Patent Publication Number: US-11397392-B2

Title: Image forming apparatus with downstream end of first feeding surface positioned above upstream end of second feeding surface

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus for forming an image on a sheet. 
     Conventionally, an image forming apparatus of an electrophotographic type includes a transfer portion where the image is transferred onto the sheet and includes a fixing portion where the image transferred on the sheet is fixed on the sheet. Further, as disclosed in Japanese Laid-Open Patent Application (JP-A) 2012-83416, there is a constitution in which a feeding means for sucking and feeding the sheet on a belt is provided between the transfer portion and the fixing portion with respect to a sheet feeding direction. 
     Further, as disclosed in JP-A 2014-44232, there is a constitution in which a loop detecting means is provided between the transfer portion and the fixing portion and a sheet feeding speed by the fixing portion is controlled on the basis of a detection result of a height of the loop. 
     However, in recent years, in order to realize a high image quality and high productivity, devices of the transfer portion and a fixing portion are upsized, and correspondingly, a distance in which the sheet is fed by a feeding means between the transfer portion and the fixing portion becomes long. In this constitution, for example, in the case where an elongated sheet longer than the distance between the transfer portion and the fixing portion is subjected to loop control, a sheet feeding distance with respect to the sheet feeding direction between a transfer nip and a fixing nip in which the sheet is nipped becomes long, so that there is a liability that behavior such that the sheet is looped cannot be stabilized and thus the loop control cannot be carried out. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide an image forming apparatus, in which an elongated sheet is subjected to loop control between a transfer portion and a fixing portion, capable of improving a sheet feeding performance. 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image bearing member configured to bear a toner image; transfer means including a transfer nip in which a sheet is nipped and fed and configured to transfer the toner image from the image bearing member onto the sheet nipped in the transfer nip; fixing means including a fixing nip in which the sheet is nipped and fed and configured to fix the toner image, on the sheet, transferred by the transfer means; first feeding means including a first endless belt having air permeability and including a first belt portion for forming a first feeding surface on which the sheet is fed, a first stretching member for rotatably stretching the first belt portion, and a first air sucking portion capable of attracting the sheet to the first feeding surface by sucking air through the first belt portion, and configured to feed the sheet from the transfer means toward the fixing means by rotating the first belt portion; second feeding means including a second endless belt having air permeability and including a second belt portion for forming a second feeding surface on which the sheet is fed, a second stretching member for rotatably stretching the second belt portion, and a second air sucking portion capable of attracting the sheet to the second feeding surface by sucking air through the second belt portion, wherein the second feeding means is provided downstream of the first feeding means with respect to a sheet feeding direction and is configured to feed the sheet, fed by the first feeding means, toward the fixing means by rotating the first belt portion; a height detecting means configured to output a signal depending on a height of the sheet from the first feeding surface at a detecting position where the height detecting means overlaps with the first feeding means as viewed in a widthwise direction of the sheet perpendicular to the sheet feeding direction and which is downstream of a center of the first feeding means with respect to the sheet feeding direction; and a controller configured to receive the signal outputted from the height detecting means and configured to control the fixing means. 
     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 structural view of an image forming apparatus of an embodiment 1 of the present invention. 
         FIG. 2  is a sectional view showing a secondary transfer portion, a belt feeding unit and a fixing potion in the embodiment 1. 
         FIG. 3  is a perspective view of the belt feeding unit in the embodiment 1. 
         FIG. 4  is a perspective view of the belt feeding unit in a state in which a belt is dismounted in the embodiment 1. 
         FIG. 5  is a block diagram showing a control constitution of the image forming apparatus of the embodiment 1. 
         FIG. 6  is a flowchart showing a flow of an operation for feeding a sheet by the belt feeding unit in the embodiment 1. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, an embodiment for carrying out the present invention will be described by making reference to the drawings. 
       FIG. 1  is a schematic structural view of an image forming apparatus  100  of an embodiment 1. First, with reference to  FIG. 1 , a structure of the image forming apparatus  100  will be described. The image forming apparatus  100  includes a feeding portion  100 B for feeding a sheet and a height feeding (conveying) portion  100   d  for feeding (conveying) the sheet fed by the feeding portion  100 B. Further, the image forming apparatus  100  includes an image forming portion  513  for forming a toner image on the sheet, a secondary transfer portion  57  where the toner image is transferred onto the sheet, and a belt feeding unit  100 E for feeding the sheet, on which the toner image is transferred, to a fixing portion  58 . Further, the image forming apparatus  100  includes a post-feeding portion  59  for feeding the sheet on which the toner image is fixed by the fixing portion  58 . The feeding portion  100 B includes a sheet cassette  51  in which sheets are stacked on a life-up device  52  and includes a sheet feeding means  53  for sending (feeding) a sheet S stacked in the sheet cassette  51 . As a sheet feeding method by the sheet feeding means  53 , for example, a friction-separation type by a roller and a separation attraction type by the air exist, but in  FIG. 1 , an example using the separation attraction type by the air is shown. Incidentally, in the image forming apparatus  100 , a constitution in which the sheet is fed by the friction-separation type by the roller may also be employed. The sheet fed from the feeding portion  100 B is successively delivered by pluralities of roller pairs provided in the sheet feeding portion  100 D and then is fed toward the secondary transfer portion  57 . 
     The image forming portion  513  is an image forming means of a so-called tandem type in which image forming stations PY, PM, PC and PK of an electrophotographic type for forming toner images of Y (yellow), M (magenta), C (cyan) and K (black), respectively, are arranged in line (series). The image forming stations PY, PM, PC and PK have a common constitution except that toner colors are different from each other. For that reason, in this embodiment, a constitution of the image forming station PY will be described as an example, and constitutions of the image forming stations PM, PC and PK will be omitted from description. Incidentally, in  FIG. 1 , constituent elements of the image forming stations PY, PM, PC and PK are represented by adding suffices “Y”, “M”, “C” and “K”, respectively. The image forming station PY includes a photosensitive drum  1 Y, an exposure device  511 Y, a developing device  510 Y, a primary transfer device  507 Y and a cleaner  509 Y. The image forming portion  513  includes an intermediary transfer belt  506  as an example of an image bearing member on which toner images formed (visualized) by the image forming stations PY, PM, PC and PK are borne. The intermediary transfer belt  506  is supported in a state in which the intermediary transfer belt  506  is stretched by a driving roller  505 , a tension roller  504  and an inner transfer roller  503  and is rotated in an arrow B direction by drive of the driving roller  505 . 
