U.S. patent application number 12/357339 was filed with the patent office on 2009-06-18 for flux orientation locating in a drilling system.
Invention is credited to John E. Mercer.
Application Number | 20090153141 12/357339 |
Document ID | / |
Family ID | 24126297 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090153141 |
Kind Code |
A1 |
Mercer; John E. |
June 18, 2009 |
Flux Orientation Locating in a Drilling System
Abstract
An above ground locator includes an apparatus for determining
the strength of the locating signal at a selected point relative to
the boring tool. The apparatus includes an antenna arrangement
configured for measuring the strength of the locating signal at the
selected point along first and second orthogonally opposed
receiving axes to produce first and second received signals. A
phase shifting arrangement phase shifts the first and second
received signals in a predetermined way to generate first and
second phase shifted signals, respectively. Thereafter, a summing
arrangement adds the first and second phase shifted received
signals to generate an output signal which is a vector sum of the
first and second received signals. In one feature, third and fourth
signals derived from the first and second signals are used to
eliminate balance point ambiguity which is present using the first
and second signals alone. In another feature, signals corresponding
to first, second, third and fourth axes are compared in a way which
confines the possible locations of an above ground point to one
particular type of region out of a plurality of different types of
regions. Tracking of the boring tool may be accomplished in a
number of described ways since the regions occur in a specific
sequence along the intended path with respect to the location of
the boring tool.
Inventors: |
Mercer; John E.; (Kent,
WA) |
Correspondence
Address: |
PRITZKAU PATENT GROUP, LLC
993 GAPTER ROAD
BOULDER
CO
80303
US
|
Family ID: |
24126297 |
Appl. No.: |
12/357339 |
Filed: |
January 21, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11936153 |
Nov 7, 2007 |
7495445 |
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12357339 |
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11561289 |
Nov 17, 2006 |
7309990 |
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11936153 |
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11369404 |
Mar 7, 2006 |
7154273 |
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11561289 |
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10990128 |
Nov 16, 2004 |
7061244 |
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11369404 |
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10747467 |
Dec 29, 2003 |
6838881 |
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10990128 |
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10453375 |
Jun 2, 2003 |
6693429 |
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10747467 |
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10171489 |
Jun 12, 2002 |
6593745 |
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10453375 |
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09533516 |
Mar 23, 2000 |
6417666 |
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10171489 |
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09058981 |
Apr 13, 1998 |
6057687 |
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09533516 |
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08731056 |
Oct 9, 1996 |
5767678 |
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09058981 |
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08442481 |
May 16, 1995 |
5633589 |
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08731056 |
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08259441 |
Jun 14, 1994 |
5444382 |
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08442481 |
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07958941 |
Oct 9, 1992 |
5337002 |
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08259441 |
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07662939 |
Mar 1, 1991 |
5155442 |
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07958941 |
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Current U.S.
Class: |
324/329 |
Current CPC
Class: |
G01V 3/08 20130101; G01V
3/165 20130101; E21B 47/0232 20200501; G01V 3/15 20130101; G01V
3/081 20130101; G01C 9/20 20130101; G01C 9/06 20130101; E21B
47/0228 20200501 |
Class at
Publication: |
324/329 |
International
Class: |
G01V 3/08 20060101
G01V003/08 |
Claims
1. In a technique for at least partially establishing a positional
relationship with respect to a transmitter configured for
transmitting a dipole field, a method comprising: positioning the
transmitter at a depth below the surface of the ground in an
orientation which at least generally establishes a particular
pattern of magnetic fluxlines in relation to the surface of the
ground, such that fore and aft signal points are defined as part of
said particular pattern, each of said fore and aft signal points
having a flux orientation which is normal to the surface of the
ground, and which particular pattern relates in certain ways to a
current position of the transmitter as characterized by a localized
slope of the fluxlines relative to the surface of the ground; and
moving an antenna arrangement, that is responsive to the localized
slope of the fluxlines, through the particular pattern in relation
to the surface of the ground to monitor the localized slope of the
fluxlines for use in generating directional indications relating to
the current position of the transmitter from a current position of
the antenna arrangement.
2. The method of claim 1 further comprising: generating at least
one directional indication and displaying the directional
indication.
3. In a system for at least partially establishing a positional
relationship, an apparatus comprising: a transmitter positioned for
transmitting a dipole field at a depth below the surface of the
ground in an orientation which at least generally establishes a
particular pattern of magnetic fluxlines in relation to the surface
of the ground, such that fore and aft signal points are defined as
part of said particular pattern, each of said fore and aft signal
points having a flux orientation which is normal to the surface of
the ground, and which particular pattern relates in certain ways to
a current position of the transmitter as characterized by a
localized slope of the fluxlines relative to the surface of the
ground; and an antenna arrangement, that is responsive to the
localized slope of the fluxlines, configured for movement through
the pattern in relation to the surface of the ground to monitor the
localized slope of the fluxlines for use in generating directional
indications relating to the current position of the transmitter
from a current position of the antenna arrangement.
4. In a technique for at least partially establishing a positional
relationship with respect to a transmitter configured for
transmitting a dipole field, a method comprising: positioning the
transmitter at a depth below the surface of the ground in an
orientation which at least generally establishes a particular
pattern of magnetic fluxlines in relation to the surface of the
ground, such that fore and aft signal points are defined as part of
said particular pattern, each of said fore and aft signal points
having a flux orientation which is normal to the surface of the
ground, and which particular pattern relates in certain ways to a
current position of the transmitter as characterized by a localized
slope of the fluxlines relative to the surface of the ground; and
moving an antenna arrangement, that is responsive to the localized
slope of the fluxlines, through the particular pattern in relation
to the surface of the ground to monitor the localized slope of the
fluxlines for use in generating directional indications relating to
a current position of at least one of the fore and aft signal
points for the current position of the transmitter from a current
position of the antenna arrangement.
5. In a system for at least partially establishing a positional
relationship with respect to a transmitter configured for
transmitting a dipole field, an apparatus comprising: a transmitter
positioned at a depth below the surface of the ground in an
orientation which at least generally establishes a particular
pattern of magnetic fluxlines in relation to the surface of the
ground, such that fore and aft signal points are defined as part of
said particular pattern, each of said fore and aft signal points
having a flux orientation which is normal to the surface of the
ground, and which particular pattern relates in certain ways to a
current position of the transmitter as characterized by a localized
slope of the fluxlines relative to the surface of the ground; and
an antenna arrangement, that is responsive to the localized slope
of the fluxlines, configured for movement through the pattern in
relation to the surface of the ground to monitor the localized
slope of the fluxlines for use in generating directional
indications relating to a current position of at least one of the
fore and aft signal points for the current position of the
transmitter from a current position of the antenna arrangement.
6. The apparatus of claim 5 further comprising: a display for
displaying said directional indications.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of copending application
Ser. No. 11/936,153 filed on Nov. 7, 2007, which is a continuation
of application Ser. No. 11/561,289 filed on Nov. 17, 2006 and
issued as U.S. Pat. No. 7,309,990 on Dec. 18, 2007; which is a
continuation of application Ser. No. 11/369,404 filed on Mar. 7,
2006 and issued as U.S. Pat. No. 7,154,273 on Dec. 26, 2006; which
is a continuation of application Ser. No. 10/990,128 filed on Nov.
16, 2004 and issued as U.S. Pat. No. 7,061,244 on Jun. 13, 2006;
which is a continuation of application Ser. No. 10/747,467 filed on
Dec. 29, 2003 and issued as U.S. Pat. No. 6,838,881 on Jan. 4,
2005; which is a divisional of application Ser. No. 10/453,375
filed on Jun. 2, 2003 and issued as U.S. Pat. No. 6,693,429 on Feb.
17, 2004; which is a divisional of application Ser. No. 10/171,489,
filed Jun. 12, 2002 and issued as U.S. Pat. No. 6,593,745 on Jul.
15, 2003; which is a divisional of application Ser. No. 09/533,516,
filed Mar. 23, 2000 and issued as U.S. Pat. No. 6,417,666 on Jul.
9, 2002; which is a Continuation-in-Part of application Ser. No.
09/058,981, filed Apr. 13, 1998 and issued as U.S. Pat. No.
6,057,687 on May 2, 2000; which is a Continuation of application
Ser. No. 08/731,056, filed Oct. 9, 1996 and issued as U.S. Pat. No.
5,767,678 on Jun. 16, 1998; which is a Continuation of application
Ser. No. 08/442,481, filed May 16, 1995 and issued as U.S. Pat. No.
5,633,589 on May 27, 1997; which is a Continuation of application
Ser. No. 08/259,441, filed Jun. 14, 1994 and issued as U.S. Pat.
No. 5,444,382 on Aug. 22, 1995; which is a Continuation of
application Ser. No. 07/958,941, filed Oct. 9, 1992 and issued as
U.S. Pat. No. 5,337,002 on Aug. 9, 1994; which is a Continuation-in
Part of application Ser. No. 07/662,939, filed Mar. 1, 1991 and
issue as U.S. Pat. No. 5,155,442 on Oct. 13, 1992, the disclosures
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to apparatus capable of
locating and/or monitoring the position (i.e., the depth below a
surface and the location within the horizontal plane at that depth)
and/or orientation (i.e., yaw, pitch, roll or a combination
thereof) of a device located out of view below a surface. More
specifically, the present invention is directed to locator/monitor
devices that are suitable for use in combination with boring
apparatus.
[0003] Utilities are often supplied from underground lines. Two
techniques are generally used to install such lines. In one
technique, the utility line pathway is excavated; the line is
installed; and the excavated material is replaced. While this
method is suitable for new developments, implementation of this
technique is not always practical in previously developed areas. As
a result, industry development efforts have been focused on
excavating tools capable of installing utilities underground
without surface disruption.
[0004] Several guided and unguided boring tools are currently on
the market. Guided tools require substantially continuous location
and orientation monitoring to provide the necessary steering
information. A prerequisite of such monitoring is, of course,
locating the tool that is to be monitored. Only once the position
of the tool is located can a proper depth measurement be obtained,
for example, from a measuring position directly above the head of
the boring tool which houses a transmitter. Unguided tools would
also benefit from periodic locating or substantially continuous
monitoring, for example, in prevention of significant deviation
from planned tool pathways and close tool approaches to utilities
or other below surface obstructions.
[0005] Locating or monitoring systems currently used in combination
with boring apparatus are either cable locating systems or are
based on cable locating technology. Although the more advanced
systems perform adequately, limitations on cable locating
technology also limit measurement accuracy.
[0006] Most cable locators involve receiver detection of an
oscillating magnetic field derived from electrical current directly
fed or induced onto the cable. The magnetic field lines emanating
from a cable are essentially cylindrical in shape, forming
concentric circles around the cable. As the current flows along the
cable, losses occur as a result of displacement and induced
currents into the soil. Consequently, the exact signal strength of
the magnetic field emanating from the cable at any point is
unknown. Although local signal peaks or nulls (depending on
receiver antennas and electronic configuration) are useful to
determine the surface position directly above the cable, signal
strength (i.e., magnetic field strength) alone is not directly
indicative of cable depth. In certain specific circumstances (i.e.,
when the rate of loss along the cable length is not great), a
signal strength ratio can be used to compute depth. If the cable
run is straight for a long distance (compared to the depth), the
magnetic field strength (B) will be inversely proportional to the
distance (d) from the cable to the receiver (i.e., B alpha. 1/d or
B=k/d, where k is a proportionality constant). By taking two signal
strength readings at different locations directly above the cable,
the proportionality constant can be eliminated and the depth
determined.
[0007] A simple device for determining the depth of a relatively
straight cable is manufactured by Dynatel, a subsidiary of the
Minnesota Mining and Manufacturing Company. The Dynatel device
includes a single antenna, a gain control knob and a gain doubling
switch. The operator determines cable depth by (1) placing the
device on the ground above the cable; and (2) adjusting the output
displayed on a meter with the gain control knob until the meter
needle lines up with a line on the meter scale; (3) doubling the
gain with the switch; and (4) vertically elevating the device until
the output returns to the original value (i.e., the needle realigns
with the meter line referred to in step (2)). Since the magnetic
field strength is inversely proportional to the distance, the
height of the unit above the ground at step (4) is equal to the
depth of the cable. This procedure is accurate, but time consuming.
It also becomes impractical for more deeply buried cables,
requiring the operator to raise the device above his head.
[0008] Other currently used cable locating devices employ two
antennas and logic circuitry to determine depth. The antennas are
separated by a fixed distance. With this known separation distance
and magnetic field strength readings at the antennas, cable depth
can be computed. The difficulty with these devices is that there
are practical limits regarding antenna separation. If the cable
depth is much larger than the antenna separation, which is
generally approximately 12 to 18 inches, signal strength
measurement accuracy becomes more critical. Measurement accuracy is
affected by differential drifting of the electronics associated
with the antennas as well as differential responses of the antennas
themselves.
[0009] Various approaches have been taken to enhance magnetic field
strength measurement precision. The accuracy of these approaches
increases as the number of components common to the two measurement
circuits increases. Current systems accomplish this by taking a
magnetic field reading at one antenna; switching the electronics
connection from one antenna to the other; and measuring the
magnetic field strength at the second antenna. Although this
switching methodology eliminates many sources of error, one major
error source remains--the antennas. To increase sensitivity,
ferrite rods are sometimes employed to enhance the effective
capture area of the antennas. As a result of the antenna
separation, both antennas may not experience the same thermal
environment. The characteristics of ferrite vary measurably with
temperature and are not consistent between rods. Alternatively,
large diameter air-core coils are employed. Such coils eliminate
the inconsistency of the ferrite rods, but still exhibit thermal
drift problems. Air-core coils also are generally larger in
diameter.
[0010] All of these spatially separated two-antenna devices must be
periodically calibrated. Any aging or drifting of an antennas will
cause rapid loss in cable depth measurement accuracy, particularly
at depths that are large compared to antenna separation. In cable
locators, this is generally not a serious problem, since most
cables are buried at depths of less than 2 or 3 times the
separation.
[0011] A device conforming to the above-described arrangement is
available from Radiodetection Ltd. (Bristol, England), the RD300.
The device includes two antennas with horizontal coil axes disposed
a fixed vertical distance from each other. In operation, the device
is placed on the ground, such that a first receiving antenna sensor
is near ground level (e.g., within about 1-2 inches) and a second
receiving antenna is located about 16 inches thereabove. The ground
therefore serves as a reference surface for depth measurement. One
disadvantage of this particular prior art device and other devices
that operate similarly thereto manifests itself when the reference
surface exhibits an obstruction such as a curb, a rock, landscaping
or the like, at a desired measurement location. Under these
circumstances, an operator must compensate for the obstruction to
obtain the depth below the reference surface. Another disadvantage
of this equipment is that the depth measurement process is time
consuming even after the device is properly located above the
transmitter (i.e., a needle must be aligned with a meter line
through a knob-actuated adjustment process). Radiodetection Ltd.
applies this technology to cable, sewer and pipe location as well
as horizontal boring tool monitoring.
[0012] The principal means of locating a boring tool head for
guidance purposes is to place a radio frequency transmitter in the
tool head, and track the tool from the surface using a radio
frequency receiver that detects the alternating magnetic field
emanating from the transmitter.
[0013] While this is similar to the cable-locating situation, the
type of measurement necessary for accurate guided boring differs,
and the requirements therefore are more stringent. Transmitters or
sondes generally emit a dipole magnetic field in the normal
measurement range, which differs from the source or source-like
magnetic field emanating from a utility cable. When a single
horizontal antenna is used to measure the strength of a dipole
magnetic field, that parameter varies as depicted in FIG. 1a.
[0014] A transmitter 10 is located directly below a maximum field
strength point 12. Nulls 14 are present in the horizontal field
directly ahead and behind maximum 12, causing local peaks 16 in
field strength. If a locator/monitor operator were to commence
operations at a location substantially ahead or behind the actual
transmitter 10 location, he might locate one of local peaks 16 and
believe the tool to be directly below. In order to be certain that
field strength maximum 12 has been located when using single
horizontal antenna devices, another peak must be found and
evaluated to be lower in strength (i.e., to be a local peak 16). An
operator failing to take this precautionary measure may conclude
that transmitter 10 is located at a position that leads or trails
its true location. Erroneous depth readings and subsequent
misplacement of the bore typically result.
[0015] A single vertical antenna fares no better. A vertical
antenna will produce a null directly above the transmitter. This
null exists along a line extending on both sides of the
transmitter, however, and therefore cannot be used to locate a
point, such as the transmitter location. Data from a combination of
two antennas may be manipulated to provide a more accurate
indication of transmitter location. An orthogonal set of antennas
can produce the monotonic signal strength variation shown in FIG.
1b.
[0016] When guiding a boring tool, the operator constantly requires
accurate depth measurements, and time consuming procedures, such as
the single antenna cable locator utilizing gain doubling, are
therefore not practical. For tool control purposes, the operator
must be able to determine the depth gradient to ascertain the
direction (i.e., up or down) in which to steer. Gradient
determinations require greater precision than depth measurement.
Also, boring depth may be a factor of 0 or more greater than
practical antenna separation limits of spatially separated two
antenna locators.
[0017] U.S. Pat. No. 7,806,869 issued to Chau et al. discusses a
5-sensor receiver apparatus capable of "locating the position of a
boring device within the ground with respect to a particular
reference location along an above ground path directly over the
intended course" of the boring device. In this receiver, four
sensors are arrayed at the four corners of a square within a
horizontal plane (i.e., parallel to the surface), the midpoint of
which is displaced vertically from the fifth sensor. Chau et al.
indicate that such a receiver is an improvement over a 4-sensor
device designed to locate/monitor electronically conductive cable,
having sensors located at the end points of two intersecting lines
of equal length within a plane that is perpendicular to the
surface.
