Abstract:
A photoconductive drum assembly according to one embodiment includes a photoconductive drum rotatable about a rotational axis in first and second rotational directions. A spring brake has a coiled portion wrapped around a portion of the photoconductive drum at its axial end and around the rotational axis of the photoconductive drum. The spring brake has a first arm and a second arm. The first arm is positioned to flex in an unwinding direction causing the coiled portion to unwind upon the first arm receiving a force in the first rotational direction. The first arm is positioned to flex in a winding direction and to push the second arm in an unwinding direction relieving winding of the coiled portion caused by the flexing of the first arm in the winding direction of the first arm upon the first arm receiving a force in the second rotational direction.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to electrophotographic image forming devices and more particularly to a bi-directional spring brake for a photoconductive drum of an electrophotographic image forming device. 
     2. Description of the Related Art 
     As is well known in the art, during a print operation by an electrophotographic image forming device a charge roll charges the surface of a photoconductive drum to a predetermined voltage. The charged surface of the photoconductive drum is then selectively exposed to a laser light source to selectively discharge the surface of the photoconductive drum and form an electrostatic latent image on the photoconductive drurnm corresponding to the image being printed. Toner is picked up by the latent image on the photoconductive drum from a developer roll creating a toned image on the surface of the photoconductive drum. The toned image is then transferred from the photoconductive drum to the print media either directly by the photoconductive drum or indirectly by an intermediate transfer member. A cleaning blade or roller removes any residual toner adhering to the photoconductive drum after the toner is transferred from the photoconductive drum. The cleaned surface of the photoconductive drum is then ready to be charged again and exposed to the laser light source to continue the printing cycle. 
     The photoconductive drum may include a spring brake that applies a uniform drag on the photoconductive drum when the photoconductive drum rotates in an operative rotational direction in order to minimize jitter and backlash of the photoconductive drum.  FIG. 1  shows a prior art photoconductive drum  20 . Photoconductive drum  20  includes a hollow cylindrical drum member  22  having an outer surface  24 . Drum member  22  is mounted on a shaft  26  that defines a rotational axis  28  of photoconductive drum  20 . An end cap  30  is positioned on an axial end  32  of drum member  22 . End cap  30  includes a circular hub  34  on an outboard side of end cap  30 . Hub  34  has an opening  36  that is centered around rotational axis  28 . Shaft  26  is attached to end cap  30  and passes through opening  36  such that shaft  26 , end cap  30  and drum member  22  rotate in unison. 
     With reference to  FIGS. 1 and 2 , photoconductive drum  20  includes a spring brake  40  mounted on end cap  30 . Spring brake  40  includes a segment of spring wire  41  that forms a coiled portion  42  and a pair of arms  44 ,  46 . Coiled portion  42  includes a middle portion of spring wire  41  coiled around a center axis  43 . Arms  44 ,  46  are formed by respective ends of spring wire  41 . Coiled portion  42  is wrapped around hub  34  of end cap  30 . Arm  44  extends beyond an outer circumference of end cap  30  and is positioned to contact a stop  48  (shown schematically) when photoconductive drum  20  rotates in an operative rotational direction indicated by arrow A in  FIG. 1 . When photoconductive drum  20  rotates in the operative rotational direction, spring brake  40  rotates with end cap  30  until arm  44  contacts stop  48 , which stops the rotation of spring brake  40  with photoconductive drum  20 . When arm  44  contacts stop  48 , the force on arm  44  from stop  48  causes arm  44  to flex counter to the operative rotational direction of photoconductive drum  20  which, in turn, causes coiled portion  42  to unwind slightly from hub  34 . Coiled portion  42  remains in contact with hub  34  but allows photoconductive drum  20  to continue rotating with coiled portion  42  applying a uniform drag on photoconductive drum  20 . Arm  46  is spaced clear of arm  44  and provides no functionality other than forming an end of spring brake  40 . 
     SUMMARY 
     A spring brake for use with a photoconductive drum of an electrophotographic image forming device according to one example embodiment includes a spring wire having a coiled portion and first and second arms extending from the coiled portion. The coiled portion is coiled around a center axis. Each of the first arm and the second arm has a winding direction around the center axis and an unwinding direction around the center axis. A force on the first arm in the winding direction of the first arm causes the coiled portion to wind and a force on the first arm in the unwinding direction of the first arm causes the coiled portion to unwind. A force on the second am in the winding direction of the second armn causes the coiled portion to wind and a force on the second arm in the unwinding direction of the second arm causes the coiled portion to unwind. In home positions of the first arm and the second arm, a portion of the second arm is positioned in close proximity to the first arm such that flexing of the first arm friom the home position of the first arm in the winding direction of the first arm causes the first arm to push the second arm from the home position of the second arm in the unwinding direction of the second arm relieving winding of the coiled portion caused by the flexing of the first arm in the winding direction of the first arm. 
