A METHOD OF CREASING SHEETS

Abstract

The invention relates to a method of creasing sheets (12) by using a creasing tool (14, 20, 21) cooperating with a counter element (22, 23), comprising the following steps: a creasing plate blank (24′) is provided with at least one creasing projection (26) by plastically deforming the material of the blank (24′) so as to form a creasing plate (24),the creasing plate (24) is mounted to a creasing tool (14, 20, 21),sheets (12) to be provided with at least one crease are advanced through a gap between the creasing tool (14, 20, 21) and the counter element (22, 23).

Description

The invention relates to a method of creasing sheets.

Creasing machines are used for generating one or more creases in a sheet from which blanks are cut which are folded. Each of the creases forms kind of a “hinge” which allows the later formed blanks to be folded at a well defined place.

The creasing machine can be formed as a device or system which is either a standalone unit or is integrated into a larger machine or system such as a printing machine or a finishing machine.

The sheets can be made from cardboard, carton or a foil, and they can be provided to the creasing machine separately or in a continuous manner as part of a web.

The creases are formed by locally applying a pressure onto the sheet. To this end, creasing knives are known which are pressed onto the surface of the sheet so as to generate the crease. It is also known to provide local projections on the creasing tool, for example by etching away those portions of the creasing tool which shall not project, or by locally applying a plastic material in a liquid condition, which is then cured.

The creasing tool can either be generally flat and be moved back and forth in a direction which is generally perpendicular with respect to the plane in which the sheet extends, or it can be generally cylindrical and be rotated so as to engage at the sheet when it is being transferred through the creasing area.

The problem with all creasing machines is that they can hardly be quickly adapted to a specific pattern of creases to be applied to a sheet. This has become more of a problem since digital printing allows changing very quickly from one printing job to a different one.

Assuming that the creasing tool is to be manufactured by means of an etching process, it may take several hours until a new creasing tool is available. Assuming that the creasing projections are formed by applying a plastic material to a carrier, the manufacturing times might be shorter, depending on the time which is necessary for curing the plastic material. However, the lifetime of such a creasing tool is significantly shorter than the lifetime of a creasing tool comprising an etched steel plate. In any case, the step of adapting the creasing machine to a new creasing job is the bottleneck when the creasing machine is used in connection with a digital printing machine.

The object of the invention is to provide a creasing method which can be quickly changed from one creasing pattern to another creasing pattern.

In order to achieve this object, the invention provides a method of creasing sheets by using a creasing tool cooperating with a counter element, comprising the following steps:

• • a creasing plate blank is provided with at least one creasing projection by plastically deforming the material of the blank so as to form a creasing plate,
  • the creasing plate is mounted to a creasing tool,
  • sheets to be provided with at least one crease are advanced through a gap between the creasing tool and the counter element.

The invention is based on the concept of using a metal creasing plate in which the creasing projection is formed by a large number of punching strokes, the individual punching strokes generating the creasing projection. This allows achieving two advantages. First, the creasing plate has a long lifetime as there is very little wear at the creasing projections, simply because they are made from metal. The strain hardening which inevitably occurs during punching contributes to the wear resistance of the creasing plate. Second, individual creasing plates can be manufactured quickly and with very little effort by for example a turret punching machine or a coil punching machine.

Preferably, the material of the creasing plate blank is deformed by means of a punching module. It is thus not necessary to install a separate punching machine. Rather, a dedicated (smaller) punching module can be integrated into the machine so as to form a self contained creasing machine which does not require any external machinery when it comes to manufacturing the creasing plates.

The punching module is preferably a turret punching machine or a coil punching machine as these types of machine allow manufacturing the creasing plates in a very flexible yet quick manner.

According to an embodiment, the punching module has a punch and a die, the die having an outer contour which extends, adjacent the open end of the recess, at an angle of between 90° and 45°, approximately 45° or less than 45° with respect to the longitudinal direction of the recess, the die being rotated so as to align the outer contour with an already generated creasing projection. The advantage of this geometry is that merging creasing projections can be generated which extend at an angle of 45° with respect to each other.

