Patent Publication Number: US-9889563-B1

Title: Systems and methods to facilitate human/robot interaction

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This disclosure is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 14/660,161, filed Mar. 17, 2015, of the same title, which is incorporated herein by reference as if fully set forth below. 
    
    
     BACKGROUND 
     Modern inventory systems, such as those in mail order warehouses, supply chain distribution centers, airport luggage systems, and custom-order manufacturing facilities, include a number of complex systems, including robots, automated shelving systems, radio frequency identification (RFID), and automated scheduling and routing equipment. Many systems, for example, comprise robots that travel to shelving systems to retrieve items, or the shelves themselves, and return them to a central location for additional processing. 
     Automated warehouses exist that use robots, for example, to move items or shelves from a storage location in the warehouse to a shipping location (e.g., for inventory items to be boxed and shipped). It is inevitable, however, that the paths of the robots and humans working in the warehouse will cross. Direct contact between the human workers and the robots, however, can be problematic, and a maintenance issue for the robots. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items or features. 
         FIG. 1  is a pictorial flow diagram of an illustrative process for maintaining a predetermined, working distance between workers and robots on an automated warehouse floor, in accordance with some examples of the present disclosure. 
         FIGS. 2A and 2B  are schematic diagrams that depict components of an automated warehouse, in accordance with some examples of the present disclosure. 
         FIG. 3  is an isometric view of a robot with multiple radio frequency identification (RFID) tags configured to be read by an RFID reader on a worker, in accordance with some examples of the present disclosure. 
         FIG. 4  is an isometric view of a worker wearing a garment with multiple RFID tags configured to be read by an RFID reader on a robot, in accordance with some examples of the present disclosure. 
         FIG. 5A  is a front view of a vest with multiple RFID tags, in accordance with some examples of the present disclosure. 
         FIG. 5B  is a front view of a baseball cap with multiple RFID tags, in accordance with some examples of the present disclosure. 
         FIG. 6  is an isometric view of a cart and a robot, each with one or more cameras to provide location information to a central control, in accordance with some examples of the present disclosure. 
         FIG. 7  is a top, detailed view of a fiducial comprising fiducial data, in accordance with some examples of the present disclosure. 
         FIG. 8  is a schematic diagram that depicts components of another automated warehouse comprising a separate server, in accordance with some examples of the present disclosure. 
         FIG. 9  is a flowchart depicting a method of maintaining a predetermined distance between workers and robots in an automated warehouse using location information, in accordance with some examples of the present disclosure. 
         FIG. 10A  is an isometric view of a stationary robotic arm comprising multiple RFID tags configured to be read by an RFID reader on a worker and a circular work zone around the stationary robotic arm, in accordance with some examples of the present disclosure. 
         FIG. 10B  is an isometric view of a worker wearing a garment with multiple RFID tags configured to be read by an RFID reader on the stationary robotic arm and a spherical work zone around the stationary robotic arm, in accordance with some examples of the present disclosure. 
         FIG. 10C  is an isometric view of a stationary robotic arm comprising multiple RFID tags configured to be read by an RFID reader on a worker and a circular work zone around the worker, in accordance with some examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of the present disclosure relate generally to automated warehouses, and specifically to one or more types of devices for use in the warehouse to provide a virtual work zone around warehouse workers and/or warehouse robots. In some examples, the system can comprise one or more radio frequency identification (RFID) tags and one or more RFID readers. In some examples, the warehouse workers can wear one or more RFID tags to enable to robots to sense their presence. In other examples, the warehouse robots can comprise one or more RFID tags and the warehouse worker can have an RFID reader. In this manner, when the robot senses an RFID reader associated with a warehouse worker is writing to its RFID tags, the robot can sense the presence of the worker. The warehouse worker, warehouse robot, or both can also include one or more RFID readers to identify nearby tags, verify tags, and establish virtual work zones as necessary. 
     While other short range transmissions technologies besides RFID, such as Bluetooth® and near field communications (NFC), could be used, one advantage of RFID tags is that they are inexpensive. In this manner, redundancy can be provided simply by using multiple RFID tags. When incorporated into a disposable garment, such as a vest or a baseball cap, for example, the whole garment can be replaced if the RFID tags have failed, or are failing. In addition, each garment and/or each robot can include multiple RFID tags to ensure readability from multiple angles and orientations. In this manner, regardless of the relative motion and orientation between the robot and the worker, at least one tag can be read and identified. 
     To this end, as shown in  FIG. 1 , examples of the present disclosure can comprise systems and methods  100  for improving efficiency and reducing maintenance in automated warehouses by, among other things, preventing collisions and other mishaps between workers  102  and robots  120 . In some examples, this can be achieved using virtual work zones  105  around the robots  120 , the workers  102 , or both. As mentioned above, in some examples, the work zones  105  can be implemented using relatively short range communications, such as RFID, and readers capable of reading these short range communications. In this manner, when a reader on a robot  120  detects the presence of an RFID tag assigned to a worker  102  (or vice versa), for example, the robot  120  can take evasive action (e.g., slow down, stop, or reroute). 
     At  110 , in the warehouse during normal operations, the robots  120  can be routed by a central control to various locations to, for example, retrieve merchandise, receive maintenance and/or recharging, or perform maintenance themselves (e.g., the robots  120  can take inventory images or provide lighting to maintenance operations). In some examples, the central control can determine the route for the robot from the robot&#39;s current location to the next assignment (e.g., to retrieve a shelving unit). In other examples, the central control can simply provide a location (e.g., a grid number, row number, or GPS location within the warehouse) to the robot  120 , enabling the robot  120  to generate its own path. 
     At  125 , the central control can receive a signal that a worker  102  has entered a portion of the warehouse floor  170 . In some cases, this may be to enable the worker  102  to leave for the day, for example, go to the bathroom, perform maintenance operations in the warehouse, or go on a lunch break. In other cases, the worker  102  may need to enter the warehouse to remove errant items on the warehouse floor  170  such as, for example, inventory items that have fallen out of shelving units or trash. In still other examples, the worker  102  may need to retrieve an inventory item manually because the shelving unit has inadvertently become too heavy or imbalanced, for example, to be transported by a robot  120 . 