     A photoconductive drum assembly for use in an electrophotographic image forming device according to one example embodiment includes a photoconductive drum rotatable about a rotational axis in a first rotational direction and a second rotational direction opposite the first rotational direction. A spring brake has a coiled portion wrapped around a portion of the photoconductive drum at an axial end of the photoconductive drum and around the rotational axis of the photoconductive drum. The spring brake has a first armn and a second artn. The first arm is positioned to flex in an unwinding direction of the first arm causing the coiled portion to unwind upon the first arm receiving a force in the first rotational direction. The first arm is positioned to flex in a winding direction of the first arm and to push the second arm in an unwinding direction of the second arm relieving winding of the coiled portion caused by the flexing of the first arm in the winding direction of the first arm upon the first arm receiving a force in the second rotational direction. 
     A photoconductive drum assembly for use in an electrophotographic image forming device according to another example embodiment includes a photoconductive drum rotatable about a rotational axis in an operative rotational direction and a direction counter to the operative rotational direction. A spring brake has a coiled portion wrapped around a portion of the photoconductive drum at an axial end of the photoconductive drum and around the rotational axis of the photoconductive drum. The spring brake has a first arm and a second arr. The first arm is positioned to flex in a direction that unwinds the coiled portion upon the first arm contacting a first stop when the photoconductive drum rotates in the operative rotational direction. The first arm is positioned to flex in a direction that winds the coiled portion and to push the second arm in a direction that unwinds the coiled portion relieving winding of the coiled portion caused by the flexing of the first arm in the direction that winds the coiled portion upon the first arm contacting a second stop when the photoconductive drum rotates in the direction counter to the operative rotational direction. 
    
    
     
       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 perspective view of a prior art photoconductive drum having a spring brake. 
         FIG. 2  is a perspective view of the spring brake shown in  FIG. 1 . 
         FIG. 3  is a perspective view of a photoconductive drum having a spring brake according to one example embodiment. 
         FIG. 4  is a perspective view of the spring brake shown in  FIG. 3 . 
         FIG. 5  is a perspective view showing an arm of the spring brake in contact with a forward stop when the photoconductive drum rotates in an operative rotational direction according to one example embodiment. 
         FIG. 6  is a perspective view showing the arm of the spring brake in contact with a rearward stop when the photoconductive drum rotates counter to the operative rotational direction according to one example embodiment. 
         FIG. 7  is a perspective view of the photoconductive drum having a spring brake according to another 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. 
       FIG. 3  shows a photoconductive drum  120  for use in an electrophotographic image forming device according to one example embodiment. Photoconductive drum  120  includes a hollow cylindrical drum member  122  having an outer surface  124 . Drum member  122  is mounted on a shaft  126  that defines a rotational axis  128  of photoconductive drum  120 . An end cap  130  is positioned on an axial end  132  of drum member  122 . End cap  130  includes a circular hub  134  on an outboard side of end cap  130 . Hub  134  has an opening  136  that is centered around rotational axis  128 . Shaft  126  is attached to end cap  130  and passes through opening  136  such that shaft  126 , end cap  130  and drum member  122  rotate in unison. Photoconductive drum  120  is rotatable in a forward operative rotational direction indicated by arrow A′ in  FIG. 3  and a reverse direction counter to the operative rotational direction indicated by arrow B′ in  FIG. 3 . 
     With reference to  FIGS. 3 and 4 , a spring brake  140  is mounted on axial end  132  of photoconductive drum  120 . Spring brake  140  includes a segment of spring wire  141  that forms a coiled portion  142  and a pair of arms  150 ,  160 . Coiled portion  142  includes a middle portion of spring wire  141  coiled around a center axis  143 . Arms  150 ,  160  may be formed by respective ends of spring wire  141 . Each arm  150 ,  160  includes a winding direction  151 ,  161  around center axis  143  and an unwinding direction  152 ,  162  around center axis  143 . A force on arm  150  in winding direction  151  causes coiled portion  142  to wind tighter and a force on arm  150  in unwinding direction  152  causes coiled portion  142  to unwind. Similarly, a force on arm  160  in winding direction  161  causes coiled portion  142  to wind tighter and a force on arm  160  in unwinding direction  162  causes coiled portion  142  to unwind. 
