Patent Publication Number: US-2002011049-A1

Title: Automatic Packaging Method

Description:
BACK GROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an automatic packaging method and an automatic packaging apparatus for packaging an article to be packaged with a film formed by resin material.  
       [0003] 2. Description of the Prior Art  
       [0004] Heretofore, a plastic tray with a plastic cover is generally used for containing foods in grocery store, drug store, food court or something like that. These plastic trays and covers are formed by plastic forming apparatus in succession, so that these are suitable for mass production. Generally, these plastic trays and covers are formed with certain form by die forming using a plastic blank material.  
       [0005] However, above-mentioned plastic forming apparatus requires own mold for each plastic product having different form. Therefore, plural sizes of molds are required if plural sizes of trays and the covers are requested, so that use and maintenance of the molds is troublesome.  
       [0006] Stretch packaging method is also usually used for containing foods. This type of packaging method can eliminate above drawback concerning the plastic forming technique. Japanese un-examined publication document no. hei 8-217008 and Japanese un-examined publication document no. hei 9-12004 introduce a stretch packaging apparatus for packaging an article using a stretching film. This type of apparatus automatically selects preset film size according to the tray size fed from an article feed unit, and packages the article with the film fed from a film unit.  
       [0007] However, this type of packaging method requires many amount of stock of a roll film. The stretch packaging apparatus is able to package the article being suitable of several sizes of the trays, which contains the article. Thus, several widths of roll films for packaging the article should be prepared in advance.  
       [0008] The stretch packaging apparatus has other drawback. The thickness of stretch film is usually uneven and some portions of the stretch film is usually very thin because the stretch film is formed by stretching the film having constant thickness so as to be suitable of the tray size. Thus, the stretch film often tears at thin portions. Also, the stretch film is not strong in nature. The stretch film is not suitable for the articles having projections, thorns or spines.  
       SUMMARY OF THE INVENTION  
       [0009] Accordingly, an object of the present invention is to provide an automatic packaging method and an automatic packaging apparatus to be capable of packaging an article without preparation of rolls of film.  
       [0010] Another object of the present invention is to provide an automatic packaging method and an automatic packaging apparatus to be capable of packaging the article using minimum amount of film material.  
       [0011] Another object of the present invention is to provide an automatic packaging method and an automatic packaging apparatus to be capable of forming the film with various kinds of width and thickness.  
       [0012] A further object of the present invention is to provide an automatic packaging method and an automatic packaging apparatus to be capable of forming the film without preparing a roll film previously.  
       [0013] These and further objects of the present invention are achieved by the novel automatic packaging method and automatic packaging apparatus of the present invention.  
       [0014] According to the present invention there is provided an automatic packaging method wherein melted resin material as raw material of a film is extruding from a resin extruding outlet, extruded resin is cooled so as to form the film, the film is immediately introduced after forming the film above a tray charged with an article to be packaged, and the article is packaged with the film. Accordingly, the article can be packaged without preparing a roll film previously because the article is packaged while the film is formed.  
       [0015] Another aspect of the present invention there is provided an automatic packaging method wherein a tray, which contains an article to be packaged, is positioned adjacent to a film extruding mechanism for extruding melted resin material as raw material of a film from a resin extruding outlet so as to form the film; and the article is packaged with the film while the film extruding mechanism forms the film. Accordingly, the article can be packaged without preparing a roll film previously because the article is packaged while the film is formed.  
       [0016] Another aspect of the present invention there is provided an automatic packaging apparatus comprises a film extruding mechanism for extruding melted resin material as raw material of a film from a resin extruding outlet, a film forming mechanism for touching the extruded resin with a surface of rotating cooling drum so as to cool and solidify the extruded resin from the resin extruding outlet, and a packaging mechanism for introducing the film immediately, after solidifying on the surface of cooling drum, above a tray charged with an article to be packaged to package the article with the film. Accordingly necessary film for packaging the article can be formed when the article is packaged so that film forming operation and article packaging operation can be done easily with same apparatus. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0017] A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which:  
     [0018]FIG. 1 is a perspective view showing an inner structure of a packaging apparatus according to an embodiment of the present invention;  
     [0019]FIG. 2 is a longitudinal sectional view showing the inner structure of the packaging apparatus;  
     [0020]FIG. 3 is a longitudinal sectional view of a film extruding mechanism;  
     [0021]FIG. 4 is a front view showing the inner structure of the packaging apparatus;  
     [0022]FIG. 5 is a perspective view of a scraper;  
     [0023]FIG. 6 is a perspective view of a mechanism for adjusting thickness of the film;  
     [0024]FIG. 7 is a longitudinal sectional view thereof;  
     [0025]FIG. 8 is a perspective view of a mechanism for adjusting width of the film;  
     [0026]FIG. 9 is a perspective view of a packaging apparatus according to other embodiment of the present invention;  
     [0027]FIG. 10 is a front view of a tray with film drawn out above the tray;  
     [0028]FIG. 11 is a front view of the tray with film positioned on the tray;  
     [0029]FIG. 12 is a front view of the tray with film portions overhanging from the tray pulled down sideways of the tray;  
