Single facer for manufacturing corrugated sheet by means of system for controlling pressing belt and related method

Abstract

A system and method for preventing drifting and twisting of a continuous flexible pressing member in a single facer, i.e. In a machine for producing a single facer corrugated board by coupling a smooth paper web and a grooved paper web together by the single facer. Systems and methods for correcting the position of a continuous flexible member in the event of drift or torsion are configured to maintain an offset adjustment to reduce or eliminate the tendency of the continuous flexible member to twist or laterally drift.

Description

Technical Field

[0001] The present invention relates to a machine for manufacturing corrugated boards. In particular, the present invention relates to improvements to a corrugating machine or a so-called single facer. Background Art

[0002] Corrugated boards are manufactured starting from a smooth paper web unrolled from a master roll. In its simplest form, a corrugated board consists of a smooth paper web and a corrugated paper web, the smooth paper web and the corrugated paper web being bonded together at the crests of the corrugated paper web. Usually, a second smooth paper web is attached to this basic structure, i.e., bonded to the corrugated paper web, such that the latter is sandwiched between two smooth paper webs referred to as liners. In some cases, other paper webs are added to this structure consisting of three paper webs, resulting in a sequence in which the corrugated paper web is sandwiched between smooth paper webs.

[0003] Single facer corrugated boards are produced by a single facer which includes a pair of intermeshing corrugating rollers, with a first smooth paper web supplied between the corrugating rollers. The first smooth paper web is thermally deformed and made corrugated, i.e., a so-called corrugated paper web, in the nip between the two corrugating rollers. Adhesive is applied to the crests of the corrugated paper web adhering to one corrugating roller, and a smooth paper web is applied to the corrugated paper web provided with adhesive by pressure and heat.

[0004] A pressing unit for bonding the corrugated paper web and the smooth paper web together is provided, the pressing unit including at least one pressing member which is pressed against one corrugating roller. The smooth paper web and the corrugated paper web are fed between the corrugating roller and the pressing member.

[0005] In some single facers, the pressing unit includes a continuous flexible member in the form of a belt which is driven around guide rollers. Examples of such single facers are disclosed in US9,545,769, EP0698752, US10,293,588, US2015 / 0122423, US5,512,020, EP2805810, US5,951,817, US2014 / 0345804, EP0850753, JP10-710, JP2001-38830, JP10-709. EP3556548 discloses a single facer provided with a mechanism for replacing corrugating rollers. The single facer also includes a pair of fixed shaft guide rollers around which a pressing belt is driven. When the corrugating roller is removed from the single facer, the pressing belt is lifted.

[0006] Using a continuous flexible member in the form of a belt requires careful control of its traction force and position during operation. This requires the use of complex control and guiding systems.

[0007] WO2021224143, WO2021224141, and WO2021224142 disclose various innovative solutions for manufacturing a belt-type single facer. These publications disclose devices for controlling the tension of a continuous flexible member and checking its correct position during operation. The single facers disclosed in these publications have significant advantages and improvements compared to the single facers of the prior art. However, there is still a need for the devices for controlling the tension and position of a continuous flexible member to be more effective and reliable during operation. Summary of the Invention

[0008] According to one aspect, there is provided a single facer including a first corrugating roll and a second corrugating roll, the first corrugating roll and the second corrugating roll meshing with each other and being supported by a support structure. The support structure includes a first arm located on a first side of the single facer and a second arm located on a second side of the single facer. The single facer further includes a first guide roll having a first axis of rotation and being supported to the first arm by a corresponding first support and to the second arm by a corresponding second support. The second guide roll has a second axis of rotation and is supported to the first arm by a corresponding first support and to the second arm by a corresponding second support.

[0009] In addition, the single facer includes a continuous flexible member that is driven around the first guide roll and the second guide roll and has a first longitudinal edge and a second longitudinal edge.

[0010] During operation of the single facer, the position of the continuous flexible member is controlled and adjusted by an adjusting and guiding device.

[0011] The adjusting and guiding device includes sensors adapted to detect the lateral drift and torsion of the continuous flexible member. In addition, an actuator and a control unit are provided, the actuator being adapted to change the relative position of the first guide roll and the second guide roll.

[0012] The control unit is configured to activate the actuator based on signals received from the sensors and perform a correction cycle by changing the relative position of the first guide roll and the second guide roll from an initial position to a correction position that causes correction of the lateral drift and / or torsion. The control unit is configured to bring the first guide roll and the second guide roll to an intermediate position between the initial position and the correction position once the lateral drift and / or torsion has been removed or corrected.

[0013] In this specification and the appended claims, "torsion of the continuous flexible member" means a state in which one of the two longitudinal edges of the flexible member advances at a greater speed than the other. "Lateral drift of the continuous flexible member" means the lateral displacement of the continuous flexible member in a direction orthogonal to the advancing direction (i.e., a direction parallel to the axis of rotation of the guide roll).

[0014] The correction cycle may include a drift correction cycle or a twist correction cycle. If both conditions occur simultaneously, the correction cycle may include a drift correction cycle and a twist correction cycle.

[0015] In fact, the fact that the control unit is configured to bring the first guide roller and the second guide roller to an intermediate position between the initial position and the correction position once the lateral drift and / or twist have been removed or corrected means that the guide rollers do not return to the original position but to an offset position that tends to counteract the factors causing the lateral drift and / or twist.

[0016] In fact, the relative movement of the guide rollers imposed by the control unit for correcting the lateral drift is not completely cancelled after the lateral drift correction. Instead, the guide rollers are brought to positions where they resist the occurrence of new lateral drift.

[0017] If the correction cycle involves, for example, bringing the axis of rotation of the guide rollers from a parallel position to an inclined position to correct the lateral drift, or to a coplanar but non-parallel position to correct the twist, then once the lateral drift and / or twist have been corrected, the guide rollers are not brought back to a position where their axes of rotation are parallel to each other, but to a position where the axes of rotation remain slightly inclined or coplanar but slightly non-parallel. The offset from the parallel position enables resistance to, slowing down of, or limitation of the occurrence of new twist and / or lateral drift.

[0018] In the case of correcting the lateral drift, when the lateral drift has been corrected, the two rollers are not brought back with their axes of rotation parallel, but their axes of rotation remain slightly inclined, with an inclination such that they resist the tendency of the continuous flexible member to drift laterally.

[0019] Similarly, the relative displacement of the guide rollers imposed by the control unit for correcting the twist is not completely cancelled after the twist correction. Instead, the guide rollers are brought to positions where they resist the occurrence of new twist. For example, in this case, the correction cycle may involve changing the length of the path traveled by one of the two side edges of the flexible member relative to the other. This can be achieved by moving the corresponding side supports of the guide rollers away from each other. Once the twist has been corrected, the two guide rollers can be brought back towards the initial position, but not with their axes parallel, but in an offset position where the path that has become longer remains longer than the other, in order to resist, prevent, or slow down the occurrence of new twist.

[0020] According to another aspect, a method for controlling a single-sided machine of the above type is provided. The method includes the following steps:

[0021] Monitoring the position of the continuous flexible member relative to the first guide roller and the second guide roller during rotation of the first guide roller and the second guide roller;

[0022] If lateral drift and / or torsion of the continuous flexible member is detected, a correction cycle is performed by changing the relative position of the first guide roller and the second guide roller from an initial position to a corrected position, causing correction of the lateral drift and / or torsion; and

[0023] Once the lateral drift and / or torsion has been corrected, the first guide roller and the second guide roller are brought to an intermediate position between the initial position and the corrected position, maintaining an offset that prevents, limits or slows new torsion and / or new lateral drift.

[0024] Further advantageous features and embodiments of the single facer and method of the present invention will be described hereinafter and defined in the appended claims.

[0025] Maintaining the offset condition after the correction cycle has been performed, rather than returning the guide rollers to the initial position where the axes of rotation are parallel, allows a significant reduction in the number of interventions for correcting the position of the flexible member. The latter is more stably held in the correct position, eliminating its tendency for lateral drift and / or torsion. For example, if external factors tend to cause lateral drift of the continuous flexible member, an offset in the position of the axes of rotation of the rollers is maintained relative to the parallel condition in order to counteract the drift, thereby stabilizing the lateral position of the continuous flexible member. The tendency for lateral drift of the continuous flexible member is eliminated or slowed, which results in better and smoother operation.

[0026] Similarly, if external factors tend to cause torsion of the continuous flexible member, an offset in the position of the axes of rotation of the rollers is maintained relative to the parallel condition in order to counteract the drift, thereby stabilizing the position of the continuous flexible member and preventing or reducing the tendency for one of its side edges to overtake the other.

