Note: Descriptions are shown in the official language in which they were submitted.
REMOTE DIGITIZATION OF ELECTROMAGNETIC TELEMETRY SIGNAL
Cross-Reference to Related Applications
[0001] N/A
Field
[0002] The present disclosure relates to technologies in wellbore drilling
operations and more
particularly to systems, apparatus, and methods for transmitting
electromagnetic telemetry signals
to facilitate drilling operations.
Background
[0003] Drilling for hydrocarbons in subterranean formations requires precise
wellbore location,
which often requires the wellbore to follow a complex non-linear path for
maximum resource
recovery. This has been the focus of measurement while drilling (MWD)
technology for several
decades. The goal of all MWD systems is to deliver measurements taken near the
drill bit to the
operators on the surface to allow them to make inform decisions as to well
path, drill bit heading,
formation properties, downhole tool condition, and anything else deemed
important for efficient
drilling. The more information that can be delivered to the operators the
better the drilling
operation can be optimized. One branch of the MWD industry seeks to create and
improve the
downhole sensors, the other branch seeks to maximize the bandwidth and
reliability of the
communication channel between those downhole sensors and the operators at
surface.
[0004] Several general technology modalities exist to convey information from
downhole sensors
to surface, one of which employs a downhole transmitter that encodes binary
information from the
downhole sensor into a modulated sinusoidal signal, then drives current
representing that signal
into the formation. The downhole sensor and the corresponding downhole
transmitter are typically
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located in the bottomhole assembly of the drill string, for example, at the
drill bit. The resulting
electromagnetic (EM) field propagates through the earth in all directions. The
component of the
field that reaches the surface can be detected by measuring the electric
potential between two
points on surface. A signal based on the measured electric potential at
surface is filtered and
processed to recover the best possible estimate of the original signal
generated by the downhole
transmitter.
[0005] With reference to FIG. 1, the above-described technology operates with
a surface receiver
22 located in a structure on the wellsite for drilling a wellbore 32, which is
typically at or near the
drilling rig 30 of the wellbore 32. The surface receiver 22 is networked to
other rig equipment like
the electronic data recorder (EDR) and various remote displays for the
operators' viewing. The
surface receiver 22 houses a sensitive analog-to-digital converter coupled to
cables 26 that run
from the surface receiver 22 out into the surrounding area on surface E and
the cables 26 are
terminated with copper ground stakes 24 driven into the earth. The surface
receiver 22 is
configured to detect the electric potential between the ground stakes 24 and
based on the electric
potential, derive an estimate of the original signal from the downhole
transmitter 34. The exact
placement strategy of the ground stakes 24 is a learned art and can vary from
positions proximal
to the drilling rig 30, to positions far away from the surface receiver 22.
The distance between the
ground stakes 24 and the surface receiver 22 is denoted by the reference
character "D" and the
distance D may range from several feet to several thousand feet.
[0006] Recovery of the original signal by the surface receiver 22 can be
inhibited by any
uncorrelated electrical noise superimposed on the downhole originated signal.
Sources of
electrical noise are primarily from high power electrical equipment, including
for example some
typical equipment at or near the drilling rig. As these equipment all rely on
an earth-ground
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electrical system, the return current always flows through the ground. The
return current
propagates in all directions and is modulated by the mechanical process using
electrical power.
For example, the top drive of a drilling rig is a massive electric motor
ranging in power from 500-
1500hp. The current consumed by the top drive is directly proportional to the
torque output. When
drilling ahead and rotating at a constant RPM the changing, unpredictable
reactionary torque of
the drill string results in a fluctuating torque demand on the motor. These
torque fluctuations are
"encoded" in the current draw and this current returns through the earth
ground to the local
generator. The torque fluctuations are in a similar bandwidth to the frequency
used to encode
downhole sensor data so they cannot be easily filtered out. To address this
issue, MWD operators
attempt to position the ground stakes 24 as far from sources of electrical
noise as possible.
However, because the ground stakes 24 are connected by continuous cables 26 to
the surface
receiver 22, placement of the ground stakes is restricted by the maximum
available length of the
cables, the required effort to drag thousands of feet of cables out to reach
the desired location, and
interception by busy roads, private properties, and impassible terrains.
Consequently, the
placement of the ground stakes 24 is usually a compromise between the above
limiting factors and
the received signal quality.
