Abstract:
A computerized base station system communicates with radio frequency tags attached to one or more objects. Included in the system is a separate position detector that determines the position of one or more of the tags within a time increment and within a field of the base station. A communication process reads information from one or more of the tags within the time increment and associates the position determined with the information of the respective tag.

Description:
RELATED PATENTS AND APPLICATIONS 
     Related U.S. Pat. Nos. include: 5,866,044; 5,521,601; 5,528,222; 5,538,803; 5,550.547; 5,552,778; 5,554,974; 5,563,583; 5,565,847; 5,606,323; 5,635,693; 5,673,037; 5,680,106;5,682,143; 5,729,201; 5,729,697;5,736,929; 5,739,754; 5,767,789; 5,777,561; 5,786,626; 5,812,065; 5,821,859; 5,828,318; 5,831,532; 5,850,181; 5,874,902; 5,889,489; 5,909,176; and 5,912,632. These U.S. patents are herein incorporated by reference in their entirety. 
    
    
     FIELD OF INVENTION 
     This invention relates to RFID or radio frequency identification applications. More specifically, the invention relates to identifying particular items when there are a multitude tags on containers of objects in the field of the RFID tag reader. 
     BACKGROUND OF THE INVENTION 
     RFID has become a pervasive technology for tracking and identifying people, vehicles, retail items, pallets etc. One of the frequent applications of RFID is that of tracking pallets as they move past a tag reader or ‘base station’. Generally pallets as used in industry contain a large number of individual boxes or crates. Each crate may contain an individual, unique RFID tag. The tag may contain generic or even detailed data relating to the contents of the crate. However, present day tag readers cannot distinguish between or amongst the multitude of tags that are presented in the field. Thus, while all the tags are read in a sequential manner, the reader output cannot distinguish which tag corresponds to the particular package or crate. This lack of correlation between the tag reader and the crate makes it impossible to know which crate to unload at a particular location unless all the crates and their contents are identical. In those cases where the crates are not all identical in content, it becomes necessary to scan each tag individually in order to know which crate to unload, a time consuming and impractical solution to today&#39;s methods of distribution. 
     However, the prior art does not disclose ways that accurately and simply correlate information obtained by reading one or more tags to the specific location of the respective tag. In particular, the correlation of information and position of tag objects is not disclosed in the art related to inventory control or processing containers and/or contents in those containers. 
     OBJECTS OF THE INVENTION 
     It is the object of this invention to modify the conventional method of scanning RFID tags to correlate tag information with tag/object position of each tagged object and/or separately packaged item (in a container). It is another object of this invention to modify the conventional method of scanning RFID tags to correlate tag information with tag/object position of each tagged object and/or separately packaged item (in a container) on pallets. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a base station system for communicating with radio frequency tags attached to one or more objects. The base station has one or more computers, each having one or more central processing units (CPUs) and one or more memories. A separate position detector determines the position of one or more of the tags within a time increment and within a field of the base station. A communication process, executed by one or more of the CPUs, reads information from one or more of the tags within the time increment and associates the position determined with the information of the respective tag in one or more of the memories. 
     In one embodiment of the invention a movable or non-stationary base station antenna providing a narrow tag interrogation beam is used as the position detector. The reflected wave from the tag may also be narrow though this is not required. The antenna of the reader is designed to have rotational motion to allow for scanning in a vertical plane. Scanning can then be accomplished as a function of position with the antenna scanning vertically while the object (e.g. pallet) moves horizontally. In this mode of scanning, each tag is scanned individually as it passes the base station antenna so that the combination of horizontal pallet motion with vertical scanning results in an xy coordinate associated with each tag readout. The horizontal motion ( x direction) can be determined by knowing the velocity of the object (pallet). This can be accomplished by way of a photocell as the pallet enters a given position and exits a second position together with the knowledge of the time interval between the two photo signals. Stationary pallets can also be scanned by an antenna which can have motion in both x and y directions. Scanning can also be accomplished with fixed or stationary antenna by using a laser beam that scans and turns on individual tags for a brief time. In that case, a wide field antenna is preferably used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram cart containing boxes (containers) that have tags passing near a focused beam antenna for reading the tags. 
     FIG. 2 a  is a block diagram showing a cart containing crates or boxes as in FIG. 1, except here passing a laser beam which activates the tags attached to the crates. 
     FIG. 2 b  is a diagram showing the logic circuit related with the light activated tag. 
     FIG. 2 c  is a table (from prior art) showing the reduced characteristics for the S-R latches. 
