Abstract:
An image forming device includes a body and one or more door assemblies. At least one door assembly may be movable between open and closed orientations. A variety of mechanical and electrical interlocks may be used to control motion of the door assemblies. A first interlock may prevent a door assembly from moving under the influence of a force between an open and closed orientation prior to a condition being satisfied. This condition may depend on the position of a second door assembly. A breakaway feature may release the first interlock when the closing force exceeds a predetermined level. A second interlock may work with the first interlock to keep a second door assembly from opening if the first door assembly is closed. An electrical interlock may disconnect power to the image forming device when the first door assembly is open.

Description:
BACKGROUND  
       [0001]     Image forming devices often have modular designs comprising a plurality of consumer replaceable units (CRUs). Some example CRUs include waste toner cartridges, developer cartridges, photoconductive members, and transport belt modules. Some of these CRUs are consumable items that are used or worn with use. Over the life of an image forming unit, these CRUs may be replaced multiple times. Replacing the CRUs typically requires access to the interior of the image forming unit.  
         [0002]     Replacement and mounting of these modules is vital to acceptable user ergonomics. The modules should be positioned in a manner to be accessible to the user. The complex design of many current devices makes accessing the components difficult. The modules may be located within the interior of the device making it very difficult to grasp and manipulate the modules. Intricate cartridge mounting locations may also result in toner spills and component damage, which may result in print defects, or the device not operating properly.  
         [0003]     In addition to replacing CRUs, there may be other times when it is necessary to access the interior of an image forming device. For instance, paper jam errors sometimes require access to interior portions of a paper feed path to clear misfeeds. To that end, image forming devices are often provided with exterior door panels. These door panels often comprise some portion of the exterior housing of the image forming device and may be opened and closed as needed to access the interior of the device.  
         [0004]     As image forming devices become smaller in size, rigid space constraints may limit placement options for internal components, including CRUs. In some cases, it may be advantageous to include multiple door panels to improve access to the interior of the image forming device. For example, in some cases, a first door may provide access to a paper path to clear paper jams while a second door may permit removal of CRUs. In these cases, one door panel may need to be opened before opening another. By the same token, the door panels may also need to be closed in a particular order. This may be particularly true if opening one of the door panels triggers a series of events, such as disengaging rotary drive components. Thus, if these door panels are not opened or closed in the proper order, device errors may ensue. Worse yet, damage to the moving components, hinges, or latch mechanisms may result, thus causing device downtime and/or expensive repairs.  
       SUMMARY  
       [0005]     Embodiments of the present invention are directed to an image forming device and methods of controlling and interlocking door assembly movement and device operation. These features may be implemented in an image forming device having a body and one or more door assemblies. A variety of mechanical and electrical interlocks may be used to control motion of the door assemblies. In certain embodiments, some of the image forming device modules may be mounted to one or more of the door assemblies.  
         [0006]     At least a first door assembly may be movably coupled to the body and positionable between a first open orientation where the first door assembly is positioned away from the body and a first closed orientation where the first door assembly is positioned in proximity to the body. A first interlock may prevent an undesired first door assembly motion. For instance, the first door assembly motion may be when the first door assembly moves under the influence of a force between the first open orientation and the first closed orientation prior to a condition being satisfied. An exemplary condition may be when a second door assembly is positioned in a second open orientation away from the body. A breakaway feature may be included to release the first interlock when the force exceeds a predetermined level. The breakaway feature may reset the first interlock if the second door assembly is moved from the second open orientation to a second closed orientation in proximity to the body. Alternatively, the breakaway feature may reset the first interlock if the first door assembly is moved from the first closed orientation back to the first open orientation.  
         [0007]     A second interlock may cooperate with the first interlock to obstruct the second door assembly from moving to the second open orientation if the first door assembly is in the first closed orientation. In one embodiment, the second interlock may unconditionally allow the first door assembly to move between the first open orientation and the first closed orientation.  
