Abstract:
An opening method for a packaging bag with a fastener enables the fastener to be surely opened with a simplified arrangement and by a simple operation as compared to the prior art. A packaging bag with a fastener is held by being gripped at the laterally opposite side edges thereof with a pair of grippers. A pair of suction cups are disposed at respective stand-by positions at both sides of the bag. The suction cups are moved to respective mutually close positions and allowed to adhere to both side surfaces of the bag at respective regions where the fastener is present. The suction cups adhering to the bag are retracted to respective intermediate positions. The movement of the suction cups between the mutually close positions and the intermediate positions is repeated a plurality of times. Thereafter, the suction cups are returned to the stand-by positions. The fastener is opened stepwise.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an opening method for opening a fastener of a packaging bag (hereinafter, a packaging bag with a fastener will be occasionally referred to as a “zippered packaging bag”). More particularly, the present invention relates to a packaging bag opening method suitable for use in an apparatus that performs automatic packaging of food or the like while moving a packaging bag by gripping the laterally opposite side edges thereof with a pair of grippers, wherein a zippered bag is used as the packaging bag.  
         [0003]     2. Discussion of Related Art  
         [0004]     There has been used a zippered bag whose mouth is closable by fitting engagement between a rib and an associated groove that constitute a fastener. More specifically, the rib is formed to extend in the width direction on one of the inner surfaces of the opposite walls of the bag near the upper edge thereof. The groove is formed to extend widthwise on the other of the inner surfaces of the bag walls. The zippered bag is usable in automatic packaging of food or the like. When the zippered bag is used, it has to be opened before filling of food. A variety of apparatus and methods for opening the zippered bag have been proposed.  
         [0005]     Japanese Patent No. 3429872 discloses an opening apparatus for a packaging bag with a fastener. In this apparatus, first, suction cups are operated to act on both side surfaces of the bag at respective positions above the fastener to open the part of the bag above the fastener. Then, the upper edges of the opposite walls of the opened part of the bag are gripped with grippers, respectively, and the grippers are rotated in opposite directions to each other about their own axes, thereby partially opening the fastener. Thereafter, the grippers are moved away from each other to fully open the fastener, thereby opening the bag. In this case, the apparatus requires, in addition to suction cups, grippers that are capable of opening and closing, and mechanisms for rotating the grippers or moving them toward or away from each other. Thus, the apparatus has a complicated structure and suffers increased costs. In addition, it takes a great deal of time to carry out maintenance or cleaning works. Because the upper edges of the bag are gripped and pulled with the grippers, the bag mouth may be damaged, causing the appearance of the bag to be degraded.  
         [0006]     Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 8-104308 discloses a fastener opening apparatus for a packaging bag with a fastener. The apparatus includes a set of driving and driven rollers disposed at both sides of a bag to be opened. The driving and driven rollers have their axes extending perpendicular to the extending direction of the bag fastener. The rotation of the driven roller is forcedly checked at a certain position against the rotation of the driving roller, thereby causing the opposite walls of the bag to slide relative to each other at the fastener part of the bag, and thus partially disengaging the male and female fastener elements from each other. This apparatus, however, only provides an automated fastener opening operation, which has heretofore been carried out by a manual operation, and is capable of opening the fastener only partially. To fully open the bag, a device for this purpose is needed separately. Therefore, the apparatus is difficult to apply to an automatic packaging machine. The arrangement of the apparatus will become extremely complicated if it is adapted to be applicable to an automatic packaging machine. In addition, because the fastener part of the bag is pressed from both sides to cause the opposite bag walls to slide relative to each other, the bag mouth is likely to be deformed, i.e. wrinkled or elongated, or damaged.  
         [0007]     Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 10-81313 discloses an opening apparatus for a bag with a fastener. With the apparatus, suction cups adhering to the opposite side walls of a bag to be opened are rotated about their own axes at respective present positions to open a part of the bag above the fastener. Then, the suction cups are retracted to pull the side walls of the bag. Meanwhile, a nozzle is lowered into the open part of the bag while injecting pneumatic pressure thereinto. Thus, the push-down force of the nozzle and the compressed air pressure are applied to open the fastener. The operation of the suction cups takes place in two steps. In addition, the apparatus uses the nozzle device. Therefore, the arrangement is complicated. Further, the bag may be deformed or damaged by forcing of the nozzle into the bag.  
         [0008]     Japanese Patent No. 3578924 discloses a method and apparatus for opening a fastener at the mouth of a bag. The apparatus is arranged as follows. After suction cups have been made to adhere to the opposite side walls of a bag, a frame rotatably supporting one of the suction cups is lowered to move the suction cup downward while tilting it, thereby turning over one side wall at the mouth of the bag to disengage the fastener. Thus, the arrangement is complicated.  
