HK1251663B

HK1251663B - Systems and methods for locating tags within a space

Info

Publication number: HK1251663B
Application number: HK18111114.8A
Authority: HK
Inventors: S‧J‧瑞纳斯福德; D‧S‧盖斯莱特
Original assignee: Sensormatic Electronics, LLC
Priority date: 2015-06-16
Filing date: 2016-06-16
Publication date: 2023-01-20

Description

System and method for locating tags in space

Technical Field

This document relates generally to wireless-based systems. More particularly, this document relates to systems and methods for locating tags within a space.

Background

Existing beacon technology provides navigation and location reference points to assist a device in determining its own position or location. Based on infrared ("IR")Wi-Fi access points, Global positioning System ("GPS") satellites, quick response ("QR") codes, ultra Wide band ("UWB") time of flight, and beacons of magnetic field contour maps all used asA known reference point to inform the device (e.g., mobile phone) of its own location. Systems that rely little or no on GPS to derive fine grid positions are commonly referred to as location-based services ("LBS") or indoor positioning systems ("IPS"). These systems are used to infer the location of other objects known to be nearby. For example, if the device is determined to be at location x, then an object known to be within y units of distance of the located device is inferred to be within y units of location x. These systems require interaction with the device being located and are not suitable for integration with radio frequency identification ("RFID") tags.

Triangulation techniques are used to determine the location of an object based on information collected by viewing the object from one or more known locations. Cellular triangulation, Wi-Fi triangulation, and various land survey techniques all gather information from one or more reference locations (such as direction to an object and/or signal strength from an object) and derive an approximation of the location of that object. This requires having multiple viewpoints with known positions. The larger the area of the unknown object, the larger the number of viewpoints needed to achieve a given accuracy.

Passive RFID is widely used for inventory assessment, providing RFID readers with information about the presence of RFID tags, but the location of RFID tags in a broad direction and signal strength information (from which an approximate location can be inferred) is little information. RFID tags are often read correctly, but the derived direction and signal strength information is corrupted due to multipath and antenna side lobe distortion. The wide beam width of the antenna of the RFID reader limits the orientation accuracy. The orientation of the antenna of the RFID tag relative to the antenna of the RFID reader has the same effect on the received signal strength indicator ("RSSI") as the distance, i.e., a near RFID tag that is turned sideways towards the RFID reader may have a lower return signal than a far RFID tag that has a favorable orientation towards the RFID reader. This possibility of distance inversion limits the value of RSSI that determines the actual location of an RFID tag based on a single tag read.

Arrays of antennas with RFID readers provide finer resolution, but are less scalable, expensive, difficult to deploy, and difficult to change. The use of beam-steered antennas (such as Impinj X-Array and sensory IDSM-1000 and IDA-3100) can be configured to provide the relative angle of the RFID tag with respect to the antenna or RFID tag location/position at the point of blockage.

Disclosure of Invention

The present disclosure relates to implementing systems and methods for determining the location of objects within a space. The method comprises the following steps: generating, by an attitude and heading reference ("AHR") device, inertial reference measurement data useful for determining a location of an RFID reader within a space at each of a plurality of RFID tag read times; performing, by the RFID reader, one or more reads of a plurality of RFID inventory tags; processing inertial reference measurement data to determine at least an RFID reader position estimate each time the RFID inventory tag is read; and defining a plurality of cones (cone) associated with each of the plurality of RFID inventory tags. Each cone has (a) a vertex that is an RFID reader position estimate at a respective one of the plurality of RFID tag read times, (b) an angle that is inversely proportional to a signal strength of a signal received from a respective one of the plurality of RFID inventory tags, and (c) an orientation that is the same as an orientation of an RFID reader antenna at a respective one of the plurality of RFID tag read times. The cone is then mapped to the model. The model may include, but is not limited to, a physical model, a mathematical model, or a graphical model. The model is analyzed to identify at least one set of cones that overlap each other and are associated with reads for respective ones of the plurality of RFID inventory tags. A location estimate is then derived for the corresponding inventory tag based on the intersection of the previously identified cones in the set of cones.

In some scenarios, the method further involves: performing, by the RFID reader, one or more reads of at least one RFID locator tag; and correcting errors in the RFID reader position estimate using the known locations of the RFID locator tags. Cones with the following features can be discarded: (a) does not overlap in the model with at least one other cone, (b) has an angle greater than a threshold, or (c) does not overlap with the cone associated with the strongest received signal strength.

In those or other scenarios, the position estimate derived for the respective inventory tag is refined using at least one predefined rule, wherein the rule defines a valid location of an object to which the respective inventory tag is attached. Additionally or alternatively, the RFID inventory tag is highly readable only from a preset and limited range of RFID reader locations, and has a weak or no response outside that limited range.

Drawings

Embodiments will be described with reference to the following drawings, wherein like numbers represent like items throughout the views, and wherein:

FIG. 1 is a schematic diagram of an exemplary system useful for understanding the present invention.

FIG. 2 is a block diagram of an exemplary architecture for a handheld reader.

FIG. 3 is a block diagram of an example architecture for a server.

FIG. 4 is a schematic diagram of an exemplary cone.

FIG. 5 is a schematic diagram illustrating the intersection of three cones narrowing the possible locations of RFID inventory tags.

Fig. 6A-6B (collectively referred to herein as "fig. 6") provide a flow chart of an exemplary method for determining the location and/or position of RFID inventory tags within an inventory space.

Detailed Description

It will be readily understood that the components of the embodiments as generally described and illustrated in the figures herein could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the disclosure, but is merely representative of various embodiments. While various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention are or should be in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean: the particular features, advantages, or characteristics described in connection with the embodiments are included in at least one embodiment of the invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. As used herein, the term "including" means "including, but not limited to".

