Patent Publication Number: US-2021163242-A1

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus for forming an image on a sheet fed from an accommodating portion for accommodating the sheet. 
     The image forming apparatus such as a printer, a copying machine or a multi-function machine is required to improve productivity of output of the image-formed sheet. As one of methods of maintaining high productivity, it is possible to cite a method in which by increasing a volume of the accommodating portion for accommodating sheets for image formation, a frequency of an occurrence of downtime for replenishing the sheets is suppressed. U.S. Patent Application Publication No. US2005/0067759 discloses that in the case where a large-volume accommodating portion of an image forming apparatus is pulled out, lifting and lowering of a lifter plate (lift plate) is controlled so that a top surface position of the sheets stacked on the lifter plate is maintained at a predetermined position between an upper-limit position and a lower-limit position of the lifter plate. According to U.S. Patent Application Publication NO. US2005/0067759, the top surface of the sheets is maintained at a proper height, so that supply and exchange of the sheets become easy. 
     However, a viewpoint of convenience varies depending on users in some instances. For example, some uses desire that sheets in a large amount close to an upper limit of a volume of the accommodating portion are supplied at one time in some instances. In such a case, advantage such that the lifting and lowering control of the lifter plate as disclosed in the above-described U.S. Patent Application Publication is poor. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: an accommodating portion configured to accommodate a sheet; an image forming portion configured to form an image on the sheet fed from the accommodating portion; an opening portion configured to open the accommodating portion to an outside for supplying a sheet; a lifter plate which is provided in the accommodating portion and on which the sheet is stacked; a lifting and lowering mechanism configured to lift and lower the lifter plate; a lower-limit detecting portion configured to detect that the lifter plate is in a lower-limit position in the accommodating portion; a control unit configured to control the lifting and lowering mechanism and the opening portion so that lowering of the lifter plate and opening of the accommodating portion are carried out in accordance with an operation in a set mode of a plurality of modes when the control unit receives an instruction to open the accommodating portion, wherein the modes includes a first mode in which the accommodating portion is opened irrespective of whether or not the lifter plate lowers to the lower-limit position and a second mode in which the accommodating portion is opened after the lifter plate lowers to the lower-limit position; and an operating portion configured to be operated by an operator for changing setting of the mode, between the modes, executed when the control unit receives the instruction to open the accommodating portion. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an image forming apparatus according to an embodiment 1. 
       Part (a) of  FIG. 2  is a schematic view of an option feeder in the embodiment 1, and part (b) of  FIG. 2  is a schematic view of a lifting mechanism in the embodiment 1. 
         FIG. 3  is a block diagram showing a control constitution of the image forming apparatus according to the embodiment 1. 
       Parts (a) and (b) of  FIG. 4  are schematic views for illustrating opening and closing of the option feeder in the embodiment 1. 
         FIG. 5  is a conceptual view showing a load exerted on the lifting mechanism during sheet supply in the embodiment 1. 
       Parts (a), (b) and (c) of  FIG. 6  are schematic views for illustrating an opening operation of the option feeder by open control after lifter lowering in the embodiment 1. 
         FIG. 7  is a flowchart showing a process when an accommodating portion open button is pressed in the embodiment 1. 
         FIG. 8  is a flowchart showing a process of normal open control in the embodiment 1. 
         FIG. 9  is a flowchart showing a process of the open control after lifter lowering in the embodiment 1. 
         FIG. 10  is a schematic view showing a switching screen of an operation in an accommodating portion open mode in the embodiment 1. 
         FIG. 11  is a chart showing a time series of automatic switching of an accommodating portion open mode in an embodiment 2. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, an exemplary embodiment for carrying out the present invention will be described while making reference to the drawings. 
     Image Forming Apparatus 
       FIG. 1  is a sectional view showing a general structure of an image forming apparatus  100 . In  FIG. 1 , the image forming apparatus  100  includes a printer main assembly  100 A which is a main assembly thereof and an image reading apparatus (image reader)  100 B provided on the printer main assembly  100 A. The image reader  100 B reads, for example, an image of an original placed on a platen glass and sends read image data, as a video signal, to a scanner unit of the printer main assembly  100 A. On the basis of image information inputted from an external PC or the image data read from the original, the printer main assembly  100 A forms an image on a state used as a recording medium. The sheet used as the recording medium includes paper such as plain paper or thick paper, a plastic film such as a sheet for an overhead projector, a sheet with a special shape, such as an example or index paper, and a cloth. 
     The printer main assembly  100 A includes a process unit  120  for forming a color image, a cassette feeding portion  150  and a normal feeding portion  210  which are used for feeding sheets S which are recording materials, and a sheet feeding system for feeding the sheets S. 
     The process unit  120  provided as an image forming means includes image forming stations Y, M, C and K juxtaposed along a horizontal direction. The image forming stations Y, M, C and K form toner images of yellow, magenta, cyan and black, respectively. The image forming stations Y, M, C and K have substantially the same constitution except for the colors of toners used in development. That is, each of the image forming stations Y to K is an electrophotographic unit including a photosensitive drum  121  which is a photosensitive member shaft-supported rotatably, and forms the toner image on a surface of the photosensitive drum  121  as an image bearing member. As regards each of the image forming stations Y to K, in order to execute steps of an electrophotographic process, a primary charging device, a developing device and a cleaning device are provided so as to oppose an outer peripheral surface of the photosensitive drum  121 . Each of the developing devices is connected to a toner supplying portion for supplying the toner of an associated color. 
     Under the process unit  120 , an endless intermediary transfer belt  130  is provided so as to contact the photosensitive drums  121  of the image forming stations Y to K. Further, four primary transfer rollers  123  are provided so as to oppose the four photosensitive drums  121  through the intermediary transfer belt  130 , so that a primary transfer portion T 1  is formed as a nip between each of the primary transfer rollers  123  and the associated one of the photosensitive drums  121 . 
     The intermediary transfer belt  130  is an intermediary transfer member functioning as an image bearing member for bearing the toner image similarly as the photosensitive drum  121 . The intermediary transfer belt  130  is rotatably stretched by a driving roller, a tension roller and a secondary transfer opposite roller  139 . A secondary transfer roller  140  is provided so as to oppose the secondary transfer opposite roller  139 , and a secondary transfer portion T 2  is formed as a nip between the secondary transfer roller  140  and the secondary transfer opposite roller  139 . 
     Below the intermediary transfer belt  130 , a sheet feeding portion for feeding the sheet S to the secondary transfer portion T 2  and the cassette feeding portion  150  for feeding the sheet S are provided. The cassette feeding portion  150  includes an upper cassette  150   a  and a lower cassette  150   b  which accommodate the sheets S and feeding units  151  for feeding the sheets S from the respective cassettes. 
     The printer main assembly  100 A is provided with the manual feeding portion  210  in addition to the cassette feeding portion  150 . The manual feeding portion  210  includes a manual feeding tray  212  on which a user manually sets the sheets and a feeding unit  213  for feeding the sheet from the manual feeding tray  212 . A position of the sheet set on the manual feeding tray  212  is regulated by a side regulating plate  215 . Further, the manual feeding tray  212  is provided with a sensor  211  for detecting that the sheet is set. The manual feeding portion  210  is used when images are formed on sheets in a relatively small number of sheets, for example about several tens of sheets. 
