Welding device for product packaging machines

Abstract

A welding device (1) for product packaging machines, comprising: a base (2); a welding tool (3) mounted on the base (2); a countertool (4), mounted on the base (2), the welding tool (3) being movable towards and away from the countertool (4) along a movement direction (X); an actuator (5) to move the welding tool (3) along said movement direction (X); a support (6) of the countertool (4); a load cell (7) interposed between the countertool (4) and the support (6) of the countertool (4) and configured to detect the thrust, or at least a variable influenced by the thrust, applied by the welding tool (3) on the countertool (4) during operation of the device. The position of the countertool (4) along the movement direction (X) is defined by the position of the support (6) of the countertool (4), so that a deformation of the load cell (7) under the thrusting action of the welding tool (3) causes a corresponding displacement of the countertool (4a) along the movement direction (X).

Description

[0001] WELDING DEVICE FOR PRODUCT PACKAGING MACHINES

[0002] Field of the art

[0003] The present invention relates to the technical field of automatic product packaging machines and it relates, in detail, to a welding device and method for product packaging machines, in particular for the automated welding of product packages, both discrete packages and flow-pack type packages.

[0004] Background art

[0005] In the article packaging industry, it is known to make longitudinal and transverse weldings using conventional systems, e.g., such as hot, cold, or ultrasonic tools.

[0006] In general, the welding is done by mutually approaching a tool and a countertool, where the tool forms an active welding member while the countertool defines a backing anvil during the compression application by the tool.

[0007] During welding, the welding tool is pressed against the countertool for a predetermined time in order to perform a sufficiently stable welding without deteriorating the material.

[0008] In detail, the welding is controlled by acting on several welding parameters, including advancing the welding tool towards the countertool. This advancing is functional in determining the distance between the mutually facing surfaces of the welding tool and countertool. In this manner, a predetermined welding action can be performed by setting the respective stroke of the actuator which moves the welding tool for each welding. Object of the invention

[0009] The Applicant found that this control method is afflicted by errors if the thickness of the material to be welded varies. In this case, an unexpected increase in thickness inevitably leads to an undesirable increase in welding pressure, with adverse effects both on the material that could be damaged and on the welding apparatus due to localized overloads that are often of such magnitude that they can damage structural members. Conversely, an unexpected reduction in material thickness leads to insufficient welding pressure and, therefore, to incomplete and nonconforming weldings. This problem substantially occurs because the position control between the welding tool and the countertool cannot compensate for variability in the thickness of the material to be welded beyond a specific tolerance. Furthermore, those undesirable effects may also arise in the case of thermal expansions related to sonotrode operation and sliding friction of the materials, which cause an alteration in the distance between sonotrode tool and countertool.

[0010] Therefore, the Applicant has found that by monitoring the thrust applied between the welding tool and the countertool, or a corresponding variable influenced by the thrust (e.g., a deformation), measured by means of an appropriate sensor (in particular, a load cell), it is possible to adapt the welding process to material thicknesses within a very wide tolerance. Indeed, this makes it possible to exactly identify the occurrence of undesirable thrust values and provides the opportunity to take appropriate corrective actions.

[0011] Furthermore, the Applicant has found that by arranging the sensor (load cell) between the countertool and a support of the countertool, it is possible to set a desired yielding in the positioning of the countertool, which determines a displacement of the countertool along the movement direction, which is a direct consequence of the force applied by the welding tool. This yielding / displacement can be measured either in terms of direct reading (signal generated by a load cell) or in terms of displacement (e.g., by detecting the change of position taken by a surface of the sensor and / or of the countertool relative to the support of the countertool).

[0012] The present invention, therefore, relates, in its first aspect, to a welding device for product packaging machines. "Product" means a generic item, e.g., but not limited to a bag, a sachet, a generic rigid or floppy packaging or related semi-finished products (e.g., for flow-pack processing).

[0013] The device comprises a base, defining a stationary and supporting part of the device and defining, for example, a component for supporting or anchoring the device on a surface.

[0014] The device further comprises a welding tool mounted on the base and defining at least one active welding surface.

[0015] The device further comprises a countertool mounted on the base and defining at least one opposing surface.

[0016] The welding tool is movable along a movement direction to reciprocally move towards and away with respect to the countertool.

[0017] Preferably, the device comprises an active actuator on the welding tool to move the welding tool and the countertool towards and away from each other.

[0018] Preferably, the device further comprises a support of the countertool, to which the countertool is connected.

