Patent Publication Number: US-9428295-B2

Title: Modular material handling system for order fulfillment

Description:
This application is a continuation of U.S. patent application Ser. No. 13/280,134, filed Oct. 24, 2011, now U.S. Pat. No. 8,892,240, which claims benefit of priority to U.S. Provisional Patent Application No. 61/502,790, filed Jun. 29, 2011, both of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     In a distribution system, a retailer or other product distributor (which may collectively be referred to as distributors) typically maintains an inventory of various items at one or more distribution centers, fulfillment centers, cross-docking facilities, materials handling facilities or warehouses (which may collectively be referred to as materials handling facilities). The inventory items are ordered from one or more vendors, received at the materials handling facilities as inbound shipments, and stocked in inventory of the materials handling facilities. In a conventional order fulfillment process, orders for items may be received from customers of the distributor. Units of the ordered items are picked from various locations in the inventory in the materials handling facilities, processed for shipping, and shipped as outbound shipments to the customers. 
     The facilities operated by the merchant may include various fulfillment processes for fulfilling orders submitted by customers. These processes may operate on items to perform various tasks, such as preparing items for shipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a logical representation of various operations of a materials handling facility, according to some embodiments of the present disclosure. 
         FIG. 2  illustrates an example of a high-level physical layout of a materials handling facility, according to some of the present embodiments. 
         FIG. 3  depicts an example of a control system that may be employed in some embodiments. 
         FIG. 4  illustrates an exemplary physical layout of a materials handling facility, according to one of the present embodiments. 
         FIG. 5  illustrates operation of an exemplary sorting station that may be used in processing modules of some of the present embodiments. 
         FIG. 6  is a flowchart illustrating a method of operation of one of the present embodiments. 
         FIG. 7  is a flowchart illustrating various aspects of one present embodiment. 
         FIG. 8  is a block diagram illustrating an example computer system that may be used in at least some embodiments of the present modular material handling system. 
     
    
    
     Specific embodiments are shown by way of example in the drawings and will be described herein in detail. It should be understood, however, that the drawings and detailed description are not intended to limit the claims to the particular embodiments disclosed, even where only a single embodiment is described with respect to a particular feature. On the contrary, the intent is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. 
     The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). The words “include,” “including,” and “includes” indicate open-ended relationships and therefore mean including, but not limited to. Similarly, the words “have,” “having,” and “has” also indicate open-ended relationships, and thus mean having, but not limited to. The terms “first,” “second,” “third,” and so forth as used herein are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.) unless such an ordering is otherwise explicitly indicated. 
     Various components may be described as “configured to” perform a task or tasks. In such contexts, “configured to” is a broad recitation generally meaning “having structure that” performs the task or tasks during operation. As such, the component can be configured to perform the task even when the component is not currently performing that task (e.g., a router module may be configured to receive inventory items, even when the items are not currently being received). In some contexts, “configured to” may be a broad recitation of structure generally meaning “having circuitry that” performs the task or tasks during operation. As such, the component can be configured to perform the task even when the component is not currently on. In general, the circuitry that forms the structure corresponding to “configured to” may include hardware circuits. 
     Various components may be described as performing a task or tasks, for convenience in the description. Such descriptions should be interpreted as including the phrase “configured to.” Reciting a component that is configured to perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, paragraph six, interpretation for that component. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various embodiments of methods and apparatus for material handling in an order fulfillment center, using a modular material handling system are described. In some of the described embodiments, an order fulfillment system includes inventory storage, a processing area, and a control system. The inventory storage may in some instances include two storage areas, and in some cases the processing area may be disposed between the two storage areas. 
     In some embodiments, the processing area may include a router module that is configured to receive inventory items that have been picked from the inventory storage. In some cases, the inventory items may be received by the router module via conveyance receptacles (e.g., totes, bins) that are conveyed using a conveyor mechanism, where the conveyance receptacles are not fixed to the conveyor mechanism. The processing area may also include a plurality of processing modules that may be configured to receive inventory items from the router module. In some instances, the processing modules may receive the inventory items via conveyance receptacles that are conveyed using the conveyor mechanism. In some cases, the processing area may also include a shipping module that is configured to receive packaged inventory items from various ones of the processing modules. 
