Cutting machine for transversal cutting of logs of paper material

Abstract

A cutting machine for transversal cutting of logs of paper material, comprising: - a structure (SC) for moving the logs thereon; - a cutting unit (CU) with a blade (2); - a grinding unit for sharpening the blade; - a device for positioning the grinding wheel with respect to the blade (2); wherein: - the positioning device comprises a main carriage (4) and two secondary carriages (42, 43) driven by respective actuators; - there is an optical sensor (100) that detects the cutting edge (200) of the blade (2); - in the operating positioning phase of the grinding wheel, which comprises sharpening the blade after the grinding wheel has come into contact with the blade, the rough side of the grinding wheel is pushed against the blade with a thrust having a predetermined value.

Description

Technical Field

[0001] This invention relates to a cutting machine for transversely cutting logs made of paper material. Background Technology

[0002] As is well known, toilet paper, kitchen paper, and similar products are obtained by transversely cutting rolls, commonly referred to as "logs," and producing them through a machine called a "rewinder," in which a predetermined amount of paper material, consisting of one or more overlapping layers of paper, is wound around itself or around a cardboard tube called a "core." Generally, the logs produced by the rewinder are conveyed to a buffer hopper and from there to a machine called a "cutting machine," which performs the aforementioned transverse cutting. Typically, the cutting machine has a platform defining a guide channel for the logs, and downstream of this channel is a cutting unit comprising disc blades that are appropriately activated and moved to determine the transverse cut of the log at a programmed rate based on the length of the roll to be obtained from the log. The blades are typically associated with a grinding wheel, which periodically intervenes to restore the cutting profile of the blade itself. The blades of the cutting machine must be replaced periodically due to wear, which gradually reduces their 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.

[0003] EP3194128B1 discloses a machine for transversely cutting logs of paper material, comprising: a forward path for the log to be cut; a cutting unit having replaceable disc blades, the cutting unit being supported to be able to rotate about its own axis while performing a cyclic motion for cutting the log and allowing the log to advance along the forward path; and a sharpening unit having two grinding wheels. The grinding wheels are configured and controlled to intervene on the disc blades when they are to be sharpened. The grinding wheels are mounted on a support system including a mechanism for controlled approach of the grinding wheels to the blades, the mechanism being configured to move each grinding wheel in a direction substantially parallel to its own axis of rotation. The mechanism operates to bring a support slider of each grinding wheel into a nominal position relative to the blade, and to bring the grinding wheel closer to the blade in a controlled manner by moving the grinding wheel relative to a relative slider held in the nominal position. Summary of the Invention

[0004] The main objective of this invention is to provide a machine for cutting logs, wherein the positioning of a sharpening wheel relative to a blade that is sharpened from time to time is automated, and wherein the positioning is substantially independent of the diameter of the blade.

[0005] Another object of the present invention is to provide a sharpening mechanism for blades used in cutting machines for transversely cutting logs of paper material, the sharpening mechanism allowing the elimination or at least significant reduction of the so-called "polygonalization" of the blade itself, i.e., the loss of its original annular shape and the presentation of a substantially polygonal shape that determines the incorrect execution of transverse cutting of logs due to the repeated grinding operations it typically undergoes.

[0006] According to the present invention, this result is achieved by employing the idea of ​​manufacturing a machine according to an embodiment of the present application.

[0007] Because of this invention, the positioning of the grinding wheel can be performed automatically in a shorter time than manual positioning and with higher operational safety, as the operation does not require the operator to enter the area of ​​the machine containing the blade. Furthermore, the device for positioning the grinding wheel in a machine according to the invention has a relatively simple structure and integrates an effective mechanism for identifying the desired position of the grinding wheel. Moreover, even if the positioning of the grinding wheel determined by the main motion frame is not particularly precise, the machine according to the invention avoids or, in any case, reduces so-called blade polygonization. Attached Figure Description

