Note: Descriptions are shown in the official language in which they were submitted.
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A HIGH-SPEED ROTARY TRANSFER DEVICE
FIELD OF INVENTION
This invention provides a rotary transfer device for transferring a material
from
one point to another point sag a conjugate cam vehicle and a transfer drive
mechanism
therein to provide transfer speed ratios of between about 1 x 104:1, about I
:1, and/or about
I :1x104, and also from a stationary position to a specified speed and vice
versa.
BACKGROUND OF INVENTION
Articles, such as disposable diapers, generally have been manufactured by a
process where discrete parts or components of different materials, such as leg
elastic,
waist elastic, tapes, and other fasteners such as hook and loop materials or
snaps, have
been applied to a continuously moving product web of interconnected articles.
Often, the
speed at which the parts are fed into the process is not the same as the speed
of the
product web itself. Thus, the speed of the parts must be changed to match the
speed of
the product web to properly apply the parts without adversely affecting the
process or the
finished articles.
Several different conventional methods for changing the speed of a part or
component of material such that it can be applied to a continuously moving web
have
been known to those skilled in the art. For example, one method has been known
as the
slip gap or slip cut method. A web of material, which is traveling at a slower
speed than
the moving web, is fed into a knife and anvil roll having a surface speed
equal to the speed
of the moving web. As the material is cut into discrete parts, vacuum in the
anvil roll is
activated to draw the parts of material to the surface of the anvil roll. The
anvil roll then
carries the parts to the moving web where the vacuum is released and the parts
are
applied to the moving web while both the parts and the moving web are
traveling at the
same speed.
Another method has utilized festoons to reduce the speed of the moving web to
match the speed of the discrete parts of material to be applied to the web.
The moving
web is temporarily slowed down to the speed of the parts with the excess
portion of the
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moving web gathering in festoons. The parts of material are then applied to
the moving
web while both the parts and the web are traveling at the same speed. The
festoons are
then released allowing the moving web to return to its original speed.
Another method has utilized a slider-crank mechanism to accomplish the speed
change. The slider-crank mechanism utilizes concentrically mounted arms or
linkages to
receive the discrete parts of material, increase the speed of the parts to
match the speed of
the moving web and apply the parts to the moving web. The slider-crank
mechanism is a
special case of a four bar linkage system.
Another such method to change the speed of a discrete part before it is
applied to
a moving web has utilized a cam actuated crank-follower mechanism. The cam
actuated
cram:-follower mechanism comprises crank levers that are mounted on a
rotatable
driving plate. Each crank lever includes a cam follower on one end and a
follower lever
connected to the other end. The other end of the follower lever is connected
to an
applicator device which is mounted concentric with the driving plate's center
of rotation.
The cam follower remains in contact with a fixed cam that is also mounted
concentric
with the driving plate's center of rotation. As the driving plate rotates, the
crank levers
pivot as their cam followers follow the cam shape. As the crank levers pivot,
the
follower levers cause the applicator devices to speed up or slow down. An
example of
this method is described in U.S. Pat. No. 4,610,751 issued September 9, 1986,
to Eschler.
Finally, another such method to change the speed of a discrete part before it
is
applied to a moving web utilizes an offset crank motion of a drive ring and
the pivoting
___ of coupler arms to vary the effective drive radius of a material transfer
segment to
provide variable speeds. More specifically, as the transfer segments rotate
about their
drive ring, they are movable along their radial arm to effect changes in their
speeds at
pick-up and transfer of elastic materials. An example of this method is
described in U.S.
Patens No. 5,716,478 issued February 10, 1998 to Boothe, et al.
Conventional methods, such as those described above, have exhibited several
drawbacks. For example, as the discrete parts of material are transferred,
they are often
subjected to a tugging action because the surface speed of the transfer means
used to
transfer the parts is greater than the speed of the parts. The tugging action
may result in
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an undesirable elongation or tear of the parts. Also, few, if any, of the
conventional
methods have the ability to achieve the high speed ratios claimed by the
invention herein;
e.g., the cut & slip method is one such conventional method and also, it
cannot provide
irregular shapes taken from one web to another. Finally, several of the
conventional
methods can be very expensive and time consuming to change as the size and
speed of
the discrete parts and the speed of the moving web change to coincide with
various
finished product sizes. Consequently, an inexpensive and adaptable apparatus
for
receiving discrete parts traveling at a speed and applying the parts to a web
traveling at a
different speed is desirable.
