Patent Publication Number: US-9411302-B2

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2014-102318, filed on May 16, 2014, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects of the disclosure relate to an electrophotographic image forming apparatus. 
     BACKGROUND 
     A known image forming apparatus has a casing, a drawer unit including a drum unit and being detachably attached to the casing, and a conveyor unit for conveying a sheet. The conveyor unit is disposed at a position shifted from the drawer unit in a direction in which the drawer unit is attached and removed. 
     The drum unit includes at least a photosensitive drum. The drawer unit includes two or more drum units. 
     The conveyor unit includes a contact member, an elastic member, and a frame. The contact member is a member contacting a sheet to be fed, such as a roller and a separation pad. The elastic member exerts an elastic force pressing the contact member against the sheet. The frame receives the elastic force directly or indirectly. 
     SUMMARY 
     The frame is a strength member shaped like a beam extending in a width direction perpendicular to both of a sheet feed direction and a sheet thickness direction. Thus, if the frame has small bending stiffness, the frame may become greatly deformed upon receipt of the elastic force. 
     When the frame becomes greatly deformed, the elastic force pressing the contact member against the sheet becomes small, and improper sheet feeding easily occurs. 
     Illustrative aspects of the disclosure provide an image forming apparatus configured to reduce a potential of a frame from becoming greatly deformed and minimize improper sheet feeding due to deformation of the frame. 
     According to an Aspect 
     of the disclosure, an image forming apparatus includes a sheet receiving portion configured to receive a sheet, a drum unit including a photosensitive drum configured to carry a developer image to be transferred onto the sheet, a contact member configured to contact the sheet fed from the sheet receiving portion toward the photosensitive drum, a roller configured to contact the contact member and to rotate in contact with the sheet to apply a feeding force to the sheet, an elastic member configured to exert an elastic force to press the contact member toward the sheet, and a frame supporting the roller. The frame receives the elastic force from the elastic member via the roller and the contact member when the roller is in contact with the contact member. The frame extends in a width direction perpendicular to a sheet feed direction and a sheet thickness direction. The drum unit is configured to move between a first position in which an image is formable and a second position shifted from the first position in a moving direction of the drum unit. The drum unit includes a restriction portion configured to restrict the frame from moving in a direction perpendicular to the width direction, the restriction portion being disposed on a side of the frame opposite to the elastic member. 
     With this structure, the potential of the frame from becoming greatly deformed can be reduced. Thus, improper sheet feeding due to deformation of the frame can be minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the following description taken in connection with the accompanying drawings, like reference numerals being used for like corresponding parts in the various drawings. 
         FIG. 1  is a sectional view of an image forming apparatus according to an illustrative embodiment. 
         FIG. 2  is a fragmentary sectional view of the image forming apparatus according to the illustrative embodiment. 
         FIG. 3  is a perspective view of a drum unit according to the illustrative embodiment. 
         FIG. 4  is an enlarged view of a first feeder mechanism and a second feeder mechanism according to the illustrative embodiment. 
         FIG. 5  is a perspective view of a first sheet supply frame according to the illustrative embodiment. 
         FIG. 6  is a perspective view of a second sheet supply frame according to the illustrative embodiment. 
         FIG. 7A  is a perspective view illustrating positional relationship between the second sheet supply frame and a restriction portion. 
         FIG. 7B  is a perspective view of the restriction portion. 
         FIG. 8  illustrates an arrangement of the restriction portion, a separation pad, a first support portion and a second support portion. 
         FIG. 9  illustrates an arrangement of the restriction portion, the separation pad, the first support portion and the second support portion. 
         FIG. 10  illustrates a sheet is fed from the second sheet supply frame. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative embodiment of the disclosure will be described with reference to the following drawings. 
     In the following description, the expressions “front”, “rear”, “upper or top”, “lower or bottom”, “right”, and “left” are used to define the various parts when an image forming apparatus  1  is disposed in an orientation in which it is intended to be used. In the embodiment, the image forming apparatus  1  is a color type image forming apparatus configured to form a color image. 