     [0030]FIG. 13 is a perspective view of the tray with film positioned on the tray;  
     [0031]FIG. 14 is a perspective view of the tray with film positioned on the tray and spread;  
     [0032]FIG. 15 is a front view of the tray with film started to converge under the jet of hot air;  
     [0033]FIG. 16 is a front view of the tray with a solid edge portion formed by film;  
     [0034]FIG. 17 is a perspective view of a packaging apparatus according to other embodiment of the present invention;  
     [0035]FIG. 18 is a functional block diagram showing a control system;  
     [0036]FIG. 19 is a block diagram showing the control system;  
     [0037]FIG. 20 is a flow chart for film forming process and film packaging process;  
     [0038]FIG. 21 is a flow chart showing a subroutine executed in an input/display controller;  
     [0039]FIG. 22 is a flow chart showing a subroutine executed in a packaging controller;  
     [0040]FIG. 23 is a flow chart showing a subroutine executed in a packaging condition setting controller;  
     [0041]FIG. 24 is a flow chart showing a subroutine executed in a film forming controller;  
     [0042]FIG. 25 is a flow chart showing a subroutine executed in the packaging controller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0043] An embodiment of the present invention is now explained with reference to FIGS.  1  to  8 . FIG. 1 shows basic structure of an automatic packaging apparatus in this embodiment. A detail of the same is mentioned below. An packaging machine  1  as the automatic packaging apparatus  201  includes uniformly a film unit  205  for forming a film  15  and a packaging unit  202  for sealing an upper surface of a tray  2  with the film  15 . The packaging machine  1  has a tray table  3  for supporting the tray  2  containing an article to be packaged. A film forming unit  4  is provide above the tray table  3 . The film forming unit  4  contains a linear actuator  5  for raising and lowering the film unit  205  according to a height of the tray  2  set on the tray table  3 , a pair of linear actuators  7  provided along a seal surface  6  of the tray  2  and a pair of linear guide rail  8  for guiding the linear actuator  7 . Such arrangement of each member, the linear actuator  5  and the linear actuator  7  operate as a packaging mechanism  51  for packaging the tray  2 . Especially, the linear actuator  5  also operates as rising/lowering mechanism  52  for rising and lowering the film forming unit  4 . A block diagram of FIG. 19 shows the linear actuator  5  and the linear actuator  7  as an actuator Act.  
     [0044] The film forming unit  4  and an extruding unit  101  will be explained with reference to FIGS. 2 and 3. The extruding unit  101  feeds heated and melted pellet into the film forming unit  4 . These film forming unit  4  and the extruding unit  101  comprises a film extruding mechanism  13 . The pellet, ethylene vinyl acetate copolymer for instance, is used for a film material. Thermo plastic synthetic resin, polyethylene, polypropylene or nylon for instance, also can be used for the film material. The film extruding unit  101  heats and melts the pellet with 170-200° C. to feed the melted pellet into a resin extruding portion  9  by pressure means. The extruding unit  101  has a housing  102  including a mandrel  103 , which feeds the melted pellet into the resin extruding portion  9  by rotation thereof. The housing  102  has a hopper  104  for introducing the pellet into a pellet transfer space of the mandrel  103 . The housing  102  also has a heater  105 , built-in it, for heating a solid pellet or the melted resin and keeping the resin in melted condition. The extruding unit  101  rotates the mandrel  103  by a motor M shown in FIG. 19 so that the mandrel  103  forwards the pellet with a screw  106  formed on a surface of the mandrel  103  while the mandrel  103  stirs the pellet. For other embodiment, pressure means for feeding the pellet into the resin extruding portion  9  of the extruding unit  101  may be used other structure such as a pressure pump.  
     [0045] The resin extruding portion  9  provided in the film forming unit  4  comprises a resin feed tube  10 . The resin feed tube  10  comprises a flexible pipe  11  formed by stainless steel for instance, and a heat insulating material  12  for covering a periphery of the flexible tube  11 . A nozzle  14  as a resin extruding outlet is provide. The nozzle  14  feeds the melted resin to a cooling drum  16  while a mechanism for controlling a thickness and width of the film  15  sets a gap and width of the nozzle  14  with desired value. For concrete value with respect to the thickness of the film  15 , 30 μm-100 μm are set so as to be suitable for packaging of the article to be packaged. The surface of the cooling drum  16  is cooled by cooling system, coolant around 20° C. for instance, when the melted resin has been fed to the cooling drum  16 . The cooling drum  16  has a hollow  17 . The cooling drum  16  is formed by machining using SUS 630. A pair of hollow supporting shafts  18  is provided at both ends of the cooling drum  16  as shown in FIG. 4. These supporting shafts  18  are attached on a supporting frame  19  via a pair of bearings  20 . A pair of pipes  22  as a passage of coolant  23  connects to the hollow supporting shafts  18  via a pair of rotary joint  21 . The coolant  23  can be introduced into the cooling drum  16  through one of the pipes  22 , rotary joints  21  and supporting shafts  18  as shown in FIG. 1. A coolant liquid such as a coolant water and coolant air can be used as the coolant  23 .  
     [0046] A film forming mechanism  24  comprises the cooling drum  16 , periphery mechanisms thereof, and the arrangement between the film extruding mechanism  13  and the cooling drum  16 . The periphery mechanisms of the cooling drum  16  include a driving mechanism for rotating the cooling drum  16 . The driving mechanism comprises a motor  26  supported on the supporting frame  19 , and transmission gears  27  for transmitting a driving power from the motor  26  to the cooling drum  16 . The motor  26  is shown as the motor M in FIG. 19. The melted resin extruding from the nozzle  14  is cooled by touch on the surface of the cooling drum  16 , so that the melted resin becomes the film  15 . The cooling drum  16  rotates when the melted resin has been extruded from the nozzle  14 , so that an front end of the film  15  on the surface of the cooling drum  16  feeds to the scraper  25 . Thus, the scraper  25  peels the front end of the film  15  from the cooling drum  16  when the front end of the film  15  was reached at the scraper  25 .  
