U.S. patent application number 17/037205 was filed with the patent office on 2021-01-14 for device for cutting a web of material.
The applicant listed for this patent is GDM S.P.A., UNIVERSITA' DEGLI STUDI DI BERGAMO. Invention is credited to Paolo CARRARA, Matteo PIANTONI, Davide RUSSO, Valerio SOLI.
Application Number | 20210007901 17/037205 |
Document ID | / |
Family ID | 1000005117754 |
Filed Date | 2021-01-14 |
United States Patent
Application |
20210007901 |
Kind Code |
A1 |
PIANTONI; Matteo ; et
al. |
January 14, 2021 |
DEVICE FOR CUTTING A WEB OF MATERIAL
Abstract
A device for cutting a web of material comprises movement means
for moving a web of material to be cut, defining a feed path for
the web at least partly rotatable about a central axis and equipped
with at least one conveyor mounted around the central axis, at
least one cutting head equipped with a laser source and an optical
system configured to direct the laser beam towards a cutting zone,
where the optical system of the cutting head comprises at least one
directing member located inside the conveyor to direct the laser
beam away from the central axis towards the cutting zone.
Inventors: |
PIANTONI; Matteo; (Albino
(Bergamo), IT) ; SOLI; Valerio; (Bologna, IT)
; RUSSO; Davide; (Firenze, IT) ; CARRARA;
Paolo; (Sovere (Bergamo), IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GDM S.P.A.
UNIVERSITA' DEGLI STUDI DI BERGAMO |
Bologna
Bergamo |
|
IT
IT |
|
|
Family ID: |
1000005117754 |
Appl. No.: |
17/037205 |
Filed: |
September 29, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15304794 |
Oct 17, 2016 |
10821032 |
|
|
PCT/IB2015/052696 |
Apr 14, 2015 |
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17037205 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 13/15723 20130101;
B23K 26/082 20151001; B23K 26/032 20130101; A61F 2013/15821
20130101; B23K 26/08 20130101; A61F 13/15764 20130101; B23K 26/0846
20130101; B23K 2103/40 20180801 |
International
Class: |
A61F 13/15 20060101
A61F013/15; B23K 26/082 20060101 B23K026/082; B23K 26/08 20060101
B23K026/08; B23K 26/03 20060101 B23K026/03 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2014 |
IT |
BO2014A000227 |
Claims
1. A device for cutting a web of material, comprising: movement
means by which a web of material to be cut is made to advance and
defining for the web a feed path which is at least partly rotatable
about a central axis; the movement means comprising at least a
conveyor mounted around the central axis and defining an at least
partly curved cutting zone; at least one laser cutting head laser
equipped with a laser source configured to generate a laser beam,
and an optical system configured to direct the laser beam towards
the cutting zone; Wherein the optical system of the cutting head
comprises at least one directing member located inside the conveyor
to direct the laser beam away from the central axis towards the
cutting zone; the directing member being rotatable about its axis
of rotation and oriented in such a way that the laser beam defines
on the web a cutting line transversal to the feed path of the
web.
2. The device according to claim 1, wherein the conveyor
constitutes a curved feed surface for the web and is equipped, at
the cutting zone, with at least one permeable portion permeable to
the laser beam and facing the directing member, so as to allow the
laser beam to pass through the feed surface.
3. The device according to claim 2, wherein the permeable portion
is defined by a through opening.
4. The device according to claim 2, wherein the permeable portion
is defined by an insert or window which is transparent to the laser
beam; the device comprising means for cleaning the insert or
window, configured to remove the dirt produced by the sublimation
of the fibrous material.
5. The device according to claim 1, wherein it comprises motion
transmission means, of mechanical or electro-mechanical type,
operatively interposed between the movement means and the directing
member to correlate a movement of the movement means along the feed
path with the rotation of the directing member about its axis of
rotation.
6. The device according to claim 1, wherein the optical system of
the cutting head comprises at least one focusing unit operatively
located upstream of the directing member and able to move
translationally in a straight line between a position close to the
directing member, where the focal point of the laser beam is distal
from the directing member itself, and a position away from the
directing member, where the focal point of the laser beam is
proximal to the directing member itself.
7. The device according to claim 1, wherein the directing member is
rotatable at least between a first angular, start-of-cutting
position and a second angular, end-of-cutting position; the
movement means and the axis of rotation of the directing member
being positioned in such a way that for each angular position of
the directing member, the optical path followed by the laser beam
between the directing member and the feed surface for the web is
substantially constant in length.
