Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to a rotary cleaner having multiple blades that contact a surface to be cleaned. The cleaning blade is particularly suited for use in xerographic or electrophotographic devices to remove residuals, such as liquid or dry toner.  
           [0003]    2. Description of Related Art  
           [0004]    There have been proposed several blade mechanisms to remove residual components from a photoreceptive surface in a xerographic or electrophotographic  10  device. One technique employed involves the use-of a compliant blade held against the surface. Such blade cleaners, often accompanied by irrigating and agitation devices, are common in low to mid-volume electrophotographic machines and digital presses equipped with liquid imaging systems. Such blade cleaners are rarely used in long-run, high reliability, high-speed systems as they have relatively short mean-time-to-failure when compared to magnetic brush-type cleaning systems employed in dry xerographic machines.  
           [0005]    Consistent, reliable cleaning performance is required to satisfy the needs of customers in the graphic arts market. Currently, production in this market is from offset presses, plate-makers (offline and direct) and high-end workstations. All of these graphic arts machines are designed to deliver hour after hour of dependable performance. Presses require less than one service call per year with outputs in the tens of millions of sheets between calls. This means that a blade-based cleaning subsystems reliability must be high, much higher than existing blade-based cleaners used today.  
           [0006]    The present mainline approach to removing residual liquid imaging material from the surface of an image carrier, such as a photoreceptor, image bearer, transfer belt, etc., in a liquid imaging system is use of a foam agitation roll, a spray bar, and a compliant blade in combination. This cleaning system has been employed to remove residual ink “cake” for reclamation, and residual ink and Isopar™ image carriers following electrostatic transfer at process speeds of 30 inches per second (ips). However, there are problems with this system.  
         SUMMARY OF THE INVENTION  
         [0007]    There is a need for an improved cleaning system that has an increased failure interval.  
           [0008]    There also is a need for such a system to retain simplicity, effectivity and low cost.  
           [0009]    It is an object of the invention to provide a rotary, multi-bladed cleaner that can provide increased life expectancy, up to 15-25 times the life of a single blade cleaner. Moreover, it is another object of the invention to provide a highly reliable cleaner due to its ability to frequently change brush surfaces and by provision of a redundant system that enables multiple blades to contact the surface to be cleaned at once.  
           [0010]    These and other objects are achieved by a blade cleaner that has a paddle-wheel type cross-sectional shape with a plurality of radially extending blades spaced around the periphery thereof. The blades are spaced to be closely adjacent one another such that one and preferably two or more blades contact the residual image at one time. The rotary blade cleaner blades are preferably skewed. The rotary blade can be rotated at a slow rotation rate with the blades being in contact for only a limited time before being displaced by the next blade(s). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The foregoing and further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is an end view of a multi-blade rotary cleaner according to the invention;  
         [0013]    [0013]FIG. 2 is a side view of the multi-blade rotary cleaner of FIG. 1 according to the invention;  
         [0014]    [0014]FIG. 3 is a perspective view of the multi-blade rotary cleaner of FIG. 1 according to the invention;  
         [0015]    [0015]FIG. 4 shows a graph of test results showing minimum cleaner speeds for dry toner and diluted ink systems, as well as 24% solids ink systems;  
         [0016]    [0016]FIG. 5 shows a schematic of a liquid electrophotographic system with the inventive multi-bladed rotary cleaner according to the invention; and  
         [0017]    [0017]FIG. 6 shows a schematic of a dry electrophotographic system with the inventive multi-bladed rotary cleaner according to the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    A first embodiment of the present invention will be described with reference to FIGS.  1 - 3 , which show a multi-bladed rotary cleaner  100  applicable to both dry and liquid toner imaging systems. For a general understanding of a printing machine in which the invention may be incorporated, reference will be made to FIG. 5, which depicts schematically various components of an exemplary liquid electrophotographic system. FIG. 6 depicts schematically an exemplary dry electrophotographic system to which the invention can be incorporated. While the rotary cleaner is well suited to these types of systems, it should become equally evident that the invention is well suited to other cleaning applications beyond the exemplary embodiments shown, such as offset presses and other graphic arts printing systems in general, and to other general applications in which residual materials on a surface need to be removed.  
