Abstract:
A device and a method is proposed whereupon the device for processing a packing material using ultrasound comprises the following elements: at least one sonotrode ( 10 ), at least one anvil ( 12 ), whereupon a gap is constructed between sonotrode ( 10 ) and anvil ( 12 ) through which the packing material can be passed for the purpose of ultrasonically sealing a packing material, at least one adjustment means ( 50 ) that adjusts the gap (s) between sonotrode ( 10 ) and anvil ( 12 ), at least one generator ( 70 ) that changes an input voltage into an output voltage, which a converter ( 74 ) transforms into mechanical oscillations in order to generate ultrasonic oscillations on the sonotrode ( 10 ), whereupon a regulation device and/or control device ( 78 ) is arranged to regulate or control the gap (s) between sonotrode ( 10 ) and anvil ( 12 ) depending on at least one electric variable (P,E,R) that acts on the sonotrode ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention is based on a device and a method for processing a packing material by means of ultrasound. DE 197 537 40 C1 discloses a device for processing a material strip, having an ultrasound unit which has a sonotrode and a counterpart tool. The material strip is guided through a gap between the sonotrode and counterpart tool, wherein the sonotrode is clamped in a carriage and can be adjusted relative to the counterpart tool by means of an adjusting device. The force with which the sonotrode is loaded in the direction of the counterpart tool is measured by means of a force sensor. By means of the pressing force of the sonotrode thus determined, the sonotrode can be moved toward the counterpart tool or away from the counterpart tool by means of a control device. The optimum pressing force is determined in advance in tests and is stored as a setpoint value in the control and/or regulating device. 
       SUMMARY OF THE INVENTION 
       [0002]    The invention is based on the object of specifying a device and a method in which adjustments and regulation of the sealing gap are further improved and consistent quality of the sealing seam is attained. 
         [0003]    In contrast to this, the device and method according to the invention have the advantage that a more uniform spacing of the sealing rolls to one another can be reliably maintained even in the event of temperature fluctuations. This permits consistent quality of the sealing seam. The regulation and/or control of the sealing gap takes place as a function of at least one electric variable which acts on the sonotrode. This may be an electric output variable of a generator which provides high-frequency electrical energy for generating mechanical ultrasound vibrations to a converter, which in turn acts correspondingly on the sonotrode. Electric variables can be very easily integrated into a regulation and/or control system and are often provided in any case. For example, the generator power or energy is available in a corresponding generator regulator. On the other hand, a targeted voltage loading of the sonotrode—as a further electric variable—may in a particularly simple manner be a constituent part of a contact detection system. 
         [0004]    With the gap measurement by means of an electric variable of the generator regulator in combination with contact detection, it is possible to dispense with an additional temperature sensor for further correction. Separate force sensors are also no longer required. The contact detection system provides the application of a voltage to the upper and lower sealing rolls, wherein an electrical sparkover would occur shortly before contact. In this way, the directly impending contact of the sealing rolls can be determined from an electrical current flow, and is therefore suitable in particular for a region to which the gap measurement by means of the electric variable of the generator regulator is not particularly well suited. All the gap sizes are therefore reliably detected. Also, the current flow upon contact can be detected particularly easily and integrated into the regulation or control of the gap. 
         [0005]    In one expedient refinement, the regulator or controller is initialized by virtue of at least one of the sealing rolls performing a parallel movement until contact occurs. Finally, only one side is lowered until contact occurs, and then the other side. In this way, it is ensured that the sealing rolls are parallel to one another. This process may take place automatically. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Exemplary embodiments of a device and method for processing a packing material by means of ultrasound are illustrated in the drawing and will be described in more detail below. 
