U.S. patent application number 11/199334 was filed with the patent office on 2006-03-30 for embossing unit.
Invention is credited to Alessandro Minarelli, Gilberto Spirito.
Application Number | 20060065033 11/199334 |
Document ID | / |
Family ID | 35169372 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060065033 |
Kind Code |
A1 |
Spirito; Gilberto ; et
al. |
March 30, 2006 |
Embossing unit
Abstract
An embossing unit, wherein sheet material is fed between a first
and a second embossing roller counter-rotating respectively about a
first and a second axis of rotation defining a plane, one of the
embossing rollers being subjected, in use, to a compression force
towards the other embossing roller; and wherein at least one of the
axes of rotation oscillates about a virtual hinge or instantaneous
centre of rotation, which is movable, in the plane defined by the
axes of rotation, in response to displacement, along a pitch line
of tangency between the embossing rollers, of a point of
application of a reaction force.
Inventors: |
Spirito; Gilberto; (Bologna,
IT) ; Minarelli; Alessandro; (Bazzano, IT) |
Correspondence
Address: |
McCarter & English, LLP;Four Stamford Plaza
107 Elm Street
Stamford
CT
06902
US
|
Family ID: |
35169372 |
Appl. No.: |
11/199334 |
Filed: |
August 8, 2005 |
Current U.S.
Class: |
72/196 |
Current CPC
Class: |
B31F 2201/0782 20130101;
B31F 2201/0753 20130101; B31F 1/07 20130101 |
Class at
Publication: |
072/196 |
International
Class: |
B21D 13/04 20060101
B21D013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2004 |
IT |
BO2004A 000519 |
Claims
1. An embossing unit comprising a first and a second embossing
roller (3, 4) counter-rotating respectively about a first and a
second axis (6, 7) of rotation defining a plane, the embossing
rollers (3, 4) being tangent to each other along a pitch line (8)
lying in said plane; and a push assembly (16) for pressing the
embossing rollers (3, 4) against each other to grip, in use, sheet
material (2) for embossing between the embossing rollers (3, 4)
with a given compression force (F); at least one of the axes (6, 7)
of rotation being an oscillating axis (7) oscillating about a third
axis (15) perpendicular to said plane and defining, in said plane,
a centre of rotation (C); characterized in that the centre of
rotation (C) is an instantaneous centre of rotation (C), which is
movable in said plane in response to displacement, along the pitch
line (8) of tangency between the embossing rollers (3, 4), of a
point (A) of application of a reaction force (R) to the compression
force (F).
2. An embossing unit as claimed in claim 1, wherein said first
embossing roller (3) is a drive embossing roller, and said second
embossing roller (4) is a driven embossing roller.
3. An embossing unit as claimed in claim 1, wherein said
oscillating axis (7) is the second axis (7); the first axis (6) is
a fixed axis; and the push assembly (16) is connected to the second
embossing roller (4).
4. An embossing unit as claimed in claim 1, wherein, of the
embossing rollers (3, 4), the one coaxial with said oscillating
axis (7) is an oscillating embossing roller (4) oscillating about
the third axis (15); a supporting unit (12) being provided to
support the oscillating embossing roller (4); and said supporting
unit (12) being interposed between the oscillating embossing roller
(4) and the push assembly (16).
5. An embossing unit as claimed in claim 4, wherein the supporting
unit (12) is an articulated unit.
6. An embossing unit as claimed in claim 5, wherein the supporting
unit (12) comprises an articulated quadrilateral.
7. An embossing unit as claimed in claim 6, wherein said
articulated quadrilateral comprises a frame (18) movable parallel
to said compression force (F) by the push assembly (16); a cross
member defined by a shaft (11) coaxial with said oscillating axis
(7) and supporting for rotation said oscillating embossing roller
(4); and two connecting rods (21) perpendicular to the third axis
(15) and having respective lines of action intersecting at said
instantaneous centre of rotation (C).
8. An embossing unit as claimed in claim 7, wherein each connecting
rod (21) is a tie.
9. An embossing unit as claimed in claim 4, wherein the supporting
unit (12) is an articulated "rocking" unit.
10. An embossing unit as claimed in claim 9, wherein the supporting
unit (12) comprises a base (26) having a first surface (25); a fork
(18) comprising a cross member (19) and two arms (20), the cross
member (19) having a second surface (24); and a shaft (11) coaxial
with said oscillating axis (7) and supporting said oscillating
embossing roller (4); at least one of said first and said second
surface (25, 24) being a curved surface (24) contacting the other
of said first and said second surface (25, 24) at a point defining
the instantaneous centre of rotation (C).
