Abstract:
The invention relates to a thermo-forming packaging machine and a method which are characterized in that the location of trays in a base film upstream of a sealing station is detected by a measuring system and that the sealing station is immediately subsequently positioned such as to allow a top film to be sealed with highest accuracy matching the tray and thereby to be able to compensate for irregularities and tolerances, for example, in the film feed, in a true-to-cycle manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority to European Application Number 12008109.6 filed Dec. 4, 2012 and European Application Number 13002228.8 filed Apr. 26, 2013, to Elmar Ehrmann and Christian Lau, currently pending, the entire disclosures of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a thermo-forming packaging machine and a method for operating the thermo-forming packaging machine. 
       BACKGROUND OF THE INVENTION 
       [0003]    A thermo-forming packaging machine is known from EP 0 569 933 A1 having work stations, for example, a forming, sealing and cutting station adjustable in the direction of production, which can be adjusted in dependence of the position of a print mark on a base film, where the print mark is detected by the forming station using a print mark sensor. The work stations have motorized adjustment drives with displacement measuring devices. Adjustable intervals between successive print marks are determined by the control unit using the print mark sensor and the position of the forming, sealing and cutting station is controlled accordingly to adjust the distances of the work stations relative to each other. This is to ensure that the forming station forms trays matching the position of the print mark, the sealing station produces sealing seams corresponding to the location of the trays and the cutting station cuts the sealed packages relative to the sealing seams and separates the packages. 
         [0004]    Any shifting of the sealing station after detection of a print mark has an effect only after many feeds or advances of the detected print mark because a loading stretch for loading products to be packaged into the formed trays is provided between the forming station and the sealing station. In this, negative influences caused by irregular film shrinkage or tolerances in the feed motions of the feed chains are unaccounted for. This requires a generous design of the width of the packing webs and edges in the feeding direction so that the sealing seam can be produced on the edges with sufficient width and the sealing seam still has a width achieving a desired seal quality after the subsequent cutting operation. This generous design leads to increased film consumption due to a large amount of film wastage. 
         [0005]    A further packaging machine is known from DE 24 37 127 A1 in which a print mark sensor is used for the top film. This print mark sensor is disposed precisely as far ahead of the sealing station as the forming station is located upstream of the sealing station, so that the print mark sensor always accurately detects the print mark corresponding to the film section of the lower tray formed precisely at that time in the same machine cycle. 
         [0006]    The non-previously published DE 10 2011 108 939 further discloses a packaging machine in which the location of the sealing seams is detected in order to be able to subsequently align a cutting device relative to the location of the sealing seams. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to improve a thermo-forming packaging machine in terms of film consumption. 
         [0008]    The thermo-forming packaging machine according to the invention during its operation works with a specific feed length for every work cycle. In one embodiment, it comprises a forming station for forming trays into a base film, a sealing station, preferably a cutting station, and a control unit, where the sealing station comprises an adjustment device along a direction of production and a displacement measuring device. 
         [0009]    According to a first aspect of the invention, a measuring system for determining the location of the reference element may be provided at the sealing station or within a feed length upstream of the sealing station (i.e., within a maximum of one feed length upstream of the sealing station) and the control unit is configured to position the sealing station according to the detected location of the reference element relative to the trays using the adjustment device. Firstly, the location of the trays that are one cycle upstream of the sealing station can be determined, or secondly, the location of the trays that are already within the sealing station when the feed motion of the base film or the trays is completed. Determining the location of the reference element when the base film is stationary has the advantage that inaccuracies in positioning the base film or the trays, respectively, in the sealing station are taken into account towards the end of the feed motion and inaccuracies of dynamic detection of the reference element can be eliminated already during the feed motion. Location control in the final position during the feed motion of the base film using a servo drive can be simplified as well as detection of the reference element. This has the advantage that the sealing station can always be positioned precisely relative to the location of the trays to be sealed. Thereby, no tolerances in relation to feed differences need to be considered and the area of the package edge necessary for sealing can be reduced to a minimum. In consequence, the length of a film feed can be reduced or the package dimensions can be increased in the feed direction, which leads to a reduction of film wastage. 
