Method and equipment for ultrasonic sealing of a continuous sheet

Abstract

Method for ultrasonic sealing, wherein a sonotrode and an anvil are operated to seal two edges of sheet arranged therebetween, said method comprising the steps of feeding a continuous sheet (S) along a packaging direction (D1); superimposing two longitudinal edges (S1, S2) of said continuous sheet (S) placing them facing each other between a sonotrode (2) and an anvil (3); dragging said continuous sheet (S) by means of dragging means (6, 7) so as to obtain the advancement of said continuous sheet (S) along a packaging direction (D1) during sealing; activating the sonotrode (2) by making it vibrate at a predetermined sealing amplitude and frequency; arranging the sonotrode (2) and the anvil (3) reciprocally in a sealing position (WP); applying a reciprocal sealing force (RF) between said sonotrode (2) and said anvil (3) to seal the two longitudinal edges (S1, S2) facing each other to form a sealed fin (SP); and interrupting the sealing by removing the application of the sealing force (RF) between said sonotrode (2) and said anvil (3), wherein during the step of interrupting the sealing, the sonotrode (2) is maintained active while simultaneously leaving said sonotrode (2) and said anvil (3) in said sealing position (WP), whereby the vibration of said sonotrode (2) generates a thrust against the anvil (3) substantially equal to the amplitude of the vibration of the sonotrode (2).

Description

[0001] METHOD AND EQUIPMENT FOR ULTRASONIC SEALING OF A CONTINUOUS SHEET

[0002] The present invention falls within the technical sector relating to ultrasonic sealing, in particular it is directed to an ultrasonic sealing method and equipment.

[0003] In the current state of the art, ultrasonic sealing methods and equipment comprising a sonotrode and an anvil are well-known, wherein the sonotrode and the anvil are simultaneously operated to seal portions of sheet metal placed between them.

[0004] Ultrasonic sealing applications can be of the rotary type, wherein the sonotrode and the anvil rotate around their respective rotation axes and the peripheral speed of the rotating sonotrode and anvil is equal to the linear speed of the fed sheet, as there is no sliding between the sheet and the rotating elements. This type of application is particularly advantageous when a continuous longitudinal seal is to be made on a sheet. Alternatively, there are ultrasonic sealing applications of the translating type, in which the sonotrode and the anvil are mutually moved towards and away from the sheet to perform the sealing operation.

[0005] The sheet portions to be sealed together are typically thin films. These sheet portions are typically made of polymeric materials, such as plastics, as well as paper with layers which are compatible with ultrasonic sealing. Ultrasonic sealing is also compatible with metallic materials and multilayer films containing both polymeric and metallic materials. A typical application of this type is the sealing of packaging films in product packaging applications, such as food, in horizontal or vertical packaging equipment.

[0006] Ultrasonic sealing typically involves several stages. First, in the preliminary stage, a continuous sheet is fed to be sealed along a packaging direction. During the feeding of the sheet, depending on the individual application, it is possible to wrap or fold the sheet around products to be packaged, orienting the longitudinal edges of the continuous sheet along the packaging direction. In a subsequent step, the longitudinal edges to be sealed are positioned in correspondence with the sonotrode and the anvil. In particular, this step consists of overlapping longitudinal flaps of the longitudinal edges of the sheet, arranging them counter-facing between the sonotrode and the anvil.

[0007] Furthermore, in order to seal correctly, it is necessary to complete a preparatory step of arranging the sonotrode and the anvil at a mutual sealing distance, aimed at eliminating the distance between the two edges of the sheet to be sealed, between a first edge of the sheet and the sonotrode and between the second edge of the sheet and the anvil. This mutual distance is normally managed by a reciprocal constraint device, which allows the sonotrode and the anvil to be brought closer by applying an external force for the closure or mutual approach of the sonotrode and the anvil. Consequently, the reciprocal constraint device is typically configured to reach a closing position wherein the distance between the sonotrode and the anvil is such as to hit the interposed counter-facing edges, putting them in mutual contact with each other and further causing compression of the same, a necessary condition for their mutual sealing. In other words, in the presence of flaps interposed between the sonotrode and the anvil, the constraint device exerts pressure on the flaps in the closed position.

[0008] In fact, in ultrasonic sealing devices with a constraint device, the mutual distance between the sonotrode and the anvil can vary from an open position, wherein the mutual distance is maximum and such as to allow the preparation of the counterfacing edges to be sealed between the sonotrode and the anvil, and a closed position for sealing, wherein the mutual distance between the sonotrode and the anvil is minimum and such as to guarantee the ultrasonic sealing thanks to the amplitude caused by the sum of displacements due to the applied forces. The applied forces are essentially two; on the one hand the vibrational force which is caused by the vibrating sonotrode, and operates in its radial direction with respect to the sonotrode, and on the other the external force for the closing or mutual approach of the sonotrode and the anvil, operating in a direction orthogonal to advancement of the film to be sealed. The sum of these forces is mechanically transmitted to the counter-facing edges, which absorb a sealing energy aimed at plastically deforming the film so as to mutually fix the closely spaced edges. The constraint device for the mutual approach / distance between sonotrode and anvil can be of the linear actuator type. In fact, in the absence of other applied forces, the sole application of force by the linear actuator acts by varying the mutual distance of the elements between the open position and the closed position for sealing.

[0009] Advantageously, once the flaps have been arranged counter-faced, the devices available in the prior art are controlled to position the sonotrode and anvil in the sealing position, and consequently the ultrasonic sealing step can be started. At this point, the ultrasonic sealing devices operate while the sheet advance with the counter-faced flaps facing each other, the sonotrode vibrates at a predetermined amplitude and frequency to interact with the anvil, to seal the flaps together, thanks to the radial excursion of the ultrasonic vibration of the sonotrode. The radial direction is understood to be the direction perpendicular to that of advancement of the sheet during sealing. In the case of rotating sealing devices, the sonotrode and anvil rotate around respective rotation axes at the sealing distance.