         [0019]    Referring back to FIGS.  1 - 3 , a cross-section of a molded, compliant multi-bladed cleaner  100  is shown having a plurality of blades  110  radiating from a base  120 , which is preferably cylindrical. Rotary cleaner  100  is used to clean residuals from a surface, such as image bearing surface  200 . Rotary cleaner  100  is suitable for installation onto a mandrel or other cylindrical mount, such as the shaft-driven mandrel  300  shown in FIG. 3, which is operatively driven by a drive source  400 , which can be any conventional or subsequently developed drive source such as a D.C. motor or servo motor, connected to a shaft  310  of the mandrel through a conventional (unshown) linkage. The driving is preferably continuous during use, but may be indexed. For example, the rotary cleaner may be incrementally indexed after a predetermined number of images have been cleaned.  
         [0020]    In this exemplary embodiment of FIGS.  1 - 3 , rotary cleaner  100  has a length L that is preferably at least as long as the transverse width of the surface being cleaned. Rotary cleaner  100  also has a predefined roll diameter D 1 , a plurality of radially projecting blades  110  spaced around the periphery of the blade cleaner at a preferably constant pitch (substantially uniform blade spacing) S, a blade thickness T, and a blade extension length E, which results in a blade cleaner having a total diameter D 2 . These variables are selected based on several criteria. The number of blades, the spacing, and the circumference D 2  are selected for a particular application based on many criteria, which can vary greatly depending on the particular application. Some of these variables are inter-related and thus not completely arbitrary. For example, the number of blades is dependent on the selected circumference and spacing. Conversely, once a desired number of blades is determined, the necessary circumference can be mathematically determined given a specified spacing.  
         [0021]    One factor in selecting the desirable number of blades is based on the expected life expectancy of the unit (i.e., printing machine) and a desirable service interval. By increasing the number of blades, the life expectancy can be increased (assuming a given wear rate per blade) as a larger number of blades will decrease the total time that each blade will be in contact with the surface given a constant rotation speed. Furthermore, the number of blades may be selected based on a desirable rotation rate and a selection of an adequate time to clean the blade surfaces before they again contact the image bearing surface during a subsequent rotation cycle. Also, the number of blades may be determined mathematically based on a maximum design s diameter of a cleaner that can fit in a given space and a predetermined minimum spacing between blades. These are just examples of various criteria that may go into the selection of an appropriate number of blades.  
         [0022]    Each vane or paddle  110  preferably represents a full width compliant blade (i.e., a blade that extends the full length of a surface to be cleaned, such as a photoreceptor  200 ). Preferably, blades  110  are oriented in a skewed fashion similar to the spiral or slightly helical pattern shown in FIG. 2 (similar to that of a gravure roll) so that only a portion of each blade is used at any one time during cleaning. A better illustration of an exemplary embodiment of the rotary cleaner  100  is shown in FIG. 3.  
         [0023]    In use, it is preferable for at least two blades  110  to contact the image bearer  200  at one time. That is, the interference between the image bearing surface and the multiple blades are adjusted so that at least one and preferably two (or more depending on application) blades are in contact With multiple blade contact, the likelihood of a damaged blade causing a streak defect is minimized. An optimum number of blades to contact has been found to be two to assure good cleaning and minimize drag on the image bearing surface.  
         [0024]    Spacing S is selected based on several criteria, including material selection, modulus of the selected material, and extension length E, which are primary factors that determine deflection of individual blades  110 . Spacing should not be so close that adjacent blades  110  contact one another during use. Moreover, the spacing should be enough to allow a sufficient flow channel for removal of the wiped material which will become entrapped between adjacent blades so as to prevent clogging or choking off of flow out of the channel. Further, spacing should be selected so that only a desired number of blades contact the surface at one time at a given section of the cleaner.  
         [0025]    Various lab experiments have been conducted to verify the capability of the multi-blade cleaner  100  with imaging materials. Cleaning was accomplished using the rotary blade cleaner shown in FIG. 3. Blade cleaner  100  was made using a soft urethane. For use in removing liquid imaging toner and similar residuals, a preferred material was found to be a 70 Shore A durometer urethane rubber having a Young&#39;s modulus of about 1000 psi. However, the invention is not limited to this material and other known, conventional or subsequently developed blade surface materials may be used or selected depending on the particular residuals or surface being cleaned.  
         [0026]    This exemplary blade cleaner  100  had a length L of about 38 mm (1.5″) for testing purposes but can be any suitable length, preferably a length that is the same as or longer than the surface to be cleaned, a diameter D of about 66 mm (2.6″) (as shown in FIG. 1), a blade spacing S of about 6.5 mm, a blade thickness T of about 2 mm (as shown in FIG. 1), and a blade extension length E of about 7 mm. With this dimensioning, the resultant rotary cleaner  100  had 30 blades  110 . However, this example is illustrative and not meant to be limiting. Similar results can be achieved with altered variables.  