In order to be able to quickly exchange one creasing plate against a different one, the creasing plate can be clamped to the cylindrical surface of a creasing cylinder of the creasing tool.

When a creasing cylinder is being used, it preferably cooperates with a counter cylinder. The counter cylinder can be provided with an elastic layer against which the sheets are pressed and which allows the creasing projections to locally deform the sheets so as to generate the creases.

The counter cylinder can alternatively be provided with a layer made from a shape memory material. This layer can be clamped to the counter cylinder in order to facilitate the installation, and can be “erased”, owing to the shape memory qualities of the material from which it is made, once a creasing job is finished.

According to a preferred embodiment, the distance between the axis of rotation of the creasing cylinder and the counter cylinder is adjusted with respect to the plane in which the sheet is transported, before a creasing job is started. This allows changing the creasing direction (from above the sheets to from below the sheets, and vice versa) so as to be able to crease carton and corrugated cardboard on one and the same machine. It is sufficient to exchange which of the cylinders is provided with the creasing plate and which is provided with the layer acting as counter element to the creasing plate, and to change the distance between the axis of rotation of the two cylinders and the plane in which the sheets are being transported through the creasing area between the cylinders.

Preferably, the creasing cylinder and the counter cylinder are driven with different speeds of rotation. This ensures that the peripheral speed of both cylinders at the radius at which they interact with the sheets is identical, despite the fact that there are different effective radii.

According to an embodiment, a driving fillet is generated on the creasing plate, the driving fillet extending around the majority of the circumference of the creasing cylinder. Providing a driving fillet avoids the problem that usually, the driving engagement between the creasing cylinder and the sheets depends from the presence of creasing projections in the gap between the two cylinders, the creasing projection entraining the sheets. If however no creasing projection is present in the gap at a certain point in time, then the sheet usually has no contact to the creasing cylinder as the outer surface of the creasing cylinder is at a distance from the surface of the sheets; it is only the creasing projections which engage at the sheets. The driving fillet ensures that a driving engagement between the creasing cylinder and the sheet is always maintained (possibly apart from a short dead zone which is used for clamping the creasing plate to the creasing cylinder). Thus, even if no creasing projection is currently engaging at the sheet, the sheets are positively driven by means of the driving fillet.

The driving fillet can be obtained by locally deforming the creasing plate in a manner similar to the creasing projections. As an alternative, the driving fillet can be obtained by applying a strip of epoxy material onto the creasing plate, which is then cured.

The method preferably comprises the further step of detecting the arrival of a sheet to be creased at the gap between the creasing tool and the counter element and controlling the rotation of the creasing tool and the counter element in dependence upon said detection.

The invention will now be described with reference to the enclosed drawings. In the drawings,

FIG. 1 schematically shows a creasing machine,

FIG. 2 schematically shows one embodiment of the creasing tool used in the creasing machine of FIG. 1,

FIG. 3 schematically shows a second embodiment of a creasing tool used in the creasing machine of FIG. 1,

FIG. 4 shows a cross section through a creasing plate mounted to the creasing tool and generating a folding crease by pressing the sheet against the counter element,

FIG. 5 schematically shows the process of creating a creasing projection on a creasing plate,

FIGS. 6a to 6c show three different embodiments of punches used in the creasing machine of FIG. 1,

FIGS. 7a and 7b show a first embodiment of a die used in the creasing machine of FIG. 1,

FIG. 8 shows a second embodiment of the die used in the creasing machine of FIG. 1,

FIG. 9 shows a die according to the prior art,

FIG. 10 shows a cross section through a punch and a die when deforming a creasing plate blank,

FIGS. 11a and 11b schematically show the die of FIGS. 7a and 7b when generating two merging creasing projections, and the folding creases generated with these folding projections, and

FIGS. 12a to 12e schematically show the die of FIGS. 7a and 7b used for manufacturing three merging folding projections, and the folding creases generated with these creasing projections as well as a corresponding blank cut from a sheet and a box manufactured from the blank,

FIGS. 13a and 13b show in more detail creasing projections obtained with the punches of FIGS. 6b and 6c,

FIGS. 14a and 14b show a cross section through creasing projections used for creasing carton,

