Abstract:
In an image forming apparatus, a timer unit measures a time interval between a current time and a time point when previous supply of toner to a developing unit ended and an adjusting unit adjusts an amount of toner to be supplied to the developing unit based on the time interval measured at the timer unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to and incorporates by reference the entire contents of Japanese priority document 2008-069260 filed in Japan on Mar. 18, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technology for supplying toner in an image forming apparatus. 
     2. Description of the Related Art 
     In an electrophotographic image forming apparatus in which a toner image is formed by using a two-component developer, toner is consumed by repeatedly performing an image formation. Therefore, a consumed amount of toner needs to be supplied successively to a developing unit. Typically, toner is stored in a toner container such as a toner cartridge and a toner bottle to be supplied to the developing unit. When the toner container becomes empty, the toner container is replaced by a new one. 
     Some toner supplying devices employ a powder pump for supplying the toner into the developing unit. Meanwhile, a toner end sensor needs to be provided to the toner supplying device for detecting a toner end. For example, a light transmission sensor is arranged at a vertical portion of a nozzle of the toner supplying device and detects whether the toner container has become empty. 
     If the image forming apparatus is always operated at normal temperature and normal humidity, the toner can be supplied appropriately. However, under a high temperature and high humidity condition, fluidity of the toner is lowered, which may cause toner blocking or other adverse phenomena inside the toner container. In the toner supplying device employing the powder pump, a toner consumption amount in the developer is estimated by fixing a time period per single driving of the powder pump. In a system having only one toner-supplying time period table, the time period per single driving of the powder pump is short, so that the pressure generated by the powder pump is relatively low. Thus, the toner blocking that has occurred inside the toner container is difficult to remove. The toner blocking causes insufficient supplying of toner, error in detecting the toner end, and the like. The error in detecting the toner end indicates that the toner container is detected to have become empty although the toner still remains therein. 
     To overcome the drawback mentioned earlier, the applicants have proposed a technology disclosed in Japanese Patent Application Laid-open No. 2007-148277, in which if it is detected that toner does not exist in the toner container, a time period per single driving of a powder pump is increased. With such technology, the toner blocking that has occurred inside the powder container can be removed. 
     In a toner supplying mechanism that includes a supplying pump, the developing unit and the supplying pump are connected by a conveying path such as a tube. Toner is supplied into the developing unit from the toner container by switching on and off the supplying pump. However, a pressure inside the supplying path is in some cases lowered due to a time interval from a previous toner supply. Due to this, a difference occurs between an actual toner supplying amount and a cumulative toner supplying amount that is calculated. In this case, the toner supplying amount can be increased by increasing the time period per single driving of the supplying pump in the similar manner to the technology mentioned earlier. Although a time period required for the toner end can be delayed, the toner supplying amount cannot be accurately determined. Thus, detection accuracy of the toner near end decreases. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to one aspect of the present invention, there is provided an image forming apparatus that includes a toner supplying unit that supplies toner from a toner container to a developing unit; a timer unit that measures a time interval between a current time and a time point when previous supply of toner by the toner supplying unit to the developing unit ended; and an adjusting unit that adjusts an amount of toner to be supplied by the toner supplying unit to the developing unit based on the time interval measured at the timer unit. 
     According to another aspect of the present invention, there is provided an image forming method that includes supplying toner from a toner container to a developing unit; measuring a time interval between a current time and a time point when previous supply of toner at the supplying ended; and adjusting an amount of toner to be supplied at the supplying based on the time interval measured at the measuring. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a schematic diagram of a toner supplying device that supplies toner from a toner cartridge to a developing unit of the image forming apparatus as shown in  FIG. 1 ; 
         FIG. 3  is a block diagram of a circuit on a control board of the image forming apparatus as shown in  FIG. 1 ; 
         FIG. 4  is a block diagram of a circuit on an identification read/write (ID-R/W) board arranged in a setting unit of the image forming apparatus as shown in  FIG. 1 ; 
         FIG. 5  is a flowchart for explaining a process performed when a toner bottle including an ID chip is replaced by a new one; 
         FIG. 6  is a flowchart for explaining a process performed at the time of supplying the toner; 
         FIG. 7  is a table indicating a relation between a toner supplying interval and a toner supplying amount for each color; and 
         FIGS. 8A and 8B  are schematic diagrams illustrating a supplying-amount correcting screen and a supplying-amount setting screen. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments according to the present invention are explained in detail below with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is a tandem-type image forming apparatus of an indirect transfer system. In the present embodiment, the image forming apparatus is used as a printer. The image forming apparatus includes a well-known mechanical structure. The configuration of the image forming apparatus is explained. Four imaging units  2  are arranged in a main body  1 . An intermediate transfer body  3 , which is formed of an endless belt, is arranged opposite each imaging unit  2 . The intermediate transfer body  3 , which is wound around a plurality of support rollers, runs in a direction of an arrow as shown in  FIG. 1 . Based on a well-known electrophotographic system, each of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image is formed on a corresponding photosensitive element  10  in the imaging unit  2 . The toner images are sequentially electrostatically transferred onto the intermediate transfer body  3  in a superimposed manner. 
     A sheet feeding unit  4  is arranged in a lower portion inside the main body  1  of the image forming apparatus. A sheet fed from the sheet feeding unit  4  is conveyed along the conveying path and is sent between the intermediate transfer body  3  and a transferring unit  6  via a pair of registration rollers  5 . When the sheet passes through the intermediate transfer body  3  and the transferring unit  6 , the toner images superimposed on the intermediate transfer body  3  are transferred onto the sheet. Subsequently, the sheet passes through a fixing unit  7  at which the toner images are fixed on the sheet by heat and pressure. The sheet that has passed through the fixing unit  7  is discharged onto a discharging unit  8 . 
     A setting unit  9  is arranged between the discharging unit  8  and the intermediate transfer body  3  of the main body  1  of the image forming apparatus. Toner cartridges  30  are attached to the setting unit  9 . The toner cartridge  30  is a powder storage container that stores therein the toner to be supplied into a developing unit  11  of the imaging unit  2 . The toner cartridges  30  are detachably attached to the setting unit  9 . 
       FIG. 2  is a schematic diagram of a toner supplying device for supplying the toner from the toner cartridge  30  to the developing unit  11  shown in  FIG. 1 . As shown in FIG.  2 , for forming the toner image on the photosensitive element  10  by the developing unit  11  of the image forming apparatus that uses the well-known electrophotographic system, a powder pump  20  of the developing unit  11  is operated to supply the toner in the toner cartridge  30  to the developing unit  11  via a tube  25  that is a toner conveying unit. The tube  25  communicates with the inside of the toner cartridge  30  via a nozzle  31 . 
     The powder pump  20  uses a suction-type single axis eccentric powder pump (commonly known as a mohno pump). The powder pump  20  includes a rotor  21  that is formed in an eccentric screw shape using a material having stiffness such as metal, a fixedly arranged stator  22  in which a double thread hole is formed of rubber, and a housing  23  that is molded of resin or the like, houses the rotor  21  and the stator  22 , and forms a powder conveying path. Due to rotation of the rotor  21 , strong self-suction force (suction pressure) is generated in the powder pump  20 . Due to this, the toner can be sucked from the toner cartridge  30 . 
     The tube  25  has an inner diameter of 4 millimeters to 10 millimeters. For the tube  25 , it is extremely effective to use rubber material such as polyurethane, nitrile, EPDM, and silicon that is flexible and excellent in toner resistance properties or plastic material such as polyethylene and nylon. The sucked toner drops into the developing unit  11  from a toner guiding aperture  12  that is arranged in a portion of the developing unit  11 . The toner is further conveyed to a developing section by using a stirring screw (not shown). If a two-component developing method is used, the toner (sucked toner) supplied during the conveying process is stirred and mixed with a developer inside the developing unit  11 . Due to this, a toner concentration can be uniform and a charge amount of the toner can be appropriate. 
     For suction conveying the toner by using the powder pump  20 , the toner needs to constantly exist in the vicinity of a toner sucking unit  29  indicated by a hatching. Thus, the toner cartridge  30  can be configured to include a coil spring inside thereof or a spiral-shaped projection on an internal wall thereof and convey the toner to a tip of the container by the rotation of the cartridge main body. 
     In such toner supplying device, conventionally, based on a result of a detection by a magnetic permeability detector (not shown) arranged in a portion of the developing unit  11 , a change in a mixing ratio of the toner and a carrier in the developing unit  11  is detected. If it is detected that the amount of the toner is low, the powder pump  20  is operated by rotating a driving shaft  24  of the powder pump  20 . When the toner that is conveyed by the powder pump  20  into the developing unit  11  is equal to or more than a predetermined amount, driving of the driving shaft  24  is interrupted by signals from the magnetic permeability detector, thus stopping the operation of the powder pump  20 . 
     Details of toner supplying control according to the present embodiment are explained below. 
       FIG. 3  is a block diagram of a circuit on a control board of the image forming apparatus according to the present embodiment. The circuit includes an operating unit  110 , an image processing unit  132 , a hard disk drive (HDD)  134 , a network controlling unit (NCU)  139 , a facsimile controlling unit (FCU)  140 , various sensors  137 , and a load  138  that are connected to and centered on an engine control unit  120 . 
     The engine control unit  120  includes a central processing unit (CPU)  121 , and a read only memory (ROM)  122 , a random access memory (RAM)  123 , a non-volatile RAM  124 , and an input output (I/O) control unit  125  that are connected to the CPU  121  via a data bus and an address bus. The ROM  122  stores therein a program code of a computer program executed by the CPU  121 . The CPU  121  uses the RAM  123  as a work area and executes the computer program. The non-volatile RAM  124  stores therein data required while executing the computer program. The CPU  121  controls the HDD  134  that is connected to the CPU  121  via an HDD control unit  131 . 
     A reading unit  135 , a writing unit  136 , and an image RAM  133  are connected to the image processing unit  132 . Image data read by the reading unit  135  is input into the image processing unit  132  and a write image data is input into the writing unit  136  from the image processing unit  132 . Image data that is temporarily stored in the image RAM  133  is read by the image processing unit  132 , and image data read by the reading unit  135  is temporarily stored in the image RAM  133 . The image processing unit  132  is also connected to the HDD control unit  131 , so that image data stored in the HDD  134  is read by the image processing unit  132  and image data subjected to the image processing by the image processing unit  132  is stored in the HDD  134 . 
     On a toner bottle for each color according to the present embodiment, an identification (ID) chip (Non-volatile memory radio frequency identification (RFID) chip)  149  is mounted. Due to this, data can be read or written from the CPU  121  of the engine control unit  120 . The toner bottle is filled with the toner and is closed with a cap, which is the toner cartridge  30 . A control board (hereinafter, “ID-read/write (R/W) board”)  150  is arranged in the setting unit  9  for carrying out reading and writing with respect to the ID chip  149 . The toner bottle is set in the setting unit  9  such that the toner bottle can communicate with the ID chip  149 . 
       FIG. 4  is a block diagram of a circuit on the ID-R/W board  150 . The ID-R/W board  150  includes a CPU  141 , a ROM  142 , a RAM  143 , a non-volatile RAM  144 , and an I/O controller  145  that are connected to the CPU  141  via a data bus and an address bus. The ROM  142  stores therein a program code of a computer program executed by the CPU  141 . The CPU  141  uses the RAM  143  as a work area and executes the computer program. The non-volatile RAM  144  stores therein data that is required while executing the computer program by the CPU  141 . The ID chip  149  is connected such that the ID chip  149  can carry out mutual wireless communication with the ID-R/W board  150 . The ID chip  149  transmits and receives data via the data bus and the address bus. Thus, a I/O control unit (not shown) is arranged for carrying out wireless communication. Because a structure related to wireless communication between the ID chip  149  and the ID-R/W board  150  is a well-known structure, which is disclosed, for example, in Japanese Patent Application Laid-open No. 2007-148006, details are omitted. In the present embodiment, communication between the ID chip  149  and the setting unit  9  is carried out using wireless communication. However, communication between the ID chip  149  and the setting unit  9  can be carried out using a connector such that the connector is directly connected to the data bus and the address bus. 
       FIG. 5  is a flowchart for explaining a process performed by the CPU  121  of the engine control unit  120  when the toner bottle including the ID chip  149  is replaced. 
     In  FIG. 5 , upon starting the process, the CPU  121  of the engine control unit  120  accesses the CPU  141  of the ID-R/W board  150 . The CPU  141  reads data stored in a memory of the ID chip  149  and transmits the data to the CPU  121 . Based on the data, the CPU  121  checks whether the toner bottle is a new bottle (Step S 101 ). If the toner bottle is a new bottle (Yes at Step  101 ), the CPU  121  initializes a cumulative toner usage amount of the ID chip  149 . In other words, the CPU  121  clears a cumulative toner-supplying amount (Step S 102 ) and subsequently, clears a cumulative counter (Step S 103 ). However, based on the data read from the ID chip  149 , if the toner bottle is not a new bottle, the cumulative toner usage amount of the bottle is used. In other words, the CPU  121  reads the cumulative toner-supplying amount (Step S 104 ) and also reads the cumulative counter (Step S 105 ). Upon reading the ID chip  149 , if the cumulative toner-supplying amount is equal to or more than a toner-near-end threshold value (Yes at Step S 106 ), the toner near end is notified to a user by displaying or the like (Step S 107 ) and the process ends by saving a supplying end time (Step S 108 ). However, if the cumulative toner-supplying amount is less than the toner-near-end threshold value (No at Step S 106 ), the process ends by saving the supplying end time (Step S 108 ) without notifying the user of the toner near end. The supplying end time is saved in the memory of the ID chip  149 . 
       FIG. 6  is a flowchart for explaining a process performed at the time of supplying the toner. Upon starting the supplying, first, the toner supplying amount is calculated (Step S 201 ). For example, it is assumed that supply of 120 milligrams (mg) toner in 200 milliseconds (ms) is a default prior set toner supplying amount. In other words, the toner of 120 mg supplied in a supplying time period of 200 ms is assumed as the prior set toner supplying amount. Next, a correction setting (adjustment setting) is referred (Step S 202 ). If correction (adjustment) is not to be carried out (No at Step S 202 ), the toner supplying is carried out by using the default condition (Step S 205 ) and the toner supplying amount is added without carrying out the correction (Step S 206 ). The value of the added amount of the toner is saved in the ID chip  149 . 
     If the correction is to be carried out (Yes at Step S 202 ), the previous toner supplying time is acquired from the ID chip  149  (Step S 203 ), and based on the previous toner supplying time, a toner supplying interval is calculated (Step S 204 ). The toner supplying amount is calculated by referring to a table stored in the non-volatile RAM  144  in advance and the toner supplying is carried out (Step S 205 ). The calculated toner supplying amount is the supplying amount that is stored in the table. Subsequently, the toner supplying amount is added (Step S 206 ) and the cumulative toner-supplying amount is compared with the toner-near-end threshold value (Step S 207 ). If the cumulative toner-supplying amount is greater than the toner-near-end threshold value (Yes at Step S 207 ), the toner near end is notified to a user (Step S 208 ). Upon notifying the toner near end, the process ends by saving the supplying end time (Step S 209 ). If the cumulative toner-supplying amount is equal to or less than the toner-near-end threshold value (No at Step S 207 ), the process ends by saving the supplying end time (Step S 209 ) without notifying the user of the toner near end. The toner near end is notified by displaying it on an operation panel of the operating unit  110 . 
