Piercing tool aiming device

A system and for providing a bore sight in a piercing tool. A transmitter emits a magnetic field. The flux lines which emanate along the transmitter axis are substantially straight. A receiver at a remote, target location can detect these flux lines. The receiver and transmitter are oriented such that the substantially straight flux line are along an intended bore path. Then, a piercing tool or other boring tool is oriented along the same path and a bore is created.

SUMMARY

The present invention is directed to a method for planning and maintaining a straight line path to an intended target when using a piercing tool or similar device.

DETAILED DESCRIPTION

The use of high frequency alternating current (“AC”) fields for short range direction finding is useful in locating subterranean devices and tools such as HDD bits. These devices are known in the art, such as in U.S. Pat. No. 7,786,731, issued to Cole, et al., the contents of which are incorporated by reference herein.

These “AC” fields can be detected using a wire wound coil and a narrow band filter receiver tuned to the transmit frequency. A coil of wire can only detect a changing magnetic field and therefore cannot detect a “DC” field.

With reference toFIG.1, such an “AC” magnetic field10emanating from a dipole field transmitter12is shown. The limitations of such a field10are dictated by the fact that magnetic lines of flux14emanating from the transmitter12are curved, flowing around a loop from one pole of the transmitter12to the other. The only flux lines14which approximate to “straight” lines are those which extend from the ends of the transmitter. These will average to a straight line when integrated by the area of a coil receiving antenna16, when that receiver is on such a “straight” line. This technique will be referred to throughout the application as “bore sighting”, with a line of straight magnetic flux14considered a bore sight line15.

It should be understood that while only two dimensions of the field10are shown inFIG.1, it represents a three dimensional field which extends into, and out of, the figure. However, if the figure represents the x-y aspect of the field10in a Cartesian coordinate system with the transmitter axis (and bore sight line15) parallel to the x axis, the x-z aspect of the field will be substantially identical. To the extent that only two dimensions of a field may be shown in any figure, it can be understood that the figure is parallel to the transmitter axis.

With reference toFIG.2, a simple job site20is shown. On the job site20, a desired bore path22exists between a first location24and a second location26. As shown, the first location24and second location26are visually separated, such that an operator at one of the first24and second26location cannot see the other location. For example, each of the first location24and second location26may be in a basement or pit.

The desired bore path22may be known roughly, but minimizing errors over a bore length is important. For example, for a twenty-foot bore, an error of three degrees at the starting location results in an error of over a foot.

The magnetic flux lines14generated by a transmitter12penetrate the ground and can be “visible” at an otherwise invisible location. If the receiving antenna16is oriented towards the transmitter12, the direction of the lines of flux14can be measured and used to determine the orientation of the transmitter12.

The transmitter12may be a standard ferrite antenna. In some embodiments, the ferrite antenna or other transmitter may be supported such that it is isolated from shock.

It may be preferable to utilize an orthogonal array of receiver coils used to measure flux direction. One such set of coils is shown in U.S. Pat. Pub. No. 2020/0142089, Cole, et al., the contents of which are incorporated by reference herein.FIG.4shows such a receiving antenna16. The antenna16comprises a first30and second32pair of antennas, each pair30,32oriented with common centers and at ninety degree angles relative to the other of the pair. In this way, the field10can be balanced across each pair30,32to align the receiving antenna16with the bore sight line15of the field10.

By orienting the transmitter12and receiver16prior to boring operations, the receiver16can detect deviation of the transmitter by detecting a “curve” in the received flux lines14. This can be accomplished by orienting both the receiver16and transmitter12to the same reference direction, then rotating the transmitter12until the rotation angle of the transmitter is equal to the measured angle of the magnetic flux lines14in the receiver16. This angle is then locked into the receiver16software and used to monitor the transmitter12motion. This operation may take place in either two dimensions or three, by using a compass direction for azimuth and an elevation sensor.

In this way, the transmitter12and receiver16can define the bore sight line15between them, for use in boring techniques, as described below. Sighting a bore is especially advantageous when used with a piercing tool50, such as tools like that found in U.S. Pat. No. 7,028,785, issued to Randa, et al., the contents of which are incorporated herein by reference. Piercing tools50typically include reciprocating strikers (not shown) which cause a front nose to move through a subsurface.

In the job site20ofFIG.2, the piercing tool50is at the first location24—a basement—with no visual sight line to the second location26in a pit. In operation, the piercing tool50will initially form a borehole52at an entry point54, and once fully in a subterranean formation, will maintain a substantially straight line. However, small mistakes in the angle at which the piercing tool50is started can result in a misaligned borehole. Thus, a misaligned piercing tool50at the first location24may miss the second location26by an unacceptable amount. Using flux lines of an emitted field to orient a piercing tool to a target may overcome these limitations.