[0007] Accordingly, the present disclosure aims to address the abovementioned
shortcomings of
the existing EM signal recovery technology.
Summary
[0008] According to a broad aspect of the present disclosure, there is
provided a method
comprising: measuring, by a remote transmitter, an electric potential between
a pair of ground
stakes positioned at a distance from a local receiver located at or near a
drilling rig, the electric
potential providing a first analog signal; converting, by the remote
transmitter, the first analog
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signal into a digital signal that represents the electric potential;
transmitting, by the remote
transmitter, the digital signal wirelessly to the local receiver; and
converting, by the local receiver,
the digital signal into a second analog signal.
[0009] In some embodiments, the method comprises transmitting, by the local
receiver, the second
analog signal to a surface receiver located at or near the drilling rig.
[0010] In some embodiments, transmitting the digital signal wirelessly
comprises transmitting the
digital signal by one or more of: radio transmission, cellular transmission,
and satellite
transmission.
[0011] In some embodiments, the distance ranges from 50 meters to 6000 meters.
[0012] In some embodiments, the method comprises synchronizing, by the remote
transmitter and
the local receiver, the first and second analog signals to maintain a constant
phase shift between
the first and second analog signals.
[0013] In some embodiments, synchronizing comprises: GPS time-stamping, by the
remote
transmitter, the digital signal to provide a time-stamped digital signal;
converting, by the local
receiver, the time-stamped digital signal into the second analog signal; and
transmitting, by the
local receiver, the second analog signal in a timing consistent with the time-
stamped digital signal
according to a GPS clock in the local receiver to a surface receiver located
at or near the drilling
rig.
[0014] According to another broad aspect of the present disclosure, there is
provided a method
comprising: installing a plurality of pairs of ground stakes in the earth,
with each pair of the
plurality of pairs of ground stakes at a respective distance from a local
receiver located at or near
a drilling rig; measuring, by a first remote transmitter, an electric
potential between a first pair of
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the plurality of pairs of ground stakes, the electric potential between the
first pair providing a first
analog signal; converting, by the first remote transmitter, the first analog
signal into a first digital
signal that represents the electric potential between the first pair, the
first digital signal having a
first signal strength; measuring, by a second remote transmitter, an electric
potential between a
second pair of the plurality of pairs of ground stakes, the second pair being
spaced apart from the
first pair, the electric potential between the second pair providing a second
analog signal;
converting, by the second remote transmitter, the second analog signal into a
second digital signal
that represents the electric potential between the second pair, the second
digital signal having a
second signal strength; and one of:
a.
comparing, by the first and second remote transmitters, the first and second
signal
strengths to determine which of the first and second signal strengths is
greater; and if
the first signal strength is greater, transmitting, by the first remote
transmitter, the first
digital signal wirelessly to the local receiver; or if the second signal
strength is greater,
transmitting, by the second remote transmitter, the second digital signal
wirelessly to
the local receiver; and
b.
transmitting, by the first and second remote transmitters, the first and
second digital
signals wirelessly to the local receiver; and comparing, by the local
receiver, the first
and second signal strengths to determine which of the first and second signal
strengths
is greater.
[0015] In some embodiments, the comparing is performed by the first and second
remote
transmitters, and the method comprises converting, by the local receiver, the
first or second digital
signal into a third analog signal.
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[0016] In some embodiments, the comparing is performed by the local receiver,
and the method
comprises: if the first signal strength is greater, converting, by the local
receiver, the first digital
signal into a third analog signal; or if the second signal strength is
greater, converting, by the local
receiver, the second digital signal into the third analog signal.
[0017] In some embodiments, the method comprises transmitting, by the local
receiver, the third
analog signal to a surface receiver located at or near the drilling rig.
[0018] In some embodiments, the respective distance ranges from 50 meters to
6000 meters.
[0019] In some embodiments, installing the plurality of pairs of ground stakes
comprises
positioning at least one pair of the plurality of pairs of ground stakes along
a planned well path of
a wellbore.
