Patent Publication Number: US-2022229385-A1

Title: Recording material cooling device, image forming apparatus, and image forming system

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a recording material cooling device that cools recording material via a belt, and to an image forming apparatus and image forming system equipped with such device. 
     In the image forming apparatus, a toner image formed on the recording material is fixed on the recording material by heating and pressurising it in a fixing device. As a result, a temperature of the recording material being conveyed from the fixing device is higher than that before fixing. If the recording material after the toner image has been fixed is discharged and stacked in a discharge tray at a high temperature, toner may stick to the other recording materials stacked on the tray. To prevent such sticking of the recording material, a recording material cooling device is provided to lower the temperature of the recording material after the toner image is fixed. (Japanese Laid-Open Patent Application No. 2009-181055). The recording material cooling device described in Japanese Laid-Open Patent Application No. 2009-181055 is a belt-cooling device, in which a heat sink cools one of a pair of belts that nip and feed the recording material that has passed through the fixing device, and the temperature of the recording material is lowered through the cooled belt. Such recording material cooling device is attached to the image forming apparatus by means of a pair of support plates that rotatably support a plurality of rollers that stretch the belt at both ends and are fixed to a main assembly frame, for example. 
     In the above-mentioned belt-cooled recording material cooling device, if one of the multiple rollers stretching the belt is not parallel to the other rollers but tilted relative to them, the rotating belt may move in a width direction crossing a recording material feeding direction (so-called belt shift). In such a case, the belt may shift too close to the support plate supporting each roller, and a belt edge may contact the support plate, which may damage the belt and the support plate. To solve this issue, steering control is used to suppress the belt shifting by tilting one of the multiple rollers that tension the belt (called a steering roller) according to a position of a belt edge portion. 
     The relative inclination of the rollers that causes the belt shifting described above can be caused by the parts tolerance of each element that constitutes a belt unit, such as, the plurality of rollers that stretch the belt and the pair of support plates that support each roller. Therefore, in the past, the relative inclination of the rollers that may be caused by component tolerances in the belt unit has been taken into account so that steering control can be performed as described above. 
     However, in the past, even though steering control was applied, the belt would lean over and the belt and support plate would be damaged. This is because the support plate is displaced during installation due to component tolerances in the parts that affect installation in the recording material cooling device, and the relative inclination of the rollers can be so great that it is difficult to control the belt shifting even with steering control. 
     In view of the above problem, the present invention aims to provide a recording material cooling device capable of correcting the relative inclination of rollers that may occur when the recording material cooling device is mounted on a support frame, and an image forming apparatus and image forming system equipped with such recording material cooling device. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a recording material cooing device configured to cool a recording material on which a toner image is fixed by heating, said recording material cooling device comprising: a supporting frame; a first unit provided with a first endless belt, a first plurality of rollers stretching said first belt, and a cooling member contacting an inner peripheral surface of said first belt and configured to cool said first belt; a second unit provided with a second endless belt contacting an outer peripheral surface of said first belt and configured to form a nip portion nipping and feeding the recording material, a second plurality of rollers stretching said second belt, a first supporting member and a second supporting member disposed in a widthwise direction crossing a feeding direction of the recording material and configured to support both end portions of said second plurality of rollers; a holding member fixed to said supporting frame and configured to rotatably hold said first supporting member; and a fixing member configured to fix said first supporting member to said holding member at any rotating position of said first supporting member. 
     Further features of the present invention 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 schematic view showing the configuration of an image forming apparatus. 
         FIG. 2  is a schematic view showing a recording material cooling device of an embodiment. 
         FIG. 3  is a perspective view showing the recording material cooling device when a first unit is in a contact position. 
         FIG. 4  is a perspective view showing the recording material cooling device when the first unit is in a separation position. 
         FIG. 5  is an exploded perspective view illustrating a pressure release lever. 
         FIG. 6  is an enlarged view illustrating a static eliminating needle. 
         FIG. 7  is an exploded perspective view showing the recording material cooling device as seen from a rear support plate side. 
         FIG. 8  is an exploded perspective view showing an adjustment operating mechanism. 
         FIG. 9  is a view illustrating roller adjustment by the adjustment operating mechanism, part (a) showing when an adjustment plate is rotated and adjusted in a J direction, part (b) showing when the adjustment plate is rotated and adjusted in an M direction, and part (c) showing after adjustment. 
         FIG. 10  is a schematic drawing showing an image forming system with a recording material cooling device outside the image forming apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     &lt;Image Forming Apparatus&gt; 
     A recording material cooling device of this embodiment will be described below. An image forming apparatus  100  shown in  FIG. 1  is an electrophotographic tandem type full colour printer which has image forming portions Pa, Pb, Pc, Pd which form yellow, magenta, cyan, and black images, respectively. The image forming apparatus  100  forms a toner image on a recording material S in response to image information from a document reader (not shown) or an external device such as a personal computer (not shown) that is communicatively connected to the image forming apparatus  100 . The recording material S can be various types of sheet materials such as plain paper, thick paper, rough paper, uneven paper, coated paper, plastic film, cloth, etc. In the case of this embodiment, the image forming portion Pa to Pd, primary transfer rollers  6   a  to  6   d , intermediate transfer belt  80 , secondary transfer inner roller  14 , secondary transfer outer roller  11 , and tensioning rollers  15  and  16  constitute an image forming unit  200  that forms a toner image on the recording material S. 
     A conveying process of the recording material S of the image forming apparatus  100  will be described. The recording material S is stored in a paper cassette  10  and is fed from the cassette  10  by a paper feed roller  13  in accordance with the image forming timing. The recording material S fed by the paper feed roller  13  is conveyed to a registration roller  12  located in the middle of a conveyance path  114 . After skew correction and timing correction of the recording material S is performed by the registration roller  12 , the recording material S is sent to the secondary transfer portion T 2 . The secondary transfer portion T 2  is a transfer nip portion formed by the secondary transfer inner roller  14  and the secondary transfer outer roller  11 , and the toner image is transferred onto the recording material S as a secondary transfer voltage is applied to the secondary transfer outer roller  11 . 