         [0009]     Japanese Patent Application Unexamined Publication (KOKAI) No. 2004-17985 discloses an opening apparatus for a bag with a fastener. The apparatus uses a pair of vacuum cups having different configurations from each other. One of the vacuum cups is provided with a trumpet-shaped recess. The other vacuum cup is provided with a rib so that the cup has a flat suction-adhering surface. The cups each have a flat suction-adhering surface. A bag to be opened is held in such a manner that the male profile side of the fastener faces the cup having the recess, whereby the male profile side of the fastener is partially distorted during suction, thereby disengaging a part of the fastener. In this arrangement, suction cups used in a pair are different in configuration from each other. Accordingly, the apparatus cannot function as desired if the bag is held in reverse orientation to that in which the bag is supposed to be held, in terms of the front and back faces.  
         [0010]     The above-described conventional apparatus are all complicated in arrangement, which causes problems in terms of maintenance and cleaning, or problems in application to an automatic packaging machine. The difference in structure between a pair of suction cups used in the conventional apparatus presents a problem that the bag opening operation cannot be performed independently of the orientation of the bag to be opened. The above-described prior art is arranged to open the fastener in one step of opening operation. Particularly, the apparatus disclosed in the last four of the above-described patent documents use frictional force between the rollers and the bag walls, the adhering force of the suction cups, or pneumatic pressure from the nozzle to open the fastener. Therefore, the force for opening the fastener cannot be said to be sufficiently strong. If the engaging force between the male and female fastener elements is strong, the apparatus may fail to open the fastener.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention was made in view of the above-described problems associated with the prior art.  
         [0012]     Accordingly, an object of the present invention is to provide an opening method for a packaging bag with a fastener that can open the bag more easily and surely than by the prior art method with a simplified arrangement. That is, the present invention is based on the knowledge the present inventor obtained in the process of carrying out research and development that a packaging bag with a fastener can be opened more easily and surely by repeating a simple opening operation a plurality of times to thereby carry out the opening process stepwise than by opening the bag in one step of opening operation.  
         [0013]     To attain the above-described object, the present invention provides a method of opening a packaging bag with a fastener that is gripped at laterally opposite side edges thereof with a pair of grippers by using a pair of suction-adhering members disposed at both sides of the packaging bag. The suction-adhering members are moved to perform a reciprocating operation a plurality of times. The reciprocating operation includes a series of operations of moving the suction-adhering members toward each other, making the suction-adhering members adhere to both side surfaces of the packaging bag at respective regions where the fastener is present, and moving the suction-adhering members adhering to the packaging bag away from each other. With this method, the process of opening the fastener proceeds gradually, and the fastener can be easily and surely opened.  
         [0014]     In one embodiment, before starting the reciprocating operation, the suction-adhering members are placed at respective stand-by positions apart from each other by a predetermined distance. When moved away from each other during the reciprocating operation, the suction-adhering members are moved to respective intermediate positions where they are closer to each other than at the stand-by positions, except for the final cycle of the reciprocating operation, which is repeated a plurality of times. This arrangement makes it possible to shorten the stroke of the reciprocating operation and to improve throughput capability.  
         [0015]     In another embodiment, the reciprocating operation is repeated at least three times. By repeating the reciprocating operation at least three times, presently used general zippered packaging bags can be surely opened, and the bag opening operation is stabilized.  
         [0016]     In still another embodiment, the pair of suction-adhering members are positioned so that the respective centers of suction-adhering surfaces of the suction-adhering members are displaced relative to each other in the longitudinal direction of the fastener. If the suction-adhering surfaces adhere to both side surfaces of the bag in a state where the fastener is closed and the opposite side walls of the bag adhere to each other in such a way that the suction-adhering surfaces are superimposed over one another, a negative pressure is created in the bag. The negative pressure acts to reduce the suction-holding force when the suction-adhering members move away from each other. By adopting the above-described arrangement, however, the reduction of the suction-holding force can be minimized.  
         [0017]     In a further embodiment, the suction-adhering members are capable of returnably tilting within a plane perpendicular to the side surfaces of the packaging bag and containing the fastener. When performing the tilting operation, the suction-adhering members apply a massage-like action to the portions of the bag to which they are adhering so as to loosen the fastener, thereby promoting disengagement of the male and female fastener elements.  
         [0018]     In a still further embodiment, the suction-adhering members are urged toward respective predetermined positions with predetermined postures by respective resilient members, and when the suction-adhering members have performed the tilting operation, they are returned by the resilient members. With this arrangement, the positions and postures of the suction-adhering members when adhering to the bag are kept constant and stabilized, and the bag opening operation becomes stabilized.  
