PROCEDURE AND EQUIPMENT FOR ULTRASONIC WELDING OF A CONTINUOUS SHEET

Description

PROCEDURE AND EQUIPMENT FOR WELDING ULTRASOUND OF A CONTINUOUS SHEET DESCRIPTION OF THE INVENTION The present invention falls within the technical sector concerning welding 5 ultrasound, in particular it is aimed at a process and equipment of ultrasonic welding. In the current state of the art, processes and equipment are known: ultrasonic welding, comprising a sonotrode and an anvil, which are operated simultaneously to weld portions of sheet placed between them. 10 Ultrasonic welding applications can be of the rotary type, where sonotrode and anvil are rotating around their respective axes of rotation and the speed peripheral of the rotating sonotrode and anvil is equal to the linear velocity of sheet advancement, as there is no sliding between the sheet and the elements rotating. This type of application is particularly advantageous when 15 wants to make a continuous longitudinal weld of a sheet. Alternatively, there are applications of ultrasonic welding of the translating type, in which sonotrode and anvils are mutually moved towards and away from each other from the sheet to carry out the welding operation and in this case it is present sliding between the sheet and the sealing means. 20 The sheet portions to be welded are typically thin films. Such sheet portions They are normally made of polymeric materials, such as plastic, which are compatible with ultrasonic welding. Ultrasonic welding is also compatible with metallic materials and with multilayer films containing both materials polymeric and metallic. A typical application of this type is the welding of films 25 from packaging in product packaging applications, e.g. food, in horizontal or vertical packaging equipment. Ultrasonic welding typically involves several stages. First, in preliminary phase a continuous sheet is fed to be welded along one direction of packaging. During the feeding of the sheet, depending on the individual 30 application, it is possible to wrap or fold said sheet around products to be package, orienting the longitudinal edges of the sheet along the direction of packaging. In a subsequent phase, the longitudinal edges to be welded are positioned in correspondence with the sonotrode and the anvil. In particular, this phase consists 5 in overlapping longitudinal flaps of the longitudinal edges of the sheet by arranging them counterfeited between the sonotrode and the anvil. Furthermore, in order to weld properly, it is necessary to complete a preparatory phase of arranging the sonotrode and the anvil at a mutual distance of welding, aimed at eliminating the distance between the two edges of the sheet respectively 10 to be welded, between a first edge of sheet and the sonotrode and between the second edge of sheet and the anvil. This mutual distance is normally managed by a mutual constraint device, which allows the sonotrode to be moved closer / further away and anvil by applying an external force for closing or mutual approach of sonotrode and anvil. Consequently, the device 15 of mutual constraint is typically configured to achieve a position of closure in which the distance between the sonotrode and the anvil is such as to affect the flaps counterfeited interposed between them, putting them in mutual contact with each other and further causing compression of the same, a necessary condition for their mutual welding. In other words, in the presence of interposed edges between 20 sonotrode and anvil, the constraint device exerts in the closed position a pressure on the flaps. In fact, in ultrasonic welding devices with constraint device, the The mutual distance between the sonotrode and the anvil can vary from an open position, in which the mutual distance is maximum and such as to allow the flaps to be prepared 25 counterfeits to be welded placed between the sonotrode and the anvil, and a position of welding closure, in which the mutual distance between sonotrode and anvil is minimum and such as to guarantee ultrasonic welding thanks to the amplitude caused sum of the applied forces. The applied forces are essentially two; one part is the vibrational force which is caused by the vibrating sonotrode, and operates 30 in its radial direction with respect to the sonotrode, and on the other the external force for the closing or mutual approach of sonotrode and anvil, operating in direction orthogonal to the edges of the film to be sealed. The sum of these forces is mechanically transmitted to the countersunk flaps, which absorb an energy welding aimed at plastically deforming the film in order to fix it the edges close together. 5 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 forces applied, the sole application of force from the linear actuator acts by varying the mutual distance of the elements between the opening position and the closed position for welding. 10 Advantageously, once the flaps have been prepared counterfeit, the devices available in the prior art are controlled to position sonotrode and anvil in the welding position, and consequently the welding phase can be started ultrasonic welding. At this point, the applications in which these devices ultrasonic welding involves the operation of the dragging means 15 which advance the sheet with the counterfeit flaps, at the same time upon actuation of the sonotrode and anvil, with the sonotrode vibrating at amplitude and predetermined frequency to interact with the anvil, to weld the edges mutually, thanks to the radial excursion of the ultrasonic vibration of the sonotrode. The radial direction is understood to be the direction perpendicular to 20 that of the sheet in the welding position. In the case of welding devices rotating, sonotrode and anvil rotate around their respective axes of rotation at the welding distance. In order to ensure a stable weld, it is usual to keep the pressure exerted on the flaps due to the external force applied for closure 25 reciprocal between the sonotrode and the anvil during the welding phase. To this end it is possible to use a controller that commands, following the monitoring of the actual pressure applied on the flaps, the constraint device, typically of the type above-mentioned linear actuator, to apply a mutual force between sonotrode and anvil in order to keep the applied mutual force stable 30 from the sonotrode and anvil constraint device, and consequently the pressure exerted on the edges for their welding. This type of configuration is particularly advantageous because it allows the use of a single controller for all elements involved in the ultrasonic welding process, such as the source to make the sonotrode vibrate with the appropriate amplitude and frequency, the constraint device and the means of transport to advance the