Abstract:
A packaging machine includes a pair of sealing members, a cutting device and a switching unit. The sealing members are configured to selectively seal a cylindrical packing material that extends therebetween. The cutting device includes a pressing member arranged on one of the pair of sealing members and a receiving member arranged on the other of the pair of sealing members. The cutting device is configured to selectively press the pressing member against the receiving member to melt and cut the cylindrical packaging material by heat and pressure. The switching unit is configured to switch the pressing member between a pressing state and a non-pressing state with respect to the receiving member when the sealing members are pressed together. The stopping unit is configured to selectively stop the pressing member from retracting from the pressing state with respect to the receiving member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional application of U.S. patent application Ser. No. 11/279,249, filed on Apr. 11, 2006. The entire disclosure of U.S. patent application Ser. No. 11/279,249 is hereby incorporated herein by reference. Moreover, this application claims priority to Japanese Patent Application No. 2005-113290. The entire disclosure of Japanese Patent Application No. 2005-113290 is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a packaging machine, and more particularly to packaging machines that have a cutting device installed on a sealing device.  
         [0004]     2. Background Information  
         [0005]     In conventional practice, packaging machines generally form bags, into which articles are placed, by sealing a heat-melting film rolled into a cylinder lengthwise and widthwise, where the heat-melting film is made of a material such as a synthetic resin. Such packaging machines are commonly equipped with a cutting device for cutting the widthwise sealed areas along the width to separate the individual bags. Known examples of such cutting devices include melting-type cutting devices as disclosed in Japanese Examined Utility Model Application No. 6-34264 (FIG. 1), wherein the film is held between a pressing member, described as a “cutter blade” in this reference, and a receiving member, described as a “cutter receiving blade” in this reference, and heat and pressure are applied to press in and cut through the film. The cut ends of the bags are thereby bonded by heat. This is advantageous in that the ends of the bags do not lift up, the appearance of the bag is not compromised, and the sealing of the bag is improved.  
         [0006]     However, with melting-type cutting devices such as those described above, since the film is melted with heat and cut through with pressure, the pressing member must be pressed into the receiving member with a relatively large amount of force. Therefore, in conventional melting-type cutting devices, the pressing member is either fastened to a widthwise sealing device, as disclosed in Japanese Examined Utility Model Application No. 6-34264, or supported by a spring with a large spring constant. However, the result of this is that a conventional melting-type cutting device has drawbacks in that it is constantly cutting bags and cannot switch back and forth from a cutting to a non-cutting mode. Thus, it is impossible to manufacture bags that are connected to each other uncut, so as to indicate, for example, the presence of one or more abnormal bags. In one suggested solution to this problem, as disclosed in Japanese Examined Utility Model Application No. 61-43687 (FIG. 2), Japanese Patent No. 2849071 (specification and FIG. 7), and Japanese Examined Utility Model Application No. 7-51454 (FIGS. 5 and 6) listed below, the pressing member is made movable, so that the pressing member is pushed into the receiving member when bags are being melted, and the pressing member is not pushed into the receiving member when bags are not being melted.  
         [0007]     However, with the cutter device disclosed in Japanese Examined Utility Model Application No. 61-43687, when either a cutting blade or a perforating blade is used, there is no support for bearing the large amount of force applied from the front of the blade, and therefore the blade retracts, and the film cannot be cut through with the large amount of force applied. In addition, in the packaging machine disclosed in Japanese Patent No. 2849071, when perforating needles configured to be capable of oscillating by means of a parallel link move forward past the sealing surface of a seal bar, there is no support for bearing the large amount of force applied from the front of the needles, and therefore the needles retract, and the film cannot be cut through with the large amount of force applied. With the cutting device disclosed in Japanese Examined Utility Model Application No. 7-51454, when perforations are created or when the bags are cut apart from each other, the knife is constantly piercing through the bags, and therefore keeping the pressing member from being pushed into the receiving member is not an option.  
         [0008]     Although it is possible for a cylinder or another such drive source for driving the pressing member to bear this large amount of pressure during melting, this will require a large and heavy drive source, and will result an increase in the cost of the cutting device and compromise the speed of the packaging machine.  
