Patent Publication Number: US-2018039801-A1

Title: Tag reading device and control program for tag reading device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-154530, filed Aug. 5, 2016, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a tag reading device and a control program for a tag reading device. 
     BACKGROUND 
     In the related art, a wireless tag reading device reads information from a radio frequency identification (RFID) tag using an RFID reader with a moving antenna. The RFID tags can be attached to items of merchandise for tracking and inventory control. 
     In an existing wireless tag reading device, if the antenna moves at a high speed, the power supply to the RFID tags from the antenna can be intermittently interrupted, and thus certain RFID tags may be missed. However, if the antenna moves at a low speed in such a device, there can be a problem in that it may consume substantial time to move the antenna throughout the entire targeted reading area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of an RFID tag reading device according to an embodiment and a merchandise sales data processing apparatus. 
         FIG. 2  is a side view illustrating a schematic configuration of the RFID tag reading device. 
         FIG. 3  is a block diagram illustrating hardware aspects of a merchandise sales data processing apparatus and a RFID tag reading device. 
         FIG. 4  is a block diagram illustrating functional aspects of a merchandise sales data processing apparatus and a RFID tag reading device. 
         FIG. 5  is a diagram illustrating a setting example of a speed change pattern for moving an RFID antenna. 
         FIG. 6  is a flowchart illustrating aspects of an RFID tag reading process that can be performed by a merchandise sales data processing apparatus and a RFID tag reading device. 
         FIG. 7  is a diagram illustrating a different setting example of a speed change pattern for moving a RFID antenna. 
         FIG. 8  is a flowchart illustrating aspects of an RFID tag reading process that can be performed by a modification of a RFID tag reading device. 
         FIGS. 9A to 9C  are diagrams illustrating a different example of the RFID tag reading device;  FIG. 9A  is a top view illustrating a schematic configuration of the RFID tag reading device;  FIG. 9B  is a diagram illustrating an example of a movement of the RFID antenna; and  FIG. 9C  is a diagram illustrating a different example of the movement of the RFID antenna. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an electronic tag reading device comprises an antenna for transmitting wireless signals to an electronic tag (e.g., an RFID tag) to initiate reading of information stored in the electronic tag. An electronic tag reader is electrically coupled to the antenna. The electronic tag reader supplies signals to the antenna and receives signals from the antenna that are used in reading the information stored in the electronic tag. A moveable stage is connected to the antenna and is configured to move the antenna during a reading process for reading the information from the electronic tag. A speed controller is configured to change a speed of moveable stage during the reading process. 
     Description of Overall Configuration of Merchandise Sales Data Processing Apparatus 
     An RFID tag reading device according to an example embodiment will be described below with reference to the drawings.  FIG. 1  is an external view illustrating an overall configuration of a merchandise sales data processing apparatus  1  equipped with an RFID tag reading device  30 . The merchandise sales data processing apparatus  1  is installed, for example, in a store such as a supermarket, and used for registration of merchandise purchased by customers and the settlement process thereof. The RFID tag reading device  30  reads the information of an RFID tag attached to merchandise by using radio waves. 
     As illustrated in  FIG. 1 , the merchandise sales data processing apparatus  1  includes a Point-of-sale (POS) terminal body  2 , a sales person-side display  3 , a customer-side display  4 , a keyboard  5 , a barcode reader  6 , a card reader  7 , a receipt printer  8 , and a drawer  9 . The merchandise sales data processing apparatus  1  is also connected to the RFID tag reading device  30 . The configuration of the RFID tag reading device  30  will be described later. 
     The POS terminal body  2  includes the sales person-side display  3 , the customer-side display  4 , the keyboard  5 , the barcode reader  6 , the card reader  7 , the receipt printer  8 , and the drawer  9 . Although not illustrated in detail, the POS terminal body  2  is connected to a store controller (e.g., server) including a merchandise database, and can acquire merchandise information such as a merchandise name, a merchandise image, and a merchandise unit price corresponding to the merchandise code of each item of merchandise read. 
     The sales person-side display  3  is attached to the upper portion of the POS terminal body  2  towards the inside (the sales person side) of a checkout counter  10 . The sales person-side display  3  displays information such as the name and price of the merchandise corresponding to a merchandise code read from a RFID tag attached to an item of merchandise. The sales person-side display  3  may have a function of a touch panel that recognizes an instruction input by a sales person&#39;s pressing of keys or buttons. 
     The customer-side display  4  is attached toward the outside of the checkout counter  10  (the customer side) with the back surface thereof facing the sales-person side display  3 . 
     The keyboard  5  includes keys such as a closing key for declaring the end of a merchandise sales data processing of a merchandise M purchased by the customer. 
     The barcode reader  6  optically reads the barcode attached to each item of merchandise M, and is disposed so as to be usable at the center portion of the checkout counter  10 . The barcode includes information such as a merchandise code which has been previously allocated to each item of merchandise for identifying the type of each item of merchandise. Either of a RFID tag T or a barcode can be affixed to each item of merchandise. Hereinafter, the RFID tag reading device  30  will be described. The description of the barcode reading process by the barcode reader  6  will be omitted. 
     The card reader  7  reads information on a points card (e.g., a customer loyalty card) or a credit card of a customer inserted from a card insertion slot not illustrated in  FIG. 1 . 
     The receipt printer  8  prints a receipt after an accounting process, and issues the receipt from a receipt issue opening not illustrated in  FIG. 1 . 
     The drawer  9  includes a drawer capable of opening and closing, and accommodates cash or the like in the drawer. 
     Description of Overall Configuration of RFID Tag Reading Device 
     Next, the configuration of the RFID tag reading device  30  will be described.  FIG. 2  is a side view illustrating a schematic configuration of the RFID tag reading device  30  (along the A arrow of  FIG. 1 ). 
