Patent Publication Number: US-10315231-B1

Title: Attribute-based container selection for inventory

Description:
BACKGROUND 
     Modern inventory systems, such as those in mail order warehouses, supply chain distribution centers, airport luggage systems, and custom-order manufacturing facilities, face significant challenges in responding to requests for inventory items. As inventory systems grow, the challenges of simultaneously completing a large number of packing, storing, sorting, retrieving, and other inventory-related tasks become non-trivial. In inventory systems tasked with responding to large numbers of diverse inventory requests, inefficient utilization of system resources, including space, equipment, and manpower, can result in lower throughput, unacceptably long response times, an ever-increasing backlog of unfinished tasks, and, in general, poor system performance. Additionally, expanding or reducing the size or capabilities of many inventory systems requires significant changes to existing infrastructure and equipment. As a result, the cost of incremental changes to capacity or functionality may be prohibitively expensive, limiting the ability of the system to accommodate fluctuations in system throughput. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which: 
         FIG. 1  is a simplified schematic diagram illustrating an example inventory system, in accordance with some embodiments; 
         FIG. 2  illustrates components of the inventory system of  FIG. 1 ; 
         FIG. 3  illustrates in greater detail the components of an example management module that can be used in the inventory system of  FIG. 1 ; 
         FIGS. 4 and 5  illustrate in greater detail an example mobile drive unit that can be used in the inventory system of  FIG. 1 ; 
         FIG. 6  illustrates in greater detail an example inventory holder that can be used in the inventory system of  FIG. 1 ; 
         FIG. 7  shows various components of an alternative inventory holder that can be used in the inventory system of  FIG. 1 ; 
         FIG. 8  shows a first example of a sorting station that can be used in the inventory system of  FIG. 1 ; 
         FIG. 9  shows a second example of a sorting station that can be used in the inventory system of  FIG. 1 ; 
         FIG. 10  is a simplified schematic diagram illustrating one example of a process for implementing feature vectors in container selection that can be used in the inventory system of  FIG. 1 ; 
         FIG. 11  is a simplified block diagram illustrating an example control system that can be used in the inventory system of  FIG. 1   
         FIG. 12  illustrates a first example process for implementing container selection using feature vectors that can be used in the inventory system of  FIG. 1 ; 
         FIG. 13  illustrates a second example process for implementing container selection using feature vectors that can be used in the inventory system of  FIG. 1 ; 
         FIG. 14  illustrates a third example process for implementing container selection using feature vectors that can be used in the inventory system of  FIG. 1 ; 
         FIG. 15  illustrates a fourth example process for implementing container selection using feature vectors that can be used in the inventory system of  FIG. 1 ; 
         FIG. 16  illustrates an environment in which various embodiments can be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, various embodiments will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the embodiments may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiment being described. 
     Inventory systems can enhance throughput by efficiently using space and by employing automation, including robotic means to lift, transport, and place inventory. One significant drawback in such automation has been the difficulty that robotic inventory handlers have in identifying specific inventory items from among collections of mixed inventory items, which may be similar to each other. This drawback competes functionally with advantages of co-locating disparate items together in an inventory system. As a result, improved methods for facilitating the retrieval of specific inventory items from groups of co-located, disparate items are desired. 
     Embodiments herein are directed to an inventory system configured for automated handling of inventory items. The inventory system can include various components, such as containers, inventory holders, dunnage, boxes, unmanned drive units for moving inventory items, and stations for automated handling of inventory items. Specifically, features herein are directed to selective placement of inventory items in storage containers in order to facilitate improved automated detection and access to the inventory items during subsequent processing of the inventory items. Inventory systems using these methods can include sensing apparatuses to obtain data about physical attributes of inventory items, and robotic manipulators for physically moving inventory items into storage containers. A destination container for storing an inventory item can be selected based on a determination by the inventory system that the attribute data corresponding to the inventory item is sufficiently unique relative to attribute data of items in the destination container to enable automated selection of the incoming inventory item from the destination container if the items were to be mixed. The attribute data corresponding to these physical attributes can be used to generate feature vectors that correspond to readily machine-identifiable physical attributes of the inventory items in a form readily accessed for comparison with feature vectors of other inventory items. 
       FIG. 1  illustrates an example inventory system  200  that utilizes sorting stations to sort inventory into containers  212  for storage in an inventory facility, in accordance with some embodiments. The sorting stations can include, e.g., induct stations  206  and/or replenishment stations  224  to move inventory items into storage  214  in the inventory system. Aspects of the system  200  are directed by a management component or controller  240 , which includes a processor and memory  242 ,  244 . Specific attributes of the controller  240 , associated modules, and processes are discussed below with greater detail with reference to  FIGS. 10-13 . The controller  240  can communicate with other system components via a network  246 , such as a wireless network. The system  200  can be used to manage inventory items in the context of a workspace of an inventory facility, which can include a storage region  214  and/or a sorting floor  218 . The workspace includes a physical workspace, in which the induct and replenishment stations  206 ,  224  are positioned, and on which unmanned drive units  20  operate in order to move and store inventory within the inventory facility. A virtual representation of the inventory facility can be maintained by the controller  240  in order to facilitate control over the drive units  20  moving therein. 
     The induct station  206  can operate in conjunction with an inbound conveyance  202 , such as a chute, conveyer belt, series of shuttles, drive units  20  carrying inventory items  210  or inventory item holders thereon, or the like. The inbound conveyance  202  can pass through or otherwise include a sensor station  204  to facilitate physical data collection about inventory items. Aspects of sensor stations are discussed below with reference to  FIG. 9 . Further sensing elements  216  can be located directly adjacent or within the induct station  206 . The inbound conveyance  202  is capable of transporting inbound inventory items for inductance into the inventory system, and can convey the items to the induct station  206  individually, on pallets, in bulk storage, in containers or the like. In some embodiments, the sensor station  204  and/or sensing elements  216  are configured to detect discrete physical attributes of the inventory items suitable for generating feature vectors. In some embodiments, one or both of the sensor station and sensing elements are capable of positively identifying an inventory item, e.g. by way of reading a machine-readable identifier on the inventory item. 
     Under the control of the controller  240 , the induct station  206  can parcel out inventory items  210  into inventory containers  212  for transit to storage  214 . In some embodiments, the inventory containers  212  are arrayed on inventory holders  208 , e.g. into first inventory holders  212   a  positioned on a first inventory holder  208   a  adjacent the induct station  206 . The inventory containers  212  that receive inventory items can be arrayed around or proximate to the induct station  206  for access by robotic manipulators of the induct station ( FIGS. 8-9 ). In some embodiments, one or more inventory holders  208  containing inventory containers  212  are transported to loading positions adjacent the induct station  206  by a drive unit(s)  20 . The inventory containers  212  can be transported to and from the induct station  206  by any suitable conveyance, e.g. via conveyor belts, shuttles, robotic gantries or grasping elements, or the like. The induct station  206  can be positioned and configured with robotic manipulators to access and place inventory items into any one of multiple inventory containers  212 . In some embodiments, approximately ten inventory containers can be accessible at any one time, or in some cases, at least 2 inventory containers, e.g., 2-10, 2-20, or more than 20 inventory containers. 
     In some embodiments, the controller  240  causes the induct station  206  to load inventory items  210  into selected inventory containers  212  based on item attribute data  210 , which can be in the form of a unique feature vector associated with the inventory item to be stored. For example, the item attribute data for each inventory item  210  can be accessed based on an identity of the inventory item, or may be generated based on sensed physical attributes as measured by the sensor station  204  or sensing elements  216 . This item attribute data can then be compared with feature vectors associated with collections of items already present in each of the inventory containers  212   a  adjacent the induct station  206 , in order to locate a destination container containing only items having feature vectors that are sufficiently distinct or machine differentiable as compared to the inventory item  210  to be stored. Specific aspects of feature vector distinctness are discussed below in greater detail with reference to  FIGS. 10-13 . Once all of the inventory containers  212   a  are full, or once a sufficient number of the inventory containers are full, the system controller  240  can direct a drive unit  20  to transfer inventory containers to storage  214  and to supply as-yet unfilled or partially unfilled inventory containers  212  to the induct station. 
     The system  200  can also replenish inventory in inventory containers  212  by way of replenishment stations  224  that are not necessarily inducting new inventory items. For example, ongoing sorting of inventory items can be conducted to optimize the contents of inventory containers by transferring inventory from existing containers to new containers according to methods described herein. In some embodiments, known inventory items  210  are transferred to storage from, e.g., other inventory systems (trans-shipped items) via conveyors  222 , or from bulk containers  220  which may be transferred via inventory holders  208   c  and/or drive units  20 . The replenishment station  224 , which includes sensing elements  226 , can select adjacent inventory containers  212   b  for storing inventory items  210  according to similar methods used to select destination containers as described above with reference to the induct station  206 . In some embodiments, the replenishment station  224  scans the inventory items  210  via sensing elements  226  to determine a specific identifier of each inventory item in order to retrieve a known, item attribute data of the inventory item. In some embodiments, the system  200  generates an item attribute data of the inventory item based on sensed physical attributes of the inventory item. Once replenished, the inventory containers  212   b  can be returned to storage  214 , e.g. by drive units  20 . 
     The replenishment of inventory items  210  into inventory containers  212  can be accomplished when the inventory system is inducting new inventory, transferring in inventory, sorting inventory, or shipping inventory. For example, requested inventory items can be transported from storage  214  to a sorting floor  218 , e.g. by drive units  20 , where the selected inventory items are removed for sorting or shipping, resulting in a continuous stream of partially emptied inventory containers  212 . These partially emptied inventory containers may be transported to replenishment stations  224  and/or to induct stations  206  where they can be refilled with additional inventory items. Partially emptied inventory containers can also be replenished while positioned on the sorting floor or even during a sorting operation when a select inventory item is removed. Specific aspects of selecting a destination container for receiving inventory items are discussed below with reference to  FIGS. 8-13 , whereas aspects of storage and transport of inventory are discussed below with reference to  FIGS. 2-7 . 
