Patent Publication Number: US-11650519-B2

Title: Image forming apparatus and method to determine control temperatures for cooling control of inside of the image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 from Japanese Patent Applications No. 2020-158295, No. 2020-158297, and No. 2020-158299 that were filed on Sep. 23, 2020. The entire subject matter of the applications is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure are related to an image forming apparatus having a controller to perform cooling control to cool an inside of a main body housing. 
     Related Art 
     Heretofore, an image forming apparatus has been known that includes a controller configured to calculate a control temperature for triggering cooling control, based on an inside temperature (i.e., a temperature inside the image forming apparatus) obtained from an inside temperature sensor, an outside temperature (i.e., a temperature of air outside the image forming apparatus) obtained from an outside temperature sensor, and a driving state of a cartridge. 
     SUMMARY 
     In the meantime, if the image forming apparatus includes a plurality of cartridges, each individual cartridge would have a different driving state and a different temperature environment inside the image forming apparatus from those of the other cartridges. Therefore, according to how to calculate the control temperature(s), the image forming apparatus might be unable to appropriately cool the plurality of cartridges. 
     Aspects of the present disclosure are advantageous to provide one or more improved techniques for an image forming apparatus to perform appropriate cooling control for cooling a plurality of cartridges. 
     According to aspects of the present disclosure, an image forming apparatus is provided, which includes a main body housing, a first cartridge configured to store first developer, a second cartridge configured to store second developer, a first temperature sensor configured to detect an inside temperature as a temperature inside the main body housing, and a controller. The controller is configured to calculate a first control temperature corresponding to the first cartridge, using the inside temperature detected by the first temperature sensor, and a first coefficient to be multiplied by the inside temperature, calculate a second control temperature corresponding to the second cartridge, using the inside temperature detected by the first temperature sensor, and a second coefficient to be multiplied by the inside temperature, the second coefficient being different from the first coefficient, and perform cooling control to cool an inside of the main body housing when at least one selected from the first control temperature and the second control temperature is higher than a particular threshold. 
     According to aspects of the present disclosure, further provided is a method implementable on an image forming apparatus including a main body housing, a first cartridge, and a second cartridge. The method includes calculating a first control temperature corresponding to the first cartridge, using an inside temperature of the main body housing and a first coefficient to be multiplied by the inside temperature, calculating a second control temperature corresponding to the second cartridge, using the inside temperature of the main body housing, and a second coefficient to be multiplied by the inside temperature, the second coefficient being different from the first coefficient, and performing cooling control to cool an inside of the main body housing when at least one selected from the first control temperature and the second control temperature is higher than a particular threshold. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a housing, a first cartridge, a second cartridge, a temperature sensor, and a controller. The controller is configured to retrieve, from the temperature sensor, an inside temperature T in  which is a temperature of air inside the housing, calculate a first differential temperature ΔT B-first  using the inside temperature T in  and a first thermal resistance R in-B-first , the first differential temperature ΔT B-first  being a change in temperature of the first cartridge, the first thermal resistance R in-B-first  being a thermal resistance between the air inside the housing and the first cartridge, and calculate a second differential temperature ΔT B-second  using the inside temperature T in  and a second thermal resistance R in-B-second , the second differential temperature ΔT B-second  being a change in temperature of the second cartridge, the second thermal resistance R in-B-second  being a thermal resistance between the air inside the housing and the second cartridge and being different from the first thermal resistance R in-B-first . 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMANYING DRAWINGS 
         FIG.  1    is a cross-sectional view showing a configuration of a color printer of which a drawer includes a first temperature sensor, in an illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  2    shows a state in which the drawer is pulled out from a main body housing of the printer, in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  3    shows a color mode in which all developing rollers are in contact with corresponding photoconductive drums, a monochrome mode in which only one developing roller for black is in contact with a corresponding photoconductive drum, and an all-separation mode in which all the developing rollers are separated from the corresponding photoconductive drums, in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  4    shows a thermal circuit illustrating heat transfer to and from a regulating blade, in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  5    is a flowchart showing a sequence of processes by a controller of the color printer, in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  6    is a flowchart showing a procedure of a first temperature calculation process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  7    is a flowchart showing a procedure of a cooling control start/end determination process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIGS.  8 A and  8 B  are flowcharts showing a procedure of a when-cover-is-open process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  9    is a flowchart showing a procedure of a second temperature calculation process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG.  10    is a cross-sectional view showing a configuration of a color printer of which the main body housing includes the first temperature sensor, in a modification according to one or more aspects of the present disclosure. 
         FIG.  11    is a cross-sectional view showing a configuration of a color printer of which a cartridge includes the first temperature sensor, in another modification according to one or more aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     (General Overview) 
     According to aspects of the present disclosure, an image forming apparatus is provided, which includes a main body housing, a first cartridge configured to store first developer, a second cartridge configured to store second developer, a first temperature sensor configured to detect an inside temperature as a temperature inside the main body housing, and a controller. The controller is configured to calculate a first control temperature corresponding to the first cartridge, using the inside temperature detected by the first temperature sensor, and a first coefficient to be multiplied by the inside temperature, calculate a second control temperature corresponding to the second cartridge, using the inside temperature detected by the first temperature sensor, and a second coefficient to be multiplied by the inside temperature, the second coefficient being different from the first coefficient, and perform cooling control to cool an inside of the main body housing when at least one selected from the first control temperature and the second control temperature is higher than a particular threshold. 
     The controller may be further configured to calculate the first control temperature and the second control temperature at particular time intervals. 
     The controller may be further configured to calculate the first control temperature at a present time, using the first control temperature calculated at a previous time, and calculate the second control temperature at the present time, using the second control temperature calculated at the previous time. 
     The image forming apparatus may further include a second temperature sensor configured to detect an outside temperature as a temperature outside the main body housing. In this case, the controller may be further configured to calculate the first control temperature using the outside temperature detected by the second temperature sensor and a third coefficient to be multiplied by the outside temperature, as well as the detected inside temperature and the first coefficient, and calculate the second control temperature using the outside temperature detected by the second temperature sensor and a fourth coefficient to be multiplied by the outside temperature, as well as the detected inside temperature and the second coefficient. 
     The controller may be further configured to calculate the first control temperature using an amount of operation of the first cartridge, as well as the detected inside temperature and the first coefficient, and calculate the second control temperature using an amount of operation of the second cartridge, as well as the detected inside temperature and the second coefficient. 
     The first cartridge may be configured to store black developer as the first developer. Further, the second cartridge may be configured to store colored developer as the second developer. In this case, the controller may be further configured to, when forming a monochrome image, operate the second cartridge without operating the first cartridge, and when forming a color image, operate the first cartridge and the second cartridge. 
     The image forming apparatus may further include a fan configured to cool the inside of the main body housing. In this case, the controller may be further configured to set an air volume of air from the fan larger than when the cooling control is not performed. 
     The controller may be further configured to set a count of pages to be printed per unit time less than when the cooling control is not performed. 
     The image forming apparatus may further include a second temperature sensor configured to detect an outside temperature as a temperature of air outside the main body housing. In this case, the controller may be further configured to, when determining that the first cartridge has been replaced with a new cartridge, set the first control temperature based on the outside temperature detected by the second temperature sensor, and when determining that the second cartridge has been replaced with a new cartridge, set the second control temperature based on the outside temperature detected by the second temperature sensor. 
     The image forming apparatus may further include a fuser configured to fix a developer image onto a sheet. In this case, the first cartridge may be positioned closer to the fuser than the second cartridge is. Further, a distance between the first temperature sensor and the first cartridge may be shorter than a distance between the first temperature sensor and the second cartridge. 
     According to aspects of the present disclosure, further provided is a method implementable on an image forming apparatus including a main body housing, a first cartridge, and a second cartridge. The method includes calculating a first control temperature corresponding to the first cartridge, using an inside temperature of the main body housing and a first coefficient to be multiplied by the inside temperature, calculating a second control temperature corresponding to the second cartridge, using the inside temperature of the main body housing, and a second coefficient to be multiplied by the inside temperature, the second coefficient being different from the first coefficient, and performing cooling control to cool an inside of the main body housing when at least one selected from the first control temperature and the second control temperature is higher than a particular threshold. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a housing, a first cartridge, a second cartridge, a temperature sensor, and a controller. The controller is configured to retrieve, from the temperature sensor, an inside temperature T in  which is a temperature of air inside the housing, calculate a first differential temperature ΔT B-first  using the inside temperature T in  and a first thermal resistance R in-B-first , the first differential temperature ΔT B-first  being a change in temperature of the first cartridge, the first thermal resistance R in-B-first  being a thermal resistance between the air inside the housing and the first cartridge, and calculate a second differential temperature ΔT B-second  using the inside temperature T in  and a second thermal resistance R in-B-second , the second differential temperature ΔT B-second  being a change in temperature of the second cartridge, the second thermal resistance R in-B-second  being a thermal resistance between the air inside the housing and the second cartridge and being different from the first thermal resistance R in-B-first . 
