Technical Field
[0001] The present invention relates to marking of a continuous strip or web, preferably
of metal. More specifically, the invention relates to a device for guiding such a
strip past a marking unit that is arranged to provide the strip with markings.
[0002] The present invention is especially useful in an arrangement for manufacture of marked
articles to be included cans, in particular beverage cans. Therefore, the technical
background of the invention, and objects and embodiments thereof, will be described
with reference to such an arrangement. However, the invention may also be applicable
in connection with marking of other articles formed from a continuous strip.
Background Art
[0003] In many situations, there is a need for indicative markings on a product, for example,
traceability markings indicating the origin of the product, or promotional markings.
Such indicative markings can be provided by non-mechanical, i.e. non-contact, marking
techniques, such as laser engraving or ink jet printing. These noncontact techniques
provide for flexibility in production and high production speeds. Often, the markings
must be precisely located in a specific area of the product. To this end, the marking
equipment must be accurately controlled in providing the markings. Further, the material
to be marked must be carefully positioned during the marking process. This is often
inconsistent with high production speeds.
[0004] One area with a need for high production speeds is the beverage can industry, for
example in the production of can ends. Typically, a production line for can ends has
a capacity of 2,000 ends per minute. A conventional production line is disclosed in
a brochure entitled "This is PLM Fosie" issued by Applicant's Swedish company PLM
Fosie AB in the mid nineties. In a first production stage of such a production line,
a thin metal strip, preferably a 0.23-mm-thick aluminium strip, is indexed into a
tab forming unit in which the strip is punched and stamped to form opening tabs or
opener rings integrated with the strip. In a second production stage, circular shells
for forming the can ends are die cut from a thin metal sheet, preferably a 0.23-mm-thick
aluminium sheet. Each shell is scored for opening, and a rivet for attachment of the
tab is formed at the center of the shell. In a third production stage, the strip with
the integrated tabs is joined with the circular shells in an attachment station, in
which the tabs are separated from the strip and attached to the shells by riveting.
A finished can end is achieved when the tab is fastened to the shell.
[0005] There is need for indicative markings on the tabs. Such markings could be provided
by marking the strip before it is fed into the tab forming unit, in which the thus-marked
strip is formed into marked tabs. However, due to the indexing motion of the strip
into the tab forming unit, the strip will swing and jump in all directions on its
way to the tab forming unit. Thus, to control the position of the strip, a guiding
device should be arranged in the area of the marking operation. This guiding device
should allow for careful positioning of the strip, but should not interfere with the
intermittent progression of the strip into the tab forming unit. Also, stretching
of the strip should be avoided, and friction should be minimized. Typically, the strip
should be positioned with a precision of at least about 5-15 µm in the lateral, or
transverse, direction, when providing markings on the surface of the tabs. The vertical
position of the strip should also be carefully controlled within the focal region
of marking equipment, typically with a precision of at least about 0.1-0.2 mm.
Summary of the Invention
[0006] The object of the invention is to at least partly fulfil the above identified needs.
[0007] This object is achieved by a guiding device and an arrangement according to the appended
independent claims. Preferred embodiments are defined in the dependent claims.
[0008] In the inventive device, by one or more guiding elements being pressed against the
strip from at least one side of the channel, the strip can be positioned with high-precision
without being subjected to excessive frictional forces during the marking operation.
Thus, the inventive device does not significantly interfere with the motion of the
strip.
[0009] According one preferred embodiment, the guiding element has a surface portion to
be pressed against the strip, and a shoulder portion adjacent to the surface portion
for guiding the strip in the channel. This guiding element performs the dual functions
of applying stabilizing forces in the lateral or the vertical direction and guiding
the strip in the longitudinal direction. Preferably, the surface portion and the shoulder
are located on a freely rotatable body.