[0027] The advantage of maintaining the correction offset compared to returning the guide rollers to the parallel position at the end of each correction cycle is twofold: the continuous flexible member is subjected to less stress and its wear is reduced. Secondly, a more stable quality of the product (single-faced corrugated board) obtained at the output of the single facer is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be better understood by following the description and the drawings, which show non-limiting embodiments of the present invention. More specifically, in the drawings:

[0029] Figure 1 A side view of the single facer in the working position is shown;

[0030] Figure 2 Shown from the opposite side relative to Figure 1 of Figure 1 a side view of the single facer;

[0031] Figure 2AShows a very simplified cross-section of a single-sided machine according to a vertical plane between two sides;

[0032] Figure 2B Shows a cross-section of a single-sided machine according to a vertical plane between two sides at Figure 1 and Figure 2 the position of;

[0033] Figure 3 Shows a side view similar to Figure 1 where the pressing unit is raised;

[0034] Figure 4 Shows a side view similar to Figure 2 where the pressing unit is raised;

[0035] Figure 5 Shows a cross-section of a single-sided machine according to a vertical plane between two sides of the single-sided machine at Figure 3 and Figure 4 the position of;

[0036] Figure 6 Shows a plan view of the pressing unit;

[0037] Figure 6A Shows a view similar to Figure 6 where the magnetic sensor and the control unit are schematically indicated;

[0038] Figure 7 Shows a view according to Figure 6 VII-VII;

[0039] Figure 8 Shows a view according to Figure 6 VIII-VIII;

[0040] Figure 9 Shows a view according to Figure 6 IX-IX;

[0041] Figure 10 Shows a cross-section according to Figure 8 X-X;

[0042] Figure 11 Shows a cross-section according to Figure 8 XI-XI;

[0043] Figure 12 Shows a partial isometric view of the pressing unit on the side where a motor for actuating a continuous flexible member is installed;

[0044] Figure 13A and Figure 13B Shows a partial isometric view of the pressing unit showing a sensor for detecting the position of a continuous flexible member;

[0045] Figure 14A 、 14B show two schematic side views of a pressing unit, showing the movement of one of two guide rollers of a continuous flexible member to adjust its tension;

[0046] Figure 15 and Figure 16 show two schematic views of a pressing unit, respectively according to Figure 16 line XV-XV of Figure 15 and line XVI-XVI of

[0047] Figure 17A 、 17B show two schematic views of a pressing unit, showing the movement of one of the two guide rollers of a continuous flexible member to correct its torsion; and

[0048] Figure 18 and Figure 19 show two flowcharts summarizing the logic for controlling and correcting the torsion and lateral drift of a continuous flexible member. DETAILED DESCRIPTION

[0049] The overall structure of the single facer 1 can be understood from Figure 1 、 Figure 2 and Figure 2A The first two figures show side views of the single facer as seen from two opposite sides, and Figure 2A shows a very simplified cross-section according to the vertical plane between the two sides, showing only the main components of the single facer 1. Figure 2B Shows a cross-section according to the vertical plane between the two sides of the single facer.

[0050] The single facer 1 includes a carrier frame 3, on which a corrugating roll and a pressing unit are supported, the pressing unit being used to press two paper webs of a sheet for forming a single facer corrugated board against each other, not shown in the drawings. The frame includes a first side portion 5 on the first side of the single facer 1 and a second side portion 7 on the second side of the single facer 1. The two side portions 5 and 7 are connected together by appropriate horizontal crossbars. Generally, the first side is the side where the automation device is provided, and the second side is the operator side, that is, the side from which the operator usually approaches the single facer 1.

[0051] A cassette or cartridge 13 is inserted into the carrier frame 3, the cassette including a first corrugating roll 15 and a second corrugating roll 17 covering the first corrugating roll. The cassette 13 is replaceable, i.e., interchangeable, to change the characteristics of the corrugated paper web produced by the single facer 1 using different corrugating rolls 15, 17. The structure of the cassette and its replacement system are known and will not be described in detail.

[0052] Each corrugating roll has a corrugated cylindrical surface, and the two corrugated cylindrical surfaces mesh with each other at a corrugation clamping portion defined by the two corrugating rolls 15, 17, where the first smooth paper web passes through and is corrugated due to the pressure exerted by the two corrugating rolls.

[0053] The first corrugating roll 15 cooperates with the adhesive applicator 16, only shown in Figure 2A a simplified cross-section, the adhesive applicator applying adhesive to the peaks of the corrugations formed in the first paper web before the smooth second paper web is applied thereto (when it is still in contact with the second corrugating roll 17). To bond the two paper webs (the corrugated paper web and the smooth paper web respectively), the single facer 1 includes a pressing unit or assembly 21, which is arranged to act on the upper part of the second corrugating roll 17 from top to bottom, and the two paper webs are guided around the second corrugating roll 17.

[0054] In the illustrated embodiment, the pressing unit or assembly 21 includes a pivoting structure, which in turn includes a first pivoting arm 23 on the first side of the carrier frame 3 and a second pivoting arm 25 on the second side of the carrier frame 3. The two pivoting arms 23, 25 can be rigidly connected to each other, for example, by a beam 27. In the illustrated embodiment, both pivoting arms 23, 25 are hinged to the carrier frame 3 about a pivoting axis 29, which is parallel to the axes of the corrugating rolls 15, 17 when the corrugating rolls 15, 17 are installed in the single facer 1.

[0055] The pressing unit or assembly 21 further includes a continuous flexible member 31, such as a continuous belt. The continuous flexible member 31 is guided around a first guide roll 32 (which rotates about a first rotation axis 33) and a second guide roll 35 (which rotates about a second rotation axis 37). In Figure 5 and Figure 8 the cross-section, the guide rolls 32, 35 and their respective rotation axes 33, 37 and the continuous flexible member 21 are particularly shown.

[0056] From Figure 2AThe simplified cross-section facilitates understanding of the general operation of the single facer. A first smooth paper web N1 is guided around a heating roller 20 and fed into a corrugation clamping section between a first corrugating roller 15 and a second corrugating roller 17, where it is permanently deformed to form corrugations parallel to the rotational axes of the corrugating rollers 15, 17. The first paper web N1 remains attached to the second corrugating roller 17 and receives an adhesive applied by an adhesive applicator 16 on the thus formed corrugations. Downstream of the adhesive applicator 16, the first corrugated web N1 is guided by the second corrugating roller 17 under a pressing unit 21 and more precisely between the corrugated surface of the second corrugating roller 17 and a continuous flexible member 31, which acts on the second corrugating roller 17. A second smooth paper web N2 is guided around a heating roller 22 and fed between the first corrugated web N1 attached to the second corrugating roller 17 and the pressing unit 21, and more precisely under the continuous flexible member 31 of the pressing unit 21. The pressure applied to the two webs N1, N2 in the clamping section between the pressing unit 21 and the second corrugating roller 17 causes the webs N1, N2 to adhere to each other. A single facer corrugated board web SF is obtained at the outlet of the single facer 1, the structure of which is visible in the Figure 2A magnified view shown. The adhesive joining the corrugated web N1 and the smooth web N2 is denoted by C.

[0057] A first guide roller 32 and a second guide roller 35 define a first branch of the continuous flexible member 31, which consists of the part of the continuous flexible member 31 between the two guide rollers 32, 35 facing the second corrugating roller 17. The first branch of the continuous flexible member 31 constitutes the active branch, i.e., the branch that is pressed against the second corrugating roller 17. On the opposite side of the guide rollers 32, 35, i.e., facing the opposite side with respect to the second corrugating roller 17, a second branch or return branch of the continuous flexible member 31 is also defined.

[0058] A gear motor 39 is mounted on a first pivot arm 23, which provides a rotational movement to the second guide roller 35 and thus to the continuous flexible member 31, while the first guide roller 32 is mounted on the pivot arms 23, 25 for free rotation.

[0059] In other embodiments not shown, the gear motor 39 is not provided and both guide rollers 32 and 35 are mounted on pivot structures for free rotation. In this case, the movement of the continuous flexible member can be provided by the friction of the second corrugating roller 17.

