Patent Publication Number: US-9409304-B2

Title: Cutting unit for a packaging machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to German patent application number DE 10 2010 019 634.7, filed May 6, 2010, which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a cutting unit for a packaging machine. 
     BACKGROUND 
     DE 10 2007 013 698 A1 and the post-published DE 10 2009 022 545 A1 disclose thermoformer packaging machines as a special type of packaging machines. In the case of these thermoformer packaging machines, packaging troughs are thermoformed in a bottom foil, filled with a product and subsequently sealed with a cover film. After having been sealed, the packages must be singulated. To this end, cutting units are normally provided in the longitudinal direction and in the transverse direction of the working direction of the packaging machine. These cutting units are subjected to high loads, since they execute fast movements and since they must exert strong forces for cutting through packaging foils, in particular if these packaging foils are thick. Hence, they are liable to fatigue and regular maintenance is necessary. In addition, conventional cutting units often consume a lot of energy and take up much space. 
     SUMMARY 
     It is an object of the present disclosure to improve, with the aid of structurally simple means, a cutting unit for a packaging machine such that the above-mentioned drawbacks will be avoided. 
     In the case of the cutting unit according to the present disclosure, a curved push rod is provided between the drive and the cutting knife. The curved shape of the push rod allows a much better transmission of the forces which are applied by the drive to the push rod and transmitted from the push rod to the cutting knife. Due to the improved transmission of forces, fatigue phenomena of the material will be reduced. 
     A particularly good distribution of the forces and stresses on the push rod will be accomplished when the push rod has a substantially U-shaped curvature. The ends of the push rod may, however, be bent outwards once more so that—when seen e.g. from one side of the push rod—the resultant whole curvature is a concave-convex-concave curvature. 
     It will be particularly advantageous when the linear guide is provided with a first lateral guide and a second guide, a transverse member extending between said guides and having the cutting knife secured thereto. Due to the fact that the transverse member is guided on both sides thereof, tilting is prevented and the cutting forces can be transmitted to the packaging films/foils in a defined orientation of the cutting knife. The lateral guides may e.g. be rods or rails. 
     Preferably, a first end of the push rod is connected to the transverse member via a swivel joint. This allows the push rod to raise the transverse member at different angular positions. 
     The second end of the push rod can be connected to at least one crank shaft via a swivel joint. This crank shaft will then predetermine the angular positions of the push rod and additionally define the vertical displacement of the push rod. 
     According to a preferred embodiment, the swivel joint is accommodated in a curved slotted link between the second end of the push rod and the crank shaft. This leads to a substantial increase in the stability of the lifting mechanism and, in addition, to a more smooth and silent running of the cutting knife. Since the movement of the swivel joint is predetermined by the crank shaft, the slotted link does not represent a further forcible control of the swivel joint, but it is primarily provided for reasons of stability. 
     The slotted link may describe at least a semicircle around an output shaft of the drive or around a gear box shaft of the drive. The swivel joint can thus perform in the slotted link a movement of 180° or more about the shaft. In this way, it can be guaranteed that the cutting movement corresponds to a length up to twice the length of the crank shaft or to a length corresponding precisely to twice the length of the crank shaft. 
     In order to increase the stability still further, the slotted link may be provided in a plate connected to both lateral guides. It is also imaginable that two plates are provided, which are arranged parallel to one another and each of which is provided with a slotted link. 
     The crank shaft may be connected to the output shaft of the drive, or it may also be connected to a gear box provided between the drive and the crank shaft. 
     In one embodiment of the present disclosure, the drive is an electric motor. In contrast to the normally used linear drives or pneumatic drives, this offers the advantage that a reduction of wear will be accomplished and that the use of compressed air can be dispensed with. Instead, the cutting unit (and possibly the whole packaging machine) can be operated with electric energy alone. 
     A particularly advantageous embodiment is obtained, when the drive is arranged within the installation space delimited by the two lateral guides. In this way, the cutting unit is rendered compact, since the drive no longer projects beyond the sides. 
     It may also be advantageous, when the longitudinal axis of the drive extends parallel to the cutting knife, when seen from above. In this way, the overall length of the cutting unit will be particularly short in the working direction of the packaging machine, so that a plurality of cutting units or other working units can be arranged in closely spaced succession. 
     Optionally, the output shaft of the drive may have arranged thereon a gear box, said gear box comprising at least one gear box shaft extending at an angle of 90° relative to the output shaft. In particular, two such gear box shafts may be provided, said gear box shafts extending from the output shaft on both sides. In the latter case, a particularly symmetric distribution of the driving forces will be accomplished. 
     Finally, the present disclosure also relates to a packaging machine having a cutting unit of the type described hereinbefore. 
