Note: Descriptions are shown in the official language in which they were submitted.
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S P EC I F I C A T I O N
TO WHOM IT MAY CONCERN:
BE IT KNOWN, That George F. Skinners and John L. Talbert both
residents of Antigo, Wisconsin, Langlade County both citizens of the United
States, have invented certain new and useful improvements in:
METHOD AND APPARATUS FOR BREAKING CONCRETE OR THE LIKE
of which the following is a specification.
Title: METHOD AND APPARATUS FOR BREAKING CONCRETE OR
- THE LIKE
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This application claims the benefit of Provisional Application Serial
No. 06/006,191 filed November 1, 1995.
BACKGROUND OF THE INVENTION
w
1. Field of the Invention
The present invention relates generally to a method and apparatus
for breaking concrete or the like, and more particularly, to a multi-head
concrete
breaker for cracking, breaking or rubblizing the concrete in existing roadways
or
other surfaces for removal or for asphalt overlay.
2. Description of the Prior Art
As highway and roadway systems mature, highway programs
change from new construction to rehabilitation and maintenance. A common
technique for rehabilitation of concrete pavement, in contrast to new
construction, is to overlay existing roadways with hot mix asphalt. One
problem
with this technique, however, is a condition referred to as reflective
cracking.
Reflective cracking is the propagation of existing cracks and joints in the
underlying concrete or pavement upwardly through the overlaid asphalt or
other layer.
Various techniques have been developed to overcome this problem.
One involves use of wire mesh or other reinforcing material in combination
with specific formulations of the overlaid asphalt mix. A second involves
cracking the underlying pavement into smaller segments and then rolling the
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segments with a roller to seat the concrete pieces into the subgrade prior to
overlaying the same with an asphalt mix.
A still further technique is to break the existing concrete into still
smaller pieces which is often referred to as "rubblizing'". Rubblizing is a
type of
concrete demolition in which the demolished pavement and broken pieces are
not substantially displaced, but are broken into pieces which are usually no
greater than approximately one to two inches in diameter at the surface and
eight
inches in the lower layer. When reinforced pavement is rubblized, the broken
pieces are substantially debonded from any reinforcement located therein.
Rubblized concrete may be rolled and compacted as a base for newly poured
concrete or asphalt layers or can be removed. A principal advantage of
rubblizing
concrete is that it provides greater flexibility to the structure and
eliminates
distinct edges at joints and cracks, thus minimizing reflective cracking or
other
deterioration of the overlaid material.
Various equipment has been developed for breaking concrete
pavement in preparation for removal or asphalt overlay. Examples include
those disclosed in U.S. Patent No. 4,402,629 issued to Gurries, U.S. Patent
No.
4,439,056 issued to Riley et al., U.S. Patent No. 4,457,645 issued to Klochko
and
U.S. Patent No. 4,634,311 issued to Jinnings et al. Other machines have
included
concrete breakers having a single, relatively large hammer or head, sometimes
as
much as eight feet wide and weighing several tons. One disadvantage of
machines of this sort is that, because of their size and weight, they have a
tendency to push the pavement down into the substrate as it is broken.
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Although these machines are generally acceptable for cracking, their use for
rubblizing is extremely limited.
Development has occurred with respect to concrete breaking
machines having one or more hammers and utilizing a cantilevered, whip arm
principle. These machines claim to have the ability to rubblize concrete,
however, they have not been particularly effective due to poor mechanical
design.
A machine currently available for rubblizing is a machine known in
the trade as a "resonant breaker". Such machine has a single head about 6-7
inches wide projecting from the front of the machine at its midpoint and thus
breaks concrete in strips about 6-7 inches wide. Thus, it breaks the roadway
concrete in longitudinal strips and necessarily requires numerous passes to
cover
the roadway width. Several limitations exist with this machine. First, it
often
leaves areas of unbroken concrete between the broken strips. Secondly, because
the vehicle is much wider than the 6-7 inch head, several feet of clearance
are
required on each side of the broken strip. Thirdly, because of the relatively
high
wheel load and because at least two of the wheels must traverse broken
concrete,
the machine can sometimes sink into the concrete which is already broken and
damage the underlying substrate and/or pavement strata.
Accordingly, there is a need for an improved method and apparatus
for breaking concrete and the like which overcomes the limitations of the
prior
art.
