Improvement of the drill head positioning accuracy using magnetic sensors

Precise measurement of drill head position is required to avoid the collision between the drill head and underground facilities, when a horizontal drilling machine is used for constructing underground gas pipes in the city. A positioning technique without special devices on the ground surface has been expected especially beneath the waterway or heavy traffic road, because it is difficult to conduct the measurement for locating the drill head position on the ground surface.The authors have studied both magnetic and pitch sensors installed inside the drilling tool for locating drill head position, and we have found that alignment of two sets of magnetic sensors is effective to reduce noise in the city which disturbs the natural magnetic field. We have confirmed that the sensors can keep the drill head position with a precision less than 10 cm, when the drill head progresses 12 m along the drill hole. Engineers and workers do not have to walk around just above the underground drilling site to locate the drill head position by using the sensors.