[0008] These and other advantages and features of the 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 but are not intended to be limiting, in which: - Figure 1 A schematic vertical sectional view of a cutting station of a cutting machine according to the present invention for transversely cutting paper material logs using a cutting unit is shown. - Figure 2 A schematic front view showing a cutting unit for a cutting machine according to the present invention; - Figure 3 and Figure 4 express Figure 2 Two schematic side views of the cutting unit; - Figure 5 and Figure 6 express Figure 2 Two schematic 3D views of the cutting unit shown; - Figure 7A Indicates along Figure 2 A sectional view of line AA; - Figure 7B It is a three-dimensional view of the auxiliary motion frame with corresponding moving devices; - Figure 8 This is a diagram showing the possible orientation of the grinding wheel relative to the plane (P2) of the blade (2); - Figure 9 It is a polygonal representation of the blade; - Figure 10 This is a qualitative diagram showing the possible variations in torque provided by the drive motor of the grinding wheel in the cutting unit shown in the previous diagram as the diameter of the blade undergoes sharpening. - Figure 11 This illustration schematically shows another embodiment of the invention, wherein the log being cut is indicated by the reference numeral "L" in the drawing. - Figure 12 It is a diagram showing some geometric parameters related to the position of the grinding wheel relative to the blade of the cutting unit; - Figure 13 A simplified block diagram showing a possible control system for an actuator of a cutting unit in a machine according to the invention; - Figure 14 It is a qualitative graph representing the constant value of the torque provided by the motor of the auxiliary actuator during the stroke of the auxiliary motion frame; - Figure 15 This is a qualitative diagram showing the possible ways to control the rotational speed of the blade during the sharpening stage. Detailed Implementation

[0009] Simplified to the main structure of the cutting machine and referring to the accompanying drawings, the cutting machine to which the cutting unit of the present invention is applicable includes the following types: - Structural member (SC), on which the logs to be cut laterally move to obtain shorter rolls; - A cutting unit (CU) is arranged at a predetermined point on the structure (SC) and includes a support plate (1) for the blade (2), which is removably connected to a corresponding rotary actuator (20) arranged at one end of the plate (1) and is capable of determining the rotation of the blade itself about its own axis (xx) at a predetermined speed. The plate (1) is constrained to another actuator that drives the plate to rotate about an axis parallel to the rotation axis (xx) of the blade (2) at a predetermined angular velocity. - A sharpening unit having two wheels (3), the sharpening unit being adapted to be set to sharpen the blade (2); - A device for positioning the grinding wheel (3) relative to the blade (2).

[0010] Figure 1The main components of a cutting machine (CM) in which the cutting unit according to the invention can be mounted are schematically shown. It should be understood that this diagram is provided only to allow identification of the position of the cutting unit relative to the path of the log. It should also be understood that the structure of the cutting machine can be manufactured in any suitable manner, as long as it is intended to laterally cut logs of paper material into shorter rolls by means of cutting units comprising blades acting laterally to the log.

[0011] exist Figure 1 In the example, according to a known construction scheme, the rotary actuator (20) is connected to the blade (2) via a belt (21), which connects the central pin (22) of the same blade to the shaft (23) of the actuator (20) via a pulley arranged on the free end of the shaft (23). Furthermore, the plate (1) rotates about an axis parallel to the axis of rotation of the blade (2) via a corresponding rotary actuator (A1), the shaft (B1) of which is parallel to the shaft (23) of the actuator (20) that controls the rotation of the blade (2). For example, the actuator (20) of an electric motor is integrated with a box-shaped body (BB) located above the structural member (SC), and the belt (21) and the shafts (23) and (B1) are arranged inside the box-shaped body. The body (BB) is connected to a corresponding actuator (BA), which controls the vertical position of the body, i.e., the positioning of the body relative to the lower structural member (SC), by a screw (VA) acting on a nut bushing arranged on the upper side of the same body (BB). Therefore, by controlling the position of the body (BB), the blade (2) can be positioned at a desired height relative to the structural member (SC). For example, an actuator (A1) consisting of an electric motor is also integrated with the body (BB).

[0012] In fact, the blade (2) rotates about a corresponding axis (xx) that is parallel to the axis of rotation of the plate (1).

[0013] A cutting unit (CU) according to a possible embodiment of the invention comprises a plate (1) having an upper side (10), a lower side (11), a front side (F1), and a rear side (R1). A central pin (22) of an annular blade (2) is mounted on the lower side (11) of the plate (1) and applied to the pin in a removable manner to allow for blade replacement when needed. The blade (2) is oriented parallel to the plate (1) and positioned at a predetermined distance from the front side (F1) of the plate (1). Two grinding wheels (3) for sharpening the blade (2) and means for positioning the grinding wheels (3) relative to the blade (2) are also mounted on the plate (1). Each grinding wheel (3) is applied to a respective support shaft (30), the axis (A30) of which 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 The figure shows the spindle (30) supporting the grinding wheel (3), the corresponding axis (A30), and the inclination of the grinding wheel (3) in the sharpened position relative to the face (A2) of the blade (2) and the plane (P2) of the blade (2).

