Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PRELOADING
A SHID PLATE FOR AN EARLY CUTTING CONCRETE SAW
Field of the Invention
This invention relates to a method and apparatus for preloading a skid plate
assembly to ensure that the skid plate asserts a predefined force on a
concrete surface
during cutting in order to reduce raveling of the groove cut in the concrete.
Background of the Invention
It is common practice to provide grooves at predetermined intervals in the
surface of poured concrete to confine crack growth along the grooves and
minimize
cracking in the remainder of the concrete. Conventional concrete e~tting saws
cut
these grooves after the concrete has hardened sufficiently to prevent undue
damage
to the concrete surface by the weight of the saw and operator as well as the
saw blade
action and water lubricant used for the saw blade.
More recent, early cutting saws use up-cut rotating blades to cut the grooves
at hardnesses lower than practical with conventional saws. These early cutt;n~
caws
support the concrete surface during cutting to reduce raveling. The support
must be
within a sufficiently close distance to the rotating cutting blade, and along
a sufficient
length of the cutting blade to reduce raveling. These distances and lengths
can vary
with the concrete hardness, but the support is most critical adjacent the up-
cutting
edge of the cutting blade where raveling, spalling and chipping more readily
occur.
One type of early cutting saw uses a skid plate to support the concrete
surface.
But as the saws become bigger and heavier in order to use larger diameter
cutting
blades, difficulties arise if a skid plate is used to support the concrete
along a
substantial length of the cutting blade. The weight of the saw causes the skid
plate
to bend so that the skid plate does not maintain sufficient contact with or
support of,
the concrete surface. A lack of contact or insufficient support of the surface
can lead
to raveling of the cut groove, especially if the lack of contact occurs
adjacent the
leading edge.
The weight of the saw also causes the skid plate to bend and exert a non-
uniform pressure on the concrete surface, resulting in non-uniform support of
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concrete surface during cutting. As the skid plate traverses uneven concrete
surfaces,
this non-uniform support can cause portions of the skid plate to loose contact
with the
concrete surface or provide insufficient support - which can cause raveling.
There is thus a need for a skid plate that maintains contact with the concrete
surface during cutting, and that exerts a sufficient force, or at least a
predetermined
force distribution, on the concrete surface along the length of the skid
plate.
These problems were previously addressed by pre-bending the skid plate in an
attempt to compensate for the deformation caused by the weight of the saw
during
operation. A truss held the skid plate in the pre-bent position. But
unfortunately
raveling of the cut groove still occurs, especially on concrete surfaces that
are not
sufficiently flat. Indeed, slight depressions or rises in the concrete surface
of about
1/16 to 1/8 of an inch over the length of the skid plate (roughly one foot or
.25 m)
could cause raveling - depending on the hardness of the concrete and the
closeness of
the support to the cutting blade during cutting.
There is, therefore, a need for an improved support for the concrete surface
that
reduces raveling during cutting. There is a further need for a reliable method
of
consistently producing or adjusting a skid plate for use in reducing that
raveling.
Where this reduction in raveling is achieved by deforming a skid plate, there
is a
further need for a method and device for achieving a desired preloading with
sufficient
accuracy, and consistently doing so, and for determining what preloading
produces the
desirable results.
Summary of the Invention
A skid plate is placed on a multi-point sensing system that can sense the
amount of deformation occurring at a plurality of points on the skid plate
when
various loads are applied to the skid plate. The amount of deformation may be
sensed
directly or it may be sensed indirectly by measuring the resistive forces the
skid plate
exerts on one or more supports. Preferably the deformation is detected by
sensors at
a plurality of locations on the central portion of the skid plate that
contacts the
concrete during cutting, and that has a slot through which the cutting blade
extends
to cut the concrete during cutting. A truss holds the skid plate in its
desired position
once a predetermined deformation or force distribution is achieved. The
deformation
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or load distribution deformed position is adjusted by moving the truss
relative to the
skid plate in response to the sensors. Preferably, the deformation is adjusted
for a
uniform force distribution from the leading end to the trailing end of the
skid plate,
and from side to side on the skid plate. Once the force or deformation is
adjusted to
° S the desired distribution, the truss is fastened into place to hold
the predetermined
deformation or force distribution until the skid plate is used.
There is thus disclosed a method of making a skid plate assembly to ensure
that, when the skid plate assembly is mounted onto a concrete saw for cutting
grooves
on a concrete surface with a saw blade, the skid plate assembly provides
adequate
support for the concrete surface to minimize or prevent raveling. The skid
plate
assembly in particular maintains adequate pressure on and supports the
concrete
surface adjacent the location where the cutting blade exits the concrete
surface, since
raveling is especially prone to occur in that region. Raveling can also occur
in an area
adjacent the location where the cutting blade enters the concrete. The skid
plate
assembly desirably provides sufficient support for the concrete surface in
that area as
well. The skid plate assembly desirably provides support, more desirably
uniform
support, for the concrete surface along the entire length from where the
cutting blade
enters the concrete to where the cutting blade exits the concrete. The skid
plate
assembly advantageously also provides uniform support for the concrete
surfaces on
both sides of the cutting blade.
There is thus advantageously provided a method of calibrating a skid plate
assembly, where the assembly comprises a skid plate having at a leading and
trailing
end with least a first mounting portion configured to be releasably fastened
to a saw.
The mounting portion is connected to a support portion which has a slot
through
which a cutting blade extends during cutting. The slot has a leading end
through
which an up-cutting edge of the blade passes during cutting. A truss connects
to
opposing portions of the skid plate to maintain it in a predetermined
configuration.
The calibration process applies a predetermined loading to the skid plate,
with the
loading causing the support portion to deform. The deformation of the skid
plate is
monitored or sensed at least at one location. The deformation of the support
portion
of the skid plate is adjusted to achieve a predetermined deformation of the
support
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portion. The truss is then connected to the skid plate to hold that
predetermined
deformation.
Advantageously the loading applied to the skid plate is selected to simulate
an
operational load exerted on the skid plate by the saw. This loading may also
be
advantageously selected to simulate the load on the skid plate during cutting
of
grooves in a concrete surface before the concrete has hardened sufficiently to
crack.
Further, the loading may advantageously be selected to apply substantially
equal loads
to opposing ends of the skid plate, wherein each of the applied loads is less
than about
50 pounds (23 kg).
The deformation of the support portion is advantageously adjusted to achieve
a deformation causing a substantially uniform force distribution along the
length of
the support portion during cutting, and also to achieve a substantially
uniform force
distribution on opposite sides of the leading end of the slot in the skid
plate. This
force distribution may be achieved by moving the truss relative to the skid
plate.
Advantageously the skid plate has a truss comprising a first truss member
located above a first side of the support portion of the skid plate, and a
second truss
member located above a second side of the skid plate. The first and second
sides of
the skid plate are located on opposing sides of the slot in the support
portion of the
skid plate. For these skid plate and truss assemblies, adjusting the force in
the first
truss member affects the deformation of the second side of the support
portion, and
vice versa. Once the desired force distribution or deformation is obtained for
this type
of skid plate assembly, opposing ends of the truss are connected to opposing
mounting
portions located at opposite ends of the skid plate, to hold the desired
deformation.
There is thus provided a truss with a first end and a second end, the first
end
being fastened to the first mounting portion of the skid plate, the second end
being
adjustably coupled to a second mounting portion of the skid plate. Because the
mounting portions are not in the plane of the support portion of the skid
plate, the
moving one of the mounting portions relative to the truss deforms the skid
plate and
adjusts the deformation. The resulting skid plate assembly provides superior
support
to the concrete surface during cutting and provides a superior finish adjacent
the
grooves cut in the concrete.
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The apparatus used to calibrate this skid plate advantageously has at least
one
support located and configured to contact the support portion of the skid
plate
assembly during calibration. A load application apparatus is configured to
apply a
predetermined load at a predetermined location on the skid plate assembly,
with at
least a portion of that load being transferred to the support. There is thus
provided
load application means for applying a predetermined load to the skid plate
assembly
to simulate predetermined operating conditions, with at least a portion of
that force
being transferred to the support.
At least one sensor cooperates with the support to detect the force exerted on
the support during calibration, with the sensor providing output information
correlated
to the magnitude of the force. There is thus provided sensor means cooperating
with
the support or with the skid plate to detect the deformation of the support
during
calibration, the sensor providing output information for use in adjusting the
force
distribution or deformation profile.
