Patent Publication Number: US-8994503-B2

Title: RFID evaluation system, target position indicating apparatus, and target position indicating program for changing a posture of an RFID tag

Description:
TECHNICAL FIELD 
     The present invention relates to RFID evaluation systems, target position indicating apparatuses, and target position indicating programs. 
     BACKGROUND ART 
     A system for evaluating an RFID (radio frequency identification) tag that evaluates the RFID tag, taking into account a degree of freedom of a relative posture which is unique to radio authentication is known in the related art. For example, as an example of the system for evaluating the RFID tag, an RFID tag evaluation system is known, including a positioning apparatus having an elongated plate-shaped radial direction rail which moveably supports a tested object fixing unit for holding the RFID tag to be evaluated; a radial driving unit which moves the tested object fixing unit back and forth on the radial direction rail to change a moving radius to an arbitrary one; an elevation angle driving unit which drives the radial direction rail in an arbitrary elevation angle direction by rotating the radial direction rail from an origin which is a base part of one end of the radial direction rail upward and downward relative to a horizontal face; and a direction angle driving unit which drives the radial direction rail so as to rotate it in an arbitrary direction angle with, as an axis, a vertical portion which is vertical relative to the horizontal face located at the origin; an antenna arranged at the origin position that transmits a radio signal for testing to the RFID tag and that receives the radio signal transmitted from the RFID tag; and a testing apparatus which transmits a radio signal from the antenna to the RFID tag for each combination of respective values of moving radii, elevation angles and direction angles and receives a radio signal received from the RFID tag to change the respective moving radii, elevation angles, and direction angles to evaluate the RFID tag (see Patent document 1, for example). 
     However, with the above described RFID tag evaluation system, it is necessary to take measures such as providing, outside a moveable range of the positioning apparatus, a fence, etc., taking into account work format, working site conditions, etc., in order to prevent danger due to humans coming into contact with the positioning apparatus in operation based on specifications such as labor safety and health regulations, etc., when the positioning apparatus is an industrial robot. 
     Therefore, with the above-described RFID tag evaluation system, there is a problem that it is not simple to take the RFID system into a location at which the RFID system is actually implemented. With the above-described RFID tag evaluation system, there is a problem that an evaluation of the RFID tag at the location at which the RFID system is actually implemented may differ from an evaluation of the RFID tag carried out by preparing, in an anechoic chamber, etc., an environment which approximates the location at which the RFID system is actually implemented, for example. 
     Patent Document 
     
         
         Patent document 1: JP4579599B 
       
    
     DISCLOSURE OF THE INVENTION 
     In light of the problems described above, an object of the present invention is to provide an RFID evaluation system, a target position indicating apparatus, and a target position indicating program that make it possible to easily evaluate an RFID system at a location at which it is implemented. 
     According to an embodiment of the present invention, an RFID evaluation system which evaluates an RFID system is provided, the RFID evaluation system including: a tag position and posture varying unit which accepts a manual operation from an operator to vary a position of an RFID tag and automatically varies a posture of the RFID tag; an antenna unit which transmits a radio signal for testing to the RFID tag and which receives the radio signal transmitted from the RFID tag; and a control unit which, for each combination of the position and the posture of the RFID tag, controls the antenna unit to measure a response radio wave strength of the RFID tag, wherein the control unit includes a position measuring unit which measures the position of the RFID tag; and an information providing unit which provides information for moving the RFID tag to a target position. 
     A form of the present invention in which elements, representations, or arbitrary combinations of the elements of the present invention are applied to a method, an apparatus, a system, a computer program, a recording medium, a data structure, etc., is also effective as a mode of the present invention. 