     For members or portions designated by numerals, at least one is provided unless “plural” or “two or more” is specifically stated otherwise. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  includes, in a casing  3 , an electrophotographic image forming unit  5  configured to form an image on a recording medium, e.g., a sheet. The image forming unit  5  includes a plurality of developing cartridges  7 , a plurality of photosensitive drums  8 , a plurality of chargers  8 A, a light exposure unit  9 , and a fixing unit  11 . 
     The developing cartridges  7  each include a storing portion  7 A in which a developer is stored. Each developing cartridge  7  or each storing portion  7 A contains a different color developer (for example, one of yellow, magenta, cyan, and black). 
     The photosensitive drums  8  and the chargers  8 A are provided in the same number as the developing cartridges  7 . Each of the chargers  8 A is configured to charge a corresponding one of the photosensitive drums  8 . The light exposure unit  9  is configured to expose each charged photosensitive drum  8  to form an electrostatic latent image thereon. 
     When a developer is supplied to each photosensitive drum  8  having the electrostatic latent image formed thereon, a developer image corresponding to the electrostatic latent image is carried on an outer surface of each photosensitive drum  8 . A belt  13  is a strip-shaped endless belt, extends between a roller  13 B and a roller  13 C, which are spaced apart from each other, and is configured to rotate. The belt  13  is configured to feed a sheet, on which an image is being formed, toward the fixing unit  11 . 
     Transfer members  15  are disposed in one-to-one correspondence with the photosensitive drums  8  such that the belt  13  is sandwiched between each of the transfer members  15  and a corresponding one of the photosensitive drums  8 . Each of the transfer members  15  is configured to transfer a developer image carried on a corresponding one of the photosensitive drums  8  to a sheet. Thus, developer images, which are carried on the corresponding photosensitive drums  8 , are sequentially transferred and overlaid one over the other on a sheet conveyed on the belt  13 . 
     The fixing unit  11  is configured to fix developer images transferred onto a sheet by heating the developer images through the application of pressure. A sheet having an image formed thereon is ejected by an ejection roller  3 A onto an ejection tray  3 B disposed in an upper portion of the casing  3 . 
     A first feeder mechanism  17  and a second feeder mechanism  19  are disposed upstream from the belt  13  in a sheet feed direction. The first feeder mechanism  17  is configured to feed sheets one by one from a sheet supply tray  21  toward the image forming unit  5 . 
     The sheet supply tray  21  is a sheet receiving portion disposed below a drum unit  25  in a vertical direction and configured to receive sheets. The sheet supply tray  21  according to the embodiment is detachably attached to a main body. 
     The main body refers to portions of the image forming apparatus  1 , such as the casing  3  and left and right main frames (not illustrated), which cannot be disassembled by a user. The main frames are strength members to which the image forming unit  5  is assembled. The main frames are board-shaped and disposed on left and right sides of the drum unit  25  in a horizontal direction, respectively, such that the drum unit  25  is sandwiched therebetween. 
     As illustrated in  FIG. 2 , the second feeder mechanism  19  is configured to feed sheets one by one from a multi-purpose tray  23  toward the image forming unit  5 . The multi-purpose tray  23  is a sheet receiving portion configured to receive a sheet temporarily for forming an image on the sheet different from a sheet received on the sheet supply tray  21 . 
     The multi-purpose tray  23  according to the embodiment is disposed to a front cover  3 D for opening and closing an opening  3 C formed at a front side of the casing  3 . The front cover  3 D is movable between a position to open the opening  3  ( FIG. 1 ) and a position to close the opening ( FIG. 2 ). 
     The multi-purpose tray  23  is movable independently relative to the front cover  3 D between a position to open the opening  3 C and a position to close the opening  3 C. The multi-purpose tray  23  is available when in the position to open the opening  3 C. 
     The developing cartridges  7 , the photosensitive drums  8  and the chargers  8 A are attached to a drawer  25 A illustrated in  FIG. 3 . The developing cartridges  7  are detachably attachable to the drawer  25 A. In other words, the drawer  25 A constitutes a support member supporting each of the developing cartridges  7  detachably. 
