Patent Publication Number: US-10315794-B2

Title: Bag mouth opening device for continuously conveyed bags

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bag mouth opening device and more particularly to a device that adheres suction members facing each other on either side of a bag conveying path to both sides of the mouths of bags continuously conveyed along the bag conveying path at a constant speed and then moves the suction members away from each other to open the mouths of the bags. 
     2. Description of the Related Art 
       FIG. 11  shows the bag mouth opening device described in Japanese Patent Application Laid-Open (Kokai) No. 2002-255119. In this the bag mouth opening device, a pair of suction cups  2 ,  3  provided so as to face each other on either side of a conveying path (bag conveying path)  1  along which the bags (not shown) are conveyed are continuously rotated along the circular moving paths  4 ,  5  in mutually opposite directions (see arrows in the circular moving paths  4 ,  5 ) at a speed equal to the conveying speed of the bags (see the leftward arrow on the conveying path  1  indicative of the bag conveying direction). The time the suction cups  2 ,  3  take to make a single rotation along the circular moving paths  4 ,  5  is adjusted to match the time a bag to be conveyed takes for an inter-bag distance (1 (one) pitch (which is the distance between two bags being conveyed)) along the bag conveying path or the time that is an integer multiple thereof. When the cups  2 , 3  continuously rotate along the circular moving paths  4 ,  5 , they keep their suction surfaces to be oriented frontally (in other words, toward the bag conveying path  1 ) at all times while maintaining mutually symmetrical positions on either side of the bag conveying path  1 . 
     In comparison with bag mouth opening devices existing previously, the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 has such advantages that it is able to offer a simpler and more compact construction, to provide a reduction in vibration and noise, and to increase the speed of operation. 
     In the bag mouth opening device described in Japanese Patent Application Laid-Open (Kokai) No. 2002-255119, the suction cups  2 ,  3  are continuously rotated along the circular moving paths  4 ,  5  in mutually opposite directions at a speed equal to the speed of the bag conveyed (which is a constant speed); and when the cups are closest to each other in the circular moving paths  4 ,  5 , they adhere with suction to both sides of a bag conveyed along the bag conveying path  1 . After adhering to the bag, the suction cups  2 ,  3  travel in the bag conveying direction (toward the left side of  FIG. 11 ) while moving away from each other (away from the bag conveying path  1 ) as the bag is conveyed. 
     The suction cups  2 ,  3  travel along the circular moving paths  4 ,  5  at a constant speed, and in position P 0 , where the suction cups  2 ,  3  come close together again, the direction of travel of the suction cups  2 ,  3  coincides with the bag conveying direction. Accordingly, in position P 0 , the speed of travel of the suction cups  2 ,  3  in the bag conveying direction is equal to the speed of bag conveyed. However, since the suction cups  2 ,  3  travel along the circular moving paths  4 ,  5 , the speed of travel of the suction cups  2 ,  3  in the bag conveying direction thereafter becomes subsequently smaller (when compared with the speed of the bag conveyed). 
     It should be noted that if the speed of bag conveyed (the speed of travel of the suction cups  2 ,  3  along the circular moving paths  4 ,  5 ) is designated as V 0 , then the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction after the suction cups  2 ,  3  have traveled through an angle of θ from the position P 0  where the two cups approach toward each other the most along the circular moving paths is shown by V=V 0  cos θ. 
     Although the bag conveying speed V 0  is constant, the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction decreases during the rotation along the circular moving paths  4 ,  5 . After the suction cups  2 ,  3  adhere to the bag in position P 0  (θ=0°), the difference (V 0  minus (−) V) between the bag conveying speed V 0  and the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction increases over time, resulting in that the suction cups  2 ,  3  start lagging behind the bag. 
     Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 describes in paragraph 13 that the flexibility of the bag absorbs the difference (V 0  minus (−) V) between the bag conveying speed V 0  and the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction, so that this speed difference does not lead to any particular problems. However, this description in Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 is based on the premise that bags processed are relatively small in width dimensions. When bags are relatively small in width dimensions, the spacing distance D (see  FIG. 11 ) between the suction cups  2 ,  3  that have reached the position to fully open the mouth of the bag is small, and as a result the traveling angle θ of the cups from the position P 0  along the circular moving paths  4 ,  5  can be small. For this reason, the speed difference between the bag and the cups does not increase very much, and this speed difference can be absorbed by the flexibility of the bag. 
     When the bag processed is relatively large in width dimensions, it is necessary to increase the spacing distance D between the suction cups  2 ,  3  to reach the position to fully open the mouth of the bag. Assuming that the radius of the circular moving paths  4 ,  5  does not change, then it is necessary to increase the traveling angle θ of the suction cups  2 ,  3  to fully open the mouth of the bag. If the traveling angle θ of the suction cups  2 ,  3  increases, the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction becomes smaller, and the speed difference (V 0 −V) between the bag conveying speed V 0  of the bag and the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction becomes larger. For this reason, positional misalignment between the bag and the suction cups  2 ,  3  in the bag conveying direction increases as much as it becomes difficult to absorb the misalignment even if the advantage of the flexibility of the bag is taken into account, resulting in that the suction cups  2 ,  3  become detached from the bag while the mouth is opened, causing mouth opening failures. In addition, even in a case that the suction cups  2 ,  3  do not become detached from the bag, since forces in a direction opposite to the conveying direction act on the bag while the mouth is being opened, various problems would arise, including that the bag is detached from the grippers, the bag is displaced from the regular holding position, and the shape of the opened bag mouth is distorted. 
     If the radius of the circular moving paths  4 ,  5  in the above-described bag mouth opening device can be increased, even if the traveling angle θ of the suction cups  2 ,  3  reached the position where the mouth of the bag is fully opened is small, the spacing distance D between the suction cups  2 ,  3  can be increased, and the speed difference between the bag conveying speed V 0  and the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction does not become excessively large even when the mouth of bag that is relatively large in width dimensions is opened, and this speed difference can be absorbed by taking (advantage of) the flexibility of the bag into account. However, in the above-described bag mouth opening device, the speed of rotation of the suction cups  2 ,  3  along the circular moving paths  4 ,  5  is adjusted to match the conveying speed of bag, and the time period the suction cups  2 ,  3  take to make a single rotation along the circular moving paths  4 ,  5  is adjusted to match the time the bag is conveyed for an inter-bag distance (1 pitch), or it is set to an integer multiple thereof. For this reason, the radius of the circular moving paths  4 ,  5  is inevitably set to a constant value. In other words, in the above-described bag mouth opening device, it is substantially difficult to vary the radius of the circular moving paths  4 ,  5  in accordance with the width dimensions of the bags to be processed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is devised by taking into account the problems with the bag mouth opening device described in Japanese Patent Application Laid-Open (Kokai) No. 2002-255119, and it is an object of the invention to provide a bag mouth opening device that is capable of opening the mouths of bags in a more reliable and stable manner regardless of the size of the width direction of bags. 