     The controller may be further configured to calculate a first control temperature corresponding to the first cartridge in accordance with a first equation, calculate a second control temperature corresponding to the second cartridge in accordance with a second equation, and perform cooling control to cool an inside of the housing when at least one selected from the first control temperature and the second control temperature is higher than a particular threshold. The first equation may be expressed as T B-first (n)=T B-first (n−1)+ΔT B-first , where T B-first (n) represents the first control temperature at a present time, T B-first (n−1) represents the first control temperature at a previous time, and ΔT B-first  represents the first differential temperature. The second equation may be expressed as T B-second (n)=T B-second (n−1)+ΔT B-second , where T B-second (n) represents the second control temperature at a present time, T B-second (n−1) represents the second control temperature at a previous time, and ΔT B-second  represents the second differential temperature. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a main body housing, a drawer configured to hold a cartridge storing developer and to be withdrawn out of an image formation position in the main body housing, a first temperature sensor disposed at the drawer, and a controller. The controller is configured to perform cooling control to cool an inside of the main body housing, based on control temperature. In a case where the drawer is placed in the image formation position after the drawer is withdrawn out of the image formation position, when an elapsed time since the drawer was withdrawn out of the image formation position is shorter than a particular time, the controller calculates the control temperature based on a temperature detected by the first temperature sensor and a previous control temperature. In this case, when the elapsed time is equal to or longer than the particular time, the controller sets the control temperature based on the temperature detected by the first temperature sensor without using the previous control temperature. 
     The controller may be further configured to, when the drawer is out of the image formation position, calculate the control temperature based on a temperature detected by the first temperature sensor immediately before the drawer is withdrawn out of the image formation position, and the previous control temperature. 
     The controller may be further configured to calculate the control temperature based on the temperature detected by the first temperature sensor, the previous control temperature, and an amount of operation of the cartridge. 
     The drawer may include a first contact conductive to the first temperature sensor. Further, the main body housing may include a second contact conductive to the controller. In this case, when the drawer is out of the image formation position, the first contact may be disconnected from the second contact. Further, when the drawer is placed in the image formation position, the first contact may be connected with the second contact. 
     The image forming apparatus may further include a fan configured to cool the inside of the main body housing. In this case, the controller may be further configured to set an air volume of air from the fan larger than when the cooling control is not performed. 
     The controller may be further configured to set a count of pages to be printed per unit time less than when the cooling control is not performed. 
     The image forming apparatus may further include a second temperature sensor configured to detect an outside temperature as a temperature of air outside the main body housing. In this case, the controller may be further configured to calculate the control temperature based on the temperature detected by the first temperature sensor, the previous control temperature, the amount of operation of the cartridge, and the outside temperature detected by the second temperature sensor. 
     The controller may be further configured to, when the drawer is placed in the image formation position, and it is determined that the cartridge is replaced with a new cartridge, regardless of the elapsed time, set the control temperature based on the outside temperature detected by the second temperature sensor, without using the previous control temperature. 
     The cartridge may include a developing roller, and a container configured to store the developer. 
     The drawer may include a photoconductive body. 
     The first temperature sensor may be disposed upstream of the cartridge in a pull-out direction in which the drawer is withdrawn. 
     The image forming apparatus may further include a fuser configured to fix a developer image onto a sheet. In this case, the first temperature sensor may be disposed between the cartridge and the fuser in the pull-out direction. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a main body housing, a cartridge configured to be removably attached to the main body housing and to store developer, a first temperature sensor disposed at the cartridge, and a controller. The controller is configured to perform cooling control to cool an inside of the main body housing, based on control temperature. In a case where the cartridge is attached to the main body housing after the cartridge is removed from the main body housing, when an elapsed time since the cartridge was removed from the main body housing is shorter than a predetermined time, the controller calculates the control temperature based on a temperature detected by the first temperature sensor and a previous control temperature. In this case, when the elapsed time is equal to or longer than the predetermined time, the controller sets the control temperature based on the temperature detected by the first temperature sensor without using the previous control temperature. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a main body housing, a drawer configured to hold a cartridge storing developer and to be withdrawn out of an image formation position in the main body housing, a first temperature sensor disposed at the drawer, and a controller. The controller is configured to start and stop cooling control to cool an inside of the main body housing, based on control temperature. The control temperature is determined based on a temperature detected by the first temperature sensor. The controller continues the cooling control when the drawer is withdrawn out of the image formation position during the cooling control. The controller stops the cooling control when an elapsed time since the drawer was withdrawn out of the image formation position is equal to or longer than a particular time, in a state where the drawer remains withdrawn out of the image formation position. 
     The controller may be further configured to, when the drawer is placed in the image formation position, if the elapsed time is shorter than the particular time, stop the cooling control based on the control temperature. 
     The image forming apparatus may further include a fan configured to cool the inside of the main body housing. In this case, the controller may be further configured to set an air volume of air from the fan larger than when the cooling control is not performed. 
     The controller may be further configured to calculate the control temperature based on the temperature detected by the first temperature sensor and an amount of operation of the cartridge. 
     The drawer may include a first contact conductive to the first temperature sensor. Further, the main body housing may include a second contact conductive to the controller. In this case, when the drawer is out of the image formation position, the first contact may be disconnected from the second contact. Further, when the drawer is placed in the image formation position, the first contact may be connected with the second contact. 
     The image forming apparatus may further include a second temperature sensor configured to detect an outside temperature as a temperature of air outside the main body housing. In this case, the controller may be further configured to calculate the control temperature based on the temperature detected by the first temperature sensor, the amount of operation of the cartridge, and the outside temperature detected by the second temperature sensor. 
     The cartridge may include a developing roller, and a container configured to store the developer. 
     The drawer may include a photoconductive body. 
     The first temperature sensor may be disposed upstream of the cartridge in a pull-out direction in which the drawer is withdrawn. 
     The image forming apparatus may further include a fuser configured to fix a developer image onto a sheet. In this case, the first temperature sensor may be disposed between the cartridge and the fuser in the pull-out direction. 
     According to aspects of the present disclosure, further provided is an image forming apparatus that includes a main body housing, a cartridge configured to be removably attached to the main body housing and to store developer, a first temperature sensor disposed at the cartridge, and a controller. The controller is configured to perform start and stop control to cool an inside of the main body housing, based on control temperature. The control temperature is determined based on a temperature detected by the first temperature sensor. The controller continues the cooling control when the cartridge is removed from the main body housing. The controller stops the cooling control when an elapsed time since the cartridge was removed from the main body housing is equal to or longer than a predetermined time, in a state where the cartridge remains removed from the main body housing. 
     It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. Aspects of the present disclosure may be implemented on circuits (such as application specific integrated circuits) or in computer software as programs storable on computer-readable media including but not limited to RAMs, ROMs, flash memories, EEPROMs, CD-media, DVD-media, temporary storage, hard disk drives, floppy drives, permanent storage, and the like. 
     Illustrative Embodiment 
     Hereinafter, an illustrative embodiment according to aspects of the present disclosure will be described with reference to the accompanying drawings. As shown in  FIG.  1   , a color printer  1  includes a main body housing  10 , a sheet feeder  20  configured to feed a sheet P, an image forming engine  30  configured to form an image on the fed sheet P, a sheet conveyor  90  configured to discharge the sheet P with the image formed thereon, and a controller  100 . 
     The main body housing  10  has a first opening  10 A, a front cover  11 , a second opening  10 B, and a rear cover  12 . The first opening  10 A is an opening through which a below-mentioned unit U is inserted and drawn out. The front cover  11  is rotatable between an open position to open the first opening  10 A and a closed position to close the first opening  10 A. 
     The second opening  10 B is an opening through which the sheet P is removed. The rear cover  12  is rotatable between an open position to open the second opening  10 B and a closed position to close the second opening  10 B. 
     The sheet feeder  20  includes a feed tray  21  that accommodates sheets P, and a sheet feeding mechanism  22  configured to feed the sheets P from the feed tray  21  to the image forming engine  30 . 
     The image forming engine  30  includes a scanner unit  40 , a unit U, a transfer unit  70 , and a fuser  80 . 
     The scanner unit  40  includes a laser emitter, a polygon mirror, a lens, and a reflective mirror, which are not shown in any drawings. The scanner unit  40  is configured to emit a laser beam onto a surface of each photoconductive drum  61 . 
     The unit U is configured to be pulled out from the main body housing  10  through the first opening  10 A. The unit U includes four cartridges  50  and a drawer  60 . 