           [0007]    In the drawing: 
           [0008]      FIG. 1  shows a perspective front view of the device for processing a packing material, 
           [0009]      FIG. 2  shows the rear view of the device according to  FIG. 1 , 
           [0010]      FIG. 3  shows a side view of a coupling means, 
           [0011]      FIG. 4  shows a side view of a further alternative coupling means, 
           [0012]      FIG. 5  shows a perspective illustration of a further exemplary embodiment of the device for processing a packing material, expanded to include an adjusting means, 
           [0013]      FIG. 6  shows a side view of a first adjusting device, 
           [0014]      FIG. 7  shows the side view of a second adjusting device, 
           [0015]      FIG. 8  shows the side view of a third adjusting device, 
           [0016]      FIG. 9  shows a flow diagram of the initialization, 
           [0017]      FIG. 10  shows a flow diagram of the gap regulation, and 
           [0018]      FIG. 11  shows a block circuit diagram of the regulation structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the device according to  FIG. 1 , a sonotrode  10  is rotatably mounted on both sides by in each case one bearing shield  14 . The two bearing shields  14  for the sonotrode  10  are laterally connected to one another at the top side of the device  8  by an upper support means  22 , designed here by way of example as a support beam. A likewise rotatably mounted anvil  12  interacts with the sonotrode  10 . The anvil  12  is mounted in two bearing shields  16 . The bearing shield  14  of the sonotrode  10  is connected by a coupling means  20  to the bearing shield  16 , situated therebelow in each case, of the anvil  12 . The two bearing shields  16  of the anvil  12  are in turn laterally connected to one another by a lower support means  24 , which is formed by way of example as a support tube. Arranged in each case on the opposite side of the coupling means  20  in relation to the axes of rotation of the sonotrode  10  and anvil  12  are force means  18  by means of which the required sealing force can be applied to the sealing surface of the sonotrode  10  and anvil  12 . Adjusting means  30  are provided in each case above the force means  18 . In this way, the sealing force or sealing gap s can be adjusted. 
         [0020]    In the rear view, shown in  FIG. 2 , of the device  8  described in  FIG. 1 , it is clear that the bearing shield  14  of the sonotrode  10  is connected in each case to the bearing shield  16 , arranged therebelow, of the anvil  12  by the coupling means  20 , which is designed by way of example as a bending beam. The coupling means  20  is connected at the top end to the end side of the bearing shield  14  by means of two fastening elements  21 , and is connected at the bottom end to the bearing shield  16  by means of two fastening elements  21 . Here, a gap is provided between the bottom edge of the bearing shield  14  of the sonotrode  10  and the top edge of the bearing shield  16  of the anvil  12 , which gap is bridged only by the coupling means  20 . Furthermore, a drive  28  is provided which, by means of a drive element  26 , drives both the sonotrode  10  and also the anvil  12  in opposite directions. 
         [0021]    In the view of  FIG. 3 , the bearing receptacles for the rotating sonotrode  10  and the rotating anvil  12  are visible as round openings. The bearing shield  14  of the sonotrode  10  is connected to the bearing shield  16  of the anvil  12  at one side by the coupling means  20 , which is designed as a bending beam. On the opposite side, the force means  18  loads the bearing shields  14 ,  16  with a force toward one another via the coupling means  20 , which acts as a joint. In the direction of the coupling means  20 , the bearing shields  14 ,  16  each have recesses  23 . The desired bending capability of the bending beam  20  can thus be influenced by the bending length formed in this way. In the arrangement shown, the bending beam acts as a center of rotation, by means of which the spacing between the sonotrode  10  and anvil  12  can be varied. The design of the coupling means  20  as a bending beam offers a relatively rigid but nevertheless articulated connection between the two bearing shields  14 ,  16 . The use of a bending beam as a coupling means  20  also acts as an overload protection means in the event of a crash. The bending beam  20  thus permits a defined opening and bending of the sealing gap s between the sonotrode  14  and anvil  16  even in the event, for example, of a product or foreign body becoming jammed between the sonotrode  10  and anvil  12 . 
