Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background Ancl Summary Of The Invention
.
This invention relates to certain improvements in
a clutch and brake mechanism particularly adapted for but not
limited to smaller horsepower application.
The applicant is a joint inventor on Canadian
application filed February 1, 1977, Serial No. 270,867 for a
clutch and brake mechanism. That earlier application relates
to and describes a low torque clutch. At least in the case
of lawn mowers, the low torque clutch has not proven to ad-
vantage. In heavy grass, a low torque clutch can be subjected
to considerable slippage between drive and driven members,
giving rise to the generation of considerable heat, and even
possible fire hazzard when operating in dry grass. Further,
the heat will serve to anneal the clutch springs and result
in an even lower clutch capacity. Shorter clutch life is also
to be expected.
Thus, for lawn mowers and other applications, a high
torque, or at least a higher torque clutch is preferred to
minimize clutch clippage and consequent heat build-up in the
clutch mechanism. With a higher toryue capability, the engine
will be lu~ged down and killed if it is overloaded and yet is
protccted when an obstruction is encountered. It is generally
an object of this invention to provide a clutch and brake
mechanism of higher torque capability.
For good clutch and brake operation, it is important
that the clutch and brake surfaces remain clean and dry.
Clippings, sawdust, dirt, oil and other foreign matter are
deleterious to proper clutch and brake engagement. It is
also an object of this invention to substantially preclude
the entry of foreign matter into the clutch-brake housing and
thus possibly interfere with the clutch and braking operations.
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The invention contemplates the use of a brake band
for declutching and stopping rotation of the driven member
without interrupting the rotation of the drive me-mber.
Further aspects of the invention relate to the mounting of the
brake band, util zation of the brake band to aid in keeping
the braking surface clean, and provision fox the cut-off of
the power source in the event the brake band should fail.
Description of the Drawing Figures
-
The drawings furnished herewith illustrate ~he best
mode presently contemplated for carrying out the invention
and are described hereinafter.
In the drawings:
Fig, 1 is a plan view of the clutch-brake mechanism
o ~his invention and is generally taken on line 1--1 of Fig. 3;
Fig. 2 is a sectional view taken,generally on line 2--2
of Fig. 3 and shows the clutch in the fully engaged position;
Fig, 3 is a sectional elevation taken generally on
line'3--3 of Fig. 1;
Fig. 4 is a sectional view similar to that of Fiy. 2
and shows the clutch at the start of its engagement with the
drive member;
Fig. ~ is a sectional view similar to that of Fig. 2
showing the clutch disengaged and the brake fully engaged;
Fig. 6 is a detail ~ection taken generally on line 6--6
of Fig. l;
Fig. 7 is a detail section showing a further embodiment
of the invention;
Fig. 8 is a detail view illustrating the provision
for cut-off of the power source in the event of a brake band
failurei
.
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Fig. 9 is a detail view showing a further embodiment
for the mounting of a brake band;
Fig. 10 is a partial side elevation of a chain saw
~hich embodies certain aspects of the invention;
Fig. 11 is a plan view of a clutch-brake mechanism
showing an emb~diment wherein the brake band is partially
-overlapped and in the de-energized or brake-off position;
Fig.'12 is a sectional elevation taken generally on
line 12--12 of Fig. 11; and
Fig. 13 is an enlarged view of the brake band as
employed in Figs. 11 and 12.
Description of-the Illustrated Embodiments
Referring to the drawings, the clutch-brake mechanism
20 of this invention is interposed between the drive shaft 21
of an engine or other power source, not shown, and a driven
shaft 22. The mechanism 20 shown in Fig. 1 is specifically
intended fo~ use on a lawn mower, but is readily adapted for
use between the drive and driven members in many other applica-
tions.
The dri~e shaft 21 carries a hub 23 that mounts
a dxum 24 having a circumferential flange 25 that projects
axially into the housing 26. Beyond the hub 23, the end
portion of the shaft 21 extends into and is piloted within
the bearing sleeve 27, as generally shown in Fig. 3.