The present disclosure relates to systems and methods for locating objects or items (e.g., RFID inventory tags) within a facility. These methods generally involve determining timely and accurate locations and locations of inventory in a facility while minimizing investment in new equipment, installation costs, and impact on the display of goods by commercial owners. As used herein, the term "location" refers to a specific coordinate (such as inventory space expressed as x, y, and z coordinates) within a reference system. As used herein, the term "location" refers to a specific named location (e.g., to an entire shelf or pole, or to a station, space, or room). Implementation of the novel method does not require installation of cables, maintenance of powered devices, a strict path or pattern that an operator must follow when using a handheld reader, and/or additional wireless locator devices that must be scanned by the handheld reader to determine the RFID inventory tag location within the facility.

Thus, the system includes an RFID locator tag, an AHR device attached to a handheld reader, and a scalable computing platform ("SCP"). The RFID locator tags define a fixed reference system in the facility for determining the location of RFID inventory tags in the facility. Thus, the RFID locator tag is strategically located at a fixed location within the facility. For example, RFID locator tags may be placed on each end of the display equipment (e.g., a shelf). The SCP converts the raw data into a database of locations and localities associated with each RFID inventory tag read by the handheld reader.

Notably, in some scenarios, the RFID locator tag includes an RFID inventory tag attached to the inventory piece and having a previously determined location with a value of some accuracy. These RFID inventory tags may move at any time, but are useful in the context of every inventory sweep (sweep).

The AHR device provides an inertial reference means for determining the orientation and position of the handheld reader antenna in three-dimensional space. In this regard, AHR generates measurements of linear acceleration, rotation rate, and local magnetic field. The AHR device can also derive its absolute orientation relative to a fixed reference frame (e.g., an earth-based system at northeast altitude). The absolute position can be derived from the measurement data, but drift can be severe because it is difficult to separate the earth's gravitational acceleration from the relatively small acceleration of the AHR device's movement. It is common for AHR devices to accumulate an error in estimated position of one hundred (100) feet of position error in ten (10) seconds. The position error comes from a double integration of the error in the acceleration data, so the position error grows exponentially with time. The position error can be limited if the correction can be made at relatively short intervals. There are other ways to correct the initial position estimate, including gait measurements. Additional corrections are presented below based on the reference RFID location tag.

The processing of the data uses the known location to reference the observations of the RFID locator tags to correct the initial location estimate generated by the SCP. The corrected location estimate is used to determine the location and/or position of other RFID inventory tags read during the same inventory scan. This location and/or position information is useful for many purposes. For example, location information may be used to fine tune the positioning of items during the inventory process. For warehouses, retailers, hospitals, and other applications where tracking of items or people is desirable, knowing the exact location of an item within a facility would be a huge feature. For example, employee and/or equipment tracking may be accomplished by (a) employing a wearable or attached RFID reader and (b) using proximity to RFID locator tags and RFID inventory tags as a proxy for the employee's or equipment's actual location.

Exemplary System

Referring now to FIG. 1, a schematic diagram of an exemplary system 100 useful for understanding the present invention is provided. The present invention is described herein with respect to a retail store environment. The invention is not limited in this respect and may be used in other environments. For example, the present invention may be used in distribution centers, factories, and other commercial environments. It is noted that the present invention may be used in any environment where it is desirable to locate and/or track objects and/or items.

The system 100 is generally configured to use RFID and sensor technology to allow improved object location within a facility. As shown in FIG. 1, system 100 includes a retail store facility ("RSF")128 in which the display equipment 102 is disposed₁-102_M. The display equipment is for displaying objects (or items) 110 to customers of the retail store₁-110_N、116₁-116_NAnd is provided. The display equipment may include, but is not limited to, shelves of RSF 128, item display cases, promotional displays, fixtures, and/or equipment securing areas. The RSF may also include emergency equipment (not shown), a checkout counter, and an EAS system (not shown). Emergency equipment, checkout counters and EAS systems are well known in the art and will not be described herein.

RFID locator tag 106₁，...，106_XStrategically located within the RSF 128 and oriented for easy reading. In some scenarios, the RFID locator tag is deployed on the display equipment 102 in a manner that prevents it from being inadvertently moved₁-102_MAbove (as shown in fig. 1). Additionally or alternatively, the RFID location tag is deployed on emergency equipment, checkout counters, walls, ceilings, and/or EAS system equipment (e.g., pedestals near the RSF and entrance/exit). RFID locator tags are well known in the art and therefore will not be described herein. It should still be appreciated that RFID locator tags are generally configured to facilitate periodic or continuous determination of the location of objects within the RSF 128.

Each RFID locator tag 106₁，...，106_XWith a unique locator ID associated therewith. When handheld reader 120 reads an RFID locator tag, it obtains a unique locator ID therefrom. The unique locator ID is then used to obtain information specifying the known location of the RFID locator tag. In this regard, it should be understood that information specifying a known location of an RFID locator tag in three-dimensional space is stored in the data store 126, may be encoded in a unique locator ID, or may be stored in another location in the tag memory. This information may be stored in the data store 126 using the server 124 and/or the memory of the handheld reader. The server 124 will be described in more detail below with respect to fig. 3. It should still be understood that the server 124 and/or handheld reader are configured to perform the following operations: determining a location estimate of a handheld reader within a facility at a plurality of RFID inventory tag read times; and use these determined location estimates to derive in-facility RFID inventory tags 112₁，...，112_N、118₁，...，118_NThe location and/or position of. The known location of the RFID locator tag is used to correct for errors in the position estimate determined for the handheld reader.

