05520255 is referenced by 166 patents and cites 6 patents.

A modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations, comprises a number of hydraulic actuators spaced apart around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. A selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, each movable thrust member is displaced outwardly at the same selected rotational position so as to bias the drill bit laterally and thus control the direction of drilling. The control valve is a disc valve comprising two relatively rotating elements having contiguous surfaces formed of polycrystalline diamond. The elements are maintained in coaxial relation by a polycrystalline diamond bearing pin which extends axially from one element and engages in a central axial bearing aperture in the other element.

Title
Modulated bias unit for rotary drilling
Application Number
8/455455
Publication Number
5520255
Application Date
May 31, 1995
Publication Date
May 28, 1996
Inventor
Robert A Russell
Barnwood
GB
Richard E Thorp
Frampton-Cotterell
GB
John D Barr
Cheltenham
GB
Assignee
Camco Drilling Group
GB
IPC
E21B 7/08
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