Abstract:
A wireless tracking system and method with a tag removal detection feature is disclosed herein. The system and method utilize a tag attached to an asset which includes a processor, a motion sensor (such as an accelerometer), a transceiver, a tag removal sensor and a power source having a limited supply of power. The tag removal sensor is an optical sensor which is activated only when the motion sensor detects motion. In this manner, the tag conserves power since the tag is typically only in motion ten percent of the day. If the tag is removed from the asset, the optical sensor confirms the removal and an alert is activated by the system.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The Present Application is a continuation application of U.S. patent application Ser. No. 11/875796, filed on Oct. 19, 2007. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention is related to wireless tracking systems and methods. More specifically, the present invention relates to a system and method for determining if a tracking tag has been removed from an asset. 
         [0005]    2. Description of the Related Art 
         [0006]    The ability to quickly determine the location of objects located within a facility is becoming a necessity of life. To the uninformed observer, the placement of transponders, also known as tags, on numerous non-stationary objects whether in an office or home would appear to be an unnecessary use of resources. However, the uninformed observer fails to appreciate the complexity of modern life and the desire for efficiency, whether at the office or home. 
         [0007]    For example, in a typical hospital there are numerous shifts of employees utilizing the same equipment. When a new shift arrives the ability to quickly locate medical equipment not only results in a more efficient use of resources, but also can result in averting a medical emergency. Thus, the tracking of medical equipment in a hospital is becoming a standard practice. 
         [0008]    The tracking of objects in other facilities is rapidly becoming a means of achieving greater efficiency. A typical radio frequency identification system includes at least multiple tagged objects, each of which transmits a signal, multiple receivers for receiving the transmissions from the tagged objects, and a processing means for analyzing the transmissions to determine the locations of the tagged objects within a predetermined environment. One exemplary method triangulates the strongest received signals to determine the location of a tagged object. This method is based on the assumption that the receivers with the strongest received signals are the ones located closest to the tagged object. However, such an assumption is sometimes erroneous due to common environmental obstacles. Multipath effects can result in a further located receiver having a stronger signal from a tagged object than a more proximate receiver to the tagged object, which result in a mistaken location determination. 
         [0009]    Yashina, U.S. Pat. No. 5,068,643, for a Burglarproof Device, discloses a device that includes a vibration sensor and an optical sensor. When the vibration sensor is activated, by vibration, a signal is sent to the optical sensor to determine the level of ambient light from relative brightness to relative darkness. If the ambient level is too dark, an alarm circuit is activated on the device to indicate that the goods to which the device is attached has been placed under or in a thief&#39;s clothing. 
         [0010]    Watters, et al., U.S. Pat. No. 6,806,808, for a Wireless Event-Recording Device With Identification Codes, discloses a passive transponder that has a sensor for detecting a physical or chemical event or state without using a power source of its own. 
         [0011]    Glick, et al., U.S. Pat. No. 7,002,473, for a Loss Prevention Device, discloses placing a RFID tag on an article and periodically interrogating each RFID tag to determine if the tag is still within a predetermined zone. 
         [0012]    Clucas, U.S. Pat. No. 7,042,359, for a Method And Apparatus To Detect A Plurality Of Security Tags discloses an electronic article surveillance system which includes a multitude of expensive RFID tags attached to expensive goods and a multitude of inexpensive RFID tags attached to inexpensive goods, and means to distinguish between the types of tags. 
         [0013]    Although the prior art has provided numerous solutions to prevent the theft of goods, the prior art has yet to resolve tag removal issues associated with location asset tracking. Further, the prior art has failed to recognize the problems associated with wireless location asset tracking. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    The present invention has recognized that tag removal in a wireless location asset tracking system complicates the asset tracking function of the system since additional components must be added to an already power exhausted and space restricted tag. The present invention is able to provide a solution that resolves the space restriction and power consumption issues. 
         [0015]    The present invention restricts the activity of the tag removal sensor by only activating the tag removal sensor when the possibility of the tag being removed is very high. This high possibility activation is performed by a motion sensor controlling the activation of the tag removal sensor through a processor. When the motion sensor registers motion, a signal is sent to the processor to activate the tag removal sensor to determine if the tag is still attached to the asset. In this manner, the power supply of the tag is conserved, while the tag removal function is optimized. 
