Abstract:
An image forming apparatus includes an image forming unit configured to form a toner image on an image bearing member, an endless belt configured to transfer and carry the toner image thereon, a transfer unit configured to transfer the toner image carried by the endless belt onto a recording sheet, a sensing unit configured to sense the toner image transferred onto the endless belt, a blocking unit mounted between the sensing unit and the endless belt and configured to block the sensing unit, a contact and separation unit configured to cause the transfer unit to reciprocally contact and separate from the endless belt. With this configuration, the blocking unit and the contact and separation unit are configured to be driven by an identical drive source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2007-169088, filed on Jun. 27, 2007 in the Japan Patent Office, the contents and disclosure of which are hereby incorporated by reference herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary embodiments of the present invention generally relate to an image forming apparatus that can effectively use a drive unit for image forming. 
     2. Discussion of the Related Art 
     A four-drum-type image forming apparatus, also called a tandem-type electrophotographic image forming apparatus, is expected to meet recent demands for an increase in print speed and image quality of color image forming apparatuses and is increasing its share of the market therefor. 
     In one known tandem-type electrophotographic image forming apparatus, four image forming units form single color toner images different from each other on respective surfaces of image bearing members provided therein, and the single color toner images are sequentially transferred either directly onto a transfer sheet carried by a sheet conveyor belt or onto an image transfer belt before the transfer sheet so as to form a composite, full-color toner image fast. In an effort to effectively increase both the print speed and the image quality further, attention has focused on an intermediate transfer unit as a transfer unit of the tandem-type electrophotographic image forming apparatus. 
     However, a related problem is that the tandem-type electrophotographic image forming apparatus can cause improper composition of the single color images resulting in color shift in a composite image, thereby degrading the quality of the composite image. 
     One approach to solve this problem is to provide a so-called “color shift correction” that can eliminate the drawback by forming toner pattern images on a transfer belt, causing an optical sensor to detect the toner pattern images, and adjusting a timing of optical writing based on the information detected by the optical sensor. Further, a shutter controlled by a solenoid, for example, is provided to cover the optical sensor unit and open only when detecting toner pattern images, so as to protect the optical sensor unit from contamination due to toner particles scattered inside the image forming apparatus, which degrades detection accuracy of the optical sensor. 
     However, it is likely that toner pattern images formed on the image transfer belt during such color shift correction adhere to and contaminate a secondary transfer roller that is held in contact with the image transfer belt used in the intermediate transfer unit, and therefore a back side of the transfer sheet is also contaminated. 
     To prevent such contamination of the back side of the transfer sheet, another known image forming apparatus further employs a mechanism to switch a position of the secondary transfer roller, i.e., to periodically contact and separate from the image transfer belt, so that the secondary transfer roller can separate from the image transfer belt during the color shift correction. Further, in such image forming apparatus the shutter is provided to prevent the detection accuracy of the optical sensor from deteriorating, a fixed motor is used as a drive source, a solenoid is provided in a drive array and disposed near the shutter, and a swing mechanism is also provided in the drive array and disposed near the fixing motor. By controlling forward and reverse rotations of the fixed motor, this configuration opens and closes the shutter and controls the contact and separation of the secondary transfer roller. 
     The above-described configuration, however, requires additional mechatronics parts and components such as solenoid and brush motor, which can cause an increase in cost, power consumption, and machine size. Moreover, the additional mechatronics parts and components can adversely affect the reliability of the image forming apparatus. 
     Therefore, there is still a need for an image forming apparatus that can effectively operate (open and close) the shutter and control the movement of the secondary transfer roller without adding mechatronics parts and components and increasing machine size, costs, and power consumption. 
     SUMMARY OF THE INVENTION 
     Exemplary aspects of the present invention have been made in view of the above-described circumstances. 
     Exemplary aspects of the present invention provide an image forming apparatus that can effectively operate (open and close) a shutter and control the movement of a secondary transfer roller without adding mechatronics parts and components and increasing machine size, costs, and power consumption. 
