Patent Publication Number: US-11048204-B2

Title: Positioning apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a positioning apparatus that positions a draw-out portion with respect to an apparatus body and an image forming apparatus including the same. 
     Description of the Related Art 
     Generally, in an image forming apparatus such as a printer, a copier, or a multifunctional apparatus, a photosensitive drum and a process unit that acts on the photosensitive drum are integrated as a cartridge, and a cartridge system in which this cartridge is attachable to and detachable from an apparatus body is employed. 
     Conventionally, in Japanese Patent Laid-Open No. 2007-178657, a color laser printer including a drum unit and a body casing to which the drum unit is attachable to and detachable from is proposed. The drum unit is a cartridge in which four drum subunits are supported by a pair of side plates. The body casing includes a standard shaft that a notch portion of the drum unit abuts to position the drum unit in an attached state. In addition, the notch portion of the drum unit is pressed against the standard shaft by being pressed toward the rear side of the apparatus by a pressing mechanism portion. 
     However, the notch portion of the drum unit described in Japanese Patent Laid-Open No. 2007-178657 abuts the standard shaft at two portions, which are an upper edge extending in the horizontal direction and a lower edge extending in the vertical direction. Therefore, a force of pressing the drum unit in the attachment direction does not act on the notch portion. Hence, the drum unit is pressed in the attachment direction by only the pressing mechanism portion, resulting in increase in the size and cost of the pressing mechanism portion. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a positioning apparatus includes an apparatus body, a draw-out portion configured to be drawn out from and attached to the apparatus body, and a positioning mechanism configured to position the draw-out portion at an attachment position with respect to the apparatus body, wherein the positioning mechanism includes a first engaging portion provided in one of the apparatus body and the draw-out portion, a first engaged portion provided in another of the apparatus body and the draw-out portion and configured to determine a position of the draw-out portion in an attachment direction by engaging with the first engaging portion, and wherein the first engaged portion includes an inclined surface that is inclined downward toward a downstream side in the attachment direction and causes a force in the attachment direction to act on the draw-out portion on a basis of a weight of the draw-out portion in a state in which the first engaged portion is engaged with the first engaging 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 an overall perspective view of a printer. 
         FIG. 2  is an overall schematic view of the printer illustrating an inner configuration thereof. 
         FIG. 3A  is a front perspective view of a process cartridge. 
         FIG. 3B  is a rear perspective view of the process cartridge. 
         FIG. 4A  is a front perspective view of a cartridge tray. 
         FIG. 4B  is a rear perspective view of the cartridge tray. 
         FIG. 5A  is a front perspective view of the cartridge tray with respective process cartridges attached thereto. 
         FIG. 5B  is a rear perspective view of the cartridge tray with the respective process cartridges attached thereto. 
         FIG. 6  is a perspective view of a frame structure of a printer body. 
         FIG. 7  is a bottom perspective view of a positioning shaft of the cartridge tray. 
         FIG. 8A  is a section view of the printer illustrating a state in which a positioning shaft on the apparatus body side is engaged with a positioning groove. 
         FIG. 8B  is a section view of the printer illustrating the positioning shaft and the positioning groove in a state in which the cartridge tray is slightly drawn out from an attached state. 
         FIG. 8C  is a section view of the printer illustrating the positioning shaft and the positioning groove in a state in which the cartridge tray is further drawn out from the state of  FIG. 8B . 
         FIG. 8D  is a section view of the printer illustrating a state in which a positioning shaft on the cartridge tray side is engaged with a positioning groove. 
         FIG. 8E  is a section view of the printer illustrating the positioning shaft and the positioning groove in a state in which the cartridge tray is slightly drawn out from the attached state. 
         FIG. 8F  is a section view of the printer illustrating the positioning shaft and the positioning groove in a state in which the cartridge tray is further drawn out from the state of  FIG. 8E . 
         FIG. 9  is a front view of a rib provided on the cartridge tray. 
         FIG. 10  is a section view of the cartridge tray taken along a line A-A of  FIG. 9 . 
         FIG. 11A  is a front perspective view of the process cartridges and the cartridge tray in a state in which a front door is closed. 
         FIG. 11B  is a front perspective view of the process cartridges and the cartridge tray in a state in which the front door is open. 
         FIG. 12A  is a rear perspective view of the process cartridges and the cartridge tray in the state in which the front door is closed. 
         FIG. 12B  is a rear perspective view of the process cartridges and the cartridge tray in the state in which the front door is open. 
         FIG. 13A  is a side view of the process cartridges and the cartridge tray in the state in which the front door is closed. 
         FIG. 13B  is a side view of the process cartridges and the cartridge tray in the state in which the front door is open. 
         FIG. 13C  is a side view of the process cartridges and the cartridge tray in the state in which the front door is open. 
         FIG. 14  is a perspective view of a pull-in apparatus according to a first exemplary embodiment. 
         FIG. 15  is a perspective view of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 16A  is a top view of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 16B  is a side view of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 16C  is a bottom view of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 17  is an exploded view of an arm and a locking member according to the first exemplary embodiment. 
         FIGS. 18A and 18B  are each a diagram for describing an operation of the pull-in apparatus according to the first exemplary embodiment. 
         FIGS. 19A and 19B  are each a diagram for describing an operation of the pull-in apparatus according to the first exemplary embodiment. 
         FIGS. 20A and 20B  are each a diagram for describing an operation of the pull-in apparatus according to the first exemplary embodiment. 
         FIGS. 21A and 21B  are each a diagram for describing an operation of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 22  is a diagram for describing an operation of the pull-in apparatus according to the first exemplary embodiment. 
         FIG. 23  is a top view of a pull-in apparatus according to a second exemplary embodiment. 
         FIG. 24  is a top view of a pull-in apparatus according to a third exemplary embodiment. 
         FIG. 25  is a top view of the pull-in apparatus according to the third exemplary embodiment. 
         FIG. 26  is a top view of the pull-in apparatus according to the third exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Exemplary Embodiment 
     Overall Configuration 
     First, a printer  100  serving as an image forming apparatus according to a first exemplary embodiment is a full-color laser beam printer of an electrophotographic system. As illustrated in  FIG. 1 , the printer  100  includes an apparatus body  100 A and a front door  31  supported to be openable and closeable with respect to the apparatus body  100 A. To be noted, for description of the printer  100 , directions are defined as follows. That is, the side of the printer  100  on which the front door  31  is provided will be referred to as the front side, the opposite side thereto will be referred to as the rear side, and a direction from the rear side toward the front side or from the front side toward the rear side will be referred to as a front-rear direction. 
     In addition, the left side, the right side, the upper side, and the lower side are defined with a state in which the printer  100  is viewed from the front side as a standard. The left side and the right side will be also respectively referred to as the non-driving side and the driving side. Further, a direction from the right side toward the left side or from the left side toward the right side will be referred to as a left-right direction, and a direction from the upper side toward the lower side or from the lower side toward the upper side will be referred to as an up-down direction. 
     As illustrated in  FIG. 2 , the printer  100  includes an image forming unit  10  that forms an image on a sheet S, a sheet feeding portion  18 , a fixing unit  23 , a discharge roller pair  24 , and a controller  200 . The printer  100  is capable of forming a full-color image or a monochromatic image on a sheet-shaped recording medium, which will be hereinafter referred to as a sheet S, on the basis of an electric image signal output from an external host apparatus  400  and input to the controller  200  via an interface portion  300 . The external host apparatus  400  is, for example, a personal computer, an image reader, or a facsimile machine. 
     The controller  200  controls an electrophotographic image formation process of the printer  100 , and communicates various electric information with the external host apparatus  400 . In addition, the controller  200  performs processing of electric information input from various process devices and sensors, processing of command signals to the various process devices, predetermined initial sequence control, sequence control of a predetermined image formation process, and so forth. 
     The sheet feeding portion  18  is provided in a lower portion of the printer  100 , and includes a cassette  19  that accommodates the sheet S, an inner plate  21  that supports the sheet S and is capable of ascending and descending, a pickup roller  20   a , and a separation roller pair  20   b . The cassette  19  is formed to be capable of being drawn out to the front side from the apparatus body  100 A and being attached to the apparatus body  100 A from the front side. The sheet S supported on the inner plate  21  is fed by the pickup roller  20   a . When a plurality of sheets S are fed at once, one sheet S is separated and fed by the separation roller pair  20   b . To be noted, a torque limiter system or a retard roller system may be applied to the separation roller pair  20   b , and a separation pad may be used instead of one of the separation roller pair  20   b.    
     The fixing unit  23  includes a fixing film  23   a  configured to be heated by a heater, and a pressurizing roller  23   b  that is in pressure contact with the fixing film  23   a , and a fixing nip Q is formed by the fixing film  23   a  and the pressurizing roller  23   b . The discharge roller pair  24  includes a discharge driving roller  24   a  and a discharge driven roller  24   b  that is rotationally driven in accordance with the discharge driving roller  24   a.    
     The image forming unit  10  serving as an image forming portion includes a cartridge tray  40 , four process cartridges PPY, PPM, PPC, and PPK, a scanner unit  11 , a transfer unit  12 , and a cleaning unit  26 . The process cartridges PPY, PPM, PPC, and PPK will be also collectively referred to as process cartridges PP. The transfer unit  12  includes a driving roller  14 , an auxiliary roller  15 , a tension roller  16 , and an intermediate transfer belt  13 . The intermediate transfer belt  13  is stretched over the driving roller  14 , the auxiliary roller  15 , and the tension roller  16 , is formed from a dielectric material, and is flexible. 