[0019] According to an aspect of the invention, the device comprises a load cell configured to detect the thrust applied between the welding tool and the countertool during the operation of the device.

[0020] Alternatively, the load cell is configured to detect a variable influenced by said thrust.

[0021] Preferably, the load cell is arranged between the countertool and the support of the countertool.

[0022] Preferably, the device is configured so that the position of the countertool along the movement direction is defined by the position of support of the countertool, where a deformation of the load cell under the thrusting action of the welding tool determines a corresponding displacement of the opposing surface along the movement direction.

[0023] This displacement of the contrast surface as a result of the thrust applied by the welding tool is a variable directly or indirectly measurable to obtain a reliable indication of the applied thrust.

[0024] In particular, this displacement can be directly measured geometrically (defining a possible "thrust-influenced variable") or it can be measured indirectly, in particular by means of direct detection of the thrust itself by means of the load cell.

[0025] Therefore, the thrust detection can be instantaneous, continuous and extremely accurate and reliable.

[0026] The present invention can also have at least one of the preferred features set forth below.

[0027] Preferably, the support of the countertool is stationary, in particular fixed to the base.

[0028] In an embodiment, the support of the countertool is fixed to the base in a non-adjustable manner. This can be achieved by means of non-adjustable fasteners or by means of non-reversible connection, e.g., by means of weldings or integral construction.

[0029] Alternatively, the support of the countertool is adjustably fixed to the base (e.g., by means of adjustable slots and threaded members), although the support of the countertool remains fixed to the base without the possibility of movement after adjustment.

[0030] In both solutions, the support of the countertool is normally integral to the base and therefore stationary, defining a reliable abutment for detecting the thrust applied by the welding tool.

[0031] Preferably, the support of the countertool comprises a support bracket fixed to the base, in which the load cell has a first end fixed to the support of the countertool, in particular to the bracket, and a second end fixed to the countertool. In this configuration, a thrusting action applied by the welding tool on the countertool translates into a mechanical action applied between the ends of the load cell, which optimally performs its measurable yielding function. Preferably, the support bracket comprises two parallel plates defining therebetween a space in which the first end of the load cell is housed. Preferably, furthermore, the two plates lie flat and parallel to the movement direction. In this configuration, the device is compact and remarkably robust.

[0032] Preferably, the support bracket is mounted at one end of the base, preferably cantilevered. This allows the bracket to be configured as an end element of the base, which is easily controllable and disassemblable.

[0033] Preferably, the load cell is arranged and / or configured to be subjected to a bending action consequent upon said thrust. In this manner, a particularly accurate and responsive solution to small changes in thrust, suitable for small measured force values, is obtained. Furthermore, a similar architecture has a low and suitable natural frequency that does not interfere with the oscillation frequency of the sonotrode and isolates the opposing structure from disturbances induced by the oscillation of the sonotrode.

[0034] Alternatively, the load cell is arranged and / or configured to be subjected to a compressive action consequent to said thrust.

[0035] Alternatively, the load cell is arranged and / or configured to be subjected to a twisting action consequent to said thrust.

[0036] Preferably, the load cell comprises two parallel foils separated by a cavity, the two foils lying perpendicularly to the movement direction and being arranged in succession along the movement direction. This architecture optimizes the deformability of the load cell by increasing measurement accuracy.

[0037] Preferably, the device comprises a first slide on which the welding tool is mounted, and the base comprises a first linear guide on which the first slide is smoothly engaged and oriented parallel to the movement direction. This achieves a precise and reliable movement of the welding tool.

[0038] Preferably, the first guide and the first slide are connected to each other by means of a shape or grooved connection, preferably a rolling connection, in particular by means of ball recirculation.

[0039] Preferably, the device comprises a second slide, on which the countertool is mounted and the base comprises a first linear guide on which the first slide is smoothly engaged and oriented parallel to the movement direction. This achieves a precise and reliable guide of the countertool during its movement consequent to the yielding of the load cell.

[0040] Preferably, the second guide and the second slide are connected to each other by means of a shape or grooved connection, preferably a rolling connection, in particular by means of ball recirculation.

[0041] Preferably, the first and second linear guides are defined by respective portions of a single guide member. This feature allows for greater robustness of the device and better compliance in the movements of the welding tool and the countertool along the movement direction.

[0042] Preferably, the single guide member is made in the form of an elongated rib which protrudes upwards from a top surface of the base.

[0043] Preferably, said guide member is stably applied to the base by means of insertion into a corresponding upper groove of the base, and preferably removably fixed therein (e.g., by means of threaded parts).

