Patent Publication Number: US-6983111-B2

Title: Image formation device and image formation method

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image formation device and an image formation method. More specifically, the invention relates to an image formation device that transfers toner images formed with toners of multiple colors onto a recording medium, such as paper, so as to form a color image, and a corresponding image formation method. 
   2. Description of the Prior Art 
   As is known in the art, a conventional image formation device that is capable of forming a color image, such as a color laser printer or a color photocopier, develops electrostatic latent images of respective colors formed on a photoreceptor as toner images with toners of respective colors, transfers the toner images of the respective colors in an overlapping manner as a composite color toner image on an intermediate transfer medium, such as a transfer belt, and transfers and fixes the composite color toner image as a resulting color image on a recording medium like paper. The toner density of each toner image formed on the photoreceptor or the intermediate transfer medium is varied with a variation in working environment, for example, the temperature or the humidity. The image formation device accordingly carries out adjustment of a toner image formation process according to the working environment. 
   A variation in toner density of the toner image less affects the picture quality of a resulting monochromatic image, compared with that of a resulting color image. The prior art image formation device, however, adopts the same procedure for adjustment of the toner image formation process in the case of formation of a monochromatic image and in the case of formation of a color image. Such adjustment applies unnecessary, excessive loads onto the respective constituents of the image formation device and thereby accelerates deterioration of the constituents. 
   SUMMARY OF THE INVENTION 
   An image formation device and a corresponding image formation method of the present invention aim to adjust the toner density adequately for formation of the composite color image or formation of the monochromatic image. The image formation device and the corresponding method of the invention also aim to effectively prevent excessive deterioration of constituents of the image formation device. 
   In order to achieve at least a part of the aforementioned aim, the image formation device is constructed as follows. 
   An image formation device of the present invention is a device that transfers toner images formed with toners of multiple colors onto a recording medium, such as paper, so as to form a color image, the image formation device comprising: a specification module that specifies either formation of a composite color image or formation of a monochromatic image; and a control module that, when the specification module specifies formation of the composite color image, controls to selectively apply a color image adjustment operation for toner density adjustment that adjusts a toner density of each toner image formed, while controlling to selectively apply a monochromatic image adjustment operation for the toner density adjustment when the specification module specifies formation of the monochromatic image. 
   The image formation device of the invention specifies either formation of a composite color image or formation of a monochromatic image and controls the toner density adjustment to be suitable for formation of the composite color image or for formation of the monochromatic image, based on the result of the specification. This arrangement ensures the adequate toner density adjustment for formation of the composite color image or formation of the monochromatic image, thus effectively preventing excessive deterioration of constituents of the image formation device involved in the toner density adjustment. The formation of the composite color image or the formation of the monochromatic image may be specified, based on external information like printing instruction information and image data input from a computer connecting with the image formation device or input through operations of an operation panel of the image formation device or based on internal information like setting information of the image formation device. 
   The image formation device of the invention, as one modified structure, may further include an information acquisition module that acquires information on color of toner filled in each toner cartridge from each of storage elements mounted on multiple toner cartridges, which are attached to the image formation device. In this modified structure, the specification module may specify formation of the composite color image or formation of the monochromatic image, based on the information on the color of toner acquired by the information acquisition module. In the modified structure, further, the composite color image may be formed with toners of at least three primary colors, cyan, magenta, and yellow, and the specification module may specify formation of the composite color image when the colors of toners filled in the multiple toner cartridges include all of the three primary colors, while specifying formation of the monochromatic image when the colors of toners filled in the multiple toner cartridges exclude at least one of the three primary colors. In the modified structure, still further, the specification module may specify formation of the composite color image when the colors of toners filled in the multiple toner cartridges include any color other than black, while specifying formation of the monochromatic image when the colors of toners filled in the multiple toner cartridges are all black. 
   In the image formation device of the present invention, the toner density adjustment may detect a toner density of a test toner image formed and set a control parameter for controlling toner image formation based on the detected toner density, the color image adjustment operation may detect toner densities of multiple test toner images formed with multiple color toners and set the control parameter, and the monochromatic image adjustment operation may detect a toner density of a test toner image formed with black toner and set the control parameter. The color image adjustment operation may detect a toner density of a test toner image formed and set a control parameter for controlling toner image formation based on the detected toner density, and the monochromatic image adjustment operation may set a preset monochromatic image parameter value to the control parameter. Here, the toner density adjustment for formation of the monochromatic image may detect the toner density of only one test toner image formed with black toner or may set a predetermined parameter value to the control parameter without detection of the toner density of a test toner image. This is because a variation in toner density less affects the picture quality of a resulting monochromatic image, compared with that of a resulting color image. The control parameter may include at least one of a charge potential of a photoreceptor, a light exposure of an exposure unit, a developing bias of a developer unit, and a charge potential of a transfer unit. 