FIGS. 15a and 15b show in a cross section a creasing projection used for creasing corrugated carton and the crease obtained therewith,

FIGS. 16a and 16b show the creasing tool of FIG. 3 in a first and in a second condition,

FIG. 17 schematically shows the creasing tool in more detail in combination with a control of the speed of rotation of the cylinders,

FIG. 18 shows a schematic cross section through the creasing tool for explaining the speed of rotation of the cylinders,

FIG. 19 shows at a larger scale the area of contact between the two cylinders of the creasing tool and the sheet to be provided with the creases,

FIGS. 20a to 20c show a top view on a creasing plate, a cross section through the creasing tool provided with a driving fillet and a cross section through part of a creasing plate provided with a driving fillet and a creasing projections,

FIGS. 21a to 21c show a perspective view of a cylinder used in the creasing tool, an enlarged view of the clamping mechanism used for clamping the creasing plate and used for clamping the elastic layer of the counter cylinder,

FIGS. 22a to 22g show different steps of using a counter cylinder according to an alternative embodiment,

FIGS. 23a to 23d show the cylinder used in the creasing tool in more detail, and

FIGS. 24a and 24b show the counter cylinder in more detail.

In FIG. 1, a creasing machine is schematically shown. It comprises a transportation system 10 for advancing sheets 12 through a creasing area 14 where folding creases can be applied to the sheets 12.

Additional processing stations 16, 18 may be provided as part of the creasing machine or associated therewith. Processing stations 16, 18 can be used for cutting, folding, gluing or otherwise processing the sheets 12 or articles produced therewith.

Sheets 12 can be made from cardboard, carton or foil, and they can later be processed so as to cut blanks from the sheets to form a package, a box, a wrapping, an envelope or a similar product.

Sheets 12 can be supplied to creasing area 14 either separately as shown in the Figure, or in the form of a continuous web guided through creasing area 14.

It is also possible to integrate into creasing area 14 a cutting system which allows separating the individual blanks from the sheet.

In creasing area 14, a creasing tool and a counter element cooperate so as to apply at least one folding crease to sheet 12. To this end, the creasing tool carries a creasing plate, the creasing plate being provided with creasing projections. The geometry and arrangement of the creasing projections on the creasing plate corresponds to the folding creases to be applied to the sheet.

A first example of the creasing tool and the counter element used in creasing area 14 is shown in FIG. 2.

The creasing tool is here in the form of a plunger 20 which can be advanced towards and pressed against a counter element 22. At plunger 20, a creasing plate 24 is mounted which is provided with at least one creasing projection 26. Only a single creasing projection 26 is shown here for increased clarity.

On the side facing plunger 20, counter element 22 is provided with an elastic layer 28 which preferably is formed from rubber or an elastomer.

The sheets 12 to be provided with a folding crease are advanced with transportation system 10 so as to be positioned between plunger 20 and counter element 22. Plunger 20 is then pressed against elastic layer 28 whereby creasing projection 26 creates a folding crease 30 by locally deforming sheet 12.

A second embodiment of the creasing tool and the counter element is shown in

FIG. 3. Here, the creasing tool is provided in the form of a creasing cylinder 21, and the counter element is in the form of a counter cylinder 23. Accordingly, creasing plate 24 is curved, and elastic layer 28 is cylindrical.

The folding creases 30 are generated by advancing sheet 12 through the gap between creasing cylinder 21 and counter cylinder 23.

The interaction between creasing plate 24 and sheet 12 is shown in more detail in FIG. 4.

Creasing projections 26 are formed at creasing plate 24 by repeatedly and locally deforming the material of creasing plate 24 so as to generate the creasing projections 26 in the desired pattern. In order to allow for the desired plastic deformation, creasing plate 24 is formed from steel, in particular from carbon steel or stainless steel. It preferably has a thickness in the order of 0.2 to 0.6 mm.

For generating the creasing projections 26, a punching module 40 is provided, in particular a turret punching machine or a coil punching machine. Punching machines of these types are generally known. They however are preferably slightly adapted for being used in combination with the creasing machine. In particular, punching module 40 may not be as versatile and powerful as a conventional punching machine as it only has to perform a very limited number of different operations (namely generating generally straight creasing projections) in a rather thin material.