[0018] The 4-sensor cable-locating apparatus was not designed for
continuous monitoring. Signals from the horizontally placed sensors
are used to locate the transmitter, while signals from the two
vertically aligned sensors are used to determine cable depth. Such
a process is impractical for continuous monitoring.
[0019] In contrast, the 5-sensor apparatus utilizes signals from
the two horizontally disposed sensors, located in the plane
perpendicular to the desired path of the boring device and within
which the boring device is actually positioned, and the vertically
displaced sensor to determine boring device depth and displacement
from its intended path.
[0020] The disadvantage of the 5-sensor device is its complexity.
This device is also susceptible to locating local peaks 16 in the
signal strength. Also, the operator of a 5-sensor device traverses
the desired boring device path, rather than locating a position
directly above the device.
[0021] Again, these 4- and 5-sensor prior art receivers incorporate
sensors that are in fixed spatial positions with respect to each
other. In contrast, U.S. Pat. No. 4,646,277 issued to Bridges et
al. includes a sensing assembly formed of three orthogonal pick up
coils. The sensing assembly of the Bridge et al. patent serves as a
homing beacon for a boring apparatus, rather than a means to
establish the position of the tool head.
[0022] U.S. Pat. No. 3,906,504 issued to Guster et al. describes a
method of locating and plotting tunnels using a portable receiver
to monitor a transmitter moving through the tunnels. Guster et al.
employ an antenna having a vertical axis in the transmitter. While
this antenna configuration eliminates nulls, such an arrangement is
not practical in a boring application, because the head of the
boring apparatus rotates. Signal strength emanating from a
vertically oriented antenna would therefore vary during boring.
[0023] Also, Guster et al. employ very complex mathematics in
determining the distance between the transmitter and the receiver.
The need for a calibration system involving complicated electronics
for use with the Guster et al. system is discussed, without further
explanation, at Column 2 of the patent. The Guster et al. estimate
regarding the complexity of calibration electronics appears to be
accurate in view of the nature of the depth determination employed
in the patent.
[0024] In addition, Guster et al. employ a pulsed transmitted
signal, so as to avoid interference with verbal communication
between the receiver operator and the transmitter operator. Pulsed
transmitted signals complicate the locating/monitoring process
carried out by the receiver.
[0025] Steering a boring device also requires information
concerning pitch (i.e., angle above or below the X-axis in an XY
plane, where the X-axis corresponds to the longitudinal axis of the
boring device and the Y-axis is parallel to the gravity vector).
Several pitch sensors are known and commercially available. Most of
these pitch sensors will not produce a pitch angle independent of
the roll orientation (about the X-axis). Those that can produce a
roll-insensitive signal are generally expensive to produce and
easily damaged by shock loads. Less expensive pitch-sensing devices
are generally not sufficiently sensitive or well damped. Because
equipment loss is common, most users are reluctant to invest a
large amount of money in components that are deployed underground.
Consequently, development of low cost pitch sensors capable of
surviving the loads and environment associated with boring through
soil, rock and debris has been pursued.
[0026] U.S. Pat. No. 4,674,579 issued to Geller et al. describes
two pitch-sensing devices. One apparatus features a transmitter
that includes a mercury switch connected in such a manner that the
transmitter is deactivated when the tip of the housing is upwardly
inclined. The inclination of the tip may be determined by an
operator by measuring the angle of rotation at which the
transmitter switches on and off. This type of pitch-sensing device
is not highly accurate as a result of inaccuracy in measuring the
roll angle of the tool head. This process is also time consuming,
thereby reducing the practicality of implementing such a
methodology.
[0027] The second pitch-sensing device shown in FIG. 8 of and
described in the Geller et al. patent includes a first common
electrode and two pad-electrode assemblies, including the second
and third electrodes, housed within a glass envelope. The glass
tube is partially filled with an electrolytic fluid, such that the
resistance between the second and third electrodes and the first
common electrode varies with the inclination (i.e., pitch) of the
device. This pitch-sensing device can be costly to implement.
[0028] An additional difficulty with locating and monitoring boring
apparatus having a transmitter housed in the boring tool head is
that the structural loads and wear experienced by the tool head
require that the head be fabricated from a high strength material
such as steel or some other metal. Since metals conduct
electricity, a transmitter contained within a metal tool head
induces a current in the metal. This induced current, in turn,
induces a magnetic field that cancels the transmitted field to some
extent and, in some circumstances, entirely.
[0029] In order to allow the signal emitted by the transmitter to
radiate to the surface, one or more windows or openings have been
fabricated or machined into the conductive boring tool head.
Employing this solution structurally weakens the tool head and may
allow debris or ground water to enter the tool head and impinge
upon the transmitter, thereby destroying the antennas and/or the
related electronics. To avoid such debris and water damage and in
an effort to bolster the strength of the windowed tool head, these
openings have been filled with composite, ceramic or plastic
materials, thereby sealing the transmitter and antennas. These
filler materials are not as durable as metal, however, and
generally fail long before a metal structure would fail. Typically,
filler material failure results in costly electronics destruction.
Since the tool structure is weakened by the window, premature tool
head failures resulting in the loss of both the tool head and the
electronics may also occur, however.
[0030] Another difficulty with the use of the window concept is
that the radiated field strength becomes a function of tool head
orientation. Specifically, in a single window configuration, the
field is strongest when emanating from the window and measurably
weaker 180.degree. therefrom. Although this result can be useful in
determining the tool head roll orientation, it makes it impossible
to determine tool depth accurately while drilling, because the tool
head is rotating during drilling. To overcome this restriction,
multiple small window or slot tool head designs have also been used
with mixed success.
[0031] In another attempt to overcome this radiated signal problem,
the entire tool head structure has been formed with non-conductive
materials such as composites and ceramics. Unfortunately, none of
these substitute materials exhibits all of the desirable
characteristics of steel or other durable conductive metals. Strong
ceramics do not handle impact loads as well, while composites do
not take abrasive wear as well. These substitute materials are also
much more costly than metals.
SUMMARY OF THE INVENTION
[0032] The present invention provides a locator/monitor capable of
locating a boring tool head for control purposes. The
locator/monitor of the present invention is compact, portable, easy
to carry and user friendly. Accurate boring tool head depth and
orientation measurements may be obtained through flexible
procedures that may be modified in accordance with the
circumstances under which a measurement is to be made. Precise and
continuous depth and periodically updated orientation measurements
provide the information necessary to locate and steer the tool
head. Depth (i.e., the distance between the reference surface and
the transmitter) may also be presented to an operator of the
locator/monitor of the present invention as range (i.e., a
monotonic function indicative of the distance between the receiver
and the transmitter). Straightforward calibration and expedited
locating methodology may also be implemented using apparatus of the
present invention.
[0033] The locator/monitor of the present invention achieves these
goals through the operation of an antenna assembly featuring two
orthogonal antennas. The antennas are located in spatial proximity
to each other (i.e., they are not disposed a fixed distance apart),
thereby decreasing the size of the locator/monitor and providing
monotonic magnetic field strength information. Once calibrated
(i.e., the value of the proportionality constant k relating
magnetic field strength and range is known), continuous measurement
of range or a gradient thereof, and periodic updated indications of
orientation are possible. No manipulation of equipment controls is
necessary to initiate or continue generating such data.
[0034] Calibration of the locator/monitor of the present invention
is achievable through a simple procedure. An operator need only
locate the transmitter; deploy the receiver of the locator/monitor
of the present invention at a first convenient height above the
transmitter location; measure the magnetic field strength emanating
from the transmitter; deploy the receiver at a second convenient
height; and measure the magnetic field strength emanating from the
transmitter. To permit the value of the proportionality constant to
be determined, an independent indicator of the distance between
magnetic field strength measurement points is provided by
locator/monitors of the present invention. A preferred independent
indicator is an ultrasonic receiver-to surface measurement
system.
[0035] The transmitter may be located in an expeditious manner by
"following" dipole magnetic flux lines to the transmitter (i.e.,
determining the minimum distance to the transmitter, indicated by a
maximum magnetic field strength reading as the receiver is rotated)
in a stepwise fashion. Staged progress is achieved, because dipole
magnetic flux lines are not typically straight line paths to the
transmitter (they are local tangents to the flux line along the
transmitter axis). Sensitivity of this locating procedure can be
enhanced by using the square of the magnetic field strength. Ease
of accomplishing the locating method is increased by a beeper or
visual function designed to indicate passage through a measurement
maximum or to predict such passage. The maximum value may be stored
in memory to permit later comparisons with new measurements, with
beeper or visual indications occurring when a measurement equals or
exceeds that held value. The signal squared procedure may also be
used to determine yaw orientation of the transmitter.
[0036] The present invention also provides a pitch sensor capable
of supplying orientation data for devices such as boring tools. The
pitch sensor of the present invention may also act as a level
reference or an accelerometer. The principal advantages of pitch
sensors of the present invention are durability and cost
effectiveness.
[0037] The pitch sensor of the present invention includes a
conductive central rod, running the length of a conductive
assembly; two sections of conductive tubing separated by a small
gap, where the length of tube sections and gap correspond
collectively to the length of the conductive assembly; and
electrically conductive fluid disposed within the conductive
assembly in an appropriate amount. The amount of conductive fluid
is selected, such that the central rod of the pitch sensor is
contacted by the conductive fluid when the pitch sensor is in a
horizontal position.
[0038] The present invention also provides a transmitter housing
formed of a conductive material such as a metal, where the magnetic
field generated by the transmitter is capable of penetrating to the
surface. In this manner, the structural strength of the housing is
preserved; the electronics are protected from debris and water
infiltration; and a symmetrical magnetic field is produced by the
transmitter.
[0039] Radiated signal strength is enhanced by increasing the
equivalent induced electrical current path length in the conductive
metal transmitter housing of the present invention. This increase
is achieved by the presence of slots in the housing structure.
Preferably, the diameter of the antenna's coil is small in
comparison with the housing diameter. In addition, an increased
number of slots consistent with maintaining the structural
integrity of the housing is also preferred.
[0040] The present invention provides further advantages in a
system for locating a boring tool which is disposed within the
ground in which the boring tool is configured for transmitting a
locating signal. An above ground locator forms part of the system
and includes an apparatus for determining the strength of the
locating signal at a selected point relative to the boring tool.
The apparatus includes an antenna arrangement configured for
measuring the strength of the locating signal at the selected point
along first and second orthogonally opposed receiving axes to
produce first and second received signals. A phase shifting
arrangement phase shifts the first and second received signals in a
predetermined way to generate first and second phase shifted
signals, respectively. Thereafter, a summing arrangement adds the
first and second phase shifted received signals to generate an
output signal which is a vector sum of the first and second
received signals.
[0041] In one aspect of the invention, an antenna pair including
first and second orthogonal antennas define an antenna plane. The
first and second antennas generate first and second signals,
respectively, from the locating signal such that, for an initial
fixed orientation of the antenna pair relative to the particular
path, in which the antenna plane extends generally along the
particular path, the locating signal exhibits two different types
of balance points for different above ground positions. At these
balance points, however, the first and second antennas each receive
the locating signal having an equal magnitude such that the
position of the antenna pair is ambiguous as to balance point type.
Accordingly, the present invention provides an improvement for
eliminating ambiguity as to the type of balance point by producing
third and fourth signals in a predetermined way. The third and
fourth signals may be obtained in one way by rotating the antenna
pair by 45.degree. from the initial fixed orientation in the
antenna plane and then measuring the locating signals with the
rotated antenna pair. A determination is made as to which type of
balance point the antenna pair is positioned based on the first,
second, third and fourth signals. In one feature, the third and
fourth signals are not measured, but are generated using the first
and second signals.
[0042] In another aspect of the invention, the signals
corresponding to the first, second, third and fourth axes are
compared in a way which confines the possible locations of the
above ground point to one particular type of region out of a
plurality of different types of regions. The regions are defined
along the intended path of the boring tool by certain
characteristics of the locating signal in proximity to the intended
path and with respect to the boring tool. Tracking of the boring
tool may be accomplished in a number of disclosed ways since the
regions occur in a specific sequence along the intended path with
respect to the location of the boring tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1a indicates magnetic field strength as measured by a
single antenna.
[0044] FIG. 1b indicates magnetic field strength, as measured by
two orthogonal antennas.
[0045] FIG. 2 shows a partial cross-sectional view of a typical
horizontal boring operation.
[0046] FIGS. 3a and 3b show block diagrams of a transmitter of the
locator/monitor of the present invention.
[0047] FIG. 4 shows a cross-sectional view of a boring tool
incorporating a transmitter of the locator/monitor of the present
invention.
[0048] FIGS. 5a and 5b show block diagrams of a receiver of the
locator/monitor of the present invention.
[0049] FIG. 6 shows a cross-sectional view of a pitch sensor of the
present invention.
[0050] FIG. 7 shows an electronic circuit that is capable of
driving a pitch sensor of the present invention.
[0051] FIG. 8 shows typical pitch response curves that a pitch
sensor of the present invention may be designed to emulate.
[0052] FIG. 9 shows a perspective view of a conductive transmitter
housing with a magnetic field transmitting antenna disposed
therein.
[0053] FIG. 10 shows a perspective view of a conductive transmitter
housing of the present invention with a magnetic field transmitting
antenna disposed therein.
[0054] FIG. 11 shows a perspective view of an embodiment of a
receiver of the locator/monitor of the present invention.
[0055] FIG. 12 shows a cross-sectional view of a receiver of an
embodiment of the locator/monitor of the present invention shown in
FIG. 11.
[0056] FIG. 13 is a schematic diagram illustrating a lag
circuit.
[0057] FIG. 14 is a schematic diagram illustrating a lead
circuit.
[0058] FIG. 15 is a schematic diagram illustrating a summing
circuit incorporating the lag and lead circuits of FIGS. 13 and 14,
respectively, wherein the lag circuit receives an input v.sub.i1
and the lead circuit receives an input v.sub.i2.
[0059] FIG. 16 is a vector diagram illustrating a sum of v.sub.i1
and v.sub.i2 performed by the summing circuit of FIG. 15 when
v.sub.i1 and v.sub.i2 are in phase.
[0060] FIG. 17 is a vector diagram illustrating a sum of v.sub.i1
and v.sub.i2 performed by the summing circuit of FIG. 15 when
v.sub.i1 and v.sub.i2 are 180.degree. out of phase.
[0061] FIG. 18 is a schematic diagram illustrating a vector sum
receiver designed in accordance with the present invention which
produces a vector sum signal from the inputs of a pair of
orthogonal antennas.
[0062] FIG. 19 is a schematic diagram illustrating one portion of
the vector sum receiver of FIG. 18 having an LC tank circuit
substituted for an electronic amplifier to show one modification
required in the circuit of FIG. 18 to provide a vector sum circuit
using passive circuitry.
[0063] FIG. 20 is a diagrammatic illustration of a planer
orthogonal antenna arrangement in an "X" configuration for
receiving a locating signal assuming the surface of the ground as
being horizontal in the figure.
[0064] FIG. 21 is a schematic diagram illustrating one embodiment
of a sum and difference generating circuit designed in accordance
with the present invention for use in generating output signals
which may otherwise be obtained from horizontal and vertical
antennas having receiving patterns centered at the center point of
the X antenna configuration of FIG. 20.
[0065] FIG. 22 is a diagrammatic elevational view, in
cross-section, showing a boring tool, its intended path with
reference to the surface of the ground and certain flux lines of a
locating field emanating from the boring tool, shown here to
illustrate characteristics of the slope orientation of the flux
within regions recognized by the present invention for use in the
disclosed highly advantageous locating procedures.
[0066] FIG. 23 is a diagrammatic illustration showing the X antenna
configuration of FIG. 20 in relation to the flux slope orientation
regions recognized by the present invention.
[0067] FIG. 24 is a diagrammatic illustration showing a "+" (plus)
antenna configuration which may be the antennas of FIG. 23 either
physically or, preferably, electronically rotated, shown here to
illustrate the + antenna configuration in relation to the flux
slope orientation regions recognized by the present invention.
[0068] FIG. 25 is a diagrammatic illustration of one possible
display which may be presented on a locating arrangement which
conveys information to an operator including indications in
accordance with the present invention as to the direction of the
various flux orientation regions of FIG. 22 in relation to a
current location of the locating arrangement and the signal
strength of the locating signal. In particular, the locating
arrangement is in a far field flux region.
[0069] FIG. 26 is the display of FIG. 25 after moving the locating
arrangement partially toward the boring tool such that a locate
point target is displayed ahead of a locator icon.
[0070] FIG. 27 is the display of FIG. 25 after still further
movement of the locating arrangement toward the boring tool such
that the locate point target is still closer to the locator
icon.
[0071] FIG. 28 is the display of FIG. 25 showing the locate point
target at the locator icon after moving the locating arrangement to
the indicated locate point.
[0072] FIG. 29 illustrates the appearance of the display of FIG. 25
at the locate point upon actuation of a calibration feature to
store a reference signal strength and showing distance of the
locator above the surface of the ground as well as a predicted
depth of the boring tool and its temperature.
[0073] FIG. 30 is the display of FIG. 25 showing the locate point
target behind the locator icon as the locating arrangement is moved
toward the boring tool beyond the locate point.
[0074] FIG. 31 is the display of FIG. 25 showing the locate point
target still further behind the locator icon as the locator
arrangement is moved increasingly closer to the boring tool.
[0075] FIG. 32 is the display of FIG. 25 showing a locate line at a
distance from the locator icon indicating the position of the
boring tool with possible lateral variation as the locating
arrangement approaches the boring tool.
[0076] FIG. 33 is the display of FIG. 25 showing the locate line
very near the locator icon as the distance to the boring tool is
further reduced.
