CA2220215A1 - An apparatus and a method for irradiating a sheet of material - Google Patents

Abstract

Disclosed is an apparatus and a method for irradiating sheets of materials, especially printing plates where the sheet is forced or pressed radially in the internal drum of the apparatus in order to obtain the desired shape of the material during irradiation while holding the sheet in a manner so that preferably no shadows are generated on the sheet during irradiation. Another aspect of the invention is a method and an apparatus for providing registering edges in a sheet of material in e.g. an internal drum image setter. The advantage of the present apparatus and method is the fact that no shadows are generated on the sheet during irradiation.

Description

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 AN APPARATUS AND A METHOD FOR IRRADIATING A SHEET OF MATERIAL

The present invention relates to an apparatus, such as an image setter, and a method in which a sheet of a material comprising a layer containing a photo sensitive substance is irradiated.

A number o~ di~erent types o~ apparatuses, such as laser image setters, per~orming this task have been suggested, but mostly ~or sheet-like materials in the ~orm o~ lengths o~
~ilm which are cut into individual pieces be~ore or a~ter irradiation thereo~ and from which part o~ the ~ilm material cannot be irradiated and is cut away subsequent to irradi-ation.

Part o~ these are o~ the so-called internal drum type, in which a sheet-like material is supported inside a concavely curved "drum" in order to obtain a circularly cylindrical shape.

The advantage o~ this type o~ image setter is obtained when the irradiation means are positioned and moved along the axis o~ symmetry o~ the circularly cylindrical sur~ace and, there-~ore, obtain the same distance ~rom the irradiation means tothe photo sensitive substance throughout the sheet-like material. This is important when optics are involved as e g a beam o~ light will have a single ~ocus and diverge on both sides thereo~. Thus, illuminating a material with this beam at di~erent positions thereo~ will generate di~erent il-luminated spot sizes. This is in no way desired and is typi-cally attempted reduced to a min~mllm An internal drum laser image setter o~ this type may be seen ~rom PCT applications with publication numbers WO 92/14609 and WO 94/00295.

Another problem in image setters, especially when producing so-called positive prints, is that o~ elements o~ the image CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 setter producing shadows on the illuminated sheet. When producing positive prints, all parts o~ the sheet, which are not to have a colour in the ~lnal version, are illuminated during illumination. Thus, in this situation, a shadow will generate a coloured area o~ the final product.

Those parts which may generate shadows in image setters are typically means ~or holding the sheet-like material during illumination.

In typical image setters, such as the image setter o~ PCT
application with publication number W0 92/14609, using thin and pliable sheets o~ material, this problem is solved by holding the sheets by means o~ vacuum during illumination.

The present invention relates to an internal drum image setter ~or sheets o~ materials. Especially ~or sheets o~
materials, problems may arise due to the ~act that, c~ above, pre~erably the whole o~ the sheet should be irradiatable.
Vacuum would be a possible solution, as this re~uires no contact on the side o~ the material pointing towards the optical elements o~ the instrument.

However, it has been ~ound that vacuum is not always su~
ciently power~ul and reliable, especially, when the photosensitive material is not very pliable - such as print-ing plates o~ e.g. aluminum.

In WO 94/00295, this problem is solved by ~orcing the material in place. However, in order to do so, means are used which make shadows on the sheet, thus not always removing the problem that the irradiated material should be cut to measure a~ter irradiation. In addition, in the solution o~ this re~erence, the material is introduced in the drum in a direc-tion along the longitudinal direction o~ the drum. This,however, is not pre~erred due to the more complex setup o~
the instrument.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 In a ~irst aspect, the present invention relates to an alter-native way o~ introducing and holding the sheet o~ material during illumination. In this aspect, the present invention relates to an apparatus ~or irradiating a sheet o~ a material comprising a layer containing a photo sensitive substance, said apparatus comprising .

- a concavely curved support sur~ace means ~or supporting the sheet and ~or de~ining at least part o~ a substan-tially circularly cylindrical sur~ace, - means ~or ~eeding, in a direction at an angle to a longi-tudinal axis o~ the support sur~ace means, the sheet into contact with the support sur~ace means in a position in which the sheet extends peripherally between ~irst and second opposite edge portions, - irradiating means ~or irradiating the photo sensitive substance o~ the sheet, - means ~or retaining the sheet in a predetermined position in relation to the support sur~ace means, the retaining means comprising means ~or abutting the opposite edge portions o~ the sheet and ~or ~orcing the edge portions substantially peripherally so as to ~orce the sheet into a substantially circularly cylindrical shape in contact with the support sur~ace means, where a sliding member is adapted to be moved between a ~irst and second position, in which the sheet in the ~irst position may be ~ed into its said position and where the sliding member in the second position is adapted to abut one o~ the ~irst and second opposite edge portions so as to constitute part o~ the abutting means.

In this manner, a problem which may be seen when using the rollers to immobilize the edge portion, a solution also seen in the art, i.e. that a roller may generate shadows on the CA 022202l~ ls97-ll-04 W096/36486 PCT~K96/00206 irradiated sheet, may be removed. It is possible to choose a sliding member which abuts the edge portion without generat-ing shadows on the sheet.

Referring to the method and apparatus of W0 94/00295, this apparatus supports only a single with o~ material and is not easily adaptable to very different widths of material. In contrast, the apparatus and method according to the present invention easily adapts to different ~m~n~ions in that any length of a sheet along and supportable by the periphery o~
the support surface may be immobilized and having any width in the axial direction o~ the support sur~ace (smaller than the width of the support surface means).

Thus, the apparatus and method of the invention is adaptable to illuminate and immobilize di~ferent widths and lengths of material.

Typically, the irradiation is an illumination with infra-red or visible light, However, depending on the type of photo sensitive substance on the sheet, the irradiation may also be performed using ultra-violet light or perhaps X-ray radi-ation. Naturally, the photo sensitive substance and theirradiation means should match so that the photo sensitive substance of the sheet is sensitive to the emitted radiatio~
from the irradiating means.

In this first aspect of the invention, the support sur~ace means de~ine a surface which, when the sheet is abutted and forced in contact therewith, makes the sheet material define the substantially circularly cylindrical shape which is preferred in order to obtain the above-mentioned advantage of the equidistancy to the irradiation means.

In the present aspect, the "opposite edge portions" are those edge portions which define the two peripheral positions in the support sur~ace means, between which the rest o~ the sheet material is positioned. Dependlng on the shape of the CA 022202l~ l997-ll-04 WO 96/36486 PCT/DK'96/00206 sheet and on how it is fed into said position, these two edge portions may vary ~rom being constituted by approximately point-shaped edge portions (as i~ the sheet had a circular shape) to being consisted by sides o~ e.g. a rectangular 5 sheet.

Naturally, the abutting means should be adapted to abut the actual shape o~ the edge portions in question.

In the present context, "~orcing" the sheet into a shape in contact with the support sur~ace means means that the abut-ment exerts such a ~orce onto the edge portions so that thesheet material contacts the substantially circularly cylin-drical sur~ace de~ined by the support sur~ace means and assumes a corresponding shape.

When the ~orce is exerted substantially peripherally in 15 relation to the support sur~ace means~ the sheet material is automatically ~orced towards the inner support sur~ace o~ the support sur~ace means.

At present, it is pre~erred that the abutting means comprise - stationary means peripherally immovable in relation to the support sur~ace means ~or abutting one o~ the ~irst and second opposite edge portions and - movable means peripherally movable in relation to the support sur~ace means between ~irst and second positions in which it is out o~ engagement with and in abutment with the other o~ the opposite edge portions, respective-ly .

In this manner, a stationary abutment means is positioned in the support sur~ace means and a movabIe means abuts the sheet and operates to generate the force exerted on to the edge portions.

Pre~erably, the sliding member, in its second position, constitute part o~ the stationary means.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 When rendering one edge portion peripherally immovable in the support surface means, and preferably at a well-defined position, the peripheral position of the sheet, when abutted, is relatively well defined. This is preferred so as to be able to irradiate images also close to the edges of the sheet, which would not be possible i~ the position of these edges was not known.

In fact, it is typically desired to have the irradiated image positioned with a precision of +0.5 mm in relation to the edges of the sheet, whereby some positioning of thereof should be performed.

The feeding means are preferably adapted to feed the sheet into said position in a first direction along a first path of which a part is defined by the substantially circularly cylindrical surface. This feeding preferably takes place so that the part of the path substantially ~ollows the periphery of the support surface.

When the apparatus according to the invention further com-prises means ~or removing the sheet having been ~ed into said position, these means are preferably adapted to remove the sheet along a second path, part of which is substantially identical to the part of the first path defined by the sub-stantially circular cylindrical sur~ace, in a direction substantially opposite to the first direction.

When transporting the sheet into and out of the support surface means along substantially the same path, part of the transportation means may perform both tasks and need, consequently, only be positioned at one position in order to feed and remove sheets therefrom.

The feeding means may comprise two rollers between which the sheet is fed.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 Preferably, one of the two rollers being adapted to contact the layer o~ the sheet containing the photo-sensitive sub-stance is displaceable between a ~irst and a second position where the roller, in the ~irst position, contacts the layer in order to be able to ~eed the sheet and, in the second position, the roller is moved away ~rom the layer in order to not create shadows on the sheet during irradiation.

It may otherwise be a problem to be able to "deliver" the sheet at a position on the support sur~ace (which normally requires that a pair o~ rollers is able to contact the sheet) and to still irradiate all parts o~ the sheet.