     Some embodiments of the present disclosure further include a control system that is operable to cause a particular inventory item to be picked from the inventory storage and to be routed (e.g., via the conveyor mechanism) to the router module of the processing area. Various embodiments include a control system that is further operable to cause the router module to route the particular inventory item to a selected processing module that may perform packaging operations for the particular inventory item. The selected processing module may in some cases be selected based at least in part on the received customer order. For example, a certain processing module may be required if the particular inventory item was part of a multi-item customer order, as opposed to a single-item customer order. 
     Various embodiments may include a control system that is operable to determine one or more inventory storage zones for storing a replenishment supply of an inventory item. These inventory storage zones may be determined based at least in part on various optimization criteria (e.g., throughput, cost, storage density). In some cases, pick-to-ship time is minimized. In some cases, receive-to-stow time is minimized. 
     The various operations of a materials handling facility may be located in one building, or alternatively may be spread or subdivided across two or more buildings. In addition, a materials handling facility may include one or multiple levels or floors. For example, a materials handling facility that includes inventory  30  may include one, two, or more levels; in multi-level facilities, inventory  30  may be spread across two or more levels. The total floor space of a materials handling facility may be anywhere from tens of thousands of square feet to more than a million square feet, although embodiments may be implemented in smaller facilities. 
       FIG. 1  illustrates a logical representation or view of the operation of a materials handling facility in which embodiments of the modular material handling system may be implemented. For example, this figure may illustrate an order fulfillment center of a product distributor. Multiple customers  10  may submit orders  20  to the product distributor, where each order  20  specifies one or more items from inventory  30  to be shipped to the customer that submitted the order. To fulfill the customer orders  20 , the one or more items specified in each order may be retrieved, or picked, from inventory  30  (which may also be referred to as stock storage) in the materials handling facility, as indicated at  40 . Picked items may be delivered or conveyed, if necessary, to one or more stations in the materials handling facility for sorting  56  into their respective orders, packing  60 , and finally shipping  70  to the customers  10 . In some embodiments of the modular material handling system, picked items may be delivered to a singulation station, where individual units of items are associated with and placed into particular conveyance receptacles, which are then inducted into a conveyance mechanism. The conveyance receptacles may then be routed to particular destinations for the items contained within the receptacles in accordance with the requests (orders) currently being processed, e.g. to sorting stations, under direction of a control system. A picked, packed and shipped order does not necessarily include all of the items ordered by the customer; an outgoing shipment to a customer may include only a subset of the ordered items available to ship at one time from one inventory-storing location. In some other embodiments, picked items may be delivered to particular destinations via other means, such as automated guided vehicles, pallet jacks, etc. 
     The picking process  40  as illustrated in  FIG. 1  may be implemented in two or more different inventory areas, for example on different floors or in different areas of a materials handling facility. Two or more separate stock storage areas may be maintained and may be physically located on different floors of a materials handling facility. For each separate stock storage area, there may be one or more associated induction stations. Types of items may be, but are not necessarily, stored in different stock storage areas. For example, units of a given type of item may be stowed to locations in storage units in both inventory areas. 
     A materials handling facility may also include a receiving  80  operation for receiving shipments of stock from one or more sources (e.g., vendors) and for placing the received stock into stock storage. The receiving  80  operation may also receive and process returned purchased or rented items or orders from customers. At least some of these items are typically returned to inventory  30 . The various operations of a materials handling facility may be located in one building or facility, or alternatively may be spread or subdivided across two or more buildings or facilities. In various instances, it should be understood that references to elements, units, items, processes (or anything else) as being located within materials handling facility  100  may easily be extended to encompass elements, units, items, processes (or anything else) proximate to but not physically located within materials handling facility. For example, various elements, units, items, or processes (or anything else) may be implemented outside of the materials handling facility, according to some embodiments. 
       FIG. 2  illustrates an example of a physical layout of a materials handling facility, such as an order fulfillment facility or center, in which embodiments of the modular material handling system may be implemented. At any one time, one or more agents  42  of the distributor may each be picking items from inventory  30  to fulfill portions or all of one or more requests or orders. This may result in a stream and/or batches of picked items for multiple incomplete or complete orders, which may then be delivered to an induction station (e.g., at routing module  52  or elsewhere within processing area  50 ). For example, in some instances, picked items in conveyance receptacles (e.g., totes), each containing one or more units of items (each possibly containing items from two or more orders) may be conveyed to any of various inductions stations that may be present, via a conveyance device (e.g., a conveyor belt). In other embodiments, picked items may be conveyed via other means. For example, large items may require transport via pallet jacks or other larger form factors. 
