Patent Publication Number: US-10766721-B2

Title: Sheet feeding device capable of using long sheets, method of controlling sheet feeding device, and image forming system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet feeding device capable of feeding long sheets to an image forming apparatus, a method of controlling the sheet feeding device, and an image forming system including the sheet feeding device. 
     Description of the Related Art 
     In recent years, as printed media diversify, there is an increasing demand for an image forming apparatus that is capable of continuously performing image formation on a large number of sheets having a longer length in a sheet feeding direction than a predetermined length (for example, the length of A3 sheets) (hereinafter referred to as “long sheets”). Examples of a sheet feeding device applied to such an image forming apparatus include one disclosed in U.S. Pat. No. 9,359,157. The sheet feeding device disclosed in U.S. Pat. No. 9,359,157 is configured such that so as to accommodate regular sheets (non-long sheets) which are not long sheets, a sheet storage can be drawn out toward the near side. Further, the sheet feeding device is configured such that so as to accommodate long sheets, an extension plate is fixed to a bottom plate of the sheet storage, and long sheets are received therein from upstream in the sheet feeding direction. In the sheet feeding device configured to fix the extension plate for long sheets to the bottom plate, as described above, the operation of drawing out the sheet storage is locked as long as the extension plate is fixed to the bottom plate, so as to provide a prevention measure against breakage of the device due to an erroneous operation by a user. 
     In the above-described related art, however, although breakage of the device can be prevented, in a case where images are formed using long sheets after images are formed using non-long sheets, it is necessary to fix the extension plate to the bottom plate to extend the same. Further, in a case where images are formed using non-long sheets after images are formed using long sheets, it is necessary to remove the extension plate fixed for temporary use. This causes a problem that user&#39;s convenience is degraded in a case where the frequency of switching between non-long sheets and long sheets is high. 
     SUMMARY OF THE INVENTION 
     The present invention provides a sheet feeding device that is capable of improving user&#39;s convenience even in a case where non-long sheets and long sheets are switchingly used, a method of controlling the sheet feeding device, and an image forming system. 
     In a first aspect of the present invention, there is provided a sheet feeding device comprising a storage configured to be openable and closable, and to store sheets to be used for image formation, a feed unit configured to feed sheets from the storage, a first lift plate and a second lift plate, provided in the storage, side by side, in a sheet feeding direction, and each configured to be capable of being lifted up and down, a lifter configured to lift up and down the first lift plate and the second lift plate, and a controller configured to determine whether or not an operation has been performed concerning storing of long sheets longer than a predetermined length in the sheet feeding direction, in the storage, and to control the lifter, in a case where it is determined that the operation has been performed, to cause a level of the first lift plate in a height direction and a level of the second lift plate in the height direction to match each other. 
     In a second aspect of the present invention, there is provided an image forming system including a sheet feeding device, and an image forming apparatus that forms images on sheets fed from the sheet feeding device, wherein the sheet feeding device comprises a storage configured to be openable and closable, and to store sheets to be used for image formation, a feed unit configured to feed sheets from the storage, a first lift plate and a second lift plate, provided in the storage, side by side, in a sheet feeding direction, and each configured to be capable of being lifted up and down, a lifter configured to lift up and down the first lift plate and the second lift plate, and a controller configured to determine whether or not an operation has been performed concerning storing of long sheets longer than a predetermined length in the sheet feeding direction, in the storage, and to control the lifter, in a case where it is determined that the operation has been performed, to cause a level of the first lift plate in a height direction and a level of the second lift plate in the height direction to match each other. 
     In a third aspect of the present invention, there is provided a method of controlling a sheet feeding device including a storage configured to be openable and closable, and to store sheets to be used for image formation, a feed unit configured to feed sheets from the storage, a first lift plate and a second lift plate, provided in the storage, side by side, in a sheet feeding direction, and each configured to be capable of being lifted up and down, and a lifter configured to lift up and down the first lift plate and the second lift plate, the method comprising determining whether or not an operation has been performed concerning storing of long sheets longer than a predetermined length in the sheet feeding direction, in the storage, and controlling the lifter, in a case where it is determined that the operation has been performed, to cause a level of the first lift plate in a height direction and a level of the second lift plate in the height direction to match each other. 
     According to the present invention, in a case where long sheets are expected to be used, preparation for storing the long sheets is performed by making the respective levels of a first lift plate and a second lift plate equal to each other. This makes it possible to improve the user-friendliness of the sheet feeding device which switchingly uses non-long sheets and long sheets. 
     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 cross-sectional view of an image forming apparatus including a sheet feeding device according to an embodiment of the invention. 
         FIG. 2  is an enlarged cross-sectional view of the sheet feeding device appearing in  FIG. 1 . 
         FIG. 3  is a control block diagram of the image forming apparatus. 
         FIG. 4  is a flowchart of a lift plate moving process performed when a sheet storage is opened. 
         FIG. 5  is a flowchart of a lift plate moving process performed when the sheet storage is closed. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention will now be described in detail below with reference to the accompanying drawings showing embodiments thereof. 
       FIG. 1  is a schematic cross-sectional view of an image forming apparatus including a sheet feeding device according to an embodiment of the invention. Referring to  FIG. 1 , the image forming apparatus  100  includes an image forming apparatus body (hereinafter referred to as the “printer”)  100 A, and an image reading device (hereinafter referred to as the “image reader”)  100 B. 
     The image reader  100 B reads an original image placed e.g. on a platen glass, not shown, and transmits image data of the original image as video signals to scanner units, described hereinafter, of the printer  100 A. 