In order to retain the typical setup o~ this type o~ instru-ments, the means ~or ~eeding the sheet into contact with the support sur~ace means are typically means ~or ~eeding the sheet in a direction substantially perpendicular to a longi-t~ n~ 1 axis o~ the support sur~ace means.

Naturally, the shape o~ the abutting means will depend on the actual shape of the edge portions to be abutted. However, it is pre~erred to have abutting means comprising means ~or abutting each o~ the two opposite edge portions at one or more positions. These means may comprise one or more means independently resiliently connected to a main holding means The resilient connection is pre~erred as all ~eeding o~ sheet will be per~ormed with a certain precision. Thus, as the edge portion to be abutted may deviate slightly ~rom its ideal position, the abutting means should be adapted to adapt to this deviation.

I~ the shape o~ the edge portion to be abutted is e.g.
straight, such as the edge o~ a square-shaped sheet, it may be pre~erred that these means comprise a main member and a 'single rigid means resiliently connected thereto and ~or abutting the edge portion.

CA 022202l~ l997-ll-04 W096/36486 PCT~X~G/~C2~6 A more complex shape o~ the edge portion may be better abutted using means which comprise several individual abut-ting means so as to better adapt to the shape o~ the edge portion.

The resilient connection between the means ~or abutting an edge portion at one or more positions and the main holding means may be a spring loaded connection. However, also other suitable resilient connections such as connections comprising rubber, ~lat springs etc. may be used.

At present, it is pre~erred that the angular position o~ the sheet in the support sur~ace means i8 de~ined by the sliding mem~ber and that a resilient connection is provided at the movable abutment means.

Furthermore, due to the possibility o~ the sheet translating in a direction parallel to the axis o~ the support sur~ace means during abutment due to the angular de~inition o~ the sliding member, the resilient connection o~ the movable means should be able to also adapt to this movement.

Using normal springs ~or the resilient connection, these may adapt to movements in all three ~im~n~ions However, it may be pre~erred to have a resilient connection only adapting to movement in two ~m~n~ions and being more rigid in the third dimension, such as in the radial direction in the support sur~ace means. Means o~ this type is a ~lat spring having an S-shape and directed so that its plane is directed radially in the support sur~ace means.

A spring o~ this type will be able to adapt to both a peri-pheral movement - the abutment - and a movement in the direc-tion parallel to the axis o~ the support sur~ace means -angular correction o~ the sheet. The more rigid direction isin the radial direction, where no movement o~ the sheet should occur.

CA 0222021~ 1997-11-04 WO 96/36486 PCTIDK'96/00206 In order to be able to control the abutment of the sheet, the abutting means may comprise ~orce measuring means ~or deter-m; nl ng the ~orce applied to the abutted edge portions. Pre-~erably, the ~orce applied depends on the thickness and sti~ness of the sheet material in order not to de~orm the sheet during abutment. De~orming the sheet will reduce the precision of the irradiated image, as the photo sensitive substance o~ the sheet material is no longer equidistantly positioned in relation to the irradiating means. It may also be more di~icult to use de~ormed sheets ~or their ~inal purpose such as during a printing process. In addition, it may not be possible to remove a deformed sheet ~rom the apparatus without ~urther de~ormation o~ the sheet or damage to the apparatus.

In order to ~acilitate the relative movement between the movable abutting means and the support sur~ace means, the abutting means pre~erably comprise ~irst engaging means engaging with second engaging means constituting part o~ the support sur~ace means, and a motor ~or driving the ~irst engaging means. Optionally, the motor may be positioned so at to drive the second engaging means.

In the presently pre~erred embodiment, the ~irst engaging means comprise a toothed wheel and the second engaging means comprise a toothed portion along a radial part o~ the support sur~ace means. However, any other suitable means, such as a ~riction engagement, arrangements utilizing belts, wires, ch~n~, etc. may be used.

When subsequently using an irradiated sheet in e.g. a print-ing process, it is o~ great importance that the irradiated image is correctly positioned during the printing process.
This criticality is especially visible when per~orming mul-tiple color prints where e.g. ~our prints are superposed.
.

This positioning o~ the irradiated image is pre~erably obtained by using registering edge portions precisely de~ined CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 in relation to the irradiated image. In this way, the image may be positioned independently o~ small deviations in the ~eeding o~ the sheet prior to irradiation. Thus, the present apparatus pre~erably ~urther comprises means ~or providing registering edge portions in the sheet.

It is presently desired by operators that the registering edge portions are positioned with a precision o~ 1/100 mm in relation to the irradiated image. O~ten, these edge portions are used in the positioning o~ the irradiated sheet and not the outer boundaries o~ the sheet due to the larger precision in the position o~ the registering edge portions.

I~ manu~acturing o~ the registering edge portions is per-f ormed while the sheet is present in the support sur~ace means, the position o~ these edge portions will be well-de~ined in relation to the irradiated image i~ both aregenerated while the sheet is in the same position.

Typically, an irradiated sheet comprises two registering edge portions, whereby it is pre~erred that the edge portion providing means comprise at least two edge portion providing tools each providing one registering edge portion and being connected to a main member.

Depending on the desired number o~ registering edge portions and the positions thereo~, the at least two edge portion providing tools and the main member may be movable between at least two positions so that each o~ the at least two edge portion providing tools may provide multiple edge portions in the sheet.

Naturally, it is possible to simply ~it the apparatus with a number o~ ~ixed edge portion providing tools i~ the positions o~ the registering edge portions never change. However, as it may be pre~erred to be able to irradiate sheets having di~-~erent sizes, the positions o~ the registering edge portions may vary. Typically, two registering edge portions are posi-CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 tioned at one side o~ the sheet and symmetrically around the middle thereo~. Thus, in order to avoid ~itting the apparatus with an excessive number o~ edge portion providing tools, the tools are pre~erably movable.

In ~act, some registering standards require that the regis-tering edge portions are positioned with one o~ a number o~
~ixed distances. This may be ~ollowed providing e.g. three tools on the member in order to be able to provide two edge portions with two di~erent distances therebetween without having to move the member between the production o~ the two registering edge portions.

In order ~or the edge portion providing tools to be able to provide registering edge portions at multiple positions o~
the sheet, the at least two edge portion providing tools and the main member are pre~erably movable along a substantially circular path, as this is the shape o~ the pre~erred edge portion o~ the sheet to receive the registering edge por-tions.

A second aspect o~ the present invention relates to a tool ~or providing a registering edge portion in a sheet o~ a material and typically ~or use in the above-mentioned appar-atus This tool comprises - a ~irst edge portion defining means having a ~irst edge portion de~ining the registering edge portion to be provided, - a second edge portion de~ining means having - a sur~ace ~or contacting the sheet on the opposite side o~ the layer containing the photo sensitive substance during production o~ the registering edge portion, - receiving means at said sur~ace ~or receiving the ~irst means and comprising a second edge portion substantially inverse o~ that o~ the ~irst means, CA 022202l~ l9s7-ll-04 W096/36486 PCT~K96/00206 where the first edge portion defining means are adapted to move between - a first position where a gap is defined between the first means and the contact surface of the second means and - a second position where the first edge portion defining means are introduced in the receiving means in a manner so that the first means to no substantial degree protrude beyond the plane of the contacting surface and so that the first and second edge portions become adjacent during the movement between the first and second positions.

The advantage of a tool of this type is the fact that, subse~uently to providing the registering edge portion, the tool cannot generate shadows on the sheet to be irradiated as substantially all of the tool is positioned on the other side o~ the sheet material.

Usually, the edge portions to be defined in the sheet are indentations or notches at an edge portion of the sheet - and typically the same edge portion thereof.

The first edge portion of the tool is preferably an outer edge portion and the receiving means preferably constitute a hole or an indentation of the second means, wherein the second edge portion constitutes part of the edge of the hole or indentation. Thus, the first means are introduced in the indentation or hole during production of the edge portion in a manner so that substantially all of the first means are received in the hole or indentation.

Preferably, the first and second means are interconnected by an interconnecting body so that this and the first means are introduced in the hole or indentation of the second means when the first means are in the second position. Naturally, in order to avoid shadows on the irradiated sheet, also the interconnecting body is preferably substantially fully intro-duced in the receiving means.

CA 022202l~ l997-ll-04 WO 96/36486 PCI'/DK96/00206 In a third aspect, the present invention relates to a method o~ irradiating a sheet o~ a material comprising a layer containing a photo sensitive substance, said method compris-ing the steps o~:

- ~eeding the sheet into contact with a support surface means de~ining at least part o~ a substantially circularly cylindrical support sur~ace in a direction at an angle to a longitudinal axis o~ the support sur~ace means and in a position in which the sheet extends peri-pherally between ~irst and second opposite edge portions, - irradiating the photo sensitive substance o~ the sheet while retaining the sheet in a predetermined position in relation to the support sur~ace means by abutting the opposite edge portions o~ the sheet and ~orcing the edge portions substantially peripherally so as to ~orce the sheet into a substantially circular cylindrical shape in contact with the support sur~ace means characterized in that a sliding member, subsequent to the ~eeding step, is moved between a ~irst and second position, where, in, the ~irst position, the sheet may be ~ed into its said position and where the sliding member, in the second position, abuts one o~ the opposite edge portions during irradiation.