     The present invention makes it possible to provide an RFID evaluation system, a target position indicating apparatus, and a target position indicating program that make it possible to easily evaluate an RFID system at a location at which it is implemented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a configuration drawing of an example of an RFID evaluation system according to the present embodiment; 
         FIG. 2  is a configuration diagram of an exemplary control unit; 
         FIG. 3  is a configuration diagram of a tag position and posture varying unit; 
         FIG. 4  is a hardware configuration diagram of an exemplary PC; 
         FIG. 5  is a flowchart of an exemplary process of the RFID evaluation system; 
         FIG. 6  is an image diagram of an example of multiple measuring points; 
         FIG. 7  is a flowchart of an example of a process which computes a posture of a crane; 
         FIG. 8  is an image of an example of a process which computes a direction angle of the crane; 
         FIG. 9  is an exemplary explanatory diagram for explaining setting of absolute and position control coordinates; 
         FIGS. 10A and 10B  are image diagrams of exemplary projection and screen patterns; 
         FIGS. 11A ,  11 B,  11 C,  11 D, and  11 E are image diagrams of an exemplary projection pattern projected onto a screen; 
         FIGS. 12A ,  12 B, and  12 C are diagrams for explaining another exemplary method of indicating target position; and 
         FIGS. 13A and 13B  are diagrams for explaining yet another exemplary method of indicating target position. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention are described in detail below. 
     When implementing an RFID system, it needs to be designed such that an RFID tag is detected at a necessary location and is not detected at an unnecessary location. More specifically, for the RFID system in UHF band that recognizes over a long distance (up to several meters), radio waves are not visible and detection is performed in a wide range, so that determining is difficult. 
     In this way, when implementing the RFID system, it is necessary to evaluate the non-visible radio waves to evaluate whether an actual RFID system operates stably, or in other words, whether the RFID tag may be read, whether no RFID tag is missed in reading, or whether no unnecessary RFID tag is read. 
     In order to determine whether the actual RFID system operates stably, it is necessary to grasp, as a response radio wave strength distribution of the RFID tag, what response radio wave strength is achieved at what posture at what position (at what position and posture) of the RFID tag in a space of a location at which the RFID system is actually implemented. 
     Grasping the response radio wave strength distribution of the RFID tag leads to stable operating conditions of the RFID tag (at what posture and at what range it is passed) being recognized. 
     If a response radio wave strength distribution of the RFID tag before operation is grasped accurately, the RFID system may, in a short time, accurately investigate causes and propose actions to be taken by grasping the response radio wave strength distribution of the RFID tag and comparing it with the response radio wave strength distribution of the RFID tag before operation even when the reading performance deteriorates due to some cause after actual operation. 
     Thus, the RFID evaluation system of the present embodiment that is easily brought into a location at which the RFID system is actually implemented, may arbitrarily designate a position and posture of the RFID tag within a space of a location at which the RFID system is actually implemented and measure the response radio wave strength to grasp the response radio wave strength distribution within the space of the location at which the RFID system is actually implemented and evaluate the RFID system. 
     (Configuration Diagram) 
       FIG. 1  is a configuration diagram of an example of an RFID evaluation system according to the present embodiment. An RFID evaluation system  1  in  FIG. 1  includes an antenna unit  10 ; a control unit  11 ; a tag position and posture varying unit  12 . In  FIG. 1 , two antenna units  10  make up a gate. The antenna units  10  are not limited to two. 
     The antenna unit  10 , whose illustration is omitted in  FIG. 1 , is communicatively connected to a PC  15  of the control unit  11 . A form of connection between the antenna unit  10  and the PC  15  may be wireless or wired. The antenna unit  10  transmits a radio signal for testing to an RFID tag  16  held by the tag position and posture varying unit  12  and receives the radio signal transmitted from the RFID tag  16  by a control from the PC  15 . The antenna unit  10  transmits the received radio signal to the PC  15 . An RFID reader/writer is embedded in the antenna unit  10 , for example. The RFID reader/writer may be separately provided between the antenna unit  10  and the PC  15 . The antenna unit  10  is an example of an RFID tag detecting unit. 
     The control unit  11  includes a projector  13 , a stereo camera  14 , and the PC  15 . The projector  13  projects, onto a screen  17  of the tag position and posture varying unit  12 , information for moving, to a target position, the RFID tag  16  with a control of the PC  15 , indicating to an operator which operates the tag position and posture varying unit  12 . Information for moving the RFID tag  16  to the target position may be displayed at a PC  20  of the tag position and posture varying unit  12 . 
     The stereo camera  14  shoots a marker  18  of the tag position and posture varying unit  12  with a control of the PC  15 . The marker  18  is fixed to a predetermined position of a crane  19  of the tag position and posture varying unit  12 . 
     The PC  15  may measure a three-dimensional position of the marker  18  from results of shooting by the stereo camera  14 . The PC  15  may set, in advance, a positional relationship between the marker  18  and the RFID tag  16  fixed to the crane  19  to compute a three-dimensional position of the RFID tag  16  from a three-dimensional position of the marker  18 . 
