Abstract:
A system tracks assets using RFID tags. A plurality of RFID readers use different frequencies to read RFID tags. A plurality of assets each have a RFID tag coupled to them. The RFID tag changes a response frequency as a function of a next RFID reader scheduled to track the corresponding asset. Assets may be components in an assembly line, patients in hospitals, containers, or other things that need to be tracked at different locations.

Description:
BACKGROUND  
       [0001]     RFID tags are finding numerous applications in asset tracking and monitoring. In assembly lines, the use of such tags can help with assembly by making sure parts are correctly identified and used in assembling products. Each part may be provided a tag to uniquely identify the part. When parts or readers are placed closely on an assembly line, reader/tag collisions between adjacent readers/tags can result in incorrect identification, or confusion in correctly identifying the parts. This can occur in many different situations, such as when the spacing between adjacent stages in an assembly line is comparable to that between a reader and tag.  
         [0002]     Prior attempts to minimize such confusion involved reducing transmit power levels. Doing so may increase a bit error rate (BER) of a link due to reduced signal to noise ratio (SNR). Attempting to implement synchronization schemes can greatly increase the cost and complexity of systems.  
       SUMMARY  
       [0003]     A system tracks assets using RFID tags on the assets. A plurality of RFID readers use different frequencies to read RFID tags. The RFID tag changes a response frequency as a function of a next RFID reader scheduled to track the corresponding asset. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a block diagram of and RFID tag and reader according to an example embodiment.  
         [0005]      FIG. 2  is a block diagram of an assembly line utilizing RFID tags and readers according to an example embodiment.  
         [0006]      FIG. 3  is a block diagram of an RFID tag according to an example embodiment.  
         [0007]      FIG. 4  is a state diagram of a component RFID tag according to an example embodiment.  
         [0008]      FIG. 5  is a state diagram of an assembly RFID tag according to an example embodiment.  
         [0009]      FIG. 6  is a state diagram of a reader according to an example embodiment.  
         [0010]      FIG. 7  is a block diagram of a computer system for implementing algorithms according to an example embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0011]     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.  
         [0012]     The functions or algorithms described herein are implemented in software or a combination of software and human implemented procedures in one embodiment. The software comprises computer executable instructions stored on computer readable media such as memory or other type of storage devices. The term “computer readable media” is also used to represent carrier waves on which the software is transmitted. Further, such functions correspond to modules, which are software, hardware, firmware or any combination thereof. Multiple functions are performed in one or more modules as desired, and the embodiments described are merely examples. The software is executed on a digital signal processor, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server or other computer system.  
         [0013]     As shown in  FIG. 1 , a basic RFID system  110  includes two components: a reader  112 , and a transponder (commonly called an RFID tag)  114 . The reader  112  and RFID tag  114  include respective antenna circuits  116 ,  118 . In one embodiment, the RFID tag  114  is an active RFID tag. It contains a power source and transmitter that is used to generate its own radio frequency energy.  
         [0014]     In operation, the reader  112  receives transmission from the RFID tag through its antenna circuit  116 . In response to successfully receiving the transmission, the reader  112  sends an acknowledgement back to the RFID tag  114 . In one embodiment, the readers receive data from RFID tags at different frequencies, resulting in frequency diversity.  
         [0015]     A typical RFID system  110  often contains a number of RFID tags  114  and one or more readers  112 . RFID tags are divided into three main categories. These categories are beam-powered passive tags, battery-powered semi-passive tags, and active tags. Each operates in different ways.  
         [0016]     The beam-powered RFID tag is often referred to as a passive device because it derives the energy needed for its operation from the interrogation signal beamed at it. The tag rectifies the energy field and changes the reflective characteristics of the tag itself, creating a change in reflectivity that is seen at the interrogator. A battery-powered semi-passive RFID tag operates in a similar fashion, modulating its RF cross-section in order to reflect a delta to the interrogator to develop a communication link. Here, the battery is the source of the tag&#39;s operational power for optional circuitry. The passive and semi-passive devices, or non-active devices, reflect the energy from the interrogation signal. In contrast, in an active RFID tag, a transmitter is used to generate its own radio frequency energy powered by the battery.  