         [0027]    The material being removed by rotary cleaner  100  during initial testing was a 24% solids CEP ink cake spread onto a glass surface. The rotary cleaning blade  100  was manually engaged and slowly rotated. Cleaning was found to be perfect, and the vanes/blades  110  were easily washed using Isopar™ by simply directing the washing fluid along and between the vanes  110 . A quick and easy clean wash of the vanes is important to assure that the blades are clean before they rotate back into the cleaning nip. It is contemplated that such cleaning can be achieved by a routine, periodic manual flushing using a squirt bottle with a cleaning fluid such as Isopar or could be achieved with a mechanical washing station provided within the machine adjacent to rotary cleaner  100 . A suitable washing station could include a mechanical sprayer positioned to move along the cleaner  100  and spray a fluid into the vanes and channels therebetween to wash the residuals to a waste tank or other removal facility (unshown). The washing station may also include a damp cloth or sponge that wicks or otherwise remove the residuals from the surface of cleaner  100 . In the case of dry residuals, such as dry toner particles, the washing station may consist of a rotary brush, a vacuum source or air assist that cleans the residuals from the cleaner  100  without contacting the image bearing surface  200 .  
         [0028]    It has been found to be preferable to rotate the blades  110  of rotary cleaner  100  at a slow rate of speed, so that the cleaner slowly advances new clean blades continuously into a cleaning nip and carry the wiped residuals (such as ink) between the vanes to a suitable washing station (unshown). A suitable cleaner roll rpm depends on several parameters, such as the process speed of the xerographic device, the input residual mass density, the amount of residual mass on the cleaner roll that has to be cleaned, and the diameter of the cleaner roll. The diameter of the roll determines the number of cleaning blades. The dimensions of the blade, such as extension and thickness determine the normal cleaning force applied to remove the toner or ink. Thus, there are a number of parameters that affect cleaner roll rpm.  
         [0029]    The inventive rotary cleaner is particularly suited for use in cleaning residual printing materials, such as dry toner, diluted ink and high solids content ink, in a xerographic or other printing or copying device. Such devices operate at one or more predefined process speeds. Additional testing was conducted to determine necessary rotary cleaner speeds to obtain adequate cleaning of such devices that operate at a given process speed. The data in FIG. 4 shows that the inventive rotary cleaner  100  can operate at a very low rpm compared to conventional brush cleaners, which typically operate at between 300 to 1000 rpm. This slower rotation allows ample time to clean the blades and eliminate toner or ink emissions from the cleaner.  
         [0030]    Studies with both toner and ink systems show that for good, reliable cleaning, the minimum number of blades contacting the image should be two. The second blade serves as a backup blade in case the first blade fails. For example, if the first blade develops a nick that allows toner to leak under the blade, the second (or subsequent) blade will clean the toner passing under the nicked blade. Another example would be if the input mass density is high and the first blade is unable to remove all the residual and allows some to leak under the first blade. The second blade&#39;s function would be to remove the residual that leaked past the first blade. The two blades contacting the surface define a cleaning nip with a width NW, which is the circumference of the roll divided by the number of blades.  
         [0031]    The rpm for the cleaner roll is typically specified in terms of the process speed of the xerographic device. When the process speed increases, the rpm of the cleaner roll correspondingly increases. This holds true generally for all types of rotary cleaners. From the studies conducted, cleaner rpm was varied with process speed. In particular, process speed was set constant and cleaner rpm was adjusted until good cleaning was achieved. This represents the minimum roll speed required for cleaning.  
         [0032]    A simple empirical relationship that works well with both toner and diluted ink systems was found to follow the formula: 
         V b =cleaner rpm=V pr /5,  [1] 
         [0033]    where V pr  is the process speed of the xerographic device and V b  is the minimum rpm to achieve good cleaning.  
         [0034]    A simple empirical relationship that works with a pasty ink having a high solids content, for example a 24% solids ink, was found to follow the formula: 
         V b =cleaner rpm=V pr /2,  [1] 
         [0035]    where V pr  is the process speed of the xerographic device and V b  is the minimum rpm to achieve good cleaning.  
         [0036]    Cleaning blades used for xerographic or electrophotographic applications usually operate using one of a doctoring mode or a wiping mode motion. In the doctoring mode, a blade edge contacts a surface at a low angle and cleans using a chiseling or pushing motion. In the wiping mode, the blade edge is closer to perpendicular to the surface and cleans using a wiping motion. Applicants have found that the wiping mode is preferable as it eliminates any stick-slip motion when the surface being cleaned has low lubrication. As such, the invention provides a rotary cleaner that provides a plurality of blades that operate in the wiping mode.  