     The RFID tag reading device  30  reads an RFID tag attached to the merchandise M, particularly, an RFID tag T operating in the UHF band, in this example. The RFID tag reading device  30  includes an RFID antenna  22  (e.g., as part of an antenna unit). As illustrated in  FIG. 2 , the RFID antenna  22  is embedded in the checkout counter  10 . 
     In  FIG. 2 , the RFID antenna  22  radiates radio waves toward a top plate of the checkout counter  10 . The top plate is made of a material that transmits radio waves, such as wood. A communication area of the RFID tag reading device  30  corresponds to region/area that can receive radio waves transmitted by the RFID antenna  22 . The RFID antenna  22  reads the tag information stored in the RFID tags T attached to the items of merchandise M placed in the reading area. As illustrated in  FIG. 1 , the item of merchandise M being purchased by the customer is placed directly on the checkout counter  10  above the RFID antenna  22 . Alternatively, a shopping basket (not specifically depicted) containing the item of merchandise M may be placed above the RFID antenna  22 . In addition, information, such as the merchandise code of the item of merchandise to which the RFID tag T is attached, is stored in the RFID tag T in advance along with identification information unique to the tag. 
     The RFID antenna  22  is installed on a moving mechanism  24  disposed under the checkout counter  10 . The RFID antenna  22  so installed is thus movable below the top plate of the checkout counter  10 . 
     The moving mechanism  24  is configured with a linear motion mechanism including a screw shaft  18 , a bearing  16  of the screw shaft  18 , a stepping motor  12 , a coupling  14 , and a moveable stage  20 . The stepping motor  12  is a rotational power source. The coupling  14  transmits the rotational power of the stepping motor  12  to the screw shaft  18 . The moveable stage  20  is formed integrally with a ball screw nut screwed to the screw shaft  18 . 
     One end of the screw shaft  18  is horizontally supported by the bearing  16  and the other end by the coupling  14  so as to be rotatable about a horizontal axis (x-axis in  FIG. 2 ). An output shaft  12   a  of the stepping motor  12  is connected to the other end of the screw shaft  18  in the coupling  14 . With this configuration, the rotational power of the stepping motor  12  is transmitted from the output shaft  12   a  to the screw shaft  18  through the coupling  14 . 
     The moveable stage  20  has a through hole, and the ball screw nut of the screw shaft  18  is embedded in the through hole. The moveable stage  20  moves forward and backward along the screw shaft  18 , that is, moves in the directions of the arrow R 1  and the arrow R 2  along the x axis in  FIG. 2 . Since a metallic ball (e.g., steel ball) is interposed in the threaded portion between the screw shaft  18  and the ball screw nut during the movement of the moveable stage  20 , smooth movement is possible. It is assumed that the moveable stage  20  moves in the range of x=0 to x=W along the x axis as illustrated in  FIG. 2 . That is, the moveable stage  20  moves between the rightmost position  20   a  and the leftmost position  20   b.    
     As described above, the moving mechanism  24  changes the rotational motion of the stepping motor  12  to a linear motion by the above-described ball screw mechanism to enable the moveable stage  20  to move forward and backward. The moveable stage  20  slides while keeping a part of the moveable stage  20  in contact with the support plate  11  such that the moveable stage  20  does not rotate as the screw shaft  18  rotates. Thus, the moveable stage  20  moves without rotating. 
     On the upper surface of the moveable stage  20 , the RFID antenna  22  is fixed so that a reading surface of the RFID antenna  22  is facing the top plate of the checkout counter  10 . Here, the reading surface of the RFID antenna  22  refers to a radiation surface from which a planar patch antenna radiates radio waves. With this disposition, the RFID antenna  22  radiates radio waves toward the reading surface, that is, toward the top plate of the checkout counter  10 . Then, the RFID antenna  22  moves along the screw shaft  18  integrally with the moveable stage  20 . 
     A reader and writer device (not illustrated) can be connected to the RFID antenna  22  using a bendable coaxial connector (e.g., coaxial cable). To improve the positioning accuracy of the moveable stage  20 , the reader and writer device may be provided with a position sensor  42  (see  FIG. 3 ) disposed along the path of the moveable stage  20 . The position sensor  42  can be used to correct the position of the moveable stage  20 . For example, the reader and writer device is provided with a position sensor  42  (for example, a micro switch, a proximity sensor, or the like) at a start position and an end position of the moveable stage  20 , and acts to stop the movement of the moveable stage  20  or corrects the movement amount of the moveable stage  20  when the position sensor  42  detects the position of the moveable stage  20  is incorrect. Thus, the reader and writer device can more reliably perform positioning of the moveable stage  20  and therefore positioning of the RFID antenna  22 . 
     With the configuration of the moving mechanism  24  described above, if the stepping motor  12  is rotated in one direction, the moveable stage  20  advances on the screw shaft  18  in the direction of the arrow R 2  in  FIG. 2 , and if the stepping motor  12  rotates in the reverse direction, the moveable stage  20  moves on the screw shaft  18  in the direction of the arrow R 1  in  FIG. 2 . Along with the movement of the moveable stage  20 , the RFID antenna  22  moves integrally with the moveable stage  20 , with the reading surface facing upward (towards the top plate of the checkout counter  10 ). With this movement, the RFID antenna  22  communicates with the RFID tag T while changing a communication range (distance) between the RFID tag T and the RFID antenna  22 . Hereinafter, regarding the direction of rotation of the stepping motor  12 , a case where the moveable stage  20  advances in the direction of the arrow R 1  is defined as forward rotation, and a case where the moveable stage  20  advances in the direction of the arrow R 2  is defined as reverse rotation. 