Punching module 40 is schematically shown in FIG. 1 with a punch 42 used for plastically deforming a creasing plate blank 24′.

Further, punching module 40 comprises a turret 44 in which a plurality of different punches 42 is stored.

FIG. 5 schematically shows how punching module 40 generates a creasing projection 26 by repeatedly plastically deforming creasing plate blank 24′. With full lines, punch 42 is shown which cooperates with a die 46 positioned on the opposite side of creasing plate blank 24′. With dashed lines, the position of punch 42 during the previous punching stroke is shown, and dotted lines indicate the position of punch 42 during the again proceeding punching stroke.

Each stroke generates a small, plastically deformed area at the creasing plate blank 24′, with the entirety of the plastically deformed areas forming the creasing projection(s) 26.

FIGS. 6a to 6c show different embodiments of the punch arranged on a carrier 43.

In FIG. 6a, a punch 42 with a comparatively short projecting portion 45 is shown. The length of the projecting portion can be in the order of one centimeter.

At its ends which are opposite each other when viewed along the longitudinal direction of the projecting portion 45, comparatively small radii are provided. They can be in the order of 0.2 to 2 millimeters.

In FIG. 6b, a punch 42 is shown in which the projection portion 45 is approximately three times the length of the projecting portion 45 of the punch 42 shown in FIG. 6a. It can be seen that the radii at the opposite ends of the projecting portion are comparatively large.

In FIG. 6c, a punch 42 is shown which has different radii at the opposite ends of the projecting portion 45. There is a small radius R₁ which is in the order of 0.2 to 2 millimeters only, and there is a large radius R₂ which can be in the order of 2 to 15 millimeters.

The height H (please see also FIG. 10) with which the projecting portion 45 projects over the forward end face of punch 42, is in the order to 1 to 2 mm.

FIGS. 7a and 7b show an embodiment of die 46 adapted for cooperating with punch 42 and mounted on a carrier 47.

Die 46 has a support surface 48 at which creasing plate blank 24′ may abut during the punching operation. Within support surface 48, a recess 50 is provided. Recess 50 is sized so as to receive the plastically deformed material of creasing plate blank 24′ forming the creasing projection 26.

As can be seen in FIGS. 7a and 7b, recess 50 is open at its opposite ends.

It can further be seen in FIG. 7a that the outer contour of die 46 adjacent one of the open ends of recess 50 extends inclined with respect to the longitudinal direction of recess 50. In particular, the outer contour at each side of recess 50 extends at an angle of 45° with respect to the longitudinal direction of recess 50.

At the opposite end of recess 50, the outer contour of die 46 extends perpendicularly with respect to the longitudinal direction of recess 50.

An elastic ejector 58 is arranged at die 46. Ejector 58 is formed as a plate from rubber or an elastomer and snugly surrounds die 46 so that it stays at the position shown in FIG. 7b without any additional measures.

In FIG. 8, a different embodiment of die 46 is shown. Here, die 46 has the inclined contour at both open ends of recess 50 (please see the portions to which arrows P point).

In FIG. 9, a conventional die 46 is shown which has a circular support surface 48.

In FIG. 10, a schematic cross section through the punch 42 cooperating with die 46 is shown.

The creasing plate blank 24′ is held, during the process of locally plastically deforming it so as to create the creasing projections 26, between die 46 and the carrier 43. Carrier 43 is here spring loaded towards die 46 so as to act in the manner of a clamp.

This avoids tension in the creasing plate blank 24′ which could result in unwanted deformations.

In FIGS. 11a and 11b, it is schematically shown how adjacent creasing projections 26 can be formed by means of the punch cooperating with die 46. For better clarity, the punch and the creasing plate are not shown in FIG. 11a. Rather, only creasing projections 26 formed at creasing plate 24 are shown.

The creasing projection 26 extending towards the left in FIG. 11a is a projection which was previously formed. The creasing projection 26 extending through the recess in die 46 is the creasing projection currently formed together with punch 42. It can be seen that the “new” creasing projection 26 can be formed to a point where it is immediately adjacent the “old” creasing projection 26.