[0020] According to another broad aspect of the present disclosure, there is
provided a digitizing
apparatus for use with a surface receiver located at or near a drilling rig
and a pair of ground stakes
installed in the earth at a distance from the surface receiver, the pair of
ground stakes having an
electric potential therebetween, the digitizing apparatus comprises: a remote
transmitter configured
to be coupled to the pair of ground stakes to measure the electric potential
and to generate a digital
signal based on the electric potential; and a local receiver configured to
convert the digital signal
into an analog signal representing the electric potential and to be coupled to
the surface receiver
to transmit the analog signal to the surface receiver, wherein the remote
transmitter is configured
to transmit the digital signal to the local receiver by wireless transmission.
[0021] In some embodiments, the remote transmitter comprises an analog-to-
digital converter for
converting the electric potential into the digital signal, and the local
receiver comprises a digital-
to-analog converter for converting the digital signal into the analog signal.
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[0022] In some embodiments, the remote transmitter comprises a remote radio
transceiver for
transmitting the digital signal via radio transmission, and the local receiver
comprises a local radio
transceiver for receiving the digital signal via radio transmission.
[0023] In some embodiments, the remote transmitter comprises a battery.
[0024] In some embodiments, the remote transmitter comprises a solar panel for
charging the
battery.
[0025] In some embodiments, the remote transmitter is configured to be
portable.
[0026] In some embodiments, the remote transmitter comprises a ruggedized
enclosure for
housing one or more components of the remote transmitter.
[0027] In some embodiments, the local receiver comprises a pair of
differential analog outputs
and the local receiver is configured to be coupled to the surface receiver by
a first set of cables via
the pair of differential analog outputs; and the remote transmitter is
configured to be coupled to
the pair of ground stakes by a second set of cables.
[0028] In some embodiments, the local receiver and remote transmitter each
comprise a respective
GPS clock.
[0029] The details of one or more embodiments are set forth in the description
below. Other
features and advantages will be apparent from the specification and the
claims.
Brief Description of the Drawings
[0030] The invention will now be described by way of an exemplary embodiment
with reference
to the accompanying simplified, diagrammatic, not-to-scale drawings. Any
dimensions provided
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in the drawings are provided only for illustrative purposes, and do not limit
the invention as defined
by the claims. In the drawings:
[0031] Figure 1 is a schematic view of a prior art system for recovering EM
signals from a
downhole transmitter.
[0032] Figure 2 is a schematic view of a system comprising a digitizing
apparatus for recovering
EM signals from the downhole transmitter, according to one embodiment.
[0033] Figure 3 is a schematic view of a system comprising a digitizing
apparatus for recovering
EM signals from the downhole transmitter, according to another embodiment.
[0034] Figure 4 is a schematic view of a remote transmitter usable in the
digitizing apparatus of
FIG. 2, according to one embodiment. In FIG. 4, the remote transmitter is
shown with ground
stakes.
[0035] Figure 5 is a schematic view of a local receiver usable in the
digitizing apparatus of FIG.
2, according to one embodiment. In FIG. 5, the local receiver is shown with a
surface receiver.
Detailed Description of the Embodiments
[0036] When describing the present invention, all terms not defined herein
have their common art-
recognized meanings. To the extent that the following description is of a
specific embodiment or
a particular use of the invention, it is intended to be illustrative only, and
not limiting of the claimed
invention. The following description is intended to cover all alternatives,
modifications and
equivalents that are included in the scope of the invention, as defined in the
appended claims.
[0037] According to embodiments herein, a system is configured to allow more
freedom in the
placement of ground stakes. In general, the system comprises two modules: a
remote digitizing
transmitter and a local synthesis receiver. The digitizing transmitter is
placed near the ground
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stakes and is coupled to the ground stakes by cables. The synthesis receiver
is placed at or near the
drilling rig and is coupled to a conventional surface receiver. The digitizing
transmitter and the
synthesis receiver are configured to communicate with each other wirelessly,
thus collectively
replacing the lengthy cables that connect the surface receiver and the ground
stakes in the prior art
system. The system of the present disclosure and related methods are described
hereinbelow in
greater detail.
[0038] With reference to FIG. 2, a system 120 according to one embodiment of
the present
disclosure has a digitizing apparatus comprising two modules: a local
synthesis receiver 142 and
a remote digitizing transmitter 144. The local synthesis receiver 142 is
operably coupled to and in
communication with a surface receiver 122. The local receiver 142 may be
coupled to the surface
receiver 122 wiredly (for example, via cables 126a) or wirelessly. Cables 126a
may be
conventional cables 26 like those used in prior art system 20. In some
embodiments, the local
receiver 142 may be located at or near the drilling rig 30, along with the
surface receiver 122. In
some embodiments, the surface receiver 122 is the same as or similar to the
surface receiver 22 of
the prior art system 20 in FIG. 1.
