Patent Description:
The present invention relates, furthermore, to a cutting plant that carries out this method. Furthermore, it relates to a structure of blade used in this plant and for carrying out this method.

Transversal cutting machines are well known and commonly used to make rolls or stacks of paper, for example for use as toilet paper, kitchen rolls, tissue paper stacks and the like, which receive as input a log or logs of paper or similar material that have been preliminarily prepared upstream. With these machines it is possible to achieve very high production rates.

In such transversal cutting machines, at least one log is normally arranged on step plane conveyors. Then, a part of the log to be cut is in turn kept still so that a sharp blade passes through the paper, thus cutting in turn the log into rolls or stacks or portions of the same length as a conveying step. More precisely, before each cutting reciprocation of the blade, the logs are shifted axially by a pitch that corresponds to a distance equal to the length of each roll or pack or portion to obtain. The logs are kept still only during the cut by a clamping device that makes it possible to avoid any misplacement during the cut, and instead allow the sliding of the log during the step-conveying phase.

Cutting machines of this type can be equipped with a circular blade, as described in <CIT> or <CIT>. These systems have the advantage of being very fast and allow very high production rates, but also have drawbacks, among which the following:.

Blades with a helical profile also exist, as described in <CIT>, which however have low practical use.

In a way more limited with respect to transversal cutting machines with circular blades, industrial transversal cutting machines with band saw have been used, with the band saw sharpened on one edge or on two edges, rotating on two flywheels rotatably mounted on a mobile reciprocating carriage, which determine the reciprocation of the band saw during a cutting stroke. The flywheels can be mounted on a mobile carriage that reciprocates horizontally, as described in <CIT> or <CIT>, or on a mobile carriage that reciprocates vertically, as described in ITMI942062A1. Other examples with band saw are known in <CIT> and <CIT>. That <CIT> discloses a method for cutting logs comprising the steps of: prearranging at least one cutting region configured to be crossed by at least one log according to a conveying direction transversal to a cutting plane; prearranging a blade having a longitudinal axis and comprising: a plane cutting portion, said cutting portion having a cross section; moving said blade parallel to said longitudinal axis and conveying said or each log in said cutting region.

Such cutting systems with band saw have the advantage of having high precision of cut even with log of large diameter and density, as well as absence of danger of fire, since the blade can be sharpened far from the cutting zone. However, they have a plurality of drawbacks, among which the following: a limited production rate, risks of hurting the operators both in occasion of the change of the blade, and when cleaning the machine from debris or when solving other operative conditions, risk of derailing of the band saw from the flywheels. Therefore, they are mainly used for cutting logs of medium-large diameters, such as industrial rolls, or large rolls for large dispensers of toilet paper.

Among the main limits of the application of the cutting machines with band saws, there is the slow reciprocating relative movement between the whole carriage with the flywheels and the paths on which the logs are conveyed.

It is therefore desirable a cutting system that achieves the high production rates of the circular blades and the high precision and the low costs of the band saws.

An object of the present invention is then to provide a method for cutting logs of paper and similar material that does not present the above identified drawbacks of both the circular blades and of the band saws.

Another object of the present invention is to provide a plant for cutting logs of paper and the like configured for carrying out such method and avoiding the above-identified drawbacks.

A further object of the present invention is to provide a blade for cutting logs of paper and the like configured for working with the plant and according to the method and avoiding the above-identified drawbacks.

These and other objects are achieved, as defined in claim <NUM>, by a method for cutting logs comprising the steps of:.

This way, the shear force has a direction in minimum part orthogonal to the log, and mainly parallel to a speed of the longitudinal axis of the blade, such that the resulting shear force is parallel to the oblique sharp profile of the blade, which penetrates gradually into the log, determining a precise and clean cut at an optimal speed of the blade with respect to the log.

This way, a plurality of advantages derives with respect to the two cutting techniques of disc blade and band saw, as described above, with a very high cutting quality like the band saw technology and very high production rate like the disc blade technology. In fact, the gradual penetration of the blade allows minimum shear stresses and minimum reactions on the blade for length unit of the cutting profile, and then a high speed of the band of the blade can be achieved, in addition to a low power installed, as well as possibility of arranging even <NUM> log feeding cradle channels, or more, for each cutting region, as well as the possibility to cut, with a same passage the blade, even logs of different diameter.

