Patent Publication Number: US-9846400-B2

Title: Image forming apparatus that executes light emission based on discharge dot count value

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 USC 119 to Japanese Patent Application No. 2015-192495 filed on Sep. 30, 2015, the entire contents which are incorporated herein by reference. 
     TECHNOLOGY FIELD 
     The present invention relates to an image forming apparatus for printing an image on a continuous medium. 
     BACKGROUND 
     In a print process of an image forming apparatus employing an electrographic system, a method for executing a discharging (waste) process of a toner (deteriorated toner) in a development device by comparing the printing rate in a period until the number of rotations of a photosensitive drum as a image carrier reaches a predetermined number of rotations (corresponds to the number of print dots) and a threshold value is proposed (for example, see Patent Document 1). 
     RELATED ART 
     [Patent Doc.] Japanese Laid-Open Application Publication 2004-45481 (for example, paragraphs 0033 to 0043, FIG. 4) 
     However, in the conventional method, the discharge process of the toner inside the development device may sometimes not be executed even when the number of rotations of the photosensitive drum in the print process reaches the predetermined number of rotations. In such a case, the quality of images to be formed in the next print process may sometimes be deteriorated from the effect of the deteriorated toner increased inside the development device. 
     The present invention was made to solve the problems in the abovementioned conventional technology and aims to provide an image forming apparatus capable of improving the quality of images to be printed on a continuous medium. 
     SUMMARY 
     An image forming apparatus disclosed in the application for forming an image on a continuous medium by a print process based on a print job includes a process execution part that executes the print process; a control part that controls an operation of the process execution part based on the print job; and a measuring part. Wherein, the process execution part includes an image carrier on which an electrostatic latent image is formed, an exposure part that is composed with a plurality of light emitting elements, the exposure part forming the electrostatic latent image on the image carrier by emitting light on the image carrier while light emission of each of the light emitting elements is controlled by the control part, and a development part that accommodates a developer and forms a developer image on the image carrier by supplying the developer to the image carrier, the measuring part measures an exposure dot number of each of the light emitting elements and a print amount executed by the print process. Wherein the control part makes the process execution part execute a discharge process to discharge the developer accommodated in the development part to an outside of the development part after completion of a print process based on a most recent print job and before initiation of a print process based on a next print job after the most recent print job, and in the discharge process, the control part makes the exposure part execute light emission based on a discharge dot count value obtained using a measurement result measured by the measuring part during the print process based on the most recent print job. 
     According to the present invention, the quality of images to be printed on a continuous medium can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view schematically showing a configuration of an image forming apparatus according to a first embodiment of the present invention. 
         FIG. 2  is a vertical cross-sectional view schematically showing a configuration of a process execution part (image forming part) shown in  FIG. 1 . 
         FIG. 3  is a block diagram schematically showing a configuration of a control system of the image forming apparatus according to Embodiment 1 of the present invention. 
         FIGS. 4A and 4B  are flowcharts showing an operation of the image forming apparatus according to Embodiment 1 of the present invention. Between the two flowcharts, “ 4   a ” and “ 4   b ” in  FIG. 4A  respectively connect to “ 4   a ” and “ 4   b ” in  FIG. 4B  so that a step following S 110  in  FIG. 4A  is S 115  in  FIG. 4B . In the same manner, step following S 119  in  FIG. 4B  is S 111  in  FIG. 4A . 
         FIG. 5  is a vertical cross-sectional view schematically showing a configuration of the image forming apparatus according to a Comparative Example. 
         FIG. 6  is a flowchart showing an operation of the image forming apparatus according to the Comparative Example. 
         FIG. 7  shows the a configuration, a discharge process, a printing rate (print duty), a print distance, and the result of smear judgment for the image forming apparatus according to Embodiment 1 (Experimental Examples #1 to #5) and the image forming apparatus of the Comparative Examples (Experimental Examples #6 to #11) in a table format. 
         FIG. 8  shows the relationship between the print distance [m] and the discharge dot count [dots] in the print process in the image forming apparatus of the Comparative Example (Experimental Examples #10, #11). 
         FIG. 9  shows the relationship between the print distance [the roll number of a 300 m rolled sheet] and the discharge dot count [dots] in the print process in the image forming apparatus according to Embodiment 1 (Experimental Examples #1, #2) and the image forming apparatus of the Comparative Example (Experimental Examples #6, #7). 
         FIG. 10  shows the relationship between the print distance [the roll number of a 300 m rolled sheet] and the discharge dot count [dots] in the print process in the image forming apparatus according to Embodiment 1 (Experimental Examples #3, #4) and the image forming apparatus of the Comparative Example (Experimental Examples #8, #9). 
         FIGS. 11A and 11B  are flowcharts showing an operation of the image forming apparatus according to a second embodiment of the present invention. 
         FIG. 12  is a flowchart showing the details of a forced discharge control shown in  FIGS. 11A and 11B . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     &lt;&lt;1&gt;&gt; Embodiment 1 
     &lt;&lt;1-1&gt;&gt; Configuration of the Image Forming Apparatus 
       FIG. 1  is a vertical cross-sectional view schematically showing a configuration of the image forming apparatus  1  according to a first embodiment of the present invention. The image forming apparatus  1  is a printer configured to form images (for example, toner images as developer images) on a continuous medium (recording medium) by a print process (print operation) based on a print job using a toner as a developer by an electrographic system. Specifically, the image forming apparatus  1  shown in  FIG. 1  is a color printer configured to perform color printing. However, the present invention can also be applied to monochromatic printers. Further, the present invention can also be applied to copiers, fax machines, and multifunction machines. 
     In this application, a “print job” is a print command (a command for executing a print process) to be sent to the image forming apparatus  1  (specifically, a later-described image data converter  67 ) from an external device. “One print job” is a command particularly for making the image forming apparatus  1  execute one set of print process. One print job is, for example, a print process for printing a one-page manuscript image once on a recording medium, a print process for printing a one-page manuscript image three times on a recording medium, a print process for printing a three-page manuscript image once on a recording medium, or a print process for printing a three-page manuscript image four times on a recording medium. 
     The image forming apparatus  1  is equipped with process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W as image forming parts conured to execute the print processes. Specifically, the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W form yellow (Y), magenta (M), cyan (C),black (K), and white (W) images, respectively. The process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W are arranged in one array tandem arrangement) in that order. The process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W have the same configuration except that the type (color) of the toners to be used is different. Therefore, each of the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W is also referred to as a process execution part  10 . Further, the number of the process execution parts equipped in the image forming apparatus  1  can be a number besides five. Furthermore, the colors of the toner of the process execution parts equipped in the image forming apparatus  1  are not limited to yellow (Y), magenta (M), cyan (C), black (K), and white (W). 
     The image forming apparatus  1  is equipped with a rolled sheet feeder  51  (rolled sheet holder) as a rolled sheet supply part held rotatably and configured to supply a rolled sheet P on the supply side, which is a recording medium before images are printed, and a rewinder  52  as a rolled sheet winding part for winding the rolled sheet P (rolled sheet P on the winding side after the images are printed) supplied by the rolled sheet feeder  51 . The image forming apparatus  1  may be equipped with a cutter  53  as a cutting part for cutting the rolled sheet P that is pulled out in the arrow AO direction from the rolled sheet feeder  51  after the completion of printing of one page. 
     An embodiment in which both ends of the rolled sheet P are fixed to the rolled sheet supporting shaft of the rolled sheet feeder  51  and the rolled sheet winding shaft of the rewinder  52  to carry out the printing on the rolled sheet P is called “roll to roll printing” (roll-to-roll printing). 
     In Embodiment 1, a case in which the width of the rolled sheet Pin the main scanning direction is 105 [mm] and the length of one roll of rolled sheet Pin the sub-scanning direction (that is, the length of one roll of the rolled sheet P) is 300 [m] will be described. However, the width and the length of the rolled sheet P are not limited to the aforementioned example. 
     The image forming apparatus  1  is equipped with an endless intermediate transfer belt  31  below the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W. The intermediate transfer belt  31  is movably supported by supporting rollers  32 ,  33 ,  34 ,  35 ,  36 , and  37 . The supporting roller  33  is a drive roller for carrying the intermediate transfer belt  31  in the arrow A 1  direction. The supporting roller  35  is also called a backup roller. The supporting roller  36  is also called a tension roller. 
     Further, the image forming apparatus  1  is equipped with primary transfer rollers  40 Y,  40 M,  40 C,  40 K, and  40 W as transfer parts (primary transfer parts) for transferring the toner images to the intermediate transfer belt  31  from the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W to the opposite side of the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W sandwiching the intermediate transfer belt  31 . The toner image formed by the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W are transferred (primary transferred) on the intermediate transfer belt  31  by the primary transfer rollers  40 Y,  40 M,  40 C,  40 K, and  40 W. Further, each the primary transfer rollers  40 Y,  40 M,  40 C,  40 K, and  40 W is also referred to as a primary transfer roller  40 . 