         [0008]     The image forming device may also have an electrical interlock to disconnect power to the image forming device when the first door assembly is positioned in the first open orientation. Conversely, the electrical interlock may supply power to the image forming device when the first door assembly is positioned in first closed orientation. An exception may be that the electrical interlock continues to remove power if the breakaway feature has released the first interlock. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIGS. 1A-1C  are schematic diagrams of an image forming device having a plurality of moveable door assemblies according to one embodiment of the present invention;  
         [0010]      FIG. 2  is a functional diagram of an image forming apparatus according to one embodiment of the present invention;  
         [0011]      FIG. 3  is a is a cut-away side view of an image forming device with a door assembly in an open orientation according to one embodiment of the present invention;  
         [0012]      FIG. 4  is a partial side view of locking members used to secure a door assembly according to one embodiment of the present invention;  
         [0013]      FIGS. 5A-5C  are schematic diagrams showing a sequence by which a locking member secures a door assembly according to one embodiment of the present invention;  
         [0014]      FIGS. 6A-6C  are schematic diagrams showing components of a door panel interlock mechanism according to one embodiment of the present invention;  
         [0015]      FIGS. 7A-7B  are frontal section views illustrating components of a breakaway feature in a door panel interlock mechanism according to one embodiment of the present invention;  
         [0016]     FIGS.  8  is a lateral view illustrating components of a breakaway feature in a door panel interlock mechanism according to one embodiment of the present invention;  
         [0017]     FIGS.  9  is a schematic diagram showing components of a door panel interlock mechanism with a released breakaway feature according to one embodiment of the present invention;  
         [0018]      FIGS. 10A-10C  are schematic diagrams showing components of a door panel interlock mechanism according to one embodiment of the present invention; and  
         [0019]      FIGS. 11A-11B  are schematic diagrams showing components of a door panel interlock mechanism actuating an electrical interlock according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]     The various embodiments disclosed herein are directed to controlling the order in which door panels of an image forming device are opened and closed. The mechanisms implemented also feature a breakaway mechanism that prevents damage to the image forming device. Also disclosed is a safety interlock that removes and reapplies system power if the door panels are opened and closed in the appropriate order. The various embodiments may be implemented in an image forming device of the type indicated generally by the numeral  10  in  FIGS. 1A-1C . The exemplary image forming device  10  comprises a main body  12  and two door assemblies  11 ,  13 . As used herein, the term “door assembly” is intended to refer to a door panel that is movably or detachably coupled to the main body  12 . Exemplary door assemblies  11 ,  13  may simply comprise a door panel and any mounting hardware that permits relative movement between the main body  12 , including but not limited to hinges and link arms or pivot arms. As indicated below, other components may be coupled to the door assemblies  11 ,  13 . The first door assembly  11  is located towards a top side of the image forming device  10  while the second door assembly  13  is located towards a lateral side of the image forming device  10 . In the exemplary image forming device  10 , a user interface panel  19  comprising a display  21  and one or more input buttons  23  is disposed on the first door assembly  11 .  
         [0021]     Each door assembly  11 ,  13  is movable between a closed position as shown in  FIG. 1A  and an open position as shown in  FIGS. 1B and 1C . In the exemplary embodiment, the door assemblies are opened in the order illustrated by the progression from  FIG. 1A  to  FIG. 1B  to  FIG. 1C . That is, access to the interior of the image forming device  10  may be provided by first opening the first door assembly  11  followed by the second door assembly  13 . The door assemblies  11 ,  13  are returned to the operating position in the reverse order. That is, the second door assembly  13  is closed before the first door assembly  11 .  
         [0022]     One or more modules may be coupled to the first and second door assemblies  11 ,  13 . For instance,  FIG. 1C  shows a belt module  20  coupled to the second door assembly  13 . The belt module  20  may be an image transfer belt, a document transport belt, or other belt commonly used in image forming devices  10 . The schematic illustration provided in  FIG. 2  shows one embodiment of an image forming device  10  where belt module  20  is implemented as a transport belt module.  
         [0023]     A schematic representation of the exemplary image forming device  10  is shown in  FIG. 2 . The image forming device  10  includes a media tray  98  with a pick mechanism  16  and a multi-purpose feeder  32 , both of which are conduits for introducing media sheets into the device  10 . The media tray  98  is preferably removable for refilling, and located on a lower section of the device  10 . Media sheets are moved from the input and fed into a primary media path. One or more registration rollers  99  disposed along the media path aligns the print media and precisely controls its further movement along the media path. The belt module  20  forms a section of the media path for moving the media sheets past a plurality of image forming units  100 . Color printers typically include four image forming units  100  for printing with cyan, magenta, yellow, and black toner to produce a four-color image on the media sheet.  