     In one exemplary embodiment, an image forming apparatus includes an image forming unit configured to form a toner image on an image bearing member, an endless belt configured to transfer and carry the toner image thereon, a transfer unit configured to transfer the toner image carried by the endless belt onto a recording sheet, a sensing unit configured to sense the toner image transferred onto the endless belt, a blocking unit mounted between the sensing unit and the endless belt and configured to block the sensing unit, and a contact and separation unit configured to cause the transfer unit to reciprocally contact and separate from the endless belt, so that the blocking unit and the contact and separation unit are configured to be driven by an identical drive source. 
     The blocking unit may close in synchronization with separation of the transfer unit from the endless belt by the contact and separation unit. 
     The blocking unit and the contact and separation unit may include a common member to synchronize operations performed by the blocking unit and the contact and separation unit. 
     The above-described image forming apparatus may further include at least one detector configured to detect opening and closing of the blocking unit and contact and separation of the transfer unit from the endless belt by the contact and separation unit. 
     The transfer unit disposed in the vicinity of the blocking unit and the contact and separation unit may be driven by the drive source for driving the blocking unit and the contact and separation unit. 
     The above-described image forming apparatus may further include a registration member configured to convey a recording medium according to a given timing. The registration member may be driven by the drive source driving the blocking unit and the contact and separation unit. 
     The above-described image forming apparatus may further include a drive blocking member provided to at least one of the drive source and the contact and separation unit. 
     The drive blocking member may include a one-way clutch. 
     The above-described image forming apparatus may further include multiple drive blocking members provided to the drive source and a drive array of a member driven by the drive source. 
     The multiple drive blocking members may include a one-way clutch. 
     The blocking unit may be in the open condition and the contact and separation unit may separate the transfer unit from the endless belt only when a toner image is being transferred on the endless belt and the sensing unit senses information of the toner image, and the blocking unit may remain closed and the transfer unit remaining contacted against the endless belt by the contact and separation unit at all other times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic cross-sectional view of a schematic configuration of a color printer according to an exemplary embodiment of the present invention; 
         FIG. 2A  is an exploded perspective view of a secondary transfer roller provided in the color printer of  FIG. 1 ; 
         FIG. 2B  is an exploded perspective view of a bracket including the secondary transfer roller of  FIG. 2A ; 
         FIG. 2C  is a side view of the bracket of  FIG. 2B , viewed from a longitudinal direction of the bracket; 
         FIG. 3A  is a perspective view of sensors provided in the color printer of  FIG. 1 ; 
         FIG. 3B  is a perspective view of a shutter provided over the sensors of  FIG. 3A , which is in a close state covering the shutters; 
         FIG. 3C  is a perspective view of the shutter in an open state showing the sensors; 
         FIG. 4A  is a perspective view of the bracket of  FIG. 2B  and a position switching mechanism for the secondary transfer roller of  FIG. 2A ; 
         FIG. 4B  is a perspective view for explaining operations of the position switching mechanism of  FIG. 4A ; 
         FIG. 5A  is a plan view for explaining an operational relation of the shutter of  FIGS. 3B and 3C  and a cam pressed contact to the shutter; 
         FIG. 5B  is a perspective view of the cam of  FIG. 5A ; 
         FIG. 6A  is a plan view for explaining a drive transmission of a motor in a forward operation; and 
         FIG. 6B  is a plan view for explaining a drive transmission of the motor in a reverse operation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of the present invention are described. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of the present invention are described. 
     Referring to  FIG. 1 , a schematic configuration of a color laser printer or laser printer  100  according to an exemplary embodiment of the present invention is described. 
       FIG. 1  is a schematic cross-sectional view of the laser printer  100  employing a tandem-electrophotographic method and an intermediate transfer method. 
     The laser printer  100  of  FIG. 1  includes four toner image forming units  1 Y,  1 M,  1 C, and  1 K, an intermediate transfer unit  600 . 