     The above object is accomplished by a unique structure of the present invention for a bag mouth opening device for bags continuously conveyed in which a pair of opposed suction members (suction cups) are adhered to both sides of the mouth of each bag continuously conveyed along a bag conveying path at a constant speed and regular intervals, and then the suction members are moved away from each other to thereby open the mouth of the bag, and in the present invention,
         the pair of suction members are continuously rotated in mutually opposite directions along their moving paths of a substantially elliptical shape while keeping their suction surfaces oriented frontally (or toward the bag conveying path) in a plane substantially parallel to the conveying path and substantially perpendicular to the surface of the bag, and   the moving paths of the suction members have their major axes inclined at substantially equal angles with respect to the bag conveying path such that they digress from the conveying path toward the anterior side, and the time the suction members take to make their single rotation along the moving paths is set to be an integer (including 1) multiple of the time a bag to be conveyed takes for an inter-bag distance (which is the distance between two bags being conveyed).       

     Needless to say, the direction of rotation of the suction members cannot be opposite to the bag conveying direction. 
     In the above structure and as used herein, the term “substantially elliptical” includes the shape of an ellipse as defined in geometry, as well as shapes close to an ellipse, for example, a racetrack shape (a shape in which two semicircles are connected by two straight lines), an oval, or a shape obtained by compressing an ellipse in the direction of its major or minor axes. 
     In the above-described structure, the pairs of (or two) suction members are provided on, for instance, a pair of (two) rotation transmission members, respectively, that make a translational motion along the moving paths of substantially elliptical shape. The rotation transmission members that make the translational motion are oriented in the same direction at all times, and the motion of the pairs of suction members provided on the rotation transmission members respectively is thus a translational motion as well, and further the suction surfaces of the suction members are oriented in the same direction (frontally) at all times during the rotation along the moving paths so that the suction surfaces always face the bag conveying path. 
     The mechanism that causes each one of the rotation transmission members to make the translational motion is comprised of, for example,
         two first rotating shafts connected to a common drive source and rotated in the same direction at a constant speed;   a first rotating lever secured to each one of the first rotating shafts;   a second rotating shaft which is journaled on each one of first rotating levers in a rotatable manner in locations offset equidistantly and in the same direction relative to the first rotating shafts and turns at a constant speed in a direction opposite to the direction of rotation of the first rotating shafts;   a second rotating lever secured to each one of the second rotating shafts; and   a support shaft provided on each one of the second rotating levers in locations offset equidistantly and in the same direction relative to the second rotating shafts, and       

     the rotation transmission members are coupled to the support shafts so as to make the translational motion. 
     Furthermore, the drive mechanism that causes each one of the second rotating shafts to turn in the same direction at a constant speed is comprised of:
         a fixed sun gear whose center is on the axial line of the first rotating shaft;   a planetary gear rotatably journaled on the first rotating lever and meshing with the sun gear; and   a driven gear secured to the second rotating shaft and meshing with the planetary gear.       

     In this structure of the drive mechanism that causes each one of the second rotating shafts to turn in the same direction at a constant speed, the gear ratio of the sun gear and the driven gear is set to 2:1. On the other hand, instead of such a planetary gear mechanism, it is possible to employ other drive sources such as, for instance, servo motors so that the drive source is provided on the first rotating lever to turn the second rotating shaft. 
     Similarly to the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119, if necessary, a plurality of sets of suction members can be installed at intervals equal to the inter-bag distance in the bag conveying direction. If only one pair (or one set) of suction members is installed along the bag conveying path as will be described below, the time the suction members take to make their single rotations is set to be equal to the time a bag is conveyed for an inter-bag distance. However, when a plurality of sets of suction members are provided, then the time those suction members take to make their single rotations is set to a time obtained by multiplying the number of sets by the time a bag is conveyed for an inter-bag distance. In addition, when a plurality of pairs or sets of suction members are provided, the circumferential lengths of the suction member moving paths of substantially elliptical shape can be increased by the same scaling factor. 
     The bag mouth opening device of the present invention is applicable mostly to cases in which the mouth of a bag is upwardly oriented and the bag is conveyed horizontally in the bag width direction in a vertical state with both side or lateral edges of the bag being held by grippers so that the bag is suspended or held with retainers, etc. The device of the present invention is, nonetheless, further applicable to cases in which bags are conveyed in the longitudinal (depth) direction or in which bags are oriented horizontally and conveyed in the width or longitudinal direction. In other words, bag mouth opening device of the present invention is applicable broadly to cases in which bags are conveyed in the width or longitudinal direction along the bag surface. In addition, the bag mouth opening device of the present invention is applicable not only to cases in which bags are conveyed substantially linearly, but also to case, for instance, in which the bags are held by numerous grippers installed around a rotating table and conveyed along a circular moving path of a relatively large diameter. In such a case, the moving paths of the suction members that are substantially elliptical shape can be defined by considering, for instance, the direction, which is tangential to the bag conveying path at a point (point of adhesion) where the moving paths of substantially elliptical shape reach the conveying path, as a bag conveying direction. 
     As seen from the above, in the bag mouth opening device of the present invention, the shape of the moving paths along which the pair of suction members rotate is substantially elliptical and not circular as seen in the prior art, and their major axes are tilted so that they digress from (or separate from) the bag conveying path toward the anterior side (which is a forward side in terms of the bag conveying direction), thereby making it possible to better prevent, in comparison with circular suction member moving paths, an increase in the difference between the conveying speed of the bag and the traveling speed of the suction members in the bag conveying direction in the process of mouth opening that occurs subsequent to adhesion of the pair of suction members to a bag. For this reason, when bags of relatively large in width dimensions are to be opened, the opening action for the mouths of such bags can be made in a more reliable and stable manner in comparison with the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119. In addition, in the same manner as in the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119, the bag mouth opening device of the present invention is able to provide a simpler and more compact construction, a reduction in vibration and noise, and an increase in the speed of operation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view of one example of a continuous transportation type bag filling and packaging apparatus that uses the bag mouth opening device of the present invention. 
         FIG. 2  is a conceptual diagram showing a comparison between the moving paths along which suction members (suction cups) of a bag mouth opening device of the present invention rotate and the moving paths along which the suction cups of the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 rotate. 