   The technique of the present invention is not restricted to the image formation device described above, but is also applicable to an image formation method. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically illustrates the structure of a color laser printer  60  in one embodiment; 
       FIG. 2  shows the electrical connection of the controller  70  with each of the storage elements  50 ; 
       FIG. 3  is a block diagram showing functional blocks of the controller  70 ; 
       FIG. 4  is a flowchart showing a color mode specification routine; 
       FIG. 5  is a flowchart showing a toner density adjustment routine; 
       FIG. 6  shows one example of the patch toner images; and 
       FIG. 7  shows a map of setting the control parameters. 
       FIG. 8  is a flowchart showing a color mode specification routine. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   One preferred embodiment of the invention is discussed below.  FIG. 1  schematically illustrates the structure of a color laser printer  60  functioning as an image formation device in one embodiment of the invention. The color laser printer  60  of the embodiment is constructed as a full-color electrophotographic image formation device that adopts a single photoreceptor system and an intermediate transfer system. As illustrated, the color laser printer  60  includes a charge roller  73  that charges a photoreceptor  63  to a fixed potential (for example, −700 V), an exposure unit  62  that irradiates the charged photoreceptor  63  with laser and thereby forms color-separated images of four colors, cyan (C), magenta (M), yellow (Y), and black (K), as electrostatic latent images on the photoreceptor  63 , and a developer unit  61  that develops the electrostatic latent images formed on the photoreceptor  63  as toner images of the respective colors with corresponding color toners respectively fed from toner cartridges  40 C,  40 M,  40 Y, and  40 K attached to the developer unit  61 . The color laser printer  60  further includes a primary transfer unit  71  that transfers the toner images of the respective colors developed on the photoreceptor  63  onto a transfer belt  64  in an overlapping manner to form a composite color toner image, a feeder unit  66  that conveys printing paper from a paper cassette  65 , a secondary transfer unit  67  that further transfers the composite color toner image formed on the transfer belt  64  onto the conveyed printing paper, a fixation unit  68  that fixes the transferred composite color toner image on the printing paper and delivers the printing paper with the fixed composite color toner image, and a controller  70  that controls all the operations of the color laser printer  60 . 
   The developer unit  61  is rotatable to make each of the toner cartridges  40 C,  40 M,  40 Y, and  40 K attached to the developer unit  61  face the photoreceptor  63 . The toner cartridges  40 C,  40 M,  40 Y, and  40 K respectively have storage elements  50 C,  50 M,  50 Y, and  50 K. The controller  70  reads information on the color of toner filled in each toner cartridge via a movable connector  69 , which connects with each of the storage elements  50  moved to be located at a lower right position in the drawing.  FIG. 2  shows the electrical connection of the controller  70  with each of the storage elements  50 . As illustrated, the storage element  50  includes a memory cell  52  that stores data, a read-write controller  54  that controls operations of reading and writing data from and into the memory cell  52 , and an address counter  56  that counts up in the process of data transmission to and from the controller  70  of the color laser printer  60  via the read-write controller  54  in response to a clock signal CLK. An EEPROM is a typical example of the storage element  50 . 
   The primary transfer unit  71  has a transfer roller  74  that rotates while holding the transfer belt  64  interposed between the photoreceptor  63  and the transfer roller  74  and pressing the transfer belt  64  against the photoreceptor  63 . The function of the transfer roller  74  charges the transfer belt  64  to a reverse polarity to the polarity of a toner image formed on the photoreceptor  63 , and thereby causes the toner image to be transferred to the transfer belt  64  by the function of an electric field and the pressing force. The primary transfer unit  71  also has a toner density sensor  72  that irradiates the toner image transferred to the transfer belt  64  with infrared light and detects a toner density of the toner image, based on an observed quantity of reflected light. The detected toner density is input into the controller  70  via a signal line and an input port (not shown). 
     FIG. 3  is a block diagram showing functional blocks of the controller  70 . As illustrated, the controller  70  is constructed as a microprocessor including a CPU  90 , a RAM  92 , and a ROM  94 . The controller  70  receives the toner density detected by the toner density sensor  72  and other input signals (for example, a print instruction signal given by an operator) via signal lines. The controller  70  controls the operations of the respective constituents of the color laser printer  60  and specifically regulates a charge potential applied on the charge roller  73 , a developing bias potential applied on the developer unit  61 , a light exposure of the exposure unit  62 , and a charge potential applied on the transfer roller  74  via a charge roller actuation controller  96 , a developer unit actuation controller  97 , an exposure unit actuation controller  98 , and a transfer roller actuation controller  99 , based on the input signals. The charge roller  73 , the exposure unit  62 , the feeder unit  66 , and the secondary transfer unit  67  are identical with those included in conventional color laser printers and color photocopiers and are not specifically described here. 
