Abstract:
A device and method of supporting a doctor blade within an image forming apparatus. The device has a housing for positioning a doctor blade such that a bottom edge contacts a developer roller. One or more extensions are positioned to support a first side of the doctor blade. The one or more extensions may include dampeners which are constructed of a resilient material. Supports are positioned on a second side of the doctor blade. The doctor blade is sized to fit between the one or more extensions and the supports. A method of supporting the doctor blade includes positioning the doctor blade to dampen vibrations and velocity fluctuations caused by sticking and slipping of the bottom edge of the doctor blade against the developer roller.

Description:
BACKGROUND 
     Image forming devices including copiers, laser printers, facsimile machines, and the like, include a drum having a rigid cylindrical surface that is coated along a defined length of its outer surface with a photoconductive material. The surface of the drum is charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the photoconductive surface exposed to light are discharged thus forming a latent electrostatic image on the photoconductive surface. A developer material, such as toner, having an electrical charge such that the toner is attracted to the photoconductive surface is brought into contact with the photoconductive surface. The drum then rotates past an intermediate transfer medium where the toner is transferred onto the medium. A recording sheet, such as a blank sheet of paper, is then brought into contact with the intermediate transfer medium and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated thereby permanently fusing the toner to it. In preparation for the next image forming cycle, the photoconductive surface is discharged and residual toner is removed. 
     The toner is stored in a toner reservoir adjacent to the drum. A doctor blade and developer roller are positioned between the toner reservoir and drum for controlling the amount of toner passed to the drum. A point created between the doctor blade and the developer roller controls the amount of toner transferred to the drum. It is important that the doctor blade make uniform and consistent contact across the entire length of the developer roller. If the doctor blade has inconsistent pressure with the developer roller during the transfer, uneven toner amounts will be transferred to the drum resulting in inconsistent and unacceptable print quality. If too much toner is transferred to the drum, printing errors may occur such as blurred images, poor color, and toner particles deposited on the background areas. Conversely, if not enough toner is transferred to the drum, the images will be too light and difficult to see. 
     A problem in maintaining consistent contact and pressure is the developer roller profile may be non-uniform requiring that the doctor blade move inward and outward to track the surface of the developer roller. Additionally, it is vital that contact be maintained across the entire length of the doctor blade to ensure even print quality across the width of the image. 
     One problem in prior systems is jitter caused by vibrations and velocity fluctuations in the developer roller during the printing process. Jitter shows up on a printed page as a repeating pattern of light and dark lines in the process direction that extend across the printed image. One cause of jitter is the doctor blade sticking to and slipping across the surface of the developer roller. The stick/slip movement causes the doctor blade to move back and forth which results in small perturbations on the developer roller which translate into small velocity variations. 
     One proposed solution is to lessen the amount of force that the doctor blade exerts on the developer roller. However, the amount of force applied by the doctor blade controls the amount of toner transferred to the developer roller. If the force is decreased to prevent or decrease jitter, toner transfer may be adversely affected. Also, it has been determined that lesser biasing force may prevent the doctor blade from sticking and skipping along the developer roller, but may not prevent vibrations that result in jitter. Further, another cause of jitter may be the electrical force between the developer roller and the drum. Lessening the amount of biasing force does not substantially reduce or eliminate this cause of jitter. 
     SUMMARY 
     The present invention includes an apparatus and method of dampening a doctor blade within an image forming apparatus. In one embodiment, the apparatus includes a developer housing having an area for housing the doctor blade, a biasing member to bias the doctor blade against a developer roller, a member connected to a developer housing on a first side of the doctor blade, an extension connected to the developer housing and positioned on a second side of the doctor blade opposite the member on the first side, and a dampener attached to the extension and positioned between the extension and the doctor blade. In this embodiment, the dampener is constructed of a resilient material to dampen the movement of the doctor blade. 
     In another embodiment, the apparatus includes a developer housing having a first edge and a second edge positioned a distance apart for positioning a doctor blade, and a support extending between the first edge and the second edge. A first extension and a second extension each extend from the support and are equally distanced from a centerline of the developer housing. 
