Abstract:
In an embodiment of the invention, a cut/weld apparatus is configured to provide optimal and limited tension of bag material even during high-speed operation. The limited tension may contribute to stronger plastic welds. Another embodiment of the invention, which may be used in combination with the first embodiment, provides a roll discharge stage in a bag manufacturing apparatus that includes a retracting spindle and may include a rotating tray. The improved discharge stage requires less floor space than conventional side-discharge manufacturing equipment.

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to plastic bags, and more particularly, but without limitation, to an apparatus and method for manufacturing a roll of interleaved bags. 
     2. Description of the Related Art 
     Plastic bags are packaged in a variety of configurations. Some packaging variations relate to how the bags are dispensed. For instance, in one known configuration, plastic kitchen garbage bags, shopping bags, or other bags are prepackaged in a roll of pre-cut (separated) bags. Bags within the roll are interleaved prior to rolling such that each bag partially overlaps another. 
     Plastic bag manufacturing is increasingly cost competitive. This is true for rolls of interleaved bags as well as for other bag configurations. 
     One known way to decrease manufacturing cost is to increase the speed of bag manufacturing. This is advantageous because fixed labor costs associated with machine operation can be spread over a higher number of products. Higher-speed bag manufacturing equipment is therefore needed. 
     Facilities are a component of overhead expense. Accordingly, another known way to decrease manufacturing cost is to improve the utilization of factory floor space. Manufacturing equipment features that improve floor space efficiencies are therefore highly desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention seek to address one or more of the cost reduction opportunities described above. In an embodiment of the invention, a cut/weld apparatus is configured to provide optimal and limited tension of bag material even during high-speed operation. The limited tension may contribute to stronger plastic welds. Another embodiment of the invention, which may be used in combination with the first embodiment, provides a roll discharge stage in a bag manufacturing apparatus that includes a retracting spindle and may include a rotating tray. The improved discharge stage requires less floor space than conventional side-discharge manufacturing equipment. 
     More specifically, one embodiment of the invention provides a method for manufacturing bags. The method includes: receiving a tube of film; folding the tube of film to produce folded film; welding one end of the folded film; cutting the folded film to produce a folded bag; interleaving a plurality of folded bags to produce a plurality of interleaved bags; and accumulating the plurality of interleaved bags on a retractable spindle to produce a roll of interleaved bags. 
     Another embodiment of the invention provides a bag manufacturing apparatus. The bag manufacturing apparatus includes a first module, the first module including a first spindle configured to accumulate a plurality of interleaved bags thereon to produce a first roll of interleaved bags during a first accumulation mode, the first spindle further configured to retract from the first roll of interleaved bags along a long axis of the first spindle during a first spindle retraction mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the detailed description below and the accompanying drawings, wherein: 
         FIG. 1  is a flow diagram of a bag manufacturing process, according to an embodiment of the invention; 
         FIG. 2  is a plan view of a formed plastic material, according to an embodiment of the invention; 
         FIG. 3  is a cross-sectional view of a tubular portion along plane A-A in  FIG. 2 , according to an embodiment of the invention; 
         FIG. 4  is a cross-sectional view of a gusset forming tool, according to an embodiment of the invention; 
         FIG. 5  is a cross-sectional view of a gusseted portion along plane B-B in  FIG. 2 , according to an embodiment of the invention; 
         FIG. 6  is a cross-sectional view of a folded portion along plane C-C in  FIG. 2 , according to an embodiment of the invention; 
         FIG. 7A  is a cross-sectional elevation view of a die set in a first position, according to an embodiment of the invention; 
         FIG. 7B  is a cross-sectional elevation view of a die set in a second position, according to an embodiment of the invention; 
         FIG. 7C  is a cross-sectional elevation view of a die set in a third position, according to an embodiment of the invention; 
         FIG. 8  is a flow diagram of a bag manufacturing process, according to an embodiment of the invention; 
         FIGS. 9A through 9F  are sequential elevation views of a roll accumulation and discharge station, according to an embodiment of the invention; 
         FIGS. 1A through 10F  are sequential plan views of a roll accumulation and discharge station, according to an embodiment of the invention; 
         FIG. 11A  is an elevation view of a dual accumulation and discharge station, according to an embodiment of the invention; 
         FIG. 11B  is a plan view of the dual accumulation and discharge station in  FIG. 10A ; 
         FIG. 12A  is a schematic diagram of a pneumatic valve in a first mode, according to an embodiment of the invention; and 
         FIG. 12B  is a schematic diagram of a pneumatic valve in a second mode, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described more fully with reference to  FIGS. 1-11B , in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, reference designators may be duplicated for the same or similar features. The figures are not drawn to scale; some features may be exaggerated for clarity. 