[0060] The first pivot arm 23 is constrained to a first linear actuator 41, such as a cylinder-piston actuator, preferably of the hydraulic type. One end 41.1 of the linear actuator 41 is pivotally connected to the carrier frame 3, and the second end 41.2 of the linear actuator 41 is pivotally connected to the first pivot arm 23. A second linear actuator 43 is provided on the opposite side of the single facer 1 (see Figure 2) The second actuator restrains the second pivot arm 25 to the carrier frame 3. One end 43.1 of the linear actuator 43 is pivotally connected to the carrier frame 3, and the second end 43.2 of the linear actuator 43 is pivotally connected to the second pivot arm 25. The two linear actuators 41, 43 control the pivotal movement of the pivotal structure including the pivot arms 23, 25 and the beam 27 about the pivot axis 29 to perform the operations described below.

[0061] Further details of the pressing unit 21 will be described hereinafter.

[0062] Reference Figures 1 to 7 , the movement performed by the single facer 1 will be described, more specifically the movement performed by the pressing unit or assembly 21 for removing the cassette 13 of the corrugating rollers 15, 17. Figure 1 and Figure 2 A side view of the first and second sides of the single facer 1 is shown, with the cassette or cylinder 13 and the corresponding corrugating rollers 15, 17. The pressing unit 21 is in the working position, i.e., in the lower position. In this position, the continuous flexible member 31 presses against the upper part of the second corrugating roller 17, i.e., the corrugating roller arranged at a higher level, which is arranged in the cassette 13 that is supported on the carrier frame 3. In the working position, the actuators 41, 43 push the pressing unit 21 downwards. In the illustrated embodiment, each of the pivot arms 23, 25 has a contact member 23A and 25A respectively. The two contact members 23A, 25A are arranged to cooperate with the contact member 13A carried by the cassette 13. The contact members 23A, 25A are particularly visible in Figure 2 , Figure 4 , Figure 5 and Figure 7 . One of the contact members 13A is particularly visible in Figure 2 .

[0063] When the single facer 1 is in the working position, the pivot arms 23, 25 are in an angular position by resting on the contact member 13A of the cassette 13 through the contact members 23A, 25A, and the cassette 13 in turn is supported on the support profiles 3.1, 3.2. The pressure applied by the actuators 41, 43 keeps the pivot arms 23, 25 in place and helps to keep the cassette 13 of the corrugating rollers 15, 17 in the correct position.

[0064] When the pressing unit 21 is in the working position, a tension actuator (to be described hereinafter) applies a traction force to the continuous flexible member 31 so that the continuous flexible member 31 adheres to a paper web (not shown), which is interposed between the continuous flexible member 31 and the second corrugating roller 17. The traction force of the continuous flexible member 31 reduces the thrust force applied by the actuators 41, 43 on the contact member 13A.

[0065] To replace the cassette 13, first rotate the pressing unit 21 upwards, performing a rotational movement about the pivot axis 29. By this movement, the pressing unit 21 is brought to a raised position, spaced apart from the cassette 13. The traction force of the lower branch of the continuous flexible member 31 (i.e., the branch facing the second corrugating roll 17) is maintained between the first guide roll 32 and the second guide roll 35 by a mechanism which will be described below.

[0066] In Figure 3 (the first side of the single facer 1) and Figure 4 (the second side of the single facer 1) two side views and Figure 5 in the cross-section of show the raised position of the pressing unit 21, thus showing the pivot structure carried thereon and the raised positions of the guide rolls 32, 35.

[0067] The pivot axis 29 of the pivot structure is arranged to be spaced apart from both the rotation axes 33, 37 of the first guide roll 32 and the second guide roll 35, allowing a larger spacing between the guide roll and the second corrugating roll 17 to be obtained, thus facilitating the removal of the cassette 13.

[0068] Providing the pressing unit 21 with a lifting movement about the pivot axis 29 allows an extremely simple and reliable system to be obtained for performing the various operations required for the single facer, in particular: maintaining the continuous flexible member 31 under pressure against the second corrugating roll 17 during the production of corrugated board; replacing the cassette 13; replacing the continuous flexible member 31.

[0069] When the pivot frame is in the raised position, the cassette 13 can be raised and removed from the single facer 1. Once the cassette 13 has been removed, it can be replaced by another cassette 13 having different corrugating rolls 15, 17 in order to manufacture different types of corrugated board.

[0070] When the single facer 1 is in the working position, the continuous flexible member 31 must be properly tensioned and guided around the guide rolls 23, 25. Compared with the length of the continuous flexible member 31, the width of the continuous flexible member 31 and the axial lengths of the guide rolls 23, 25 are very large. This makes guiding the continuous flexible member 31 particularly critical.

[0071] To keep the continuous flexible member 31 properly tensioned and guided, devices for adjusting and guiding the continuous flexible member 31 are provided, which will be specifically referred to below Figures 6 to 17BDescribe the device. The system is used to maintain the correct tension of the continuous flexible member 31 to prevent or correct any lateral drift, i.e., displacement along the axes of the guide rollers 32, 35, and to avoid or correct any torsion of the continuous flexible member 31. Torsion occurs when the two edges of the continuous flexible member 31 advance at non-uniform speeds, i.e., one speed is faster than the other, such that the line of the continuous flexible member 31 that was originally parallel to the rotational axes of the guide rollers 32, 35 is displaced and thus is in a position no longer parallel to these rotational axes.

[0072] In the illustrated embodiment, corresponding actuators are associated with the pivot arms 23, 25 to independently adjust the distance between the rotational axes of the two guide rollers 32, 35 for both sides of the single-sided machine 1. Additionally, additional actuators are provided on either side of the single-sided machine 1, the additional actuators being associated with one end of one of the two guide rollers 32, 35, and the additional actuators adjusting the inclination of the axis of this guide roller in the lateral direction, the lateral direction being preferably substantially orthogonal to the adjustment direction of the center distance of the guide rollers.

[0073] More specifically, the first guide roller 32 is supported on the first pivot arm 23 by the first support 32.1 and on the second pivot arm 25 by the second support 32.2. Similarly, the second guide roller 35 is supported on the first pivot arm 23 by the corresponding first support 35.1 and on the second pivot arm 25 by the corresponding second support 35.2.

[0074] In the illustrated embodiment, the supports 35.1 and 35.2 of the second guide roller 35 are mounted in fixed positions relative to the first pivot arm 23 and relative to the second pivot arm 25, while the supports 32.1 and 32.2 of the first guide roller 32 are mounted such that they can move relative to the first pivot arm 23 and the second pivot arm 25 in a controlled manner, as described below.

[0075] In the illustrated embodiment, the first support 32.1 of the first guide roller 32 and the second support 32.2 of the first guide roller 32 are mounted in respective movable units, one of which is Figure 9 shown in detail in the part of, denoted by reference numeral 71. The supports 32.1 and 32.2 are pivot supports, i.e., they allow a change in the inclination of the rotational axis 33 of the first guide roller 32 for the purposes described below and in the manner described below.

[0076] The movable unit 71 contains the first support 32.1 of the first guide roller 32 and connects it to the first pivot arm 23 as described below. By means of a similar movable unit 72, the second support 32.2 of the first guide roller 32 is mounted on the second pivot arm 25 in the same manner, see in particular Figure 6 、Figure 6A , Figure 7 , Figure 8 and Figure 9 .

[0077] Specifically referring to Figure 9 , the movable unit 71 has a seat 71.1 for the first support 32.1 of the first guide roller 32. The movable unit 71 is constrained to the pivot arm 23 by a rocker arm 73, which is pivotally connected to the movable unit 71 at one end and to the pivot arm 23 at the opposite end. The axes for pivotally connecting the rocker arm 73 to the arm 23 and the movable unit 71 are denoted by 73.1 and 73.2, respectively.

[0078] The movable unit 71 is also constrained to the pivot arm 23 by a first actuator 75 for adjusting the traction force of the continuous flexible member 31. In the illustrated embodiment, the first actuator 75 is a linear actuator, such as a cylinder-piston actuator, preferably of the double-acting hydraulic type.

[0079] In the illustrated embodiment, the actuator 75 includes a cylinder 75.1 formed within the movable unit 71, in which a piston 75.2 slides. The rod of the piston 75.2 is pivotally connected to the first pivot arm 23 at 75.3. The movement of the actuator 75 causes the pivoting of the rocker arm 73 and the corresponding movement of the axis of rotation 33 of the first guide roller 32 relative to the pivot arm 23.

[0080] A similar arrangement is provided to connect the second support 32.2 of the first guide roller 32 to the second pivot arm 25.

[0081] By acting on two actuators 75 associated with the two supports 32.1 and 32.2, the traction force of the continuous flexible member 31 due to the change in the distance between the axes of rotation 33 and 37 of the two guide rollers 32, 35 can be changed.

