Abstract:
A system and method for stacking battery cells or related assembled components. Generally planar, rectangular (prismatic-shaped) battery cells are moved from an as-received generally vertical stacking orientation to a generally horizontal stacking orientation without the need for robotic pick-and-place equipment. The system includes numerous conveyor belts that work in cooperation with one another to deliver, rotate and stack the cells or their affiliated assemblies. The belts are outfitted with components to facilitate the cell transport and rotation. The coordinated movement between the belts and the components promote the orderly transport and rotation of the cells from a substantially vertical stacking orientation into a substantially horizontal stacking orientation. The approach of the present invention helps keep the stacked assemblies stable so that subsequent assembly steps—such as compressing the cells or attaching electrical leads or thermal management components—may proceed with a reduced chance of error.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was supported by the government under a grant under Contract No. DE-EE0002217 awarded by the Department of Energy. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to a way to improve the manufacture of individual battery cells into assembled modules, and more particularly to the assembly of prismatically-shaped cans of cells using high-speed battery stacking. 
         [0003]    The increasing demand to improve vehicular fuel economy and reduce vehicular emissions has led to the development of both hybrid vehicles and pure electric vehicles. Pure electric vehicles may be powered by a battery pack (which is made up of numerous smaller modules or cells), while hybrid vehicles include two or more energy sources, such as a gasoline (also referred to as an internal combustion) engine used as either a backup to or in cooperation with a battery pack. There are two broad versions of hybrid vehicles currently in use. In a first version (known as a charge-depleting hybrid architecture), the battery can be charged off a conventional electrical grid such as a 120 VAC or 240 VAC power line. In a second version (known as a charge-sustaining hybrid architecture), the battery receives all of its electrical charging from one or both of the internal combustion engine and regenerative braking. In one form of either version, the pack is made from numerous modules, which in turn are made up of numerous individual cells. 
         [0004]    Typically, the individual cells that make up a module are of a generally rectangular, planar (or prismatic) structure that includes alternating stacks of sheet-like positive and negative electrodes having a similarly-shaped electrolytic separator disposed between each positive and negative electrode pair; these separators are used to prevent physical contact between positive electrodes and negative electrodes within each cell while enabling ionic transport between them. In one form, the separators are configured to absorb the liquid electrolyte of the cell. Cooling features are also frequently employed to convey away the heat generated by the various individual cells during the charging and discharging activities associated with battery operation; in one form, such cooling features may be formed as yet another generally planar sheet-like device that can be added between the various cells as part of the stacked arrangement of components that make up the module. Connection tabs extend from a peripheral edge of each cell to allow mechanical and electrical connection between the electrodes of the individual battery cells. Proper alignment of the various tabs is generally required to ensure low electrical resistance to bus bars or related conductors, as well as for robust mechanical connectivity. These prismatic cells typically have either a soft, flexible case (called “pouch” cells) or a hard rigid case (called “can” or “cannular” cells). Depending on the application, the individual battery cells may be arranged in series, parallel or combinations thereof to produce the desired voltage and capacity. Numerous frames, trays, covers and related structure may be included to provide support for the various cells, modules and packs, and as such help to define a larger assembly of such cells, modules or packs. 
         [0005]    Due to the prismatic dimensions, the current common practice for handling the rigid cannular cells during assembly is by stacking them along a generally vertical axis (for example, along the so-called y-axis in the well-known Cartesian coordinate system) such that the cells and frames are loaded with their largest flat surfaces laying down. However, the slightly bulged flat cells and the nesting geometries of the frames require them be stacked with the subassemblies standing up on their narrow, but flat edge surfaces. The cells may become bulged for various reasons; one such reason is due to increases in mechanical pressure that may arise from electrode expansion during operation that presses on the can walls, or internal gaseous pressure. In one particular instance, such expansion may be caused by electrolyte evaporation as heat is generated during operation, while in another, electrochemical reactions within the cell may create gaseous byproducts. As such, changes in stacking orientation may be required. Unfortunately, such changes in orientation can be a complex, expensive and inefficient process. 
         [0006]    In one form, it is known to manufacture a battery module assembly by using robotic pick-and-place component transport systems. Such approaches remove the cells from the shipping dunnage, transfer the cells via conveyor to an initial process step (typically in the form of electrical verification) and then transfer them via robotic pick-and-place equipment to the high precision carrier. Such approaches are useful for assembling layered cells that have tight placement tolerance requirements, as well as those with special handling needs. While this method is effective for protecting the cell during the assembly operation, it also leads to expensive tooling and wasted assembly time to locate the carrier in position, remove the part for the specific station operation and then return the part to the carrier to move to the next operation. This in turn forces packaging and tooling operations to become more complex and expensive. 