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SUMMARY OF THE INVENTION
In contrast to the prior art, the present invention relates to a
method and apparatus for breaking concrete which overcomes the deficiencies of
the prior art and facilitates the performance of all pavement breaking
techniques
~ 5 including the cracking of pavement prior to an asphalt overlay, the
breaking of
pavement for removal or the rubblizing of pavement for removal or for asphalt
or concrete overlay.
In general, the apparatus of the present invention includes a multi-
head or multi-hammer concrete breaker having one or more hammer pairs or
hammer assemblies in which the operation cycle for each hammer assembly is
independently controlled. By using multiple hammers or heads with staggered
operation cycles, or with operation cycles which are initially the same but
which
become staggered during use, significantly smaller hammers can be utilized and
an irregular striking pattern can be achieved. This allows the apparatus to
spread
out the relatively low impact force levels of the smaller hammers and thus
eliminate or substantially reduce vibration concerns without sacrificing, and
often improving, performance.
Further, in the apparatus of the present invention, the plurality of
hammers are mounted transversely, across the machine, to permit the apparatus
to break concrete across its entire width, which can extend 8-12 feet or more.
This
eliminates the strips of unbroken concrete often present when using the
"resonant breaker" machine of the prior art. Such structure also substantially
eliminates any side-by-side clearance restrictions and enables the apparatus
to
function without requiring the vehicle to be supported by broken concrete.
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More specifically, the concrete breaking apparatus of the present
invention includes a frame or chassis assembly adapted for carrying a
plurality of
hammer assemblies whose break cycle (lift and drop cycle) is controlled
independently of other hammer assemblies. In the preferred embodiment, each
hammer assembly comprises a pair of hammers spaced transversely across the '
machine from one another. Each hammer is guided for generally vertical up and
down movement along a pair of guide members fixed to the frame. Each pair of
hammers is associated with an actuating or lift cylinder which functions to
raise
the hammers to a desired height and then allows the same to drop by gravity as
part of the operation or breaking cycle. Preferably the cylinder is positioned
between the pair of hammers and is operatively connected to the hammers
through a yoke and connection means which facilitates relative movement
between the hammers and thus limited tilting movement of the yoke.
Associated with each of the lift cylinders is a hydraulic system
comprising a source of fluid pressure to lift the hammers to their desired
height
and to release the hammers for free fall by gravity toward the pavement at a
particular time in the cycle. The hydraulic system is in turn controlled by an
electronic control which controls the entire breaking (lift/drop) cycle
including
the time at which the hammers are lifted, the time during which the hammers
are lifted and thus the height to which the hammers are lifted, and the time
at
which the hammers are dropped. The apparatus of the preferred embodiment of
the present invention is capable of operating at up to 40 cycles per minute.
In the
preferred embodiment, the apparatus is attached to a towing vehicle at its
forward end and is provided with support wheels at its rearward end.
Y
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The method aspect of the present invention includes providing a
plurality of hammers in the form of one or more hammer assemblies or pairs
and operating the break cycles of such hammer assemblies independently of one
,
another.
~ 5 Accordingly, an object of the present invention is to provide a
method and apparatus for breaking concrete or the like which overcome
limitations of prior machines in the art and which can perform all desired
concrete breaking functions.
Another object of the present invention is to provide an improved
method and apparatus for breaking concrete or the like which includes multiple
breaking heads whose breaking cycles are controlled or operated independently
of
one another.
Another object of the present invention is to provide a concrete
breaker having one or more hammer assemblies in which each hammer
assembly includes a pair of spaced hammers and a single lift mechanism
associated therewith including a lift cylinder and a yoke member.
A still further object of the present invention is to provide a multi-
hammer concrete breaking method and apparatus in which each hammer or
group of hammers is independently controlled or operated.
These and other objects of the present invention will become
apparent with reference to the drawings, the description of the preferred
embodiment and the appended claims.
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DESCRIPTION OF THE DRAWINGS
Figure 1 is an elevational side view of the concrete breaking
apparatus of the present invention connected with a towing vehicle.
Figure 2 is an elevational plan view of the apparatus of the present
invention and towing vehicle as shown in Figure 1.
Figure 3 is an elevational plan view of two of the hammer
assemblies of the apparatus of the present invention.
Figure 4 is an enlarged elevational front view of one of the hammer
assemblies of the present invention.
Figure 5 is a schematic of the hydraulic circuit associated with each
of the lift cylinders.