         [0019]     In a still further embodiment, the suction-adhering members are disposed so that their respective suction-adhering surfaces face obliquely upward. With this arrangement, when the suction-adhering members adhere to the bag, the mouth at the upper edge of the bag is always opened. Accordingly, once the fastener has been opened, even partially, air can immediately flow into the bag, whereby the following fastener opening and bag opening operations are facilitated.  
         [0020]     According to the present invention, a packaging bag with a fastener can be opened simply by moving a pair of suction-adhering members to perform the above-described reciprocating operation. Therefore, an apparatus for carrying out the opening method is extremely simplified in arrangement. The opening operation can be accomplished simply by repeating the reciprocating operation of the suction-adhering members a plurality of times. Accordingly, the opening operation can be performed extremely easily, simply and surely. Further, the process of opening the bag is carried out stepwise by repeating the reciprocating operation a plurality of times, unlike the conventional practice of opening the bag in only one step of opening operation. Therefore, the bag can be surely opened. Once a part of the fastener has been opened, the rest of it can be opened very easily. Because the arrangement of the apparatus is simplified, the apparatus is excellent in maintainability, cleanability, and so forth.  
         [0021]     Other objects and advantages of the present invention will become apparent from the following detailed description of illustrated embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a perspective view showing the conceptual arrangement of an automatic packaging machine for carrying out a bag opening method according to a first embodiment of the present invention.  
         [0023]      FIGS. 2   a  and  2   b  are partially-sectioned plan and side views, respectively, showing suction cups at their respective stand-by positions.  
         [0024]      FIGS. 3   a  and  3   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have advanced to their respective positions where they adhere to a bag to be opened.  
         [0025]      FIGS. 4   a  and  4   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have advanced to their respective final, mutually close positions.  
         [0026]      FIGS. 5   a  and  5   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have returned to their respective intermediate positions.  
         [0027]      FIGS. 6   a  and  6   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have advanced to their mutually close positions again.  
         [0028]      FIGS. 7   a  and  7   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have returned to their respective intermediate positions again.  
         [0029]      FIGS. 8   a  and  8   b  are partially-sectioned plan and side views, respectively, showing the suction cups that have returned to their respective stand-by positions after completion of opening the bag.  
         [0030]      FIGS. 9   a  and  9   b  are diagrams showing an essential part of an apparatus for carrying out a second embodiment of the present invention, in which  FIG. 9   a  shows suction cups at their respective stand-by positions, and  FIG. 9   b  shows the suction cups at their mutually close positions.  
         [0031]      FIG. 10  is a diagram showing a part of a bag opening process according to a third embodiment of the present invention.  
         [0032]      FIG. 11  is a diagram showing another part of the bag opening process according to the third embodiment of the present invention.  
         [0033]      FIG. 12  is a diagram showing another part of the bag opening process according to the third embodiment of the present invention.  
         [0034]      FIG. 13  is a diagram showing another part of the bag opening process according to the third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted, however, that the following embodiments are for illustrative purposes only, and that the scope of the present invention is not limited to these embodiments.  
         [0036]      FIG. 1  is a perspective view conceptually showing an automatic packaging machine for food that employs an opening method for a packaging bag with a fastener according to one embodiment of the present invention. In the figure, a turntable  2  is secured to a rotating shaft  3  driven by a driving device (not shown) so that the turntable  2  is rotatable together with the rotating shaft  3  as one unit. In this embodiment, the turntable  2  rotates intermittently in the direction indicated by the arrow in the figure. A pair of grippers  5  are disposed underneath the turntable  2  near the outer periphery thereof with a predetermined spacing in the circumferential direction to grip the laterally opposite side edges of a bag  4 . The grippers  5  receive the bag  4  supplied from the outside of the turntable  2  and move it in a vertically held position to various steps successively to perform operations such as opening the bag, filling the bag with contents, sealing the bag mouth, and discharging the finished product. For these operations or arrangements therefor, publicly known techniques can be used satisfactorily, except a bag opening apparatus (described later). Therefore, a detailed description thereof is omitted. The arrangement for securing the grippers  5  to the turntable  2  and the operation thereof are also publicly known; therefore, a detailed description thereof is omitted.  
         [0037]     Suction cups  6  and  7  serving as suction-adhering members are secured to respective arms  8  and  9  and disposed facing each other across the bag  4 . The way in which the suction cups  6  and  7  are secured to the arms  8  and  9  and the operation of the suction cups  6  and  7  will be detailed later. A driving mechanism  11  for operating the arms  8  and  9  will be explained first. It should be noted the driving mechanism  11  is not necessarily limited to the one that is arranged as stated below, but any driving mechanism capable of driving the suction cups  6  and  7  to perform an operation that will be described later.  
