Patent Publication Number: US-11665292-B2

Title: Sheet conveyance device and program for sheet conveyance device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/096,723, filed on Nov. 12, 2020, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-011484, filed on Jan. 28, 2020, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a sheet conveying apparatus and a program. 
     BACKGROUND 
     Conventionally, an image forming apparatus conveys a sheet from a sheet cassette or a manual feeding tray and then forms an image on the conveyed sheet. In some examples, sheets of a certain type incorporate a wireless tag (e.g., an RFID tag). In order to read and write information to and from a wireless tag of such a sheet, the image forming apparatus incorporates a wireless tag communication device along the sheet conveyance path. 
     A technique of performing reading and writing to tags while the resonance frequency of the transmission antenna is changed such that the frequency deviation between the resonance frequency of the transmission antenna and the transmission signal being supplied to the transmission antenna falls within an allowable range in order to prevent the deterioration in the antenna communication performance due to a decrease in the resonance current is known. 
     However, if information is to be written to a wireless tag of a sheet while moving on a conveyance path, the communication area of the wireless tag communication apparatus becomes relatively wide. As such, the wireless tag communication device may also inadvertently communicate with other wireless tags on the sheet or on the conveyance path, and may thus write information to these other wireless tags in error. For example, the wireless tag communication device may inadvertently write information to a wireless tag on a sheet that is not yet on the conveyance path, such as a sheet still in a sheet cassette. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is schematic diagram of an image forming apparatus according to an embodiment. 
         FIG.  2    is a schematic diagram of a sheet flow for double-sided printing. 
         FIG.  3    is a block diagram of a sheet conveying apparatus according to an embodiment. 
         FIG.  4    is a schematic diagram depicting phase data stored in a phase storage portion. 
         FIG.  5    is a flowchart of a process related to reading and writing of information from and to a wireless tag. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, a sheet conveying apparatus of an embodiment comprises a conveyance path along which a sheet can be conveyed, and a plurality of conveyance rollers configured to move a sheet along the conveyance path. A wireless tag reader/writer is configured to read information from, and write information to, a wireless tag of a sheet on the conveyance path. A phase change detector is configured to detect a phase change in response waves received by the wireless tag reader/writer from a wireless tag. A tag specifying unit is configured to identify whether a wireless tag is moving along the conveyance path based on the detected phase change in response waves from the wireless tag. A controller is configured to control the wireless tag reader/writer to write information to the wireless tag identified as moving along the conveyance path. 
     A sheet conveyance apparatus of an embodiment can appropriately write information to a wireless tag on a sheet that is being moved along a conveyance path. Hereinafter, an image forming apparatus incorporating a sheet conveying apparatus according to an embodiment will be described as an example. 
     First, a configuration of the image forming apparatus  10  according to an embodiment will be described with reference to  FIG.  1   .  FIG.  1    depicts an image forming apparatus  10  according to an embodiment. 
     In  FIG.  1   , the image forming apparatus  10  includes a control panel  13 , a wireless tag communication device  201 , and a printer unit  18 . The printer unit  18  includes an image forming controller  100 , a sheet cassette  16   a , and a sheet cassette  16   b . The image forming controller  100  controls the control panel  13 , the wireless tag communication device  201 , and the printer unit  18 . The image forming controller  100  controls conveyance of sheets in the printer unit  18 . In particular, control of the conveyance of the sheets is to control the conveyance timing of a sheet, the stop position of a sheet, the conveyance speed of a sheet, and the like. 
     The control panel  13  includes an input key and a display unit. For example, the input key accepts input from a user. For example, the display unit is a touch panel type. The display unit receives an input and displays the input. For example, the control panel  13  displays an item of information related to the operation of the image forming apparatus  10  on the display unit so as to be able to set or adjust parameters or settings associated with the item. The control panel  13  notifies the image forming controller  100  of inputs and changes to settings made by the user. 
     The sheet cassettes  16   a  and  16   b  store sheets on which a wireless tag is provided. The sheet cassettes  16   a  and  16   b  can also store sheets on which a wireless tag is not provided (e.g., a normal or standard sheet of paper or the like). In the following description, unless otherwise specified, references to a sheet refer to a sheet in or on which a wireless tag is provided. For example, a material such as paper or a plastic film can be used as the sheet. 
     The printer unit  18  performs operations for forming an image on the sheet. For example, the printer unit  18  prints an image corresponding to image data on a sheet. In the following description, forming an image on a sheet will also be referred to as “printing”. In the present embodiment, the printer unit  18  is a device for fixing a toner image to the sheets, but the present disclosure is not limited thereto, and the printer unit may be an ink jet type device or the like. 
