Note: Descriptions are shown in the official language in which they were submitted.
FORCE MODIFYING DEVICE ~ 3 ~ 7
Field of the Invention
m e present invention relates generally to spring driven systems
for article dispensing devices, and more particularly to a force modifying
arrangement to produce a more uniform output force in a spring actuated
biasing system. The arrangement is particularly applicable for use in a
dlspenser for dispensing very thin planar articles, such as currency
notes, sheet paper, or the like, ~nd will be described with partict~ar
reference thereto, altho~gh it will be appreciated that the invention has
other broader applications where planar articles are driven by a push
plate tcwards a dispensing position.
Backqround of the Invention
~ he present invention finds advantageous application in a currency
dispenser as used in automatic teller machines (AqMS). In such machines,
a stack of bills of a parti¢ular denomination is generally disposed within
an elongated canister having a dispensing position at one end thereof.
From this dispensing position, the bills are dispensed individually by a
transfer mechanism. The sta¢k of bills is urged towards the dispensing
position by means of a push plate. Generally, the push plate is biased
(pulled) toward the dispensing position by means of a tension spring
system. With such a system, the removal of currency and the resultant
contraction of the tension spring inevitably leads to a reduction of the
biasing force exerted on the push plate. In other words, the force on the
push plate at the position where the canister lS fully loaded continuously
2S decreases as the push plate moves toward the dLtspensing position. In this
respect, it is not un sual for the blas mg force in such devices to ~
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~~` decrease 67% or more as the push plate travels from a fully loaded
position to an empty position. This change in the biasing force places
severe requirements on the transfer mechanism which picks or removes the
b;lls from the dispensing position, and generally leads to degraded
performance of the transfer mechanism when the canister is fully loaded or
near empty. The present invention overcomes this and other problems and
provides a simple, reliable device for use with a spring force system,
which device modifies the force generated by such system to produce a more
uniform output biasing force.
Su~mary of the Invention
In accordance with the present invention there is provided a
system for transmitting a biasing force from a force generating component
to a lcad remote from the fcrce com~onent. The system includes a first
elongated flexible element having a first end and a second end, the first
end of the first flexible element being connectable to the force
generating component, and a second elongated flexible element having a
first end and a second end, the first end of the second flexible element
being connectable to the load. A force modifying member rotatable about a
fixed axis îs provided and includes first and second outwardly facing
surfaces of predetermined length which curve about the axis. The second
ends of the elongated flexible elements are connected respectively to the
first and second surfaces at one end of each surface. The flexible
elements are operable to be wound or unwound on the respective surfaces as
~ the ~Ember rotates about the axis. The first flexible element produces a
force moment about the axis in a first direction biasing the force
modifying member into rotation in the first direction. The second element
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exerts a resultant biasing force on the load. The first and second
surfaces are dimensioned such that rotation of the member about the axis
in the first direction causes one of the elements to be wound onto its
respective surface as the other element is unwound from its respective
surface in a manner which varies the force mcments about the axis.
In accordance with another aspect of the present invention, there
is provided a device for moving a stack of generally planar articles
toward a dispensing position where individual articles are to be
dispensed, which device includes means for maintaining a generally uniform
force on the stack in the direction of the dispensing position. The
device includes plate means movable along a predetermined path between a
first position remote fr~m the dispensing cpening and a second position
adjacent the dispensing opening for pushing the stack toward the
dispensing position; a plate cable means having a first end and second
end, the irst end being connected to the plate means; a tension spring
having a stationary end fLxed relative to the dispensing position and a
free end movable along a predetermuned spring path between a first
position wherein the spring is extended a predetermined distance and a
second contracted position, the spring defining a tension force having a
predetermined value when in the first position, which tension force
diminishes as the spring retracts along the spring path t~ward the second
position; spring cable means having a first end and a second end, the
first end being connected to the free end of the tension spring; and a
force modifying member for transmitting the tension force in the spring
to the plate means to move ~he plate means along the plate path. ~he
modifying member is rotatable akout an axis fixed relative to the
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dispensing opening, and includes first and second
outwardly facing contoured surfaces to receive the
tension spring cable means and the plate cable means,
respectively. The second ends of the cable means are
attached to the modifying member such that the spring
cable means is disposed on the first surface when the
spring is in the first position. The tension force of
the spring biases the modifying member to rotate in a
predetermined direction, which rotation produces a
resultant biasing force on the plake means via the plate
cable means to force the plate means toward the
dispensing position. The first surface is dimensioned to
vary the distance between the spring cable means and the
axis as the modifying member rotates, wherein the
resultant biasing force acting on the plate means is
maintained generally more uniform as the plate moves
between the first position and the second position.