[0010] In order to ensure a stable seal, it is usual to keep the pressure exerted on the edges fixed due to the external force applied for the mutual closure between the sonotrode and the anvil during the sealing step. To this end, it is possible to use a controller that controls, following the monitoring of the actual pressure applied on the edges, the constraint device, typically of the above-mentioned linear actuator type, to apply a reciprocal force between the sonotrode and the anvil so as to keep the reciprocal force applied by the constraint device to the sonotrode and the anvil stable, and consequently the pressure exerted on the edges for their sealing. This type of configuration is particularly advantageous because it allows the use of a single controller for all the elements involved in the ultrasonic sealing method, such as the power source to vibrate the sonotrode with the appropriate amplitude and frequency, the constraint device and the dragging means to advance the sheet whose edges are sealed. If the sealing device is of the rotating type, the controller is also responsible for the means to rotate the sonotrode and anvil. The sealing can be requested to be interrupted for various reasons, including an external command from a user, either due to the lack of product to be packaged or due to automatic detection by a controller, such as the interruption of the feeding of the film, which require an immediate interruption of the sealing. If an interruption of the sealing occurs, the state of the art provides the switching off of the sealing device, which entails stopping the vibration of the sonotrode and the separation of the sonotrode from the anvil. In particular, the switching off of the sealing device comprises the switching off of the vibratory source of the sonotrode. Usually, the switching off the means which advance the sheet occurs simultaneous with the switching off of the sealing device. Moreover, typically the distance between the sonotrode and anvil is increased by acting on the constraint device, until reaching an open position.

[0011] For example, document WO2016 / 160752 teaches an ultrasonic sealing apparatus with a rotating sonotrode and anvil and a linear actuator for moving them closer to / farther away from each other. This apparatus is configured to control the actuator so as to block the mutual distance between the sonotrode and the anvil while sealing takes place, or in any case while the sonotrode is controlled to vibrate towards the anvil, and is controlled to allow the reciprocal movement in distance / approach between the sonotrode and the anvil when the sonotrode has been turned off, and therefore the sealing operation has been suspended. In fact, document WO2016 / 160752 teaches, after a shutdown, to bring the sonotrode and the anvil back to an open position, so as to allow the appropriate maintenance operations.

[0012] With the configuration just described, a quick verification operation in the machine implies that, following a positive response to this verification, the sealing method must comprise a reciprocal reapproach operation between sonotrode and anvil. In some cases, this reapproach operation, as well as the initial approach prior to sealing, is controlled in feedback to calibrate the actual reciprocal distance between sonotrode and anvil. This calibration is due to the fact that, in the absence of a correct reciprocal distance in the sealing position, the quality of the sealing itself may be poor and consequently part of the production may be discarded with consequent material losses and plant productivity. These reapproach operations, with possible calibration of the position, of the sealing device require time and consequently have repercussions on the productivity of the plant.

[0013] In summary, quick shutdown / restart operations for timely checks are more common than long downtimes such as those due to scheduled maintenance, format changes or failures in the sealing equipment. Unfortunately, the ultrasonic sealing methods of the state of the art are unable to guarantee a quick restart following a timely check of the sealing method, and if the restart of the dragging of the sheet to be sealed occurs at the same time as the activation of the sonotrode, the quality of the sealing may not satisfy the required parameters, such as when hermetic seal is required. A lack of quality detected in the sealing would result in the consequent rejection of the package or packages until acceptable sealing conditions are restored.

[0014] There is therefore a need to improve an ultrasonic sealing method that can overcome the drawbacks of the prior art. To do this, it is necessary to solve the technical problem of creating an ultrasonic sealing method that is effective, fast and efficient in its operation, with particular reference to the restart phase.

[0015] The main aim of this invention is to solve the above problems by proposing an ultrasonic sealing method that allows for a timely restart after a brief interruption of the sealing and dragging steps.

[0016] Within the aim of this task, an aim of the invention is to propose an ultrasonic sealing method that does not require long reciprocal approach paths of the sonotrode and anvil and related recalibrations after timely sealing interruptions, and consequently a shortening of the related restart times.

[0017] Another aim of the present invention is to provide an ultrasonic sealing method that does not require long times to reach the required vibration amplitude of the sonotrode.

[0018] Another aim of the invention is to propose a method that guarantees high productivity of the plant in which it is applied thanks to the drastic reduction of waste product due to the restart procedure. Another aim of the invention is to propose an ultrasonic sealing method that, after a quick restart, guarantees the quality of the sealing thanks to a rapid restart of the sealing parameters.

[0019] A further aim of the present invention is to guarantee hermeticity from the very first moment in which the sealing restarts following a brief interruption, eliminating packaging waste.

[0020] These aims are achieved by a sealing method according to claim 1 . These aims are also achieved by means of an ultrasonic sealing apparatus according to claim 9.

[0021] Further features and advantages of the invention will become more evident in light of the detailed description of a preferred but non-exclusive embodiment of an ultrasonic sealing method and apparatus according to the invention, illustrated by way of a non-limiting example with the aid of the attached drawing tables in which:

[0022] - Fig. 1 represents, in a schematic top view, an ultrasonic sealing apparatus according to the present invention;

[0023] - Fig. 2 represents, in isometric view, an ultrasonic sealing device of the ultrasonic sealing apparatus of Fig.1 ;

[0024] - Fig. 3 shows a top view of the ultrasonic sealing device of the present invention;

[0025] - Fig. 4 represents the ultrasonic sealing device in an open position OP, with a force application device shown in cut view relative to the linear travel relative to the open position OP;

[0026] - Fig. 5 represents the ultrasonic sealing device in a sealing position WP, with the force application device shown in cut view relative to the linear travel relative to the sealing position WP;

[0027] - Fig. 6 represents a control diagram relating controller of the apparatus with respect to the controlled elements thereof;

[0028] - Fig. 7 represents a cut view taken along the line VII-VII of Fig. 1 of the sealing apparatus before the edges S1 , S2 are sealed together; - Fig. 8 represents a cut view taken along the line VIII-VIII of Fig. 1 of the sealing apparatus after sealing has taken place;

[0029] - Figs. 9A, 9B, 9C, 9D, 9E, 9F represent different steps of the ultrasonic sealing method provided by the present invention;

[0030] - Fig. 10 represents a graph of the reciprocal force applied to the force application device and the mutual distance between sonotrode and anvil during steps of the ultrasonic sealing method according to the invention.