         [0010]    According to a second aspect of the invention, a measuring system may be provided within a maximum of one feed length upstream of the sealing station for detecting the location of those trays that are fed to the sealing station in the direction of production during a following work cycle and the control unit is configured to control the sealing station according to the determined location of the trays in a true-to-cycle manner in its position relative to the trays using the adjustment device. This likewise has the advantage that the sealing station can always be positioned precisely relative to the location of the trays to be sealed. Thereby, no tolerances in terms of feed differences need to be considered and the area of the package edge necessary for sealing can be reduced to a minimum. In consequence, the length of a film feed can be reduced or the package dimensions can be increased in the feed direction, which leads to a reduction of film wastage. 
         [0011]    The measuring system can be provided for contactless detection of the location of the trays or of the reference element. 
         [0012]    The forming station can comprise a device or the device is positioned upstream of the forming station for introducing a reference element into the base film, where the location of the trays can be detected via the measuring system by detecting the reference element. The device may be coupled to the forming station. One the one hand, the forming station and the device can be driven using a common drive, on the other hand, the reference element has a defined and same distance relative to the trays formed during the same work cycle. Thereby, there is a fixed relation between the location of the trays of a common cycle and the associated reference element. This allows the use of low-cost measuring systems, as only the reference element must be detected, since the trays have a predetermined location relative to the reference element. The reference element can be, for example, a punching in the shape of a hole being created by the device that is part of the forming station, or be an embossing in the shape of a knob. It is also conceivable to have a plurality of punchings applied, for example, on both sides of the trays in proximity to the clip chain provided on both sides for film transport. For this purpose, two measuring systems are provided upstream of or at the sealing station for detecting such reference elements from both sides. 
         [0013]    The measuring system may comprise a camera or a reflex sensor, such as a light barrier. The reflex sensor can be especially suited to detect a reference element in the form of a punching. A camera allows detection of the trays themselves directly from above or below in the absence of a reference element. A camera can also suited for detecting the location of the reference element at a standstill after a feed motion of the base film and thereby of the trays. 
         [0014]    According to one embodiment, the displacement measuring device of the sealing station is a magnetostrictive linear transducer for providing a hygienic embodiment. Such a linear transducer cooperates contactlessly with a sensor such that even the gap between the linear transducer and the sensor is easy to clean and resistant to common detergents. 
         [0015]    An adjustment range of the sealing station of up to 1000 mm, preferably larger than 300 mm can be provided in order to compensate not only variations in and counter to the direction of production, but to be able, for example, to also move the sealing station to a tool changing position in which a sealing tool lower and/or upper part can be removed laterally or towards the top from the thermo-forming packaging machine for maintenance, cleaning or exchange purposes. 
         [0016]    A further measuring system may be provided for contactless detection of the location of those trays that are fed to the sealing station during a following work cycle and the control unit is configured to control the sealing station according to the detected location of the trays in a true-to-cycle manner in its position relative to the trays using a further adjustment device. This ensures that the cutting station can be positioned true-to-cycle in relation to the location of the trays or the sealing seams produced in the sealing station. It is conceivable for a cutting station disposed directly downstream of the sealing station, that the control unit positions the cutting station according to the detection of the trays or the reference element or elements, respectively. 
         [0017]    In one embodiment, trend control is provided by the control unit for the forming station. The term trend control means that repeated positioning of the sealing station again and again in only one direction is detected by the control unit, and the control unit in counteracting this adjusts (i.e., displaces) the forming station in the opposite direction such that further continuous positioning of the sealing station in one direction can be avoided. 
         [0018]    The forming station and/or the sealing station may be movable into a tool exchange position or against the direction of production to adjust it into a laterally accessible position relative to the thermo-forming packaging machine in order to be able to ergonomically perform a tool exchange without affecting a film. 
