WO1998002273A1

WO1998002273A1 - Web cutting and/or sealing method and apparatus

Info

Publication number: WO1998002273A1
Application number: PCT/GB1997/001855
Authority: WO
Inventors: Alan Michael Aindow; Michael John Cahill; Philip Gordon Haddow; Geoffrey William Vernon
Original assignee: Molins Plc
Priority date: 1996-07-11
Filing date: 1997-07-10
Publication date: 1998-01-22
Also published as: AU3454197A; EP0958096A1

Abstract

Laser cutting and/or sealing appparatus, particularly for webs of paper, comprises means for scanning a beam (2; 202) relative to a travelling web (4; 204) to define cuts and/or seals of predetermined shape (121; 121A) in the web. The scanning means includes first and second mirrors (18, 18A; 22, 22A; 206, 208) cyclically movable about mutually inclined axes (19, 19A; 23, 23A; 241, 222). There may be two such scanning means defining separate paths to the web and a switching disc (10) may direct the beam along each path in turn: in this way the beam may be used to cut and/or seal webs substantially continuously while still allowing cutting of discontinuous shapes. The apparatus may be used to cut out and/or seal packages from a web containing packages of tea or other infusible material.

Description

l Web Cutting and/or Sealing Method and Apparatus

2

3 This invention relates to a web cutting and/or sealing method and

4 apparatus, particularly but not exclusively for cutting and/or sealing webs

5 of paper or paper-like material (including board) suitable for use in

6 packaging or wrapping processes.

7 According to one aspect of the invention a method of making at a least one cut and/or seal in a travelling web comprises feeding the web at a predetermined (preferably constant) speed, directing a beam of ιo laser radiation along a path towards the moving web, and causing the π beam to scan relative to web so as to make a cut and/or seal having a i2 predetermined shape in the web, wherein the beam is redirected at i3 spaced positions on said path by means cyclical ly movable about i4 mutually inclined axes so as to cause said scanning of the beam The is beam may be used to make a cut in the web and/or, particularly where i6 the web comprises multiple layers, may be used to make a seal in the i7 web, e.g by causing the layers to bond together The beam could be is arranged, e g by variation of its effective action on the web at adjacent i9 locations on the web, to cut the web at one location and seal it at another

20 location Preferably the rate at which the beam scans relative to the web

2i is maintained approximately constant along the length of the cut and/or

22 seal . In one preferred arrangement the p redete rmin ed shape is

23 substantially closed so that cut-outs of a defined shape, e.g. circular, 2<. may be subsequently removed from the web This arrangement has

25 particular application for production of packages containing tea or other

26 infusible material. The method may therefore be used as an alternative

27 to that disclosed in PCT Patent Application No W094/1 583 for cutting

28 out round tea bags.

29 According to another aspect of the invention apparatus for making

30 at least one cut and/or seal in a travelling web comprises means for 3i feeding the web at a predetermined speed, means for directing a beam

32 of laser radiation along a path towards the moving web, and means for

33 controlling the directing means so as to scan the beam relative to the 3-; m ovi n g we b to mak e a c ut an d/o r s e a l i n th e we b h av i n g a

35 predetermined shape, wherein the directing means includes first and

36 second movable beam directing elements, e g mirrors, which are

37 cyclically movable about mutually inclined, preferably perpendicular,

38 axes. The first and second elements may thus comprise successive mirrors in the beam path, arranged so that the first element scans the

2 beam across the face of the second elem ent. In one preferred

3 arrangement the elements are pivotable about axes respectively

4 perpendicular and parallel to the path of web. The cyclic movement of

5 the elements may be control led by cam means synch ronised with

6 movement of the web.