     A secondary transfer roller  56  press-contacts the intermediary transfer belt  506  supported by the inner transfer roller  503  from an inside of the intermediary transfer belt  506  and forms a secondary transfer nip N 2  between itself and the intermediary transfer belt  506 . The secondary transfer portion  57  as a transfer means in this embodiment is constituted by the secondary transfer roller  56 , the intermediary transfer belt  506  and the inner transfer roller  503 . Transfer residual toner and paper dust and the like which remain on a surface of the intermediary transfer belt  506  after passing through the secondary transfer nip N 2  are removed by a cleaning device. The fixing portion  58  provided on a side downstream of the secondary transfer portion  57  with respect to a sheet feeding direction FD is a fixing means for fixing the toner image on the sheet by heat and pressure. The fixing portion  58  includes a heating roller  582  including a heater therein and an opposite roller  583  which is provided contactable to the heating roller  582  and which forms a fixing nip N in cooperation with the heating roller  582 . Further, the fixing portion includes a heating roller temperature sensor for detecting a surface temperature of the heating roller  582  and a pressing roller temperature sensor for detecting a surface temperature of the opposite roller  583 . The heating roller temperature sensor and the pressing roller temperature sensor are provided so as to maintain the surface temperatures of the heating roller  582  and the opposite roller  582 , respectively, at appropriate temperatures. 
     With respect to the sheet feeding direction FD, between the secondary transfer portion  57  and the fixing portion  58 , the belt feeding unit  100 E is provided. The belt feeding unit  100 E is constituted by a first belt feeding portion  10  provided on an upstream side with respect to the sheet feeding direction FD and a second belt feeding portion  20  provided on a side downstream of the first belt feeding portion  10  with respect to the sheet feeding direction FD. A constitution of the belt feeding unit  100 E will be described later. 
     The post-feeding portion  59  discharges the sheet, discharged from the fixing portion  58 , to an outside of an apparatus main assembly  100 A of the image forming apparatus  100 . The post-feeding portion  59  includes a reverse feeding portion  501  for reversely feeding the sheet and a double-side feeding passage  502  where the sheet reversed by the reverse feeding portion  501  is fed and which is merged with a sheet feeding passage of the sheet feeding portion  100 D. 
     Next, a series of a flow of formation of the image on the sheet in the image forming apparatus  100  will be described. On the basis of an image forming job inputted to the image forming apparatus  100 , first, the photosensitive drum  1 Y is exposed to light by the exposure device  511 Y, so that an electrostatic latent image is formed on a surface of the photosensitive drum  1 Y. The electrostatic latent image is developed by the developing device  510 Y and thus is visualized as a toner image. The toner image carried on the surface of the photosensitive drum  1 Y is primary-transferred onto the intermediary transfer belt  506 . Similarly, the toner images carried on the surfaces of other photosensitive drums are successively primary-transferred superposedly onto the intermediary transfer belt  506  by the primary transfer device  507 Y. The toner images primary-transferred on the intermediary transfer belt  506  are secondary-transferred onto the sheet S, fed from the feeding portion  100 B, in the secondary transfer nip N 2  as a transfer nip in this embodiment. Incidentally, the intermediary transfer belt  506  is rotationally driven by the driving roller  505  rotating at a certain speed and thus is rotated in a state in which a peripheral speed thereof is kept so as to be a certain transfer speed. Accordingly, a feeding speed of the sheet in the secondary transfer nip N 2  is the peripheral speed of the intermediary transfer belt  506 . Hereinafter, the feeding speed of the sheet in the secondary transfer portion  57  is referred to as a “transfer speed (velocity) VT”. The transfer speed VT is the sheet feeding speed when the toner image is transferred at the secondary transfer portion  57 . 
     A registration roller pair  7  of the sheet feeding portion  100 D receives the sheet S in a state in which rotation thereof is stopped, and then, the rotation is started by being timed to the toner images on the intermediary transfer belt  506 , so that the sheet S is sent toward the secondary transfer nip N 2 . In the secondary transfer nip N 2 , the toner images are transferred onto the sheet S. The sheet S on which the toner images are transferred is fed from the secondary transfer nip N 2  toward the fixing portion  58  by the belt feeding unit  100 E. In the fixing portion  58 , the sheet S is nipped in the fixing nip N and the (unfixed) toner images are fixed on the sheet S under application of heat and pressure. The sheet S sent from the fixing portion  58  is discharged by the post-feeding portion  59 . 
     In the case where images are formed on both surfaces (front surface and back surface) of the sheet, the sheet sent from the fixing portion  58  is fed to the reverse feeding portion  501 , and is fed toward the double-side feeding passage  502  after being reversed by the reverse feeding portion  501 . The sheet is fed to the feeding path of the sheet feeding portion  100 D via the double-side feeding passage  502 . Then, similarly as in the case of a first surface (front surface), the toner image is formed on a second surface (back surface). 
     Next, a detailed constitution of the belt feeding unit  100 E and a peripheral portion thereof in this embodiment will be described.  FIG. 2  is a sectional view showing the secondary transfer portion  57 , the belt feeding unit  100 E and the fixing portion  58 . The belt feeding unit  100 E includes the first belt feeding portion as a first feeding means and the second belt feeding portion  20  as a second feeding means in this embodiment. With respect to the sheet feeding direction FD, the first belt feeding portion  10  is disposed downstream of the secondary transfer nip N 2  and the second belt feeding portion  20  is disposed downstream of the first belt feeding portion  10  and upstream of the fixing nip N. 
     With respect to the sheet feeding direction FD, between the belt feeding unit  100 E and the secondary transfer nip N 2 , a transfer separation guide  561  for separating the sheet fed from the secondary transfer nip N 2  and for guiding the sheet toward the belt feeding unit  100 E is provided. Further, with respect to the sheet feeding direction FD, between the belt feeding unit  100 E and the fixing nip N, a pre-fixing guide  581  for guiding, toward the fixing nip N, the sheet fed by the belt feeding unit  100 E is provided. As shown in  FIG. 2 , when the first belt feeding portion  10  is viewed in a widthwise direction of the sheet perpendicular to the sheet feeding direction FD, the first belt feeding portion  10  is capable of being disposed at a position lower than the fixing nip N. When the second belt feeding portion  20  is viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD, the second belt feeding portion  20  is capable of being disposed at a position lower than the fixing nip N. By such a constitution, a leading end of the sheet passed through the secondary transfer nip N is fed toward the first belt feeding portion  10  along the transfer separation guide  561 . Further, as viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD, a downstream end of a feeding surface  10 A of the first belt feeding portion  10  is positioned above an upstream end of a feeding surface  20 A of the second belt feeding portion  20 . By such an arrangement, bucking of the sheet, fed by the first belt feeding portion  10 , by the second belt feeding portion  20  is prevented. In this embodiment, a first feeding surface is the feeding surface  10 A, and a second feeding surface is the feeding surface  20 A. 
