Patent Publication Number: US-9904224-B2

Title: Image forming apparatus, and method and computer-readable medium for the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2015-170106 filed on Aug. 31, 2015. The entire subject matter of the application is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The following description relates to aspects of an image forming apparatus, and a method and a computer-readable medium for controlling the image forming apparatus. 
     Related Art 
     An image forming apparatus has been known that includes a process unit, a fuser, and a re-conveyor and is configured to perform duplex printing. In the image forming apparatus, the process unit forms a toner image on a first side of a sheet being conveyed, and the fuser thermally fixes the toner image onto the first side of the sheet. The re-conveyor again conveys the sheet passed through the fuser to the process unit, with the sheet being turned upside down. The process unit forms a toner image on a second side of the sheet re-conveyed, and the fuser thermally fixes the toner image onto the second side of the sheet. Thus, an image is formed on each side of the sheet. 
     In the known image forming apparatus, the sheet heated by the fuser is re-conveyed to the process unit by the re-conveyor. Therefore, for instance, when an ambient temperature of the process unit rises, it might result in a lower quality of image. In order to solve the problem, an image forming apparatus has been proposed that is configured to cool a sheet being re-conveyed by a re-conveyor with an air current flowing through an air guide formed at the re-conveyor. 
     SUMMARY 
     A temperature of the re-conveyed sheet varies depending on a temperature of the fuser. Hence, when the temperature of the fuser is relatively high, there is a risk that the re-conveyed sheet might not be adequately cooled. 
     Aspects of the present disclosure are advantageous to provide one or more improved techniques, for an image forming apparatus, which make it possible to adequately cool a re-conveyed sheet. 
     According to aspects of the present disclosure, an image forming apparatus is provided, which includes a process unit configured to form a toner image on a sheet, a fuser configured to heat the sheet passed through the process unit thereby thermally fixing the toner image onto the sheet, a re-conveyor configured to convey the sheet passed through the fuser to the process unit, and a controller configured to perform particular duplex printing including controlling, when a temperature of the fuser is a first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a first period of time, and controlling, when the temperature of the fuser is a second temperature higher than the first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a second period of time, which is longer than the first period of time. 
     According to aspects of the present disclosure, further provided is a method adapted to be implemented on a processor coupled with an image forming apparatus including a process unit, a fuser, and a re-conveyor, the method including controlling, when a temperature of the fuser is a first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a first period of time, and controlling, when the temperature of the fuser is a second temperature higher than the first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a second period of time, which is longer than the first period of time. 
     According to aspects of the present disclosure, further provided is a non-transitory computer-readable medium storing computer-readable instructions that are executable by a processor coupled with an image forming apparatus, which includes a process unit, a fuser, and a re-conveyor. The instructions are configured to, when executed by the processor, cause the processor to perform particular duplex printing including controlling, when a temperature of the fuser is a first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a first period of time, and controlling, when the temperature of the fuser is a second temperature higher than the first temperature, the re-conveyor to convey the sheet passed through the fuser to the process unit in a second period of time, which is longer than the first period of time. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is a cross-sectional side view schematically showing an overall configuration of a printer in an illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG. 2  is a block diagram schematically showing an electrical configuration of the printer in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG. 3  is a flowchart showing a procedure of a print control process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG. 4  is a timing chart showing a timing relationship among temperature control for a fuser, drive control for each of a process motor, a scanner motor, and a discharge motor, and sheet feeding control for a sheet feeder, in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG. 5  is a flowchart showing a procedure of a pre-simplex-printing process in the illustrative embodiment according to one or more aspects of the present disclosure. 
         FIG. 6  is a flowchart showing a procedure of a pre-duplex-printing 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 re-conveyance process in the illustrative embodiment according to one or more aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Hereinafter, a printer  10  of an illustrative embodiment according to aspects of the present disclosure will be described with reference to the accompanying drawings.  FIG. 1  is a cross-sectional view schematically showing an overall configuration of the printer  10 .  FIG. 1  shows an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other. In the following description, for the sake of explanatory convenience, a positive direction along the Z-axis will be referred to as an upward direction. A negative direction along the Z-axis will be referred to as a downward direction. A positive direction along the X-axis will be referred to as a frontward direction. A negative direction along the X-axis will be referred to as a rearward direction. A positive direction along the Y-axis will be referred to as a rightward direction. A negative direction along the Y-axis will be referred to as a leftward direction. The same will apply to  FIG. 2  and the following drawings. 
     The printer  10  is an electrophotographic printer configured to form an image on a sheet W such as a recording paper and a transparency with toner (developer) of a single color (e.g., black). 
     As shown in  FIG. 1 , the printer  10  includes a casing  100 , a sheet feeder  200 , a sheet conveyor  300 , and an image forming device  400 . The casing  100  accommodates the sheet feeder  200 , the sheet conveyor  300 , and the image forming device  400 . Further, at an upper surface of the casing  100 , a discharge port  110  and a discharge tray  120  are formed. Discharge rollers  130  are disposed in a position close to the discharge port  110  of the casing  100 . 
     The sheet feeder  200  includes a tray  210 , a pickup roller  220 , a separation roller  221 , and a separation pad  222 . The tray  210  accommodates one or more sheets W. The pickup roller  220  is configured to pick up and feed one or more sheets W placed on the tray  210 . The separation roller  221  and the separation pad  222  are configured to pinch therebetween the sheets W fed by the pickup roller  220 , and feed the sheets W toward the sheet conveyor  300  on a sheet-by-sheet basis. 
     The sheet conveyor  300  includes conveyance rollers  310  and registration rollers  320 . The conveyance rollers  310  are configured to convey the sheets W fed by the sheet feeder  200 , toward the registration rollers  320 . The registration rollers  320  are configured to perform skew correction for the sheets W conveyed by the conveyance rollers  310 , and convey the sheets W toward the image forming device  400 . 
     The image forming device  400  includes an exposure device  500 , a process unit  600 , and a fuser  700 . The exposure device  500  is configured to emit a laser beam L onto a photoconductive body  610  of the process unit  600 . Specifically, the exposure device  500  includes a light source (not shown), a polygon mirror  511 , and a scanner motor  510 . The light source is configured to emit a laser beam L. The polygon mirror  511  is driven to rotate by the scanner motor  510 , and configured to deflect the laser beam L emitted by the light source, to be incident onto the photoconductive body  610 . 