     The sheet feeding portion is principally constituted by a supply passage  131  and a discharge passage  231 . The supply passage  131  is a feeding passage along which the sheet S fed from the cassette feeding portion  150 , the manual feeding portion  210  or an option feeder  250  is fed to the secondary transfer portion T 2 . The discharge passage  231  is a feeding passage along which the sheet S after the image formation is fed to an outside of the printer main assembly  100 A. 
     The supply passage  131  is provided with feeding roller pairs  153 ,  154  and  155 , and a registration roller pair  161 . On a side upstream of the registration roller pair  161  with respect to a feeding direction of the sheet S, a registration sensor  160  is provided. The registration sensor  160  is used for determining timing when the feeding of the sheet S once stopped by contact with the registration roller pair  161  is resumed and the image is transferred from the intermediary transfer belt  130  onto the sheet S. 
     Further, on a side (right-hand side in  FIG. 1 ) of the printer main assembly  100 A, the option feeder  230  is connected to the printer main assembly  100 A. The option feeder  250  constitutes the image forming apparatus  100  (image forming system) in combination with the printer main assembly  100 A. 
     The printer main assembly  100 A and the option feeder  250  are connected to each other through a deck supply passage  132 . The deck supply passage  132  is connected to the supply passage  131  on a side upstream of the feeding roller pair  154  and feeds the sheet S, accommodated in the option feeder  250 , to the supply passage  131 . 
     The option feeder  250  is capable of stacking many elongated sheets longer in size with respect to the sheet feeding direction than regular size sheets, in addition to the sheets with regular size such as A3 or A4. A user uses the option feeder  250  in the case where the image is formed on the sheet with a size other than the regular size or in the case where the image is formed on a sheet with a size different from the size(s) of the sheet(s) already accommodated in the upper cassette  150   a  and the lower cassette  150   b.  Further the option feeder  250  is larger in maximum number of sheets S stackable on the upper cassette  150   a  and the lower cassette  150   b,  and therefore, is also usable for the purpose of improving operational efficiency by, for example, reducing a frequency of surface supply. Details of the option feeder  250  will be specifically described later. 
     On the other hand, the discharge passage  231  is provided with a fixing provided  170 , and on a side downstream of the fixing device  170 , a reverse passage  230  is connected to the discharge passage  231 . Further, to the reverse passage  231 , a double-side feeding passage  235  is connected. At a connecting portion between the discharge passage  231  and the reverse passage  230 , a reverse flap  172  is provided. The reverse flap  172  divides a destination of the sheet S discharged from the fixing provided  170 , into a plurality of destinations. 
     The discharge passage  231  branches into an upper discharge passage  181  and a lower discharge passage  180  on a side downstream of the connecting portion thereof to the reverse passage  230 , and a reverse flap  190  is provided at a branch portion. The reverse flap  190  divides a destination of the sheet S into the upper discharge passage  181  and the lower discharge passage  180 . The upper discharge passage  181  permits discharge of the sheet S onto an upper discharge tray  196 . The lower discharge passage  180  permits discharge of the sheet S onto a lower discharge tray  200 . Each of the discharge passage  231 , the reverse passage  230 , the double-side feeding passage  235 , the upper discharge passage  181  and the lower discharge passage  180  is provided with a feeding roller pair or a discharging roller pair. 
     Image Forming Operation 
     Next, an image forming operation by the image forming apparatus  100  will be described. When a job (print job) requiring the image forming apparatus  100  to output the instruction is inputted to the image forming apparatus  100 , sheets are fed one by one to the feeding passage  131  from either one of the cassette feeding portion  150 , the manual feeding portion  210  and the option feeder  250 . At this time, on the basis of detection timing of the sheet S by feeding sensors  152  and  603 , whether or not the sheet S is fed normally is discriminated. 
     The sheet S fed to the feeding passage  131  is fed toward the registration roller pair  161  by the feeding roller pairs  154  and  155  and the like. A leading end and a trailing end of the sheet S are detected by the registration sensor  160  at a position between the feeding roller pair  155  and the registration roller  161 . The registration sensor  160  is used for controlling feeding of the sheet S by the registration roller pair  161  in synchronism with timing when the toner image carried on the intermediary transfer belt  130  reaches the secondary transfer portion T 2 . Further, the registration sensor  160  is also used as a means for detecting a length of the sheet S with respect to the feeding direction of the sheet S. 
     In each of the image forming stations Y to K of the process unit  120 , the surface of the photosensitive drum  121  is electrically charged uniformly, and then an electrostatic latent image is formed on the drum surface by irradiating the drum surface with laser light emitted from the scanner unit  122 . The electrostatic latent image carried on the photosensitive drum  121  is developed with toner supplied from the developing device, so that a toner image is formed on the surface of each of the photosensitive drums  121 . Resultant toner images are successively transferred from the photosensitive drums  121  onto the intermediary transfer belt  130  at the primary transfer portions T 1 , so that the toner images of the respective colors are superposed on each other and thus a full-color toner image is formed on the intermediary transfer belt  130 . The toner image formed on the intermediary transfer belt  130  is moved to the secondary transfer portion T 2  by rotation of the intermediary transfer belt  130 . 
     On the other hand, the sheet S detected at the leading end thereof by the registration sensor  160  contacts the registration roller pair  161  and stops. At this time, the sheet S forms a loop shape (flexure) by being fed in a predetermined amount in a state in which the leading end of the sheet S is abutted against the registration roller pair  161 , so that oblique movement of the sheet S is corrected. As regards the sheet S subjected to the correction of the oblique movement, in consideration of a time when the leading end of the sheet S reaches the registration sensor  160  and a time required for forming the loop for registration, feeding of the sheet S is resumed so that a leading end of an effective print region and the leading end of the toner image on the intermediary transfer belt  130  coincide with each other at the secondary transfer portion T 2 . 
     To the sheet S reached the secondary transfer portion T 2  and the toner image on the intermediary transfer belt  130 , a transfer voltage is applied from the secondary transfer roller. By this, the toner image is transferred from the intermediary transfer belt  130  onto the sheet S. The sheet S on which the toner image is transferred is fed to the fixing device  170 . The sheet S fed into the fixing device  170  is heated and pressed, whereby the toner image is fixed on the sheet S. The sheet S on which the toner image is fixed is fed toward an outlet of the printer main assembly  100 A. 
     Incidentally, when the leading end of the sheet S on which the toner image is transferred reaches a feeding sensor  171  provided on a side upstream of the fixing device  170 , a designation of the sheet S is switched between the reverse passage  230  and the discharge passage  231  in accordance with an instruction of the print job. In the case of a double-side printing job in which images are formed on double surfaces (sides) of the sheet S, the surface S is fed to the reverse passage  230 , and in a state in which a front surface and a back surface of the sheet S are changed to each other, the sheet S is fed again toward the secondary transfer portion T 2 , and then the image is formed on the back surface of the sheet S. In the case of a one-side printing job or back-side printing in the double-side printing job, the sheet S is fed to the discharge passage  231 . 
     The sheet S fed to the discharge passage  231  is fed by a feeding roller pair  232  and is guided by the reverse flap  190  positioned in accordance with the instruction of the print job, so that the sheet S is fed to the lower discharge passage  180  or the upper discharge passage  181 . In the case where a discharge destination is the lower discharge tray  200 , the sheet S is fed to the lower discharge passage  180 , and in the case where, the discharge destination is the upper discharge tray  196 , the sheet S is fed to the upper discharge passage  181 . Further, to the image forming apparatus  100 A, a sheet processing device for subjecting the image formed sheet to binding or the like is connected, the sheet is delivered from the lower discharge passage  180  to the sheet processing device. 