[0031] It is specified that in the description the phraseology and terminology used, as well as the figures of the attached drawings, even as described, have the sole function of illustrating and explaining the present invention better, having a nonlimiting exemplifying function of the invention itself, the scope of protection being defined by the claims.

[0032] For ease of understanding, identical reference numerals have been used, where possible, to identify identical common elements in the figures. It should be understood that elements and features of one embodiment may be conveniently combined or incorporated into other embodiments without further specification.

[0033] With reference to fig. 1 , the ultrasonic sealing apparatus 10 comprises

[0034] - a sealing device 1 comprising o a sonotrode 2 and an anvil 3 configured to be operated to seal together two longitudinal edges S1 , S2 of a continuous sheet S arranged therebetween, and o a force application device 4 configured to apply a sealing force RF between the sonotrode 2 and the anvil 3 to seal the two longitudinal edges S1 , S2 forming a sealed fin SP; wherein the sonotrode 2 is configured to be vibrated at a predetermined sealing amplitude and frequency so that when the sonotrode 2 and the anvil 3 are arranged in a sealing position WP, with the two longitudinal edges S1 , S2 of the continuous sheet S arranged therebetween, the sealing device 1 is able to seal the longitudinal edges S1 , S2 together;

[0035] - feeding means 8 configured to feed the continuous sheet S; - dragging means 6, 7 configured to drag the continuous sheet S to advance said continuous sheet S along a packaging direction D1 during sealing; and

[0036] - a controller 5 connected to the force application device 4 and configured and programmed to command the force application device 4 to interrupt the application of the sealing force RF during a step of interrupting the sealing,

[0037] Preferably, the feeding means 8 comprises a rotatable element configured to house a reel of sheet of packaging material and to rotate the reel, thus unwinding the continuous sheet towards the transport means 6, 7 and the sealing device 1 .

[0038] According to the invention, the controller 5 is further programmed to maintain the vibration of the sonotrode 2 active while simultaneously leaving the sonotrode 2 and the anvil 3 in the sealing position WP when commanding the force application device 4 to interrupt the application of the sealing force RF, thereby the vibration of the sonotrode 2 generates a thrust against the anvil 3 substantially equal to the amplitude of the vibration of the sonotrode 2.

[0039] In this way, the sealing apparatus 10 can restart sealing quickly instead of having to undergo a restart procedure with mutual approach of the sonotrode 2 and the anvil 3. In this way, it is not necessary to reactivate the sonotrode 2 and wait for the vibration amplitude to reach the nominal value.

[0040] The sealing device 1 is of the ultrasonic type, wherein a sonotrode 2 and an anvil 3 interact to seal longitudinal edges S1 , S2 of said continuous sheet S, wherein the edges S1 , S2 are interposed between the sonotrode 2 and the anvil 3.

[0041] According to a particular aspect of the invention, the sonotrode 2 and the anvil 3 comprise a respective rotary body (see figure 2). To simplify the current disclosure, embodiments that provide for the use of a rotating sonotrode and anvil will be presented below for purely illustrative and non-limiting purposes. Clearly, a person skilled in the art using the teachings of the present invention would be able to apply the solution to other types of applications, such as cases in which the sonotrode and the anvil are operated without rotation and are translated at least towards and away from the sheet for the mutual sealing of edges interposed therebetween. Consequently, the scope of protection of the present invention extends to any type of ultrasonic sealing.

[0042] Accordingly, the controller 5 is further configured and programmed to rotate the sonotrode 2 and the anvil 3 around respective rotation axes X2, X3 during the sealing step. In particular, the sonotrode 2 and the anvil 3 are arranged parallel, with the rotation axes X2, X3 parallel to each other.

[0043] In this way the controller 5 can coordinate the driving of the dragging means 6, 7 and the sonotrode 2 and the anvil 3 of the sealing device 1 .

[0044] Preferably, the controller 5 of the apparatus 10 is configured to maintain the vibration of the sonotrode 2 3 during the step of interrupting the sealing. During such step, the rotation of the sonotrode 2 and the anvil is stopped, so as to prevent the stationary sheet S from tearing. This operating logic allows the sealing apparatus 10 to restart promptly after an intermediate step of interrupting the sealing.

[0045] Preferably, the sealing device 1 comprises a cylindrical joint 21 configured to limit the position of the sonotrode 2 relative to a frame of the sealing device 1. Preferably the cylindrical joint 21 is mounted on a fixed axis X21 .

[0046] Preferably, the sonotrode 2 is mounted on a sonotrode support flange 22. The flange 22 comprises a seat to host the cylindrical joint 21 . Preferably, the flange 22 is mounted with play so that it rotates about the fixed axis X21 .

[0047] Preferably, the cylindrical joint 21 is arranged substantially parallel to the rotation axis X2 of the sonotrode. Preferably, the sonotrode 2 is mounted so that it can rotate with respect to the cylindrical joint 21 , so that it can orbit around it.

[0048] Preferably, the X3 axis on which the rotating anvil 3 is mounted is fixed with respect to the sealing device 1 .

[0049] Preferably, the sonotrode 2 used in the sealing method of the present invention comprises a disk-shaped head 23 whose centre coincides with the axis X2 of the same. The sonotrode head 23 comprises a lateral surface 24. Similarly, the anvil 3 preferably comprises a disk-shaped head 33 whose centre coincides with the axis X3 of the same. The anvil head 33 comprises a lateral surface 34.

[0050] Preferably, the heads 23, 33 will be aligned and facing close to each other, so that portions of the lateral surfaces 24, 34 are parallel and close to each other, so as to be in contact with the portions S1 , S2 of the continuous sheet S during the step of sealing.

[0051] The lateral surface 34 of the anvil 3 is suitably shaped with grooves configured to optimize the quality of the sealing, in particular, obtained through a dedicated process; by way of example but not limitation, it is possible to carry out a knurling process on the surface 34. The effect obtained by the interaction between the lateral surface 34 of the anvil 3 and the lateral surface 24 of the sonotrode 2 is to obtain a sealed fin in which at least the edge S1 of the sheet arranged in contact with the anvil 3 is knurled due to the mutual interaction between the lateral surfaces 24, 34.