         [0019]    A first method according to the invention for operating a thermo-forming packaging machine, comprising a forming station for forming trays into a base film, a sealing station and a control unit, provides that a device introduces a reference element into the base film, the position of the reference element, and thereby at least indirectly also the position of the trays, is determined by a measuring system and the control unit positions the sealing station in a predetermined or predeterminable position relative to the trays using an adjustment device. Firstly, the location of those trays can be determined that are one cycle upstream of the sealing station, or secondly, the location of those trays that are already within the sealing station when the feed motion is completed. Thereby, the sealing station can always be positioned precisely in relation to the position of the trays to be sealed and tolerances can be disregarded, which results in a reduction of film consumption. 
         [0020]    A second method according to the invention for operating a thermo-forming packaging machine, comprising a foaming station for forming trays into a base film, a sealing station and a control unit, provides that, during a given work cycle, the location of the trays being fed to the sealing station in a directly subsequent work cycle is determined by a measuring system, and the control unit positions the sealing station using an adjustment device prior to the next work cycle or at the latest within the next work cycle in a true-to-cycle manner in its position relative to the trays. 
         [0021]    The measuring system may comprise a reference element which was introduced into the base film using a device in the forming station or a device which is arranged upstream of the forming station, in order to determine the location of the trays for the control unit. 
         [0022]    The control unit can determine a trend from a changing location of the trays and adjusts the position of the forming station in relation to a direction of production using a further adjustment device. As a variant, a parameter for the length of the intermittent feeds can be adjusted in the control unit. 
         [0023]    In a particular variant of the method according to the invention, the control unit detects the position of the sealing station using a displacement measuring device of the adjustment device aligned longitudinally along the direction of production. 
         [0024]    As a further variant for contactless determination of the location of the trays, a mechanical scanning device is conceivable to scan a punching or a knob as a reference element. 
         [0025]    A camera may capture the location of the reference element at a standstill after a feed motion of the base film using a film transport chain. With such a detection of the reference element during the subsequent standstill, any consideration of the feed motion of the film transport chain can be dispensed with, thereby further increasing the accuracy when positioning the sealing station. Any inaccuracies or varying positionings of the film transport chain, respectively, which occur due to varying friction conditions along the guides of the film transport chain, are all entirely taken into account, since detection of the location of the reference element, and thereby the location of the trays, is performed only subsequent to the positioning of the film transport chains at standstill of the trays to be sealed. 
         [0026]    The option is also conceivable, that the operator stores target positions in the control unit in programs for the processes as a default for various forming tools and thereby also different feed lengths. 
         [0027]    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 
         [0028]    In the accompanying drawing, which forms a part of the specification and is to be read in conjunction therewith in which like reference numerals are used to indicate like or similar parts in the various views: 
           [0029]      FIG. 1  is a schematic side view a thermo-forming packaging machine in accordance with one embodiment of the present invention; 
           [0030]      FIG. 2  is a partial top perspective view of a sealing station in accordance with one embodiment of the present invention; 
           [0031]      FIG. 3  is a partial plan view of the base film upstream of, in, and downstream of the sealing station in accordance with one embodiment of the present invention; 
           [0032]      FIG. 4  is a schematic side view a thermo-forming packaging machine in accordance with a further embodiment of the present invention; and 
           [0033]      FIG. 5  is a plan view of the forming station in accordance with one embodiment of the present invention. 
       
    
    
       [0034]    Identical components are throughout the figures designated with the same reference numerals. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    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. 
         [0036]    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. 
         [0037]      FIG. 1  shows an intermittently (cyclically) operating thermo-forming packaging machine  1  according to one embodiment of the present invention, comprising a machine frame  2  being oriented along a direction of production R. At the beginning of the thermo-forming packaging machine  1 , shown at the right in  FIG. 1 , a roll-off device  3  is provided for a base film  4 . The base film  4  can be fed at a feed length V for every work cycle in the direction of production R to a forming station  5  using two feed chains—not illustrated. Furthermore, a loading stretch  6  for loading a product  7  into formed trays  8  is shown downstream of the forming station  5 . A sealing station  9  for closing the trays  7  filled with a product  7  having a top film  10 , and a first cutting station  11  being embodied as a transverse cutting device may follow in the further course of production. A second cutting device  12  being disposed downstream of the first cutting device  11  can be embodied as a longitudinal cutting device and separates the packages  13 . 