     Each cartridge  50  is attachable to and removable from the drawer  60 . Each cartridge  50  includes a toner container  51 , a developing roller  52 , and a regulating blade  53 . The toner container  51  is configured to store toner. The regulating blade  53  is configured to contact the developing roller  52  to regulate the layer thickness of toner on the developing roller  52 . The toner containers  51  of the four cartridges  50  store therein toner of different colors, i.e., yellow, magenta, cyan, and black, respectively. 
     Hereinafter, the four cartridges  50  containing the toner of the different colors (i.e., yellow, magenta, cyan, and black) may be represented by different reference characters  50 Y,  50 M,  50 C, and  50 K, respectively. As shown in  FIG.  1   , the four cartridges  50 Y,  50 M,  50 C, and  50 K are arranged in this order from the upstream in a sheet conveyance direction. It is noted that, in the present disclosure, to identify a specific element corresponding to a specific one of the toner colors from among, e.g., the photoconductive drums  61  or the developing rollers  52 , the specific element will be represented by the reference numeral with a corresponding one of the characters Y, M, C, and K added. 
     When the unit U is placed in a position for image formation in the main body housing  10 , the cartridge  50 Y is closest to the first opening  10 A, and the cartridge  50 K is farthest from the first opening  10 A. In the following description, the cartridge  50 K may be referred to as the “first cartridge  50 K,” and the cartridge  50 Y may be referred to as the “second cartridge  50 Y” The first cartridge  50 K is closer to the fuser  80  than the second cartridge  50 Y is. Further, it is noted that hereinafter, the position for image formation may be referred to as the “image formation position.” 
     The drawer  60  is configured to be pulled out in a direction perpendicular to the vertical direction from the image formation position in the main body housing  10 . The image formation position is a position of the drawer  60  when image formation is performed. The drawer  60  includes the four photoconductive drums  61 , four chargers (not shown), a frame  62  that holds the four cartridges  50  detachably attached thereto, a first temperature sensor SE 1 , and a first contact CN 1 . The four photoconductive drums  61  and the four chargers are disposed in the frame  62 , corresponding to the four developing rollers  52 . 
     The frame  62  is supported by the main body housing  10  to be movable in the direction perpendicular to the vertical direction. The first temperature sensor SE 1  is, for instance, a thermistor. The first temperature sensor SE 1  is configured to detect an inside temperature that is a temperature inside the main body housing  10 . The first contact CN 1  is conductive to the first temperature sensor SE 1  via wiring. 
     The first temperature sensor SE 1  and the first contact CN 1  are disposed upstream of the first cartridge  50 K as the most upstream one of the cartridges  50  in a pull-out direction D for the drawer  60 . In other words, the first temperature sensor SE 1  and the first contact CN 1  are positioned between the first cartridge  50 K and the fuser  80  in the pull-out direction D for the drawer  60 . In the pull-out direction D for the drawer  60 , a distance between the first temperature sensor SE 1  and the first cartridge  50 K is shorter than a distance between the first temperature sensor SE 1  and the second cartridge  50 Y. 
     The main body housing  10  has a second contact CN 2  that is conductively connected with the controller  100  via wiring. The first contact CN 1  is connected with the second contact CN 2  in a state where the drawer  60  is in the image formation position in the main body housing  10 . Specifically, the first contact CN 1  is connected to the second contact CN 2  when the drawer  60  is placed in the image formation position. 
     As shown in  FIG.  2   , the first contact CN 1  is apart from the second contact CN 2  in a state where the drawer  60  is pulled out from the main body housing  10 . Specifically, when the drawer  60  is out of the image formation position, the first contact CN 1  is separated from the second contact CN 2 . 
     Referring back to  FIG.  1   , the transfer unit  70  includes a driving roller  71 , a driven roller  72 , a conveyance belt  73 , and four conveyance rollers  74 . The transfer belt  73  is an endless belt. The driving roller  71  and the driven roller  72  are configured to rotate the conveyance belt  73 . Each of the four conveyance rollers  74  is disposed to face a corresponding one of the photoconductive drums  61  across the conveyance belt  73  and pinch the conveyance belt  73  with the corresponding photoconductive drum  61 . 
     The fuser  80  is configured to fix a toner image onto a sheet P. The fuser  80  includes a heating roller  81  and a pressure roller  82 . The heating roller  81  is heated by a heater H. The pressure roller  82  is pressed against the heating roller  81 . 
     When the drawer  60  is in the image formation position in the main body housing  10 , the color printer  1  is allowed to perform image formation. When the drawer  60  is in the image formation position, the photoconductive drums  61  and the transfer unit  70  are in contact with each other, and the scanner unit  40  is allowed to expose a particular position of each photoconductive drum  61 . In the image forming engine  30 , first, a surface of each photoconductive drum  61  is uniformly charged by the corresponding charger and then exposed by the scanner unit  40 . Thereby, an electrostatic latent image based on image data is formed on each photoconductive drum  61 . Thereafter, the toner in the corresponding toner container  51  is supplied, via the corresponding developing roller  52 , to the electrostatic latent image on each photoconductive drum  61 . Thus, a toner image is formed on each photoconductive drum  61 . 
     Next, the toner image formed on each photoconductive drum  61  is transferred onto the sheet P as the sheet P fed on the conveyance belt  73  passes between each photoconductive drum  61  and the corresponding transfer roller  74 . Then, as the sheet P passes between the heating roller  81  and the pressure roller  82 , the toner image transferred on the sheet P is thermally fixed. 
     The sheet conveyor  90  serves as a discharge mechanism to discharge the sheet P fed out from the image forming engine  30  onto the discharge tray  13  of the main body housing  10 . The sheet conveyor  90  also serves as a re-conveyance mechanism to invert the surfaces of the sheet P with an image on one side thereof and re-convey the inverted sheet P to the image forming engine  30 . Specifically, the sheet conveyor  90  has a conveyance path  91 , a discharge roller  92 , and a re-conveyance path  93 . 
     The conveyance path  91  is configured to guide the sheet P from the fuser  80  toward the discharge tray  13 . 
     The discharge roller  92  is configured to rotate both forward and backward. When rotating forward, the discharge roller  92  discharges the sheet P fed out from the image forming engine  30  toward the discharge tray  13 . When rotating backward, the discharge roller  92  conveys the sheet P in such a manner as to pull the sheet P back into the main body housing  10 . 
     The re-conveyance path  93  is configured to guide the sheet P with an image formed on one side thereof by the image forming engine  30 , back to the image forming engine  30  through under the sheet feeder  20 . 
     In the sheet conveyor  90 , after completion of image formation, the sheet P fed out from the image forming engine  30  is conveyed along the conveyance path  91 , and is discharged onto the discharge tray  13  outside the main body housing  10  by the discharge roller  92  rotating forward. Further, when another image needs to be formed on the other side of the sheet P with an image formed on one side thereof, the discharge roller  92  is rotated backward before the whole sheet P is completely discharged out of the main body housing  10 . Thereby, the sheet P is pulled back into the main body housing  10  again and is conveyed from the conveyance path  91  to the re-conveyance path  93 . Thereafter, the sheet P is conveyed along the re-conveyance path  93  and is again conveyed to the image forming engine  30  by the sheet feeder  20 . 
     The main body housing  10  has a fan  14 , an intake port  15 , and a second temperature sensor SE 2 . 
     The fan  14  is for cooling the inside of the main body housing  10 . Specifically, the fan  14  is configured to suck out air inside the main body housing  10  and exhaust the air outside the main body housing  10 . The fan  14  is disposed above the fuser  80 . The fan  14  is located between the fuser  80  and the drawer  60  in the pull-out direction D for the drawer  60 . 
     The intake port  15  is an opening for introducing outside air into the main body housing  10 . The intake port  15  is disposed on an opposite side of the drawer  60  across the fuser  80 . The intake port  15  is located below the fuser  80 . Namely, the intake port  15  is disposed in such a position that the intake port  15  is not easily affected by the heat generated by the fuser  80  and the cartridges  50 . 
     For instance, the second temperature sensor SE 2  is a thermistor. The second temperature sensor SE 2  is disposed to face an inside of the intake port  15 . The second temperature sensor SE 2  is configured to detect a temperature of the air introduced via the intake port  15 , thereby obtaining an outside temperature that is a temperature of air outside the main body housing  10 . The second temperature sensor SE 2  is connected with the controller  100  via wiring. 
     The color printer  1  further includes a front cover opening/closing sensor  11 A and a rear cover opening/closing sensor  12 A. The front cover opening/closing sensor  11 A is for detecting opening and closing of the front cover  11 . The rear cover opening/closing sensor  12 A is for detecting opening and closing of the rear cover  12 . 