It is an object of an aspect of the invention
to provide a device to modify the force generated by a
spring system or the like into a more uniform force with
a less radical drop-off as the spring contracts.
Another object of an aspect of the invention is
to provide a dispensing canister for currency, documents
or the like wherein the force exerted on the currency or
documents to move the same toward a dispensing position
remains more uniform between a full canister condition
and an empty canister condition.
A still further object of an aspect of the
invention is to providP a device for moving planar
articles toward a dispensing location.
According to aspect of the invention, an
elongated, generally rectangular currency canister for
moving a stack of sheet currency toward a dispensing
position at one end thereof where individual sheets are
dispensed, the canister having a first lengthwise
compartment for holding the stack of currency, a second
lengthwise compartment, and a device for biasing the
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stack in the direction of the dispensing position, the
biasing means comprises:
plate means disposed within the first and
second compartments movable along a predetermined plate
path between a first position remote from the dispensing
opening and a second position adjacent the dispensing
opening for pushing the stack in the first compartment
toward the dispensing position,
plate cable means having a first end and a
second end, the first end is connected to the plate means
in the second compartment,
a tension spring disclosed in the second
compartment having a stationary end fixed relative to the
dispensing position and a free end movable along a
predetermined spring path within the second compartment
between a first position wherein the spring is extending
a predetermined distance and a second contracted
position, the spring defining a tension force having a
predetermined value when in the first position which
diminishes as the spring retracts along the spring path
toward the second position,
spring cable means having a first and a second
end, the first end is connected to the free end of the
tension sprin~, and
a force modifying member disposed in the second
compartment for transmitting the tension force in the
spring to the plate means to move the plate means
along the plate path, the modifying member is rotatable
through at least 270 degrees about an axis fixed relative
to the dispensing opening from a first rotation position
corresponding to the first spring position and second
rotation position corresponding to the second spring
position and having ~irst and second outwardly facing
non-circular arcuate surfaces to receive the tension
spring cable means and the plate cable means
respectively, the first arcuate surface is
generalIy helical in shape and spiralling outwardly, the
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second ends of the cable means is attached to the
modifying member wherein the spring cable means is
disposed on the first surface when the spring is in the
first position, the tension force biasing the modifying
member to rotate in a predetermined direction wherein the
plate cable means is wound onto the second arcuate
surface and the spring cable means is unwound from the
first arcuate surface and the rotation of the member
producing a resultant force on the plate means via the
plate cable means to force the plate means toward the
dispensing position, the first and second surfaces is
dimensioned to vary the respective distances between the
spring cable means and the plate cable means and the axis
as the modifying member rotates, the ratio of the
distance between the spring cable and the axis relative
to the distance between the plate cable and the axis
continually increasing as the modifying member rotates
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Brief Description of the Drawinas
The invention may take physical form in certain parts and
arrangement of parts, a preferred embodiment of which will be described in
detail in the specification and illustrated in the accompanying drawings
wherein:
FIG. 1 is a perspective view of a currency dispensing canister
illustrating a preferred embcdiment of the present invention;
FIG. 2 is an enlarged sectional view taken along 2-2 of FIG. 1
illustrating the position of various components of the currency
dispensing canister when the canister is in a fully loaded condition;
FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG.
l;
FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;
FIG. 5 is an enlarged side elevational view illustratIng a force
m~difying eleme~t incorporating another concept of t~e present invention;
FIG. 6 is a sectional vlew taken alo~g line 6-6 of FIG. 5;
FIG. 7 is an enlarged sectional view taken along line 7-7 of FIG.
4; and
FIG. 8 is a sectional view, similar to that shcwn in FIG. 2,
illustrating the position of the various ccmponents of the currency
dispensLng canister when the dispensing canister is in a nearly empty
con~ition.
Detailed Description of a Preferred Embodiment
Referring now to the drawings wherein the showin~s are for the
purpose of illustrating a preferred e~bodLment of the pr~sent invention
and not for the purpose of limiting~same, FIG. I shows a currency
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~ispensing canister 10 for use in an automatic teller machine (AIM).
