Patent ID: 7350593

Claim:
An earth drilling rig comprising: a hydraulically operated drill head for rotating a hollow drill string, an elongated mast for supporting the drill head; a hollow drill string comprising at least one pipe section connected to, and rotatable by, the drill head; a hydraulically operated hoist for moving the drill head longitudinally along the mast; a hydraulic pump mechanism for supplying hydraulic fluid under pressure for driving the drill head and said hoist; a pneumatic hammer connected to the drill string; a drill bit rotatable with the drill string and subject to repeated impact by the pneumatic hammer; an air compressor, connected to the drill head, for causing compressed air to flow through the drill string for operation of the pneumatic hammer; valving and regulators for controlling and regulating the flow of hydraulic fluid to the drill head and the hoist; a sensor, comprising a transducer in direct fluid communication with to the hydraulic fluid for operating the hoist, said transducer providing an output signal representative of the pressure of the hydraulic fluid operating the hoist; and a programmed electronic control for controlling the flow of hydraulic fluid through said valving to the hoist and drill head, said control being responsive to said output signal of the transducer, connected to control operation of the hoist and drill head, and programmed to: operate the hoist and drill head, while the bit is in a bore hole, to rotate the drill string, and raise the drill string to a fixed position by an amount sufficient to ensure that the bit is free to move vertically in the bore hole; and measure the hydraulic pressure required to hold the drill string in said fixed position, thereby obtaining a pressure measurement corresponding to the actual weight of the drill string.