     The process unit  600  includes the photoconductive body  610 , a charger  620 , a developer  630 , and a transfer roller  640 . The photoconductive body  610  is a drum-shaped member configured to rotate around an axis. The charger  620  is disposed to face a surface of the photoconductive body  610 . The charger  620  is configured to evenly charge the surface of the photoconductive body  610 . The developer  630  includes a toner box  631  and a development roller  632 . The toner box  631  accommodates toner. The development roller  632  is configured to supply toner stored in the toner box  631  to the surface of the photoconductive body  610 . The transfer roller  640  is disposed to face the photoconductive body  610 . The transfer roller  640  is configured to, when supplied with a voltage, transfer a toner image formed on the surface of the photoconductive body  610  onto a sheet W. 
     When the laser beam L from the exposure device  500  is emitted onto the surface of the photoconductive body  610  charged by the charger  620 , an electrostatic latent image is formed on the surface of the photoconductive body  610 . When toner is supplied to the surface of the photoconductive body  610  by the developer  630 , the electrostatic latent image formed on the surface of the photoconductive body  610  is developed. Thereby, a toner image is formed on the surface of the photoconductive body  610 . The toner image formed on the surface of the photoconductive body  610  is transferred by the transfer roller  640  onto a sheet W passing through a position where the photoconductive body  610  and the transfer roller  640  face each other. Hereinafter, the position where the photoconductive body  610  and the transfer roller  640  face each other may be referred to as a “transfer position X 1 .” 
     The fuser  700  is configured to heat the sheet W passed through the process unit  600 , and fix onto the sheet W the toner image transferred onto the sheet W. Thereby, an image is formed on the sheet W. Specifically, the fuser  700  includes a fixing belt  710 , a halogen heater  720 , a nip member  730 , a pressing roller  750 , and a thermistor  770 . The fixing belt  710  is a tube-shaped band configured to rotate. The halogen heater  720  is a heat generating body configured to, when supplied with electricity from an alternate-current power supply (not shown), generate heat. The halogen heater  720  is disposed in a region surrounded by the fixing belt  710 . The pressing roller  750  is disposed to contact the fixing belt  710 . The pressing roller  750  is pressed against the fixing belt  710 . The nip member  730  includes a metal plate. The nip member  730  is configured to pinch the fixing belt  730  with the pressing roller  750 . A nip P is defined as a portion between the fixing belt  710  and the pressing roller  750 . The thermistor  770  is disposed in such a position as to contact the nip member  730 . The thermistor  770  is a temperature sensor configured to output a temperature signal depending on a temperature of the nip member  730  to a controller  800 . 
     When the halogen heater  720  generates heat, the fixing belt  710  is heated by the halogen heater  720  through the nip member  730 . Thus, the temperature of the fixing belt  710  increases. Further, when the pressing roller  750  is driven to rotate by a driving force from the process motor  811 , the fixing belt  710  moves in accordance with the rotation of the pressing roller  750 . When the sheet W passed through the process unit  600  reaches the nip P between the fixing belt  710  and the pressing roller  750 , the sheet W is heated by the fixing belt  710  while being conveyed by the fixing belt  710  and the pressing roller  750 . Thereby, the toner image formed on the surface of the sheet W is thermally fixed. The discharge rollers  130  discharge the sheet W passed through the fuser  700  onto the discharge tray  120  via the discharge port  110 . Hereinafter, a conveyance path of the sheet W, which extends from the sheet feeder  200  to the discharge rollers  130  via the sheet conveyor  300 , the transfer position X 1 , and the nip P of the fuser  700 , will be referred to as a “conveyance path R 1 .” A direction in which the sheet W is conveyed along the conveyance path R 1  will be referred to as a “conveyance direction.” 
     The casing  100  further includes a conveyance guide  150 . The conveyance guide  150  is disposed downstream of the fuser  700  in the conveyance direction. As shown in  FIG. 1 , the conveyance guide  150  includes a curved portion  151  positioned behind (i.e., on a rear side of) the conveyance path R 1 . The curved portion  151  is concave substantially in a rearward direction. In other words, the curved portion  151  is concave substantially in a direction of a specific surface of the sheet W being guided by the conveyance guide  150  in contact between the curved portion  151  and the specific surface. Thus, the conveyance guide  150  (more specifically, the curved portion  151 ) is configured to guide the sheet W to the discharge rollers  130  in contact with the specific surface of the sheet W passed through the fuser  700 . The specific surface of the sheet W is a surface that faces the pressing roller  750  when the sheet W passes through the fuser  700 . 
     The casing  100  further includes a re-conveyor  160 . The re-conveyor  160  is configured to re-convey the sheet W passed through the fuser  700  to the process unit  600 , with the sheet being turned upside down. Specifically, the re-conveyor  160  includes the aforementioned discharge rollers  130 , a first re-conveyance guide  161 , a second re-conveyance guide  162 , a third re-conveyance guide  163 , a fourth re-conveyance guide  164 , and a plurality of rollers  165 . The first to fourth re-conveyance guides  161  to  164  are configured to define a re-conveyance path R 2 . The re-conveyance path R 2  extends from the discharge rollers  130 , and passes by a position behind the conveyance guide  150 , a position below the image forming device  400 , and a position behind the sheet conveyor  300 . Hereinafter, a direction in which the sheet W is re-conveyed along the re-conveyance path R 2  will be referred to as a “re-conveyance direction.” 