     The front cover opening/closing sensor  11 A is configured to be in contact with a part of the front cover  11  when the front cover  11  is closed, thereby outputting an ON signal to the controller  100 . Further, the front cover opening/closing sensor  11 A is configured to be separated from the front cover  11  when the front cover  11  is open, thereby outputting an OFF signal to the controller  100 . Likewise, the rear cover opening/closing sensor  12 A is configured to be in contact with a part of the rear cover  12  when the rear cover  12  is closed, thereby outputting an ON signal to the controller  100 . Further, the rear cover opening/closing sensor  12 A is configured to be separated from the rear cover  12  when the rear cover  12  is open, thereby outputting an OFF signal to the controller  100 . 
     The controller  100  includes a CPU  101 , a ROM  102 , and a RAM  103 , and is configured to perform various processes in response to receipt of commands (e.g., a print command), in accordance with pre-prepared programs  104 . The programs  104  may be stored in the ROM  102 . As shown in  FIG.  3   , the controller  100  is configured to execute a color mode for forming a multi-color image, a monochrome mode for forming a monochrome image, and an all-separation mode. The controller  100  controls a separation mechanism  200  for causing each individual developing roller  52  to be in contact with or separate from the corresponding photoconductive drum  61 , thereby switching the mode to be executed from one mode to another among the above three modes. 
     Specifically, in the color mode, the controller  100  brings all the developing rollers  52 Y,  52 M,  52 C, and  52 K into contact with the corresponding photoconductive drums  61 Y,  61 M,  61 C, and  61 K, respectively, and rotates all the developing rollers  52  and all the photosensitive drums  61 . Namely, when forming a multi-color image, the controller  100  operates all the cartridges  50  including the first cartridge  50 K and the second cartridge  50 Y. 
     In the monochrome mode, the controller  100  brings only the developing roller  52 K for black into contact with the photoconductive drum  61 K, and makes the developing rollers  52 Y,  52 M, and  52 C for the other three colors separate from the corresponding photoconductive drums  61 Y,  61 M, and  61 C. Further, in the monochrome mode, the controller  100  rotates only the developing roller  52 K and stops the other developing rollers  52 Y,  52 M, and  52 C, while rotating all the photoconductive drums  61 . Namely, when forming a monochrome image, the controller  100  operates the first cartridge  50 K without operating the cartridges  50 Y,  50 M, and  50 C including the second cartridge  50 Y. 
     Further, for instance, when cleaning the photoconductive drums  61 , the controller  100  executes the all-separation mode to separate all the developing rollers  52 Y,  52 M,  52 C, and  52 K from the corresponding photoconductive drums  61 Y,  61 M,  61 C, and  61 K. 
     The controller  100  is configured to perform cooling control to cool the inside of the main body housing  10  based on temperatures for control. Here, the temperatures for control are temperatures estimated as temperatures of the cartridges  50 . More specifically, in the illustrative embodiment, the temperatures for control are estimated as temperatures T B  of the regulating blades  53 . It is noted that hereinafter, the temperatures for control may be referred to as the “control temperatures.” 
     The controller  100  is configured to calculate a first control temperature corresponding to the first cartridge  50 K and a second control temperature corresponding to the second cartridge  50 Y. The controller  100  performs the cooling control based on a higher one of the first and second control temperatures. 
     Specifically, the controller  100  calculates a differential temperature, which is a change in temperature of the regulating blade  53  from the time of previous calculation to the present time, at particular time intervals, based on the inside temperature, the outside temperature, and a driving state of the corresponding developing roller  52 . Then, the controller  100  calculates the sum of the obtained differential temperature and the previously calculated temperature of the regulating blade  53  as a current temperature of the regulating blade  53 . 
     Specifically, a current temperature T B (n) [° C.] of the regulating blade  53  is calculated using a previously calculated temperature T B (n−1) [° C.] and a differential temperature ΔT B  [° C.] of the regulating blade  53  in accordance with the following equation (1).
 
 T   B ( n )= T   B ( n− 1)+Δ T   B   (1)
 
     Here, the differential temperature ΔT B [° C.] of the regulating blade  53  in the equation (1) is calculated, as shown in  FIG.  4   , using a heat quantity ΔE in-B (n)[J] transferred from the air inside the main body housing  10  (more specifically, from around the first temperature sensor SE 1 ) to the regulating blade  53 , a heat quantity ΔE out-B (n)[J] transferred from the regulating blade  53  to the outside air, and a heat generation amount Q B [W] of the regulating blade  53  (i.e., an amount of heat generated at the regulating blade  53 ), in accordance with the following equation (2):
 
Δ T   B =(Δ E   in-B ( n )−Δ E   out-B ( n )+ Q   B   ×Δt )/ C   B ,  (2)
 
where C B [J/° C.] is a heat capacity of the regulating blade  53 , and Δt [sec] is a time from the time of previous calculation to the present time.
 
     The heat quantity ΔE in-B (n)[J] transferred from the air (hereinafter referred to as the “inside air”) inside the main body housing  10  to the regulating blade  53 , in the equation (2), is calculated using a previously obtained inside temperature (i.e., a temperature inside the main body housing  10 ) T in (n−1)[° C.], the previously calculated temperature T B (n−1)[° C.] of the regulating blade  53 , and a thermal resistance R in-B [° C./W] between the inside air and the regulating blade  53 , in accordance with the following equation (3).
 
Δ E   in-B ( n )=( T   in ( n− 1)− T   B ( n− 1))×Δ t/R   in-B   (3)
 
     The heat quantity Δ E   out-B (n)[J] transferred from the regulating blade  53  to the outside air, in the equation (2), is calculated using a previously obtained outside temperature T out (n−1)[° C.], the previously calculated temperature T B (n−1)[° C.] of the regulating blade  53 , and a thermal resistance R out-B [° C./W] between the outside temperature and the regulating blade  53 , in accordance with the following equation (4).
 
Δ E   out-B ( n )=( T   B ( n− 1)− T   out ( n− 1))×Δ t/R   out-B   (4)
 
     R in-B  in the equation (3) is set to different values between when the first control temperature is calculated and when the second control temperature is calculated. Likewise, R out-B  in the equation (4) is set to different values between when the first control temperature is calculated and when the second control temperature is calculated. In other words, R in-B  in a first function used to calculate the first control temperature is different from R in-B  in a second function used to calculate the second control temperature. Further, R out-B  in the first function used to calculate the first control temperature is different from R out-B  in the second function used to calculate the second control temperature. 
     Specifically, a distance between the first temperature sensor SE 1  and the first cartridge  50 K is different from a distance between the first temperature sensor SE 1  to the second cartridge  50 Y. Therefore, a coefficient 1/R in-B  is set to different values between the first function and the second function. The coefficient 1/R in-B  is a coefficient to be multiplied, for instance, by the inside temperature as the temperature value previously obtained by the first temperature sensor SE 1 . Here, 1/R in-B  in the first function corresponds to a first coefficient. Further, 1/R in-B  in the second function corresponds to a second coefficient. 
     In addition, a distance between a particular location outside the main body housing  10  and the first cartridge  50 K is different from a distance between the particular location outside the main body housing  10  and the second cartridge  50 Y. Therefore, a coefficient 1/R out-B  is set to different values between the first function and the second function. The coefficient 1/R out-B  is a coefficient to be multiplied, for instance, by the outside temperature T out (n−1) as the temperature value previously obtained by the second temperature sensor SE 2 . Here, 1/R out-B  in the first function corresponds to a third coefficient. Further, 1/R out-B  in the second function corresponds to a fourth coefficient. 
     The heat generation amount Q B  of the regulating blade  53  in the equation (2) is a parameter varying depending on an amount of operation of the cartridge  50 . Namely, the heat generation amount Q B  corresponds to the amount of operation of the cartridge  50 . The heat generation amount Q B  may be set, for instance, based on a drive time, a stop time, and a rotation speed of the developing roller  52 . 
     From the equations (2) to (4), the controller  100  calculates the temperature T B  of the regulating blade  53 K, that is, the first control temperature, based on the inside temperature T in (n−1) (i.e., the temperature value previously obtained by the first temperature sensor SE 1 ), the first coefficient 1/R in-B , the previous temperature T B (n−1) (i.e., the previous first control temperature) of the regulating blade  53 K, the heat generation amount Q B  (which corresponds to the amount of operation of the first cartridge  50 K), the outside temperature T out (n−1) (i.e., the temperature value previously obtained by the second temperature sensor SE 2 ), and the third coefficient 1/R out-B . 