Figure 6 is a schematic of the electronic control for the apparatus of
the present invention.
Figure 7 is an elevational front view of one of the hammer
assemblies showing an alternate embodiment for connecting the hammers to the
lift cylinder assembly.
Figure 8 is an elevational plan view of a further embodiment
showing the concrete braking apparatus with steerable wheels.
Figure 9 is an elevational plan view, similar to that of Figure 3,
showing a further embodiment of a hammer lifting mechanism.
Figure 10 is an elevational front view showing the further
embodiment of Figure 9 with the hammers in down position.
Figure 11 is an elevational side view of the hammer assembly and
lifting mechanism of Figure 10.
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Figure 12 is an elevational front view of the embodiment of Figure
10, with the hammers in a partially raised position.
DESCRIPTION OF THE PREFERRED EMBODIMENT AND METHOD
The method and apparatus of the present invention relates to a
device commonly referred to as a concrete breaker. Although its primary use is
in connection with the cracking, breaking or rubblizing of concrete highways
and
roadways for subsequent removal or asphalt overlay, it is not intended that
the
method and apparatus be limited to such use. For example, the method and
apparatus of the present invention can be used in connection with the
cracking,
breaking and rubblizing of concrete other than highways or roadways. It is
intended that the method and apparatus of the present invention can be used
for
cracking, breaking or rubblizing materials other than concrete such as asphalt
substrates. Further, the preferred embodiment is described with reference to a
hydraulic system for driving the lift cylinders, however, it is to be
understood
that other sources of fluid pressure such as a pneumatic pressure source may
be
used as well. It is also to be understood that many of the features of the
present
invention can be achieved via a lift mechanism other than a fluid power lift
mechanism, such as a mechanical lift mechanism.
Reference is first made to Figures 1 and 2 in which the concrete
breaker apparatus 10 is shown as being connected with a towing vehicle 11. The
vehicle 11 may be a wheeled vehicle as shown or an endless track vehicle, if
desired. Although it is possible for the apparatus 10 of the preferred
embodiment
to be designed as an attachment to a tractor or other vehicle, it is intended
that
the apparatus would normally be connected to a dedicated vehicle designed only
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for use with the apparatus of the present invention. Such vehicle should
preferably have multiple (at least three) output shafts for driving the
hydraulic
pumps and be capable of very slow, consistent and accurate travel speed on the
order of 36 inches per minute or less.
The apparatus 10 includes a frame assembly 12 and a plurality of '
head or hammer assemblies 14 operatively mounted to the frame assembly 12.
The preferred embodiment includes three rearwardly positioned hammer
assemblies positioned in transversely or laterally spaced relationship in a
rearward portion of the frame 12 and three forwardly positioned hammer
assemblies positioned in transversely or laterally spaced relationship in a
forward
portion of the frame 12. As shown best in Figure 2, the forward and rearward
hammer assemblies are staggered across the width of the apparatus 10 so that a
slab of concrete the width of the apparatus 10 can be cracked or rubblized in
one
travel pass.
The forward end of the apparatus 10 includes means 19 for
connection with the towing vehicle 11 and plurality of hydraulic distribution
units 20 for lifting and dropping the plurality of hammer assemblies in
accordance with predetermined cycle parameters as will be described below. A
control box 13 is connected with the vehicle 11. The rearward end of the
apparatus 10 is provided with a pair of wheel supports 15 and a pair of wheels
16.
Preferably the wheel supports 15 are pivotally secured to a rearward portion
of
the frame assembly 12 and a piston/cylinder assembly 18 extends between an
upper portion of the frame assembly 12 and the outer end of the wheel support
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15 for adjusting the height of the frame 12 relative to the wheels 16 and thus
the
ground level.
The frame assembly illustrated in Figures 1 and 2 by the general
reference character 12 is shown in Figures 3 and 4 as including a plurality of
upper, lower, side and intermediate frame members. The upper frame members
26 and the lower frames members 28 are interconnected by a plurality of side
frame members 29 and intermediate vertical frame members 33 (Figure 4). As
illustrated best in Figure 3, the upper frame is shown as comprised of three
frame
members 26 extending across the width of the apparatus and connected in fixed
relationship to similar lower frame members 28 by a plurality of side and
intermediate frame members 29 and 33.