The driven shaft 22 is aligned with the shaft 21 and
piloted on the exterior of the bearing sleeve 27. The shaft 22
projects from the housing 26 through the opening 28 and is
rotationally supported by the ball bearing 29 seated adjacen-t
the opening 28 in the annular housing projection 30. Within
the housing 26, the shaft 22 carries a pair of axially spaced~
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generally parallel plates 31 and 32. Plates 31 and 32 are
generally oval-shaped and are aligned axially and form a peri-
pheral recess 33 on the shaft 22 which is radially aligned
with the circumferential flange 25 of the drive shaft drum 24.
S The driven shaft 22 carries a pair of diametrically
opposed clutch shoes 34 for engagement with the drum 24. The
shoes 34 are disposed symmetrically with respect to the axis
of shaft 22 and a portion thereof is slidably disposed in
the peripheral recess 33 between the plates 31 and 32. The
respective shoes.34 are pivoted on corresponding pins 35
supporked between the radially extended portions of the plates 31
and 32. In relation to the forward direction of travel of the
shoes 34 as indicated by the direction arrow 36 in Fig. 1, the
shoes are pivoted adjacent to their leading end.
Corresponding portions of each shoe 34 are st~pped
axially outwardly beyond the radial confines of plates 31 and
.32 to provide the shoe.s with axially spaced shoulders.37 which
are engageable with the corresponding edges of the plates to
establish the limiting clutch disengaged position of the shoes.
The side of the shoes 34 facing the drum 24 are provided with
an arcuate ~ecess 38 for receiving the projecting drum flange 25.
When the shoes 34 are pivoted to their outermost position, the
inner face 3g of the recesses 38 are disposed in a circular
configuration to generally match and drivingly engage the inner
face 40 of the flange 25. When so engaged by the clutch shoes 34,
~he powered drive shaft effects rotation of the driven shaft 22.
The shoes 34 are each provided with an oversize hole 41
at the pivot mounting to provide a substantial clearance on
the pins 3S. When the pins 35 are 1/4 inch in diameter, the
30. hole 41 should be about 9/32 inch providing a clearance of
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about 1/32 inch as perhaps more clearly shown in Fig. 6 for
reasons hereinafter explained.
Shoes 34 are normally biased outwardly toward
engagement with the drum flange 25 on the drive shaft 21. The
.capacity of the clutch is at least in part de~ermined by the
spring-load imposed on thè shoes 34 and is generally tailored
in accordance with the application of -the clutch-brake
mechanism ~0. The application for the mechanism 20 generally
.depicted in Figs. 1-5 relates to a walk-behind lawn mower and
inc.ludes the compression springs 42 disposed between the drive
shaft 22 and the respective shoes.34. The springs 4~ exert
their biasing force generally radially wi-th respect to the
shaft.22.and toward the leading end of the shoes 34 on a line
about 45 removed from the radial lines through the axis of the
respecti.ve pivot pins.35. . The respective springs 42 extend
between the recessed seat g3 on the shoes 34 and the peripheral
recess 44 on the driven shaft.22 between the plates 31 and 3Z~
For some applications the springs 42 alone will provide
adequate torque capacit~ for the clutch. For other applications
compression springs 45 alone may be utilized . .For applications
requiring a still greater torque capacity, a combination of
springs 42 and 45 may be utilized as generally shown in Fig. 1.
The respective springs 45 are disposed between the opposed
seats.46 and 47 provided at the leading end of one shoe 34 and
the trailing end of the opposed shoe, respectively. Springs 45
are so disposed to place their line of force generally parallel
to. and spaced inwardly from a line through the axis of the pivot
pins 35 and extending normal to the opposed spring seats 46
and 47 when the shoes 34 are in the clutch engaged position
as generally shown in Fig~ 1 by the dot-dash line 48. With the
line of force of springs 45 clisposed inwardly relative to the
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axis of pivot pins.35 and with the springs 42 exerting a force
toward the leading ends of the shoes 34, the~springs tend to
move the leading end of the shoes 34 outwardly on a radial
line through the axis of the pivot pins 35 as provided for by
.the shoe clearance on the pivot pins.
