include
one or more reinforcement layers (not shown) that strengthen the
article 18, and an outer cover 19 that protects the article 18 and
its interior components. Because the inner tube 20 directly
contacts the fluid, the material from which the inner tube 20 is
formed must be chemically compatible with the fluid contained by
the article 18. As a result, various materials may be employed for
the inner tube 20, including nitrile-butadiene, chloroprene,
copolymer of ethylene and propylene, polytetrafluoroethylene
(PTFE), etc. The reinforcement layer generally promotes the
strength of the article 18. Any number of reinforcement layers may
be present in the article 18, and reinforcement layers may be
constructed from a variety of materials in a variety of
configurations. Typical materials include metals such as steels,
bronze, and aluminum, synthetic materials such as rayon, nylon,
polyethylene terephthalate (PET) fiber, and glass fiber, and
textile yarns such as cotton. If multiple reinforcement layers are
used, rubber separation layers may be placed between the
reinforcement layer to reduce abrasion and wear there between.
Suitable materials for the outer cover 19 will depend on the
operating environment of the article 18 with typical materials
including synthetic rubbers.
[0034] As illustrated in FIG. 2, the sensor sleeve 10 includes a
first electrode layer 14 covering at least a portion of a surface
of an article 18. An insulator (dielectric) layer 12 covers a least
a portion of the first electrode layer 14. A second electrode layer
16 is illustrated covering at least a portion of the dielectric
layer 12. When damage to the surface of the article 18 occurs, the
first electrode layer 14 is caused by fluid pressure exerted
through the inner tube 20 and the sidewalls of the article 18 to
contact the second electrode layer 16. When the electrode layers
14, 16 make contact, the impedance measured between the electrode
layers decreases from the mega-Ohms range when the electrode layers
14, 16 are not in contact (and isolated) to near zero when the
electrode layers 14, 16 are in contact with each other.
[0035] The sensor sleeve 10 is also responsive to damage caused by
external sources (e.g., force impact). When damage to the electrode
layer 16 occurs, the electrode layer 16 is caused by the external
force to penetrate the insulator layer 12 and contact the first
electrode layer 14. When the electrode layers 14, 16 make contact,
the impedance measured between the electrode layers decreases from
the mega-Ohms range when the electrode layers 14, 16 are not in
contact (and isolated) to near zero when the electrode layers 14,
16 are in contact with each other.
[0036] In order to facilitate contact between the electrode layers
14, 16, one or more of the electrode layers may include contacts 22
(also referred to herein as protrusions, penetrators, etc.)
embedded in and/or formed from the electrode layer 14, 16. For
example, referring to FIGS. 3 and 4, the electrode layer 14 may
include one or more contacts 22 spaced apart, wherein the contacts
are configured to puncture through the dielectric layer 12 and make
contact with the second electrode layer 16 when a crack and/or leak
develops in the article 18.
[0037] Any shape of contact 22 may be used in accordance with
aspects of the present invention. For example, as shown in FIG. 3,
the contacts 22 have a saw-tooth shape. With respect to FIG. 4, the
contacts 22 have a semi-circle shape. One of ordinary skill in the
art will readily appreciate that the contacts 22 may be any desired
size and shape and may be dependent on application. Likewise, the
contacts 22 may be spaced apart a prescribed uniform distance
and/or a non-uniform distance. The contacts 22 facilitate contact
between the electrode layers 14, 16 upon initiation of a damage
condition associate with the article 18. In another embodiment,
illustrated in FIG. 5, the contacts 22 may take the form of a wire
embedded in the dielectric layer 12, for example.
[0038] The sensor sleeve 10 may be designed to change electrical
impedance (or resistance) due to a fluid pressure (e.g., oil
pressure) initiating a pin hole through the sensor sleeve 10. The
sensor sleeve 10 will detect the fluid leak when the pin hole
penetrates the sensor sleeve 10 and brings the two elastic
electrode layer 14, 16 in contact with each other. The flexibility,
thickness and geometry of the electrode layers 14, 16 should be
designed based on the material the sensor sleeve is monitoring,
e.g. an article in the form of a hydraulic hose. As an example, to
monitor a composite material for impact damage, the sensor skin may
have thinner and stiffer electrode layers to match the mechanical
impedance (stiffness) of the base composite material (e.g., the
components that form the hose, composite airplane wing, etc.).