     The printer  100 A includes a process unit  120  for forming color images. 
     The process unit  120  includes a plurality of image forming stations Y, M, C, and K arranged side by side in a horizontal direction. The image forming stations Y to K form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming stations Y to K have the same configuration, and include photosensitive drums as photosensitive members which are rotatably supported on rotating shafts, not shown, respectively. The photosensitive drums each function as an image bearing member. In opposed relation to outer peripheral surfaces of the respective photosensitive drums, there are arranged primary charging devices, the scanner units  122 , reflection mirrors, developing devices, and cleaners, respectively. Each developing device is connected to an associated one of toner replenishing sections. 
     An intermediate transfer belt  130  in the form of an endless belt is arranged such that it is in sliding contact with the respective photosensitive drums of the image forming stations Y to K. Similar to each photosensitive drum, the intermediate transfer belt  130  functions as an image bearing member, and is rotatably stretched by a drive roller  401 , a tension roller  402 , and a secondary transfer opposed roller  403 , for example. A secondary transfer roller  404  is disposed in opposed relation to the secondary transfer opposed roller  403 . A contact portion of the secondary transfer roller  404  and the secondary transfer opposed roller  403  forms a secondary transfer section Te. 
     Four primary transfer rollers are disposed in opposed relation to the four photosensitive drums via the intermediate transfer belt  130 , respectively. Respective contact portions of the primary transfer rollers and the photosensitive drums form primary transfer sections Ty to Tk. Toner images of the four colors to be transferred to the same sheet are sequentially formed on associated ones of the four photosensitive drums. 
     Arranged below the intermediate transfer belt  130  are a sheet storage section  150  for storing sheets S and a sheet conveying section  305  (see  FIG. 3 ) for conveying each sheet S to the secondary transfer section Te and discharging the same out of the printer  100 A. The sheet storage section  150  is comprised of an upper cassette  150   a  and a lower cassette  150   b . The upper cassette  150   a  and the lower cassette  150   b  are capable of stacking a large number of sheets S therein. Regular sheets e.g. of the same size or different sizes are stored in the upper and lower cassettes  150   a  and  150   b . In addition to the upper cassette  150   a  and the lower cassette  150   b , there are provided a sheet feeding deck (sheet feeding device)  250  and a manual feed tray  210 . 
     The sheet feeding deck  250  is disposed on the right side of the printer  100 A as viewed in  FIG. 1 , and is capable of stacking not only sheets of regular sizes, such as the A3 size and the A4 size, but also a large number of long sheets which are longer in length in a sheet feeding direction than the regular sheets. A user uses the sheet feeding deck  250  in a case where images are formed on sheets other than the regular sheets, or in a case where images are formed on sheets of a size different from the size of sheets which have already been stored in the upper cassette  150   a  and the lower cassette  150   b , or in a case where images are formed on a large number of sheets. The sheet feeding deck  250  will be described in detail hereinafter. Note that the manual feed tray  210  is suitably used in a case where images are formed on a relatively small number, e.g. approximately several tens, of sheets which are temporarily used. 
     A conveying path of the sheet conveying section  305  includes a supply path  131  and a discharge path  231 . The supply path  131  is a conveying path along which conveys sheets S are conveyed from the upper cassette  150   a , the lower cassette  150   b , the sheet feeding deck  250 , or the manual feed tray  210 , to the secondary transfer section Te. The discharge path  231  is a conveying path along which sheets S having been subjected to image formation are conveyed to the outside of the image forming apparatus. 
     The supply path  131  is provided with pickup rollers  151   a  and  151   b  and conveying roller pairs  154  and  153 , which are associated with the upper and lower cassettes  150   a  and  150   b , respectively, as well as a conveying roller pair  155  and a registration roller  161 . A registration sensor  160  is disposed at a location upstream of the registration roller  161 . The registration sensor  160  detects a sheet being conveyed so as to determine a timing at which the sheet reaches the registration roller  161 . The registration sensor  160  also functions as a size detecting section for detecting the size of the sheet S being conveyed. That is, the registration sensor  160  outputs signals on respective occasions of detection of the leading edge and the trailing edge of the same sheet S. A CPU  301  as a controller, referred to hereinafter, detects the sheet size of the sheet S in the conveying direction of the sheet S using the output signals from the registration sensor  160 . 
     The printer  100 A and the sheet feeding deck  250  are connected by a deck supply path  132 . The deck supply path  132  is connected to the supply path  131  on the upstream side of the conveying roller pair  154 . Each of the sheets S stored in the sheet feeding deck  250  is conveyed into the supply path  131  via the deck supply path  132 . 
     On the other hand, a fixing device  170  including a heating roller  410  and a pressing roller  411  is provided in an intermediate portion of the discharge path  231 , and an inversion path  230  branches from a portion of the discharge path  231  downstream of the fixing device  170 . Further, a double-sided conveying path  235  is connected to the inversion path  230 . At a connection portion between the discharge path  231  and the inversion path  230 , there is disposed an inversion flapper  172 . According to the conveying destination of a sheet S discharged from the fixing device  170 , the inversion flapper  172  guides the sheet S either toward an upper discharge path  181  and a lower discharge path  180  or into the inversion path  230 . 