     In another embodiment, the apparatus is incorporated within an image forming apparatus which includes a developer roller, a doctor blade having a top edge and a bottom edge that contacts the developer roller, a biasing member that contacts the top edge of the doctor blade and biases the doctor blade against the developer roller, members positioned to contact a front side of the doctor blade, extensions positioned on a back side of the doctor blade, and dampeners positioned on the first extension. In this embodiment, the front side of the doctor blade contacts the members and the back side of the doctor blade contacts the dampeners. 
     The invention further includes a method of dampening a doctor blade by placing a dampening material against the doctor blade to dampen movement caused by sticking and slipping of a bottom edge of the doctor blade against the surface of a developer roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view illustrating an image forming apparatus constructed according to one embodiment of the present invention; 
     FIG. 2 is a perspective view of a developer housing having a doctor blade and developer roller according to one embodiment of the present invention; 
     FIG. 3 is a partial perspective view illustrating a front side of the developer housing having two extensions according to one embodiment of the present invention; 
     FIG. 4 is a partial perspective view illustrating the two extension illustrated in FIG. 3; 
     FIG. 5 is a side view illustrating the developer housing and extension relative to the doctor blade and developer roller according to one embodiment of the present invention; and 
     FIG. 6 is a schematic diagram illustrating the forces exerted on the doctor blade in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates the basic elements of an image forming apparatus and is incorporated for an understanding of the overall electrophotogr process. A four cartridge c color laser printer is illustrated as  100 , however on e skilled in the art will understand that the present invention is applicable to other types of image forming devices using toner for printing with a photoconductor. The printer, image forming apparatus or image forming device, generally designated  100 , includes a plurality of similar toner cartridges  110 ,  210 ,  310 , and  410 . Each toner cartridge  110 ,  210 ,  310  and  410  i s of a similar construction but is distinguished by the toner color contained therein. In the preferred embodiment, the device  100  includes a black (K) cartridge  110 , a magenta (M) cartridge  210 , a cyan (C) cartridge  310 , and a yellow (Y) cartridge  410 . Each different color toner forms an individual image of a single color that is combined in layered fashion to create the final multi- colored image. 
     Each of the toner cartridges  110 ,  210 ,  310  and  410  is substantially identical and includes a photoconductor, a developer device, and a cleaning device. As the toner cartridges  110 ,  210 ,  310  and  410  are identical except for the toner color, the toner cartridge  110  and elements for forming black images will be described, with the other color image forming units being omitted for simplification. 
     A photoconductor  114  is generally cylindrically-shaped with at least one end that intermeshes with the image forming device drive gears to provide for a rotational force. The photoconductor  114  has a smooth surface for receiving an electrostatic charge over the surface as the photoconductor  114  rotates past charging device  116 . The photoconductor  114  uniformly rotates past a scanning laser  120  directed onto a selective portion of the photoconductor  114  surface forming an electrostatically latent image across the width of the photoconductor representative of the outputted image. The drive gears rotate the photoconductor  114  continuously so as to advance the photoconductor  114  about 1/600 th  or 1/1200 th  of an inch between laser scans. This process continues as the entire image pattern is formed on the photoconductor surface. 
     After receiving the latent image, the photoconductor  114  rotates to a developer which has a toner bin, illustrated generally as  122  in FIG. 1, for housing the toner and a developer roller  124  for uniformly transferring toner to the  114  photoconductor. The toner is transferred from the toner bin  122  to the photoconductor  114  through a doctor blade nip formed between the developer roller  124  and a doctor blade  121 . The toner is a fine powder usually constructed of plastic granules that are attracted and cling to the areas of the photoconductor  114  that have been discharged by the scanning laser  120 . 