     FIG. 2 d  is a flow diagram of the tag activation by a light source. 
     FIG. 3 a  is a flow diagram of tag reading by a narrow beam antenna for the case where the cart containing the tagged crates is at rest. 
     FIG. 3 b  is the same as FIG. 3 a  except that each tag is turned off after the first interrogation and reading of a tag. 
     FIGS. 4 a  and  4   b  are alternative embodiments of those flow charts shown in FIG. 3 except that a scanning laser is used to turn on the tags sequentially to determine the position of the crate as a function of time for the pallet or cart being addressed. 
     FIGS. 5 a  and  5   b  are alternative embodiments of those shown in FIGS. 3 a  and  3   b,  respectively, except here the cart is moving past the antenna, preferably though not necessarily at a constant velocity. 
     FIGS. 6 a  and  6   b  are alternative embodiments of those shown in FIGS. 4 a  and  4   b,  respectively, except here the cart is moving past the antenna, preferably though not necessarily at a constant velocity. 
     FIG. 7 is a block diagram describing the overall operation of a preferred system. 
     FIG. 8 is a flow diagram of the system&#39;s operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, areas (e.g. pallets) having RFID tagged containers (e.g. crates) can be interrogated as they pass a base station which is designed to send out an RF wave and receive the reflected wave from the tags. However, the difficult problem is identifying which crate has been read and what position that crate has on the pallet because the detection volume is generally quite large. Therefore, the reader will read all the tags in a matter of milliseconds but additional action is needed to identify which tag reading corresponds to a particular crate on the cart or pallet. Traditionally, knowledge of a particular crate requires a bar code attached to the crate or any one of several methods to make an additional close range measurement or visual inspection to correlate the RFID reading with the particular box or package on the pallet. 
     The present invention describes several techniques to facilitate the operation that is presently tedious while also providing a method that is suitable for a fully automated distribution system. The invention determines a one to one correspondence between the tag identification presented to the base station and the position of the scanned item. When the containers are moved from a storage area (e.g. a pallet is unloaded), it will be clear which box (container) relates to the particular tag and the description that the tag offers of the item or items within the tagged container. 
     In FIG. 1 the stationary pallet  101  contains crates  102 , each of which has an RF tag  103  attached to the end of the box facing an antenna  104 , the antenna attached to a base station  105 . The antenna  104  is designed to be directional and have a far field beam diameter of 30 cm at ˜1 meter from tag. At a greater distance between antenna and tag, the beam diameter can be made even smaller. When the cart is in a position such that one box end faces the antenna, that is the beam of the antenna  106  is approximately perpendicular to the face of the box, the antenna is able to scan the boxes. The scanning is achieved by having the antenna mounted on two axes that permit vertical and horizontal motion. This type of motion is well known in the field of radar. The amplitude of the motion is controlled so that the entire cart is scanned while the cart or pallet is stationary but in a prescribed location in order that the scanning beam can access all the tags on the pallet. The scanning and retrieval of the information from the tags is controlled by a computer  107 . 
     In a second embodiment, also shown FIG. 1, the tags on the boxes need not be addressed in a predetermined cart position. Here the cart can be in motion, either step wise or continuous with a starting and ending temporal flag  110  that can be sensed for example by an electric or acoustic sensor or sensors, a photocell  111 , a pressure sensor in the floor etc. well known by those skilled in the art for determining time intervals. In this embodiment the need for the horizontal scan is avoided since the timing between the two flag intervals determines the velocity of the pallet and hence offers a simple means for determining the position of the cart or pallet as a function of time. 
     In yet another embodiment FIG. 2 a,  the tag reading is achieved by a wide RF beam rather than a focused antenna. In this case the tags  202  contain a light sensitive switch mechanism or photocell so that when illuminated they are switched on. A laser  203  is used to scan the tags which switches the heretofore quiescent tag to an active state or ‘on’ state when the laser beam  204  is incident on a particular tag. After the laser is no longer incident on the tag, the tag can stay active for a set duration and return to its quiescent state thereby preventing it from being read more than once by the wide beam antenna. With only one tag turned on at a time, the wide beam antenna  205  will only read one tag at a time whose position is then known in both space and time by computing the angular detection of the laser. This mode of operation makes it possible to leave the antenna fixed in space while the laser scans in the plane of the tags, turning them on sequentially. The tags can be configured so that they turn off after a set period after the laser no longer is incident on them or can be turned off by a command from the computer. The laser scans in two dimensions by computer control. As in the previous case, a set of flags  110  can be used to determine the position of the cart, for both the case of a stationary or moving cart. 