       FIG. 1  is a flow diagram of a bag manufacturing process, according to an embodiment of the invention. As shown therein, the process begins in step  105 . Then, the process receives a tube of film in step  110  and folds the tube of film to produce folded film in step  115 . In step  120 , the process welds a first portion of the folded film. The process cuts a second portion of the folded film to produce a bag in step  125 . Next, in step  130 , the process interleaves a plurality of the bags to produce a plurality of interleaved bags. In step  135 , the process provides a vacuum at a plurality of holes on a spindle surface. Then, in step  140 , the process accumulates the plurality of interleaved bags onto the spindle to produce a roll of interleaved bags. The process discharges the roll of interleaved bags in step  145  and terminates in step  150 . 
     Variations to the process illustrated in  FIG. 1  are possible. For example, step  115  may be omitted, according to design choice. In such an instance, the process would operate on the tube of film. In an alternative embodiment, the order of steps  120  and  125  may be reversed. Moreover, in embodiments of the invention, steps  120  and  125  may be performed together. For example, a top of one bag may be cut at the same time a bottom of another bag is sealed. 
       FIGS. 2-6  below illustrate the configuration of a tube of film during the folding step  115 , according to an embodiment of the invention. 
       FIG. 2  is a plan view of a formed plastic material, according to an embodiment of the invention.  FIG. 2  illustrates the progression of formed plastic film (sometimes referred to as a web) in a bag manufacturing process. In sequence,  FIG. 2  shows a tubular portion  205 , a gusseted or 4-layered portion  210 , and a folded or 8-layered portion  215 . The tubular portion  205  may be as received in step  110 . The gusseted or 4-layered portion  210  or the 8-layered portion  215  may be as output from step  115 .  FIGS. 3 ,  4 , and  5  provide cross sectional views of the tubular portion  205 , 4-layered portion  210  and 8-layered portion  215 , respectively. 
       FIG. 3  is a cross-sectional view of the tubular portion  205  along plane A-A in  FIG. 2 , according to an embodiment of the invention. The tubular portion  205  may be, for example, several inches or several feet in diameter, according to application demands. 
       FIG. 4  is a cross-sectional view of a gusset forming tool, according to an embodiment of the invention;  FIG. 5  is a cross-sectional view of the gusseted portion  210  along plane B-B in  FIG. 2 , according to an embodiment of the invention. As shown in  FIG. 4 , the tubular portion  205  may be deformed using gusset forming tools  405  and  410 . In the illustrated embodiment, the gusseting tools  405  and  410  substantially meet along a center line  220  of the 4-layered portion  210 . The gusseting tools  405  and  410  may be, for instance, constructed of wood or other thermal insulator. The resulting structure of the 4-layered portion  210  is shown in  FIG. 5 . As illustrated therein, except at the center line  220 , the 4-layered portion  210  includes a first, second, third, and fourth layer  505 ,  510 ,  515 , and  520 , respectively. Layers  510  and  515  are the gusset layers. 
