U.S. patent application number 13/819389 was filed with the patent office on 2014-05-29 for rock drill.
This patent application is currently assigned to ROCKDRILL SERVICES AUSTRALIA PTY LTD.. The applicant listed for this patent is Dechun Kang, Alexander Sangster, Geoffrey Whyte. Invention is credited to Dechun Kang, Alexander Sangster, Geoffrey Whyte.
Application Number | 20140144660 13/819389 |
Document ID | / |
Family ID | 45810007 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140144660 |
Kind Code |
A1 |
Sangster; Alexander ; et
al. |
May 29, 2014 |
ROCK DRILL
Abstract
A rock drill including a first control valve (80), a first fluid
circuit (70) suppliable with fluid via the first control valve
(80), an impact piston (66) driveable by fluid pressure in the
first fluid circuit, a plurality of first fluid circuit feedback
paths (72) from the impact piston (66) to the control valve (80), a
damping body (50) for damping backpressure from a rock face, a
damping fluid chamber (52), associated with the damping body (50),
characterised in a second fluid circuit (56) in fluid communication
with the damping fluid chamber (52) and a stroke length control
mechanism (91) actuable by fluid pressure in the second fluid
circuit (56), wherein flow of fluid in said first fluid circuit
feedback paths (72) is controllable by the stroke length control
mechanism (91), whereby the driveable stroke length of said impact
piston 66 may be adjusted.
Inventors: |
Sangster; Alexander;
(Victoria, AU) ; Kang; Dechun; (West Heidelberg,
AU) ; Whyte; Geoffrey; (West Heidelberg, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sangster; Alexander
Kang; Dechun
Whyte; Geoffrey |
Victoria
West Heidelberg
West Heidelberg |
|
AU
AU
AU |
|
|
Assignee: |
ROCKDRILL SERVICES AUSTRALIA PTY
LTD.
West Heidelberg
AU
|
Family ID: |
45810007 |
Appl. No.: |
13/819389 |
Filed: |
February 28, 2011 |
PCT Filed: |
February 28, 2011 |
PCT NO: |
PCT/AU11/00220 |
371 Date: |
May 2, 2013 |
Current U.S.
Class: |
173/112 |
Current CPC
Class: |
B25D 9/18 20130101; E21B
6/08 20130101; E21B 44/06 20130101; B25D 9/26 20130101 |
Class at
Publication: |
173/112 |
International
Class: |
E21B 44/06 20060101
E21B044/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 2010 |
AU |
2010904066 |
Claims
1-14. (canceled)
15. A rock drill including an impact piston; a fluid system for
driving the impact piston; a stroke length adjustment mechanism
including at least one element moveable to vary a stroke length of
the impact piston; structure defining a chamber such that a back
pressure from a rock face is applied to fluid in the chamber; and
wherein the chamber is fluidly connected to the stroke length
adjustment mechanism such that the moveable element(s) is driven by
the fluid, to which the back pressure is applied, to vary the
stroke length in response to the back pressure.
16. The rock drill of claim 15, wherein the fluid system is
responsive to the impact piston passing a trigger point.
17. The rock drill of claim 15, wherein the fluid system reverses a
direction of the impact piston in response to the impact piston
passing a trigger point.
18. The rock drill of claim 16, wherein the stroke length
adjustment mechanism is configured to move the trigger point to so
vary the stroke length.
19. The rock drill of claim 16, wherein: the fluid system includes
flow paths opening to the impact piston at locations spaced along
its direction of travel; and at least one of the flow paths is
selectively blocked by the moveable element(s) to so vary the
stroke length.
20. The rock drill of claim 19, wherein the moveable element(s)
includes a balancing port to alleviate the effect on the moveable
element(s) of fluid pressure changes in the fluid system.
21. The rock drill of claim 15, wherein the moveable element(s)
includes a balancing port through which the fluid, to which the
back pressure is applied, may pass.
22. The rock drill of claim 15, wherein the moveable element(s) is
so driven against a spring.
23. The rock drill of claim 15, wherein the chamber is a damping
chamber for damping the back pressure.
24. The rock drill of claim 15, wherein the fluid system is a
hydraulic system.
25. The rock drill of claim 15, wherein the moveable element(s) is
hydraulically driven by the fluid to which the back pressure is
applied.
