Patent Publication Number: US-8539739-B2

Title: Method of palletizing items

Description:
RELATED U.S. APPLICATION DATA 
     Division of application Ser. No. 12/512,897, filed on Jul. 30, 2009, now U.S. Pat. No. 8,220,229, which is a division of application Ser. No. 12/476,124, filed on Jun. 1, 2009, now U.S. Pat. No. 8,074,431. 
    
    
     BACKGROUND 
     The present invention relates generally to item manipulation, and particularly to manipulation of entire layers of items during handling operations. 
     Palletizing generally refers to a process of constructing a stack of items organized as layers on a pallet. A pallet is a standard support and carrier structure used in shipping and provides a support surface for receiving items stacked for transport. Efficient shipping of palletized items calls for efficient stacking of items on the pallet to minimize open space within the stack. Accordingly, a variety of “item patterns” have emerged for efficient and stable packing together of items in item layers on a pallet. In some applications unit loads are built effectively identical to loads on pallets absent the pallet itself with a slip sheet providing load support or without any underlying support structure. Whether loads are built on pallets or without pallets, the common art name is palletizing. 
     Two common methods on palletizing consist of layer building palletizers and robotic pick and place palletizing. Layer building palletizers typically employ various mechanisms to manipulate items into rows of items spaced and turned appropriately to construct rows. Rows of items are then transferred to a layer assembly platform through various means until a layer is completed. Depending on the location of the of the layer assembly device, the completed layer is transferred to the load under construction. Typically the layer construction device has a layer support surface commonly called an apron. The apron can be rigid or flexible and in either style the apron is pulled from under the layer of items to deposit the layer on the pallet or previously deposited layer. Prior to deposit it is common to condition the layer that may be loosely assembled using various clamping means. Where the layer is assembled relative to the load under construction varies. Layers can be built horizontally offset then raised or lowered then moved horizontally for deposit. The layer can be assembled above the load under construction and either the layer assembly device is lowered to the load under construction for deposit or the load itself is raised to the fixed layer assembly device that opens to deposit the layer. A third method is to build less than complete layers that are transferred to the layer assembly device that vertically positions above the load under construction. All methods and techniques used are common in the art of layer building palletizing. 
     Robotic pick and place palletizing utilizes a programmable mechanism to pick and place an item, item groups or previously constructed layers from a picking location to pallet load under construction. Unless the layer was previously constructed by other means, the pick and place device picks and places items into their finished position on the load under construction. A characteristic of such pick and place actions is the item or items are picked in such a manner that the actual gripping device does not hinder final positioning of items or items on the load. Top picking vacuum gripping systems are most common where there is no gripping mechanism below the top of the item or items being picked and placed allowing tight placement of item or items adjacent to each other on the load under construction. Side gripping devices or bottom support devices are alternative gripping devices. Side grippers are effective and more positive than top picking vacuum methods, but whatever the thickness of the side gripper is becomes a void in the finished load unless the pick and place device performs a secondary bump to remove the void. Bottom support devices are more problematic if a tight-finished load is desired as the bottom support must have horizontal clearance to disengage from supporting the item or items bottom when depositing. Typically, a horizontal space at the periphery of the load or the load pattern is required and this space interior to the load limits load pattern flexibility. Regardless of the item or items, known pick-and-place gripping device typically need to slow down for accurate final placement: And, in most instances, move items or items at speeds slower than the programmable mechanism is capable of due to insecure gripping. The most common top picking vacuum gripping method is especially susceptible to insecure handling requiring slower speeds. 
     There are two deviations to the above generalities about item or items gripper technologies employed by pick and place palletizers that apply to bag handling and full layer handling. A first deviation is that bags are typically handled with a basket style gripper that surrounds the bag in a clamp or vise-type grip and this clamp or grip includes providing some sort of support element to engage a substantial part of the bag bottom. For stacking on a pallet, the basket style gripper opens and drops the bag into position onto the load under construction from an elevation that allows for clearance for the basket. Dropping the bag is often preferred as dropping allows the pliable bag content to deform to the previously deposited bags creating a tighter load. Because the bag is contained in the basket and final placement accuracy is less critical the pick and place device often can operate at higher speeds than the same pick and place device will operate with previously discussed item or items handling devices. Often speeds are 20% faster when an identical programmable item pick and place device is assembling an identical pattern of bags compared to rigid containers indicative of the advantage of bottom support and less accurate final positioning provides. 
     A second differentiating method of pick and place palletizing is full layer handling. Commonly the full layer is preassembled by various means into a tight configuration then the layer is picked and placed using top vacuum, side clamping or bottom support means so that the layer can be picked and place onto the load. Some bottom supporting methods will receive a loosely assembled layer and perform secondary layer conditioning into a tight configuration during the pick and place cycle. 
     Regardless of the method and devices used to stack items on a pallet, nearly all finished loads are stretch wrapped prior to shipment to secure the load against disruption from the rigors of transportation. As such, if palletizing and stretch wrapping can be combined into one location there are benefits in space savings in that space for secondary stretch wrapping operations are unnecessary and many less stable loads benefit from the stability imparted by stretch wrapping while load building. There are three primary prior art patents related to palletizing and stretch wrapping that employ palletizing methods discussed earlier. For example, Yourgalite, in U.S. Pat. No. 4,995,224, teaches picking and placing an item or groups of items on an offset turntable where wrapping occurs as the load is built. Items or groups of items are positioned in the final load build position only if the turntable is not rotating; this requires that no items be palletized when the stretch wrapping operation is active. Second, Denley in U.S. Pat. No. 5,758,471 teaches building a full layer of rows of items at a horizontally offset position below the finished load height then transferring the layer for deposit to the load under construction. During layer construction at an adjacent offset position the stretch wrapper can operate providing concurrent layer building and load wrapping. And thirdly, Heston in U.S. Pat. No. 6,533,533 teaches building a full layer of rows of items with items entering at an elevation above the finished load height in the same vertical space as the stretch wrap turntable occupies. Layers can be simultaneously built while palletizing occurs. 
     Yet, despite the current state of the art, there remains a need for a compact palletizer that more quickly and more efficiently creates layers for palletizing and more quickly builds an entire pallet of items. One attempt to create a more efficient palleting device includes the device of Corsini in U.S. Pat. No. 6,238,173. Corsini teaches an apparatus for placing items in groups on pallets according to a pre-set planar configuration. An up-stream forming machine discharges items pre-grouped into stacks. The apparatus comprises a pallet loading station with a movable arm fitted with a claw for gripping at least one rank of stacks and positions the rank onto the plane of the pallet. In yet another example, Yourgalite in U.S. Pat. No. 5,005,335 instructs that a set of boxes should be accumulated before they are picked up by a robotic palletizer and transferred to a turntable. 
     TopTier, Inc of Portland, Oreg. manufacturers several palletizer models including two row building palletizers with concurrent stretch wrapping. High and low infeed models build rows that are transferred to a layer build table that vertically reciprocates above the stretch wrapper turntable. While the turntable is wrapping, subsequent layers can be built on the layer head. Another low infeed version used for higher speeds assembles less than a layer on a vertically reciprocating deck. The pre-arranged item groupings of partial layers are then transferred to a layer assembly device that occupies the vertically space above the turntable. Once sufficient partial layer groups are transferred to the layer assembly device the layer is deposited onto the load under construction. Layer groupings can continue to be transferred to the layer assembly device while the turntable is wrapping allowing concurrent stretch wrapping. 