     In this example, the printer unit  18  includes an intermediate transfer belt  21 . The printer unit  18  supports the belt  21  by the driven roller  41 , the backup roller  40 , and the like. The printer unit  18  rotates the intermediate transfer belt  21  in the direction indicated by the arrow m in  FIG.  1   . The printer unit  18  includes four sets of image forming stations  22 Y,  22 M,  22 C, and  22 K. The image forming stations  22 Y,  22 M,  22 C, and  22 K correspond to Y (yellow), M (magenta), C (cyan), and K (black), respectively. The image forming stations  22 Y,  22 M,  22 C and  22 K are arranged on the lower side of the intermediate transfer belt  21  in order along the rotation direction of the intermediate transfer belt  21 . 
     Hereinafter, the image forming station  22 Y of Y (yellow) from among the image forming stations  22 Y,  22 M,  22 C, and  22 K will be described as an example. The image forming stations  22 M,  22 C and  22 K have the same configuration as that of the image forming station  22 Y, and therefore detailed description thereof will be omitted. 
     The image forming station  22 Y includes an electrostatic charger (charger)  26 , an exposure scanning head  27 , a developing device  28 , and a photosensitive cleaner  29 . The charger  26 , the exposure scanning head  27 , the developing device  28 , and the cleaner  29  are disposed around the photosensitive drum  24  that rotates in the direction of the arrow n in  FIG.  1   . 
     The image forming station  22 Y includes a first transfer roller  30 . The first transfer roller  30  is disposed so as to face the photosensitive drum  24  via the intermediate transfer belt  21 . 
     The charger  26  uniformly charges the photosensitive drum  24 . The exposure scanning head  27  selectively exposes the uniformly charged photosensitive drum  24  to form an electrostatic latent image on the photosensitive drum  24 . The developing device  28  develops the electrostatic latent image on the photosensitive drum  24  by supplying a two-component developer (formed of a toner and a carrier) to the photosensitive drum  24 . 
     The first transfer roller  30  transfers the toner image formed on the photosensitive drum  24  to the intermediate transfer belt  21  (this may be referred to as a primary transfer). The first transfer roller  30  of each of the image forming stations  22 Y,  22 M,  22 C, and  22 K transfers the respective toner images onto the intermediate transfer belt  21 , thereby forming a color toner image on the intermediate transfer belt  21 . The color toner image is a toner image formed by sequentially supplying toner images of Y (yellow), M (magenta), C (cyan), and K (black). The cleaner  29  removes the toner remaining on the photosensitive drum  24  after the primary transfer. 
     The printer unit  18  includes a second transfer roller  32 . The second transfer roller  32  is disposed so as to face the backup roller  40  via the intermediate transfer belt  21 . The second transfer roller  32  transfers all of the color toner images on the intermediate transfer belt  21  to the sheet (this may be referred to as a secondary transfer). In the following description, the term “toner image” may refer a multi-color toner image or a toner image of only one color (monochromatic). The toner image may be a toner image formed using a decolorable toner. 
     The conveyance path  33  is a path through which a sheet is conveyed by conveyance rollers (for example, the conveyance rollers  330  and the like). In this example, the conveyance path  33  includes a first conveyance path  33   a , a second conveyance path  33   b , and a third conveyance path  33   c . The first conveyance path  33   a  is a conveyance path from a merging portion  44   a  to a branch portion  44   b . The second conveyance path  33   b  is a conveyance path passing through the inside of an inversion unit  38  (also referred to as a reversing unit), and is a conveyance path that is different from the branch portion  44   b  to the merging portion  44   a  and is different from the first conveyance path  33   a . The third conveyance path  33   c  is a conveyance path from the branch portion  44   b  to a sheet discharge tray  20 . 
     The sheet to be processed can be taken out from any one of the sheet cassette  16   a , the sheet cassette  16   b , or a manual feeding tray  16   c . After being taken out, the sheet is temporarily stopped at a portion where the two registration rollers  31  are in contact with each other. At this time, the leading edge of the sheet is brought into contact with the registration roller  31 , and any inclination (angling) of the sheet edge is also corrected. The image forming controller  100  starts the rotation of the registration roller  31  in accordance with the expected position of the toner image on the rotating intermediate transfer belt  21 , and thus moves the sheet to the position of the second transfer roller  32  at an appropriate timing to receive the toner image from the intermediate transfer belt. 