     The image forming apparatus  1  is equipped with a secondary transfer roller  54  as a transfer part (secondary transfer part) arranged sandwiching the intermediate transfer belt  31  below the supporting roller  35  (backup roller) arranged on the inner side of the intermediate transfer belt  31 . The secondary transfer roller  54  transfers the toner image formed on the intermediate transfer belt  31  on the rolled sheet P. 
     The image forming apparatus  1  is equipped with a belt cleaning member  38  for scraping the toner remaining on the intermediate transfer belt  31  from the intermediate transfer belt  31  after the transfer by the secondary transfer roller  54 , a waste toner collection part  24  for accommodating the toner (waste toner) scraped by the belt cleaning member  38 , and a toner carrying part  23  for carrying the waste toner to the waste toner collection part  24  from the belt cleaning member  38 . The toner carrying part  23  is equipped with, for example, a carrying path for carrying the waste toner, a spiral member for sending the waste toner, and a spiral drive part for rotating the spiral member. 
     The image forming apparatus  1  is equipped with a fuser part  55  for fusing the toner image transferred on the rolled sheet P by applying heat and pressure. The fuser part  55  is equipped with a heat application roller  55   a  and a pressure application roller  55   b.    
       FIG. 2  is a vertical cross-sectional view schematically showing a configuration of the process execution part  10 . The process execution part  10  is equipped with cylindrical photosensitive drums  11  ( 11 Y,  11 M,  11 C,  11 K, and  11 W) as image carriers to which electrostatic latent images are formed on the surface thereof The photosensitive drums  11  are, for example, equipped with a cylindrical conductive support and a photoreceptive layer equipped on the surface of the conductive support. The photosensitive drum  11  rotates in one direction (counterclockwise in  FIG. 2 ) by a driving force produced at a driving force generation part such as a photosensitive drum motor  11   a  (see later-described  FIG. 3 ) and transmitted by a driving force transmission part such as a gear, etc. 
     The process execution part  10  is equipped with a photosensitive drum  11 , a charge roller  12  as a charging part, an optical head  13  ( 13 Y,  13 M,  13 C,  13 K,  13 W) as an exposure part, and a development part  14  ( 14 Y,  14 M,  14 C,  14 K, and  14 W). 
     The process execution part  10  is equipped with a cartridge  140  configured to accommodate an unused toner (also referred to as “toner”) and a waste toner. Specifically, the cartridge  140  is equipped with an unused toner accommodation part  140   a  for accommodating an unused toner (first toner accommodation part) and a waste toner accommodation part  140   b  for accommodating a waste toner (second toner accommodation part). 
     The charge roller  12  is equipped with, for example, a metal shaft and a semiconductive elastic layer formed on the surface of the shaft. A predetermined bias voltage is applied to the charge roller  12  from a charge roller power source  72 . The charge roller  12  is driven to rotate in accordance with the rotation of the photosensitive drum  11  to uniformly charge the surface of the photosensitive drum  11 . 
     The optical head  13  is equipped with a light emitting element array having a plurality of light emitting elements  13   a  arranged in the main scanning direction (in a direction of the rotation axis of the photosensitive drum  11 ) and a rod lens array. For example, each of the light emitting element  13   a  is a light emitting diode (LED: Light Emitting Diode), and the light emitting element array is an LED array. The optical head  13  emits light (dot shaped light) on the photosensitive drum  11  to form an electrostatic latent image on the photosensitive drum  11 . Specifically, the optical head  13  forms an electrostatic latent image on the photosensitive drum  11  by forming an image with the light of the light emitting elements  13   a  emitted according to the image data on a uniformly charged photosensitive drum  11  with a rod lens array. In the present application, a case in which the LED array pitch of the LED array is 1200 dpi (dots per inch) will be described. Further, in this application, a case will be described, in which the light emission amount of the plurality of light emitting elements  13   a  is constant and either a lighting state in which the light emitting element  13   a  is emitting light or a non-lighting state in which it is not emitting light is selected. However, the optical head  13  as an exposure part can be any parts employing any methods such as a laser scanning part. 
     The development part  14  is equipped with a casing  141 , a supply roller  142  as a developer supply member, a development roller  143  as a developer carrier, a development blade  144  as a developer regulatory member and an agitating member  145 . 
     The casing  141  accommodates the supply roller  142 , the development roller  143 , the development blade  144 , and the agitating member  145 . Further, the casing  141  accommodates an unused toner, which is a developer supplied from the unused toner accommodation part  140   a.    
     The development roller  143  is equipped with, for example, a metal shaft and a semiconductive elastic layer formed on the surface of the shaft. In this embodiment, a urethane rubber having an ASKER C hardness of 78 degrees is used as a semiconductive elastic layer and a conducting agent in which carbon black is mixed is used. It is preferable that the surface layer covering the surface of the elastic layer is selected in consideration of, e.g., wear resistance and application of electric charge to the toner. In this embodiment, a case in which a urethane resin is used as a surface layer is described. The surface roughness and the resistance value of the development roller  143  needs to be set so that the toner layer thickness and the toner amount on the development roller  143  is a desired amount. In this embodiment, it is preferable that the ten-point average surface roughness measurement Rz is within a range of 2 [μm] to 8 [μm], and the measurement of the resistance value including the elastic layer and the surface layer is set within a range of 1×10 6 [Ω] to 1×10 8 [Ω]. 
     A predetermined bias voltage is applied to the development roller  143  from the development roller power source  73  (see later-described  FIG. 3 ). The development roller  143  rotates in the same direction as the photosensitive drum  11  at the contact part with the photosensitive drum  11  (direction opposite to the rotation direction of the development roller  143  and rotation direction of the photosensitive drum  11 ) and forms a toner image on the photosensitive drum  11  by supplying the toner to the surface of the photosensitive drum  11 . 
     A supply roller  142  as a developer supply part and a development blade  144  as a developer regulatory member are arranged adjacent to the development roller  143 . In the supply roller  142 , for example, a foamed silicon rubber layer is formed on the metal shaft. A predetermined bias voltage is applied to the supply roller  142  from the supply roller power source ( 74  of the later-described  FIG. 3 ), and the supply roller  142  rotates in the opposite direction of the development roller  143  at the contact part with the development roller  143  and supplies a toner to the surface of the development roller  143 . The overlap amount of the supply roller  142  and the development roller  143  at the nip part is, for example, 1.0 [mm]. 
     The development blade  144  is formed by, for example, bending a plate-shaped member elongated in the axial direction of the development roller  143  and stainless steel is used as the material. The thickness of the plate is, for example, 0.08 [mm]. The curved surface of the bent part of the development blade  144  is pressed against the surface of the development roller  143 , and the thickness of the toner layer is regulated by the pressing force to form a toner thin layer on the development roller  143 . A predetermined bias voltage is applied to the development blade  144  from the supply roller power source  74  (see later-described  FIG. 3 ). 
     The photosensitive drum  11  of the process execution part  10  integrated in the image forming apparatus  1  is in contact with the intermediate transfer belt  31 , and a primary transfer roller  40  is provided on the opposite side of the photosensitive drum  11  sandwiching the intermediate transfer belt  31 . A predetermined bias voltage is applied to the primary transfer roller  40  from the transfer roller power source  71  (see later-described  FIG. 3 ), and the primary transfer roller  40  transfers the toner image formed on the surface of the photosensitive drum  11  to the intermediate transfer belt  31 . 
     The process execution part  10  is equipped with a cleaning member  15  provided on the downstream side in the rotation direction of the photosensitive drum  11 , a carrying spiral  21  configured to carry the toner (waste toner) scraped by the cleaning member  15 , and a carrying path  22  on which the waste toner is carried. The cleaning member  15  is, for example, a blade made of polyurethane rubber in contact with the photosensitive drum  11 , and removes the toner remaining on the surface of the photosensitive drum  11  after the execution of the primary transfer. The carrying path  22  is connected to the waste toner accommodation part  140   b . The carrying spiral  21  can carry the toner (waste toner) scraped with the cleaning member  15  to the waste toner accommodation part  140   b.    
     The process execution part  10  is equipped with a discharging light irradiation part  16  provided more on the downstream side in the rotation direction than the cleaning member  15  of the photosensitive drum  11 . The discharging light irradiation part  16  is arranged so as not to be in contact with the photosensitive drum  11  and removes the residual electric charge on the surface of the photosensitive drum  11 . The discharging light irradiation part  16  is, for example, constituted with an LED. 
     Hereinafter, the toner used for the Experimental Examples #1 to #11 will be described. The toner used is a nonmagnetic one-component negatively chargeable toner. The toner is constituted by mother particles in which a coloring agent, a binder resin, and a wax are agglomerated, and an external additive added to the mother particles. The mother particle of the toner is produced using a pulverization method and uses, for example, pigment yellow (Y), quinacridone (M), copper phthalocyanine (C), carbon black (K), titanium oxide (W), etc. For the binder resin, polyester is used, for example, with the purpose of improving the dispersiveness of the pigments. The wax is used for the purpose of, e.g., preventing the toner from adhering to the heat application roller  55   a  at the time of fusing. 