     [0047] The packaging mechanism  51  will be explained. The linear actuator  7  drives the film unit  205  while the above-mentioned film forming operation has been done, so that the film unit  205  moves along the tray  2  on the tray table  3  in arrow direction of FIG. 2. The movement of the film unit  205  synchronizes the rotation of the cooling drum  16 , so that the peeled film  15  drops on the seal surface  6  of the tray  2 . In this embodiment, the seal surface  6  has adhesive so as to adhere the film  15  to the seal surface  6 . The width of the film  15  can be easily suitable for the width of the tray  2  by the above-mentioned mechanism for controlling the thickness and width of the film  15 . This mechanism includes a pair of slidable obstructing member  36  disposed at both sides in the nozzle  14  as mentioned below. The packaging mechanism  51  is able to be suitable for several height of the tray  2  because, as mentioned above, the linear actuator  5  raises and lowers the film unit  205  according to the height of the tray  2  on the tray table  3 .  
     [0048] The cooling system using the cooling drum  16  will be explained. The coolant  23  can be introduced into the cooling drum  16  through one of the pipes  22 , rotary joints  21  and one end of the supporting shafts  18  as shown in FIG. 1, so that the surface of the cooling drum  16  is cooled. The warmed coolant  23  in the cooling drum  16  drains through other end of the supporting shaft  18 . There is provided a temperature sensor (not shown) for detecting a temperature of the cooling drum  16 . In this embodiment, the flow rate of the coolant  23  can be adjusted according to detected temperature value of the sensor, so that the temperature on the surface of the cooling drum  16  can be kept in certain temperature.  
     [0049] In this embodiment, the nozzle  14  of the resin extruding portion  9  is arranged upward, disposed toward the cooling drum  16  with little gap, and inclined, so that the nozzle  14  is positioned at upper position more than an axis of the cooling drum  16 . Thus, the melted resin from the nozzle  14  can be touched as soon as the melted resin is extruded from the nozzle  14 , so that the thickness of the film  15  can be kept in constant.  
     [0050] The film  15  on the cooling drum  16  can be easily peeled. This is because the surface of the cooling drum  16  has fluoro resin treatment. Also, the scraper  25  touches the peripheral surface of the cooling drum  16  with its acute-angled edge portion at film peeling point with certain angle. For other embodiment, the scraper  25  may be disposed toward the cooling drum with little gap. The scraper  25  is preferably made by fluoro resin material whose peeling characteristics with film  15  are well. For other embodiment, fruoro resin may be treated on the surface of the metal scraper  25 .  
     [0051] Pealing characteristics can be improved by adding micro-vibration to the scraper  25 . FIG. 5 shows a scraper supporting structure with means for driving the scraper  25  so as to arise the micro-vibration. As shown in FIG. 5, the pair of supporting frames  19 , for supporting the supporting shafts  18  of the cooling drum  16  (refer FIG. 4), have a pair of fixing seats  107 . There are provided a pair of scraper holder  109  for holding both ends of the scraper  25 . The scraper holders  109  are attached to the fixing seats  107  via a pair of leaf springs  108 . A pair of piezoelectric elements  110  is attached on the leaf springs  108 . Poly vinyliden fluoride (PVDF) for instance is used for the piezoelectric elements  110 . A length of the scraper  25  is set as two leaf springs  108  urges preload each other in static condition. Thus, the piezoelectric elements  110  strain by supplying voltage, so that one of the leaf springs  108  is deflects toward the other one of the leaf springs  108 . Accordingly, the micro-vibration can be arose in the scraper  25  by applying the alternative voltage to the piezoelectric elements  110  frequently.  
     [0052] The driving source for giving micro-vibration in the scraper  25  is not limited as the piezoelectric elements  110 . Electric strain elements for instance may be used.  
     [0053] The film  15  should have certain rigidity for keeping its form when the film  15  is peeled from the cooling drum  16  because the film  15  is formed by cooling process of the melted resin extruded from the nozzle  14  to the cooling drum  16  with certain width and thickness. However, cooling process completes depending on the width and thickness of the film  15 . Thus, in this embodiment, the velocity of the cooling drum  16  can be adjusted, so that the cooling period for cooling process can be controlled.  
     [0054] An obstructing plate driving mechanism will be explained with reference to FIGS.  6  to  8 . There is provided an obstructing plate  29  at the nozzle  14 . The obstructing plate  29  has a width, which is longer than maximum width of the nozzle  14 . As shown in FIGS. 6 and 7, the obstructing plate  29  is attached slidable in the nozzle  14 . The obstructing plate  29  is urged in a direction so as to shut the nozzle  14  by a pair of springs  30  at both ends thereof. An ellipse opening  31  is formed around center portion of the obstructing plate  29 . An eccentric cam  33  driven by a motor  32  is disposed at the ellipse opening  31 , so that the Scotch yoke mechanism is formed. Thus, the obstructing plate  29  can be raised and lowered by rotation of the eccentric cam  33  driven by the motor  32  so as to adjusting the gap of the nozzle  14 . Then, the extruding amount of the melted resin from the nozzle  14  is adjusted, so that the thickness of the film  15  can be controlled.  
     [0055] As other method for controlling the thickness of the film  15 , the velocity of the cooling drum  16  can be adjusted.  
