Abstract:
An Oldham coupler assembly capable of transferring rotary power between two shafts in a developer unit of an image forming apparatus that includes an input plate and an output plate made of metal and a star plate made in plastic mechanically coupled and positioned in between the input plate and the output plate. A spline component made of metal is rigidly and integrally attached to the input plate, the spline component including a tubular spline portion that includes a plurality of wear strips made of plastic, the output plate having a plastic material coated along a portion of an outside diameter of the output plate. The input and output plates further include a plurality of openings to receive a plurality of wheels and pins. This structure allows a sufficiently stiff drive system to substantially eliminate fine line jitter by raising the natural frequency of the drive system.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     This application claims the benefit of the earlier filing date of Application Ser. No. 61/177,441, filed May 12, 2009, entitled “Printing Device.” The present application hereby incorporates by reference the above identified patent applications in their entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to image formation devices, and in particular to a coupling retraction mechanism for a color electrophotographic printer. Specifically, the present invention discloses an Oldham coupler for transferring rotary power between two shafts in a developer unit of the image formation device including an input metal plate, a plastic star plate and an output metal plate. 
     2. Description of the Related Art 
     Oldham couplers have been employed for many years in drive systems of diverse machines for transferring torque or rotary power between two parallel but non-collinear and/or non-radially aligned rotating shafts. In the past, Oldham couplers with retraction splines have all the components made out of plastic. This leads to a weak design from the standpoint of the stiffness of the drive connections in the drive system. Since mono or color machines are sensitive to low frequency oscillations of the drive connections, the all-plastic components can cause banding in the range of 0.5 to 2 mm on a media sheet as the drive system oscillates which appear as light and dark bands on the printed media sheet. 
     Given the foregoing, there is a need for an improved Oldham coupler that possesses the requisite stiffness, is simple in construction and is relatively easy to manufacture. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, there is provided an Oldham coupler assembly capable of transferring rotary power between two shafts in a developer unit of an imaging apparatus including an input plate and an output plate made of a first material, a star plate made of a second material positioned in between and mechanically coupled to the input plate and the output plate and a spline component made of the first material rigidly and integrally attached to the input plate. The spline component is an elongated tubular spline portion including a plurality of wear strips, the wear strips providing an area to engage with a mating spline. The second material may be a plastic composition. One or both of the input plate and the output plate may have overmolded plastic features. 
     In some embodiments, the first material provides a stiffness ranging from approximately 14 in-oz/degree to approximately 24 in-oz/degree. 
     In some embodiments, the output plate further includes a plurality of openings having a first width and a second width, the first width being different from the second width. The plurality of openings increase in width from the first width to the second width from a center of the openings. 
     In yet another aspect of the invention, a composite torque transfer assembly is disclosed including a metal input plate and a metal output plate, a plastic star plate coupled to the metal input plate and the metal output plate, a metal drive spline rigidly and integrally attached to the metal input plate, the metal drive spline including a plurality of plastic wear strips providing an area to engage with a mating spline, and a plastic material coated along a portion of an outside diameter of the metal output plate. 
     In another embodiment, the plurality of plastic molded openings are symmetrically arranged to receive a plurality of pins for securing wheels to the output plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of the various embodiments of the invention, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein: 
         FIG. 1  is a representative image forming apparatus having a plurality of pairs of separate developer units and photoconductor units and an openable and closable subunit; 
         FIG. 2  is a perspective view of an assembly of an Oldham coupler assembly according to one embodiment of the present invention; 
         FIG. 3  is an exploded view of the Oldham coupler of  FIG. 2  with a plastic over molded coated on the input plate and the output plate; 
         FIG. 4  is a perspective view of a pivoting coupling retraction plate assembly according to an embodiment of the present invention; and 
         FIG. 5  is a perspective view of the output plate of  FIGS. 2 and 3  prior to overmolding. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
     Reference will now be made in detail to the exemplary embodiment(s) of the invention as illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  depicts an image forming apparatus  10  including a housing  12  with a top portion  14 , a subunit  16  separated from the housing  12  by pivoting about a hinge point  18 . The media sheet transport belt  20  and the photoconductor units  24  are mounted to the subunit  16 . To allow the photoconductor units  24  to clear the housing  12  when the subunit  16  is opened, the photoconductor units  24  are first decoupled from the drive mechanism couplings  26  within the housing  12  that supply rotary power to the photoconductor units  24 . Additionally, to remove or insert a developer unit  28  from or into the housing  12 , at least the developer unit  28  of interest must be decoupled from the drive mechanism couplings  26  that supply rotary power to it. Furthermore, since the developer units  28  are inserted and removed from the housing  12  in a direction at approximately right angles to the axes of the rollers within the cartridges, the drive mechanism couplings  26  must be decoupled to provide mechanical clearance for the removal or insertion of the developer unit  28  cartridges. 
