Abstract:
An image forming apparatus includes an image transfer unit that transfers a reversed image onto an image bearing member as a toner image, a secondary transfer roller that transfers the toner image onto a recording medium, a contact and separation unit that brings the secondary transfer roller into contact with and separates the secondary transfer roller from the image bearing member, a secondary-transfer-roller housing unit that houses the secondary transfer roller, a lubricant applying brush that applies a lubricant thereto, a lubricant-applying-brush housing unit that houses the lubricant applying brush and is configured to be movable along a groove, and an lifting and lowering member that lifts and lowers the lubricant-applying-brush housing unit, wherein the secondary transfer roller and the lubricant applying brush come into contact with and separate from each other in response to a contact and separation operation of the secondary transfer roller and the image bearing member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of U.S. Provisional Applications No. 60/940,254, filed May 25, 2007; and No. 60/969,587, filed Aug. 31, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus including, in a secondary transfer unit having a mechanism for bringing a secondary transfer roller into contact with and separating the secondary transfer roller from an image bearing member, a mechanism for further bringing the secondary transfer roller into contact with and separating the secondary transfer roller from a fur brush and an image forming method therefor. 
     2. Description of the Related Art 
     A transfer device includes a contact and separation mechanism for bringing a secondary transfer roller into contact with an image bearing member when the transfer device transfers a toner image formed on the image bearing member onto a sheet and separating the secondary transfer roller from the image bearing member when the transfer device does not transfer the toner image onto the sheet. 
     There is known a contact and separation driving device for a secondary transfer roller in which, in a secondary transfer unit having a mechanism for bringing a secondary transfer roller into contact with and separating the secondary transfer roller from an image bearing member, the number of components of a mechanism unit configuring the mechanism for performing a contact and separation operation is not increased and a device such as an electromagnetic clutch that requires electric control is not used (JP-A-2007-264546). 
     BRIEF SUMMARY OF THE INVENTION 
     An image forming apparatus according to a first aspect of the present invention includes an image transfer unit that transfers a reversed image based on a scanned original image onto an image bearing member as a toner image, a secondary transfer roller that comes into contact with the image bearing member and transfers the toner image onto a recording medium, a contact and separation unit that brings the secondary transfer roller into contact with and separates the secondary transfer roller from the image bearing member, a secondary-transfer-roller housing unit that houses the secondary transfer roller, a lubricant applying brush that comes into contact with the secondary transfer roller and applies a lubricant thereto, a lubricant-applying-brush housing unit that houses the lubricant applying brush and is configured to be movable along a groove provided in the secondary-transfer-roller housing unit, and an lifting and lowering member that is provided in another member not associated with the secondary-transfer-roller housing unit and lifts and lowers the lubricant-applying-brush housing unit, wherein the secondary transfer roller and the lubricant applying brush come into contact with and separate from each other in response to a contact and separation operation of the secondary transfer roller and the image bearing member. 
