Patent Publication Number: US-10766655-B2

Title: Thermoform packaging machine with film punch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority to German Patent Application Number 102015211622.0 filed Jun. 23, 2015, to Elmar Ehrmann and Robert Maier, currently pending, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a thermoform packaging machine as well as to a method comprising the features of the machine. 
     BACKGROUND OF THE INVENTION 
     DE 198 41 415 A1 discloses a film punch suitable for cutting plastic films/foils by means of a knife and a counter knife. A lift drive including a linear motor is provided. The lift drive includes a means of an articulated lever arrangement in combination with a straightening lever arrangement comprising together a large number of mechanical levers. Forces which are effective for cutting the film can increase rapidly and towards the end of the punching stroke, the increase of these forces becomes less steep. This is advantageous insofar as the film punch is intended to be suitable for reliably cutting different film/foil thicknesses without complicated knife adjustment operations being necessary. 
     The prior art discloses a film punch, type FS 08, produced by the applicant&#39;s company (see  FIG. 1 ), which comprises a pneumatic cylinder as a lifting mechanism drive and which cuts through a film web by means of a squeeze knife and a counter-pressure bar. In order to reduce the load on and the wear of the squeeze knifes as far as possible when they come into contact with the counter-pressure bar and in order to be nevertheless able to cut through thick films/foils, the counter-pressure bar is provided with a fine adjustment device so that the counter-pressure bar can be adjusted with an accuracy of at least 0.02 mm relative to the end position of the squeeze knife. 
     As the squeeze knife is operated over time, the cutting edge of the squeeze knife dulls and the counter-pressure bar and/or the squeeze knife must be readjusted in order to guarantee a reliable, high-quality cut through of the film so as to ensure reliable processing. When such a film punch is used on thermoform packaging machines, the squeeze knifes, and perhaps also the counter-pressure bar, are often replaced in the case of a change of format, and, subsequently, the counter-pressure bar and the squeeze knife, respectively, have to be newly adjusted. This is done in a first test phase, with the thermoform packaging machine running, and requires a certain effort until cutting or cutting through of the film is accurately adjusted. 
     The load on the squeeze knife caused by the contact with the counter-pressure bar during each cutting or squeezing process may be very high, as can be seen from the time-force diagram according to  FIG. 2 . In order to be able to establish this kind of diagram, pressure sensors were provided in the area of the fine adjustment device in an experimental set-up, so as to detect the load on the counter-pressure bar and the squeeze knife, respectively. The diagram shows that, after cutting through of the film at the moment in time t 2 , the force increases still further, since the pneumatic cylinder with its force, which can be generated through the pressure applied, presses the squeeze knife and the counter-pressure bar against one another. In the exemplary case shown, this force F 1  is more than twice as strong as would be necessary for the cutting process. A fundamental reduction of the pressurized air supply to the pneumatic cylinder is, however, not desired, since, if the pressure were for example halved, this would also lead to a reduction of the speed of the lift drive, whereby the performance per work cycle of the film punch would be reduced. The reduced speed with which the squeeze knife impacts the film also has a negative influence on the cutting quality when the film is being cut through. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to improve a thermoform packaging machine including a film punch with respect to a longer service life of the tools and an easier adjustment of the tools relative to one another in the case of tool changing. 
     The thermoform packaging machine according to one embodiment of the present invention comprises a controller and a film punch, which includes a lever mechanism, a tool upper part and a tool lower part. The tool upper part and/or the tool lower part are movable by means of the lever mechanism such that the tool upper part and the tool lower part approach each other. In the thermoform packaging machine, according to one embodiment, the film punch comprises a servo drive. A measuring unit may be provided, which is configured to detect the contact between the tool upper part and the tool lower part. With regard to this contact position of the movable tool, for example, through a calibration procedure, the end position of the movable tool which is most suitable for the punching process and thus the position of the two tools relative to one another can be ascertained in the controller and can then be accessed and established during the subsequent punching processes. Due to the accurate end position of the movable tool, unnecessarily higher forces or loads on the squeeze knife will no longer occur. 
     The controller may be connected to the measuring unit, and the position of the tool upper part and of the tool lower part at the working position can be calculated by means of the controller. This supports a fully automated calibration mode. An additional option provided is the possibility of configuring the lower position and the open tool position, respectively, such that they can be changed by the operator and can also be stored in programs so as to reduce unnecessary lifting movements, for example, in the case of small package depths. 