     The discharge path  231  is bifurcated into the upper discharge path  181  and the lower discharge path  180  at a location downstream of the connection portion between the discharge path  231  and the inversion path  230 . At the branching point, there is disposed an inversion flapper  190 . According to the conveying destination of a sheet S, the inversion flapper  190  guides the sheet S into the upper discharge path  181  or the lower discharge path  180 . The upper discharge path  181  is a conveying path along which the sheet S is conveyed to be discharged onto an upper discharge tray  196 . Further, the lower discharge path  180  is a conveying path along which the sheet S is conveyed to be discharged onto a lower discharge tray  200 . The discharge path  231  is provided with a conveying roller pair  232  at a location downstream of a connection portion between the discharge path  231  and the inversion path  230 , and each of the inversion path  230 , the double-sided conveying path  235 , the upper discharge path  181 , and the lower discharge path  180  is also provided with a conveying roller pair or a discharge roller pair. 
     Next, a description will be given of the configuration of the sheet feeding deck  250 . 
       FIG. 2  is a cross-sectional view of the sheet feeding deck (sheet feeding device) of the image forming apparatus shown in  FIG. 1 . Referring to  FIG. 2 , the sheet feeding deck  250  includes a casing  250 A, a box-like sheet storage  506  for storing a large number of sheets S, two lift plates  507   a  and  507   b  which are mounted in the sheet storage  506  in a manner such that they can be lifted up and down, and the deck supply path  132  for feeding sheets S to the printer  100 A. The sheet storage  506  is configured to be capable of being drawn out from and pushed into the casing  250 A. 
     The lift plate  507   a  and the lift plate  507   b  are arranged side by side in the sheet feeding direction in the sheet storage  506 . The lift plate  507   a  covers e.g. the left half of the sheet storage  506 , and is configured to be capable of being lifted up and down by a lift mechanism (lifter)  530 . The lift mechanism  530  is an elevator that lifts up and down the lift plate  507   a , and includes a wire  530   a  for suspending and supporting the lift plate  507   a , a plurality of pulleys  530   b  around which the wire  530   a  extends, and a wire pulley  530   c  to which one end of the wire  530   a  is fixed. The wire pulley  530   c  is driven for rotation by a lifter motor M 500 , and lifts up and down the lift plate  507   a.    
     The lift plate  507   b  has a length approximately half the length of the sheet storage  506  in the sheet feeding direction. The lift plate  507   b  is lifted up and down within a predetermined range in accordance with the lifting (up and down motion) of the lift plate  507   a . More specifically, the lifting down motion of the lift plate  507   b  is limited by a mechanical stopper  609  provided at a side of the sheet storage  506 , which is close to the lift plate  507   b , and the lift plate  507   b  is configured to be capable of being lifted up and down above the mechanical stopper  609 . In other words, the mechanical stopper  609  serves as a restriction member configured to cause the lift plate  507   b  to stay at a long sheet lower limit position (predetermined position), referred to hereinafter. The lift range of the lift plate  507   b  is smaller than the lift range of the lift plate  507   a . The lift plate  507   b  functions as an extension lift plate for extending the length of the lift plate  507   a.    
     A lifting down limit position (long sheet lower limit position) of the lift plate  507   b  is a lift plate position where the sheet feeding deck  250  can stack the maximum number of long sheets, for example, a position where the sheet feeding deck  250  can stack 1000 long sheets. The bottom dead center of the lift plate  507   b  is the home position (HP) of the lift plate  507   b , the HP is provided with an extension lifter HP sensor  607  at the side of the sheet storage  506 , which is close to the lift plate  507   b.    
     The extension lifter HP sensor  607  determines whether or not the lift plate  507   b  is at the HP. If the lift plate  507   b  is at the HP, the extension lifter HP sensor  607  is turned on, whereas if the lift plate  507   b  is not at the HP, the extension lifter HP sensor  607  is turned off. 
     Note that if the lift plate  507   b  is configured to be capable of being lifted down below the HP, there is a fear that a user stacks 1000 or more long sheets. In such a case, a motor having a higher power is required. Therefore, the mechanical stopper  609  is provided to limit the lifting down of the lift plate  507 . The HP of the lift plate  507   b  is defined by taking into account the strength of the lift plates  507   a  and  507   b , the strength of the sheet storage  506 , and the capability of the lift mechanism  530  (power of the motor). However, the lifting down limit position of the lift plate  507   b  is not particularly limited, but it can also be configured to be changeable, as required. 
     Non-long sheets are stacked on the lift plate  507   a . The lift plate  507   a  is singly capable of stacking e.g. approximately 3000 sheets. Long sheets longer than a predetermined length are stacked such that they extend over the lift plate  507   a  and the lift plate  507   b . A sheet stacking surface is thus formed by the two lift plates  507   a  and  507   b , and hence the user can easily switch between a state in which a large number of non-long sheets are stacked and a state in which long sheets are stacked. 
     A sheet partition plate  500  is disposed perpendicular to the lift plate  507   a  and the lift plate  507   b , and also movable along sheet stacking surfaces of the lift plate  507   a  and the lift plate  507   b . The sheet partition plate  500  is for restricting the trailing edge of sheets S in the sheet feeding direction, and is movable in a left-right direction, as viewed in  FIG. 2 . The user manually moves the sheet partition plate  500  according to the size of stacked sheets. In a case where long sheets are used, the user moves the sheet partition plate  500  to a position which corresponds to the position of the trailing edges of long sheets stacked on the lift plate  507   a  and the lift plate  507   b.    
