Patent Publication Number: US-2023150770-A1

Title: Automated shuttle materials handling and storage systems and methods of using the same

Description:
FIELD OF THE INVENTION 
     Example embodiments of the present invention relate generally to material handling systems for handling items, and, more particularly, to techniques for using a plurality of shuttles to move objects to and/or from various storage locations within a material handling system. 
     BACKGROUND 
     Automated Storage and Retrieval Systems (ASRS), such as ASRS product lifts and automated shuttles configured to move along shuttle guide tracks, are used as material handling systems to facilitate movement of high volumes of articles and maximize the use of valuable storage space. ASRSs are key components in material handling environments by combining automation, software, and labor to optimize the productivity and throughput in a variety of operations. Furthermore, ASRSs provide flexibility and speed allowing use in applications ranging from e-commerce and omnichannel fulfillment to article distribution. Applicant has identified several technical challenges associated with utilizing automated shuttles in an ASRS to retrieve objects stored at discrete storage locations within a storage rack arrangement. Through applied effort, ingenuity, and innovation, many of these identified challenges have been overcome by developing solutions that are included in embodiments of the present invention, many examples of which are described in detail herein. 
     BRIEF SUMMARY 
     Various embodiments are directed to an automated storage and retrieval system and methods of using the same. Various embodiments re directed to an automated storage and retrieval system comprising: a plurality of storage aisles, each storage aisle comprising a plurality of storage locations positioned adjacent to an aisle track that extends along an aisle length; a plurality of shuttles configured to travel throughout the automated storage and retrieval system to execute a materials handling operation; at least one vertical lift; a plurality of inter-aisle shuttle outlet tracks configured to facilitate shuttle traffic flow in at least substantially the same direction, the plurality of inter-aisle shuttle outlet tracks comprising: a first inter-aisle shuttle outlet track configured to facilitate shuttle traffic flow to the at least one vertical lifts via at least one lift interface position defined along the first inter-aisle shuttle outlet track; and a second inter-aisle shuttle outlet track arranged in an at least substantially parallel configuration relative to the first inter-aisle shuttle outlet track; wherein the plurality of inter-aisle shuttle outlet tracks is configured to enable a transfer of at least one of the plurality of shuttles between the first inter-aisle shuttle outlet track and the second inter-aisle shuttle outlet track at one or more transfer locations along the first inter-aisle shuttle outlet track; wherein the aisle track of each storage aisle of the plurality of storage aisles is configured to facilitate shuttle traffic flow along the aisle length thereof in a first shuttle travel direction such that each of the plurality of storage aisles is defined in part by a unidirectional shuttle traffic flow pattern. 
     In various embodiments, the automated storage and retrieval system may further comprise a central controller configured to transmit instructional signals to each of the plurality of shuttles to cause the plurality of shuttles to travel throughout the automated storage and retrieval system. In various embodiments, the plurality of storage aisles may be defined by further comprising a rack arrangement comprising a plurality of storage racks, each storage rack being defined by a plurality of storage shelves arranged in a vertically stacked configuration such that the rack arrangement comprises a plurality of rack arrangement levels, wherein each of the plurality of storage aisles is provided within a first rack arrangement level. In certain embodiments, the plurality of storage racks may be arranged in an at least substantially parallel configuration such that each of the plurality of storage aisles is parallel to one another. 
     In various embodiments, the automated storage and retrieval system may further comprise an inter-aisle shuttle inlet track operatively connected to a respective aisle inlet end of each of the plurality of storage aisles such that each of the plurality of storage aisle is accessible to the plurality of shuttles via the inter-aisle shuttle inlet track, wherein the inter-aisle shuttle inlet track is configured to facilitate unidirectional shuttle traffic flow along a shuttle inlet track length thereof. In certain embodiments, the automated storage and retrieval system may further comprise a shuttle transport track extending from the plurality of inter-aisle shuttle outlet tracks to the inter-aisle shuttle inlet track so as to facilitate transportation of the plurality of shuttles from the plurality of inter-aisle shuttle outlet tracks to the inter-aisle shuttle inlet track. Further, in certain embodiments, the automated storage and retrieval system may be configured to enable a shuttle recirculation traffic flow pattern defined at least in part by respective unidirectional shuttle traffic flow patterns along each of the shuttle transport track, the inter-aisle shuttle inlet track, the plurality of inter-aisle shuttle outlet tracks, and at least one of the plurality of storage aisles. 
     In various embodiments, the automated storage and retrieval system may further comprise a shuttle storage position that is defined by a shuttle guide track segment along which the automated storage and retrieval system is configured to store one or more of the plurality of shuttles that are configured in a standby configuration at a particular instance. In certain embodiments, the shuttle storage position may be defined along a secondary shuttle transport track extending at least partially between the plurality of inter-aisle shuttle outlet tracks and an inter-aisle shuttle inlet track operatively connected to each of the plurality of storage aisles. In various embodiments, the first inter-aisle shuttle outlet track may be defined at least in part by a first track length and the second inter-aisle shuttle outlet track is defined at least in part by a second track length that is at least substantially equal to the first track length. 
     Various embodiments are directed to a method of operating an automated storage and retrieval system using a unidirectional shuttle traffic flow pattern, the method comprising: providing an automated storage and retrieval system comprising a first storage aisle, the first storage aisle comprising an aisle track extending along an aisle length and a plurality of storage locations positioned at least substantially adjacent the aisle track, wherein the aisle track is configured to facilitate movement of a plurality of shuttles along the first storge aisle in a shuttle travel direction defined along the aisle length; causing a first shuttle to travel to a first storage location provided within the first storage aisle such that the first shuttle moves along an aisle track of the first storage aisle in a first shuttle travel direction; causing a second shuttle to travel to a second storage location provided within the first storage aisle such that the second shuttle moves along the aisle track of the first storage aisle in the first shuttle travel direction and such that both the first shuttle and the second shuttle are positioned within the first storage aisle at a first instance; and causing the first shuttle to travel in the first shuttle travel direction from the first storage location to a first storage aisle outlet of the first storage aisle. 
     In various embodiments, the method may further comprise causing the second shuttle to travel along the aisle track in the first shuttle travel direction to the first storage aisle outlet. In various embodiments, the method may further comprise accessing, via the first shuttle, a first vertical lift of a plurality of vertical lifts by causing the first shuttle to travel from the first storage aisle to a first lift interface position defined along a first inter-aisle shuttle outlet track. Further, in various embodiments, the method may further comprise determining that the first shuttle is stopped along the first inter-aisle outlet track at a first lift interface position; identifying that the second shuttle traveling along the first inter-aisle outlet track is in an upstream position relative to the first shuttle; and causing the second shuttle to transfer from the first inter-aisle outlet track to a second inter-aisle outlet track arranged in an at least substantially parallel configuration relative to the first inter-aisle shuttle outlet track. In certain embodiments, the method may further comprise upon determining that the second shuttle has moved along the second inter-aisle shuttle outlet track so as to pass the first shuttle, causing the second shuttle to transfer from the second inter-aisle outlet track to the first inter-aisle outlet track; and accessing, via the second shuttle, a second vertical lift of the plurality of vertical lifts by causing the second shuttle to travel to a second lift interface position defined along the first inter-aisle shuttle outlet track, wherein the second lift interface position is arranged downstream from the first lift interface position along the first inter-aisle shuttle outlet track. 
     In various embodiments, the method may further comprise determining a system bandwidth of the automated storage and retrieval system based at least in part on a number of shuttles of the plurality of shuttles determined to be executing a materials handling operation at a measurement instance; identifying a third shuttle of the plurality of shuttles this is configured in a standby configuration; providing instructions to the third shuttle to execute a third materials handling operation, so as to increase the number of shuttles of the plurality of shuttles in operation within the automated storage and retrieval system. In various embodiments, the method may further comprise causing a third shuttle to travel to a third storage location provided within the first storage aisle such that the third shuttle moves along the aisle track of the first storage aisle in the first shuttle travel direction and such that each of the first shuttle, the second shuttle, and the third shuttle are positioned within the first storage aisle at the first instance. In various embodiments, the method may further comprise upon determining that that the first shuttle has executed a first materials handling operation, providing instructions to the first shuttle to execute a second materials handling operation, including causing the first shuttle to travel to a third storage location provided within the first storage aisle such that the first shuttle moves along the aisle track of the first storage aisle in the first shuttle travel direction. Further, in certain embodiments, the automated storage and retrieval system comprises a plurality of storage aisles, and wherein the method may further comprise identifying that first storage aisle outlet of the first storage aisle is arranged in an upstream position from a first lift interface portion corresponding to a first vertical lift relative to a unidirectional shuttle recirculation traffic flow pattern defined by the automated storage and retrieval system; and wherein causing the first shuttle to travel to the first storage location provided within the first storage aisle comprises selectively causing the first shuttle to travel to the first storage aisle of the plurality of storage aisles based at least in part on the upstream position of the first storage aisle outlet relative to the first lift interface portion corresponding to the first vertical lift. 