     Description of Hardware Configuration of an Example 
     Next, the hardware configurations of the merchandise sales data processing apparatus  1  and the RFID tag reading device  30  will be described.  FIG. 3  is a hardware block diagram illustrating aspects of hardware configurations of the merchandise sales data processing apparatus  1  and the RFID tag reading device  30  in the present embodiment. 
     The merchandise sales data processing apparatus  1  includes a control unit  26  such as a computer including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. The ROM stores various programs executed by the CPU and various types of data. The RAM temporarily stores data and programs when the CPU executes various programs. 
     The control unit  26  is connected to the sales person-side display  3 , the customer-side display  4 , the keyboard  5 , the barcode reader  6 , the card reader  7 , the drawer  9  and the receipt printer  8  through various input and output circuits (I/O). The function of each hardware unit is as described above. 
     Furthermore, a storage unit  27  and a communication interface (I/F)  28  are connected to the control unit  26 . 
     The storage unit  27  is a storage device including a nonvolatile storage medium such as a hard disk drive (HDD) or a solid state drive (SSD). The storage unit  27  stores various programs and various types of data related to the operation of the merchandise sales data processing apparatus  1 . Examples of the data stored in the storage unit  27  include a merchandise master list registering merchandise information on each possible item of merchandise in association with a merchandise code identifying the merchandise. Such merchandise information includes, for example, the merchandise name, the price, and the like of the corresponding merchandise. The communication interface (I/F)  28  is an interface for transmitting and receiving various data to and from the RFID tag reading device  30 . 
     The RFID tag reading device  30  includes a control unit  32  such as a computer including a CPU, a ROM, a RAM, and the like. The ROM stores various programs executed by the CPU and various types of data. The RAM temporarily stores data and programs when the CPU executes various programs. 
     Furthermore, the control unit  32  is connected to a reader and writer unit  38 , a storage unit  34 , a communication interface (I/F)  36 , a motor driver  40 , a position sensor  42 , and the like through various input and output circuits. 
     The reader and writer unit  38  communicates with the RFID tag T through the RFID antenna  22  under the instruction from the control unit  32 . The communication with the RFID tag T is generally performed as in the following example. 
     If the RFID tag T, for example, is a passive type that does not have a battery, the RFID antenna  22  amplifies unmodulated carrier waves supplied from the reader and writer unit  38  and radiates the carrier waves as radio waves. Then, in response to the interrogation radio waves, the RFID antenna  22  receives a response signal including tag information, such as an identification code, modulated (e.g., encoded) in the reflected radio wave, from the RFID tag T existing within the response range of the RFDI tag reading device. The RFID antenna  22  sends the received radio waves to the reader and writer unit  38 , and the reader and writer unit  38  demodulates (e.g., decode) the received the carrier wave, and then transmits the demodulated tag information to the control unit  32 . Thus, the tag information stored in the RFID tag T can be read with the RFID antenna  22 . 
     The storage unit  34  is a storage device including a nonvolatile storage medium such as an HDD or an SSD. The storage unit  34  stores various programs and various types of data related to the operation of the RFID tag reading device  30 . The communication interface (I/F)  36  is an interface for transmitting and receiving various types of data to and from the merchandise sales data processing apparatus  1 . 
     The motor driver  40  is a driver circuit that operates the stepping motor  12 . The motor driver  40  outputs a pulse signal for rotating the stepping motor  12  by a predetermined angle (e.g., step angle) based on an instruction from the control unit  32 . 
     The position sensor  42  detects whether or not the moveable stage  20  is at a predetermined position, as described above. 
     Description of Functional Configuration 
     Next, the functional aspects of configurations of the merchandise sales data processing apparatus  1  and the RFID tag reading device  30  will be described.  FIG. 4  is a block diagram illustrating functional aspects of the merchandise sales data processing apparatus  1  and the RFID tag reading device  30 . 
     The control unit  26  (CPU) of the merchandise sales data processing apparatus  1  cooperates with a program stored in the storage unit  27  to realize the display control unit  100 , the input reception unit  102 , the sales registration unit  104 , and the communication control unit  106  as functional units. 
     The display control unit  100  controls the sales person-side display  3  so as to display various screens on the sales person-side display  3 . For example, the display control unit  100  displays a screen including a button, an icon, or the like for instructing the start of the reading of the merchandise code (the RFID tag T) (also referred to as a reading start button) and a button, an icon, or the like for instructing the end of the reading (also referred to as a reading end button). Further, the display control unit  100  reads the merchandise information corresponding to the merchandise code from the merchandise master list, based on the merchandise code transmitted from the RFID tag reading device  30 , and displays the merchandise name and price of the merchandise M, the tendered amount, the change due amount, and the like on the sales person-side display  3 . Further, the display control unit  100  controls the customer-side display  4  so as to display various screens on the customer-side display  4 . For example, the display control unit  100  displays the merchandise name, the price, and the like of the item of merchandise M being purchased by the customer on both the sales person-side display  3  and the customer-side display  4 , based on the merchandise code transmitted from the RFID tag reading device  30 . 
     The input reception unit  102  receives an input through the keyboard  5  or the touch panel. For example, if a button or key is pressed on the operation screen displayed on the sales person-side display  3 , the input reception unit  102  outputs an instruction corresponding to the pressed button or key to the control unit  26 . 
