CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior U.S. Patent Application No. 61/331,137 filed on May 4, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    Embodiments described herein relate generally to an image forming apparatus and an image forming method. 
       BACKGROUND 
       [0003]    In general, in order to stabilize image characteristics in electrophotography, an image forming condition is controlled based on information from a toner density sensor, an optical sensor, a temperature and humidity sensor or the like. 
         [0004]    On the other hand, when toner in a developing device is not consumed for the volume of copy, or the agitating time of the toner and carrier becomes long, the toner electric charge increases, and defects, such as reduction in image density and fogging, occur. Against such a phenomenon, the amount of toner consumed for a specific period is estimated from a copy counter, a developing device drive counter, a pixel counter or the like. When the replacement amount of toner is low as compared with the estimated toner amount, after a copy job is ended, the toner is forcibly discharged. In this way, the highly charged toner is discharged, and a new toner is supplied, so that stable image formation can be performed. 
         [0005]    However, according to the forcible discharge of toner as stated above, there is a problem that a large amount of toner, which is not printed on a transfer medium, is discarded, the replacement frequency of a toner cartridge becomes high, and the running cost becomes high. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a structural view of an image forming apparatus as a four-drum tandem color printer of an embodiment; 
           [0007]      FIG. 2  is a schematic structural view of an image forming unit of the embodiment; 
           [0008]      FIG. 3  is a block diagram of the embodiment; 
           [0009]      FIG. 4  is a table of addresses and information content of a memory on a body side; 
           [0010]      FIG. 5  is a table of addresses and information content of a memory on a toner cartridge side; and 
           [0011]      FIG. 6  is a flowchart of the embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Reference will now be made in detail to the present embodiment of the invention, an example of which is illustrated in the accompanying drawing. 
         [0013]      FIG. 1  is a structure view of an image forming apparatus of a four-drum tandem color printer, which is an example of an image forming apparatus of an embodiment. As shown in  FIG. 1 , a secondary transfer roller  11  to transfer an image on an intermediate transfer belt  10  onto a transfer medium  12 , and respective image forming units  20 Y,  20 M,  20 C and  20 K of yellow, magenta, cyan and black are arranged along the conveyance direction (arrow direction) of the intermediate transfer belt  10 . 
         [0014]    The image forming units  20 Y,  20 M,  20 C and  20 K include photoreceptors  21 Y,  21 M,  21 C and  21 K as image carriers. Further, charging devices  22 Y,  22 M,  22 C and  22 K as charging portions, developing devices  23 Y,  23 M,  23 C and  23 K including developing rollers as developing members and having developers including color toner particles of yellow, magenta, cyan and black and carrier particles, primary transfer rollers  24 Y,  24 M,  24 C and  24 K as transfer portions, and cleaner units  25 Y,  25 M,  25 C and  25 K are provided around the respective photoreceptors. These are respectively arranged along the rotation directions of the corresponding photoreceptors  21 Y,  21 M,  21 C and  21 K. 
         [0015]    The primary transfer rollers  24 Y,  24 M,  24 C and  24 K are disposed inside the intermediate transfer belt  10 , and nip the intermediate transfer belt  10  against the corresponding photoreceptors  21 Y,  21 M,  21 C and  21 K. Exposure devices  26 Y,  26 M,  26 C and  26 K are arranged so that exposure points are formed on the outer peripheral surfaces of the photoreceptors  21 Y,  21 M,  21 C and  21 K between the charging devices  22 Y,  22 M,  22 C and  22 K and the developing devices  23 Y,  23 M,  23 C and  23 K. The secondary transfer roller  11  is arranged outside the intermediate transfer belt  10  so as to contact therewith. 
         [0016]    A print operation is performed as described below by the image forming apparatus constructed as stated above. A toner image is formed in the image forming unit  20 Y. The same process is performed also in the image forming units  20 M,  20 C and  20 K in synchronization with the timing of the toner image formation in the image forming unit  20 Y. The toner images of magenta, cyan and black formed on the photoreceptors of the image forming units  20 M,  20 C and  20 K are also sequentially primarily transferred onto the intermediate transfer belt  10 . 
         [0017]    The transfer medium  12  is conveyed from a cassette (not shown), and is sent to the intermediate transfer belt  10  by an aligning roller (not shown) in timing with the toner images on the intermediate transfer belt  10 . 
         [0018]    A bias (+) of a reverse polarity to a charging polarity of a toner is applied to the secondary transfer roller  11  by a power source (not shown). As a result, the toner images on the intermediate transfer belt  10  are transferred onto the transfer medium  12  by a transfer electric field formed between the intermediate transfer belt  10  and the secondary transfer roller  11 . A fixing device (not shown) to fix the toner transferred onto the transfer medium  12  is disposed, and the transfer medium  12  is made to pass through the fixing device so that a fixed image is obtained. 
         [0019]    Incidentally, although the description is made on the example in which the image forming units are arranged in color sequence of yellow, magenta, cyan and black, the color sequence is not limited. 
         [0020]      FIG. 2  is a schematic structural view of an image forming unit in the image forming apparatus which is constructed as stated above and in which an image is formed. Incidentally, the image forming units  20 Y,  20 M,  20 C and  20 K have the same structure. 
         [0021]    As shown in  FIG. 2 , a charging charger  22 , a developing device  23  and a cleaning unit  25  are arranged around a photoreceptor  21 . A toner cartridge  27  is mounted on the developing device  23 . Further, a print counter  28 A to count the number of prints, output pixels or the like, a toner supply drive counter  28 B to count the drive time of the toner cartridge, and a developing device drive counter  28 C to count the drive time of the developing device  23  are installed. 
         [0022]    Further, the image forming unit  20  includes a memory  29  in which values of the print counter  28 A, the toner supply drive counter  28 B and the developing device drive counter  28 C and a threshold used to determine the necessity of a toner replacement operation are stored. 
         [0023]    The toner cartridge  27  includes a memory  30  in which characteristic data of a manufacturing lot of toner stored in the toner cartridge  27  is previously stored. Incidentally, the memory  30  is not necessarily required to be attached to the toner cartridge  27 . The memory may be attached to an integrated unit of a developing unit including the toner cartridge  27  and the developing device. Besides, the memory  30  may be separated and mounted on the image forming unit. 
         [0024]    The respective components of the image forming unit are connected to an arithmetic control mechanism (not shown) to control these. 
         [0025]    In the image forming unit as stated above, the control of a forcible toner supply operation is performed as described below.  FIG. 3  is a block diagram of a component portion in which the control of a toner replacement operation is performed. As shown in  FIG. 3 , a CPU  31  as an arithmetic control mechanism is connected to the memory  29  of the image forming unit  20 . The memory  29  is connected to the print counter  28 A, the toner supply drive counter  28 B and the developing device drive counter  28 C. 
         [0026]    Further, the CPU  31  is connected to the memory  30  of the toner cartridge  27  through a transmission and reception part  32  via wired or wireless, and controls the image forming apparatus including the respective components of the image forming unit  20  such as a toner cartridge drive motor  33 . Incidentally, the CPU  31  is not required to be integrated, and may be separate from a motor driver to drive the toner cartridge drive motor  33 , an ASIC to process data from the memory  29 , an ASIC to process data from the memory  30 , or the like. Besides, the memory  29  may be incorporated. 
         [0027]      FIG. 4  shows a correspondence table of addresses and information content of the memory  29  on the image forming unit side, and  FIG. 5  shows a correspondence table of addresses and information content of the memory  30  on the toner cartridge side. 
         [0028]    As shown in the table of  FIG. 4 , the memory  29  on the image forming unit side includes, for the respective addresses, an area (A 001 ) in which an identification code is inputted, an area (A 002 ) in which a data selection code for selecting a toner replacement amount according to an after-mentioned toner characteristic partitioned code is inputted, a writing area (A 003 ) in which a characteristic partitioned code from the memory  30  on the toner cartridge  27  side is written, and a toner refresh history writing area (A 004 ) in which history of execution of the toner replacement operation is written. Besides, print counter value writing areas (A 005 , A 006 ) in which print counter values in a monochrome mode and a color mode are respectively written are provided. 