     According to one embodiment, the measuring unit is a governor of the servo drive, so that, on the basis of current consumption over time, namely during the calibration movement of the movable tool, the working position can be detected and evaluated, since, at the point where the tools come into contact with one another, the current consumption will increase strongly and it may also exhibit other characteristic features. 
     Alternatively, the measuring unit can be a pressure sensor or an impact-sound or vibration sensor for detecting the pressure between the tool upper part and the tool lower part. The impact-sound sensor or the vibration sensor are preferably suitable for detecting, through the suddenly occurring impact, the collision of the two tools and for detecting the resultant vibration. 
     The servo drive may comprise a servomotor with a governor and a spindle, for example a ball screw, for positioning the movable tool with high speed in combination with high accuracy. 
     A method according to one embodiment of the present invention used for determining the working position, in particular the working position of the tool lower part of the film punch, is characterized in that the tool lower part and the tool upper part are caused to approach each other, and that the contact between the tools is ascertained by means of the controller on the basis of an evaluation of data of the measuring unit. 
     The measuring unit can be a governor for a servomotor of the servo drive, and, on the basis of the current consumption of the servomotor, the force progression of the force acting on the movable tool may be detected. Hence, a suitable position, namely an end position, can be ascertained in the controller in an automated manner on the basis of the current profile over time with simultaneous detection of the position of the tools relative to one another. 
     Alternatively, the measuring unit may be a pressure sensor and a measurement of force is carried out at a tool. 
     According one embodiment, the controller calculates an end position for the movable tool, so that the forces produced during the punching process will not be (substantially) higher than the forces required for the punching process, so as to extend the service life of the tools. 
     Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description. 
    
    
     
       DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       In the following, an advantageous embodiment of the thermoform packaging machine according to the present invention and of the method according to the present invention will be explained in more detail making reference to a drawing. The individual figures show: 
         FIG. 1  is a sectional view of a film punch according to the prior art; 
         FIG. 2  is a time-force diagram of the conventional film punch and of a film punch according to one embodiment of the present invention; 
         FIG. 3  is a schematic side view of a thermoform packaging machine according to one embodiment of the present invention; 
         FIG. 4  is a sectional view of a film punch according to one embodiment of the present invention in the production direction at an initial position; 
         FIG. 5  is a sectional view of the film punch of  FIG. 4  at a partially closed position; and 
         FIG. 6  is a sectional view of the film punch of  FIG. 4  at an end position. 
     
    
    
     Like components are provided with like reference numerals throughout the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. For purposes of clarity in illustrating the characteristics of the present invention, proportional relationships of the elements have not necessarily been maintained in the drawing figures. 
     The following detailed description of the invention references specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The present invention is defined by the appended claims and the description is, therefore, not to be taken in a limiting sense and shall not limit the scope of equivalents to which such claims are entitled. 
       FIG. 1  shows, in a sectional view, a film punch  1  according to the prior art, comprising a lever mechanism  2  for allowing a tool lower part  3  to be moved vertically upwards. A pneumatic cylinder  4  is used as a drive for the lever mechanism  2 . The lever mechanism  2  transmits the movement of a piston of the pneumatic cylinder  4  to the tool lower part  3 . The lift and the force of the tool lower part  3  are determined by the structural design of the lever mechanism  2 . The tool lower part  3  is shown at its maximum upper position in  FIG. 1 . At this position, a counter-pressure bar  6  of the tool lower part  3  is in contact with a knife  7   a  of a tool upper part  7 . In order to allow an adjustment of the pressure, which the counter-pressure bar  6  applies to the knife  7   a , the film punch  1  comprises adjustment wheels  8 , so that the knife  7   a  can be adjusted with an accuracy of a few 1/100 millimeters with respect to its height and thus relative to the counter-pressure bar  6  of the tool lower part  3 . Due to the constant contact of the knife  7   a  with the counter-pressure bar  6  after cutting through of a film/foil, the cutting edge of the knife  7   a  blunts and the knife  7   a  must be displaced downwards for still achieving a good punching and cutting result. Misadjustments may have a strongly negative effect on the service life of the knife  7   a  and the counter-pressure bar  6 . 