With continuing reference to Figures 3 and 4, each hammer
assembly includes a pair of hammers 21 and 22, a lift cylinder 24 and a tower
or
yoke member 25 connecting the lift cylinder 24 with each of the hammers 21 and
22. The lift cylinder 24 of each of the hammer assemblies 14 is connected with
and carried by the frame assembly 12 by means of a cross support brace 31
extending between adjacent frame members 26 as shown best in Figures 3 and 4.
Each cross brace 31 is connected with the lift cylinder 24 by a trunion mount
for
supporting the cylinder and thus the yoke 25 and the pair of hammers 21 and 22
as well. The trunion mount includes a pivot 37 connected with the brace 31 and
the cylinder 24 enabling the cylinder to accommodate limited relative movement
between the hammers 21 and 22 and to permit limited side-to-side tilting
movement of the cylinder 24. The lift cylinder assembly 24 includes an
hydraulic
cylinder 27 with a fluid power/exhaust port 23 at its lower end and a
hydraulic
fluid line 17 connected thereto. The port 23
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function to provide a source of fluid power to, and to exhaust fluid from, the
interior of the cylinder 27. A piston rod 32 extends outwardly from the
cylinder
27 and is connected to the yoke 25 by an appropriate connection means 34.
In the preferred embodiment, the piston rod 32 includes a
connection end 45 with a diameter smaller than the diameter of the piston rod
32, a pair of donut-shaped members 48 and 49 positioned on opposite sides of a
top mount plate 50 of the yoke 25 and a nut 51 threaded onto the externally
threaded connection end 45. Preferably, a pair of steel washers are also
provided
on opposite sides of the donut members 48 and 49 and a brass bushing is
positioned between the connection end 45 and the top 50.
The yoke 25 includes a pair of outwardly extending wings or
connection members 35 for connection with the top end of each of the weights
or
hammers 21 and 22. The connection between the outer ends of the wings 35 and
the hammers 21 and 22 provide for limited relative movement between such
elements to accommodate slight tilting movement of the yoke 25 caused by one
of the hammers dropping further than the other. As illustrated best in Figures
3
and 4, the connection means 36 includes a threaded member 54 extending
upwardly from each of the hammers 21 and 22 through an opening in a lower
hammer mount plate 55 of each wing 35. The connection means 36 further
includes a pair or donut-shaped rubber mounts 56, 56 positioned on opposite
sides of the mount plate 55.
Figure 7 is an alternate embodiment of a connection means to
interconnect the cylinder assembly 24 with the hammers 21 and 22. In Figure 7,
the connection means includes a lift bar 92 connected with the top end of the
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piston rod 32 and a pair of cables 94, 94 connecting the outer ends of the
lift bar 92
with the hammers 21 and 22. The lift bar 92, as shown, is pivotally connected
to
the piston rod to facilitate tilting of the bar caused by the hammers 21 and
22
being lifted to different heights. Other connection means may also be provided
including various lost motion types of connections.
Each of the hammers 21 and 22 is guided by a pair of angle iron
guide members 38, 38 which are positioned on opposite sides of the hammer and
which extend generally vertically long the entire travel path of the hammers
21
and 22. As illustrated best in Figure 3, each cooperating pair of angle guides
38
include an angled corner surface facing toward each other and designed to
cooperate in sliding relationship with a pair of corresponding angled grooves
39
in each of the hammers 21 and 22. Each of the guides 38 may be rigidly secured
to
a guide mounting bracket 30 which is in turn connected to the upper and lower
frame members by a plurality of threaded members 41 or other connecting
means. The connection between the bracket 30 and the frame members allows
some adjustability of the bracket position relative to the frame members so
that
the position of the guides 38 can also be adjusted. However, the guides 38 can
be
welded or otherwise connected directly to the frames 26 and 28. Additional
frame members and support can also be provided for the guides 38 if desired.
As shown best in Figure 4, the bottom end of each of the hammers
21 and 22 is provided with a striking bar 43. The striking bar has a bottom
edge
for striking the concrete or the material to be broken. The configuration of
the
bottom edge can be whatever is desired. Preferably the bottom edge has a
rectangular cross-sectional configuration. The striking bar is preferably
connected
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with the hammer 21 or 22 in a manner which allows the orientation of the
striking bar 43 to be adjusted. In the preferred embodiment, a steel plate is
secured to the bottom of each of the hammers 21 and 22 by threaded members or
the like and the striking bar is welded to the bottom of the steel plate. The
striking bar may be positioned transversely so that it extends laterally
relative to
the apparatus, diagonally or in line with the movement of the apparatus. When
positioned in line with the movement of the apparatus, the concrete will tend
to
be broken into strips.
