Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to counterbalancing means for the
drive system of a reciprocating blade saw 9 and particularly
a heavy duty high speed saw wherein a motor rotates an eccen-
tric which rocks a bell crank to reciprocate the saw blade,
the counterbalancing means including masses which rotate and
rock 180 out of phase with the eccentric and bell crank to
counterbalance the centrifugal and inertial forces developed
thereby and thus to minimize the vibration of the system in
operation.
10A heavy duty high speed saw of the type designed for
splitting an animal carcass comprises a frame, a blade about
30" long and drive means including a motor ~preferably hy-
draulic) rotating a drive shaft which carries an eccentric
connected by a pitman to one arm of a bell crank, the other
arm of which is connected to one end of the blade. Rotating
: movement of the drive shaft is thus converted to reciprocating
linear movement of the blade. At operating speeds of 2000
r.p.m. or more the eccentric creates centrifugal vibrations of
the same frequency and the rocking of the bell crank to re-
ciprocate the saw blade creates inertial vibrations at its
points of reversal. Such vibrations tend to make the saw noisy
and uncomfortable to use, and to reduce the service life of
some parts. Counterbalancing elements for a single eccentric
cam driving directly a reciprocating saw blade are known, as
shown in Mandell patent No. 3,270,369, but the interposition
of the bell crank connection shown herein creates different
vibration problems.
' It is accordingly an object of the invention to provide
counterbalancing elements which are effective to eliminate or
substantially reduce the vibration caused by imbalance of the
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rotating and reciprocating parts of the saw by providing a
system of eccentric drive cams and levers so disposed as to
counteract the vibrating forces generated in the reciprocating
blade saw.
It is another object of the invention to divide the
counterbalancing elements and mount them in positions strad-
dling the working parts of the drive train, to prevent the
development of any lateral torque.
It is a further object of the invention to provide
couterbalancing elements which are so proportioned and lo-
cated that they are equally effective at all speeds of opera- . :
tion.
It is still a further object of the invention to
provide certain improvements in the form, construction and arrange- :
ment of the several parts whereby the above named and other .~ .
objects may effectively be attained.
The invention accordingly comprises the features of .
constru~tion, combination of elements, and arrangement of parts
which will be exemplified in the construction hereinafter set
forth, and the scope of the invention will be indicated in the
claims.
In one aspect of the present invention there is ;
provided a reciprocating blade saw compris.ing an eccentric
mounted on a drive shaft, means for dri~ing said shaft, a :~
bell crank on a second shaft, a pitman connecting the eccentric
to one arm of the bell crank, a saw blade connected to the -
other end of the bell crank and supported for substantially :.
linear reciprocation upon rocking of the bell crank, constituting ~ ....
the saw drive train, and counterbalancing means including at .
least one additional eccentric mounted on the drive shaft ad~
jacent the first eccentric and oriented angularly 180 therefrom, - : . .:
at least one lever pivoted intermediate its ends on the second
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shaft, a second pitman connecting the additional eccentric to
one end of the lever, and a mass carried by the other end of
said lever, the sizes and location of the counterbalancing
means being calculated to substantially counterbalance the
centrifugal and inertial forces developed by operation of the
saw drive train.
In a further aspect of the present invention there
is provided the combination with a drive train, comprising a
drive shaft, a first eccentric fixed thereon, a bell crank
pivotally supported intermediate its ends, a first pitman
connecting the eccentric to one arm of the bell crank and an
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element connected to the other arm of the bell crank for re~
ciprocation thereby, of counterbalancing means which comprises
a pair of second eccentrics fixed on the drive shaft each side
of the first eccentric and angularly displaced 180 therefrom,
a pair of levers pivotally supported each side of the bell
,
crank, a pair of second pitmans each connecting a second
eccentric to one end of a respective lever and a pair of masses
each carried by the other end of a respective lever, the di- -
mensions of the elements comprising the counterbalancing means
being calculated to counteract centrifugal and inertial forces
developed in the operation of the drive train.
A practical embodiment o~ the invention is shown in
; the accompanying drawings wherein:
FIG. 1 represents a top plan view of the saw,
FIG. 2 represents a side elevation of the saw, on a
larger scale, part of the housing being broken away and parts ; ~-
~ eing in sections
1 FIG- 3 represents a seGtionl)on line III-III of Fig~ 2,
FIG. 4 represents a section on line IV-IV of Fig. 2, and
FIG. 5 represents a detail elevation, similar to the left
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side of Fig. 2, showing the driving and counterbalancing
elemen~s in 180 different positions.
