Technical area

The present invention relates to a cutting device for cutting off, perforating or folding of an advancing track of a thin bendable material according to the preamble of patent claim 1 and a method of cutting off, perforating or folding an advancing track of a thin bendable material according to the preamble of patent claim 8.

Background of the invention

The present invention discloses a cutting device and a method of cutting off, perforating or folding an advancing track of a thin bendable material to sheets. This type of equipment comprises two drums equipped with knives that interact with each other and is used primarily in printing works for cutting off sheets from a paper roll that is running from a printing press. It is also used to produce a non- printed paper material, such as napkins, to produce printed or non-printed paper material, to produce filter material or other technical material, etc. Cutting off is often combined with perforating in order to later on facilitate tearing off manually, or combined with bending in order to facilitate later bending of the material. In order to achieve a clean cutting surface and in order to minimize dust that is produced when the knife cuts through the sheet when cutting off the sheet, it is important for these types of cutting devices that the velocity of the knives at the cutting moment corresponds to the velocity of the advancing track of a thin bendable sheet material.

A problem with known cutting devices is that it is difficult in an easy way to adjust the device so that the length of a waste strip and the length of the sheet is independent of the distance between the knives along the peripheries of the drums, at the same time as the velocity of the knives corresponds to the velocity of the sheet track at the cutting moment.

US4009626 discloses a cutting unit with two oppositely driven rolls, where each roll has a knife and an anvil. The rolls are connected by means of gear wheels and one of the rolls with its gear wheel may be axially displaced in order to facilitate placing it in an amended twisted direction in relation to the other roll. Therefore, the distance between the two cuts may be amended. A drawback with this cutting unit is that the distance between the cut of the first and the second drum is limited to the different gearings between the different connected gear wheels that are connected to the two rolls. A further drawback with the cutting unit according to US4009626 is that the rolls may not be adjusted to move with the velocity of the paper track at the cutting moment and will be driven faster or slower during the rest of the turn depending on the appropriate length of the cutted sheet and of the waste strip.

EP0035462 discloses a cutting unit with two oppositely driven rolls with one knife on each roll. The knives are working against each other as a pair of scissors. The rolls are driven by an electrical motor that is regulated by rotation speed such that they are moving at the velocity of the paper track at the cutting moment, but will be driven faster or slower during the rest of the turn in order to provide appropriate length of the cutted sheet. The adaption of the velocity is achieved by means of micro processors, velocity sensors or position sensors. The length of the sheet is noted with a thumbwheel or similar, there after the micro processors are calculating an appropriate scheme of velocity. A drawback with the cutting device according to EP0035462 is that only one cut is made for every turn, which means that cuts with very short distances are difficult to achieve and that the said cutting unit is not appropriate to cut off waste strips between the different sheets. This cutting unit is also expensive since a plurality of sensors is needed in order to adapt the velocity of the rolls.

Purpose of the invention

The purpose with the present invention is thus, to provide a cutting device and a method of cutting off, perforating or folding of an advancing track of paper or similar thin bendable material, which may be adjusted that the length of the cutted sheets and the length of the waste strips is independent of the distance between the knives along the periphery of the drums, and at the same time the velocity of the knives corresponds to the velocity of the sheet track at the cutting moment.

Summary of the invention

The purpose mentioned above and other purposes, which will be made clear in the description below, is achieved for the present invention as it is defined in the independent claims 1 and 8. Preferred embodiments of the invention are defined in the dependent claims 2-7 and 9-17. Thus, the present invention defines a cutting device for repeatedly lateral cutting off an advancing material track comprising a first rotating drum comprising at least one knife and a second rotating drum comprising at least one knife, which at least one knife on said first rotating drum cooperates with at least one anvil or with at least one knife arranged on said second rotating drum in such a way that said at least one knife on said first rotating drum cuts off the material track against said at least one anvil or at least one opposite knife of said second rotating drum and that said at least one knife on said second rotating drum cooperates with at least one anvil or at least one opposite knife arranged on said first rotating drum in such a way that said at least one knife on said second rotating drum cuts off the material track against said at least one anvil or at least one opposite knife of said first rotating drum, said advancing material track may be cut off at least twice on each turn of the drum, characterised in, that said first drum is arranged to be driven by a first electric servo motor and said second drum is arranged to be driven by a second electric servo motor, which first and second electric servo motors are connected to at least one programmable control unit that is arranged in order to control the peripheral speed of at least one of said drums, and said at least one control unit is arranged to control the peripheral speed of at least said first and second drum such that the peripheral speed of the drum/-s may deviate from the velocity of the material track at times when no cutting takes place.

