| 摘要 |
A drill rig (10) comprises a tower (12) and a drill head (14) that is able to travel linearly up and down the tower (12). The drill head (14) provides torque to a drill string (16) attached to the drill head (14) ad thus to a drill bit (18) coupled to a distal end of the drill string (16). The drill head (14) is traversed along the tower (12) by a plurality of rams (22a, 22b) and (22c) (hereinafter referred to in general as "rams 22"). The rams (22) provided hold back and pull down for the drill bit (18) via the drill head (14). The rams (22) are selectively operable to enable the hold back and pull down applied to the drill bit to be selectively varied. Thus for example a first of the rams (22a) is selected to operate when drilling to a first depth, then the rams (22b) and (22c) are selected to operate when drilling to a second greater depth; and finally all three rams (22a, 22b) and (22c) are selected to operate when drilling to a third greater depth. |