     Management module  15  assigns tasks to appropriate components of inventory system  10  and coordinates operation of the various components in completing the tasks. These tasks may relate not only to the movement and processing of inventory items, but also to the management and maintenance of the components of inventory system  10 . For example, management module  15  may assign portions of workspace  70  as parking spaces for mobile drive units  20 , the scheduled recharge or replacement of mobile drive unit batteries, the storage of empty inventory holders  30 , or any other operations associated with the functionality supported by inventory system  10  and its various components. Management module  15  may select components of inventory system  10  to perform these tasks and communicate appropriate commands and/or data to the selected components to facilitate completion of these operations. Although shown in  FIG. 2  as a single, discrete component, management module  15  may represent multiple components and may represent or include portions of mobile drive units  20  or other elements of inventory system  10 . As a result, any or all of the interactions between a particular mobile drive unit  20  and management module  15  that are described below may, in particular embodiments, represent peer-to-peer communication between that mobile drive unit  20  and one or more other mobile drive units  20 . The components and operation of an example embodiment of management module  15  are discussed further below with respect to  FIG. 3 . 
     Mobile drive units  20  move inventory holders  30  between locations within workspace  70 . Mobile drive units  20  may represent any devices or components appropriate for use in inventory system  10  based on the characteristics and configuration of inventory holders  30  and/or other elements of inventory system  10 . In a particular embodiment of inventory system  10 , mobile drive units  20  represent independent, self-powered devices configured to freely move about workspace  70 . Examples of such inventory systems are disclosed in U.S. Pat. No. 9,087,314, issued on Jul. 21, 2015, titled “SYSTEM AND METHOD FOR POSITIONING A MOBILE DRIVE UNIT” and U.S. Pat. No. 8,280,547, issued on Oct. 2, 2012, titled “METHOD AND SYSTEM FOR TRANSPORTING INVENTORY ITEMS”, the entire disclosures of which are herein incorporated by reference. In alternative embodiments, mobile drive units  20  represent elements of a tracked inventory system configured to move inventory holder  30  along tracks, rails, cables, crane system, or other guidance or support elements traversing workspace  70 . In such an embodiment, mobile drive units  20  may receive power and/or support through a connection to the guidance elements, such as a powered rail. Additionally, in particular embodiments of inventory system  10  mobile drive units  20  may be configured to utilize alternative conveyance equipment to move within workspace  70  and/or between separate portions of workspace  70 . The components and operation of an example embodiment of a mobile drive unit  20  are discussed further below with respect to  FIGS. 4 and 5 . 
     Additionally, mobile drive units  20  may be capable of communicating with management module  15  to receive information identifying selected inventory holders  30 , transmit the locations of mobile drive units  20 , or exchange any other suitable information to be used by management module  15  or mobile drive units  20  during operation. Mobile drive units  20  may communicate with management module  15  wirelessly, using wired connections between mobile drive units  20  and management module  15 , and/or in any other appropriate manner. As one example, particular embodiments of mobile drive unit  20  may communicate with management module  15  and/or with one another using 802.11, Bluetooth, or Infrared Data Association (IrDA) standards, or any other appropriate wireless communication protocol. As another example, in a tracked inventory system  10 , tracks or other guidance elements upon which mobile drive units  20  move may be wired to facilitate communication between mobile drive units  20  and other components of inventory system  10 . Furthermore, as noted above, management module  15  may include components of individual mobile drive units  20 . Thus, for the purposes of this description and the claims that follow, communication between management module  15  and a particular mobile drive unit  20  may represent communication between components of a particular mobile drive unit  20 . In general, mobile drive units  20  may be powered, propelled, and controlled in any manner appropriate based on the configuration and characteristics of inventory system  10 . 
     Inventory holders  30  store inventory items. In a particular embodiment, inventory holders  30  include multiple storage bins with each storage bin capable of holding one or more types of inventory items. Inventory holders  30  are capable of being carried, rolled, and/or otherwise moved by mobile drive units  20 . In particular embodiments, inventory holder  30  may provide additional propulsion to supplement that provided by mobile drive unit  20  when moving inventory holder  30 . 
     Additionally, in particular embodiments, inventory items  40  may also hang from hooks or bars (not shown) within or on inventory holder  30 . In general, inventory holder  30  may store inventory items  40  in any appropriate manner within inventory holder  30  and/or on the external surface of inventory holder  30 . 
     Additionally, each inventory holder  30  may include a plurality of faces, and each bin may be accessible through one or more faces of the inventory holder  30 . For example, in a particular embodiment, inventory holder  30  includes four faces. In such an embodiment, bins located at a corner of two faces may be accessible through either of those two faces, while each of the other bins is accessible through an opening in one of the four faces. Mobile drive unit  20  may be configured to rotate inventory holder  30  at appropriate times to present a particular face and the bins associated with that face to an operator or other components of inventory system  10 . 
     Inventory items represent any objects suitable for storage, retrieval, and/or processing in an automated inventory system  10 . For the purposes of this description, “inventory items” may represent any one or more objects of a particular type that are stored in inventory system  10 . Thus, a particular inventory holder  30  is currently “storing” a particular inventory item if the inventory holder  30  currently holds one or more units of that type. As one example, inventory system  10  may represent a mail order warehouse facility, and inventory items may represent merchandise stored in the warehouse facility. During operation, mobile drive units  20  may retrieve inventory holders  30  containing one or more inventory items requested in an order to be packed for delivery to a customer or inventory holders  30  carrying pallets containing aggregated collections of inventory items for shipment. Moreover, in particular embodiments of inventory system  10 , boxes containing completed orders may themselves represent inventory items. 
     In particular embodiments, inventory system  10  may also include one or more inventory stations  50 . Inventory stations  50  represent locations designated for the completion of particular tasks involving inventory items. Such tasks may include the removal of inventory items from inventory holders  30 , the introduction of inventory items into inventory holders  30 , the counting of inventory items in inventory holders  30 , the decomposition of inventory items (e.g. from pallet- or case-sized groups to individual inventory items), the consolidation of inventory items between inventory holders  30 , and/or the processing or handling of inventory items in any other suitable manner. In particular embodiments, inventory stations  50  may just represent the physical locations where a particular task involving inventory items can be completed within workspace  70 . In alternative embodiments, inventory stations  50  may represent both the physical location and also any appropriate equipment for processing or handling inventory items, such as scanners for monitoring the flow of inventory items in and out of inventory system  10 , communication interfaces for communicating with management module  15 , and/or any other suitable components. Inventory stations  50  may be controlled, entirely or in part, by human operators or may be fully automated. Moreover, the human or automated operators of inventory stations  50  may be capable of performing certain tasks to inventory items, such as packing, counting, or transferring inventory items, as part of the operation of inventory system  10 . 
     Workspace  70  represents an area associated with inventory system  10  in which mobile drive units  20  can move and/or inventory holders  30  can be stored. For example, workspace  70  may represent all or part of the floor of a mail-order warehouse in which inventory system  10  operates. Although  FIG. 2  shows, for the purposes of illustration, an embodiment of inventory system  10  in which workspace  70  includes a fixed, predetermined, and finite physical space, particular embodiments of inventory system  10  may include mobile drive units  20  and inventory holders  30  that are configured to operate within a workspace  70  that is of variable dimensions and/or an arbitrary geometry. While  FIG. 2  illustrates a particular embodiment of inventory system  10  in which workspace  70  is entirely enclosed in a building, alternative embodiments may utilize workspaces  70  in which some or all of the workspace  70  is located outdoors, within a vehicle (such as a cargo ship), or otherwise unconstrained by any fixed structure. 
     In operation, management module  15  selects appropriate components to complete particular tasks and transmits task assignments  18  to the selected components to trigger completion of the relevant tasks. Each task assignment  18  defines one or more tasks to be completed by a particular component. These tasks may relate to the retrieval, storage, replenishment, and counting of inventory items and/or the management of mobile drive units  20 , inventory holders  30 , inventory stations  50  and other components of inventory system  10 . Depending on the component and the task to be completed, a particular task assignment  18  may identify locations, components, and/or actions associated with the corresponding task and/or any other appropriate information to be used by the relevant component in completing the assigned task. 
     In particular embodiments, management module  15  generates task assignments  18  based, in part, on inventory requests that management module  15  receives from other components of inventory system  10  and/or from external components in communication with management module  15 . These inventory requests identify particular operations to be completed involving inventory items stored or to be stored within inventory system  10  and may represent communication of any suitable form. For example, in particular embodiments, an inventory request may represent a shipping order specifying particular inventory items that have been purchased by a customer and that are to be retrieved from inventory system  10  for shipment to the customer. Management module  15  may also generate task assignments  18  independently of such inventory requests, as part of the overall management and maintenance of inventory system  10 . For example, management module  15  may generate task assignments  18  in response to the occurrence of a particular event (e.g., in response to a mobile drive unit  20  requesting a space to park), according to a predetermined schedule (e.g., as part of a daily start-up routine), or at any appropriate time based on the configuration and characteristics of inventory system  10 . After generating one or more task assignments  18 , management module  15  transmits the generated task assignments  18  to appropriate components for completion of the corresponding task. The relevant components then execute their assigned tasks. 
