Cutting machine for cross-cutting logs of paper material

Abstract

A cutting machine for cross-cutting a log of paper material, comprising: - a structure (SC) for moving the log; - a cutting unit (CU) with a blade (2); - a grinding unit for sharpening the blade; - a device for positioning a grinding wheel with respect to the blade (2); - the positioning device comprises a first carriage (4) and two second carriages (42, 43) driven by respective actuators; - an optical sensor (100) is provided for detecting the cutting edge (200) of the blade (2); - during the operational positioning phase of the grinding wheels, which includes sharpening the blade following contact of the grinding wheel with the blade, the grinding surface of the grinding wheel is pressed against the blade with a thrust having a predetermined value.

Description

[Technical Field]

[0001] The present invention relates to a cutting machine for cross-cutting logs made of paper material. [Background technology]

[0002] It is known that rolls of paper for toilet paper, kitchen paper, and similar uses are commonly called "logs" and are produced by a machine called a "rewinder" and are obtained by cross-cutting a longer length of roll. In said logs, a predetermined amount of paper material consisting of one or more overlapping paper plies is wound around itself or around a cardboard tube called a "core." Generally, the logs produced by the rewinder are transported to a buffer magazine and from there to a machine called a "cutting machine" which performs the aforementioned cross-cutting.

[0003] Generally, the sawing machine has a platform in which a guide channel for the log is defined and a cutting unit located downstream of the channel, which includes a disk-shaped blade that operates and moves appropriately to determine the cross-cut of the log at a speed programmed according to the length of the roll obtained from the log. The blade is usually associated with a grinding wheel that periodically intervenes to restore the blade's own cutting profile. The blade of the sawing machine must be replaced periodically due to wear, which gradually reduces both its diameter and cutting performance. Whenever a worn blade is replaced with a new one, the position of the grinding wheel relative to the blade must be adjusted.

[0004] Patent document 1 discloses a cross-cutting machine for logs of paper material, which includes a path of travel for the logs to be cut, a cutting unit with an exchangeable disc-shaped blade supported so as to be able to rotate about its own axis while performing a periodic movement for cutting the logs and advancing the logs along the path of travel, and a sharpening unit with two grinding wheels configured and controlled to interpose on the disc-shaped blade when the disc-shaped blade is sharpened.

[0005] The grinding wheels are mounted on a support system including a mechanism for controlled approach of the grinding wheels to the blade. The approach mechanism is configured to move each grinding wheel in a direction substantially parallel to its axis of rotation. The mechanism acts to controllably approach the grinding wheels to the blade by moving each grinding wheel's support slide to a nominal position relative to the blade and moving the grinding wheel relative to the associated slide, which is held in the nominal position. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] EP3194128B1 Summary of the Invention [Problem to be solved by the invention]

[0007] The main object of the present invention is to propose a machine for cutting logs in which the positioning of the sharpening wheel relative to the blade, which is sharpened from time to time, is automated and this positioning is substantially independent of the diameter of the blade.

[0008] A further object of the present invention is to provide a sharpening mechanism for blades, used in cutting machines for cross-cutting logs of paper material, that makes it possible to eliminate or at least significantly reduce the so-called "polygonization" of the blades themselves, i.e. the phenomenon in which the blades lose their original circular shape due to the repeated grinding operations they are usually subjected to and take on a substantially polygonal shape, which determines the incorrect execution of the cross-cutting of the logs. [Means for solving the problem]

[0009] This object has been achieved according to the invention by adopting the idea of ​​producing a machine having the features set out in claim 1. Further features of the invention are the subject of the dependent claims. [Effects of the Invention]

[0010] According to the present invention, the positioning of the grinding wheel can be performed automatically in less time and with greater operational safety than manual positioning, since this operation does not require an operator to access the area of ​​the machine that houses the blade. Furthermore, the device for positioning the grinding wheel in the machine according to the present invention has a relatively simple structure and incorporates an effective mechanism for recognizing the desired position of the grinding wheel. Furthermore, the machine according to the present invention eliminates or at least significantly reduces the so-called polygonization of the blade, even when the positioning of the grinding wheel determined by the first carriage is not particularly accurate.