     The first re-conveyance guide  161  is disposed in a position opposite to the fuser  700  with respect to the conveyance guide  150 . The first re-conveyance guide  161  includes a section extending from a position closer to the discharge rollers  130  than the conveyance guide  150  to a position behind the conveyance guide  150 . The second re-conveyance guide  162  is disposed behind (i.e., on a rear side of) the conveyance guide  150 . The second re-conveyance guide  162  includes a section extending substantially in the vertical direction. The third re-conveyance guide  163  is disposed between the process unit  600  or the fuser  700 , and the sheet feeder  200  in the vertical direction. The third re-conveyance guide  163  includes a section extending substantially in the front-to-rear direction. The fourth re-conveyance guide  164  is disposed between the third re-conveyance guide  163  and the registration rollers  320  in the vertical direction. The fourth re-conveyance guide  164  includes a U-shaped section extending from a position close to the third re-conveyance guide  163  toward the registration rollers  320 . The rollers  165  are disposed along the third re-conveyance guide  163 . The rollers  165  are driven to rotate by the driving force from the process motor  811 . Further, the aforementioned discharge rollers  130  are configured to be driven to rotate in both of a forward direction and a backward direction by the driving force from a discharge motor  812 . Hereinafter, a position where the discharge rollers  130  are opposed to each other will be referred to as a “discharge position X 2 .” A position between the discharge position X 2  and the rollers  165  on the re-conveyance path R 2  will be referred to as a “before-roller position X 3 .” A position between the rollers  165  and the registration rollers  320  on the re-conveyance path R 2  will be referred to as an “after-roller position X 4 .” 
     Further, the casing  100  includes a duct  105  formed therein. An end of the duct  105  communicates with a fan  106  for exhaust. The other end of the duct  105  communicates with the outside of the casing  100  via a ventilation hole  166  formed at the third re-conveyance guide  163  and a gap  211  between the casing  100  and the tray  210 . When the fan  106  rotates, the outside air is introduced into the duct  105  via the gap  211  and the ventilation hole  166 . Thereby, an air current V crossing the conveyance path R 1  and the re-conveyance path R 2  is generated inside the casing  100 . 
     The printer  10  further includes a temperature sensor  170 . The temperature sensor  170  is disposed close to the ventilation hole  166 . The temperature sensor  170  is configured to output a signal depending on an outside air temperature. 
       FIG. 2  is a block diagram showing an electrical configuration of the printer  10 . The printer  10  further includes the controller  800 , a display  820 , a user interface  830 , and a communication interface  840 , as well as the sheet feeder  200 , the sheet conveyor  300 , and the image forming device  400 . 
     The controller  800  includes a CPU  801 , a ROM  802 , a RAM  803 , a nonvolatile memory  804 , an ASIC (which is an abbreviated form of Application Specific Integrated Circuit)  805 , and a motor driver  810 . The ROM  802  stores therein control programs  802   a  and various setting information for controlling the printer  10 . The RAM  803  is used as a work area and/or a temporary data storage area when the CPU  801  executes programs. The nonvolatile memory  804  includes a rewritable memory such as an NVRAM, a flash memory, an HDD, and an EEPROM. The ASIC  805  includes a hardware circuit for image processing. The CPU  801  is configured to control each of elements included in the printer  10  in accordance with one or more control programs  802   a  read out from the ROM  802  and signals from various sensors. The motor driver  810  is configured to drive the scanner motor  510 , the process motor  811 , and a discharge motor  812 . The controller  80  is further configured to acquire an outside air temperature based on a signal output from the temperature sensor  170 . 
     The process motor  811  is configured to drive the pickup roller  220 , the registration rollers  320 , the photoconductive body  610 , the development roller  632 , the pressing roller  750  of the fuser  700 , and the rollers  165  of the re-conveyor  160 . The process motor  811  is rotatable in a forward direction and a backward direction. The process motor  811  is configured to rotate the discharge rollers  130  in both of the forward direction and the backward direction. When the process motor  811  rotates in the forward direction, the discharge rollers  130  are driven to rotate in the forward direction such that a sheet W is discharged out of the casing  100 . Meanwhile, when the process motor  811  rotates in the backward direction, the discharge rollers  130  are driven to rotate in the backward direction such that the sheet W is pulled into the casing  100 . 
     The display  820  may be a liquid crystal display. The display  820  is configured to display various kinds of information in accordance with instructions from the controller  800 . The user interface  830  includes various buttons configured to accept user operations. The communication interface  840  is hardware that enables communication with external devices. The communication interface  840  may include at least one of a network interface, a serial communication interface, and a parallel communication interface. 
     Subsequently, a print control process by the controller  800  will be described. In response to accepting a print instruction to form images on sheets W, e.g., via the user interface  830  or the communication interface  840 , the controller  800  launches a print control process. More specifically, the print control process may be performed by the CPU  801  (see  FIG. 2 ) executing one or more control programs  802   a  stored in the RAM  802 . 
       FIG. 3  is a flowchart showing a procedure of the print control process.  FIG. 4  is a timing chart showing a timing relationship among temperature control for the fuser  700 , drive control for each of the motors  510 ,  811 , and  812 , and sheet feeding control for the sheet feeder  200 . Regarding the aforementioned controls except for the drive control of the discharge motor  812 , each dashed line indicates a change in time of a control parameter for the corresponding control in duplex printing. Additionally, each alternate long and short dash line indicates a change in time of the control parameter for the corresponding control in simplex printing. Further, each solid line indicates a change in time of the control parameter for the corresponding control in common with the duplex printing and the simplex printing. Regarding the drive control for the discharge motor  812 , a dashed line indicates a change in time of a control parameter (i.e., a control voltage) for second re-conveyance control in the duplex printing. Additionally, an alternate long and short dash line indicates a change in time of the control voltage for first re-conveyance control in the duplex printing. Further, a solid line indicates a change in time of the control voltage in common with the first re-conveyance control and the second re-conveyance control. Further,  FIG. 4  shows a graph line G 2  representing a change in time of the temperature of the sheet W in the duplex printing and a graph line G 1  representing a change in time of the temperature of the sheet W in the simplex printing. The following description will be provided under assumptions that, before a print instruction is accepted, driving the motors  510 ,  811 , and  812  and supplying sheets W from the sheet feeder  200  are stopped. Further, it is assumed that, before a print instruction is accepted, the temperature control for the fuser  700  is stopped, or the fuser  700  is maintained at a particular temperature (e.g., a temperature in a sleep mode or a standby mode) lower than a target fixing temperature (see timing t 0  in  FIG. 4 ). 
     Firstly, in response to accepting a print instruction, the controller  800  determines whether the accepted print instruction is directed to the simplex printing or the duplex printing (S 110 ). When determining that the accepted print instruction is directed to the simplex printing (S 110 : simplex printing), the controller  800  goes to S 120 . In S 120 , the controller  800  performs a pre-simplex-printing process. 