Moreover, it is desirable that the receiving and applying of the parts occurs
while
the respective surface speeds are maintained substantially constant for a
fixed duration.
For example, it is desirable to apply the parts to the substrate web while the
parts and
substrate web are traveling at substantially the same surface speed or at
match speed.
Such a substantially constant speed dwell allows precise control of the length
and
placement of the part on the substrate web especially if the part is fragile
and/or elastic.
In addition, it is desired herein that the radius between the transfer shafts
and the
center of the rotatable drum remains constant.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a transfer device comprising a
conjugate cam vehicle for achieving a speed ratio ranging from about 1x10':1,
about 1:1,
- and/or about 1:1x10' at pick-up or stationary at some speed and transfer of
materials
about the device. This speed ratio range is achieved about a pair of points of
pick-up and
transfer spaced at least 10° and preferably at least 90° apart
on the conjugate cam vehicle.
The conjugate cam vehicle comprises a first cam having a center point, an
outer
perimeter, an inner perimeter, and irregularly shaped teeth faced inwardly
toward the
center point. The conjugate cam also comprises a second cam having a center
point, an
outer perimeter, an inner perimeter, and irregularly shaped teeth faced
inwardly toward
the center point. The first cam and the second cam are positioned adjacent to
one-
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another to form a conjugate cam vehicle having a center, an outer perimeter,
an inner
perimeter and irregularly shaped teeth faced inwardly toward the center.
The conjugate cam vehicle is configured to provide substantially inconstant
acceleration about the irregularly shaped teeth such that the conjugate cam
vehicle
provides acceleration from between about 0° to about 180° of the
outer perimeter and a
deceleration from between about 180° to about 360° of the outer
perimeter.
The transfer device also comprises a rotary transfer drive mechanism or
transfer
drive that picks up and transfers material. The transfer drive is positioned
within the
conjugate cam and operates partially therein. The transfer drive comprises a
main drive
shaft for driving the transfer drive mechanism which extends through the
center of the
conjugate cam. Further, the transfer drive comprises a rotatable drum having a
perimeter, a center, a first side, and a second side opposed to the first
side. The rotatable
drum is attached to the main drive shaft at its center and rotates thereabout
as the drive
shaft rotates.
At least one transfer shaft is placed onto and through the rotatable drum
adjacent
to or near the drum perimeter. Each transfer shaft comprises a first end and a
second end.
The first end of each transfer shaft is positioned above the first side of the
rotatable drum
and the second end of each rotatable shaft is positioned below the second side
of the
rotatable drum. Also, at least one transfer head is positioned about the first
end of each
transfer shaft above the first side of the rotatable drum, each transfer head
preferably but
not necessarily being rotatable about each transfer shaft.
A cam follower mechanism is positioned about the second end of each transfer
shaft below the second side of the rotatable drum. Each cam follower mechanism
comprises a cam follower plate having a perimeter, a first side and a second
side opposed
to the first side, and at least two cam followers attached to each cam
follower plate. At
least one cam follower is attached to the first side of the cam follower plate
with the
other cam followers being attached to the second side of the cam follower
plate. Each
cam follower mechanism is rotatable about one transfer shaft.
The transfer drive mechanism fits at least partially within the conjugate cam
vehicle whereby the cam followers move about the irregularly shaped teeth of
the
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conjugate cam as the rotary transfer drive mechanism is rotated by the main
drive shaft
within the conjugate cam..