7 The controlling means is preferably arranged to impart cyclic s movement to said directing means, so that a series of said cuts and/or seals of predetermined shape is made in successive portions of the web. ιo In another preferred arrangement the elements are rotatable about π mutually perpendicular axes, preferably including a first axis parallel to i2 the path of an incident beam of laser radiation and a second axis lying in i a plane parallel to that of the web and transverse to its direction of i movement. is The controlling means preferably includes means for redirecting i6 or intercepting the laser beam so that discontinuous cuts and/or seals, i7 e.g. a series of separate circular cuts, may be made in the web. In a is preferred arrangement there are at least two directing means, with the i9 beam being supplied to each directing means in turn: in this way the

20 beam may be used to cut and/or seal webs substantially continuously

2i while still allowing cutting and/or sealing of discontinuous shapes.

22 Where there are two separate directing means these may conveniently

2 be arranged to make cuts and/or seals (e.g. circular cut-outs) in separate

24 tracks along the web.

25 The term "laser" has been used herein for convenience; the

26 invention is applicable to any i ntense beam of radiation capable of

27 cutting and/or sealing paper or other material forming the web.

28 The invention will be further described, by way of example only,

29 with reference to the accompanying diagrammatic drawings, in which:

30 Figure 1 is a plan view of laser web cutting and/or sealing 3i apparatus,

32 Figure 2 is another pl an view s h owing further detail of the

33 apparatus of Figure 1 ,

3 Figure 3 is a view in the direction of arrow III in Figure 1 , Figure 4 is a part-sectional view of a first mirror mounting and cam

36 mechanism of the Figure 1 apparatus, 7 Figure 5 is a part-sectional view of a second mirror mounting of 8 the Figure 1 apparatus, 1 Figure 6 is a part-sectional view on the line VI-VI in Figure 5,

2 Figure 7 is a view in the direction of arrow VII in Figure 5,

3 Figure 8 shows part of the drive means for the apparatus of Figure

1 ,

5 Figure 9 shows the paths scanned by the laser beams, relative to

6 the apparatus of Figure 1 ,

? Figure 10 shows the paths scanned by the beams, relative to the s moving web in the apparatus of Figure 1 , o Figure 1 1 is a side view of further laser web cutting and/or sealing ιo apparatus, and ιι Figure 12 shows a detail from the apparatus of Figure 1 1 i2 For convenience, the apparatus will be d escribed in general

3 hereinafter with reference to use as web cutting apparatus, although it

14 should be understood that the apparatus may be used for cutting and /or is sealing depending on the material of the web and the intensity of the i6 beam at the location of the web it is intended to cut and/or seal

I ? Figure 1 shows optical apparatus for focusing and scanning an is incident laser beam 2 relative to a moving web 4 The beam 2 passes i through a first lens 6 and is brought to an intermediate focus 8 adjacent

20 to a rotary switching disc 10 The disc 10 has a reflective surface facing

2i the beam and, as shown in Figure 3, has a periphery comprising first

22 and second coaxial semi circular edges 10A and 1 0B lying at different

23 radii from the axis 1 0C of rotation of the disc Thus the disc has a

24 rad ial ly o ute r po rtio n 1 0D b etween t h e ed g e 1 0A and a rad i us

25 corresponding to that of the edge 10B. The path of beam 2 is situated at

26 such distance from the axis 10C that the beam is intercepted only by the

27 portion 10D of the disc

28 In rotational positions of the disc 10 where it does not intercept the

29 beam 2 the latter impinges on a stationary mirror 1 2 resulting in a 0 reflected beam 14, which passes by way of a final focusing lens 16 to a 3i first oscillating mirror 18 whence a further reflected beam 20 is directed

32 to a second oscillating mirror 22

33 The first oscillating mirror 18 is capable of pivotal movement about

34 a vertical axis 19 and for this purpose is connected to one end of an arm

35 24 carrying at its other end a cam roller 26 maintained in contact with a

36 first cam 28 rotatable about a vertical axis 30 Rotation of the cam 28

37 thus causes the mirror 18 to pivot about its axis 19.

38 Referring now also to Figure 2, the mirror 22 is capable of pivotal 1 movement about a horizontal axis 23 extending parallel to the direction of

2 movement of the web 4. This movement is derived from a second cam

3 32, rotatable about the vertical axis 30, and transmitted by way of a cam

4 roller 34 carried by a first arm 36 which, together with a second arm 38

5 which is rigidly connected to the first arm, is pivoted about the vertical

6 axis 19. A push-rod 40 is connected by way of ball-joints between the outer end of the arm 38 and part of the support structure for the mirror

₈ 22.

