Welding device and method for product packaging machines

Abstract

A welding device (1) for product packaging machines, comprising: a welding tool (3) defining at least one active welding surface (3a); a countertool (4) defining at least one opposing surface (4a), the welding tool (3) and the countertool (4) being movable relative to each other along a movement direction (X) to perform a movement towards and away from each other; an actuator (5) active on the welding tool (3) and / or on the countertool (4) to move the welding tool (3) and the countertool (4) towards and away from each other; a load cell (7) configured to detect the thrust, or at least a variable influenced by the thrust, applied between the welding tool (3) and the countertool (4) during the operation of the device (1), said load cell (7) being disposed between the countertool (4) and a support (6) of the countertool (4); a control unit (U), connected to the load cell (7) to receive from the 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.

Description

[0001] DESCRIPTION

[0002] WELDING DEVICE AND METHOD FOR PRODUCT PACKAGING

[0003] MACHINES

[0004] Field of the art

[0005] 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.

[0006] Background art

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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

[0011] 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, the undesirable effects may also arise in the case of thermal expansion related to sonotrode operation and sliding friction of the materials, which cause an alteration of the gap width between sonotrode tool and countertool.

[0012] Therefore, the Applicant has found that by operating a control based on the thrust applied between the welding tool and the countertool, or on a variable influenced by the thrust (e.g., a deformation), in particular measured by means of a load cell arranged between the countertool and a countertool support, it is possible to adapt the welding process to material thicknesses within a very wide tolerance. Indeed, the control allows early or late reaching of the optimum welding thrust by adapting other welding parameters (e.g., the distance between welding tool and countertool) as a function of the thrust to be obtained, so that the thrust is the reference parameter to be achieved.

[0013] 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). 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 and the countertool are mutually movable along a movement direction to move them towards and away from each other.

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

[0018] 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.

[0019] Alternatively, the load cell is configured to detect a variable influenced by said thrust.

[0020] Preferably, the load cell is placed between the countertool and a countertool support.

[0021] Preferably, the device comprises a control unit connected to the load cell to receive from the load cell a signal identifying the detected thrust or the variable influenced by the thrust.

[0022] Preferably, the control unit is further connected to the actuator to regulate the actuator as a function of said signal.

[0023] The presence of the control unit connected to the load cell and active on the actuator makes it possible to set a target value for the thrust, correcting the mutual positioning between the welding tool and the countertool (thus varying the mutual distance) following variations in the thickness of the material to be welded, in particular when the thickness of the material to be welded has variations over time, e.g., in the case of a sequence of products whose portion to be welded has a thickness with a variability exceeding a predetermined tolerance.

[0024] Therefore, the present invention relates, in its first aspect, to a welding method in product packaging machines.

[0025] The method is performed by means of a device comprising a welding tool and a countertool, in particular arranged facing each other.

[0026] Preferably, at least either the welding tool or the countertool is operationally movable along a movement direction to move the welding tool and the countertool towards and away from each other.

[0027] The method involves preparing a material or aggregate to be welded, which is subjected to welding action by means of said welding tool and countertool.

[0028] According to an aspect of the invention, the method involves regulating the mutual movement of the welding tool and countertool towards and away from each other as a function of the thrust applied between the welding tool and the countertool during welding.

[0029] Alternatively, the method involves regulating the movement of welding tool and the countertool towards and away from each other as a function of at least one variable influenced by the thrust.

[0030] Preferably, the thrust (or the variable influenced thereby) is detected by a sensor applied to the countertool.

[0031] By means of this method, it is possible to regulate the welding by setting the thrust value as a target, either directly or indirectly, so as to obtain a welding having an optimal thrust value. The remaining welding control parameters (e.g., the gap between the welding tool and the countertool) can be determined accordingly so as to adapt the welding process to materials or aggregates having different thicknesses, in particular beyond a predetermined tolerance.

[0032] In at least one of the above aspects, the present invention may also have at least one of the preferred features set forth below.

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

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

[0035] Preferably, the countertool is mounted on the base movably along the movement direction and is kept stationary along said movement direction by means of the load cell, so that a deformation of the load cell under the thrusting action of the welding tool determines a corresponding displacement of the opposing surface () along said movement direction.

[0036] This simplifies the structure of the device and at the same time allows the entire force applied by the sonotrode on the opposing surface to be measured without measuring the effect of further constraints in the direction of the force itself.

[0037] Preferably, the direction of mutual movement between the welding tool and the countertool is straight.

[0038] In this case, the countertool is preferably mounted on the base by means of a linear guide, having extension parallel to the movement direction. In this manner, the guide determines a free movement of the countertool along the movement direction and an interaction, along the movement, so that the thrust is discharged entirely onto the load cell.

[0039] Alternatively, the movement direction could be defined by a rotational or rototranslation movement.