[0039] As set forth above, the sensor sleeve 10 utilizes an
electrical impedance approach to detect small initiating damage
over large surfaces. As stated above, the sensor skin includes two
electrode layers 14, 16 separated by an insulator layer 12 (e.g., a
dielectric material), thereby forming a capacitor. The sensor
sleeve 10 is thin (e.g., 10-1000 microns thick) and can be
attached, sprayed, extruded and/or co-extruded onto the surface of
an article 18. Exemplary articles in accordance with aspect of the
present invention include: a hose assembly, tire assembly, belt
assembly, etc. Electrical impedance measurements are used to detect
damage to the sensor sleeve 10 due to impact or high pressure, or
cracking of the article underneath the sleeve. Such damage will
puncture the dielectric layer 12, which results in the electrode
layers 14, 16 contacting each other. This contact will cause the
electrical impedance of the sensor sleeve 10 to change from
initially a high impedance range (e.g., Mega-Ohms, Kilo-Ohms, etc.)
to near zero, for example. Thus, initiating damage can be
identified early and the component can be repaired or taken out of
service before it fails.
[0040] Advantages of the sensor sleeve 10 include that it can
detect a small amount of damage over very large areas that may have
complex structural shapes and features, and only one or a small
number of channels of data acquisition are needed to monitor the
impedance. The sensor sleeve 10 can be very low cost and tailored
to each application. No damage from external loading can occur to
the structure without first being detected by the change in
impedance of the sensor sleeve 10 or by damage to the sensor sleeve
10.
[0041] The type of material for the dielectric layer may include,
for example, silicone rubber, epoxy, nanotube elastomer, plastic,
honeycomb, polymer nanocomposite, etc. Such materials will allow
use of the sensor sleeve 10 for different structural and component
applications including flexible components like hoses, tires and
belts, rigid structures like concrete, and stiff composite
components and structures like aircraft and spacecraft.
[0042] The type of material for the electrode layer may include,
for example, aluminum, steel, titanium, or any other suitable
conductive material. Many variations of the electrode material,
thickness, size of protrusions (e.g. contacts, penetrators, etc.),
and the dielectric material and thickness are possible. A general
guideline is that the mechanical impedance of the sensor sleeve 10
should match the mechanical impedance of the article in which it is
used with. For example, when monitoring composite materials, a
stiffer and thinner sensor sleeve is appropriate because the
displacements and strains may be small and the loads may be large
such as due to impact. For elastomer material, the sensor sleeve
should be softer and thicker because the displacements and strains
are larger and the loads are lower.
[0043] Different electrode configurations are possible for use with
the sensor sleeve. FIG. 6 illustrates an embodiment wherein the
sensor sleeve 10 includes a deformable (e.g. ductile like aluminum)
metals in which the thickness of the electrode can vary so that
damage would cause the outer electrode to deform into, and remain
attached to the inner electrode thus shorting the sensor. Carbon
nanotube arrays on one electrode surface, carbon nanotubes
dispersed in the dielectric or insulator material, and different
shape electrode surfaces could be built using nanotube synthesis on
different substrates, dispersion of nanotubes in polymer and
elastomers, and magnetron sputtering or other thin film deposition
systems can be used to put patterns on the electrodes.
[0044] A few exemplary designs of a sensor sleeve 10 in accordance
with aspects of the present invention are illustrated in FIGS. 6-9.
With respect to FIG. 6, a piezoresistive elastomer or polymer that
changes resistance with pressure and strain is illustrated in the
insulator layer 12. A nanotube elastomer may be one example of such
material. For example, nanotubes are dispersed in the insulator
layer (e.g., within the elastomer/polymer) to provide the
piezoresistivity. If the nanotube loading is at the percolation
level, a large scale change in electrical impedance (or resistance)
will occur with strain. This allows the sensor skin to be used as a
pressure or strain sensor, as opposed to a binary (e.g., fault
condition or no-fault condition) damage sensor.
[0045] FIG. 7 illustrates spike contacts 22 formed in one electrode
layer (e.g., electrode layer 14). When a failure condition arises,
the contacts stay attached to the opposing electrode layer (e.g.,
electrode layer 16).