The result of the immediately adjacent creasing projections 26 is visible in FIG. 11b where folding creases 30 are shown which are arranged at a 90° angle with respect to each other and which almost merge into each other. Since very little uncreased material remains in the corner between the folding creases 30, a very precise fold can be achieved in this area.

In FIGS. 12a to 12e, it is shown how three creasing projections 26 can be formed at a creasing plate. Due to the particular contour at one of the open ends of recess 50, the three creasing projections 26 can almost merge into each other at an intersection point. It can be seen in FIG. 12d where such creasing projections 26 can be used for forming folding creases 30 at a sheet 12.

These creasing projections are aimed to fold a composite flap of a crash lock bottom box or of a four corner or six corner tray.

Punching module 40 is capable of producing different creasing plates 24 by appropriately deforming a creasing plate blank 24′ at the required locations. It is in particular possible for the creasing machine, in particular for a schematically shown control 60 of the creasing machine, to determine, upon receipt of data for a new creasing job, whether a new creasing plate 24 is to be manufactured or whether an “old” creasing plate used in a previous creasing job can be used. Depending on the determination, control 60 either initiates that punching module 40 manufactures a new creasing plate 24, or that the “old” creasing plate 24 is retrieved from an inventory 62 where the previously manufactured creasing plates 24 are being stored.

The creasing plate 24 (either newly manufactured or retrieved from inventory 62) is taken over by handling system 64 and is then mounted at the creasing tool.

If the creasing tool is a punch, the plate is mounted in a flat shape. If the creasing tool is a creasing cylinder, creasing plate 24 can be either bent and clamped to creasing cylinder 23, or a circumferentially closed creasing sleeve can be formed which can then be mounted to creasing cylinder 23.

As is explained above, a punch having larger radii at opposite sides (to be precise: having larger radii at opposite sides of its projecting portion 45) is used for obtaining creasing projections 26 which have a smooth transition between the material deformed with each stroke of the punch. FIG. 13a shows creasing projections 26 which terminate at a larger distance from each other. The creasing projections 26 very smoothly merge into the creasing plate 24.

FIG. 13b shows two creasing projections 26 which terminate in a very small distance from each other so as to almost merge into each other. These creasing projections 26 are obtained by using a punch 42 which has at least at its “forward” end (referring to the direction in which the creasing plate blank 24′ is displaced during consecutive strokes) a small radius. The small radius allows for a comparatively steep rise of the creasing projection 26 from the creasing plate 24 so that a small distance between adjacent ends of the creasing projections 26 is possible.

It can be seen that the ends of the creasing projections which are at the opposite ends, terminate with a larger radius.

FIGS. 14a and 14b show cross sections through creasing projections 26 which have been proven to be very effective for creasing carton.

In FIG. 14a, the creasing plate has a thickness in the range of 0.4 mm while the height h of the creasing projection is in the range of 0.6 to 1.6 mm.

Depending from the particular carton to be creased, the radius R at the apex of the creasing projection 26 can be in the range of 0.25 to 0.7 mm. In other words, the apex matches an inscribed circle with a diameter of 2R.

Preferred values for the height h are in the region of 1.2 mm, while preferred radii can be 0.35 mm and 0.525 mm.

In FIG. 15a, a creasing projection 26 for creasing corrugated cardboard is shown. It can be seen that a much wider creasing projection is used as compared to the profiles shown in FIGS. 14a and 14b. In particular, the angle α is more than 90°. According to a preferred embodiment, this angle can be in the range of 110 to 120°, in particular 114°.

The wider conical shape of the profile of creasing projection 26 is effective to compress the carton on each side of the crease so as to create the space which is necessary for folding the corrugated cardboard (because of its increased thickness), thereby reducing the tension which is generated when the carton is folded.

Here again, a typical height of the creasing projection 26 is in the region of 1.2 mm. As the radius R at the apex of the profile, a value in the order of 0.5 to 0.6 mm is suitable, in particular 0.53 mm.

As a radius R at the base of creasing projection 26, a value in the order of 0.5 mm has been proven to be beneficial.