         [0009]     In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved packaging machine that can switch between cutting and not cutting the bags, and bear the large amount of pressure necessary for cutting, without increasing the size or weight of the drive source of the pressing member. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.  
       SUMMARY OF THE INVENTION  
       [0010]     In order to resolve these problems, a packaging machine according to a first aspect of the present invention includes a pair of sealing members configured so as to selectively seal a cylindrical packing material that extends therebetween; a cutting device comprising a pressing member arranged on one of the pair of sealing members and a receiving member arranged on the other of the pair of sealing members, the cutting device configured to selectively press the pressing member against the receiving member and cut the cylindrical packing material; a switching unit configured to switch the pressing member between a pressing state and a non-pressing state with respect to the receiving member when the sealing members are pressed together; and a stopping unit configured to selectively stop the pressing member from retracting from the pressing state with the receiving member.  
         [0011]     The packing material may be cut by applying pressure alone, or it may be cut by applying heat and pressure.  
         [0012]     A packaging machine according to a second aspect of the present invention is the packaging machine of the first aspect, wherein the switching unit includes a drive source configured to cause the pressing member to protrude a predetermined distance from the sealing surface of the sealing member, and a force augmenting mechanism configured to transmit the motive energy of the drive source to the pressing member. The stopping unit employs the force augmenting mechanism to stop the pressing member from retracting.  
         [0013]     A packaging machine according to a third aspect of the present invention is the packaging machine of the second aspect, wherein the force augmenting mechanism is comprised of a toggling mechanism, and the pressing member is stopped from retracting by reducing the angle formed by the longitudinal direction of the links of the toggling mechanism and the movement direction of the pressing member.  
         [0014]     A packaging machine according to a fourth aspect of the present invention is the packaging machine of the second aspect, wherein the force augmenting mechanism is comprised of a cam mechanism, and the pressing member is stopped from retracting by reducing the angle formed by the tangential direction of the cams of the cam mechanism and the direction orthogonal to the movement direction of the pressing member.  
         [0015]     A packaging machine according to a fifth aspect of the present invention is the packaging machine of the first aspect, wherein the switching unit comprises an urging unit that urges the pressing member forward, a mobile member that moves freely between an inhibiting position that inhibits the pressing member from retracting and a permitting position that permits the pressing member to retract, and a drive source configured to drive the mobile member to the inhibiting position and the permitting position. The mobile member is employed as the stopping unit.  
         [0016]     A packaging machine according to a sixth aspect of the present invention is the packaging machine of any of the first through the fifth aspects, wherein the packaging machine is provided with an adjusting unit configured to adjust the pressing force of the pressing member when the pressing member is pressed together with the receiving member.  
         [0017]     A packaging machine according to a seventh aspect of the present invention is the packaging machine of any of the first through the sixth aspects, wherein the switching unit is configured to switch the pressing member from the pressing state to the non-pressing state when the sealing members are pressed together.  
         [0018]     According to the first aspect, in a packaging machine comprising a cutting device, it is possible to switch between cutting and not cutting the bags because the pressing member is switched between a pressing state with the receiving member and a non-pressing state. In addition, when the bags are being cut, the pressing member will not retract and a large amount of pressure necessary for cutting can be secured, because the stopping unit is provided in order to stop the pressing member from retracting when the pressing member is in the pressing state. Moreover, it is possible to avoid an increase in the size and weight of the drive source of the pressing member because the stopping unit is provided separately from the drive source of the pressing member.  
         [0019]     Next, according to the second aspect, the large amount of pressure necessary for cutting can be secured with a small amount of force, because the force augmenting mechanism for transmitting the motive energy of the drive source to the pressing member is used as the stopping unit. In addition, an increase in the number of components can be suppressed because the force augmenting mechanism is also employed as the stopping unit.  
         [0020]     Next, according to the third aspect, when a toggling mechanism is employed as the force augmenting mechanism, the large amount of pressure necessary for cutting is reliably secured with a small amount of force because the longitudinal direction of the links of the toggling mechanism and the movement direction of the pressing member are made to substantially coincide.  
