Abstract:
A cleaning mechanism for an image forming apparatus can assure stable cleaning performance, constantly maintain surface condition of an intermediate transfer body and a photoconductor to be removed an ink or the like by the intermediate transfer body clean, and thus stably obtain satisfactory quality of printed products. The cleaning mechanism has a cleaning roll being contacted with the intermediate transfer body under pressure with a predetermined load and rotated with firm contact with the intermediate transfer body for removing residual ink, toner or impurity on the intermediate transfer body after a transfer process and a sheet member being urged onto the cleaning roll for slip contact with a predetermined load.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a cleaning mechanism for an image forming apparatus. More particularly, the invention relates to a cleaning mechanism for an image forming apparatus for cleaning an intermediate transfer body used upon formation of an image in an electrophotographic apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    In an electrophotographic apparatus or the like, a toner image is electrostatically carried on a transfer member. Therefore, after transfer, substantial amount of toner resides on a surface of a photoconductor (transfer ratio is about 80 to 90%) to lower an image density. On the other hand, since the toner is transferred electrostatically, it is no possible to completely prevent flying of toner to potentially cause degradation of clearness of the image or to contaminate the inside of the apparatus. For avoiding such defects, there has been proposed a pressure type transfer means. This type of apparatus employs appropriately 200 kg/cm 2  of pressure for transferring and fixing the image, it is difficult to directly transfer the toner image on the surface of the photoconductor onto a medium to be printed the image to require transfer of electrostatic latent image to a dielectric layer as an intermediate transfer body. Therefore, apparatus can become bulky and mechanism can be complicate. Also, in order to transfer the electrostatic latent image, resolution of the image can be lowered.  
           [0005]    On the other hand, there has been proposed an apparatus for developing the latent image formed on the photoconductor and transferring the developed image to the intermediate transfer body having a silicon rubber layer, and then transferring the transferred image onto the medium to be printed the image, which medium will be hereinafter referred to as “printing medium”. However, such apparatus requires large amount of calorie for transferring and fixing the image. Also, the head inherently elevates temperature of the photoconductor via the intermediate transfer body, the characteristics of the photoconductor may possibly be degraded.  
           [0006]    Conventional cleaning mechanism of the image forming apparatus will be discussed in detail with reference to the drawing.  
           [0007]    [0007]FIG. 6 is a side elevation showing the first prior art disclosed in Japanese Unexamined Patent Publication No. Showa 62-286082. In FIG. 6, an intermediate transfer body  503  is in belt form which is formed by coating a surface of rigid roll of stainless or the like with a silicon rubber or the like.  
           [0008]    The intermediate transfer body  503  is clamped between a cleaning roll  501  heated by an internal heater and a pressure roll  507  positioned in opposition to the cleaning roll  501  and is fed therethrough. Thus, a residual toner  508  on the intermediate transfer body  503  is molten by the cleaning roll  501  and deposit thereon. On the cleaning roll  501 , a cleaning blade  504  which is formed with a thin plate of stainless steel or phosphor bronze, is contacted under pressure exerted by a spring  505  for removing the toner depositing on the surface thereof. The toner thus scraped is received in a waste toner box  509 . On the other hand, in order to prevent the waste toner from scattering, a sheet  506  formed with a heat resistant resin film, such as polyimide film or the like, is urged onto the cleaning roll  501 .  
           [0009]    The toner on the intermediate transfer body  503  is soften in certain extent by heat and pressure applied from the cleaning roll  501 . Furthermore, since a surface free energy of the surface of metal is greater than that of the silicon rubber, softened toner is efficiently deposited on the surface of the metal of the cleaning roll  501 . Furthermore, the softened toner is removed a pressure after passing through a nip portion between the cleaning roll  501  and the pressure roll  507  to be quickly hardened to be easily removed by the metallic cleaning blade  504 .  
           [0010]    One employing a cleaning belt in place of the cleaning roll  501  for removing residual ink or stain or dirt on the surface of the transfer body may possibly cause fluctuation in pressure upon contacting the cleaning belt onto the transfer body. Also, for low absorbing speed of the ink, fluctuation may be caused in removal of residual ink or stain or dirt on the surface of the transfer body to form stain on the printed product.  