     The external additive is added to the mother particles of the toner for the purpose of controlling the flowability and the chargeability of the toner, and for example, titanium oxide, alumina, silica, melamine, etc., are used. Furthermore, for silica, silica subjected to a surface reforming such as silicone oil processing and disilazane processing to improve the hydrophobicity and the flowability may be used. The volume mean particle diameter of the toners of each color is, for example, 5.6 [μm] for yellow (Y), magenta (M), cyan (C), and black (K), and 7.0 [μm] for white (W). The volume mean particle diameter can be measured using a grain size distribution measurement device (Coulter Multisizer II manufactured by Coulter, Inc.) The circularity degree of the toner of each color is, for example, 0.97. The circularity degree is measured using a flow-type particle image analysis device (FPIA-3000 manufactured by Sysmex Corp.) and the following formula is used for the calculation of the circularity degree. Circularity degree=(circumference length of the circle having the same area as the particle image projection image)/(circumference length of the particle image projection image). From this formula, a value between 0 and 1 showing the circularity degree is calculated. The value of the circularity degree in the case of a perfect sphere shape is 1, and the value of the circularity degree is smaller as the shape becomes complex. 
     The blow-off charge amount of the toner in each color is, for example, −36 [μC/g]. The blow-off charge amount can be obtained by using a power charge amount measurement device (TYPE TB-203 manufactured by Kyocera Corp.) to mix 0.5 [g] of the toner and 9.5 [g] of a ferrite carrier (F-60 manufactured by Powder Tech Co., Ltd.) and by measuring the saturated charge amount under the condition of flow pressure of 7.0 [kPa] and suction pressure of −4.5 [kPa] after agitating for 30 minutes. 
       FIG. 3  is a block diagram schematically showing a configuration of the control system of the image forming apparatus  1  according to a first embodiment. The image forming apparatus  1  is equipped with a control part  60  as a main control part and a measuring part  64 . 
     The control part  60  is equipped with a print control part  61  managing various controls, a print data monitoring part  62  for monitoring the changing of the page in the print data, and a calculation part  63  for performing various calculations. For example, the control part  60  (specifically the print control part  61 ) controls the operation of the process execution part  10  based on the print job. For example, the control part  60  (specifically, the print control part  61 ) controls the light emission of each light emitting element  13   a  of the optical head  13  via the head drive control part  75 . 
     The measuring part  64  is equipped with a drum rotation number measuring part  65  for measuring the rotation number of the photosensitive drum  11  and a dot light emitting number measuring part  66  for measuring the light emitting number of the light emitting element  13   a  corresponding to the image data of the optical head  13 . For example, the measuring part  64  (specifically the dot light emitting number measuring part  66 ) measures exposure dot number of the light emitting elements  13   a.    
     The image forming apparatus  1  is equipped with an image data converter  67  for receiving a print job (image data) D 0  from an external device, for example, a personal computer (PC) and generating a control signal (head light emission command data D 1  for the optical head  13 ) based on the print job D 0 , and a memory part  68  for storing the results of the calculations of the control part  60 , etc. 
     The image forming apparatus  1  is further equipped with a transfer roller power source  71  configured to apply a predetermined voltage to the primary transfer roller  40  and the secondary transfer roller  54 , a charge roller power source  72  configured to apply a predetermined voltage to the charge roller  12 , a development roller power source  73  configured to apply a predetermined voltage to the development roller  143 , a supply roller power source  74  configured to apply a predetermined voltage to the supply roller  142  and the development blade  144 , a head drive control part  75  as a drive part to make the optical head  13  emit light, and a discharge power source  76  configured to apply voltage to make the discharging light irradiation part  16  emit light. 
     The image forming apparatus  1  is further equipped with a fusing control part  77  configured to control the operation of the heat application roller  55   a  and the pressure application roller  55   b , a carrying motor control part  78  configured to control the rolled sheet feeder motor  51   a , a drive motor control part  79  configured to control the rotation drive of the intermediate transfer belt motor  31   a , the secondary transfer roller motor  54   a , and the photosensitive drum motor  11   a , a cutter operation control part  80  configured to control the cutter drive part  80   a  which operates the cutter  53 , and a separating operation control part  81  configured to control the secondary transfer roller cam  81   a  for contacting and separating the intermediate transfer belt  31  to and from the secondary transfer roller  54 . 
     The print control part  61 , the print data monitoring part  62 , and the calculation part  63  constitute the control part  60 . The drum rotation number measuring part  65  and the dot light emitting number measuring part  66  constitute the measuring part  64 . 
     &lt;&lt;1-2&gt;&gt; Print Operation 
     Next, the print operation of the image forming apparatus  1  will be described with reference to  FIG. 1 ,  FIG. 2 , and  FIG. 3 . 
     In the image forming apparatus  1 , the print job D 0  is sent from a host device such as a personal computer (PC) and a scanner and received by the image data converter  67 . The image data converter  67  converts the image data included in the received print job D 0  to head light emission command data D 1 . 
     The print control part  61  starts the print operation when the head light emission command data D 1  based on the print job D 0  is received from the image data converter  67 . The print control part  61  drives the photosensitive drum motor  11   a  as a driving force generation part via the drive motor control part  79  and rotates the photosensitive drum  11  at a constant peripheral velocity in the arrow direction of  FIG. 2 . The driving force by the rotation of the photosensitive drum  11  is transmitted to a gear array as a driving force transmission part, etc., and rotates the development roller  143  and the supply roller  142  in the arrow direction of  FIG. 2 . The charge roller  12  rotates in the arrow direction of  FIG. 2  together with the photosensitive drum  11 . At this time, a direct current voltage is applied to the charge roller  12  provided so as to be in contact with or pressed against the surface of the photosensitive drum  11  from the charge roller power source  72 , so that the surface of the photosensitive drum  11  is uniformly (evenly) charged. In this embodiment, the aluminum raw tube of the photosensitive drum  11  is grounded, and the surface of the photosensitive drum  11  is charged to around −500 [V] by applying a direct current voltage of −1000 [V] to the charge roller  12 . 
     Next, in the exposure process, dot-shaped lights corresponding to the head light emission command data D 1  is irradiated from a plurality of LEDs of the optical heads  13  onto the surface of the charged photosensitive drum  11 , so that an electrostatic latent image is formed on the photosensitive drum  11 . In this embodiment, the electrical potential of the photosensitive drum  11  at the exposed portion is around −50 [V]. Further, the irradiation by the optical head  13  is also executed during the generation of the head light emission command data D 1  of one print job and not after all of the head light emission command data D 1  of one print job are generated. 
     Furthermore, an electrostatic latent image on the photosensitive drum  11  is developed by the toner and a toner image is formed on the photosensitive drum  11  from the operation of the development part  14 . In this embodiment, a direct current voltage of −200 [V] is applied to the development roller  143  from the development roller power source  73 . Further, the electrical potential of the toner layer on the development roller  143  made into a thin layer is around −50 [V]. Since the total of the electrical potential of the toner thin layer and the voltage applied to the development roller  143  exceeds the electrical potential of the exposure part on the photosensitive drum  11 , the exposure part on the photosensitive drum  11  is developed by the toner. Since the total of the electrical potential of the toner thin layer and the voltage applied to the development roller  143  does not exceed the electrical potential of the unexposed part on the photosensitive drum  11 , the unexposed part on the photosensitive drum  11  is not developed by the toner. 
     Further, the drive motor control part  79  controls the intermediate transfer belt motor  31   a , so that the intermediate transfer belt  31  rotates in the arrow A 1  direction of  FIG. 1 . A direct current voltage +2000 [V] is applied to the primary transfer roller  40  provided so as to face the photosensitive drum  11  from the transfer roller power source  71 . The toner image formed on the photosensitive drum  11  is primary transferred onto the intermediate transfer belt  31  from the electric field generated between the primary transfer roller  40  (+2000 [V]) and the raw tube of the photosensitive drum  11  (grounded electrical potential). From the rotation of the intermediate transfer belt  31 , toner images in a maximum of five colors, Y, M, C, K, and W, are laminated on the intermediate transfer belt  31  after passing the white process execution part  10 W. 
     On the other hand, the rolled sheet P is sent to the secondary transfer part, that is, between the intermediate transfer belt  31  and the secondary transfer roller  43  by the drive of the rolled sheet feeder motor  5  la connected to the carrying motor control part  78 . At this time, the secondary transfer roller  54  is in contact with the intermediate transfer belt  31  by the separation operation control part  81 . Further, the supporting roller  35  is grounded. A direct current voltage of +2000 [V] is applied to the secondary transfer roller  54  provided so as to face the supporting roller  35  from the transfer roller power source  71 . The toner image formed on the intermediate transfer belt  31  is transferred on the rolled sheet P by the electric field generated between the secondary transfer roller  54  (+2000 [V]) and the supporting roller  35  (grounded). 
     After passing the secondary transfer part, the rolled sheet P further passes between the heat application roller  55   a  and the pressure application roller  55   b  constituting the fuser part  55 . And from the heat and the pressure, the toner on the rolled sheet P melts and permeates between the fibers of the rolled sheet to perform the fuser of the toner image on the rolled sheet P. The rolled sheet P in which the toner image is fused is winded by the rewinder  52 . 
     The print data monitoring part  62  recognizes a change of page by detecting that the light emission of the optical head  13  by the head light emission command data D 1  converted in the image data converter  67 , and after that, the cutter  53  is operated by the cutter operation control part  80  and the rolled sheet is cut at a position behind by a margin than the position on the rolled sheet P in which the printing was completed. 