         [0021]     Next, according to the fourth aspect, when a cam mechanism is employed as the force augmenting mechanism, the large amount of pressure necessary for cutting is reliably secured with a small amount of force, because the tangential direction of the cams of the cam mechanism and the movement direction of the pressing member are made to be substantially orthogonal.  
         [0022]     Next, according to the fifth aspect, since the mobile member that moves freely between an inhibiting position that inhibits the pressing member from retracting and a permitting position that permits the pressing member to retract is used as the stopping unit, the large amount of pressure necessary for cutting can be reliably secured by this mobile member.  
         [0023]     Next, according to the sixth aspect, since the pressing force of the pressing member is adjusted, the cutting pressure can be altered in various degrees according to, for example, the type and the thickness of the packing materal, the cutting time, and any other factors, thus making it possible to cut the bags quickly and precisely.  
         [0024]     According to the seventh aspect, since the pressing member is switched from the pressing state to the non-pressure position during the scaling operation of the sealing members in mutual contact, the time period during which the pressing force of the scaling members decrease due to the pressing member being in the pressing state is shortened, the large amount of pressing force between the sealing members necessary for sealing the cylindrical packing material is maintained for a long period of time, and the cylindrical packing material is sealed reliably and firmly.  
         [0025]     These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Referring now to the attached drawings which form a part of this original disclosure:  
         [0027]      FIG. 1  is a schematic side view showing the primary configuration of a packaging machine according to an embodiment of the present invention;  
         [0028]      FIG. 2  is an enlarged plan view of the periphery of a widthwise sealing device in the packaging machine;  
         [0029]      FIG. 3  is a cross-sectional side view taken along line I-I in  FIG. 2 ;  
         [0030]      FIG. 4  is a partial enlarged view of  FIG. 3  when the pressing member is in contact under pressure with the receiving member;  
         [0031]      FIG. 5  is a time chart showing the operation timing of the sealing jaws and the pressing member in the packaging machine;  
         [0032]      FIG. 6  is a side view showing the configuration of one of the sealing jaw units of a widthwise sealing device in the packaging machine according to the second embodiment of the present invention;  
         [0033]      FIG. 7  is a view from line II-II in  FIG. 6 , showing the bearings of the sealing jaw units, the cam mechanical housings, the heat insulating blocks  53 , and the sealing jaws, all in two-dot chain lines; and  
         [0034]      FIG. 8  is a cross-sectional plan view showing the configuration of one of the sealing jaw units of the widthwise sealing device in the packaging machine according to the third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.  
       First Embodiment  
       [0036]     In this embodiment, the present invention is applied to a packaging machine  1  shown in  FIG. 1 . Specifically, this packaging machine  1  is a conventional lengthwise pillow-type bag making machine, comprising a former  2 , a tube  3 , pull-down belts  4 ,  4  (only one is shown), a lengthwise sealing device  5 , and a widthwise sealing device  6 . A heat-melting film F made of a synthetic resin or the like is conveyed as shown by the arrow, and rolled into a cylinder by the former  2 . The cylindrical film F is suspended down along the periphery of the tube  3 , and as the film is conveyed further downward by the pull-down belts  4 ,  4 , the overlapping lateral edges of the film are sealed along the length thereof by being heated and welded by the lengthwise sealing device  5 , and the film is further sealed along the width thereof by being heated and welded by the widthwise sealing device  6 . While the bag W is thereby being manufactured, articles are filled into the bag W from above via the tube  3 .  
         [0037]     The widthwise sealing device  6  has a pair of sealing jaws  11  and  12  that come in mutual contact with the cylindrical film F, and the film is sandwiched therebetween. These sealing jaws  11  and  12  do not block the continuous conveyance of the film F, because they move in symmetrical D-shaped trajectories (D motion) when viewed from the side. In addition, the sealing jaws  11  and  12  turn around the rotational axes X, X while pivoting around the pivotal axes O, O so that the same orientation is always maintained, that is, an orientation in which the sealing surfaces of the sealing jaws  11  and  12  face each other.  
