Patent Publication Number: US-10759599-B2

Title: Inventory management

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 16/056,919 filed on Aug. 7, 2018, which is a continuation of U.S. patent application Ser. No. 15/222,606 filed on Jul. 28, 2016, the entire contents of each of which are incorporated herein by reference, as if fully set forth in this description. 
    
    
     BACKGROUND 
     One or more robotic devices and/or other actors can move throughout a storage environment to perform actions related to the storage and shipment of items. One example storage environment is a warehouse, which may be an enclosed building having rows of storage racks on which items may be stored. In some cases, the items may be stored on pallets, and the pallets may be stacked vertically. The warehouse may also include a loading dock used for loading and/or unloading items and pallets from delivery trucks or other types of vehicles. 
     The pallet may include a barcode that identifies the pallet. A centralized system may store information corresponding to the barcode, such as the number of items on the pallet, type of item, and location of the pallet within the warehouse. The centralized system may include similar information for all pallets included in the warehouse, such that the centralized system contains an inventory of the warehouse. 
     SUMMARY 
     Example systems, methods, and devices may help build and maintain an accurate inventory of pallets, boxes, shelves, robotic devices, and other items located in a warehouse environment. The systems, methods, and devices may include a robotic device that can navigate through the warehouse by using a camera. The camera may capture image data that can be used to determine whether one or more objects may obstruct movement of the robotic device. This image data can then be used to generate navigation instructions for the robotic device. Using the same image data used to generate navigation instructions, the systems, methods, and devices described herein may detect one or more on-item visual identifiers, such as barcodes or the like that are located on one or more items within the warehouse environment. These detected visual identifiers may then be used to build and/or maintain an accurate inventory. The camera thus can perform a dual purpose, by enabling both navigation and the capture of information related to items within the warehouse, possibly simultaneously or at nearly the same time. As the robotic device navigates throughout the warehouse environment, more and more on-item visual identifiers may be detected, allowing for more comprehensive inventory to be built and/or maintained. 
     In one example, a method is disclosed. The method involves receiving image data captured by a camera mounted on a robotic device, during navigation of the robotic device through a warehouse environment, wherein a plurality of inventory items are located within the warehouse environment. The method also involves, based on the received image data, generating navigation instructions for navigation of the robotic device within the warehouse environment. The method further involves analyzing the received image data to detect one or more on-item visual identifiers corresponding to one or more of the inventory items. The method still further involves, for each detected visual identifier, (i) using the image data as a basis for determining a warehouse location of the inventory item corresponding to the detected visual identifier, (ii) comparing the determined warehouse location of the corresponding inventory item to an expected location of the corresponding inventory item, and (iii) initiating an action based on the comparison between the determined warehouse location and the expected location. 
     In another example, a system is disclosed. The system includes a robotic device deployed in a warehouse environment, wherein a plurality of inventory items are located within the warehouse environment. The system also includes a camera mounted on the robotic device, wherein the camera is configured to capture image data. The system also includes a computing system configured to receive the captured image data. The computing system is further configured to, based on the received image data, generate navigation instructions for navigation of the robotic device within the warehouse environment. The computing system is yet further configured to analyze the received image data to detect one or more on-item visual identifiers corresponding to one or more of the inventory items. The computing system is still further configured to, for each detected visual identifier, (i) use the image data as a basis for determining a warehouse location of the inventory item corresponding to the detected visual identifier, (ii) compare the determined warehouse location of the corresponding inventory item to an expected location of the corresponding inventory item, and (iii) initiate an action based on the comparison between the determined warehouse location and the expected location. 
     In a third example, a robotic device is disclosed. The robotic device is deployed in a warehouse environment, wherein a plurality of inventory items are located within the warehouse environment. The robotic device includes a camera configured to capture image data. The robotic device also includes a computing system configured to receive the captured image data. The computing system is also configured to, based on the received image data, generate navigation instructions for navigation of the robotic device within the warehouse environment. The computing system is also configured to analyze the received image data to detect one or more on-item visual identifiers corresponding to one or more of the inventory items. The computing system is further configured to, for each detected visual identifier, (i) use the image data as a basis for determining a warehouse location of the inventory item corresponding to the detected visual identifier, (ii) compare the determined warehouse location of the corresponding inventory item to an expected location of the corresponding inventory item, and (iii) initiate an action based on the comparison between the determined warehouse location and the expected location. 
     In another example, a control system is described. The control system includes means for receiving image data captured by a camera mounted on a robotic device, wherein the robotic device is deployed in a warehouse environment, wherein a plurality of inventory items are located within the warehouse environment. The control system also includes means for, based on the received image data, generating navigation instructions for navigation of the robotic device within the warehouse environment. The control system further includes means for analyzing the received image data to detect one or more on-item visual identifiers corresponding to one or more of the inventory items. The control system still further includes, for each detected visual identifier, means for (i) using the image data as a basis for determining a warehouse location of the inventory item corresponding to the detected visual identifier, (ii) comparing the determined warehouse location of the corresponding inventory item to an expected location of the corresponding inventory item, and (iii) initiating an action based on the comparison between the determined warehouse location and the expected location. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the figures and the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  illustrates a robotic fleet, according to an example implementation. 
         FIG. 1B  illustrates a functional block diagram showing components of a robotic fleet, according to an example implementation. 
         FIG. 2A  illustrates a robotic truck unloader, according to an example embodiment. 
         FIG. 2B  illustrates a robotic arm on a pedestal, according to an example embodiment. 
         FIG. 2C  illustrates an autonomous guided vehicle, according to an example embodiment. 
         FIG. 2D  illustrates an autonomous fork truck, according to an example embodiment. 
         FIG. 3  illustrates a system, according to an example implementation. 
         FIG. 4  illustrates a warehouse aisle according to an example implementation. 
         FIG. 5  illustrates the warehouse aisle of  FIG. 4  according to another example implementation. 
         FIG. 6  illustrates a flowchart of an example method, according to an example implementation. 
     
    
    
     DETAILED DESCRIPTION 
     Example methods, systems, and devices are described herein. Any example embodiment or feature described herein is not to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. 
     Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments might include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example embodiment may include elements that are not illustrated in the Figures. 
     I. Overview 
     During normal or typical operation of a warehouse, pallets and items are routinely moved from one location to another by robotic devices, such as pallet jacks. Within this specification, the term “pallet jack” may be used as a stand in for any applicable robotic device, and any description of a pallet jack may apply to one or more other types of robotic devices operating within the warehouse environment. As such, acts, functions, and operations of the pallet jack may include interactions with both palletized and non-palletized objects. 