RFID locator tag 106₁，...，106_XIt may also have a known angular electromagnetic response pattern for the handheld reader 120. Additional information may also be pre-encoded at each RFID locator tag 106₁，...，106_X. The additional information may include, but is not limited to, the indicia that the RFID tag is an RFID locator tag, the location of the RFID locator tag within the inventory space, and/or the location of the RFID locator tag within the inventory space. As used herein, the term "inventory space" refers to the final frame of reference of RFID inventory tag location information. The inventory space may have limits or constraints that define the range of RFID inventory tags stored in the inventory (e.g., walls of a store exclude RFID inventory tags in adjacent stores).

RFID inventory tags and RFID locator tags are described herein as including single technology tags that are only RFID enabled. The invention is not limited in this respect. The RFID inventory tags and locator tags may alternatively or additionally include dual technology tags with EAS and RFID capabilities. Further, the RFID inventory tags and RFID locator tags may be passive or active devices.

When the handheld reader 120 scans the RSF 128, it records certain information in internal memory (not shown in fig. 1) and/or the external data store 126 along with a timestamp. Such information includes, but is not limited to, data from each RFID inventory tag read, parameters controlling the RFID inventory tag read, measurements related to the read process, and AHR device measurement data (also referred to herein as "inertial reference measurement data"). The AHR measurement data is obtained by an AHR device 150 attached to the handheld reader 120. The AHR device 150 is attached to the handheld reader 120 such that it scans or reads on tagsThere is no relative movement between the antenna of the handheld reader (not shown in figure 1) and the AHR device 150 during the reading operation. AHR measurement data includes acceleration measurement data, rotation measurement data, and magnetic field measurement data. AHR measurement data is measured from each RFID inventory tag 112₁，...，112_N、118₁，...，118_NAnd/or RFID locator tag 106₁，...，106_XCollected at each point of the read data. During inventory scanning, each RFID tag 106 is performed and recorded in the inventory space₁，...，106_X、112₁，...，112_N、118₁，...，118_NOne or more observations of (a). Due to the sweeping nature of scanning with the handheld reader 120, each observation is made from a unique location and orientation of the handheld reader 120.

When the inventory scan is complete, the collected data is processed to derive each RFID inventory tag 112 in the inventory space₁，...，112_N、118₁，...，118_NThe location and the position of the device. The observed data from the AHR device is used to derive an initial estimate of the path (sequence of positions) and orientation of the handheld reader 120. The initial or corrected location of the handheld reader 120 may then be interpolated to know it is at the RFID inventory tag 112₁，...，112_N、118₁，...，118_NThe position and orientation at each reading. The RFID inventory tag 112 is then₁，...，112_N、118₁，...，118_NMay be combined with the RFID inventory tag 112 based on the estimated location of the handheld reader 120 at each reading₁，...，112_N、118₁，...，118_NThe recorded data (e.g., time, decoded tag data, received signal strength indicator ("RSSI"), RF power, RF frequency, antenna polarity, beam width, orientation, location of the handheld reader, location of the antenna of the handheld reader is used to determine an estimate of the location of the RFID tag).

The processing of the data may be iterative and adaptive. In an iterative process, a model of the RFID tag and handheld reader locations is constructed from the observed data for the first time during the scan through the inventory space. Subsequent scans use this model as a starting point to improve the estimation of all locations of the minimum energy or entropy model using simulated annealing, physical modeling, or other iterative system solvers.

Referring now to fig. 2, a detailed block diagram of an exemplary architecture for a handheld reader 200 is provided. The handheld reader 120 of fig. 1 is the same as or similar to the handheld reader 200. Thus, the discussion of handheld reader 200 is sufficient for understanding handheld reader 120.

Handheld reader 200 may include more or fewer components than shown in fig. 2. The components shown, however, are sufficient to disclose an illustrative embodiment for practicing the invention. Some or all of the components of handheld reader 200 may be implemented in hardware, software, and/or a combination of hardware and software. The hardware includes, but is not limited to, one or more electronic circuits. The electronic circuit may include passive components (e.g., capacitors and resistors) and active components (e.g., processors) arranged and/or programmed to implement the methods disclosed herein.

The hardware architecture of fig. 2 represents an embodiment of a representative handheld reader 200 configured to facilitate improved object positioning within an RSF (e.g., RSF 128 of fig. 1). In this regard, the handheld reader 200 includes a mechanism for allowing communication with external devices (e.g., the RFID locator tag 106 of FIG. 1) via RF technology₁，...，106_XAnd/or RFID inventory tags 112₁，...，112_N、118₁，...，118_N) An RF-enabled device 250 that exchanges data. The components 204 and 216 shown in fig. 2 may be collectively referred to herein as RF-enabled devices 250 and include a power source 212 (e.g., a battery).

The RF-enabled device 250 includes an antenna 202 for allowing data to be exchanged with external devices via RF technology (e.g., RFID technology or other RF-based technology). The external device may include the RFID locator tag 106 of FIG. 1₁，...，106_XAnd/or RFID inventory tags 112₁，...，112_N、118₁，...，118_N. In this case, the antenna 202 is configured to transmit an RF carrier signal (e.g., an interrogation signal) to the listed external devices and/or transmit a data response signal (e.g., an authentication reply signal) generated by the RF-enabled device 250. In this regard, RF-enabled device 250 includes RF transceiver 208. RFID transceivers are well known in the art and will not be described herein. However, it should be understood that the RF transceiver 208 receives an RF signal including information from a transmitting device and forwards it to the logic controller 210 to extract information therefrom.

Notably, the memory 204 can be volatile memory and/or non-volatile memory. For example, memory 204 may include, but is not limited to, random access memory ("RAM"), dynamic random access memory ("DRAM"), static random access memory ("SRAM"), read only memory ("ROM"), and/or flash memory. Memory 204 may also include unsecure memory and/or secure memory. As used herein, the phrase "unsecure memory" refers to memory configured to store data in plain text form. As used herein, the phrase "secure memory" refers to memory configured to store data in encrypted form and/or memory having or disposed in a secure or tamper-resistant enclosure.