     Primary transfer rollers  17 Y,  17 M,  17 C, and  17 K respectively opposing photosensitive drums of the process cartridges PPY, PPM, PPC, and PPK are provided in a space enclosed by the intermediate transfer belt  13 . A secondary transfer roller  27  is provided opposite to the driving roller  14  with the intermediate transfer belt  13  interposed therebetween. A secondary transfer nip T 2  is formed by the intermediate transfer belt  13  and the secondary transfer roller  27 . 
     The four process cartridges PPY, PPM, PPC, and PPK respectively form toner images of four colors of yellow, magenta, cyan, and black. Y, M, C, and K respectively represent yellow, magenta, cyan, and black. To be noted, the four process cartridges PPY, PPM, PPC, and PPK have the same configuration except for the image to be formed. Therefore, only the configuration and image formation process of the process cartridge PPY will be described, and description of the process cartridges PPM, PPC, and PPK will be omitted. 
     As illustrated in  FIGS. 2 to 3B , the process cartridge PPY is a unit in which a drum unit OP and a developing unit DP are integrated. The drum unit OP as a unit includes a photosensitive drum  1  serving as a photosensitive member capable of bearing a toner image. The developing unit DP as a unit includes a developing roller  3  that develops a latent image formed on the photosensitive drum  1  into a toner image, and an accommodating portion  3   b  that accommodates a developer. A drum coupling  1   c  and a developing coupling  3   c  are respectively provided on the driving side, that is, the right side of the photosensitive drum  1  and the developing roller  3  in the longitudinal direction, and drive is transmitted thereto from an unillustrated drive source of the apparatus body  100 A. In addition, a contact  2  is provided on the non-driving side, that is, the left side of the developing roller  3  in the longitudinal direction, and a developing bias is applied to the contact  2  in contact with a contact  38  provided in the apparatus body  100 A as illustrated in  FIG. 12B . A contact  1   b  for connecting to the ground potential is provided on the non-driving side of the photosensitive drum  1  in the longitudinal direction. 
     The process cartridges PPY, PPM, PPC, and PPK are held by the cartridge tray  40 , and a user can access the cartridge tray  40  by opening the front door  31 . Further, the user can replace the process cartridges PPY, PPM, PPC, and PPK by drawing out the cartridge tray  40  to the front side. 
     Image Forming Operation 
     Next, an image forming operation of the printer  100  configured in this manner will be described. When the controller  200  of the printer  100  receives a job signal from the interface portion  300 , an unillustrated developing separation mechanism provided in the apparatus body  100 A moves in the front-rear direction. The developing separation mechanism causes the developing roller  3  to abut the photosensitive drum  1 . 
     To be noted, in a job in which a monochromatic image is formed, only the photosensitive drum of the process cartridge PPK abuts the developing roller, and in a job in which a full-color image is formed, the photosensitive drums of the process cartridges PPY, PPM, PPC, and PPK abut respective developing rollers. Then, the photosensitive drums, the developing rollers, and the intermediate transfer belt  13  are driven by an unillustrated drive source. 
     The scanner unit  11  radiates laser light corresponding to an image signal onto the photosensitive drum  1  of the process cartridge PPY. In this case, the surface of the photosensitive drum  1  is uniformly charged to a predetermined polarity and predetermined potential in advance by a charging roller  5 , and an electrostatic latent image is formed thereon as a result of being irradiated by the laser light from the scanner unit  11 . The electrostatic latent image formed on the photosensitive drum  1  is developed by the developing roller  3 , and thus a yellow toner image is formed on the photosensitive drum  1 . 
     To be noted, a light guide  57  illustrated in  FIG. 5B  serving as a pre-exposing portion is provided in the cartridge tray  40 . The light guide  57  is formed from, for example, transparent acrylic resin or the like. Before charging the surface of the photosensitive drum  1  by the charging roller  5 , light is emitted from an unillustrated light source, and is radiated onto the surface of the photosensitive drum  1  in a state of being uniformly diffused in the longitudinal direction by the light guide  57 . As a result of this, the potential of the surface of the photosensitive drum  1  is stabilized, and thus a good toner image can be formed. 
     Similarly, the laser light is also radiated onto the photosensitive drums of the process cartridges PPM, PPC, and PPK from the scanner unit  11 , and toner images of magenta, cyan, and black are formed on the respective photosensitive drums. The toner images of respective colors formed on the respective photosensitive drums are transferred onto the intermediate transfer belt  13  by primary transfer bias applied to the primary transfer rollers  17 Y,  17 M,  17 C, and  17 K. The full-color toner image transferred onto the intermediate transfer belt  13  is conveyed to the secondary transfer nip T 2  by the intermediate transfer belt  13  rotated by the driving roller  14 . To be noted, the image formation process of each color is performed at such a timing that each toner image is superimposed on an upstream toner image that has been already transferred onto the intermediate transfer belt  13  through primary transfer. 
     The skew of the sheet S fed out by the sheet feeding portion  18  is corrected by the registration roller pair  22  in parallel with this image formation process. Further, the registration roller pair  22  conveys the sheet S toward the secondary transfer roller  27  at a timing matching conveyance of the toner image on the intermediate transfer belt  13 . The full-color toner image on the intermediate transfer belt  13  is transferred onto the sheet S at the secondary transfer nip T 2  by a secondary transfer bias applied to the secondary transfer roller  27 . In addition, after the transfer of the toner image, toner remaining on the surface of the intermediate transfer belt  13  is removed by the cleaning unit  26 , and is collected into an unillustrated waste toner collection container. 
     The sheet S onto which the toner image has been transferred is subjected to predetermined heat and pressure in the fixing nip Q of the fixing unit  23 , thus the toner melts and then adheres to the sheet S, and thereby an image is fixed to the sheet S. The sheet S having passed through the fixing unit  23  is discharged onto a discharge tray  25  by the discharge roller pair  24 . 
     Cartridge Tray 
     Next, a configuration of the cartridge tray  40  serving as a draw-out portion will be described. As illustrated in  FIGS. 4A and 4B , the cartridge tray  40  includes a tray side plates  41 L and  41 R arranged in the left-right direction with an interval therebetween, coupling members  42 ,  43 ,  44 ,  45 , and  46  that couple the tray side plates  41 L and  41 R to each other, and guide members  47 L and  47 R. To be noted, in the description below, a pair of members respectively provided on the left side and the right side will be distinguished by adding “L” or “R” to the end of the reference sign. 
     The coupling members  42  to  46  are formed from a resin material, and are arranged in this order from the front side to the rear side. The light guide  57  described above is provided on each of the coupling members  42  to  45 . The tray side plates  41 L and  41 R are formed from a metal material, the guide member  47 L is supported by the tray side plate  41 L, and the guide member  47 R is supported by the tray side plate  41 R. The guide members  47 L and  47 R are respectively slidable on a plurality of rollers  56 L and  56 R respectively provided on holders  52 L and  52 R illustrated in  FIGS. 11A to 12B . Further, guide grooves  47   a L and  47   a R are respectively defined in the guide members  47 L and  47 R, and guide the cartridge tray  40  in a draw-out direction and in the attachment direction with respect to the apparatus body  100 A. In addition, the guide grooves  47   a L and  47   a R engage with unillustrated stoppers provided in the apparatus body  100 A to restrict drawing out of the cartridge tray  40  beyond a predetermined position. 
     The coupling member  42  includes receiving portions  42   b  and a grip portion  42   d , and the user can draw out the cartridge tray  40  from the apparatus body  100 A by gripping the grip portion  42   d . In addition, when an impact toward the front side is applied to the printer  100  in a state in which the front door  31  is closed, the receiving portions  42   b  abut the front door  31  and thus suppress damage to components inside the printer  100 . Similarly, the coupling member  46  include receiving portions  46   a , and, when an impact toward the rear side is applied to the printer  100 , the receiving portions  46   a  abut a fixing stay  35  illustrated in  FIG. 6  and thus suppress damage to the components inside the printer  100 . 
     The tray side plates  41 L and  41 R have shapes in which the upper portions thereof extend further to the outside than the lower portions thereof, and the distance between the tray side plates  41 L and  41 R in the left-right direction is smaller in the upper portion than in the lower portion. As a result of this, the width of the cartridge tray  40  in the left-right direction can be reduced without degrading the insertability/ejectability of the process cartridges PPY, PPM, PPC, and PPK, which contributes miniaturization of the printer  100 . 
     Further, the lower side of the tray side plates  41 L and  41 R are bent into L shapes to secure the strength. Although the tray side plates  41 L and  41 R and the coupling members  42  to  46  are each fastened by screws, the configuration is not limited to this, and thermal caulking or the like may be used. In addition, a configuration in which only the coupling members  42  and  46  are fastened to the tray side plates  41 L and  41 R and the coupling members  43  to  45  are not fastened to the tray side plates  41 L and  41 R may be employed. 
     As illustrated in  FIGS. 4A to 5B , cartridge engagement portions  41   g R,  41   h R,  41   i R, and  41   j R are provided in the tray side plate  41 R, and the cartridge engagement portions  41   g R,  41   h R,  41   i R, and  41   j R are each formed in an approximately V shape. Specifically, the cartridge engagement portions  41   g R,  41   h R,  41   i R, and  41   j R are each formed such that an inclined surface thereof on the front side in the draw-out direction has an angle of 65° and an inclined surface thereof on the rear side has an angle of 45°. 