26. A rock drill including an impact piston; a fluid system,
including fluid paths, for driving the impact piston; a stroke
length adjustment mechanism including at least one element moveable
to reconfigure the fluid paths to vary a stroke length of the
impact piston; structure defining a damping chamber such that a
back pressure from a rock face is applied to fluid in the chamber;
and wherein the chamber is fluidly connected to the stroke length
adjustment mechanism such that the moveable element(s) is driven by
the fluid, to which the back pressure is applied, to vary the
stroke length in response to the back pressure.
27. The rock drill of claim 26, wherein the fluid system is
responsive to the impact piston passing a trigger point.
28. The rock drill of claim 26, wherein the fluid system reverses a
direction of the impact piston in response to the impact piston
passing a trigger point.
29. The rock drill of claim 27, wherein the stroke length
adjustment mechanism is configured to move the trigger point to so
vary the stroke length.
30. The rock drill of claim 26 wherein: the fluid paths open to the
impact piston at locations spaced along its direction of travel;
and at least one of the flow paths is selectively blocked by the
moveable element(s) to so reconfigure the fluid paths.
31. The rock drill of claim 26, wherein the moveable element(s)
includes a balancing port to alleviate the effect on the moveable
element(s) of fluid pressure changes in the fluid system.
32. The rock drill of claim 26, wherein the moveable element(s)
includes a balancing port through which the fluid, to which the
back pressure is applied, may pass.
33. The rock drill of claim 26, wherein the moveable element(s) is
so driven against a spring.
34. The rock drill of claim 26, wherein the fluid system is a
hydraulic system.
35. The rock drill of claim 26, wherein the moveable element(s) is
hydraulically driven by the fluid to which the back pressure is
applied.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to industrial ore mining drill
tools and specifically to rock drills that provide percussive and
rotary energy to a drill string.
BACKGROUND
[0002] Rock drills drive a drill rod (also known as a drill shank)
that transmits (via a drill string) rotary and percussive energy to
a drill bit which has a working or rock facing end. The drilling
tool also supplies flushing medium (commonly air or water) via the
drill rod and drill string.
[0003] Typically a mining rig has a `central` pump supplying fluid
into a `central` pressurised hydraulic system. Various parts of the
rig and rock drill are operated using the pressurised hydraulic
system. The `central` pump may be driven by an electric `central`
motor.
[0004] The rock drill also has another motor (which may receive
hydraulic supply from the `central` hydraulic system), which
generates high speed rotary motion of the drill rod via a gearing
arrangement involving an offset drive shaft. Typically the drill
rod rotates at speeds of up to around 220 rpm. This rotation is
transmitted via the drill string to the drill bit at the rock face
to enable holes to be drilled in the rock.
[0005] Rock drills also generate percussive force on the drill rod,
by generating a shock wave that is transmitted via the drill string
to the drill bit and rock face. This percussive force or shock wave
is generated by impact force from an impact piston (housed in an
impact body) aligned on the same axis as the drill rod. The impact
piston is hydraulically driven back and forth so that an end
impacts an end of the drill rod. The hydraulic driving circuit is
usually supplied by the `central` hydraulic system. Force on the
order of 2.8 tonnes at 60 Hz is typical. To cope with the
percussive shock wave returned up the drill string from the rock
face, a damping body cushions the chuck holding the end of the
drill rod.
[0006] Such rock drills are frequently required to drive a drill
string of around 3 to 6 metres weighing around 35 kilograms.
Depending on the nature of the rock, they may drill through up to
around 60 metres of rock per hour.
[0007] The rock drill is advanced along a beam towards the rock
face, keeping the tip of the drill bit in contact with the working
face. The drill bit rotation and percussive shockwaves break up the
rock face, in some circumstances fluidising the rock at the tip of
the drill bit.
[0008] Rock drills suffer from numerous problems in actual
operation. The operating conditions are difficult and dirty, the
loads and forces involved are significantly high, and a number of
failure modes are common.
[0009] It is important to match parameters including the rate the
drill advances along the beam, the type of rock being drilled,
rotational speed, frequency and level of percussive force being
used. Otherwise the drill can become uncontrolled. The pressure
experienced at the rock face is related to these parameters and
also experienced by the rock drill damping body. This is known as
the back pressure. The back pressure experienced by the drill is
thus related to these parameters.