An inscribed circle here again can have a diameter of 1.05 mm.

It is important to note that the creasing projections 26 on one and the same creasing plate 24 can have different heights, depending from the particular requirements.

FIGS. 16a and 16b show an advantageous aspect of the creasing tool.

When changing from creasing cardboard to creasing corrugated carton, it is necessary to change the crease direction. This can very easily be done by changing the function of the two cylinders 21, 23.

In FIG. 16a, the upper cylinder acts as the counter cylinder 23 while the lower cylinder is the creasing cylinder 21. Accordingly, the elastic layer 28 is mounted to the upper cylinder while creasing plate 24 is mounted to the lower cylinder.

In the configuration shown in FIG. 16b, this arrangement is reversed. The elastic layer 28 is mounted to the lower cylinder while creasing plate 24 is mounted to the upper cylinder. Thus, the upper cylinder acts as creasing cylinder 21 while the lower cylinder acts as counter cylinder 23.

It is however the same set of cylinders which is being used. The function of the cylinder is simply determined by the “tool” mounted to it (either creasing plate 24 or elastic layer 28). Accordingly, both cylinders are provided with identical clamping mechanisms (here very briefly indicated with reference numeral 60), and the cylinders have the same diameter.

The functional outer radius of both cylinders depends from the tool mounted to it. In particular, the functional outer radius of the cylinder provided with the elastic layer 28 is larger than the functional radius of the cylinder provided with creasing plate 24. Accordingly, the plane in which sheet 12 is advanced through the creasing area between the cylinders has to be adjusted depending from the particular configuration. The respective Δ is indicated between FIGS. 16a and 16b.

The vertical adjustment of the plane in which sheets 12 are provided can either be obtained by vertically adjusting the feeding device which advances the sheets, or by vertically adjusting the two cylinders 21, 23 with respect to the feeding plane.

Another consequence from the functional radius of the two cylinders being different is that the speed of rotation of the cylinders is slightly different as the tangential speed at the point of engagement at the sheets 12 has to be the same. Further, it has to match the speed with which the sheets 12 are advanced through the creasing tool.

In order to allow for an individual control of the speeds of rotation, each cylinder is provided with a servo motor 62 which is controlled by means of a machine control 64. Machine control 64 is also provided with a signal relating to the position of the clamping devices 60 as they form a dead zone where no creasing can be made.

Machine control 64 is furthermore provided with a signal relating to the position of the sheets 12 advanced through the creasing tool. This signal can be obtained via a sensor 66 which for example detects the leading edge of the sheets 12 upstream of the creasing tool.

Based on the effective radii R_E, the speed V with which the sheets 12 are advanced through the creasing tool, and the signal from sensor 66, machine control 64 suitably controls the servo motors 62 so as to achieve the proper speed of rotation U for each of the cylinders and also the correct position of the dead zone with respect to the individual sheets.

For manufacturing creasing plate 24, it has to be kept in mind that the creasing plate blanks 24′ are deformed when being in a flat shape while the creasing plates are mounted, when installed on a creasing cylinder 21, in a curved shape. This results in the creasing projections 26 having, when the creasing plate is mounted to the creasing cylinder 21, a distance from each other which is larger than in the flat configuration of the creasing plate.

As can be seen in FIGS. 18 and 19, the creasing projections 26 are pressed into the carton to be creased by a certain distance (for example 1 mm) which however is less than the total height of the creasing projection. It is however preferred that the outer surface of creasing plate 24 does not touch the upper surface of sheets 12. Accordingly, a gap exists between the outer surface of creasing plate 24 and the upper surface of sheet 12.

FIG. 18 shows in an example the straight real length L between two creases 30, measured in parallel with the feeding direction of sheet 12. The same curved real length L can be measured between the apex of the corresponding creasing projections 26 on the functional, effective radius R_E. It can be seen that in a developed, flat condition of creasing plate 24, because of the difference between the development radius R_D and the functional, effective radius R_E, the developed length L_D is less than the real length L. Accordingly, two creasing projections 26 have to be formed on the creasing plate 24 in a distance, parallel to the feeding direction, which is less than the actual distance which the respective creases shall have on sheet 12.