9 Referring now also to Figure 1 , when the disc 10 is in a rotational ιo position such that the portion 1 0D intercepts the beam 2 a reflected π beam 14A is directed to a final focusing lens 16A and subsequently to i2 oscillating mirrors 18A and 22A. Oscillation of the mirrors 18A, 22A by i3 the respective cams 28 , 32 ι s sιmι lar to th at of the mιrrors 1 8, 22. i Corresponding parts have been given the same reference numbers with is the addition of the suffix "A". i6 Oscillation of the mirrors 18, 18A causes scanning of the beams i7 20, 20A in a direction parallel to the web 4 and oscillation of the mirrors is 22, 22A causes scanning in a direction transverse to the web. The resul- i9 tant beam 21 (Figure 6) directed at the web 4 thus follows a path on the

2o web determined by the shapes of the cams 28, 32. Generation of the

2i shapes of the cams 28,32 to provide the desired beam paths was carried

22 out using a computer program CAMLINKS available from Limacon,

23 Meadow Farm, Horton, Malpass, Cheshire, SY14 7EU, UK.

2 Figure 9 shows in full lines the path 121 of the beam 21 directed

25 from the mirror 22, and also the path 121 A of the beam directed from the

26 mirror 22A The paths 121 and 121 A shown in Figure 9 are as traced

27 relative to the apparatus. The start 1 1 0 and end 1 1 1 of the path 121 is

28 determined by switching of the beam 2 caused by the disc 10. Similarly,

29 the path 121 A has a start 1 1 0A and end 1 1 A. The beam is active on

30 only one of the paths 1 21 or 1 21 A at any one time, the return path 3i 123, 1 23A of the notιonal beam on the other path being indicated in

32 dotted lines in Figure 9. It will be appreciated therefore that when the

3 beam reaches the end 1 1 1 of the path 121 it is switched by operation of

3 the disc 10 to the start 1 1 0A of the path 121 A; when the beam reaches 5 the end 1 1 1 A of the path 121A it is switched to the start 1 1 0 of the path

36 121 , and so on.

37 The traversing speed of the beam in space along the path 121 or 8 121 A during a cutting cycle and of the notional beam along the return l path 123 or 123A during a non-cutting cycle are constant. The length of

2 the cutting path 121 , 121 A is slightly longer than the circumference of the

3 circles on which paths 121 and 121A lie: hence, there is a slight overlap

4 at the beginning and end of the cutting path (i.e. in the region between start 1 10, 1 10A and end 1 1 1 , 1 1 1 A the web 4 may be cut twice). This

6 improves reliability of the joining up of the cut into a closed periphery, and may also compensate for lower power of the beam at the start and s end of the cutting cycle, due to transition of the beam across the leading or trailing edge of the radially outer portion of the switching disc 10. ιo Figure 10 shows the effect of the beam paths 121 , 121 A when ιι applied to the moving web 4. The active, or cutting, cycles of the beams i2 on the paths 121 , 121 A describe circles, and cut through the web so that i circular portions of the web may be subsequently removed from the i remainder of the web. is Each rotation of the disc 10 produces two cut-out portions of the i6 web 4: hence the disc 10 rotates at a rate which is half the production

I? rate of the apparatus. Each rotation of cams 28, 32 produces four is cut-out portions from web 4: hence, the cams rotate at one quarter i9 production rate.

20 Figure 8 shows in plan view drive means for the cams 28, 32 and

2i disc 10, including a drive shaft 42 from a main drive for the apparatus,

22 and a bevel gearbox 44 including a first output shaft (on axis 30) leading

23 to the cams and a second output shaft 46 leading to a reduction belt

24 drive 48 for the disc 10.