sheet to which 5 flaps are welded. If the welding device is of the rotating type, the controller is also responsible for the means to rotate the sonotrode and anvil. The welding phase in this type of process can be interrupted for several reasons, including an external user command, or the lack of the 10 product to be packaged, both for automatic detection by the controller of anomalies / faults, such as the interruption of the film transport, which require the immediate interruption of the welding phase. If this occurs an interruption of the welding phase, the welding procedures known to the state of the art provide for the switching off of the welding device, which includes 15 the vibrating sonotrode, the mutual constraint device and the rotation means of sonotrode and anvil in the particular case of rotary welding. In particular, Switching off the welding device includes switching off the vibratory source of the sonotrode. Normally, the procedure involves, in following the shutdown of the sheet transport means, the shutdown 20. Contextual information on the welding device. Ultrasonic welding processes are typically configured to space the sonotrode and anvil, acting on the constraint device, until it returns to the position of initial opening once the sheet dragging was interrupted, and in any case downstream of the sonotrode shutdown. 25 For example, document WO2016160752 teaches a welding apparatus ultrasonic with rotating sonotrode and anvil and a linear actuator for their mutual approach / distance. This device is configured to control the actuator so as to block the mutual distance between the sonotrode and anvil while welding is taking place, or in any case while the sonotrode is 30 commanded to vibrate towards the anvil, and is commanded to allow the reciprocal movement of the sonotrode and the anvil away from each other / towards each other when the sonotrode was turned off, and thus the welding operation was suspended. In fact, the document WO2016160752 teaches, following a shutdown, to bring the sonotrode and anvil back into a position of opening, so as to allow for appropriate maintenance operations. 5 With the configuration just exposed, a quick verification operation in the machine implies that, following a positive result from this check, the welding process must include a re-approach operation reciprocal action between sonotrode and anvil. In some cases this operation reapproach, as well as the initial approach prior to welding is 10 controlled in feedback to calibrate the actual mutual distance between sonotrode and anvil. This calibration is due to the fact that, in the absence of a correct mutual distance in the welding position the quality of the same can to fail and consequently to discard part of the production with resulting in material losses and plant productivity losses. Such operations 15 re-approach, with possible calibration of the position, of the device Welding takes time and consequently has an impact on productivity of the plant. In summary, quick shutdown / shutdown operations for timely checks are more common than long downtimes such as those due to scheduled maintenance, 20 format changes or due to failures in the production equipment. Unfortunately, the procedures state-of-the-art ultrasonic welding systems are unable to ensure a quick restart following a timely process check of welding, and in case the drag restart occurs at the same time as the of the sonotrode the welding quality may not meet the parameters 25 required, such as that of its hermetic integrity. A failure quality detected in the welding would result in the consequent rejection of the package or packages until the welding conditions are restored to normal operating conditions necessary to achieve the required quality. There is therefore a need to perfect a welding process 30 ultrasound that can overcome the drawbacks of the prior art. To do so this is necessary to solve the technical problem of realizing a procedure of ultrasonic welding that is effective, fast and efficient in its operation, with particular reference to the restart phase. The main task of this invention is to solve the above problems exposed, proposing an ultrasonic welding process that allows a 5 timely restart following a short interruption of the welding phases and dragging. Within the scope of this task, an object of the invention is to propose a ultrasonic welding process that does not require long travel distances mutual approach of sonotrode and anvil and related recalibrations downstream of 10 short welding interruptions, and consequently a shortening of the related restart times. Another object of the present invention is to provide a process for ultrasonic welding that does not require long times to achieve of the vibration amplitude required of the sonotrode. 15 Another aim of the invention is to propose a process that guarantees the high productivity of the plant in which it is applied thanks to the drastic reduction of the waste due to the restart procedure. Another aim of the invention is to propose a process of ultrasonic welding which, after a quick restart, guarantees quality 20 of welding thanks to a quick restoration of the welding parameters. A further aim of this invention is to guarantee the hermetic nature of the weld from the very beginning. first moment in which the welding process restarts downstream of a short interruption, eliminating packaging waste and consequently the products packaged inside them. 25 This task and these goals are achieved by the welding process according to claim 1. This task and these purposes are also achieved by means of an ultrasonic welding apparatus according to the claim 9. Further features and advantages of the invention will become more evident in light of the detailed description of a preferred embodiment but non-exclusive of a process for ultrasonic welding according to the invention, illustrated as a non-limiting example with the aid of the attached drawing tables 5 in which: − Fig. 1 represents, in a schematic view from above; a device of horizontal ultrasonic welding; − Fig. 2 represents, in isometric view, a welding device ultrasound; 10 − Fig. 3 shows, in top view, the welding device ultrasound; − Fig. 4 represents the ultrasonic welding device 1 in a OP open position, with force application device 4 represented in cut view relative to the linear travel relative to the 15 open position OP; − Fig. 5 represents the ultrasonic welding device 1 in a WP welding position, with force application device 4 represented in cut view relative to the linear travel relative to the WP welding position; 20 − Fig. 6 represents a control diagram relating to controller 5 with respect to the controlled elements of the welding equipment; − Fig. 7 represents a cut view of Fig. 1 