The absence of reciprocating parts between logs and blade and a very low number of accessories allows limited costs, rapidity of production and installation of the plant that carries out the method, as well as minimum maintenance, in addition to simplicity of use and setting, as well as safety of manipulation of the blade in case of replacement or cleaning.

Furthermore, the blade has very long duration, since the consumption for sharpening of the blade does not require any setting adjustments and it does not cause a reduction in width or thickness of the blade, but it simply determines a different ratio between the length of the cutting portion and the length of the connection portion. The blade can also be chosen very thin, for example even a few tenth of mm for soft products, up to avoiding the need of sharpening.

Advantageously, the blade can be selected from the group consisting of:.

In an advantageous variated method, the blade can be selected among:.

If the plane cutting portion comprises a plane band and the connection portion is a connecting element connected to the plane cutting portion, the connection portion can be selected from the group consisting of:.

In an alternative implementation of the method, the blade comprises a conveying portion having a larger width than the cutting portion, the conveying portion defining at least one elongated hole on which both the at least one cutting profile and the connection portion are facing, the elongated hole defined by a connection belt which extends opposite to the at least one cutting profile.

This solution, which can be provided for each of the embodiments above described, both with a single cutting profile and with more than one cutting profile, both with continuous or discontinuous connection portion, determines a band with fixed width and the cutting profile only in the cutting portion, allowing to convey the blade very steadily and quickly, owing to the presence of the connection belt.

In case of a conveying portion having a larger width than the plane cutting portion, the elongated hole can be a first elongated hole and the plane cutting portion provides a second elongated hole, for lightening the blade. In this case the plane cutting portion provides a band portion that has a first end connected to the first connection belt and a second end that is connected to a second connection belt, and extends obliquely between the two connection belts, the band portion extending obliquely between the first connection belt and the second connection belt, in order to have said cutting profile facing towards the first connection belt. In a particular embodiment, the band portion may also have a cutting profile facing towards the second connection belt, in case of reciprocating movement of the blade, in this case at least one further log feeding cradle provided in the second elongated hole.

Preferably, a conveying solution is selected from the group consisting of:.

The solution of stepped conveying of the log, even if it is a traditional stepped log feeding system, can permit an increase of the number of cradles, for example up to <NUM>, or more, and a subsequent evacuation of a corresponding number of cut portions. The stepped movement can be triggered simply with a measurement, using for example an optical or magnetic sensor of the movement of the front end of the cut portion at a predetermined point, and then computing the time for transit of the connection portion.

Instead, the solution of continuous conveying has the advantage of reduced dynamic stresses for the stepped advancing, with lower wear, lower energy consumption, in addition to higher production rates, avoiding the idle times of stop, wait and start of the log. In fact, the movement of moving back the blade to the first position and the transit of the connection portion overlap the time of continuous moving of the log, allowing even very high speed, and production rates of the cut portions much higher than a maximum available with respect to a stepped movement.

In case of continuous conveying and of a conveying device in the cutting region that causes a bending of the blade in the conveying direction, a system can be provided for tensioning the blade, selected from the group consisting of: a spring-loaded blade tensioning device and a mechanism of synchronous shifting of at least one axis of the pulley drums, either motorized or idle, that convey the blade.

In some possible exemplary embodiments, to avoid the need of a blade tensioning device, and in order to double the production rate, two respective opposite conveying devices can be provided, similar to what above described, which move integrally in an alternated way, but according to two opposite sides of the blade path. This way, the two conveying devices, causing a bending of the blade in one or in the other conveying direction, are set to cut according to phases opposite to each other. In this way, the tension of the blade does not require further compensations, since the blade is constantly tensioned. Furthermore, the production rate is doubled.

Further sides of the blade and further dispositions of the cradles of the log can be implemented by the skilled person, and preferably even with further systems when the blade extends on a wide working area, for example polygonal with more than four sides.

In a possible implementation of the method, the blade is looped around a plurality of flywheels or pulleys arranged in polygonal layout, in particular quadrilateral, wherein on one edge of a polygonal path a sharpening device is provided, and wherein on at least another edge of the polygonal path at least one cutting region is provided, in particular the cutting region arranged downstream of a log storage region produced through a log production line comprising at least one rewinding machine, or an interfolding machine, or a machine for stacking packs of folded sheets. Such solution makes it possible to eliminate bottleneck delays due to cutting waiting times, arranging a cutting region at each edge of the blade polygonal path, or cutting, with a single blade, logs exiting from two different production lines.