         FIG. 3  is a conceptual diagram showing the operation of the suction cups in the bag mouth opening device of the present invention. 
         FIG. 4  is a conceptual diagram of a time-sequential description of the bag mouth opening steps performed by the suction cups of the bag mouth opening device of the present invention. 
         FIG. 5  is a perspective view of the bag mouth opening device of the present invention. 
         FIG. 6  is a perspective of the main portion thereof, showing one of four mechanisms that make a translational motion of rotation transmission members of the bag mouth opening device of the present invention, four of such mechanism provided therein being substantially the same. 
         FIG. 7  is also a perspective of the main portion thereof, looking the same from another side. 
         FIG. 8  is a conceptual top view of the construction of the bag mouth opening device of the present invention. 
         FIG. 9  is a conceptual top view showing moving paths along which the suction cups of the bag mouth opening device of the present invention rotate. 
         FIG. 10  is a conceptual top view showing a time-sequential description of the operation of a crank mechanism that rotates the suction cups of the bag mouth opening device of the present invention. 
         FIG. 11  is a conceptual diagram showing the moving paths along which the suction cups of the bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 rotate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The bag mouth opening device according to the present invention is described below with reference to  FIG. 1  through  FIG. 10 . 
     A continuous transportation type bag filling and packaging apparatus that uses the bag mouth opening device of the present invention is illustrated in  FIG. 1 . 
     The continuous transportation type bag filling and packaging apparatus of  FIG. 1  includes an endless chain  11  which travels along a racetrack-shaped annular path comprised of arcuate sections at both ends and rectilinear sections between the arcuate end sections, and it also includes multiple sets of grippers  12  (two of or a pair of grippers constitutes one set of grippers), which are installed at equal intervals in the lengthwise direction of the endless chain  11  and travel along a similarly racetrack-shaped annular moving path together with the endless chain  11 . A bag feeding device  13 , a printer  14 , a print testing device  15 , a bag mouth opening device (only the suction cups  16 ,  17  are illustrated), a filling device  18 , a sealing device  19 , an empty bag discharging device (not illustrated), a product bag discharging device (not illustrated), and the like are disposed along the annular moving path for the grippers  12 . 
     As the grippers  12  rotationally travel along the annular moving path, various operations are carried out to bags: feeding bags  20  to the grippers  12  using the bag feeding device  13 , holding both side or lateral edges of each one of the bags using the grippers  12 , printing, for instance, a manufacturing date on the surface of the bag using the printer  14 , print testing using the print testing device  15 , opening the mouth of the bag using the bag mouth opening device (only suction cups  16 ,  17  are illustrated), filling the bag with the material to be packaged using the filling device  18 , sealing the mouth of the bag (including cooling) using the sealing device  19 , discharging a product bag  20 A (a bag filled with the material to be packaged) using the product bag discharging device, and the like. 
     The endless chain  11  and the grippers  12 , as well as the mechanism that moves the endless chain  11 , are identical to those employed in the devices described in Japanese Patent Application Laid-Open (Kokai) Nos. 2002-302227 and 2009-161230. More specifically, the endless chain  11  is a chain formed by numerous links connected via connecting shafts in endless form such that one set (one pair) of grippers  12  is provided on the outside of each link. The grippers  12  are installed at regular intervals along the endless chain  11 , and, as the endless chain  11  moves, the grippers continuously rotate at a constant speed in a horizontal plane along the racetrack-shaped annular moving path (clockwise as viewed from above in  FIG. 1 , see two curved and straight arrows). The bags  20  held by the grippers  12  are continuously conveyed at a constant speed and regular intervals in a horizontal plane along the racetrack-shaped conveying path. 
     The bag feeding device  13  is identical to the empty bag feeding device described in Japanese Patent Application Laid-Open (Kokai) Nos. 2002-308223 and 2009-161230. The bag feeding device  13  is combined with a conveyor magazine type bag supplying device  13   a , and it simultaneously supplies four bags  20  to four sets of grippers  12  in a one-by-one manner. 
     The printer  14  and the print testing device  15  are publicly known devices. 
     The bag mouth opening device (only the suction cups  16 ,  17  are illustrated in  FIG. 1 ) will be described below. 
     The filling device  18  includes numerous hoppers  21  movable up and down and disposed at equal angular intervals. The hoppers  21  rotate at a constant speed along the circular moving path and at the same time move up and down at predetermined timing. A weighing hopper  22  and a weighing box  23  are installed at equal angular intervals for each hopper  21  and rotate at a constant speed along the circular moving path together with the hoppers  21 . At the lower end of each weighing hopper  22 , there is installed a shutter (not illustrated) that opens and closes the lower end opening of the weighing hopper  22 . Inside the weighing box  23 , a weight sensor (for example, a load-cell type sensor), not shown, that measures the weight of the material to be packaged fed to the weighing hopper  22  is provided. One half of the circular portion of the moving path of the hoppers  21  is in overlying alignment with the conveying path (semicircle portion) of the bags  20  held by the grippers  12 . With the speed of rotation of the hoppers  21  being coincide with the speed of travel of the grippers  12 , the hoppers  21  rotationally travel in synchronism with the transport of the bags  20  directly above the conveying path (semicircle portion) of the bags  20  held by the grippers  12 . 
     In the filling device  18 , when the material to be packaged is fed into the weighing hopper  22  from a feeding means, which is not shown, at a predetermined timing, the weight of the material to be packaged is measured by the weight sensor installed in the weighing box  23 . Subsequently, the hopper  21  is moved down, its lower end is inserted into a bag  20 , the shutter of the weighing hopper  22  is opened, and thus the material to be packaged falls through the hopper  21  into the bag  20  and filled therein. Once the lower end portion of the hopper  21  is inserted into the bag  20 , all operations until the bag  20  is filled with the material to be packaged are carried out while the hopper  21  is rotationally traveling in synchronism with the bag  20  being conveyed. 
     The sealing device  19  is comprised of first sealing devices  19   a ,  19   a  (only the sealing bar of the first sealing device  19   a  on the downstream side is illustrated), which heat-seals the mouth of a filled bag  20  by clamping it with sealing bars, second sealing devices  19   b ,  19   b  (only the two sealing bars are illustrated), and sealed portion cooling devices  19   c ,  19   c  (only the two cooling bars are illustrated), which cool the sealed portion by clamping it with cooling bars. In the same manner as the sealing device described in Japanese Patent Application Laid-Open (Kokai) No. 2001-72004, the sealing device  19  operates such that it follows the grippers  12  for a predetermined distance at the same speed as the grippers, and the sealing bars or cooling bars of the sealing device  19  clamp the mouth of the bag  20  during such time and then release the mouth, and, subsequently, return to the original position. In the shown example, two bags are simultaneously heat-sealed by the first sealing devices  19   a ,  19   a , whereupon they are simultaneously heat-sealed (for the second time) by the second sealing devices  19   b ,  19   b , and then simultaneously cooled by the sealed portion cooling devices  19   c ,  19   c.    