     In some examples, the central control can receive a signal from a supervisor with access to the inventory control system that one or more workers  102  are on the warehouse floor  170 . In other examples, the workers  102  may pass by an RFID scanner, light beam sensor, motion sensor, or other sensor to signal to the central control that workers  102  are present on the warehouse floor  170 . In still other examples, the workers  102  can simply enter the warehouse floor  170  and the robots  120  can simply scan continuously for RFID tags associated with workers  102  (as opposed to other robots  120 ). 
     The worker  102 , the robot  120 , or both can be equipped with RFID tags and/or RFID readers. In some examples, the worker  102  can wear garments or other wearable devices that include RFID tags such as, for example, a shirt, vest, jacket, baseball cap, bracelet, necklace, ring, band, watch, etc. Similarly, the robot  120  may have one or more RFID tags located in various orientations (e.g., the right, left, top, bottom, forward and reverse sides). In either case, the RFID tags can be situated such that they can be read from many angles and orientations. 
     At  135 , the robot  120  can detect the presence of a worker  102  due to RFID interaction between the robot  120  and the worker  102 . In other words, depending on the configuration, of which several are discussed below, if the robot  120  (1) senses, by an RFID reader, one or more RFID tags associated with a worker  102 , or (2) senses that the RFID tags on the robot  120  are being written to by an RFID reader associated with the worker  102 , this indicates that the robot  120  is within the worker&#39;s work zone  105  and/or that the worker  102  is in the robot&#39;s work zone  105 . In some examples, the tags and/or readers can simply sense that they are within range based on emitted signals, rather than actually performing a write to the tags. 
     In some examples, the robot  120  can send a detection signal to the central control that an RFID interaction exists. The central control can then send instructions to the robot establishing one or more work zones around the worker  102  and/or the robot  120 . In other examples, a processor on the robot  120  can detect and process the RFID interaction. Regardless, in response, the robot  120  can take an appropriate “evasive” action. 
     In some examples, the robot  120  can simply stop until all RFID tags (or RFID readers) associated with a worker  102  are no longer in range of the RFID reader (or RFID tags) on the robot  120 . In other examples, the robot  120  can detect its distance from the worker—using RFID tags, fiducials, or other means—as discussed below—to establish multiple, concentric work zones  105 . In this manner, the robot  120  can try to reroute around the worker  102  upon initial contact with an outer work zone  105   a  (e.g., 10 feet), for example, slow down upon contact with an intermediate work zone  105   b , and then stop upon detection of an inner work zone  105   c  (e.g., 5 feet). At  145 , when the robot  120  (1) ceases to detect, with the RFID reader, RFID tags associated with the worker  102  (or any worker  102 ), or (2) ceases to detect a reader associated with the worker writing to its RFID tags, it can return to normal operation (e.g., continue on its route at a normal speed). 
     As shown in  FIG. 2A , an inventory control system  200  can include a plurality of robots  120  to transport inventory items  140 , shelving units, or inventory holders  130 , or other objects for additional processing. In some examples, the robots  120  can retrieve inventory holders  130 , for example, and deliver them to work stations  150 . At the work stations  150 , workers  102  can, for example, retrieve inventory items  140  from the inventory holders  130 , restock the inventory holders  130 , or conduct inventory for the inventory holders  130 , among other things. 
     As mentioned above, despite the robots  120 , in some cases it may nonetheless be necessary, or desirable, for workers  102  to enter the warehouse floor  170 . This may simply enable the worker  102  to leave for the day, go to the bathroom, perform maintenance operations in the warehouse, or go on a lunch break. In other cases, the worker  102  may need to enter the warehouse floor  170  to remove errant items on the warehouse floor  170  such as, for example, inventory items  140  that have fallen out of shelving units or trash. In still other examples, the worker  102  may need to retrieve an inventory item  140  because the shelving unit has inadvertently become too heavy or imbalanced, for example, to be transported by a robot  120 . Workers  102  may also simply need to leave or go to the break room via the warehouse floor  170 . 
     Regardless of the reason, it is desirable to prevent incidents between workers  102  and robots  120 . To this end, examples of the present disclosure can comprise an inventory control system  200  for establishing work zones  105  around the robots  120  and the workers  102 . As mentioned above, the work zones  105  can be established with a variety of short range transmission technologies such as, for example, Bluetooth®, near field communication (NFC), or RFID technology. Thus, while discussed herein with respect to RFID, it should be understood that other communications protocols could be used and are contemplated herein. It should also be noted that, while they are generally referred to as “RFID readers,” it is understood that RFID readers generally also have the ability to write to RFID tags. 
     RFID technology tends to have a relatively short range—e.g., on the order of approximately 10 feet. Within this range, RFID tags can be detected, read, and written to by an RFID reader. As a result, this limited range can also be used to establish approximate distances between the RFID tags and the RFID reader. In addition, RFID tags can be both passive and active. A passive RFID tag is powered by electromagnetic induction created when the reader reads the RFID tag. An active RFID tag is powered by a local power source (e.g., the battery for the robot  120 ) and thus, requires less power to read and can often be read over greater distances, among other things. 
     Based on the relatively short range of RFID tags, therefore, in some examples, the worker  102  can wear a garment, hat, accessory, or other wearable device that includes multiple RFID tags (e.g., in the pockets or sewn into the garment) to enable an RFID reader on the robots  120  to identify the worker  102 . In this configuration, the robot  120  can slow down or stop anytime it reads an RFID tag associated with a worker  102 . When the robot  120  no longer detects the presence of RFID tags associated with the worker  102 , it can continue on its normal course of business. 
     In other examples, the robot  120  can comprise multiple RFID tags and the worker  102  can be equipped with the RFID reader. In this configuration, detection is provided when a processor in the robot  120 , and in communication with the RFID tags on the robot  120 , detects that one or more RFID tags on the robot  120  are being written to with a reader associated with the worker  102  (or simply that the reader is within range). As before, the robot  120  can slow down or stop anytime it detects that its RFID tags are being written to by a worker&#39;s RFID reader. In other words, in either case, the range of the RFID tags can establish the work zone  105 . In this manner, when the RFID tags are within the range of the reader (i.e., are detected or written to, respectively), then the robot  120  can take action (slow down, divert, or stop). 
