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The invention relates to the field of paper industry, and more in detail it relates to a cutting machine of the disc blade type for cutting long staffs, interleaved sticks or paper rolls, also called logs, into small sized portions.

In particular, the invention relates to a kinematic mechanism for moving such blade.

According to the prior art, cutting machines for obtaining paper logs or packages for civil or industrial use substantially comprise a step feed structure for the logs, a cutting section provided with rotating blade and a mechanism for ejecting the cut products.

Normally, the blade is provided with a first moving system that enables it to rotate about an axis, and with a second system that imparts an oscillating movement thereto, rotary or alternating, suitable for moving the blade near to and away from the logs prepared for cutting following mostly elliptical or circular trajectories. The use of rotary electric motors and the use of lever mechanisms and additional mechanical components, such as connecting rods, cranks, arms, plates, etc., are widely known for these kinematic mechanisms.

In most cases, the log feeding system provides for the use of a continuous chain device capable of preparing multiple logs in a sequence for cutting. Sometimes, multiple logs are also prepared in parallel, side by side, so that the blade may cut multiple logs in a sequence with a single orbit. Most machines use independent log feed and cutting systems, actuated by control units provided with different software applications.

Some types of machines are furtherly provided with blade sharpening means, particularly subject to wear depending on the work condition and time, and wear compensation means, for example jacks, which move the blade arm by the extent required to compensate exactly the worn portion.

Normally, the sharpening means are associated to the blade support arm and follow the same trajectory thereof, causing an increase in weight, vibrations and unbalance of the mobile system in relation to the blade wear.

Such machines for cutting paper logs and interleaved sticks have some limits or drawbacks, especially due to the use of rotary motors connected to complex kinematic mechanisms with leverisms that make the machine more cumbersome, heavy to manage, expensive to maintain and particularly subject to vibrations.

In particular, vibrations disadvantageously cause a considerable loss in the process quality and productivity: due to the vibration phenomenon, in fact, the blade edge has some thickness irregularities, impairing the cutting accuracy.

Some machines use reduction gears or special systems, such as for example toothed belts or racks, for transforming the blade rotary movement into a linear movement, trying to obtain a more accurate kinematic mechanism with a smoother and faster operation. Unfortunately, these additional systems in any case introduce heavy mechanical clearances, disadvantageously limiting the cutting speed and eliminating the desired advantages.

A further disadvantage consists in the difficulty of synchronising the two different software applications that separately manage the blade movement and the log feeding.

The complete orbit covered by the blade, moreover, is of the circular or elliptical type, and as a consequence the trajectory followed by the blade inside the log corresponds to a wide circle or ellipse arch: the long permanence of the blade into the log disadvantageously causes the overheating of the same, with the unavoidable vibration and inaccuracy problems. In fact, for a good log cutting it is necessary for the blade to stay cold and thus remain as shortly as possible inside the log.

If multiple logs are arranged in parallel, according to the material diameter and density, the arch covered by the rotating blade inside the paper logs is furtherly extended, with the harmful consequences of overheating and vibrations already described.

Moreover, the configuration of traditional machines and the respective arrangement of the parts thereof do not allow making use of the blade return movement for carrying out a further cut, thus not optimising the work times.

The invention aims to overcome these limits by providing a cutting machine for cutting paper logs which:

- uses a quick, accurate and smooth kinematic mechanism for moving the blade; - minimises the problems of space occupied due to unnecessary leverisms;

- eliminates vibrations and reduces the blade overheating problems; - perfectly adjusts the blade wear and the compensation of distance between cutting edge and log dimensions, using a sharpening device independent of the blade movement kinematic mechanisms;

- properly manages the interference between rotating blade and log feed conveyor belt so as to not create interferences; - optimises the work times, using a complete blade movement cycle for cutting multiple logs without affecting accuracy;

- eliminates the possibility of machine downtime due to the complexity of mechanical parts;

- reduces construction and maintenance costs. Such aims are achieved by a machine for cutting paper logs supported by a support and feed structure, comprising:

- a blade;

- first motor means arranged for giving said blade a rotary movement around an axis z; - a kinematic mechanism arranged for moving said blade near to and away from said paper logs;

- a kinematic mechanism for sharpening said blade;

- a control unit with movement control software; characterized in that said kinematic mechanism comprises second motor means arranged for giving said blade a translation movement with linear trajectory.