[0010] In a further preferred embodiment, the guiding elements are arranged to be pressed
against the opposite longitudinal edges of the strip. This will minimize the bearing
surfaces between the guiding elements and the strip, to further reduce friction. Preferably,
each guiding element comprises a freely rotatable body having a cylindrical portion
for abutment against the longitudinal edges, so that both friction and wear can be
minimized. It is also preferred that the rotatable body comprises a circumferential
shoulder adjacent to the cylindrical portion for guiding the strip in the channel.
Preferably, the shoulder is arranged to guide a portion of one of the upper and lower
surfaces adjacent to the longitudinal edges. This guiding element is compact and capable
of controlling the position of the strip in both the vertical and the lateral direction.
[0011] In a further preferred embodiment, the guiding device comprises an intake and an
outlet assembly, each including first and second intake rollers which receive the
strip and abuttingly engage the upper and lower surfaces thereof, respectively. Such
an assembly will isolate the strip portion in the channel from twisting and tugging
motions in the strip fed to and from the guiding device.
Brief Description of the Drawings
[0012] A presently preferred embodiment of the invention will now be described in more detail,
reference being made to the accompanying schematic drawings.
[0013] Fig. 1 is a side view of a laser engraving apparatus in a system for manufacturing
opening tabs for can ends, the laser engraving apparatus including a guiding device
according to the invention.
[0014] Fig. 2 is a plan view of a portion of a metal strip provided with indicative markings.
[0015] Fig. 3 is a bottom view of a tab having markings on its bottom surface.
[0016] Fig. 4 is a plan view of a strip guiding device according to a preferred embodiment
of the invention.
[0017] Fig. 5 is a cross-sectional view taken along the line V-V in Fig. 4.
[0018] Fig. 6 is an end view taken in the direction of the arrows VI-VI in Fig. 4.
[0019] Fig. 7 is an end view taken in the direction of the arrows VII-VII in Fig. 4.
[0020] Figs 8a-8d illustrate alternative embodiments.
Description of Preferred Embodiments
[0021] Fig. 1 shows part of an arrangement for manufacture of marked opener rings or tabs
T (Figs 2-3) to be included in ends for beverage cans (not shown). A blank in the
form of a thin, continuous metal strip S is fed from a supply 1 to a laser unit 2
supported by a supporting member 3. The laser unit 2 is of a high-power and highspeed
type and is capable of providing laser engraved markings in the surface of the strip
S. The laser unit 2 is adapted to generate laser radiation at a suitable wavelength,
and to focus and direct the generated radiation to an engraving area on the surface
of the strip S. After the engraving operation in the engraving area, the strip S is
fed to an adjacent tab forming apparatus 4 which is of a type known per se and which
forms tabs by punching and stamping the strip S. When passing the laser unit 2, the
strip S is guided by a guiding unit 5 secured to the supporting member 3. Further,
a dust protection device 6 is connected to the laser unit 2 to protect the laser unit
2 from dust or debris produced during the engraving operation.
[0022] Fig. 2 shows a portion of the strip S after the laser engraving operation at the
laser unit 2, but before the punching and stamping operation in the tab forming apparatus
4. The laser unit 2 has provided the engraved markings WIN, A, 8, 9 on one surface
of the strip S. The approximate periphery of the tab T to be produced in the following
tab forming steps in the apparatus 4 has been indicated with ghost lines in Fig. 2.
In practice, the size of the laser engraved markings is about 1.4 x 1.2 mm which makes
them easily readable. In Fig. 3, the final tab T is shown from below after processing
in the tab forming apparatus 4. The markings WIN, A, 9, 8 are now precisely located
on a respective tab surface, in this case intermediate an opening T1 and peripheral
edge portions T2, T3, T4 of the tab T.
[0023] Figs 4-7 shows in some detail a preferred embodiment of the strip guiding device
5. The device 5 comprises a main block 200, an intake mechanism 210, a guiding channel
220, and an outlet mechanism 240.