   The following describes operations of the color laser printer  60  in the embodiment and specifically an operation of regulating the toner density of each toner image formed.  FIG. 4  is a flowchart showing a color mode specification routine, which is executed by the controller  70  in response to a power ON operation of the color laser printer  60  or in response to attachment of the toner cartridge  40  to the color laser printer  60 . The color mode specification routine sets a color mode CMode, one of control parameters used for controlling toner density adjustment discussed later. When the color mode specification routine starts, the controller  70  first reads color information of the toner filled in the toner cartridge  40  from the storage element  50  of the toner cartridge  40  attached to the color laser printer  60  (step S 100 ). According to a concrete procedure, the controller  70  outputs a read signal to the read-write controller  54  of the storage element  50  of the toner cartridge  40  connecting with the movable connector  69  of the color laser printer  60 . 
   The controller  70  subsequently determines whether toners of cyan (C), magenta (M), and yellow (Y) are all included in the toner filled in the toner cartridge  40  attached to the color laser printer  60 , based on the read-out color information of the toner (step S 110 ). When the toners of all these colors are included in the toner cartridge  40 , the controller  70  specifies formation of a composite color image, sets a value Co (representing a color image formation mode) to the color mode CMode, and writes the setting of the color mode CMode at a preset address in the RAM  92  (steps S 120  and S 140 ). When the toners of all these colors are not included in the toner cartridge  40 , that is, when any of the toners of cyan (C), magenta (M), and yellow (Y) is absent, on the other hand, the controller  70  specifies formation of a monochromatic image, sets a value Mo (representing a monochromatic image formation mode) to the color mode CMode, and writes the setting of the color mode CMode at the preset address in the RAM  92  (steps S 130  and S 140 ). After the processing, the color mode specification routine is terminated. 
   The following describes a toner density adjustment process to adjust the toner density of each toner image formed.  FIG. 5  is a flowchart showing a toner density adjustment routine. The toner density adjustment routine is executed by the controller  70 , when the color mode specification routine executed in response to the power ON operation of the color laser printer  60  is concluded or when the number of printed images reaches a preset value after a previous cycle of the toner density adjustment routine. When the toner density adjustment routine starts, the controller  70  first reads the setting of the color mode CMode from the RAM  92  (step S 200 ) and specifies the setting of the color mode CMode as either the value Co (the color image formation mode) or the value Mo (the monochromatic image formation mode) (step S 210 ). The value of the color mode CMode has been set in advance according to the color mode specification routine discussed above. 
   When the setting of the color mode CMode is the value Co (the color image formation mode), the controller  70  uses all the toners of cyan (C), magenta (M), yellow (Y), and black (K) to form test toner images or patch toner images Pc, Pm, Py, and Pk on the transfer belt  64  (step S 220 ). When the setting of the color mode CMode is the value M (the monochromatic image formation mode), on the other hand, the controller  70  uses only the toner of black (K) to form only a patch toner image Pk on the transfer belt  64  (step S 230 ). The procedure of the embodiment reads image data, which correspond to the respective patch toner images and are stored in advance in the ROM  94 , forms the electrostatic latent images on the photoreceptor  63 , develops the electrostatic latent images with the developer unit  61 , and transfers the developed patch toner images onto the transfer belt  64 .  FIG. 6  shows one example of the patch toner images formed on the transfer belt  64 . As illustrated, when the setting of the color mode is the color image formation mode, the patch toner images of the respective colors are successively formed at preset intervals. When the setting of the color mode is the monochromatic image formation mode, only the patch toner image of black (K) is formed. In the color image formation mode, four cycles of toner image formation are required to implement the processing from the formation of the electrostatic latent images on the photoreceptor  63  to the transfer of the patch toner images onto the transfer belt  64 . In the monochromatic image formation mode, on the other hand, only one cycle of toner image formation is sufficient. 