[0014] According to the present invention, the positioning device for the grinding wheel (3) includes: - The main motion frame (4) can move parallel to the plate (1) according to the main movement direction (PD); - Two auxiliary motion frames (42, 43) are restricted to the main motion frame (4) and can move independently according to the auxiliary motion direction (SD) orthogonal to the main motion direction (PD). Each auxiliary motion frame (42, 43) has a seat for supporting the shaft (30) of the corresponding grinding wheel (3).

[0015] In fact, the main moving direction (PD) is parallel to the plane (P2) where the blade (2) is located, that is, the radial direction about the blade (2), while the secondary moving direction (SD) is parallel to the rotation axis (xx) of the blade (2).

[0016] According to the embodiment shown in the attached drawings, the main motion frame (4) consists of two independent units (40, 41), and the corresponding auxiliary motion frames (42, 43) are constrained to each independent unit (40, 41). Alternatively, the main motion frame may consist of a single unit, and both auxiliary motion frames (42, 43) are constrained to that single unit.

[0017] refer to Figure 2 In the embodiment shown in Figure 7, the main motion frame (4) consists of two independent units, each consisting of a body (40, 41). The bodies (40, 41) are constrained to the inner side (F1) of the plate (1) by linear guides (LG), allowing guided sliding of the bodies (40, 41) along the main motion direction (PD). The sliding of each body (40, 41) along the main motion direction (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), which engages with a corresponding nut bushing (MV) formed on each body (40, 41). Thus, each body (40, 41) can move along the main motion direction (PD) by the corresponding motor (M0, M1).

[0018] 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) orthogonal to the first side (4P) and located below the first side (4P). The first side (4P) slides along a corresponding guide (LG). The second side (4H) forms a cantilever structure, the function of which is as follows. In fact, each of the bodies (40, 41), viewed from the side, has a structure with a portion (4P) parallel to the inner side (F1) of the plate (1) and a portion (4H) orthogonal to the same inner side (F1) of the plate (1), thereby defining a support above the blade (2). In the above example, due to the presence of the guide (LG) that constrains the bodies (40, 41) to the inner side (F1) of the plate (1), the movement of the bodies (40, 41), that is, the movement of the two units constituting the main motion frame (4), is a guided movement.

[0019] According to the example shown in the attached figures, each sub-motion frame (42, 43) is located below the corresponding support (4H) and has an upper vertical attachment (U4) passing through a longitudinal slot (4C) formed on the same support. Motors (M2, M3) are located above the support (4H) such that each motor (M2, M3) is fixed to the upper surface of the corresponding support (4H) via the housing of a corresponding linear actuator (A2, A3) driven by the same motor (M2, M3). Each actuator (A2, A3) is, for example, a known screw actuator, i.e., an actuator comprising a rod (SA) that moves a screw (not visible in the figure) operated by the corresponding motor (M2, M3). The rod (SA) is attached to a flange (FA), the rear side of which is fixed to a slider (CA) mounted on the upper surface of the actuator housing, while the front side of the flange is fixed to the vertical attachment (U4) of the corresponding motion frame (42, 43).

[0020] The shafts (30) of the grinding wheels (3) are each fixed to their respective auxiliary motion frames (42, 43). In this way, each motor (M2, M3) moves its respective auxiliary motion frame (42, 43) along the lower side of the support (4H) in the secondary direction (SD). And since the auxiliary motion frames are connected to the main motion frame, each auxiliary motion frame and its corresponding grinding wheel can move along the main direction (PD) and the secondary direction (SD).

[0021] In other words, each grinding wheel (3) is supported by a cutting unit (CU) so that it can move in the main direction of movement (PD) and in the secondary direction of movement (SD). In fact, the main body (40, 41) constituting the main motion frame (4) can move in the direction (PD) by motors (M0, M1), while the secondary motion frames (42, 43) can move along the direction (SD) on the main motion frame by motors (M2, M3).

[0022] The grinding wheels (3) are oriented so that their respective rough sides (31) face the plane (P2) where the blade (2) is located.