         [0037]    In view of this testing, the exemplary rotary cleaner  100  has been found to be particularly applicable to single or multiple color liquid development electrophotographic imaging systems, such as the exemplary one shown in FIG. 5. The imaging system is formed by an electrophotographic or ionographic printer  500 , with the associated printer housing and framework being omitted for clarity. Such electrophotographic printers are well known and as such, their operation will only be briefly mentioned to provide context for the type of residuals being cleaned by the inventive rotary cleaner  100 . Printer  500  employs as an image retention member  514  an endless conductive belt having a dielectric layer (serving as an image bearing surface) on which multiple electrostatic images are created by an ion deposition process. Belt  514  moves in the direction of arrow  515  to advance successive portions of its surface through various processing stations disposed about the path of movement at a process speed of about 10 inches/second. Belt  514  is supported by rollers  558 ,  560  and  552 . Roller  558  is rotatably driven by a suitable motor (unshown) to move belt  514 . Rolls  544 ,  545 ,  548 ,  550 ,  554  and  556  are idler rolls provided to keep the belt taut and on track.  
         [0038]    Initially, a portion of belt  514  passes through a primary color charging station  521  where an image forming subsystem  521 A and imager  582  (which could be a laser) deposits charge of sufficient magnitude to form a latent image on the dielectric surface of belt  514 . Then, belt  514  passes a first liquid development system  536  with the belt surface containing the latent image confronting but uniformly spaced from the system  536  to form a first development zone  511 . Development system  536  passes a developing liquid comprising an insulating carrier and a predetermined concentration of toner particles into the development zone to develop the electrostatic image into a visible image as well known in the art.  
         [0039]    Next, belt  514  is advanced to second primary charging station  523  where an electrostatic latent image corresponding to a second color is formed by imager  584 , which image is subsequently developed by second development system  537  at second development zone  512 . The belt  514  then advances past a third primary charging station  525  and third imager  586 , followed by belt  514  passing a third development system  540 , and third development zone  516 . Then, belt  514  advances past a fourth and final black charging station  527  and fourth imager  588 , followed by black development at development station  541  and fourth developing zone  517 ″. The second, third and fourth stations and associated development systems are substantially the same as the first mentioned corresponding station so additional details are omitted for brevity.  
         [0040]    After full color development, belt  514  advances the developed full image contained in the surface thereof to a transfer station  563  where a sheet of copy paper  568  is advanced from a paper stack  569  along paper path  571  by a sheet feeder  566 . The copy paper advances in synchronism with movement of the belt  514  so that the developed image and the sheet arrive simultaneously at transfer station  563  for transfer. After transfer, the copy sheet with transferred image thereon is advanced to a fusing station  570  which has a series of fuser rolls  570 A that vaporize any remaining liquid carrier on the paper surface and permanently fuse the toner particles onto the copy sheet. Upon completion, the copy sheet is advanced to an output catch tray (unshown). A rotary cleaner  100  is provided downstream from transfer station  563  to remove any residuals, such as adhering toner particles or carrier fluid from belt  514  prior to creation of a new image. Rotary cleaner  100  may be opposed to an idler roller  556 . Rotary cleaner  100  corresponds to the rotary cleaner disclosed in FIGS.  1 - 3 . While a full color system has been shown, it is obvious that the invention also applies to monochrome printing and copying systems.  
         [0041]    The liquid electrophotographic system of FIG. 5 operates at a predetermined process speed. The rotary cleaner is rotated at a speed commensurate with the process speed and preferably is rotated at a minimum rotation speed as set forth in equation 1 when the liquid is diluted and rotated at a minimum speed as set forth in equation 2 when the ink has a high solids content.  
         [0042]    [0042]FIG. 6 depicts schematically an exemplary dry xerographic system to which the invention may also be particularly suited. As xerographic systems are well known, the various processing stations thereof will only be briefly described. A reproduction machine  600  is shown having a photoreceptor belt  610  having a photoconductive surface that serves as an image bearing surface. While a belt architecture is shown, the invention is equally applicable to a drum photoreceptor architecture. Photoreceptor belt  610  moves in the direction of arrow  612  to advance successive portions of belt  610  sequentially through the various processing stations disposed about the path of the belt. The belt  610  is entrained about a stripping roller  614 , a tension roller  616 , and a drive roller  620 . Drive roller  620  is coupled to a suitable motor  621  by an appropriate linkage such as a belt drive (unshown). The belt  610  is maintained in tension by a pair of unshown springs that resiliently urge tension roller  616  against belt  610  with a desired force. Both stripping roller  614  and tension roller  616  are idler rollers that are rotatably mounted for free movement.  