     The photosensitive drums  8  and the chargers  8 A are non-detachable relative to the drawer  25 A except for repair. In short, the user can detach or attach the developing cartridges  7  relative to the drawer  25 A, but cannot detach or attach the photosensitive drums  8  and the chargers  8 A relative to the drawer  25 A. 
     The drawer  25 A is a member shaped like a box opening upward, and is movably assembled to the main body. Specifically, the drawer  25 A is movable between a first position ( FIG. 1 ) where an image is formable and a second position ( FIG. 2 ) where the drawer is moved from the first position. 
     Thus, only by moving the drawer  25 A relative to the main body, the user can move the developing cartridges  7 , the photosensitive drums  8  and the chargers  8 A simultaneously relative to the main body. Hereinafter, units unified by the drawer  25 A are collectively referred to as a drum unit  25 . 
     The drum unit  25  (the drawer  25 A) according to the embodiment is detachably attachable relative to the main body. As illustrated in  FIG. 2 , when the front cover  3 D is open and the opening  3 C is open, the user can attach or remove the drum unit  25  through the opening  3 C. 
     The first position is a position where image formation on a sheet is reliably performed. Specifically, the photosensitive drums  8  assembled to the drawer  25 A are located in regular positions relative to the transfer members  15  assembled to the main body. 
     As illustrated in  FIG. 4 , the first feeder mechanism  17  includes a pickup roller  17 A, a separation roller  17 B, and a separation pad  17 C. The pickup roller  17 A feeds at least one of sheets received in the sheet supply tray  21  toward the image forming unit  5  or the photosensitive drums  8 . 
     The separation pad  17 C functions as a contact member that contacts a sheet fed toward the photosensitive drums  8  to apply feeding resistance to the sheet. The separation roller  17 B is a roller disposed facing the separation pad  17 C and rotates in contact with the sheet to give a feeding force to the sheet. 
     With this structure, when two or more sheets are fed by the pickup roller  17 A, a sheet of the two or more sheets just contacting the separation roller  17 B is fed toward the photosensitive drums  8 , and the remaining sheets undergo the feeding resistance directly or indirectly from the separation pad  17 C and stop. 
     The separation roller  17 B is assembled to a first sheet supply frame  18 A via a drive shaft (not illustrated). The first sheet supply frame  18 A is a strength member shaped like a beam extending in the width direction and left and right ends of the first sheet supply frame  18 A in the extending direction are fixed to the main frames, respectively. 
     The width direction refers to a direction perpendicular to the sheet feed direction and a sheet thickness direction. In this embodiment, the width direction agrees with a left-right direction of the image forming apparatus  1 . The drive shaft extends in the width direction, supports the separation roller  17 B, and transmits a rotation force supplied from an electric motor (not illustrated) to the separation roller  17 B. 
     The pickup roller  17 A is pivotally assembled to the drive shaft via a first roller holder  17 D, and receives a rotation force from the drive shaft via a rotation force transmitting portion (not illustrated) such as gears. 
     The separation pad  17 C is movable close to or away from the separation roller  17 B and pressed against a sheet by an elastic force of a spring (not illustrated). In short, the spring exerts the elastic force to move the separation pad  17 C to the separation roller  17 B. The separation pad  17 C and the spring are assembled to the sheet supply tray  21 . 
     As illustrated in  FIG. 5 , a pair of registration rollers  20 A,  20 B, and an auger  20 C are assembled in the first sheet supply frame  18 A. The registration rollers  20 A,  20 B exert the following registration function. 
     In short, the registration rollers  20 A,  20 B, which stop rotating, contact a sheet fed from the first feeder mechanism  17  or the second feeder mechanism  19  to temporarily stop feeding of the sheet. 
     Then, the registration rollers  20 A,  20 B resume rotating and feed the sheet. The sheet is corrected such that the front end is oriented perpendicular to the sheet feed direction, and then enters the image forming unit  5  at a specified time. 
     The outer surface of the registration roller  20 A is provided with a covering portion made of fluorine resin. The outer surface of the registration roller  20 A is configured to slidingly contact a frictional member  20 D illustrated in  FIG. 4 . 