         [0038]    A plurality of formed trays  8  can be arranged in the base film in the direction of production R, which are in the format of, for example, three trays  8  arranged adjacently to each other, each being transported downstream in one cycle and intermitting by one tray  8 . It is also conceivable that the forming station  5  forms a plurality of rows of trays  8  and that this respective format of trays  8  being formed in one work cycle in the forming station  5  into the base film  4  is further transported in an intermittent manner in the direction of production R. 
         [0039]    In the following, the mode of operation of the thermo-forming packaging machine  1  shall be illustrated in more detail. The base film  4  being rolled off from the roll-off device  3  may be gripped by the feed chains on both sides and supplied to the forming station  5 . In the forming station  5 , one or more trays  8  are formed into the base film  4  and a reference element  40  (see  FIG. 3 ) is introduced into the base film  4  at a defined position relative to the trays  8  using a punching device  14  in a region that is located outside of the trays  8  and outside of or between the sealing seams  41  to be created at a later time. For example, the reference element  40  can be a hole having a diameter of 5 mm. 
         [0040]    In the following work cycle, the base film  4  may be further transported with the formed trays  8  intermittingly along the loading stretch  6 . The trays  8  are manually or automatically filled with products, for example, using pickers  7 . In one cycle, directly prior to reaching the sealing station  9  (i.e., at a maximum of one feed length V upstream of the sealing station  9 ) a measuring system  15  can be attached above the base film  4  to detect the reference element  40  during the cyclic feed motion of the base film  4 , or at a standstill, in order to determine the location of the reference element  40 , for example, by using a camera  15   a.    
         [0041]    The information about the location of the reference element  40  in cycle Tx is transmitted to a control unit  16 . The position of the tray  8  relative to the reference element  40  is stored in the control unit  16  so that the control unit  16  adjusts the sealing station  9  for cycle Ty using an adjustment device  17  such that those trays  8  being detected in cycle Tx are in the subsequent cycle Ty in the sealing station  9  in exact correspondence it terms to their location. The adjustment device  17  may be operated after the sealing operation for sealing the top film  10  onto the base film  4  is terminated and a sealing tool lower part  18  has moved downwardly away from the collision area of the trays  8  in order to allow the next base film  8  feed motion. 
         [0042]    Therefore, adjustment of the sealing station  9  is always true-to-cycle in relation to the location of the trays previously detected in the cycle, since detection of the trays  8  in cycle Tx results in adjustment of the sealing station  9  in the immediately following cycle Ty. 
         [0043]    The control unit  16  can, in addition to adjustment (displacement) of the sealing station  9 , also perform an adjustment of the first cutting station  11 , to partially separate the packages  13  or the base film  4  and the cover film  10 , respectively, directly at the sealing seam  41  aligned transversely to the direction of production R. For this, detection of the trays  8  in cycle Tx by use of the measuring system  15  can be provided upstream of the sealing station  9 , or a further measuring system  19  in cycle Tz upstream of the cutting station  11  determines the location of the trays  8  or the sealing seams  41  created in the sealing station  9  (see  FIG. 3 ). The second cutting device  12  disposed towards the end of the thermo-forming packaging machine  1  may be embodied as a longitudinal cutting device and separates the packages  13  in the longitudinal direction along the direction of production R, so that the separated packages  13  can be supplied in a separated manner to the further production process. 
         [0044]    In  FIG. 2 , the sealing station  9  is shown without a sealing tool upper part and the sealing tool lower part  18 . The sealing station  9  may be attached to the machine frame  2  with six fastening elements  20 . A lifting device  22  may be movable along guide rails  21  in and against the direction of production R. The lifting device  22  can be adjustable relative to the machine frame  2  via a toothed belt  25  along the direction of production R using a servo drive  23  and a belt drive  24 . In one embodiment, the position of the sealing station  9  or the lifting device  22 , respectively, is detectable relative to the machine frame  2  using a displacement measuring device  26 , where the displacement measuring device  26  is a non-contact linear transmitter being oriented along the machine frame  2 . As shown, an associated measurement sensor  27  is attached to the lifting device  22 . The lifting device  22  can comprise a toggle lifting unit  28  with a servo drive  29  for vertically lifting or lowering the sealing tool lower part  18  (not shown in  FIG. 2 ) being provided on the supports  30 . 
