Patent Publication Number: US-9411303-B1

Title: Positioning stop assembly for a replaceable unit of an electrophotographic image forming device

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/145,642, filed Apr. 10, 2015, entitled “Handle and Positioning Stop Assembly for a Replaceable Unit of an Electrophotographic Image Forming Device,” the content of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to image forming devices and more particularly to a positioning stop assembly for a replaceable unit of an electrophotographic image forming device. 
     2. Description of the Related Art 
     In order to reduce the premature replacement of components traditionally housed within a toner cartridge for an image forming device, toner cartridge manufacturers have begun to separate components having a longer life from those having a shorter life into separate replaceable units. The image forming device&#39;s main toner supply, which is consumed relatively quickly, is provided in a large reservoir in a first replaceable unit, which may be referred to as a toner cartridge. Relatively longer life components are provided in one or more additional  20  replaceable units. For example, the developer roll, toner adder roll, doctor blade and a relatively small reservoir of toner (in the case of a single component development image forming device) or the magnetic roll and a relatively small reservoir containing a mix of toner and magnetic carrier beads (in the case of a dual component development image forming device) may be provided in a second replaceable unit, which may be referred to as a developer unit. The photoconductive drum, charge roll and cleaner blade/roll may be provided in a third replaceable unit, which may be referred to as a photoconductor unit. This configuration allows replenishment of the image forming device&#39;s toner supply without replacing the developer unit or the photoconductor unit. This configuration also allows the developer unit and the photoconductor unit to be repaired or replaced independent of the image forming device&#39;s main toner supply. 
     It is important that the replaceable units are precisely aligned within the image forming device for proper operation. The requirement for precise alignment must be balanced with the need to permit a user to easily load and unload the replaceable units into and out of the image forming device. 
     SUMMARY 
     A replaceable unit for an electrophotographic image forming device according to one example embodiment includes a housing and a positioning stop on the housing that is translatable between a latching position and an unlatching position. The positioning stop is positioned to limit the travel of the replaceable unit in the image forming device when the positioning stop is in the latching position. A compression spring is positioned in line with the translation of the positioning stop between the positioning stop and a first side of a post on the housing. The compression spring biases the positioning stop toward the latching position. A deflectable arm extends from the positioning stop in line with the translation of the positioning stop proximate the compression spring. The deflectable arm includes a hook that wraps over the post in position to contact a second side of the post opposite the first side of the post to limit translation of the positioning stop away from the post. 
     A replaceable unit for an electrophotographic image forming device according to another example embodiment includes a housing and a positioning stop on the housing that is slidable between a latching position and an unlatching position. The positioning stop is biased toward the latching position. The positioning stop is positioned to limit the travel of the replaceable unit in the image forming device when the positioning stop is in the latching position. A pair of guides running in line with the sliding movement of the positioning stop on opposite sides of the positioning stop guide the sliding movement of the positioning stop between the latching position and the unlatching position. A deflectable arm extends from the positioning stop in line with the sliding movement of the positioning stop. The deflectable arm includes a hook that wraps over a post on the housing in position to contact a first side of the post to limit the sliding movement of the positioning stop away from the post. 
     A replaceable unit for an electrophotographic image forming device according to another example embodiment includes a housing having a photoconductive drum rotatably mounted thereon. The photoconductive drum has a rotational axis. A guide channel on an exterior of the housing extends parallel to the rotational axis of the photoconductive drum and is positioned to guide insertion of the housing into the image forming device. A positioning stop on the housing is translatable perpendicular to the rotational axis of the photoconductive drum between a latching position and an unlatching position. In the latching position the positioning stop obstructs at least a portion of the guide channel to limit the travel of the replaceable unit in the image forming device parallel to the rotational axis of the photoconductive drum. A compression spring is positioned in line with the translation of the positioning stop between the positioning stop and a first side of a post on the housing. The compression spring biases the positioning stop toward the latching position. A deflectable arm extends from the positioning stop in line with the translation of the positioning stop proximate the compression spring. The deflectable arm includes a hook that wraps over the post in position to contact a second side of the post opposite the first side of the post to limit translation of the positioning stop away from the post toward the latching position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present disclosure, and together with the description serve to explain the principles of the present disclosure. 
         FIG. 1  is a block diagram depiction of an imaging system according to one example embodiment. 
         FIG. 2  is a schematic diagram of an image forming device according to one example embodiment. 
         FIG. 3  is a perspective view of an imaging unit including a developer unit and a photoconductor unit according to one example embodiment. 
         FIG. 4  is a perspective view of the imaging unit showing the developer unit separated from the photoconductor unit according to one example embodiment. 
         FIG. 5  is a perspective view of a rear end of the imaging unit with the imaging unit installed in the image forming device according to one example embodiment. 