     As discussed above, in some cases, the RFID tags can also provide location or range information. In this configuration, the inventory control system  200  can establish outer  105   a , intermediate  105   b , and inner  105   c  work zones. In this manner, the robot  120  can escalate its evasive action as it gets closer and closer to the worker  102 . So, for example, the robot  120  can attempt to divert around the worker  102  upon detection of the outer work zone  105   a , slow down upon detection of the intermediate work zone  105   b , and stop completely upon detection of the inner work zone  105   c.    
     As shown in  FIG. 2B , the inventory control system  200  can further comprise a central control  115 , a plurality of robots  120 , one or more inventory containers, pods, or holders  130 , and one or more inventory work stations  150 . The robots  120  can transport the inventory holders  130  between points within the warehouse floor  170  on their own, or in response to commands communicated by the central control  115 . Each inventory holder  130  can store one or more types of inventory items  140 . As a result, the inventory control system  200  is capable of moving inventory items  140  between locations within a workspace, such as a storage facility or warehouse floor  170  to facilitate the entry, processing, and/or removal of inventory items  140  from inventory control system  200  and the completion of other tasks involving the inventory items  140 . 
     The central control  115  can assign tasks to the appropriate components of the inventory control system  200  and coordinate operation of the various components in completing the tasks. These tasks may relate both to the movement and processing of inventory items and the management and maintenance of the components of inventory control system  200 . The central control  115  may assign portions of the warehouse floor  170 , for example, as parking spaces for the robots  120 , for the scheduled recharge or replacement of robot  120  batteries, for the storage of inventory holders  130 , or any other operations associated with the inventory control system  200  and its various components. 
     The central control  115  may also select components of the inventory control system  200  to perform these tasks and communicate appropriate commands and/or data to selected components to facilitate completion of these operations. Although shown in  FIG. 2B  as a single, discrete component, the central control  115  may represent multiple components and may represent, or include, portions of the robots  120 , inventory holders  130 , or other elements of the inventory control system  200 . As a result, any or all of the interaction between a particular robot  120  and the central control  115  that is described below may, for example, represent peer-to-peer communication between that robot  120  and one or more other robots  120 , or may comprise internal commands based on memory in the robot  120 , for example. 
     As mentioned above, the robots  120  can be used to move inventory holders  130  between locations within the warehouse floor  170 . The robots  120  may represent many types of devices or components appropriate for use in inventory control system  200  based on the characteristics and configuration of inventory holders  130  and/or other elements of inventory control system  200 . In a particular embodiment of inventory control system  200 , the robots  120  can represent independent, self-powered devices, such as wheeled or tracked robots or robotic carts, for example, configured to freely move about warehouse floor  170 . Examples of such inventory control systems are disclosed in U.S. Patent Publication No. 2012/0143427, published on Jun. 7, 2012, titled “SYSTEM AND METHOD FOR POSITIONING A MOBILE DRIVE UNIT,” and U.S. Pat. No. 8,280,547, issued on Oct. 2, 2012, titled “METHOD AND SYSTEM FOR TRANSPORTING INVENTORY ITEMS,” the entire disclosures of which are herein incorporated by reference. 
     In other examples, the robots  120  can comprise track guided robots configured to move inventory holders  130  along tracks, rails, cables, a crane system, or other guidance or support elements traversing the warehouse floor  170 . In this configuration, the robot  120  may receive power, communications, and/or support through a connection to guidance elements such as, for example, a powered rail, slot, or track. Additionally, in some examples of the inventory control system  200 , the robot  120  may be configured to utilize alternative conveyance equipment to move within warehouse floor  170  and/or between separate portions of warehouse floor  170 . 
     Additionally, the robots  120  may be capable of communicating with the central control  115  to receive tasks, inventory holder  130  assignments, transmit their locations or the locations of other robots  120 , or exchange other suitable information to be used by central control  115  or robots  120  during operation. The robots  120  may communicate with central control  115  using, for example, wireless, wired, or other connections. In some examples, the robots  120  may communicate with central control  115  and/or each other using, for example, 802.11 specification wireless transmissions (e.g., a/b/g/n), Bluetooth, radio frequency (RF), Infrared Data Association (IrDA) standards, or other appropriate wireless communication protocols. 
     In other examples, such as in an inventory control system  200  using tracks, the tracks or other guidance elements (e.g., slots or rails) along which robot  120  moves may be wired to facilitate communication between robot  120  and other components of inventory control system  200 . Furthermore, as noted above, the robot  120  may include components of the central control  115  such as, for example, processors, modules, memory, and transceivers. Thus, for the purposes of this description and the claims that follow, communication between central control  115  and a particular robot  120  may also represent communication between components within a particular robot  120 . In general, the robots  120  can be powered, propelled, and controlled in many ways based on the configuration and characteristics of a particular inventory control system  200 . 
     The inventory holders  130  are used to store inventory items and can include additional features as part of the inventory control system  200 . In some examples, each of the inventory holders  130  can include multiple dividers to create multiple bins or bays within the inventory holders  130 . In this configuration, each inventory holder  130  can store one or more types of inventory items  140  in each bin or bay (e.g., each inventory holder  130  may store the same inventory item  140  in all bins or bays, or different inventory items  140  in each bin or bay, or have no bins or bays and store just one type of item  140 ). Additionally, in particular examples, inventory items  140  may also hang from hooks or bars within, or on, the inventory holders  130 . In general, the inventory holders  130  may store inventory items  140  in any appropriate manner within the inventory holders  130  and/or on the external surface of the inventory holders  130 . 
