Note: Descriptions are shown in the official language in which they were submitted.
` ~ 1052951
Low energy electrically-powered impact tools
are quite commonplace and are used for such applications as
driving small nails and staples, loosening and tightening
nuts, and setting deformable fasteners like small brass and
S copper rivets. Up to now, however, most all high energy im-
pact tools, at least the hand held type, have been operated
by compressed air. There are many obvious disadvantages to
air-operated hand tools, not the least of which is the
necessity for large hoses and a relatively stationary high
volume air supply. The pressure regulators, lubricators,
filters and the like ordinarily used with pneumatic equipment
all serve to complicate the situation as well as make it more
cumbersome and expensive.
While the concept of a high energy hand-held
electrically-powered impact tool is, to say the least, an
attractive one, it poses a number of problems which have hereto-
fore remained unsolved. For instance, it can be demonstrated
, rather simply through the use of an arbor press and a scale
that a peak force of about 1000 lbs. is required to drive a
16 penny (3.25") nail into semihard wood up to the point where
its head lies flush with the surface of the latter. Since the
nail obviously exerts an equal and opposite force on the driver
and the operator could not possibly oppose a 1000 lb. peak
~' force, a low velocity driver will not work regardless of the
force developed thereby as it would merely be pushed back
away from the workpiece rather than forcing the nail through
it. Thus, both the time required to drive the nail and the
mass of the driver become most important considerations,
especially if the design parameters call for recoilless opera-
tion which is highly desirable.
Other practical parameters can be chosen for
the tool such as, for example, its mass and contact velocity
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lOSZ95~
for the purpose of calculating the amount of latent energy
that must be stored in the system as well as the type of
mechanism that is required to transfer such energy to the
workpiece in the brief time allotted for essentially recoilless
operation. When this is done, such calculations reveal the fact
that a considerable energy storage capability coupled to a
very fast and efficient power transfer mechanism becomes an
absolute necessity. Furthermore, such calculations reveal
the utter futulity of applying conventional approaches like
solenoids to the solution of the problem because an electro-
magnetic unit capable of generating the required average
power over the allotted time span would be so large and heavy
as to be utterly impractical to say nothing of its cost.
The flywheel comes to mind as a mechanism which
s 15 is both compact and lightweight yet, at the same time, possesses
3 high energy storage capabilities. Unfortunately, however, it
also constitutes a high speed rotating system with large un- -
desirable precession moments that become most difficult to cope
with and, in fact, almost insurmountable in a hand-held tool ~ ~.
that must be positioned with considerable accuracy. The
problems presented to the operator in coping with such forces
as these make a single flywheel tool a very dangerous, if not
in fact a lethal, instrument when loaded with nails or other
fasteners that are ejected therefrom at high speeds because
of the considerable difficulty associated with controlling
same.
It has now been found in accordance with the
teaching of the instant invention that a high energy, pre-
ferably electrically-driven and hand-held impact tool can,
in fact, be constructed that is capable of developing the
75 horsepower or so required to drive a 3-1/4 nail during a
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lOSZ951
brief interval lasting a few thousandths of a second. In
fact~ a small fractional horsepower electric motor will be
entirely adequate to answer the power requirements of a duty
cycle calling for more than one actuation per second.
Not one, but a pair of preferably substantially
identical counterrotating rotating bodies or flywheels store
the necessary energy and, in addition, when properly matched
and oriented relative to one another, co-operate to cancel out
the bothersome precession moments inherent in high speed
` 10 rotating systems having flywheels. These same flywheels, .
; when one is moved relative to the other so as to engage a
friction ram positioned therebetween, coact to define an
efficient high speed power transfer mechanism capable of
i~ imparting a considerable driving force to the ram in a matter
of a few milliseconds. What's more, the clutch thus produced
requires no synchronous engagement and, when properly designed,
is free of slippage.
The preferred incorporation of mechanical inter-
locks which require that the nose of the tool to be held firmly
against the workpiece while the trigger is actuated to engage
the clutch make the tool a safer one to operate while, at the
same time, disabling it from discharging a fastener should it
-~ be dropped accidently. The motor speed control, while not
exactly a safety feature, does provide the operator with the
means by which he can reduce the ram energy to an appropriate
level commensurate with the job being performed thus preventing
~ damage to the workpiece.
t Ordinary household current is entirely adequate
' as a power source and, in fact, the power demands are such
~ 30 that they could easily be supplied by batteries or a small
; self-contained generator, especially in the case of a low de-
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~OS2951
mand duty cycle. The problem becomes one of the time involved to get the
flywheel drive motors up to speed rather than the dissipation of energy
during the drive cycle which is minimal even with a small fractional horse-
power motor.
