U.S. patent application number 13/466216 was filed with the patent office on 2012-12-06 for low-frequency viscosity, density, and viscoelasticity sensor for downhole applications.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Sunil Kumar.
Application Number | 20120304758 13/466216 |
Document ID | / |
Family ID | 47260178 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120304758 |
Kind Code |
A1 |
Kumar; Sunil |
December 6, 2012 |
LOW-FREQUENCY VISCOSITY, DENSITY, AND VISCOELASTICITY SENSOR FOR
DOWNHOLE APPLICATIONS
Abstract
Disclosed is an apparatus for estimating a property of a fluid
downhole. The apparatus includes a carrier configured to be
conveyed through a borehole penetrating the earth. A cantilever is
disposed at the carrier and configured to move in the fluid upon
receiving a stimulus. An actuator is disposed at the cantilever and
configured to provide the stimulus at a frequency less than a
lowest resonant frequency of the cantilever. A sensor is disposed
at the cantilever and configured to sense a strain imposed on the
cantilever due to movement of the cantilever in the fluid in order
to estimate the property.
Inventors: |
Kumar; Sunil; (Celle,
DE) |
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
47260178 |
Appl. No.: |
13/466216 |
Filed: |
May 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61491409 |
May 31, 2011 |
|
|
|
Current U.S.
Class: |
73/152.55 |
Current CPC
Class: |
E21B 49/08 20130101;
G01N 9/002 20130101; G01N 11/16 20130101; E21B 47/00 20130101 |
Class at
Publication: |
73/152.55 |
International
Class: |
E21B 49/08 20060101
E21B049/08 |
Claims
1. An apparatus for estimating a property of a fluid downhole, the
apparatus comprising: a carrier configured to be conveyed through a
borehole penetrating the earth; a cantilever disposed at the
carrier and configured to move in the fluid upon receiving a
stimulus force; an actuator disposed at the cantilever and
configured to provide the stimulus force at a frequency less than a
lowest resonant frequency of the cantilever; and a sensor disposed
at the cantilever and configured to sense a strain imposed on the
cantilever due to movement of the cantilever in the fluid in order
to estimate the property.
2. The apparatus according to claim 1, wherein the property
comprises at least one of density, viscosity, and visco
elasticity.
3. The apparatus according to claim 1, wherein the frequency is
zero Hertz.
4. The apparatus according to claim 3, further comprising a
feedback control circuit configured to receive the strain as input
and to control a signal to the actuator to maintain the strain at a
constant value wherein a change in magnitude of the signal
necessary to maintain the strain at the constant value is used to
derive viscosity or density of the fluid.
5. The apparatus according to claim 1, wherein the cantilever and a
base supporting the cantilever is formed from a substrate.
6. The apparatus according to claim 1, wherein the cantilever
defines a first hole and a second hole with a center bridge element
disposed between the holes, the cantilever further defining a first
side bridge element adjacent to the first hole and a second side
bridge element adjacent to the second hole, the first, second, and
center bridge elements extending from a base to a distal end of the
cantilever.
7. The apparatus according to claim 6, wherein the sensor is
disposed at the center bridge element.
8. The apparatus according to claim 6, wherein sensor comprises a
first sensor disposed at the first side bridge element, a second
sensor disposed at the second side bridge element, and a third
sensor disposed at the center bridge element.
9. The apparatus according to claim 6, wherein the actuator
comprises a conductive element extending from the first side bridge
element to the second side bridge element and configured to conduct
current to interact with a magnetic field in order to move the
cantilever.
10. The apparatus according to claim 6, wherein the actuator
comprises a layer of magnetic material extending from the first
side bridge element to the second side bridge element and
configured to interact with a magnetic field in order to move the
cantilever.
11. The apparatus according to claim 1, wherein the actuator
comprises at least one of a piezoelectric material, a conductive
material, a magnetostrictive material, and a photostrictive
material.
12. The apparatus according to claim 11, wherein the conductive
material is configured to conduct current that interacts with a
magnetic field to move the cantilever.
13. The apparatus according to claim 12, wherein the actuator
further comprises a source of the magnetic field configured to
interact with a current or magnetic material disposed at the
cantilever in order to move the cantilever.
