Abstract:
A system includes an asset tag associated with an asset, the asset tag having a motion sensor to detect a movement of the asset. The system also includes a plurality of readers, each reader receiving one or more signals from the asset tag and measuring a distance between the asset tag and the reader based on the signals. The system further includes a controller receiving a measured distance from each of the plurality of readers and determining a location of the asset based on the measured distances.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to asset tracking systems and more specifically to an apparatus and method for tracking assets using asset tags with motion sensors. 
     BACKGROUND 
     Asset tracking systems are used to track the locations of assets in a facility. These systems may be used as part of a process control system or as part of a security system allowing the systems to identify when assets enter predefined areas or when assets are moved to or from their designated locations. 
     Asset tracking systems may be implemented using an asset tag attached or fixed to an asset. The asset tag periodically sends signals or “beacons” that are received by any number of readers at fixed locations throughout the facility. The readers use the signals to measure the distance between the asset tag and the readers. The readers then send the measurements to a central location, for example, by way of a mesh network. A system at the central location then uses the measurements from the readers to calculate the location of the asset. 
     Although such asset tracking systems are useful in keeping track of assets, they suffer from a lack of scalability and are prone to flooding as the number of asset tags increase. Accordingly, the capacity of the system (measured in terms of the number of tags that can be tracked/second) may be lower than desired for many applications. Although the beaconing rate of the asset tag could always be reduced in order to accommodate a higher number of tags, reducing the beaconing rate results in an increased lag time in providing a reliable location estimate because the most current information is not available should an asset start moving. 
     SUMMARY 
     This disclosure provides a system and method for tracking assets. 
     In a first embodiment, a system includes an asset tag associated with an asset, the asset tag having a motion sensor to detect a movement of the asset. The system also includes a plurality of readers, each reader receiving one or more signals from the asset tag and measuring a distance between the asset tag and the reader based on the signals. The system further includes a controller receiving a measured distance from each of the plurality of readers and determining a location of the asset based on the measured distances. 
     In particular embodiments, the asset tag is attached to the asset. 
     In other particular embodiments, the asset tag transmits the signals at a first rate when the asset is stationary. 
     In other particular embodiments, the asset tag transmits the signals at a second rate when the asset is in motion. 
     In yet other particular embodiments, the first rate is different from the second rate. 
     In still other particular embodiments, the second rate is faster than the first rate. 
     In a second embodiment, a method includes detecting a movement of an asset using an asset tag having a motion sensor. The method also includes transmitting one or more signals at a second rate in response to detecting a movement of the asset. 
     In a third embodiment, an apparatus includes a motion sensor detecting a movement of an asset. The apparatus also includes a controller transmitting one or more signals at a second rate in response to the motion sensor detecting a movement of the asset. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example of an asset tracking system according to an embodiment of this disclosure; 
         FIG. 2  illustrates an example of an asset tag according to an embodiment of this disclosure; and 
         FIG. 3  is a flow chart illustrating a method of tracking an asset according to an embodiment of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 3 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the invention may be implemented in any type of suitably arranged device or system. 
       FIG. 1  illustrates an example system  100  according to this disclosure. The embodiment of the system  100  shown in  FIG. 1  is for illustration only. Other embodiments of asset tracking system  100  could be used without departing from the scope of this disclosure. 
     As shown in  FIG. 1 , an asset tag  102  is attached or fixed to an asset  104 . Upon detecting a movement of the asset  104 , the asset tag  102  emits signals or “beacons” that are detected by any number of readers  106  placed at fixed locations throughout the facility. The readers  106  then use the signals to measure the distance between the asset tag  102  and the respective reader  106 . The readers  106  then send the measurements to a controller  108 . The controller  108  uses the measurements from readers  106  to calculate the location of asset  104 . The location of asset  104  may be calculated, for example, by triangulation from the readers  106 . Of course, the location of asset  104  may be calculated by any method or system known to one of ordinary skill in the art. 
     Because the asset tag  102  will only beacon when it detects a movement of the asset  104 , a significant increase in the number of asset tags tracked by the asset tracking system  100  is realized. For example, depending on how often the assets are moved, whether the assets are moved independently or in tandem, and the duration of the movement, the capacity of asset tracking system  100  can be increased by several orders of magnitude in some embodiments. 