11. An embossing unit as claimed in claim 10, wherein said push
assembly (16) is connected to the base (26).
12. An embossing unit as claimed in claim 11, wherein said curved
surface (24) has a radius of curvature equal to at least twice the
distance between the instantaneous centre of rotation (C) and the
pitch line (8).
13. An embossing unit as claimed in claim 1, the embossing unit (1)
having, at any instant and in use, an instantaneous centre of
stability (SC) defined as the point which lies in said plane, is
integral with said oscillating axis (7), and, following
infinitesimal oscillation of said oscillating axis (7), moves, in
said plane and parallel to the pitch line (8), by the same amount
as the instantaneous centre of rotation (C); the pitch line (8)
being located, in use, between the instantaneous centre of
stability (SC) and the oscillating axis (7).
Description
[0001] The present invention relates to an embossing unit.
[0002] The present invention may be used to advantage for embossing
strips (or sheets) of packing material (e.g. aluminium or foil or
other materials) in the tobacco industry, to which the following
description refers purely by way of example.
[0003] More specifically, the present invention relates to an
embossing unit of the type comprising a first and second embossing
roller counter-rotating respectively about a first and second axis
of rotation defining a plane, the embossing rollers being tangent
to each other along a pitch line lying in said plane; and a push
assembly for pressing the embossing rollers against each other to
grip, in use, the sheet material for embossing between the
embossing rollers with a given compression force; at least one of
the axes of rotation being an oscillating axis oscillating about a
third axis perpendicular to said plane and defining, in said plane,
a centre of rotation.
BACKGROUND OF THE INVENTION
[0004] In known embossing units of the type described above, one of
the two embossing rollers is normally a drive roller mounted to
rotate about a fixed axis of rotation, while the other embossing
roller is normally a driven roller, which is mounted for rotation
on a support, oscillates about a fixed pivot or hinge, and is
subjected to said compression force which necessarily passes
through the hinge axis.
[0005] To minimize axial displacement of the driven embossing
roller in response to oscillation of the driven embossing roller
about its fixed hinge, the fixed hinge is normally located as close
as possible to the axis of the driven embossing roller and,
therefore necessarily, on the opposite side of the driven embossing
roller to the drive embossing roller.
[0006] In such a structure, if, as a result of any anomaly, e.g.
transverse slip of the work strip with respect to a central
reference position, the point at which the reaction force is
applied is moved along the pitch line of tangency, the compression
force--still passing through the fixed hinge--is misaligned with
respect to the reaction force, thus producing a moment which tends
to amplify the effects of the anomaly. In other words, a
destabilizing moment is produced, which tends to rotate the driven
embossing roller away from its parallel position with respect to
the drive embossing roller. When this occurs and the elastic
reaction of the work material between the two embossing rollers
fails to restore the system to its initial condition, i.e. in which
the two embossing rollers are parallel, the system, being unable to
rebalance itself, assumes an improper position, which results in
creasing of the work strip and/or in uneven embossing caused by the
difference in compression to which the strip is subjected along the
pitch line of tangency.
[0007] By way of a solution to the problem, the structure is
normally subjected to a number of intricate adjustments designed to
restrict the oscillation range of the driven roller to a narrow
stable "region", in which the elastic reaction of the work material
is sufficient to compensate the negative effects induced by any
anomaly in the original balance of the system.
[0008] Despite the care and precision with which the adjustments
are made, however, it is obviously impossible to predict the
precise actual response of the work material, with the result that
the structure remains highly unreliable.
[0009] To solve the problem, the structure could be modified so
that the fixed hinge is located on the opposite side of the drive
embossing roller to the driven embossing roller. In which case, the
driven embossing roller would theoretically come close to the
condition of a "suspended" body, thus resulting in an intrinsically
stable system. In such a structure, however, the distance between
the fixed hinge and the axis of the driven embossing roller would
result in unacceptable axial displacement of the driven embossing
roller in response to even relatively minor oscillation of the
driven embossing roller about the fixed hinge. Moreover, in the
event the system becomes destabilized, rebalancing again depends
entirely on the elastic reaction of the work material.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide an
embossing unit of the type described above, designed to eliminate
the aforementioned drawbacks.