14. The apparatus according to claim 1, further comprising an
electronic device coupled to the actuator and configured to actuate
the actuator at the frequency less than the lowest resonant
frequency of the cantilever.
15. The apparatus according to claim 14, wherein the electronic
device is configured to provide at least one of a voltage, a
current, and light to actuate the actuator.
16. The apparatus according to claim 1, wherein the sensor
comprises a strain gauge.
17. The apparatus according to claim 16, where in the strain gauge
uses a change in resistance or a magnetostrictive effect to measure
the strain.
18. The apparatus according to claim 1, wherein the carrier
comprises at least one of a wireline, a slickline, a drillstring,
and coiled tubing.
19. A method for estimating a property of a fluid downhole, the
method comprising: conveying a carrier through a borehole
penetrating the earth; moving a cantilever in the fluid with an
actuator at a frequency less than a lowest resonant frequency of
the cantilever, the cantilever being disposed at the carrier; and
sensing a strain imposed on the cantilever due to movement of the
cantilever in the fluid using a sensor in order to estimate the
property.
20. The method according to claim 19, wherein the property
comprises at least one of density, viscosity, and
viscoelasticity.
21. The method according to claim 19, wherein sensing comprises
measuring the strain as a function of time with respect to a
stimulus applied to the cantilever by the actuator.
22. The method according to claim 19, wherein the frequency
comprises a first frequency and a second frequency and the strain
comprises a first strain corresponding to movement of the
cantilever at the first frequency and a second strain corresponding
to movement of the cantilever at the second frequency, the first
strain and the second strain being used to identify the fluid and
to estimate viscoelasticity of the fluid.
23. A non-transitory computer-readable medium comprising
computer-executable instructions for estimating a property of a
fluid downhole by implementing a method comprising: moving a
cantilever in the fluid with an actuator at a frequency less than a
lowest resonant frequency of the cantilever, the cantilever being
disposed at the carrier configured to be conveyed through a
borehole penetrating the earth; and sensing a strain imposed on the
cantilever due to movement of the cantilever in the fluid using a
sensor in order to estimate the property.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM
[0001] This application claims the benefit of Provisional
Application No. 61/491,409, entitled "LOW-FREQUENCY VISCOSITY,
DENSITY, AND VISCOELASTICITY SENSOR FOR DOWNHOLE APPLICATIONS",
filed May 31, 2011, which is incorporated herein by reference in
its entirety.
BACKGROUND
[0002] In geophysical industries such as for hydrocarbon
exploration and production, geothermal energy, and carbon
sequestration, it is important to characterize fluids deep in the
earth. Boreholes are drilled into the earth in order to access
these fluids. Borehole tools are then conveyed through the
boreholes to perform measurements on downhole fluids. Typically,
very high pressures and temperatures are encountered by the tools
when they are disposed in a downhole environment.
[0003] Physical properties such as density, viscosity, and
viscoelasticity of downhole fluids are important to know when
performing measurements on particle and polymer laden fluid as in
fracking fluid as well as in some drilling muds. It is also
important to know the density and viscosity of reservoir fluids at
the pressure and temperature of the reservoir in order to determine
the permeability and flow characteristics of the reservoir. It
would be well received in the drilling industry if a sensor would
be developed to measure physical properties of downhole fluids at
ambient conditions.
BRIEF SUMMARY
[0004] Disclosed is an apparatus for estimating a property of a
fluid downhole. The apparatus includes a carrier configured to be
conveyed through a borehole penetrating the earth. A cantilever is
disposed at the carrier and configured to move in the fluid upon
receiving a stimulus force. An actuator is disposed at the
cantilever and configured to provide the stimulus force at a
frequency less than a lowest resonant frequency of the cantilever.
A sensor is disposed at the cantilever and configured to sense a
strain imposed on the cantilever due to movement of the cantilever
in the fluid in order to estimate the property.
[0005] Also disclosed is a method for estimating a property of a
fluid downhole. The method includes conveying a carrier through a
borehole penetrating the earth and moving a cantilever disposed at
the carrier in the fluid with an actuator at a frequency less than
a lowest resonant frequency of the cantilever. The method further
includes sensing a strain imposed on the cantilever due to movement
of the cantilever in the fluid using a sensor in order to estimate
the property.