Again, it is pre~erred that the abutting comprises - peripherally immobilizing one o~ the opposite edge por-tions o~ the sheet in relation to the support sur~ace means and - moving a movable means peripherally in relation to the support sur~ace means ~rom a ~irst position where there 3 0 iS no engagement with the sheet to a second position where the movable means abut the other o~ the opposite edge portions.

CA 0222021~ 1997-11-04 W096/36486 PCT~K~96100206 As mentioned above, the feeding of the sheet into said posi-tion is pre~erably per~ormed in a ~irst direction along a ~irst path o~ which a part is de~ined by the substantially circularly cylindrical sur~ace.

Where the method also comprises removal o~ the sheet having been ~ed into said position, this removal is, naturally, pre~erably per~ormed subsequent to irradiation thereof, and the sheet is pre~erably removed along a second path, part o~
which is substantially identical to the part o~ the ~irst path de~ined by the substantially circular cylindrical sur-~ace, in a direction substantially opposite to the first directlon .

As described above, the ~orce applied to the abutted edge portions is preferably determined by force measuring means.
This determined force may then be compared to a predetermined ~orce, and the result of the comparison may be used ~or controlling the abutment o~ the edge portions. This predeter-mined ~orce will typically depend on the thickness and stiff-ness of the sheet and the size o~ the edge portions to be abutted. Naturally, thin materials may not require abutment with the ~orce required in order to force a thicker material into shape. On the other hand, exerting the force required t Q
~orce a given material into shape may de~orm the sheet, if the ~orce is exerted on a too small edge portion Thus, the material thickness and stiffness should correspond to the force required/desired and the area o~ the edge portion receiving the ~orce.

Even though it is contemplated that this ret~;nm~nt o~ the sheet will ~unction using almost every thickness/sti~fness o~
materials, the advantage o~ using the present invention is largest when relatively sti~, and, thus, usually relatively thick, sheet are irradiated. Using e.g. vacuum ret~nm~nt of the sheet may not ~unction i~ the sheet material is too thick or sti~. This problem is overcome by using the apparatus and method o~ the invention.

CA 022202l~ l997-ll-04 Thus, it is pre~erred that the sheet comprises a sheet-shaped base material having a thickness o~ 0.1-0.5 mm, pre~erably 0.1-0.4 mm, more pre~erably 0.3 mm onto which a photo sensi-tive layer has been applied. The sti~fness o~ the sheet pre~erably corresponds to that o~ a sheet o~ ~ully hardened (de~ormation hardened) aluminium having a thickness of 0.1-0.5 mm, pre~erably 0.1-0.4 mm, more pre~erably 0.3 mm. The base material may be made o~ any suitable material such as metal, pre~erably aluminium, alloys, pre~erably steel, plas-tics, pre~erably polyester, etc. Naturally, a more stif~material may be made thinner compared to that o~ a more so~t material in order to obtain the ~ull advantage o~ the present abutment.

Again, it is pre~erred to provide at least one registering edge portion by edge portion providing means while the sheet is retained by the retaining means.

In order to have the edge portion providing means provide the edge portions in the sheet, it is presently pre~erred to have the sheet ~ed into said position in a manner so that a part thereo~ projects beyond the support sur~ace means in a direc-tion parallel to a longitudinal axis thereo~, so that the edge portion providing means may be positioned so as to provide the at least one registering edge portion in that part o~ the sheet.

In this situation, where the sheet extends outside the sup-port sur~ace means, the edge portion providing means may be movable between a ~irst and a second position, the movement being at an angle to the periphery o~ the support sur~ace, and the second position being ~urther away ~rom the support sur~ace means than the ~irst position.

I~ the edge portion providing means are in the second posi-tion when the sheet is ~ed into position and is moved into the ~irst position be~ore the sheet is irradiated, a longi-tudinal positioning o~ the sheet is per~ormed at an angle to CA 022202l~ ls97-ll-04 W096/36486 PCT~Ks''002J6 the periphery o~ the support sur~ace. Thus, this positioning together with the peripheral positioning o~ the sheet using the abutment means is pre~erred in order to position the sheet in a well-de~ined position.

Thus, the edge portion providing means may help in position-ing the sheet ln the support sur~ace means together with the abutting means. In ~act, as the ~eeding o~ the sheet will always be per~ormed within certain tolerances, the required tolerances may be reduced due to the positioning per~ormed by the edge portion providing means.

In order to ~acilitate the positioning by the edge portion providing means, a ~irst predetermined force is pre~erably applied during abutment to the sheet while moving the edge portion providing means ~rom the second position to the ~irst position, and this ~orce is pre~erably smaller than a second predetermined ~orce applied during irradiation o~ the sheet.
Translating the sheet while abutting it with an excessive ~orce will increase the risk o~ de~orming the sheet during this process.

Alternatively, the translation o~ the sheet may be provided by not the edge portion providing means but an other element, such as an element rigidly connected thereto, which per~orms a similar movement prior to irradiation o~ the sheet.

Even though the positioning provided by the edge portion providing means or a similar means, the angular positioning o~ the sheet in the support sur~ace means is pre~erably determined by the abutment means and more pre~erably by the stationary part thereo~.

A typical sheet is substantially rectangularly shaped and the edge portion providing means abut and provide registering edge portions in an edge o~ the sheet which is not abutted by the retaining means.

, CA 022202l~ l997-ll-04 Alternatively, it may be pre~erred to provide the registering edge portions at the edge portions abutted by the abutting means. In this situation, the edge portion providing means may be incorporated in or at the abutting means.

When it is desired that each o~ the edge portion providing tools should be able to provide multiple edge portions in the sheet it is pre~erred that the edge portion providing means are movable substantially along the periphery o~ the support sur~ace between at least two positions. In this manner, the edge portion providing means may provide substantially any number o~ registering edge portions at substantially any position in the part o~ the sheet extending outside the support sur~ace means.

In a ~ourth aspect, the present invention relates to a method o~ providing a registering edge portion in a sheet o~ a material, the method comprising - providing a first edge portion providing means having a ~irst edge portion de~ining the registering edge portion to be provided, - providing a second edge portion de~ining means having - a sur~ace ~or contacting the sheet during production o~ the registering edge portion, - receiving means at said sur~ace ~or receiving the first means and comprising a second edge portion substantially inverse o~ that o~ the ~irst means, - moving the ~irst means into a position where a gap is de~ined between the contact sur~ace and the ~irst means, - positioning the sheet on said sur~ace so that a part thereo~ is introduced in said gap, - moving the ~irst means into a second position where the first edge portion moves through said gap, the ~irst edge CA 022202l~ l997-ll-04 W096l36486 PCT~K96/00206 portion de~ining means being introduced in the receiving means in a manner so that the ~irst means to no substan-tial degree protrude beyond the plane o~ the contacting sur~ace.

The ~irst and second edge portions pre~erably become adjacent during the movement o~ the ~irst means ~rom the ~irst to the second position.

In the most pre~erred embodiment, the ~irst and second edge portions are positioned adjacent to said gap so that these edge portions become adjacent when the ~irst means is intro-duced in said receiving means. In this manner, these two edge portions are the ones actually providing the edge portion.
When these edge portions are substantially congruent, the best possible indentation o~ the sheet is obtained without de~ormation o~ the adjacent sheet material.

A preferred embodiment o~ the ~our aspects o~ the invention will now be described with re~erence to the drawing where Fig. 1 is a cross-section o~ the pre~erred embodiment o~ the apparatus according to the invention, Fig. 2 is a cross-section o~ a detail o~ Fig. 1 illustrating the operation o~ the stationary abutting means, Fig. 3 is a cross-section o~ a detail o~ Fig. 1 illustrating the operation of the movable abutting means, Fig. 4 is a block diagrammatic top view o~ a pre~erred embo-diment o~ the irradiation means, Fig. 5 is a side view o~ the pre~erred registering edge portion providing means according to the invention, Fig. 6 is a top view o~ the pre~erred registering edge por-tion providing means according to the invention, CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 Fig. 7 is a side view o~ the edge portion providing means o~
Fig. 6, Fig. 8 is a cross-sectional view o~ a pre~erred alignment detector according to the invention, Fig. 9 is a schematic view o~ a quadrant detector, Fig. 10 is a cut-away illustration an alignment setup ~or the alignment detector o~ Fig. 7, Fig. 11 is a cross-sectional view o~ the alignment setup o~
Fig. 10 through line A and the center o~ the outer tube, and Fig. 12 is a cross-sectional view o~ the alignment setup o~
Fig. 10 seen ~rom the end thereo~ ~rom arrow B.

Fig. 13 illustrates a pre~erred method o~ controlling the illuminated spot size by controlling the output power of the laser.

In Fig. 1, a cross-section o~ the presently pre~erred inter-nal drum laser image setter 2 according to the invention is illustrated. In this instrument, the sheets, typically sheets o~ aluminum comprising a layer containing a photo sensitive substance and having a total thickness o~ at least 0.1 mm, such as 0.15 mm or 0.3 mm, are positioned on a tray 4.

When ~eeding a sheet o~ the material into the instrument 2, a suction means 6 is moved ~rom its position as shown in Fig. l by moving means 8 to a position ad]acent to the tray 4 so as to contact a sheet o~ the sheet. Subse~uently, the suction means 6 are translated to their ~irst position in order to have the sheet contacted by a pair rollers 10 so as to start ~eeding the sheet into the instrument 2.

