PRESSURE CONTROL OF A DRILLING APPARATUS

DISPOSITIF DE COMMANDE DE LA PRESSION D'UN APPAREIL DE FORAGE

English Abstract

Apparatus for blast hole drilling includes a hammer and drill bit driven by a hydraulic drive motor outside the hole through a drill string extending along the drilled hole to the drill bit. The drive motor is carried on a mast with a telescopic hydraulic cylinder driving the motor 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 cylinder assembly has a pulldown pressure side fed at a constant supply rate and a holdback pressure side controlled to discharge the fluid when moving downwards and to supply the fluid at a constant rate when pulling up. The control system includes a first valve for controlling a rate of supply of fluid to the motor for controlling the rate of rotation of the drill bit, a drilling valve operable to supply fluid to the pulldown side or to the holdback side, a second valve for controlling the rate of supply of fluid to the pulldown side, a third valve for controlling the rate of discharge of fluid from the holdback side, a hydraulic feedback line for communicating an increase in pressure of the fluid at the motor, caused by an increase in resistance to the rotation of the drill bit, to the holdback side of the so that the rate of forward movement of the drill bit is varied in proportion to changes in the pressure at the motor and a pressure switch responsive to pressure of the fluid at the hydraulic drive assembly exceeding a predetermined pressure limit to repeatedly cycle an upward and downward movement of the drill bit until the overpressure condition clears or until a number of cycles is completed.

French Abstract

Un appareil pour le forage de trou de mine comprend un marteau et un trépan entraînés par un moteur d'entraînement hydraulique à l'extérieur du trou à travers une rame s'étendant le long du trou foré au niveau du trépan. Le moteur d'entraînement est monté sur un mât avec un cylindre hydraulique télescopique entraînant le moteur le long du mât vers l'avant pour acheminer le trépan le long du trou face à la paroi et pour appliquer une force d'alimentation sur le trépan face à la paroi et dans une direction vers l'arrière pour réduire la force d'alimentation et pour retirer le trépan du trou. L'ensemble de cylindre a un côté de pression déroulant alimenté à un taux d'alimentation constant et un côté de pression de retenue commandé pour décharger le fluide lors du déplacement vers le bas et pour fournir le fluide à un taux constant lors de la remontée. Le système de commande comprend une première soupape pour commander un taux d'alimentation de fluide vers le moteur pour commander le taux de rotation du trépan, une soupape de forage pouvant être actionnée pour fournir du fluide au côté déroulant ou au côté de retenue, une deuxième soupape pour commander le taux de décharge de fluide au côté déroulant, une troisième soupape pour commander le taux de décharge de fluide depuis le côté de retenue, une ligne de retour hydraulique pour communiquer une augmentation de la pression du fluide au niveau du moteur, provoquée par une augmentation de résistance au niveau de la rotation du trépan, sur le côté de retenue de sorte que le taux de déplacement vers l'avant du trépan varie en proportion à des changements de pression au niveau du moteur et un commutateur de pression réagissant à la pression du fluide au niveau de l'ensemble d'entraînement hydraulique supérieur à une limite de pression prédéterminée pour fluctuer à plusieurs reprises un déplacement vers le haut et vers le bas du trépan jusqu'à ce que la condition de surpression se calme ou jusqu'à ce qu'un nombre de cycles se termine.

Claims

12

CLAIMS:

1. 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


13

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.

2. The drilling apparatus according to Claim 1 wherein the drill bit
includes a percussion hammer operable to cause forward and rearward
reciprocation of a hammer piston to apply percussive force to the drill bit.

3. The drilling apparatus according to Claim 1 wherein the
holdback side is connected to a directional control valve movable between a
first




14

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.

4. The drilling apparatus according to Claim 3 wherein the
hydraulic feedback line is connected to the holdback side between the
directional
control valve and the third valve.

5. The drilling apparatus according to Claim 3 wherein the control
system includes a third input for selecting a speed of rearward movement of
the drill
bit.

