Abstract:
A test fixture for evaluating an RF identification system and related methods for evaluating an RF tag and/or an RF antenna, are disclosed. The test fixture provides predefined RF tag positions that can be used to test: read position, distance and antenna capability and adjustments. By placing an actual RF tag in each of the predefined positions, a read of the tag information can be performed. A three dimensional plot can then be established for the sensitivity field of the antenna. By placing the RF tag in various positions and orientations, the antenna can be adjusted until an optimum field is produced. The invention can also be used to determine RF tag performance within the optimized field.

Description:
BACKGROUND OF INVENTION 
   1. Technical Field 
   The present invention relates generally to radio frequency (RF) identification systems, and more particularly, to a test fixture for evaluating an RF identification system and related methods. 
   2. Related Art 
   Highly automated manufacturing facilities, such as those in the semiconductor industry, track product movement of a product throughout a facility using a radio frequency (RF) identification system. Typically, these systems include an RF tag mounted to the product and RF antennas placed at load ports within a manufacturing facility to sense and read RF tags on the product containers. The ability to read RF tags repeatedly and accurately within the manufacturing facility is a critical component of the automation system. An antenna&#39;s sensing field is three dimensional. The alignment of an antenna to the RF tag enables each load port that receives the product container having an RF tag to read the information contained on the RF tag. Tag reading, however, is affected by external fields, metal objects, and positioning and alignment of the antenna. 
   One challenge for these automation systems is making “in-the-field” adjustments to ensure proper reading of RF tags. “In-the-field” adjustments are difficult because, inter alia, surrounding metal, obstructions and other RF field parameters affect the shape of the antenna sensing fields. One approach to provide “in-the-field” adjustments is to conduct testing using a hand held field strength meter, which senses the strength and location of an antenna&#39;s sensing field. This approach, however, suffers from a number of drawbacks. First, field strength meters use a different antenna than the in-situ antenna. As a result, they do not replicate the actual tag and actual antenna interaction. Second, field strength meters are hand held and, therefore, prevent accurate repeatability of positioning during testing. As a result, field strength meters provide only a general indication of antenna performance because they do not accurately replicate the read capability of the RF tag in situ. Finally, since field strength meters evaluate an antenna&#39;s sensing field only, they provide no functioning that allows verification of tag performance. 
   In view of the foregoing, there is a need in the art for a solution that addresses the problems of the related art. 
   SUMMARY OF INVENTION 
   The invention includes a test fixture for evaluating an RF identification system and related methods for evaluating an RF tag and/or an RF antenna. The test fixture provides predefined RF tag positions that can be used to test: read position, distance and antenna capability and adjustments. By placing an actual RF tag in each of the predefined positions, a read of the tag information can be performed. A three dimensional plot can then be established for the sensitivity field of the antenna. By placing the RF tag in various positions and orientations, the antenna can be adjusted until an optimum field is produced. The invention can also be used to determine RF tag performance within the optimized field. 
   A first aspect of the invention is directed to an apparatus for evaluating a radio frequency (RF) identification system, the apparatus comprising: a test fixture including a base having a plurality of tag positions for locating an RF tag relative to an RF antenna. 
   A second aspect of the invention is directed to a method of evaluating a radio frequency (RF) identification system, the method comprising the steps of: placing a test fixture proximate an RF antenna of the RF identification system; positioning an RF tag at a plurality of tag positions on the test fixture; and evaluating sensing of the RF tag by the RF antenna at each of the tag positions. 
   A third aspect of the invention is directed to a method of evaluating a radio frequency (RF) identification system including an RF tag and an RF antenna for sensing the RF tag, the method comprising the steps of: placing a test fixture in proximity to the RF antenna; positioning the RF tag at a plurality of tag positions on the text fixture; evaluating sensing of the RF tag by the RF antenna at each of the tag positions; determining at least one of: a sensing field of the RF antenna and a sensitivity strength of the RF tag; and adjusting one of the RF tag and the RF antenna to ensure reading of the RF tag by the RF antenna during operation of the RF identification system. 
   The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
       FIG. 1  shows a perspective view of a test fixture according to one embodiment of the invention. 
       FIG. 2  shows a perspective view of an underside of one stackable member of the test fixture of  FIG. 1 . 
       FIG. 3  shows a plan view illustrating positions for either placing an RF tag or holding a stackable member of  FIG. 1  according to one embodiment of the invention. 
       FIG. 4  shows a three-dimensional sensitivity field for an RF antenna and various tag positions for generating the sensitivity field. 
   

   DETAILED DESCRIPTION 
   With reference to the accompanying drawings,  FIG. 1  shows a perspective view of a test fixture  8  for evaluating a radio frequency (RF) identification system, according to one embodiment of the invention. Test fixture  8  includes a base  10  having a plurality of tag positions  12  for locating an RF tag  14  relative to an RF antenna  20 . Test fixture  8  also preferably includes a height adjustable mount  22  configured to hold RF tag  14  at a selected vertical position relative to RF antenna  20 . Mount  22  is positionable at a selected one of a set  30  of mount positions  32  provided on base  10 . Mount positions  32  extend in a linear direction such that the mount can be moved to a selected one of the mount positions  30 , for reasons to be explained below. As used herein, “tag positions”  12  include a number of different positions, i.e., general position relative another structure, and/or a number of different orientations, i.e., angular position relative to another structure, for an RF tag  14 . The different orientations may be provided, for example, by tag position  12  openings being angled or placed in the side of mount  22  ( FIG. 2  only). 