     Incidentally, the above-described process unit  120  is an example of an image forming means, and may also be an electrophotographic unit of a monochromatic type or may also be of another printing type such as an ink jet type. 
     Option Feeder 
     Next, a structure of the option feeder  250  which is a sheet feeding device in this embodiment will be described. Part (a) of  FIG. 2  is an enlarged sectional view of the option feeder  250  in the image forming apparatus  100  of  FIG. 1 . The option feeder  250  includes a casing  250 A as a housing and an accommodating portion unit  508  openable and closable relative to the casing  250 A. The accommodating portion unit  508  includes a box-like accommodating portion main body  506  for accommodating a large number of sheets S, a lifter plate (lift plate)  507  mounted in the accommodating portion main body  506  so as to be capable of being lifted and lowered, and a lifting mechanism  530  for lifting and lowering the lifter plate  507 . The accommodating portion unit  508  is an accommodating portion in this embodiment, and the lifting mechanism  530  is a lifting and lowering means in this embodiment. 
     At an upper portion of the option feeder  250 , a pick-up roller  501  and a separation and feeding roller  502  which constitute an upstream portion of the deck supply passage  132 . The pick-up roller  501  which is a feeding means in this embodiment is provided above the lifter plate  507  and contacts a top surface of an uppermost sheet of the sheets S stacked on the lifter plate  507 , and feeds the sheet S toward the separation and feeding roller  502 . The separation and feeding roller  502  feeds the sheet S, received from the pick-up roller  501 , toward the feeding roller pair  504  of the printer main assembly  100 A. At this time, a separation roller opposing the separation and feeding roller  502  exerts frictional force on the sheet entering a nip between itself and the separation and feeding roller  502 , and thus prevents double (multiple-)feeding of the sheets other than the sheet contacting the separation and feeding roller  502 . The separation roller is, for example, a retard roller to which rotational drive (rotation driving force) with respect to, for example, a direction opposite to the feeding direction of the sheet S, but another separation member (for example, a pad-like frictional member) may also be used. 
     Part (b) of  FIG. 2  is a schematic view showing a structure of the lifter plate  507  and the lifting mechanism  530  for lifting and lowering the lifter plate  507 . As shown in parts (a) and (b) of  FIG. 2 , the lifting mechanism  530  in this embodiment includes two wires  530   a  and  530   e,  a plurality of pulleys  530   b,    530   c,    530   f  and  530   g,  a wire winding-up shaft  532 , and a lifter motor M 500 . 
     The lifter plate  507  is hung by the wire  530   a  at one end portion thereof, and is hung by the wire  530   e  at the other end portion thereof, so that the lifter plate  507  is supported in a substantially horizontal attitude. The wires  530   a  and  530   e  are wound about the pulleys  530   b  and  530   c  and about the pulleys  530   g  and  530   f,  respectively, and end portions thereof opposite from connecting portions thereof to the lifter plate  507  are fixed to wire pulleys  530   d  and  530   h,  respectively, provided on the wire winding-up shaft  532 . The wire winding-up shaft  532  is connected to an output shaft of the lifter motor M 500 . Accordingly, by power of the lifter motor M 500  which is a driving source, winding-up and feeding of the wires  530   a  and  530   e  by the wire winding-up shaft  532  are carried out, so that the lifter plate  507  is lifted and lowered. 
     The lifter motor M 500  is provided in the accommodating portion unit  508 , and when the accommodating portion unit  508  is opened and closed, the lifter motor M 500  moves together with the accommodating portion unit  508  relative to the casing  250 . The lifter motor M 500  is connected to a power source provided on the casing  250 A side through a flexible cable following movement of the accommodating portion unit  508 , and is moved by electric power supplied from the power source. Incidentally, in part (b) of  FIG. 2 , the wire winding-up shaft  532  is directly connected to the output shaft of the lifter motor M 500  but may also be connected to the lifter motor output shaft through a transmission mechanism such as a gear train. Further, as the lifter motor M 500 , for example, a DC mode can be used. The lifter motor M 500  is a mode in this embodiment, and the wire winding-up shaft  532  is a winding-up shaft in this embodiment. 
     Incidentally, the pulley  530   b  is shaft-supported by a supporting member  531   b,  the pulley  530   c  is shaft-supported by a supporting member  531   c,  the pulley  530   f  is shaft-supported by a supporting member  531   f,  and the pulley  530   g  is shaft-supported by a supporting member  531   g.  The respective supporting members  531   b,    531   c,    531   f  and  531   g  are connected (fixed) to an inner wall of the accommodating portion unit  508 . As the supporting members  531   b,    531   c,    531   f  and  531   g,  for example, metal plate members secured to the inner wall of the accommodating portion unit  508  with screws can be used. 
     In this embodiment, the lifting mechanism  530  for lifting and lowering the lifter plate  507  by the two wires is described as an example, but the number of the wires may be changed or a lifting and lowering means of a type other than the wire type may also be used. For example, a constitution in which upper and lower belts are stretched around pulleys supported by a frame of the accommodating portion unit  508  and in which the lifter plate  507  is not only fixed to the belts but also lifted and lowered by rotationally driving the belts by a mode may also be employed. 
     In the accommodating portion unit  508 , a space above the lifter plate  507  and enclosed by the inner wall of the accommodating portion unit  508  is a sheet accommodating portion. At an uppermost portion of the sheet accommodating portion, a sheet presence/absence sensor  601  and a feeding position sensor  602  are provided. The sheet presence/absence sensor  601  is a sensor for detecting whether or not at least one sheet S is present on the lifter plate  507 . The feeding position sensor  602  is a sensor for detecting that a top surface of the sheets S stacked on the lifter plate  507  (or an upper surface of the lifter plate  507  in the case where there is no sheet on the lifter plate  507 ) is in a position (feeding position) where the pick-up roller  501  contacts and feeds the uppermost sheet. 
     As the sheet presence/absence sensor  601  and the feeding position sensor  602 , an optical sensor constituted by a flag member swingable by being pressed against the sheet S and a photo-interrupter light-blocked by a light-blocking portion provided on the flag member can be used. Then, for example, at a position of the lifter plate  507  corresponding to a flag member (A) of the sheet presence/absence sensor  601 , a cut-away portion is provided, so that the lifter plate  507  and the flag member (A) are prevented from interfering with each other. On the other hand, at a position of the lifter plate  507  corresponding to the flag member (B) of the feeding position sensor  602 , no cut-away portion is provided, so that the lifter plate  507  is made contactable to the flag member (B). 
     In this case, when the lifter plate  507  is lifted in a state in which at least one sheet is stacked on the lifter plate  507 , both the sheet presence/absence sensor  601  and the feeding position sensor  602  are in a state (ON state) in which these sensors detect that their flag members are swung by being pressed by the sheet S. When the lifter plate  507  is lifted in a state in which no sheet is stacked on the lifter plate  507 , the sheet presence/absence sensor  601  is in an OFF state and the feeding position sensor  602  is in the ON state. In the case where the sheets) S on the lifter plate  507  and the lifter plate  507  do not reach the feeding position (in the case where there is room to lift the lifter plate  507 ), both the sheet presence/absence sensor  601  and the feeding position sensor  602  are in the OFF state. Accordingly, a CPU  301  ( FIG. 3 ) described later is capable of acquiring pieces of information indicating presence or absence of the sheet on the lifter plate  507  and the top surface position of the sheet(s) stacked on the lifter plate  507 , on the basis of patterns of detection states of these sensors. 