         [0007]    A previous horizontal battery stacking mechanism, which is described in co-pending application entitled LARGE FORMAT CELL HANDLING FOR HIGH SPEED ASSEMBLY, application Ser. No. 13/835,858 filed on Mar. 15, 2013 that is owned by the Assignees of the present invention and incorporated herein by reference, discloses the use of a conveyor belt with cams, lifters and guides to enable high speed assembly for large format cells that go through cell re-orientation and part sequencing steps. While useful for its intended purpose, the cams and the lifters that move in response to the cams still need to go through retracting and recirculating movements once the assemblies have been pressed together at the stacking stand. This in turn requires that the lifters, cam-followers and related equipment be returned to the place where they first engages the assemblies; during this return trip, they are not being used to help the assemblies being carried along the system. 
         [0008]    What is needed is a battery stacking approach that permits low cost, high speed continuous assembly that eliminates the need for high precision packaging and tooling, and that allows for reduced part cost by permitting larger dimensional variation. A battery stacking system employing such an approach would also occupy a relatively small manufacturing floor space footprint. 
       SUMMARY OF THE INVENTION 
       [0009]    According to an aspect of the present invention, a system for stacking numerous prismatic-shaped battery cells includes conveyor belts cooperative with one another to transport, rotate and stack the cells. The cooperation includes transporting the cells along a first of these belts while one or more lifting devices coupled to a second of these belts causes the cells to rotate. In this way, the largest, generally planar surface of cells is oriented in a substantially horizontal stacking direction. The system also includes one or more driving devices to operate the belts; as well as a receptacle to receive the rotated cells from the first belt. The movement of the belts are coordinated to have cell transporting, rotating and stacking operations take place in an orderly, registered manner without the need for the cells to be robotically picked from or added back to the belts of the system. In particular, the stacking system receives the cells (or their corresponding assemblies) such that when each cell arrives, its stacking surface is oriented along a substantially non-horizontal direction. The system moves the cells along a first conveyor belt such that a lifter (also called a flipper or flipping device) situated on a second conveyor belt causes the cells to rotate into a substantially horizontal direction; in this way, a subsequent facingly adjacent contact between successive cells (or a frame that is used as part of each cell assembly) can take place along a substantially horizontal direction. Once this stacking is completed, the aligned cell (or their respective assemblies) can then be compressed or otherwise secured along this horizontal axis, after which electrical, mechanical or cooling connection may be implemented to form an assembled battery module, section or related component. Benefits of the system of the present invention include low cost, high speed assembly of battery modules and battery packs by eliminating the need for high precision packaging and tooling. Furthermore, the system promotes reduced part cost by allowing more dimensional variation than from a traditional pick-and-place system. In the present context, the stacking of battery cells is meant to include situations where the cell is part of a larger assembly (such as a cell attached to a companion frame). As such the terms “cells”, “assemblies” and their variants can be used interchangeably in this disclosure unless the particular context dictates otherwise. 
         [0010]    According to another aspect of the present invention, a system for assembling a battery module is disclosed. The system includes a first conveyor belt with numerous backstops arranged in a spaced, repeating fashion on its cell-engaging surface, as well as a second conveyor belt with numerous flippers spaced in a similar repeating fashion along its respective cell-engaging surface. The first and second belts cooperate with one another such that one of the backstops facilitates translation of the cells from a receiving end of the system (i.e., where the system first encounters or picks up the individual cells) to a stacking end of the system. Likewise, a corresponding one of the flippers facilitates rotation of the largest, generally planar surface of the prismatic shape of the cells from a substantially non-horizontal direction at the receiving end of the system to a substantially horizontal direction at the stacking end of the system. The system also includes one or more driving devices to provide motive power to one or more of the belts. The system further includes a stacking stand situated at the stacking end of the system to receive the translated and rotated cells. The stacking stand may also be used to either compress the stack or cooperate with a compressing mechanism to compress the stack. Additional equipment may also be included to place a support structure onto the stack while the stack is in its compressed state. 