     The product bag discharging device, which is identical to the opening/closing device (comprised of an opening/closing member and a drive mechanism therefore, etc.) described in Japanese Patent Application Laid-Open (Kokai) Nos. 2002-302227 and 2009-161230, opens the gripping portion of the grippers  12  upon arrival at a predetermined position, drops the product bag (a bag filled with the material)  20 A into a chute (not illustrated), and outputs it on an output conveyor (not illustrated). Such an opening/closing device as described above can be provided in the bag feeding device  13 ; and when the bags  20  are fed to the grippers  12 , the gripping portions of the grippers  12  are opened (operates simultaneously on four sets of grippers  12 ) thereby. 
     The empty bag discharging device (not illustrated) is the same as the defective bag discharging device described in Japanese Patent Application Laid-Open (Kokai) No. 2009-161230, and it is disposed somewhat upstream side of the product bag discharging device. Being equivalent to the product bag discharging device from a functional standpoint, the empty bag discharging device opens the gripping portion of the grippers  12  to drop the empty bags  20 . 
     Next, the bag mouth opening device of the present invention will be described with reference to  FIG. 2  through  FIG. 4 . 
     In the continuous transportation type bag filling and packaging apparatus of  FIG. 1  in which the bag mouth opening device of the present invention is utilized, numerous bags  20  are vertically suspended with both side or lateral edges thereof held by the grippers  12 , and these bags are continuously conveyed along the racetrack-shaped conveying path at a constant speed and at regular intervals. The bag mouth opening device of the present invention opens the mouth of the bag  20  being conveyed along the rectilinear regions of the conveying path. 
     The differences between the bag mouth opening device of the present invention and the conventional bag mouth opening device of Japanese Patent Application Laid-Open (Kokai) No. 2002-255119 will be described first with reference to  FIG. 2 . 
     The bag mouth opening device of the present invention includes a pair of suction cups (suction members)  16 ,  17 . As shown in  FIG. 2 , the suction cups  16 ,  17  continuously rotate at a constant speed (speed V 0 ) in mutually opposite directions along the respective elliptical moving paths  24 ,  25  in a horizontal plane, with their suction surfaces oriented frontally at all times in other words to face the conveying path  1 . In the shown example, the moving paths  24 ,  25  of the suction cups  16 ,  17  are defined symmetrically on ether side of the conveying path  1 , and their major axes  26 ,  27  are inclined at the same angle relative to the conveying path  1 , such that the major axes  26 ,  27  digress from the conveying path  1  toward the anterior side (which is a forward side in terms of the bag conveying direction), In addition, the suction cups  16 ,  17  that travel along the moving paths  24 ,  25 , respectively, maintain symmetrical positions on ether side of the bag conveying path  1  at all times. The speed of the bags  20  (not illustrated in  FIG. 2 ) conveyed along the conveying path  1  is V 0 . 
     The circular moving paths  4 ,  5  of  FIG. 11  of the conventional suction cups  2 ,  3  is superimposed on  FIG. 2 , and they have the same circumferential length as the elliptical moving paths  24 ,  25  and also are defined symmetrically on ether side of the conveying path  1 . The suction cups  2 ,  3  continuously rotate in a horizontal plane at a constant speed (speed V 0 ) in mutually opposite directions along the circular moving paths  4 ,  5 , respectively, with their suction surfaces oriented frontally at all times to face the bag conveying path  1 . The suction cups  2 ,  3  traveling along the moving paths  4 ,  5  are provided so as to maintain symmetrical positions on ether side of the conveying path  1  at all times. 
     As seen from  FIG. 2 , if the traveling speed of the suction cups  2 ,  3  in the bag conveying direction (toward left in  FIG. 2 ) is designated as V (which is the component of the conveying speed V 0  of the bag in the bag conveying direction) and the traveling speed of the suction cups  16 ,  17  in the bag conveying direction is designated as U (which is the component of the conveying speed V 0  of the bag in the bag conveying direction), then V=U=V 0  in position P 0  where the suction cups  2 ,  3  and the suction cups  16 ,  17  approach the bag conveying path  1  the most (and where the cups suction-hold the bag). On the other hand, once adhered to a bag by suction, the suction cups  2 ,  3  move away from each other as they travel along the circular moving paths  4 ,  5 , and the suction cups  16 ,  17  also move away from each other as they travel along the moving paths  24 ,  25  (for the spacing distance D), and it is clear that in this case U&gt;V (U is greater than V). Then, the more the spacing distance D increases, the greater the difference between the traveling speed U of the suction cups  16 ,  17  and the traveling speed V of the suction cups  2 ,  3  becomes (U&gt;&gt;V). In other words, during the bag opening process, the traveling speed U of the suction cups  16 ,  17  in the bag conveying direction is, in comparison with the traveling speed V of the suction cups  2 ,  3  in the bag conveying direction, set such that the speed difference with respect to the bag conveying speed V 0  is kept smaller (V 0 −U&lt;V 0 −V). As a result, the positional misalignment of the suction cups  16 ,  17  and the bag in the bag conveying direction is kept smaller. Therefore, even if the width dimensions of the bags are relatively large and it is necessary to make the spacing distance D between the suction cups  16 ,  17  larger to open the mouth of the bag, the compliance of the suction cups  16 ,  17  with respect to the bags in the conveying direction is better, and the opening of the mouth of the bag can be carried out in a stable manner. 
     Next, the mouth opening steps performed by the above-described bag mouth opening device of the present invention will be described in greater detail with reference to  FIGS. 3 and 4 . 
     In the continuous transportation type bag filling and packaging apparatus in which the bag mouth opening device of the present invention is utilized, numerous bags  20  are vertically suspended with both side edges or lateral edges thereof being held by the grippers  12 , and they are continuously conveyed along the conveying path  1  (see  FIG. 2 ) at a constant speed and at regular intervals (the conveying direction is indicated by the arrow). Pairs of suction members (suction cups  16 ,  17 ), which form part of the bag mouth opening device of the present invention, are installed on the opposite sides (or on either side) of the conveying path  1  of the bags  20 , respectively. 