The instant impact tool, when designed for use as a nailer, is
readily adapted to accept commercially-available strips or belts of nails
without modification. The same is true of other types of fasteners such as
rivets and the like when similarly packaged. In general, such items would
~ be housed in a spring-fed magazine of conventional design.
- 10 Thus, according to one aspect of the present invention there is
provided an impact tool having driving fasteners comprising: a) a housing
defining a drive path; b) a pair of counter-rotating flywheels; c) power
means for rotating said flywheelc; d) ram means movable in said drive path;
e) feed means including a magazine containing a supply of fasteners for
supplying fasteners in sequence to said drive path; f) clutch means for
drivingly coupling said flywheels and ram means to propel said ram means in
j a drive stroke along said drive path toward a fastener disposed in said drive
.
~ path to impact the fastener; and g) control means for controlling the clutch
; means.
According to another aspect of the present invention there is pro-
vided a fastener driving method comprising the steps of: counter-rotating -
a pair of flywheels of equal mass about parallel axes at equal speeds, so as
to cancel precession moments, and transferring energy from said flywheels to
a fastener driving ram by moving one of said flywheels toward the other to
pinch said ram between them.
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105Z951 ~J
: In the accompanying drawings which illustrate an exemplary
embodiment of the present invention:
Figure 1 is a schematic representation of the principle
operating parts of an embodiment of the invention;
Figure 2 is a perspective view of the tool as seen from a
vantage point above and to the left of its rear end;
Figure 3 is a top plan view of the tool to an enlarged scale,
portions having been broken away to both conserve space and better reveal
the interior construction;
.`
f
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~OS2951
Figure 4 is a transverse section taken along
line 4--4 of Figure 3 to a further enlarged scale;
. Figure 5 is a longitudinal section to the
: same scale as Figure 4 taken along line 5--5 of Figure 3;
Figure 6 is a section taken along line 6--6 of
., Figure 5 and to the same scale as the latter figure, portions
again having been broken away to conserve space;
Figure 7 is a fragmentary section similar to
Figure 6, but showing ram advanced into its fully-extended
position;
Figure 8 is a fragmentary section taken along
line 8--8 of Figure 3 to an even further enlarged scale;
"
.. Figure 9 is a framentary perspective view to
the same scale as Figure 8 and with portions broken away and
shown in section to better reveal the interior construction; ~ -
-: Figure 10 is a fragmentary section similar to
.~ Figure 5 and to the same scale as the latter showing the
` trigger actuated, but the nosepiece still extended;
~; Figure 11 is a fragmentary section like Figure
10 except that the nosepiece is shown in retracted position; and
; Figure 12 is a schematic of a representative ~
motor speed control circuit. ~-
. Before turning to a detailed description of a
:~ preferred nail-driving embodiment of the present invention .
, 25 that has been broadly designated by reference numeral 10,
reference will be made to the schematic view of Figure 1
for the purpose of outlining the more important design features
and parameters of the tool, some of which are quite critical.
~I First of all, to get an idea of the force that must be
generated by the tool and the time interval within which this
~' force must be expended, a simple experiment coupled with a
., . ; ~
.. ' ' ~ :
lOS~:9S~. `
detailed mathematical analysis will be helpful.
It can be demonstrated experimentally with a
simple arbor press that a 16 penny nail which is 3.25 inches
long requires a peak force of about 1000 lbs. to drive it all
the way up to the point where its head is flush with the
; surface of a piece of medium hard lumber. Furthermore, a ~ -
graph of the force applied versus the degree of penetration
shows a substantially linear relationship up to the 1000 lb.
limit above noted. Therefore, the total energy expended (Eo)
can be represented mathematically as follows:
Equation (1) Eo = ~ F dL ~ 125 ft lbs.
Since, in operation, the nail exerts an equal
and opposite force upon the impact tool or driver, the time
required to drive the nail and the mass of the driver become
important considerations. If, therefore, we assume a 10 lb.
i weight for the driver which is reasonable for a hand-held
si tool, and we further assume a contact velocity of 5 ft./sec.,
! the time available to insert the nail into the wood can be
defined as follows where F(t) is the time varying force
exerted on the tool by the nail, then,
, Equation (2) F(t) = MA = ~
where M is the mass of the driver and td is
time required to drive the nail. Accordingly,
Equation (3) F(t) dt = dv
or,expressed another way
Equation (4) M ~d F(t) dt = Yf dv
Where Vi is the impact velocity of the tool and Vf is its final
velocity.
