Patent Publication Number: US-11385578-B2

Title: Image forming apparatus

Description:
BACKGROUND 
     Field 
     The present disclosure relates to an image forming apparatus such as a printer, a copying machine, a facsimile, and a multifunction peripheral. More particularly, the present disclosure relates to an image forming apparatus having a fixing apparatus for fixing a toner image to a recording material, and a recording material cooling apparatus for cooling down the recording material discharged from the fixing apparatus. 
     Description of the Related Art 
     A conventional image forming apparatus for forming an image on a recording material employs a belt conveyance apparatus that nips and conveys a recording material by using an endless belt (hereinafter simply referred to as a belt) stretched around a plurality of rollers. For example, there is proposed a recording material cooling apparatus that cools down a belt that is nipping and conveying a recording material conveyed from a fixing apparatus to lower the temperature of the recording material with a toner image fixed thereon, via the cooled belt, thus preventing adhesion between recording materials to be stacked as discussed in Japanese Patent Application Laid-Open No. 2009-181055. 
     The recording material cooling apparatus using a belt, as discussed in Japanese Patent Application Laid-Open No. 2009-181055, performs steering control in which at least one of a plurality of rollers for suspending the belt is inclined to reciprocate the belt in the roller axis direction, thus preventing the belt from shifting all the way to an end of the roller. The recording material cooling apparatus constantly performs such steering control while the belt is rotating, and stops the steering control when stopping rotating the belt. Accordingly, the roller may stop in an inclined state depending on the timing of stopping the steering control. 
     A recording material cooling apparatus using a belt requires a periodical belt replacement for maintenance. There has been an issue that the belt is difficult to be replaced if the roller stops in an inclined state as described above. 
     In particular, when the roller is stopping at a position where the roller inclines to move the belt toward the back side, as illustrated in  FIG. 13 , the pressure applied to the front side in the roller axis direction has been increased to move the belt toward the back side in the roller axis direction. If an attempt is made in this state to pull out the belt from the front side in the roller axis direction, the belt will be caught on the front side, making it difficult to replace the belt. 
     SUMMARY 
     According to an aspect of the present disclosure, an image forming apparatus including an image forming unit configured to form a toner image on a recording material, and configured to perform a state transition to a power-off state and to a standby state where image forming by the image forming unit is possible, includes a fixing unit configured to fix the toner image on the recording material, a belt, a conveyance unit configured to form a conveyance nip portion with the belt and to nip and convey the recording material that has passed through the fixing unit, a heat sink configured to be in contact with an inner circumferential surface of the belt, first and second rollers configured to suspend the belt, each having a rotational axis, a belt position detection unit configured to detect a position of the belt in a widthwise direction perpendicular to a thickness direction of the belt and a conveyance direction of the recording material nipped by the conveyance nip portion, a steering unit configured to swing the first roller relative to the second roller based on a detection result by the belt position detection unit to widthwisely move the belt relative to the first roller, and a control unit configured to control the steering unit, wherein, when the image forming apparatus enters the power-off state, the control unit controls the steering unit to make the rotational axis of the first roller approximately parallel to the rotational axis of the second roller. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an image forming apparatus according to an exemplary embodiment. 
         FIG. 2  is a block diagram illustrating an example hardware configuration of the image forming apparatus according to the exemplary embodiment. 
         FIG. 3  illustrates a cooling apparatus according to the exemplary embodiment. 
         FIG. 4  illustrates the cooling apparatus according to the exemplary embodiment. 
         FIG. 5  illustrates the cooling apparatus according to the exemplary embodiment. 
         FIG. 6  illustrates the cooling apparatus according to the exemplary embodiment. 
         FIGS. 7A and 7B  illustrate the cooling apparatus according to the exemplary embodiment. 
         FIG. 8  illustrates a belt steering mechanism of the cooling apparatus according to the exemplary embodiment. 
         FIG. 9  illustrates the belt steering mechanism of the cooling apparatus according to the exemplary embodiment. 
         FIG. 10  is a flowchart illustrating a steering roller control when power of the cooling apparatus according to the exemplary embodiment is OFF. 
         FIG. 11  is a flowchart illustrating the steering roller control when power of the cooling apparatus according to the exemplary embodiment is ON. 
         FIG. 12  illustrates a configuration in which a recording material cooling apparatus is disposed outside the image forming apparatus. 
         FIG. 13  illustrates an issue in the prior art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     &lt;Image Forming Apparatus&gt; 
     An exemplary embodiment of the present disclosure will be described below with reference to the accompanying drawings. An image forming apparatus to which a cooling apparatus according to the present exemplary embodiment is applicable will be described with reference to  FIG. 1 . An image forming apparatus  100  illustrated in  FIG. 1  is an electrophotographic tandem type full color printer. The image forming apparatus  100  includes image forming units Pa, Pb, Pc, and Pd for forming a yellow, a magenta, a cyan, and a black image, respectively. The image forming apparatus  100  forms a toner image on a recording material S according to image information from a document reading apparatus (not illustrated) or an external apparatus (not illustrated), such as a personal computer, communicably connected to the image forming apparatus  100 . Examples of recording materials S include plain paper, thick paper, rough paper, uneven paper, coated paper, and other types of paper, and include plastics films, cloths, and other various types of sheet materials. 
     A recording material conveyance process of the image forming apparatus  100  will be described. Recording materials S are stored in a paper cassette  10  in a stacked manner Each of the recording materials S is sent out from the paper cassette  10  by a feed roller  13  in synchronization with the image forming timing. The recording material S sent out by the feed roller  13  is conveyed to a registration roller  12  disposed in the middle of a conveyance path  114 . Then, the recording material S is subjected to skew correction and timing correction by the registration roller  12  and then sent to a secondary transfer portion T 2 . The secondary transfer portion T 2  is a transfer nip portion formed by a secondary inner transfer roller  14  and a secondary outer transfer roller  11 . At the secondary transfer portion T 2 , a toner image is transferred to the recording material S by a secondary transfer voltage being applied to the secondary outer transfer roller  11 . 
     The process of conveying the recording material S to the secondary transfer portion T 2  has been described above. The process of forming an image transmitted to the secondary transfer portion T 2  at a similar timing will be described. Firstly, the image forming units will be described. The image forming units Pa, Pb, Pc, and Pd have approximately similar configurations except for the colors of the used toner. More specifically, the image forming units Pa, Pb, Pc, and Pd use yellow, magenta, cyan, and black toner, respectively. The image forming unit Pd for black will be described as a representative, and descriptions of other image forming units Pa, Pb, and Pc will be omitted. 
     The image forming unit Pd mainly includes a development unit  1   d , a charging unit  2   d , a photosensitive drum  3   d , a photosensitive drum cleaner  4   d , and an exposure unit  5   d . Referring to  FIG. 1 , the surface of the photosensitive drum  3   d  rotating in the direction of the arrow R 1  is uniformly pre-charged by the charging unit  2   d . Then, an electrostatic latent image is formed on the photosensitive drum  3   d  by the exposure unit  5   d  driven based on an image information signal. Next, the electrostatic latent image formed on the photosensitive drum  3   d  is developed into a toner image by using developer by the development unit  1   d . Then, when a primary transfer voltage is applied to a primary transfer roller  6   d  disposed across the image forming unit Pd and the intermediate transfer belt  20 , the toner image formed on the photosensitive drum  3   d  is primarily transferred onto an intermediate transfer belt  20 . A small amount of primary transfer residual toner on the photosensitive drum  3   d  is collected by the photosensitive drum cleaner  4   d , and then the image forming unit Pd prepares for the next image forming process again. 