[0006] Further disclosed is a non-transitory computer-readable
medium having computer-executable instructions for estimating a
property of a fluid downhole by implementing a method that
includes: moving a cantilever in the fluid with an actuator at a
frequency less than a lowest resonant frequency of the cantilever,
the cantilever being disposed at the carrier configured to be
conveyed through a borehole penetrating the earth; and sensing a
strain imposed on the cantilever due to movement of the cantilever
in the fluid using a sensor in order to estimate the property.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The following descriptions should not be considered limiting
in any way. With reference to the accompanying drawings, like
elements are numbered alike:
[0008] FIG. 1 illustrates an exemplary embodiment of a downhole
tool disposed in a borehole penetrating the earth;
[0009] FIG. 2 depicts aspects of an embodiment of a sensor
configured to measure physical properties of a fluid;
[0010] FIG. 3 depicts aspects of another embodiment of a sensor
configured to measure physical properties of a fluid;
[0011] FIG. 4 depicts aspects of a feedback control circuit for
providing a constant strain to the sensor; and
[0012] FIG. 5 presents one example of a method for estimating a
property of a downhole fluid.
DETAILED DESCRIPTION
[0013] A detailed description of one or more embodiments of the
disclosed apparatus and method presented herein by way of
exemplification and not limitation with reference to the
Figures.
[0014] FIG. 1 illustrates an exemplary embodiment of a logging tool
10 disposed in a borehole 2 penetrating the Earth 3. The Earth 3
includes an earth formation 4 that includes layers 4A-4C, each
layer having a property distinguishable from the property of
another layer. As used herein, the term "formation" includes any
subsurface materials of interest that may be analyzed to estimate a
property thereof. The logging tool 10 is supported and conveyed
through the borehole 2 by a carrier 5. In an operation referred to
as wireline logging, the carrier 5 is an armored wireline 6. In
addition to supporting the logging tool 10, the wireline 6 can be
used to communicate information between the logging tool 10 and
equipment at the surface of the Earth 3. In another operation
referred to as logging-while-drilling (LWD), the logging tool 10 is
disposed at a drilling tubular such as a drill string or coiled
tubing and is conveyed through the borehole 2 while the borehole 2
is being drilled. In LWD, the logging tool 10 performs a
measurement of a property of a subsurface material generally during
a temporary halt in drilling.
[0015] Still referring to FIG. 1, the logging tool 10 includes a
formation fluid extraction device 11. The formation fluid
extraction device 11 is configured to extract a sample of a fluid
from the formation 4 through the wall of the borehole 2. The sample
is then provided to an instrument 7, which is configured to perform
a measurement of a physical property of the formation fluid.
Non-limiting examples of the property include density, viscosity,
and viscoelasticity.
[0016] Still referring to FIG. 1, the formation fluid extraction
device 11 includes a probe 12 configured to extend from the device
11 and seal to the wall of the borehole 2. In order to keep the
device 11 in place while sealing, the device 11 includes a brace 13
configured to extend from the device 11 and contact the wall of the
borehole 2 opposite of the location where the sealing is being
performed. After a seal is formed, pressure within the probe 12 is
reduced to extract the fluid from the formation 4 and to cause it
to flow into the device 11 from which it can be provided to the
instrument 7.
[0017] Still referring to FIG. 1, the logging tool 10 includes a
downhole electronics unit 8. The downhole electronics unit 8 can be
configured to operate the logging tool 10 and/or communicate data
14 between the logging tool 10 and a computer processing unit 9 at
the surface of the Earth 3. The data 14 can include measurement
data and/or commands.
[0018] Reference may now be had to FIG. 2, which depicts aspects of
the instrument 7. The instrument 7 includes a cantilever 20
configured to be moved in a fluid of interest by an actuator 21
disposed at the cantilever 20. The cantilever is configured to be
at least partially disposed within the fluid and to move within the
fluid when receiving a stimulus force from the actuator 21.
Movement or deflection of the cantilever 20 can be related to a
physical property of the fluid of interest. In one or more
embodiments, the cantilever 20 extends from a base 22 that can be a
substrate from which both the cantilever 20 and the base 22 are
built. In one or more embodiments, the cantilever 20 moves or
deflects about an edge of the base 22 from which the cantilever 20
extends.