[0011] These and further advantages and features of the present invention will become more apparent to those skilled in the art from the following description and accompanying drawings, which are provided by way of example and should not be considered in a limiting sense. [Brief explanation of the drawings]

[0012] [Figure 1] 1 represents a schematic vertical cross-section of a cutting station of a cutting machine for cross-cutting a log of paper material by means of a cutting unit according to the invention; [Figure 2]1 shows a schematic front view of a cutting unit for a cutting machine according to the invention; [Figure 3] 3 shows a first schematic side view of the cutting unit of FIG. 2; [Figure 4] 3 shows a second schematic side view of the cutting unit of FIG. 2. [Figure 5] 3 shows a first schematic perspective view of the cutting unit shown in FIG. 2; [Figure 6] 3 shows a second schematic perspective view of the cutting unit shown in FIG. 2; [Figure 7A] 3 shows a cross-sectional view taken along line AA in FIG. 2. [Figure 7B] FIG. 10 is a perspective view of a second carriage with respective movement means. [Figure 8] FIG. 10 shows possible orientations of the grinding wheel relative to the plane (P2) of the blade (2). [Figure 9] FIG. 10 is a diagram showing the polygonal shape of the blade. [Figure 10] 10 is a qualitative graph illustrating possible variations in torque provided by the drive motor of the grinding wheel in the cutting unit shown in the previous figure, along with variations in the diameter of the blade being sharpened. [Figure 11] 10 schematically represents a further embodiment of the invention, in which the cut log is designated with the reference "L". [Figure 12] FIG. 10 is a diagram illustrating the geometric parameters for the position of the grinding wheel relative to the blade of the cutting unit. [Figure 13] 3 shows a simplified block diagram of a possible control system for the actuators of the cutting unit in a machine according to the invention; [Figure 14] 10 is a qualitative graph illustrating the constant value of the torque provided by the motor of the second actuator during a stroke of the second carriage. [Figure 15] 10 is a qualitative graph illustrating a possible method for controlling the rotational speed of the blade during the sharpening stage. DETAILED DESCRIPTION OF THE INVENTION

[0013] The cutting machine according to the invention, to which the cutting unit can be applied, modified in its essential structure and with reference to the accompanying drawings, comprises: - Structure for moving logs to be cut transversely to obtain rolls of shorter length (SC); - a cutting unit (CU) placed in a predetermined position on the structure (SC) and comprising a support plate (1) for blades (2), said blades (2) being removably connectable to respective rotary actuators (20) placed at one end of said plate (1) and capable of determining the rotation of said blades themselves about their own axes (xx) at a predetermined speed, said plate (1) being likewise constrained to a further actuator which rotates said plate at a predetermined angular speed around an axis parallel to the rotation axis (xx) of said blades (2); - a sharpening unit having two wheels (3) suitably arranged to sharpen said blade (2); - a device for positioning the grinding wheel (3) relative to said blade (2).

[0014] 1 shows diagrammatically the main components of a cutting machine (CM) on which a cutting unit according to the invention can be mounted, it being understood that this drawing is provided only to make it possible to identify the position of said cutting unit with respect to the path of said log, and that said cutting machine configuration can be manufactured in any suitable way, as long as it is intended for the transverse cutting of a log of paper material in order to obtain rolls of shorter length by means of a cutting unit with a blade acting transversely on said log.

[0015] In the example of Figure 1, according to a construction scheme known per se, the rotary actuator (20) is connected to the blade (2) by a belt (21) which connects the central pin (22) of the blade to the shaft (23) of the actuator (20) via a pulley arranged at the free end of the shaft (23). Furthermore, the plate (1) is rotated about an axis parallel to the axis of rotation of the blade (2) by a corresponding rotary actuator (A1) with an axis (B1) parallel to the axis (23) of the actuator (20) which controls the rotation of the blade (2).

[0016] The actuator (20), e.g., an electric motor, is integrated with a box-shaped body (BB) located above the structure (SC) and containing the belt (21) and the shafts (23) and (B1). The body (BB) is connected to a corresponding actuator (BA), which controls its vertical position, i.e., its positioning relative to the underlying structure (SC), via a screw (VA) acting on a nut bushing located on the upper side of the body (BB). Thus, by controlling the position of the body (BB), the blade (2) can be positioned at a desired height relative to the structure (SC). The actuator (A1), e.g., an electric motor, is also integrated with the body (BB).

[0017] In practice, said blades (2) rotate about respective axes (xx) parallel to the axis of rotation of said plate (1).

[0018] A cutting unit (CU) according to a possible embodiment of the present invention comprises a plate (1) having an upper side (10), a lower side (11), a front side (F1), and a rear side (R1). The central pin (22) of the circular blade (2) is attached to the lower side (11) of the plate (1) and is removably attached to this pin so that the blade can be replaced when necessary. The blade (2) is oriented parallel to the plate (1) and is positioned a predetermined distance from the front side (F1) of the plate (1). Also attached to the plate (1) are two grinding wheels (3) for grinding the blade (2) and a device for positioning the grinding wheels (3) relative to the blade (2).