     An image forming method according to a second aspect of the present invention is an image forming method for an image forming apparatus including an image transfer unit configured to transfer a reversed image based on a scanned original image onto an image bearing member as a toner image, a secondary transfer roller that comes into contact with the image bearing member and transfers the toner image onto a recording medium, and a contact and separation unit configured to bring the secondary transfer roller into contact with and separate the secondary transfer roller from the image bearing member, comprising: contacting the secondary transfer roller and a lubricant applying brush with and separating from each other in response to a contact and separation operation of the secondary transfer roller and the image bearing member, wherein the image forming apparatus includes a secondary-transfer-roller housing unit configured to house the secondary transfer roller, the lubricant applying brush that comes into contact with the secondary transfer roller and applies a lubricant thereto, a lubricant-applying-brush housing unit configured to house the lubricant applying brush and to be movable along a groove provided in the secondary-transfer-roller housing unit, and an lifting and lowering member that is provided in another member not associated with the secondary-transfer-roller housing unit and lifts and lowers the lubricant-applying-brush housing unit. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram of an image forming unit of an image forming apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing the structure of a secondary transfer unit; 
         FIG. 3  is a side view of the secondary transfer unit; 
         FIG. 4  is a diagram showing ends of a secondary transfer roller and a fur brush unit in a state in which a pre-transfer guide is removed; 
         FIG. 5  is a diagram for explaining a contact and separation operation of the secondary transfer roller; 
         FIG. 6  is a diagram showing the secondary transfer roller, the fur brush unit, and the like in a state in which the pre-transfer guide is removed; 
         FIG. 7  is a diagram showing a state in which the secondary transfer roller is separate from a transfer belt; 
         FIG. 8  is a diagram showing a state in which the secondary transfer roller is in contact with the transfer belt; 
         FIG. 9  is a diagram showing the secondary transfer roller, the fur brush unit, and the like in a state in which a part of the pre-transfer guide is not shown; 
         FIG. 10  is a perspective view showing a lifting and lowering member; 
         FIG. 11  is a diagram showing a state in which the lifting and lowering member is attached to the pre-transfer guide; 
         FIG. 12  is a diagram showing a state in which the secondary transfer roller is separate from the transfer belt; and 
         FIG. 13  is a diagram showing a state in which the secondary transfer roller is in contact with the transfer belt. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       FIG. 1  is a schematic diagram of an image forming unit of an image forming apparatus according to a first embodiment of the present invention.  FIG. 2  is a perspective view showing the structure of a secondary transfer unit.  FIG. 3  is a side view of the secondary transfer unit. 
     As shown in  FIG. 1 , an image forming unit  10  includes a laser unit  12 , developing devices  14 , a transfer belt (an image bearing member)  16 , a counter roller  17 , a sheet conveying path  18 , registration rollers  20 , a secondary transfer roller  22 , a fur brush  40 , a conveyance guide  24 , and a fixing device (a fixing unit)  26 . 
     The laser unit  12  irradiates a laser beam optically modulated according to an image signal of an original scanned by a not-shown scanner unit or an image signal inputted from an external apparatus and forms electrostatic latent images on the developing devices  14 . The developing devices  14  reversely develop the electrostatic latent images and transfer toner images onto the transfer belt  16 . 
     The sheet conveying path  18  is a conveying path for a sheet fed from a not-shown paper feeding unit. The registration rollers  20  correct inclination of the sheet immediately before an image is transferred thereon. The secondary transfer roller  22  is arranged downstream of the registration rollers  20  and opposed to the counter roller  17  to be capable of coming into contact with the transfer belt  16 . When the sheet passes between the transfer belt  16  and the secondary transfer roller  22 , the toner images are collectively transferred onto the sheet. The conveyance guide  24  guides the sheet, which is conveyed out from the secondary transfer roller  22 , to the fixing device  26 . The fixing device  26  fixes an image transferred by the secondary transfer roller  22  on the sheet. 
     As shown in  FIGS. 2 and 3 , the fur brush  40  and a lubricant case  41  that comes into press contact with the fur brush  40  and supplies a lubricant (zinc stearate) thereto are provided below the secondary transfer roller  22 . In the following explanation, a unit configured by integrating the fur brush  40  and the lubricant case  41  is referred to as fur brush unit  42 . A cleaning blade  43  that scrapes off a residual toner adhering to the secondary transfer roller  22  is in contact with the secondary transfer roller  22 . A pre-transfer guide  44  is fixedly provided between the fur brush unit  42  and the sheet conveying path  18 . 
       FIG. 4  is a diagram showing ends of the secondary transfer roller  22  and the fur brush unit  42  in a state in which the pre-transfer guide  44  is removed. 
     A bearing of the secondary transfer roller  22  is held by a secondary-transfer-roller holding case  45 . The secondary-transfer-roller holding case  45  has a guide groove  46  for guiding the fur brush unit  42  up and down. In the fur brush unit  42 , two shafts are provided on each of a front side and a rear side of the secondary transfer unit. The two shafts provided on each of the front side and the rear side move up and down along the guide groove  46 , whereby the fur brush unit  42  is capable of moving up and down. 