Instructions 222 are stored in memory for execution by RF-enabled device 250 and to cause RF-enabled device 250 to perform any one or more of the methods of the present disclosure. The instructions 222 are generally operable to facilitate determining where RFID inventory tags are located within a facility. Other functions of the RF-enabled device 250 will become apparent as the discussion proceeds.

AHR device 280 is attached to handheld reader 200. The AHR device 150 of fig. 1 may be the same as or similar to the AHR device 280. Thus, the discussion of the AHR device 208 is sufficient for understanding the AHR device 150. AHR device 280 includes one or more quantitative sensors 282 that have phenomena such as magnetic field, acceleration, and rotation. The AHR device 280 is configured to process the sensor data to obtain a position and orientation within a reference frame. As used herein, the term "reference frame" refers to any consistent coordinate system that may be transformed to another coordinate system.

The extracted information may be used to determine an RFID inventory tag (e.g., RFID inventory tag 112 of FIG. 1) within a facility (e.g., RSF 128 of FIG. 1)₁，...，112_N、118₁，...，118_N) The location of (a). In this regard, the extracted information includes the RFID data from the RF-enabled device 250 as well as the AHR and clock information in the handheld reader 200. Thus, the logic controller 210 may store the extracted information in the memory 204 and execute an algorithm using the extracted information. For example, the logic controller 210 may perform correlating RFID inventory tag reads with RFID locator tag reads to determine the location of RFID inventory tags within a facility.

Output device 216 generally provides a means for outputting information to a user of handheld reader 200. For example, the output device 216 includes a display on which graphics are displayed that directs the user to a location where better scanning is desired or where a particular item is located. Also, the map may be presented to the user via a display. The map may include a three-dimensional map showing estimated locations of RFID inventory tags within the virtual facility, and/or a heat map overlaid on the image inventory space showing uncertainty in the RFID inventory tag locations. Additionally or alternatively, the output device 216 includes means for revealing well scanned areas of the facility, poorly scanned areas of the facility, and/or missing scanned areas of the facility. Employee efficiency in a scan may be derived from the quality of the scanned data relative to the aggregated data scanned by all employees.

Referring now to FIG. 3, a detailed block diagram of an exemplary architecture for a server 300 is provided. The server 124 of fig. 1 is the same as or substantially similar to the server 300. Thus, the following discussion of the server 300 is sufficient for understanding the server 124.

It is noted that the server 300 may include more or fewer components than shown in fig. 3. The components shown, however, are sufficient to disclose an illustrative embodiment for practicing the invention. Hardware architecture representation of FIG. 3One embodiment of a server configured to facilitate (a) determining a location and a position of an RFID inventory tag within a facility and/or (b) providing a display showing RFID inventory tags (e.g., RFID inventory tags 112 of FIG. 1) within an RSF (e.g., RSF 128 of FIG. 1)₁，...，112_N、118₁，...，118_N) A three-dimensional map of the location of (a). Accordingly, the server 300 of fig. 3 implements at least a portion of a method for providing such RIFD inventory tag locations and locations according to an embodiment of the present invention.

Some or all of the components of the server 300 may be implemented as hardware, software, and/or a combination of hardware and software. The hardware includes, but is not limited to, one or more electronic circuits. The electronic circuit may include, but is not limited to, passive components (e.g., resistors and capacitors) and/or active components (e.g., amplifiers and/or microprocessors). The passive and/or active components may be adapted, arranged and/or programmed to perform one or more of the methods, processes or functions described herein.

As shown in FIG. 3, server 300 includes a user interface 302, a central processing unit ("CPU") 306, a system bus 310, a memory 312 connected to and accessible by other portions of server 300 via system bus 310, and a hardware entity 314 connected to system bus 310. The user interface may include input devices (e.g., keypad 350) and output devices (e.g., speaker 352, display 354, and/or light emitting diodes 356) that facilitate user-software interaction for controlling the operation of server 300.

At least some of the hardware entities 314 perform actions that involve accessing and using the memory 312, where the memory 312 may be random access memory ("RAM"), a disk drive, and/or a compact disk read-only memory ("CD-ROM"). The hardware entities 314 may include a disk drive unit 316, the disk drive unit 316 including a computer-readable storage medium 318 having stored thereon one or more sets of instructions 320 (e.g., software code) configured to implement one or more of the methods, processes, or functions described herein. The instructions 320 may also reside, completely or at least partially, within the memory 312 and/or within the CPU 306 during execution thereof by the server 300. The memory 312 and the CPU 306 may also constitute machine-readable media. As used herein, the term "machine-readable medium" refers to a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions 320. The term "machine-readable medium" as used herein also refers to any medium that is capable of storing, encoding or carrying the set of instructions 320 for execution by the server 300 and that cause the server 300 to perform any one or more of the methodologies of the present disclosure.

In some embodiments of the invention, hardware entity 314 comprises electronic circuitry (e.g., a processor) programmed to facilitate (a) determining the location and location of RFID inventory tags within a facility and/or (b) providing a three-dimensional map showing the location and/or location of RFID inventory tags within a facility. In this regard, it should be understood that the electronic circuitry may access and run a location/position determination application 324 installed on the server 300. The software application 324 is generally operable to facilitate: determination of the location and/or position of RFID inventory tags within a facility; and mapping of RFID inventory tag locations in the virtual three dimensional space. Other functions of the software application 324 will become apparent as the discussion proceeds.