           [0011]    [0011]FIGS. 7A and 7B are perspective view and side elevation of the second prior art disclosed in Japanese Unexamined Patent Publication No. Heisei 04-016978, for example.  
           [0012]    A cleaner  613  is constructed with a cleaning puff  610 , a cleaning roll  622  and a take-up roll  631 . A cleaning agent supplier  609  is formed with a plurality of conduits or one or more grooves to impregnate a cleaning agent stored therein into the cleaning puff  610 . Impregnating method of the cleaning agent in the cleaning puff  610  may be capillary force, a pressure difference between inside and outside of the cleaning agent supplier  609 , difference of concentration of the cleaning agent, heating by an electric heater, ultrasonic vibration or pumps.  
           [0013]    The cleaning puff  610  impregnated the cleaning agent is pressed onto a photoconductor drum  606  by a cleaning roll  622  in the vicinity of an ink absorbing portion  620 . The cleaning puff  610  absorbing contaminants is taken up by the take-up roll  631 . After absorbing contaminants, the cleaner  613  may rewind the almost dried cleaning puff  610  to the cleaning agent supplier  609  for reuse. Furthermore, when the same image is to be printed for a plurality of sheets simultaneously, cost may be saved by performing cleaning at a given interval or by reducing impregnating amount of the cleaning agent.  
           [0014]    The cleaning puff  610  may be formed with fibric paper, cloth, plastics. However, by containing metallic or ceramic fiber, effect of removal of static electricity or removal of solid deposit may be expected. On the other hand, the cleaning puff  610  may also be formed with porous sheet or sheet working into particular pattern.  
           [0015]    The cleaning agent is made of a material which may solve an ink to be used for printing. For example, in case of water soluble ink, a mixture prepared by adding a surface active agent and an antioxidant to solution of higher alcohols or glycol esters is taken as a primary component. In addition, depending upon composition of the ink, amines, ethyl&#39;s or other esters may be used.  
           [0016]    On the other hand, when a dispersion type ink which is prepared by dispersing a pigment into a liquid component, a solvent having the same polarity with dispersed particle or solvent easily solving the pigment may be used.  
           [0017]    The conventional cleaning mechanism of the image forming apparatus set forth above employs the roll form cleaning means. The conventional roll type cleaning means merely remove the residual ink on the intermediate transfer body by coating the ink component on the roll for removing the ink utilizing the fact that binding power between the ink component on the cleaning roll and the residual ink on the intermediate transfer body is greater than that between the residual ink and the surface of the intermediate transfer body. However, on the surface of the cleaning roll, impurity other than the ink, substance contained in the ink component and degrading transfer performance, paper dust of the printing paper and so forth may deposit to lower cleaning performance. On the other hand, even assuming that the substance depositing on the surface of the cleaning roll is only ink, ink amount is not uniform over axial direction of the roll in some image to be printed to form irregularity on the surface of the cleaning roll to cause failure in firm fitting between the cleaning roll and the intermediate transfer body resulting in cleaning failure.  
         SUMMARY OF THE INVENTION  
         [0018]    Therefore, it is an object of the present invention to provide a cleaning mechanism for an image forming apparatus which can assure stable cleaning performance, constantly maintain surface condition of an intermediate transfer body and a photoconductor to be removed an ink or the like by the intermediate transfer body clean, and thus stably obtain satisfactory quality of printed products.  
           [0019]    According to one aspect of the present invention, a cleaning mechanism of an image forming apparatus which transfers an ink or a toner image formed on a photoconductor to a roll form intermediate transfer body and then transfers to a printing medium for obtaining a printed product, the cleaning mechanism comprises:  
           [0020]    a cleaning roll being contacted with the intermediate transfer body under pressure with a predetermined load and rotated with firm contact with the intermediate transfer body for removing residual ink, toner or impurity on the intermediate transfer body after a transfer process; and  
           [0021]    a sheet member being urged onto the cleaning roll for slip contact with a predetermined load.  