     In the following, an advantageous embodiment of the present disclosure will be explained in more detail on the basis of the below drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a packaging machine according to the present disclosure in the form of a thermoformer packaging machine; 
         FIG. 2  is a view of the cutting unit at a position in which the cutting knife has been lowered; 
         FIG. 3  is a view of the cutting unit according to the present disclosure at a position in which the cutting knife has been raised; and 
         FIG. 4  is a side view of the cutting unit according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Identical components are provided with identical reference numerals throughout the figures. 
       FIG. 1  shows a schematic view of a packaging machine  1  according to the present disclosure in the form of a thermoformer packaging machine. This thermoformer packaging machine  1  comprises a forming station  2 , a sealing station  3 , a transverse cutting unit  4  and a longitudinal cutting unit  5 , which are arranged in this order in a working direction R on a machine frame  6 . In the present embodiment, the transverse cutting unit  4  is configured as a cutting unit according to the present disclosure, which will be described in detail hereinbelow. 
     On the input side, a supply roll  7  is provided on the machine frame  6 , from which a first web material  8  is unwound. In the area of the sealing station  3 , a material storage unit  9  is provided, from which a second web material  10  used as a cover film is unwound. On the output side, a discharge device  13  in the form of a transport conveyor is provided at the packaging machine, with which finished, singulated packages are transported away. Furthermore, the packaging machine  1  comprises a feeding device which is not shown, said feeding device gripping the first web material  8  and transporting it cyclically in a main work cycle in the working direction R. The feeding device can be realized, for example, by laterally arranged transport chains. 
     In the embodiment shown, the forming station  2  is realized as a thermoforming station in which containers  14  are formed in the first web material  8  by thermoforming. The forming station  2  can be configured such that in the direction perpendicular to the working direction R several containers are formed side by side. In the working direction R behind the forming station  2 , a filling area  15  is provided, in which the containers  14  formed in the first web material  8  are filled with the product  16 . 
     The sealing station  3  is provided with a closable chamber  17  in which the atmosphere in the containers  14  can be substituted, prior to sealing, by an exchange gas or by an exchange gas mixture, e.g. by gas flushing. 
     The transverse cutting unit  4  is configured as a punch separating the first web material  8  and the second web material  10  in a direction transversely to the working direction R between neighbouring containers  14 . In so doing, the transverse cutting unit  4  works such that the first web material  8  is not cut across the whole width of the web, but remains uncut in at least an edge area. This allows controlled further transport by the feeding device. 
     In the embodiment shown, the longitudinal cutting unit  5  is configured as a blade arrangement by means of which the first web material  8  and the second web material  10  are cut between neighbouring containers  14  and at the lateral edge of the first web material  8 , so that, downstream of the longitudinal cutting unit  5 , singulated packages are obtained. 
     The packaging machine  1  is additionally provided with a controller  18 . It is used for controlling and monitoring the processes taking place in the packaging machine  1 . A display device  19  with operating controls  20  serves to make the sequences of process steps in the packaging machine  1  visible to an operator and to influence them by the operator. 
     The general mode of operation of the packaging machine  1  will be described briefly in the following. 
     The first web material  8  is unwound from the supply roll  7  and conveyed into the forming station  2  by the feeding device. In the forming station  2 , containers  14  are formed in the first web material  8  by thermoforming. Together with the material of the first web material  8  surrounding them, the containers  14  are advanced, in a main work cycle, to the filling area  15  where they are filled with the product  16 . 
     Subsequently, the filled containers  14  are, together with the material of the first web material  8  surrounding them, advanced by the feeding device into the sealing station  3  during the main work cycle. After having been sealed onto the first web material  8 , the second web material  10  is advanced as a cover film when the feed motion of the first web material  8  takes place. In the course of this process, the second web material  10  is unwound from the material storage unit  9 . By sealing the cover film  10  onto the containers  14 , closed packages  21  are obtained. 
     In the cutting units  4 ,  5  the packages  21  are singulated by cutting through the web materials  8 ,  10  in the transverse direction and in the longitudinal direction. The transverse cutting unit  4  is an example of a cutting unit according to the present disclosure. 
       FIG. 2  shows a view of a transverse cutting unit  4  in the direction of the conveying direction R of the packaging machine  1 . The cutting unit  4  is provided with a cutting knife  22  having a cutting edge  23  on the upper side thereof. The cutting knife  22  is mounted on a transverse member  25  via two fastening elements  24 . The cutting knife  22  may in particular be releasably fastened to the fastening elements  24  so that a damaged or worn-out cutting knife  22  can be replaced. 