Radially outward from the recess 38, the shoes 34
are provided with an arcuate braking surface 49 engageable
by the brake band 50~ The brake band 50 extends around the
outside periphery of the shoes 34 and has one end thereof
.secured to a fixed anchor pin 51 and the opposite end
secured to the movable anchor pin 52. The movable anchor
pin 52 is carried by the lever 53 pivoted on the pin 54. The
lever.53 is movable between positions corresponding to the
extended or brake-off condition of the brake band 50 as
genera~ly shown in Figs.. 1 and 2 and the fully co~tracted or
brake-on condition for the band as generally shown in Fig. 5.
With the:lever 53 in the extended or brake-o~f condi-
. tion of the brake band 50, the band lies adjacent to the wall
. of housing.26 and clear of the clutch shoes 34 in their clutch
. engaged position. When the lever 53 is moved to the fully
contracted or brake-on condition, as shown in Fig. 5,.the band 50
. engaged with the outer surface 49 of the shoes.34 and pi~ots
the shoes inwardly against the biasing force of the springs 42
and 45 to effect a disengagement of the shoes from the drum
flange.25 to declutch the driven shaft 22 from the drive shaft 21
and to stop rotation of the driven shaft without interruption
of the rotation of the drive shaft and its power source. In
the braking sequence from the forward direction of travel for
the shoes.34 as indicated by the direction arrow.36, the
contracting brake band 50 is initially brought into contact
with the shoes and then frictionally tightens itself thereon
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so as to be self~energizing and thus effect a quiak clutch
release and a quick stop of the driven shaft 22. When braking,
the inward pivotal movement of the shoes 34 is interrupted when
the shoulders 37 on the shoes en~age with the peripheral edges
5 of plates :31 and 32 as ~enerally shown in Fig. 5. In the
inne~most braking position, the outer surfaces 49 of the shoes 3
are generally disposed in a circular configuration or are
symmetrical relative to the axes of shafts 21 and 22.
When the lever 53 is moved to restore clutch engage-
ment in the forward direction of travel for the clutch shoes 34,
the clutch.faces 39 adjacent to the leading ends of the shoes
make the initial contact with the inner face 40 of the drum
flange 25 as the clearance formed by the oversize hole 41 of
the shoes on the pivot pins 35 is restored outwardly by the
springs 42 and 45 as generally shown in Fig. 4. The friction
resulting from the initial contact at the leading end of the
shoes.34 with the rotating drum flange 25, causes the shoes
to cam and grab the drum 24 to quickly restore full engagement
and power to the driven shaft 22. If desired, the oversized
hole 41 in the shoes.34 may be replaced by a slot.55 e~tending
at about.30~ from the symmetrical centerline through the clutch
as generally shown in FigO 7.
The brake-clutch mechanism 20 can also be used in
applications requiring a reversible power source. When the
drive shaft 21 is rotating in a direction opposite from direction
arrow 36, howeverr the brake band 50 will not be self-energizing
but nevertheless will be effective to provide for clutch release
and stopping of the driven shaft 22 without interruption of the
drive shaft 21 and its power source. Clutch engagement in
reverse will also be effective but will involve more slippage
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or chatter between the shoes 34 and the drum flange 25 and
requires more time since initial camming of the shoes cannot
be expected.
The lever 53 for extending and contracting the brake
band 50 is normally biased to the braking position by the torsion
spring 56. The lever 53 can be connected by a control cable 57
or the like to a deadman's handle 58 which when engayed by the
operator pulls the lever to the braking position shown in Fig. 1
against the bias of spring 56~ When the deadman's handle is
released, the torsion spring 56 moves the handle to the
brake-on position and effects a contraction of the brake
band 50 to disengage the clutch and stop the driven shaft 22
without interruption in the rotation of the drive shaft 21.