     As shown in FIG. 2 b,  the tag of FIG. 2 a  uses a photovoltaic cell  231  in one of the preferred embodiments. The cell  231  is connected to an AND gate  232  while a second terminal of  232  is connected to a battery or voltage source  233  that supplies a constant voltage equivalent to a logical ‘1’. The output of  232  is connected to the ‘C’ input of a S-R-NOR latch described in detail in Modern Digital Designs by R. S. Sandige, McGraw Hill (1990) which is incorporated by reference in its entirety. The ‘S’ input is also connected to  233  and the ‘R’ input is connected to the disconnect circuit  236 . This circuit when activated put a temporary ‘1’ on input ‘R’. 
     When the laser light powers the photocell  231 , a ‘1’ is set on input ‘C’ of  234 . That in turn sets ‘Q’ equal to ‘1’ in  234 . This ‘1’ is applied to the base  240  of a transistor  235  or to any device with a similar function. This last step produces a conducting path between collector and emitter in transistor  235  connecting  238  with  237  which closes a circuit in a critical part  239  of the tag to disable the tag. Note that in alternative preferred embodiments, the photovoltaic cell has a filtering device, e.g. any well known optical filter, that discriminates ambient light from the laser light signal. 
     For the description of the critical part  239  that enables/disables the tag, refer to Docket Y0996-037, entitled Radio Frequency Identification Transponder with Electronic Circuit Enabling/Disabling Capability, to Capek et al., U.S. patent application Ser. No. 08/681,741. After the tag has been interrogated one option is that the tag shuts itself off after a short period time in a manner well known to those skilled in the art. Alternatively, the tag can set a a temporary ‘1’ in  236  which sets ‘R’ equal to ‘1’ and therefore the latch  234  resets ‘Q’ equal to zero, thereby opening the path between  238  and  237 , thereby disabling the tag. It is well known to those skilled in the art that similar enabling/disabling functions can be facilitated using a photodiode in series with the battery  233  while the AND gate  232  can be replaced by an OR gate with one terminal connected to ground. Other combinations of logical devices to carry out this function are well known to those skilled in the art. The characteristic table for the S-R latches is shown in FIG. 2 c , generally known in the prior art. See for example Modern Digital Designs by R. S. Sandige, McGraw Hill (1990). 
     FIG. 2 d  describes the flow diagram for the process that starts  250  with the tag in an off position where ‘S=1 and C,R,Q’ are set to zero in latch  234 . In  251  the laser or light source illuminates the photocell setting  252 , S=1, Q=1 in  234  connecting  253 , the parts  238  and  237  which close the circuit in  239  enabling  254 , a critical part of the circuit making the tag active from its previous quiescent state. The tag remains active even though the light is no longer incident and the tag is read  255 . After the tag is read, the tag can be shut via its own circuit as is well known in the art or alternatively, set ‘R’ =1 in  234  temporarily, which will open the transistor disabling the critical circuit  239  thus putting the tag back into its quiescent state. 
     FIG. 3 shows a flow diagram indicating the logic steps for FIG. 1 for the case that the pallet is stationary in a predetermined position. Step  301  the starting flag signals the start of the reading process. The variable, j, determining the horizontal movement of the antenna is set to zero,  302 . The next step determining the vertical scan given by letter i, is set to 0, 303. In the next step,  304 , the antenna is pointed in a direction given by coordinates, i, j in a direction given by the variable H ij . In the following step  305  the signal ID ij  designating the identification of the i,j tag is queried and read by the base station. If ID ij  is non-zero, the system  306  reads H ij , ID ij  and INFO ij , which describes the content of each crate which has a tag ID ij . In the next step  307  the computer compares ID ij  with ID 1−l, j . If these two readings are the same, then the average value between H i−1,j  and H ij , represented by &gt;H i−1,j , H ij , step  308 . Next, the comparator compares  309  ID ij  with ID 1j−l . If they are the same, then the average value &lt;H ij−1 , H ij .&gt; is assigned to H ij , step  310 . In the next step  311  the variable ‘i’ is incremented by one and its value is compared with the upper limit, n. If the value of ‘i’ is greater or equal to n, then in the next step  313 , the horizontal value j is incremented by one. In the next step  314  the value of ‘j’ is compared with an upper limit ‘m’. If ‘j’ is larger or equal than m then H ij , ID ij , and INFO ij  are displayed in step  315 . Commands are issued in step  316  to unload specified boxes by means of a robot or manually and the process stops  317 . To address the case of level  305  where ID ij  is equal to zero, the next logic step is step  311 . If ID ij  is not equal to ID i−1,j , level  307  the next logic step is step  308 . If ID ij−1  is not equal to ID ij , then the next logic step is  311 . If i&lt;n in level  312  then the next logic step is  304 . Finally if j&lt;m in level  314 , the next logic step is  303 . 