     In one embodiment, each of the drive mechanism couplings  26  to developer units  28  and photoconductor units  24  are decoupled and/or retracted substantially simultaneously, allowing for removal and replacement without individually retracting each drive mechanism coupling  26 . In particular, the drive mechanism couplings  26  are automatically retracted relative to developer units  28  and photoconductor units  24  whenever the subunit  16  is opened to allow access to such units, without requiring further action on the part of the operator. According to various embodiments of the present invention, all of the drive couplers supplying rotary power to the developer units  28  and the photoconductor units  24  are retracted simultaneously, by actuation of a translatable retraction plate  30  within a coupling retraction mechanism, as described in further detail below. 
       FIGS. 2 and 3  illustrate an assembly of an Oldham coupler  32 , according to an exemplary embodiment of the present invention. The assembly  32  generally includes an input plate  34 , a star plate  36 , and an output plate  38 . A spline component  40  in the form of an elongated tubular spline portion is integrally attached to the input plate  34  and the output plate  38 . 
     The star plate  36  of the assembly  32  is coupled in between the input plate  34  and the output plate  38 . The star plate  36  is made of a first material, such as a molded plastic material, such as acetal. Alternatively, star plate  36  is made from Nylon, Nylon with glass, ABS, or the like. 
     The input plate  34  and the output plate  38  of the assembly  32  are made of a second material that is different from the first material of the star plate  36 . The second material has a stiffness greater than that of the first material. By way of example, the greater stiffness of the second material over that of the first material can provide the assembly  32  with stiffness ranging from approximately 14 in-oz/degree to approximately 24 in-oz/degree. The second material can be zinc, steel, aluminum, magnesium, brass, bronze or the like. In one exemplary embodiment, the second material of the assembly  32  is cast zinc, which can be readily manufactured and provides the desired stiffness at relatively low cost. The star plate  36  in plastic form gives an added advantage since it provides lower mass and inertia when the star plate  36  rotates off its center of gravity during operation. Due to the lower mass and inertia of the star plate  36 , less side forces are transmitted by the assembly  32  of the Oldham coupler which causes less movement to the photoconductor drum being driven by the Oldham coupler. This leads to better print quality. Also, due to the reduced movement of the photoconductor drum the chance of loosing the nip force between the photoconductor drum and the developer roll is substantially averted. 
     The spline component  40 , rigidly and integrally attached to the input plate  34 , is an elongated tubular spline portion extending from the input plate  34 . The spline component  40  further includes a plurality of wear strips  42  disposed along an inner surface thereof. The wear strips  42  are made of the first material discussed above. The wear strips  42  serve two purposes. First, wear strips  42  provide an area for a mating spline to ride on that has better wear characteristics because of the wear strips  42  being plastic in nature. Second, the wear strips  42  provide lower friction when compared to metal wear strips. The wear strips  42  also act as a centering device for the mating splines when not transmitting torque. 
       FIG. 3  illustrates an exploded view of the assembly  32  that includes the input plate  34 , the star plate  36  and the output plate  38 . The assembly  32  also includes a plurality of wheels  44  and pins  46  that are secured to the input plate  34  and output plate  38 . The plurality of wheels  44  move within slots  48  defined in the star plate  36 . Spline  40  on the input plate  34  mates with similar features on the inside of a mating receiver spline (not shown). 
     As shown in  FIG. 3 , output plate  38  includes an over molded feature  50  made of a plastic coating along a portion of the outside diameter. The over molded feature may cover not only the outside circumference of output plate  38  but also a major portion of the outwardly facing surface thereof. The over molded feature  50  further includes a plurality of molded openings  52  formed for allowing the plurality of pins  46  to be pressed therein, and one or more anchors  62  for securing over molded features  50  to output plate  38 . Specifically, the areas where the plurality of pins  46  are to be pressed into the output plate  38  are coated with over molded feature  50  to form the plurality of molded openings  52  to avoid any secondary operations on the molded part apart from simply pressing the plurality of pins  46  into the plurality of molded openings  52 . Rotatable wheels  44  are secured to output plate  38  via pins  46 . 
     Input plate  34  may include plastic overmolded features forming a ring  53  ( FIG. 2 ) formed along the outer surface of input plate  34 , a plurality of molded openings  52  ( FIG. 3 ) for receiving pins  46  to secure wheels  44  to input plate  34 , and one or more anchors  62  for securing the above overmolded features thereto. 
     Coating a plastic over molded feature  50  on the input plate  34  and the output plate  38  has an advantage that the plurality pins  46  can be simply pressed into the input plate  34  and the output plate  38  because of the plastic coating on the input plate  34  and the output plate  38 . If the input plate  34  and the output plate  38  are not coated with over molded features  50 , the plurality of molded openings  52  would have to be drilled to achieve an appropriate press fit on the pins  46 , since the input plate  34  and the output plate  38  are made of metal. 