         [0038]     A cam  12  is secured to a cam shaft  13  driven to rotate by a driving device (not shown) so that the cam  12  rotates together with the cam shaft  13  as one unit. A cam lever  14  is secured to a lever shaft  16  rotatably supported appropriately so that the cam lever  14  pivots together with the lever shaft  16  as one unit. The cam lever  14  rotatably supports a cam roller  15  at a longitudinally intermediate position thereon. One end of a return spring  17 , which is a tension coil spring, is attached to the distal end of the cam lever  14 . The other end of the spring  17  is attached to a spring hook  18  secured to a frame (not shown). Accordingly, the cam lever  14  is constantly urged in a direction in which the cam roller  15  contacts the outer peripheral surface of the cam  12 . The outer profile of the cam  12  has the following portions (not denoted by reference numerals in the figure): a small diameter portion formed over a certain angular range with a small diameter from the axis of the shaft  13 ; a first displacement portion having a diameter gradually increasing from one end of the small diameter portion; a large diameter portion maintaining the length of the diameter at the terminating end of the first displacement portion over a certain angular range; and a second displacement portion having a diameter gradually decreasing from the large diameter portion to the other end of the small diameter portion.  
         [0039]     A hollow stand  19  is stood on the top of a machine base (not shown). The stand  19  rotatably supports a driving shaft  20 . A connecting lever  21  is secured at one end thereof to the lower end of the driving shaft  20  so that the lever  21  is rotatable together with the driving shaft  20  as one unit. One end of an air cylinder  22  is pivotably attached to the other end of the lever  21 . The other end of the air cylinder  22  is pivotably attached to the cam lever  14  at a longitudinally intermediate position between the cam roller  15  and the end thereof to which the spring  17  is attached. The air cylinder  22  is connected to a compressed air source (not shown). Compressed air is supplied into and discharged from the air cylinder  22  under appropriate control, causing a rod  22   a  to extend and contract in response to the supply and discharge of compressed air, thereby moving the suction cups  6  and  7  between their respective mutually close positions and intermediate positions as explained hereinafer.  
         [0040]     A plate-shaped gear holder  23  is secured to the upper end of the stand  19  as shown in the figure. A pinion  24  is positioned in a recess (no reference numeral) formed in an approximately central portion of the gear holder  23  and fixed to the upper end of the driving shaft  20 . Racks  25  and  26  are disposed and guided in respective slots (no reference numeral) formed on the gear holder  23 . The racks  25  and  26  extend parallel to each other across the pinion  24 . As the pinion  24  rotates, the racks  25  and  26  move opposite to each other in their longitudinal directions. The above-described arms  8  and  9  are integrally secured to the respective distal ends of the racks  25  and  26 . The arms  8  and  9  both have an L-shape as shown in the figure. The arm  8  associated with the suction cup  6  is longer than the other arm  9 , so that the suction cups  6  and  7  are positioned facing each other across the bag  4  as illustrated in the figure. Piping tubes  27  and  28  are connected to the suction cups  6  and  7 , respectively. The tubes  27  and  28  are each connected to a vacuum pump (not shown) through appropriate members, such as a switching valve and a filter (not shown). A nozzle  29  is disposed so that an opening end  29   a  thereof is positioned slightly above the upper edge of the bag  4 . The nozzle  29  injects air to assist in the operation of opening the bag  4  that is performed by the action of the suction cups  6  and  7 .  
         [0041]     The bag  4  is opened as follows. When the cam roller  15  is on the small diameter portion of the rotating cam  12 , the suction cups  6  and  7  are at rest at their respective stand-by positions apart from each other. When the bag  4  held by the grippers  5  has moved to and stopped at a bag opening position, the cam roller  15  moves along the first displacement portion toward the large diameter portion in response to the rotation of the cam shaft  13 . The cam lever  14  moves in the direction of the arrow in the figure, causing the suction cups  6  and  7  to move to their mutually close positions at which the suction cups  6  and  7  abut against each other across the bag  4 . A vacuum is applied to the suction cups  6  and  7  so that the suction cups  6  and  7  adhere to the outer surfaces of the opposite side walls of the bag  4 . While the cam roller  15  is moving along the large diameter portion of the cam  12 , the cam lever  14  remains at the present position. Meanwhile, the air cylinder  22  operates so that the suction cups  6  and  7  are returned from the mutually close positions to respective intermediate positions between the mutually close positions and the stand-by positions and moved to the mutually close positions again and then returned to the intermediate positions again. The reciprocating operation of the suction cups  6  and  7  between the mutually close positions and the intermediate positions is repeated a plurality of times. When the suction cups  6  and  7  are finally returned to the mutually close positions, the cam roller  15  is located at the end of the large diameter portion opposite to the leading end thereof. Then, the cam roller  15  moves along the second displacement portion toward the small diameter portion. Consequently, the cam lever  14  pivots in a direction opposite to the arrow direction shown in the figure to return to the previous position. Thus, the suction cups  6  and  7  are also returned to the stand-by positions. While the cam roller  15  is moving along the small diameter portion of the cam  12 , the bag  4  moves to the subsequent step. The operations of the arms  8  and  9  and the suction cups  6  and  7  in this embodiment will be explained below in detail with reference to  FIGS. 2   a  and  2   b  and the following figures.  