[0019] The actuator 21 can be built integral to the cantilever 20
or the actuator 21 can be attached to the cantilever 20 such as by
an adhesive. In one or more embodiments, the actuator 21 includes
materials that can provide a moving force responsive to a stimulus
applied to the materials. Non-limiting embodiments of materials for
the actuator 21 include electrically conductive materials, magnetic
materials, piezoelectric materials, joule heating materials,
magnetostrictive and photostrictive materials. With a conductive
material, an electric current flowing through the conductive
material can interact with a magnetic field to cause the cantilever
20 to move. With a magnetic material, varying the intensity of an
external magnetic field, such as by varying a magnetizing current
through an electromagnet, can cause the cantilever 20 to move in
relation to the magnitude of the magnetizing current. With a
piezoelectric material, applying a voltage to that material can
cause the cantilever 20 to move. With a magnetostrictive material,
varying an intensity of a magnetic field in that material can cause
the cantilever 20 to move. With a photostrictive material, applying
light to that material can cause the cantilever 20 to move. It can
be appreciated that the various materials used for the actuator 21
can be built integral to (i.e., within) the cantilever 20 or they
can be deposited in one or more layers on the cantilever 20.
[0020] Still referring to FIG. 2, a sensor 24 is disposed at the
cantilever 20 and configured to provide an output responsive to
movement of the cantilever 20. In one or more embodiments, the
sensor 24 is configured to measure a strain of the cantilever 20
caused by movement of the cantilever 20 in the fluid of interest.
Hence, the measured strain of the cantilever 20 is indicative of an
amount of movement, deformation, or flexing of the cantilever
20.
[0021] In one or more embodiments, the sensor 24 is a resistance
strain gauge in which a resistance of the strain gauge is related
to the strain experienced by the strain gauge. In one or more
embodiments of the resistive strain gauge, as the cantilever 20
flexes, the resistance material of the strain gauge either
compresses decreasing total resistance or stretches increasing the
total resistance. Hence, a change of resistance of this strain
gauge is related to a change in the measured strain and
displacement or movement of the cantilever 20. In one or more
embodiments, the sensor 24 is a magnetostrictive strain gauge,
which uses a magnetostrictive material to sense strain. The
magnetostrictive material has a magnetization that is related to
the strain experienced by that material. Thus, in one or more
embodiments, a coil can have a voltage induced in it by a changing
magnetic field of the magnetostrictive material (related to the
changing strain) as the cantilever 20 moves back and forth. As with
the actuator 21, it can be appreciated that the sensor 24 can be
built into the cantilever 20, such as with solid-state electronic
fabrication techniques, or attached post-fabrication such as with
an adhesive.
[0022] Still referring to FIG. 2, the cantilever 20 defines a first
hole (or opening) 25 and a second hole (or opening) 26 and a center
bridge element 29 between the two holes. In addition, the
cantilever 20 in the embodiment of FIG. 2 defines a first side
bridge element 27 and a second side bridge element 28. The bridge
elements extend from the base 22 to a distal end of the cantilever
20. It can be appreciated that actuator(s) 21 and sensor(s) 24 can
be at any of the bridge elements or combination of the bridge
elements.
[0023] As noted above, movement or deflection of the cantilever 20
can be related to a physical property of the fluid of interest.
Generally, measurement of the movement or deflection of the
cantilever 20 as a function of time is made with respect to the
stimulus force applied by the actuator 21. That is, displacement of
the cantilever 20 over time is measured with respect to the
stimulus applied by the actuator 21 in order to determine a damping
factor of the cantilever 20 caused by the fluid of interest.
Movement of the cantilever 20 can include the effects of bulk
movement of the fluid and shearing of the fluid. The bulk movement
is related to the density of the fluid and the shearing is related
to the viscosity of the fluid. It can be appreciated that the sizes
of the holes 25 and 26 can be selected or tuned to predominantly
measure density or viscosity. Smaller holes result in a larger
cross-sectional area of the cantilever 20 for predominantly
measuring density. Larger holes result in a smaller cross-sectional
area of the cantilever 20 for predominantly measuring viscosity. It
can also be appreciated that the size of the holes 25 and 26 can be
selected to provide a balance between measurements of density and
viscosity. It can also be appreciated that holes 25 and 26 provide
insulation between the various materials used for the actuator 21
on the various bridge elements.