[0046] FIGS. 8A-8B illustrate use of an auxetic material 30,
similar to a honeycomb material, that has a negative Poisson's
ratio and an elastomer 32 positioned between the auxetic material
to achieve a desired stiffness of the insulator layer 12. In one
embodiment, the auxetic material may be used to provide a
non-linear stiffness dielectric layer. In another embodiment, the
auxetic material 30 may be used to facilitate collapsing of the
sensor if used as an insulating layer. FIG. 8B illustrates the
auxetic material collapsing due to an external impact force
imparted on one portion of the sensor sleeve 10. The external
impact force imparts sufficient force to collapse the auxetic
material and enables the electrode layers 14, 16 to make contact
with each other, which changes the impedance measured between the
electrode layers 14, 16.
[0047] FIG. 9, illustrates a fuse 34 or alarm in series with a
battery (not shown). Once the electrodes contact each other, the
fuse is blown, which interrupts some process or stops the hydraulic
system, or an alarm can sound in place of or with the fuse. Further
implementation of system that uses aspects of this embodiment will
be discussed below.
[0048] Another embodiment of the invention is illustrated in FIGS.
10A and 10B. In FIG. 10, the sensor sleeve 10 is identical to the
sensor sleeve illustrated in FIGS. 1 and 2, except that the
dielectric layer 12 is made of a porous and non-absorbent material.
Such material may include, for example, a mesh fabric made of
nylon, acrylic, polyester, or acetate, such material may also
include porous polymers. Such a dielectric layer 12 allows fluid
leaking from the article (e.g., a hydraulic hose) to create a
conductive path through the dielectric layer and between the first
electrode layer and the second electrode layer, which will change
the impedance measured across the electrode layer 14, 16 from a
high impedance range (e.g., mega-Ohms, kilo-Ohms, etc) to near zero
Ohms. The dielectric layer 12 has conductive coating (e.g.,
electrode layers 14, 16) coated on both sides of the surface of the
layer 12. Since the fabric is non-conductive, porous and
non-absorbent, fluid leakage (conductive fluid) will be trapped in
the pores and create a conductive path between the coating layers
14, 16. Therefore, the impedance (e.g., resistance) between the
layers 14, 16 drops. Benefits of such sensor sleeve include
detecting fluid leakage. Such sleeves are durable, sensitive, false
positive resistive, low cost, easily implemented, thin and
lightweight.
[0049] If the location of the leakage is desired, the conductive
layer may have a small resistance. When there is a leakage at a
location, the measured resistance can be correlated with the
distance from the leakage point of the resistive layer to the
measurement point, as illustrated in FIG. 10B (e.g.,
distance=(1/2).times.Resistance/(Resistance/ft)).
[0050] An exemplary system 100 in accordance with aspects of the
present invention is illustrated in FIG. 11. In the system 100,
three embodiments of the sensor sleeve 10 are illustrated. The
article 18-A includes sensor sleeves 10-A and 10-B, which cover a
portion of the article 18A. In article 18-B, the sensor sleeve 10-B
covers substantially the entire article 18B. In article 18-C, the
sensor sleeve 10-C is an internal sensor sleeve integrally formed
in at least a portion of the article 18-C, for example. The sensor
sleeve 10 has one or more couplers 102 that are conductively
coupled to the electrode layers 14, 16 of the sensor sleeve. The
one or more couplers 102 may output their respective signals to a
data acquisition device 104. In addition or alternatively, the one
or more couplers may be coupled to external or internal sensor
sleeves that output their respective signals to the data
acquisition and processing device 104.
[0051] The information received by the data acquisition and
processing device 104 may be stored in memory (not shown). The data
acquisition information may also be compared to operation
parameters 106 associated with the article 18 in which the sensor
sleeve 10 is attached. The operation parameters 106 may be stored
locally, for example by a storage device coupled to data
acquisition and processing device 104 and/or received from a host
server 108 coupled to the system 100. Preferably, the operation
parameters 106 are stored locally. The operation parameters 106 may
vary based on the type of article, environment in which the article
is used, application of the article, etc. Such parameters include
operating temperature, fluid pressure, bending rate, etc. and may
be provided a separate storage device 110, for example.
[0052] The data acquisition and processing device 104 and host
server 108 establish a wired or wireless communication link.
Depending on the system configuration, preferably, data is
processed locally through data acquisition and processing device
104, and only resulting information is sent to host server 108.