[0039] The remote transmitter 144 is operably coupled to and in communication
with ground
stakes 124. The remote transmitter 144 may be wiredly coupled to the ground
stakes 124 via cables
126b. In some embodiments, the ground stakes 124 are the same as or similar to
the copper ground
stakes 24 of the prior art system 20 in FIG. 1. In other embodiments, the
ground stakes 124 may
be any earthed metallic structure, such as an existing well(s), situated near
the downhole
transmitter 34. In some embodiments, the ground stakes 124 are spaced apart by
about 10 meters
to about 50 meters. The remote transmitter 144 may have connections like those
of the prior art
surface receiver 22 of system 20 in FIG. 1 for connecting with cables 126b.
For example, the
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remote transmitter 144 may have two ports for connecting a pair of cables 126b
terminated in
ground stakes 124. Cables 126b may be the same as conventional cables 26 like
those used in
prior art system 20. In some embodiments, cables 126b are shorter than
conventional cables 26
and may be, for example, about 100 meters in length.
[0040] In some embodiments, the remote transmitter 144 is configured to
measure and digitize the
electric potential between the ground stakes 124 into a real-time digital
signal. The electric
potential measured between the ground stakes 124 may be referred to herein as
the "original analog
signal". In some embodiments, instead of copper stakes, an existing well(s)
that is connected to
the remote transmitter 144 may function as the ground stakes 124. Using an
existing well(s) as
.. ground stakes 124 may provide a strong original analog signal if the
existing wells are in close
proximity to the downhole transmitter 34.
[0041] With reference to FIG. 4, in some embodiments, the remote transmitter
144 comprises an
analog-to-digital converter 152 that operates to convert the original analog
signal into a digital
signal. In some embodiments, the remote transmitter 144 comprises power
management hardware
154, a radio transceiver 156, and a battery 158 for supplying power to the
components of the
transmitter 144. In some embodiments, a solar panel 162 is used to charge the
battery 158. In
some embodiments, at least some of the components of the transmitter 144 are
housed in a
ruggedized weatherproof enclosure 160 and the transmitter 144 is configured to
be portable. In
some embodiments, the enclosure 160 may protect the remote transmitter 144
from the elements
such as water, dust, and extreme temperatures. As a skilled person in the art
can appreciate, the
remote transmitter 144 may comprise a processor, a memory, software, hardware,
firmware, and/or
any other component that can facilitate the operation of the transmitter 144.
Date Regue/Date Received 2021-05-28
[0042] Referring back to FIG. 2, the remote transmitter 144 can be placed at a
desired location at
surface E, such as somewhere along the planned well path of the wellbore 32,
at some distance D'
from the remote transmitter 144 away from the rig 30. The remote transmitter
144 is configured to
communicate with the local receiver 142 wirelessly, for example, by radio
transmission via its
.. radio transceiver. Being portable and free of a physical cable connection
to any equipment at or
near the rig 30, the remote transmitter 144, along with the ground stakes 124,
may be placed almost
anywhere along the planned well path with little or no restriction. In a
sample embodiment,
distance D' may range from about 50 meters to about 6000 meters. In another
sample embodiment,
distance D' may range from about 500 meters to about 4000 meters.
.. [0043] With reference to FIG. 5, in some embodiments, the local receiver
142 comprises a digital-
to-analog converter 172 and a radio transceiver 176. In some embodiments, the
local receiver 142
comprises one or more of: a serial port 174, a USB connection port 178, and a
pair of differential
analog outputs 180 for connection to surface receiver 122 via cables 126a. In
some embodiments,
an operator at the rig 30 may connect to the local receiver 142 by wired
connection via the serial
port 174 and/or the USB connection port 178 to adjust operating parameters of
one or both of the
local receiver 142 and the remote transmitter 144 and/or to monitor the status
of the remote
transmitter 144. In other embodiments, the operator may connect to the local
receiver 142 by
wireless connection, such as Wi-fl, cellular, etc., to adjust operating
parameters of one or both of
the local receiver 142 and the remote transmitter 144. In some embodiments,
the local receiver
142 may include or may be connected to a human-machine interface (HMI) (not
shown) to
facilitate the operator's interaction with the local receiver 142. As a
skilled person in the art can
appreciate, the local receiver 142 may comprise a processor, a memory,
software, hardware,
firmware, and/or any other component that can facilitate the operation of the
receiver 142.