         [0042]      FIGS. 2   a  and  2   b  are partially-sectioned plan and side views, respectively, showing the bag  4  having moved to and stopped at the bag opening position and the suction cups  6  and  7 , together with the arms  8  and  9 , at the stand-by positions. The bag  4  is a packaging bag with a fastener as stated above. As shown in  FIG. 2   b , a fastener  4   a  is formed on the inner surfaces of the opposite side walls of the bag  4  at a position slightly away from the upper edge of the bag  4  to extend in the width direction of the bag  4 . The fastener  4   a  consists essentially of a male fastener element  4   b  formed on the inner surface of one side wall of the bag  4  and a female fastener element  4   c  formed on the inner surface of the other side wall of the bag  4 . The arrangement of the fastener  4   a  is publicly known. Therefore, a detailed description thereof is omitted. Regarding the arms  8  and  9 , only the bent distal end portions  8   a  and  9   a  thereof are shown in the figures.  
         [0043]     The suction cup  6  has a suction cup body portion  6   a  having a suction-adhering surface that is adapted to adhere to the bag  4  by suction, for which a publicly known arrangement can be employed. The suction cup  6  further has a shaft portion  6   b  extending rearward from the rear end of the body portion  6   a , and a flange  6   c  provided at the rear end of the shaft portion  6   b  to extend radially outward of the shaft portion  6   b . The shaft portion  6   b  is fitted in a slot  8   b  formed in the bent portion  8   a  of the arm  8 . The slot  8   b  has a predetermined length in the width direction of the bag  4 . The suction cup  6  is urged forward, i.e. toward where the bag  4  is positioned, by a compression spring  10  disposed around the shaft portion  6   b  between the body portion  6   a  and the bent portion  8   a . The suction cup  6  is positioned with the flange  6   c  abutting on the bent portion  8   a . In this embodiment, the suction cup  6  has the shaft portion  6   b  abutting on the upper end of the slot  8   b  as viewed in  FIG. 2   a  owing to the way in which the spring  10  is installed. It should be noted, however, that the illustrated arrangement of the suction cup  6  is not essential. The arrangement of the other suction cup  7  and the way in which it is attached to the bent portion  9   a  are the same as in the case of the suction cup  6 . Portions of the suction cup  7  corresponding to those of the suction cup  6  are denoted by adding the same letters of English alphabet as used for the corresponding portions of the suction cup  6  to reference numeral  7 . It should be noted, however, that the shaft portion  7   b  abuts on the lower end of the slot  9   b  as viewed in  FIG. 2   a.    
         [0044]     As shown in  FIGS. 2   a  and  2   b , the suction cups  6  and  7  stand by at respective positions at both sides of the bag  4  a predetermined distance away from each side of the bag  4  such that the respective centers of the suction-adhering surfaces  6   d  and  7   d  face approximately the center of the bag  4  in the width direction thereof at substantially the same position as the fastener  4   a  of the bag  4  in the height direction thereof. As will be clear from  FIG. 2   a , however, the suction cups  6  and  7  are positioned so that the respective axes are slightly displaced relative to each other in the width direction of the bag  4 . Further, as will be understood from  FIG. 2   b , the suction cups  6  and  7  are disposed so that the respective axes slightly tilt at the same angle to a horizontal plane and the suction-adhering surfaces  6   d  and  7   d  face slightly obliquely upward.  