     Drum flanges  1   a  of the process cartridges PPY, PPM, PPC, and PPK illustrated in  FIG. 3A  respectively engage with the cartridge engagement portions  41   g R,  41   h R,  41   i R, and  41   j R. As a result of this, the process cartridges PPY, PPM, PPC, and PPK are positioned with respect to the cartridge tray  40  by the weight thereof or by being pressed downward by pressing units  33  and  34  illustrated in  FIG. 11A . The pressing units  33  and  34  serving as second pressing units press the process cartridges downward at the time of image formation, and thus the process cartridges and the cartridge tray  40  integrated with the process cartridges are positioned with respect to the apparatus body  100 A. To be noted, unillustrated cartridge engagement portions are similarly formed in the tray side plate  41 L, and the process cartridges PPY, PPM, PPC, and PPK are also positioned with respect to the tray side plate  41 L. 
     In addition, boss portions  42   a L,  43   a L,  44   a L, and  45   a L are respectively formed on left end portions of the coupling members  42 ,  43 ,  44 , and  45 , and boss portions  42   a R,  43   a R,  44   a R, and  45   a R are respectively formed on right end portions of the coupling members  42 ,  43 ,  44 , and  45 . To be noted, the groove portions  1   d  are defined in left and right end portions of the process cartridge of each color as illustrated in  FIGS. 3A and 3B . Further, the groove portions  1   d  of the process cartridges PPY, PPM, PPC, and PPK respectively engage with the boss portions  42   a L,  43   a L,  44   a L, and  45   a L on the left end side and with the boss portions  42   a R,  43   a R,  44   a R, and  45   a R on the right end side. As a result of this, rotation of the process cartridges PPY, PPM, PPC, and PPK with respect to the cartridge tray  40  is restricted. 
     In this manner, the process cartridges PPY, PPM, PPC, and PPK are mounted on the cartridge tray  40 , and are grounded via a wire material  48  serving as a drum ground wire provided in the guide member  47 L. 
     Positioning Configuration of Cartridge Tray 
     Next, a positioning configuration of the cartridge tray  40  will be described. To be noted, the apparatus body  100 A and the cartridge tray  40  constitute a positioning apparatus  140  illustrated in  FIG. 2 . As illustrated in  FIG. 6 , the apparatus body  100 A illustrated in  FIG. 1  includes a pair of body side plates  36 L and  36 R respectively on the left side and the right side, and the fixing stay  35  that couples the body side plates  36 L and  36 R to each other and define a process region and a fixing region. The process region is a region where the process cartridges PPY, PPM, PPC, and PPK are accommodated, and the fixing region is a region where the fixing unit  23  is accommodated. The body side plates  36 L and  36 R and the fixing stay  35  are formed from a metal material. 
     The body side plates  36 L and  36 R respectively serving as a first support portion and a second support portion respectively include shaft support portions  50   a L and  50   a R on the rear side of the apparatus, and the shaft support portions  50   a L and  50   a R support a positioning shaft  50  serving as a first engaging portion and a shaft. To be noted, although the positioning shaft  50  is fixed so as to be immobile with respect to the shaft support portions  50   a L and  50   a R, the positioning shaft  50  may be rotatably supported as long as the positioning shaft  50  is immobile in the front-rear direction and in the up-down direction. 
     In addition, the body side plates  36 L and  36 R respectively have positioning grooves  36   a L and  36   a R on the apparatus front side. The positioning grooves  36   a L and  36   a R will be also collectively referred to as a body positioning portion  36   a . As illustrated in  FIG. 7 , shaft support portions  41   d L and  41   d R are respectively formed on the front side of the tray side plates  41 L and  41 R of the cartridge tray  40 . The shaft support portions  41   d L and  41   d R support a positioning shaft  49  serving as a second engaged portion. The positioning shaft  49  penetrates through the tray side plates  41 L and  41 R, and an unillustrated left end portion and a right end portion  49   a  of the positioning shaft  49  project to the outside from the tray side plates  41 L and  41 R. To be noted, although the positioning shaft  49  is fixed so as to be immobile with respect to the shaft support portions  41   d L and  41   d R, the positioning shaft  49  may be rotatably supported as long as the positioning shaft  49  is immobile in the front-rear direction and in the up-down direction. In addition, although the positioning shafts  49  and  50  are formed as round rod shafts that extend in the left-right direction and have circular shapes in a section view, the shapes thereof are not limited. 
     Further, a shaft contact portion  42   c  that supports an approximate center portion of the positioning shaft  49  in the axial direction thereof from below is formed on the coupling member  42 , and the shaft contact portion  42   c  regulates downward warpage of the positioning shaft  49 . To be noted, the shaft contact portion  42   c  may support a different position of the positioning shaft  49  from below instead of the approximate center portion of the positioning shaft  49  in the axial direction. However, it is preferable to regulate the downward warpage of the positioning shaft  49  at the center portion of the positioning shaft  49 . In addition, the shaft contact portion  42   c  may be formed in a shape elongated in the axial direction. 
     As illustrated in  FIG. 8D , the positioning groove  36   a R serving as a second engaging portion in the body side plate  36 R is defined along an attachment direction Y 1  of the cartridge tray  40 , and includes a fitting groove  37   a R defined on the rear side and a guide groove  37   b R defined on the front side. 
     The fitting groove  37   a R has a width equal to or slightly smaller than the outer diameter of the positioning shaft  49 , and the end portion  49   a  of the positioning shaft  49  fits in the fitting groove  37   a R when the cartridge tray  40  is positioned at an attached position. The guide groove  37   b R has a width larger than the outer diameter of the positioning shaft  49 , and guides the end portion  49   a  of the positioning shaft  49  to the fitting groove  37   a R when attaching the cartridge tray  40  to the apparatus body  100 A. To be noted, the guide groove and the fitting groove are also similarly defined in the body side plate  36 L, and guide or engage with a left end portion of the positioning shaft  49 . 
     As illustrated in  FIG. 5B , positioning grooves  41   b L and  41   b R are respectively defined on the rear side of the tray side plates  41 L and  41 R. The positioning grooves  41   b L and  41   b R are provided between the tray side plates  41 L and  41 R in the axial direction of the positioning shaft  50 , and engage with the positioning shaft  49  to position the cartridge tray  40 . The positioning grooves  41   b L and  41   b R will be also collectively referred to as a tray positioning portion  41   b .  FIGS. 8A to 8C  are enlarged views of the positioning groove  41   b L. To be noted, the positioning grooves  41   b L and  41   b R have similar configurations, and therefore only the positioning groove  41   b R will be described and description of the positioning groove  41   b L serving as a third engaged portion will be omitted. The positioning groove  41   b L is provided at a position different from the positioning groove  41   b R in the axial direction of the positioning shaft  50 . 
     As illustrated in  FIGS. 8A to 8C , the positioning groove  41   b R serving as a first engaged portion includes an inclined surface  41   f  and a positioning surface  41   e  formed continuously from the inclined surface  41   f . The positioning surface  41   e  extends in a direction approximately perpendicular to the attachment direction Y 1  of the cartridge tray  40 , and positions the cartridge tray  40  in the attachment direction by abutting the positioning shaft  50 . The inclined surface  41   f  is inclined downward toward the downstream side in the attachment direction Y 1 . In addition, a sliding surface  46   d  illustrated in  FIG. 5B  is formed on the coupling member  46  of the cartridge tray  40  such that the sliding surface  46   d  is continuous to the front side from the inclined surface  41   f . The sliding surface  46   d  is inclined upward toward the downstream side in the attachment direction Y 1 . 
     As illustrated in  FIG. 8A , when the cartridge tray  40  is attached, a downward force is applied to the cartridge tray  40  by the weight thereof and by the pressing units  33  and  34  illustrated in  FIG. 11A , and thus the inclined surface  41   f  receives a reaction force F 1  from the positioning shaft  50 . Since the reaction force F 1  includes a component force F 2  in the attachment direction Y 1 , the cartridge tray  40  is pulled in the attachment direction Y 1  by the component force F 2 . As a result of this, the positioning surface  41   e  is pressed against the positioning shaft  50 , and thus the cartridge tray  40  can be precisely positioned with respect to the apparatus body  100 A. As described above, the inclined surface  41   f  is formed to generate the component force F 2 , which is a force in the attachment direction Y 1 , on the cartridge tray  40 . 
     As illustrated in  FIG. 9 , the positioning shaft  50  is rotatably supported by the shaft support portions  50   a L and  50   a R. In a state in which the cartridge tray  40  is attached to the apparatus body  100 A, the positioning grooves  41   b L and  41   b R are positioned further on the inside than the shaft support portions  50   a L and  50   a R in the axial direction. Therefore, the center portion of the positioning shaft  50  receives a downward force applied by the weight of the cartridge tray  40  and by the pressing unit  33  and  34  illustrated in  FIG. 11A , and may be warped downward, that is, in a direction indicated by a hollow arrow in  FIG. 9 . In the case where the positioning shaft  50  is deformed, the positioning precision of the cartridge tray  40  is degraded. Regarding the related art described above, the standard shaft of Japanese Patent Laid-Open No. 2007-178657 receives a force in the gravity direction from the notch portion of the drum unit, and may be warped downward. In the case where the standard shaft is warped, the positioning precision of the drum unit itself is degraded. 
     Therefore, in the present exemplary embodiment, a rib  46   b  serving as a contact portion is formed in an approximate center portion of the coupling member  46  in the axial direction, that is, in the left-right direction. That is, the rib  46   b  is provided at a position between the body side plates  36 L and  36 R and between the positioning grooves  41   b L and  41   b R in the axial direction of the positioning shaft  50 . The rib  46   b  abuts an approximate center portion of the positioning shaft  50  in the axial direction to support the positioning shaft  50  from below, and thus regulates downward warpage of the positioning shaft  50 . To be noted, the rib  46   b  may support a different position of the positioning shaft  50  from below instead of the approximate center portion of the positioning shaft  50  in the axial direction. However, it is preferable to regulate the downward warpage of the positioning shaft  50  at the center portion of the positioning shaft  50 . In addition, the rib  46   b  may be formed in a shape elongated in the axial direction, or a plurality of ribs  46   b  may be provided in the axial direction. In addition, although the downward warpage of the positioning shaft  50  is regulated by the rib  46   b  because the positioning shaft  50  receives a force in the gravity direction, the rib  46   b  does not have to contact the lower portion of the positioning shaft  50  as long as the member regulates the warpage of the positioning shaft  50  by receiving the force in the warping direction. 