The supply of fluid power to, and the exhaust of fluid from, each
lift cylinder 24 via the port 23 is controlled by an hydraulic distribution
unit 20
which is schematically illustrated in Figure 5. The operation of each
hydraulic
unit 20, in turn is controlled by an electronic control mechanism which is
schematically illustrated in Figure 6.
The hydraulic distribution system illustrated by the hydraulic
schematic of Figure 5 is provided with each of the hammer assemblies and thus
each of the lift cylinders 24. The hydraulic schematic includes a source of
hydraulic fluid 59, a filter 60 and an hydraulic pump 61. The supply of
pressurized hydraulic fluid from the pump 61 to the cylinder 24 is controlled
by
the lifting valve 65. The lifting valve 65 is normally open which allows the
fluid
to flow through the valve 65 and to a fluid reservoir or sump 70. When the
lifting valve 65 is closed, hydraulic pressure flows through a check valve 62
and
into the cylinder through the line 71. When the piston 32 within the cylinder
24
has reached the desired height, the lifting valve 65 is opened, thus
preventing
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further supply of fluid pressure to the cylinder 24. If the systems is in a
jog mode,
the valve 65 will remain open and the piston 32 will remain in its lifted
position.
If the system is in a normal operation cycle, opening of the valve 65
will also result in opening of a pilot valve 66. The pilot valve 66 is
normally in a
S closed position and when in such closed position holds pressure on a drop
valve
68 to maintain the drop valve 68 in a closed position as well. When pressure
in
the pilot valve 66 is lowered, the drop valve 68 is allowed to open, thus
exhausting fluid from within the cylinder 24 to the sump 70. The valve 68 is
sufficiently large to permit the hammers connected with the rod 32 to
essentially
free fall by gravity, causing fluid within the cylinder 24 to be exhausted
through
the valve 68 in the process. A relief valve 69 is provided to direct
pressurized
fluid to the sump 70 if the pressure within the system exceeds a predetermined
level. In the event the operator desires to lift the piston, and thus the
hammers
and to maintain the same in a lifted position such as in the jog mode, the
pilot
valve 66 can be maintained in its closed position.
Reference is next made to Figure 6 illustrating the control box
schematic for controlling the hydraulic distribution units associated with
each of
the hammer assemblies. As shown, Figure 6 discloses an identical timer circuit
74 associated with each of the hydraulic distribution units. Specifically, the
outputs from each timer circuit 74, namely the lift output 75 and the drop
output
76 control the lifting valve 65 and the pilot valve 66, respectively, of the
hydraulic circuit of Figure 5.
Each timer circuit includes a switch 78 which can be switched either
to a cycle mode 79 or a jog mode 80. When switched to a cycle mode 79, the
timer
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circuit 74 functions to start the timer to begin the lift cycle at a preset
time, to lift
the cylinder and thus the hammer assembly for a preselected time (and thus to
a
predetermined height), to drop the hammer assembly and to then repeat the
cycle again repeatedly. When the switch is switched to the jog mode 80, the
cylinder 24 and thus the associated hammer assembly are lifted to a desired '
height and retained in that position.
Each timer circuit includes a cycle timer 81, a start timer 82 and a
solenoid relay 84. When the switch 78 is switched to the cycle mode 79, the
cycle
timer 81 is energized. This results in the commencement of a lift/drop cycle.
Tnitially, at a preset time following activation of the cycle timer, the
lifting valve
65 (Figure 5) will be closed as a result of a signal from the cycle timer 81
via the
output 75 (Figure 6). Such signal is provided via the line 89, through the
relay
84 via the contacts 86 and 87a and then to the output 75. When the lift
portion of
the cycle is completed, the signal from the cycle timer 81 is de-energized.
This
results in the relay 84 switching from contact 87a to contact 87, thus
resulting in
the lift valve returning to its normal open position and the pilot valve 66
being
opened via the signal at the output 76 via the lines 90 and 88 and through the
contacts 87 and 87a of the relay 84. The cycle timer includes input means by
which the initiation of the lift cycle, the lift cycle duration (and thus the
lift
height) and the drop time can be set and predetermined. The drop time is the
time period between the opening of the lift valve 65 and the pilot valve 66 to
drop the hammer and the start of the lift cycle by closing the valve 65.