[0044] This feature allows the guide member to be replaced quickly and easily.

[0045] According to a different embodiment solution, the first and second linear guides are separated from each other and arranged with preferably coincident or parallel alignment.

[0046] Preferably, the support bracket is connected to the base at a lower level than the second linear guide and the support bracket and / or the load cell extend above the level of the second linear guide allowing the load cell to be connected to the countertool. In this architecture, the support bracket and / or the load cell define a bridge-like structure that connects the lower zone to the second linear guide (base) with the upper zone to it (support of the countertool), making an end structure which is easily controllable or accessible during the step of assembly or repair.

[0047] Preferably, the actuator is mounted on the base and arranged below the first linear guide and is connected to the first slide by means of side connecting elements that are arranged on opposite sides of the base.

[0048] Preferably, these side connecting elements are configured in the form of plates or arms. This configuration allows for a compact structure which can be easily accessed during the step of assembly or repair because the side connecting elements are externally arranged relative to the first linear guide.

[0049] Preferably, the actuator is a screw-and-nut actuator with rotary servomotor. This solution is particularly suitable to be transversely compact with prevalent longitudinal extension, which allows the installation under the first linear guide. Indeed, in the preferred configuration, the base has a substantially elongated shape along the movement direction.

[0050] Preferably, the load cell is connected to the countertool by means of an adapter frame defining a reference front surface on which the load cell is abutted. In particular, the reference surface is planar and more preferably perpendicular to the movement direction. This solution allows for high accuracy in positioning the load cell, whose position along the movement direction can thus be determined with high precision.

[0051] Preferably, the device further comprises a control unit, connected to the load cell to receive from the load cell a signal identifying the detected thrust or variable and also connected to the actuator to regulate the actuator as a function of said signal.

[0052] Preferably, the load cell is configured to perform a continuous or variable detection of the thrust at least during a welding operation. In more detail, it is understood that the load cell is capable of monitoring the time trend of the thrust applied between the welding tool and the countertool, in particular to make a detection which lasts for the time required to apply thrust control on the welding, thus preferably at least during the entire approach movement between the welding tool and the countertool, and not therefore a punctual and isolated detection. This allows a complete and accurate monitoring of the thrust, so that situations in which the thrust may remain above an optimal or maximum value are avoided.

[0053] Preferably, furthermore, the control unit is configured to perform a continuous regulation on the actuator at least during the welding operation. This achieves a continuous control during at least part of the welding operation, so to prevent the generation of thrusts in excess of the maximum or optimum value, in particular by stopping the approach movement between the welding tool and the countertool when the optimum thrust value or a threshold value is reached.

[0054] Preferably, the control unit is configured to regulate the actuator so as to keep the thrust below a maximum threshold value, in particular by moving the welding tool and the countertool away from each other when the thrust value exceeds said threshold value. This allows welding to be performed under optimal conditions for the product to be welded and avoiding unwanted overloads on the device which could lead to damage to the device.

[0055] Preferably, the control unit is further configured to regulate the actuator so as to keep the thrust above a minimum threshold value, in particular by moving the welding tool and the countertool towards each other when the thrust value detected drops under the minimum threshold value. This makes it possible to weld under optimal conditions for the product to be welded and to avoid the formation of nonconforming welds or the formation of zones with insufficient or no welding.

[0056] Preferably, the device further comprises at least one additional sensor configured to detect a positional parameter of the active welding surface relative to the countertool and the control unit is also connected to the additional sensor to receive from the additional sensor a supplementary signal identifying the detected positional parameter or the corresponding detected variable, and configured to regulate the actuator also as a function of said supplementary signal. This makes it possible to perform a regulation as a function of a plurality of control parameters, optimizing the welding process.

[0057] The additional sensor may comprise a position transducer, e.g., a linear transducer, applied to the welding tool and / or countertool.

[0058] The additional sensor may comprise at least a photocell or other optical sensor adapted to detect the spatial position of the active welding and / or opposing surface (direct detection) or of a moving portion of the welding tool and / or countertool (indirect detection).

[0059] According to a different embodiment, the device comprises at least one additional sensor configured to detect a variable influencing the position of the active welding surface with respect to the countertool, i.e., their mutual position. As an example, this sensor may be a temperature sensor, suitable for identifying a temperature change which, due to the thermal expansion of the components, influences the mutual position between the active welding surface and the opposing surface along the movement direction.