         [0024]     An optical scanning device  22  forms a latent image on photoconductive members  51   a - d  within the image forming units  100 . Toner from the developer units  40  is supplied to develop the respective latent images. The developed images are then transferred from the photoconductive members  51   a - d  to the media sheet being transported by the belt module  20 . The media sheet with loose toner is then moved through a fuser  24  that adheres the toner to the media sheet. Exit rollers  26  rotate in a forward direction to move the media sheet to an output tray  28 . Optionally, the rollers  26  may rotate in a reverse direction to move the media sheet to a duplex path  30 . The duplex path  30  directs the inverted media sheet back through the image formation process for forming an image on a second side of the media sheet.  
         [0025]     As indicated above, at least one internal module may be attached to the second door assembly  13  and travel with the second door assembly  13  as it moves between an open and closed position.  FIG. 1C  shows at least a belt module  20  being coupled to the second door assembly  13 . Other modules may be coupled to the second door assembly as well. For example, some portion or the entire image forming unit  100  may be coupled to the second door assembly  13 .  FIGS. 2 and 3  show exemplary image forming units  100  that are constructed of a separate developer unit  40  and a photoconductor unit  50 . The developer unit  40 , including a developer member  45 , may be positioned within the main body  12  whereas the photoconductor unit  50  may be mounted to the second door assembly  13  along with the aforementioned belt module  20 . In a closed orientation as illustrated in  FIGS. 1A and 2 , the second door assembly  13  is positioned adjacent to the main body  12  with the photoconductive member  51  of the photoconductor unit  50  positioned adjacent the developer unit  40 . In an open orientation as illustrated in  FIG. 3 , the second door assembly  13  is moved away from the main body  12  separating the photoconductor unit  50  and belt module  20  from the developer unit  40 . This configuration provides direct and easy user access to the developer unit  40 , photoconductor unit  50 , and the belt module  20 . It has been determined that the highest user intervention rates are at the developer unit  40 , photoconductor unit  50 , and media path in the vicinity of the belt module  20 .  
         [0026]     As illustrated in  FIGS. 1C and 3 , the main body  12  has enclosed sides forming an opening  18  for mounting the developer units  40 . Developer units  40  are positioned within the opening  18  with the developer roll  45  extending outward to contact the photoconductive member  51  during image formation. Opening  18  may be sized to encompass the entire side of the main body  12 , or may comprise only a limited portion of one side. In the embodiment of  FIG. 3 , opening  18  is positioned on a lateral side of the main body  12 . Opening  18  may also be positioned on the top or bottom side of the main body  12  depending upon the application. For instance, in image forming devices  10  that orient the image forming units  100  in a more horizontal configuration, the opening  18  may be advantageously placed towards a top side of the main body  12 .  
         [0027]     The second door assembly  13  is movably attached relative to the main body  12  between an opened orientation as illustrated in  FIGS. 1C and 3  and a closed orientation as illustrated in  FIGS. 1A and 2 . The second door assembly  13  may be attached to the main body  12  in a variety of manners.  FIG. 3  illustrates one embodiment with the second door assembly  13  pivotally attached to the main body  12  through a pivot  14 . Pivot  14  may attach the main body  12  and second door assembly  13  at a variety of locations, such as towards a lower edge  15 . In the open orientation, the door assembly upper edge  16  is spaced from the main body  12 . This orientation provides access to the developer units  40 , photoconductor units  50 , and media path, including belt module  20 . In the closed orientation, the upper edge  16  is in proximity to the main body  12 . The upper edge  16  may be in contact with the main body  12 , or slightly spaced apart from the main body  12 .  
         [0028]     Referring to  FIGS. 1C and 3 , the belt module  20  is coupled, at least loosely, to second door assembly  13 .  FIG. 3  further shows the photoconductor units  50  coupled to the door assembly  13 . The photoconductor units  50  are omitted from  FIG. 1C  for clarity. A roller frame  34  is coupled to the door assembly  13  and configured so that rollers  38   a - 38   d  substantially span the width of belt module  20 . An endless belt  48  extends around the rollers  38   a - 38   d . In one embodiment, the rollers  38   a - 38   d  are transfer rollers that are electrically biased to promote the transfer of a developed image from an associated photoconductive member  51  to a media sheet being carried by the belt  48 . Alternatively, the endless belt  48  may be an image transfer belt and developed images may be transferred to the endless belt  48  for subsequent transfer to a media sheet.  