[0024] Still referring to FIG. 2, an electronic device 23 is
coupled to the actuator 21 and the sensor 24. The electronic device
23 is configured to apply an electrical, magnetic, or photonic
stimulus to a material of the actuator 21. In order to perform
displacement versus time measurements of movement or deflection of
the cantilever 20, the actuator provides the stimulus at a
frequency less than the lowest resonant frequency of the cantilever
20. This prevents resonance effects from affecting the measurement.
In one or more embodiments, the measurement frequency is zero
Hertz. It can be appreciated that low-frequency measurements
provide for multiple measurements in a short time period resulting
in measurements having increased precision and accuracy in addition
to an increase in the signal-to-noise ratio of the
measurements.
[0025] Reference may now be had to FIG. 3, which depicts aspects of
another embodiment of the cantilever 20. In the embodiment of FIG.
3, a conductive element 31 extends or runs from the first side
bridge element 27 to the second side bridge element 28 in a U-shape
configuration. Current flowing in the conductive element 31
interacts with an external magnetic field created by a magnetic
field source 30 to impart a force on the cantilever 20 causing the
cantilever 20 to move in the fluid of interest. In one or more
embodiments, the magnetic field source 30 is an electromagnet where
the strength of the magnetic field is controlled by a magnetic
field control signal, such as magnetizing current, from the
electronic device 23. Hence, the electronic device 23 can control
the amplitude and the frequency of movement of the cantilever 20 by
controlling magnetizing current to the magnetic field source 30
that is an electromagnet. Further, in the embodiment of FIG. 3,
each of the bridge elements 27, 28 and 29 includes one sensor 24.
It can be appreciated that multiple sensors 24 provide for strain
measurements having increased precision, accuracy, and
signal-to-noise ratio.
[0026] Once measurements of the fluid of interest are performed
using the cantilever 20, the resulting strain measurements of the
cantilever 20 are used to estimate a physical property of the fluid
of interest. Disclosed are at least two methods to estimate the
physical property from the strain measurements. In one method, the
instrument 7 is calibrated in a laboratory using samples of
expected downhole fluids having known physical properties such as
density, viscosity, and viscoelasticity. Hence, a measured response
of the instrument 7 can be compared to the calibrated responses of
the laboratory samples to estimate the physical properties. In
another method, the strain measurements are input into mathematical
relationships that use basic principles to relate the strain
measurements to the physical properties.
[0027] One example of mathematical relationships relating a strain
measurement to density is now presented where .epsilon. represents
the strain measured by the sensor 24 where the sensor 24 is a
resistive strain gauge.
= .DELTA. R / R G GF ##EQU00001##
where .DELTA.R is the change in resistance caused by strain,
R.sub.G is the resistance of the undeformed sensor 24, and GF is
the gauge factor.
.tau. = .mu. u y ##EQU00002##
where .tau. is the shear stress exerted by the fluid (Pa), .mu. is
the fluid viscosity--a constant of proportionality (Pas), and
u y ##EQU00003##
is the velocity gradient perpendicular to the direction of shear,
or equivalently the strain rate (s.sup.-1).
[0028] The shear stress is calculated from the measured strain
using .tau.=.epsilon./A.sub.plate
[0029] where A.sub.plate is the area of the cantilever 20 moving in
the fluid of interest, assuming a pure shear motion. The estimation
of viscosity above is for a Newtonian fluid (temperature and
pressure effects are neglected). For non-Newtonian (viscoelastic)
fluids, the stress is given by a tensor and various models such as
Kelvin-Voigt are used to estimate visco elastic properties.
[0030] In one or more embodiments, the cantilever 20 can be
actuated at two or more different frequencies that provide for
measuring the viscosity of the fluid of interest at two different
shear rates. By measuring the viscosity at two or more different
shear rates, the fluid of interest can be identified and the
viscoelasticity determined.
[0031] In one or more embodiments, the actuation force or stimulus
force applied by the actuator 21 to the cantilever 20 is controlled
to maintain the strain measured by the sensor 24 at a constant
value. The constant value of strain relates to maintaining the
cantilever 20 in a constant position after deflection in the fluid.