[0052] Preferably, the sealing device 1 used in the sealing method of the present invention can advantageously comprise a rotary actuator 35 associated at least with the anvil 3. In figure 2 the rotary actuator 35 is schematically represented as a functional block, such rotary actuator 35 can be aligned with the anvil 3 along its own rotation axis X3, for example by being associated directly with a joint 36, substantially coaxial with the anvil 3 and the rotary actuator 35. Alternatively, the rotary actuator 35 can be associated with the anvil 3 according to any other kinematic chain.

[0053] Preferably, the rotary actuator 35 is configured to provide a rotary motion about its rotation axis X3. The actuator 35 of the sealing device 1 , preferably comprises an electric motor and a frequency variation drive for controlling the same. The drive is configured to vary the power and the mechanical torque applied by the motor on the rotary actuator 35. The drive is preferably connected to the controller 5. However, it is not excluded that the drive is configured as a logic element belonging to the controller 5. The sealing device 1 further comprises a motion transmission device 37, configured to constrain the rotation of the anvil 3 around its axis X3 to the rotation of the sonotrode 2 around its axis X2. The motion transmission device 37 preferably comprises a pair of parallel gears with mating profiles. Preferably, the motion transmission device 37 is configured to force the sonotrode 2 and the anvil 3 to rotate in opposite directions around their respective rotation axes X2, X3. Preferably, the linear speed of the sonotrode head 23 is substantially equal to the speed of the anvil head 33 in the portion in contact with the edges S1 , S2 of the continuous sheet S. Such linear speed of the heads 23, 33 is substantially equal to the speed of the sheet S and slightly lower than the speed of the dragging means 6, 7 to advance the sheet S along the packaging direction D1 when the dragging means 6, 7 are active, in order to allow the dragging to be performed by their own dragging means 6, 7 while the interaction between the heads 23, 33, of the sonotrode 2 and the anvil 3 takes care of the mutual sealing of the edges S1 , S2 of the continuous sheet. In particular, the linear speed of the dragging means 6, 7 is preferably higher by up to about 1 % than the linear speed of the heads 23, 33 and of the sheet S, even more preferably by up to about 0.5%.

[0054] The sealing device 1 also comprises a vibration transducer 27. The vibration transducer 27 is mechanically constrained to the sonotrode 2 and is configured to transform electrical energy into mechanical energy, so as to cause the rotating sonotrode 2, and consequently its head 23, to vibrate, with particular reference to the radial direction DR with respect to the rotation axis X2 of the sonotrode 2. The transducer 27 is configured to modulate, by increasing or decreasing up to zero, the vibration amplitude as a function of the sealing power required to be transmitted to the sheet S. The transducer 27 is appropriately connected to the controller 5 for the actuation and modulation of the transducer 27.

[0055] As reported above, the sealing device 1 comprises a force application device 4, configured to exert a reciprocal force between the sonotrode 2 and the anvil 3, and in particular the head 23 of the sonotrode with respect to the head 33 of the anvil. Preferably the sonotrode 2 comprises a protrusion 28 in a radial direction with respect to the rotation axis X2 and axially phased with respect to the sonotrode head 23. Preferably the anvil 3 comprises a respective protrusion 38 in a radial direction with respect to the rotation axis X3 and axially phased with respect to the anvil head 33. Preferably, each of the radial protrusions 28, 38 is configured and dimensioned to accommodate at least one constraint element 11 , 12 between the force application device 4 and the respective sonotrode 2 and anvil 3.

[0056] Preferably, the constraint elements 11 , 12 will be rotary joints 11 , 12 with their respective axes arranged substantially parallel to the rotation axes X2, X3 of the sonotrode and anvil. Advantageously, the force application device 4 and the protrusions 28, 38 will comprise seats configured and dimensioned to accommodate cylindrical elements of the constraint elements 11 , 12 with their axis parallel to the sonotrode 2 and anvil 3, which allow the mutual rotation between the force application device 4 and the sonotrode 2 and between the force application device 4 and the anvil 3.

[0057] Preferably, the degree of freedom of movement between the sonotrode 2 and the anvil 3 introduced by the cylindrical joint 21 of the sonotrode 2 can be combined by actuating the force application device 4. In particular, in the steps in which the transducer 27 is active, the vibrational force applied to the sealing device 1 has the effect of generating a mutual repulsion force between the sonotrode 2 and the anvil 3. The force application device 4 is appropriately configured to apply a force such as to substantially eliminate the dynamic effects of the vibrational force when the device 1 is in the sealing position WP. The force application device 4 in any of the embodiments of the present invention is connected to the controller 5. In this way it is possible to control the force application device 4 independently of the other elements connected to the controller 5.

[0058] Preferably, the force application device 4 is of the linear actuator 4 type. Such linear actuator 4 is dimensioned to provide a linear actuation stroke LS. Since the rotary joints 11 , 12 are arranged with their respective axes substantially parallel to the rotation axes X2, X3 of the sonotrode and anvil , the actuator 4 can act on a plane substantially perpendicular to both rotation axes X2, X3 of the sonotrode and anvil, so that the force applied to the actuator 4 results in a variation of the position in the stroke LS, causing a mutual approach / distancing between the sonotrode 2 and the anvil 3, in particular between the close portions of the lateral surfaces 24, 34 of the heads of the sonotrode and the anvil.

[0059] With reference to Figures 2-5 and 7A-7F, and according to an embodiment of particular interest for the invention, the linear actuator 4 is a cylindrical pneumatic actuator 4. Such pneumatic actuator 4 is preferably of the double-acting type. The double-acting pneumatic actuator 4 comprises a piston 43 connected to a stem 44. The piston 43 of the actuator 4 is mounted for sliding on a cylindrical seat 45 along the stroke LS. The double-acting pneumatic actuator 4 has two inlet ports 41 , 42, the first inlet port 41 being positioned on the body of the actuator 4 containing the stem 44 and the second inlet port 42 on the body of the actuator 4 containing the terminal side of the cylindrical sliding seat 45.

[0060] Preferably, the body of the actuator 4 containing the stem 44 is positioned oriented towards the first rotary joint 11 associated with the sonotrode 2, while the body of the actuator 4 containing the terminal side of the cylindrical sliding seat 45 is positioned oriented towards the second rotary joint 12 associated with the anvil 3. Alternatively, the body containing the stem 44 is associated with the second rotary joint 12 and the body containing the terminal side of the cylindrical seat 45 is associated with the first joint 11 .