In particular, the cutting region is configured in a way selected from the group consisting of:.

All the above-described solutions, which are some among the possible applications of the cutting layout with the method according to the invention, allow increasing remarkably the production rate of existing lines or permit a new production line design with very high production rate.

Advantageously, in the cutting region a pressing element is provided selected from the group consisting of:.

Such two solutions for blocking the log, which are only exemplary solutions among other blocking possibilities, allow to block the log with simplicity and rapidity for permitting a stop and start of the stepped movement, since the method according to the invention allows a cut without that high shear stresses are generated, and then without that high force components are generated that would require a stronger block. This avoids leaving undesired markings or deformations on the cut portions. The solution with conveyor belts opposite is also suitable to be used in case of continuous movement of the log.

Owing to the very low shear stresses on the log, it is also possible that there is no need of blocking the log, and the shape of the cradle is configured to keep the log, by a simple positive engagement or by the aid of suction holes or air jets.

Preferably, a sharpening step is provided of the blade, carried out only on the cutting profile of the cutting portion and not on the connection portion, in particular the sharpening step being selected from the group consisting of:.

The above-described sharpening systems allow an easy sharpening action that is carried out only on the cutting profile, and they can be mounted at a sufficient distance from the cutting region that avoids risks of fire.

According to another aspect of the invention, a plant is provided for cutting logs as defined in claim <NUM>.

According to another aspect of the invention, a blade is provided for cutting logs as defined in claim <NUM>.

The invention will be now shown with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings in which:.

With reference to <FIG> a method according to the invention for cutting a log <NUM> comprises the steps of:.

In case of logs <NUM> of large diameter, in a way not shown but easily implemented by a skilled person, it is also possible that the cradle <NUM> causes a rotation of the log <NUM> about itself when the cutting profile 12c passes above the cradle <NUM>. In this case, the cutting height <NUM> can be equal to half the diameter of the log <NUM>, or equal to the difference between the radius of the log <NUM> and the radius of the core of the log <NUM>.

With reference to <FIG>, the blade can have the cutting portion <NUM> having a single cutting profile 12c (<FIG>). In the cutting region logs <NUM> can be fed, which are arranged as shown in <FIG> or as shown in <FIG>, or arranged in a similar way to <FIG> (as described hereinafter) aligned in respective cradles <NUM>, providing up to, for example, eight cradles parallel to each other, also that they can be each cradle <NUM> with log of different diameter, or of different material.

Alternatively, the blade can have cutting portion <NUM> having two cutting profiles 12c, <NUM>'c opposite to each other with respect to the longitudinal axis <NUM> (<FIG>). This way, in the cutting region <NUM> logs <NUM> can be fed opposite to each other with respect to the longitudinal axis <NUM>, so that the logs are cut from both the respective cutting profiles 12c,<NUM>'c. Such solution can be particularly suited for industrial rolls or jumbo rolls.

In a further solution, as shown in <FIG>, the blade can have the cutting portion <NUM> with two cutting profiles 12c,<NUM>"c, arranged at a same side with respect to the longitudinal axis <NUM>, the two cutting profiles 12c,<NUM>"c cutting the log <NUM> (arranged on cradles not shown, for example similar to the cradles <NUM> of <FIG>) when the blade <NUM> carries out the movement in respective opposite directions.

It is also possible, in a way not shown but easily implemented by a skilled person, to combine the above described profiles, for example a blade with two cutting profiles arranged at a same side with respect to the longitudinal axis as shown in <FIG> and duplicated on the other part of the longitudinal axis as shown in <FIG>. Such blade can for example be used with alternated movement in a vertical plane for carrying out the cut on two cradles both with movement of the blade towards below and towards the above.