         [0029]    There are provided a toner supply drive counter value writing areas (A 007 -A 010 ) in which counter values of drive times of the respective toner cartridges of black, yellow, cyan and magenta are written, and a developing device drive counter value writing area (A 011 -A 014 ) in which counter values of drive times of the respective developing devices are written. These count values are respectively parameter values for obtaining the use amount of toner. 
         [0030]    Further, there are provided a writing area (A 015 ) of print count thresholds which are respectively thresholds for executing the toner replacement operation, and a writing area (A 016 ) of a toner refresh threshold as a threshold for the toner use amount obtained from the parameter values detected by the toner supply drive counter  28 B and the developing device drive counter  28 C. 
         [0031]    Besides, as shown in the table of  FIG. 5 , the memory  30  on the toner cartridge  27  side includes, for respective addresses, an area (B 001 ) in which an identification code is inputted and an area in which a partitioned code partitioned based on a toner resistance value as a toner characteristic is inputted. Incidentally, as the toner characteristic, a charge amount, a particle diameter or the like can be used in addition to the toner resistance value. Besides, the characteristic value itself is inputted, and may be partitioned by the CPU  31 , or may be inputted as a partitioned code of toner replacement amount. 
         [0032]    By the structure as stated above, the control of the toner replacement operation is performed as described below.  FIG. 6  shows a flowchart. As shown in  FIG. 6 , when printing starts, power supply is turned ON, or a front cover is opened and closed in order to replace the toner cartridge (Act  1 ). It is determined whether an identification code inputted in A 001  of the memory  29  and an identification code inputted in B 001  of the memory  30  are coincident with each other (Act  2 ). When they are coincident, it is determined whether a toner replacement operation (toner refresh) function in the image forming apparatus body is effective (Act  3 ). When it is effective, the following operation is performed. When the identification codes are not coincident, and when the toner replacement operation function is ineffective, a print operation in which the function is stopped is performed or the toner cartridge is replaced. 
         [0033]    The partitioned code written in B 002  is read into the CPU  31  through the transmission and reception part  32 , and the corresponding control code of A 002  is selected and is written to A 003  (Act  4 ). By this, the image forming apparatus body is place in a Ready state, and a print job is performed (Act  5 ). 
         [0034]    After the print job is ended, it is determined whether the print counter values written in A 005  and A 006  reach the print counter thresholds written in A 015  (Act  6 ). 
         [0035]    When they reach the print counter thresholds, the toner use amount is obtained from the toner supply drive counter values written in A 007 -A 010  and the developing device drive counter values written in A 011 -A 014  (Act  7 ). It is determined whether the obtained toner use amount reaches the toner refresh threshold written in A 016  (Act  8 ). 
         [0036]    When it reaches the toner refresh threshold, the toner replacement operation is executed based on the control code written in A 003  (Act  9 ). The execution history is written to A 004  (Act  10 ), and the counter values of the print counter  28 A, the toner supply drive counter  28 B and the developing device drive counter  28 C are reset (Act  11 ). 
         [0037]    As described above, in the toner replacement operation, although a constant amount of toner is discharged and supplied until now, the control can be performed so that the discharge amount (supply amount) is adjusted according to, for example, the charging characteristic of toner, and the use amount of toner can be suppressed. 
         [0038]    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 omission, 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.
An image forming apparatus includes an image forming unit including a developing device, a toner cartridge to supply a toner to the developing device, a first memory which is provided in the toner cartridge and in which data of a toner characteristic is previously stored, a toner use amount detection mechanism to detect a parameter value for obtaining a toner use amount, a second memory which is provided in the image forming unit and in which the parameter value and a threshold of a toner use amount for performing a toner replacement operation are stored, and an arithmetic control mechanism which obtains the toner use amount based on the parameter value, compares the toner use amount with the threshold, determines necessity of the toner replacement operation, and executes the toner replacement operation based on the characteristic data.