Having already determined that
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'
lOS~951
Equation (5) F(t) = 1,000 (td~ lbs.
it follows from Equation (4~ that
Equation (6) 12 td = Vf - Vi
Solving for td in Equation (6) we f ind
Equation (7) td = 2M ~Vf - Vi )
1000
Now, substituting the assumed value of 5 ft./sec. for the impact
velocity (Vi~, a zero terminal or final velocity (Vf) and a
mass M of 10/32, we find that
Equation (i) td = 2 (10/32) (5) = 003
Accordingly, using a 10 lb. tool with an initial velocity of
~ 5 ft./sec. and recoilless operation (Vf = o), three milliseconds
; of time are available to drive the nail.
The average power required during the drive
. time td can be calculated as follows:
15 Equation (9) PaVe 550 x .003 = 75 hp.
~ It becomes readily apparent from the above calculations that
;~ the tool must possess a considerable energy storage capability ~
and, in addition, the ability to release said energy over a ~ .
very short period of time, namely, a few milliseconds.
Now, if a flywheel adopted as the energy
storage mechanism, and we use a 3 inch diameter on and assume
an angular velocity of w, a meaningful comparison can be made
between the peripheral flywheel velocity and the nail insertion
speed, and the flywheel energy and required energy.
Assuming a 3 inch nail is driven in .003
seconds, this is a velocity of:
Equation (lQ) 003 = 1000 in/sec.
The angular velocity of a 3 inch flywheel with
1000 in.~sec. peripheral velocity is:
:
_ g _
, . .
:, ~ . . . ; . . . .
; . , .
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1052951
Equation (11) w = 15 = 666 rad./sec.
= 106 rev. sec.
= 6366 r.p.m.
This is a reasonable velocity and could be
increased if necessary.
The energy of the flywheel is:
Equation (12) E - .5 I w
where I is the angular inertia of the flywheel.
For a solid disc, 3 inch in diameter, the
inertia is expressed as follows:
Equation (13) I = .5mr
If, for example, brass is chosen for the fly-
wheel and it is 1 inch thick, its mass is:
Equation (14) M = w = (535/1728) (/4) (9) (1? .0684 ft.
Thus, substituting in Equation (13),
Equation (15) I = .5 (.0684~ (1.5/12)2 = 5.34 x 10 41b. ft. sec.
Using w = 666 rad./sec. the energy becomes:
Equation (16) E = .5(5.34 x 10 4) (666)2 = 118.43 ft. lb.
Having already determined that approximately 125 ft. lbs. of
.:'
' 20 energy was needed to drive a 3.25 inch nail up to the head in
- semihard wood, it becomes apparent that a 3 inch solid brass
flywheel 1 inch thick rotating 7000 r.p.m. has ample energy
i' and peripheral velocity to satisfy the needs of a high energy
- nailer. ~ ;
Such a tool, however, if hand held, would likely
develop significant precession moments when subject to angular
rotation about axes perpendicular to the flywheel spin axis.
` The magnitude of this moments can be calculated as follows:
Equation (17~ Mp = IQw
where Mp is the precession moment acting upon
the nailer
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1052951
I is the inertia of the nailer's flywheel
w is the angular velocity of the flywheel
Q is the angular velocity that the operator
attempts to rotate the nailer.
; 5 By way of example, assume the operator has a
nailer with t~e previously-mentioned flywheel parameters and
he attempts to reorient the nailer 180 in 0.1 sec., the
resulting moment on the nailer due to gyroscopic precession
~'~ is calculated as follows:
Equation (18) = ~ c = 31.4 rad./sec.
Equation (19) Mp = (31.4 rad./sec.) 5.34 x 10 4 lb. ft. sec. )
~666 rad./sec.) = 11.2 ft. lb.
~, This is a significant torque and would make it
very difficult for the operator to position the nailer at any
desired location.
Accordingly, two functionally identical fly-
wheels rotating in opposite directions about parallel axes at
~; the same speed can be used to cancel out the precession moments
.~ ~
I that are most unwelcome in a hand-held tool that must be posi-
j 20 tioned carefully and accurately relative to a workpiece. It
has now been found in accordance with the teaching of the
instant invention that there are a number of other, more or
~, less critical parameters that must be reconnected with.
