CA1145173A - Apparatus for generating pulsed light beams - Google Patents

Abstract

582=899A

LIGHT ENERGY PERFORATION
APPARATUS AND SYSTEM
ABSTRACT

Apparatus for generating pulsed light beams from a focused continuous laser beam includes reflector discs which are rotated about a common rotational axis. The discs include peripheral reflective facets which confront the laser beam in the course of rotation and also have light transmissive por-tions between adjacent facets. The facets and transmissive portions of successive discs are selectively misaligned such that pulsed beams issue successively from different discs. A
system employing the apparatus for perforation of a web also includes a common lens per disc pair and a prism for deviating light issuing from one disc of the disc pair.

Description

11~5173 1 This invention relates genPrally to perforating material by the use of light energy and pertains more part-icularly to apparatus and systems providing spatially precise matrices of perforations in sheet material.
In perforating sheet material, a two-dimensional hole matrix is frequently sought with rigorous limits on per-foration spacing uniformity as between rows and columns of the matrix. An illustrative field of current interest is that of perforating cigarette filter tipping paper, where h~e matrix 1~ unlformity enables consistency of cigarette dilution charac-ter~stics. In various known mechanical puncture and electric arc perforating practices, row spacing is rendered precise by providing an individual perforating device for each row. Uni-formity in the spacing of perforations made in each row, and hence precise column spacing is achieved by synchronizing op-eration of each perforating device. Since the perforating devices, e.g., pin or electrode pair, are physically limited in size, these practices can readily accommodate quite close spacing of adjacent rows of the matrix.
2U The prior art has also encompassed perforating prac-tices involving lasers providing pulsed or continuous light I ;
energy in row-column perforation. In these efforts, however, t~ere generally has been an apparent preference, for economic `
and physical size reasons, for use of a single laser serving ~oth row and column perforation. Rnown single laser prac-tices of type affording spacing uniformity have involved the splltting of the laser beam into plural ~eams, one for each rowl and the focusing of light onto a sheet member by use of It .

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~5~73 1 an individual lens for each row. Spacing of perforations by precise limits within each row has been sought by inclusion of a movable reflective element in each of the plural beam paths. Complexity attends precision movement, e.g., vibra-tion or pivoting, of such reflective element into and out of its reference plane, to uniformly locate holes in rows, and the present state of the art is accordingly limited.
The present invention has, as its primary object, the provision of improved apparatus and systems f'or perfor-ating sheet material by the use of light energy.
A more particular object of the invention is toprovide for expeditious perforation of cigarette filter tipping paper by laser.
In attàining these and other objects, the invention provides apparatus for generating pulsed light beams from a continuous light beam, the apparatus including a lens for focusing the continuous beam and one or more light reflective devices supported for rotation and having a plurality of light reflectors disposed in a circular locus and mutually spaced by light transmissive portions. In the course of rotation, the reflectors confront the focused beam whereby light pulses are issued. The reflectors of one such reflec-tive device are aligned with light transmissive portions of other participating reflective devices, and vice versa, such that the light pulses issue successively, or in other pattern, from the participating reflective devices.

` ~1 51'73 In perforating systems of the ~nvention, light pulses issuing from each pair of participating reflective devices are received by a common focusing lens, wi`th a prism or like light deviating member disposed between one of the devices and such common focusing lens to provide for adjacent rows of uniformly spaced perforations in a web or like perforatable member.