     In addition, as illustrated in  FIGS. 9 and 10 , locking portions  46   c  capable of locking onto the fixing stay  35  are formed on the coupling member  46 . The locking portions  46   c  can regulate the downward warpage of the cartridge tray  40  including the coupling member  46  by locking onto the fixing stay  35 . By reducing downward warpage of the cartridge tray  40 , deformation of the cartridge tray  40  at the positioning grooves  41   b L and  41   b R can be also reduced, and thus the cartridge tray  40  can be positioned with high precision with respect to the positioning shaft  50 . To be noted, the locking portions  46   c  do not hinder the attachment operation of the cartridge tray  40 , and the number thereof may be only one or three or more. In addition, one locking portion  46   c  elongated in the axial direction, that is, in the left-right direction, may be formed. 
     Draw-out Operation and Attachment Operation of Cartridge Tray 
     Next, the draw-out operation and attachment operation of the cartridge tray  40  will be described. The product values of the process cartridges PPY, PPM, PPC, and PPK are lost when the developer is consumed to such a degree that it becomes impossible to form an image of a quality satisfactory the user that has purchased the process cartridges. 
     Therefore, an unillustrated detection portion that detects the amount of remaining developer of each process cartridge may be provided, and the detected amount of remaining developer may be compared by the controller  200  with a threshold value for cartridge lifetime notification or lifetime warning that is set in advance. In this case, when the detected amount of remaining developer of a process cartridge is smaller than the threshold value, a lifetime notification or lifetime warning is displayed for the process cartridge to prompt the user to replace the process cartridge. Then, the user opens the front door  31  of the printer  100 , draws out the cartridge tray  40  to the outside of the apparatus, and replaces the process cartridge. The draw-out operation and attachment operation of the cartridge tray  40  will be described in detail below. 
     The front door  31  serving as a door member is supported so as to be openable and closeable with respect to the apparatus body  100 A as illustrated in  FIGS. 11A to 12B , and can be held in an open state by door links  32 L and  32 R coupling the front door  31  to the apparatus body  100 A. 
     When the user opens the front door  31 , a plurality of unillustrated link members move in an interlocked manner via the door links  32 L and  32 R, and the transfer unit  12  rotates around the driving roller  14  by about 1°. As a result of this, the photosensitive drum  1  of each process cartridge is separated from the intermediate transfer belt  13  as illustrated in  FIG. 13C . 
     Next, as illustrated in  FIG. 12B , each of contacts  38  provided on the left side, that is, the non-driving side of the apparatus body  100 A is separated from the contact  2  of each developing roller  3  illustrated in  FIG. 3B , and the pressurization by the pressing units  33  and  34  is cancelled. Next, the engagement with the drum coupling  1   c  and the developing coupling  3   c  illustrated in  FIG. 3A  on the driving side of each process cartridge is cancelled, and the pressurization of the cartridge tray  40  by tray pressing units  51  is cancelled as illustrated in  FIGS. 11B and 13B . As a result of this, it becomes possible to take the cartridge tray  40  out of the apparatus body  100 A. 
     Here, the tray pressing units  51  serving as first pressing units are respectively provided on the holders  52 L and  52 R respectively supported by the body side plates  36 L and  36 R, and press the cartridge tray  40  from the rear side to the front side during image formation. The tray pressing units  51  each include a tray pressing lever  53 , a tray pressing link  54 , and an urging spring  55  as illustrated in  FIGS. 13A and 13B . 
     As illustrated in  FIG. 13A , the tray pressing lever  53  is pressed by the tray pressing link  54  urged by the urging spring  55  in a state in which the front door  31  is closed. As a result of this, the tray pressing lever  53  presses a pressed portion  41   c  formed on the tray side plate  41 R of the cartridge tray  40  to the rear side. 
     As illustrated in  FIG. 13B , when the front door  31  is opened, the tray pressing lever  53  is retracted downward by the door links  32 L and  32 R and unillustrated link members. As a result of this, the pressurization of the cartridge tray  40  to the rear side by the tray pressing lever  53  is cancelled, and it becomes possible to take the cartridge tray  40  out of the apparatus body  100 A. 
     Next, although motion of the surroundings of the positioning shafts  49  and  50  will be described with reference to  FIGS. 8A to 8F , since the positioning configuration of the cartridge tray  40  is the same between the left side and the right side of the positioning shafts  49  and  50 , only the right side of the apparatus will be described, and description of the left side of the apparatus will be omitted. As illustrated in  FIGS. 8A to 8F , when the cartridge tray  40  starts being drawn out, the inclined surface  41   f  slides on the positioning shaft  50 , and therefore the rear side of the cartridge tray  40  is slightly lifted. Then, the cartridge tray  40  moves in a draw-out direction Y 2  while the sliding surface  46   d  provided on the coupling member  46  of the cartridge tray  40  slides on the positioning shaft  50 . 
     At the same time, the end portion  49   a  of the positioning shaft  49  of the cartridge tray  40  is released from the fitting groove  37   a R of the positioning groove  36   a R, and moves on to the guide groove  37   b R. The cartridge tray  40  is drawn out in the draw-out direction Y 2  while the end portion  49   a  of the positioning shaft  49  is guided by the guide groove  37   b R.  FIGS. 8A and 8D  each illustrate a state in which the cartridge tray  40  is in the attached position.  FIGS. 8B and 8E  each illustrate a state in which the cartridge tray  40  is drawn out from the attached position by about 3 mm  FIGS. 8C and 8F  each illustrate a state in which the cartridge tray  40  is drawn out from the attached position by about 10 mm. 
     When the cartridge tray  40  is drawn out to some extent, the guide members  47 L and  47 R of the cartridge tray  40  are guided on the rollers  56 L and  56 R as illustrated in  FIGS. 11B and 12B . Then, the cartridge tray  40  is drawn out of the apparatus body  100 A. To be noted, at the time of image formation, the cartridge tray  40  is not in contact with the rollers  56 L and  56 R, and a clearance of about 0.5 mm is secured. 
     After the cartridge tray  40  is drawn out and a process cartridge is replaced, the cartridge tray  40  is attached to the apparatus body  100 A. The attachment operation of attaching the cartridge tray  40  to the apparatus body  100 A is the reverse of the draw-out operation. At this time, first, the sliding surface  46   d  starts sliding on the positioning shaft  50 , and the end portion  49   a  of the positioning shaft  49  is passed onto the fitting groove  37   a R from the guide groove  37   b R after the positioning shaft  50  has passed the sliding surface  46   d , as illustrated in  FIGS. 8B and 8E . 
     Since the boundary portion between the guide groove  37   b R and the fitting groove  37   a R has upward inclination and the end portion  49   a  of the positioning shaft  49  fits in the fitting groove  37   a R, an operation force for the user to attach the cartridge tray  40  is large. However, since the positioning shaft  49  enters the fitting groove  37   a R after the positioning shaft  50  has passed the sliding surface  46   d , the timing when the operation force of the user increases does not concentrate, and therefore the operation force can be reduced. To be noted, the cartridge tray  40  is configured to be automatically pulled in to the attached position by a pull-in apparatus that will be described later when the cartridge tray  40  is inserted to a position at a predetermined distance from the attachment position on the front side. 
     When the cartridge tray  40  is inserted to the attached position and the front door  31  is closed, the tray pressing units  51  press the cartridge tray  40  to the rear side as illustrated in  FIGS. 11A, 12A, and 13A . Then, the drum coupling  1   c  and the developing coupling  3   c  on the driving side of each process cartridge illustrated in  FIG. 3A  connect to the drive source of the apparatus body  100 A, and the pressing units  33  and  34  press the process cartridges from above. Further, the contacts  38  come into contact with the contacts  2  of the respective developing rollers  3  illustrated in  FIG. 3B , and the transfer unit  12  rotates upward about the driving roller  14 . As a result of this, the photosensitive drum  1  of each process cartridge comes into contact with the intermediate transfer belt  13 . 
     As described above, in a state in which the front door  31  is closed and the printer  100  is capable of forming an image, the positioning shaft  50  engages with the positioning grooves  41   b L and  41   b R on the front side of the cartridge tray  40 . At this time, since the positioning grooves  41   b L and the  41   b R are provided with the inclined surface  41   f , the cartridge tray  40  is pulled in the attachment direction Y 1  on the basis of the weight of the cartridge tray  40  and the downward force from the pressing units  33  and  34 . As a result of this, the positioning surface  41   e  is pressed against the positioning shaft  50 , and thus the cartridge tray  40  can be positioned in the attachment direction Y 1  with a high precision. 
     In addition, the positioning shaft  49  engages with the positioning grooves  36   a L and  36   a R on the rear side of the cartridge tray  40 . At this time, since the end portion  49   a  of the positioning shaft  49  fits in the fitting grooves of the positioning grooves  36   a L and  36   a R, rotation of the cartridge tray  40  in a direction perpendicular to the attachment direction Y 1 , that is, rotation of the cartridge tray  40  about the positioning shaft  50  can be restricted. 
     The positioning shaft  50  and the positioning grooves  36   a L and  36   a R that are provided in the apparatus body  100 A and the positioning shaft  49  and the positioning grooves  41   b L and  41   b R that are provided in the cartridge tray  40  constitute a positioning mechanism  60  illustrated in  FIGS. 8A and 8D . The positioning mechanism  60  positions the cartridge tray  40  with respect to the apparatus body  100 A. 