     The above methods can successfully palletize and stretch wrap or palletize and concurrently stretch wrap with limitations. The current state of the art of pick and place methods and known devices must cease load building while wrapping occurs. These known construction and layer deposit methods include many complex mechanisms to accomplish palletizing and their throughput speed is limited by the inability to queue more than one layer without increasing machine complexity during final wrap and load pallet exchange time limiting total load throughput speeds to about a layer every 45 seconds. 
     However, Denley, in U.S. Pat. No. 5,758,471, teaches one means to queue more than one layer during wrapping operation utilizing more than one stacked apron. 
     Yet, there still remains a need for a palletizing devices and methods that improve total load throughput speeds, reduce complexity of components, maintain or improve upon a compact footprint and that can provide the benefits of more effective concurrent stretch wrapping. There is a need for a hybrid palletizer adapted to overcome the limitations of the known state of the art and provide a palletizing solution that is smaller, faster, and lower cost (to manufacture, operate, and maintain) compared to the current devices. Such an improved hybrid palletizer should further provide new capabilities unavailable utilizing the best attributes of established methods of palletizing. 
     As discussed, pick and place palletizers are often constrained to lower speeds than the mechanism are capable of operating at because speed must be reduced to perform exact placement of an item or items as the load stack is built directly on the load under construction. Proper finished loads require tight uniform stacks of items on the pallet so precise positioning is a necessity. Furthermore methods of gripping an item or items can also reduce speed potential as the gripper is not capable of retaining items or items at higher speed potential. Or, gripper methods that allow fast speeds compromise item or items placement by requiring gaps or clearance for gripper removal. 
     Thus, there also is a need for a hybrid palletizing solution that employs a pick and place device depositing an item or items to an intermediate oversized layer assembly platform that provides cures for the shortcomings discussed above. 
     SUMMARY OF THE INVENTION 
     The present invention relates to compact palletizers that include an infeed conveyer at a fixed vertical height or elevation relative to the finish load height. Further, this invention relates to compact palletizers that include a stretch-wrap operation to wrap layers of the partially built load as the load continues to be built. Specifically, the present invention uses a robot to pick and place items from a fixed infeed elevation either above or, alternatively, below the height of the finished load. An item or items are picked and placed loosely to a layer assembly device that is larger than the finished layer, so a four-sided compaction mechanism compresses the rough built load to the final pallet size and then the entire layer is released to the pallet. 
     To overcome the limitations of the current state of the art, the present invention in a preferred embodiment comprises a hybrid palletizer system. This hybrid palletizer system includes an oversized layer assembly platform, which provides additional space for an item or items to be roughly positioned as the oversize layer assembly platform utilizes secondary layer conditioning that compacts the layer prior to deposit. Furthermore, in one preferred embodiment the item or items gripper can provide both bottom support and a pinch-like grip. This requires that there is clearance available for the bottom supporting aspect of the gripper to be removed from under the item or items. The item or items can also be tightly gripped for maximum speed movement. 
     A further advantage of the hybrid solution is the pick and place layer construction on an oversized layer assembly device is not restricted to assembling one level on the device. Higher rates can be achieved by reducing the number of layer deposit cycles by stacking more than one layer between each deposit. 
     Additionally the oversized layer assembly platform can receive an item or items immediately adjacent to the pick and place device then index the layer support surface presenting new unoccupied layer support surface for more items until a layer is completed. Pick and place motion travel distance of each cycle is substantially reduced to further increase speeds. Such capabilities can allow the use of a smaller less expensive and faster pick and place devices because the range of motion requirements of the pick and place device is less. Additional speed increases are possible by stacking more than one level of items with each index cycle reducing time required for layer deposit while utilizing the above methods. 
     Concurrent wrapping can occur while layers are constructed on the oversized layer assembly device as pick and place palletizing to the oversized layer assembly platform can continue during wrapping operations. When the method of stacking more than one layer either directly or on an indexing layer support platform is utilized with concurrent wrapping throughput potential is increased as layer condition and deposit cycles are reduced. Completion of final load wrap and pallet exchange is time consuming requiring about 45 seconds. The ability to assemble more than one layer during that time using either method further enhances the viability of concurrent wrapping as potential throughput is increased. 
     Some items or items that are particularly well suited for top picking with vacuum eliminating the advantage of bottom support and necessary bottom support removal clearance or bag items that are dropped with or without side constraints do not necessarily benefit from an oversized layer assembly platform. Such item or items can be deposited directly onto a layer assembly platform with or without fixed side constraints simplifying the mechanism. While the platform is loaded with one or more layers concurrent wrapping can occur. Because concurrent wrapping occurs when the unwrapped load height is equal to or greater than the film width, the layer support platform can be open during deposit while one or more than one layer is directly deposited to the load until the necessary load height is achieve for wrapping, then the floor can close continuing to receive items until a layer or layers are assembled while wrapping occurs. The methods above minimize time required for layer clamping when utilized and floor removal optimizing throughput potential when concurrently wrapping. 
     Layer conditioning and layer deposit can impact potential throughput if the time required is greater than a single pick and place cycle. Throughput speed can also be compromised if the pick and place device must perform significant vertical movement due to increasing load height as the load is built. Accordingly, a second preferred embodiment of the present invention provides additional elements that counter this travel-distance imposed time delay. In this second preferred embodiment an intermediate shuttle device, such as a partial layer build platform adapted to selectively position vertically adjacent to both the infeed conveyor and the build platform, selectively positions at an optimal elevation relative to the pick and place device and receives items or items and, thus, stages one or more partial layers prior to deposit and thereby improves overall throughput time. 
     For example, if the intermediate platform is approximately half the size of the oversized layer build platform horizontal pick and place reach requirements are reduced and vertical travel can be optimized as the intermediate platform can always position at an ideal height relative to the pick and place device. Once the intermediate platform has received one or more partial layers the intermediate platform can quickly vertically shuttle to transfer its items to the oversized layer build platform where a completed layer can be conditioned and deposited while the intermediate platform continues to receive items. The combination of optimized pick and place motions with reduced horizontal and vertical reach requirements and quick transfers to the oversized layer build platform increases throughput potential with and without concurrent stretch wrapping. 
     The pick and place methods discussed in relation to the various preferred embodiments (above) can occur when items are entering the hybrid palletizer at a level below or above the finished load height. If the items enter the palletizer above the finished load height an item or items do not necessarily need to be picked and placed. A programmable device can just as easily slide an item or items into a rough position on the oversized layer support platform positioned at the same or slightly lower elevation as the item infeed elevation. Sliding avoids time consuming pick and place so throughput is improved. Sliding distance is reduced and speed increases if the layer support platform indexes as described earlier. Similarly if an adjacent static platform roughly equal to about half a layer size with a secondary items sweep mechanism capable of transferring already positioned items into the oversized layer build platform, item or items sliding can continue during layer conditioning and deposit increasing rate potential. Another alternative to a static intermediate platform that allows continued partial layer assembly during layer condition and deposit is to use an extended apron where the very short slide strokes combined with an indexing apron creates an assembled layer that indexes into the layer conditioning and deposit zone. Remaining apron is available for additional positioning of items as the already completed layer is conditioned and deposited. During layer deposit when the apron retracts from under the layer being deposited a means must be employed to resist substantial movement of already positioned items that are part of the next layer already positioned on the extended apron. Those items already positioned as part of the next layer on the apron can be held in position resisting the apron sliding motion by a second stop that comes from below or above or by the ledge created by an elevation difference when the indexing apron is slightly below the infeed elevation. An advantage of a stop that comes from below such as a tilting dead plate or a static ledge created by an elevation difference between the infeed and apron elevation is that items can continue to be slid into position over the ledge or tilting dead plate while the apron is being retracted allowing uninterrupted item positioning for higher rate potential. Some of the iterations discussed in this paragraph can occur with concurrent wrapping when the layer is lowered to the load under construction. If the pallet is raised to the load build height then lowered as layers are deposited throughput is further increased because down stacking palletizers are inherently faster due to quicker layer deposits than high infeed palletizers that lower the layer for deposit. Finally, addition of more than one programmable device capable of sliding an item or items will provide further increase in throughput potential. 