         [0022]    The gap s between the sonotrode  10  and anvil  12  can be varied according to adjustment. The force means  18  has the effect of moving the upper and lower bearing shields  14 ,  16  toward one another about the center of rotation  56 , and thereby imparting a force to the sealing surfaces. For this purpose, a plunger  48  is connected at one side to the bearing shield  14  of the sonotrode  10  such that a movement of the plunger  48  also causes a movement of the bearing shield  14 . The plunger  48  is guided through an opening in the bearing shield  16  of the anvil  12 , so as to be movable relative to the bearing shield  16 , and ends with a flange  51 . The flange  51  serves as a support surface for a spring  49  which, at the other side, is supported against the underside of the bearing shield  16  of the anvil  12 . The spring  49  is designed as a spiral spring and surrounds the plunger  48 . The force means  18  is preferably designed to be adjustable. For this purpose, it would for example be possible for the adjusting means  30  in the form of a screw to vary the preload of the spring  49  and thereby ultimately the sealing force. 
         [0023]    In the exemplary embodiment of  FIG. 4 , as a coupling means  20 , a bush-pin connection is provided which permits a rotational movement of the two bearing shields  14 ,  16  relative to one another about a center of rotation  56 . It is however essential that the coupling means  20  permits a relative movement between the bearing shield  14  of the sonotrode  10  and the bearing shield  16  of the anvil  12  in such a way that the sonotrode  10  and anvil  16  can be moved relative to one another in order to realize the adjustment of a gap s depending on the packing material. The axis of rotation about the center of rotation  56  is parallel to the axis of rotation of the sonotrode  10  and anvil  12 . 
         [0024]    The exemplary embodiment of  FIG. 5  differs from that of  FIGS. 1 and 2  substantially in that adjusting means  50  are additionally shown. The adjusting means  50  comprise a coupling  52  and a threaded bolt  54  for gap adjustment by virtue of the bearing shield  14  of the sonotrode  10  being adjusted relative to the bearing shield  16  of the anvil  12 . Furthermore, in the exemplary embodiment of  FIG. 5 , the coupling means  20  is in a lateral arrangement. Here, a bolt is coupled to the bearing shield  14  of the sonotrode  10 , and a bush which engages correspondingly into the bolt is coupled to the bearing shield  16  of the anvil  12  at the center of rotation  56 . 
         [0025]    The exemplary embodiments of  FIGS. 6 to 8  show different variants of the adjustment possibilities between the bearing shield  14  of the sonotrode  10  and the bearing shield  16  of the anvil  12 .  FIG. 6  corresponds to the variant illustrated in  FIG. 5 , where the adjusting means  50  presses via the coupling  52  and the threaded bolt  54  against the lower edge of the bearing shield  14  of the sonotrode  10  and thereby effects a relative movement about the center of rotation  56 . The adjusting means  50  is arranged relatively distant from the center of rotation  56 . As an adjusting device  50 , a servo motor is for example provided which, via the threaded bolt  54 , imparts a translatory movement to the bearing shield  14 . Here, the lower bearing shield  16  will function, in effect, as a base, and push the upper bearing shield  14  upward via the threaded bolt  54  as the latter is unscrewed. The force means  18  furthermore ensure that the upper bearing shield  14  always bears against the threaded bolt  54  and thus also moves downward as the threaded bolt  54  is screwed in. On account of the pressure acting continuously from above, the thread play does not have a noticeable adverse effect. The use of in each case one servo motor with threaded bolt  54  in the left-hand and right-hand bearing shields  14 ,  16  makes it possible for the sonotrode  10  and the anvil  12  to be automatically aligned parallel to one another. In the exemplary embodiment of  FIG. 6 , very small and also relatively large adjustment travels can be attained very accurately. 
         [0026]    In the exemplary embodiment of  FIG. 7 , the spacing can be varied by means of an eccentric  58  which is rotatably mounted parallel to the axis of rotation of the sonotrode  10  and anvil  12 . The force means  18  again effects a preload between the two bearing shields  14 ,  16 . The rotational movement of a servo motor is converted by means of the eccentric disk  58  into a translatory movement. Whereas the eccentric disk  58  is fixedly mounted, the upper bearing shield  14  are raised and lowered by means of the eccentric disks  58 . 