[0024] The intake mechanism 210 includes an upper and a lower intake roller 211, 212, each
comprising a spindle 213, 214 having a number of cylindrical, laterally spaced radial
projections 215, 216. The intake rollers 211, 212 are arranged to receive the strip
S with the projections 215, 216 abuttingly engaging the upper and lower surfaces of
the strip S, respectively. Each spindle 213, 214 is mounted in the main block 200
for free rotation therein. The clearance between the projections 215, 216 corresponds
to the thickness of the strip S with nearly zero tolerance, in order to avoid a twisting
motion of the incoming strip S being transmitted to the strip portion received in
the guiding channel 220. The lower spindle 214 is provided with guiding shoulders
217, 218 with a mutual distance essentially corresponding to the width of the strip
S, typically with a tolerance of about 0.5 mm.
[0025] In an alternative embodiment (not shown), the clearance between the projections 215,
216 is adjustable to accommodate strips of different thickness. Preferably, the upper
intake roller 211 is adjustable in the vertical direction, while the lower intake
roller 212 is fixed to remain level with the guiding path in the subsequent channel
220. The upper intake roller 211 could be adjusted by means of an eccentric mechanism
(not shown) or be spring-biased towards the lower intake roller 212.
[0026] Returning to the embodiment of Figs 4-7, the guiding channel 220 is defined by a
guiding shoe 221, a number of guiding elements 222, 222' arranged in pairs on both
sides of the channel 220 in the longitudinal direction, and a guiding cover 223. The
distance between the guiding shoe 221 and the guiding cover 223 is such that the strip
S can move essentially without interference. The guiding shoe 221 will guide the front
end of the strip S in proper place on entering the intake mechanism 210. An opening
or window 224 is defined in the cover 223 so that one surface of the strip S is accessible
for engraving by means of the laser unit 2.
[0027] The guiding elements 222 on a first side of the channel 220 are mounted for rotation
at a fixed location in the main block 220, whereas the guiding elements 222' on a
second, opposite side of the channel 220 are mounted for both rotation and lateral
displacement in the main block 200. Each guiding element 222, 222' comprises a rotatable
guiding roller 225 which has a cylindrical portion with a circumferential surface
226 for abutment on the longitudinal edges of the strip S and an adjacent circumferential
shoulder 227 for defining the guiding path of the strip S in the vertical direction.
Thus, a small portion of the strip surface will be carried on the shoulders 227.
[0028] The displaceable guiding elements 222' further comprises a mounting block 228, which
receives the guiding roller 225 and is displaceably arranged on a common pin 229 extending
in the longitudinal direction of the guiding device 5. Spring-biased pusher arrangements
230 are arranged to urge the guiding elements 222' towards the first side of the channel
220. Before the strip S enters the channel 220, the guiding elements 222' are pressed
onto the guiding shoe 221, which has a slightly smaller width than the strip S. On
entering the channel 220, the strip S will displace the guiding elements 222' against
the biasing action of the pusher arrangements 230, thereby locating the strip S in
the lateral direction. Typically, the mounting block 228 allows for a movement of
±3 mm in the lateral direction. As an alternative (not shown), all guiding elements
222, 222' can be displaceable and biased towards the center of the channel 220.
[0029] The components of the outlet mechanism 240 are illustrated in Figs 4, 5 and 7, and
are identified by reference numerals 241-248 corresponding to reference numerals 211-218
of the identical intake mechanism 210. The above description of the intake mechanism
210 is equally applicable to the outlet mechanism 240 and will not be repeated.
[0030] The strip guiding device 5 as described above and shown in Figs 4-7 forms a self-adjusting
system for careful positioning of the strip S during the laser engraving operation,
independently of the subsequent tab forming unit 4. The strip S will move in a defined
path through the guiding device 5, the path being delimited in the vertical direction
by the guiding shoulders 227, and to some extent by the guiding shoe 221 and the guiding
cover 223. In the lateral direction, the path is delimited by the circumferential
surfaces 226 abutting against the longitudinal edges of the strip S. The intake and
outlet mechanisms 210, 240 has the ability of precluding any twisting motion from
being transferred to the strip portion in the marking area defined by the window 224.