     In contrast to the process of conveying the recording material S up to the secondary transfer portion T 2  described above, the process of forming an image that is sent up to the secondary transfer portion T 2  at the same timing is described below. First, the image forming portions Pa, Pb, Pc, and Pd are described. The image forming portions Pa, Pb, Pc, and Pd of each colour are constructed in almost the same way, except that the toner colours used in developing units  1   a ,  1   b ,  1   c , and  1   d  are different: yellow, magenta, cyan, and black. Therefore, in the following, the image forming portion Pd of black will be explained as a representative, and other image forming portions Pa, Pb, and Pc will be omitted. 
     The image forming portion Pd mainly consists of the developing unit  1   d , a charger  2   d , a photosensitive drum  3   d , a photosensitive drum cleaner  4   d , and an exposure device  5   d . The surface of the photosensitive drum  3   d , which is rotated in a direction of arrow R 1 , is uniformly charged in advance by the charger  2   d , and then an electrostatic latent image is formed by the exposure device  5   d , which is 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 the developing unit  1   d  using a developer agent. Then, the toner image formed on the photosensitive drum  3   d  is primary transferred onto the intermediate transfer belt  80  in response to the application of a primary transfer voltage to the primary transfer roller  6   d , which is positioned between the image forming portion Pd and the intermediate transfer belt  80 . The toner remaining from the primary transfer, which remains slightly on the photosensitive drum  3   d , is collected by the photosensitive drum cleaner  4   d . As previously mention, image forming portions Pa, Pb and Pc are arranged similarly to image forming portion Pd, and include respective ones of chargers  2   a / 2   b / 2   c , photosensitive drums  3   a / 3   b / 3   c , photosensitive drum cleaners  4   a / 4   b / 4   c , and exposure devices  5   a / 5   b / 5   c.    
     The intermediate transfer belt  80  is stretched by the secondary transfer inner roller  14  and the tensioning rollers  15  and  16 , and is driven in a direction of an arrow R 2 . In the case of this embodiment, the tensioning roller  16  also serves as the drive roller that drives the intermediate transfer belt  80 . The image forming process of each colour, which is processed in parallel by image forming portion Pa to Pd, is performed by sequentially overlapping the toner image of the upstream colour that has been primary transferred onto the intermediate transfer belt  80 . As a result, a full-colour toner image is finally formed on the intermediate transfer belt  80  and is conveyed to the secondary transfer portion T 2 . A residual toner from the secondary transfer after passing through the secondary transfer portion T 2  is removed from the intermediate transfer belt  80  by a belt cleaner  22 . 
     With the conveying process and image formation process described above, the timing of the recording material S and the full-colour toner image matches at the secondary transfer portion T 2 , and secondary transfer is performed. After that, the recording material S is fed to a fixing device  30 , where the toner image is fixed on the recording material S by applying a predetermined amount of pressure and heat. The fixing device  30  nips and feeds the recording material S on which the toner image has been formed, and heats and pressurises the conveyed recording material S to fix the toner image on the recording material S. In other words, the toner of the toner image formed on the recording material S is melted and mixed by heat and pressure, and is fixed to the recording material S as a full-colour image. In this way, the series of image formation process is completed. In the case of this embodiment, the recording material S on which the toner image has been fixed is conveyed from the fixing device  30  to a recording material cooling device  50  for cooling. For example, the temperature of the recording material S is about 90° C. immediately before the recording material cooling device  50 , but it is lowered to about 60° C. after passing through the recording material cooling device  50 . 
     In the case of single-sided image formation, the recording material S cooled by the recording material cooling device  50  is conveyed between a pair of discharge rollers  105  and discharged directly onto a discharge tray  120 . On the other hand, in the case of double-sided image formation, a feeding path is switched from a path leading to the discharge tray  120  to a double-sided conveying device  111  by means of a switching member  110  (called a flapper, etc.), and the recording material S held and fed by the discharge rollers  105  is sent to the double-sided conveying device  111 . After that, a reversing roller  112  switches the front and back ends of the recording material S, and the recording material S is sent to the conveyance path  114  again via a duplex path  113 . 
     The subsequent conveyance and the image formation process for the reverse side (second side) are the same as described above, so the explanation is omitted. 
     &lt;Recording Material Cooling Device&gt; 
     Next, the recording material cooling device  50  of this embodiment will be explained using  FIGS. 2 to 9  ( c ). The recording material cooling device  50  of this embodiment is a belt cooling type recording material cooling device. As shown in  FIG. 2 , the recording material cooling device  50  has a first unit  501 U and a second unit  502 U. The first unit  501 U has an endless first belt  501 , first belt tensioning rollers ( 501   a  to  501   e ) as first rollers, a heat sink  503 , a sensor portion  390 , etc. On the other hand, the second unit  502 U has an endless second belt  502 , second belt tensioning rollers ( 502   a  to  502   e ) as second rollers, pressure rollers ( 509   a ,  509   b ), sensor portion  390 , etc. 
     Both the first belt  501  and the second belt  502  are film-like endless belts formed using, for example, a strong polyamide resin. The second belt  502  is hung on a plurality of second belt tensioning rollers  502   a  to  502   e , and one of the second belt tensioning rollers  502   a  to  502   e  is rotated by a belt drive motor  511 . In this embodiment, the second belt tensioning roller  502   e , which is rotated by the belt drive motor  511 , corresponds to a drive roller that drives the second belt  502 . The second belt tensioning roller  502   e  is, for example, an aluminum roller with a diameter of 24.8 mm, and silicone rubber with a thickness of 100 μm is formed on the peripheral surface, so that the coefficient of friction with the second belt  502  is set to “1.1”. 
     The second belt tensioning roller  502   a  corresponds to a steering roller described below, and is, for example, an aluminum roller with a diameter of 25 mm, and the coefficient of friction with the second belt  502  is set to “0.5”, which is smaller than that of the second belt tensioning roller  502   e  (drive roller). The second belt tensioning rollers  502   b  through  502   d  correspond to idler rollers that tension the second belt  502 , and are aluminum rollers with a diameter of 25 mm, for example, and the coefficient of friction with the second belt  502  is set to “0.1”. When the second belt tensioning roller  502   e  is rotated by the belt drive motor  511 , the second belt  502  rotates in a direction of an arrow C in the figure. 