As shown in <FIG>, the blade can also have (<FIG>) a plane cutting portion <NUM> and a connection portion <NUM> connected to the cutting portion <NUM> consisting of a single plane band, which can be a band continuously looped about at least two flywheels (for example implemented by a skilled person as the flywheels 23a,23b of the <FIG>), which provide a continuous movement, or a reciprocating band, as that of <FIG>. Such solution of continuous band is particularly advantageous for simplicity for making the blade, which can be a simple band of a shaped sheet, and sharpened only on the cutting profile, even very thin (a few tenth of mm) in such a way that it does not need to be sharpened further.

Alternatively, a blade (<FIG>) can be provided, where the plane cutting portion <NUM> comprises a plane band <NUM> and the connection portion <NUM> is a connecting element connected to the plane cutting portion, and where the blade can be selected from the group consisting of: a continuous blade looped about at least two flywheels that provide a continuous movement, a discontinuous blade having reciprocating movement, and where the connection portion <NUM> can be selected from the group consisting of: a band portion, a chain portion, a rope portion, a belt portion. The connection portion <NUM> can be connected to the cutting portion for example by a link <NUM>, or the belt, chain, rope, in addition to form the connection portion <NUM>, can also extend integrally along the cutting portion <NUM>, to ensure continuity of traction, through pulleys, gears, spools, not shown, which provide a torque and guide the path of the cut or the blade path. Such solution makes it possible to replace easily the cutting portion without to replace also the connection portion.

The examples of <FIG> can be fixed at a desired blade as above described or as described hereinafter, both with only one cutting profile that with two cutting profiles, in a way easily implemented by a skilled person.

In case of the example of <FIG>, in a way easily implemented by a skilled person, the connection portion can be chosen as a discontinuous element, consisting of connecting portions <NUM> that are discontinued at the connections <NUM> with the plane cutting portion, or alternatively as a continuous element <NUM> that extends also between the connections <NUM> of the plane cutting portion <NUM> parallel to it.

Alternatively, or in addition, as shown in <FIG> and <FIG>, for cutting logs <NUM> the blade can comprise a conveying portion <NUM> having a larger width than the cutting portion, the conveying portion <NUM> defining at least one elongated hole <NUM> on which the at least one cutting profile 12c and the connection portion face, the elongated hole defined by a connection belt 18a that extends opposite to at least one cutting profile 12c. This way, both with a single cutting profile 12c (<FIG>) as well as with more cutting profiles 12c,<NUM>'c (<FIG>) for each connection portion <NUM>, on the one hand a band <NUM> is obtained with fixed width even if maintaining a cutting profile 12c or 12c,<NUM>'c in the cutting portion <NUM> with adjustable cross section, allowing to convey the blade <NUM> in a way that is very steady and quick, owing to the presence of the connection belt 18a.

The conveying the log <NUM>, or each log <NUM>, on a respective cutting cradle <NUM> in the cutting region <NUM>, can be made stepwise, each step being carried out when in the cutting region <NUM> the connection portion <NUM> is moved, and is then stopped when in the cutting region <NUM> the cutting portion <NUM> moves, so that the cutting profile 12c that extends obliquely cuts the log <NUM> obtaining cut portions <NUM> for a length corresponding to one step.

In the possible embodiment of <FIG> the cutting portion <NUM> is arranged in turn in an elongated hole, with an elongated hole <NUM>', which allows lightening the cutting portion <NUM> same. In particular, the elongated hole <NUM> can be a first elongated hole and the plane cutting portion <NUM> provides a second lightening elongated hole <NUM>'. In this case, the plane cutting portion <NUM> provides a band portion 12d that has a first end <NUM>'d connected to the first connection belt 18a and a second end <NUM>"d that is connected to a second connection belt <NUM>'a, the band portion 12d extending obliquely between the first connection belt 18a and the second connection belt <NUM>'a, in order to have said cutting profile 12c facing towards the first connection belt 18a. In a particular production configuration, the band portion may also have a cutting profile facing towards the second connection belt, in case of reciprocating movement of the blade, the band portion extending obliquely between the first connection belt and the second connection belt.

In a specific example of an exemplary embodiment of <FIG>, not shown but easily implemented by a skilled person, the band portion 12d may also have a cutting profile facing towards the second connection belt <NUM>'a, in case of reciprocating movement of the blade, in this case at least one further cradle can be provided, for feeding logs in the second elongated hole <NUM>'.

