Patent Publication Number: US-9405262-B2

Title: Image forming apparatus eliminating static electricity from photoconductor surface

Description:
INCORPORATION BY REFERENCE 
     This application claims priority to Japanese Patent Application No. 2014-174240 filed on Aug. 28, 2014, the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus, and more particularly to an image forming apparatus that eliminates static electricity from a photoconductor surface by light irradiation. 
     Image forming apparatuses based on Xerography are thus far known, which are configured to evenly charge a photoconductor with a charging device, form a latent image with an exposure device, visualize the latent image with toner using a developing device, transfer the toner image to a sheet with a transfer device, and fix the toner on the sheet with a fixing device. In such image forming apparatuses, a ghost may appear in the image owing to disturbance of potential on the photoconductor surface taking place before the charging process, originating from a residual charge of the previous image forming operation. Accordingly, it is a normal practice to eliminate static electricity from the photoconductor surface, before the charging process of the next image forming operation. 
     Many of such image forming apparatuses include a plurality of illuminating devices respectively opposed to a plurality of photoconductors used for different colors, and each configured to irradiate the photoconductor surface with static elimination light. Normally, a light source is provided for each of the illuminating devices in this type of image forming apparatuses, and hence the same number of light sources as the number of photoconductors are necessary. Therefore, a larger space is required to accommodate the plurality of light sources, which naturally leads to an increase in cost. As a solution thereto, a technique of eliminating static electricity from a plurality of photoconductors with a single light source has been disclosed. 
     SUMMARY 
     In an aspect, the disclosure proposes further improvement of the foregoing technique. 
     The disclosure provides an image forming apparatus including a plurality of image forming units, a static eliminator, and a controller. 
     The plurality of image forming units each include a photoconductor, and charge a surface of the photoconductor to form an image. 
     The static eliminator is provided for each of the plurality of photoconductors, and outputs static elimination light to eliminate a residual charge remaining on the surface of the photoconductor after an image formation operation of the image forming unit. 
     The controller controls the image forming unit and the static eliminator. 
     The static eliminator includes a light source, a light guide unit, and a light shield unit. 
     The light source emits the static elimination light. 
     The light guide unit guides the static elimination light emitted from the light source to the plurality of photoconductors, and outputs the guided static elimination light to the surface of the photoconductors. 
     The light shield unit is provided inside the light guide unit or between the light guide unit and the surface of each of the photoconductors in an optical path formed between the light source and the surface of each of the photoconductors, and transmits or blocks the static elimination light. 
     Further, the controller controls the static eliminator, when the image forming unit performs the image formation, so as to transmit the static elimination light to the surface of the photoconductor on which the image formation is being performed among the plurality of photoconductors, and to block the static elimination light directed to the surface of the photoconductor on which the image formation is not being performed among the plurality of photoconductors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front cross-sectional view showing a configuration of an image forming apparatus according to a first embodiment of the disclosure; 
         FIG. 2A  is a side view of a static eliminator according to the first embodiment of the disclosure,  FIG. 2B  is a cross-sectional view taken along a line A-A in  FIG. 2A  and showing a light shield unit located at an emitting position, and  FIG. 2C  is a cross-sectional view taken along a line B-B in  FIG. 2A  and showing the light shield unit located at a shielding position; 
         FIG. 3  is a functional block diagram showing an essential internal configuration of the image forming apparatus according to the first embodiment of the disclosure; 
         FIG. 4  is a flowchart showing an image forming process and a static elimination process according to the first embodiment of the disclosure; 
         FIG. 5A  is a side view of a static eliminator according to a second embodiment of the disclosure,  FIG. 5B  is a cross-sectional view taken along a line A-A in  FIG. 5A  and showing the light shield unit located at the distribution position, and  FIG. 5C  is a cross-sectional view taken along a line B-B in  FIG. 5A  and showing the light shield unit located at the shielding position; 
         FIG. 6A  is a side view of a static eliminator according to a third embodiment of the disclosure,  FIG. 6B  is a cross-sectional view taken along a line A-A in  FIG. 6A  and showing the light shield unit located at the transmission position, and  FIG. 6C  is a cross-sectional view taken along a line B-B in  FIG. 6A  and showing the light shield unit located at the shielding position; 
         FIG. 7A  is a side view of a static eliminator according to a fourth embodiment of the disclosure,  FIG. 7B  is a cross-sectional view taken along a line A-A in  FIG. 7A  and showing the light shield unit located at the emitting position, and  FIG. 7C  is a cross-sectional view taken along a line B-B in  FIG. 7A  and showing the light shield unit located at the shielding position; 
         FIG. 8  is a side view of a static eliminator according to a variation of the first embodiment of the disclosure; and 
         FIG. 9A  is a side view of a static eliminator according to an additional embodiment of the disclosure,  FIG. 9B  is a cross-sectional view taken along a line A-A in  FIG. 9A  and showing the light shield unit transmitting static elimination light, and  FIG. 9C  is a cross-sectional view taken along a line B-B in  FIG. 9A  and showing the light shield unit blocking the static elimination light. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, an image forming apparatus according to a first embodiment of the disclosure will be described with reference to the drawings. 