In accordance with a broad aspect, the invention relates to apparatus for generation of pulsed light beams from a continous light beam, comprising:
(a) lens means f-or receiving said continuous light beam and issuing a focused continuous beamL
(b) first reflective means arranged to receive said focused continuous beam and supported for rotation about a preselected rotational axis;
(1) having light reflective facets mutually spaced in a circular locus about the periphery of said disc to confront said focused continuous beam indivi-dually in the course of rotation of said first disc; all such light reflective facets being disposed in mutually identical first attitude with respect to said rotational axis, and ~2) having apertures between adjacent such light re-flective elements to define light transmissive portions; and (c) second reflective means disposed mutually conti-gously with said first reflective means, said second reflective means including a second reflective disc having light reflective facets mutually spaced in a circular locus about the periphery of said second disc to confront said focused continuous beam indivi-dually in the course of rotation of said second disc, said light reflective facets of said second disc all ,.,,,~

~S173 being disposed in mutually identical second attitude diverse from said first attitude with respect to said rotational axis, said second disc further having apertures between adjacent such light reflective facets defining reflective portions, said light reflective facets and said second disc being in alignment respectively with said apertures and said light reflective ~acets of said first disc, whereby first and second ~ pulsed light beams issue successively alternately from said first and second discs;
(d) common focusing means for receiving said first and second pulsed light beams issuing from said first and second discs and focusing said pulsed beams at first and second spaced locations; and (e) light deviating means disposed between said second disc and said common focusing means for controlling the path of said second beam to said common focusing means, and thereby said second location relative to said first location.

The foregoing and other objects and features of the invention will be further understood from the following de-tailed description of preferred methods and systems and from the drawings wherein like reference numerals identify like parts throughout.
Fig. 1 is a block diagrammatic showing of a pre-ferred system embodiment.
Fig. 2 is a perspective view of the reflective discs of Fig. 1, the discs being shown side-by-side for purposes of explanation.

Fig. 3 is an optical diagram applicable to the Fig.
1 system.
Fig. 4 is an optical diagram applicable to the .^ Fig. 1 system as expanded to include additional reflective discs. ~
_ 3~_ 5~73 Fig. 5 is a plan elevation of such expanded system.

Fig. 6 shows the respective configurations of the xeflective discs of the expanded system.
Fig. 7 is a geometric drawing explanatory of perforating activities with the expanded system set as in Fig. 5.
Referring to Fig. 1, a web 10 of sheet material is collected by take-up drum 12 following horiæontal transport from a payout drum, not shown. Take-up drum 12 is rotated by 3b -.

