Patent ID: 8393413

Claim:
A steerable bore hole drilling tool comprising: a tool body having a first end connectable to a drive member and a second end connectable to a drill bit, the tool body arranged to transmit rotary motion from said first end to said second end; a deflection member disposed on the tool body to deflect said second end away from a longitudinal axis of the tool body; a sensor unit; estimation means arranged to estimate the direction and/or position of the tool body on the basis of the output of said sensor unit; control means for calculating the difference between the estimated direction and/or position and corresponding pre-stored direction and/or position information and for controlling said deflection member so as to deflect said second end on the basis of said difference; and a counter-rotating platform disposed on the tool body, said sensor unit being disposed on said counter-rotating platform, wherein said counter-rotating platform is arranged to mechanically decouple said sensor unit from the tool body, and said counter-rotating platform is further arranged to decouple said sensor unit from the rotary motion of said tool body, such that in use, the sensor unit does not move relative to an Earth fixed reference frame.