[0060] According to an embodiment, the at least one additional sensor comprises an encoder associated with the actuator to detect the instantaneous position of the actuator, which directly influences the instantaneous mutual position between the active welding surface and the opposing surface along the movement direction.

[0061] Preferably, in the case of an actuator with a rotary servomotor and screw- and-nut mechanism, the additional sensor comprises an angular encoder associated with the servomotor or screw of the screw-and-nut mechanism. This allows for a compact and protected structure of the measuring devices.

[0062] Preferably, the welding tool is an ultrasonic tool.

[0063] Alternatively, the welding tool is a hot, cold or induction welder.

[0064] However, the invention is applicable to any type of welding tool of the type suitable for cooperating with a countertool. Preferably, in the case of ultrasonic solution, the control unit is further connected to the ultrasonic tool, in particular to a respective ultrasonic generator, to receive at least one working signal identifying at least one respective working parameter of the ultrasonic tool and configured to regulate the actuator also as a function of said at least one working signal.

[0065] Preferably, the working parameter is at least one parameter among amplitude, frequency, voltage, power.

[0066] Brief description of the drawings Further features and advantages of the present invention will be more apparent from the following detailed description of preferred embodiments thereof, made with reference to the accompanying drawings.

[0067] In the drawings:

[0068] - figure 1 is a perspective view of the welding device according to the present invention, with functional control connections highlighted;

[0069] - figure 2 is an enlarged view of a first portion of the device in figure 1 ;

[0070] - figure 3 is an isolated view of second portion of the device in figure 1 ;

[0071] - figure 4 is an isolated view of a third portion of the device in figure 1 .

[0072] With reference to the accompanying figures, a welding device according to the invention is indicated by reference numeral 1 . Detailed description of preferred embodiments of the invention

[0073] The welding device 1 comprises a supporting base 2, preferably stationary, e.g., fixed or mounted on a supporting surface or structure, e.g., fixed.

[0074] In the illustrated embodiment, the base 2 has a plate-like base portion 2a suitable for mounting to a preferably horizontal resting surface.

[0075] Furthermore, the device 1 comprises a welding tool 3 and a countertool 4, which are mounted on the base 2. The welding tool 3 defines at least one active welding surface 3a while the countertool 4 defines at least one opposing surface 4a. The wording "at least one welding surface" means that the welding tool 3 may have a single continuous welding surface 3a or a plurality of separate and coplanar or non-coplanar welding surfaces, which may operate simultaneously or may define successive welding actions which are mutually distinct and consecutive. The same applies to the at least one opposing surface 4a of the countertool 4.

[0076] In the illustrated embodiment, the welding tool 3 has two active welding surfaces 3a each having a prevalent extension direction where the prevalent extension directions are parallel to each other so that a recess 3b is defined between the two active welding surfaces 3a. The two active welding surfaces 3a may be structurally identical, e.g., to make weldings which are mutually identical (in which case recess 3b may serve to receive the blade of a cutting tool during a cutting action) or they may be structurally different, e.g., have different surface structures and / or shapes, to make weldings of mutually different types (e.g., a cosmetic welding and a hermetic welding).

[0077] The at least one active welding surface 3a and the at least one opposing surface 4a either face or can face each other to compress a material or aggregate interposed between them during a welding operation.

[0078] The opposing surface 4a is stationary or, alternatively, it can be an idle or motorized rolling surface (e.g., a caster or roll) that is dragged by the material or motorized around its own axis.

[0079] The welding tool 3 is movable from and to the countertool 4 along a movement direction "X". For this purpose, the device 1 comprises an actuator 5 which is active on the welding tool 3 to move the welding tool 3 along the movement direction "X" defining a movement of the welding tool 3 and countertool 4 towards and away from each other.

[0080] The countertool 4 is preferably stationary, i.e., without a respective active movement (subjected to an actuation) along the movement direction "X”.

[0081] The device 1 further comprises a support 6 of the countertool 4, intended to define an abutment portion against which the countertool 4 is positioned. In other words, the position of the countertool 4 along the movement direction "X” is defined by the position of the support 6 of the countertool 4, to which the countertool 4 is connected.

[0082] In the illustrated embodiment, the support 6 of the countertool 4 is stationary, in particular fixed to the base 2. Preferably, the support of the countertool 4 is fixed to the base 2 in a non-adjustable manner.

[0083] Alternatively, the support 6, while remaining operationally stationary, may be adjustable (off-line) to vary its position along the movement direction "X".