Advantageously, the support comprises at least at two locations adjacent to
and
on opposite sides of the leading end of the slot when the skid plate assembly
is placed
on the apparatus for calibration. More advantageously, the support is located
at least
at the leading and trailing ends of the support portion of the skid plate, and
at a
location between the leading and trailing ends of the support portion of the
skid plate.
There is thus provided a support means for supporting the skid plate assembly
during
calibration.
The adjustment device is configured to deform the skid plate assembly to vary
the sensor output, thus achieving the desired force distribution or
deformation. There
is thus advantageously provided adjustment means for varying the skid plate
deformation. The adjustment device contacts adjacent ends of the skid plate
and truss
to move them relative to one another. Because the truss is offset from the
support
portion of the skid plate, the skid plate deforms and allows adjustment of the
force
distribution or deformation profile of the skid plate. Preferably, the
adjustment device
grips one end of the truss and pushes the corresponding end of the skid plate
to cause
relative movement between the truss and skid plate. The adjustment device
could be
modified to grip the skid plate and push the truss, or it could be modified to
apply
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forces to opposing ends of the skid plate or truss.
In accordance with an aspect of the present invention, there is provided a
method of calibrating a skid plate assembly comprising a skid plate having at
least a
leading and trailing end with least a first mounting portion configured to be
releasably
S fastened to a saw, the mounting portion being connected to a support portion
which
has a slot through which a cutting blade extends during cutting, the slot
having a
leading end through which an up-cutting edge of the blade passes during
cutting, and
a truss for maintaining the skid plate in a predetermined configuration,
comprising the
steps o~
applying a predetermined loading to the skid plate, the loading causing
the support portion to deform;
monitoring the deformation of the skid plate at least at one location;
adjusting the deformation of the support portion to achieve a
predetermined deformation of the support portion; and
connecting the truss to the skid plate to hold that predetermined
deformation.
In accordance with another aspect of the present invention, there is provided
an apparatus for calibrating a skid plate assembly for use with a concrete
saw, the skid
plate assembly comprising a skid plate with at least a first mounting portion
configured to be releasably fastened to the saw, and a truss with a first end
fastened to
the skid plate and a second end and fasteners to hold the second end in a
predetermined position, the skid plate comprising a support portion which has
a slot
through which a cutting blade extends during cutting, comprising:
at least one support located and configured to contact the support
portion of the skid plate assembly during calibration;
a load application apparatus configured to apply a predetermined load
at a predetermined location on the skid plate assembly, with at least a
portion
of that load being transferred to the support;
at least one sensor cooperating with the support to detect the force
exerted on the support during calibration, the sensor providing output
information correlated to the magnitude of the force; and
an adjustment device configured to deform the skid plate assembly to
vary the sensor output.
In accordance with another aspect of the present invention, there is provided
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an apparatus for calibrating a skid plate assembly for use with a concrete
saw, the skid
plate assembly comprising a skid plate with at least a first mounting portion
configured to be releasably fastened to the saw, and a truss with a first end
fastened to
the skid plate and a second end and fasteners to hold the second end in a
S predetermined position, the skid plate having a support portion which has a
slot
through which a cutting blade extends during cutting, comprising:
at least one support located and configured to contact the support
portion of the skid plate assembly during calibration;
load application means for applying a predetermined load to the skid
plate assembly to simulate predetermined operating conditions, with at least a
portion of that force being transferred to the support;
at least one sensor cooperating with the support to detect the
deformation of the support during calibration, the sensor providing output
information; and
adjustment means for deforming the skid plate assembly in response to
the sensor output information to achieve a predetermined deformation of the
support portion.
There is thus provided method and apparatus for calibrating the forces in a
skid plate assembly, to achieve predictable and repeatable performance of the
skid
plate during cutting.
Brief Description of the Drawings
Figure 1 is a perspective view of the concrete saw in operation.
Figure 2 is an up side view of the saw in operation.
Figure 3 is an exploded side perspective view of the skid plate assembly.
Figure 4 is a side perspective view of the assembled skid plate assembly of
Figure 3.
Figure 5 is a bottom plan view of the skid plate.
Figure 6 is a side perspective view of a different embodiment of a skid plate
and a truss.
Figure 7 is an exploded perspective view of the skid plate assembly support.
Figure 8 is a cut away view of the blade housing, cutting blade, and skid
plate
with supports.
Figure 9 is a partially exploded perspective view of a calibration apparatus
for
calibrating the skid plate assembly.
7
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Figure 10 is a perspective view of an apparatus assembly of the skid plate
assembly mounted on the calibration apparatus of Figure 9.
Figure 11 is a partial top plan view of the apparatus assembly of Figure 10
taken along line A-A.
Figure 12 is a partial perspective view of the apparatus assembly of Figure 10
illustrating the mounting of the adjustment unit.
Figure 13 is an exploded perspective of the adjustment unit.
Figure 14 is a front elevational view of the apparatus assembly of Figure 10.
Figure 15 is a side elevational view of the apparatus assembly of Figure 10 in
a disengaged position.
Figure 16 is a side elevational view of the apparatus assembly of Figure 10 in
an engaged position.
Detailed Description of the Preferred Embodiment
As the method and apparatus involves a skid plate assembly, for a saw, one
illustrative embodiment will be briefly described first. Figures 1 and 2 show
a skid
plate assembly 20 removably connected to a concrete cutting saw 24. The saw 24
includes a motor 28 mounted thereon for rotating a concrete cutting blade 30,
preferably in an upcut direction. The concrete cutting blade 30 may have a
diameter
of 8-14 inches (20-35 cm), although larger and smaller blades can be used to
cut the
concrete. The saw 24 has a plurality of wheels 34 for supporting the saw 24 on
the
concrete surface 38 during cutting of grooves 42 in the concrete surface. A
saw of this
general type is described in more detail in U.S. Patent No. 5,305,729 portions
of
which are described in further detail later in this specification.
Referring also to Figures 3 and 4, the skid plate assembly 20 includes a skid
plate 50 connected to a truss 52 and mounting portions 56, 58 by fasteners
146, 148.
The truss 52 may be fastened by other means known in the art, such a rivets,
adhesives, welding, interference fits or frictional engagements. The leading
mounting
block 56 and a trailing mounting block 58 are attached to the skid plate 50
and truss
52 for mounting onto the saw 24. As used herein, "leading" corresponds to the
direction that the saw 24 moves during cutting, while "trailing" in the
opposite
direction. Basically, the skid plate 50 is deformed to offset the deformation
that
occurs when the skid plate 50 is used. The truss 52 holds the deformation in
place
until the saw 24 is in use.
The skid plate 50 has leading and trailing skid plate mounting portions 82,
84,
7a
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respectively, parallel to but offset from the central portion 66 of the skid
plate 50.
Curved portions 62, 74 connect the mounting portions 82, 84 to opposing ends
of the
central portion 66. Central portion 66 contains slot 90 through which the
cutting blade
30 extends during cutting to cut the concrete. A leading end 96 is located in
the
S direction that the saw travels during cutting, and is located adjacent the
up-cutting
edge of the cutting blade as it exits from the concrete surface during
cutting. A trailing
end 98, and a recessed portion or tunnel 100 are located at the trailing end
of the slot
90.
The skid plate assembly 20 is movably mounted relative to the saw 24, as
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shown in Figures 1, 7 and 8. Shafts 160 are slidably constrained to move in
cylindrical bores (Fig. 8) in the saw 24, with each opposing end of the skid
plate 50
being mounted to one of these shafts 160 through the pins 164 and mounting
holes
and slots 154, 152, respectively. It is this mounting that exerts a force on
the skid
plate assembly 20 during operation, which causes the skid plate 50 to deform.
The
force exerted on the skid plate SO can be varied by turning screws 196 to vary
the
compression of springs 188 resiliently urging the shafts 160 and skid plate 50
against
the concrete, as apparent to one skilled in the art from the teachings of this
application
and Figures 7-8.