Alternatively, data processing can be done at the host server 108,
and device 104 may function solely as a data acquisition device,
for example.
[0053] The host server 108 may include a database of relevant
information associated with the article 18. The host server 108 may
be updated and be utilized to provide information regarding the
operation parameters 106, and establish reporting and aid decision
making in regard to proper maintenance actions. In addition,
information acquired through the data acquisition and processing
device 104 may be stored at the host server 108.
[0054] An exemplary method 120 for detecting failure of an article
illustrated in FIG. 12. At block 122, the method includes
monitoring impedance of an article 18, wherein the article includes
a sensor sleeve 10 including a first electrode layer 14 covering at
least a portion of a surface of the article; a dielectric layer 12
covering a least a portion of the first electrode layer 14; and a
second electrode layer 16 covering at least a portion of the
dielectric layer 12, wherein damage to the surface of the article
covered by the first electrode layer 14, the dielectric layer 12
and the second electrode layer 16 causes the first electrode layer
14 to contact the second electrode layer 16, wherein the impedance
is measured between the first electrode layer and the second
electrode layer.
[0055] At block 124, the method includes detecting a failure in the
article 18 based at least in part on the monitored impedance across
the first electrode layer 14 and the second electrode layer 16. A
failure in the article may be defined as any non-desirable
performance characteristic of the article. In one embodiment, a
failure is detected by comparing the impedance measured across the
first electrode layer and the second electrode layer and when a
prescribed difference in impedance is detected, a failure may be
said to occur. A prescribed difference may be a change in impedance
value of 10% or more, for example. Such a difference in impedance
may occur if one or more contacts in the first electrode layer is
in contact with the second electrode layer, for example.
[0056] In another embodiment, a failure is detected by comparing
the impedance measured across the first electrode layer and the
second electrode layer with a database of information including
operation parameters associated with the article, for example the
host server 108.
[0057] At block 126, upon determining a failure condition, it is
desirable to terminate fluid input to the article and/or terminate
operation of the machinery in which the article is attached.
Therefore, upon failure of the hose, a control signal may be
generated by a processor in the data acquisition and processing
device 104, for example, to turn off machinery and/or flow fluid
associated with the failed article. Thus, the sensor sleeve 10 may
be used in a feedback loop to control one or more processes in
which the article 18 is used. In addition or alternatively, it may
be desired to output an audible notification and/or an electronic
notification that the article has failed upon detecting the failure
of the article.
[0058] An exemplary method 130 is illustrated in FIG. 13 for
detecting conductive fluid leaking in an article. At block 132, the
method includes: monitoring impedance of an article 18, wherein the
article includes a sensor sleeve 10 including a first electrode
layer 14 covering at least a portion of a surface of the article; a
dielectric layer 12 covering a least a portion of the first
electrode layer, wherein the dielectric layer is porous and
non-conductive; and a second electrode layer 16 covering at least a
portion of the dielectric layer, wherein a leak of conductive fluid
creates a conductive path through the dielectric layer 12 and
between the first electrode layer and the second electrode layer,
wherein the impedance is measured between the first electrode layer
and the second electrode layer; and
[0059] At block 134, the method includes detecting the leak of
conductive fluid in the article based at least in part on the
monitored impedance across the first electrode layer and the second
electrode layer. In one embodiment, the leak of conductive fluid is
detected by comparing the impedance measured across the first
electrode layer and the second electrode layer and when a
prescribed difference in impedance is detected, a failure may be
said to occur. A prescribed difference may be a change in impedance
value of 10% or more, for example. Such a difference in impedance
may occur if one or more contacts in the first electrode layer is
in contact with the second electrode layer, for example.
[0060] At block 136, upon determining a fluid leak, it is desirable
to terminate fluid input to the article and/or terminate operation
of the machinery in which the article is attached. Therefore, upon
determination of a failure of the hose, a control signal may be
generated by a processor coupled to the data acquisition device
104, for example, to turn off machinery and/or flow fluid
associated with the failed article. Thus, the sensor sleeve 10 may
be used in a feedback loop to control or more processes in which
the article 18 is used. In addition or alternatively, it may be
desired to output an audible notification and/or an electronic
notification that the article has failed upon detecting the failure
of the article.