[0084] In other embodiments, not shown, the support 6 of the countertool 4 can be (either in addition to or as an alternative to moving the welding tool 3 along the movement direction "X") movable along the movement direction "X" by means of a respective actuator so that, as a result, the countertool 4 is movable along the movement direction "X".

[0085] According to a variant embodiment, the welding tool 3 and the countertool 4 (in particular, the support 6 of the countertool 4) can be moved by means of a single actuator, preferably by means of a mechanical transmission acting simultaneously on both (e.g., by meshing).

[0086] According to an aspect of the invention, the device 1 further comprises a sensor 7 interposed between the countertool 4 and the support 6 of the countertool 4 and configured to detect the thrust, or at least a variable influenced by the thrust, applied by the welding tool 3 onto the countertool 4 during operation of the device 1 .

[0087] Preferably, the sensor 7 is a load cell.

[0088] The countertool 4 is connected to the respective support 6 by means of the load cell 7, and preferably exclusively by means of the load cell 7, so that the position of the countertool 4 along the movement direction "X" is defined by the position of the support 6 of the countertool 4, while a deformation of the load cell 7 under the thrusting action of the welding tool 3 determines a corresponding displacement of the countertool 4, thus of the opposing surface 4b, along the movement direction "X". In this context, in the scope of the present invention, "countertool 4" is identifiable with the part of the device 1 defining the at least one opposing surface 4a and which is provided with movement along the movement direction "X" as a result of a deformation of the load cell 7. In other words, the countertool 4 can be identified as the portion of device 1 which extends between the at least one opposing surface 4a and the load cell 7.

[0089] In the illustrated embodiment (figure 2), the support 6 of the countertool 4 comprises a support bracket 8 fixed to the base 2, in which the load cell 7 has a first -lower- end fixed to the support 6 of the countertool 4, in particular to the bracket 8, and a second -upper- end fixed to the countertool 4.

[0090] Preferably, the bracket 8 comprises two mutually parallel plates 8a defining therebetween a space in which the first end of the load cell 7 is housed.

[0091] In greater detail, the two plates 8a are connected to each other by means of a connecting plate 8b that partially delimits the space so that the first end of the load cell 7 is inserted into the space and preferably connected to the connecting plate 8b, e.g., by one or more threaded members 8c.

[0092] The plates 8a are fixed at one end to base 2, in particular to one end of the base 2 (preferably to a vertical wall of the base 2) and, at another preferably opposite end, to the aforementioned connecting plate 8b. In this manner, a configuration can be achieved in which the support 6 is mounted at one end of the base 2, in particular cantilevered.

[0093] In the illustrated embodiment, the load cell 7 is shaped and arranged to operate under bending. In particular, the load cell 7 is oriented so as to lie along a vertical direction and configured to receive a thrust in a horizontal direction on its second upper end, so that a bending load is formed on the load cell 7 due to the fact that the first -lower- end of the load cell 7 is fixed to the support 6.

[0094] In more detail, the load cell 7 has a central portion comprised between the aforementioned two ends and comprising two portions or foils 7a, preferably parallel to each other, separated by a cavity 7b. Preferably, the two portions or foils 7a lie perpendicular to the movement direction "X" and / or are arranged in succession along the movement direction "X". In this manner, the thrusting action along the movement direction "X" combined with the increased yielding of the central portion of the load cell 7, presenting the cavity 7b, operates a controlled and measurable bending of the load cell 7.

[0095] Preferably, the load cell 7 is connected to the countertool 4 by means of an adapter frame 9 defining a reference surface 10 on which the load cell 7 is abutted.

[0096] Preferably, the reference surface 10 is planar and more preferably perpendicular to the movement direction "X".

[0097] Preferably, the adapter frame 9 has a hollow or lattice conformation, in particular, it is equipped with a face plate 9a defining the aforesaid reference surface 10 and a plurality of arms 9b parallel to the movement direction "X" and such to fix the face plate 9a to the countertool 4 at a predetermined distance from the countertool 4.

[0098] The device 1 further comprises (figure 3) a first slide 11 on which the welding tool 3 is mounted, slidingly engaged on a first linear guide 12 applied to the base 2, in particular by means of preferably rolling (ball recirculation) form or grooved connection. The first linear guide 12 is oriented parallel to the movement direction "X".

[0099] Similarly, the device 1 further comprises a second slide 13 on which the countertool 4 is mounted, slidingly engaged on a second linear guide 14 applied to the base 2, in particular by form-fit or splined connection, preferably of the rolling type (ball recirculation). The second linear guide 14 is oriented parallel to the movement direction "X".