[0031] In the illustrated preferred embodiment, the strip S is only subjected to guiding
forces at its longitudinal edges. Therefore, friction is minimal between the guiding
device 5 and the strip S, and the indexing movement of the strip S is essentially
undisturbed. In fact, tests show that the illustrated guiding device 5 improves the
operation of the subsequent tab forming unit 4 by eliminating twitches and tugs in
the strip S.
[0032] Friction in the guiding device 5 is also minimized by making the guiding elements
222, 222' freely rotatable, thereby eliminating any sliding friction between the strip
S and the guiding elements 222, 222'. This also improves the service life of the device
5. Further, by applying the guiding forces on the longitudinal edges of the strip
S, the area of the strip surface accessible for marking is maximized.
[0033] An alternative, simplified embodiment is shown in the plan view of Fig 8a. Here,
the guiding elements 222, 222' are provided in the form of blocks or wall portions.
Either one, or both, of the guiding elements 222, 222' is displaceable and biased
onto a longitudinal edge of the strip S. Although not shown on the drawing, each of
the guiding elements 222, 222' is preferably provided with a guiding shoulder carrying
the strip S in a defined path through the channel 220.
[0034] The plan view of Fig. 8b shows another alternative embodiment, which is a combination
of the embodiment shown in Figs 4-7 and the one shown in Fig 8a. Each of the guiding
elements 222', and/or the guiding element 222, is biased to abut on a longitudinal
edge of the strip S.
[0035] In a further alternative embodiment, shown in the plan view of Fig. 8c and the side
view of Fig. 8d, guiding elements 222, 222' are arranged in pairs and biased (as indicated
by arrows in fig. 8d) to abut on the strip surface from opposite sides of the strip
S in the channel 220. The guiding elements 222, 222' comprise a freely rotating body
with a circumferential surface 226 for abutment on the surface of the strip S. One
guiding element 222' in each pair has a guiding shoulder 227 adjacent to the surface
226. Thus, the surfaces 226 are pressed against the strip surface, thereby defining
the path of the strip S in the vertical direction, whereas the shoulders 227 define
the path in the longitudinal direction. Compared to the embodiment of Figs 4-7, the
bearing surface of the guiding elements 222, 222' on the strip S is increased, and
consequently friction is increased as well. Further, a larger portion of the strip
surface will be blocked by the guiding elements 222, 222', thereby also reducing the
strip surface accessible for marking.
[0036] Finally, it should be emphasized that the invention by no means is restricted to
the embodiments described in the foregoing, and modifications are feasible within
the scope of the appended claims. For example, to allow for marking of both sides
of the strip S, the guiding shoe 221 could be substituted for a cover similar to the
guiding cover 223.
[0037] Although the invention is described in connection to laser engraving equipment, it
may also be applicable in connection with equipment for any other type of nonmechanical
marking, such as ink jet printing.
1. A device for guiding a continuous strip (S) past a marking unit (2), said strip (S)
having two opposite longitudinal edges and an upper and a lower surface, said marking
unit (2) being arranged to non-mechanically provide said strip (S) with markings on
at least one of said surfaces, said device comprising a longitudinal channel (220)
for receiving said strip (S), the channel (220) being at least partly defined by guiding
elements (222, 222') which are arranged for abutment against the strip (S) from opposite
sides of the channel (220), wherein at least one of the guiding elements (222, 222')
is displaceable and biased towards the channel (220).
2. A device as set forth in claim 1, wherein said guiding element (222, 222') has a surface
portion (226) to be pressed against said strip (S), and a shoulder portion (227) adjacent
to said surface portion (226) for guiding said strip (S) in said channel (220).
3. A device as set forth in claim 2, wherein said surface portion (226) and said shoulder
(227) are located on a freely rotatable body.
4. A device as set forth in any one of claims 1-3, wherein said guiding elements (222,
222') are arranged to be pressed against said opposite longitudinal edges of the strip
(S).
5. A device as set forth in claim 1, wherein each guiding element (222, 222') comprises
a freely rotatable body (225) having a cylindrical portion for abutment against said
opposite longitudinal edges of the strip (S) .