ll~S173 1 drive unit 14 with drum speed being established by a control signal provided on line 16 as furnished by potentiometer 18 or like settable device. A further control signal, derived on line 20 from potentiometer 22 controls drive unit 24 of light-reflector assembly 26, which comprises shaft 28, rotated by drive unit 24 and light-reflective discs 30 and 32 keyed to shaft 28 for rotation therewith.
Laser 34 generates a continuous output beam ~6 which is focused by lens 38 at a location adjacent discs 30 and 32.
Light beams reflected ~y the discs are conducted by a common focus~ng element, shown as lens 40, to web 10.
~ ig. 2 shows in side-by-side perspective disc 30 and disc 32, as the latter would be seen rightwardly of disc 30 in Fig. 1. T~e discs are keyed to shaft 28 in position wherein lines 42 and 44 are in common plane with shaft axis 46. In the illustrative embodiment wherein two discs are used and are intended to confront beam 36 (Fig.l) alternately, the discs have light-transmissive uniformly spaced peripheral por-tions 48 and 50 which are mutualiy staggered, defining reflec-tive facets 52 and 54 therebetween. Forty-five such facets are typically employed with each facet subtending four degrees of arc ~angles 56 and 58) and each transmissive portion also subtending four degrees o~ arc (angles 60 and 62). With transimissive portion 48a having its leading edge aligned with line 42 and transmissive portion 50a spaced from line 44 b-~ ~acet angle 58, the discs are properly aligned for alter-nate reflectron of the laser beam, the beam passing through tXansmiss~ve portlon 48a to be reflected by the facet clock-~-~se of transmissive portion 50a. The light-transmissive ll.1 ~5~7;3 1 portions are typically opening in the discs of size sufficient to freely pass the laser beam. While disc 32 might be con-structe`dwith no light-transmissive portions since it is the last disc from the laser, the described construction mitigates against spurious reflection of the laser output beam by disc 32 during confrontation of facets of disc 30 with the laser beam, i.e., laser output beam spillage beyond disc 30 simply passes through disc 32 openings. In this respect, such beam spillage may be desired in applications wherein different spacing lengths are required in adjacent rows and beam usage is not strictly alternate as in the practice under discussion.
Referring to Fig. 3, each confrontation of a facet of disc 30 with beam 36 will give rise to the propagation of a modified version of the laser output beam, such modified beam being shown at 64 and having central axis 64a, which is incident on lens 40 at angle set by the selected orientation of disc 30. Beam 64 has outer rays 64b and 64c, which diverge respectively oppositely from ~eam central axis 64a. Where ~eam 36 converges and then di~erges between discs 30 and 32, ~o the beam is then con~ergent as to disc 30, and modified beam 64 will be convergent at the outset and then divergent.
Lens 40 also has within its fiald of view, through prism 33, the facets of disc 32 and hence collects further modified versions o laser output beam 36 on each confronta-: tion of a facet of disc 32 with beam 36. Such fur~her modi-fied beam 66, as it issues from disc 32, has central axis 66a and divergent outer rays 66b and 66c.
In copending, commonly-assigned application Serial No.329,184, filed onJune 6/79 and entitled "Method and Appar-3U atus for Perforation of Sheet Material by Laser", all reflec-11~5~73 1 tive discs couterpart to discs 30 and 32 herein have theirreflective facets disposed at one identical attitude with respect to the axis of rotation thereof. Accordingly, beams counterpart to beams 64 and 66 herein issuing from such counterpart discs are each inclusive of an axis of symmetry parallel to the optical axis ~axis 40a) of the common focusing element. Based on optical considerations discussed in said copending application, such counterpart beams thereof are processed directly by such common focusing element without 1~ other intervening optics.
In contrast to the disc structure and practice of such copending application, system use herein of the apparatus for generation of pulsed light beams involves diverse attitudes for the facets of different discs and the use of intervening optics. Referring to Fig. 3, surface 30a of disc 30 is fully planar across t~e diameter of the disc. Surface 32a of disc 32 is ~eveled at t~e disc periphery. Thus, the facets of disc 30 are each at first identical attitude with respect to the disc rotational axis and the facets of disc 32 are each at second ldentical attitude, aiverse from such first attitude, with respect to such rotational axis.
Beam 64 is collected airectly by lens 4U and focused at locatlon ~8. ~eam 66 is incident o~ prism 33, and upon de~iation by the prism is focused at location 7U, both such locations being outward of focal plane FP40 of lens 40. In its functlon, prism ~3 confronts beam 66 and modifies the place and angle of incidence of the beam on lens 40, effectively dis-placing beam lncidence place rightwardly in Fig. 3, from that ;bta~ning if beam 6~ were directly applied to the lens, and ~ 5~73 accordingly controlling the position of location 70. For var~able control of the position of location 70, the prism is cemented as at 33a to ring 35, which is supported for rotation about the ring axis~ Locations 68 and 70 may accordingly be arranged to be in juxtaposition ~ith a plane through which web 10 is conveyed, thereby to effect perforations therein.
