Abstract:
A vacuum holder for use with an automated carton erecting and packing line and mountable on a rotary carton placer for removing cartons into which product is to be placed includes vacuum cup for removing a carton from a store of cartons. The cartons including a foldable flap. The vacuum holder includes a set of vacuum cups that will engage a flap and at an appropriate time in the carton erection sequence will be positively actuated under control of a power actuator to fold the flap to a desired position prior to depositing the carton on a conveyor line. A rotary manifold carries both vacuum for vacuum cups holding the carton, and fluid pressure for the power actuators to the rotating carton placer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/259,581, filed Mar. 1, 1995, now abandoned, which is a divisional of U.S. application Ser. No. 08/718,142, filed Sep. 18, 1996, which referred to and claimed priority on U.S. Provisional Application Ser. No. 60/022,110, filed Jul. 17, 1996, which claim of priority is continued. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a vacuum cup carton handler for a carton loading machine which has a handling section that will bend a flap on a carton to be filled along its score line automatically before depositing the carton onto a conveyor for inserting product. 
     Rotary placers have long been used for handling cartons and carton loading machines. One such device is shown in U.S. Pat. No. 5,456,570. It includes a vacuum holder for receiving cartons from a store or supply, and then moves the carton to a position where it will be deposited on a conveyor for subsequent loading of products into the carton. Vacuum cups are used for holding the carton while the rotary placer moves the carton to the conveyor, and then a control is used for releasing the vacuum so that the carton can be moved along the conveyor. However, U.S. Pat. No. 5,456,570 does not include any structure for positively moving or “breaking” a carton flap between two positions. 
     Carton formation systems of various kinds have been used for erecting cartons so that they can be appropriately packed, and for example U.S. Pat. No. 5,106,359 shows such a provision. The present invention fulfills a need for properly breaking or bending a carton flap along a score line for ease in subsequent handling and loading. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a vacuum gripper used for handling cartons, and which is preferably mounted onto a rotary type placer that will pick a carton at a store station, and will move the carton to a station where it will be released onto a conveyor so that the carton can subsequently be packed. The carton is preferably erected at the time it is deposited on the conveyor, and normally this is done by “breaker bars” or other devices that will engage the carton and cause the carton to be folded from a flat position to an erected position. Cartons have to be closed after they are filled, and normally flaps are provided on at least some of the side panels of the carton along score lines which permit folding the flaps from a flat position to an “open” position where it does not cover the end of the carton. 
     The present handler includes an auxiliary set of vacuum cups that will engage a carton flap, and by actuation of a power actuator, in the form shown, a pneumatic cylinder operated under air pressure, will be moved through a linkage to bend a carton flap substantially 90° about its score line. The flap will then be in an open position when deposited on a conveyor and thereafter can be maintained in such position by guides on the conveyor. 
     The present placer includes the provision of both vacuum and air pressure to the rotary carton handler disclosed, so that the operation of the power actuator can be at any desired annular location in the rotation of the unit. As shown, a vacuum and air pressure slip ring assembly is mounted onto a mounting shaft of the rotary placer on which the carton handling device of the present invention is used, using interfacing surfaces, one stationary and one rotating, that will provide a vacuum and air pressure seal between a stationary member and a rotating member that rotates with the rotary placer. The provision of both vacuum and air pressure to control the handling of the carton provides an efficient way of having actuators mounted on a rotating element for carton manipulation. The manifold forms an important part of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a rotary placer having a carton erecting assembly made according to the present invention installed thereon; 
     FIG. 2 is a side elevational view of the device of FIG. 1 schematically shown with parts in section and parts broken away; 
     FIG. 2A is a fragmentary sectional view of a guide slot for controlling arm movement taken on line  2 A— 2 A in FIG. 2; 
     FIG. 3 is a fragmentary enlarged side elevational view of a vacuum cup linkage mechanism used with the present invention in an actuated position; 
     FIG. 4 is a top plan view of the linkage in FIG. 3 in an initial position; 
     FIG. 4A is a front elevational view of the linkage of FIG. 4; 