         [0011]    According to yet another aspect of the present invention, a method of assembling battery pack components into a battery module assembly is disclosed. In particular, the method includes a stacking mechanism (also referred to herein as a stacking system) that employs conveyor belts and a flipping device or related mechanism that permit battery assemblies to be stacked horizontally irrespective of their initial stacking orientation. As mentioned above, the cells and their related assemblies define a generally rectangular or prismatic shape; in this way, the cell or assembly has a generally planar surface that forms the largest projected area, as well as numerous edges formed around the generally rectangular periphery of the planar surface; it is the large, generally planar surface that is used as the stacking surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The following detailed description of specific embodiments can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0013]      FIG. 1  shows a notional vehicular propulsion system in the form of a battery pack; 
           [0014]      FIG. 2  shows a vertical stacking orientation of numerous battery cell/frame assemblies according to the prior art; 
           [0015]      FIG. 3  shows a partially exploded view of a horizontal stacking orientation of numerous battery cell/frame assemblies according to an aspect of the present invention; 
           [0016]      FIG. 4  shows a simplified perspective view of the stacking mechanism according to an aspect of the present invention with some details removed for clarity; 
           [0017]      FIG. 5  shows a simplified elevation view of a portion of the changes in stacking orientation of one of the assemblies as it traverses the stacking mechanism of  FIG. 4 ; 
           [0018]      FIG. 6  shows the cooperation of the various belts that make up the stacking mechanism of  FIG. 4 , including placement of numerous assemblies along a horizontal stacking axis; 
           [0019]      FIG. 7A  shows a side elevation view of an alternate embodiment of the stacking mechanism of the present invention, with some details removed for clarity; and 
           [0020]      FIG. 7B  shows a top-down view of the alternate embodiment of  FIG. 7A , emphasizing how the belt with the flippers engages the cells or assemblies from a different orientation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring initially to  FIG. 1 , a battery pack  1  employing numerous battery modules  10  with cells  100  is shown in a partially-exploded view. Depending on the power output desired, numerous battery modules  10  may be combined into larger groups or sections; such may be aligned to be supported by a common tray  2  that can also act as support for coolant hoses  3  where supplemental cooling may be desired. In the present context, the terms “battery cell”, “battery module” and “battery pack” (as well as their shortened variants “cell”, “module” and “pack”) are use to describe different levels of components of an overall battery-based power system, as well as their assembly. For example, numerous individual battery cells form the building blocks of battery modules. Numerous battery modules (in conjunction with ancillary equipment) in turn make up the completed battery pack. 
         [0022]    A bulkhead  4  may define a primary support structure that can function as an interface for the coolant hoses  3 , as well as house a battery disconnect unit in the event battery service is required. In addition to providing support for the numerous battery modules  10 , tray  2  and bulkhead  4  may support other modules, such as a voltage, current and temperature measuring module  5 . Placement of individual battery cells  100  within one of battery modules  10  is shown, as is the covering thereof by a voltage and temperature sub-module  6  in the form of plug connections, busbars, fuses or the like. Although shown notionally in a T-shaped configuration, it will be appreciated by those skilled in the art that battery pack  1  may be formed into other suitable configurations as well. Likewise, battery pack  1  may include—in an exemplary configuration—between about two hundred and three hundred individual battery cells  100 , although (like the arrangement) the number of cells  100  may be greater or fewer, depending on the power needs of the vehicle. In one exemplary form, battery pack  1  is made up of three sections a first of which consists of two modules  10  with thirty six cells  100  in each module  10  to make a seventy two cell section located along the vehicular longitudinal axis of the T-shaped battery pack  1 , a second of which consists of two modules  10  with thirty six cells  100  in each module  10  and one module with eighteen cells  100  to make a ninety cell section (also located along the vehicular longitudinal axis) and a third (located on the vehicular lateral axis of the T-shaped battery pack  1 ) made up of three modules  10  with thirty six cells  100  in each module  10  and one module with eighteen cells  100  to make a one hundred and twenty six cell section for a total of two hundred and eighty eight such cells. Other features, such as manual service disconnect  7 , insulation  8  and a cover  9  are also included in the battery pack  1 . In addition to the aforementioned battery disconnect unit, other power electronic components (not shown) may be used, including a battery management system or related controllers. 