In the instance where the brake band 50 should fail
by reason of its severance at some cross-section along its
length, the clutch might unwittingly become engaged to drive
the driven shaft 22 when no~ expected, giving rise to a possible
dangerous circumstance. To avoid such a problem, the lever 5~
can be designed so that it can rotate in avoidance of the ~ixed
anchor pin 51 as generally shown in Fig. 8. In case of sever-
ance of the brake band 50, the lever 59 will be rotated under the
influence of the torsion spring 56, as generally shown by the
dashed lines in Fig. 8, past the normal brake-on position, to
engage with a grounding pin 60 connected into the ignition
circuitry 61 of an engine, not shown, to short out the ignition
circuit and so stop the engine to preclude possible injury by
reason of the unwitting engagement of the driven shaft 22.
In the case of an electric motor drive, a micro-switch could be
provided in place of the grounding pin 60 to short out a make~
and-bra~e circuit for the motor.
A low torque clutch is generally not favored when
applied to a lawn mower. When a low torque clutch is over-
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loaded, as when cutting heavy grass for example, there willbe considerable clutch slippage which will generate a consider-
able heat in -the clutch elements and its housing. Such heat
will have an annealing effect on the one or more clutch
springs to make .then even less effective. Such heat may
also weaken and/or shorten the life of the brake band. A
high or higher torque clutch, however, as herein described
seems generally f.avored and will offer slippage only when an
obstruction is encountered to generally protect the drive parts
- 10 and power source. In the case of overloading a high or higher
.torque clutch, as when cutting heavy grass r for example, the
engine will.generally be lugged down and might ultimately
die with a minimum of slippage and heat generation.
For the proper functioning of the brake-clutch
mechanism 20, it is essential that the brake and clutch
surfaces remain relatively clean and dry. Moisture, oil,
~irt, clippings, saw dust and other foreign matter are likely
to prove deleterious for proper functioning of the mechanism.
.Referring particularly to Fig. 3, the cup-like hous-
ing 26 is suspended beneath the deck, not shown, of a lawn
mower. by a plurality of spaced hangers 62. A seal plate 63
is disposed on the upper open side of the housing 26 and has
a circular opening 64 which generally provides an open
exposure to the brake-clutch mechanism 20. The edge of the
circular opening-64 is pr.ovided with an upturned lip 65 generally
aligned radially with the radially extending portion of the
drum 24~ A generally circular slinger plate 66 is carried
by the drive hub 23 and extends radially over and in close
proximity to the edge of lip .65 to in effect provide a rotary
closure for the opening 64. Possible oil drippings from the
engine or other motive source, clippings or other dirt and
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foreign matter al1ghting on the slinger plate 66 are substan-
tially precluded from enfry into the housing 26 and cast
centrifugally by the slinger plate clear of the opening 64.
The slinger plate 66 and drum 24 may be fabricated and
assembled inkegrally on the drive hub 23~
In the embodiment of Fig. 9, the brake band 67 is
connected to a pair of movable anchors 68 and 69 carried by
the lever 70 on opposite sides of the piv¢t pin 71 mounting the
lever. The lever 70 is normally biased by the torsion spring 72
to move the anchors 68 and 69 counterclockwise about the pivot
pin 71 to contract the brake band 67 into the braking position.
Movement of the lever 70 in the opposite direction against the
biasing force of the spring 72, as by a deadman's handle or the
like, not shown, through the control cable 73 extends the brake
band 67 to the brake-off position allowing the clutch to engage
to drive the driven member.
Figs. 10-13 indicate how the clutch-brake mechanism
- of this invention can be applied to a chain saw 74 with several
additional features being shown.
The stepped drive shaft 75 extends through the
circular opening 76 of the seal plate 77 secured to the
housing 77a. A bearing sleeve 78 is disposed on the shaft 75
and extends between the shoulder 79 spaced from the end of
the shaft and the nut 8~ threaded onto the end of the shaft.
The drive shaft 75 carries a drum 81 wh-ich may be integral with
the end nut 80.