       FIG. 6  is a cross-sectional view of the folded portion  215  along plane C-C in  FIG. 2 , according to an embodiment of the invention. The 8-layered portion  215  is formed by folding the 4-layered portion  210  onto itself. The center line  220  is the fold line. The resulting 8-layered structure  215  includes first, second, third, fourth, fifth, sixth, seventh, and eighth layers  605 ,  610 ,  615 ,  620 ,  625 ,  630 ,  635 , and  640 , respectively. 
       FIGS. 7A-7C  illustrate a die set than can be used, for instance, in executing welding step  120  and cutting step  125 . 
       FIG. 7A  is a cross-sectional elevation view of a die set in a first position, according to an embodiment of the invention. As shown therein, a web  705  is disposed between an upper die set  700  and a lower die set  745 . The upper die set  700  includes outer-holding knives  715  and  740 , inner-holding knives  725  and  735 , heating tip  720 , and cutting knife  730 . As illustrated in  FIG. 7A , the web  705  may be positioned, for instance by a conveyer, between the upper die set  700  and the lower die set  745 . 
       FIG. 7B  is a cross-sectional elevation view of a die set in a second position, according to an embodiment of the invention. As shown therein, in the second position, the outer-holding knives  715  and  740 , and the inner-holding knives  725  and  735  are disposed in a lower position to secure the web  705  with limited tension prior to welding step  120  and cutting step  125 . 
       FIG. 7C  is a cross-sectional elevation view of a die set in a third position, according to an embodiment of the invention. As shown therein, the outer-knives  715  and  740  and inner-holding knives  725  and  735  remain in the lower position to secure the web  705 . Additionally, the cutting knife  730  and the heating tip  720  are disposed in a lower position. In operation, the cutting knife  730  separates the web  705  into webs  707  and  709  in cutting step  125 . The outer-holding knife  715  and the inner holding knife  725  secure the web  709  as the heating tip  720  seals a portion of the web  709  during welding step  120 . 
     The outer holding knives  715  and  740 , and the inner holding knives  725  and  735 , may enable optimal and limited tension on the web  705  even during high-speed operation. Limited tension can be beneficial during welding step  120  because it produces a more robust plastic weld than one formed under a relatively higher degree of tension. 
     Variations to the configurations illustrated in  FIGS. 7A-7C  are possible. For instance, in an alternative embodiment, a portion of the lower die  745  that is opposite the heating tip  720  may be heated and may also move in a vertical plane so that it only contacts the web  705  ( 709 ) during the welding step  120 . 
       FIG. 8  is a flow diagram of a bag manufacturing process, according to an embodiment of the invention.  FIG. 8  illustrates a process for performing the discharge step  145 , according to one embodiment of the invention. As shown in  FIG. 8 , the process begins in step  805 , and then disposes a tray in a first position under the roll of interleaved bags in step  810 . The process then produces an exhaust at multiple holes on a surface of a spindle in step  815 . Next, in step  820 , with continued exhaust from the spindle, the process retracts the spindle from the roll of interleaved bags. The process cradles the roll of interleaved bags on a tray in step  825 , and then rotates the tray to a second (discharge) position in step  830 . In step  835 , the process disposes a retaining bar behind the roll of interleaved bags. The process then retracts the tray in step  845 , which discharges the roll of interleaved bags. The process terminates in step  850 . 
     Variations to the process illustrated in  FIG. 8  are possible. For instance step  810  could include producing an exhaust at a single elongated hole in the spindle, instead of at multiple holes in the spindle. Alternatively, step  810  could be omitted.  FIGS. 9A-9F ,  10 A- 10 F,  11 A,  11 B,  12 A, and  12 B illustrate components of an apparatus that can be used in executing the accumulation step  140  and/or the discharge step  145 . 
       FIGS. 9A through 9F  are sequential elevation views of a roll accumulation and discharge station, according to an embodiment of the invention. The sequence illustrated in  FIGS. 9A through 9F  may be consistent with the process flow illustrated in  FIG. 8 . For clarity, only selected components of an accumulation and discharge station are illustrated. 