BRIEF DESC lPTrnN pF THE FI RED
While the specification concludes with claims particularly pointing out and
distinctly claiming the subject matter which is regarded as forming the
present invention,
it is believed that the invention will be better understood from the following
description
taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a perspective view of the high-speed rotary transfer device;
Fig. 2 is a side view of the high-speed rotary transfer device;
Fig. 3 is a plan view of the conjugate cam vehicle;
Fig. 4 is a plan view of the conjugate cam vehicle;
Fig. 5 is a plan view of the conjugate cam vehicle;
Fig. 6 is a plan view of the conjugate cam vehicle;
Fig. 7 is a plan view of the conjugate cam vehicle;
Fig. 8 is a plan view of the conjugate cam vehicle;
Fig. 9 is a plan view of the conjugate cam vehicle;
Fig. 10 is a plan view of the conjugate cam vehicle;
Fig. 11 is a graph relating the planet or cam followers displacement,
velocity, and
acceleration as compared to the drum angle; and
Fig. 12 is .
DETAILED DI C .(Wi 1RF F TH . INVENTION
The present invention provides a transfer device that comprises a conjugate
cam
vehicle for achieving a speed ratio ranging from about 1x10':1, about 1:1,
andlor about
1:1 x 10° at pick-up and transfer of materials about the device. This
speed ratio range is
achieved about a pair of points of pick-up and transfer spaced at least
10° and preferably
at least 45° apart on the conjugate cam vehicle from the center of the
vehicle.
As shown in Fig. 1, the conjugate cam vehicle 20 comprises a first cam 21
having
a center point, an outer perimeter, an inner perimeter, and irregularly shaped
teeth 25
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faced inwardly toward the center point. The conjugate cam vehicle 20 also
comprises a
second cam 22 having a center point, an outer perimeter, an inner perimeter,
and
irregularly shaped teeth faced inwardly toward the center point. The first cam
21 and the
second cam 22 are positioned adjacent to one-another to form a conjugate cam
vehicle 20
having a shared and common center, outer perimeter, inner perimeter and
irregularly
shaped teeth faced inwardly toward the center.
The conjugate cam vehicle 20 is configured to provide substantially inconstant
acceleration about the irregularly shaped teeth 25 such that the conjugate cam
vehicle 20
provides accelerations through the conjugate cam vehicle 20 ranging from
between about
0° to about 180° of the outer perimeter and decelerations
ranging from between about
180° to about 360° of the outer perimeter.
The transfer device 10 also comprises a rotary transfer drive mechanism 28 or
transfer drive 28 that picks up and transfers material about the device 10.
The transfer
drive 28 is positioned within the conjugate cam vehicle 20 and operates
partially therein.
The transfer drive 28 comprises a main drive shaft 32 for driving the transfer
drive 28
which extends through the center of the conjugate cam vehicle 20. Further, the
transfer
drive 28 comprises a rotatable drum 30 having a perimeter, a center, a first
side, and a
second side opposed to the first side. The rotatable drum 30 is attached to
the main drive
shaft 32 through its center and rotates thereabout as the drive shaft 32
rotates.
At least one transfer shaft 35 is placed onto and through the rotatable drum
30
adjacent to or near the drum perimeter. Each transfer shaft 35 comprises a
first end 35A
___(not shown) and a second end 35B (not shown). The first end 35A of each
transfer shaft
is positioned above the first side 30A of the rotatable drum 30 and the second
end 35B of
each rotatable shaft 35 is positioned below the second side 30B of the
rotatable drum 30.
Also, at least one transfer head 40 is positioned about the first end 35A of
each transfer
shaft 35 above the first side 30A of the rotatable drum 30, each transfer head
40,
preferably but not necessarily, being rotatable about each transfer shaft 35
to
accommodate product size changes.
A cam follower mechanism 34 is positioned about the first end 35A of each
transfer shaft 35 above the first side 30a of the rotatable drum 30. Each cam
follower
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mechanism 34 comprises a cam follower plate 38 having a perimeter, a first
side 38' and
a second side 38" opposed to the first side 38', and at least four cam
followers 36
attached to each cam follower plate 38. At least two cam follower 36 are
attached to the
first side 38' of the cam follower plate 38 and at least two cam followers 36
are attached
to the second side 38" of the cam follower plate 38. For every one cam
follower 36 on
one side (either first or second) of the cam follower plate 38 there is
another cam
follower 36 positioned on the opposite side (either first or second) of the
cam follower
plate 38 Each cam follower mechanism 34 is rotatable on one transfer shaft 35.