     The inventory holders  130  can be configured to be carried, rolled, and/or otherwise moved by the robots  120 . In some examples, the inventory holders  130  may also provide propulsion to supplement that provided by robot  120  when moving multiple inventory holders  130 , for example. Additionally, each inventory holder  130  may include a plurality of sides, and each bin or bay may be accessible through one or more sides of the inventory holder  130 . For example, in a particular embodiment, the inventory holders  130  include four sides. In such an embodiment, bins or bays located at a corner of two sides may be accessible through either of those two sides, while each of the other bins or bays is accessible through an opening in one of the four sides and a free-standing inventory holder  130  with no bins or bays may be accessible via all four sides. The robot  120  may be configured to rotate inventory holders  130  at appropriate times to present a particular face and the bins, bays, shelves or dividers associated with that face to an operator or other components of inventory control system  200  to facilitate removal, storage, counting, or other operations with respect to inventory items  140 . 
     In particular examples, the inventory control system  200  may also include one or more inventory work stations  150 . Inventory work stations  150  represent locations designated for the completion of particular tasks involving inventory items. Such tasks may include the removal of inventory items  140 , the addition, or restocking, of inventory items, the counting of inventory items  140 , the unpacking of inventory items  140  (e.g. from pallet- or case-sized groups to individual inventory items), the consolidation of inventory items  140  between inventory holders  130 , and/or the processing or handling of inventory items  140  in any other suitable manner. The work stations  150  may represent both the physical location and also any appropriate equipment for processing or handling inventory items, such as work benches, packing tools and supplies, scanners for monitoring the flow of inventory items in and out of inventory control system  200 , communication interfaces for communicating with central control  115 , and/or any other suitable components. Inventory work stations  150  may be controlled, entirely or in part, by human operators or may be partially or fully automated. 
     In operation, the central control  115  selects appropriate components to complete particular tasks and transmits task assignments  118  to the selected components. These tasks may relate to the retrieval, storage, replenishment, and counting of inventory items and/or the management of robots  120 , inventory holders  130 , inventory work stations  150 , and other components of inventory control system  200 . Depending on the component and the task to be completed, a particular task assignment  118  may identify locations, components, and/or actions associated with the corresponding task and/or any other appropriate information to be used by the relevant component in completing the assigned task. 
     In particular examples, the central control  115  generates task assignments  118  based, in part, on inventory requests that central control  115  receives from other components of inventory control system  200  and/or from external components in communication with central control  115 . For example, in particular examples, an inventory request may represent a shipping order specifying particular inventory items that have been purchased by a customer and that are to be retrieved from inventory control system  200  for shipment to the customer. The central control  115  may also generate task assignments  118  in response to the occurrence of a particular event (e.g., in response to a robot  120  requesting a space to park), according to a predetermined schedule (e.g., as part of a daily start-up or cleaning routine), or at any appropriate time based on the configuration and characteristics of inventory control system  200 . 
     The central control  115  may, in some cases, communicate task assignments  118  to a robot  120  that include one or more destinations for the robot  120 . In this vein, the central control  115  may select a robot  120  based on the location or state of the robot  120 , an indication that the robot  120  has completed a previously-assigned task, a predetermined schedule, and/or any other suitable consideration. For example, the task assignment may define the location of an inventory holder  130  to be retrieved, an inventory work station  150  to be visited, a storage location where the robot  120  should park until receiving another task, or a location associated with any other task appropriate based on the configuration, characteristics, and/or state of inventory control system  200 , as a whole, or individual components of inventory control system  200 . 
     As part of completing these tasks, the robots  120  may dock with various inventory holders  130  within the warehouse floor  170 . The robots  120  may dock with inventory holders  130  by connecting to, lifting, and/or otherwise interacting with inventory holders  130  such that, when docked, the robots  120  are coupled to the inventory holders  130  and can move inventory holders  130  within the warehouse floor  170 . While the description below focuses on particular examples of robots  120  and inventory holders  130  that are configured to dock in a particular manner, alternative examples of robots  120  and inventory holders  130  may be configured to dock in any manner suitable to allow robots  120  to move inventory holders  130  within warehouse floor  170 . 
     Components of inventory control system  200  may provide information to the central control  115  regarding their current state, the state of other components of inventory control system  200  with which they are interacting, and/or other conditions relevant to the operation of inventory control system  200 . This may allow central control  115  to utilize feedback from the relevant components to update algorithm parameters, adjust policies, or otherwise modify its decision-making to respond to changes in operating conditions or the occurrence of particular events. In addition, while central control  115  may be configured to manage various aspects of the operation of the components of inventory control system  200 , in particular examples, the components themselves may also be responsible for some decision-making relating to certain aspects of their operation, thereby reducing the processing load on central control  115 . 
     In some examples, the warehouse floor  170  floor can also comprise a plurality of markers, or fiducials  175 , to enable the robots  120  to establish their location in the warehouse. Because the robots  120  are generally low enough to travel under inventory holders  130  (i.e., to be able to lift them), in some examples, the fiducials  175  can also continue under the inventory holders  130 , substantially spanning the entire floor. In some examples, the area between the fiducials  175  can define grid areas  175   a  with a fiducial  175  at each corner. When attempting to locate a particular inventory holder  130 , therefore, the robot  120  can locate the fiducial  175 , or grid  175   a , associated with the inventory holder&#39;s location by scanning the floor with a downward facing scanner or camera and then confirm that it is in the right location by scanning an identifier, e.g., a 2D or 3D bar code, an RFID tag, or other identifier, on the bottom of the inventory holder  130  with an upward facing scanner or camera, for example. In some examples, the inventory holder  130  and/or the fiducials  175  can include 2D or 3D bar codes, an RFID tag, or other identifiers. 
     As shown in  FIG. 3 , examples of present disclosure can comprise a system  300  for maintaining a predetermined, or threshold, working distance between workers  102  and robots using RFID, or other short-range transmission technologies. In some examples, the robot  120  can be equipped with one or more passive or active RFID tags  305  and the worker  102  can be equipped with an RFID reader  310 . In some examples, the RFID tags  305  on the robot  120  can comprise active RFID tags  305  (i.e., tags with a power source) and can be powered by a battery  320  on the robot  120  (e.g., the battery that powers the robot  120  or a separate battery). The robot  120  can also comprise a processor  315  in communication with the one or more RFID tags  305  to monitor the status of the RFID tags  305 . 