[0061] Preferably, the double-acting pneumatic actuator 4 is mounted normally open, that is, in the absence of pressures applied by the inlet ports 41 , 42 the reciprocal force RF applied by the actuator 4 between the sonotrode 2 and the anvil 3 is zero, the sealing device 1 is therefore not able to perform the sealing. According to the preferred embodiment, in the absence of other external forces the application of manometric pressure from the first inlet port 41 results in the application of a pressure force of the surface 24 of the sonotrode 2 on the surface 34 of the anvil 3. Conversely, in the absence of other external forces the application of manometric pressure from the second port 42 results in the removal of the surface 34 of the anvil with respect to the surface 24 of the sonotrode. In this regard, the controller 5 is further configured and programmed to balance the pressures applied through the two inlet ports 41 , 42, for instance by removing any pressure applied through both ports 41 , 42, when the application of the sealing force RF is interrupted.

[0062] Preferably, the sealing device 1 may comprise a pressure sensor mounted on the sonotrode 2 (not shown in the figures) configured to send signals to the controller 5. By doing so the controller 5 sends a feedback signal to the linear actuator 4 so as to regulate the force acting between the sonotrode and the anvil to keep a stable functioning of the apparatus 10.

[0063] The driving means 6, 7 used in the sealing method of the present invention are of the rotating type. Preferably, the driving means 6, 7 may comprise first front driving means 6, arranged upstream of the sealing device 1 , and second rear driving means 7, arranged downstream of the sealing device 1. Alternatively, the driving means may only be arranged either upstream of the sealing device, or downstream of the sealing device 1.

[0064] Each driving means 6, 7, comprises a pair of rollers 61 , 71 , arranged parallel and close to each other; with the front driving means 6 comprising a pair of front rollers 61 and the rear driving means 7 comprising a pair of rear rollers 71. Each roller of the pair of rollers 61 , 71 is arranged to rotate around a respective axis X6, X7 and configured to rotate in the opposite direction to the other roller 61 , 71 of the pair of rollers 61 , 71 .

[0065] The axis X6, X7 of each roller 61 , 71 is substantially parallel to the axis X6, X7 of the other roller 61 , 71 of the pair. It is possible to move the pair of axes X6 of the front drive means 6 away from each other to allow the insertion of the sheet edges S1 , S2 and then bring them closer together to allow the dragging of the edges. Furthermore, it is possible to adjust the closing pressure between the two axes X6. Similarly, it is possible to move the axes X7 of the rear drive means away from and closer together, as well as adjust the closing pressure between these axes X7. Each of the driving means 6, 7 comprises constraint means configured to force rotation of each roller 61 , 71 of the pair in the opposite direction to the other roller 61 , 71. Preferably, the constraint means comprise a pair of parallel gears with mating profiles. Preferably, the diameter of the rollers 61 , 71 of each pair of rollers is substantially the same as the other roller 61 , 71 of the same pair of rollers 61 , 71 , in which case the transmission ratio of the constraint means is substantially 1 :1.

[0066] Preferably, each of the driving means 6, 7 comprises a rotary actuator configured to rotate each roller 61 , 71 of the pair of rollers 61 , 71 . Preferably, the actuator of the driving means 6, 7 is connected to and controlled by the controller 5.

[0067] Each roller 61 , 71 of the pair of rollers contacts the sheet S in a portion substantially tangential and opposite to the portion of the other roller 61 , 71 of the pair. The front rollers 61 will contact the edges S1 , S2 to be sealed, while the rear rollers 71 will be able to advantageously drag a sealed fin SP of said sheet. The linear peripheral speed of the rollers in the portion in contact with the sheet S is slightly higher than that of the sheet S itself, being dragged along the packaging direction D1.

[0068] Preferably, the sealing device 1 is aligned with respect to the driving means 6, 7, along the packaging direction D1. In this configuration, the continuous sheet S can be interposed along a straight segment in the direction D1 between each pair of rollers 61 , 71 , of the driving means 6, 7, and between the sonotrode 2 and the anvil 3 of the sealing device.

[0069] The present disclosure extends its scope of protection to a method for ultrasonic sealing.

[0070] The method for ultrasonic sealing, in accordance with the present invention, involves the use of a sonotrode and an anvil which are operated to seal two edges of sheet arranged therebetween comprises the steps of: feeding a continuous sheet S along a packaging direction D1 ; superimposing two longitudinal edges S1 , S2 of said continuous sheet S placing them facing each other between a sonotrode 2 and an anvil 3; - dragging said continuous sheet S by means of dragging means 6, 7 so as to obtain the advancement of said continuous sheet S along a packaging direction D1 during sealing;

[0071] - activating the sonotrode 2 by making it vibrate at a predetermined sealing amplitude and frequency;

[0072] - arranging the sonotrode 2 and the anvil 3 reciprocally in a sealing position WP;

[0073] - applying a reciprocal sealing force RF between the sonotrode 2 and the anvil 3 to seal the two longitudinal edges S1 , S2 facing each other to form a sealed fin SP; and

[0074] - interrupting the sealing by removing the application of the sealing force RF between the sonotrode 2 and the anvil 3.

[0075] In the preferred but not exclusive embodiment wherein the sonotrode 2 and the anvil 3 are of the rotating type, the sonotrode 2 and the anvil 3 are set in rotation by the activation of the rotary actuator 35. Preferably the rotary actuator 35 is associated with the rotating anvil 3.

[0076] Accordingly, the sonotrode 2 is made vibrate towards the anvil 3. In particular, in the embodiments wherein the sonotrode 2 and the anvil 3 are of the rotating type, the sonotrode 2 vibrates in a radial direction following the activation of the vibration transducer 27.

[0077] In fact, the sonotrode 2 and the anvil 3 are constrained by the application of a reciprocal force RF to exert a pressure on the sheet edges S necessary for sealing and to maintain the sealing position WP. Preferably, the application of such reciprocal force allows the surface 24 of the sonotrode 2 to be pressed against the surface 34 of the anvil 3 with the sheet edges S arranged in between.