     In the embodiment illustrated, coiled portion  142  is wrapped around hub  134  of end cap  130 . In other embodiments, coiled portion  142  is wrapped around shaft  126 . In the embodiment illustrated, arm  150  extends beyond an outer circumference of end cap  130 . Arm  150  includes a front side  154  and a rear side  155 . Front side  154  leads in the operative rotational direction of photoconductive drum  120  and rear side  155  trails. A portion of front side  154  of arm  150  is positioned to contact a forward stop when photoconductive drum  120  rotates in the operative rotational direction and a portion of rear side  155  of arm  150  is positioned to contact a rearward stop when photoconductive drum  120  rotates counter to the operative rotational direction as discussed in greater detail below. In the example embodiment illustrated, arm  150  includes a tab  156  positioned beyond the outer circumference of end cap  130 . In this embodiment, the front side  154  of tab  156  contacts the forward stop when photoconductive drum  120  rotates in the operative rotational direction and the rear side  155  of tab  156  contacts the rearward stop when photoconductive drum  120  rotates counter to the operative rotational direction. 
       FIGS. 3 and 4  show arms  150 ,  160  in their home positions without any external forces, such as from the forward stop or the rearward stop, on arm  150  or arm  160 . In the embodiment illustrated, when arms  150 ,  160  are in their home positions, a portion of arm  160  is positioned in close proximity to front side  154  of arm  150 . In some embodiments, a portion of arm  160  rests against front side  154  of arm  150 . In other embodiments, a portion of arm  160  is spaced by a few millimeters (e.g., from less than 1 mm up to about 6 mm) ahead of front side  154  of arm  150  with respect to the operative rotational direction of photoconductive drum  120 . In the example embodiment illustrated, arm  160  includes a tab  164  positioned in close proximity to front side  154  of arm  150 . Arm  160  and tab  164  may be contained within the outer circumference of end cap  130  as illustrated or a portion of arm  160  including tab  164  may extend beyond the outer circumference of end cap  130 . 
     With reference to  FIG. 5 , when photoconductive drum  120  rotates in the operative rotational direction indicated by arrow A′ in  FIG. 5 , spring brake  140  rotates with end cap  130  until front side  154  of arm  150  contacts a forward stop  170  (shown schematically), which stops the rotation of spring brake  140  with photoconductive drum  120 . When front side  154  of arm  150  contacts forward stop  170 , the force F 1  on arm  150  from forward stop  170  counter to the operative rotational direction of photoconductive drum  120  causes arm  150  to flex in unwinding direction  152  which, in turn, causes coiled portion  142  to unwind slightly from hub  134 . Coiled portion  142  remains in contact with hub  134  but allows photoconductive drum  120  to continue rotating in the operative rotational direction of photoconductive drum  120  with coiled portion  142  applying a uniform drag on photoconductive drum  120 . 
     With reference to  FIG. 6 , when photoconductive drum  120  rotates counter to the operative rotational direction indicated by arrow B′ in  FIG. 6 , spring brake  140  rotates with end cap  130  until rear side  155  of arm  150  contacts a rearward stop  172  (shown schematically), which stops the rotation of spring brake  140  with photoconductive drum  120 . When rear side  155  of arm  150  contacts rearward stop  172 , the force F 2  on arm  150  from rearward stop  172  in the operative rotational direction of photoconductive drum  120  causes arm  150  to flex in winding direction  151 . The flexing of arm  150  in winding direction  151  causes front side  154  of arm  150  to push arm  160  in unwinding direction  162 . The force F 3  from arm  150  on arm  160  in unwinding direction  162  relieves any tightening of coiled portion  142  around hub  134  that would otherwise result from the flexing of arm  150  in winding direction  151 . As a result, coiled portion  142  remains in contact with hub  134  but allows photoconductive drum  120  to continue rotating counter to the operative rotational direction of photoconductive drum  120  with coiled portion  142  applying a uniform drag on photoconductive drum  120 . 
     In some embodiments, forward stop  170  and rearward stop  172  are positioned on the housing of a replaceable unit that holds photoconductive drum  120 . In other embodiments, forward stop  170  and rearward stop  172  are positioned on the frame of the electrophotographic image forming device or on another replaceable unit of the image forming device. 