of the apparatus welding before welding of edges S1, S2 is carried out; − Fig. 8 represents a cut view of Fig. 1 of the apparatus 25 welding after welding has taken place; fig. 9A, 9B, 9C, 9D, 9E, 9F represent different possible stages of the welding process ultrasound provided for by this invention; − Fig. 10 represents a graph of the reciprocal force applied to the force application device 4 and the mutual distance between sonotrode 30 2 and anvil during ultrasonic welding process phases according to the finding. Please note that in this description the phraseology and terminology used, as well as the figures of the attached drawings also as described have the sole function of illustrating and explaining the present invention better by having a non-limiting exemplary function of the invention itself, being the scope of 5 protection defined by the claims. For ease of understanding, identical reference numbers have been used, where possible, to identify identical common elements in the figures. It is understood that elements and features of an embodiment may be conveniently combined or incorporated into other embodiments without 10 further clarifications. With reference to fig. 1, the ultrasonic welding process involves the use of at least one welding device 1, dragging means 6, 7 of a continuous sheet S and a controller 5 connected to the device 1 and to the means 6, 7. The welding device 1 is of the ultrasonic type, in which a sonotrode 2 and 15 an anvil 3 interact to weld longitudinal edges S1, S2 of said sheet continuous S, in which the edges S1, S2 are interposed between the sonotrode 2 and the anvil 3. In particular, the ultrasonic welding device 1 shown in the figures It is of the rotating type. To simplify the current disclosure, the following will be embodiments are presented that include the use of sonotrode and anvils 20 rotating for purely illustrative and non-limiting purposes. Clearly, a person expert in the field using the teachings of this invention would be in able to apply the solution to other types of applications, such as cases where sonotrode and anvil are operated without rotation and are translated at least in approaching and moving away from the sheet for the mutual welding of edges 25 interposed. Consequently, the scope of protection of this invention extends to any type of ultrasonic welding. With reference to figure 2, the sonotrode 2 and the anvil 3 are preferably rotatable around respective rotation axes X2, X3. Sonotrode 2 and anvil 3 are arranged parallel, with the rotation axes X2, X3 parallel to each other. Preferably, the welding device 1 comprises a cylindrical joint 21 configured to limit the position of the sonotrode 2 relative to a frame of the welding device 1. Preferably the cylindrical joint 21 is mounted on a X21 axis fixed. 5 Preferably, the sonotrode 2 is mounted on a supporting flange 22 of the sonotrode. Preferably, the flange 22 is mounted so that it can rotate around the axis X21 fixed. Preferably, the cylindrical joint 21 is arranged substantially parallel to the rotation axis X2 of the sonotrode. Preferably the sonotrode 2 is mounted 10 rotatable with respect to the cylindrical joint 21, so as to be able to orbit around it. Preferably, the X3 axis on which the rotating anvil 3 is mounted is fixed with respect to the welding device 1. Preferably, the sonotrode 2 used in the welding process of the The present invention comprises a disc-shaped head 23 whose center coincides 15 with the X2 axis thereof. The head 23 of the sonotrode comprises a surface lateral 24. Similarly, the anvil 3 preferably comprises a head 33 disc-shaped whose center coincides with the X3 axis of the same. The head 33 of the anvil comprises a lateral surface 34. Preferably, the heads 23, 33 will be aligned and facing close to each other. 20 with respect to the 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 welding phase. The lateral surface 34 of the anvil 3 is suitably shaped with grooves configured to optimize the quality of the weld, in particular, 25 obtained through a dedicated process; by way of example but not limitation it is possible to perform a knurling process of the surface 34. The effect obtained from the interaction between the lateral surface 34 of the anvil 3 and the surface lateral 24 of the sonotrode 2 is to obtain a welded fin in which at least the edge S1 of the sheet placed in contact with the anvil 3 is knurled by effect 30 of the mutual interaction between the lateral surfaces 24, 34. Preferably, the welding device 1 used in the welding process welding of the present invention can advantageously comprise an actuator rotating 35 associated at least with the anvil 3. Figure 2 represents schematically the rotary actuator 35 as a functional block, such 5 rotary actuator 35 can be aligned with the anvil 3 along its axis of rotation X3, for example being directly associated 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 another any kinematic chain. 10 Preferably, the rotary actuator 35 is configured to impart a rotary motion around its own axis X3 of rotation. The actuator 35 of the welding device 1, preferably comprises an electric motor and a variator drive of frequency for its control. The drive is configured to vary the power and mechanical torque applied by the motor to the rotary actuator 35. 15 The drive is preferably connected to the controller 5. However, this is not excluded. that the drive is configured as a logical element belonging to the controller 5. The welding device 1 further comprises a transmission device of the motion 37, configured to constrain the rotation of the anvil 3 around its own 20 axis X3 to the rotation of the sonotrode 2 around its own axis X2. The device of motion transmission 37 preferably comprises a pair of gears parallel with conjugated profiles. Preferably, the transmission device of the motion 37 is configured to force sonotrode 2 and anvil 3 to rotate in reverse directions around their respective rotation axes X2, X3. Preferably, the 25 linear velocity of the sonotrode head 23 is substantially equal to the velocity of the anvil head 33 in the portion in contact with the edges S1, S2 of the continuous sheet S. This linear speed of the heads 23, 33, is substantially equal to the speed of the sheet S and slightly slower than the speed of the dragging means 6, 7 to advance the sheet S along the direction D1 of 30 packaging when the dragging means 6, 7 are active, in order to allow the dragging to be done by your own dragging means 6, 7 while the interaction between the heads 23, 33, of the sonotrode 2 and the anvil 3 is they are responsible for the mutual welding of the edges S1, S2 of the continuous sheet. in particular, the linear speed of the driving means 6, 7 is preferably higher by up to about 1% compared