       FIG. 5  is a flowchart showing a procedure of the pre-simplex-printing process. The controller  800  starts rotation control for controlling the scanner motor  510  to rotate at a scanner speed VS by the motor driver  810  (S 310 , see timing t 1  in  FIG. 4 ). Subsequently, the controller  800  sets the target fixing temperature to an activation temperature TH, and starts temperature control for bringing a temperature of the fixing belt  710  closer to the activation temperature TH based on a temperature signal from the thermistor  770  (S 320 , see timing t 3  in  FIG. 4 ). The activation temperature TH is higher than a temperature suitable for fixing. Further, the controller  800  starts rotation control for controlling the process motor  811  to rotate at a process speed VN by the motor driver  810  (S 300 , see timing t 3  in  FIG. 4 ). The process speed VN is a rotational speed of the process motor  811  when the process unit  600  forms an image on a sheet W. Thereby, the pickup roller  220 , the registration rollers  320 , the photoconductive body  610 , the development roller  632 , and the pressing roller  750  of the fuser  700  are driven to rotate at respective speeds corresponding to the process speed VN in respective rotational directions such as to convey the sheet W along the conveyance path R 1 . The controller  800  may execute S 320  and S 330  at the same timing or mutually-different timings. 
     A reason why the target fixing temperature is set to the activation temperature TH in the pre-simplex-printing process will be described below. In the pre-simplex-printing process, by making the timing to start the rotation control for the process motor  811  as late as possible, it is possible to prevent deterioration of the toner stored in the toner box  631  and/or the development roller  632  due to rotation of the development roller  632 . Nonetheless, the fuser  700  needs to be driven in a state where a lubricant between the fixing belt  710  and the nip member  730  is thermally melted. Therefore, the fixing belt  710  begins to be rotated provided that the temperature control for the fuser  700  has been started. Further, the fixing belt  710  and the development roller  632  are driven to rotate by the same process motor  811 . Accordingly, when the timing to start the rotation control for the process motor  811  (e.g., the development roller  632 ) is delayed, the timing to start the temperature control for the fuser  700  is delayed as well accordingly. As the temperature control for the fuser  700  is delayed, there is a risk that a period of time required for completing a printing operation after acceptance of a print instruction might be longer. Thus, in order to prevent the required period of time from being longer, the target fixing temperature is set to the activation temperature TH higher than the temperature suitable for fixing. 
     After completing the pre-simplex-printing process, the controller  800  goes to S 130  in  FIG. 3 . In S 130 , the controller  800  controls the sheet feeder  200  to feed one sheet W (see timing t 4  in  FIG. 4 ). Then, the controller  800  controls the process unit  600  to start transferring a toner image onto a single side of the sheet W passing through the transfer position X 1  (S 140 ). Afterward, the sheet W with the toner image transferred thereon is heated for a period of time during which the sheet W is passing through the nip P of the fuser  700  (see timings t 5  to t 7  in  FIG. 4 ). During this period of time, since the target fixing temperature is set to the activation temperature TH, the temperature of the sheet W is higher than when the duplex printing is performed, as indicated by the graph line G 1  in  FIG. 4 . 
     Subsequently, when determining that a particular timing (see timing t 6  in  FIG. 4 ) at which a leading end of the sheet W in the conveyance direction is between the fuser  700  and the discharge rollers  130  has come, the controller  800  starts rotating the discharge motor  812  in the forward direction (S 150 ). Further, when determining that a particular timing (see timing t 8  in  FIG. 4 ) at which a trailing end of the sheet W in the conveyance direction passes through the discharge position X 2  has come, the controller  800  stops the discharge motor  812 . Thereby, the simplex-printed sheet W is discharged onto the discharge tray  120 . The controller  800  may determine whether each of the timings t 6  and t 8  has come, e.g., based on a signal from a sheet sensor (not shown) or a period of time elapsed since the registration rollers  320  fed the sheet W. 
     Subsequently, the controller  800  determines whether all of the pages specified by the print instruction have been completely printed (S 160 ). When determining that all of the pages specified by the print instruction have not been completely printed (S 160 : No), the controller  800  goes back to S 130 . In S 130 , simplex printing is performed on a next sheet W. Meanwhile, when determining that all of the pages specified by the print instruction have been completely printed (S 160 : Yes), the controller  800  performs post processing (S 170 ). For instance, the post processing includes stopping the temperature control for the fuser  700  and stopping the motors  510 ,  811 , and  812 . Thereafter, the controller  800  terminates the print control process. 
     In S 110 , when determining that the accepted print instruction is directed to the duplex printing (S 110 : duplex printing), the controller  800  goes to S 180 . In S 180 , the controller  800  performs a pre-duplex-printing process.  FIG. 6  is a flowchart showing a procedure of the pre-duplex-printing process. The controller  800  determines whether an outside air temperature is equal to or lower than a threshold temperature (e.g., 15° C.), based on a temperature signal from the temperature sensor  170  (S 410 ). When determining that the outside air temperature is equal to or lower than the threshold temperature (S 410 : Yes), the controller  800  sets the target fixing temperature to a particular high temperature TNH, and sets a first target reverse speed VR 1  to a particular low speed VR 1 L (S 420 ). The particular high temperature TNH is equal to or higher than the temperature suitable for fixing, and is lower than the activation temperature TH. The target reverse speed is a rotational speed of the discharge motor  812  rotating in the backward direction. Meanwhile, when determining that the outside air temperature is higher than the threshold temperature (S 410 : No), the controller  800  sets the target fixing temperature to a particular low temperature TNL, and sets the first target reverse speed VR 1  to a particular high speed VR 1 H (S 430 ). The particular low temperature TNL is equal to or higher than the temperature suitable for fixing and lower than the particular high temperature TNH. Namely, the lower the outside air temperature is, the higher the target fixing temperature is set to be, and the lower the first target reverse speed VR 1  is set to be accordingly. 