     In addition, the controller  100  calculates the temperature T B  of the regulating blade  53 Y, that is, the second control temperature, based on the inside temperature T in (n−1) (i.e., the temperature value previously obtained by the first temperature sensor SE 1 ), the second coefficient 1/R in-B , the previous temperature T B (n−1) (i.e., the previous second control temperature) of the regulating blade  53 Y, the heat generation amount Q B  (which corresponds to the amount of operation of the second cartridge  50 Y), the outside temperature T out (n−1) (i.e., the temperature value previously obtained by the second temperature sensor SE 2 ), and the fourth coefficient 1/R out-B . 
     The controller  100  obtains the aforementioned constants (e.g., Q B , C B , R in-B , and R out-B ) from a memory, according to each of states regarding the color printer  1 . The states regarding the color printer  1  may include, but are not limited to, the driving state of the corresponding developing roller  52 , an open/closed state of the rear cover  12 , a case where simplex/duplex printing is performed, a size of the sheet(s) P, an operating state of the fan  14 , and an operating state of the fuser  80 . Then, using the obtained constants, the controller  100  calculates the temperature of the corresponding regulating blade  53 . Here, examples of the memory may include, but are not limited to, the ROM  102  and the RAM  103 . For instance, the memory may store a map showing the aforementioned plurality of constants associated with each of a plurality of combinations of the aforementioned states regarding the color printer  1 . For instance, for the closed state of the rear cover  12 , the aforementioned constants are set to predetermined values, respectively. When the rear cover  12  is in the open state, R in-B  and R out-B  among the aforementioned constants are set to values different from the respective predetermined values. 
     In the illustrative embodiment, the driving state of the developing roller  52  is a state depending on whether a motor for driving the developing roller  52  is driven or stopped and a rotational speed of the developing roller  52 . The states of the fuser  80  may include, but are not limited to, a state in which printing is in progress, a ready state in which a temperature of the fuser  80  is maintained at a lower level than when printing is performed, and a sleep state in which the fuser  80  is turned off. 
     In principle, the controller  100  determines the first control temperature and the second control temperature by calculation using the first function and the second function. However, in some exceptional circumstances, the controller  100  may set the first control temperature and the second control temperature without using any of the first and second functions. 
     Further, in principle, the controller  100  starts and terminates the cooling control based on the first control temperature and the second control temperature. However, in some exceptional circumstances, the controller  100  may terminate the cooling control without depending on any of the first and second control temperatures. 
     The controller  100  is configured to continue the cooling control when the drawer  60  is out of the image formation position during the cooling control. 
     Operations by the controller  100  will be described in detail below. The controller  100  repeatedly performs a process shown in  FIG.  5   . 
     In the process shown in  FIG.  5   , the controller  100  first performs a first temperature calculation process (S 1 ). As shown in  FIG.  6   , in the first temperature calculation process, the controller  100  first obtains the inside temperature and the outside temperature from the first temperature sensor SE 1  and the second temperature sensor SE 2 , respectively, and also obtains the constants (e.g., Q B , C B , R in-B , and R out-B ) for each of the first and second functions from the memory (S 101 ). Specifically, in S 101 , the controller  100  determines the states regarding the color printer  1  such as the driving state of each developing roller  52  in the first cartridge  50 K and the second cartridge  50 Y, and obtains, based on the determined states, the constants (e.g., Q B , C B , R in-B , and R out-B ) to be used in each of the first and second functions. 
     After S 101 , the controller  100  calculates the temperature T B (n) of the regulating blade  53 K, that is, the first control temperature based on the first function, and calculates the temperature T B (n) of the regulating blade  53 Y, that is, the second control temperature based on the second function (S 102 ). Specifically, in S 102 , the controller  100  calculates the first control temperature by substituting the temperature T B  of the regulating blade  53 K, the inside temperature Tin, and the outside temperature Tout, which are stored in the memory, into T B (n−1), T in (n−1), and T out (n−1) in the first function, respectively. Further, in S 102 , the controller  100  calculates the second control temperature by substituting the temperature T B  of the regulating blade  53 Y, the inside temperature Tin, and the outside temperature Tout, which are stored in the memory, into T B (n−1), T in (n−1), and T out (n−1) in the second function, respectively. 
     T B , T in , and T out  in the first execution of S 102  (i.e., when the calculation in S 102  is made for the first time in the color printer  1 ) may be previously stored as initial values in the memory, or may be set based on the inside temperature and the outside temperature obtained this time, respectively. 
     After S 102 , the controller  100  updates T B , T in , and T out  by overwriting T B , T in , and T out  in the memory with the temperature T B (n) of each of the regulation blades  53 K and  53 Y calculated this time and the inside temperature T in (n) and the outside temperature T out (n) obtained this time (S 103 ). Thereafter, the controller  100  terminates the first temperature calculation process. In the illustrative embodiment, T B , T in , and T out  are overwritten as described above. However, a particular number of values, for each of the temperatures T B , T in , and T out , may be stored in a time-series order. 
     Referring back to  FIG.  5   , after S 1 , the controller  100  performs a cooling control start/end determination process (S 2 ). As shown in  FIG.  7   , in the cooling control start/end determination process, the controller  100  first obtains, from the memory, the temperature T B  of the regulating blade  53 K in the first cartridge  50 K and the temperature T B  of the regulating blade  53 Y in the second cartridge  50 Y (S 201 ). After S 201 , the controller  100  selects a higher one of the temperature T B  of the regulating blade  53 K and the temperature T B  of the regulating blade  53 Y (S 202 ). 
     After S 202 , the controller  100  determines whether or not the selected temperature T B  is equal to or lower than a first threshold T 1  (S 203 ). When determining that the temperature T B  is not equal to or lower than the first threshold T 1  (i.e., the temperature T B  is higher than the first threshold T 1 ) (S 203 : No), the controller  100  determines whether or not the temperature T B  is equal to or lower than a second threshold T 2  which is higher than the first threshold T 1  (S 204 ). 
     Here, the second threshold T 2  is a temperature equal to or lower than a melting point of the toner. The second threshold T 2  may be the same value as the first threshold T 1 . 
     When determining in S 204  that the temperature T B  is not equal to or lower than the second threshold T 2  (i.e., the temperature T B  is higher than the second threshold T 2 ) (S 204 : No), the controller  100  starts the cooling control (S 206 ). Then, the controller  100  terminates the cooling control start/end determination process. If the controller  100  begins to execute S 206  during the cooling control, the controller  100  continues the cooling control. When making an affirmative determination in S 203  (i.e., S 203 : Yes) or S 204  (i.e., S 204 : Yes), the controller  100  terminates the cooling control (S 205 ). Thereafter, the controller  100  terminates the cooling control start/end determination process. 
     The controller  100  performs the following process based on the temperature T B  during the cooling control. During the cooling control, when the temperature T B  is equal to or lower than a third threshold T 3  that is higher than the second threshold T 2 , the controller  100  sets an air volume of air from the fan  14  larger than when the cooling control is not performed. Specifically, in the cooling control, the controller  100  rotates the fan  14  at a higher rotational speed than a rotational speed before the cooling control is started. 
     Further, during the cooling control, when the temperature T B  is higher than the third threshold T 3  and is equal to or lower than a fourth threshold T 4  that is higher than the third threshold T 3 , the controller  100  sets the number of pages to be printed per unit time in printing control to be less than when the cooling control is not performed. Applicable methods for reducing the number of pages to be printed may include, but are not limited to, a method of setting the rotational speed of each photoconductive drum  61  and the rotational speed of each developing roller  52  lower than when normal printing is performed, thereby setting a conveyance speed for the sheet P lower than when the normal printing is performed, and a method of setting a conveyance interval between the sheets P wider than when the normal printing is performed. In the normal printing, the controller  100  performs such printing control as to maximize the number of pages printed per unit time, that is, printing control before the cooling control is started. 
     In the method of reducing the conveyance speed for the sheet P, the rotational speed of each developing roller  52  is reduced. Herewith, it is possible to suppress generation of heat due to friction between the developing rollers  52  and the regulating blades  53 , thereby cooling the cartridges  50 . In this case, as an example, the conveyance speed for the sheet P may be set to half of a conveyance speed applied when the cooling control is not performed. In the method of increasing the conveyance interval between the sheets P, a frequency with which the sheet P, which takes heat from the heating roller  81 , is fed to the fuser  80  is reduced. Herewith, it is possible to suppress an amount of heat generated by the fuser  80  and suppress an increase in the inside temperature Tin, thereby cooling the cartridges  50 . 
     When the temperature T B  is higher than the fourth threshold T 4  during the cooling control, the controller  100  stops printing. Herewith, it is possible to suppress generation of heat due to the friction between the developing rollers  52  and the regulating blades  53  and suppress the amount of heat generated by the fuser  80 , thereby cooling the cartridges  50 . 