8. (canceled)
9. The device according to claim 7, wherein the conveyor is defined
at least partly by a cylindrical drum rotatable about the central
axis having a peripheral surface at least partly defining the
cutting zone; the directing member being located at the central
axis of the drum and being oriented in such a way that, between the
first and the second angular position of the directing member, the
laser beam remains in a plane at right angles to the central
axis.
10. The device according to claim 9, wherein the movement means are
structured to direct the web feed path around the drum along a
partly helicoidal line.
11. The device according to claim 10, wherein the drum defines a
guide shaped to divert the feed path of the web around the drum
itself along a portion of a helicoid extending for approximately
180.degree..
12. The device according to claim 7, wherein the conveyor comprises
a semi-elliptic guide extending at least partly around the central
axis and a belt slidable on the semi-elliptic guide; the directing
member being rotatable about its axis of rotation which is incident
on the central axis at an angle such that for each angular position
of the directing member, the laser beam intercepts a point on the
semi-elliptic guide located at the same predetermined distance from
the directing member itself.
13. The device according to claim 12, wherein the area subtended by
the laser beam between the first and the second angular position of
the directing member, measured in a plane at right angles to the
axis of rotation of the directing member itself, defines a circular
sector perimetrically delimited by the semi-elliptic guide.
14. The device according to claim 1, wherein the directing member
is rotatable about the central axis.
15. The device according to claim 1, wherein the directing member
and the conveyor are rotatable as one about the same axis of
rotation corresponding to the central axis.
Description
TECHNICAL FIELD
[0001] This invention relates to a device for laser cutting a web
of material, preferably a continuous web.
[0002] More specifically, this invention applies to the manufacture
of sanitary underwear such as baby nappies, sanitary towels or the
like.
BACKGROUND ART
[0003] These sanitary articles typically comprise an absorbent pad
which is normally sandwiched between a permeable inner layer of
non-woven fabric and an impermeable outer layer of
polyethylene.
[0004] The manufacture of such articles involves the formation
initially of a continuous web incorporating the aforementioned
layers, then shaping the web and finally separating the web into
single items ready for packaging.
[0005] Shaping consists mainly in the cutting of leg contours and,
more generally, serves to give the article an outline appropriate
for the specified use.
[0006] Prior art devices used for this type of operation comprise a
rotating drum, around which the web is looped partially as it
advances in a predetermined direction, and a laser cutting head
that operates on the web in the course of its passage over the
drum. Laser cutting heads are especially suitable for processes
used in the manufacture of sanitary underwear products, by virtue
of their low maintenance requirements and their ease of control and
adjustment, especially when compared with rotary blade cutter
systems adopted in this same technical field, which require
frequent replacement of the blades, or at all events, frequent
sharpening of the blades.
[0007] While the pros of such an application are evident, one
disadvantage of using laser cutting is, without doubt, that
connected with the movement of the cutting head and/or of the
optical systems, since the very high speed of web feed and the mass
production of these articles involves the use of extremely rapid
reciprocating drives and the consequent need to move masses which
are all but negligible and which undergo very significant
acceleration.
[0008] In other words, one of the major disadvantages of this
technology is due to the high inertia loads involved, requiring
high-powered (and high-cost) drive systems and very high-strength
structures.
[0009] A further solution of the prior art is disclosed in document
EP0549357, which illustrates the use a laser cutting head within a
rotary drum, by directing the laser beam on the inner surface of
the drum, carved, in order to make cuts or incisions on the web
translating with the drum.
[0010] In particular, said document specifies that the cutting head
comprises a fixed directioning element positioned at the center of
the drum to deflect the laser beam towards the drum surface,
widening it so as to cover the drum entire width.
[0011] In this light, additional mirrors are placed inside the drum
to intercept the portions of the laser refracted/reflected
diverting them again on the surface.
[0012] Disadvantageously, this solution requires high power laser
sources as the fixed position of the deflector element implies the
need to complete the cut instantaneously or, at the most, to stop
the movement of the drum during the cut, which is clearly
undesirable in the technical field of interest.
[0013] Moreover, it is not to be underestimated also the problem of
the security, which is particularly critical in light of the
widespread distribution of the laser beam of EP0549357, which is
designed to cover the entire width of the drum resulting active
only in correspondence of the notches and being therefore
reflected/refracted for the greater part.