     Thus, when the registration roller  20 A rotates and the outer surface of the registration roller  20 A slides on the frictional member  20 D, the registration roller  20 A becomes charged by friction. Static electricity builds up on the registration roller  20 A, causing a suction force thereon so that foreign matter clinging to the sheet, such as paper dust particles, becomes adhered to the charged registration roller  20 A. 
     The paper dust adhered to the registration roller  20 A is scraped by the frictional member  20 D and transferred by the auger  20 C to a paper dust collecting portion, which is not illustrated. The auger  20 C is a kind of liquid pump, e.g., a screw pump. 
     A movable member  22  is disposed downstream of the registration roller  20 A,  20 B and upstream of the image forming unit  5  in the sheet feed direction. The movable member  22  is a member that moves in contact with a sheet fed thereto for detecting presence or absence of a sheet. 
     Specifically, as illustrated in  FIG. 4 , the movable member  22  is a pivotable member such that one end is pivotally supported by the first sheet supply frame  18 A and the other end is located such that the other end can contact a sheet to be fed. A shielding plate (not illustrated) is disposed on a pivot of the movable member  22  such that the shielding plate is movable together with the movable member  22 . 
     The shielding plate moves between a light shielding position where the shielding plate shields light emitting from a photo interrupter and a position shifted from the light shielding position. Detection as to presence or absence of a sheet is made based on whether a light receiving portion of the photo interrupter receives the light. The movable member  22 , the shielding plate, and the photo interrupter are collectively referred to as a post-registration sensor. 
     As illustrated in  FIG. 4 , the second feeder mechanism  19  includes a pickup roller  19 A, a separation roller  19 B and a separation pad  19 C. The pickup roller  19 A feeds at least one of sheets received in the multi-purpose tray  23  toward the image forming unit  5  or the photosensitive drums  8 . 
     The separation pad  19 C functions as a contact member that contacts a sheet fed to apply feeding resistance to the sheet. The separation roller  19 B is disposed facing the separation pad  19 C and rotates in contact with the sheet to give a feeding force to the sheet. 
     With this structure, when two or more sheets are fed by the pickup roller  19 A, a sheet of the two or more sheets just contacting the separation roller  19 B is fed toward the photosensitive drums  8 , and the remaining sheets undergo the feeding resistance directly or indirectly from the separation pad  19 C and stop. 
     The separation roller  19 B is assembled in a second sheet supply frame  18 B via a drive shaft  19 E illustrated in  FIG. 6 . The second sheet supply frame  18 B is a strength member shaped like a beam extending in the width direction and left and right ends of the second sheet supply frame  18 B in the extending direction are fixed to the first sheet supply frame  18 A. 
     Thus, in the embodiment, the second feeder mechanism  19  (the second sheet supply frame  18 B) and the first feeder mechanism  17  (the first sheet supply frame  18 A) are unified and assembled to the main frames as one sheet supply unit. 
     The drive shaft  19 E extends in the width direction, supports the separation roller  19 B, and transmits a rotation force supplied from the electric motor (not illustrated) to the separation roller  19 B. The second sheet supply frame  18 B includes a first support portion  18 C and a second support portion  18 D, which are disposed to left and right ends of the separation roller  19 B in an axial direction thereof, respectively. 
     The first support portion  18 C and the second support portion  18 D are sliding bearing members rotatably supporting the drive shaft  19 E. In short, the separation roller  19 B is supported via the drive shaft  19 E to the second sheet supply frame  18 B by the first support portion  18 C and the second support portion  18 D. 
     The pickup roller  19 A is pivotally assembled to the drive shaft  19 E via a second roller holder  19 F, and receives a rotation force from the drive shaft  19 E via a rotation force transmitting portion (not illustrated) such as gears. 
     As illustrated in  FIG. 4 , the separation pad  19 C is movable close to or away from the separation roller  19 B. A spring  19 D is an elastic member that exerts an elastic force to press the separation pad  19 C toward the sheet. In short, the spring  19 D exerts elastic force F to move the separation pad  19 C to the separation roller  19 B. 