     Further, a slight amount of toner sometimes remains on the photosensitive drum  11  after the primary transfer, but the remaining toner is removed by the cleaning member  15 . Further, the unexposed electric charge on the photosensitive drum  11  is removed by light irradiating the photosensitive drum  11  by the discharging light irradiation part  16 . The surface of the photosensitive drum  11  in which the electric charge was removed is charged again by the charge roller  12 . In this way, the photosensitive drum  11  is repeatedly used for image forming. 
     Further, a slight amount of toner sometimes remains on the intermediate transfer belt  31  after the secondary transfer, but the remaining toner is removed by the belt cleaning member  38 . The toner removed by the belt cleaning member  38  is carried by a waste toner carrying member, for example, a toner carrying part  23  such as a spiral for carrying toners (rotating spiral shape blade part), a toner carrying paddle, etc., and collected by the waste toner collection part  24 . In this way, the intermediate transfer belt  31  is repeatedly used for image forming. 
     Next, the operation of the development part  14  in the print step will be described. The development roller  143  and the supply roller  142  receive the rotation driving force of the photosensitive drum  11  and rotate in the arrow direction of  FIG. 2 . The toner accommodated in the unused toner accommodation part  140   a  is sent to the development roller  143  by the rotation of the supply roller  142 . Since the supply roller  142  and the development roller  143  rotate in the opposite direction at the contact part thereof, the toner is negatively charged by the friction. When the toner sent to the development roller  143  passes the contact part with the development blade  144  by the rotation of the development roller  143 , the toner is made into a thin layer while being frictionally charged by the development roller  143  and the development blade  144 . In this embodiment, a direct current voltage of −300 [V] is applied to the supply roller  142  and the development blade  144  from the supply roller power source  74 . After that, the toner on the development roller  143  made into a thin layer is developed corresponding to the electrostatic latent image formed on the photosensitive drum  11  and furthermore, the electrostatic latent image becomes a toner image. 
     The toner is rubbed at the contact part of the development roller  143  and the supply roller  142  and the contact part of the development roller  143  and the development blade  144 . When the print operation in a state in which the optical head  13  is unexposed continues, the toner continuously moves around the development roller  143  without being used, repeating the rubbing with the supply roller  142  and the development blade  144 , gradually causing deterioration of the toner to due to peeling of the external additives. In the deteriorated toner, the flowability and the chageability are decreased different from the beginning and since it is in a state in which electric charge is easily retained in the toner due to agglomeration of the toners, staining can easily occur. Further, the deteriorated toner is easily retained around the development roller  143 . Specifically, when the electrical potential of the toner layer when the metal shaft on the development roller  143  is grounded becomes −100 [V] or below (for example, when the development voltage is not applied), white contamination occurs. 
     &lt;&lt;1-3&gt;&gt; Toner Discharging (Disposing) Operation 
     Next, the toner discharging (disposing) operation (toner discharging process) in the image forming apparatus  1  will be described.  FIGS. 4A and 4B  are flowcharts showing the toner discharging (disposing) operation in the image forming apparatus  1 . The toner discharging operation shown in  FIGS. 4A and 4B  is carried out in the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W. 
     In the present application, the “*” in the symbols E*, F*, H*, I*, J*, R* can be replaced by the toner colors Y, M, C, K, and W used in the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W. That is, the drum count E* of the process execution parts  10 Y,  10 M,  10 C,  10 K and  10 W are E Y , E M , E C , E K , and E W , respectively. The light emitting dot count F* of each process execution parts  10 Y,  10 M,  10 C,  10 K and  10 W is F Y , F M , F C , F K , and F W , respectively. The slicing print rate (slicing duty) H* of each process execution part  10 Y,  10 M,  10 C,  10 K and  10 W is H Y , H M , H C , H K , and H W , respectively. That is, the discharge dot count I* of each process execution part  10 Y,  10 M,  10 C,  10 K and  10 W is I Y , I M , I C , I K  and I W , respectively. That is, the print dot count J* of each process execution part  10 Y,  10 M,  10 C,  10 K and  10 W is J Y , J M , J C , J K , and J W , respectively. That is, the slicing dot light emitting number R* of each process execution part  10 Y,  10 M,  10 C,  10 K and  10 W is R Y , R M , R C , R K , and R W , respectively. 
     The drum count E* shows the print amount executed during the print process based on one print job in each of the process execution parts  10 Y,  10 M,  10 C,  10 K and  10 W. In the present embodiment, the drum count E*=1 means that the outer circumferential portion of the photosensitive drum  11  has rotated by a length of 148 [mm] in the circumferential direction (that is, corresponding to print distance=148 [mm]). The time between the print processes is the time from when the control part  60  (specifically the print control part  61 ) receives a print job from an external device to when the image forming on a rolled sheet P based on the received print job is completed. 
     The light emission dot count F* is the total value of the exposure dot number (dot light emitting number) of each light emitting element  13   a  (for example, LEDs) measured between the print processes based on one print job in each of the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W. Further, 1 [dot] corresponds to one light emitting element  13   a  (for example, LED). The dot light emitting number is the number of dots irradiated on the surface of the photosensitive drum  11  by each light emission (also referred to as “dot light emission”) of the light emitting elements  13   a  of the optical head  13  (for example, LEDs). That is, the light emission dot count F* shows a cumulative value of the number of dots irradiated on the surface of the photosensitive drum  11  by the optical head  13  between the print processes based on one print job in any of the process execution parts  10 Y,  10 M,  10 C,  10 K, and  10 W. 
     The slicing printing rate H* is a predetermined coefficient (print rate), which was set in advance, for calculating the discharge dot count I* and is a printing rate (print duty) set as a standard to determine whether or not to carry out the toner discharging operation (toner discharging process). 
     The discharge dot count I* is a value obtained by using the measurement result measured by the measuring part  64  between the print processes based on a print job. The specific calculation method will be described later. 
     The print dot count J* is a dot count [dot] when printing is performed for a print amount corresponding to drum count E*=1 at 1% duty. 
     The slicing dot light emitting number R* is a dot count [dot] when printing for an amount shown by the drum count E* is performed at a predetermined slicing printing rate H*. It is a value calculated by multiplying the print amount (drum count E*) measured between the printing processes based on one print job to a predetermined conversion factor. 
     At S 101 , when printing starts, the print control part  61  reads the discharge dot count I* stored in the memory part  68  at S 102 . When carrying out the toner discharging operation (first time) of  FIGS. 4A and 4B , the discharge dot count I* stored in the memory part  68  is 0. When carrying out the toner discharging operation (second time and beyond) of  FIGS. 4A and 4B , the discharge dot count I* stored in the memory part  68  is a value (count value) stored in the memory part  68  at S 113  to be described later. 
     At S 103 , the measuring part  64  starts to measure the print amount being executed by the print process. Specifically, the drum rotation number measuring part  65  starts the measurement of the rotation number of the photosensitive drum  11  and counts up (adds) the drum count E* based on the measured rotation number. In this embodiment, the print amount is a length (print distance) in the carrying direction of the rolled sheet P on which printing was performed by the print process based on one print job. In this embodiment, “1” is added to the drum count E* when the outer circumferential portion of the photosensitive drum  11  rotates for a length of 148 [mm] in the circumferential direction in the print process. That is, in this embodiment, the drum count E* is shows the print amount. Further, the initial value of the drum count E* is 0. The print control part  61  receives the drum count E*. 
     In this embodiment, the print amount is set to the length (print distance) of the printed rolled sheet P in the carrying direction, but the rotation number of the photosensitive drum  11  in the print process based on one print job can be set as the print amount. 
     At S 104 , the dot light emitting number measuring part  66  starts to measure the exposure dot number (dot light emission number) of each LED of the optical head  13  and counts up (adds) the light emitting dot count F*. In this embodiment, for example, “1” is added to the light emission dot count F* when one LED of the optical head  13  emits 1 dot of light. 
     At S 105 , the print data monitoring part  62  checks whether or not the light emission by the LED of the optical head  13  based on the head light emission command data D 1  is completed (that is, whether or not the print process based on one print job is complete), and when it is not completed, it repeats the process of Step S 105  until the print process based on one print job is completed. While the process At S 105  is repeated, the drum count E*, a value showing the print distance, and the light emission dot count F* showing the dot light emitting number is continuously added accordingly with the print operation. 
     At S 105 , in a case in which the print process based on one print job is determined to be completed (YES at S 105 ), the measurement of the drum count E* is completed at S 106  and the measurement of the light emission dot count F* is completed at S 107 . That is, the measurement of the print amount by the measuring part  64  in the print process is executed for every print job. 
     At S 109 , the control part  60  (specifically, the calculation part  63 ) calculates the discharge dot count I* as a value for calculating the toner discharging amount from the drum count E*, which is a value showing the print amount (for example, print distance), the light emission dot count F* showing the dot light emitting number, and the slicing printing rate H*. 
     Here, the print dot count J* will be described. In an A6 size sheet, the length in the main scanning direction is 105 [mm] and the length in the sub-scanning direction is 148 [mm]. That is, in this embodiment, an A6 size sheet is a print amount corresponding to a drum count E*=1 (print distance=148 [mm]). For the printing, the top, bottom, left, and right margins are 2 [mm]. In this case, the area of the printable region of the A6 size sheet [mm 2 ] can be shown by the following formula.
 