     In some warehousing systems, a pallet jack may include a camera or sensor that can read a barcode or other identifier, as described herein, identifying an item or pallet. However, in some cases, an identifier may be obscured, misplaced, or otherwise difficult for the pallet jack to read. This is especially so in the case of an item that a pallet jack is itself transporting, since its cameras or other sensors, as described herein, may be oriented outward to capture the pallet jack&#39;s environment. As such, the items a pallet jack is carrying may be outside of the pallet jack sensor&#39;s field of view. In addition, during transit from one location to the other, one or more items may fall off the pallet. As a result, it may be difficult for a given pallet jack to determine the correct pallet to transport from one location to another, or to determine if the pallet contains the correct number of items. In an environment where a pallet jack is an autonomous or semi-autonomous vehicle, and a human is not able to observe every item and action carried out by a pallet jack, the above problems may be significant. Further, in some cases the location of a given pallet in the warehouse may differ from the location of the pallet stored by a robotic device and/or centralized system. This may be due to an unintentional movement of the pallet, a mistake in updating information, mislabeling a pallet or location of a pallet, or other error. As a result, a percentage of the inventory of the warehouse may be lost or misplaced, which can cause delays in shipping items to customers and can require resources to find the lost or misplaced items. Example embodiments described herein may help to address such issues. 
     An example warehouse may be a fulfillment warehouse in which items are selected, sorted, and packaged for shipment to customers. Items may be arranged or organized within the warehouse to improve efficiency of this process based on customer demand, product size, weight, shape, or other characteristic. Items may be stored on pallets, which may be stacked on top of each other and/or on shelves that extend upwards (e.g., multi-level shelving). Further, each item, pallet, and/or shelf may include a visual identifier such as a barcode or Quick Response (QR) code that identifies the item, pallet, and/or shelf. 
     A computer-based warehouse management system (WMS) may be implemented for the warehouse. The WMS may include a database for storing information related to the items, pallets, and shelves, as well as one or more actors operating in the warehouse. For instance, the WMS may include information about the location of each item, pallet, shelf, and/or actor. This information may be used to coordinate the actors to allow them to carry out one or more functions, such as fulfilling an order for a customer. It may also be used to build and/or maintain an inventory of the warehouse. 
     The actors operating in the warehouse may include robotic devices such as autonomous guided vehicles (AGVs). Example AGVs may include pallet jacks, fork trucks, truck loaders/unloaders, and other devices. Each device may be autonomous or partially autonomous. Human-operated devices are also possible. Further, each device may include a vision system having a camera, such that the device can navigate through the warehouse. 
     A. Multipurpose Camera 
     Advantageously, an example robotic device may be deployed in a warehouse environment, and may use its pre-existing camera system for both navigation and inventory management. Specifically, a pallet jack may already be equipped with a stereo vision camera system (e.g., a stereo camera pair), which the pallet jack may use to sense its environment and navigate through the warehouse. The image data captured for navigation purposes may include images of pallets, other pallet jacks or devices, and other objects in the environment. As such, barcodes on the pallets may be detected in the image data, and combined with location information to determine the locations of the pallets in the warehouse. When numerous pallet jacks are moving about in a warehouse, the WMS may combine such information from the pallet jacks to improve inventory management of pallets in the warehouse. 
     In one example, a robotic device operating in the warehouse may be an autonomous pallet jack. The autonomous pallet jack may include a guidance system used to guide the autonomous pallet jack through the warehouse. The guidance system may include a camera, a GPS receiver, and/or other devices or systems. The camera may be mounted in a fixed position on the pallet jack, or may be mounted such that it can be turned or aimed in two or three dimensions, such as on a gimbal or swiveling mechanism. The camera may be configured to receive visual data about the surroundings of the autonomous forklift. Based on the received visual data, the autonomous pallet jack may be able to determine its position and orientation within the warehouse, and may be able to move from one location to another location while avoiding obstacles along the way. 
     The guidance system camera may be specially configured for the task of guidance. For example, the camera may include two optical receivers (i.e., a stereo camera), which may allow for more accurate depth perception and better position and orientation measurement, as well as better object avoidance. The guidance system camera may also be angled downward toward the ground, where objects are more likely to obstruct the autonomous forklift. 
     In some examples, the autonomous forklift may use the guidance system camera for other purposes in addition to guidance. For instance, when the autonomous forklift is near an item, pallet, or shelf the guidance system camera may capture an image of a barcode corresponding to the item, pallet, or shelf. When a barcode associated with a pallet is captured, the location of the pallet within the warehouse may be determined based on the location of the guidance system camera that captured the barcode. The barcode, location of the pallet, location of the autonomous forklift, and/or other information may be transmitted to the WMS, which may then compare with an expected location of the pallet. Where there is a discrepancy, the WMS may take action to fix the issue by dispatching an agent, generating and/or sending an alert, adding the pallet to a list of misplaced pallets, or taking another action. 
     In some examples, a guidance system camera may capture the barcode of each item, pallet, and/or shelf that it can see. Data may be transmitted to the WMS constantly or at regular intervals to provide a continuous check on the location of items, pallets, and shelves within the warehouse. Further, some examples may include the guidance system camera of multiple robotic devices operating within the warehouse environment, such that each robotic device transmits data to the WMS, and a constant or regular inventory location check is being performed. 
     In further examples, the movement of an AGV and/or the orientation of a guidance system camera on an AGV may be actively steered in order to obtain more item inventory data. For instance, the guidance system camera may be angled upwards and/or to the side of the AGV while it moves through the warehouse in order to attempt to capture barcodes of items that are placed above and to the side of the AGV (such as on shelves placed along an aisle). Further, the AGV and/or camera may be steered toward items that have not been updated recently, to provide the WMS with more up-to-date information on those items. For example, the north side of shelves in an aisle may include items that have not been scanned or checked recently. When an AGV travels down this aisle, the guidance camera may be angled toward the north side of shelves to capture barcodes of the items stored thereon, in order to update the information in the WMS. 
     Still further examples may include balancing the need for an inventory update with the need for safe and accurate navigation of a robotic device. This may involve weighing the value or importance of information that could be gained by using the guidance camera to scan items against the expected decrease in accuracy of navigation of the robotic device. A guidance camera on an AGV may be angled upwards in order to capture information about items stored on higher shelves. But this information may come at a cost, because the camera may no longer be able to see obstacles on the ground as easily. This trade-off may be beneficial, especially where the item information gained by angling the camera upward is valuable and the likelihood of running into an obstacle is small. 
     In some embodiments a specially tailored robotic device may be used to gather data about the location of items, pallets, shelves, and robotic devices within the warehouse. The specially tailored robotic device may include a standalone camera that can be used to capture the barcodes of items, pallets, shelves, and/or robotic devices that it views. The standalone camera may have a wide angle lens and/or may include the ability to rasterize such that barcodes may be captured more accurately and easily. 
     B. Using Multiple Sensors 
     Items and pallets may be transported from location to location within the warehouse. In one example, an autonomous pallet jack may be tasked with moving a pallet of items from a first location to a second location. To carry out this task, several steps may be performed. First, the pallet jack may determine the location of the pallet it seeks to move. Next, it may travel to that location and find the pallet, such as by reading nearby barcodes and identifying the sought after pallet. Then, the pallet jack may transport the pallet from the first location to the second location. 
     Several issues may arise when the pallet jack attempts to carry out this task. First, the location of the pallet may be incorrect. This may be due to incorrect information or a misplaced pallet, among other reasons. Second, the barcode identifying the pallet may be obscured, misplaced on the pallet, or otherwise difficult or impossible for the pallet jack to read. For instance, the pallet may be located on a shelf with the barcode placed on the side of the pallet opposite an aisle in which the pallet jack is located. Third, during transit from the first location to the second location, one or more items may fall off the pallet. 