     When the payment is confirmed upon settlement process for each item of merchandise corresponding to the merchandise codes transmitted from the RFID tag reading device  30 , the sales registration unit  104  registers the sales of the item of merchandise purchased by the customer. Specifically, the sales registration unit  104  registers the merchandise code of each item of merchandise in the database for registration together with the tendered amount, change due, and transaction date and time. The database for registration may be provided in the storage unit  27  of the merchandise sales data processing apparatus  1  or may be provided in an external device capable of communicating with the merchandise sales data processing apparatus  1 . 
     The communication control unit  106  controls the communication interface (I/F)  28 , and transmits and receives various types of information to and from the RFID tag reading device  30  through the communication interface (I/F)  28 . For example, if the reading start button is pressed, the communication control unit  106  transmits instruction information for instructing the start of the reading to the RFID tag reading device  30 . Furthermore, the communication control unit  106  receives the merchandise code transmitted from the RFID tag reading device  30 . If the reading end button is pressed, the communication control unit  106  transmits instruction information for instructing the end of the reading to the RFID tag reading device  30 . 
     The control unit  32  (CPU) of the RFID tag reading device  30  cooperates with the program stored in the storage unit  34  to realize an antenna position detection unit  110 , a reader and writer control unit  112 , an antenna movement control unit  114 , an antenna movement speed control unit  116 , and a communication control unit  118  as functional units. 
     The reader and writer control unit  112  controls the reader and writer unit  38  so as to perform reading of the RFID tags T (attached to the items of merchandise) and performs writing to the RFID tags T through the RFID antenna  22 . 
     Specifically, the reader and writer control unit  112  starts a reading cycle for reading the RFID tag T, when the start of reading is instructed from the merchandise sales data processing apparatus  1 . The tag information read from the RFID tag T is transmitted to the merchandise sales data processing apparatus  1  from the reader and writer control unit  112  at any time during or after the reading. 
     Further, when the end of reading is instructed from the merchandise sales data processing apparatus  1 , the reader and writer control unit  112  ends the reading by the reader and writer unit  38 . Then, when a registration completion is instructed from the merchandise sales data processing apparatus  1 , the reader and writer control unit  112  controls the reader and writer unit  38  and performs a writing (writing cycle) of the registration completion flag. Here, the registration completion flag is information indicating that the sales registration has been completed for the particular RFID tag(s) T. The completion flag is written to a predetermined storage area of each RFID tag T. 
     The antenna position detection unit  110  receives an instruction from the control unit  32  and monitors the output of the position sensor  42 . Then, is the antenna position detection unit  110  determines whether or not the moveable stage  20  is at a predetermined position. The antenna position detection unit  110  further passes the output of the position sensor  42  to the control unit  32 . 
     The antenna movement control unit  114  controls the motor driver  40  when reading the RFID tag T. Specifically, during the execution of reading of the RFID tag T by the reader and writer control unit  112 , the antenna movement control unit  114  drives the motor driver  40  according to a predetermined operation pattern. Specifically, the antenna movement control unit  114  acquires information on the position of the moveable stage  20  detected by the antenna position detection unit  110 , and moves the moveable stage  20  according to the predetermined operation pattern. For example, the predetermined operation pattern may be reciprocating the moveable stage  20  between positions x=0 and x=W (see  FIG. 2 ). 
     The antenna movement speed control unit  116  performs control to change the movement speed of the RFID antenna  22 , when the antenna movement control unit  114  controls the motor driver  40 . Specifically, when the moveable stage  20  (on which RFID antenna  22  is supported/attached) is moved, the movement speed of the RFID antenna  22  is changed according to the number of round trips (movement cycles) of the moveable stage  20 . Further, the movement speed of the RFID antenna  22  is changed according to the position of the moveable stage  20  (or RFID antenna  22 ). A specific pattern of changing movement speed will be described later. The movement speed of the RFID antenna  22  is changed by changing the frequency of the pulse signal applied to the stepping motor  12 . That is, if the frequency of the pulse signal applied to the stepping motor  12  is increased, the movement speed of the RFID antenna  22  increases. Conversely, if the frequency of the pulse signal applied to the stepping motor  12  is decreased, the movement speed of the RFID antenna  22  decreases. The specific frequency of a pulse signal is determined by referring to the relationship between the frequency of the pulse signal, acquired in advance, and the movement speed of the RFID antenna  22 . 
     The communication control unit  118  controls the communication interface (I/F)  36 , and transmits and receives various types of information to and from the merchandise sales data processing apparatus  1  through the communication interface (I/F)  36 . For example, the communication control unit  118  receives the instruction information for instructing to start reading which is transmitted from the merchandise sales data processing apparatus  1 . Further, the communication control unit  118  transmits the merchandise code read from the RFID tag T by the reader and writer control unit  112 , to the merchandise sales data processing apparatus  1 . In addition, the communication control unit  118  receives the instruction information for instructing to end reading which is transmitted from the merchandise sales data processing apparatus  1 . 
     Description of Speed Change Pattern of RFID Antenna 
     Next, a specific speed change pattern of the RFID antenna  22  in the RFID tag reading device  30  will be described.  FIG. 5  is a diagram illustrating a setting example of a movement speed when moving the RFID antenna  22 . 
     As described above, the RFID antenna  22  receives tag information such as an identification code modulated (e.g., encoded) in the reflected radio wave, from the RFID tag T existing within the response range of the RFDI tag reading device. Therefore, if the RFID antenna  22  moves at a high speed, the power supply to the RFID tags T from the RFID antenna  22  is intermittently interrupted. Therefore, reflected waves from certain RFID tags T may not be obtained. 
     Conversely, if the RFID antenna  22  moves at a low speed, the RFID antenna  22  can also supply power to the RFID tags T overlapping one another. Therefore, reflected waves from the overlapping RFID tags T can reliably be obtained. However, since the movement speed of the RFID antenna  22  is low, the reading time increases. 