[0019] Each grinding wheel (3) is applied to a support shaft (30) whose axis (A30) has a predetermined inclination relative to the front side (F1) of the plate (1) and therefore relative to the corresponding face of the blade (2). Figure 8 shows the shafts (30) supporting the grinding wheels (3), their respective axes (A30), the inclination of this grinding wheel (3) in the grinding position relative to the face (A2) of the blade (2) and the plane (P2) of the blade.

[0020] According to the present invention, the positioning device for the grinding wheel (3) has the following configuration: - a first carriage (4) movable parallel to said plate (1) according to a first direction of movement (PD); - two second carriages (42, 43) constrained to the first carriage (4) and independently movable according to a second direction of movement (SD) perpendicular to the first direction of movement (PD), each second carriage (42, 43) having a seat for supporting the shaft (30) of a respective grinding wheel (3).

[0021] In practice, the first direction of movement (PD) is parallel to the plane (P2) in which the blade (2) is located, i.e. radially relative to the blade (2), while the second direction of movement (SD) is parallel to the axis of rotation (xx) of the blade (2).

[0022] According to the embodiment shown in the drawings, the first carriage (4) consists of two independent units (40, 41) each of which has a corresponding constrained second carriage (42, 43). Alternatively, the first carriage can consist of a single unit, with both second carriages (42, 43) constrained.

[0023] In the embodiment shown in Figures 2 to 7, the first carriage (4) consists of two independent units, each of which includes a body (40, 41) restrained by a linear guide (LG) on the inner side (F1) of the plate (1) to enable guided sliding along the first direction of movement (PD). The sliding of each body (40, 41) along the first direction of movement (PD) is controlled by a corresponding electric motor (M0, M1). Each motor (M0, M1) is fixed to the inner side (F1) of the plate (1) and drives a threaded shaft (TS) that engages with a corresponding nut bush (MV) formed on each body (40, 41). Therefore, each body (40, 41) can be moved along the first direction of movement (PD) by its respective motor (M0, M1).

[0024] Each of the bodies (40, 41) has a first side (4P) parallel to the inner side (F1) of the plate (1) and a second side (4H) perpendicular to the first side (4P) and located below. The first side (4P) slides along the respective guide (LG). The second side (4H) forms a cantilever structure, the function of which will be explained below. In fact, each of the bodies (40, 41) has a structure with a part (4P) parallel to the inner side (F1) of the plate (1) and a part (4H) perpendicular to the inner side (F1) of the plate (1) when viewed laterally, which defines a bracket above the blade (2). In the above example, the movement of the main body (40, 41), i.e., the movement of the two units constituting the first carriage (4), is guided by the presence of the guide (LG) that restrains the main body (40, 41) to the inner side (F1) of the plate (1).

[0025] According to the embodiment shown in the accompanying drawings, each second carriage (42, 43) has an upper vertical appendix (U4) arranged below the respective bracket (4H) and passing through a longitudinal slot (4C) made in said bracket. The motors (M2, M3) are arranged above the bracket (4H) and are fixed to the upper surface of the corresponding bracket (4H) via the outer casing of the respective linear actuator (A2, A3) driven by said motor (M2, M3). Each actuator (A2, A3) is, for example, a screw actuator known per se, i.e., an actuator comprising a stem (SA) moved by a screw (not shown) operated by the respective motor (M2, M3). The stem (SA) is attached at its rear to a flange (FA) fixed to a slide member (CA) attached to the upper surface of the actuator casing, while its front is fixed to the vertical appendix (U4) of the respective carriage (42, 43).

[0026] The shafts 30 of the grinding wheels 3 are fixed to the respective second carriages 42, 43. Thus, the motors M2, M3 move the respective second carriages 42, 43 in the second movement direction SD along the underside of the bracket 4H. And, since the second carriages are connected to the first carriages, the respective second carriages, and consequently the respective grinding wheels, can move in both the first movement direction PD and the second movement direction SD.

[0027] In other words, each grinding wheel (3) is supported by the cutting unit (CU) so as to be movable in both the first direction of movement (PD) and the second direction of movement (SD). In fact, the bodies (40, 41) constituting the first carriage (4) can be moved in the direction (PD) by the motors (M0, M1), while the second carriages (42, 43) can be moved on the first carriage along the direction (SD) by the motors (M2, M3).