     Individual items or group of items will be picked and placed or slid onto a layer support device in a loose orientation. The loose orientation (also referred to as a rough build or rough finish layer or loosely constructed) enables a much faster palletizing operation over known prior art devices because the robotic arm that pick-and-places or slides the item or items can operate much faster as it does not have to precisely locate the item or items. 
     During the time that a layer is being loosely constructed on the layer support device concurrent wrapping can occur. When concurrent wrapping is used the wrapper turntable remains at a fixed elevation. If concurrent wrapping is not used, the load build position remains stationary or can be hoisted to the layer support device height in higher speed down stacking high-infeed palletizers. 
     A pick and place operation by the robot to rough finished position so that motion can be as rapid as possible allowing higher throughput. Because the pick and place device does not need to perform final positioning more items can be handled in a time span compared to other known methods and devices. And, a rough position deposit with adjacent space around items allows rapid use of a bottom support picker for more secure item handling. 
     In one preferred embodiment of the present invention a robot picks and places items from a fixed infeed elevation. This infeed elevation invariably is at some height that differs from the height of the finish load and depends on the needs of a particular production line. Accordingly, the infeed conveyor, although fixed in vertical elevation, may be either below the height of the finished load or above the finished load. 
     Individual items or group of items are picked and placed onto a layer support device in a loose orientation. The layer support device is substantially larger than the finished layer after conditioning. The layer support device has the ability to condition the load with layer clamping. The preferred picking device is a gripper that provides support from the bottom of the item allowing very fast movement as the item is contained. Vacuum top picking is an option, but vacuum is less reliable because speeds must be slower to reduce the chance of vacuum grip loss. 
     Bottom support requires clearance from adjacent previously deposited item on the layer support device so that the bottom support can move out from under the item when deposited. 
     During the time that a layer is being loosely constructed (oriented, or rough-built) on the layer support device concurrent wrapping can occur on previously deposited layers. Then, known and existing concurrent wrapping technology, which is fully automated, can occur as would be understood by those having ordinary skill in this art. When concurrent wrapping is used the wrapper turntable remains at a fixed elevation. If concurrent wrapping is not used, the load build position remains stationary. 
     The robot base remains stationary. The vertical and horizontal reach of the arm allows the robot to pick and place items from the fixed infeed elevation to various heights of the layer support device as it moves up always remaining above the height of the load under construction for applications where the infeed elevation is below the height of the finished load. When the in-feed elevation is above the height of the finished load the layer assembly platform and the infeed maintain a similar vertical relationship during item transfer to the layer assembly platform. 
     The present invention overcomes some limitations of known devices. For example, Yourgalite U.S. Pat. No. 5,005,335 instructs that a set of boxes should be accumulated before they are picked up by a robotic palletizer and transferred to the turntable. This teaches away from the present invention because Yourgalite requires a set of boxes to accumulate and only then can the robotic palletizer transfer the set of boxes to an awaiting pallet on the turntable. Further, Yourgalite does not contemplate or suggest a “compaction” of items as defined in the present invention and, further lacks means for layer queuing, which eliminates the possibility of concurrent wrapping without stopping palletizing. 
    
    
     
       DRAWING 
         FIG. 1  is an offset front view of a hybrid palletizer including an item handling and stacking system at a first position according to a first preferred embodiment of the present invention. 
         FIG. 2  is a top-view of the hybrid palletizer system of  FIG. 1 . 
         FIG. 3  is an offset front view of the hybrid palletizer system of  FIG. 1  at a second position. 
         FIG. 4  is a top-view of the system of  FIG. 3 . 
         FIG. 5  is an offset front view of the hybrid palletizer system of  FIG. 1  at a third position. 
         FIG. 6  is a drawing of the chute style layer support device. 
         FIG. 6A  is the layer support device in  FIG. 5  with the layer conditioning clamps in the X direction extended for clamping. 
         FIG. 7  is a top view of the system of  FIG. 5 . 
         FIG. 8  shows an apron of the system of  FIG. 5  in a closed position. 
         FIG. 8A  shows the apron of  FIG. 8  in an open position. 
         FIG. 9  is an offset frontal view of the embodiment of  FIG. 1  in a fourth position with the gripper shown picking two items. 
         FIG. 10  is a top view of the embodiment of  FIG. 9 . 
         FIG. 11  is an offset frontal view of the embodiment of  FIG. 1  in a fifth position and showing two items being roughly positioned. 
         FIG. 12  is a top view of the embodiment of  FIG. 11 . 
         FIG. 13  is an offset frontal view of the embodiment of  FIG. 1  in a sixth position. 
         FIG. 14  is a top view of the embodiment of  FIG. 13 . 
         FIG. 15  is a detailed view of a sliding end effector in a first position according to a preferred embodiment of the present invention. 
         FIG. 16  shows a second position of the end-effector of  FIG. 15 . 
         FIG. 17  shows a third position of the end-effector of  FIG. 15 . 
         FIG. 18  shows a fourth position of the end-effector of  FIG. 15 . 
         FIG. 19  is a detailed view of a pick and place end-effector having an under-side-support gripping element. 
         FIG. 20  shows the end-effector of  FIG. 19  in another position. 
         FIG. 21  illustrates a stretch-wrap device according to one embodiment of the present invention. 
         FIG. 22  is an offset top view detailing a compression device according to one preferred embodiment of the present invention. 
         FIG. 23  shows a completed layer being conditioned and the first subsequent 
         FIG. 24  is a flow chart of a first preferred method of the present invention. 
         FIG. 25  is a flow chart of a second preferred method of the present invention. 
         FIG. 26  is an offset frontal view of a second preferred embodiment of the present invention. 
         FIG. 27  is another view of the embodiment of  FIG. 26  and illustrates a full build layer. 
         FIG. 28  is another view of the embodiment of  FIG. 26  and illustrates a full build layer being deposited on a pallet. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Possible preferred embodiments will now be described with reference to the drawings and those skilled in the art will understand that alternative configurations and combinations of components may be substituted without subtracting from the invention. Also, in some figures certain components are omitted to more clearly illustrate the invention. 
     A known device that exemplifies the level of skill and understanding of those in this art includes the article handling device and system as described by Heston in U.S. Pat. No. 6,533,533 issued on 18 Mar. 2003, the entire contents are incorporated by reference as if fully set forth herein. 
       FIGS. 1-20  show a first preferred embodiment and related elements of a hybrid palletizer including an item handling and stacking system  10  according to the present invention.  FIGS. 1 and 2  provide a general overview of major sub-systems of the hybrid palletizer system  10 . Some of the major sub-systems include an infeed system  14 , such as a roller conveyer, adapted to transfer items  12  within a range of operation of a robotic pick-and-place device  30 . The infeed system locates at a given height relative to the system, such as a first (infeed) height  16 . Other sub-systems include an out-feed system  40 , a layer queuing device  50  and a stretch-wrapping device  60 . 