DISCLOSURE OF THE INVENTION
[0014] In light of the above, the primary technical purpose of this
invention is to devise a device for laser cutting a web of material
and capable of overcoming the above mentioned disadvantages.
[0015] In the context of this technical purpose, one important aim
of the invention is to provide a device for laser cutting a web of
material and capable of reducing the resources necessary for
cutting in motion.
[0016] A further aim of the invention is to devise a device for
laser cutting a web of material where the movements associated with
the cutting head are minimized.
[0017] The technical purpose and aims specified are substantially
achieved by a device for laser cutting a web of material comprising
the technical features set out in claim 1.
BRIEF DESCRIPTION OF DRAWINGS
[0018] Further features and advantages of this invention are more
apparent in the non-limiting description of a preferred but
non-exclusive embodiment of a device for laser cutting a web of
material, as illustrated in the accompanying drawings, in
which:
[0019] FIG. 1 shows a schematic view of a first embodiment of the
device according to this invention for laser cutting a web of
material;
[0020] FIG. 2 shows a schematic view of a second embodiment of the
device according to this invention for laser cutting a web of
material;
[0021] FIGS. 3a-3c illustrate a third embodiment of the device
according to this invention for laser cutting a web of material in
schematic top and side views, respectively;
[0022] FIGS. 4a-4c are a schematic front view, a schematic side
view and a perspective view, respectively, of a fourth embodiment
of the device according to this invention for laser cutting a web
of material.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0023] With reference to the accompanying drawings, the numeral 1
denotes a device for laser cutting a web 2 of material.
[0024] Preferably, the device 1 is fitted in a machine for making
sanitary underwear such as baby nappies or sanitary towels.
[0025] The device thus comprises an unwinder (not illustrated) at
which a web 2, preferably continuous and padded, is made, for
example by juxtaposing a first layer of permeable material with a
second layer of impermeable material and interposing between the
two a portion of absorbent material, not illustrated, constituting
the padding. This operation is done, for example, by two feed
rollers and a device of known type, not illustrated in the
drawings, for adding the pad.
[0026] It should be noted, however, that the cutting device
according to this invention may be used to divide and cut any
component, even an accessory one, of the sanitary article, provided
it can be fed from a web of material, irrespective of its
composition.
[0027] Thus, the continuous web 2 is made to advance by means of
suitable movement means 3 configured to impart motion to the web 2
of material to be cut.
[0028] More precisely, the movement means 3 by which the web 2 of
material to be cut is made to advance define for the web 2 a feed
path "P" which is at least partly rotatable about a central axis,
hereinafter referred to as central axis "A". The central axis "A"
is thus transversal to the web 2.
[0029] More in detail, the movement means 3 comprise at least a
conveyor 4 mounted around the central axis "A" and defining an at
least partly curved cutting zone "Z".
[0030] Thus, the conveyor 4 is structured to define in the feed
path "P" a curve whose concavity faces the central axis "A".
[0031] Preferably, as will become clearer as this description
continues, the conveyor 4 comprises at least a drum 5 rotatable
about its axis of rotation which preferably corresponds to the
central axis "A" (FIGS. 1, 2, 3a, 3b).
[0032] Alternatively, the conveyor 4 may be defined by a curved
central core 6a slidably associated with a sliding belt 6b or the
like (FIGS. 4a-4c).
[0033] To guarantee processing precision, the device is equipped
with tensioning means (not illustrated) preferably operatively
located both upstream and downstream of the conveyor.
[0034] More preferably, the tensioning means define for the web 2
(at least partly) a feed unit 12 and a pickup unit 13,
respectively, associated with the conveyor 4.
[0035] The feed unit 12 is operatively located upstream of the
conveyor 4 to direct the web 2, that is, the feed path "P" thereof,
towards the conveyor at a predetermined entry angle.
[0036] Similarly, the pick-up unit 13 is operatively located
downstream of the conveyor 4 to pick up the web 2, that is, to
determine its feed path "P" on leaving the conveyor 4, at a
predetermined exit angle.
[0037] In order to cut the material, the device 1 also comprises a
laser cutting head 7, equipped with a laser source 7a configured to
generate a laser beam "F", and an optical system 7b configured to
direct the laser beam "F" towards the cutting zone "Z".
[0038] According to the invention, the optical system 7b of the
cutting head 7 comprises at least one directing member 8 located
inside the conveyor 4 to direct the laser beam "F" away from the
central axis "A" towards the cutting zone "Z".
