U.S. patent number 3,632,104 [Application Number 04/853,304] was granted by the patent office on 1972-01-04 for balanced folder assembly.
This patent grant is currently assigned to Harris-Intertype Corporation. Invention is credited to Charles H. Dufour.
United States Patent |
3,632,104 |
Dufour |
January 4, 1972 |
BALANCED FOLDER ASSEMBLY
Abstract
An improved sheet-folding apparatus includes a folder blade
which is reciprocated by operation of a first crank assembly to
move sheets into a nip formed by a pair of folder rollers. A second
crank assembly is connected to a crankshaft for operating the first
crank assembly. This second crank assembly is operable to maintain
the torque load applied to the crankshaft substantially constant by
applying to the crankshaft a fluctuating torque load which offsets
a fluctuating torque load applied to the crankshaft by the first
crank assembly.
Inventors: |
Dufour; Charles H. (Westerly,
RI) |
Assignee: |
Harris-Intertype Corporation
(Cleveland, OH)
|
Family
ID: |
25315672 |
Appl.
No.: |
04/853,304 |
Filed: |
August 27, 1969 |
Current U.S.
Class: |
493/444 |
Current CPC
Class: |
B65H
45/18 (20130101) |
Current International
Class: |
B65H
45/18 (20060101); B65H 45/12 (20060101); B65h
045/18 () |
Field of
Search: |
;270/83,84,85,30,67,61,32,62,79 ;74/603 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Michell; Robert W.
Assistant Examiner: Dyer; R. P.
Claims
Having described a specific preferred embodiment of the invention,
the following is claimed:
1. A sheet-folding apparatus comprising a pair of folder rollers
cooperating to form a nip, means for positioning sheets in a
predetermined relationship with said folder rollers, blade means
for engaging the sheets and moving them into the nip formed by said
folder rollers, means for reciprocating said blade means including
a shaft operatively connected with said blade means and drive means
for rotating said shaft to effect reciprocation of said blade
means, and counterweight means for offsetting torque fluctuation
resulting from reciprocation of said blade means, said
counterweight means being operatively connected with said shaft
whereby rotation of said shaft operates said counterweight means to
effect the offsetting of the torque fluctuations resulting from
reciprocation of said blade means to thereby tend to minimize
torque loading on said shaft during operation of said folding
apparatus.
2. A sheet-folding apparatus as set forth in claim 1 wherein said
counterweight means includes a mass which is operatively connected
with said shaft and is reciprocated approximately 90.degree. out of
phase with reciprocation of said blade means upon rotation of said
shaft by said drive means.
3. A sheet-folding apparatus as set forth in claim 1 wherein said
blade means includes a first pivotally mounted arm and a folder
blade mounted on said first arm, said means for reciprocating said
blade means includes a first crank assembly operatively connected
with said shaft and said first arm for reciprocating said first arm
to move said folder blade relative to said folder rollers, and said
counterweight means includes a second pivotally mounted arm and a
second crank assembly operatively connected with said shaft and
said second arm for reciprocating said second arm to operate said
counterweight means to offset torque fluctuations resulting from
reciprocation of said folder blade relative to said folder rollers
by operation of said first crank assembly.
4. A sheet-folding apparatus as set forth in claim 1 wherein said
counterweight means includes means for statically balancing said
blade means and means for reciprocating said blade means to provide
static equilibrium of said folding apparatus for positions through
which said blade means is moved by said means for reciprocating
said blade means during operation of said sheet-folding
apparatus.
5. A sheet-folding apparatus as set forth in claim 1 wherein said
counterweight means includes a mass which is reciprocated to offset
torque fluctuations resulting from reciprocation of said blade
means, said mass and blade means being operatively interconnected
in such a manner that the acceleration of said mass is
substantially zero when said blade means is experiencing its
greatest acceleration and the acceleration of said blade means is
substantially zero when said mass is experiencing its greatest
acceleration.