       FIG. 1  is a front cross-sectional view showing a configuration of an image forming apparatus according to the first embodiment of the disclosure. The image forming apparatus  1  according to the first embodiment of the disclosure is a multifunction peripheral having a plurality of functions, such as copying, printing, scanning, and facsimile transmission. The image forming apparatus  1  includes an operation unit  47 , an image forming unit  12 , a fixing unit  13 , a paper feed unit  14 , a document feeder  6 , and a document reading unit  5 , which are mounted inside a main body  11 . 
     The operation unit  47  receives instructions from the user, for operations and processes that the image forming apparatus  1  is configured to perform, such as image forming and document reading. The operation unit  47  includes a display unit  473  for displaying a guidance and so forth to the operator. 
     When the image forming apparatus  1  performs the document reading operation, the document reading unit  5  optically reads the image on a source document delivered from the document feeder  6  or placed on a platen glass  161 , and generates image data. The image data generated by the document reading unit  5  is stored in a built-in HDD or a computer connected to a network. 
     When the image forming apparatus  1  performs the image forming operation, the image forming unit  12  forms a toner image on a sheet P serving as a recording medium and delivered from the paper feed unit  14 , on the basis of the image data generated in the document reading operation and received from the computer connected to the network, or stored in the built-in HDD. In the case of color printing, an image forming subunit  12 M for magenta, an image forming subunit  12 C for cyan, an image forming subunit  12 Y for yellow, and an image forming subunit  12 Bk for black in the image forming unit  12  form a toner image based on the corresponding color component, on photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk respectively, through charging, exposing, and developing processes, and the toner image is transferred onto an intermediate transfer belt  125  via a primary transfer roller  126 . In the case of monochrome printing, the image forming subunit  12 Bk for black in the image forming unit  12  forms a toner image based on the image represented by the image data on the photoconductor drum  121 Bk through charging, exposing, and developing processes, and the toner image is transferred onto the intermediate transfer belt  125  via the primary transfer roller  126 . The image forming subunit  12 M, the image forming subunit  12 C, the image forming subunit  12 Y and the image forming subunit  12 Bk are examples of the image forming unit in the disclosure. 
     The image forming apparatus  1  includes the four photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, to form the four toner images of magenta (M), cyan (C), yellow (Y), and black (Bk), respectively. The photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk are examples of the photoconductor in the disclosure. A static eliminator  50  is provided for each of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, to emit static elimination light for eliminating electric charge on the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, remaining after the image formation with the image forming subunit  12 M, the image forming subunit  12 C, the image forming subunit  12 Y, and the image forming subunit  12 Bk. 
     The toner images of the respective colors are superposed at an adjusted timing when transferred onto the intermediate transfer belt  125 , so as to form a colored toner image. A secondary transfer roller  210  transfers the colored toner image formed on the surface of the intermediate transfer belt  125  onto the sheet P transported along a transport route  190  from the paper feed unit  14 , at a nip region N of a drive roller  125 A engaged with the intermediate transfer belt  125 . Then the fixing unit  13  fixes the toner image on the sheet P by thermal pressing. The sheet P having the colored image formed and fixed thereon is discharged to an output tray  151 . 
     The paper feed unit  14  includes a plurality of paper feed cassettes. A controller  100  (see  FIG. 3 ) rotates a pickup roller  145  of one of the paper feed cassettes in which the sheets of the size designated by the operator are placed, to thereby transport the sheet P in the paper feed cassette toward the nip region N. 
     In the case of performing duplex printing with the image forming apparatus  1 , the sheet P having an image formed by the image forming unit  12  on one of the surfaces is nipped between a discharge roller pair  159 , and then switched back by the discharge roller pair  159  to be delivered to a reverse transport route  195  and is again transported by a transport roller pair  19  to the upstream side with respect to the nip region N and the fixing unit  13  in the transport direction of the sheet P. Thus, the image is formed by the image forming unit  12  on the other surface of the sheet P. 
       FIG. 2A  is a side view of a static eliminator according to the first embodiment of the disclosure.  FIG. 2B  is a cross-sectional view taken along a line A-A in  FIG. 2A .  FIG. 2C  is a cross-sectional view taken along a line B-B in  FIG. 2A . As shown in  FIG. 2A , the static eliminator  50  includes a single light source  51 , a light guide unit  52 , and light shield units  53 M,  53 C,  53 Y, and  53 Bk. An arrow X in  FIG. 2A  indicates the longitudinal direction of light emitters  521 M,  521 C,  521 Y, and  521 Bk respectively extending parallel to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and a directional symbol Y indicates the direction orthogonal to the longitudinal direction of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The light source  51  is constituted of a light emitting diode (LED) for example, and emits the static elimination light. 