to the linear speed of heads 23, 33 and the sheet 5 S, even more preferably up to about 0.5%. The welding device 1 further comprises a vibration transducer 27. The vibration transducer 27 is mechanically coupled to the sonotrode 2 and It is configured to transform electrical energy into mechanical energy, so that vibrate the rotating sonotrode 2, and consequently its head 23, with 10 particular reference to the radial direction DR with respect to its own axis of X2 rotation of the sonotrode 2. The transducer 27 is configured to modulate, increasing or decreasing the amplitude of the vibration to zero function of the welding power required to be transmitted to the sheet S. The transducer 27 is conveniently connected to controller 5 for actuation and 15 transducer modulation 27. Preferably, the welding device 1 comprises a clamping 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 one direction 20 radial with respect to the rotation axis X2 and axially phased with respect to the head 23 of the sonotrode. Preferably the anvil 3 comprises a respective protrusion 38 in a radial direction with respect to the rotation axis X3 and axially phase-shifted with respect to the anvil head 33. Preferably, each of the protrusions 28, 38 radials is configured and sized to accommodate at least one element of 25 constraint 11, 12 between the force application device 4 and the respective sonotrode 2 and anvil 3. Preferably the constraint elements 11, 12 will be rotary joints 11, 12 with the respective axes arranged substantially parallel to the rotation axes X2, X3 of sonotrode and anvil. Advantageously, the force application device 4 30 and the protrusions 28, 38 will include seats configured and sized for accommodate cylindrical elements of the constraint elements 11, 12 with their own axis parallel to the sonotrode 2 and anvil 3, which allow mutual rotation between force application device 4 and sonotrode 2 and between force application device application of force 4 and anvil. 5 Preferably, the degree of freedom of movement between sonotrode 2 and anvil 3 introduced by the cylindrical joint 21 of the sonotrode 2 can be combined via the operation of the constraint device 4. In particular, in the phases in which the transducer 27 is active, the vibrational force applied on the welding device 1 has the effect of generating a mutual repulsive force between sonotrode 2 and 10 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 device 1 is in the welding position. The force application device 4 in any of the embodiments of the This finding is connected to controller 5. This way it is possible 15 control the force application device 4 independently of the others elements connected to the controller 5. Preferably, the force application device 4 is of the linear actuator type. 4. This linear actuator 4 is sized to have a linear stroke LS of implementation. Since the rotary joints 11, 12 are arranged with their respective axes 20 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 X2, X3 axes of rotation of sonotrode and anvil, so that the applied force on actuator 4 results in a change in position in the LS stroke, causing a mutual approach / distance between sonotrode 2 and anvil 3, plus 25 concretely between the close portions of the lateral surfaces 24, 34 of the heads of sonotrode and anvil. With reference to figures 2-5 and 7A-7F, and according to an embodiment of Of particular interest to the invention, the linear actuator 4 is a pneumatic actuator cylindrical 4. This pneumatic actuator 4 is preferably of the double-acting type 30 effect. The double-acting pneumatic actuator 4 comprises a piston 43 connected to a stem 44. The piston 43 of the actuator 4 is slidably mounted on a cylindrical seat 45 along the LS stroke. The double pneumatic actuator 4 effect has two input ports 41, 42, the first port 41 being positioned on the actuator body 4 containing stem 44 and second port 42 on the body of the actuator 4 containing the terminal side of the cylindrical sliding seat 45. 5 Preferably the actuator body 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 it is positioned oriented towards the second rotary joint 12 associated with the anvil 3. Alternatively the body containing the stem 44 is associated with a second rotary joint 10 12 and the body containing the terminal side of the cylindrical seat 45 is associated with the first joint 11. Preferably, the double-acting pneumatic actuator 4 is mounted normally open, that is, in the absence of pressure applied from the input ports 41, 42 the mutual force RF applied by actuator 4 between sonotrode 2 and anvil 3 is zero, 15 the welding device 1 is therefore not able to perform welding. According to the preferred embodiment, in the absence of other external forces the application of manometric pressure from the first port 41 results in the application of a pressure force of the surface 24 of the sonotrode 2 on surface 34 of the anvil 3. Conversely, in the absence of other external forces 20 the application of manometric pressure from the second port 42 results in the separation of the surface 34 of the anvil from the surface 24 of the sonotrode. Preferably, the welding device 1 may comprise a sensor pressure mounted on sonotrode 2 (not shown in figures) configured for 25 The dragging means 6, 7 used in the welding process of the present found are of the rotating type. Preferably the driving means 6, 7, may include first front drag means 6, arranged upstream of the welding device 1, and second rear driving means 7, arranged downstream of the welding device 1. Alternatively, the means of 30 dragging can only be arranged upstream of the welding device, advantageously the dragging means can be placed only downstream of the welding device. Each driving means 6, 7, comprises a pair of rollers 61, 71, arranged parallel and close to each other; with the front drag means 6 5 comprising a pair of front rollers 61 and the rear drive means 7 comprising a pair of rear rollers 71. Each roller of the pair of rollers 61, 71 is arranged to be rotated around a respective axis X6, X7 and configured for rotate in the opposite direction to the other roller 61, 71 of the pair of rollers 61, 71. The X6, X7 axis of each roller 61, 71 is substantially parallel to the X6, X7 axis 10 of the other roller 61, 71 of the pair. It is possible to move the pair of X6 axles of the front drag means 6 to allow the insertion of the edges of the sheet S1, S2 and then bring them closer together to allow the dragging of these flaps. Furthermore, it is possible to adjust the closing pressure between the two X6 axes. Similarly, it is possible to move away and towards 15 mutually the X7 axes of the rear drag means, as well as adjust the closing pressure between these axes X7. Each of the dragging