[0010] It is important for effective drilling that the percussive
force transmitted is matched to the particular rock face. Where the
rock is very hard, greater force is required to be concentrated at
the rock face. This is achieved by using a longer impact piston
stroke length. The longer stroke length (also known as "throw"),
results in a higher final impact velocity of the piston and thus in
the impact force (Force=Mass.times.Velocity/Time) being greatly
increased than for a shorter throw. It is noted that a longer throw
is associated with a lower frequency at that back pressure (i.e.
fewer impacts per time period) for the impact piston cycle than a
shorter throw at the same back pressure.
[0011] Where the rock is soft, a lesser force is used by using a
shorter impact piston stroke length, and thus a lower final impact
velocity when the impact piston impacts the drill rod and thus a
reduced impact force, compared to using a longer throw.
[0012] In operation, the main way in which back pressure is
affected is by a change in the actual rock--hard rock will provide
high back pressure as the drill tip advances along the beam against
the hard rock. Where the rock is soft, but the drill is set for
hard rock and the drill tip advances at a hard rock rate, there is
an almost total loss in back pressure as rock is cracked or
fluidised at a greater distance in advance of the drill bit tip in
soft rock than in hard rock, resulting in the drill bit tip working
against a non-resistive substance rather than a surface against
which pressure may be exerted.
[0013] The drill rod associated with the rock drill in use is held
in a chuck. Rotation of the chuck is generated via a gear box, thus
rotating the drill rod. The chuck is cushioned against backpressure
and vibration by a damping body. Typically the chuck presses
against a damping piston located in a hydraulic fluid chamber in
the damping body, acting as the cushion. This damping fluid chamber
is independent of the `central` hydraulic fluid system--movement of
the damping piston simply increases or decreases pressure to absorb
the vibration and backpressure. In this way, the forces exerted
during operation are, to the extent possible, isolated from the
main parts of the drill or at least are damped.
[0014] The more force exerted on the chuck, the harder it will push
into the damping body. Where back pressure is increased due to more
pressure being applied at the rock face by the tip of the drill,
more force is exerted on the chuck, and where less pressure is
applied at the rock face, less force is exerted on the chuck.
Pressing harder at the rock face causes higher back pressure, while
softer rock face pressure reduces back pressure.
[0015] A loss in back pressure causes the chuck to move forward
relative to the damping body and impact body, moving the end of the
drill rod forward away from the impact body and thus changing the
impact piston stroke length to a longer throw. Thus an even higher
impact force is then applied to the drill rod. This increases the
force at the rock face, further reduces the back pressure and an
over-stroking loop quickly develops. The impact piston throw
increases but since there is no back pressure through the drill rod
the frequency may also increase.
[0016] Uncontrolled over-stroking of the impact piston can result
in significant and expensive damage to the drill, including damage
to the `central` hydraulic pump and its motor. Matching the impact
piston throw length to type of rock is sometimes achieved by using
a set of regulating pins that can be changed over in an onsite
workshop or even in the field. Each pin is shaped to reconfigure
the hydraulic circuit driving the impact piston, to change piston
stroke length to be long, medium or short. However, this does not
solve the problem where a drill tip suddenly punches through hard
rock into soft. The over-stroking problem remains. Furthermore,
operators forget to change pins, lose pins and in the dirty mining
environment there is a risk dirt or contaminants will enter the
impact piston hydraulic driving circuit and result in expensive
damage.
[0017] Electronic control and monitoring systems have been
attempted in the past to alleviate the over-stroking problem.
However these systems are themselves prone to failure in the
extreme field conditions (usually very hot or very cold, and very
dirty) and they are also very expensive, in addition to causing
operations to cease for a period of time.
[0018] It is an object of the invention to provide an improved or
alternative means of reducing the impact of over-stroking on
drilling operations.
[0019] Use of the terms `forward`, `rearward` or other relative
terms is made for ease of understanding of the relative disposition
of components and is not to be taken as limiting the drill or
components to operation in a particular orientation.
[0020] Any reference to prior art in this specification is not, and
should not be taken as, an acknowledgement or admission that the
prior art forms part of the common general knowledge of a person
skilled in the relevant art or could reasonably be expected to be
ascertained, understood or regarded as relevant by a person skilled
in the relevant art.