     The light guide unit  52  serves to guide the static elimination light emitted from the light source  51  toward the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and emits the guided static elimination light onto the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. The light guide unit  52  includes a distribution member  520  having branch portions  5201  that respectively distribute the static elimination light emitted from the light source  51  to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The distribution member  520  extends in a direction orthogonal to the axial direction of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. The distribution member  520  includes, for example, a light inlet  5200  protruding toward the light source  51  from a central portion in the extending direction of the distribution member  520 . The distribution member  520  is constituted of, for example, a light-transmissive resin material. The distribution member  520  includes, as shown in  FIG. 2A , a plurality of reflection patterns  520 P each constituted of an inverted V-shaped prism projecting toward the corresponding branch portion  5201 , from one of the sides of the distribution member  520 . The reflection patterns  520 P each reflect the static elimination light that has entered the distribution member  520  through the light inlet  5200  in a direction orthogonal to the longitudinal direction of the distribution member  520  (toward the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk), to thereby conduct the static elimination light to the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The light emitters  521 M,  521 C,  521 Y, and  521 Bk are respectively opposed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, with a predetermined gap therebetween. The light emitters  521 M,  521 C,  521 Y, and  521 Bk are each disposed in a longitudinal direction so as to extend along the rotational axis (X-direction) of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. An end portion of each of the light emitters  521 M,  521 C,  521 Y, and  521 Bk in the longitudinal direction is connected to the corresponding branch portion  5201  of the distribution member  520 , so that the static elimination light distributed by the branch portion  5201  is introduced into each of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. The light emitters  521 M,  521 C,  521 Y, and  521 Bk emit the static elimination light distributed as above, to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, respectively. The light emitters  521 M,  521 C,  521 Y, and  521 Bk are formed of the same material as the distribution member  520 . The light emitters  521 M,  521 C,  521 Y, and  521 Bk each include a reflection pattern  521 P constituted of an inverted V-shaped prism like those shown in  FIG. 2A , and formed on the face opposite to the face opposed to the corresponding one of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. The reflection patterns  521 P serve to reflect the static elimination light that has entered the light emitters  521 M,  521 C,  521 Y, and  521 Bk through the distribution member  520  in a direction orthogonal to the longitudinal direction of the light emitters  521 M,  521 C,  521 Y, and  521 Bk (toward the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk), to thereby conduct the static elimination light to the light emitters  521 M,  521 C,  521 Y, and  521 Bk. A plurality of arrows O in  FIG. 2A  each indicate the optical path of the light reflected by each of the reflection patterns  521 P toward the surface of the corresponding one of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. 
     The light shield units  53 M,  53 C,  53 Y, and  53 Bk are formed of a non-transmissive material. The light shield units  53 M,  53 C,  53 Y, and  53 Bk are respectively located between the pairs of the light emitters  521 M,  521 C,  521 Y, and  521 Bk and the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, in the optical path from the light source  51  to the surface of the respective photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. The light shield units  53 M,  53 C,  53 Y, and  53 Bk serve to transmit or block the static elimination light emitted from the light emitters  521 M,  521 C,  521 Y, and  521 Bk, respectively. The light shield units  53 M,  53 C,  53 Y, and  53 Bk each include a moving mechanism. The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk move the respective light shield units  53 M,  53 C,  53 Y, and  53 Bk to an emitting position deviated from the optical path of the static elimination light emitted from the light emitters  521 M,  521 C,  521 Y, and  521 Bk, or to a shielding position where the light shield units  53 M,  53 C,  53 Y, and  53 Bk interfere with the optical path of the static elimination light directed toward the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk respectively, to thereby block the static elimination light. For example, the moving mechanism  54 M includes a moving element  540 M having a rack, a pinion gear  541 M meshed with the rack of the moving element  540 M, and an electric motor  542 M that serves as a drive source for independently rotating the pinion gear  541 M. Like the moving mechanism  54 M, the moving mechanisms  54 C,  54 Y, and  54 Bk respectively include moving elements  540 C,  540 Y, and  540 Bk, pinion gears  541 C,  541 Y, and  541 Bk, and electric motors  542 C,  542 Y, and  542 Bk. The light shield units  53 M,  53 C,  53 Y, and  53 Bk are respectively attached to the moving elements  540 M,  540 C,  540 Y, and  540 Bk, so as to linearly move together with the moving elements  540 M,  540 C,  540 Y, and  540 Bk by the rotation of the pinion gears  541 M,  541 C,  541 Y, and  541 Bk, thus to be positioned at the emitting position or the shielding position. 
     The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk are controlled by the controller  100  (see  FIG. 3 ). In the case of the monochrome printing, for example, the controller  100  causes the moving elements  540 M,  540 C, and  540 Y to linearly move in the Y-direction, the moving elements  540 M,  540 C, and  540 Y being respectively connected to the light shield units  53 M,  53 C, and  53 Y corresponding to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed by the image forming subunit  12 M, the mage forming subunit  12 C, and the image forming subunit  12 Y respectively, to thereby move the light shield units  53 M,  53 C, and  53 Y to the shielding position.  FIG. 2C  illustrates the light shield unit  53 Y which has reached the shielding position. In the case of the monochrome printing, further, the controller  100  causes the moving element  540 Bk to linearly move in the Y-direction, the moving element  540 Bk being connected to the light shield unit  53 Bk corresponding to the photoconductor drum  121 Bk on which the image formation is being performed by the image forming subunit  12 Bk, to thereby move the light shield unit  53 Bk to the emitting position.  FIG. 2B  illustrates the light shield unit  53 Bk which has reached the emitting position. 