     Referring generally to  FIGS. 1-8   a , the first preferred embodiment of an item handling and stacking system  10 , adapted to receive at least one item  12  from an infeed system  14  presented an infeed height  16 , includes a frame  20 . As  FIG. 3  shows, the frame  20  consists of a base  201  consisting of four horizontal members arranged to form a rectilinear box with intermediate members  209  intersecting with and running generally perpendicular to two oppositely positioned horizontal members  202 . Additional base support members may be included, as deemed necessary by a particular layout of sub-systems, as would be well understood by those skilled in this art. Extending from the base  201 , at four vertical uprights  203  position at the respective four corners of the rectilinear base. The box frame further includes four horizontal beams  205  arranged to mirror the base. And, as would be understood in the art, each frame element couples to the adjacent element to form a rigid structure. The individual frame elements may be coupled by fasteners to enable disassembly and repair, or alternatively, may be permanently coupled by welding or riveting, for example, to provide a more permanent joining of adjacent members. 
     A portion of the frame  20  defines a vertical column of space, which is useful to describe the layout, location, and interaction of certain sub-systems of the present invention. This vertical column of space is best physically defined by a portion of the base  201  and the pair of oppositely positioned intermediate vertical uprights  207  and two, opposite corner vertical uprights  203   a  and  203   b , which are linked by a common horizontal beam  205   a , as  FIG. 3  shows. Accordingly, the robot  30  and infeed system  14  are adjacent to the vertical column of space despite their physical location within the overall frame structure  20 .  FIG. 4  further details this juxtaposition of the vertical column defined by a portion of oppositely positioned horizontal beams  205  and the vertical corner uprights  203   a  and  203   b  and joining beam  205   a  and vertical uprights  207 . As  FIG. 4  shows, the infeed system  14  and robot  30  are adjacent to this vertical column. 
     In this first preferred embodiment, a layer queuing device  50  locates within the vertical column of space. The layer queuing device is operable to independently and selectively reciprocate vertically (that is selectively position at any intermediate location within a vertical column of space, the intermediate position defined by opposing extreme ends of the vertical column of space as physically limited by the structure) between a first position and a second position within the vertical column of space. 
     The layer queuing device  50 , detailed in  FIG. 6 , for example, consists of an apron  53  (detailed in  FIGS. 8 and 8   a , for example) with a static compaction mechanism. The static compaction mechanism comprises two opposing x-direction arms or walls that funnel items from a first rough build position to a second, tighter position merely by using gravity as the item is released from the robot. An additional pair of y-direction barriers arranged perpendicular to the oppositely facing x-direction arms may be used in certain circumstances to further restrict the load of items (layer) being deposited from the assembly platform to the pallet. The apron comprises a flexible or inflexible support surface, such as the assembly platform  503 , and at provides a downward opening so that items constructed into a layer can exit when the support surface is removed. 
     The apron  53  has a motive device to position the apron in the downward opening and remove the apron from the downward opening to allow items to travel through. In the preferred embodiment the motive force is an electric gear motor that rotates a shaft with two chain loops connected. Rollers or slats create a flexible apron that occupies part of the chain loop roughly equal to the size of the downward facing opening. The shaft rotation causes the two chain loops to move in unison transporting the flexible apron from a position occupying the downward facing opening when items are being accumulated and out of the downward facing opening when items are being deposited. 
     With specific reference to  FIGS. 8 and 8   a , the apron  53  includes a roller curtain flexible assembly platform  503 . The roller curtain comprises a plurality of linearly aligned roller tubes  54 . Each roller tube has a distal and proximal end and each end, respectively, couples to a first and second roller chain  55   a  and  55   b . The assembly platform  503  is selectively operable between an open and a closed position, and can stop at any intermediate position including being operable to selectively index to intermediate positions anywhere in the range from fully open (fully retracted) to fully closed (fully extended). A gear-motor  56  links to the pair of roller chains  55   a  and  55   b  as would be understood in the art, using associated bearings, sprockets, and bushings. A drive shaft  57  with associated bearing sprockets, and bushings at a distal end links the gear motor  56  to the distal roller chain  55   b.    
     Stationary or moveable surfaces immediately above the plane of the flexible apron and positioned in direction of loop movement when provide a stop to retain items from moving with the apron  53  when it is removed from the downward facing opening effectively causing the apron to shear from under the items. 
     It shall be appreciated by those skilled in the art that the flexible curtain can be made operable to selectively travel horizontally in a single plane in increments. Accordingly, the pick and place robot end effector can place all items in a predetermined position in a first grouping. Then, the flexible curtain can advance a sufficient distance to move the deposited grouping of items over, presenting an open space on the platform  503 , thus allowing the robot to place additional items and minimizing robot travel, which would increase the operational speed of the entire palletizing operation. 
     Another variation of this first preferred embodiment includes providing a flexible apron comprising at least two roller curtain floors operable to selectively index in the same horizontal plane (as  FIG. 22  illustrates, for example), the first roller curtain floor  503   a  following a first continuously looped path and operable in a clockwise direction and the second roller curtain floor  503   b  following a second continuously looped path and operable in an anti-clockwise direction. 
     In the first preferred embodiment, the layer support platform consists of a single chain loop pair. That design effectively urges all items against a backstop on the side the apron travels towards when floor removal occurs. Because the apron is the entire length of the downward facing opening time required to move the floor is twice the time required for two half aprons to move in opposite directions. Furthermore it is desired to position items consistently in all four corners of the completed layer. Some layer patterns have spaced items in the direction of floor removal and if a full-length apron is removed spaced items can collect tightly against the backstop or each other creating a void in the corner of the load. 
     However, in other contemplated embodiments, other apron designs would work equally well. For example, In one variation, the layer queuing device  50  includes a rigid apron comprising at least one floor panel, and preferably two floor panels, operable to slide horizontally when moving out from under the layer from a closed position to an open position. A rigid apron works equally well as a flexible apron and in some instances has advantages. Some items such as non rigid bags sometimes do not work well with flexible surfaces due to the propensity of the flexible bags surface to conform to the necessary gaps in-between each apron roller or slat that must be used to create a flexible apron. If the bag conforms to the gaps then removal of a flexible apron can damage or tear the bag. 
     Mechanically, rigid aprons operate substantially the same as a flexible apron with the exception that flexible aprons can transition to vertically travel as the apron rollers or slats move from the horizontal downward facing opening allowing a smaller machine. Inflexible apron designs require horizontal space at least equal to the downward facing opening when a single rigid or two panel bi-parting apron is used resulting in a larger machine. 
     An apron system when closed can create a layer support platform and when layer deposit occurs by opening the downward facing opening. Bi-parting apron designs move half the apron, each half moves in opposite directions and is, therefore, twice as fast which allows higher rates and items that have gaps in the direction of apron removal are pulled towards each side maintaining the desired positioning of items in each corner of the load. 
     The layer queuing device  50  can be stationary occupying the top of the vertical column of space with the pallet raised to have layers deposited then lower with each subsequent layer deposit until the load is completed. Or, it can position at the top of the vertical column of space when receiving items then descend to the load under construction for layer deposit returning to receive subsequent layers or vertically travel in the vertical column of space remaining above the height of the load being constructed and receiving items at different elevations. Layer queuing devices that travel vertically are effectively platforms that are attached to hoist devices for which there are many known designs. In the preferred embodiment, as detailed in  FIG. 6A  for example, a gear motor  529  is attached to a driven shaft and associated sprockets and connecting drive chains. Each sprocket drives a chain length with one end connected to each corner of the layer queuing device. Forward and reverse rotation of the shaft driven by the gear motor causes the chain lengths to raise and lower the layer queuing platform including the assembly platform  50  and apron  503 . The identical construction can be used to raise and lower a pallet when the layer assembly queuing device remains stationary at the top of the vertical column of space. 