[0077] FIG. 34 is the display of FIG. 25 showing the locate line
superimposed on the locator icon, indicating that the locator is at
the overhead point directly above the boring tool with possible
lateral variation.
[0078] FIG. 35 illustrates the appearance of the display of FIG. 25
at the overhead point upon actuation of the calibration feature
showing distance of the locator above the surface of the ground as
well as a measured depth of the boring tool and its
temperature.
[0079] FIG. 36 is the display of FIG. 25 showing the locate line
behind the locator icon as the locating arrangement is moved ahead
of the boring tool along its intended path.
[0080] FIG. 37 is the display of FIG. 25 showing the locate line
still further behind the locator icon as movement of the locating
arrangement continues in the forward direction.
[0081] FIG. 38 is the display of FIG. 25 showing an arrow
indication pointing to the rear from the locator icon as the
locating arrangement moves into a far field region ahead of the
boring tool.
[0082] FIG. 39 is a schematic in block diagram form of a locator
manufactured in accordance with the present invention.
DETAILED DESCRIPTION
[0083] While the following preferred aspects of the present
invention are described with reference to use thereof in
combination with boring apparatus operating in a generally
horizontal plane, these aspects are amenable to other uses and
applications, as will be recognized by practitioners in the
relevant arts. For example, the apparatus of the present invention
may be designed to determine the magnetic field strength-depth
relationship based on an inverse proportionality (i.e., magnetic
field strength .alpha. 1/depth) for cable locating purposes.
[0084] Boring apparatus that may be used in combination with the
locator/monitor of the present invention are any apparatus capable
of or modifiable to be capable of generally horizontal boring and
housing a transmitter in a manner allowing a signal emanating from
the transmitter to penetrate sufficiently for surface signal
detection. Such boring apparatus are known and commercially
available. Exemplary boring apparatus useful with the present
invention include Ditch Witch P40 and P80, Tru-Trac, and Jet-Trac
(Charles Machine Works), Direct Line (Straight Line Manufacturing)
or GuideDrill (Utilx, Kent, Wash.).
[0085] A typical horizontal boring operation is shown in FIG. 2.
The operation generally requires two or more operators. A first
operator 20, who may be located in the vicinity of a starting pit
22, is responsible for operation of a boring machine 24. A second
locator/monitor operator 26 is responsible for locating a boring
tool head 28 and determining steering commands therefor. Tool head
28 is guided around an obstacle 30 at a generally constant depth
beneath a reference surface 32 until it reaches a termination pit
34. Locator/monitor operator 26 holds a receiver 36 and uses it to
locate the surface position directly above tool head 28. Once
locator/monitor operator 26 finds this position, receiver 36 is
used to determine the depth of tool head 28. Using a
locator/monitor of the present invention, operator 26 can also
determine the orientation (yaw, pitch and roll) of tool head
28.
[0086] As stated above, the boring apparatus houses the transmitter
component of an embodiment of the locator/monitor of the present
invention that includes a receiver and a transmitter.
Alternatively, the locator/monitor of the present invention may
consist of a receiver component designed to cooperate with a
transmitter that is already in place or has been obtained
separately. In either case, transmitters useful in the present
invention are known and commercially available. Exemplary
transmitters are 10/SC 0412-8 and 10/SC 0322-8 (Radiodetection
Limited, Bristol, England) and Flocator (Utilx, Kent, Wash.). A
preferred transmitter of the present invention includes a pitch and
roll sensor, as described herein. Such preferred transmitters may
be used with other receivers or as accelerometers or level
references in related or unrelated applications.
[0087] Transmitted dipole magnetic fields are preferred for use in
the practice of the present invention, because, in part, such
fields are fairly constant with time. For the low transmission
frequencies used in boring applications, ground attenuation is
generally not significant. In contrast to the horizontal cable
situation, the magnetic field strength-distance relationship for a
dipole magnetic field-generating or -approximating transmitter is
inversely cubic along a straight line from the dipole.
Specifically, the magnetic field strength (B) at a distance (d)
from the transmitter may be represented as follows:
B.alpha.1/d.sup.3
or
B=k/d.sup.3
where k is a proportionality constant related to the transmitter
signal strength. Because of the inverse cube--relationship between
the parameters, the strength of a dipole magnetic field is a very
sensitive indicator of transmitter depth changes. As set forth
above, a proportionality constant based on an inverse relationship
may alternatively be determined for cable locating or other
appropriate applications.
[0088] FIG. 3a shows a block diagram for a preferred embodiment of
transmitter 10 useful in the practice of the present invention.
Transmitter 10 incorporates a low frequency oscillator 40 operating
from about 4 kHz to about 100 kHz, with about 33 kHz preferred.
Oscillator 40 drives an amplifier 42 that is amplitude modulated by
a modulator 44. The modulated output of amplifier 42 drives an
antenna 46. Modulator 44 provides amplifier 42 with a series of
digitally encoded signals derived from a pitch sensor 48 and a roll
sensor 50. Specifically, digital output signals from sensors 48 and
50 are multiplexed by a multiplexer 52 which, in turn, drives a
Dual-Tone MultiFrequency (DTMF) generator 54. The tone pair
produced by DTMF generator 54 modulates the output signal of
modulator 44. Specifically, the output of modulator 44 includes the
carrier and two side tones. A tone pair is preferred over a single
tone as input to modulator 44, because the dual tone requirement
lessens the probability that a random signal could be interpreted
as data by the receiver. In this system, two legitimate tones are
required to constitute data. An analogous system is used in
touch-tone telephones to eliminate noise. While this invention will
be described with reference to a DTMF generator, it should be
understood that other techniques, such as a pulsed signal on a
separate carrier frequency can be used to advantage in this
context.
[0089] A block diagram of an alternative and preferred electronics
configuration of transmitter 10 of the present invention is shown
in FIG. 3b. Transmitter 10 consists of a pitch sensor 48 to measure
the attitude of tool head 28 relative to gravity. Pitch sensor 48
provides an analog signal through line 60 to an A/D converter 62.
The digitized output of A/D converter 62 is fed by a data bus 64 to
multiplexer 52.
[0090] Roll or tool head 28 angle is also measured relative to
gravity by means of roll sensor 50, a 12-position mercury switch.
The output signal of roll sensor 50 is in digital format, so it can
be directly fed to multiplexer 52 by a bus 66. Multiplexer 52 is
switched between buses 64 and 66 by a timer 68. The output signal
of timer 68 is dependent upon oscillator 40 frequency fed to timer
68 by a line 70 (i.e., oscillator 40 frequency is divided to a much
lower frequency by timer 68).
[0091] Multiplexer 52 provides four, 4-bit nibbles of data through
a bus 72 to DTMF generator 54 which produces tone pairs from a
selection of frequencies that differ from the carrier frequency.
For example, tone pairs may be chosen from 8 frequencies below 1
kHz. As a result, the transmitter of the present invention may
employ the same or similar DTMF chips as are used in touch-tone
telephone applications, with the chip being clocked at a slower
frequency by timer 68 than would be the case in a telephone
application. The tone pair is fed to an amplitude modulation
amplifier 74 through a line 76. The output signal from modulation
amplifier 74 controls the voltage of an output amplifier 78 and is
fed to output amplifier 78 through a line 80. Output amplifier 78
is driven, for example, in class D operation (i.e., output
amplifier 78 is turned on and off at the carrier frequency, thereby
decreasing power dissipation) at, for example, 32768 Hz by
oscillator 40. The amplitude modulated signal is fed to a
capacitor-inductor pair (82, 84) operating at series resonance of,
for example, 32768 Hz. Inductor 84 is preferably an antenna
producing a dipole magnetic field. Oscillator 40 frequency may be
any frequency that does not interfere with the DTMF generator 54
tone pair and that is not subject to substantial ground
attenuation.
[0092] Regulated 5 volt power is provided to transmitter 10 by a
voltage-controlled switching regulator 86 to which current is
supplied by a battery 88. The individual components of transmitter
10 are known and commercially available, with the exception of the
preferred pitch sensor described below. As a result, one of
ordinary skill in the art could construct and implement transmitter
10, as contemplated by the present invention.
[0093] A cross-sectional view of transmitter 10 housed within a
typical directional drilling tool head 28 is shown in FIG. 4.
Transmitter 10 is sized and configured for sliding engagement
within an elongated opening 100 formed in a steel tool body 102. A
keyed end section 104 of transmitter 10 consists of a semicircular
element 106 which engages a similar keyed head element 108 located
on tool head 28. Battery 88 is also slidingly engaged within
opening 100 and contacts transmitter 10, thereby making one
electrical connection. The other electrical connection is made
through a spring 110 attached to a remaining drill string 112
through a set of threads 114. One or more elongated slots 116 in
steel tool body 102 provide for penetration of steel tool body 102
by the magnetic field generated by transmitter 10.
[0094] While the interface between transmitter 10 and tool body 102
is described and depicted as a keyway/key arrangement, any other
interfacing mechanism capable of stabilizing transmitter 10 within
tool body 102 at an appropriate orientation may be used. The
appropriate orientation of transmitter 10 is any one in which data
from pitch sensor 48 and roll sensor 50 may be properly related to
the pitch and roll of tool head 28. Similarly, a specific set of
electrical connections and structure for making them are described
and depicted. Any similar mechanism may be employed to achieve this
end. One of ordinary skill in the art could therefore interface
transmitter 10 with boring apparatus 24 and provide power thereto
to produce a dipole magnetic field.
[0095] Receiver 36 of a preferred embodiment of the present
invention involves a single antenna location employing two
orthogonally disposed antennas. If two orthogonal antennas are used
to measure the horizontal and vertical components of a dipole
magnetic field, and those components are vectorially added, the
magnetic field strength varies as shown in FIG. 1b. The orthogonal
pair of receiving antennas provide the total magnetic field
strength in the plane of the orthogonal antennas axes. As a result,
the indicated distance to transmitter 10 will be a monotonic
function of the true distance to transmitter 10 along dipole flux
lines. Once the location directly above transmitter 10 is
determined, a depth reading taken at that position will indicate
the true depth, because the field strength perpendicular to
transmitter 10 is approximately zero at that point.
[0096] The surface location directly above transmitter 10 can be
found by searching for the minimum distance reading on the receiver
36 display. Since the monotonic function exhibits only one peak,
maximum point 12, locator/monitor operator 26 cannot be misled with
respect to transmitter 10 location. Two orthogonal antennas in
close spatial relationship are useful in the practice of the
present invention, because locator/monitor operator 26 almost
always knows the general direction of the bore. If this direction
were also unknown, a third antenna, orthogonal to the plane defined
by the other two, could be incorporated in receiver 36. In the
three-antenna embodiment of receiver 36 of the present invention,
the three dimensional components of the magnetic field strength are
vectorially added to eliminate all ambiguity regarding transmitter
10 position (i.e., true depth or range is indicated at all times,
because the total field is being measured).
[0097] Preferably, the two antennas functioning as depth receivers
in the present invention are oriented such that one is disposed at
a 45.degree. angle to a horizontal plane passing through receiver
36 parallel to the base thereof, and the other is oriented
orthogonally thereto. When the antennas are oriented in this
configuration and are balanced, and receiver 36 is located directly
over transmitter 10, the induced signal (i.e., the amplified
receiving antenna output signal) will be the same for both
antennas. Antennas are not always balanced, however. If the
antennas are not balanced, inaccurate transmitter 10 location will
result.
[0098] As a result, the present invention may include an automatic
antenna balancing means that may be initiated in or as a
prerequisite to receiver 36 modes, such as antenna balancing,
transmitter locating or calibration, for example. Specifically, an
automatic adjustment may be made to amplified antenna output signal
gain of a first antenna to balance it with a second antenna
amplified output. If the output signal from a first antenna
(OS.sub.1) is not equal to the output signal from a second antenna
(OS.sub.2) at a location where it should be equal, OS.sub.1 will be
adjusted by a factor of OS.sub.2/OS.sub.1 for each subsequent
measurement. Consequently, the amplified output signals from the
two antennas (i.e., the antenna/amplifier systems) will be
balanced.
[0099] Antenna balancing may be accomplished at any point relative
to transmitter 10 that equal signal strength is expected at each
antenna. Receiver 36 antenna balancing may be conducted, for
example, at a point directly over transmitter 10, directly behind
or in front of transmitter 10 along the longitudinal axis thereof,
or the like.
[0100] If a spatially-separated, prior art two antenna device is
used with a dipole field, the sensitivity of that device (i.e., the
percentage change in output signal divided by the percentage change
in distance) depends on the ratio of antenna separation to depth.
Measurement sensitivity therefore decreases with increasing depth.
On the other hand, if signal strength alone is used in computation
as contemplated by the present invention, the locator/monitor
measurement sensitivity becomes depth-independent. As a result, a
locator/monitor operating on signal strength in an antenna
separation-insensitive manner, such as that of the present
invention, could be as much as an order of magnitude more sensitive
at a depth of 10 feet. To achieve depth-independent measurement
sensitivity, the proportionality constant relating distance to the
cube root of magnetic field strength must be conveniently
determinable, however.
[0101] The aforementioned factors and parameter relationships
indicate, and the prior art has recognized, that the distance
between transmitter 10 and receiver 36 can be obtained using
magnetic field strength measurements alone once the proportionality
constant has been determined.
[0102] The proportionality constant depends upon a variety of
parameters, such as soil characteristics, tool body attenuation and
battery strength. As a result, locator/monitors of the present
invention should be calibrated (i.e., the proportionality constant
should be determined) before use under new conditions or after a
substantial period of continual use. Since calibration is required
often, a simple procedure therefor, as provided by the present
invention, is desirable.
[0103] A method to accurately determine the proportionality
constant in an antenna separation-insensitive manner is to measure
the magnetic field strength at two positions using a "single
antenna location" device (e.g., two orthogonal antennas disposed in
close spatial proximity), such as the locator/monitor of the
present invention. In such a device, the single antenna location is
moved between two measurement positions by an operator.
Consequently, the spacing between the two measurement positions can
be much larger than that of a spatially separated two-antenna
device, since packaging requirements do not limit the distance
between measurement positions in locator/monitors of the present
invention.
[0104] In the practice of the present invention, the magnetic field
strength (B.sub.1) is measured by the orthogonally disposed
antennas at a first position that is located a distance d.sub.1
from transmitter 10. Similarly, magnetic field strength (B.sub.2)
is measured at a second position that is vertically displaced from
the first position and located a distance d.sub.2 from transmitter
10. If the distance d between the first and second positions is
known, the variables k, d.sub.1 and d.sub.2 may be calculated by
solving the following equations:
B.sub.1=k/d.sub.1.sup.3
B.sub.2=k/d.sub.2.sup.3
d=(d.sub.1-d.sub.2)
An important feature of this process is that d is accurately
ascertainable. As a result, an accurate independent measurement
system is incorporated into receiver 36 of locator/monitors of the
present invention, so that the distance between the two measurement
positions can be determined. The independent distance measuring
means could also be separate from the receiver, but such a
configuration is not preferred.
[0105] One method of achieving such accurate measurement is the use
of an ultrasonic measuring device to precisely reference the
elevation of receiver 36 above surface 32. An ultrasonic system
measures distance by monitoring the time it takes a signal to
travel from an ultrasonic transmitter to the surface and back to an
ultrasonic receiver. A temperature sensor is preferably included in
the ultrasonic measuring device to measure the ambient temperature
and correct for the speed of sound variation with temperature.
Knowing the distance between the measurement locations d and the
two magnetic field strengths B.sub.1 and B.sub.2, the
proportionality constant k and transmitter 10 depth can be
determined.
[0106] FIG. 5a shows a block diagram of a preferred embodiment of a
receiver 36 useful in the present invention. Receiver 36 includes
three separate receiving units: a first range receiver 122, a
second range receiver 124 and a roll/pitch receiver 126. First and
second range receivers 122 and 124 preferably involve antennas
arranged orthogonally with respect to each other, measuring the
vertical and horizontal components, respectively, of the magnetic
field emanating from transmitter 10. Range receivers 122 and 124
have very narrow band-pass filters preferably centered on the
carrier frequency that strip the modulation side-bands from
received signal to provide a steady amplitude carrier signal used
for range computation by a CPU 128. Roll/pitch receiver 126
demodulates the received signal and decodes it into 4-bit nibbles
that provide roll and pitch orientation information.
[0107] The roll-pitch data and the range signals are fed into a CPU
interface 130 that converts the analog signals into digital format
for processing by CPU 128. CPU interface 130 also sets the gain in
range receivers 122 and 124 to maintain the signals in the dynamic
range of an A/D converter within CPU interface 130. CPU interface
130 also accepts signals from switches 132 that control receiver 36
functions. Other functions of CPU interface 130 are to drive a
display system 134, a signal beeper 136 and an ultrasonic ranging
system 138, such as an ultrasonic transducer.
[0108] Antenna range receivers 122 and 124 used in receiver 36 of
the present invention differ from the spatially separated antennas
used in prior art devices. Antenna range receivers 122 and 124
measure different components of the magnetic field emanating from
transmitter 10 and are located in spatial proximity to each
other.
[0109] The block diagram of an alternative and preferred embodiment
of receiver 36 is shown in FIG. 5b. In this embodiment of the
present invention, roll-pitch receiver 126 includes a tuned antenna
system 150 composed of a coil 152 and a variable capacitor 154.
Receiver 126 communicates with CPU 128 through data bus 156 and
data strobes 158. Each range receiver 122, 124 has associated
linear antennas 160 and 162, respectively, which are orthogonally
disposed. The axes of antennas 160 and 162 may, for example, be
offset 45.degree. from a horizontal plane passing through receiver
36 parallel to the base thereof. Gain control buses 164 and 166
permit CPU 128 to set the gain values of range receivers 122 and
124. Range receivers 122 and 124 produce an output voltage related
to the range from receiver 36 to transmitter 10 and the controlled
gain setting of CPU 128. These voltages are fed to a multiplexer
and analog-to-digital (A/D) converter 168 through a set of wires
170 and 172. Multiplexer-A/D converter 168 is controlled by a
control bus 174 from CPU 128. Channel selection is performed by CPU
128 through control bus 174, and the digitized data are returned to
CPU 128 by means of a data bus 176.