     A partition plate position sensor  606  is provided substantially in the center of the bottom of the sheet storage  506 . The partition plate position sensor  606  is turned on when the sheet partition plate  500  is detected. The partition plate position sensor  606  is turned on by the movement of the sheet partition plate  500  to the lift plate  507   b , whereby it is known that the trailing edge of sheets S which the user intends to use has reached the lift plate  507   b , in other words, that the user intends to use long sheets. 
     A sheet storage section is formed above the lift plates  507   a  and  507   b , and a sheet sensor  601  and a sheet feed position sensor  602  are disposed in the uppermost part of the sheet storage section. The sheet sensor  601  detects whether or not there is any sheet S on the lift plate  507   a . If any sheet S is detected, the sheet sensor  601  is turned on, whereas if no sheet S is detected, the sheet sensor  601  is turned off. 
     The sheet feed position sensor  602  detects the uppermost surface of sheets S on the lift plate  507   a . With this, it is determined whether or not the uppermost surface of sheets S stacked on the lift plate  507   a  is at a position where a sheet can be fed by a sheet feed pickup roller  501 . During image forming operation, the CPU  301  monitors the sheet feed position sensor  602 . In a case where the sheet feed position sensor  602  is turned off, the CPU  301  drives the lifter motor M 500  until the sheet feed position sensor  602  is turned on, whereby the top surface of sheets S stacked on the lift plate  507   a  is controlled to be maintained at a fixed level. 
     The deck supply path  132  formed on the top of the sheet storage  506  is provided with the sheet feed pickup roller  501 , a sheet feed roller  502 , and a retard roller  503  opposed to the sheet feed roller  502 . Further, the deck supply path  132  is provided with a conveying roller pair  504  and a sheet feed sensor  603 . Sheets S stacked on the lift plate  507   a  or on the lift plates  507   a  and  507   b  are conveyed, one by one, to the supply path  131  of the printer  100 A via the deck supply path  132 . At this time, the sheet feed pickup roller  501  feeds sheets S on the lift plate  507   a . The retard roller  503  separates a single uppermost one of sheets S to be fed, from the others. 
     A lift level sensor  605  is provided at a side of the sheet storage  506 , which is close to the lift plate  507   a  and opposed to the mechanical stopper  609 , and at the same level as the mechanical stopper  609 . The lift level sensor  605  monitors the lift plate  507   a , and when the lift plate  507   a  is detected, the lift level sensor  605  is turned on, whereas when the lift plate  507   a  is not detected, it is turned off. That is, when the lift level sensor  605  is turned on from off, the lift plate  507   a  is at the long sheet lower limit position (predetermined position). 
     As described hereinabove, the lift level sensor  605  is disposed at the side of the sheet storage  506 , which is close to the lift plate  507   a , and the extension lifter HP sensor  607  is disposed at the side of the same, which is close to the lift plate  507   b . In a case where both the lift level sensor  605  and the extension lifter HP sensor  607  are on in a state where no sheets S are stored in the sheet storage  506 , the lift plate  507   a  is located at the same level as that of the lift plate  507   b , and the lift plates  507   a  and  507   b  form the same sheet stacking surface. By positioning the lift plate  507   a  and the lift plate  507   b  at the same level, the lift plates  507   a  and  507   b  are ready for having long sheets stacked thereon. On the other hand, in a case where the lift level sensor  605  is off, and the extension lifter HP sensor  607  is on, the lift plate  507   a  is located below the lift plate  507   b . In this case, there is a level difference between the lift plate  507   a  and the lift plate  507   b , and the lift plates  507   a  and  507   b  are in a state in which no long sheets can be stacked thereon. 
     A bottom position sensor  604  is provided on the bottom of the sheet storage  506 . The bottom position sensor  604  is turned on if the lift plate  507   a  is on the bottom of the sheet storage  506 , and is turned off if the lift plate  507   a  is not on the bottom of the sheet storage  506 . 
     Further, the sheet storage  506  is configured such that it can be drawn out toward the near side, as viewed in  FIG. 2 . The sheet storage  506  is provided with a storage open button  510 , and when the user presses the storage open button  510 , the fixed state of the sheet feeding deck  250  and the sheet storage  506  is released. That is, a storage latch member, not shown, is released, thereby making it possible to draw the sheet storage  506  toward the near side. The sheet storage  506  is provided with a storage opening/closing sensor  608 . The storage opening/closing sensor  608  detects whether or not the sheet storage  506  is in a state drawn toward the near side. If the sheet storage  506  is drawn toward the near side, the storage opening/closing sensor  608  is turned on, whereas if the sheet storage  506  is not drawn toward the near side, in other words, if the sheet storage  506  is received in the casing  250 A, the storage opening/closing sensor  608  is turned off. 
     Next, a description will be given of the control configuration of the image forming apparatus  100  including the sheet feeding deck  250  configured as above. 
       FIG. 3  is a control block diagram of the image forming apparatus  100  shown in  FIG. 1 . Referring to  FIG. 3 , the image forming apparatus  100  includes a CPU circuit section  300 . The CPU circuit section  300  incorporates the CPU  301 , a ROM  302 , and a RAM  303 . The CPU  301  is connected to the ROM  302  and the RAM  303  by an address bus and a data bus. 
     The CPU circuit section  300  is connected to a console section  310  and a printer controller  304 . The printer controller  304  is connected to an image signal controller  308 , and an external interface  309  via the image signal controller  308 . Further, the printer controller  304  is connected to the sheet conveying section  305 , an image forming section  306 , and a storage controller  311 , respectively. Note that the image signal controller  308  is also directly connected to the CPU circuit section  300 . 