[0028] The grinding wheels (3) are oriented with their respective grinding faces (31) facing towards the plane (P2) in which the blades (2) lie.

[0029] The first carriage may be provided with an optical sensor 100, the function of which will be described later, on its underside, i.e., the side facing the blade 2. For example, the optical sensor 100 may be attached under the bracket 4H of either of the aforementioned bodies 40, 41. For example, the optical axis of the sensor 100 is spaced a predetermined distance b from a reference line (which may be the so-called "sink line" (L3) of the grinding wheel 3) so that it intercepts the cutting edge 200 of the blade 2 when the first carriage approaches the blade 2 before the grinding wheel 3 is positioned in the sharpening position on the blade.

[0030] The sink line is the reference line of each grinding wheel (3) and is a known geometric parameter provided by the manufacturer. This parameter specifies the correct position of the grinding wheel relative to the blade for sharpening purposes. In practice, to accurately sharpen the blade, the sink line of the grinding wheel must be tangential to the cutting edge of the blade, as shown in Figure 12. In this condition, the grinding surface of the grinding wheel precisely interfaces with the area of ​​the blade to be sharpened, i.e., optimal contact is created between the grinding wheel and the blade during the sharpening process.

[0031] According to the above-described embodiment, the movement of the first carriage (4) along the first movement direction (PD) is controlled by the sensor (100) which detects the actual diameter of the blade (2), so that, regardless of the actual diameter of the blade (2), the grinding wheel (3) is guided to the exact sharpening position where the sink line of the grinding wheel contacts the cutting edge of the blade.

[0032] 12, in the first stage of operational positioning of the grinding wheel (3), the movement of the first carriage (4) is controlled by the sensor (100), which detects the radius of the blade (2) and controls the interruption of the travel of the first carriage along the first direction of movement (PD) when the grinding wheel is positioned with its axis at a distance (h) equal to the radius (r2) of the blade increased by the radius (r3) of the wheel and decreased by a predetermined value (b) relative to the axis of the blade, the radius (r3) of the grinding wheel (3) being a known value.

[0033] Similarly, the value (b) is a known value provided by the grinding wheel manufacturer. This value (b) defines the position of the reference line (L3) relative to the edge of the grinding wheel, or equivalently, relative to its axis. In fact, the above value (b) represents the difference along the first direction of movement (PD) of the first carriage movement between the position of the optical sensor (100) projected onto the plane (P2) of the blade (2) and the position of the sinking line (L3) of the grinding wheel (3) projected onto the same plane (P2).

[0034] According to the present invention, while moving the second carriages (42, 43) along the direction (SD) to bring the grinding wheels (3) into contact with the blade (2), and thus during the sharpening phase, the respective motors (M2, M3) are controlled to provide a predetermined torque. In other words, the motors (M2, M3) are controlled so that the respective grinding wheels (3) exert a predetermined amount of thrust on the blade (2) during the sharpening phase. In further words, during the second phase of operatively positioning the grinding wheels (3), the grinding wheels are pressed toward the blade (2) by applying a predetermined amount of thrust that is maintained during the sharpening phase.

[0035] In this specification, a first stage of operational positioning of the grinding wheel (3) corresponds to a stroke of the grinding wheel towards the blade (2) along the first direction of movement (PD), while a second stage of operational positioning of the grinding wheel (3) corresponds to a stroke of the grinding wheel towards the blade (2) along the second direction of movement (SD).

[0036] In the example shown in Figure 13, the electric motors (M2, M3) are controlled by a programmable control unit (MC) to which the motors (M0) and (M1), the sensor (100), the motor (20) and the rotary actuator (A1) are also connected. In this figure, a sensor (20S) for detecting the rotational speed of the blade (2) is also connected to the control unit (MC).

[0037] Possible modes of operation of the above described device are as follows:

[0038] To sharpen the blade attached to the cutting unit, the first carriage moves along the first movement direction (PD) and performs a first stage of operational positioning of the grinding wheel (3). The optical sensor (100) then detects the edge (200) of the blade (2), and the movement of the first carriage is stopped, for example, when the sensor (100) passes the edge (200) by a value corresponding to the aforementioned value (b). For this purpose, the optical sensor (100) is connected to the motors (M0, M1) via the programmable control unit (MC). In this way, the grinding wheel (3) is positioned as desired, spaced apart from the two sides of the blade (2) for the subsequent sharpening stage.