         [0027]    In the exemplary embodiment of  FIG. 8 , an actuator  60  is provided which engages relatively close to the center of rotation  56 . The actuator is for example a piezoelectric actuator  60  which converts electrical energy into a mechanical change in travel. Piezoelectric actuators  60  are advantageous because they can carry out movements in the sub-nanometer range. Furthermore, piezoelectric actuators  60  are maintenance-free and wear-free. In static operation, they require no power. Furthermore, high loads can be moved. 
         [0028]    The input voltage of 50 Hz, 220 V is converted by an electric generator  70  into high-frequency electric alternating-current voltage. Most systems operate with 20, 30 or 35 kHz. The sound converter (converter  74 ) is connected to said generator  70  and in turn converts the electrical energy into high-frequency mechanical vibrations. By means of an amplitude transformation piece (booster  76 ), the amplitudes are amplified or reduced. Here, the change in amplitude is inversely proportional to the change in cross section of the booster  76 . The high-frequency vibrations at the converter  74  are transmitted from the booster  76  to the fusion tool, specifically the sonotrode  10 . The sonotrode  10  is screwed on with frictional engagement and so as to be easily exchangeable. One option for determining the change in the gap dimension s exists in the generator regulator  72  which is provided in any case. The generator  70  contains an electric oscillator circuit in which the behavior of the mechanical oscillator circuit is directly reflected. As long as the oscillator circuit, both the mechanical and the electric oscillator circuit, oscillates at its natural frequency, only the amount of energy lost through friction losses in the material and through resistance need be supplied to said oscillator circuit. If the sonotrode  10  is hindered in its natural movement by the sealing and/or cutting, this is also manifested in the electrical oscillator circuit. The energy extracted from the system in this way is proportional to the fusion amplitude and force and, in this respect, also to the fusion gap s. By parameter adjustment upon the start of operation, it is possible for a reliable range for the power P or energy E to be defined (Pmin, Pmax; Emin, Emax) in which good quality fusion takes place. If said range is departed from, the generator regulator  72  outputs a corresponding signal to a regulator or controller  78  to adapt the gap dimension s correspondingly. Corresponding to said change As, the regulator or controller  78  activates the adjusting device  50 , as a result of which the sealing gap s is varied in the desired way. The generator regulator  72  generates for example the rectangular profile of the power P over time illustrated in  FIG. 11 . The power P assumes its maximum at the times at which the sealing surfaces of the sonotrode  10  and anvil  12  are situated directly opposite one another and ultrasound sealing is to be carried out. To obtain the desired power profile, the generator regulator  72  constantly measures the actual power P_act of the generator  70 . 
         [0029]    The regulator or controller  78  is also supplied an output signal R from a contact detection system  82 , by means of which directly impending contact of the sonotrode  10  and anvil  12  is detected. For this purpose, a preferably low voltage is applied to the sonotrode  10  and anvil  12  by means of a voltage source  80 . If contact occurs or is impending, the current circuit is closed, which can be identified on the basis of the output signal R. In the event of impending contact, the regulator or controller  78  increases the sealing gap s, as described in more detail below. 