SUMMARY OF THE INVENTION
[0021] A first aspect of the invention provides a rock drill
including: [0022] a) a first control valve 80; [0023] b) a first
fluid circuit 70 suppliable with fluid via the first control valve
80; [0024] c) an impact piston 66 driveable by fluid pressure in
the first fluid circuit 70; [0025] d) a plurality of first fluid
circuit feedback paths 72 from the impact piston 66 to the control
valve 80; [0026] e) a damping body 50 for damping backpressure from
a rock face; [0027] f) a damping fluid chamber 52, associated with
the damping body 50;
[0028] characterised in: [0029] g) a second fluid circuit 56 in
fluid communication with the damping fluid chamber 52; and [0030]
h) a stroke length control mechanism 91 actuable by fluid pressure
in the second fluid circuit 56;
[0031] wherein flow of fluid in said first fluid circuit feedback
paths 72 is controllable by the stroke length control mechanism 91,
whereby the driveable stroke length of said impact piston 66 may be
adjusted.
[0032] Advantageously, the stroke length of the impact piston is
automatically adjustable or controllable in response to a change in
drill backpressure communicated to the damping body fluid chamber.
Problems associated with sensitive electronic detection and control
equipment are avoided. The lack of automatic response, loss of
manual pins, and the dirt and contamination problems associated
with manual reconfigurations are avoided--the fluid circuits may be
sealed during normal field use, rather than being vulnerable to
contamination when parts are changed over.
[0033] In a preferred embodiment, said stroke length control
mechanism 91 is hydraulically actuable by fluid pressure in the
second fluid circuit 56 to hydraulically open and/or close said
plurality of first fluid circuit feedback paths 72 to adjust the
driveable stroke length of said impact piston 66.
[0034] Preferably said stroke length control mechanism 91 includes
an actuator piston 94 in fluid communication with and actuable by
fluid pressure in the second fluid circuit 56. Preferably said
stroke length control mechanism 91 includes an adjustor pin 92
driveable by the actuator piston 94, whereby movement of the
adjustor pin 92 opens and/or closes said plurality of first fluid
circuit feedback paths 72. Preferably said adjustor pin 92 is in
fluid communication with the first fluid circuit 70. Preferably
said adjustor pin 92 has a balancing port 92b. Preferably said
actuator piston 94 has a balancing port 94b. Preferably said stroke
length control mechanism 91 includes a return spring 95.
[0035] In a preferred embodiment, the rock drill has four forward
first circuit fluid feedback paths 72 and two rearward first
circuit fluid feedback paths 72.
[0036] A second aspect of the invention provides a rock drill
including: [0037] a) a first fluid circuit 70 for driving an impact
piston 66; [0038] b) a second fluid circuit 56 isolated from the
first fluid circuit, the second fluid circuit in fluid
communication with a damping chamber 52 for damping backpressure
from a rock face; and [0039] c) a stroke length control mechanism
91 in fluid communication with each of the first fluid circuit and
the second fluid circuit, the stroke length control mechanism 91
actuable by fluid pressure in the second fluid circuit 56 to
reconfigure fluid paths in the first fluid circuit 70;
[0040] whereby the driveable stroke length of the impact piston 66
is automatically adjustable in response to backpressure from the
rock face.
[0041] A third aspect of the invention provides a rock drill
including: [0042] a) a first fluid circuit 70 for driving an impact
piston 66; [0043] b) a second fluid circuit 56 in fluid
communication with a damping chamber 52 for damping backpressure
from a rock face; and [0044] c) a stroke length control mechanism
91 hydraulically actuable by fluid pressure in the second fluid
circuit 56 to hydraulically open and/or close fluid paths in the
first fluid circuit 70;
[0045] whereby the driveable stroke length of the impact piston 66
is automatically controllable in response to backpressure from the
rock face.
[0046] A fourth aspect of the invention provides a method of
adjusting the drivable stroke length of an impact piston 66 in a
rock drill, the method including the steps of: [0047] a) causing a
pressure change in fluid in a damping chamber 52 in fluid
connection with a damping fluid circuit 56, the damping chamber 52
associated with a rockdrill damping body 50; [0048] b) in response
to said pressure change, hydraulically actuating a mechanism 91 in
fluid communication with both the damping fluid circuit 56 and a
driving fluid circuit 70 for driving the impact piston 66; and
[0049] c) moving one or more components of the mechanism in
response to said hydraulically actuation of the mechanism 91,
thereby opening and/or closing fluid paths 72 in the driving fluid
circuit 70;
[0050] whereby the driveable stroke length of the impact piston 66
is adjusted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] A preferred embodiment of the invention will now be
described by way of example only with reference to the accompanying
drawings in which:
[0052] FIG. 1 is a perspective view of a rock drill according to an
embodiment of the invention, mounted upon a cradle movable along a
beam;
[0053] FIG. 2 is a front elevation of the embodiment of FIG. 1;
[0054] FIG. 3 is a cross-sectional view of the embodiment of FIG.