     Various embodiments are directed to an automated storage and retrieval system comprising: at least one storage aisle comprising a plurality of storage locations positioned adjacent to an aisle track that is defined by an aisle length, wherein the storage aisle is defined in part by a unidirectional shuttle traffic flow pattern that extends along the aisle length; a plurality of shuttles configured to travel throughout the automated storage and retrieval system to execute a materials handling operation; a plurality of shuttle outlet tracks configured to facilitate shuttle traffic flow from the storage aisle to each of object disposal positions, the plurality of shuttle outlet tracks comprising: an object disposal track configured to facilitate shuttle traffic flow in a first shuttle travel direction along the object disposal track to at least one of a plurality of object disposal positions defined along the object disposal track; and a parallel passing track arranged in an at least substantially parallel configuration relative to the object disposal track and configured to facilitate shuttle traffic flow in the first shuttle travel direction along the parallel passing track; wherein the plurality of shuttle outlet tracks is configured to enable a transfer of at least one of the plurality of shuttles between the object disposal track and the parallel passing track at one or more transfer locations along a track length of the object disposal track. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG.  1    illustrates a schematic view of an exemplary automated storage and retrieval system according to various embodiments described herein; 
         FIG.  2    illustrates a schematic view of an exemplary automated storage and retrieval system according to various embodiments described herein; 
         FIGS.  3 A- 3 B  illustrate various schematic views of exemplary automated storage and retrieval systems according to various embodiments described herein; 
         FIG.  4    is a flowchart of operating an automated storage and retrieval system in accordance with an example embodiment; and 
         FIG.  5    is a flowchart of operating the automated storage and retrieval system in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure more fully describes various embodiments with reference to the accompanying drawings. It should be understood that some, but not all embodiments are shown and described herein. Indeed, the embodiments may take many different forms, and accordingly this disclosure should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     It should be understood at the outset that although illustrative implementations of one or more aspects are illustrated below, the disclosed assemblies, systems, and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents. While values for dimensions of various elements are disclosed, the drawings may not be to scale. 
     The words “example,” or “exemplary,” when used herein, are intended to mean “serving as an example, instance, or illustration.” Any implementation described herein as an “example” or “exemplary embodiment” is not necessarily preferred or advantageous over other implementations. 
     The words “lateral,” longitudinal,” and “vertical,” when used herein, are intended to be used for referential and/or illustrative purposes in order to provide context for one or more aspects of the present invention, and should be strictly interpreted as being limited a particular universal direction. By way of non-limiting example, as described herein with reference to the directional references provided in the figures, the “lateral” direction may extend along an x-axis, a “longitudinal” direction may extend perpendicularly within at least substantially the same plane as a lateral direction, such as, for example, along a y-axis, and a “vertical” direction may extend perpendicularly within an at least substantially perpendicular plane relative to both the lateral and longitudinal directions, such as, for example, along an a z-axis. 
     The components illustrated in the figures represent components that may or may not be present in various embodiments of the invention described herein such that embodiments may include fewer or more components than those shown in the figures while not departing from the scope of the invention. 
     Overview 
     Automated storage and retrieval systems may utilize various material handling products such as various carriages, carts, lifts, conveyors, and/or the like to facilitate the transportation of objects to a desired delivery location within a factory or a warehouse. For example, automated shuttles may be used to transport objects to and/or from various storage locations organized along storage aisles arranged within a storage environment. Further, a vertical lift assembly may be used to facilitate the vertical transportation of one or more objects between different levels of a storage rack or other storage environment. Various automated storage and retrieval systems may include a shuttle provided within each storage aisle of the system that is configured execute a retrieval operation by moving in a first direction along the storage aisle to a storge location, retrieving an object disposed within the storage location, and returning to a vertical lift provided adjacent the storage aisle by moving in a second direction opposite the first direction along the storage aisle to the vertical lift. For example, such automated storage and retrieval systems may provide a vertical lift adjacent each storage aisle defined therein such that the shuttle configured for bidirectional travel within that particular storage aisle can access a respective vertical lift adjacent thereto in order to facilitate the transportation of an object between the storage aisle and a remote location within a materials handling environment. 
     The present invention relates to an automated storage and retrieval system comprising a plurality of storage aisles, each comprising an aisle track configured to facilitate shuttle traffic flow of a plurality of shuttles along the aisle length thereof in a first shuttle travel direction such that each of the plurality of storage aisles is defined in part by a unidirectional shuttle traffic flow pattern. As described herein, the exemplary AS/RS is configured such that the plurality of shuttles are transported throughout the AS/RS according to a shuttle recirculation traffic flow pattern defined at least in part by the unidirectional shuttle traffic flow pattern of each of the plurality of parallel storage aisles. The present invention is preferrable to automated storage and retrieval systems comprising shuttles that are limited to bidirectional travel along respective storage aisles, as the unidirectional shuttle traffic flow pattern in each of the storage aisles of the AS/RS at least substantially eliminates the risk of gridlock and/or traffic backup caused by two shuttles simultaneously positioned within the same storage aisle that are moving in opposing directions and/or along conflicting shuttle traffic paths. As such, the present invention allows for the AS/RS to be operated such that a plurality of shuttles executing respective materials handling operations may be positioned within the same storage aisle at the same time, thereby increasing system output by minimizing the inefficiencies associated with the travel time of bidirectional shuttles to and from various storage locations within a single storage aisle. 
     Further, the present invention includes an AS/RS comprising a plurality inter-aisle shuttle outlet tracks configured to facilitate shuttle traffic flow in at least substantially the same direction, including a first inter-aisle shuttle outlet track configured to facilitate shuttle traffic flow to each of a plurality of vertical lifts via corresponding lift interface positions defined along the first inter-aisle shuttle outlet track, and a second inter-aisle shuttle outlet track arranged in an at least substantially parallel configuration relative to the first inter-aisle shuttle outlet track. As described herein, the plurality of inter-aisle shuttle outlet tracks is configured to enable a transfer of at least one of the plurality of shuttles between the first inter-aisle shuttle outlet track and the second inter-aisle shuttle outlet track at one or more transfer locations along the first inter-aisle shuttle outlet track. In such an exemplary configuration, the plurality of inter-aisle shuttle outlet tracks of the AS/RS may embody parallel passing lanes that provide access for each of the plurality of shuttles within a particular level of the AS/RS to access each of the plurality of vertical lifts for executing various storage and/or retrieval operations, thereby maximizing the efficiency and collective output of the plurality of vertical lifts. Further, the plurality of inter-aisle shuttle outlet tracks of the present invention, as described herein, may facilitate an at least substantially continuous flow of shuttle traffic throughout the AS/RS by providing the second inter-aisle shuttle outlet track that may be selectively used as a passing lane to which at least a portion of the shuttles may be transferred (e.g., from the first inter-aisle shuttle outlet track) to avoid a shuttle stopped at a lift interface position along the first inter-aisle shuttle outlet track, thereby at least substantially maximizing system throughput by minimizing bottlenecks that my result from traffic interferences within the AS/RS. 
     In various embodiments, a material handling system may include an exemplary automated storage and retrieval system (AS/RS) comprising a rack arrangement comprising a plurality of storage racks. For example, a storage rack of the AS/RS may be defined as a series of vertically arranged shelves, each supported by a support frame (e.g., a post and beam rack). The support frame may comprise vertical support members separating various levels within the storage rack, and horizontal support members supporting individual shelves. Each shelf may define and/or comprise a plurality of storage locations (e.g., separated into one or more bays) configured for storing at least one object (e.g., a storage container, a product, a spool, and/or other object configurations) therein. In various embodiments, wherein the rack arrangement of the AS/RS comprises a plurality of storage racks, the rack arrangement may be defined at least in part by a plurality of rack arrangement levels, each corresponding to a respective level of the rack arrangement defined within a corresponding at least substantially horizontal plane. For example, in an exemplary circumstance wherein a rack arrangement of an exemplary AS/RS comprises a plurality of storage racks, each comprising a plurality of storage shelves arranged in a vertically stacked configuration such that each storage rack is defined by a plurality of storage rack levels, a rack arrangement level may be defined collectively by each of the storage rack levels from the storage racks of the rack arrangement that are defined within a common (e.g., at least substantially the same) horizontal plane (e.g., level). Further, a rack arrangement level defined within an at least substantially horizontal plane may be defined by each storage shelf (e.g., each of the storage locations provided therein) of the plurality of storage racks that is provided within the least substantially horizontal plane. 
     In various embodiments, the plurality of racks of a rack arrangement of the AS/RS may be arranged such that two adjacent storage racks are provided in an at least substantially parallel configuration relative to one another. As described in further detail herein, two adjacent storage racks may be arranged such that an aisle is provided therebetween. For example, the aisle may be defined at least in part by the perpendicular separation distance between adjacent storage racks. 