Applicants have discovered that one way to reduce raveling is to calibrate the
skid plate assembly 20 of Figures 3-5 under simulated operational conditions
to ensure
that a sufficient pressure is applied by the saw 24 through the skid plate 50
to the
concrete surface 38 during operation. Applicants have found that it is
advantageous
to calibrate the skid plate assembly 20 to ensure the skid plate 50 is pressed
against
IS the concrete surface 38 with adequate pressure in an area adjacent the
location where
the upcut cutting blade 30 exits the concrete. It is desirable to further
ensure
sufficient pressure in an area adjacent the location where the cutting blade
30 enters
the concrete. It is more desirable to calibrate the skid plate assembly 20 to
distribute
the pressure on the concrete surface 38 generally uniformly along the length
of the
middle portion 66 of the skid plate 50 which contacts the concrete surface 38
during
operation. It is also advantageous to distribute the pressure on the concrete
surface
38 generally evenly across the width of the middle portion 66 of the skid
plate 50.
One method of calibrating the skid plate assembly 20 illustrated in Figures 3-
6
is to precisely adjust the preloading or initial deformation of the skid plate
50 by the
truss 52. The preloading can be calibrated by adjusting the position of the
elongated
holes 128 on the trailing mounting portion 124 of the truss 52 through which
the
fasteners 148 are attached with respect to the circular holes 86 on the skid
plate 50.
The adjustment is performed with the leading mounting portion 122 of the truss
52
generally fixed with respect to the leading mounting portion 82 of the skid
plate 50.
The elongated holes 128 preferably have a sufficient length and are disposed
at a
location to allow adjustment of both tensile and compressive preloading on the
skid
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plate 50 by the truss 52.
By fastening the skid plate assembly 20 such that the fasteners 148 are
located
adjacent the leading ends 129a of the elongated holes 128, i.e., the holes 86
are
aligned with the leading ends 129a of the elongated holes 128, the arms 132
and 134
of the truss 52 are stretched in tension longitudinally. Through the fasteners
146 and
148, the truss 52 exerts a compressive longitudinal preloading on the skid
plate 50.
On the other hand, if the fasteners 148 are located adjacent the trailing ends
129b of
the elongated holes 128, i.e., the holes 86 are aligned with the trailing ends
129b of
the elongated holes 128, the arms 132 and 134 of the truss 52 experience
longitudinal
compression. As a result, the truss 52 exerts a longitudinal tensile force on
the skid
plate 50. It is understood, however, that other means of adjusting th,~
preloading on
the skid plate 50 may be employed without departing from the spirit and scope
of this
embodiment.
The following device and method are used to set the amount of deformation
to offset or counteract the deformation that occurs during cutting of the
concrete.
Calibration Apparatus
Referring to Figures 3-4, previously, the leading end 122 of truss 52 was
fastened to skid plate 52 and leading mounting block 56 by fasteners 146. At
the
trailing end, fasteners 148 loosely held trailing mounting block 58 to the
trailing
portion of truss 52 and skid plate 50. A spring scale was connected to hole
130 in the
truss 52 to apply a known preload to the truss. Then the fasteners 148 were
tightened.
But this preloading was never consistent. It did not control the force or
deformation
because it had no way to determine the deformation or force along the length
or width
of the skid plate. Thus, the deformation and resulting support of the concrete
varied
along the length of the skid plate, and from side to side on the skid plate.
The
resulting distribution of the loads and deformation was not uniform and was
not
repeatable. It resulted in raveling (spalling, chipping, cracking, etc.)
during normal
use, and when the skid plates traversed either depressions or mounds in the
concrete.
To precisely, repeatedly and predictably adjust the preload or initial
- 30 deformation on the skid plate assembly 20 a calibration apparatus 210 is
used as
illustrated in Figures 9-16. As best seen in Figure 9, the apparatus 210
comprises ~
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loading module 212 which simulates actual loading exerted on the skid plate 50
by
the saw 24 (Figure 2) when in operation; a detection module 214 for sensing
the force
profile throughout the middle or support portion 66 of the skid plate 50, and
an
adjustment unit 216 for adjusting the preloading or deformation of the skid
plate 50
and the truss 52. The assembled apparatus 210 is illustrated in Figure 10.
The loading module 212 advantageously has a structure configured to simulate
the actual magnitude and application of the loads applied to the skid plate
assembly
20 by the saw 24 during cutting. As shown in Figures 9 and I0, the loading
module
212 desirably includes a left frame 222 and a right frame 224 extending along
a first
axis, perpendicular to the skid plate 50. A support base 226 is preferably
parallel to
support portion 66 of skid plate 50, and supports frames 222, 224.
Advantageously, the frames 222 and 224 are substantially identical in
structure
and configured with a leading shaft 232 extending through a bore (not shown)
at the
distal end of left frame 222, and a trailing shaft 234 extending through a
bore (not
shown) at the distal end of right frame 224. The shafts 232, 234 can slide
along a
direction parallel to the first axis. A leading weight 236, preferably of
lead, is placed
on a top end 238 of the leading shaft 232. A trailing weight 240 is placed on
a top
end 242 of the trailing shaft 234. Screws 244 extend through the weights 236,
240
and frictionally engage the ends 238, 242 to secure the weights 236 and 240 to
the
shafts 232, 234.
The shafts 232, 234 have bottom ends 246, 248 configured to mount the skid
plate assembly 20 (Figures 3-4). The bottom end 246 of the leading shaft 232
is
constructed to attach the leading mounting block 56, and the bottom end 248 of
the
trailing shaft 234 to attach the trailing mounting block 58. As configured,
the leading
mounting portion 82 of the skid plate 50 is advantageously disposed directly
under the
leading weight 236 through the leading shaft 232 and the trailing mounting
portion 84
directly under the trailing weight 240 through the trailing shaft 234. To
simulate
actual operational conditions, the shafts 232, 234 of the loading module 212
are
preferably substantially the same as the shafts 160 of the saw 24.
The skid plate assembly 20 is placed into the calibration apparatus 210 as
shown in Figures 9 and I0. The skid plate assembly 20 is positioned so that
the
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shafts 232, 234 extend into the mounting blocks 56, 58 (Fig. 3-4) on the skid
plate
assembly. The bottom end 246 of the leading shaft 232 has a pin 254 through
its
diameter producing an end on each opposing side of shaft 232. Advantageously,
the
pin 254 is fixed to the shaft 232. The pin 254 preferably corresponds in
diameter to
the pins 154 used in the saw {Fig. 7). The ends of the pin 254 slide into the
mounting
slot 152 of the mounting block 56. The bottom end 248 of the trailing shaft
234 has
a hole 256 through which a pin 258 (Figures 10 and 11 ) can pass to attach the
mounting block 58. One skilled in the art with knowledge of this disclosure
would
recognize that different connections between the skid plate and calibration
assembly
could be used, especially if the skid plate assembly 20 used a different
mounting
structure to connect to the saw 24.
Referring to Figures 9, 10, and 14-16, a linkage is used to move the shafts
232,
234. The linkage is moved by a pair of actuators, such as solenoids or other
electric,
hydraulic or pneumatic actuators. Preferably hydraulic actuators are used to
move a
pair of members 262 having a first end rotatably mounted to the support base
225.
The second end of each member 262 is connected to a first end of pivotally
mounted
lever arms 264. The lever arms 264 are rotatably mounted at pivot 266 to
frames 222,
224. The second end of lever arms 264 each have a circular ball bearing 265
that is
located so that it can be urged against one of the weights 236, 240 to lift
the weight.
The hydraulic members 262 are advantageously actuated with a hand-held control
(not
shown) easily accessible by a technician operating the calibration apparatus
210.
Below the skid plate 50 are a plurality of support blocks 268a-268d. The
support blocks 268a-268d are preferably in a plane substantially parallel to
the skid
plate 50, to simulate a flat surface that does not cause the skid plate 50 to
twist when
the skid plate is urged against the blocks 268. Movement of the shafts 232,
234
determines whether the skid plate 50 contacts the blocks 268.
Figures 10 and 1 S show the shafts 232, 234 at a disengaged position lifted
away from the support blocks 268. In this disengaged position the hydraulic
members
262 are fully retracted, causing the linkage to pivot and urge the ball
bearings 26~
against the weights 236, 240 to lift the weights, shafts 232, 234, and
attached skid
plate assembly 20. Thus, the skid plate 50 does not contact the blocks 268 and
is held
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only by the shafts 232, 234. Referring to Figures 14 and 16, an engaged or
loaded
position is shown when the hydraulic members 262 are extended, the lever arms
264
rotate toward the support blocks 268, moving the bearings 265 out of contact
with the
weights 236, 240 so that the weights urge shafts 232, 234 and attached skid
plate
assembly 20, toward the support blocks 268. When the skid plate 50 fully
engages
or contacts support blocks 268, the operational loading that the saw 24 exerts
on the
skid plate assembly 20, is simulated.
The weights 236, 240 are selected to simulate the load the saw 20 exerts on
the leading mounting block 56 and trailing mounting block 58 of the skid plate
assembly 20. The shafts 232, 234 are mounted to move freely in the frames 222,
224
once released by the lifting mechanism. The connection between the shafts 232,
234
and the skid plate assembly 20 simulates the connection used on the saw 20.
Thus,
the apparatus 210 is designed to cause the central portion 66 of skid plate 50
that
normally contacts the concrete to bend as it would bend during cutting of the
concrete.
15Referring to Figures 9 and 10, the detection module 214 includes sensors
278a-
278d disposed on the surfaces of or inside the support blocks 268a-268d for
sensing
the pressure applied on the blocks 268a-268d by the skid plate assembly 20
through
the middle portion 66 of the skid plate 50 when the loading apparatus 212 is
in the
engaged or DOWN position for loading. A variety of sensors can be used, such
as
strain gages, load cells or other types of force sensors. Because the force is
related
to the amount of skid plate deformation, motion or displacement sensors can
also be
used, such as photo cells, laser interferometers, or other types of motion and
displacement sensors. Similarly, because the force can be correlated to a
deformation
that would occur if the support blocks 268 were not there, the sensors 278 may
also
be considered to be measuring deformation, and a reference to detecting the
deformation will be used to also include detecting the force, and vice versa.
Suitable
modification to the apparatus would be made to suit the particular type of
sensor used.
Preferably though. load cells are used, specifically Chatillon digital force
gages with
a 200 pound capacity.
The sensors 278 are ideally distributed along the entire length of the middle
portion 66 of the skid plate 50 along its longitudinal axis to obtain a force
distribution,
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force profile or deformation profile on the middle portion 66, but it is
generally not
feasible to do so. As a result, selective sensing of the forces or deformation
at
discrete locations on the skid plate 50 is used.
Because the pressure at the region where the cutting blade 30 exits the
concrete
surface 38 is believed to be most critical, at least one support block is
advantageousl5-
located to support the skid plate SO adjacent the leading end 96 of the slot
90, as best
seen in Figures 10, 11 and 14. There are advantageously first and second
support
blocks 268a and 268b adjacent the leading end 96 of the slot 90, one on each
side of
the slot 90 in order to measure the force or to indicate the deformation on
each side
of the slot 90. The use of a support block and sensor on each side of the slot
90
allows balancing of the loads across the width or lateral dimension Qf the
skid plate
50 to adjust for twisting of the skid plate.
Referring to Figure 11, the support blocks 268a, 268b are preferably
positioned
slightly away from the end 96 of the slot 90 so that the center of the blocks
268a.
268b correspond to the location at which the cutting blade 30 exits the
concrete during
cutting. During cutting, the blade 30 can move relative to the concrete as it
hits
aggregate entrained in the concrete. Thus, a reading over the variable
location of the
cutting edge is desirable. It is believed suitable, but less preferable, to
position the
blocks 268a, 268b elsewhere, even in front of the leading end 96 of the slot
90. Of
course, the force or deformation sensors 278a-278d are preferably positioned
with the
support blocks 268a-268d, and sense the deformation or force at those same
locations.
An approximately even load distribution along the length of the middle portion
66 of the skid plate 50 is believed preferable. As shown in Figures 9-11, a
third
support block 268c is placed at a location to support the middle portion 66 of
the skid
plate 50 adjacent the trailing end 98 of the slot 90, close to where the blade
30 enters
the concrete surface 3 8 during cutting as depicted in Figure 7. A fourth
support block
268d is placed approximately midway between the leading end 96 and trailing
end 98
of the slot 90. The third and fourth support blocks 268c, 268d, extend across
the slot
90 to support the skid plate 50 on opposing sides of the slot 90. Using two
separate
support blocks and sensors at each of these locations, with sensors on
opposing sides
of the slot 90. is also believed suitable, but using a single sensor at each
location is
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simpler and has proven adequate.
The sensors 278a-278d are desirably electronic digital force gage sensors that
provides accurate force readings over the surfaces of the support blocks 268a-
268d.
The sensors 278a-278d in the preferred embodiment are 200-lb load cells.
Sensors
278a-278d with different capacities would be selected as amount of weight on
the skid
plate 30 varies. Each sensor (278a-278d) is connected through a cable 280 to
corresponding electronic digital meter 282 to visually display the force
readings. The
digital meters 282 are desirably placed on the calibration apparatus 210 so
that a
person can see the force readings during calibration. As shown in Figure 10,
the
electronic meters 282 may be mounted on a mounting frame 286 extending
horizontally from the left and right frames 222, 224 of the loading module
212. Other
mating configurations are also suitable.
As the support surfaces on supports 268a-268d are in the same plane, there is
thus provided a means for measuring the force that the skid plate 50 exerts on
a flat
surface. Preferably, the force exerted is measured at the leading and trailing
ends of
the portion of the skid plate contacting the concrete, and also in the middle
of the skid
plate. That measured force can be correlated to a deformation that would occur
if the
support were not there, and thus the sensor may also be considered to be
measuring
deformation. One skilled in the art who uses the teachings of the present
disclosure
could devise suitable apparatus, sensors and sensor location to measure the
desired
forces or deformations of other skid plate assemblies having different
configurations.
Force Or Deformation Adjustment Unit
Figures 11 and 12 illustrate the adjustment unit 216 mounted onto the trailing
mounting portion 124 of the skid plate assembly 20. The adjusting unit 216 is
used
to adjust the preloading of the skid plate 50 held by the truss 52 by
adjusting the
deformation of the support portion 66 or by adjusting the resulting forces the
support
portion 66 exerts on a known surface or know sensor array. The skid plate is
adjusted so that the support portion provides a predetermined support to the
concrete
surface during cutting, advantageously reducing and preferably eliminating
raveling.
Simply described, one end of the truss 52 is fastened to the skid plate 50.
Then the other end of the truss 52 and skid plate 50 are moved relative to one
another
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causing the skid plate SO to bend. The sensors 278 on the support blocks 268
detect
this deformation or the resulting forces exerted on the sensors 278.
Preferably, an
array of sensors 278 is used. When the desired force profile or deformation is
obtained, the truss 52 is fastened to the skid plate 50 to lock that force
profile or
deformation profile into place. This produces a skid plate assembly 20 with a
precisely predetermined deformation that can be selected to offset the
deformation
occurring when the skid plate 50 is used during cutting of the concrete.
Because the skid plate assembly 20 is a pre-fabricated, pre-existing assembly,
the adjustment unit 216 was configured to fit that pre-existing assembly. One
skilled
in the art, applying the teachings of this specification, can readily devise
other ways
of adjusting the forces or deformation for different configuration" of skid
plate
assemblies. For the depicted skid plate assembly, the adjustment unit 216
shown in
Figures 11-13 is an example of a suitable adjustment device.
As shown in Figures 3 and 12, the skid plate assembly 20 uses a truss 52 with
a triangular trailing portion 124. Referring to Figures 11-14, the adjustment
unit 216
engages or otherwise grips the trailing mounting portion 124 of the truss 52.
A pair
of adjustment devices that take the form of threaded knobs 334 are supported
by the
adjustment unit 216 and configured to adjust the position of the trailing
mounting
portion 84 of the skid plate 50 relative to the trailing mounting portion 124
of the
truss 52. The end portion 124 of truss 52 is placed into a cavity 306 formed
between
a metal top plate 296 and a metal bottom plate 298 that are held together,
preferably
by fasteners such as rivets or screws 302. The cavity 306 is advantageously
slightly
larger than the size and thickness of the trailing mounting portion 124. The
metal is
preferably aluminum.
Two screws 308 extend through threaded holes 310 in the bottom plate 298
and extend into the cavity 306 toward the top plate 296. The trailing mounting
portion 124 is placed into this cavity 306 and the screws 308 tightened to
press the
trailing mounting portion 124 against the top plate 296. The friction created
by the
screws 308 pressing the trailing mounting portion 124 against the top plate
296 is
sufficient to grip that mounting portion prevent the trailing mounting portion
124 from
slipping from the top plate 296 during calibration. Hand tightening the screws
308
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by knobs on the ends of the screws 308 is sufficient to achieve this gripping.
The
screws 308 thus clamp the mounting portion 124 to the adjustment unit 216.
Preferably the screws 308 pass through threaded holes 310 located along the
mid-axis
of the bottom plate 298. A longitudinal block or ridge 312 is provided in the
bottom
plate 298 to provide enough threaded area to enable the clamping.
Still referring to Figures 11-14, but primarily to Figure 13, the aluminum
bottom plate 298 of the calibration apparatus 216 has two slots 328 running
the length
of the plate 298 in a plane substantially parallel to the plane of the portion
66 of skid
plate 50. A third slot is formed in the bottom of the plate 298, and extends
perpendicular to these slots 328 and through the middle ridge 312. A stainless
steel
bar 342 is placed into this third slot. Two threaded holes 340 extend trough
the bar
342 in a plane substantially parallel to the plane of the portion 66 of the
skid plate 50.
Threaded adjustment screws 318 extend through these holes 40. Two generally
rectangular, steel plates 316 are sized to slidably fit in the slots 328 on
the opposite
side of the bar 342 as the adjustment screws 334 and knobs 334. The ends 336
of
adjustment screws 318 abut the ends of plates 316 and by turning the knob 334
the
adjustment screws 318 can move the plates 324 along the 'slots 328. The tops
of the
sliding plates 316, the steel bar 342 and the middle ridge 312 are all in
substantially
the same plane so they do not obstruct insertion of the trailing mounting
portion 124
into the cavity 306 of the adjustment unit 216.
The plates 316 have pins 324 at the side of the plate that is closest to the
periphery of adjustment unit 216. Each pin 324 extends into a longitudinal
slot 326
located in the bottom of the plate 298. The pins 324 limit the movement of the
plates
316 along the slots 328, and keep the plates 316 from exiting the adjustment
unit 216.
As best seen in Figures 10-14, when the adjustment unit 216 grips the trailing
mounting portion 124, one end of the top plate 296 abuts the trailing mounting
block
58. This abutment aligns the adjustment unit 216 as the mounting block 58 is
at a
predetermined orientation relative to the skid plate assembly. Preferably, the
mounting
block 58 abuts the adjustment unit 216 so the mounting block 58 and adjustment
unit
216 are orientated along a line substantially parallel to the longitudinal
axis of skid
plate S0. The bottom plate 298 of adjustment unit 216 abuts the end of the
trailing
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mounting portion 84 of skid plate 50. Further, the sliding plates 316 can be
moved
by screws 318 to push against the trailing mounting portion 84 of skid plate
50, thus
creating relative movement between the truss 52 and skid plate 50. In essence,
the
truss 52 is being placed in tension while the skid plate 50 is being placed in
compression, causing the skid plate 50 to bend. This bending is achieved by
moving
one of truss 52 of skid plate 50 relative to the other. In the depicted
embodiment, the
truss 52 is held while the skid plate 50 is moved, but one skilled in the art
can devise
other suitable structures and methods to achieve the desired force
distribution or
deformation given the present disclosures.
Referring to Figures 10-14, the skid plate assembly 20 is mounted onto the
loading apparatus 21'? at the mounting blocks 56, 58 by the bottom ends 246,
248 of
the shafts 232, 234. The adjustment or calibration unit ~.t~ ran hP
nnnnant4,r1 .~ .~,~
skid plate assembly 20 either before or after the assembly 20 is placed on the
loading
apparatus 212, but is preferably done after the skid plate assembly 20 is
mounted to
the loading apparatus 212.
Figure 15 shows the loading apparatus 212 at the disengaged or UP position
wherein no loading is applied to the skid plate assembly 20 by the weights
236, 240
of the loading apparatus 212. In this disengaged position, the skid plate
assembly 20
is not supported by the support blocks 268a-268d. This position simulates the
position
when the cutting blade 30 (Figure 3) is not engaged with the concrete to cut
grooves.
Figure 16 shows the loading apparatus 212 at the engaged, or DOWN position at
which point the skid plate assembly 20 rests on the supports blocks 268a-268d
and the
load from the weights 236, 240 is applied at the two mounting blocks ~6, 58 of
the
skid plate assembly 20. This engaged position simulates the loads on the skid
plate
assembly 20 that occur when cutting concrete on a flat surface.
Calibration Procedure
To calibrate the skid plate assembly 20 for a desired cutting performance, the
skid plate assembly 20 is mounted onto the calibration apparatus 210, as shown
in
Figures 10 and 14-16. The loading module 212 is set at the disengaged position
for
mounting the skid plate assembly 20 (Figure 1 S). Suitable weights 236. 240
are
selected and positioned on top of the loading shafts 232, 234. The weights are
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selected to achieve the desired loading of the skid plate assembly 20.
Preferably the
weights are selected to simulate the forces applied to the skid plate 20
during
operation of the saw 24. The leading mounting block 56 of the skid plate
assembly
20 is rotatably and slidably connected to the bottom end 246 of the leading
shaft 232
by sliding the ends of pin 254 into the mounting slot 152. The trailing
mounting
block 58 is attached to the bottom end 248 of the trailing shaft 234 by the
pin 258.
The adjustment unit 216 is mounted onto the truss 52 by slipping the trailing
mounting portion 124 into the gap or cavity 306 between the top plate 296 and
the
bottom plate 298. The sliding blocks 316 are disposed to bear against the
trailing
edge 88 of the skid plate 50. The screws 308 are tightened to urge the
trailing
mounting portion 124 against the top plate 296, gripping and fixing the
mounting
portion 124 with respect to the adjustment unit 216. The fasteners 148 (Fig.
3) that
attach the trailing mounting portion 124 to the trailing mounting portion 84
of the skid
plate 50 are slightly loosened during this period so that the truss 52 can
move relative
to the skid plate 50. The fasteners 148 travel along the elongated holes 128
in the
truss 152 to allow this movement.
The hydraulic members 262 are activated by the motors 274 to move the
loading module 212 from the disengaged, UP position to the engaged, DOWN
position, such that the skid plate assembly 20 rests on the support blocks
268a-268d
(Figure 16) to simulate the desired loading on the skid plate assembly 20. The
loading by the weights 236, 240 is now applied to the skid plate assembly 20
due to
the constraint and reaction force provided by the support blocks 268a-268d
against the
middle portion 66 of the skid plate 50. The detection module 214 is activated
so the
sensors 278a-278d each provide a signal in response to the skid plate's middle
portion
66 being urged against the support blocks 268a-268d. These sensor signals can
be
correlated to force or deformation, depending on the sensor type and display
type.
The signals are preferably visually displayed on electronic meters 282 (Figure
14).
The readings provide the forces or deformation at predetermined points along
the
length of the middle portion 66 and over the width of the middle portion 66 at
a
location adjacent the leading end 96 of the slot 90. Preferably, the forces
the support
portion 66 exerts on the supports 268 are displayed.
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From the force readings shown on the digital meters 282, the adjustment unit
216 can be used to adjust the preloading on the skid plate 50 to calibrate the
skid plate
assembly 20 for a desired force or deformation profile. Preferably a generally
uniform
force distribution along the length and across the width of the middle portion
66 of
S the skid plate 50 is believed desirable to eliminate raveling. In the saw 24
illustrated
in Figures 1, 2, 7, and 8, the weight or force applied to both ends of the
skid plate
assembly 20 through the shafts 160, is substantially equal. Thus, the weights
236 and
240 are preferably the same in the calibration apparatus 2I0 shown in Figures
9-16.
In this situation where the weights are the same, the substantial symmetry of
loading
on the skid plate 50 by the loading module 212 results in the force or
deformation
readings being substantially symmetrical when the skid plate 50 is properly
adjusted.
The sensors 278c, 278d reflect the force or deformation on both sides of the
slot 90
in the skid plate 50. But each of the sensors 278a, 278b at the leading end of
the skid
plate 50 indicate the force or deformation on only one side of the slot 90,
thus the
readings of sensors 278a, 178b are combined for the total force on, or
deformation of,
the skid plate at that location. Therefore, preferably the combined readings
of the
sensors 278a . and 278b will be approximately equal to the reading from the
sensor
278c, and approximately equal to the reading of the sensor 278d, when the
sensors are
located at the ends and middle of the support portion 66 of skid plate 50.
If the sensor 278d at the middle indicates a larger value or reading than that
of the sensor 278c, and of the combined reading of sensors 278a, 278b, then
the
middle portion 66 of skid plate 52 is bowing slightly toward the middle sensor
-
which would correspond to bowing toward the concrete surface 38. The skid
elate
would thus be exerting more support of the concrete surface at the middle than
at the
ends of the skid plate. If the reading of the sensor 278d at the middle is
smaller than
the reading of the sensor 278c (and of the combined reading of sensors 278a,
278b),
then the support portion 66 of the skid plate 50 is bowing away from the
sensor 278 -
which would correspond to bowing away from the concrete surface 38. In this
situation the skid plate would be exerting more support on the concrete
surface at the
ends of the skid plate than in the middle. Other combinations of readings
indicate
other bowing configurations land corresponding variations in the support
provided by
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the skid plate to the concrete surface 38.
To change the preloading on the skid plate 50 the adjustment screws 3l 8 of
the
adjustment unit 216 are used to move the truss 52 relative to the skid plate
50, causing
the skid plate central portion 66 to bend in varying degrees and directions.
Specifically, the sliding plates 316 are pushed toward the trailing edge 88 of
the skid
plate 50. The adjustment screws 318 are turned while the readings on the
digital
meters 282 are monitored until the desired preloading is achieved. For the
illustrated
configuration, tightening the screws 318 increases the tension in the truss 52
and bows
the central portion 66 of the skid plate SO for the depicted skid plate
assembly 20.
Loosening the screws 318 decreases the tension in the truss 52 for the
depicted skid
plate assembly 20.
When the desired force profile or deformation profile are achieved, the
fasteners 148 are then tightened to lock-in this force distribution and skid
plate
deformation by firmly attaching the trailing mounting portion 124 of the truss
52 to
the trailing mounting portion 84 of the skid plate 50. The skid plate 50 is
thus
preloaded to a desired condition.
The amount of deformation of the skid plate 50 that can result in raveling of
the concrete during cutting is often not visually detectable because of the
strength of
the skid plate 50. A skid plate that looks perfectly flat to the unaided eye,
isn't, and
even those small differences that are not visually perceptible can cause
raveling. For
example, the skid plates 50 are stamped from sheet metal. But the sheet metal
comes
in rolls, and inherently has a bend. Despite efforts to straightened the
metal, or even
grind it flat, the resulting skid plates have some residual bow, twist or
uneven
deformation that can cause raveling. The detection module 214 thus
advantageously
provides a preferred method of detecting and setting the preloading to achieve
not
only predictable, but repeatable force or deformation profiles over the skid
plate in
order to improve the support of the concrete surface 38 by the skid plate 50.
Further, during stamping and handling, the skid plates 50 are twisted, and
they
are thin enough and long enough that the twisting causes a permanent
deformation that
is also not always visible to the unaided eye. The result is that the amount
of support
provided to the concrete surface adjacent the up-cutting edge of the cutting
blade 30
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can vary on opposite sides of the cutting blade because of this twisted skid
plate. This
variation in support may be significant. On one side of the blade 30 the
support may
be adequate, but on the other side of the blade the support may be inadequate
and
raveling will occur constantly, or sometimes occur when traversing bumps or
S depressions.
The two adjustment screws 318 are also used to adjust the preloading across
the width of the skid plate 50 as measured by the sensors 278a and 278b, in
order to
compensate for this undesirable twist in the skid plates. Adjusting one of the
adjustment screws 318 independently of the other will effect a diagonal lift
across the
length of the skid plate 50 by the truss 52 to compensate for the twist and
correct the
preloading. For example, referring to Figures 3, 4, 10 and 11, tightenipg
screw 334a
will cause the leading end of side 104b to move away from the support 268a and
sensor 278a. Tightening screw 334b will cause the leading end of side 104a to
move
away from the support 268b and sensor 278b. Loosening screws 334a, 334b have
the
opposite effect.
The relation between the amount of tightening and the amount of movement
on the diagonally opposite end of the skid plate varies with the strength and
location
of the truss 52, the strength and configuration of skid plate 50, and the
location of
screws 334. Locating the screws 334 outward, toward the lateral sides of the
skid
plate SO and away from the plane of the slot 90 and cutting blade 30,
increases the
skid plate deformation for a given turn of screws 334a, 334b. Thus, in Figures
12-13,
the screws 334 are located toward the outer sides of the adjustment unit 216
and skid
plate S0, in order to achieve greater movement for fewer turns and smaller
movements
of the screw 304.
As seen best in Figures 4 and 9-13, the truss 52 comprises opposing members
104a, 104b that are located toward the lateral sides of skid plate 50, as far
from the
plane of the slot 90 and cutting blade 30 as possible. The truss members 104a,
104b
are also relatively narrow so the force transmitted by those members is
concentrated
far away fiom the plane containing the slot 90 and cutting blade 30. For,
example,
a skid plate 50 has a middle support section 66 about 9.5 inches (24 cm) long
for a
10 inch (25 cm) diameter cutting blade 30 (Fig. 1-3). The skid plate 50 is
about 2.5 .
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inches (6.4 cm) wide and a thickness of about 14 gage (.075 inches, .19 cm}
steel,
with an end to end length of about 13 inches ( 10.5 cm). The truss members
132, 134
are metal, preferably steel, and located in a plane about .6 inches ( 1.3 cm)
above and
substantially parallel to the plane of the support portion 66. The truss
members 132,
134 are about .03 to .04 inches thick (.08 to .1 cm), and preferably cadmium
coated
to prevent rusting.
As discussed above, raveling can be significantly reduced by preloading the
skid plate SO to achieve a predetermined force distribution when the middle
portion
66 is pressed against the concrete surface 38 by the saw 24 as in Figures 1
and 2.
Having the force distributed uniformly over the support portion 66 of skid
plate 52 is
preferred. For instance, one commercial embodiment of the saw 24.exerts about
24
pounds (11 kg) of force at each mounting block 56, 58, during cutting for a
total of
about 48 pounds (22 kg). These forces can be determined by methods known to
those
of ordinary skill in the art, and are not described in detail herein. The skid
plate 52
is about 12 inches (30.5 cm) between pins 164 (Fig. 7), with support portion
66 about
9.5 inches (24 cm) long. To simulate that loading by the saw 24 on the skid
plate 52,
each of the weights 236 and 240 is also about 24 pounds (11 kg). A uniform
distribution of this weight on the skid plate 52 will have about 1/6 the
weight on each
of the supports 268a, 268b and sensors 278a and 278b, about 1/3 the weight on
each
of the supports 268c, 268d and sensors 278c and 278d. For the 48 pound (22 kg)
weight, this amounts to a force of about 8 pounds (3.6 kg) detected by each of
the
sensors 278a, 278b, and a force of about 16 pounds (7.3 kg) detected by each
of the
sensors 278c and 278d.
A variation of about ~20% at each of the leading and trailing ends of the
support portion 66 are believed to produce suitable results during cutting.
For the
above described commercial embodiment, that amounts to amounts to as little as
12.8
pounds (5.8 kg), or as much as 19.3 pounds (8.8 kg) detected by sensor 278c,
and by
sensors 278a and 278b combined. A variation of about +20% and -30% is believed
suitable for the central sensor 278d. It is preferred to have the center of
the support
portion 66 lighter, rather than heavier; alternately phrased, the center of
support
portion 66 can bend more away from the concrete than it can toward it before
raveling
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occurs. Similarly, it is preferred to have the leading end of the skid plate
heavier or
more deformed toward the concrete, rather than urged against the concrete with
less
face. This is because raveling is more sensitive to the deformation or lack of
support
at the leading end 96 of the skid plate 50.
The acceptable variation in the force or deformation across the width of the
skid plate 50 adjacent the region where the saw blade 30 exits the concrete is
smaller
than for the remainder of the skid plate. This is also because raveling is
most
sensitive to the support of the concrete at this location, and thus more
likely to occur
for unsymmetrical preloading at this location, or insufficient support on one
side of
the skid plate 50 at this location. Thus, it is believed possible that the
variation on
opposite sides of the slot 90 is advantageously less than about 20% at tlge
leading edge
96 of slot 90, but may vary as much as 40% from side to side along the
remaining
length of the sides 104a, 104b, while still producing suitable results during
cutting.
Thus, for example the leading sensor 278a might detect as little as 12.8
pounds (5.8
kg) while the adjacent sensor 278b might detect as much as 19.3 pounds (8.8
kg).
It is also believed suitable, but with less desirable control over raveling,
to have
the force vary by 40% at the leading and trailing edge sensors 278a, 278b and
278c,
with the force varying at the central sensor 278d by +30% and -50%. If the
sensors
278 detect deformation rather than force as in this example, then a suitable
deformation profile and variation corresponding to these forces would be
determined.
The precise amount of force variation that will permit suitable results will
vary
with the size and configuration of the skid plate assembly 20, as well as the
hardness
of the concrete during cutting. But give the teachings of this specification,
one skilled
in the art can determine suitable force or deformation variations within which
to adjust
the preloading in order to achieve the desired control of raveling during
cutting.
Referring to Figures 8 and 9, it may be desirable in some cutting situations
to
adjust the force applied on the ends of the skid plate assembly 20
independently and
produce more or less force at the leading or trailing end of the skid plate
52. The
adjustment screws 196 may be independently adjusted to vary the downward
forces
applied to the two shafts 160 connected to the ends of the skid plate assembly
20.
Thus the desired force distribution may be adjusted so that it is no longer
uniform but
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produces desirable cutting results. The amount of permissible variation will
depend
on the particular needs and circumstances. Suitable variations to accommodate
such
non-uniform forces or deformation can be obtained by calibrating the skid
plate
assembly 20 with the calibration apparatus 210 and observing the performance
of the
S skid plate assembly 20 in operation. To simulate such non-uniform loading of
the
skid plate assembly 20, the calibration apparatus 210 can use weights 236, 240
of
suitable, and likely different, values to simulate the loading from the saw
24.
Alternatively, a variable loading mechanism can be incorporated into the
calibration apparatus 210. For example, the adjustment screws 196 and springs
188
illustrated Figures 7 and 8 for mounting the skid plate assembly 20, can be
adapted
to replace the shafts 32, 234 (Figs. 9-10), with the adjustment screws~196
being used
to produce the desired simulated force or deformation profile. This is another
example
of the advantages of the ability of the calibration apparatus 210 to simulate
the actual
operational conditions of the skid plate assembly 20.
Operation of the Calibrated Skid Plate Assembly
Referring to Figures 1 and 2, the skid plate assembly 20 is mounted onto the
saw 24 for cutting the groove 42 in the concrete as the saw moves across a
portion
of the concrete surface 38. The amount of raveling has been shown to vary with
the
force distribution over the middle portion 66 adjacent the groove 42 being cut
in the
concrete surface 38.
Applicants have found that raveling can be reduced when the skid plate
assembly 20 provides adequate support for the concrete surface 38 adjacent the
location where the cutting blade 30 exits the concrete surface 38 to minimize
or
prevent raveling, since raveling is especially prone to occur in that region.
To a lesser
extent, raveling also tends to occur in an area adjacent the location where
the cutting
blade 30 enters the concrete surface 38. The skid plate assembly 20 desirably
provides sufficient support for the concrete surface 38 in that area as well.
The skid
plate assembly 20 desirably provides support, more desirably uniform support,
for the
concrete surface 38 along the entire length from where the cutting blade 30
enters to
where the cutting blade 30 exits the concrete surface 38. The skid plate
assembly 20
advantageously also provides even support on both sides of the cutting blade
30.
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The calibration apparatus 210 of Figures 9-16 is able to calibrate the skid
plate
assembly 20 to produce a desired force or deformation distribution on the
concrete
surface 38 through the support portion 66 of the skid plate assembly 20 by
adjusting
the preloading on the skid plate 50 by the truss 52. Given the disclosure
herein,
however, various other ways of implementing the skid plate assembly 20 to
achieve
the preloading of the skid plate 50 to achieve the desired support of the
concrete
surface 38 could be devised by one of skill in the art without undue
experimentation.
The present method and apparatus are especially suitable for cutting concrete
before it has reached its typical, rock-like hardness. This cutting preferably
begins
immediately after finishing of the concrete surface, and is often referred to
as "early
cutting." Suitable saws are described in more detail in U.S. Patent Nos.
4,769,201 and
5,429,109. As described in greater detail in those patents, because the
concrete can be
cut by the saw 24 while the concrete is not yet hard, the size of the slot 90
surrounding the cutting blade 30 must be designed so the skid plate 52
provides
sufficient support to the concrete surface 38 surrounding the cutting blade to
reduce
raveling of the groove 90.
When properly calibrated, the skid plate assembly 20 is believed suitable for
cutting grooves 42 without raveling when the concrete has a hardness such that
a steel
rod weighing about 5.75 pounds, having a diameter of 1.125 inches, when
dropped
from a height of about 24 inches from the surface 38 of the concrete, makes an
indentation of about 0.5 inch (1.27 cm) with a flat end of the rod. The skid
plate
assembly 20, when properly calibrated, is also believed suitable for cutting
grooves 42
in harder concrete without raveling, as where the above-described rod produces
indentations of 1/32 of an inch or less. Preferably, the saw 24 and skid plate
assembly
20 are used before the concrete 38 cracks, and ideally, before the concrete
reaches a
hardness at which conventional saws can cut the concrete without supporting
the
surface adjacent the cut groove. As the saw 24 is used to cut harder concrete,
the
downward force on the cutting blade 30 may need to be increased, while the
force on
the skid plate 50 may be reduced, so long as sufficient force is applied by
the skid
plate 52 to support the concrete surface 38 adjacent the groove 42 to inhibit
raveling
of the concrete at the cut groove 42.
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Detailed Description of Skid Plate & Truss Assembly
In order to ensure that one skilled in the art appreciates the details of
construction of the illustrated skid plate assembly 22, the following
disclosure is
given. Referring to Figures 3 and 4, the skid plate 50 has a leading edge 62
at one
end, a trailing edge 64 at the other end, and a middle or support portion 66
between
the leading edge 62 and trailing edge 64. The leading and trailing edges 62
and 64
are advantageously inclined upwardly away from the concrete surface 38 and
toward
the saw 24 with an incline slope, forming a leading inclined portion 72 and a
trailing
inclined portion 74. The leading inclined portion 72 has one end connected to
the
leading edge 62 and another end connected to a leading mount portion 82. The
trailing inclined portion 74 has one end connected to the trailing edga.64 and
another
end connected to a trailing mounting portion 84. The mounting portions 82 and
84
are also referred to as ends of the skid plate 50. The trailing mounting
portion 84 has
a trailing edge 88, as best seen in Figure 3.
As shown in Figures 3 and 4, the mounting portions 82 and 84 are offset
vertically by a distance from the concrete surface 38. The middle portion 66
thus
depends from the saw 24 a distance sufficient to contact the concrete surface
38 to
support the concrete surface 38 during cutting and to inhibit raveling of the
concrete
surface 38 adjacent the groove 42. The mounting portions 82 and 84 can be
configured to adapt to the particular mounting configuration of the saw 24. In
the
embodiment shown in Figures 1 and 2, the mounting portions 82 and 84 of
Figures
3 and 4 are parallel to the middle portion 66 of the skid plate 50.
The slot 90 has inner side edges 94a and 94b which extend through the
thickness of the skid plate 50 to the bottom of the skid plate 50 that faces
and contacts
the surface 38 of the concrete, as best seen in Figure 5. The slot 90 has a
leading end
96 and a trailing end 98. At a point near the trailing end 98 of the slot 90,
a recess
100 extends into the bottom surface of the skid plate 50 and stretches from
the trailing
end 98 of the slot 90 to the trailing edge 64 of the skid plate 50.
As illustrated in Figures 3-5. the skid plate 50 has side portions i 04 which
extend from the slot 90 outwardly. The middle portion 66 is desirably about
9.5
inches (24 cm) long and 2 inches (~ cm) wide, for a total area of about 19
square
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WO 98/02278 PCT/US97/12583
inches (120 cmz), when used with a cutting blade 30 of about 10 inches (25 cm)
in
diameter. Advantageously, the middle portion 66 is made of 12 gage stainless
steel,
which has a thickness of about 0.1046 inch (0.266 cm). Accordingly, the slot
90
depth is also 0.1046 inch. The skid plate 50 is advantageously made of
stainless steel
so that it will not wear at an excessive rate.