     FIG. 5 is a schematic perspective view of the linkage of the present invention in a carton receiving position; 
     FIG. 6 is a schematic perspective view of the device in the present invention in a position where it will deliver a carton with a folded flap to a conveyor; 
     FIG. 7 is a sectional view of a manifold used for transferring both vacuum and air pressure to a rotary placer with parts in section and parts broken away; 
     FIG. 8 is a view taken as on line  8 — 8  in FIG. 7; 
     FIG. 9 is a view taken as on line  9 — 9  in FIG. 7 with parts broken away to show a second portion of the assembly; 
     FIG. 10 is a sectional view taken as on line  10 — 10  in FIG. 7; and 
     FIG. 11 is a sectional view taken as on line  11 — 11  in FIG. 7, which is the same line as the view of FIG. 10 but looking in an opposite direction. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the particular type of rotary placer that is utilized is not essential or part of the invention, the rotary placer is partially shown in FIGS. 1 and 2 schematically. Rotary placer  10  is to be used to pick up a carton or other item  11  in a desired position, called a “pick” position from a supply or store  13  having a plurality of cartons and moves the carton to a conveyor that is shown only schematically in FIG. 6 at a place position to place a carton on the conveyor for opening and filling. The rotary placer  10  has a frame  12  mounted on a shaft  14  for rotation about a central axis indicated generally at  15 . A hub  16  and suitable locking members drivably connect the frame  12  to the shaft  14 . Motor and drive  17  rotates the shaft  14  and thus the frame  12  about the central axis  15 . The shaft  14  is mounted on suitable bearings  18  to the machine frame  19  shown only schematically. The pick and place positions are at desired locations to fit the carton loading machine used. 
     As shown, the frame  12  includes three sections for mounting three separate arm assemblies  22 ,  23  and  24 , respectively 120° apart. There can be two or more, for example up to eight arms assemblies on the frame. Only one arm assembly is shown completely, but it is to be understood that each of the arm assemblies is constructed identically. The arm assemblies  22 ,  23  and  24  are controlled in their motion during rotation of the frame  12 , by a gear set shown generally at  26 , which includes a fixed gear  27  and planet gears  28  that are mounted on suitable shafts which will rotate on bearings relative to the frame  12 . The fixed gear  27  is supported on a hub  30  that is mounted through bearings to the shaft  14  and then held from rotation in a suitable manner, as shown schematically with an arm  32  that is supported relative to the machine frame  19  in a suitable manner. The shaft  14  thus can rotate relative to the gear  27 . The planet gears  28 , as shown, are mounted on suitable shafts  34  and bearing housings  36  mounted on the frame  12 . The planet gears  28  rotate about the central or sun gear  27  when the frame  12  is rotated, and as they do, they also rotate about the axis of the shafts  34  in a known manner. It should be noted that the gear  27  is also mounted on suitable bushings on the shaft  14 , so that the gear can remain stationary as the shaft  14  and the frame  12  rotate. 
     Each of the shafts  34  has a crank arm  38  fixed at an end thereof on an opposite side of the frame  12  from the gears  27  and  28 . Crank arms  38  are used to control movement of a carton pickup assembly indicated generally at  40 , mounted at an outer end of a slider shaft  42 . The slider shaft  42  is reciprocated by the crank arm  38  as the crank arm rotates. A crank pin  44  at the end of the crank arm  38  drives the slider shaft through suitable bearings on the crank pin. The slider shaft  42  is slidably mounted in a hub or housing  46  supported at the outer end of an arm  55  forming one arm of a bell crank assembly  48 . The hub  46  is pivotally mounted on a suitable pin  50  in bearings, at the end of arm  55  of the bell crank assembly  48 . The bell crank assembly  48  in turn is mounted at the inner end of arm  55  on a pivot pin  52  that is secured to the rotating frame  12 . A control arm portion  54  is fixed to an arm  55 . Control arm  54  has a cam follower roller  61  at its outer end (see FIG. 2A) on an opposite side of the arm  54  from that shown in FIG.  2 . The roller rides in a cam track  60  formed in the side of the plate  12  and will move along the cam track  60  to cause the arm  55  and thus hub  46  to move in a desired path as the crank  38  rotates. 
     As the crank arm  38  rotates about the axis of the crank pin  34 , it will cause the slider  42  to move in and out relative to the slider hub  46 . Because of the needed geometry for the operation of the carton pickup assembly  40 , the cam track  60  is provided to permit the arm  52  of the bell crank to move about the axis of the mounting pin  52 , which causes the arm  55  to move and control the position of the carton pickup assembly. 