         [0038]     As shown in  FIG. 2 , the sealing jaws  11  and  12  are connected to bearing boxes  15 ,  15  by means of left and right pairs of thermal insulating blocks  13 ,  13  and mounting blocks  14 ,  14 . The bearing boxes  15 ,  15  rotatably support shafts, not shown in the figure, that serve as the rotational axes X, and these shafts extend between the pivoting ends of left and right pairs of pivoting arms  16 ,  16 . Units  17  for rotating the sealingjaws  11  and  12  around the rotational axes X are provided adjacent to one pair of pivoting arms  16 . Timing belts  18  for constantly maintaining the sealing jaws  11  and  12  in the same orientation are wound between the units  17  and the pivotal axes O.  
         [0039]     As shown in  FIG. 3 , the bearing boxes  15 ,  15  are fixed in place between the top and bottom jaw frames  20  and  21 . The rear surfaces of the thermal insulating blocks  13  and the mounting blocks  14  are formed into arcuate concavities (similar to base members  36  described below), as shown in  FIG. 3 . This is to avoid interference with the shafts, shown by the two-dot chain line, that serve as the rotational axes X.  
         [0040]     As shown in  FIG. 3 , a gap that expands horizontally is formed in the vertical middle of one scaling jaw  11 , hereinafter referred to as the first jaw, and a pressing member  22  is provided inside this gap. A horizontal concave groove is formed in the vertical middle of the other sealing jaw  12 , hereinafter referred to as the second jaw, and a receiving member  23  is embedded in this concave groove. The pressing member  22  moves freely in the horizontal direction, particularly in the horizontal direction that extends towards and away from both the second jaw  12  and the receiving member  23 , whereas the receiving member  23  is fixed in place in the second jaw  12 .  
         [0041]     The top and bottom pairs of heaters  19 ,  19  are embedded in the first jaw  11  and the second jaw  12  in order to sandwich the pressing member  22  and the receiving member  23 . These heaters  19  are used to heat the jaws  11  and  12 , the pressing member  22 , and the receiving member  23  by heat conduction. Alternatively, heaters for the jaws  11  and  12  and heaters for the pressing member  22  and receiving member  23  can be provided separately.  
         [0042]     In this embodiment, the distal end of the pressing member  22  is formed to be flat, because the first jaw  11  and the second jaw  12  are both flat jaws with flat sealing surfaces. The shape of the pressing member  22  is not limited thereto, and forming the distal end to protrude in an arcuate shape, or forming the distal end into a sharp knife shape or any other shapes, will be acceptable as alternatives.  
         [0043]     The configuration of the pressing member  22  is summarized below. The pressing member  22  is allowed to move freely in the horizontal direction. As shown in  FIG. 2 , a pair of left and right leg members  24 ,  24  is attached to the back of the jaw frames  20  and  21 , and attached to a pair of top and bottom supporting frames  25 ,  25 . A first support shaft  27  extends vertically between the supporting frames  25 ,  25 , with the rear portion of the first link  26  rotatably supported on the first support shaft  27 . Similarly, a supporting bracket  28  is attached on the rear side of the jaw frames  20  and  21  on the same side as the leg members  24 . The tail end of an air cylinder  30  is rotatably supported on a support shaft  29  in a supporting bracket  28 . The distal end (rod end)  32  of a rod  31  of this air cylinder  30  and the front portion of the first link  26  are connected via a second support shaft  33 . The front portion of the first link  26  is composed of a top and a bottom level, and the rod end  32  is connected so as to be sandwiched in between the top and the bottom levels of the front portion of the first link  26 , as shown in  FIG. 3 .  
         [0044]     The parts of the second links  34 ,  34  on the back side are also connected to the second support shaft  33 , as shown in  FIG. 2 . A pair of top and bottom second links  34  is provided, as shown in  FIG. 3 . This is to avoid interference with the shaft, shown by a two-dot chain line, that serves as the rotational axis X. The parts of the second links  34 ,  34  on the front side are connected to a base member  36  via a third support shaft  35 , as shown in  FIG. 2 . The rear portion of the pressing member  22  is screwed in place on the base member  36  and supported so that, through the four top and bottom oscillating links  37  on both the left and the right side, it is able to oscillate back and forth at an incline in the horizontal direction. The pressing member  22  is thereby able to move horizontally, toward the second jaw  12  or the receiving member  23 , and protrude a specific distance out from the sealing surface of the first jaw  11 , and also away from the second jaw  12  or the receiving member  23  in order to retract into the first jaw  11 , away from the sealing surface thereof.  