[0100] Preferably, the first and second linear guides 12, 14 are defined by respective portions of a single guide member "C", preferably defining an elongated rib which protrudes upwards from a top surface 2a of the base 2. This guide member "C" is preferably removably applied to the base 2, in particular by inserting a base portion of the guide member "C" into a corresponding groove made in the base 2.

[0101] According to a variant embodiment, not shown, the first and second linear guides 12, 14 are mutually separated and / or parallel (offset).

[0102] Furthermore, as shown in figure 2, the support bracket 8 is connected to the base 2 at a level below the second linear guide 14. Furthermore, the support bracket 8 and / or the load cell 7 extend above the level of the second linear guide 14 allowing the load cell 7 to be connected to the countertool 4, which is instead arranged at a level above the second linear guide 14.

[0103] Preferably, in the device 1 , the actuator 5 is mounted on the base 2 and arranged below the first linear guide 12 and is connected to the first slide 12 by means of side connecting elements 15a, 15b which are arranged on opposite sides of the base 2.

[0104] Preferably, the side connecting elements 15a, 15b are in the form of plates and / or arms.

[0105] In more detail (figures 3 and 4), the connecting elements 15a, 15b have first connecting elements 15a (in the form of arms) oriented substantially parallel to the movement direction "X" and connected to the actuator 5, and second connecting elements 15b in the form of parallel plates arranged to connect the first connecting elements 15a and the first slide 12.

[0106] Preferably, the actuator 5 is a screw-and-nut actuator with rotary servomotor 5a. The actuator 5, arranged with its rotation axis parallel to the movement direction "X", switches the rotational movement of a screw 5b into a translation of a nut 5c, preferably connected directly to the aforementioned connecting elements 15a, 15b, in particular to the first connecting elements 15a.

[0107] According to the invention, the device 1 further comprises a control unit "U", connected to the sensor -load cell- to receive a signal identifying the detected thrust or variable and also connected to the actuator 5 to regulate the actuator 5 as a function of the received signal. The variable influenced by the thrust may be, for example, a displacement or a deformation.

[0108] The load cell 7 is configured to perform a continuous or variable detection of the thrust at least during a welding operation. In particular, it is configured to output a continuous signal (or a signal at a predetermined frequency) for at least the time required for the welding operation.

[0109] Similarly, the control unit "U" is configured to perform a continuous adjustment on the actuator 5 at least for the time required for the welding operation.

[0110] In this manner, it is possible to continue regulating the actuator 5 during the course of the welding operation (reciprocal approaching between welding tool 3 and countertool 4 and / or step of holding the compression of the material or aggregate therebetween), managing the mechanical strains on the material or aggregate and also on the device 1 .

[0111] The control unit "U" is configured to regulate the actuator 5 so as to keep the thrust below a threshold value, in particular by interrupting the mutual advancement between the welding tool 3 and the countertool 4 and / or performing a mutual distancing between the welding tool 3 and the countertool 4 when the detected thrust value exceeds the threshold value. Preferably, the control unit “U” is further configured to regulate the actuator 5 so as to keep the thrust above a minimum threshold value, in particular by moving the welding tool 3 and the countertool 4 away from each other when the thrust value drops under the minimum threshold value.

[0112] Preferably, the control unit "U" is connected to the rotary servomotor 5a for regulating the rotation of the servomotor 5a. This allows the advancement of the welding tool 3 to be regulated accordingly by stopping it when a thrust equal to the threshold value is reached, thus controlling the welding as a function of the thrust and not of the geometry (breadth) of the gap between welding tool 3 and countertool 4.

[0113] According to an aspect of the invention, the device 1 further comprises at least one additional sensor configured to detect a positional parameter of the active welding surface 3a with respect to the opposing surface 4a and / or with respect to the countertool 4, in particular the position of a portion of the active welding surface 3a along the movement direction "X". In this case, the additional sensor comprises a position transducer configured to detect the position of the welding tool 3 along the movement direction "X", preferably to directly detect the position of the active welding surface 3 along the movement direction "X".

[0114] Alternatively, the device 1 further comprises at least one additional sensor configured to detect a variable influencing the position of the active welding surface 3a relative to the opposing surface 4a and / or relative to the countertool 4.

[0115] In this situation, the control unit "U" is also connected to the additional sensor to receive from the additional sensor a supplementary signal identifying the detected positional parameter or the corresponding detected variable and configured to regulate the actuator 5 (in particular, the servomotor 5a) also as a function of the supplementary signal.