     Moreover, the PC  15  measures the three-dimensional position of the marker from the results of shooting by the stereo camera  14  to compute a direction angle of the crane  19  and transmit the direction angle of the crane  19  to the tag position and posture varying unit  12 . 
     The tag position and posture varying unit  12  includes a moving mechanism which moves a position of the RFID tag  16  which is fixed to a tip of the crane  19 ; a posture control mechanism which controls a posture of the RFID tag  16  fixed to the tip of the crane  19 , and a PC  20 . 
     To the crane  19  is fixed the RFID tag  16 , a screen  17 , the marker  18 , the PC  20 , and a gravitational acceleration sensor (not shown). For example, the marker  18  may be implemented with LEDs. For example, the marker  18  is desirably implemented with the LEDs of different colors. 
     The moving mechanism of the tag position and posture varying unit  12  moves a position of the RFID tag  16  fixed to the tip of the crane  19  by the operator manually moving a position of the tag position and posture varying unit  12 , or manually changing elevation and direction angles of the crane  19 . The posture control mechanism of the tag position and posture varying unit  12  automatically changes the posture of the RFID tag  16  with a control of the PC  20 . 
     In this way, with the moving mechanism of the tag position and posture varying unit  12 , the operator manually changes the position of the tag position and posture varying unit  12  or changes the elevation and direction angles of the crane  19 , so that it is necessary to take a measure such as providing, rather than an industrial robot, a fence, etc., outside a moving range of the tag position and posture varying unit  12 . Therefore, it becomes easy for the tag position and posture varying unit  12  to be taken into a location at which the RFID evaluation system  1  is actually implemented. 
     As described above, the direction angle of the crane  19  is received from the control unit  11  side. The elevation angle (pitch angle) of the crane  19  is measured with a gravitational acceleration sensor. The PC  20  may calculate the posture of the crane  19  with the direction and elevation angles of the crane  19 . Therefore, the PC  20  may control the posture of the RFID tag  16  fixed to the tip of the crane  19  such that a relative posture of the RFID tag  16  relative to the antenna unit  10  takes a predetermined posture based on the computed posture of the crane  19 . 
     After controlling the relative posture of the RFID tag  16  relative to the antenna unit  10  to a predetermined posture, the PC  20  requests the PC  15  of the control unit  11  to measure a response radio wave strength. The PC  15  controls the antenna unit  10  to measure the response radio wave strength of the RFID tag  16 . After the measuring of the response radio wave strength is completed, the PC  15  reports a completion of the measuring of the response radio wave strength to the PC  20  of the tag position and posture varying unit  12 . 
     The PC  15  of the control unit  11  and the PC  20  of the tag position and posture varying unit  12  are communicatively connected. A form of connecting the PC  15  of the control unit  11  and the PC  20  of the tag position and posture varying unit  12  may be wired or wireless. 
     Therefore, with the RFID evaluation system  1  in  FIG. 1 , the posture of the RFID tag  16  is automatically controlled, so that the response radio wave strength may be measured by the operator of the tag position and posture varying unit  12  moving the RFID tag  16  fixed to the tip of the crane  19  to an arbitrary position within a space of a location to be implemented according to an indication projected onto the screen  17 . 
       FIG. 2  is a configuration diagram of an exemplary control unit. For the control unit  11  in  FIG. 2 , the projector  13  and the stereo camera  14  are fixed to a tripod  21 . The projector  13  and the stereo camera  14  are communicatively connected with the PC  15  via a cable. While the PC  15  is not fixed to the tripod  21  in the control unit  11  in  FIG. 2 , it may be arranged to fix the PC  15  to the tripod  21 . 
       FIG. 3  is a configuration diagram of a tag position and posture varying unit. For the tag position and posture varying unit  12  in  FIG. 3 , the crane  19  is fixed to a pedestal  22  such that the crane can be moved with respect to the direction and elevation angles. The pedestal  22 , which is provided with a wheel, facilitates moving the position of the tag position posture varying unit  12 . The moving mechanism which moves the position of the RFID tag  16  is realized by moving the position of the tag position and posture varying unit  12  by the pedestal  22  and movability of the crane  19  with respect to the direction and elevation angles. 