         [0017]     In one embodiment, active RFID tags are utilized to track assets, such as components and assemblies. Assets that may be tracked also include patients that are monitored in hospitals, container tracking in shipping environments, and other assets that are tracked in different locations. In the present embodiment, the term “assemblies” is used to refer to a major component of a product being assembled, such as an engine. Other components are added to the engine as the engine or assembly progresses down an assembly line  200  as shown in  FIG. 2 . A plurality of readers  205 ,  210  and  215 , correspond to successive stages on the assembly line  200 . Each reader operates at a different frequency, f 1  f 2  and f 3  respectively. The readers may be coupled by a network  220 , which may be hardwired, or wireless, and in turned coupled to a controller  225  for controlling or tracking assembly line operations.  
         [0018]     An engine  230  is shown on the assembly line  200  at a first station or stage. It has an assembly RFID tag  235 . The engine is also shown at second and third stages at  240  and  250 , with corresponding RFID tags  245  and  255 . The various engines at the stages are representative of the same engine, or different engines, each receiving components that are assembled at the various stages. An assembly section  260  associated with the first stage contains various components that are added to engine  230  at the first stage. Successive stages may have further assembly sections.  
         [0019]     The components are also equipped with component RFID tags. In one embodiment, each of the RFID tags for both components and assemblies are programmed to transmit at a frequency corresponding to the station it is at, or in the case of some components, the station where it is to be added to or assembled in the assembly. Assembly RFID tags change frequencies as the engine progresses down the assembly line and moves to different stages. The frequencies may be preprogrammed into the RFID tags, and may be successively increasing frequencies, or otherwise. In one embodiment, frequencies for successive stages may be selected to minimize interference between stages. RFID tags for components may be removed upon assembly, and transmit at that time, or may be transmitting prior to assembly if desired. The tags may be reused after removing from one component, and information in the tags about the components may be updated, or frequencies changed if required.  
         [0020]      FIG. 3  is a diagram of an RFID tag  300  formed in accordance with one embodiment of the present invention. The RFID tag  300  includes a transceiver, and has an antenna  305  is coupled to a demodulator  310 , which receives transmitted radio-frequency signals from the antenna  305  and extracts data contained therein. The demodulator  310  is coupled to a processor  315 , which analyzes the data extracted from the radio frequency signal. In one embodiment, the processor  315  is coupled to a memory  320 , such as a non-volatile programmable memory, and the processor  315  generates control signals to store data in the memory  320  based on the data extracted from the transmitted radio-frequency signal, such as an acknowledgement from a reader. The processor  315  is coupled to a modulator  325  and generates control signals to control the modulation of a radio-frequency signal by the modulator  325 , based on the data extracted from the received radio-frequency signal. The modulator  325  is coupled to the antenna  305  for transmission of the signal. In one embodiment, power circuitry  330  includes a batter for powering the RFID circuitry.  
         [0021]     Component tags are reusable, and may be mounted on critical components that need to be assembled on the engine. Programming of memory  320 , as illustrated in a state diagram of  FIG. 4 , may be done through a user interface in which a component type and ID are provided. Based on the stage in which the component is going to be assembled, its transceiver is tuned to the desired frequency at  400  of the corresponding assembly stage. Once programmed, the component tag will be using this frequency for communication. The tag will be removed from the component at  405  once the component gets assembled. When the tag is removed from the component, it comes to an ON state, tunes to the reader&#39;s frequency and starts transmitting to the reader at that stage at the proper frequency  410 . The tag keeps sending its data until it gets an acknowledgement or for a predetermined timeout period, whichever occurs earlier. Once this happens, the tag will again go to the OFF state at  415 .  