     In this embodiment, a drive chain  504   a  is provided at the shaft end portion of the second belt tensioning roller  502   e . This drive chain  504   a  forms a part of the drive gear chain for transmitting the rotational driving force of the belt drive motor  511  to rotate the first belt  501 . 
     On the other hand, the first belt  501  is hung around the plurality of first belt tensioning rollers  501   a  to  501   e  so that it can contact the second belt  502 . At least one of the first belt tensioning rollers  501   a  to  501   e  is rotated by the driving power of the belt drive motor  511  through a drive gear chain comprising drive chains  504   a  to  504   d . In the case of this embodiment, the first belt tensioning roller  501   e  rotated by the drive chain  504   d  corresponds to a drive roller that drives the first belt  501 . The first belt tensioning roller  501   e  is, for example, an aluminum roller having a diameter of 24.8 mm, and silicone rubber having a thickness of 100 μm is formed on the outer surface, so that the coefficient of friction with the first belt  501  is set to “1.1”. This causes the first belt  501  to rotate in a direction of arrow B in the figure. In other words, 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 , which is the same drive source. 
     The first belt tensioning roller  501   a  corresponds to a steering roller described below. The first belt tensioning roller  501   a  is, for example, an aluminum roller with a diameter of 25 mm, and an acrylic layer with a thickness of 100 μm is formed on its outer peripheral surface, so that the coefficient of friction with the first belt  501  is set to “0.5”, which is smaller than that of the first belt tensioning roller  501   e  (drive roller). The first belt tensioning rollers  501   b - 501   d  correspond to idler rollers that tension the first belt  501 , for example, they are aluminum rollers with a diameter of 25 mm, and the coefficient of friction with the first belt  501  is set to “0.1”. The first belt tensioning roller  501   e  and the second belt tensioning roller  502   e  do not form a nip with each other. When the friction coefficient of the drive rollers ( 501   e ,  502   e ) is greater than that of the steering rollers ( 501   a ,  502   a ) as described above, the belt shifting is more pronounced when the drive roller is tilted relative to the other rollers. 
     &lt;One-Way Clutch&gt; 
     Each of the drive chains  504   a  through  504   d  that transmit the rotational driving force of the belt drive motor  511  is a gear. And any of the drive chains  504   a  to  504   d  has a one-way clutch  505  that shuts off the transmission of the drive force depending on the direction of the drive force. In the case of this embodiment, the one-way clutch  505  is press-fitted into the inner circumference of the drive chain  504   d  and is arranged so that the center of rotation of the drive chain  504   d  and the center of rotation of the one-way clutch  505  are the same. In other words, the drive chain  504   d  is installed on the rotational axis of the first belt tensioning roller  501   e  via the one-way clutch  505 . 
     The one-way clutch  505  does not transmit the driving force by the drive chain  504   d  to the rotational shaft of the first belt tensioning roller  501   e  when the first belt tensioning roller  501   e  and the drive chain  504   d  are moving in opposite directions relative to each other. That is, when the moving speed of the first belt  501  becomes faster than that of the second belt  502 , the one-way clutch  505  causes the drive chain  504   d  and the rotating axis of the first belt tensioning roller  501   e  to enter a drive cutoff state. In this case, the first belt tensioning roller  501   e  rotates freely (idle) with respect to the drive chain  504   d . In other words, regardless of the drive transmission by the drive chains  504   a  to  504   d , the first belt tensioning roller  501   e  and thus the first belt  501  rotates. 
     When a one-way clutch  505  is provided, if the moving speed of the first belt  501  becomes faster than that of the second belt  502 , the drive chain  504   d  receives the driving force of the belt drive motor  511  and rotates, and the first belt tensioning roller  501   e  receives the rotation of the first belt  501  and rotates. In this case, the first belt  501  is only accompanied by the second belt  502  which is in contact with it at the cooling nip portion T 4 , and no driving force is added by the belt drive motor  511 . Therefore, the moving speed of the first belt  501  follows the moving speed of the second belt  502  and gradually decreases so that it becomes equal to the speed of the second belt  502 . 
     As the moving speed of the first belt  501  decreases as described above, the circumferential speed of the first belt tensioning roller  501   e  decreases to less than the circumferential speed of the drive chain  504   d  which is driven by the belt drive motor  511  through the drive chains  504   a  to  504   c . Then, the drive chain  504   d  and the rotational axis of the first belt tensioning roller  501   e  become drive transmission state again by the one-way clutch  505 . When the drive train  504   d  and the rotational axis of the first belt tensioning roller  501   e  become the drive transmission state by the one-way clutch  505 , the drive power of the belt drive motor  511  is transmitted to the first belt tensioning roller  501   e , and the first belt tensioning roller  501   e  is rotated according to the power. At this time, the moving speed of the first belt  501  is the same as the moving speed of the second belt  502 . When the moving speed of the first belt  501  becomes faster than the moving speed of the second belt  502  again, the drive is shut off by the one-way clutch  505  as described above. 
     In this way, the one-way clutch  505  is provided to change the transmission and interruption of the drive in the drive chain  504   d  and the rotational axis of the first belt tensioning roller  501   e . Then, when there is a speed difference between the moving speed of the first belt  501  and that of the second belt  502 , the one-way clutch  505  repeats whether or not the driving force is transmitted between the drive chain  504   d  and the rotating shaft of the first belt tensioning roller  501   e . This prevents a speed difference from occurring between the first belt  501  and the second belt  502 . 
     &lt;Heat Sink&gt; 
     The recording material S, on which the toner image has been fixed, is held between the first belt  501  and the second belt  502 , and is conveyed in a conveyance direction (arrow D direction) by the rotation of these belts. At that 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 this embodiment, the first belt  501  is cooled by heat sink  503 . The heat sink  503  is disposed so as to contact the inner surface of the first belt  501  at the point where the cooling nip portion T 4  is formed in order to efficiently cool the recording material S. The recording material S is cooled through the first belt  501  as it passes through the cooling nip portion T 4 . For example, if the temperature of the recording material S is about 90° C. before passing through the recording material cooling device  50 , the recording material S is cooled so that it becomes about 60° C. after passing through the recording material cooling device  50 . As the recording material S is cooled, the toner on the recording material S is cooled and adheres to it. 
     The heat sink  503  as a cooling member is a heat sink made of metal, such as aluminum. The heat sink  503  has a heat-receiving portion  503   a  for contacting the first belt  501  to take heat from the first belt  501 , a heat-dissipating portion  503   b  for dissipating the heat, and a fin base  503   c  for conducting the heat from the heat-receiving portion  503   a  to the heat-dissipating portion  503   b . The heat-dissipating portion  503   b  is formed by a large number of heat-dissipating fins in order to promote efficient heat dissipation by increasing the contact area with the air. For example, the heat-dissipating fins are set to have a thickness of 1 mm, a height of 100 mm, and a pitch of 5 mm, and the fin base  503   c  is set to have a thickness of 10 mm. In order to forcibly cool the heat sink  503  itself, one or more cooling fans  513  are provided to blow air toward the heat sink  503  (in detail, the heat-dissipating portion  503   b ). The air volume of the cooling fans  513  is set to 2 m3/min, for example. The cooling of the heat sink  503  is not limited to the cooling fans  513 . 
     On the other hand, pressure rollers  509   a  and  509   b  are provided on the inner circumference side of the second belt  502  to pressurise the second belt  502  toward the heat sink  503  of the second unit  502 U. The pressure rollers  509   a  and  509   b  as pressure members pressurise the second belt  502  with a pressurising pressure of, for example, 9.8 N (1 kgf). This ensures that the first belt  501  through the second belt  502  is in contact with the heat sink  503  (heat-receiving portion  503   a  to be described in detail later). 
     &lt;Steering Control&gt; 
     In such a recording material cooling device  50 , when an endless belt such as the first belt  501  and the second belt  502  is supported and rotated by a plurality of rollers, a meandering phenomenon in which the rotating belt moves in the width direction may occur. Therefore, one of the multiple rollers supporting the first belt  501  and the second belt  502  is tilted as a steering roller, and the first belt  501  and the second belt  502  are reciprocated in the width direction to suppress the meandering phenomenon. 
     In this embodiment, the first belt tensioning roller  501   a  and the second belt tensioning roller  502   a  are steering rollers provided to control the shifting of the first belt  501  and the second belt  502 , respectively. These steering rollers ( 501   a ,  502   a ) press the first belt  501  and the second belt  502  from the inner circumference to the outer circumference so that the tension of the first belt  501  and the second belt  502  is, for example, about 39.2 N (about 4 kgf). To do so, the first belt tensioning roller  501   a  is driven by a spring  507   a  and the second belt tensioning roller  502   a  is urged by a spring  508   a . The steering rollers ( 501   a ,  502   a ) are separately steered by a steering mechanism  400  to control the meandering of the first belt  501  and the second belt  502  (steering control) by cutting the steering angle with the center portion of its rotational axis direction (width direction) as the turning fulcrum. 
     At one point in the rotation path of the first belt  501  and the second belt  502 , respectively, the sensor portion  390  is provided to detect the end position of the first belt  501  and the second belt  502 , respectively. Based on the detection signal of the sensor portion  390 , the end positions of the first belt  501  and the second belt  502  during rotation are detected. Then, the steering angle of the steering rollers ( 501   a ,  502   a ) is adjusted by operating the steering mechanism  400  described above based on the detected end positions. 
     &lt;About Belt Connection and Disconnection&gt; 
     The first unit  501 U is movable to the contact position where the first belt  501  and the second belt  502  are in contact with each other to form the cooling nip portion T 4 , and to the separation position where the first belt  501  and the second belt  502  are separated from each other to not form the cooling nip portion T 4 .  FIG. 3  shows the case where the first unit  501 U is in the contact position, and  FIG. 4  shows the case where the first unit  501 U is in the separation position. 
     In this embodiment, the first unit  501 U is provided so that it can be rotated up and down with respect to the second unit  502 U with the rotational axis (not shown) of a rotation mechanism  510  as a rotation means as a rotation center. This means that when a so-called jam occurs in the recording material cooling device  50  where the recording material S stays in the device, the operator can separate the first belt  501  from the second belt  502  to remove the recording material S jammed in the cooling nip portion T 4 . The purpose is also to allow the operator to loosen the first belt  501  and the second belt  502  in order to replace the first belt  501  and the second belt  502 , as described later. 
     As shown in  FIG. 3  and  FIG. 4 , a first front support plate  524  is disposed on one end side of the first belt tensioning rollers  501   a  to  501   e . The first front support plate  524  rotatably supports one end side of the first belt tensioning rollers  501   a - 501   e , and also supports one end side of the heat sink  503 . A first rear support plate  525  rotatably supports the other end side of the first belt tensioning rollers  501   a - 501   e , and also supports the other end side of the heat sink  503 . The first front support plate  524  as a third supporting member and the first rear supporting plate  525  as a fourth supporting member are each a single member formed of sheet metal. 
     On the other hand, a second front support plate  526  is disposed on one end side of the second belt tensioning rollers  502   a  to  502   e , and the second front support plate  526  rotatably supports one end side of the second belt tensioning rollers  502   a  to  502   e  and the pressure rollers  509   a  and  509   b  (see  FIG. 2 ). A second rear support plate  527  rotatably supports the other end sides of the second belt tensioning rollers  502   a - 502   e  and the pressure rollers  509   a ,  509   b . The second front support plate  526  as a first supporting member and the second rear support plate  527  as a second supporting member are each a single member formed of sheet metal. 
     &lt;Pressure Release Lever&gt; 
     In the recording material cooling device  50  of this embodiment, the steering roller ( 501   a ) can be moved between the tensioned position where the first belt  501  is tensioned and the non-tensioned position where the first belt  501  is loosened in order to facilitate replacement of the first belt  501  by the operator. When the steering roller ( 501   a ) is in the non-tensioned position, the contact pressure on the first belt  501  is smaller than when the steering roller ( 501   a ) is in the tensioned position, and the tensioning of the first belt  501  is loosened. Similarly, in order for the operator to replace the second belt  502 , the steering roller ( 502   a ) can be moved by manual operation between the tensioned position where the second belt  502  is tensioned and the non-tensioned position where the second belt  502  is loosened. 