(105−(2×2))×(148−(2×2))[mm 2 ]  Formula 1
 
     When the entire printable region is irradiated with the dot-shaped lights at a printing rate of 100% (when all LEDs are irradiated, the irradiation dot number (dot light emitting number) in the main scanning direction is shown by the formula 2 and the irradiation dot number (dot light emitting number) in the sub-scanning direction is shown by the formula 3.
 
(105−(2×2))/25.4×1200=4771.6535 [dots]  Formula 2
 
(148−(2×2))/25.3×1200=6803.1496 [dots]  Formula 3
 
     Here, 25.4 [mm/inch] is a conversion of units inches and millimeters, and 1200 [dot/inch] is the number of LEDs per 1 inch of LED arrays of the optical heads  13 . 
     The print dot count J* (1% duty) is shown by the following formula 4 when a region of only 1% of the area among the entire printable area is irradiated with dot-shaped lights.
 
 J*= 4771.6536×6803.1496×0.01=324622.726 [dots]  Formula 4
 
     The number of dot-shaped lights J* is 324622 [dots] when the decimal points are rounded off. The value J* is a dot count when printing at a printing rate of 1% is performed on one A6 size sheet (corresponding to drum count E*=1). 
     Therefore, for example, the print dot count J* (5% duty)=J5* when printing at a printing rate of 5% is performed on one A6 size sheet is shown by the following formula 5, and the print dot count J* (10% print duty)=J10* when printing at a printing rate of 10% is performed on one A6 size sheet is shown by the following formula 6.
 
 J 5*= J 1*×5=324622×5 [dots]  Formula 5
 
 J 10*= J 1*×5=324622×10 [dots]  Formula 6
 
     Next, the slicing printing rate H* will be described. The slicing printing rate H* a printing rate (print duty) set as a standard on whether or not to carry out the toner discharging operation (toner discharging process). When a state in which the toner is not consumed continues, deteriorated toners with changed properties increase around the development roller  143  and become the cause of occurrences of print contamination. Therefore, when the printing rate (print duty) is low, it is preferable to carry out the toner discharging process (discharge process) for discharging the deteriorated toner. When the print process is executed at a printing rate below the slice printing rate H*, the toner discharge process is executed after the completion of the print process. In Embodiment 1, the slicing printing rate H* is set to 5%. Not to mention, the rate H* may vary according to various conditions. The rate H* may be determined to be within 0% to 20%. 
     The calculation method of the discharge dot count I* (discharge dot count value) for calculating the toner discharging amount will be described. 
     First, the control part  60  calculates the slicing dot light emitting number R* using the following formula in which the dot count E* is multiplied by the conversion factor.
 
 R*=J* ×( H*× 100)× E*  
 
Instead of using dot count E*, a drum rotation time (or period) may be available.
 
     Next, the control part  60  calculates the discharge dot count I* by the difference in the light emission dot count F* and the slicing dot light emitting number R* (formula 7) in the print process based on the most recent print job.
 