Beam axis 36a and shaft 28 are positioned at a common acute angle to the Fig. 3 plane and lens 40 and prism 33 are moved throu~h such angle outwardly of the Fig. 3 plane into registry with discs 30 and 32. Web 10 has a marginal edge co-inciding with the Fig~ 3 plane~ Operation of the system then gives rise to a first ro~ of perforations created by modified beam 64 at locations 68 and a second perforation row spaced therefrom and created by modified beam 66 at locations 70. Such practice will be understood further by detailed consideration of an expanded syste~ embodiment, shown and explained in Figs.
4-.7~
In Fig~ 4, four reflective discs, 30~. 32', 72 and 74, are spa.ced along shaft 28 by spacer 76.. An additional prism is s~bwn at 78 and a further focus~ng element for modified beams is ; sho~n as lens 80~ Modified beams 82 and 84 are propagated re-spect~.~ely by the facets of disas 72 and 74~ Modified beam 82 has central axis 82a and outer divergent rays 82b and 82c~
; Discs 72 and 74 h~ve. their reflective facets arranged at attitudes to the rotational axis respectively as in the case of discs 30 and 32 discussed above. Lens 80 is positioned closer to web 10 than.lens 40~ based on the increased extent of diver-gence of beam 36 as it is confronted by discs 72 and 74. Lens 80 position and prism 78 position are adjusted to provided for disposition of focus locations 86 and 88 of beams 82 and 84 , 1~ ~5173 Closely adjacent web 10, and generally juxtaposed with locations 68 and 70, as indicated. Spacing Dl exists between locations 68 and 70 based on the selection of facet attitudes of discs 30 and 32 and optics (lens 40 and prism 33) therefor. Spacing D2 between locations 70 and 86 is set by the length of spacer 76~ Spacing D3 exists between locations 86 and 88 based on the selection of facet attitudes of discs 72 and 74 and optics (lens 80 and prism 78) therefor.
In Fig. 5, the plane of Fig. 4 is orthogonal to web 10 and coincident with web maxgin lOa and laser output beam axis 36a makes acute angle Z therewith. The axis of shaft 28 is in a common plane with beam axis 36a orthogonal to web 10. By set-ting of system parameters as discussed below, the illustrated four row-column matrix may be reached with column spacings D4 and D5 applicable to respective upper and lower adjacent row pairs and spacings Sl-S3 applicable as between the rows.
Fig. 6 shows the configurations of discs 30', 32', 72 and 74. With all discs keyed to common plane keying lines 90, 92, 94 and 96, and assuming forty-five facets per disc as in the system of Figs. 1-3, facets of all discs each subtend two degrees of arc and openings thereof each subtend six degrees of arc. Facet 98 of disc 32' has its leading clockwise edge coincident with keying line 92. Facets 100, 102 and 104 of discs 30', 72 and 74, have their leading clockwise edges spaced from keying lines 90, 94 and 96 respectively by two, six and four degree angles 106, 108 and 110. By this configuration, it will be seen that clockwise rotation of shaft 28 will give rise to successive propagation of modified beams 66, 64, 84 ~ and 82 (Fig. 4). Such firing order is chosen for convenience of explanation since it gives rise to time-successive perfora-tions in rows 112, 114, 116 and 118 of Fig. 5. The firing order ca~ be changed, as desired, from such convenient order. As noted for the two disc embodiment above, the last successive disc may be arranged without light-transmissive portions, but same are preferred to mitigate against spurious light energy reflections from such last disc. The laser beam is focused to its divergence origin 360 (Fig. 4), such that the beam cross-section clears the openings of the penultimate disc (disc 72), thereby assuring that the full beam can be incident on each disc.
Fig. 7 shows four solid line perforations 120, 122, 124 and 126 made in time succession. The time spacing between each successively made perforation is readily calculated since the propagation rate of modified beams is determined solely by reflector assembly parameters, i.e., for one revolution of shaft 28 in the given embodiment, four times forty-five, or one hundred eighty, modified beams are propagated. The time spacing (t) between successively-made perforations, i.e., perforations 120 and 122, is thus 1/180R, where R is the number of revolutions of shaft 26 per unit time.
Perforations 120 and 122 are spaced in distance by the measure (Fig. 7) Dl cos Z plus D6. Dl is the spacing in the Fig. 4 plane between the perforations 120 and 122, with web 10 stationary. The cast image separation of Dl is greater in Fi~.
7, based on angle Z and is the measure Dl cos Z. D6 represents the distance travelled by web 10 during the interperforation time period (t) and is simply web speed (distance- travelled per unit time) multiplied by t, derived as above. Since per-forations in row 112 are all made at the same location (68 - Fig.
4) with respect to lens 40, and do not have cast image spacing, they may all be spaced by a distance (D4j which is shown as .