         [0030]    Both the sonotrode  10  and also the anvil  12  rotate in opposite directions and are designed, in effect, as sealing rolls. They have a plurality of sealing surfaces into which may also be integrated a cutting function for cutting the packing material. Depending on the type of packing material, a sealing gap must be set with high accuracy. A sealing gap or gap s denotes the spacing of the sealing surface of the sonotrode  10  from the sealing surface of the anvil  12 . Said sealing gap s is adjusted to the desired size by adjusting means, illustrated by way of example in  FIGS. 5 to 8 , such as an adjusting drive  50 , eccentric  58  or actuator  60 . Said adjusting means act on at least one bearing shield  14  relative to the other bearing shield  16 . If the size of the gap s varies during ongoing operation, the adjusting means  50  can adjust said gap back to the desired setpoint size. The force means  18 , designed for example as a spring, on the end of the bearing shields  14 ,  16  serves to press the bearing shields  14 ,  16  together and impart the required sealing and/or cutting force. Furthermore, by means of the toothed belt drive, forces act on the sonotrode  10  which seek to raise the upper bearing shields  14 , which is prevented by the force means  18 . The force means  18  could also be of pneumatic or hydraulic design instead of a spring. The coupling means  20  serve to movably connect the bearing shield  14  of the sonotrode  10  to the bearing shield  16  of the anvil. In addition to the described variants, linear guides such as for example column guides could also be provided, which permit a relative linear movement of the bearing shields  14 ,  16  with respect to one another. 
         [0031]    The bearing shields  14  form side cheeks which are connected to one another by the support means, specifically the support beam  22 . The support tube  24  could also serve for stabilization and as a holding facility in the packaging machine. The drive coupling of the upper and lower sealing rolls (sonotrode  10  and anvil  12 ) is realized by means of toothed belts. The rotational speed of the sealing rolls is dependent on the speed of the strip of the packing tube to be sealed and may for example be event-controlled. Said dynamics are attained by means of the drive  28 , for example a servo motor, which transmits the forces and torques by means of a drive element  26  designed as a toothed belt. The described device allows the parameters required for the joining process by means of ultrasound, such as for example the sealing gap s, sealing force and sealing time, to be set very precisely and in a manner appropriate to the application. The adjustment of the sealing force can be realized via the force means  18 . The force means are designed for example as springs, such that it is possible for the sealing force to be adjusted linearly with respect to the spring characteristic curve. The force means  18  act on the two bearing shields  14 ,  16 , such that the sealing force between the upper sealing roll, the sonotrode  10 , and the lower sealing roll, the anvil  12 , can be set. 
         [0032]    In the contact detection system  82 , a voltage of approximately 5 to 10 V is applied to the upper and lower sealing rolls, that is to say the sonotrode  10  and anvil  12 . Shortly before metallic contact of the sonotrode  10  and anvil  12  occurs, the current circuit is closed, specifically in the form of an electrical sparkover. At the stated voltage, the electric strength in the case of air and atmospheric pressure is a distance of 0.6 to 1.0 μm, depending on the temperature, humidity and the presence of foreign bodies. If heating of the sonotrode  10  and anvil  12  leads to a reduction in the gap dimension s, the signal provided by the regulator or controller  78  would trigger a defined backward stroke of the upper sealing roll, specifically the sonotrode  10 . Too large a gap s cannot be detected by means of the contact detection system  78 . 
         [0033]    Below, the initialization of the regulator and/or controller  78  will be described in more detail on the basis of  FIG. 9 . Upon the start of operation of the device  8  for processing a packing material by means of ultrasound, it must be ensured that the sealing rolls, specifically the sonotrode  10  and anvil  12 , are parallel to one another. After the start of the initialization (step  101 ), the sealing rolls  10 ,  12  are placed into the sealing position (step  102 ). For this purpose, the sealing rolls  10 ,  12  should be manually aligned with one another such that the lugs of the sonotrode  10  and anvil  12  are situated opposite one another. Said position is stored in the machine controller. The sonotrode  10  and anvil  12  are moved relative to one another such that they are brought into contact with one another, wherein the side at which contact takes place is not known. For this purpose, both sides are lowered in parallel until contact occurs (steps  102 ,  103 ). Subsequently, the sonotrode  10  is raised by Δha to a starting gap. It is detected by means of the contact detection system  82  whether the sonotrode  10  and anvil  12  are in contact, because in this case, a current flows via the sealing rolls  10 ,  12 . Thereafter, firstly the right-hand side (step  104 ) and then the left-hand side (step  105 ) are lowered until contact occurs and in each case raised again by the change in travel ΔHr and ΔHI respectively registered here. If the sonotrode  10  and anvil  12  are not parallel to one another, the corrective factor K can be calculated (steps  108  and  111 ) from said two changes in travel ΔHr and ΔHI respectively, from the bearing spacing B and from the roll width b of the sonotrode  10 : 
         [0000]        K= ( ΔHr−ΔHI )*( B+b )/2 b )   (step 108)
 
         [0000]      and 
         [0000]        K =( ΔHI−ΔHr )*( B+b )/2 b )   (step 111).