The kinematic mechanism suitable for moving the blade near to or away from the log prepared for cutting preferably is of the type comprising a rail and a slide, wherein said slide is associated to the first motor means used for giving the blade rotation around axis z.

Moreover, said second motor means preferably are of the linear type, controlled by the control unit, so as to accelerate or decelerate the slide along the rail according to a predetermined criterion.

A preferred embodiment of said cutting machine provides for the kinematic mechanism for moving the blade near to and away from the log to be associated to a linear encoder arranged for detecting and providing the measurement of the movement of the blade itself to the control unit.

According to a further aspect of the invention, also the sharpening system is associated to a kinematic mechanism comprising motor means, preferably of the linear type, arranged for providing a translatory movement thereto, and a proximity sensor arranged for detecting wear of the blade and for sending a signal to the control unit.

Preferably, said control unit, according to the signals received from the linear encoder and from the proximity sensor, modifies the amplitude of the translatory movement of the blade and the sharpening system.

Possible embodiments of the invention provide for the addition of a second blade moved by the same translation kinematic mechanism, or the insertion of at least a second support and feed structure for the logs, positioned at the side opposite the first structure already in use, with reference to a plane passing by the rotation axis z of the blade and normal to the kinematic mechanism rail.

In such last version, it is preferable that the position of the support structures be such that the cutting speed the logs are subject to, equivalent to the sum of the components projected along the blade feeding direction of the translation speed and rotation speed vectors of the blade, be maximised.

The invention has several advantages: - the blade covers a rectilinear trajectory, shorter than the traditional elliptical or circular trajectories, with reduction of the permanence time of the blade itself inside the logs and elimination of the drawbacks due to overheating, such as for example vibrations;

- a precise, clean and fast cutting is achieved; - using separate linear motors for the blade movement and sharpening functions there is not need to use further leverings and mechanical gears for managing the blade motion and sharpening, with consequent reduction of the overall dimensions, of any mechanical problems and of the relevant maintenance costs; - the machine uses encoder and sensor technology for synchronising the log feeding and cutting steps without interference problems between the parts;

- the work times are optimised, using multiple blades at the same time managed by a single translation kinematic mechanism, or using the rectilinear return trajectory of the blade for cutting multiple logs, that is, the cutting process is improved if the logs are arranged so that the sum of the blade feeding and rotation vectorial components is maximised.

The advantages of the invention shall appear more clearly from the following description of preferred embodiments, by way of a non- limiting example, and with the help of the figures, wherein:

Fig. 1 shows a front view of the machine for cutting paper logs according to a first embodiment of the invention;

Fig. 2 shows the side view of the same machine of Fig. 1 ; Fig. 3 shows a front view of a preferred embodiment version of the machine.

With reference to Figs. 1-2, there is shown a sliding and feeding structure 1 for paper rolls, or logs L, to be cut into smaller portions by a blade 2, turnably supported and moved by motor means 3 and translation kinematic mechanisms 4.

In particular, blade 2 moved by the rotary motor 3, rotates about an axis z and concurrently translates along a rectilinear trajectory T in the direction of logs L prepared for cutting. Said trajectory T belongs to a plane perpendicular to the rotation axis z. The dashed line I represents the space occupied by blade 2 during the simple path covered by the blade itself, between two extreme stop positions corresponding to a position of total sinking into log L and of total exit from the log itself.