         FIG. 6  is an exploded view of a rear end of the photoconductor unit according to one example embodiment. 
         FIG. 7  is a perspective view of the rear end of the photoconductor unit with an end cap and a handle of the photoconductor unit removed to illustrate a positioning stop of the photoconductor unit according to one example embodiment. 
         FIG. 8  is a perspective view of an inner side of a rear end cap of the photoconductor unit according to one example embodiment. 
         FIG. 9  is a perspective view of the rear end of the photoconductor unit installed in the image forming device with the rear end cap removed to illustrate the handle and the positioning stop in their latching positions according to one example embodiment. 
         FIG. 10  is a perspective view of the rear end of the photoconductor unit installed in the image forming device with the rear end cap removed to illustrate the handle in and the positioning stop in their unlatching positions according to one example embodiment. 
         FIG. 11  is a perspective view of the rear end of the photoconductor unit installed in the image forming device with the rear end cap removed to illustrate the handle in its latching position and the positioning stop in its unlatching position according to one example embodiment. 
         FIG. 12  is a side cross-sectional view of an access door of the image forming device showing an interference feature on an inner side of the access door contacting the handle of the photoconductor unit when the photoconductor unit is not installed completely in the image forming device and the handle is in its unlatching position according to one example embodiment. 
         FIG. 13  is a side cross-sectional view of the access door of the image forming device showing multiple interference features on the inner side of the access door positioned to contact the handles of multiple photoconductor units when the photoconductor units are not installed completely in the image forming device according to one example embodiment. 
         FIG. 14  is a side cross-sectional view of the access door showing the interference feature clearing the handle of the photoconductor unit when the photoconductor unit is installed in the image forming device and the handle is in its latching position according to one example embodiment. 
         FIG. 15  is a side cross-sectional view of the access door in a closed position with the interference feature clear of the handle of the photoconductor unit according to one example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present disclosure. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present disclosure is defined only by the appended claims and their equivalents. 
     Referring now to the drawings and more particularly to  FIG. 1 , there is shown a block diagram depiction of an imaging system  20  according to one example embodiment. Imaging system  20  includes an image forming device  100  and a computer  30 . Image forming device  100  communicates with computer  30  via a communications link  40 . As used herein, the term “communications link” generally refers to any structure that facilitates electronic communication between multiple components and may operate using wired or wireless technology and may include communications over the Internet. 
     In the example embodiment shown in  FIG. 1 , image forming device  100  is a multifunction machine (sometimes referred to as an all-in-one (AIO) device) that includes a controller  102 , a print engine  110 , a laser scan unit (LSU)  112 , one or more toner bottles or cartridges  200 , one or more imaging units  300 , a fuser  120 , a user interface  104 , a media feed system  130  and media input tray  140  and a scanner system  150 . Image forming device  100  may communicate with computer  30  via a standard communication protocol, such as, for example, universal serial bus (USB), Ethernet or IEEE 802.xx. Image forming device  100  may be, for example, an electrophotographic printer/copier including an integrated scanner system  150  or a standalone electrophotographic printer. 
     Controller  102  includes a processor unit and associated memory  103  and may be formed as one or more Application Specific Integrated Circuits (ASICs). Memory  103  may be any volatile or non-volatile memory or combination thereof such as, for example, random access memory (RAM), read only memory (ROM), flash memory and/or non-volatile RAM (NVRAM). Alternatively, memory  103  may be in the form of a separate electronic memory (e.g., RAM, ROM, and/or NVRAM), a hard drive, a CD or DVD drive, or any memory device convenient for use with controller  102 . Controller  102  may be, for example, a combined printer and scanner controller. 
     In the example embodiment illustrated, controller  102  communicates with print engine  110  via a communications link  160 . Controller  102  communicates with imaging unit(s)  300  and processing circuitry  301  on each imaging unit  300  via communications link(s)  161 . Controller  102  communicates with toner cartridge(s)  200  and processing circuitry  201  on each toner cartridge  200  via communications link(s)  162 . Controller  102  communicates with fuser  120  and processing circuitry  121  thereon via a communications link  163 . Controller  102  communicates with media feed system  130  via a communications link  164 . Controller  102  communicates with scanner system  150  via a communications link  165 . User interface  104  is communicatively coupled to controller  102  via a communications link  166 . Processing circuitry  121 ,  201 ,  301  may include a processor and associated memory such as RAM, ROM, and/or NVRAM and may provide authentication functions, safety and operational interlocks, operating parameters and usage information related to fuser  120 , toner cartridge(s)  200  and imaging unit(s)  300 , respectively. Controller  102  processes print and scan data and operates print engine  110  during printing and scanner system  150  during scanning. 