According to the present invention the advantage is achieved that the peripheral speed of a drum corresponds to the velocity of the material track at the cutting moment and may deviate there from under other parts of the rotational turn of the drum. In this way a good cutting without dust creation is achieved and the distance between the cuts may also be controlled infinitely variable without regarding the circumference of the drums and the distance between the knives on a drum.

According to a preferred embodiment the peripheral speed of at least one of said first and second drum may be controllable such that the cutting takes place on certain distances of the material track, which may be set by programming of said at least one control unit. In this way the length of the waste strip is handled in relation to the length of the sheet. According to a preferred embodiment the peripheral speed of the drums may be controllable such that the angle position of the drums in relation to each other remains the same under the turn, which is settable by programming of said at least one control unit. Thereby, the length of the waste strip remains the same, at the same time as the length of the sheet may be adapted to different sizes.

According to a further preferred embodiment the velocity scheme of the drums may be automatically determined of said at least one control unit according to predetermined rules after the operator has indicated desired distances between the cuts.

According to a further preferred embodiment position sensors sense the position of the material track and by said at least one control unit the velocities of the drums is precisely adapted so that the cut may take place on predetermined points on the material track independently of possible variations of velocity of the track.

According to a further preferred embodiment the cutting device comprises a vacuum assembly and said lower drum is equipped with a channel in which said vacuum assembly is arranged in order to create a negative pressure for keeping hold against the periphery surface of the lower drum of those parts of the advancing material track that have been cut off by said at least one knife of the upper drum from said advancing material track. Thereby, a controlled handling of the waste strip is created down into the subsequent exhaust.

According to a further preferred embodiment the cutting device comprises a pressure assembly that is arranged to create a pressure shock in said channel after a predetermined time after the vacuum creation.

According to a further aspect of the invention a method is defined for repeatedly lateral cutting off an advancing material track.

Short description of the drawings

The invention will now be closer described by means of no limiting embodiments and with reference to the accompanied drawings, where;

Figure 1 discloses a perspective view of an embodiment of a cutting device 1 according to the present invention, where the material track is cut off both by the knife of the upper drum and by the knife of the lower drum, where the knife of the lower drum has cut off the material track creating a sheet shown to the right of the cutting device and where the knife of the upper drum has cut off the material track creating a waste strip situated against the periphery of the lower drum, and Figure 2 discloses a schematically view of a cutting device where each of the two cylindrical drums are connected to an electric servo motor. The two electric servo motors driving the two cylindrical drums are connected to a control unit for each one that controls said drums.

Detailed description of the invention

In the figures 1 and 2 an embodiment of the present invention is disclosed, applied on a cutting device dedicated for cutting off, perforating or folding of an advancing track of a thin bendable material. Already here shall be emphasized that the invention is in no way limited to this sort of cutting device, but may be applied on all sorts of cutting devices.

Figure 1 discloses a perspective view of a cutting device 1 according to the present invention. In this embodiment the cutting device 1 comprises two drums 2, 3 rotatable mounted in a frame 13 (only partly shown). At operation a material track 10 of e.g. paper is fed with a certain velocity between these drums 2, 3 and is cut off with knives 4, 5 arranged on drums 2, 3. Each one of the two drums 2, 3 in fig. 1 comprises a knife 4, 5 and an anvil arranged along the periphery of each drum 2, 3, wherein the knife 4 of the first drum 2 cooperates with the anvil of the second drum 3 in such a way that the knife 4 cuts off the material track 10 against the anvil and the knife 5 of the second drum 3 cooperates with the anvil of the first drum 2 in such a way that the knife 5 cuts off the material track 10 against the anvil. It is also of course possible to use opposite knives instead of anvils and each drum 2, 3 may of course comprise more than one knife. Since the drums 2, 3 are equipped with anvils or opposite knives in order to cooperate with the knives 5 of the opposite drum 3, a compact cutting device 1 that requires a small amount of space and low manufacturing costs is achieved. In the description is stated that the material of the material track 10 is paper, but of course is it possible to use other thin bendable materials, such as plastic, felt material, metal or a combination of these. By cutting is not only meant completely cutting through the material track 10 that results in the sheet 11 being separated, but also cutting through piece by piece in order to facilitate later tearing off or folding, so called perforating, and also partly cutting through in the direction of thickness that gives a weakening in the material in order to facilitate folding in a later stage, so called bending. The two drums 2, 3 are not limited to have the same circumference, but may of course have different circumferences.