A tubular driven member 82 is freely rotatable on
the bearing sleeve 78 and generally extends between the
shoulder 79 on the drive shaft 75 and the drum 81. The end
portion of the driven member 82 adjacent to the shoulder 79
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is provided with spline grooves 83 to dri~inyly mount the
cutting chain sprocket 84. ~djacent to the sprocket 84 the
driven member 82 carries a circular slinger plate 85 which
extends radially outward beyond the circular l.ip 86 of the
seal plate.77. . Thus, the slinger plate 85 rotates w.ith the
driven member 83 to generally preclude entry of sawdust, oil
and other deleterious matter to the brake-clutch mechanism 87
disposed between the slinger plate and the drive drum 81.
. The mechanism 87 is in many respects similar to
the brake-clutch mechanism 20 of Fig. l and includes a pair
of diametrically opposed clutch shoes 88 disposed generally
symmetrically with respect to the axes of the drive and driven
members..75 and 82. In relation to the forward direction of
travel of the shoes 8B as indicated by the direction arrow 89,
the respective shoes are pivoted adjacent to their leading
end on the axially extending pins 90 carried between the
generally oval-shaped side plate 91 formed integrally with
the driven member 82 and the slinyer plate 85. . The shoes 88
are provided with an oversize hole 92 at the pivot mounting
to provide a substantial clearance on the pins 90 as generally
shown in Figs. ll and 12.
The side of the shoes 88 facing the dri~e drum 81
are stepped axially outward beyond the radial confines of
the side plate 91 to provide the shoes with a shoulder 93
2S engageable with the peripheral edge of the side plate to establish
-the limiting clutch disengaged position for the shoes. Out-
wardly from shoulders 93, the same side of shoes 88 are provided
with an arcuate recess 94 opening toward the drum 81 for
recei~ing the axially projecting drum flange 95.
The shoes 88 are biased outwardly into the clutch
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engaged position by a centxal spring 96 and end springs 97
to place the inner face 98 of the shoe recesses 94 in clutching
engagement with the inner face 99 of the drum flange 95.
The compression springs 96 extend generally radially between
5 the recessed seat 100 on the shoes 88 and the peripheral
recess 101 on the driven member 82. As in the case of
springs 42 of Fig. 1, the springs 96 exert their biasing
force generally radially on a line about 45 removed from
the radial lines through the axis of the respective pivot
10 pins 90. The respective compression springs 97 are aisposed
between opposed seats 102 and 103 provided at the leading end
of one shoe 88 and the trailing end of the other shoe, respect-
ively. As in the case of springs.45 of Fig. 1, the springs 97
are so disposed to place their line of force generally parallel
15 to and spaced inwardly from a line through the axes of the pivot
pins 90 and extending normal to the opposed seats 102 and 103
r when the shoes 88 are in the clutch engaged position. When the
.shoes 88 are biased i.nto their clutch engaging position, the
inner faces 98 of the shoe recesses 94 define a circular con-
20 figuration to complement and drivingly engage with the circular
face 99 of the drum flange 95.
A brake band 104 extends around the outer periphery
of the shoes 88 and is engageable with the extexnal surfaces 105
of the shoes~ One end of the brake band lD4 is connected to a
25 fixed anchor pin 106 rom which the band extends completely
around the shoes 88 and overlaps with a portion of itself. A
loop 107 is secured to an intermediate portion of the brake
band 104 for connection to a movable anchor pin. 108 carried by
the lever 109 which is pivotally mounted on the pin 110. In
30 the brake-off posi-tion of the lever lQ9 as generally shown in
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Fig.. 11, the brake band 104 is extended and out of contact
with the shoe surface 105 to thus allow the shoes 88 to
assume their clutch engaged position under the biasing force
of the springs 96 and 97. The lever 109 is normally biased
by the torsion spring 111 to the brake-on position, generally
shown by dot-dash lines in Fig. 11~ in which position the
brake band 104 is contracted into engagement with the shoe
surfaces 1.05 forcing the shoes 88 to pivot inwardly out of
clutching engagement with the drum flange 95 and to stop
lQ the rotation of the driven member 82 without interruption of the
rotation of the drive shaft 75 and its power source. When the
brake band 104 contracts for braking from the direction of
travel indicated by the direction arrow 89, it is lnltially
brought into contact with the shoe surfaces 105 and then
frictionally tightens itself thereon so as to be self-energizing
and thus effect a rapid release of the clutch and a rapid stop
of the driven member 82. The outer surfaces 105 of the shoes ~8
assume a generally circular or concentric configuration when the
shoes are pivoted to their limiting clutch disengaged position
wherein the shoulders 93 engage upon the peripheral edge of
.ide plate 91.
