Apparatus for eliminating net drill bit torque and controlling drill bit walk

摘要

The drilling apparatus comprises an axial thrust module 107; a drilling module 111 having inner 115 and outer 113 drill bits; and a rotary coupling 109 which incorporates a rotary encoder 201 to determine relative rotation between the thrust and drilling modules. A control module uses information from the rotary encoder, ie. the angular rotation of the drilling module with respect to the thrust module, in order adjust the torque associated with the drill bit by making adjustments to the relative rotational velocity of the inner and outer drill bits. In this way the reaction torque in manipulated in order to prevent loss of penetration, due to undesired rotation of the drilling apparatus, and "drill bit walk" is controlled.