In FIGS. 20a and 20b, another aspect of the creasing tool is shown.

Typically, sheet 12 is driven between the creasing cylinder 21 and the counter cylinder 23 by the contact of the creasing projections 26 with the sheet and also because of the contact of the sheet with the counter cylinder. However, there are creasing configurations where at a certain point in time, no creasing projection 26 engages at sheet 12. Because of the gap G explained with reference to FIGS. 18 and 19, no proper driving force would be exerted onto sheet 12 in these points in time.

To ensure that sheet 12 is always positively driven irrespective of the particular position of creasing projections 26, a driving fillet 27 is provided which extends in a circular direction along the entire creasing plate 24. Driving fillet 27 can be a plastically deformed portion of creasing plate 24 in the same manner as the creasing projections 26.

It is however also possible to create driving fillet 27 in a different manner. As an example, an epoxy fillet could be added to the creasing plate in a separate manufacturing operation. Such driving fillet can be seen in FIG. 20c.

Driving fillet 27 does not have to project over the surface of creasing plate 24 in a manner which creates a distinct crease in sheet 12. The height can be chosen mainly in view of the intended driving force which shall be generated.

FIGS. 21a to 21c show the clamping mechanism 60 in more detail.

The clamping mechanism 60 is effective to anchor both ends of either creasing plate 24 or elastic layer 28 and force both ends towards each other equally. This ensures that the respective sleeve is correctly located around the cylinder. Further, this avoids problems with air pockets being trapped under the sleeve. Such air pockets could result in damage to the creasing plate 24 or the elastic layer 28 when the respective sleeve is put under pressure in operation.

FIGS. 22a to 22g show an additional aspect of the creasing machine.

In this embodiment, a sleeve of a shape memory material 29 is used on counter cylinder 23 instead of elastic layer 28. Shape memory material layer 29 is plastically deformed by means of creasing plate 24.

In FIG. 22a, creasing plate 24 has been mounted to creasing cylinder 21 while layer 29 having in a starting condition with a flat surface is mounted to counter cylinder 23.

For shaping layer 29, the two cylinders 21, 23 are advanced towards each other so that creasing projections 26 on creasing plate 24 penetrate into layer 29 (please see FIG. 22b).

After increasing the distance between cylinders 21, 23 (and after curing, if necessary), layer 29 has the shape of a counter die to creasing plate 24 (please see FIG. 22c).

Subsequently, creasing cylinder 21 with creasing plate 24 and counter cylinder 23 with layer 29 can be used for creasing sheets 12 (please see FIG. 22d).

After a certain creasing job has been finished, layer 29 is restored to its original condition. To this end, layer 29 can be heated (schematically indicated with reference numeral H in FIGS. 22e and 220 so that the depressions in layer 29 are “erased”.

When layer 29 has been restored to its original flat shape (please see FIG. 22g), the creasing machine is ready for the next creasing job which starts by creating a new counter die by deforming layer 29 with the new creasing plate 24.

FIG. 23a shows the creasing cylinder 21 in more detail.

The clamping mechanism 60 has clamping pins 62 which are moveable between a clamping position (shown in FIG. 23c) and a release position (shown in FIG. 23d).

In the release position, the clamping pins 62 are spread apart as compared with the clamping position. Looking at FIGS. 23c and 23d, the distance between the clamping pins 62 in the clamping position is less than in the release position. In other words, a creasing plate 24 having holes into which the clamping pins 62 engage, is pulled to the outer circumference of the creasing cylinder when the clamping pins are in their clamping position.

The clamping pins 62 are mounted to sliding elements 64 which are arranged in a groove 66 formed in the creasing cylinder 21. The sliding elements 64 are biased by means of schematically shown springs 68 towards the center of the groove 66 and thus towards each other (and into the clamping position).

A release mechanism is provided for moving the clamping pins 62 from the clamping position into the release position. The release mechanism is here formed as a cam mechanism.

The cam mechanism has a plurality of cams 70 which are mounted non-rotatably on a shaft 72. The shaft is mounted rotatably in groove 66. Cams 70 are symmetrical with respect to the center of shaft 72. Thus, there are two apexes spaced by 180°.