means 6, 7 comprises configured constraint means to force the rotation of each roller 61, 71 of the pair in the direction opposite to the other roller 61, 71. Preferably, the constraint means 20 comprise a pair of parallel gears with conjugated profiles. Preferably, the diameter of the rollers 61, 71 of each pair of rollers is substantially equal to the other roller 61, 71 of the same pair of rollers 61, 71, in in this case the transmission ratio of the constraint means is substantially 1:1. Preferably, each of the driving means 6, 7 comprises a 25 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 commanded by controller 5. Each roller 61, 71 of the pair contacts the sheet S in a portion substantially tangential and opposite to the portion of the other roller 61, 71 30 of the pair. The front rollers 61 will contact the edges S1, S2 to be welded, while the rear rollers 71 will be able to advantageously drag a welded 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 sheet S itself, being dragged along the packaging direction D1. 5 Preferably, the welding device 1 is aligned with respect to the means of dragging 6, 7, along the packaging direction D1. In this configuration, the continuous S-sheet can be interposed along a segment straight in the direction D1 between each pair of rollers 61, 71, of the means of drag 6, 7, and between the sonotrode 2 and the anvil 3 of the welding device. 10 The ultrasonic welding process, according to the present invention, It includes the following phases: - Feed a continuous sheet S along a direction D1 of packaging; - Overlap two longitudinal edges S1, S2 of the continuous sheet S 15 counterfeiting them between the sonotrode 2 and the anvil 3; - Drag the continuous sheet S using dragging means 6, 7 in so as to obtain the advancement of the continuous sheet S along a D1 packaging direction during welding; - Activate sonotrode 2 by making it vibrate at an amplitude and frequency 20 predetermined welding; - Arrange the sonotrode 2 and the anvil 3 in a mutually exclusive position of WP welding; and - Apply a reciprocal RF welding force between the sonotrode 2 and the anvil 3 adequate to allow correct welding of the two edges S1, S2 25 longitudinal countersunk to form a welded fin SP; In the preferred but not exclusive embodiment where sonotrode 2 and 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 rotating anvil 3. In this process the sonotrode 2 is made to vibrate towards the anvil 3. In particular according to the embodiments in which sonotrode 2 and anvil 3 are of the type rotating, the sonotrode 2 vibrates in radial direction following the activation of the vibration transducer 27. 5 In this process the sonotrode 2 and the anvil 3 are arranged reciprocally in the WP welding position by the control of the constraint device 4. In this process the sonotrode 2 and the anvil 3 are connected by means of the application of a reciprocal RF force to exert pressure on the flaps of S sheet needed for welding and maintaining the welding position WP 10 from the implementation of the constraint device 4. Preferably the application of such mutual force allows to press the surface 24 of the sonotrode 2 against the surface 34 of the anvil 3 with the edges of sheet S arranged between them. Furthermore, the process includes a welding interruption phase. by interrupting the application of the RF welding force between the 15 sonotrode 2 and anvil 3, and a phase of keeping sonotrode 2 active leaving at the same time said sonotrode 2 and said anvil 3 in said position of WP welding, where the vibration of said sonotrode 2 generates a thrust against the anvil 3 is substantially equal to the amplitude of the vibration of the sonotrode 2. In other words, the welding interruption phase involves the unlocking of the 20 block between sonotrode 2 and anvil 3, leaving sonotrode 2 and anvil 3 in the WP welding position while the sonotrode 2 remains active, where said unlocking involves the interruption of the reciprocal RF force related to the actuation of the constraint device 4. Leaving the sonotrode always active instead of turning it off during the 25 interruption, has the advantage of not having to wait for this sonotrode to reach the vibration amplitude again following the restart of the same. Preferably, before or simultaneously with the withdrawal phase of the welding the procedure involves interrupting the sheet feed continuous S along the packaging direction D1. The radial vibration of the active sonotrode 2 generates a push-away force between the sonotrode 2 and the anvil 3 substantially equal to the radial amplitude of the vibration of sonotrode 2, until the contact between sonotrode 2 and anvil is eliminated following a plurality of vibration cycles. 5 This push away that occurred downstream of the unlocking is small. Typically, in ultrasonic welding devices for applications of product packaging the operating frequency of the transducer 27 is of the order of 10-50 kHz and has a radial amplitude of the order of approximately 30-80 µm. As mentioned above, the effect generated is a small distance 10 reciprocal between sonotrode 2 and anvil 3 substantially equal to the radial amplitude, or equal to or less than this radial amplitude of vibration. Consequently it can be considered that for the practical purposes of the further functioning of the force application device 4 following the interaction between sonotrode 2 and anvil 3 after unlocking, sonotrode 2 and anvil 3 remain in the position of 15 WP welding. It is specified that the welding position can be defined as a window of tolerance. In fact, it is specified that while the linear stroke LS of the application device of force 4 is a few millimeters, as is the difference between the open position OP and WP welding position, the mutual distancing due to the 20 vibration transmitted by transducer 24 is of the order of magnitude of tens of micrometers, the ratio between the two parameters being about two orders of size. This limited distance from each other allows for a prompt restore the process without having to turn off the transducer 24 or make any changes 25 again the phase of mutual approach between sonotrode 2 and anvil 3. In this configuration, sonotrode 2 could still contact the edges S1, S2 however without affecting the anvil 3 and consequently not hitting or causing wear to the anvil. During the welding interruption phase it is possible, even if not necessary, stop the operation of the rotary actuator responsible for the rotation of the sonotrode 2 and the anvil 3 around their respective axes X2, X3. According to embodiments of the present invention, the welding process, before or simultaneously with the application discontinuation phase of the 5 RF mutual force welding, provides to stop the sheet dragging