Also, the solutions of <FIG>, <FIG> can provide the possible increase of the number of cradles, for example up to eight cradles, or more, and the subsequent evacuation of a corresponding number of cut portions (see for example the layout of <FIG>).

Alternatively to what above defined, the conveying of log <NUM> can be continuous (<FIG>). The continuous conveying can be made according to a conveying direction <NUM> in <FIG>, or in two opposite directions for conveying two separate series of log <NUM>, as described hereinafter.

With reference to <FIG>, on each cutting cradle of logs1 in the cutting region <NUM>, by using a preferred exemplary embodiment of the blade <NUM> as above described, in order to avoid interferences with the cutting portion <NUM>, in the cutting region <NUM>, a conveying device <NUM> can be provided, for example consisting of small rollers <NUM> that roll on the blade <NUM> and that move integrally in an alternated way according to arrow <NUM>. This way, the conveying device <NUM> causes a bending of blade <NUM> in the conveying direction <NUM> between a first position 40A and a second position 40B. In this bending, the tension of the blade is for example compensated by a blade tensioner <NUM>, which can oscillate according to an arrow 42a.

According to this exemplary embodiment, when the conveying device <NUM> causes the bending in the direction 7b in the same conveying direction <NUM> from the first position 40A to the second position 40B (<FIG>), this bending is carried out with a movement synchronous to the continuous conveying of the log <NUM> in the direction <NUM>, and this synchronous movement is carried out when in the cutting region <NUM> the cutting portion <NUM> moves, so that the cutting profile 12c that extends obliquely, cuts the log <NUM> obtaining cut portions <NUM> having a same length as a predetermined conveying length.

Instead, with reference to <FIG>, the conveying device <NUM> can cause the bending in an opposite direction 7a to the conveying direction <NUM> from the second position 40B to the first position 40A when in the cutting region <NUM> the connection portion <NUM> moves, so that the connection portion moves next to the log <NUM> without impeding the continuous conveying of the log <NUM>. Such movement 7a can be made in the quickest possible way, for increasing the production rate and the need of a connection portion <NUM> as short as possible, while the pitch of the cut is determined by the combination between the speeds of movement according to arrows <NUM> and 7a.

In these exemplary embodiments with continuous movement of the log <NUM>, alternatively to a blade tensioner, the bending of blade <NUM> caused by the variation of position of the conveying device <NUM> can be compensated, in a way not shown but easily implemented by a skilled person, with the movement of at least one, or both the flywheels 23a, 23b, or other flywheels arranged for rotating the blade <NUM>, in synchronism with the movement of the conveying device <NUM>. In this case, the drums or the flywheels should be mounted to a support whose axis can move parallel to itself.

With reference to <FIG>, in a possible exemplary embodiment of the two solutions of <FIG>, in order to avoid the need of a blade tensioner, and to double the production rate, two respective conveying devices can be provided <NUM>, <NUM>', similar to that above described, that move integrally in an alternated way, but according to two opposite phases shown respectively in <FIG>. This way, the two conveying devices <NUM>, <NUM>' cause a bending of the blade <NUM> in the conveying direction <NUM> or in the conveying direction <NUM>' between the two above described positions, or in a similar way to that described in <FIG>, provided according to phases opposite to each other. In this bending, the tension of the blade <NUM> does not require further compensations, since the blade is fixedly tensioned. Furthermore, the production rate is doubled. Further sides of the blade <NUM> and further dispositions of the cradles of the logs <NUM> can be implemented by the skilled person, and preferably even with further systems <NUM> when the blade <NUM> extends on a wide surface, for example polygonal with more than four sides.

With reference to the figures from <NUM> to <NUM>, in possible production layouts, the blade <NUM> is looped around a plurality of flywheels or pulleys 23a,23b,23c,23d arranged as a polygon <NUM>, in particular a quadrilateral, wherein, on one side of the polygon a sharpening device is provided <NUM>, and wherein on at least another side 100a of the polygon at least one cutting region is provided <NUM>. In particular, the cutting region <NUM> is located downstream of a storage region <NUM> of log ready to be cut, in turn, downstream of a production line of paper material comprising at least one production machine, for example a rewinding machine, or an interfolding machine, or a machine for stacking packages of folded sheets. Other machines can be unwinding, transversal cutting, gluing machines, etc., as well known in plants of paper converting.