         [0029]     The roller frame  34  is attached to a subframe  60  that is pivotally attached to the second door assembly  13  at a second pivot  25 . The second pivot  25  allows the subframe  60  to move relative to the second door assembly  13  when the second door assembly  13  is in the open orientation. In the closed orientation, the roller frame  34  and subframe  60  are accurately aligned with the main body  12  such that the photoconductive members  51  are aligned with the developer rolls  45 . One or more locks  17  maintain the second door assembly  13  in the closed orientation and secure the roller frame  34  and subframe  60  in this aligned position when the second door assembly  13  is in the closed orientation. In one embodiment, a total of four locks  17  connect the roller frame  34 , subframe  60 , and second door assembly  13  to the main body  12 . As shown in  FIG. 3 , the two upper locks are designated  17   a,    17   c,  while the two lower locks are designated  17   b ,  17   d . The following discussion focuses primarily on the upper locks  17   a ,  17   c . Thus, for the sake of clarity in the following discussion, lock  17   a  will be referred to as the upper right lock. The upper right lock  17   a  is depicted in  FIG. 1C . The nomenclature “upper right” is derived from the fact that the lock is positioned at the upper right corner of the opening  18  when looking into the opening from the right side of  FIGS. 1C and 3 . Similarly, the other upper lock  17   c  located at the upper left corner of opening  18  (not visible in  FIG. 1 ) is designated as the upper left lock  17   c . These left/right distinctions are offered merely for the sake of clarity and should not be construed as limiting. The locking and interlock features described below may be implemented in any of a right side, left side, top side, or bottom side of a door panel opening.  
         [0030]      FIG. 4  illustrates a more detailed representation of locks  17   a ,  17   b  located at the right side of door opening  18 . Specifically,  FIG. 4  shows the upper right lock  17   a  and the lower right lock  17   b  used to secure the right side of roller frame  34  to an interior frame  36 . The interior frame  36  is disposed within the interior of the image forming device housing  12 . The remaining portions of the image forming device  10 , including image forming units  100 , and second door assembly  13  are omitted from  FIG. 4  for clarity. The roller frame  34  is depicted in the closed orientation in  FIG. 4 . The upper right lock  17   a  and lower right lock  17   b  are depicted in a locked orientation, thereby securing the roller frame  34  in this closed orientation.  
         [0031]     In one embodiment, the upper right lock  17   a  and lower right lock  17   b  comprise over-center clamps  58   a  and  58   b , respectively, that are pushed over center by motion of the roller frame  34  when the second door assembly  13  is opened and closed. The upper right lock  17   a  includes a first biasing member  62   a  that provides some nominal first securing force when the roller frame  34  is moved from the open orientation to the closed orientation as shown in  FIG. 4 . Lower right lock  17   b  also includes a corresponding biasing member  62   b  that performs a similar function. Biasing members  62   a  and  62   b  are selected to limit the amount of user force that is required to move the second door assembly  13  and roller frame  34  into the closed position. Notably, the upper left lock  17   c  and lower left lock  17   d  (not visible in  FIG. 4 ) also include corresponding biasing members  62   a  and  62   b . Additional securing force may be provided by the locks  17   a - d  by actuating a locking sequence exemplified in  FIGS. 5A-5C . This sequence is initiated by first closing second door assembly  13  and completed by closing the first door assembly  11 .  FIGS. 5A-5C  illustrate this locking sequence for only one of the four locks (i.e., the upper left lock  17   c ). The lower locks  17   b ,  17   d  operate in a manner similar to upper locks  17   a ,  17   c  and a detailed description thereof is not provided herein. Note also that the illustration provided in  FIG. 5C  shows cutaway portions of a first pivot arm  64  and a second pivot arm  66  to reveal the other components of the upper left lock  17   c.    
         [0032]      FIGS. 5A-5C  illustrate relevant parts of the image forming device  10  involved in securing the roller frame  34  and door assembly  13  in a closed position. The upper left lock  17   c  is coupled to interior frame  36  similar to the upper right lock  17   a  as described above and as shown in  FIG. 4 .  FIGS. 5A-5C  also show a first pivot arm  64  and a second pivot arm  66  that are coupled to the first door assembly  11 . The first pivot arm  64  and second pivot arm  66  are also visible (on the near side) in  FIG. 1C . FIGS.  1 C and  5 A- 5 C also show a shaft  68  that rotates in conjunction with the motion of first pivot arm  64  and second pivot arm  66 . A more detailed description of the movement of pivot arms  64 ,  66  and shaft  68  is provided below.  