     In the case where a print job in which the sheet S is supplied form the option feeder  250  to the printer main assembly  100 A of the image forming apparatus  100  and in which the image is formed on the sheet S, a lifting operation of the lifter plate  507  is performed. That is, the lifter motor M 500  rotates the wire winding-up shaft  532 , and thus the wire pulleys  530   d  and  530   h  wind up the wires  530   a  and  530   e,  so that the lifter plate  507  is lifted. When the state of the feeding position sensor  602  changes from the OFF state to the ON state and the sheet presence/absence sensor  601  is in the ON state, the CPU  301  discriminates that the sheet S is present on the lifter plate  507  and the top surface of the sheet reaches the feeding position. Then, a feeding mode which is a driving source for the pick-up roller  501  and the separation and feeding roller  502  starts rotation thereof. By this, the sheets S stacked on the lifter plate  507  are fed one by one to the supply passage  131  through the deck supply passage  132  including the pick-up roller  501 , the separation and feeding roller  502  and the feeding roller pair  504 . 
     During execution of the print job, on the basis of a detection result of the feeding position sensor  602 , the CPU  301  monitors the top surface position of the sheet S in the option feeder  250 . Then, when the state of the feeding position sensor  602  changes from the ON state to the OFF state by consumption of the sheets S, the CPU  301  discriminates that the top surface position of the sheet S lowers from the feeding position, so that the CPU  301  drives the lifter motor M 500  again so that the top surface of the sheets S is lifted to the feeding position. Thus, during execution of the print job, control such that the top surface position of the sheets S in the option feeder  250  is kept at a substantially constant level is carried out. 
     The accommodating portion unit  508  including the accommodating portion main body  506  is openable and closable relative to the casing  250 A. A state in which the accommodating portion unit  508  is closed (closed state of the accommodating portion unit  508 ) refers to a state in which the accommodating portion unit  508  is inserted to a predetermined mounting position of the casing  250 A so that feeding of the sheets S can be executed. Further, a state in which the accommodating portion unit  508  is open (open state of the accommodating portion unit  508 ) refers to a state in which the accommodating portion unit  508  is pulled out of the casing  250 A so as to enable replenishment and exchange of the sheet S. Incidentally, in the open state of the accommodating portion unit  508 , a state in which a latch member for locking the accommodating portion unit  508  to the closed state is released and thus the user is capable of manually pulling out to a position where the user has access to the sheet accommodating portion is included. In the following, irrespective whether or not the entirety of the sheet accommodating portion is pulled out to an outside of the casing  250 A, the state in which the accommodating portion unit  508  is pulled out and the state in which the accommodating portion unit  508  is pullable out are referred to as the open state. Further, the state in which the accommodating portion unit  508  is locked to the mounting position of the casing  250 A is referred to as the closed state. 
     The casing  250 A is provided with an accommodating portion open button  510 , and the user presses the accommodating portion open button  510 , whereby locking of the accommodating portion unit  508  to the casing  250 A is released. Specifically, an accommodating portion open solenoid  610  ( FIG. 3 ) which is an actuator is actuated, so that the latch member physically latching the casing  250 A and the accommodating portion unit  508  is moved, so that the accommodating portion unit  508  is capable of being pulled out to a front side in part (a) of  FIG. 2 . An accommodating portion open solenoid  610  is an openable (open/close) means for switching the state of the accommodating portion unit  508  in this embodiment between the open state and the closed state, and the accommodating portion open button  510  is an open instruction means in this embodiment for sending a signal (open instruction) providing an instruction to open the accommodating portion. Incidentally, the accommodating portion open button  510  is an example of the open instruction means, and an open instruction may also be provided by pressing a bottom of a display operation portion  310 . In this case, the display operation portion  310  functions as the open instruction means. Further, a constitution in which the open of the accommodating portion can be instructed through an external device connected through an external I/F  309 . 
     Incidentally, at the contact portions of the accommodating portion unit  508  and the casing  250 A, urging portions such as spring members for urging the accommodating portion unit  508  in the pulling-out direction can be provided. In this case, when the latch member is released by pressing-down of the accommodating portion open button  510 , the accommodating portion unit  508  starts to automatically move in the pulling-out direction relative to the casing  250 A. For that reason, an operation load of the user is reduced, and in addition, the open state of the accommodating portion unit  508  is quite obvious to the eyes of the user. 
     Further, the casing  250 A is provided with an accommodating portion open close sensor  608 . The accommodating portion open/close sensor  608  detects whether or not the accommodating portion unit  508  is in the pulled-out state. In the case where the accommodating portion unit  508  is pulled out, the accommodating portion open/close sensor  608  is turned on. Further, in the case where the accommodating portion unit  508  is not pulled out (i.e., in the case where the accommodating portion unit  508  is accommodated in a mounting position of the casing  250 A), the accommodating portion open/close sensor  608  is turned off 
     Further, the accommodating portion unit  508  is provided with a supply position sensor  605 , a bottom position sensor  604  and a bottom position sheet presence/absence sensor  606 . 
     The supply position sensor  605  which is an intermediary detecting means in this embodiment is provided on the inner wall (a side surface of the lifter plate  507 ) of the accommodating portion main body  506 . The supply position sensor  605  detects that the top surface of the sheets stacked on the lifter plate or the upper surface of the lifter plate is in a detection range between an upper-limit position and a lower-limit position of the lifter plate  507  in the accommodating portion main body  506  and is in an ON state. In the case where each of the sheets stacked on the lifter plate  507  and the lifter plate  507  is not in the supply position (the lower-limit position of the detection range), the supply position sensor  605  is in an OFF state. That is, at the time when the state of the supply position sensor  605  changes from the ON state to the OFF state during lowering of the lifter plate  507 , it is understood that the top surface of the sheets stacked on the lifter plate  507  (the upper surface of the lifter plate  507  in the case where there is no sheet on the lifter plate  507 ). In normal open control described later, a lowering operation of the lifter plate  507  is stopped at the time when the top surface of the sheet or the upper surface of the lifter plate  507  is lowered to the supply position, so that the supply of the sheet by the user is made easy and thus convenience can be enhanced. 
     As the supply position sensor  605 , an optical sensor including a flag member which has a certain length with respect to a vertical direction and which projects toward an inside of the accommodating portion main body  506  and a photo-interrupter light-blocked by a light-blocking portion provided on this flag member. In this case, the length of the flag member defines a detection range, and a lower end portion of the flag member is the supply position. In the case where the sheet on the lifter plate  507  or the lifter plate  507  is present at a height not less than the supply position, the flag member is pressed by the sheet or the lifter plate  507 , and is retracted from an inside space (sheet accommodating portion) of the accommodating portion main body  506 . On the other hand, when the sheet and the lifter plate  507  is in a position lower than the supply position, the flag member projects toward the inside of the accommodating portion main body  506  without being obstructed by the sheet and the lifter plate  507 . Accordingly, a detection state of the photo-interruptor changes depending on whether at least one of the sheet and the lifter plate  507  is in a position equal to or higher than the supply position or in a position lower than the supply position. Incidentally, in this embodiment, the optical sensor using the flag member was described as an example, but by another known detecting mechanism, detection that the top surface of the sheet stacked on the lifter plate  507  or the upper surface of the lifter plate  507  is in the supply position may also be made. 