     Computer  30 , which is optional, may be, for example, a personal computer, including memory  32 , such as RAM, ROM, and/or NVRAM, an input device  34 , such as a keyboard and/or a mouse, and a display monitor  36 . Computer  30  also includes a processor, input/output (I/O) interfaces, and may include at least one mass data storage device, such as a hard drive, a CD-ROM and/or a DVD unit (not shown). Computer  30  may also be a device capable of communicating with image forming device  100  other than a personal computer such as, for example, a tablet computer, a smartphone, or other electronic device. 
     In the example embodiment illustrated, computer  30  includes in its memory a software program including program instructions that function as an imaging driver  38 , e.g., printer/scanner driver software, for image forming device  100 . Imaging driver  38  is in communication with controller  102  of image forming device  100  via communications link  40 . Imaging driver  38  facilitates communication between image forming device  100  and computer  30 . One aspect of imaging driver  38  may be, for example, to provide formatted print data to image forming device  100 , and more particularly to print engine  110 , to print an image. Another aspect of imaging driver  38  may be, for example, to facilitate the collection of scanned data from scanner system  150 . 
     In some circumstances, it may be desirable to operate image forming device  100  in a standalone mode. In the standalone mode, image forming device  100  is capable of functioning without computer  30 . Accordingly, all or a portion of imaging driver  38 , or a similar driver, may be located in controller  102  of image forming device  100  so as to accommodate printing and/or scanning functionality when operating in the standalone mode. 
       FIG. 2  illustrates a schematic view of the interior of an example image forming device  100 . For purposes of clarity, the components of only one of the imaging units  300  are labeled in  FIG. 2 . Image forming device  100  includes a housing  170  having a top  171 , bottom  172 , front  173 , rear  174  and a pair of sides (one facing out of the page and one facing into the page as viewed in  FIG. 2 ). Housing  170  includes one or more media input trays  140  positioned therein. Trays  140  are sized to contain a stack of media sheets. As used herein, the term media is meant to encompass not only paper but also labels, envelopes, fabrics, photographic paper or any other desired substrate. Trays  140  are preferably removable for refilling. A media path  180  extends through image forming device  100  for moving the media sheets through the image transfer process. Media path  180  includes a simplex path  181  and may include a duplex path  182 . A media sheet is introduced into simplex path  181  from tray  140  by a pick mechanism  132 . In the example embodiment shown, pick mechanism  132  includes a roll  134  positioned at the end of a pivotable arm  136 . Roll  134  rotates to move the media sheet from tray  140  and into media path  180 . The media sheet is then moved along media path  180  by various transport rollers. Media sheets may also be introduced into media path  180  by a manual feed  138  having one or more rolls  139 . 
     In the example embodiment shown, image forming device  100  includes four toner cartridges  200  removably mounted in housing  170  in a mating relationship with four corresponding imaging units  300 , which are also removably mounted in housing  170 . Each toner cartridge  200  includes a reservoir  202  for holding toner and an outlet port in communication with an inlet port of its corresponding imaging unit  300  for transferring toner from reservoir  202  to imaging unit  300 . Toner is transferred periodically from a respective toner cartridge  200  to its corresponding imaging unit  300  in order to replenish the imaging unit  300 . In the example embodiment illustrated, each toner cartridge  200  is substantially the same except for the color of toner contained therein. In one embodiment, the four toner cartridges  200  contain yellow, cyan, magenta and black toner, respectively. 
     In the example embodiment illustrated, image forming device  100  utilizes what is commonly referred to as a dual component development system. Each imaging unit  300  includes a reservoir  302  that stores a mixture of toner and magnetic carrier beads. The carrier beads may be coated with a polymeric film to provide triboelectric properties to attract toner to the carrier beads as the toner and the carrier beads are mixed in reservoir  302 . Reservoir  302  and a magnetic roll  306  collectively form a developer unit. Magnetic roll  306  includes a stationary core that includes one or more permanent magnets and a rotatable sleeve that encircles the core. Reservoir  302  may include toner agitators, such as paddles, augers, etc., that stir the developer mix and present the developer mix to magnetic roll  306 . Each imaging unit  300  also includes a charge roll  308 , a photoconductive drum (PC drum)  310  and a cleaner blade or roll (not shown) that collectively form a photoconductor unit. PC drums  310  are mounted substantially parallel to each other when the imaging units  300  are installed in image forming device  100 . In the example embodiment illustrated, each imaging unit  300  is substantially the same except for the color of toner contained therein. 