     The four toner image forming units  1 Y,  1 M,  1 C, and  1 K form respective toner images of different colors that are yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, the suffixes “Y”, “M”, “C”, and “K” indicate that a member having a specific suffix includes a corresponding one of respective colors of yellow, magenta, cyan, and black. 
     The four toner image forming units  1 Y,  1 M,  1 C, and  1 K include four photoconductor drums  11 Y,  11 M,  11 C, and  11 K, respectively, and respective developing units, not shown. 
     The intermediate transfer unit  600  is disposed above the toner image forming units  1 Y,  1 M,  1 C, and  1 K, and includes an intermediate transfer belt  6 . The intermediate transfer belt  6  forms an endless loop as an endless belt, and transfers the toner images formed on the photoconductor drums  11 Y,  11 M,  11 C, and  11 K by the toner image forming units  1 Y,  1 M,  1 C, and  1 K, respectively, onto the intermediate transfer belt  6 . When transferred, the toner images are sequentially overlaid onto a surface of the intermediate transfer belt  6  to form a composite, full-color toner image. The intermediate transfer belt  6  is supported and spanned around by a drive roller  6   a , and drive rollers  6   c  and  6   d , and sandwiched by the drive roller  6   a  and a secondary transfer roller  6   b  disposed facing the drive roller  6   a.    
     The laser printer  100  according to an exemplary embodiment of the present invention further includes an optical writing unit  2 , sheet feeding cassettes  3  and  4 , a pair of registration rollers  5 , the intermediate transfer belt  6 , a fixing unit  7 , a pair of sheet discharging rollers  8 , and a manual sheet feeding tray MF. 
     The optical writing unit  2  includes a light source, a polygon mirror, an f-theta lens, reflection mirrors, and so forth, and scans and emits laser light beams to respective surfaces of the photoconductor drums  11 Y,  11 M,  11 C, and  11 K based on image data, to form respective electrostatic latent images on the surfaces of the photoconductor drums  11 Y,  11 M,  11 C, and  11 K. 
     Arrows shown in  FIG. 1  indicate a sheet conveying path of a recording sheet  10  accommodated in the sheet feeding cassettes  3  and  4 , and the manual sheet feeding tray MF. The recording sheet  10  is fed by a feed roller  71  from any one of the sheet feeding cassettes  3  and  4 , and the manual sheet feeding tray MF, guided by a conveyance guide, not shown, and conveyed by a pair of conveyance rollers  72  to the pair of registration rollers  5 . At the pair of registration rollers  5 , the recording sheet  10  is stopped for a given period while forming a bow shape between the pair of conveyance rollers  72  and the pair of registration rollers  5 . After the given period has elapsed, the recording sheet  10  is conveyed by the pair of registration rollers  5  toward a nip contact formed between the drive roller  6   a  and the secondary transfer roller  6   b . Affected by a transfer electrical field of the secondary transfer roller  6   b  and a nip pressure exerted to the nip contact between the drive roller  6   a  and the secondary transfer roller  6   b , the composite toner image formed on the surface of the intermediate transfer belt  6  is transferred onto a surface of the recording sheet  10 . 
     The recording sheet  10  having the full-color toner image thereon is then conveyed to the fixing unit  7  to fix the full-color toner image to the surface of the recording sheet  10 , and conveyed via the pair of sheet discharging rollers  8  to an outside of the color laser printer  100 . By performing a series of the above-described operations, a copy or print of full-color image can be produced. 
     The color laser printer  100  further includes image sensors  12  and a shutter plate  13 . Details of the image sensors  12  and the shutter plate  13  will be described later. 
     Next, a detailed description is given of main parts and components of the laser printer  100  according to an exemplary embodiment of the present invention. 
       FIGS. 2A ,  2 B, and  2 C show exploded perspective views of details of the intermediate transfer unit  600 . 