         [0023]    Referring next to  FIG. 2 , a conventional vertical battery stacking approach according to the prior art is shown. The battery assembly  110  (also referred to herein as a subassembly to signify it being the building-block of a larger module, pack or the like) includes repetitive stacking of the battery cells  100 , frames  105  and end plates  107 . Unfortunately, a charged battery cell with prismatic can has a tendency to bulge on both sides of the stacking surfaces, which reduces the generally planar nature of contact between adjacent cells  100 . This in turn impacts the stability of the vertical stacking approach, especially as the stack height increases along the y-axis. This reduced stability is shown presently in the form of the stacked battery assembly  110  leaning to the right. 
         [0024]    Referring next to  FIG. 3 , assembly  110  made up of a cell  100  and a frame  105  is shown in an exploded view along a substantially horizontal (i.e., x-axis) direction. In both  FIGS. 2 and 3 , it can be seen that the assemblies  110  define a generally prismatic construction made up of an anode and a cathode (with corresponding positive and negative tabs or related contacts  100 A,  100 B) separated by an electrolytic membrane (details not shown). Additional details, such as cooling plates, fins and related structure—although not shown—may also form a part of each assembly  110 . As mentioned above, horizontal stacking does not have the stack height problem that plagues the vertically-stacked approach of  FIG. 2 . 
         [0025]    Referring next to  FIG. 4 , a battery stacking mechanism (or system)  200  defines a cell-receiving end  200 A and a stacking end  200 B. Stacking mechanism  200  includes numerous conveyor belts  210 ,  220  and  230  cooperative with one another such that upon receipt of numerous individual frame/cell assemblies  110 , stacking mechanism  200  reorients the assemblies  110  from a generally vertical stacking direction to a generally horizontal stacking direction as a way to avoid the misalignment and related stacking problems that may arise when the numerous battery cells  100  are in a bulged condition. Additional components, including backstops  215  (on the main belt  210 ) and  235  (on the upper belt  230 ), assembly flippers  225 , stabilizers (described below) and one or more access windows  285  for retrieving a battery assembly  110  may also be used. The backstops  215  and  235 —by virtue of being affixed or otherwise fastened to their respective belts  210  and  230 —provide a secure lower mounting surface for the assemblies  110  to help carry them forward (i.e., in a left-to-right registered pattern as shown in  FIGS. 4 through 6 ) until such time as they reach a suitable stacking receptacle (discussed below), while backstops  235  provide additional support at the upper edge of the assemblies  110  once they have been tilted upward in a 90° position relative to the surface of main belt  210 ; this latter support is shown with particularity in  FIG. 6 . One attribute that is significant in helping to establish and maintain registry between the belts  210 ,  220  and  230  is the pitch P; this is a measure of the distance between similar spots on adjacent backstops  215  or  235  (on the main belt  210  and the upper belt  230 ) or adjacent flippers  225  (on flipper belt  220 ). In one exemplary form, such a pitch P could be on the order of 150 millimeters. Significantly, the present invention does away with the need for cams, lifters or related protuberances that would otherwise cause an undulation or related deviation from the generally planar construction in the travel path of the conveyor belts  210 ,  220  and  230 . 
         [0026]    A series of gears, pulleys and related equipment  250  is also included to provide registered (i.e., meshed, synchronous) interaction of the various belts  210 ,  220  and  230 . These components may make up part of (or in the alternative be coupled to) one or more drives (including a central drive  260 ) can be used to impart rotational motion to the conveyor belts  210 ,  220  and  230 ; such drives may be part of (or in turn receive motive power through) a suitable engine (not shown). The pulley and gear train making up equipment  250  enables the three (or four) belts  210 ,  220  and  230  to run synchronously with central drive  260  where arrows show one exemplary form of cooperative movement between them. 
         [0027]    The aforementioned receptacle is in the form of a stacking stand  270  that is placed at a remote end of stacking mechanism  200 ; stacking stand  270  is configured to receive the horizontally-stacked assemblies  110  such that subsequent assembly operations (such as attaching electrical connections, cooling connections or the like) may be performed. In one form, stacking mechanism  200  is placed on a sled or frame  280  to facilitate modular construction. The stacked cells or assemblies  110  that have accumulated on the stacking stand  270  will exit through the enclosure  295  (as shown at the stacking end  200 B of stacking mechanism  200 ) and continue for further processing. To be suitable for pack assembly, the stacked cells or assemblies  110  may be subjected to a compressing operation through cooperation between movable and stationary holding tools (not shown); additional lateral support may be provided through mounted guides (not shown). This compression may be configured to impart one of a predetermined force or distance, depending on cell  100  structural needs, cooling fin design or the like. In one preferred embodiment, the compression forces range from between about one hundred Newtons and about four thousand Newtons, while a compressive displacement may be between about one and thirty millimeters. Once this predetermined level is reached, a box-like frame (not shown, but for example configured as a U-shaped structure with its own end plate with interlocking features) is secured around the compressed stack, after which a cover (which may include wiring harnesses, busbars, connectors and ancillary electronic equipment) is attached to the stack and frame that in turn may be secured through known means, such as welding (for example, ultrasonic welding, resistance welding or laser welding) mechanical fastening or the like. It will be appreciated by those skilled in the art that some of the details of stacking mechanism  200  are either not shown (for example, certain belts or other conveying or connectivity mechanisms) or simplified in order to promote clarity in the remaining features. 
