Gyro-stabilized single-axis platform

Claim 1

An instrument for measuring the direction of a borehole comprising a case having a longitudinal axis coincident, in use, with the axis of the borehole, a single-degree-of-freedom gyro comprising an outer gimbal mounted in the case with its axis coincident with the longitudinal axis thereof, an inner gimbal mounted in the outer gimbal with its axis coincident with the outer gimbal axis, a gyro rotor mounted in the inner gimbal, means for sensing angular movement of the inner gimbal relative to the outer gimbal and applying a torque to the outer gimbal to rotate it about its axis so that the inner gimbal precesses back to its initial position, means for measuring the angle of rotation of the case about its longitudinal axis relative to the outer gimbal and a gravity sensor unit for measuring three components of gravity in three non-coplanar directions.

Claim 6

A method of surveying a borehole comprising: moving a survey instrument along the borehole, said survey instrument comprising a case having a longitudinal axis coincident, in use, with the axis of the borehole, a single-degree-of-freedom gyro comprising an outer gimbal mounted in the case with its axis coincident with the longitudinal axis thereof, an inner gimbal mounted in the outer gimbal with its axis perpendicular to the outer gimbal axis, a gyro rotor mounted in the inner gimbal; continually sensing angular movement of the inner gimbal relative to the outer gimbal as the instrument moves along the borehole and applying a torque to the outer gimbal to rotate it about its axis so that the inner gimbal precesses back to its initial position; determining at each of a series of survey stations spaced along the borehole a set of three components of gravity in three non-coplanar directions relative to the outer gimbal; calculating, from the sensed components of gravity at each of said survey stations, the inclination of the borehole and the non-rotative high-side angle of the instrument relative to a reference direction which does not rotate about the longitudinal axis of the instrument as it travels along the borehole at each station; and calculating, from said inclination and non-rotative high-side angle, the azimuth of the borehole at each station.

Claim 7

A method of surveying a borehole comprising: moving a survey instrument along the borehole, said survey instrument comprising a case having a longitudinal axis coincident, in use, with the axis of the borehole, a single-degree-of-freedom gyro comprising an outer gimbal mounted in the case with its axis coincident with the longitudinal axis thereof, an inner gimbal mounted in the outer gimbal with its axis perpendicular to the outer gimbal axis, a gyro rotor mounted in the inner gimbal; continually sensing angular movement of the inner gimbal relative to the outer gimbal as the instrument moves along the borehole and applying a torque to the outer gimbal to rotate it about its axis so that the inner gimbal precesses back to its initial position; determining at each of a series of survey stations spaced along the borehole a set of three components of gravity in three non-coplanar directions relative to the outer gimbal; calculating, from the sensed components of gravity at each of said survey stations, the inclination of the borehole and the non-rotative high-side angle of the instrument relative to a reference direction which does not rotate about the longitudinal axis of the instrument as it travels along the borehole at each station; and calculating, from said inclination and non-rotative high-side angle, the azimuth of the borehole at each station.