     The cutting knife  22  is guided in a vertical linear guide  26  for carrying out a vertical movement. This linear guide comprises the transverse member  25 , two vertically oriented lateral guides  27  configured as rods as well as two sleeves  28 , each of them provided on one end of the transverse member  25  and enclosing a respective lateral guide  27 . Since the sleeves  28  are higher than the transverse member  25  in the axial direction of the lateral guides  27 , they prevent tilting of the transverse member  25 , and guarantee thus a more smooth and silent running of the cutting knife  22  as well as a defined, horizontal orientation of the cutting edge  23 . 
     The two lateral guides  27  are, at the upper end thereof, interconnected by an (optionally slotted) counter pressure bar or a counter knife  29  having, at the lower end thereof, a horizontal (cutting) edge  30  cooperating with the cutting edge  23  of the cutting knife  22 . The lower ends of the two lateral guides  27  are interconnected by two vertically oriented support plates  31 , which are arranged parallel to one another. The support plates  31  substantially have the shape of a parallelogram. 
     As can especially be seen from  FIG. 3 , a projection on the transverse member  25  is connected to a curved push rod  33  via a first swivel joint  32 . The push rod has a substantially U-shaped curvature. The ends, however, are bent outwards once more relative to the U-shaped curvature. Seen from the left side in  FIG. 3 , a concave-convex-concave curvature of the whole push rod thus results. Seen from the right side in  FIG. 3 , a convex-concave-convex curvature of the push rod  33  results. 
     A second, lower end of the push rod  33  is connected to the crank shaft  35  via a second swivel joint  34 . Actually, a respective crank shaft  35  can be provided on either end of the second swivel joint  34 . 
     The support plates  31  have secured thereto a drive  36  for driving the movement of the cutting knife  22 . In the present embodiment, the drive  36  is an electric motor. This electric motor  36  is provided with an output shaft which is directed in the axial direction of the drive  36 . The output shaft (not shown) ends at a gear box  37 . The gear box comprises two gear box shafts  38  extending respectively from the output shaft of the drive  36  at an angle of 90° to the right and to the left. The gear box shafts  38  are operated by means of the output shaft. The gear box shafts  38  may also be implemented as hollow shafts through which an axle is passed. 
     Each of the two horizontally oriented gear box shafts  38  is connected to a crank shaft  35 . A rotation of the gear box shafts  38  results in a rotation of the crank shafts  35  about the gear box  37 . 
     When seen in the conveying direction R, i.e. in the view according to  FIGS. 2 and 3 , the drive  36  is located fully within the installation space which is delimited at the right and at the left by the two lateral guides  27 . The output shaft of the drive  36  is located between the two support plates  31 . When seen from the side, also the push rod  33  is located between the two support plates  31 , whereas the crank shafts  35  are arranged on the outer sides of the two support plates  31 . The gear box shafts  38  as well as the second swivel joint  34  extend through the two support plates  31 . 
     A semicircular slotted link  39  is provided in the support plates  31 . The slotted link  39  extends over an angle of 180° around the gear box shafts  38  of the gear box  37 . 
     In the following, the operation of the cutting unit  4 ,  5  according to the present invention will be explained. 
     In  FIG. 2  the cutting unit  4 ,  5  occupies a position in which the cutting knife  22  has been lowered. The distance between the cutting edge  23  of the cutting knife  22  and the cutting edge  30  of the counter knife  29  is large enough for allowing filled and sealed packages  21  to be conveyed between the two cutting edges  23 ,  30  and between the two lateral guides  27 . 
     As soon as the advance movement of the packages  21  has been stopped, the cutting knife  22  is moved to the raised position (or cutting position) shown in  FIG. 3 . To this end, the output shaft of the drive  36  moves the gear box shafts  38  such that they rotate about their respective axes. This rotation has the effect that the crank shafts  35  connected to the gear box shafts  38  are pivoted about the gear box shafts  38 . In the course of this process, the second swivel joint  34 , which extends through the support plates, moves from the lower end of the slotted link  39  through the whole slotted link  39  up to the upper end thereof. In  FIG. 3 , the swivel joint  34  has reached this position at the end of the slotted link  39 . The crank shaft  35  moves here from a downwardly directed position to an upwardly directed position, starting from the gear box shaft  38  in each case. The stroke of the cutting knife  22  thus corresponds to twice the distance between the axis of the gear box shaft  38  and the axis of the second swivel joint  34 . 
     The second swivel joint  34  has the push rod  33  connected thereto. Due to the forcible control exerted by the linear guide  26 , the transverse member  25  and the cutting knife  22  move vertically upwards, when the lower swivel joint  34  and, together therewith, the push rod  33  are raised. The sleeves  28  guarantee that the horizontal orientation of the transverse member  25  and of the cutting knife  22  is always maintained. The angle of the push rod  33  adjusts itself in a suitable manner between the two swivel joints  32 ,  34 . 