Subsequently, the system consisting o~ the pairs o~ ~eeding rollers 10, 12, 14, 16 and 18 together with guides 20, 22, CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 24, 26 and 28 and helping rollers 30, 32, 34, 36, 38, 40, 42 and 44 will translate and guide the sheet into a support sur-~ace means or drum 50 of the instrument 2. It is pre~erred to contact the sheet in a manner so that the side having the photo sensitive substance predom;n~ntly is contacted by rollers in order not to scratch and stress this surface.
Feeding o~ the sheet ends, when the rollers 18 no longer engage the sheet.

Retainment and illumination o~ the said sheet will be described ~urther below.

When removing the illuminated sheet ~rom the drum 50, the pair o~ rollers 18 again engage the sheet and together with guides 58, 60 and 62 as well as helping rollers 64, 66, 68 and 70 and removal roller pairs 72 and 74 cooperate in order to remove the sheet ~rom the drum 50 and deliver this to an output tray (not shown).

In the presently pre~erred instrument 2, the guide 62 is pre~erably an endless conveyer belt which, when no material is present between this and the rollers 66, 68 and 70, fol-lows a path defined by rollers 66, 68 and 70, the roller 76o~ the pair o~ rollers 74, roller 78 of the pair o~ rollers 72, and the helping roller 69. This path is shown in a full ~~
line. When a sheet is guided by guide 62, the path thereof is slightly changed due to the presence of the sheet. This changed path is shown in a broken line.

In order not to stress the sheet, a body 75 holding the rollers 74 and 70 is pre~erably movable by operating means 77 so that the body 75 is in a more vertical position when the sheet is introduced between rollers 72 and moved to the more horizontal position shown in Fig. 1 before the sheet contacts the roller 76 of the pair o~ rollers 74.

In order to be able to ~eed the sheet into the drum 50 and especially in order to be able to remove the illuminated CA 022202l~ l997-ll-04 sheet therefrom, the roller 52 of the pair of rollers 18 preferably comprises a number of rollers positioned along a common axis (not shown). This will allow a comb-shaped part 79 of the drum 50 to extend between the individual rollers and thereby also support the sheet in these positions.

The support provided with the part 79 should, naturally, be suf~icient in order to have the sheet retain the preferred shape. At present, the roller 52 consists o~ a total of four rollers having a length o~ 40 mm. This has been found to provide a part 79 giving sufficient support for the sheet.

This setup will enable ~eeding o~ the sheet into the drum 50 into a position where substantially all of the sheet may be supported by the drum 50. Furthermore, after illumination, the sheet may be contacted by the pair o~ rollers 18 and be removed from the drum 50.

Retaining a sheet fed into the drum 50 is performed by trans-lating rollers 52 and 54 out of engagement with the sheet and away therefrom, as may best be seen from Fig. 2 where refer-ence numerals 52' and 54' re~er to the retracted positions o~
the rollers 52 and 54, respectively.

Abutment of the sheet is performed by translating a sliding member 60 between a first position as shown in Fig. 2 in ~ull line and second, abutting position shown in a dashed line and re~erred to re~erence numeral 60' in which it is adapted to abut an end portion o~ the sheet.

At the opposite end portion o~ the sheet, the means ~or abutment are shown on Fig. 3, where a movable means 70 is movable along a support surface 56 of the drum 50 ~rom a first position which is substantially at the end of the drum 50 opposite to that at the sliding means 60 to a second position wherein a substantially straight and rigid contact-ing means 72 of the movable means 70 contacts and abuts the opposition edge portion of the sheet.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 At present, it is pre~erred that the movable means 70 com-prise two toothed wheels 74 positioned at the opposite peri-pheral side portions of the drum 50 and engaging with a toothed rim portion 76 on the outer side of the drum 50. The two toothed wheels 74 are interconnected by a common axel and driven by a motor 78.

As the abutted edge portion o~ the sheet may not be per~ectly plane and co-linear with the means 72, the means 72 are pre~erably resiliently connected, such as through springs, to the rest of the movable means 70 in order to compensate for small deviations in the angle between the sheet and the means 72.

The means 70 are ~urthermore preferably equipped with ~orce measuring means (not shown) in order to determine the force exerted by the means 70, that is of the springs thereof, onto the edge portion of the sheet ln order to keep this below a predetermined maximum ~orce, which would otherwise lead to deformation of the sheet.

Thus, abutment of the sheet comprises, subsequent to feeding the sheet, a translation o~ the rollers 52 and 54 and the sliding means 60 into positions 52', 54' and 60', respective-ly, and subsequent movement of the moving means 70 from a ~irst position to the second position, wherein a predeter-mined ~orce is exerted on the two opposite edge portions of the sheet.

When the predetermined desired force is suitably selected, the sheet will now be ~orced outwards toward the support surface 56 o~ the drum 50 and, thus, closely resemble the substantially circular cylindrical shape of the inner sur~ace o~ the drum 50.

Illumination o~ the sheet is per~ormed, as it is known ~ se using a carriage moving along a linear track 81 and on which a laser and suitable optical elements are positioned as well CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 as a rotatable mirror, which directs the laser light onto the photo sensitive substance o~ the sheet.

An irradiation means 80 O~ this type is illustrated on Fig.
4, where they comprise a laser 82 positioned on a base plate 5 84 which is adjustably mounted on the means 80 by means of three adjusting screws 86, 88 and 90, a collimating lens 92, and an acousto-optic modulator 94, lenses 96, 98 and 100, a rotatable mirror 102 and a motor 104 ~or rotating the rotatable mirror 102.

As is known ~_ se and as may be seen ~rom Fig. 4 the trans-mission o~ the light through the acousto-optic modulator 94 introduces a small angular displacement of the laser beam, whereby the laser 82 and lens 92 are at a small angle to the optical axis o~ the remainder o~ the means 80.

As is also known, in order to ~unction optimally, the light entering the modulator 94 should be ~ocused in the middle thereo~ and have a diameter o~ at the most 50 - 100 ~m. As the laser beam of the presently used laser is collimated with a beam diameter on the order o~ 0.7 mm, the lens 92 ~ocuses 20 this beam in the modulator 94.

Even though the lens 92 iS positioned in a housing 93 ~ixed to the means 80 and extending over the base plate 84 in order to be correctly positioned in relation to the laser 82, a position this close to the laser 82 may not be required.

25 Illumination of the photo sensitive substance is consequently per~ormed by rotating the rotating mirror 102, modulating the laser and translating the means 80 in a manner so that the rotating mirror 102 translates along the symmetry axis o~ the substantially circular cylindrical sur~ace 56 O~ the drum 50 in order to have the same ~ocused laser beam on all parts o~
the illuminated sheet.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 In order to be able to precisely position the illuminated sheet during a subsequent process wherein it ~orms the basis o~ e.g. a printing process, it is pre~erred to provide regis-tering notches in the sheet, which notches are precisely positioned in relation to the illuminated image.

Providing these notches is pre~erably per~ormed while the sheet is in the illumination position and, thus, in connec-tion with the illumination thereo~ and most pre~erably be~ore illumination c~. below.

In the present instrument, the sheet is pre~erably ~ed into the drum 50 in a manner so that a part thereo~ extends beyond a side o~ the drum 50 in a direction parallel to a longitudi-nal axis thereo~. Thus, part o~ the sheet extends beyond the drum 50, whereby this part is ~ree ~or the engagement o~
notch providing means 200 which may engage with the sheet without inter~ering with the drum 50.

As is illustrated in Fig. 5, the notch providing tools 200 comprise a base part 202 and a movable part 204 between which a gab is de~ined wherein the sheet is introduced before making the notch. By operating a motor 206 which through a worm gear 208 and an eccentric 209 translates the movable means 204 ~rom its ~irst position illustrated in Fig 5 to its second position, wherein it is submerged in the base means 202, and back, indentation o~ the sheet is per~ormed.

One center axis o~ the eccentric 209 is connected to the movable part 204 and the other center axis o~ the eccentric 209 is connected to the worm gear 208.

The movement o~ the movable means 204 is monitored by moni-toring means 210 in a manner which will be described below.

The base part 202 is ~astened to the apparatus along an axis C. Due to the movement o~ the eccentric 208, the motor 206 may rock during the provision of the edge portion. In ~act, CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 the movement o~ the motor 206 and eccentric 208 is the move-ment detected by the monitoring means 210, as this means is positioned so as to detect movement between the base part 202 and the eccentric 208.

The movement o~ the motor 206 is, due to the position o~ the eccentric 208 into and out o~ the plane o~ Fig. 5, and is monitored by the means 210, which detects the movement 90~
out o~ phase with the movement o~ the movable part 204.

Thus, the means 210 is activated when the movable means 204 moves from the ~irst position to the second position - that is, during provision o~ a registering edge portion - and de-activated during the opposite movement. The means 210 shi~ts its mode when the moving means 204 is in its ~irst and second position.

Using a means 210 in this manner, only a single means is su~icient ~or monitoring the movement o~ the moving means 204.

The notch providing means 200 are pre~erably movable in a direction transverse to the edge to be indented o~ the sheet so that the indenting or notch providing means 200 are posi-tioned away ~rom the sheet and wherein the movable means 204 are in their ~irst position when the sheet is ~ed into its position. This is illustrated on Fig. 6.

Subsequently, the indenting means 200 are translated into contact with the sheet, initially having a position as shown in a dashed line with the re~erence numeral 212, and trans-lated into its ~inal position shown in a dashed line with re~erence numeral 214, so that the indenting means 200 take part in the defining o~ the ~inal position o~ the sheet prior to illumination thereo~.