     At an induction station, each item may be pulled individually from each conveyance receptacle. Alternatively, all items may be “dumped” into a common receptacle (a bin, basket, shelf, etc.), and individual units may then be pulled from the common receptacle. In various embodiments, each pulled unit is then placed into a conveyance receptacle (e.g., a tote or tray) by itself. This process may be referred to as singulating the item. Receptacles, as used herein, may include, but are not limited to, any tote, basket, box, tray, or similar mechanism configured to receive individual units of items or groups of units of items in a materials handling facility. A conveyance receptacle need not be fixed to any conveyance mechanism. 
     The pulled unit of an item may be associated with the particular conveyance receptacle that it is placed in. In one embodiment, the association of a unit of an item with a particular conveyance receptacle may be performed by reading, scanning or otherwise entering an item identifier associated with the item and a conveyance receptacle identifier associated with the particular conveyance receptacle into which the unit is placed. The item identifier and receptacle identifier may be communicated to a control system  190  of the materials handling facility via wired and/or wireless communications. Each conveyance receptacle may include a unique conveyance receptacle identifier that uniquely identifies the particular conveyance receptacle in the materials handling facility. The conveyance receptacle identifier may, for example, be indicated by a bar code, QR code, Radio Frequency Identifier (RFID) device, or some other scannable or readable mechanism, mark, or tag attached to or integrated with the conveyance receptacle. 
     Each unit of each item carried in inventory  30  may include an item identifier. A type of item held in inventory  30  may be referred to herein as simply an item. The term item identifier may refer to a unique identifier associated with each particular type of item carried in inventory  30  of a distribution system. The term unit may be used to refer to one (unit) of a type of item. Typically, but not necessarily, each unit is tagged or otherwise marked with the item identifier. For example, units or collections of items in inventory may be marked or tagged with a bar code, Universal Product Code (UPC), Stock-Keeping Unit (SKU) code, serial number, and/or other designation (including proprietary designations) that may be used as item identifiers to facilitate materials handling facility operations, including, but not limited to, stowing, rebinning, picking, sorting, packing and shipping. These designations, or codes, may identify items by type, and/or may identify individual units within a type of item. 
     Cases, boxes, bundles, or other collections of units of items may similarly be marked or tagged with item identifiers. The units of items in a collection may all be of the same type of item, for example a case of twelve units of a particular item, or may be a collection of one or more units of each of two or more heterogeneous items. A collection of units of item(s) (e.g., a case containing twelve units of an item, or a bundle containing one or more units of each of two or more heterogeneous items, such as a boxed or bundled set of three different books) may thus be considered or treated as a “unit” in the order fulfillment process. A designation, or code, may thus also identify a collection of units of item(s) as a “unit” in the order fulfillment process. Thus, various, in addition to sorting individual units of items, may also process collections of units of item(s) designated as units. Therefore, the conveyance receptacles described herein may receive collections of units of item(s) that are designated as units as well as individual units of items. 
     A materials handling facility may include a control system  190  which may include, but is not limited to, one or more computer systems, one or more data storage devices, one or more wired and/or wireless networks, control system software (programs, modules, drivers, user interfaces, etc.), and one or more hand-held, mobile and/or fixed readers, scanners or scanning devices that may be able to scan, receive, or otherwise detect the marks or tags (e.g., bar codes, radio frequency identification (RFID) tags, etc.) on individual items (units) or collections of items (e.g., cases) and communicate with a control station or stations of the control system to, for example, determine and record the item and/or item type of the items. The hand-held, mobile and/or fixed readers, scanners or scanning devices may also be able to scan, receive, or otherwise detect the marks or tags (e.g., bar codes, radio frequency identification (RFID) tags, etc.) attached to or integrated with the conveyance receptacles. An exemplary computer system that may be used in a control system  190  is illustrated in  FIG. 8 . An exemplary network topology that may be used in control system  190  is shown in  FIG. 3 . 
     At the induction station, a pulled unit of an item may be associated with a particular conveyance receptacle by reading, scanning, etc. the item identifier associated with the item and the conveyance receptacle identifier associated with the conveyance receptacle into the control system  190 . This may be performed manually (e.g., by an operator or agent using a hand-held scanner), via an automated scanning/reading process using fixed scanners/readers, or by a combination of manual and automatic scanning/reading. For example, an operator at an induction station may use a hand-held scanner to scan a code off the unit of the item before or during placement of the unit into a “staged” conveyance receptacle, while an automated reader may read (or may have already read) the conveyance receptacle identifier from the new conveyance receptacle that is “staged” for the operator to place the unit of the item into. 