[0082] The two actuators 75 on both sides of the single-sided machine 1 can be actuated independently of each other, meaning that they allow independent adjustment of the respective supports 32.1 and 32.2 of the first guide roller 32 relative to the respective supports 35.1 and 35.2 of the second guide roller 35. This allows the continuous flexible member 31 to be kept properly tensioned and also allows its torsion to be controlled and corrected. The independent actuation of the actuators 75 allows the inclination of the axis of rotation 33 of the first guide roller 32 to be changed so that it is not exactly parallel to the axis of rotation 37 of the second guide roller 35. This change in inclination can be used to balance or correct the torsion of the continuous flexible member 31.

[0083] The actuator 75 can be controlled by a control unit 101( Figure 6A ), based on signals from sensors with which the single-sided machine 1 is equipped, some of which will be specifically referred to belowFigure 6 and Figure 6A Description. For example, to control the tension of the continuous flexible member 31, a load sensor that detects the traction force on the continuous flexible member 31 can be provided. This traction force corresponds to a determined pressure on the second corrugating roll 17 and thus corresponds to a determined bonding pressure between the smooth paper web and the corrugated paper web. Alternatively, the traction force can simply be determined as a function of the pressure of the hydraulic fluid used to control the actuator 75.

[0084] Figure 14A and Figure 14B More specifically shows how to perform the control of the traction force of the continuous flexible member by simultaneously actuating the actuator 75.

[0085] In Figure 14A , the continuous flexible member 31 is not in a traction state, while in Figure 14B , due to the equal elongation of the two actuators 75 and the corresponding movement of the guide roll 32 away from the guide roll 35, it is in a traction state while keeping the axes of the two guide rolls parallel to each other.

[0086] In addition to the system for controlling the tension and torsion of the continuous flexible member 31, the single facer 1 further includes members that properly hold the continuous flexible member 31 in place during the operation of the single facer 1 to avoid its lateral drift. For this purpose, as described in detail below, sensors can be provided that detect the positions of the two longitudinal edges of the continuous flexible member 31 and interface with the control unit 101 to perform, through the latter, a cycle for correcting the position of the continuous flexible member 31 when needed. More specifically, based on the signals from these sensors, possible displacements of the continuous flexible member 31 can be corrected by differentially acting on the two actuators 75, thereby causing a change in the inclination of the rotational axis 33 of the first guide roll 32 in order to correct any torsion of the continuous flexible member 31, as described below.

[0087] Furthermore, any lateral drift of the continuous flexible member 31 can be corrected by the same sensors. For this purpose, members are provided that allow the rotational axis of one guide roll to move orthogonally with respect to the plane in which the rotational axes of the two guide rolls 32, 35 are located under the normal operating conditions of the single facer 1.

[0088] In the illustrated embodiment, the members that enable such movement are described below. In the illustrated example, the guide roll for correcting the movement of the lateral drift of the continuous flexible member 31 is the guide roll 32. The pivot axis 73.1 of the rocker arm 73 associated with the pivot arm 25 is fixed (see Figure 7 ). In contrast, the pivot axis 73.1 of the rocker arm 73 associated with the pivot arm 23 is movable in order to impart a further adjustment movement to the first guide roll 32. Refer to Figure 8, Figure 9 and Figure 10 This further movement will be better understood. The pivot axis 73.1 of the rocker arm 73 associated with the first pivot arm 23 is constituted by an eccentric 73.3 which is received in a seat 73.4 of the pivot arm 23 (see Figure 9 ). The eccentric 73.3 rotates in the seat 73.4 about an axis 73.5 which is parallel to but spaced from the pivot axis 73.1 of the rocker arm 73. In the illustrated embodiment, the rotation of the eccentric 73.3 is controlled by a linear actuator 77 (such as an electric jack) via a rod 79 (see Figure 8 ).

[0089] The rotation of the eccentric 73.3 about the axis 73.5 causes a displacement of the pivot axis 73.1 of the rocker arm 73 relative to the pivot arm 23. In Figure 9 , the general direction of this displacement is indicated by f73. This direction is perpendicular to the direction of the displacement imparted by the linear actuator 75 (indicated by f75). In this way, on one side of the first pivot arm 23, the first support 32.1 of the first guide roller 32 can be displaced in two directions which are substantially orthogonal to each other. The displacement imparted by the actuator 75 according to the arrow f75 ( Figure 9 ) is used to adjust the traction and torsion of the continuous flexible member 31 and can be coordinated with the corresponding movement imparted by the corresponding actuator 75 of the second support 32.2. The displacement imparted by the actuator 77 via the eccentric 73.3 can be used to correct the displacement of the continuous flexible member 31, for example, a lateral drift parallel to the rotational axes of the guide rollers 32, 35. A corresponding displacement of the support 32.2 on the side of the second pivot arm 25 is not necessary.

[0090] Figure 6A , Figures 13A to 17B Shows further details for understanding the control of the position of the continuous flexible member 31 by the movement imparted to the guide rollers by the above mechanical members and actuators 75, 77.

[0091] More specifically, Figure 6A , Figure 13A and Figure 13B Show an axonometric view of the details of the pivot arms 23, 25 and the continuous flexible member 31 driven around the guide rollers 32 and 35. Figure 6A Similar to Figure 6 , but shows the continuous flexible member 31 with a part removed to show the sensors for detecting the positions of the two longitudinal edges 31A, 31B of the continuous flexible member 31. When the single-sided machine 1 is operating and the continuous flexible member 31 is correctly positioned, the latter is in accordance with the forward direction f31 ( Figure 6A) movement, which is oriented at 90° with respect to the axes of rotation 33 and 37 of the guide rollers 32 and 35 and is parallel to the longitudinal edges 31A, 31B. Additionally, the continuous flexible member 31 is substantially centered with respect to the intermediate plane (i.e., the intermediate vertical plane M-M of the single-sided machine 1( Figure 6 , Figure 6A )) and thus centered with respect to the pivot arms 23, 25.

[0092] Figure 6A , Figure 13A and Figure 13B show sensors for detecting the displacement of the continuous flexible member 31, which sensors supply signals to a control unit 101 that controls the above actuators to keep the continuous flexible member 31 in the correct position.

[0093] In the following description, reference will be made specifically to an embodiment of a particularly advantageous sensor system that employs magnetic sensors. These magnetic sensors are highly reliable and insensitive to factors that may adversely affect the operation of other types of sensors, such as optical sensors that may be affected by dust or other dirt. Alternatively, capacitive sensors, for example, may be used. Even though they are currently less preferred due to their sensitivity to dust, optical sensors may also be used.

[0094] In the illustrated embodiment, a set of magnetic sensors is arranged on each side of the pressing unit 21 and is schematically shown in Figure 6A where a portion of the continuous flexible member 31 is removed on both sides to show the underlying magnetic sensors.

[0095] More specifically, in the embodiment of Figure 6A , a first group 103A of three magnetic sensors is provided, associated with one side of the pressing unit 21 where the pivot arm 23 is arranged, and a second group 103B of magnetic sensors is provided on the side of the pressing unit 21 where the pivot arm 25 is arranged. In the example shown, each magnetic sensor group 103A, 103B includes three magnetic sensors. Each individual magnetic sensor is denoted by the reference numeral 103. The six magnetic sensors of the two magnetic sensor groups 103A, 103B are aligned in a direction D that is orthogonal to the forward direction f31 of the continuous flexible member 31 and thus orthogonal to the vertical intermediate plane M-M. However, this arrangement is not strictly necessary. In other embodiments, the magnetic sensors 103A are aligned with each other in the direction D, the magnetic sensors 103B are aligned with each other in the direction D, but the two sensor groups 103A, 103B may be offset from each other by a known distance in a direction orthogonal to the direction D. In fact, as will be clearly apparent below, it is important that the distance between the two sensor groups in the forward direction of the continuous flexible member 31 is known.

[0096] The first set 103A of magnetic sensors is adapted to detect the passage of magnets 104A fixed to or embedded in a continuous flexible member 31, near the longitudinal edge 31A. The second set 103B of magnetic sensors is adapted to detect magnets fixed to or embedded in the continuous flexible member 31, near the longitudinal edge 31B. For this purpose, the magnetic sensors 103 are mounted on the pressing unit 21 in a side position, near the pivot arms 23, 25. For example, the sensors 103 may be mounted to protrude on the sliding surface 106 ( Figure 6A ) of the continuous flexible member 31. In the illustrated embodiment, the sliding surface 106 is formed by the upper surface of a beam 27 connecting the pivot arms 23, 25.