[0023] The main motion frame may be equipped with an optical sensor (100) corresponding to its lower side, i.e., the side facing the blade (2), the function of which is as described below. For example, the optical sensor (100) may be mounted below the support (4H) of either of the aforementioned bodies (40, 41). For example, the optical axis of the sensor (100) is spaced from the reference line by a predetermined value (b) so that it intersects the cutting edge (200) of the blade (2) when the main motion frame approaches the blade (2) before the grinding wheel (3) is placed in the sharpening position on the blade. This reference line may be the so-called "sink line" (L3) of the grinding wheel (3). The sink line is a reference line for each grinding wheel (3), and the sink line is a known geometric parameter provided by the manufacturer. This parameter determines the correct position of the grinding wheel relative to the blade for sharpening purposes. In fact, in order to properly sharpen the blade, the sink line of the grinding wheel must be in a position tangent to the cutting edge of the blade, such as Figure 12 As shown. In this case, the rough side of the grinding wheel correctly interferes with the area of ​​the blade to be sharpened, that is, optimal contact conditions are formed between the grinding wheel and the blade during the sharpening stage. According to the above embodiment, the movement of the main motion frame (4) along the main direction (PD) is controlled by a sensor (100) that detects the actual diameter of the blade (2), so that regardless of the actual diameter of the blade (2), the grinding wheel (3) is brought to the correct sharpening position, in which the sink mark of the grinding wheel is tangent to the cutting edge of the blade. Reference Figure 12 In the diagram, during the first stage of the operation positioning of the grinding wheel (3), the movement of the main motion frame (4) is controlled by a sensor (100). The sensor (100) detects the radius of the blade (2) and controls the interruption of the stroke of the main motion frame along the main direction (PD) when the grinding wheel is positioned at a distance (h) relative to the axis of the blade with its respective axis. This distance (h) is equal to the radius of the blade (r2) plus the radius of the wheel (r3) minus a predetermined value (b). It should be noted that the radius (r3) of the grinding wheel (3) is a known value. Similarly, the value (b) is a known value provided by the grinding wheel manufacturer, and the 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) measures the difference between the position of the optical sensor (100) projected onto the plane (P2) of the blade (2) along the main direction of movement (PD) of the main motion frame and the position of the sunken line (L3) of the grinding wheel (3) projected onto the same plane (P2).

[0024] According to the invention, during the movement of the auxiliary motion frame (42, 43) in the directional (SD) direction, the grinding wheel (3) is brought into contact with the blade (2), so that during the sharpening stage, each motor (M2, M3) is controlled to provide a predetermined torque. In other words, the motors (M2, M3) are controlled in such a way that each grinding wheel (3) applies a predetermined amount of thrust to the blade (2) during the sharpening stage. In other words, in the second step of the operation positioning of the grinding wheel (3), the grinding wheel is pushed toward the blade (2) by applying the predetermined amount of thrust maintained during the sharpening stage.

[0025] In the context of this specification, the first step of the operation positioning of the grinding wheel (3) corresponds to the same grinding wheel traveling toward the blade (2) in the main direction (PD), while the second step of the operation positioning of the grinding wheel (3) corresponds to the same grinding wheel traveling toward the blade (2) in the secondary direction (SD).

[0026] exist Figure 13 In the figure shown as an example, electric motors (M2, M3) are controlled by a programmable control unit (MC), and electric motors (M0 and M1), sensor (100), motor (20) and rotary actuator (A1) are also connected to the programmable control unit (MC). In this figure, a sensor (20S) that detects the rotational speed of the blade (2) is also connected to the control unit (MC).

[0027] One possible operating mode of the above-mentioned device is as follows.