         [0016]    One aspect of the present invention is a method for determining if a tracking tag has been removed from an asset within an indoor facility. The method includes tracking a location of an asset bearing a tag. The tag includes a processor, a motion sensor, a transceiver, a tag removal sensor, and a power source having a limited supply of electrical power. The motion of the tag is detected by the motion sensor and communicated to the processor. An activation signal is activated from the processor to the tag removal sensor. The activation signal activates the tag removal sensor from a low power consumption state to an activation state. The tag removal sensor is an optical sensor that emits light from the tag to the asset and receives the light reflected from a surface of the asset indicating that the tag is attached to the asset. The method includes determining if the tag is currently attached to the asset. The method includes transmitting an unattached signal from the tag removal sensor to the processor and from the processor to the transceiver to indicate that the tag is currently unattached to the asset. The method includes broadcasting the unattached signal from the transceiver of the tag to a plurality of network sensors positioned within an indoor facility. The method includes transmitting the unattached signal from at least one of the plurality of network sensors to a positioning engine to generate a warning. 
         [0017]    Another aspect of the present invention is a tracking and security device comprising a microcontroller, a wireless network interface, a power supply, a motion sensor and a tag removal sensor. The tag also includes a housing for protecting the components of the tag. The optical sensor includes an emitter for emitting a light beam through a window of the housing of the tag. The optical sensor also includes a photodiode for receiving a reflected light beam generated by the emitter. The optical sensor has a resting mode to conserve power consumption and an activation mode to determine if the tag is attached to an object. During the activation mode, the emitter generates the light beam which is reflected off a reflective panel of an asset and received by the photodiode if the tag is attached to the object. The optical sensor has means for informing the microcontroller that the tag is attached to the asset. The motion sensor has means for transmitting a signal to the microcontroller when the tag is in motion. The microcontroller activates the optical sensor when the motion sensor transmits a motion signal. The wireless network interface transmits a broadcast from the tag using a wireless communication format. The microcontroller has means for transmitting at a motion rate and at a stationary rate. The housing is preferably composed of a hard plastic material and the window is preferably transparent. 
         [0018]    Another aspect of the present invention is a system for determining if a tracking tag has been removed from an asset within an indoor facility. The system comprises a plurality of sensors, a positioning engine, a plurality of assets with each of the assets having a tag with a tag removal sensor, and a plurality of access points for receiving the signals from the plurality of sensors and transmitting the signals to the positioning engine. Each tag of each of the plurality of assets has means for determining if the tag has been removed from the asset, and means for broadcasting a signal to each of the plurality of sensors. The positioning engine includes means for tracking each asset within the indoor facility and means for warning an operator of the system if a tag is removed from an asset. 
         [0019]    Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]      FIG. 1  is schematic view of a wireless asset tracking system. 
           [0021]      FIG. 2  is a multi-floor view of a facility employing a wireless asset tracking system. 
           [0022]      FIG. 3  is a floor plan view of a single floor in a facility employing a wireless asset tracking system. 
           [0023]      FIG. 4  is a block diagram of a tag. 
           [0024]      FIG. 5  is a schematic diagram of a tag attached to an object. 
           [0025]      FIG. 6  is a flow chart of a method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    As shown in  FIGS. 1-3 , a wireless asset tracking system is generally designated  50 . The system  50  is capable of determining real-time location of an asset  100  within an indoor facility  70 . The system  50  preferably includes a plurality of sensors  55 , a plurality of bridges  56 , a plurality of tags  60  and at least one server  65 . One example of the components of the system  50  is disclosed in U.S. patent application Ser. No. 10/968814, filed on Oct. 18, 2004 for a Wireless Position Location And Tracking System, which is hereby incorporated by reference in its entirety. A more specific example of the sensors  55  is disclosed in U.S. patent application Ser. No. 11/008802, filed on Dec. 8, 2004 for a Plug-In Network Appliance, which is hereby incorporated by reference in its entirety. Another example of a system  50  is set forth in U.S. Pat. No. 6,751,455 for a Power-And Bandwidth-Adaptive In-Home Wireless Communications System With Power-Grid-Powered Agents And Battery-Powered Clients, which is hereby incorporated by reference in its entirety. 
         [0027]    The system  50  is preferably employed within an indoor facility  70  such as a business office, factory, home, hospital and/or government agency building. The system  50  is utilized to track and locate various assets (objects) positioned throughout the facility  70 . The tags  60  preferably continuously transmit signals on a predetermined time cycle, and these signals are received by sensors  55  positioned throughout the facility  70 . In a preferred embodiment, the tags  60  transmit a single every five seconds when in motion, and a signal every ten minutes when stationary. The sensors  55  preferably transmit the data to a bridge  56  for transmission to a server  65 . If a sensor  55  is unable to transmit to a bridge  56 , the sensor  55  may transmit to another sensor  55  in a mesh network-like system for eventual transmission to a bridge  56 . In a preferred embodiment, a transmission may be sent from a transmission distance of six sensors  55  from a bridge  56 . The server  65  preferably continuously receives transmissions from the sensors  55  via the bridges  56  concerning the movement of assets  100  bearing a tag  60  within the facility  70 . The server  65  processes the transmissions from the sensors  55  and calculates a real-time position for each of the assets  100  bearing a tag  60  within the facility  70 . The real-time location information for each of the assets  100  bearing a tag  60  is preferably displayed on an image of a floor plan of the indoor facility  70 , or if the facility  70  has multiple floors, then on the floor plan images of the floors of the facility  70 . The floor plan image may be used with a graphical user interface so that an individual of the facility  70  is able to quickly locate assets  100  within the facility  70 . 