[0097] In the illustrated embodiment, the magnets 104A, 104B are fixed to the continuous flexible member 31, for example, embedded in its thickness, in such a position that when the continuous flexible member 31 is correctly positioned on the guide rollers 32, 35, the magnets 104A, 104B are aligned with each other according to the direction D, that is, parallel to the alignment of the two sets of magnetic sensors 103A, 103B and orthogonal to the forward direction f31 of the continuous flexible member 31. However, such an arrangement is not strictly necessary. What is important is that when the continuous flexible member 31 is correctly positioned on the guide rollers 32, 35, the distance between the magnet 104A and the magnet 104B in the forward direction of the continuous flexible member 31 is known.

[0098] When the continuous flexible member 31 is centered relative to the pivot arms 23, 25 and thus relative to the vertical intermediate plane M-M, the mutual positions of the magnets 104A, 104B relative to the magnetic sensors 103A, 103B are such that when the continuous flexible member 31 moves around the guide rollers 32, 35, the trajectory along which the magnet 104A moves intercepts the central magnetic sensor 103 in the set of magnetic sensors 103A, and the trajectory along which the magnet 104B moves intercepts the central magnetic sensor 103 in the set of magnetic sensors 103B.

[0099] Furthermore, since the magnets 104A, 104B are aligned along the direction D under appropriate operating conditions, they simultaneously intercept the corresponding central magnetic sensors in the sets of magnetic sensors 103A, 103B. The simultaneous signals from the magnetic sensors 103A, 103B indicate the absence of torsion. However, as described above, the two magnets 104A, 104B do not have to be aligned along the direction D. They may be offset by a known distance. An explanation of how the offset arrangement of the magnets still allows control of the torsion of the continuous flexible member 31 will be given below.

[0100] The assembly formed by the magnetic sensors 103A, 103B, the magnets 104A, 104B, and the control unit 101 allows the correct position of the continuous flexible member 31 to be controlled and maintained during the operation of the single-sided machine 1, as described below.

[0101] As mentioned, when one of the longitudinal edges 31A, 31B of the continuous flexible member 31 advances more slowly than the other, torsion of the continuous flexible member 31 occurs. This causes the two magnets 104A, 104B to be offset from each other along the advancing direction of the continuous flexible member 31. In fact, in the case of torsion of the continuous flexible member 31, the two magnets 104A, 104B no longer align along the direction D orthogonal to the direction f31, but the line connecting them will be arranged at an angle other than 90° with respect to the direction f31. The control unit detects the occurrence of this situation based on the time offset of the signals from the two sensor groups 103A, 103B.

[0102] If the two magnets 104A, 104B are not aligned but are offset from each other in the longitudinal direction (i.e., the extending direction of the edge of the continuous flexible member 31), the control unit 101 can determine the correct time interval between the detection of the magnet 104A passing in front of the sensor 103A and the detection of the magnet 104B passing in front of the sensor 103B based on the offset amount and the speed of the continuous flexible member 31. In the case of torsion of the continuous flexible member 31, this time interval changes, and the control unit 101 can detect the change in the time interval, thereby obtaining information about the occurrence of torsion. If an encoder is provided on the main motor that controls the movement of the continuous flexible member 31, in addition to detecting the time interval indicating torsion, the degree of offset (expressed in length) between the two longitudinal edges of the continuous flexible member 31 can also be detected.

[0103] Generally, the torsion condition is detected by the delay of the signal from one of the sensor groups 103A, 103B with respect to the signal from the other sensor group among the sensor groups 103A, 103B. For example, if the longitudinal edge 31A moves forward faster than the longitudinal edge 31B, the magnet 104A will pass in front of the magnetic sensor 103A earlier than the magnet 104B passes in front of the magnetic sensor 103B, and thus the signal of the magnetic sensor 103A will be earlier in time than the signal of the magnetic sensor 103B. Even in the case of initially misaligned magnets, torsion still causes a change (increase or decrease) in the time offset of the signals generated by the two sensors.

[0104] This time offset provides the control unit 101 with information about the need to perform a correction cycle by the differential actuation of the two actuators 75.

[0105] Calibration is performed in the following manner. The control unit 101 acts on the actuator 75 to increase the tension of the continuous flexible member 31 on the side where deceleration is detected. If the slower moving longitudinal edge is the longitudinal edge 31B, the control unit 101 will cause such a differential tension between the two sides of the continuous flexible member 31 that the tension on the side of edge 31A is less than the tension on the side of edge 31B. For this purpose, the tension on edge 31A is appropriately maintained and the tension on edge 31B is increased by acting on the corresponding actuator 75, such that the supports of the guide rollers 32, 35 move away from each other on the side of the longitudinal edge 31B. If the slower moving longitudinal edge is the longitudinal edge 31A, the opposite action should be performed.

[0106] This adjustment is based on the following consideration. If one of the two longitudinal edges is slower (i.e., the passage of the magnet associated with the slower edge is detected later than the passage of the magnet on the other side), then considering that the tangential velocity of the flexible member 31 is the same across the entire span (i.e., the entire width of the continuous flexible member 31), this means that the delayed edge of the continuous flexible member 31 is traveling a longer path. Therefore, it is necessary to extend the path of the edge on the opposite side to compensate for the torsion of the flexible member.

[0107] The control unit 101 detects the gradual realignment of the two magnets 104A, 104B along the direction D, which is detected by a decrease in the time offset between the signals generated by the sensor group 103A and the sensor group 103B.

[0108] Once the time offset of the signals becomes zero, i.e., when the torsion has been corrected, the control unit 101 can theoretically return the actuator 75 whose tension it has increased to its original value, i.e., it can return the two actuators 75 to applying the same tension to the continuous flexible member 31. This is the neutral position of the actuator responsible for controlling the torsion.

[0109] However, this operating mode is not optimal. In fact, the torsion of the continuous flexible member 31 is caused by one or more external causes that are neither detected nor eliminated. Therefore, once the control unit 101 has returned the actuator 75 to the state before the start of the calibration cycle, the continuous flexible member 31 will tend to twist again. As a result, in a short period of time, the control unit 101 will intervene again to perform a new torsion correction cycle.

[0110] The situation where repeated and frequent interventions may be required to correct the torsion of the continuous flexible member 31 may even persist for a long time, resulting in stress on the continuous flexible member 31 and adversely affecting the quality of the obtained product (corrugated board).

[0111] To avoid this negative situation and prevent the continuous flexible member 31 from twisting again, the control unit 101 is programmed (i.e., configured) to maintain an offset between the tensions applied to the continuous flexible member 31 by the two actuators 75.

[0112] In fact, the position reached by the actuator 75 after the twist has been corrected is an intermediate position between the initial position (i.e., the position it was in at the start of the correction cycle) and the position it was in during the correction cycle. The initial position can be a neutral position where the two actuators 75 have positions such that the path traveled by the edge 31A of the continuous flexible member 31 is equal to the path traveled by the edge 31B of the continuous flexible member 31. However, this is not always the case. In fact, a correction cycle can be started after the control unit 101 has executed a previous correction cycle that did not end with the two actuators 75 returned to the same position relative to each other (the paths of the two edges 31A, 31B are not the same), but with some offset to compensate for the twisting tendency of the continuous flexible member 31.

[0113] It is also possible that a twist correction cycle started at a given time makes it perform a correction opposite to the correction made by a previous correction cycle. This can happen if the factors causing the continuous flexible member 31 to twist change substantially over time. For example, the first correction cycle causes the path traveled by the edge 31A to be longer relative to the path traveled by the edge 31B, with the actuator 75 arranged on the side of the edge 31A being extended. The offset maintained at the end of this correction cycle causes the actuator 75 on the side of the edge 31A to be more extended than the actuator 75 on the side of the edge 31B. If the operating conditions change, it is possible that the continuous flexible member 31 undergoes a twist opposite to the previous twist at some point. In this case, the offset set in the previous correction cycle accelerates the twist, causing the control unit 101 to intervene faster to correct the twist, shortening the path of the edge 31A and / or extending the path of the edge 31B. However, this situation is rare, and typically, the offset set in the previous correction cycle compensates for the twisting tendency, thus actually reducing the frequency of interventions for correcting the twist.