           [0022]    In the construction set forth above, a relative speed may be provided between the cleaning roll and the sheet member for slip contact to transfer ink or impurity from a surface of the cleaning roll to the sheet member.  
           [0023]    According to another aspect of the invention, a cleaning mechanism of an image forming apparatus which transfers an ink or a toner image formed on a photoconductor to a roll form intermediate transfer body and then transfers to a printing medium for obtaining a printed product, the cleaning mechanism comprises:  
           [0024]    a cleaning roll being contacted with the intermediate transfer body under pressure with a predetermined load and rotated with firm contact with the intermediate transfer body for removing residual ink, toner or impurity on the intermediate transfer body after a transfer process; and  
           [0025]    a back-up roll arranged in opposition to the cleaning roll;  
           [0026]    a sheet member being inserted between the back-up roll and the cleaning roll and slip-contacting with the cleaning roll;  
           [0027]    a feeding roll feeding the sheet member wound thereon;  
           [0028]    a take-up roll taking up the sheet member;  
           [0029]    a housing receiving the back-up roll, the sheet member, the feeding roll and the take-up roll; and  
           [0030]    an actuator connected to the housing and driving the sheet member toward and away from the cleaning roll for establishing and releasing slit contact therebetween.  
           [0031]    A heat source, such as halogen lamp or the like may be built-in the cleaning roll for differentiating a surface temperature of the cleaning roll from a surface temperature of the intermediate transfer roll for providing large binding force with an ink for the cleaning roll.  
           [0032]    Liquid supply means for supplying a liquid serving as a lubricant and a cleaning aiding agent to sheet member, may be arranged within the housing. The liquid maybe one of water, isopropyl alcohol and an insulative solvent.  
           [0033]    The sheet member may be in endless form.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of the preferred embodiment of the present invention, which, however, should not be taken to be limitative to the invention, but are for explanation and understanding only.  
         [0035]    In the drawings:  
         [0036]    [0036]FIG. 1 is a diagrammatic illustration showing an overall construction of one embodiment of a cleaning mechanism for an image forming apparatus according to the present invention;  
         [0037]    [0037]FIG. 2 is an illustration showing an image transfer portion and a fixing portion incorporating the preferred embodiment of the cleaning mechanism according to the present invention;  
         [0038]    [0038]FIG. 3 is a diagrammatic side elevation showing one embodiment of a cleaning mechanism for an image forming apparatus according to the present invention;  
         [0039]    [0039]FIG. 4 is an illustration showing a modification of one embodiment of the embodiment of a cleaning mechanism for an image forming apparatus according to the present invention;  
         [0040]    [0040]FIG. 5 is an illustration showing another modification of one embodiment of the embodiment of a cleaning mechanism for an image forming apparatus according to the present invention;  
         [0041]    [0041]FIG. 6 is a side elevation showing the first prior art; and  
         [0042]    [0042]FIGS. 7A and 7B are a perspective view and a side elevation showing the second embodiment.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0043]    The present invention will be discussed hereinafter in detail in terms of the preferred embodiment of the present invention with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without these specific details. In other instance, well-known structure are not shown in detail in order to avoid unnecessary obscurity of the present invention.  
         [0044]    [0044]FIG. 1 is a diagrammatic illustration showing an overall construction of an image forming apparatus incorporating the preferred embodiment of a cleaning mechanism according to the present invention. FIG. 1 illustrates a color electrophotographic printer as one example of the image forming apparatus. However, the present invention should be applicable for color/monochrome electrophotographic printer, facsimile machine, copy machine and so forth. In FIG. 1, around a photoconductor  1 , a charging portion  2 , an exposure portion  3 , a developing portion  4 , an ink drying portion  5  and transferring and fixing portion  6 . Since the shown embodiment illustrates the color printer, the exposure portion  3  and the developing portion  4  are respectively consisted of exposure portions  3   a ,  3   b ,  3   c  and  3   d  and developing portions  4   a ,  4   b ,  4   c  and  4   c  adapting for respective colors of inks of yellow, magenta, cyan and black. By means of these mechanisms, a sequence of electrophotography process is performed to form an image on a printing paper  8  fed from a paper feeding hopper  7 .  