     That is, the toner image formed on the intermediate transfer belt  21  is secondarily transferred to the sheet at the second transfer roller  32 . Subsequently, the transferred toner image is fixed to the sheet by a fixing device  34 . In this way, an image is formed (printed) on the sheet under the control of the image forming controller  100 . The image forming controller  100  then conveys the printed sheet to the third conveyance path  33   c , and discharges the sheet. 
     The wireless tag communication device  201  includes an arithmetic device, a storage device, and an antenna. The wireless tag in this example, is a radio frequency identifier (RFID) tag. The wireless tag communication device  201  transmits radio waves along the arrow k direction depicted in  FIG.  1   . The wireless tag communication device  201  is able to communicate with a wireless tag provided in a sheet being conveyed. Specifically, the wireless tag communication device  201  reads information from the wireless tag and writes information to the wireless tag. 
     The information written to the wireless tag includes, for example, information indicating an identification of the printed sheet/document, information indicating an intended destination of the sheet/document, and/or contents printed on the sheet/document for when the sheet is subsequently distributed or the like. In the present embodiment, the wireless tag communication device  201  uses, for example, a radio wave system (UHF) in the 900 MHz band. However, the communication method/protocol and the frequency band are not limited, and other methods and frequency bands may be employed in other examples. 
     Next, double-sided printing operations will be described. 
       FIG.  2    is an explanatory diagram illustrating an example of double-sided printing. 
     In the case of the double-sided printing, the sheet  250  is taken out from any one of sheet feeding locations, such as the sheet cassette  16   a , the sheet cassette  16   b , or the manual feeding tray  16   c . The sheet  250  is then conveyed to the first conveyance path  33   a . More specifically, the sheet  250  fed from one of the sheet feeding locations is corrected in inclination at the registration roller  31 . Then, the sheet  250  is conveyed to the position of the second transfer roller  32  to match with the position of the toner image formed on the intermediate transfer belt  21 . The toner image formed on the intermediate transfer belt  21  is transferred to the front side of the sheet  250  by the second transfer roller  32 . Then, the toner image on the front side of the sheet  250  is fixed by the fixing device  34 . 
     The sheet  250  on which the image has been formed on the front side next enters the third conveyance path  33   c . Then, under the control of the image forming controller  100 , the sheet  250  is switched back and conveyed to the second conveyance path  33   b . Thereafter, the sheet  250  is conveyed to the merging portion  44   a  via the second conveyance path  33   b  in the inversion unit  38 . The sheet  250  is next conveyed to the first conveyance path  33   a  via the registration roller  31 . Accordingly, the sheet  250  passing through the second conveyance path  33   b  is conveyed to the first conveyance path  33   a  so that the back surface side now faces toward the intermediate transfer belt  21  side. 
     Then, a toner image formed on the intermediate transfer belt  21  is transferred to the back surface side of the sheet  250  by the second transfer roller  32 . The toner image transferred to the back surface side of the sheet  250  is fixed by the fixing device  34 . Then, the sheet  250  is supplied to the third conveyance path  33   c , and is sent out to the sheet discharge tray  20 . 
     Next, a sheet conveying apparatus  50  included in the image forming apparatus  10  will be described with reference to  FIG.  3   .  FIG.  3    is a block diagram illustrating an example of a functional configuration of the sheet conveying apparatus  50  according to an embodiment. 
     In  FIG.  3   , the sheet conveying apparatus  50  includes an image forming controller  100 , a wireless tag communication device  201 , a storage device  220 , and a conveyance path  33 . The image formation control unit  100  controls the wireless tag communication device  201  in accordance with a sheet conveyance program stored in the storage device  220 . 
     The image forming controller  100  is realized by, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), or the like. The storage device  220  is realized by a read only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), a solid-state drive (SSD), or the like. 
     The wireless tag communication device  201  attempts to read an identification code (ID) of a wireless tag  251  (provided in a sheet  250 ) within a communication area at a certain, fixed interval (for example, at a 10 msec interval). Specifically, the wireless tag communication device  201  transmits a signal (carrier wave) at a predetermined interval. When a wireless tag  251  in the communication area receives a signal from the wireless tag communication device  201 , the wireless tag  251  receives electric power from this signal and starts up. The wireless tag communication device  201  can be a wireless tag reader/writer device. Then, the wireless tag  251  transmits a response wave including the ID of the wireless tag communication device  201  previously written or otherwise stored in the wireless tag  251 . Accordingly, the wireless tag communication device  201  receives a response wave from the wireless tag  251  and acquires the ID data corresponding to the wireless tag  251  ID. 