In a first possible exemplifying embodiment (<FIG>), downstream of the cutting region <NUM> a downhill conveying path <NUM> is provided along which cut portions <NUM> of the logs move. A first side 100a of polygon <NUM> of the path of blade <NUM> crosses the cutting region <NUM> upstream of the downhill conveying path <NUM>, and a second side 100b of the polygon consisting of the path of blade <NUM> is opposite to the first side 100a and extends above the downhill conveying path <NUM> so that the blade <NUM> has the cutting edge <NUM> with the cutting profile 12c that do does not impede the cut portions of log <NUM>, whereas when the cutting edge <NUM> with the cutting profile 12c passes through the side 100a of polygon <NUM>, it cuts the log <NUM> into portions <NUM>. Such solution allows a very high production rate.

Another alternative layout shown in <FIG> provides upstream of the cutting region <NUM> a conveying path <NUM> of log <NUM>, for example providing up to eight cradles of log <NUM> or even more. In this layout a first side 100a of polygon <NUM> of the blade path, consisting of the blade <NUM> and of the drums or pulleys 23a,23b, etc., crosses the cutting region <NUM> so that the cutting profile 12c cuts them into rolls <NUM>, and other sides of polygon <NUM> extend upstream of and at the sides of the conveying path <NUM>, so that the blade <NUM> does not impede cut portions of log <NUM>. The length of the sides of polygon <NUM> does not affect the efficiency of the method, since the angle of the cutting portion <NUM> can be also of a few degrees, up to <NUM> degree, and the speed <NUM> of the blade (<FIG>) can be also of hundreds of metres per minute.

In a further layout shown in <FIG>, there are provided two cutting regions <NUM> and two conveying paths <NUM> of logs upstream of the cutting region, wherein a first and a second side 100a and 100b of polygon <NUM> provide blade <NUM> crossing the conveying paths <NUM> of log <NUM> in two respective cutting regions, in order to cut the log coming from the two conveying paths, and a third side 100c of polygon <NUM> passes above two respective paths of downhill evacuation 8a,8b of cut portions, so that the blade <NUM> does not impede respective cut portions of log <NUM>. Such solution allows, with a single blade <NUM>, a production rate doubled with respect to <FIG>, with up to <NUM> logs (or more) cut by a single passage of blade <NUM>. Obviously, other similar layouts and with a production rate even higher can be provided similarly, with a polygon with different shape and different size, but easily obtainable by a skilled person.

With reference to all these exemplary embodiments, with references <NUM> and <NUM>-<NUM> a production line of paper material is shown comprising at least one machine for paper converting, for example a rewinding machine, or an interfolding machine, or a machine for stacking packages of folded sheets. Other machines can be unwinding machines, transversal web cutting machines, gluing machines, etc., as well known in paper converting plants.

With reference to the <FIG>, a cutting region <NUM> can be provided wherein polygon <NUM> is arranged in a vertical plane and the blade <NUM> has at least one couple of cutting profiles 12c,<NUM>'c opposite to the longitudinal axis (as described for <FIG>). Upstream of the cutting region <NUM> there being provided a conveying path <NUM> of at least two logs <NUM>, in a way in which they are located at opposite sides with respect to the blade <NUM> in the cutting plane. Such solution is particularly suitable to cut industrial rolls very thick and jumbo rolls.

In possible exemplary embodiments according to <FIG>, in the cutting region <NUM> in the various ways above described, at the cradles <NUM> an element of pressure <NUM> can be provided, commonly called presser.

In a possible solution, as shown in <FIG>, the pressing element <NUM> comprises an upper pressing member <NUM> having at least one couple of plane upper pressing plates, configured to contact a respective generatrix of the log (not shown), opposite to the cradle <NUM>. This way, the upper pressing member <NUM> can carry out a blocking movement 70a in a direction that is orthogonal to the conveying direction, according to a blocking stroke simultaneously to the movement of the cutting portion into the cutting plane. There can be provided a mechanism <NUM> of adjustment in height of the upper pressing member, which allows both adjusting a rest position of the plane pressing plates and adapting to different diameters of the log, carrying out the stroke of blocking/unlocking the log. Advantageously, as shown in the figure, a pressing device <NUM> can be provided of a support structure <NUM> of a plurality of cradles <NUM> adjacent to each other and relative pressing devices.