This translation o~ the sheet is per~ormed while the retain-ing means 60 and 70 retain the sheet. However, it is pre-CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 ~erred that the ~orce exerted by the abutting means thereo~
is smaller than the predetermined ~orce exerted during illum-ination thereo~, as this translation o~ sheet while exerting a relatively large ~orce thereon, may result in de~ormation o~ the sheet.

Subsequent to translation o~ the sheet into its ~inal posi-tion, the movable means 204 are translated ~rom its ~irst to its second position, whereby a suitable indentation is made in the sheet.

In order not to de~orm the sheet during indentation thereo~, the stationary means 202 pre~erably comprise a support sur-~ace 220 on which the sheet may rest during indentation.
Pre~erably, this sur~ace 220, into which the movable means 204 are received subsequent to indentation o~ the sheet, has an edge 222 ~itting the indenting edge 224 o~ the means 204.
In this situation, only the part o~ the sheet closest to the position o~ indentation is in~luenced (and, thus, has a small risk o~ de~ormation) by the indentation.

As described above, it is pre~erred to be able to illuminate all parts o~ the sheet. Thus, it is desired not to have any kind o~ shadowing elements positioned over the sheet during illumination thereo~. Thus, it is pre~erred that, subsequent to indentation, no part o~ the indentation or notch providing means 200 to any substantial degree extend beyond the plane o~ the sheet positioned on the sur~ace 220.

As may be seen ~rom Figs. 5 and 6, the moving means 204 and the stationary 202 are manu~actured so that the moving means 204 may be introduced completely into the stationary means 202 so as to not pro~ect above the support sur~ace 220 o~ the stationery means 202. Thus, no part o~ the indentation means 200 may provide shadows during illumination o~ the sheet.

The axial positions o~ ~the indentation o~ the sheet may, naturally, be adapted to the individual needs or requirements CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 the operator. However, at present, a rectangular ihdentation and an indentation as illustrated where parts o~ the outer contour of the movable means 204 comprise an edge portion de~ining part o~ a circle are provided. These indentations help in positioning the illuminated sheet in e.g. a printing machine.

A widely used European industry standard requires a distance between the two indentations of 220 or 425 mm and that these indentations be positioned symmetrically about the middle o~
the sheet.

Thus, it may be required to provide either multiple indenta-tion tools 200 or that one or more of these tools be movable so as to be able to each produce multiple indentations.

In Fig. 7, a first position of three indenting tools 200 positioned on a main member 225 are illustrated in a first position in full lines and in a second position in broken lines.

Providing three tools 200 on the member 225 ~acilitates providing the two notches with the two different distances of a widely used European industry standard without having to move the means 225 between the indentations of the sheet.

When moving the main member 225 and the tools 200 between these two positions, each indenting means 200 may, alterna-tively, produce two indentations in the sheet. This provides the use of also other indenting standards in the present apparatus.

Providing a movable main member 225 and, thus, one or more movable indentation means 200, the instrument will be more versatile and will be able to accommodate different lengths of sheet. This is, naturally, highly preferred when the length of the sheet is often changed.

CA 022202l~ l997-ll-04 W096/36486 PCT~GI~~2-6 EXAMPLE 1: Alignment o~ the laser beam on the carriage In the presently pre~erred embodiment o~ the internal drum plotter o~ the invention, alignment o~ the laser beam on the carriage (o~ Fig. 4) is per~ormed by altering the position and direction o~ the laser.

It is presently contemplated that a method comprising introducing an alignment detector in the beam at one or more well-de~ined positions on the carriage will produce su~icient in~ormation concerning the direction and position o~ the laser beam to ensure a proper alignment o~ the beam.
This alignment detector should produce in~ormation o~ the beam direction and location relative to the alignment detector.

The presently pre~erred alignment detectar comprises a hollow tube 300 and an optical grating 302 - pre~erably a holo-graphic grating - positioned so that its perpendicular is at an angle (~) to the axis 304 o~ the tube 300. The tube 300 is positioned in a manner on the carriage so that the laser beam should pre~erably ~ollow the axis o~ the tube 300.

The laser beam is launched on to the grating 302, which will consequently di~ract the laser beam in at least a zeroth and a ~irst order beam. If the laser beam coincides with the axis 304 o~ the tube 300, the di~racted beams will impinge on detectors 306 and 308. I~ a holographic grating 302 is used, this may be manu~actured to only re~lect the zeroth and ~irst order so that the amount o~ disturbing stray light in the tube 300 is reduced.

The detectors 306 and 308 pre~erably have a certain area so that the di~racted laser beam will impinge thereon even i~
this does not exactly coincide with the axis 304 o~ the tube CA 022202l~ l997-ll-04 WO 96/36486 PCT/I)K96/00206 The function of the presently preferred tube 300 will now be described in more detail:

On Fig. 8, a cross section of the presently preferred cali-bration tube 300 is shown. In this tube 300, a tilted grating 5 302 is positioned which will diffract at least the zeroth and the first order of the incoming laser light in two different directions and, in the case where the laser beam coincides with the symmetry axis 304 of the tube 300, directly onto the center of two quadrant sensors 306 and 308 positioned at the wall of the tube 300. The reason that the grating 302 is tilted is the fact that, otherwise, the zeroth order beam would be emitted in a direction close to the symmetry axis of the tube 300 (and in the situation where the laser light coincides with the symmetry axis 304, the zeroth order will 15 also coincide with this axis), which makes it more difficult to detect.

If a coordinate system with an origo as shown on Fig. 8 is chosen, D and ~ are known. (x0, D, z0) and (x1, D, z1) are the positions of the zeroth and ~irst dif~racted order, where 20 Xo, zo, xl and zl are measured at the inner wall of the tube 300 at the points o~ impingement of the laser beams. Knowing one coordinate (y or z) of the position of impact of the laser beam on the grating 3 02, the other coordinate may be found from y tan~ = z (1) 25 For the zeroth order beam which impinges a position detecto~-306 at (x0, D, z0) the following equation applies:

(z-z0) tan (~+~)+ y = D (2) ~ where o~ is the angle between the diffracted laser beam and the perpendicular of the grating 302 and, thus, ~+~ the angle CA 022202l~ l997-ll-04 W096t36486 PCTtDK~Gt~20G

between the diffracted beam and the axis 304 of the tube 300.
This gives (y tan~-zO)tan(e+o~)+y = D (3) for the zeroth order beam.

Equation (4) is general for the angles of beams diffracted ~rom gratings. (a is the grating constant denoting the sepa-ration between the lines of the grating 302 and ~ and ~ are as defined in Fig. 8) a (sina+sin~) =n~ (4) For the first order (n=1), this gives sin~ sin~ (5) For the first order beam being di~racted at an angle ~, resulting from a beam impinging on the grating 302 at (x, y, z), and impinging on a position detector positioned at (x1, D, z1), common geometry gives (z-z1)tan(e+~)+y=D (6) Introducing equation (5) gives (z-z1)tan (~+Arctan ( ~ -sin~))+y=D (7) which, using (1), may be transformed to (y tan~ )tan (~+A~ctan ( ~ -sin~) ) +y=D (8) CA 022202l~ l997-ll-04 WO 96/36486 PCTII)K96/00206 This equation and the corresponding equation (3 ) for the zeroth order give a system of two equations having two unknown variables, y and ~. Determ;n;ng the y-coordinate of the position of impact of the laser beam on the grating 3 02 will automatically determine the corresponding z-value.

Furthermore, ~ (the angle between the incoming laser beam and the plane of Fig. 8) may be determined from the equation (9) (Zl-zO)tan~ = x1-xO

Thus, from the positions of impact of the diffracted beams on the detectors 306 and 308, the position of impact (x,y,z) of the laser beam on the grating 302 and the angles of impact (~
and ~) may be determined.

X - Xl I Z (Xl Xo) (10) These values are the values required in order to determine the path of the laser beam on the carriage.

Naturally, as described above, it is preferred to use detectors having a certain area in order to be able to also detect laser beams not exactly coinciding with the axis 304 of symmetry of the tube 300. In fact, in order to be able to not only detect the diffracted laser beam, which would nor-mally be the situation i~ typical simple detectors were used, 20 but to also be able to determine in which direction this beam deviates from its desired path, the used detectors are pre-ferably position sensitive.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 At present, the so-called quadrant sensors are pre~erred.
This type o~ sensor 306 comprises ~our quadrants being ~our individual sensors 320, 322, 324 and 326 positioned as ~our quarters o~ a circle (See Fig. 9).

The advantage o~ this type o~ detector is that the actual position o~ impingement o~ a laser beam or the like on a detector 306 o~ this type may be calculated ~rom the output o~ the ~our sensors 320, 322, 324 and 326.

The coordinates x and y are now used in a Cartesian coordinate system with origo in the center o~ a quadrant detector.

The power o~ a laser beam is gaussian, whereby the intensity o~ the beam impinging in position XL~ YL may be ~ound ~rom (X--X~ ) 2 _ 2 ( Y--YL) 2 ( 1 1 ) IL(X~Y)=e W e W

Looking at Fig 9, ~rom a simple circle, where capital x (X) and y (Y) denotes the outer limits o~ the detector 306 in question:

X2+y2=r2 ~ X=~2_y (12) Thus, integrating the total intensity, the power detected by the sensors 320, 322, 324 and 326 may be ~ound ~rom:

Y ~
P320=J J IL (X, Y) dx dy (13 ) o o CA 022202l~ l997-ll-04 W096/36486 PCT~K'96/00206 Y o P32Z=¦ J IL(X,Y) dx dy (14) o -~

o o P324=J J IL(X,Y) dx dy (15) -Y

o P326=J J IL(X~Y) dx dy (16) y o From these ~our outputs o~ the sensors, the position (XL~ YL) o~ impact o~ the laser beam on or near the detector may be determined.