[0061] In order to test the above concepts, a simple configuration
of materials for the sensor sleeve was selected and tested to
validate the proof of concept. A rubber sheet was chosen as the
structure that the sensor skin would monitor for damage. The rubber
simulates the material of a hydraulic hose and the sensor is placed
near the inner layer of the hose. The sensor layer would have a
protective rubber layer over it so the sensor skin is not in
contact with hydraulic fluid. The sensor sleeve in this experiment
includes two thin aluminum electrodes, and a dielectric medium
(paper in this case to form a capacitor). Electrical alligator
clamps were attached to the two aluminum electrodes and were also
connected to the measurement device (a multimeter).
[0062] As expected, the initial electrical resistance of the sensor
sleeve 10 was infinite, as there was no contact between the two
electrodes. A probe in the form of a rod having about 1/10 inch
diameter with a rounded tip that was electrically insulated by a
polymer film was used as the tool to produce damage in the sensor
skin.
[0063] When the load and damage was applied to the outer electrode,
the electrical resistance and capacitance changed as the distance
between the two electrodes narrowed. Thus, the closer the
electrodes became to one another, the impedance decreased. The load
was applied continuously until damage (similar to a pin hole)
occurred to the outer electrode. This damage penetrated the
dielectric medium and resulted in the contact of the two aluminum
electrodes. This caused the electrical impedance properties
(resistance and capacitance) of the skin sensor to immediately go
from infinite to zero.
[0064] Different trials were conducted to test the repeatability
and it was observed that every time the damage penetrated through
the electrodes, the resistance went from infinite to zero. A
NI-Data Acquisition module NI-9219 and LabVIEW software were used
to monitor the on-line data and the change in electrical resistance
due to the application of load onto the surface of the outer
electrode. The data obtained from LabVIEW software was then plotted
using Microsoft Excel and is shown in FIG. 14. FIG. 14 clearly
shows the resistance drop from infinite (e.g., 10 KOhms) to zero at
about 14.5 seconds, which is when the damage occurred. A person
having ordinary skill in the art will readily appreciate that
reference to an impedance of infinite means that the impedance is
at least an order of magnitude higher when in a open circuit state
than in a short circuit state, when the impedance is said to be
near zero Ohms, for example.
[0065] Note that as soon as the sensor sleeve is penetrated, the
sensor sleeve reports damage. Still the damage is only to the
sensor sleeve--there is no damage to the underlying rubber layer.
Thus damage is detected before the structure is actually damaged
and this provides time for the operator to repair or take the
structure (e.g. hydraulic hose) out of service.
[0066] The concept of sensor sleeve was tested by using the
electrical impedance, e.g., mainly the electrical resistance, of
the sensor sleeve. Initial experiments were conducted to determine
the feasibility of having an external sensor sleeve on the hose
that could indicate the damage in the hose like pin holes, oil
leak, etc. Aluminum was used as a conductive material and Kapton
film and wax paper were used as different dielectric/insulating
materials for the sensor sleeve. Two different designs were
conceptualized for the hose application.
[0067] Design 1: Sensor sleeve on the outer layer of the hose.
[0068] Design 2: Sensor sleeve between the innermost rubber layer
and steel layer (inside the hose).
[0069] The following section describes the process involved in the
development of sensor skin on the hose. For demonstration purpose,
a section of hose was cut (about 15 cm in length) and a layer of
sensor skin was developed on it. First, the innermost rubber layer
was cut, as shown in FIG. 15A. Next, an insulating layer was glued
to the innermost steel layer with an adhesive. On top of the
insulating layer, a first layer of conductive aluminum was attached
along the length of the hose as shown in FIG. 15B. Next, an
insulating layer (wax paper or Kapton film) was put on top of the
first conductive layer as shown in FIG. 15C. A second conductive
layer was then added on top of the insulating layer thereby forming
the sensor skin as shown in FIG. 15D. Finally, the innermost rubber
layer was attached on top of the sensor skin as shown in FIG. 15E.
Lead wires were attached to the conductive layers for impedance
measurements.
[0070] This design utilizes the concept of developing a sensor
sleeve layer on the outside of the hose. This concept can also be
visualized as putting an external sensor on the hose like the
sensor sleeve. The sensor sleeve can be manufactured as a separate
product and can be placed on top of the outer layer of the hose.