     The suction cups  16 ,  17  rotate in a horizontal plane in mutually opposite directions along the elliptical moving paths  24 ,  25  with their suction surfaces frontally oriented so as to face both surfaces of the bag at all times. This motion of the suction cups  16 ,  17  is translational motion. In the shown example, the elliptical moving paths  24 ,  25  are defined symmetrically on ether side of the bag conveying path  1  with their major axes  26 ,  27  (see  FIG. 2 ) inclined at the same angle with respect of the bag conveying path  1 , such that the major axes  26 ,  27  digress from the bag conveying path  1  toward the anterior side (with respect to the bag conveying direction). The suction cups  16 ,  17  rotate along the moving paths  24 ,  25  at a constant speed, which is the same speed as the conveying speed V 0  of the bags  20 , and, at the same time, rotate by maintaining mutually symmetrical positional relationship as viewed from the conveying path  1  of the bags  20 . In addition, the time the suction cups  16 ,  17  take to make a single rotation is set to be equal to the time a bag  20  takes to be conveyed for an inter-bag distance (which is the distance between two bags being conveyed) s (1 pitch), and also the circumferential length of the moving paths  24 ,  25  of the suction cups  16 ,  17  is set to be equal to the inter-bag distance s. Furthermore, the timing of conveying the bag  20  and rotating the suction cups  16 ,  17  is set such that when the suction cups  16 ,  17  reach the conveying path  1  of the bags  20  (where the suction cups come close the most), they abut the mouth area of the bag  20  substantially in its central portion and adhere thereto by suction. 
       FIG. 4 , including illustrations (a)-(l), shows the relationship between one (1) cycle of moving of the suction cups  16 ,  17  (one (1) rotation) and the conveyance of the bag  20  in the mouth opening procedure. These diagrams are described below in simple terms.
         (a)-(d) The suction cups  16 ,  17  initiate their approach while rotating from the position of maximum separated distance towards the bag conveying path  1 , and, on the other hand, an unopened bag  20  is approaching a predetermined position of cup adhesion in a rectilinear manner.   (e)-(f) The suction cups  16 ,  17  approach the mouth of the bag  20  and vacuum suction is initiated.   (g) The suction cups  16 ,  17  reach the bag conveying path  1 , the suction surfaces of the cups are resiliently pressed against the mouth of the bag  20  from either side, and suction is applied. At such time, the traveling speed of the suction cups  16 ,  17  in the bag conveying direction is equal to the bag conveying speed V 0 .   (h)-(i) The suction cups  16 ,  17 , traveling along the elliptical moving paths  24 ,  25 , start moving away from each other while adhering by suction to the bag mouth, resulting in that the mouth of the bag  20  is opened (opened bag  20   a ). The travelling speed of the suction cups  16 ,  17  in the bag conveying direction is gradually reduced in the process of rotation; however, in comparison with the conventional suction cups  2 ,  3  rotating along circular moving paths (see  FIG. 2 ), in a case involving the same spacing distance, the difference relative to the bag conveying speed V 0  is smaller, which makes it possible to maintain substantially the same speed and ensure superior compliance with the bag  20   a  being conveyed at the constant speed V 0 . It should be noted that if multiple pairs of suction cups  16 ,  17  are provided, the circumferential length of the elliptical moving paths  24 ,  25  is proportionally increased, and as a result of which the speed difference of the bag and the suction cups becomes even smaller.   (j) The vacuum suction of the suction cups  16 ,  17  is stopped, and the suction surfaces of the suction cups are detached from the mouth of the bag  20   a.      (k)-(l) The suction cups  16 ,  17  are moved even farther away from each other, and one (1) cycle of the suction cups ends.       

     Next, a specific preferred construction of the bag mouth opening device of the present invention will be described with reference to  FIG. 5  through  FIG. 10 . In  FIG. 5  through  FIG. 10 , parts that are substantially equivalent to those of the bag mouth opening device illustrated in  FIGS. 1 through 4  are assigned with the same reference numerals. 
     As shown in  FIGS. 5 through 7 , the suction cups  16 ,  17  are secured to the distal ends of mouth opening arms  31 ,  32 , respectively, so that they are provided on plate-shape rotation transmission members  35 ,  36 , respectively, via the mouth opening arms  31 ,  32  and attachment holders  33 ,  34 . The mouth opening arms  31 ,  32  are hollow pipes, the suction cups  16 ,  17  are secured to the distal ends thereof, respectively, vacuum pipes, not shown, are connected to their back ends, respectively, and the vacuum pipes are placed in communication with vacuum sources through filters, change-over valves, and the like. The attachment holders  33 ,  34  are secured to the front ends of the rotation transmission members  35 ,  36 , respectively, and the back end portions of the mouth opening arms  31 ,  32  are secured thereto, respectively. 
     A drive shaft  37  and four first rotating shafts  38  through  41  are vertically provided on a base frame, not shown, in a rotatable manner. A drive gear  42  is secured to the drive shaft  37 , and linkage gears  43  through  46  are secured to the first rotating shafts  38  through  41 , respectively. The linkage gears  43  through  46  have the same number of teeth. Among these linkage gears  43  through  46 , the linkage gears  43 ,  44  mesh with the drive gear  42 ; and the linkage gear  45  meshes with the linkage gear  43 , and the linkage gear  46  meshes with the linkage gear  44 . The drive shaft  37  is coupled to a drive source, not shown, and is rotated at a constant speed; and when the drive gear  42  is rotated by the drive shaft  37 , the first rotating shafts  38  through  41  are simultaneously rotated at a constant speed via the linkage gears  43  through  46 . 
     First rotating levers  47  through  50  are secured in the vicinity of the upper ends of the first rotating shafts  38  through  41 , respectively. The first rotating levers  47  through  50  are rotated in a horizontal plane at a constant speed when the first rotating shafts  38  through  41  are rotated. As shown in  FIGS. 7 and 8 , the first rotating lever  47  (the other first rotating levers  48 ,  49  and  50  have the same construction as the first rotating lever  47  and thus will not be described in detail in the below) is comprised of top and bottom plate-shaped members  47   a ,  47   b  and a connecting member  47   c  that connects the plate-shaped members  47   a  and  47   b , thus taking a frame-like configuration. Second rotating shafts  51  through  54  are provided vertically on the top and bottom plate-shaped members of the first rotating levers  47  through  50 , respectively, in a rotatable fashion. The above-described first rotating shafts  38  through  41  (corresponding to a crank journal), the first rotating levers  47  through  50  (corresponding to a crank arm), and the second rotating shafts  51  through  54  (corresponding to a crankpin) form a type of crank mechanism (or first crank mechanisms  55  through  58 , each comprising the first rotating shaft, the first rotating lever, and the second rotating shaft). In the first crank mechanisms  55 ,  56 , the second rotating shafts  51 ,  52  are provided in locations offset equidistantly and in the same direction relative to the first rotating shafts  38 ,  39  respectively. Likewise, in the first crank mechanisms  57 ,  58 , the second rotating shafts  53 ,  54  are provided in locations offset equidistantly and in the same direction relative to the first rotating shafts  40 ,  41 , respectively. 