     The storage controller  311  is connected to the lifter motor M 500 , the storage open button  510 , the extension lifter HP sensor  607 , the bottom position sensor  604 , the storage opening/closing sensor  608 , and the sheet feed position sensor  602 , respectively. Further, the storage controller  311  is connected to the sheet sensor  601 , the lift level sensor  605  and the partition plate position sensor  606 . 
     The CPU  301  controls the overall operation of the image forming apparatus  100 . The ROM  302  stores control programs. Data used for control is written in the RAM  303 . The printer controller  304  instructs the image forming section  306  to form an image, based on instructions from the CPU  301 . The image forming section  306  forms the image based on input video signals. Further, the printer controller  304  controls the sheet conveying section  305  to perform feeding, conveying, and so forth of sheets, based on instructions from the CPU  301 . During printing operation, the image signal controller  308  performs various kinds of processing on digital image signals input via the external interface  309 , converts the processed digital image signals to video signals, and stores the video signals in the RAM  303 . The console section  310  receives user&#39;s instructions for selection of a color mode, input of sheet information, start of copying, and so forth, before starting image formation, and further displays a state of the image forming apparatus, warning messages, etc. 
     The storage controller  311  receives information from the extension lifter HP sensor  607 , the storage opening/closing sensor  608 , the lift level sensor  605 , the storage open button  510 , the bottom position sensor  604 , the sheet sensor  601  and the sheet feed position sensor  602 . Then, the storage controller  311  controls the lifter motor M 500  based on instructions from the CPU  301 . 
     Next, a description will be given of the operation of the image forming apparatus  100  including the sheet feeding deck  250  configured as above. 
     When a print job for supplying sheets from the sheet feeding deck  250  to the printer  100 A is started, the lifter motor M 500  rotates the wire pulley  530   c  to wind the wire  530   a  around the wire pulley  530   c , whereby the lift plate  507   a  is lifted up. Further, a sheet feed motor, not shown, is operated which serves as the drive sources of the sheet feed pickup roller  501  and the sheet feed roller  502 . With this, the sheet feed pickup roller  501 , the sheet feed roller  502 , and the conveying roller pair  504  are rotated, whereby sheets S placed on the lift plate  507   a  are conveyed one by one into the supply path  131  via the deck supply path  132 . 
     At this time, if two or more sheets S are fed by the sheet feed pickup roller  501 , and are caught in a separation nip formed by the sheet feed roller  502  and the retard roller  503 , a second sheet S and following sheets, if any, are blocked by the retard roller  503 . As a consequence, only a first and uppermost sheet S is conveyed toward the conveying roller pair  504 . It is monitored by the sheet feed sensor  603  whether or not the operation for feeding the sheets S has been normally performed. 
     The sheet S having been conveyed into the supply path  131  is conveyed to the secondary transfer section Te by the conveying roller pairs  154  and  155 , etc. The registration sensor  160  monitors for arrival of the sheet S at the secondary transfer section Te. Further, the size of the sheet S is determined based on the signals indicative of detection of the leading edge and the trailing edge of the sheet S by the registration sensor  160  or based on a sheet size input by the user via the console section  310 . 
     In the image forming stations Y to K of the process unit  120 , after the surfaces of the photosensitive drums are uniformly charged, electrostatic latent images are formed on the photosensitive drums by laser light irradiated from the scanner units  122 . The electrostatic latent images formed on the photosensitive drums are developed with toners by the developing devices. Through application of a primary transfer voltage to each of the primary transfer sections Ty to Tk, toner images formed by developing the electrostatic latent images are sequentially transferred onto the intermediate transfer belt  130 , whereby a color image is formed. The color image formed on the intermediate transfer belt  130  is moved to the secondary transfer section Te by rotation of the intermediate transfer belt  130 . 
     On the other hand, the sheet S which has been brought into abutment with the registration roller  161  and stopped after the leading edge thereof was detected by the registration sensor  160  is conveyed by a predetermined amount with the leading edge held in abutment with the registration roller  161 . This bends the sheet S, and thereby corrects a skew of the sheet S. The sheet S having the skew corrected is conveyed by the registration roller  161  such that the leading edge of the sheet S and the leading edge of a toner image on the intermediate transfer belt  130  meet at the secondary transfer section Te. 
     A transfer voltage is applied from the secondary transfer roller  404  to the sheet S which has reached the secondary transfer section Te and the color image on the intermediate transfer belt  130 . With this, the color image is transferred to the sheet S. The sheet S having the color image transferred thereon is conveyed to the fixing device  170 . The sheet S conveyed to the fixing device  170  is heated and pressurized by the heating roller  410  and the pressing roller  411 , whereby the toner image is fixed on the sheet S. The sheet S having the color image fixed thereon is conveyed toward an discharge port of the printer  100 A. 
     Note that when the leading edge of the sheet S having the color image transferred thereon reaches a sheet conveyance sensor  171  disposed upstream of the fixing device  170 , control is started so as to convey the sheet S into to the inversion path  230  or the discharge path  231  according to a conveying destination of the sheet S, which is set in advance. In a case where front-side printing has been performed in a double-sided printing job, the sheet S is conveyed into the inversion path  230 , whereas in the case of a single-sided printing job or in a case where reverse-side printing has been performed in the double-sided printing job, the sheet S is conveyed into the discharge path  231 . 
     Hereinafter, a description will be given of the case where the sheet S having the color image fixed thereon is conveyed into the discharge path  231  in the single-sided printing job or when reverse-side printing has been performed in the double-sided printing job. 