     Referring back to  FIG.  5   , after S 2 , the controller  100  determines whether there is a print job to be executed (S 3 ). When determining that there is a print job to be executed (S 3 : Yes), the controller  100  performs a printing process based on the print job (S 4 ). After S 4 , or when determining that there is not a print job to be executed (S 3 : No), the controller  100  determines whether the front cover  11  is open, based on the signal from the front cover opening/closing sensor  11 A (S 5 ). 
     When determining in S 5  that the front cover  11  is not open (S 5 : No), the controller  100  goes back to S 1 . Meanwhile, when determining that the front cover  11  is open (S 5 : Yes), the controller  100  performs a when-cover-is-open process (S 6 ). Thereafter, the controller  100  goes back to S 1 . 
     As shown in  FIGS.  8 A and  8 B , in the when-cover-is-open process, the controller  100  first determines whether there is a response from the first temperature sensor SE 1  disposed in the drawer  60 , that is, whether the first contact CN 1  is disconnected from the second contact CN 2 , thereby determining whether the drawer  60  has been withdrawn out of the image formation position in the main body housing  10  (S 601 ). When determining that the drawer  60  has been withdrawn out of the image formation position in the main body housing  10  (S 601 : Yes), the controller  100  determines whether or not an elapsed time TM since the drawer  60  was withdrawn out of the image formation position is equal to or longer than a particular time Tth (S 602 ). 
     When determining that the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is not equal to or longer than the particular time Tth (S 602 : No), the controller  100  performs a second temperature calculation process (S 603 ). As shown in  FIG.  9   , the second temperature calculation process includes S 111  and S 113  which are partially different from S 101  and S 103  in the aforementioned first temperature calculation process (see  FIG.  6   ), respectively, and further includes S 102  which is substantially the same as S 102  in the first temperature calculation process. 
     In S 111 , the controller  100  obtains the outside temperature from the second temperature sensor SE 2  and obtains the constants (e.g., Q B , C B , R in-B , and R out-B ) used for each of the first and second functions from the memory, but does not obtain the inside temperature from the first temperature sensor SE 1 . After S 111 , the controller  100  executes S 102 , and then goes to S 113 . 
     In S 113 , the controller  100  overwrites T B  and T out  in the memory with the temperature T B (n) of each of the regulating blades  53 K and  53 Y calculated this time and the outside temperature T out (n) obtained this time, thereby updating T B  and T out . However, the controller  100  does not update the inside temperature Tin in the memory. Thus, the inside temperature Tin in the memory is maintained at the detected value of the first temperature sensor SE 1  that has been obtained by the controller  100  immediately before the drawer  60  is withdrawn out of the image formation position. Therefore, when determining in S 601  that the drawer  60  has been withdrawn out of the image formation position in the main body housing  10  (S 601 : Yes), the controller  100  calculates in S 102  the temperature T B (n) of each of the regulating blades  53 K and  53 Y, based on the detected value of the first temperature sensor SE 1  that has been obtained immediately before the drawer  60  is withdrawn out of the image formation position, and the previous temperature T B  of each of the regulating blades  53 K and  53 Y. 
     Referring back to  FIGS.  8 A and  8 B , when determining that the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is equal to or longer than the particular time Tth (S 602 : Yes), the controller  100  stops the cooling control regardless of the temperatures T B  of the regulating blades  53 K and  53 Y (S 604 ). Namely, the controller  100  stops the cooling control when the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is equal to or longer than the particular time Tth, in a state where the drawer  60  remains withdrawn out of the image formation position. 
     After S 603  or S 604 , the controller  100  determines whether there is a response from the first temperature sensor SE 1 , that is, whether the first contact CN 1  is connected with the second contact CN 2 , thereby determining whether the drawer  60  has been placed in the image formation position in the main body housing  10  (S 605 ). When determining that the drawer  60  has not been placed in the image formation position in the main body housing  10  (S 605 : No), the controller  100  goes back to S 602 . 
     When determining that the drawer  60  has been placed in the image formation position in the main body housing  10  (S 605 : Yes), the controller  100  determines whether at least one of the first cartridge  50 K and the second cartridge  50 Y, which are the targets for the temperature calculation, has been replaced with a new one (S 606 ). Here, the determination in S 606  as to whether at least one of the first cartridge  50 K and the second cartridge  50 Y has been replaced with a new one may be made, for instance, based on information stored in an IC chip attached to each of the cartridges  50 K and  50 Y, or by detecting a position of a protrusion provided at each of the cartridges  50 K and  50 Y and configured to move from a new-cartridge position to an old-cartridge position. 
     When determining that at least one of the first cartridge  50 K and the second cartridge  50 Y has been replaced with a new one (S 606 : Yes), the controller  100  rewrites the temperature T B  in the memory that corresponds to the new cartridge  50 , with the outside temperature T out (n) obtained this time (S 607 ). Namely, when the drawer  60  is moved to the image formation position (S 605 : Yes), and it is determined that at least one of the first cartridge  50 K and the second cartridge  50 Y has been replaced with a new one (S 606 : Yes), regardless of the elapsed time TM, the controller  100  sets (updates) at least one, corresponding to the new cartridge  50 , of the temperatures T B  in the memory as the corresponding control temperature(s), based on the value obtained by the second temperature sensor SE 2 . In other words, in this case, the controller  100  does not use at least one, corresponding to the new cartridge  50 , of the temperatures T B  stored in the memory as the previous first control temperature and the previous second control temperature. When determining that none of the first cartridge  50 K and the second cartridge  50 Y has been replaced with a new one (S 606 : No), the controller  100  determines whether or not the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is equal to or longer than the particular time Tth (S 608 ). 
     When determining that the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is not equal to or longer than the particular time Tth (S 608 : No), the controller  100  performs the first temperature calculation process shown in  FIG.  6    (S 609 ). Namely, when the drawer  60  is moved to the image formation position (S 605 : Yes) after the drawer  60  is withdrawn out of the image formation position (S 601 : Yes), if the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is shorter than the particular time Tth (S 608 : No), the controller  100  calculates the respective temperatures T B (n) of the regulating blades  53 K and  53 Y, based on the previous temperature values stored in the memory, such as the previous value (Tin) obtained by the first temperature sensor SE 1  and the previous temperatures T B  of the regulating blades  53 K and  53 Y. 
     In the first temperature calculation process (see  FIG.  6   ) immediately after it is determined in S 605  that the drawer  60  has been placed in the image formation position, the inside temperature Tin in the memory, which is maintained at the value obtained by the first temperature sensor SE 1  immediately before the drawer  60  is withdrawn out of the image formation position, is used as the previous inside temperature T in (n−1). However, in S 103 , the inside temperature Tin in the memory is overwritten with the inside temperature T in (n) obtained this time in S 101  of the first temperature calculation process in this control cycle, and is updated. Therefore, in the first temperature calculation process in the subsequent control cycles, the inside temperature Tin obtained by the first temperature sensor SE 1  during a previous control cycle is used as the previous inside temperature T in (n−1). 
     When determining that the elapsed time TM since the drawer  60  was withdrawn out of the image formation position is equal to or longer than the particular time Tth (S 608 : Yes), the controller  100  obtains the inside temperature Tin from the first temperature sensor SE 1 , and overwrites the temperature T B  corresponding to each of the cartridges  50 K and  50 Y in the memory with the inside temperature T in (n) obtained this time, thereby updating each temperature T B  in the memory (S 610 ). Namely, when the drawer  60  is moved to the image formation position (S 605 : Yes) after the drawer  60  is withdrawn out of the image formation position (S 601 : Yes), if the elapsed time TM is equal to or longer than the particular time Tth (S 608 : Yes), the controller  100  sets (updates) the temperatures T B  in the memory as the control temperatures based on the value obtained by the first temperature sensor SE 1  (S 610 ), without using the temperatures T B  (i.e., the temperatures T B  before updating in S 610 ) stored in the memory as the previous control temperatures. 
     After S 609  or S 610 , the controller  100  determines whether stop conditions for stopping the cooling control are satisfied (S 611 ). Here, the stop conditions for the cooling control include a condition defined by a process of S 201  to S 203  in the cooling control start/end determination process shown in  FIG.  7   . Namely, in S 611 , the controller  100  determines whether the higher one of the temperatures T B  corresponding to the cartridges  50 K and  50 Y that are stored in the memory is equal to or lower than the first threshold T 1 . 
     When determining that the stop conditions for the cooling control are satisfied (S 611 : Yes), the controller  100  stops the cooling control (S 612 ). If the cooling control has already been stopped in S 604 , which is a process prior to S 612 , the controller  100  does nothing in S 612 . 