[0114] In other words, if the detected torsion is caused by the deceleration of the edge 31B of the continuous flexible member 31, and thus the correction results in an increase in the tension on the side of the edge 31A (and thus an increase in the path of this edge), then when the torsion has been corrected and the two magnets 104A, 104B are again aligned in the direction D parallel to the advancing direction f31 of the continuous flexible member 31 (or their offset has been restored to the initial value), the control unit 101 can reduce the traction force applied by the actuator 75 on the faster side, that is, the side whose path has been extended to correct the torsion (in the example, the side of the edge 31A), but keep this traction force slightly higher than the slower side (the side of the edge 31B). This offset compensates for the factors causing the torsion, thus preventing the continuous flexible member 31 from twisting again, or at least it reduces the amplitude or speed of the torsion.

[0115] Therefore, generally, torsion correction involves applying a differential tension between the two longitudinal edges 31A, 31B of the continuous flexible member 31 to elongate the path traveled by the faster edge. At the end of the correction, that is, when the two magnets 104A, 104B return to their alignment positions with respect to each other in the direction D (or the original mutual distance in the direction orthogonal to the direction D), the control unit 101 reduces the tension difference, maintaining a residual difference to counteract the newly corrected torsion.

[0116] It should be understood that for smooth operation, when the time offset of the signals from the two sensor groups 103A, 103B exceeds the tolerance time threshold, the control unit 101 should intervene to correct the torsion in order to avoid continuous correction even in the case of slight torsion. The time interval between torsion correction intervals, its duration, and the entities (the force applied to the piston, the correction time, the amount of torsion detected by the sensors) allow the control unit 101 to continuously refine the offset value to achieve maximum system stability. Variable temperature, the characteristics of the processed paper web, the wear of the continuous flexible member 31, and changes over time will always cause small changes that need to be compensated for.

[0117] In some embodiments, when the actuator 75 performs a correction action by applying a higher pressure from an appropriate side, the direct action of the control unit 101 is not used to maintain the pressure. Instead, the pressure can be maintained by closing the pressure fluid circuit (usually oil) that actuates the actuator 75. A specific cut-off valve can be provided for this purpose. The set pressure is monitored by a pressure sensor for each actuator 75. When the torsion correction is completed, or if for any reason the target pressure deviates from the desired threshold, the system first intervenes by bringing its pressure to the same pressure level in the cylinders of the two actuators 75, opening the cut-off valve, and regulating the pressure to the correct value through a hydraulic control unit.

[0118] In a further embodiment, instead of the cylinder-piston actuator 75, other types of actuators can be used, preferably linear actuators. For example, the same operation as described above can be achieved by a jack equipped with a load cell for detecting tension.

[0119] Figure 18 The flowchart of summarizes the cycle for correcting the torsion of the continuous flexible member 31. Briefly, the process of controlling and correcting the torsion is performed as follows. The position of the continuous flexible member 31 is detected by the sensor 103 (block 311). Based on the signal received from the sensor 103, the control unit 101 checks whether the continuous flexible member 31 is twisted (block 312). If not, no correction is made. If so, the cycle for correcting the torsion is executed by activating any of the actuators 75 (block 313). At this stage, any of the actuators 75 changes the length of the path traveled by the corresponding longitudinal edges 31A, 31B according to the received signal. In principle, the intervention can also be performed by two actuators 75 that can move in opposite directions. Once the correction cycle is completed, the control unit 101 checks whether the torsion has been eliminated based on the signal received from the sensor 103 (block 314). If not, the actuator 75 activated during the correction cycle remains in the activated position. If so, that is, if the torsion has been eliminated, the actuator 75 activated during the correction cycle returns to an intermediate position between the initial position and the position at which it was in block 312 (block 315). In practice, the previously activated actuator 75 is brought to the neutral position, except for a slight offset. The correction cycle is completed and the control returns to block 310.

[0120] As described below, any lateral drift of the continuous flexible member 31 is detected and corrected using the magnetic sensors 103 and the control unit 101.

[0121] When the continuous flexible member 31 translates or drifts laterally relative to the forward direction and moves towards either of the two pivot arms 23, 25, the longitudinal edges 31A, 31B translate along the alignment direction D of the magnetic sensors 103. Such lateral drift can be detected by one of the two groups of magnetic sensors 103A, 103B. In fact, the position of the magnetic sensors 103 is such that in the centered position, when the flexible member 31 is centered with respect to the vertical intermediate plane of the two pivot arms 23, 25 and the two side edges 31A, 31B are equidistant from the vertical intermediate plane, the trajectories of the magnets 104A, 104B pass through the central magnetic sensors of each of the two groups of magnetic sensors 103A, 103B.

[0122] Thus, if the continuous flexible member 31 drifts laterally, i.e., moves parallel to the rotational axes of the guide rollers 32, 35, both magnets 104A, 104B move and intercept one lateral magnetic sensor in each lateral magnetic sensor group 103A, 103B. If the continuous flexible member 31 drifts laterally towards the pivot arm 25, the magnet 104B adjacent to the longitudinal edge 31B translates until its trajectory intercepts the outermost sensor 103 in the sensor group 103B, while the magnet 104A translates until its trajectory intercepts the innermost sensor 103 in the sensor group 103A. Depending on the size of the magnet and the distance between the magnetic sensors, the lateral drift can be intercepted by only one magnetic sensor (thus the passage from the central magnetic sensor to one of the lateral magnetic sensors) or can be intercepted by both magnetic sensors simultaneously.

[0123] The control unit 101 can be programmed to detect such displacement by signals from the magnetic sensors 103. For this purpose, it is sufficient to process the signals of only the magnetic sensors 103 of group 103A or the magnetic sensors 103 of group 103B.

[0124] In a practical embodiment, only one of the two sensor groups 103A, 103B is used for drift control. Thus, although the initial position of the flexible member 31 is perfectly centered, during operation, the drift is controlled by controlling only one of the two longitudinal edges of the flexible member 31. In fact, during operation, when on the controlled edge, for example, the central sensor detects the magnet, on the opposite edge, the magnet may be detected by the outermost sensor due to the possible expansion of the flexible member in the lateral direction, which is sensitive to temperature changes. The sensors 103 are arranged at an appropriate distance such that even in the case of maximum expansion of the flexible member 31, one of the three sensors placed on each side can always detect the corresponding magnet. This ensures continuous torsion control regardless of the lateral expansion of the flexible member.

[0125] Any thermal expansion of the continuous flexible member may cause a negligible drift of the continuous flexible member relative to the intermediate plane, due to the fact that the lateral position of the continuous flexible member is detected by reading only one longitudinal edge. Basically, by keeping the lateral position of one of the two longitudinal edges of the continuous flexible member under control, the thermal expansion can cause the other of the two longitudinal edges to drift laterally. However, this drift is small and acceptable. The use of a system that detects any lateral drift of the continuous flexible member by checking the position of one of its longitudinal edges is substantially simpler.

[0126] When the control unit 101 detects a lateral displacement caused by the drift of the continuous flexible member exceeding a threshold, it initiates a correction cycle. The correction includes actuating the actuator 77, which causes the axis of rotation of the guide roller 32 to move in such a direction that the axis of rotation 33 is inclined with respect to the axis of rotation 37. If the axis of rotation 33 and the axis of rotation 37 are initially coplanar, the correction cycle involves moving the axis of rotation 33 away from the original plane in which the axes of rotation 33 and 37 lie.

[0127] The displacement of the axis of rotation 33 gradually returns the continuous flexible member 31 to its central position. When the control unit 101 detects, through the signal from the magnetic sensor 103, that the continuous flexible member 31 is centered again, in theory, the axis of rotation 33 of the guide roller 32 can be returned to a position coplanar with the axis of rotation 37 of the guide roller 35. This position is the neutral position of the actuator for controlling the lateral drift.

[0128] However, this operating mode is not optimal. In fact, the lateral drift of the continuous flexible member 31 is caused by one or more external causes that are neither detected nor eliminated. Therefore, once the control unit 101 has returned the actuator 77 to the conditions before the start of the correction cycle, with the axes of rotation 33 and 37 coplanar, the continuous flexible member 31 tends to drift again in the same direction that led to the previous correction intervention. As a result, in a short period of time, the control unit 101 will again correct the lateral position of the continuous flexible member 31 with a new cycle.

[0129] This situation, which requires repeated and frequent intervention to correct the drift (i.e., lateral translation) of the continuous flexible member 31, can last for a long time, resulting in stress on the continuous flexible member 31 and affecting the quality of the obtained product (corrugated board).

