Abstract:
A system and method for tracking consumables associated with an image forming device is described. An RFID reader is positioned to read RFID tags associated with the consumables when the consumables are inserted into, stationary in, or removed from the image forming device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-224548, filed on Sep. 29, 2009, the entire subject matter of which is incorporated herein by reference. 
     FIELD 
     Aspects of the disclosure relate to an image forming apparatus including a reading portion that is configured to read information from a wireless tag attached to a consumable unit. 
     BACKGROUND 
     A known image forming apparatus, e.g., an inkjet printer, is configured to read information from a wireless tag attached to an ink cartridge. Based on the information read from the wireless tag, the image forming apparatus determines a manufacturer of the instant ink cartridge for consumables management. 
     Another known image forming apparatus, e.g., a laser printer, includes an accommodating unit, e.g. a drawer, to accommodate a plurality of consumable units, e.g. consumable cartridges, which are detachable. The accommodating unit may be slidable from a predetermined position inside the printer to outside the printer. When the accommodating unit is slid outside the printer, the user can replace a cartridge with a new one. 
     Even in the image forming apparatus having such an accommodating unit, a wireless tag may be attached to each cartridge for consumables management. In this case, a reading portion that reads information from the wireless tag is required to have a high degree of accuracy of reading in consideration of that each cartridge accommodated in the accommodating unit moves in accordance with movement of the accommodating unit. 
     SUMMARY 
     Aspects of the disclosure provide an image forming apparatus including a reading portion that reads information from a wireless tag attached to a consumable unit, wherein the image forming apparatus has a high degree of accuracy of reading with an inexpensive structure even if consumable units accommodated in an accommodating unit move in accordance with movement of the accommodating unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative aspects will be described in detail with reference to the following figures in which like elements are labeled with like numbers and in which: 
         FIG. 1  is a side sectional view of an internal structure of a laser printer as an illustrative example of an image forming apparatus using features described herein; 
         FIG. 2  is a top view schematically illustrating arrangement of cartridge tags according to a first illustrative embodiment. 
         FIG. 3  illustrates a structure of a cartridge tag according to the first illustrative embodiment. 
         FIG. 4  is a block diagram illustrating a control system of a laser printer. 
         FIG. 5  is a flowchart of a reading range setting program. 
         FIG. 6  is a side sectional view of the laser printer for process cartridge replacement. 
         FIG. 7  is a side sectional view of the laser printer for process cartridge replacement. 
         FIG. 8  is a side sectional view of the laser printer for process cartridge replacement. 
         FIG. 9  is a flowchart of a toner error handling program. 
         FIG. 10  is a top view schematically illustrating an arrangement of cartridge tags according to a second illustrative embodiment. 
         FIGS. 11A to 11D  illustrate structures of the cartridge tags according to the second illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A first illustrative embodiment will be described in detail with reference to the accompanying drawings. An image forming apparatus according to aspects of the disclosure applies to a laser printer  1  as shown in  FIG. 1 . The laser printer  1  is an electrophotographic color laser printer that forms a color image on a recording sheet P. The recording sheet may include plain paper, cardboards, postcards, and transparency sheets. 
     For ease of discussion, in the following description, the “top” or “upper side”, the “bottom” or “lower side”, the “left” or “left side”, the “right” or “right side”, the “front” or “front side”, and the “rear” or “rear side” are used to define the various parts when the laser printer  1  is disposed in an orientation in which it is intended to be used. In  FIG. 1 , the right side is referred to as the front or front side, the left side is referred to as the rear or the rear side, the upper side is referred to as the top or upper side, the down side is referred to as the bottom or lower side, and an up and down direction is referred to as a top-bottom direction or vertical direction. 
     As shown in  FIG. 1 , the laser printer  1  may include a generally box-shaped main body  2 . A front side of the main body  2  contains an opening  2 A. The main body  2  accommodates an image forming unit  10 , a sheet supplying unit  50 , a sheet feeding unit  60 , a fixing unit  70 , an wireless tag reader  80 , and a controller  90  ( FIG. 4 ). 
     The main body  2  includes a frame member (not shown) inside. The image forming unit  10 , the sheet supplying unit  50 , the sheet feeding unit  60 , and the fixing unit  70  are assembled to the frame member. The frame member includes a pair of side frames along right and left side surfaces of the main body  2 . The side frames support a drawer case  35  such that the drawer case  35  slidably moves in the front-rear direction. 
     A top surface of the main body  2  contains an output tray  4  and a display  95 . The output tray  4  is configured to store recording sheets  4  each having an image thereon such that they are overlaid, one over the other. The display  95  is configured to display various information, e.g. an error message relating to image formation, based on the controller  90 . 
     The front side of the main body  2  contains a front cover  5  which opens and closes the opening  2  as shown in  FIGS. 6-8 . Specifically the front cover  5  is pivotally supported by the main body  2  in such a manner as to pivot on a shaft  5 A which is disposed at a lower end defining the opening  2 A. The front cover  5  is movable between a closed position in which the opening  2 A is closed ( FIG. 6 ) and an open position in which the opening  2 A is open ( FIG. 8 ). 
     The front cover  5  includes a cover tag  6  in a predetermined position of an end opposite to the shaft  5 A. The cover tag  6  is disposed above the drawer case  35  when the front cover  5  is in the closed position. The cover tag  6  is a wireless tag, e.g. a passive radio frequency identification (RFID) tag, which may be configured to receive radio waves from the wireless tag reader  80  as its operating power. The cover tag  6  stores various kinds of information specific thereto, such as identification information. 