     Each charge roll  308  forms a nip with the corresponding PC drum  310 . During a print operation, charge roll  308  charges the surface of PC drum  310  to a specified voltage, such as, for example, −1000 volts. A laser beam from LSU  112  is then directed to the surface of PC drum  310  and selectively discharges those areas it contacts to form a latent image. In one embodiment, areas on PC drum  310  illuminated by the laser beam are discharged to approximately −300 volts. The permanent magnet(s) of magnetic roll  306  attract the carrier beads in reservoir  302  having toner thereon to the outer surface of the sleeve of magnetic roll  306 . The sleeve of magnetic roll  306  transports the carrier beads having toner thereon past a trim bar that trims the mix of carrier beads and toner to a predetermined average height on the outer surface of the sleeve. The sleeve of magnetic roll  306  then transports the carrier beads having toner thereon to the corresponding PC drum  310 . Electrostatic forces from the latent image on PC drum  310  strip the toner from the carrier beads to form a toner image on the surface of PC drum  310 . 
     An intermediate transfer mechanism (ITM)  190  is disposed adjacent to the PC drums  310 . In this embodiment, ITM  190  is formed as an endless belt trained about a drive roll  192 , a tension roll  194  and a back-up roll  196 . During image forming operations, ITM  190  moves past PC drums  310  in a clockwise direction as viewed in  FIG. 2 . One or more of PC drums  310  apply toner images in their respective colors to ITM  190  at a respective first transfer nip  197 . In one embodiment, a positive voltage field attracts the toner images from PC drums  310  to the surface of the moving ITM  190 . ITM  190  rotates and collects the one or more toner images from PC drums  310  and then conveys the toner images to a media sheet at a second transfer nip  198  formed between a transfer roll  199  and ITM  190 , which is supported by back-up roll  196 . The cleaner blade/roll removes any toner remnants on PC drum  310  so that the surface of PC drum  310  may be charged and developed with toner again. 
     A media sheet advancing through simplex path  181  receives the toner image from ITM  190  as it moves through the second transfer nip  198 . The media sheet with the toner image is then moved along the media path  180  and into fuser  120 . Fuser  120  includes fusing rolls or belts  122  that form a nip to adhere the toner image to the media sheet. The fused media sheet then passes through exit rolls  126  located downstream from fuser  120 . Exit rolls  126  may be rotated in either forward or reverse directions. In a forward direction, exit rolls  126  move the media sheet from simplex path  181  to an output area  128  on top  171  of image forming device  100 . In a reverse direction, exit rolls  126  move the media sheet into duplex path  182  for image formation on a second side of the media sheet. 
     While the example image forming device  100  shown in  FIG. 2  illustrates four toner cartridges  200  and four corresponding imaging units  300 , it will be appreciated that a monocolor image forming device  100  may include a single toner cartridge  200  and corresponding imaging unit  300  as compared to a multicolor image forming device  100  that may include multiple toner cartridges  200  and imaging units  300 . Further, although image forming device  100  utilizes ITM  190  to transfer toner to the media, toner may be applied directly to the media by the one or more photoconductive drums  310  as is known in the art. 
     While the example image forming device  100  shown in  FIG. 2  utilizes a dual component development system, in another embodiment, image forming device  100  utilizes what is commonly referred to as a single component development system. In this embodiment, a toner adder roll in each developer unit has an outer surface that is in contact with and forms a nip with the outer surface of a corresponding developer roll. As the toner adder roll and the developer roll rotate, the toner adder roll supplies toner in reservoir  302  to the developer roll. The developer roll is electrically charged and electrostatically attracts the toner particles supplied by the toner adder roll. A doctor blade positioned along each developer roll provides a substantially uniform layer of toner on the developer roll. The outer surface of the developer roll is also in contact with and forms a nip with the outer surface of a corresponding PC drum  310 . As the developer roll and PC drum  310  rotate, toner particles are electrostatically transferred from the developer roll to the latent image on PC drum  310  forming a toned image on the surface of PC drum  310 . PC drum  310  is charged by charge roll  308  and cleaned by a cleaner blade/roll as discussed above. 
       FIGS. 3 and 4  show imaging unit  300  according to one example embodiment. Imaging unit  300  includes a developer unit  320  and a photoconductor unit (PC unit)  330 . In the example embodiment illustrated, developer unit  320  is removably coupled to PC unit  330  to permit repair or replacement of developer unit  320  independent of PC unit  330  and vice versa. In other embodiments, developer unit  320  and PC unit  330  are fixed together such that imaging unit  300  is replaced as a single unit. PC unit  330  includes a housing  332  having PC drum  310  as well as charge roll  308  ( FIG. 2 ) and a cleaner blade/roll (not shown) mounted thereto. Housing  332  may also include one or more user-actuated latches  334  that couple developer unit  320  to PC unit  330  as shown in  FIG. 3  for operation in image forming device  100  and that permit a user to separate developer unit  320  from PC unit  330  when imaging unit  300  is removed from image forming device  100  as shown in  FIG. 4 . Developer unit  320  includes a housing  322  having reservoir  302  therein. Housing  322  extends generally along an axial dimension of magnetic roll  306 , which is substantially parallel to an axial dimension of PC drum  310 . A portion of magnetic roll  306  is exposed from reservoir  302  at one side of housing  322  for mating with PC drum  310  when developer unit  320  is coupled to PC unit  330 . When developer unit  320  is coupled to PC unit  330 , imaging unit  300  is insertable into image forming device  100  via a sliding motion along an insertion direction  326  as indicated in  FIG. 3 . 