     The outer end of the slider  42  supports the carton pickup assembly  40 , which includes vacuum cup frame assembly  64 . The vacuum cups are provided with a vacuum through a hose in a conventional manner, as can be seen schematically in FIGS. 5 and 6. Suitable vacuum is provided through a control manifold  68  that transfers both vacuum and air under pressure, as will be explained. The vacuum hoses are just shown schematically at  69  in FIGS. 5 and 6, because they are conventionally used. 
     The vacuum cup frame  64  includes a main cross member  70  that is supported fixedly on a threaded portion and nut at the end of the slider shaft  42 . The cross member  70  thus reciprocates in and out with slider shaft  42  as the crank  38  rotates when above frame  12  is rotating. The position of the cross member  70  is selected to mate with the carton store  13  for holding the cartons  11  at a pick position, to position above a conveyor which is shown schematically in FIG.  6 . 
     The cross member  70  carries a pair of vacuum cups  72  (or more) that are spaced apart a suitable distance and have cup edges that lie on a common plane that is the plane of an exterior surface of a carton  11 . 
     The cross member  70  has a pair of depending brackets  74  fixed thereon as can be seen in FIGS. 2 and 2A. These brackets in turn support a carton flap folding assembly  76 . The carton flap folding assembly  76  includes a pair of pivoting angled brackets  78  that as shown have angularly offset portions. The brackets have mounting shank portions  80  that adjustably mount an auxiliary vacuum cup cross member  82 . The mountings can be adjusted as to length. The cross member  82  in turn mounts suitable vacuum cups  84 . As shown in FIGS. 5 and 6 there can be three such vacuum cups  84 , and each of them is connected to a suitable vacuum line  69  in a normal manner coming from the manifold assembly  68 . 
     The position of the flap folding vacuum cup cross member  82  about the pivots of the pins  79 , which mount members  78  in position is controlled by a control linkage indicated generally at  86 . The control linkage  86  includes a pair of arms  88 ,  88  which are fixed to the cross member  70  in a suitable manner. The arms can be welded to the cross member  70  or can be integrally cast with the cross member. The support arms  88  extend away from the plane of the vacuum cups  84  and the carton  11 , and toward the support hub  46  for the slider shaft  42 . The support arms  88  in turn mount a pivoting shaft  90 , at outer end of the arms. The shaft  90  pivots relative to the arms. The shaft  90  forms a bell crank pivot for an arm  92  fixed to one end of the shaft. A pair of long actuator arms are also fixed to the shaft  90  and move when arm  92  pivots the shaft. A short actuator arm  96  is also attached to the shaft  90  and is positioned between support arms  88 . 
     The long actuator arms  92  are pivotally connected to links  98  through a suitable pivot pin  99 . The links have opposite ends connected through pivot pins  100  to brackets  102  fixed to carton flap folding assembly cross member  82 . 
     The actuator arm  92  is operated through the use of a double action fluid pressure actuator  106 , comprising an air cylinder that is mounted at a base end on a support arm  108 . The actuator  106  is held in this position so that it cannot rotate about the pin mounting at the base end. The actuator  106  in turn has an extendible and retractable rod  110  with a rod end  112  that connects through a suitable pin to the actuator arm  92 . In the position shown in FIGS. 2 and 3, the auxiliary carton flap folding vacuum cup lies on a plane with the edges of the vacuum holding cups  72 . 
     When the rod  110  is extended, under suitable control as will be explained, the actuator arm  92  will move forwardly position represented in direction by the arrow adjacent the rod end  112  in FIG. 2, and this will cause shaft  90  to pivot, moving the long actuator arms  94 . The arms  94  pull the link  98  upward to a position wherein the cross member  88  is in the location shown in solid lines in FIG.  3 . This will move the vacuum cups  84  to move substantially 90° and to hold a flap represented in dotted lines in FIG. 3 to a 90° position from the main portion of the carton. This will be done in a desired location during the cycles or rotation of the rotary frame  12 . The pivot axis indicated at  114  in FIG. 3 between the flap folding frame  76  and the support brackets or hubs  74  will be located in a position where axis will lie even with a score line of a carton  11  that is held in the vacuum cups  72 . When the vacuum cups  84  move to the position shown in FIG. 3, the fold will come be made at the score line. It should be noted that the score line is actually offset forwardly (or downwardly) slightly from this pivot, but the score line will fold around the end of the brackets so that a neat, useable fold of the flap indicated at  11 A in FIG. 3 will be made. 