In another possible solution, as shown in <FIG>, the pressing element <NUM> comprises two conveyor belts 71a, 71b facing each other that move for pushing a log not shown in the conveying direction <NUM>, in order to cause it to advance. Furthermore, the belts 71a, 71b can move in a direction 70a orthogonal to the conveying direction <NUM>, for carrying out a blocking stroke of the log, simultaneously to the movement of the cutting portion of the blade <NUM> in the cutting plane by it defined. For carrying out the blocking movement in the direction 70a, there can be provided a mechanism of pushing and adjusting in height <NUM> the conveyor belts 71a, 71b, in order to both adjusting a rest position of the conveyor belts and adapting to different diameters of the log, as well as carrying out the blocking stroke during the movement of the cutting portion of the blade <NUM>. Such a configuration of the clamping device can also be used in case of continuous movement, according to <FIG>.

In possible embodiments, according to <FIG>, a step can be provided of sharpening the blade, carried out only on the cutting profile 12c of the cutting portion and not on the connection portion <NUM>. This determines that portions of the blade are not sharpened, and then easily handled in case of mounting and maintenance.

In particular, the sharpening step can be made through at least one sharpening knob <NUM> mounted to an oscillating arm <NUM>, configured to oscillate by translating (<FIG>) or by rotating (<FIG>) with respect to a fixed frame, under the push of the knob <NUM>, in order to follow the cutting profile 12c during the movement of the cutting portion <NUM>.

Alternatively, as shown in <FIG>, the sharpening can be made through a couple of abrasive sharpening sticks <NUM> arranged slanted and opposite to each other, and configured for closing or widening from each other according to arrow 51a respectively, for carrying out the sharpening of the cutting profile 12c (normally called bevel) or releasing the blade when the sharpening has not to be done.

As further alternative, as shown in <FIG>, the sharpening can be made by an elongated abrasive strip <NUM> mounted to a support 55a having an approaching movement and arranged laterally so that the cutting profile 12c contacts with an own side face against the strip <NUM>, allowing that different portions of the cutting profile 12c contact different portions of the strip <NUM>.

Claim 1:
A method for cutting logs (<NUM>) comprising the steps of:
- prearranging at least one cutting region (<NUM>) configured to be crossed by at least one log (<NUM>) according to a conveying direction (<NUM>) transversal to a cutting plane (<NUM>);
- prearranging a blade (<NUM>) having a longitudinal axis (<NUM>) and comprising:
- a plane cutting portion (<NUM>) and a connection portion (<NUM>) connected to said plane cutting portion (<NUM>);
- said plane cutting portion (<NUM>) having a cross section of minimum width (12a), a cross section of maximum width (12b) and at least one cutting profile (12c) that extends obliquely between said cross section of minimum width (12a) and said cross section of maximum width (12b), so that said cutting profile (12c) forms an angle with respect to said longitudinal axis (<NUM>) set between <NUM>° and <NUM>°, in particular between <NUM>° and <NUM>°, much more in particular, between <NUM>° and <NUM>°, preferably between <NUM>° and <NUM>°,
- said cutting profile (12c) having a cutting height (<NUM>) in a direction that is orthogonal to said longitudinal axis (<NUM>) equal to at least the difference between said cross section of maximum width (12b) and said cross section of minimum width (12a), and said connection portion (<NUM>) having a width less than or equal to said minimum width (12a);
- moving (<NUM>) said blade (<NUM>) parallel to said longitudinal axis (<NUM>) so that said connection portion (<NUM>) and said plane cutting portion (<NUM>) cross in turn said cutting region (<NUM>) and said plane cutting portion (<NUM>) passes through said cutting region (<NUM>) according to said cutting plane (<NUM>);
- conveying said or each log (<NUM>) on a respective cutting cradle (<NUM>) in said cutting region (<NUM>), said or each log (<NUM>) having a height less than said cutting height (<NUM>) so that said cutting profile (12c) that extends obliquely cuts said logs (<NUM>) during said movement (<NUM>) starting from a point in which it comes in contact with said log (<NUM>), causing a cut in said logs (<NUM>) and obtaining cut portions (<NUM>) having a same length as a predetermined conveying length.