One of the most significant is the fact that if
25 a ram element 12 is pinched between a pair of counterrotating
flywheels 14 and 16 which drive same forwardly against a work- -~
`' piece as illustrated in the diagram of Figure 1, then no -
slippage of any consequence can be tolerated if, as previously
3 noted, the entire work stroke of the ram must be completed in
30 a few milliseconds. In other words, if the tool is to be used
' to drive a 16 penny nail, it must be capa~le of transmitting a
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lOSZ95S
1000 lb. force to the ram in a .003 second ram engagement time.
While a driving connection between the flywheels
and the ram can be accomplished in more than one way, the only
practical one seems to be frictionally as it requires no
synchronous engagement as would a rack and pinion and the like.
Furthermore, a clutch of some nature is necessary to bring the
already spinning flywheels into instant driving engagement
~` with the ram, it being an obvious impossibility to bring the
flywheels up to the required speed and drive the ram all with-
in a few milliseconds, yet, such would be necessary if the
flywheels stayed in driving engagement therewith.
Now, such a clutch could either operate to shift
; both flywheels toward and away from one another to engage and
disengage the flywheel or, alternatively, only one need move
relative to the other, the movable one engaging the ram and
:~ pushing it sideways against the fixed one. Of the two, the
latter approach is much to be preferred over the former for
the reason that if the ram floats between two relatively
movable flywheels, one will reach it ahead of the other each
actuation rather than simultaneously. As this happens one
flywheel of the pair will have to yield to the other in which
the overbalancing force is present. It can be shown that
these ram engaging forces are of the order of three times the
s force necessary to drive the nail, i.e. 3000 lbs. as compared
with 1000 lbs; therefore, a yieldable flywheel mounting system
becomes a most difficult mechanism to properly design and engi-
neer. Furthermore, one is never sure what path the ram will
follow on its forward excursion or work stroke as it may be
on either side of its guidewa~s depending upon which of the
two flywheels has taken precedence over the other on the
particular actuation. For the reasons above noted, one fly-
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... ~ ~ ,. ............ . ~
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105Z951
wheel mounted for rotation ahout a fixed spin axis and
clutch attached to the other operative upon actuation to narrow
the gap therebetween is much the better way of solving the
; problem.
While it is certainly possible to shift the mov-
able flywheel toward the fixed one along a line perpendicular
to the direction of ram travel into its extended position, -
-: developing a ram-engaging force nearly three times the maximum
work force developed in the ram becomes a serious problem.
It has been found, however, that ram-gripping forces of suf-
ficient magnitude can easily be developed by swinging the
movable flywheel arcuately into engagement about an axis of
. pivotal movement lying to the rear of its spin axis. As the
surface of the movable flywheel engages the adjacent ram sur-
face and forces the ram over against the surface of the fixed
flywheel, its direction of rotation is such as to roll it
rearwardly thereby increasing the pressure it exerts against the
ram. Such flywheel action upon engagement with the opposite --
; ram surfaces instantly and easily develops the requisite ram-
gripping forces even though they exceed the maximum driving -~
force developed in the ram by a three-fold factor.
The theoretical arcuate excursion of the
movable flywheel's spin axis is back into a plane passing through ~ `~
its axis of pivotal movement that is perpendicular to the
direction of ram travel into its extended position. Once the
spin axis passes rearwardly beyond this plane, however, the
clutch loosens its grip on the ram and the driving connection -
is lost. If the system is to accommodate even minimal wear on
` the mating parts, therefore, the spin axis of the arcuately
movable flywheel must be stopped short of this position. How
far short presents an interesting question and one that is
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:.: - : . . . - ,
'~ 1052951
susceptible of precise, though unobvious, solution in
accordance with the teaching found herein.
The force tending to propel the ram upwardly as
schematically represented in Figure 1 can be expressed as
follows:
Equation (20~ Fd ~ 2 F Kf
where Fn is the normal force between the
flywheel and ram surface, and
Kf is the coefficient of friction between the y
ram and flywheel.
In the same diagram, the downward force on the arcuately
movable flywheel 16 is:
EquatiOn (21) Fu = FnKf
From the geometry of the system, the force ~-
Equation (22) Fn = u
Tan ~ -
where ~ is the acute angle at the intersection
of a plane defined by the spin axis of the arcuately-movable
?i flywheel and its axis of pivotal movement and a second plane
perpendicular to the direction of movement of the ram 12 into
extended position.