     In order to fix these problems, as well as others, an example system may utilize multiple pallet jacks collecting and sharing information with a warehouse management system (WMS) and/or amongst one another. In some cases the pallet jacks may be connected to a WMS storing inventory information related to the items, pallets, and shelves, as well as the pallet jacks and other robotic devices operating in the warehouse. The WMS may also coordinate between the pallet jacks to keep an updated list of the locations and other characteristics of the items, pallets, shelves, and robotic devices. In other cases, pallet jacks may form a peer-to-peer network communicating with each other to store and update information related to items, pallets, shelves, and each other. 
     In one example, a first pallet jack may be carrying a pallet from one location to another in a warehouse. The warehouse may also include a second pallet jack and a WMS to manage the warehouse. While the first pallet jack is carrying the pallet, it may be unable to verify which pallet it is carrying and/or the contents of the pallet. This may be due to the positioning and view of the first pallet jack&#39;s camera. Although the first pallet jack could set the pallet down to get a different view, it may be advantageous to verify the identity and/or contents of the pallet via another means. The first pallet jack and/or WMS may transmit a message to the second pallet jack requesting verification of the identity and/or contents of the pallet. The second pallet jack may have a camera with a better view of the pallet, and may be able to scan a barcode or identify the contents of the pallet. This information may then be shared with the WMS and/or first pallet jack. In this manner the second pallet jack may act as a “mirror” for the first pallet jack, allowing the first pallet jack to gather information about the pallet it is carrying that it would otherwise not be able. The first pallet jack may thus be able to “see” itself by utilizing the resources of the second pallet jack. 
     In some examples, this “mirroring” may be performed without an explicit request from a first pallet jack. In a warehouse that includes multiple pallet jacks, each pallet jack may verify the contents of one or more other pallet jacks as they pass each other or otherwise travel near each other during ordinary operation or performance of tasks. Still further, the WMS may coordinate the routes or positions of one or more pallet jacks such that they pass each other and perform a verification on each other. 
     Some examples may include pallet jacks that can measure the weight of pallets they are carrying. The measured weight may be used as an indicator that a first pallet jack should request that a second pallet jack verify the contents of the first pallet jack. An expected weight of the pallet may be stored by the WMS. The pallet jack may weigh a pallet to determine an actual weight. When a discrepancy between the expected weight and actual weight is detected, the pallet jack and/or WMS may take action. This action may include dispatching a second pallet jack to verify the pallet and/or contents of the pallet. It may also include causing the pallet jack to bring the pallet to predetermined location or along a predetermined route, such that one or more cameras or other devices can verify the pallet and/or contents of the pallet. 
     During typical warehouse operations, pallets and items are routinely moved from one location to another by robotic devices, such as pallet jacks. Within this specification, the term “pallet jack” may be used as a stand in for any applicable robotic device, and any description of a pallet jack may apply to one or more other types of robotic devices operating within the warehouse environment. As such, acts, functions, and operations of the pallet jack may include interactions with both palletized and non-palletized objects. 
     II. Example Environment 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure and the described embodiments. However, the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
     Example embodiments may involve a robotic fleet deployed within a warehouse environment. More specifically, a combination of fixed and mobile components may be deployed within the environment to facilitate automated processing of boxes, packages, or other types of objects. Example systems may involve automated loading and/or unloading of boxes and/or other objects, such as into storage containers or to and from delivery vehicles. In some example embodiments, boxes or objects may be automatically organized and placed onto pallets. Within examples, automating the process of loading/unloading trucks and/or the process of creating pallets from objects for easier storage within a warehouse and/or for transport to and from the warehouse may provide a number of industrial and business advantages. 
     According to various embodiments, automating the process of loading and/or unloading delivery trucks at the warehouse and/or the process of creating pallets may include the deployment of one or more different types of robotic devices to move objects or perform other functions. In some embodiments, some of the robotic devices can be made mobile by coupling with a wheeled base, a holonomic base (e.g., a base that can move in any direction), or rails on the ceiling, walls, or floors. In additional embodiments, some of the robotic devices may be made fixed within the environment as well. For instance, robotic manipulators can be positioned on elevated bases at different chosen locations within a warehouse. 
     As used herein, the term “warehouse” may refer to any physical environment in which boxes or objects may be manipulated, processed, and/or stored by robotic devices. In some examples, a warehouse may be a single physical building or structure, which may additionally contain certain fixed components, such as pallet racks or shelving for storing pallets of objects. In other examples, some fixed components may be installed or otherwise positioned within the environment before or during object processing. In additional examples, a warehouse may include multiple separate physical structures, and/or may also include physical spaces that are not covered by a physical structure as well. 
     Further, the term “boxes” may refer to any object or item that can be placed onto a pallet or loaded onto or unloaded from a truck or container. For example, in addition to rectangular solids, “boxes” can refer to cans, drums, tires or any other “simple” shaped geometric items. Additionally, “boxes” may refer to totes, bins, or other types of containers which may contain one or more items for transport or storage. For instance, plastic storage totes, fiberglass trays, or steel bins may be moved or otherwise manipulated by robots within a warehouse. Examples herein may also be applied toward objects other than boxes as well, and toward objects of various sizes and shapes. Additionally, “loading” and “unloading” can each be used to imply the other. For instance, if an example describes a method for loading a truck, it is to be understood that substantially the same method can also be used for unloading the truck as well. As used herein, “palletizing” refers to loading boxes onto a pallet and stacking or arranging the boxes in a way such that the boxes on the pallet can be stored or transported on the pallet. In addition, the terms “palletizing” and “depalletizing” can each be used to imply the other. 
     Within examples, a heterogeneous warehouse robot fleet may be used for a number of different applications. One possible application includes order fulfillment (e.g., for individual customers), in which cases may be opened and individual items from the cases may be put into packaging within boxes to fulfill individual orders. Another possible application includes distribution (e.g., to stores or other warehouses), in which mixed pallets may be constructed containing groups of different types of products to ship to stores. A further possible application includes cross-docking, which may involve transporting between shipping containers without storing anything (e.g., items may be moved from four 40-foot trailers and loaded into three lighter tractor trailers, and could also be palletized). Numerous other applications are also possible. 
     Referring now to the figures,  FIG. 1A  depicts a robotic fleet within a warehouse setting, according to an example embodiment. More specifically, different types of robotic devices may form a heterogeneous robotic fleet  100  that may be controlled to collaborate to perform tasks related to the processing of items, objects, or boxes within a warehouse environment. Certain example types and numbers of different robotic devices are shown here for illustration purposes, but robotic fleet  100  may employ more or fewer robotic devices, may omit certain types shown here, and may also include other types of robotic devices not explicitly shown. Additionally, a warehouse environment is shown here with certain types of fixed components and structures, but other types, numbers, and placements of fixed components and structures may be used in other examples as well. 