         [0033]     The progression from  FIG. 5A  to  FIG. 5B  to  FIG. 5C  shows a locking sequence that provides an adequate securing force to hold the roller frame  34  in the closed position while minimizing the amount of user input force needed to initiate the illustrated motions. Initially, as shown in  FIG. 5A , the roller frame  34  is in an open orientation and is spaced away from the upper left lock  17   c . As the second door assembly  13  and roller frame  34  are pushed into a closed orientation (in the direction indicated by arrow C in  FIG. 5A ), a protrusion  70  on the roller frame  34  engages a gap  72  between a first clamp arm  74  and a second clamp arm  76 . The contact between the protrusion  70  and the second clamp arm  76  causes the clamp  58   c  to rotate about a clamp pivot  78  in the direction indicated by the arrow labeled R.  
         [0034]     In the embodiment shown, the first biasing member  62   a  is implemented as a torsion spring. The rotation of clamp  58   c  is resisted by a bias force F applied by the first biasing member  62   a . As the clamp  58   c  rotates in the direction indicated by the arrow labeled R, the first biasing member  62   a  moves upward in the direction indicated by the arrow labeled B. Ultimately, the roller frame  34 , the clamp  58   c , and first biasing member  62   a  move to the position shown in  FIG. 5B .  
         [0035]     The remaining locking force is actuated as the first door assembly  11  is closed. This motion is illustrated in the sequence from  FIG. 5B  to  5 C. When the first door assembly  11  is closed, the first pivot arm  64  and the second pivot arm  66  rotate in the directions indicated by the arrows labeled M and N in  FIG. 6B , respectively. Note that the first pivot arm  64  and the second pivot arm  66  rotate relative to one another about an arm pivot  65 . The crank shaft  68  has a substantially D-shaped cross section that fits within a similarly shaped aperture within the first pivot arm  64 . Thus, the rotational motion imparted on the first pivot arm  64  by the second pivot arm  66  and the first door assembly  11  is transmitted to the crank shaft  68 . An over-center clamping mechanism is actuated by the rotation of the crank shaft  68 . Thus, when the first door assembly  11  is completely closed, a locking force L is applied by the first clamp arm  74  on the protrusion  70 . A more thorough description of the over-center locking mechanism used in upper locks  17   a  and  17   c  is provided in commonly assigned U.S. patent application Ser. No. 11/231,859 entitled “Securing Mechanism for an Image Forming Device Module” filed Sep. 21, 2005, the relevant portions of which are incorporated by reference herein.  
         [0036]      FIG. 6A  shows an interlock mechanism  200   a  that works in conjunction with the upper right lock  17   a  to control the order in which the door assemblies  11 ,  13  are opened and closed. For the sake of generality, the following discussion will presume different configurations for an upper right interlock  200   a  and an upper left interlock  200   c  (not shown in  FIGS. 6A-6C , but see  FIGS. 10A-10C ). However, in at least one alternative implementation, the structure used in the upper right interlock  200   a  may be used in both the right and left sides of the exemplary image forming device  10 . However, some advantages to having slightly different configurations for the upper right interlock  200   a  and the upper left interlock  200   c  are discussed in detail below.  
         [0037]     The upper right interlock  200   a  includes a pawl  118  that is fixedly attached to the previously described crank shaft  68 . A D-shaped opening in the pawl  118  mates with the D-shaped crank shaft  68 . Thus, as the first door assembly  11  opens and closes as shown in  FIGS. 5A-5C , the pawl  118  also rotates. The pawl  118  fits within a retraction pinion cam  102 . In most instances, rotation of the crank shaft  68  and pawl  118  induces rotation of the retraction pinion cam  102 . The retraction pinion cam  102  rotates about crank shaft  68  but is not keyed to the crank shaft  68  in the same way the pawl  118  is keyed. Thus, the retraction pinion cam  102  moves through contact between the pawl  118  and surfaces  116  or first or second catches  122 ,  124 . For instance,  FIG. 6A  shows the condition where the first door assembly  11  and the second door assembly  13  are closed and the image forming device  10  is ready to print. If at this point, the first door assembly  11  is opened, the crank shaft  68  and pawl  118  rotate in a direction indicated by the arrow labeled H. The physical contact between the pawl  118  and surface  116  causes the retraction pinion cam  102  to rotate in the direction of arrow H as well. When the first door assembly  11  is completely open, the crank shaft  68 , pawl  118 , and retraction pinion cam  102  move to the position shown in  FIG. 6B . At this point, the second door assembly  13  remains closed so the upper right lock  17   a  and roller frame  34  remain in the same position as in  FIG. 6A .  