     Further, as described herein, an exemplary AS/RS may comprise a plurality of shuttle guide tracks extending along and/or between each of the plurality of storage racks of the rack arrangement. The plurality of shuttle guide tracks may be configured such that a plurality of automated shuttles configured for travel thereon may move along the tracks between various racks (e.g., storage locations) within the rack arrangement. In various embodiments, the plurality of shuttle guide tracks of the AS/RS may comprise a plurality of aisle tracks, each provided along a respective aisle length between a respective pair of two adjacent storage racks. As described in further detail herein, an exemplary AS/RS may comprise a plurality of storage aisles, each comprising a first storage shelf and a second storage shelf, defined by respective portions of adj acent first and second storage racks that are provided in the same rack arrangement level (e.g., within at least substantially the same horizontal plane), and an aisle track extending between the first storage shelf and the second storage shelf along an aisle length such that each of the storage locations within the first and second storage shelves are accessible to a shuttle via the aisle track provided therebetween. 
     In various embodiments, a shuttle of the AS/RS may be configured for movement along each of the plurality of shuttle guide tracks provided within a rack arrangement level of the system (e.g., within a singular horizontal plane). For example, the plurality of shuttle guide tracks may comprise a first plurality of shuttle guide tracks provided within a first rack arrangement level and configured to enable shuttle transportation of a first plurality of shuttles to and/or from a first storage aisle defined by a first storage shelf, a second storage shelf, and a first aisle track provided within the first rack arrangement level. In such an exemplary circumstance, the plurality of shuttle guide tracks of the same AS/RS may further comprise a second plurality of shuttle guide tracks provided within a second rack arrangement level and configured to enable shuttle transportation of a second plurality of shuttles to and/or from a second storage aisle defined by a third storage shelf, a fourth storage shelf, and a second aisle track provided within the second rack arrangement level. Further, in various embodiments, as described in further detail herein, a rack arrangement of an exemplary AS/RS may comprise a plurality of storage racks arranged such that each rack arrangement level of the AS/RS comprises a plurality of storage aisles, each of which may be accessible to a shuttle configured to travel along the plurality of shuttle guide tracks within the rack arrangement level. 
       FIG.  1    illustrates a schematic view of an exemplary automated storage and retrieval system according to various embodiments described herein. In particular,  FIG.  1    illustrates a schematic view of an exemplary rack arrangement level  10  of an AS/RS 1, the rack arrangement level  10  comprising a storage aisle  100 . As shown, a storage aisle  100  may be defined by various components of an exemplary rack arrangement that are provided within at least substantially the same horizontal plane, including, for example, a first storage shelf  101  and a second storage shelf  102  of adjacent first and second storage racks, respectively. As illustrated, the first and second storage shelves  101 ,  102  of an exemplary storage aisle  100  may each extend in an at least substantially longitudinal direction, such as, for example, in the y-direction, as illustrated, and may be arranged in an at least substantially parallel configuration relative to one another. An exemplary storage aisle  100  may further include an aisle track  110  extending between the first and second storage shelves  101 ,  102  in at least substantially the same longitudinal direction as the first and second storage shelves  101 ,  102  provided on either side thereof. For example, the aisle track  110  of a storage aisle  100  may be arranged in an at least substantially parallel configuration relative to one or both of the first and second storage shelves  101 ,  102  adjacent thereto. As shown, an aisle track  110  may be defined at least in part by an aisle length that extends between the first aisle end  111  and the second aisle end  112  thereof. 
     In various embodiments, the AS/RS 1 may comprise a plurality of automated shuttles  50  configured to travel along the plurality of shuttle guide tracks provided within a rack arrangement level to facilitate the retrieval, storage, and/or transportation of various objects throughout the AS/RS 1. In various embodiments, a plurality of shuttles  50  may be disposed along each rack arrangement level of the rack arrangement. As such, the shuttle(s)  50  may be configured to move along the plurality of shuttle guide tracks provided within a rack arrangement level  10  in order to selectively remove and/or place objects into a storage location within a storage shelf (e.g., first storage shelf  101 , second storage shelf  102 ) provided within the rack arrangement level  10 . For example, as illustrated, an exemplary aisle track  110  may be configured to enable shuttle traffic along the aisle length thereof in order to facilitate movement of one or more of the plurality of automated shuttles  50  to and/or from one or more storage locations within the storage aisle  100 . In such an exemplary configuration, a shuttle  50  may travel along aisle track  110  in order to retrieve and/or dispose an object into one of the plurality of storage locations provided within either the first storage shelf  101  (e.g., first storage location  101   a , second storage location  101   b , third storage location  101   n , and/or the like) or the second storage shelf  102 . 
     In various embodiments, the shuttle  50  may be any type of one-level shuttle (OLS) vehicle typically used in a AS/RS, such as a shuttle, a carrier, a bot, and/or the like. In various embodiment, the shuttle  50  may be a self-contained unit, receiving power (e.g., 48 VDC) from a bus bar located inside a shuttle guide track that may be mounted to the storage rack. In various embodiments, the power guide track (e.g., 48 VDC power supplied to the track) may be powered from a DC power panel. In various embodiments, a single DC power panel can power a plurality of shuttles (e.g., up to six shuttles). In various embodiments, the shuttle  50  may receive control system commands over a Wireless Local Area Network (WLAN). In various embodiments, a shuttle  50  may have one or more wheels to facilitate movement thereof along a shuttle guide track via a motor. In various embodiments, the shuttle guide track may be affixed to the storage rack. However, it should be understood that any of a variety of movement mechanisms may be utilized for moving the shuttle  50  (e.g., belt-drive systems, magnetic movement mechanisms, chain-drive systems, and/or the like). Moreover, it should be understood that the movement mechanisms may be defined within the shuttle  50  (e.g., a motor positioned on the shuttle) or within the storage rack (e.g., motors within the storage rack). In various embodiments, an exemplary shuttle  50  may comprise one or more sensors configured movement of the shuttle  50  to an intended storage location and/or engagement of the shuttle  50  with a particular object in a given storage location. For example, the shuttle  50  may be equipped with a proximity sensor to determine the longitudinal and/or lateral position of the shuttle  50  within a given rack arrangement level (e.g., by identifying the storage aisle in which the shuttle  50  is positioned, identifying one or more storage locations disposed at least substantially adjacent the shuttle  50 , and/or the like, or any combination thereof), and/or the position of the shuttle  50  relative to one or more other shuttles of the plurality provided within the same rack arrangement level  10 . In various embodiments, the shuttle  50  may also be equipped with sensors and onboard devices, such as Wi-Fi antenna for communication with a Warehouse Control System (WCS) and/or Warehouse Execution System (WES), overload protection, one or more power supplies (e.g., 24 Volt power supply and/or 48 volt power supply), digital input and output modules, and/or the like. 
     Further, an exemplary AS/RS 1 may comprise a plurality of vertical lifts  200  configured to facilitate the vertical transportation of objects between the multiple levels of the AS/RS 1. For example, at least a portion of the plurality of lifts  200  of the AS/RS 1 may be configured to receive an object retrieved by a shuttle  50  from a storage aisle  100  provided within a rack arrangement level  10  (e.g., from an exemplary storage location  101   a  within a first storage shelf  101  of the storage aisle  100 ) and vertically move (e.g., lower) the retrieved object to a lift drop-off station  60 . The lift drop-off station  60  may be connected to an out-feed conveyor  42  that is configured to deliver the object retrieved by the shuttle  50  from within the rack arrangement level  10  to a downstream location, such as, for example, a destination location within a manufacturing environment. Alternatively, and/or additionally, at least a portion of the plurality of lifts  200  of the AS/RS 1 may be configured to receive an object to be stored at a storage location within the first rack arrangement level  10  of the AS/RS 1 at the lift drop-off station  60 , wherein the object to be stored may be delivered to the lift drop-off station  60  via an in-feed conveyor  41  configured to deliver the object to be stored from an upstream location to the lift drop-off station  60 . At least a portion of the plurality of lifts  200  may be configured to vertically move (e.g., raise) the object to be stored from the lift drop-off station  60  to a first rack arrangement level  10 , wherein it may be transferred to one of the plurality of shuttles  50  provided along the plurality of tracks within the rack arrangement level  10  and delivered to a storage location within an exemplary storage aisle  100 . As described in further detail herein, at least a portion of the plurality of lifts provided within the AS/RS 1 may be positioned in an at least substantially aligned configuration, such as, for example, along a second aisle end (e.g., an aisle outlet end) such that the plurality of shuttles provided in the AS/RS 1 may access the at least a portion of the plurality of lifts  200  upon exiting a storage aisle (e.g., storage aisle  100 ). Additionally, or alternatively, in various embodiments, one or more of the plurality of lifts may be positioned along an aisle length of one or more storge aisles (e.g., adjacent one or more of the storage shelves aligned along the corresponding aisle track), so as to embody an intra-aisle lift that may be accessed by a shuttle travelling in a shuttle travel direction along the corresponding aisle track. 