continuous S along the packaging direction D1. In this way, the flaps S1, S2 will remain stationary in the position along the packaging direction so that in a possible resumption there are no longitudinal segments of sheet continuous S not welded following the sliding of sheet through the device 10 welding while the latter is not controlled for welding. According to embodiments of the present invention, the welding process according to the invention, it also comprises a welding recovery phase by means of the restoration of the reciprocal welding RF force applied between the sonotrode 2 and the anvil 3 in the welding position WP, in which the sonotrode 2 always remains 15 active. In this way, device 1 promptly recovers its capabilities weld the edges S1, S2 together, since the vibration of the sonotrode 2 remains always active as there is no need for an amplitude reactivation time of the vibration. According to embodiments of the present invention, the welding recovery phase 20 also includes the reactivation of the continuous sheet dragging S along the packaging direction D1 with said driving means 6, 7. In this way, since the mutual welding RF force has been restored and that a real reciprocal re-approach phase between the sonotrode is not required 2 and anvil 3, the welding phase restarts promptly. 25 According to embodiments of the present invention, the step of applying a force reciprocal welding RF between sonotrode 2 and anvil 3 of the process is such as maintain contact between the sonotrode 2 and the anvil 3 with the two flaps in between S1, S2 longitudinal to be welded. This reciprocal force RF is useful to apply a compression on the S1, S2 flaps to enable the transfer of the necessary energy 30 for welding due to the vibrating actuation of the sonotrode 2 on the anvil 3. Preferably, the reciprocating force RF is performed by a linear actuator 4. Preferably, the linear actuator 4 is of the double-acting pneumatic type as the one reported above. During the welding interruption phase, the manometric pressure is 5 equal in the two ports 41 and 42, and preferably zero, i.e. the pressure is substantially equal to that of atmospheric pressure. Atmospheric pressure at the inlet ports 41, 42 of the actuator is reached interrupting the operation of the pneumatic linear actuator 4, i.e. by interrupting the electrical power associated with actuator 4. 10 Alternative embodiments of the present invention provide that the actuator linear 4 is of the type one chosen between mechanical, electromechanical or hydraulic. 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. 15 In particular, the pneumatic actuator 4 can be equipped with a regulator electronic pressure. Preferably, during the phase of applying a reciprocal RF force the actuator increases the manometric pressure in a first port 41. The difference of pressures between the first port 41 and a second port 42 allows the sonotrode 2 20 to press against the anvil 3. In the welding interruption phase, the force reciprocal RF is zeroed by balancing the manometric pressure in the two ports 41 and 42, preferably reset by unloading both doors 41, 42. As previously mentioned, preferred embodiments of the present invention 25 provide that the sonotrode 2 and the anvil 3 are used in the process for the ultrasonic welding are of the rotating type around respective rotation axes X2, X3, which are operated to weld two edges of sheet metal placed between them. According to embodiments of the present invention, the sonotrode 2 and the anvil 3 will preferably be rotated at an angular velocity such that their respective surfaces in contact with the two longitudinal edges S1, S2 have a speed tangential substantially equal to the speed of dragging of said sheet continuous S. In particular, they will be portions of the lateral surfaces 24, 34 of the respective heads 23, 33 of sonotrode 2 and anvil 3 to tangentially contact the 5 edges S1, S2 of the continuous sheet during welding. The surface portions of the lateral surfaces 24, 34 will have a linear velocity equal to the velocity angle of sonotrode 2 and anvil 3 multiplied by the radius of their respective heads 23, 33. The linear velocity of said portions of the lateral surfaces 24, 34 in contact is slightly lower than the speed of the drag means 6, 7, in 10 way to weld, keeping pace with the speed of the sheet S without dragging it. As mentioned above the drag means 6, 7 will be responsible for moving the S1, S2 edges of the sheet at the process speed desired. Preferably, the procedure may provide that the anvil 3 remains in a 15 fixed position both in the locking and unlocking phases. As mentioned previously, the anvil 3 is mounted rotatably around its own axis X3. Preferably, the X3 axis is fixed, so as to keep the anvil in a fixed position of the welding device 1. With reference to figure 10, a graph is shown with the evolution 20 time of the different phases of the welding process, both by mutual force applied that for mutual distance between sonotrode 2 and anvil 3. In particular in the initial phase F1 a reciprocal closing force is exerted to bring the two together sonotrode 2 and anvil 3 from the open position OP, with mutual distance maximum, until reaching the WP welding position. This phase is 25 represented in figure 9A. In a subsequent phase F2, the procedure may include a waiting time before starting welding where no force is applied on the welding device constraint 4. Remember that sonotrode 2 is already active, i.e. able to vibrate to the desired width. 30 In a subsequent F3 welding phase the procedure requires that the a reciprocal force between sonotrode 2 and anvil 3 while transducer 27 vibrates according to predetermined welding parameters, in order to maintain the mutual welding distance WP and to exert a compression on the edges of the sheet S suitable for transmitting the necessary welding energy (figure 9B). specifies that in the case of using the pneumatic actuator 4, the reciprocal force 5 RF is applied by increasing the manometric pressure of port 41, while the port 42 is kept substantially unloaded, i.e. at pressure atmospheric. As mentioned before, the procedure includes a F4 phase of interruption of the welding by unlocking the lock between the sonotrode 2 and the anvil 3, 10 leaving sonotrode 2 and anvil 3 in the WP welding position while the sonotrode 2 remains active (figure 9C). During the interruption phase F4 the force The applied RF reciprocal is zero. During the F4 interruption phase, the transducer 27 vibrates the sonotrode 2, gradually separating, but only slightly, sonotrode 2 and anvil 3. This displacement is shown in figure 8 during the phase 15 F4 interruption. It is specified that in the case of using the pneumatic actuator 4, the elimination of the mutual RF force occurs by balancing the pressure of ports 41, 42. Preferably, the pressure balance occurs by unloading both ports 41, 42, i.e. bringing them to pressure atmospheric. 