6. A sheet-handling apparatus comprising a member for engaging
sheets, a first crank assembly operatively connected to said member
for reciprocating said member to thereby effect movement of the
sheets, a mass, a second crank assembly operatively connected to
said mass for reciprocating said mass, a shaft operatively
interconnecting said first and second crank assemblies, and drive
means for rotating said shaft to effect operation of said first and
second crank assemblies, said first crank assembly including means
for effecting maximum acceleration of said member when said mass is
being subjected to substantially zero acceleration by said second
crank assembly, said second crank assembly including means for
effecting maximum acceleration of said mass when said member is
being subjected to substantially zero acceleration by said first
crank assembly.
7. A sheet-handling apparatus as set forth in claim 6 wherein said
member is mounted on a first arm mounted for pivotal movement under
the influence of said first crank assembly, said mass including a
second arm mounted for pivotal movement under the influence of said
second crank assembly, said first arm being pivoted in a first
direction by operation of said first crank assembly to move sheets
engaged by said member in said first direction, said first arm
being pivoted in a second direction by operation of said first
crank assembly to move said member out of engagement with the
sheets.
8. A sheet-handling apparatus as set forth in claim 6 wherein said
member for engaging the sheets is a folder blade, said
sheet-handling apparatus further including a pair of folder rolls
which cooperate to define a nip, said folder blade being movable by
operation of said first crank assembly to move the sheets into said
nip.
9. A sheet-handling apparatus as set forth in claim 6 wherein said
second crank assembly and mass statically balances said first crank
assembly and member to provide static equilibrium when said drive
means is ineffective to rotate said shaft.
10. A sheet-handling apparatus as set forth in claim 6 wherein said
first crank assembly includes means for applying a fluctuating
torque load to said shaft upon reciprocation of said member under
the influence of said first crank assembly and said second crank
assembly includes means for applying to said shaft a fluctuating
torque load which is equal and opposite to the fluctuating torque
load applied to said shaft by said first crank assembly.
11. A folder assembly for folding sheet material along a
predetermined fold line, said folder assembly comprising a pair of
cooperating folder rollers defining a nip, conveyor means for
transporting sheets of material to a position overlying said nip, a
first pivotally mounted arm, a folder blade mounted on said arm, a
crankshaft, first crank means for reciprocating said arm to move
said blade and sheets toward said nip and then to move said blade
away from said nip while the sheets are folded by passing through
said nip, said first crank means including a first member fixedly
connected to said crankshaft and a first link pivotally connected
at one end portion to said first member and at another end portion
to said arm whereby rotation of said crankshaft and first member
moves said first link to reciprocate said first arm and said blade,
a second pivotally mounted arm, second crank means operatively
connected to said crankshaft for reciprocating said second arm,
said second crank means including a second member fixedly connected
to said crankshaft and a second link pivotally connected at one end
portion of said second member and at another end portion to said
second arm whereby rotation of said crankshaft and said second
member moves said second link to reciprocate said second arm, and
drive means for rotating said crankshaft to thereby operate said
first and second crank means to reciprocate said first and second
arms and said blade, said first crank means including means for
subjecting said first arm to maximum acceleration when said second
arm is being subjected to substantially zero acceleration by
operation of said second crank means and said second crank means
including means for subjecting said second arm to maximum
acceleration when said first arm is being subjected to
substantially zero acceleration by operation of said first crank
means so that said first and second crank means apply to said
crankshaft fluctuating torque loads which offset each other.
12. A folder assembly as set forth in claim 11 wherein said pivot
connection between said first link and said first arm is moved
along a first path by operation of said first crank means and
wherein said pivot connection between said second link and said
second arm is moved along a second path extending transversely to
said first path by operation of said second crank means.
13. A folder assembly as set forth in claim 11 wherein said first
crank means, first arm, and blade are statically balanced by said
second crank means and second arm.