       FIG. 9A  illustrates that a roll of bags  905  has accumulated on a spindle  910 . The spindle  910  includes multiple holes  912 .  FIG. 9A  further illustrates a retaining arm  915  having a pivot point  920 . In  FIG. 9A , the retaining arm  915  is not in a retention position.  FIG. 9A  further illustrates an end view of a tray  925  and an elevation view of a discharge ramp  930 .  FIG. 9A  may thus illustrate an apparatus configuration associated with the accumulation step  140 . 
       FIG. 9B  illustrates the apparatus configuration during process steps  810 ,  815 , and  820 . As shown therein, the spindle  910  has begun to retract in a direction  935 . In addition, the tray  925  is disposed to support the roll of bags  905 . In one embodiment, the apparatus is configured so that the roll of bags  905  falls onto the tray  925  once the spindle  910  has fully retracted. In another embodiment, the apparatus is configured so that the tray  925  also supports the roll of bags  905  while the spindle  910  is being retracted. 
       FIG. 9C  illustrates the apparatus configuration upon completion of step  830 , for instance. As shown in  FIG. 9C , the tray  925  fully supports the roll of bags  905  and has rotated 90 degrees as compared to the position illustrated in  FIG. 9B . In  FIG. 9C , the roll of bags  905  and tray  925  are in a discharge position. 
       FIG. 9D  illustrates the apparatus configuration upon completion of step  835 . As shown therein, the retaining bar  915  has rotated about the pivot point  920  to retain the roll of bags  905 . 
       FIG. 9E  illustrates the apparatus configuration upon completion of step  840 . In  FIG. 9E , the tray  925  has retracted (into the page) from the discharge position. The roll of bags  905  has dropped to contact the discharge ramp  930 . 
       FIG. 9F  illustrates the apparatus configuration at or near the conclusion of step  845 . As shown in  FIG. 9F , the retaining bar  915  has rotated about the pivot point  920  away from a retaining position. Accordingly, the roll of bags  905  is free to follow the slope of the discharge ramp  930 . 
     Variations to the apparatus illustrated in  FIGS. 9A-9F  are possible. For instance, in an alternative embodiment, the discharge ramp  930  could be replaced by a collection bin. 
       FIGS. 10A through 10F  are sequential plan views of a roll accumulation and discharge station, according to an embodiment of the invention. The station illustrated in  FIG. 10A  illustrates the relative positions of a roll of bags  1005 , spindle  1010 , a tray  1025 , a discharge ramp  1030 , and a conveyor  1070  that is configured to move in a direction  1075 . The station in  FIG. 10A  illustrates relative component positions during accumulation step  140 , for instance. 
     Upon completion of the accumulation step  140 , the tray  1025  may first extend as illustrated in  FIG. 10B , and rotate in a clockwise direction about pivot point  1065  as illustrated in  FIG. 10C , until the tray  1025  is disposed under the roll of bags  1005  as illustrated in  FIG. 10D . Together,  FIGS. 10B ,  10 C, and  10 D illustrate sequential operations of an accumulation and discharge station during process step  810 . 
       FIG. 10D  also illustrates the relative positions of components of an accumulation and discharge station during process steps  815 ,  820 , and  825 , except of course that the spindle  1010  is retracted in process step  820 . 
       FIG. 10E  illustrates that, during the execution of process step  830 , the roll of bags  1005  is rotated to a second position by the tray  1025 . As shown, the tray  1025  may be rotated in a counter-clockwise direction about the pivot point  1065 . 
       FIG. 10F  illustrates the relative position of components at the conclusion of step  840 . The retaining bar  1020  is disposed at one end of the roll of bags  1005  in process step  835 . The tray  1025  is retracted into the illustrated position in process step  840 . At the conclusion of process step  840 , the roll of bags  1005  has been discharged onto the discharge ramp  1030 . 