     Once a pulled unit of an item is associated with and placed into a particular conveyance receptacle, that conveyance receptacle may be inducted into a conveyance mechanism (e.g., a conveyor belt, roller system, or other conveyance mechanism). In various embodiments, the conveyance mechanism may include a mechanism that includes some method of diverting a product off a conveyance path under control of the control system. Examples of such diversion mechanisms may include, but are not limited to, sliding shoe sorter mechanisms and pop up diversion mechanisms, such as pop up wheel sorter mechanisms. A pop up wheel sorter includes powered wheels that rise up out of the conveyor to divert product off the conveyor onto a different path or to a location. Other types of mechanisms may be used in various embodiments. 
     A conveyance receptacle may already be on the conveyance mechanism when the unit is associated with and placed into the receptacle. Alternatively, a conveyance receptacle may be retrieved from a conveyance receptacle storage, stack, or other supply, the unit may be associated with and placed into the receptacle, and the receptacle may then be inducted into or placed on the conveyance mechanism. The conveyance receptacles need not be fixed to the conveyance mechanism; instead, the receptacles may be removable bins, trays, totes, or similar devices. The conveyance mechanism may be coupled to and controlled by the materials handling facility control system  190  via wired and/or wireless communications. The control system  190  may receive input from and send commands to the conveyance mechanism to direct or control various operations of the conveyance mechanism. 
     The above describes aspects of an induction station  210  in which a human operator performs at least a portion of the pulling of units of items from groups of picked items, scanning/reading the items and receptacles to associate single units of items to particular conveyance receptacles, and placing the units into the conveyance receptacles. In alternative embodiments, some or all of the activities described as being performed by a human operator may be performed by automated mechanisms, which may be coupled to and under control of the materials handling facility control system  190 . 
     The conveyance mechanism, under direction of control system  190 , may deliver the conveyance receptacles, each including an individual unit of an item, to various order processing modules  55 . Various ones of the processing modules  55  (or elsewhere in processing area  50 ) may include one or more sorting stations. Portions of an order may be received from the agents  42 , or from other stations, at a processing area  50  at different times. Thus, processing at a station may have to wait for one or more items for some orders to be delivered to the station from picking and/or from another station before completion of processing of a multi-item order at the sorting station. 
     The picked units of items that in some cases are delivered to a processing area via the conveyance receptacles may be processed at routing module  52 . For example, routing module  52 , under the direction of control system  190 , may in some embodiments sort the individual picked units in accordance with their respective orders. In other embodiments, the picked units may be sorted into their respective orders at one or more of processing modules  55  under the direction of control system  190 . As discussed in greater detail below, various processing modules  55  may provide differing types of packaging operations that may be suitable for differing picked items (e.g., based on the size of the item), or differing order category (e.g., multi-item orders, single-item orders) 
     An order fulfillment center may also include one or more receiving  80  operations for receiving shipments  90  of stock from various vendors. The received stock may then be placed into stock storage. The receiving  80  operation may also receive and process returned, purchased, or rented items from customers. The various operations and stations of an order fulfillment center may be located in one building or facility, or alternatively may be spread or subdivided across two or more buildings or facilities. 
     Turning now to  FIG. 3 , one exemplary embodiment of control system  190  is depicted. Control system  190  may in some cases include a host warehouse management system (Host WMS) in coordination with various localized control system components, such as one or more warehouse control systems (WCS), sensors, conveyor-specific controllers (e.g., programmable logic controllers), and other motion-control components. For example, the Host WMS may in some embodiments provide high-level instruction as to routing and scheduling of items to particular modules of the system, whereas the WCS may execute lower-level tasks related to execution of the routing and scheduling the conveyance of the inventory items in accordance with the routing dictated by the Host WMS (e.g., messaging proper zones within the modular material handling system). Other embodiments may include a more centralized configuration in which a central host oversees most or all of the material handling functions, of alternately a more distributed configuration in which most or all of the material handling functions are handed off between area-specific controller components. 
