| 摘要 |
<p num="1"><br/><br/><br/>The present invention provides a directional drilling apparatus for use in the <br/>directional drilling of bore holes. In one embodiment the apparatus comprises <br/>a plurality of cutting elements movably mounted with respect to a rotatable <br/>body member, wherein the cutting elements are movable between first, radially <br/>retracted, positions and radially extended, positions for cutting. A rotary <br/>valve is provided for synchronising the movement of the cutting elements <br/>between their respective extended and retracted positions in accordance with <br/>the rotational position of the body member in the bore hole being drilled. <br/>Control of the directional drilling system is effected by synchronised <br/>movement of the cutting elements from an inner to an outer radial position in <br/>accordance with the angular position of the drill bit.<br/>
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