     Therefore, the RFID tag reading device  30  according to the present embodiment changes the movement speed of the RFID antenna  22 , according to the number of round trips (corresponding to a total movement distance D) of the RFID antenna  22 . 
     Specifically, as illustrated in  FIG. 5 , when the RFID antenna  22  is moved, the RFID antenna  22  is moved at a high speed (for example, 100 mm/s) in the first two round trips (0≦D≦4W). The RFID antenna  22  is moved at a low speed (for example, 50 mm/s) in the next one round trip (4W≦D≦6W). 
     The RFID antenna  22  moves at a high speed during the first two round trips so as to receive tag information from the RFID tags T, from which reflected waves can be obtained with a short time power supply, among the RFID tags T attached to the items of merchandise M. Then, the RFID antenna  22  moves at a lower speed during the next round trip so as to supply power to the RFID tags T for a longer time. Thus, tag information is received from the RFID tags T that have smaller reading areas of the RFID tag reading device  30 , for example, the RFID tags T overlapping one another. Therefore, in the third round trip, the RFID antenna  22  receives the tag information that could not be received during the first two round trips. 
     For example, in  FIG. 2 , the movement range of the RFID antenna  22  is W=200 mm, if the RFID antenna  22  is moved with a movement speed V, as depicted in  FIG. 5 , the RFID antenna  22  reads the tag information during a total reading time of 16 seconds: 4 seconds per round trip for the first two round trips and 8 seconds for the third round trip. 
     Next, the flow of a series of processes performed by the merchandise sales data processing apparatus  1  and the RFID tag reading device  30  will be described with reference to  FIG. 6 .  FIG. 6  is a flowchart illustrating aspects of a reading process of the RFID tag T that can be performed by the merchandise sales data processing apparatus  1  and the RFID tag reading device  30 . 
     Description of Aspects of Process Performed by Merchandise Sales Data Processing Apparatus 
     First, aspects of a process performed by the merchandise sales data processing apparatus  1  will be described. The sales person instructs the input reception unit  102  of the merchandise sales data processing apparatus  1  to start reading the RFID tag T (step S 10 ). Specifically, the sales person places the merchandise M on the checkout counter  10  and instructs to start reading the RFID tag T by operating the keyboard  5  or the button or the like for instructing to start reading the RFID tag T displayed on the sales person-side display  3  provided with the touch panel function. 
     The communication control unit  106  receives the reading result of the RFID tag T from the RFID tag reading device  30  (step S 12 ). 
     The display control unit  100  displays the reading result of the RFID tag T on the sales person-side display  3  and the customer-side display  4  (step S 14 ). 
     The merchandise sales data processing apparatus  1  determines whether or not the movement of the RFID antenna  22  has been completed (step S 16 ). When the merchandise sales data processing apparatus  1  determines that the movement of the RFID antenna  22  has been completed (step S 16 : Yes), the process proceeds to step S 18 . Otherwise (step S 16 : No), the process returns to step S 12 . 
     The sales registration unit  104  performs settlement process (step S 18 ). Thereafter, the merchandise sales data processing apparatus  1  ends the process of  FIG. 6 . 
     Description of Aspects of Process Performed by RFID Tag Reading Device 
     Next, the flow of the process performed by the RFID tag reading device  30  will be described. First, the antenna movement control unit  114  sets a counter value X for counting the number of round trips of the RFID antenna  22  to X=0 (step S 30 ). 
     With reference to the output of the position sensor  42 , the antenna position detection unit  110  determines whether or not the RFID antenna  22  is at a position of x=0, that is, at a home position (step S 32 ). When the antenna position detection unit  110  determines that the RFID antenna  22  is at the home position (step S 32 : Yes), the process proceeds to step S 34 . Otherwise (step S 32 : No), the process proceeds to step S 36 . 
     The RFID tag reading device  30  displays an error output (step S 36 ). The error output may be displayed on, for example, the sales person-side display  3 . Thereafter, the process of  FIG. 6  is ended. 
     In step S 32 , if it is determined that the RFID antenna  22  is at the home position (step S 32 : Yes), the RFID tag reading device  30  determines whether or not the start of reading of the RFID tag T has been instructed from the merchandise sales data processing apparatus  1  (step S 34 ). If the RFID tag reading device  30  determines that the start of reading of the RFID tag T has been instructed (step S 34 : Yes), the process proceeds to step S 38 . Otherwise (step S 34 : No), the process of step S 34  is repeated. 
     The antenna movement control unit  114  determines whether or not the counter value X is smaller than  2  (step S 38 ). If the antenna movement control unit  114  determines that the counter value X is smaller than  2  (step S 38 : Yes), that is, if the RFID antenna  22  has not reciprocated twice, the process proceeds to step S 40 . Otherwise (step S 38 : No), the process proceeds to step S 42 . 
     The antenna movement speed control unit  116  sets the frequency of the pulse signal applied to the stepping motor  12  to a predetermined value, thereby setting the movement speed of the RFID antenna  22  to V=100 mm/s (step S 40 ). Thereafter, the process proceeds to step S 44 . 
     The antenna movement speed control unit  116  sets the frequency of the pulse signal applied to the stepping motor  12  to a predetermined value, thereby setting the movement speed of the RFID antenna  22  to V=50 mm/s (step S 42 ). Thereafter, the process proceeds to step S 44 . 
     The antenna movement control unit  114  forwardly rotates the stepping motor  12  (step S 44 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave of the radio wave radiated by the RFID antenna  22  (step S 46 ). 