     The layer queuing device includes a frame structure  501  (of  FIGS. 5 and 6A , for example) sized to fit within the frame  20  and includes accommodation for the drive motor  529 , at least one drive shaft, and associated components. 
     As  FIGS. 1-5 ,  7 , and  9  show, the layer queuing device  50  includes a layer assembly platform  503  where items  12  are placed for layer assembly and the layer assembly platform, being part of the layer queuing device, moves vertically in the vertical column. Thus, the assembly platform&#39;s location defines a selectively adjustable assembly platform layer-build height so as a pallet is built with multiple layers, the build platform moves upward to always stay above the last build-layer positioned on the pallet. Necessarily, the assembly platform layer-build height is always intermediate to the first and second positions representing the range of vertical movement of the layer queuing device within the frame  20 . 
     The layer queuing device  50  further includes a compaction mechanism, or more accurately, a compaction mechanism  90  operable to include relative movement in at least two directions in a single plane. The compaction mechanism  90  is more generally referred to as a layer conditioning mechanism, which is a more generic term. Items are conditioned from a loose orientation into a tight layer grouping, compression or compaction, may or may not be part of layer conditioning. However, as used herein, the compaction mechanism  90  refers to a set of cooperating mechanical systems that aligns and conditions items arranged on a layer. For example, a pick-and-place robot rapidly deposits a sequence of items on for a layer build in a first “loose” position and the compaction mechanism adapts the layer into a second “tighter” position—this does not necessarily mean that the physical items are “compacted” or compressed (as used when referring to bagged items, for instance). 
     In this embodiment, the compaction mechanism  90  includes a first x-direction arm  521  and a second, oppositely disposed x-direction arm  523 , and a first y-direction barrier  525  arranged generally perpendicular to the first x-direction arm and cooperating with both arms to define a generally rectilinear space. A compaction device, such as a cylinder and hinged lever assembly coupled to the first x-direction arm selectively operates the x-direction arm, or preferably a pair of oppositely facing x-direction arms, to include relative movement toward the center of the assembly platform and retract. 
     Compaction of loosely or roughly positioned items to the center of the assembly platform will be the normal, preferred operation. However, the present invention contemplates that certain pallet loading operations may necessitate off-center or other configurations of items. Accordingly, if the layer assembly platform center is not be coincident with the center of the load build position, then centering to that position will be another preferred capability. Compacting items to either centered positions will require both X &amp; Y direction movement of arm sets, whereas non-centered layer conditioning will only require at least movement of one arm (x or y) and a rigid barrier opposite the moving arm. 
     Each respective x-direction movable arm  521  and  523  includes an associated link mechanism consisting of a pair of cross-linked members  522  coupled at a proximal end to the associated arm  521   523  and coupled to a motivating means, such as a drive chain or pulley, at their respective distal end. A common, central link pin enables each cross link arm to rotate relative to the cooperating arm, operating much like a scissors and thus enabling the x-direction arm  521  or  523  to move evenly and remain parallel to its corresponding portion of the rectilinear space. A single drive motor ( 529  is the motor that moves the flexible apron) operable in forward or reverse, couples to each x-direction arm by drive shafts, pulleys, sprockets, bushings and the like, as well-understood in the art. Thus, the single motor, causes both x-direction arms to simultaneously move inward or, selectively, outward to compress or compact or, more broadly, condition items on the platform  503 , as required. 
     In an alternate preferred embodiment, the first y-direction arm  525  is a rigid barrier and a second y-direction arm  527  is operable to move inwards and outwards, and arranges generally perpendicular to the x-direction arms. Arm  527  is a single y-direction conditioning clamp extended to a position, this position, in certain embodiments would interfere with the robot&#39;s movement. 
     Further, the frame  20  includes pallet-build position located within the vertical column and under the layer queuing device (as shown by lead-arrow  70  in  FIG. 9 , for example).  FIG. 21  details a turntable assembly  80  contemplated by this first preferred embodiment, arranged in the pallet build area  70  and adapted to receive layers of items from the layer queuing device, and a stretch wrapping device  60  comprising a means for automatic wrap start and wrap cut after wrapping completion. 
     With particular reference to  FIG. 21 , and as generally shown in  FIGS. 1-5 ,  7  and  9 , there is a load supporting turntable  80  positioned at the bottom of the vertical column of space supported by a slewing ring bearing. A gear motor  83  and chain loop assembly rotates the turntable  81 . Rotation occurs when there is an adequate vertical stack of items roughly equal to the film width. Rotation also occurs while the layer queuing device is being filled with items and returns the turntable to a known position prior to deposit of the next completed layer. The turntable has a powered roller  88  driven top deck that supports the pallet and load of items under construction. The powered roller  88  is motivated in either a forward or a reverse direction by a gear motor  85 . The roller deck  87  provides transport means to move empty pallets into position and transfer completed loads off the turntable. 
     The stretch wrapping mechanism  60  disposes adjacent to the turntable assembly  80 . Adjacent to the turntable  81  is a mast  61  that has a hoist mechanism and film dispensing head and film cutting arm  63  with a hot wire to cut film vertically throughout the vertical column of space a partial or completed load occupies when on the turntable. A hoist motor  64  raises and lowers the film dispensing head assembly  62 . The film dispensing head has rollers capable of metering out film to wrap the load while the load is being constructed. The rollers are driven by a motor whose speed is manipulated to coordinate film dispensing rate to the needs of the load as it rotated on the turntable. The film dispensing head also travels vertically to spiral wrap the load with varying amounts of film overlap. 
     Automatic film dispensing and film wrap completion requires the means to start the film by attaching the film tail to the turntable or load so that turntable rotation pulls film from the dispenser until rotation begins to wrap the load after which the film initially contacting the load continues to pull the film from the dispenser whenever rotation occurs until the load is wrapped to the desired amount. In the preferred embodiment the film is not attached to the turntable, but is blown onto the empty pallet or one of the first layer of items then subsequent layers are deposited to secure the film to the load. Another method is to use a clamp on the turntable to grip the film tail. 
     After the desired load wrap sequence occurs that may wrap the entire load of some part of the load the film must be cut creating a tail for the next load sequence. In the preferred embodiment, an arm with a hot wire cutter  63  is a single hot wire cutter supported on a vertical extension of arm  65  actuated to swing into the film in-between the dispenser and the load that cuts the film. 
     In this first preferred embodiment, the stretch wrapping system includes the turntable  80  positions in the vertical column of space and remains in a fixed vertical location within the column but is adapted to selectively rotate a pallet or a layer of items. (It would be understood in the art that the pallet layer would likely be placed on a pallet, however, other embodiments contemplate stacking a layer of items directly on a platform or on the turntable, or slidable sheet). 
     The stretch-wrapping device  60  includes a conventional stretch wrappings system such as the Q-series automatic system available from Lantech, Inc. of Louisville Ky., USA. Modifications to such a conventional system include sensors and machine-executable operating instructions and software programming to enable the stretch-wrapping device  60  to wrap one or more layers (each layer comprising one or more items arranged in x and y rows in an a single plane) while the pick-and-place robot continues to place individual items or groups of items on the layer queuing device. 