     Further, since the positioning shaft  50  is supported from below by the rib  46   b  provided on the coupling member  46  of the cartridge tray  40 , downward warpage, that is, deformation of the positioning shaft  50  is regulated. In addition, the locking portions  46   c  provided on the coupling member  46  reduce deformation of the cartridge tray  40  itself. Further, since the positioning shaft  49  on the rear side of the cartridge tray  40  is also supported from below by the shaft contact portion  42   c , downward warpage of the positioning shaft  49  is regulated. According to such a configuration, the shaft diameter of the positioning shafts  49  and  50  can be reduced, the positioning shafts  49  and  50  can be formed from a cheaper resin material, and thus the cost and size can be reduced. 
     According to these, the cartridge tray  40  can be positioned at the attached position with high precision with respect to the apparatus body  100 A, and the positioning precision of the cartridge tray  40  can be improved. Particularly, although the process cartridges held by the cartridge tray  40  are pressed from above by the pressing units  33  and  34  during image formation, this does not affect the positioning precision of the cartridge tray  40 . Therefore, the positioning precision of each process cartridge held by the cartridge tray  40 , specifically, the positioning precision between the photosensitive drum  1  and the intermediate transfer belt  13  is improved, and thus an image of high quality can be formed. 
     In addition, the cartridge tray  40  is urged to the front side at the attached position by the effect of the inclined surface  41   f  on the front side of the cartridge tray  40  and pressurization by the tray pressing units  51  on the rear side. Therefore, displacement of the cartridge tray  40  caused by vibration at the time of image formation or the like can be suppressed. In addition, by generating pressing force on the front side and rear side of the cartridge tray  40 , the pressing force can be distributed, and thus the urging springs  55  of the tray pressing units  51  can be configured to have smaller elasticity. As a result of this, the size and cost of the tray pressing units  51  can be reduced. 
     To be noted, the positioning shaft  50  and the positioning grooves  41   b L and  41   b R that are included in the positioning mechanism  60  may be interchanged as long as the positioning shaft  50  is provided in one of the apparatus body  100 A and the cartridge tray  40  and the positioning grooves  41   b L and  41   b R are provided in the other. In addition, the positioning shaft  49  and the positioning grooves  36   a L and  36   a R that are included in the positioning mechanism  60  may be interchanged as long as the positioning shaft  49  is provided in one of the apparatus body  100 A and the cartridge tray  40  and the positioning grooves  36   a L and  36   a R are provided in the other. 
     In addition, the positioning shaft  49  does not have to be a penetrating shaft that extends in the entirety of the cartridge tray  40  in the left-right direction, and may be in any form as long as two projections projecting from the both sides of the cartridge tray  40  are formed. 
     In addition, although each process cartridge is formed by integrating the drum unit OP and the developing unit DP, these may be separately provided. Further, for example, a configuration in which the cartridge tray  40  only holds the drum unit OP and a configuration in which the cartridge tray  40  only holds the developing unit DP may be employed. 
     Pull-in Apparatus 
     A pull-in apparatus  90  of the present exemplary embodiment will be described below. As illustrated in  FIGS. 14 and 15 , the pull-in apparatus  90  has a function of pulling in the cartridge tray  40 , which is an example of a unit that can be drawn out from the apparatus body, to a predetermined position in the apparatus body. In the present exemplary embodiment, the attached position of  FIG. 15  serves as the predetermined position. 
       FIG. 14  illustrates a state before the pull-in apparatus  90  pulls in the cartridge tray  40  as viewed from above. The pull-in apparatus  90  includes a holder  91 , an arm  92 , an arm spring  93 , a locking member  94  that will be described later, and a first action portion  46   s   1  and a second action portion  46   s   2  that are provided in the cartridge tray  40 . The arm  92  serves as an arm member of the present exemplary embodiment, the locking member  94  serves as a restriction member of the present exemplary embodiment, and the arm spring  93  serves as an urging member of the present exemplary embodiment. In addition, the first action portion  46   s   1  serves as a first abutting portion of the present exemplary embodiment, and the second action portion  46   s   2  serves as a second abutting portion of the present exemplary embodiment. 
     The holder  91  is fixed to the fixing stay  35  of the apparatus body, and pivotably holds the arm  92  at a pivot support portion  91   o . The arm  92  is always urged in a clockwise direction in  FIG. 14  by the arm spring  93 . The arm  92  pulls in the first action portion  46   s   1  by this urging force to move the cartridge tray  40  toward the rear side of the apparatus, and thus a pulled-in state illustrated in  FIG. 15  is achieved. In the pulled-in state, the tray positioning portion  41   b  described above engages with the positioning shaft  50 , the positioning shaft  49  engages with the body positioning portion  36   a , and thus the cartridge tray  40  is positioned. To be noted, in a stand-by state illustrated in  FIG. 14  in which the cartridge tray  40  is drawn out to a position where attachment/detachment of a process cartridge PP is performed, pivoting of the arm  92  is restricted by a locking mechanism that will be described later. 
     The urging force that the arm spring  93  applies to the arm  92  is adjusted in accordance with the total weight of the cartridge tray  40  including the process cartridges PP. In the configuration example to which the present exemplary embodiment is applied, a good operability can be obtained in the case where the urging force of the arm  92  is set to 2 kgf. This value is about 1 kgf to 1.5 kgf in terms of a force of pulling the cartridge tray  40  in the attachment direction. This is set to be smaller than force in the same direction generated by the tray pressing units  51  described above and by the contact between the inclined surface  41   f  and the positioning shaft  50 . Meanwhile, the magnitude of the urging force of the arm spring  93  is set such that the cartridge tray  40  can be pulled in to the attached position against the frictional drag between the sliding surface  46   d  illustrated in  FIGS. 8A to 8C  described above and the positioning shaft  50 . 
       FIGS. 16A, 16B, and 16C  illustrate components of the pull-in apparatus  90  on the apparatus body side as viewed from above, as viewed horizontally, and as viewed from below, respectively. In the figures, the left-right direction of the image forming apparatus is set as an X-axis direction, the front-rear direction, that is, the attachment direction of the cartridge tray  40 , is set as a Y-axis direction, and the vertical direction (i.e., gravity direction) perpendicular to the X-axis direction and the Y-axis direction is set as a Z-axis direction. 
     The arm  92  is capable of pivoting between the position of the stand-by state illustrated in  FIGS. 14 and 16A to 16C  and the position of the pulled-in state illustrated in  FIG. 15  about the pivot support portion  910  extending in the Z-axis direction. That is, the direction of the pivot axis of the arm  92  (i.e., rotation axis of the arm member) of the present exemplary embodiment approximately coincides with the vertical direction. In the description below, the position of the arm  92  in the stand-by state will be referred to as a “stand-by position”, and the position of the arm  92  in the pulled-in state will be referred to as a “pulled-in position”. In addition, the pivot direction of the arm  92  serving as a first direction from the stand-by position toward the pulled-in position will be referred to as a “pull-in direction”, and the pivot direction of the arm  92  serving as a second direction from the pulled-in position toward the stand-by position will be referred to as a “returning direction”. 
     In the stand-by position, the arm  92  projects toward the front side of the image forming apparatus through an opening portion  35   o  illustrated in  FIG. 14  provided in a front side wall surface  35   a  of the fixing stay  35 . When the arm  92  moves to the pulled-in position, the arm  92  is retracted toward the rear side of the image forming apparatus together with the first action portion  46   s   1  and the second action portion  46   s   2  with respect to the opening portion  35   o  as illustrated in  FIG. 15 . In addition, the arm spring  93  of the present exemplary embodiment is configured to urge the arm  92  in a pull-in direction R 1  in the entire region from the stand-by position to the pulled-in position. 
     As illustrated in  FIGS. 16A to 16C , a first engagement surface  92   s  and a second engagement surface  92   d  that abut the first action portion  46   s   1  are provided on the arm  92 . The first engagement surface  92   s  is a portion that abuts the first action portion  46   s   1  to release the locking by the locking mechanism in an initial stage of a pull-in operation. The second engagement surface  92   d  is a portion that abuts the first action portion  46   s   1  to receive the force to pull in the cartridge tray  40  from the arm  92  pivoted by the urging force of the arm spring  93  after the locking by the locking mechanism is released. 
       FIG. 17  is an exploded view of the arm  92  and the locking member  94 . The arm  92  is formed by integrating an arm upper portion  92   a  serving as a first portion of the present exemplary embodiment and an arm lower portion  92   b  serving as a second portion of the present exemplary embodiment by fastening members such as screws and by engagement between an elastic claw portion  92   m  and a hole portion  92   n . The locking member  94  is held between the arm upper portion  92   a  and the arm lower portion  92   b . In addition, the locking member  94  includes a pressing portion  94   s  pressed by the second action portion  46   s   2  at the time of inserting the cartridge tray  40 , and an abutting portion  941  that abuts an abutted portion  911  illustrated in  FIGS. 18A and 18B  that is provided in the holder  91 , that is, fixed with respect to the apparatus body. 
     The locking member  94  and a locking spring  95  constitute a locking mechanism that locks the arm  92  in the stand-by position in the drawn-out state of the cartridge tray  40 . In the description below, the position of the locking member  94  at which the abutting portion  941  faces the abutted portion  911  to restrict pivoting of the arm  92  will be referred to as a “locked position”, and the position of the locking member  94  at which the abutting portion  941  is separated from the abutted portion  911  to allow the pivoting of the arm  92  will be referred to as a “lock-release position”. 