     The bottom position sensor  605  is provided at the bottom of the accommodating portion main body  506 . The bottom position sensor  604  is constituted so that the bottom position sensor  604  is turned on when the lifter plate  507  is positioned at the bottom of the accommodating portion main body  506  (i.e., the lower-limit position of the lifter plate  507  in the accommodating portion main body  506 ) and so that the bottom position sensor  604  is turned off when the lifter plate  507  is not positioned at the bottom of the accommodating portion main body  506 . As the bottom position sensor  604 , a switch which actuates in contact with the lower portion of the lifter plate  507  or a photo-interruptor light-blocked by a light-blocking portion provided at the lower portion of the lifter plate  507 . 
     Further, the bottom position sheet presence/absence sensor  606  is also provided at the bottom of the accommodating portion main body  506 . The bottom position sheet presence/absence sensor  606  is constituted so that the bottom position sheet presence/absence sensor  606  is turned on when the sheets are stacked on the lifter plate  507  in a state in which the lifter plate  507  is positioned at the bottom of the accommodating portion main body  506  and so that the bottom position sheet presence/absence sensor  606  is turned off when no sheet is stacked on the lifter plate  507  in the state in which the lifter plate  507  is positioned at the bottom of the accommodating portion main body  506 . As the bottom position sheet presence/absence sensor  606 , for example, an optical sensor which includes a flag member swingable depending on presence or absence of the sheet in the state in which the lifter plate  507  is positioned at the bottom of the accommodating portion main body  506  and which includes a photo-interruptor light-blocked by a light-blocking portion of the flag member. In the state in which the lifter plate  507  is positioned at the bottom of the accommodating portion main body  506 , the flag member is disposed so as to project upward from the upper surface of the lifter plate  507  through an opening provided in the lifter plate  507  and is swung downward by being pressed by the sheet. 
     Control Constitution of Image Forming Apparatus 
     Next, a control constitution of the image forming apparatus  100  provided with the above-constituted option feeder  250  will be described.  FIG. 3  is a block diagram showing the control constitution of the image forming apparatus  100  of  FIG. 1 . In  FIG. 3 , the image forming apparatus  100  includes a CPU circuit portion  300 . The CPU circuit portion  300  includes the CPU  301 , a ROM  302 , a RAM  303  and a timer  312 . The CPU  301  is connected to the ROM  302  and the RAM  303  through an address bus or a data bus. 
     The CPU circuit portion  300  is connected to the display operation portion  310  and a printer controller  304 , and the printer controller  304  is connected to an image signal controller  308  and the external I/F (interface)  309  through the image signal controller  308 . Further, the printer controller  304  is connected to each of a sheet feeding portion  305 , an image forming portion  306  and an accommodating portion controller  311 . Further, the image signal controller  308  is also connected directly to the CPU circuit portion  300 . 
     The accommodating portion controller  311  is connected to each of the lifter motor M 500 , the accommodating portion open button  510 , the sheet presence/absence sensor  601 , the feeding position sensor  602  and the accommodating portion open/close sensor  608 . The accommodating portion controller  311  is connected to each of the bottom position sensor  604 , the supply position sensor  605 , the bottom position sheet presence/absence sensor  606 , a lifter motor over current detecting sensor  609  and the accommodating portion open solenoid  610 . The accommodating portion controller  311  is a control circuit including a processor and volatile and non-volatile memories. 
     The CPU  301  reads and executes a control program stored in the ROM  302 , so that the CPU  301  controls entirety of the image forming apparatus  100 . The ROM  302  stores the control programs. The ROM  302  is an example of a non-transient storing medium in which the control programs for operating the sheet feeding device and the image forming apparatuses are stored and which is readable by a computer. In the RAM  303 , data used for control is written. Incidentally, the RAM  303  is a rewritable memory and includes a non-volatile storing area such as EEPROM. On the basis of an instruction from the CPU  301 , the printer controller  304  provides an instruction to form the image to the image forming portion  306 . The image forming portion  306  forms the image on the basis of a video signal inputted from the printer controller  304 . Further, on the basis of the instruction from the CPU  301 , the printer controller  304  controls the sheet feeding portion  305 , so that the sheet is fed and conveyed. The image signal controller  308  subjects digital image signals, inputted through the external I/F  309 , to various processes during the printing operation, and then converts the processed digital image signals into video signals, so that the converted video signals are stored in the RAM  303 . 
     The display operation portion  310  which is a user interface of the image forming apparatus  100  is an operating portion in this embodiment. The display operation portion  310  includes a display such as a liquid crystal panel for displaying an image, bottoms such as a print start bottom and ten keys, and a touch panel, and functions as an input means through which the user is capable of inputting information to the image forming apparatus  100  and as a display means presenting information to the user. The CPU  301  controls contents of information displayed on the display operation portion  310  and receives information inputted by the user, so that the CPU  301  makes settings relating to functions, operation conditions and the like of the image forming apparatus  100  and setting (print setting) when a print job is executed. For example, the display operation portion  310  receives instructions from the user, such as selection of a color mode, input of sheet information, a copy start and the like when the image formation is carried out. Further, the display operation portion  310  has a function of displaying a state, a warning message and the like of the image forming apparatus. 
     The accommodating portion controller  311  receives pieces of information from the feeding position sensor  602 , the accommodating portion open/close sensor  608 , the supply position sensor  605 , the accommodating portion open button  510 , the bottom position sensor  604 , and the sheet presence/absence sensor  601 . Further, on the basis of the instruction from the CPU  301  the accommodating portion controller  311  controls the lifter motor M 500  and thus controls the position of the sheet in the accommodating portion main body  506 . That is, the CPU controller  300  and the accommodating portion controller  311  function in cooperation with each other as a control means for controlling the option feeder  250 . 
     Mode of Accommodating Portion Open Control 
     Next, a mode in an operation of the option feeder  250  when the accommodating portion open button  510  is pressed in a state in which the accommodating portion unit  508  is closed will be described. 
     First, a normal open mode which is a first open mode in this embodiment will be described. Parts (a) and (b) of  FIG. 4  are sectional views showing the option feeder  250  as seen from a right-hand side of part (a) of  FIG. 2 . As shown in part (a) of  FIG. 4 , when the user presses down the accommodating portion open button  510  in a state in which the accommodating portion unit  508  is closed, in the operation in the normal open mode, locking between the casing  250 A and the accommodating portion unit  508  is released. Then, as shown in part (b) of  FIG. 4 , the accommodating portion unit  508  is drawn from the casing  250 A. 
     In the operation in the normal open mode, after the state of the accommodating portion unit  508  is switched from the closed state to the open state, the lifter plate  507  is subjected to lifting and lowering control so that the top surface of the sheets stacked on the lifter plate  507  (the upper surface of the lifter plate  507  in the case where there is no sheet on the lifter plate  507  is maintained at the supply position. Thus, the lifter plate  507  is maintained at a proper height, so that the user can easily carry out replenishment and exchange of the sheets. 
     Incidentally, after the accommodating portion unit  508  is opened in the operation in the normal open mode, in a state in which the lifter plate  507  is maintained at the proper height, it would be also considered that sheets in a large amount are stacked on the lifter plate  507  at one time. The sheets in the large amount refer to sheets, for example, in an amount which exceeds a height from the upper surface of the lifter plate  507  positioned at the supply position to an upper stacking limit of the sheets in the accommodating portion main body  506 . 