       FIG. 3  is a functional block diagram showing an essential internal configuration of the image forming apparatus  1 . The image forming apparatus  1  includes a control unit  10 , the document feeder  6 , the document reading unit  5 , the image forming unit  12 , an image memory  32 , a HDD  92 , the fixing unit  13 , a drive motor  70 , the operation unit  47 , a facsimile communication unit  71 , a network interface unit  91 , the static eliminator  50 , and moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk. The constituents described above with reference to  FIG. 1  are given the same numeral, and the description thereof will not be repeated. 
     The document reading unit  5  includes a reading mechanism  163  (see  FIG. 1 ) including a light emitting unit and a CCD sensor, to be controlled by the control unit  100  in the controller  10 . The document reading unit  5  illuminates the source document with the light from the light emitting unit and detects the reflected light with the CCD sensor, to thereby read the image on the source document. 
     The image memory  32  is a region for temporarily storing the image data of the source document acquired by the document reading unit  5 , and data to be printed by the image forming unit  12 . 
     The HDD  92  is a large-capacity storage device for storing source images acquired by the document reading unit  5 , and so forth. 
     The driving motor  70  is a drive source that provides a rotational driving force to rotational components and the transport roller pair  19  of the image forming unit  12 . 
     The facsimile communication unit  71  includes, though not shown, an encoding/decoding unit, a modem, and a network control unit (NCU), to perform facsimile transmission through a public circuit. 
     The network interface unit  91  includes a communication module such as a LAN board, to transmit and receive data to and from an external device  20  such as a personal computer in the local area or in the Internet, through the LAN connected to the network interface unit  91 . 
     The control unit  10  includes a central processing unit (CPU), a RAM, a ROM, and an exclusive hardware circuit. The control unit  10  includes the controller  100 . The controller  100  serves to control the overall operation of the image forming apparatus  1 . 
     In the case of the monochrome printing, for example, the controller  100  controls the static eliminator  50  so as to allow the light shield unit  53 Bk to transmit the static elimination light emitted from the light guide unit  52  to the surface of the photoconductor drum  121 Bk on which the image formation is being performed, among the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and to cause the light shield units  53 M,  53 C, and  53 Y to block the static elimination light, when it is necessary to block the light directed to the surface of the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed. To be more detailed, the controller  100  controls the moving mechanism  54 Bk to drive the electric motor  542 Bk so as to linearly move the moving element  540 Bk connected to the light shield unit  53 Bk in the Y-direction, thereby moving the light shield unit  53 Bk to the emitting position. At this point, the light shield unit  53 Bk is deviated from the optical path of the static elimination light emitted from the light emitter  521 Bk. Accordingly, the static elimination light reaches the photoconductor drum  121 Bk. In addition, the controller  100  controls the moving mechanisms  54 M,  54 C, and  54 Y to drive the electric motors  542 M,  542 C, and  542 Y so as to linearly move the moving elements  540 M,  540 C, and  540 Y respectively connected to the light shield units  53 M,  53 C, and  53 Y in the Y-direction, thereby moving the light shield units  53 M,  53 C, and  53 Y to the shielding position. At this point, the light shield units  53 M,  53 C, and  53 Y respectively interfere with the optical path of the static elimination light toward the surface of the photoconductor drums  121 M,  121 C, and  121 Y thus to block the static elimination light. Therefore, the static elimination light is restricted from being transmitted to the surface of the photoconductor drums  121 M,  121 C, and  121 Y. 
     The control unit  10  acts as the controller  100  by operating in accordance with an image processing program installed in the HDD  92 . However, the controller  100  may be constituted of hardware circuits instead of the operation by the control unit  10  in accordance with the image processing program. This also applies to other embodiments, unless otherwise specifically noted. 
     Referring now to  FIG. 4 , description will be given about the image forming operation and the static elimination for the photoconductor according to the first embodiment of the disclosure.  FIG. 4  is a flowchart showing the image forming process and the static elimination process according to the first embodiment of the disclosure. 
     Upon receipt of an instruction to perform the monochrome printing (S 1 ), the controller  100  controls the image forming subunit  12 Bk for black so as to charge the surface of the photoconductor drum  121 Bk, thereby forming an image (S 2 ). In this image forming process, only the photoconductor drum  121 Bk is charged, and the remaining photoconductor drums  121 M,  121 C, and  121 Y are not charged. Then the controller  100  controls the moving mechanism  54 Bk so as to move the light shield unit  53 Bk, corresponding to the photoconductor drum  121 Bk charged by the image forming subunit  12 Bk, to the emitting position, and controls the moving mechanisms  54 M,  54 C,  54 Y so as to move the light shield units  53 M,  53 C, and  53 Y respectively corresponding to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed, to the shielding position (S 3 ). The controller  100  then receives an instruction to finish the operation, and finishes the image forming process and the static elimination process for the photoconductor. 