[0011] According to the present invention, there is provided an
embossing unit as claimed in the attached claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A number of non-limiting embodiments of the invention will
be described by way of example with reference to the accompanying
drawings, in which:
[0013] FIG. 1 shows a schematic, partly sectioned, functional vies
of a first preferred embodiment of the embossing unit according to
the present invention;
[0014] FIG. 2 shows a schematic, partly sectioned, functional vies
of a second preferred embodiment of the embossing unit according to
the present invention;
[0015] FIGS. 3 and 4 show operating graphs of the FIGS. 1 and 2
embossing units respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Number 1 in FIGS. 1 and 2 indicates as a whole an embossing
unit for embossing a continuous strip (or a sheet) 2 of packing
material (normally a strip or sheet of foil).
[0017] Embossing unit 1 comprises two known embossing rollers 3 and
4, which are fitted to a frame 5 to rotate about respective axes 6
and 7, and have respective cylindrical outer surfaces having
respective numbers of tips (not shown) meshing along a pitch line 8
of contact coplanar with axes 6 and 7 of embossing rollers 3 and
4.
[0018] More specifically, embossing roller 3 is a drive roller
fitted to a respective shaft 9, which is coaxial with axis 6, is
fitted to frame 5 with the interposition of bearings 10, and is
connected angularly to an output shaft (not shown) of a known motor
(not shown), fixed to frame 5 to receive a given drive torque from
the motor.
[0019] Embossing roller 4 is fitted in rotary manner, with the
interposition of internal bearings (not shown), to a shaft 11
coaxial with axis 7 and fitted in angularly fixed manner to a
supporting unit 12, and is rotated by embossing roller 3 via a gear
transmission comprising a gear 13 fitted to shaft 9, and a gear 14
coaxial with axis 7 and integral with embossing roller 4.
[0020] Supporting unit 12 allows embossing roller 4 to oscillate
about an instantaneous centre of rotation or hinge C--in the
example shown, a virtual hinge--having an axis 15 perpendicular to,
and movable transversely in, a fixed plane defined by axes 6 and 7.
Supporting unit 12 is interposed between embossing roller 4 and a
push assembly 16, which in turn is interposed between supporting
unit 12 and frame 5, and transmits to embossing roller 4 a
compression force F passing at all times through instantaneous
centre of rotation or hinge C and directed onto embossing roller 3
in a direction substantially perpendicular to axis 6 to grip strip
2 between embossing rollers 3 and 4.
[0021] At least in an original balanced embossing condition, axes 6
and 7 are parallel to each other and perpendicular to a reference
axis 17 through the centre line of embossing rollers 3 and 4 and,
in use, through the centre line of work strip 2 between embossing
rollers 3 and 4.
[0022] Supporting unit 12 comprises a U-shaped fork 18 defined by a
cross member 19, located on the opposite side of embossing roller 4
to embossing roller 3, and by two arms 20 perpendicular to cross
member 19 and located on opposite sides of embossing roller 4 and
symmetrically with respect to reference axis 17.
[0023] In the FIG. 1 example, supporting unit 12 is an articulated
unit defined by an articulated quadrilateral whose frame is defined
by fork 18, which is fitted to frame 5 to move towards drive
embossing roller 3 perpendicularly to axis 6 and in the direction
of compression force F, and with cross member 19 positioned
parallel to axis 6. The articulated quadrilateral also comprises a
cross member defined by shaft 11; and two connecting rods 21 (or
ties, given that, in the articulated structure defined by the above
quadrilateral, the two connecting rods 21 are mounted to operate in
traction) perpendicular to axis 15 and converging with each other
towards embossing roller 3. More specifically, the intersection of
the lines of action of connecting rods 21 defines, at any instant,
the position of instantaneous centre of rotation or hinge C. Each
connecting rod 21 is hinged, by two pins 22 and 23 parallel to axis
15, at one end to a respective end of shaft 11, and at the other
end to the free end of respective arm 20.
[0024] In a variation not shown, the two connecting rods 21 are
mounted to operate in traction, but diverge, i.e. arms 20 are
located outwards of relative pins 22 with respect to reference axis
17.