 I*=R*=F*   Formula 7
 
     The discharge dot count I* read at S 102  is added to the calculated discharge dot count I* to update the discharge dot count I* used in the toner discharging process. When the discharge dot count I* has a positive value, it means that deteriorated toner exists in the casing  141  from the continuation of low duty printing, for example. 
     At S 110 , the control part  60  determines whether or not the discharge dot count I* updated at S 109  is 0 or lower. It is the same as determining whether or not deteriorated toner exists in the casing  141 . When the discharge dot count I* (YES at S 110 ) is 0 or lower, the drum count E* is set to 0 [counts] at S 111  (or reset the drum count), the light emitting dot count F* is set to 0 [counts] at S 112  (or reset the light emitting dot count F*), and the discharge dot count I* is set to 0 [counts] at S 113  to store the discharge dot count I* in the memory part  68 . At this time, the value of the stored discharge dot count I* is 0 [counts]. And the print operation is completed at S 114 . 
     At S 110 , when the discharge dot count I* updated at S 109  is determined to be larger than 0 [counts] (NO at S 110 ), the control part  60  starts the execution of the toner discharging process. Specifically, the control part  60  (print control part  61 ) makes the process execution part  10  execute the toner discharging process between after the print process (first print process) based on the most recent print job (first print job) is completed and until the print process (second print process) based on the next print job (second print job) is started. 
     At S 115 , according to the control signal of the control part  60 , the separating operation control part  81  drives the secondary transfer roller cam  81   a  to separate the secondary transfer roller  54  from the intermediate transfer belt  31 . 
     At S 116 , the control part  60  determines whether or not the discharge dot count I* is below the predetermined first standard dot count N 1  [counts]. The first standard dot count N 1  is, for example, 588779520 [counts]. The first to fourth standard dot counts N 1  to N 4  are determined based on lengths by which the control part  60  is able to continue to print without wasting toners. From the first to the fourth, the counts increase. 
     When the discharge dot count I* is below the first standard dot count N 1  (YES at S 116 ), at S 117 , the control part  60  (for example, the print control part  61 ) makes each part including the process execution part  10  execute the toner discharging process based on the discharge dot count I*. The discharge amount of the toner is calculated by multiplying the discharge dot count I* by the amount of toner supplied to the photosensitive drum  11  from the development part  14  by the light emission (dot light emission) of one light emitting element  13   a  in a plurality of light emitting elements  13   a  in the optical heads  13 . That is, the control part  60  (for example, the print control part  61 ) makes the optical head  13  execute the dot light emission based on the discharge dot count I*, and an amount of toner to be discharged is discharged from the development part  14 . Specifically, an amount of toner to be discharged is supplied to the photosensitive drum  11  from the development part  14 . The toner (waste toner) supplied to the photosensitive drum  11  is removed by the cleaning member  15  or the belt cleaning member  38  and accommodated by the waste toner accommodation part  140   b  or  24 . 
     Since all deteriorated toner to be discarded may be regarded to be discharged at S 117 , at S 118 , the control part  60  updates the discharge dot count I* to 0 [counts] (that is, the discharge dot count I* is overwritten to 0 [counts]). Further, the first standard dot count N 1  is not limited to the aforementioned value. 
     At  116 , when the discharge dot count I* is the first standard dot count N 1  or larger (NO at S 116 ), at S 120 , the control part  60  determines whether or not the discharge dot count I* is below the predetermined second standard dot count N 2  [counts]. The second standard dot count N 2  is a value larger than the first standard dot count N 1  The second standard dot count N 2  is, for example, a value twice the first standard dot count N 1  [count], that is, 1177559040 [counts]. When the discharge dot count I* is below the second standard dot count N 2  (YES at S 120 ), at S 121 , the control part  60  (for example, the print control part  61 ) makes each part including the process execution part  10  execute the toner discharging process based on the discharge dot count I*. In  FIG. 4B , the process is simply shown as Execute TDP. Other processes at S 124 , S 127  and S 129  are the same. The discharge amount of the toner is calculated by multiplying the standard dot count value (first standard dot count N 1 ) by the amount of toner supplied to the photosensitive drum  11  from the development part  14  by the light emission (dot light emission) of one light emitting element  13   a  in a plurality of light emitting elements  13   a  in the optical head  13 . That is, the control part  60  (for example, the print control part  61 ) makes the optical head  13  execute the dot light emission based on the first standard dot count N 1 , and an amount of toner to be discharged is discharged from the development part  14 . 
     Since a part of the deteriorated toner to be discarded is considered to be discharged at S 121 , at S 122 , the control part  60  updates the discharge dot count I* to (I*−N 1 ) [counts]=(I*−588779520) [counts] (that is, the discharge dot count I* is overwritten to (I*−N 1 ) [counts]). Further, the second standard dot count N 2  is not limited to the aforementioned value. 
     At  120 , when the discharge dot count I* is the second standard dot count N 2  or larger (NO at S 120 ), at S 123 , the control part  60  determines whether or not the discharge dot count I* is below the predetermined third standard dot count N 3  [counts]. The third standard dot count N 3  is a value larger than the second standard dot count N 2  [counts]. The third standard dot count N 3  is, for example, a value three times the first standard dot count N 1  [count], that is, 1766338560 [counts]. When the discharge dot count I* is below the third standard dot count N 3  (YES at S 123 ), at S 124 , the control part  60  (for example, the print control part  61 ) makes each part including the process execution part  10  execute the toner discharging process based on the second standard dot count N 2 . The specific calculation method of the toner discharging amount is same as the calculation method at S 121 . 
     Since a part of the deteriorated toner to be discarded is considered to be discharged at S 124 , at S 125 , the control part  60  updates the discharge dot count I* to (I*−N 2 ) [counts]=(I*−1177559040) [counts] (that is, the discharge dot count I* is overwritten by (I*−N 2 ) [counts]). Further, the third standard dot count N 3  is not limited to the aforementioned value. 
     At  123 , when the discharge dot count I* is the third standard dot count N 3  or larger (NO at S 123 ), at S 126 , the control part  60  determines whether or not the discharge dot count I* is below the predetermined fourth standard dot count N 4  [counts]. The fourth standard dot count N 4  is a value larger than the third standard dot count N 3  [counts]. The fourth standard dot count N 4  is, for example, a value four times the first standard dot count N 1  [count], that is, 2355118080 [counts]. When the discharge dot count I* is below the fourth standard dot count N 4  (YES at S 126 ), at S 127 , the control part  60  (for example, the print control part  61 ) makes each part including the process execution part  10  execute the toner discharging process based on the third standard dot count N 3 . The specific calculation method of the toner discharging amount is same as the calculation method at S 121 . 
     Since a part of the deteriorated toner to be discarded is considered to be discharged at S 127 , at S 128 , the control part  60  updates the discharge dot count I* to (I*−N 3 ) [counts]=(I*−1766338560) [counts] (that is, the discharge dot count I* is overwritten by (I*−N 3 ) [counts]). Further, the fourth standard dot count N 4  is not limited to the aforementioned value. 
     When the discharge dot count I* is above the fourth standard dot count N 4  (NO at S 126 ), at S 129 , the control part  60  (for example, the print control part  61 ) makes each part including the process execution part  10  execute the toner discharging process based on the fourth standard dot count N 4 . The specific calculation method of the toner discharging amount is same as the calculation method at S 121 . 
     Since a part of the deteriorated toner to be discarded is considered to be discharged at S 129 , at S 130 , the control part  60  updates the discharge dot count I* to (I*−N 4 ) [counts]=(I*−2355118080) [counts] (that is, the discharge dot count I* is overwritten by (I*−N 4 ) [counts]). 
     After the toner discharging is executed and the discharge dot count I* are updated at S 118 , S 122 , S 125 , S 128 , and S 130 , the secondary transfer roller  54  is moved at S 119  by the separating operation control part  81  to come into contact with the intermediate transfer belt  31  so that the next print operation can be performed. 
     At S 111 , the measuring part  64  resets the drum count E* to 0 [counts] and resets the light emitting dot count F* to 0 [counts] at S 112 . 
     At S 113 , the control part  60  stores the discharge dot count I* in the memory part  68  and carries over the value of the discharge dot count I* at the time of Step S 113  to the time of the execution of the next toner discharging process. The print operation is completed at S 114 . 
     Next, the toner discharging operation (toner discharging process) in this embodiment will be described. At the time of executing the toner discharging operation, the bias applied to the primary transfer roller  40 , the charge roller  12 , the development roller  143 , the supply roller  142 , and the development blade  144  is the same bias as in the printing step. The whole surface of the discharging light irradiation part  16  is exposed, and continuously emits light until the dots for the toner discharging as instructed in each of Step S 117 , Step S 121 , Step S 124 , Step S 127 , and Step S 129  are consumed. The drive motor control part  79  drives the intermediate transfer belt  31  and the photosensitive drum  11  but does not drive the secondary transfer roller  54  since it is separated. The operation of the heat application roller  55   a  and the pressure application roller  55   b  by the fusing control part  77 , the operations of the rolled sheet feeder  51  by the carrying motor control part  78 , and the operations of the cutter  53  by the cutter operation control part  80  are also not performed so that the sheet feeding operation is not performed. 
     The movement of the toner at the time of toner discharging operation will be described. In the exposure process by the optical head  13 , by executing the dot light emission based on the standard dot count value (for example, the discharge dot count I*), first, toner is supplied (discharged) to the photosensitive drum  11  from the development device. The discharged toner on the photosensitive drum  11  is transferred to the intermediate transfer belt  31 , and since the secondary transfer roller  54  is separated, the discharged toner is scraped from the intermediate transfer belt  31  by the belt cleaning member  38  and accommodated in the waste toner collection part  24 . However, the discharged toner on the photosensitive drum  11  can be removed by the cleaning member  15  and accommodated by the waste toner accommodation part  140   b.    
     When the discharge dot count I* is larger than a value of 0 [counts] in a plurality of colors, the discharging operation is performed simultaneously at process execution parts  10  having a value of 0 or larger. 
     In the image forming apparatus  1 , when the image data of the next print job is received by the image data converter  67  during a print process based on one print job, the print operation of the second print job and the discharging operation are performed after the aforementioned print operation and the toner discharging operations are over. 
     Next, using  FIG. 5 , the operation of the print step in Comparative Example will be described.  FIG. 5  is a vertical cross-sectional view schematically showing a configuration of the image forming apparatus according to Comparative Example. The image forming apparatus  2  is different from the image forming apparatus  1  in that it is not provided with a rewinder  52  but provided with a stacker  56 . As in the image forming apparatus  2 , a printing embodiment in which a rolled sheet P is cut by a cutter  53  every few hundred [mm] and sheets are accommodated in the stacker  56  is called “roll to sheet printing” (roll-to-sheet printing). Other configurations (including control systems) are the same as the image forming apparatus  1 . 
     The head light emission command data of the first print job is shown as D 1 , and the head light emission command data of the second print job is shown as D 2 , and similarly so forth. The other operations (print process and the toner discharging process) are basically the same as the operations of the image forming apparatus  1 . 
       FIG. 6  is a flowchart showing an operation of the image forming apparatus according to Comparative Example. Next, the toner discharging control operation in Comparative Example will be described using the flowchart shown in  FIG. 6 . The flowchart of  FIG. 6  is carried out independently in each process execution part  10 Y,  10 M,  10 C,  10 K, andlOW, and the “*” in the flowchart represents Y, M, C, K, and W (each color). 
     At S 201 , when printing starts, the print control part  60  reads the discharge dot count I* from the memory part  68  at S 202 . Further, the discharge dot count I* is 0 [count] when the process shown in  FIG. 6  is carried out for the first time (first execution), but for the second time and thereafter, the value stored in the memory part  68  is used. The meaning of the discharge dot count I* is the same as in the image forming apparatus  1 . 
     At S 203 , the drum rotation number measuring part  65  starts the measurement of the rotation number of the photosensitive drum  11  and adds as a drum count E*. In this Comparative Example, for example, 1 is added to the drum count E* when the outer circumferential portion of the photosensitive drum  11  rotates by a length of 148 [mm] in the circumferential direction in the print process. Further, the initial value of the drum count E* is 0. 
     At S 204 , the dot light emitting number measuring part  66  starts to measure the exposure dot number (dot light emission number) of the LEDs of the optical head  13  and adds them up as the light emitting dot count F*. In this Comparative Example, for example, 1 is added to the light emission dot count F* when one LED of the optical head  13  emits 1 dot of light. 