     Spring brake  140  allows rotation of photoconductive drum  120  in both the forward operative direction and the reverse direction counter to the operative direction. It may be desirable to periodically rotate photoconductive drum  120  counter to its operative rotational direction in order to dislodge toner fragments that tend to accumulate on a cleaning blade that is positioned against outer surface  124  of photoconductive drum  120  and that removes residual toner from outer surface  124 . Photoconductive drum  120  may also be rotated counter to its operative rotational direction in order to introduce slack into a gear train that drives photoconductive drum  120  in order to make it easier for a user to remove a replaceable unit that holds photoconductive drum  120  from the image forming device. 
     In contrast, if photoconductive drum  20  shown in  FIG. 1  is driven counter to its operative rotational direction as indicated by arrow B in  FIG. 1  far enough for arm  44  of spring brake  40  to contact a rear side  49  (shown schematically) of stop  48 , the force on arm  44  from stop  48  causes arm  44  to flex in the operative rotational direction of photoconductive drum  20  which, in turn, causes coiled portion  42  to tighten around hub  34 . Damage may result if photoconductive drum  20  continues to be driven counter to its operative rotational direction against the tightening of coiled portion  42  around hub  34 . For example, arm  44  of spring brake  40  may tend to bend against stop  48  to the point of permanently deforming spring brake  40 . Continued rotation of photoconductive drum  20  counter to its operative rotational direction may also damage end cap  30  of photoconductive drum  20  or a gear train or motor driving photoconductive drum  20 . The positioning of arm  160  of spring brake  140  in close proximity to front side  154  of arm  150  prevents coiled portion  142  of spring brake  140  from excessively tightening around hub  134 . The flexing of arm  150  against arm  160  in unwinding direction  162  of arm  160  relieves tightening of coiled portion  142  around hub  134  permitting photoconductive drum  120  to continue rotating counter to its operative rotational direction. 
       FIG. 7  shows a photoconductive drum  120  according to another example embodiment that includes a spring brake  240  that allows rotation of photoconductive drum  120  in both an operative forward direction and a reverse direction. Spring brake  240  includes a segment of spring wire  241  that forms a coiled portion  242  and a pair of arms  250 ,  260  like spring brake  140  discussed above. Spring brake  240  also includes an intermediate member  280  positioned on end cap  130 . Intermediate member  280  includes a front end wall  282  positioned behind and in close proximity to arm  260  with respect to the operative rotational direction of photoconductive drum  120  and a rear end wall  284  positioned in front of and in close proximity to arm  250  with respect to the operative rotational direction of photoconductive drum  120 . In the example embodiment illustrated, front end wall  282  is formed in a front slot  286  in intermediate member  280  that receives arm  260  and rear end wall  284  is formed in a rear slot  288  in intermediate member  280  that receives arm  250 . 
     When photoconductive drum  120  rotates in the operative rotational direction indicated by arrow A′ in  FIG. 7 , spring brake  240  rotates with end cap  130  until a front side  254  of arm  250  contacts forward stop  170  as discussed above. When front side  254  of arm  250  contacts forward stop  170 , the force on arm  250  from forward stop  170  counter to the operative rotational direction of photoconductive drum  120  causes arm  250  to flex in an unwinding direction  252  of arm  250  which, in turn, causes coiled portion  242  to unwind slightly from hub  134 . Rear slot  288  provides sufficient clearance to allow arm  250  to flex in unwinding direction  252 . When photoconductive drum  120  rotates counter to the operative rotational direction indicated by arrow B′ in  FIG. 7 , spring brake  240  rotates with end cap  130  until a rear side  255  of arm  250  contacts rearward stop  172  as discussed above. When rear side  255  of arm  250  contacts rearward stop  172 , the force on arm  250  from rearward stop  172  in the operative rotational direction of photoconductive drum  120  causes arm  250  to flex in a winding direction  251  of arm  250 . The flexing of arm  250  in winding direction  251  causes front side  254  of arm  250  to push against rear end wall  284  of intermediate member  280  in the operative rotational direction of photoconductive drum  120  which, in turn, causes front end wall  282  of intermediate member  280  to push against arm  260  in an unwinding direction  262  of arm  260 . The force on arm  260  from front end wall  282  of intermediate member  280  in unwinding direction  262  relieves any tightening of coiled portion  242  around hub  134  that would otherwise result from the flexing of arm  250  in winding direction  251 . In this manner, intermediate member  280  allows photoconductive drum  120  to rotate counter to its operative rotational direction without damaging spring brake  240 . 
     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.