     Further, the second belt feeding portion  20  feeds the sheet toward the fixing portion  58  along the feeding surface  20 A. A phantom line  200 A′ extended from the feeding surface  2 A toward a downstream side of the sheet feeding direction FD crosses a nip line N′ of the fixing nip N on a side downstream of the fixing nip N with respect to the sheet feeding direction FD. The nip line N′ of the fixing nip N refers to a tangential line, of tangential lines of the fixing nip N, contacting the heating roller  582  and the opposite roller  583 . By such a constitution, the sheet fed by the second belt feeding portion  20  is fed in a crossing direction extending from below toward above in  FIG. 2 . Further, with respect to the sheet feeding direction FD, between the second belt feeding portion  20  and the fixing portion  58 , the pre-fixing guide  581  as a guiding member in this embodiment is provided. The pre-fixing guide  581  includes a guiding surface  581 A for guiding the sheet, toward the fixing nip N, a leading end of the sheet fed along the feeding surface  20 A. As viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD, the guiding surface  581 A of the pre-fixing guide  581  is positioned downstream of the second belt feeding portion  20  and crosses the phantom line  20 A′ of the feeding surface  20 A. By such a constitution, the sheet fed by the second belt feeding portion  20  is guided to the fixing nip N by the pre-fixing guide  581  in a state in which the pre-fixing guide  581  crosses the nip line N′ from below toward above in  FIG. 2 . 
     Incidentally, of the tangential lines of the fixing nip N, the nip line N′ exists on a flat surface formed by the tangential line contacting the heating roller  582  and the opposite roller  583 . That is, the sheet is fed to the fixing nip N in the state in which the pre-fixing guide  581  crosses the nip line N′ from below toward above in  FIG. 2 , and therefore, it is possible to suppress contact of the heating roller  582  to the unfixed toner on the sheet. 
     The first belt feeding portion  10  includes a first feeding belt  101  as a first belt portion, a first driving roller  102  rotatably stretching the first feeding belt  101 , and follower rollers  103 ,  104  and  105  in this embodiment. A first stretching member in this embodiment is constituted by the first driving roller  102  and the follower rollers  103 ,  104  and  105 . Further, the first belt feeding portion  10  includes a motor for rotating the first feeding belt  101  by rotating the first driving roller  102 . The first feeding belt  101  is a member which includes endless belts (belts  101   a ,  101   b ,  101   c ,  101   d  ( FIG. 3 ) each provided with many holes and which has air permeability such that air is capable of passing through the first feeding belt  101  between inner and outer peripheral surfaces of the first feeding belt  101  via the holes. Further, inside the inner peripheral surface of the first feeding belt  101 , a first suction fan  106  for attracting the sheet to the outer peripheral surface of the first feeding belt  101  is provided. 
       FIG. 4  is a perspective view of the belt feeding unit  100 E in a state in which the first feeding belt  101  and the second feeding belt  201  are dismounted. As shown in  FIG. 4 , the first belt feeding portion  10  is provided with the first suction fan  106  for sucking the air through air bent holes. The first suction fan  106  sucks the air from the outer peripheral surface toward the inner peripheral surface of the first feeding belt  101  through many holes formed in the first feeding belt  101 . The first suction fan  106  is provided with the air bent holes which open from the inside of the first feeding belt  101  toward the feeding surface  10 A ( FIG. 2 ) and is capable of attracting the sheet, fed by the first feeding belt  101 , to the feeding surface  10 A by sucking the air through the air bent holes. That is, a first air sucking portion in this embodiment is the first suction fan  106  capable of attracting the sheet to the feeding surface  10 A. 
     As shown in  FIG. 2 , as viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD, the sheet passed through the secondary transfer nip N 2  is fed to an upper surface of the first feeding belt  101 . That is, the sheet is fed to the feeding surface  10 A formed by the first feeding belt  101  after passed through the secondary transfer nip N 2 . As a result, the sheet is fed in a state in which the sheet is attracted to the feeding surface  10 A by the influence of air suction by the first suction fan  106 . Further, in this embodiment, the first driving roller  102  is rotated so that a feeding speed V 1  of the sheet by the first feeding belt  101  becomes slightly higher than the transfer speed VT. By doing so, buckling of the sheet can be prevented by a speed difference between the secondary transfer nip N 2  and the first feeding belt  101 . Incidentally, the feeding speed V 1  of the sheet by the first feeding belt  101  is a peripheral speed of the first feeding belt  101 . 
     The second belt feeding portion  20  includes a second feeding belt  201  as a second belt portion, a second driving roller  202  rotatably stretching the second feeding belt  201 , and follower rollers  203 ,  204  and  205  in this embodiment. A second stretching member in this embodiment is constituted by the second driving roller  202  and the follower rollers  203 ,  204  and  205 . Further, the second belt feeding portion  20  includes a motor for rotating the second feeding belt  201  by rotating the second driving roller  202 . The second feeding belt  201  is a member which includes endless belts (belts  201   a ,  201   b ,  201   c ,  201   d  ( FIG. 3 ) each provided with many holes and which has air permeability such that air is capable of passing through the second feeding belt  201  between inner and outer peripheral surfaces of the second feeding belt  201  via the holes. Further, inside the inner peripheral surface of the second feeding belt  201 , a second suction fan  206  for attracting the sheet to the outer peripheral surface of the second feeding belt  201  is provided. 