     The locking member  94  is supported by the arm  92  so as to be pivotable about a pivot  92   o , and is always urged in a counterclockwise direction in  FIG. 17  by the locking spring  95 . The urging force of the locking spring  95  may be set such that free pivoting of the locking member  94  with respect to the arm  92  is restricted, and the urging force is set to a smaller load than that of the arm spring  93 . In the configuration example to which the present exemplary embodiment is applied, it is preferable to set the urging force of the arm spring  93  to 50 gf. 
     As illustrated in  FIG. 16B , the locking member  94 , which is a plate-like member, is sandwiched between the arm upper portion  92   a  and the arm lower portion  92   b , which are two plate-like members, in an orientation perpendicularly intersecting the Z-axis direction. That is, the thickness of the locking member  94  is smaller than an interval z 1  between the arm upper portion  92   a  and the arm lower portion  92   b  in the Z-axis direction. The interval z 1  is set to such a value that the fingertip of a person does not get caught between the arm upper portion  92   a  and the arm lower portion  92   b , for example, a value equal to or smaller than 5 mm. 
     As a guide shape for guiding the second action portion  46   s   2  in the cartridge tray, inclined surfaces  92   a   1  and  92   b   1  of the arm upper portion  92   a  and the arm lower portion  92   b  are provided at an upstream end portion of the arm  92  in the attachment direction Y 1  at the stand-by position. The inclined surfaces  92   a   1  and  92   b   1  are opposed to each other in the Z-axis direction, and are each inclined with respect to the X-Y plane such that the interval therebetween in the Z-axis direction is smaller on the more downstream side in the attachment direction Y 1 . In addition, the inclined surfaces  92   a   1  and  92   b   1  are formed in a region that overlaps with a position p 1  in the X-axis direction where the second action portion  46   s   2  first abuts the locking member  94 . 
     As illustrated in  FIGS. 14 and 18A , the first action portion  46   s   1  and the second action portion  46   s   2  are provided on the coupling member  46  positioned on the most rear side in the cartridge tray  40 . The first action portion  46   s   1  and the second action portion  46   s   2  of the present exemplary embodiment are each a resin molded product  46   s  integrally molded from a resin material, and projects from the coupling member  46  toward the downstream side in the attachment direction Y 1  of the cartridge tray  40 . The first action portion  46   s   1  has a columnar shape extending in the Z-axis direction, and the second action portion  46   s   2  has a plate-like shape perpendicular to the Z-axis direction. The thickness of the second action portion  46   s   2  is set to a value smaller than the interval z 1  between the arm upper portion  92   a  and the arm lower portion  92   b  described above. 
     Operation of Pull-in Apparatus 
     An operation of the pull-in apparatus  90  will be described below with reference to  FIGS. 18A to 21B .  FIGS. 18A and 18B  correspond to the stand-by state in which the cartridge tray  40  is drawn out of the apparatus body,  FIGS. 19A and 19B  correspond to a first stage of a locking cancellation operation,  FIGS. 20A and 20B  correspond to a second stage of the lock-release operation, and  FIGS. 21A and 21B  correspond to the pulled-in state in which the cartridge tray  40  is pulled in to the attached position. In addition,  FIGS. 18A, 19A, 20A, and 21A  illustrate the pull-in apparatus  90  as viewed from above, and  FIGS. 18B, 19B, 20B, and 21B  are perspective views of the pull-in apparatus  90  in which a part of the arm upper portion  92   a  is made invisible. 
     In the stand-by state illustrated in  FIGS. 18A and 18B , the first action portion  46   s   1  and the second action portion  46   s   2  are separated from the arm  92 , and the arm  92  is in the stand-by position. To be noted, although the cartridge tray  40  is illustrated in  FIGS. 18A and 18B  for the sake of description, in the case of performing attachment/detachment of a process cartridge, the cartridge tray  40  is at a position lower than the position illustrated in  FIGS. 18A and 18B  with respect to the arm  92 . In the stand-by state, the locking member  94  is engaged with the holder  91  as illustrated in  FIG. 18B , and the arm  92  is in a locked state in which pivoting in the pull-in direction R 1  is restricted. That is, although an urging force in the clockwise direction in  FIGS. 18A and 18B  is applied to the arm  92  from the arm spring  93 , the locking member  94  pivotably supported by the arm  92  is abutting the abutted portion  911  of the holder  91  at the abutting portion  941 . Therefore, the pivot  92   o  of the locking member  94  cannot move in the pull-in direction R 1  with respect to the pivot support portion  910  of the arm  92 , and thus the arm  92  does not pivot in the pull-in direction R 1 . 
     In addition, in the stand-by state, although the locking member  94  is pressed in a counterclockwise direction r 1  in  FIGS. 18A and 18B  by a reaction force from the abutted portion  911 , the locking member  94  abuts a wall surface  912  illustrated in  FIG. 20B  adjacent to the abutted portion  911 . Therefore, pivoting of the locking member  94  in the counterclockwise direction in the stand-by state is restricted, and the locking member  94  is kept at the locked position. 
       FIGS. 19A and 19B  illustrate a first stage of a lock-release operation of releasing the locking of the arm  92  in the course of inserting the cartridge tray  40  in the apparatus body. When the cartridge tray  40  moves in the attachment direction Y 1  of the tray to approach the arm  92 , first, the first action portion  46   s   1  abuts the first engagement surface  92   s  of the arm  92 . When the arm  92  is in the stand-by position, the first engagement surface  92   s  is inclined from the outside to the inside of a range of the first action portion  46   s   1  in the X-axis direction toward the downstream side in the attachment direction Y 1 , that is, inclined upward to the left side in  FIGS. 19A and 19B . Therefore, the first action portion  46   s   1  presses the first engagement surface  92   s  to the left side in  FIGS. 19A and 19B  in accordance with the insertion of the cartridge tray  40 , and thus pivots the arm  92  in a returning direction R 2  against the urging force of the arm spring  93 . 
     Then, as illustrated in  FIG. 19B , the abutting portion  941  of the locking member  94  is separated from the abutted portion  911  of the holder  91 , thus a gap g is generated, and it becomes possible to move the locking member  94  with respect to the arm  92 , that is, to pivot the locking member  94  in the clockwise direction in  FIG. 19B . However, also in this state, the locking member  94  is urged in the clockwise direction r 1  in  FIG. 19B  by the urging force of the locking spring  95 , and abuts the wall surface  912  of the holder  91 . Therefore, the locking member  94  stays in the locked position, and the locked state of the arm  92  is not released. That is, even if it is attempted to manually pivot the arm  92  in the pull-in direction R 1  without moving the cartridge tray  40 , the abutting portion  941  of the locking member  94  abuts the abutted portion  911  of the holder  91  again to restrict the pivoting of the arm  92 . 
       FIGS. 20A and 20B  illustrate the lock-release operation having proceeded to the second stage as a result of the cartridge tray  40  being further inserted into the apparatus body. In this stage, the second action portion  46   s   2  presses the pressing portion  94   s  of the locking member  94  in a state in which the first action portion  46   s   1  of the cartridge tray  40  has pivoted the arm  92  in the returning direction R 2  from the stand-by position. As a result of this, the locking member  94  pivots in a clockwise direction r 2  in  FIGS. 20A and 20B  against the urging force of the locking spring  95 , and the locking member  94  is retracted to a lock-release position where the abutting portion  941  does not face the abutted portion  911  of the holder  91 . 
     While the locking member  94  is pivoting from the locked position to the lock-release position, the arm  92  is kept in a state in which the arm  92  has been pivoted in the returning direction R 2 . In other words, the shape of the first engagement surface  92   s  is designed so as to secure such a pivot amount of the arm  92  that the locking member  94  can pivot to the lock-release position without interfering with the abutted portion  911 . For example, this is satisfied in the case where the minimum distance from the pivot  92   o  of the locking member  94  to the abutted portion  911  is smaller than the pivoting radius of the abutting portion  941  about the pivot  92   o  during a period from the time when the second action portion  46   s   2  abuts the locking member  94  to the time when the abutting portion  941  is separated from the abutted portion  911 . 
     As a result of the second action portion  46   s   2  moving the locking member  94  to the lock-release position, a state in which pivoting of the arm  92  in the pull-in direction R 1  is not hindered by the locking member  94 , that is, the lock-release state is taken. That is, if the cartridge tray  40  is vanished while maintaining the positions of the arm  92  and the locking member  94  of  FIGS. 20A and 20B , the arm  92  is pivoted in the pull-in direction R 1  by the urging force of the arm spring  93 . 
     The second engagement surface  92   d  of the arm  92  engages with the first action portion  46   s   1  in a state in which the locking of the arm  92  is released by the second action portion  46   s   2 . When the second engagement surface  92   d  engages with the first action portion  46   s   1 , the pull-in force in the attachment direction Y 1  starts acting on the cartridge tray  40  from the arm  92  due to the urging force of the arm spring  93 . In other words, the second engagement surface  92   d  starts abutting the first action portion  46   s   1  in a surface region of the arm  92  that abuts the first action portion  46   s   1  and in a direction whose normal vector includes a positive component in the Y-axis direction, in the course of inserting the cartridge tray  40 . 
     As illustrated in  FIGS. 21A and 21B , when the arm  92  pivots from the stand-by position by a predetermined angle, which is about 45° in the present exemplary embodiment, while pulling in the cartridge tray  40  in the attachment direction Y 1  by the urging force of the arm spring  93 , the arm  92  reaches the pulled-in position. As a result of this, the cartridge tray  40  is attached to the attached position in the apparatus body. 