The significant advantage is the simplicity of this design as it is
likely that there would be no modification to the hose itself. The
sensor skin can be protected from the outside environment by
covering the sensor skin with a protective rubber layer probably
like the same polymer material as that of the outer layer of the
hose. By this protective layer, it is possible to prevent any
damage to the sensor skin from any environmental conditions and
might prevent any false positive alarms from the sensor sleeve.
[0071] This design might not prevent damage happening to the hose
because the sensor sleeve is going to identify the damage only
after the hose has failed. But this design will prevent damage
penetrating from the hose to the outside environment. The entire
system can be modeled in such a way that the moment the signal from
the sensor sleeve deviates from the nominal value, an alarm can be
activated or the entire system can be shut down and the hose can be
replaced. This design thus prevents any significant damage to the
outside environment.
[0072] A prototype of this concept was constructed and tested. The
prototype used aluminum as the conductive material and either
Kapton film or wax paper as the insulating material. As described
in the previous section, first layer of aluminum was attached to
the outer layer of the hose followed by the insulating layer and
another conductive aluminum layer on top of the insulating layer.
All the layers were attached to each other using commercially
available adhesive. Lead wires were taken out from the first and
second conductive layers. The electrical impedance between the two
layers could then be measured. Two different orientations of sensor
skin were tested; sensor skin placed along the length of the hose
(FIG. 16A) and the other placed circumferentially (FIG. 16B). For
the second case, it can be visualized as having a sensor sleeve
tape that can be attached circumferentially along the entire length
of the hose.
[0073] Another design is form the sensor sleeve within the hose
assembly. This design utilizes the concept of putting a layer of
sensor sleeve on the inside of the hose. For example, the sensor
sleeve can be built between the innermost rubber layer and first
reinforcement layer. The significant advantage of this design is
that it prevents damage in the hose, as any damage to the hose will
have to penetrate the sensor sleeve. Such penetration will cause
failure of the sensor sleeve. Thus, any damage like pin holes, oil
leak, etc., beyond the innermost rubber layer can be prevented from
occurring and the hose can be inspected and replaced, if
necessary.
[0074] In order to prove the concept, a prototype was developed and
tested. In this experiment, a portion of the inner rubber layer
(about 15 cm in length) was cut thus exposing the steel
reinforcement layer. Then, as described earlier, the layers of the
sensor skin were attached in the proper sequence using the
adhesive, as shown in FIG. 17A. The thickness of the entire sensor
skin comprising of two conductive layers and insulating layer was
only between 10-1000 microns. Finally, the rubber layer was glued
back to its initial position as shown in FIG. 17B. Lead wires were
taken out from the first and second conductive layers and the
electrical impedance between the two layers was measured. The
sensor sleeve was placed in the longitudinal orientation. For this
experiment, there was no end fitting in the hose being tested.
Hence, there was no issue of the electrode layers of the sensor
sleeve coming in contact with each other due to crimping.
[0075] Test results were obtained in LabVIEW to automatically store
the data from the sensor sleeve and indicate the damage occurring
to the sensor skin by activating a LED signal. Two experiments were
conducted; first was to simulate the pin hole damage and second was
to simulate the a fluid leak (e.g., an oil leak). In the first
experiment, a pin hole was simulated using a sharp pointed tool and
the electrical resistance was monitored continuously. The moment
the pin hole damage penetrated through the inner rubber layer and
hit the sensor skin, the resistance dropped from infinite (10.5
k.OMEGA.--maximum resistance capability for NI-DAQ 9219) to zero
and activating the LED signal, which indicated damage to the hose.
It can be observed that the damage did not penetrate the steel
reinforcement layer. This further validates an advantage the sensor
sleeve in predicting and preventing the damage to the hose.
[0076] In the second experiment, an oil leak was simulated by
injecting oil using syringe into the hose until damage occurred.
Approximately, 0.5 to 1 cc of oil was injected to the hose. Similar
to the previous experiment, the resistance dropped from infinite to
zero and activated the LED signal, indicating the damage to the
hose. However, it was difficult to measure the exact amount of oil
injected in the inner rubber layer. The experiments were repeated
for several times and the response was repeatable. The change in
resistance of the sensor sleeve is shown in FIG. 18. It can be seen
that the resistance of the sensor sleeve is consistent when the
hose is in the healthy condition. The sharp drop in resistance can
be seen when the damage occurred to the hose. Similar result was
observed for both pin hole and oil leak situations.