     The main body  2  accommodates the wireless tag reader  80  slightly above an upper end defining the opening  2 A. When the front cover  5  is placed in the closed position as shown in  FIG. 1 , the wireless tag reader  80  is disposed above the cover tag  6 . The wireless tag reader  80  is located in a central portion with respect to a width direction that is a right-left direction of the main body  2  or the front door  5  placed in the closed position. The wireless tag reader  80  has a reading range having a directivity directed downward to a center of the opening  2 A, e.g. a first reading range R and a second reading range L as shown in  FIG. 1 . 
     The wireless tag reader  80  is configured to read information from wireless tags, e.g. passive RFID tags, which are located within the reading range, e.g. the cover tag  6 , a first drawer tag  36 A, a second drawer tag  36 B, and a cartridge tag  45 . Specifically, the wireless tag reader  80  emits radio waves including a command toward a wireless tag. The wireless tag responds by emitting radio waves, and the wireless tag reader  80  reads information stored in the wireless tag by receiving and decoding the radio waves received from the wireless tag. The reading range means a range in which the wireless tag reader  80  transmits and receives radio waves to and from the wireless tag. The wireless tag reader  80  is connected to an auxiliary power supply of the laser printer  1 , and is capable of reading the wireless tag even when the laser printer  1  is not in operation. 
     The image forming unit  10  of the laser printer  1  will be described. 
     The image forming unit  10  is located in substantially a central portion inside the main body  2  and is configured to form an image on a recording sheet P. The image forming unit  10  includes a scanner unit  20  and a photosensitive member unit  30 . 
     The scanner unit  20  is disposed in the top portion within the main body  2  and includes laser light sources, a polygon mirror, fθ lenses, and reflecting mirrors. The scanner unit  20  has, e.g. four, laser light sources, which are provided for a plurality of colors, e.g. four colors of black, yellow, magenta, and cyan. A laser beam emitted from each laser light source, based on image data, may be deflected by the polygon mirror, pass through the fθ lenses, and be folded by the reflecting mirror to be directed to a surface of each photosensitive drum  31 , on which an electrical latent image is formed. The electrical latent image formed on each photosensitive drum  31  is to be developed with one of black, yellow, magenta, and cyan. 
     The photosensitive member unit  30  is disposed below the scanner unit  20  and above the sheet feeding unit  60 . The photosensitive member unit  30  includes process cartridges  40 , photosensitive drums  31 , and chargers  32 , which all are provided for a plurality of colors, e.g., four colors of black, yellow, magenta, and cyan. The photosensitive member unit  30  further includes the drawer case  35 . The drawer case  35  holds four process cartridges  40  arranged in tandem in the front-rear direction. Process cartridges  40  are one type of consumable product (hereinafter “consumables”). Photosensitive drums  31  may also be considered a consumable. 
     As shown in  FIGS. 6-8 , the drawer case  35  is slidable along guides formed on the frame member in the front-rear direction of the laser printer  1 . The drawer case  35  is movable between a use position shown in  FIG. 6  and a replacement position shown in  FIG. 8  in the front-rear direction. As shown in  FIGS. 1 and 6 , when the drawer case  35  is in the use position or located in the main body  2 A, image is formed using the process cartridges  40 . As shown in  FIG. 8 , when the drawer case  35  is in the replacement position or located outside the main body  2 A, the process cartridges  40  can be attached to or removed from the drawer case  35  for replacement. 
     As shown in  FIG. 1 , each process cartridge  40  includes a toner chamber  41 , a supply roller  42 , a developing roller  43 , a layer-thickness regulating blade  44 , and a cartridge tag  45 . Each process cartridge  40  is configured to be attached to and removed from the drawer case  35 , independently. The toner chamber  41  forms an upper portion of the process cartridge  40 , and is configured to store black, yellow, magenta, or cyan toner. The supply roller  42  is configured to supply toner in the toner chamber  41  to a surface of the developing roller  43 . The developing roller  43  is configured to supply the toner supplied from the supply roller  42  to a surface of the photosensitive drum  31 . The layer-thickness regulating blade  44  is configured to regulate the toner carried on the surface of the developing roller  43  to a uniform thickness. 
     The four process cartridges  40  are provided for colors of toner stored in the toner chamber  41 : black, yellow, magenta, and cyan. In the first illustrative embodiment, the process cartridges  40  are attached to the drawer case  35  such that a first process cartridge  40 K storing black toner, a second process cartridge  40 Y storing yellow toner, a third process cartridge  40 M storing magenta toner, and a fourth process cartridge  40 C storing cyan toner are arranged in this order from front to rear of the laser printer  1 . 
     Each process cartridge  40  includes its corresponding cartridge tag  45  on the top surface thereof. The cartridge tag  45  is a wireless tag, e.g. a passive RFID tag, which includes an antenna  46  and an IC chip  47  ( FIG. 3 ). The cartridge tag  45  stores identification information. 
     The drawer case  35  includes four photosensitive drums  31  and four chargers  32 . Each photosensitive drum  31  is rotatably supported below the corresponding process cartridge  40  and is disposed such as to contact a conveying belt  63  of the sheet feeding unit  60 . Each charger  32  is a scorotron charger and is disposed in a position facing the corresponding photosensitive drum  31 . The charger  32  is configured to positively charge the surface of the photosensitive drum  31  to form an electrostatic latent image on the photosensitive drum  31 . 
     In the first illustrative embodiment, as is the case with the process cartridges  40 , the four photosensitive drums  31  includes a first photosensitive drum  31 K corresponding to black toner, a second photosensitive drum  31 Y corresponding to yellow toner, a third photosensitive drum  31 M corresponding to magenta toner, and a fourth photosensitive drum  31 C corresponding to cyan toner, which are arranged in this order from front to rear of the laser printer  1 . 