     In this manner, as the robot  120  travels through the warehouse, if the RFID tags  305  are sensed, scanned, or written to, by the worker&#39;s RFID reader  310 , the RFID tag  305  can send a signal to the processor  315  reporting same. The robot  120  can then take evasive action because it senses it is within range of the worker  102 . In other words, because the robot  120  must be within range of the RFID reader  310  for the RFID tag  305  to sense or be written to by the RFID reader  310 , the robot  120  knows it is within the work zone  105 . As mentioned above, the robot  120  can then attempt to reroute, slow down, or stop, as appropriate. 
     Of course, the predetermined, or threshold, distance to be maintained between the worker  102  and the robot  120  can vary widely depending on the size of the warehouse floor  170 , the number of workers  102  and robots  120 , and the level of activity at a particular time on the warehouse floor  170 . If, for example, the warehouse floor  170  is particularly large, maintaining a relatively large work zone  105  (e.g., 25 feet) may be easier to manage and require less system  300  resources, while having little impact on the efficiency of the inventory control system  200 . On smaller warehouse floors  170  or inventory control systems  200  with a large number of robots  120  or very busy warehouse floors  170 , it may be desirable to reduce the size of the work zone (e.g., to 10 feet) to reduce the effect on robots  120  retrieving inventory holders  130  and performing other duties. Of course, many predetermined distances can be chosen to suit many warehouse and traffic configurations. 
     In some examples, the robot  120  can also be equipped with an RFID reader  310 . The RFID reader  310  can be in communication with the processor  315  and can periodically scan for RFID tags  305  that are within range. In this manner, the robot  120  can run self-checks on the RFID tags  305  located on the robot  120  (i.e., its own RFID tags  305 ). In other examples, the RFID tags  305  on the robot  120  can be checked when the robot  120  docks to be recharged (approximately once per hour) or is otherwise maintained. 
     If one or more RFID tags  305  on the robot  120  fails, the robot  120  can report the failure to the central control  115 . The central control  115  can then schedule maintenance for the robot  120  to have the failed RFID tags  305  replaced. Some, or all, of the RFID tags  305  can be replaced when any RFID tags  305  fail. In other words, because RFID tags  305  are inexpensive, it may be prudent to simply replace them all. In other examples, the central control  115  may replace the RFID tags  305  only when a certain number or percentage of RFID tags  305  fail, or when the number of operating RFID tags  305  out of the total number of RFID tags  305  reaches a predetermined level (e.g., based on the desired level of redundancy). 
     Because RFID tags  305  are relatively inexpensive (less than $1), the robot  120  can be equipped with multiple RFID tags  305  to provide redundancy. In this manner, a significant number of RFID tags  305  can fail without posing a concern because a significant number of RFID tags  305  remain operational. In some examples, the processor  315  and/or the central control  115  can monitor the locations of failed RFID tags  305  to ensure that at least one RFID tag  305  in each orientation (e.g., at least one RFID tag  305  on each face of the robot  120 ) is operational. 
     Similarly, as shown in  FIG. 4 , examples of present disclosure can comprise another system  400  for maintaining a predetermined distance between workers  102  and robots using RFID, or other short-range transmission technologies. In some examples, the worker  102  can wear a garment  405  or other wearable device, such as a vest, a hat, or coveralls that includes one or more RFID tags  305 . In some examples, the RFID tags  305  can comprise surface RFID tags  305   a  that can be sewn or adhered, for example, to the surface of the garment  405 . In other examples, the RFID tags  305  can be embedded RFID tags  305   b  that are sewn into, or otherwise incorporated into the garment  405 . Embedded RFID tags  305   b  may improve the aesthetics of the garment  405 , for example, or may simply provide some protection to the RFID tags  305  from abrasion or other damage. In this configuration, the RFID reader  310  on the robot  120  constantly polls for RFID tags  305  at a predetermined interval (e.g., once every second, once every 0.5 seconds) that are within range. When the robot  120  receives a return from a RFID tag  305  associated with a worker  102 , the robot  120  can take evasive action. 
     As before, initially the robot  120  can attempt to deviate from its current route slightly to avoid the worker  102 . If the worker  102  remains in range, however, or the signal gets stronger, for example, the robot  120  can slow down and eventually stop, as necessary. The robot  120  can remain in this mode of operation until the RFID reader  310  on the robot  120  no longer detects any RFID tags  305  associated with the worker  102  (or any worker  102 ) and then return to normal operation. 
     To provide additional redundancy, the robot  120  can also include one or more RFID tags  305 . The RFID reader  310  on the robot  120  can then scan these RFID tags  305  to ensure that the RFID reader  310  is functioning properly. If the RFID reader  310  on the robot  120  fails to detect a predetermined number or percentage of RFID tags  305  on the robot  120 , the robot  120  can alert the central control  115 . The central control  115  can then take the robot  120  offline, enter a maintenance request, or stop the robot  120  immediately, among other things. 
     In some examples, the system  400  can also include an RFID reader  310  that can be worn by the worker  102  to ensure that a sufficient number of the RFID tags  305  in the garment  405  or other wearable device are functioning properly to meet system guidelines. In some examples, the RFID reader  310  can further comprise an indicator  325 . In some examples, the indicator  325  can comprise a transceiver (e.g., a wireless transceiver) to communicate with the central control  115  to report a high number of failed RFID tags  305 . The central control  115  can then provide a message to the worker  102  or a supervisor, for example, that the worker  102  needs a new garment  405  or other wearable device. In other examples, the indicator  325  can comprise a light or an audible alarm to directly alert the worker  102  of the failure. The worker  102  can then retrieve a new garment  405  or other wearable device. 
     Regardless of the configuration (i.e.,  FIG. 3  or  FIG. 4 ), in some examples, the systems  300 ,  400  can also use fiducials  175  in the warehouse floor  170  to establish appropriate work zones  105  based, at least in part, on the range of the RFID readers  310  and tags  305  in the system  300 ,  400 . In other words, in some examples, the fiducials  175  can also include RFID tags  305  to provide location information to RFID readers  310  on the robots  120  and/or workers  102  to establish the range of the RFID readers. When the RFID reader reports to the central control  115 , for example, it can include all of the fiducials  175  it can “see” at any given time. Based on location information associated with the reported fiducials  175 , therefore, the central control  115  can determine the range of a particular RFID reader  310  or the average range of all RFID readers  310  in the system  300 ,  400 , for example. 