         [0045]     The operation of the packaging machine  1 , according to the first embodiment configured as described above, will be described below. As shown in  FIG. 1 , in this packaging machine  1 , the cylindrical film F is continuously conveyed, and the first jaw  11  and second jaw  12  continuously pivot synchronously and symmetrically around the pivotal axes O, O. The cylindrical film F is sandwiched and sealed at the top first by the jaws  11  and  12 . The, while the cylindrical film F is continuously conveyed downward, and before the bottom edge of the cylindrical film F passes by the jaws  11  and  12 , the jaws  11  and  12  will come together to press and seal cylindrical film F therebetween along the width thereof to form a bag W. In addition, during this sealing operation, the distance between the pivotal axes O, O is controlled, and the cylindrical film F is conveyed straight downward.  
         [0046]     When the first jaw  11  and the second jaw  12  come together to press and seal the cylindrical film F together, the jaws  11  and  12  draw near each other as shown by the arrows A 1  and A 2  in  FIG. 2 , and the sealing surfaces are pressed together as shown in  FIG. 4 . During the sealing operation, the air cylinder  30  turns on, the rod  31  advances forward, and the rod end  32  moves into a position directly in front of the first support shaft  27 , as shown by the arrow A 3  in  FIG. 2 . Accordingly, the rod end  32 , the second support shaft  33 , the front portion of the first link  26 , and the parts of the second links  34  in the rear side move forward, and the parts of the second links  34  on the front side and the third support shaft  35  cause the base member  36  and the pressing member  22  to move forward. As a result, the base member  36  and the pressing member  22  oscillate forward at an incline in the horizontal direction via the oscillating links  37 , in the direction shown by the arrows A 4 , A 4  in  FIG. 2 , and the pressing member  22  protrudes a specific distance from the sealing surface of the first jaw  11  so as to draw near the second jaw  12  or the receiving member  23 . The pressing member  22  is then pressed together with the receiving member  23 , as shown by the arrow A 5  in  FIG. 4 , and the cylindrical film F sealed by the first jaw  11  and second jaw  12  is cut through and melted along the width by means of the heat and pressure in the horizontal sealing area.  
         [0047]     On the other hand, when the air cylinder  30  is turned off the rod  31  will retract and the rod end  32  will move in the opposite direction of the arrow A 3 , which causes the base member  36  and pressing member  22  to oscillate in the direction opposite the arrow A 4 , A 4 . As a result, the pressing member  22  retracts inward from the sealing surface of the first jaw  11 , separates from the second jaw  12  and the receiving member  23 , and is no longer pressed together with the receiving member  23 .  
         [0048]     The toggling mechanism, which is the force augmenting mechanism, is composed of the cylinder rod  31 , the first link  26 , and the second links  34 . When the pressing member  22  is pressed together with the receiving member  23 , the three support shafts  27 ,  33 , and  35  are aligned substantially in the pressure contact direction e. As a result, the longitudinal direction of the first link  26 , the longitudinal direction of the second links  34 , and the moving direction of the pressing member  22 , are approximately in the same direction as the pressing direction e.  
         [0049]     In the first embodiment, the packaging machine  1  has a melting-type cutting device, where the pressing member  22  can either be pressed together with the receiving member  23 , or not in contact with the receiving member  23 , by switching the air cylinder  30  on or off. Therefore, it is possible to cut or not cut the bags W. Moreover, when the pressing member  22  is pressed together with the receiving member  23 , that is, when the bags W are being cut, the longitudinal direction of the first link  26  of the toggling mechanism and the longitudinal direction of the second links  34  substantially coincide with the moving direction e of the pressing member  22 , and therefore these links  26  and  34  act as a stopping unit for preventing the pressing member  22  from retracting inward. As a result, when the bags W are being melted, the pressing member  22  does not retract, and the large amount of pressure necessary for melting is reliably transmitted. In this case, because the stopping unit is separate from the air cylinder  30 , a considerable increase in the size and weight of the air cylinder  30 , as the drive source of the pressing member  22 , can be avoided. It is also possible to secure the large amount of pressure necessary for melting with a small amount of force, because the stopping unit is provided by the force augmenting mechanism, or the toggling mechanism in the first embodiment, that transmits the motive energy of the air cylinder  30  to the pressing member  22 . Furthermore, an increase in the number of components in the packaging machine  1  will be inhibited because the force augmenting mechanism is also utilized also as the stopping unit.  