     One example type of robotic device shown within robotic fleet  100  is an autonomous guided vehicle (AGV)  112 , which may be a relatively small, mobile device with wheels that may function to transport individual packages, cases, or totes from one location to another within the warehouse. Another example type of robotic device is an autonomous fork truck  114 , a mobile device with a forklift that may be used to transport pallets of boxes and/or to lift pallets of boxes (e.g., to place the pallets onto a rack for storage). An additional example type of robotic device is a robotic truck loader/unloader  116 , a mobile device with a robotic manipulator as well as other components such as optical sensors to facilitate loading and/or unloading boxes onto and/or off of trucks or other vehicles. For instance, robotic truck unloader  116  may be used to load boxes onto delivery truck  118 , which may be parked adjacent to the warehouse. In some examples, movements of delivery truck  118  (e.g., to deliver packages to another warehouse) may also be coordinated with robotic devices within the fleet. 
     Other types of mobile devices than those illustrated here may also be included as well or instead. In some examples, one or more robotic devices may use different modes of transportation besides wheels on the ground. For instance, one or more robotic devices may be airborne (e.g., quadcopters), and may be used for tasks such as moving objects or collecting sensor data of the environment. 
     In further examples, the robotic fleet  100  may also include various fixed components that may be positioned within the warehouse. In some examples, one or more fixed robotic devices may be used to move or otherwise process boxes. For instance, a pedestal robot  122  may include a robotic arm elevated on a pedestal that is fixed to the ground floor within the warehouse. The pedestal robot  122  may be controlled to distribute boxes between other robots and/or to stack and unstack pallets of boxes. For example, the pedestal robot  122  may pick up and move boxes from nearby pallets  140  and distribute the boxes to individual AGV&#39;s  112  for transportation to other locations within the warehouse. 
     In additional examples, robotic fleet  100  may employ additional fixed components positioned within a warehouse space. For instance, high density storage racks  124  may be used to store pallets and/or objects within the warehouse. The storage racks  124  may be designed and positioned to facilitate interaction with one or more robotic devices within the fleet, such as autonomous fork truck  114 . In further examples, certain ground space may be selected and used for storage of pallets or boxes as well or instead. For instance, pallets  130  may be positioned within the warehouse environment at chosen locations for certain periods of time to allow the pallets to be picked up, distributed, or otherwise processed by one or more of the robotic devices. 
       FIG. 1B  is a functional block diagram illustrating components of a robotic warehouse fleet  100 , according to an example embodiment. The robotic fleet  100  could include one or more of various mobile components, such as AGV&#39;s  112 , autonomous fork trucks  114 , robotic truck loaders/unloaders  116 , and delivery trucks  118 . The robotic fleet  100  may additionally include one or more fixed components positioned within a warehouse or other environment, such as pedestal robots  122 , density storage containers  124 , and battery exchange/charging stations  126 . In further examples, different numbers and types of the components illustrated within  FIG. 1B  may be included within a fleet, certain types may be omitted, and additional functional and/or physical components may be added to the examples illustrated by  FIGS. 1A and 1B  as well. To coordinate actions of separate components, a warehouse management system  150 , such as a remote, cloud-based server system, may communicate (e.g., through wireless communication) with some or all of the system components and/or with separate local control systems of individual components. 
     Within examples, certain of the fixed components  120  may be installed before deployment of the rest of the robotic fleet  100 . In some examples, one or more mobile robots may be brought in to map a space before determining placement of certain fixed components  120 , such as the pedestal robots  122  or battery exchange stations  126 . Once map information is available, the system may determine (e.g., by running simulations) how to layout the fixed components within the space available. In certain cases, a layout may be chosen to minimize the number of fixed components needed and/or the amount of space used by those components. The fixed components  120  and mobile components  110  may be deployed in separate stages or all at once. In additional examples, certain of the mobile components  110  may only be brought in during particular time periods or to complete particular tasks. 
     In some examples, warehouse management system  150  may include a central planning system that assigns tasks to different robotic devices within fleet  100 . The central planning system may employ various scheduling algorithms to determine which devices will complete which tasks at which times. For instance, an auction type system may be used in which individual robots bid on different tasks, and the central planning system may assign tasks to robots to minimize overall costs. In additional examples, the central planning system may optimize across one or more different resources, such as time, space, or energy utilization. In further examples, a planning or scheduling system may also incorporate particular aspects of the geometry and physics of box picking, packing, or storing. 
     Planning control may also be distributed across individual system components. For example, warehouse management system  150  may issue instructions according to a global system plan, and individual system components may also operate according to separate local plans. Additionally, different levels of detail may be included within a global plan, with other aspects left for individual robotic devices to plan locally. For instance, mobile robotic devices may be assigned target destinations by a global planner but the full routes to reach those target destinations may be planned or modified locally. 
     In additional examples, a central planning system may be used in conjunction with local vision on individual robotic devices to coordinate functions of robots within robotic fleet  100 . For instance, a central planning system may be used to get robots relatively close to where they need to go. However, it may be difficult for the central planning system to command robots with millimeter precision, unless the robots are bolted to rails or other measured components are used to precisely control robot positions. Local vision and planning for individual robotic devices may therefore be used to allow for elasticity between different robotic devices. A general planner may be used to get a robot close to a target location, at which point local vision of the robot may take over. In some examples, most robotic functions may be position-controlled to get the robots relatively close to target locations, and then vision and handshakes may be used when needed for local control. 
     In further examples, visual handshakes may enable two robots to identify one another by barcode, QR code, augmented reality tag (AR tag), or other characteristics, and to perform collaborative operations within fleet  100 . In additional examples, items (e.g., packages to be shipped) may be provided with visual tags as well or instead, which may be used by robotic devices to perform operations on the items using local vision control. In particular, the tags may be used to facilitate manipulation of the items by the robotic devices. For instance, one or more tags on particular locations on a pallet may be used to inform a fork lift where or how to lift up the pallet. 
     In additional examples, deployment and/or planning strategies for fixed and/or mobile components may be optimized over time. For instance, a cloud-based server system may incorporate data and information from individual robots within the fleet and/or from external sources. Strategies may then be refined over time to enable the fleet to use less space, less time, less power, less electricity, or to optimize across other variables. In some examples, optimizations may span across multiple warehouses, possibly including other warehouses with robotic fleets and/or traditional warehouses. For instance, global control system  150  may incorporate information about delivery vehicles and transit times between facilities into central planning. 
     In some examples, a warehouse management system may sometimes fail, such as when a robot gets stuck or when packages get dropped in a location and lost. Local robot vision may also therefore provide robustness by inserting redundancy to handle cases where the warehouse management system fails in part. For instance, as an automatic pallet jack passes and identifies an object, the pallet jack may send information up to a remote, cloud-based server system. Such information may be used to fix errors in central planning, help to localize robotic devices, or to identify lost objects. 
     In further examples, a warehouse management system may dynamically update a map of the physical environment containing robotic fleet  100  and objects undergoing processing by the robotic devices. In some examples, the map may be continuously updated with information about dynamic objects (e.g., moving robots and packages moved by robots). In additional examples, a dynamic map could contain information on both the current configuration or placement of components within a warehouse (or across multiple warehouses) as well as information about what is anticipated in the near term. For instance, the map could show current locations of moving robots and anticipated locations of the robots in the future, which may be used to coordinate activity between robots. The map could also show current locations of items undergoing processing as well as anticipated future locations of the items (e.g., where an item is now and when the item is anticipated to be shipped out). In addition, the map could show the current location of all items within the warehouse (or across multiple warehouses). 