         [0043]    Initially, a portion of belt  610  passes through a charging station A, where a corona device  622  charges a portion of belt  610  to a relatively high, substantially uniform potential (which can be either positive or negative depending on application). At exposure station B, an original document is positioned face down on a transparent platen  630  for illumination with flash lamps  632 . Light rays reflected from the original document are reflected through a lens  633  and projected onto the charged portion  611  of the photoreceptor belt  610  to selectively dissipate the charge thereon. This records an electrostatic latent image on the belt that corresponds to the informational area contained within the original document. Alternatively, a laser may be provided to imagewise discharge the photoreceptor belt  610  in accordance with stored electronic information.  
         [0044]    Thereafter, belt  610  advances the electrostatic latent image to development station C, where at least one of two developer housings  634  and  636  is brought into contact with belt  610  for the purpose of developing the latent image. Housings  634  and  636  may be moved into and out of developing position by corresponding cams  638  and  640  selectively driven by motor  621 . Each developer housing  634  and  636  supports a developing system such as magnetic rolls  642  and  644 , which provides a rotating magnetic member to advance developer mix (i.e., carrier beads and toner) into contact with the electrostatic latent image. The electrostatic latent image attracts toner particles from the carrier beads, thereby forming toner powder images on the photoreceptor belt  610 . If only a single color developing system is used, the second developer housing may be omitted.  
         [0045]    Photoreceptor belt  610  then advances the developed latent image to transfer station D, where a sheet of support material such as paper copy sheets  649  is advanced into contact with the developed images on belt  610 . A corona generating device  646  charges the copy sheet to the proper potential so that it becomes tacked to the photoreceptor belt  610  and the toner powder image is attracted from photoreceptor belt  610  to sheet  649 .  
         [0046]    After transfer, corona generator  648  charges the copy sheet to an opposite polarity to detach the copy sheet from belt  610 , whereupon the copy sheet is stripped from belt  610  at stripping roller  614 . Sheets of support material  649  are advanced to transfer station D from a supply tray  650 . Sheets are fed from tray  650  with sheet feeder  652  and advanced to transfer station D along conveyor  656 .  
         [0047]    After transfer, the sheet continues from stripping roller  614  toward a fusing station E, which includes a fuser assembly  670  that permanently affixes the transferred toner powder images to the sheets. The fuser assembly may be a heated fuser roller  672  in pressure engagement with a backup roller  674 . From the fuser, sheet  649  passes gate  662  to an output tray  680 .  
         [0048]    Residual particles remaining on the photoreceptor belt  610  after each copy is made are removed by cleaning station F, which includes the inventive rotary cleaner  100 . A roll  690  may oppose cleaner  100 . All of the various movements may be controlled by machine controller  696 .  
         [0049]    The dry xerographic system of FIG. 6 operates at a predetermined process speed. The rotary cleaner is rotated at a speed commensurate with the process speed and preferably is rotated at a minimum rotation speed as set forth in equation 1.  
         [0050]    While the systems of the invention have been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.  
         [0051]    For example, the blades do not necessarily have to be continuous in their length and may be discontinuous. To prevent gaps in cleaning with such a configuration, discontinuous regions in adjacent blades should be offset so that the entire length of the surface is covered by at least one of the two or more blades that contact the surface at any one time.  
         [0052]    Moreover, it is not necessary for the blade cleaner  100  to be fixedly mounted adjacent and in contact with surface  200 . Rather, it is possible for rotary blade cleaner  100  to be pivotally or translatably movable toward and away from surface  200 .  
         [0053]    Further, while the base  120  and blades  110  may be integrally formed from a suitable material, it is also possible for base  120  and blades  110  to be formed of differing materials, with the blades  110  being bonded, adhered or otherwise affixed to base  120  so as to be radially provided around the periphery of base  120 .  
         [0054]    Additionally, while base  120  is preferably cylindrical, the invention is not limited to this and acceptable results may be achieved using a semispherical or other surface. However, in such a case, full rotation would not be achievable and an indexing mechanism would be required to index the cleaner back to a first blade when the cleaner has advanced to the last blade element.  
         [0055]    Moreover, the inventive rotary cleaner is applicable as a cleaning tool for many general purposes, even those outside of the graphic arts or printing field, as the cleaner has been found to adequately clean residual materials of many types from a surface.

Technology Category: 3