[0130] To avoid this inconvenience, instead of precisely returning the two guide rollers 32, 35 and their respective axes of rotation to coplanarity, the control unit 101 is configured to maintain a slight offset, i.e., a slight inclination of the guide roller 32 with respect to the coplanar condition between the axes of rotation, such that its axis of rotation 33 is slightly inclined from its nominal position parallel to the axis of rotation 37 of the guide roller 35. The offset is used to compensate (i.e., counteract) the tendency of the continuous flexible member 31 to translate by slowing down or eliminating the translational movement. Basically, if the drift correction cycle is carried out by moving the axis of rotation 33 of the guide roller 32 to a plane above the original plane in which the axes of rotation 33, 37 lie, then once the continuous flexible member 31 returns to the central position, the axis of rotation 33 returns to a coplanar condition with the axis of rotation 37, but not completely coplanar, rather remaining slightly above the coplanar plane. If the drift correction is carried out by moving the axis of rotation 37 downwards, then vice versa.

[0131] A slight offset in the angular position of the axis of rotation 33 that is maintained once the continuous flexible member 31 reaches the central position compensates for stray factors that tend to cause lateral drift of the continuous flexible member, such as mechanical tolerances, characteristics of the processed paper, and accumulation of dirt on moving parts. By maintaining this offset, new offset movements are slowed down or eliminated.

[0132] There may also be a situation where the execution of a drift correction cycle initiated at a given time makes a correction opposite to the correction made by a previous correction cycle. This can occur when the factors causing the drift of the continuous flexible member 31 change substantially over time. For example, in the first correction cycle, the axis of rotation 33 of the guide roller 32 may have been raised to return the continuous flexible member 31 to its central position. The offset maintained at the end of this first correction cycle causes the actuator 77 to slightly raise the axis of rotation 33 relative to the neutral position coplanar with the axis of rotation 37 of the guide roller 35. If the operating conditions change, it is possible that the continuous flexible member 31 experiences a drift opposite to the previous drift at some point. In this case, the offset set in the previous correction cycle accelerates the drift movement, leading to faster intervention by the control unit 101 to correct the drift. In this case, the control unit 101 activates the actuator 77 to tilt the axis of rotation 33 below the neutral position, that is, below the coplanar plane of the axes of rotation 33, 37. However, this situation is rare, and typically, the offset set in the previous correction cycle compensates for the drift tendency and thus actually reduces the frequency of intervention to correct the drift.

[0133] Figure 19 The flowchart of summarizes the cycle for correcting the lateral drift of the continuous flexible member 31. Briefly, the process of controlling and correcting the drift is performed as follows. The position of the continuous flexible member 31 is detected by the sensor 103 (block 301). Based on the signal received from the sensor 103, the control unit 101 checks whether the continuous flexible member 31 is laterally translated (block 302). If not, no correction is made. If so, a cycle for correcting the drift is executed by activating the actuator 77 (block 303). At this stage, the actuator 77 causes the axis of rotation 33 of the guide roller 32 to tilt based on the received signal. The displacement may be upward or downward, depending on the direction in which the lateral drift of the continuous flexible member 31 occurs. Once the correction cycle has been initiated, the control unit 101 checks based on the signal received from the sensor 103 whether the drift has been eliminated (block 304) and whether the continuous flexible member 31 has returned to its central position. If not, the actuator 77 remains in the activated position. If so, that is, if the drift has been eliminated, the actuator 77 returns to an intermediate position between the initial position and the position it was in at block 302 (block 305). In practice, the actuator 77 is brought to the neutral position, except for a slight drift. The correction cycle is completed and the control returns to block 301.

[0134] Figure 15 and Figure 16 shows the displacement of the first guide roller 32 for correcting the lateral drift of the continuous flexible member 31 caused by the linear actuator 77. More specifically, Figure 15 is the rear view of the pressing unit 21 according to Figure 16 XV-XV, and Figure 16 is its side view according to Figure 15 XVI-XVI. 32X and 32Y indicate two inclined positions of the first guide roller 32. For clarity, the displacements are shown much larger than they actually are.

[0135] Figure 17A and Figure 17B show, in the top view of the pressing unit 21, the displacement of the first guide roller 32 controlled by the differential stroke of the actuator 75 to correct any torsion of the continuous flexible member 31. 32Z and 32W indicate the positions of the first guide roller 32 inclined in opposite directions obtained by the differential actuation of the actuator 75. For clarity, as in Figure 15 and Figure 16 , in Figure 17A , 17B , the displacements are also shown much larger than they actually are.

[0136] The present invention has been described in various embodiments. However, it will be apparent to those skilled in the art that many modifications, changes, and omissions can be made to the present invention without departing from the scope of protection defined in the appended claims.

Claims

1. A single facer (1) for producing single-sided corrugated board, comprising: a) a first corrugating roll (15) and a second corrugating roll (17) that mesh with each other; b) a support structure, which includes a first arm (23) on the first side of the single facer (1) and a second arm (25) on the second side of the single facer (1); c) a first guide roll (32) having a first axis of rotation (33), which is supported on the first arm (23) by a corresponding first support (32.1) and on the second arm (25) by a corresponding second support (32.2); d) a second guide roll (35) having a second axis of rotation (37), which is supported on the first arm (23) by a corresponding first support (35.1) and on the second arm (25) by a corresponding second support (35.2); e) a continuous flexible member (31), which is driven around the first guide roll (32) and the second guide roll (35), and has a first longitudinal edge (31A) and a second longitudinal edge (31B), the first longitudinal edge and the second longitudinal edge extending parallel to the advancing direction of the continuous flexible member (31); and f) an adjusting and guiding device for adjusting and guiding the continuous flexible member (31), which includes: f1. a sensor (103), which is adapted to detect the lateral drift and torsion of the continuous flexible member (31); and f2. actuators (75, 77), which are adapted to change the relative positions of the first guide roll (32) and the second guide roll (35); f3. a control unit, which is configured to: (a) start the actuators (75, 75, 77) based on the signals received from the sensor (103) and perform a correction cycle by changing the relative positions of the first guide roll (32) and the second guide roll (35) from an initial position to a correction position that causes the correction of the lateral drift and / or torsion; and (b) once the lateral drift and / or torsion has been removed or corrected, bring the first guide roll (32) and the second guide roll (35) to an intermediate position between the initial position and the correction position.

2. The single facer according to claim 1, wherein the adjusting and guiding device for adjusting and guiding the continuous flexible member (31) includes: a first actuator (75) associated with the first arm (23), which is adapted to adjust the distance between the first support (32.1) of the first guide roll (32) and the first support (35.1) of the second guide roll (35); a second actuator (75) associated with the second arm (25), which is adapted to adjust the distance between the second support (32.2) of the first guide roll (32) and the second support (35.2) of the second guide roll (35), the first actuator (75) and the second actuator (75) being able to be actuated independently of each other; wherein the control unit (101) is configured to act differentially on the first actuator and the second actuator based on the signals from the sensor (103) to correct the torsion of the continuous flexible member (31).

3. The single-sided machine according to claim 2, wherein the control unit (101) is programmed such that when the sensor (103) detects a torsion of the continuous flexible member (31), the control unit (101) performs a correction cycle for correcting the torsion, causing a change in the distance between the first support (32.1) of the first guide roller (32) and the first support (35.1) of the second guide roller (35) relative to the distance between the second support (32.2) of the first guide roller (32) and the second support (35.2) of the second guide roller (35); the change changes the relative position of the first guide roller (32) and the second guide roller (35) from an initial position to a corrected position; the change reduces or removes the torsion of the continuous flexible member (31).

4. The single-sided machine according to claim 3, wherein the control unit (101) is configured such that once the torsion has been corrected or removed, the first guide roller (32) and the second guide roller (35) are brought to an intermediate position between the initial position and the corrected position.

5. The single-sided machine (1) according to claim 2, 3 or 4, wherein the first actuator (75) and the second actuator (75) are linear actuators, in particular cylinder-piston actuators or mechanical jacks.

6. The single-sided machine (1) according to one or more of claims 2 to 5, wherein: The first support (32.1) of the first guide roller (32) is movably mounted on the first arm (23), and the second support (32.2) of the first guide roller (32) is movably mounted on the second arm (25); wherein the movement of the first support (32.1) of the first guide roller (32) on the first arm (23) and the movement of the second support (32.2) of the first guide roller (32) on the second arm (25) are respectively controlled by the first actuator (75) and the second actuator (75); and wherein the first support (35.1) of the second guide roller (35) is fixedly mounted on the first arm (23), and the second support (35.2) of the second guide roller (35) is fixedly mounted on the second arm (25).