         [0028]    The assets  100  are preferably items of value to the owners or users of the system  50  and/or the facility  70 . In a hospital setting, the assets  100  could include vital sign monitoring devices, kidney dialysis machines, imaging devices, and other like items that are valuable and mobile. In an office setting, the assets  100  could be computers, copiers, printers, and like devices. Those skilled in the pertinent art will recognize that the assets are anything of value to a user and mobile. 
         [0029]    As shown in  FIG. 1 , the system  50  utilizes sensors  55  to monitor and identify the real-time position of non-stationary assets  100  bearing or integrated with tags  60 . The sensors  55   a - f  preferably wirelessly communicate with each other (shown as double arrow lines) and with a server  65  through a wired connection  66  via at least one bridge  56 , such as disclosed in the above-mentioned U.S. patent application Ser. No. 11/008802, filed on Dec. 8, 2004 for a Plug-In Network Appliance. The tags  60   a - c  transmit signals (shown as dashed lines) which are received by the sensors  55   a - e,  which then transmit signals to bridges  56  for eventual transmission to a server  65 . The server  65  is preferably located on-site at the facility  70 . However, the system  50  may also include an off-site server  65 , not shown. 
         [0030]    Each tag  60  preferably transmits a radio frequency signal of approximately 2.48 GigaHertz (“GHz”). The communication format is preferably IEEE Standard 802.15.4. Those skilled in the pertinent art will recognize that the tags  60  may operate at various frequencies without departing from the scope and spirit of the present invention. 
         [0031]    As shown in  FIGS. 2-3 , the facility  70  depicted is a hospital. The facility  70  has a multitude of floors  75   a - c.  An elevator  80  provides access between the various floors  75   a,    75   b  and  75   c.  Each floor  75   a,    75   b  and  75   c  has a multitude of rooms  90   a - i,  with each room  90  accessible through a door  85 . Positioned throughout the facility  70  are sensors  55   a - o  for obtaining readings from tags  60   a - d  attached to or integrated into non-stationary assets  100   a,    100   b  (see  FIGS. 2 and 4 ). A bridge  56  is also shown for receiving transmissions from the sensors  55  for processing by the server  65 . 
         [0032]    As shown in  FIG. 4 , a tag  60  preferably includes a microcontroller or processor  101 , a wireless network interface  103  having an antenna, a power supply  104 , a motion sensor  105  and an optical sensor  106 . The processor  101  is in communication with the optical sensor  106 , motion sensor  105  and wireless network interface  103 . The power supply  104  preferably provides power to the processor  101 , the motion sensor  104 , the optical sensor  106  and the wireless network interface  103 . The power supply  104  is preferably a battery such as a lithium battery. The power supply  104  is preferably the only source of power for the tag  60 . Conserving the energy use of the tag  60  allows the tag  60  to have greater use period before needing to be recharged or replaced. In order to conserve the energy use of the tag  60 , it is preferably to activate the motion sensor  105  and the optical sensor  106  only when necessary. Preferably the components of the tag are enclosed within a housing indicated by the dashed line. Preferably a transparent window is positioned by the optical sensor  106 . 
         [0033]    A preferred optical sensor  106  is a TCND5000 from VISHAY SEMICONDUCTORS, which is a reflective optical sensor with PIN photodiode output. The emitter  107  is preferably an infrared emitter having a wavelength of approximately 940 nanometers (“nm”). The emitter  107  preferably has a voltage of 5 Volts, a peak current of 500 milliAmps, and a power dissipation of 190 milliWatts. The photodiode  108 , or detector, preferably has a voltage of 60 Volts and a power dissipation of 75 milliWatts. A marking area of the optical sensor  106  preferably separates the emitter  107  from the photodiode  108 . The optical sensor  106  preferably has dimensions of a length of 6 millimeters (“mm”), a height of 4.3 mm and a width of 3.75 mm. The photodiode  107  preferably has a spectral range of 840 nm to 1050 nm. Those skilled in the pertinent art will recognize that other optical sensors may be used without departing from the scope and spirit of the present invention. 