         [0045]    [0045]FIG. 2 is an illustration showing a construction of the transferring and fixing portion  6 , to which the cleaning mechanism according to the present invention is applied. The photoconductor  1  is transferred between a pair of rolls contacted under pressure and between an intermediate transfer body  62  and a transfer back-up roll  61 . An ink image on the photoconductor  1  is transferred to the intermediate transfer body  62 . On the other hand, onto the intermediate transfer body  62 , a fixing roll  63  is contacted under pressure. By feeding the printing paper  8  between these rolls, the ink image on the intermediate transfer body  62  is transferred to the printing paper  8 . The intermediate transfer body  62  constantly transfers the ink from the photoconductor  1  to the printing paper  8  upon printing. However, it is quite difficult to constantly transfer the ink image from the intermediate transfer body  62  to the printing paper  8  at a transfer efficiency of 100%. Therefore, the intermediate transfer body  62  constantly holds possibility to be contaminated. Accordingly, in order to clean up the residual ink image or impurity on the intermediate transfer body  62 , the preferred embodiment of the cleaning mechanism  100  according to the present invention is arranged.  
         [0046]    [0046]FIG. 3 is a diagrammatic side elevation showing the preferred embodiment of the cleaning mechanism according to the present invention. The cleaning mechanism is constructed with a back-up roll  103  arranged in opposition to a cleaning roll  101 , a sheet member  104  disposed between the back-up roll  103  and the cleaning roll  101  for cleaning the cleaning roll  101 , a feeding roll  105  for feeding the sheet member  104  wound thereon, a take-up roll  106  taking up the sheet member  104  passed between the back-up roll  103  and the cleaning roll  101 , a housing receiving these back-up roll, the sheet member, the feeding roll and the take-up roll, and an actuator  108  connected to the housing for driving the latter for reciprocal movement in a direction shown by an arrow  202  and thus for movement toward and away from the cleaning roll  101 .  
         [0047]    During printing operation of the image forming apparatus, the housing  107  is located away from the cleaning roll  101  by the actuator  108 . At this condition, the intermediate transfer body  62  is driven to rotate by the photoconductor  1 . Furthermore, the cleaning roll  101  in pressure contact with the intermediate transfer body  62  is also driven to rotate.  
         [0048]    By repeating printing operation, stain by the ink or impurity should be deposited on the surface of the cleaning roll  101  which cleans the intermediate transfer roll  62 . When only ink is deposited on the surface of the cleaning roll  101 , since binding force between ink is greater than that between the ink and the intermediate transfer roll  62 , good cleaning performance can be maintained. However, in practice, impurity other than ink, substances contained in the ink component interfering transfer performance, paper dust of the printing paper and so forth may deposit on the surface of the cleaning roll  101  to degrade cleaning performance. On the other hand, even if the only ink deposit on the surface of the cleaning roll  101 , amount of ink depositing on the surface if the cleaning roll cannot be uniform in the axial direction of the roll in certain image to form unevenness on the surface of the cleaning roll  101  to cause contact failure between the cleaning roll  101  and the intermediate transfer body  62  to cause cleaning failure.  
         [0049]    Therefore, upon completion of printing of a predetermined number of sheets, cleaning of the cleaning roll  101  is performed by means of the sheet member  104 . Namely, upon completion of printing of the predetermined number of sheets, the actuator  108  is activated to move the back-up roll  103  together with the housing  107  frontwardly to contact the sheet member  107  onto the cleaning roll  101  under pressure. By rotating the intermediate transfer body  62  at this condition, the cleaning roll  101  is driven to rotate in the direction of allow  201  to cause a relative speed between the cleaning roll  101  and the sheet member  104  to establish slip contacting state. By this, the substance on the cleaning roll  101  is removed and transferred to the sheet member  104 .  