     [0056] A mechanism for adjusting the width of the film  15  will be explained with reference to FIGS. 4, 7 and  8 . The width of the film  15  should be adjusted according to a size or kind of the tray  2 . As shown in FIGS. 4 and 8, a pair of linear actuator  34  is fixed to the pair of supporting plates  19 . As described above, the pair of obstructing members  36  is disposed in the nozzle  14  as showing in FIG. 7. Each linear actuator  34  and the obstructing member  36  are connected with connecting plate  37 . This is a basic structure of the mechanism for adjusting the width of the film  15 . An interval of the ends of the obstructing members  36  determines effective nozzle width because the obstructing members  36  cover the opening of the nozzle  14  completely. Thus, the melted resin can be merely extruded from the effective nozzle width. As shown in FIG. 8, each linear actuator  34  for driving the obstructing member  14  includes linear actuator shaft  35  having screw on its periphery and guide shaft  112  having smoothness on its periphery. Each linear actuator shaft  35  and guide shaft  112  are movably contained in an actuator housing  111 . Each linear actuator shaft  35  and guide shaft  112  are connected to the obstructing members  36  via the connecting plate  37 . Each linear actuator shaft  35  is mounted at the connecting plate  37 . There is provided a floating nut (not shown) driven by the motor M shown in FIG. 19 in each actuator housing  111 . Each floating nut transmits rotation power from the motor M to the linear actuator shaft  35  so as to rotate the linear actuator shaft  35 . Each linear actuator shaft  35  moves right or left direction according to the rotation of each floating nuts, so that each obstructing member  36  slides in the nozzle  14  with the linear actuator shaft  35 . Thus, the interval of the ends of the obstructing members  36  can be adjusted, so that the width of the film  15  can be controlled. That is, it is possible to form the film  15  having a size being suitable for the tray  2  and the article to be packaged.  
     [0057] A film forming process will be explained below.  
     [0058] The film forming process of the present invention is similar to conventional extrusion technique. However, the pellet amount for one extrusion is very little. And the pellet, which became the melted resin, is not extruded continuously. These features identify the extruding method used in the present invention from the conventional extrusion technique. These features contribute compactness of the apparatus, so that the film unit  205  can be built into the automatic packaging apparatus  201 .  
     [0059] As mentioned above, the extruding unit  101  drives the mandrel  103  by the motor M, and forwards the pellet with the screw  106  formed on the periphery surface of the mandrel  103  while the mandrel  103  stirs the pellet. Then, the nozzle  14  provided in the film forming unit  4  is filled with the pellet, which became the melted resin, so that preparation for film forming completes. After the preparation of it, the mandrel  103  is forward and backward driven so as to keep the end position of the melted resin in the nozzle  14 . This is named waiting condition. The film forming unit  4  starts up the film forming operation according to start up signal from the automatic packaging apparatus  201 . After starting up, the cooling drum  16  is driven by the motor  26  to rotate. The mandrel  103  is also driven by the motor M as shown in FIG. 19 to rotate, so that the melted resin is extruded from the nozzle  14 . Extruded resin is cooled by the touch to the periphery surface of the cooling drum  16 , so that the melted resin solidifies and becomes the film  15 . The film  15  is fed to left direction in FIG. 3 so as to be peeled from the cooling drum  16  by the scraper  25 . Peeled film  15  can be handled as ordinary film. A film forming controller  301 , shown in FIG. 18, watches rotary operation of the mandrel  103 . The film forming controller  301  rapidly drives the motor M for the mandrel  103  backward when the film forming controller  301  determines that enough amount of the melted resin for the film  15  to be formed is extruded from the nozzle  14 . Then, the mandrel  103  is rapidly driven backward. Thus, the supply of the melted resin to the nozzle  14  is rapidly broken off, so that the last end of the film  15  on the cooling drum  16  is also separated from the melted resin. The melted resin is drawn back into the nozzle  14  uniformly in the width direction thereof because the nozzle  14  is disposed upward. Thus, the straightness at last end of the film  15 , as well as at front end of the next film to be formed, can be improved.  
     [0060] Next, whole process of the packaging operation will be described.  
     [0061] (1) Keep the pellet as resin material for the film  15  in heated and melted condition with certain temperature.  
     [0062] (2) Set the tray  2  charged with the article to be packaged on the tray table  3  at standard position for packaging. It is preferable to obtain size of the tray  2  by measuring the size using a sensor S, an optical sensor or image-processing sensor for instance (refer FIG. 19). The size data to be obtained is used as a basic data for determining the width and the thickness of the film  15  to be formed.  
     [0063] (3) Start up the mandrel  103  for obtaining waiting condition. Heated and melted resin material is extruded into the nozzle  14  and kept in the nozzle  14 .  
     [0064] (4) Move the film unit  205  to a packaging start up position. The packaging start up position is adjacent to the standard position. It is preferable to return the film unit  205  at the packaging start up position after one cycle of the packaging operation because the packaging start up position identifies the starting point. Then, dispose the film unit  205  at certain height by driving the linear actuator  5 .  
     [0065] (5) Determine the width of the film  15  to be formed, by moving the obstructing members  36 , according to the measured data of the tray  2 . The linear actuator  34  can move the obstructing members  36  via the connecting plate  37 . The obstructing members  36  at right side and left side can be moved toward inner side and outer side in certain amount. Thus, the width of the film  15  is determined as center standard.  
     [0066] (6) Drive the cooling drum  16 . Adjust the thickness of the film  15  by driving the eccentric cam  33 . The eccentric cam  33  drives the obstructing plated  29 .  