       FIG. 2  shows the force progression of the pressure F applied by the counter-pressure bar  6  to the knife  7   a , on the basis of a time-force diagram with a solid line, taking the film punch  1  according to  FIG. 1  as an example. At the moment in time t 0 , the tool lower part  3  is at the lower initial position, at which the pneumatic cylinder  4  is fully retracted. The pneumatic cylinder  4  has then pressure applied thereto and moves the tool lower part  3  upwards up to the film to be cut. At t 1 , the counter-pressure bar  6  of the tool lower part  3  meets the film and presses the film with a force F 1  against the knife  7   a . t 2  represents the moment at which the knife penetrates into and passes through, i.e., cuts through, the film. Subsequently, the knife  7   a  is in contact with the counter-pressure bar  6  and the force F increases to a maximum value F 2 , which is influenced by the pneumatic cylinder  4  and its pressurized air supply and also by the upper end position of the pneumatic cylinder. At t 3 , the punching process comes to an end and the pressure of the pneumatic cylinder  4  is no longer applied and, consequently, the pressure F will decrease up until t 4 . From the moment t 4  onwards, the tool lower part  3  and the counter-pressure bar  6  move away from the knife  7   a  and return to the initial position. 
     As can be seen from the diagram, the force F 1  required for cutting the film is less than half the maximum occurring force F 2  with which the counter-pressure bar  6  still acts on the knife  7   a  after the cutting process. For a direct comparison with the prior art, the force progression according to one embodiment of the present invention is shown as a dot-and-dash line L. With reference to the figures following herein below, it will be explained in more detail how this force progression is accomplished. 
       FIG. 3  shows a schematic side view of a thermoform packaging machine  10  according to one embodiment of the present invention. The thermoform packaging machine  10  may comprise a forming station  11 , a sealing station  12 , a transverse cutting unit in the form of a film punch  1  and a longitudinal cutting unit  13 , which are arranged in this order in a production direction Ron a machine frame  14 . On the input side, a supply roll  15  can be provided on the machine frame  14 , from which a film web  16  is unwound. In the area of the sealing station  12 , a material storage unit  17  may be provided, from which a cover film  18  is unwound. On the output side, a discharge device  19  in the form of a conveyor belt can be provided at the thermoform packaging machine  10 , with which finished, singulated packages  20  are transported away. Furthermore, the thermoform packaging machine  10  may comprise a feeding device, which grips the film web  16  and advances it in the production direction R during each main work cycle. The feeding device may include, for example, clamp chains arranged on both sides. 
     In the embodiment shown, the forming station  11  is configured as a thermoforming station, in which troughs  21  are formed in the film web  16  by thermoforming. The forming station  11  may be configured such that, in the direction perpendicular to the production direction R, several troughs  21  are formed side by side. Downstream of the forming station  11 , when seen in the production direction R, an infeed line  22  may be provided, along which the troughs  21  formed in the film web  16  are filled with products  23 . 
     The transverse cutting unit  1  is configured as a film punch cutting through the film web  16  and the cover film  18  in a direction transversely to the production direction R between neighboring troughs  21 . In so doing, the film punch  1  may work such that the film web  16  is not cut across the whole width of the film, but remains uncut in at least an edge area thereof. This allows controlled further transport by the feeding device. 
     In the embodiment shown, the longitudinal cutting unit  13  is configured as a blade arrangement that may comprise a plurality of rotating circular blades by means of which the film web  16  and the cover film  18  are cut through between neighboring troughs  21  and at the lateral edge of the film web  16 , so that, downstream of the longitudinal cutting unit  13 , singulated packages  20  are obtained. 
     The thermoform packaging machine  10  may additionally be provided with a controller  26 . It has the function of controlling and monitoring the processes taking place in the thermoform packaging machine  10 . A display device  27  with operating controls  28  serves to make the sequences of process steps in the thermoform packaging machine  10  visible to an operator and to influence them by the operator. 
     The film punch  1  and its function will be explained in more detail making reference to the figures following herein below. 
       FIG. 4  shows a sectional view of the film punch  1  according to one embodiment of the present invention in the production direction R at an initial position at which the tool lower part  3  is at its lower position. A servomotor  29  can be provided as a drive for the lever mechanism  2 , the servomotor  29  transmitting via a belt drive  30  the torque to a spindle  31 , such as a ball screw, thus converting the rotation of the motor into a linear movement. The spindle  31  lifts a carriage  32  guided on a vertical guide  33 . Alternatively, it is also imaginable to use a linear servo drive instead of the servomotor  29 , the belt drive  30  and the spindle  31 . The servomotor  29  in combination with the belt drive  30  and the spindle  31  are referred to as servo drive  50 . The servo drive  50  can also comprise a governor  51  for the servomotor  29 , the governor  51  communicating with the controller  26 . Alternatively, a gear drive may be provided instead of the belt drive  30 . The servo drive  50  may additionally comprise an incremental encoder or an absolute encoder on the spindle  31  for detecting the linear movement of the spindle  31 . 