     As shown in  FIG. 4 , the second belt feeding portion  20  is provided with the second suction fan  206  for sucking the air through air bent holes. Further, as shown in  FIGS. 2 and 4 , with respect to the sheet feeding direction FD, a position of a center of the second suction fan  206  may also be downstream of a center of the second feeding belt  201 . By doing so, in a state in which the sheet is attracted to the feeding surface  20 A, the sheet can be fed to the fixing nip N. The second suction fan  206  is provided with the air bent holes which open from the inside of the second feeding belt  201  toward the feeding surface  20 A ( FIG. 2 ) and is capable of attracting the sheet, fed by the second feeding belt  201 , to the feeding surface  20 A by sucking the air through the air bent holes. That is, a second air sucking portion in this embodiment is the second suction fan  206  capable of attracting the sheet to the feeding surface  20 A. 
     Further, a suction force of the air by the second suction fan  206  can be switched between a suction force for attracting the sheet toward the feeding surface  20 A and a suction force smaller than this suction force. The suction force of the air by the second suction fan  206  capable of attracting the sheet toward the feeding surface  20 A is a first suction force in this embodiment. The suction force smaller than the suction force for attracting the sheet toward the feeding surface  20 A refers to, for example, a suction force of a degree such that the sheet attracted to the feeding surface  20 A is capable of freely moving on the feeding surface  20 A. The air suction force, by the second suction fan  206 , smaller than the suction force capable of attracting the sheet to the feeding surface  20 A is a second suction force in this embodiment. In this embodiment, control may also be carried out so that the air suction force by the first suction fan  106  and the air suction force by the second suction fan  206  are the same suction force. 
     As shown in  FIG. 2 , as viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD, the sheet passed through the first feeding belt  101  is fed to an upper surface of the second feeding belt  201 . That is, the sheet is fed to the feeding surface  20 A formed by the second feeding belt  201  after having passed through the feeding surface  10 A. As a result, the sheet is fed in a state in which the sheet is attracted to the feeding surface  20 A by drive of the second suction fan  206 . Further, in this embodiment, the second driving roller  202  is rotated so that a feeding speed V 2  of the sheet by the second feeding belt  201  becomes slightly higher than the feeding speed V 1  of the sheet by the first feeding belt  101 . By doing so, buckling of the sheet can be prevented by a speed difference between the first feeding belt  101  and the second feeding belt  201 . Incidentally, the feeding speed V 2  of the sheet by the second feeding belt  201  is a peripheral speed of the second feeding belt  201 . 
     Further, in this embodiment, a height detecting means  30  for detecting a height of the sheet from the feeding surface  10 A in a detecting position PL positioned on a state downstream of the first suction fan  106  of the first belt feeding portion  10  with respect to the sheet feeding direction FD is provided. Incidentally, the detecting position PL of the height detecting means  30  in this embodiment is a position, where formation of looseness (loop) of the sheet is most visible, for example, is positioned on a side slightly downstream of the first suction fan  106  with respect to the sheet feeding direction FD. However, as regards the detecting position PL of the height detecting means  30 , the detecting position PL may also be any position between the secondary transfer nip N 2  and the fixing nip N with respect to the sheet feeding direction FD. Further, in this embodiment, the detecting position of the height detecting means  30  overlaps with the belt feeding unit  100 E with respect to the sheet feeding direction FD as viewed in the widthwise direction of the sheet perpendicular to the sheet feeding direction FD. By doing so, with respect to the sheet feeding direction FD, a height of the sheet from the feeding surface  10 A can be detected with reliability. 
       FIG. 3  is a perspective view of the belt feeding unit  100 E. As shown in  FIG. 3 , the first feeding belt  101  includes belts  101   a ,  101   b ,  101   c  and  101   d . Each of the belts  101   a ,  101   b ,  101   c  and  101   d  is an endless belt in which numbers of holes are formed and constitutes the feeding surface  10 A of the first feeding belt  101  on which the sheet is fed. As shown in  FIG. 3 , the belts  101   a ,  101   b ,  101   c  and  101   d  are disposed with intervals therebetween with respect to the widthwise direction W perpendicular to the sheet feeding direction FD, and the detecting position PL of the height detecting means  30  is disposed between the belt  101   b  and the belt  101   c . That is, in this embodiment, a first endless belt is the belt  101   b  and a second endless belt is the belt  101   c , and the detecting position PL of the height detecting means  30  is disposed between the belts  101   b  and  101   c  with respect to the widthwise direction W. Incidentally, a locating position of the detecting position PL of the height detecting means  30  may also be between adjacent belts (for example, the belt  101   a  and the belt  101   b ) with respect to the widthwise direction W, in addition to the locating position shown in  FIG. 3 . Further, a center of the sheet with respect to the widthwise direction W on the first feeding belt  101  may also be disposed between the belts  101   b  and  101   c . By such an arrangement, in the case where feeding of the sheet in the image forming apparatus  100  is made on a center(-line) basis with respect to the widthwise direction W, with respect to the widthwise direction W, it becomes possible to reliably detect the height of the sheet from the feeding surface  10 A. 
     As shown in  FIG. 3 , the second feeding belt  201  includes, as examples of a second endless belt in this embodiment, belts  201   a ,  201   b ,  201   c  and  201   d . Each of the belts  201   a ,  201   b ,  201   c  and  201   d  is an endless belt in which numbers of holes are formed and constitute the feeding surface  20 A of the second feeding belt  201  on which the sheet is fed. As shown in  FIG. 3 , the belts  201   a ,  201   b ,  201   c  and  201   d  are disposed with intervals therebetween with respect to the widthwise direction W perpendicular to the sheet feeding direction FD. 
     The height detecting means  30  includes a detecting flag  301  capable of being displaced depending on the height of the sheet from the feeding surface  10 A as viewed in the widthwise direction W perpendicular to the sheet feeding direction FD. A position where the detecting flag  301  as a flag member in this embodiment and the sheet fed by the belt feeding unit  100 E are in contact with each other is an example of the detecting position PL of the height detecting means  30 . The detecting flag  301  is displaced depending on the height of the sheet from the feeding surface  10 A, fed by the belt feeding unit  100 E. In  FIG. 2 , as the height of the sheet, from the feeding surface  10 A, fed by the belt feeding unit  100 E, S 1  and S 2  lower than S 1  are shown as an example in the order of height as viewed in the widthwise direction W perpendicular to the sheet feeding direction FD. A first position in this embodiment is a position of the detecting flag  301  when the sheet is detected above S 1  relative to the feeding surface  10 A. Further, a second position in this embodiment is a position of the detecting flag  301  when the sheet is detected between S 1  and S 2  relative to the feeding surface  10 A, and a third position in this embodiment is a position of the detecting flag  301  when the sheet is detected below S 2  relative to the feeding surface  10 A. That is, in this embodiment, the detecting flag  301  is capable of being displaced to the first position, the second position and the third position in the order of height. 
