| 摘要 |
<p>A drilling rig (10) including a mast assembly (12) supported on a support frame (11), and a tool (24) suspended by a cable (23) from the mast assembly (12). The tool (24) is caused to reciprocate by a rotatable crank arm (28) carrying a sheave (25) around which the cable passes and the crank arm (28) may be driven for the cycle of rotation to raise and lower the tool (24) or may be driven for only part of its cycle to raise the tool (24) and allow it to free fall. </p> |