Shaft 72 is provided with a bore for receiving an actuating tool 74 which can be a simple rod. The actuating tool 74 allows rotating the shaft and thus the cams 70 from the rest position shown in FIG. 23c to the spreading position shown in FIG. 23d.

In the rest position, the cams 70 do not exert notable forces on the sliding elements 64 so that they are urged by springs 68 towards each other into the clamping position.

In the spreading position, the cams urge the sliding elements 64 apart into the release position, against the force of the springs 68.

The amount of rotation of shaft 72 for transferring the cams 70 from the rest position into the spreading position is approx. 90°. It can be seen that in the spreading position, the cams 70 are moved “beyond” the dead center position in which the two apexes are arranged horizontally when looking at FIG. 23d, ensuring that the release mechanism reliably remains in the spreading position with the clamping pins 70 in the release position.

For mounting a creasing plate, the clamping pins 62 are brought into their release position. Then, the creasing plate is mounted at the creasing cylinder 21 such that the clamping pins engage into holes provided close to the edges of the creasing plate which are arranged opposite each other. Then, the release mechanism is returned into the rest position such that the clamping pins 62, under the effect of springs 68, pull the creasing plate 24 tight against the outer circumference of the creasing cylinder.

The clamping pins 62 are in the form of hooks so there is a slight undercut into which the creasing plate engages. This ensures that the creasing plate is mechanically held “under” the clamping pins 62 and cannot disengage axially outwardly when being clamped to the ceasing cylinder.

FIGS. 24a and 24b show the same clamping mechanism 60 which is known from the creasing cylinder.

The elastic layer 28 has a reinforcement plate 80 which is provided with holes 82 into which the clamping pins 62 engage.

Claims

1. A method of creasing sheets (12) by using a creasing tool (14, 20, 21) cooperating with a counter element (22, 23), comprising the following steps: a creasing plate blank (24′) is provided with at least one creasing projection (26) by plastically deforming the material of the blank (24′) so as to form a creasing plate (24),the creasing plate (24) is mounted to a creasing tool (14, 20, 21),sheets (12) to be provided with at least one crease are advanced through a gap between the creasing tool (14, 20, 21) and the counter element (22, 23).

2. The method of claim 1 wherein the material of the creasing plate blank (24′) is deformed by means of a punching module (40).

3. The method of claim 2 wherein the punching module (40) has a punch (42) and a die (46), the die having an outer contour which extends, adjacent the open end of the recess (50), at an angle of between 90° and 45°, approximately 45° or less than 45° with respect to the longitudinal direction of the recess, the die (46) being rotated so as to align the outer contour with an already generated creasing projection (26).

4. The method of claim 1, wherein the step of mounting the creasing plate (24) to the creasing tool (21) involves clamping the creasing plate (24) to the cylindrical surface of a creasing cylinder (21).

5. The method of claim 4 wherein a counter cylinder (23) is used for cooperating with the creasing cylinder (21).

6. The method of claim 5 wherein a layer (29) made from elastomeric material is clamped to the counter cylinder (23).

7. The method of claim 5 wherein a layer (29) made from a shape memory material is clamped to the counter cylinder (23).

8. The method of claim 5, wherein the distance between the axis of rotation of the creasing cylinder (21) and the counter cylinder (23) is adjusted with respect to the plane in which the sheet (12) is transported, before a creasing job is started.

9. The method of claim 5, any of claims 5 to 8 wherein the creasing cylinder (21) and the counter cylinder (23) are driven with different speeds of rotation.

10. The method of claim 1, wherein a driving fillet (27) is generated on the creasing plate (24), the driving fillet (27) extending around the majority of the circumference of the creasing cylinder (21).

11. The method of claim 10 wherein the driving fillet (27) is formed by applying a strip of epoxy material onto the creasing plate (24), which is then cured.

12. The method of claim 1, comprising the further step of detecting the arrival of a sheet to be creased at the gap between the creasing tool (14, 20, 21) and the counter element (22, 23) and controlling the rotation of the creasing tool and the counter element in dependence upon said detection.