         [0050]     In this case, the operation timing of the sealing jaws  11  and  12  and the pressing member  22  is preferably set so that during a sealing operation under low pressure between the sealing jaws  11  and  12 , the pressing member  22  is switched from pressed under high pressure with the receiving member  23  to not being in contact, as shown in  FIG. 5 . When the pressing member  22  is pressed together with the receiving member  23 , it is unavoidable that the sealing jaws  11  and  12  will tend to rise upward and lose some of the contact force, which compromises the sealing of the cylindrical film F, as shown by the time period T 1  in the figure. In view of this, the cylindrical film F can be sealed reliably and firmly by reducing the time period T 1  during which the pressure is reduced. This is achieved by switching the pressing member  22  to not being pressed together with the receiving member  23  before the sealing jaws  11  and  12  are no longer pressed together, which will ensure that there is a large pressing force between the sealing jaws  11  and  12  necessary for sealing the cylindrical film F for a long period of time, shown by the time period T 2  in the figure.  
         [0051]     The bags W can be cut without certain undesirable defects because of the sliding motion of the pressing member  22 , i.e., the pressing member  22  oscillates in the direction opposite the arrows A 4 , A 4  and slides backward at an incline when the pressing member  22  is switched to the non-pressing position.  
       Second Embodiment  
       [0052]     A second embodiment of the present invention will be described with reference to  FIGS. 6 and 7 . The same reference numbers are used for structural elements identical to or resembling those of the first embodiment, and only the characteristics unique to this embodiment are described below. In the first embodiment, a toggling mechanism was used as the force augmenting mechanism for transmitting the motive energy of the air cylinder  30  to the pressing member  22 ; however, in the second embodiment, a cam mechanism is used as the force augmenting mechanism.  
         [0053]     In the second embodiment, a widthwise sealing device  6  has sealing jaw units. Two of these jaw units come in contact and sandwich the film F, where the pressing members  22  are provided on the first jaws  11  and the receiving members  23  are provided on the second jaws  12 . However, only a jaw unit of the first jaws  11  is described below as an example, shown in  FIG. 6 .  
         [0054]     Specifically, this jaw unit includes two bearings  51 ,  51 , only one shown in the figure, for axially supporting a shaft, not shown in the figure, that serves as a pivotal axis O, two cam mechanism housings  52 ,  52  extending between the bearings  51 ,  51  in point symmetry to the pivotal axis O, heat insulating blocks  53 ,  53  mounted on the housings  52 ,  52 , and sealing jaws  11 ,  11  mounted on the heat insulating blocks  53 ,  53 .  
         [0055]     As the arcuate motion, the jaw unit of the first jaws  11  and the jaw unit of the second jaws  12  rotate synchronously and symmetrically in the direction of the arrows A 6 , A 6  while sandwiching the cylindrical film F, whereby the two first jaws  11 ,  11  and the two second jaws  12 ,  12  pivot around the pivotal axes O, O, and the jaws  11  and  12  meet and come into mutual contact once every half rotation of the jaw units, in order to form a widthwise seal. Therefore, in the second embodiment, the widthwise sealing device  6  does not hinder the film F from being continuously conveyed. In addition, the sealing surfaces of the sealing jaws  11  and  12  are formed into arcuate protrusions, similar to the front edge of the pressing members  22 .  