     Namely, when the drawer  60  is moved to the image formation position (S 605 : Yes) after the elapsed time TM is equal to or longer than the particular time Tth, the controller  100  does nothing in S 612  since the controller  100  has already stopped the cooling control in S 604 . On the other hand, when the drawer  60  is moved to the image formation position (S 605 : Yes) when the elapsed time TM is shorter than the particular time Tth, since the controller  100  has not executed S 604 , the controller  100  stops the cooling control based on the respective temperatures T B  (i.e., the first and second control temperatures) corresponding to the cartridges  50 K and  50 Y. 
     After S 612  or when making a negative determination in S 611  (S 611 : No), the controller  100  determines whether the front cover  11  has been closed, based on the signal from the front cover opening/closing sensor  11 A (S 613 ). When determining that the front cover  11  has been closed (S 613 : Yes), the controller  100  terminates the when-cover-is-open process shown in  FIGS.  8 A and  8 B . When determining that the front cover  11  has not been closed (S 613 : No), the controller  100  goes back to S 601 . 
     When determining that the drawer  60  has not been withdrawn out of the image formation position in the main body housing  10  (S 601 : Yes), the controller  100  performs the first temperature calculation process shown in  FIG.  6    (S 614 ). After S 614 , the controller  100  proceeds to S 611 . 
     The following describes operations and advantageous effects of the color printer  1  configured as above. When the developing rollers  52  rotate during a printing operation or in a warming operation performed before the printing operation, the temperature of each regulating blade  53  rises due to the friction between each regulating blade  53  and the corresponding developing roller  52 . In addition, when the fuser  80  is in an ON state, the heat from the fuser  80  warms the regulating blades  53 . 
     In the color printer  1 , the controller  100  calculates the temperatures of the regulating blades  53  based on the inside temperature detected by the first temperature sensor SE 1 , the outside temperature detected by the second temperature sensor SE 2 , and the driving states of the developing rollers  52 . Then, when the temperature of at least one of the regulating blades  53  becomes higher than the second threshold T 2 , the controller  100  performs the cooling control. Thus, the cooling control is appropriately performed to suppress deterioration of the toner. 
     The controller  100  changes the constants used to calculate the temperatures of the regulating blades  53  according to the driving states of the developing rollers  52 . Thus, in calculating the temperatures of the regulating blades  53 , the controller  100  is enabled to take into account the difference in temperature changes of the cartridges  50  due to the difference in the driving states of the developing rollers  52 . Thereby, the cooling control is appropriately performed. 
     There is a difference in the temperature changes of the cartridges  50  between when only cold sheets P are fed to the image forming engine  30  (e.g., when simplex printing is performed) and when sheets P heated through the fuser  80  are fed to the image forming engine  30  through the fusing unit  80  (e.g., when duplex printing is performed). The controller  100  changes the constants used to calculate the temperatures of the regulating blades  53  depending on which, of simplex printing and duplex printing, is performed. Thus, in calculating the temperatures of the regulating blades  53 , the controller  100  is enabled to take into account the difference in temperature changes of the cartridges  50  between when simplex printing is performed and when duplex printing is performed. 
     When printing is performed on a small-size sheet P, which has a small thermal capacity, an amount of heat transferred from the cartridges  50  to the sheet P is smaller, and the temperatures of the cartridges  50  tend to rise more easily, than when printing is performed on a sheet P that is larger in size than the small-size sheet P. In the illustrative embodiment, the controller  100  changes the constants used to calculate the temperatures of the regulating blades  53  between when printing is performed on the small-size sheet P and when printing is performed on the sheet P with a larger size. Thus, in calculating the temperatures of the regulating blades  53 , the controller  100  is enabled to take into account the difference in temperature changes of the cartridges  50  due to the difference in size of the sheet P. 
     The controller  100  changes the constants used to calculate the temperatures of the regulating blades  53  according to the operating state of the fan  14 . Thus, in calculating the temperatures of the regulating blades  53 , the controller  100  is enabled to take into account the difference in temperature changes of the cartridges  50  due to the difference in cooling effects for cooling the inside of the main body housing  10  by the fan  14 . 
     The controller  100  changes the constants used to calculate the temperatures of the regulating blades  53  according to the operating state of the fuser  80 . Thus, in calculating the temperatures of the regulating blades  53 , the controller  100  is enabled to take into account the difference in temperature changes of the cartridges  50  due to the operating state of the fuser  80 . 
     In the illustrative embodiment, none of the cartridges  50  has a temperature sensor. Therefore, it is possible to reduce a cost of each cartridge  50 . 
     The first temperature sensor SE 1  is positioned between the fuser  80  and the cartridges  50  in the pull-out direction D for the drawer  60  inside the main body housing  10 . Thus, it is possible to measure the heat transferring from the fuser  80  toward the cartridges  50  by the first temperature sensor SE 1 . 
     The second temperature sensor SE 2  is disposed to face the intake port  15 . Thus, it is possible to properly measure the temperature of the outside air introduced into the main body housing  10  via the intake port  15  by the second temperature sensor SE 2 . 
     When the drawer  60  is again placed in the image formation position, and the elapsed time TM since the drawer  60  was withdrawn is shorter than the particular time Tth, the value obtained by the first temperature sensor SE 1  is likely to be not so different from that before the drawer  60  was withdrawn. Therefore, in this case, proper control temperatures are obtained by calculating the control temperatures based on the value obtained by the first temperature sensor SE 1  and the previous control temperatures. Meanwhile, when the drawer  60  is again placed in the image formation position, and the elapsed time TM since the drawer  60  was withdrawn is equal to or longer than the particular time Tth, the value obtained by the first temperature sensor SE 1  is likely to be significantly different from that before the drawer  60  was withdrawn. Therefore, in this case, proper control temperatures are obtained by setting the control temperatures based on the value obtained by the first temperature sensor SE 1  without using the previous control temperatures. 
     When the drawer  60  is withdrawn out of the image formation position, the control temperatures are calculated based on the value obtained by the first temperature sensor SE 1  immediately before the drawer  60  is withdrawn out of the image formation position and the previous control temperatures. Therefore, it is possible to more accurately calculate the control temperatures in the first temperature calculation process after the drawer  60  is again placed in the image formation position. 
     The first contact CN 1  and the second contact CN 2 , which are connected with each other when the drawer  60  is placed in the image formation position and are disconnected from each other when the drawer  60  is out of the image formation position, are disposed at the drawer  60  and the main body housing  10 , respectively. Therefore, it is possible to determine that the drawer  60  is out of the image formation position when the controller  100  is unable to obtain a response from the first temperature sensor SE 1 . 
     The controller  100  increases the air volume of air from the fan  14  in the cooling control. Therefore, it is possible to cool the inside of the main body housing  10  by the airflow from the fan  14 . 
     The controller  100  decreases the number of pages printed per unit time in the cooling control, thereby, for instance, reducing the amount of operation of each cartridge  50  and reducing the amount of the heat generated by the fuser  80 . Therefore, it is possible to cool the cartridges  50  in a favorable manner. 
     A new cartridge  50  has a temperature close to the outside temperature. Hence, by setting the control temperatures based on the value (i.e., the outside temperature) obtained by the second temperature sensor SE 2 , it is possible to properly calculate the control temperatures. 
     The first temperature sensor SE 1  is disposed upstream of the cartridges  50  in the pull-out direction D for the drawer  60 . Hence, when the drawer  60  is placed in the image formation position inside the main body housing  10 , the first temperature sensor SE 1  is placed around a center of the main body housing  10  where the temperature tends to be high. Accordingly, the controller  100  is allowed to properly calculate the control temperatures based on the temperature of a portion, at which the temperature tends to be high, inside the main body housing  10 , thereby performing appropriate cooling control. 
     Even in a situation where the drawer  60  is out of the image formation position, and the controller  100  is unable to obtain the value detected by the first temperature sensor SE 1 , the controller  100  stops the cooling control when the elapsed time TM is equal to or longer than the particular time Tth. Therefore, the cooling control is prevented from being continued unnecessarily. When the elapsed time TM is equal to or longer than the particular time Tth, it is highly likely that the cartridges  50  have been exposed to the outside air for a long time and have been sufficiently cooled. Thus, in this case, there is no problem even if the controller  100  stops the cooling control. 
     If the drawer  60  is placed in the image formation position when the elapsed time TM is shorter than the particular time Tth, the controller  100  stops the cooling control based on the control temperatures (more specifically, based on a higher one of the temperatures T B ). Therefore, it is possible to stop the cooling control based on the proper control temperatures. 
     The controller  100  performs the cooling control based on the control temperature corresponding to a cartridge  50 , which has a higher temperature, of the cartridges  50 K and  50 Y that are under respective different installation conditions. Therefore, the first cartridge  50 K and the second cartridge  50 Y are cooled favorably. 