1~ 5173 being fractional to the spatial measure Dl cos Z plus D6, and a multiple of D6 times the number of discs.
In the Fig. 7 example, on rightward movement of web 10, -row 112 perforations 128 and 130 are made spatially prior to, and row 112 perforation 132 is made spatially coincident with, row 114 perforation 122, but later in time than row 114 perfor-ation 122. Such phenomena is attributable to the combined effects of cast image separation as between time-successive per-forations and angle Z.
One may define a number N indicating the number of row 112 perforations made spatially prior (or coincident with) and timewise later than the ~ow 114 perforation made time successive to an initial row 112 perforation, and establish the following relation, for a four disc arrangement:
,. N D4 = Dl cos Z + D6 (1) N = Dl cos Z + D6 (2) D
or Dl cos Z = D4 N - D6 (3) or Dl = D4 N D6 ~4) ', cos Z
In the given instance, N is three and D4 is four times D6. In such instance:
1 11 D6 (5) cos Z
In expression (4) with Dl, Z and N preselected constants, D4 and D6 may be established as mutually variable to effect the same pattern. Since D4 is proportional to t and since D6 is deter-mined by web speed, one may establish a series of respective values for drive unit 24 (reflector assembly speed, line 20 ll~S173 signal of Fig. 1) and drive unit 14 (web transport speed, line 16 of Fig. 1) which will yield the Fig. 7 configuration for rows 112 and 114. A common control input may adjust the wiper positions of pots 18 and 22.
The number N is integral in the foregoing example and is selected as the number three. Any integer may be selected to provide for column perforation registry. Lower values of N, i.e., lesser perforations in row 112 between time successive (row 112-row 114) perforations will give rise to a lesser number of per-forations per unit distance in web 10. Conversely, higher values of N will increase perforation density in the web.
If N is selected to be non-integral, the above-noted column registration is not provided. By way of example, if N is selected as three and one-half, perforation density as between rows 112 and 114 decreases from the N equals three situation and the perforations in rows 112 and ll4 are mutually uniformly staggered, i.e., are 180 out of phase, as is the case with all N
values which have a one-half fractional part.
In the N equals three situation above, column registry in rows 116 and 118 also applies, and column registry as among all of rows 112 through 11~ may be achieved by making D2 cos Z
plus D6 an integral multiple of D6 times the number of discs and by making D3 equal to Dl. On the other hand, non-uniform ma-trices may be achieved by other parameter selections however, with consistency of both row spacing uniformity and uniformity in intrarow perforation spacing. The spacing parameters may likewise be modified to compensate for optics aberrations to attain desired perforation matrices.
In its embodiments depicted in the drawings, the ap-paratus for pulsed beam generation involves plural discs or the ll~S~73 like which are disposed mutually contiguously, with facet atti-tude diversity enabling generation of non-interfering pulsed beams. In the above-noted copending application, such discs are spaced from one another along the common rotational axis. The apparatus hereof will thus be seen to be changeable in various manners in leading to the generation of pulsed beams. Further, while system usage of the apparatus disclosed herein and in said above-noted copending application look to the use of common fo-cusing of beams issuing from plural discs, individual processing of such beams may be undertaken. As will be clear, beams in number greater than two may be collected by a common focusing element, giving rise to a corresponding number of perforation rows greater than the two rows obtained in the illustrated practice for each lens.