     In the above-described conveyance and image forming processes, timing is synchronized between the recording material S and the full color toner image at the secondary transfer portion T 2 , and then secondary transfer is performed. Subsequently, the recording material S is conveyed to the fixing apparatus  30  and applied with a predetermined pressure and heat, and the toner image is fixed onto the recording material S. The fixing apparatus  30  nips and conveys the recording material S with a toner image formed thereon, and then heats and pressurizes the conveyed recording material S to fix the toner image to the recording material S. More specifically, toner of the toner images formed on the recording material S through heating and pressurization is melted and mixed, and then the toner images are fixed on the recording material S as a full color image. In this way, a series of image forming processes ends. According to the present exemplary embodiment, the image forming units Pa, Pb, Pc, and Pd, the intermediate transfer belt  20 , the secondary inner transfer roller  14 , and the secondary outer transfer roller  11  are an example of an image forming unit for forming an image on the recording material S by using toner. 
     According to the present exemplary embodiment, the recording material S with a toner image fixed thereon is conveyed from the fixing apparatus  30  to the recording material cooling apparatus  50  and then cooled. For example, the temperature of the recording material S is around 90° C. immediately before entering the recording material cooling apparatus  50 , and decreases to around 60° C. after exiting the recording material cooling apparatus  50 . The recording material cooling apparatus  50  will be described in detail below. 
     In single-sided image forming, the recording material S with a toner image fixed thereon is nipped and conveyed by a discharge roller pair  105  and then discharged on a discharge tray  120 . On the other hand, in double-sided image forming, the conveyance path is changed from the path leading to the discharge tray  120  to a double-sided conveyance path  111  by a switching member  110  (flapper), and the recording material S nipped and conveyed by the discharge roller pair  105  is sent to the double-sided conveyance path  111 . Subsequently, the leading and trailing ends are exchanged by a reversing roller  112  and then sent to the conveyance path  114  again via a double-sided path  113 . The subsequent conveyance and image forming processes for the rear surface (second surface) are similar to the above-described processes, and redundant descriptions thereof will be omitted. 
     An example hardware configuration of the image forming apparatus  100  according to the present exemplary embodiment will be described below with reference to  FIG. 2 .  FIG. 2  is a block diagram illustrating an example hardware configuration of the image forming apparatus  100  according to the present exemplary embodiment. 
     The image forming apparatus  100  includes a main control unit  600  as a portion for controlling the operations of the image forming apparatus  100 . For example, the main control unit  600  is a substrate having a central processing unit (CPU)  601  as a control element. The main control unit  600  collectively controls the entire image forming apparatus  100 . The main control unit  600  performs turning on/off and the like of a portion for controlling the entire apparatus, a portion for controlling communication, a portion for performing image processing, a portion for image forming, and a motor for rotating various rotating members. The main control unit  600  may be divided into a plurality of different control units for respective functions, for example, an engine control unit for controlling printing. In the following descriptions, these control units are collectively configured. The main control unit  600  is an example of a control unit. 
     The main control unit  600  includes a storage unit  602  that stores programs and data for controlling the image forming apparatus  100  as well as image data. For example, the storage unit  602  includes a combination of volatile and nonvolatile storage devices, including a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), and a flash ROM. The CPU  601  performs calculation processing, and transmits and receives control signals based on programs and data stored in the storage unit  602 , to control the image forming apparatus  100 . Paper type settings such as plain paper and coated paper input from the operation panel  40  by the user are also stored in the storage unit  602  by the CPU  601 . 
     The main control unit  600  is communicably connected to a document conveyance unit  900 , an image reading unit  901 , and other units of the image forming apparatus  100  to control each unit. The main control unit  600  is also communicably connected with the operation panel  40 . In this way, settings and inputs made on the operation panel  40  are transmitted to the main control unit  600 . The main control unit  600  issues operation instructions to respective units according to the settings to operate each unit of the image forming apparatus  100 . 
     The main control unit  600  is further connected with a communication unit  903 , which is as an interface for communicating with a computer  200  (e.g., a personal computer) and a remote facsimile apparatus  300  via a network, a cable, or a communication network. Thus, the image forming apparatus  100  receives image data from the computer  200  and performs printing (printer function). Image data read by the image reading unit  901  is accumulated in the storage unit  602  and then transmitted to the computer  200  (scanner function). Image data is also transmitted and received to/from the external facsimile apparatus  300  (facsimile function). 
     The image forming apparatus  100  is provided with a power source unit  420 . For example, the power source unit  420  is connected to a commercial power supply to generate various voltages. A main switch  410  for turning ON and OFF the main power source for connecting and disconnecting the commercial power supply and the power source unit  420  is provided (e.g., on the side face of the image forming apparatus  100 ). The main switch  410  can be operated by a user or service engineer. The operation for turning the main switch  410  OFF from ON serves as a trigger for shifting the image forming apparatus  100  to the power OFF state. The operation for turning the main switch  410  ON from OFF serves as a trigger for shifting the image forming apparatus  100  to the standby state. 
     The power source unit  420  includes a plurality of power conversion circuits  422  including, for example, a rectifier circuit, a transformer, a converter, and a smoothing circuit to generate a plurality of different voltages required to operate the image forming apparatus  100 . For example, the power source unit  420  generates 24 VDC for motor drive and 5 VDC and 3.3 VDC for driving circuit elements such as the main control unit  600 , and applies these voltages to the units of the image forming apparatus  100 . 
     When the image reading unit  901 , the image generation unit  902 , and other units of the image forming apparatus  100  do not operate for a predetermined time period, the main control unit  600  enters a power-saving state providing a smaller power consumption than a standby state that can immediately start the image forming operation upon reception of an image forming instruction. Then, the main control unit  600  stops supplying power to portions predetermined by a power control unit  421 , thus implementing power-saving. According to the present exemplary embodiment, the main control unit  600  monitors the image reading unit  901 , the image generation unit  902 , and other units of the image forming apparatus  100  and then enters the power-saving state. However, the monitoring targets are not limited thereto. The main control unit  600  may follow an instruction for entering the power-saving state from the operation panel  40 . The present exemplary embodiment has been described above centering on the image forming apparatus  100  capable of performing state transitions to three different states: the power-off state, the power-saving state, and the standby state. However, the image forming apparatus  100  may have two different power-saving states. 
     &lt;Recording Material Cooling Apparatus&gt; 
     Next, the recording material cooling apparatus  50  will be described with reference to  FIG. 3 . As illustrated in  FIG. 3 , the recording material cooling apparatus  50  includes a first unit  501  U having an endless first belt  501 , and a second unit  502  U having an endless second belt  502  for nipping with the first belt  501  and conveying the recording material S. For example, the first belt  501  and the second belt  502  are made of polyimide having high strength. These belts are set to 100 μm in thickness and 942 mm in circumference. The recording material cooling apparatus  50  includes a heat sink  503  for cooling down the first belt  501 . The heat sink  503  is an example of a cooling member for cooling down the first belt  501 . 
     According to the present exemplary embodiment, the heat sink  503  contacts the first belt  501  that is in contact with the recording material S on the surface where a toner image is formed at the secondary transfer portion T 2  (see  FIG. 1 ). 
     The first belt  501  is stretched around a plurality of the first belt suspension rollers  501   a  to  501   e . Either one of the first belt suspension rollers  501   a  to  501   e  is rotated by a belt drive motor  511 . The second belt  502  is stretched around a plurality of the second belt suspension rollers  502   a  to  502   e . Either one of the second belt suspension rollers  502   a  to  502   e  is rotated by the belt drive motor  511 . More specifically, the first belt  501  is suspended by the first belt suspension rollers  501   a  to  501   e , and the second belt  502  is suspended by the second belt suspension rollers  502   a  to  502   e.    
