Electronic guidance system and method for locating a discrete in-ground boring device

A navigation system for determining the position of a boring device within the ground, the navigation system comprising:

• (a) a navigation computer;
• (b) a primary navigation package comprising:
• (i) a triaxial accelerometer located in said boring device and producing a first set of data signals representative of a rotation of said boring device;
• (ii) a triaxial magnetometer located in said boring device and producing a second set of data signals representative of a strength of a magnetic field intersecting the triaxial magnetometer in said boring device;
• and
• (iii) a transmitter for transmitting the first set of data signals representative of the rotation of the boring device and the second set of data signals representative of the strength of the magnetic field intersecting the triaxial magnetometer to the navigation computer, wherein the navigation computer can manipulate the first and the second set of data signals to determine a calculated position of said boring device within the ground;
• and
• (c) a secondary navigation package comprising:
• (i) radiating means located in said boring device for emitting an electromagnetic field having a predetermined radiation pattern;
• (ii) a locator for detecting the electromagnetic field emitted from the radiating means and for determining an actual position of the radiating means by measuring the strength of the received electromagnetic field;
• and
• (iii) a transmitter for transmitting the actual position of the radiating means to the navigation computer, wherein the navigation computer periodically sets the calculated position of the boring device generated by the primary navigation package to the actual position of the radiating means generated by the secondary navigation package to correct an error that has occurred in the calculated position as determined by the primary navigation package.

A method of accurately following a predetermined borehole path by monitoring the position of a boring device beneath the ground, the boring device containing a primary navigation package containing means for generating a first set of signals indicative of the position of the boring device and a secondary navigation package containing means for generating a second set of signals indicative of the position of the boring device, the method comprising the steps of:

• (a) receiving the first set of signals indicative of the position of the boring device;
• (b) calculating a first position of the boring device;
• and
• (c) guiding the boring device along the predetermined borehole path based on the calculated first position, the first position being periodically cleared of accumulated error by:
• (i) receiving the second set of signals indicative of the position of the boring device;
• (ii) calculating a second position of the boring device;
• and
• (iii) setting the first position of the boring device equal to the second position of the boring device to remove any error present in the first position.

A method of accurately following a predetermined borehole path by monitoring the position of a boring device beneath the ground, the boring device containing a primary navigation package comprising a triaxial magnetometer and a triaxial accelerometer and a secondary navigation package comprising a radiating means for emitting an electromagnetic field having a predetermined radiation pattern and a locator for determining a position of the radiating means by measuring a strength of the electromagnetic field emitted from the radiating means at a point distant from the radiating means, the method comprising the steps of:

• (a) receiving a first set of signals from said triaxial magnetometer indicative of a magnetic field intersecting the triaxial magnetometer and a second set of signals from said triaxial accelerometer indicative of a rotation of said boring device;
• (b) calculating a first position of the boring device from the first set of signals, and the second set of signals;
• and
• (c) guiding the boring device based on the calculated first position, the first position being periodically corrected of an accumulated error by:
• (i) determining a second position of the boring device by using the locator to determine the position of the radiating means;
• and
• (ii) setting the first position equal to the second position.