By substituting Equation (21) into Equation (22)
~ and simplifying, unexpectedly one finds that: ~-
;~ Equation (23) Tan ~ = Kf
Thus, knowing that slippage is critical and cannot be tolerated
for all practical purposes, if Kf > tan ~, the flywheels will
not slip once engaged with the ram. It now becomes quite
~ simple to select the angle ~ or the coefficient of friction
s Kf so that the foregoing critical relationship is present.
, Note also that the flywheels are cylindrical
and the engaged faces of the ram are planar so that they mate
..
- 14 -
lOSZ951
in tangential relation making straight-line contact with one
another along a line parallel to the spin axis. Other comple-
mentary surfaces are unsatisfactory and to be avoided for the
reason that points thereon at different distances from the spin
axis will, of necessity, have different peripheral velocities
and slippage is bound to result.
A few other points are worthy of specific mention
before proceeding with a detailed description of the nail-
driving embodiment of the impact tool. Motor size is a con- -
sideration and it depends upon the required duty cycle. As
previously noted, the average power consumed is approximately
75 hp to drive a 16 penny nail so as to bury the head flush
with the surface of the workpiece. Since energy is stored in
the flywheels, the actual motor size required to drive them may
vary from 0 - 75 hp depending upon the required duty cycle. If
a duty cycle of 5 actuations/sec. is chosen and friction ignored,
the required motor would be: -
Equation (24~ Preq = 75 (lj = 1.125 hp
In other words, a 1.125 hp motor could maintain flywheel speed
even using five actuations per second. Obviously, this is an
excessive duty cycle from a practical standpoint and it becomes
quite obvious that a small fractional horsepower electric
motor would be entirely adequate. Furthermore, the amount of
energy dissipated per actuation is such that battery power would
be quite adequate to power the motors in light to medium duty
applications over moderate time spans of a few hours or so.
~ Excessive ram energy can be a problem and pro-
-~ vision may be needed for controlling same. The first of two
provisions for doing so is by means of a speed control 18 for
the motor or motors driving the flywheels such as that shown
schematically in Figure 12 and upon which no novelty whatsoever
is predicated, it being merely representative of one such speed
(~
- 15 -
lOSZgSl
control that could be used. The various positions of the
control knob 20 can be indexed to positions on the scale 22
(Figure 2~ that are calibrated directly in nail sizes, for
example. ~-
Since enough energy must be imparted to the ram
to insure completion of the work assigned thereto, a slight
excess is ordinarily employed. To avoid damaging the workpiece
due to the presence of this excess energy, however, means are
preferably provided for dissipating some before it can cause the
ram to dent, gouge, puncture, sear or otherwise damage the
workpiece. An energy-absorbing cushion 24 is placed in the
nosepiece 26 on the front end of the nozzle 28 of the case
effective to receive and absorb some of the excess energy
left in the ram as it nears completion of its work stroke.
If, however, the ram is still being positively driven by the
flywheels, such a cushion is inadequate. Accordingly, the
length of the ram is preferably such in relation to the
location of the flywheels behind the nosepiece that the
ram has moved out of positive driven engagement therewith
prior to its completing its work stroke or striking the cushion
24 as shown most clearly in Figure 7. This means, of course,
that the cushion is no longer required to absorb the direct
energy being supplied to the ram by the flywheels at the end
of its stroke, but only that energy left over due to its mass
and velocity. Obviously, the lighter the ram, the less residual
energy it has at the end of its stroke, all other factors
being equal.
At the instant the ram moves forward beyond the
flywheels and becomes disengaged therefrom, at least insofar as
a driving connection therebetween is concerned, the clutch
is free to reopen the gap between the flywheels and allow the
- 16 -
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1052951
ram to complete its cycle of movement by passing back there-
between under the influence of tension spring 30 connected
thereto. In the particular form shown, the clutch actuating
means comprises the nosepiece 26 which is mounted for re-
S tractable movement relative to the nozzle 28, and a rigidlink 32 which operative connects the nosepiece to the pivoted
frame 34 journalling the movable flywheel 16 for arcuate
movement. As the nosepiece moves rearwardly into retracted
position upon being pressed against a workpiece W in the
manner shown in Figure 7, link 32 acts upon the pivoted frame
34 to swing the mova~le flywheel rearwardly into engaged
ram-driving relation. Once engaged, the ram cannot be released
until it leaves the flywheels even if it were possible to return
the nosepiece to its extended position during the few milli-
seconds it takes to complete the power stroke. Once the ram
7, has, in fact, moved out of driving engagement therewith, the
clutch is free to reopen the gap between the flywheels. This
is accomplished automatically by a clutch release means con-
nected to normally bias the pivoted frame 34 in a direction
to open the gap between the flywheels. In the particular form
shown, the clutch release means takes the form of a compression
spring 36 normally biasing the retractable nosepiece 26 into
, extended position. Thus, before this particular clutch
-` release means can function, the biasing force it exerts on the
nosepiece must exceed the opposing retracting force exerted
thereon by the workpiece W. As a practical matter, as soon
as the ram has completed its work stroke, the operator will
usually remove the nosepiece from engagement with the workpiece
thus permitting the clutch release means to open the gap
between the flywheels so spring 30 can retract the ram there-
between.