     Further, the height detecting means  30  includes sensors  302  and  303 , such as photo-interruptors which are switchable between a light-blocking state and a light-transmission state depending on the position of the detecting flag  301  and which output a signal depending on the state thereof. The sensor  302  as a first sensor in this embodiment becomes the light-transmission state when the height of the sheet from the feeding surface  10 A is higher than S 1 , and outputs an OFF signal. On the other hand, the sensor  302  becomes the light-blocking state when the height of the sheet from the feeding surface  10 A is S 1  or lower (in a state in which the sheet is closer to the feeding surface  10 A than S 1  is), and outputs an ON signal. Further, the sensor  303  as a second sensor in this embodiment becomes the light-transmission state when the height of the sheet from the feeding surface  10 A is lower than S 2 , and outputs an OFF signal. On the other hand, the sensor S 303  becomes the light-blocking state when the height of the sheet from the feeding surface  10 A is S 2  or higher (in a state in which S 2  is closer to the feeding surface  10 A than the sheet is), and outputs an ON signal. That is, from the height detecting means  30 , a signal depending on a combination of the signal outputted from the sensor  302  and the signal outputted from the sensor  303 . 
     In the case where the height of the sheet from the feeding surface  10 A, in other words, in the case where the detecting flag  301  is positioned above S 1 , the signal outputted from the height detecting means  30  is a combination of the OFF signals of the sensors  302  and  303 . Further, when the sensor  302  outputs the OFF signal, the detecting flag  301  is positioned above S 1 , and therefore, the sensor  303  becomes the light-blocking state and outputs the OFF signal. Thus, in this embodiment, when the sensor  302  outputs the OFF signal, the sensor  303  also outputs the OFF signal. A first signal in this embodiment corresponds to a signal outputted from the height detecting means  30  when a combination of the OFF signals of the sensors  302  and  303  is formed. Further, when the detecting flag  302  is positioned between S 1  and S 2 , the signal outputted from the height detecting means  30  is a combination of the ON signal of the sensor  302  with the OFF signal of the sensor  303 . That is, a second signal in this embodiment corresponds to a signal outputted from the height detecting means  30  when a combination of the ON signal of the sensor  302  and the OFF signal of the sensor  303  is formed. Further, when the detecting flag  301  is positioned below S 2 , the signal outputted from the height detecting means  30  is a combination of the ON signals of the sensors  302  and  303 . Further, the sensor  302  is put in the light-blocking state by the detecting flag  301  when the sensor  303  outputs the ON signal, and therefore, when the sensor  303  outputs the ON signal, the sensor  302  also outputs the ON signal. That is, a third signal in this embodiment corresponds to a signal outputted from the height detecting means  30  when a combination of the ON signals of the sensors  302  and  303  is formed. The signal depending on output values of the sensors  302  and  303  is sent to a controller  305  ( FIG. 5 ). 
     Incidentally, a state in which the sheet height is S 1  refers to, for example, a state in which the sheet is fed at a position spaced from the feeding surface  10 A before the sheet is stretched between the fixing portion  58  and the secondary transfer portion  57  with respect to the sheet feeding direction FD. Further, a state in which the sheet height is S 2  refers to a state in which the sheet is fed at a position closest to the feeding surface  10 A before the sheet is excessively loosened between the fixing portion  58  and the secondary transfer portion  57  with respect to the sheet feeding direction FD. That is, when the sheet is positioned between S 1  and S 2 , the sheet is fed not only in a state in which the sheet is spaced from the feeding surface  10 A but also in a state in which the sheet is loosened. Accordingly, when the combination of signals outputted from the height detecting means  30  is the ON signal of the sensor  302  and the OFF signal of the sensor  303 , the detecting flag  301  is positioned between S 1  and S 2  as viewed in the widthwise direction W perpendicular to the sheet feeding direction FD. Further, when the combination of the signals outputted from the height detecting means  30  is the ON signal of the sensor  302  and the OFF signal of the sensor  303 , the sheet is fed not only in the state in which the sheet is spaced from the feeding surface  10 A but also in the state in which the sheet is loosened. In other words, when the detecting flag  301  is positioned between S 1  and S 2  as viewed in the widthwise direction W perpendicular to the sheet feeding direction FD, the sheet is in a spaced state from the feeding surface  10 A and in a loosened state. 
     Incidentally, with respect to the sheet feeding direction FD, between the registration roller pair  7  and the secondary transfer nip N 2 , a sheet detecting sensor for detecting the sheet may also be provided. The sheet detecting sensor detects the presence or absence of the sheet at a detecting position between the registration roller pair  7  and the secondary transfer nip N 2  with respect to the sheet feeding direction FD. The signal outputted from the sheet detecting sensor is sent to the controller  305  ( FIG. 5 ) and is used for discriminating passing of the sheet. 
     The sheet passed through the detecting position PL is fed from the second feeding belt  201  to the fixing portion  58 . In the fixing portion  58 , for example, the heating roller  582  is rotationally driven by a heating roller driving motor such as a DC brush-less motor. A sheet feeding speed in the fixing nip N can be changed. Incidentally, the sheet feeding speed in the fixing nip N refers to a peripheral speed of the heating roller  582 . In the following, the feeding speed in the fixing portion  58 , i.e., the feeding speed of the sheet in the fixing nip N is referred to as a “fixing speed (velocity) VF”. Here, the feeding speed refers to the sheet feeding speed when the toner image is fixed on the sheet in the fixing portion  58 . That is, in the fixing nip N formed between the heating roller  582  and the opposite roller  583 , the toner image is fixed on the sheet while the sheet is fed at the fixing speed VF. 
     Next, a control constitution when the sheet is fed by the belt feeding unit  100 E in the image forming apparatus  100  of this embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a block diagram showing the control constitution of the image forming apparatus  100  of this embodiment. The controller  305  as a control means in this embodiment is constituted by including a processing unit containing a CPU and a memory and including an interface for establishing communication between itself and an external device, and the like. The controller  305  receives job data  306  and is capable of controlling the feeding portion  100 B, the image forming portion  513 , the fixing portion  58 , the secondary transfer portion  57  and the like. To the controller  305 , as the job data  306 , information on a kind of the sheet, for example, pieces of the information such as a basis weight of the sheet, a size of the sheet, plain paper or coated paper are sent. Incidentally, as the job data  306 , one in which information on the kind of the sheet is included in information sent as an image forming job from the external device, one generated depending on an operation of an operating portion of the image forming apparatus  100 , and the like data are used. Here, the coated paper is a sheet of which surface is subjected to resin coating. Further, the controller  305  receives the signal outputted from the height detecting means  30 , in other words, the signals consisting of combinations of the ON signal and the OFF signals of each of the sensors  302  and  303 . The controller  305  controls, on the basis of the received signal, operations of a fixing motor MF, a transfer motor MT, a motor FM 1  for driving the first suction fan  106 , a motor FM 2  for driving the second suction fan  206 , a driving motor for driving the heating roller, and the like motor. The controller  305  is capable of adjusting the fixing speed VF by controlling drive of the fixing motor MF. Further, the controller  305  is capable of adjusting the transfer speed VT by controlling drive of the transfer motor MT. 
     Next, a flow of control of the belt feeding unit  100 E in the image forming apparatus  100  of this embodiment will be described with reference to  FIG. 6 .  FIG. 6  is a flowchart showing a flow of an operation for feeding the sheet by the belt feeding unit  100 E in this embodiment. The flow is started by inputting information, such as the size, the basis weight and the like, on the sheet in the image forming job from the operating portion of the image forming apparatus  100  or by inputting the image forming job from the external device to the image forming apparatus  100 . Further, the flag is executed principally by the controller  305 . When the image forming job is started, the controller  305  executes control at the time of the start of the job (S 11 ). In the control at the time of the start of the job in this embodiment, the controller  305  sets the transfer speed VT, a sheet feeding speed V 1  at the first belt feeding portion  10 , a sheet feeding speed V 2  at the second belt feeding portion  20 , and the fixing speed VF so as to satisfy V 2 &gt;V 1 &gt;VT and VF&gt;VT. Further, the controller  305  starts feeding of the sheet under a condition of V 2 &gt;V 1 &gt;VT and VF&gt;VT. Further, the controller  305  puts the second suction fan  206  in an ON state in the control at the time of the start of the image forming job. Incidentally, together with the second suction fan  206 , the first suction fan  106  may also be put in an ON state. 
     Subsequently, the controller  305  acquires information on a length of the sheet with respect to the sheet feeding direction FD from information included in the image forming job, and discriminates whether or not the length of the sheet with respect to the sheet feeding direction FD is longer than a length between the secondary transfer nip N 2  and the fixing nip N (S 12 ). In the case where the length of the sheet with respect to the sheet feeding direction FD is shorter than the length between the secondary transfer nip N 2  and the fixing nip N (S 12 : N), the sequence goes to S 23 . Then, when the image forming job is not ended (S 23 : N), the sequence returns to S 02 , and when the image forming job is ended (S 23 : Y), the flow is ended. 
     Further, when the length of the sheet with respect to the sheet feeding direction FD is longer than the length between the secondary transfer nip N 2  and the fixing nip N with respect to the sheet feeding direction FD (S 12 : Y), the belt feeding unit  100 E awaits until a leading end of the sheet reaches the fixing nip N (S 13 ). As regards discrimination as to whether or not the leading end of the sheet reaches the fixing nip N, first, after the feeding of the sheet is started, the belt feeding unit  100 E awaits until the leading end of the sheet is detected by the sheet detecting sensor. Then, when the leading end of the sheet reaches the detecting position of the sheet detecting sensor, an elapsed time from the time when the leading end of the sheet reaches the detecting position is measured, and the controller  305  discriminates whether or not a time necessary for the leading end of the sheet to reach the fixing nip N has elapsed. When the elapsed time from the time when the leading end of the sheet reaches the detecting position exceeds the time necessary for the leading end of the sheet to reach the fixing nip, the controller  305  discriminates that the leading end of the sheet reaches the fixing nip N (S 13 : Y). 
     When the leading end of the sheet reaches the fixing nip N, the controller  305  switches the state of the second suction fan  206  from the ON state to the OF state (S 14 ). Here, an operation mode of the sheet relative to the feeding surface  20 A by the switching of the second suction fan  206  between the ON state and the OFF state will be described. In the case where an operation of the second suction fan  206  is in the OFF state, a suction force (attraction force) for sucking the air through the second feeding belt  201  by the second suction fan  206  is a suction force of a degree such that the sheet is freely movable relative to the feeding surface  20 A of the second feeding belt  201 . An example of the second suction force is the suction force of the degree such that the sheet is freely movable relative to the feeding surface  20 A of the second feeding belt  201 . On the other hand, in the case where the operation of the second suction fan  206  is in the ON state, the suction force for sucking the air through the second feeding belt  206  by the second suction fan  206  is a suction force of a degree such that the sheet is attracted to the feeding surface  20 A of the second feeding belt  201 . This is because the air suction force is increased by driving the second suction fan  206  and thus a phenomenon such that air stream generates from the outer peripheral surface toward the inner peripheral surface of the second feeding belt  201  and the sheet is attracted to the feeding surface  20 A occurs. An example of the first suction force in this embodiment is the suction force for sucking the sheet to the feeding surface  20 A of the second feeding belt  201 , and the second suction force is smaller than the first suction force. 
     Further, the OFF state of the second suction fan  206  is not limited to a state in which the operation of the second suction fan  206  is at rest. That is, the second suction fan  206  is in the OFF state when the air suction force by the second suction fan  206  is smaller than the suction force of the degree such that the sheet is attracted to the feeding surface  20 A and is the suction force of the degree such that the sheet is freely movable relative to the feeding surface  20 A. By doing so, in a state in which the sheet is nipped in the secondary transfer nip N 2  and the fixing nip N, it becomes possible to suppress attraction of the sheet to the feeding surface  20 A. That is, a state in which the height of the sheet from the feeding surface  10 A of the first feeding belt  101  is detectable without attracting the sheet to the feeding surface  20 A. Incidentally, when the air suction force by the second suction fan  206  is made smaller than a sheet nipping force in the fixing nip N, the sheet nipped in the fixing nip N is prevented from being attracted to the feeding surface  20 A. By doing so, the sheet nipped in the fixing nip N is not pulled toward an upstream side of the sheet feeding direction FD, and therefore, positional deviation of the (unfixed) toner on the sheet can be suppressed. 
     When the second suction fan  206  is put in the OFF state, the controller  305  discriminates the height of the sheet from the feeding surface  10 A on the basis of the signal received from the height detecting means  30 . Specifically, the controller  305  discriminates the sheet height from the feeding surface  10 A depending on the combination of the signals of the sensors  302  and  303  received from the height detecting means  30 . In the case where the signal of the sensor  302  is the OFF signal (S 15 : N), as described above, the OFF signal is also outputted from the sensor  303 , and therefore, the controller  305  discriminates that the sheet is positioned above the feeding surface  10 A than S 1  is. Further, in this case, the sheet is in a stretched state between the fixing portion  58  and the secondary transfer portion  57  with respect to the sheet feeding direction FD and in a state in which the sheet is fed at a position remotest from the feeding surface  10 A. In the case where the signal of the sensor  302  is the ON signal (S 15 : Y), the controller  305  decreases a drive amount of the fixing motor MF and establishes a speed relationship of VF&lt;VT between the transfer speed VT and the fixing speed VF (S 16 ). By this, it is possible to prevent the sheet from being excessively stretched toward the fixing portion  58 . A second speed in this embodiment is the sheet feeding speed of the fixing portion  58  when being lower than the sheet feeding speed at the secondary transfer portion  57 , i.e., the fixing speed VF when the speed relationship between the transfer speed VT and the fixing speed VF is VF&lt;VT. 
     On the other hand, the signal from the sensor  302  is the ON signal (S 15 : N), the controller  305  discriminates whether or not the signal from the sensor  303  is the ON signal (S 17 ). In the case where the signal of the sensor  302  is the ON signal and the signal of the sensor  303  is also the ON signal (S 17 : Y), the controller  305  discriminates that the sheet is positioned below the feeding surface  10 A than S 2  is. Further, in this case, the sheet is in an excessively loosened state between the fixing portion  58  and the secondary transfer portion  57  with respect to the sheet feeding direction FD and in a state in which the sheet is fed at a position closest to the feeding surface  10 A (such as in a contact state with the feeding surface  10 A). In the case where the signal of the sensor  302  is the ON signal and the signal of the sensor  303  is the ON signal (S 17 : Y), the controller  305  increases the drive amount of the fixing motor MF and establishes a speed relationship of VF&gt;VT between the transfer speed VT and the fixing speed VF (S 18 ). By this, the sheet is pulled toward the fixing portion  58 , and therefore, looseness formed on the sheet is gradually eliminated, so that it is possible to prevent that a state in which a loop amount of the sheet becomes excessive is formed. A first speed in this embodiment is the sheet feeding speed at the secondary transfer portion  57 , i.e., the transfer speed VT. Further, a third speed in this embodiment is the sheet feeding speed of the fixing portion  58  when being lower than the sheet feeding speed at the secondary transfer portion  57 , i.e., the fixing speed VF when the speed relationship between the transfer speed VT and the fixing speed VF is VF&gt;VT. 
     In the case where the signal of the sensor  302  is the ON signal and the signal of the sensor  303  is the OFF signal (S 17 : N), the controller  305  discriminates that the sheet is positioned between S 1  and S 2  relative to the feeding surface  10 A. Further, in this case, with respect to the sheet feeding direction FD, between the fixing portion  58  and the secondary transfer portion  57 , the sheet is in a spaced state from the feeding surface  10 A and is in a loosened state. In the case where the signal of the sensor  302  is the ON signal and the signal of the sensor  303  is the OFF signal (S 17 : N), the controller  305  continues the feeding of the sheet without changing the fixing speed VF and the sequence goes to S 19 . Thus, in this embodiment, in a state in which the sheet is nipped in the secondary transfer nip N 2  and in the fixing nip N and in which the height of the sheet from the feeding surface  10 A is such that the sheet is spaced from the feeding surface  10 A and is loosened, the feeding of the sheet is continued by maintaining the feeding speed VF. 
     As in the steps S 16  and S 18 , in this embodiment, the fixing speed VF is adjusted depending on the signal outputted from the height detecting means  30 , and therefore, during execution of the image forming job, the relationship of VF&lt;VT changes in some instances. That is, in a state in which the sheet is nipped in the secondary transfer nip N 2  and in the fixing nip N, the state of the sheet changes from a state in which the sheet is pulled toward a downstream side of the sheet feeding direction FD to a state in which the sheet is loosened in some instances. At this time, as in the step S 14 , the suction force for attracting the sheet to the feeding surface  20 A is decreased, so that abrupt displacement of the sheet relative to the feeding surface  20 A is suppressed. 
     The controller  305  discriminates whether or not a trailing end of the sheet passes through the secondary transfer nip N 2  (S 19 ), and repeats the steps from S 15  to S 18  until the trailing end of the sheet passes through the secondary transfer nip N 2 . Specifically, as regards discrimination as to whether or not the trailing end of the sheet passes through the secondary transfer nip N 2 , for example, first, the controller  305  awaits until the leading end of the sheet is detected by the sheet detecting sensor after the feeding of the sheet is started. Then, when the leading end of the sheet reaches the detecting position of the sheet detecting sensor, an elapsed time from the time when the leading end of the sheet reaches the detecting position is measured, and the controller  305  discriminates whether or not a time necessary for the trailing end of the sheet to pass through the secondary transfer nip N 2  has elapsed. When the elapsed time from the time when the leading end of the sheet reaches the detecting position exceeds the time necessary for the trailing end of the sheet to pass through the secondary transfer nip N 2 , the controller  305  discriminates that the trailing end of the sheet passes through the secondary transfer nip N 2  (S 19 : Y). When the controller  305  discriminates that the trailing end of the sheet passes through the secondary transfer nip N 2  (S 19 : Y), the controller  305  ends the execution of the adjusting operation (S 15  to S 19 ) of the fixing speed VF adjusted depending on the signal outputted from the height detecting means  30  (S 20 ). 
     Next, the controller  305  awaits until the trailing end of the sheet passes through the fixing nip N (S 21 ). Specifically, as regards discrimination as to whether or not the trailing end of the sheet passes through the secondary transfer nip N 2 , for example, first, the controller  305  awaits until the leading end of the sheet is detected by the sheet detecting sensor. Then, when the leading end of the sheet reaches the detecting position of the sheet detecting sensor, an elapsed time from the time when the leading end of the sheet reaches the detecting position is measured, and the controller  305  discriminates whether or not a time necessary for the trailing end of the sheet to pass through the fixing nip N. When the elapsed time from the time when the leading end of the sheet passes through the detecting position exceeds the time necessary for the trailing end of the sheet to pass through the fixing nip N, the controller  305  discriminates that the trailing end of the sheet passes through the fixing nip N (S 21 : N). 