Server 300 also includes a data processing and modeling engine ("DPME") 326. DPME is generally configured to determine: an estimate of the location and position of the handheld reader; and an estimate of the location and position of the RFID inventory tags. In this regard, DPME performs the following operations: estimating a process and a location of a handheld reader (e.g., handheld reader 200 of FIG. 2) and an AHRD device (e.g., AHRD device 280 of FIG. 2) at each read time defined by the timestamp; defining a cone using data for each read of the RFID inventory tag; placing the cone in a three-dimensional physical, graphical or mathematical model; and determining an estimate of the location and position of the RFID inventory tag based on the overlapping cones associated therewith. Physical, graphical and mathematical modeling are well known in the art and therefore will not be described in detail herein.

The progress, location and location of the handheld reader and the AHRD device (e.g., AHRD device 280 of figure 2) are derived using inertial navigation and the known locations of the RFID locator tags read by the handheld reader. Inertial navigation is well known in the art and therefore will not be described in detail herein. In some scenarios, the position and orientation of the handheld reader is constrained by the actual maximum translation and rotation speed. These constraints may be defined as additional relationships between entities in a physical or graphical model. For example, constraints may include hard stops or non-linear spring forcing when mapping to a physical model. Notably, any refinement in the precision or accuracy of the location and/or position estimates of RFID inventory tags may be used to refine the location and/or position of the handheld reader.

The relative signal strengths of the co-located horizontally polarized RFID locator tag and the vertically polarized RFID locator tag are used as an indication of the scrolling of the handheld reader. This information may be used as an additional input to an estimation system, such as a kalman filter, for example. Compensation of the relative signal strength read by the handheld reader from each RFID locator tag under ideal conditions may be required.

Referring now to FIG. 4, a schematic diagram is provided that is useful for understanding how RFID inventory tag locations and locations are determined by a system (e.g., the system 100 of FIG. 1). In an RFID inventory tag (e.g., RFID inventory tag 112 of FIG. 1)₁，...，112_N、118₁，...，118_N) The data recorded at each reading of (a) is used to define the cone 400. Presumably, RFID inventory tags may be found within the boundaries of the cone 400. The apex 402 of the cone 400 is the estimated location of the handheld reader (e.g., handheld reader 120 of fig. 1) when an RFID inventory tag is read. The axis 404 of the cone 400 coincides with the estimated orientation of the handheld reader when reading RFID inventory tags (in line with). The angle 406 of the cone 400 is defined to be inversely proportional to the RSSI recorded for the RFID inventory tag at that read with possible modifications to the RFID reader antenna directional gain and/or tag directional sensitivity. When the RSSI is high, the angle 406 is small, and when the RSSI is low, the angle 406 is large. RSSI is affected by several factors: distance between the RFID reader and the tag; RFID readerObtaining the transmitting power of the device; and the orientation of the tag toward the RFID reader antenna. For example, nearby tags that turn to the side of the RFID reader may respond with a lower RSSI than more distant tags aligned with the broadside of the RFID reader. Colloquially, a wide-side tag presents a larger area to the RFID reader antenna.

The set of RFID inventory tag reads is ranked by the RSSI associated with it. The RFID inventory tag read with the highest RSSI maps to a cone with a narrow angle (essentially defining the line on which the RFID inventory tag is expected to be located). The data from the additional RFID inventory tag reads defines a cone whose width is inversely proportional to the RSSI associated with the strongest signal for that RFID inventory tag. Data for RFID inventory tag reads that are substantially lower than the strongest RSSI values for other reads of the same RFID inventory tag may be discarded.

Data from each read of the same RFID inventory tag results in multiple cones 500, 502, 504 with different attributes. Each of the cones 500-504 may contain the location of the RFID inventory tag. The intersection of these cones 500-504 narrows the possible locations for RFID inventory tags, as shown in FIG. 5. The estimated location of the RFID inventory tag is determined to be within the intersection area 506.

All cones of estimated locations for each RFID inventory tag are linked to each other by segments of the estimated path and orientation of the handheld reader (e.g., handheld reader 120 of fig. 1). Certain points of the system (e.g., system 100 of fig. 1) are well known, including the location of each RFID locator tag, and are considered fixed. Other fixed locations may be the starting point of the handheld reader. Other locations defined by the system are constrained, in part, to the inventory space reference frame, or to another point within a distance or angular range.

In some scenarios, a minimum number of cones are used to determine the location of the RFID locator tag, regardless of how different the angle of intersection is. In other scenarios, only cones with an angle of intersection approaching ninety degrees (90 °) are used to determine the location of the RFID locator tag. Thus, cones with small axis intersection angles with the cone with the strongest RSSI and cones that do not intersect are ignored or rejected, i.e., not used to determine the location of the RFID locator tag.

Refinement of the width of the cone of possible locations determined by one read of an RFID inventory tag may be based on the intersection of that cone with the cone of another read of the same RFID inventory tag. For each RFID inventory tag, the farther it intersects with the estimate of the handheld reader location, the narrower the estimated cone of the location may be. The width of the cone may be adjusted based on the difference between low RSSI due to distance from the handheld reader's antenna and low RSSI due to off-axis reading from the handheld reader antenna.

As noted above, the estimated location of the RFID inventory tag is then mapped to a physical model, a graphical model, and/or a mathematical model. Each of these types of models is well known in the art and therefore will not be described in detail herein. Still, some examples are provided below for physical model scenarios and graphical model scenarios.

Physical modeling method

Mapping the most likely inventory location problem to a constrained physical body problem allows for the extraction of location information from the physical model solution. The result after all reads are mapped is an articulated rigid body model that will start with various tensile elements and will be reduced through iteration to a configuration with the least energy (as defined by the stop and spring constants). The location of each tag may then be available from the physical model.