[0040] 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.

[0041] 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.

[0042] Preferably, the control unit is configured to regulate the actuator so as to keep the thrust below a 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.

[0043] In an embodiment, the actuator is active only on the welding tool. In this situation, the countertool is stationary, in particular connected (by interposition of the load cell) to a respective support, which is also stationary and more in particular integral to the base.

[0044] In an alternative embodiment, the actuator is active on the countertool support to move the countertool to and from the welding tool. In this case, the load cell, interposed between the countertool and its support, can thus always detect the thrust applied between the welding tool and the countertool. In a further embodiment, both the welding tool and the countertool are associated with relative actuators which determine respective, preferably independent, movements along the movement direction.

[0045] Preferably, the actuator comprises a rotary servomotor and a screw-and- nut mechanism driven by the servomotor, in which the control unit is connected to the servomotor to regulate the rotation of said servomotor. This allows a precise and reliable actuator movement by means of the rotational control of the servomotor.

[0046] 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.

[0047] The additional sensor may comprise a position transducer, e.g., a linear transducer, applied to the welding tool and / or countertool.

[0048] 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).

[0049] 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. 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.

[0050] 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.

[0051] Preferably, the welding tool is an ultrasonic tool.

[0052] Alternatively, the welding tool is a hot, cold or induction welder.

[0053] However, the invention is applicable to any type of welding tool of the type suitable for cooperating with a countertool.

[0054] 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. Preferably, the working parameter is at least one parameter among amplitude, frequency, voltage, power.

[0055] With reference to the method according to the invention, the sensor in charge of thrust detection is preferably a load cell. This choice allows a reliable and direct thrust detection by means of a configuration which is structurally simple and compact.

[0056] Preferably, the countertool is movable along the base and is kept stationary along the movement direction by means of the load cell, when 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. This simplifies the structure of the device and at the same time allows the entire force applied by the sonotrode on the opposing surface to be measured without measuring the effect of further constraints in the direction of the force itself.

[0057] Preferably, the countertool is movable along the movement direction by means of a preferably horizontal linear guide, the guiding direction of which is parallel to the movement direction. In this situation, during a welding operation, the thrust applied between the welding tool and the countertool has the effect of making the countertool retract along the guide while the weight of the countertool is discharged onto the guide. This minimizes friction, by means of the guide, allowing the load cell to detect only the thrust of the welding tool.

[0058] Preferably, said regulating the movement of the welding tool and countertool towards and away from each other is performed uninterruptedly during the welding of the material or aggregate. 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.

[0059] Preferably, furthermore, said regulating the movement of the welding tool and countertool towards and away from each other is performed so as to keep the thrust under a threshold value. This has the effect of preventing thrusts in excess of the maximum or optimum value from being generated, 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. This results in a welding operation in optimal conditions for the product to be welded and avoiding unwanted overloads on the device which could lead to damage to the device.

[0060] In an embodiment, the welding of the material or aggregate by means of compression applied between the welding tool and the countertool is accomplished by actively moving only the welding tool. In an alternative embodiment, the welding of the material or aggregate by compression applied between the welding tool and the countertool is accomplished by actively moving only the countertool.

[0061] In a further alternative embodiment, the welding of the material or aggregate by compression applied between the welding tool and the countertool is accomplished by actively moving both the welding tool and the countertool.

[0062] Preferably, the welding tool and / or the countertool is / are moved along the movement direction by means of a respective actuator, when said regulating the movement of the welding tool and countertool towards and away from each other is performed by regulating said actuator.

[0063] Preferably, the actuator is a screw-and-nut actuator with rotary servomotor.

[0064] Preferably, said regulating the movement of the welding tool and countertool towards and away from each other is performed by regulating the rotation of the servo motor.

[0065] Preferably, said regulating the movement of the welding tool and countertool towards and away from each other is also performed as a function of a positional parameter of the welding tool relative to the countertool. This makes it possible to perform a regulation as a function of a plurality of control parameters, optimizing the welding process.

[0066] This positional parameter may comprise the position of the active welding and / or opposing surface (direct detection) or the position of a moving portion of the welding and / or countertool (indirect detection).

[0067] Alternatively, said regulating the movement of the welding tool and countertool towards and away from each other is also performed as a function of a variable influencing the position of the welding tool relative to the countertool. For example, this variable is the temperature of the welding tool and / or countertool, the variation of which causes a shift in the respective active welding and / or opposing surface. Preferably, said regulating the movement of the welding tool and countertool towards and away from each other comprises detecting, via an additional sensor, said positional parameter or said variable influencing the position of the welding tool relative to the countertool, and in which regulating the movement of the welding tool and countertool towards and away from each other comprises regulating said actuator, and in particular, said servomotor as a function of said detected positional parameter or said detected variable.