     After execution of S 420  or S 430 , the controller  800  starts temperature control for bringing the temperature of the fixing belt  710  close to the particular high temperature TNH or the particular low temperature TNL on the basis of the temperature signal from the thermistor  770  (S 440 , see timing t 1  in  FIG. 1 ). In  FIG. 4 , the particular high temperature TNH and the particular low temperature TNL are indicated by the same dashed line. Further, the controller  800  starts rotation control for controlling the process motor  811  to rotate at a low process speed VL by the motor driver  810  (S 450 , see timing t 1  in  FIG. 4 ). The low process speed VL is lower than the aforementioned process speed VN. Thereby, the pickup roller  220 , the registration rollers  320 , the photoconductive body  610 , the development roller  632 , and the pressing roller  750  of the fuser  700  are driven to rotate at respective speeds corresponding to the low process speed VL in respective rotational directions such as to convey the sheet W along the conveyance path R 1 . Further, the plurality of rollers  165  of the re-conveyor  160  are driven to rotate at respective speeds corresponding to the low process speed VL in respective rotational directions such as to convey the sheet W along the re-conveyance path R 2 . Subsequently, the controller  800  starts rotation control for controlling the scanner motor  510  to rotate at the scanner speed VS by the motor driver  810  (S 460 , see timing t 2  in  FIG. 4 ). Thereafter, the controller  800  starts rotation control for controlling the process motor  811  to rotate at the process speed VN by the motor driver  810  (S 470 , see timing t 3  in  FIG. 4 ). 
     A reason why it is possible to prevent a delay on sheet feeding timing even though the target fixing temperature is set to the particular high temperature TNH or the particular low temperature TNL, which are lower than the activation temperature TH, in the pre-duplex-printing process will be provided below. As shown in  FIG. 4 , in the pre-duplex-printing process, the timing to start the temperature control for the fuser  700  is earlier than that in the pre-simplex-printing process. Therefore, in the pre-duplex-printing process, it is possible to secure a longer period of time between the timing to start the temperature control for the fuser  700  and the sheet feeding timing (see timing t 4  in  FIG. 4 ) in comparison with the pre-simplex-printing process. Hence, even when the target fixing temperature is set to the particular high temperature TNH or the particular low temperature TNL, it is possible to make the temperature of the fixing belt  710  equal to or higher than the temperature suitable for fixing before the sheet W reaches the nip P. 
     Further, a reason why the timing to start the rotation control for the scanner motor  510  in the pre-duplex-printing process is later than that in the pre-simplex-printing process will be provided below. Each of the process motor  811  and the scanner motor  510  needs a large amount of electricity for starting the rotation control therefor. Therefore, a short time interval between the timing to start the rotation control for the process motor  811  and the timing to start the rotation control for the scanner motor  510  results in a great load placed on the motor driver  810 . Hence, in the duplex printing, the scanner motor  510  is driven to rotate after the process motor  811  begins to be rotated at the low process speed VL. Thereby, it is possible to reduce the load placed on the motor driver  810 . 
     After completing the pre-duplex-printing process, the controller  800  goes to S 190  in  FIG. 3 . In S 190 , the controller  800  controls the sheet feeder  200  to feed one sheet W (see timing t 4  in  FIG. 4 ). Then, the controller  800  controls the process unit  600  to start transferring a toner image onto a first side of the sheet W passing through the transfer position X 1  (S 200 ). Afterward, the sheet W with the toner image transferred thereon is heated for a period of time during which the sheet W is passing through the nip P of the fuser  700  (see timings t 5  to t 7  in  FIG. 4 ). During this period of time, since the target fixing temperature is set to the particular high temperature TNH or the particular low temperature TNL, the temperature of the sheet W is lower than when the simplex printing is performed, as indicated by the graph line G 2  in  FIG. 4 . 
     Subsequently, when determining that a particular timing (see timing t 6  in  FIG. 4 ) at which a leading end of the sheet W in the conveyance direction is positioned between the fuser  700  and the discharge rollers  130  has come, the controller  800  starts rotating the discharge motor  812  in the forward direction (S 210 ). Thereafter, the controller  800  determines whether a trailing end of the sheet W in the conveyance direction has passed by the conveyance guide  150  (S 220 ). Immediately before the trailing end of the sheet W in the conveyance direction passes by the conveyance guide  150 , the sheet W is bent in a U-shape by the conveyance guide  150  and the discharge rollers  130 . Therefore, after the trailing end of the sheet W in the conveyance direction has passed by the conveyance guide  150 , the trailing end of the sheet W in the conveyance direction moves from the conveyance guide  150  to the first re-conveyance guide  161  by a restoring force of the sheet W. Thereby, the re-conveyor  160  is allowed to re-convey the sheet W. When determining that the trailing end of the sheet W in the conveyance direction has not passed by the conveyance guide  150  (S 220 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the trailing end of the sheet W in the conveyance direction has passed by the conveyance guide  150  (S 220 : Yes), the controller  800  performs a re-conveyance process. 
       FIG. 7  is a flowchart showing a procedure of the re-conveyance process. The re-conveyance process is for controlling the re-conveyor  160  to perform a re-conveyance operation. Firstly, the controller  800  starts a stop operation to stop the discharge motor  812  (S 510 , see timing t 8  in  FIG. 4 ). At this time, the leading end of the sheet W in the conveyance direction is exposed to the outside of the casing  100  via the discharge port  110 , whereas the trailing end of the sheet W in the conveyance direction is pinched by the discharge rollers  130 . The controller  800  determines whether the target fixing temperature is equal to or higher than a reference temperature (S 520 ). In the illustrative embodiment, when the temperature (i.e., the particular high temperature TNH or the particular low temperature TNL) set in the pre-duplex-printing process is equal to or higher than the reference temperature, the controller  800  determines that the target fixing temperature is equal to or higher than the reference temperature (S 520 : Yes). Meanwhile, when the temperature (i.e., the particular high temperature TNH or the particular low temperature TNL) set in the pre-duplex-printing process is made lower than the reference temperature (see S 270  in  FIG. 3 ), the controller  800  determines that the target fixing temperature is not equal to or higher than the reference temperature (S 520 : No). 
     When determining that the target fixing temperature is not equal to or higher than the reference temperature (S 520 : No), the controller  800  performs first re-conveyance control for controlling the re-conveyor  160  to re-convey the sheet W passed through the fuser  700  to the process unit  600  in a first period of time ΔT 1 . 