[0116] Examples of variables influencing the position of the active welding surface 3a are: the position (angular / linear) of the actuator; the temperature of the welding tool 3; the deformation of the load cell; the position of a load cell surface; the temperature of the material to be welded, measured near the welding; generator parameters (power, amplitude); position of the opposing surface 4a and / or the active welding surface 3a.

[0117] In this case, the at least one additional sensor comprises one or more of: an encoder associated with the actuator 5 to detect the instantaneous position of the actuator 5, in particular an angular encoder associated with the servomotor 5a or the screw 5b of the screw-and-nut mechanism; a temperature sensor, in particular configured and / or arranged to detect the temperature of a portion of the welding tool 3 or the material to be welded, in a zone close to the welding; an active displacement sensor on a surface of the load cell; an active displacement sensor on the opposing surface 4a and / or the active welding surface 3a; a sensor of operating parameters of the welding tool (amplitude / power of the ultrasonic generator).

[0118] In the illustrated embodiment, the welding tool 3 is an ultrasonic tool.

[0119] In an embodiment of the invention, the control unit "U" can also be connected to the ultrasonic welding tool 3, in particular to a respective ultrasonic generator "G", to receive at least one working signal identifying at least one respective working parameter of the ultrasonic welding tool 3, in particular at least one parameter among amplitude, frequency, voltage, power. In this situation, the control unit "U" is also configured to regulate the actuator 5 also as a function of the at least one received work signal.

[0120] By virtue of this regulation, it is also possible to perform a regulation of the welding which takes into account the operating mode of the ultrasonic generator.

[0121] In an embodiment of the invention, the control unit "U" is also connected to the ultrasonic generator "G" to regulate the generator "G" according to the thrust identification signal or detected variable. In this manner, it is possible to perform a regulation of the welding process as a function of the detected thrust, in particular by acting on the ultrasonic generator "G" in order to perform a regulation of the positioning of the active welding surface 3a along the movement direction "X".

[0122] In more detail, the control unit "U" is configured to vary the amplitude and / or power of oscillation of the generator "G", in particular to reduce the oscillation amplitude and / or power, as a function of the thrust identification signal or detected variable and, specifically, when the detected thrust value exceeds a threshold value, or to increase the oscillation amplitude and / or power as a function of the thrust identification signal or detected variable and, specifically, when the detected thrust value falls below the minimum threshold value.

[0123] Preferably, the control unit comprises a decision routine configured to determine, as a function of the thrust value detected by the sensor -load cell- 7 or the detected variable influencing thrust, whether to regulate the generator "G", the actuator 5 or both. Indeed, it turns out that if the thrust were to reach the threshold value, the control unit "U" could intervene to reduce this thrust by retracting the welding tool 3 and / or the countertool 4 (by acting on the actuator 5) or by reducing the oscillation amplitude or power (by acting on the generator "G"). However, there may be cases in which one of the two actions is not feasible or less convenient, e.g., if one of the two actions may lead to a worsening of the welding quality, e.g., by making the device 1 work in conditions outside the ideal range. In this case, the decision routine implemented in the control unit "U" provides the optimal choice in order to maximize the final product quality while safeguarding the structural integrity of the device at the same time.

[0124] In use, a material or aggregate to be welded is prepared and interposed between the welding tool 3 and the countertool 4. This is common to both discrete component weldings (bags, sachets or the like) and weldings in flow-pack contexts.

[0125] Successively, the welding tool 3 and the countertool 4 are moved towards each other to compress the material or aggregate between the welding tool 3 and the countertool 4.

[0126] During the entire compression, and preferably also during the approach movement between the welding tool 3 and the countertool 4, the thrust, or at least a variable influenced by the thrust applied between the welding tool 3 and the countertool 4 during welding () is detected by means of a sensor -load cell- 7 and, consequently, the reciprocal approach movement between welding tool 3 and countertool 4 is regulated in real time according to this detected thrust or variable. In particular, when compression causes the thrust to exceed a threshold value, the welding tool 3 and the countertool 4 are moved away in order to reduce the thrust until the detected thrust or variable returns to a value below the threshold value.

[0127] After the expiration of a time required for the completion of welding, the welding tool 3 and the countertool 4 are moved away from each other and the welded material or aggregate is removed.

[0128] The present invention achieves its intended purposes, overcoming the drawbacks highlighted in the prior art.

[0129] The welding control based on the force (thrust) applied during the welding compression allows the process to be adapted to different thicknesses of the material or aggregate to be welded, eliminating the risks that unexpected and undesirable variations in the material could lead to nonconforming weldings or damage to the material itself or the device.