     In the operation in the normal open mode, it is typically assumed that the user supplies the sheets every one package (for example,  500  sheets of plain paper). On the other hand, for the purpose of shortening an operation time of sheet supply by the user or for the like purpose, it would be also considered that the user intends to stack, for example, sheets in an amount corresponding to several packages collectively. In such a case, even when the lifter plate  507  is maintained at the supply position, an advantage such that the sheet supply is made easy is not readily obtained. On the other hand, the sheets in the large amount are stacked on the lifter plate  507  at one time, so that a relatively large load is exerted on the lifting mechanism  530 . 
       FIG. 5  is a conceptual view showing loads exerted on constituent elements of the lifting mechanism  530  by forces received by the lifter plate  507  when the sheets in the large amount are stacked at one time on the lifter plate  507 . When a sheet bundle S 1  in the large amount is stacked at one time on the lifter plate  507 , a relatively large downward force N 1  acts on the lifter plate  507  by a weight of the sheet bundle S 1  and the inertia of the sheet bundle S 1  lowered. 
     By this force N 1 , loads are exerted on the respective members constituting the lifting mechanism  530 , so that stress acts on the respective members. For example, downward forces N 2 , N 3 , N 4  and N 5  are exerted on the supporting members  531   b,    531   c,    531   f  and  531   b  supporting the wires  530   a  and  530   e  through the pulleys  530   b,    530   c,    530   f  and  530   g.  Accordingly, as the supporting members  531   b,    531   c,    531   f  and  531   g,  supporting members having strength not causing deformation and breaking due to stress generated by the forces N 2 , N 3 , N 4  and N 5  when the sheet supply normally carried out by the user is assumed. Similarly, also as regards the wires  530   a  and  530   e,  the pulleys  530   b,    530   c,    530   f  and  530   g,  and the wire winding-up shaft  532  and the like on which stress due to the force N 1  is actable, those having strength not causing the deformation and breakage due to the stress are used. 
     Incidentally, a magnitude of the force N 1  fluctuates depending on momentum of an operation of lowering the sheet bundle S 1  by the user. Accordingly, in order not to exert an overload on the supporting members  531   b  and the like, in the case where the user intends to constitute the lifting mechanism  530  so as to not to exert the overload on the supporting members even when the user supplies the sheet in any manner, each of the members is provided with strength move than necessary. However, the supporting members  531   b  and the like are provided each strength only for meeting a relatively rare case, and therefore, as a result, it leads to increase in size, weight and cost of the option feeder  250 . 
     Therefore, in this embodiment, as a mode of control (accommodating portion open control) when the accommodating portion open button  510  is pressed down, in addition to the normal open mode, an open mode after lifter lowering is prepared. When the normal open mode is a first mode, the open mode after lifter lowering is a second mode. Parts (a), (b) and (c) of  FIG. 6  are sectional views, showing the option feeder  250  as seen from the right-hand side of part (a) of  FIG. 2 , for illustrating contents of the open mode after lifter lowering. 
     Part (a) of  FIG. 6  shows a state in which the accommodating portion unit  508  is closed. In this state, when the user presses down the accommodating portion open button  510 , in an operation in the open mode after lifter lowering, as shown in part (b) of  FIG. 6 , a lowering operation of the lifter plate  507  is started while maintaining the closed state of the accommodating portion unit  508 . Then, when the bottom position sensor  604  detects that the lifter plate  507  reaches the lower-limit position (the bottom of the accommodating portion main body  506 ), the locking between the casing  250 A and the accommodating portion unit  508  is released, so that the accommodating portion unit  508  is drawn out shown in part (c) of  FIG. 6 . 
     Thus, when the accommodating portion open button  510  is operated, before the locking between the casing  250 A and the accommodating portion unit  508  is released, the lifter plate  507  is moved to the lower-limit position of the accommodating portion main body  506  in advance. This is the operation in the open mode after lifter lowering. 
     In the operation in the open mode after lifter lowering, when the sheet supply by the user is carried out, the lifter plate  507  is in the lower-limit position and is supported by the bottom portion (supporting portion) of the accommodating portion main body  506 . For this reason, even if the user stacks the sheet bundle in the large amount on the lifter plate  507  at one time, the force N 1  ( FIG. 5 ) received by the lifter plate  507  is distributed to the bottom portion of the accommodating portion main body  506 . For that reason, compared with the operation in the normal open mode in which there was a need to receive the force N 1  principally by the lifting mechanism  530 , the overload is not readily exerted on the constituent elements of the lifting mechanism  530  including the supporting member  531   b.  Accordingly, durability of the accommodating portion unit  508  as a whole can be ensured without changing the strength of the supporting members  531   b  and the like. Further, for users employing a supplying method in which sheets in a large amount are supplied at one time, it would be considered that the operation in the open mode after lifter lowering is not inferior in convenience to the operation in the normal open mode. 
     Control Method of Option Feeder 
     In the following, a control method of the option feeder  250 , in this embodiment, capable of switching operations in a plurality of modes including the normal open mode (first mode) and the open mode after lifter lowering (second mode), as a mode defining the operation when the accommodating portion open button  510  is operated will be described. Incidentally, description will be made that the operation of the option feeder  250  in this embodiment is switched between the two modes consisting of the first mode and the second mode, but may also be switchable to another mode. Further, the following process is periodically executed by the CPU  301  mounted in the printer main assembly  100 A. 
       FIG. 7  is a flowchart showing a process in which on the basis of preset mode setting, the accommodating portion unit  508  is opened in response to pressing-down of the accommodating portion open button  510  by the operation in the normal open mode or in the open mode after lifter lowering. The CPU  301  checks whether or not the accommodating portion unit  508  is accommodated in a predetermined mounting position of the casing  250 A by checking the accommodating portion open/close sensor  608  (S 10 ). In the case where the CPU  301  discriminated that the accommodating portion unit  508  is not accommodated (is not in the closed state), the control is ended as it is. In the case where the CPU  301  discriminated that the accommodating portion unit  508  is accommodated (is in the closed state), the CPU  301  checks whether or not an output state of the accommodating portion open button  510  is changed from an ON state to an OFF state (S 11 ). 
     When the accommodating portion open button  510  is not changed in state from the ON state to the OFF state, the CPU  301  is capable of discriminating that the accommodating portion open button  510  is not pressed down by the user, so that the control is ended as it is. On the other hand, when the accommodating portion open button  510  is changed in state from the ON state to the OFF state, the CPU  301  is capable of discriminating that the accommodating portion open button  510  is pressed down. In this case, the CPU  301  checks whether or not by the mode setting of the accommodating portion open control stored in the RAM  303  is the normal open mode (S 12 ). Incidentally, a mode setting method of the accommodating portion open control will be described later. In S 12 , in the case where the normal open modes set, normal open control is carried out (S 13 ). In S 12 , in the case where the open mode after lifter lowering is set, open control after lifter lowering is carried out (S 14 ). 
     Normal Open Control 
     Next, a procedure of the accommodating portion open control (normal open control) by the operation in the normal open mode will be described using  FIG. 8 . When the normal open control is started, first, the CPU  301  performs a process of switching the state of the accommodating portion unit  508  from the closed state to the open state. Specifically, locking between the casing  250 A and the accommodating portion unit  508  is released by moving a latch member locking the accommodating portion unit  508  to the casings  250 A by turning an accommodating portion open solenoid  610  on (energization) (S 21 ). Then, the CPU  301  waits for a time t 1  in which sufficient pulling of the accommodating portion open solenoid  610  can be confirmed (S 22 ). After waiting for the time t 1 , the accommodating portion open solenoid  610  is turned off (stop of the energization) (S 23 ). In the timed, it is assumed that the accommodating portion unit  508  is moved in a drawing direction to a position where the accommodating portion unit  508  is not locked by the latch member even when the accommodating portion open solenoid  610  is returned to an original position. 