     More specifically, the controller  800  determines whether a first stop period of time Δts 1  has elapsed since the stop operation to stop the discharge motor  812  was started (S 530 ). When determining that the first stop period of time Δts 1  has not elapsed (S 530 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the first stop period of time Δts 1  has elapsed (S 530 : Yes), the controller  800  starts rotation control for controlling the discharge motor  812  to reversely rotate at a third target reverse speed VR 3  by the motor driver  810  (S 540 , see timing t 9  in  FIG. 4 ). The third target reverse speed VR 3  is higher than the first target reverse speed VR 1 . Thereby, each discharge roller  130  is reversely rotated at a rotational speed corresponding to the third target reverse speed VR 3 , and the sheet W begins to be conveyed to the re-conveyance path R 2 . 
     Afterward, the controller  800  determines whether a leading end of the sheet W in the re-conveyance direction has reached the before-roller position X 3  (S 570 ). The controller  800  may make the determination in S 570 , e.g., based on a signal from a sheet sensor (not shown) disposed along the re-conveyance path R 2  or a period of time elapsed since the timing to start reversely rotating the discharge rollers  130 . When determining that the leading end of the sheet W in the re-conveyance direction has not reached the before-roller position X 3  (S 570 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the leading end of the sheet W in the re-conveyance direction has reached the before-roller position X 3  (S 570 : Yes), the controller  800  starts rotation control for controlling the discharge motor  812  to rotate at a second target reverse speed VR 2  by the motor driver  810  (S 580 , see timing t 11  in  FIG. 4 ). The second target reverse speed VR 2  is lower than the third target reverse speed VR 3 . The rotational speed of the discharge rollers  130  corresponding to the second target reverse speed VR 2  is identical to the rotational speed of the rollers  165  corresponding to the process speed VN. Namely, the rotational speed of the discharge motor  812  (the discharge rollers  130 ) in the backward direction is higher than the process speed VN until the leading end of the sheet W in the re-conveyance direction reaches the most upstream one of the rollers  165  in the re-conveyance direction. Therefore, it is possible to shorten a period of time required for re-conveying the sheet W. Meanwhile, after the leading end of the sheet W in the re-conveyance direction has passed through the before-roller position X 3 , the leading end of the sheet W in the re-conveyance direction comes into contact with the most upstream one of the rollers  165  in the re-conveyance direction, and the trailing end of the sheet W in the re-conveyance direction comes into contact with the discharge rollers  130 . However, since the rotational speed of the rollers  165  is identical to the rotational speed of the discharge rollers  130  in the backward direction, the sheet W is stably re-conveyed without being crinkled. 
     Thereafter, when the trailing end of the sheet W in the re-conveyance direction has passed through the discharge position X 2 , the sheet W is re-conveyed only by the rollers  165  and guided toward the registration rollers  320  by the fourth re-conveyance guide  164 . The controller  800  determines whether the trailing end of the sheet W in the re-conveyance direction has passed through the after-roller position X 4  (S 590 ). The controller  800  may make the determination in S 590 , e.g., based on a signal from a sheet sensor (not shown) disposed along the re-conveyance path R 2  or a period of time elapsed since the timing to start reversely rotating the discharge rollers  130 . When determining that the trailing end of the sheet W in the re-conveyance direction has not passed through the after-roller position X 4  (S 590 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the trailing end of the sheet W in the re-conveyance direction has passed through the after-roller position X 4  (S 590 : Yes), the controller  800  starts a stop operation to stop the discharge motor  812  (S 600 , see timing t 13  in  FIG. 4 ). Thereafter, the controller  800  terminates the re-conveyance process. The first period of time ΔT 1  for the first re-conveyance control is a period of time between the timing t 7  and the timing t 13  in  FIG. 4 . 
     When determining that the target fixing temperature is equal to or higher than the reference temperature (S 520 : Yes), the controller  800  performs the second re-conveyance control. The second re-conveyance control is for controlling the re-conveyor  160  to convey the sheet W passed through the fuser  700  to the process unit  600  in a second period of time ΔT 2 . The second period of time ΔT 2  is longer than the first period of time ΔT 1 . 
     More specifically, the controller  800  determines whether a second stop period of time Δts 2  has elapsed since the stop operation to stop the discharge motor  812  was started (S 550 ). The second stop period of time Δts 2  is longer than the first stop period of time Δts 1 . When determining that the second stop period of time Δts 2  has not elapsed (S 550 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the second stop period of time Δts 2  has elapsed (S 550 : Yes), the controller  800  starts rotation control for controlling the discharge motor  812  to rotate at the first target reverse speed VR 1  (i.e., VR 1 H or VR 1 L) set in the pre-duplex-printing process (S 560 , see timing t 10  in  FIG. 4 ). Thereby, the discharge rollers  130  are reversely rotated at the first target reverse speed VR 1 , and the sheet W begins to be conveyed to the re-conveyance path R 2 . Namely, in the second re-conveyance control, a period of time during which the sheet W stops in the discharge position X 2  is longer than that in the first re-conveyance control. Further, in the second re-conveyance control, a re-conveyance speed in a section from the discharge position X 2  to the before-roller position X 3  on the re-conveyance path R 2  is lower than that in the first re-conveyance control. Therefore, in the second re-conveyance control, since a period of time required for re-conveying the sheet W passed through the fuser  700  to the before-roller position X 3  is longer than that in the first re-conveyance control, it is possible to more adequately cool the sheet W for the longer period of time. 
     Afterward, when determining that the leading end of the sheet W in the re-conveyance direction has not reached the before-roller position X 3  (S 570 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the leading end of the sheet W in the re-conveyance direction has reached the before-roller position X 3  (S 570 : Yes), the controller  800  starts rotation control for controlling the discharge motor  812  to rotate at the second target reverse speed VR 2  (S 580 , see timing t 12  in  FIG. 4 ). Thereafter, when determining that the trailing end of the sheet W in the re-conveyance direction has not passed through the after-roller position X 4  (S 590 : No), the controller  800  waits in a standby state. Meanwhile, when determining that the trailing end of the sheet W in the re-conveyance direction has passed through the after-roller position X 4  (S 590 : Yes), the controller  800  starts a stop operation to stop the discharge motor  812  (S 600 , see timing t 14  in  FIG. 4 ). Thereafter, the controller  800  terminates the re-conveyance process. The second period of time ΔT 2  is a period of time between the timing t 7  and the timing t 14 . As described above, the second period of time ΔT 2  is longer than the first period of time ΔT 1 . Therefore, in the second re-conveyance control, it is possible to more efficiently cool the re-conveyed sheet W than in the first re-conveyance control. 