         [0045]     Next, as the cam  12  rotates, the cam roller  15  moves along the first displacement portion, causing the suction cups  6  and  7  to move toward each other as far as respective positions where the suction cups  6  and  7  contact the opposite sides of the bag  4 , as shown in  FIGS. 3   a  and  3   b , as has been stated above. In this embodiment, a vacuum is applied to the suction cups  6  and  7  slightly before the suction cups  6  and  7  reach the above-described positions. The vacuum is kept applied to the suction cups  6  and  7  until completion of a series of opening operations (described later). When the suction cups  6  and  7  are moved to the above-described positions, because the suction-adhering surfaces  6   d  and  7   d  of the suction cups  6  and  7  face obliquely upward as stated above, the lower portions of the suction cups  6  and  7  abut against each other across the bag  4 , but the upper portions of the suction cups  6  and  7  are separate from each other. In this case, however, because the vacuum is acting on the suction cups  6  and  7 , side wall portions of the bag  4  above the fastener  4   a , at least near where the suction cups  6  and  7  are positioned, are opened by being sucked to the suction cups  6  and  7 , as shown in  FIG. 3   b . The inner surfaces of side wall portions of the bag  4  below the fastener  4   a  also slightly separate from each other, as shown in the figure, owing to the presence of the fastener  4   a  in an area where the suction-adhering surfaces  6   d  and  7   d  of the suction cups  6  and  7  overlap each other. It should be noted that in this embodiment the cam roller  15  has not yet reached the large diameter portion of the cam  12  even when the suction cups  6  and  7  have reach the above-described positions.  
         [0046]     As the cam  12  rotates further, the cam roller  15  reaches the large diameter portion. Thereupon, the suction cups  6  and  7  assume respective positions as shown in  FIGS. 4   a  and  4   b . That is, when in the positions shown in  FIGS. 3   a  and  3   b , the suction cups  6  and  7  have already abutted against each other across the bag  4  at their lower portions and cannot further advance as a whole. The arms  8  and  9 , however, further advance against the forces of the springs  10  from the positions shown in  FIGS. 3   a  and  3   b  to the respective positions in  FIGS. 4   a  and  4   b , thus separating from the flanges  6   c  and  7   c , respectively. Meanwhile, the suction cups  6  and  7  have their axes displaced relative to each other as stated above, and the shaft portions  6   b  and  7   b  are respectively fitted in the slots  8   b  and  9   b  of the arms  8  and  9 . Therefore, the shaft portions  6   b  and  7   b  move within the slots  8   b  and  9   b  to abut on the respective ends thereof opposite to the above as shown in  FIG. 4   a , causing the suction cups  6  and  7  to tilt slightly (the tilting action may be regarded as tilting of the suction cups  6  and  7  within a plane perpendicular to the side surfaces of the bag  4  and containing the fastener  4   a ). Thus, the suction cups  6  and  7  pinching the fastener  4   a  of the bag  4  from both sides shift from the respective positions shown in  FIGS. 3   a  and  3   b  to the positions shown in  FIGS. 4   a  and  4   b , thereby providing a massage-like action to loosen the fastener  4   a  at the pinched portion. As a result, the fastener  4   a  is slightly elastically deformed. That is, the mouth of the female fastener element  4   c  widens a little, making it easy for the male fastener element  4   b  to disengage from the female fastener element  4   c.    
         [0047]     The large diameter portion of the cam  12  is formed to extend over a certain angular range, as has been stated above. While the cam roller  15  is moving along the large diameter portion, the following operation takes place: When the state shown in  FIGS. 4   a  and  4   b  is reached, the above-described air cylinder  22  is activated at a predetermined timing to withdraw the rod  22   a  into the air cylinder  22  by a predetermined length. In response to the contraction of the rod  22   a , the pinion  24  rotates through a predetermined angle in a direction opposite to the above, causing the suction cups  6  and  7  to retract to respective. intermediate positions as shown in  FIGS. 5   a  and  5   b . During the retracting movement to the positions shown in  FIGS. 5   a  and  5   b , the suction cups  6  and  7  are adhering to the opposite side walls of the bag  4 . Thus, the suction cups  6  and  7  pull the bag  4  from both sides thereof and hence act to open the fastener  4   a  at the portion thereof where the suction cups  6  and  7  are adhering. Even if the fastener  4   a  is not fully opened at that portion by the above-described action, the male fastener element  4   b  begins to disengage from the female fastener element  4   c , as shown in  FIGS. 5   a  and  5   b . It should be noted that if the suction cups  6  and  7  were disposed in such a way that their respective axes coincide with each other unlike in this embodiment, the following problem might arise: While the suction cups  6  and  7  are adhering to the bag  4 , a negative pressure is created in the bag  4  at the suction-held portion below the fastener  4   a . Consequently, when the bag  4  is pulled from both sides thereof, the pulling force is canceled by the negative pressure, so that the suction holding of the bag  4  by the suction cups  6  and  7  becomes incomplete. In such a case, the suction cups  6  and  7  cannot pull the bag  4  sufficiently and may separate from the bag  4  undesirably. With this embodiment, however, a sufficiently strong suction-holding force can be maintained.  