       FIG. 5  is a diagram for explaining a contact and separation operation of the secondary transfer roller  22 . 
     As shown in  FIG. 5 , both ends of the secondary transfer roller  22  are rotatably supported by a pair of lever-like members  28  serving as a contact and separation mechanism. In other words, the secondary transfer roller  22  is supported to be movable between a first position and a second position. The respective lever-like members  28  are capable of swinging with these substantially upper positions in a longitudinal direction as fulcrums. The respective lever-like members  28  are always urged by an elastic force of not-shown springs in a direction of bringing the secondary transfer roller  22  into contact with the transfer belt  16 . 
     Pushers  32  are disposed near lower ends  28   a  of the lever-like members  28 , respectively. Distal ends  32   a  of the pushers  32  press the lower ends  28   a  of the lever-like members  28 , whereby the lever-like members  28  swing against the elastic force of the springs. Consequently, the secondary transfer roller  22  can be separated from the transfer belt  16 . On the other hand, the distal ends  32   a  of the pushers  32  separate from the lever-like members  28 , whereby the lever-like members  28  swing with the elastic force of the springs to positions for bringing the secondary transfer roller  22  into contact with the transfer belt  16 . 
       FIG. 6  is a diagram showing the secondary transfer roller  22 , the fur brush unit  42 , and the like in a state in which the pre-transfer guide  44  is removed. 
     The entire secondary transfer unit is supported by a secondary-transfer-unit holding frame  47 . A fulcrum  48  is provided in an upper part of the secondary-transfer-unit holding frame  47 . The fulcrum  48  is connected to the secondary-transfer-roller holding case  45 . Therefore, the secondary-transfer-roller holding case  45  can rotate around the fulcrum  48 . A not-shown sheet metal is provided in the secondary-transfer-roller holding case  45 . As described above, the pushers  32  push the sheet metal, whereby the secondary-transfer-roller holding case  45  swings between the first position and the second position with the fulcrum  48  as a rotation axis. 
     A rack  49  is provided below the fur brush unit  42 . Two compression springs  50   a  and  50   b  (compression springs  50 ) are attached between the rack  49  and the fur brush unit  42 . The compression springs  50   a  and  50   b  press the fur brush unit  42 . 
     Operations of the fur brush unit  42  during the contact and separation operation are explained. 
       FIG. 7  is a diagram showing a state in which the secondary transfer roller  22  is separate from the transfer belt  16 . 
     During the separation, the fur brush unit  42  is pushed up by the compression springs  50  provided in the rack  49  and comes into contact with the secondary transfer roller  22 . The fur brush unit  42  moves up and down along the guide groove  46 . Therefore, a position where an upper shaft  52   a  comes into contact with an upper end of the guide groove  46  is an upper limit position of the operation. 
     As shown in  FIG. 7 , a member of a wedge shape in section (hereinafter referred to as an lifting and lowering member)  54  is provided in the pre-transfer guide  44 . During the separation, the lifting and lowering member  54  and the fur brush unit  42  are in a non-contact state. 
     During transition from a separation state shown in  FIG. 7  to a contact state, the secondary transfer roller  22 , the fur brush unit  42 , and the rack  49  integrally move in the left direction. Then, a distal end of a wedge of the lifting and lowering member  54  approaches a lower shaft  52   b . A cylindrical member  53  made of synthetic resin such as plastic is arranged on an outer periphery of the lower shaft  52   b . The cylindrical member  53  is configured to freely rotate around the lower shaft  52   b . When the transition to the contact state progresses, the cylindrical member  53  and a slope of the lifting and lowering member  54  come into contact with each other. 
       FIG. 8  is a diagram showing a state in which the secondary transfer roller  22  is in contact with the transfer belt  16 . 