The transfer drive mechanism 28 fits at least partially within the conjugate
cam
vehicle 20 whereby the cam followers 36 move about the irregularly shaped
teeth 25 of
the conjugate cam vehicle 20 as the transfer drive mechanism 28 is rotated by
the main
drive shaft 32 within the conjugate cam vehicle 20.
In practice the first and second cams each comprise a minor cam diameter
ranging from about 3.0 inches to about 200 inches. Preferably, the minor cam
diameters
range from about 22 inches to about 28 inches. Also, the first and second cams
each
comprise a major cam diameter ranging from about 4.0 inches to about 260.0
inches.
Preferably, the major cam diameters of the first and second cams range from
about 30
inches to about 34 inches. The minor cam diameter is that diameter measured
from the
inner perimeter of the conjugate cam (i.e., from the tips of the cam teeth) to
the center of
the conjugate cam vehicle 20. The major cam diameter is that diameter measured
from
the deepest points of the irregularly shaped teeth (i.e., the bottom of the
teeth) to the
--center of the conjugate cam vehicle 20.
Additionally, the conjugate cam comprises 20 an outer diameter ranging from
about 4.5 inches to about 180 inches. Preferably, the outer diameters of the
conjugate
cam vehicle 20 range from about 35 inches to about 37 inches. The first and
second
cams each comprise a cam width ranging from about 0. 25 inches to about 8
inches.
Preferably, the cam widths range from about 0.3125 inches to about 2.0 inches.
The first
cam 21 and second cam 22, and thus the conjugate cam vehicle 20, also each
comprise a
harmonic deviation ranging from about 0° to about 10,000°. As
used herein, the term
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"harmonic deviation" refers to the maximum rotational deviation of the planet
per
rotatable drum 30 cycle, or 360° rotation, due to the harmonic change
in position.
The rotatable drum 30 of the transfer device 10 comprise a diameter ranging
from
about 2.5 inches to about 160 inches, preferably from about 15 inches to about
35 inches.
The thickness of the rotatable drum 30 may range from about 0.25 inches to
about 20
inches.
Figure 1 provides a perspective view of the high-speed rotary transfer device
or
transfer device 10 taken at an angle behind the conjugate cam vehicle 20, the
cam
followers 36, the cam follower plates 38 and the rotatable drum 30. Also shown
is the
main drive shaft 32 extending through the transfer device 10 and the conjugate
cam
vehicle 20. Recall that the conjugate cam vehicle 20 is comprised of a first
cam 21 and a
second cam 22. Also shown are the transfer shafts 35 attached to the cam
follower plates
38 at one end and attached to the transfer heads 40 at the other end. Fig. 1
shows a
preferred embodiment wherein the transfer shafts 35 are attached to a
rotatable guide
plate 42 such that the transfer shafts 35 are stabilized at each of their
respective ends.
The preferred motion of the transfer shafts 35 is that first, they rotate
about the main
drive shaft 32 as the cam followers 36 move along the conjugate cam's
irregularly
shaped teeth 25 of the first and second cams within and without of the
conjugate cam
vehicle 20 and second, the transfer shafts 35 themselves rotate such that the
transfer
heads 40 rotate about the transfer shafts 35.
Figure 2 provides a side view of the transfer device 10. In an alternative
__ embodiment, holding plates 15 (not shown) may secure the device 10 to the
ground or to
some other structure while the transfer device 10 is in operation. As is shown
in Fig. l,
the main drive shaft 32 is shown herein extending through the device 10 and
being
connected to the rotatable drum 30 and the rotatable guide plate 42. Transfer
shafts 35
are shown in spaced relationship to the main drive shaft 32.