     When drawing the cartridge tray  40  out of the apparatus body, the pull-in apparatus  90  changes from the pulled-in state illustrated in  FIGS. 21A and 21B  to the stand-by state illustrated in  FIGS. 18A and 18B  by tracking back the pull-in operation described above. That is, the user or the like pulls the cartridge tray  40  in a draw-out direction opposite to the attachment direction Y 1 , and thus the first action portion  46   s   1  presses the second engagement surface  92   d  of the arm  92  in the draw-out direction. As a result of this, the arm  92  pivots in the returning direction R 2 , and the state of  FIGS. 21A and 21B  transitions to the state of  FIGS. 20A and 20B . The locking member  94  pivots in the counterclockwise direction in  FIGS. 20A and 20B  by the urging force of the locking spring  95  while maintaining the state in which the pressing portion  94   s  is in contact with the second action portion  46   s   2 , and returns to the locked position as illustrated in  FIG. 19B . 
     When the cartridge tray  40  is drawn out further, the second action portion  46   s   2  is separated from the pressing portion  94   s  of the locking member  94 . In addition, the first action portion  46   s   1  pivots the arm  92  in the returning direction R 2  to a position beyond the stand-by position. Then, the arm  92  pivots in the pull-in direction R 1  to the stand-by position while sliding on the first action portion  46   s   1  at the first engagement surface  92   s , thus the abutting portion  941  of the locking member  94  abuts the abutted portion  911  of the holder  91 , and the pull-in apparatus  90  takes the stand-by state illustrated in  FIGS. 18A and 18B . 
     Summary of Pull-in Apparatus 
     The pull-in apparatus  90  of the present exemplary embodiment, having a configuration in which the pivoting of the arm  92  is locked in the stand-by state, requires two actions of (1) pivoting of the arm  92  in the returning direction R 2  and (2) pivoting of the locking member  94 . That is, in the case where (1) and (2) described above do not act on the pull-in apparatus  90  in this order, normally the locking of the arm  92  is not released. As a result of this, in the stand-by state as illustrated in  FIGS. 18A and 18B  in which the locking is yet to be released, high stability of the pull-in apparatus  90  can be realized. Here, high stability is defined by unlikeliness of occurrence of an event in which the locking of the arm  92  is accidentally released and the arm  92  unintentionally pivots, which may be caused in a case where, for example, the user&#39;s finger touches the pull-in apparatus  90  in the stand-by state. 
     Further, in the configuration of the present exemplary embodiment, the locking member  94  is held in a gap between two portions of the arm  92 , and this gap needs to be accessed to move the locking member  94 . If it is attempted to release the locking by one action of moving the locking member  94  to the lock-release position in the state in which the arm  92  is in the stand-by position, the locking member  94  needs to be strongly pressed in an arrow direction of  FIG. 22  as illustrated in  FIG. 22 . However, in the stand-by state, the locking member  94  is pressed against the abutted portion  911  of the holder  91  by the urging force of the arm spring  93 , and a strong force is required for pivoting the locking member  94  in the clockwise direction in  FIG. 22 . Therefore, although an operation of inserting and pushing an object such as a ruler that is rigid and thinner than the interval z 1  between the arm upper portion and the arm lower portion illustrated in  FIG. 16B  in the gap of the arm  92  is required, such an event occurring accidentally is unrealistic. Meanwhile, it is also unimaginable that a two-step operation of inserting an object such as a ruler in the gap of the arm  92  to pivot the locking member  94  after pivoting the arm  92  in the returning direction R 2  is accidentally performed. 
     Therefore, according to the configuration of the present exemplary embodiment in which the locking member  94  is surrounded and protected by the arm  92 , the stability of the pull-in apparatus  90  can be further improved. To be noted, in the present exemplary embodiment, the second action portion  46   s   2  is used as a second abutting portion, and the possibility of an object other than the second action portion  46   s   2  getting into the gap of the arm  92  is reduced by setting the thickness of the second action portion  46   s   2  to be smaller than the interval z 1  of the arm  92 . Even in the case of using a second abutting portion not having a plate-like shape instead of this, an effect similar to that of the present exemplary embodiment can be obtained by disposing the second abutting portion between a plurality of parts of the arm member. 
     In addition, in the pull-in apparatus  90  of the present exemplary embodiment, at least the arm spring  93  and the pivot support portion  910  of the arm  92  are disposed further on the rear side than the front side wall surface  35   a  of the fixing stay  35  illustrated in  FIG. 14 . According to such a configuration in which the number of members projecting toward the space in which the cartridge tray  40  is accommodated is small in the stand-by state, accidental contact with the pull-in apparatus  90  can be suppressed, and thus the stability can be further improved. To be noted, as illustrated in  FIG. 16C , it is preferable to provide the arm  92  with a covering portion  92   k  that covers at least part of the locking spring  95  as viewed in the Y-axis direction in the stand-by state and provide the holder  91  with a covering portion  91   k  that overlaps with the locking member  94  as viewed in the vertical direction in the stand-by state. These elements also contribute to the improvement in the stability of the pull-in apparatus  90  by suppressing unintentional contact with the locking spring  95  or the locking member  94 . In addition, a cover that covers a movable portion other than the arm  92  may be provided by using other plate metal frames or the holder  91  in addition to the fixing stay  35 . 
     In addition, in the configuration of the present exemplary embodiment, the arm spring  93  urges the arm  92  in the pull-in direction R 1  in the entire region from the stand-by position to the pulled-in position. Therefore, compared with a configuration used for a pull-in apparatus of a so-called toggle type in which the urging direction of the arm by the spring member changes within the range from the stand-by position to the pulled-in position, the distance to which the arm  92  is capable of pulling in the cartridge tray  40  can be set to be long. In the case of the pull-in apparatus of a toggle type, the pull-in action occurs after the arm passes a middle position. The pull-in action is weak near the middle position, and rather a force in a direction of pushing back the cartridge tray is applied before passing the middle position. In contrast, in the case of the present exemplary embodiment, the urging force of the arm spring  93  is efficiently transmitted as a force of moving the cartridge tray  40  in the attachment direction Y 1  at the stage of  FIGS. 20A and 20B  before the pull-in action starts being in effect. As a result, the distance in which sufficient pull-in force can be exerted can be elongated as compared with the pull-in apparatus of a toggle type while avoiding increase in the size of the pull-in apparatus. 
     In addition, the present exemplary embodiment also has a good space-saving characteristic. In the state illustrated in  FIGS. 21A and 21B  in which the pull-in apparatus  90  has pulled in the cartridge tray  40  to the attached position, a range occupied by the pull-in apparatus  90  in the attachment direction Y 1  is approximately a half of that in the stand-by state illustrated in  FIGS. 18A and 18B . In addition, in the pulled-in state, the cartridge tray  40  is present in at least part of the space occupied by the arm  92  in the stand-by state. These characteristics enable securing an accommodation space for the cartridge tray  40  without increasing the size of the casing of the image forming apparatus, resulting in contribution to miniaturization of the apparatus. 
     To be noted, the pull-in apparatus  90  of the present exemplary embodiment has a configuration in which the force the cartridge tray  40  receives from the arm  92  in the course of the lock-release operation and the pull-in operation includes a component toward one side in the X-axis direction, which is the left side in  FIGS. 20A and 20B . Although the illustrated structure may be disposed in the pull-in apparatus  90  in a state of being inverted with respect to the X-axis direction, in the present exemplary embodiment, the arrangement in which the component of the force in the X-axis direction is in a direction from the right side plate  37  to the left side plate  36  is employed as illustrated in  FIG. 14 . 
     Here, in the present exemplary embodiment, positioning of a photosensitive drum in the longitudinal direction in the case of performing an image forming operation after attaching the cartridge tray  40  to the apparatus body is performed by pressing the photosensitive drum leftward. Specifically, a driving coupling provided in the apparatus body presses the drum coupling  1   c  illustrated in  FIG. 3A  leftward, which is coaxially provided with the photosensitive drum. 
     In such a configuration, the pull-in apparatus  90  of the present exemplary embodiment is provided such that the direction of a component force applied to the cartridge tray  40  in a direction perpendicular to the attachment direction in the course of the pull-in operation coincides with the direction in which the photosensitive drum is pressed in the longitudinal direction in a state after the tray is attached. If these are opposite to each other, a guide shape that regulates the position of the cartridge tray  40  in the left-right direction at the time of inserting the cartridge tray  40  and another guide shape that receives a force that the cartridge tray  40  receives via the photosensitive drum after being attached and regulates the position of the cartridge tray  40  need to be provided separately. For example, the guide shape is a side wall that opposes the guide member  47 L of the cartridge tray  40  in the left-right direction. In contrast, in the present exemplary embodiment, the directions of these forces coincide with each other, and therefore the position regulating function at the time of inserting the cartridge tray  40  and the position regulating function after the attachment can be realized by the same guide shape, and thus the configuration of the apparatus can be simplified. 
     In addition, as illustrated in  FIG. 14 , a contact t 1  for connecting the photosensitive drums to the ground potential is provided on the cartridge tray  40 , and a wire spring t 2  connected to the ground potential is provided in the apparatus body. The contact t 1  is electrically connected to a contact  1   b  of each process cartridge PP illustrated in  FIG. 3B  mounted on the cartridge tray  40 , via a wire material  48  illustrated in  FIG. 5  attached to the cartridge tray  40 . When the cartridge tray  40  is attached to the attached position in the apparatus body, the wire spring t 2  comes into pressure contact with the contact t 1 , and thus the photosensitive drums are grounded. 