6. A device as set forth in claim 5, wherein said rotatable body (225) further comprises
a circumferential shoulder (227) adjacent to said cylindrical portion for guiding
said strip (S) in said channel (220).
7. A device as set forth in claim 6, wherein said shoulder (227) is arranged to guide
a portion of one of said upper and lower surfaces adjacent to said longitudinal edges
of the strip (S).
8. A device as set forth in any one of claims 5-7, wherein each of said displaceable
guiding elements comprises a mounting block (228), which receives at least one of
said rotatable bodies (205) and is biased towards the channel (220).
9. A device as set forth in claim 8, wherein said mounting blocks (228) are arranged
for displacement on a common rod element (229) extending in a longitudinal direction
of the guiding device.
10. A device as set forth in any one of claims 1-9, wherein the channel (220) is further
defined by at least one cover element (221) which is arranged between the guiding
elements (222, 222') to provide a small clearance with respect to one of said upper
and lower surfaces of the strip (S).
11. A device as set forth in claim 10, wherein the cover element (221) defines an opening
(224) allowing the marking unit (2) to provide markings on said one surface of the
strip (S).
12. A device as set forth in any one of claims 1-9, comprising two cover elements (221,
223) which are arranged to at least partly define said channel (220), the distance
between the cover elements (221, 223) being such that the strip (S) can move essentially
without interference in said channel (220).
13. A device as set forth in claim 12, wherein an opening (224) is defined in at least
one of said cover elements (221, 223) allowing the marking unit to provide markings
on at least one of said surfaces of the strip (S) .
14. A device as set forth in any one of claims 1-13, further comprising an intake assembly
(210) which includes first and second intake rollers (211, 212) which are arranged
to receive the strip (S) and abuttingly engage the upper and lower surfaces thereof,
respectively.
15. A device as set forth in claim 14, wherein each intake roller (211, 212) is mounted
in a supporting structure (200) for free rotation therein.
16. A device as set forth in claim 14 or 15, wherein a clearance is defined between the
intake rollers (211, 212), said clearance corresponding with essentially zero tolerance
to the distance between the upper and lower surfaces of the strip (S).
17. A device as set forth in any one of claims 14-16, wherein each intake roller (211,
212) comprises a spindle (213, 214) having cylindrical, laterally spaced radial projections
(215, 216), the projections (215, 216) being arranged to abuttingly engage the upper
and lower surfaces of the strip (S), respectively.
18. A device as set forth in claim 17, wherein one of said spindles (213, 214) is provided
with guiding shoulders (217, 218) having a mutual distance that essentially corresponds
to a distance between the longitudinal edges of the strip (S).
19. A device as set forth in any one of claims 1-18, further comprising an outlet assembly
(240) which includes first and second outlet rollers (241, 242) which are arranged
to receive the strip (S) and abuttingly engage the upper and lower surfaces thereof,
respectively.
20. A device as set forth in claim 19, wherein each outlet roller (241, 242) is mounted
in a supporting structure (200) for free rotation therein.
21. A device as set forth in claim 19 or 20, wherein a clearance is defined between the
outlet rollers (241, 242), said clearance corresponding with essentially zero tolerance
to the distance between the upper and lower surfaces of the strip (S).
22. A device as set forth in any one of claims 19-21, wherein each outlet roller (241,
242) comprises a spindle (243, 244) having cylindrical, laterally spaced radial projections
(245, 246), the projections (245, 246) being arranged to abuttingly engage the upper
and lower surfaces of the strip (S), respectively.
23. A device as set forth in claim 22, wherein one of said spindles (243, 244) is provided
with guiding shoulders (247, 248) having a mutual distance that essentially corresponds
to a distance between the longitudinal edges of the strip (S).
24. An arrangement for shaping and marking a continuous strip (S) of metal, comprising
a marking unit which non-mechanically provides said strip (S) with markings on at
least one of said surfaces, a processing apparatus (4) which mechanically shapes the
thus-marked strip (S) into marked articles (T), and a guiding device (5) according
to any one of the preceding claims.