Canister 10 is camprised of a generally rectangular housing 12 having side
walls 14, 16, end walls 18, 20 and bottam wall 22. End wall 18 includes a
generally rectangular opening 24 in the upper portion thereof, which
opening 24 defines a dispensing opening from which individual bills are to
be removed by a transfer n~chanism (not shown). A pair of generally Lr
shaped tracks 30, 32 extend along the length of side walls 14, 16 and are
secured thereto by fasteners 33. Tracks 30, 32 include horizontal leg
portions 30a, 32a and vertical leg portions 30b, 32b. Tracks 30 and 32
are positioned such that horizontal leg portions 30a, 32a are generally
coplanar and define a surface 34, best seen in FIG. 3. Tracks 30, 32
generally divide the canister into an upper compartment 36 and a lower
ccmpartment 3&. Upper compartment 36 is dimensioned to hold a stack of
planar, sheet like material such as currency, which stack is designated
"S" in the drawings. In this respe¢t, sta¢k S rests on surface 34 as
shown in the drawings, and a push plate 40 is prcvided to move stack S
along surface 34 tcward cpening 24.
Push plate 40 includes a front side 42 adapted to engage sta¢k S
and a back side 44. As best seen in FIG. 3, push pla~e 40 includes an
upper portion 46 adapted to move within upper ccmpartment 36 and a-lower
portion 48 dimensioned to travel in lower ccn~Lrtnent 38. In this
respect, notches 50, 52 are provided in the sides of push plate 40 to
accommcdate horizontal legs 30a, 32a of tracks 30, 32, respectively. A
rectangular notch 54 is also provided at the bottom of lower portion 48,
as seen in FIG. 3. PUsh plate 40 is mounted for horizontal travel along
parallel cylindrical guides 60, 62 which ext~nd between end walls 18 and
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20; Guides 60, 62 are secured to end walls 18, 20 in a known manner.
Secured to back side 44 of lower portion 48 of push plate 40 is a
generally U-shaped bracket 64, best seen in FIGS. 2, 4 and 8. Bracket 64
has a closed end 66 an opened end 68, with mounting feet 70, 72 adjacent
opened end 68. Bracket 64 is mounted to push plate 40 such that mounting
feet 70, 72 are on opposite sides of rectangular notch 54, as shcwn in
FIG. 3. 8racket 64 may be secured to push plate 40 by soldering, welding
or by conventionally-known fastener means.
A flexible element 80 is provided and secured at one end to
closed end 66 of bracket 64. Flexible element 80 may be comprised of a
cord, rope, cable or timing chain. In the preferred embodiment, flexible
element 80 is comprised of a flexible wire cable. Flexible element 80
extends æound a pair of pulleys 82, 84 as shown in FIGS. 2, 4 and 7.
Pulleys 82, 84 are slightly elongated in shape to allow verti~al travel of
flexible element 80 along the bearing surface thereof. Pulleys 82, 84 a~e
fixedly se~ured to bottom wall 22 of housing 12 by threaded fasteners in a
conventional manner. The other end of flexible element 80 is secured to a
force mcd~ifyin~ unit 90 which is rota W le about a fixed axis designated
"A" in the drawings (see FIGS. 2 and 4). ElemQnt 90 is fixe~ly mounted to
housing 12 as will be described in greater detail below. Flexible
element 80 operatively engages force modifying unit 90 to one side of axis
A.
Another elongated flexible element 92 is connected to force
modifying element 90. As with flexible element 80, flexible element 92
may be comprised of a cord, rope, cable or timing chain. In the preferred
embcdiment, flexible element 92 is also formed of a flexible wire cable.
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m e other end of flexible element 92 is connected to an elongated tension
sprin~ 94. Tension spring 94 extends around a pulley 96 which is secured
by conventional means in a fixed position to bottom wall 22. The other
end of tension spring 94 is attached to a vertical post 98 which is
fixedly secured to bottom wall 22. Spring 94 has a predetermined
configuration, which will be discussed in greater detail below, and is
dimensioned to maintain at all times tension on flexible element 92.
Referring now to FIGS. 5, 6 and 7, force mcdifying umt 90 is
shcwn. Unit 90 is generally comprised of three disk-shaped elements 102,
104, 106, best seen in FIG. 7. Disk-shaped elements 102 and 106 also
include, respectively, cam portions 108, 110, which are molded, machined
OE otherwise formed thereon. Disk-shaped elements 102, 104, 106 are
securel together by threaded fasteners 114, 116 (best seen in FIGs~ 6 and
7) to form an integral unit. Cam portion 108 includes an outward facing
arcuate cam surface 120 and two yenerally planar surfa¢es 122, 124, best
seen in FIG. 6. In similar resF~cts, cam element llO includes an outwan~
fa~in~ ar~uate ¢am surface 130 and two generally planar surfaces 132,
134, best seen in FIG. 6. Cam surfaces 120, 130 are of a predetermined
length and shape, and have a predetermined a~gular orientation wlth
respect to ea¢h~other.