         [0038]     Motion of the retraction pinion cam  102  is further constrained by an assist spring  114  that is attached to the retraction pinion cam  102  at a first anchor point  112 . The assist spring  114  travels around the pawl  118  and connects at a second end to the interior frame  36  of the image forming device  10 . As will be discussed below, the retraction pinion cam  102  is only loosely coupled to the crank shaft  68 . Thus, the assist spring  114  serves at least two purposes. First, as the first door assembly  11  is closed, the assist spring  114  helps pull the retraction pinion cam  102  back to the closed position shown in  FIG. 6A . Second, the assist spring helps maintain contact between pawl  118  and either the first  122  or second  124  catches. Thus, when the pawl  118  rotates between the open position shown in  FIG. 6B  and the closed position shown in  FIG. 6A , the pawl  118  can drive the retraction pinion cam  102  as well.  
         [0039]     In the closed orientation shown in  FIG. 6A , the retraction pinion cam  102  is oriented so that an interference point  110  exists between the retraction pinion cam  102  and the over-center clamp  58   a . Thus, if the second door assembly  13  is pulled open as indicated by the arrow labeled D, motion of the over-center clamp  58   a  in the direction of arrow T is impeded at the interference point  110 . This interference  110  serves to remind users that the second door assembly  13  should not be opened until the first door assembly  11  is completely open.  
         [0040]     The retraction pinion cam  102  also includes a series of pinion gear teeth  104  disposed opposite from the catches  122 ,  124 . These pinion gear teeth  104  engage mating gear teeth  106  on a retraction rack  108 . The respective teeth  104 ,  106  induce lateral motion of the retraction rack  108  that is dependent upon the motion of the retraction pinion cam  102 . Thus, as  FIG. 6A  shows, when the first door assembly  11  opens and the retraction pinion cam  102  rotates in the direction of arrow H, the retraction rack  108  moves in the direction of arrow J. Similarly, as illustrated in  FIG. 6B , when the first door assembly  11  closes and the retraction pinion cam  102  rotates in the direction of arrow M, the retraction rack  108  moves in the direction of arrow K. This lateral motion of the retraction rack  108  induces coupling and de-coupling of a drive train system and electrical motors that are used to apply rotary motion to the four developer members  45 , the four photoconductive members  51 , and the belt module  20  shown in  FIGS. 2 and 3 . These drive train components are located within a gearbox (not shown) that is connected to the developer members  45 , the four photoconductive members  51 , and the belt module  20  by means of axially retractable couplings (also not shown). A thorough description of this coupling mechanism is provided in commonly assigned U.S. patent application Ser. No. 10/810,139 entitled “Coupling Retraction Mechanism for an Image Forming Device” filed Mar. 26, 2004, the relevant portions of which are incorporated by reference herein. It will suffice to say here that the motion of the retraction rack  108  engages and disengages the developer members  45 , the four photoconductive members  51 , and the belt module  20  so that these components may be removed once the door assemblies  11 ,  13  are opened. Further, since the roller frame  34  and the rotating belt module  20  are coupled to the second door assembly  13 , the releasing action induced by the retraction rack  108  allows users to open the door assembly  13  without damaging drive couplings and drive train components.  
         [0041]     The progression from  FIG. 6B  to  FIG. 6C  represents the step of opening the second door assembly  13  after the first door assembly  11  is open.  FIG. 6C  represents the condition where both door assemblies  11 ,  13  are open. Opening the second door assembly  13  causes the roller frame  34  to move in the direction of arrow D, which in turn, causes the over-center clamp  58   a  to rotate in the direction of arrow T. At this point, a user may access the internals of the image forming device to clear paper jams or remove consumable CRUs. Once the image forming device  10  has been serviced, the process of closing the door assemblies  11 ,  13  should follow the reverse order as opening. That is, the second door assembly  13  should be closed before the first door assembly  11 . To that end, a second interference point  120  shown in  FIG. 6C  is created between the retraction pinion cam  102  and the over-center clamp  58   a . Thus, if a user attempts to close the first door assembly  11 , thereby attempting to rotate the pawl  118  and retraction pinion cam  102  in the direction of arrow M, the interference  120  between the retraction pinion cam  102  and the over-center clamp  58   a  may serve as a reminder that the second door assembly  13  should be closed first.  