     Thus, the second sheet supply frame  18 B receives the elastic force F via the separation pad  19 C, the separation pad  19 B and the drive shaft  19 E. In short, a center portion of the second sheet supply frame  18 B in the extending direction is pressed by the elastic force F from the lower side toward the upper side. 
     The spring  19 D is assembled in the first sheet supply frame  18 A via a mounting frame, not illustrated. Thus, reaction of the elastic force F is received at the first sheet supply frame  18 A. The spring  19 D according to the embodiment is a torsion coil spring having a coil portion. A central axis of the coil portion agrees with a central axis of the separation pad  19 C. 
     As illustrated in  FIG. 4 , the second sheet supply frame  18 B includes a guide portion  18 E. The guide portion  18 E guides a sheet fed from the sheet supply tray  21  or the multi-purpose tray  23  toward the image forming unit  5 . The movable member  22  moves in contact with the sheet guided by the guide portion  18 E. 
     As illustrated in  FIG. 7A , the drum unit  25  (the drawer  25 A) includes a restriction portion  25 B. The restriction portion  25 B restricts the movement of the second sheet supply frame  18 B in a direction perpendicular to a longitudinal direction of the second sheet supply frame  18 B, that is, in a direction of the elastic force F. 
     As illustrated in  FIG. 7B , the restriction portion  25 B is constituted by a protrusion protruding from the drum unit  25  (the drawer  25 A) toward the second sheet supply frame  18 B when the drum unit  25  is in the first position. 
     The restriction portion  25 B according to the embodiment restricts the second sheet supply frame  18 B from moving by more than a predetermined dimension. Specifically, as illustrated in  FIG. 4 , when the drum unit  25  is in the first position, there is a clearance between an end of the restriction portion  25 B and the second sheet supply frame  18 B. 
     Thus, even in a case where the second sheet supply frame  18 B becomes deformed toward the restriction portion  25 B, the second sheet supply frame  18 B contacts the restriction portion  25 B to restrict further deformation of the second sheet supply frame  18 B. In short, the amount of deformation of the second sheet supply frame  18 B is restricted to be lower than or equal to the dimension for the clearance. 
     The restriction portion  25 B is located above the second sheet supply frame  18 B in the vertical direction. The drum unit  25  (the drawer  25 A) has sufficiently high stiffness and mass compared with the second sheet supply frame  18 B. 
     For this reason, the drum unit  25  (the drawer  25 A) is not deformed, nor moved upwardly by a force to deform the second sheet supply frame  18 B, that is, the elastic force F. 
     As illustrated in  FIG. 1 , the restriction portion  25 B is disposed on a side of the frontmost photosensitive drum  81  opposite to the photosensitive drum  82  adjacent to the photosensitive drum  81 . Specifically, the restriction portion  25 B is disposed to one end of the drum unit  25  in a moving direction thereof (toward the opening  3 C in the embodiment). 
     In short, as illustrated in  FIG. 1 , the drum unit  25  includes the photosensitive drums  8  and the photosensitive drums  8  are arranged in a direction perpendicular to axial directions of the respective photosensitive drums  8 , that is, in the moving direction of the drum unit  25  (the front-rear direction in the embodiment). 
     Of the photosensitive drums  8 , a photosensitive drum  8  located at an end in an arrangement direction where the photosensitive drums  8  are arranged is regarded as a most-end photosensitive drum ( 81 , in the embodiment, disposed at the left end of the  FIG. 1 ), and a photosensitive drum  8  adjacent to the most-end photosensitive drum  81  is regarded as an adjacent photosensitive drum ( 82 , in the embodiment, the second one from the left end of  FIG. 1 ). The restriction portion  25 B is disposed on a side of the most-end photosensitive drum  81  opposite to the adjacent photosensitive drum  82 . 