7. The single-sided machine (1) according to at least claims 2 and 6, wherein the first support (35.1) of the second guide roller (35) is fixed relative to the first arm (23), and the second support (35.2) of the second guide roller (35) is fixed relative to the second arm (25); wherein the first support (32.1) of the first guide roller (32) and the second support (32.2) of the first guide roller (32) are respectively mounted in a first movable unit (71) and a second movable unit (72), the first movable unit being fixed to the first arm (23), and the second movable unit being fixed to the second arm (25); wherein the first movable unit (71) is fixed to the first pivot arm (23) by a first actuator (75) and by a first pivot axis about a first pivot axis substantially parallel to the hinge axis (29) of the support structure and hinged to a first rocker arm (73) of the first arm (23); wherein the second movable unit (72) is fixed to the second arm (25) by a second actuator (75) and by a second pivot axis about a second pivot axis substantially parallel to the hinge axis (29) of the support structure to the carrier frame (3) and hinged to a second rocker arm (73) of the second arm (25); and wherein the pivot axis of at least one of the first rocker arm (73) and the second rocker arm (73) can be adjusted by a third actuator (77).

8. The single-sided machine according to claim 7, wherein the first actuator (75) is a linear actuator having a first end hinged to the first arm (23) about an axis substantially parallel to the hinge axis (29) of the support structure and a second end rigidly coupled to the first movable unit (71); and wherein the second actuator (75) is a linear actuator having a first end hinged to the second arm (25) about an axis substantially parallel to the support structure of the carrier frame (3) and a second end rigidly coupled to the second movable unit (72).

9. The single-sided machine according to one or more of the preceding claims, wherein the adjusting and guiding means for adjusting and guiding the continuous flexible member (31) comprises at least a third actuator (77) provided on one of the first arm (23) and the second arm (25) to tilt the rotation axis of at least one of the first guide roller (32) and the second guide roller (35) in an adjusting direction transverse to a plane, when the rotation axes of the first guide roller (32) and the second guide roller (35) are parallel to each other, the rotation axis (33) of the first guide roller (32) and the rotation axis (37) of the second guide roller (35) are on the plane.

10. The single-sided machine according to claim 9, wherein the control unit (101) is programmed such that when the sensor (103) detects a lateral drift of the continuous flexible member (31), the control unit (101) executes a correction cycle for correcting the lateral drift, causing a change in the inclination of the rotation axis of at least one of the first guide roller (32) and the second guide roller (35) in the adjustment direction by the third actuator (77); the change causes the relative position of the first guide roller and the second guide roller to change from the initial position to the correction position; the change in the inclination reduces or removes the lateral drift of the continuous flexible member (31).

11. The single-sided machine according to claim 10, wherein the control unit (101) is programmed such that once the correction cycle for correcting the lateral drift is completed, the first guide roller (32) and the second guide roller (35) are brought to an intermediate position between the initial position and the correction position.

12. The single-sided machine (1) according to one or more of the preceding claims, wherein the second guide roller (35) is motorized.

13. The single-sided machine (1) according to one or more of the preceding claims, wherein the sensor (103) is a magnetic sensor adapted to detect magnets fastened near the first longitudinal edge (31A) and the second longitudinal edge (31B) of the continuous flexible member (31).

14. The single-sided machine according to claim 13, wherein the magnetic sensor comprises: A first group (103A) of magnetic sensors on the first side of the pressing unit (21), which are aligned with each other in a direction (D) orthogonal to the advancing direction (f31) of the continuous flexible member (31); and a second group (103B) of magnetic sensors on the second side of the pressing unit (21), which are aligned with each other in a direction (D) orthogonal to the advancing direction (f31) of the continuous flexible member (31); wherein the magnetic sensors are adapted to detect the lateral drift of the longitudinal edges of the continuous flexible member (31) in the direction (D) orthogonal to the advancing direction (f31), and to detect the torsion of the continuous flexible member (31).

15. The single-sided machine according to claim 14, wherein the first group (103A) of magnetic sensors is adapted to detect the passage of the magnet (104A) fixed to the continuous flexible member (31) near the first longitudinal edge (31A) of the continuous flexible member; and the second group (103B) of magnetic sensors is adapted to detect the passage of the magnet (104B) fixed to the continuous flexible member (31) near the second longitudinal edge (31B).

16. The single facer according to claim 15, wherein the control unit is configured to: detect a lateral drift of the continuous flexible member (31) based on a signal from either the first set (103A) of magnetic sensors or the second set (103B) of magnetic sensors, the signal being generated by the passage of a respective magnet fixed to the continuous flexible member (31); and detect a twist in the continuous flexible member based on signals from both the first set (103A) of magnetic sensors and the second set (103B) of magnetic sensors, the signal being generated by the passage of a magnet fixed to the continuous flexible member (31).

17. A method for controlling a single facer (1) for producing single-sided corrugated board, the single facer comprising: A first corrugating roll (15) and a second corrugating roll (17) that mesh with each other; A support structure having a first arm (23) on a first side of the single facer (1) and a second arm (25) on a second side of the single facer (1); a first guide roll (32); a second guide roll (35); a continuous flexible member (31) that is driven around the first guide roll (32) and the second guide roll (35) and pressed against the second corrugating roll (17); the method comprising the steps of: Monitoring the position of the continuous flexible member (31) relative to the first guide roll (32) and the second guide roll (35) during rotation of the first guide roll (32) and the second guide roll (35); If a lateral drift and / or twist of the continuous flexible member (31) is detected, performing a correction cycle by changing the relative position of the first guide roll (32) and the second guide roll (35) from an initial position to a correction position, thereby causing correction of the lateral drift and / or twist; and Once the lateral drift and / or twist has been corrected, bringing the first guide roll (32) and the second guide roll (35) to an intermediate position between the initial position and the correction position.

18. The method according to claim 17, wherein, If a twist of the continuous flexible member (31) is detected, the correction cycle includes a lateral drift correction cycle, which includes the steps of: Changing the distance between the first support (32.1) of the first guide roll (32) on the first arm (23) and the first support (35.1) of the second guide roll (35) on the first arm (25) relative to the distance between the second support (32.2) of the first guide roll (32) on the second arm and the second support (35.2) of the second guide roll (35) on the second arm (25); this change causes the relative position of the first guide roll (32) and the second guide roll (35) to change from the initial position to the correction position; wherein the change reduces or eliminates the twist of the continuous flexible member (31); Once the twist has been eliminated or corrected, bringing the first guide roll (32) and the second guide roll (35) to an intermediate position between the initial position and the correction position.

19. The method according to claim 17 or 18, wherein, If a lateral drift of the continuous flexible member (31) is detected, performing a lateral drift correction cycle, which includes the steps of: causing a change in the inclination of the rotation axis of at least one of the first guide roller (32) and the second guide roller (35), the change causing the relative position of the first guide roller (32) and the second guide roller (35) to change from an initial position to a corrected position; wherein the change in the inclination reduces or eliminates the lateral drift of the continuous flexible member (31); Once the lateral drift has been corrected or eliminated, the first guide roller (32) and the second guide roller (35) are brought to an intermediate position between the initial position and the corrected position.

20. The method according to any one of claims 17 to 19, wherein the position of the continuous flexible member (31) is detected by a magnetic sensor, the magnetic sensor being adapted to detect the lateral drift and torsion of the continuous flexible member (31).

21. The method according to claim 20, wherein the lateral drift and torsion of the continuous flexible member (31) are detected by a first group (103A) of magnetic sensors and a second group (103B) of magnetic sensors, the first group of magnetic sensors being aligned with each other on a first side of the continuous flexible member (31) and in a direction (D) orthogonal to the advancing direction (f31) of the continuous flexible member (31), and the second group of magnetic sensors being aligned with each other on a second side of the continuous flexible member (31) and in a direction (D) orthogonal to the advancing direction (f31) of the continuous flexible member (31).

22. The method according to claim 21, comprising the following steps: Detecting the passage of the magnet (104A) fixed to the continuous flexible member (31) near the first longitudinal edge (31A) of the continuous flexible member by the first group (103A) of magnetic sensors; and detecting the passage of the magnet (104B) fixed to the continuous flexible member near the second longitudinal edge (31B) of the continuous flexible member by the second group (103B) of magnetic sensors.

23. The method according to claim 21 or 22, comprising the following steps: Detecting the lateral drift of the continuous flexible member (31) based on a signal from any one of the first group (103A) of magnetic sensors and the second group (103B) of magnetic sensors generated by the passage of the respective magnet (104A, 104B) fixed to the continuous flexible member (31); and detecting the torsion of the continuous flexible member (31) based on signals from both the first group (103A) of magnetic sensors and the second group (103B) of magnetic sensors generated by the passage of the magnets fixed near the first and second edges of the continuous flexible member (31).

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