The two knives 4, 5 of the drums 2, 3 are cutting off the advancing material track 10 into sheets 11 and into waste parts 12. The knife 5 of the second, lower drum 3 cuts off the material track 10 into sheets 11 and the knife 4 of the second, upper drum 2 cuts off the material track 10 into waste parts 12, where the peripheral speed of the two drums 2, 3 in relation to the velocity of the material track 10 settles the sheet length and the length of the waste strip 12 respectively.

In fig. 2 a schematically view of a cutting device 1 according to the present invention is shown. In fig. 2 the two drums 2, 3 are each connected to its own electric servo motor 6, 7, which in turn are connected and are controlled by its own electric control unit 8, 9. In this way the peripheral speed of the two drums 2, 3 may be precisely varied also within one turn, which makes it possible that the peripheral speed of a drum 2, 3 may be controlled such that it corresponds to the velocity of the material track 10 in the cutting moment, but that it may deviate there from under other parts of the rotational turn of the drum 2, 3. The advantage with this is that the distance between the cuts is not dependent of the distance between the knives arranged along the periphery of the drums 2, 3 and that the sheets 10 get a cut with high quality.

The peripheral speed of a drum 2, 3 depends on the desired length of the sheet 11 and the waste strip 12 respectively. If the length of the sheet 11 shall be equal to the circumference of said drums 2, 3 the velocity of the knife 5 of the second drum 3 may be invariable such that its peripheral speed is equal to the velocity of the material track 10. If, on the other hand the length of the sheet 11 shall be longer than the periphery of the drums 2, 3 the velocity of the knife 5 of the second drum 3 shall be equal to the velocity of the material track 10 at the moment of cutting, but be slower than the velocity of the material track 10 between the cuts until the right length of the sheet 11 has passed the second drum 3 and thereafter the velocity of the knife 5 has to be accelerated to the velocity of the material track 10 at the moment of cutting.

If the length of the sheet 11 shall be shorter than the circumference of the second drum 3 the velocity of the knife 5 will be the same as the velocity of the material track 10 at the moment of cutting, but there after the knife 5 has to be accelerated to a higher velocity between the intervals of cutting such that a shorter part of the material track 10 will pass the second drum 3 between the intervals of cutting.

The precise velocity scheme of the drums 2, 3 does not have to be set by an operator, it is automatically determined by said electric control unit 8, 9 according to predetermined parameters that are controlled by the distance of the sheets 11 fed in by the operator. Thus, no change of neither drums 2, 3 nor knives 4, 5 are required when the distance between the cuts shall be changed, instead it is controlled by the operator. In this way cost of components and setup time is saved.

Said second drum 3 comprises a channel (not shown in the figures) that discharges into an opening at the knife 5 of said second drum 3. In the channel a negative pressure is created in order to keep hold of a strip formed part 12 that has been cut loose from the advancing paper track 10. The negative pressure in said channel may keep hold of said strip formed part, the waste strip 12 until the rotating knife 5 has rotated about half a turn, where after the strip formed parts 12 may be shocked by an instantaneous pressure shock in the channel such that the strip formed parts are exhausted and are removed from the cutting device by e.g. a suction apparatus (not shown in the figures). The strip formed parts are removed from the cutting device and are collected preferably in some sort of collecting device (not shown in the figures). The channel is preferably connected to a vacuum/ compressed air apparatus (not shown in the figures) in order to create said vacuum and said pressure shock in the channel.