     In the embodiment, as illustrated in  FIG. 8 , an outer dimension W 1  of the restriction portion  25 B of which is parallel to the width direction is greater than an outer dimension W 2  of the separation pad  19 C of which is parallel to the width direction. When the drum unit  25  is in the first position, the following three requirements are satisfied in the embodiment: 
     First, at least a part of the restriction portion  25 B is disposed between a first imaginary plane S 1  and a second imaginary plane S 2  (see  FIG. 8 ). Second, at least a part of the restriction portion  25 B is disposed between a third imaginary plane S 3  and a fourth imaginary plane S 4  (see  FIG. 9 ). Third, the movable member  22  is disposed between a fifth imaginary plane S 5  and a sixth imaginary plane S 6  (see  FIG. 8 ). 
     The first imaginary plane S 1  is an imaginary plane, which is perpendicular to the axial direction of the separation roller  19 B (a direction parallel to the width direction in the embodiment) and includes the first support portion  18 C. The second imaginary plane S 2  is an imaginary plane, which is perpendicular to the width direction and includes the second support portion  18 D. 
     The third imaginary plane S 3  is an imaginary plane, which is perpendicular to the width direction and includes one end of the separation pad  19 C in the width direction. The fourth imaginary plane S 4  is an imaginary plane, which is perpendicular to the width direction and includes the other end of the separation pad  19 C in the width direction. 
     The fifth imaginary plane S 5  is an imaginary plane, which is perpendicular to the width direction and includes one end of the restriction portion  25 B in the width direction. The sixth plane S 6  is an imaginary plane, which is perpendicular to the width direction and includes the other end of the restriction portion  25 B in the width direction. 
     In the embodiment, the drum unit  25  includes the restriction portion  25 B that restricts the second sheet supply frame  18 B from moving in a direction perpendicular to the longitudinal direction. 
     With this structure, as the restriction portion  25 B restricts the deformation of the second sheet supply frame  18 B beyond the specified dimension, the second sheet supply frame  18 B does not become greatly deformed. Thus, improper sheet feeding resulting from the excessive deformation of the second sheet supply frame  18 B can be minimized. 
     The disclosure is effective especially for an image forming apparatus, as in the image forming apparatus  1  according to the embodiment, in which the drum unit  25  moves above the second sheet supply frame  18 B when the drum unit  25  is pulled out of the casing  3 . 
     If the vertical dimension of the second sheet supply frame  18 B is increased unconditionally in order to enhance the stiffness of the second sheet supply frame  18 B, the vertical dimension of the image forming apparatus  1  is increased. 
     In the embodiment, as the restriction portion  25 B of the drum unit  25  restricts the deformation of the second sheet supply frame  18 B, the need to increase the vertical dimension of the second sheet supply frame  18 B can be reduced and improper sheet feeding resulting from the deformation of the second sheet supply frame  18 B can be reduced. 
     In the embodiment, the elastic force F of the spring  19 D acts on the second sheet supply frame  18 B via the first support portion  18 C and the second support portion  18 D. Thus, a portion of the second support portion  18 B corresponding to an area between the first imaginary plane S 1  and the second imaginary plane S 2  may become most greatly deformed. 
     In the embodiment, however, as the restriction portion  25 B is disposed between the first imaginary plane S 1  and the second imaginary plane S 2 , the deformation of the second sheet supply frame  18 B can be reliably restricted. 
     In the embodiment, the elastic force F of the spring  19 D acts on the second sheet supply frame  18 B via the separation pad  19 C. Thus, the second sheet supply frame  18 B may be deformed such that a portion thereof corresponding to a space between the first imaginary plane S 1  and the second imaginary plane S 2  is most greatly deformed. 
     In the embodiment, however, as at least a part of the restriction portion  25 B is disposed between the third imaginary plane S 3  and the fourth imaginary plane S 4 , the deformation of the second sheet supply frame  18 B can be reliably restricted. 
     In the embodiment, the outer dimension W 1  of the restriction portion  25 B of which is parallel to the width direction is greater than the outer dimension W 2  of the separation pad  19 C of which is parallel to the width direction. With this structure, the deformation of the second sheet supply frame  18 B can be reliably restricted. 
     The restriction portion  25 B according to the embodiment is disposed above the second sheet supply frame  18 B in the vertical direction. 