Thus, when the cycle switch 79 is turned on, the following occurs:
1. The hammers drop;
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2. The start timer begins to time out adjustable preset time
before the cycle begins;
3. The cycle timer starts, closing the relay, sending electric power
to the hydraulic lift valve 65 causing the hammers to be lifted to the height
determined by time duration of the adjustable lift timer;
4. The lift timer stops and the drop timer starts, opening the
relay, sending electric power to the valve 66 causing the hammers to drop for
time duration of adjustable drop timer;
5. The lift cycle starts and cycling repeats until cycle switch is
turned off.
With the control mechanism and hydraulic system illustrated in
Figures 5 and 6, the lift and drop cycle of each hammer assembly can be
controlled or operated independent of one another. For example, it might be
desirable to lift some hammers higher than the others to break thicker
concrete
such as at the edges of a roadway. Each cycle includes variables relating to
the
period of time during which the hammers are lifted and thus the height to
which the hammers are lifted and the time at which the hammers are dropped.
The fully raised height of the hammers is about 40 inches. The drop time may
also be controlled. By coordinating the lift and drop cycles for each of the
plurality of hammer assemblies, or by providing random lift and drop patterns,
the impact forces of the hammers can be spread out, thus substantially
reducing,
. if not eliminating vibration concerns. Further, because multiple hammers and
multiple hammer assemblies are utilized, each hammer can be substantially
reduced in size without sacrificing overall machine performance. It should
also
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be understood that the cycle speed and other parameters are to be coordinated
with the travel speed of the towing vehicle 11 so that the desired degree of
cracking or rubblizing may be achieved.
A further embodiment of the apparatus of the present invention is
illustrated in Figures 8-12. Figure 8 shows an embodiment of the invention in
which the support wheels 16 are steerable. This is accomplished via a
piston/cylinder assembly 95 positioned between a rearward portion of the
apparatus and one of the wheel support members 96 which are in turn pivotally
connected to the apparatus frame 12. A tie rod 98 extends between the wheel
support members 96,96.
Figures 9-11 illustrate top, front and side elevational views of a
further embodiment of the means for transferring the lifting force from the
lift
cylinder 24 to the hammers 21 and 22. As shown, the top end of the piston rod
32
is pivotally connected with a pair of spaced cross arms 99,99 by a pair of
plates 100,
a support post 101 and a transversely extending pin or bolt 102 extending
between
the cross-arms 99,99. The outward ends of each of the cross-arms 99,99 is
provided with means in the form of the bolts 104 and 105 and corresponding
rubber bushings 106 and 108 for pivotally connecting the outer ends of the
cross-
arms 99,99 to a pair of torque arms or rods 109 and 110. The bottom ends of
the
torque arms 109 and 110 are pivotally connected with the top ends of the
hammers 21 and 22, respectively, by a hammer connection assembly. In the
embodiment of Figures 9-11, the hammer connection assembly includes a pair of
support posts 111,111 connected with the top of each hammer, a rubber bushing
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112 and a support pin 115 extending outwardly from the bottom end of each
torque arm 109 and 110 for pivotal connection with the support posts 111,111.
As shown in Figure 12, this structure enables the hammers 21 and
22 to be lifted to different heights and thus to drop to different levels as
well.
~ 5 During operation, one hammer may fall to a different level because of
uneven
terrain or the existence of a raised portion in the concrete, etc. When this
occurs,
the hammers may be raised to different heights as shown in Figure 12. However,
during the next cycle, the hammers will be lifted to approximately the same
height unless the condition which caused their unevenness continues to exist.
In the embodiment of Figures 9-12, the hammer guides 116 are
generally square tubes which are welded to the various frame members such as
the frame members 26 as illustrated in Figure 9. It should also be noted that
in
the embodiment of Figures 9-12, the lift cylinder 24 is connected with the
frame
members 26 via the support block 118 and the fluid port 23 is positioned
approximately at the mid-point of the cylinder 24.
Although the description of the present invention has been quite
specific, it is contemplated that various modifications could be made without
deviating from the spirit of the present invention. Accordingly, it is
intended
that the scope of the present invention be dictated by the appended claims
rather
20° than by the description of the preferred embodiment and method.
. _ . _19_
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