     In the first embodiment, as described above, when the monochrome printing is performed for example, the controller  100  controls the moving mechanisms  54 M,  54 C,  54 Y so as to move the light shield units  53 M,  53 C, and  53 Y, respectively corresponding to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed by the image forming subunit  12 M, the image forming subunit  12 C, and the image forming subunit  12 Y, to the shielding position. 
     In the first embodiment, accordingly, in the case of the monochrome printing the static elimination light is not transmitted to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed by the image forming subunit  12 M, the image forming subunit  12 C, and the image forming subunit  12 Y, and therefore the photoconductor drums  121 M,  121 C, and  121 Y which are not used in the monochrome printing can be exempted from optical fatigue. Consequently, the configuration according to the first embodiment eliminates the need to drive or charge the photoconductor drums  121 M,  121 C, and  121 Y in order to prevent the optical fatigue. 
     With conventional image forming apparatuses unlike the one according to this embodiment, the static elimination light is emitted not only to a photoconductor for single-color printing but also to unused photoconductors that are not charged in the single-color printing, even when the photoconductor for single-color printing is used. Accordingly, the photoconductors not used in the single-color printing may incur optical fatigue. In order to prevent the optical fatigue it is necessary to drive or charge the photoconductors that are not used in the single-color printing, which leads to shortened life span of the photoconductor. 
     The configuration according to this embodiment, however, enables the static elimination of a plurality of photoconductors to be performed with a single light source, and restricts the static elimination light from reaching the photoconductors that are not used in the single-color printing, thereby preventing the optical fatigue of the photoconductors. Thus, the foregoing problem can be eliminated. 
     Hereunder, an image forming apparatus according to a second embodiment of the disclosure will be described with reference to the drawings. 
       FIG. 5A  is a side view of a static eliminator according to a second embodiment of the disclosure. The same constituents as those of the image forming apparatus according to the first embodiment will be given the same numeral, and the description thereof will not be repeated. The light shield units  53 M,  53 C,  53 Y, and  53 Bk of the first embodiment are respectively located between the pairs of the light emitters  521 M,  521 C,  521 Y, and  521 Bk and the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk (see  FIG. 2 ), however the light shield units  53 M,  53 C,  53 Y, and  53 Bk according to the second embodiment of the disclosure are different from those of the first embodiment in being located at the corresponding branch portions  5201  of the distribution member  520 , in the optical path from the light source  51  to the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. Arrows X in  FIGS. 5A to 5C  indicate the longitudinal direction of light emitters  521 M,  521 C,  521 Y, and  521 Bk, and a directional symbol Y and arrows Y indicate the direction orthogonal to the longitudinal direction of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk are controlled by the controller  100  (see  FIG. 3 ). In the case of the monochrome printing, for example, the controller  100  causes the moving elements  540 M,  540 C, and  540 Y to linearly move in the Y-direction, the moving elements  540 M,  540 C, and  540 Y being respectively connected to the light shield units  53 M,  53 C, and  53 Y corresponding to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed by the image forming subunit  12 M, the mage forming subunit  12 C, and the image forming subunit  12 Y respectively, among the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, to thereby move the light shield units  53 M,  53 C, and  53 Y to the shielding position where the light shield units  53 M,  53 C, and  53 Y interfere with the optical path of the static elimination light directed to the light emitters  521 M,  521 C, and  521 Y, thereby blocking the static elimination light.  FIG. 5C  illustrates the light shield unit  53 Y which has reached the shielding position. In the case of the monochrome printing, further, the controller  100  causes the moving element  540 Bk to linearly move in the Y-direction, the moving element  540 Bk being connected to the light shield unit  53 Bk corresponding to the photoconductor drum  121 Bk on which the image formation is being performed by the image forming subunit  12 Bk, among the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, to thereby move the light shield unit  53 Bk to a distribution position deviated from the optical path of the static elimination light distributed from the branch portion  5201 .  FIG. 5B  illustrates the light shield unit  53 Bk which has reached the distribution position. 
     In the case of the monochrome printing, for example, the controller  100  (see  FIG. 3 ) causes the moving elements  540 M,  540 C, and  540 Y, respectively connected to the light shield units  53 M,  53 C, and  53 Y corresponding to the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed, to linearly move in the Y-direction, to thereby move the light shield units  53 M,  53 C, and  53 Y to the shielding position. At this point, the light shield units  53 M,  53 C, and  53 Y interfere with the optical path of the static elimination light toward the light emitters  521 M,  521 C, and  521 Y respectively, thus to block the static elimination light. Therefore, the static elimination light is restricted from being transmitted to the light emitters  521 M,  521 C, and  521 Y. Further, the controller  100  causes the moving element  540 Bk, connected to the light shield unit  53 Bk corresponding to the photoconductor drum  121 Bk on which the image formation is being performed, to linearly move in the Y-direction, to thereby move the light shield unit  53 Bk to the distribution position.  FIG. 5B  illustrates the light shield unit  53 Bk which has reached the distribution position. At this point, the end portion of the light emitter  521 Bk on the side of the distribution member  520  is spaced from the distribution member  520 . The size of the spacing may be determined so as to allow the static elimination light distributed from the distribution member  520  to be transmitted to the light emitter  521 Bk. At this point, the light shield unit  53 Bk is deviated from the optical path of the static elimination light distributed from the branch portion  5201 . Therefore, the static elimination light can be distributed to the light emitter  521 Bk from the branch portion  5201 . 