     To the crane  19  of  FIG. 3  is fixed the RFID tag  16 , the screen  17 , three markers  18 , the PC  20 , a gravitational acceleration sensor  23 , a battery  24 , and a balance weight unit  25 . 
     The RFID tag  16  is fixed to the tip of the crane  19  such that the posture may be controlled from the PC  20 . For example, a posture control mechanism which controls the posture of the RFID tag  16  may be realized by controlling, from the PC  20  with a motor, etc., a direction of a part to which the RFID tag  16  is fixed. 
     The screen  17  is fixed to the crane  19  such that it may be oriented to a direction which is easy to view from an operator. The marker  18  may be realized with an LED. The gravity acceleration sensor  23  measures an elevation angle (a pitch angle) of the crane  19  to transmit the measured results to the PC  20 . The battery  24  supplies electric power used by the marker  18  or the posture control mechanism. Moreover, the balance weight unit  25  is a balance weight for reducing power needed to move the crane  19  with respect to the direction and elevation angles. 
     The PC  15  of the control unit  11  and the PC  20  of the tag position and posture varying unit  12  are realized by a hardware configuration as shown in  FIG. 4 , for example.  FIG. 4  is a hardware configuration diagram of an exemplary PC. Here, the PC  15  is explained as an example. 
     The PC  15  is configured to include an input apparatus  31 , an output apparatus  32 , a recording medium reading apparatus  33 , an auxiliary storage apparatus  34 , a main storage apparatus  35 , an arithmetic processing apparatus  36 , and an interface apparatus  37  that are mutually connected via a bus  39 . 
     The input apparatus  31  includes a keyboard, a mouse, etc. The input apparatus  31  is used for inputting various signals. The output apparatus  32  includes a display apparatus, etc. The output apparatus  32  is used for displaying various windows, data, etc. The interface apparatus  37  includes a modem, a LAN card, a USB (universal serial bus), etc. The interface apparatus  37  is used for connecting to a network such as the Internet and a LAN, and to other equipment units such as the projector  13 , the stereo camera  14 , for example. 
     The target position indicating program for realizing the control unit  11  is at least a part of various programs which control the PC  15 . The target position indicating program is provided by distributing the recording medium  38 , downloading from the network, etc., for example. 
     For the recording medium  38 , various types of recording media may be used such as a recording medium which optically, electrically, or magnetically records information such as a CD-ROM, a flexible disk, a magneto-optical disk, etc.; a semiconductor memory which electrically records information such as a ROM, a flash memory, etc. 
     When the recording medium  38  having recorded the target position indicating program therein is set to the recording medium reading apparatus  33 , the target position indicating program is installed from the recording medium  38  to the auxiliary storage apparatus  34  via the recording medium reading apparatus  33 . The target position indicating program which is downloaded from the network, etc., is installed in the auxiliary storage apparatus  34  via the interface apparatus  37 . 
     The auxiliary storage apparatus  34  stores therein data, files, programs including the target position indicating program, etc. The main storage apparatus  35  reads the target position indicating program from the auxiliary storage apparatus  34  at the time of launching the target position indicating program to store therein the read results. The arithmetic processing apparatus  36  implements various processes according to the target position indicating program stored in the main storage apparatus  35 . 
     (Processing Procedure) 
     The RFID evaluation system  1  performs a process according to a procedure of a flowchart shown in  FIG. 5 , for example.  FIG. 5  is a flowchart of an exemplary process of the RFID evaluation system. The process of the flowchart in  FIG. 5  is started by an operator instructing from the PC  20 , for example. 
     In step S 1 , the PC  15  controls the stereo camera  14  to shoot the marker  18  of the tag position and posture varying unit  12 . The PC  15  measures the three-dimensional position of the marker  18  from results of shooting with the stereo camera  14 . The PC  15  may compute the three-dimensional position of the RFID tag  16  from the measured three-dimensional position of the marker  18  and a positional relationship between the marker  18  and the RFID tag  16  fixed to the crane  19 . 
     In step S 2 , based on a target position, which is a next measuring point, and the three-dimensional position of the RFID tag  16  calculated, the PC  15  creates information for the operator to move the RFID tag  16  to the target position. Details of the information for the operator to move the RFID tag  16  to the target position are described below. Then, the PC  15  controls the projector  13  to project information for the operator to move the RFID tag  16  to the target position onto the screen  17  of the tag location position varying unit  12 . 