     When the carriage  32  moved upwards, a respective toggle lever  34  provided on either side of the guide  33  may be operated and forced apart (see  FIG. 5 ) by means of a lever linkage  35  connecting the carriage  32  to the toggle lever  34 . The forcing apart of the respective toggle levers  34  causes a lifting plate  36  to move vertically upwards, since the two toggle levers  34  are each rotatably supported on a frame  39  via a respective lower lever element  37  and on the lifting plate  36  via a respective upper lever element  38 . The lifting plate  36  can be vertically guided via rollers  40  by means of the guide  33 . 
       FIG. 6  shows the film punch  1  at an end position after the film web  16  has been cut through. Just before this end position, the carriage  32  executes a lift movement H 1  of, for example, 20 mm, while the lifting plate  36  executes simultaneously only a lift H 2  of, for example, 1 mm in the same direction. 
       FIG. 6  additionally shows the governor  51  for the servomotor  29 , the governor  51  being connected to the controller  26 . The governor  51  may detect the motor current of the servomotor  29  and transmits this information to the controller  26 . The motor current is approximately proportional to the pressure F, which is shown in the diagram in  FIG. 2 . 
     Alternatively or additionally, the pressure may also be detected by a pressure sensor  42  as a measuring unit, the pressure sensor  42  being arranged in the power flow from the lever mechanism  2 , the tool upper part  7  and the tool lower part  3 , for example, as shown in  FIG. 6 , between the lower end of a holder  43  for the tool upper part  7  and an accommodation part  44  of the frame  39  for the holder  43 . It is also possible to provide two pressure sensors  42  symmetrically on the right and on the left hand side on the holders  43 . 
     According to another alternative embodiment of the measuring unit, a vibration sensor  45  or an impact-sound sensor may be provided on the tool upper part  7 , so as to detect the contact or the impact of the tool lower part  3  and the counter-pressure bar  6  with/on the tool upper part  7  and the knife  7   a.    
     For determining the working position, the tool lower part  3  is moved upwards, as shown in  FIGS. 4 to 6 , up to the tool upper part  7 . The speed of travel may here be lower and therefore more gentle than during the rest of the production process. According to one embodiment of the method, a film web  16  is not yet present during this procedure, so that the tool lower part  3  can be moved up to the tool upper part  7  without a cutting force being applied. 
     In all these cases, the controller  26  may ascertain, on the basis of the detected data of the measuring unit  41 ,  42  or  45 , the end or also the contact position as working position of the tool lower part  3  and of the carriage  32 , which corresponds to a specific position of the servomotor  29  and of the spindle  31 , respectively. The controller  26  positions the tool lower part  3  for the punching process at the working position, but not further than that. In this way, a force progression L is obtained (see  FIG. 2 ) shown as a dot-and-dash line L in direct comparison with an embodiment according to the prior art. In comparison with the prior art, this force progression has the advantage that the maximum force is hardly higher than the force ensuring that the film is cut through. 
     The spindle  31  may optionally (see  FIG. 6 ) be provided with a housing  60  with an IP 65 type of protection. A pressure compensation device  61  in the form of a line may be provided, the line being extended outwards to the surroundings. This kind of structural design is particularly hygienic, since the housing  60  is here configured such that it is dustproof and adapted to be cleaned by a water jet. 
     Instead of a spindle  31 , the servo drive  50  may comprise a connecting rod drive. 
     According to one variant, the knife  7   a  may be provided on the tool lower part  3  and the counter-pressure bar  6  on the tool upper part  7 . 
     The method according to the present invention may be carried out regularly, for example, once a week, once a day or whenever the machine is started. The film punch  1  will then always be adjusted optionally for the subsequent operation, irrespectively of a possible wear of the knife  7   a . In this way, a manual readjustment or replacement of the cutting tools of the film punch is required much less frequently than in the prior art, whereby the operation of the film punch  1  and of the packaging machine in its entirety is substantially optimized. 
     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. It will be understood that certain features and sub combinations are of utility and may be employed without reference to other features and sub combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments of the invention may be made without departing from the scope thereof, it is also to be understood that all matters herein set forth or shown in the accompanying drawings are to be interpreted as illustrative and not limiting. 
     The constructions and methods described above and illustrated in the drawings are presented by way of example only and are not intended to limit the concepts and principles of the present invention. Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “having” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required”. Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.