         [0042]     The pivot arms  64 ,  66  described above (and shown in  FIGS. 5A-5C ) may offer a substantial amount of mechanical advantage. Thus, it may be possible for a user to force the first door assembly  11  closed despite the resistance offered by interference point  120 . Accordingly, a breakaway feature is built into the upper right interlock  200   a . The section views provided in FIGS.  7 A and  7 B, identified by the section lines in  FIG. 6C , help illustrate this breakaway feature.  
         [0043]      FIGS. 7A and 7B  illustrate various components of the upper right interlock  200   a  described above. These include the retraction pinion cam  102 , the pawl  118 , the assist spring  114 , and the crank shaft  68  about which these other components rotate. As discussed above, the retraction pinion cam  102  is not keyed to the crank shaft  68 . It was also mentioned that the retraction pinion cam  102  is only loosely coupled to the crank shaft  68 . The left side of  FIG. 7A  shows a diameter dimension ØE reflecting the diameter of the crank shaft  68 . At the left side of the retraction pinion cam  102 , near the pinion gear teeth  104 , there exists a relatively tight fit between the retraction pinion cam  102  and the crank shaft  68  as identified by the lack of an apparent gap at locations  126  and  128 . However, towards the right side of the retraction pinion cam  102 , nearest the pawl  118 , there exists a gap  130  between the crank shaft  68  and the retraction pinion cam  102 . This gap  130  permits relative movement, identified by the arrow S, between the retraction pinion cam  102  and the crank shaft  68  and pawl  118 . In fact, the representation shown in  FIG. 7B  illustrates the condition where the retraction pinion cam  102  has moved in the direction of arrow S. This movement results in a reduction in the previously mentioned gap  130  and a formation of a second gap  132  opposite to the first gap  130 .  
         [0044]     As a result of this rocking motion of the retraction pinion cam  102 , the pawl  118  releases from the first catch  122  and second catch  124 . This situation is illustrated in  FIG. 8 , where the pawl  118  begins to slide past the first catch  122  in the direction of arrow M. In actuality, the rocking motion of the retraction pinion cam  102  may be caused when the first door assembly  11  is forced to close while both door assemblies  11 ,  13  are open. Comparing  FIGS. 6C and 9 , the retraction pinion cam  102  is restrained from rotating in the direction of arrow M by the interference  120 . However, since pawl  118  is keyed to crank shaft  68 , the pawl  118  begins to rotate as door assembly  11  closes. The interference between the pawl  118  and the first catch  122  causes the retraction pinion cam  102  to rock in the direction identified by the arrow S in  FIG. 7A . Ultimately, if enough of a closing force is applied to close the first door assembly  11 , the pawl  118  will break away from the retraction pinion cam  102  and the crank shaft  68  and pawl  118  will move to the position shown in  FIG. 9 .  
         [0045]     Two possible modes of correction are provided to reset this breakaway feature. The first simply consists of re-opening the first door assembly  11  so that the crank shaft  68  and the pawl  118  rotate back from the orientation shown in  FIG. 9  towards the orientation shown in  FIG. 6A . A second mode of correction is provided by the assist spring  114  in the event the second door assembly  13  is closed enough to cause the over-center crank  58   a  to move out of interference with the retraction pinion cam  102 . In this case, the assist spring  114  pulls the retraction pinion cam  102  towards the displaced pawl  118  and forces engagement of either the first catch  122  or second catch  124 . Two separate catches  122 ,  124  are provided to accommodate part size and placement variations caused by manufacturing tolerances. The second catch  124  is positioned to accommodate a worst case tolerance stack up. In cases where resetting the breakaway feature results in the pawl  118  engaging the second catch  124 , the pawl  118  will ultimately push up against surface  116  (likely when the first door assembly  11  is next opened) to completely reset the breakaway feature.  
         [0046]     As discussed above, the features of the upper right interlock  200   a  just described may be incorporated at or near the other locks  17   b ,  17   c ,  17   d . In an alternative embodiment, a modified upper left interlock  200   c  may be incorporated to increase the effectiveness of the breakaway feature of the upper right interlock  200   a . This modified upper left interlock  200   c  is illustrated in  FIGS. 10A-10C . These Figures also illustrate the upper left lock  17   c , which operates using the same principals discussed above for the upper right lock  17   a , albeit with an over-center clamp  58   c  having a slightly different configuration.  