     Although the turn-table  80  and stretch-wrapping device  60  are discussed relative to the first preferred embodiment, it will be appreciated by those skilled in the art that a similar stretch wrapping mechanism could be adapted for use with other preferred embodiments as described herein. 
     The first preferred embodiment of the present invention includes a robot  30 . The robot includes a stationary base  301  and an articulating arm assembly  303  adapted to provide 180-degrees of rotation in a three-coordinate space. At a distal end of the arm, an end-effector enables transfer of the items  12  from the infeed system  14  to the layer queuing device  50 . One suitable end-effector includes a gripping element. A gripping element includes a vacuum-assisted end-effector, or a claw-type gripping element, or a combination of vacuum and claw, or other similar end-effectors as would be understood in the art. In the first preferred embodiment, the gripping element  321  as  FIGS. 19 and 20  show, for example, includes a top portion  324  coupled to the distal end of the arm  303  and a rigid perpendicular rear-wall  322 . An oppositely positioned front wall  323  hingeably couples to the top portion at its proximal end. The front wall includes claws  32  at its distal end. The claws extend generally perpendicular to this front gripping wall  323 . In other embodiments of the claw-type gripping element, the claws can be any feature that extends under an item, for example, a cut-piece of rolled bar stock welded to a bottom edge of the front wall will restrict an item from sliding out of the grip. A pair of cylinders  326  actuate between an open and a closed position, which enables the claws to manipulate under an item  12  on the infeed conveyor  14 , grip (by closing the actuating cylinders) and pick up the item when the robot arm  303  moves upward. 
     The gripping element  321  arranges at the distal end of the arm  303  of the robot  30  and is operable to pick and place the at least one item  12  from the infeed system  14  and transfer the at least one item to a predetermined location on the layer queuing device  50 . The gripping element further includes a bottom support picker  323 . Thus, the gripping element positions adjacent to the item on the infeed conveyor in a first, open position and lowers to surround the item and close upon it. The picker  323  positions under the item. 
     In nearly all instances any method of item picking that does not support some portion of the bottom of the item is inferior to a device capable of bottom support because securing the item for pick and place transport is compromised. Bottom support overcomes deficiencies of top vacuum picking because the variable of vacuum seal is eliminated. Similarly clamping is not always reliable due to variations of item integrity. 
     Top picking vacuum devices are very common, but for many products such picking is impractical due to the item top construction being unsuitable for vacuum sealing required for picking. Many other items with some variable porosity of the top surface such as cardboard cases often require slower movements than might be possible because vacuum seal to the case top is inconsistent. 
     Item clamping for pick and place is another common method of item gripping. Many items are suitable for clamp picking, but the space occupied by the clamp surface on the item side creates voids in the finished load unless secondary time consuming item bumping occurs. 
     Building a loose layer on a layer support apron rather than directly on the load provides the option for the preferred embodiment of bottom support item picking because there is adequate clearance for the bottom support element of the picking device to disengage from the item when it is deposited. 
     Bottom support advantages are realized with only a minimal amount of bottom support as dramatic deformity of the item must occur before picker support capabilities are compromised. Furthermore only one side bottom support achieves nearly the same reliability as two sided bottom support picking as the item cannot slide out the bottom of the picker in either case without substantial deformity of the picked item. 
     The bottom support aspect of the gripper can engage by pivoting or lineal motion for which there are many methods of design. One or both sides of the picker can pivot or travel laterally to clamp and engage the item or items bottom and release the item or items. In the simplest design there is one fixed side and another side that pivots to open and close actuated by a pneumatic cylinder. Nearly the same device can be designed so that one side is slid horizontally to clamp and position the bottom support slide of the picker to the item or items. 
     In another variation of the first preferred embodiment, the layer queuing device  50  includes an oversized layer assembly platform and a compaction mechanism or layer conditioning mechanism  90 . Thus, when used with the gripping element  321 , this embodiment enables rapid placement of a layer of items on the platform  503 . Although the robot places each item of a given layer in a predetermined position, the positioning can be less precise (so called “rough or loose positioning”) and, therefore, the robot can move the arm more rapidly. Because the gripping element  321  requires clearance to release the grip of the item, the layer of items necessarily needs to be placed with space between each item picked or group of items picked on a given layer. In the prior art where items are placed directly on a load, such gripping of items required a subsequent bump or nudge into final position before the robot could return to the infeed conveyor. However, in this embodiment, the robot need only loose or rough position the items. Final positioning of all items of a layer is done at one time by the compaction mechanism or layer conditioning mechanism  90  on the oversized build platform  503 . 
     Accordingly, the apron comprises an oversized layer assembly platform  503   a  having an at least two-axis compaction mechanism or layer conditioning mechanism  90  operable to position the at least one item on the oversized layer assembly platform from a first loosely placed position to a second compressed position, the second compressed position approximating a finished layer dimension when deposited on a pallet. 
     It will be appreciated that the various variations of this first embodiment may be combined in different combinations. Importantly, this first embodiment with its variations can be adapted for many different palletizing operations wherein the infeed system is in a fixed position relative to the vertical column. In certain palletizing operations, the infeed system may present items at a low-feed height, while other systems may present items at a high-feed height. This first embodiment can readily adapt to any given infeed system height because the robot transfers the items from the infeed system to the build platform and the infeed height and variable build height need not be at the same elevation. 
     In certain installations, such as an operation that presents an infeed system a high-infeed position, a sliding transfer of items from an infeed conveyor  14  to the palletizer may be desired. Accordingly, a specialized end-effector as  FIGS. 15-18  illustrate may be preferred. Accordingly, the robot  30  includes an end effector  320  that is adapted to slide items from the infeed conveyor to the vertical transport platform, the end effector comprising a variable sized push bar  333 , the push bar comprising a positionable hand  335 , the hand being operable from 0-degrees rotation to 90-degrees rotation relative to the push bar whereby a rotation of 0-degrees enables the hand to be folded on the push bar for a cupped position facilitating item rotation in cooperation with robot gripper rotation capability and whereby 90-degrees rotation enables the hand and push bar to cooperatively extend the effective length of the push bar. A pneumatic strut  337 , and associated controllers and programming sequences can be used to position the hand  335  in the desired position as required for a particular palletizing operation. 
     The robotic end effector  320  is further operable to rotate the at least one item 90-degrees from a first orientation to a second orientation ( FIG. 15 ). As would be well-understood in the art, the robot arm and/or the end effector includes a wrist mechanism that enables 360-degrees of rotation about one axis. Additionally, the robot is operable to transfer a plurality of items from the infeed conveyor to the layer queuing device ( FIG. 17 ). 
     And although not shown in  FIGS. 1-20 , the end effector can be programmed to deposit multiple layers on the layer queuing device before the being deposited on the pallet. Thus, the layer queuing device adapts to receive the plurality of items to form multiple layers whereby fewer layer deposit cycles occur between the layer queuing device and the oversized layer assembly platform thereby increasing item throughput speed. For example,  FIG. 5  illustrates a representative double stand and double stack indexing operation, the technique and operation of which is well suited to this first preferred embodiment. 