The amplitude of said path may be adjusted according to the diameter of blade 2 and of the paper log L to be cut and to the wear of the blade itself.

Trajectory T is covered thanks to second motor means 5 whereto said blade 2 is connected: in particular, a linear motor controls the sliding, on a rail 6, of a slide 7 whereto motor 3 is associated, which causes the rotation of blade 2 around axis z.

The feeding system 1 for feeding rolls L is of the known type and comprises, for example, two longitudinal guiding planes 19-20, arranged sideways for forming a containment cradle for said logs. These logs L are moved along said cradle by means of a conveyor belt or a chain system 16 set in rotation by toothed wheels or rollers 18 according to the prior art. Thrusting paddles 17, in jargon called studs, are fixed on the conveyor belt or chain 16, arranged for feeding logs L towards the cutting system and keeping them into position during the sinking of blade 2. The guiding planes 19-20, in fact, are arranged spaced from one another, for allowing the passage of paddles 17 sliding with chain 16.

The position of structure 1 is such that the components, along the feeding direction of blade 2, of the blade rotation speed and translation speed vectors are positively summed, so as to speed up the cutting of log L.

The coordination between the rotary motor means 3, the translation kinematic mechanism 4 and the feeding system 1 of logs L is controlled by a control unit (not shown) which, according to a preloaded software program moves blade 2 near to or away from logs L in an accelerated or decelerated manner, receiving information from a linear encoder (not shown), provided on kinematic mechanisms 4, which detects and transmits all the movements.

Said control unit further controls speed, stroke, acceleration and deceleration of the entire cutting system along trajectory T, ensuring good cutting quality.

The cutting machine is furtherly provided with kinematic mechanisms 11 for sharpening blade 2 and compensating the amplitude of trajectory T covered by the same. In particular, said kinematic mechanisms 11 comprise linear translation motor means 12, a rail 14, a slide 13 whereon two abrasive discs 10 are turnably mounted, according to axes parallel to axis z, which act on the cutting edge of blade 2.

A proximity sensor (not shown) is placed associated to said kinematic mechanisms 11 , which detects the position of the cutting edge of blade 2, sending a signal to the control unit which accordingly modifies the reciprocal position of said blade 2 with said sharpening discs 10 for compensating the wear of the blade itself.

Fig. 3 shows a particular version of the cutting machine, wherein a second structure 1' is provided for feeding and sliding second paper logs L ¹ .

In order to keep the cutting speed high, said second structure is positioned parallely to the first one, but diametrically opposite it, with reference to the extreme translation positions assumed by blade 2.

The operation of the cutting system is as follows. At least one paper log L is positioned on a structure 1 , is fed by paddles 17, turning on a conveyor belt or chain 16, and moved near the cutting section. A blade 2 cuts log L into smaller portions, disposed of and removed from the work position by a known ejection system. Before the cutting step, the paper log L is pushed and moved beyond the cutting plane represented by blade 2, by an amount to be cut.

Blade 2 is moved by kinematic mechanisms 3-4 suitable for giving a rotary-translation movement thereto and covers its trajectory T sinking and retracting from the paper log L, orthogonally to its axis, carrying out a clean and precise cutting.

The operation of the embodiment shown in Fig. 3 provides for the trajectory T covered by axis z of blade 2 to be extended: the return path from the first position of sinking to the stop position continues, up to reach a second position of sinking into the second log L' arranged on the additional feeding structure 1'.

As is clear to the man skilled in the art, the invention has been described with exemplary reference to the cut of a paper log into smaller portions of the same, but it may also be used for other purposes, such as for example only for finishing the heads of said logs.

Moreover, the cutting machine according to the invention refers to the cutting of paper logs but it may be applied more in general to the cutting of rolls of any type, for example plastic film rolls, or any elongated, tubular or non, element, to be divided into portions of predetermined size.

Finally, the means and the materials for carrying out the various functions described may be of a different type, always achieving the advantages described above.