Cam surface 120 is adapted to receive flexible element 80 thereon
with one end of element 80 being secured thereto by fastener 126 as shcwn
in FIG. 6. In simllar respects, cam surface 130 is adapted to receive
flexible element 92 thereon, with one end of element 92 being secured to
surface 130 by means of a fastener 136. In this respect, flexible
elements 80, 92 are adapted to be wound or unwound on cam surfaces 120,
:
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130 respectively as force modifying unit 90 rotates about axis A. In this
respect, each of the disk-shaped elements 102, 104, 106 includes an
aperture therethrough, which aperture is in registry with apertures of the
other elements to define a cylindrical opening or bore 138 through unit
9o. Bore 138 is dimensioned to receive a pin 140 therein. PLn 140
includes a head portion 142, a shank portion 144 and a threaded fastener
portion 146. Threaded fastener portion 146 has a smaller diameter than
shank portion 144 and defines a shoulder 148 at the juncture therewith. A
conventional nut fastener 150 secures pin 140 to bottom wall 22 of housing
12 as best seen in FIG. 7, wherein shoulder 148 is maintained agains'c wall
22 by fastener nut 150. Force modifying unit 90 is adapted for pivotal
movement ab~ut pin 140, the axis of pin 140 being axis A as defined above.
A bearing member 152 is provided to elevate unit 90 above bottom wall 22
and to Eermit free rotation of unit 90 3bcut pin 140.
The operation of force modifying unit 90 can best be des~ribed
with reference to FIG. 6. Force mcdifyin~ unit 90 basically operates by
varying the force moment arms acting thereon about axis A. The tension
force created by tension spring 94 acts through one of the mament arms,
acting on unit 90, and the output or resultant force generate~ in flexible
element 80 is determined by the other mcment arm acting on unit 90. More
specifically, as seen in the drawings, flexible element 92 wraps around
cam surfaoe 130 and lS attached to tension sprLng 94 which exerts a force
thereon. The tension force is exerte: along the axis of tension spring
94, and in FIG. 6, an arrow designated "TF" depicts the tension force and
its direction relative to unit 90. ~ension force IF produces a force
:: :
;~ momnt about axis A which is a function of;the tension on spring 94 and
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the perpendicular distance from flexible element 92 to axis A. ~his
force moment biases unit 90 into clockwise rotation about axis A. This
rotation of unit 90 produces a resultant force designated "RF" on
flexible element 80, and rotation of unit 90 causes flexible element 80 to
wrap around or be wound onto surface 120 of cam portion 108~ Element 80
is attached to a load (in the present ~mbodiment, the load being push
plate 40) remote from unit 90. The resultant force RF exerted on push
plate 40 is a function of the tension force TF exerted on unit 90 by
spring 94 and the relative lengths of the two moment arms. In this
respect, the resultant tension force RF can be determined by dividing the
force mcment generated by tension force TT, by the perpendicular distance
between axis A and flexible element 80. In other words, resultant force
RF = force moment generated by tension spring 94 divided by the distance
between axis A and flexible element 80.
As best seen in FIG. 6, surface 130 of cam portion 110 is
gene~ally helical in shape and spirals outwar~ly from surface 134 to
surface 132. In this respect, as force unit 90 rotates, the moment arm
between tension force TF and axis A gradually increases. Simultaneously,
tension spring 94 contracts. Thls, as tension spring 94 contracts and the
tension force TF diminishes, the moment arm between such tension force and
axis A increases thereby maintaining a more uniform force moment about
axis A generally. With respect to cam portion 108, as can be seen from
FIG. 6 cam surface 120 spirals outwardly slightly about axis A for an
angular sweep of about 180 after which cam surface 120 decreases slightly
as it approaches surface 122. In this respect, cam surface 120 also
varies the moment arm between flexible element 80 and axis A and thereby
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modifies the resultant force acting on the remote load. Cam portions 10~,
110 are oriented relative to each other such that rotation of force
modifying unit 90 modifies tension force TF in a manner such that
r~lltant force RF exhibits a substantially less radical force drop-off
than that exhibited in tension spring 94 as the spring contracts.