     The drawer case  35  further includes a first drawer tag  36 A and a second drawer tag  36 B, which are wireless tags, e.g. passive RFID tags, and store identification information respectively. In the drawer case  35 , the first drawer tag  36 A and the second drawer tag  36 B are disposed above the cartridge tags  45 . The first drawer tag  36 A is disposed in a front upper end portion of the drawer case  35  and the second drawer tag  36 B is disposed in a rear upper end portion of the drawer case  35 . As shown in  FIG. 2 , the first and second drawer tags  36 A,  36 B are disposed on a centerline C of the drawer case  35  in the width direction. The first and second drawer tags  36 A,  36 B pass under the wireless tag reader  80  as the drawer case  35  moves as shown in  FIGS. 6-8 . 
     The sheet supplying unit  50  of the laser printer  1  will be described. 
     The sheet supplying unit  50  includes a sheet supply tray  51 , a sheet supply roller  52 , a separation pad  53 , a pair of feed rollers  54 , and a pair of registration rollers  55 . 
     The sheet supply tray  51  is configured to store a stack of recording sheets P and is disposed in a lower portion of the main body  2 . The sheet supply cassette  51  may be configured to be attached to and removed from the front of the main body  2 . The pick up roller  52  is rotatably disposed in a front upper portion of the sheet supply cassette  51  and configured to pick up sheets P in the sheet supply tray  51  and feed them toward the image forming unit  10 . The separation pad  53  is configured to separate the sheets P picked up by the pickup roller  52  one by one. The feed rollers  54  are disposed downstream of the separation pad  53  in a sheet feeding direction, and configured to contact the sheet P separated by the separation pad  53  and feed it to the image forming unit  10 . The registration rollers  55  are disposed at a downstream side from the feed rollers  54  in the sheet feeding direction and configured to contact the leading edge of the recording sheet P, correct skew of the recording sheet P and feed it further to the image forming unit  10 . 
     The sheet feeding unit  60  of the laser printer  1  will be described. 
     The sheet feeding unit  60  is disposed below the image forming unit  10  and above the sheet supply tray  51 . The sheet feeding unit  60  is configured to feed the recording sheet P supplied by the sheet supplying unit  50  toward the fixing unit  70 . The sheet feeding unit  60  includes a drive roller  61 , a driven roller  62 , the conveying belt  63  and four transfer rollers  64 . 
     The driven roller  61  and the driven roller  62  are spaced apart in the front-rear direction and parallel to each other under the image forming unit  10 . The conveying belt  63  is an endless belt made of a conductive rubber and is stretched around the drive roller  61  and the driven roller  62 . Thus, the conveying belt  63  rotates along with rotation of the drive roller  61 . The upper surface of the conveying belt  63  contacts the photosensitive drums  31 . The transfer rollers  64  are disposed within the conveying belt  63  and under the respective photosensitive drums  31  such that the conveying belt  63  is sandwiched between the transfer rollers  64  and the photosensitive drums  31 . 
     The fixing unit  70  of the laser printer  1  will be described. 
     The fixing unit  70  is disposed behind the image forming unit  10 . The fixing unit  70  includes a heat roller  71  and a pressure roller  72 . The heat roller  71  is configured to feed the recording sheet P toward the output tray  4  disposed downstream in the sheet feeding direction, while heating toner transferred onto the recording sheet P. The pressure roller  72  is disposed facing the heat roller  71  and configured to rotate while pressing the recording sheet P toward the heat roller  71 . Thus, the fixing unit  70  is configured to melt the toner transferred onto the recording sheet P by heat and fix it to the recording sheet P, while feeding the recording sheet P toward the output tray  4 . 
     An ejection roller  75  is disposed upward from the fixing unit  70  such as to rotate along a rear end of the output tray  4 . The ejection roller  75  is configured to eject the recording sheet P fed by the fixing unit  70  to the output tray  4 . 
     In the printer  1 , an image is formed on a recording sheet P as follows. 
     When the image formation starts, the sheet supplying unit  50  and the sheet feeding unit  60  operate to feed a recording sheet P from the sheet supply tray  51  to the image forming unit  10 . During this time, the surfaces of the rotating photosensitive drums  31 K,  31 Y,  31 M and  31 C are uniformly and positively charged by the respective chargers  32 , and exposed to laser beams emitted from the scanner unit  20 , so that latent images based on image data are formed on the surfaces of the photosensitive drums  31 K,  31 Y,  31 M and  31 C. 
     In each of the process cartridges  40 K,  40 Y,  40 M, and  40 C, toner in the toner chamber  41  is supplied through the supply roller  42  and the developing roller  43  to the surface of the corresponding one of the photosensitive drums  31 K,  31 Y,  31 M and  31 C. As a result, the electrostatic latent image formed on the surface of each photosensitive drum  31  becomes visible and a reversal takes place. In this manner, toner images are carried on the surfaces of the photosensitive drums  31 K,  31 Y,  31 M and  31 C. 
     The toner images carried on the surfaces of the photosensitive drums  31  are transferred onto a recording sheet P, which is fed along the surface of the conveying belt  63  from front to rear, by a voltage applied to the transfer rollers  64 . When the recording sheet P having toner images is fed to the fixing unit  70 , the fixing unit  70  melts toner by the application of heat, so that the toner images are fixed onto the recording sheet P as an image. The recording sheet P having the image is fed upward from the fixing unit  70  and ejected to the output tray  4 . 
     The cartridge tags  45  attached to the process cartridges  40  will be described. 
     As described above, each of the process cartridges  40 K,  40 Y,  40 M, and  40 C includes one cartridge tag  45 . In the following description, a cartridge tag  45  attached to the first process cartridge  40 K is referred to as a first cartridge tag  45 K, a cartridge tag  45  attached to the second process cartridge  40 Y is referred to as a second cartridge tag  45 Y, a cartridge tag  45  attached to the third process cartridge  40 M is referred to as a third cartridge tag  45 M, and a cartridge tag  45  attached to the fourth process cartridge  40 C is referred to as a fourth cartridge tag  45 C. 