     The communication control unit  118  transmits the information of the RFID tag T read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 48 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 50 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=0 to the position of x=W, by applying 3000 pulses. The number 3000 of pulses represents the number of pulses applied to the stepping motor  12  to move the moveable stage  20  from the position of x=0 to the position of x=W. This number 3000 of pulses is an example and varies depending on the stepping motor  12  being used, the pitch of screws formed on the screw shaft  18 , and the like. 
     The antenna movement control unit  114  reversely rotates the stepping motor  12  (step S 52 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave from the RFID antenna  22  (step S 54 ). 
     The communication control unit  118  transmits the information of the RFID tag T read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 56 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 58 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=W to the position of x=0, by applying 3000 pulses. 
     The antenna movement control unit  114  increments the counter value X (step S 60 ). 
     The antenna movement control unit  114  determines whether or not the counter value X is 3 (step S 62 ). If the antenna movement control unit  114  determines that the counter value X is 3 (step S 62 : Yes), that is, if the RFID antenna  22  has reciprocated three times, the process proceeds to step S 64 . Otherwise (step S 62 : No), the process returns to step S 32 . 
     The RFID tag reading device  30  transmits to the merchandise sales data processing apparatus  1  through the communication control unit  118  that the movement of the RFID antenna  22  has been completed (step S 64 ). Thereafter, the process of  FIG. 6  is ended. 
     Description of Different Speed Change Pattern of RFID Antenna 
     The speed change pattern of the RFID antenna  22  in the RFID tag reading device  30  is not limited to the particular pattern described above. A different speed change pattern of the RFID antenna  22  will be described later with reference to  FIG. 7 . 
     In  FIG. 7 , the movement speed of the RFID antenna  22  is reduced, when the RFID antenna  22  is in the vicinity of the center of the movement range (x=0 to W). When the items of merchandise M are placed on the top plate of the checkout counter  10 , the merchandise items are generally gathered and placed in the vicinity of the center of the movement range of the RFID antenna  22 . That is, there is a high likelihood that a plurality of RFID tags T will overlap each other in the vicinity of the center of the movement range of the RFID antenna  22 . Therefore, it is possible to more reliably read the tag information from the plurality of overlapping RFID tags T by slowing down the movement speed of the RFID antenna  22  in the vicinity of the center of the movement range of the RFID antenna  22 . 
     According to the speed change pattern of the RFID antenna  22 , as illustrated in  FIG. 7 , the antenna movement speed control unit  116  ( FIG. 4 ) sets the movement speed V of the RFID antenna  22  to V=50 mm/s in the range of p≦D≦W−p, within the movement range 0≦D≦W of the RFID antenna  22 . Here, p is a preset constant. Then, in the other movement range, that is, in the range of 0 ≦D≦p and W−p≦D≦W, the antenna movement speed control unit  116  sets the movement speed V of the RFID antenna  22  to V=100 mm/s. 
     The RFID antenna  22  reads the RFID tags (attached to the items of merchandise M) while moving the predetermined movement range (0≦D≦W) over two reciprocating cycles according to the speed change pattern illustrated in  FIG. 7 . 
     Description of Modification of Embodiment 
     Hereinafter, a modification of the embodiment described above will be described with reference to  FIG. 8 . According to the configuration of the above-described embodiment, even after reading of all the tag information has been completed, the RFID antenna  22  reciprocate for a predetermined number of times. In a modification described below, the movement speed V of the RFID antenna  22  is lowered when a RFID tags T are detected unread. 
     Since this modification has substantially the same configuration (e.g.,  FIGS. 3 and 4 ) as the merchandise sales data processing apparatus  1  provided with the RFID tag reading device  30  described above, a descriptions of the function of each hardware unit is omitted. 
       FIG. 8  is a flowchart illustrating aspects of a reading process of the RFID tag T performed by the RFID tag reading device  30 , in a modification of the merchandise sales data processing apparatus  1  provided with the RFID tag reading device  30 . Since the aspects of process performed by the merchandise sales data processing apparatus  1  is substantially the same as illustrated in  FIG. 6 , only the aspects of the process performed by the RFID tag reading device  30  will be described here. 
     First, the reader and writer control unit  112  sets a counter value J, indicating the number of RFID tags T read by the RFID antenna  22 , to J=0 (step S 70 ). 
     With reference to the output of the position sensor  42 , the antenna position detection unit  110  determines whether or not the RFID antenna  22  is at a position of x=0, that is, at the home position (step S 72 ). When the antenna position detection unit  110  determines that the RFID antenna  22  is at the home position (step S 72 : Yes), the process proceeds to step S 74 . Otherwise (step S 72 : No), the process proceeds to step S 76 . 
     The RFID tag reading device  30  displays an error output (step S 76 ). The error output may be displayed on, for example, the sales person-side display  3 . Thereafter, the process of FIG.  8  is ended. 
     If, in step S 72 , the antenna position detection unit  110  determines that the RFID antenna  22  is at the home position (step S 72 : Yes), the RFID tag reading device  30  determines whether or not the start of reading of the RFID tag T has been instructed from the merchandise sales data processing apparatus  1  (step S 74 ). If the RFID tag reading device  30  determines that the start of reading of the RFID tag T has been instructed (step S 74 : Yes), the process proceeds to step S 78 . Otherwise (step S 74 : No), the process of step S 74  is repeated. 
     The antenna movement speed control unit  116  sets the movement speed of the RFID antenna  22  to V=100 mm/s (step S 78 ). 
     The antenna movement control unit  114  forwardly rotates the stepping motor  12  (step S 80 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave of the radio wave radiated by the RFID antenna  22  (step S 82 ). 
     The reader and writer control unit  112  determines whether or not the information of the read RFID tag T is information which has newly been read (step S 84 ). When the information is newly read information (step S 84 : Yes), the process proceeds to step S 86 . Otherwise (step S 84 : No), the process proceeds to step S 90 . 