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[0044] Referring back to FIG. 2, the remote transmitter 144 operates to
transmit the digital signal
to the local receiver 142 by radio transmission, such as ISM-band radio
transmission. When the
local receiver 142 receives the digital signal by radio transmission via its
radio transceiver, the
digital-to-analog converter of the receiver 142 converts the digital signal
back into an analog signal
(the "converted analog signal") that represents the original analog signal
with high fidelity. In
some embodiments, the remote transmitter 144 processes the digital signal to
improve the quality
thereof prior to transmitting the digital signal to the local receiver 142. In
additional or alternative
embodiments, the local receiver 142 may process the digital signal to improve
specific qualities
thereof before converting the digital signal into the converted analog signal.
The converted analog
signal is then input into the surface receiver 122 via, for example, cables
126a. From the
perspective of the surface receiver 122, the analog signal input is identical
to that provided by the
ground stakes via the conventional cables 26 in the prior art system 20. The
surface receiver 122
can thus process the converted analog signal in the same way as the prior art
surface receiver 22.
In some embodiments, the local receiver 142 and the remote transmitter 144 may
be configured to
communicate with each other by additional or alternative means of wireless
transmission,
including for example cellular, satellite, etc.
[0045] Therefore, existing surface receivers 22 and ground stakes 24 can be
retrofitted with the
digitizing apparatus comprising the local receiver 142 and the remote
transmitter 144 to eliminate
the need for the lengthy conventional cables 26. Further, without the
limitations imposed by the
conventional cables 26, the ground stakes 124 in system 120 can be placed as
far away from the
rig 30 as possible to eliminate or at least reduce corruption of the original
analog signal by the
electrical noise generated by the drilling equipment.
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[0046] Surface receiver 122 synchronizes its decoding algorithm to the input
analog signal without
the benefit of an explicit high-fidelity timing signal. This problem can be
overcome by transmitting
a header pattern in the input signal and performing an autocorrection on
surface with that known
pattern. Then, the resulting timing is assumed for all subsequent data signal.
One drawback of this
approach is that once the surface receiver 122 is synchronized, any temporal
shift in the input
signal will corrupt the decoding. The insertion of the digitizing apparatus in
the signal path between
the downhole transmitter 34 and the surface receiver 122 may introduce a
temporal delay as a
result of wireless communication overhead. If the temporal delay is consistent
then decoding by
the surface receiver 122 will not be adversely affected. A method to maintain
a consistent temporal
delay involves using a GPS clock in each of the remote transmitter 144 and the
local receiver 142.
More specifically, the remote transmitter 144 time-stamps the digital signal
that corresponds to the
original analog signal according to its GPS clock. Upon receiving the time-
stamped digital signal
from the remote transmitter 144, the local receiver 142 outputs the
corresponding analog signal at
a predetermined, consistent time offset to the surface receiver 122 for
processing. Accordingly,
the remote transmitter 144 and the local receiver 142 may be GPS time
synchronized so that the
phase shift between the original analog signal and the converted analog signal
remains constant.