     The short actuator arm  96  is used for controlling a breaker bar  116  pivoted on a shaft  117  that is supported on arms  88  through a link  118  that will push a carton held by the vacuum cups  72  away from these cups at the time of folding the flap and aid in release of the carton when it is in its position adjacent the conveyor as shown in FIG.  6 . The vacuum to the vacuum cups  72  and  84  will be released when the carton is properly placed. 
     The vacuum-fluid pressure manifold assembly  68  is shown in FIGS. 7 through 11. Referring specifically to FIG. 7, the manifold assembly  68  is mounted onto the main shaft  14 , and includes a non-rotatable or stationary hub  170 , which is rotatably mounted on the shaft  14  through a suitable bushing  172 . The hub  170  has an end plate  174 , and a sleeve like hub  176  surrounding the bushing  172 . A thrust bearing  178  is fixed adjacent the end of the shaft  14  and is used for reacting the loads that are created on plate  70 , as will be explained, between the rotating and stationary portions of the manifold assembly  68 . A pressure valve piston  180  is mounted on the interior of an outer support ring or sleeve  182  that is also fixed to the plate  174  on an opposite side from bearing  178 . The sleeve or ring  182  is concentric with and spaced radially outwardly from the hub  176 . 
     The piston  180  has an inner cylindrical surface that rides on the outer surface of the sleeve like hub  176 , and is provided with a pair of O-rings indicated at  184  that are spaced axially, and slidably seal against the hub  176 . The outer surface of the piston  180  is slidably mounted on the interior of the support sleeve or ring  182  and is also sealed relatively to the interior surface of the sleeve  182  with a pair of O-rings shown generally at  186 . 
     The piston  180  is slidably mounted for axially movement in direction along the axis of the shaft  14 , and is held from rotation relative to the hub on a plurality of pins  188  that are fixed in three radial locations around the central axis of the plate  174 . The pins  188  are slidably mounted in suitable receptacles or bores  190  formed in the side of the piston that faces the plate  174 . A spring  192  is mounted on each of these pins  188  and provides a resilient urging tending to move the piston along the inner surface of the sleeve  182  and the outer surface of the hub  176  away from the plate  174 . 
     The hub plate  174  is also used for supporting a vacuum valve ring indicated generally at  198 . The vacuum valve ring  198  includes a low friction material portion  200 , which can be a suitable plastic, and a steel plate  202  that is used for a backing plate. 
     The valve ring  198  is used for providing ports or openings (see FIG. 9) for threading in vacuum fittings. These bores are shown at  202 A and  202 B in FIG. 9, and serve the function of providing a vacuum from a source to the rotating portions of the rotary pick and place unit, as well as providing for a vacuum exhaust. 
     The vacuum valve ring  198  is held from rotation in a suitable manner relative to the hub  170 , and is urged axially away from the plate  174  through the use of springs  204  that are mounted onto pins  205  located radially outwardly from the pins  188 . 
     The vacuum valve ring portion  200  has a pair of part annular slots defined therethrough, and these are on the opposite side of the steel backing plate  202 , as shown generally in FIG. 10, from ports or bores  202 A and  202 B and open to the bores  202 A and  202 B. These slots indicated at  206 , which is a long part annular slot that extends all the way through the unit, and a vacuum relief slot or exhaust slot indicated generally at  208  that is relatively shorter. 
     The surface  201  of the vacuum valve portion  200 , and the surface  181  of the piston  180  face in the same direction and are coplanar in use. Both surfaces  181  and  201  ride against a mating surface  211  of a distribution manifold section  210  that is fixed in position on the shaft  14  and rotates with the shaft. Set screws and a drive key are used for fixing the manifold section in position. For example, set screws  213  can be used for clamping onto the shaft  14  axially. A drive key is used to drive the manifold section. 