While other tools may be used with the transmitter12and determination of a bore sight line15, such tools will need to operate on substantially straight lines such that the straight bore sight line15is useful.

The operator initially orients the transmitter12to point to the receiver16. As shown inFIG.3, the transmitter12is mounted to a bracket52which is temporarily attached to the piercing tool50. The bracket52may be magnetically attached to the piercing tool50such that the transmitter12axis is parallel to the axis of the piercing tool.

As shown, the bore sight line15is offset some distance from the desired bore path22. The receiver22may be positioned at a similar offset from the target at the second location26. Further, the bracket52may be at a small enough offset such that the error between the transmitter12position and the centerline of the piercing tool50is negligible.

Other apparatus could be used, for example, the transmitter12could be disposed internally in a housing located behind, and in line with, the piercing tool50. A ring-shaped harness may be used for attaching the transmitter. In any case, the transmitter12should be oriented such that its longitudinal axis is parallel to the longitudinal axis of the piercing tool12.

The field10, and flux lines14, generated by the transmitter12are received at the receiver16. The bore sight line15is found and the receiver16oriented accordingly, with the proper angle and orientation locked into the receiver16. This orientation will define the desired bore path22, which extends along the bore sight line15between the first24and second26location. The receiver16, locked into position and orientation, can subsequently monitor the transmitter coil12orientation as the piercing tool50is inserted into the subsurface.

As shown inFIG.2, the proper orientation is achieved, with the transmitter and receiver oriented along the bore sight line15, which is substantially identical to the desired borepath22. The path shown is substantially horizontal, but it should be understood that the planned borepath may have a vertical component, and a component “into the page”—that is, the bore sight line15is determined in three dimensions. Likewise, angle64is shown from vertical from illustrative purposes, but the angle at which the sight line15(and thus the borepath52) is oriented may have components in three dimensions.

A compass may be used to orient the receiver16to a cardinal compass direction. Orientation data may be fed back to an operator via a wire or an RF transmitter from the receiver16. The transmitter12may be mounted on a protractor or goniometer which is oriented to the same cardinal direction. The operator may then rotate the transmitter12until the measured angle64on the protractor is equal to the flux direction measured by the receiver16. The receiver16is then nulled relative to this direction to find the bore sight line15.

Since the tool may be in a basement, normal Bluetooth signals to communicate between the receiver16and transmitter12may not be sufficient. One transmission method would be to transmit Multi-Use Radio Service (“MURS”) packet signals. The lower frequency and higher power allow for longer ranges and greater penetration than Bluetooth.

An application or program in a common smart phone device or other hand-held device may be used for the processing and alignment. As these devices usually do not receive multi-use radio service signals, a relay device6omay be necessary if such a signal is utilized. This relay device6owould be located near the operator and would translate the radio data to Bluetooth for use by the hand-held device. This relay60could also have LEDs which would indicate bore sight errors as the piercing tool50is used.

The transmitter12may initially be paired with a protractor or goniometer or other sort of orientation sensor, such that it may be matched to the angle of the receiver16. The transmitter12and receiver16are oriented along the proper angle64on opposing sides of the bore sight path15, which is substantially the desired bore path22.

If the operation of the piercing tool50makes continued pairing with the transmitter12unfeasible, it may be mounted in an offset, parallel position to keep the tool aligned as it is inserted into the ground. Alternatively, the transmitter12may continue to be paired with the piercing tool50until the alignment of the piercing tool is assured, such as after a length of the borehole is created. An alignment cradle62may be used with the piercing tool50to orient the tool to the proper angle. Such an alignment cradle62may be helpful in matching the measured angle of the piercing tool50to the angle of the protractor.

Prior to use at a job site20, the transmitter12and receiver16may be calibrated to reduce measurement errors. Calibration may occur by many techniques. One such technique to first orient the transmitter12and receiver16to the same direction. For example, both may be oriented toward magnetic north. The transmitter12is then angled such that the flux angle measured by the receiver16equals the angle of the transmitter as measured by a goniometer or protractor. This condition indicates the transmitter12is pointing to the center of the receiver16antenna array. The receiver16is then “zeroed” to this angle and subsequently measures the deviation of transmitter16heading from this “boresite” line. Preferably, this calibration technique would be performed for both azimuth and elevation.

Changes may be made in the construction, operation and arrangement of the various parts, elements, steps and procedures described herein without departing from the spirit and scope of the invention as described in the following claims. For example, as shown inFIG.5, the positions of the transmitter12and receiver16at a job site20a, are alternated. The steps for operating the system are similar in this orientation, with the bore sight line15determined in the same manner. However, with the transmitter located on the opposite side of the planned bore path from the transmitter, it is the angle at the receiver16which must be matched by the insertion of the piercing tool50.