Abstract:
A releasable security tag for attachment to an article of merchandise includes: a locking mechanism with a release for attaching the tag to the article of merchandise; an EAS resonant circuit or an RFID circuit for responding to a first RF signal at a predetermined frequency corresponding to the resonant circuit or to the RFID circuit; an ambient RF energy harvesting circuit; a release signal detection circuit coupled to and powered by the ambient RF energy harvesting circuit and an electro-mechanical actuator electrically coupled to the release signal detection circuit. The electro-mechanical actuator releases the locking mechanism whenever the release signal detection circuit receives a release signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This utility application claims the benefit under 35 U.S.C. §119(e) of Provisional Application Ser. No. 60/778,646 filed on Mar. 3, 2006 entitled RF POWERED RELEASE MECHANISM FOR HARD TAG the entire disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The current invention relates to security tags and more particularly, discloses a security tag that can be removed from an article to which it is attached by transmission of a wireless (e.g., radio frequency) signal to the tag. 
     2. Description of Related Art 
     Electronic article surveillance (EAS) security tags, typically comprise a resonant circuit that utilizes at least one coil and at least one capacitor that operate to resonate when exposed to a predetermined electromagnetic field (e.g., 8.2 MHz) to which the EAS tag is exposed. Scanning equipment transmits a signal at the frequency of the tag and detects the signal created by the resonant circuit. Such tags are applied to merchandise to prevent theft and for inventorying. Various different resonant tag products are commercially available and described in issued patents, for example, U.S. Pat. Nos. 5,172,461; 5,108,822; 4,835,524; 4,658,264; and 4,567,473 all describe and disclose electrical surveillance tag structures. 
     One form of EAS tag is known as a “hard tag.” A hard tag is typically a reusable device that contains the resonant circuitry and that can be attached to an article with means for keeping the tag attached until released by a special apparatus. By way of example only, the coil and the capacitor are enclosed in a first device having a retaining device to accept a pin. A second device containing a pin and looking like a large thumb tack can be inserted through an article of clothing, for example, and into the retaining device of the first device. In an exemplary design the pin is retained by a ball clutch in the tag that prevents removal once the pin is inserted. In this manner, the hard tag is affixed to an article and remains attached such that it cannot be removed by a customer. In typical prior art hard tags having a ball clutch, pressure is applied to the balls by an iron slug backed by a spring. Upon application of a large magnetic field at a point of sale, the slug retracts, relieving pressure from the ball clutch, allowing the pin to be removed by store personnel. 
     Another type of RF security device is an RFID device. Such a device contains active circuitry to produce an encoded RF signal when energized by an external RF signal. Circuitry for an RFID device can also be contained in a hard tag as described above. 
     One problem with magnetically-releasable hard tags is that thieves sometimes carry magnets strong enough to remove the tags. Another problem is that of untrustworthy store personnel, who remove the tags for an accomplice customer, without the customer ever paying for the item. Thus, there exists a need for an EAS or RFID hard tag with a more secure removal mechanism. 
     The present invention is a hard tag powered by harvesting ambient radio frequency energy with circuitry that allows removal only upon application of an encoded RF signal at the appropriate frequency. Such a device prevents thieves from removing the hard tags, and, when linked to a system which tracks an article identification number for each time the RF signal is applied to allow release of a hard tag, can be used to track removal of tags by store personnel. 
     All references cited herein are incorporated herein by reference in their entireties. 
     BRIEF SUMMARY OF THE INVENTION 
     A security tag or other device for affixing to an object is disclosed, wherein the tag can only be removed by activation of a release mechanism that is triggered by an external radio frequency signal, where the device is powered by harvesting ambient radio frequency energy. 
     One embodiment of such a tag includes a ball clutch for receiving a pin, which is inserted through an article to be tracked by the tag. The ball clutch is held in a locked position by spring pressure. A releasing mechanism, such as a low power solenoid, is activated by an external RF signal. The release circuitry within the tag can be supplied by a current source that receives power from external ambient RF energy. If the tag is an EAS tag, the tag can include a resonant circuit that produces a signal that allows detection of the tag when in the presence of a sufficiently large RF field at the frequency to which the resonant circuit is tuned. If the tag is an RFID tag, it may include a transmitter to send a unique signal when the tag is in the presence of an RF interrogation field at a particular frequency. The receiving and transmitting circuitry of the RFID part of the tag can be self-powered by the RF interrogation signal, or can be powered by the RF energy harvesting circuitry. 