[0078] According to the invention, the step of interrupting the sealing involves that the sonotrode 2 is maintained active while simultaneously leaving the same and the anvil 3 in the sealing position WP, whereby the vibration of the sonotrode 2 generates a thrust against the anvil 3 substantially equal to the amplitude of the vibration of the sonotrode 2. Maintaining the sonotrode always active instead of turning it off during the step of interrupting the sealing has the advantage of not having to wait for the sonotrode to reach the vibration amplitude again after the sonotrode is restarted.

[0079] Preferably, before or simultaneously with the step of interrupting the sealing, the method involves interrupting the feeding of the continuous sheet S along the packaging direction D1 .

[0080] The radial vibration of the active sonotrode 2 generates a repelling force between the sonotrode 2 and the anvil 3 substantially equal to the radial amplitude of the vibration of the sonotrode 2, until the contact between the sonotrode 2 and the anvil is eliminated following a plurality of vibration cycles.

[0081] In this regard, the repelling force occurring during the step of interrupting the sealing is small. Typically, in ultrasonic sealing devices for product packaging applications, the operating frequency of the transducer 27 is in the range of I Q- 50 kHz and has a radial amplitude in the range of approximately 30-80 pm.

[0082] As mentioned above, the effect generated is a small mutual separation between the sonotrode 2 and the anvil 3 substantially equal to the radial amplitude, or equal to or less than such radial amplitude of vibration. Consequently, it can be considered that for the step of applying the reciprocal sealing force RF following the interaction between the sonotrode 2 and the anvil 3 during the step of interrupting the sealing, the sonotrode 2 and the anvil 3 remain in the sealing position WP. It is specified that the sealing position can be defined as a tolerance interval.

[0083] In fact, it is specified that while the linear stroke LS is of a few millimetres or centimetres, as is the difference between the open position OP and the sealing position WP, the mutual separation due to the vibration transmitted by the transducer 24 is in the order of magnitude of tens of micrometres, the ratio between the two parameters being approximately of at least two orders of magnitude.

[0084] This limited separation of the mutual distance allows a prompt resumption of the sealing without having to switch off the transducer 24 or perform the step of reciprocally arranging the sonotrode 2 and the anvil 3 in a sealing position WP again. In this configuration, the sonotrode 2 could still contact edges S1 , S2 but without impacting the anvil 3 and consequently without hitting or causing wear to the anvil 3.

[0085] According to an aspect of the present invention, the sealing method, before or simultaneously to the step of interrupting the sealing, comprises a step of interrupting the dragging of the continuous sheet S along the packaging direction D1. In this way, the edges S1 , S2 will remain still in the position along the packaging direction so that in the event of resumption of the sealing there are not unsealed longitudinal segments of continuous sheet S following the sliding of the sheet through the sealing device 1 while the latter is not operated for sealing (i.e. the step of interrupting the sealing).

[0086] According to an aspect of the present invention, the sealing method further comprises a step of resuming the sealing by reinstating the sealing force RF between the sonotrode 2 and the anvil 3 kept at the sealing position WP, while keeping the sonotrode 2 active. In this way, the device 1 promptly recovers the ability to mutually seal the edges S1 , S2, since the vibration of the sonotrode 2 always remains active, as a reactivation time of the vibration amplitude is not necessary.

[0087] According to an aspect of the present invention, the sealing method further comprises, when the sealing is resumed, a step of reinstating the dragging of the continuous sheet S along the packaging direction D by means of the dragging means 6, 7. In this way, given that the reciprocal sealing force RF has been restored and that the step of arranging the sonotrode 2 and the anvil 3 in the sealing position WP is not required, the sealing restarts promptly (i.e.: the step of applying the reciprocal sealing force RF).

[0088] According to yet another aspect of the present invention, the method provides that, during the step of applying the reciprocal sealing force RF, the sonotrode 2 and the anvil 3 are pushed against each other to maintain their reciprocal contact with the two longitudinal edges S1 , S2 to be sealed in between. This reciprocal RF force is useful for applying compression on edges S1 , S2 to enable the transfer of the energy necessary for sealing due to the vibrating actuation of the sonotrode 2 onto the anvil 3.

[0089] According to yet another aspect of the present invention, the reciprocal sealing force RF is performed by a force application device 4, more in particular a linear actuator 4. Preferably, the linear actuator 4 can be of the double-acting pneumatic type as reported above, namely comprising two inlet ports 41 , 42, wherein during the step of interrupting the sealing force RF the pressures applied through the two inlet ports 41 , 42 are balanced, preferably by removing any pressure applied through each of the two ports 41 , 42.

[0090] The atmospheric pressure at the inlet ports 41 , 42 of the actuator, which means the force applied in the inlet ports 41 , 42 is removed, is achieved by interrupting the operation of the pneumatic linear actuator 4, i.e. by interrupting the electrical power associated with the actuator 4.

[0091] Alternative embodiments of the present invention provide that the linear actuator 4 is of the type chosen between mechanical, electromechanical or hydraulic.

[0092] The actuator 4 ensures fine control of the reciprocal RF force applied between sonotrode 2 anvil 3. In particular, the pneumatic type linear actuator 4 is very fast in dynamic responses to apply the required forces. In particular, the pneumatic type actuator 4 can be equipped with an electronic pressure regulator.

[0093] Preferably, during the step of applying a reciprocal force RF the actuator increases the manometric pressure in a first port 41 . The difference in pressures between the first port 41 and a second port 42 allows the sonotrode 2 to press against the anvil 3. In the step of interrupting the sealing, the reciprocal force RF is zeroed by balancing the manometric pressure in the two ports 41 and 42, preferably zeroed by venting both ports 41 , 42.

[0094] According to yet another aspect of the present invention, the method provides that the sonotrode 2 and the anvil 3 comprise respectively rotary bodies 23, 33 rotating about respective rotation axes X2, X3. A rotary actuator 35 may be arranged to rotate the sonotrode 2 and the anvil 3. During the step of interrupting the sealing, it is possible, even if not necessary, to interrupt the operation of the rotary actuator 35 responsible for the rotation of sonotrode 2 and anvil 3 around their respective axes X2, X3.