     The PC  15  repeats the process of steps S 1 -S 3  until the calculated three-dimensional position of the RFID tag  16  takes a target position, which is the next measuring point. The operator moves the RFID tag  16  to the target position with a moving mechanism of the tag position and posture varying unit  12  while checking information projected onto the screen  17 . When, in step S 3 , the PC  15  determines that the three-dimensional position of the RFID tag  16  became the target position which is the next measuring point, or, in other words, the RFID  16  moved to the target position, the process of step S 4  is performed. 
     In step S 4 , the PC  15  measures the three-dimensional position of the marker  18  from shooting results with the stereo camera  14  to compute the direction angle of the crane  19 . The PC  15 , when it determines that the RFID tag  16  moved to the target position, may transmit the direction angle of the crane  19  to the PC  20  to report that the RFID tag  16  moved to the target position. 
     The PC  20  computes the posture of the crane  19  with the elevation angle of the crane  19  that is measured by the gravitational acceleration sensor and the direction angle of the crane  19 . Details of the process in step S 4  are described below. The process of step S 4  is for determining, from the posture of the crane  19 , the posture of the RFID tag  16  which changed at the same time the elevation and direction angles of the crane  19  were changed. 
     In step S 5 , the PC  20  controls the posture of the RFID tag  16  fixed to the tip of the crane  19  such that a relative posture of the RFID tag  16  relative to the antenna unit  10  takes a predetermined posture based on the computed posture of the crane  19 . After controlling the relative posture of the RFID tag  16  relative to the antenna unit  10  to a predetermined posture, the PC  20  requests the PC  15  of the control unit  11  to measure the response radio wave strength. The PC  20  may request measurement of the response radio wave strength to the PC  15  to report that the relative posture of the RFID tag  16  relative to the antenna unit  10  became a predetermined posture. 
     In step S 6 , the PC  15  controls the antenna unit  10  to measure the response radio wave strength of the RFID tag  16 . After the measuring of the response radio wave strength is completed, the PC  15  reports the completion of the measuring of the response radio wave strength to the PC  20  of the tag position and posture varying unit  12 . 
     In step S 7 , at the measuring point moved to in step S 3 , the PC  20  determines whether the measuring of the response radio wave strength at all postures of the RFID tag  16  is completed. The posture of the RFID tag  16  for measuring the response radio wave strength is set in multiple numbers in advance. At the measuring point moved to in step S 3 , if the measuring of the response radio wave strength at all postures of the RFID tag  16  is not completed, the PC  20  returns to step S 5 . 
     At the measuring point moved to in step S 3 , if the measuring of the response radio wave strength at all postures of the RFID tag  16  is completed, the PC  20  in step S 8  determines whether the measuring of the response radio wave strength at all measuring points is completed. When the measuring of the response radio wave strength at not all the measuring points is not completed, the PC  20  returns to step S 1 , and starts a process for the next measuring point. When measuring of the response radio wave strength of all the measuring points are completed, the PC  20  completes the process. 
     In the process of the flowchart shown in  FIG. 5 , the RFID evaluation system  1  may measure the response radio wave strength of all postures of the RFID  16  at multiple measuring points such as shown in  FIG. 6 , for example. 
       FIG. 6  is an image diagram of an example of multiple measuring points.  FIG. 6  shows measuring points for a range of 1.2 meters and measuring intervals of 30 cm. In  FIG. 6 , the measuring point is represented by a crossing point. the RFID evaluation system  1  performs measuring in an order of x, then z, and then y, until measuring a tip of a space to be measured, and then turns around to perform the measuring.  FIG. 6  shows an order of the measuring in arrows. 
       FIG. 7  is a flowchart of an example of a process which computes a posture of a crane.  FIG. 8  is an image of an example of a process which computes a direction angle of the crane. Here, the process which computes the direction angle of the crane included in the flowchart in  FIG. 7  is described with reference to  FIG. 8 . 
     In step S 11 , the PC  15  controls the stereo camera  14  to shoot markers  18 - 1  and  18 - 2  of the tag position and posture varying unit  12 . The PC  15  measures the three-dimensional position [x 1 , y 1 , z 1 ] of the marker  18 - 1  and the three-dimensional position [x 2 , y 2 , z 2 ] of the marker  18 - 2  from results of shooting with the stereo camera  14 . 