     The piston  181  for the pressure actuation is made of a suitable low friction material such as plastic as well, and the distribution manifold section is made of steel but has a smooth surface against which the plastic parts ride to effect a fluid pressure seal as the manifold section rotates with the shaft  14 . 
     The valve slots  202 A and  202 B in the vacuum valve section  200  extend all the way through to the surface  201 , and as will be explained open to suitable ports in the manifold section  210  as the manifold section rotates. 
     As perhaps best seen in FIG. 10, the piston  180  is provided with a number of annular grooves on the surface  181 , that are used for carrying pressure to the manifold section  210 . Since the actuators  106  for actuating are double acting, it is necessary to provide a pressure connection to opposite ends of the actuators. In other words, pressure to a base end of an actuator  106  will cause the rod to extend, but at the same time an exhaust passage has to be provided at the port at the rod end of the actuator  106 . This is done by having a part annular groove for carrying fluid pressure to or permitting pressure to bleed from the base end port of the actuators  106 , and separate part annular groove sections, spaced at a different radial location, for carrying the pressure to or from the rod end of the actuators  106 . As shown in FIG. 10, a first part annular groove section indicated at  214 A is used for permitting air to exhaust from the base end of the cylinders, and is called an “extend” pressure exhaust. This groove  214 A has a number of radially extending passageways  215  that discharge to the periphery of the piston  180  and then are capable of being bled out of the manifold through passageways  216  adjacent the inner diameter of the vacuum valve ring section  200  and its backing plate  202 . 
     On the same radius, but separated therefrom, a second base end groove  214 B is provided in surface  181  as a pressure providing groove for the base end of each of the actuators  106 , and this groove  214 B has a plurality of passageways  217  that extend axially, and as shown in FIG. 7 communicate with a sealed plenum  218  formed within support sleeve  182  and between piston  181  and plate  174 . The plenum  218  is connected to communicate a source of pressure  220 . The groove or recess  214 B is separated from the ends of the groove or recess  214 A with a surface portion  214 C (which is part of surface  181 ) at opposite ends thereof. The grooves  214 A and  214 B are positioned so that there is proper timing for holding the base end of the respective actuators  106  under pressure to extend the appropriate rod for actuating the bracket that controls the auxiliary vacuum cups  82  to pull the carton flap substantially 90° at the proper position. 
     A part annular groove  222 A is formed in piston  180  radially inwardly from the groove sections  214 A and  214 B, and the part annular groove  222 A has a plurality of exhaust passageways indicated at  223  to bleed to the exterior of the piston  180 , and thus also exhaust to the atmosphere when it is desired to extend the rod of the actuator  106 . Annularly aligning (at the same radial position), part annular groove  222 B is the pressure carrying groove for providing pressure to the rod end of the actuators  106 . As can be seen, groove section  222 B is at the same radially distance as the groove section  222 A and has a plurality of pressure ports  224  formed axially in the piston  181 , and leading to plenum  218  and source of pressure  220 . It should be noted that the part annular groove  222 A providing exhaust for the rod end of the actuators  106 , overlaps one portion of the groove section  214 A that provides exhaust for the base end of the actuators in order to obtain proper operation. The positions where pressure is applied to either the rod or the base end of the actuator is also selected by the length of the groove sections  222 A and  222 B. The part annular groove sections  222 A and  222 B are separated by surface portions  225 , to provide a time when there would be no pressure or exhaust provided to the port on the rod end of the actuator. 
     The distribution manifold section  210  for both vacuum and pressure receives the pressure and vacuum from the piston pressure valve  181  and vacuum valve ring  198 , respectively. As shown in FIG. 11, the distribution manifold section  210 , which rotates with the shaft  14  and which has the surface  111  that is formed flat and true and is used as a sealing surface relative to the piston  181  and vacuum valve  198  is provided with three vacuum outlet ports indicated generally at  230 A,  230 B and  230 C, and each of these ports is made for use with one of the actuators  106  and the associated vacuum cups. The vacuum ports  230 A,  230 B and  230 C are each connected through a radial bore  231 A,  231 B and  231 C to the exterior or peripheral surface  232  of the distribution manifold section. 