     The present invention contemplates a method using a hybrid palletizer according to the first preferred embodiment.  FIGS. 1-14  show various stages of this first contemplated method using a hybrid palletizer of the present invention. For example,  FIGS. 1 and 2  show a first item  12  arriving on an infeed system  14 . The infeed system includes a transfer device, such as a roller conveyor, at a given infeed height  16 . The transfer device, illustrated as a roller conveyor, can be any type of infeed device including a free-rolling roller conveyor, a mechanized roller conveyor, a belt, or a flat surface for sliding items, for example. Appropriate stop bars or other mechanical devices and sensors may be included to locate an incoming item at a particular location on the infeed device, as would be well understood by those skilled in the art. Also, the infeed height  16  can vary depending on the particular application of use of the palletizer. As illustrated in  FIGS. 1-14 , the infeed height is at an intermediate height, higher than the pallet build height represented by the turntable  70 , and lower than the top of the frame structure  20 . However, a high-infeed height (above or near the top portion of the frame), or alternatively, a low-infeed height (at or near the floor or turntable height) would work as well for this first method. Variations to this method based on the location of the infeed conveyor are discussed subsequently. However, for the first embodiment of the preferred method, an intermediate infeed-height, as depicted in  FIGS. 1-14 , will be discussed. 
       FIGS. 1 and 2  show a first item  12  at the infeed system  14  conveyor. The robot  30  picks the item using its end-effector, here a gripping element  321  with picker fingers (claws)  32  arranged under a portion of the item. An empty platform  503  consisting of a flexible apron comprising a roller curtain of layer queuing device  50  awaits the first item. Below the layer queuing device, two previous layers of items already are completed on a pallet resting on the turntable  70 . It will be understood that the first two layer positioned on the pallet as depicted in the various figures would have been placed on the pallet according to this method in a previous iteration. 
       FIGS. 3 and 4  show the transfer or placement of the first item  12  from the infeed system  14  to the build platform  503  in first, pre-determined position. This first position, as illustrated, is in the front right-hand corner of the platform, however any number of layer build patterns is contemplated and this method should not be limited to the literal version depicted in the Figures. As this first item  12   a  is being placed, a second item  12   b  arrives at the infeed system. 
       FIGS. 5 and 7  illustrate a layer under construction. Each item on the platform  503  is located in a predetermined position according to a layer build pattern. However, each item is placed in a rough or loose position. This allows the robot to travel more quickly and transfer more items to the layer queuing device  50 . However, this rough build position results in a layer that is oversized when compared to the finished build layer required to fit on the pallet below. Accordingly, this layer will need subsequent conditioning prior to deposit on the pallet. 
       FIGS. 9-12  show another layer under construction. Each item on the platform  503  is located in a predetermined position according to a layer build pattern. However, some items ( 12   a    12   b    12   c ) are placed in a rough or loose position, each item being placed individually by the robot. But, items  12   d  and  12   e  are transferred simultaneously by the robot in a single pick and place operation. The robot picked both  12   e  and  12   d  at the same time, rotated the items 90-degrees and transferred the items to the layer queuing device. Meanwhile additional items arrive on the infeed conveyor ( FIGS. 9-10 ) and are subsequently transferred to the layer queuing device ( FIGS. 11-12 ). Thus, an oversized build layer is complete and will need subsequent conditioning prior to deposit on the pallet. 
     It will be appreciated, that the method of the present invention contemplates building at least one, preferably two, or alternately, a plurality of layers concurrently on the assembly platform prior to layer deposit on the pallet. The pattern of items deposited on the assembly platform in this concurrent building scenario will depend on a pre-determined positioning plan. One such plan includes building a first horizontal layer, then a second horizontal layer, and so one until the plurality of layers is built, then depositing the plurality of layers simultaneously. More likely, and preferably, the concurrent layer building operation is be optimized by building partial horizontal layers, such as stacking one item on top of a previously placed item before the first horizontal layer is completed. 
       FIGS. 13-14  show a complete layer under construction consisting solely of loose positioned items, wherein the robot individually transferred each item. This finished, albeit oversized, layer will need subsequent conditioning prior to deposit on the pallet. 
     This preferred method, accordingly, includes steps for palletizing a plurality of items from an infeed system using a hybrid palletizer and item-handling system includes presenting the plurality of items  12  at an infeed system first height  16 . Then, using a pick and place robot  30 , transferring at least one item from the plurality of items to a predetermined position on a layer queuing device  50  having an apron, the layer queuing device being arranged at a built-layer deposit height within a vertical column. Then, vertically hoisting the layer queuing device from the built-layer deposit height to a layer deposit height within the vertical column and opening the apron and depositing a first layer comprising at least one item on an pallet-build position or previously deposited layer within the vertical column. 
     In one iteration, a second layer of items is built on the layer queuing device  50  after the first layer of items is deposited on the pallet. Simultaneous to the building of the second layer, a stretch-wrapping device  60  operates a turntable  80  and wraps the first layer. 
     Accordingly, the method further includes the steps of building a second layer of items on the layer queuing device, the second layer comprising at least a second item from the plurality of items and concurrently stretch wrapping the first layer while the second layer is being built. 
     In another embodiment, the layer queuing device includes a flexible apron with a selectively positionable assembly platform. This apron, in one embodiment, positions in a fully closed arrangement and the pick and place puts each item in a pre-determined and unique x and y coordinate position in the single plane defined by the layer-build platform. In an alternate embodiment, the apron floor indexes incrementally as the layer is built. Thus, the robot places each item at a unique x direction but the same y or approximately similar y coordinates, when one item grouping is complete, the floor indexes forward horizontally to present an open portion of the platform. This method, accordingly, includes steps for providing a selectively and horizontally indexable apron floor arranged on the layer queuing device within the vertical column; using the pick and place robot, transferring at least one item on the indexable apron floor at assembly-platform layer-build height; indexing the apron floor horizontally to a second apron floor position; and transferring a second at least one item to the layer queuing device at the second apron floor position. 
     In yet another configuration, the more than one layer of items is built on the layer queuing device before being deposited on the pallet. This method includes additional steps of: building a first layer comprising a first plurality of items on the layer queuing device by using the pick and place robot to transfer each item to a pre-determined position; building a second or more layers comprising a second or more plurality of items on the layer queuing device by using the pick and place robot to transfer each item to a pre-determined position; and opening the apron and simultaneously depositing more than one layer on the pallet-build position or previously deposited layers within the vertical column. The description above is not meant to preclude stacking items to create more than one layer prior to completing the first layer rough positioning. 
     Further, items may be rough-positioned on the assembly platform, allowing the robot to move quickly and, thus, sacrificing precision. Items are placed in a pre-determined position, but have clearance between each item and may present a build layer that is bigger than the finished pallet dimensions. However, a compaction mechanism or layer conditioning mechanism, operating independent of the robot, operates to compress or compact or, more broadly, condition the layer before depositing it on the pallet. The method, therefore, includes further steps comprising: using the pick and place robot, transferring a first plurality of items to predetermined rough-build positions on an apron floor of a layer queuing device; compressing the first plurality of items from the rough-build positions to a built-layer deposit height by actuating at least one x-arm and one y-arm inward to compress or compact or, more broadly, condition the first plurality of items to a smaller x and y dimension on the apron floor; and depositing the first plurality of items in the built-layer deposit height to the pallet-build position within the vertical column. 
       FIGS. 26-28  illustrate a second preferred embodiment of a hybrid palletizer  11  having an apron with a pair of rigid platforms  513   a  and  513   b  that slideably and selectively open to deposit a build layer at a finished pallet build height. The remaining structure and operation of the layer queuing device, previously described in the first embodiment, remains unchanged and any differences are discussed here, without repeating the previous description. These elements include pallet-build position disposed within the vertical column of space, a robot operable to pick and place at least one item from the infeed system to the vertical transport platform. 