         [0028]    Significantly, each of the conveyor belts  210 ,  220  and  230  define a continuous, closed loop construction. As such, once each belt  210 ,  220  and  230  has completed its portion of the delivery or reorientation of the assemblies  110 , its members return to an initial takeup point to gather up a new batch of cells  100  or their related assemblies  110 . Significantly, features included in at least the main belt  210  and the upper belt  230  are used on both the feed and return trips. In particular, periodically-spaced backstops  215 ,  235  that are mounted into or on top of the main and upper belts  210 ,  230  help ensure accurate positioning of the assemblies  100  both before and after reorientation. Thereby significantly increasing speed over conventional systems such as pick-and-place, where—in addition to empty return trips for incoming parts—the opening and closing of grippers and related components tend to slow down movement in approaching or positioning parts. In fact, the prismatic nature of the cans used to encase the individual battery cells  100  are inherently easy to handle by the present invention due to their rigid structure and well defined dimensions. 
         [0029]    The first of the conveyor belts  210  is referred to as the main belt  210  that carries forward the assemblies  110  of battery cells  100  and cooling frames  105  to be stacked. In a preferred form, there are two flipper conveyor belts  220  that straddle main belt  210  along its opposing lateral sides; while delivering the assemblies  110  for stacking, all three belts move in the same general left-to-right direction as shown in the figure, although the flipper belts  220  may be inclined by a small amount (for example, about 5° relative to the x-axis) relative to the main belt  210 . Flippers  225  and backstops  215  are mounted onto their respective belts  220 ,  210  in a repeating, periodic pattern. Upper belt  230  assists the main belt  210  in transporting and stacking the battery assemblies  110  with backstops  235  that are generally similar to backstops  215 ; this assistance is particularly helpful once the cells  100  or assemblies  110  have been rotated into their substantially upright (i.e., where the largest planar surface of the cell or assembly is oriented 90° relative to the surface of main belt  210 ) position. The central drive  260  is engaged with the belts  210 ,  220  and  230  such that they can all be moved simultaneously and synchronously through the gears, pulleys and related equipment  250 . By virtue of this geared relationship, all of the conveyor belts  210 ,  220  and  230  move continuously and synchronously, thereby facilitating high speed meshed operation. 
         [0030]    Referring next to  FIGS. 5 and 6  in conjunction with  FIG. 4 , flippers  225  act as moving lifters by being attached at a fixed pitch relative to the flipper belt  220  that flanks the main belt  210  on both sides. Moreover, the flippers  225  define a generally arcuate shape such that upon engagement with the battery assemblies  110  and progression from left-to-right as shown, the flippers  225  that straddle the main belts  210  gradually coax the assemblies  110  into successively more edgewise placement on the main belt  210 . In this way, the flippers  225  act like moving cam lifters on opposing sides of the main belt  210  to promote the horizontal stacking orientation of the assemblies  110 ; as shown in  FIG. 6 , three representative angular snapshots of the assembly  110  at 61°, 81° and 86° relative to the horizontal (i.e., x-axis) respectively are shown. In one form, the two flipper belts  220  may be driven by a coaxial pulley; such a device simplifies the drive train; to unload a stacked set of assemblies from the stacking stand&#39;s backstop  270  with such an axle arrangement will require a stack exit window  285  situated along a sideways (i.e., z-axis) exit. Battery stacking mechanism  200  uses the backstops  215  that are situated on main belt  210  along with one of the flippers  225  that pass by on the flipping belt  220  to keep each of the cells  100  (or their respective assembly  110 ) registered with respect to the immediately preceding and succeeding cells that are traversing main belt  210 . In the present context, adjacent cells  100  or their assemblies  110  are considered to be registered as long as they maintain their intended position and orientation while traversing the stacking mechanism  200 ; in one form, such registration may be judged by the various cells  100  maintaining a desired degree of horizontal (x-axis) spacing or rotational orientation between them to ensure a predetermined stacking configuration. Geared cooperation between various components (such as the various conveyor belts  210 ,  220  or  230 ) are considered to be registered as long as they maintain the timing, spacing, meshing or related operation to ensure delivery of the cells  100  or assembles  110  from start to finish. Contrarily, when one or more cells  100  or assemblies  110  gets out of registry, the potential for misalignment or other stacking problems may arise. 