[0068] In an embodiment, said positional parameter or said variable influencing the position of the welding tool relative to the countertool comprises a position of said actuator, in particular the angular position of the servomotor or of the screw of said screw-and-nut mechanism.

[0069] Preferably, said welding is performed by means of an ultrasonic welding tool.

[0070] Preferably, in this solution, the method further comprises detecting at least one working parameter of the ultrasonic welding tool, in particular of a respective ultrasound generator, in which said regulating the movement of the welding tool and countertool towards and away from each other is performed also as a function of said at least one working parameter.

[0071] Preferably, the working parameter comprises at least one parameter among amplitude, frequency, voltage, power.

[0072] Alternatively, said welding is performed by means of a hot, cold or induction welder.

[0073] However, the invention is applicable to any type of welding tool of the type suitable for cooperating with a countertool.

[0074] Brief description of the drawings

[0075] 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.

[0076] In the drawings: - figure 1 is a perspective view of the welding device according to the present invention, with functional control connections highlighted;

[0077] - figure 2 is an enlarged view of a first portion of the device in figure 1 ;

[0078] - figure 3 is an isolated view of second portion of the device in figure 1 ;

[0079] - figure 4 is an isolated view of a third portion of the device in figure 1 .

[0080] With reference to the accompanying figures, a welding device according to the invention is indicated by reference numeral 1 .

[0081] Detailed description of preferred embodiments of the invention

[0082] 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.

[0083] In the illustrated embodiment, the base 2 has a plate-like base portion 2a suitable for mounting to a preferably horizontal resting surface.

[0084] 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.

[0085] 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).

[0086] 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.

[0087] 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.

[0088] 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

[0089] 3 and countertool 4 towards and away from each other.

[0090] The countertool 4 is preferably stationary, i.e., without a respective active movement (subjected to an actuation) along the movement direction "X”.

[0091] 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.

[0092] 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.

[0093] Alternatively, the support 6, while remaining operationally stationary, may be adjustable (off-line) to vary its position along the movement direction "X".

[0094] 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

[0095] 4 is movable along the movement direction "X". 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).

[0096] 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 .

[0097] Preferably, the sensor 7 is a load cell.

[0098] 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.

[0099] 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.

[0100] 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. 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] Preferably, the reference surface 10 is planar and more preferably perpendicular to the movement direction "X".

[0106] 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.

[0107] 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".

[0108] 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 means of preferably rolling (ball recirculation) form or grooved connection. The second linear guide 14 is oriented parallel to the movement direction "X".

[0109] 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. The 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.

[0110] According to a variant embodiment, not shown, the first and second linear guides 12, 14 are mutually separated and / or parallel (offset).

[0111] 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.

[0112] 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. Preferably, the side connecting elements 15a, 15b are in the form of plates and / or arms.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] The variable influenced by the thrust may be, for example, a displacement or a deformation.

[0117] 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.

[0118] 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.

[0119] 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 .

[0120] 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.

[0121] 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.

[0122] 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".

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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).

[0127] In the illustrated embodiment, the welding tool 3 is an ultrasonic tool.

[0128] 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.

[0129] 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. 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".

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] The present invention achieves its intended purposes, overcoming the drawbacks highlighted in the prior art.

[0137] 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 supporting 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) and the countertool (4) being movable relative to each other along a movement direction (X) to perform a movement towards and away from each other;- an actuator (5) active on the welding tool (3) and / or on the countertool (4) to move the welding tool (3) and the countertool (4) towards and away from each other;- a load cell (7) configured to detect the thrust, or at least a variable influenced by the thrust, applied between the welding tool (3) and the countertool (4) during the operation of the device (1 ), said load cell (7) being disposed between the countertool (4) and a support (6) of the countertool (4);- a control unit (U), connected to the load cell (7) to receive from the 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.

2. The device (1 ) according to claim 1 , wherein said load cell (7) is disposed and / or configured to be subjected to a bending action consequent upon said thrust.

3. The device (1 ) according to claim 1 or 2, wherein the countertool (4) is mounted on the base (3) movably along said movement direction (X), preferably via a respective linear guide (14), and is kept stationary along said movement direction (X) by the load cell (7), a deformation of the load cell (7) under the thrusting action of the welding tool (3) causing acorresponding displacement of the opposing surface (4a) along said movement direction (X).

4. The device (1 ) according to any one of the preceding claims, wherein the load cell (7) is configured to perform a continuous detection of the thrust or the variable at least during a welding operation and wherein the control unit (U) is configured to perform a continuous regulation of said actuator (5) at least during a welding operation.

5. The device (1 ) according to any one of the preceding claims, wherein the control unit (U) is configured to regulate the actuator (5) in such a way as to keep said thrust below a threshold value, in particular by moving the welding tool (3) and the countertool (4) away from each other when the thrust value exceeds said threshold value.