       FIG. 4  depicts a pivoting coupling retraction mechanism according to one embodiment of the present invention, indicated by numeral  54 . The pivoting coupling retraction mechanism  54  includes a gearbox frame  56  housing various drive components such as motors, gears, and the like, and a retraction plate  30 . Mounted to gearbox  56 , and axially retained by the pivoting retraction plate  30 , are a plurality of Oldham coupler assemblies  32  according to embodiments of the present invention, which mate and provide rotational power to the corresponding plurality of developer units  28  ( FIG. 1 ). The Oldham coupler assemblies  32  transfer rotary power between two parallel, but not necessarily radially aligned shafts. Additionally mounted to gearbox frame  56 , and axially retained by the pivoting retraction plate  30 , is a plurality of photoconductor unit couplers  60 , each of which couples with and provides rotary power to a corresponding photoconductor unit  24  ( FIG. 1 ). 
     The Oldham coupler assemblies  32  and photoconductor unit couplers  60  are biased by springs. The couplers  32  and  60  mate with their respective input members on the removable cartridges (developer units  28  and photoconductor units  24 , respectively) when the retraction plate  30  is in an engaged position. According to embodiments of the present invention, Oldham coupling assemblies  32  and photoconductor unit couplers  60  (four of each in the embodiment as shown in  FIG. 4 ) are simultaneously retracted in an axial direction of the coupler shafts as the retraction plate  30  moves from an engaged to a retracted position. The retraction plate  30  retracts both the Oldham coupler  32  and the photoconductor unit couplers  60  laterally, in an axial direction, thus disengaging the couplers  32  and  60 . With the couplers  32  and  60  thus retracted, the subunit  16  holding the photoconductor units  24  are opened and the developer units  28  may be freely removed from, or inserted into, the housing  12  of the image forming apparatus  10  ( FIG. 1 ). 
       FIG. 5  illustrates output plate  38  prior to being subjected to the overmolding process. Output plate  38  includes a plurality of openings  52 ′ from which openings  52  are formed during the overmolding process. Each opening  52 ′, when viewed from either major surface of output plate  38 , is substantially symmetrical about either or both of a horizontal (longitudinal) axis and a vertical (lateral) axis extending through a center point of opening  52 ′. For instance, each opening  52 ′ may have a substantially oblong shape—curved and/or semicircular, concave shape at each side of opening  52 ′, and curved, convex shapes at upper and lower portions thereof. It is understood, however, that openings  52 ′ may have any of a number of substantially symmetrical shapes, such as a clover shape. 
     With further reference to  FIG. 5 , output plate  38  includes a plurality of openings  62 ′ from which anchors  62  are formed during the overmolding process. In one embodiment, a size of opening  62 ′ along one surface of output plate  38  may be larger than a size of the opening  62 ′ along the second surface thereof. In another embodiment, a size of opening  62 ′ along a center of output plate  38  may be smaller or larger than a size of opening  62 ′ along each surface of output plate  38 . It is understood that the size of opening  62 ′ may vary in other ways from one surface of output plate  38  to the other surface. 
     It is understood that input plate  34  has openings  52 ′ and  62 ′ as illustrated in  FIG. 5  and described herein for forming overmolded openings  52  and anchors  62 , respectively. 
     In particular, each opening  52 ′ may have a first width and a second width, the first width being different from the second width. The plurality of openings  52 ′ decrease in width from the first width to the second width when viewed from the horizontal (longitudinal) axis extending through a center of the openings  52 ′. This resulting feature of the plurality of molded openings  52  allows for a good locking between output plate  38  and overmold feature  50  as well as between input plate  34  and overmold feature  50 . The plurality of molded openings  52  are symmetrically aligned to receive the plurality of pins  46  ( FIG. 3 ). A plurality of anchors  62  are defined around the input plate  34  and output plate  38  to keep the location of the overmolded parts relative thereto as the over molded feature  50  shrinks. Because of the shape of the plurality of openings  52 ′, the over molded feature  50  on each plate  34  and  38  would not shrink away from the metal parts and does not cause looseness between the parts. Since the Oldham coupler  32  rides in the metal retraction plate  30  during movement from retraction and non-retraction, there is some rotation during the process. The over molded feature  50  on output plate  38  being in plastic gives a good low friction wear surface for the output plate to rotate. Since the over molded feature  50  surrounds the outside circumference of the output plate  38 , the over molded feature  50  is held tight by its shrinkage during cooling in the mold that gives a strong clamp between the overmold and each of plates  34  and  38 . Similarly, anchors  62  are held tight by its shrinkage during cooling in the mold. 
     The structural elements employed in the present invention of metal and plastic combination control the location and firmly secure the components together in a manner that will transmit high torque loads required to drive the developer unit  28 . The composite torque transfer assembly of the present invention demonstrates a substantial elimination of jitter of about 0.6 to about 0.75 mm on a media sheet. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.