     According to the present exemplary embodiment, the second belt suspension roller  502   e  rotated by the belt drive motor  511  corresponds to a drive roller for driving the second belt  502 . For example, the second belt suspension roller  502   e  is composed of an aluminum roller with a diameter of 24.8 mm, and silicon rubber with a thickness of 100 μm formed on the outer circumferential surface of the roller, with the friction coefficient for the polyimide belt set to 1.1. In this way, the second belt  502  rotates in the direction of the arrow C in  FIG. 3 . 
     A drive train  504   a  is disposed at a shaft end portion of the second belt suspension roller  502   e . Drive trains  504   a  to  504   d  transmit a driving force to the first belt  501 . According to the present exemplary embodiment, the second belt suspension rollers  502   a  to  502   d  correspond to idler rollers for suspending the second belt  502 . For example, the second belt suspension rollers  502   a  to  502   d  are aluminum rollers with a diameter of 25 mm, with the friction coefficient for the polyimide belt set to 0.1. On the other hand, the first belt  501  is stretched around the plurality of the first belt suspension rollers  501   a  to  501   e  and is in contact with the second belt  502 . 
     At least either one of the first belt suspension rollers  501   a  to  501   e  is rotated by a driving force of the belt drive motor  511  via the drive trains  504   a  to  504   d . According to the present exemplary embodiment, the first belt suspension roller  501   e  rotated by the drive train  504   d  corresponds to a drive roller for driving the first belt  501 . For example, the first belt suspension roller  501   e  is composed of an aluminum roller with a diameter of 24.8 mm, and silicon rubber with a thickness of 100 μm formed on the outer circumferential surface of the roller, with the friction coefficient for the polyimide belt set to 1.1. In this way, the first belt  501  rotates in the direction of the arrow B in  FIG. 3 . 
     In this way, the first belt  501  and the second belt  502  are rotated in the same direction at a cooling nip portion T 4  by the belt drive motor  511  as the same drive source. According to the present exemplary embodiment, the second belt suspension rollers  502   a  to  502   d  correspond to idler rollers for suspending the second belt  502 . For example, the second belt suspension rollers  502   a  to  502   d  are aluminum rollers with a diameter of 25 mm, with the friction coefficient for the polyimide belt set to 0.1. In addition, the first belt suspension roller  501   e  and the second belt suspension roller  502   e  do not form a nip portion. 
     The drive trains  504   a  to  504   d  are gears. Any one of the drive trains  504   a  to  504   d  has a one-way clutch  505  that disconnects the driving force transmission depending on the driving force direction. According to the present exemplary embodiment, the one-way clutch  505  is embedded in the drive train  504   d , and the rotation shaft of the drive train  504   d  and the rotation shaft of the one-way clutch  505  are coaxially positioned. 
     Setting is made so that, when the first belt suspension roller  501   e  is rotated clockwise in  FIG. 3 , the one-way clutch  505  is not locked with the shaft end portion of the first belt suspension roller  501   e . For example, when the rotating belt drive motor  511  is rotated to rotate the second belt  502  in the direction of the arrow C in  FIG. 3 , the drive train  504   a  rotates counterclockwise in  FIG. 3 , the drive train  504   b  rotates clockwise in  FIG. 3 , the drive train  504   c  rotates counterclockwise in  FIG. 3 , and the drive train  504   d  rotates clockwise in  FIG. 3 . 
     When the drive train  504   d  rotates clockwise, the one-way clutch  505  locks with the shaft end portion of the first belt suspension roller  501   e , and the first belt suspension roller  501   e  rotates clockwise. When the first belt suspension roller  501   e  rotates clockwise, the first belt  501  rotates in the direction of the arrow B in  FIG. 3 . 
     The recording material cooling apparatus  50  will be described with reference to  FIGS. 4 and 5 . The first unit  501  U for suspending the first belt  501  by the first belt suspension rollers  501   a  to  501   e  and the second unit  502  U for suspending the second belt  502  by the second belt suspension rollers  502   a  to  502   e  form the cooling nip portion T 4 . The cooling nip portion T 4  is an example of a conveyance nip portion that nips and conveys a sheet. 
     &lt;Fixing Apparatus&gt; 
     The second unit  502  U includes the drive train  504   a  rotatably supported by a shaft end portion of the second belt suspension roller  502   e  via a bearing (not illustrated), and a rotation support member  506 . The rotation support member  506  is provided with a second idler shaft  507  fixed thereto, and the second idler shaft  507  is provided with the drive train  504   b  rotatably supported via a bearing (not illustrated). The drive trains  504   a  and  504   b  are disposed to transmit a driving force. 
     The first unit  501  U includes a first idler shaft  512  fixed thereto, and the drive train  504   c  rotatably supported by the first idler shaft  512  via a bearing (not illustrated). A shaft end portion of the first belt suspension roller  501   e  is provided with the drive train  504   d  rotatably supported via the one-way clutch  505  illustrated in  FIG. 1 . The drive trains  504   c  and  504   d  are disposed to transmit a driving force. 
     According to the present exemplary embodiment, the first belt suspension roller (also referred to as a steering roller)  501   a  and the second belt suspension roller (also referred to as a steering roller)  502   a  are steering rollers disposed to control the deviations of the first belt  501  and the second belt  502 , respectively. For example, the steering roller  501   a  is composed of an aluminum roller with a diameter of 24.8 mm, and an acrylic layer with a thickness of 100 μm formed on the outer circumferential surface of the roller, with the friction coefficient for the polyimide belt set to 0.5. These steering rollers  501   a  and  502   a  press the first belt  501  and the second belt  502 , respectively, from the inner circumferential side outward so that the first belt  501  and the second belt  502  provide a tension of about 39.2 N (about 4 kgf). 
     To accomplish this, the steering roller (second belt suspension roller)  501   a  is biased by a spring  507   a  (see  FIG. 3 ), and the steering roller  502   a  is biased by a spring  508   a  (see  FIG. 3 ). 
       FIG. 7A  is a perspective view illustrating the recording material cooling apparatus  50  viewed from the back side (rear surface side) of the image forming apparatus  100 .  FIG. 7B  is a cross-sectional view schematically illustrating the steering roller  501   a . As for each of the steering rollers  501   a  and  502   a , steering mechanisms  400  are provided on the back side of the recording material cooling apparatus  50 , as illustrated in  FIG. 7A . When the steering rollers  501   a  and  502   a  are swung around the center thereof in the rotational axis direction (widthwise direction), steering control of the first belt  501  and the second belt  502  can be performed. The steering mechanisms  400  are examples of steering units. 
     As illustrated in  FIG. 7B , the steering roller  501   a  is rotatably supported by a roller holder  800 . The roller holder  800  is swingable around a swing axis  802  relative to a support sheet metal  801 . The swing axis  802  is provided at the center between the front and the back side ends of the roller holder  800  in the rotational axis direction of the steering roller  501   a . When a shaft  465  fixed to the roller holder  800  is operated by a steering mechanism  400 , the roller holder  800  is swingable around the swing axis  802 . The support sheet metal  801  is supported by a back side plate  461  disposed on the back side of the recording material cooling apparatus  5  and a front side plate  462  disposed on the front side thereof. When an operation lever (not illustrated) is operated, the support sheet metal  801  moves the steering roller  501   a  toward the inner circumferential side together with the roller holder  800 , thus releasing the pressing of the steering roller  501   a  on the first belt  501 . In other words, this operation enables canceling the state where the first belt  501  is suspended with tension. The steering roller  501   a  has been described above as an example. The steering roller  502   a  of the second unit  502  U has a similar configuration to the steering roller  501   a.    