     As shown in  FIG. 2 , the first cartridge tag  45 K is disposed on the centerline C of the drawer case  35  in the width direction on the top surface of the first process cartridge  40 K. Thus, the first cartridge tag  45 K passes under the wireless tag reader  80  when the drawer case  35  moves between the use position and the replacement position. 
     The second, third and fourth cartridge tags  45 Y,  45 M,  45 C are positioned on the top surfaces of the second, third and fourth process cartridges  40 Y,  40 M,  40 C such as to be gradually spaced away from the centerline C in the width direction. Of the second, third and fourth cartridge tags  45 Y,  45 M,  45 C, the second cartridge tag  45 Y is disposed closest to the center line C and the fourth cartridge tag  45 C is disposed farthest from the centerline C. When the drawer case  35  moves between the use position and the replacement position, the second, third and fourth cartridge tags  45 Y,  45 M,  45 C pass within the reading range of the wireless tag reader  80 , which is directed downward. 
     As each cartridge tag  45  has a different distance to the centerline C, the distance from the centerline C to each cartridge tag  45  passing under the wireless tag reader  80  becomes longer in this order: the first cartridge tag  45 K, the second cartridge tag  45 Y, the third cartridge tag  45 M, and the fourth cartridge tag  45 C. 
     Each cartridge tag  45  has an antenna  46  and an integrated circuit (IC) chip  47 . In the first illustrative embodiment, the first to fourth cartridge tags  45 K,  45 Y,  45 M,  45 C are identical in shape and structure. 
     In the cartridge tag  45  according to the first illustrative embodiment, the antenna  46  is a loop antenna that is configured to allow the cartridge tag  45  to transmit and receive radio waves to and from the wireless tag reader  80 . When the antenna  46  receives radio waves including a command, it creates electromotive force by resonance. The IC chip  47  energizes the circuits by the electromotive force, and reads information stored in the cartridge tag  45 . The IC chip  47  transmits the read information to the wireless tag reader  80  via the antenna  46 . The IC chip  47  stores identification information specific to the cartridge tag  45  and information specific to the corresponding process cartridge  40 . The information specific to the process cartridge  40  includes a date of manufacture of the process cartridge  40  and a manufacturer, and is written in the IC chip  47  when the cartridge tag  45  is attached to the process cartridge  40 . 
     As described above, the wireless tag reader  80  reads information stored in the wireless tag by transmitting and receiving radio waves to and from the wireless tag. As each cartridge tag  45  is positioned at a different distance to the centerline C and the antenna  46  of each cartridge tag  45  is identical in configuration, a radio wave transmitted from each cartridge tag  45  arrives at the wireless tag reader  80  at a different intensity. Thus, the wireless tag reader  80  can identify each of the first to fourth cartridge tags  45 K,  45 Y,  45 M,  45 C from the received radio wave intensities. 
     A control system of the laser printer  1  will be described. 
     As shown in  FIG. 4 , the laser printer  1  includes a controller  90 . The controller  90  is made up of a central process unit (CPU)  91 , a read-only memory (ROM)  92 , a random access memory (RAM)  93 , and an electrically erasable programmable read only memory (EEPROM)  94 . The CPU  91  is the core part that controls all the data relating to the laser printer  1 , and performs control programs, e.g., a reading range setting program ( FIG. 5 ), and a toner error handling program ( FIG. 9 ). The ROM  92  stores the control programs and data tables required for controlling the laser printer  1 . The reading range setting program and the toner error handling program are stored in the ROM  92 . The RAM  93  is a volatile memory that temporarily stores computation results by the CPU  91 . 
     The EEPROM  94  is a non-volatile memory that stores data, e.g. user configuration settings, relating to image formation of the laser printer  1 . Specifically, the EEPROM  94  stores identification information read from the cartridge tags  45 , and the number of pages which have been output since each process cartridge  40  was attached. In addition, the EEPROM  94  may store error information for each identification information based on the toner error handling program. 
     The controller  90  is connected to the wireless tag reader  80 . Thus, the controller  90  may process information read by the wireless tag reader  80  based on the control programs. For example, the controller  90  may allow the EEPROM  94  to store information of the cartridge tags  45  read by the wireless tag reader  80  by identification information. 
     The controller  90  is also connected to the display  95 . Thus, the controller  90  may allow the display  95  to display various messages in accordance with the control programs. For example, the controller  90  may display various error messages on the display  95  in accordance with the toner error handling program (e.g. S 13 , S 17 , and S 19  in  FIG. 9 ). 
     The controller  90  is further connected to the image forming unit  10 , the sheet supplying unit  50 , the sheet feeding unit  60 , and the fixing unit  70 . Thus, the controller  90  controls the image forming unit  10  to form an image on a recording sheet P based on print data. 
     Replacement of the process cartridge  40  will be described with reference to  FIGS. 6-8 . 
     When the laser printer  1  is in normal operation or in a state where image formation is normally performed, the drawer case  35  holding the four process cartridges  40  is placed in the use position, and the front cover  5  is placed in the closed position ( FIGS. 1 and 6 ). In this case, the cover tag  6  and the first drawer tag  36 A are positioned within the first reading range R of the wireless tag reader  80 , and located above the cartridge tags  45  or closer to the wireless tag reader  80  than the cartridge tags  45  ( FIGS. 1 ,  6 , and  8 ). That is, the laser printer  1  is detecting the cover tag  6  and the first drawer tag  36 A when in normal operation. 