25 Figure 4 shows part of the apparatus in the vicinity of the vertical

26 axis 19 in more detail. A spindle 50 is supported for rotation about the

27 axis 1 9 in bearings carried by horizontal frame members 52 of the

28 apparatus. The mirror 18 is attached to a member 54 connected for

29 rotation with the spindle 50. The arm 24 carrying the cam roller 26, by

30 means of which the mirror 18 is oscillated, is integrally formed with a 3i sleeve member 56 keyed to the spindle 50. The arms 36 and 38

32 associated with the cam roller 34 for the mirror 22 are integrally formed with a further sleeve member 58, which is also coaxial with the spindle

3 50 but which is rotatable relative to it.

35 Figures 5-7 show mounting of the mirror 22. A mounting block 60

36 is supported in a recess 62 in one of the horizontal frame members 52

37 and supports a spindle 64 rotatable about the axis 23. Pivotally carried

38 at th e ends of the spi ndl e 64 are two depend ing l im bs 66, 68 l interconnected at their lower ends by a cross member 70 supporting the mirror 22 in an inclined position. The limbs 66, 68 pass through slots 72

3 in the mem ber 52 , the slots exte nd ing s uffi ci ently in a directio n

4 transverse to the axis 23 to allow the limbs to pivot (by up to about 12°)

5 on the spindle 64 The limb 68 extends upwards, beyond its connection

6 with the spindle 64, to a position at which the push-rod 40 is attached to

7 it. a In one embodiment typical of the illustrated arrangement, in which

9 the web 4 consists of a double layer of tea bag paper (the portions of the ιo web to be cut out forming individual tea bags), the laser beam 2 is of ιι about 8mm diameter and generated by a laser of 240 watts output i2 power. The diameter of the beam 2 at the disc 10 is about 2mm: this is i3 sufficiently compact to allow switching of the beam by the disc 10 but i not so small that the power intensity damages the reflective surface of is the disc At the final focus position the spot diameter is about 0 18mm i6 Typically the system allows a usable depth of focus of about 4mm- this is i sufficient to accommodate the beam path length change as the mirrors is oscillate, which is typically about 2mm. i9 Where the apparatus forms part of a machine for producing tea

20 bags a typical production speed is 2000 bags per minute. At this speed

2i the cams 28, 32 rotate at 500 rpm and the disc 10 at 1000 rpm. A typical

22 bag diameter is 67mm , this gives a required average tracking speed for

23 the cutting beam of about 7m/sec; at lower required rates of cut the

2 power output of the laser may be reduced

25 The disc 1 0 and mirrors 1 8, 1 8A and 22, 22A have reflective

26 surfaces formed from diamond-cut gold-plated aluminium

27 The apparatus shown in Figure 1 1 is capable of producing a

28 single row of circular cut-outs in a moving web 204. A parallel beam 202

2 is directed at a first rotary optical unit 206 comprising a first mirror 208, so second mirror 21 0 and focusing lens 21 2 The unit 206 is rotatable i about an axis 214 parallel to and aligned with the beam 202 2 A focused beam 21 6 is di rected from the lens 21 2 towards a 3 second rotary optical unit 21 8 carrying opposed mirrors 220 and

3 rotatable about an axis 222 which is transverse to the axis 214 5 As the unit 206 rotates about the axis 214 the beam 216 describes

36 a conical surface and is scanned across the moving surface of one of

37 the mirrors 220. The resultant beam 224 directed by the mirror 220 at

38 the web 204, lying in the plane of focus of the beam, scans a shape 1 similar to that of the beam path 121 or 121 A in Figure 9. The shape is

2 determined by the relative speeds of the units 206 and 220. The beam 202 is switched on and off at times corresponding to positions of the focused beam 224 which themselves correspond to the positions 1 1 0 and 1 1 1 in Figure 9. Typically for each individual cut-out

6 the unit 206 will make substantially one revolution and the unit 21 8 will

7 move one of the mirrors 220 through the path of the beam 21 6. In this a respect is should be noted that although in Figure 1 1 the unit 21 8 is 9 shown as having two mirrors 220, it preferably has more, typically six, so ιo that the mirrors form a regular polygonal shape around the axis 222. ιι Switching of the beam 202 may be performed electrically or i2 mechanically, e.g. by means of a rotating disc 226 (Figure 12) provided i3 with castellations 228 to intercept the beam, i. e. during periods which

1 correspond with transitions between the mirrors 220 of the unit 21 8. is During the period when the beam is switched off or intercepted the web i6 204 moves on, so providing for the gap between cut-outs. Switching on i7 (and off) of the beam occurs at the same rotary position of the unit 206 is for each cut-out and corresponding similar positions for the respective i9 mirrors 220 on the unit 218.