The two positions (one ~rom each detector 306, 308) are introduced in equations (3) and (8) in order to give the position of impact o~ the incoming laser beam on the grating 302 and the angle under which the laser beam enters the tube 300.

The angle and position o~ the laser beam may then be cor-rected while monitoring the output o~ the two detectors 306 and 308 so as to obtain the desired reading ~rom these detectors.

Thus, when positioning the tube 300 in a given position on the carriage 80 o~ the presently pre~erred plotter 2, where the x-axis o~ the tube coordinate system is horizontal, the position and direction o~ the laser may be corrected in order to have the correct illumination o~ the sheet.

It may be pre~erred to per~orm the alignment o~ the laser beam in more than one step where the tube 300 is positioned at more than one location on the carriage 80 at di~erent positions ~urther and ~urther away ~rom the laser 82. This CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 method may be pre~erred as the above-described tube 300 has a limited "area o~ sight" whereby a too mis-aligned laser may not be detected by the detectors 306 and 308. When per~orming a coarse alignment using the tube 300 at a position closer to the laser 82, it is ensured that the laser beam will be detectable at the position ~urther away ~rom the laser 82.

Thus, it may be pre~erred to ~irst remove the lens 92 and the housing on the carrier 80 (See Fig. 4) and here per~orm a coarse alignment o~ the laser beam. Subsequently, the ~inal alignment is per~ormed by removing lenses 96, 98 and 100 and replacing the spinner-motor 104 and mirror 102, which are positioned on a re~erence sur~ace, with the tube 300. Final-ly, the position o~ the carriage 80 in the apparatus may a~terwards be adjusted by launching the laser into the tube 300, while the carriage 80 is mounted on the apparatus 2. The tube should in this case be connected to the support sur~ace means 50 and be centered along the axis thereo~.

At present, it is pre~erred that the inner diameter D of the tube 300 is o~ the order o~ 28 mm, the outer diameter on the order o~ 38 mm, and that the length thereo~ is on the order o~ 12 cm. This geometry o~ the tube 300 limits the maximum ~irst order di~raction angle to 45~. The required grating constant should consequently be higher than 700 nm when using a laser beam with a wavelength o~ 532 nm.

The precision obtainable using the present alignment sensor may be described by:

I~ the laser on the carriage 80 is coarsely adjusted so that the laser beam at a distance o~ 1 m is within 5 cm ~rom its aligned direction, this corresponds to an angular error o~
under 5 cm/1 m = 0.05 rad. Along the length o~ the tube 300 (12 cm), this angular error corresponds to under 6 mm. This will also correspond to the maximum displacement o~ the laser beam spots near the detectors 306 and 308 o~ the tube 300 Due to the area o~ the pre~erred detectors (which may have a CA 0222021~ 1997-11-04 radius of several millimetres if desired) and to the area of the reflected laser beam, a laser beam impinging 6 mm from the center of a detector 306 or 308 may easily be detected and, thus, aligned.

Thus, even this very coarse initial alignment will allow the tube 3 00 to detect the beam and to allow for this to be properly aligned. As a quadrant detector may detect the position of a laser beam within ~m's, the final precision of the alignment having positioned the laser beam within e.g.

2.4 ~m will be 2.4 ~m/12 cm = 20 ~rad.

At present, the typical manner of adjusting the laser 82 on the carriage 80 is to position two small apertures spaced approx. 0.5 m and thereby to adjust the laser to obtain maximum intensity therethrough. This manoeuvre may take hours, and the final precision typically corresponds to 3 cm over 10 m, that is on the order of 3 mrad.

In fact, the present alignment is not only contemplated to be better but also faster, as the instrumentation translating the detected positions of the reflected laser beams may be made to not only inform the operator of these positions but also of the alignment knobs or the like to operate in order to align the laser beam. In its last consequence, this align-ment may be fully automated.

Even though the above was illustrated using a quadrant sensor having a circular detector area, the same, naturally, applies to similar detectors, such as quadrant sensors having a quadratic or square detector area.

Also other setups are contemplated to give similar results.
These setups differ from the above-mentioned by employing 3 0 different optical elements for performing the diffraction or other modification of the incoming laser beam. Naturally, this will in some cases require other positions for the detectors.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 In a ~irst alternative setup, the grating is replaced by a prism (such as a Melles Griot wedge 02 PRW 009) which will re~lect part o~ the incoming laser beam and transmit the rest thereo~. Again, it may be pre~erred to have the ~ront sur~ace o~ the prism tilted so that its perpendicular is at an angle to the axis 304 o~ the tube 300.

Two position sensitive detectors may, thus, be positioned so as to detect the two beams. The angle and position o~ inci-dence o~ the incoming laser beam on the ~ront sur~ace o~ the prism may be determined ~rom Snell's law.

In a second alternative setup, two thin, light transmitting gratings are used, where the zero-order beam ~rom the ~irst grating impinges onto the second grating. One ~irst order beam ~rom each of the two gratings are detected in order to generate the in~ormation.

I~ the angle o~ the incoming beam is not perpendicular to the gratings, the beam will impinge on the two gratings at di~-~erent positions. Furthermore, the position and angle o~
impingement o~ the beam on the ~irst grating may be deter-mined ~rom the positions o~ impingement on the tube 300 o~the two di~racted beams in much the same way as described above using two equations similar to (8).

The above method is contemplated to ~unction independently o~
the grating constants of the two gratings being equal or not.

In a third setup, the laser beam is di~racted by a thin transmission grating. The ~irst and zeroth order o~ the di~racted beam are projected onto a screen, making two spots. The distance between these spots vary as a ~unction o~
the angle o~ the incoming beam, whereby this angle may be determined. From the positions o~ these two spots relative to the axis o~ the tube, the position o~ the beam on the grating may be determined. The grating may be tilted in order to improve the resolution o~ the determination, as it may be CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 calculated that a tilt angle of approx. 90~ to the axis of the tube 300 is optimal using a grating constant of 1 ~m. The detection of the spots may be accomplished using e.g. a CCD-array, a diode array or a PSD (position sensitive device).

5 When producing an alignment detector of the above-described type, production imperfections will typically render it necessary to calibrate this instrument before using it to align lasers on e.g. sensitive plotters. If positioning of the laser beam on the detectors is desired to a precision of ~m's, the positioning of these detectors should, naturally, be within at least the same precision.

Calibrating the present alignment detector is presently contemplated to be per~ormed by launching a laser beam in a direction along the symmetry axis 304 of the tube 300 and 15 determ;n~ng the positions of the re~lected beams on the two detectors 306, 308. These positions are thereafter the cali-brated positions, which the reflected laser beams to be aligned are to obtain.

Aligning the tube 300 after a given laser beam may be 20 obtained using the setup o~ Figs. 10 and 11, where a laser beam is produced by a laser 330 and directed as the zero-order beam from a grating 332 into the tube 300. Positioning of the tube 300 iS per~ormed by way o~ manipulating a total of twelve positioning rods 340, 342, 344, 346, 348, 350, 352, 25 354, 356 and 358, of which two are not shown. These position-ing rods are connected to an outer tube 336 to which the laser 330 and grating 332 are also connected in order to provide a frame for the calibration of the alignment detector.

30 It may be preferred to first perform a coarse positioning with the rods 340, 342, 344, 346, 348, 350, 352 and 354 with no engagement to the ~our other rods, as an adjustment o~ one o~ these rods may include the loosening o~ a fastening device (not shown) introducing a small error. Subsequently, a finer CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 adjustment using the ~our rods 356 and 358 (the other two, which are not shown, are similarly positioned at the other end o~ the tube 300) which are positioned so as to abut the lower side o~ the tube 300 wherea~ter the rods 340, 342, 344, 346, 348, 350, 352 and 354 are removed.

As the ~irst-order beams ~rom the grating 332 have well-de~ined directions in relation to the zero-order beam, these may be used in order to position the tube 300 in relation to the zero-order beam inside the outer tube 336. To this e~ect, a total o~ ~our detectors 360, 362, 364 and 366 are temporarily positioned on the outer side o~ the tube 300 to detect the ~irst-order beams. Naturally, as the ~irst-order beams and the zero-order beams diverge away ~rom the grating 332, the two detectors 360 and 362 positioned on the ~ront end o~ the tube 300 closer to the grating 332 are positioned closer to the tube 300 than the detectors 364 and 366 posi-tioned at the farther end o~ the tube 300 Having ~irstly positioned one end o~ the tube 300 correctly, this is rotated 90~ so as to have the two other detectors detect the ~irst order beams and in order to be able to position the other end o~ the tube 300.

By positioning the tube 300 so as to obtain optimum reading ~rom the ~our detectors 360, 362, 364 and 366, the zero-order beam entering the tube 300 should coextend with the symmetry axis 304 o~ the tube 300, whereby the calibrated position o~
the two detectors 306 and 308 o~ the tube 300 may be deter-mined.