     After completing the re-conveyance process, the controller  800  goes to S 240  in  FIG. 3 . In S 240 , the controller  800  controls the process unit  600  to start transferring a toner image onto a second side of the sheet W passing through the transfer position X 1 . Afterward, the sheet W with the toner image transferred thereon is heated for a period of time during which the sheet W is passing through the nip P of the fuser  700 . Next, when determining that the timing at which the leading end of the sheet W in the conveyance direction is positioned between the fuser  700  and the discharge rollers  130  has come, the controller  800  starts rotating the discharge motor  812  in the forward direction (S 250 ). Subsequently, the controller  800  determines whether all of the pages specified by the print instruction have been completely printed (S 260 ). When determining that all of the pages specified by the print instruction have been completely printed (S 260 : Yes), the controller  800  performs the aforementioned post processing (S 170 ). Thereafter, the controller  800  terminates the print control process. When determining that all of the pages specified by the print instruction have not been completely printed (S 260 : No), the controller  800  sets again the target fixing temperature based on an elapsed period of time (S 270 ). Thereafter, the controller  800  goes back to S 190 , in which the controller  800  performs duplex printing for a next sheet W. Here, when a particular period of time has elapsed since the temperature control for the fuser  700  was started, and heat is accumulated at the fuser  700 , the controller  800  sets the target fixing temperature to be further lower than the particular high temperature TNH or the particular low temperature TNL. 
     According to the illustrative embodiment, when the target fixing temperature is equal to or higher than the reference temperature (S 520 : Yes), a re-conveyance period of time required for the re-conveyor  160  to convey the sheet W passed through the fuser  700  to the process unit  600  is longer than when the target fixing temperature is lower than the reference temperature (S 520 : No) (see ΔT 1  and ΔT 2  in  FIG. 4 ). Therefore, even when the target fixing temperature is equal to or higher than the reference temperature, it is possible to more adequately cool the sheet W being conveyed by the re-conveyor  160  than when the re-conveyance period of time is the same as when the target fixing temperature is lower than the reference temperature. 
     Suppose, for instance, that the first re-conveyance control is performed even when the target fixing temperature is equal to or higher than the reference temperature. In such a case, particularly, a first sheet W is re-conveyed after heated to a high temperature by the fuser  700 . Then, in the first re-conveyance control, since the re-conveyance period of time is the first period of time ΔT 1  shorter than the second period of time ΔT 2 , the first sheet W again passes through the fuser  700  without being adequately cooled. Thus, the first sheet W, which is still at a high temperature, is guided by the conveyance guide  150 . Hence, there is a risk that toner on the first side of the first sheet W might be melted by heat and attached to the conveyance guide  150 , and it might cause deterioration in accuracy for guiding sheets W by the conveyance guide  150 . In contrast, according to the illustrative embodiment, when the target fixing temperature is equal to or higher than the reference temperature, the second re-conveyance control is performed in which the re-conveyance period of time is longer than in the first re-conveyance control. Therefore, the first sheet W again passes through the fuser  700  after adequately cooled. Thus, as indicated by the graph line G 2  in  FIG. 4 , the first sheet W, which is cooled to a relatively low temperature, is guided by the conveyance guide  150 . Hence, it is possible to prevent the accuracy for guiding sheets W along the conveyance guide  150  from being deteriorated due to attachment of toner on the first side of the first sheet W to the conveyance guide  150 . It is noted that, in the illustrative embodiment, as described above, the air current V crossing the conveyance path R 1  and the re-conveyance path R 2  is generated in the casing  100  (see  FIG. 1 ). By the air current V, it is possible to further cool the re-conveyed sheet W. 
     Further, in the illustrative embodiment, it is possible to differentiate the re-conveyance period of time between the first re-conveyance control and the second re-conveyance control, by changing the rotational speed of the discharge motor  812  (the discharge rollers  130 ) in the backward direction depending on whether the target fixing temperature is equal to or higher than the reference temperature (see S 540  and S 560  in  FIG. 7 ). Thereby, it is possible to more efficiently prevent the user from misunderstanding that a sheet W has been discharged when a state where the sheet W is partially exposed to the outside of the casing  100  is maintained for a long time, than when the re-conveyance period of time is differentiated between the first re-conveyance control and the second re-conveyance control only by differentiating the stop period of time therebetween. 
     Further, in the illustrative embodiment, when the target fixing temperature is equal to or higher than the reference temperature, it is possible to cool the sheet W by making the re-conveyance period of time longer. Meanwhile, when the target fixing temperature is lower than the reference temperature, it is possible to shorten the period of time required for duplex printing by making the re-conveyance period of time shorter. 
     Further, in the illustrative embodiment, it is possible to differentiate the re-conveyance period of time between the first re-conveyance control and the second re-conveyance control by differentiating the stop period of time (see S 530  and S 550  in  FIG. 7 ) depending on whether the target fixing temperature is equal to or higher than the reference temperature. 
     Further, in the illustrative embodiment, at least the target fixing temperature for the first sheet W to pass through the fuser  700  for the first time may be set to a temperature equal to or higher than the reference temperature. Therefore, it is possible to cool the sheet W while bringing the temperature of the fuser  700  to a fixable temperature (e.g., the temperature suitable for fixing) earlier after acceptance of a print instruction for duplex printing, than when the target fixing temperature for the first sheet W is set to be lower than the reference temperature. It is noted that the target fixing temperature for the first sheet W to pass through the fuser  700  for the second time may be set to a temperature lower than the reference temperature. Further, the target fixing temperature for one or more subsequent sheets W to continuously pass through the fuser  700  may be still set to the temperature lower than the reference temperature. 
     Further, the higher the target fixing temperature is, the larger the quantity of heat accumulated in the fuser  700  is. Therefore, there is a risk that the sheet W might be heated to a higher temperature as a larger quantity of heat is applied to the sheet W while the sheet W is passing through the fuser  700 . In view of the risk, in the illustrative embodiment, the higher the target fixing temperature is, the lower the first target reverse speed VR 1  is set to be (see S 420  and  430  in  FIG. 6 ). Thereby, the second period of time ΔT 2  is set to be longer. Thus, it is possible to more certainly prevent the sheet W passed through the fuser  700  from being re-conveyed to the process unit  600  although the sheet W is still at a high temperature, than when the second period of time ΔT 2  is always constant. 