Force modifying unit 90 finds advantageous application in a money
dispensing canister as described above. The operation of such a money
canister can kest be described with reference to FIGS. 2 and 8 wherein
FIG. 2 shows the money dispensing canister 10 in a fully loaded condition.
In this condition, push plate 40 is disposed away from dispensing opening
24 and tension sprlng 94 is fully extended with flexible element 92
wrapped around cam surface 130 of cam portion 110. Flexible element 80
connected to cam p~rtion 10~ exerts the resultant biasing force RF on push
plate 40 t¢ uLge a sta¢k of bills S (not shown) t¢ward dispersing opening
24. As understoo~, tension spri~g 94 maintains the r~tant biasing
for¢e ~F ¢n push plate 40. ~s individual bills are indi~idually dispensed
by a t~ansfer mechanism (not shGwn), the tension on spring 94 ¢auses force
modlfyLng unit 90 to rotate ¢lockwise, which in turn ~raps flexible
element 80 onto cam portion 108 thereby pulling push plate 40 toward
opening 24. As force modifying unit 90 rotates, the moment arm between
the tension force TF exerted by spring 94 and a~is A increases as a result
of cam portion 110. Thus, although the tension force TF exerted by the
spring is constantly decreasing, the moment arm between the tension force
and axis A continually increases to generally mQintain a more uniform
resultant force on push plate 40. FIG. 8 shows the configuration of the
dispensing canister when push plate 40 is near, or at, an e~pty position.
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As seen in this drawing, tension spring 94 has contracted a substantial
length and rotated force modifying unit 90 approximately 270. m is
rotation has caused flexible element 80 to be wrapped onto cam surface 110
of cam portion 108 and thereby pulled push plate 40 to dispensing opening
24. In this respect, the rectangular notch 54 on the lower portion of
push plate 40 facilitates movement of push plate 40 over pulley 82.
As will be appreciated from the preceding discussion, the relation
ketween tension force TF and resultant force RF is a function of the
shapes of respective cam portions 108, 110 of modifying unit 90, and the
spring constant of tension spring 94. In addition, with respect to the
shape of unit 90, cam surfaces 120, 130 are relat~d to the desired travel
of push plate 40 between a fully loaded position and a fully empty
~osition, as well as the le~gth of tension spring 94.
Consider as an example with respect to the currency disEensing
canister disclosed in the drawings, it was desired: to produce a m~ney
dispensing canister wherein the travel of the push plate 40 would be
approximately 34 centimeters, to provide a m mimum resultant force RF of
approxImately 600 grams on push plate 40 when the canister was nearly
empty, and to maintain the resultant tension force within several hundred
grams (approximately 300) throughout the travel push plate 40 from a fully
loaded condition to a fully empty condition. With respect to such a
device, a stack of currency approximately 34 centimeters long weighs
approximately 2,900 grams. Therefore to compensate for an estimated 290
grams of frictional force resistance, the force on~the push plate 40 when
the;canister is fully loaded is preferably approximately 890 grams. To
provide the tension force, a tension spring 94 having a sprlng constant of
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approximately 34 grams (force)/centimeter of spring extension was
selected. As set forth above, the tension spring 94 is installed in such
a manner that a tension is constantly maintained on flexible element 92
even when the push plate is in an empty condition as shcwn in FIG. 8.
With respect to the embodiment shown, a spring with the aforementioned
spring constant wais installed such that the spring would be extended 14.7
centimeters and provide a 500 gram force when the canister and push plate
were a~ an empty condition. An additional extension beyond ~his empty
condition establishes the "working range" of tension spring 94. The
working range of spring 94 is illustrated by~the position of spring 94 in
FIGS. 2 and 8. With respYct to the embcdiment shown, the working range of
tenston s~ring 94 is approximately 27 centi~eters. Accordi~gly, for~e
mc~ifying unit 90 was dimensione~ su~h thiat ai ¢ontrai~tlon of 27
centimeters by tension spring 94 produGes a tra~el of appr~ximately 34
centimeters by push plate 40, and at thie same time, exerted on push plate
40 a force varying between 890 grams at thie fully loa~ied;c3n~ tionito
approximately 600 grams at the fully empty position. With respect to thie
aforementioned tension sprin~ 94, at its f~ly exten~ied Fosition, the
force of spring 94 i9 approxlmately 1,400 grams and as set forth akcve,
and at the end of its "working rcmge" (i.e~ at its contracted Ecsition) is
approximately 500 grams. Cam portions 108, 110 have been dimensioned to
modify the tension ~orce exerted by spring 94 into a more uniform
resultant force RF exerted on push plate 40. ~he following table provides
speclfic information on force modifying unit 90 shown in the drawings.