     In additional examples, some or all of the robots may scan for labels on objects at different points within the process. The scans may be used to look for visual tags that may be applied to individual components or specific items to facilitate finding or keeping track of components and items. This scanning may yield a trail of items constantly moving around as the items are manipulated or transported by robots. A potential benefit is added transparency, both on the supplier side and the consumer side. On the supplier side, information about current locations of inventory may be used to avoid overstocking and/or to move items or pallets of items to different locations or warehouses to anticipate demand. On the consumer side, the information about current locations of particular items may be used to determine when a particular package will be delivered with improved accuracy. 
     In some examples, some or all of the mobile components  110  within robotic fleet  100  may periodically receive charged batteries from a battery exchange station  126  equipped with multiple battery chargers. In particular, the station  126  may replace a mobile robot&#39;s old batteries with recharged batteries, which may prevent robots from having to sit and wait for batteries to charge. The battery exchange station  126  may be equipped with a robotic manipulator such as a robotic arm. The robotic manipulator may remove batteries from an individual mobile robot and attach the batteries to available battery chargers. The robotic manipulator may then move charged batteries located at the station  126  into the mobile robot to replace the removed batteries. For instance, an AGV  112  with a weak battery may be controlled to move over to battery exchange station  126  where a robotic arm pulls a battery out from the AGV  112 , puts the battery in a charger, and gives the AGV  112  a fresh battery. 
     In further examples, battery exchanges may be scheduled by a warehouse management system. For instance, individual mobile robots may be configured to monitor their battery charge status. The robots may periodically send information to the warehouse management system indicating the status of their batteries. This information may then be used by the warehouse management system to schedule battery replacements for individual robots within the fleet when needed or convenient. 
     In some examples, a fleet  100  may contain a number of different types of mobile components  110  that use different types of batteries. A battery exchange station  126  may therefore be equipped with different types of battery chargers for different types of batteries and/or mobile robots. The battery exchange station  126  may also be equipped with a robotic manipulator that can replace batteries for different types of robots. In some examples, mobile robots may have battery containers containing multiple batteries. For instance, an autonomous fork truck  114  such as a pallet jack may have a steel bucket with 3 or 4 batteries. The robotic arm at the station  126  may be configured to lift out the entire bucket of batteries and attach individual batteries to battery chargers on a shelf at the station  126 . The robotic arm may then find charged batteries to replace the old batteries, and move those batteries back into the bucket before reinserting the bucket into the pallet jack. 
     In further examples, warehouse management system  150  and/or a separate control system of the battery exchange station  126  may also automate battery management strategies. For instance, each battery may have a barcode or other identifying mark so that the system can identify individual batteries. A control system of the battery exchange station  126  may count how many times individual batteries have been recharged (e.g., to determine when to change water or empty batteries completely). The control system may also keep track of which batteries have spent time in which robotic devices, how long the batteries took to recharge at the station  126  in the past, and other relevant properties for efficient battery management. This battery usage information may be used by the control system to select batteries for the robotic manipulator to give to particular mobile robots. 
     In additional examples, a battery exchange station  126  may also involve a human operator in some cases. For instance, the station  126  could include a rig where people can safely perform manual battery changing or deliver new batteries to the station for deployment into the fleet  100  when necessary. 
       FIGS. 2A-2D  illustrate several examples of robotic devices that may be included within a robotic warehouse fleet. Other robotic devices which vary in form from those illustrated here as well as other types of robotic devices may also be included. 
       FIG. 2A  illustrates a robotic truck unloader, according to an example embodiment. In some examples, a robotic truck unloader may include one or more sensors, one or more computers, and one or more robotic arms. The sensors may scan an environment containing one or more objects in order to capture visual data and/or three-dimensional (3D) depth information. Data from the scans may then be integrated into a representation of larger areas in order to provide digital environment reconstruction. In additional examples, the reconstructed environment may then be used for identifying objects to pick up, determining pick positions for objects, and/or planning collision-free trajectories for the one or more robotic arms and/or a mobile base. 
     The robotic truck unloader  200  may include a robotic arm  202  with a gripping component  204  for gripping objects within the environment. The robotic arm  202  may use the gripping component  204  to pick up and place boxes to load or unload trucks or other containers. The truck unloader  200  may also include a moveable cart  212  with wheels  214  for locomotion. The wheels  214  may be holonomic wheels that allow the cart  212  to move with two degrees of freedom. Additionally, a wrap-around front conveyor belt  210  may be included on the holonomic cart  212 . In some examples, the wrap around front conveyer belt may allow the truck loader  200  to unload or load boxes from or to a truck container or pallet without having to rotate gripper  204 . 
     In further examples, a sensing system of robotic truck unloader  200  may use one or more sensors attached to a robotic arm  202 , such as sensor  206  and sensor  208 , which may be two-dimensional (2D) sensors and/or 3D depth sensors that sense information about the environment as the robotic arm  202  moves. The sensing system may determine information about the environment that can be used by a control system (e.g., a computer running motion planning software) to pick and move boxes efficiently. The control system could be located on the device or could be in remote communication with the device. In further examples, scans from one or more 2D or 3D sensors with fixed mounts on a mobile base, such as a navigation sensors  216 , safety sensor  218 , and one or more sensors mounted on a robotic arm, such as sensor  206  and sensor  208 , may be integrated to build up a digital model of the environment, including the sides, floor, ceiling, and/or front wall of a truck or other container. Using this information, the control system may cause the mobile base to navigate into a position for unloading or loading. 
     In further examples, the robotic arm  202  may be equipped with a gripper  204 , such as a digital suction grid gripper. In such embodiments, the gripper may include one or more suction valves that can be turned on or off either by remote sensing, or single point distance measurement and/or by detecting whether suction is achieved. In additional examples, the digital suction grid gripper may include an articulated extension. In some embodiments, the potential to actuate suction grippers with rheological fluids or powders may enable extra gripping on objects with high curvatures. 
     The truck unloader  200  may additionally include a motor, which may be an electric motor powered by electrical power, or may be powered by a number of different energy sources, such as a gas-based fuel or solar power. Additionally, the motor may be configured to receive power from a power supply. The power supply may provide power to various components of the robotic system and could represent, for example, a rechargeable lithium-ion or lead-acid battery. In an example embodiment, one or more banks of such batteries could be configured to provide electrical power. Other power supply materials and types are also possible. 
       FIG. 2B  illustrates a robotic arm on a pedestal, according to an example embodiment. More specifically, pedestal robot  220  may be positioned within an environment such as a warehouse environment and used to pick up, move, and/or otherwise manipulate objects within reach. In some examples, the pedestal robot  220  may be specialized for heavy lifting without requiring batteries to operate. The pedestal robot  220  may include a robotic arm  222  with an end-effector-mounted gripper  224 , which may be of the same type as the robotic manipulator  202  and gripper  204  described with respect to the robotic truck unloader  200 . The robotic arm  222  may be mounted on a pedestal  226 , which may allow the robotic arm  222  to easily pick up and move nearby packages, such as to distribute packages between different mobile robots. In some examples, the robotic arm  222  may also be operable to construct and/or deconstruct pallets of boxes. In additional examples, the pedestal  226  may include an actuator to allow a control system to change the height of the robotic arm  222 . 