     The second rotating shafts  51  through  54  project above the first rotating levers  47  through  50 , respectively, and the second rotating levers  59  through  62  (see second rotating lever  60  in  FIG. 8 ) are secured to the upper ends of the second rotating shafts  51  through  54 , respectively, and further the support shafts  63  through  66  are provided on the rotating levers  59  through  62 , respectively, in a rotatable manner. The above-described second rotating shafts  51  through  54  (corresponding to a crank journal), the second rotating levers  59  through  62  (corresponding to a crank arm), and the support shafts  63  through  66  (corresponding to a crankpin) form a type of crank mechanism (or second crank mechanisms  68  through  70 , each comprising the second rotating shaft, the second rotating lever, and the support shaft. In the second crank mechanisms  67 ,  68 , the support shafts  63 ,  64  are provided in locations offset equidistantly and in the same direction relative to the second rotating shafts  51 ,  52 , respectively. Likewise, in the second crank mechanisms  69 ,  70 , the support shafts  65 ,  66  are provided in locations offset equidistantly and in the same direction relative to the second rotating shafts  53 ,  54 , respectively. 
     A rotation transmission member  35  is secured to the upper ends of the support shafts  63 ,  64 , and a rotation transmission member  36  is secured to the upper ends of the support shafts  65 ,  66 . 
     The first rotating shafts  38  through  41  are hollow inside and have sun gear shafts installed in the hollow interiors, respectively (only sun gear shaft  71  inside the first rotating shaft  38  is shown in  FIGS. 6, 7 , and the other sun gear shafts, not shown, are provided in the first rotating shafts  39  through  41 , respectively, in the same manner as the sun gear shaft  71 ). The lower ends of the sun gear shafts pass through the centers of the linkage gears  43  through  46 , respectively, and are secured to a base frame, not shown, while the upper ends of the respective sun gear shafts project inside the frames of the first rotating levers  47  through  50 , respectively, and sun gears are secured to the upper ends of the sun gear shafts, respectively (only the sun gear  72  is shown in  FIGS. 6 and 7  for the first rotating lever  47 , the sun gear for the first rotating lever  48  is not shown, and the sun gears  73 ,  74  for the first rotating lever  49 ,  50  are shown in  FIG. 5 ). The centers of the sun gears coincide with the axial lines of the first rotating shafts  38  through  41 , respectively. 
     Planetary gears meshing with sun gears are journaled inside the frames of the first rotating levers  47  through  50 , respectively, in a rotatable manner (only planetary gears  75 ,  76  are shown in  FIGS. 5 through 7 ). Furthermore, driven gears are secured to the second rotating shafts  51  through  54 , respectively (only driven gears  78  through  80  are shown in  FIGS. 5 through 7 ), and these driven gears mesh with the planetary gears, respectively. 
     The above-described sun gears, planetary gears, and driven gears constitute drive mechanisms that rotate the second rotating shafts  51  through  54 , respectively (although not indicative for all, as can be seen from the above description, four sun gears, planetary gears, and driven gears are provided in the shown example, with each for each one of the drive mechanisms that rotate the second rotating shafts). Also, in the shown example, the gear ratio of the sun gears, planetary gears, and driven gears is set to 2:1:1. However, since the planetary gears are substantially idle gears, the gear ratio of the sun gears and planetary gears does not have to be 2:1. 
     In the above-described bag mouth opening device, when the drive gear  42  is rotated, it rotates the first rotating shafts  38  through  41  via the linkage gears  43  through  46 , and the first rotating levers  47  through  50  are also rotated. As a result, in the first crank mechanisms  55  through  58 , the second rotating shafts  51  through  54  are rotated around the first rotating shafts  38  through  41 , respectively. On the other hand, when the first rotating levers  47  through  50  rotate, the planetary gears and the driven gears within the first rotating levers  47  through  50  turn while rotating (revolving) around the sun gears, respectively, and the second rotating shafts  51  through  54  turn while rotating (revolving) around the first rotating shafts  38  through  41 , respectively, and the second rotating levers  59  through  62  are rotated, respectively, as well. As a result, in the second crank mechanisms  67  through  70 , the support shafts  63  through  66  rotate around the second rotating shafts  51  through  54 , respectively. 
     In the first crank mechanisms  55  through  58 , the second rotating shafts  51  through  54  make two rotations (turns) on the first rotating levers  47  through  50 , respectively, while the first rotating shafts  38  through  41  (and the respective first rotating levers  47  through  50 ) make a single rotation. Therefore, the second rotating levers  59  through  62 , which rotate together with the second rotating shafts  51  through  54 , respectively, make two rotations relative to the first rotating levers  47  through  50  while the first rotating levers  47  through  50  make a single rotation. In addition, since the direction of rotation of the second rotating levers  59  through  62  is opposite to the direction of rotation of the first rotating levers  47  through  50 , respectively, each of the second rotating levers  59  through  62 , in an absolute sense, make a single counter-rotation relative to the first rotating levers  47  through  50 , respectively, while the first rotating levers  47  through  50  make a single rotation. 
       FIG. 10  shows the positional relationship between the first rotating levers  47  through  50  (only the first rotating levers  47 ,  49  are illustrated) and the second rotating levers  59  through  62  (only the second rotating levers  59 ,  61  are illustrated) in a time-sequential manner, from right to left or ( 1 ) to ( 7 ). While the first rotating lever  47  rotates 90 degrees to the right about the first rotating shaft  38  as seen from (a)( 1 ) to (a)( 7 ), the second rotating lever  59  rotates 90 degrees to the left about the second rotating shaft  51  in an absolute sense, and at the same time it rotates 180 degrees to the left with respect to the first rotating lever  47  (The rotational relationship between the first rotating lever  48  and the second rotating lever  60  is the same as that of the first rotating lever  47  and the second rotating lever  59 ). On the other hand, while the first rotating lever  49  rotates 90 degrees to the left about the first rotating shaft  40 , the second rotating lever  61  rotates 90 degrees to the right about the second rotating shaft  53  in an absolute sense, and at the same time it rotates 180 degrees to the right with respect to the first rotating lever  49  (The rotational relationship between the first rotating lever  50  and the second rotating lever  62  is the same as that of the first rotating lever  49  and the second rotating lever  61 ). 