[0110] A temperature sensor 180 and associated electronics 178 form
a part of ultrasonic ranging system 181, including an ultrasonic
transmitter 186, an ultrasonic receiver 188 and associated
electronics 182 and 184, respectively. Ultrasonic transmitter 186
generates an ultrasonic pulse of sufficient strength and duration
to facilitate accurate ultrasonic receiver 188-to-surface 32
measurements. Such pulses may, for example, range from about 30 kHz
to about 60 kHz and extend from about 0.25 ms to about 5 ms. A
transmitted ultrasonic pulse of approximately 40 kHz and 1 ms
duration, for example, is initiated by CPU 128 through a strobe
line 190. CPU 128 measures the time between pulse transmission and
pulse return, communicated to CPU 128 through a line 192. CPU 128
then calculates the receiver 36-surface 32 range based on the time
and ambient temperature.
[0111] A control switch 194 provides operator input signals to CPU
128 to control power switching and the various operational modes
(e.g., calibration, location, depth measurement, peak signal
holding, and range compensation).
[0112] Beeper 136 provides operational mode information as well as
confirmation and error signaling. Beeper 136 may also be activated
during transmitter 10 locating processes as described herein. Data
are presented on display 134. Display 134 is preferably configured
to supply information on location and orientation of transmitter 10
as well as receiver 36 battery status. Other useful data may also
be displayed, if desired.
[0113] Receiver 36 is capable of constantly comparing rates of
change (i.e., gradients) of the vectorially added magnetic field
strength components to provide locator/monitor operator 26 with an
indication of his direction of motion relative to transmitter 10
(i.e. toward or away from transmitter 10). Once positioned
substantially directly above transmitter 10, operator 26 can rotate
receiver 36 to the left or right to determine the yaw orientation
of boring apparatus 24 using the displayed field strength rate of
change. This operator 26 position is also appropriate for obtaining
accurate depth measurements.
[0114] The individual components of receiver 36 are known and
commercially available. For example, ultrasonic measurement devices
useful in receiver 36 are ME 251-1603 (Mouser) and P9934-ND and
P9935-ND (Panasonic). As a result, one of ordinary skill in the art
could construct and implement receivers 36 as contemplated by the
present invention.
[0115] Optical means, such as used for camera focusing, or
mechanical means may alternatively be employed to determine the
distance between magnetic field strength measurement positions. One
of ordinary skill in the art would be able to design and implement
these distance measuring means.
[0116] Since receiver 36 of the locator/monitor of the present
invention has only one antenna location, it can be very compact.
The prior art two antenna location systems, for example, must
accommodate the antennas and the fixed separation therebetween.
[0117] The locator/monitor of the present invention is
self-calibrating, in that the proportionality constant between
magnetic field strength and the inverse cube of the distance
between transmitter 10 and receiver 36 can be recomputed at any
time. Recalibration might be undertaken when concern about
transmitter 10 output or ground attenuation deviation, receiver
antennas 122 or 124 alterations resulting from thermal effects, for
example, or when any other concern regarding measurement accuracy
arises. The calibration procedure uses the transmitter signal from
the boring tool, so that the calibration can be conducted during
boring. That is, the calibration process of the present invention
is not so distinct from normal operation as to require a cessation
of normal operation therefor. Since the locator/monitor of the
present invention involves only one antenna location, there is only
one antenna location/electronics path. As a result, only the
linearity of the response in receiver 36 electronics affects
measurement accuracy. Fortunately, with modern electronic circuits,
linearity is generally not a problem.
[0118] Calibration of receiver 36 is performed by holding it close
to surface 32 and switching it into calibration mode as described
herein. Receiver 36 measures field strength and the ultrasonic
range to surface 32. Receiver 36 is raised a vertical distance
above the first measurement location, and a second set of
measurements is recorded. CPU 128 combines the data from the
measurement sets; calculates the range proportionality constant;
and stores the information. Notification of correct calibration
procedures are accomplished by display 134 and beeper 136.
[0119] Digital processing allows for verification of signals by
comparing readings and other tests as described herein. Also, CPU
128 circuitry can compensate for the height that operator 26 holds
receiver 36 above surface 32. This feature is important when
surface 32 obstructions, such as rocks or landscaping, are located
at a measurement position. Such an obstruction falsely alters the
level of surface 32, thereby falsely increasing or decreasing (if
the obstruction is a ditch or hole of some sort) the depth of
transmitter 10. In this situation, operator 26 will employ
ultrasonic ranging system 138 of the locator/monitor of the present
invention at a location adjacent to but free from the obstruction
and at a height greater than that of the obstruction. This distance
measurement is stored in CPU 128 memory. Operator 26 deploys
receiver 36 over the obstruction at substantially the same height
that it was deployed at the closely adjacent location. CPU 128 uses
the stored distance-to-surface value and displays the depth of
transmitter 10 below reference or extended surface 32, despite the
obstruction.
[0120] A preferred pitch sensor useful in the practice of the
present invention is durable and cost effective. Components used to
produce a prototype device were obtained from plumbing supply,
hardware, or hobby stores and constituted standard fittings and
tubing. When used as a pitch sensor for horizontal boring
applications, the sensor of the present invention is insensitive to
roll orientation.
[0121] As shown in FIG. 6, a pitch sensor 200 consists of two
insulating end caps 202 and 204, two outer conductive lengths of
tubing 206 and 208, an insulating center coupling 210, a conductive
central rod or tube 212 and a conductive fluid 214. Conductive
fluid 214 provides a current path between central rod 212 and outer
tubes 206 and 208. Tubes 206 and 208 are prevented from
electrically contacting each other by a gap or ring 216 in center
coupling 210. As pitch sensor 200 orients to mimic the orientation
of tool head 28, conductive fluid 214 flows to one end of sensor
200 or the other. A larger conductive path will exist between
central rod 212 and whichever outer tube 206 or 208 holds the
greater volume of fluid 214. By comparing the conductivities
between central rod 212 and outer tubes 206 and 208, the pitch
angle of pitch sensor 200 can be determined.
[0122] A prototype pitch sensor 200 was constructed from 1/2-inch
cpvc plastic water pipe fittings available from plumbing supply and
hardware stores. End caps 202 and 204 were drilled in a lathe to
accept central rod 212, a 3/16-inch brass tube purchased from a
hobby shop. Outer tubes 206 and 208 were short lengths of standard
copper water tubing. Conductive fluid 214 was glycerin, with a
small quantity of saline solution added to provide for
conductivity. Glycerin exhibits a low freezing point and the
viscosity necessary for sufficient damping. Prototype pitch sensor
200 was cemented together to prevent leakage of fluid 214. The use
of readily available household parts and simple machining allowed
prototype pitch sensor 200 to be manufactured at low cost. One of
ordinary skill in the art would be able to construct pitch sensor
200 of the present invention.
[0123] FIG. 7 shows an electronic circuit 220 capable of driving
pitch sensor 200 and providing a digital output. An analog output
can also be derived from circuit 220 by eliminating an A/D
converter 222. Circuit 220 consists of an oscillator 224 producing
an alternating voltage output. Oscillator 224 may produce any
convenient alternating voltage output. Outputs ranging from about
50 Hz to about 10 kHz are appropriate for use in the practice of
the present invention. For the prototype, the output was a 2 kHz
square wave. The output is a.c. coupled to sensor 200 through a
capacitor 226. Sensor 200 is preferably driven without any d.c.
component to prevent dissociation of conductive fluid 214.
Oscillator 224 output is rectified, filtered and scaled by device
228. Output from device 228 is used as a reference voltage 230 for
A/D converter 222 to compensate for any changes in oscillator 224
output level.
[0124] One outer tube 206 or 208 is coupled to capacitor 226. The
other outer tube 208 or 206, respectively, is connected to an
analog ground 232, provided by an operational amplifier 234. Analog
ground 232 voltage level is sufficiently high that the a.c. peaks
remain within the operational range of circuit 220. This voltage
level is determined by a resistor pair 236 and 238.
[0125] Pitch sensor output 240 is taken from central rod 212 at an
electrical connection 242. Output signal 240 amplitude is related
to the pitch angle of tool head 28. The exact relationship
therebetween is determined by pitch sensor 200 geometry as
discussed herein. Output signal 240 is fed into a peak detector
244, including an operational amplifier 246, a diode rectifier 248
and a capacitor 250. A peak detected signal 252, analog ground 232
and reference signal 230 are fed into A/D converter 222 that
converts the signals to a digital output 254. Since output signal
254 is referenced to oscillator 224 output voltage, any changes in
output signal 254 due to fluctuations in oscillator 224 output
voltage will be cancelled.
[0126] All of the components of electronic circuits 220 capable of
driving pitch sensor 200 are known and commercially available. As a
consequence, a practitioner in the art could implement pitch sensor
200 of the present invention.
[0127] FIG. 8 shows characteristic output signal 254 curves. For
applications where high accuracy over a limited range of pitch is
desired, a curve 260 would be preferred. For applications where a
broad range of pitch is desired, a curve 262 would be preferred.
The variation between curves 260 and 262 is controlled by pitch
sensor 200 geometry. Pitch sensors 200 of the present invention may
be sized and configured to produce an output signal 254 over the
full range of +90 to -90 degrees, if required (e.g., curve 262).
Pitch sensors 200 may also be designed to produce its full output
signal 254 over an extremely small range (e.g., curve 260).
[0128] The alterable geometric parameters are the
length-to-diameter ratio of outer tubes 206 and 208, the diameter
ratio of central rod 212-to-outer tubes 206 and 208 and the
relative level of conductive fluid 214 in pitch sensor 200. A very
narrow, highly sensitive pitch resolution may be achieved by
broadening the separation between outer tubes 206 and 208 and
constructing pitch sensor 200 with a high outer tube 206 and 208
length-to-diameter ratio.
[0129] Other pitch sensor 200 characteristics could be achieved
through structural alternatives thereof. For example, increasing
the amount of fluid 214 in sensor 200 may be undertaken to limit
the voltage range.
[0130] A well-damped output signal 254 can be obtained using a
viscous fluid 214 in sensor 200. Glycerin or a polymer exhibiting
the desired elevated viscosity may be used for this purpose. If a
nonconductive liquid is used to provide the viscosity, a conductive
liquid or a salt must be added to form conductive fluid 214. The
required degree of fluid 214 conductivity required depends on the
associated electronic circuitry 220. Since output signal 254 is
based on a ratio of conductive paths, pitch sensor 200 performance
is insensitive to fluid 214 conductivity. As the conductivity
increases, the drive current from oscillator 224 or circuit 220
shown in FIG. 7 will increase, however. If low power is desired,
then fluid 214 should exhibit low conductivity.
[0131] Sensor 200 can be used as an accelerometer, since an
acceleration along the axis of central rod 212 will cause fluid 214
displacement in the same manner as a pitch rotation. In an
accelerometer application, signal damping assumes greater
significance. As a consequence, viscosity of conductive fluid 214
must be carefully adjusted for this application. Baffles, porous
foam or other known damping devices may be employed to obtain
proper fluid 214 characteristics. Alternatively, fluid 214 may be
replaced with conductive balls or other flowing conductive material
capable of acceleration-induced displacement in the manner of
conductive fluid 214.
[0132] Pitch sensor 200 may be plated with gold or another
appropriate material to prevent corrosion or reaction between
conductive fluid 214 and the internal surfaces of pitch sensor 200.
Such plating would greatly extend the life of sensor 200 and
provide stability to conductive fluid 214 by preventing additional
conductive ions from going into solution.
[0133] As demonstrated above, the geometry of and the geometric
relationships between pitch sensor 200 components dictate the
performance characteristics of pitch sensor 200 of the present
invention. A practitioner in the art would therefore be able to
design and implement an appropriate pitch sensor 200 for the
particular application in which it is to be used.
[0134] Although the discussion above is directed to electrically
conductive fluid 214, a dielectric fluid or other flowing
dielectric medium may also be employed in pitch sensors 200 of the
present invention. In the dielectric fluid embodiment of pitch
sensor 200, a voltage output is derived from a comparison of the
capacitance between outer tubes 206 and 208 and rod 212. A
dielectric fluid useful in the present invention is, for example,
glycerin, petroleum oils and synthetic fluids. Input impedance
should be high, greater than about 10 mega-ohms, for pitch sensors
200 employing dielectric fluids. Since the geometric configuration
of pitch sensor 200 components impacts dielectric fluid sensors 200
in substantially the same manner as conductive fluid 214 sensors
200, and the nature and properties of dielectric fluids are known,
a practitioner in the art would also be able to design and
implement appropriate dielectric pitch sensors 200.
[0135] In another device which operates on the same principle, the
inner conductive member is not located within the first and second
outer conductive members, but is instead located between them. For
example, the inner member can be a cylinder of approximately the
same dimensions as the outer members and be joined to the outer
members by appropriate coupling means. In use, fluid flows from one
of the outer members to the other via the inner member, thereby
altering the conductance or resistance between the inner member and
each of the outer members. These electrical properties can be
measured in much the same manner as described earlier.
[0136] The operational characteristics of this device can be
adjusted by varying the dimensions of the three members, in
particular the length/diameter ratios and the separation between
the conductive members. Also, the sensitivity of the device can be
adjusted by varying the amount of fluid which is placed within the
device.
[0137] FIG. 9 shows a configuration of magnetic transmitting
antenna 46 contained in a conductive housing 270. A magnetic field
272 derived from antenna 46 induces a voltage in housing 270 that
causes electrical current 274 to flow. Current 274 is depicted, for
simplicity, as a single line in FIG. 9, but, in actuality, it is a
distribution on the surface of housing 270 ascertainable from
Maxwell's equations. Surface current 274 induces a counter magnetic
field that tends to cancel field 272 derived from antenna 46. As
the conductivity of housing 270 decreases, the intensity of current
274 decreases, thereby diminishing the countering field intensity.
If a perfect insulating housing 270 were used, no current 274 would
flow, and the entire magnetic field 272 induced by antenna 46 would
radiate unattenuated. Unfortunately, a conductive metal such as
steel produces an amount of current 274 sufficient to virtually
eliminate radiated magnetic field 272.
[0138] FIG. 10 shows a means of reducing surface current 274 in
conductive housing 270 to substantially increase radiated magnetic
field 272. The principal difference between housing 270' (FIG. 10)
and housing 270 (FIG. 9) is that one or more narrow elongated slots
280 are formed in housing 270'. Slots 280 increase current path
length which, because housing 270' is not a perfect conductor, will
increase apparent resistance. This increase in resistance, in turn,
reduces surface current 274 and the resulting, opposing magnetic
field. Alternatively, slots 280 may be replaced by a plurality of
elongated apertures of any configuration sufficient to increase
current path length.
[0139] Slot(s) 280 need only be wide enough to disrupt current 274
flow. Such narrow gap(s) do not readily allow debris penetration
and are easily filled to prevent water intrusion. The filler
material need only be strong enough to withstand the torque loads
on housing 270', or, alternatively, elastic enough to deform in
response to those loads and restore to its original shape once the
loads have been removed. Since slot(s) 280 are narrow, the filler
material is also substantially protected from abrasion caused by
the rock and soil material being bored. Composite or ceramic
materials could therefore be used as filler materials to restore
most of the torsional rigidity and strength to housing 270'.
[0140] As stated previously, antennas 46 useful in transmitter 10
of the present invention are known and commercially available.
Similarly, slotted housing 270' of the present invention may be
fabricated from commercially available steel tubing using known
techniques. As a result, a practitioner in the art would be capable
of producing and implementing slotted housing 270' of the present
invention.
[0141] Housing 270 and 270' tests were conducted using steel tubes
with inside diameters of approximately 1 inch and a 1.25 inch
outside diameter. An antenna consisting of a ferrite rod,
approximately 0.29 inches in diameter by 1 inch long with windings
having an outside diameter of about 0.45 inches, was centrally
placed in each tube. Four tubes were tested having zero slots
(housing 270), one slot (housing 270'), two slots (housing 270')
and four slots (housing 270'). Slots were 0.125 inches wide by 4.5
to 5.5 inches long. Data were taken using a precision receiver of
the present invention located 85 inches from the antenna. Table 1
shows the results of this testing. All signal strengths are
referenced to an antenna not contained in a housing, representing
100% of the signal generated by the antenna.
TABLE-US-00001 TABLE 1 Signal Configuration Signal Ratio
Orientation Strength Strength No cover -- 4.920 0.0 dB No slots --
0.000 -Inf. dB 1 slot 1 1.139 -12.7 dB 2 1.098 -13.0 dB 3 1.060
-13.3 dB 4 1.103 -13.0 dB 2 slots 1 1.945 -8.1 dB 2 1.940 -8.1 dB 4
slots 1 2.835 -4.8 dB 5 2.835 -4.8 dB Orientation Notation 1--Slot
toward receiver 2--Slot perpendicular to receiver (90.degree.)
3--Slot away from receiver 4--Slot perpendicular to receiver
(-90.degree.) 5--Slot 45.degree. to receiver
[0142] The results indicate that the antenna disposed within the
housing without slots (housing 270) generated no measurable signal
at the receiver. One slot (housing 270') allowed about 22% of the
signal to penetrate the housing, with about 0.6 dB variation in
signal strength dependent upon orientation. With 2 slots (housing
270'), virtually no variation in the signal strength with
orientation was observable, and better than 39% of the signal
penetrated the housing. With 4 slots (housing 270'), no variation
in signal strength was observed, and more than 57% of the signal
penetrated the housing.