     As previously described, the intermediate transfer belt  6  is extended by three supporting rollers: the drive roller  6   a , the driven roller  6   c  disposed upstream from the drive roller  6   a , and the driven roller  6   d  disposed downstream from the drive roller  6   a.    
     The secondary transfer roller  6   b  of  FIG. 2A  includes a shaft, both ends of which are supported by a guide bracket  6   e  as shown in  FIG. 2B . The guide bracket  6   e  also serves as a sheet conveyance guide plate, and can open and close about a fulcrum  6   f  to remove jammed papers during paper jam. When the guide bracket  6   e  is closed, a pressing member, not shown, presses the secondary transfer roller  6   b  in a direction indicated by an arrow in  FIG. 2C  to position the secondary transfer roller  6   b.    
     In the vicinity of the driven roller  6   c , the image sensors  12  to read and detect toner pattern images formed on the intermediate transfer belt  6  are disposed. As shown in  FIG. 3A , the image sensors  12  are integrally mounted on a bracket, not shown, at given intervals. The bracket with the image sensors  12  is positioned at front and rear side plates, not shown, of a main body of the laser printer  100 . 
     Between the image sensors  12  and the driven roller  6   c , the shutter plate  13  is disposed. As shown in  FIGS. 3B and 3C , the shutter plate  13  is disposed slidably in a longitudinal axis of the driven roller  6   c  along a guide rail, not shown. 
     Further, as shown in  FIGS. 4A and 4B , a lever  14  and a cam  15  are provided in the vicinity of the guide bracket  6   e . The lever  14  is engaged with both ends of the secondary transfer roller  6   b.    
     The cam  15  presses contact one end of the lever  14  to move the secondary transfer roller  6   b  in synchronization with a movement of the cam  15  in directions indicated by a bi-directional arrow shown in  FIG. 3B . For example, when an apex of the cam  15  having a longest distance on a flat part (see  FIG. 5B ) from a center of the cam  15  comes to contact with the lever  14 , the secondary transfer roller  6   b  is pressed to a contact position to contact with the intermediate transfer belt  6 . When the lever  14  is in contact with a part other than the apex of the cam  15 , the secondary transfer roller  6   b  separates from the intermediate transfer belt  6  to a non-contact position. 
     Thus, the lever  14  and the cam  15  interact with each other to serve as a contact and separation unit. 
     Next, a description is given of operations of the shutter plate  13 , in reference to  FIGS. 5A and 5B . 
     As described above, the shutter plate  13  moves in the longitudinal axis of the driven roller  6   c . As shown in  FIG. 5B , the cam  15  includes a slanted part on the flat part. The shutter plate  13  is pressed by a pressing member to be held in contact with the slanted part of the cam  15  so as to move the shutter plate  13  reciprocally (for push and retreat) while the cam  15  rotates. As shown in  FIG. 5B , a tip of the slanted part of the cam  15 , which is indicated by “b”, is arranged apart from the apex of the cam  15 , which is indicated by “A”, by 180 degrees, and therefore a timing that the shutter plate  13  moves to an open position to expose the image sensors  12  is equal to a timing that the secondary transfer roller  6   b  separates from the intermediate transfer belt  6 . 
     Specifically, when the cam  15  comes to a position indicated by A/a shown in  FIG. 5B , the shutter plate  13  moves to a close position and the secondary transfer roller  6   b  comes to the contact position to contact the intermediate transfer belt  6 . By contrast, when the cam  15  comes to a position indicated by B/b shown in  FIG. 5B , the shutter plate  13  moves to the open position and the secondary transfer roller  6   b  comes to the non-contact position to separate from the intermediate transfer belt  6 . 
     Thus, the shutter plate  13  and the cam  15  interact with each other to serve as a blocking unit. 
     As described above, the cam  15  may be used as a common member to synchronize operations of the blocking unit and the contact and separation unit. 