20 In an F5 recovery phase the procedure provides that you can resume timely mutual welding by applying a force mutual RF such as to counteract the effects of mutual interaction between sonotrode 2 and anvil 3 (figure 9D). Preferably, during the recovery phase F5 the sonotrode remains active. It is specified that in the case of using the actuator 25 tire 4, the F5 recovery phase involves increasing the pressure manometric of port 41, while port 42 is kept substantially in exhaust, that is, at atmospheric pressure. Finally, it is possible to apply a new final F6 break, to which preferably follows a final phase F7 of mutual distancing, applying 30 a mutual force (figure 9E). At the end of the final phase F7, sonotrode 2 and anvil 3 will again be placed in an open position OP, where the mutual distance is maximum (Figure 7F). It is specified that in the form implementation which involves the use of the pneumatic actuator 4 the phase of mutual distancing F7 provides for an increase in manometric pressure of the second door 42 while the first door 41 is kept substantially in 5 exhaust, or at atmospheric pressure. The present invention extends its scope of protection to an apparatus 10 of rotary type ultrasonic welding, including - a welding device 1 comprising a sonotrode 2 and an anvil 3 configured to be operated to weld two flaps together 10 S1, S2 longitudinals of a continuous sheet S interposed between these, - 8 feed means configured to feed the sheet continuous; and - dragging means 6, 7 configured to drag the sheet continuous S so as to obtain the advancement of the continuous sheet S along 15 a D1 packaging direction during welding. Preferably, the sonotrode 2 is configured to be vibrated at a predetermined amplitude and frequency of welding so that when the sonotrode 2 and anvil 3 are placed in a welding position WP the welding device 1 is capable of welding two overlapping longitudinal edges 20 arranged along the said edges S1, S2 counter-facing each other and interposed between the sonotrode 2 and anvil 3. Preferably, the welding device 1 further comprises a welding device force application 4 configured to apply a reciprocal RF force of welding between sonotrode 2 and anvil 3 to allow correct welding 25 of the two longitudinal flaps S1, S2 counter-faced to form a welded fin SP; Preferably, the welding apparatus 10 further comprises a controller 5 connected to the constraint device 4. Controller 5 is configured and programmed to stop applying reciprocal RF force to welding during a welding interruption phase without deactivating the 30 sonotrode 2, so that the vibration of sonotrode 2 generates a thrust against the anvil 3 is substantially equal to the amplitude of the vibration of the sonotrode 2. In this way, the welding equipment 10 can restart with welding quickly rather than having to go through a restart procedure with mutual approach of sonotrode 2 and anvil 3. In this way, it is not reactivate sonotrode 2 and wait for the vibration amplitude to reach 5 the nominal value. Preferably, the sonotrode 2 and the anvil 3 of the welding apparatus 10 will be of the rotating type. Preferably, the controller 5 is configured and programmed to rotate the sonotrode 2 and the anvil 3 around their respective axes of rotations X2, X3 during the welding phase. In this way the controller 5 10 can coordinate the driving means 6, 7 and the sonotrode 2 and the anvil 3 of the welding device 1. Preferably the controller 5 of the apparatus 10 is configured to maintain the vibration of the sonotrode 2 3 during the interruption phase of the welding. During the welding interruption phase, the stop command is given. 15 of the rotation of the sonotrode 2 and the anvil, to prevent the stationary sheet S from tears. This operating logic allows the welding equipment 10 to restart promptly after an intermediate phase of interruption of the welding. Preferably, the power supply means 8 comprises a rotatable element 20 configured to accommodate a roll of sheet packaging material and to rotate said reel by unwinding the continuous sheet towards the means of drag 6, 7 and welding device 1. The welding apparatus 10 can be advantageously integrated into a packaging machine, which further comprises a device 25 trainer 9. Preferably, the forming device 9 is arranged along the line of conveying of products. Preferably, the forming device 9 comprises bending means arranged between an input section and a section output of the forming device 9. Preferably, the bending means of the forming device 9 will be configured to intercept and detect the continuous sheet S and fold the sheet continuous S so as to form a tubular casing around the products comprising respective folded and mutually counter-facing end flaps. 5 According to embodiments of the present invention, the apparatus 10 of welding can be integrated into a horizontal packaging machine, such as the flow pack type, in which a forming device 9 is interposed between the continuous sheet S feeding means and the welding device 1. The forming device 9 is configured to arrange the sheet around the products to be 10 package, typically delivered along a supply direction parallel to the packaging direction D1. This way you can easily wrap the continuous S sheet around the products to be packaged, leaving the longitudinal edges S1, S2 below the product to be packaged along the line product conveyance. 15 Alternative embodiments of the present invention provide that the welding equipment 10 is integrated into a welding machine vertical packaging, in which the product to be packaged is supplied in bulk from above and inserted into a tubular or prismatic dosing device. forming device 9 in such machines can be the same dosing device, 20 alternatively the forming device 9 is external to the dosing device, normally concentric, so as to arrange the continuous sheet around the bulk product dosed through the dosing device. In the case of the vertical packaging machine before dosing bulk product a transversal welding phase takes place in order to close from the 25 low the package, In any case the longitudinal welding of the flaps S1, S2 proceeds in parallel. It is clear that the ultrasonic welding process and the equipment For the ultrasonic welding described above, modifications can be made. and / or additions of parts or phases, without thereby departing from the scope of this 30 found as defined by the claims. In the following claims, the references in parentheses are for the sole purpose of facilitate reading and should not be considered as limiting factors for as regards the scope of protection underlying the specific claims.