     In the various preferred embodiments, the hybrid palletizer ( 10  or  11 ) includes a pick-and-place robot  30 . The robot  30  includes an end-effector. One suitable end-effector includes a sliding-transfer mechanism for the unique situation when the infeed conveyor is at a high position so that the layer build platform that defines the layer-build height and the subsequent layer-deposit height will always be at or lower than the infeed conveyor height. In this embodiment, the pick-and-place robot further comprises a robotic end effector adapted for sliding items from the infeed conveyor to the layer assembly platform, the end effector comprising a variable sized push bar, the push bar comprising a positionable hand, the hand being operable from 0-degrees rotation to 270-degrees rotation relative to the push bar whereby a rotation of 0-degrees enables the hand to be folded on the push bar (for a compact position) and whereby 180-degrees rotation enables the hand and push bar to cooperatively extend the effective length of the push bar, and whereby 270-degrees rotation creates a right-angle with the push bar. The robot further includes a wrist mechanism and being operable to rotate the at least one item 90-degrees from a first orientation to a second orientation. 
     Another suitable end-effector is a gripping element  321  disposed at the end of an arm  303 , the gripping element and arm being operable to pick and place the at least one item from the infeed conveyor  14  to the vertical transport platform  100 , the gripping element further comprising a bottom support picker  32 . Similarly, the layer queuing device  50  further comprises an apron defining the assembly platform layer-build height, the apron operable from a first closed position to a second open position and a compaction mechanism or layer conditioning mechanism disposed in the vertical column and operable to include relative movement in at least two directions in a single plane, the compaction mechanism or layer conditioning mechanism comprising a first x-direction arm and a second, oppositely disposed x-direction arm, transfer mechanism  110  provides first y-direction conditioning, and a second, oppositely disposed y-direction conditioning occurs when apron removal urges the item layer against backstop  525  to create a generally rectilinear space, the four sided conditioning elements cooperatively operable to condition the item layer from a first, loose-build position to a second compressed-build position. And, the system further includes a stretch wrap device positioned in the vertical column of space and being operable for concurrent and automated stretch wrapping of a plurality of pre-positioned items within the vertical column while at least one item is being transferred from the infeed system to the layer queuing device. 
     Additionally, the layer queuing device includes a four-axis compaction element  90  wherein the first x-direction arm and the second, oppositely disposed x-direction arm are operable to selectively move toward each other to compact a plurality of items from a rough-build x-direction to a compact-build x direction and wherein the first transfer mechanism  110  and oppositely disposed y-direction backstop  525  arm are operable to selectively move to compact a plurality of items from a rough-build y-direction to a compact-build y direction. 
     Other elements contemplated by the preferred embodiments of the present invention include an infeed conveyor stop mechanism to restrict movement of at least one item in a pre-determined x-direction so robotic arm moves item/items to y-direction of loose-build position on the build platform, an oversized layer build platform  503  larger in the x and y directions than the finished pallet layer size. 
     A tilt-up dead plate  37  disposes normally in the same plane as the apron and infeed. During floor removal it pivots up to prevent already positioned items from sliding off the apron so that they then become the first items for the next layer. While it is tipped up additional items can be slid over the top if necessary. A similar, but simpler design is to position the infeed at an elevation slightlyabove the apron so there is always a barrier ledge due to the elevation difference that item or items can be slid across avoiding secondary mechanisms such as the tilt up dead plate. Alternatively to the tilt-up dead plate  37  can be a barrier that actuates from above. The purpose is to allow continual item positioning of new items destine for the next layer on the same apron mechanism while layer compression and deposit occurs on an already completed layer in a minimal amount of space. 
       FIG. 24 , a flowchart, illustrates a first and second preferred method according to the present invention. They hybrid palletizer is selectively pre-programmed to build one layer at a time on a layer queuing device (first preferred embodiment) or more than one layer (second preferred embodiment) prior to depositing the build layer on the pallet. According to the first preferred method a sequence starts (box  601 ) with items arriving on an infeed conveyor (box  603 ). The items may continually arrive any many well-understood arrival sequences as necessitated by the particular use and installation of the system  10  or  11  of the present invention. According to a predetermined programming, an item or group of items is/are presented to the robot (box  605 ). Initially, the layer queuing device is selectively positioned within the vertical column and within a range of motion of the robot (box  607 ). Once the layer queuing device is in place, the robot begins transferring individual items or groups of items to a predetermined rough position on the layer queuing device (box  609 ). This continues until the predetermined layer is built (box  611 ). In the first preferred method, only one layer is built before being deposited (box  613 ), so the layer queuing device is now free to travel in the vertical column to deposit the recently built layer on the pallet (box  615 ). 
     It should be understood that the infeed conveyor can position at any height relative to an empty pallet height in the vertical column of space. Thus, if the infeed conveyor is at the same height as an empty pallet (low infeed), the layer queuing device will continually travel upward as layers are built. Conversely, if the infeed conveyor locates towards the top of the frame structure (high infeed), the layer queuing device would initially travel downwards the full range of movement in the vertical column to deposit the first built layer and subsequently decrease the travel distance as the pallet is built up. Optionally, a pallet build area could be programmed to move downward as it builds in this high-infeed example, however, concurrent shrink wrapping (boxes  617 ,  619 , and  621 ) would be disabled. Additionally, the infeed conveyor could locate at an intermediate position, which would require the layer queuing device to move downward at first to deposit at least one build layer and then position itself above the build layer as the pallet was built. 
     When a layer is completed in this first preferred method, the apron floor retracts, depositing the newly build layer on the pallet. As soon as at least one layer is deposited on the pallet (box  615 ) a concurrent shrink wrap operation can begin (box  619 ). At any time after a first layer is deposited, stretch wrapping can occur concurrent with subsequent building of additional layers on the layer queuing device. Immediately after a layer is deposited and the layer queuing device clears the immediate vertical space above the last deposited layer, the turntable rotates. Prior to deposit of a first layer, film is automatically connected so that the turntable rotation pays out fill for wrapping. More than one concurrent stretch wrap sequence occurs during load build. After the last layer of the pallet load is deposited, wrapping is completed, the film is cut, the full (wrapped) pallet is discharged from the palletizer and the palletizer is ready or the next load (empty pallet). 
     In the second preferred method, multiple layers of items are built on the layer queuing device prior to layer deposit (box  613 ). Otherwise, this second method is similar to the first preferred method. 
       FIG. 25 , another flow diagram, illustrates a third and fourth preferred method according to the present invention. Similar operations to the first two preferred methods use the same box reference numerals. The third and fourth preferred methods contemplate an indexing apron floor as a build layer progresses. This increases the speed at which the robot can operate because the robot&#39;s travel distance is minimized to one x-direction instead of multiple x and multiple y directions of the first and second preferred methods. The indexing apron floor, therefore, moves into a second and subsequent x location as each partial layer is built. Accordingly, after the layer queuing device selectively positions within the vertical column and within range of the robot (box  607 ), the apron floor is set to the first index position (box  608 ). The robot places items or plurality of items on the apron at the first position (box  609 ) until this first position is full (box  614 ). Once the partial layer is built, the apron indexes to the second position (box  610 ), and this process repeats until an entire layer is built on the layer queuing device (box  611 ). In the fourth preferred method, more than one layer is built on the layer queuing device before being deposited on the pallet. Accordingly, before the apron indexes to the next position (box  610 ) the subsequent partial layer is built on top of the first partial layer (box  614 ). Otherwise, the third and fourth preferred methods are the same as the first and second preferred methods and concurrent wrapping occurs as described (box  616 ). 
     Although the invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.