Claims

CLAIMS1 . A welding device (1 ) for product packaging machines, comprising:- a base (2);- a welding tool (3) mounted on the base (2) and defining at least one active welding surface (3a);- a countertool (4), mounted on the base (2) and defining at least one opposing surface (4a), the welding tool (3) being movable towards and away from the countertool (4) along a movement direction (X);- an actuator (5) active on the welding tool (3) to move the welding tool (3) along said movement direction (X) to define a movement of the welding tool (3) towards and away from the countertool (4);- a support (6) of the countertool (4);- a load cell (7), interposed between the countertool (4) and the support (6) of the countertool (4) and configured to detect the thrust, or at least a variable influenced by the thrust, applied by the welding tool (3) on the countertool (4) during the operation of the device; and wherein the position of the countertool (4) along said movement direction (X) is defined by the position of the support (6) of the countertool (4), a deformation of the load cell (7) under the thrusting action of the welding tool (3) causing a corresponding displacement of the opposing surface (4a) along said movement direction (X).

2. The device according to claim 1 , wherein the support (6) of the countertool (4) is stationary, being in particular fixed to the base (2).

3. The device according to claim 1 or 2, wherein the support (6) of the countertool (4) is fixed to the base (2) nonadjustably.

4. The device according to any one of the preceding claims, wherein the support (6) of the countertool (4) comprises a mounting bracket (8) fixed to the base (2), the load cell (7) having a first end which is fixed to thesupport (6) of the countertool (4), in particular, to the bracket (8), and a second end which is fixed to the countertool (4).

5. The device according to claim 4, wherein the mounting bracket (8) comprises two parallel plates (8a) defining between them a space which houses said first end of the load cell (7).

6. The device according to claim 4 or 5, wherein the mounting bracket (8) is mounted, preferably cantilevered, to one end of the base (2).

7. The device according to any one of the preceding claims, wherein the load cell (7) is structured and disposed to operate by bending.

8. The device according to claim 7, wherein the load cell (7) comprises two parallel foils (7a) separated by a cavity (7b), the two foils (7a) lying perpendicularly to the movement direction (X) and being disposed in succession along said movement direction (X).

9. The device according to any one of the preceding claims, comprising a first slide (11 ) on which the welding tool (3) is mounted and wherein said base (2) comprises a first linear guide (12) on which the first slide (11 ) is slidably engaged and which is oriented parallel to said movement direction (X), in particular, said first linear guide (12) and said first slide (11 ) being connected to each other by a shape or grooved connection, preferably roll grooved.

10. The device according to claim 9, comprising a second slide (13) on which the countertool (4) is mounted and wherein said base (2) comprises a second linear guide (14) on which the second slide (13) is slidably engaged and which is oriented parallel to said movement direction (X), in particular, said second linear guide (14) and said second slide (13) beingconnected to each other by a shape or grooved connection, preferably roll grooved.

11. The device according to claim 10, wherein said first and second linear guides (12, 14) are defined by respective portions of a single guide member (C), preferably defining an elongated rib which protrudes upwards from a top surface (2a) of the base (2).

12. The device according to claims 4 and 10, wherein the mounting bracket (8) is connected to the base (2) at a level below the second linear guide (14) and wherein the mounting bracket (8) and / or the load cell (7) extend above the level of the second linear guide (14), allowing the load cell (7) to be connected to the countertool (4).

13. The device according to any one of claims 9 to 13, wherein the actuator (5) is mounted on the base (2) and disposed under the first linear guide (12) and is connected to the first slide (11 ) by lateral connecting elements (15a, 15b), preferably in the form of plates or arms, which are disposed on opposite sides of the base (2).

14. The device according to any one of the preceding claims, wherein the actuator (5) is a screw-and-nut actuator (5b) with a rotary servomotor (5a).

15. The device according to any one of the preceding claims, wherein the load cell (7) is connected to the countertool (4) by an adapter frame (9) defining a reference surface (10) abutted against the load cell (7), in particular, said reference surface (10) being planar and preferably perpendicular to the movement direction (X).

16. The device according to any one of the preceding claims, further comprising a control unit (U), connected to the load cell (7) to receive fromthe load cell (7) a signal identifying the detected thrust or variable and also connected to the actuator (5) to regulate the actuator (5) as a function of said signal.

17. The device (1 ) according to any one of the preceding claims, wherein the welding tool (3) is an ultrasonic welding tool.

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