     When a process cartridge  40  is replaced because of, e.g. toner exhaustion, the front cover  5  is moved from the closed position to the open position ( FIGS. 6 and 7 ). When the front cover  5  is moved to the open position, the cover tag  6  moves outside of the reading range of the wireless tag reader  80 . Thus, when the front cover  5  is located in the open position, the wireless tag reader  80  can not detect the cover tag  6 . 
     After the front cover  5  is moved to the open position, the drawer case  35  is moved from the use position inside the main body  2  to the front side of the laser printer  1 . The drawer case  35  is slidingly moved through the opening  2 A toward the replacement position ( FIG. 8 ). At this time, the first drawer tag  36 A moves outside of the reading range of the wireless tag reader  80  along with the movement of the drawer case  35  to the replacement position ( FIG. 7 ). In other words, while the drawer case  35  is moved from the use position to the replacement position, the first drawer tag  36 A changes from a state being detected by the wireless tag reader  80  (hereinafter referred to as a detected state) to a state being not detected by the wireless tag reader (hereinafter referred to as an undetected state). 
     When the drawer case  35  is moved from the use position to the replacement position, the first, second, third, and fourth cartridge tags  45 K,  45 Y,  45 M,  45 C pass, in this order, the second reading range L of the wireless tag reader  80  along with the movement of the drawer case  35  ( FIG. 7 ). During the movement of the drawer case  35 , the wireless tag reader  80  reads information of the first, second, third, and fourth cartridge tags  45 K,  45 Y,  45 M,  45 C in this order. 
     When the drawer case  35  reaches the replacement position, the second drawer tag  36 B enters the first reading range R of the wireless tag reader  80  as shown in  FIG. 8 . The laser printer  1  can detect the drawer case  35  in the replacement position by detecting the second drawer tag  36 B. 
     When the drawer case  35  is located in the replacement position, the process cartridges  40  can be individually removed from the drawer case  35 . In the replacement position, a process cartridge  40  in which an error occurs due to, e.g., toner exhaustion, is replaced with a new process cartridge  40 . 
     After the new process cartridge  40  is attached to the drawer case  35 , the drawer case  35  is moved inside the main body  2  toward the use position. That is, the drawer case  35  is slidingly moved through the opening  2 A toward the use position ( FIG. 6 ). At this time, the second drawer tag  36 B moves outside of the reading range of the wireless tag reader  80  along with the movement of the drawer case  35  to the use position ( FIG. 7 ). When the drawer case  35  is moved from the replacement position to the use position, the second drawer tag  36 B changes from the detected state to the undetected state. 
     When the drawer case  35  is moved from the replacement position to the use position, the fourth, third, second, and first cartridge tags  45 C,  45 M,  45 Y,  45 K pass, in this order, the second reading range L of the wireless tag reader  80  along with the movement of the drawer case  35  ( FIG. 7 ). During the movement of the drawer case  35 , the wireless tag reader  80  reads information of the fourth, third, second, and first cartridge tags  45 C,  45 M,  45 Y,  45 K in this order. 
     When the drawer case  35  reaches the use position, the first drawer tag  36 A is located within the first reading range R of the wireless tag reader  80  ( FIG. 6 ). Thus, the laser printer  1  can detect the drawer case  35  in the use position by detecting the first drawer tag  36 A. 
     After the drawer case  35  is located in the use position, the front cover  5  is moved from the open position to the closed position ( FIG. 6 ). When the front cover  5  is moved in the closed position, the cover tag  6  moves within the first reading range R of the wireless tag reader  80 . Thus, when the front cover  5  is located in the closed position, the wireless tag reader  80  is capable of detecting the cover tag  6 . In other words, the laser printer  1  is capable of detecting that it can normally form an image on the recording sheet P by detecting the cover tag  6 . Replacement of the process cartridge  40  is finished by moving the front cover  5  to the closed position. 
     The reading range setting program will be described with reference to  FIG. 5 . 
     This program is executed by the CPU  91  normally while the laser printer  1  is in operation. 
     In the initial state, the reading range of the wireless tag reader  80  is set to the first reading range R. As shown in  FIGS. 1 and 6 , the first reading range R has a directivity toward the central portion of the opening  2 A, and includes the positions of the cover tag  6  and the first drawer tag  36 A when the front cover  5  is in the closed position. The first reading range R does not include the positions of the cartridge tags  45  when passing through the opening  2 A ( FIGS. 1 and 6 ). 
     In S 1 , the CPU  91  determines whether the cover tag  6  is undetected by the wireless tag reader  80  or the cover tag  6  is located outside the first reading range R. Specifically, the CPU  91  determines whether the front cover  5  is moved to the open position in S 1 . When the cover tag  6  is undetected (S 1 : Yes), the CPU  91  proceeds to S 2 . When the cover tag  6  is detected and the front cover  5  is in the closed position (S 1 : No), the CPU  91  returns to S 1 . 
     In S 2 , the CPU  91  determines whether a drawer tag has changed from the detected state to the undetected state. In S 2 , the drawer tag includes both the first and second drawer tags  36 A,  36 B. In other words, the CPU  91  determines whether the drawer case  35  has started to move between the use position and the replacement position in S 2 . The movement of the drawer case  35  between the use position and the replacement position includes both movement from the use position to the replacement position and movement from the replacement position to the use position. When the drawer tag has changed from the detected state to the undetected state (S 2 : Yes), the CPU  91  proceeds to S 3 . When the drawer tag has not changed from the detected state to the undetected state (S 2 : No), the CPU  91  proceeds to S 5 . 
     In S 3 , the CPU  91  performs a second reading range setting process. In the second reading range setting process (S 3 ), the CPU  91  sets the reading range of the wireless tag reader  80  to the second reading range L which is greater than the first reading range R. The second reading range L has a directivity toward the central portion of the opening  2 A and includes the positions of the cartridge tags  45  when passing through the opening  2 A ( FIGS. 1 and 7 ). Specifically, the CPU  91  changes the intensity of radio waves including a command that the wireless tag reader  80  transmits, and sets the reading range of the wireless tag reader  80  to the second reading range L. After setting to the second reading range L, the CPU  91  proceeds to S 4 . 