[0039] In other words, the directing member 8 faces the concavity
defined by the conveyor 4. More precisely, the directing member 8
is located in the proximity of the central axis "A".
[0040] It should be noted that the directing member 8 is preferably
a mirror 8a or lens operatively associated with the laser source 7a
by a system of mirrors 9 or lenses.
[0041] In other words, the directing member 8 preferably defines an
end element of the cutting head 7 from which the laser beam "F" is
projected in the direction of the material to be cut.
[0042] The directing member 8 may also be constituted by a metallic
component made of molybdenum, aluminium or copper.
[0043] Advantageously, the possibility of moving a single directing
member 8 (that is, a single mirror 8a) located inside the conveyor
4 allows considerably reducing not only the dimensions of the
device but also the inertias involved during cutting.
[0044] In this regard, the directing member 8 is preferably
rotatable about its axis of rotation "B" and is oriented (or
orientable) in such a way that the laser beam "F" defines on the
web 2 a cutting line "T" transversal to the feed path "P" of the
web 2 itself.
[0045] More precisely, the directing member 8 is rotatable at least
between a first angular, start-of-cutting position "T1" and a
second angular, end-of-cutting position "T2".
[0046] Thus, the directing member 8 is mounted along an optical
path of the laser beam "F" to intercept and deflect it in the
direction of the cutting zone "Z" starting from the inside of the
conveyor 4 and away from the central axis "A".
[0047] In order to make a cut which is transversal to the feed path
"P" of the web 2 along the conveyor 4, the directing member 8 is
rotatable about its axis of rotation "B".
[0048] Advantageously, using the movement of the web 2 along its
longitudinal direction, imparted by the conveyor 4 (that is, along
the feed path "P"), it is sufficient for the directing member 8 to
be made to rotate about its axis of rotation "B" to obtain a cut
which is transversal to that direction and to easily control
cutting along both axes.
[0049] It should be noted that positioning the directing member 8
inside the conveyor 4 considerably reduces the change of distance
between the directing member 8 itself and the cutting zone Z,
thereby allowing a reduction in the movements of the components
and, consequently, in the stresses on the structure of the
device.
[0050] It should be noted that to allow correctly cutting the web 2
without impairing the structure of the device 1, the conveyor 4
(which constitutes a curved feed surface for the web 2), is
equipped at the cutting zone "Z", with at least one permeable
portion 4a permeable to the laser beam "F" and facing the directing
member 8, so as to allow the laser beam "F" to pass through the
feed surface.
[0051] In other words, the conveyor 4 is equipped with at least one
laser transparent portion shaped at least like the cutting line to
allow the laser beam "F" to pass from the inside of the conveyor 4,
in which the directing member 8 is situated, to the outside of the
conveyor 4, on which the web 2 rests (and thus constituting the
feed surface for the web 2).
[0052] More in detail, the permeable portion 4a made in the
conveyor 4 extends at least between one end, corresponding to the
first angular (or start-of-cutting) position "T1" of the directing
member 8, and a second end, corresponding to the second angular (or
end-of-cutting) position "T2" of the directing member 8.
[0053] Depending on the embodiment, the permeable portion 4a may
differ in structure and shape.
[0054] In the embodiment illustrated in FIG. 1, the permeable
portion 4a is defined by a through opening. More precisely, the
opening is a slot extending transversely to the feed path "P". More
precisely, in this embodiment (as in other preferred embodiments)
the slot extends in a direction substantially parallel to the
central axis "A".
[0055] Alternatively, the permeable portion 4a might be defined by
an insert or window which is transparent to the laser beam "F".