Figures 3-5 provide top plan views of the conjugate cam vehicle 20, the
rotatable
drum 30, one end of the main drive shaft 32 the cam follower plates 38 and the
cam
followers 36 attached thereto and moving about the irregularly-shaped teeth 25
of the
conjugate cam vehicle 20. In these views, the front most cam is the second cam
22 and
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the first cam 21, although not shown here, would be positioned behind the
second cam
22. Fig. 3 provides an embodiment wherein three cam followers 36 are
positioned on
either side of the cam follower plate 38 giving a total of six cam followers
36 positioned
onto each cam follower plate, three of which are not seen in this view. The
shape and
form of the cam teeth 25 in Fig. 3 provide a suitable cam profile through
which the
followers may travel (by rotation) throughout the conjugate cams to meet the
designed
transfer speed and pick-up speed requirements. It is noted herein that the cam
followers
36 freely rotate about either a rotatable or stationary shaft 52 (not shown)
connecting
each cam follower to its resident cam follower plate. By the term "cam
profile" it is
meant herein the structure and shape of the cam teeth 25 of each cam in the
conjugate
cam vehicle 20.
In another embodiment herein, Fig. 4 shows four cam followers 36 on the second
side 38" of the cam follower plate 38. Therefore, four other cam followers 36
(not
shown herein) are also attached to the first side 38' (not shown) of the cam
follower plate
38 making a total of eight cam followers positioned onto each cam follower
plate. As in
the embodiment for Fig. 3, the cam profile shown in Fig. 4 was constructed to
meet the
design criteria (e.g., speed) of the transfer device 10 operating within the
conjugate cam
vehicle 20.
Figure 5 provides an additional component to that of Figure 4, the transfer
head
40. The transfer heads 40 herein are used to transfer a material from one
source to
another. For example, in Fig. 5 the transfer head 40 is shown to be contacting
a source
A, conceivably for either transfer or pick-up of a material. In practice, the
transfer heads
40 will always be aligned with the source A as they are rotated about transfer
shafts 35
which in turn rotate about the main drive shaft 32. Preferably, each transfer
head 40 is
independently rotatable about its transfer shaft 35.
Figure 6 provides a plan view of the conjugate cam which shows the first cam
21
and the second cam 22. Also, four cam follower plates 38 with the cam
followers 36
thereon are shown. The shaded cam followers 36 represent those cam followers
which
are positioned on the second side 38" of the cam follower plate 38. The
unshaded cam
followers 36 are positioned on the first side 38' of the cam follower plate
38. Eight cam
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followers 36 for each cam follower plate 38 are shown. Additionally, each cam
follower
plate 38 has a rotatable transfer head 40 positioned thereon. As shown, each
transfer
head 40 will follow the path of rotation 50 shown by the heads 40 located on
each
transfer shaft 35. As is also shown, the path 50 for the transfer heads 40
develops from
the design of the conjugate cam vehicle 20 and the speed requirements for the
pick-up
and transfer of a material about the conjugate cam vehicle 20 from one point
about the
vehicle 20 to another point about the vehicle 20.
At the flattened out or bulbous portion of the ''teardrop" path formed, the
transfer
heads 40 are moving at their slowest rotation about the conjugate cam vehicle
20. As the
transfer heads 40 make their way back up to transfer/pick-up area A, they are
beginning
to travel with greater rotational speed until they reach transfer/pick-up area
A, the point
or area of their greatest speed. Note, all of these speeds will correspond to
the speeds of
material to be picked up and transferred; i.e., when the transfer heads 40
pick-up and
deliver materials, the heads surface will be moving at substantially the same
speed as the
pick-up and transfer sources. Also note that the closer that the irregularly-
shaped teeth
25 are, the faster the transfer heads 40 will travel. Correspondingly, the
more spread-out
the teeth 25 are, the slower the heads will travel. Generally, the speed of
the main drive
shaft 32 remains constant.
Fig. 7 shows a plan view of a "cloverleaf' configuration; i.e., the path of
the
transfer heads 40 about the conjugate cam and at a look at the conjugate cam
vehicle 20
from behind the second cam 22. Where the teeth of the conjugate cam 25 are
smallest
---- and closest together, the transfer heads 40 are moving at their fastest.
Correspondingly,
where the teeth of the conjugate cam vehicle 20 are at its widest and most
spaced apart,
the transfer heads 40 are moving at their slowest. The "cloverleaf' path of
the transfer
heads 40, as in the "teardrop" path configuration, results from calculations
determining
the number of transfer head revolutions per drum revolutions. The "cloverleaf'
path
relates to the speed, and the orientation of the pick-up and transfer of
materials from one
point to another point. It is noted herein that one skilled in the art can
construct various
types of transfer head paths 50 to suit her design criteria. Any such path
design therefore
falls within the scope of the invention herein.
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The transfer device may achieve times of transfer ranging from less than one
millisecond to about 10 seconds between a point or points of pick-up.
In one embodiment herein, one'pair of cam followers are attached to the first
side
of the cam follower plate and another pair of cam followers is attached to the
second side
of the cam follower plate. Preferably, each cam follower is positioned
equidistant or
proportionately from the other cam followers on the cam follower plate. In
another
embodiment herein, each cam follower mechanism comprises at least three cam
followers placed equidistant apart about the cam follower plate perimeter on
the first side
of the cam follower plate and also at least three cam followers placed
equidistant on the
second side of the cam follower plate.
The rotatable drum may take-on any number of shapes per the designer's
preferences and needs. For example, the rotatable drum may be in the shape of
a circle,
cross, star, bar, triangle or whatever shape might be useful for the operation
of the device
described herein.
Rotational Displacement & Ha_r_m__onic Deviation
Rotational displacement is the amount of rotation of the top dead center
(t.d.c.)
point on the transfer head relative to the radius of the drum which passes
through the
center of the head (Fig. 6). By top dead center point it is meant herein that
point (or area)
on a transfer head that contacts material along or adjacent to the transfer or
pick-up
points adjacent to the conjugate cam. Rotational displacement is measured by
the
-- angular rotation of the top dead center point from the radius of the drum
passing through
the center of the transfer head 40.
The cam profile is driven by the harmonic deviation required. The higher the
harmonic deviation, the greater the speeds will be at various points about the
conjugate
cam vehicle 20, and specifically at the pick-up and/or transfer points about
the conjugate
cam vehicle 20. Harmonic deviation is the amount of rotational displacement of
top dead
center point over one-half revolution about the conjugate cam, i.e.,
180° from a point
midway between the transfer and pick-up points to a point 180° from
that point 90° to
270° on the cam. Furthermore, harmonic deviation dictates how slowly or
quickly the
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transfer head will spin about the transfer shafts 3~ at the pick-up and
transfer points
about the conjugate cam vehicle 20. In this way harmonic deviation is said to
drive the
cam profile or determine the shape, height and contour of the teeth 25 of the
conjugate
cam vehicle 20.
As is shown in Fig. 6, the 180° revolution about the conjugate cam
begins from
0° (a point of pick-up or transfer) and goes to 180° ( another
point of transfer or pick-up).
Obviously if the pick-up point is set at 180°, then the transfer point
for the particular
profile shown in Fig. 6 will be located at the 180° point. It is noted
herein that the points
of pick-up and transfer do not have to be 180° apart. More
specifically, depending upon
the size of a material to be picked-up, the transfer point may be less than or
greater than
180°. For example, a discrete component pitch length and an
interconnected article pitch
length at about 20 inches at about 1 inch, respectively, will, in one
embodiment herein,
have a range between transfer points at about 166° ~ 5°. In one
alternative embodiment
herein, a material having a length at about 1 inch which is transferred to a
product having
a length at about 1 ~ inches will have transfer points about the conjugate cam
vehicle
ranging from about 131 ° ~ 5°. Likewise, a material having a
length at about 3 inches
which is transferred to a product having a length at about 15 inches will have
range
between transfer points of about 130° ~ 5.
In practice, the cam followers will move about the conjugate cams in certain
prescribed configurations. Each of these configurations is created based upon
various
criteria specific to each transfer device design. For example, Fig. 6 shows a
conjugate
w- cam vehicle 20 and cam followers 36 moving about the conjugate cam in a
"teardrop"
configuration. This prescribed configuration is determined by various factors
which
include the speed of the transfer device moving within the cam, the number of
cam
followers used, and the teeth profile of the conjugate cam vehicle 20. In
designing the
transfer device, all of these factors combine to produce the "teardrop"
configuration or
path of travel of the transfer heads 40.
Fig. 7 shows another configuration called the "cloverleaf'. Like the
"teardrop",
the "cloverleaf' is determined by the speed of the transfer device moving
within the cam,
the number of cam followers used, and the teeth profile of conjugate cam.
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1n one example, the fewer the number of head revolutions per 360°
revolutions of
the drum produces less motion of the cam followers about the conjugate cam. In
the
"teardrop" configuration, the transfer head rotates fewer times within one
360° revolution
of the rotatable drum. Generally, fewer transfer head revolutions within one
360° drum
revolution results in fewer teeth being built, machined or carved into the
conjugate cam.
Such a design would generally result in less contact stress being applied to
the conjugate
cam as a whole and on the teeth specifically. Also, less forces would be
placed on the
- cam followers. This can result in greater product reliability in pick-up and
transfer of
materials about the conjugate cam.
Figures 8, 9, and 10 provide illustrations regarding use of the invention for
a
range of sizes of interconnected articles 202, 206 and a range of sizes of
discrete
components 201, 205. Interconnected articles 202, 206 may be, for example,
uncut or
unreleased articles within a web. In one example, this web could be a diaper
web or that
of any of the known absorbent articles. The discrete components 201, 205 may
be
component parts like tape tabs, waist features and other types of known
elements
commonly applied to sanitary napkins.
The range of pitch lengths of discrete components 201, 205 which the transfer
device 10 is capable of applying and the range of pitch lengths of
interconnected articles
202, 206 on which the discrete components will be applied is determined by the
conjugate cam vehicle 200. The maximum discrete component pitch length and
maximum interconnected article pitch length have been set forth prior to the
design of
the conjugate cam vehicle 200. The transfer device 10 is able to apply
discrete
components having a pitch length equal to or less than the maximum discrete
component
pitch length and is able to apply the discrete components onto interconnected
articles
having a pitch length equal to or less than the maximum interconnected article
pitch
length.
Referring now to Figures 8, 9, and 10, in practice, when it becomes necessary
either to apply a discrete component of which its size is not equal to the
maximum
discrete component pitch length or to apply a discrete component to an
interconnected
article of which its size is not equal to the maximum interconnected article
pitch length,
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or the distance between similar points of adjacent product parts, adjustments
should be
made to the transfer device 10. Specifically, cam shift, the fixed rotational
position of
the conjugate cam vehicle 200 must be adjusted. The pick up heads 208 (Fig. 8)
must be
replaced with new pick up heads 210 matching the shape of the new discrete
components
205 and having a new top dead center head radius. By the term "top dead center
head
radius" it is meant herein the distance between the top dead center of the
pick-up head
surface and the center of the pick-up head shaft. The new pick-up heads must
be phase
rotationally aligned to match their placement with the interconnected articles
202, 206.
Anvil roll 203 must be adjusted in position and rotational phase to align with
the pick-up
heads 208. The vertical position and machine direction phasing of the
interconnected
articles 202, 206 must be adjusted to be aligned with the pick-up heads 208.
It is usually desirable that the supply rate of interconnected articles is
equal to the
number of heads on the drum 209 per every one revolution of said drum. By the
term
"supply rate" it is meant herein the rate at which one interconnected article
202, 206 is
delivered to the point of transfer, i.e., pick-up head 208. It is also usually
desirable that
the rotational speed of the anvil roll is such that the discrete components
205 are supplied
at a rate of one discrete component per one interconnected article.