     The wireless tag communication device  201  is capable of communicating with the image forming controller  100 . The wireless tag communication device  201  receives a response wave from the wireless tag  251  provided in the sheet  250  at regular intervals and transmits phase data indicating the phase of the received response wave to the image formation controller  100 . 
     The image forming controller  100  includes an acquisition unit  101 , a detect unit  102 , a specifying unit  103 , and a communication controller  104 . The respective units  101  to  104  are not limited to being provided within the image forming controller  100  and may be provided in another control unit (another CPU, an ASIC, or the like) different from the image forming controller  100 . 
     The acquisition unit  101  acquires the phase data of the response wave received from the wireless tag  251  by the wireless tag communication device  201 . More specifically, the acquisition unit  101  acquires the phase data of the response wave from the wireless tag communication device  201  at a certain interval (for example, at a 10 msec interval). The acquisition unit  101  starts acquisition of the phase data every time a sheet  250  begins to be printed. 
     The acquisition unit  101  stores the acquired phase data of the response waves in a phase storage portion  221  of the storage device  220  for each interval (for example, at a 10 msec interval). Here, when the sheet  250  (more particularly, the wireless tag  251  of the sheet  250 ) moves, the phase of the response wave from the wireless tag  251  changes. For example, the response wave from a sheet  250  (the wireless tag  251  therein) moving on the first conveyance path  33   a  tends to change according to a common change pattern of specific phases. On the other hand, if a sheet  250  (wireless tag  251 ) is not moved, the phase of the response wave from the wireless tag does not change substantially. 
     In addition, in the present embodiment, the information can be written to the wireless tag  251  while the sheet  250  is moving through the conveyance path  33 . Therefore, the communication area of the wireless tag communication device  201  needs to be set relatively wide. More specifically, the communication area of the wireless tag communication device  201  is a wider than would be the case if the sheet  250  could be completely stopped and information written to the wireless tag  251  only while the sheet is stationary at a specific location. For this reason, if information is to be written to the wireless tag  251  while the sheet  250  is moving along the conveyance path  33 , the potential for information to be inadvertently written to another wireless tag  251  within the communication area instead of the intended target wireless tag  251  to which the information is to be written increases. 
     Therefore, to compensate for this increase potential for inadvertent writing, the detect unit  102  refers to the phase data stored in the phase storage portion  221 , and detects a phase change amount of the response wave acquired from wireless tags  251  within the communication area at regular intervals. The phase change amount is, for example, a value indicating a difference in phase acquired at different times from an initial, previous, or reference time. More specifically, in this example, the phase change amount is a difference between the response wave phases stored at a timing interval of 10 msec. 
     The specifying unit  103  identifies a wireless tag  251  to be read/written (hereinafter referred to as a “target wireless tag  251   a ”) based on the amount of phase change of the response wave detected by the detect unit  102 . Specifically, when the phase change amount of the response wave is equal to or larger than some predetermined value (for example, 10°), the specifying unit  103  specifies the wireless tag  251  for which such a phase change amount is obtained as the target wireless tag  251   a.    
     A wireless tag  251  (the target wireless tag  251   a ) for which the phase change amount of the response wave is equal to or more than the predetermined value is considered to be on a sheet  250  is being moved along some portion of the conveyance path  33  (for example, the first conveyance path  33   a ). Accordingly, the specifying unit  103  can identify the wireless tag  251  being moved as the target wireless tag  251   a.    
     The communication controller  104  controls the wireless tag communication device  201  so as to write information to the target wireless tag  251   a  as specified by the specifying unit  103 . The wireless tag communication device  201  writes information to the target wireless tag  251   a  in accordance with the control of the communication controller  104 . 
     (Comparison of Change Patterns of the Phase of the Response Wave) 
     A reference value storage portion  222  stores in advance a reference value of the phase of the response wave when the sheet  250  moves on the conveyance path (hereinafter referred to as a “phase reference value”). Specifically, the phase reference value is a change pattern (reference pattern) of the phase of the response wave associated with the normal conveyance of a sheet  250 . In the present embodiment, the reference pattern is, for example, a change pattern that increases by 20° for each 10 msec. 
     The phase reference value can be obtained by conveying one test sheet  250  in an environment in which other wireless tags  251  are not present around the sheet. For example, such phase reference value(s) can be provided before shipment of the image forming apparatus  10  from a factory or the like. The phase reference value is, for example, a value that can be different for different image forming apparatuses  10 . The phase reference value is not necessarily required to be a factory setting, and for example, the phase reference value may be obtained by prompting a user to obtain a reference value by operation of the image forming apparatus  10  during a user setup mode or the like. 