     In various embodiments, an exemplary AS/RS 1 may be operated such that each shuttle  50  that is moved throughout a storage aisle  100  travels in the same singular direction (e.g., a shuttle travel direction) along the aisle track  110  from the first aisle end  111  to the second aisle end  112 . As such, each storage aisle  100  of an exemplary AS/RS 1 may be defined in part by a unidirectional shuttle traffic flow pattern that is defined along the aisle track  110  thereof. For example, in various embodiments, the plurality of shuttle guide tracks within a particular rack arrangement level of an AS/RS 1 may be configured such that a shuttle  50  executing a retrieval operation relating to an object disposed within a storage location  101   a  provided within the storage aisle  100  may be received by the aisle track  110  of the storage aisle  100  at a first aisle end  111  thereof. The storage aisle  100  may be configured to facilitate a unidirectional shuttle traffic flow along the aisle length of the aisle track  110 , such that each shuttle  50  traveling along the aisle track  110  moves in a shuttle travel direction, such as, for example, in a first longitudinal direction  11  (e.g., in the negative y-direction as illustrated). For example, the shuttle  50  may stop at a position along the aisle track  110  that is adjacent to the designated storage location  101   a  defined within the first storage shelf  101  of the storage aisle  100  in order to access to object disposed therein. In such an exemplary configuration, upon retrieving the object from the storage location  101   a , the shuttle  50  may continue travelling in the shuttle travel direction (e.g., the first longitudinal direction  11 ) towards the second aisle end  112  of the aisle track  110 . As described herein, in an exemplary circumstance wherein an AS/RS 1 is operated such that each storage aisle  100  provided therein defines a unidirectional shuttle traffic flow pattern from a first aisle end  111  to a second aisle end  112 , a plurality of shuttles  50  may at least substantially simultaneously travel to a respective plurality of storage locations (e.g., storage locations  101   a ,  101   b ,  101   n ) with the same storage aisle  100  such that the plurality of shuttles  50  are each positioned along the aisle track  110  at substantially the same time. By operating the AS/SR 1 that each of the shuttles  50  travel along the aisle track  110  of a storage aisle  100  in the same shuttle travel direction (e.g., the first longitudinal direction  11 ) the risk of shuttle collision and/or shuttle traffic flow bottlenecks caused by two or more shuttles  50  being moved along intersecting, overlapping, and/or otherwise incompatible shuttle travel paths along the same aisle track  110  may be at least substantially mitigated. 
     In various embodiments, such a unidirectional shuttle traffic flow pattern of each storage aisle  100  within a rack arrangement level  10  may be enabled by a looped track configuration of the plurality of shuttle guide tracks provided within the rack arrangement level  10 . For example, the plurality of shuttle guide tracks provided within a rack arrangement level  10  may be arranged so as to define an looped track circuit comprising an at least partially closed looped configuration, wherein an exemplary shuttle  50 , upon having travelled along the aisle length of the aisle track  110  in the first longitudinal direction  11  to the second aisle end  112 , may exit the storage aisle  100  and travel along at least a portion of the looped track circuit to be recirculated to the first aisle end  111  of the aisle track  110 . In various embodiments, an exemplary AS/RS 1 comprising a storage aisle  100  provided within a rack arrangement level  10  and configured to facilitate shuttle transportation along an aisle track  110  thereof according to a unidirectional shuttle traffic flow pattern defined at least in part by the first longitudinal direction  11  may further include a plurality of shuttle guide tracks provided within the rack arrangement level  10  that collectively facilitate a shuttle recirculation traffic flow pattern. In various embodiments, as illustrated in  FIG.  1   , such an exemplary rack arrangement level  10  of an AS/RS 1 may include a plurality of shuttle guide tracks comprising the aisle track  110  of the storage aisle  100 , a shuttle transport track  130 , an inter-aisle shuttle inlet track  140 , and a plurality of inter-aisle shuttle outlet tracks  120 . 
     In various embodiments, the aisle track  110  of a storage aisle  100 , the shuttle transport track  130 , the inter-aisle shuttle inlet track  140 , and the plurality of inter-aisle shuttle outlet tracks  120  provided within the rack arrangement level  10  may collectively define a looped track circuit configured such that the plurality of shuttles  50  provided within the rack arrangement level  10  may travel along the aforementioned shuttle guide tracks so as to define a shuttle recirculation traffic flow pattern defined at least part by a plurality of shuttles  50  serially travelling along the aisle track  110  in the first longitudinal direction  11  (e.g., from the first aisle end  111  to the second aisle end  112 ). For example, the shuttle recirculation traffic flow pattern exhibited by the illustrated plurality of shuttles  50  travelling throughout the rack arrangement level  10  may be defined at least in part by two or more shuttles  50  of the plurality being at least substantially simultaneously positioned within the storage aisle  100  (e.g., travelling along the aisle track  110  in the first longitudinal direction  11 ) at respective positions along the aisle length thereof. In various embodiments, each of the plurality of shuttle guide tracks that define at least a portion of the looped track circuit provided within a rack arrangement level  10  may be configured to define a unidirectional shuttle traffic flow pattern along the track length thereof. For example, each of the shuttle transport track  130 , the inter-aisle shuttle inlet track  140 , and the plurality of inter-aisle shuttle outlet tracks  120  are configured for unidirectional shuttle traffic along their respective track lengths such that a shuttle travelling thereon moves in a respective singular direction along the length of the shuttle guide track. Accordingly, in various embodiments wherein the shuttle transport track  130 , the inter-aisle shuttle inlet track  140 , the plurality of inter-aisle shuttle outlet tracks  120 , and the aisle track  110  are arranged in an at least substantially continuous looped track circuit that connects the second aisle end  112  of the aisle track  110  to the first aisle end  111 , as illustrated in  FIG.  1   , the plurality of shuttle guide tracks within the rack arrangement level  10  are configured to facilitate an at least generally clockwise-or, alternatively, counterclockwise—shuttle recirculation traffic flow pattern through the looped track circuit, as described herein. 
     In various embodiments, a plurality of inter-aisle shuttle outlet tracks  120  may collectively define a segment of shuttle guide tracks extending between a second aisle end  112  of a storage aisle  100  and a shuttle transportation track  130 . Further, the plurality of inter-aisle shuttle outlet tracks  120  may be arranged to as to facilitate transportation of a shuttle  50  from a storge aisle  100  and to each of a plurality of vertical lifts  200  provided within an AS/RS 1. For example, the plurality of inter-aisle shuttle outlet tracks  120  may be arranged so as to extend in a direction that at least substantially intersects a second aisle end  112  of each of the storage aisles  100  provided within a rack arrangement level  10  (e.g., in an at least substantially a perpendicular direction relative to the aisle length). Accordingly, in various embodiments, the plurality of inter-aisle shuttle outlet tracks  120  may be at least substantially immediately downstream from each of the storage aisles  100  within the rack arrangement level  10  such that a shuttle  50  travelling along the aisle track  110  according to the unidirectional shuttle traffic flow pattern, as described herein, may exit the storage aisle  100  via a respective second aisle end  112  and be received by the plurality of inter-aisle shuttle outlet tracks  120 . Further, the plurality of inter-aisle shuttle outlet tracks  120  may be arranged to extend at least substantially between each of the plurality of lifts  200  of the AS/RS 1 such that each of the plurality of lifts  200  is accessible to a shuttle  50  via the plurality of inter-aisle shuttle outlet tracks  120 . For example, in various embodiments, each of the plurality of lifts  200  is accessible to a shuttle  50  via a corresponding lift interface position defined along the plurality of inter-aisle shuttle outlet tracks  120 , such that a shuttle  50  travelling in the first lateral direction  21  along the plurality of inter-aisle shuttle outlet tracks  120  may be stopped at a lift interface position thereon in order to dispense and/or retrieve an object from a corresponding lift  200  adjacent thereto. 
     As illustrated in  FIG.  1   , an exemplary AS/RS 1 may comprise a plurality of lifts  200  arranged in an at least substantially aligned configuration in one or more directions, such as, for example, in a substantially lateral distribution (e.g., distributed along the x-axis, as illustrated). As such, the plurality of inter-aisle shuttle outlet tracks  120  may be arranged in an at least substantially perpendicular configuration relative to the aisle track  110  such that a shuttle  50  traveling along one of the plurality of inter-aisle shuttle outlet tracks  120  moves along the track length thereof in a first lateral direction  21  (e.g., in the negative x-direction as illustrated). In various embodiments, the plurality of inter-aisle shuttle outlet tracks  120  may comprise a first inter-aisle shuttle outlet track  121  and a second inter-aisle shuttle outlet track  122  arranged in an at least substantially parallel configuration relative to one another. Each of the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122  may be configured to define a unidirectional shuttle traffic flow pattern along a respective track length thereof. For example, both the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122  may be configured such that exemplary shuttles  50  travelling along the respective inter-aisle shuttle outlet tracks  121 ,  122  may move in a first lateral direction  21 . 