     [0067] (7) The cooling drum  16  is kept cool because the coolant  23  is introduced to the hollow  17  of the cooling drum  16  via the pipe  22  and rotary joint  21 . The extruded resin touches the periphery surface of the cooling drum  16 , so that the heated and melted resin is cooled to become the film  15  having certain rigidity for keeping its form. The film  15  is fed to the standard position for packaging.  
     [0068] (8) The scraper  25  having sharp edge is disposed at opposite side of the resin extruding portion  9  with width longer than the width of the film  15  in order to peel the film  15  easily from the cooling drum  16 . The film  15  on the periphery surface of the cooling drum  16  is effectively peeled from the cooling drum  16  by micro-vibration of the scraper  25 .  
     [0069] (9) The film unit  205  is controlled so as to move opposite direction to the standard position by the pair of linear guide rails  8  and the pair of linear actuators  7  while the film unit  205  executes above (5)-(8) processes.  
     [0070] (10) Formed film  15  moves while the film  15  touches the seal surface  6  of the tray  2 . It is possible to seal the film  15  strongly to the tray  2  when a moving roller (not shown) for instance put pressure on the tray  2 . In this case, the actuator Act shown in FIG. 19 drives the moving roller.  
     [0071] (11) The film unit  205  moves upward or downward, while the film unit  205  moves packaging direction, by driving the linear actuator  5  depending on the height of the article to be contained in the tray  2 . The width of the film  15  also can be adjusted according to the moving amount of the film unit  205 . In such case, the film  15  having different width through its forming direction is issued.  
     [0072] (12) The resin supply is rapidly stopped and the obstructing plate  29  is rapidly shut after forming the film  15  and packaging, so that the extruding unit  101  stops extruding the resin completely.  
     [0073] (13) Move the film unit  205  upward and stop the same. Then, the packaged tray  2  can be removed from the tray table  3 .  
     [0074] (14) One cycle of the packaging process has been ended.  
     [0075] Other embodiment of the present invention is now explained with reference to FIGS.  9  to  16 . The same parts as those in the former embodiment are designated by the same reference numerals, and are not again explained herein. This embodiment relates to the automatic packaging apparatus  201  which packages the article to be packaged automatically after forming the film  15 . The former embodiment introduces the automatic packaging apparatus  201 , which drops the forming film  15  from the cooling drum  16  on the seal surface  6  of the tray  2  so as to adhere the film  15  to the seal surface  6  of the tray  2 . The former embodiment also introduces the pressure roller, which puts pressure on the tray  2  for seal the film  15  to the tray  2  strongly. This embodiment will introduce automatic packaging apparatus  201  of which film grippers  207  grips the film  15  extruded by the film forming unit  4  for packaging operation. More specifically, the film grippers  207  feed the film  15  above the tray  2  disposed in the packaging unit  202 , and move the film  15  downward so as to dispose the gripping position of the film  15  lower than the upper surface of the tray  2 . Then, packaging operation is executed by heating the edge portion of the film  15 . The detail description of this embodiment is now explained below.  
     [0076] What is illustrated in FIG. 9 is the automatic packaging apparatus  201 . The automatic packaging apparatus  201  comprises the packaging unit  202 , a tray feed unit  203  and a tray discharge unit  204  disposed on the left and right sides, respectively, of the packaging unit  202 , and the film unit  205  disposed behind the packaging unit  202 . With this arrangement, the automatic packaging apparatus  201  can package continuously a large number of articles to be packaged. The tray feed unit  203  feeds a tray  2  to the packaging unit  202  in a continuous manner, the tray discharge unit  204  discharges the tray  2  after packaged, and the film unit  205  feeds the film  15  to the packaging unit  202  in a successive manner. As to detailed structures of the tray feed unit  203  and tray discharge unit  204 , explanations thereof are here omitted. The detailed structure of the film unit  205  is substantially the same as the former embodiment, so that explanations thereof are also here omitted.  
     [0077] The packaging unit  202  is provided with a tray table  3  on which the tray  2  is placed. Four blowers  206 , whose heaters H are built in it, are arranged so as to surround four sides of the tray  2  put on the tray table  3 . Also mounted are four film grippers  207  (only two are shown in FIG. 9) for gripping four corners of the film  15  pulled out from the film unit  205 .  
     [0078] The tray  2  is formed with an upper opening  209  having a peripheral fitting edge  208  and is in the shape of an upwardly expanded tray as a whole.  
     [0079] In such a construction, as shown in FIG. 10, the tray  2  charged with an article (not shown) to be packaged is fed from the tray feed unit  203  onto the tray table  3  in the packaging unit  202  and at the same time the film  15  is fed from the film unit  205 . The film  15  is gripped at four corners thereof by the film grippers  207 . In this state, the film grippers  207  move down into contact with the tray  2  while pulling the film so as not to wrinkle the film, to cover the opening  209  of the tray  2 , as shown in FIGS. 11 and 12. Further, as shown in FIG. 13, the film grippers  207  turn and move down, causing overhanging portions of the film  15  overhanging from the tray  2  to approach the side faces of the tray  2 . At this time, as shown in FIG. 12, it is desirable that the gripping direction of the film grippers  207  is an upward direction toward the fitting edge  208 .  