20 The apparatus of Figure 1 1 may be used in a machine in which

2i multiple tracks of cut-outs are made in a web, in a manner analogous to

22 that employed in the apparatus of Figure 1 . Thus, during periods when

23 the laser beam 202 is required to be switched off or intercepted in the

24 Figure 1 1 apparatus, the beam may be redirected to similar apparatus

25 operating 1 80° out of phase with the illustrated apparatus , so as to

26 provide two rows of cut-out portions in the web 204, similar to those

2 shown in the web 4 in Figure 10.

28 Both illustrated embodiments of the invention are capable of

29 producing cut-outs having closed curved non-circular shapes. The 0 shapes and relative rotational speeds of the cams 28,32 or the rotational 3i speeds of the units 206 and 218, together with the beam path geometry

32 and the speed of the web, are factors in determining the shapes of the

3 cut-outs.

34 The apparatus of Figure 1 or Figure 1 1 could be used to seal the

35 web 4 or 204, e.g. to bond two or multiple layers of web together,

36 instead of or as well as cutting it. Generally a lower beam intensity is

37 required to seal the web as opposed to cutting it. Where the beam is

38 intended to cut and seal the web the beam may have a first region or ι part where the beam is of high intensity to cut the web and a second

2 region or part of lower intensity to seal the web, preferably in a position

3 adjacent the cut. Beams having regions or parts of different intensities

4 may be produced in several ways, e.g. from different laser sources, by

5 attenuation of part of a beam, or by directing a beam having a first, e.g.

6 central, region where the beam is focused on the web, and a second,

7 e.g. peripheral, region where the beam is slightly defocused, so that the s web is cut when the focused beam impinges on it and sealed where the 9 defocused beam impinges on it. Defocusing of the beam on peripheral ιo regions may be achieved by appropriate selection of beam path, e.g. so π that the depth of focus is relatively large, and/or by appropriate selection i2 of the final processing element, i.e. lenses 16, 16A or 212.

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Claims

Claims:

3 1. A method of making at least one cut and/or seal in a travelling web, comprising feeding the web (4; 204) at a predetermined

5 speed, directing a beam (2; 202) of laser radiation along a path

6 (14,20,21 , 14A.20A; 216,224) towards the moving web, and causing the

7 beam to scan relative to the web so as to make a cut and/or seal having

8 a predetermined shape (121 , 121 A) in the web, wherein the beam is

9 redirected at spaced positions on said path by means (1 8, 18A,22,22A; ιo 206, 21 8) cycl ical ly m ovab l e a bout m utu a l ly i ncl i ned axes ιι (19,19A,23,23A; 214,222) so as to cause said scanning of the beam.

1 2 ι 2. A method as claimed in claim 1 , wherein said beam (2; i4 202) is caused to scan a substantially closed shape (121 ,121 A) so that is cut-outs of said shape may be removed from the web (4; 204).

16 i7 3. A method as claimed in claim 1 or claim 2, wherein the is beam (2) is cyclically redirected along a second path (14A.20A) on i9 which it is caused to scan relative to the web to make a further cut and/or

20 seal of predetermined shape (121 A) in the web adjacent the cut and/or

2i seal made by the beam on the first path (14,20,21 ).

22

23 4. A method as claimed in claim 3, wherein the beam (2) is

24 caused to cut and/or seal substantially closed shapes (121 ,121 A) in the

25 web (4; 204) substantially continuously by alternate redirection along

2 said first and second paths (14,20,21 ; 14A.20A).