     The sheet S conveyed into the discharge path  231  is conveyed by a conveying roller pair  232 , and is conveyed into the lower discharge path  180  or the upper discharge path  181  by switching the inversion flapper  190  according to an instruction set in advance. In a case where a designated discharge destination is the lower discharge tray  200 , the sheet S is conveyed into the lower discharge path  180 , and in a case where the designated discharge destination is the upper discharge tray  196 , the sheet S is conveyed into the upper discharge path  181 . 
     Next, a description will be given of a lift plate moving process performed when the sheet storage  506  of the sheet feeding deck  250  is opened and closed. 
       FIG. 4  is a flowchart of the lift plate moving process performed when the sheet storage is opened. This lift plate moving process is performed when the storage open button  510  has been pressed, and is executed by the CPU  301  of the CPU circuit section  300  according to a lift plate moving process program stored in the ROM  302 . 
     Referring to  FIG. 4 , after the sheet feeding deck  250  is powered on, the CPU  301  always determines whether or not the storage open button  510  has been pressed (step S 401 ), and waits until the storage open button  510  is pressed. If it is determined in the step S 401  that the storage open button  510  has been pressed (YES to the step S 401 ), the CPU  301  proceeds to a step S 402 , wherein the CPU  301  determines whether or not the partition plate position sensor  606  has detected the sheet partition plate  500  (step S 402 ). If the partition plate position sensor  606  detects the sheet partition plate  500 , it means that the sheet partition plate  500  has been moved to the lift plate  507   b , i.e. that an operation concerning the storage of long sheets has been performed, and it is supposed that long sheets are to be stored. If it is determined in the step S 402  that the partition plate position sensor  606  has not detected the sheet partition plate  500  (NO to the step S 402 ), the CPU  301  proceeds to a step S 403 . In this case, it is not supposed that long sheets are to be stored, but it is supposed that non-long sheets are to be stored. Therefore, the CPU  301  determines whether or not the bottom position sensor  604  is off, in order to lower the lift plate  507   a  below the long sheet lower limit position (step S 403 ). 
     If it is determined in the step S 403  that the bottom position sensor  604  is off (YES to the step S 403 ), the lift plate  507   a  is not at the bottom position of the sheet storage  506 . Therefore, the CPU  301  controls the lifter motor M 500  to start driving in a direction of lowering the lift plate  507   a  (step S 404 ). After causing the lifter motor M 500  to start lowering the lift plate  507   a , the CPU  301  determines again whether or not the bottom position sensor  604  is turned on (step S 405 ), and continues to lower the lift plate  507   a  until the bottom position sensor  604  is turned on. Then, after the bottom position sensor  604  is turned on (YES to the step S 405 ), the CPU  301  stops the driving of the lifter motor M 500  (step S 406 ), followed by terminating the present process. 
     If the bottom position sensor  604  is turned on, it indicates that the lift plate  507   a  has reached the bottom of the sheet storage  506 , and it is impossible to further lower the lift plate  507   a . Therefore, the CPU  301  stops the driving of the lifter motor M 500  for lowering the lift plate  507   a . With this flow of operations, when the sheet storage  506  is opened by the user, the lift plate  507   a  moves downward in the sheet storage  506 , and stops at the bottom position, whereby the lift plate  507   a  is ready for the user to stack non-long sheets thereon. 
     Note that if it is determined in the step S 403  that the bottom position sensor  604  is on (NO to the step S 403 ), there is no need to lower the lift plate  507   a , and hence the CPU  301  immediately terminates the present process. In this case, the lift plate  507   a  is already ready for the user to stack non-long sheets on the lift plate  507   a.    
     On the other hand, if it is determined in the step S 402  that the partition plate position sensor  606  is on (YES to the step S 402 ), it is supposed in this case that long sheets are to be stored, and hence the CPU  301  proceeds to a step S 407 , wherein the CPU  301  controls the lifter motor M 500  to start driving in the direction of lowering the lift plate  507   a  (step S 407 ). After causing the lifter motor M 500  to start to lower the lift plate  507   a , the CPU  301  determines whether or not the lift level sensor  605  is turned on (step S 408 ). If it is determined in the step S 408  that the lift level sensor  605  is turned on (YES to the step S 408 ), the CPU  301  stops the driving of the lifter motor M 500  (step S 409 ), followed by terminating the present process. At this time, the lift plate  507   a  is at the level of the lift level sensor  605 , and the lift plate  507   b  as well is at the level of the extension lifter HP sensor  607 , which is at the same level as that of the lift level sensor  605 . In this state, the lift plate  507   a  and the lift plate  507   b  are located at the same level, and they are in a state ready for stacking long sheets. 
     On the other hand, if it is determined in the step S 408  that the lift level sensor  605  is not turned on (NO to the step S 408 ), the CPU  301  continues to lower the lift plate  507   a , and then determines whether or not a predetermined time period has elapsed (step S 410 ). The predetermined time period is a time period long enough for the lift plate  507   a , which is located above the lift level sensor  605 , to be lowered to the position of the lift level sensor  605 . 
     If it is determined in the step S 410  that the predetermined time period has not elapsed (NO to the step S 410 ), the CPU  301  returns to the step S 408 , and waits until the lift level sensor  605  is turned on. On the other hand, if it is determined in the step S 410  that the predetermined time period has elapsed (YES to the step S 410 ), the CPU  301  controls the lifter motor M 500  to stop lowering the lift plate  507   a , and start driving in a direction of lifting up the lift plate  507   a  (step S 411 ). If the lift level sensor  605  is not turned on even when the predetermined time period has elapsed (NO to the step S 408 ), it is considered that the lift plate  507   a  is located below the lift level sensor  605 . Note that in this case, the lift plate  507   b  is stationary at the position of the extension lifter HP sensor  607 , which is the HP. Therefore, in this case, the CPU  301  causes the lift plate  507   a  to be lifted to the position of the lift level sensor  605 . 