     As a position of contact of the cylindrical member  53  and the slope of the lifting and lowering member  54  moves, the fur brush unit  42  is pushed downward. Therefore, at a point when this contact operation is completed, the fur brush unit  42  and the secondary transfer roller  22  are separated from each other. 
     According to the progress of the contact operation, the cylindrical member  53  changes the position of contact with the lifting and lowering member  54  while rotating around the lower shaft  52   b . Therefore, the fur brush unit  42  smoothly moves downward without being affected by an unnatural force. The lower shaft  52   b  and the lifting and lowering member  54  do not come into direct contact with each other. A material (synthetic resin) of the cylindrical member  53  is softer than a material (metal) of the lifting and lowering member  54  and the lower shaft  52   b . Therefore, there is little abrasion between the lower shaft  52   b  and the lifting and lowering member  54  and it is possible to consume only the cylindrical member  53 . 
     During transition from the contact state shown in  FIG. 8  to the separation state shown in  FIG. 7 , the wedge of the lifting and lowering member  54  moves away from the lower shaft  52   b  in a manner opposite to the above explanation. Therefore, the fur brush unit  42  is pushed upward by the compression springs  50   a  and  50   b  (compression springs  50 ). At a point when the separation operation is completed, the fur brush unit  42  and the secondary transfer roller  22  come into contact with each other. 
     In the first embodiment explained above, the fur brush  40  separates from the secondary transfer roller  22  when the secondary transfer roller  22  comes into contact with the transfer belt  16 . The fur brush  40  comes into contact with the secondary transfer roller  22  when the secondary transfer roller  22  separates from the transfer belt  16 . As a result, compared with the system in the past in which the fur brush  40  is always in contact with the secondary transfer roller  22 , it is possible to prevent the lubricant from being excessively applied to the secondary transfer roller  22 . 
     Second Embodiment 
     In a second embodiment of the present invention, a contact and separation operation of the secondary transfer roller  22  and the fur brush  40  and a mechanism therefor are different from those in the first embodiment. Therefore, components identical with those in the first embodiment are denoted by the same reference numerals and signs and explanation of details of the components is omitted. 
       FIG. 9  is a diagram showing the secondary transfer roller  22 , the fur brush unit  42 , and the like in a state in which a part of the pre-transfer guide  44  is not shown. 
     The entire secondary transfer unit is supported by the secondary-transfer-unit holding frame  47 . The fulcrum  48  is provided in the upper part of the secondary-transfer-unit holding frame  47 . The fulcrum  48  is connected to the secondary-transfer-roller holding case  45 . Therefore, the secondary-transfer-roller holding case  45  can rotate around the fulcrum  48 . The not-shown sheet metal is provided in the secondary-transfer-roller holding case  45 . As described above, the pushers  32  push the sheet metal, whereby the secondary-transfer-roller holding case  45  swings between the first position and the second position with the fulcrum  48  as a rotation axis. 
     Leaf spring members (hereinafter referred to as lifting and lowering members)  56   a  and  56   b  (lifting and lowering members  56 ) are provided on a front side and a rear side below the fur brush unit  42 . The lifting and lowering members  56   a  and  56   b  are attached to the pre-transfer guide  44 . When the secondary transfer roller  22  comes into contact with the transfer belt  16 , the lifting and lowering members  56   a  and  56   b  press the fur brush unit  42 . 
       FIG. 10  is a perspective view showing one of the lifting and lowering members  56 .  FIG. 11  is a diagram showing a state in which the lifting and lowering member  56  is attached to the pre-transfer guide  44 . 
     The lifting and lowering member  56  includes an attaching section  57 , an intermediate section  58 , and a distal end section  59 . A hole for inserting a member for connecting the lifting and lowering member  56  to the pre-transfer guide  44 , for example, a bolt is provided in the attaching section  57 . The intermediate section  58  is folded in two stages and has two areas. An area close to the distal end section  59  of the intermediate section  58  and the fur brush unit  42  come into contact with each other. The intermediate section  58  is folded in two stages in order to effectively show a function of the leaf spring by setting a contact angle of the intermediate section  58  and the fur brush unit  42  to a predetermined angle. Therefore, the number of folding stages is not limited to two and may be three or more. In other words, two or more areas may be formed in the intermediate section  58 . 