     The reader and writer control unit  112  increments the counter value J (step S 86 ). 
     The communication control unit  118  transmits the information of the RFID tag T read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 88 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 90 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=0 to the position of x=W, by applying 3000 pulses. 
     The antenna movement control unit  114  reversely rotates the stepping motor  12  (step S 92 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave of the radio wave radiated by the RFID antenna  22  (step S 94 ). 
     The reader and writer control unit  112  determines whether or not the information of the read RFID tag T is newly read information (step S 96 ). When the information is first read information (step S 96 : Yes), the process proceeds to step S 98 . Otherwise (step S 96 : No), the process proceeds to step S 100 . 
     The reader and writer control unit  112  increments the counter value J (step S 98 ). 
     The communication control unit  118  transmits the information of the RFID tag T read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 100 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 102 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=W to the position of x=0, by applying 3000 pulses. 
     The reader and writer control unit  112  determines whether or not the value of the counter value J is 0 (step S 104 ). In a case where the value of the counter value J is 0 (step S 104 : Yes), the process proceeds to step S 110 . Otherwise (step S 104 : No), the process proceeds to step S 106 . 
     The reader and writer control unit  112  sets the value of the counter value J to 0 (step S 106 ). Thereafter, the process returns to step S 80 . 
     When in step S 104 , the reader and writer control unit  112  determines that the value of the counter value J is 0 (step S 104 : Yes), the antenna movement speed control unit  116  sets the movement speed of the RFID antenna  22  to V=50 mm/s (step S 110 ). 
     The antenna movement control unit  114  forwardly rotates the stepping motor  12  (step S 112 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave of the radio wave radiated by the RFID antenna  22  (step S 114 ). 
     The reader and writer control unit  112  determines whether or not the information of the read RFID tag T is newly read information (step S 116 ). When the information is newly read information (step S 116 : Yes), the process proceeds to step S 118 . Otherwise (step S 116 : No), the process proceeds to step S 122 . 
     The reader and writer control unit  112  increments the counter value J (step S 118 ). 
     The communication control unit  118  transmits the information (of the RFID tag T) read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 120 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 122 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=0 to the position of x=W, by applying 3000 pulses. 
     The antenna movement control unit  114  reversely rotates the stepping motor  12  (step S 124 ). 
     The reader and writer control unit  112  reads the information of the RFID tag T by receiving the reflected wave of the radio wave radiated by the RFID antenna  22  (step S 126 ). 
     The reader and writer control unit  112  determines whether or not the information of the read RFID tag T is newly read information (step S 128 ). When the information is newly read information (step S 128 : Yes), the process proceeds to step S 130 . Otherwise (step S 128 : No), the process proceeds to step S 132 . 
     The reader and writer control unit  112  increments the counter value J (step S 130 ). 
     The communication control unit  118  transmits the information of the RFID tag T read by the reader and writer control unit  112  to the communication control unit  106  of the merchandise sales data processing apparatus  1  (step S 132 ). 
     After applying 3000 pulses to the stepping motor  12 , the antenna movement control unit  114  stops the stepping motor  12  (step S 134 ). The stepping motor  12  moves the moveable stage  20 , that is, the RFID antenna  22 , from the position of x=W to the position of x=0, by applying 3000 pulses. 
     The reader and writer control unit  112  determines whether or not the value of the counter value J is 0 (step S 136 ). In a case where the value of the counter value J is 0 (step S 136 : Yes), the process proceeds to step S 138 . Otherwise (step S 136 : No), the process proceeds to step S 140 . 
     The reader and writer control unit  112  sets the value of the counter value J to 0 (step S 140 ). Thereafter, the process returns to step S 112 . 
     In a case where in step S 136 , the reader and writer control unit  112  determines that the value of the counter value J is 0 (step S 136 : Yes), the RFID tag reading device  30  transmits to the merchandise sales data processing apparatus  1  through the communication control unit  118  that the movement of the RFID antenna  22  has been completed (step S 138 ). Thereafter, the process of  FIG. 8  is ended. 
     Since the RFID tag reading device  30  reduces the movement speed V of the RFID antenna  22  when new tag information has not be read, it is possible to change the movement speed V of the RFID antenna  22  depending on the reading status of the RFID tag information T, thereby shortening the reading time of the tag information. 
     Description of Alternative Movement Locus of RFID Antenna 
     Next, another speed change pattern of the RFID antenna  22  in the RFID tag reading device  30   b  will be described with reference to  FIGS. 9 . 
     In the above-described example, the RFID tag reading device  30  moves the RFID antenna  22  along with the moveable stage  20  along the x-axis direction (a one-dimensional path). However, the movement direction of the RFID antenna  22  is not restricted to the x-axis direction.  FIG. 9A  is a top view illustrating a schematic configuration of an RFID tag reading device  30   b,  which is a modification of the RFID tag reading device  30 . As illustrated in  FIG. 9A , the moving mechanism  24  is configured to be movable in the y-axis direction by moving mechanism  24   b.    
     Here, the screw shaft  18 , the bearing  16 , the stepping motor  12 , the coupling  14 , and the moveable stage  20  (all of which make up a moving mechanism  24 ) are supported by a support member  25   a . The moveable stage  20  slides while keeping a part of the moveable stage  20  in contact with the support member  25   a  such that the moveable stage  20  does not rotate as the screw shaft  18  rotates. Thus, the moveable stage  20  moves in the x-axis direction without rotating. 