   After formation of the patch toner images, the controller  70  detects the toner density of each patch toner image formed with the toner density sensor  72  (step S 240 ). The controller  70  then sets control parameters (for example, the charge potential of the photoreceptor  63 , the light exposure of the exposure unit  62 , the developing bias of the developer unit  61 , and the transfer potential of the transfer roller  74 ) used for controlling the operations of the respective constituents involved in formation of the toner images, based on the detected toner densities and writes the settings of the control parameters into the RAM  92  (step S 250 ). After the processing, the toner density adjustment routine is terminated. The procedure of this embodiment experimentally or otherwise specifies relations between the detected toner density and the settings of the control parameters and stores in advance the relations in the form of control parameter setting maps into the ROM  94 . The settings of the control parameters corresponding to the detected toner density are read from the control parameter setting maps. One example of the control parameter setting maps is given as  FIG. 7 .  FIG. 7  shows a map of settings for the charge potential of the transfer roller  74 , where voltage  1  (V 1 ), voltage  2  (V 2 ), and voltage  3  (V 3 ) are an example of various charge potentials for the transfer roller  74 . Similar maps are given to set the other control parameters, that is, the charge potential of the photoreceptor  63 , the light exposure of the exposure unit  62 , and the developing bias of the developer unit  61 . The toner images are formed with the settings of the control parameters written in the RAM  92 , in response to the operator&#39;s print instruction. The arrangement of the embodiment ensures formation of the toner images having the adequate toner densities, regardless of a variation in working environment, for example, the temperature or the humidity. 
   As described above, the color laser printer  60  of the embodiment reads the color of toner filled in the toner cartridge  40  from the storage element  50  of the toner cartridge  40 , specifies either formation of a composite color image or formation of a monochromatic image, sets the control parameters for the toner density adjustment according to the result of the specification, and carries out the toner density adjustment process with the settings of the control parameters. The arrangement of the embodiment ensures adequate toner density adjustment for formation of the composite color image or for formation of the monochromatic image. This desirably relieves the load on the constituents of the color laser printer  60  involved in the toner density adjustment process and prevents the excessive deterioration of the constituents. The arrangement also ensures easy specification of either formation of the composite color image or formation of the monochromatic image, based on the information on the color of toner read from the storage element  50  of the toner cartridge  40 . 
   The movable connector  69  included in the color laser printer  60  of the embodiment corresponds to the information acquisition module of the invention. The controller  70  executing the color mode specification process and the toner density adjustment process corresponds to the specification module and the control module of the invention. 
   The color laser printer  60  of the embodiment determines whether the toners of cyan (C), magenta (M), and yellow (Y) are all included in the toner filled in the toner cartridge  40  attached to the color laser printer  60 , based on the color information of the toner read from the storage element  50  of the toner cartridge  40 , and specifies either formation of a composite color image or formation of a monochromatic image. Another method may alternatively be applied to specify formation of the composite color image or formation of the monochromatic image, as long as the specification is based on the read-out color information of the toner. One modified procedure may specify formation of a composite color image when the toner of any color other than black (K) is included in the toner filled in the toner cartridge  40  attached to the color laser printer  60 , while specifying formation of a monochromatic image when only the toner of black (K) (step S 110 B) is included, as shown in  FIG. 8 . 
   In the monochromatic image formation mode, the color laser printer  60  of the embodiment detects the toner density of the formed patch toner image of black (K) and sets the control parameters of the toner image formation, based on the detected toner density. One possible modification may set the control parameters without detection of the toner density of the patch toner image. Namely this modified procedure sets predetermined values to the control parameters in the monochromatic image formation mode. 
   In the color printer  60  of the embodiment, the control parameters of the toner image formation to be set are the charge potential of the photoreceptor  63 , the light exposure of the exposure unit  62 , the developing bias of the developer unit  61 , and the transfer potential of the transfer roller  74 . The control parameters are however, not restricted to this example but may be any parameters affecting the toner density of each toner image formed. 
   The color laser printer  60  of the embodiment reads the color of the toner from the storage element  50  of the toner cartridge  40  and specifies formation of a composite color image or formation of a monochromatic image. Another method may be applied to specify formation of the composite color image or formation of the monochromatic image. For example, specification of either formation of a composite color image or formation of a monochromatic image may be based on printing instruction information or image data input from a computer connecting with the color laser printer  50  or input through operations of an operation panel of the laser printer  60 . 
   The color laser printer  60  of the embodiment is constructed as a full-color electrophotographic image formation device that adopts the single photoreceptor system and the intermediate transfer system. The requirement is simply to read the information on the color of the toner from the storage element  50  of the toner cartridge  40 . The technique of the invention is thus also applicable to a color laser printer or a color photocopier constructed as a full-color electrophotographic image formation device that adopts a multiple photoreceptor system or a direct transfer system. 
   The embodiment regards the color laser printer  60  that fixes toner images transferred with toners of multiple colors onto a recording medium, such as paper, so as to form a color image. The technique of the invention is also actualized by a corresponding image formation method of forming a color image in such a way. 
   The above embodiment is to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. All changes within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.