     Next, the moving paths along which the suction cups  16 ,  17  are rotated in the bag mouth opening device of  FIGS. 5 through 7  will be described below with reference to  FIGS. 8 through 10 . 
     As shown in  FIG. 8 , in this bag mouth opening device, the first rotating shafts  38 ,  39  for the cup  16  are provided in a line perpendicular to the bag conveying path  1 , and, in a similar manner, the first rotating shafts  40 ,  41  for the cup  17  are provided in a line perpendicular to the bag conveying path  1 . 
     In the first crank mechanisms  55 ,  56  for the cup  16 , the second rotating shafts  51 ,  52  are installed in positions offset equidistantly and in the same direction relative to the first rotating shafts  38 ,  39 , respectively; and in the second crank mechanisms  67 ,  68  for the cup  16 , the support shafts  63 ,  64  are respectively installed in positions offset equidistantly and the support shafts  63 ,  64  are installed in positions offset equidistantly and in the same direction relative to the second rotating shafts  51 ,  52 , respectively. On the other hand, in the first crank mechanisms  57 ,  58  for the cup  17 , the second rotating shafts  53 ,  54  are installed in positions offset equidistantly and in the same direction relative to the first rotating shafts  40 ,  41 , respectively; and in the second crank mechanisms  69 ,  70  for the cup  17 , the support shafts  65 ,  66  are installed in positions offset equidistantly and in the same direction relative to the second rotating shafts  53 ,  54 , respectively. 
     In addition, the distance d 1  between the first rotating shaft  38  and the second rotating shaft  51  for the cup  16  (the distance between the first rotating shaft  39  and the second rotating shaft  52  for the cup  16  has the same length d 1 ) is set to be slightly shorter than the distance d 2  that is between the first rotating shaft  40  and the second rotating shaft  53  for the cup  17  (the distance between the first rotating shaft  41  and the second rotating shaft  54  for the cup  17  has the same length d 2 ). Further, the distance d 3  between the second rotating shaft  51  and the support shaft  63  for the cup  16  (the distance between the second rotating shaft  52  and the support shaft  64  for the cup  16  has the same length d 3 ) is set to be slightly shorter than the distance d 4  between the second rotating shaft  53  and the support shaft  65  for the cup  17  (the distance between the second rotating shaft  54  and the support shaft  66  for the cup  17  has the same length d 4 ). 
     The direction of rotation of the first rotating shafts  38 ,  39  for the cup  16  and the direction of rotation of the first rotating shafts  40 ,  41  for the cup  17  are mutually opposite, and the direction of rotation of the second rotating shafts  51 ,  52  for the cup  16  and the direction of rotation of the second rotating shafts  53 ,  54  for the cup  17  are also mutually opposite. 
     The first rotating shafts  38 ,  39  and support shafts  63 ,  64 , all for the cup  16 , can be considered as four joints of a parallel linkage mechanism, and the rotation transmission member  35  that corresponds to a linkage in such a parallel linkage mechanism rotates in a horizontal plane while being oriented perpendicularly to the bag conveying path  1  at all times. Likewise, the first rotating shafts  40 ,  41  and support shafts  65 ,  66 , all for the cup  17 , can be considered as four joints of another parallel linkage mechanism, and the rotation transmission member  36  that corresponds to a linkage in such a parallel linkage mechanism rotates in a horizontal plane while being oriented perpendicularly to the bag conveying path  1  at all times. The direction of rotation of the rotation transmission member  35  for the cup  16  and the direction of rotation of the rotation transmission member  36  for the cup  17  are mutually opposite. This rotation of the rotation transmission members  35 ,  36  is a translational motion, and thus, as the rotation transmission members  35 ,  36  rotate, the suction cups  16 ,  17  rotate in mutually opposite directions, with their suction surfaces oriented frontally at all times to face the surface of the bag. 
     As shown in (a)-( 1 ) of  FIG. 10 , the second rotating shaft  51  and the first rotating shaft  38  of the first crank mechanism  55  for the cup  16  are arranged along a line perpendicular to the conveying path  1  (see  FIG. 8 ), and, at the same time, when the second rotating shaft  51  comes to closest to the conveying path  1 , the support shaft  63  and the second rotating shaft  51  of the second crank mechanism  67  for the cup  16  are on a line parallel to the conveying path  1 , and, in addition, the support shaft  63  is positioned on the posterior side of the second rotating shaft  51  (posterior side relative to the bag conveying direction). The same positional relationship applies to the first crank mechanism  56  and the second crank mechanism  68  both for the cup  16 . 
     On the other hand, as far as the first crank mechanisms  57 ,  58  and the second crank mechanism  69 ,  70 , which are all for the cup  17 , are concerned, the directions of rotation of the first rotating shafts  40 ,  41  and the second rotating shafts  53 ,  54  are opposite to those of the first rotating shafts  38 ,  39  and the second rotating shafts  51 ,  52  all for the cup  16 . As shown in (b)-( 1 ) of  FIG. 10 , the second rotating shaft  53  and the first rotating shaft  40  of the first crank mechanism  57  for the cup  17  are on a line perpendicular to the conveying path  1 , and, at the same time, when the second rotating shaft  53  comes farthest from the conveying path  1 , the support shaft  65  and the second rotating shaft  53  of the second crank mechanism  69  for the cup  17  are on a line parallel to the conveying path  1 , and, in addition, the support shaft  65  is positioned on the posterior side of the second rotating shaft  53 . The same positional relationship applies to the first crank mechanism  58  and the second crank mechanism  70  both for the cup  17 . 