     With reference to  FIG. 4 , housing  332  includes a front end  336  that leads during insertion of PC unit  330  into image forming device  100  and a rear end  337  opposite front end  336  that trails during insertion of PC unit  330  into image forming device  100 . In the embodiment illustrated, the axis of PC drum  310  extends along a front-to-rear dimension of housing  332  (i.e., along a horizontal dimension of housing  332  extending from front end  336  to rear end  337 ). Housing  332  also includes a top  338 , a bottom  339  and a pair of sides  340 ,  341 . In the embodiment illustrated, a portion of PC drum  310  is exposed at top  338  of housing  332  where PC drum  310  transfers the toner image formed on the surface of PC drum  310  to ITM  190  or to the print media. A portion of PC drum  310  is also exposed on side  340  of housing  332  facing magnetic roll  306  where toner is transferred to the surface of PC drum  310  by magnetic roll  306  when developer unit  320  is mated with PC unit  330 . 
       FIG. 5  shows rear end  337  of housing  332  in closer detail. A guide channel  342  is formed in the bottom  339  of housing  332  and runs along the length of housing  332  from front end  336  to rear end  337 . Guide channel  342  receives and rides on a corresponding guide rail  400  in image forming device  100  when imaging unit  300  is inserted into image forming device  100 . The engagement between guide rail  400  and guide channel  342  guides the sliding movement of imaging unit  300  into image forming device  100  and provides coarse alignment of PC unit  330  in a side-to-side dimension (i.e., along a horizontal dimension of housing  332  extending from side  340  to side  341 ) and a vertical dimension of housing  332  during installation of imaging unit  300  into image forming device  100 . 
       FIG. 6  shows an exploded view of rear end  337  of housing  332 . As shown in  FIG. 6 , in one embodiment, rear end  337  includes an end cap  344  mounted on a rear wall  346  of housing  332 . With reference to  FIGS. 5 and 6 , a positioning stop  348  is positioned at rear end  337  of housing  332 . In the embodiment illustrated, positioning stop  348  is mounted on an outer side of rear wall  346  and positioned between an inner side of end cap  344  and the outer side of rear wall  346 . In the embodiment illustrated, positioning stop  348  is slidable and translatable up and down between an unlatching position ( FIGS. 10 and 11 ) and a latching position ( FIGS. 5, 7 and 9 ). Positioning stop  348  provides a datum surface that defines the position of PC unit  330  and imaging unit  300  in image forming device  100  along the front-to-rear dimension of housing  332  (the axial dimension of PC drum  310  in the embodiment illustrated) as discussed in greater detail below. In other embodiments, positioning stop  348  is mounted on end cap  344  instead of rear wall  346 ; however, the mounting of positioning stop  348  on rear wall  346  provides more accurate positioning of PC drum  310  relative to image forming device  100  than the mounting of positioning stop  348  on end cap  344  due to the tolerance stack up between end cap  344  and the portion of housing  332  that supports PC drum  310 . A release handle  350  is exposed on an outer side of end cap  344  through an opening  352  in end cap  344 . Release handle  350  is operatively connected to positioning stop  348 , e.g., by a bell crank  354 , to permit a user to move positioning stop  348  from its latching position to its unlatching position as discussed in greater detail below. 
       FIG. 7  shows rear end  337  of housing  332  with end cap  344  and release handle  350  removed in order to illustrate the mounting of positioning stop  348  on the outer side of rear wall  346  according to one example embodiment. The features of positioning stop  348  obscured by bell crank  354  in  FIG. 7  are shown in broken line. Positioning stop  348  is biased downward toward its latching position as shown in  FIG. 7 . In the latching position of positioning stop  348 , a bottom surface  348   a  of positioning stop  348  is positioned lower than a top surface  342   a  of guide channel  342  such that positioning stop  348  obstructs at least a portion of the rear end of guide channel  342 . In one embodiment, positioning stop  348  clears guide channel  342  in its unlatching position. In the embodiment illustrated, a compression spring  356  biases positioning stop  348  toward its latching position. Spring  356  is positioned in line with or substantially parallel to the translation of positioning stop  348  between a top surface  348   b  of positioning stop  348  and a bottom surface  358   a  of a post  358  on rear wall  346 . In the embodiment illustrated, spring  356  is positioned around a boss  357  on top surface  348   b  of positioning stop  348 . Although a compression spring  356  is illustrated, any suitable biasing member may be used to bias positioning stop  348  toward its latching position such as, for example, an extension or leaf spring or a material having resilient properties. 