     The specifying unit  103  identifies the target wireless tag  251   a  based on the result of the comparison between the phase change amount detected by the detect unit  102  and the phase reference value stored in the reference value storage portion  222 . Specifically, for example, the specifying unit  103  compares the change pattern indicated by the phase change amount detected by the detect unit  102  with the reference pattern stored in the reference value storage portion  222 . As a result of the comparison, the specifying unit  103  is able to identify a particular wireless tag  251  that has output a response wave corresponding to the phase reference pattern as the target wireless tag  251   a  when the detected and reference patterns are approximately the same. 
     (Control of Wireless Tags  251  which are not Subject to Reading and Writing) 
     Further, the specifying unit  103  identifies a non-target wireless tag  251  (hereinafter referred to as a “non-target wireless tag  251   b ”) that is not a target for reading and writing, based on the phase change amount detected by the detect unit  102 . The non-target wireless tag  251   b  is, for example, a wireless tag  251  provided in a sheet  250  still in the sheet cassettes  16   a ,  16   b , or on the manual feed tray  16   c.    
     The communication controller  104  requests the non-target wireless tag  251   b  specified by the specifying unit  103  to suppress the output of response waves. More specifically, the communication controller  104  controls the wireless tag communication device  201  to transmit a response suppression command to the non-target wireless tag  251   b  for suppressing the output of response waves. In response to this response suppression command, the non-target wireless tag  251   b  turns on a response suppression flag for prevent the output of a response wave from the non-target wireless tag  251   b  until subsequent commands. 
     The response suppression flag can be reset by cutting off the output of radio waves from the wireless tag communication device  201 . The output of radio waves from the wireless tag communication device  201  is thus cut every time a new printing of a sheet  250  is to be performed. Thus, the response suppression flag can be reset every time the printing of a sheet  250  is performed. 
     (A Position to Write Information to the Target Wireless Tag  251   a ) 
     In some examples, the position at which the information is written to the target wireless tag  251   a  may be set to be on the first conveyance path  33   a , but in the present embodiment, this position is on the second conveyance path  33   b . In the present embodiment, the conveyance path  33  includes a first conveyance path  33   a , a second conveyance path  33   b , and a third conveyance path  33   c , which may be considered portions and/or branches of the overall conveyance path  33 . 
     The first conveyance path  33   a  is the portion of the conveyance path  33  used for forming an image on a sheet  250 . The first conveyance path  33   a  can be used for performing a front surface printing on a sheet  250  fed directly from one the cassettes  16   a ,  16   b , but may also be used for a back surface printing on a sheet  250  returned via the inversion unit  38 . The second conveyance path  33   b  is the path by which a sheet  250  is returned through the inversion unit  38  after previously passing through the first conveyance path  33   a . In this example, the second conveyance path  33   b  is a position closer to the wireless tag communication device  201  than is the first conveyance path  33   a.    
     The detect unit  102  is used to detect the phase change amount in the response wave from sheets  250  traveling along the first conveyance path  33   a . The specifying unit  103  identifies a target wireless tag  251   a  based on the phase change amount(s) detected by the detect unit  102 . The communication controller  104  controls the wireless tag communication device  201  to write the information to the target wireless tag  251   a  when the target wireless tag  251   a  identified by the specifying unit  103  moves to the second conveyance path  33   b.    
     The communication controller  104  determines whether or not the sheet  250  with the target wireless tag  251   a  has moved to the second conveyance path  33   b . The communication controller  104  may determine that the sheet  250  with the target wireless tag  251   a  has moved to the second conveyance path  33   b  based on, for example, the timing of switching functions along the conveyance path  33  for switch back (inversion) processing. 
     The sheet  250  on the second conveyance path  33   b  is subsequently returned to the first conveyance path  33   a  again. When a single-sided printing is set, backside printing (second printing) is not performed on the sheet  250  returned to the first conveyance path  33   a . However, when the backside printing is set to be performed, the backside printing is performed. 
     (Phase Data Example Stored in the Phase Storage Portion  221 ) 
       FIG.  4    is an explanatory diagram illustrating an example of phase data stored in the phase storage portion  221 . As illustrated in  FIG.  4   , phase data  400  includes items corresponding to an “Index”, an “elapsed time”, a “tag ID”, and a “Phase”. 