     A boss  60  as a projecting section is formed in the distal end section  59 . When the fur brush unit  42  comes into contact with the intermediate section  58 , the boss  60  and the pre-transfer guide  44  come into contact with each other, whereby the lifting and lowering member  56  functions as the leaf spring and presses the fur brush unit  42  upward. A shape of the boss  60  is a spherical surface such that the boss  60  and the pre-transfer guide  44  come into contact with each other at one point. However, since the contact of the boss  60  and the pre-transfer guide  44  only has to be a point contact, the shape of the boss  60  is not limited to the spherical surface and only has to be a shape of a convex curved surface. 
     Operations of the fur brush unit  42  during the contact and separation operation are explained. 
       FIG. 12  is a diagram showing a state in which the secondary transfer roller  22  is separate from the transfer belt  16 . 
     During the separation, the fur brush unit  42  is in a non-contact state with the lifting and lowering member  56 . During transition from the separation state shown in  FIG. 12  to the contact state, the secondary transfer roller  22  and the fur brush unit  42  integrally moves in the left direction. When the transition to the contact state progresses, a lower part of the fur brush unit  42  approaches the intermediate section  58  and, before long, the lower part of the fur brush unit  42  and the intermediate section  58  come into contact with each other. 
     Then, the lifting and lowering member  56  is pressed and the boss  60  and the pre-transfer guide  44  come into contact with each other, whereby the lifting and lowering member  56  functions as the leaf spring and presses the fur brush unit  42  upward. As a result, the fur brush unit  42  is pushed up and comes into contact with the secondary transfer roller  22 . 
     In this way, the lifting and lowering member  56  approaches to come into contact with the pre-transfer guide  44  while bending during the contact of the secondary transfer roller  22 . However, after the boss  60  and the pre-transfer guide  44  come into contact with each other, the lifting and lowering member  56  receives a reaction from the pre-transfer guide  44  and deformation of the leaf spring is controlled. Since the reaction is received from the pre-transfer guide  44 , a stress is prevented from being concentratedly exerted on the leaf spring. 
       FIG. 13  is a diagram showing a state in which the secondary transfer roller  22  is in contact with the transfer belt  16 . 
     As a position of contact of the fur brush unit  42  and the intermediate section  58  of the lifting and lowering member  56  moves, the fur brush unit  42  is pushed upward. At a point when this contact operation is completed, the fur brush unit  42  and the secondary transfer roller  22  are in contact with each other. 
     During transition from the contact state shown in  FIG. 13  to the separation state shown in  FIG. 12 , the position of contact of the fur brush unit  42  and the intermediate section  58  of the lifting and lowering member  56  changes in a direction opposite to the direction in the above explanation. Therefore, a pressing force by the lifting and lowering member  56  gradually decreases. During the separation, the fur brush unit  42  is separate from the lifting and lowering member  56 . 
     In the second embodiment explained above, the fur brush  40  comes into contact with the secondary transfer roller  22  when the secondary transfer roller  22  comes into contact with the transfer belt  16 . The fur brush  40  separates from the secondary transfer roller  22  when the secondary transfer roller  22  separates from the transfer belt  16 . 
     In the related art in which the fur brush  40  is always in contact with the secondary transfer roller  22 , problems described below are pointed out. When recording paper causes jamming or when the recording paper is not supplied because of paper empty or the like, the secondary transfer roller  22  continues to rotate with a transferred toner kept applied thereto. In such a case, it is possible to clean the secondary transfer roller  22  to a certain degree by the cleaning blade  43 . However, when the toner remains, the toner soils the fur brush  40  that is always in contact with the secondary transfer roller  22 . In the second embodiment, such soiling of the fur brush  40  can be prevented. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.