       FIG. 11A  is an elevation view of a dual accumulation and discharge station, according to an embodiment of the invention. As shown therein, a dual accumulation and discharge station services two bag manufacturing lines. For instance, one line is serviced by the first accumulation and discharge station  1001 ; a second line is serviced by a second accumulation and discharge station  1002 . 
     The first accumulation and discharge station  1001  includes a spindle  1010  configured to accumulate a roll of bags  1005 . The spindle  1010  is further configured to move in a direction  1015 .  FIG. 11A  also illustrates that a retaining arm  1020  is disposed in a non-retaining position and that a tray  1025  is disposed over a discharge ramp  1030 . The second accumulation and discharge station  1002  includes a spindle  1040  configured to accumulate a roll of bags  1035 . The spindle  1040  is configured to move in a direction  1045 . The direction  1045  is opposite the direction  1015 . The second discharge station  1002  also includes a retaining arm  1050 , a tray  1055 , and a discharge ramp  1060 . 
     An advantage of the configuration illustrated in  FIG. 11A  is that two bag manufacturing lines can be disposed next to each other. Such a configuration is enabled by the retractable spindles  1010  and  1040  and by the rotating trays  1025  and  1055  that facilitate discharge of the rolls  1005  and  1035 , respectively, from the end of each manufacturing line. 
       FIG. 11B  is a plan view of the dual accumulation and discharge station in  FIG. 11A . As illustrated in  FIG. 10B , the first bag accumulation and discharge station  1001  also includes a conveyer  1070  that is configured to move in a direction  1075 . Additionally,  FIG. 11B  illustrates that the second accumulation and discharge station  1002  includes a conveyer  1085  that is configured to move in a direction  1090 .  FIG. 11B  further illustrates a pivot point  1065  associated with the tray  1025 , the pivot point  1065  allowing the tray to move between a catching position and a discharge position. Likewise,  FIG. 11B  illustrates a pivot point  1080  associated with the tray  1055  that permits the tray  1055  to move between a catching position and a discharge position. 
       FIGS. 11A and 11B  thus highlight how two accumulation and discharge stations  1001  and  1002  can be disposed next to each other in a manufacturing facility. Such a layout may improve layout efficiencies compared to conventional bag manufacturing equipment that is configured to discharge a roll of bags to the side. 
       FIGS. 12A and 12B  illustrate a pneumatic valve  1200  that is coupled between an air supply  1225  and holes  912  in the spindle  910 . The same valve  1200  could be used in conjunction with spindles  1010  and/or  1040 . 
       FIG. 12A  is a schematic diagram of a pneumatic valve in a first mode, according to an embodiment of the invention. As shown therein, the pneumatic valve  1200  includes ports  1205 ,  1210 , and  1215 . The valve  1200  further includes an actuator  1220  coupled to each of the ports  1205 ,  1210 , and  1215 . In the configuration illustrated in  FIG. 12A , an air supply  1225  is coupled to the port  1205 . A spindle  910  is coupled to the port  1210 . Port  1215  is vented. In the configuration illustrated in  FIG. 12A , a vacuum is created at the spindle  910 . The configuration shown in  FIG. 12A  may be used, for instance, during accumulation step  140 . 
       FIG. 12B  is a schematic diagram of a pneumatic valve in a second mode, according to an embodiment of the invention. In the configuration illustrated in  FIG. 12B , the exhaust port  1215  is in a closed position. Accordingly, an air supply  1225  at the port  1205  is exhausted at port  1210  to the spindle  910 . The configuration illustrated in  FIG. 12B  may be used, for instance, during discharge step  145 . 
     It will be apparent to those skilled in the art that modifications and variations can be made without deviating from the spirit or scope of the invention. For example, features described herein could be combined in ways not explicitly illustrated or disclosed. Thus, it is intended that the present invention cover any such modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.