     At the point in time when the drawer case  35  has started to move between the use position and the replacement position, the reading range of the wireless tag reader  80  is set to the second reading range L. The cartridge tags  45  pass within the second reading range L along with the movement of the drawer case  35  ( FIG. 7 ). At this time, the wireless tag reader  80  reads information of the first to fourth cartridge tags  45 K,  45 Y,  45 M,  45 C. The CPU  91  stores the information read from the cartridge tags  45  in the EEPROM  94  in association with identification information of the respective cartridge tags  45 . 
     In S 4 , the CPU  91  determines whether the wireless tag reader  80  has read information of all cartridge tags  45 . When reading is completed (S 4 : Yes), the CPU  91  determines that all cartridge tags  45  are detected, and proceeds to S 5 . When reading is not completed (S 4 : No), the CPU  91  returns to S 3 . Thus, the reading range of the wireless tag reader  80  remains set to the second reading range L until the wireless tag reader  80  completes reading of information of all cartridge tags  45 . 
     In S 5 , the CPU  91  executes a first reading range setting process. In the first reading range setting process (S 5 ), the CPU  91  sets the reading range of the wireless tag reader  80  to the first reading range R. Specifically, the CPU  91  changes the intensity of radio waves including a command that the wireless tag reader  80  transmits, and sets the reading range of the wireless tag reader  80  to the first reading range R. After setting to the first reading range R, the CPU  91  returns to  51 . 
     As described above, the laser printer  1  sets the reading range of the wireless tag reader  80  to the second reading range L only when the process cartridges  40  pass through the opening  2 A along with the movement of the drawer case  35 , by executing the reading range setting program. Thus, the laser printer  1  reliably allows the wireless tag reader  80  to read information of the cartridge tags  45 . At other times, the laser printer  1  sets the reading range of the wireless tag reader  80  to the first reading range R. The first reading range R is set to detect the drawer tags  36 A,  36 B and the cover tag  6 , and is narrower than the second reading range L. In other words, the laser printer  1  can detect the movements of the front cover  5  and the drawer case  35 , while minimizing power consumption of the wireless tag reader  80 . 
     The toner error handling program will be described with reference to  FIG. 9 . 
     This program is executed by the CPU  91  when a condition for a toner error (hereinafter referred to as toner error condition) is satisfied. A confirmation as to whether the toner error condition is satisfied is carried out at a predetermined time, e.g., at power-on, at the time when a predetermined number of sheets has been printed, and after the elapse of a predetermined time. 
     The toner error condition includes that the amount of toner remaining in a process cartridge  40  is smaller than a predetermined amount (hereinafter referred to as a toner empty condition) and that toner in a process cartridge  40  suffers deterioration (hereinafter referred to as a toner deterioration condition). The toner error condition is satisfied by either the toner empty condition or the toner deterioration condition, and the CPU  91  determines that a toner error occurs in the laser printer  1 . 
     The toner empty condition is determined based on the number of recoding sheets P printed from a process cartridge  40  since the process cartridge  40  has been attached to the drawer case  35 . When the number of recording sheets P printed from a process cartridge  40  exceeds a predetermined number, the CPU  91  determines that the process cartridge  40  satisfies the toner empty condition. 
     The toner deterioration condition is determined based on the elapsed time since the manufacture date of the process cartridge  40 , the number of rotations of the photosensitive drum  31 , and the number of recording sheets P printed from the process cartridge  40  since start of use. For example, the CPU  91  specifies the manufacture date of the process cartridge  40  from information obtained from its cartridge tag  45 , and determines that the toner deterioration condition is satisfied when a period of time since the manufacture date until now is longer than a predetermined period of time. 
     When the toner error condition is satisfied, the CPU  91  sets a toner error flag in the RAM  93  in S 11 . The toner error flag means that a process cartridge  40  satisfies the toner error condition and that the toner error occurs in the laser printer  1 . After setting the toner error flag, the CPU  91  proceeds to S 12 . 
     In S 12 , the CPU  91  executes an error information storage process. In the error information storage process (S 12 ), the CPU  91  specifies a process cartridge  40  that satisfies the toner error condition (hereinafter referred to as a target process cartridge), and stores error information in the EEPROM  94  by associating the error information with identification information which has been obtained from a cartridge tag  45  of the target process cartridge  40 . The error information indicates that the process cartridge  40  satisfies the toner error condition and that the error occurs in the process cartridge  40 . When the error information storage process is finished, the CPU  91  proceeds to S 13 . 
     When the drawer case  35  holding the process cartridges  40  is moved from the replacement position to the use position, identification information of the cartridge tags  45  attached to the respective process cartridges  40  is read by the wireless tag reader  80  and stored in the EEPROM  94  in association with the process cartridges  40 . 
     In S 13 , the CPU  91  executes a toner error notification process. In the toner error notification process (S 13 ), the CPU  91  causes the display  95  to display messages indicating for example that a toner error occurs and that the target cartridge needs replacement. When the toner error notification process is finished, the CPU  91  proceeds to S 14 . 
     In S 14 , the CPU  91  determines whether cartridge replacement is completed. Specifically, the CPU  91  causes the wireless tag reader  80  to always detect the cover tag  6 , the first drawer tag  36 A, and the second drawer tag  36 B. Thereby, the CPU  91  detects the movement of the front cover  5  to the open position, the movement of the drawer case  35  to the replacement position, the movement of the drawer case  35  to the use position, and the movement of the front cover  5  to the closed position, in this order and determines whether the cartridge replacement is completed. When the cartridge replacement is completed (S 14 : Yes), the CPU  91  proceeds to S 15 . When the cartridge replacement is not completed (S 14 : No), the CPU  91  returns to S 13 , and causes the display  95  to display a toner error. 