27

28 5. A method as claimed in any preceding claim, wherein the

2 beam (2) is caused to simultaneously make a substantially parallel cut

30 and seal having said predetermined shape (121 , 121 A) in adjacent 3i regions of the web (4; 204).

32

33 6. A method as claimed in any preceding claim, wherein the

34 beam (2; 202) is caused to have a first region of relatively high intensity

3 to cut the web, and a second region of relating low intensity to seal the

36 web.

37

38 7. Apparatus for making at least one cut and/or seal in a travelling web, comprising means for feeding the web (4; 204) at a predetermined speed, means (1 8, 18A,22,22A, 206,21 8) for directing a beam (2;202) of laser radiation along a path (14,20,21 , 14A.20A; 21 6,224) towards the moving web, and means (28,32) for controlling the directing

5 means so as to scan the beam relative to the moving web to make a cut

6 and/or seal in the web having a predeterm ined shape ( 1 21 .1 21 A),

7 wherein the directing means includes first (1 8.1 8A; 206) and second a (22.22A; 218) movable beam directing elements which are cyclically 9 movable about mutually inclined axes (19, 19A,23,23A; 214,222).

10 π 8. Apparatus as cl aimed in claim 7, wherein the first and i second elements comprise successive mirrors (1 8, 18A,22,22A, 206,218) i in said beam path, arranged so that the first element scans the beam i4 across the face of the second element

15 i6 9. Apparatus as clai med in clai m 8, wherein the elements

I? (18, 18A,22,22A) are pivotable about axes (1 9, 19A,23,23A) respectively is perpendicular and parallel to the path of the web (4, 204)

19

20 10. Apparatus as claimed in any of claims 7-9, wherein the

2i cyclic movement of the beam directing elements (1 9, 1 9A,23,23A) is

22 controlled by cam means (28,32) synchronised with movement of the

2 web (4; 204).

24

25 1 1 . Apparatus as claimed in any of claims 7- 1 0, wherein the

26 controlling means (28,32) is arranged to impart cyclic movement to said

27 directing means (1 8, 18A,22,22A; 206,21 8) , so that a series of said cuts

28 of predetermined shape (121 , 121 A) is made in successive portions of

29 the web (4; 204).

30

3 12. Apparatus as claimed in any of claims 7-9, wherein said

32 beam directing elements (206 ,21 8) are rotatable about m utually

33 perpendicular axes, including a first axis (214) parallel to the path of the

3 incident beam (202) and a second axis (222) lying in a plane parallel to

35 that of the web (204) and transverse to its direction of movement.

36

37 13. Apparatus as claimed in any of claims 7-12, wherein the

38 controlling means i ncludes means ( 1 0 ; 226) for redirecting or 1 intercepting the laser beam (2; 202) so that discontinuous cuts and/or

2 seals may be made in the web (4; 204).

3

4 14. Apparatus as claimed in claim 1 3, wherein said directing

5 means includes said first and second movable beam directing elements

6 (1 8,22) for directing the beam along a first path (20,21 ) and further first

7 and second movable beam directing elements (1 8A,22A) for directing

8 the beam (2) along a second path (20A), said redirecting means ( 1 0)

9 being arranged to redirect the beam along said first and second paths in ιo turn. ι ι 15. Apparatus as claimed in claim 1 4, wherein substantially i2 closed shapes (121 , 121 A) are cut from the web (4; 204) substantially i continuously.

1 4 i5 16. Apparatus as claimed in any of claims 7-1 5, wherein said i6 beam directing means ( 1 8 , 1 8A, 22, 22A; 206, 21 8) is arranged to i7 provide a beam (2; 202) having a first region of relatively high intensity is and a second region of relatively low intensity at the web (4; 204).

19

2o 17. Apparatus as claimed in claim 1 6, wherein said beam

2i directing means (1 8, 18A, 22, 22A; 206, 21 8) includes focusing means

22 (16, 16A; 212) arranged so as to provide said first and. second regions at

2 the web (4; 204) by focusing the beam differentially at the web.

24 25 26 27 28 29 30 31 32 33 34 35 36 37 38