     For example, as illustrated, the first inter-aisle shuttle outlet track  121  of the plurality  120  may extend at least substantially between the plurality of lifts  200  of the AS/RS 1 such that each of the plurality of lifts  200  may be accessed by a shuttle  50  travelling along the first inter-aisle shuttle outlet track  121  via a corresponding plurality of lift interface positions defined along the first inter-aisle shuttle outlet track  121 . As described herein, a shuttle  50  travelling in the first lateral direction  21  along the first inter-aisle shuttle outlet track  121  may stop along the first inter-aisle shuttle outlet track  121  at a lift interface position adjacent a corresponding lift (e.g., adjacent a first vertical lift  200   a  or a second vertical lift  200   b  of the plurality  200 ) in order to dispense and/or retrieve an object from the corresponding lift of the plurality  200 . As further illustrated in  FIG.  1   , the second inter-aisle shuttle outlet track  122  of the plurality of inter-aisle shuttle outlet tracks  120  may be arranged at least substantially adjacent the first inter-aisle shuttle outlet track  121  and configured to extend at least substantially parallel direction relative to the first inter-aisle shuttle outlet track  121 . A plurality of inter-aisle shuttle outlet tracks  120  defined by such an exemplary configuration may enable parallel shuttle traffic flow patterns in the first and second inter-aisle shuttle outlet tracks  121 ,  122  that are defined by respective unidirectional traffic flows in the first lateral direction  21  along each of the parallel track lengths. In various embodiments, the plurality of inter-aisle shuttle outlet tracks  120  are configured such that a shuttle  50  travelling in the first lateral direction  21  along either the first inter-aisle shuttle outlet track  121  or the second inter-aisle shuttle outlet track  122  may be selectively transferred to the adjacent, parallel inter-aisle shuttle outlet track of the plurality  120 . For example, in various embodiments, wherein a first shuttle  50  is traveling in the first lateral direction  21  along the first inter-aisle shuttle outlet track  121  and a second shuttle  50  is stopped along the first inter-aisle shuttle outlet track  121  in a downstream position relative to the first shuttle  50  at a lift interface position corresponding to a second vertical lift  200   b , the plurality of inter-aisle shuttle outlet tracks  120  may be configured such that the first shuttle  50  may be transferred to the second inter-aisle shuttle outlet track  122 . Upon being moving from the first inter-aisle shuttle outlet track  121  to the second inter-aisle shuttle outlet track  122 , the first shuttle  50  may continue to travel in the first lateral direction  21  (e.g., along the second inter-aisle shuttle outlet track  122 ) according to the shuttle recirculation traffic flow pattern, thereby avoiding a traffic stoppage along the first inter-aisle shuttle outlet track  121  that may result from the at least temporarily stationary second shuttle  50  being engaged with the second lift  200   b . 
     In such an exemplary configuration, wherein the plurality of inter-aisle shuttle outlet tracks  120  are arranged in an at least substantially parallel configuration and configured for unidirectional shuttle traffic thereon in the same direction (e.g., the first lateral direction  21 ), the plurality of inter-aisle shuttle outlet tracks  120  may function as parallel passing lanes between which an exemplary shuttle  50  may be transferred in order to facilitate shuttle engagement with each of a plurality of lifts  200  of the AS/RS 1 via the lift interface positions defined along the first inter-aisle shuttle outlet track  121 , while simultaneously enabling an at least substantially continuous shuttle traffic flow of at least a portion of the plurality of shuttles  50  travelling from the storage aisle  100  (e.g., the second aisle end  112 ) to the shuttle transport track  130 . The plurality of inter-aisle shuttle outlet tracks  120  may be configured such that a shuttle  50  travelling there along may be selectively transferred between the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122  (e.g., from the first inter-aisle shuttle outlet track  121  to the second inter-aisle shuttle outlet track  122  and/or from the second inter-aisle shuttle outlet track  122  to the first inter-aisle shuttle outlet track  121 ) in order to avoid a shuttle interference that is detected along one of the plurality of inter-aisle shuttle outlet tracks  120 . For example, the parallel passing lanes defined by the configuration of the plurality of inter-aisle shuttle outlet tracks  120  enables the plurality of shuttles  50  provided within the rack arrangement level  10  to access each of the plurality of lifts  200  for executing various storage and/or retrieval operations, while avoiding shuttle traffic bottlenecks that impede the shuttle recirculation traffic flow pattern during the use of one or more of the lifts  200  by using the passing lane configuration of the second inter-aisle shuttle outlet track  122  to facilitate the at least substantially continuous flow of shuttle traffic along the plurality of inter-aisle shuttle outlet tracks  120 . 
     As a non-limiting example,  FIG.  5    is a flowchart that illustrates an exemplary operation of an automated storage and retrieval system using a unidirectional shuttle traffic flow pattern and a plurality of parallel inter-aisle shuttle outlet tracks, such described herein in reference to  FIGS.  1 - 3 B , in accordance with various embodiments. Referring to Block  502  of  FIG.  5   , the exemplary method  500  of operating the automated storage and retrieval system 1 includes accessing, via a first shuttle, a first vertical lift of a plurality of vertical lifts by causing the first shuttle to travel from a first storage aisle to a first lift interface position defined along a first inter-aisle shuttle outlet track. Referring now to Block  504  of  FIG.  5   , the method  500  of operating the AS/RS 1 includes determining that the first shuttle is stopped along the first inter-aisle outlet track at a first lift interface position. Referring now to Block  506 , the method  500  further includes identifying a second shuttle traveling along the first inter-aisle outlet track in an upstream position from the first shuttle relative to the unidirectional shuttle traffic flow pattern of the first inter-aisle outlet track. The method  500  may further include causing the second shuttle to transfer from the first inter-aisle outlet track to a second inter-aisle outlet track arranged in an at least substantially parallel configuration relative to the first inter-aisle shuttle outlet track, as shown at Block  508 . Referring now to Block  510 , the method  500  of operating the AS/RS 1 may include, upon determining that the second shuttle has moved along the second inter-aisle shuttle outlet track so as to pass the first shuttle, causing the second shuttle to transfer from the second inter-aisle outlet track to the first inter-aisle outlet track. Further, the method  500  may include accessing, via the second shuttle, a second vertical lift of the plurality of vertical lifts by causing the second shuttle to travel to a second lift interface position defined along the first inter-aisle shuttle outlet track, wherein the second lift interface position is arranged downstream from the first lift interface position along the first inter-aisle shuttle outlet track, as shown at Block  512 . 
     Although the plurality of inter-aisle shuttle outlet tracks  120  shown in the exemplary embodiment depicted in  FIG.  1    comprises two inter-aisle shuttle outlet tracks (e.g., the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122 ), it should be understood that the plurality of inter-aisle shuttle outlet tracks  120  may comprise at least substantially more than two inter-aisle shuttle outlet tracks arranged in an at least substantially parallel configuration so as to embody parallel passing lanes. As a non-limiting example, in various embodiments, the plurality of inter-aisle shuttle outlet tracks  120  may comprise three, four, five, seven, ten, or any number of inter-aisle shuttle outlet tracks sufficient to facilitate the operability of the AS/RS described herein. 
     Further, in various embodiments, the selective transfer of a shuttle  50  between the plurality of inter-aisle shuttle outlet tracks  120  (e.g., from the first inter-aisle shuttle outlet track  121  to the second inter-aisle shuttle outlet track  122 , or from the second inter-aisle shuttle outlet track  122  to the first inter-aisle shuttle outlet track  121 ) may be enabled by one or more transfer tracks extending between the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122 . For example, in various embodiments, one or more of the transfer tracks  201   a ,  201   b  may enable a bidirectional traffic flow therethrough, such that a shuttle  50  traveling along the plurality of inter-aisle shuttle outlet tracks  120  may be transferred in either a first transfer direction from the first inter-aisle shuttle outlet track  121  to the second inter-aisle shuttle outlet track  122 , or a second transfer direction from the second inter-aisle shuttle outlet track  122  to the first inter-aisle shuttle outlet track  121 . In various embodiments, the one or more transfer tracks  201   a ,  201   b  may be defined within the plurality inter-aisle shuttle outlet tracks  120 , as illustrated in the exemplary rack arrangement level  10  shown in  FIG.  1   . Alternatively, or additionally, as illustrated in the exemplary rack arrangement level  20  shown in  FIG.  2   , the one or more transfer tracks  201   a ,  201   b  may comprise distinct shuttle track guide segments extending in an at least partially perpendicular direction between the first and second inter-aisle shuttle outlet tracks  121 ,  122 . 