         [0048]     Next, the air cylinder  22  is activated in reverse to the above to extend the rod  22   a , causing the suction cups  6  and  7  to assume respective positions as shown in  FIGS. 6   a  and  6   b . More specifically, the suction cups  6  and  7  move toward the bag  4  again to adhere to the bag  4  and perform the massaging operation to loosen the fastener  4   a , as has been stated above in connection with  FIGS. 4   a  and  4   b , to reach the respective positions shown in  FIGS. 6   a  and  6   b . Then, the rod  22   a  of the air cylinder  22  contracts again, causing the suction cups  6  and  7  to retract to the intermediate positions again. The air cylinder  22  repeats the contacting-extending operation a predetermined number of times while the cam roller  15  is moving along the large diameter portion of the cam  12 . During this operation, a part of the fastener  4   a  is fully opened, and the extent of the opening of the fastener  4   a  gradually extends as shown in  FIG. 7   a . Once a part of the fastener  4   a  has been opened, it is easy to open the rest of it. Finally, with the air cylinder  22  kept extended, the cam roller  15  moves along the second displacement portion of the cam  12 , causing the suction cups  6  and  7  to return to the respective previous stand-by positions. Thus, the fastener  4   a  of the bag  4  is opened over the entire length thereof, and the bag  4  is fully opened as shown in  FIGS. 8   a  and  8   b.    
         [0049]     It should be noted that air is injected from the nozzle  29  during the above-described opening operation. As has been stated above, the suction-adhering surfaces  6   d  and  7   d  of the suction cups  6  and  7  face obliquely upward so as to act to open the upper edge portion of the bag  4  at all times. Therefore, once the fastener  4   a  has been opened, even partially, flowing of air injected from the nozzle  29  into the bag  4  is promoted to facilitate and ensure the opening operation. Eventually, the bag  4  can be fully opened as far as the bottom thereof. It should be noted that, during the above-described operation, the grippers  5  gripping the laterally opposite side edges of the bag  4  move toward each other by a predetermined distance at a predetermined timing so as not to interfere with the operation of opening the bag  4 . The use of the air cylinder  22  makes it possible to adopt an arrangement in which the suction cups  6  and  7  are not retracted beyond the respective intermediate positions except the final retracting operation. Consequently, it is possible to shorten the reciprocating stroke of the suction cups  6  and  7  and to eliminate useless movement of the suction cups  6  and  7  and hence possible to improve throughput capability.  
         [0050]      FIGS. 9   a  and  9   b  are diagrams showing a second embodiment of the present invention.  FIG. 9   a  is a plan view corresponding to  FIG. 2   a .  FIG. 9   b  is a plan view corresponding to  FIG. 4   a . In this embodiment, suction cups  41  and  42  are secured to respective holders  47  and  48  that are pivotably supported to arms  43  and  44  (only partially shown) by shafts  45  and  46 , respectively. The holders  47  and  48  are subjected to forces from tension springs  49  and  50  retained each at one end thereof by spring retainers  51  and  52 , and positioned by abutting on respective stoppers  53  and  54 . The operations of the arms  43  and  44  and the suction cups  41  and  42  are substantially the same as in the first embodiment. It should be noted, however, that the operation of tilting the suction cups  41  and  42  as shown in  FIG. 9   b  is effected by pivoting of the holders  47  and  48  about the respective shafts  45  and  46  against the forces of the springs  49  and  50 . The other operations in this embodiment will be understood from the description of the first embodiment. Therefore, a description thereof is omitted. It should be noted that in this embodiment the suction cups  41  and  42  are placed in predetermined positions when retracted. Therefore, the suction cups  41  and  42  can surely adhere to the same positions on bags, and the opening operation can be performed stably.  
         [0051]     Although in the above-described first and second embodiments the arms and the suction cups move further from the respective positions shown in  FIGS. 3   a  and  3   b  to those shown in  FIGS. 4   a  and  4   b , it should be noted that the arms and the suction cups may move from the positions shown in  FIGS. 3   a  and  3   b  directly to the intermediate positions, not moving to the positions shown in  FIGS. 4   a  and  4   b , and finally retract to the stand-by positions. That is, the interlocking force of the fastener depends on the arrangement thereof. In a case where the interlocking force of the fastener is relatively small so that the fastener can be opened without performing the above-described massaging operation, it is unnecessary to carry out the massaging operation. In the first and second embodiments, the fastener opening operation is performed twice in total. That is, the operation of returning the suction cups to the respective intermediate positions while pulling the bag from both sides thereof is performed once. In the second suction cup returning operation, the suction cups are returned to the respective stand-by positions. The present applicant confirmed that ordinary zippered packaging bags presently used in automatic packaging can be surely opened by performing the above-described opening operation at least three times. The number of times of repeating the opening operation, however, is not necessarily limited to the above but may be determined according to the specifications of bags to be used. Whether or not to perform the massaging operation may also be determined according to need. In the first and second embodiments, the operation of moving the suction cups between the mutually close positions and the intermediate positions is performed by using an air cylinder. It is, however, also possible to effect the operation by using the cam itself, for example. If the cam alone is used to perform all the operations of moving the suction cups between the stand-by positions and the mutually close positions and moving them between the mutually close positions and the intermediate positions, however, the cam has to be changed when the number of times of repeating the opening operation is changed. In the case of the foregoing embodiments, however, the number of times of repeating the opening operation can be readily changed simply by controlling the air cylinder.  