     Although the present exemplary embodiment will be described centering on an example configuration in which the steering mechanisms  400  are disposed in the recording material cooling apparatus  50 , the steering mechanisms  400  may be disposed on the frame (not illustrated) of the image forming apparatus  100  that supports the recording material cooling apparatus  50 . Steering control of the first belt  501  and the second belt  502  will be described below. Although, in the above-described exemplary embodiment, the steering mechanism  400  is configured to be operated by the shaft  465  disposed on the roller holder  800 , the steering mechanism  400  may be directly operated by the axis of the steering roller  501   a  to perform steering control. 
     According to the present exemplary embodiment, the steering rollers  501   a  and  502   a  are examples of first rollers, and the first belt suspension rollers  501   b  to  501   e  and the second belt suspension rollers  502   b  to  502   e  are examples of second rollers. As described above, according to the present exemplary embodiment, the first belt suspension rollers  501   b  to  501   e  and the second belt suspension roller  52   b  to  502   e  do not swing, and both ends of the roller axes are supported by the front and the back side frames of the first unit  501  U and the second unit  502  U. The steering roller  502   a  is an example of a third roller, and the second belt suspension rollers  502   b  to  502   e  are examples of fourth rollers. 
     Pressure rollers  509   a  and  509   b  for pressurizing the second belt  502  toward the heat sink  503  are disposed on the inner circumferential side of the second belt  502 . For example, the pressure rollers  509   a  and  509   b  apply a pressure of 9.8 N (1 kgf) to the second belt  502  to reliably bring the first belt  501  to contact the heat sink  503  (heat reception unit  503   a  to be described below) via the second belt  502 . 
     The recording material S with a toner image fixed thereon is nipped between the first belt  501  and the second belt  502  and conveyed in the conveyance direction (the arrow D in  FIG. 3 ) due to the rotations of these belts. At this time, the recording material S passes through the cooling nip portion T 4  formed by the first belt  501  and the second belt  502  in contact with each other. According to the present exemplary embodiment, the first belt  501  is cooled by the heat sink  503 . 
     To efficiently cool the recording material S, the heat sink  503  is disposed to be in contact with the inner surface of the first belt  501  at a position where the cooling nip portion T 4  is formed. When the recording material S passes through the cooling nip portion T 4 , the recording material S is cooled by the heat sink  503  via the first belt  501 . For example, when the temperature of the recording material S is around 90° C. before passing through the recording material cooling apparatus  50 , the recording material S is cooled so that its temperature decreases to around 60° C. after passing through the recording material cooling apparatus  50 . As the recording material S is cooled down, toner on the recording material S is also cooled down and fixed. 
     The heat sink  503  is made of a metal such as aluminum. The heat sink  503  includes a heat reception unit  503   a  for drawing heat from the first belt  501  by contacting the first belt  501 , a heat radiation unit  503   b  for radiating heat, and a fin base  503   c  for transferring heat from the heat reception unit  503   a  to the heat radiation unit  503   b.    
     The heat radiation unit  503   b  is formed of a number of radiating fins to promote efficient heat radiation with a large area of contact with the air. For example, a radiating fin is set to be 1 mm in thickness, 100 mm in height, and 5 mm in pitch, and the fin base  503   c  is set to be 10 mm in thickness. 
     A cooling fan  513  for sending air toward the heat sink  503 , more specifically, the heat radiation unit  503   b , is provided to forcibly cool the heat sink  503  itself. The air volume of the cooling fan  513  is set, for example, to 2 m 3 /min. The cooling method for the heat sink  503  is not limited to the cooling fan  513 . The heat sink  503  may be cooled, for example, by a cooling medium. 
     In such the recording material cooling apparatus  500 , the first belt  501  shifts to widthwise end sides of the first belt suspension rollers  501   a  to  501   e  by the dispersion of the dimensional tolerance of the first belt suspension rollers  501   a  to  501   e  supporting the first belt  501  and the dispersion of the dimensional tolerance of a pair of frames supporting both ends of the first belt suspension rollers  501   a  to  501   e . Likewise, the second belt  502  shifts toward widthwise end sides of the first belt suspension rollers  501   a  to  501   e  by the dispersion of the dimensional tolerance of the second belt suspension rollers  502   a  to  502   e  supporting the second belt  502  and the dispersion of the dimensional tolerance of a pair of frames supporting both ends of the second belt suspension rollers  502   a  to  502   e . As a result, an end of the first belt  501  or the second belt  502  may possibly be in friction with either one of a pair of frames disposed at both widthwise ends of the recording material cooling apparatus  50 . Therefore, by swinging one of the plurality of rollers supporting the first belt  501  and the second belt  502 , as a steering roller, relative to other rollers, the present exemplary embodiment performs steering control to reciprocate the first belt  501  and the second belt  502  in the widthwise directions. This prevents the widthwise ends of the first belt  501  and the second belt  502  from being in friction with the above-described frame. 
     To perform steering control in this way, there are provided sensor units  390  and  391  for detecting widthwise end positions of the first belt  501  and the second belt  502 . The widthwise direction of the first belt  501  is the rotational axis direction of the first belt suspension rollers  501   a  to  501   e , and the widthwise direction of the second belt  502  is the rotational axis direction of the second belt suspension rollers  502   a  to  502   e . Based on the detection signals of the sensor units  390  and  391 , the widthwise end positions of the rotating first belt  501  and the rotating second belt  502  are detected. The sensor unit  390  is capable of detecting the widthwise end positions of the first belt  501  at a plurality of positions to detect how much the widthwise center of the first belt  501  deviates from the widthwise centers of the first belt suspension rollers  501   a  to  501   e . Likewise, the sensor unit  391  is capable of detecting widthwise end positions of the second belt  502  at a plurality of positions to detect how much the widthwise center of the second belt  502  deviates from the widthwise centers of the second belt suspension rollers  502   a  to  502   e . Then, based on the end positions detected by the sensor units  390  and  391 , the above-described steering mechanisms  400  are operated so that the first belt  501  and the second belt  502  are positioned at the widthwise center, respectively. More specifically, the angles of the steering rollers  501   a  and  502   a  are adjusted based on the detection signals of the sensor units  390  and  391 , respectively. The sensor units  390  and  391  are examples of belt position detection units. The “widthwise direction” according to the present exemplary embodiment refers to the direction perpendicular to the thickness direction of the first belt  501  and the conveyance direction of the sheet nipped by the cooling nip portion T 4 , and is the rotational axis direction of the steering rollers  501   a  and  502   a . The “widthwise direction” refers to the rotational axis direction of the first belt suspension rollers  501   b  to  501   e , and also to the rotational axis direction of the second belt suspension rollers  502   b  to  502   e.    
     The steering mechanisms  400  for the first unit  501  U and the second unit  502  U have almost similar configurations. Therefore, the steering mechanism  400  for the first unit  501  U will be described as a representative with reference to  FIG. 8 . 
     A steering control stepping motor  452 , a worm gear  466 , and a sector gear  460  are supported by the back side plate  461  on the back side of the cooling apparatus  500 . The shaft  465  is fixed to the roller holder  800  supporting the shaft of the first belt suspension roller  501   a . The sensor unit  390  is a belt end detection sensor. 
     When the steering control stepping motor  452  is driven in the clockwise (CW) direction, the worm gear  466  rotates, and then the sector gear  460  is downwardly oriented around the shaft. Accordingly, the shaft  465  downwardly moves and hence the roller holder  800  with the shaft  465  fixed thereto swings around the swing axis  802 . As a result, the steering roller  501   a  supported by the roller holder  800  is inclined toward the back side in the rotational axis direction of the steering roller  501   a . Then, the first belt  501  moves toward the back side with the rotation of the first belt  501 . According to the present exemplary embodiment, the back side refers to the side closer to an opening/closing mechanism  510  in the rotational axis direction of the steering roller  501   a , and the back side refers to the rear surface side of the image forming apparatus  100 . 