Referring to the drawings, the saw is shown as comprising
the frame 11 connecting the distal end housing 12 to the drive
assembly housing 13. The saw blade 14 is supported at one
end by a link 15 in the distal end housing and is movable
longitudinally in a slot or guideway 16 in the lower portion
of the end housing. The opposite end portion of the saw blade
extends through an opening 17 into the drive assembly housing
where it is attached at 18 to the drive train.
The working elements of the drive train include the main `~
drive shaft 20, the eccentric cam 21, the drive link or pit-
man 22 and the bell crank 23, pivotally supported on the
shaft 24 and comprising a first arm 25 connected at 26 to the
.
end of the link or pitman 22 and a second arm 27 to which the
saw blade is attached at 18.
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The drive assembly housing 13 is constituted by side
plates 30, 31 fixed to the frame 11 and the drive shaft 20 is - ~ -
journaled in bearings 32, 33 in the side plates, as shown in ~ -
Fig. 3. The drive shaft is driven by a hydraulic motor 35
which is controlled through connections, not shown, by the -
trigger 36 in the handle 37. The eccentric cam 21 is keyed on
the drive shaft as indicated at 38. The drive train so far --~ I : : :
described is known, but the housing 13 is here enlarged to
accommodate the counterbalancing elements.
The counterbalancing system includes a pair of éccentric
cams 40, 41, somewhat smaller than the cam 21 fixed on the
.
drive shaft 20 each side of the cam 21 and offset angularly
therefrom by 180. Drive links or pitmans 42~ 43 are mounted
3Q on the cams 40, 41 and are connected by pins 44, 45 to levers
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46, 47 which are carried by the shaft 24, on each side of
the bell crank 23. Each lever 46, 47 extends downward beyond
its pivot point and supports a counterweight 48, 49. The
levers 46, 47 may suitably be keyed to the shaft 24 which is ~ -
rotatably mounted in bearings 50, 51 in the side plates 30,
31, as shown in Fig. 4.
Each eccentric cam 21, 40, 41 is provided with a suitable -
ball or roller bearing, not shown, in its periphery and the
washers 53, shown in Fig. 3, aid in locating and supporting
oil seal rings, not shown, adjacent the bearings which are
lubricated in a conventional manner through the drive shaft.
In operation, the drive shaft is driven by the motor 35
to reciprocate, by means of the cams~ the pitmans 22, 42, 43;
the pitmans rock, respectively, the bell crank 23 and levers
46, 47; the bell crank 23 reciprocates the saw blade 14 and
the leveTs 46, 47 oscillate the counterweights 48, 49.
Vibrational forces are generated, in the basic drive
train, by the rotation of the eccentric cam 21 which exerts `~
centrifugal force in all direceions within its plane of rota-
` 20 tion, by the rotation of the larger end of the pitman 22 which
; adds to the centrifugal forces generated by the cam, by the
linear reciprocation of the pitman 22 which exerts inertial
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orces at each end of its travel, and by the bell crank 23
` which exerts inertial forces of acceleration and decelera~ion
at every point in its cycle of movement. The mass of the saw
blade, moving with the bell crank, adds to the inertial forces
thereof. From the description of the counterbalancing system,
and assuming that the mass and location of its elements have
been accurately calculated, it will be apparent that the ~`
eccentric cams 40, 41 each side of the cam 21 form with said
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cam 21 a symmetrical assembly which can rotate around the
axis of the drive shaft without vibration, because the mass
of cam 21, extending in one direction, is exactly balanced
by the masses of cams 40, 41, extending in the opposite
direction. The annular ends of the pitmans, each surrounding
a cam and movable therewith, add to the centrifugal forces
but are designed not to unbalance the assembly. The pitmans
42, 43 and levers 46, 47 are so disposed that their masses,
including counterweights 48, 49, correspond kinetically, but
in the opposite sense, to the masses of the bell crank, saw
blade and pitman 22, the movements of these elements being
linear on short arcs.
The arrangement of elements as disclosed can be operated ~ ~
at any desired speed with minimal vibration of the whole sys- ~ -
; tem due to the inherent counterbalancing of all eccentric,
oscillatory or reciprocatory parts. ~
Where a working element is reciprocated directly by an ;
eccentric along a single axis the vibratory forces are mainly
in the direction of said axis, but when an eccentric acts
along an axis lying in a first direction, to reciprocate
~through a bell crank) a working element which moves on an
axis lying in a second direction at an angle to the first,
the ~ibratory forces become complex. Such forces are, how-
ever, substantially completely counterbalanced by the means
disclosed herein, where every move of every part of the dri~e
train is accompanied by a corresponding move, in the opposite
sense, by equivalent masses in the counterbalancing system.
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