     Physical Layout of Modular Material Handling System 
       FIG. 4  presents greater detail of the physical layout of one embodiment of the present disclosure. In the depicted embodiment, processing area  420  is located between inventory areas  410   a  and  410   b , with router module  422  of processing area  420  receiving/sending inventory items to/from each of inventory areas  410   a  and  410   b  via conveyor mechanisms. By virtue of this layout, which includes multiple smaller individual inventory areas distributed around the processing area, the maximum distances that picked inventory items must travel (e.g., from the farthest end of an inventory area to the router module of the processing area) are lower than distances that may be encountered in configurations having a single equivalent, larger inventory area (e.g., an inventory area having a volume equal to the combined volume of inventory areas  410   a  and  410   b ) located adjacent to the processing area. Accordingly, pick-to-ship times may be minimized by use of this physical layout. Other embodiments may provide similar benefits by use of more than two inventory areas disposed around a processing area. In some embodiments, multiple inventory areas may be located adjacent to various sides of processing area  420  in an asymmetric layout. 
     The physical layout of fulfillment center  400  depicted in  FIG. 4  may further improve inventory item throughput by virtue of the availability of additional conveyance paths between processing area  420  and the two inventory areas  410   a  and  410   b . For example, twice as many conveyor lines of a minimal length L between the two inventory areas and router module  422  may be possible in the embodiment of  FIG. 4 , as compared to an embodiment in which only a single inventory area is employed on one side of router module  422 . In some embodiments, control system  190  may maximize material throughput by exploiting the availability of additional conveyance paths. For example, a high demand item may be stored in both inventory area  410   a  and in the oppositely disposed inventory area  410   b  to take advantage of the availability of a maximum number of conveyance mechanisms. In such a way, it may be possible to double the throughput of extremely high demand items. 
     The factory layout may provide additional opportunities for efficiency improvement, based on a more centralized distribution of personnel that may be achieved by the central location of processing area  420 . For example, the greater concentration of operators due to centrally located processing area  420  may provide for more efficient management of those operators (e.g., via lower ratios manager to operator ratios). 
     Embodiments of fulfillment center  400  may include control system  190  that is configured to dynamically adjust inventory placement strategies as demands change. For example, it may initially be beneficial to store inventory of a particular low demand product at inventory area zones that are relatively distant from router module  422 . Such an arrangement may allow higher demand items to be stored at inventory locations that are nearer router module  422 . This may be desirable because an item at storage zone  412   a  will have a longer pick-to-ship time than an item picked at storage zone  412   e ). It may also be desirable for simplicity reasons to store the particular low demand product together at one particular storage zone  412  within inventory area  410 . 
     Now consider a scenario in which demand increases dramatically for the above-discussed item. It may be beneficial to relocate the suddenly high-demand product to a more desirable area of the inventory areas (e.g., storage zone  412   e ). If demand is exceptionally high, it may also be desirable to relocate the high demand product across multiple storage zones  412 , in order to avoid possible backlog at conveyance mechanisms (e.g., due to excessive conveyance receptacles/totes overwhelming a particular conveyor line) and/or at a picking module. In such a case, relocating the high demand product to multiple storage zones (e.g., storage zones  412   e  and  412   f  of inventory area  410   a , as well as additional zones in inventory area  410   b ) may eliminate the sources of backlog. Inventory items may be relocated within the inventory areas by use of, for example, bypass lines  414   a  and  414   b , which route materials through router module  422 . 
     Continuing with  FIG. 4 , router module  422  serves as the interface between inventory areas  410  and the various processing modules  426 . As discussed above, router module  422  receives conveyed inventory items from pick modules within inventory areas  410 . In some embodiments, the inventory items are received via conveyance receptacles (e.g., standardized totes) that are transported via conveyance mechanisms (e.g., conveyor lines). The conveyance receptacles may not be fixed to the conveyance mechanism in various embodiments. In some cases, other methods for conveying the inventory items are employed (e.g., various robotic form factors, automated guided vehicles). Control system  190  may govern the conveyance of the inventory items (e.g., via the a Host WMS and a supporting WCS) to router module  422 , and the subsequent routing of inventory items to processing modules  426 . Various identifying methods (e.g., RFID tags, barcode scanner, QR scanners located, for example, on the conveyance receptacles) may be employed to track the movement of the inventory items). 
     In some embodiments, router module  422  provides one or more standardized interfaces (e.g., physical conveyer interface, data interface, power interface) to various processing modules  426  that are coupled to router module  422  for receiving inventory items. These standardized interfaces may be expandable to accommodate varying numbers of processing modules  426 . In this way, router module  422  may support flexible configuration of the type and number of processing modules  426  employed in a fulfillment center. 
     Various embodiments of router module  422  pass along received conveyance receptacles. In other cases, router module  422  may perform some redistribution (e.g., re-toting) of inventory items prior to conveying materials to one or more processing modules  426 . 
     Processing Modules 
     Various processing modules  426  provide configurable functionality that may include processing and packaging inventory items and customer orders of various types. For example,  FIG. 4  depicts a configuration of processing area  420  that includes three multi-item material handling system modules  426   a , four flex-pack modules  426   b , three auto-box modules  426   c , and two gift-wrap modules  426   d . These modules are configured in a modular manner to interface with router module  422  and shipping module  424 . 
     Multi-item material handling system modules  426   a  may provide capabilities for handling inventory items that are received in conveyance receptacles containing, for example, multiple inventory items corresponding to multiple customer orders. These inventory items may also correspond to customers orders containing multiple inventory items.  FIG. 5  illustrates operation of an exemplary sorting station that may be used for assembling these multi-item orders in embodiments of multi-item material handling system modules  426   a , or in other processing modules  426  or router module  422  in some embodiments. Initially, conveyance receptacles containing multiple items are divided to single item conveyance receptacles  104 . Once the conveyance receptacles  104 , each containing an individual unit  108  of an item and each associated with the item it contains, are inducted into the conveyance mechanism  200 , at least some of the receptacles  104  may be conveyed to sorting station  152 . In one embodiment, the conveyance mechanism may be directed by the control system  190  as to the disposition of each particular conveyance receptacle  104 . Each conveyance receptacle  104  may be associated with the particular item it contains. Thus, the control system  190  may, by tracking a particular conveyance receptacle  104  via its unique conveyance receptacle identifier  106 , direct the conveyance mechanism to route the particular conveyance receptacle  104  and its associated unit  108  of the item to sorting station  152 . 
     There may be one or more order processing stations  155  associated with sorting station  152 . In this example, an order processing station  155  is located on the other side of order sorting bin  154 . Order processing station  155  may, for example, be a packing station at which one or more units  108  of items for an order are processed, packed, and labeled for shipping to the customer. The order slots  156  may be pass-through slots into one side of which units  108  of items may be placed, and out of which individual or collections of units  108  of items may be removed for processing. In one embodiment, units  108  of items may be removed from conveyance receptacles  104  and placed into a particular slot (e.g., item  108  is illustrated as being placed into slot ( 3 ,  2 )) as indicated by the control system  190 , for example by the control system  190  activating an indicator  158  associated with the slot  156  into which the unit  108  is to be placed to indicate to the operator that the unit  108  from the current receptacle  104  is to be placed into that slot  156 . Sorting bin  154  may also include indicators associated with the slots  156  on the order processing station  155  side which control system  190  may activate to indicate to operators at the order processing station  155  that a particular slot  156  is ready to be processed (e.g., that all units  108  of all items for an order have been placed into that slot). In this example, control system has indicated to operator(s) at order processing station  155  that an order  160  in slot ( 2 ,  1 ) has been completed. An operator may then pull the order  160  from the slot  156  for further processing (e.g., shipping). 
     Continuing with  FIG. 4 , flex-pack modules  426   b  may provide functionality for processing items that are inappropriate for other processing modules  426  due to, for example, size and/or weight of the items. In some embodiments, an operator may remove a tote from the conveyor and places it on a work shelf to perform manual operations. Carts may be utilized to assist in processing large items. 
     Auto-box modules  426   c  may provide for automated packaging of items conforming to certain particular dimensional constraints. In some cases, applicability of auto-box modules  426  may be limited to packaging of single-item orders. Other embodiment include auto-box modules  426  that may provide automated packaging of multi-item orders. 
     Gift-wrap modules  426   d  may facilitate gift wrap of packages corresponding to customer orders requesting gift wrapping. In some embodiments, personnel may perform the required packaging as directed by the control system  190 . However, in some embodiments automated wrapping of packaging conforming to particular dimensional constraints, similar to the auto-box modules  426   c , may be performed. 
     Continuing with  FIG. 4 , receiving modules  430  may be arranged in some embodiments to minimize receive-to-stow time. For example, multiple receiving modules  430  may be implemented to optimally correspond to the various inventory areas  410 . These receiving modules may convey replenishment supply to replenishment sorter  440 , that may serve to optimize storage of items (e.g., under control of control system  190 ) based on various criteria, such as minimization of pick and/or stow times. 