[0047] With reference to FIG. 3, a system 220 according to another embodiment
comprises a
digitizing apparatus comprising a local synthesis receiver 242 and two or more
remote digitizing
transmitters 244a,244b,244c. In the illustrated embodiment, system 220
comprises three remote
transmitters 244a,244b,244c, each terminated at a respective pair of ground
stakes 224a,224b,224c
via cables. It can be appreciated that system 220 may have fewer or more
remote transmitters and
respective pairs of ground stakes in other embodiments. In some embodiments,
each of the remote
transmitters 244a,244b,244c and its respective pair of ground stakes
224a,224b,224c are the same
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as or similar to the remote transmitter 144 and ground stakes 124,
respectively, of system 120
described above with respect to FIG. 2. Each remote transmitter 244a,244b,244c
is configured to
detect an electric potential between the respective pair of grounds stakes
224a,224b,224c and
convert a original analog signal representing the electric potential into a
digital signal. Each remote
transmitter 244a,244b,244c then transmits the digital signal to the local
receiver 242 via radio
transmission. In some embodiments, the pairs of ground stakes 224a,224b,224c
are sporadically
or intermittently placed along the planned well path to provide multiple
measurement points for
the downhole transmitter 34. As the downhole transmitter 34 moves with the
drill bit (not shown)
along the well path, at least one pair of the ground stakes 224a,224b,224c is
closer to the downhole
transmitter 34 than the other ground stakes at any given time. The pair of
ground stakes that is the
closest to the downhole transmitter 34 at a given time is likely to provide
the best quality signal
compared to the other ground stakes, and the corresponding remote transmitter
is likely to generate
the strongest digital signal at that given time. Accordingly, the strength of
the digital signal of each
remote transmitters 244a,244b,244c may indicate the proximity of the
respective ground stakes
224a,224b,224c to the downhole transmitter 34.
[0048] In some embodiments, the local receiver 242 may be the same as or
similar to the local
receiver 142 of system 120 described above with respect to FIG. 2. The local
receiver 242 is
operably coupled to a surface receiver 222 via, for example, cables. Surface
receiver 222 may be
the same as or similar to surface receiver 122 described above with respect to
FIG. 2. In some
embodiments, the remote transmitters 244a,244b,244c are configured to
communicate amongst
themselves to determine which remote transmitter has the strongest digital
signal at any given time
(i.e., which pair of ground stakes 224a, 224b, or 224c is the closest to the
downhole transmitter
34), and only the remote transmitter with the strongest signal transmits its
digital signal to the local
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receiver 242. In alternative embodiments, the local receiver 242 receives the
digital signals from
all the remote transmitters 244a,244b,244c and the local receiver 242 is
configured to determine
which of the received digital signals is the strongest at any given time. The
local receiver 242 then
converts the strongest digital signal at that given time into a converted
analog signal that is input
.. into the surface receiver 222 for processing.
[0049] Unless the context clearly requires otherwise, throughout the
description and the
"comprise", "comprising", and the like are to be construed in an inclusive
sense, as opposed to an
exclusive or exhaustive sense; that is to say, in the sense of "including, but
not limited to";
"connected", "coupled", or any variant thereof, means any connection or
coupling, either direct or
indirect, between two or more elements; the coupling or connection between the
elements can be
physical, logical, or a combination thereof; "herein", "above", "below", and
words of similar
import, when used to describe this specification, shall refer to this
specification as a whole, and
not to any particular portions of this specification; "or", in reference to a
list of two or more items,
covers all of the following interpretations of the word: any of the items in
the list, all of the items
in the list, and any combination of the items in the list; the singular forms
"a", "an", and "the" also
include the meaning of any appropriate plural forms.
[0050] Where a component is referred to above, unless otherwise indicated,
reference to that
component should be interpreted as including as equivalents of that component
any component
which performs the function of the described component (i.e., that is
functionally equivalent),
.. including components which are not structurally equivalent to the disclosed
structure which
performs the function in the illustrated exemplary embodiments.
[0051] The previous description of the disclosed embodiments is provided to
enable any person
skilled in the art to make or use the present invention. Various modifications
to those embodiments
Date Regue/Date Received 2021-05-28
will be readily apparent to those skilled in the art, and the generic
principles defined herein may
be applied to other embodiments without departing from the spirit or scope of
the invention. Thus,
the present invention is not intended to be limited to the embodiments shown
herein but is to be
accorded the full scope consistent with the claims. All structural and
functional equivalents to the
elements of the various embodiments described throughout the disclosure that
are known or later
come to be known to those of ordinary skill in the art are intended to be
encompassed by the
elements of the claims. Moreover, nothing disclosed herein is intended to be
dedicated to the
public regardless of whether such disclosure is explicitly recited in the
claims. It is therefore
intended that the following appended claims and claims hereafter introduced
are interpreted to
include all such modifications, permutations, additions, omissions, and sub-
combinations as may
reasonably be inferred. The scope of the claims should not be limited by the
preferred embodiments
set forth in the examples but should be given the broadest interpretation
consistent with the
description as a whole.
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