     The moving mechanism  24   b  includes a linear motion mechanism including a screw shaft  18   b,  a bearing  16   b  of the screw shaft  18   b,  a stepping motor  12   b  having an output shaft  12   c  as a rotational power source, a coupling  14   b  that transmits the rotational power of the stepping motor  12   b  to the screw shaft  18   b,  a ball screw nut threadedly engaged with the screw shaft  18   b,  a support member  25   a  constituting a moving mechanism  24 . The support member  25   a  slides while keeping a part of the support member  25   a  in contact with the support member  25   b  such that the support member  25   a  does not rotate as the screw shaft  18   b  rotates. Thus, the support member  25   a  moves in the y-axis direction without rotating. 
     The RFID antenna  22  is movable along the x-axis (in the directions of the arrow R 1  and the arrow R 2 ) by the moving mechanism  24 , and is movable along the y-axis direction (in the direction of the arrow R 3  and the arrow R 4 ) by the moving mechanism  24   b.  That is, the RFID antenna  22  is freely movable on the xy plane (i.e., along a two-dimensional path). 
     With moving mechanisms  24  and  24   b,  the RFID tag reading device  30   b  can move the RFID antenna  22  on distinct forward and backward paths. 
     For example, in the example as illustrated in  FIG. 9B , the RFID tag reading device  30   b  moves the RFID antenna  22  from the position of x=0 to the position of x=W (movement path Q 1 ) while maintaining y=y 1 , and thereafter, moves the RFID antenna  22  from the position of y=y 1  to the position of y=y 2  (movement path Q 2 ) while maintaining x=W. Then, the RFID tag reading device  30   b  moves the RFID antenna  22  from the position of x=W to the position of x=0 while keeping y=y  2  (a movement path Q 3 ). 
     Thereafter, the RFID tag reading device  30   b  moves the RFID antenna  22  to the original position (x=0, y=y  1 ) by moving the moving paths Q 3 , Q 2 , and Q 1  in the opposite directions. 
     In this way, since the movement paths of the RFID antenna  22  are different in the forward and backward paths, it is possible to supply radio waves from different directions to the plurality of RFID tags T, thereby improving the probability of reading the tag information of the RFID tags T. 
       FIG. 9C  illustrates a different example of the movement path of the RFID antenna  22 . In the example as illustrated in  FIG. 9C , the RFID tag reading device  30   b  moves the RFID antenna  22  simultaneously along two axis directions. That is, the RFID tag reading device  30   b  moves the RFID antenna  22  from the position of x=0 and y=y 1  to the position of x=W and y=y 3  (a movement path Q 4 ), and thereafter, moves the RFID antenna  22  from the position of x=W and y=y 3  to the position of x=0 and y=y 2  (a movement path Q 5 ). Thereafter, the RFID tag reading device  30   b  moves the RFID antenna  22  to the original position (x=0, y=y 1 ) by moving the moving paths Q 5  and Q 4  in the opposite directions. By adopting such a movement path, radio waves can be radiated over a wider range within the movement range of the RFID antenna  22 . 
     As described above, according to the RFID tag reading device  30 , the reader and writer control unit  112  reads the information of the RFID tag T from the item of merchandise M to which the RFID tag T is attached, while the moving mechanism  24  changes the communication distance between the RFID antenna  22  and the RFID tag T. Furthermore, the antenna movement speed control unit  116  changes the speed of changing the communication distance between the RFID antenna  22  and the RFID tag T. Therefore, it is possible to reliably read the information of the RFID tag T in a short time. 
     According to the RFID tag reading device  30 , the antenna movement speed control unit  116  changes the speed of changing the communication range between the RFID antenna  22  and the RFID tag T, based on at least one of the movement distance of the moving mechanism  24 , the position of the communication distance, and the reading result of the reader and writer control unit  112 . Therefore, it is possible to reliably read the information of the RFID tag T in a short time. 
     According to the RFID tag reading device  30 , the antenna movement speed control unit  116  reduces the speed of changing the communication range, when in the communication range between the RFID antenna  22  and the RFID tag T, a movement of a predetermined movement distance has been completed. Therefore, even when RFID tags T overlap each other, it is possible to reliably read the information of the RFID tags T, by reducing the movement speed of the RFID antenna  22 . 
     According to the RFID tag reading device  30  of the embodiment, the antenna movement speed control unit  116  reduces the speed of changing the communication range, when the communication range between the RFID antenna  22  and the RFID tag T is in the vicinity of the center of the predetermined movement range. Therefore, since the RFID antenna  22  moves at a low speed at a position where there is a high possibility that a plurality of RFID tags T overlap and are placed, the information of the RFID tag T can be reliably read. 
     According to the RFID tag reading device  30   b  t, the antenna movement speed control unit  116 ) reduces the speed of changing the communication range between the RFID antenna  22  and the RFID tag T, when the reader and writer control unit  112  has not read the information of a new RFID tag T for a predetermined time. Therefore, it is possible to further shorten the time for reading the information of the RFID tag T. Further, since the total movement distance of the RFID antenna  22  can be shortened, the durability of the moving mechanism  24  including the stepping motor  12  can be improved. 
     Specific examples are described above in which an RFID tag reading device  30 , or  30   b  is applied to a case of reading information stored in RFID tags T attached to items of merchandise M. However, the RFID tag reading device  30 , or  30   b  can also be used as an RFID tag writing device that writes information into the RFID tags T. That is, after tag information is read, the RFID antenna  22  writes information into the RFID tag T indicating that the merchandise has been registered. Such information written to the RFID tags T can be used not only as information indicating that the merchandise is registered but also as information for crime prevention. Even when at least one of the RFID tag reading devices  30  and  30   b  are used as the RFID tag writing devices, it is possible to reliably write information into the RFID tags T, by making the movement speed of the RFID antenna  22  variable. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.