     Additionally, the distribution manifold section  210  has a set of retract pressure ports which essentially are rod end pressure ports  234 A,  234 B and  234 C, which are the same radial distance out from the center of shaft  14  as the respective groove portions  222 A and  222 B on the piston pressure valve  180 . That means that as the piston pressure valve  180  is held stationary and the distribution manifold section rotates past the groove sections  222 A and  222 B, the ports  234 A,  234 B and  234 C will alternately be provided with fluid under pressure from the source  220  through the piston grooves and as they rotate past groove section  222 B will be permitted to exhaust to atmosphere through the radial passages  223  that open to the groove section  222 A. The outer ends of each of the radial bores  235 A,  235 B and  235 C, which are open to the ports  234 A- 234 C is provided with a threaded outer end for attaching suitable pressure lines such as that shown at  236  through a suitable fitting. There are separate pressure lines to each of the passageways  235 A- 235 C leading to a separate one of the actuators  106  for the separate vacuum cup assemblies. 
     The base ends of each of the actuators  106  is provided with the fluid under pressure, or connection to exhaust passageways through a plurality of axially extending ports  238 A,  238 B and  238 C that are spaced radially outwardly from the center of rotation of the shaft  214  a greater distance than the ports  224 , so that the ports  238  align with the part annular grooves  214 A and  214 B. The ports  238 A- 238 C are connected to radial passageways  239 A,  239 B and  239 C that have threaded ends for connection to suitable threaded fittings such as that shown at  240 , which provide pressure lines connected to the base ends of the respective actuators  106 . 
     Since the distribution manifold section  210  rotates with the shaft  214 , it also rotates with the frame that supports the vacuum cup assemblies, so that the transfer of fluid pressure between the stationary member and the rotating member occurs right at the interface between the surfaces  181  and the surface  211 . By having the part annular grooves  214 A and  214 B for connection to the base end of the actuators  106 , and the grooves  222 A and  222 B connected to the rod end of the actuators, and then having the arcuate length of the grooves properly arranged for the three ports  234 A- 234 C and  238 A- 238 C, respectively, the actuators can be operated at the desired position during the cycles of rotation of frame  12  to pick up a carton, and at the appropriate position the actuator will be extended to cause the auxiliary vacuum cups to “break” or move the flap of a carton to its appropriate position. 
     The manifold assembly  68  carries both vacuum and pressure, across the same interface surface. This is aided in part by having the vacuum acting at a greater radius from the center of rotation of the stationary and rotating members, than the pressure. The total axial force from the pressure acting in the grooves  214 B and  222 B is counteracted by the force acting on the piston  180  from chamber  218 . The pressure in the chamber  218  is the same as that in the grooves  214 A and  222 A but the area of the back side of the piston is greater than the area of the part annular grooves. Thus the pressure in the chamber urges the surfaces of the piston and the manifold section together. The vacuum force and the differential pressure force will keep the system sealed, but springs  192  and  204  are used for assuring sealing is maintained. 
     The vacuum is supplied to the vacuum cups at the appropriate time to pick up the cartons, during a portion of the rotary cycle, and release the vacuum at an appropriate time so the cartons will be deposited on the conveyor appropriately. 
     The present rotary placer is the first to use pneumatic or air pressure for operating actuators, carried by the rotary device, and at the same to carrying vacuum to vacuum cups for operation. 
     It should be noted that the hub plate  174  has a recess for permitting a vacuum fitting to be attached directly to the vacuum port of the steel backing plate of the vacuum valve ring. 
     In FIGS. 6 and 7, the carton handling assembly is shown moved from a pick position wherein all of the vacuum cups  84  and  72  are on a plane to the place position. As can be seen in FIG. 6, the cups are connected with vacuum lines  69  that come from the manifold assembly  68 . In FIG. 4 the carton handling components are shown in approximately the position for picking up a carton at a carton store. 
     FIG. 6 is a perspective view with the carton handling assembly  40  after rotating from the pick position to the place position. The auxiliary or flap folding vacuum cups have moved 90° to hold a flap  11 A that is shown only schematically on one part, with the main part of the carton held as shown with a fragmentary portion  11 B. In FIG. 6, the conveyor chain  160  for a carton loading machine  162  is shown, and a guide or pusher  163  as illustrated. The flap would be lifted to its folding position for transporting by the conveyor  160 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.