2, taken along the line A-A on FIG. 2;
[0055] FIG. 4 is a cross-sectional view of the embodiment of FIG.
2, taken along the line B-B on FIG. 2;
[0056] FIG. 5 is a detail view of part of FIG. 4;
[0057] FIG. 6 is an exploded view of the embodiment of FIG. 1;
[0058] FIG. 7a is a sectional and schematic view of the impact
piston and associated hydraulic driving circuit, in which the
stroke adjustor is shown in a minimum stroke position;
[0059] FIG. 7b is a sectional and schematic view of the impact
piston and associated hydraulic driving circuit, in which the
stroke adjustor is shown in an intermediate stroke position;
[0060] FIG. 7c is a sectional and schematic view of the impact
piston and associated hydraulic driving circuit, in which the
stroke adjustor is shown in a maximum stroke position;
[0061] FIG. 8 is a schematic of a hydraulic circuit according to an
embodiment of the invention; and
[0062] FIG. 9 is a block diagram of a method according to an
embodiment of the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0063] FIGS. 1 and 2 show a rock drill 2 in drill operation
configuration, the drill 2 having a front head 20, cover plate 30,
housing of a rotation generation mechanism or gear box 40, a
percussive or back pressure damping mechanism for damping a drill
rod (also known as back pressure damping body 50), stroke adjustor
90 for adjusting the stroke length of an impact piston 66 and
impulse generating mechanism or impact body 60. They are supported
on cradle assembly 110, which in operation moves longitudinally
along a beam 120.
[0064] A drill rod or shank adaptor 10 associated with the rock
drill is also shown in the operational position. In use, drill rod
10 is connected to a drill string (not shown) for transmission of
rotary motion and percussive force to a drill bit (not shown)
working at a rock face. The rock drill 2 advances along the beam
120 to keep the tip of the drill bit (not shown) under pressure at
the rock face. As rock is fluidised, the rock drill continues to
move forward, drilling a hole in the rock. When the drill 2 has
advanced to the forward end of the beam 120 it is repositioned at
the rear end, and the beam and drill string reconfigured to
recommence operations.
[0065] As shown in FIG. 3, the drill rod or shank adaptor 10 is
held by a drill chuck 42. The drill chuck 42 is rotatable about the
central drill axis 4, and can also move through a limited range
longitudinally along the drill axis 4. During operation, as the
rock drill 2 advances along the beam 120, the tip of the drill bit
(not shown) works at the rock face. The continued advancement of
the rock drill 2 creates a back pressure along the drill string and
drill rod 10 from the drill bit at the rock face to the drill chuck
42. The drill chuck 42 moves in a limited range forwardly or
rearwardly relative to the back pressure damping body 50 along the
longitudinal axis 4, in response to the back pressure, i.e. the
pressure at the working rock face. The back pressure, and
vibrational forces or percussive shock imparted to and reflecting
from the working face, are as far as possible isolated or damped
from the rest of the drill by back pressure damping body 50. These
vibrational forces may also be known as reflex waves.
[0066] A rotary drive shaft 46 drives gearbox 40 having cover plate
30, gears 48 and tapered thrust bearings 47, 49. This in turn
drives chuck 42 and drill rod 10. The front head 20 has a flushing
seal carrier 150 via which flushing medium is supplied to the
hollow centre 12 of the drill rod 10.
[0067] Back pressure damping body 50 has or is associated with a
back pressure damping fluid chamber 52, and a damping piston 54.