     In the example embodiment illustrated, positioning stop  348  is retained in the side-to-side and front-to-rear dimensions of housing  332  by a pair of guide slots  360 ,  361  positioned on opposite sides of positioning stop  348 . Guide slots  360 ,  361  receive corresponding guide ribs  359   a ,  359   b  of positioning stop  348 . Guide ribs  359   a ,  359   b  extend outward from opposite sides of positioning stop  348  (perpendicular to the translation of positioning stop  348 ) and run vertically between top surface  348   b  and bottom surface  348   a  of positioning stop  348  (in line with or substantially parallel to the translation of positioning stop  348 ). In one embodiment, guide ribs  359   a ,  359   b  are relatively thin in the front-to-rear dimension of housing  332 . In other embodiments, this configuration is reversed and guide slots on positioning stop  348  receive corresponding guide wings on rear wall  346 . 
     In the embodiment illustrated, positioning stop  348  includes a deflectable arm  362  that extends upward from top surface  348   b  of positioning stop  348  (in line with or substantially parallel to the translation of positioning stop  348 ). Arm  362  includes a hook  363  that wraps above a top surface  358   b  of post  358 . Contact between hook  363  and top surface  358   b  of post  358  limits the travel of positioning stop  348  downward toward its latching position. Contact between boss  357  and bottom surface  358   a  of post  358  limits the travel of positioning stop  348  upward toward its unlatching position. 
     The use of deflectable arm  362  along with guide ribs  359   a ,  359   b  and corresponding guide slots  360 ,  361  reduces the amount of space occupied by positioning stop  348  in the front-to-rear dimension of housing  332  thereby reducing the footprint of PC unit  330 . Deflectable arm  362 , guide ribs  359   a ,  359   b  and guide slots  360 ,  361  also permit relatively easy assembly of positioning stop  348  onto PC unit  330 . In the example embodiment illustrated, positioning stop  348  is assembled to rear wall  346  of housing  332  by first sliding positioning stop  348  upward between guide slots  360 ,  361  with guide ribs  359   a ,  359   b  positioned in guide slots  360 ,  361  and spring  356  positioned between top surface  348   b  of positioning stop  348  and bottom surface  358   a  of post  358 . Positioning stop  348  is then slid further upward until hook  363  of deflectable arm  362  clears and catches on top surface  358   b  of post  358 . 
       FIG. 8  shows the inner side of end cap  344  according to one example embodiment. In the example embodiment illustrated, release handle  350  is mounted on the inner side of end cap  344 . In the example embodiment, release handle  350  is translatable up and down between a latching position ( FIGS. 5-7, 9 ) and an unlatching position ( FIGS. 8 and 10 ) of release handle  350 . Guides  372 ,  374  positioned on the inner side of end cap  344  on opposite sides of release handle  350  retain release handle  350  in the side-to-side dimension of housing  332 . In the embodiment illustrated, guide  372  includes a rib on the inner side of end cap  344  that is positioned against a side surface of handle  350  and guide  374  includes a post on the inner side of end cap  344  that travels in an elongated vertical slot  375  in handle  350 . However, guides  372 ,  374  may take any suitable form. In the embodiment illustrated, release handle  350  also includes a vertical groove  364  that receives a corresponding guide  376  on the inner side of end cap  344 . The engagement between groove  364  and guide  376  aids in guiding the movement of release handle  350  between the latching and unlatching positions of release handle  350 . One or more of guides  372 ,  374  and  376  may include a lip  378  that extends over an inner surface of release handle  350  in order to retain release handle  350  against the inner side of end cap  344  in the front-to-rear dimension of housing  332 . Further, in one embodiment, a rear face  358   c  ( FIGS. 7, 10 and 11 ) of post  358  on rear wall  346  is positioned to retain release handle  350  against the inner side of end cap  344  in the front-to-rear dimension of housing  332  when end cap  344  is mounted on rear wall  346 . In one embodiment, the inner side of end cap  344  includes an upstop  380  and a downstop  382  that limit the upward and downward travel of release handle  350  toward its latching and unlatching positions. In some embodiments, a top or bottom surface of guide  372 ,  374  or  376  may form downstop  382  or upstop  380 . For example, in the embodiment illustrated, a bottom surface of guide  374  forms upstop  380  and a top surface of guide  374  forms downstop  382 . In other embodiments, a top or bottom surface of opening  352  may limit the upward or downward travel of release handle  350 . Release handle  350  also includes a boss  366  that extends forward from release handle  350 , away from the inner side of release handle  350  and toward the outer side of rear wall  346 . 