     At S 205 , the print data monitoring part  62  checks whether or not it is a break of the print job, and when it is not a break, Step S 205  is repeated until it becomes a break of the print job (that is, until one print job is completed). Herein, the break of the print job is determined by finding that the next print job D 0  has not been delivered when the emission of the head light emission command data D 1  is completed. While the process at S 205  is repeated, the drum count E* and the light emission dot count F* are continuously added according to the print operation. 
     When the print data monitoring part  62  detects a break of the print job (YES at S 205 ), the discharge dot count I* is calculated using a similar method as at S 109  at S 206 . After that, at S 207 , the drum count E* is set to 0 [counts] and the light emitting dot count F* is set to 0 [counts] at S 208 . In  FIG. 6 , these processes are recited as “Reset” 
     At S 209 , the control part  60  determines whether or not the discharge dot count I* is 0 [counts] or larger, and in case of 0 or smaller (YES at S 209 ), at S 210 , the discharge dot count I* is reset to 0 [count]. 
     At S 211 , the control part  60  confirms whether or not data remains in the image data converter  67 , and when there is no data remaining (NO at S 211 ), it shifts to Step S 212  and stores in the memory part  69  that the discharge dot count I* is 0 [count] and completes the printing at S 213 . 
     At S 209 , when the discharge dot count I* has a value that is larger than 0 (NO at S 209 ), the control part  60  separates the secondary transfer roller  54  from the intermediate transfer belt  31  at S 214 . 
     Next, at S 215 , the control part  60  makes the optical head  13  execute the dot light emission for 154828800 [dots] that was set in advance and executes the toner discharging process (or Execute TDP at S 215  in  FIG. 6 ). 
     At S 216 ,  154828800  [counts] are subtracted from the discharge dot count at the time of Step S 216  (updates the discharge dot count I*). 
     At S 217 , when the discharge dot count I* obtained at S 216  is 0 or smaller (YES at S 217 ), at S 218 , the discharge dot count I* is reset to 0 [count]. 
     At S 219 , the control part  60  makes the secondary transfer roller  54  come in contact with the intermediate transfer belt  31  and shifts to Step S 211 . 
     At S 211 , the control part  60  checks whether or not the head light emission command data D 1  remains in the image data converter  67 . When there is no head light emission command data D 1  remaining (NO at S 211 ), it shifts to Step S 212 , and when the head light emission command data D 1  remains (YES at S 211 ), it returns to Step S 205 ). 
     &lt;&lt;1-4&gt;&gt; Evaluation Experiment 
     In the image forming apparatus of Comparative Example, when the discharge dot count I* is a value of 0 [counts] or larger, the toner discharging process is executed for every period between a print process based on a print job and a print process based on the next print job (break of print process), and the toner discharging amount in this toner discharging process is a constant amount that is not dependent on the discharge dot count I*. 
     Hereinafter, the evaluation and the results for confirming the effects of this embodiment by the toner discharging process (the toner discharging control shown in  FIGS. 4A and 4B ) will be shown. In this evaluation, after performing continuous printing under various conditions, halftone images were printed by dot forming and the occurrences of contamination were checked visually. Specifically, continuous printing was performed under the following conditions (Embodiment, Comparative Example). Further, when the print distance is referred in “rolls”, it shows the roll number of the rolled sheet when a rolled sheet having a length of 300 [m] for one roll is used as a print medium, and one print job is one roll. Only Experimental Example #10 (Comparative Example) performs roll-to-sheet printing, and one print job is a print job on 500 A6 size sheets. 
     Further, the method in which halftone images are printed by dot forming and the occurrences of contamination are checked visually will be described. In a halftone image, since the intervals of dots are narrow and the electrostatic latent images by dots on the photosensitive drum  11  are not isolated, the electrostatic latent image of the photosensitive drum  11  by dot forming overlap with the electrostatic latent image by dots around them. The surface electrical potential −500 [V] of the photosensitive drum  11  that should originally be white becomes larger, for example, −400 [V] from the overlapping of electrostatic latent image. And when the development roller  143  in which deteriorated toner is adhered on the perimeter and the photosensitive drum  11  come in contact by the rotation, the electrical potential by the development roller  143  and the deteriorated toner comes closer to −400 [V] of the photosensitive drum  11 , and halftone smear occurs, which is a smear in which the deteriorated toner is transferred to the overlapping part of the electrostatic latent image of the dots on the photosensitive drum  11 . 
     In this way, the determination of contamination when halftone printing is performed is judged based on whether or not toner that should not be adhered is adhered between the dots in the halftone images, and it is judged to have a smear (×) when the adherence of the toner between the dots is seen. When no toner adhered between the dots, it is judged to have no smear (◯). 
       FIG. 7  shows the a configuration, a discharge process, a printing rate (print duty), a print distance, and the result of smear judgment for the image forming apparatus according to Embodiment 1 (Experimental Examples #1 to #5) and the image forming apparatus of Comparative Example (Experimental Examples #6 to #11). Those experimental examples #1 to #5 are related to the invention. 
       FIG. 8  shows the relationship between the print distance [m] and the discharge dot counts I* [counts] in the print process in the image forming apparatus of Comparative Example (Experimental Example #10, #11). In  FIG. 8 , the discharge dot count when a halftone smear is generated is shown with a dotted line. In the roll-to-sheet printing, the toner discharging process is executed once per printing of 500 sheets of A6 size sheet (print distance of 75 [m]). On the other hand, in the roll-to-roll printing, since the toner discharging process is executed once per printing of a roll (printing distance of 300 [m], the number of execution of the toner discharging process is less than the roll-to-sheet printing. Therefore, in roll-to-roll printing, the discharge dot count I* is more likely to increase. For example, in the configuration of the process execution part  10  of this embodiment, when 3 rolls of rolled sheet (print distance 900 m) are subjected to continuous printing at 0.3% duty (toner discharging process is not executed), halftone smear occurs. The discharge dot count I* when the halftone smear occurs is, for example, 9088450560 [counts] (≈9.1×10 9  [counts]). 
       FIG. 9  shows the relationship between the print distance [the roll number of a 300 m rolled sheet] and the discharge dot count [counts] in the print process in the image forming apparatus according to Embodiment 1 (Experimental Examples #1, #2) and the image forming apparatus of the Comparative Example (Experimental Examples #6, #7). In  FIG. 9 , the discharge dot count when a halftone smear is generated is shown with a dotted line. When continuous printing (the toner discharging process is not executed) is performed at 0.3% duty, as described above, a halftone smear occurs after the third roll, so in the second roll of Experimental Example #6 (Comparative Example), smearing did not occur, and in the fourth roll of the Experimental Example #7, smearing occurs. On the other hand, in Experimental Example #1 (Embodiment) and Experimental Example #2 (Embodiment) with toner discharging, the discharge dot count I* at the time of completing the printing after the first roll was 3029120026 [counts], and the toner discharging process of Step S 129  in  FIG. 4B  is executed. Since the toner discharging process of Step S 129  is carried out after the second roll, as seen in Experimental Example #2 (Embodiment) at the time of completing the fourth roll, the halftone smear did not occur. 
       FIG. 10  shows the relationship between the print distance [the roll number of a 300 m rolled sheet] and the discharge dot count [counts] in the print process in the image forming apparatus according to Embodiment 1 (Experimental Examples #3, #4) and the image forming apparatus of Comparative Example (Experimental Examples #8, #9). In  FIG. 10 , the discharge dot count when a halftone smear is generated is shown with a dotted line. When continuous printing (the toner discharging process is not executed) is performed at 0.3% duty without toner discharging, as described above, a halftone smear occurs in the middle of the eighth roll, so in the sixth roll of Experimental Example #8 (Comparative Example), smearing did not occur, and in the tenth roll of Experimental Example #9, smearing occurred. On the other hand, in Experimental Example #3 (Embodiment) and Experimental Example #4 (Embodiment) in which the toner discharging process is executed, the discharge dot count I* at the time of completing the printing after the first roll was 1289016983 [counts], and the toner discharging process of Step S 124  in  FIG. 4B  is executed. The toner discharging process of Step S 124  is carried after the second roll up to the fifth roll. The discharge dot count I* at the time of completing the printing after the sixth roll was 1846306699 [counts], and the toner discharging process of Step S 127  in  FIG. 4B  is executed. For the toner discharging process from the seventh roll up to the ninth roll, a toner discharging process of Step S 124  is executed. At this time, as seen in Experimental Example #4 (Embodiment), there is no occurrence of the halftone smear after the completion of the tenth roll. 
     Experimental Example #5 (Embodiment) is a case in which the toner discharging process is executed at 5% duty. In Experimental Example #5, since the discharge dot count I* does not increase, the toner discharging process is not carried out and there is no smearing. When comparing Experimental Examples #1 and #2 (Embodiment), Experimental Examples #3 and #4 (Embodiment), and Experimental Examples #5 (Embodiment), Experimental Examples #3 and #4 are higher duty printing than Experimental Examples #1 and #2 (Embodiment). Further, the Experimental Example #5 (Embodiment) is higher duty printing when compared to Experimental Examples #3 and #4 (Embodiment). Further, the toner discharging amount at the time of the completion of printing the first roll is less for Experimental Examples #3 and #4 (Embodiments) than Experimental Examples #1 and #2 (Embodiments). Further, the toner discharging amount at the time of the completion of printing the first roll is less for Experimental Example #5 (Embodiment) than Experimental Examples #3 and #4 (Embodiments). 
     &lt;&lt;1-5&gt;&gt; Effects 
     As described above, according to Embodiment 1, since the toner discharging process (discharge of the deteriorated toner) is executed every time a print process based on one print job is completed, the quality of the printed images can be improved. 
     In the toner discharging process, when a low printing rate printing continued for a long time, the amount of toner discharged from the development part  14  is controlled to increase, so the deteriorated toner in the development part  14  can be sufficiently discharged. 
     When a high printing rate printing is executed, the amount of toner discharged from the development part  14  is controlled to decrease, so the discharging of the deteriorated toner can be effectively performed. 
     &lt;&lt;2&gt;&gt; Embodiment 2 
     &lt;&lt;2-1 &gt;&gt; Configuration of the Image Forming Apparatus 
     The basic configuration of an image forming apparatus  2  is the same as Embodiment 1. For this reason, in describing Embodiment 2,  FIGS. 1 to 3  will be referred. 
     &lt;&lt;2-2&gt;&gt; Operation of The Image Forming Apparatus 
       FIGS. 11A and 11B  are flowcharts showing an operation of the image forming apparatus according to Embodiment 2. The operation of the print process of the image forming apparatus of Embodiment 2 and that of the toner discharging process are basically the same as the operation of the image forming apparatus  1  according to Embodiment 1 as shown in  FIGS. 4A and 4B . Therefore, S 301 -S 307 , S 310 -S 313  and S 315 -S 330  in  FIGS. 11A and 11B  correspond to S 101 -S 107 , S 110 -S 113  and S 115 -S 130  in  FIGS. 4A and 4B , respectively. In Embodiment 2, the differences compared to the operation of the image forming apparatus  1  according to Embodiment 1 will be described. 
     The process shown in  FIGS. 11A and 11B  is different from the process of Embodiment 1 ( FIGS. 4A and 4B ) as described in the following. The first difference is that the calculation of the discharge dot count I* of Step S 109  in Embodiment 1 is performed before the completion of the print process based on one print job, that is, while the print process based on one print job is being carried out (Step S 309 ). The second difference is that, in Embodiment 1, the toner discharging process is executed after the completion of the print process based on one print job (Step S 105 ), but in Embodiment 2, the forced discharge control (forced discharge process) (Step S 332 ) is executed at the time it is determined that the discharge dot count I* has exceeded a predetermined threshold value (Step S 331 ) even if the print process based on one print job is not completed (Step S 305 ). Hereinafter, the conditions in which the forced discharge control is executed will be described. 
     At S 305 , when the control part  60  determines that a print process based on one print job has not yet be completed (NO at S 305 ), at S 331 , the control part  60  further determines whether or not the discharge dot count I* is a predetermined threshold value N 5  or higher (for example, 2355118080 [count]). When the discharge dot count I* is below the threshold value N 5  (for example, 2355118080 [count]) (NO at S 331 ), it shifts to Step S 309  and the print process is continued. When the discharge dot count I* reaches the threshold value N 5  (for example, 2355118080 [count]) (YES at S 331 ), at S 332 , the forced discharge control described below will be performed. After the completion of the forced discharge control, it goes back to Step S 309  and the print process is continued. The threshold value N 5  is also determined in the same fashion as the first to fourth standard dot counts N 1  to N 4  are determined. The value N 5  is determined such that the value is to be smaller than a discharge dot count at a timing when a halftone smear is generated, see  FIG. 8 . The value N 5  is not necessarily equal to the fourth standard dot count N 4 , but it is preferred that value N 5  is equal to or larger than the maximum value among the first to fourth standard dot counts N 1  to N 4 . Namely, the following formula is satisfied:
 