     “Index” items are information (e.g. an index number or a counting value) for identifying each piece of data. The “elapsed time” is the elapsed time since the start of a printing operation corresponding to when the particular tag ID and phase value were detected. For example, the time elapsed since the wireless tag communication device  201  transmits the first signal (carrier wave) in the printing operation can be used as the elapsed time value. The “tag ID” value is unique identification information allocated for each of the different wireless tags  251 . In this context, “Phase” information indicates a detect phase value (0° to 180°) for a response wave. 
     In the phase data  400  depicted in  FIG.  4   , wireless tags  251  two different “tag IDs”, “AAAABBBB0001” and “CCCCDDDD0002,” are illustrated. That is,  FIG.  4    shows that two different “tag IDs” corresponding to two different the wireless tags  251  are in the communication area. When there are 3 or more types of “tag IDs” in the communication area of the wireless tag communication device  201 . The phase data  400  can include “tag IDs” corresponding to any number of wireless tags  251  detected in the communication area, but here only two different tags  251  are represented in  FIG.  4   . 
     Next, the phase change amount of the wireless tag  251  having the tag ID “AAAABBBB0001” will be described. As indicated at the value “1” in the “Index” column, the “Phase” of the response wave of the wireless tag  251  with the tag ID “AAAABBBB0001” at elapsed time of 0 msec is 20°. As indicated at the value “3” in the “Index” column, the “Phase” of the response wave of the wireless tag  251  with the tag ID “AAAABBBB0001” at 10 msec is 40°. Thus, the phase change amount for the response wave of the wireless tag  251  with the tag ID AAAABBBB0001 is +20° from 0 msec to 10 msec. This phase change amount (magnitude change) is equal to or larger than a predetermined value (for example, 10°) indicating travel/movement of the wireless tag  251 . 
     As indicated by value “5” in the “Index” column, the “Phase” of the response wave of the wireless tag  251  with the tag ID “AAAABBBB0001” at the 20 msec is 60°. For this reason, the phase change amount of the response wave of the wireless tag  251  with the tag ID “AAAABBBB0001” from 10 msec to 20 msec is again+20° (magnitude change of 20°). 
     The phase change amount is again equal to or larger than the predetermined value (for example, 10°). That is, the wireless tag  251  (“AAAABBBB0001”) is estimated to be a wireless tag  251  on a sheet  250  being moved. The comparison between the phase change amount and the predetermined value is, for example, a comparison of absolute values. The phase change pattern obtained from the phase change amounts over time for a particular wireless tag  251  can be compared to a reference pattern stored in the reference value storage portion  222 , for example. 
     Accordingly, it can be estimated that the sheet  250  with the wireless tag  251  having the tag ID “AAAABBBB0001” is moving along the conveyance path  33 . Therefore, the specifying unit  103  identifies the wireless tag  251  having the tag ID “AAAABBBB0001” as target wireless tag  251   a.    
     Next, the phase change amount of the wireless tag  251  having the tag ID “CCCCDDDD0002” will be described. As indicated by value “2” in the “Index” column, the “Phase” of the response wave of the wireless tag  251  with the tag ID “CCCCDDDD0002” at 1 msec is 162°. As indicated by value “4” in the “Index” column, the “Phase” of the response wave of the wireless tag  251  with the tag ID “CCCCDDDD0002” at 11 msec is 161°. Therefore, the phase change amount of the response wave of the wireless tag  251  with the tag ID “CCCCDDDD0002” from 1 msec to 11 msec is −1° (the absolute size change is 1′). This amount of phase change is less than the predetermined value (for example, 10°). 
     As indicated by the value “6” in the “Index” column, the “Phase” of the wireless tag  251  with the tag ID “CCCCDDDD0002” at the 21 msec is 163 degrees. Thus, the amount of phase change in the response wave of the wireless tag  251  with the tag ID “CCCCDDDD0002” from 11 msec to 21 msec is +2° (the absolute size is 2°). The amount of phase change is less than the predetermined value (for example, 10°). The difference in the detected phase change amount is presumably due to a minor error in measurement or the like. That is, it can be considered that there has been almost no change in the phase change amount for the wireless tag  251  with the tag ID “CCCCDDDD0002”. 
     Accordingly, it can be estimated that the sheet  250  with the wireless tag  251  having the tag ID “CCCCDDDD0002” is not on the conveyance path  33 . More specifically, it can be estimated that the sheet  250  with the wireless tag  251  having the tag ID “CCCCDDDD0002” is in one of the sheet cassettes  16   a ,  16   b , or on the manual feed tray  16   c . Therefore, the specifying unit  103  identifies the wireless tag  251  having the tag ID “CCCCDDDD0002” as the non-target wireless tag  251   b.    