     As described above, in the second embodiment the light shield units  53 M,  53 C,  53 Y, and  53 Bk are each located at the corresponding branch portion  5201  of the distribution member  520 . The light shield units  53 M,  53 C,  53 Y, and  53 Bk can block the static elimination light directed to the photoconductor drums  121 M,  121 C, and  121 Y from the light emitters  521 M,  521 C, and  521 Y, simply by blocking the static elimination light from the branch portion  5201 . Such an arrangement eliminates the need to provide the light shield units  53 M,  53 C,  53 Y, and  53 Bk over the entire length of the light emitter  521 M,  521 C,  521 Y, and  521 Bk in the longitudinal direction, as in the first embodiment. Consequently, the light shield units  53 M,  53 C,  53 Y, and  53 Bk can be formed in a smaller size than those of the first embodiment. 
     Hereunder, an image forming apparatus according to a third embodiment of the disclosure will be described with reference to the drawings. 
       FIG. 6A  is a side view of a static eliminator according to a third embodiment of the disclosure.  FIG. 6B  is a cross-sectional view taken along a line A-A in  FIG. 6A .  FIG. 6C  is a cross-sectional view taken along a line B-B in  FIG. 6A . The same constituents as those of the image forming apparatus according to the first embodiment will be given the same numeral, and the description thereof will not be repeated. In the first embodiment, the light shield units  53 M,  53 C,  53 Y, and  53 Bk are provided for transmitting or blocking the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk (see  FIG. 2 ). The third embodiment of the disclosure is different from the first embodiment in transmitting or blocking the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk without utilizing the light shield units  53 M,  53 C,  53 Y, and  53 Bk. 
     As shown in  FIG. 6A , the static eliminator  50  includes the single light source  51 , the distribution member  520 , the light emitters  521 M,  521 C,  521 Y, and  521 Bk, and the moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk. Arrows X in  FIGS. 6A to 6C  indicate the longitudinal direction of light emitters  521 M,  521 C,  521 Y, and  521 Bk, and a directional symbol Y and arrows Y indicate the direction orthogonal to the longitudinal direction of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The distribution member  520  includes branch portions  5201  that each distribute the static elimination light emitted from the light source  51  to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and transmission surfaces  5201 A formed on the respective branch portions  5201  so as to transmit the static elimination light. The distribution member  520  allows the static elimination light to be transmitted to the light emitters  521 M,  521 C,  521 Y, and  521 Bk only via the transmission surface  5201 A, by means of the reflection pattern  521 P, and the static elimination light is transmitted through no other route. 
     The light emitters  521 M,  521 C,  521 Y, and  521 Bk each include an incident surface  5210  and an output surface  5211 . The incident surface  5210  allows the distributed static elimination light to be introduced, when the incident surface  5210  is in contact with the transmission surface  5201 A. The output surfaces  5211  are respectively opposed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, so as to emit the static elimination light introduced through the incident surface  5210  to the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. 
     The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk respectively move the light emitters  521 M,  521 C,  521 Y, and  521 Bk to a transmission position that allows the static elimination light to be transmitted from the transmission surface  5201 A of the distribution member  520  to the incident surface  5210  of the light emitters  521 M,  521 C,  521 Y, and  521 Bk, and to the shielding position that restricts the static elimination light from being transmitted from the transmission surface  5201 A of the distribution member  520  to the incident surface  5210  of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk are controlled by the controller  100  (see  FIG. 3 ). In the case of the monochrome printing, for example, the controller  100  causes the moving elements  540 M,  540 C, and  540 Y to linearly move in the Y-direction, the moving elements  540 M,  540 C, and  540 Y being respectively connected to the light emitters  521 M,  521 C, and  521 Y, the respective output surfaces  5211  of which are opposed to the surface of the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed, to thereby move the light emitter  521 M,  521 C, and  521 Y to the shielding position.  FIG. 6C  illustrates the light emitter  521 Y which has reached the shielding position. At this point, the incident surface  5210  of the light emitter  521 Y is not in contact with the transmission surface  5201 A of the distribution member  520 , and therefore the static elimination light is not transmitted from the transmission surface  5201 A to the incident surface  5210 . Accordingly, the static elimination light directed to the surface of the photoconductor drum  121 Y is blocked, and thus restricted from reaching the surface of the photoconductor drum  121 Y. In the case of the monochrome printing, further, the controller  100  causes the moving element  540 Bk to linearly move in the Y-direction, the moving element  540 Bk being connected to the light emitter  521 Bk, the output surface  5211  of which is opposed to the surface of the photoconductor drum  121 Bk on which the image formation is being performed, to thereby move the light emitter  521 Bk to the transmission position.  FIG. 6B  illustrates the light emitter  521 Bk which has reached the transmission position. At this point, the incident surface  5210  of the light emitter  521 Bk is in contact with the transmission surface  5201 A of the distribution member  520 , and therefore the static elimination light is transmitted from the transmission surface  5201 A to the incident surface  5210 . Accordingly, the static elimination light can reach the surface of the photoconductor drum  121 Bk, from the light emitter  521 Bk. 