     With respect to mobile drive units  20  specifically, management module  15  may, in particular embodiments, communicate task assignments  18  to selected mobile drive units  20  that identify one or more destinations for the selected mobile drive units  20 . Management module  15  may select a mobile drive unit  20  to assign the relevant task based on the location or state of the selected mobile drive unit  20 , an indication that the selected mobile drive unit  20  has completed a previously-assigned task, a predetermined schedule, and/or any other suitable consideration. These destinations may be associated with an inventory request the management module  15  is executing or a management objective the management module  15  is attempting to fulfill. For example, the task assignment may define the location of an inventory holder  30  to be retrieved, an inventory station  50  to be visited, a storage location where the mobile drive unit  20  should park until receiving another task, or a location associated with any other task appropriate based on the configuration, characteristics, and/or state of inventory system  10 , as a whole, or individual components of inventory system  10 . For example, in particular embodiments, such decisions may be based on the popularity of particular inventory items, the staffing of a particular inventory station  50 , the tasks currently assigned to a particular mobile drive unit  20 , and/or any other appropriate considerations. 
     As part of completing these tasks mobile drive units  20  may dock with and transport inventory holders  30  within workspace  70 . Mobile drive units  20  may dock with inventory holders  30  by connecting to, lifting, and/or otherwise interacting with inventory holders  30  in any other suitable manner so that, when docked, mobile drive units  20  are coupled to and/or support inventory holders  30  and can move inventory holders  30  within workspace  70 . While the description below focuses on particular embodiments of mobile drive unit  20  and inventory holder  30  that are configured to dock in a particular manner, alternative embodiments of mobile drive unit  20  and inventory holder  30  may be configured to dock in any manner suitable to allow mobile drive unit  20  to move inventory holder  30  within workspace  70 . Additionally, as noted below, in particular embodiments, mobile drive units  20  represent all or portions of inventory holders  30 . In such embodiments, mobile drive units  20  may not dock with inventory holders  30  before transporting inventory holders  30  and/or mobile drive units  20  may each remain continually docked with a particular inventory holder  30 . 
     While the appropriate components of inventory system  10  complete assigned tasks, management module  15  may interact with the relevant components to ensure the efficient use of space, equipment, manpower, and other resources available to inventory system  10 . As one specific example of such interaction, management module  15  is responsible, in particular embodiments, for planning the paths mobile drive units  20  take when moving within workspace  70  and for allocating use of a particular portion of workspace  70  to a particular mobile drive unit  20  for purposes of completing an assigned task. In such embodiments, mobile drive units  20  may, in response to being assigned a task, request a path to a particular destination associated with the task. Moreover, while the description below focuses on one or more embodiments in which mobile drive unit  20  requests paths from management module  15 , mobile drive unit  20  may, in alternative embodiments, generate its own paths. 
     Components of inventory system  10  may provide information to management module  15  regarding their current state, other components of inventory system  10  with which they are interacting, and/or other conditions relevant to the operation of inventory system  10 . This may allow management module  15  to utilize feedback from the relevant components to update algorithm parameters, adjust policies, or otherwise modify its decision-making to respond to changes in operating conditions or the occurrence of particular events. 
     In addition, while management module  15  may be configured to manage various aspects of the operation of the components of inventory system  10 , in particular embodiments, the components themselves may also be responsible for decision-making relating to certain aspects of their operation, thereby reducing the processing load on management module  15 . 
     Thus, based on its knowledge of the location, current state, and/or other characteristics of the various components of inventory system  10  and an awareness of all the tasks currently being completed, management module  15  can generate tasks, allot usage of system resources, and otherwise direct the completion of tasks by the individual components in a manner that optimizes operation from a system-wide perspective. Moreover, by relying on a combination of both centralized, system-wide management and localized, component-specific decision-making, particular embodiments of inventory system  10  may be able to support a number of techniques for efficiently executing various aspects of the operation of inventory system  10 . As a result, particular embodiments of management module  15  may, by implementing one or more management techniques described below, enhance the efficiency of inventory system  10  and/or provide other operational benefits. 
       FIG. 3  illustrates in greater detail the components of a particular embodiment of management module  15 . As shown, the example embodiment includes a resource scheduling module  92 , a route planning module  94 , a segment reservation module  96 , an inventory module  97 , a communication interface module  98 , a processor  90 , and a memory  91 . Management module  15  may represent a single component, multiple components located at a central location within inventory system  10 , or multiple components distributed throughout inventory system  10 . For example, management module  15  may represent components of one or more mobile drive units  20  that are capable of communicating information between the mobile drive units  20  and coordinating the movement of mobile drive units  20  within workspace  70 . In general, management module  15  may include any appropriate combination of hardware and/or software suitable to provide the described functionality. 
     Processor  90  is operable to execute instructions associated with the functionality provided by management module  15 . Processor  90  may comprise one or more general purpose computers, dedicated microprocessors, or other processing devices capable of communicating electronic information. Examples of processor  90  include one or more application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), digital signal processors (DSPs) and any other suitable specific or general purpose processors. 
     Memory  91  stores processor instructions, inventory requests, reservation information, state information for the various components of inventory system  10  and/or any other appropriate values, parameters, or information used by management module  15  during operation. Memory  91  may represent any collection and arrangement of volatile or nonvolatile, local or remote devices suitable for storing data. Examples of memory  91  include, but are not limited to, random access memory (RAM) devices, read only memory (ROM) devices, magnetic storage devices, optical storage devices or any other suitable data storage devices. 
     Resource scheduling module  92  processes received inventory requests and generates one or more assigned tasks to be completed by the components of inventory system  10 . Resource scheduling module  92  may also select one or more appropriate components for completing the assigned tasks and, using communication interface module  98 , communicate the assigned tasks to the relevant components. Additionally, resource scheduling module  92  may also be responsible for generating assigned tasks associated with various management operations, such as prompting mobile drive units  20  to recharge batteries or have batteries replaced, instructing inactive mobile drive units  20  to park in a location outside the anticipated traffic flow or a location near the anticipated site of future tasks, and/or directing mobile drive units  20  selected for repair or maintenance to move towards a designated maintenance station. 
     Route planning module  94  receives route requests from mobile drive units  20 . These route requests identify one or more destinations associated with a task the requesting mobile drive unit  20  is executing. In response to receiving a route request, route planning module  94  generates a path to one or more destinations identified in the route request. Route planning module  94  may implement any appropriate algorithms using any appropriate parameters, factors, and/or considerations to determine the appropriate path. After generating an appropriate path, route planning module  94  transmits a route response identifying the generated path to the requesting mobile drive unit  20  using communication interface module  98 . 
     Segment reservation module  96  receives reservation requests from mobile drive units  20  attempting to move along paths generated by route planning module  94 . These reservation requests request the use of a particular portion of workspace  70  (referred to herein as a “segment”) to allow the requesting mobile drive unit  20  to avoid collisions with other mobile drive units  20  while moving across the reserved segment. In response to received reservation requests, segment reservation module  96  transmits a reservation response granting or denying the reservation request to the requesting mobile drive unit  20  using the communication interface module  98 . 
     The inventory module  97  maintains information about the location and number of inventory items  40  in the inventory system  10 . Information can be maintained about the number of inventory items  40  in a particular inventory holder  30 , and the maintained information can include the location of those inventory items  40  in the inventory holder  30 . The inventory module  97  can also communicate with the mobile drive units  20 , using task assignments  18  to maintain, replenish or move inventory items  40  within the inventory system  10 . 
     Communication interface module  98  facilitates communication between management module  15  and other components of inventory system  10 , including reservation responses, reservation requests, route requests, route responses, and task assignments. These reservation responses, reservation requests, route requests, route responses, and task assignments may represent communication of any form appropriate based on the capabilities of management module  15  and may include any suitable information. Depending on the configuration of management module  15 , communication interface module  98  may be responsible for facilitating either or both of wired and wireless communication between management module  15  and the various components of inventory system  10 . In particular embodiments, management module  15  may communicate using communication protocols such as 802.11, Bluetooth, or Infrared Data Association (IrDA) standards. Furthermore, management module  15  may, in particular embodiments, represent a portion of mobile drive unit  20  or other components of inventory system  10 . In such embodiments, communication interface module  98  may facilitate communication between management module  15  and other parts of the same system component. 
     In general, resource scheduling module  92 , route planning module  94 , segment reservation module  96 , inventory module  97 , and communication interface module  98  may each represent any appropriate hardware and/or software suitable to provide the described functionality. In addition, as noted above, management module  15  may, in particular embodiments, represent multiple different discrete components and any or all of resource scheduling module  92 , route planning module  94 , segment reservation module  96 , inventory module  97 , and communication interface module  98  may represent components physically separate from the remaining elements of management module  15 . Moreover, any two or more of resource scheduling module  92 , route planning module  94 , segment reservation module  96 , inventory module  97 , and communication interface module  98  may share common components. For example, in particular embodiments, resource scheduling module  92 , route planning module  94 , segment reservation module  96 , and inventory module  97  represent computer processes executing on processor  90  and communication interface module  98  comprises a wireless transmitter, a wireless receiver, and a related computer process executing on processor  90 . 
       FIGS. 4 and 5  illustrate in greater detail the components of a particular embodiment of mobile drive unit  20 . In particular,  FIGS. 4 and 5  include a front and side view of an example mobile drive unit  20 . Mobile drive unit  20  includes a docking head  110 , a drive module  120 , a docking actuator  130 , and a control module  170 . Additionally, mobile drive unit  20  may include one or more sensors configured to detect or determine the location of mobile drive unit  20 , inventory holder  30 , and/or other appropriate elements of inventory system  10 . In the illustrated embodiment, mobile drive unit  20  includes a position sensor  140 , a holder sensor  150 , an obstacle sensor  160 , and an identification signal transmitter  162 . 