[0028] To sharpen the blade mounted on the cutting unit, the main motion frame moves along the main direction (PD) to perform the first operational positioning stage of the grinding wheel (3). Then, an optical sensor (100) detects the edge (200) of the blade (2), and the main motion frame stops its travel, for example, when the sensor (100) has passed the edge (200) to a value corresponding to the aforementioned value (b). For this purpose, the optical sensor (100) is connected to the motors (M0, M1) via a programmable control unit (MC). In this way, the grinding wheel (3) is positioned as needed, spaced apart from both sides of the blade (2) for the subsequent sharpening stage. At this time, the auxiliary motion frames (42, 43) move along the secondary direction (SD) via motors (M2, M3) to perform the second operational positioning stage of the grinding wheel, such that the corresponding rough side (31) of each grinding wheel (3) contacts the corresponding side of the blade (2), and the blade (2) rotates about its own axis (xx). This contact (in technical terms, "in-situ" position recognition) is detected by the same blade (2), which in fact experiences deceleration due to the contact itself. Typically, the motor (20) driving the blade is controlled by a system equipped with a control function (FC) that ensures a constant rotational speed of the blade around the axis (xx) during transverse cutting of the log. When the grinding wheel positioning device is in operation, the grinding wheel moves in the direction (SD) as described above, and the aforementioned motor control function (20) is temporarily deactivated. The contact between the grinding wheel (3) and the blade (2) causes the blade to decelerate, which is considered a sign of contact between the grinding wheel and the blade. When this situation is detected, the thrust applied to the grinding wheel (3) is not interrupted, that is, the thrust is maintained throughout the sharpening stage. For this purpose, the torque of the motors (M2, M3) is controlled in such a way that it remains at a predetermined value throughout the sharpening stage of the blade (2). Because the grinding wheel (3) is actively and controlled to push against the blade (2) during the sharpening stage, the vibrations typically caused by the contact between the grinding wheel and the rotating blade are reduced, thus reducing the contact between the blades and improving the grinding wheel. This avoids the so-called "polygonalization" of the blade's cutting edge and allows for more precise log crosscutting and optimizes blade wear, which is an expensive component of the cutting unit. As mentioned earlier, "polygonalization" refers to the phenomenon where a blade loses its original ring shape and takes on a substantially polygonal shape after repeated grinding operations typically performed before replacement. Figure 9 In the schematic diagram, the solid line (PC) represents the ideal annular profile of the blade (2), while the dashed line (PP) represents the profile of the polygonal blade. Figure 9 In the image, the dashed outline (PP) of the blade (2) is deliberately enlarged to highlight its non-circular shape. Figure 9 In the reference, "VP" indicates that a certain vertex has a polygonal shape due to the polygon effect.

[0029] In an alternative implementation, the identification of the “starting” position (i.e., the contact position between the grinding wheel and the blade) is operated in a different manner: during the phase where the grinding wheel approaches the blade, the control motors (M2, M3) are used to provide a predetermined limited torque during sharpening, and the control function (FC) of the motor (20) that moves the blade is not deactivated, so that the contact between the grinding wheel and the blade is identified by the stopping of the motors (M2, M3) caused by the contact between the grinding wheel and the blade. In any case, during the sharpening phase, the grinding wheel is pushed towards the blade with a constant thrust.

[0030] Preferably, the motors (M2, M3) move the auxiliary motion frame (42, 43) via a mechanical transmission, particularly a screw drive as in the example above. This avoids or, in any case, greatly reduces the possibility of the grinding wheel bouncing during sharpening. In other words, using a mechanical linear actuator—such as the type described above, which determines the movement of the auxiliary motion frame via a screw driven by an electric motor—is superior to a pneumatic linear actuator, in which the return of the grinding wheel relative to the blade is more likely to occur.

[0031] Since the stroke of the main motion frame toward the blade (2) is controlled by an optical sensor (100) that detects the cutting edge (200) of the blade, the stopping point of the main motion frame at the end of the stroke is not predetermined, but depends on the diameter, and therefore on the wear of the blade installed in the cutting unit.

[0032] In fact, in the first stage of the operation positioning of the grinding wheel (3), the movement of the main motion frame (4) is controlled by an optical sensor (100) that detects the cutting edge (200) of the blade (2), so that the first operation positioning stage of the grinding wheel (3) means the stroke of the main motion frame (4), the length of which is related to the actual diameter of the blade (2). Furthermore, in the second step of positioning the grinding wheel (3), the auxiliary motion frames (42, 43) are controlled to make the rough side of the grinding wheel (3) contact the blade (2).

[0033] According to the invention, during the second step of the operational positioning of the grinding wheel (3), the motors (M2, M3) are controlled to provide a fixed predetermined torque. In fact, the applicant observed that this control mode of the motors (M2, M3) during the second stage of positioning of the grinding wheel (3) determines a more accurate sharpening of the blade (2), and even if the first stage of operational positioning by the main motion frame is affected by errors (e.g., if the positioning determined by the activation of the main motion frame controlled by the sensor 100 is affected by an error of 0.5 mm, or more generally, by an error between 0 mm and 3 mm), so-called polygonization of the blade is avoided.

[0034] More generally, according to the invention, as described above, during the sharpening of the blade (2), the grinding wheel (3) is pushed toward the same blade with a predetermined and controlled thrust by means of an actuator that moves the motion frame on which the grinding wheel is mounted. In the example above, the actuator that moves the secondary motion frame is driven by an electric motor (M2, M3), but more generally, these actuators can be of any suitable type, as long as they can be controlled to push the grinding wheel (3) toward the blade (2) in the secondary direction (SD) and apply a predetermined and controlled thrust during sharpening.