         [0056]     As shown in  FIG. 7 , the air cylinder  30  is housed inside the jaw unit, and a drive link  56  is rotatably connected to the distal end (rod end)  32  of the rod  31  via a pin  55 . Two cam mechanisms corresponding to the two first jaws  11 ,  11  are disposed in point symmetry in relation to the pivotal axis O on both sides of the air cylinder  30 . The air cylinder  30  is attached to the cam mechanism housings  52 ,  52  via a bracket  54 .  
         [0057]     Driven links  58  are rotatably connected to driving links  56  via pins  57 . Note that there are two driven links  58  in point symmetry. The driven links  58  can oscillate around oscillating shafts  59 . The oscillating shafts  59  are fixed to the cam mechanism housings  52 .  
         [0058]     First cams  60  are laid over the driven links  58 . In this case, arcuate long holes  61 ,  61  are formed in the first cams  60 , and the first cams  60  are coupled with the driven links  58  in a manner allowing for phase adjustment by bolts  62 ,  62  and press plates  63  via the long holes  61 ,  61 .  
         [0059]     Pins  64  are placed on the driven links  58 , and coupling links  65  interlock with these pins  64 . Also, second and third driven links  67 ,  67  are provided adjacent to the driven links  58  at substantially equal intervals and are allowed to oscillate around oscillating shafts  68 ,  68 . These second and third oscillating shafts  68 ,  68  are also fixed to the cam mechanism housings  52 .  
         [0060]     Second and third cams  69 ,  69  are also laid over and coupled with the second and third driven links  67 ,  67  in a manner that allows for phase adjustment, and the coupling links  65  interlock with the pins  66 ,  66  provided on the second and third driven links  67 ,  67 .  
         [0061]     Guide rails  70  and overhanging blocks  71 ,  71  are provided to the back surfaces of the base members  36  for supporting the pressing members  22 . The second cams  69  engage with the guide rails  70 , and the ends of the two coil springs  72 ,  72  at one end are fixed to the cam mechanism housing  52 , while the ends at the other end are coupled with each of the two overhanging blocks  71 ,  71 . The base members  36  are thereby urged towards the cams  60 ,  69 ,  69 , and the base members  36  are constantly in contact with the cams  60 ,  69 ,  69 .  
         [0062]     In the configuration described above, when the air cylinder  30  is turned on, the rod  31  advances forward, and the rod end  32  and driving link  56  move in the direction of the arrow A 7  in  FIG. 7 . Accordingly, the driven links  58  and the first cams  60  rotate in the direction of the arrow A 8 , and the second and third driven links  67 ,  67  and the second and third cams  69 ,  69  rotate together in the direction of the arrow A 8  via the coupling links  65 . The degree of lift by the cams  60 ,  69 ,  69  increases. The base members  36  and the pressing members  22  are pushed outward in a horizontal plane in the direction of the arrows A 9 , and the pressing members  22  protrude a specific distance from the sealing surfaces of the first jaws  11  so as to draw near to the second jaws  12  and the receiving members  23 . The pressing members  22  are then pressed together with the receiving members  23 , and the cylindrical film F sealed by the first jaws  11  and the second jaws  12  is cut through and melted along its horizontally sealed areas by the heat and pressure.  
         [0063]     On the other hand, when the air cylinder  30  is turned off, the rod  31  retract back inward, the rod end  32  and the driving link  56  move in the direction opposite the arrow A 7 , and the links  58 ,  67 ,  67  and the cams  60 ,  69 ,  69  rotate in the direction opposite the arrow A 8 . As a result, the pressing members  22  retract in the direction opposite the arrows A 9  from the sealing surfaces of the first jaws  11  that are separating from the second jaws  12  and receiving members  23 , to be in the non-pressing position with the receiving members  23 .  
         [0064]     In the second embodiment, the cam mechanism is used as the force augmenting mechanism. When the pressing members  22  are pressed together with the receiving members  23 , or in the position when the bags W are being cut, the tangential directions of the cams  60 ,  69 ,  69  of the cam mechanism and the movement directions i of the pressing members  22  are made to be substantially orthogonal, and the large amount of pressure necessary for melting is thereby reliably secured with a small amount of force.  
