Automatic sequencing system for earth drilling machine

In an earth drilling machine of the type comprising a mast, a drive assembly movable along the mast, a boom mounted adjacent the mast to move between a lower boom position and an upper boom position, a plurality of boom clamps mounted to the boom to grip a length of down hole tubular, a tubular storage device at a lower level, and a lifter configured to move a length of down hole tubular between a lower lifter position aligned with the tubular storage device and an upper lifter position aligned with the lower boom position, the improvement comprising:

• an automatic sequencing system comprising:
• a plurality of position sensors responsive to position of at least the boom, the lifter, and a length of down hole tubular at selected positions;
• means, responsive to the position sensors, for automatically coordinating movement of the lifter and the boom such that the boom raises a first tubular from the lower to the upper boom positions and the lifter raises a second tubular from the lower to the upper lifter positions, said boom and lifter being controlled such that movement of the boom overlaps movement of the lifter;
• wherein said coordinating means controls the boom and the lifter such that upward movement of the first tubular in the boom overlaps upward movement of the second tubular in the lifter;
• said position sensors comprising a plurality of pilot pressure control valves operative to control pilot pressure at least in part in response to position of the boom clamps and the lifter;
• said movement coordinating means comprising a plurality of mechanically controlled hydraulic valves responsive to pilot pressure as controlled at least in part by the pilot pressure control valves to automatically open and close the boom clamps, raise and lower the lifter, and raise and lower the boom.