To use the physical model (these are virtual mappings of RFID inventory tag read parameters to the physical model), the following operations are implemented.

Each view of the RFID inventory tag is modeled as a body with the position and orientation of the handheld reader antenna when read in the reference frame. The watchers are linked together according to a time-ordered sequence of reads, and constrained in position and orientation according to estimates of position and orientation between successive reads.

RFID locator tags have known locations and have additional constraints because they are fixed within the reference frame, i.e., their locations are not adjusted during optimization. The anchoring effect of its fixed position is one of the biggest impacts on the final solution.

Each reading of the RFID inventory tag has data defining a link between the location and orientation of the handheld reader's antenna and the tag body at that reading.

One link is a sliding link with a constraint fixed at one end of the sliding range at the handheld reader antenna and another constraint at the maximum reasonable reading range (e.g., ten meters). The possible locations of the RFID inventory tag for that reading are defined as the end of the slider opposite the end of the reader antenna.

In series with the sliding link, the second constraint defined by the tag reading is a ball-and-socket joint (ball-joint) located at the body of the handheld reader. The ball and socket constraint may be a combination of hard angle limits and a spring constant forced to a read centerline defined by the orientation of the handheld reader body. The limits and spring constants are proportional to the RSSI values read, the antenna beam width of the handheld reader, and other factors. This allows the sliding link to rotate around the central axis of the antenna of the handheld reader, thereby defining the cone of possible positions mentioned above.

Each RFID inventory tag is modeled as a principal, constraining the link to the physical embodiment of each read of the RFID inventory tag. The position of each tag body is constrained by each reading of that RFID inventory tag by defining a slip joint for each reading, with a spring constant forced to a minimum length, and a slider attached to the body of the tag and the other end attached to the end of each slider defined by each reading of that RFID inventory tag. The spring constant force may be controlled by RSSI and other estimates of the quality of a particular read.

Each location of the handheld reader is constrained by the initial measurement of the AHRS and the known location of the RFID locator tag. The observation of the RFID locator tag provides a strong constraint on the adjustment of the initial observation path. The handheld reader is further constrained by docking at a fixed location to reference the AHRS, by a portal with known coordinates, reading one or more RFID inventory tags or locator tags from a known location and orientation, and by lanes and corridors, etc.

In some scenarios, a physics modeling engine is used to iteratively adjust the relevant RFID inventory tag locations to the most likely solution. To model convergence, the following parameters are defined to minimize oscillation: quality; a spring constant; and viscosity/friction.

Graphic modeling method

In some scenarios, the most likely RFID inventory tag locations are mapped to a graphical model of the inventory space. The uncertainty in the location of the RFID inventory tags is iteratively reduced according to an optimization algorithm. The optimization algorithm may include, but is not limited to, a simulated annealing ("SA") heuristic algorithm. SA heuristics are well known in the art and therefore will not be described herein. It should still be understood that the SA heuristic defines constraints as mathematical relationships. The system is optimized for a minimum value defined by a constraint, where the minimum value indicates a best fit of the RFID inventory tag location to the collected data.

Further, the newly estimated location of the RFID inventory tag or handheld reader may be constrained by using its previously determined location. The forcing strength may decay linearly or exponentially with the distance between the previous location and the new estimated location.

Additional rules

In all modeling scenarios, additional rules may be used to refine the location estimate for RFID inventory tags. These rules may be used to refine the location and position estimates of the RFID inventory tags determined in the modeling process. Alternatively or additionally, rules may be used during the modeling process to determine location and position estimates for RFID inventory tags. The rules may limit the effective location of a particular object (to which the RFID inventory tag is attached) based on the contents of the inventory storage system. For example, an object (e.g., an article of clothing) is typically hung from a pole or on a shelf. However, the determined location and/or position for the corresponding RFID inventory tag indicates that the object is floating in the middle of a known aisle. In this case, rules are used to refine the initial and/or final estimates of the location and/or position of the RFID inventory tag by removing invalid locations and positions from the location estimate, i.e., by removing location and/or position information indicating that the object is floating in the middle of a known aisle. The location of the RFID inventory tag must eventually be resolved to a valid location or rejected. These rules improve the rejection of multi-path reads, antenna side lobe reads, and/or RFID inventory tag movement and reading in both locations.

The rules also provide a means to place RFID inventory tags in the reference frame near physical constraints. This allows for more accurate location of RFID inventory tags. For example, the rules ensure that RFID inventory tags are placed as close as possible to the hook because the hook is placed on a pole with a fixed position within the reference frame.

In some scenarios, the processing of tag read data is done in separate steps to improve convergence. For example, the first step corrects the path and orientation of the handheld reader using only tag read data for the RFID locator tags. Successive steps estimate the location and/or position of the RFID inventory tags in the group. And finally, checking or fine-tuning the result.

The processing of the tag read data to determine the location and/or position of the RFID inventory tags may be performed as it is received. Deriving the location of the RFID inventory tag requires one or more reads of that RFID inventory tag coupled with one or more reads of the RFID locator tag. Once the minimum information is available for a single RFID inventory tag, an estimate of its location may be made and stored. When performing additional scans, the estimated locations of some RFID inventory tags may be improved, and a first estimated location of additional RFID inventory tags may be derived.

Calibration techniques

In some scenarios, calibration techniques are employed to ensure that only a relatively narrow cone is generated for certain location tags. The calibration technique develops a highly oriented set of reference tags. Let us consider a situation where multiple RFID location tags are present in close proximity. Each RFID location tag has a unique ID. Regardless of the beam width of the handheld reader antenna, each RFID location tag is readable only under a narrow beam width. In addition to the known location of the RFID locator tag, this concept also correlates known angular patterns for calibration and/or correction of other tag data. The separation between sectors need only be sufficient to clearly distinguish between stronger/weaker tag responses. Because these RFID locator tags are closely spaced, the RSSI effectively distinguishes the most direct path tags.