         [0047]      FIG. 10A  illustrates the condition where both door assemblies  11 ,  13  are closed. In this condition, an interference point  140  exists between the over-center clamp  58   c  and a second retraction cam  134 . As opposed to the retraction pinion cam  102 , the second retraction cam  134  is keyed to the crank shaft  68  and therefore moves with the crank shaft  68  at all times. The interference  140  between the second retraction cam  134  prevents rotation of the over-center clamp  58   c  in the direction of arrow T. This, in turn, prevents the second door assembly  13  from being pulled open in the direction of arrow D. Thus, both the upper left interlock  200   c  and the upper right interlock  200   a  include similar interference points  120 ,  140  that prevent users from opening the second door assembly  13  before the first door assembly  11  is opened.  
         [0048]      FIG. 10B  illustrates the condition where both door assemblies  11 ,  13  are opened. This condition corresponds to the condition shown in  FIG. 6C . Note that once the first door assembly  11  is opened and the crank shaft  68  and second retraction cam  134  move out of the way of the over center clamp  58   c , the second door assembly  13  may be opened to the position shown in  FIG. 10B . In contrast with the upper right interlock  200   a , the upper left interlock  200   c  does not create a second interference that serves to prevent closing the first door assembly  11  before closing the second door assembly  13 . Instead, the second retraction cam  134  is actually configured so that it clears the over-center clamp  58   c  if forced to move in the direction of arrow M when the first door assembly  11  is forced closed. This clearance between the second retraction cam  134  and the over-center clamp  58   c  is shown in  FIG. 10C , which represents the condition where the second door assembly  13  is open and the first door assembly  11  is closed. This clearance in the upper left interlock  200   c  may contribute to the effectiveness of breakaway feature in the upper right interlock  200   a  described above.  
         [0049]      FIGS. 11A and 11B  illustrates an electrical interlock switch  136  that is actuated by the motion of the retraction pinion cam  102 . The electrical interlock switch  136  is a safety feature that removes power from the image forming device  10  to prevent device operation or electrical shock when the first door assembly  11  is open. Specifically,  FIGS. 11A and 11B  illustrate the upper right lock  17   a  and upper right interlock  200   a  from a direction reverse to that provided in  FIGS. 6A-6C  and  9 . As described previously, the retraction pinion cam  102  includes a series of pinion gear teeth  104 . Notably, the pinion gear teeth  104  do not span a full circumference around the axis of rotation, which happens to be the crank shaft  68 . As such, the pinion gear teeth  104  provide an eccentric feature that may be used to trip a lever arm  138  on the electrical interlock switch  136 . This is illustrated in  FIG. 11B , where the door assemblies  11 ,  13  are closed as compared to the open state shown in  FIG. 11A . In  FIG. 11A , the pinion gear teeth  104  are rotated away from the switch lever  138 . In this position, the electrical interlock switch  136  is open and power is removed from the image forming device  10 . The arrow M shown in  FIG. 11A  indicates the direction of rotation of the retraction pinion cam  102 , and the pinion gear teeth  104 , when the first door assembly  11  is closed. Once closed, the pinion gear teeth  104  engage the switch lever  138 , thereby closing the electrical interlock switch  136  and reapplying power to the image forming device  10 .  
         [0050]     The electrical interlock switch  136  is actuated by the motion of the retraction pinion cam  102  and not by the motion of the crank shaft  68  or the pawl  118 . Thus, power should not be reapplied to the image forming device  10  if the breakaway feature in the upper right interlock  200   a  is tripped when the first door assembly  11  is inadvertently closed before closing the second door assembly  13 . Note that in  FIG. 9 , which shows the tripped breakaway feature of the upper right interlock  200   a , the retraction pinion cam  102  remains in the “open” position due to interference  120 . Therefore, the electrical interlock  136  also remains open.  
         [0051]     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For example, embodiments of the mechanical interlocks  200   a ,  200   c  and electrical interlock  136  have been described according to their position in the exemplary image forming device  10 . Thus, the terms upper right, upper left, lower right, and lower left have been included merely for clarity in the detailed description. The features described herein may be implemented in any appropriate location depending on the device configuration as well as the configuration of door panels in the device. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.