6. The drilling apparatus according to Claim 1 wherein 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.

7. The drilling apparatus according to Claim 6 wherein 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.

8. The drilling apparatus according to Claim 7 wherein 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.

9. A drilling apparatus comprising:
a drill bit operable to break rock to produce a hole in a forward




15

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:




16

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
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;
and a pressure switch responsive to pressure of the fluid at the
hydraulic drive assembly exceeding a predetermined pressure limit;
the control system being arranged in response to the pressure
exceeding said limit to effect supply of fluid to the holdback side to drive
rearward
movement of the drill bit, to drive said rearward movement for a predetermined
time



17

and then to supply fluid to the pulldown side to drive forward movement of the
drill
bit.

10. The drilling apparatus according to Claim 9 wherein the drill bit
includes a percussion hammer operable to cause forward and rearward
reciprocation of a hammer piston to apply percussive force to the drill bit.

11. The drilling apparatus according to Claim 9 wherein 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.

12. The drilling apparatus according to Claim 11 wherein the
hydraulic feedback line is connected to the holdback side between the
directional
control valve and the third valve.

13. The drilling apparatus according to Claim 12 wherein the control
system includes a third input for selecting a speed of rearward movement of
the drill
bit.

14. The drilling apparatus according to Claim 9 wherein 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.

15. A method for drilling comprising:
providing a drill bit operable to break rock to produce a hole in a
forward direction;



18

providing a hydraulic drive assembly arranged to be mounted exteriorly
of the hole for communicating drive force to the drill bit;
providing 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;
providing 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;
providing 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 controlling the rotation rate of the drill bit and the feed force on the
drill bit by:
controlling a rate of supply of fluid to the hydraulic drive assembly for




19

controlling the rate of rotation of the drill bit;
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;
controlling a rate of discharge of fluid from the holdback side of the
hydraulic cylinder assembly;
controlling the first and second valves to select a rate of rotation of the
drill bit and to select a rate of forwarding movement of the drill bit;
and 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.

Description

CA 02310893 2000-06-OS
PRESSURE CONTROL OF A DRILLING APPARATUS
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
s 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
Io 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
is 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;
2o 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;


CA 02310893 2000-06-OS
2
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
s 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
io 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
is 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
2o 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;


CA 02310893 2000-06-OS
3
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
s 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
io 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
is 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.
2o 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


CA 02310893 2000-06-OS
4
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
s 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.
io 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
is 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
20 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


CA 02310893 2000-06-OS
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
s 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
io 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;
is 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;
2o 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


CA 02310893 2000-06-OS
6
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
s 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;
and a pressure switch responsive to pressure of the fluid at the
hydraulic drive assembly exceeding a predetermined pressure limit;
io the control system being arranged in response to the pressure
exceeding said limit to effect supply of fluid to the holdback side to drive
rearward
movement of the drill bit, 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.
is According to a third aspect of the invention there is provided a method
for drilling comprising:
providing a drill bit operable to break rock to produce a hole in a
forward direction;
providing a hydraulic drive assembly arranged to be mounted exteriorly
20 of the hole for communicating drive force to the drill bit;
providing 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;
providing a mast for supporting the drive assembly for movement of


CA 02310893 2000-06-OS
7
the drive assembly with the drill string and the drill bit carried thereby in
a direction
longitudinally of the hole;
providing a hydraulic cylinder assembly for causing movement of the
drive assembly along the mast in a forward direction for forwarding the drill
bit along
s 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
io 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
is dependent upon the pressure differential between the pulldown and holdback
sides;
and controlling the rotation rate of the drill bit and the feed force on the
drill bit by:
controlling a rate of supply of fluid to the hydraulic drive assembly for
controlling the rate of rotation of the drill bit;
2o 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;
controlling a rate of discharge of fluid from the holdback side of the


CA 02310893 2000-06-OS
8
hydraulic cylinder assembly;
controlling the first and second valves to select a rate of rotation of the
drill bit and to select a rate of forwarding movement of the drill bit;
and communicating an increase in pressure of the fluid at the hydraulic
s 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.
The arrangement as described herein has two main functions: a)
io automatic control of feed force, rotation speed and torque according to the
resistance encountered by the drill bit, and b) prevent the drill bit from
jamming. It is
supplied as an added feature along with manual controls. The main components
of
the arrangement as described herein are rotation and feed control interfaces,
a
rotation pressure monitoring device, and a PLC. A ladder logic program and
Is hydraulic feedback are used to control all intended functions.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is a side elevational view of a typical drilling apparatus
2o according to the present invention.
Figure 2 is a schematic illustration of the operating components and
the control system of the apparatus of Figure 1.