     The basic elements of an exemplary RF releasable security tag are: 1) an energy harvesting circuit that is powered by external ambient RF energy; 2) an energy storage element for storing power from the energy harvesting circuit; 3) Detection circuitry for receiving a release signal; 5) a switch for applying power to a solenoid from the energy storage element and 6) a solenoid for releasing a security tag attachment element. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is a drawing of an exemplary prior art hard tag system; 
         FIG. 2  is a drawing of the locking mechanism of a prior art hard tag shown in an unlocked position; 
         FIG. 3  is a detail drawing of an exemplary RF releasable hard tag release mechanism in a locked position; 
         FIG. 3   a  is a detail drawing of an exemplary RF releasable hard tag mechanism in an unlocked (released) position; 
         FIG. 4  is a block diagram of the electronics for an exemplary RF releasable hard tag; 
         FIG. 5  is a block diagram of an exemplary RF releasable hard tag having a clamping device for attachment to an article; and 
         FIG. 6  is a block diagram of the electronics for an exemplary RF releasable hard tag system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a typical prior art hard tag system includes an electronics housing H and a locking pin assembly  5 , the pin  6  of which is inserted thorough an article of clothing A.  FIG. 2  is a cross section drawing of a prior art hard tag and locking pin assembly. Pin  6  is inserted into opening  7  in the housing. A plurality of balls  40  are arranged in ball housing  70  such that there is space in the middle of the balls for pin  6  to be inserted between them. The inside walls  75  of ball housing  70  are tapered slightly such that the inside diameter of the housing is smaller at opening end  7  than at the opposite end. Plunger  50  is urged toward the opening end of the ball housing by spring  60 , forcing the balls  40  toward the inserted pin  6 . The size of the balls and the dimensions of the ball housing are such that the balls tightly grip the pin when they are forced toward the opening by the plunger and spring, and also that the balls do not grip the pin when the plunger is pulled away from the opening end, for example, by a magnet. With the plunger and spring in the extended position (no magnet present) any effort to remove the pin forces the balls tighter against the pin as they are pulled into the narrower end of the ball housing. When the plunger is pulled upward, away from the ball housing opening, the balls rest loosely in the ball housing and the pin can be removed with little effort. 
     Mechanical Components of an Exemplary RF Releasable Hard Tag 
       FIG. 3  is a cross section drawing of the lock mechanism of an exemplary RF powered releasable hard tag. The tag includes electronics housing H 1 , which includes ball housing  170 , housing locking balls  140 . The locking balls are in contact with plunger base  150 . Plunger base  150  is in contact with spring  160 . Behind spring  160  is plunger plate  165 , having a detent  166 . Activating plunger  168  passes through an opening  169  in the electronics housing H 1 .  FIG. 3  shows the hard tag in a locked position. In the locked position, plunger plate  166  is locked into position by a spring loaded pin  191  of solenoid  190  which is engaged into detent  166  in plunger plate  165 . Chamfer  167  in the plunger plate  165  allows the plate to be pushed down while forcing the solenoid pin  191  into the detent once the plate  165  is pushed sufficiently far to allow it to be locked in place by the solenoid pin  191 . In the locked position, plunger plate  165  places spring  160  in a compressed state, such that a force is applied to plunger base  150 , urging balls  140  toward the narrow end of ball housing  170 . With the balls in the narrow end of the ball housing  170 , the pin  6  is held captive against any retraction force. With the tag in a locked position, the pin  6  can be inserted into the tag because an upward force against the balls pushed them to the wider end of the ball housing leaving room for the pin  6  to be inserted. One skilled in the art will readily appreciate the size of spring  160  necessary to hold plunger base  150  against the balls  140  with sufficient force to prevent retraction of the pin, while not presenting so much force as to make insertion of the pin difficult. The size of spring  160  must also be compatible with the amount of energy available from the RF harvesting circuitry to retract solenoid pin  191 . 