     In various embodiments, as further illustrated in  FIG.  1   , the plurality of shuttle guide tracks provided within an exemplary rack arrangement level  10  of an AS/RS 1 may include a shuttle transport track  130  extending between the plurality of inter-aisle shuttle outlet tracks  120  and the inter-aisle shuttle inlet track  140  so as to facilitate transportation of the plurality of shuttles  50  from the plurality of inter-aisle shuttle outlet tracks  120  to the inter-aisle shuttle inlet track  140 . In various embodiments, the shuttle transport track  130  may be defined at least in part by a track length that extends between a first track end connected to one or more of the plurality of inter-aisle shuttle outlet tracks  120  and a second track end connected to the inter-aisle shuttle inlet track  140 . For example, as illustrated, an exemplary shuttle transport track  130  may be configured to enable shuttle traffic along the track length thereof so as to define a portion of a looped track circuit and facilitate a shuttle recirculation traffic flow pattern relative to one or more storage aisles  100  provided within a given rack arrangement level  10  of an AS/RS 1. As described herein, the shuttle transport track  130  is configured to define a unidirectional shuttle traffic flow pattern along the track length thereof. For example, the shuttle transport track  130  may be configured such that exemplary shuttles  50  travelling along the shuttle transport track  130  (e.g., from the plurality of inter-aisle shuttle outlet tracks  120  to the inter-aisle shuttle inlet track  140 ) may move in a second longitudinal direction  12 . As illustrated, the second longitudinal direction  12  may be defined by a longitudinal direction that is at least partially opposite the first longitudinal direction  11  defined by the aisle track  110  of a storage aisle  100 , such as, for example, in the positive-y direction, as illustrated. For example, as shown, the shuttle transport track  130  may be configured to facilitate movement of a shuttle  50  there along in the second longitudinal direction  21  in order to direct the movement of the shuttle  50  received from the plurality of inter-aisle shuttle outlet tracks  120  towards the first aisle end  111  of the aisle track  110  of storage aisle  100  (e.g., towards the inter-aisle shuttle inlet track  140 ). 
     Further, the plurality of shuttle guide tracks provided within an exemplary rack arrangement level  10  of an AS/RS 1 may include an inter-aisle shuttle inlet track  140  extending between the shuttle transport track  130  and a first aisle end  111  of the aisle rack  110  of each of the storage aisles  100  defined within the rack arrangement level  10 . The inter-aisle shuttle inlet track  140  is configured to operatively connect the shuttle transport track  130  to aisle track  110  of a storage aisle  100  (e.g., the first aisle end  111 ) in order to facilitate transportation of the plurality of shuttles  50  from shuttle transport track  130  to the aisle track  110  of a particular storage aisle  100 . In various embodiments, the inter-aisle shuttle inlet track  140  may be defined at least in part by a track length that extends between a first track end connected to the shuttle transport track  130  and a second track end connected to the first aisle end  111  of an aisle track  110  defining part of a storage aisle  100 . For example, as illustrated, an exemplary inter-aisle shuttle inlet track  140  may be configured to enable shuttle traffic along the track length thereof so as to define a portion of a looped track circuit, as described herein, and facilitate a shuttle recirculation traffic flow pattern relative to one or more storage aisles  100  provided within a given rack arrangement level  10  of an AS/RS 1. For example, the inter-aisle shuttle inlet track  140  may be arranged so as to extend in a direction that at least substantially intersects a first aisle end  111  of each of the storage aisles  100  provided within a rack arrangement level  10  (e.g., in an at least substantially a perpendicular direction relative to the aisle length). Accordingly, in various embodiments, the inter-aisle shuttle inlet track  140  may be at least substantially immediately upstream from each of the aisle track  110  provided within the rack arrangement level  10  such that a corresponding storage aisle  100  may selectively be accessed by a shuttle  50  via the inter-aisle shuttle inlet track  140 . As described herein, the inter-aisle shuttle inlet track  140  is configured to define a unidirectional shuttle traffic flow pattern along the track length thereof. For example, the inter-aisle shuttle inlet track  140  may be configured such that exemplary shuttles  50  travelling along the inter-aisle shuttle inlet track  140  (e.g., from the shuttle transport track  130  to an aisle track  110  of a particular storage aisle  100 ) may move in a second lateral direction  22 . As illustrated, the second lateral direction  22  may be defined by a lateral direction that is at least partially opposite the first lateral direction  21  defined by the plurality of inter-aisle shuttle outlet tracks  120 , such as, for example, the positive-x direction, as illustrated. For example, as shown, the inter-aisle shuttle inlet track  140  may be configured to facilitate movement of a shuttle  50  there along in the second lateral direction  22  in order to direct the movement of the shuttle  50  received from the shuttle transport track  130  towards a first aisle end  111  of an aisle track  110  of storage aisle  100 . For example, a shuttle  50  travelling along the inter-aisle shuttle inlet track  140  in the second lateral direction  22  according to the unidirectional shuttle traffic flow pattern thereof may be directed to one or more positions along the track length of the inter-aisle shuttle inlet track  140  that are connected to a first aisle end  111  of an aisle track  110 , such that the shuttle  50  may access the corresponding storage aisle  100  therefrom. The aisle track  110  of each storage aisle  100  may be configured to receive a shuttle  50  transferred thereto from the inter-aisle shuttle inlet track  140  such that movement of the shuttle  50  is redirected from the second lateral direction  22  to the first longitudinal direction  11  as the shuttle  50  travels along the aisle track  110 . 
       FIG.  2    illustrates a schematic view of an exemplary automated storage and retrieval system according to various embodiments described herein. In particular,  FIG.  2    illustrates a schematic view of an exemplary rack arrangement level  10  of an AS/RS 1, the rack arrangement level  10  comprising a plurality of storage aisles  100 . In various embodiments, the rack arrangement of an exemplary AS/RS 1 may comprise a plurality of storage racks arranged so as to define a plurality of adjacent storage rack pairs, each adjacent storage rack pair defining a central aisle provided between the adjacent storage racks, as described herein. In such an exemplary circumstance, as shown in the exemplary embodiment illustrated in  FIG.  2   , an exemplary rack arrangement level  20  may comprise a plurality of storage aisles  100  provided therein, each of which may be accessible to a shuttle  50  configured traveling along the plurality of shuttle guide tracks within the rack arrangement level  20  according to the shuttle recirculation traffic flow pattern, as described herein. For example, the exemplary rack arrangement level  20  illustrated in  FIG.  2    includes a plurality of storage aisle  100  comprising a first storage aisle  100   a , a second storage aisle  100   b , a third storage aisle  100   c , and a fourth storage aisle  100   d . In various embodiments, each of the plurality of storage aisles  100  within a rack arrangement level  20  may comprise a first storage shelf and a second storage shelf of adjacent storage racks, respectively. In the illustrated exemplary embodiment, the first storage aisle  100   a  comprises a first storage shelf  101  and a second storage shelf  102 , the second storage aisle  100   b  comprises a third storage shelf  103  and a fourth storage shelf  104 , the third storage aisle  100   c  comprises a fifth storage shelf  105  and a sixth storage shelf  106 , and the fourth storage aisle  100   d  comprises a seventh storage shelf  107  and an eight storage shelf  108 . Further, the first, second, third, and fourth storage aisles  100   a ,  100   b ,  100   c , and  100   d  of the plurality of storage aisles  100  provided in the rack arrangement level  20  may comprise a first aisle track  110   a , a second aisle track  110   b , a third aisle track  110   c , and a fourth aisle track  110   d , respectively, each of which may extend along a respective aisle length between the two storage shelves of the corresponding storage aisle in at least substantially the same longitudinal direction as the storage shelves provided on either side thereof. 
     In various embodiments, the rack arrangement of the AS/RS 1 may comprise a plurality of racks provided in a laterally distributed arrangement wherein each of the plurality of racks is arranged in an at least substantially parallel configuration relative to one another, such that each of the respective storage shelves provided within the rack arrangement level  20  (e.g., first storage shelf  101 , second storage shelf  102 , third storage shelf  103 , fourth storage shelf  104 , fifth storage shelf  105 , sixth storage shelf  106 , seventh storage shelf  107 , eighth storage shelf  108 ) are similarly arranged in an at least substantially parallel configuration relative to one another. Accordingly the storage aisles of the plurality of storage aisles  100  may be arranged in a parallel configuration, wherein the aisle length of each of the plurality of storage aisles  100  is parallel to each of the other aisle lengths defined by the other storage aisles of the plurality  100 . For example, as illustrated in  FIG.  2   , the first, second, third, and fourth storage aisles  100   a ,  100   b ,  100   c ,  100   d  may each extend in an at least substantially longitudinal direction, such as, for example, in the y-direction, as illustrated. 