[0025] In the FIG. 2 example, supporting unit 12 is an articulated
"rocking" unit, in which the opposite ends of shaft 11 are fixed to
the free ends of arms 20, and a surface 24 of cross member
19--which surface may be flat, as in the embodiment shown, or, in a
variation not shown, may be an outwardly convex curved
surface--rocks on a surface 25 of a base 26, which, together with
fork 18, defines supporting unit 12 and is fitted to frame 5 with
the interposition of push assembly 16 to move, on frame 5, in the
direction of compression force F. In the example shown, surface 25
is curved with its convexity facing cross member 19, but, in a
variation (not shown) in which surface 24 is curved, may also be
flat or even curved with its concavity facing cross member 19. In a
variation not shown, surface 24 may be curved with its concavity
facing base 26, and surface 25 may be curved with its convexity
facing cross member 19.
[0026] In actual use, surfaces 24 and 25 roll, without sliding, on
each other, and the point of contact between cross member 19 and
surface 25 defines the instantaneous centre of rotation or hinge C
(a virtual hinge in this case too), which is movable along surfaces
24 and 25 as a function of the angular position of embossing roller
4 about axis 15.
[0027] Operation of embossing unit 1 will now be described with
reference to FIGS. 3 and 4, which show graphically the way in which
embossing unit 1 is restabilized automatically when destabilized by
any anomaly--e.g. sideslip of, or a crease in, strip 2--capable of
moving a reaction force R application point A--originally located
along reference axis 17--laterally along pitch line 8 to a point A'
which, by way of example, is located to the right of point A.
[0028] It should be pointed out that, for reasons of clarity,
oscillation of embossing roller 4 is greatly amplified in FIGS. 3
and 4. In actual fact, oscillation is normally in the order of
fractions of a degree (not illustratable graphically) and to all
intents and purposes may be considered "infinitesimal".
[0029] Theoretically, if a system--in this case, driven embossing
roller 4--subjected to a compression force F and a reaction force
R, both acting parallel to the same fixed plane, rotates-translates
generically in this fixed plane, and oscillates infinitesimally as
a result of a point A of application of reaction force R moving
along a fixed line--in this case, pitch line 8--extending in the
fixed plane, it is always possible to determine an instantaneous
centre of rotation C movable in the fixed plane both in absolute
terms and relative to the system; and an instantaneous centre of
stability SC, which by analogy with boats may be defined as a
pseudo-metacentre, which is the point which lies in the fixed
plane, is integral with the system, and, following infinitesimal
oscillation of the system, moves, in the fixed plane and parallel
to the fixed line (pitch line 8), by the same amount as
instantaneous centre of rotation C.
[0030] Graphically, the pseudo-metacentre or instantaneous centre
of stability SC is the point through which compression force F
passes before and after said rotation-translation. In other words,
and with reference to FIGS. 3 and 4, the instantaneous centre of
stability SC is the point defined by the intersection of two lines
along which force F is assumed to be applied after each of the two
movements into which rotation-translation of driven embossing
roller 4 may be divided: a line through C and A' and which
infinitesimal oscillation rotates about C with respect to reference
axis 17; and a line through point C' and translated parallel to
reference axis 17 by displacement of C to C'. By definition,
therefore, in a fixed-pivot system, instantaneous centre of
rotation C and pseudo-metacentre or instantaneous centre of
stability SC are fixed and coincide.
[0031] Since, as stated in the introduction, to stabilize the
system, it is not enough that driven embossing roller 4 be mounted
to oscillate about a fixed pivot or hinge (in this case, C and SC
coincide) located on the opposite side of pitch line 8 to driven
embossing roller 4, the only way of achieving a permanently stable
system, in which translation of driven embossing roller 4 may be
rendered less important, is to support driven embossing roller 4 on
a supporting unit, e.g. articulated or articulated rocking
supporting unit 12, which allows driven embossing roller 4 to
oscillate about an instantaneous centre of rotation C detached from
pseudo-metacentre or instantaneous centre of stability SC, i.e. an
instantaneous centre of rotation C movable in said fixed plane.
[0032] In fact, only using a supporting unit of this type, can the
average engineer determine the countless physical-geometric
variables of embossing unit 1 to ensure permanent stability of the
embossing unit (pseudo-metacentre or instantaneous centre of
stability SC on the opposite side of pitch line 8 to driven
embossing roller 4) and that the instantaneous centre of rotation C
remains permanently at an acceptable distance from driven embossing
roller 4.
[0033] As shown in FIGS. 3 and 4, embossing unit 1 responds to
displacement of point A to A' by rotation-translation (clockwise
rotation and leftward translation) of axis 7 in said fixed plane,
i.e. in the FIG. 3, 4 plane, and by displacement of instantaneous
centre of rotation or hinge C in the same direction as point A.