       FIG. 3A  shows the RF releasable tag in an unlocked position. In the unlocked position, plunger plate  165  is not engaged by solenoid pin  166  and is at the far end of the electronics housing H 1  from the balls  140 . In this position, spring  160  is completely relaxed, such that it does not apply any force on plunger base  150 , releasing balls  140  from the narrow end of the ball housing  140  so that the pin  6  can be removed. To return the tag to a locked position, an external force is applied to plunger  168  until plunger plate  165  is forced far enough toward the spring that detent  166  is opposite solenoid pin  190 . Solenoid pin  190  is spring-loaded such that the solenoid pin  190  moves into the detent when the plunger plate  165  is pushed in, thus locking the plunger plate  165  in a position forcing spring  150  in a compressed state. 
     Electronic Components 
     With reference to the block diagram in  FIG. 4 , the basic electronic elements of an exemplary RF releasable security tag are: an antenna for receiving ambient RF energy  410 ; RF harvesting circuitry  420  for converting the received ambient RF energy to a direct current signal; a charge storage component  430 ; release signal receiving circuitry  440 , which may have an antenna  445 ; an electro-mechanical release mechanism  460 , (e.g. solenoid  190 ) and an electronic switch  450  for supplying power to the electro-mechanical release mechanism. Electronic circuitry (e.g. RFID or EAS circuitry)  470  for providing tag detection response can be electrically separate and apart from those described above for the hard tag release. Such components that are well known in the art can include EAS passive resonant circuits incorporating an inductor/antenna and a capacitor. RFID circuits that are powered by an external RF signal and produce a coded RF signal are also well known and can be housed in the hard tag. 
     RF harvesting circuits that supply DC power from ambient RF energy are well known in the art. For example, U.S. Patent Application Publication US 2005/0104553, Mickle et al., whose entire disclosure is incorporated by reference herein, discloses a means for receipt of ambient RF energy to energize power storage elements for powering wireless devices. This publication discloses the reception and conversion of a wide band of ambient radio frequency energy into direct current. Another approach harvests RF energy from a single frequency source, which may be transmitted in the vicinity of the device or devices to be powered from that energy. U.S. Pat. No. 6,856,291, (Mickle et al.), and U.S. Patent Application Publication No. US 2004/0053584, (Mickle et al.), both disclose charging apparatuses based on reception of limited bandwidth RF energy, and both of whose entire disclosures are incorporated by reference herein. 
     In an exemplary embodiment, RF harvesting circuitry  420  powers a charge storage element  430  which can be a large value storage capacitor with low leakage or a rechargeable battery. The storage element supplies DC power to release signal receiver circuitry  440 , which can be an RF receiver tuned to a particular frequency, with an antenna  445  for receiving the release signal. Upon receipt of a signal at that frequency, the receiver circuit activates electronic switch  450 , which connects power from the storage element  430  to the electro-mechanical release mechanism  460 . In an exemplary design, the receiver  440  is a low power integrated circuit and the electronic switch  450  is a MOSFET or other type of semiconductor switch with a low voltage drop. 
     In another embodiment, the release circuitry can be more sophisticated than the simple reception of an RF signal at a single frequency. In this embodiment, the release is conditioned on reception of a code broadcast at an RF carrier frequency by any of various known means of modulation. The use of a code to trigger tag release reduces the chances of inadvertent release of a tag and enhances the user&#39;s ability to track removal of tags from merchandise. For example, a tag requiring reception of a unique identification code before release can be associated with piece of inventory. A transmitter for sending a release signal can be connected to a cash register system and product identification hardware, such that the unique release code associated with the piece of inventory is only transmitted when a valid sale transaction is recorded for the identified piece of inventory. Such a system would allow, for instance, customers to remove tags on their own after they have paid for items at self-service checkout stations by sending the release signal once the product has been identified and paid for. This type of system would also prevent employee theft whereby employees remove tags from merchandise for illegitimate “customers” without the accomplice paying for the item. 