     In various embodiments, an exemplary rack arrangement level  20  may be configured such that each of the plurality of storage aisles  100  provided within the rack arrangement level  20  may comprise a respective aisle track  110   a ,  110   b ,  110   c ,  110   d  that extends along an aisle length thereof in a longitudinal direction that is at least substantially parallel to the adjacent storage shelves of the corresponding storage aisle. As illustrated in  FIG.  2   , the aisle tracks  110   a ,  110   b ,  110   c ,  110   d  of each of the plurality of storage aisles  100   a ,  100   b ,  100   c ,  100   d  may be configured to enable shuttle traffic of at least one shuttle provided within the storage aisle along the aisle length thereof in a first shuttle travel direction in order to facilitate movement of one or more of the plurality of automated shuttles  50  to and/or from one or more storage locations provided within the storage aisle  100 . For example, as illustrated, each of the aisle tracks  110   a ,  110   b ,  110   c ,  110   d  are configured to enable shuttle traffic of at least one shuttle  50  along the respective aisle length thereof in a first shuttle travel direction, such as, for example, the first longitudinal direction  11  (e.g., in the negative-x direction, as illustrated). In various embodiments, each of the plurality of storage aisles  100  provided within a rack arrangement level  20  may be configured to facilitate shuttle transportation along a corresponding aisle track thereof (e.g., aisle tracks  110   a ,  110   b ,  110   c ,  110   d ) according to a unidirectional shuttle traffic flow pattern, wherein the unidirectional shuttle traffic flow pattern is defined by the movement of each of the plurality of shuttles  50  along the corresponding aisle track thereof in at least substantially the same shuttle travel direction, such as, for example, in the first longitudinal direction  11 . 
     In various embodiments, an exemplary rack arrangement level  20  comprising a plurality of storage aisles  100  provided therein may comprise a plurality of inter-aisle shuttle outlet tracks  120 , as described herein, that extends in a direction is at least substantially perpendicular to at least a portion of the parallelly-configured plurality of storage aisles  100  (e.g., in a lateral direction, such as the x-direction, as illustrated) and is arranged so as to be connected to each of the plurality of storage aisles  100  (e.g., at the second aisle end of each respective aisle track). Accordingly, in various embodiments, the plurality of inter-aisle shuttle outlet tracks  120  may comprise a second inter-aisle shuttle outlet track  122  that is at least substantially immediately downstream from each of the plurality of storage aisles  100  within the rack arrangement level  20  such that a plurality of shuttles  50  travelling along any one of the aisle tracks  110   a ,  110   b ,  110   c ,  110   d  according to the unidirectional shuttle traffic flow pattern defined by each of the plurality of storage aisles  100 , as described herein, may be received by the second inter-aisle shuttle outlet track  122  upon plurality of shuttles  50  being transported beyond the second aisle end of the aisle track of a storage aisle  100 . Further, the first inter-aisle shuttle outlet track  121  of the plurality of inter-aisle shuttle outlet tracks  120  may be configured to facilitate transportation of the plurality of shuttles  50  from each of the plurality of storage aisles  100  provided within the rack arrangement level  20  to one or more of a plurality of vertical lifts  200  of the AS/RS 1. For example, the first inter-aisle shuttle outlet track  121  may define a vertical lift access track along which a plurality of shuttles  50  may be received from at least one of the plurality of storage aisles  100  (e.g.,  100   a ,  100   b ,  100   c ,  100   d ) and transported according to a unidirectional shuttle traffic flow pattern in a first latitude direction  12  (e.g., in the negative-x direction, as illustrated) to one of a plurality of lift interface positions defined along the first inter-aisle shuttle outlet track  121 , as described herein, from which a shuttle  50  may access an adjacent lift  200   a ,  200   b ,  200   c ,  200   d  of the plurality of lifts  200 . 
     As described herein in further detail in reference to the plurality of inter-aisle shuttle outlet tracks  120  of the exemplary rack arrangement level  10  depicted in  FIG.  1   , the plurality of inter-aisle shuttle outlet tracks  120  configured to facilitate transportation of the plurality of shuttles  50  from the plurality of storage aisles  100  to one or more of the plurality of lifts  200 , or, alternatively and/or additionally, to the shuttle transport track  130  as the result of the shuttle recirculation traffic flow pattern defined within the rack arrangement level  20 . For example, of the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122  may be configured to facilitate a respective unidirectional shuttle traffic flow pattern defined at least in part along a respective track length thereof in the first lateral direction  21  (e.g., the negative-x direction, as illustrated). As described herein, the second inter-aisle shuttle outlet track  122  spans laterally across each of the plurality of storage aisles  100  provided within the rack arrangement system  20 , and is arranged in an at least substantially parallel and adjacent configuration relative to the first inter-aisle shuttle outlet track  121  such that the second inter-aisle shuttle outlet track  122  embodies a parallel passing track that functions as an alternative shuttle travel path to that of the first inter-aisle shuttle outlet track  121 . The plurality of inter-aisle shuttle outlet tracks  120  may be configured such that a shuttle  50  travelling there along may be selectively transferred between the first inter-aisle shuttle outlet track  121  and the second inter-aisle shuttle outlet track  122  in order to facilitate an at least substantially continuous (e.g., unobstructed) shuttle traffic flow towards the shuttle transport track  130 . Further, an exemplary second inter-aisle shuttle outlet track  122  embodying a parallel passing track may be utilized for transportation of at least a portion of the plurality of shuttles  50  determined to be executing a portion of a storage and/or retrieval operation that does not require access to one of the plurality of lifts  200 . For example, such exemplary shuttles  50  may be transported along the second inter-aisle shuttle outlet track  122  directly to the shuttle transport track  130  without being transferred to the first inter-aisle shuttle outlet track  121 , thereby minimizing the risk that the movement of said exemplary shuttles  50  along the plurality of inter-aisle shuttle outlet tracks  120  will be impeded and/or slowed by another shuttle  50  of the plurality that is stopped at a lift interface position along the first inter-aisle shuttle outlet track  121 . 
     As further illustrated in  FIG.  2   , an exemplary rack arrangement level  20  comprising a plurality of storage aisles  100  provided therein may comprise an inter-aisle shuttle inlet track  140 , as described herein, that extends in a direction is at least substantially perpendicular to at least a portion of the parallelly-configured plurality of storage aisles  100  (e.g., in a lateral direction, such as the x-direction, as illustrated) and is arranged so as to be connected to each of the plurality of storage aisles  100  (e.g., at the first aisle end of each respective aisle track). The inter-aisle shuttle inlet track  140  may be configured to operatively connect the shuttle transport track  130  to each of the plurality of storage aisles  100   a ,  100   b ,  100   c ,  100   d  (e.g., each of the respective aisle tracks  110   a ,  110   b ,  110   c ,  110   d ) at a respective first aisle end thereof in order to facilitate transportation of the plurality of shuttles  50  from shuttle transport track  130  to a particular storage aisle of the plurality of storage aisles  100 . In various embodiments, the inter-aisle shuttle inlet track  140  may be defined at least in part by a track length that extends between a first track end connected to the shuttle transport track  130  and a second track end operatively connected to first aisle end of the storage aisle of the plurality  100  that is arranged in a position farthest away from the shuttle transport track  130 , such as, for example, the fourth storage aisle  100   d  in the exemplary rack arrangement  20  illustrated in  FIG.  2   . Accordingly, in various embodiments, the inter-aisle shuttle inlet track  140  may be arranged at least substantially immediately upstream (e.g., relative to the shuttle recirculation traffic flow pattern, as described herein) from each of the aisle tracks  110   a ,  110   b ,  110   c ,  110   d  provided within the rack arrangement level  20  such that one or more shuttles  50  instructed (e.g., via a central controller of the AS/RS 1) to execute a storage and/or retrieval operation with respect to an object stored at a storage location provided within a particular storage aisle of the plurality  100  may travel along the inter-aisle shuttle inlet track  140  in the second lateral direction  22  according to the unidirectional shuttle traffic flow pattern thereof to a position at least substantially adjacent a first aisle end of the particular storage aisle, where the one or more shuttles  50  may turn into the particular storage aisle comprising the designated storage location. 
     In various embodiments, the plurality of vertical lifts  200  of an exemplary AS/RS 1 may include a first portion of the plurality of vertical lifts  200  may be operatively connected to a first conveyor configured to transport objects between the AS/RS 1 and a first remote location, and a second portion of the plurality of vertical lifts  200  may be operatively connected to a second conveyor configured to transport objects between the AS/RS 1 and a second remote location. For example, as illustrated, the plurality of vertical lifts  200  may comprise a first portion of the plurality of vertical lifts  200  including a first vertical lift  200   a  and a second vertical lift  200   b  that are operatively connected to a first conveyor  61  that is configured to transport objects between the AS/RS 1 and a first remote conveyor  41 . As illustrated, the plurality of vertical lifts  200  may further include a second portion of vertical lifts including a third vertical lift  200   c  and a third vertical lift  200   d  that are operatively connected to a second conveyor  62  that is configured to transport objects between the AS/RS 1 and a second remote conveyor  42 . In such an exemplary circumstance, one or more shuttles of the plurality of shuttles  50  instructed to execute a storage and/or retrieval operation that requires accessing either the first vertical lift  200   a  or the second vertical lift  200   b  may be selectively transported along the second inter-aisle shuttle outlet track  122  in the first lateral direction  21  so as to pass the lift interface positions corresponding to the third vertical lift  200   c  and the fourth vertical lift  200   d . The one or more shuttles  50  may be selectively transferred from the second inter-aisle shuttle outlet track  122  to the first inter-aisle shuttle outlet track  121  so as to avoid track interferences caused by other shuttles of the plurality  50  being positioned in the lift interface positions corresponding to the third vertical lift  200   c  and the fourth vertical lift  200   d , while facilitating the transportation of the one or more shuttles to a particular one of the designated vertical lifts  200   a ,  200   b . 