To create a cam which produces rotary motion of a planet that is attached to a
drum rotating at a fixed speed, it is necessary only to describe the paths of
the centers of
the cam followers that ride along the cam. Each cam follower of the planet
will have its
own unique path that it will travel through once for every revolution of the
drum. By
-- using a cutting device with the same diameter as the cam followers, these
same paths can
be used to fabricate the cam. Therefore, the task of defining the cam profile
becomes a
matter of mathematically describing the paths of the followers and hence the
cam cutters
that will create the profile. A pair of equations for each follower path
should be found
and a list of coordinates for each path should be created, these being the
outputs of said
equations given some incremental step of drum rotation.
To aid in describing the mathematics involved with the invention, the
description
can be broken down into several concepts that can be understood individually
more
easily. The invention can be thought of as two wheels in space that spin in
opposite
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directions. One is the main drum. The other is one of the planets. The total
number of
planets is not of concern here because if one planet can be modeled correctly
then
modeling the others is simply a matter of copying the first. The following
three examples
explain the two essential concepts to the design of the cam, Planet Speed
Factor and
Harmonic Deviation.
Example One: The drum spins at constant velocity. The planet spins at constant
velocity
and at twice the rotational velocity of the drum in the opposite direction. In
this example,
Planet Speed Factor is 2. Harmonic Deviation is 0 because there is no change
in planet
velocity.
Example Two: Again the drum spins at constant velocity. The planet has no
initial
rotational velocity, but begins accelerating up to some rotational speed,
slows back to
zero velocity, accelerates in the opposite direction up to the same rotational
speed in the
opposite direction, and then slows back to zero velocity. This cycle repeats
for every
revolution of the drum. In this example, the Planet Speed Factor is 0 because
the planet
makes no cumulative revolutions. The Harmonic Deviation is at some value, not
zero.
This example illustrates that Harmonic Deviation is the amount of rotation the
planet
experiences from rotational stopping point to rotational stopping point.
- Example Three: Combine Example One and Example Two. The drum spins at
constant
velocity. The planet begins at twice the rotational velocity of the drum in
the opposite
direction. 1t accelerates to some speed and then returns to the two times
speed, then
decelerates to some slower speed (without reversing), and returns to the two
times speed.
Speed Factor is 2 and Harmonic Deviation is some value. Fig. 11 shows a graph
of planet
rotational displacement, velocity, and acceleration.
The planet is placed on the edge of and in the same plane as the drum. At this
point in the discussion the drum and planet motion have been described.
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16
The next step is to track a point on the edge of the planet, representing the
center
of a cam follower. The total number of cam followers is not of concern here
because if
one follower can be modeled correctly then modeling the others is simply a
matter of
copying the first as with the planets. The path that this point will trace
will be one of the
cam follower paths.
The pair of equations that gives the position of the cam follower, namely the
angle and distance from the center of the drum, for any given Drum Angle is
dependent
on a set of five fixed variables. The names and definitions for these
variables follows:
Drum Radius - Distance from center of drum to center of planet.
Planet Radius - Distance from center of planet to center of cam follower.
Planet Speed Factor - Average rotational speed of planet divided by the speed
of
drum.
Harmonic Deviation - Mathematically, the greatest amount of rotational
displacement that planet will experience from constant rotation defined by the
Planet Speed Factor. Qualitatively, the amount of change in rotational speed
of
planet as drum makes constant rotation.
Follower Shift - Position of each follower on its planet. On a four follower
planet
configuration, follower shift equals 0° for follower one, 90°
for follower two,
180° for follower three, and 270° for follower four. For the
conjugate cam,
follower shift equals 45° for follower one, 135° for follower
two, 225° for
----. follower three, and 31 S° for follower four.
Fig. 12 shows the cam paths 55 (four) which can be used to fabricate the cam
itself. Note that this is only one of two cams, a conjugate pair. In fact,
second cam 22 is
showing. The first cam 21 is created by shifting the four followers 36 by
45°, half the
spacing of the followers 36 to create four new paths 55. For a four follower
per cam
design, adding 45° to each of the follower shift values 0°,
90°, 180°, & 270°, will give
new values of 45°, 135°, 225°, & 315° which will
yield four new pairs of equations.
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While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention.