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Claims (9)

1. Apparatus for generation of pulsed light beams from a continuous laser beam for perforating a moving web at certain predetermined spaced-apart locations, comprising:
(a) first reflective means arranged to receive said continuous beam and supported for rotation about a preselected rotational axis, said first reflective means including a first disc (1) having light reflective elements mutually spaced in a circular locus on said disc for confronting said continuous beam individually in the course of rotation of said first disc, each of such light reflective elements being disposed in a mutually identical first attitude with respect to said rotational axis, and (2) having apertures between adjacent said light reflective elements to define light transmissive portions;
(b) second reflective means disposed mutually contiguously with said first reflective means including a second reflective disc having reflective portions mutually spaced in a circular locus on said second disc for confronting said continuous beam individually in the course of rotation of said second disc, said light reflective portions of said second disc each being disposed in a mutually identical second attitude diverse from said first attitude with respect to said rotational axis, said light reflective portions of said second disc being in alignment with said apertures of said first disc, whereby first and second pulsed light beams issue successively alternately from said first and second discs, said diverse attitudes of said light reflective elements on said first disc and of said light reflective portions on said second disc cooperating to cause divergence of the paths of said first and said second pulsed beams;

(c) common focusing means for receiving said first and second pulsed light beams issuing from said first and second discs and focusing said pulsed beams at first and second predetermined spaced-apart locations on said moving web; and (d) light deviating means disposed between said second disc and said common focusing means for controlling the path of said second beam to said common focusing means, and thereby controlling the spacing of said second relative to said first location on said moving web.

2. The apparatus of claim 1, further comprising:
lens means for receiving said continuous laser beam and issuing a focused continuous beam, wherein said focused continuous beam is received by said first reflective means for confronting said light reflective elements of said first reflective means and by said second reflective means for confronting said light reflective portions of said second reflective means.

3. The apparatus of claim 1, wherein said second disc further includes apertures between adjacent said light reflective portions to define light transmissive portions, and wherein said light reflective portions and said apertures of said second disc are respectively aligned with said aper-tures and said light reflective elements of said first disc.

4. Apparatus for generation of pulsed light beams from a continuous light beam for perforating a moving web at certain predetermined spaced-apart locations, comprising:
(a) first reflective means arranged to receive said continuous beam and supported for rotation about a pre-selected rotational axis, said first reflective means includ-ing a first disc (1) having light reflective facets mutually spaced in a circular locus about the periphery of said disc to confront said continuous beam individually in the course of rotation of said first disc, each of said light reflective facets being disposed in a mutually identical first attitude with respect to said rotational axis, and (2) having apertures between adjacent said light reflective facets to define light transmissive portions;
(b) second reflective means disposed mutually contiguously with said first reflective means, said second reflective means including a second reflective disc having light reflective facets mutually spaced in a circular locus about the periphery of said second disc to confront said continuous beam individually in the course of rotation of said second disc, said light reflective facets of said second disc each being disposed in a mutually identical second attitude diverse from said first attitude with respect to said rotational axis, said second disc further having aper-tures between adjacent said light reflective facets to define light transmissive portions, said light reflective facets and said apertures of said second disc being in alignment respectively with said apertures and said light reflective facets of said first disc, whereby first and second pulsed light beams issue successively alternately from said first and second discs, said diverse dispositions of said light reflective facets on said first and second discs cooperating to cause divergence of the paths of said first and said second pulsed beams;
(c) common focusing means for receiving said first and second pulsed light beams issuing from said first and second discs and focusing said pulsed beams at first and second predetermined spaced-apart locations on said moving web; and (d) light deviating means disposed between said second disc and said common focusing means for controlling the path of said second beam to said common focusing means, and thereby controlling the spacing of said second location relative to said first location on said moving web.

5. The apparatus claimed in claim 4 wherein all said facets are planar elements disposed coplanar with said discs.

6. The apparatus claimed in claim 4 wherein said discs are supported for rotation about a rotational axis intersecting the axis of said focused continuous beam.

7. The apparatus claimed in claim 4 wherein said second disc is supported for joint rotation with said first disc about said rotational axis.

8. The apparatus claimed in claim 4 wherein said light deviating means is movable with respect to said second disc for selective deviation of said second beam paths, thereby to adjust the spacing of said second location relative to said first location on said moving web.

9. The apparatus of claim 8 wherein said light deviating means comprises a prism.