A change in the current, voltage, magnetic field, or other
actuation parameter or stimulus signal necessary to maintain the
constant value of strain is then proportional to the damping effect
of the fluid of interest and can be used to derive the viscosity
and density of the fluid. A feedback control circuit 40 as
illustrated in FIG. 4 can be used to control the actuation force to
maintain the constant value of strain and to determine a change in
the actuation parameter or signal necessary to maintain the
constant value of strain. The feedback control circuit 40 receives
an input signal 41 (i.e., feedback signal) from the one or more
sensor(s) 24 and controls a stimulus signal 42 to the actuator 21,
which can include the magnetic field source 30.
[0032] FIG. 5 presents one example of a method 50 for estimating a
physical property of a fluid of interest. The method 50 calls for
(step 51) conveying a carrier through a borehole penetrating the
earth. Further, the method 50 calls for (step 52) moving a
cantilever in the fluid with an actuator at a frequency less than a
lowest resonant frequency of the cantilever, the cantilever being
disposed at the carrier. Further, the method 50 calls for (step 53)
sensing a strain imposed on the cantilever due to movement of the
cantilever in the fluid using a sensor in order to estimate the
property.
[0033] It can be appreciated that solid-state components such as
the cantilever 20, the actuator 21, the sensor 24 and the
electronic device 23 enable the instrument 7 to function in the
high temperature and pressure environment experienced downhole.
[0034] In support of the teachings herein, various analysis
components may be used, including a digital and/or an analog
system. For example, the downhole electronics 8, the surface
computer processing 9, the electronic device 23 or the feedback
control circuit 40 may include the digital and/or analog system.
The system may have components such as a processor, storage media,
memory, input, output, communications link (wired, wireless, pulsed
mud, optical or other), user interfaces, software programs, signal
processors (digital or analog) and other such components (such as
resistors, capacitors, inductors and others) to provide for
operation and analyses of the apparatus and methods disclosed
herein in any of several manners well-appreciated in the art. It is
considered that these teachings may be, but need not be,
implemented in conjunction with a set of computer executable
instructions stored on a non-transitory computer readable medium,
including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic
(disks, hard drives), or any other type that when executed causes a
computer to implement the method of the present invention. These
instructions may provide for equipment operation, control, data
collection and analysis, data and analysis presentation and other
functions deemed relevant by a system designer, owner, user or
other such personnel, in addition to the functions described in
this disclosure.
[0035] Further, various other components may be included and called
upon for providing for aspects of the teachings herein. For
example, a power supply (e.g., at least one of a generator, a
remote supply and a battery), cooling component, heating component,
magnet, electromagnet, sensor, electrode, transmitter, receiver,
transceiver, antenna, controller, optical unit, electrical unit or
electromechanical unit may be included in support of the various
aspects discussed herein or in support of other functions beyond
this disclosure.
[0036] The term "carrier" as used herein means any device, device
component, combination of devices, media and/or member that may be
used to convey, house, support or otherwise facilitate the use of
another device, device component, combination of devices, media
and/or member. Other exemplary non-limiting carriers include drill
strings of the coiled tube type, of the jointed pipe type and any
combination or portion thereof. Other carrier examples include
casing pipes, wirelines, wireline sondes, slickline sondes, drop
shots, bottom-hole-assemblies, drill string inserts, modules,
internal housings and substrate portions thereof.
[0037] Elements of the embodiments have been introduced with either
the articles "a" or "an." The articles are intended to mean that
there are one or more of the elements. The terms "including" and
"having" are intended to be inclusive such that there may be
additional elements other than the elements listed. The conjunction
"or" when used with a list of at least two terms is intended to
mean any term or combination of terms. The terms "first," "second"
and "third" are used to distinguish elements and are not used to
denote a particular order. The term "couple" relates to a first
component being coupled to a second component either directly or
indirectly through an intermediate component. The term "disposed
at" relates to a first component being disposed in or on a second
component.
[0038] It will be recognized that the various components or
technologies may provide certain necessary or beneficial
functionality or features. Accordingly, these functions and
features as may be needed in support of the appended claims and
variations thereof, are recognized as being inherently included as
a part of the teachings herein and a part of the invention
disclosed.
[0039] While the invention has been described with reference to
exemplary embodiments, it will be understood that various changes
may be made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications will be appreciated to adapt a particular
instrument, situation or material to the teachings of the invention
without departing from the essential scope thereof. Therefore, it
is intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *