Abstract:
The present invention aims at performing, in a color image forming apparatus, image adjustment processes with adequate amounts of toners remaining in the developers. The color image forming apparatus of the present invention comprises: an image adjuster operable to perform an image adjustment process under a predetermined condition; and a supply controller operable to make a judgment, with respect to each developer prior to the image adjustment process, on need for toner supply based on the quantity of the toner detected by a toner quantity detector, and to cause a supplier to perform the toner supply if the judgment is affirmative.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application is based application No 2006-268027 filed in Japan, the content of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a color image forming apparatus. 
       RELATED ART 
       [0003]    In conventional color image forming apparatuses, the remaining quantity of toner in the developer is monitored when the developer is being driven—i.e. when a printing job is in process, and toner is supplied when it is judged necessary. 
         [0004]    Image forming apparatuses, such as printers, are prone to cause change in image density due to change in the temperature and humidity in the apparatuses and/or deterioration of the photosensitive drum or other parts. 
         [0005]    Therefore, when predetermined conditions (e.g. for each printing job with a certain number of printout sheets) are satisfied, image adjustment (image stabilization) is performed in which control variables for each unit of the apparatus are changed to thereby maintain the quality of the printed images at a certain level. 
         [0006]    In the case of, for example, successively performing printing in monochrome, only the black developer being driven is a target for monitoring the remaining quantity of toner, as described above. 
         [0007]    Although, as to the other color developers being not driven, their remaining toner quantities are not monitored and toner supplies are not provided, the color toners of these color developers are also used in the image adjustment process, which leads to a progressive decrease in color toners. 
         [0008]    Accordingly, there is a possibility that the image adjustment process is performed with inappropriate quantities of toners in the color developers and then inappropriate control variables are created. 
         [0009]    If color printing is subsequently performed, the printing is based on the inappropriate control variables, which may result in poor quality of printed images. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in view of the problem, and aims at offering a color image forming apparatus capable of maintaining an appropriate quantity of toner in each developer in the image adjustment process. 
         [0011]    In order to realize the above object, the present invention is a color image forming apparatus comprising: a plurality of developers; a plurality of toner bottles, each of which contains a toner of a color corresponding to a different one of the developers; a toner quantity detector operable to detect, with respect to each of the developers, quantity of a toner therein; a supplier operable to perform toner supply in which the toner in one of the toner bottles is supplied to a corresponding one of the developers; an image adjuster operable to perform an image adjustment process under a predetermined condition; and a supply controller operable to make a judgment, with respect to each of the developers prior to the image adjustment process, on need for the toner supply based on the quantity of the toner detected by the toner quantity detector, and to cause the supplier to perform the toner supply if the judgment is affirmative. 
         [0012]    This structure prevents an image adjustment process from being carried out when the remaining toner quantity in each developer is low. Accordingly, an appropriate adjustment process is carried out, which enhances the quality of printed images obtained after the process. 
         [0013]    Additionally, one of the developers may be for a black toner. Here, the color image forming apparatus further comprises: a developer controller operable to drive only the developer for the black toner in a case of forming a monochrome image. 
         [0014]    According to the structure, even if printing in monochrome, for example, is successively performed, the image adjustment process can be carried out after toners of the developers, except for black, are supplied. 
         [0015]    In addition, the toner quantity detector may detect the quantity of the toner only when the developer is being driven 
         [0016]    In addition, the color image forming apparatus may further comprise: a storage operable to store therein toner quantity information for each of the developers, the toner quantity information including the developer and the detected quantity of the toner in the developer. Here, the supply controller makes the judgment based on the toner quantity information. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    These and other objects, advantageous effects and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. In the drawings: 
           [0018]      FIG. 1  shows a structure of an MFP  1  according to an embodiment; 
           [0019]      FIG. 2  is a functional block diagram showing a controller  140 ; 
           [0020]      FIG. 3  is a cross-sectional diagram showing a structure of a developer  103 Y; 
           [0021]      FIG. 4  schematically shows a buffer  303  of the developer  103 Y; 
           [0022]      FIG. 5  is a waveform chart showing an example of the result of sensor outputs of an optical receiver; 
           [0023]      FIG. 6  is a flowchart showing an image adjustment control process performed by the controller  140 ; and 
           [0024]      FIG. 7  is a flowchart showing a toner supply process during a printing job performed by the controller  140 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    The following describes an embodiment of the image forming apparatus of the present invention with reference to drawings, taking an MFP  1  (Multi Function Peripheral) as an example. 
         [0026]      FIG. 1  shows a structure of the MFP  1  according to an embodiment. 