     Further, in the illustrative embodiment, the casing  100  includes the conveyance guide  150  configured to contact the first side of the sheet W passed through the fuser  700 . It is noted that the first side of the sheet W is opposite to the second side that faces the fixing belt  710  when the sheet W once passed through the fuser  700  again passes through the fuser  700 . After the sheet W has passed through the fuser  700  by which the toner image was fixed onto the first side, the sheet W is cooled while being conveyed by the re-conveyor  160 . Therefore, it is possible to prevent toner on the first side of the sheet W from being attached to the conveyance guide  150 . 
     Further, in the illustrative embodiment, the trailing end in the conveyance direction of the sheet W conveyed by the discharge rollers  130  is guided by the first re-conveyance guide  161  after completely passing by the conveyance guide  150 . Then, when the rotational directions of the discharge rollers  130  are reversed, the sheet W is guided to the re-conveyor  160  by the first re-conveyance guide  161 . Accordingly, it is possible to guide the sheet W to the re-conveyor  160  without having to provide a separate switching mechanism for switching between the conveyance path R 1  from the fuser  700  to the discharge rollers  130  and the re-conveyance path R 2  from the discharge rollers  130  to the re-conveyor  160 . 
     Further, in the illustrative embodiment, when simplex printing is performed, the target fixing temperature is set to the activation temperature TH higher than the particular high temperature TNH (see S 320  in  FIG. 5 ). Thereby, it is possible to promptly bring the temperature of the fuser  700  to a fixable temperature (e.g., the temperature suitable for fixing). Further, in the illustrative embodiment, when the target fixing temperature is set to the activation temperature TH, the timing to start the rotation control for the process motor  811  is made later than that in duplex printing (see timings t 1  and t 3  in  FIG. 4 ). Thereby, it is possible to shorten a period of time for preparatory driving of the process unit  600  or the fuser  700 . 
     Hereinabove, the illustrative embodiment according to aspects of the present disclosure has been described. The present disclosure can 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 the present disclosure can 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 the present disclosure is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. For instance, according to aspects of the present disclosure, the following modifications are possible. 
     [Modifications] 
     In the aforementioned illustrative embodiment, the target fixing temperature in the temperature control for the fuser  700  has been exemplified as a temperature of the fuser  700 . However, the temperature of the fuser  700  may be a temperature acquired based on a temperature signal from a temperature sensor such as the thermistor  770 . 
     In the aforementioned illustrative embodiment, the re-conveyance period of time is differentiated between the first re-conveyance control and the second re-conveyance control, by the difference therebetween in the rotational speed of the discharge motor  812  (the discharge rollers  130 ) in the backward direction (see S 540  and S 560  in  FIG. 7 ) and the difference therebetween in the stop period of time during which the discharge motor  812  is stopped (see S 530  and S 550 ). However, the re-conveyance period of time may be differentiated between the first re-conveyance control and the second re-conveyance control, by only one of the difference therebetween in the rotational speed of the discharge motor  812  (the discharge rollers  130 ) in the backward direction and the difference therebetween in the stop period of time. Further, the printer  10  may be configured to perform rotation control for the rollers  165  of the re-conveyor  160  independently with a motor different from the process motor  811 . In such a configuration, the sheet W may be stopped or conveyed at a lower speed on the re-conveyance path R 2  in the casing  100 . 
     In the aforementioned illustrative embodiment, the controller  800  determines in S 410  whether the outside air temperature is equal to or lower than the threshold temperature (e.g., 15° C.). Nonetheless, the controller  800  may determine whether the temperature of the fixing belt  710  before receipt of the print instruction is equal to or lower than a threshold temperature (e.g., 152° C.), based on a temperature signal from the thermistor  770 . The higher the temperature of the fuser  700  before receipt of the print instruction for duplex printing, the larger the quantity of heat accumulated in the fuser  700  is. Therefore, there is a risk that the sheet W might be heated to a higher temperature as a larger quantity of heat is applied to the sheet W while the sheet W is passing through the fuser  700 . In view of the risk, the higher the temperature of the fuser  700  before receipt of the print instruction for duplex printing is, the lower the first target reverse speed VR 1  may be set to be. Thereby, it is possible to make the second period of time ΔT 2  longer. Thus, it is possible to more certainly prevent the sheet W passed through the fuser  700  from being re-conveyed to the process unit  600  although the sheet W is still at a high temperature, than when the second period of time ΔT 2  is always constant. 
     Further, in the processes (see  FIGS. 3 and 5 to 7 ) exemplified in the aforementioned illustrative embodiment, some steps may be omitted. Further, the operations to be executed in some steps may be changed. Further, the order of some steps may be changed. 
     In the aforementioned illustrative embodiment, the printer  10  is configured to perform printing using a single color (black) of toner. However, the color of the toner to be used for printing is not limited to the color (black) exemplified in the illustrative embodiment. Further, the number of colors to be used for printing may be two or more. 
     Further, aspects of the present disclosure may be applied to copy machines, facsimile machines, and multi-function peripherals, as well as printers. 
     In the aforementioned illustrative embodiment, the photoconductive body  610  is a roller-shaped body. However, for instance, the photoconductive body  610  may be a belt-shaped body. 
     The exposure device  500  may be a device having a plurality of LED elements arranged in a main scanning direction parallel to the rotational axis direction of the photoconductive body  610 . 
     In the aforementioned illustrative embodiment, the fuser  700  includes the fixing belt  710 . However, the fuser  700  may include a fixing roller instead of the fixing belt  710 . 
     The operations and/or the processes described as being executed by the single CPU  801  in the aforementioned illustrative embodiment may be executed by one or more hardware elements such as a single CPU, a plurality of CPUs, one or more ASICs, and a combination of one or more CPUs and one or more ASICs. The controller  800  is a generic term that represents hardware elements (e.g., the CPU  801 ) for controlling the printer  10 . The controller  800  may not necessarily be a single hardware unit existing in the printer  10 .