[0143] Tests with other antennas were conducted to explore other
structural/functional relationships involving housing 270' and
components disposed therein. If the antenna diameter was increased
until it became a large fraction of the inside diameter of housing
270' (approximately 80%), a noticeable loss of Q (i.e., the ratio
of stored energy to dissipated energy) in the antenna and a
substantial decrease in radiated magnetic field were observed. As a
result, the housing diameter is preferably large in comparison to
the antenna diameter.
[0144] An antenna having a core that was 0.2 inches in diameter by
0.72 inches long and an outer winding diameter of 0.40 inches
showed almost identical results for signal strength ratios. This
indicates that slot length-to-antenna length ratio is not critical
beyond a minimum ratio. The ratio of housing 270' inside
diameter-to-antenna diameter does not appear to be critical below a
maximum ratio. Preferred embodiments of the present invention
employ a housing 270' inside diameter-to-antenna diameter ratio of
approximately 2.5 or more. Once these ratios are achieved, the
number of slots and the length thereof assumes greater importance.
An increase in slot number produces narrower conductor paths,
increasing the effective resistance and therefore reducing signal
losses. The length of the slots increase the conductive path length
and therefore increase the resistance. The number of slots in the
cover will be restricted by structural considerations and will vary
from one tool design to another. The minimum slot length
corresponds to approximately 1.5 antenna lengths.
[0145] A preferred receiver 36 of the present invention is shown in
FIG. 11. Receiver 36 is preferably a convenient size for portable
use. Preferred receiver 36 may, for example, be approximately 1
foot square (X and Y dimensions) by approximately 5 inches wide (Z
dimension). A case 290 is formed from a non-magnetic,
non-conductive material such as fiberglass or a styrene plastic,
such as ABS, so that the magnetic field generated by transmitter 10
is able to penetrate case 290 without attenuation. A handle 292 is
provided to allow operator 26 to hold and manipulate receiver 36. A
trigger switch 294 provides all control functions for the operation
of receiver 36 including power switching, calibration, range
compensation and locating functions. Specifically, trigger switch
294 has a variety of settings and/or may be depressed for certain
time periods or at specific times during use to initiate specific
receiver functions or as a prerequisite to such functions. Displays
296, 298 and 300 provide information to operator 26 regarding range
to transmitter 10, transmitter 10 orientation and receiver 36
battery condition. Beeper 136 provides audible cues to facilitate
calibration and locating functions as well as to identify errors in
procedures or functions. Cover plate 302 provides access to
receiver 36 electronics.
[0146] A cross-sectional view of receiver 36 is shown in FIG. 12.
Displays 296, 298 and 300 and associated electronic drives are
arranged on a printed circuit card 304. An orthogonal set of
antennas 122 and 124 are attached to the side of case 290. Power is
supplied by a set of batteries (not shown) loaded into an assembly
306 and held in place by battery cover 308. An additional set of
printed circuit cards 310 are arranged above an electronics
assembly support 312. Attached to electronics assembly support 312
is roll-pitch receiving antenna 126. Two ultrasonic transducers 314
(i.e., ultrasonic transmitter 186 and ultrasonic receiver 188) are
mounted to the bottom of case 290. Temperature sensor 178 is also
mounted to the bottom of case 290.
[0147] Equipment cases having handles, triggers, displays,
battery-containing assemblies and the like are known in the art.
Such equipment may be fabricated from known materials and
components to achieve a portable apparatus. In addition, the
electronic/mechanical interface at trigger switch 294 and
electronics relating to displays 296, 298 and 300 are within the
purview of a practitioner in the art. As a result, one of ordinary
skill in the art could design and implement preferred cases 290 of
the present invention.
[0148] In operation, the transmitter is installed in the head of a
boring tool used to drill a predominately horizontal hole. The
transmitter provides an amplitude modulated signal that consists of
the carrier frequency (e.g., 32768 Hz) and two tones that are
changed four times over a one-second interval followed by a single
tone lasting one second used as a delimiter. The tones preferably
range in frequency from about 400 to about 900 Hz, for example, so
that the entire signal is contained in a bandwidth of less than 2
kHz, for example. Roll-pitch electronics in the receiver of the
present invention has a bandwidth of less than 2 kHz, for example,
to receive the transmitter signal. The depth receivers have a
bandwidth of about 20 Hz, for example, so that roll/pitch
modulation does not influence the depth output signal. The depth
output signal is a function only of the strength of the received
carrier frequency.
[0149] The inductor-antenna in the transmitter emits a signal that
approximates a dipole field at distances greater than a few antenna
coil lengths. The signal strength of a dipole field is known to
vary as the inverse cube of the distance. This relationship is used
to measure depth and calibrate the system. Since the transmitter
has a well regulated power supply and stable components, the
transmitted signal remains constant with time so that frequent
recalibration is not required.
[0150] When necessary or desired, calibration is achieved by first
holding the receiver unit near the surface above the transmitter
and depressing the switch for approximately 2 seconds, for example.
The CPU in the receiver measures the magnetic signal strength of
the carrier and uses the ultrasonic system to measure the distance
to the surface. The receiver is then raised and the switch again
briefly depressed. A second set of magnetic and acoustic
measurements are taken. The relationship between the signal
strength and the range is then computed by the CPU and the
proportionality constant stored. The distance between the receiver
and transmitter will be shown on the receiver display in one inch
increments. If the operator were to again briefly depress the
switch, the receiver would measure the distance to the surface
using the ultrasonic ranging system and subtract this value from
the magnetic range to obtain the distance of the transmitter below
the surface.
[0151] An expedited transmitter location process is also provided
by the present invention. This process takes advantage of the fact
that the orthogonal antenna system measures the total magnetic
field strength in the plane of the antennas. When the receiver case
(antenna plane) is pointed in a direction parallel to one of the
dipole flux lines emanating from the transmitter, the measured
field will be a maximum. The operator can therefore hold the
receiver at a fixed location above the surface and rotate the case
until a minimum distance to the transmitter is indicated. The
operator can then move in the indicated direction for a distance
related to the indicated distance and repeat the process.
Repetition continues until the operator passes over the
transmitter, as indicated by an increase in range. The location
process must be accomplished in stages, because flux lines are not,
in general, straight lines to the transmitter.
[0152] The sensitivity of the expedited locating process can be
increased by using the square of the signal strength rather than
the range which has an inverse cube root relation to the signal
strength. Since the square of the signal strength is available from
the vector sum process used to obtain the total in-plane signal
strength, its use does not add significantly to the computational
process. By comparing the current signal strength with the
previously measured one, a sensitive signal peak can be
determined.
[0153] The process consists of arming a beeper activation circuit
after several consecutive signal strength increases are measured,
indicating a peak searching mode. When the signal ceases to
increase or decreases, a brief activation of the beeper occurs.
With a measurement cycle time of 0.1 of a second, for example, the
indication is quite accurate for moderate rates of signal strength
change. In order to enhance the accuracy at faster rates of change,
a predictor method may be used to estimate the rate of change of
signal strength. If the predictor method determines the peak will
occur before the next measurement, the routine measurement cycle is
halted, and the beeper is activated after a delay estimated to be
that required to reach peak signal.
[0154] The predictor may, for example, fit a quadratic function to
three prior magnetic field strength readings to determine whether
the field strength will pass through a maximum (i.e., zero slope
point) prior to the next reading. If the predictor determines that
a maximum will occur prior to the next reading, it suspends the
next measurement cycle; waits until the estimated time to the
maximum passes; and initiates the beeper. The predictor of the
present invention is also preferably capable of ascertaining
circumstances when extrapolation will not be accurate. Under these
conditions, the predictor will not suspend the measurement cycle.
If the predictor does not suspend the measurement cycle, and the
subsequent measurement is less than the prior measurement, the
predictor will initiate the beeper.
[0155] A case rotation process is used to determine the direction
that the transmitter is pointed once the location of the
transmitter has been found. The case rotation process may operate
in the same manner as the locator process described above.
Specifically, a predictor-controlled extrapolation process may be
employed.
[0156] The peak signal squared value derived from the searching
process may be held in memory. This peak held signal corresponds to
the last measured magnetic field strength reading, rather than the
extrapolated value. The receiver of the present invention will hold
the signal for a specified time period, for example, 2 seconds, to
allow the operator the option to further refine the searching
process by comparing the current signal strength to the peak value.
This is accomplished by the operator, for example, by depressing
the switch within the time period for holding the peak signal after
the peak signal beep sounds. As long as the switch remains
depressed, the receiver will compare the current signal with the
peak value and activate the beeper if the current signal strength
equals or surpasses the peak held value.
[0157] This feature is useful for accurately locating the
transmitter. If the operator holds the receiver closer to the
surface than it was when the peak beep was heard, there will be an
area above the surface where the beeper will sound. As the receiver
is raised the area will become smaller. Eventually, a beep will
sound at only one location. This process provides a very accurate
location. A similar process can be used to establish the pointing
direction (i.e., yaw) of the transmitter, replacing lateral and
longitudinal displacements with rotation. Specifically, an initial
wide angle in which the beeper function is activated will narrow as
the receiver is elevated, until the yaw orientation is
pinpointed.
[0158] The signal strength comparison may also be presented
visually using a +/- sign on a display, for example. If the signal
strength is increasing, indicating a reduction in range, the - sign
is displayed. If the signal strength is decreasing, indicating an
increase in range, the + sign is displayed.
[0159] The digital signals received by the roll-pitch receiver and
sent to the CPU are decoded and displayed. The roll orientation
may, for example, be represented as clock positions in 30 degree
increments, 1 through 12. The pitch may, for example, be displayed
in degrees from +90 to -90. An indication may additionally be
provided when the roll and pitch displays are updated by flashing a
sign on the pitch display.
[0160] A sign may also be used to indicate that the a receiver
should be recalibrated. This determination is established whenever
the temperature of the receiver has changed at least 10.degree. C.
since the last calibration. Any other appropriate criteria may also
be used in making the recalibration determination.
[0161] A timer in the CPU determines whether the switch has been
activated in the past 5 minutes, for example. If the switch has not
been activated within the appropriate time frame, the receiver is
switched off. Depressing the switch returns power to the
receiver.
[0162] The bandwidth values, time constraints, trigger switch
activation particulars and the like presented above are exemplary.
Other appropriate and substantially equivalent indicators or
procedures may be used to accomplish these tasks. A practitioner in
the art could produce and implement a receiver case housing with
appropriate operational mechanics, electronics and
electromechanics.
[0163] A procedure for locating the transmitter is based on having
the two receiving antennas oriented at a 45 degree angle to level.
With this orientation the signal strength in the two antennas will
balance at three locations along a line in a vertical plane
containing the axis of the transmitting antenna. One location will
be approximately above the transmitting antenna, one will be behind
the transmitting antenna and one will be ahead of the transmitting
antenna. Referring to FIG. 12, if the receiving antennas are moved
forward (to the left) along the line starting from a substantial
distance from the transmitting antenna, the signal strength would
be greater in antenna 124 than in antenna 122 assuming that the
transmitting antenna was to the left of the receiving antenna. As
the receiving antennas are moved forward (to the left) the signal
strength will reach a balance point where the flux line from the
transmitting antenna through the receiving antennas is vertical. As
the receiving antennas are moved farther toward the transmitting
antenna, the signal strength will be greater in antenna 122 until
the point where the strengths in both antennas are balanced. At
this point, the flux line is horizontal and the receiving antennas
are substantially over the transmitter. The exact location of the
balance will vary slightly due to the pitch angle of the
transmitting antenna. Beyond this mid-balance point, the signal in
antenna 124 will be greater until a third balance point is reached
when the flux line through the receiving antennas is again
vertical. Beyond this fore-balance point, the signal strength will
again be greater in antenna 122.
[0164] By noting the transition of greater signal strength between
antennas 122 and 124 at the balance point, it is possible to
distinguish the point substantially over the transmitting antenna
from the other two points of balance. That is, there is only one
transition of greater signal strength from antenna 122 to antenna
124 while there are two transitions from 124 to 122.
[0165] The two locations where greater signal strength transitions
from antenna 124 to antenna 122 can be used to provide two lateral
locates which are in planes perpendicular to the axis of the
transmitting antenna, one ahead and one behind. This locating
procedure indicates the lateral position and direction of the
transmitter. At these two balance points, the magnetic flux lines
from the transmitting antenna extend in a radial direction along a
circle passing through the receiving antennas contained in the
planes which are substantially perpendicular to the axis of the
transmitter. If the receiving antennas are rotated about a vertical
axis such that the receiving antennas axes are in the same plane as
the radial flux line, then another signal strength balance point
can be found. This point will be on the line formed by the
intersection of the vertical plane through the transmitting antenna
and the plane of the radial flux lines. A mark or flag can be
placed on the surface of the ground directly below the point. A
corresponding point can also be found on the other end of the
transmitting antenna and the surface of the ground marked
accordingly. The line connecting the two points will be in the
vertical plane containing the axis of the transmitter and therefore
provide the lateral locate. Then the balance point at the
transition of greater signal strength from antenna 122 to antenna
124 as the receiver is moved forward along the line will provide a
location substantially over the center of the transmitting
antenna.
[0166] An important feature of the procedure just outlined for the
lateral locate is the use of the vertical component of the flux
field to obtain a balance when the plane of the receiving antenna
is perpendicular to the axis of the transmitting antenna. This
means that any point behind or ahead of the balance point
substantially above the transmitting antenna could be used since
the flux lines at any other location except substantially over the
transmitting antenna would have a vertical component. Although the
best sensitivity will be obtained by using the fore and aft balance
points, the procedure will work without having to find these
points.
[0167] In practice, acceptable lateral locates have been obtained
by first finding the mid-balance point above the transmitting
antenna, then marking the location by having the locating operator
place their foot on the ground below the receiving unit and then
pivoting on that foot so as to be able to move the receiver
perpendicular to the axis of the transmitter within normal reach
ahead or behind the marked location.
[0168] A similar locating process can be accomplished employing
only one horizontal receiving antenna. With the single antenna
configuration, the locations where the flux lines are substantially
vertical would cause a null signal in the receiving antenna, and
the location substantially over the transmitting antenna would
cause a maximum or peak in the induced signal strength in the
receiving antenna. One difference between the single-antenna and
the dual-antennas locating methods is that with the single-antenna
method there is no indication as to the direction to move to find
the null or maximum such as the relative signal strength described
above.
[0169] In practice, a "+" and "-" symbol have been used on the
receiver's display to denote which receiving antenna has the
greater induced signal strength. If antenna 124 has the greater
signal strength, a "+" is displayed, and if antenna 122 has the
greater signal strength, a "-" is displayed. Moving the receiver
forward toward the transmitting antenna from a great distance, the
display will first show a "+" then switch to a "-" at the aft
balance point where the flux line is substantially vertical. Moving
on in the same direction, the display will then transition to a "+"
at the balance point substantially over the transmitting antenna
where the flux line is level. Moving on farther, the display will
finally transition to a "-" at the fore balance point where the
flux line is again substantially vertical. By finding "-" to "+"
transition, the balance point substantially over the transmitting
antenna can be distinguished from the other two balance points
which will be "+" to transitions.
[0170] The complete locating procedure using the fore and aft
signal balance points have been found to provide very good accuracy
not only for the location of the transmitting antenna but also for
the direction that the antenna is pointing.
[0171] A receiver as is described in this application can also be
used to identify and measure the angular and horizontal
displacement of a transmitter. When used for this purpose, the
orthogonally oriented antennas are in a horizontal plane. The two
antennas detect the signal from the transmitter which is
horizontally displaced from the receiver and at a distance from the
receiver. For example, the receiver may be located at a position to
which a boring tool is directed. The boring tool can be started
towards the location of the receiver from a location at a distance
from the receiver. As the boring device progresses towards the
receiver, the receiver can detect when the flux line from the
transmitting antenna through the receiving antennas are deflected
so as not to cause equal signals to be induced. Such a deflection
can be caused by an angular deflection, a lateral deflection or a
combination of both.
[0172] When the boring device is angularly and/or laterally
displaced from a direct flux line path towards the receiver, one of
the two orthogonally oriented antennas will detect a stronger
signal than the other antenna and this will be indicative of the
direction in which the boring device must be steered. An
appropriate visual indication can be given to the operator as to
which of the two antennas is receiving the greater signal and thus
the direction to which the boring device must be steered. This
enables the operator to correct the direction of the boring
device's progress.
[0173] Optionally, the CPU can calculate the displacement of the
boring tool from a flux line heading to the receiver as a function
of the ratio between the signal strengths measured by the two
antennas. This information can be useful in helping the operator to
determine the degree of correction which is required. It is also
possible to reduce or eliminate the need for an operator by
providing an appropriate connection between the receiving unit and
the boring control device. When the receiver senses that the boring
tool is displaced from a flux line course to the receiver, it can
transmit to the boring control device an indication of the
direction and, optionally, the magnitude of the error. In response
to this input, the boring control device can automatically adjust
the direction in which the boring tool moves in order to bring the
tool back into a flux line path towards the receiver.
[0174] In yet another version of such a control device, the
receiver includes two pairs of receiving antennas, the antennas in
each pair being orthogonally oriented to each other, with one pair
in a horizontal plane and the other pair in a vertical plane. The
antenna pair in the horizontal plane functions to provide an
indication of the displacement of the boring tool as described
above, and the vertically oriented pair provides an indication of
the vertical displacement of the boring tool in a similar manner.
Such a device can provide simple, reliable and automatic control
progress of a boring tool.
[0175] Referring again to FIG. 1a, certain characteristics of the
locating field are pertinent to the discussion which follows.