     On the other hand, when the steering control stepping motor  452  is driven in the counterclockwise (CCW) direction, the worm gear  466  rotates, and then the sector gear  460  is upwardly oriented around the shaft. Accordingly, the shaft  465  upwardly moves and hence the roller holder  800  with the shaft  465  fixed thereto swings around the swing axis  802 . As a result, the steering roller  501   a  is slightly inclined toward the front side in the rotational axis direction of the steering roller  501   a . Then, the first belt  501  moves toward the front side (right direction in  FIG. 7B ) with the rotation of the first belt  501 . 
       FIG. 9  illustrates a case where the steering roller  501   a  is inclined to move back the position of the first belt  501  of the first unit  501  U from a back side position to a front side position. The drive for inclining the steering roller  501   a  is positioned on the back side, as described above, an end of the steering roller  501   a  is raised by the steering control stepping motor  452 . Hereinafter, the displacement amount of the end of the steering roller  501   a  is referred to as a displacement amount D of the end of the steering roller  501   a . The positive (+) direction of the displacement amount D is the upward direction in which the first belt  501  is moved toward the front side in the rotational axis direction of the steering roller  501   a . The negative (−) direction of the displacement amount D is the downward direction in which the first belt  501  is moved toward the back side in the rotational axis direction of the steering roller  501   a.    
     When the displacement amount D of the end changes, the widthwise position of the first belt  501  tends to move following the change. Ideally, the first belt  501  is positioned at a position where the widthwise center of the first belt  501  coincides with the widthwise center of the steering roller  501   a . At this ideal position, the angle of the steering roller  501   a  is approximately horizontal, and the above-described displacement amount D is the reference displacement amount ±0. 
     Ideally, when the displacement amount D is the reference displacement amount ±0, the belt does not widthwisely move from that position. Actually, however, the first belt  501  shifts to either end of the steering roller  501   a  because of the above-described dimensional tolerance and other various factors. As a result, the first belt  501  moves in the widthwise direction of the first belt suspension roller. Therefore, the position of the reference displacement amount ±0 is set to be the reference position of the steering roller  501   a , at which the steering HP sensor  453  turns OFF from ON by the sector gear  460 . The CPU  601  determines that the steering HP sensor  453  is ON when it is shielded from light and OFF when it is not shielded from light. The steering HP sensor  453  is an example of a steering position detection unit for detecting the positions (displacements) of the steering rollers  501   a  and  501   b , i.e., the angles relative to other rollers. 
     The displacement amount D of the steering roller  501   a  is determined by the position of the first belt  501  detected by the sensor unit  390 . More specifically, when the first belt  501  is positioned more on the front side than the widthwise center, a negative displacement amount of the steering roller  501   a  is set, and the first belt  501  is moved back to the widthwise center. When the first belt  501  is positioned more on the back side than the widthwise center, a positive displacement amount of the steering roller  501   a  is set, and the first belt  501  is moved back to the widthwise center. According to the present exemplary embodiment, the sensor unit  390  enables detecting a total of seven belt positions, i.e., the center position, three positions on the back side, and three positions on the front side. When the first belt  501  is positioned at the center, the steering mechanism  400  sets the steering roller  501   a  to the reference position. When the first belt  501  is positioned at either one of the six positions except for the center, the steering mechanism  400  inclines the steering roller  501   a  to set the angle of the steering roller  501   a  corresponding to each position. For example, when the first belt  501  is positioned more on the back side than the center, the steering mechanism  400  gradually changes the angle of the steering roller  501   a  (+0.75°, +1.5°, and +1.8°) corresponding to the position of the first belt  501 . When the first belt  501  is positioned more on the front side than the center, the steering mechanism  400  gradually changes the angle of the steering roller  501   a  (−0.75°, −1.5°, and −1.8°) corresponding to the position of the first belt  501 . In this way, the steering mechanism  400  can swing the steering roller  501   a  within a range from +1.8° to −1.8°. Although the present exemplary embodiment defines the swing angles of the steering roller  501   a  as described above, it is not limited thereto. 
     When the steering rollers  501   a  and  501   b  are inclined in the recording material cooling apparatus  50  having the steering mechanism  400 , the first belt  501  or the second belt  502  is hard to pull out in replacing the first belt  501  or the second belt  502 , respectively. This means that inclined steering rollers degrade the workability in belt replacement. In particular, when the first steering roller  501   a  or the second steering roller  501   b  is stopping at such an inclination angle that the first belt  501  or the second belt  502  moves toward the back side of the recording material cooling apparatus  50 , the workability in belt replacement degrades because of the increased pressure in the pulling direction for the first belt  501  or the second belt  502 . 
     When the heat sink  503  is provided in the inner circumferential surface of a conveyance belt, like the first belt  501  in the recording material cooling apparatus  50 , the heat sink  503  occupies a large area in the conveyance belt to improve the cooling efficiency. Accordingly, even when the steering mechanism  400  is configured to move the steering roller  501   a  toward the inner circumferential side of the first belt  501  against the biasing force of the spring  507   a  that presses the steering roller  501   a  toward the inner circumferential surface of the first belt  501  in replacing the first belt  501 , a sufficient moving amount of the steering roller  501   a  cannot be obtained because of the presence of the heat sink  503 . 
     Accordingly, when changing the first belt  501  in a state where the steering roller  501   a  is inclined, the first belt  501  is hard to pull out against the suspension rollers  501   a  to  501   d , making it hard to attach a new belt. 
     According to the present exemplary embodiment, the steering roller  501   a  is moved back to the reference position so that the axis line of the steering roller  501   a  becomes approximately parallel to the axis lines of other suspension rollers  501   b  to  501   d  before the image forming apparatus  100  requiring the replacement of the first belt  501  enters the power-off state or the power-saving state. According to the present exemplary embodiment, “approximately parallel” also includes, for example, a position deviated from the reference displacement amount ±0 within a range of ±0.5° when the state of the reference displacement amount ±0 is assumed to be the parallel state. A sequence for moving the steering roller  501   a  to the reference position will be described in detail below. 
     The first belt  501  of the first unit  501  U has been described above with reference to  FIGS. 8 and 9 , and the second belt  502  of the second unit  502  U has a similar basic configuration. 
     A method for removing the recording material S from the recording material cooling apparatus  50  when the recording material S is clogged in the recording material cooling apparatus  50 , and the swing configuration provided for the drive trains  504   a  to  504   d  will be described with reference to  FIGS. 4 and 5 . 
       FIG. 4  illustrates a state where the recording material S is conveyed in the recording material cooling apparatus  50 . The cooling nip portion T 4  is formed by the first unit  501  U for suspending the first belt  501  by using the first belt suspension rollers  501   a  to  501   e , and the second unit  502  U for suspending the second belt  502  by using the second belt suspension rollers  502   a  to  502   e  (see  FIG. 3 ). 
     The second unit  502  U is provided with the drive train  504   a  rotatably supported by a shaft end portion of the second belt suspension roller  502   e  via a bearing (not illustrated), and the rotation support member  506 . The rotation support member  506  is provided with the second idler shaft  507  fixed thereto. The second idler shaft  507  is provided with the drive train  504   b  rotatably supported via a bearing (not illustrated). The drive trains  504   a  and  504   b  are disposed to transmit a driving force. 
     The rotation support member  506  is connected with the spring member  509  connected with a fixing member  508 , and applies tension to the rotation support member  506  rotatably supported by a shaft end portion of the second belt suspension roller  502   e  via a bearing (not illustrated). 
     The first unit  501  U is provided with the first idler shaft  512  fixed thereto, and is provided with the drive train  504   c  rotatably supported by the first idler shaft  512  via a bearing (not illustrated). A shaft end portion of the first belt suspension roller  501   e  is provided with the drive train  504   d  rotatably supported via the one-way clutch  505  illustrated in  FIG. 3 . The drive trains  504   c  and  504   d  are disposed to transmit a driving force. 