         [0027]    As shown in  FIG. 1 , the MFP  1  includes: image forming units  100 Y,  100 M,  100 C and  100 K for yellow (Y), cyan (C), magenta (M) and black (K), respectively; an intermediate transfer belt  112 ; a secondary transfer roller  113 ; an intermediate transfer belt cleaner  114 ; a waste toner bottle  115 ; a toner bottles  120 Y,  120 M,  120 C and  120 K; a paper storage  131 ; a paper feed roller  132 ; a timing roller  133 ; a fixing roller  134 ; an eject roller  135 ; a loop sensor  137  that detects surface waviness on paper; a controller  140 ; and an automatic reversing unit  143 . 
         [0028]    The image forming unit  100 Y includes: a charging unit  101 Y; an exposing unit  102 Y; a developing unit  103 Y; and a photosensitive drum  111 Y. The charging unit  101 Y charges the photosensitive drum  111 Y. The exposing unit  102 Y exposes the photosensitive drum  111 Y to form an electrostatic latent image. The developing unit  103 Y develops the electrostatic latent image formed on the photosensitive drum  111 Y. 
         [0029]    The image forming units  100 M,  100 C and  100 K have the same structure as the image forming unit  100 Y. 
         [0030]    On the intermediate transfer belt  112 , images of four toners each formed on the photosensitive drums  111 Y,  111 M,  111 C and  111 K are subsequently overlaid to thereby form a multi-color toner image. 
         [0031]    The secondary transfer roller  113  transfers the toner image formed on the intermediate transfer belt  112  to paper. The intermediate transfer belt cleaner  114  separates toner particles that were not transferred and remained from the intermediate transfer belt  112 . The waste toner bottle  115  collects the separated toner particles. 
         [0032]    The toner bottles  120 Y,  120 M,  120 C and  120 K have agitating blades  121 Y,  121 M,  121 C and  121 K, respectively, and supply a toner to corresponding image forming units  100 Y,  100 M,  100 C and  100 K. 
         [0033]    The paper storage  131  stores therein paper. The paper feed roller  132  feeds paper stored in the paper storage  131 . 
         [0034]    The timing roller  133  determines the timing of sending out paper brought thereto, to the secondary transfer roller  113 . 
         [0035]    The fixing roller  134  fixes the toner image transferred to paper. The paper with the fixed toner image is ejected by the eject roller  135 . 
         [0036]    The controller  140  controls operations of the MFP  1 . 
         [0037]    The automatic reversing unit  143  includes transport rollers  141  and  142 , and is used in two-sided printing. 
         [0038]      FIG. 2  is a functional block diagram showing the controller  140  of the MFP  1 . 
         [0039]    The CPU  150  includes: paper feeding controller  151 ; a storage medium controller  152 ; a toner supply controller  153 ; an image forming controller  154 ; a fixing controller  155 ; and an I/F controller  156 . 
         [0040]    The paper feeding controller  151  controls various loads  160 , such as a transport motor, and paper detection sensor  161  that detects a paper position. 
         [0041]    The storage medium controller  152  controls data input and output of a RAM  162  and an EEPROM  163 . The RAM  162  and EEPROM  163  store therein data measured by the CPU and information of consumable goods, such as the remaining quantities of toners. 
         [0042]    Note that, other than an EEPROM, consumable goods with an IC chip can be used to store information of these consumable goods. 
         [0043]    The toner supply controller  153  carries out toner supplies by controlling toner supply motors  165 Y,  165 M,  165 C and  165 K based on the detection result of the remaining quantities of toners obtained by the toner-remaining-quantity detection sensors  164 Y,  164 M,  164 C and  164 K. 
         [0044]    The image forming controller  154  controls a developer, a photoreceptor, a polygon motor, and various sensors  166 . 
         [0045]    The fixing controller  155  controls the temperature and the number of rotations of a heater and a fixing motor  168 . 
         [0046]    The I/F controller  156  controls an interface controller  169 . 
         [0047]      FIG. 3  is a cross sectional diagram showing a structure of the developer  103 Y. Note that, since other developers  103 M,  103 C and  103 K have the same structure, here only the developer  103 Y will be explained as a representative of them. 
         [0048]    The developer  103 Y includes: a toner supplier  302 ; a toner agitation/transport screw  401 ; a buffer  303 ; a supply roller  402 ; a developing roller  403 ; an emitter  404  and an optical receiver  406  of the toner-remaining-quantity detection sensor; and a light guide  405 . 