     Next, the CPU  301  checks whether or not the sheet remains in the accommodating portion main body  506  (S 24 ). Whether or not the sheet remains in the accommodating portion main body  506  is discriminated by checking the output state of the sheet presence/absence sensor  601  stored in the RAM  303  before the normal open control is carried out. Incidentally, by a relative position of the lifter plate  507  in the accommodating portion main body  506 , the presence or absence of the sheet may also be discriminated. 
     In the case where the CPU  301  discriminated that the sheet does not remain in the accommodating portion main body  506 , the control in this embodiment is ended. In the case where the CPU  301  discriminated that the sheet remains in the accommodating portion main body  506 , drive of the lifter motor M 500  is start in a direction of lowering the lifter plate  507  (S 25 ). Next, the lowering operation of the lifter plate  507  is continued while checking stop conditions of S 26  and S 27 . In S 26 , whether or not a state of the supply position sensor  605  is changed from the ON state to the OFF state, i.e., whether or not the top surface of the remaining sheet(s) lowers to the supply position by the lowering of the lifter plate  507 . In S 27 , whether or not a state of the bottom position sensor  604  is changed from the OFF state to the ON state, i.e., whether or not the lifter plate  507  reached the lower-limit position of the accommodating portion main body  506 . In a period in which both of the conditions in S 26  and S 27  are not satisfied, the lowering of the lifter plate  507  is continued, and when either one of the conditions in S 26  and S 27  is satisfied, the drive of the lifter motor M 500  is stopped and thus the lowering of the lifter plate  507  is stopped (S 28 ). Thus, a normal open control flow is ended. 
     Incidentally, when the sheet bundle is set on the lifter plate  507  after the top surface of the remaining sheet(s) or the lifter plate  507  lowers to the supply position in the step (S 26 : Y), the state of the supply position sensor  605  changes from the OFF state to the ON state. In this case, the processes which are the same contents as those in S 25  to S 28  are executed, so that the top surface of the sheets after being supplied lowers to the supply position or the lifter plate  507  lowers until the lifter plate  507  reaches the lower-limit position of the accommodating portion main body  506 . By this the top surface position of the sheets on the lifter plate  507  is maintained at a height where the user is easy to supply the sheets. Further, in this embodiment, the lifter plate  507  starts to lower after the state of the accommodating portion unit  508  switches to the open state in the operation in the normal open mode, but switching between the open state and the closed state may also be carried out in parallel to the lowering of the lifter plate  507 . 
     Open Control after Lifter Lowering 
     Next, by using  FIG. 9 , a procedure of accommodating portion open control (open control after lifter lowering) by the operation in the open mode after lifter lowering will be described. When the open control after lifter lowering is started, first, the CPU  301  causes the lifter motor M 500  to start to drive in a direction in which the lifter plate  507  lowers (S 31 ). Different from the operation in the normal open control, at this time, the accommodating portion open solenoid  610  is not turned on, so that the accommodating portion unit  508  is kept in the closed state. 
     Then, the CPU  301  checks whether or not the state of the bottom position sensor  604  changed from the OFF state to the ON state, i.e., whether or not the lifter plate  507  reached the lower-limit position of the accommodating portion main body  506  (S 32 ). The lowering of the lifter plate  507  is continued in a period in which the lifter plate  507  does not reach the lower-limit position of the accommodating portion main body  506 , and in the case where the lifter plate  507  reached the lower-limit position, the CPU  301  causes the lifter motor M 500  to stop the drive of the lifter motor M 500 , and thus causes the lifter plate  507  to stop (S 33 ). 
     Next, the CPU  301  performs a process of switching the state of the accommodating portion unit  508  from the closed state to the open state. Specifically, locking between the casing  250 A and the accommodating portion unit  508  is released by moving a latch member locking the accommodating portion unit  508  to the casings  250 A by turning an accommodating portion open solenoid  610  on (S 34 ). Then, the CPU  301  waits for a time t 1  in which sufficient pulling of the accommodating portion open solenoid  610  can be confirmed (S 35 ). After waiting for the time t 1 , the accommodating portion open solenoid  610  is turned off S 36 ). By the above, a flow of the open control after lifter lowering is ended. 
     Thus, in the open control after lifter lowering, in the case where the accommodating portion open button  510  is pressed down, the lifter plate  507  is lowered to the lower-limit position in the accommodating portion main body  506 , and thereafter, the state of the accommodating portion unit  508  is constituted so that the state thereof is switched from the closed state to the open state. 
     Incidentally, depending on a detection range of the bottom position sensor  604 , it would be considered that the state of the bottom position sensor  604  becomes the ON state before the lifter plate  507  contacts the bottom portion of the accommodating portion main body  506 . In this case, the drive of the lifter motor M 500  is stopped by providing a slight time after the state of the bottom position sensor  604  becomes the ON state, so that the lifter plate  507  stops in a state in which the lifter plate  507  is supported by the bottom portion of the accommodating portion main body  506 . On the other hand, a period from the time when the state of the bottom position sensor  604  becomes the ON state until the drive of the lifter motor M 500  stops is short, and therefore, a process in which the state of the accommodating portion unit  508  is changed to the open state may also be started at the time when the state of the bottom position sensor  604  becomes the ON state. That is, in  FIGS. 9 , S 33  and S 34  may also be changed to each other. Even when such a constitution is employed, the lifter plate  507  can be expected to become the state of contacting the bottom portion of the accommodating portion main body  506  until the accommodating portion unit  508  is drawn out, so that an advantage such that durability of the option feeder  250  is improved is achieved. 
     Mode Switching Method of Accommodating Portion Open Control 
     Next, a method of switching mode setting of the accommodating portion open control will be described. In this embodiment, a service person (or the user him(her)self) is capable of switching the mode setting of the accommodating portion open control through the display operation portion  310 . 
       FIG. 10  is a schematic view showing a mode switching screen for changing the mode setting of the accommodating portion open control in the display connect operation portion  310 . On the mode switching screen, a normal mode bottom  701  showing the normal open mode and an “open after lifter lowering” bottom  702  showing the open mode after lifter lowering are displayed as selectable bottoms. Incidentally, when each of the modes is selected, the selected mode bottom (in this embodiment, the “open after lifter lowering” bottom  702 ) is highlighted in black as shown in  FIG. 10 . When an end bottom  703  is pressed down in a state in which either one of the bottoms is selected, information on mode setting is stored in the RAM  303 , so that the mode setting of the accommodating portion open control is completed. 
     Incidentally, as regards the switching method of the accommodating portion open mode, the display operation portion  310  may also be directly connected to the option feeder  250  (not as a value interface of entirety of the image forming apparatus). Further, a constitution in which the mode switching of the accommodating portion open control can be made by input from an information processing terminal (personal computer, smartphone or the like) connected to a network through the external I/F  309  may also be employed. 
     Further, in place of the switching method through the screen display, for example, a toggle switch is provided on the option feeder  250  and depending on the position of this toggle switch, the normal open mode and the open mode after lifter lowering may also be switched to each other. 
     Embodiment 2 
     An embodiment 2 will be described. This embodiment is different from the embodiment 1 in that the mode switching of the accommodating portion open control in the option feeder is automatically performed. In the following, constituent elements represented by reference numerals or symbols common to the embodiments 1 and 2 substantially have the same constitutions and functions as those described in the embodiment 1. 