     The contact t 1  and the wire spring t 2  are provided in a left end portion of the cartridge tray  40 , and are not provided on the right side thereof. In such a configuration, the position at which the arm  92  presses the first action portion  46   s   1  in the attachment direction of the cartridge tray  40  in the attached state of the cartridge tray  40  is offset to the left side with respect to the center position of the cartridge tray  40  in the X-axis direction. Therefore, a force of the wire spring t 2  pressing the cartridge tray  40  via the contact t 1  and a force that the cartridge tray  40  receives from the pull-in apparatus  90  cancel each other, and thus inclination of the cartridge tray  40  is suppressed. 
     Further, as described above, the process cartridges PPY, PPM, PPC, and PPK are positioned not with respect to the apparatus body of the image forming apparatus but with respect to the cartridge tray  40 . In such a case, the precision of the positioning may be degraded if the user is let perform the final positioning of the cartridge tray  40  by an insertion operation. In the case where the positioning precision of the cartridge tray  40  with respect to the body is low, the laser light irradiation position on the surface of the photosensitive drum  1  is displaced from an ideal position, resulting in displacement of an image position on the sheet. In contrast, according to the exemplary embodiment described above, since the positioning of the cartridge tray  40  with respect to the body is performed by the urging force of the arm spring  93  and the like, such a problem can be suppressed. 
     MODIFICATION EXAMPLE 
     In the present exemplary embodiment, as illustrated in  FIGS. 20A and 20B , the first action portion  46   s   1  comes into frictional contact with the first engagement surface  92   s  of the arm  92  in the course of inserting the cartridge tray  40  in the pull-in apparatus  90 . Therefore, it can be considered that the operational load of inserting the cartridge tray  40  becomes large depending on conditions such as the materials of the first action portion  46   s   1  and the first engagement surface  92   s  and the humidity. To address this, a rotary member having a columnar shape similarly to the first action portion  46   s   1  and pivotably supported by the cartridge tray  40  may be used instead of the first action portion  46   s   1  of the present exemplary embodiment. In addition, although the first action portion  46   s   1  serves as both of the portion that acts on the arm  92  in the initial stage of the lock-release operation and the portion that receives a pull-in force from the arm  92  after releasing the locking in the present exemplary embodiment, these portions may be provided as separate members. 
     In addition, the first engagement surface  92   s  of the arm  92  preferably has a shape that reduces fluctuation of the operational load of inserting the cartridge tray  40  to a position where pulling in of the cartridge tray  40  is started. For example, it is preferable that the first engagement surface  92   s  has an arcuate shape centered in a position away from the pivot support portion  910  of the arm  92  by a certain distance as viewed in the Z-axis direction. In addition, although all the components other than the springs  93  and  95  are formed from a resin material in the present exemplary embodiment, it can be also considered to form components that receive strong force, such as the arm  92 , from a metal material. In addition, it can be also considered to use torsion coil springs or compressive springs for the springs instead of tension springs. 
     In addition, a pull-in operation similar to that of the present exemplary embodiment can be realized also in the case where the arm  92  and the locking member  94  are disposed in the cartridge tray  40  and the first action portion  46   s   1  and the second action portion  46   s   2  are disposed in the apparatus body. That is, the arm member and the restriction member may be disposed in one of the apparatus body and the unit, and the first abutting portion and the second abutting portion may be disposed in the other of the apparatus body and the unit. However, disposing the arm  92  and the locking member  94  that are movable members in the apparatus body as in the present exemplary embodiment is advantageous for reducing the weight and size of the cartridge tray  40  and suppress damage to the members. 
     Second Exemplary Embodiment 
     A pull-in apparatus according to a second exemplary embodiment will be described. In the first exemplary embodiment, since only one arm  92  is provided, the cartridge tray  40  is pressed leftward or rightward by the arm  92  when inserting the cartridge tray  40  in the apparatus body, which is a cause of generation of a frictional force between the apparatus body and the cartridge tray  40 . 
     In the present exemplary embodiment, two arms  92 L and  92 R are symmetrically arranged in the left-right direction as illustrated in  FIG. 23 . In addition, locking mechanisms similar to that of the first exemplary embodiment and including locking members  94 L and  94 R are symmetrically arranged in the left-right direction in correspondence with the arms  92 L and  92 R. Therefore, a pivot direction R 3  of the arm  92 R on the right side upon pulling in the cartridge tray  40  serving as a third direction is a rotational direction opposite to the pull-in direction R 1  of the arm  92 L on the left side. In addition, the arms  92 L and  92 R are respectively connected to two ends of the arm spring  93  serving as a common urging portion and receive urging force. In the case where the arm  92 L and the locking member  94 L on the left side serve as a first arm member and a first restriction member, the arm  92 R and the locking member  94 R on the right side serve as a second arm member and a second restriction member. 
     In the present exemplary embodiment, detailed configurations of the arms  92 L and  92 R and the locking members  94 L and  94 R and operations of the arms  92 L and  92 R and the locking members  94 L and  94 R at the time of inserting the cartridge tray are the same as those of the arm  92  and the locking member  94  of the first exemplary embodiment. Therefore, also according to the configuration of the present exemplary embodiment, a pull-in apparatus capable of suppressing erroneous release of the locking can be provided. 
     In addition, in the configuration of the present exemplary embodiment, in forces that the two arms  92 L and  92 R apply to two first action portions  46   s   1 , components in the X-axis direction perpendicular to the attachment direction of the cartridge tray  40  cancel each other. As a result of this, friction between the cartridge tray  40  and the apparatus body can be reduced, and thus the operational load can be reduced. In addition, inclination of the cartridge tray  40  as viewed from above caused by the force received from the pull-in apparatus  90  during the inserting operation can be suppressed. Further, in the case where the same spring member as in the first exemplary embodiment is used as the arm spring  93 , since the tension of the arm spring  93  acts on the cartridge tray  40  through the arms  92 L and  92 R respectively connected to the two ends of the arm spring  93 , the force in the attachment direction received by the tray is approximately doubled. As a result, the required pull-in force can be secured even in the case where a spring member weaker than in the first exemplary embodiment is used, and therefore the cost of the arm spring  93  can be reduced. 
     Third Exemplary Embodiment 
     A pull-in apparatus according to a third exemplary embodiment will be described. Whereas the arm  92  holds the locking member  94  in the first exemplary embodiment, in the present exemplary embodiment a locking member  94 A is pivotably supported by the holder  91  as illustrated in  FIG. 24 . That is, the restriction member of the present exemplary embodiment is pivotably supported by the apparatus body separately from the arm member. 
     In the stand-by state, an engagement portion  92   e  of the arm  92  abuts the locking member  94 A, and thus pivoting of the arm  92  in the pull-in direction R 1  is restricted. When the cartridge tray  40  is inserted, the first action portion  46   s   1  provided on the tray presses the first engagement surface  92   s  of the arm  92  to pivot the arm  92  in the returning direction R 2  from the stand-by position against the arm spring  93  as illustrated in  FIG. 24 . As a result of this, the engagement portion  92   e  of the arm  92  is released from the locking member  94 A, and therefore it becomes possible to pivot the locking member  94 A in the clockwise direction in  FIG. 24 . However, in the state illustrated in  FIG. 24 , the orientation of the locking member  94 A is maintained by the urging force of the locking spring  95 , and therefore the locking of the arm  92  is not released. 
     When the cartridge tray  40  is further inserted, the second action portion  46   s   2  abuts the locking member  94 A to pivot the locking member  94 A in the clockwise direction in  FIG. 25  against the locking spring  95  as illustrated in  FIG. 25 . As a result of this, locking of the arm  92  by the locking member  94 A is released. Then, the arm  92  pivots in the pull-in direction R 1  in accordance with the urging force of the arm spring  93  in a state in which the second engagement surface  92   d  of the arm  92  is abutting the first action portion  46   s   1 , and thus the cartridge tray  40  is eventually pulled in to the position of  FIG. 26 . 
     Also in the present exemplary embodiment, two actions of (1) pivoting of the arm  92  in the returning direction R 2  and (2) pivoting of the locking member  94 A are required for releasing the locking of the arm  92 . Therefore, also according to the configuration of the present exemplary embodiment, a pull-in apparatus capable of suppressing erroneous release of locking can be provided. 
     OTHER EMBODIMENTS 
     Although the pull-in apparatus  90  that pulls the cartridge tray  40  into the apparatus body has been described in the first to third exemplary embodiments above, this pull-in apparatus  90  is applicable to an arbitrary apparatus including a unit that can be drawn out of the apparatus body. For example, this can be applied to a configuration in which the cassette  19  illustrated in  FIG. 2  serving as an example of a sheet accommodating portion that accommodates a sheet used as a recording medium is pulled into the apparatus body. In addition, the positioning mechanism of the cartridge tray  40  may be applied to other draw-out portions such as the cassette  19 . 
     In addition, for example, this can be applied to a configuration in which a sheet processing apparatus or an option feeder attachable to and detachable from the apparatus body of an image forming apparatus is pulled into the apparatus body. The sheet processing apparatus is an apparatus that performs processing such as binding on sheets, and the option feeder is an apparatus that supplies a sheet to the apparatus body. In addition, the apparatus to which the pull-in apparatus is applicable is not limited to an image forming apparatus, and the pull-in apparatus is also applicable to, for example, a configuration in which a drawer of a desk for an office or a drawer of storage furniture is pulled into the apparatus body, that is, a casing. 
     In addition, although description has been given by using the printer  100  of an electrophotographic system in all of the embodiments described above, the present invention is not limited to this. For example, the present invention can be also applied to an image forming apparatus of an inkjet system that forms an image on a sheet by ejecting an ink liquid through a nozzle. 
     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. 2019-027865, filed Feb. 19, 2019, and Japanese Patent Application No. 2019-027866, filed Feb. 19, 2019, which are hereby incorporated by reference herein in their entirety.