In the case of a chain saw 74, the lever 109 is
control.led by a deadman's handle in the form of a bell crank
or thumb lever 112 which is pivotally mounted on a generally
horizontal axis on the horizontal carrying handle. 113 of the
saw. The projection 114 o~ lever 112. carries a pin 115 which
is engageable within the slot 16 of the lever projection 117
of lever 109. Under the influence of the torsion spring 111,
the levers 109 and 112 normally assume the brake-on position
generally shown in dot-dash lines in Fig. 11. When the thumb
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projection 118 of lever, 112 is depressed, the levers 109 and
112 assume the bxake-off position to place the brake band 104
in its extended condition providing for clutch engagement -ko
power the driven member 82 and chain sprocket 84.
The loop 107 secured to an in-termediate portion of
the brake band 104 for attachment to -the movable anchor pin 108
is formed with a stiffening member 119. The member 119 is
superposed onto the lower reach 120 of the loop material
and extends under the upper reach:121 of the loop material to a
.position adjacent to the ancho.r pin attachment. The stifening
member,'.ll9 is made of a heavier gauge spring metal and has a
slight normal S-shape configuration (reverse S-shape as viewed
in Fig~ 11) which is imparted to the loop 107 when the braXe
band, 104 is in the brake-off, clutch engaged position as genexally
shown in Fig. 11. When the lever moves to the brake-on, clutch
disengaged position under the influence of torsion spring 111
and the self-energizing charac-ter of the brake band 104, the '
S-shape configuration of the'loop'107 is distorted with a snap
action to a generally arcuate coniguration. When the brake
band 104 is again extended by pressure on the th~nb lever 112
to re-engage the clutch, the'loop.'107 snaps back to its normal
S-shape configuration to thereby reduce the thumb pressure
requirement and help pxevent the possibility of the brake
band assuming a position bf less than full extension where the
25 ,. band might interfere with complete clutch engagement.
In Fig. 11, the brake band 104 is shown to be overlapped
inwardly approximately 210 with :the end thereof having a proje~-
tion 122 turned outwardly for engagement within a recess 123
provided in the outer layer of the band. The recess 123 is
sufficiently long to accommodate relative movement of the
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projection 122 ~s the brake band 104 is extended and contr~cted.
Overlap in the brake band 104 appears to materially reduce -th~
braking time. The amount or length of overlap in the brake
band 104 will likely have to be determined empirically and
may vary considerably in accordance with tha application for the
brake-clutch mechanism.
According to Fig. 13, the brake band 104 is provided
~ith a plurality of spaced holes 124. The holes 124 aid in
wiping oil, chips and other deleterious matter from the outer
surface 105 of the shoes 88 to thus aid in maintaining the
surfaces generally dry and clean.
As applied to a chain saw 74, the clutch-brake mechan-
ism 87 generally avoids the hazzard of chain motion or creep
at idle speed common in conventional chain saws when the engine
is adjusted to a higher idle speed to improve starting and prevent
the engine from dying out. In the operation of chain saw 74,
braking can be applied at any speed when a dangerous situation
develops. No throttling down of the engine is required, nor
a chain coasting to a stop as in conventional chain saws.
Thus, the clutch-brake mechanism 87 renders the chain saw 74 a
far safer implement.
While the several improvements comprising the invention
have been variously and specifically applied to lawn mowers and
chain saws, they likely will find further application in presses,
rototillers, snowblowers and numerous other implements.
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. Various modes of carrying out the invention are
contemplated as being within the scope of the following
claims particularly pointing out and distinctly claiming
the subject matter which is regarded as the invention.
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