     The transverse member  25  is raised until the cutting edges  23 ,  30  of the cutting knife  22  and of the counter knife  29  strike against one another, whereby the films/foils of the packages  24  between the two cutting edges  23 ,  30  are cut through. 
     In  FIGS. 2 and 3  it can be seen that the cutting edges  23 ,  30  do not extend over the whole distance between the two lateral guides  27 . Hence, an area of the packaging films/foils  8 ,  10 , which is used for further conveying the packages  21 , can remain uncut laterally next to the two cutting edges  23 ,  30 . It is also possible that a chain guide used for conveying the packaging films/foils  8 ,  10  extends in the area next to the two cutting edges  23 ,  30 . 
     The cutting unit shown in  FIGS. 2 to 4  may also be used as a longitudinal cutting unit  5 , instead of as a transverse cutting unit  4 , in the packaging machine  1 . For example, the entire device shown in  FIG. 2  may be oriented so that the cutting knife  22  extends in the longitudinal direction or conveying direction R, and the lateral guides  27  may be offset with respect to the cutting knife  22  in the transverse direction so that the lateral guides  27  do not obstruct the transport of the packaging films/foils  8 ,  10 . 
     As another example, the cutting knife  22  shown in  FIG. 2  may be oriented in the longitudinal direction (i.e., rotated 90 degrees with respect to the transverse member  25  shown in  FIG. 2 ), and the cutting knife  22  may be connected to the transverse member  25  with a single fastening element that extends in the longitudinal direction in order to provide support to the cutting knife  22  in the longitudinal direction. With this configuration, the lateral guides  27  would remain disposed on opposite sides of the films/foils  8 ,  10 . One or more additional cutting knives oriented in a similar manner may also be attached to the transverse member  25  so that the cutting unit  5  may be used to cut multiple longitudinal cuts in the films/foils  8 ,  10 . 
     As yet another example, a cutting unit  5  may be provided with four lateral guides  27 , such that two lateral guides  27  are disposed on each side of the films/foils  8 ,  10 ; two transverse members  25  that are spaced apart from each other in the longitudinal direction and that each extend between two lateral guides  27  disposed on opposite sides of the films/foils  8 ,  10 ; and one or more cutting knives  22  that extend in the longitudinal direction between the transverse members  25  and that are fastened to the transverse members  25  with fastening elements  24 , for example. Such a cutting unit  5  may also be provided with a single push rod and drive assembly that is connected to both transverse members  25 , such as via a longitudinal member that extends between the transverse members  25 . As an alternative, the cutting unit  5  may be provided with two push rod and drive assemblies, each of which is connected to a respective transverse member  25 . 
     With any of the above embodiments, the upper pressure bar or counter knife  29  with its blade or edge  30  should, of course, always be adapted to reflect the configuration and orientation of the lower cutting knife  22  and its cutting edge  23 . Likewise, if a particular cutting unit  5  is provided with multiple cutting knives, then the cutting unit  5  may also include multiple counter knives oriented in the longitudinal direction, such that each cutting knife is aligned with a respective counter knife. 
     Starting from the embodiment shown, the cutting unit  4 ,  5  according to the present disclosure may also be modified in other respects. For example, the lateral guides  27  need not be implemented as rods, but one or both lateral guides may also be implemented as rail/rails. Instead of the sleeves  28 , an adequate sliding member may be used, said sliding member being connected to the transverse member  25 . Instead of two support plates  31 , it is also possible to provide only one support plate  31 . Instead of two crank shafts  35 , only a single crank shaft  35  may be provided in a different embodiment. It is also imaginable to connect the lower end of the crank shaft  35  not to a gear box shaft  38 , but directly to the output shaft of the drive  36 . The longitudinal axis of the drive  36 , i.e. the axis of the output shaft of the drive  36 , may extend horizontally or—as shown in  FIGS. 2 and 3 —at an angle to the horizontal. 
     Deviating from the embodiment shown, the drive  36  may also be implemented as an electric motor with a disc-shaped rotor in the case of which a cylindrical hollow axis is driven. This hollow axis of the electric motor  36  with a disc-shaped rotor may be coupled directly to the push rod  33  so that the crank shaft  35  can be dispensed with in this embodiment. 
     The gear box is preferably very stable in the case of the cutting unit  4  according to the present disclosure. By supporting the gear box casing on the support plates  31  and by connecting the crank shafts  35  directly to the gear box shafts  38 , the gear box  37  can be provided with a stability that is so high that no additional bearing parts or bearing points are necessary for absorbing, when the transverse cutting unit  4  is in operation, the process forces occurring due to the cutting process and due to the weight of the crank shafts  35  and of the push rod  33 . In order to increase the stability of the gear box  37  still further, the gear box can be supported in special (e.g. hardened) bearings having a higher load bearing capacity. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.