CA 02310893 2004-12-30
9
DETAILED DESCRIPTION
Figure 1 illustrates a in the hole (ITH) drill. The rotation motor 4 rotates
the drill string 2 and the drill bit 1 through the top drive assembly 3 at a
predetermined RPM. The drill bit 1 is advanced into a rock mass by the feed
cylinder 5. It breaks rocks due to percussive actions of the hammer 22. Forces
exerted on the bit can be varied either by the operator or by the arrangement
as
described herein. The hydraulic pump 8, driven by a motor 9, is the source of
energy for the rotation motor 4 and the feed cylinder 5.
The feed cylinder 5 is a compound or telescopic cylinder where two
inputs are provided on the pull down side and two inputs are provided on the
holdback side so that compound movement of the top drive assembly 3 on the
mast
6 occurs from the top to the bottom of the mast.
Feed force, rotation speed and torque are set and maintained by
means of hydraulic valves and electrical controls shown in Figure 2. The
rotation
valve 10 controls rotation speed and the drilling valve 11 controls feed rate.
The
amount of feed force and torque on rocks depends on the differential pressure
between the pulldown pressure P1 and the holdback pressure P1. The pulldown
pressure P1 is the supply line pressure to the feed cylinder 5 tending to move
the
top drive assembly 3 downwardly on the mast 6 and it usually remains unchanged
during drilling. The holdback pressure P2 tending to move the top drive
assembly 3
upwardly on the mast 6 is the return line pressure of the feed cylinder 5 and
it is
usually adjusted either manually or automatically by the control system.
When the drill is intended to be used in manual mode, the control


CA 02310893 2000-06-OS
system is turned off, the pulldown pressure P1 is set at a predetermined level
by
adjusting the relief valve 16. The holdback pressure P2 is controlled by the
relief
valve 12. The joysticks 13 and 14 are used to control the rotation valve 10
and the
drilling valve 11 respectively.
s When the control system is turned on, feed force, rotation speed and
torque are set by the potentiometers 18 and 19 respectively. The PLC 17
receives a
preset level of signal from the potentiometer 18 and accordingly energizes the
coil of
the rotation valve 10. Rotation speed remains at this set value until it is
changed by
the potentiometer 18.
to Maximum feed rate is set by the potentiometer 19, which sends signal
to the PLC 17 to energize the drilling valve 11 accordingly.
The hydraulic feedback line and the directional control valve 21 allow
the holdback pressure P2 to vary in direct proportion to the rise or fall of
the rotation
pressure P3. If the drill bit 1 encounters greater resistance, then the
rotation
is pressure P3 will increase causing the holdback pressure P2 to increase and
feed
force and torque to decrease proportionately. This control of feed force helps
maximize the drill bit life.
The pressure switch 20 monitors the rotation pressure P3 and sends a
signal to the PLC 17 to energize the reverse feed coil of the drilling valve
11 once
2o the rotation pressure P3 reaches the preset limit. The feed cylinder 5
retracts to
withdraw the drill bit 1 from engagement at a speed set by the Potentiometer
23.
Once the preset time is elapsed, the PLC 17 resets the drilling valve 11 to
resumes
drilling again. This drilling and reversing will continue until any one of the
following


CA 02310893 2000-06-OS
11
conditions is met: a) rotation pressure drops below the preset limit, b)
drilling and
reversing cycles exceeds the preset value, and c) the drill operator shuts off
the
control system.
The control system responds very quickly to the geological conditions
s of the rock mass. It decreases feed force and rotation torque when drilling
in harder
rocks and prevents over feeding in broken rocks or voids. As a result of this,
arrangement as described herein has been proven to be an effective control
system
for producing straight holes with minimal drill bit wear.
Since various modifications can be made in my invention as herein
to above described, and many apparently widely different embodiments of same
made
within the spirit and scope of the claims without department from such spirit
and
scope, it is intended that all matter contained in the accompanying
specification shall
be interpreted as illustrative only and not in a limiting sense.

Representative Drawing