     Next, schematic configuration and functions of the drive array from a motor  50  serving as a drive source to the cam  15  according to an exemplary embodiment of the present invention are described, in reference to  FIGS. 6A and 6B . 
       FIG. 6A  shows a drive transmission of the motor  50  in a forward direction, and  FIG. 6B  shows a drive transmission of the motor  50  in a reverse direction. The drive array further includes two one-way clutches: a one-way clutch  61  is disposed on a shaft of the registration roller  63 , and a one-way clutch  62  is disposed on a shaft of the cam  15 . The one-way clutches  61  and  62  lock the movements of the registration roller  63  serving as a registration member and the cam  15  when rotating in a specific direction. 
     Specifically, as shown in  FIG. 6A , when the motor  50  rotates in the forward direction, the one-way clutch  61  locks or engages with the registration roller  63  to rotate in a direction to convey the recording sheet, and the one-way clutch  62  idles or does not engage with the cam  15 , thereby causing the cam  15  to remain unrotated. By contrast, when the motor  50  rotates in the reverse direction, the one-way clutch  62  locks or engages with the cam  15  to rotate, and the one-way clutch  61  idles or does not engage with the registration roller  63 , thereby causing the registration roller  63  to remain unrotated. 
     The position of the cam  15  is detected by a filler  64  and a sensor  65  each serving as a detector and disposed on the one-way clutch  62 . When the cam  15  reaches a desired position, the motor  50  stops. 
     If the color shift correction is allowed to interrupt conveyance of the recording sheet  10 , when the recording sheet arrives to the registration roller  63 , the one-way clutch  62  may be needed so as not to convey the recording sheet in a direction opposite to the sheet conveyance direction when the motor  50  rotates in an opposite direction. Therefore, when the sequence is controlled not to perform the color shift correction during the conveyance of the recording sheet  10 , the one-way clutch  62  is not necessary. Further, a spring-type one-way clutch and a needle type one-way clutch can achieve the same effect. 
     As described above, a use of identical drive source to drive the blocking unit and the contact and separation unit can reduce the number of mechatronics parts, thereby achieving a reduction of cost and of power consumption. 
     Further, synchronization of an open state of the blocking unit with a non-contact state of the contact and separation unit can prevent contamination of a secondary transfer roller during the color misregistration correction or the density correction. 
     Further, by detecting the open and close states of the blocking unit and the contact and non-contact states of the contact and separation unit, the blocking unit can surely open and close and the contact and separation unit can surely control the contact and separation of the secondary transfer roller. 
     Further, by causing the drive source of the blocking unit and the contact and separation unit to also drive the conveyance roller disposed nearby, a simpler drive array can be formed, which can achieve an increase of efficiency and a reduction of cost. 
     Furthermore, by causing the drive source of the blocking unit and the contact and separation unit to also drive the registration roller, a simpler drive array can be formed, which can achieve an increase of efficiency and a reduction of cost. 
     Further, by including at least one drive blocking member in the drive array from the drive source to the contact and separation unit, the switching of the contact state and the non-contact state of the contact and separation unit can be performed easily. 
     Further, when the drive array from the drive source to a member driven by the drive source includes multiple drive blocking members, the color misregistration correction and the density correction can be performed without being affected by the sheet conveyance operation and state. When a one-way clutch serves as the drive blocking member, the cost can be most effective and the switching can be surely performed. 
     Further, when the blocking unit moves to the close state while the color misregistration correction and the density correction are not performed, a degradation of detection accuracy due to contamination of the sensor can be prevented. 
     Furthermore, by separating the secondary transfer roller during the color misregistration correction and the density correction, the background contamination of the transfer sheet can be reduced. 
     The above-described example embodiments are illustrative, and numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative and exemplary embodiments herein may be combined with each other and/or substituted for each other within the scope of this disclosure. It is therefore to be understood that, the disclosure of this patent specification may be practiced otherwise than as specifically described herein. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, the invention may be practiced otherwise than as specifically described herein.