     The central control  115  can then use this information, in part, to establish the radius used for the outer work zone  105   a . The ranges of various RFID components  305 ,  310  can vary widely based on, for example, atmospheric conditions, local interference, placement, battery charge levels, and angle of incidence between the reader and tag. In addition to RFID range, the size of work zones  105  can also be based on the number of robots  120  and/or workers  102  on the warehouse floor  170 , the travel speed of the robots  120 , and the size of the warehouse floor  170 , among other things. Because some of these variables can change, in some examples, the system  300 ,  400  can periodically reset work zones  105  based on current conditions. 
     In some examples, if the range of the RFID readers  310  and/or RFID tags  305  falls below a predetermined threshold, on the other hand, the system  300 ,  400  can instruct one or more of the robots  120  to take evasive action. In other words, if the range for one or more RFID components  305 ,  310  in the system  300 ,  400  fall below a predetermined distance (e.g., 10 feet), then an appropriate work zone  105  may not be possible or practical. To prevent unwanted interactions between robots  120  and workers  102 , therefore, the system  300 ,  400  can instruct some or all of the robots  120  to stop or slow down until the range issue can be rectified (e.g., with new batteries). 
     As shown in  FIGS. 5A and 5B , the system  400  can include a vest  505 , hat  510 , coveralls, belts, or other item of clothing (collectively, “garment”) that can be easily worn and can include a plurality of RFID tags  305 . In some examples, as shown, the garment can include RFID tags  305  arranged in multiple orientations and locations to enable the RFID tags  305  on the garment to be detected by RFID readers  310  regardless of their relative positions. In other words, the RFID readers  310  can detect at least one tag  305  regardless of whether the worker  102  is walking away or towards the robot  120  and regardless of the worker&#39;s relative position to the robot (e.g. in front, behind, or to either side of the robot  120 ). 
     Using multiple RFID tags  305  in each garment also increases the redundancy of the system, such that multiple RFID tag  305  failures are required before the effectiveness of the garment is significantly affected. In some examples, the garment can be disposable such that when the number of RFID tag  305  failures reaches a predetermined number or percentage, for example, the worker  102  can simply throw the vest  505  or hat  510  away and retrieve a new one. In some examples, the vest  505  and/or hat  510  can also include reflective tape or other features enabling the garment to serve multiple purposes. 
     In some examples, the garment can comprise RFID tags  305   a  mounted on the surface. In other embodiments, the garment can comprise RFID tags  305   b  embedded (e.g., sewn into) the garment. In still other embodiments, the garment can include multiple types of RFID tags  305   a ,  305   b  such as, for example, passive, active, and semi-active RFID tags  305 . 
     In still other embodiments, as shown in  FIG. 6 , the robot  120  can comprise an onboard imaging device, or camera  605 , and a transceiver  610 . As the robot  120  traverses the warehouse floor  170 , the camera  605  can detect and identify fiducials  175  on the warehouse floor  170 . The robot  120  can communicate with the central control  115  using the transceiver  610  and can provide, for example, location, direction, and speed information. 
     As shown in  FIG. 7 , the fiducials  175  can comprise, for example, stickers or plaques attached to the warehouse floor  170 . In some examples, the fiducials  175  can provide their location in the warehouse (e.g., they can include a coordinate, row and column number, grid number, GPS location, or other information). In some examples, the location of the fiducial  175  can be printed on the fiducial  175  and can be read by the camera  605  on the robot  120 . 
     In other examples, as shown in detail in  FIG. 7 , the fiducials  175  can also comprise additional fiducial data  705 . The fiducial data  705  can comprise, for example, a fiducial identification number (ID)  175   b  (e.g., “fiducial 186143a”). In some examples, the robot  120  can read the fiducial ID  175   b  with the camera  605 , or other suitable device, and can cross-reference the fiducial ID  175   b  with an onboard database to establish its location. In other embodiments, the central control  115  can include a fiducial database and the robot  120  can transmit the fiducial ID  175   b  to the central control  115  and the central control  115  can provide the location of the fiducial  175  to the robot  120 . 
     In other examples, the fiducial data  705  can also comprise, for example, a bar code  175   c  and/or an RFID tag  305 , among other things, that can be read by the robot  120 . In some examples, the bar code  175   c  or RFID tag  305  can have embedded location information to directly provide location information to the robot. In other embodiments, as discussed above, the robot  120  can read or scan the bar code  175   c  or RFID tag  305 , transmit the fiducial data  705  to the central control, and receive location information for the fiducial  175  from the central control  115  to determine the location of the robot  120  on the warehouse floor  170 . 
     Referring back to  FIG. 6 , in some examples, the worker  102  can also be equipped with one or more cameras  605 . In some examples, the worker  102  can wear a camera  605  on a headband, armband, or a necklace. In other examples, the worker  102  can utilize a cart  615  equipped with one or more cameras  605 . The cart  615  can also include one or more carrying trays  630  to enable the worker  102  to, for example, retrieve merchandise from inventory holders  130 , carry tools for maintenance operations, or retrieve trash or inventory items  140  from the warehouse floor  170 . Like the robot  120 , therefore, as the worker  102  moves across the warehouse floor  170 , the camera(s)  605  can identify and report the fiducials  175  proximate the cart  615 . 
     The cart  615  can also comprise a processor  650  and a transceiver  655  to transmit the location of the cart  615  to the central control  115 . In some examples, the processor  650  can perform some or all of the image processing (e.g., parsing) required for the images from the one or more cameras  605  to reduce bandwidth between the cart  615  and the central control  115 . Thus, the central control  115  can receive periodic updates from both the robot  120  and the cart  615  regarding their location and/or including imagery or data related to imagery from the one or more cameras  605  on the robots  120  and cart  615 . This can enable the central control  115  track the locations of the robots  120  and the cart  615  and instruct the robot  120  to take evasive action when necessary. In some cases, the central control  115  can track the robot  120  and the cart  615 , determine when the robot  120  and the cart  615  are on a collision course, and reroute the robot  120  as necessary, for example. 