         [0031]    As shown with particularity in  FIG. 5 , assemblies  110  with their largest planar surfaces oriented in a substantially vertically-facing direction are introduced to the stacking mechanism  200  along the main belt  210  at the left side (not shown). Because the assembly  110  defines a width that is greater than the main belt  210 , the flippers  225  are able to contact the assembly  110  from below. Because of the angled relationship mentioned above between the belts  210  and  220 , the flippers  225  start off on the left side of the stacking mechanism  200  being below the main belt  210 , during this early stage, flippers  225  have no engagement with the subassemblies  110 . As the belts move simultaneously to the right, the flippers  225  move up progressively above the main belt  210 , thereby lifting the assemblies  110  such that the surface of their largest planar dimension goes from being aligned to a vertical (i.e., y-axis) to a horizontal (i.e., x-axis) with the help of stops  215  on the main belt  210 . When the flipper  225  moves to a point higher along the y-axis than the assembly  110 , the two become disengaged, this allows the assembly  110  to proceed to the stacking stand  270  on the far right of the stacking mechanism  200 . A stabilizer  290  (which may be outfitted with brushes or soft friction pads), lightly contacts the side edges of the cells  100  or assemblies  110  to prevent them from tipping forward before stacking. 
         [0032]    As the assemblies  110  move from the conveyor belts  210 ,  220  to the stacking stand  270 , the stacking stand  270  slides by the conveyor force until the backstops  215 ,  235  disengage from the cells  100  or assembly  110 . The inertial forces also move the backstop  270  in the stacking direction. The backstop  270  of the stacking stand is keyed to the stacking stand plate  275  to allow movement in the x-axis and is held with an adjustable friction device (e.g. spring loaded) to provide resistance as the assemblies  110  exit the conveyor belts  210 ,  220 . Furthermore, the stacking stand plate  275  is adjustable to a negative angle (i.e. −5 degrees) to allow the assemblies to fall against each other and use gravity to rest against the backstop  270 . Thus, the stacking stand plate  275  acts as the base plate that the cells  100  or assemblies  110  move onto when they come off of the main belt  210 . 
         [0033]    Significantly, the use of the approach depicted in  FIGS. 4 through 6  facilitates high speed stacking for assemblies  110  by positioning the parts to stack without the individual (i.e., robotic) manipulations associated with conventional pick-and-place-based equipment. Moreover, by conveying parts that are loosely assembled at high speeds along edgewise orientations (with concomitant small component footprint), a much smaller amount of manufacturing floor space is required. 
         [0034]    Referring next to  FIGS. 7A and 7B , an alternative embodiment shows that the two conveyor belts  220  with the flippers  225  can be driven by parallel axles, which allow the stacked cells  100  or assemblies  110  to exit more conveniently in the direction of stacking as they approach the stacking end  200 B of the system  200 .  FIG. 7A  shows the embodiment in a side elevation view and  FIG. 7B  shows a top elevation view. Referring with particularity to  FIG. 7B , the two conveyor belts  220  with the flippers  225  may be oriented such that rather than the selective engagement of the flippers  225  and cells  100  or assemblies  110  taking place through an angled intersection of their respective belts  210  and  220 , they engage through a sideways cooperation of the belts. In this embodiment, the flipper  225  is mounted to the face of the conveyor belt  220 , rather than being mounted to a lateral (i.e., side) as described above. This mounting strategy results in less twist and tension in the conveyor belt  220 , which helps improve the life of the belt and allow better assembly  110  alignment for stacking. A different view of the stabilizer  290  with brushes shows how it contacts the side edges of the cells  100  or assemblies  110  to prevent them from tipping forward prior to stacking against backstop  270 . 
         [0035]    While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention, which is defined in the appended claims.