,
- 17 -
~05Z951
Turning next to Figure 2 where the nail-driving
embodiment 10 of the tool has been shown in perspective,
reference numeral 40 has been selected to designate the case
or housing in its entirety, nozzle 28 forming a part thereof.
; 5 Immediately behind the nozzle is an enlargement which will
henceforth be referred to as the "flywheel cavity" 42 for lack
of a better term. Within this cavity is housed the drive
means in the form of a pair of identical electric motors 44, -
the movable mounting 34 for one of them, and the fixed mounting
46 for the other. Extending on rearwardly of the flywheel
cavity as an integral part of the housing aligned longitudinally
with the nozzle is the upper limb 48 of the handle 50. Limb
i 48 is hollow and adapted to receive the ram 12 in its retracted
position as shown in Figures 5 and 6. In the particular form
shown, speed selector switch 20 of the speed control 18 along
with the scale 22 calibrated in nail sizes or the like are
,~
provided on the rearwardly-forcing wall 52 on the back of handle
; 50. The handle 50, as a whole, has the usual C-shaped config-
;~ uration commonly associated with many electrically-driven
hand tools. The handle 50 also carries the trigger 54 and the
line cord 56 to the source of electrical power in the event
a self-contained power source is not used. ~ -
As illustrated, the case has a removable cover
plate 58 which provides access to the interior thereof and, in
addition, it is shown die cast in two halves which are bolted
together. The nail gun form of the tool, of course, requires
an opening 60 (Figures 7, 8 and 9) into which the nails or
other fasteners 62 are fed into the path of the advancing ram
12. A magazine 64 of conventional design has been shown
feeding a commercially-available belt of nails into opening
60 in the side of the nozzle.
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:
. .
- -
` lOSZ951 -
Figures 3-7, inclusive, to which reference ~
will now be made, show the interior construction of the tool ~ -
; most clearly. Resting in the bottom of flywheel cavity 42
is a fixed endplate 66 which carries a bearing 6E journalling
~5 5 the shaft 70~ of fixed motor 44F. An upstanding partition
wall 72 divides the flywheel cavity into two motor compartments
74 and 76. A horizontal wall 78 formed integral with the
partition wall 72 separates the motor compartments 74 and 76
from the flywheel compartment 80. The horizontal wall is shown
supported on ledges 82 on the inside of the flywheel cavity.
Additional shaft bearings 68 are mounted in fixed position in
one half of the flywheel compartment, one being recessed in
the top of the horizontal wall while the other is recessed
into the lid. Fixed flywheel 14 is mounted on the portion of
motor shaft 70F pro~ecting from motor compartment 74 up into
the flywheel compartment. Thus, the fixed motor 44F and its
flywheel 14 are housed in one side of the flywheel cavity
alongside ram 12.
-~ In the other side of the flywheel cavity, is
; 20 mounted movable motor 44M, its shaft 70M and movable flywheel ~-
, 16. Fixed endplate 66 is replaced by movable endplate 84 that
carries bearing 68 journalling the lower end of shaft 70M of
the movable motor 44M. This endplate together with verti-
cally-spaced parallel arms 86 co-operate to define the pivoted
~' 25 mounting means 34 that carries motor 44M and its flywheel for
pivotal movement in a direction to vary the width of the gap
q so as to engage and form a driving connection with the ram.