Description
This invention relates generally to a sheet-handling apparatus and
more particularly to an apparatus for folding sheets.
A known sheet folder of the knife- or "chopper"-type folds sheets
by passing them through a nip formed by a pair of cooperating
rollers or cylinders. A blade or knife is moved downwardly into
engagement with the sheets and forces them into the nip. The blade
is then withdrawn upwardly. The blade is reciprocated through these
down and up operating strokes by operation of a crank assembly.
The reciprocative movement of the blade produces torque
fluctuations in the load applied to the crank assembly and thus on
the folder drive train. Torque fluctuations on the drive train tend
to vibrate the folder assembly and a printing press associated with
the folder assembly. This vibration tends to adversely effect the
operation of mechanical components of the folder and printing
press.
Accordingly, it is an object of this invention to provide a new and
improved sheet-handling apparatus wherein a substantially constant
torque load is applied to a drive train for a reciprocating mass
system.
Another object of this invention is to provide a new and improved
statically and dynamically balanced sheet folder apparatus having a
blade which is reciprocated to effect a folding of the sheets.
Another object of this invention is to provide a new and improved
sheet folder apparatus having a blade which is reciprocated to move
sheets into the nip of a pair of folder rollers and a counterweight
means for offsetting torque fluctuations resulting from
reciprocation of the blade.
Another object of this invention is to provide a new and improved
sheet folder apparatus having a first crank assembly for
reciprocating a blade to move sheets into the nip of a pair of
folder rollers and a second crank assembly for offsetting torque
fluctuations resulting from reciprocation of the blade.
These and other objects and features of the invention will become
more apparent upon a consideration of the following description
taken in connection with the accompanying drawings wherein:
FIG. 1 is a schematic illustration of a knife-type folder
construction in accordance with the present invention;
FIG. 2 is a schematic elevational view, taken generally along the
line 2--2 of FIG. 1, illustrating the relationship between a
"chopper" or knife assembly and a folder crank assembly for
operating the knife assembly;
FIG. 3 is a schematic illustration, taken generally along the line
3--3 of FIG. 2, illustrating the relationship between the folder
crank assembly of FIG. 2, a crankshaft, a crankshaft drive train,
and a counterweight crank assembly of the folder of FIG. 1;
FIG. 4 is a schematic illustration, taken generally along the line
4--4 of FIG. 3, further illustrating the counterweight crank
assembly;
FIG. 5 is a schematic illustration, taken generally along the line
5--5 of FIG. 4, illustrating the relationship of the counterweight
crank assembly to a mounting or support bracket;
FIGS. 6-9 are graphic illustrations approximating variations in
velocity, acceleration, torque arm, and load torque, respectively,
for the folder crank assembly during operation of the folder of
FIG. 1; and
FIGS. 10-13 are graphic illustrations approximating variations in
velocity, acceleration, torque arm, and load torque, respectively,
for the counterweight crank assembly during operation of the folder
of FIG. 1.
Although it is contemplated that the present invention will be used
in many different types of sheet-handling devices, such as packers
and folders, it is disclosed herein in a knife- or "chopper"-type
folder. A knife-type folder constructed in accordance with the
present invention includes a pair of folder rollers or cylinders
and a blade which is reciprocated to move sheets into a nip defined
by these rollers. A counterweight assembly is provided for
offsetting torque fluctuations resulting from reciprocation of the
blade. This counterweight assembly can take many different forms
including that of a crank assembly which reciprocates a mass in an
out-of-phase relationship with reciprocative movement of the
blade.
A knife- or "chopper"-type folder 20 forming a specific preferred
embodiment of the invention as illustrated in FIGS. 1 and 2. The
folder 20 includes a pair of folder rollers or cylinders 22 and 24
which cooperate to define a nip 26 through which sheets of material
30 pass either singularly or in groups or gathers. As the sheets 30
pass through the nip 26 a fold is formed along a predetermined fold
line. The blade 34 is moved from a raised position (shown in dashed
lines in FIG. 2) to a lowered position (shown in solid lines in
FIG. 2) to press the sheets into the nip 26. The blade 34 is
reciprocated between the raised and lowered positions by means of a
folder crank assembly 36 which is driven by a crankshaft 38.