     It is, of course, possible that the worker  102  could walk away from the cart  615 , rendering their location unknown to the central control  115 . In other words, when the worker  102  walks away from the cart, the cameras  605  on the cart  615  provide the central control  115  with the location of the cart  615 , but not the location of the worker  102 . As a result, in some examples, the system  600  can also comprise a “tether”  625  between the cart  615  and the worker  102 . 
     In some examples, the tether  625  can be a physical tether  625 , similar to those used on boats and jet skis, for example, and can comprise a physical connection between the cart  615  and the worker  102 . The tether  625  can comprise, for example, a lariat or harness around the worker&#39;s wrist, or attached to the worker&#39;s clothes, and then attached to a switch on the cart  615 . In other examples, the tether  625  can comprise an electromechanical connection between the cart  615  and the worker  102 . In some examples, the handle  635  of the cart  615  can comprise one or more electrical contact pads for measuring the temperature, resistance, or capacitance of the handle  635 , for example. In this configuration, the central control  115  can determine that the worker  102  has one or both hands on the handle. 
     In still other embodiments, the tether  625  can comprise what is essentially an “electromagnetic” tether. In other words, using RFID technology, or other short range link, in a similar manner to that discussed above, the tether  625  can determine whether the worker  102  is within a certain distance of the cart  615 . So, for example, as discussed above, the system  600  can include a garment for the worker  102  (e.g., a vest  505 ) comprising one or more RFID tags  305  and the cart  615  can comprise a RFID reader  310 . When the worker  102  is within range of the RFID reader  310 , therefore, the tether  625  can be considered “latched,” and the system  600  can operate normally. 
     If the worker  102  is out of range of the RFID reader  310 , on the other hand, the tether  625  can be considered “unlatched,” send an unlatched signal to the central control  115 , which may require the central control  115  to stop all robots  120  in the warehouse, or in a portion of the warehouse, until the worker  102  can be “found.” In other words, if the tether  625  is unlatched, the location of the worker  102  on the warehouse floor  170  is essentially unknown. If this is the case, the central control  115  cannot accurately route robots  120  around the worker  102  and may have no choice but to shut down all of the robots  120 . In some cases, when the worker  102  returns to the cart  615 , the tether  625  can automatically “relatch,” send a relatch signal to the central control  115 , and normal warehouse operations can resume. In some examples, to prevent a total shutdown, the system  600  can include a secondary location system using, for example, RFID, proximity sensors, infrared cameras, or facial recognition, to locate the worker  102 . In a preferred example, workers  102  can simply be trained to stay within range of their cart  615  at all times. 
     In some examples, a similar system  600  can be used in a work station  150 . In other words, while the worker  102  in a work station  150  is theoretically stationary, in some instances, the worker  102  may need to temporarily leave the bounds of the work station  150  to retrieve a dropped item, for example. Thus, while a “permanent” work zone  105  may exist with respect to the work station  150  (to keep robots  120  from driving through the work station  150 ), if the worker  102  leaves the work station  150 , the robots  120  may need to take additional evasive action. 
     To this end, if the system  600  detects that the worker  102  has left the work station  150 , the system  600  can instruct one or more robots  120  to slow down or stop, for example. In this situation, the tether  625  can comprise, for example, a light curtain, light beam, or proximity sensor to determine when the worker  102  leaves the work station  150 . In some examples, the work station  150  can also comprise an additional RFID reader  310  to provide additional range information to the central control  115 . 
     In some examples, as shown in  FIG. 8 , it may be desirable to have a warehouse system  800  with separate management and interaction systems. In other words, the system  800  can comprise a central control  115  for managing overall routing and work flow and a second server  805  for managing worker  102 /robot  120  interactions. In this manner, a higher level of redundancy can be provided and each system  100 ,  800  can be optimized for the purpose at hand. 
     To this end, in addition to the redundancy provided by the use of multiple RFID tags  305  and RFID readers  310 , as discussed above, in some examples, the work zones  105 , robots  120 , and workers  102  can be monitored and managed by a dedicated interaction server  805 . In this configuration, the central control  115  can handle the routing and scheduling of robots  120  during normal operation—e.g., retrieving inventory holders  130  and delivering them to work stations—while the interaction server  805  can monitor workers  102  and robots  120  solely for the purpose of preventing incidents. In this manner, the operations of the robots  120  and the workers  102  are not in conflict, reliability is increased via redundant communications and control systems, and downtime and maintenance is reduced by reducing the number of robot  120 /worker  102  interactions, among other things. 
     In some examples, the robots  120  can be in communication with the central control  115  via a first, dedicated communications network  810  and in communication with the interaction server  805  via a second, dedicated communications network  815 . Both networks can comprise, for example, wireless LANs (e.g., 802.11x networks), or other suitable networks. In some examples, the interaction server  805  and second network  815  can also be on dedicated internet, power, or network connections, as necessary. 
     In some examples, therefore, the second network  815  can also comprise a network with a higher level of reliability and/or security than the first network  810 . The second network  815  may also be able to override the first network  810 . In other words, if the interaction server  805  determines that an incident between a worker  102  and a robot  120  is imminent, the interaction server  805  can send a command to the robot  120  regardless of whether the robot  120  is currently receiving a command from the central control  115 . In this case, the robot  120  can ignore the command from the central control  115 , take evasive action, if necessary, and then reconnect with the central control  115  when the worker is no longer proximate the robot  120 . 
     As shown in  FIG. 9 , examples of the present disclosure can also comprise a method for using the location information from the fiducials  175  to maintain a predetermined distance between workers and robots. At  905 , a worker enters the floor of the warehouse. As mentioned above, there are several reasons the worker may need or want to enter the warehouse floor. 