     The photoconductor  114  next rotates past an adjacently-positioned intermediate transfer mechanism belt  500  (hereinafter, ITM belt) to which the toner is transferred from the photoconductor  114 . As illustrated in FIG. 1, the ITM belt  500  is endless and extends around a series of rollers adjacent to photoconductors  114 ,  214 ,  314  and  414 . The ITM belt  500  and each photoconductor  114 ,  214 ,  314 ,  414  are synchronized providing for the toner from each photoconductor  114 ,  214 ,  314  and  414  to precisely align on the ITM belt  500  during a single pass. By way of example as viewed in FIG. 1, the yellow toner will be placed on the ITM belt  500 , followed by cyan, magenta, and black. 
     After depositing the toner on the ITM belt  500 , the photoconductor  114  rotates through a cleaning area where residual toner is removed from the surface via a brush or scraper  126 . The residual toner is moved along the length of the photoconductor  114  to a waste toner reservoir. In one embodiment, the photoconductor  114  further passes through a discharge area (not shown) having a lamp or other light source for exposing the entire photoconductor surface to light to remove any residual charge and image pattern formed by the scanning laser  120   
     As the photoconductors  114 ,  214 ,  314  and  414  are being charged and gathering toner, a recording sheet, such as a blank sheet of paper, is being routed to intercept the ITM belt  500 . The paper may be placed in one of the trays  510 , or introduced into the image forming device through a side track tray  520 . A series of rollers and belts transport the paper to point Z where the sheet contacts the ITM belt  500  and receives the toner. The sheet may receive an electrostatic charge prior to contact with the ITM belt  500  to assist in attracting the toner from the ITM belt  500 . The sheet and attached toner next travel through a fusser  530  having a pair of rollers and a heating element that heats and fuses the toner to the sheet. The paper with fused image is then transported out of the printer  100  for receipt by a user. 
     FIG. 2 illustrates one embodiment of a developer housing  20  with the doctor blade  121  positioned against the developer roller  124 . In one embodiment, the structure adjacent to the first and second ends of the doctor blade  121  maintains the position relative to the developer roller  124 . Stop posts  12  extend over the doctor blade  121  and are each positioned within an aperture  26  in the developer housing  20 . The stop post  12  is positioned above the doctor blade  121  opposite the developer roller  124  and functions to control the maximum movement of the doctor blade  121  away from the developer roller  124 . The stop post  12  is especially effective for safety concerns during handling of the cartridge to keep the doctor blade  121  within the cartridge. By way of example, if the cartridge is dropped, the stop post  12  prevents the doctor blade  121  from separating from the developer housing  20  and possibly damaging the cartridge, image forming apparatus, or injuring a person handling this equipment. 
     Retention posts  14  are positioned at each end of the doctor blade  121  to control one aspect of lateral movement of the doctor blade  121  relative to the developer roller  124 . A pair of retention blocks  16  extend from the developer housing  20  along the doctor blade  121  to further maintain the lateral position. As the developer roller  124  rotates in the direction of arrow  101  in FIG. 5, the doctor blade  121  is pushed against the retention post  14  and retention block  16 . The retention post  14  and retention block  16  work in combination and the doctor blade  121  may contact one or both during the toner transfer process. The stop post  12 , retention post  14 , and retention block  16  are mounted to support each end of the doctor blade  121 . The stop post  12 , retention post  14 , and retention block  16  may have a variety of shapes to effectively control the positioning of the doctor blade  121 . 
     In one embodiment, the stop post  12 , retention post  14 , and retention block  16  are constructed as a unitary piece having a common back section  18 . Preferably, the piece is constructed of a low friction material, and in one preferred embodiment the piece is constructed from acetal. The distance the stop post  12 , retention post  14 , and retention block  16  extend outward along the doctor blade  121  may vary. 
     A biasing member  50  attached to the developer housing  20  is positioned above the doctor blade  121  to maintain a continuous force for biasing the doctor blade  121  against the developer roller  124 . The amount of force applied by the biasing member  50  also controls the amount of toner transferred to the developer roller  124 . The drawings illustrate the doctor blade  121  substantially perpendicular to the developer roller  124 , however, other orientations may also provide for transfer of proper toner amounts. The biasing member  50  may contact the doctor blade  121  at one or more locations along the length of the doctor blade  121  to ensure an even and distributed force is applied across the entire width of the developer roller  124 . In one embodiment, the biasing member  50  provides about 1400 grams of force to the developer roller  124 . U.S. pat. No. 6,078,771, assigned to the Lexmark International, Inc., the assignee of the present application, discloses various structure for an image forming apparatus and is incorporated by reference herein in its entirety. 