     [0080] When end portions of the film  15  have reached a position lower than the opening  209  of the tray  2  in a fully pulled state of the film  15 , the blowers  206  positioned around the tray  2  are driven to blow hot air against the four sides of the container. Taking the influence on the article to be packaged into account, a jet of hot air at 120° C. for about 3 seconds is desirable. With this hot air, end portions of the film  15  become hot and shrink. As a result of this thermal shrinkage the overhanging portions of the film  15  overhanging from the tray  2  converge to enhance their rigidity and extend inside along the fitting edge  208  to form a solid edge portion  210  below the fitting edge  208 . In this case, an appropriate timing for ungripping the film  15  from the gripped state by the film grippers  207  is set in synchronism with shrinkage of the film positioned at the side portions of the tray  2 . The solid edge portion  210  is formed also by the four corners of the film  15 . AS a result of formation of the solid edge portion  210  there is formed a cover member  18  by the film  15 . The solid edge portion  210  is fitted with the fitting edge  208  of the tray  2  and is not heat-fused to the tray  2 . Of course, the solid edge portion  210  may be heat-fused to the tray  2  to such an extent that it can be stripped off easily. Therefore, when the article to be packaged is to be taken out from the tray  2 , a finger is put on the solid edge portion  210  and is moved in a direction to come off the fitting edge  208 , whereby the film  15  is separated easily from the tray  2  and the upper surface of the tray  2  can be opened without damaging the tray  2 .  
     [0081] Another method for pulling a film, which covers a tray  2  according to the present invention, will now be described with reference to FIG. 17. The same parts as those in the former embodiments are designated by the same reference numerals, and are not again explained herein.  
     [0082] What is illustrated in FIG. 17 is the automatic packaging apparatus  201  provided with the packaging unit  202  for stretching the film  15 . The automatic packaging apparatus  201  comprises the tray feed unit  203  and the tray discharge unit  204  disposed on the left and right sides, respectively, of the packaging unit  202  and the film unit  205  disposed behind the packaging unit  202 . According to this arrangement, a large number of articles to be packaged can be packaged in a continuous manner. The tray feed unit  203  feeds trays  2  to the packaging unit  202  continuously one by one, the tray discharge unit  204  discharges packaged trays  2 , and the film unit  205  feeds the film  15  to the packaging unit  202  in a successive manner. As to detailed structures of the tray feed unit  203  and the tray discharge unit  204 , explanations thereof are here omitted. The detailed structure of the film unit  205  is substantially the same as the former embodiments, so that explanations thereof are also here omitted.  
     [0083] The packaging unit  202  comprises the tray table  3  which includes a container raising/lowering mechanism (not shown) for moving the tray  2  up and down while carrying it thereon, film grippers  207 , for drawing out the film  15  to the packaging unit  202  and gripping four corners of the film, the film grippers  207  being also used for stretching, film pulling mechanisms  211 , as the film gripper, and linear-acting actuators  112 . The film pulling mechanisms  211  themselves, which are provided four, can move back and forth and turn vertically and the film pulling mechanisms  211  located on the linear-acting actuators  112  which are disposed two at right and left positions can also move in the longitudinal direction of the automatic packaging apparatus  201 , whereby the formed film  15  can be gripped, stretched and ungripped.  
     [0084] The detailed structure of the film unit  205  is substantially the same as the film unit  205  shown in FIGS.  1  to  8 . A front end portion of the film  15 , formed by the film unit  205 , is fed to a film delivery section  213 . In this case, a control is made so that the front end portion of the film is set at an initial position at which it slightly overhangs to the packaging unit  202  side with respect to the film delivery section  213 .  
     [0085] In such a configuration, when the tray  2  charged with an article (not shown) has been fed onto the tray table  3  in the packaging unit  202 , the linear-acting actuator  212  operates and two film grippers  207  located on the linear-acting actuators  112  and on the front side of the apparatus grip the film  15  overhanging from the film delivery section  213 , then the film  15  is drawn out to above the tray  2 . Thereafter, two film grippers  207  located at rear positions grip the film  15 . The amount of the film  15  to be drawn out differs depending on the size of the tray  2  and a film forming controller  301  described below controls the film drawing-out operation (refer FIG. 18). At this time, the film pulling mechanisms  211  not concerned in drawing out the film  15  are located at positions not obstructing the drawing-out operation.  
     [0086] After the film  15  has been drawn out to above the tray  2 , the film pulling mechanisms  211  grasp the centers in each side of the film  15 , both film pulling mechanisms  211  and film grippers  207  stretches the film  15 . As a result, as shown in FIG. 17, the four corners of the film  15 , which is rectangular, are grasped by the film grippers  207  and a central portion of the film is grasped at four points by the film pulling mechanisms  211 . For stretching the film  15  from the central portion of the film, as shown in FIG. 17, the film pulling mechanisms  211  move outwards crosswise from the central portion of the film  15 , while the film grippers  207  move in diagonal directions. As a result, the film  15  whose central portion and four corners are thus grasped at eight points can be stretched by being pulled from its central portion. The pulling operation is performed by actuators Act provided in the film pulling mechanisms  211  and the film grippers  207  (refer FIG. 19), conditions such as pulling speed and pulling quantity differ depending on the properties of the film  15  and the specification of actuators Act.  
     [0087] It is also possible to provide rotating mechanisms in the film grasping portions of both film pulling mechanisms  211  and film grippers  207  and effect film stretching through the rotating mechanisms. To be more specific, by grasping the film  15  at eight points through the film pulling mechanisms  211  and the film grippers  207  and causing the film grasping portions of the actuators to turn downward.  