     As described above, in the third embodiment the controller  100  can transmit or block the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk with a simple mechanism for moving the light emitters  521 M,  521 C,  521 Y, and  521 Bk with respect to the distribution member  520 , without employing additional components such as the light shield units  53 M,  53 C,  53 Y, and  53 Bk. 
     Hereunder, an image forming apparatus according to a fourth embodiment of the disclosure will be described with reference to the drawings. 
       FIG. 7A  is a side view of a static eliminator according to the fourth embodiment of the disclosure.  FIG. 7B  is a cross-sectional view taken along a line A-A in  FIG. 7A .  FIG. 7C  is a cross-sectional view taken along a line B-B in  FIG. 7A . The same constituents as those of the image forming apparatus according to the third embodiment will be given the same numeral, and the description thereof will not be repeated. In the third embodiment, the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk is transmitted or blocked by moving the light emitters  521 M,  521 C,  521 Y, and  521 Bk (see  FIG. 6 ). The fourth embodiment of the disclosure is different from the third embodiment in that shielding members  53 M,  53 C,  53 Y, and  53 Bk are provided. 
     As shown in  FIG. 7A , the static eliminator  50  includes the single light source  51 , the distribution member  520 , the light emitters  521 M,  521 C,  521 Y, and  521 Bk, the shielding members  53 M,  53 C,  53 Y, and  53 Bk, and the moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk. Arrows X in  FIGS. 7A to 7C  indicate the longitudinal direction of light emitters  521 M,  521 C,  521 Y, and  521 Bk, and a directional symbol Y and arrows Y indicate the direction orthogonal to the longitudinal direction of the light emitters  521 M,  521 C,  521 Y, and  521 Bk. 
     The shielding members  53 M,  53 C,  53 Y, and  53 Bk are formed of a non-transmissive material. As shown in  FIGS. 7B and 7C , the shielding members  53 Y and  53 Bk are located adjacent to the incident surface  5210  of the respective light emitters  521 Y and  521 Bk, and each include a shielding surface  530  that can be moved in the Y-direction along the transmission surface  5201 A of the distribution member  520  together with the incident surface  5210 , so as to block the static elimination light from the distribution member  520  upon contacting the transmission surface  5201 A. Although not shown in  FIGS. 7B and 7C , the shielding members  53 M and  53 C also include the shielding surface  530  like the shielding members  53 Y and  53 Bk. 
     The moving mechanisms  54 M,  54 C,  54 Y, and  54 Bk are controlled by the controller  100  (see  FIG. 3 ). In the case of the monochrome printing, for example, the controller  100  controls the moving mechanisms  54 M,  54 C, and  54 Y to cause the moving elements  540 M,  540 C, and  540 Y to linearly move in the Y-direction, the moving elements  540 M,  540 C, and  540 Y being respectively connected to the light emitters  521 M,  521 C, and  521 Y, the respective output surfaces  5211  of which are opposed to the surface of the photoconductor drums  121 M,  121 C, and  121 Y on which the image formation is not being performed, to thereby move the light emitters  521 M,  521 C, and  521 Y to the shielding position (see  FIG. 7C ). At this point, the respective incident surfaces  5210  of the light emitters  521 M,  521 C, and  521 Y are in contact with the shielding surfaces  530 , and therefore the static elimination light directed to the light emitters  521 M,  521 C, and  521 Y from the distribution member  520  is blocked. Thus, the static elimination light directed to the surface of the photoconductor drums  121 M,  121 C, and  121 Y is blocked and hence the static elimination light is restricted from being transmitted to the surface of the photoconductor drums  121 M,  121 C, and  121 Y.  FIG. 7C  illustrates the light emitter  521 Y which has reached the shielding position. In the case of the monochrome printing, further, the controller  100  controls the moving mechanism  54 Bk to causes the moving element  540 Bk to linearly move in the Y-direction, the moving element  540 Bk being connected to the light emitter  521 Bk, the output surface  5211  of which is opposed to the surface of the photoconductor drum  121 Bk on which the image formation is being performed, to thereby move the light emitter  521 Bk to the transmission position.  FIG. 7B  illustrates the light emitter  521 Bk which has reached the transmission position. At this point, the incident surface  5210  of the light emitter  521 Bk is in contact with the transmission surface  5201 A of the distribution member  520 , and therefore the static elimination light is transmitted from the distribution member  520  to the incident surface  5210 . Accordingly, the static elimination light can reach the surface of the photoconductor drum  121 Bk, from the light emitter  521 Bk. 
     As described above, in the fourth embodiment the static elimination light directed to the light emitters  521 M,  521 C, and  521 Y from the distribution member  520  is blocked by the respective shielding surfaces  530  of the shielding members  53 M,  53 C, and  53 Y. Such a configuration ensures that the static elimination light is restricted from being transmitted to the surface of the photoconductor drums  121 M,  121 C, and  121 Y from the light emitters  521 M,  521 C, and  521 Y. 