     FIG. 3 illustrates the developer housing  20  with the doctor blade  121  and developer roller  124  removed for clarity. The developer housing  20  contains the toner and provides a structure for mounting the doctor blade  121  and developer roller  124 . In one embodiment, the developer housing  20  includes an area  23  for housing the doctor blade  121  that includes openings  24  through which developer roller axles extend for positioning the developer roller  124 . A support  22  extends along at least a section of the area  23  and includes extensions  25  extending outward for supporting the doctor blade  121  as will be explained below. The developer housing  20  forms an inner sidewall  28  that provides for laterally maintaining the doctor blade  121  over the developer roller  124 . In one embodiment, apertures  26  are positioned within the inner sidewalls  28 . The developer housing  20  may be constructed of any rigid material for supporting the toner and doctor blade  121 , and in one embodiment is constructed of polystyrene. 
     FIG. 4 illustrates one embodiment having a pair of extensions  25  mounted on the support  22  of the developer housing  20 . In this embodiment, the extensions  25  are equally spaced from a centerline C of the developer housing  20 . The distance between the extensions  25  may vary depending upon the parameters of the printing device. In one embodiment, the inner edges  25   a  are separated by a total of about 25.02 mm (i.e., the inner edge  25   a  of each extension is about 12.51 from the centerline C). The extensions  25  may have a variety of shapes and sizes. In one embodiment, the extensions  25  are substantially rectangular in shape and have a width w of about 4.98 mm and a thickness t of about 1.50 mm. In one embodiment, a stiffening rib  27  extends between the developer housing  20  and a back of the extension  25  for additional stiffness and strength. In one embodiment, a shoulder  21  extends outward from the face of the extension  25  to support a dampener  40  (FIG.  5 ). In one embodiment, both extensions  25  have the same shape and size and dimensions to equally support the doctor blade  121 . 
     In another embodiment, only one extension  25  extends from the developer housing  20  to support the doctor blade  121 . In this embodiment, the extension  25  is centered about the centerline C. In another embodiment, more then two extensions  25  are mounted on the developer housing  20  to support the doctor blade  121 . The extensions  25  are spaced about the support  22  to equally support the length of the doctor blade  121 . The sizes and shapes of the extensions  25  may vary depending upon their position on the support  22 , and the total number of extensions  25 . 
     FIG. 5 illustrates a side view of one embodiment with the extension  25  having a dampener  40  mounted on the front side to contact the doctor blade  121 . Dampener  40  has a damping capacity to absorb vibrations from the doctor blade  121 . In one embodiment, dampener  40  is constructed of a resilient material that is compressed by the doctor blade  121  and thus applies a force to the doctor blade  121 . In one embodiment, the dampener  40  is constructed of PORON foam, a polyurethane foam commercially available from Rogers Corp. as 4790-92-2008104. The dampener  40  has a thickness such that the doctor blade  121  contacts the dampener  40  on a first side and a retention block  16  on the opposite side. In one embodiment, dampener  40  is about 2.06 mm thick. Dampener  40  may have a variety of shapes and sizes. In one embodiment, dampener  40  extends beyond the extension  25 , either on the lower edge, upper edge, or one or both side edges. In one embodiment, dampener  40  is positioned on the front of the extension  25  and rests on a shoulder  21  adjacent to a bottom edge of the extension  25 . In one embodiment, dampener  40  has a uniform cross-section thickness with the front surface that contacts the doctor blade  121  being substantially parallel to the front surface of the extension  25 . In one embodiment, dampener  40  has a width of about 4.98 mm. 
     In one embodiment, the distance between an inside edge of the front support and an inside edge of the extension  25  is less than a thickness of the doctor blade  121  and a thickness of the dampener  40 . Therefore, the dampener  40  is maintained in a compressed state. 