[0039] At this point, to perform a second operational positioning step of the grinding wheels, the second carriages (42, 43) are moved by the motors (M2, M3) along the second movement direction (SD), so that each grinding wheel (3) is transported with its respective grinding surface (31) in contact with the corresponding side of the blade (2) rotated about its own axis (xx). This contact (in technical terms, a "home" position identification) is detected via the blade (2), which in fact undergoes a deceleration as a result of the contact itself.

[0040] Typically, the motor (20) driving the blade is controlled by a system with a control function (FC) that ensures a constant rotational speed of the blade around the axis (xx) during the cross-cutting of the log. When the grinding wheel positioning device is activated and the grinding wheel is moved along the aforementioned direction (SD), the control function of the motor (20) is temporarily stopped. Contact between the grinding wheel (3) and the blade (2) causes the blade (2) to decelerate, and this condition is assumed to be an indication of contact between the grinding wheel and the blade. When this condition is detected, the thrust force applied to the grinding wheel (3) is not interrupted, i.e., this thrust force is maintained throughout the sharpening phase.

[0041] For this purpose, the torque of the motors (M2, M3) is controlled so as to remain at a predetermined value throughout the sharpening phase of the blade (2). During the sharpening phase, the grinding wheel (3) is pressed in a positive and controlled manner towards the blade (2), thereby reducing the vibrations normally caused by the contact between the grinding wheel and the rotating blade and thus improving the contact between the blade and the grinding wheel. This makes it possible to avoid the so-called "polygonization" of the cutting edge of the blade and to obtain a more accurate cross-cut of the log and to optimize the wear of the blade, which is an expensive component of the cutting unit.

[0042] As mentioned above, "polygonalization" refers to the phenomenon in which the blade loses its original circular shape and assumes a substantially polygonal shape due to repeated grinding operations, which the blade typically undergoes before being replaced. In the schematic diagram of FIG. 9, the solid line (PC) represents the ideal circular outline of the blade (2), and the dotted line (PP) represents the polygonalized outline of the blade. In FIG. 9, the dotted outline (PP) of the blade (2) has been intentionally enlarged to emphasize its non-circular shape. In FIG. 9, the reference characters "VP" indicate some vertices of the polygonal shape assumed by the blade due to the polygonalization effect.

[0043] In another embodiment, the identification of the "home" position, i.e., the contact position between the blade and the grinding wheel, is operated differently: during the phase in which the grinding wheel approaches the blade, the motors (M2, M3) are controlled to provide a predetermined limited torque during grinding, and the control function (FC) of the motor (20) that moves the blade is not stopped, so that contact between the grinding wheel and the blade is identified by the stopping of the motors (M2, M3) resulting from contact between the grinding wheel and the blade. In any case, during the sharpening phase, the grinding wheel is pressed towards the blade with a constant thrust.

[0044] Preferably, the motors (M2, M3) move the second carriage (42, 43) by means of a mechanical transmission, in particular a screw transmission as in the example described above, thereby avoiding or in any case significantly reducing the possibility of the grinding wheel bouncing during the sharpening process. In other words, the use of a mechanical linear actuator, such as the type described above, that determines the movement of the second carriage via a screw driven by an electric motor, is preferred to a pneumatic linear actuator, which is more likely to cause bouncing of the grinding wheel relative to the blade.

[0045] The stroke of the first carriage towards the blade (2) is controlled by the optical sensor (100) which detects the cutting edge (200) of the blade, so that the stopping point of the first carriage at the end of this stroke is not predefined but depends on the diameter and therefore on the degree of wear of the blade attached to the cutting unit.

[0046] In practice, in the first stage of operational positioning of the grinding wheel (3), the movement of the first carriage (4) is controlled by the optical sensor (100) that detects the cutting edge (200) of the blade (2), so that the first operational positioning stage of the grinding wheel (3) means a stroke of the first carriage (4) whose length correlates with the actual diameter of the blade (2). And in the second stage of positioning of the grinding wheel (3), the second carriages (42, 43) are controlled to bring the grinding surface of the grinding wheel (3) into contact with the blade (2).

[0047] According to the invention, during the second stage of operational positioning of the grinding wheel 3, the motors M2, M3 are controlled to provide a fixed predetermined torque. Indeed, the Applicant has observed that this control mode of the motors M2, M3 during the second stage of operational positioning of the grinding wheel 3 determines a more accurate sharpening of the blade 2, which avoids so-called polygonization of the blade, even when the first stage of operational positioning performed by the first carriage is affected by an error (for example, if the positioning determined by the actuation of the first carriage controlled by the sensor 100 is affected by an error of 0.5 mm, more generally an error between 0 mm and 3 mm).