         [0045]      FIG. 3 , in a plan view onto the base film  4 , shows two trays  8  each being arranged in two lanes, and a single-lane cycle or feed. The reference element  40 , when viewed in the direction of production R, is located at the right edge of the base film  4  adjacent to or outside of the sealing seam  41 , respectively. With a feeding motion, cycle Tx upstream of the sealing station  9  transforms into the next cycle Ty in the sealing station. 
         [0046]    A trend control for the forming station  5  is explained in more detail using  FIG. 1 . If the control unit  16  determines that the sealing station  9  has for several times been moved repeatedly in the same direction, then the forming station  5  can be adjusted in the opposite direction using a separate adjustment device to minimize or end continuous adjustment of the sealing station  9  in only one direction. Adjustment of the sealing station  9  serves primarily to compensate for irregularities in the feed motion of the base film  4  or irregularities in the base film  4  itself, in that the location of the tray  8  is referenced true-to-cycle. 
         [0047]      FIG. 4  shows a variant according to the invention of the thermo-forming packaging machine  1  shown in  FIG. 1 . A device  14   a  for creating a reference element  40   x,    40   y  can be disposed upstream of the forming station  5  and mechanically connected to the forming station  5 . Trays  8  of a cycle Tx are in one work cycle simultaneously thermo-formed in the forming station  5 , while device  14   a  forms a reference element  40   x  into the right edge of the base film  4 . The two juxtaposed trays  8  of cycle Tx have a defined distance to the associated reference element  40   x.  This distance can be entered into the control unit  16  and, during detection of the reference element  40   x  upstream of the sealing station  9  using a camera  15   a,  is offset in the control unit  16  in order to position the sealing station  9  according to the trays  8  of cycle Tx located therein. 
         [0048]      FIG. 5  shows a top view of the forming station of the variant of  FIG. 4  according to the invention. In the forming station  5 , two trays  8  of cycle Tx are created and device  14   a  forms a reference element  40   x  in the shape of a knob  40   x  having a diameter of, for example, 3 mm into the base film  4 . Trays  8  of a cycle Ty and a reference element  40   y  were created in a previously performed work cycle. 
         [0049]    Since the respective reference element  40   x,    40   y  has a distance A upstream of the trays  8  in the direction of production R, the reference element  40   x,    40   y  can be detected outside or upstream of the sealing station  9  after the associated trays  8  are located in the sealing station. In this, the feed motion is completed and the trays  8  and the reference element  40   x,    40   y  are at a standstill. The camera  15   a  has a defined distance to the sealing station  9  and this distance can be entered into the control unit  16  and is offset accordingly. A reference image of the reference element is  40   x,    40   y  may be stored in or taught to the camera  15   a,  respectively. Any deviation of the actual location of the reference element  40   x,    40   y  with respect to the reference image may be offset in the control unit  16  together with the distance of the camera  15   a  to the sealing station  9  and the distance A of the reference element  40   x  to the trays  8 , and the sealing station  9  is positioned such that the sealing seam  41  subsequently produced is in an exact location relative to the trays  8 . 
         [0050]    The distance A can, for example, be the distance from the center of a circular knob deformation of the reference element  40   x  to the center axis of the trays  8  of cycle Tx. But other alternative definitions of the distance A between the reference element  40   x  and the trays  8  of cycle Tx are conceivable. 
         [0051]    The reference element  40   x  can have various shapes, preferably concentric shapes such as a circle or a circular knob being formed upwardly or downwardly into the base film  4 . Punchings are also conceivable, preferably circular hole punchings. 
         [0052]    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. 
         [0053]    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.