     In further examples, a bottom surface of the pedestal robot  220  may be a pallet-shaped structure. For instance, the bottom surface may have dimension and shape roughly equivalent to other pallets used for object transport or storage within a warehouse. By shaping the bottom of the pedestal robot  220  as a pallet, the pedestal robot  220  may be picked up and moved to different locations within a warehouse environment by a pallet jack or different type of autonomous fork truck. For instance, when a delivery truck arrives at a particular docking port of the warehouse, a pedestal robot  220  may be picked up and moved to a location closer to the delivery truck to more efficiently process boxes coming from or going to the delivery truck. 
     In additional examples, the pedestal robot  220  may also include one or more visual sensors to identify boxes and/or other robotic devices within the vicinity of the pedestal robot  220 . For instance, a control system of the pedestal robot  220  or a global control system may use sensor data from sensors on the pedestal robot  220  to identify boxes for the robotic arm  222  and gripper  224  of the pedestal robot  220  to pick up or manipulate. In further examples, the sensor data may also be used to identify mobile robotic devices in order to determine where to distribute individual boxes. Other types of robotic fixed manipulation stations may also be used within a heterogeneous robotic fleet as well. 
       FIG. 2C  shows an autonomous guided vehicle (AGV), according to an example embodiment. More specifically, AGV  240  may be a relatively small, mobile robotic device that is capable of transporting individual boxes or cases. The AGV  240  may include wheels  242  to allow for locomotion within a warehouse environment. Additionally, a top surface  244  of the AGV  240  may be used to places boxes or other objects for transport. In some examples, the top surface  244  may include rotating conveyors to move objects to or from the AGV  240 . In additional examples, the AGV  240  may be powered by one or more batteries that can be quickly recharged at a battery charging station and/or exchanged for fresh batteries at a battery exchange station. In further examples, the AGV  240  may additionally include other components not specifically identified here, such as sensors for navigation. AGVs with different shapes and sizes also may be included within a robotic warehouse fleet, possibly depending on the types of packages handled by a warehouse. 
       FIG. 2D  shows an autonomous fork truck, according to an example embodiment. More specifically, autonomous fork truck  260  may include a forklift  262  for lifting and/or moving pallets of boxes or other larger materials. In some examples, the forklift  262  may be elevated to reach different racks of a storage rack or other fixed storage structure within a warehouse. The autonomous fork truck  260  may additionally include wheels  264  for locomotion to transport pallets within the warehouse. In additional examples, the autonomous fork truck may include a motor and power supply as well as a sensing system, such as those described with respect to robotic truck unloader  200 . The autonomous fork truck  260  may also vary in size or shape from the one illustrated in  FIG. 2D . 
       FIG. 3  illustrates a system  300 , according to an example implementation. System  300  may include a robotic device  302 , which may be deployed in a warehouse environment, and a computing system  310 . 
     Robotic device  302  may be an AGV, or may take the form of one or more other robotic devices such as those shown in  FIGS. 2A-D . Other forms are possible as well. Robotic device  302  may be configured to move throughout a warehouse environment based on information gathered by one or more sensors mounted on robotic device  302 . For example, one or more sensors may be positioned on robotic device  302  such that it can build a full or partial 3D model of its surroundings, which may be used to generate a route or path for movement of robotic device  302 . Alternatively, robotic device  302  may move based on commands from a computing system communicatively coupled to robotic device  302 . For instance, one or more sensors positioned on robotic device or positioned within the warehouse environment may transmit data to a computing system (e.g., a warehouse management system), which may then generate a route, path, or other navigation instructions for robotic device  302 . In additional examples, robotic device  302  may move and/or navigate the warehouse environment based on a combination of both local sensing information and centralized commands from the computing system. 
     Robotic device  302  may be deployed in a warehouse environment such as the warehouse environment shown in  FIG. 1A . As discussed above, the warehouse environment may include a single or multiple room structure, and/or covered or uncovered areas such as a loading dock area. The warehouse environment may include a plurality of inventory items, such as pallets, boxes, shelves, or other items. These inventory items may be arranged and stored on shelves organized into aisles within the warehouse environment. This organization may allow a robotic device to navigate through the aisles to access one or more inventory items. The warehouse environment may also include one or more tags, fiducial markers, visual identifiers, beacons, markings, or other indicators that may be used for navigation of a robotic device. 
     In some examples, each inventory item may have a location stored by a computing system. The location may be an expected location of the item based on a stored inventory. The expected location may be updated in the computing system at any time, such as when an item is moved, for example. During regular use of the warehouse, inventory items may be selected for one or more purposes, and moved from one location to another. This may change the true or actual location of the items. However, the computing system may not always be updated correctly or in a timely manner, which can result in a mismatch between the true location and the expected location. As such, the computing system may not always have correct or current information. 
     The computing system may also store other information in addition to the expected location, such as the contents of the item, size, weight, color, history associated with the item, and various other characteristics. This information may be used to build a virtual warehouse that can be used to keep track of the inventory items. 
     In some examples, each inventory item in the warehouse environment may include an identifier that a sensor can detect, allowing the sensor and/or a connected computing device to identify the item. The identifier may be a barcode, QR code, RFID chip, or other identifier that can be placed on or in the item. In other examples, an inventory item&#39;s shape, size, color, texture, or other characteristic of the item itself may be used to identify the item. 
     In some examples, barcodes may be used as visual identifiers associated with each inventory item. Each barcode may be placed on the outside of the inventory item, such as on the packaging or wrapping. It may be beneficial to place the identifier for each item in the same or similar location on the items, such as in the upper right corner of one face, such that a robotic device can find the identifiers faster and more reliably. In other examples, an RFID tag identifier or other tag may be placed inside the item packaging itself. 
     Robotic device  302  may include a camera  304 , which may be configured to capture image data. The captured image data may be used for one or more purposes discussed herein, such as navigation, obstacle avoidance, item identification, and robotic device identification. Camera  304  may include one or more optical sensors configured to capture visual information, such as size, shape, depth, texture, and color, for example. In one embodiment, camera  304  may include a stereo pair of lenses, which may operate in tandem to provide a 3D image of the field of view of the camera. Camera  304  may also or alternatively include one or more lenses, RADAR sensors, LIDAR sensors, 3D sensors, or other type of sensing equipment. More or fewer lenses may be used as well. 
     Camera  304  may be mounted on robotic device  302  such that it can be positioned to have a plurality of different fields of view. For example, camera  304  may be mounted on the front of robotic device  302  (i.e., such that the camera is forward facing when robotic device  302  moves, as shown in  FIG. 3 ). Camera  304  may also be mounted such that it can swivel, turn from side to side and/or up and down, or change position on robotic device  302 . Camera  304  may be mounted on a controllable robotic arm, or on a track such that it can move positions on the robotic device. In this way, camera  304  may be positioned to have multiple different fields of view. 
