Patent ID: 6293359
Filing Date: 2001-09-25
Classification: E21B

Abstract:
A drilling apparatus comprising:a drill bit operable to break rock to produce a hole in a forward direction;a hydraulic drive assembly arranged to be mounted exteriorly of the hole for communicating drive force to the drill bit;a drill string attached to and supported by the drive assembly for extending from the drive assembly along the drilled hole to the drill bit;a mast for supporting the drive assembly for movement of the drive assembly with the drill string and the drill bit carried thereby in a direction longitudinally of the hole;a hydraulic cylinder assembly for causing movement of the drive assembly along the mast in a forward direction for forwarding the drill bit along the hole to the rock face and for applying a feed force on the drill bit at the rock face and in a rearward direction for reducing the feed force and for withdrawing the drill bit from the hole;the hydraulic cylinder assembly having a pulldown pressure side and a holdback pressure side arranged such that the supply of fluid under pressure to the pulldown pressure side tends to move the drive assembly in the forward direction and to cause discharge of fluid from the holdback side and the supply of fluid under pressure to the holdback pressure side tends to move the drive assembly in the rearward direction and to cause discharge of fluid from the pulldown side so that a resultant force on the drive assembly in the forward and rearward directions is dependent upon the pressure differential between the pulldown and holdback sides;and a control system for controlling the rotation rate of the drill bit and the feed force on the drill bit, the control system comprising:a first valve for controlling a rate of supply of fluid to the hydraulic drive assembly for controlling the rate of rotation of the drill bit;a second valve for controlling a rate of supply of fluid to the pulldown side of the hydraulic cylinder assembly for controlling the rate of movement of the drill bit in the forward direction;a third valve for controlling a rate of discharge of fluid from the holdback side of the hydraulic cylinder assembly;a control unit for controlling the first and second valves having a first input for setting a selected rate of rotation of the drill bit and a second input for setting a selected rate of forwarding movement of the drill bit;and a hydraulic feedback line for communicating an increase in pressure of the fluid at the hydraulic drive assembly, caused by an increase in resistance to the rotation of the drill bit, to the holdback side of the hydraulic cylinder assembly such that the rate of forward movement of the drill bit is varied in proportion to changes in the pressure of the fluid at the hydraulic drive assembly.