Several of these characteristics are described in U.S. Pat. Nos.
5,155,442, 5,337,002, 5,444,382 and 5,633,589 (collectively
referred to herein as the "Mercer patents"), all of which are
incorporated herein by reference. One of these characteristics is
seen in FIG. 1a as nulls 14 in the locating field, as described
above for a single horizontal antenna. Outside the null points, a
local peak in signal strength which may be referred to as a "ghost"
is present. As described in the Mercer patents, the locating field
is vertically oriented at these null points such that a single
horizontally oriented antenna loses the locating signal. These null
points, sometimes referred to in the Mercer patents as negative
locate points, may also be referred to more simply as locate points
herein. In particular, the locate point which is ahead of the
boring tool may be referred to as a forward locate point (FLP) and
the locate point which is behind or to the rear of the boring tool
may be referred to as a rear locate point (RLP). For present
purposes, it is sufficient to note that the locate points arise as
a result of the use of an elongated electromagnetic radiation
dipole transmitter in the boring tool used to produce the locating
signal, as described in the Mercer patents.
[0176] Referring to FIG. 13 and the prior discussions regarding the
vector sum of components of a locating signal, further advances in
this subject are described. FIG. 13 illustrates a lag circuit
generally indicated by reference number 400. Circuit 400 includes a
resistor R402 and a capacitor R404 in a series connection. An input
voltage v.sub.i1 is provided. The output of the circuit is
v.sub.o(lag). It can be shown that:
v o ( lag ) = v i 1 2 - j .pi. 4 ( 6 ) ##EQU00001##
[0177] Referring to FIG. 14, a lead circuit 410 includes R402 and
C404 interchanged in position relative to FIG. 13 and with an input
voltage v.sub.i2 and an output voltage V.sub.o(lead). For circuit
410, it can be shown that:
v o ( lead ) = v i 2 2 j .pi. 4 ( 7 ) ##EQU00002##
[0178] FIG. 15 illustrates a summing circuit 420, which is a
combination of previously described lag circuit 400 and lead
circuit 410, each of which are indicated within dashed lines, along
with summing junction 422. Summing junction 422 receives
v.sub.o(lag) and v.sub.o(lead) to produce a sum voltage v.sub.s.
Using equations 6 and 7:
v s = v i 1 2 - j .pi. 4 + v i 2 2 j .pi. 4 ( 8 ) ##EQU00003##
[0179] Referring to FIGS. 16 and 17, if v.sub.i1 and v.sub.i2 are
in phase or 180.degree. out of phase, v, is the vector sum of
v.sub.i1 and v.sub.i2. FIG. 16 illustrates an in phase vector sum
424 while FIG. 17 illustrates a 180.degree. out of phase vector sum
426. The magnitude of v.sub.s is the same irrespective of v.sub.i1
and v.sub.i2 being in phase or 180.degree. out of phase; however,
the phase angle of the vector sum varies with respect to v.sub.i1
and v.sub.i2.
[0180] Referring to FIG. 18, a first embodiment of a vector sum
receiving circuit 450, manufactured in accordance with the present
invention, is generally indicated by the reference number 450,
which includes previously described lag circuit 400 and lead
circuit 410. A pair of orthogonally arranged antennas 452 includes
antennas 452a and 452b. These antennas are shown in a vertical and
a horizontal orientation, respectively, for illustrative purposes.
One useful implementation for providing orthogonal antennas having
centered radiation patterns is disclosed in U.S. Pat. No. 6,005,532
entitled ORTHOGONAL ANTENNA ARRANGEMENT AND METHOD which is
incorporated herein by reference and which is commonly assigned
with the present application. The overall orientation of the
antenna pair can be varied in any suitable manner such as, for
example, by placing the antennas in an "X" configuration with
respect to horizontal and vertical. The dipole locating signal to
be received is indicated as Be.sup.j.omega.t and is oriented at
angle .theta. to horizontal. Horizontal antenna 452a provides a
signal s.sub.1, serving as a first component of the locating
signal, to an amplifier 454a. The amplified first component is then
sent to lag circuit 400 to produce v.sub.o(lag) which is then
provided to a summing amplifier 456, forming part of a summing
amplifier section 457, via a DC blocking capacitor C458a and a
series resistor R460a. Vertically oriented antenna 452b provides a
signal s.sub.2, serving as an orthogonal, second component of the
locating signal, to an amplifier 454a. The amplified second
component is then sent to lead circuit 410 to produce V.sub.o(lead)
which is then provided to a summing amplifier 456 via a DC blocking
capacitor C458b and a series resistor R460b. Series resistors R460a
and R460b each have a value R.sub.s. A feedback resistor R462
cooperates with series resistors R460 to set the gain of summing
amplifier 456. The value of R462 is set to {square root over (2)}R,
so as to provide a summing amplifier gain of {square root over (2)}
for reasons to become evident. Also, the product of C404 and R402
is set to 1/.omega..
[0181] With the input of the locating signal taken as
Be.sup.j.omega.t:
s1=Be.sup.j.omega.t cos .theta. (horizontal antenna), and (10)
s2=Be.sup.j.omega.t sin .theta. (vertical antenna). (11)
[0182] V.sub.sum, the output of summing amplifier 456 is equal to
the sum of the amplified and phase shifted s1 and s2 components of
the locating signal multiplied by {square root over (2)}:
v sum = 2 [ B j .PI. t cos .theta. 2 - j .pi. 4 + B j .PI. t sin
.theta. 2 j .pi. 4 ] ( 12 ) ##EQU00004##
[0183] This expression can be reduced to:
v sum = B j ( .PI. t + .theta. - .pi. 4 ) ( 13 ) ##EQU00005##
which is equal to the total locating field, as described above.
Thus, the orthogonally measured components of the locating field
have been used to produce a true vector sum.
[0184] Referring to FIGS. 5A and 18, vector sum receiving circuit
450 is advantageous since only a single receiving circuit is
required to detect the vector sum of the magnetic field. As can be
seen in FIG. 5A, separate range receivers 122 and 124 are each
associated with one of the antennas in receiver 36. Alternatively,
vector sum receiving circuit 450 may be used in receiver 36 so as
to eliminate the need for one range receiver. This improvement
serves to simplify the circuitry with an attendant increase in
reliability. At the same time, the single receiver vector sum
circuit does not allow for detecting the locate points described
above. This may be offset, however, since there are drilling
applications which are particularly well suited to locating without
the use of the locate points. One such application, for example, is
that of locating to a shallow bore. Shallow bore drilling is
prominent in certain instances including installing utility
services from a curb to a residence. The advantage of the vector
sum receiving circuit, in this instance, resides in the elimination
of the aforementioned ghosts, seen in FIG. 1a and described above.
This advantage is provided since the vector sum exhibits a
monotonic variation in signal strength (see FIG. 1b), even though a
single receiving circuit is employed.
[0185] Referring to FIG. 5A, the vector sum receiving circuit is
advantageous in roll-pitch receiver 126 since receiving circuit 450
eliminates nulls in the signal strength introduced by a single
antenna configuration. That is, at a null point, the roll and pitch
information cannot be received when a single horizontal antenna is
used. Of course, use of the vector sum receiving circuit assumes
the use of a pair of input antennas. These antennas can be shared
for both the range and roll-pitch receivers by connecting both
receivers to the v.sub.sum output of amplifier section 457. In
addition, the circuit shown in FIG. 17 may be used solely for the
roll-pitch receiver to eliminate the null while connecting the same
two antennas to the two depth receivers as previously
described.
[0186] Referring to FIGS. 18 and 19, vector sum receiving circuit
450 is partially illustrated in an embodiment which does not
require the use of active components. To that end, summing
amplifier section 457 has been replaced by a tuned LC tank circuit
464 including resistors R460a and R460b connected to the LC tank
circuit at a node 470. The opposing end of the tank circuit is
connected to ground. In addition, amplifiers 454a and 454b are
eliminated (not shown) such that antenna 452a is connected directly
to R402 of lag circuit 400 and antenna 452b is connected directly
to C404 of lead circuit 410. In this configuration, the impedance
of antennas R452a and R452b must be low enough to drive the
required network or buffer amplifiers (not shown). Consideration
must also be given to the drive requirements of a receiver (not
shown) which accepts v.sub.sum from the vector sum circuit in this
tank circuit configuration. That is, for the summing circuit to
function properly, the input impedance of any receiver receiving
vsum from this tank circuit configuration must be high compared to
R, or the equivalent parallel dissipation resistance of the tank,
whichever is greater. Otherwise, the Q of the tank will be reduced
and the attenuation of the signal will be increased.
[0187] FIG. 20 illustrates planer orthogonal antenna arrangement
480 that may also be referred to as an "X" antenna configuration
for purposes of simplicity. Thus, the first and second antennas for
range receivers 122 and 124, respectively, of FIG. 12 may be
replaced by X configuration 480 and accompanying circuitry.
[0188] Still referring to FIG. 20, X antenna configuration 480
includes orthogonal antennas 482a and 482b. Antenna 482a produces
an output signal s.sub.1' while antenna 482b produces an output
signal s.sub.2' from the locating signal. For an input locating
signal given as Be.sup.j.omega.t and oriented at an angle .theta.
to horizontal, s.sub.1' and s.sub.2' are given as:
s'.sub.1=-Be.sup.j.omega.t cos(.pi./4+.theta.), and (14)
s'.sub.2=Be.sup.j.omega.t cos(.pi./4-.theta.). (15)
[0189] The sum of s.sub.1' and s.sub.2' is expressed in the
following equation:
s'.sub.1+s'.sub.2=Be.sup.j.omega.t[-cos(.pi./4+.theta.)+Cos(.pi./4-.thet-
a.)]. (16)
[0190] Expanding the expression and canceling terms leaves:
s'.sub.1+s'.sub.2=2Be.sup.j.omega.t sin .pi./4 sin .theta., or
(17)
s.sub.1+s'.sub.2= {square root over (2)}Be.sup.j.omega.t sin
.theta.. (18)
[0191] Referring to FIGS. 18 and 20, comparison of equations 11 and
18 reveals that the sum of s.sub.1' and s.sub.2' is equivalent to
the output of a vertically oriented antenna having a gain of
{square root over (2)}. In essence, the sum signal represents the
output of an "electronically rotated" vertical antenna.
[0192] The difference between s.sub.1' and s.sub.2' is expressed in
the following equation:
s'.sub.1-s'.sub.2=Be.sup.j.omega.t[-cos(.pi./4+.theta.)-cos(.pi./4-.thet-
a.)] (19)
expanding and canceling terms leads to:
s'.sub.1-s'.sub.2=-2Be.sup.j.omega.t cos .pi./4 cos .theta., or
(20)
s'.sub.1-s'.sub.2=- {square root over (2)}Be.sup.j.omega.t cos
.theta.. (21)
[0193] A comparison of equations 10 and 21 shows that the
difference signal is equivalent to the output of a horizontally
oriented antenna having a gain of - {square root over (2)}. Thus,
the sum signal represents the output of an electronically rotated
horizontal antenna. The use of the sum and difference signals forms
an integral part of the techniques to be described below. While the
use of signals provided by electronic rotation is considered to be
highly advantageous, the use of first and second signals measured
along first and second intersecting receiving axes in an initial
orientation defining an antenna plane in combination with third and
fourth signals, that may be produced in one way by an actual
physical rotation of the receiving axes by a predetermined amount
such as, for example, 45.degree. about the intersection point
within the receiving plane, is considered to be within the scope of
the appended claims. That is, the third and fourth signals may be
produced in any suitable manner for use in the methods that follow,
including the highly advantageous electronic rotation method
described immediately above. Moreover, the use of a rotated antenna
arrangement allows for the determination of the slope of the
magnetic field lines within a 180.degree. ambiguity using a pair of
range receivers that detect only peak or average signal strength
and not the phase relationship as would be otherwise required. This
rotation technique allows for more simple receivers to be
employed.
[0194] Referring to FIG. 21, circuit 500 is an embodiment of a sum
and difference generating circuit designed in accordance with the
present invention. Capacitors C502 all serve the purpose of DC
blocking. Resistors R504 are all of the value R.sub.s while
resistors R506 have a value of {square root over (2)}R.sub.s.
Buffers 454a and 454b receive s.sub.1' and s.sub.2' from orthogonal
antennas 482a and 482b (so as to present a high input impedance to
the high output impedance of the antennas) and have a gain G. A
first amplifier 508 with its biasing resistors is configured to
provide a gain of 1/ {square root over (2)} such that the output of
the amplifier is the sum signal G (s.sub.1'+s.sub.2')/ {square root
over (2)}. A second amplifier 510 receives s.sub.2' at its
inverting input. The amplifier cooperates with its biasing
resistors as an inverter to provide a gain of -1 such that the
output is -s.sub.2'. By setting the gain of the amplifiers with
R506 and R504 to be 1/ {square root over (2)}, the vector sum
signal strength from the rotated antennas is equivalent to the
vector sum signal strength of the output of the buffers 454a and
454b, that is the product of G multiplied by B.
[0195] Still referring to FIG. 21, the output, -s.sub.2', of
amplifier 510 is provided to a third amplifier 512 and its biasing
resistors via one of resistors R504. Amplifier 512 cooperates with
its biasing resistors to provide a gain of 1/ {square root over
(2)} such that the output of this amplifier is the difference
signal G, (s.sub.1'-s'.sub.2')/ {square root over (2)}. Thus,
circuit 500 has produced the sum and difference signals
contemplated above and equivalent to those signals which could
otherwise be generated by a vertical antenna and a horizontal
antenna, respectively, when the actual antennas measuring s.sub.1'
and s.sub.2' are in an X configuration with respect to horizontal.
In this manner, four field measurement values are available rather
than only two, even though the need to physically measure two of
the values has been advantageously eliminated. Although it might
appear to be a simple matter to merely add another pair of
orthogonal antennas in the + configuration to measure the third and
fourth signals, the task is complicated by a number of factors,
including space limitations, undesirable weight increase, and the
need to have substantially common centers for the various antennas
in order to provide optimum accuracy. A highly advantageous
solution for this difficult antenna centering problem is been
disclosed in the above incorporated U.S. Pat. No. 6,005,532. At the
same time, it is to be understood that the methods below may be
practiced using four separate antennas oriented appropriately
irrespective of the fact that overall accuracy may be affected.
[0196] The advantages derived from using four magnetic field values
derived, for example, using circuit 500 (FIG. 21), as described
above, are made clear in FIG. 22 which illustrates boring tool 28
transmitting a dipole locating signal in a region 448 from an
internal transmitter (not shown) producing a dipole field 550. Four
selected flux lines of dipole field 550 are shown as indicated by
the reference numbers 552, 554, 556 and 558 and are distorted from
their true representation for purposes of illustration only. In
this regard and in accordance with the present invention, the
depicted flux lines have been selected based on their slope in the
vicinity of ground surface 560 (only partially shown), which is
parallel to and below the line of travel of the locating antennas.
The boring tool is depicted traveling in a forward direction as
indicated by an arrow 562, and angular measurements are taken
herein with respect to the forward direction. Specifically, flux
line 552 is horizontally oriented at the surface at a point A
directly above boring tool 28. Flux line 554 is oriented at an
angle of 135.degree. from horizontal at a point B measured
clockwise (CW) from the forward direction at the locator above the
surface of the ground. Point B is also ahead of the boring tool
with respect to forward direction 562. A mirror image of the entire
flux field ahead of the boring tool is present behind the boring
tool, assuming ground surface 560 is level and boring tool 28 is
also horizontally oriented. Therefore, at a point B', which is
behind the boring tool, flux line 554 is oriented at 45.degree.
from horizontal measured CW from the forward direction (note the
flux angles may just as readily be specified in other ways such as,
for example, measurement CCW from the forward direction. In this
instance, 45.degree. is added to the angular measurements described
per the adopted conventions currently used with regard to FIG. 22).
At a point C, flux line 556 is oriented vertically. Similarly, a
vertical flux orientation is present at point C' behind the boring
tool on flux line 556. C is the forward locate point and C' is the
rear locate point.
[0197] Still referring to FIG. 22, at a point D on the surface of
the ground at flux line 558, the flux line has a slope orientation
of 45.degree. from horizontal measured CW from the forward
direction. At D' on flux line 558, a flux slope orientation of
135.degree. is encountered measured CW from the forward direction.
At points E and E', which represent an infinite distance from the
boring tool, the flux line slope theoretically approaches
horizontal.
[0198] Points A-E and B'-E' serve to define a series of regions
which are numbered as regions 0-7. Within each of these regions, a
predetermined flux line slope orientation is present, depending
upon the flux line orientations at the points which define the
boundaries of the regions at the surface of the ground. FIG. 22
indicates the range of flux line slope within each of regions 0-7.
As the slopes of the flux lines are measured in a clockwise
direction with respect to forward direction 562, region 0 (points
E-D) includes a flux slope ranging from 0.degree. (horizontal) to
45.degree.; region 1 (points D-C) includes a flux slope ranging
from 45.degree. to 90.degree.; region 2 (points C-B) includes a
flux slope ranging from 90.degree. to 135.degree.; and region 3
(points B-A) includes a flux slope ranging from 135.degree. to
horizontal or 180.degree.. These regions do not include the
defining boundary points such that the flux slope within each
region ranges up to, but does not include the flux slope at the
defining boundary points. For reasons which are made evident below,
flux orientation characteristics a-d have been assigned to regions
0-3, respectively.
[0199] Continuing in a progression through regions 0-7 of FIG. 22,
after having passed above boring tool 28, region 4 (points A-B')
includes a flux orientation slope ranging from 180.degree. to
225.degree. measured CW from the forward direction, which is the
same range of flux slope orientation in region 0, except for the
addition of 180.degree.. Because the magnetic field continuously
oscillates, the slope will switch 180.degree. during each complete
oscillation cycle. For example, a flux line that has a slope of
45.degree. will have a slope of 225.degree. one-half cycle later.