     (Processing Related to Reading and Writing of Information with the Wireless Tag  251  Performed by the Image Forming Apparatus  10 ) 
     Next, an example of processing related to reading and writing of information from and to the wireless tag  251  performed by the image forming apparatus  10  (or more particularly a sheet conveyance device  50 ) will be described with reference to  FIG.  5   .  FIG.  5    is a flowchart illustrating an example of a process related to reading and writing of information with respect to the wireless tags  251  as performed by the image forming apparatus  10 . 
     In  FIG.  5   , the image forming apparatus  10  determines whether a printing has been started (ACT 501 ). The printing in this context is, for example, a printing on a single sheet  250 . The image forming apparatus  10  waits (ACT 501 : NO) until the start of printing. When the image forming apparatus  10  starts the printing (ACT 501 : YES), the image forming apparatus  10  starts RFID reading (ACT 502 ). Specifically, the image forming controller  100  controls the wireless tag communication device  201  to start transmission of a carrier wave signal at regular intervals and begins reception of any response wave(s). 
     Then, the image forming apparatus  10  determines whether or not the wireless tag  251  has been detected (ACT 503 ). In ACT 503 , specifically, the image forming controller  100  determines whether or not the wireless tag communication device  201  has received a response wave from a wireless tag  251 . When the wireless tag communication device  201  does not detect any wireless tag  251 , the image forming apparatus  10  stands by (ACT 503 : NO). When the wireless tag communication device  201  detects a wireless tag  251  (ACT 503 : YES), the image forming apparatus  10  stores the relevant data items (that is, values for the “elapsed time”, “tag ID”, and “Phase”) of the phase data  400  as obtained by receiving the response wave from a wireless tag  251 . 
     Then, the image forming apparatus  10  detects, measures, or calculates the phase change amount for a wireless tag  251  indicated by a previously received tag ID (ACT 505 ) if available. Then, the image forming apparatus  10  determines whether or not the phase change amount is equal to or larger than some predetermined value (ACT 506 ). When the phase change amount is equal to or larger than the predetermined value (ACT 506 : YES), the image forming apparatus  10  proceeds to ACT 508 . When the phase change amount is not equal to or larger than the predetermined value (ACT 506 : NO), the image forming apparatus controls the wireless tag communication device  201  to transmit a response suppression command addressed to the particular (estimated as none moving) wireless tag  251  (ACT 507 ), and returns to ACT 503 . 
     Then, the image forming apparatus  10  compares the phase change pattern for a particular wireless tag estimated as possibly moving in the prior step(s) with the reference pattern stored in the reference value storage portion  222  (ACT 508 ). Next, the image forming apparatus  10  determines whether or not the phase change pattern matches, or substantially coincides with, the reference pattern (ACT 509 ). When the phase change pattern does not match the reference pattern (ACT 509 : NO), the image forming apparatus  10  returns to ACT 507 . 
     When the phase change pattern matches the reference pattern (ACT 509 : YES), the image forming apparatus  10  next determines whether or not the sheet  250  having the wireless tag  251  has been passed to the second conveyance path  33   b  (ACT 510 ). A sheet  250  passing through the second conveyance path  33   b  can be determined, for example, by detecting that the entire sheet  250  has passed the branch portion  44   b  and being conveyed to the second conveyance path  33   b  by switching back the sheet  250 . 
     The image forming apparatus  10  waits until the sheet  250  is on the second conveyance path  33   b  (ACT 510 : NO). When the sheet  250  is deemed on the second conveyance path  33   b  (ACT 510 : YES), the image forming apparatus  10  controls the wireless tag communication device  201  to write information to the wireless tag  251  (ACT 511 ). 
     Then, the image forming apparatus  10  determines whether or not the printing is finished (ACT 512 ). The image forming apparatus  10  stands by until the printing is completed (ACT 512 : NO). Once the printing is finished (ACT 512 : YES), the image forming apparatus  10  controls the wireless tag communication device  201  to reset the communication with the wireless tags  251  (ACT 513 ), and ends the present series of processes. 
     By resetting the communication with the wireless tags  251 , the outputting of radio waves from previously suppressed wireless tags  251  is reset since the response suppression flag in any of the wireless tags  251  is reset. The collected phase data  400  can also be reset by the reset of the communication with the wireless tag  251 . 
     In the flowchart illustrated in  FIG.  5   , the processing of the ACT 506  (determination of the amount of phase change) and the processing of the ACT 508  and ACT 509  (the comparison of the change pattern to a reference pattern) are performed, but the processing is not limited to this. For example, the processes may be performed together or just one of the processes may be performed. 