     [0088] After the film  15  grasped at its four corners has thus been stretched by being pulled from its central portion through the film pulling mechanisms  211 , the stretched film  15  is applied over the tray  2  and is made integral with the container, whereby there is formed a packaged trays  2 , in which the stretched film  15  constitutes a cover portion as is the case with the description of the former embodiment. The process for forming the cover portion of the packaged trays  2  is as follows.  
     [0089] First, when such a state as shown in FIG. 17 has been attained, the container raising/lowering mechanism of the tray table  3  causes the tray  2  charged with the article to be packaged to rise toward the stretched film  15 . It is preferable that the rising speed be 50 mm or so per second.  
     [0090] Upon contact of the article to be packaged or the opening  121  of the tray  2  with the stretched film  15 , the rising speed is decreased to 20 mm or so per second to cover the opening  121  little by little. The opening  121  of the tray  2  is a fitting edge  208 . Further, the stretched film  15  is pushed upward with the pressure of the tray  2  of the article to be packaged and the film grippers  207  and the film pulling mechanisms  211  turn slightly, causing the overhanging portions of the film  15  overhanging from the opening  121  to approach the side faces of the tray  2 . At this time it is preferable that the film grasping direction of the film grippers  207  and film pulling mechanisms  211  is upward toward the container opening.  
     [0091] When end portions of the stretched film  15  have arrived at a position lower than the opening  121 , blowers  206  positioned within the packaging unit  202  are driven to blow hot air to the four sides of the tray  2 , thereby allowing the stretched film  15  to be fitted with the opening  121 , whereby a solid edge portion  210  is formed and it is possible to form a packaged trays  2 .  
     [0092] A control system for controlling the above structure of the automatic packaging apparatus  201  is now explained with reference to FIGS.  18  to  25 .  
     [0093] The former embodiment described first has a different packaging manner to the other two former embodiments. The control system described hereafter is suitable for latter two embodiments of the present invention. However, the film unit  205  is commonly used for all former embodiments. Thus, the control system described hereafter is suitable for all former embodiments with respect to a control of the film unit  205 .  
     [0094]FIG. 18 is a functional block diagram showing a control system of the automatic packaging apparatus  201 . The automatic packaging apparatus  201  comprises an input/display device  302 , whose outer structure is not shown, for inputting driving and packaging condition data and displaying necessary information. The driving and packaging condition data, input by the input/display device  302 , are input into an input/display controller  303  to be controlled in the input/display controller  303 , so that the driving and packaging condition data are displayed on the input/display device  302 . The driving and packaging condition data input by the input/display device  302  are the driving condition data, packaging number of the tray  2  for instance, and the packaging condition data, the thickness and width of the film  15  to be formed by the film unit  205  for instance.  
     [0095] The input/display controller  303  transmits the input driving and packaging condition data into an information inputting controller  304 . The information inputting controller  304  transmits the input driving and packaging condition data into an packaging condition setting controller  305 . The packaging condition setting controller  305  refers a packaging condition data base  306  to obtain setting condition of each portion corresponding to the input packaging condition data. The packaging condition data are the data, for instance, data for diving the motor  32 , the motor M in FIG. 19, of the film unit  205  so as to limit the thickness of the film  15  corresponding to the input thickness data as packaging condition data, and data for driving the actuator Act of the film unit  205  so as to form the film having the width corresponding to the input width data as packaging condition data and so on. The packaging condition setting controller  305  transmits the obtained packaging condition data to a packaging controller  307  and the film forming controller  301  which controls each portions of the film unit  205 .  
     [0096] The film forming controller  301  transmits the packaging condition data into the input/display controller  303  according to transmittal request from the input/display controller  303 . The input/display controller  303  converts the packaging condition data to readable information for operators to display the same on the input by the input/display device  302 .  
     [0097] The packaging controller  307  transmits a film forming start-up signal into the film forming controller  301 , when the packaging condition data was transmitted from the packaging condition setting controller  305 , on condition that the packaging controller  307  was received a tray detecting signal, which identifies tray supply into the tray feed unit  203 , from a tray unit  308 . The film forming controller  301  drives the extruding unit  101  and the film forming unit  4  according to the film forming start-up signal, causing the extruding unit  101  and the film forming unit  4  to start up. As to following film forming operation and packaging operation, explanations thereof are here omitted because these operations are described above. As to data processing for film forming operation and packaging operation will be explained below.  
     [0098]FIG. 19 is a block diagram showing the control system for executing data processing with respect to the operation shown in FIG. 18. Each portion  301 ,  303 ,  304 ,  305 ,  307  and  308  shown in functional diagram of FIG. 18 identify a microcomputer comprises a CPU (central processing unit)  401 , RAM (random access memory)  402  and ROM (read-only memory)  403 . The microcomputer controls peripheral devices by processing of the CPU  401  according to operating program and application program stored in the ROM  403 . As to a recording medium for storing the operating program and the application program, it may be used, for instance, the ROM  403 , a hard disk drive (HDD)  404  connected to the CPU  401 , MO (magnetic optical disk), DVD-ROM (digital video disk), DVD-RAM (digital video disk) and so on. The HDD  404  stores the packaging condition data base  306  shown in FIG. 18. The peripheral devices is driven by control of the each portion  301 ,  303 ,  304 ,  305 ,  307  and  308 , shown in functional diagram of FIG. 18, according to the operating program and the application program stored in the recording medium, so as to execute the film forming operation and the packaging operation.  