[0077] The sensor sleeve may also be used on a wide range of
structures. For example, the sensor sleeve may be used in
connection aerospace structures like aircraft, satellites, unmanned
vehicles, missiles, etc. The damage to these structures from
external sources like lightning, debris, and large pressure loading
can be detected.
[0078] The sensor sleeve's thinness makes it suitable for such
applications. The sensor sleeve can be made of different materials
to meet the demands of the application such as high or low
temperature, abrasion, electrical conductivity, and corrosion
resistance, for example.
[0079] A sensor sleeve for use on composite materials was
fabricated using a Kapton film sheet between two aluminum film
electrodes (0.016 mm thick), which is one way that a dry capacitor
is formed. Also, wax paper was used as dielectric material and was
placed between the two aluminum electrodes. Initial testing was
performed to validate the proof of concept of the sensor skin using
a hydraulic press. Three different spherical indenters were used in
the experiment to create damage to the sensor sleeve covering the
composite material. In this experiment, the sensor sleeve was
placed on a loading station in the hydraulic press. The spherical
indenter was attached to the top of the loading station. The load
was gradually applied until the sensor sleeve was damaged. The
electrical impedance of the sensor sleeve was measured using a
multimeter as the load was applied. It was observed that the
electrical resistance of the sensor sleeve changed from infinite to
zero as the damage penetrated the dielectric medium and resulted in
the contact of the two electrodes in the sensor skin. At the sensor
sleeve, the composite plate showed indentation damage with the
diameter of indentation measured to be 0.33''.
[0080] The response of the sensor skin versus loading for three
different indenter sizes is shown in FIG. 19. The graph shows
change in the resistance of the sensor sleeve due to loading with
the applied load shown in the x-axis and resistance of the sleeve
shown on the y-axis. It can be seen from the plot that the
electrical resistance of the sleeve was large in the beginning and
the resistance suddenly dropped to zero as the sleeve was damaged
due to loading, due to contact of the two electrodes. It is also
observed that as the diameter of the spherical indenter was
increased (0.187'', 0.374'', 0.55''), the load at which the
resistance of the sensor sleeve changed from infinite to zero also
increased from 1.250 klbs to 4.0 klbs, to 8.5 klbs. It can thus be
concluded that the sensor sleeve is sensitive to any size of
damage. For instance, the sensor sleeve will be sensitive to small
damage like pin holes or large damage from impact with large
particles. Having sensitivity to different size of damage is
explained by considering the stress applied to the sensor sleeve.
The diameter of indentation on the composite is measured and was
found to be 0.128'', 0.23'' and 0.33'' for the 0.187'', 0.374'' and
0.55'' spherical indenters respectively. Then, the stress applied
to the sleeve was calculated by knowing the area of indentation and
the force applied to the sleeve. The applied stress on the sleeve
due to damage was found to be around 680 MPa for all three
spherical indenters. With a small diameter sphere, the area of
indentation is small and the sleeve fails at a small load. With a
larger diameter sphere, the area of indentation is larger and a
larger load is required to cause the sleeve to fail. However, it
was observed that the stress is similar for all cases. The surface
of the fiberglass panel also sustained minor localized spherical
shaped damage but the damage area was smaller than the area of
indentation in the sensor sleeve.
[0081] From this experiment, it can be concluded that the sensor
sleeve had been used as a protective layer to prevent excessive
damage in the composite plate due to continuous loading as the
damage in the composite plate was limited to only 0.0134'' even at
a very high stress level.
[0082] An experiment was also conducted to study the feasibility of
the sensor sleeve to detect impact damage. A fiberglass panel was
simply supported on two angle sections. A spherical indenter (steel
ball) was dropped from a certain height onto the sensor skin and
the variation in the resistance of the sleeve was monitored online
using a data acquisition device and LabVIEW software. It was
observed that the resistance of the sleeve dropped from the M-Ohms
range to zero as the impact resulted in the contact of the two
electrodes. This experiment shows that the sensor skin can detect
dynamic loading and impact damage.
[0083] Although the principles, embodiments and operation of the
present invention have been described in detail herein, this is not
to be construed as being limited to the particular illustrative
forms disclosed. They will thus become apparent to those skilled in
the art that various modifications of the embodiments herein can be
made without departing from the spirit or scope of the
invention.
* * * * *