Claims

1. Ultrasonic welding process, wherein a sonotrode and an anvil are operated to weld two edges of sheet placed between them, said process comprising the steps of: - feeding a continuous sheet (S) along a packaging direction (D1); - overlapping two longitudinal edges (S1, S2) of said continuous sheet (S) by counter-facing them between said sonotrode (2) and said 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 welding; - activating the sonotrode (2) by making it vibrate at a predetermined welding amplitude and frequency; - mutually arranging the sonotrode (2) and the anvil (3) in a welding position (WP);and - applying a reciprocal welding force (RF) between said sonotrode (2) and said anvil (3) adequate to allow correct welding of the two longitudinal flaps (S1, S2) facing each other to form a welded fin (SP); characterised in that said process also comprises a welding interruption phase by interrupting the application of the welding force (RF) between said sonotrode (2) and said anvil (3), and a phase of keeping the sonotrode (2) active while leaving said sonotrode (2) and said anvil (3) in said welding position (WP), wherein 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. Process according to the previous claim, characterised in that before or simultaneously with the welding interruption phase, the process involves stopping the transport of said continuous sheet (S) along the packaging direction (D1).

3. Process according to claim 1 or 2, characterised in that it comprises a welding resumption phase by restoring the welding force (RF) applied between the sonotrode (2) and the anvil (3) in said welding position (WP), in which the sonotrode (2) always remains active.

4. Process according to claim 3 when it depends on claim 2, characterised in that the welding resumption phase also comprises the reactivation of the dragging of the continuous sheet (S) along the packaging direction (D1) with said dragging means (6, 7).

5. Process according to any of the preceding claims, characterised in that the reciprocal welding force (RF) of said step of applying a reciprocal welding force (RF) is such as to maintain contact between the sonotrode (2) and the anvil (3) with said two longitudinal flaps (S1, S2) to be welded interposed.

6. A method according to claim 5, characterised in that said reciprocal force (RF) is carried out by a linear actuator (4), preferably of the double-acting pneumatic type with two input ports (41, 42), wherein the phase of interrupting the application of the welding force (RF) comprises the balancing of the pressures applied in the two input ports (41, 42), preferably by subjecting both ports (41, 42) to atmospheric pressure.

7. Method according to any of the preceding claims, characterised in that said sonotrode (2) and said anvil (3) are of the type rotating around respective rotation axes (X2, X3).

8. Process according to claim 7, characterised in that said sonotrode (2) and anvil (3) are rotated at an angular velocity such that their respective surfaces in contact with the two longitudinal edges (S1, S2) to be welded have a tangential velocity substantially equal to the dragging velocity of said continuous sheet (S).

9. Ultrasonic welding apparatus (10), comprising - a welding device (1) comprising a sonotrode (2) and an anvil (3) configured to be operated to weld together two longitudinal edges (S1, S2) of a continuous sheet (S) interposed therebetween, - feeding means (8) configured to feed said continuous sheet (S); - driving means (6, 7) configured to drive said continuous sheet (S) so as to achieve advancement of said continuous sheet (S) along a packaging direction (D1) during welding; wherein said sonotrode (2) is configured to be vibrated at a predetermined welding amplitude and frequency so that when the sonotrode (2) and the anvil (3) are placed in a welding position (WP) with the two longitudinal edges (S1, S2) of the continuous sheet (S) interposed therebetween, said device (1) is capable of weld them;wherein said welding device (1) further comprises a force application device (4) configured to apply a welding force (RF) between said sonotrode (2) and said anvil (3) to enable correct welding of the two longitudinal flaps (S1, S2) facing each other to form a welded fin (SP); characterised in that it further comprises a controller (5) connected to said force application device (4) and configured and programmed to interrupt the application of the welding force (RF) during a welding interruption phase, said controller (5) being further programmed to maintain the vibration of said sonotrode (2) active while leaving said sonotrode (2) and said anvil (3) in said welding position (WP), so that 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. Apparatus (10) according to claim 9, characterised in that said sonotrode (2) and said anvil (3) are of the rotating type and 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 welding phase.

11. Apparatus according to claim 10, characterised in that said force application device (4) is a linear actuator (4) of the double-acting pneumatic type comprising two input ports (41, 42) and in that said controller (5) is further configured and programmed to reset the reciprocal welding force (RF) applied by said device (4), preferably by balancing the pressures applied in the two input ports (41, 42), e.g. 5 by subjecting both ports (41,42) to atmospheric pressure.