     [0099] The microcomputer, comprises CPU  401 , RAM  402  and ROM  403 , is connected with each portion provided in the packaging unit  202 , a conveyance unit  406  comprising the tray feed unit  203  and the tray discharge unit  204 , and film unit  205 , via a system bus  405 . Each portion connected with the microcomputer identify the actuator Act, the motor M, piezoelectric element  110  and heater  105  provided in the film unit  205 , the actuator Act, the heater H and the blower  206  provided in the packaging unit  202 , and the motor M and the sensor S provided in the conveyance unit  406 .  
     [0100] FIGS.  20  to  25  are flow charts showing summary of the data processing with respect to the film forming process and the packaging process in the automatic packaging apparatus  201 . The data processing of the film forming process and the packaging process is now described with reference to these flow chats.  
     [0101]FIG. 20 shows main routine executed in the packaging controller  307 . First, the packaging controller  307  reads the initial conditions (step S 101 ), and starts up each subroutine (step S 102 ). Then each subroutine shown in FIGS.  21  to  22  is started up.  
     [0102] The subroutine shown in FIG. 21, executed in the input/display controller  303 , determines whether the driving condition is input (step S 201 ), and whether the packaging condition is input (step S 203 ). The input/display controller  303 , which determines the driving condition is input and the packaging condition is input, executes setting operation with respect to the input driving condition (step S 202 ) and the input packaging condition (step s 204 ). The subroutine shown in FIG. 23, executed in the packing condition setting controller  305 , determines the conditions are input (Y of step S 401 ), so that the packing condition setting controller  305  refers the packaging condition data base  306  stored in the HDD  404  according to the input packaging condition to obtain the setting conditions of each portion, setting each portion according to obtained setting conditions (step S 402 ). The main routine, executed in the packaging controller  307 , shown in FIG. 20 executes reading process of setting conditions from the packaging condition setting controller  305  (step S 103 ). Then the packaging controller  307  sets a desired packaging number to “n” (step S 104 ). The desired packaging number is set in counter area presented in work area of the RAM  402 . The packaging controller  307  determines whether the tray is present (step S 105 ).  
     [0103]FIG. 22 is a flow chart showing a subroutine executed in the packaging controller  307 . The packaging controller  307  drives the actuator Act to convey the tray  2  certain amount (step S 303 ) and cause the conveyed tray  2  raising (step S 304 ), when the packaging controller  307  was received the tray detecting signal from the feed unit  308  (Y of step S 301 ), on condition that last packaging operation completed (Y of step S 302 ). The packaging controller  307  transmits the film forming start-up signal into the film forming controller  301  (step S 305 ), and waits for a packaging completion signal (step S 306 ). The main routine executed in the packaging controller  307  shown in FIG. 20 determines that the tray is fed according to the film forming start-up signal (Y of step S 105 ). Then the packaging controller  307  increments counter value (step S 106 ). The packaging controller  307  returns the process of step S 103  until the counter value will become “n” as desired packaging number set in step S 104 .  
     [0104]FIG. 24 is a flow chart showing a subroutine executed in a film forming controller  301 . The film forming controller  301  determines whether the film forming start-up signal is received (step S 411 ). The film forming controller  301  starts up the film forming operation (step S 412 ) when the film forming controller  301  is received the film forming start-up signal from the packaging controller  307 . The film forming controller  301  drives the piezoelectric element  110  (step S 413 ), just before completion of the film forming operation, to urge smooth separation of the film  15  from the melted resin. Then the film forming controller  301  transmits the film forming completion signal to the CPU  401  after the film forming operation (step S 414 ). The CPU  401  uses the film forming completion signal for the packaging controller  307 .  
     [0105]FIG. 25 is a flow chart showing a subroutine executed in the packaging controller  307 . The packaging controller  307  waits for receiving the film forming completion signal transmitted from the film forming controller  301  (step S 414  of FIG. 24). The packaging controller  307  drives actuator Act to execute the film grasping operation (step S 502 ), the film moving operation (step S 503 ), and the film stretching operation (step S 504 ) in the successive manner when the packaging controller  307  received the film forming completion signal. Then the packaging controller  307  drives the actuator Act to raise the tray (step S 505 ), and drives the heater H and the blower  206  to heat and shrink the overhanging portion of the film  15  overhung from the opening  121  of the tray  2 , so that the solid edge portion  210  is formed at the peripheral of the film  15  (step S 506 ). Thus, the tray  2  charged with the article is packaged with the film  15 .  
     [0106] As next process, the packaging controller  307  transmits the packaging completion signal to the CPU  401  (step S 507 ). Thus, the subroutine for executing the control of the conveyance unit  406  executed in the packaging controller  307  shown in FIG. 22 determines that the packaging completion signal is received (Y of step S 306 ). Then the packaging controller  307  drives the motor M to lower the tray  2  (step S 307 ) and covey the tray  2  with certain amount (step S 308 ).  
     [0107] Whole process for packaging the tray  2  with the film  15  completes after completion of the operation according to the process of step  308  (refer FIG. 22).  
     [0108] The main routine shown in FIG. 20 determines that the counter value reaches “n”, so that the packaging controller  307  excutes stop process of the subroutine (step S 109 ), on condition that the last tray  2  is discharged from the tray discharge unit (Y of step S 108 ).  
     [0109] The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the present invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.  
     [0110] The present application is based on Japanese Priority Documents hei 11-82942 filed on Mar. 26, 1999 and 2000-079623 filed on Mar. 22, 2000, the content of which are incorporated herein by reference.