     In another embodiment the tag is turned off after it is read and stays off for a predetermined interval consistent with the other time-dependent parameters of the scanning system. For that case, the flow diagram is shown FIG. 3 b.  The step  321  signals the start of the reading process. The antenna continues scanning  322  until it detects the signal containing the ID of a tag at position ‘i,j’. The time required for reading the tag is kept small compared to the scanning time, that is the time to traverse the diameter of the tag. The following steps comprise reading the position of the tag, H ij ,  324  reading the ID ij    325 , reading INFO ij    326  and turning the tag off,  327 . The next step requires checking to see that the end flag  328  has been reached. If so, the system displays all the H ij &#39;s, ID ij &#39;s and INFO ij &#39;s. The following step issues commands  330  and stops the process  331 . If the end flag is not detected, the system continues to scan  322 . 
     FIG. 4 a  shows the flow diagram similar to that shown in FIG. 3 a  where the cart is stationary and a scanning laser is used to turn on the tags sequentially to determine the position of the crate as a function of time for the pallet or cart being addressed. The difference between FIGS. 4 a  and  3   a  is that in FIG. 4 a  the laser scans while the antenna remains stationary. In  404  the laser points at position H ij . In step  405  the antenna receives a signal that causes the laser to remain stationary while the tag is powered and the variables H, ID and INFO are read  406 . The subsequent steps  407 - 417  are similar to the steps  307 - 317  respectively. 
     FIG. 4 b  contains similar steps as those found in  3   b  with the exception that step  423  is different from the corresponding step  323  in so far as pinging signifies the laser has identified the presence of a tag leads to  424  which powers the tag and then  425 - 428  are again similar  324 - 327  in which the variables are read for H, INFO ID are again read and the tag is turned off. The process continues with steps  429 - 432  which are similar to steps  328 - 321 . 
     So far, the flow diagrams have dealt only with the antenna or the laser moving or scanning elements while the pallet or cart is stationary. In FIG. 5 a,  the steps are similar to those in FIGS. 3 a  except here the pallet or cart is moving, preferably at constant velocity past the scanning devices. For this case, the scanning of the antenna as described in FIG. 3 again scans the pallet but can also be made to scan in only the vertical plane. The steps in the flow diagram corresponding to FIG. 5 a  are similar to steps of the flow diagram of FIG. 3 a,  with the addition that in FIG. 5 a,  step  515  is added in which the position of the variable ‘j’ is computed with respect to the pallet or cart velocity. Step  516  determines the position of ‘i,j’ with respect to the pallet or cart reference. Step  517  displays the variables H, ID, INFO with respect to the pallet or cart reference frame. Commands are again issued  518  and the system terminates with step  519 . FIG. 5 b  is similar to FIG. 3 b  except here the pallet or cart is moving, preferably at constant velocity past the scanning devices; the additional steps are labeled  529 - 533 . 
     FIG. 6 a  corresponds to the steps of FIG. 4 a  except that the pallet or cart is now in motion. For this case, the scanning of the laser as described in FIG. 4 again scan the pallet but can also be made to scan in only the vertical plane The overall scanning and tag reading process follows in steps  616 - 619  which are identical to  515 - 519 . The flow steps of FIG. 6 b  are similar to those of FIG. 4 with the addition of steps  640 - 644  which are the same as  616 - 619 . 
     FIG. 7 shows the pallet or cart  701  stopping or passing in proximity to base station  702  where the tags are read and the position of the crates are determined with respect to a reference frame fixed to the pallet. Instruction for further cart movement and robot action are issued and the pallet starts a preprogrammed path  703  where unloading at selected storage or transport areas  704  or to a loading dock  705 . 
     FIG. 8 shows the flow diagram of the system operation. In step  801  the pallet or cart is scanned. The ID of the boxes or crates are determined with respect to the pallet  802  and the positions are recorded in the computer memory  803 . In step  804  an output of the information is produced. In step  805  the distribution information is conveyed to robots or people for  806  and the instructions are executed.