6. The device (1 ) according to any one of the preceding claims, wherein said actuator (5) acts only on the welding tool (3).

7. The device (1 ) according to any one of the preceding claims, wherein said actuator (5) comprises a rotary servomotor (5a) and a screw-and-nut mechanism (5b, 5c) driven by said servomotor (5a), said control unit (U) being connected to the servomotor (5a) to regulate the rotation of said servomotor (5a).

8. The device (1 ) according to any one of the preceding claims, further comprising at least one additional sensor configured to detect a positional parameter of the active welding surface (3a) relative to the opposing surface (4a) and / or to the countertool (4) or a variable influencing the position of the active welding surface (3a) relative to the countertool (4), wherein the control unit (U) is also connected to the additional sensor to receive from the additional sensor a supplementary signal identifying thedetected positional parameter or the corresponding detected variable, and configured to regulate the actuator (5) also as a function of said supplementary signal.

9. The device (1 ) according to claim 8, wherein said at least one additional sensor comprises 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 with said screw (5b) of said screw- and-nut mechanism (5b, 5c).

10. The device (1 ) according to claim 8 or 9, wherein said at least one additional sensor comprises a temperature sensor, in particular configured and / or arranged to detect the temperature of a portion of the welding tool (3).11 . The device (1 ) according to any one of claims 8 to 10, wherein said at least one additional sensor comprises a position transducer configured to detect the position of the welding tool (3) along said movement direction (X), preferably the position of the active welding surface (3a).

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

13. The device (1 ) according to any one of the preceding claims, wherein said control unit (U) is also connected to said ultrasonic welding tool (3), in particular to a respective ultrasound 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 between amplitude, frequency, voltage and power, said control unit being also configured to regulate the actuator (5) also as a function of said at least one working signal.

14. A welding method for product packaging machines, in particular carried out using a device (1 ) according to any one of the preceding claims, comprising:- providing a material or an aggregate to be welded;- welding said material or aggregate by compression applied between a welding tool (3) and a countertool (4), wherein at least one between said welding tool (3) and said countertool (4) is operatively movable along a movement direction (X) to move the welding tool (3) and the countertool (4) towards and away from each other;- regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other as a function of the thrust or of at least one variable influenced by the thrust, applied between the welding tool (3) and the countertool (4) during welding and detected by a sensor (7) mounted on the countertool (4).

15. The method according to claim 14, wherein said sensor (7) is a load cell.

16. The method according to claim 15, wherein the countertool (4) is movable along the movement direction (X), preferably via a respective linear guide (14), and is kept stationary along said movement direction (X) by the load cell (7), 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).

17. The method according to any one of claims 14 to 16, wherein regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other is carried out uninterruptedly during welding of the material or aggregate.

18. The method according to any one of claims 14 to 17, wherein regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other is carried out in such a way as to keep said thrust under a threshold value.

19. The method according to any one of claims 14 to 18, wherein welding the material or aggregate by compression applied between the welding tool (3) and the countertool (4) is accomplished by moving only said welding tool (3).

20. The method according to claim 19, wherein the welding tool (3) is moved along said movement direction (X) by a respective actuator (5), in particular a lead screw actuator (5) with a screw-and-nut (5b, 5c) and a rotary servomotor (5a), and wherein regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other is carried out by regulating said actuator (5), in particular by rotating said servomotor (5a).

21. The method according to any one of claims 14 to 20, wherein regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other is carried out also as a function of a positional parameter of the welding tool (3) relative to the countertool (4) or as a function of a variable influencing the position of the welding tool (3) relative to the countertool (4).

22. The method according to claims 20 and 21 , wherein regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other comprises detecting, via an additional sensor, said positional parameter or said variable influencing the position of the welding tool (3) relative to the countertool (4), and wherein regulating the movement of the welding tool (3) and the countertool (4) towards andaway from each other comprises regulating said actuator (5), and in particular, said servomotor (5a) as a function of said detected positional parameter or said detected variable.

23. The method according to claim 22, wherein said positional parameter or said variable influencing the position of the welding tool (3) relative to the countertool (4) comprises a position of said actuator (5), in particular the angular position of the servomotor (5a) or of said screw (5b) of said screw-and-nut mechanism (5b, 5c).

24. The method according to any one of claims 14 to 23, wherein welding is carried out by an ultrasonic welding tool (3).

25. The method according to claim 24, further comprising receiving or detecting at least one working parameter of the ultrasonic welding tool, in particular of a respective ultrasound generator (G), preferably at least one parameter between amplitude, frequency, voltage and power, regulating the movement of the welding tool (3) and the countertool (4) towards and away from each other is carried out also as a function of said at least one working parameter.

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