     When the controller  305  discriminates that the trailing end of the sheet passes through the fixing nip N (S 21 : Y), the controller  305  switches the state of the second suction fan  206  from the OFF state to the ON state (S 22 ). By this, a leading end of a subsequent sheet is attracted to the feeding surface  20 A, so that it is possible to improve feeding efficiency of the subsequent sheet. Then, when the image forming job is not ended (S 23 : N), the sequence returns to S 12 , and when the image forming job is ended (S 23 : Y), the flow is ended. 
     In this embodiment, when a sheet of which length with respect to the sheet feeding direction FD is longer than a length between the secondary transfer nip N 2  and the fixing nip N with respect to the sheet feeding direction FD, so-called an elongated sheet is fed, excessive looseness and excessive stretch of the sheet can be superposed. Further, by suppressing the excessive looseness and the excessive stretch of the sheet, it becomes possible to suppress improper transfer at the secondary transfer portion  57 , improper sheet feeding and the like, and therefore, it is possible to compatibly realizing an improvement in sheet feeding performance and an improvement in image quality. 
     Further, in this embodiment, a speed relationship between the transfer speed VT and the fixing speed VF is changed depending on the height of the sheet, from the feeding surface  10 A, nipped in the secondary transfer nip N 2  and the fixing nip N. Specifically, in a state in which the sheet is excessively stretched by the fixing nip N, the fixing speed VF is decreased, so that a degree of the excessive stretch of the sheet toward the fixing portion  58  is alleviated. Further, in a state in which the sheet is excessively loosened, the fixing speed VF is increases, so that a degree of the excessive looseness is alleviated. Further, when the height of the sheet from the feeding surface  10 A is detected, the sheet is prevented from being attracted to the second feeding belt  201 , so that it is possible to detect the height of the sheet from the feeding surface  10 A with reliability. 
     Further, in this embodiment, in the case where the sheet is fed between the fixing portion  58  and the secondary transfer portion  57  in a state in which the sheet is spaced from the feeding surface  10 A and is loosened, the feeding of the sheet is continued without changing the fixing speed VF. Accordingly, without making unnecessary change in fixing speed VF, the sheet can be stably fed between the fixing portion  58  and the secondary transfer portion  57  with no contact thereof with the feeding surface  10 A. Further, the change in fixing speed VF may only be required to be made minimally, and therefore, a degree of deviation of alignment between the first driving roller  102  and the follower rollers  103 ,  104  and  105  due to a frequent change in fixing speed VF can be reduced. Further, also, as the second driving roller  202  and the follower rollers  203 ,  204  and  205 , a degree of deviation of alignment therebetween can be reduced. 
     Incidentally, in this embodiment, the length between the secondary transfer nip N 2  and the fixing nip N is designed so as to be 19 inches (483 mm) or more. Accordingly, in the case where a sheet with a size such that a length thereof with respect to the sheet feeding direction FD is 19 inches or less, the sheet is fed without being put in a state in which the sheet is nipped in both the secondary transfer nip N 2  and the fixing nip N. Here, with respect to the sheet feeding direction FD, a length from the second suction fan  206  to the fixing nip N is set at a length of a degree such that a sheet with a length with respect to the sheet feeding direction FD is shorter than a predetermined length. Here, the sheet with the length shorter than the predetermined length is, for example, about 148 mm with respect to the sheet feeding direction FD, and refers to a sheet, of sheets usable in the image forming apparatus  100 , shortest in length with respect to the sheet feeding direction FD. 
     Further, with respect to the sheet feeding direction FD, lengths of the first feeding belt  201  and the second feeding belt  201  are designed so as to be always equal to each other. Incidentally, in this embodiment, the first feeding belt  101  and the second feeding belt  201  have the same constitution, and commonality of component parts thereof is realized, but the lengths of the first feeding belt  101  and the second feeding belt  202  may also be different from each other. For example, the length of the first feeding belt  101  with respect to the sheet feeding direction FD is made 3/10 of the length between the secondary transfer nip N 2  and the fixing nip N. At this time, the length of the second feeding belt  201  with respect to the sheet feeding direction FD may also be made ½ of the length between the secondary transfer nip N 2  and the fixing nip N. 
     Other Embodiments 
     In the embodiment 1, an example in which the belt feeding unit  100 E is constituted by including the first belt feeding portion  10  and the second belt feeding portion  20  was described, but three or more belt feeding portions may also be included in the belt feeding unit  100 E. In this case, a sheet feeding speed in a downstream belt feeding portion with respect to the sheet feeding direction FD is made higher than a sheet feeding speed in an upstream belt feeding portion with respect to the sheet feeding direction FD. By doing so, it becomes possible to suppress buckling of the sheet due to a difference in sheet feeding speed between the belt feeding portions. Further, in this case, a constitution corresponding to the height detecting means  30  may desirably be disposed on a side somewhat downstream of the center of the belt feeding unit  100 E with respect to the sheet feeding direction. 
     Further, the constitution of the embodiment 1 is also applicable to a printer of a direct transfer type in which toner is directly transferred from the photosensitive drum as the image bearing member onto the sheet by a primary transfer roller as a transfer means. 
     The controller  305  in the embodiment 1 includes the central processing unit (CPU) and the memory. The CPU reads and executes a program stored in the memory and carries out integrated control of the image forming apparatus in cooperation with various functional portions for achieving specific functions. The memory includes a non-volatile memory medium such as a read-only memory (ROM) and a volatile memory medium such as a random-access memory (RAM), and not only constitutes a storage area of programs and data but also constitutes an operational (working) area when the CPU executes the program. Further, the memory is an example of a non-transient memory medium in which a program for controlling the image forming apparatus  100  is stored. Incidentally, the various functions of the controller  305  may also be mounted, as an independent hardware such as ASIC, on a circuit of the controller, or may also be mounted, as a functional unit of a program executed by the CPU or another processing device, in the form of a software. 
     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. 2020-087088 filed on May 19, 2020, which is hereby incorporated by reference herein in its entirety.