DB9 5 88US 13
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Ratio "RF" Travel '~F" Sprir~ ~ ~-
TF A~m of Push ~tal Device A~ tension at Given Fo~e
Arm to ~ngth ~late Rotation I~r~th (workir~ Bctension (g=
Driven ~cm) 40 ~?adians/Cegr~s ~cm) ra~e) (gra~ for~e)
A~m ~ rcnl rCn) for~)
Full Canist~
.633 6.0 0 0 3~80 26.65 1406.1 890
1.36
.640 6.125 .224 12.8 3.92 25.78 1376.5 881
2.72
.647 6.25 .444 25.4 4.045 24.91 1346.9 871
4.08
.654 6.38 .659 37.8 4.175 24.03 1317.0 861
5.44
.662 6.51 .870 49.8 4.31 23.19 1288.5 853
6.8
.665 6.69 1.076 61.6 4.45 22.23 1255.8 835
8.16
.673 6.82 1.277 73.2 4.59 21.32 1224.9 824
9.52
.680 6.956 1.475 84.5 4.73 20.40 1193.6 812
10.88
.687 7.10 1.668 95.6 4.88 19.47 1162.0 798
12.24
.695 7.24 1.858 106.5 5.035 18.53 1130.0 785
13.6
.706 7.36 2.04~ 117.1 g.l9S 17.58 1097.7 775
14.95
.717 7.476 2.22& 127.7 5.36 16.61 1064.7 763
16.32
.7}2 7.54 2.409 138.0 5.52 15.52 1031.1 755
}7.68
.745 7.61 2.588 l4a.3Q 5.68 14.62 997.1 744
19.04
.76} 7.674 2.766 158.sQ 5.84 13.60 962.4 7}2
20.4
.776 7.732 2.943 16&.6 6.00 12.55 925.7 719
21.76
.790 7.797 3.118 17a.6 6.16 11.48 890.3 703
23.12
.809 7.812 3.292 188.6Q 6.32 10.40 85}.6 691
24.48
.8}8 7.733 3.467 198.6C~ 6.48 9.28 815.5 683
2S .84
.868 7.6S 3.644 208.8Q 6.64 8.12 776.1 674
27.2
.897 7.6b 3.822 219.0~ 6.82 6.92 735.3 660
28.56
.934 7.S44 4.002 229.3 7.046 5.67 692.8 647
29.92
.978 7.44 4.184 239.7 7.27S 4.37 648.6 634
31.28
1.037 7.242 4.369 2S0.3 7.51 3.00 602.0 624
32.64
1.103 7.026 4.SS9 261.2 7.75 l.SS 552.7 610
34.00
1.18 ~ 6.80S 4.7S6 272.S 8.00 0 S00 S90
*with allowance to ~nQen~ate for friction of ~ o~en~ on sLIpporting su~facQ.
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Table 1 sets forth the respective dimensions of the moment arms
between axis A and tension force TF and resultant force-RF for cam
portions 108, 110 at various positions of rotation of unit ga fram its
initial position. Table 1 shaws that as force modifying unit 90 rotates
fram its initial position shawn in FIG. 2, the moment arm of tension
force TF continuously increases (to ccmpensate for the decreasing tension
force TF in spring 94) and the moment arm of resultant force RF increases
slightly, then decreases. Table 1 also illustrates the force degradation
in tension spring 94, i.e. fram 1,400 grams to 500 grams as the tension
spring contracts, and shaws the resultant force RF as modified by
modifying unit 90, i.e. from 890 grams to 590 grams. Thus, whereas the
tension force TF ~enerated by spring 94 aver its "working ran~e" has a net
chanye of 900 grams between its fully extended position and its contracted
position, the output force on the push plate varies by only 300 grams
between the fully loaded position and the fully empty position. m e
present invention thus provides a force modifying unit which substantially
reduces the force degradation in the illustrated spring biasing system and
produces a more uniform biasing force on the push plate.
The invention has been described with respect to a preferre~
embodiment. Modifications may occur to others skilled in the art upon
their reading and understanding of the specification. It is intended that
all such modifications and alterations be included in so far as they come
within ~he scope of the invention as claimed or the equiv21ent thereof.
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