[0034] As shown in FIGS. 3 and 4, however, instantaneous centre of
rotation or hinge C moves in the same direction as point A
(rightwards in the example shown) but further (i.e. faster) than
point A, thus generating a torque which tends to restore the system
as a whole to its original equilibrium condition (both forces F and
R located opposite each other along reference axis 17) which is
therefore shown to be the stable equilibrium condition.
[0035] To determine the theoretical position assumed by
pseudo-metacentre or instantaneous centre of stability
SC--originally located along axis 17--of embossing unit 1 following
response of embossing unit 1 to an anomaly capable of moving from A
to A' the point of application of reaction force R (indicated R'),
the response is shown graphically as though it were performed in
two successive movements.
[0036] During the first of the two movements, driven embossing
roller 4 (only axis 7 is shown in FIG. 3, and only surface 24,
parallel to and integral with axis 7, of cross member 19 is shown
in FIG. 4) rotates about instantaneous centre of rotation or hinge
C, which is considered fixed, taking with it reference axis 17,
which assumes a new configuration 17' through A'. Since
pseudo-metacentre or instantaneous centre of stability SC is
originally located along axis 17 and, as stated, is integral with
the oscillating system, rotation of axis 17 to 17' draws
pseudo-metacentre or instantaneous centre of stability SC into a
new position along axis 17'.
[0037] During the second of the two movements, instantaneous centre
of rotation or hinge C moves to C', and compression force F
(indicated F') assumes the correct position through C' and
perpendicular to pitch line 8, thus compensating reaction force R'
and normally generating a moment.
[0038] Since, as stated, pseudo-metacentre or instantaneous centre
of stability SC is located along axis 17' and, by definition, is
the point, integral with the oscillating system, which moves
parallel to pitch line 8 like instantaneous centre of rotation or
hinge C, the position along axis 17' of pseudo-metacentre or
instantaneous centre of stability SC is defined by the intersection
of reference axis 17' and the line of action of compression force
F'.
[0039] Since the FIGS. 3 and 4 graphs apply to finite oscillation a
theory which can only be applied to infinitesimal oscillation, the
graphic result does not exactly correspond to reality, but serves
to show clearly the tendency of the system, in response to an
anomaly moving point A, to move instantaneous centre of rotation or
hinge C in the same direction as point A and to simultaneously
produce a stabilizing torque.
[0040] As regards the physical-geometric characteristics of the
supporting units 12 shown, it should be pointed out that, in the
case of the FIG. 1 supporting unit 12, the main stability condition
(pitch line 8 located between driven embossing roller 4 and
pseudo-metacentre or instantaneous centre of stability SC) is
normally achieved by operating connecting rods 21 as ties and never
as push-rods. In the latter case, in fact, the system would be
unstable. In the case of the FIG. 2 supporting unit 12, on the
other hand, it is important to bear in mind that the smaller is the
radius of curvature of the curved surface--in the example shown,
surface 25--on which driven embossing roller 4 "rocks", the closer
the system comes to instability (fixed pivot, i.e. fixed SC and C,
both located on the same side of pitch line 8 as driven embossing
roller 4). Said radius of curvature should therefore be fairly
ample, e.g. equal to at least twice the distance between
instantaneous centre of rotation or hinge C and pitch line 8. If
both surfaces 24 and 25 are curved (as referred to previously but
not shown), the above consideration applies to the one with the
smaller radius of curvature.
[0041] Given the above considerations, a number of variations (not
shown) may be made to embossing unit 1. For example, driven
embossing roller 4 may be fixed, and drive embossing roller 3
oscillating. This solution would involve no theoretical
complications, only a certain amount of difficulty--resolvable in
known manner--as regards drive torque transmission.
[0042] Alternatively, both embossing rollers 3 and 4 may be
oscillating. In an embossing unit of this sort, there would still
be difficulty in transmitting the drive torque, and oscillation of
the two embossing rollers, not being limited by a
fixed-rotation-axis embossing roller, may be fairly considerable.
Nevertheless, the above theory, relative to an embossing unit in
which the pitch line of contact between the two embossing rollers
is fixed, would clearly indicate the possibility of producing, and
relatively easily, an embossing unit with a movable pitch line of
contact (with both embossing rollers oscillating).
[0043] The above theory relates to a two-roller embossing unit. It
should be pointed out that, in an embossing unit comprising more
than two rollers, the same also applies to all or some of the pairs
of rollers.
* * * * *