     According to the embodiment described above, the wireless tag communication device  201  can be controlled so that the target wireless tag  251   a  is first identified based on the phase change amount of the response wave and then the information is written to the target wireless tag  251   a . Accordingly, the sheet conveyance device  50  can appropriately write information to the intended wireless tag  251  of a sheet  250  actually moving on the conveyance path  33 . That is, erroneous (unintended) writing of information to a wireless tag  251  of a sheet  250  in the sheet cassettes  16   a ,  16   b , or on the manual feed tray  16   c  can be avoided. 
     In addition, in the present embodiment, the sheet conveyance apparatus  50  specifies the target wireless tag  251   a  based on a result of the comparison between the phase change pattern of the response wave output from the wireless tag  251  and a reference pattern for the phase of the response wave of a sheet  250  moved on the conveyance path  33 . Accordingly, it is possible to more accurately identify a sheet  250  moving on the conveyance path  33 , and thus it is possible to more appropriately write information to the wireless tag  251  of the sheet  250  that moves on the conveyance path  33 . 
     In addition, in the present embodiment, the sheet conveyance device  50  specifies the non-target wireless tag(s)  251   b  on the basis of the phase change amount of the response wave output from the wireless tag  251 , and controls the non-target wireless tag(s)  251   b  to suppress the output of a response wave. Accordingly, it is possible to prevent a response wave from being output from the wireless tag  251  that is not required. Here, if the wireless tag communication device  201  receives a response wave from a wireless tag  251  that is not targeted for writing, an operation of reading the ID of the wireless tag  251  is still performed accordingly, and the operation of reading the ID of a wireless tag  251  may still require an interval longer than, for example, 10 msec to perform associated processing. 
     However, according to the present embodiment, it is possible to suppress the output of the unnecessary response wave from the untargeted wireless tags  251 , and therefore, it is possible to prevent unnecessary operations associated with reading the ID of such wireless tags  251 . In other words, it is possible to suppress the processing load (and delays) related to the reception of the unnecessary response waves by the wireless tag communication device  201 . Therefore, it is possible to more appropriately detect the phase changes of the response wave(s), and thus it is possible to more appropriately write the information to the intended wireless tag  251  of a sheet  250  moving on the conveyance path  33 . 
     In the present embodiment, the sheet conveyance device  50  specifies the non-target wireless tag  251   b  based on the phase change amount of the response wave while on the first conveyance path  33   a , and then writes the information to the wireless tag  251  when the sheet  250  moves to the second conveyance path  33   b . Accordingly, it is possible to secure a period for detecting the phase change amount of the response wave on the first conveyance path  33   a . That is, it is possible to appropriately detect the phase change amount of the response wave. Therefore, it is possible to more accurately determine that a particular sheet  250  is moving on the conveyance path  33 . In addition, it is possible to secure a period in which information is written to the wireless tag  251  when on the second conveyance path  33   b . Therefore, it is possible to appropriately write information to the wireless tag  251  of the sheet  250  while on the second conveyance path  33   b.    
     In the present embodiment, the first conveyance path  33   a  is first used for performing front surface printing, and the second conveyance path  33   b  is used for performing the back surface printing (that is, the conveyance path  33   b  is the sheet reversing or return path). This makes it possible to efficiently write information to the wireless tag  251  of a moving sheet  250  using an existing conveyance path  33  without separately providing a conveyance path specifically dedicated to reading and writing information to and from the wireless tag  251 . 
     In the present embodiment, the second conveyance path  33   b  is at a position closer to the wireless tag communication device  201  than the first conveyance path  33   a . Accordingly, it is possible to shorten the communication distance to the wireless tag  251 , and thus it is possible to more appropriately write the information to the wireless tag  251  of the sheet  250  on the second conveyance path  33   b.    
     The function(s) of a sheet conveying apparatus  50  in the above-described embodiment may be realized by a computer. In this case, a program for realizing the function(s) may be recorded in a non-transitory, computer-readable recording medium, and the program recorded in the recording medium may be loaded into a computer system and then executed by the computer system. In this context, a “computer system” includes, for example, an operating system, hardware, a peripheral device, and the like. A “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, and a storage device such as a hard disk built in the computer system. Further, the “computer-readable recording medium” may include a cloud-based storage system or the like and a program can be transmitted via a network such as the Internet or a communication line such as a telephone line from a computer system serving as a server or a client. The program may be a program for realizing a part of the functions described above or may be a program for realizing the above-described functions in combination with a program already recorded in the computer system. 
     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.