 
         [0034]    After the higher side is lowered by K (or the lower side is raised by K), the sonotrode  10  and anvil  12  are parallel. In step  110 , both sides are lowered until contact occurs and then both sides are raised, in parallel, to the fusion gap s. The initialization is thereby complete (step  113 ). 
         [0035]    After the initialization according to  FIG. 9 , the sealing rolls  10 ,  12  move into the start position (the sealing lugs are not in contact in order to thread in the packing material and start the machine). The gap regulation realized in the regulator or controller  78  is now explained in more detail in  FIG. 10 . 
         [0036]    After the sealing gap s has been set to the predefined sealing gap s by means of the initialization (step  202  according to the approach of  FIG. 9 ), heating of the sonotrode  10  and anvil  12 , and therefore a reduction in the gap dimension s, occur during the course of operation. The corresponding regulating circuit for gap regulation with the already described gap measurement and gap adjustment to the required sealing gap is illustrated in  FIG. 10  as a function of environmental influences, the adjusting device  50 , the ambient temperature, the sealing roll temperature etc. (cf. step  203 ). The desired gap dimension is determined from the environmental influences (step  204 ). At the sealing time, the gap s is measured (step  206 ), specifically when the sealing surfaces of the sonotrode  10  and anvil  12  are adjacent to one another. At this time, it is checked whether the sonotrode  10  and anvil  12  are in contact (step  208 ). This takes place by means of the contact detection system  82 . If it is concluded, on account of a current flow, that the sonotrode  10  and anvil  12  are in contact, the gap s is increased (step  207 ). The gap measurement by means of the generator regulator  72  takes place in parallel. For this purpose, upon every (m+1) th  (m is equal to the number of sealing lugs) engagement of the sealing rolls  10 ,  12 , at the sealing time, the power P_act delivered by the generator regulator  72  is compared with the admissible power Pmin, Pmax. The admissible power, which lies within the limits Pmin and Pmax, is defined by the parameter setting upon the start of operation and encompasses the power range Pmin to Pmax in which good quality fusion takes place. If the measured electrical power P_act deviates in the upward direction from the admissible range Pmax (P_act&gt;Pmax), the gap is too narrow (query  213 ) and the gap is increased (step  214 ). As a result of this, the adjusting drive  50  is triggered so as to increase the gap s by a few μm. If the power P_act is lower than the admissible power Pmin (P_act&lt;Pmin; query  212 ), the gap must be reduced (step  215 ). It would alternatively also be possible for further suitable electric variables as output variables of the generator  70 , such as for example the energy E (as an integral of the power P), to be compared with corresponding limit values Emax, Emin, or else current, voltage etc. 
         [0037]    Independently of the generator regulator  72 , the contact detection system  82  monitors in parallel the spacing between the sonotrode  10  and anvil  12  (step  208 ). When the current circuit of the contact detection system  82  closes, that is to say the sealing rolls  10 ,  12  come into contact, a backward stroke of the upper roll, in this case the sonotrode  10 , is triggered independently of the generator regulator  72 , such that the gap s is increased (step  207 ). 
         [0038]    The described device  8  is suitable in particular for the formation of a transverse sealing seam for tubular bags, but is not restricted to this. Tubular bag machines of said type may be arranged horizontally or vertically depending on the product to be packed.