     In one embodiment, dampener  40  is attached to the extension  25  by an adhesive that may be applied in a variety of manners. In one embodiment, the adhesive comprises a pressure sensitive material applied to one side of the dampener  40  facing the extension  25 . In one embodiment, the adhesive is Model No.  7953  manufactured by 3M. Extension  25  may include a knurled surface to improve the adhesion of the adhesive. 
     In one embodiment as illustrated in FIG. 5, a flap seal  133  extends along the back side of the doctor blade  121 . The flap seal  133  includes an upper edge  134  attached to the developer housing  20  to prevent toner from leaking across the top edge  127  of the doctor blade  121 . A bottom edge  132  extends along the doctor blade  121  to prevent toner from leaking along the back edge of the doctor blade  121 . The flap seal  133  is positioned against the back edge of the doctor blade  121 . In one embodiment, the flap seal  133  is positioned between the doctor blade  121  and the dampener  40 . In another embodiment, flap seal  133  is positioned between the extension  25  and the dampener  40 . The flap seal  133  may extend beyond the length of both the dampener  40 , beyond the length of the extension  25 , or both. In one embodiment, flap seal  133  may extend a distance less than the length of either the dampener  40  or extension  25 . The material of the flap seal  133  provides for a low to zero friction contact with doctor blade  121 . In one embodiment, the flap seal  133  is constructed of mylar, however, other low friction materials may also be used. In one embodiment, flap seal  133  is not attached to the doctor blade  121 . 
     FIG. 6 is a schematic diagram illustrating the forces acting on the doctor blade  121 . Spring  50  applies a force that is countered by the force applied by the developer roller  124 . Extension  25  and dampener  40  and the frictional force  129  of the doctor blade  121  contacting the developer roller  124  apply a force that is countered by the force of the retention block  16 . 
     In one embodiment, the doctor blade  121  and the front surfaces of the extension  25  and dampener  40  are aligned substantially perpendicular to the surface of the developer roller  124 . A force applied by the extension  25  and dampener  40  is in a direction tangent to the surface of the developer roller  124 . The angle of the doctor blade  121  relative to the developer roller  124 , and the angle of the dampener  40  and extensions  25  relative to the doctor blade  121  may vary. The extensions  25  and dampener  40  are positioned to provide a force on the doctor blade  121  in a direction tangent to the surface of the developer roller  124 , or in a direction away from the surface of the developer roller  124 . 
     In use, as the developer roller  124  rotates in the direction of arrow  101  illustrated in FIG. 5, toner from the toner bin  122  is transferred at the nip point between the lower edge  125  of the doctor blade  121  and the developer roller  124 . The pressure of the doctor blade  121  against the developer roller  124  controls the mass flow and charge level of the toner. The biasing member  50  provides a predetermined force on the doctor blade  121  that is transferred to the nip point. Because of the non-uniform profile of the developer roller  124 , the doctor blade  121  may move in and out. The doctor blade  121  may be positioned at a variety of angles relative to the developer roller  124 . Any vibrations or variations in the relative position of the doctor blade  121  relative to the developer roller  124  are lessened or dampened by the dampener  40 . Consistent positioning and consistent pressure provides for toner transfer through the nip formed between the doctor blade lower edge  125  and the developer roller  124  to be consistent and reduce or eliminate jitter. Without the dampening, vibrations result in variations in the pressure amounts within the nip, and variations in the spacing of the nip result in toner deviations that cause print defects. 
     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. In one embodiment, one or all of the stop post  12 , retention post  14 , and retention block  16  are part of the developer housing  20  and are not separately mounted to the developer housing  20 . In one embodiment, the front surface of the extension  25  is substantially flat to support the doctor blade  121  equally across the width of the extension  25 . In another embodiment, the surface of the extensions  25  are knurled to assist in receiving the adhesive. In one embodiment, the extensions  25  do not include a dampener  40  as the extensions  25  alone provide a dampening force on the doctor blade  121 . 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.