     Although  FIG. 1  shows asset tracking system  100  with one asset tag  102 , one controller  108 , and four readers  106 , one of ordinary skill in the art would recognize that any number of asset tags  102 , controllers  108 , and readers  106  could be implemented in asset tracking system  100 . 
       FIG. 2  illustrates an example of an asset tag according to an embodiment of this disclosure. As shown in  FIG. 2 , the asset tag  102  comprises a motion sensor  202 , which signals whether the asset tag  102  is stationary or in motion. The motion sensor  202  is coupled to a controller  204 . Upon detecting a movement of the asset by the motion sensor  202 , the controller  204  transmits signals or beacons using a transceiver  206 , which is coupled to an antenna. As described earlier, the signals or beacons transmitted by controller  204  are received by any number of readers  106  and are used to calculate the location of the asset. 
     The controller  204  is also coupled to a memory  208 . The memory  208  stores applications and data for implementing various functions of the controller  204 . The memory  208  also stores data generated by the operation of the controller  204 . 
     A power supply  210  provides electrical power as needed to the components of the asset tag  102  via electrical connections that are not shown in  FIG. 2 . It will be understood that certain components shown as distinct entities in  FIG. 2  may be combined into integrated components. For example, the memory  208  and the controller  204  could be constructed as a single processing element. 
     In one embodiment, the asset tag  102  transmits an occasional signal or beacon even when no motion is detected by the motion sensor  202 . This occasional signal or beacon serves to indicate that the asset tag  102  is functioning properly and is still within range of the readers  106 . In such an embodiment, the asset tag  102  also may start transmitting signals or beacons at a significantly higher rate upon the detection of movement and continue to do so until the movement stops. This would allow controller  108  to be instantly informed during movement with up-to-date measurements. 
     Even for a stationary asset tag, the distance measurements are plagued by errors due to shadowing, multipath distortion, and so forth. Accordingly, it is advantageous to average several measurements in order to arrive at a location estimate with higher confidence even for a stationary asset tag. Moreover, if a signal or beacon contains information on whether the asset tag is stationary, a localization algorithm may utilize this information and treat it accordingly. 
     In some embodiments, the movement information would be displayed on a user interface, for example, at the controller  108 . The user interface would also highlight the asset tags are that currently in motion. In other embodiments, an alarm may be signaled, for example, at the controller  108  upon a movement of any asset tag. 
       FIG. 3  is a flow chart illustrating a method  300  of tracking an asset according to an embodiment of this disclosure. In step  301 , an asset tag transmits signals or beacons at a first rate when no motion is detected. The signals or beacons transmitted at step  301  may contain information indicating that the asset tag is stationary or the stationary nature of the asset tag may be inferred simply from the rate at which the signals or beacons are transmitted. If a movement of the asset tag is detected in step  303 , the asset tag transmits signals or beacons at a second rate, which is higher than the first rate, at step  305 . The signals or beacons transmitted at step  305  may contain information indicating that the asset tag is moving or the movement of the asset tag may be inferred simply from the rate at which the signals or beacons are transmitted. 
     Movement information is displayed on a user interface at step  307 , and the asset tags that are currently in motion are highlighted in step  309 . An alarm is signaled in step  311 . If movement of the asset tag is still detected in step  313 , the method repeats steps  305  to  311 . If movement of the asset tag is no longer detected in step  313 , the movement information displayed on the user interface is updated to reflect that the asset tag is no longer in motion in step  315 , and the alarm is disengaged in step  317 . The method then returns to step  301  where the asset tag transmits signals or beacons at the first rate until a movement of the asset tag is detected again. 
     Although  FIG. 3  illustrates an example of a method for tracking an asset, various changes may be made to  FIG. 3 . For example, while shown as a series of steps, various steps in  FIG. 3  could overlap, occur in parallel, occur in a different order, or occur multiple times. Further, note that these steps could occur at any suitable time, such as in response to a command from a user or external device or system. 
     In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. 
     It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. The term “controller” means any device, system, or part thereof that controls at least one operation. A controller may be implemented in hardware, firmware, software, or some combination of at least two of the same. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. 
     While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.