The damping piston 54 is longitudinally aligned with the drill
chuck 42 and is driven by the drill chuck 42. As the drill chuck 42
moves rearwardly along the longitudinal axis 4 due to the back
pressure transmitted through the drill rod 10, the damping piston
54 also moves rearwardly and compresses the cushioning hydraulic
fluid in the back pressure damping fluid chamber 52. The greater
the compression, the greater the pressure in the damping fluid
chamber and the greater the resistance to further movement in a
rearward direction. Where the back pressure is low or none, the
damping piston 54 is driven to a forward position by the hydraulic
fluid. The longitudinal movement of the drill chuck 42 thus changes
the position of the drill rod 10 relative to the impact body 60 and
impact piston 66. It is noted that the back pressure damping fluid
chamber 52 is a generally annular chamber extending around the
impact piston 66, and that the damping piston 54 also extends in an
annular manner around the impact piston 66. The damping body 50 and
its associated back pressure damping chamber 52 are not in fluid
communication with any hydraulic circuits associated with the motor
for driving the gear box 40.
[0068] Turning to FIGS. 4 and 5, the impact piston 66 is driven by
fluid in a fluid circuit 70 which in this embodiment is a hydraulic
circuit receiving pressure supply from a `central` hydraulic system
(not shown). The terms "driving fluid circuit" 70 and "first fluid
circuit" 70 are used herein to distinguish it from the "damping
fluid circuit" 56 (also referred to as "second fluid circuit" 56)
associated with the back pressure damping chamber 52. The "damping
fluid circuit" 56 is isolated from the driving fluid circuit and
does not receive pressure supply from the `central` hydraulic
system, but rather pressure changes are due to movement of the
damping piston 54, responding to the drill chuck holding drill rod
10. Use of the term "driving fluid circuit" 70 should not be taken
to require a particular fluid path of the paths within that circuit
to drive an impact piston.
[0069] Turning to FIGS. 7a to 7c which are in a mirror image
orientation compared to FIGS. 4 and 5, the hydraulic driving fluid
circuit 70 has an associated control valve, being first spool valve
80 which is not visible in FIGS. 4 and 5. The impact piston 66 is
driven forward and rearward within impact piston housing 60 at
around 60 Hz. Fluid is supplied through the first control spool
valve 80 into the impact piston housing 60 via ports 210 or 214 and
drives the impact piston 66. Fluid is returned from the impact
piston 66 via ports 210, 211 and/or 214. The position of the 6
port, 2 position spool determines the path through which fluid is
supplied and thus the direction of travel of the impact piston 66.
The control spool valve 80 has pressure supply port 202, and return
or drain ports 201 and 203. It also has working side ports 204, 205
and 206, through which fluid is supplied to and returned from the
impact piston 66. The spool valve 80 is a directional valve in
which a position change is triggered via fluid flow to end port 207
or 208.
[0070] A change in direction of the impact piston 66 is triggered
by hydraulic feedback from the impact piston 66 caused by opening
and closing of a forward and a rearward port such as forward ports
215, 216, 217, 218 and rearward ports 212, 213 due to movement of
the impact piston 66. The feedback to a respective end 207, 208 of
the spool valve 80 causes the spool to move to another position. By
providing at least two forward (or rearward) hydraulic feedback
ports a change in the stroke length of the impact piston 66 can be
obtained depending on which of the ports is connected to an end of
the spool valve. A regulating pin can be used to block or open a
fluid path to reconfigure the circuit, determines which port is
connected and thus the impact piston stroke length.
[0071] In prior art arrangements, provision of a regulating pin to
manually reconfigure the driving circuit to a particular stroke
length was of use to manually set the drill 2 to work at a known
rock face hardness level. However, where for example hard rock is
suddenly changed to a soft rock section, the drill 2 still suffers
from over-stroking of the impact piston. The over-stroking can
result in the impact piston cycling at an unreasonably high
frequency and is most undesirable. While it was possible to change
the regulating pin manually, this did not prevent over-stroking
incidents, but rather in the event that the drill was not damaged,
simply enabled the drill to be put back into service with a
different regulating pin giving a new stroke length setting for the
apparent new conditions. The regulating pin was manually removed
from the drill housing with an associated risk that dirt and
contaminants would enter the hydraulic fluid circuit driving the
impact piston.