         [0065]     In addition, since the cams  60 ,  69 ,  69  are provided respectively to the links  58 ,  67 ,  67  in a manner that allows phase adjustment, the amount of pressure applied by the pressing members  22  can be adjusted, the melting pressure can be altered to various levels according to the type and the thickness of the film F, the melting time, or any other factors, for example, and the bags W can be cut quickly and precisely.  
         [0066]     A step motor or a servomotor, for example, may be used instead of the air cylinder  30 . In addition, the sealing jaw unit shown in  FIG. 6  is a double-type configuration provided with two first jaws  11  or second jaws  12 , one at every 180°. However, the configuration is not limited thereto, and could be another configuration as well. For example, it may be a triple-type configuration provided with three first jaws  11  or second jaws  12 , one at every 120°.  
       Third Embodiment  
       [0067]     A third embodiment of the present invention will be described with reference to  FIG. 8 . The same reference numbers will be used to denote structural elements identical or similar to those in the first and second embodiments, and only the characteristics unique to the third embodiment will be described. In the first and second embodiments, the toggling mechanism or the cam mechanism were used as the force augmenting mechanism, as the stopping unit for stopping the pressing members  22  from behind when the pressing members  22  were in contact under pressure, i.e., when the bags W were being cut; however, in the third embodiment, a mobile member is used.  
         [0068]     As shown in  FIG. 8 , the sealing jaw unit has a unit case  81  through which runs a shaft, shown by the two-dot chain line, that serves as a rotational axis X. An air cylinder  84  is housed in this case  81 , and a bracket  86  is connected to the rod end  85  thereof. The bracket  86  extends past the opening  83  formed in a dividing plate  82 , and is coupled with a mobile member  87 . The mobile member  87  moves freely along a rail  88 . In addition, in this embodiment, the mobile member  87  is an on/off type translation cam.  
         [0069]     The pressing member  22  and the base member  36  are constantly being urged forward in the direction of the arrow A 10  by a number of springs  89 . However, the force of the springs that urges them forward is restricted by the two ends of the base member  36  in contact with the front walls of the unit case  81 . Switching the air cylinder  84  on and off causes the mobile member  87  to move in either the direction A 11  or A 12 , shown by the arrows. When the convex part on the front side of the mobile member  87  and the convex part on the rear side of the base member  36  come into contact, the pressing member  22  w 111  not retract in the direction opposite the arrow A 10 . On the other hand, when the convex parts (or the concave part) on the front side of the mobile member  87  and the concave part (or the convex parts) on the rear side of the base member  36  mesh together, the pressing member  22  is allowed to retract in the direction opposite to the arrow A 10 .  
         [0070]     In the third embodiment, the large amount of pressure necessary for melting can be reliably secured by the mobile member  87 . This is because the stopping unit for stopping the pressing member  22  from behind when the pressing member  22  is being pressed together with the receiving member  23 , or when the bags W are being cut, is the mobile member  87  that is able to move to a position that blocks the pressing member  22  from retracting, and can also move into a position that allows the pressing member  22  to retract.  
         [0071]     These embodiments are the preferred embodiments of the present invention; however, various revisions and modifications can be made so long as they do not deviate from the scope of the claims. For example, in the third embodiment, the mobile member  87  was an on/off type translation cam, but the mobile member  87  is not limited thereto. For example, a rotating cam whose profile has two levels of lift, which are on (large) and off (small) can be used, as well as any other possible substitutions.  
         [0072]     In addition, in the embodiments described above, the present invention was applied to a packaging machine  1  with a melting-type cutting device, but the present invention can also be applied to a packaging machine with a cutting device that cuts a cylindrical film F along the width by applying only pressure but not heat.  
         [0073]     As described in detail by the embodiments above, the present invention has a wide range of industrial applications in the field of packaging machines in which a cutting device is provided to a sealing device. This is because the present invention provides a packaging machine that has a cutting device able to switch between cutting and not cutting the bags, to prevent the pressing member from retracting when the bags are being cut, to secure the large amount of pressure necessary for cutting, and to prevent the size and weight of the drive source of the pressing member from increasing.  
         [0074]     Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention.  
         [0075]     The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.  
         [0076]     While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Thus, the scope of the invention is not limited to the disclosed embodiments.