     The toner supplying amount stored in the table is set by estimating a required toner supplying amount based on the previous toner supplying interval. In other words, every time the image forming operation is carried out on a single sheet, the toner is supplied based on the necessity. In the present embodiment, because the image forming apparatus is a four-color image forming apparatus, the toner supplying is carried out only for the time period of 200 ms for each color. In the present embodiment, the default toner supplying amount is 120 mg. Thus, if the toner supplying amount is large, the toner supplying interval becomes short. Thus, the toner supplying interval and the toner supplying amount of each color is set. The toner supplying interval is set by considering a printing rate and an output of a toner concentration sensor of the developing unit  11  for each color. In the present embodiment, as shown in  FIG. 7 , a relation between the toner supplying interval and the toner supplying amount is defined for each color of K, Y, C, and M. The relation between the toner supplying interval and the toner supplying amount is indicated in a table and the table is stored in the non-volatile RAM  144 . 
     For example, when the toner supplying interval from the previous toner supplying end time to a current toner supplying is “a” (toner supplying interval is equal to or shorter than 3 seconds), in the current supplying, the toner supplying amount, which is by default 120 mg for 200 ms, is corrected to 125 mg for 200 ms for black (K) toner and toner supplying is carried out. When the toner supplying interval is “d” (toner supplying interval is between 20 seconds and 30 seconds), the toner supplying amount is corrected to 108 mg for 200 ms for yellow toner (Y) and the toner supplying is carried out. Thus, the toner supplying amount is calculated by referring to the table and the toner supplying is carried out. 
     In other words, the toner supplying amount that is used for supplying during a first correction is prior set as default value. Normally, based on the default value, the toner supplying is carried out in the interval that is based on the consumed amount. In other words, the toner near end can be estimated according to the toner supplying amount and the toner supplying interval. However, because the consumed toner amount differs, due to the printing rate or the like, depending on the toner supplying interval, the toner supplying amount is corrected. Thus, with respect to the toner supplying amount (for example, default toner supplying amount of 120 mg for 200 ms) that is set from the printing rate and the output of the toner concentration sensor of the developing unit  11  for each color, the toner supplying amount (toner supplying amount indicated in  FIG. 7 ) is corrected by further considering the toner supplying interval. Consequently, a highly accurate toner near end is estimated by accumulating the corrected supplying amount. 
     In the present embodiment, the toner supplying amount is corrected based on the default value. A user can set from the operation panel of the operating unit  110 , whether the toner supplying amount is to be corrected.  FIG. 8A  is a schematic diagram of a supplying-amount correcting screen  110   a  and  FIG. 8B  is a schematic diagram of a supplying-amount setting screen  110   b.  Upon selecting to carry out the correction in the supplying-amount correcting screen  110   a  shown in  FIG. 8A , a user can set the toner supplying amount by shifting to the supplying-amount setting screen  110   b  shown in  FIG. 8B . For example, if the toner supplying amount of the yellow toner is set to another value from 120 mg when the toner supplying interval is 0 second to 3 seconds, and if the other value is entered using a numerical keypad  110   c  from the supplying-amount setting screen  110   b,  the other value is displayed in a display column  110   d.  Accordingly, the corrected amount changes as in the table shown in  FIG. 7 . Although the other value is entered during 3 seconds to 6 seconds using the numerical keypad  110   c,  the other value is displayed in a display column  110   e  and changed. 
     Thus, according to the embodiment of the present invention, a difference between an actual toner usage amount of each color and the estimated toner usage amount is reduced and the highly accurate toner near end can be detected without using a toner near-end sensor. Due to this, a cost can also be reduced. 
     The present invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concepts as defined by the appended claims and their equivalents. 
     According to an aspect of the present invention, detection accuracy of a toner near end can be enhanced without using a sensor. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.