The lower end of pin 88 is non-rotatably fastened in an inte-
grally-foxmed foot 90 provided on the underside of the movable
endplate 88 which skids back and forth on the bottom of the
housing. The housing is shown provided with an enlargement
-- 19 --
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:'' . ~ ; ,
105'~95~
92 to accommodate the pivot pin, the upper end of which is
rotatably mounted in a socket 94 in the coverplate 58. As
shown, arms 86 are joined together by a web 96 to define a
unitary structure which is non-rotatably fastened to the
pivot pin 88. These arms and movable endplate 84 each carry
bearings 68 journalling the shaft 70 of motor 44M. An oversize
aperture 98 in the horizontal wall 78 accommodates the shaft 70
of the movable motor and permits the entire pivoted mount 34
therefore to swing arcuately relative thereto between its
engaged and disengaged positions. Note in Figures 1 and 3
that the axis of pivotal movement defined by the pivot pin 88
is located to the rear of the spin axis of the movable flywheel
defined by movable motor shaft 70. Thus, even when fully en-
gaged as shown in Figure 7, the spin axis still lies well
ahead of a plane passing through the axis of pivotal movement
of the mount that is perpendicular to the path followed by the
ram during its excursion into extended position or work
stroke. As will be seen presently, the ram is loosely fitted
;
for longitudinal slidable movement in the opposed track-
forming grooves 100 of the clutch actuating means 32 so that
it can move aside the fraction of an inch required to bring
it into engagement with the fixed flywheel. Once thus engaged,
however, the ram follows a straight-line path determined by
the shoulders 102 of the track-forming grooves or guideway
remote from the movable flywheel that is urging the latter
thereagainst. It is for this reason that the angle ~ in
Figure 1 and the normal plane have been defined in terms of
the forward excursion of the ram. The return stroke of the
ram, while confined to the guideway, need not follow a straight
line and, in fact, can be slightly canted therein.
Directing the attention next to Figures 3-11,
inclusive, it can be seen that a pair of rearwardly-extending
,
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iO52951
parallel arms 104 are attached to the rear face of the nose-
piece 26 and mount same within the nozzle for limited re-
ciprocating movement between its normally extended position
and a retracted one. These arms perform a dual function, the
first of which is that of guiding the ram between its extended
and retracted position due to the track-forming grooves 100
formed in the opposed surfaces thereof. Secondly, it is these
same arms that are operatively linked to the arms 86 of the
pivoted mount 34 and thus co-operates with the nosepiece to
define the clutch actuating means 32.
These arms, while forming the guideway for the
ram, are, in themselves, guided for limited reciprocating
3 slidable movement in opposed grooves 106 formed on the under-
side of the lid 58 to the housing and the bottom walls of the
t 15 nozzle 28 and upper handle limb 48 into which they telescope.
A
q In contrast to the ram 12, arms 104 are closely confined
within the grooves 106 in the housing so that its movement
.
`~ is restricted to essentially straight-line motion.
As revealed most clearly in Figures 10 and 11,
a fixed limit stop 108 provided on the underside of lid 58
` engages a movable stop 110 carried by the upper arm 104 to
limit the forward excursion of the clutch-actuating means 32.
The rearward movement of the latter is stopped when the nose-
piece 26 engages the front end of the nozzle. One or more
9. 25 compression springs 36 positioned between the opposed faces
of the nozzle and nosepiece normally bias the latter into
extended position. These springs constitute a clutch release
mechanism automatically operative to disengage the clutch in
a manner to be explained in detail presently as soon as the
clutch actuating means 32 is deactuated by permitting the
nosepiece to return to its normally-extended position.
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~ ~052951
Now, in ~igures 3--7 it can be seen that the ends
of arms 86 of the pivoted mount 34 remote from pivot pin 88
are provided with vertically-aligned ears 112 that are re-
ceived in notches 114 formed in the boss 116 provided on one
side of arms 104. The connection thus formed between the
clutch actuating means 32 consisting of the nosepiece 26 and
arms 104 operatively links the latter to the clutch means
consisting of the flywheels and pivoted mount 34. As the
clutch actuating means 32 is actuated by pressing the nosepiece
against a workpiece with sufficient force to overcome the bias
exerted thereon by springs 36 and retract same, it will swing
the mounting means 34 rearward arcuately to close the gap
separating the flywheels thus engaging the clutch by gripping
the ram therebetween. As previously noted, once engaged,
the clutch will remain so until the ram clears the flywheels
as shown in Figure 7. When this happens, the clutch can be
; disengaged and it will do so automatically under the influence
of the clutch release springs 36 provided the clutch actuating
means 32 has been deactuated. In other words, so long as the
nosepiece remains pressed against the workpiece, ram retraction
spring 30 will be pulling it back into contact with the fly-
~ wheels, but they will not spread apart to allow it to pass
't therebetween. As soon as the pressure on the nosepiece is re-
lieved to a point when the bias on the latter by clutch re-
~' 25 lease springs 36 can extend it, the gap between the flywheels
will reopen and the ram can complete its return stroke.