     The field of view of camera  304  may depend on the position and orientation of camera  304 , which may be controlled by computing system  310 .  FIG. 4 , discussed in further detail below, illustrates an example field of view  406  of camera  404 . As such, the field of view may include one or more boundaries. Image data captured by the camera may thus be limited by the boundaries of the field of view. 
     In some examples, camera  304  may be used as a vision system to aid in the navigation of robotic device  302 . Aiding navigation may be a primary purpose of camera  304 . Camera  304  may capture image data about the surroundings of robotic device  302 , which may be used by computing system  310  to generate navigation instructions. In order capture image data that can be used in aiding navigation, camera  304  may be positioned such that the field of view includes the ground around and in front of robotic device  302 . In this position, image data captured by camera  304  may include objects and/or obstacles that obstruct the forward movement of robotic device  302 . The image data captured for the purpose of generating navigation instructions may also include shelves, inventory items, other robotic devices, and other objects located within the field of view. 
     System  300  may also include a computing system  310 , which may be configured to perform one or more functions described herein. As shown in  FIG. 3 , computing system  310  may be separate from robotic device  302 , and may be communicatively coupled to robotic device  302  via a wireless connection. Alternatively, in some examples computing system  310  may be coupled to robotic device  302  via a wired connection, and/or may be a component of robotic device  302  itself. In other examples, computing system  310  may include components located in both robotic device  302  and elsewhere, such that performance of the functions of computing device  310  described herein may be done by either a component on robotic device  302 , a central computing device, or a combination thereof. In still other examples, computing system  310  may be distributed across two or more robotic devices, such that a peer-to-peer network of robotic devices including a computing system is formed. 
     Computing system  310  may be configured to receive captured image data. In some examples, the image data may be captured by camera  304 , and in other examples, may come from one or more other sensors mounted on robotic device  302  or placed within the warehouse environment (e.g., cameras or sensors placed at locations throughout the warehouse). Based on the received image data, computing system  310  may generate navigation instructions for robotic device  302 . Generating navigation instructions for robotic device  302  may involve analyzing the received image data to detect objects, obstructions, inventory items, and other robotic devices that may obstruct a path of robotic device  302 . Generating navigation instructions may also involve retrieving information such as the locations or expected locations of one or more target inventory items, robotic devices, or other items. 
     In some examples, the navigation instructions for a robotic device may include both large scale instructions as well as small scale instructions. Large scale instructions may include the broad instructions needed to move a robotic device from one location to another within the warehouse, such as “move south two aisles and west three rows.” Small scale instructions, on the other hand, may include the instructions needed for a robotic device to avoid running into an obstacle while carrying out its large scale instructions. Both large and small scale instructions may be needed for the robotic device to operate properly. 
     Computing system  310  may also be configured to analyze the received image data to detect one or more visual identifiers corresponding to one or more inventory items. The visual identifiers may be on-item visual identifiers, such as barcodes, QR codes, or the like as described above. In some examples, detecting the identifiers may include scanning or searching the image data for barcodes and/or object that look like barcodes. The barcode may then be extracted or “read,” and a corresponding inventory item may be determined. In some examples, the same image data captured by camera  304  that is used to generate navigation instructions may also be analyzed to detect one or more on-item visual identifiers. As such, the image data may be dual purpose in that the generation of navigation instructions and detection of visual identifiers may be performed contemporaneously by computing system  310 . 
     After detecting one or more on-item visual identifiers, computing system  310  may identify the inventory item(s) corresponding to the detected visual identifier(s) and perform one or more actions in response. The actions described below may be performed for each visual identifier detected. 
     A first action performed responsive to detecting one or more visual identifiers may include computing system  310  using the image data as a basis for determining a warehouse location of the inventory item (i.e., the true or actual location of the item). In some examples, the warehouse location of the inventory item may be determined based on the known location of the robotic device  302  and or camera  304  at or near the time the image data was captured. In other examples, the image data captured by camera  304  and analyzed by computing system  310  may include embedded information about the location of the robotic device  302  and/or one or more items included in the image data. 
     A second action performed responsive to detecting one or more visual identifiers may include computing system  310  determining an expected location of the inventory item. Determining the expected location may include retrieving a stored location from memory or communicating with one or more computing devices to receive the expected location. 
     A third action may include computing system  310  comparing the warehouse location to the expected location. In some examples, this comparison may involve determining whether the warehouse location is within a threshold distance from the expected location. This comparison may indicate whether the identified inventory item is at an expected location or whether the inventory item has been misplaced. 
     A fourth action may include computing system  310  initiating a further action based on or responsive to the comparison between the warehouse location and the expected location. In some examples, this may include instructing the robotic device to pick up and move the inventory item to another location. It may also or alternatively include dispatching a second robotic device or human operator to go to the warehouse location or expected location of the inventory item. In other examples, the further action may include adding the inventory item to a list or queue of misplaced items, which may be moved or dealt with appropriately at a later time. In still other examples, computing device  310  may update the expected location of the inventory item to correct any errors or differences between the warehouse location and the expected location. 
       FIG. 4  illustrates an example warehouse aisle  400  according to an example implementation. Aisle  400  may include one or more shelves  410 , which may be multiple levels in height and may have one or more inventory items  412  stored thereon. Each inventory item  412  may include an on-item visual identifier  414 , which may be used to differentiate the inventory items from each other and identify which item is which. 
     A robotic device such as autonomous guided vehicle (AGV)  402  may be located in aisle  400 . Robotic device  402  may be similar or identical to robotic device  302  in one or more respects. Robotic device  402  may include a camera  404  that may have a field of view  406 . Field of view  406  may change depending on the position and orientation of camera  404 . Robotic device  402  may also include or be communicatively coupled to a computing system (not shown) that may perform one or more functions such as generating navigation instructions, analyzing image data, and others. 
     In some examples, the computing system may determine a target inventory item that is located in a target location, and may dispatch robotic device  402  to the target location. The computing system may retrieve a target (or expected) location of the target item, and generate a path for robotic device  402  to travel to move to the target location. Once robotic device  402  is positioned at the target location, it may be configured to use camera  404  to capture image data including a visual identifier corresponding to the target inventory item. 
     While robotic device  402  is moving, camera  404  may capture image data that may be used by the computing device to generate navigation instructions that may be new instructions, or may update or alter previous instructions. For instance, robotic device  402  in  FIG. 4  may receive navigation instructions to move to the end of aisle  400 . Camera  404  may be angled downward in a first position to capture image data with a field of view including the ground in front of robotic device  402 . Camera  404  in this first position may capture image data including obstacle  420 . In response, the computing device may generate navigation instructions that cause robotic device  402  to change its movement direction to avoid obstacle  420 . 
       FIG. 5  shows the warehouse aisle  400  as described with reference to  FIG. 4 . However, in  FIG. 5 , camera  404  of robotic device  402  is in a second position, angled upward, such that the field of view  506  is higher than the field of view  406 . Field of view  506  may include visual identifiers corresponding to inventory items located on the second level of shelves  410 , in addition to the visual identifiers located on the first level. However, the camera in the second position may have reduced visibility of the ground in front of robotic device  402 , or may not be able to see the ground at all. As such, the positioning and resulting field of view of camera  404  may include a trade-off between capturing the ground or obstacles for purposes of navigation and capturing additional visual identifiers. 