[0056] Provided below by way of example (non exhaustive) are some
lists of materials which can be used for this purpose, according to
the type of laser:
TABLE-US-00001 CO2 LASER: Barium fluoride BaF2 Zinc selenide ZnSe
Gallium arsenide GaAs Germanium Ge Cadmium telluride CdTe Cadmium
magnesium telluride CdMgTe Cadmium manganese mercury CdMnHgTe
telluride Cadmium manganese telluride CdMnTe Amorphous quartz SiO2
Potassium bromide KBr Potassium chloride KCl Silver bromide AgBr
Silver chloride AgCl Sodium chloride NaCl Thallium bromo-iodide
TlBr-TII DIODE: Barium fluoride BaF2 Zinc selenide ZnSe Gallium
arsenide GaAs Germanium Ge Cadmium magnesium telluride CdMgTe
Cadmium manganese mercury CdMnHgTe telluride Cadmium manganese
telluride CdMnTe Amorphous quartz SiO2 Potassium bromide KBr
Potassium chloride KCl Silver bromide AgBr Silver chloride AgCl
Sodium chloride NaCliBr Thallium bromo-iodide TlBr Borosilicate
glass BK-7 Calcium fluoride CaF2 Magnesium fluoride MgF2 Sapphire
Al2O3 QCL: Barium fluoride BaF2 Zinc selenide ZnSe Gallium arsenide
GaAs Germanium Ge Cadmium magnesium telluride CdMgTe Cadmium
manganese mercury CdMnHgTe telluride Cadmium manganese telluride
CdMnTe Amorphous quartz SiO2 Potassium bromide KBr Potassium
chloride KCl Silver bromide AgBr Silver chloride AgCl Sodium
chloride NaCliBr Thallium bromo-iodide TlBr Cadmium telluride CdTe
Calcium fluoride CaF2 Magnesium fluoride MgF2 Sapphire Al2O3
Silicon Si
[0057] In these embodiments, the device 1 preferably comprises
means for cleaning the insert or window, configured to remove the
dirt produced by the sublimation of the fibrous material (i.e. the
material of the web).
[0058] As mentioned previously, the directing member 8 is
preferably rotatable (or, in any case, movable) inside the conveyor
in order to direct the laser beam "F" along a predetermined
direction.
[0059] Preferably, the device 1 is equipped with motion
transmission means 9, of mechanical or electro-mechanical type,
operatively interposed between the movement means 3 and the
directing member 8 to correlate a movement of the movement means 3
along the feed path "P" with the rotation of the directing member 8
about its axis of rotation "B".
[0060] Advantageously, there is thus no need for a specific drive
for the cutting head 7, but it is possible to use only the rotation
of the conveyor 4 (or more in general, the advancing motion of the
movement means 3) to produce and control the movement of the
directing member 8.
[0061] Preferably, the transmission means 9 are defined by a system
of toothed wheels and/or belts (not illustrated).
[0062] Alternatively, the transmission means 9 might comprise a
galvo (electro-mechanical) system.
[0063] The galvo system comprises a limited-rotation DC motor to
drive the laser beam "F" directing member 8.
[0064] Preferably, an internal position sensor is provided for
closed-loop control of the motor by means of a signal proportional
to the rotation position of the motor shaft.
[0065] Advantageously, such a system allows digital control which
is rapid and modifiable remotely.
[0066] Alternatively, or in conjunction, the directing member 8
might be attached to the conveyor 4 in such a way as to rotate as
one therewith.
[0067] For example, in the embodiment shown in FIG. 1, the
directing member is attached to the drum 5 to rotate therewith
about the central axis "A", but also rotates about its own axis of
rotation "B" in order to make a cutting line "T" transversal to the
feed direction.
[0068] In this embodiment (FIG. 1), the optical system 7b of the
cutting head 7 comprises at least one focusing unit 10 operatively
located upstream of the directing member 8 and able to move
translationally in a straight line between a position close to the
directing member 8, where the focal point of the laser beam "F" is
distal from the directing member 8 itself, and a position away from
the directing member 8, where the focal point of the laser beam "F"
is proximal to the directing member 8 itself.
[0069] Advantageously, the linear movement of the focusing unit 10
allows compensating for variations in effective distance between
the directing member 8 and the cutting zone "Z".
[0070] In effect, in this embodiment, the conveyor 4 is defined by
a cylindrical drum 5 rotatable about its longitudinal axis,
defining the central axis "A". The directing member 8 is preferably
located at the central axis "A".
[0071] As mentioned above, in order to make a cut which is
transversal to the feed path "P" of the web 2, the directing member
8 rotates about an axis of rotation "B" which is transversal to the
central axis "A", thus, during cutting, varying its distance from
the cutting zone "Z" itself, that is, from the point on the web 2
where cutting occurs.
[0072] It should be noted that since the axis of rotation "B" is
incident upon the central axis "A" of the drum 5, the variation in
the distance between the directing member 8 and the cutting zone
"Z" during cutting is much more limited than in the prior art
(where cutting is effected from the outside of the conveyor).