     With this structure, in the embodiment, if the restriction portion  25 B is pressed upward in the vertical direction by the deformation of the second sheet supply frame  18 B, the second sheet supply frame  18 B can be pressed downward in the vertical direction by the gravity acting on the drum unit  25  and thus the deformation of the second sheet supply frame  18 B can be reliably restricted. 
     In the embodiment, as the second sheet supply frame  18 B includes the guide portion  18 E, if the second sheet supply frame  18 B becomes excessively deformed, it is difficult to feed a sheet through a proper sheet feed path. 
     If a sheet is fed through a path shifted from the proper sheet feed path, the movable member  22  cannot be brought in contact with the sheet properly, resulting in failure in detecting presence or absence of the sheet. 
     In short, when the amount of deformation of the second sheet supply frame  18 B is small and the position of the guide portion  18 E is not greatly shifted from the regular position or when the guide portion  18 E is in the regular position, the sheet fed by the guide portion  18 E is fed as illustrated by a solid line in  FIG. 10 . 
     However, if the amount of deformation of the second sheet supply frame  18 B becomes great and the position of the guide portion  18 E is shifted greatly upward from the regular position, the sheet fed by the guide portion  18 E is fed as illustrated by a two-dot chain line in  FIG. 10 . 
     Thus, when the amount of deformation of the second sheet supply frame  18 B becomes great, a trailing end portion of the sheet in the sheet feed direction is separated from the movable member  22  at an early time compared with a case in which the second sheet supply frame  18 B does not become deformed. This will result in failure in detecting the presence or absence of the sheet. 
     In the embodiment, however, as the second sheet supply frame  18 B is restricted from becoming excessively deformed, sheets can be fed through a proper sheet feed path. As the movable member  22  is disposed between the fifth imaginary plane S 5  and the sixth imaginary plane S 6 , the presence or absence of the sheet can be detected. 
     The above embodiment shows, but is not limited to, the restriction portion  25 B restricting the second sheet supply frame  18 B from moving. The restriction portion  25 B may restrict the first sheet supply frame  18 A from moving. 
     The above embodiment shows, but is not limited to, that there is a clearance between the restriction portion  25 B and the second sheet supply frame  18 B. The restriction portion  25 B and the second sheet supply frame  18 B may contact each other with the contact pressure being greater than or equal to zero. 
     The above embodiment shows, but is not limited to, that, when the drum unit  25  is in the first position, at least a part of the restriction portion  25 B is disposed between the first imaginary plane S 1  and the second imaginary plane S 2 . 
     The above embodiment shows, but is not limited to, that, when the drum unit  25  is in the first position, at least a part of the restriction portion  25 B is disposed between the third imaginary plane S 3  and the fourth imaginary plane S 4 . 
     The above embodiment shows, but is not limited to, that, when the drum unit  25  is in the first position, the movable member  22  is disposed between the fifth imaginary plane S 5  and the sixth imaginary plane S 6 . 
     The above embodiment shows, but is not limited to, the separation pad  19 C as a contact member. Instead, a retard roller, a reverse roller, a reverse belt, or a gate roller may be used as a contact member. 
     The above embodiment shows, but is not limited to, the restriction portion  25 B being disposed in a front portion of the drum unit  25  (the drawer  25 A). For example, if the second sheet supply frame  18 B is disposed to a rear portion of the casing  3 , the restriction portion  25 B may be disposed in a rear portion of the drum unit  25  (the drawer  25 A). 
     The embodiment shows, but is not limited to, the image forming apparatus  1  including the photosensitive drums  8  for forming images in color. The disclosure may be applied to an image forming apparatus for forming images in monochrome. 
     The above embodiment shows, but is not limited to, the drum unit  25  being detachably attachable to the main body. The drum unit  25  may only move relative to the main body. 
     While the features herein have been described in connection with various example structures and illustrative aspects, it will be understood by those skilled in the art that other variations and modifications of the structures and aspects described above may be made without departing from the scope of the inventions described herein. Other structures and aspects will be apparent to those skilled in the art from a consideration of the specification or practice of the features disclosed herein. It is intended that the specification and the described examples only are illustrative with the true scope of the inventions being defined by the following claims.