     In S 15 , the CPU  91  determines whether information of all cartridge tags  45  is obtained by the movement of the drawer case  35  during cartridge replacement. As described above, information of each cartridge tag  45  is read by the wireless tag reader  80  when each cartridge tag  45  passes through the second reading range L along with the movement of the drawer case  35 , and the information is stored in the EEPROM  94 . In S 15 , the CPU  91  determines whether the EEPROM  94  stores information of all cartridge tags  45 . When the EEPROM  94  stores information of all cartridge tags  45  (S 15 : Yes), the CPU  91  proceeds to S 16 . When the EEPROM  94  does not store the information of all cartridge tags  45  (S 15 : No), the CPU  91  proceeds to S 17 . 
     In S 16 , the CPU  91  determines whether the target cartridge has been replaced with a new one. Specifically, the CPU  91  compares the information of the cartridge tag  45  of the target cartridge  40 , which has been already stored in the EEPROM  94 , with information of a cartridge tag  45  of a new cartridge  40 , which is newly obtained during cartridge replacement. When the target cartridge has been replaced with a new one (S 16 : Yes), the CPU  91  proceeds to S 18 . When the target cartridge is not replaced (S 16 : No), the CPU  91  proceeds to S 19 . 
     In S 17 , the CPU  91  executes a reading error notification process. In the reading error notification process (S 17 ), the CPU  91  causes the display  95  to display messages indicating for example that information of all cartridge tags  45  could not be read and that the drawer case  35  should be moved again between the use position and the replacement position. When the reading error notification process is finished, the CPU  91  returns to S 15 . The CPU  91  repeats S 15  and S 17  until information of all cartridge tags  45  is obtained. 
     In S 18 , the CPU  91  clears the toner error flag. By cleaning the toner error flag, the laser printer  1  is ready for image formation in normal operation. After clearing the flag, the CPU  91  finishes the toner error handling program. 
     In S 19 , the CPU  91  executes a cartridge error notification process. In the cartridge error notification process (S 19 ), the CPU  91  causes the display  95  to display messages indicating for example that the target cartridge, which becomes a cause of a toner error, is not replaced with a new one. When the cartridge error notification process is finished, the CPU  91  returns to S 14 . 
     As described above, the laser printer  1  according to the first illustrative embodiment is provided with the wireless tag reader  80  in the vicinity of the upper end defining the opening  2 A. The wireless tag reader  80  has the first reading range R and the second reading range L each having the directivity toward the central portion of the opening  2 A. The laser printer  1  further includes the drawer case  35  that holds four process cartridges  40  therein. The drawer case  35  is configured to move through the opening  2 A between the use position and the replacement position. Each process cartridge  40  is provided with a corresponding cartridge tag  45 . 
     As shown in  FIGS. 6-8 , as the drawer case  35  moves between the use position and the replacement position, each process cartridge  40  moves together. At this time, the cartridge tag  45  attached to each process cartridge  40  passes within the second reading range L of the wireless tag reader  80 . Thus, the laser printer  1  can obtain information of the first to fourth cartridge tags  45 K- 45 C serially from one wireless tag reader  80 . 
     In the laser printer  1 , the cover tag  6 , the first drawer tag  36 A, the second drawer tag  36 B and the cartridge tags  45  are wireless tags, e.g. passive RFID tags. Thus, the laser printer  1  is relatively inexpensive to manufacture. 
     The drawer case  35  is provided with the first drawer tag  36 A and the second drawer tag  36 B. When the drawer case  35  is attached to the main body  2 , the first drawer tag  36 A and the second drawer tag  36 B are located above the first to fourth cartridge tags  45 K- 45 C, under the wireless tag reader  80 , and closer to the wireless tag reader  80  than the cartridge tags  45 . In other words, when the drawer case  35  is placed in the use position or in the replacement position, the wireless tag reader  80  is disposed above the first drawer tag  36 A and the second drawer tag  36 B, and the first drawer tag  36 A and the second drawer tag  36 B are disposed above the first to fourth cartridge tags  45 K- 45 C. Thus, when the drawer case  35  passes under the wireless tag reader  80 , the wireless tag reader  80  reliably detects the first drawer tag  36 A and the second drawer tag  36 B, and thereby the laser printer  1  grasps the state of the drawer case  35  (as to whether the drawer case  35  is located in the use position or the replacement position). 
     The front cover  5  is provided with the cover tag  6 . The cover tag  6  is located within the reading range of the wireless tag reader  80  when the front cover  5  is in the closed position. Thus, as the wireless tag reader  80  detects the cover tag  6 , and thereby the laser printer  1  detects the position of the front cover  5 . 
     The laser printer  1  sets the reading range of the wireless tag reader  80  in response to the position of the drawer case  35 , which moves between the use position and the replacement position, by executing the reading range setting program. With this program, the wireless tag reader  80  reliably reads information of target wireless tags that are the cover tag  6 , the first and second drawer tags  36 A and  36 B, and the cartridge tags  45 , and the laser printer  1  minimizes power consumption required for reading information. 
     The cartridge tags  45  of the first illustrative embodiment have antennas  46  of the same shape. Thus, as the same type of wireless tags can be used in the laser printer  1 , the cost of the cartridge tags  45  can be minimized. In addition, the cartridge tags  45  are disposed such that a distance between the wireless tag reader  80  and each cartridge tag  45  located within the reading range is different among the process cartridges  40 . Thus, the laser printer  1  can distinguish the cartridge tags  45  and the process cartridges  40  in response to the intensity of radio waves from each of the cartridge tags  45 . 