[0072] In the embodiment of the invention shown the Figures, the
stroke adjustor 90 includes a stroke length control mechanism 91,
in this embodiment a hydraulic control valve also referred to
herein as stroke length control valve 91, second control valve 91
or switch 91. The stroke length control valve 91 includes a stroke
adjustor pin 92, residing in adjustor housing 98, an actuator or
stroke adjustor piston 94 for driving the pin 92 and a return
spring 95. The stroke length control mechanism 91 is operable to
reconfigure the driving fluid circuit. Movement of the pin 92 opens
and/or closes the first fluid circuit feedback paths 72. The
position of the hydraulically driven stroke adjustor pin 92
controls or switches the forward feedback fluid path through which
hydraulic fluid will travel in the driving fluid circuit 70. This
in turn changes the point in the impact piston's travel or stroke
at which the first control spool valve 80 triggers a direction
change in the movement of the impact piston 66 within impact piston
housing 60. The four forward feedback ports 215, 216, 217, and 218
in impact housing 60 are spaced at a distance from the two rearward
feedback ports 212, 213 that, in conjunction with the configuration
of the impact piston 66, they provide an adjustment in the impact
piston stroke length of 0 mm, 9 mm, 17.5 mm, 31 mm respectively.
Thus in the embodiment shown the impact piston 66 may have any of
four stroke lengths corresponding to the four forward fluid ports
220, 221, 222 and 223 in impact housing 98.
[0073] Each of the four forward feedback ports 215, 216, 217, and
218 has a respective fluid path connecting to respective ports 220,
221, 222 and 223 in adjustor pin housing 98. The adjustor pin
position determines which of ports 220, 221, 222 and 223 are open
to connect to directional feedback take-off 224 and thus to fluid
path 224-207 to supply pressure to the first control valve 80 at
the forward end of the spool to trigger a spool position change and
thus an impact piston direction change.
[0074] Thus as shown in FIG. 7a, the impact piston 66 is triggered
in a direction change when the fluid path connecting ports 215-220
is open at both ends, and thus has a shorter stroke length than in
FIG. 7b where a direction change is not triggered until the impact
piston 66 has travelled far enough to open fluid path 216-221, as
in FIG. 7b fluid path 215-220 is blocked by the stroke adjustor pin
92. Similarly, a maximum stroke length is obtained in FIG. 7c as
the impact piston 66 moves until it opens fluid path 218-224, as
the adjustor pin 92 blocks fluid paths 215-220, 216-221, and
217-222.
[0075] Importantly as shown in FIGS. 7a to 7c, the stroke length
control mechanism 91 is hydraulically operated, driven by the
pressure in the damping fluid chamber 52 and damping fluid circuit
56 to reconfigure the driving fluid circuit 70. The stroke adjustor
pin 92 is driven by an actuator or stroke adjustor piston 94,
located in housing 96 (see FIG. 5). The stroke adjustor piston 94
has an associated return spring 95. Where the pressure in the
damping fluid chamber 52 is increased, fluid from the damping fluid
chamber 52 will flow through damping fluid path 56 into piston
housing 96 at an end zone 97 via port 225, hydraulically driving
the piston 94 against the return spring 95. This also drives the
adjustor pin 92. Movement of adjustor pin 92 results in switching
of the forward feedback fluid paths as described above in response
to the pressure in damping fluid chamber 52.
[0076] The stroke adjustor piston 94 has a working face which
together with an end wall of the piston housing 96 defines an end
zone 97, into which damping fluid path 56 enables passage of
damping fluid from the damping chamber 52. The working face of the
piston 94 is prevented from "sticking" to the end wall of the
housing by the left end of stroke adjustor pin 92 reaching its
maximum travel within adjustor housing 98, preventing the piston 94
from contacting the end wall.
[0077] The stroke adjustor piston 94 has a return spring 95 which
seats against piston shoulder 94a. The piston 94 also has a
balancing port 94b, being a hollow centre channel that functions as
a passage through the piston 94, from the end zone 97 side of the
piston 94 to the return spring 95 side of the piston 94. The
balancing port 94b allows equalisation of fluid pressure to either
side of the piston 94, which can significantly reduce the force
acting on the return spring 95. The fatigue life of the return
spring 95 can thus be significantly increased.
[0078] The stroke adjustor piston housing 96 has seals 99 between
it and the adjustor pin housing 98, which prevent damping fluid
from exiting the housing 96 while allowing the piston 94 to extend
into the adjustor pin housing 98 and drive the adjustor pin 92
[0079] As best viewed in FIG. 7c the adjustor pin housing 98 has a
small stepped shoulder 98a which defines a first end zone 93a.