The reciprocation of the blade 34 under the influence of the crank
assembly 36 results in the crank assembly applying a fluctuating or
uneven torque load to the crankshaft 38. Since the crankshaft 38
and folder rollers 22 and 24 are driven by common drive train, a
part of which is indicated at 42 in FIG. 1, the fluctuating torque
load tends to cause the folder rollers 22 and 24 to be driven at
varying speeds by the drive train. In addition, the fluctuating
torque load on the crankshaft 38 results in the folder drive train
being vibrated or shaken while it is being operated thereby causing
variations in perforations in the sheets, cut off of the sheets,
and folds.
A counterweight assembly 46 is connected to the crankshaft 38 (see
FIGS. 3 and 4) to maintain the torque load on the crankshaft 38
substantially constant. Accordingly, the counterweight assembly 46
applies to the crankshaft 38 a fluctuating torque load which is
equal and opposite to the torque load applied to the crankshaft 38
by the crank assembly 36. In the illustrated embodiment of the
invention, the counterweight assembly 46 includes a crank assembly
50 which is operated by rotation of the crankshaft 38 to
reciprocate a mass or arm 52. The arm 52 is reciprocated with the
same frequency and 90.degree. out of phase, in either a leading or
lagging sense, with the reciprocation of the blade 34. The mass and
rotational inertia of the counterweight assembly 46 is such that
the torque load applied to the crankshaft 38 by the crank assembly
50 is equal and opposite to the torque load applied to the
crankshaft 38 by the crank assembly 36. Therefore, the combined
torque load on the crankshaft 38 is substantially constant.
During operation of the folder assembly 20, sheets 30 are fed
either one at a time or in groups to a folder station 56 by
rotation of a plurality of feed rollers 58 through 68 (FIG. 1). The
forward movement of the sheets is arrested by engagement with a
stop member 72 while the sheets are supported on a plate 74
overlying the folder rollers 22 and 24. The sheets are retained in
place with their leading end portions engaging the stop 72 by
suitable brushes 78 which function in a known manner to prevent the
sheets from "jumping back."
During this positioning of the sheets at the folder station 56, the
crank assembly 36 maintains the blade 34 in a position above the
support plate 74 by pivoting the blade arm 82 upwardly about a
support shaft 84 (see the dash line position of FIG. 2). Once the
sheets 30 are positioned at the folder station 56 by engagement
with the stop member 72, the crank assembly 36 moves the blade 34
downwardly so that it engages the sheets 30 along a predetermined
fold line and presses the sheets through a slot 86 in the support
plate 74 and into the nip 26 between the rollers 22 and 24. The
rollers 22 and 24 are rotated continuously in the direction
indicated by the arrows in FIG. 2 and engage the sheets to move
them downwardly while folding them along the predetermined fold
line. As the sheets are being folded by the rollers 22 and 24, the
crank assembly 36 pivots the arm 82 upwardly to move the blade 34
out of engagement with the sheets 30 and enable the next group of
sheets to enter the fold station 56. Although the movement of the
blade 34 has been described as including two separate strokes, that
is a downward stroke and an upward stroke, it should be understood
that the crankshaft 38 is continuously rotating so that the crank
assembly 36 is continuously reciprocating the blade between the
raised and lowered positions to enable sheets to be quickly folded
by the folder 20.
The crank assembly 36 includes a wheel member 88 which is rotated
at a substantially constant speed by the crankshaft 38 during
operation of the folder assembly 20. A crank link 90 is pivotally
connected to the crank wheel 88 at a pivot connection 92. The
opposite end portion of the link 90 is pivotally connected at 94 to
the blade arm 82. Of course, rotation of the crank wheel 88 raises
and lowers the pivot connection 92 to reciprocate the arm 82 and
blade 34 about the support shaft 84 to thereby raise and lower the
blade. This reciprocative movement of the blade 34 and arm 82
results in their downward movement being arrested when the pivot
connection 92 is adjacent a point designated 90.degree. in FIG. 2.
The blade is then moved upwardly until the pivot connection 92 is
adjacent the point designated 270.degree. in FIG. 2. The upward
movement is then arrested and the next downward stroke
initiated.
This reciprocative movement of the blade 34 and arm 82 applies a
fluctuating torque load to the crankshaft 38. This fluctuating
torque load is offset by the counterweight assembly 46. The crank
assembly 50 of the counterweight assembly 46 includes a crank wheel
or member 100 which is fixedly connected to the crankshaft 38 (see
FIG. 4). The crank wheel 100 is connected with the mass or arm 52
by a connector link 102 which is pivotally connected at 104 to the
crank wheel and at 106 to the arm 52. The opposite end portion of
the arm 52 is pivotally connected at 110 to a support or mounting
bracket 112 (see FIG. 5). The mounting bracket 112 is connected to
a frame 114 of the folder assembly 20.
The drive train 42 rotates the crankshaft 38 to operate the crank
assemblies 36 and 50. The drive train 42 includes a gear 118 (see
FIG. 1) which is fixedly connected to the crankshaft 38. The
crankshaft 38 is supported for rotation by a bracket 120 (FIG. 3)
which is connected to the frame 114. The gear 118 is driven by a
gear 122 of a gear train which also drives the folder rollers 22
and 24. Since the counterweight assembly 46 balances the
fluctuating torque load applied to the crankshaft 38 by the crank
assembly 36, the load on the drive train 42 is maintained
substantially constant so that the drive train is operated in a
smooth manner without undue jerking to thereby tend to minimize
vibration of the folder 20 and a printing press associated with the
folder.
Simplified operating characteristics for the crank assembly 36 and
blade arm 82 are illustrated graphically in FIGS. 6 through 9. Thus
as the blade 34 is moved downwardly, the velocity of the blade
reaches a maximum when the pivot connection 92 is approximately
adjacent the point indicated at 0.degree. in FIG. 2. As the
downward movement of the blade 34 continues, the velocity is
decreased until the blade 34 reaches its lowermost position and the
pivot connection 92 is approximately adjacent the point designated
90.degree.. The direction of movement of the blade is then reversed
and the velocity in the upward direction increased until the pivot
connection 92 passes the point approximately indicated at
180.degree. in FIG. 2. The upward velocity of the blade is then
decreased until the pivot connection 92 reaches the point
designated 270.degree. when the blade 34 again begins to move
downwardly. Thus, the velocity of the blade 34 varies in a manner
which is approximated by the sinusoidal curve 130 in FIG. 6.
To provide the sinusoidally varying velocity illustrated in FIG. 6,
the acceleration of the blade 34 must vary in a sinusoidal manner
approximated by the curve 134 in FIG. 7. It should be noted that
the acceleration of the blade 34 is substantially zero when the
blade is experiencing its maximum velocity and the pivot connection
92 is approximately adjacent either the point indicated at
0.degree. or at 180.degree. in FIG. 2. Similarly, the blade 34 is
subjected to its maximum acceleration when the pivot connection 92
is approximately adjacent to either the 90.degree. or 270.degree.
designation of FIG. 2.
Since the extent to which the pivot connection 92 is located
sidewardly of the center of the crankshaft 38 varies in a
sinusoidal manner as the crankwheel 88 is rotated, the lever or
torque arm for moving the blade 34 and blade arm 82 varies in a
sinusoidal manner as approximated by the curve 136 of FIG. 8. It
should be noted that the torque or lever arm is a maximum when the
pivot connection 92 is adjacent to either the 0.degree. or
180.degree. designation of FIG. 2. It should also be noted that the
torque or lever arm is substantially zero when the pivot connection
92 adjacent to either the 90.degree. or 270.degree.
designation.
The torque load applied by the crank assembly 36 to the crankshaft
38 fluctuates relative to a predetermined torque load (designated X
in FIG. 9) in the manner approximated by the curve 140. A
simplified explanation of the torque load is that it is the product
of the torque arm (FIG. 8) the acceleration (FIG. 7) and the mass
being accelerated. If the mass of the sheets 30 is ignored, the
mass being accelerated remains substantially constant. Therefore,
the torque load (FIG. 9) applied to the crankshaft 38 varies as a
direct function of variations in the product of the torque arm and
acceleration. Thus, there will be substantially zero variable
torque load when either the value of the torque arm (FIG. 8) or the
value of the acceleration (FIG. 7) is zero.
The velocity, acceleration, torque or lever arm and torque load
characteristics for the counterweight assembly 46 are graphically
illustrated in FIGS. 10 through 13. It should be noted that the
characteristics for the counterweight assembly 46 are 90.degree.
out of phase with the corresponding characteristics for the crank
assembly 36, blade arm 82 and blade 34. Thus, the velocity (FIG.
10) of the pivot connection 106 of the crank assembly 50 is zero
when the pivot connection 104 is adjacent to the 0.degree.
designation of FIG. 4. The pivot connection 92 (FIG. 2) is offset
180.degree. from the pivot connection 104 (FIG. 4). Therefore, when
the pivot connection 104 is adjacent to the 0.degree. designation
of FIG. 4 which has the same location relative to the frame 114 as
does the 180.degree. designation of FIG. 2, the pivot connection 92
is adjacent to the point indicated 0.degree. in FIG. 2 and knife
blade 34 is being moved downwardly with its maximum velocity.
Continued rotation of the crankshaft 38 through 90.degree. of
movement moves the pivot connection 104 adjacent to the 90.degree.
designation of FIG. 4 and the pivot connection 106 is moving at its
maximum velocity (FIG. 10). This 90.degree. of rotation of the
crankshaft 38 moves the pivot connection 92 (FIG. 2) adjacent to
the 90.degree. designation and the blade 34 is being moved with
substantially zero instantaneous velocity. Thus, it can be seen
that the velocity curve 130 for the knife blade 34 is 90.degree.
out of phase with the velocity curve 144 for the pivot connection
106 of the counterweight crank assembly 50.
Variations in the acceleration of the pivot connection 106 are
illustrated graphically by the curve 148 in FIG. 11. It should be
noted that the pivot connection 106 is subjected to maximum rate of
acceleration when the pivot connection 104 is adjacent to either
the point designated 0.degree. or 180.degree. in FIG. 4. Thus, the
acceleration curve 148 is 90.degree. out of phase with the
acceleration curve 134 for the blade 34. Therefore, the blade 34 is
subjected to its maximum acceleration when the pivot connection 106
is being subjected to substantially zero acceleration. Similarly,
when the pivot connection 106 is being subjected to its maximum
acceleration, the blade 34 is being subjected to substantially zero
acceleration.
The torque or lever arm for the connection 106 relative to the
crankshaft 38 varies in a sinusoidal manner approximated by curve
150 in FIG. 12. It should be noted that the curve 150 is 90.degree.
out of phase with the torque or lever arm curve 136 of FIG. 8.
Since the mass of the counterweight assembly 46 remains constant,
the torque load which is applied to the crankshaft 38 fluctuates in
accordance with fluctuations in the product of the torque arm (FIG.
12) and acceleration of the mass (FIG. 11). Variations in this
product are approximated by the torque load curve 154 in FIG. 13.
It should be noted that the torque load curve 154 is 90.degree. out
of phase with the torque load curve 140 approximating the
fluctuations in the torque load applied to the crankshaft 38 by the
crank assembly 36. The maximum and minimum torque illustrated
graphically by the curves 140 and 154 are substantially equal.
Therefore, the fluctuations in the torque load applied to the
crankshaft 38 by the crank assembly 36 are effectively cancelled by
the equal and opposite fluctuations in the torque load applied to
the crankshaft 38 by the crank assembly 46. This is illustrated in
FIGS. 9 and 13 wherein the torque load curve 140 and 154 are
90.degree. out of phase and have equal and opposite magnitudes at
any given time.
As will no doubt be understood by those skilled in the art the
foregoing is a simplified explanation of the operation of crank
assembly 36 and counterweight assembly 46. Also, the curves of
FIGS. 6-13 represent only simplified approximations of the
operating characteristics. These operating characteristics will
vary somewhat from the simplified graphs of FIGS. 6-13 due to
weight and rotational inertia effects which are present in the
actual crank and counterweight assemblies. While the graphic
illustrations of FIGS. 6-13 only approximate the operating
characteristics which they depict, it is believed that they are
sufficiently informative since the depicted operating
characteristics will vary between embodiments of the invention
which differ only slightly from each other. It should also be
understood that the indications of the 0.degree., 90.degree.,
180.degree. and 270.degree. positions in FIGS. 2 and 4 of the
drawings are only approximate and are not exactly located.
In view of the foregoing remarks, it can be seen that the
sheet-folder assembly 20 includes a crank assembly 36 which is
driven by a crankshaft 38 to reciprocate a folder blade 35 and move
sheets into the nip 26 defined by the folder rollers 22 and 24. The
fluctuating torque load which is applied to the crankshaft 38 by
the crank assembly 36 as a result of this reciprocation of the
blade 34 is offset by a fluctuating torque load which is applied to
the crankshaft 38 by the counterweight assembly 46. In the
illustrated embodiment of the invention, the counterweight assembly
46 includes a crank assembly 50 which is operable to pivot a mass,
i.e., the arm 52, if a 90.degree. out of phase relationship with
the pivotal movement of the blade arm 82 by the crank assembly 36.
This out of phase relationship between the arms 52 and 82 results
in the fluctuating torque loads (see FIGS. 9 and 13) offsetting
each other to maintain the torque load on the crankshaft 38
substantially constant.
In addition to dynamically balancing the fluctuating torque load
applied to the crank shaft 38 by the crank assembly 36, the
counterweight assembly 46 balances the static load applied to the
crankshaft 38 by the crank assembly 36. This static balancing
results from the 180.degree. offset relationship between the pivot
connection 92 to the crank wheel 88 of the crank assembly 36 and
the pivot connection 104 to the crank wheel 100 of the crank
assembly 50. Therefore, the static loads applied to the crankshaft
38 by the two crank assemblies 36 and 50 are located on opposite
sides of the centerline of the crankshaft 38 and tend to balance
each other. The static load applied to the crank wheel 100 of the
pivot connection 104 can be adjusted to equal the load applied to
the crank wheel 88 by means of a suitable counterweight 160 (see
FIG. 4) which is connected to the arm 102. Thus, the counterweight
assembly 46 both statically and dynamically balances the load
applied to the crankshaft 38 by the crank assembly 36.
Although a specific preferred embodiment of the counterweight
assembly 46 has been illustrated herein, it is contemplated that
other specific embodiments of the counterweight assembly could be
utilized. For example the pivot connection 110 (FIG. 4) could be
located below the center of the crankshaft 38 or on the opposite
side of the crankshaft. In addition, it is contemplated that
various spring arrangements would be substituted for the
illustrated counterweight assembly. It is also contemplated that
the counterweight assembly 46 could be used in conjunction with
other types of mechanisms, such as packers.
* * * * *