[0035] The applicant further points out that, preferably, the thrust applied to the blade (2) by the grinding wheel (3) is changed as the diameter of the blade (2) decreases, while maintaining this thrust constant during each sharpening stage. More specifically, it is preferred that the thrust applied to the blade by the grinding wheel be increased as the diameter of the blade decreases. Experimental tests were conducted using blades of the type with an initial diameter of 600 mm, which gradually decreased to a final value of 480 mm due to wear during use. The motors (M2, M3) used during the tests were motors providing a nominal torque of 0.31 Nm. During the tests, the torque of the motors (M2, M3) remained constant in each sharpening stage, but increased by a predetermined value in each subsequent sharpening stage (from 10% of the nominal value when the first sharpening was performed on an unworn blade to 90% of the nominal value when the final sharpening was performed on a fully worn blade). The applicant believes that a constant and continuous rolling thrust applied to the blade by the grinding wheel during each sharpening helps stabilize the blade itself, reduce its vibration, and reduce the polygonization tendency reduced due to the present invention. In other words, constant thrust ensures that the grinding wheel is always in proper contact with the blade during the sharpening process.

[0036] exist Figure 10 The diagram provided illustrates the possible variations (M) of the torque supplied by the motors (M2, M3) as the diameter of the blade (2) varies according to the test performed. The symbols used in this diagram have the following meanings: -C: Connect -CN: Rated torque of the motor (M2, M3), equal to 0.31 Nm; -Cm: The minimum torque provided by the motor (M2, M3), equal to 10% of the rated torque CN; -CM: The maximum torque provided by the motor (M2, M3) is equal to 90% of the nominal torque CN; -D: Diameter -Dm: The minimum diameter of the blade (2) is 480 mm; -DM: The maximum diameter of the blade (2) is equal to 600 mm.

[0037] Figure 10 The graph shows a basic linear change (M) in the torque provided by the motors (M1, M2) as the diameter of the blade (2) changes, but it should be understood that this change can also be nonlinear.

[0038] Preferably, between one sharpening and the next, the rotational speed of the blade varies between a value below the nominal rotational speed (e.g., 95%) and a value above the nominal rotational speed (e.g., 105%). In fact, the applicant observed that the polygonization phenomenon can be further contrasted by combining a predetermined and controlled thrust of the grinding wheel on the blade and varying the rotational speed of the blade within predetermined limits.

[0039] The applicant conducted experimental tests using commercially available blades sold under the trade name Chromalit IKS ø610 and K10R 150 grit grinding wheels sold by InternationalKnife&Saw, Inc.

[0040] exist Figure 14 In the chart, the horizontal segment (CSD) represents the constant value of the torque (Cc) provided by the motors (M1, M2) throughout the entire stroke along the auxiliary motion carrier until contact with the blade, represented by segment 0-Xc on the XSD axis. The values ​​CN, CM, and Cm on the vertical axis C are as previously referenced. Figure 10 The value indicated by the graph. The “Cc” value represents the torque value provided by the motor (M1, M2) corresponding to the actual diameter of the blade, as described above.

[0041] exist Figure 15 In the diagram, the slanted line (VV2) represents the possible variation of the blade rotation speed (V2) during the continuous sharpening operation performed between time t=0 and time (ta). At time t=0, the blade rotation speed has a value lower than the nominal speed (V2n) (V2m), and at time (ta), the blade rotation speed has a value higher than the nominal speed (V2n) (V2M). In the example above: V2m = 0.95 * V2n and V2M = 1.05 * V2n. Figure 15 The linear velocity variation of the blade rotation speed is shown, but it should be understood that the variation can also be non-linear.