     As shown in (a)-( 1 ) through ( 7 ) and (b)-( 1 ) through ( 7 ) of  FIG. 10 , in the first crank mechanisms  55 ,  57  for the cups  16 ,  17 , respectively, the first rotating shafts  38 ,  40  rotate, and the second rotating shafts  51 ,  53  rotate about the first rotating shafts  38 ,  40 , respectively, (or they revolve around first rotating shafts  38 ,  40 , respectively) forward relative to the bag conveying direction; and, in the second crank mechanisms  67 ,  69  for the cups  16 ,  17 , respectively, the second rotating shafts  51 ,  53  turn in a direction opposite to that of the first rotating shafts  38 ,  40 , respectively, and the support shafts  63 ,  65  rotate about the second rotating shafts  51 ,  53 , respectively, forward relative to the bag conveying direction. The rotational trajectory of the support shaft  63  for the cup  16  is the one obtained by combining the motions of the first crank mechanism  55  and the second crank mechanism  67 , while the rotational trajectory of the support shaft  65  for the cup  17  is the one obtained by combining the motions of the first crank mechanism  57  and the second crank mechanism  69 . The symbols “+” shown in  FIG. 10  indicate, at regular time intervals, the rotational trajectories of the support shafts  63  (in (a)),  65  (in (b)) obtained when the first rotating shafts  38 ,  40  for the cups  16  and  17  make the quarter-turn. The same as described above occurs in the first crank mechanism  56 ,  58  and in the second crank mechanisms  68 ,  70 . 
     When the first rotating shafts  38  through  41  make their single rotations, the rotational trajectories of the support shafts  63  through  66  draw a substantially elliptical path. As a result, the rotation transmission member  35  coupled to the support shafts  63 ,  64  for the cup  16  and the rotation transmission member  36  coupled to the support shafts  65 ,  66  for the cup  17  make translational motions along the substantially elliptical moving paths. Therefore, as shown in  FIG. 9 , the suction cup  16  continuously rotates along the substantially elliptical moving path  81  (which is the same as the trajectory of motion and shape of the support shafts  63  and  64  viewed from above), and the suction cup  17  continuously rotates along the substantially elliptical moving path  82  (which is the same as the trajectory of motion and shape of the support shafts  65  and  66  viewed from above) while maintaining the substantially mutually symmetrical positions relative to the suction cup  16 . The symbols “+” in  FIG. 9  that draw the moving paths  81 ,  82  of substantially elliptical shape indicate, at regular time intervals, the rotational trajectories of the suction cups  16 ,  17 . 
     The traveling speed of the suction cups  16 ,  17  is set to closely match the conveying speed V 0  of the bag at the moment when the suction cups  16 ,  17  are closest to the bag conveying path  1 . In addition, as can be seen from the “+” symbols used to draw the moving paths  81 ,  82 , in the bag mouth opening device of the present invention, the traveling speed of the suction cups  16 ,  17  along the moving paths  81 ,  82  becomes higher in the regions where the curvature of the moving paths  81 ,  82  is smaller and becomes lower in the regions where the curvature is larger. In other words, during the bag opening process, the traveling speed of the suction cups  16 ,  17  along the moving paths  81 ,  82  becomes higher as the moving paths  81 ,  82  digress from the conveying path  1 . As a result, when the suction cups  16 ,  17  travel along the moving paths  81 ,  82  after adhering to both sides of the bag  20  by suction, the traveling speed of the suction cups  16 ,  17  in the conveying direction of the bag  20  is maintained at substantially the same speed as the traveling speed of the bag  20 , and their compliance with the bags  20  being conveyed is superior in comparison with a case in which the suction cups  16 ,  17  travel along the moving paths  24 ,  25  at a constant speed (see  FIG. 2 ). 
     The major axes of the moving paths  81 ,  82  are inclined at 45 degrees with respect to the bag conveying path  1 . This is due to the fact that the angle made by the first crank mechanisms  55  through  58  and the respective second crank mechanisms  67  through  70  is set such that when the second rotating shafts  51  through  54  and the first rotating shafts  38  through  41  of the first crank mechanisms  55  through  58  are arranged along the line perpendicular to the bag conveying path  1 , the support shafts  63  through  66  and the second rotating shafts  51  through  54  of the second crank mechanisms  67  through  70  are on the lines parallel to the conveying path  1 , respectively. The angles of inclination in the major axes of the moving paths  81 ,  82  can be changed by changing the angles of the first and second crank mechanisms. 
     In the bag mouth opening device of the present invention, the distance d 1  between the first and second rotating shafts  38  and  51  and between the first and second rotating shafts  39  and  52  (all for the cup  16 ) is set to be slightly shorter than the distance d 2  between the first and second rotating shafts  40  and  53  and between the first and second rotating shafts  41  and  54  (all for the cup  17 ); and further the distance d 3  between the second rotating shaft  51  and the support shaft  63  and between the second rotating shaft  52  and the support shaft  64  (all for the cup  16 ) is set to be slightly shorter than the distance d 4  between the second rotating shaft  53  and the support shaft  65  and between the second rotating shaft  54  and the support shaft  66  (all for the cup  17 ). Because of this arrangement, the circumferential length of the moving path  81  is slightly shorter than that of the moving path  82 , and therefore the traveling speed of the suction cup  16  traveling along the moving path  81  is slightly lower than that of the suction cup  17  traveling along the moving path  82 . Due to this fact that the traveling speeds of the suction cups  16 ,  17  upon their adhesion to the film sheets of both sides of the bag  20  differs slightly, a relative shift, though very minimum, occurs in the bag conveying direction between the two film sheets upon adhesion; and as a result, the close adhesion between the two film sheets is weakened, and the bag  20  can be opened smoothly. 
     In the bag mouth opening device of the present invention, the moving path  81  of the suction cup  16  is defined somewhat more towards the posterior side (toward right in  FIG. 9 ) in the conveying direction of the bags  20  in comparison with the moving path  82  of the suction cup  17 . Therefore, there is a fore-and-aft shift in the bag conveying direction between the positions in which the moving paths  81 ,  82  are closest to the bag conveying path  1 ; and when the suction cups  16 ,  17  come closest to the bag conveying path  1  and adhere by suction to both sides of the bag  20 , there is a slight fore-and-aft shift between the positions of adhesion in the conveying direction of the bag  20 . As a result, when the suction cups  16 ,  17  are moved away from each other, air can easily penetrate between the two film sheets of both sides of the bag  20 , and the bag  20  can be opened smoothly for this reason as well. 
     It should be noted that while a planetary gear mechanism (a sun gear, planetary gears, and driven gears) is employed in the above-described bag mouth opening device of the present invention as a drive mechanism for the second rotating shafts  51  through  54 , it is also possible to provide other drive sources such as servo motors instead of the planetary gear mechanism on the first rotating levers  47  through  50  in order to turn the second rotating shafts  51  through  54 , respectively. In such a structure, the traveling speed of the suctions cups  16 ,  17  along the respective moving paths  81 ,  82  can be adjusted more freely by adjusting the speed of rotation of the second rotating shafts  51  through  54 , and, for example, the speed of travel of the suction cups  16 ,  17  in the conveying direction of the bags  20  during the bag mouth opening process can be set at the same speed as the conveying speed of the bags  20 .