     In the first to the fourth embodiments, the light guide unit  52  includes the distribution member  520  that distributes the static elimination light emitted from the light source  51  to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and the light emitters  521 M,  521 C,  521 Y, and  521 Bk that respectively emit the static elimination light distributed by the distribution member  520  to the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk (see  FIG. 2 ), the disclosure is not limited to the foregoing embodiments. The light guide unit  52  shown in  FIG. 8  includes a passage formed from an incident end  5230 A opposed to the light source  51  to the distal end  5230 F of a light guide member  5230  that guides the static elimination light from the light source  51 . The passage is disposed so as to oppose all of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, along the rotational axis of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, and includes the output surfaces respectively opposed to the surface of the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. The output surfaces  5230 B,  5230 C,  5230 D, and  5230 E reflect the static elimination light toward the surface of the respective photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk. In this case, the light guide unit  52  can be formed with the single light guide member  5230  alone, without the need to employ a plurality of members including the distribution member  520  and the light emitters  521 M,  521 C,  521 Y, and  521 Bk as in the first to the fourth embodiments. 
     In the first and second embodiments, the controller  100  controls the moving mechanism  54  to move the light shield units  53 M,  53 C,  53 Y, and  53 Bk to the emitting position or the shielding position, to thereby transmit or block the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, however the disclosure is not limited to those embodiments.  FIG. 9A  is a side view of a static eliminator according to an additional embodiment of the disclosure.  FIG. 9B  illustrates the light shield unit transmitting the static elimination light.  FIG. 9C  illustrates the light shield unit blocking the static elimination light. For example as shown in  FIG. 9A ,  FIG. 9B , and  FIG. 9C , the light shield units  53 Bk,  53 Y,  53 C, and  53 M may each include a mechanism that transmits or blocks light by control of the orientation of liquid crystal. To be more detailed, the light shield units  53 Bk,  53 Y,  53 C, and  53 M may each include a mechanism including a pair of substrates each having an electrode on the opposing surface and a liquid crystal layer formed of liquid crystal molecules encapsulated between the pair of substrates, so as to control the orientation direction of the liquid crystal molecules by applying a first electric field or a second electric field to the pair of substrates. In this example, the controller  100  can set the orientation direction of the liquid crystal molecules parallel to the proceeding direction of the static elimination light, by applying the first electric field to the pair of substrates provided in the light shield units  53 Bk,  53 Y,  53 C, and  53 M respectively corresponding to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk on which the image formation is being performed by the image forming subunit  12 M, the image forming subunit  12 C, the image forming subunit  12 Y, and the image forming subunit  12 Bk, to thereby transmit the static elimination light along the orientation direction of the liquid crystal molecules as shown in  FIG. 9B . The controller  100  can also set the orientation direction of the liquid crystal molecules perpendicular to the proceeding direction of the static elimination light, by applying the second electric field to the pair of substrates provided in the light shield units respectively corresponding to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk on which the image formation is not being performed by the image forming subunit  12 M, the image forming subunit  12 C, the image forming subunit  12 Y, and the image forming subunit  12 Bk, to thereby cause the liquid crystal molecules to block the static elimination light, as shown in  FIG. 9C . 
     Further, a separation unit that can cause the intermediate transfer belt  125  to contact or move away from the photoconductor drums  121 M,  121 C, and  121 Y for color printing may be provided. Then the light shield units  53 M,  53 C, and  53 Y of the first embodiment may be moved to a position where the separation unit separates the intermediate transfer belt  125  from the photoconductor drums  121 M,  121 C, and  121 Y. In this case, the light shield units  53 M,  53 C, and  53 Y may be moved to the shielding position, in other words the separation unit may be moved to the shielding position for interfering with the optical path of the static elimination light directed to the surface of the photoconductor drums  121 M,  121 C, and  121 Y. In addition, when the separation unit brings the intermediate transfer belt  125  into contact with the photoconductor drums  121 M,  121 C, and  121 Y, the light shield units  53 M,  53 C, and  53 Y may be moved together with the intermediate transfer belt  125  so as to move the light shield units  53 M,  53 C, and  53 Y to the emitting position, in other words the position deviated from the optical path of the static elimination light emitted from the light emitters  521 M,  521 C, and  521 Y. By moving thus the separation unit, the moving mechanisms  54 M,  54 C, and  54 Y for moving the light shield units  53 M,  53 C, and  53 Y to the shielding position or the emitting position can be excluded. 
     Further, in the first to the fourth embodiments the controller transmits or blocks the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, when performing the monochrome printing, however the disclosure is not limited to those embodiments. The controller may transmit or block the static elimination light directed to the photoconductor drums  121 M,  121 C,  121 Y, and  121 Bk, on which the image formation is not being performed, when the single-color printing is performed with magenta (M), cyan (C), and yellow (Y). 
     It is to be understood that the configurations and operations described in the foregoing embodiments with reference to  FIG. 1  to  FIG. 8  are merely exemplary, and in no way intended to limit the configuration and operation of the present disclosure. 
     Various modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein.