Boring or penetrating the earth – With tool drive prime mover or above-ground mechanical... – Rotary drive for a relatively advancing tool
Reexamination Certificate
2000-06-05
2001-09-25
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
With tool drive prime mover or above-ground mechanical...
Rotary drive for a relatively advancing tool
C173S147000
Reexamination Certificate
active
06293359
ABSTRACT:
This invention relates to a drilling apparatus and particularly to an improved control system which controls force on the drill bit.
BACKGROUND OF THE INVENTION
The present invention is primarily but not exclusively concerned with drilling of holes for receiving explosives in a blast hole operation. One of the primary objectives of blast hole drilling is to produce straight holes and to increase drill bit life. For uniform breaking of a rock mass in the resulting explosion, it is important to have blast holes that are straight and accurately positioned. Production of straight holes depends on the feed force, rotation speed and torque applied through a “down the hole” (DTH) “in the hole” (ITH) percussion hammer to a drill bit. These drilling parameters are set according to the geological conditions of the rock mass.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a drilling apparatus aimed at the production of straight holes by a drill.
According to a first aspect of the invention there is provided 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.
Preferably the percussion hammer causes forward and rearward reciprocation of the hammer piston to apply percussive force to the drill bit.
Preferably the holdback side is connected to a directional control valve movable between a first position in which the fluid from the hydraulic cylinder assembly is discharged to the third valve and to a second position in which fluid from a supply valve is directed to the hydraulic cylinder assembly for driving rearward movement of the drill bit.
Preferably the hydraulic feedback line is connected to the holdback side between the directional control valve and the third valve.
Preferably the control system includes a third input for rearward movement of the drill bit.
Preferably the control system further includes a pressure switch responsive to pressure of the fluid at the hydraulic drive assembly exceeding a predetermined pressure limit and wherein the control system is arranged in response to exceeding said limit to effect supply of fluid to the holdback side to drive rearward movement of the drill bit.
Preferably the control system is arranged to drive said rearward movement for a predetermined time and then to supply fluid to the pulldown side to drive forward movement of the drill bit.
Preferably the control system is arranged to repeat the rearward movement and the forward movement over a set number of cycles and then to halt said movements in the event that the pressure continues to reach said limit.
According to a second aspect of the invention there is provided 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 drilling valve operable into two positions for controlling supply of fluid to the pulldown side and to the holdback side respectively so as to control forward and rearward movement of the drill bit respectively
a second valve for controlling a rate of supply of fluid to the pulldown side 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 drilling valve and the first and second valves, the control unit 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;
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
Desrosiers Georges J.
Dobran Mauro F.
McIvor James Wilfred
Battison Adrian D.
Cubex Limited
Pezzuto Robert E.
Williams Michael R.
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