         [0052]     In the foregoing first and second embodiments, the table of the automatic packaging machine intermittently rotates, and the above-described opening operation is performed while the bag is at rest at the first step of the automatic packaging process. Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-255119, for example, discloses a bag mouth opening apparatus for a bag with no fastener that is conveyed continuously. It is useful for realizing a high-speed automatic packaging machine that various operations are performed on a bag being moved continuously as disclosed in the JP(A) publication. The present invention is also applicable in a case where a bag with a fastener is moved not intermittently but continuously as in the above-described JP(A) publication. More specifically, in Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-255119, one apparatus for opening the bag mouth is provided along the bag conveying path. When the present invention is applied to an automatic packaging process in which a bag with a fastener is moved continuously, however, a plurality, for example, two, of bag mouth opening apparatuses are disposed along the bag conveying path. With the plurality of apparatuses, the opening operation is repeated a plurality of times, whereby a packaging bag with a fastener can be surely opened. The opening operation will be explained below briefly with reference to FIGS.  10  to  13 .  
         [0053]     An opening apparatus  71  used in this example may be the same as disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-255119. A pair of suction cups  74  and  75  are disposed facing each other across a bag  72  held with grippers  73  and moved continuously. The suction cups  74  and  75  are positioned in symmetry with respect to the travel line (shown by arrows in the figure) of the bag  72 . The suction cups  74  and  75  rotate in opposite directions to each other about their respective axes  76  and  77  extending perpendicular to the plane of the figure. During the rotation of the suction cups  74  and  75 , the suction-adhering surfaces thereof constantly face the bag  72 . During the movement of the suction cups  74  and  75 , their positions are kept symmetric with respect to the travel line of the bag  72  at all times. A second opening apparatus  81  placed next to the first opening apparatus  71  has the same arrangement and performs the same operation as the first opening apparatus  71 .  
         [0054]     Numerals shown in the right-top corners in two rectangular frames in each of FIGS.  10  to  13  indicate the order in which the suction cups  74  and  75  move to open the bag  72 . Regarding the first apparatus  71 , the suction cups  74  and  75  gradually move toward each other and toward the bag  72  from position “ 1 ” to “ 2 ” and further to “ 3 ” while rotating in opposite directions to each other. At position “ 4 ”, the suction cups  74  and  75  come closest to each other and abut against each other across the bag  72 . Thus, the suction cups  74  and  75  adhere to the respective outer surfaces of the opposite side walls of the bag  72  at the fastener (not shown). It should be noted that the peripheral velocity of the suction cups  74  and  75  at the positions of the suction-adhering surfaces when the suction cups  74  and  75  rotate about their axes  76  and  77  coincides with the travel speed of the bag  72 . Therefore, there is no discrepancy between the movement of the suction cups  74  and  75  and that of the bag  72 . Thus, the suction-adhering operation takes place smoothly. Then, the suction cups  74  and  75  move toward position “ 5 ” while continuing to rotate and moving away from each other, thereby pulling the bag  72  from both sides thereof. When they reach position “ 6 ”, the suction cups  74  and  75  separate from the bag  72 . At this time, a part of the fastener has been disengaged or has begun to disengage. Then, the suction cups  74  and  75  move from position “ 7 ” to “ 8 ” where they are remotest from each other, and then return to position “ 1 ”. Meanwhile, the bag  72  that has been treated by the apparatus  71  moves to the position of the second opening apparatus  81 , and a subsequent bag  72  is fed to the position of the first apparatus  71 . The operation of the second apparatus  81  is the same as that of the apparatus  71 . Therefore, a description thereof is omitted. It should be noted, however, that the fastener has been partially opened by the first apparatus  71 , or at least a part of the fastener has begun to open. Therefore, the fastener is fully opened easily and thus the bag  72  is fully opened by the second apparatus  82  as shown at “ 7 ” in  FIG. 13 . In this embodiment also, the fastener opening operation and hence the bag opening operation can be facilitated and ensured effectively by employing the nozzle used in the first embodiment.  
         [0055]     It should be noted that the present invention is not limited to the foregoing embodiments but can be modified in a variety of ways.