[0095] According to yet another aspect of the present invention, the sonotrode 2 and the anvil 3 rotate at an angular speed such that their respective surfaces in contact with the two longitudinal edges S1 , S2 to be sealed have a tangential speed substantially equal to the speed at which said continuous sheet S is dragged along the packaging direction D1 during sealing. In particular, portions of the lateral surfaces 24, 34 of the respective heads 23, 33 of sonotrode 2 and anvil 3 will tangentially contact the edges S1 , S2 of the continuous sheet during sealing. The surface portions of the lateral surfaces 24, 34 will have a linear velocity equal to the angular velocity of sonotrode 2 and anvil 3 multiplied by the radius of the respective head 23, 33. The linear velocity of said portions of the lateral surfaces 24, 34 in contact is slightly lower than the speed of the dragging means 6, 7, so as to seal, keeping pace with the speed of the sheet S without dragging it. As mentioned above, the dragging means 6, 7 will be responsible for moving the edges S1 , S2 of the sheet at the desired speed.

[0096] Preferably, the method provides that the anvil 3 remains in a fixed position both during the steps of applying a reciprocal force RF and the interrupting the sealing. As previously mentioned, the anvil 3 is mounted so that it rotates around its own axis X3. Preferably, the axis X3 is fixed, so as to maintain the anvil in a fixed position of the sealing device 1.

[0097] With reference to figure 10, a graph is shown with the temporal evolution of the different steps of the sealing method, both for the reciprocal force RF applied and for the reciprocal distance between sonotrode 2 and anvil 3. In particular, in the initial step F1 , a reciprocal closing force RF is applied to bring the sonotrode 2 and the anvil 3 closer together from the open position OP, with maximum reciprocal distance, until the sealing position WP is reached. This step is shown in figure 9A.

[0098] In a subsequent step F2, the method may foresee a waiting time before starting sealing in which no force is applied by the force application device 4. It should be remembered that the sonotrode 2 is already active, i.e. vibrating at the desired amplitude.

[0099] In a subsequent sealing step F3 the method provides for the application of a reciprocal force RF between sonotrode 2 and anvil 3 while the transducer 27 vibrates according to predetermined sealing parameters, in order to maintain the reciprocal sealing position WP and to exert a compression on the edges S1 , S2 of the sheet S suitable for transmitting the necessary sealing energy (see figure 9B). It is specified that in the case of using the pneumatic actuator 4, the reciprocal force RF is applied by increasing the manometric pressure of the port 41 , while the port 42 is kept substantially unloaded, i.e. at atmospheric pressure.

[0100] As mentioned above, the method comprises a step of interrupting the sealing F4 by unlocking the block between the sonotrode 2 and the anvil 3, leaving the sonotrode 2 and the anvil 3 in the sealing position WP while the sonotrode 2 remains active (figure 9C). During the step of interrupting the sealing F4 the applied reciprocal force RF is zero as the transducer 27 makes the sonotrode 2 vibrate, gradually separating the sonotrode 2 and the anvil 3, but just slightly, which is practically inappreciable to the naked eye. This movement is shown in figure 8 during the step of interrupting the sealing F4. It is specified that in the case of using the pneumatic actuator 4, the interruption of the reciprocal force RF occurs by balancing the pressure of the ports 41 , 42. Preferably, the balancing of the pressures occurs by unloading both ports 41 , 42, i.e. by bringing them to the atmospheric pressure.

[0101] In a step of resuming the sealing F5 the method provides that the reciprocal sealing can be promptly resumed by applying a reciprocal force RF such as to counteract the effects of the reciprocal interaction between sonotrode 2 and anvil 3 (figure 9D). Preferably, during the step of resuming the sealing F5 the sonotrode remains active. It is specified that in the case of using the pneumatic actuator 4, the step of resuming the sealing F5 provides for the increase of the pressure of the port 41 , while the port 42 is kept substantially unloaded, i.e. at atmospheric pressure. It is possible to apply a new final step of interrupting the sealing F6, which is preferably followed by a final step F7 of mutual distancing, by applying a reciprocal force (figure 9E). At the end of the final step F7, the sonotrode 2 and the anvil 3 will again be arranged in an open position OP, in which the mutual distance is maximum (Figure 9F). It is specified that in the embodiment that involves the use of the pneumatic actuator 4, the step of mutual distancing F7 involves increasing the pressure of the second port 42 while the first port 41 is kept substantially unloaded, i.e. at the atmospheric pressure.

[0102] The sealing apparatus 10 can be advantageously integrated into a packaging machine, which further comprises a forming device 9.

[0103] Preferably, the forming device 9 comprises folding means arranged between an input section and an output section thereof so as to bring the longitudinal edges S1 , S2 of the sheet S close to and facing each other.

[0104] Preferably, the forming device 9 is arranged upstream of and aligned with the ultrasonic sealing device 1 along the packaging direction D1.

[0105] Preferably, the forming device 9 is arranged downstream of and aligned with the feeding means 8 along the packaging direction D1 .

[0106] Preferably, the folding means of the forming device 9 will be configured to intercept and detect the continuous sheet S and fold the continuous sheet S so as to form a tubular casing around the products comprising respective folded and mutually opposite end flaps.

[0107] According to embodiments of the present invention, the sealing apparatus 10 can be integrated into a horizontal packaging machine, such as the flow pack type, in which a forming device 9 is interposed between the means for feeding the continuous sheet S and the sealing device 1 . The forming device 9 is configured to arrange the sheet around the products to be packaged, typically delivered along a supply direction parallel to the packaging direction D1. In this way, it is possible to easily wrap the continuous sheet S around the products to be packaged, with the longitudinal edges S1 , S2 remaining underneath the product to be packaged along the product conveyor line. Alternative embodiments of the present invention provide that the sealing apparatus 10 is integrated into a vertical packaging machine, in which the product to be packaged is dispensed loose from above and inserted into a tubular or prismatic dosing device. The forming device 9 in such machines can be the same dosing device, alternatively the forming device 9 is external to the dosing device, normally concentric, so as to arrange the continuous sheet around the loose product dosed through the dosing device.

[0108] In the case of the vertical packaging machine, before the dosing of loose product, a transverse sealing step takes place in order to close the package from below. In any case, the longitudinal sealing of the flaps S1 and S2 proceeds in parallel.

[0109] It is clear that modifications and / or additions of parts or steps may be made to the ultrasonic sealing method and the ultrasonic sealing apparatus described herein, without thereby departing from the scope of the present invention as defined by the claims. In the claims that follow, the references in brackets are for ease of reading only and should not be considered as limiting factors with respect to the scope of protection underlying the specific claims.