[0080] The adjustor pin 92 also has a piston shoulder 92a which in
the maximum stroke position shown in FIG. 7c is seated against the
end wall of the housing 98. When not in the maximum stroke position
the shoulder 92a and housing 98 define a second end zone 93b, as
viewed in FIGS. 7a and 7b.
[0081] The stroke adjustor pin 92 also has a balancing port 92b as
shown in FIGS. 7a, 7b and 7c, being a hollow centre channel that
functions as a passage through the pin 92 from the first end zone
93a side to the second end zone side 93b.
[0082] The balancing port 92b allows equalisation of fluid pressure
to either side of the adjustor pin 92, which alleviates the effect
of high percussion pressure in the driving or first fluid circuit
acting on stroke adjustor pin 92 as the impact piston 66 is
operated. Thus the stroke adjustor mechanism is primarily
controlled or affected by pressure in the damping or second fluid
circuit i.e. back pressure.
[0083] Thus the feedback fluid ports and paths, and adjustor pin 92
have been arranged (in conjunction with return spring 95 and the
sizing of the faces of piston 94 etc) to result in the stroke
length of the impact piston 66 being automatically matched to the
back pressure from the rock face (as back pressure determines the
pressure in damping fluid chamber 52).
[0084] It should be noted for clarity that the damping fluid
circuit including damping fluid chamber 52 and damping fluid path
56 is a separate fluid circuit from the driving fluid circuit
70--the stroke adjustor piston 94 and stroke adjustor pin 92 have
associated seals preventing leaks from one system to the other.
[0085] Thus the hydraulically actuated stroke length control
mechanism or switch 91 (including stroke adjustor pin 92), is
directly responsive to changes in pressure in the damping fluid
chamber, enabling the stroke length of the impact piston to be
automatically and hydraulically adjusted during operations. This
can avoid the over-stroking feedback loop which causes problems in
the prior art, since stroke length is continually adjusted
according to back pressure. The hydraulic operation avoids the need
for expensive and delicate electronic instrumentation and controls
to shut down the drill if it over-strokes.
[0086] The embodiment disclosed has four fluid paths defining four
stroke length settings. However, greater or fewer fluid paths could
be provided to change the number of stroke length settings
available, and the difference in stroke length enabled by each path
may be selected to suit particular requirements.
[0087] The arrangement of driving fluid circuit 70, stroke length
control mechanism 91, adjustor pin 92, impact piston 66 and spool
valve 80 can be made in a variety of configurations. For example
the size and location of cavities defined between the impact piston
and its housing, or between the adjustor pin and its housing, type
and configuration of the directional valve and the location of
fluid ports, may be varied in a number of ways to achieve the same
or similar result. The above is thus a description of one
embodiment of such a driving fluid circuit.
[0088] The arrangement of the damping fluid circuit 56 can also be
made in a variety of configurations. Depending on mechanical
configuration, the stroke length control mechanism 91 could be
located directly adjacent the damping fluid chamber 52 and remove
the need for a conduit, fluid channel or path between chamber 52
and piston 94. Nonetheless, in such a case the damping chamber 52
is considered to comprise the second fluid circuit 56.
[0089] Pneumatic, rather than hydraulic, operation may also be
feasible in some applications.
[0090] FIG. 9 shows a block diagram of a method of adjusting the
driveable stroke length of an impact piston. In step 1, fluid
pressure in the damping chamber 52 alters in response to movement
of the drill rod due to rock backpressure. In step 2, the fluid
pressure change hydraulically actuates the stroke length control
mechanism 92 to a new position via the damping fluid circuit 56. In
step 3, movement of the adjustor pin 92 in the mechanism 92 opens
and/or closes forward feedback paths 72 connected to ports 215,
216, 217 and 218 in the driving fluid circuit 70. This adjusts the
paths and ports through which fluid is fed back to the control
valve 80 that triggers a direction change to the impact piston, and
thus the position of the impact piston when a direction change is
triggered. Thus the driveable stroke length of the impact piston is
hydraulically adjusted in response to rock face back pressure in
the damping body.
[0091] While the above description refers to one embodiment of a
rock drill, it will be appreciated that other embodiments can be
adopted by way of different combinations of features. Such
embodiments fall within the spirit and scope of this invention.
[0092] The term "comprises" and its grammatical variants have a
meaning that is determined by the context in which they appear.
Accordingly, the term should not be interpreted restrictively
unless the context dictates so.
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