[0073] In order to completely eliminate any axial movement of the
optical system 7b, the feed path "P" and the axis of rotation "B"
of the directing member 8 are preferably positioned (FIGS. 2, 3a,
3b, 4a-4c) in such a way that for each angular position of the
directing member 8 (at least between the first angular position
"T1" and the second "T2") a line joining the directing member 8
itself and the feed surface for the web 2 travelled by the laser
beam "F" is substantially constant.
[0074] More precisely, the movement means 3 and the directing
member 8 are positioned in such a way that for each angular
position of the directing member 8, the optical path followed by
the laser beam "F" between the directing member 8 and the feed
surface for the web 2 is substantially constant in length.
[0075] In other words, the feed means 3 (that is, the conveyor 4)
and the optical system 7b are structured in such a way that the
optical path of the laser beam "F" defines, between the first
angular position "T1" and the second "T2" of the directing member
8, a circular sector, that is, a portion of a circle (whose vertex
is preferably inside the directing member 8).
[0076] Advantageously, that way, the distance between the directing
member 8 and the cutting zone "Z" (that is, the feed surface for
the web 2) remains constant without having to adjust the focal
distance (and thus without the need for axial movements of the
optical system 7b).
[0077] In accordance with the above, in a first embodiment (FIGS.
3a-3c), where the conveyor 4 is again defined at least partly by a
cylindrical drum 5 rotatable about the central axis "A", the
cutting zone "Z" is defined on a peripheral surface 5a of the drum
5 itself.
[0078] In this embodiment, the directing member 8 is located at the
central axis "A" of the drum 5 and is oriented in such a way that,
between the first angular position "T1" and the second "T2" of the
directing member 8, the laser beam "F" remains in a plane at right
angles to the central axis "A".
[0079] Thus, the directing member 8 is rotatable about the central
axis "A".
[0080] In other words, in this embodiment, the directing member 8
(that is, the mirror) is positioned in such a way as to direct the
laser beam "F" in a plane of rotation of the drum 5.
[0081] Thus, the area subtended by the laser beam "F" between the
first angular position "T1" and the second "T2" of the directing
member 8 defines a circular sector in the same plane as a
transversal section of the drum 5.
[0082] In other words, the direction of rotation of the laser beam
"F" is substantially circumferential.
[0083] Preferably, also, the directing member 8 and the drum 5 are
rotatable as one about the same axis, corresponding to the central
axis "A".
[0084] Advantageously, that means there is no need for a mechanical
transmission operating between the movement means 3 and the
directing member 8. In effect, in this embodiment, the transmission
means 9 are defined by a rigid coupling between the directing
member 8 and the drum 5.
[0085] In order to make a cut which is transversal to the feed
direction of the web 2, the movement means 3 are structured in such
a way as to direct the feed path "P" of the web 2 around the drum 5
along a partly helicoidal line. Thus, the web 2 forms a tie around
the drum 5.
[0086] More precisely, the feed unit 12 and the pick-up unit 13 of
the movement means 3 are structured in such a way as to direct the
web 2 (that is, the feed path "P") towards the drum 5 or to pick up
the web 2 from the drum 5 at an entry angle and an exit angle
substantially at right angles to the central axis "A".
[0087] The feed path "P" going in, however, is offset (that is,
shifted) along the central axis "A" relative to the feed path going
out.
[0088] Preferably, the extent of the shift is equal to the width of
the web 2.
[0089] Thus, the drum 5 is structured to divert the feed path "P"
along a helicoid until reaching a web release zone.
[0090] In other words, the drum 5 defines a guide shaped to divert
the feed path "P" of the web 2 around the drum 5 itself along a
portion of a helicoid extending for approximately 180.degree..
[0091] Advantageously, it is thus the web 2 which moves
transversely relative to the laser beam "F", allowing a transversal
cut to be made.
[0092] Also, in this embodiment, all the movements of the directing
member (except for rotation as one with the drum 5) are eliminated,
with considerable advantages in terms of costs and simplicity of
design.
[0093] Also, in this embodiment, the laser beam "F" remains at all
times at right angles to the cutting zone "Z", that is, to the web
2 to be cut, thus increasing process efficiency.
[0094] Preferably, the larger the entry (and exit) angle of the
feed path "P" is, the smaller the circular sector "swept" (that is,
covered) by the laser beam "F" between the first angular position
"T1" and the second "T2" of the directing member 8.