     In various embodiments, shipping module  424  may provide for sorting and/or routing of processed inventory items (e.g., packaged items) based on factors such as, for example, package type (e.g., flat packages, large crates, standard boxes, expedited delivery, cross-shipment of items to other fulfillment centers), and, in some cases, for further processing that may be required prior to shipment (e.g., verification of labeling). Some embodiments may include shipping modules  424  having various discrete modules that respectively correspond to one or more particular package types. As one example configuration, shipping modules  424  depicted in  FIG. 4  may include flat package module  424   a  for sortation of flat packages, carton module  424   b  for sortation of standard cartons, and special handling module  424   c  for sortation of items that may require custom handling (e.g., large items, items corresponding to expedited orders). In some other embodiments, a single shipping module  424  may be used for shipments of all package types processed by processing modules  426 . 
     Shipping module  424  may include one or more standardized interfaces (e.g., physical conveyer interface, data interface, power interface) to various processing modules  426  that deliver processed inventory items to shipping module  424 . These standardized interfaces may be expandable to accommodate configurations having varying numbers of processing modules  426 . In this way, shipping module  424  may support flexible configuration of the type and number of processing modules  426  employed in a fulfillment center. 
     Various embodiment of the present disclosure may be configured to receive and process items from other fulfillment centers. As one example, a particular fulfillment center may receive cross-shipped items from one or more other fulfillment center to replenish stock of the particular fulfillment center. As another example, cross-shipped items may be received by the particular fulfillment center in order to complete an order that is processed at the particular fulfillment center (e.g., packaged as part of a multi-item order, packaged as a single-item order). In such cases, a cross-shipped item may be received and appropriately routed via, for example, one or more of a storage area, a routing module, a processing module, a shipping module, etc. 
     In some embodiments, the conveyance mechanisms may be configured to convey received items to a storage area for inventory replenishment purposes, deliver picked items from a storage area to the processing area for order processing, and for transporting empty conveyance receptacles to areas of need. For example, a particular conveyance mechanism, such as a conveyor, may be employed to perform each of the above-mentioned tasks of transporting items for storage and for processing, as well as transporting empty receptacles for from, for example, the packaging or shipping modules to the receiving module or inventory areas for further use. 
       FIG. 6  is a flowchart illustrating a method of operation in a modular material handling system for use in a fulfillment center, according to one embodiment. This flowchart illustrates how the various components described herein, such as a controller system, routing module, processing module, shipping module, inventory area, processing area, and processing modules, for example, may be integrated to form a modular material handling system for use a fulfillment center. The method as illustrated in  FIG. 6  may be performed as a continuous or near-continuous process by modular material handling system to process incoming items for replenishment, or to process items picked from storage to fulfill customer orders. 
     At  602 , an inventory item (e.g., inventory replenishment) may be transported from an inventory receiving area to a storage area of the fulfillment center. Transportation may be by way of a non-linear conveyor system (e.g., conveyance totes are not fixed to a conveyor, and therefore items need not be linearly delivered). In other embodiments, transportation may involve automated guided vehicles, robotics, manual transfer, etc. At  604 , the item may be stored at the storage area (e.g., placed in inventory). 
     At  606 , the inventory item may be picked from the storage area in response to a received order. For example, based on a customer&#39;s order for a particular item, that item may be picked from inventory. The picking may be performed using a computer system, and may also in some cases involve various automated picking systems. The picking process may be performed using a computer system that may, in some embodiments, optimize material throughput through methods that result in mixed groupings of items (e.g., items corresponding to different orders being grouped together). 
     At  608 , the picked inventory item may be routed to one or more processing modules with the fulfillment center. The routing may be accomplished by way of the controller system and a routing module that may provide a standard interface to various processing modules. At  610 , the picked inventory item may be processed using, for example, one or more modular processing modules that interface to the routing module and a shipping module. In some embodiments, the processing may be in accordance with various information corresponding to a customer order. For example, customer selection of gift wrapping with an order may result in processing of items in that order via a gift-wrapping module. As another example, customer selection of a group of various items within a single customer order may in some cases result in processing via one or more modules that facilitate combining multiple parts into a single shipment. 