 N   5 ≧max ( N   1   , N   2   , N   3   , N   4 )
 
       FIG. 12  is a flowchart showing the operation of the forced discharge control (Step S 332 ) in detail, in which the rolled sheet P is a label sheet. At S 400 , when the forced discharge control is started, at S 401 , the cutter operation control part  80  makes the cutter  53  cut the label sheet (more specifically a middle section between the labels) in front of the next writing position (that is, the middle section means a space between the labels). 
     At S 402 , the print operation up to the cut position is executed and the printed label sheet is ejected outside the image forming apparatus so that it becomes a state in which the label sheets do not remain at least at the secondary transfer position. 
     At S 403 , the control part  60  suspends the operation of the printing process (print step operation). The operations executed at S 403  are, for example, stopping of the drive of the rolled sheet feeder  51  by the carrying motor control part  78 , the stopping of the drive of the intermediate transfer belt  31 , the secondary transfer roller  54 , and the photosensitive drum  11  by the drive motor control part  79 , the stopping of the drive of the optical head  13  by the head drive control part  75 , etc. 
     At S 404 , the secondary transfer roller  54  is separated from the intermediate transfer belt  31  by the separating operation control part  81 . 
     At S 405 , the control part  60  makes the parts including the process execution parts  10  execute the forced discharge control based on the discharge dot count I*. The discharge amount of the toner is calculated by multiplying the standard dot count value (discharge dot count I*) by the amount of toner supplied to the photosensitive drum  11  from the development part  14  by the light emission (dot light emission) of one light emitting element  13   a  in a plurality of light emitting elements  13   a  in the optical head  13 . That is, the control part  60  (for example, the print control part  61 ) makes the optical head  13  execute the dot light emission based on the discharge dot count I*, and an amount of toner to be discharged is discharged from the development part  14 . 
     At S 405 , since all toner to be discharged by the forced discharge control is discharged, at S 406 , the discharge dot count I* is reset to 0 [count]. 
     At S 407 , to execute the continuation of the print process based on the suspended print job, the secondary transfer roller  54  is brought into contact with the intermediate transfer belt  31  by the separating operation control part  81 . 
     At S 408  and S 409 , the drum count E* and the light emission dot count F* are reset to 0 [count]. 
     At S 410 , the print process based on the suspended print job is restarted. The operations executed at S 410  are, for example, restarting the drive of the rolled sheet feeder  51  by the carrying motor control part  78 , restarting the drive of the intermediate transfer belt  31 , the secondary transfer roller  54 , and the photosensitive drum  11  by the drive motor control part  79 , restarting the drive of the optical heads  13  by the head drive control part  75 , etc. With the aforementioned steps, the forced discharge control is completed (Step S 411 ). 
     In Embodiment 2, an example in which the label sheet is cut when carrying out the forced discharge control is shown, but the force discharge control can be executed without executing Step S 401  and Step S 402  (that is, the label sheet is not cut), and for example, in a state in which the label sheet remains in the fusing position and the secondary transfer positions, at S 403 , the heat application roller  55   a  and the pressure application roller  55   b  can be separated from the label sheet by the drive system, and at S 404 , the secondary transfer roller  54  and the intermediate transfer belt  31  can be separated from the label sheet. In that case, for example, at S 410 , the heat application roller  55   a  and the pressure application roller  55   b  are brought into contact with the label sheet. 
     &lt;&lt;2-3&gt;&gt; Effects 
     As described above, according to Embodiment 2, even while executing a print process based on one print job, when the discharge dot count I* reaches a predetermined threshold, the print process is suspended and a forced discharge process is executed, so the deteriorated toner can be discharged from the development part  14  before the quality of the print image decreases. Therefore, even in a case in which a print process based on one print job continues for a long time, the forced discharge process is executed at an appropriate timing and the print process is restarted after the deteriorated toner is discharged, the quality of the print image can be improved. 
     &lt;&lt;3&gt;&gt; Modified Example 
     In the aforementioned Embodiment, a color printer of a tandem system using a nonmagnetic one-component toner was described, but the present invention can be applied to an image forming apparatus using an electrographic system such as a direct transfer system printer or a printer using a two-component toner. 
     In Embodiments 1 and 2, examples in which the discharging location of the toner is the waste toner collection part  24  in the intermediate transfer belt  31  were described, but the toner (deteriorated toner) on the photosensitive drum  11  can be scraped off without transferring the toner (deteriorated toner) on the intermediate transfer belt  31  at the primary transfer part to accommodate the waste toner (deteriorated toner) in the waste toner accommodation part  140   b.