         [0050]    After performing cleaning for a given period, the back-up roll  103  is moved away from the cleaning roll  101  together with the housing  107  by means of the actuator  108 . Also, the take-up roll  106  is driven to rotate for a predetermined angle to take up the sheet member  104  in the direction of arrow  203 . With such construction, cleaning of the cleaning roll  101  at the next cleaning operation can be performed with a clean surface of the sheet member  104 .  
         [0051]    When cleaning operation is performing during printing operation, friction load and load fluctuation due to slip contact between the sheet member  104  and the cleaning roll  101  becomes significant to cause fluctuation in speed (irregularity) upon image formation. Therefore, the cleaning of the cleaning roll  101  by means of the sheet member  104  is regularly performed at an interval between printing scan. However, if the friction load and load fluctuation can be made reasonably small, the cleaning by the sheet member  104  may be constantly performed even during printing.  
         [0052]    In the shown embodiment, as a material of the intermediate transfer body  62 , a silicon rubber having hardness in a range of 50 to 75 (JIS-A) is used. As a material of the cleaning roll  104 , a material having greater binding force than the silicon rubber forming the intermediate transfer member  62  is required. Therefore, it is desirable to form the cleaning roll  101  with a material, such as a another silicon rubber or the like having greater binding force with the ink than that between the silicon rubber of the intermediate transfer roller  62 . On the other hand, when substance contained in the ink or ink component and interfering or degrading transfer performance is present between the intermediate transfer body  62  and the cleaning roll  101  or between the intermediate transfer body  62  and the ink on the cleaning roll  101 , and if the substance has a property to be easily transferred to one having higher or lower temperature, greater binding force than that of the intermediate transfer roll  62  can be provided for the cleaning roll  101  by differentiating the surface temperature of the cleaning roll  101  from that of the intermediate transfer roll  62  with incorporating heat source, such as halogen lamp or the like within the cleaning roll  101 .  
         [0053]    A material of the sheet member  104  for performing cleaning of the cleaning roll  101  may be wettable material, such as a wrapping film, a non-woven fabric of fiber or resin, felt and the like.  
         [0054]    [0054]FIG. 4 shows a modification of the preferred embodiment of the cleaning mechanism according to the present invention. In the former embodiment, cleaning is performed simply by slip contact between the cleaning roll  101  and the sheet member  104 . In contrast to this, in the shown modification in FIG. 4, a liquid supply means  109  is arranged within the housing  107  for supplying a lubricant and cleaning aiding agent for reduction of friction load in the slip contacting portion between the cleaning roll  101  and the sheet member  104  and enhancing cleaning performance. By automatically supplying a liquid to the sheet member  104  from the liquid supply means  109  at the feeding roll  105  or between the feeding roll  105  and the back-up roll  103 , more stable cleaning performance can be obtained. As a liquid to be supplied from the liquid supply means  109 , water, isopropyl alcohol, an insulative solvent or the like.  
         [0055]    [0055]FIG. 5 shows another modification of the preferred embodiment of the cleaning mechanism according to the present invention. In FIG. 5, the sheet member  104  is formed into endless form for permitting repeated use. In this case, after cleaning the sheet member  104 , residual substance on the sheet member  104  (e.g. residual ink or the like) may be washed out in certain extent by the liquid supplied from the liquid supply means  107  to certainly maintain satisfactory cleaning performance.  
         [0056]    As set forth above, the cleaning mechanism of the image forming apparatus according to the present invention constantly performs cleaning of the intermediate transfer roll by means of the cleaning roll, and regularly perform cleaning of the cleaning roll by means of the sheet member to certainly provide stable cleaning performance. The surface conditions of the intermediate transfer roll and the photoconductor which is collected the ink or the like by the intermediate transfer roll can be maintained clean to attain stable image formation.  
         [0057]    Although the present invention has been illustrated and described with respect to exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omission and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiment set out above but to include all possible embodiments which can be embodied within a scope encompassed and equivalent thereof with respect to the feature set out in the appended claims.