The flywheel engaging surfaces of the ram will
~oth be seen to include friction pads 118 formed from some
tough abrasion resistant material having a reasonably high
coefficient of friction when placed in contact with a metal
flywheel ~uch as, for example, ordinary brake lining material.
.
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lOSZ951
As ram retraction spring 30 biases the ram rearwardly, it
strikes limit stop 120 shown in Figure 5.
The front end of the ram is shaped to define a
nose 122 bordered both top and bottom by forwardly-facing
~ 5 shoulders 124 best seen in Figures 5, 8 and 9. The nose 122
; passes through an aperture 126 sized to receive same in the
nosepiece while the shoulders engage the shock-absorbing
cushion 24 bordering the latter. Whatever energy is left in
~ the ram at the completion of its workstroke is, hopefully,
- 10 dissipated in this cushion, otherwise the nose of the ram will
; impact against the workpiece itself.
.~
Particular reference will next be had to Figures
5, 6, 7, 11 and 12 for a detailed description of the trigger
54 and an important safety interlock between the latter and the
clutch actuating means 32. Trîgger 54 is pivotally mounted
`s within the opening in the handle in the usual manner and is
normally biased forwardly by spring 128. As the trigger is
~ manually actuated into retracted position it closes the
'~A normally-open on/off switch 130 in the motor speed control
3 20 circuit 18, the latter having been shown located in the lower
~ limb 132 of the handle.
$ A vertically disposed T-shaped slot 134 is formed
integral with web 136 on the inside of the handle above the
trigger. Mounted within this slot for limited vertically
slidable movement is a limit stop 138 operatively connected ~ ;
to the trigger by link 140. As the trigger 54 is retracted
into its actuated position, it acts through connecting link
140 to raise the stop 138 and move its forwardly-projecting
abutment 142 from behind the lower arm 104, thus allowing the
clutch actuating means 32 to move rearwardly so as to engage
the clutch. With the trigger released, abutment 142 blocks
- - . . . ......................... .
:- - ~ .,
7.
-
lOS2951
the retraction of the nosepiece 26 which, as previously noted,
is necessary to engage the clutch. Thus, if the tool is
running and dropped on its nose by the operator, he will, of
necessity, let go of the trigger thus interpositioning the
abutment 142 and prevented the clutch from engaging which,
otherwise, would have actuated the ram to discharge a nail.
In Figures 6, 7, 8 and 9, the magazine 64 will
be seen to be of more or less conventional design including
upper and lower parallelogram-shaped plates 144 and 146
connected along the front edge by a wall 148 that co-operates
therewith to produce a rearwardly-opening channel. Tracks
150 spaced to receive the shanks of the nails 62 therebetween
and hold same for slidable movement in alignment with the nose
~i 122 of the ram are located just inside the opening in the rear
edge. The nail heads butt up against this track and are
` advanced into position to be driven by a follower 152 which is
, pulled by a coiled tension spring 154.
The nails themselves are joined together to
form a belt by paper tapes 156 in the conventional way as
shown. The lead nail of the chain abuts a stop 158 inside the
i nozzle across from opening 60 that holds it in alignment with
the nose of the ram. The second nail, on the other hand, is
still held back by the track 150. Therefore, as the ram ad-
i vances, it strips the lead nail from the belt and drives it
on into the workpiece; whereupon, the follower moves the next
nail into position to be driven as soon as the clutch actuating
means is deactuated, the clutch release means opens the clutch,
and the ram retraction spring pulls it back to clear the
nozzle. To reload the magazine, the follower is pulled all
the way out in much the same way a stapler is loaded. Since
no novelty is predicated upon the magazine per se, a detailed
;
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:
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1052951
description of its structural features would serYe no useful
purpose. The same is true of the motor speed control circuit
of Figure 12 which has no details identified other than those
:
components which have mechanical significance in the tool itself.
In closing, it should be noted that while the
,
tool shown is specifically designed for driving nail-like
,. ~
fasteners, it is by no means so limited and the ram can
impact directly upon an external workpiece in the manner of
a stamp, punch or chisel just as well as through the medium of
a fastener. It can easily be seen that a tool having the
following parameters is praçtical and, in addition, will
perform adequately in any of the previously mentioned
, applications: -
Flywheel Diameter 3" ~-s
Flywheel Speed 7000 r.p.m.
,. .
Ram Speed 1000 in./sec.
, Motor Horsepower 1.125
Total Instrument Wt. 10 lb. ~`
:
.', '`` '' .
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-, ' ;