         [0022]     An engine or assembly tag follows a state diagram as shown in  FIG. 5 . Engine tags are mounted on the engine body and are programmed with the engine ID and frequency of the first stage in one embodiment. In the first stage of the assembly line, when the operator triggers the engine tag, it will send out the engine ID information to the reader at  500 . Once it gets an acknowledge (ACK) at  505  from the reader, it changes at  510  to the frequency of the next, stage 2 reader. The sequence of frequencies of the various stages may be stored in nonvolatile memory of the engine tag while programming. Once the frequency is changed, it goes to the OFF state or sleep mode at  510 . The engine tag periodically comes to the ON state at  500  and looks for the reader. The period may be determined by the speed at which the conveyor belt moves. If the engine tag does not get a reply from the expected reader (perhaps the reader is not functioning correctly) within the expected time period, it changes to the next frequency—that of the third stage. The present frequency of operation of the tag will be stored in the flash, so that if the tag gets reset accidentally, it can recover. In one embodiment, the engine tag scans all channels and synchronizes with the closest reader frequency at  515  following a timeout  520 .  
         [0023]     Readers may be connected to the controller through a multi-drop network as shown in  FIG. 2 . Each of the stages in the assembly which has at least one critical component to be tracked will have a tag at that stage. Each of the readers knows what components need to be assembled at a corresponding stage for the type of engine. This information may be obtained from the controller through a serial port, or other network connection. Thus, the reader at a stage “n” will have a table containing all the engine types as well as all the components that need to be assembled at that stage.  
         [0024]     An example table structure stored at the reader is as follows:  
                                                                           Struct EngineDetails{                int   Engine ID;           int   Number of Components;           int[20]   Component IDs;                }                      
 
         [0025]     There may be other tables that map the engine ID and component. ID&#39;s to their equivalent character representations for display purposes. Each of the readers may be programmed to communicate in a predefined fixed frequency as shown at  600  in a state diagram of  FIG. 6 . The frequency is selected in such a way that the frequency separation between adjacent readers is maximized. This will ensure that the communication happening in adjacent stages will have minimum impact on a given reader. The readers are programmed to have a range of approximately 10 meters in one embodiment, but the range may be varied significantly. The same frequency may be used for two readers that are sufficiently distant from each other to avoid interference. The series of frequencies may also be repeated if there are an insufficient number of available frequencies for the number of stations required for proper assembly.  
         [0026]     When a packet is received from a component RFID tag at  605 , the reader verifies at  610  whether the component is the right one for the engine currently assembled using one of the table structures described above. A packet  615  may then be received from an engine RFID tag, at which point the reader identifies the engine at  620  and displays the list of components to be mounted on the engine.  
         [0027]     A block diagram of a computer system, such as the controller, or processor and memory combinations in the RFID tags, that executes programming for performing the above algorithms is shown in  FIG. 7 . A general computing device in the form of a computer  710 , may include a processing unit  702 , memory  704 , removable storage  712 , and non-removable storage  714 . Memory  704  may include volatile memory  706  and non-volatile memory  708 . Computer  710  may include—or have access to a computing environment that includes—a variety of computer-readable media, such as volatile memory  706  and non-volatile memory  708 , removable storage  712  and non-removable storage  714 . Computer storage includes random access memory (RAM), read only memory (ROM), eraseable programmable read-only memory (EPROM) &amp; electrically eraseable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD ROM), Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing computer-readable instructions. Computer  710  may include or have access to a computing environment that includes input  716 , output  718 , and a communication connection  720 . The computer may operate in a networked environment using a communication connection to connect to one or more remote computers. The remote computer may include a personal computer (PC), server, router, network PC, a peer device or other common network node, or the like. The communication connection may include a Local Area Network (LAN), a Wide Area Network (WAN) or other networks.  
         [0028]     Computer-readable instructions stored on a computer-readable medium are executable by the processing unit  702  of the computer  710 . A hard drive, CD-ROM, and RAM are some examples of articles including a computer-readable medium. For example, a computer program  725  capable of providing a generic technique to perform access control check for data access and/or for doing an operation on one of the servers in a component object model (COM) based system according to the teachings of the present invention may be included on a CD-ROM and loaded from the CD-ROM to a hard drive. The computer-readable instructions allow computer system  700  to provide generic access controls in a COM based computer network system having multiple users and servers.  
         [0029]     The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.