   In one embodiment, mount  22  includes a plurality of stackable members  24 . As shown in  FIGS. 1 and 2 , a lowermost stackable member  24 L includes a positioner  26  configured to mate with at least one of a set of complementary mount positioners  32  on base  10  of test fixture  8 . At least each other stackable member  24  (and perhaps lowermost stackable member  24 L) includes at least one positioner  26  configured to mate with a complementary positioner  28  located on another stackable member  24 . Stackable members  24  can be stacked to position RF tag  14  at a variety of vertical positions relative to RF antenna  20 . The thickness of stackable member  24  can be selected to accommodate different vertical positions. 
   In one embodiment, shown in  FIGS. 1 and 2 , each positioner  26 ,  28  includes one of a male coupler  26  and a female coupler  28  configured to mate with a complementary female coupler  28  and a complementary male coupler  26 , respectively. Linearly disposed set  30  of mount positions  32  may be provided on base  10  to position height adjustable mount  22  in a selected one of mount positions  32  on base  10 . In this fashion, RF tag  14  position can be adjusted in one horizontal direction and vertically. While one particular mechanism has been shown for positioning stackable members  24 , it should be recognized that a variety of different mechanisms exist for positioning and holding member  24  in place. 
   With regard to the plurality of tag positions  12 , each tag position is configured to receive RF tag  14 . Referring to  FIGS. 1 and 3 , in one embodiment, a first set  34  of the plurality of tag positions  12  is provided on mount  22 , i.e., at least an uppermost stackable member, in a first linear direction. Mount position  32  extend in a second linear direction that is substantially perpendicular to the first linear direction such that RF tag  14  can be positioned in a variety of three-dimensional tag positions  12  via first set  34 , mount positions  32  and height adjustable mount  22 . A second set  36  of the plurality of tag positions  12  may extend in a radial fashion on base  10 . As shown, each tag position  12  of sets  32 ,  34 ,  36  is spaced at equal distances from adjacent positions, e.g., 15° in the radial set  36 , however this is not necessary. In addition to linear set  34 , each mount position  32  may also be used for positioning RF tag  14 . In this case, each mount position  32  is preferably configured to have substantially the same shape and dimensions as a cross-section of RF tag  14 , so that mount positions  32  can be used for either purpose. In this case, a first set  34  of the plurality of tag positions  12  extends in a first linear direction, and another set  30  of the plurality of tag positions  12  extends in a second linear direction that is substantially perpendicular to the first linear direction. In addition, a second set  36  of the plurality of tag positions  12  extend in a radial fashion on base  10 . 
   Test fixture  8  is preferably made of a material that has no RF effect on the RF antenna, e.g., any non-metallic material. As shown in  FIG. 3 , test fixture  8  may also include a coupler  40  for positioning test fixture  8  as an element to which RF tag  14  is to be coupled in operation. The “element” could be any automation system component to which an RF tag  14  may be coupled. In the semiconductor industry, the element could be, for example, a front opening unified pod (FOUP), a front opening shipping boxes (FOSBs) or a reticle standard mechanical interface pods (RSPs). In this fashion, test fixture  8  can be used in-the-field of concern, e.g., on an automation system, such that any RF affecting parameter  50 , e.g., surrounding machinery, metal, etc., that could affect RF antenna  20  sensing field can be evaluated. 
   The invention also includes a system for using test fixture  8  including an RF antenna  20  sensing field determinator  44 , which may include any conventional computer system, a software program or other hardware. In one embodiment, since test fixture  8  is capable of locating RF tag  14  in three-dimensions, a sensing field can be modeled in three-dimensions, which adds accuracy to any adjustment made.  FIG. 4  shows a three-dimensional sensitivity field  100  for an RF antenna and illustrative tag positions  12  (no all inclusive) for generating the sensitivity field. 
   The invention also includes method of evaluating a radio frequency (RF) identification system. In operation, test fixture  8  is placed proximate RF antenna  20  of the RF identification system. An RF tag  14  is then positioned at a plurality of tag positions  12  on test fixture  8 . One of the tag positions  12  can be designated as an origin (i.e., 0,0,0 co-ordinate) such that all readings reference to the origin, i.e., depth, width, height and radial positioning. Evaluation of whether RF antenna  20  senses RF tag  14  at the plurality of tag positions  8  is conducted for each tag position. Additional steps of the method may include determining at least one of: a sensing field of RF antenna  20  and a sensitivity strength of RF tag  14 . Another step may include, adjusting one of RF tag  14  and RF antenna  20  to ensure reading of RF tag  14  by RF antenna  20  during operation of the RF identification system. By placing RF tag  14  in known bad read points, RF antenna  20  can be adjusted until a good read is made. Where the sensing field of RF antenna  20  is determined, this step may include obtaining a three dimensional plot of the sensing field, as discussed above. In this case, at least one vertically different tag position is used, and preferably a number of vertically different tag positions are used. Where a sensitivity strength of RF tag  14  is determined, this step allows evaluation of RF tag  14  performance rather than simply providing a good/bad indication of RF tag  14  operation. As a result, the invention is able to eliminate weak or poor performing tags  14  by evaluating them with an optimized antenna  20 . As noted above, where test fixture  8  is coupled by coupler  44  to an element of an automation system, the evaluating step includes consideration of the presence of an RF field affecting parameter  50  such as other machinery, etc. RF field affecting parameter  50  may exist in-the-field or be generated within a laboratory setting. 
   While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.