     With this trade-off in mind, some examples may include determining the position of camera  404  based on the benefits and drawbacks of each position, with regard to navigation and detecting visual identifiers. For instance, the position of camera  404  may be determined based on (1) the value of one or more visual identifiers that may be captured by camera  404  in a selected position, and (2) the accuracy of navigation of robotic device  402  when the camera is in the selected position. The value of the one or more visual identifiers may be based on whether the visual identifier(s) have been scanned recently, the additional number of visual identifiers that may be scanned when the camera is in a first position compared to a second position, a priority associated with one or more visual identifiers and/or inventory items, the importance of one or more visual identifiers and/or inventory items (such as popular or high-selling items), or any other metric. Further, the accuracy of navigation of robotic device  402  may be based on a likelihood of running into an obstacle, a reduction in navigational precision when the camera is in a first position compared to a second position, or other metrics. 
     In some examples, the position of camera  404  may change dynamically. For instance, while robotic device  402  is carrying out navigation instructions determined based on image data captured when camera  404  in a first position, camera  404  may be put in a second position to capture additional visual identifiers. Camera  404  may initially be angled downward as shown in  FIG. 4 , and the computing system may determine that robotic device  402  must move right one foot to avoid obstacle  420 , and then that the path forward is clear for 20 feet. Robotic device  402  may then proceed to execute these navigation instructions. But before or during the execution of these navigation instructions, camera  404  may be put in a second position, such as the upward angle shown in  FIG. 5 , which may include visual identifiers that would not be visible for camera  404  in the first position. Alternatively, camera  404  may scan back and forth, up and down, or otherwise change its field of view during movement of robotic device  402 , or while robotic device  402  is stationary. 
       FIG. 6  shows a flowchart of an example method  600  according to an example embodiment. Method  600  may be carried out by any of the devices or systems described herein, such as robotic devices shown in  FIGS. 2A-2D, 3, 4, and 5 , and/or computing systems described herein. 
     Furthermore, it is noted that the functionality described in connection with the flowcharts described herein can be implemented as special-function and/or configured general-function hardware modules, portions of program code executed by a processor for achieving specific logical functions, determinations, and/or steps described in connection with the flowchart shown in  FIG. 6 . Where used, program code can be stored on any type of computer-readable medium, for example, such as a storage device including a disk or hard drive. Method 
     In addition, each block of the flowchart shown in  FIG. 6  may represent circuitry that is wired to perform the specific logical functions in the process. Unless specifically indicated, functions in the flowchart shown in  FIG. 6  may be executed out of order from that shown or discussed, including substantially concurrent execution of separately described functions, or even in reverse order in some examples, depending on the functionality involved, so long as the overall functionality of the described method is maintained. 
     At block  602  of  FIG. 6 , method  600  may include receiving image data, which may be captured by a camera mounted on a robotic device. The camera may be a stereo camera that may capture depth information. As described above, the robotic device may be deployed in a warehouse environment that includes a plurality of inventory items. The received image data may encompass the field of view of the camera, and may include one or more obstacles, inventory items, visual identifiers, or other objects. 
     At block  604 , method  600  may include generating a navigation instruction. The navigation instruction may be generated based on the received image data, and may be used for the navigation of the robotic device within the warehouse environment. 
     At block  606 , method  600  may include detecting on-item visual identifiers. The received image data used to generate navigation instructions at block  604  may also be analyzed to detect one or more on-item visual identifiers. The on-item visual identifiers may correspond to one or more inventory items located within the warehouse environment. In some examples, the image data used to generate navigation instructions may also be analyzed to detect on-item visual identifiers, such that the navigation instructions are generated contemporaneously with the detection of the on-item visual identifiers. 
     At block  608 , method  600  may include, for each detected on-item visual identifier, (i) determining a warehouse location of the corresponding inventory item, (ii) comparing the determined warehouse location to an expected location, and (iii) initiating an action based on the comparison. Determining the warehouse location of a corresponding inventory item may include receiving GPS location data, and/or other location data corresponding to the inventory item, the camera that captured the image data, the robotic device, and/or another object. Comparing the determined warehouse location to an expected location may include retrieving an expected location for the inventory item, and determining a difference between the expected location and the warehouse location. Based on this comparison, an action may be performed. These actions may be any action discussed herein, such as dispatching a human operator, updating the expected or warehouse location, moving the inventory item, or adding the inventory item to a list, for example. 
     In some examples, method  600  may also include determining a target inventory item having a target on-item visual identifier, and corresponding to a target location. Generating navigation instructions in these examples may include generating navigation instructions to move the robotic device to the target location. The method may then include moving the robotic device to the target location, and capturing the target on-item visual identifier. 
     In carrying out method  600 , the camera mounted to the robotic device may be positionable. The position of the camera may vary, and may be determined based on one or more factors described above, including (1) the value of one or more visual identifiers captured by the camera in a selected position, and (2) the accuracy of navigation of the robotic device when the camera is in the selected position. Other considerations are possible as well. 
     III. Example Variations 
     In some examples, the generation of navigation instructions may include consideration of the resulting route that a robotic device will take. It may ordinarily be beneficial for a robotic device to take a more direct route, to reduce the time of transit. However, in some examples it may be beneficial for the robotic device to take a circuitous or less direct route, because the robotic device will be exposed to a greater number of inventory items and visual identifiers. This may allow more visual identifiers to be detected, and thus for a more accurate and up to date inventory to be maintained. 
     A first set of navigation instructions may be generated to cause the robotic device to move from a first location to a second location. The number of visual identifiers the robotic device may be exposed to along this first route may be determined. A second set of navigation instructions may also be determined, as well as a second number of visual identifiers the robotic device may be exposed to. The second route may be selected for execution by the robotic device, because in carrying out the second set of navigation instructions the robotic device may obtain valuable information about the inventory items along that route. In other examples, particular navigation instructions may be selected for other reasons as well. 
     The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. 
     The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying figures. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The example embodiments described herein and in the figures are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     A block that represents a processing of information may correspond to circuitry that can be configured to perform the specific logical functions of a herein-described method or technique. Alternatively or additionally, a block that represents a processing of information may correspond to a module, a segment, or a portion of program code (including related data). The program code may include one or more instructions executable by a processor for implementing specific logical functions or actions in the method or technique. The program code and/or related data may be stored on any type of computer readable medium such as a storage device including a disk or hard drive or other storage medium. 
     The computer readable medium may also include non-transitory computer readable media such as computer-readable media that stores data for short periods of time like register memory, processor cache, and random access memory (RAM). The computer readable media may also include non-transitory computer readable media that stores program code and/or data for longer periods of time, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. A computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device. 
     Moreover, a block that represents one or more information transmissions may correspond to information transmissions between software and/or hardware modules in the same physical device. However, other information transmissions may be between software modules and/or hardware modules in different physical devices. 
     The particular arrangements shown in the figures should not be viewed as limiting. It should be understood that other embodiments can include more or less of each element shown in a given figure. Further, some of the illustrated elements can be combined or omitted. Yet further, an example embodiment can include elements that are not illustrated in the figures. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.