A more simple calibration setup ~or the tube 300 may be one where only the eight rods 340, 342, 344, 346, 348, 350, 352 and 354 are used and where the rods 340, 342, 348 and 352 are replaced by spring-biased elements so that operation o~ the other ~our rods will provide su~icient displacement o~ the tube 300.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 In the above suggested calibration setups, the detectors are positioned so as to be able to detect the first order beams, that is, in positions so that the rods are not in the way.
However, it may be preferred to have the detectors positioned so as to receive light transmitted through the rods. Thus, it may be preferred that at least part of the rods are shaped so as to allow the laser light to pass. A suitable shape may be a shape comprising a throughbore for the laser light.

The present alignment detector may be used for detecting the position and direction of a laser beam or any other substan-tially monochromatic beam relative to a reference direction Naturally, the wavelength of the laser 330 should be one detectable by the detectors 360, 362, 364 and 366.

The present alignment detector may be used in the adjustment of a ruby laser. This is presently performed using a heat sensitive sheet of paper for detecting the invisible beam.
This procedure can be replaced using the above-mentioned third alternative setup, which allows for a large percentage o~ the energy of the laser beam to be transmitted through the detector. In fact, any laser adjustment may benefit from the present alignment detector, especially the cumbersome adjust-ment procedures of power lasers.

Additionally, the alignment detector may be used in the alignment of optics o~ any kind, such as where optical elements are to be centered around an optical axis.

EXAMPLE 2: Controlling the spot size o~ the laser beam on the photo sensitive substance Usually, the controlling o~ the spot size o~ a spot illumi-nated by the laser beam on the photo sensitive layer of the sheet is per~ormed by controlling the size of an aperture positioned at a given position in the laser beam.

CA 022202l~ l997-ll-04 WO9.'~6~186 PCTIDK96/00206 However, as this method has a number o~ disadvantages, an alternative method is suggested.

At present, it is pre~erred to control the spot size oE a spot illuminated by the laser beam on the photo sensitive 5 substance by regulating the power o~ the laser beam according to the below procedure.

A typical photo sensitive layer as used in the art has a certain burn threshold (o~) deEining the lowest amount o~
energy required in order to expose the sheet material. At 10 present, an o~ o~ 1.3 J/m2 is assumed, but this number may, naturally change Erom material to material.

At present, the procedure will be described with reEerence to the characteristics of~ the pre~erred D~ 620 internal drum laser image setter f~rom ESKOFOT A/S, Denmark and o~ a typical 15 size and type o~ sheet. However, these characteristics may easily be changed in order to adapt the procedure to another apparatus.

The present apparatus comprises an internal drum having a diameter o~ 320 mm. A typical material is a 0.15 mm Aluminum 20 material comprising a photo sensitive layer having the above-mentioned burn threshold and having a length (plate-length) oi~ 720 mm along the direction oE the lines illuminated during the rotation o~ the movable mirror. This constellation gives that the sheet extends 257.8~ in the drum.

25 The angular velocity o~ the rotating mirror in the apparatus is 20,000 rpm and the spot radius o~ the laser beam on the photo sensitive layer oi~ the sheet is 16 ,~Lm. The manu~acturer (Coherent) of~ the presently pre~erred laser, Coherent DPSS
532, gives a correction coeE~icient (M2-coef~icient) of~ 1.1, 30 which means that the spot size is actualIy 1.1 times the 16 m due to the beam o~ the laser not being ideal. This coei~Ei-cient is described in detail in "Beam Characteristics and Measurement oi~ Propagation Attributes" by M. W. Sasnett and CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 T. F. Johnston, Jr., SPIE Proceedings, Vol. 1414, 1991. This correction, however, has not been taken into account in the following procedure.

The spot size is de~ined as the size o~ the spot where the intensity is e~2 (approx. 13.5~) o~ the maximum intensity o~
the beam in the center thereo~.

Usually, the resolution (res) desired in this type of appa-ratus is in the area o~ 750-3600 dpi (dots per inch) Assuming that the laser beam is per~ectIy Gaussian, the volume o~ normalized Gaussian rotational body is ~w2/2.

The intensity distribution of the laser beam is:
-2 r (17) f(r) = e W2 The desired exposed radius o~ an illuminated spot (in meters) is R(res) = 1 25.4-10-3 (18) 2 res The total energy required in order to expose a dot having the radius o~ equation 18 - that is to bring the intensity at this point over the burn threshold - is tocal f(R(res) ) 2 (19) where the intensity o~ the laser beam at the radius R(res) is ~, as required. From the ~act that the intensity at the radius R(res) is the maximum intensity o~ the beam multiplied ---~(R(res)), ~/~(R(res)) is the maximum power in the center o~the beam. Equation 19 is derived ~rom an integration o~ the power o~ the spot.

CA 022202l~ l997-ll-04 W096/36486 42 PCT~K96/00206 The time required for making a single rotation (in seconds) o~ the mirror is Tro t = ~,~ ( 20) As the sheet extends a total o~ 257.8~ in the drum, TL is the time required in order to make a line along the ~ull length thereo~ along the direction o~ movement o~ the mirror 360 rot (21) Knowing the resolution, the number o~ spots (N) along the length o~ the material may be found ~rom N(res) = plate 1 ength.reS (22) The time available ~or making one o~ these spots may be found ~rom TspOt(res) N(res) (23) Thus, in order to be able to expose the sheet in the time available ~or generating the spot, the power ~rom the laser required is P (reS) = Ptotal (res) (24) From Fig 13, a curve describing the relation between the resolution desired and the laser output (in W) required is shown.

As the rotation o~ the rotatable mirror is not altered by a change in resolution, the velocity o~ the carriage carrying CA 022202l~ l997-ll-04 W096/36486 PCT~K96100206 the laser is. Thus, the dif~erence in the situations o~ Fig 13 both having the same output power but di~erent resolu-tions are situations having different carriage velocities.

In the art, one may desire that the spot size illuminated is slightly larger than the resolution of the illumination in order to have an overlap between the generated spots. Thus, e.g. a spot size o~ 1.2 times the resolution may be desired.
In order to facilitate this, a lower resolution should be entered in the above calculation in order to give the desired result.

From Fig. 13 it may be seen that a small power variation o~
the output of the laser will have a large e~ect on the ~inal resolution, if this is in the area o~ 1200-1800 dpi, whereby it is desired to have a precise monitoring and control of this output power and a suitable power supply ~or the laser, as this also has an effect on the power emitted.

Naturally, the precision of the spot size o~ the instrument depends on both the mechanics o~ the instrument and on the optics thereo~. This precision may be made larger or smaller depending on the apparatus and is o~ten de~ined in order to provide an instrument honouring this de~inition Knowing this defined or pre-defined uncertainty (~res/res), the power stability (~p/p) may be calculated ~rom = Qres ~ res dp(res) 1 (25) p res L P ( res) dres where dpres/dres may be found from Fig. 13 or the pertaining equation 24.

Thus, i~ ~res/res is de~ined to a ~ew percent, ~p/p would be on the order of a ~ew tenth of a percent outside the interval of 1200-1300 dpi and even smaller in this interval.

CA 022202l~ l997-ll-04 W096/36486 PCT~K96/00206 This will give the requirements ~or the laser and its power supply.

One drawback o~ the present method compared to the above-mentioned prior art method is the ~act that the sharpness o~
the illuminating spot o~ the laser light will depend on the power o~ the laser. Thus, as this power will vary with vary-ing spot size, the sharpness thereo~ will vary.

The reason ~or this is the sharpness o~ the Gaussian inten-sity distribution o~ the beam. I~ the burn threshold o~ the material is at a position on the Gaussian curve where this is steep, the de~ined spot will be very sharp On the other hand, i~ the Gaussian curve is relatively ~lat, such as at the top or bottom thereo~, the edges o~~the spot may be less well-de~ined due to the more ~lat intensity distribution.

However, this may not have a serious e~ect on the illumina-tion. Some o~ the widely used photo sensitive emulsions used have a very steep illumination curve which means that i~ the intensity is above the burn threshold, whereby the illumi-nated spot will be ~ully coloured, and no coloration will take place even i~ the intensity is ~uite near the burn threshold - as long as it is below this threshold.

Using emulsions o~ this type, a less well-de~ined spot size will only have a very limited e~ect on the ~inal result.

Thus, simply by altering the output power o~ the laser and the velocity o~ the carriage, the resolution o~ the illuml-nated image may be controlled.

Claims (48)

1. An apparatus for irradiating a sheet of a material comprising a layer containing a photo sensitive substance, said apparatus comprising - a concavely curved support surface means for supporting the sheet and for defining at least part of a substantially circularly cylindrical surface, - means for feeding, in a direction at an angle to a longitudinal axis of the support surface means, the sheet into contact with the support surface means in a position in which the sheet extends peripherally between first and second opposite edge portions, - irradiating means for irradiating the photo sensitive substance of the sheet, - means for retaining the sheet in a predetermined position in relation to the support surface means, the retaining means comprising means for abutting the opposite edge portions of the sheet and for forcing the edge portions substantially peripherally so as to force the sheet into a substantially circularly cylindrical shape in contact with the support surface means, characterized in that a sliding member is adapted to be moved between a first and second position, in which the sheet in the first position may be fed into its said position and where the sliding member in the second position is adapted to abut one of the first and second opposite edge portions so as to constitute part of the abutting means.