     At  910 , the aforementioned camera(s) can begin to provide location information for the worker to the central control or the interaction server. In some examples, the cameras can be located on the worker or on a cart used by the worker and can be activated manually by the worker, or automatically upon entering the warehouse. In some examples, the cart can comprise a motion sensor, for example, which can signal the cameras and transceiver to begin sending location information. In still other examples, the system can include light beams, sensors, infrared sensors, motions sensors, or other means to detect workers in the warehouse. The location information from the worker can be updated periodically at a constant or variable rate, which can change based on the number of workers and robots in motion in the warehouse, the level of activity in the warehouse, and other factors. 
     At  915 , the central control or interaction server can also receive location information from a plurality of robots on the warehouse floor. In the case of the central control, the location information may already be provided automatically as part of the inventory management system. In other cases, the interaction server, for example, may begin polling robots for location information upon receiving location information from the worker or upon receiving a notification that a worker has entered the warehouse (e.g., from a motion sensor in the warehouse). Again, the location information from the robot can be updated periodically at a constant or variable rate, which can change based on the number of workers and robots in motion in the warehouse, the level of activity in the warehouse, and other factors. 
     At  920 , based on the location information from the worker, the system can establish a virtual work zone around the worker. As discussed above, this can comprise a single work zone at a predetermined distance (e.g., 10 feet), or can comprise a multi-level work zone within which the level of evasive action is escalated as the robot gets closer to the worker. At  925 , the system can determine whether the robot is within the work zone based on the location information. If the robot is not within the work zone, the system can simply wait for the next location update from the worker, at  910 , and the robot, at  915 . 
     At  930 , if the robot is within the work zone, on the other hand, the system (i.e., the central control or interaction server) can send a command to take evasive action. In some examples, such as with a single layer work zone, the system can simply command the robot to stop. In other examples, the system can take escalating evasive action—e.g., reroute→slow down→stop—as the robot enters an outer, intermediate, and inner work zone, respectively. In this manner, when a robot and a worker are merely traveling close to one another or at an oblique angle, a slight deviation can enable the robot to miss the worker with little interruption to the system. If the worker and the robot are on a collision course, on the other hand, the robot may need to simply stop and yield the right-of-way to the worker. At  935 , the system can continue to monitor and control the robots, as necessary, until the worker leaves the warehouse floor. 
     In yet other examples, the robot can switch to a different navigation/sensing system. In other words, part of the evasive action can comprise switching over to a sensor with higher resolution, such as a high resolution video camera, to enable more precise robot maneuvering. In other examples, the robot can switch over to a second, more precise navigation system or algorithm. In this manner, rather than simply moving from one fiducial to the next along a travel direction, the robot can utilize additional inputs to enable the robot to accurately reroute, slow, or stop, as necessary. 
     In still other examples, the systems described herein can also be used to provide a work zone  105 ,  1005  around a stationary robotic arm  1020  ( FIGS. 10A and 10B ) or around a worker  102  in proximity to the robotic arm  1020  ( FIG. 10C ). A stationary robotic arm  1020  may be used in the warehouse, for example, to unload boxes, perform maintenance, or handle other tasks that can be completed in a relatively consistent area. In other examples, the robotic arm  1020  may be moveable, but not mobile per se, to perform jobs in a limited number of places, for example, or for longer work intervals. Regardless, while the robotic arm  1020  is not mobile, the robotic arm  1020  nonetheless has a circle or sphere of motion, depending on its capabilities, within which it operates. Direct contact between workers  102  and the robotic arm  1020  can be problematic, reduce efficiency, and increase maintenance for the robotic arm  1020 . 
     To this end, as with the mobile robots  120  discussed above, it can be useful to establish one or more work zones  1005 , which can include circles  105  ( FIG. 10A ) or spheres  1005  ( FIG. 10B ). As before, in some examples, the system  1000  can include an outer work zone  105   a , an intermediate work zone  105   b , and an inner work zone  105   c . This can enable the robotic arm  1020  to take one or more evasive actions as a worker  102  (or robot  120 ) enters the work zone  105 . In some examples, the system  1000  can use multiple spherical work zones  1005   
     In some examples, the system  1000  may slow down the robotic arm  1020  when a worker  102  enters the outer work zone  105   a . The system  1000  may then apply brakes and/or assume a predetermined position when a worker  102  enters the intermediate work zone  105   b . Finally, the system  1000  may remove power from the robotic arm  1020  when a worker  102  enters the inner work zone  105   c . In some examples, the robotic arm  1020  may put objects down on the floor, or other work surface, and wait for the worker  102  to leave the work zone  105  or take other additional actions during this process. 
     As with the systems  300 ,  400 ,  600  discussed above, the system  1000  can comprise one or more RFID readers/tags and/or imaging devices to maintain a work zone  1005  around the robotic arm. In some examples, as shown in  FIG. 10A , the system  1000  can comprise one or more RFID tags  305  disposed on the robotic arm  1020  and an RFID reader  310  on the worker  102  to detect an RFID interaction. In other examples, as shown in  FIG. 10B , the system  1000  can utilize multiple surface mount  305   a , or embedded  305   b , RFID tags on the worker  102  and an RFID reader  1030  on the robotic arm  1020  to detect RFID interactions. In still other examples, the robotic arm  1020  can comprise one or more imaging devices  1025  to provide information related to the position of the robotic arm  1020  and/or work zones  105 ,  1005 . 
     While several possible examples are disclosed above, examples of the present disclosure are not so limited. For instance, while a system for maintaining a predetermined distance between robots and workers in an automated warehouse is disclosed, the system could also be used anytime humans and automated machines or fixed robotic systems interact. In addition, the location and configuration used for various features of examples of the present disclosure such as, for example, the location and configuration of RFID tags and readers, the types of cameras or other sensors used, and the layout of the warehouse can be varied according to a particular warehouse, location, or robot that requires a slight variation due to, for example, size or power constraints, the type of robot required, or regulations related to transmission interference, for example. Such changes are intended to be embraced within the scope of this disclosure. 
     The specific configurations, choice of materials, and the size and shape of various elements can be varied according to particular design specifications or constraints requiring a device, system, or method constructed according to the principles of this disclosure. Such changes are intended to be embraced within the scope of this disclosure. The presently disclosed examples, therefore, are considered in all respects to be illustrative and not restrictive. The scope of the disclosure is indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.