       FIG. 7  presents a flowchart illustrating a method of operation in a modular material handling system that may be used to optimize inventory storage strategies. Such strategies may provide, for example, reduced receive-to-stow time and/or reduced pick-to-ship time. At  702 , inventory storage locations (zones) within one or more inventory storage areas of a fulfillment center are determined. In some embodiments, this determination is based on minimizing distances that the item must be conveyed in order to stow or to subsequently pick and process the item. In some cases, the determination may estimate effects of the storage density of the particular item, or the storage density as to all items in the vicinity of the various storage zones. Storage densities may be meaningful because high storage density of high-demand items may increase probabilities that heavy pick activity or heavy stow activity within a localized area (e.g., the storage zone) may create bottlenecks. 
     Illustrative System 
     In at least some embodiments, a system that implements one or more components of modular materials handling system that implements the techniques described herein may include a general-purpose computer system that includes or is configured to access one or more computer-accessible media, such as computer system  800  illustrated in  FIG. 8 . In the illustrated embodiment, computer system  800  includes one or more processors  810  coupled to a system memory  820  via an input/output (I/O) interface  830 . Computer system  800  further includes a network interface  840  coupled to I/O interface  830 . 
     In various embodiments, computer system  800  may be a uniprocessor system including one processor  810 , or a multiprocessor system including several processors  810  (e.g., two, four, eight, or another suitable number). Processors  810  may be any suitable processors capable of executing instructions. For example, in various embodiments, processors  810  may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors  810  may commonly, but not necessarily, implement the same ISA. 
     System memory  820  may be configured to store instructions and data accessible by processor(s)  810 . In various embodiments, system memory  820  may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated embodiment, program instructions and data implementing desired functions, such as those methods and techniques described above for a control system in a robotic induction technique and/or in a non-linear, unit-level materials handling system that implements the robotic induction technique, are shown stored within system memory  820  as code  825  and data  826 . 
     In at least some embodiments, I/O interface  830  may be configured to coordinate I/O traffic between processor  810 , system memory  820 , and any peripheral devices in the device, including network interface  840  or other peripheral interfaces. In some embodiments, I/O interface  830  may perform any necessary protocol, timing or other data transformations to convert data signals from one component (e.g., system memory  820 ) into a format suitable for use by another component (e.g., processor  810 ). In some embodiments, I/O interface  830  may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface  830  may be split into two or more separate components, such as a north bridge and a south bridge, for example. Also, in some embodiments some or all of the functionality of I/O interface  830 , such as an interface to system memory  820 , may be incorporated directly into processor  810 . 
     Network interface  840  may be configured to allow data to be exchanged between computer system  800  and other devices attached to a network  800 , such as other computer systems, communications devices, control mechanisms, readers, scanners and so on that are components of a robotic induction technique and/or of a non-linear, unit-level materials handling system that implements the robotic induction technique. The communications channels may include, but are not limited to conventional and mobile telephone and text messaging communications channels. Network interface  840  may commonly support one or more wireless networking protocols (e.g., Wi-Fi/IEEE 802.11, or another wireless networking standard). However, in various embodiments, network interface  840  may support communication via any suitable wired or wireless general data networks, such as other types of Ethernet network, for example. Additionally, network interface  840  may support communication via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks, via storage area networks such as Fibre Channel SANs, or via any other suitable type of network and/or protocol. 
     In some embodiments, system memory  820  may be one embodiment of a computer-accessible medium configured to store program instructions and data as described above for  FIGS. 1 through 7  for implementing a control system for, or possibly other components of, modular material handling in a fulfillment center. However, in other embodiments, program instructions and/or data may be received, sent or stored upon different types of computer-accessible media. Generally speaking, a computer-accessible medium may include storage media or memory media such as magnetic or optical media, e.g., disk or DVD/CD coupled to computer system  800  via I/O interface  830 . A computer-accessible medium may also include any volatile or non-volatile media such as RAM (e.g. SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc, that may be included in some embodiments of computer system  800  as system memory  820  or another type of memory. Further, a computer-accessible medium may include transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link, such as may be implemented via network interface  840 . 
     Various embodiments may further include receiving, sending or storing instructions and/or data implemented in accordance with the foregoing description upon a computer-accessible medium. Generally speaking, a computer-accessible medium may include storage media or memory media such as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.), ROM, etc., as well as transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as network and/or a wireless link. 
     The various methods as illustrated in the Figures and described herein represent exemplary embodiments of methods. The methods may be implemented in software, hardware, or a combination thereof. The order of method may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. 
     Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. It is intended that the invention embrace all such modifications and changes and, accordingly, the above description to be regarded in an illustrative rather than a restrictive sense.