[0095] In an alternative embodiment (FIG. 2), the constancy of the
optical path travelled by the laser beam "F" between the directing
member 8 and the cutting zone "Z" is obtained by curving the
lateral surface of the drum 5.
[0096] More precisely, in some embodiments, the lateral surface of
the drum 5, which constitutes a sliding surface for the web 2 (as
well as the cutting zone "Z") has an at least partly spherical
shape, where the directing member 8 is located at the centre of the
sphere in such a way as to remain equidistant from all points of
the cutting zone "Z".
[0097] It should be noted that the drum 5 can be connected
removably to the conveyor 4. In other words, the drum 5 can be
substituted for another of a different shape according to
requirements.
[0098] The spherical surface may be obtained by keying an annular
insert (at least partly spherical) on the drum 5, or by shaping the
surface of the drum 5.
[0099] In this embodiment, the directing member 8 has,
advantageously associated with it, motion transmission means
configured to impart to it rotational motion about at least two,
preferably three, axes at right angles to each other, thereby
allowing complete freedom in the movement of the laser beam "F"
(and thus in the geometry of the part to be made).
[0100] In a further embodiment (FIGS. 4a-4c), the conveyor 4 has a
semi-elliptic guide 6a extending at least partly around the central
axis "A" and a belt 6b slidable on the semi-elliptic guide 6a.
[0101] In other words, the semi-elliptic guide 6a defines for the
web 2 a feed path "P" curved around the central axis "A".
[0102] This feed path "P" along the semi-elliptic guide 6a defines
an elliptic line of movement.
[0103] It should be noted that the guide 6a is positioned around
the central axis "A" but remains fixed relative thereto. In effect,
it is the belt 6b which slides along the guide, taking the material
to be cut, that is, the web 2, along with it.
[0104] In this embodiment, the directing member 8 is rotatable
about its axis of rotation "B", which is incident at an angle
".alpha." on the central axis "A".
[0105] More specifically, the value of the angle ".alpha." is such
that for each angular position of the directing member 8, the laser
beam "F" intercepts a point on the semi-elliptic guide 6a located
at the same predetermined distance from the directing member 8
itself.
[0106] In other words, since the guide 6a has an elliptic shape,
the distance between the directing member 8 and the guide 6a,
measured in a plane at right angles to the central axis "A" varies
with changes in the angular position.
[0107] However, the presence of an angle ".alpha." between the axis
of rotation "B" of the directing member 8 and the central axis "A"
allows the laser beam "F" to rotate in a cutting plane which is
inclined at an angle to the central axis "A" and which, together
with the guide 6a, defines a circle.
[0108] It should be noted that the value of the angle ".alpha." is
a function of the eccentricity of the semi-elliptic guide 6a.
[0109] More precisely, the angle ".alpha." of inclination of the
axis of rotation "B" of the directing member 8 can be calculated
using the following relation:
a=arcsin(e)
where "e" is the eccentricity of the guide 6a.
[0110] Advantageously, that way, the area subtended by the laser
beam "F" between the first angular position "T1" and the second
"T2" of the directing member 8, measured in a plane at right angles
to the axis of rotation "B" of the directing member 8 itself,
defines a circular sector perimetrically delimited by the
semi-elliptic guide 6a.
[0111] The invention achieves the preset aims and brings important
advantages.
[0112] In effect, the use of a directing member, that is, a mirror,
mounted inside the conveyor, be it a drum or a curved guide, allows
compacting the dimensions of the machine and cutting device and
reducing the need to move the directing member itself.
[0113] In effect, whatever the embodiment, any variation in the
distance between the directing member and the cutting zone, during
the rotation of the directing member itself, is considerably
reduced compared to the situation of the prior art, where the
directing member was mounted outside the drum.
[0114] Moreover, linking the structure of the conveyor and of the
movement means to the rotation of the directing member makes it
possible to keep such distance unchanged during the entire cutting
operation, that is to say, between the first and the second angular
position of the directing member.
[0115] Thus, thanks to these solutions, the driving movement of the
optical system and, in particular, of the directing member, is
greatly reduced, if not substantially cancelled, with considerable
advantages in terms of operating speed and limiting the inertias
involved.
[0116] Furthermore, by combining the cylindrical shape of the drum,
the tie feed system and the rotation of the directing member as one
with the selfsame drum, it is possible to keep the laser beam at
right angles to the cutting surface, that is, to the web, at all
times, with considerable advantages in terms of process efficiency
and efficacy.
* * * * *