An upper row of values for flux slope in regions 5 through 7 shows
the slopes of the flux lines in dipole field 550 together
considering the full range (i.e., 0.degree. to 360.degree.) of
possible flux orientation across regions 0-7. In parentheses,
angular ranges are shown for regions 5-7 which indicate
corresponding ranges over a 0.degree. to 180.degree. range, not
attempting to account for the 180.degree. angular ambiguity. Region
4 has been assigned flux orientation characteristic a. In
continuing through regions 5, 6 and 7, region 5 exhibits flux
orientation characteristic b, as with region 1; region 6 exhibits
flux orientation characteristic c, as with region 2; and region 7
exhibits flux orientation characteristic d, as with region 3.
Because a pair of regions shares one of the flux orientation
characteristics, use of the flux orientation characteristic of the
locating field at any one point above the path (or intended path)
of the boring tool is ambiguous. For example, if flux orientation
characteristic c is detected at a particular above ground location,
that location may be in either region 2 or region 6, since both of
these regions exhibit flux orientation characteristic c. With
regard to the boundary points which define these regions, the same
ambiguity also exists. For example, the same flux line slope is
present at point D as is present at point B'. Similarly, the same
slope is present at the pairs of points C-C' and B-D'. Therefore,
the present invention provides a number of approaches for resolving
this ambiguity discussed below.
[0200] Still referring to FIG. 22, one method of dealing with the
ambiguity of the flux slope resides in identification of balance
points, as can best be explained by referring to the balance
signals produced by the "X" configuration (see FIG. 20) of the
antennas at specific locations above ground. The balance points of
signal strength will occur at three different above ground
locations for most locating situations. Assuming that the locating
signal transmitter is level (as shown in FIG. 22), that the
receiver is moved along above ground surface 560, and that the
ground above and in the vicinity of the transmitter is level, one
balance point is located at A, which is substantially above the
boring tool transmitter. The other two balance points are the
aforementioned forward located point (FLP) and rear locate point
(RLP), which are located at point C and point C', respectively. To
resolve whether the receiver is at one of the locate points or at
the overhead point, one method uses actual physical rotation of the
antenna pair. Another method, as described above, uses electronic
rotation. In the former method, the X antenna configuration can be
rotated by 45.degree. degrees about the intersection point of the
orthogonal antennas with the receiving plane defined by the
antennas continuing to extend generally along the intended path of
the boring tool. However, the electronic rotation method is
considered to be highly advantageous. Therefore, its use is
discussed below even though equivalent signals obtained in other
techniques may also be used.
[0201] Continuing with a discussion relating to resolving the flux
slope ambiguity seen in FIG. 22, if the X configuration antenna
arrangement is at point A above the boring tool transmitter,
electronic rotation of the antennas will yield a horizontal antenna
signal receiving the entirety of the signal strength at point A
while the vertical antenna signal will exhibit a null. In contrast,
at the forward and rear locate points, C and C', respectively, this
signal pattern will be reversed, and the vertical antenna signal
will receive the entire signal strength of the locating signal
while the horizontal antenna signal will receive none and show a
null. Therefore, the balance points are divisible into two
different types for an "X" antenna: 1) at the overhead point A, and
2) at the FLP and RLP. In theory, two additional balance points of
the first type exist at points E and E', which are at an infinite
distance from the boring tool transmitter. However, because the
signal strength of the locating signal is so low at E and E', these
points are of no practical consequence to the present discussion.
Thus, by switching the antenna rotation circuit in and out of the
overall circuitry in a portable locator to obtain four relative
values of the locating signal, the ambiguity as to type of balance
point at which the receiver is positioned may be resolved. However,
because the flux appears the same at both the FLP and the RLP,
there still remains an additional ambiguity that must be resolved
in order to determine the position of the receiver relative to the
transmitter.
[0202] Referring to FIG. 2, this ambiguity can be resolved based on
the absolute phase of the transmitted locating signal relative to
the received signal. The absolute phase can be determined by using
an arrangement which sends out phase information regarding the
locating signal to the above ground receiver/locator. One approach
is to transmit the locating signal through drill pipe 564 using an
induced signal on the pipe or by means of a separate wire within
the pipe. See, for example, U.S. patent application Ser. No.
09/317,308, filed Jun. 1, 1999, entitled AUTO-EXTENDING/RETRACTING
ELECTRICALLY ISOLATED CONDUCTORS IN A SEGMENTED DRILL STRING, which
is incorporated herein by reference and which discloses a number of
highly advantageous "wire in the pipe" arrangements. The signal
transmitted through the pipe to the drill rig is encoded or used to
modulate a radio frequency (RF), audio, ultrasonic or infrared
signal (IR) that is sent to the receiver. In some cases, the signal
could also be sent to the receiver using a direct connection such
as a conductive wire or fiber optic line. In the present example,
FIG. 2 illustrates a tripod 600 supporting a transmitter 602 which
is connected with the drill rig via a cable 603 to receive the wire
in the pipe data. Transmitter 602 transmits a phase signal 604 to
locator 36. The latter is configured with a phase receiver 608 for
receiving phase signal 604. Receiver/locator 36 then compares phase
signal 604 with the phase of the locating signal being received
directly from the boring tool transmitter to obtain an absolute
phase of the received locating signal. In one implementation, the
phase signal may simply be in the form of a multiplication factor
of +1 or -1. That is, with one multiplication factor and a
particular instantaneous locating field polarity, the locator is at
the FLP while the presence of the opposite multiplication factor
with the same instantaneous locating field polarity indicates that
the locator is at the RLP. This arrangement functions to indicate
whether the locator is ahead of or behind the boring tool with
respect to forward direction 562 at any position of the locator
above the intended path of the boring tool.
[0203] Referring again to FIG. 22, the field slope detection
capability of the present invention, in and by itself, provides
valuable information regarding the location of the boring tool even
lacking absolute phase determination as described above. That is,
the field slope detection capabilities of the present invention
serve to direct an operator to the locate points C and C' and/or to
the overhead point A using a number techniques to be described.
[0204] Still referring to FIG. 22, a first flux orientation
locating technique in accordance with the present invention, relies
on the use of regions 0-7 in conjunction with the aforedescribed
four orientation characteristics of the locating signal. These
characteristics may be obtained using an X antenna configuration to
directly measure two of the values and then generate the other two
values equivalent to a + antenna configuration. In this regard, it
is recognized that regions 0 through 7 occur in a predetermined
sequence along the intended path of the boring tool. As described
above, one of four specific flux orientation characteristics a-d
occur in each of the regions as shown in FIG. 22. In approaching
the boring tool, for example, from some point in region 0,
traveling in forward direction 562, an operator carrying locator 36
(not shown) will pass through a portion of region 0 and then
successively pass through regions 1 through 3. In doing so, flux
orientation characteristics a-d, will be observed prior to arriving
at point A, substantially above the boring tool. Should the
operator continue in the forward direction, the flux orientation
characteristics will repeat in passing through regions 4 through 7.
So long as the operator successively tracks the flux orientation
while progressing along the path, a repetition of the flux
orientation characteristics is an indication to the operator that
the locator has passed over and is now ahead of the boring tool
thereby avoiding any problem resulting from repetition of the flux
orientation regions on the boring tool path. Moreover, this
ambiguity is resolvable by monitoring the signal strength of the
locating signal, preferably in the form of a vector sum. As the
operator approaches the boring tool from point E, the signal
strength should monotonically increase in value. Immediately upon
passing over the boring tool, the signal strength will begin to
decrease in value. While this first technique relies on beginning
in regions 0 or 7, other techniques may begin at arbitrary points
in any of the regions, as will be described. In addition, region 7
"becomes" region 0 upon reversal of the orientation of the locator
by 180.degree. such that the approach of the boring tool from
either of the outer regions is similar with regard to flux
orientation.
[0205] Continuing to refer to FIG. 22, a second flux orientation
locating technique in resolving the ambiguity as to repetition of
the flux orientation regions is to initially log a reference value
of signal strength of the locating signal. For example, the signal
strength of the locating field at either locate point C or locate
point C' may be measured and stored. Thereafter, for any measured
value of locating field strength which is greater than the stored
value, it is known that such a measurement will be produced only at
locations between the locate points (regions 2-5). If, the measured
signal strength is less than the stored reference value, such a
measurement will only be encountered outside the locate points on
the boring tool's intended path (regions 0, 1, 6 or 7). In this
regard, flux orientation ambiguity is eliminated, since each of the
flux orientation regions positioned between the locate points
(regions 2-5) have higher signal strengths compared to flux
orientation regions outside the locate points (regions 0, 1, 6, 7).
Furthermore, only one of each type of flux orientation region a-d
is present between the locate points while only one of each type of
flux orientation region is present outside of the locate points.
For example, region 0 and region 4 both exhibit flux orientation
characteristic a. However, the signal strength in region 0 is
greatly reduced compared to the signal strength in region 4. A
similar situation exists with certain pairs of the boundary points
which define the regions. For example, points D and B' share an
identical flux orientation, but the signal strength at point D is
greatly reduced compared with that at point B'.
[0206] Briefly considering the first flux orientation locating
technique with regard to FIG. 22, it should be appreciated that by
beginning at a sufficient distance from the boring tool, an
operator is reasonably assured of being in the far field region of
the locating signal (region 0 between points E and D or region 7
between points E' and D'). For purposes of clarity, the present
example begins by initially considering the approach of the boring
tool from region 0 such that the locating signal flux orientation
is between 0.degree. and 45.degree. CW from horizontal in the
forward direction. The operator will become certain of beginning in
region 0 as progression through the various flux orientation events
proceeds in route to the boring tool, particularly when a
combination of flux orientation and signal strength readings are
used. It should be appreciated, however, that flux orientation
values alone will serve in effectively locating the boring tool
using the technique.
[0207] Referring to FIGS. 22 and 23, having generally described
procedures used in flux slope orientation locating performed in
accordance with the present invention, it is now appropriate to
discuss specific details regarding the use of locating signal
strength values obtained, for example, using circuit 500 of FIG.
21. FIG. 23 illustrates an X antenna configuration 565 consisting
of antennas 482a and 482b. For purposes of simplicity, antenna 482a
is denoted by a + symbol while antenna 482b is denoted by a -
symbol. Dashed vertical and horizontal lines serve to divide the
quadrants defined by the antennas into sub quadrants. By comparing
FIGS. 22 and 23, it is observed that, as antenna configuration 565
is moved along the boring tool path, each of the flux lines
corresponding to the particular one of the flux orientation
characteristics a-d pass through or are oriented within a single
sub quadrant of the antenna configuration, with respect to the
horizontal direction. Specifically, as shown in FIG. 23, the flux
lines for orientation characteristic a are located in a sub
quadrant 570; the flux lines for orientation characteristic b are
present in a sub quadrant 572; the flux lines for orientation
characteristic c are present in a sub quadrant 574; and the flux
lines for orientation characteristic d are present in a sub
quadrant 576.
TABLE-US-00002 TABLE 2 X Configuration + Configuration Axes Axes
Flux Slope REGION Dominant Signal Dominant Signal Characteristic 0
+ -' a 1 + +' b 2 - +' c 3 - -' d 4 + -' a 5 + +' b 6 - +' c 7 - -'
d
[0208] Referring to Table 2 in conjunction with FIGS. 22 and 23,
the + and - nomenclature referring to antennas 482a and 482b is
used throughout Table 2. Within each of regions 0-7, one of either
the + or - antennas will detect the locating signal with a greater
or dominant signal strength, compared to the other one of the
antennas. In this regard, the balance points, at which each antenna
receives an equal signal strength, occur at points C (FLP), C'
(RLP) and the overhead point A. These balance points, however, are
not within but rather serve to define the regions. Table 2 includes
a "Region" column, an "X Axes Dominant Signal" column, a "Flux
Slope Characteristic" column and one additional column to be
described below. The table indicates, for each region, which
antenna receives the dominant signal strength for the X axes
configuration. For example, in region 0, the + antenna signal is
dominant, in region 1, the + antenna signal is dominant, in region
2, the - antenna signal is dominant and in region 3, the - antenna
signal is again dominant. This pattern then repeats in regions
4-7.
[0209] Referring to FIGS. 22-24 and Table 2, FIG. 24 illustrates a
+ antenna configuration generally indicated by the reference number
580 which consists of "virtual" antennas 482a' and 482b' that
represent electronically rotated antennas 482a and 482b producing
signals which may be obtained, for example, using circuit 500 of
FIG. 21. For purposes of simplicity, antenna 482a' is indicated by
a +' symbol while antenna 482b' is indicated by a -' symbol. The
third column of Table 2 is a "+' Axes Dominant Signal" column that
indicates which of antennas +' or -' receives the dominant signal
strength. For example, in region 0, the -' antenna signal is
dominant; in region 1, the +' antenna signal remains dominant; in
region 2, the +' antenna signal is dominant; and in region 3, the
-' antenna signal remains dominant. The region 0-3 pattern then
repeats in regions 4-7, respectively.
[0210] Still referring to FIGS. 22-24 and Table 2, the flux slope
orientation characteristic at the position of a portable locator is
established in accordance with the present invention in a highly
advantageous way by identifying the dominant antenna in each of the
X and + antenna configurations at the position of the locator.
Accordingly, having identified one of characteristics a-d, the
position of the locator is limited to only two of the eight regions
associated with the intended path. The foregoing techniques are
used to resolve ambiguities regarding which region the locator is
positioned in. For example, in one technique, the boring tool is
approached from the far field regions such that the predetermined
sequence of regions may be monitored up to and past the position of
the boring tool. In another technique, signal strength may be used
to resolve the ambiguity. A reference value is stored, for example,
as measured at one of locate points C or C'. Because one of the two
possible regions is always between the locate points while the
other region is outside of the locate points, the locator will
measure a signal strength at an unknown position between the locate
points which is greater than the reference value while the locator
will measure a signal strength that is less than the reference
value at an unknown position that is not within the area between
the locate points. Therefore, the ambiguity as to the two possible
regions can be resolved based on signal strength. Still other
techniques for establishing the reference value may be based on
signal strength relationships at other known locations in the
field.
[0211] Attention is now directed to FIGS. 22 and 25 for purposes of
describing a third flux orientation locating technique. The third
technique applies various concepts related to flux slope
orientation (not described above) in combination, for example, with
signal strength measurements in a highly advantageous way, serving
to quickly and accurately locate the boring tool. This technique
will be described in conjunction with the presentation of a series
of figures beginning with FIG. 25, which illustrates the appearance
of a display 700 produced in accordance with the present invention.
Display 700 may be used in place of displays 296, 298 and 300 shown
in FIG. 11. Alternatively, the information conveyed by display 700
may be displayed by any suitable combination of displays 296, 298
and 300 of FIG. 11. Display 700 includes a roll orientation display
702, illustrating the roll orientation of boring tool 28 using an
arrow 704 on a clock face 706. A pitch orientation display 708
includes a boring tool symbol 710 upon which is superimposed a
numerical pitch reading 712. In the present example, boring tool
symbol 710 is pitched upward at 10 percent grade; however, the
display is also capable of showing a boring tool symbol pitched
downward (not shown) in view of the sign of numerical pitch reading
712. Display 700 further includes a temperature icon 714 which is
generally shaped in the form of a thermometer for indicating the
temperature measured within the boring tool. This temperature is
indicated by a bar type display within the icon. An arrow 716
indicates whether recent changes in the boring tool temperature are
rising or falling (a rising indication presently provided). A
battery icon 718 indicates the remaining capacity of the locator
battery using a bar graph style therein.
[0212] Continuing with a description of FIG. 25, a telemetry
activation icon 720 illustrates the telemetry system is functioning
and sending data to the drill rig from locator 36. One arrangement
describing the use of such a telemetry signal is described in U.S.
Pat. No. 5,698,981, TECHNIQUE FOR ESTABLISHING AT LEAST A PORTION
OF AN UNDERGROUND PATH OF A BORING TOOL. A telemetry channel
display 722 is shown indicating that the system is using channel 2.
In accordance with the present invention, a locator icon 724 is
illustrated in display 700. The areas above and below locator icon
724 are substantially open and that these areas will be used in
position indication scenarios to be described at appropriate points
below. In this regard, arrow 726 will be further described below
following a description of the remaining portions of display
700.
[0213] Display 700 further includes a boring tool icon 728 having a
bar graph display 730 indicating the capacity remaining in the
battery within the boring tool which powers the locating signal
transmitter. Moreover, a series of four signal transmission arcs
732 illustrate whether locating signal strength is increasing
(lines radiate outwardly) or decreasing (lines radiate inwardly).
Immediately above arcs 732 is a digital signal strength display 734
comprised of three digits and a +/- sign indication such that the
maximum displayable signal strength is plus or minus 999 (not
shown). A signal strength of "+250" is shown. The +/- portion of
display of signal strength display 734 is used for the purpose of
indicating which antenna in the X or X-equivalent configuration has
the greater signal strength as described above.
[0214] Referring to FIGS. 22 and 25, assuming that receiver 36 is
positioned at some unknown point on ground surface 560 when the
receiver is initially powered on, the locator will make an initial
determination as to which type of flux orientation characteristic
type a-d it is positioned within. Since no reference signal
strength value for the locating signal has been measured, the
maximum signal strength value is initially stored (i.e., "999"). If
the flux slope is initially detected as less than 45.degree. (which
corresponds to flux slope characteristic a), it will be assumed
that the receiver is in region 0. Therefore, all locate information
is ahead of the operator at the present position facing the boring
tool. Previously described arrow 726 is then displayed indicating
to the operator to move ahead (in the reverse direction with
respect the boring tool forward direction). Conversely, if the
operator were to begin in region 7 with the locator oriented in the
forward direction facing the boring tool, the flux slope is
indistinguishable from that in region 0 without further
information. For example, the operator may determine the
approximate length of the drill string and position the locator at
a distance sufficient from the boring tool so as to insure that the
locator is in region 0. In any event, regions 0 and 7 are readily
distinguished by other characteristics. For example, flux intensity
will increase when moving toward the drill rig in region 0 while
flux intensity will decrease when moving toward the drill rig in
region 7. The locating logic also functions properly even if the
receiver is almost directly above the transmitter when initially
powered on.