     As shown in  FIG. 5 , in each of the first unit  501 U and the second unit  502 U, a pressure release lever ( 560 ,  570 ) is freely rotatable on one end side of the steering rollers ( 501   a ,  502   a ). As the operator grasps and rotates the pressure release levers ( 560 ,  570 ), the steering rollers ( 501   a ,  502   a ) move between a tensioned position and a non-tensioned position. For example, when the pressure release lever  560  of the first unit  501 U is rotated in a direction of an arrow V by the operator, the first belt  501  becomes taut, and when the pressure release lever  560  is rotated in the direction opposite to the arrow V, the first belt  501  becomes loose and not taut. On the other hand, when the pressure release lever  570  of the second unit  502 U is rotated by the operator in the direction of the arrow W, the second belt  502  becomes taut, and when the pressure release lever  570  is rotated in the opposite direction of the arrow W, the second belt  502  becomes unstretched and loose. 
     In this embodiment, the front surface of the first unit  501 U is covered by a front cover  550  which is attached by screws or the like to each of cover mounting portions  530  and  531  provided on the first front support plate  524 . The front cover  550  can be detachably attached to the cover mounting portions  530  and  531  so as to cover the pressure release lever  560  of the first unit  501 U. Therefore, in the case of the first unit  501 U, the operator needs to remove the front cover  550  in order to access and operate the pressure release lever  560 . 
     On the other hand, the front surface of the second unit  502 U is covered by a sheet metal cover  555  that is attached to a main assembly frame (not shown). The sheet metal cover  555  is arranged to cover the pressure release lever  570  of the second unit  502 U, and is detachably attached to the main assembly frame. Therefore, it is necessary to remove the sheet metal cover  555  in order for an operator to access the pressure release lever  570 . However, in the second unit  502 U, in order to restrain the rotation of the pressure release lever  570 , a gripping portion  570   a  of the pressure release lever  570 , which is grasped by the operator, is fitted into a fitting hole  851   a  formed in a front retaining plate  851  of a unit retaining portion  850  described below. This fitting hole  851   a  is formed in a shape that follows the outline of the gripping portion  570   a . That is, when the gripping portion  570   a  is fitted into the fitting hole  851   a , the pressure release lever  570  is not rotated in either the direction of the arrow W or the opposite direction of the arrow W. Therefore, in the case of the second unit  502 U, the operator needs to remove not only the sheet metal cover  555  but also the front retaining plate  851  in order to access and operate the pressure release lever  570 . 
     Thus, in this embodiment, in the first unit  501 U, the pressure release lever  560  can be operated only by the operator removing the front cover  550 . On the other hand, in the second unit  502 U, the pressure release lever  570  cannot be operated unless the operator removes the sheet metal cover  555  and the front retaining plate  851 . This is because the pressure release lever  560  of the first unit  501 U is used more frequently than the pressure release lever  570  of the second unit  502 U. That is, since the first belt  501  rubs against the heat sink  503 , it wears more easily than the second belt  502 , which does not rub against the heat sink  503 . Therefore, the replacement frequency of the first belt  501  is higher than that of the second belt  502 . From the viewpoint of improving the replaceability of the first belt  501 , which is frequently replaced by the operator, the pressure release lever  560  is made easier to operate in the first unit  501 U as described above. 
     &lt;Static Charge Eliminator Needle&gt; 
     In the case of the belt-cooled recording material cooling device  50 , the first belt  501  is easily charged by the heat sink  503  rubbing against it during rotation, and the second belt  502  is easily charged by rotating in contact with the first belt  501 . When the first belt  501  or the second belt  502  is electrically charged, the recording material S may stick to the first belt  501  or the second belt  502 , or the recording material S may curl, causing the recording material S to be jammed in the equipment. In addition, when the first belt  501  or the second belt  502  is electrically charged, the recording material S that passes through the cooling nip portion T 4  (see  FIG. 2 ) may be also electrically charged. If the recording material S is electrically charged, it may be difficult to discharge the recording material S to the discharge tray  120  (see  FIG. 1 ) in a correct posture, and the recording material S may not be properly stacked on the discharge tray  120 . 
     Therefore, as shown in  FIG. 6 , in the first unit  501 U and the second unit  502 U, static eliminating needles  600  and  601  are provided at the downstream side of the recording material S conveyance direction from the cooling nip portion T 4  (see  FIG. 2 ), respectively. Specifically, in the first unit  501 U, the static eliminating needle  600  is attached to a connecting sheet metal  701  connecting the first front support plate  524  and the first rear support plate  525  by means of an attaching member  602  (e.g., a sticker). The static eliminating needle  600  suppresses the electrification of the first belt  501  by contacting the outer peripheral surface of the rotating first belt  501  with its tip portion. 
     Similarly, in the second unit  502 U, the static eliminating needle  601  is attached to a connecting sheet metal  702  connecting the second front support plate  526  and the second rear support plate  527  by means of an attachment member  603  (e.g., a sticker). The static eliminating needle  601  suppresses the electrification of the second belt  502  by contacting the outer peripheral surface of the rotating second belt  502  with the tip portion. The connecting sheet metal  701  and the connecting sheet metal  702  are each provided with a pair of discharge guides  700  for discharging the recording material S that has passed through the cooling nip portion T 4  while suppressing it from both sides. 
     As shown in  FIG. 7 , in this embodiment, the steering mechanism  400  and the cooling fan  513  (one here) described above are attached to the first rear support plate  525  of the first unit  501 U. On the other hand, the steering mechanism  400  is also mounted on the second rear support plate  527  of the second unit  502 U. In addition, the rotation mechanism  510  is attached across the first rear support plate  525  of the first unit  501 U and the second rear support plate  527  of the second unit  502 U. Therefore, the steering mechanism  400  and the cooling fan  513  rotate together with the first unit  501 U as the first unit  501 U is rotated by the rotation mechanism  510 . 
     The second rear support plate  527  has a positioning portion  590  for positioning the recording material cooling device  50  when it is mounted on a main assembly  100 A (see  FIG. 1 ) as the support frame of the image forming apparatus  100 . The positioning portion  590  has a plurality of fitting portions  591  that are spaced apart in the recording material conveyance direction D and extended in the width direction. These fitting portions  591  are formed in the shape of cylindrical shafts, for example, and are fitted to fitted portions provided in the main assembly  100 A. In this way, the recording material cooling device  50  is attached to the main assembly  100 A with the second rear support plate  527  side of the second unit  502 U as a reference. 
     The recording material cooling device  50  has the unit retaining portion  850 . The unit retaining portion  850  forms a holding frame to hold the second unit  502 U by means of the front retaining plate  851  that holds the second front support plate  526 , a rear holding plate  853  that holds the second rear support plate  527 , and two connecting plates  852  that connect the front holding plate  851  and the rear holding plate  853 . 
     The front retaining plate  851  and the connecting plate  852  each have a plurality of mounting holes through which mounting screws can be inserted. In this embodiment, the recording material cooling device  50  is fixed to the main assembly  100 A by screwing the front retaining plate  851  and the two connecting plates  852  to the main assembly frame with mounting screws while the plurality of fitting portions  591  are fitted to the fitted portions respectively. In this way, the recording material cooling device  50  is fixed to the main assembly  100 A. As described in detail below, the second front support plate  526  is movable relative to the front retaining plate  851  (see  FIG. 8  and part (c) of  FIG. 9  below). The front retaining plate  851  is detachable from the connecting plate  852 . This is because, as described above, in the present embodiment, the rotation of the pressure release lever  570  is restrained by the front retaining plate  851 , and the operator needs to remove the front retaining plate  851  in order to operate the pressure release lever  570 . 
     By the way, in the conventional belt-cooling method recording material cooling device, the belt may shift off and damage the belt and the front and rear support plates that support the rollers that stretch the belt in spite of the steering control. This was particularly noticeable in the second unit  502 U, which does not have a heat sink  503 . This is due to the following reasons. 
     In the first unit  501 U having the heat sink  503 , the first front support plate  524  and the first rear support plate  525  are formed from highly rigid sheet metal to support the heavy heat sink  503 . On the other hand, in the second unit  502 U, the second front support plate  526  is formed from low-rigidity sheet metal because it is not necessary to support the heat sink  503 . As for the second rear support plate  527 , it is formed using high-rigidity sheet metal in order to attach the rotation mechanism  510 . Therefore, in the past, the second front support plate  526  has been deformed and tilted relative to the second rear support plate  527  due to component tolerances of the recording material cooling device  50  and parts affecting the installation in the main assembly  100 A. 
     For example, the fitting portion  591  of the positioning portion  590  in the recording material cooling device  50 , the mounting holes of the unit retaining portion  850 , the fitted portions provided in the main assembly  100 A that are fitted into the fitting portion  591 , holes into which screws are screwed, and other parts tolerances cause the second front support plate  526  to deform. In such a case, each roller that stretches the second belt  502  is inclined more than expected, and it becomes difficult to control the shifting of the second belt  502  even when steering control is performed to tilt the steering roller ( 502   a ) in the second unit  502 U. 
     As shown in  FIG. 2 , suppose that the recording material cooling device  50  is fixed to the main assembly  100 A with the second front support plate  526  tilted in the direction of arrow G against the second rear support plate  527  (see  FIG. 3 ). Then, the steering roller ( 502   a ) tilts outward of the second belt  502  so that one end portion supported by the second front support plate  526  of the steering roller ( 502   a ) is located lower than the other end portion supported by the second rear support plate  527  of the steering roller ( 502   a ). Hence, the second belt  502  stretched on the steering roller ( 502   a ) is more likely to move toward the second rear support plate  527 . 
     Conversely, suppose that the recording material cooling device  50  is fixed to the main assembly  100 A with the second front support plate  526  tilted in the direction of arrow H against the second rear support plate  527  (see  FIG. 3 ). Then, the steering roller ( 502   a ) is tilted inwardly of the second belt  502  so that one end portion supported by the second front support plate  526  of the steering roller ( 502   a ) is located above the other end portion supported by the second rear support plate  527  of the steering roller ( 502   a ). Hence, the second belt  502  stretched on the steering roller ( 502   a ) is more likely to move toward the second front support plate  526 . 
     The greater the inclination of the second front support plate  526  toward the second rear support plate  527  in the direction of the arrow G, the faster the movement speed of the second belt  502  toward the second front support plate  526  in accordance with the steering control than the movement speed toward the second rear support plate  527 . On the contrary, the greater the inclination of the second front support plate  526  toward the second rear support plate  527  in the direction of the arrow H, the slower the movement speed of the second belt  502  toward the second front support plate  526  becomes in accordance with the steering control than the movement speed toward the second rear support plate  527 . Thus, as the inclination of the second front support plate  526  with respect to the second rear support plate  527  increases, the difference between the movement speed of the second belt  502  when it moves toward the second front support plate  526  and the movement speed of the second belt  502  when it moves toward the second rear support plate  527  becomes faster. If the moving speed of the second belt  502  becomes too fast, even if steering control is applied to reverse the moving direction of the second belt  502  in the width direction, the second belt  502  may cause transient slippage and lean away without reversing. 
     &lt;Adjustment Operating Mechanism&gt; 
     In view of the above, this embodiment allows the operator to adjust the relative inclination of the rollers supported by the second front support plate  526  (and the second rear support plate  527 ) when mounting the recording material cooling device  50  on the main assembly  100 A. The operator can adjust the relative inclination of the rollers supported by the second front support plate  526  (and the second rear support plate  527 ) after fixing the unit retaining portion  850  (in detail, the front retaining plate  851 , the connecting plate  852 , and the rear holding plate  853 ) to the main assembly  100 A. To be able to do so, the recording material cooling device  50  is provided with an adjustment operating mechanism  800 . When the adjustment operating mechanism  800  is operated by the operator, the second front support plate  526  is rotated relative to the front retaining plate  851 , and the relative inclination of the rollers supported by the second front support plate  526  is changed accordingly. This point will be explained below using  FIGS. 8 to 9  ( a ). 
     As shown in  FIG. 8 , in the second unit  502 U, the second front support plate  526  is attached to the front retaining plate  851  that is screwed to the main frame. The front retaining plate  851  as a holding member has a plurality of mounting holes  970  (two in this case) through which mounting screws (not shown) are inserted when screwing it to the main assembly frame. These mounting holes  970  are long holes in the width direction, so that the front retaining plate  851  can be fixed to the main assembly frame by correcting the misalignment in the width direction of the second front support plate  526  caused by component tolerance at the upstream and downstream sides of the recording material conveyance direction D. 
     The second front support plate  526  has an axially shaped first protruding shaft  520  and a second protruding shaft  521  that protrude toward the front retaining plate  851 . The first protruding shaft  520  has its tip fitted into a fitting hole  529  formed in the front retaining plate  851  so that the second front support plate  526  can be rotated with respect to the front retaining plate  851  with the first protruding shaft  520  as the center of rotation. In the second front support plate  526 , two support holes  957  are formed between the second protruding shaft  521  and one mounting portion  952  between the first protruding shaft  520  and the second protruding shaft  521 . After adjusting the relative inclination of the rollers as described below, the operator can fix the second front support plate  526  to the front retaining plate  851  at any rotational position by attaching a fixing screw  950  as a fixing member to the mounting portion  952 . The front retaining plate  851  has a through-hole  951  with a long hole for inserting the fixing screw  950  used for fixing the second front support plate  526 . 
     On the front retaining plate  851 , on the side opposite to the side facing the second front support plate  526 , the adjustment operating mechanism  800  is rotatably provided on the front retaining plate  851 . The adjustment operating mechanism  800  as an operating member has an adjustment plate  801  and an eccentric cam  802 . The adjustment plate  801  as a pivoting portion is formed in an abbreviated L-shape and has a gripping portion  801   a  to be grasped by the user. The adjustment plate  801  has an abbreviated D-shaped fitting hole  801   b  to fit the eccentric cam  802 , and two arc-shaped insertion holes  801   c  to insert screws  955  between the fitting holes  801   b . The eccentric cam  802  is fitted in the fitting hole  801   b , and rotates and displaces together with the adjustment plate  801  in accordance with the rotation of the adjustment plate  801 . A cam surface  802   b  of the eccentric cam  802  is engaged with a hole portion  518   a  formed in the front retaining plate  851 . The eccentric cam  802  also has a support hole  802   a  that supports the tip of the second protruding shaft  521  of the second front support plate  526 . In other words, the second front support plate  526  and the eccentric cam  802  are connected by the second protruding shaft  521  as a connecting member so that they can operate together. 
     The moving range of the adjustment operating mechanism  800  is limited by two screws  955  inserted into each of the insertion holes  801   c  formed in the adjustment plate  801 . The screws  955  are passed through the insertion holes  801   c  and through holes  956  formed in the front retaining plate  851 , and are attached to the support holes  957  formed in the second front support plate  526 . 
     According to the above-mentioned structure, the second front support plate  526  is not fixed to the front retaining plate  851  by the fixing screw  950 , but is rotated to the front retaining plate  851  with the first protruding shaft  520  as the center of rotation by the operation of the adjustment plate  801  by the user. Parts (a) to (c) of  FIG. 9  show specific examples. 
     As shown in part (a) of  FIG. 9 , suppose that the second front support plate  526 , which supports the second belt tensioning rollers  502   a  to  502   e  (see  FIG. 2 ), is deformed in a direction of an arrow L, and the unit retaining portion  850  is fixed to the main assembly  100 A. In this case, at least one of the second belt tensioning rollers  502   a  to  502   e  can be tilted relatively due to the deformation of the second front support plate  526  caused by the parts tolerance of the second unit  502 U and the main assembly  100 A (see  FIG. 1 ). The (initial) position of the adjustment operating mechanism  800  at this time varies according to the degree of deformation of the second front support plate  526 , and more particularly according to the degree of inclination of the second front support plate  526  with respect to the second rear support plate  527 . 
     In the state shown in part (a) of  FIG. 9 , the operator rotates the adjustment plate  801  of the adjustment operating mechanism  800  in a direction of arrow J before fixing the second front support plate  526  to the front retaining plate  851  using the fixing screw  950 . When the adjustment plate  801  is rotated in the direction of arrow J by the operator, the eccentric cam  802  pushes up the second protruding shaft  521  of the second front support plate  526  in the direction of gravity. This causes the second front support plate  526  to be rotated in a direction of arrow M. Part (a) of  FIG. 9  shows the state in which the rotation of the adjustment plate  801  in an arrow K direction is limited by the two screws  955 . 
     Alternatively, as shown in part (b) of  FIG. 9 , suppose that the unit retaining portion  850  is fixed to the main assembly  100 A with the second front support plate  526  deformed in the direction of arrow M. Even in this case, at least one of the second belt tensioning rollers  502   a  to  502   e  can be tilted relatively due to the deformation of the second front support plate  526  caused by the component tolerance of the second unit  502 U and the main assembly  100 A. 
     In the state shown in part (b) of  FIG. 9 , the operator rotates the adjustment plate  801  of the adjustment operating mechanism  800  in the direction of arrow K before fixing the second front support plate  526  to the front retaining plate  851  using the fixing screw  950 . When the adjustment plate  801  is rotated in the direction of arrow K by the operator, the eccentric cam  802  pushes down the second protruding shaft  521  of the second front support plate  526  in the direction of gravity. This causes the second front support plate  526  to be rotated in the direction of the arrow L. In part (b) of  FIG. 9 , the state in which the rotation of the adjustment plate  801  in the arrow J direction is limited by the two screws  955  is shown. 
     As described above, when the operator rotates the adjustment plate  801  in the direction of arrow J or K, the second front support plate  526  is rotated in the direction of arrow M or L, and the deformation of the second front support plate  526  caused by the component tolerance of the second unit  502 U or the main assembly  100 A is corrected. When the deformation of the second front support plate  526  is corrected, even if the second belt tensioning rollers  502   a  to  502   e  supported by the second front support plate  526  are relatively tilted before the correction, the second belt tensioning rollers  502   a  to  502   e  are adjusted to an abbreviated parallel state as shown in part (c) of  FIG. 9 . The operator then fixes the second front support plate  526  to the front retaining plate  851  using the fixing screws  950 . By fixing the second front support plate  526  to the front retaining plate  851  with the fixing screws  950 , the second front support plate  526  is maintained in the corrected state in which deformation caused by component tolerance is suppressed. Thus, by adjusting the second belt tensioning rollers  502   a  to  502   e  to an abbreviated parallel state, belt shifting of the second belt  502  can be suppressed by steering control. 
     In the embodiment described above, the second unit  502 U is provided with an adjustment operating mechanism  800  to allow the operator to compensate for the deformation of the second unit  502 U and the main assembly  100 A caused by the part tolerance of the second unit  502 U and the main assembly  100 A when installing the recording material cooling device  50  on the main assembly  100 A. In contrast, the first unit  501 U is not provided with the adjustment operating mechanism  800 . This is because, as described above, the first unit  501 U uses the highly rigid first front support plate  524  and first rear support plate  525  to support the heat sink  503 , and the first belt tensioning rollers  501   a - 501   e  are supported by them. If the first front support plate  524  and the first rear support plate  525  are highly rigid, even if the first unit  501 U is mounted on the main assembly  100 A, the first front support plate  524  and the first rear support plate  525  are hardly deformed. Therefore, in the first belt tensioning rollers  501   a - 501   e  of the first unit  501 U, the relative inclination of the rollers is less likely to occur to the extent that it becomes difficult to control the belt shifting by steering control compared to the second belt tensioning rollers  502   a - 502   e  of the second unit  502 U. In the case of the first unit  501 U having the heat sink  503 , the steering control can sufficiently suppress the belt shifting of the first belt  501 . Since this is the case, the first unit  501 U is not provided with an adjustment operating mechanism  800 . 
     As described above, in this embodiment, in the second unit  502 U which does not have a heat sink  503 , the front side plate is composed of two plates, the second front support plate  526  and the front retaining plate  851 . The front retaining plate  851  is fixed to the main assembly  100 A (main frame, etc.), and the second front support plate  526 , which supports the second belt tensioning rollers  502   a  to  502   e , is pivotable with respect to the front retaining plate  851 . An adjustment operating mechanism  800  is provided in the second unit  502 U so that the operator can manually rotate the second front support plate  526  while the front retaining plate  851  is fixed to the main assembly  100 A. The operator can rotate the adjustment plate  801  of the adjustment operating mechanism  800  to move the second front support plate  526  relative to the front retaining plate  851 . When the second front support plate  526  is moved relative to the front retaining plate  851 , the deformation of the second front support plate  526  caused by the component tolerance of the second unit  502 U and the main assembly  100 A is corrected. As a result, the second belt tensioning rollers  502   a  to  502   e  supported by the second front support plate  526  are adjusted to an abbreviated parallel state. Thus, by adjusting the second belt tensioning rollers  502   a  to  502   e  to an abbreviated parallel state, the belt shifting of the second belt  502  can be suppressed by steering control. 
     Other Embodiments 
     In the above-mentioned embodiment, an example is shown in which a first protruding shaft  520  and a second protruding shaft  521  are provided in the second front support plate  526  and the fitting hole  529  and the hole portion  518   a  are formed in the front retaining plate  851  in order to rotate the second front support plate  526  against the front retaining plate  851  (see  FIG. 8 ), but the present invention is not limited to this. For example, instead of the first protruding shaft  520 , a rotating shaft protruding from the front retaining plate  851  to the second front support plate  526  may be provided, and a hole portion to support the rotating shaft rotatably may be formed in the second front support plate  526 . Also, instead of the second protruding shaft  521 , a cam protruding shaft projecting from the eccentric cam  802  to the second front support plate  526  may be provided, and a hole portion for fixing the cam protruding shaft may be formed in the second front support plate  526 . 
     In the above-mentioned embodiment, a case in which the recording material cooling device  50  is installed inside the image forming apparatus  100  is shown as an example (see  FIG. 1 ), but the present invention is not limited to this case. For example, the recording material cooling device  50  may be installed outside of the image forming apparatus  100 .  FIG. 10  shows an image forming system  1 X where the recording material cooling device  50  is installed outside the image forming apparatus  100 . 
     The image forming system  1 X shown in  FIG. 10  has an image forming apparatus  100  and an external cooling unit  101  connected to the image forming apparatus  100 . The external cooling unit  101  is configured to be connected to the image forming apparatus  100  as one of the peripheral devices that can be retrofitted to expand the functions of the image forming apparatus  100  (referred to as optional units, etc.). The external cooling unit  101  is arranged to cool the recording material S discharged from the image forming apparatus  100  to lower the temperature of the recording material S, which is higher than that before fixing, to a predetermined temperature or lower. The external cooling unit  101  has the recording material cooling device  50  described above for cooling the recording material S. 
     The recording material S that has been cooled by the external cooling unit  101  is discharged from the external cooling unit  101  by a discharge roller  85  and stacked onto the discharge tray  120 . The discharge tray  120  is freely removable from the external cooling unit  101  and the image forming apparatus  100 . In other words, the discharge tray  120  is attached to the image forming apparatus  100  when the external cooling unit  101  is not connected to the image forming apparatus  100  (see  FIG. 1 ). When the external cooling unit  101  is connected to the image forming apparatus  100 , it is removed from the image forming apparatus  100  by the operator and replaced with the external cooling unit  101 . A plurality of external cooling units  101  may be connected as peripheral units. The operator can easily improve the cooling capacity of recording material S for the existing image forming apparatus  100  by increasing the number of connected external cooling units  101 . The same effect as that of the first embodiment can be obtained by adopting the first embodiment described above when mounting the recording material cooling device  50  on the support frame of such an external cooling unit  101 . 
     According to the present invention, it is possible to compensate for the relative tilt of the rollers that may occur when mounting the recording material cooling device with a simple configuration. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention 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. 2020-100038 filed on Jun. 9, 2020, which is hereby incorporated by reference herein in its entirety.