It is preferred that the slot 90 have a width such that the side edges 94a and
94b of the slot 90 are as close to the sides of the cutting segments of the
cutting blade
30 as possible, without contact between the cutting segments and slot side
edges 94a
and 94b. A slot width of about 0.118 to 0.120 inches (0.23-0.30 cm) is
believed
advantageous for the illustrated skid plate 50, although a slightly wider slot
width of
0.13 inch (0.33 cm) is believed to perform satisfactorily while being slightly
easier to
manufacture.
Referring to Figures 3-5, the truss 52 has a leading mounting portion 122 and
a trailing mounting portion 124. The leading mounting portion 122 has a
generally
rectangular shape and desirably includes holes 126 located for attachment with
the
leading mounting portion 82 of the skid plate 50. The trailing mounting
portion 124
has a generally triangular shape and desirably includes holes 128 provided for
attachment with the trailing mounting portion 84 of the skid plate 50. The
holes 128
are not circular, but advantageously are elongated, each with a leading end
129a and
a trailing end 129b, to allow preloading of the skid plate 50 by the truss 52
and the
adjustment thereof as discussed below.
A pair of arms 132 and 134 extend between the mounting portions 122 and
124. The arms 132 and 134 are used to exert the preloading on the skid plate
50, and
are desirably the same in construction for balance in preloading on the skid
plate 50.
The arms 132 and 134 can be a variety of shapes and sizes, but are desirably
thin
strips. As discussed below, the width of the arms 132 and 134, as well as the
thickness of the truss 52, is chosen according to the load exerted on the skid
plate 50
by the particular saw 24. The truss 52 is advantageously cut or punched out of
thin
metal, preferably steel, that is subsequently cadmium coated to prevent
rusting. Steel
sheets about 0.03 to 0.04 inch thick (0.08 to 0.1 cm) are believed suitable.
As best seen in Figure 3, the leading mounting block 56 and trailing mounting.
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block 58 are advantageously U-shaped. The leading mounting block 56 has holes
142
and the trailing mounting block 58 has holes 144 through which threaded
fasteners
146 and 148 are used to attach the skid plate 50 and truss 52 with the
mounting
blocks 56 and 58. The fasteners 146 pass through holes 85 of the skid plate 50
and
holes 126 of the truss 52 to fasten the skid plate 50 and truss 52 to the
leading
mounting block 56. The fasteners 148 pass through holes 86 of the skid plate
50 and
holes 128 of the truss 52 to fasten the skid plate 50 and the truss 52 to the
trailing
mounting block 58. The fastened structure forms the skid plate assembly 20
that can
be mounted onto the saw 24 of Figures l and 2.
Referring to Figure 6, another embodiment of the skid plate 50' is shown for
use with a larger commercial embodiment of the saw illustrated in~Figure 6.
The
superscript prime (') is used to denote like components with the skid plate 50
of
Figures 3 and 4, but the details of the skid plate and truss will not be
repeated. To
accommodate larger diameter cutting blades 30, the skid plates 52 become
larger, and
the truss 52 becomes so large that the thin metal trusses 132, 134 (Figures 3-
4) are
easily bent or damaged during manufacturing, handling, assembly and shipping.
Thus,
wider truss arms 132', 134' as shown in Figure 6 are used to avoid or reduce
this
damage. The width of truss arms 132', 134' is .375 inches (.95 cm).
But it is more difficult to adjust the preloading on the skid plate 50', in
part
because the force transmitted by the truss arms 132', 134' are not as far away
from
the plane of the cutting blade. To facilitate calibration of the skid plate
assembly 20'
for a desired preloading, a transverse cut or recess 150 is advantageously
provided at
both ends of the arms 132' and 134'. The recess 150 may be cut by a saw after
the
truss 52 is stamped out of sheet metal and flattened. This provides a more
rigid truss
52 for manufacturing, assembly, handling and shipping, but requires that all
forces be
transferred through the uncut portion adjacent recess 150. As the uncut
portion
adjacent recess or cut 150 is further away from the plane of the cutting blade
30,
adjusting the preload is easier. Thus, the recess 150 facilitates adjustment
of the
tensile or compressive stress of the arms 132', 134' to create the necessary
preloading
on the skid plate 50'. It is believed possible to use the recesses 150 at only
the
leading end of the skid plate 52, but this is not as desirable as having the
recesses at
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opposing ends of arms 132', 134'.
The skid plate assembly 20 of Figures 7 and 8 as described is movably
mounted relative to the concrete cutting saw 24. In this manner, the skid
plate
assembly 20 may float relative to the saw 24 while maintaining support of the
surface
38 of the concrete as the concrete saw 24 traverses the concrete surface 38
during
cutting, while providing a predetermined force on the skid plate 50 to support
the
concrete surface 38. This is important since the skid plate 50 acts as a
support for the
concrete surface 38 surrounding the groove 42 being cut. If the skid plate 50
is
pressed against the concrete too hard, it will unacceptably mark or damage the
concrete surface 38. If insufficient support is provided to the concrete
surface 38
being cut, the surface 38 will ravel adjacent the groove 42.
As shown in Figure 7 and 8, springs i 88, one inside each bore 168 of the
housing 170, rest on smaller top ends I92 of the shafts 160. Adjustment screws
196
are positioned above the springs 188 in each bore 168 at a point near the top
of the
1 S blade housing 170, thus sandwiching the springs 188 against the top ends
192 of the
shafts 160. The springs 188 are desirably coil springs so they can easily be
inserted
into the bores I68. The springs 188 are compressed into the bores 168 with the
adjustment screws 196. Each adjustment screw 196, as illustrated, is a
threaded plug
196 that engages the top portion of the bore 168, which has corresponding
threads.
The adjustment screws 196 may be advanced into the bores 168 to compress the
springs 188 against the shafts 160 and vary the force with which the shaft 160
is
angled downwards towards the surface 38 of the concrete.
The compression of the springs 188 between the top ends 192 of the shafts 160
and the adjustment screws 196 resiliently urges the shafts 160 away from the
saw 24
and towards the concrete surface 38. The shafts 160 thus correspondingly force
the
skid plate 50 toward the surface 38 of the concrete. This is necessary to
assist in
pressing the skid plate 50 against the concrete surface 38 with a
predetermined force.
The spring size and amount of compression can be used to vary the force.
Because each of the two shafts 160 has its own independent adjustment screw
196, the compression of each spring 188 may be adjusted so that an
individualized
downward force may be applied to each of the shafts 160. Further
individualized
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WO 98/02278 PCT/US97/12583
adjustments may be made by using stiffer or weaker springs I88. Locating the
rods
180 at different positions in the housing 170 relative to the location of the
slots 178
allows adjustment of the position of each end of the skid plate 50 relative to
the blade
housing 170. The rods 180 also act as limiting stops to limit the motion of
the skid
plate 50. These individualized adjustments permit the skid plate 50 to be
adjusted so
that the ends of the skid plate 50 are at different vertical positions in
relation to the
concrete surface 38 when the skid plate SO is not in contact with the concrete
surface
38, and allow adjustment of the force with which the skid plate 50 is urged
against
the concrete surface 3 8.
It will be understood that the above-described arrangements of apparatus and
the methods therefrom are merely illustrative of applications of the
principles of this
invention and many other embodiments and modifications may be made without
departing from the spirit and scope of the invention as defined in the claims.
Thus,
for example, a skid plate 50 may be connected to the saw at only one location.
1 ~ Similarly, the leading end of the skid plate 50 could be used to adjust
the pre-loading
rather than the trailing end. Alternatively, both ends of the truss 52 and/or
the skid
plate SO could be used to adjust the pre-loading. Likewise, the module 212
could be
oriented to accommodate a skid plate assembly 20 that is vertically oriented.
Similarly, different methods and apparatus for applying the desired loads,
forces or
deformations could be devised by persons of skill in the art without undue
experimentation, given the present disclosure, including the use of hydraulic
or
pneumatic actuators, springs, levers, gears, magnets, electric motors or
solenoids.
Moreover, the present description allows manual adjustment of the skid plate
50 in
response to visually observed sensor readings, but the adjustment process
could be
2~ automated to eliminate or minimize personal involvement. Finally, if the
skid plate
50 mounts to the saw 24 at a single location rather than at opposing ends as
illustrated, suitable modifications could be made by one of ordinary skill in
the art to
have a truss attached toward opposing ends of the skid plate and adjusted to
achieve
the desired deformation or force profile given the present teachings.
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