     In another exemplary version of the RF releasable tag (either EAS or RFID), the release signal receiver  440  can also be used as a means for receiving a tag interrogation signal. With reference to  FIG. 6 , detection device  600  transmits an RF interrogation signal  610  through antenna  630 . Typically the detection device, or at least antenna  630  is placed at a store exit point to detect tagged items that are being removed from the store. The RF interrogation signal is tuned to the same frequency used to release the hard tag. The interrogation signal is received by receiver  440 . Reception of the signal can be through antenna  445 . Upon reception of the interrogation signal, receiver  440  activates RFID transmitter  475 , which sends an RF signal  620 , preferably modulated with a code identifying the tag. The detection device  600  receives the RFID signal and activates an alert device  640 . If the receiver  440  and the RFID transmitter  475  operate at similar frequencies, then the same antenna  445  can be used for both devices. A directional coupler  446  is used to ensure that signals received by the antenna  445  only go to the receiver  440  and signals transmitted by the RFID transmitter  475  only go out the antenna  445  and are not fed back into the receiver  440 . This signal  620  sent by the RFID transmitter  475  is received by the detection device  600 , which then causes an alert  640  that the tag was detected. In this embodiment, the RFID transmitter is powered from the charge storage device  430 , which is charged by the RF harvesting circuitry  420 . As long as the RF release circuitry  440  requires reception of a code, which is not sent with the tag interrogation signal  610 , then there is no risk that the interrogation signal  610  will trigger the release circuitry  440  and mechanism. The response from the RFID transmitter  475  can either be a generic signal identifying a tag&#39;s presence, or can be modulated with a code associated with each individual tag. It is advantageous that the tag responds to an interrogation with a unique identifier code as this allows for the tag to be affirmatively identified at a point of sale before a release signal is sent to the tag. 
     FURTHER EMBODIMENTS 
     The tag can be attached to an article by means other than placing a pin through the article. For example, the same pin and ball clutch type locking device as described above can be used to control the arms of a jaw-shaped clamp as depicted in  FIG. 5 . In an exemplary embodiment, the clamp  500  includes two jaws  530 ,  538  coupled by a hinge  525 . When the clamp  500  is closed over an article A, a pin  510 , which is rotatably attached at pivot point  515  to an upper clamp jaw  530  is moved into and is held from retracting by a ball clutch  520 , which is rotatably attached to lower jaw  538 . The pin  510  is held in the ball clutch  520  as described above, which contains an RF release mechanism as described above, locking the jaws  530  and  538  closed over article A. The ball clutch  520  is released in the same manner as described above, once spring pressure on the balls is released, the jaws  530  and  538  of the clamp can be separated to remove the tag from the article A. 
     Other means for releasing the RF tag from an article with the application of an RF signal to release circuitry are possible and the invention is not limited to the embodiments described above. For example, instead of a solenoid being used as the electro-mechanical release mechanism, a micro-motor linear actuator can retract a locking pin that holds a clamp or other fixing device closed. Depending on the amount of electrical power available through the RF harvesting circuitry  420 , the locking pin can either be a trigger pin that holds back a much stronger force like the spring holding the ball clutch closed as described above and shown in  FIG. 4 , or the locking pin can be the sole means of holding a clamp closed. Another such embodiment employs a spring-loaded ratcheting mechanism in place of the ball clutch in  FIG. 5 . As the jaws of the clamp are closed, a spring-loaded ratchet prevents the jaws from opening. Each click of the ratchet allows the jaws to close tighter. The ratchet pawl is released by an electro-mechanical device, e.g. a solenoid, linear actuator or the like, upon reception of a release command. 
     Another embodiment of the security tag incorporates a locking device, which can be similar to a padlock for securing an item so that it cannot be physically removed, or a reusable safer that encloses the item, such as are commonly used with CDs and DVDs. The locking device operates in the same way as the security tag described above, wherein the device is powered by ambient RF energy, and is released (unlocked) upon receipt of a release signal. The release signal could be from a portable device like a cellular phone or a portable digital assistant with wireless capability or a sales terminal or cash register based transmitter. A detailed disclosure of locking devices that unlock in response to an external signal is contained in U.S. provisional application Ser. No. 60/750,194 filed Dec. 14, 2005, and whose entire disclosure is incorporated by reference herein. Instead of being powered by the release signal as disclosed in that application, the locking devices as described in application 60/750,194 can be powered by an ambient RF harvesting circuit  420  as disclosed herein. In some instances, an RF harvesting circuit is expected to be able to generate and store significantly more energy than the signal receiving circuitry disclosed in that application. Use of an RF harvesting circuit can therefore enhance the locking mechanism such that a more powerful actuator can be used to secure the hardware components of the locking mechanisms as disclosed in application Ser. No. 60/750,194. 
     While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.