       FIGS. 9-11  show rear end  337  of housing  332  with end cap  344  removed but release handle  350  included to more clearly illustrate the operation of release handle  350  and positioning stop  348 . Handle  350  is shown in broken line in  FIGS. 9 and 10  in order to more clearly illustrate the features of positioning stop  348  and bell crank  354 . With reference to  FIGS. 7 and 9 , bell crank  354  is pivotally mounted to the outer side of rear wall  346  (as shown) or the inner side of end cap  344  about a pivot axis  355 . Bell crank  354  is coupled at its first end to release handle  350  such that bell crank  354  pivots when release handle  350  moves up or down between its latching and unlatching positions. For example, in the embodiment illustrated, bell crank  354  includes an engagement slot  368  that receives boss  366  of release handle  350 . Bell crank  354  includes an engagement surface  369  at its second end that moves positioning stop  348  from its latching position toward its unlatching position when bell crank  354  pivots as a result of release handle  350  moving from its latching position to its unlatching position. 
       FIG. 9  shows both release handle  350  and positioning stop  348  in their latching positions. In the example embodiment illustrated, when bell crank  354  pivots clockwise as viewed in  FIG. 9  as a result of release handle  350  moving downward from its latching position toward its unlatching position, engagement surface  369  pushes upward on a boss  370  located on positioning stop  348  thereby moving positioning stop  348  from its latching position toward its unlatching position as shown in  FIG. 10 , which shows both release handle  350  and positioning stop  348  in their unlatching positions. Further, in the embodiment illustrated, bell crank  354  includes sufficient clearance to permit positioning stop  348  to move upward toward its unlatching position independent of bell crank  354  as shown in  FIG. 11  and as discussed in greater detail below. In other embodiments, bell crank  354  is coupled to positioning stop  348  such that bell crank  354  pivots when positioning stop  348  moves up or down. 
     With reference to  FIGS. 5 and 9 , as imaging unit  300  is inserted into image forming device  100  along insertion direction  326 , when PC unit  330  nears its final front-to-rear position in image forming device  100 , bottom surface  348   a  of positioning stop  348  contacts a tapered top surface  401  of guide rail  400 . The forward travel of imaging unit  300  and contact between bottom surface  348   a  of positioning stop  348  and tapered top surface  401  of guide rail  400  result in an upward force on positioning stop  348  that overcomes the bias applied to positioning stop  348  causing positioning stop  348  to translate upward from its latching position toward its unlatching position where positioning stop  348  is positioned on top of guide rail  400 . In one embodiment, bottom surface  348   a  of positioning stop  348  includes a corresponding taper to that of tapered top surface  401  in order to facilitate the rise of positioning stop  348  as imaging unit  300  advances. As positioning stop  348  moves upward, hook  363  separates from top surface  358   b  of post  358 . As discussed above, in one embodiment, positioning stop  348  is free to move toward its unlatching position without rotating bell crank  354  as shown in  FIG. 11  so that release handle  350  may be in its upward latching position, its downward unlatching position or anywhere in between when imaging unit  300  is inserted into image forming device  100 . This allows a user to slide imaging unit  300  into position while holding release handle  350  without worrying about the position on release handle  350  relative to housing  332 . 
     With reference back to  FIGS. 5 and 9 , as imaging unit  300  is inserted further into image forming device  100 , when PC unit  330  reaches its final front-to-rear position in image forming device  100 , positioning stop  348  reaches an opening  402  in the top surface of guide rail  400 . The bias applied to positioning stop  348  causes positioning stop  348  to translate downward into opening  402  from its unlatching position to its latching position. In one embodiment, PC unit  330  is biased rearward by one or more biasing features in image forming device  100  such that when positioning stop  348  enters opening  402 , a rear surface  348   c  of positioning stop  348  is pressed against a corresponding surface inside of opening  402 . The contact between rear surface  348   c  of positioning stop  348  and the corresponding surface in opening  402  defines the front-to-rear position of imaging unit  300  to ensure that PC unit  330  and developer unit  320  are accurately positioned for operation in image forming device  100 . The movement of positioning stop  348  into opening  402  in guide rail  400  may produce an audible clicking or snapping sound providing feedback to the user that imaging unit  300  is fully installed in image forming device  100 . It will be appreciated that positioning stop  348  functions without interaction from the user other than the user pushing imaging unit  300  into image forming device  100 . A user does not need to separately actuate positioning stop  348  to install imaging unit  300 . 