         [0034]    As shown in  FIG. 5 , when the optical sensor  106  is in its activation mode, an emitter  107  of the optical sensor  106  transmits a light beam  109   a  through a window  115  of the tag  60  towards a reflective panel  120  attached to the asset  100 . The transparent window  115  is positioned on a housing  114  of the tag  60  by the emitter  107  and the photodiode  108 . The reflective panel  120  is preferably positioned from 2 mm to 25 mm, and most preferably approximately a distance of  6 mm from the emitter  107 . The reflective panel  120  is preferably a KODAK grey card having 20% reflectivity. The reflective panel  120  preferably has a length of approximately 30 mm. The transmitted light beam  109   a  strikes the reflective panel  120  and a reflected light beam  109   b  is received by a photodiode  108  of the optical sensor  106 . In this manner, the optical sensor  106  is able to determine if the tag  60  is attached to the asset  100 . If the tag  60  were removed, the transmitted light beam  109   a  would not strike a reflective panel  120  and a reflected light beam  109   b  would not be received by the photodiode  108 . The failure of the photodiode  108  to receive the reflected light beam  109   b  would result in an unattached signal sent from the optical sensor  106  to the processor  101 . The signals preferably sent from the optical sensor  106  to the processor  101  are simple ones (1s) and zeros (0s). If the tag  60  is attached, a 1 is sent from the optical sensor  106  to the processor  101 . If the tag  60  is unattached, a 0 is sent from the optical sensor  106  to the processor  101 . 
         [0035]    Reducing the power consumption of the tag  60  is an important aspect of the present invention. Typically, an asset  100  bearing a tag  60  is in motion ten percent of the day. The optical sensor  106  is only in its activation mode when the tag  60  is in motion as indicated by the motion sensor  105 . Thus, ninety percent of the day, the optical sensor  106  is in a resting mode and using little or no energy from the power supply  104 . When the tag  60  is in motion, the optical sensor  106  is preferably queried every five seconds by the processor  101  concerning the attachment of the tag  60  to the asset  100 . When the tag  60  is stationary, the optical sensor  106  is in its resting mode and not queried by the processor  101 . By operating in this manner, the power efficiency of the tag  60  is ten times greater than constantly querying the optical sensor  106  throughout the day concerning the attachment status of the tag  60 . However, the tag  60  is still able to provide continuous security monitoring since the motion sensor  105  transmits a motion signal when motion of the tag  60  is detected thereby resulting in an activation signal transmitted from the processor  101  to the optical sensor  106 . 
         [0036]    In one preferred embodiment, the optical sensor  106  consumes 3 milli-amps-milli-seconds of power from the power supply  104  when the optical sensor  106  is in the activation mode. On a per day power consumption, the optical sensor  106  consumes 0.0018 milli-amps-hours/day. 
         [0037]    A method  200  of the present invention is illustrated in  FIG. 6 . At block  202 , the tracking of a location of an asset  100  bearing a tag  60  is performed by the sensors  55  of the system  50  which receive readings from each tag  60 . For location tracking, a sensor  55  receives a signal which includes reading inputs from a tag  60 . The reading inputs from the tag  60  preferably include the tag identification, the signal strength, the link quality and the time of the reading, all of which are inputted as a single sensor reading. In this manner, the system is able to track the location of the asset  100  bearing the tag  60 . At block  204 , motion is detected by the motion sensor  105  of the tag  60 , which transmits a signal to the processor  101 . The motion could be the asset  100  being moved from one location to another, or the motion could be the removal of the tag  60  from the asset  100 . At block  206 , an activation signal is transmitted from the processor  101  to the tag removal sensor  106 , which is an optical sensor  106 . The activation signal activates the optical sensor  106  from a low power or resting mode to a high power or activation mode. In this manner, the limited power supply  104  of the tag  60  is not quickly exhausted by having the optical sensor  106  in a constant high power activation mode. At decision  208 , a determination is made concerning the attachment status of the tag  60 . This determination is performed by the reflected light  109   b  of the emitter  107  being received by the photodiode  108 . If the reflected light  109   b  is received by the photodiode  108 , then at block  210 , a signal is sent that the tag  60  is attached to the asset  100 , and the tag  60  continues to broadcast location readings to the sensors  55 . If the reflected light  109   b  is not received by the photodiode  108 , then at block  212 , a signal is sent from the optical sensor  106  to the processor  101  that the tag  60  has been removed from the asset  100 . At block  214 , the processor  101  transmits an unattached signal through the wireless network interface  103 , which at block  216  is broadcast to the plurality of network sensors  55  of the system  50 . At block  218 , at least one of the plurality of network sensors  55  transmits the unattached signal to the positioning engine  65  which generates an alert warning to the users of the system  50  informing the users that a tag  60  has been removed from an asset  100 . 
         [0038]    In the above-described manner, the tag  60  can operate longer on its limited power supply  104  while providing an optimized tag removal security function. 
         [0039]    From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes modification and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claim. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.