     When the first unit  501  U illustrated in  FIG. 4  contacts the second unit  502  U, the drive train  504   b  of the second unit  502  U can transmit a driving force with the drive train  504   c  of the first unit  501  U. 
     The first unit  501  U is supported to be openable and closable by a rotation shaft (not illustrated) provided in the opening/closing mechanism  510 , to enable maintaining a state where the cooling nip portion T 4  in  FIG. 4  is formed and a state where the cooling nip portion T 4  in  FIG. 5  is not formed.  FIG. 5  illustrates a state where the recording material S clogged in the recording material cooling apparatus  50  is to be removed. The first unit  501  U and the second unit  502  U are separated without forming the cooling nip portion T 4  illustrated in  FIG. 3 . 
     When the first unit  501  U illustrated in  FIG. 5  is separated from the second unit  502  U, the drive train  504   b  of the second unit  502  U cannot transmit a driving force with the drive train  504   c  of the first unit  501  U. The rotation support member  506  rotatably supported by a shaft end portion of the second belt suspension roller  502   e  via a bearing (not illustrated) receives tension from the spring member  509  connected with the fixing member  508 , and rotates counterclockwise around the rotation center of the second belt suspension roller  502   e.    
     When the rotation support member  506  rotates counterclockwise, a rotation regulation portion (not illustrated) of the rotation support member  506  interferes with a second unit front upper plate  519 , and the rotation support member  506  is regulated at a constant angle. This constant angle is set so that, when a state where the cooling nip portion T 4  is not formed (see  FIG. 5 ) is changed to a state where the cooling nip portion T 4  is formed (see  FIG. 4 ), the drive train  504   c  of the first unit  501  U and the drive train  504   b  of the second unit  502  U are engaged with each other to enable transmitting a driving force again. 
     In addition, when the belt drive motor  511  rotates the second belt in the direction of the arrow C in  FIG. 3 , the drive train  504   b  rotates around the shaft end portion of the second belt suspension roller  502   e  by the force generated by the drive trains  504   b  and  504   c . The drive trains  504   b  arranged to be constantly biased relative to the drive train  504   c  attached to the first unit  501  U. 
     How the recording material cooling apparatus  50  is fixed will be described with reference to  FIGS. 1, 5, 6, 7A, and 7B . As illustrated in  FIG. 1 , the recording material cooling apparatus  50  is disposed in an apparatus body  100 A. 
     The recording material cooling apparatus  50  is provided with positioning support members  514  and  515  illustrated in  FIGS. 5 and 6 , and positioning support members  516  and  517  illustrated in  FIGS. 7A and 7B . The recording material cooling apparatus  50  is supported by the apparatus body  100 A with these positioning support members  514 ,  515 ,  516 , and  517 . According to the present exemplary embodiment, as illustrated in  FIGS. 5 and 6 , a second unit front lower plate  518  is provided with hole portions as the positioning support members  514  and  515 . The recording material cooling apparatus  50  is fixed so that the hole portions are in contact with a convex portion of the apparatus body  100 A. More specifically, the positioning support members  514  and  515  are used to determine positions relative to the support frame of the image forming apparatus  100  at positions on the front side of the recording material cooling apparatus  50 . 
     As illustrated in  FIGS. 7A and 7B , there are provided axial portions as the positioning support members  516  and  517 . The recording material cooling apparatus  50  is fixed so that the positioning support members  516  and  517  are engaged with holes on the vertical wall of the apparatus body  100 A. Thus, the positioning support members  516  and  517  are used to determine the position the recording material cooling apparatus  50  relative to the frame of the image forming apparatus  100  at the positions on the back side of the recording material cooling apparatus  50 . 
     &lt;Sequence for Moving Steering Roller to Reference Position&gt; 
       FIG. 10  illustrates a sequence for moving the steering roller  501   a  according to the present exemplary embodiment to the reference position (the displacement amount D ±0 in  FIG. 9 ). The first unit  501  U and the second unit  502  U have approximately the same configurations. The steering roller  501   a  of the first unit  501  U will be described as a representative. 
     In step S 1001 , the CPU  601  starts monitoring the status of the image forming apparatus  100 . More specifically, the CPU  601  monitors whether the main switch  410  is OFF (a trigger for shifting the image forming apparatus  100  to the power-off state), whether the image reading unit  901 , the image generation unit  902 , and other units of the image forming apparatus  100  do not operate for a predetermined time period, or whether a request for entering the power-saving state is input from the operation panel  40  (a trigger for shifting the image forming apparatus  100  to the power-saving state). 
     In step S 1002 , the CPU  601  monitors whether the OFF state of the main switch  410  is detected. When the CPU  601  detects that the main switch  410  is OFF (YES in step S 1002 ), the processing proceeds to step S 1003 . On the other hand, when the CPU  601  does not detect the OFF state of the main switch  410  (NO in step S 1002 ), the processing proceeds to step S 1010 . In step S 1010 , the CPU  601  determines whether the transition to the power-saving state is required. As described above, the CPU  601  determines that the transition to the power-saving state is required when the image reading unit  901 , the image generation unit  902 , and other units of the image forming apparatus  100  do not operate for a predetermined time period or when a request for entering the power-saving state is input from the operation panel  40 . 
     When the CPU  601  determines that the transition of the image forming apparatus  100  to the power-saving state is required (YES in step S 1010 ), the processing proceeds to step S 1003 . On the other hand, when the CPU  601  determines that the transition to the power-saving state is not required (NO in step S 1010 ), the processing returns to step S 1002 . In step S 1002 , the CPU  601  continues monitoring the status of the image forming apparatus  100 . In step S 1003 , the CPU  601  determines whether the steering HP sensor  453  is ON. The CPU  601  detects that the steering HP sensor  453  is ON when it is shielded from light by the sector gear  460  and OFF when it is not shielded from light. 
     When the CPU  601  determines that the steering HP sensor  453  is ON (YES in step S 1003 ), the processing proceeds to step S 1004 . In step S 1004 , the CPU  601  starts driving the steering control stepping motor  452  in the CCW direction. 
     Then, the CPU  601  continues driving until the steering HP sensor  453  turns OFF. In step S 1005 , the CPU  601  determines whether the steering HP sensor  453  is OFF. When the CPU  601  detects that the steering HP sensor  453  is OFF (YES in step S 1005 ), the processing proceeds to step S 1006 . In step S 1006 , the CPU  601  stops the steering control stepping motor  452 . Then, the CPU  601  sets the stop position as the reference position. Although, in the present exemplary embodiment, the CPU  601  stops the steering control stepping motor  452  based on the OFF state of the steering HP sensor  453 , the CPU  601  may stop the motor when a predetermined time period has elapsed since the OFF state of the steering HP sensor  453  has been detected. More specifically, the steering roller  501   a  may move over a predetermined distance from the position where the OFF state of the steering HP sensor  453  has been detected. 
     On the other hand, when the CPU  601  detects that the steering HP sensor  453  is OFF (NO in step S 1003 ), the processing proceeds to step S 1020 . In step S 1020 , the CPU  601  starts driving the steering control stepping motor  452  in the CW direction. In step S 1021 , the CPU  601  continues driving the motor until the steering HP sensor  453  turns ON. 
     In step S 1021 , the CPU  601  determines whether the steering HP sensor  453  is ON. When the CPU  601  detects that the steering HP sensor  453  is ON (YES in step S 1021 ), the processing proceeds to step S 1022 . In step S 1022 , the CPU  601  stops the steering control stepping motor  452 . In step S 1023 , the CPU  601  determines whether a predetermined time period (the time period until the vibration when the motor stops becomes stable) has elapsed since the CPU  601  has detected the stop of the steering control stepping motor  452 . When the CPU  601  determines that the predetermined time period has not elapsed (NO in step S 1023 ), the CPU  601  waits until the predetermined time period has elapsed. 
     On the other hand, when the CPU  601  determines that the predetermined time period has elapsed (YES in step S 1023 ), the processing returns to step S 1004 . In step S 1004 , the CPU drives the steering control stepping motor  452  in the CCW direction. In step S 1005 , the CPU  601  continues driving the motor until the steering HP sensor  453  turns OFF. When the CPU  601  detects that the steering HP sensor  453  is OFF (YES in step S 1005 ), the processing proceeds to step S 1006 . In step S 1006 , the CPU  601  stops the steering control stepping motor  452 . Then, the CPU  601  sets the stop position as the reference position. In step S 1007 , the CPU  601  shifts the image forming apparatus  100  to the power-off state or the power-saving state. 
     When the image forming apparatus  100  enters the power-off state (the main switch  410  turned OFF) or the power-saving state, the present exemplary embodiment moves the steering roller  501   a  to the reference position (the position where the axis line of the steering roller  501   a  is approximately parallel to the axis lines of other first belt suspension rollers  501   b  to  501   d ), thus facilitating belt replacement. Although the present exemplary embodiment is configured to move the steering roller  501   a  to the reference position when the image forming apparatus  100  enters the power-off state or the power-saving state, it is not limited thereto. For example, the present exemplary embodiment may be configured to move the steering roller  501   a  to the reference position only when the image forming apparatus  100  enters the power-off state. The present exemplary embodiment may also be configured to move the steering roller  501   a  to the reference position only when the image forming apparatus  100  enters the power-saving state. The present exemplary embodiment may also be configured to, when the image forming apparatus  100  enters the power-saving state and then the power-off state, move the steering roller  501   a  to the reference position at the timing before the image forming apparatus  100  enters the power-saving state and at the timing before the image forming apparatus  100  enters the power-off state. The present exemplary embodiment may also be configured to move the steering roller  501   a  to the reference position when the image forming apparatus  100  enters the power-off state or the power-saving state and when the image forming apparatus  100  stops operating in a state where the steering roller  501   a  is inclined relative to the reference position. More specifically, when the steering roller  501   a  stops operating at the reference position when the image forming apparatus  100  enters the power-off state or the power-saving state, the CPU  601  does not need to perform the above-described control. 
     &lt;Sequence When Main Switch Is ON&gt; 
       FIG. 11  illustrates a sequence when the main switch  410  according to the present exemplary embodiment is turned ON. Since the first unit  501  U and the second unit  502  U have approximately the same control configurations, the first unit  501  U will be described as a representative. 
     In step S 2001 , the CPU  601  monitors the status of the main switch  410 . When the main switch  410  is not ON (NO in step S 2002 ), the CPU  601  waits until the main switch  410  is turned ON. On the other hand, when the main switch  410  is ON (YES in step S 2002 ), the processing proceeds to step S 2003 . In step S 2003 , the CPU  601  acquires the detection result by the sensor unit  390 . 
     In step S 2004 , the CPU  601  drives the belt drive motor  511  to rotate the first belt  501 . In step S 2005 , the CPU  601  drives the stepping motor  452  based on the detection result by the sensor unit  390  acquired in step S 2003  to perform steering control. Detailed steering control is similar to the above-described steering control, and redundant descriptions thereof will be omitted. 
     In step S 2006 , the CPU  601  determines whether a predetermined time period has elapsed since the steering control has been started. When the predetermined time period has elapsed (YES in step S 2006 ), the processing proceeds to step S 2007 . In step S 2007 , the CPU  601  stops the stepping motor  452 . In step S 2008 , the CPU  601  stops the belt drive motor  511 . 
     In this way, the CPU  601  also performs the steering control for the steering roller  501   a  when the main switch  410  is turned ON, and then the image forming apparatus  100  enters the standby state (when the image forming apparatus  100  is activated). This is because the widthwise position of the first belt  501  may possibly change by a replacement work during the power-off state of the image forming apparatus  100 . This is because, even if the first belt  501  is not replaced, performing control to move the steering roller  501   a  back to the reference position before the image forming apparatus  100  enters the power-off state may possibly deviate the angle of the steering roller  501   a  relative to the position of the first belt  501 . 
     Thus, performing the steering control during activation of the image forming apparatus  100  enables preventing the first belt  501  or the second belt  502  from shifting all the way to an end of the steering roller  501   a  or  502   a , respectively. Performing the steering control during activation of the image forming apparatus  100  also enables setting the angle of the steering roller  501   a  or  502   a  suitable for the position of the first belt  501  or the second belt  502 , respectively. The above-described predetermined time period in step S 2006  needs to be set to a time period during which the angle of the steering roller  501   a  or  502   a  suitable for the position of the first belt  501  or the second belt  502  can be resumed even with the maximum amount of deviation of the position of the first belt  501  or the second belt  502  from the steering roller  501   a  or  502   a , respectively. 
     For example, when the main switch  410  of the image forming apparatus  100  is turned OFF in a state where the first belt  501  is positioned more on the back side than the center of the image forming apparatus  100 , the steering roller  501   a  returns to the reference position by the above-described control. However, depending on the timing when the first belt  501  stops rotating, the position of the first belt  501  in the rotational axis direction of the steering roller  501   a  deviates from the angle of the steering roller  501   a . However, even if the position of the first belt  501  is more on the back side than the center, performing the steering control when the main switch  410  is turned ON as described above swings the steering roller  501   a  to the position where the first belt  501  is moved back to the center based on the detection result by the sensor unit  390 . This enables preventing the position of the first belt  501  from deviating from the angle of the steering roller  501   a , thus preventing the first belt  501  from deviating all the way to an end. 
     When the steering control is performed in response to the main switch  410  being turned ON, the first belt  501  and the second belt  502  rotate since the first belt suspension roller  501   e  and the second belt suspension roller  502   e  are rotating. In this case, the CPU  601  may determine whether a sheet is nipped by the cooling nip portion T 4  by sensors (not illustrated) disposed on the upstream and downstream sides of the cooling nip portion T 4  in the sheet conveyance direction. In this case, if a sheet is nipped by the cooling nip portion T 4 , the CPU  601  may display a message for prompting the user to remove the sheet. With this message, even if power is turned ON in a state where a sheet remains nipped by the cooling nip portion T 4  because of a conveyance failure, removing the sheet enables normally starting the operation of the recording material cooling apparatus  50 . The above-described predetermined time period in step S 2006  may be set to a time period during which the CPU  601  can determine whether a sheet is nipped by the cooling nip portion T 4  by sensors (not illustrated). 
     Although the above-described exemplary embodiment performs the steering control when the main switch  410  is turned ON, it is not limited thereto. The present exemplary embodiment may also be configured to perform the steering control when the image forming apparatus  100  changes from the power-saving state to the standby state. In this case, even if the CPU  601  performs control to move the steering roller  501   a  back to the reference position before the image forming apparatus  100  enters the power-saving state, the positional difference between the steering roller  501   a  and the first belt  501  can be dissolved. 
     Although the above-described exemplary embodiment is configured to move the steering roller  501   a  to the position where the axis line of the steering roller  501   a  is approximately parallel to the axis lines of other first belt suspension rollers  501   b  to  501   d  before the image forming apparatus  100  enters the power-off state or the power-saving state, the present exemplary embodiment may also be configured to move the steering roller  501   a  to the reference position upon reception of an operator&#39;s instruction for replacing the first belt  501  (or the second belt  502 ) from the operation panel  40 . More specifically, the present exemplary embodiment may also be configured to move the steering roller  501   a  to the position where the axis line of the steering roller  501   a  is approximately parallel to the axis lines of other first belt suspension rollers  501   b  to  501   d  by an input from the operation panel  40 . This also enables improving the workability in replacing the first belt  501  (or the second belt  502 ). 