         [0049]    The toner supplier  302  receives supply of toner from the toner bottle  120 Y. The toner of the toner supplier  302  is pushed out to the buffer  303  due to the rotation of the toner agitation/transport screw  401 . The toner in the buffer  303  is supplied to the developing roller  403  by the rotation of the supply roller  402 . 
         [0050]    The light guide  405  guides the inspection light emitted from the emitter  404  to the optical receiver  406 . As shown in  FIG. 4 , the guideway shown by the dotted line goes through the buffer  303 . 
         [0051]    On the other hand, an agitation blade  501  is provided in the buffer  303 . As the agitation blade  501  rotates, a toner level  502  goes up and down to block the inspection light. In addition, the agitating blade  501  itself blocks the inspection light. 
         [0052]    When the agitation blade  501  is performing agitation (i.e. when the developer  103 Y is being driven to rotate), the toner level  502  in the buffer  303  is determined by monitoring the sensor output of the inspection light of the optical receiver  406 . 
         [0053]    Specifically speaking, the toner level  502  in the buffer  303  can be determined based on the length of the time during which the inspection light is blocked (the light blocking period) in one agitation cycle. 
         [0054]      FIG. 5  is a waveform chart showing examples of the result of the sensor output of the optical receiver. 
         [0055]    The “agitation cycle” in  FIG. 5  means an agitation cycle of the agitating blade  501  of the buffer  303 . 
         [0056]    In the case when the quantity of toner remaining in the buffer  303  is low, the toner level  502  goes down. As a result, the duration of the time during the inspection light being blocked (i.e. the sensor output is off) becomes shorter. 
         [0057]    It can be therefore determined that, when the result of the sensor output is one as shown in  FIG. 5A , the quantity of toner remaining in the buffer  303  is low. 
         [0058]    As the quantity of toner in the buffer  303  is higher, the light blocking period becomes longer. Therefore, it can be determined that a moderate quantity of toner remains in the case of  FIG. 5B  while a high quantity of toner remains in the case of  FIG. 5C . 
         [0059]      FIG. 6  is a flowchart showing an image adjustment control process carried out by the controller  140 . 
         [0060]    First, when a time for conducting image adjustment arrives (e.g. after a specific number of prints are produced, and when the power is turned on) (S 10 : Yes), the controller  140  does not immediately carry out image adjustment and moves to a judgment of whether toner needs to be supplied. 
         [0061]    That is, the controller  140  judges whether the remaining toner of each color, the information of which is stored in the EEPROM  163 , is a specific quantity or lower (S 11 ). In the case when the remaining toner is the specific quantity or lower (S 11 : Yes), the controller  140  supplies toner of a corresponding color to the developer (S 12 ). 
         [0062]    Then, the controller  140  carries out an image adjustment process, such as resist correction and gamma correction (S 13 ). 
         [0063]      FIG. 7  is a flowchart showing a toner supply process carried out by the controller  140  during printing. 
         [0064]    In the toner supply process during printing, if the developers  103 Y,  103 M,  103 C and  103 K are being driven (S 21 : Yes), the controller  140  detects the quantity of toner in each developer being driven (S 22 ). If the detected quantity is a specific quantity or lower (S 23 : Yes), the controller  140  supplies toner of a corresponding color to the developer (S 24 ). Here, the specific quantity is, for example, a moderate or lower quantity remaining in the developer. 
         [0065]    When the developer being driven is stopped (S 21 : No) and the controller  140  determines that printing is finished (S 25 : Yes), the controller  140  stores, in the EEPROM  163 , information indicating the remaining quantity of toner that has been detected by that point (S 26 ). 
         [0066]    When the developers are being driven—e.g. when an image adjustment process is carried out, besides when printing is being performed, the remaining quantity is detected in each case, and the information of the detected quantity is stored in the EEPROM  163 . 
         [0067]    As has been described, the need of toner supply is judged prior to the execution of an image adjustment process, and therefore the present application is able to prevent an image adjustment process from being carried out when the remaining toner quantities in the developers are insufficient 
         [0068]    [Other Particulars] 
         [0069]    (1) The embodiment above is explained with the case of determining the quantity of toner in the buffer based on the time during which the light is blocked. It is a matter of course, however, that the present invention is not limited to this case, and a different method can be employed to determine the quantity remaining in the buffer. For example, the remaining toner quantity may be determined from dot-counter reading corresponding to the toner quantity having been transferred to paper. 
         [0070]    (2) It is preferable not to perform toner supply during image adjustment although the embodiment above does not give details of this. This is because, if toner is supplied during image adjustment, the toner in the developer and the newly supplied toner are not sufficiently agitated, which results in improper image adjustment. 
         [0071]    Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be constructed as being included therein.