     Since the first control temperature is calculated based on the first function, it is possible to accurately calculate the first control temperature. Since the second control temperature is calculated based on the second function, it is possible to accurately calculate the second control temperature. 
     In the monochrome mode, the first cartridge  50 K, which is operated in this mode, is set as a target of which the temperature (more specifically, the temperature T B  of the regulating blade  53 K) is calculated as the first control temperature. Further, in the monochrome mode, the second cartridge  50 Y, which is not operated in this mode, is set as a target of which the temperature (more specifically, the temperature T B  of the regulating blade  53 Y) is calculated as the second control temperature. Therefore, even when the amount of operation of each cartridge  50  varies depending on a type of the image to be formed, it is possible to accurately calculate the first control temperature and the second control temperature. 
     Hereinabove, the illustrative embodiment according to aspects of the present disclosure has been described. Aspects of the present disclosure may be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present disclosure. However, it should be recognized that aspects of the present disclosure may be practiced without reapportioning to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present disclosure. 
     Only an exemplary illustrative embodiment of the present disclosure and but a few examples of their versatility are shown and described in the present disclosure. It is to be understood that aspects of the present disclosure are capable of use in various other combinations and environments and are capable of changes or modifications within the scope of the inventive concept as expressed herein. For instance, the following modifications may be feasible. 
     (Modifications) 
     In the aforementioned illustrative embodiment, when the drawer  60  is again placed in the image formation position, and the elapsed time TM is equal to or longer than the particular time Tth, the value obtained by the first temperature sensor SE 1  is set as the control temperatures (i.e., the temperatures T B  corresponding to the cartridges  50 K and  50 Y). However, for instance, each control temperature may be set based on the value obtained by the first temperature sensor SE 1 , more specifically, set to the value obtained by the first temperature sensor SE 1  multiplied by a particular coefficient. 
     In the aforementioned illustrative embodiment, the controller  100  determines whether the drawer  60  is placed in the image formation position, based on whether the first contact CN 1  and the second contact CN 2  are connected with or disconnected from each other. However, for instance, the controller  100  may determine whether the drawer  60  is placed in the image formation position, using a sensor configured to detect the position of the drawer  60 . 
     In the aforementioned illustrative embodiment, when determining that at least one of the first cartridge  50 K and the second cartridge  50 Y has been replaced with a new one, the controller  100  sets the value obtained by the second temperature sensor SE 2  as the control temperature (i.e., the temperature T B ) corresponding to the new cartridge  50 . However, for instance, the control temperature corresponding to the new cartridge  50  may be set based on the value obtained by the second temperature sensor SE 2 , more specifically, set to the value obtained by the second temperature sensor SE 2  multiplied by a particular coefficient. 
     In the aforementioned illustrative embodiment, an example is shown in which each of the cartridges  50  does not include a photoconductive drum  61 . However, each of the cartridges  50  may include a photoconductive drum  61 . 
     In the aforementioned illustrative embodiment, the photoconductive drum  61  corresponding to each cartridge  50  is shown as an example of a photoconductive body. However, a belt-shaped photoconductive body, as well as the photoconductive drum  61 , may be included in examples of the photoconductive body. 
     In the aforementioned illustrative embodiment, the controller  100  performs, as the cooling control, controlling the fan  14 , reducing the number of pages to be printed per unit time, and stopping printing in stages according to a higher one of the temperatures T B . However, for instance, the cooling control may include only controlling the fan  14  or only reducing the number of pages to be printed per unit time. 
     In the aforementioned illustrative embodiment, in principle, the control temperatures are determined by calculation using the first function and the second function. However, for instance, the value obtained by the first temperature sensor may be set as a control temperature. 
     In the aforementioned illustrative embodiment, the toner of yellow is illustrated as an example of colored developer. However, examples of the colored developer may include toner of a color such as magenta other than yellow. 
     In the aforementioned illustrative embodiment, the two cartridges  50 K and  50 Y among the four cartridges  50  are set as targets for temperature calculation. However, three or more cartridges  50  may be set as targets for temperature calculation, or a single cartridge  50  may be set as a target for temperature calculation. 
     In the aforementioned illustrative embodiment, in S 602  and S 608 , the elapsed time TM is compared with the same threshold, that is, the particular time Tth. However, for instance, in S 602 , the controller  100  may determines whether or not the elapsed time TM is equal to or longer than a first particular time Tth 1 . In this case, in S 608 , the controller  100  may determines whether or not the elapsed time TM is equal to or longer than a second particular time Tth 2  that is different from the first particular time Tth 1 . 
     In the aforementioned illustrative embodiment, an example is shown in which the drawer  60  includes the first temperature sensor SE 1 . However, the main body housing  10  may include the first temperature sensor SE 1 . In this case, as shown in  FIG.  10   , the first temperature sensor SE 1  may be positioned between the drawer  60  and the fuser  80  in the pull-out direction D for the drawer  60 . In other words, the first temperature sensor SE 1  may be positioned between the cartridge  50 K, which is closest to the fuser  80 , and the fuser  80  in the pull-out direction D for the drawer  60 . Thus, in the case where the main body housing  10  includes the first temperature sensor SE 1 , the controller  100  is allowed to obtain the inside temperature by the first temperature sensor SE 1  even when the drawer  60  is withdrawn from the main body housing  10 . 
     In the aforementioned illustrative embodiment, the drawer  60  includes the first temperature sensor SE 1 . However, a cartridge  50  may include the first temperature sensor SE 1 . For instance, as shown in  FIG.  11   , the cartridge  50 K may include the first temperature sensor SE 1 . In this case, when the drawer  60  is pulled out from the main body housing  10 , the cartridge  50 K may be removed from the main body housing  10 . Further, when the drawer  60  is placed into the image formation position, the cartridge  50 K may be attached to the main body housing  10 . 
     When an elapsed time since the cartridge  50 K was removed from the main body housing  10  is shorter than a predetermined time, the controller  100  may calculate the control temperatures based on the value obtained by the first temperature sensor SE 1  and the previous control temperatures. Meanwhile, when the elapsed time since the cartridge  50 K was removed from the main body housing  10  is equal to or longer than the predetermined time, the controller  100  may calculate the control temperatures based on the value obtained by the first temperature sensor SE 1 . 
     The controller  100  may continue the cooling control when the cartridge  50 K is removed from the main body housing  10  during the cooling control. In addition, the controller  100  may stop the cooling control when the elapsed time since the cartridge  50 K was removed from the main body housing  10  is equal to or longer than the predetermined time, in a state where the cartridge  50 K remains removed from the main body housing  10 . 
     In the modification shown in  FIG.  10   , the temperature sensor SE 1  is disposed at the cartridge (e.g.,  50 K) detachably attached to the drawer  60 . However, for instance, a temperature sensor may be disposed at a cartridge detachably attached to a main body housing of a monochrome printer. In this case, the monochrome printer may perform control processes according to aspects of the present disclosure. 
     In the aforementioned illustrative embodiment, aspects of the present disclosure have been applied to the color printer  1 . However, aspects of the present disclosure may be applied to other image forming apparatuses such as copy machines and multi-function peripherals. 
     In the aforementioned illustrative embodiment, the controller  100  is configured to change the constants used to calculate the control temperatures between when simplex printing is performed and when duplex printing is performed. However, for instance, the controller  100  may be configured to change the constants used to calculate the control temperatures between when printing is performed of a first surface of the sheet P and when printing is performed on a second surface of the sheet P. 
     The configuration of the fuser  80  is not limited to that shown in the aforementioned illustrative embodiment. For instance, the fuser  80  may include a fixing belt, a nip plate, and a pressure member configured to sandwich the sheet P between the nip plate and the pressure member. 
     Aspects of the present disclosure may be practiced by arbitrarily combining elements described in the aforementioned illustrative embodiment and modifications. 
     The following shows examples of associations between elements exemplified in the aforementioned illustrative embodiments and modifications and elements according to aspects of the present disclosure. The color printer  1  may be an example of an “image forming apparatus” according to aspects of the present disclosure. The main body housing  10  may be an example of a “main body housing” according to aspects of the present disclosure. The cartridge  50 K may be an example of a “first cartridge” according to aspects of the present disclosure. The cartridge  50 Y may be an example of a “second cartridge” according to aspects of the present disclosure. The first temperature sensor SE 1  may be an example of a “first temperature sensor” according to aspects of the present disclosure. The second temperature sensor SE 2  may be an example of a “second temperature sensor” according to aspects of the present disclosure. The controller  100  may be an example of a “controller” according to aspects of the present disclosure. The fan  14  may be an example of a “fan” according to aspects of the present disclosure. The fuser  80  may be an example of a “fuser” according to aspects of the present disclosure.