     Similarly, in an exemplary circumstance wherein a shuttle  50  is executing a storage and/or retrieval operation that requires the shuttle  50  to access a particular lift of the plurality of lifts  200 , such as, for example, the fourth lift  200   d , the shuttle  50  may be selectively transported along the inter-aisle shuttle inlet track  140  to a particular storage aisle of the plurality of storage aisles  100 , such as, for example, the fourth storage aisle  100   d , that defines a portion of the shuttle recirculation traffic flow pattern defined within the rack arrangement level  20  that is in an upstream position relative to the lift interface position corresponding to the particular vertical lift to be accessed (e.g., the fourth lift  200   d ). 
     In various embodiments, the plurality of shuttles provided within a rack arrangement level of an exemplary AS/RS may include one or more shuttles that are at least temporarily in a standby configuration wherein the one or more shuttles are not being used to execute a storage and/or retrieval operation at a given time. For example, an exemplary AS/RS may comprise a central controller that is in communication with each of the plurality of shuttles  50  and configured to determine an optimal number of shuttles of the plurality  50  to be used in operation within a particular rack arrangement level at a given time based at least in part on an identified and/or estimated bandwidth of the AS/RS 1 (e.g., within the particular rack arrangement level at that time. For example, in various embodiments, the central controller of the AS/RS may identify that less than the total number of shuttles  50  in the plurality of shuttles provided at a rack arrangement level is needed to execute one or more storage and/or retrieval operations, and therefore, may cause at least a portion of the plurality of shuttles  50  to be transported to a shuttle storage position defined along a portion of the shuttle travel racks of the rack arrangement level. Further, in various embodiments, the central controller of the AS/RS may identify that the number of shuttles needed to execute one or more storage and/or retrieval operations is more than the total number of shuttles of the plurality  50  in operation at a given time, and therefore, may cause one or more shuttles of the plurality  50  that are being stored in a shuttle storage position within the rack level arrangement to be dispatched from the shuttle storage position for use in a storage and/or retrieval operation. 
       FIGS.  3 A- 3 B  illustrate various schematic views of exemplary automated storage and retrieval systems that include rack arrangement levels comprising a shuttle storage position according to various embodiments described herein. As illustrated in  FIG.  3 A , in various embodiments an exemplary rack arrangement level  30  may comprise a shuttle storage position  135  that is defined along the shuttle transport track  130  thereof. For example, at least a portion of the plurality of shuttles  50  provided within the rack arrangement level  30  may be at least temporarily stored at a shuttle storage position  135  defined along at least a portion of the track length of the shuttle transport track  130 . The at least a portion of the plurality of shuttles  50  being stored at the shuttle storage position  135  along the shuttle transport track  130  may be positioned in a serial arrangement along the track length thereof so as to define a queue of shuttles  50  that are not executing a storage and/or retrieval operation at a given time. In various embodiments, one or more shuttles  50  may be dispatched from the shuttle storage position as needed to execute one or more storage and/or retrieval operations. In such an exemplary circumstance, a central controller of the AS/RS 1 may provide instructions to at least the shuttle positioned in a frontmost position (e.g., furthest downstream, as defined along the unidirectional shuttle traffic flow) within the shuttle storage position  135  that may cause the shuttle to be transported (e.g., dispatched) from the shuttle storage position  135  to a designated storage aisle of the plurality  100  (e.g., via the inter-aisle shuttle inlet track  140 ). For example, upon successfully executing the storage and/or retrieval operation, the shuttle  50  may be transported to the shuttle transport track  130  (e.g., via the plurality of inter-aisle shuttle outlet tracks  120 ) such that it may returned to the shuttle storage position  135 . Such an exemplary shuttle  50  may be returned to the shuttle storage position  135  such that it is arranged in a back-most position in the queue of shuttles  50  provided within the shuttle storage position  135 . 
     As a further non-limiting example,  FIG.  3 B  illustrates an exemplary rack arrangement level  30  comprising a shuttle storage position  135  that is defined along a secondary shuttle transport track  130   a . In various embodiments, an exemplary rack arrangement level  30  may comprise a shuttle transport track  130 , as described herein in further detail with respect to  FIGS.  1  and  2   , and a secondary shuttle transport track  130   a  along which at least a portion of the plurality of shuttles  50  provided within the rack arrangement level  30  may be at least temporarily stored at a shuttle storage position  135 . For example, the at least a portion of the plurality of shuttles  50  being stored along the secondary shuttle transport track  130   a  may be positioned in a serial arrangement along the track length of the secondary shuttle transport track  130   a  so as to define a queue of shuttles  50  that are not executing a storage and/or retrieval operation at a given time. The secondary shuttle transport track  130   a  may comprise a distinct segment of shuttle guide track that is at least substantially separate from the shuttle transport track  130  such that the shuttles  50  provided at the shuttle storage position  135  along the secondary shuttle transport track  130   a  do not interrupt, interfere with, and/or otherwise obstruct the shuttle recirculation traffic flow pattern defined in part by the shuttle transportation track  130 . In various embodiments, upon determining that an additional shuttle  50  is required in order to execute a storage and/or retrieval operation, a central controller of the AS/RS 1 may provide instructions to the shuttle positioned in a frontmost position (e.g., furthest downstream, as defined along the unidirectional shuttle traffic flow) within the shuttle storage position  135  that may cause the shuttle to be transported (e.g., dispatched) from the shuttle storage position  135  to a designated storage aisle of the plurality  100  (e.g., via the inter-aisle shuttle inlet track  140 ). 
       FIG.  4    is a flowchart that illustrates an exemplary operation of an automated storage and retrieval system using a unidirectional shuttle traffic flow pattern, such described herein in reference to  FIGS.  1 - 3 B , in accordance with various embodiments. Referring to Block  402  of  FIG.  4   , the exemplary method  400  of operating the automated storage and retrieval system 1 includes causing a first shuttle to travel to a first storage location provided within the first storage aisle such that the first shuttle moves along an aisle track of the first storage aisle in a first shuttle travel direction. In various embodiments, wherein the AS/RS 1 comprises a plurality of storage aisles, causing a first shuttle to travel to a first storage location provided within the first storage aisle may comprise selectively causing the first shuttle to travel to a storage location within the first storage aisle from the plurality of storage aisles based at least in part on a relative position of the first storage aisle within a unidirectional shuttle recirculation traffic flow pattern defined by the automated storage and retrieval system. Referring now to Block  404  of  FIG.  4   , the method  400  of operating the AS/RS 1 includes causing a second shuttle to travel to a second storage location provided within the first storage aisle such that the second shuttle moves along the aisle track of the first storage aisle in the first shuttle travel direction and such that both the first shuttle and the second shuttle are positioned within the first storage aisle at a first instance. As described herein, the unidirectional shuttle traffic flow pattern defined by the first storage aisle enables an operation wherein the first shuttle executing a first materials handling operation and the second shuttle executing a second materials handling operation may each be positioned along the aisle track of the first storage aisle at the same time by eliminating the possibility that two shuttles simultaneously positioned within the same storage aisle are executing instructions to move in opposing directions and/or along conflicting shuttle traffic paths. Referring now to Block  406  of  FIG.  4   , the method  400  of operating the AS/RS 1 includes causing the first shuttle to travel in the first shuttle travel direction from the first storage location to a first storage aisle outlet of the first storage aisle. Further, in reference to Block  408  of  FIG.  4   , the method  400  of operating the AS/RS 1 may include causing the second shuttle to travel along the aisle track in the first shuttle travel direction to the first storage aisle outlet. As illustrated in the exemplary embodiment shown in  FIG.  1   , the first storage aisle outlet of the first storage aisle  100  may be defined by the second aisle end  112 . Further, in various embodiments, the method  400  of operating the AS/RS 1 may include, upon determining that that the first shuttle has executed a first materials handling operation, providing instructions to the first shuttle to execute a second materials handling operation, as shown at Block  410  of  FIG.  4   . In various embodiments, providing instructions to the first shuttle to execute the second materials handling operation may comprise causing the first shuttle to travel to a third storage location provided within the first storage aisle such that the first shuttle moves along the aisle track of the first storage aisle in the first shuttle travel direction. 
     Many modifications and other embodiments will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.