In some cases, vertical dipole RFID inventory tags may be arranged about a vertical axis, with a field absorbing splitter dividing the field of view of each RFID inventory tag. Horizontal RFID inventory tags may be similarly arranged about a horizontal axis. In other cases, limited directivity is found in crossed dipoles. Each dipole terminates in a separate RFID tag integrated circuit ("IC"). The RFID inventory and locator tag are aligned as a chord along the circumference of a circle. These RFID inventory tags and locator tags will have RSSI that varies with distance from the handheld reader. The center of the circle may be derived from the combined tag response. In still other cases, one or more labels having a flat print orientation (e.g., Yagi) may be secured to the non-conductive surface.

Although the present invention has been described above with respect to a handheld reader carried by a person through a facility, the present invention is not limited in this respect. For example, additionally or alternatively, an automatic and autonomous scrolling ("AAR") platform is employed to carry the RFID reader through the facility. The AAR platform follows a prescribed path and uses a simple mechanism to sweep the RFID reader. The translating portion of the inertial reference system may be partially replaced with an odometer-type motion sensing system mounted on the AAR platform, with an absolute angle reference built into the sweeping mechanism, with reference to the ground-referenced platform. This AAR platform based system may only operate when the store is closed. Larger batteries and longer and more thorough scans are possible, the consistency of which is incomparable for human operators. Antenna gain and pattern can be optimized to microscopic positioning.

Exemplary methods for determining the location and/or position of RFID inventory tags in a facility

Referring now to fig. 6A-6B, a flow diagram of an exemplary method 600 for determining the location and/or position of RFID inventory tags within an inventory space is provided. The method 600 begins at step 602 and continues to step 604, where a plurality of RFID locator tags (e.g., the RFID locator tags 106 of FIG. 1)₁，...，106_X) Is placed around a facility (e.g., RSF 128 of fig. 1). Information specifying the known location of the RFID locator tag is stored. This information is stored in a data store (e.g., data store 126 of fig. 1 and/or memory 204 of fig. 2) internal to the RFID handheld reader (e.g., handheld reader 120 of fig. 1 or handheld reader 200 of fig. 2) and/or external to the handheld reader.

In a next step 606, handheld readers are carried around the facility. The handheld reader may be carried by a person (e.g., employee 122 of fig. 1) or a mobile device (e.g., an unmanned vehicle). As the handheld reader is carried through the facility, step 608 is performed in which an AHR device (e.g., AHR device 150 of fig. 1 or 280 of fig. 2) generates inertial reference measurement data. The inertial reference measurement data is useful for determining the orientation, position and/or location of the handheld reader at multiple RFID tag read times. Inertial reference measurement data is also useful in determining a path through a facility.

Next in optional step 610, a press of a trigger of the handheld reader is detected. In response to such detection, step 612-618 is performed. In some scenarios, step 612 and 618 are performed sequentially at each tag read and completed before the next tag read is initiated. Step 612 involves performing, by the handheld reader, one or more reads of the AHR device and the following RFID-enabled devices: (a) attaching to multiple objects within a facility (e.g., object 110 of FIG. 1)₁，...，110_N、116₁，...，116_N) A plurality of RFID inventory tags (e.g., RFID inventory tag 112 of fig. 1)₁，...，112_N、118₁，...，118_N) (ii) a And/or (b) at least one RFID locator tag (e.g., RFID locator tag 106 of FIG. 1)₁，...，106_N). Step 614-: generating a timestamp for each RFID tag read performed in step 612; and determining the RSSI of the signal received from the RFID locator tag and/or the RFID inventory tag.

After completing step 612-. Similarly, the RFID signals received from the RFID locator tags are processed to obtain unique location identifiers therefrom. The inertial reference measurement data, the unique tag identifier, the location identifier, the timestamp, and the RSSI are optionally transmitted from the handheld reader to a remote data store.

In a next step 622, at each of a plurality of RFID inventory tag read times, an initial estimate of the location, position, and/or orientation of the handheld reader within the three-dimensional space is determined. The initial estimate is determined by processing the inertial reference measurement data and the time stamp. After completing step 622, method 600 continues with step 624 of FIG. 6B.

Referring now to FIG. 6B, step 624 involves using the unique location identifier to obtain information specifying the known location of the RFID locator tag. The known locations of the RFID locator tags are used in step 626 to correct the initial position, location and/or orientation estimate derived in the previous step 622. The estimated position/location/orientation of the handheld reader is then used to define a plurality of cones in step 628. Furthermore, the following information is used to define the pyramid: a unique tag identifier received from the RFID inventory tag; a time stamp; RSSI; and/or other data. Each cone has a vertex that is an estimated location of the handheld reader when reading the respective RFID inventory tag and an angle that is inversely proportional to the RSSI for the respective RFID inventory tag at a given reading. Some cones may be discarded in step 630. For example, cones having angles greater than a threshold may be discarded.

The cone is then mapped to a physical, graphical and/or mathematical model, as shown in step 632. The mapping is analyzed in step 634 to identify intersecting cones associated with the reads for each RFID inventory tag. A position estimate and/or location estimate is derived for each RFID inventory tag using the corresponding intersecting cones, as shown in step 636. The location and/or position estimate is then stored in step 638. Wherein the data storing the position and/or location estimate is stored internally and/or externally to the handheld reader. In a next step 640, information indicative of an estimated location and/or position for at least one RFID inventory tag is output from the handheld reader. Subsequently, step 642 is performed, wherein the method 600 ends or performs other processing.