     Docking head  110 , in particular embodiments of mobile drive unit  20 , couples mobile drive unit  20  to inventory holder  30  and/or supports inventory holder  30  when mobile drive unit  20  is docked to inventory holder  30 . Docking head  110  may additionally allow mobile drive unit  20  to maneuver inventory holder  30 , such as by lifting inventory holder  30 , propelling inventory holder  30 , rotating inventory holder  30 , and/or moving inventory holder  30  in any other appropriate manner. Docking head  110  may also include any appropriate combination of components, such as ribs, spikes, and/or corrugations, to facilitate such manipulation of inventory holder  30 . For example, in particular embodiments, docking head  110  may include a high-friction portion that abuts a portion of inventory holder  30  while mobile drive unit  20  is docked to inventory holder  30 . In such embodiments, frictional forces created between the high-friction portion of docking head  110  and a surface of inventory holder  30  may induce translational and rotational movement in inventory holder  30  when docking head  110  moves and rotates, respectively. As a result, mobile drive unit  20  may be able to manipulate inventory holder  30  by moving or rotating docking head  110 , either independently or as a part of the movement of mobile drive unit  20  as a whole. 
     Drive module  120  propels mobile drive unit  20  and, when mobile drive unit  20  and inventory holder  30  are docked, inventory holder  30 . Drive module  120  may represent any appropriate collection of components operable to propel mobile drive unit  20 . For example, in the illustrated embodiment, drive module  120  includes motorized axle  122 , a pair of motorized wheels  124 , and a pair of stabilizing wheels  126 . One motorized wheel  124  is located at each end of motorized axle  122 , and one stabilizing wheel  126  is positioned at each end of mobile drive unit  20 . 
     Docking actuator  130  moves docking head  110  towards inventory holder  30  to facilitate docking of mobile drive unit  20  and inventory holder  30 . Docking actuator  130  may also be capable of adjusting the position or orientation of docking head  110  in other suitable manners to facilitate docking. Docking actuator  130  may include any appropriate components, based on the configuration of mobile drive unit  20  and inventory holder  30 , for moving docking head  110  or otherwise adjusting the position or orientation of docking head  110 . For example, in the illustrated embodiment, docking actuator  130  includes a motorized shaft (not shown) attached to the center of docking head  110 . The motorized shaft is operable to lift docking head  110  as appropriate for docking with inventory holder  30 . 
     Drive module  120  may be configured to propel mobile drive unit  20  in any appropriate manner. For example, in the illustrated embodiment, motorized wheels  124  are operable to rotate in a first direction to propel mobile drive unit  20  in a forward direction. Motorized wheels  124  are also operable to rotate in a second direction to propel mobile drive unit  20  in a backward direction. In the illustrated embodiment, drive module  120  is also configured to rotate mobile drive unit  20  by rotating motorized wheels  124  in different directions from one another or by rotating motorized wheels  124  at different speeds from one another. 
     Position sensor  140  represents one or more sensors, detectors, or other components suitable for determining the location of mobile drive unit  20  in any appropriate manner. For example, in particular embodiments, the workspace  70  associated with inventory system  10  includes a number of fiducial marks that mark points on a two-dimensional grid that covers all or a portion of workspace  70 . In such embodiments, position sensor  140  may include a camera and suitable image- and/or video-processing components, such as an appropriately-programmed digital signal processor, to allow position sensor  140  to detect fiducial marks within the camera&#39;s field of view. Control module  170  may store location information that position sensor  140  updates as position sensor  140  detects fiducial marks. As a result, position sensor  140  may utilize fiducial marks to maintain an accurate indication of the location mobile drive unit  20  and to aid in navigation when moving within workspace  70 . 
     Holder sensor  150  represents one or more sensors, detectors, or other components suitable for detecting inventory holder  30  and/or determining, in any appropriate manner, the location of inventory holder  30 , as an absolute location or as a position relative to mobile drive unit  20 . Holder sensor  150  may be capable of detecting the location of a particular portion of inventory holder  30  or inventory holder  30  as a whole. Mobile drive unit  20  may then use the detected information for docking with or otherwise interacting with inventory holder  30 . 
     Obstacle sensor  160  represents one or more sensors capable of detecting objects located in one or more different directions in which mobile drive unit  20  is capable of moving. Obstacle sensor  160  may utilize any appropriate components and techniques, including optical, radar, sonar, pressure-sensing and/or other types of detection devices appropriate to detect objects located in the direction of travel of mobile drive unit  20 . In particular embodiments, obstacle sensor  160  may transmit information describing objects it detects to control module  170  to be used by control module  170  to identify obstacles and to take appropriate remedial actions to prevent mobile drive unit  20  from colliding with obstacles and/or other objects. 
     Obstacle sensor  160  may also detect signals transmitted by other mobile drive units  20  operating in the vicinity of the illustrated mobile drive unit  20 . For example, in particular embodiments of inventory system  10 , one or more mobile drive units  20  may include an identification signal transmitter  162  that transmits a drive identification signal. The drive identification signal indicates to other mobile drive units  20  that the object transmitting the drive identification signal is in fact a mobile drive unit. Identification signal transmitter  162  may be capable of transmitting infrared, ultraviolet, audio, visible light, radio, and/or other suitable signals that indicate to recipients that the transmitting device is a mobile drive unit  20 . 
     Additionally, in particular embodiments, obstacle sensor  160  may also be capable of detecting state information transmitted by other mobile drive units  20 . For example, in particular embodiments, identification signal transmitter  162  may be capable of including state information relating to mobile drive unit  20  in the transmitted identification signal. This state information may include, but is not limited to, the position, velocity, direction, and the braking capabilities of the transmitting mobile drive unit  20 . In particular embodiments, mobile drive unit  20  may use the state information transmitted by other mobile drive units to avoid collisions when operating in close proximity with those other mobile drive units. 
     Control module  170  monitors and/or controls operation of drive module  120  and docking actuator  130 . Control module  170  may also receive information from sensors such as position sensor  140  and holder sensor  150  and adjust the operation of drive module  120 , docking actuator  130 , and/or other components of mobile drive unit  20  based on this information. Additionally, in particular embodiments, mobile drive unit  20  may be configured to communicate with a management device of inventory system  10  and control module  170  may receive commands transmitted to mobile drive unit  20  and communicate information back to the management device using appropriate communication components of mobile drive unit  20 . Control module  170  may include any appropriate hardware and/or software suitable to provide the described functionality. In particular embodiments, control module  170  includes a general-purpose microprocessor programmed to provide the described functionality. Additionally, control module  170  may include all or portions of docking actuator  130 , drive module  120 , position sensor  140 , and/or holder sensor  150 , and/or share components with any of these elements of mobile drive unit  20 . 
     Moreover, in particular embodiments, control module  170  may include hardware and software located in components that are physically distinct from the device that houses drive module  120 , docking actuator  130 , and/or the other components of mobile drive unit  20  described above. For example, in particular embodiments, each mobile drive unit  20  operating in inventory system  10  may be associated with a software process (referred to here as a “drive agent”) operating on a server that is in communication with the device that houses drive module  120 , docking actuator  130 , and other appropriate components of mobile drive unit  20 . This drive agent may be responsible for requesting and receiving tasks, requesting and receiving routes, transmitting state information associated with mobile drive unit  20 , and/or otherwise interacting with management module  15  and other components of inventory system  10  on behalf of the device that physically houses drive module  120 , docking actuator  130 , and the other appropriate components of mobile drive unit  20 . As a result, for the purposes of this description and the claims that follow, the term “mobile drive unit” includes software and/or hardware, such as agent processes, that provides the described functionality on behalf of mobile drive unit  20  but that may be located in physically distinct devices from the drive module  120 , docking actuator  130 , and/or the other components of mobile drive unit  20  described above. 
     While  FIGS. 4 and 5  illustrate a particular embodiment of mobile drive unit  20  containing certain components and configured to operate in a particular manner, mobile drive unit  20  may represent any appropriate component and/or collection of components configured to transport and/or facilitate the transport of inventory holders  30 . As another example, mobile drive unit  20  may represent part of an overhead crane system in which one or more crane assemblies are capable of moving within a network of wires or rails to a position suitable to dock with a particular inventory holder  30 . After docking with inventory holder  30 , the crane assembly may then lift inventory holder  30  and move inventory to another location for purposes of completing an assigned task. 
     Furthermore, in particular embodiments, mobile drive unit  20  may represent all or a portion of inventory holder  30 . Inventory holder  30  may include motorized wheels or any other components suitable to allow inventory holder  30  to propel itself. As one specific example, a portion of inventory holder  30  may be responsive to magnetic fields. Inventory system  10  may be able to generate one or more controlled magnetic fields capable of propelling, maneuvering and/or otherwise controlling the position of inventory holder  30  as a result of the responsive portion of inventory holder  30 . In such embodiments, mobile drive unit  20  may represent the responsive portion of inventory holder  30  and/or the components of inventory system  10  responsible for generating and controlling these magnetic fields. While this description provides several specific examples, mobile drive unit  20  may, in general, represent any appropriate component and/or collection of components configured to transport and/or facilitate the transport of inventory holders  30 . 
       FIG. 6  illustrates in greater detail the components of a particular embodiment of inventory holder  30 . In particular,  FIG. 6  illustrates the structure and contents of one side of an example inventory holder  30 . In a particular embodiment, inventory holder  30  may comprise any number of faces with similar or different structure. As illustrated, inventory holder  30  includes a frame  310 , a plurality of legs  328 , and a docking surface  350 . 
     Frame  310  holds inventory items  40 . Frame  310  provides storage space for storing inventory items  40  external or internal to frame  310 . The storage space provided by frame  310  may be divided into a plurality of inventory bins  320 , each capable of holding inventory items  40 . Inventory bins  320  may include any appropriate storage elements, such as bins, compartments, or hooks. 
     In a particular embodiment, frame  310  is composed of a plurality of trays  322  stacked upon one another and attached to or stacked on a base  318 . In such an embodiment, inventory bins  320  may be formed by a plurality of adjustable dividers  324  that may be moved to resize one or more inventory bins  320 . In alternative embodiments, frame  310  may represent a single inventory bin  320  that includes a single tray  322  and no adjustable dividers  324 . Additionally, in particular embodiments, frame  310  may represent a load-bearing surface mounted on mobility element  330 . Inventory items  40  may be stored on such an inventory holder  30  by being placed on frame  310 . In general, frame  310  may include internal and/or external storage space divided into any appropriate number of inventory bins  320  in any appropriate manner. 
     Additionally, in a particular embodiment, frame  310  may include a plurality of device openings  326  that allow mobile drive unit  20  to position docking head  110  adjacent docking surface  350 . The size, shape, and placement of device openings  326  may be determined based on the size, the shape, and other characteristics of the particular embodiment of mobile drive unit  20  and/or inventory holder  30  used by inventory system  10 . For example, in the illustrated embodiment, frame  310  includes four legs  328  that form device openings  326  and allow mobile drive unit  20  to position mobile drive unit  20  under frame  310  and adjacent to docking surface  350 . The length of legs  328  may be determined based on a height of mobile drive unit  20 . 
     Docking surface  350  comprises a portion of inventory holder  30  that couples to, abuts, and/or rests upon a portion of docking head  110 , when mobile drive unit  20  is docked to inventory holder  30 . Additionally, docking surface  350  supports a portion or all of the weight of inventory holder  30  while inventory holder  30  is docked with mobile drive unit  20 . The composition, shape, and/or texture of docking surface  350  may be designed to facilitate maneuvering of inventory holder  30  by mobile drive unit  20 . For example, as noted above, in particular embodiments, docking surface  350  may comprise a high-friction portion. When mobile drive unit  20  and inventory holder  30  are docked, frictional forces induced between docking head  110  and this high-friction portion may allow mobile drive unit  20  to maneuver inventory holder  30 . Additionally, in particular embodiments, docking surface  350  may include appropriate components suitable to receive a portion of docking head  110 , couple inventory holder  30  to mobile drive unit  20 , and/or facilitate control of inventory holder  30  by mobile drive unit  20 . 
     Holder identifier  360  marks a predetermined portion of inventory holder  30  and mobile drive unit  20  may use holder identifier  360  to align with inventory holder  30  during docking and/or to determine the location of inventory holder  30 . More specifically, in particular embodiments, mobile drive unit  20  may be equipped with components, such as holder sensor  150 , that can detect holder identifier  360  and determine its location relative to mobile drive unit  20 . As a result, mobile drive unit  20  may be able to determine the location of inventory holder  30  as a whole. For example, in particular embodiments, holder identifier  360  may represent a reflective marker that is positioned at a predetermined location on inventory holder  30  and that holder sensor  150  can optically detect using an appropriately-configured camera. 
     Depending on the configuration and characteristics of mobile drive unit  20  and inventory system  10 , mobile drive unit  20  may move inventory holder  30  using a variety of appropriate methods. In a particular embodiment, mobile drive unit  20  is capable of moving inventory holder  30  along a two-dimensional grid, combining movement along straight-line segments with ninety-degree rotations and arcing paths to transport inventory holder  30  from the first location to the second location. Additionally, while moving, mobile drive unit  20  may use fixed objects located in the workspace as reference points to assist in navigation. For example, in particular embodiments, inventory system  10  includes multiple fiducial marks. Mobile drive unit  20  may be configured to detect fiducial marks and to determine the location of mobile drive unit  20  and/or measure its movement based on the detection of fiducial marks. 
     After mobile drive unit  20  arrives at the second location, mobile drive unit  20  may perform appropriate operations to facilitate access to inventory items  40  stored in inventory holder  30 . For example, mobile drive unit  20  may rotate inventory holder  30  to present a particular face of inventory holder  30  to an operator of inventory system  10  or other suitable party, such as a packer selecting inventory items  40  from inventory holder  30 . Mobile drive unit  20  may also undock from inventory holder  30 . Alternatively, instead of undocking at the second location, mobile drive unit  20  may transport inventory holder  30  back to the first location or to a third location after any appropriate actions have been taken involving inventory items  40 . For example, after a packer has removed particular inventory items  40  from inventory holder  30 , mobile drive unit  20  may return inventory holder  30  to its original storage location, a new storage location, or another inventory station. Mobile drive unit  20  may then undock from inventory holder  30  at this new location. 
     Systems and methods for transporting inventory via mobile drive units  20  as described above with respect to inventory holder  30  are applicable to various forms of inventory holders  30  discussed with reference to  FIG. 2 . For example, suitable inventory holders  30  can include any suitable container or stage for holding inventory, either directly or via intermediate containers. Suitable containers can include pallets, bulk containers, bins, or gaylords, platforms that may be adapted to hold one or more containers thereon, or other suitable holders.  FIG. 7  shows various components of an alternative inventory holder  370  that may be used in particular embodiments of the inventory systems shown in  FIGS. 1 and 2 . 
     For example,  FIG. 7  illustrates one example of an alternative inventory holder  370 , which is adapted for use with a drive unit  20  and can carry inventory containers  366 . The inventory holder  370  includes a stage  364  adapted to support the inventory containers  366 . In one embodiment, the stage  364  is capable of supporting the inventory containers  366  in an array; but in various other embodiments, the stage can carry one or more alternative forms of inventory container as described above, or can carry individual inventory items thereon. The stage  364  can also include a docking surface  352  similar to docking surface  350  ( FIG. 6 ) and a holder identifier  362  (similar to holder identifier  360 ,  FIG. 6 ) to facilitate the alignment of the inventory holder  370  with drive unit  20 . 
       FIG. 7  illustrates mobile drive unit  20  and inventory holder  370  prior to docking. As noted above with respect to  FIGS. 1 and 2 , mobile drive unit  20  may receive a command that identifies a location for a particular inventory holder  370 . Mobile drive unit  20  may then move to the location specified in the command. Additionally, mobile drive unit  20  may utilize position sensor  140  to determine the location of mobile drive unit  20  to assist in navigating to the location of inventory holder  370 . 
     In particular,  FIG. 7  shows mobile drive unit  20  and inventory holder  370  as mobile drive unit  20  approaches the storage location identified by the received command. In the illustrated embodiment, the reference point is marked by fiducial mark  450 , which includes a surface operable to reflect light and which, as a result, can be detected by particular embodiments of position sensor  140  when mobile drive unit  20  is positioned over or approximately over fiducial mark  450 . As noted above, the illustrated embodiment of mobile drive unit  20  utilizes optical sensors, including a camera and appropriate image- and/or video processing components, to detect fiducial marks  450 , holder identifier  362 , or both. Once connected, the mobile drive units  20  can transport the inventory holder  370  to an induct station  206  or replenishment station  224 , ( FIG. 1 ) to storage  212 , to a sorting floor  218 , or other station in an inventory system. 
       FIG. 8  shows a first example of a sorting station  800  that may be used in particular embodiments of the inventory system shown in  FIG. 1  in a side view. The sorting station  800  may be used, e.g., for inducting new items into an inventory system (e.g., induct station  206  as shown in  FIG. 1 ) and/or for replenishing depleted inventory containers with inventory items already inducted (e.g., as in replenishment station  224 ,  FIG. 1 ). 
     In an embodiment, the sorting station  800  includes a conveyance  802  (e.g. conveyor belt  812 ) for introducing items  810 , a robotic manipulator  804  for transferring inventory items, a sensing element  808  for sensing attributes of the items, a controller  240  for controlling the operation of the sorting station, and a collection of destination containers  806  positioned on a stage or comparable inventory holder  820 . Sorting station  800  represents a simplified example of a sorting station. Under the control of the controller  240 , the inventory sorting station  800  can remove the inventory item  810  from the conveyance  802  via, e.g., a robotic grasper  814  of a manipulator  816 , or other comparable robotic manipulator. The sensing element  808 , which can include a camera  818 , can scan the inventory item  810  before or after the item has been manipulated by the robotic manipulator  804 . 
     In at least one embodiment, the sensing element  808  can detect an identifier associated with the inventory item  810 , such as a machine-readable label or the like, from which the controller  240  can retrieve item information or item attribute data about the inventory item  810 , including a feature vector. In alternative embodiments, the sensing elements  808  can also, or alternatively, scan the inventory item  810  to collect physical attribute data, from which the controller  240  can construct a feature vector. The scoring station  800  can then compare the feature vector of the inventory item  810  to be sorted with feature vectors of the stored inventory items  824 ,  826 ,  830 ,  832 . Feature vectors of stored inventory items can be stored in conjunction with the inventory containers  822 ,  828  in which they are stored, thus allowing the controller  240  to readily access the feature vectors of each stored item based on the inventory containers. The feature vector of the inventory item  810  can be compared with the feature vectors of each stored inventory item  824 ,  826 ,  830 ,  832 , in order to determine whether one of the potential destination containers  822 ,  828  has a collection of items sufficiently distinct from the inventory item  810 . Once this determination is made, the inventory item  810  can be placed in the destination container containing the sufficiently distinct collection. 
     Although  FIG. 8  shows sorting of inventory items from a conveyor  812  to storage containers, sorting station  800  can also transfer items from one storage container to another. For example, in an embodiment, the sorting station  800  can identify the item  810  from a container, e.g. by way of positive identification, and then proceed to transfer the item to a destination container based on the distinctness of the item&#39;s feature vector with respect to the feature vectors of items in the destination container. This selection may be aided by use of the feature vector of the inventory item  810 . For example, in an embodiment, the sorting station  800  can identify, via the sensing element  808 , one or more physical attributes of the inventory item  810 . By accessing inventory data of a container containing the inventory item  810 , the controller  240  can compare the identified physical attributes with the feature vectors of items stored with inventory item  810 , in order to pick the inventory item. Positive identification may be used to verify that the correct inventory item was selected. 
     Alternative sorting stations may provide additional sensing elements for identifying an inventory item and/or for generating a feature vector, as described below with reference to  FIG. 9 . A more detailed discussion of feature vectors follows with reference to  FIG. 10 . 
       FIG. 9  shows a second example of a sorting station  900  that may be used in particular embodiments of the inventory system shown in  FIG. 1 . The sorting station  900  may be used, e.g., for inducting new items into an inventory system (e.g., induct station  206  as shown in  FIG. 1 ) and/or for replenishing depleted inventory containers with inventory items already inducted (e.g., as in replenishment station  224 ,  FIG. 1 ). 
     In an embodiment, the sorting station  900  includes a conveyer  912  for introducing items  810  that passes through a sensor station  902 . In an embodiment, the sensor station  902  contains sensors  906 ,  908 ,  910  for collecting data corresponding to physical attributes of the inventory item  904  in the sensor station. In at least one embodiment, the sensor station  902  can include some or all of the features of a vision tunnel as described in U.S. Pat. No. 9,663,294, which is hereby incorporated by reference. The sensors  906 - 910  can include, e.g., any suitable subset of the following sensors: optical cameras, infrared cameras, infrared heat sensors and/or emitters, acoustic sensors and/or emitters, a weight scale, or other comparable sensor. The sensors  906 - 910  can include sensors positioned to capture images or data from inventory items at different angles (e.g., sensors  906 ,  908 ), or can be positioned to contact the inventory item or to support the inventory item through the conveyor  912  (e.g. sensor  910 ). The sorting station  900  can include all of the components of the sorting station  800  ( FIG. 8 ), including a robotic manipulator  804  for transferring inventory items, a controller  240  for controlling the operation of the sorting station, and a collection of destination containers  806  positioned on a stage or comparable inventory holder  820 , any or all of which may operate in the same manner as described above with reference to  FIG. 8 . 
     Some or all of the processes  1000 ,  1200 ,  1300  (or any other processes described herein, or variations, and/or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) executing collectively on one or more processors, by hardware or combinations thereof. The code may be stored on a computer-readable storage medium, for example, in the form of a computer program comprising a plurality of instructions executable by one or more processors. The computer-readable storage medium may be non-transitory. 
       FIG. 10  is a simplified schematic diagram illustrating one example of a process  1000  for implementing feature vectors in container selection, in accordance with at least one embodiment. The process  1000  can be implemented in an inventory system such as inventory system  200  ( FIG. 1 ), or by a system such as system  1100  ( FIG. 11 , below).  FIG. 10  is presented as a simplified and non-limiting example of a process for generating unique feature vectors for inventory items based on a small number of physical attributes, which will typically be generated based on additional physical attributes. 
     In an embodiment, the process  1000  includes retrieving and/or generating feature vectors associated with select inventory items. For purposes of clarity, selected inventory item data  1024 ,  1026 ,  1030  and  1032  correspond, via like number, with representative inventory items  824 ,  826 ,  830 ,  832  as shown above with reference to  FIGS. 8 and 9 . Selections  1022  and  1028  corresponding to containers  822  and  828 . Each instance of inventory data is associated with a respective feature vector, e.g., inventory data  1024  with feature vector  1008 , inventory data  1030  with feature vector  1010 , inventory data  1026  with feature vector  1012 , and inventory data  1024  with feature vector  1014 . 
     Feature vectors can be generated for each inventory item and stored in a data store in conjunction with data about that item, which may be indexed by any suitable form of item identifier. One method of generating feature vectors, as described above, is to scan the inventory item (e.g. at time of induct or during a sorting operation) to obtain data reflecting at least two distinct physical attributes. For purposes of this simplified example process  1000 , two such physical attributes can include shape (presented here as a distinction between square and round item shape), and color (presented here as a distinction between shaded and unshaded). The feature vectors  1008 - 1014  roughly reflect these illustrative physical attributes in the Y-axis and X-axis, respectively (with “squareness” vertical, “shading” right), with a potential third vector aspect represented in the Z-direction. 
     Suitable feature vectors for actual use in sorting inventory items can encompass potentially many additional dimensions, including but not limited to: independent size attributes such as width, height, thickness, or mass; calculated size attributes such as volume or density; surface information including reflectivity or matte appearance; color information such as hue, saturation, vibrancy, color composition, or specific unique color content; tactile information such as weight, compressibility, or roughness; shape information identifiable from visual inspection, such as but not limited to parallel edges, amorphous edges, contour count, flaps; thermal properties such as heat dissipation or infrared spectrum; internal structure properties such as acoustic density; or text-based features such as identifiable textual content or text density, among other attributes. In embodiments, one or more physical attribute may be reduced to a representative numerical value, e.g. an intensity value, for generating an aspect of the feature vector; or multiple intensity values may be combined (e.g., averaged, multiplied, weighted average, etc.) to advantageously form feature vectors with more consistent properties. For example, in one embodiment, height, width, and thickness attributes may be reduced to intensity values (lengths) and multiplied to obtain a vector aspect corresponding to item volume, which is advantageous over any of the component values for its invariance with the item&#39;s orientation in storage. In another embodiment, volume and mass intensity values may be combined by division to form a vector aspect corresponding to item density, which is similarly invariant. The physical attributes selected for a particular feature vector may also be selected to ensure the inclusion of adequately diverse attributes in the feature vector, e.g. density and color are likely to both be included because these attributes are typically independent of each other. 
     In the example process  1000 , the feature vectors  1008 - 1014  correspond to a collection of intensity values associated with physical attributes, and are stored in conjunction with item data  1024 - 1032 . These item data are each associated with one of the selections  1022 ,  1028 . Item data  1004 , corresponding to the item  810  ( FIGS. 8-9 ), is selected for sorting  1002  into one of the selections  1022 ,  1028 . The system can either retrieve or generate the unique feature vector  1006  for the inventory item  810  to be sorted. In an embodiment, the system can both retrieve a stored feature vector corresponding with an identifier of the item  810 , and generate a new feature vector, in order to verify or update the feature vector. The unique feature vector  1006  can then be compared with each respective feature vector  1008 - 1014  of the collections of inventory items. As shown, the feature vector  1006  is distinct from each of the feature vectors  1008 ,  1010  of the first selection  1028 , by virtue of the feature vector being markedly different in at least one vector aspect from each of the feature vectors  1008 ,  1010 . The feature vector is not distinct from each of the feature vectors  1012 ,  1014  of the second selection  1022  by virtue of similarity to the feature vector  1014 . 
     In one embodiment, distinctness can be determined by quantifying a difference between each respective feature vector aspect, and comparing each difference to a defined threshold value for that aspect. However, the specific threshold value for each vector aspect can differ based on the relative accuracy of sensing techniques to measure the corresponding physical attribute, the presence or absence of additional calculations to generate the feature vector from the corresponding physical attribute, and the relative value of a specific feature vector aspect in accurately distinguishing between different inventory items. In an embodiment, the threshold value for a feature vector aspect is determined empirically based on a confidence interval associated with the accuracy of selecting the intended item from a container of mixed items based on the select feature vector aspect. 
     Storing inventory items in containers based on these methods results in the storage of mixed items together that are readily distinguishable from one another by automated means according to physical attributes that are detectable via automated sensing. Preferably, these automated sensing means (e.g., weighing, image processing, etc.) can be conducted without necessitating manipulation of the item, or with only a partial view of the item. Thus, pre-sorting items according to the described methods can reduce or eliminate the need for mechanical manipulation of inventory items in storage during later retrieval, greatly reducing sort times. 
       FIG. 11  is a simplified block diagram illustrating an example system  1100  for controlling an inventory system like the system  200  of  FIG. 1 , in accordance with embodiments. The system  1800  may be operable to control any suitable number of drive units  20  for transporting inventory holders  208  ( FIG. 1 ) or  30  ( FIG. 2 ), to control any suitable number of sorting stations, e.g. at item induct stations  206  and/or replenishment stations  224 , as well as other system elements. 
     For example, the system  1100  includes a controller  240 , similar to controller  240  as described with reference to  FIG. 1 , including a processing module  242  and memory  244  operable to maintain any or all of, or any suitable combination of the following modules: a user I/O module  1104 , a routing module  1106 , and a network communication module  1108 . Any or all of said modules may be configured to enable automated or semiautonomous actions by the drive units  20  and/or item induct and replenishment stations  206 ,  224  described above. The system  1100  can also include individual control modules for each aspect of the system, such as a drive unit controller  1150 , replenishment station controller  1130 , and induct station controller  1110  for controlling operation of the induct station. 
     The controller  240  can include a computer system configured to receive instructions via a network  246  and cause drive units, modular sorting stations, and other robotic elements to act in accordance with those instructions. For example, the user I/O module can receive user input and generate outputs from received data, e.g., the I/O module can include a switch, keyboard, screen, touchscreen, microphone, or any other suitable device for entering a user input or for displaying a visual or audible output. User input can include, e.g., instructions from a user to store or retrieve inventory items. Data can also include a status message, such as any suitable error message or status update. The routing module  1106  can direct pathfinding for drive units, can instruct drive units to retrieve or transport particular inventory holders from site to site within an inventory system, and can direct routing of select inventory items out of the inventory system or into storage. A network communication module  1108  can facilitate communication of instructions from the controller  240  to the various other components via the network  246 , as well as the transfer of data from the various components back to the controller  240 . 
     The drive unit controller  1150  can include at least the following components and subsystems. A sensing module  1152  can detect the local position of each drive unit, e.g. by way of fiducial markings with respect to a workstation floor, with respect to select workstations such as the induct station  206  ( FIG. 1 ) or replenishment station  224  ( FIG. 1 ), or at other stations or locations in an inventory system including in a storage region of the workstation floor or in a sorting or outbound processing region of a workstation floor. A retention module  1150  can cause drive unit to engage or disengage from an inventory holder in order to lift, transport, and deposit inventory holders in the inventory system. A displacement module can respond to routing instructions form the routing module  1106  by causing the drive unit to move within the inventory system according to the routing instructions. In one embodiment, the drive unit controller can cause the drive unit to displace based on routing instructions from the controller  240 , e.g. by calculating specific routes using onboard processing  1158  and memory  1160 . In alternative embodiments, each drive unit can be directly controlled by the controller via the network  246 . 
     The induct station controller  1110  can include a sensing module  1112  for controlling sensors associated with the induct station  206  and a displacement module  1116  for controlling any robotic manipulators associated with the induct station. The modules of the induct station controller  1110  may be implemented via one or more onboard controllers at the induct station possessing local processing  1118  and memory  1120 , or may be implemented by the controller  240  via the network  246 . 
     In an embodiment, the sensing module  1112  can control one or more sensors associated with the induct station  206  ( FIG. 1 ) to collect physical attribute data about an inventory item being inducted into the inventory system, as discussed above. The sensing module  1112  can operate multiple types of sensors simultaneously, e.g., optical sensors operating in any suitable visible or sub-visible wavelength, optical or electromagnetic readers, acoustic sensors, tactile sensors, or the like. In some cases, the sensors may be positioned to scan an inventory item while it is conveyed through a controlled environment, such as a vision tunnel as described in U.S. Pat. No. 9,663,294, which is incorporated by reference. The sensing module  1112  may be further configured to utilize image based identification techniques as discussed in U.S. Pat. No. 9,665,960, or attribute identification techniques as described in U.S. Pat. No. 9,569,700, (both hereby incorporated by reference,) to associate specific attributes with an inventory item when the inventory item is scanned. In one embodiment, the sensing module  1112  can also collect the various physical attribute data of the inventory item in order to generate a feature vector based on the data. 
     The displacement module  1116  can control mechanical systems of the induct station to transfer inventory items into the inventory system, e.g. by controlling actuation of a robotic manipulator, such as a robotic grasper, gantry robot, conveyor, or the like, to transfer inventory items into or out of containers. In some cases, the displacement module  1116  can work in concert with the sensing module  1112 , with the sensing module providing location data for target inventory items. In some cases, the displacement module  1116  may also move inventory items in order to improve item visibility to sensors associated with the sensing module  1112 . 
     Similarly, the replenishment station controller  1130  can include a comparable sensing module  1132  and displacement module  1134  that can act to collect data on inventory items and to transfer inventory items into, out of, or between storage containers. The modules of the replenishment station controller  1130  may be implemented via one or more onboard controllers at the induct station possessing local processing  1138  and memory  1140 , or may be implemented by the controller  240  via the network  246 . 
     In an embodiment, the sensing module  1132  of the replenishment station controller  1130  can perform similar operations using similar sensors to those described above with respect to the induct station controller  1110 . Likewise, the displacement module  1134  of the replenishment station controller  1130  can perform similar operations to those described with respect to the induct station controller  1110 . Although each station may be capable of performing the same functions with the same equipment, the stations may typically be assigned different tasks. For example, in one embodiment, the induct station controller  1110  may perform more detailed scans of inducted items than those required at the replenishment station. In some cases, the replenishment station may receive containers containing known inventory items with established inventory data, in which case, the sensing module  1132  of the replenishment station  1130  may confirm the identity of an inventory item and its associated feature vector based on contextual information such as an identified container in which replenishment items are provided. 
     Techniques described herein include methods of selecting a destination container for placing inventory items in an inventory system. For example,  FIGS. 12 and 13  illustrate example processes  1200  and  1300  for implementing container selection using feature vectors. Aspects of the processes  1200 ,  1300  may be performed, in some embodiments, by a similar system to the systems  200  or  1100  discussed with reference to  FIGS. 1 and 11 . 
       FIG. 12  illustrates a first example process  1200  for implementing container selection using item attribute data, e.g. feature vectors. In an embodiment, the process  1200  includes receiving instructions to place an inventory item (act  1202 ). In some cases, the instruction may specify a range of available containers, or the system may provide a continuous throughput of potential destination containers which can be assessed for suitability for placing the inventory item. In some cases, approximately ten available containers may be available for placement of any one inventory item, though certain systems may provide as few as two containers, or many containers, e.g. up to 20, up to 30, or up to 40 containers, or more. 
     Next, the system can retrieve a unique feature vector of the inventory item to be placed (act  1204 ). In some embodiments, retrieving the item attribute data can include generating a unique feature vector of the inventory item as discussed above with reference to  FIG. 10 , e.g. by retrieving inventory data based on sensed information, and converting the inventory data into a feature vector. The system can also retrieve stored feature vectors of the inventory items already contained by the inventory containers serving as potential destination containers for the inventory item. 
     The system can then perform a set of comparisons in order to determine the correct inventory container in which to deposit the inventory item. First, the system compares the item attribute data for the particular inventory item to be placed with corresponding item attribute data for inventory items in at least one of the potential destination containers (act  1208 ). The system may perform this comparison step on each contained item of one destination container at a time, or may perform the comparison step on all stored items in the potential destination containers. The comparison step determines whether detectable distinctness, i.e. distinctness with a confidence greater than a particular predetermined threshold, exists between the inventory item to be placed and all of the items in the selected container (act  1210 ). If there is insufficient distinctness, e.g. if at least one item in the container is too similar to the inventory item to be placed, the system can select a different destination container for comparison (act  1212 ). In some alternative embodiments, the system may also recruit an empty container or a container with known distinctness with respect to the inventory item, which may be from outside the set of partially filled potential destination containers. 
     When the system has identified a destination container with a selection of items that are sufficiently distinct from the inventory item to be placed (act  1210 ), the system can select the identified destination container for placement of the inventory item  1214 . Once selected, the system may also cause mechanical systems, such as a robotic displacement mechanism, to physically transfer the inventory item into the specified container (act  1216 ), and may also signal to the inventory system to transfer the specified container (e.g., if filled), for storage, transport, or further sorting via one or more drive units, conveyances, or other suitable mechanism. 
     While the process  1200  described above provides for one aspect of selecting a container for placement of an inventory item, more sophisticated selection methods may be employed in conjunction with, or replacing, those described above. For example, the process  1200  includes selecting the container based on a pass condition, in which the comparison step does not exclude any individual item contained in the container as having too small an item distinctness value. This pass condition may be included with other conditions for selecting an inventory container. For example,  FIG. 13  illustrates a second process  1300  for implementing container selection using item attribute data, aspects of which may be used in conjunction with, or instead of, those in process  1200 . 
     In an embodiment, the process  1300  includes comparing the item attribute data of the item to be placed with the feature vector of each inventory item in a potential destination container (act  1302 ). Based on the comparison step, an item distinctness score or value is determined for each of the stored inventory items of the potential destination container with respect to the inventory item to be valued (act  1304 ). These distinctness values can be combined, e.g. averaged, summed, subjected to a weighted average, or otherwise combined to generate a cumulative distinctness value for the potential destination container reflective of the relative ease of detectability of the inventory item to be stored with reference to the items already present in the potential destination container (act  1306 ). The process steps for generating cumulative distinctness values for a potential destination container may be repeated for any suitable number of potential destination containers. Additional destination containers may be analyzed until a predetermined number of destination containers have been assessed, e.g. all available containers, or a subset of the available containers. In some embodiments, additional containers may be analyzed until a cumulative distinctness value is generated that is above a predetermined threshold, or other suitable criteria. 
     Next, the system can also compare the item distinctness values of the individual items for item distinctness values below a threshold, the threshold being indicative of items that are more similar, i.e. less detectably distinct from the inventory item to be stored (act  1310 ). The potential destination containers containing these items, which may be potentially problematic, can then be excluded as candidates for storing the inventory item, thus preventing similar inventory items from being stored together in the same container. The system can also compare the cumulative distinctness values of the potential destination containers against a cumulative distinctiveness threshold, and exclude those destination containers which do not meet a minimum distinctness value (act  1312 ). The system can then select a destination container for placement of the inventory item based in part on the cumulative distinctiveness values of the remaining destination containers, e.g., by selecting the destination container with the highest cumulative distinctiveness (act  1314 ). However, in some alternative embodiments, other criteria may be employed in addition to, or instead of, the cumulative distinctness of the container. For example, in some cases a selection of the potential destination containers may pass any one of the above-referenced exclusion criteria, and may be selected from among passing destination containers based on other attributes such as: the number of items already contained in a destination container (e.g., prioritizing filled containers in order to cycle additional containers back to storage, or prioritizing containers with fewer items). In some embodiments, a container may also selected based on container-specific criteria, such as, the expected frequency of access of a container (e.g., placing frequently-accessed items together), the remaining volume in a container (e.g., placing large items in emptier containers), the remaining weight capacity of a container (e.g., placing heavy items with light items), and the like. 
     While the processes  1200  and  1300  described above provide for methods of sorting one incoming item into a container from a selection of containers, process variants can also take into account multiple incoming items when selecting a container (i.e. a “many to one” case), or can select multiple destination containers from among multiple items (i.e. a “many to many” case). These methods can be used in concert or combination with the above-referenced methods. For example, by using exclusion criteria for individual items as described with reference to  FIG. 12 or 13 . For example,  FIG. 14  illustrates a third process  1400  for implementing container selection using feature vectors that considers multiple inventory items to select a single destination container; and  FIG. 15  illustrates a fourth process  1500  for implementing container selection that considers the allocation of multiple inventory items among multiple potential destination containers. 
     In an embodiment, the process  1400  includes comparing item attribute data, e.g. feature vectors, of multiple incoming inventory items with stored inventory items in a potential destination container. First, the system receives instructions to place multiple inventory items into one or more containers of a selection of containers (act  1402 ). The system can retrieve item attribute data corresponding to each of the incoming inventory items (act  1404 ) as well as stored item attribute data corresponding to each inventory item already contained in a container (act  1406 ). Once the data has been retrieved, the system can determine item distinctness values for each item in a container with respect to each incoming item (act  1408 ). The distinctness values corresponding to the items can be combined to generate cumulative distinctness values for each incoming inventory item with respect to the container (act  1410 ). An inventory item can then be selected from among the multiple incoming inventory items for placing into the container (act  1412 ). In some embodiments, the system can generate instructions to cause the physical placement of the selected inventory item in the container (act  1414 ), e.g. via a robotic manipulator. 
     In various embodiments, the process  1400  can continue iteratively by adding new items whenever an item is placed; and by advancing selection to a new container when a given container has been filled. In some cases, all of the items may be unsuitable for placement into the selected container, in which case the system may advance to the next container, and/or may add new items for comparison. In some embodiments, multiple containers may be assessed simultaneously, as described below with reference to  FIG. 15 . 
     In an embodiment, the process  1500  includes comparing attribute data multiple incoming inventory items, simultaneously, with attribute data from items contained among multiple potential destination containers. First, the system receives instructions to allocate multiple inventory items among the containers of a collection of containers (act  1502 ). The system can retrieve item attribute data corresponding to each of the incoming inventory items (act  1504 ) as well as stored item attribute data corresponding to each inventory item already contained in each container of the collection (act  1506 ). Once the data has been retrieved, the system can determine item distinctness values for each item among all contained items with respect to each incoming item (act  1508 ). The distinctness values can be combined to generate cumulative distinctness values for each incoming inventory item with respect to each of the containers of the collection (act  1510 ). The system can then iteratively determine a total distinctness value, based on the cumulative distinctness values, for each potential arrangement of incoming inventory items among the available containers (act  1512 ), and can maximize the item uniqueness for each placement by selecting the arrangement that maximizes the distinctness value (act  1514 ). In various embodiments, the process  1500  can be combined with individual item assessments as described above with reference to  FIGS. 12-14 . For example, potential arrangements can be ignored or removed as candidates if one or more placements in the potential arrangement would violate one or more exclusion as described in  FIG. 14 . 
       FIG. 16  illustrates aspects of an example environment  1600  for implementing aspects in accordance with various embodiments. As will be appreciated, although a Web-based environment is used for purposes of explanation, different environments may be used, as appropriate, to implement various embodiments. The environment includes an electronic client device  1602 , which can include any appropriate device operable to send and receive requests, messages, or information over an appropriate network  1604  and convey information back to a user of the device. Examples of such client devices include personal computers, cell phones, handheld messaging devices, laptop computers, set-top boxes, personal data assistants, electronic book readers, and the like. The network can include any appropriate network, including an intranet, the Internet, a cellular network, a local area network or any other such network or combination thereof. Components used for such a system can depend at least in part upon the type of network and/or environment selected. Protocols and components for communicating via such a network are well known and will not be discussed herein in detail. Communication over the network can be enabled by wired or wireless connections and combinations thereof. In this example, the network includes the Internet, as the environment includes a Web server  1606  for receiving requests and serving content in response thereto, although for other networks an alternative device serving a similar purpose could be used as would be apparent to one of ordinary skill in the art. 
     The illustrative environment includes at least one application server  1608  and a data store  1610 . It should be understood that there can be several application servers, layers, or other elements, processes or components, which may be chained or otherwise configured, which can interact to perform tasks such as obtaining data from an appropriate data store. As used herein the term “data store” refers to any device or combination of devices capable of storing, accessing, and retrieving data, which may include any combination and number of data servers, databases, data storage devices and data storage media, in any standard, distributed or clustered environment. The application server can include any appropriate hardware and software for integrating with the data store as needed to execute aspects of one or more applications for the client device, handling a majority of the data access and business logic for an application. The application server provides access control services in cooperation with the data store and is able to generate content such as text, graphics, audio and/or video to be transferred to the user, which may be served to the user by the Web server in the form of HyperText Markup Language (“HTML”), Extensible Markup Language (“XML”) or another appropriate structured language in this example. The handling of all requests and responses, as well as the delivery of content between the client device  1602  and the application server  1608 , can be handled by the Web server. It should be understood that the Web and application servers are not required and are merely example components, as structured code discussed herein can be executed on any appropriate device or host machine as discussed elsewhere herein. 
     The data store  1610  can include several separate data tables, databases or other data storage mechanisms and media for storing data relating to a particular aspect. For example, the data store illustrated includes mechanisms for storing information which can be used by modules described herein, such as resource scheduling information  1612 , route planning information  1614 , segment reservation information  1616 , and/or inventory information  1618 . It should be understood that there can be many other aspects that may need to be stored in the data store, such as for page image information and to access right information, which can be stored in any of the above listed mechanisms as appropriate or in additional mechanisms in the data store  1610 . The data store  1610  is operable, through logic associated therewith, to receive instructions from the application server  1608  and obtain, update or otherwise process data in response thereto. 
     Each server typically will include an operating system that provides executable program instructions for the general administration and operation of that server and typically will include a computer-readable storage medium (e.g., a hard disk, random access memory, read only memory, etc.) storing instructions that, when executed by a processor of the server, allow the server to perform its intended functions. Suitable implementations for the operating system and general functionality of the servers are known or commercially available and are readily implemented by persons having ordinary skill in the art, particularly in light of the disclosure herein. 
     The environment in one embodiment is a distributed computing environment using several computer systems and components that are interconnected via communication links, using one or more computer networks or direct connections. However, it will be appreciated by those of ordinary skill in the art that such a system could operate equally well in a system having fewer or a greater number of components than are illustrated in  FIG. 16 . Thus, the depiction of the system  1600  in  FIG. 16  should be taken as being illustrative in nature and not limiting to the scope of the disclosure. 
     The various embodiments further can be implemented in a wide variety of operating environments, which in some cases can include one or more user computers, computing devices or processing devices which can be used to operate any of a number of applications. User or client devices can include any of a number of general purpose personal computers, such as desktop or laptop computers running a standard operating system, as well as cellular, wireless and handheld devices running mobile software and capable of supporting a number of networking and messaging protocols. Such a system also can include a number of workstations running any of a variety of commercially-available operating systems and other known applications for purposes such as development and database management. These devices also can include other electronic devices, such as dummy terminals, thin-clients, gaming systems and other devices capable of communicating via a network. 
     Most embodiments utilize at least one network that would be familiar to those skilled in the art for supporting communications using any of a variety of commercially-available protocols, such as Transmission Control Protocol/Internet Protocol (“TCP/IP”), Open System Interconnection (“OSI”), File Transfer Protocol (“FTP”), Universal Plug and Play (“UpnP”), Network File System (“NFS”), Common Internet File System (“CIFS”) and AppleTalk. The network can be, for example, a local area network, a wide-area network, a virtual private network, the Internet, an intranet, an extranet, a public switched telephone network, an infrared network, a wireless network, and/or any combination thereof. 
     In embodiments using a Web server, the Web server can run any of a variety of server or mid-tier applications, including Hypertext Transfer Protocol (“HTTP”) servers, FTP servers, Common Gateway Interface (“CGI”) servers, data servers, Java servers and business application servers. The server(s) also may be capable of executing programs or scripts in response requests from user devices, such as by executing one or more Web applications that may be implemented as one or more scripts or programs written in any programming language, such as Java®, C, C# or C++, or any scripting language, such as Perl, Python or TCL, as well as combinations thereof. The server(s) may also include database servers, including without limitation those commercially available from Oracle®, Microsoft®, Sybase® and IBM®. 
     The environment can include a variety of data stores and other memory and storage media as discussed above. These can reside in a variety of locations, such as on a storage medium local to (and/or resident in) one or more of the computers or remote from any or all of the computers across the network. In a particular set of embodiments, the information may reside in a storage-area network (“SAN”) familiar to those skilled in the art. Similarly, any necessary files for performing the functions attributed to the computers, servers or other network devices may be stored locally and/or remotely, as appropriate. Where a system includes computerized devices, each such device can include hardware elements that may be electrically coupled via a bus, the elements including, for example, at least one central processing unit (“CPU”), at least one input device (e.g., a mouse, keyboard, controller, touch screen or keypad) and at least one output device (e.g., a display device, printer or speaker). Such a system may also include one or more storage devices, such as disk drives, optical storage devices and solid-state storage devices such as random access memory (“RAM”) or read-only memory (“ROM”), as well as removable media devices, memory cards, flash cards, etc. 
     Such devices also can include a computer-readable storage media reader, a communications device (e.g., a modem, a network card (wireless or wired), an infrared communication device, etc.) and working memory as described above. The computer-readable storage media reader can be connected with, or configured to receive, a computer-readable storage medium, representing remote, local, fixed, and/or removable storage devices as well as storage media for temporarily and/or more permanently containing, storing, transmitting, and retrieving computer-readable information. The system and various devices also typically will include a number of software applications, modules, services or other elements located within at least one working memory device, including an operating system and application programs, such as a client application or Web browser. It should be appreciated that alternate embodiments may have numerous variations from that described above. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets) or both. Further, connection to other computing devices such as network input/output devices may be employed. 
     Storage media and computer readable media for containing code, or portions of code, can include any appropriate media known or used in the art, including storage media and communication media, such as but not limited to volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage and/or transmission of information such as computer readable instructions, data structures, program modules or other data, including RAM, ROM, Electrically Erasable Programmable Read-Only Memory (“EEPROM”), flash memory or other memory technology, Compact Disc Read-Only Memory (“CD-ROM”), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices or any other medium which can be used to store the desired information and which can be accessed by the a system device. Based at least in part on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the various embodiments. 
     The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the disclosure as set forth in the claims. 
     Other variations are within the spirit of the present disclosure. Thus, while the disclosed techniques are susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this disclosure are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 
     All references, including publications, patent applications and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.