     A second illustrative embodiment will be described with reference to  FIGS. 10 and 11 . The second illustrative embodiment of the disclosure also applies to the laser printer  1 . 
     The laser printer  1  of the second illustrative embodiment is identical in structure to that of the first illustrative embodiment. The reading range setting program and the toner error handling program of the second illustrative embodiment are the same as those of the first illustrative embodiment, and thus descriptions thereof will be omitted. 
     The second illustrative embodiment is different from the first illustrative embodiment in structure and arrangement of the cartridge tags  45  attached to the process cartridges  40 . The second illustrative embodiment will mainly describe the cartridge tags  45 . 
     The cartridge tags  45  of the second illustrative embodiment are disposed in predetermined positions on the top surfaces of the respective cartridges  40 . As is the case with the first illustrative embodiment, the cartridge tags  45  are wireless tags, e.g. passive RFID tags, and each have an antenna  46  and an IC chip  47 . In addition, each cartridge tag  45  contains identification information. 
     As shown in  FIG. 10 , the first cartridge tag  45 K, the second cartridge tag  45 Y, the third cartridge tag  45 M, and the fourth cartridge tag  45 C are located on the centerline C of the drawer case  35  in the width direction. Thus, when the drawer case  35  is moved between the use position and the replacement position, the first to fourth cartridge tags  45 K,  45 Y,  45 M, and  45 C pass directly below the wireless tag reader  80 . 
     The cartridges  45  of the second illustrative embodiment have antennas  46  which are different in shape. As shown in  FIG. 11A , the antenna  46  of the first cartridge tag  45 K is a loop antenna. As shown in  FIGS. 11B ,  11 C, and  11 D, the antennas  46  of the second to fourth cartridge tags  45 Y,  45 M, and  45 C are spiral antennas having different number of turns. 
     As described above, the wireless tag reader  80  reads information stored in the wireless tags by transmitting and receiving radio waves to and from the wireless tags. The cartridge tags  45  are equal in distance from the wireless tag reader  80  when passing under the wireless tag reader  80  and different in shape of the antennas  46 . Thus, the radio waves transmitted from the cartridge tags  45  reach the wireless tag reader  80  with different intensities, and the wireless tag reader  80  can identify each cartridge tag  45  with the intensity of the radio waves the wireless tag reader  80  receives. 
     As described above, the laser printer  1  of the second illustrative embodiment can produce effects similar to those brought about by the laser printer  1  of the first illustrative embodiment. In the laser printer  1  of the second illustrative embodiment, each cartridge tag  45  is located in a predetermined position of the corresponding process cartridge  40 . Thus, the laser printer  1  of the second illustrative embodiment can improve the workability in attachment of the cartridge tags  45  to the respective process cartridges  40 . Each cartridge tag  45  contains an antenna having a different number of turns. Thus, the laser printer  1  of the second illustrative embodiment can distinguish the cartridge tags  45  and the process cartridges  40  in response to the intensity of radio waves transmitted from each cartridge tag  45 . 
     The above illustrative embodiments show, but are not limited to, that the cover tag  6 , the drawer tags  36 A,  36 B, the cartridge tags  45  are wireless tags, e.g. passive RFID tags. Active and semi-passive RFID tags may be used instead of the passive RFID tags. 
     In the toner error handling program, a determination is made as to whether the target cartridge, which is a cause of a toner error, has been replaced with a new one and then the cartridge error notification process (S 19 ) is executed. However, the disclosure is not limited to this embodiment. For example, the toner error handling program may proceed as follows: each cartridge tag  45  may store information regarding a toner color of the corresponding process cartridge  40  to which the cartridge tag  45  is attached, and a determination may be made as to whether each process cartridge  40  is disposed in a predetermined position in the drawer case  35 . The laser printer  1  is configured to obtain information of each cartridge tag  45  from the movement of the drawer case  35  and to find the position of each process cartridge  40  in the drawer case  35  based on the information regarding the toner color. In this case, it is preferable that, if the process cartridge  40  is incorrectly disposed in the drawer case  35 , such a message is displayed on the display  95 . 
     The first illustrative embodiment shows, but is not limited to, that the antennas  46  of the cartridge tags  45  are loop antennas identical in shape. The antennas  46  may be formed in any shape, e.g., spiral antennas and helical antennas, as long as they are identical in shape. In addition, the cartridge tags  45  may be located in any positions on the process cartridges  40  as long as a distance between the wireless tag reader  80  and each process cartridge  45  passing under the wireless tag reader  80  is different. 
     In the second illustrative embodiment, the antennas  46  of the cartridge tags  45  are loop antenna and spiral antennas having different number of turns. However, the antennas  46  may be configured only with the same type of antennas, e.g., spiral antennas or helical antennas, as long as the number of turns differs among the antennas  46 . In addition, the cartridge tags  45  may be located in any position on the process cartridges  40  as long as the distance between each cartridge tag  45  and the wireless tag reader  80  is equal. 
     This illustrative embodiment shows, but is not limited to, the direct-tandem type color laser printer. It will be appreciated that this illustrative embodiment also applies to other types of image forming apparatuses, an intermediate transfer type color laser printer, four-cycle color laser printer, and monochrome printer as well. In addition, development may be performed with not only single component development method but also two-component development method. 
     While the features herein have been described in connection with various example structures and illustrative aspects, it will be understood by those skilled in the art that other variations and modifications of the structures and aspects described above may be made without departing from the scope of the disclosures described herein. Other structures and aspects will be apparent to those skilled in the art from a consideration of the specification or practice of the features disclosed herein. It is intended that the specification and the described examples only are illustrative with the true scope of the disclosures being defined by the following claims.