All of the devices, methods, and algorithms disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the invention has been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations may be applied to the apparatus, methods and in the sequence of steps of the method without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain components may be added to, combined with, or substituted for the components described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined.

The above-disclosed features and functions, and alternatives, may be combined in many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.

Claims

1. A method for determining a location of an object within a space, comprising:

generating inertial reference measurement data by an attitude and heading reference AHR device, the inertial reference measurement data being useful for determining an orientation and a position of an RFID reader within a space at each of a plurality of RFID tag read times;

performing, by the RFID reader, one or more reads of a plurality of RFID inventory tags;

processing the inertial reference measurement data to determine at least an orientation and a location estimate of an RFID reader each time the RFID inventory tag is read;

defining a plurality of cones associated with each of the plurality of RFID inventory tags, each cone having a vertex and an angle, wherein the vertex is an RFID reader location estimate at a respective time of the plurality of RFID tag read times and the angle is inversely proportional to a signal strength of a signal received from a respective RFID inventory tag of the plurality of RFID inventory tags;

mapping the plurality of cones to a model;

analyzing the model to identify at least one set of cones that overlap each other and are associated with reads for respective ones of the plurality of RFID inventory tags; and

deriving a location estimate for a respective inventory tag based on previously identified intersections of cones in the set of cones.

2. The method of claim 1, further comprising performing, by the RFID reader, one or more reads of at least one RFID locator tag.

3. The method of claim 2, further comprising correcting errors in the RFID reader position estimate using the known locations of the RFID locator tags.

4. The method of claim 1, wherein each cone of the plurality of cones has an orientation that is the same as an orientation of an RFID reader at a respective time of the plurality of RFID tag read times.

5. The method of claim 1, wherein the model is a physical model, a mathematical model, or a graphical model.

6. The method of claim 1, further comprising storing the RFID reader orientation and location estimates for the respective RFID inventory tags in a data store internal or external to the RFID reader.

7. The method of claim 1, further comprising outputting, from the handheld reader, information indicative of the RFID reader orientation and location estimate for the respective RFID inventory tag.

8. The method of claim 1, wherein one or more RFID location tags have a strong response within a known range of locations and/or orientations relative to the RFID reader antenna and a substantially attenuated response outside the known range.

9. A method for determining a location of an object within a space, comprising:

processing the inertial reference measurement data to determine at least an orientation and a location estimate of an RFID reader each time the RFID inventory tag is read,

defining a plurality of cones associated with each of the plurality of RFID inventory tags, each cone having a vertex and an angle, wherein the vertex is an RFID reader location estimate at a respective one of the plurality of RFID tag read times, the angle being inversely proportional to a signal strength of a signal received from the respective one of the plurality of RFID inventory tags,

mapping the plurality of cones to a model,

analyzing the model to identify at least one set of cones that overlap each other and are associated with reads for respective ones of the plurality of RFID inventory tags;

the cone with the following characteristics is discarded: (a) does not overlap with at least one other cone in the model, (b) has an angle greater than a threshold, or (c) does not overlap with a cone associated with a strongest received signal strength; and

10. A method for determining a location of an object within a space, comprising:

mapping the plurality of cones to a model;

deriving a location estimate for a respective inventory tag based on previously identified intersections of cones in the set of cones; and

refining the position estimate derived for the respective inventory tag using at least one predefined rule that limits the effective position of the object to which the respective inventory tag is attached.

11. A system, comprising:

a plurality of RF1D inventory tags coupled to objects disposed within the space;

an RFID reader configured to read a plurality of RFID inventory tags one or more times;

an attitude and heading reference "AHR" device configured to generate inertial reference measurement data useful for determining an orientation and a position of an RFID reader within a space at each of a plurality of RFID tag read times; and

electronic circuitry configured to:

mapping the plurality of cones to a model,

analyzing the model to identify at least one set of cones that overlap each other and are associated with reads for respective ones of the plurality of RFID inventory tags, an

12. The system of claim 11, wherein the RFID reader also reads the at least one RFID locator tag one or more times.

13. The system of claim 12, wherein the electronic circuitry further uses the known location of the RFID locator tag to correct errors in the RFID reader position estimate.

14. The system of claim 11, wherein each cone of the plurality of cones has an orientation that is the same as an orientation of an RFID reader at a respective time of the plurality of RFID tag read times.

15. The system of claim 11, wherein the model is a physical model, a mathematical model, or a graphical model.

16. The system of claim 11, wherein the orientation and location estimates for the respective RFID inventory tags are stored in a data store internal or external to the RFID reader.

17. The system of claim 11, wherein the handheld reader outputs information indicative of the orientation and position estimates for the respective RFID inventory tags.

18. The system of claim 11, wherein one or more RFID location tags have a strong response within a known range of locations and/or orientations relative to an antenna of the RFID reader and a substantially attenuated response outside the known range.

19. A system, comprising:

a plurality of RFID inventory tags coupled to objects disposed within a space;

electronic circuitry configured to:

mapping the plurality of cones to a model,

Deriving a location estimate for a respective inventory tag based on previously identified intersections of cones in the set of cones:

wherein the electronic circuit discards cones having the following characteristics: (a) does not overlap with at least one other cone in the model, (b) has an angle greater than a threshold, or (c) does not overlap with the cone associated with the strongest received signal strength.

20. A system, comprising:

a plurality of RFID inventory tags coupled to objects disposed within a space;

electronic circuitry configured to:

mapping the plurality of cones to a model,

Deriving a location estimate for a respective inventory tag based on previously identified intersections of cones in the set of cones;

wherein the electronic circuitry refines the position estimate derived for the respective inventory tag using at least one predefined rule that limits the effective position of the object to which the respective inventory tag is attached.