     In this embodiment, as a default, the normal open mode is set. In a state in which the normal open mode is not, for example, when impact more than assumption is exerted such that the user vigorously stacks a large amount of the sheet bundle on the lifter plate  507  at one time, there is a possibility that an over load acts on constituent elements of the lifting mechanism  530  including the supporting member  531   b  and the like. Therefore, in this embodiment, in the operation in the normal open mode, a magnitude of the load exerted on the lifting mechanism  530  is monitored, and in the case where the CPU  301  discriminated that the load (overload) which is a threshold or more is exerted on the lifting mechanism  530 , the open mode after lifter lowering is automatically set. 
     In this embodiment, as a load detecting means for detecting the magnitude of the load exerted on the lifting mechanism  530 , a lifter motor over current detecting sensor  609  ( FIG. 3 ) which is an ammeter for measuring a current value of the lifter motor M 500 . The lifter motor overcurrent detecting sensor  609  is connected to the accommodating portion controller  311 . The CPU  301  acquires the value of the current, flowing through the lifter motor M 500 , measured by the lifter motor over current detecting sensor  609  through the accommodating portion controller  311 . 
       FIG. 11  is a time-series chart showing a driving state of the lifter motor M 500 , the current value measured by the lifter motor overcurrent detecting sensor  609 , discrimination of the overcurrent of the lifter motor M 500 , and accommodating portion open mode setting. When the lifter motor M 500  is in the driven state, the current value starts to increase toward a set current value as a target value. At this time, as the mode setting of the accommodating portion open control, the normal open mode is set. 
     When the user supplies the large amount of the sheets at one time in this state, a relatively large load is exerted on the lifter motor M 500  through the lifting mechanism  530 . This load acts in a direction in which a rotational speed of the lifter motor M 500  is made faster than a target value and therefore, the current value of the lifter motor M 500  temporarily increases. The CPU  301  grasps this phenomenon that the current value of the lifter motor M 500  temporarily increases and thus makes the overcurrent discrimination of the lifter motor M 500 . That is, when the current value of the lifter motor M 500  exceeds a preset reference value (overcurrent limit), the CPU  301  discriminates that the overcurrent flowed through the lifter motor M 500 . Then, the CPU  301  automatically switches the mode setting of the accommodating portion open control to the open mode after lifter lowering (second mode) in place of the normal open mode (first mode), and then stores the mode switching in the RAM  303 . 
     By this, in subsequent and later accommodating portion open control, the open mode after lifter lowering is executed, so that the accommodating portion unit  508  is opened in a state in which the lifter plate  507  is lowered to the lower-limit position of the accommodating portion main body  506 . Accordingly, even when the user supplies the large amount of the sheets at one time, exertion of the large load on the lifting mechanism  530  is prevented, so that the durability of the option feeder  250  can be improved. On the other hand, in the case of users who do not use the sheets in a manner such that the large amount of the sheets are supplied at one time, the normal open mode is continued, and therefore, a state in which convenience during the sheet supply is high is maintained. Accordingly, also by this embodiment, compatibility between improvement in convenience during the sheet supply and improvement in durability can be realized. 
     Incidentally, as regards automatic switching timing of the accommodating portion open mode, hysteresis such that the number of times of cumulative detection of the overcurrent is stored in RAM  303  and the accommodating portion open mode is switched to the open mode after lifter lowering when this number of times of cumulative detection of the overcurrent exceeds a predetermined threshold may also be provided. 
     Further, in this embodiment, it is assumed that the overcurrent is detected during the lowering of the lifter plate  507 , but after the lifter plate  507  is stopped at the supply position or the like, detection that a current which is a reference value or more flowed through the lifter motor M 500  may also be made. That is, when the user supplies the large amount of the sheets at one time in the state in which the lifter plate  507  is at rest, it would be considered that the lifter motor M 500  rotates although the CPU  301  provides no instruction. In this case, the lifter motor M 500  function as a generator and utilizing that the current flows, the CPU  301  discriminates that a high load is exerted on the lifting mechanism  530  on the basis of the current value measured by the lifter motor overcurrent detecting sensor  609 , and then sets the open mode after lifter lowering. 
     Further, a load detecting means for detecting that the overload was exerted on the constituent elements of the lifting mechanism  530 , such as the supporting members  530   b  and the like is limited to a means for detecting the mode current. For example, the supporting member  531   b  is provided with a strain gauge, and then an output value of the strain gauge is compared with a reference value, so that whether or not the overload is exerted may also be discriminated. 
     Further, in this embodiment, description was made that the mode switching of the accommodating portion open control is automatically made when the overload is detected, but the mode switching may also be presented to the user through the display operation portion  310  when the overload is detected. Further, in the case where the mode switching of the accommodating portion open control is automatically made when the overload is detected, the mode switching may also be notified to the user through the display operation portion  310 . 
     Summary of Embodiments 
     In the embodiments 1 and 2 and their modified embodiments which are described above, as the modes of the accommodating portion open control carried out when the accommodating portion open button  510  is pressed down, the two modes consisting of the normal open mode and the open mode after lifter lowering are prepared. In the operation in the normal open mode, irrespective of whether or not the lifter plate  507  is in the lower-limit position in the accommodating portion main body  506 , a process in which the accommodating portion unit  508  is put in the open state by the accommodating portion open solenoid  610  is carried out (S 21  to S 23  of  FIG. 8 ). On the other hand, in the operation in the open mode after lifter lowering, after the lifter plate  507  is lowered until the bottom position sensor  604  detects the lifter plate  507 , a process in which the accommodating portion unit  508  is put in the open state by the accommodating portion open solenoid  610  is carried out (S 34  to S 36  of  FIG. 9 ). In other words, the sheet feeding device includes a control means for controlling the open/close means and the lifting and lowering means by either one of the operations in the plurality of the modes including the first mode and the second mode. In the operation in the first mode, in the case where the CPU receives the open instruction from an open instruction means, the accommodating portion is is put in the open state by the open/close means irrespective of whether or not the lifter plate is in the lower-limit position. In the operation in the second mode, in the case where the CPU receives the open instruction from the open instruction means, after the lifter plate is lowered until the lower limit detecting means detects the lifter plate, the accommodating portion is put in the open state by the open/close means. 
     By this constitution, the mode is switched depending on the use method of the user, so that the compatibility between the convenience during the sheet supply and the durability can be realized. That is, in the case of users who do not desire that the users do not supply the sheet bundle in a large amount at one time, the sheet supply is made easy by setting the first mode. On the other hand, in the case of users who desire that the users supply the sheet bundle in the large amount at one time, by setting the second mode, the load when the sheets are stacked on the lifter plate is distributed to the accommodating portion, so that the durability of the device can be improved. 
     Incidentally, in the above-described embodiments, as an example of the sheet feeding device, the option feeder  250  connected to the side of the printer main assembly of the image forming apparatus was described as an example, but the present invention is also applicable to other sheet feeding devices. For example, a sheet feeding device incorporated into a lower portion of the printer main assembly. 
     Other Embodiments 
     The present invention is also capable of being realized in a process in which a program for realizing one or more functions in the above-described embodiments is supplied to a system or an apparatus through a network or a recording medium and in which one or more processor in a computer of the system and the apparatus reads and executes the program. Further, the present invention is also capable of being realized by a circuit (for example, ASIC) for realizing one or more function. 
     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. 2019-218302 filed on Dec. 2, 2019, which is hereby incorporated by reference herein in its entirety.