Advanced underground homing system, apparatus and method

Abstract

A boring tool that is moved by a drill string to form an underground bore. A transmitter transmits a time varying dipole field as a homing field from the boring tool. A pitch sensor detects a pitch orientation of the boring tool. A homing receiver is positionable at a target location for detecting the homing field to produce a set of flux measurements. A processing arrangement uses the pitch orientation and flux measurements with a determined length of the drill string to determine a vertical homing command for use in controlling depth in directing the boring tool to the target location such that the vertical homing command is generated with a particular accuracy at a given range between the transmitter and the homing receiver and which would otherwise be generated with the particular accuracy for a standard range, different from the particular range. An associated system and method are described.

What is claimed is: 
     
         1 . In a system including a boring tool that is moved by a drill string using a drill rig that selectively extends the drill string to the boring tool to form an underground bore such that the drill string is characterized by a drill string length which is determinable, the transmitter configured for transmitting a including a pitch sensor for detecting a pitch orientation of the boring tool and for transmitting a dipole electromagnetic field, a homing apparatus comprising:
 a homing receiver that is positionable at least proximate to a target location for detecting the dipole electromagnetic field to produce a set of flux measurements that are subject to a measurement error; and   a processing arrangement that is configured for (i) determining a vertical homing command and a horizontal homing command such that a measurement error accumulates as the boring tool is moved through a series of positions and (ii) compensating for the measurement error by determining the vertical homing command based on the detected pitch orientation and the set of flux measurements, subject to the measurement error, in conjunction with a determined length of the drill string to establish the vertical homing command to compensate for the measurement error.   
     
     
         2 . The homing apparatus of  claim 1  wherein the vertical homing command has a particular accuracy that is greater than another accuracy associated with the horizontal homing command for use in controlling depth in directing the boring tool to said target location. 
     
     
         3 . The homing apparatus of  claim 1  wherein the homing receiver is configured in a way which produces an inaccuracy in said set of flux measurements as said measurement error which inaccuracy increases as a range between the homing receiver and the transmitter increases. 
     
     
         4 . The homing apparatus of  claim 1  wherein said processing arrangement is configured to establish an uncorrected position of the boring tool along a nominal drill path in a vertical plane that contains an initial position of the transmitter and the homing receiver and to introduce a correction to that uncorrected position to establish a corrected position as part of generating the vertical homing command. 
     
     
         5 . The homing apparatus of  claim 1  wherein said homing receiver includes an antenna arrangement having a set of three orthogonally opposed antennas for determining the set of flux measurements to provide three flux measurements taken along three orthogonally opposed directions.