     With reference to  FIG. 10 , in order to remove imaging unit  300  from image forming device  100 , a user simply presses down on release handle  350  to move release handle  350  from its latching position to its unlatching position and pulls imaging unit  300  from image forming device  100 . The downward movement of release handle  350  causes bell crank  354  to pivot clockwise as viewed in  FIG. 10 , which, in turn, causes positioning stop  348  to rise from its latching position to its unlatching position clear of opening  402  in guide rail  400 . With positioning stop  348  in its unlatching position, a user is free to pull imaging unit  300  from image forming device  100  with guide channel  342  sliding along guide rail  400  to guide the removal of imaging unit  300 . 
     A problem may occur if imaging unit  300  is not installed completely in image forming device  100 , i.e., if a user inserts imaging unit  300  into image forming device  100  without pushing imaging unit  300  far enough for positioning stop  348  to pass into opening  402  in guide rail  400 . With reference to  FIG. 12 , image forming device  100  includes an access door  410  positioned at rear end(s)  337  of PC unit(s)  330  that permits a user to install and remove imaging unit(s)  300  into and out of image forming device  100 . In the example embodiment illustrated, access door  410  is positioned on the side of image forming device  100  facing out of the page as viewed in  FIG. 2 . In one embodiment, an inner side of access door  410  includes an interference feature  412  positioned to contact release handle  350  if release handle  350  is in its unlatching position. If imaging unit  300  is installed in image forming device  100  close to, but short of, its final position, bottom surface  348   a  of positioning stop  348  will rest on the top surface of guide rail  400  upstream from opening  402  with respect to insertion direction  326  with positioning stop  348  in its unlatching position. In the example embodiment illustrated in  FIGS. 5-11 , release handle  350  will tend to be in its unlatching position when positioning stop  348  is in its unlatching position due to the weight of release handle  350 . When the user closes access door  410  with imaging unit  300  not completely installed in image forming device  100 , a face  413  of interference feature  412  contacts a face  351  of release handle  350  as shown in  FIG. 12 . As the user pushes access door  410  closed, the contact between face  413  of interference feature  412  and face  351  of release handle  350  pushes imaging unit  300  forward to its final position in image forming device  100  where positioning stop  348  is aligned with opening  402  in guide rail  400 . 
     With reference to  FIG. 13 , where image forming device  100  includes more than one imaging unit  300 , access door  410  includes an interference feature  412  for the release handle  350  of each PC unit  330 . In one embodiment, the interference features  412  are arranged such that as access door  410  is closed, interference features  412  contact their corresponding release handles  350  one at a time if the release handles  350  are in their unlatching positions so that a user only needs to overcome the force of one imaging unit  300  at a time instead of all imaging units  300  at once in order to reduce the force required to move access door  410  toward its closed position. 
     With reference back to  FIG. 12 , in one embodiment, face  413  of interference feature  412  is angled downward and face  351  of release handle  350  is angled upward so that interference feature  412  tends to exert a slight downward force on release handle  350  in order to prevent release handle  350  from rising to its latching position before positioning stop  348  reaches opening  402 . If release handle  350  were to rise to its latching position prematurely, interference feature  412  would clear release handle  350  before imaging unit  300  reached its final position in image forming device  100 . 
     The contact between interference feature  412  and release handle  350  prevents access door  410  from closing all the way. However, when the user opens access door  410  far enough to separate interference feature  412  from release handle  350  upon recognizing that access door  410  is not closed all the way, positioning stop  348  moves into opening  402  in guide rail  400  as a result of the bias applied to positioning stop  348  thereby securing imaging unit  300  in its final position in image forming device  100 . Release handle  350 , in turn, moves to its latching position clear of interference feature  412  as shown in  FIG. 14 . Once release handle  350  clears interference feature  412 , the user is able to fully close access door  410  as shown in  FIG. 15 . 
     Although the example embodiment illustrated shows positioning stop  348  and release handle  350  positioned on PC unit  330 , it will be appreciated that a similar configuration may be used on any replaceable unit of image forming device  100  such as, for example, toner cartridge  200  or developer unit  320 . Further, although the positioning stop  348  in the embodiment illustrated translates up and down between its latching and unlatching positions, other configurations are possible. For example, positioning stop  348  may translate side-to-side, pivot, etc. Similarly, although the release handle  350  in the embodiment illustrated translates up and down between its latching and unlatching positions, other configurations are possible. For example, release handle  350  may translate side-to-side, translate in-and-out, pivot about an axis that is parallel to the axis of PC drum  310 , pivot about an axis that is perpendicular to the axis of PC drum  310 , etc. Further, although the example embodiment illustrated shows positioning stop  348  positioned on the replaceable unit and opening  402  that receives positioning stop  348  positioned on housing  170  of image forming device  100 , it will be appreciated that this configuration may be reversed by placing positioning stop  348  on housing  170  in position to engage a corresponding opening or surface on the replaceable unit. 
     The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.