[0042] Regarding the description provided above, the cutting machine according to the present invention includes: -Structure (SC), on which the logs to be cut laterally move to obtain a shorter length of roll; - A cutting unit (CU) is arranged at a predetermined position on the structural member (SC), and the cutting unit (CU) includes a support plate (1) for a blade (2), the support plate being removably connected to a corresponding rotary actuator (20) arranged at one end of the plate (1), and the support plate being adapted to control the blade to rotate at a predetermined speed about its own axis (xx), the blade (2) being arranged in the predetermined position (CU) in the cutting unit along a plane (P2) orthogonal to the axis of rotation (xx); - Sharpening unit, the sharpening unit having two grinding wheels (3), the two grinding wheels (3) being adapted to sharpen the blade (2) on the opposite side relative to the plane (P2) and equipped with rough sides (31). - A positioning device for positioning the grinding wheel (3) relative to the blade (2), wherein each grinding wheel (3) is arranged in contact with the blade (2) during the step of sharpening the blade (2) from an initial non-operating position; in - The positioning device includes a main motion frame (4) and two auxiliary motion frames (42, 43). The main motion frame (4) can move from an initial waiting position along a main direction (PD) relative to the radial direction of the blade (2) by one or more main actuators (M0, M1). Each auxiliary motion frame is supported by the main motion frame (4) and can move along a secondary direction (SD) parallel to the rotation axis of the blade (2) by corresponding auxiliary actuators (M2, A2; M3, A3).

[0043] - In the first stage of the operation positioning of the grinding wheel (3), the one or more actuators (M0, M1) for moving the main motion frame (4) are controlled by an optical sensor (100), which detects the cutting edge (200) of the blade (2) and, upon detection, interrupts the operation of the main motion frame along the main direction (PD), such that the operation of the main motion frame (4) along the main direction (PD) is related to the actual diameter of the blade (2); and - In the second stage of the operation positioning of the grinding wheel (3), which involves sharpening the blade after the grinding wheel comes into contact with the blade (2), the auxiliary actuator is controlled by the control unit (MC) to push the rough side of the grinding wheel (3) against the blade (2) with a thrust having a predetermined value.

[0044] In one embodiment of the invention, a secondary actuator comprising two electric motors (M2, M3) is used to perform the second operational positioning phase of the grinding wheel, preferably, the electric motors are controlled to provide a predetermined value of torque.

[0045] Furthermore, according to the invention, the thrust applied to the blade (2) by the grinding wheel (3) is preferably related to the diameter of the blade (2), and the thrust increases particularly when the diameter of the blade decreases. In fact, the blade is worn during use, and therefore the diameter of the blade decreases. The invention preferably provides a modification of the thrust applied to the blade by the grinding wheel according to the blade diameter during the sharpening stage, which constitutes a known value due to detection performed by the sensor (100). Therefore, according to the invention, the variable thrust value of the grinding wheel on the blade can be programmed when the blade diameter changes by correspondingly programming the control on the actuator of the drive sub-motion frame (42, 43). In one embodiment of the invention, this embodiment uses an actuator including an electric motor (M2, M3) for moving the sub-motion frame, and the variable thrust value of the grinding wheel (3) on the blade (2) can be programmed by correspondingly programming the control of the drive provided by the electric motor (M2, M3) when the blade diameter changes.

[0046] Furthermore, preferably, between one sharpening stage and the next sharpening stage, the rotational speed of the blade varies between 95% and 105% of the blade's nominal rotational speed.

[0047] The optical sensor (100) can be replaced by other types of sensors, such as inductive sensors or ultrasonic sensors.

[0048] The cutting machine can also be equipped with two sharpening units of the type described above. In this case, the two sharpening units are placed in different positions relative to the blade (2) to act on different areas of the blade, respectively. This is useful in the case of large-diameter annular blades or annular blades with bevels of different shapes along the radius, so that each sharpening unit can act on a corresponding area of ​​the blade. Preferably, the two sharpening units are identical to each other.

[0049] refer to Figure 11 In the example shown, the sensor (100) is associated with a slider (S10) mounted on a guide (G10), which is tilted relative to the direction of movement (DS) of another slider (S1) on which the plate (1) is mounted. In a manner known per se, the plate (1) is lowered along the direction of the structure (SC) according to the diameter of the blade (2) detected by the sensor (100). As previously stated, the current diameter of the blade (2) is used to control the main motion frame (4) (in... Figure 11 (Not visible in the middle) The stroke is directed toward the same blade to sharpen the blade.

[0050] 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 constant, so that the detection of the cutting edge of the blade corresponds to the detection of the diameter of the plate.

[0051] In the context of this specification, a primary actuator is an actuator that controls the primary motion frame to move along the primary direction, while a secondary actuator is an actuator that controls the secondary motion frame to move along the secondary direction.

[0052] In fact, the details of implementation can vary in any case with respect to the various elements described and shown in an equivalent manner without departing from the idea of ​​the solution adopted, and thus remain within the scope of protection granted by this patent under the appended claims.