Claims

CLAIMS1. Method for ultrasonic sealing, wherein a sonotrode and an anvil are operated to seal two edges of sheet arranged therebetween, said method comprising the steps of:- feeding a continuous sheet (S) along a packaging direction (D1 );- superimposing two longitudinal edges (S1 , S2) of said continuous sheet (S) placing them facing each other between a sonotrode (2) and an anvil (3);- dragging said continuous sheet (S) by means of dragging means (6, 7) so as to obtain advancement of said continuous sheet (S) along a packaging direction (D1 ) during sealing;- activating the sonotrode (2) by making it vibrate at a predetermined sealing amplitude and frequency;- arranging the sonotrode (2) and the anvil (3) reciprocally in a sealing position (WP);- applying a reciprocal sealing force (RF) between said sonotrode (2) and said anvil (3) to seal the two longitudinal edges (S1 , S2) facing each other to form a sealed fin (SP); and- interrupting the sealing by removing the application of the sealing force (RF) between said sonotrode (2) and said anvil (3), said method being characterized in that during the step of interrupting the sealing, the sonotrode (2) is maintained active while simultaneously leaving said sonotrode (2) and said anvil (3) in said sealing position (WP), whereby the vibration of said sonotrode (2) generates a thrust against the anvil (3) substantially equal to the amplitude of the vibration of the sonotrode (2).

2. The method according to claim 1 , characterized in that before or simultaneously to the step of interrupting the sealing, the method comprises a step of interrupting the dragging of said continuous sheet (S) along the packaging direction (D1 ).

3. The method according to claim 1 or 2, characterized by further comprising a step of resuming the sealing by reinstating the sealing force(RF) between the sonotrode (2) and the anvil (3) kept at said sealing position (WP), while keeping the sonotrode (2) active.

4. The method according to claim 3 when it depends on claim 2, characterized by further comprising, when the sealing is resumed, a step of reinstating the dragging of the continuous sheet (S) along the packaging direction (D1 ) by means of said dragging means (6, 7).

5. The method according to any of the previous claims, characterized in that during the step of applying the reciprocal sealing force (RF), the sonotrode (2) and the anvil (3) are pushed against each other to maintain their reciprocal contact with the two longitudinal edges (S1 , S2) to be sealed in between.

6. The method according to claim 5, characterized in that said reciprocal sealing force (RF) is generated by a linear actuator (4), preferably a double-acting pneumatic actuator having two inlet ports (41 , 42), wherein during the step of interrupting the sealing force (RF), the pressures applied through the two inlet ports (41 , 42) are balanced, preferably by removing any pressure applied through both ports (41 , 42).

7. The method according to any of the previous claims, characterized in that said sonotrode (2) and said anvil (3) comprise, respectively, rotary bodies (23, 33) rotating about respective rotation axes (X2, X3).

8. The method according to claim 7, characterized in that said sonotrode (2) and said anvil (3) rotate at an angular speed such that their respective surfaces in contact with the two longitudinal edges (S1 , S2) to be sealed have a tangential speed substantially equal to the speed at which said continuous sheet (S) is dragged along the packaging direction (D1 ) during sealing.

9. Ultrasonic sealing apparatus (10), comprising:- a sealing device (1 ) comprising o a sonotrode (2) and an anvil (3) configured to be operated to seal together two longitudinal edges (S1 , S2) of a continuous sheet (S) arranged therebetween, ando a force application device (4) configured to apply a sealing force (RF) between said sonotrode (2) and said anvil (3) to seal the two longitudinal edges (S1 , S2) forming a sealed fin (SP) wherein said sonotrode (2) is configured to be vibrated at a predetermined sealing amplitude and frequency so that when the sonotrode (2) and the anvil (3) are arranged in a sealing position (WP), with the two longitudinal edges (S1 , S2) of the continuous sheet (S) arranged therebetween, said sealing device (1 ) is able to seal said longitudinal edges (S1 , S2) together;- feeding means (8) configured to feed said continuous sheet (S);- dragging means (6, 7) configured to drag said continuous sheet (S) to advance said continuous sheet (S) along a packaging direction (D1 ) during sealing; and- a controller (5) connected to said force application device (4) and configured and programmed to command the force application device (4) to interrupt the application of the sealing force (RF) during a step of interrupting the sealing, characterized in that said controller (5) is further programmed to maintain the vibration of said sonotrode (2) active while simultaneously leaving said sonotrode (2) and said anvil (3) in said sealing position (WP) when commanding the force application device (4) to interrupt the application of the sealing force (RF), thereby the vibration of said sonotrode (2) generates a thrust against the anvil (3) substantially equal to the amplitude of the vibration of the sonotrode (2).

10. The apparatus (10) according to claim 9, characterized in that said sonotrode (2) and said anvil (3) comprise a respective rotary body, and in that said controller (5) is further configured and programmed to rotate said sonotrode (2) and said anvil (3) around respective rotation axes (X2, X3) during the step of applying a sealing force.11 . The apparatus according to claim 9 or 10, characterized in that said force application device (4) is a linear actuator (4).

12. The apparatus according to claim 11 , characterized in that said linear actuator (4) is a double-acting pneumatic actuator having two input ports (41 , 42), and in that said controller (5) is further configured and programmed to balance the pressures applied through the two input ports (41 , 42), for instance by removing any pressure applied through both ports (41 , 42), when the application of the sealing force (RF) is interrupted.

13. Packaging machine, comprising- an ultrasonic sealing apparatus (10) according to any of claims 9-12; and- a forming device (9) comprising folding means arranged between an input section and an output section so as to bring the longitudinal edges (S1 , S2) of the sheet (S) close to and facing each other, wherein the forming device (9) is arranged upstream of and aligned with the ultrasonic sealing device (1 ) along the packaging direction (D1 ), wherein the forming device (9) is arranged downstream of and aligned with the feeding means (8) along the packaging direction (D1 ), the forming device (9) being configured to abut the continuous sheet (S) while the same advances along the packaging direction (D1 ) so that the central part (SC) of the continuous sheet (S) adopts a tubular shape for hosting inside a product to be packed.

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