     Although the present exemplary embodiment stops the steering control stepping motor  452  based on the OFF state of the steering HP sensor  453 , the motor may be stopped when a predetermined time period has elapsed since the OFF state of the steering HP sensor  453  has been detected. Performing control in this way enables reliably moving the steering roller  501   a  to the reference position regardless of the displacement amount of the steering roller  501   a  when control has been started. 
     Moving the steering roller  501   a  to the reference position before the image forming apparatus  100  enters the power-off state or power-saving state as is in the present exemplary embodiment enables preventing the operation from stopping in a state where the steering roller  501   a  is inclined during replacement of the first belt  501 . This reduces the load on the inclined steering roller  501   a  applied when the first belt  501  is pulled out, making it possible to provide an image forming apparatus that facilitates belt replacement. 
     Although, in the above-described exemplary embodiment, the recording material cooling apparatus  50  is disposed in the image forming apparatus  100  as an example (see  FIG. 1 ), it is not limited thereto. For example, the recording material cooling apparatus  50  may be disposed outside the housing of the image forming apparatus  100 , as an optional apparatus. More specifically, the recording material cooling apparatus  50  may be supported by an independent frame different from the frame of the image forming apparatus  100 .  FIG. 12  illustrates a configuration in which the recording material cooling apparatus  50  is disposed outside the image forming apparatus  100 . According to the present exemplary embodiment, when an external cooling apparatus  101  is connected to the image forming apparatus  100  as an external apparatus, as illustrated in  FIG. 12 , the image forming apparatus  100  and the external cooling apparatus  101  are collectively referred to as an image forming apparatus. In other words, according to the present exemplary embodiment, all of apparatuses related to feeding of a sheet to be subjected to image forming to discharging of the sheet to the outside of the apparatus is collectively referred to as an image forming apparatus. When a sheet processing apparatus for performing bookbinding processing and perforation processing on a sheet on the downstream side of the external cooling apparatus  101 , the configuration including all of the image forming apparatus  100 , the external cooling apparatus  101 , and the sheet processing apparatus is referred to as an image forming apparatus for forming an image on a sheet. 
     The external cooling apparatus  101  illustrated in  FIG. 12  is configured to be connectable to the image forming apparatus  100  as one of peripheral devices (referred to as optional units) that can be attached to expand the function of the image forming apparatus  100 . The external cooling apparatus  101  is disposed to cool the recording material S discharged from the image forming apparatus  100  and lower the temperature of the recording material S passing through the fixing apparatus  30  to a predetermined temperature or below. The external cooling apparatus  101  includes the above-described recording material cooling apparatus  50  to cool the recording material S. Units included in the image forming apparatus  100  have similar configurations to the configuration in  FIG. 1  and are assigned the same reference numerals, and redundant descriptions thereof will be omitted. 
     The recording materials S cooled by the external cooling apparatus  101  is discharged from the external cooling apparatus  101  by a discharge roller  85 , and then is stacked on a discharge tray  120 . The discharge tray  120  is disposed detachably attached to the external cooling apparatus  101  and the image forming apparatus  100 . More specifically, when the external cooling apparatus  101  is not connected to the image forming apparatus  100 , the discharge tray  120  is attached to the image forming apparatus  100  (see  FIG. 1 ). When the external cooling apparatus  101  is to be connected to the image forming apparatus  100 , the discharge tray  120  is removed from the image forming apparatus  100  and then attached to the external cooling apparatus  101  by the operator. A plurality of external cooling apparatuses  101  may be connected as peripheral devices. By increasing the number of external cooling apparatuses  101  to be connected, the operator can easily improve the capability of cooling down the recording material S for the existing image forming apparatus  100 . 
     The external cooling apparatus  101  may be connected to the image forming apparatus  100  incorporating the recording material cooling apparatus  50 . In addition, other sheet processing apparatuses, such as a curl correction apparatus, may be provided between the image forming apparatus  100  and the external cooling apparatus  101 . The sheet processing apparatus may be further connected to the external cooling apparatus  101  on the downstream side of the sheet conveyance direction. 
     When the present exemplary embodiment is applied to such an image forming apparatus, the steering rollers  501   a  and  502   a  are moved to the reference position when the external cooling apparatus  101  having the recording material cooling apparatus  50  enters the power-off state or the power-saving state. Moving the steering rollers  501   a  and  502   a  to the reference position depending on the power state of the apparatus having the recording material cooling apparatus  50  enables improving the workability in replacing the first belt  501  or the second belt  502 . In addition, when power is supplied to the external cooling apparatus  101  via the image forming apparatus  100 , the external cooling apparatus  101  enters the power-off state in association with the OFF (power-off) state of the main switch  410  of the image forming apparatus  100 . Even in this configuration, the steering rollers  501   a  and  502   a  are moved to the reference position before the image forming apparatus  100  enters the power-off state or the power-saving state, as described above. In this way, moving the steering rollers  501   a  and  502   a  to the reference position depending on the state of the image forming apparatus  100  enables improving the workability in replacing the first belt  501  or the second belt  502  disposed in the recording material cooling apparatus  50  of the external cooling apparatus  101 . 
     Although the above-described exemplary embodiment is configured to perform a similar control on both the steering rollers  501   a  and  502   a  of the first unit  501  U and the second unit  502  U, respectively, the exemplary embodiment may perform this control only on either one unit. For example, the exemplary embodiment may perform the above-described control only on the first unit  501  U in which the moving distance of the steering roller  501   a  toward the inner circumferential side of the first belt  501  is limited because of the existence of the heat sink  503 . 
     Although the above-described exemplary embodiment is configured to nip and convey a recording material S by the first belt  501  and the second belt  502 , the second belt  502  may be replaced with a plurality of conveyance rollers. More specifically, the exemplary embodiment may also be configured to form a conveyance nip portion by the first belt  501  in contact with the heat sink  503  on the inner circumferential surface thereof and the conveyance unit having a plurality of conveyance rollers, and to nip and convey the recording material S. 
     Although the above-described exemplary embodiment is configured to swing the steering rollers  501   a  and  502   a  around the center in the rotational axis direction, the exemplary embodiment may be configured to swing the steering rollers  501   a  and  502   a  around the back side or the front side end in the rotational axis direction. Even in such a configuration, the first belt  501  or the second belt  502  becomes hard to be replaced depending on the swing angles of the rollers in the power-off state. For example, in a configuration in which the steering rollers  501   a  and  502   a  swing around the back side end thereof, when the steering roller  501   a  is swinging so that the front side end of the steering roller  501   a  is separated from the heat sink  503 , the first belt  501  becomes hard to be pulled out from the front side. Thus, even in a configuration in which the steering rollers  501   a  and  502   a  swing around an end in the rotational axis direction, moving the steering roller  501   a  or  502   a  back to the angle parallel to other rollers before the image forming apparatus  100  enters the power-off state like the present exemplary embodiment enables improving the workability in replacing the first belt  501  or the second belt  502 , respectively. 
     The image forming apparatus  100  that makes it possible to restores an inclination of a belt to a reference position when power is turned OFF, and to improve the workability in replacing the belt. The present disclosure makes it possible to provide an image forming apparatus having improved workability in replacing a belt of a cooling apparatus. 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2020-128078, filed Jul. 29, 2020, and Japanese Patent Application No. 2021-090149, filed May 28, 2021, each of which is hereby incorporated by reference herein in their entirety.