     Then, the CPU  301  determines whether or not the lift level sensor  605  is turned on (step S 412 ), and continues the driving of the lifter motor M 500  in the direction of lifting up the lift plate  507   a  until the lift level sensor  605  is turned on. Then, when the lift level sensor  605  has been turned on (YES to the step S 412 ), the CPU  301  stops the driving of the lifter motor M 500  (step S 413 ), followed by terminating the present process. In this state, the lift plate  507   a  and the lift plate  507   b  are located at the same level, and they are in a state ready for stacking long sheets. 
     After termination of the lift plate moving process shown in  FIG. 4 , the sheet storage  506  is opened, whereby the user is enabled to draw out the sheet storage  506 . 
     According to the process in  FIG. 4 , in a case where the storage open button  510  is pressed and not long sheets but non-long sheets are supposed to be used (NO to the step S 402 ), the lift plate  507   a  is moved to the bottom of the sheet storage  506  (steps S 404  and S 406 ). This makes the lift plate  507   a  ready for stacking non-long sheets thereon, and hence operability is improved. 
     On the other hand, in a case where the storage open button  510  is pressed and long sheets are supposed to be used (YES to the step S 402 ), the lift plate  507   a  and the lift plate  507   b  are moved to the level of the HP of the lift plate  507   b  and stopped (steps S 408  and S 409 , and steps S 412  and S 413 ). This makes the lift plates  507   a  and  507   b  ready for stacking long sheets thereon, and hence operability is improved when non-long sheets and long sheets are switchingly used. 
     Next, a description will be given of the lift plate moving process performed when the sheet storage is closed. 
       FIG. 5  is a flowchart of the lift plate moving process performed when the sheet storage is closed. This lift plate moving process is performed when the user, who is about to perform image formation using e.g. long sheets, closes the sheet storage after removing non-long sheets stored in the sheet storage  506 , and moving the sheet partition plate  500  to the lift plate  507   b . The lift plate moving process is executed by the CPU  301  of the CPU circuit section  300  according to a lift plate moving process program stored in the ROM  302 . 
     Referring to  FIG. 5 , after the sheet feeding  250  is powered on, and the lift plate moving process is started, the CPU  301  monitors whether or not the storage opening/closing sensor  608  is off, i.e. whether or not the sheet storage  506  is in a closed state (step S 501 ). Then, the CPU  301  waits until the sheet storage  506  is closed. If it is determined in the step S 501  that the sheet storage  506  is in the closed state (YES to the step S 501 ), the CPU  301  proceeds to a step S 502 , wherein the CPU  301  determines whether or not the sheet feed position sensor  602  is off, in other words, whether or not the lift plate  507   a  is not in a sheet feed-enabled state in which the lift plate  507   a  is in the uppermost part of the sheet storage section (step S 502 ). If it is determined in the step S 502  that the sheet feed position sensor  602  is off, i.e. if the lift plate  507   a  is not in the sheet feed-enabled state (YES to the step S 502 ), the CPU  301  proceeds to a step S 503 , to control the lifter motor M 500  to start driving in the direction of lifting up the lift plate  507   a  (step S 503 ). 
     After causing the lifter motor M 500  to start lifting up the lift plate  507   a  (step S 503 ), the CPU  301  determines whether or not the lift level sensor  605  is off, and also the extension lifter HP sensor  607  is on (step S 504 ). By thus determining the on/off of the lift level sensor  605  and the extension lifter HP sensor  607 , it is possible to determine whether or not the lift plate  507   a  is positioned lower than the HP, which is the lifting down limit position (long sheet lower limit position), of the lift plate  507   b . More specifically, if the conditions of the step S 504  are satisfied, the lift plate  507   a  is lower than the HP of the lift plate  507   b , but if the conditions of the step S 504  are not satisfied, the lift plate  507   a  and the lift plate  507   b  are positioned at the same level, i.e. or lift plate  507   a  and the lift plate  507   b  are positioned at the level of the HP of the lift plate  507   b  or higher than the same. 
     If it is determined in the step S 504  that the conditions are satisfied, i.e. if the lift plate  507   a  is lower than the HP of the lift plate  507   b  (YES to the step S 504 ), the CPU  301  proceeds to a step S 505  to determine whether or not the partition plate position sensor  606  is on, in other words, whether or not long sheets are going to be used (step S 505 ). If the sheet partition plate  500  has been moved to a position corresponding to the sheet stacking surface of the lift plate  507   b , it is supposed that the user is about to use long sheets stacked to extend over the lift plate  507   a  and the lift plate  507   b . Therefore, if it is determined in the step S 505  that the partition plate position sensor  606  is on (YES to the step S 505 ), the CPU  301  proceeds to a step S 506 . 
     More specifically, the CPU  301  determines whether or not the lift level sensor  605  is turned on, and continues to lift up the lift plate  507   a  until the lift level sensor  605  is turned on (step S 506 ). Then, after the lift plate  507   a  is lifted up to the position of the lift level sensor  605 , causing the lift level sensor  605  to be turned on (YES to the step S 506 ), the CPU  301  stops the driving of the lifter motor M 500  (step S 507 ), followed by terminating the present process. 
     By lifting up the lift plate  507   a  until the lift level sensor  605  is turned on, the level of the lift plate  507   a  and that of the lift plate  507   b  match each other at the position of the lift level sensor  605 , i.e. the position of the extension lifter HP sensor  607 . With this, in a case where the user is supposed to stack long sheets and also the sheet storage  506  is temporarily closed, the lift plate  507   a  and the lift plate  507   b  are controlled such that the levels thereof match each other, whereby the lift plates  507   a  and  507   b  are ready for stacking long sheets. 
     On the other hand, if it is determined in the step S 504  that the conditions are not satisfied (NO to the step S 504 ), the CPU  301  proceeds to a step S 508 . In this case, the lift plate  507   a  and the lift plate  507   b  are in a state positioned at the same level, there is no need to adjust the levels of the two lift plates. Therefore, in the step S 508 , the lift plates  507   a  and  507   b  are directly subjected to processing for making them ready for feeding sheets S. More specifically, the CPU  301  causes the lift plates  507   a  and  507   b  to be lifted up until the sheet feed position sensor  602  is turned on (YES to the step S 508 ), to thereby place the lift plates  507   a  and  507   b  in a state enabled to feed long sheets. 
     Further, if it is determined in the step S 505  that the condition mentioned therein is not satisfied (NO to the step S 505 ), the CPU  301  proceeds to the step S 508 . In this case, it is supposed that the user is not going to use long sheets. Therefore, in the step S 508 , the CPU  301  causes the lift plate  507   a  to be lifted up until the sheet feed position sensor  602  is turned on (YES to the step S 508 ), to thereby place the lift plate  507   a  in a state enabled to feed non-long sheets. Then, the CPU  301  stops the driving of the lifter motor M 500  (step S 507 ), followed by terminating the present process. 
     Further, if it is determined in the step S 502  that the sheet feed position sensor  602  is on (NO to the step S 502 ), the lift plate  507   a  is in the sheet feed-enabled state and the lift plate  507   a  cannot be lifted up any further, so that the CPU  301  terminates the present lift plate moving process. 
     According to the process in  FIG. 5 , in a case where the sheet storage  506  is closed, the CPU  301  determines whether or not the lift plate  507   a  and the lift plate  507   b  are positioned at the same level (step S 504 ). In a case where the lift plate  507   a  and the lift plate  507   b  are not positioned at the same level, and also in a case where long sheets are supposed to be used (YES to the step S 505 ), the CPU  301  causes the lift plate  507   a  to be lifted up to thereby adjust the lift plate  507   a  to the same level as the lift plate  507   b  (steps S 506  and  507 ). With this, after opening the sheet storage  506  and then moving the sheet partition plate  500  to the position corresponding to the lift plate  507   b , the user only closes the sheet storage  506 , whereby the lift plates  507   a  and  507   b  become ready for storing long sheets thereon. This improves operability when long sheets are used, whereby even in a case where non-long sheets and long sheets are switchingly used, it is possible to improve the user-friendliness of the sheet feeding deck  250 . 
     Note that in the present embodiment, after the lift plate moving process in  FIG. 5  is once performed to make the lift plates  507   a  and  507   b  ready for stacking long sheets thereon, even if the sheet storage  506  is opened in order to stack the long sheets, the lift plate moving (lowering) process in  FIG. 4  is subjected to control such that it is not executed in this case. This makes it possible to maintain the state of the sheet storage  506  once made ready for stacking long sheets, without requiring any adjustment. The above-mentioned control may be realized by adding a step for determination of the above-mentioned state, to the start of the lift plate moving process in  FIG. 4 . 
     In the present embodiment, the user may set a size of sheets to be stored in the sheet storage  506  using the console section  310 , and the CUP can determine, based on the set size, that the user is going to store long sheets in the sheet storage  506 . 
     In the present embodiment, in a case where image formation is to be performed using non-long sheets after performing image formation using long sheets, the user presses the storage open button  510 , and after the sheet storage  506  is opened, long sheets are removed. Thereafter, the user moves the sheet partition plate  500  to the lift plate  507   a . With this, a stored state of long sheets prepared by the lift plate moving process in  FIG. 5  is released, whereby the lift plate  507   a  is lowered to the bottom position of the sheet storage. Therefore, it is possible to smoothly shift from an image forming operation using long sheets to an image forming operation using non-long sheets, and hence it is possible to improve the user&#39;s convenience when switching between sheets for use. 
     In the present embodiment, the lift mechanism  530  is configured such that above the long sheet lower limit position, the lift plate  507   b  is lifted up and down in accordance with the lifting (up and down motion) of the lift plate  507   a . Further, the mechanical stopper  609  for restricting a range of lifting (down motion) of the lift plate  507   b  is provided. With this, a lift capability required of the lift mechanism  530  can be made relatively small, but not too large. 
     In the present embodiment, the lift plate for stacking sheets S is formed by two lift plates, and non-long sheets are stacked on the lift plate  507   a , and long sheets are stacked to extend over the lift plate  507   a  and the lift plate  507   b . Therefore, strength required of the lift plate  507   a  and the lift plate  507   b  can be made relatively small. 
     The sheet feeding device (sheet feeding deck)  250  according to the present embodiment forms an image forming system together with the image forming apparatus that forms images on sheets fed from the sheet feeding device  250 . 
     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. 2017-099931 filed May 19, 2017 which is hereby incorporated by reference herein in its entirety.