[0048] More generally, as mentioned above, according to the invention, during the sharpening process of the blade (2), the grinding wheel (3) is pressed towards the blade with a thrust of a predetermined and controlled value by an actuator which moves the carriage on which the grinding wheel is mounted. In the above example, the actuators which move the second carriage are driven by the electric motors (M2, M3), but more generally, these actuators can be of any suitable type, as long as they can be controlled in such a way that they are able to press the grinding wheel (2) towards the blade (3) along the second direction of movement (SD) with a thrust of a predetermined and controlled value during the sharpening process.

[0049] The applicant has also noted that during the sharpening stage, it is preferable to maintain constant the thrust force exerted by the grinding wheel (3) on the blade (2) as the diameter of the blade (2) decreases, while modifying it accordingly. More specifically, it is preferable to increase the thrust force exerted by the grinding wheel on the blade as the blade diameter decreases. Experimental tests were conducted using a blade type having an initial diameter of 600 mm, which gradually decreased to a final value of 480 mm during use due to wear. The motors (M2, M3) used during the tests were motors providing a nominal torque of 0.31 Nm.

[0050] During testing, the torque of the motors (M2, M3) was kept constant during each sharpening step, but increased by a predetermined amount during each subsequent sharpening step (from 10% of the nominal value during the first sharpening step on an unworn blade to 90% of the nominal value during the final sharpening step on a fully worn blade). Applicant believes that the constant, controlled thrust exerted by the grinding wheel on the blade during each sharpening step stabilizes the blade itself, reducing its vibration and contributing to the reduction in polygonal tendencies that are reduced by the present invention. In other words, the constant thrust ensures that the grinding wheel always makes precise contact with the blade during the sharpening process.

[0051] In figure 10 a qualitative graph is provided showing the possible modes (M) of variation of the torque provided by the motors (M2, M3) when the diameter of the blade (2) is varied according to the tests carried out. In this graph the symbols used have the following meaning: -C: Couple -CN: the nominal torque of the motors (M2, M3), equal to 0.31 Nm; Cm: the minimum torque provided by said motors (M2, M3), equal to 10% of the nominal torque CN; CM: the maximum torque provided by the motors (M2, M3), equal to 90% of the nominal torque CN; -D: Diameter Dm: the minimum diameter of said blade (2), equal to 480 mm; - DM: the maximum diameter of said blade (2), equal to 600 mm.

[0052] Although the graph of Figure 10 shows a substantially linear change (M) in the torque provided by the motors (M1, M2) as the diameter of the blade (2) changes, it is understood that this change may also be non-linear.

[0053] Preferably, between one sharpening process and the next, the rotational speed of the blade is varied between a value lower than the nominal rotational speed (for example 95%) and a value higher than the nominal rotational speed (for example 105%). Indeed, the Applicant has observed that the divergence phenomenon is further enhanced by combining a predetermined and controlled thrust of the grinding wheel on the blade with varying the rotational speed of the blade within predetermined limits.

[0054] The experimental tests were conducted by the applicant using a blade commercially available under the trade name Chromalit IKS Φ610 and a grinding wheel of type K10R 150 grit commercially available from International Knife & Saw, Inc.

[0055] In the diagram of Figure 14, the horizontal line segment (CSD) represents the constant value of the torque (Cc) provided by the motors (M1, M2) along the entire stroke of the second carriage until contact with the blade, represented by the line segment 0 to Xc on the XSD axis. The values ​​CN, CM, Cm on the vertical axis C have already been indicated above with reference to the graph of Figure 10. The "Cc" value represents the value of the torque provided by the motors (M1, M2) that corresponds to the actual diameter of the blade, in accordance with what has been said above.

[0056] In Figure 15, the sloped line (VV2) represents the possible changes in blade rotation speed (V2) in the course of sharpening processes carried out between time t = 0 when the blade rotation speed has a value (V2m) lower than the nominal speed (V2n) and time (ta) when the blade rotation speed has a value (V2M) higher than the nominal speed (V2n). In the above example, V2m = 0.95 * V2n and V2M = 1.05 * V2n. Although Figure 15 shows a linear change in blade rotational speed, it is understood that this change may be non-linear.