2. An apparatus according to claim 1, wherein the abutting means comprise - stationary means peripherally immovable in relation to the support surface means for abutting one of the first and second opposite edge portions and - movable means peripherally movable in relation to the support surface means between first and second positions in which it is out of engagement with and in abutment with the other of the opposite edge portions, respectively.

3. An apparatus according to claim 1 or 2, wherein the feeding means are adapted to feed the sheet into said position in a first direction along a first path of which a part is defined by the substantially circularly cylindrical surface.

4. An apparatus according to any of claims 1-3, further comprising means for removing the sheet having been fed into said position.

5. An apparatus according to claim 4, wherein the removing means are adapted to remove the sheet along a second path, part of which is substantially identical to the part of the first path defined by the substantially circular cylindrical surface, in a direction substantially opposite to the first direction.

6. An apparatus according to any of the preceding claims, wherein the feeding means comprise two rollers between which the sheet is fed.

7. An apparatus according to claim 6, wherein one of the two rollers being adapted to contact the layer of the sheet containing the photo-sensitive substance is displaceable between a first and a second position where the roller, in the first position, contacts the layer in order to be able to feed the sheet and, in the second position, the roller is moved away from the layer in order to not create shadows on the material during irradiation.

8. An apparatus according to any of the preceding claims, wherein the means for feeding the sheet into contact with the support surface means are means for feeding the sheet in a direction substantially perpendicular to a longitudinal axis of the support surface means.

9. An apparatus according to any of the preceding claims, wherein the abutting means comprise means for abutting each of the two opposite edge portions at one or more positions.

10. An apparatus according to claim 9, wherein the means for abutting an edge portion at one or more positions comprise one or more means independently resiliently connected to a main holding means.

11. An apparatus according to claim 10, wherein the means for abutting an edge portion at one or more positions comprise a main member and a rigid means resiliently connected thereto and for abutting the edge portion.

12. An apparatus according to claim 10 or 11, wherein the resilient connection between the means for abutting an edge portion at one or more positions and the main holding means is a spring loaded connection.

13. An apparatus according to any of the preceding claims, wherein the abutting means comprise force measuring means for determining the force applied to the abutted edge portions.

14. An apparatus according to any of the preceding claims, wherein the abutting means comprise first engaging means engaging with second engaging means constituting part of the support surface means and a motor for driving the first engaging means.

15. An apparatus according to claim 14, wherein first the engaging means comprise a toothed wheel and where the second engaging means comprise a toothed portion along a radial part of the support surface means.

16. An apparatus according to any of the preceding claims, further comprising means for providing registering edge portions in the sheet.

17. An apparatus according to claim 16, wherein the edge portion providing means comprise at least two edge portion providing tools each providing one registering edge portion and being connected to a main member.

18. An apparatus according to claims 16 or 17, wherein the at least two edge portion providing tools and the main member are movable between at least two positions so that each of the at least two edge portion providing tools may provide multiple edge portions in the sheet.

19. An apparatus according to claim 18, where the at least two edge portion providing tools and the main member are movable along a substantially circular path.

20. A tool for providing a registering edge portion in a sheet of a material and for use in an apparatus according to any of the preceding claims, the tool comprising - a first edge portion defining means having a first edge portion defining the registering edge portion to be provided, - a second edge portion defining means having - a surface for contacting the sheet on the opposite side of the layer containing the photo sensitive substance during production of the registering edge portion, - receiving means at said surface for receiving the first means and comprising a second edge portion substantially inverse of that of the first means, where the first edge portion defining means are adapted to move between - a first position where a gap is defined between the first means and the contact surface of the second means and - a second position where the first edge portion defining means are introduced in the receiving means in a manner so that the first means to no substantial degree protrude beyond the plane of the contacting surface and so that the first and second edge portions become adjacent during the movement between the first and second positions.

21. A tool according to claim 20, wherein the edge portion to be defined in the sheet is an indentation or notch at an edge portion of the sheet.

22. A tool according to claim 20 or 21, wherein the first edge portion is an outer edge portion and wherein the receiving means constitute a hole or an indentation of the second means, wherein the second edge portion constitutes part of an edge of the hole or indentation.

23. A tool according to claim 22, wherein the first and second means are interconnected by an interconnecting body and wherein this and the first means are introduced in the hole or indentation of the second means when the first means are in the second position.

24. A method of irradiating a sheet of a material comprising a layer containing a photo sensitive substance, said method comprising the steps of:

- feeding the sheet into contact with a support surface means defining at least part of a substantially circularly cylindrical support surface in a direction at an angle to a longitudinal axis of the support surface means and in a position in which the sheet extends peripherally between first and second opposite edge portions, - irradiating the photo sensitive substance of the sheet while retaining the sheet in a predetermined position in relation to the support surface means by abutting the opposite edge portions of the sheet and forcing the edge portions substantially peripherally so as to force the sheet into a substantially circular cylindrical shape in contact with the support surface means characterized in that a sliding member, subsequent to the feeding step, is moved between a first and second position, where, in, the first position, the sheet may be fed into its said position and where the sliding member, in the second position, abuts one of the opposite edge portions during irradiation.

25. A method according to claim 24, wherein the abutting comprises - peripherally immobilizing one of the opposite edge portions of the sheet in relation to the support surface means and - moving a movable means peripherally in relation to the support surface means from a first position where there is no engagement with the sheet to a second position where the movable means abut the other of the opposite edge portions.

26. A method according to claim 24 or 25, wherein the feeding of the sheet into said position is performed in a first direction along a first path of which a part is defined by the substantially circularly cylindrical surface.

27. A method according to any of claims 24-26, further comprising removal of the sheet having been fed into said position.

28. A method according to claim 27, wherein the sheet is removed subsequent to irradiation thereof.

29. A method according to any of claims 27 or 28, wherein the sheet is removed along a second path, part of which is substantially identical to the part of the first path defined by the substantially circular cylindrical surface, in a direction substantially opposite to the first direction.

30. A method according to any of claims 25-29, wherein the feeding is performed using two rollers between which the sheet is transported.

31. A method according to claim 30, wherein one of the two rollers being adapted to contact the layer of the sheet containing the photo-sensitive substance is displaceable between a first and a second position where the roller during the feeding step is in the first position where it contacts the layer and, during the irradiating step, is in the second position where the roller is moved away from the layer in order to not create shadows on the material during irradiation.

32. A method according to any of claims 24-30, wherein the sliding member in the second position abuts and peripherally immobilizes one of the opposite edge portions.

33. A method according to any of claims 24-32, wherein the force applied to the abutted edge portions is determined by force measuring means.

34. A method according to claim 33, wherein the determined force is compared to a predetermined force, and where the result of the comparison is used for controlling the abutment of the edge portions.

35. A method according to claim 34, wherein the predetermined force depends on the thickness of the sheet.

36. An apparatus according to any of claims 24-35, wherein the sheet comprises a sheet-shaped base material having a thickness of 0.1-0.5 mm, preferably 0.1-0.4 mm, more preferably 0.3 mm onto which a photo sensitive layer has been applied.

37. A method according to any of claims 24-36, where at least one registering edge portion is provided by edge portion providing means while the sheet is retained by the retaining means.

38. A method according to claim 37, wherein the sheet is fed into said position in a manner so that a part thereof project beyond the support surface means in a direction parallel to a longitudinal axis thereof, and wherein the edge portion providing means are positioned so as to provide the at least one registering edge portion in that part of the sheet.

39. A method according to claims 37 or 38, wherein the edge portion providing means are movable between a first and a second position, the movement being at an angle to the periphery of the support surface, and the second position being further away from the support surface means than the first position.

40. A method according to claim 39, wherein the edge portion providing means are not in engagement with the sheet in the second position and where it is in abutment with the sheet when in the first position.

41. An apparatus according to any of claims 37-40, wherein the registering edge portions are defined by holes, notches or indentations in the sheet.

42. A method according to any of claims 39-41, wherein the edge portion providing means are in the second position when the sheet is fed into position and is moved into the first position before the sheet is irradiated.

43. A method according to claim 42, wherein a first predetermined force is applied during abutment to the sheet while moving the edge portion providing means from the second position to the first position, and where this force is smaller than a second predetermined force applied during irradiation of the sheet.

44. A method according to any of claims 40-43, wherein the sheet is substantially rectangularly shaped and wherein the edge portion providing means abut and provide registering edge portions in an edge of the sheet which is not abutted by the retaining means.

45. A method according to any of claims 37-44, wherein the edge portion providing means are movable substantially along the periphery of the support surface between at least two positions so that each of at least two edge portion providing tools of the edge providing means may provide multiple edge portions in the sheet.

46. A method of providing a registering edge portion in a sheet of a material, the method comprising - providing a first edge portion providing means having a first edge portion defining the registering edge portion to be provided, - providing a second edge portion defining means having - a surface for contacting the sheet during production of the registering edge portion, - receiving means at said surface for receiving the first means and comprising a second edge portion substantially inverse or congruent of that of the first means, - moving the first means into a position where a gap is defined between the contact surface and the first means, - positioning the sheet on said surface so that a part thereof is introduced in said gap, - moving the first means into a second position where the first edge portion moves through said gap, the first edge portion defining means being introduced in the receiving means in a manner so that the first means to no substantial degree protrude beyond the plane of the contacting surface.

47. A method according to claim 46, wherein the first and second edge portions become adjacent during the movement of the first means from the first to the second position.

48. A method according to claim 46 or 47, wherein the first and second edge portions are positioned adjacent to said gap so that these edge portions become adjacent when the first means is introduced in said receiving means.