     In step S 12 , the PC  15  computes the direction angle w of the crane  19  using Equation (1) below from the three-dimensional positions of the markers  18 - 1  and  18 - 2 .
 
 w =tan −1 {( x 2 −x 1)/( z 2 −z 1)}  (1)
 
     In step S 13 , the PC  15  transmits the computed direction angle w of the crane  19  to the PC  20 . In step S 14 , the PC  20  measures the elevation angle of the crane  19  from the gravitational acceleration sensor  23  fixed to the crane  19 . In step S 15 , the PC  20  computes the posture of the crane  19  with the elevation angle and the direction angle w of the crane  19 . 
     Details of the process which computes the posture of the crane  19  with respect to direction w and elevation angles of the crane  19  are described below. The PC  20  sets posture control coordinates Σs of the crane  19  and absolute coordinates Σc as shown in  FIG. 9 .  FIG. 9  is an exemplary explanatory diagram which describes setting of the absolute and position control coordinates. 
     The absolute coordinates Σc become coordinates (xc, yc, zc) of the stereo camera  14  around a rotating angle of a camera platform fixed to a tripod  21 . The posture control coordinates Σs are coordinates (xs, ys, zs) of the crane  19 . For the elevation angle (pitch angle) p of the crane  19 , a direction in which the tip of the crane moves upward is defined to be positive. For the direction angle (yaw angle) w of the crane  19 , a clockwise rotating direction as viewed from the top is defined to be positive. 
     Moreover, the posture of the posture control coordinates Σs in the absolute coordinates τc is defined to be
 
 c   R   s .
 
       c R s , when the pitch angle p=0 and the direction angle w=0, is defined to be a default posture of the posture control coordinates τs 
               R     s   ⁢           ⁢   0                         c     =       [         0       0         -   1             1       0       0           0         -   1         0         ]     .           
A rotation matrix Rpw, which rotates by p around an xc axis and by w around a yc axis, is defined to be
 
               R   pw     =         [         cw       0       sw           0       1       0             -   sw         0       cw         ]     ⁡     [         1       0       0           0       cp         -   sp             0       sp       cp         ]       =       [         cw       spsw       cpsw           0       cp         -   sp               -   sw         spcw       cpcw         ]     .             
The posture of the posture control coordinates τs in the absolute coordinates τc of the crane  19  which rotated by the pitch angle p and the yaw angle w becomes
 
     
       
         
           
             
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     As described above, the PC  20  may compute the posture of the crane  19  in the absolute coordinates τc of the crane  19  with the elevation angle w and the direction angle w of the crane  19 . 
     Moreover, an example of information for moving the RFID tag  16  to the target position is described here with reference to  FIGS. 10A ,  10 B,  11 A,  11 B,  11 C,  11 D, and  11 E.  FIGS. 10A and 10B  are image diagrams of exemplary projection and screen patterns.  FIG. 10A  is an image diagram of the projection pattern projected onto the screen  17  from the projector  13 .  FIG. 10B  is an image diagram of the screen pattern to be displayed on the screen  17 . 
       FIGS. 11A ,  11 B,  11 C,  11 D, and  11 E are image diagrams of an exemplary projection pattern projected onto a screen. For example, when the RFID tag  16  is offset in the back direction from the target position, a projection pattern as shown in  FIG. 11A  is displayed on the screen  17 . When the RFID tag  16  is offset in the front direction from the target position, a projection pattern as shown in  FIG. 11B  is displayed on the screen  17 . 
     When the RFID tag  16  is offset in the left direction from the target position, a projection pattern as shown in  FIG. 11C  is displayed on the screen  17 . When the RFID tag  16  is offset in the upward direction from the target position, a projection pattern as shown in  FIG. 11D  is displayed on the screen  17 . 
     When the RFID tag  16  is aligned with the target position, projection patterns as shown in  FIG. 11E  are displayed on the screen  17 . When the projection patterns as shown in  FIG. 11E  are displayed, the operator completes moving of the RFID tag  16 . In this way, a shape of the projection pattern displayed on the screen  17  may be checked to determine the direction in which to move the RFID tag  16 . 
     The PC  15  may change the projection pattern to be displayed on the screen  17  from red to orange to yellow to green as the target position is approached, for example, to make it easier for the operator to understand a distance between the target position and the RFID tag  16 . 