[0057] In relation to the above description, the cutting machine according to the present invention has the following features: - a structure (SC) for moving the logs to be cut transversely to obtain rolls of shorter lengths; - a cutting unit (CU) arranged at a predetermined position on the structure (SC) and comprising a support plate (1) for blades (2) removably connectable to respective rotary actuators (20) arranged at one end of the support plate (1) and adapted to control the rotation of the blades about their axes (xx) at a predetermined speed, the blades (2) being arranged along a plane (P2) perpendicular to the rotation axis (xx) at a pre-established position within the cutting unit (CU); a sharpening unit having two grinding wheels (3) with grinding surfaces (31) mounted on opposite sides of the plane (P2) for sharpening the blade (2); - a positioning device for positioning the grinding wheels (3) relative to the blades (2), by means of which each grinding wheel (3) is placed in a position in contact with the blades (2) during the sharpening stage of the blades (2), starting from an initial non-operating position; and In the above cutting machine, - the positioning device comprises a first carriage (4) movable by one or more first actuators (M0, M1) starting from an initial standby position in a radial direction relative to the blade (2) in a first movement direction (PD), and two second carriages (42, 43) supported by the first carriage (4) and movable by corresponding second actuators (M2, A2; M3, A3) in a second movement direction (SD) parallel to the rotation axis of the blade (2); - the one or more actuators (M0, M1) used to move the first carriage (4) during the first stage of operational positioning of the grinding wheel (3) are controlled by an optical sensor (100) that detects the cutting edge (200) of the blade (2) and interrupts the travel of the first carriage (4) along the first direction of movement (PD) after this detection, so that the travel of the first carriage (4) along the first direction (PD) is correlated to the actual diameter of the blade (2); and In a second stage of operational positioning of the grinding wheel (3), which includes bringing the grinding wheel (3) into contact with the blade (2) and then grinding the blade (2), the control unit (MC) controls the second actuator to press the grinding surface of the grinding wheel (3) against the blade (2) with a predetermined thrust.

[0058] In one embodiment of the invention providing for the use of a second actuator comprising two electric motors (M2, M3) to perform the second operational positioning step of the grinding wheel, preferably said motors are controlled to provide a torque of a predetermined value.

[0059] Furthermore, according to the invention, the thrust exerted by the grinding wheel (3) on the blade (2) is preferably related to the diameter of the blade, in particular, the thrust increases as the diameter of the blade decreases. Indeed, during its use, the blade is subject to wear and therefore a decrease in its diameter. The invention preferably provides for modifying the thrust exerted by the grinding wheel on the blade during the sharpening stage as a function of the diameter of the blade, which constitutes a known value due to the detection performed by the sensor (100).

[0060] Thus, according to the invention, a variable thrust value of the grinding wheel on the blade can be programmed in response to changes in the diameter of the blade by correspondingly programming the control of the actuator driving the second carriage (42, 43).In one embodiment of the invention providing for the use of an actuator comprising an electric motor (M2, M3) for moving the second carriage, a variable thrust value of the grinding wheel (2) on the blade (3) can be programmed in response to changes in the diameter of the blade by correspondingly programming the control of the drive provided by the electric motor (M2, M3).

[0061] Furthermore, preferably, between one sharpening stage and the next, the rotational speed of the blade varies between 95% and 105% of its nominal rotational speed.

[0062] The optical sensor (100) can be replaced by another type of sensor, for example an inductive sensor or an ultrasonic sensor.

[0063] The cutting machine may also comprise two sharpening units of the type described above, which are arranged at different positions relative to the blade (2) and each act on a different area of ​​the blade. This is advantageous for large diameter circular blades or circular blades with differently shaped bevels along their radius, as each sharpening unit can act on a corresponding area of ​​the blade. Preferably, the two sharpening units are identical to each other.

[0064] With reference to the example shown in Figure 11, the sensor (100) is associated with a slide (S10) mounted on a guide (G10) oriented obliquely to the direction of movement (DS) of a further slide (S1) on which the plate (1) is mounted. In a manner known per se, the plate (1) is lowered towards the structure (SC) as a function of the diameter of the blade (2) detected by the sensor (100). As previously mentioned, the current diameter of the blade (2) is used to control the stroke of the first carriage (4) towards the blade in order to sharpen it, although this is not shown in Figure 11.

[0065] The sensor (100) detects the current diameter of the blade (2). In fact, the position of the center of the blade relative to the plate (1) is known and invariable, so that detecting the cutting edge of the blade corresponds to detecting the diameter of the blade.

[0066] In this specification, the first actuator is an actuator that controls the movement of the first carriage along the first movement direction, while the second actuator is an actuator that controls the movement of the second carriage along the second movement direction.