[0215] It is considered to be advantageous to perform locating from
ahead of the boring tool, for example, beginning in region 0. This
consideration is founded in the value of predicting the position of
the boring tool subsequent to its current position. In other words,
locating from the drill rig toward the boring tool is readily
performed in accordance with the teachings herein using flux
orientation locating; however, it should be appreciated that
positions are being located which the boring tool has already
passed. By locating from ahead of the boring tool, predictions as
to the future position provide valuable information to the
operator. For instance, locating can be performed from the forward
locate point. Tracking positional changes in the forward locate
point indicate the heading of the boring tool. Even a small torque
applied to the drill head in being oriented for a turn can produce
a large change in the location of the forward locate point. At
least one other advantage derived from locating beginning ahead of
the tool will be described at an appropriate point below.
[0216] Referring to FIGS. 22 and 26, the latter shows display 700
after movement of the locator toward the boring tool. As in
previous examples, the forward direction is considered to be the
forward direction along the intended path of the boring tool such
that this movement may be referred to as being in the reverse
direction. It should be appreciated that for purposes of positional
analysis, the boring tool is considered to be static. Since FIG.
26, like FIG. 25, shows display 700, only changes in the display
will be described for purposes of brevity. If locator 36 is moved
into a region with flux characteristic b, a locate point target 740
appears in display 700 ahead of locator icon 724. At the same time,
signal strength display 734 now displays the value "+280",
increasing above the previous value in FIG. 25. Intuitively, the
operator will continue moving the locator in the reverse direction
toward locate point target 740 and thereby the boring tool.
[0217] Referring to FIGS. 22 and 27, flux slope monitoring occurs
throughout movement of the locator using, (for example, circuit 500
of FIG. 21) without the active intervention of the operator. FIG.
27 illustrates the appearance of display 700 with the locator at a
point midway between points D and C in region 1. Note that locate
point target 740 has moved closer to locator icon 724 and that
signal strength display 734 has increased to "+300". At this
juncture, it is noted that any time a region is entered from region
a having flux slope characteristic b (regions 1 or 5), a locate
point (C or C') will be encountered with continuing movement toward
the drill rig.
[0218] Referring to FIGS. 11, 22 and 28, by continuing to move the
locator toward the boring tool so as to move locate point target
740 toward locator icon 714, locate point target 740 will be placed
into a display area 742 of locator icon 724. Accordingly, the
operator is at locate point C, assuming the locator is
substantially above the intended path of the boring tool, as will
be further discussed. Note that signal strength display 734 has now
increased to "+320". Having arrived at a locate point, it is now
useful to store a reference signal strength measurement. The
operator does so by actuating trigger 294 (FIG. 11) on the locator
to record the reference signal strength value as "+320". In one
embodiment, the reference signal strength is stored automatically
responsive to two conditions: 1) trigger 294 is actuated and 2) the
locating field flux is oriented either vertically or horizontally.
In fact, one-half the measured signal strength is stored to
accommodate measurement of higher values, for example, if the
reference value is taken at a locate point or slightly off position
from the overhead point directly above the boring tool.
[0219] Referring to FIGS. 11, 22 and 29, with trigger 294 actuated,
display 700 appears as shown in FIG. 29 in the vicinity of a locate
point. Specifically, locator icon 740 is shown at a distance above
the surface of the ground which is indicated by the reference
number 744. Additionally, a height display 746 gives a digital
readout of this height which is indicated in the present example as
two feet, zero inches. Below the height display, a boring tool
depth display 748 shows the predicted depth of the boring tool at
target point 740. The procedure for computing the predicted depth
is described U.S. patent application Ser. No. 09/047,874, BORING
TECHNIQUE USING LOCATE POINT MEASUREMENTS FOR BORING TOOL DEPTH
PREDICTION, which by reference is incorporated herein. Since the
depth of the boring tool measured from a locate point is a
predicted depth, boring tool depth display 748 illustrates this
predicted depth measurement as being ahead of the boring tool using
an arrow 750 displayed so as to emphasize to the operator that this
is a predicted depth. It is noted that the predicted depth obtained
by locating ahead of the boring tool is highly advantageous in
guiding the boring tool. Generally, the operator will have a fairly
certain idea of the required depth of the bore. If the predicted
depth violates, for example, a minimum depth requirement, the
operator is able to take corrective action before any violation of
the minimum depth actually occurs. In the present example, a
predicted depth reading of 27 feet, 1 inch is displayed. A
temperature indication 749 also apprises the operator of the boring
tool temperature which is shown in this example as 157.degree.
F.
[0220] Referring to FIGS. 22 and 30, after having stored a
reference signal strength at locate point C, the operator continues
to move locator 36 toward the boring tool causing display 700 to
show locate point target 740 behind locator icon 724. With the
signal strength increasing to the value "-330" in signal strength
display 734; however, the sign of the reading has changed from plus
to minus indicating that the operator has moved past the locate
point and into region 2 having flux orientation characteristic
c.
[0221] Directing the reader's attention to FIGS. 22 and 31, locate
point target 740 is left still further behind locator icon 724 as
the operator moves away from locate point C towards point B. The
signal strength in signal strength display 734 has now risen to
"-340".
[0222] Turning to FIGS. 22 and 32, and after passing point B,
display 700 presents a locate line 752 ahead of locator icon 724.
Locate line 752 is intended to be centered on the locating signal
transmitter within the boring tool and perpendicular to the axis of
the transmitter (i.e., perpendicular to the intended path). The
signal strength in display 734 is up to "-350".
[0223] Referring to FIGS. 22 and 33, as the locator is moved
further toward the boring tool, locate line 752 has approached
locator icon 724 while signal strength display 734 has increased to
"-355" approximately midway into region 3.
[0224] FIG. 34 illustrates display 700 at point A (FIG. 22) with
the locator substantially above the boring tool such that locate
line 752 is within display 742 of locator icon 724. The signal
strength is now "-360" on signal strength display 734. At this
point, the operator once again actuates trigger 294.
[0225] Referring to FIGS. 11, 22 and 35, actuation of trigger 294
causes display 700 to display depth indications. Specifically, as
in FIG. 29, locator icon 740 is shown at a distance above the
surface of the ground which is indicated by reference number 744.
Additionally, height display 746 again gives a digital readout of
this height as two feet zero inches. Below the height display,
boring tool depth display 748 shows the depth of the boring tool as
29 feet, 1 inch. Arrow 750 is now extending directly between ground
surface 744 and boring tool icon 728 so as to indicate an actual
current measured depth, rather than a predicted depth. It should be
noted that the predicted depth shown in FIG. 29 is determined in
view of the pitch of the boring tool. In this instance the boring
tool is pitched upward at a 10 percent grade such that the
predicted depth (FIG. 29) is less than the measured depth (FIG. 35)
directly over the boring tool. As noted above, in one embodiment, a
new reference signal strength is automatically stored when trigger
294 is actuated at point A.
[0226] Referring to FIGS. 22 and 36, having located point A,
substantially above the boring tool, the operator may continue
moving the locator along and above the intended path of the boring
tool, in order to confirm the location of the boring tool by
finding the rear locate point and/or using that rear locate point
in some manner for future locating. Should the operator continue,
moving into region 4, locate line 752 will appear behind locator
icon 724. The signal strength in signal strength display 734 has
decreased in magnitude to "355" while the sign has changed from -
to +, as a result of passing the overhead point. It should be
appreciated that signal strengths at symmetric points in the
locating field ahead of and behind the boring tool, such as at the
forward and rear locate points, will exhibit equal signal strength
readings only if the boring tool is traveling horizontally and the
ground is level above the boring tool. For purposes of clarity, the
variation in signal strength attributable to non-zero pitch of the
boring tool has been ignored in the present example.
[0227] Referring to FIGS. 22 and 37, upon approaching point B' with
continuing movement away from the location of the boring tool,
locate line 752 will appear still further behind locator icon 724.
The signal strength in signal strength display 734 has decreased to
"+350".
[0228] As the operator continues moving forward, region 5 is
entered exhibiting flux slope characteristic b. As described above,
a locate point is always ahead of a region having flux slope
characteristic b as one moves in the reverse direction. Therefore,
display 700 may appear as in FIG. 26 except that signal strength
display 734 displays a value that is greater than the signal
strength at a locate point but less than the signal strength at
point B (within the range between "+320" to "+340"). Continuing
movement will provide a display corresponding to FIG. 27, with
locate point target 740 closer to locator icon 724, however, the
signal strength will continue to decrease to a value approaching
"+320". When the locator is at point C', display 700 will appear as
in FIG. 28. At this time the operator has found both locate points
and point A overhead of the boring tool. Should the operator
continue moving ahead, the forward locate point at point C' will
fall behind the locator icon in a manner similar to that shown in
FIGS. 30 and 31 with appropriately lower signal strength values. It
is noted that the operator may actuate trigger 294 at the RLP.
Display 700 will be similar to the illustration of FIG. 29 with
some variations. For example, the locator will be behind the boring
tool rather than ahead of it. Moreover, the "predicted" depth at
the RLP is less meaningful than that at the FLP since it does not
really represent a prediction of a future depth, but a previous
depth behind the boring tool. Additionally, the predicted depth at
the RLP should be determined including the step of changing the
sign of the pitch, since such predicted depth determinations
performed herein assume a position ahead of the boring tool.
[0229] Referring to FIGS. 22 and 38, should the operator move into
region 7, having flux slope orientation characteristic d, arrow 726
on display 700 will point in a rearward direction from locator icon
724 indicating to the operator that all of the locate information
is now behind the locator with a signal strength of "-250" or less
on signal strength display 734.
[0230] Referring to FIG. 22, while the third locating technique is
described with regard to following the entire intended path of the
boring tool, this technique is readily adaptable to beginning at
essentially any point relative to the intended path. Upon power up,
the locator of the present invention will set its signal strength
reference value to a maximum, identify the flux slope orientation
characteristic at its present location and measure the signal
strength of the locating signal. As a first example, it will be
assumed that locating is initiated within a region characterized by
flux slope orientation characteristic b. Therefore, a locate point
will be found by moving in the reverse direction irrespective of
whether the locator is in region 1 or region 5. Accordingly,
display 700 may be configured to show locate point target 740 ahead
of the locator icon in the manner illustrated by FIG. 26. The
operator may then move the locator to the locate point, placing the
locate point target within locator icon 724, as described with
regard to FIG. 28. At the locate point, a signal strength reference
value should be stored. The locate point can be identified as a
forward or rear locate point based on signal strength. If the
signal strength increases upon moving from the locate point, the
operator is entering region 2 headed toward the boring tool. If the
signal strength decreases, the operator is leaving point C',
heading into region 6. In either instance, the operator may readily
back track to point A in view of the foregoing descriptions.
[0231] Still referring to FIG. 22, as a second example of the
flexibility of the third locating technique, it will be assumed
that locating begins in a region having flux slope orientation
characteristic c. In this situation, a locate point is always ahead
with respect to the forward direction. Thus, if the locator is
oriented in the reverse direction, a target locate point will be
displayed behind the locator in a manner similar to that shown in
FIG. 30 or 31 to guide the operator in the forward direction to the
locate point. Once the locate point has been found and a reference
signal strength value stored, the operator will immediately
discover whether the forward or rear locate point was found by
proceeding as described immediately above.
[0232] Having described locating beginning in regions having flux
slope orientation characteristics b and c, beginning in an a or d
type region will now be considered with reference to FIG. 22. For
an a type flux region 0 or 4, at least one locate point will always
be ahead of the locator in the reverse (or forward) direction. In
this event, continuing to orient the locator in the reverse
direction, display 700 may present arrow 726 directed forward as
shown in FIG. 25. To guide the operator to the locate point, the
forward and rear locate points may be distinguished as described
above. For a d type flux region 3 or 7, it is recognized that at
least one locate point will always be behind the locator in the
forward direction. Therefore, display 700 may present arrow 726
directed rearward as shown in FIG. 38. Upon finding the locate
point, a reference signal strength value may be stored and the
locate point may be distinguished as a forward or rear locate
point. The locating procedure may then be completed. It should be
noted that the locating procedure may be sufficiently complete with
the identification of one of the locate points. That is, a
predicted depth is known and the lateral distance to the boring
tool can readily be estimated. Using this information, a drilling
operation may be controlled from either of the locate points, but
the forward locate point provides a more accurate prediction of the
bore path.
[0233] The descriptions referencing FIGS. 13-38 are limited to
locating with the locator properly oriented and directly above the
intended path of the boring tool. That is, the plane defined by the
orthogonal antennas within the locator is vertically oriented to
extend generally along the intended path. It should be appreciated
that the operator may be assisted in any suitable manner in
maintaining the orientation of the locator. For example, a
direction sensor (not shown) may be provided on the locator such as
a compass or magnetometer to help eliminate problems associated
with rotations of the locator about a vertical axis during the
locating process.
[0234] Referring briefly to FIG. 28, in an off path orientation,
the operator may receive the indication shown in FIG. 28 (locate
point target within locator icon 724) even though the locator is to
the side of the intended path rather than directly above.
Therefore, at each vertical balance point (forward locate point C'
or rear locate point C, as shown in FIG. 22), an operator should
turn the locator by 90.degree. to the intended path. If the locator
is directly above the intended path, locate point target 740 will
remain within display window 742 of locator icon 714. If, however,
the locator is to either side of the intended path, locate point
target 740 will move ahead or behind locator icon 724 as shown, for
example, in FIGS. 27 and 30, respectively. By moving the locator
perpendicular to the intended path, locate point target 740 may be
moved back into locator icon 724, ensuring that the locator is now
substantially above the intended path with reference to the actual
locate point. The horizontal flux balance for a level transmitter
is a plane perpendicular to the axis of the transmitter. If the
transmitter is not level then there is a corresponding plane
perpendicular to the axis of the transmitter that has a flux slope
equal to the slope of the transmitter's axis. This flux
relationship can be used to locate the transmitter from the side
when access above the transmitter is restricted. Locating to the
side with the above described procedure is the same as for Regions
3 and 4, except the signal strength at the horizontal balance point
(point A extended) is used for reference.
[0235] With reference to FIG. 21 it should be appreciated that the
present invention contemplates the use of circuit 500 cooperating
with additional circuitry (not shown) for electronically rotating
antennas 482a and 482b in an automated manner. That is, the use of
the four locating field measurements obtained using these antennas
in conjunction with the circuit is completely transparent to an
operator using locator 36. In this regard, signal strength
monitoring is performed in a particular way when a balance point is
approached using the X or + antenna configuration. Specifically, if
the configuration exhibits a substantially weaker signal in one of
the antennas, then the other configuration is favored. For example,
on approaching a locate point, the + antenna configuration exhibits
a null on the horizontal antenna. Therefore, the X antenna
configuration is preferring in traversing such a balance point.
This switching function is automated. It is to be understood that
programming for implementation of the methods described herein is
considered to be within the ability of one having ordinary skill in
the art in view of this overall disclosure. It is also possible to
interface (not shown) antennas 482a and 482b of FIG. 21 with the
circuitry of FIG. 18. This may be accomplished, for example, by
connecting the output of amplifier 454a, at a node 760 (FIG. 21),
to a node 762 at one side of capacitor C404 (FIG. 18). At the same
time, the output of amplifier 454b, at a node 764 (FIG. 21), is
connected to a node 766 (FIG. 18) at one side of capacitor C502. In
such an implementation, antennas 452a and 452b, including
associated amplifiers 454a and 454b in FIG. 18, may be eliminated.
By combining the circuitry of FIGS. 18 and 21, a vector sum signal
is available in addition to the sum and difference signals
generated by receiver 500 of FIG. 21.
[0236] Referring to FIG. 39, a block diagram of a locator
manufactured in accordance with the present invention is generally
indicated by the reference number 800. Locator 800 includes a
microprocessor 802 interfaced with a telemetry section 804 which
may, for example, receive phase signal 604 (FIG. 2). Further
components include a display 806 and a locating signal
receiving/switching section 808 which is configured for automatic
switching of antennas 482a and 482b and which incorporates the
circuitry of FIGS. 18 and 21, described above. The cooperating
switching circuitry within section 808 may be designed by one
having ordinary skill in the art in view of this disclosure. A
bi-directional connection 809 connects microprocessor 802 with
receiving section 808. Other bi-directional lines 810 connect
receiving section 808 to a first depth/range receiver 812, a second
depth/range receiver 814 and a roll/pitch receiver 816. In this
way, antennas 482a and 482b are connectable directly to depth
receivers DR1 and DR2 when it is desired to use the X antenna
configuration. When the + antenna configuration is needed, the
circuitry of FIG. 21 is interposed between antennas 482a and 482b
and depth receivers DR1 and DR2, respectively, so as to provide sum
and difference signals to the depth receivers. The vector sum
signal generated by the circuitry of FIG. 18 is provided to
roll/pitch receiver 816.
[0237] While in the foregoing specification this invention has been
described in relation to certain preferred embodiments thereof, and
many details have been set forth for purposes of illustration, it
will be apparent to those skilled in the art that the invention is
susceptible to additional embodiments and that certain of the
details described herein may be varied considerably without
departing from the basic principles of the invention.
* * * * *