     Below, a different example of indicating target position for the operator to move the RFID tag  16  to the target position and a different example of a process of computing the posture of the crane  19  are described. 
     For indicating the target position for the operator to move the RFID tag  16  to the target position, there are methods down below other than the methods shown in  FIGS. 10A ,  10 B,  11 A,  11 B,  11 C,  11 D, and  11 E. 
       FIGS. 12A ,  12 B, and  12 C are diagrams for explaining another exemplary method of indicating target position. In the method of indicating target position in  FIGS. 12A ,  12 B, and  12 C, directive lights may be irradiated such that they cross each other to indicate, as the target position, a position at which the lights overlap. When the RFID tag  16  is farther than the target position, an irradiating pattern as shown in  FIG. 12A  is displayed on the screen  17  on the tag position and posture varying unit  12  side. When the RFID tag  16  is at the target position, an irradiating pattern as shown in  FIG. 12B  is displayed on the screen  17  on the tag position and posture varying unit  12  side. When the RFID tag  16  is nearer than the target position, an irradiating pattern as shown in  FIG. 12C  is displayed on the screen  17  on the tag position and posture varying unit  12  side. 
     The target position indicating method in  FIGS. 12A ,  12 B, and  12 C may be realized inexpensively as it suffices to provide, in lieu of the projector  13 , a target position indicating unit which irradiates a directive light and provide the target position indicating unit with a pan and tilt mechanism. 
       FIGS. 13A and 13B  are diagrams for explaining another exemplary method of indicating target position. The method of indicating target position in  FIGS. 13A and 13B  may project a projection pattern which is the same as a screen pattern displayed on the screen  17  from the projector  13 , indicating a position at which the screen pattern and the projection pattern overlap as the target position. 
       FIG. 13A  shows projection patterns displayed onto the screen  17  on the tag position posture varying unit  12  side when the RFID tag  16  is nearer than the target position, when the RFID tag  16  is at the target position, and when the RFID tag  16  is farther than the target position. 
     Moreover,  FIG. 13B  shows a projection pattern displayed on the screen  17  on the tag position and posture varying unit  12  when the RFID tag  16  is at the target position, and when the RFID tag  16  is offset laterally from the target position. 
     The operator may determine a direction in which to move the RFID tag  16  from a difference in size of the projection pattern and the screen pattern. Moreover, the operator may determine a direction in which to move the RFID tag  16  from the projection pattern projected onto the screen  17 . The target position indicating method in  FIGS. 13A and 13B  projects the projection pattern with the projector  13 , making the apparatus configuration simpler and making it possible to provide complicated indications to the operator. 
     Besides, a different example of the method of indicating target position is a method of indicating a direction in which to operate the tag position and posture varying unit  12  to the indicating panel provided at hand of the operator of the tag position and posture varying unit  12 . It suffices for the operator to operate according to the indicating panel, so that the operation becomes simple. 
     Moreover, as a different example of the method of indicating target position, there is a method of making an operator wear a head mount display (HMD) and displaying an unmeasured measuring point (target position) on the HMD to indicate a direction in which to operate the tag position and posture varying unit  12 . The operator may intuitively determine a direction in which to operate the tag position and posture varying unit  12 . 
     For the process of computing the posture of the crane  19 , a method as described below may also be used besides the above-described method. For example, a geomagnetic sensor and a gravitational acceleration sensor as posture sensors may be mounted to the tag position and posture varying unit  12  to compute the posture of the crane  19  based on measured values from the posture sensors. 
     Moreover, the tag position and posture varying unit  12  may have mounted thereto a camera to shoot an external marker, etc., to compute the position and posture of the crane  19 . Furthermore, the tag position and posture varying unit  12  may have mounted to the crane  19  an ultrasonic transmitter in lieu of the marker  18  and have, in lieu of the stereo camera  14 , three ultrasonic receivers arranged at a distance to receive ultrasonic waves to compute the posture of the crane  19  from a difference in arriving times of the ultrasonic waves. Moreover, the control unit  11  may also measure the three-dimensional position of the marker  18  from results of shooting with the stereo camera  14  to measure the direction and elevation angles of the crane  19  and compute the posture of the crane  19 . 
     The present application is based on Japanese Priority Application No. 2011-187603 filed on Aug. 30, 2011, the entire contents of which are hereby incorporated by reference.