[0067] Indeed, the details of the implementation have been described and illustrated in each case without departing from the idea of ​​the solution adopted and may therefore be modified in an equivalent manner with respect to the individual elements remaining within the scope of protection granted by this patent in accordance with the following claims.

Claims

1. 1. A cutting machine for cross-cutting a log of paper material, comprising: - a structure (SC) for displacing the logs to be cut transversely to obtain rolls of shorter length; - a cutting unit (CU) arranged at a predetermined position in said structure (SC) and comprising a support plate (1) for blades (2) removably connectable to respective rotary actuators (20) arranged at one end of the support plate (1) and adapted to control the rotation of the blades about their own axes of rotation (x-x) at a predetermined speed, said blades (2) being arranged at a predetermined position in said cutting unit (CU) along a plane (P2) perpendicular to said axes of rotation (x-x); a sharpening unit having two grinding wheels (3) with grinding surfaces (31) mounted on opposite sides of said plane (P2) for sharpening said blade (2); - a positioning device for positioning the grinding wheels (3) relative to the blades (2), by means of which each grinding wheel (3) is placed in a position in contact with the blades (2) during the sharpening phase of the blades (2), starting from an initial non-operating position; and In the cutting machine, the positioning device comprises a first carriage (4) movable by one or more first actuators (M0, M1) starting from an initial standby position in a radial direction relative to the blade (2) in a first direction of movement (PD), and two second carriages (42, 43) supported by the first carriage (4) and movable by corresponding second actuators (M2, A2; M3, A3) in a second direction of movement (SD) parallel to the axis of rotation of the blade (2); - the one or more actuators (M0, M1) used to move the first carriage (4) during the first stage of operational positioning of the grinding wheel (3) are controlled by an optical sensor (100) that detects the cutting edge (200) of the blade (2) and interrupts the travel of the first carriage (4) along the first direction of movement (PD) after this detection, so that the travel of the first carriage (4) along the first direction of movement (PD) is correlated to the actual diameter of the blade (2); and - In a second stage of operational positioning of the grinding wheel (3), which includes bringing the grinding wheel (3) into contact with the blade (2) and then grinding the blade (2), the control unit (MC) controls the second actuator to press the grinding surface of the grinding wheel (3) against the blade (2) with a predetermined thrust.

2. 2. The cutting machine of claim 1, wherein the sensor (100) is constrained to the first carriage (4).

3. 2. Cutting machine according to claim 1, wherein the first carriage is formed by two independent units (40, 41).

4. 2. A cutting machine according to claim 1, wherein the thrust force exerted by the grinding wheel (3) on the blade (2) increases as the diameter of the blade (2) decreases.

5. 2. The cutting machine according to claim 1, wherein the second actuators are driven by corresponding electric motors, and the electric motors provide a predetermined torque during the second stage of the operative positioning of the grinding wheel (3).

6. 6. A cutting machine according to claim 5, wherein the torque provided by the electric motor increases as the diameter of the blade (2) decreases.

7. 7. A cutting machine according to any one of claims 1 to 6, wherein between the sharpening stage of the blade and the subsequent sharpening stage of the blade, the rotational speed of the blade varies between 95% and 105% compared to a predetermined nominal value.

8. 2. Cutting machine according to claim 1, wherein the first carriage is constrained on the inner side (F1) of the plate (1) by means of a linear guide (LG) that allows it to slide along the first direction of movement (PD).

9. 4. Cutting machine according to claim 3, wherein each of the independent units (40, 41) has a first side (4P) parallel to the inner side (F1) of the plate (1) and a second side (4H) perpendicular to and below the first side (4P), the first side (4P) sliding along a respective guide (LG) and the second side (4H) forming a bracket structure.

10. 10. The cutting machine according to claim 9, wherein the second carriages (42, 43) are each arranged below a respective bracket structure (4H) of the first carriage (4), and the second actuator is arranged above the bracket structure (4H).

11. 2. The cutting machine according to claim 1, wherein the contact between the grinding surface (31) of the grinding wheel (3) and the blade (2) is detected by detecting the deceleration of the blade (2).

12. 6. Cutting machine according to claim 5, wherein contact between the grinding surface (31) of the grinding wheel (3) and the blade (2) is detected by detecting the stopping of the electric motor.

13. 2. The cutting machine of claim 1, wherein the optical sensor (100) is replaced by an inductive sensor or an ultrasonic sensor.

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