Claims

1. A cutting machine for transverse cutting of logs used for paper materials, the cutting machine comprising: -Structure (SC), on which the log to be transversely cut moves to obtain a shorter length of roll; - A cutting unit (CU) is arranged at a predetermined position on the structural member (SC), and the cutting unit (CU) includes a support plate (1) for a blade (2), the support plate being removably connected to a corresponding rotary actuator (20) arranged at one end of the support plate (1), and the support plate being adapted to control the rotation of the blade about its own axis (xx) at a predetermined speed, the blade (2) being arranged at a predetermined position in the cutting unit (CU) along a plane (P2) orthogonal to the axis (xx); - A sharpening unit having two grinding wheels (3) adapted to sharpen the blade (2) on opposite sides of the plane (P2) and the grinding wheels (3) being equipped with roughened sides (31). - A positioning device for positioning the grinding wheel (3) relative to the blade (2), wherein each grinding wheel (3) is positioned in contact with the blade (2) by the positioning device during the step of sharpening the blade (2) from an initial non-operating position; in, - The positioning device includes a main motion frame (4) and two auxiliary motion frames (42, 43). The main motion frame (4) can move from an initial waiting position along a main direction (PD) relative to the radial direction of the blade (2) by one or more main actuators (M0, M1). Each of the auxiliary motion frames is supported by the main motion frame (4) and can move along a secondary direction (SD) parallel to the axis of the blade (2) by a corresponding auxiliary actuator (M2, A2; M3, A3). - In the first stage of the operation positioning of the grinding wheel (3), the one or more main actuators (M0, M1) used to move the main motion frame (4) are controlled by a sensor (100) that detects the cutting edge (200) of the blade (2) and interrupts the operation of the main motion frame along the main direction (PD) after detecting the cutting edge, so that the operation of the main motion frame (4) along the main direction (PD) is related to the actual diameter of the blade (2); Its features are, - In the second stage of the operation positioning of the grinding wheel (3), which includes sharpening the blade after the grinding wheel comes into contact with the blade (2), the auxiliary actuator is controlled by the control unit (MC) to push the rough side of the grinding wheel (3) against the blade (2) with a thrust of a predetermined value. The thrust provided by the auxiliary actuator is uninterrupted during the second stage of the operation positioning of the grinding wheel.

2. The cutting machine according to claim 1, characterized in that, The sensor (100) is located on the lower side of the main motion frame (4).

3. The cutting machine according to claim 1, characterized in that, The main motion frame is made of two independent units (40, 41).

4. The cutting machine according to claim 1, characterized in that, The thrust exerted by the grinding wheel (3) on the blade (2) increases as the diameter of the blade (2) decreases.

5. The cutting machine according to claim 1, wherein, Each of the auxiliary actuators is driven by a corresponding electric motor, characterized in that, in the second stage of operatively positioning the grinding wheel (3), the electric motor provides a predetermined torque.

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

7. The cutting machine according to any one of claims 1 to 6, characterized in that, Between the sharpening step that sharpens the blade and the subsequent sharpening step that sharpens the blade, the rotational speed of the blade varies between 95% and 105% of a predetermined nominal value.

8. The cutting machine according to claim 1, characterized in that, The main motion frame is restricted to the inner side (F1) of the support plate (1) by a linear guide (LG) that allows the main motion frame to slide along the main direction (PD).

9. The cutting machine according to claim 3, characterized in that, Each of the independent units (40, 41) has a first side (4P) parallel to the inner side (F1) of the support plate (1) and a second side (4H) orthogonal to the first side (4P) and located below the first side (4P), wherein the first side (4P) slides along a corresponding linear guide (LG) and the second side (4H) forms a support structure.

10. The cutting machine according to claim 9, characterized in that, The auxiliary motion frames (42, 43) are each arranged below the corresponding support structure of the main motion frame (4), and the auxiliary actuator is arranged above the support structure.

11. The cutting machine according to claim 1, characterized in that, The contact between the rough side (31) of the grinding wheel (3) and the blade (2) is detected by the deceleration of the blade (2).

12. The cutting machine according to claim 5, characterized in that, The contact between the rough side (31) of the grinding wheel (3) and the blade (2) is detected by stopping the electric motor.

13. The cutting machine according to claim 1, characterized in that, The sensor (100) is an inductive sensor.

14. The cutting machine according to claim 1, characterized in that, The sensor (100) is an optical sensor or an ultrasonic sensor.

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