Patent Publication Number: US-11392070-B2

Title: Driving-force-transmitting mechanism and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2020-159392 filed Sep. 24, 2020. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a driving-force-transmitting mechanism and an image forming apparatus. 
     (ii) Related Art 
     There are several known apparatuses relating to a driving-force-transmitting mechanism intended for an image forming apparatus or the like, such as those disclosed by Japanese Unexamined Patent Application Publications Nos. 2006-350285, No. 2010-32742, and No. 2016-126152. 
     The apparatus disclosed by Japanese Unexamined Patent Application Publication No. 2006-350285 includes a coupling member that is slidably fitted on a driving-force input shaft and is rotatable together with the driving-force input shaft to transmit a driving force to a rotation object, an urging component that urges the coupling member toward a first position where the coupling member is coupled to a coupling provided on the rotation object, and a coupling switching component that selectively positions the coupling member between the first position and a second position where the coupling member is decoupled from the rotation object and is retracted toward the driving-force input shaft. 
     The apparatus disclosed by Japanese Unexamined Patent Application Publication No. 2010-32742 includes a transmission disabling mechanism in which an operating force of attaching or detaching a detachable unit to or from the apparatus causes at least one of a driving coupling and a driven coupling to be tilted with respect to a rotation axis thereof in such a manner as to disable the transmission of a driving force to the other. 
     The apparatus disclosed by Japanese Unexamined Patent Application Publication No. 2016-126152 includes a body-side coupling that is movable in a direction of a rotation axis thereof. The body-side coupling includes a tapered portion at an end thereof nearer to a unit in the direction of the rotation axis. The diameter of the tapered portion increases toward a side away from the unit in the direction of the rotation axis. The unit includes a disabling member that is movable in a direction intersecting a rotation axis of a unit-side coupling. When the disabling member is moved, the disabling member comes into contact with and slides on the tapered portion of the body-side coupling in such a manner as to retract the body-side coupling from the unit. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a simpler mechanism of assuredly enabling and disabling the transmission of a driving force than a mechanism including a disabling member that retracts a body-side coupling from a unit by coming into contact with and sliding on a tapered portion of the body-side coupling. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a driving-force-transmitting mechanism including a driving-force-transmitting component that transmits a driving force from an apparatus body to an attaching object, the attaching object being attachable to and detachable from the apparatus body; and a plurality of operating components that enables or disables the transmission of the driving force from the apparatus body to the attaching object when the attaching object is attached to or detached from the apparatus body, the operating components operating sequentially with delays in such a manner as to move the driving-force-transmitting component in a direction intersecting attaching and detaching directions in which the attaching object is attached to and detached from the apparatus body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates an outline of an image forming apparatus to which a driving-force-transmitting mechanism according to a first exemplary embodiment of the present disclosure is applied; 
         FIG. 2  illustrates an imaging device included in the image forming apparatus; 
         FIG. 3  is a perspective view of an intermediate transfer unit; 
         FIG. 4  is a perspective view of the driving-force-transmitting mechanism provided on an apparatus body; 
         FIG. 5  is a perspective view of an intermediate-transfer-member master coupling; 
         FIG. 6  is a sectional view of the driving-force-transmitting mechanism according to the first exemplary embodiment of the present disclosure; 
         FIG. 7  is a perspective view of relevant part of the intermediate transfer unit; 
         FIG. 8  is a perspective view of a grip member and an operating member; 
         FIG. 9  is a perspective view of the driving-force-transmitting mechanism provided on the apparatus body, with the grip member and the operating member; 
         FIG. 10  is another perspective view of the grip member and the operating member; 
         FIG. 11  illustrates how the driving-force-transmitting mechanism according to the first exemplary embodiment of the present disclosure operates; 
         FIG. 12  is yet another perspective view of the grip member and the operating member; 
         FIG. 13  illustrates an outline of an image forming apparatus to which a driving-force-transmitting mechanism according to a second exemplary embodiment of the present disclosure is applied; and 
         FIG. 14  is a perspective view of an image forming unit included in the image forming apparatus according to the second exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
       FIG. 1  illustrates an outline of an image forming apparatus to which a driving-force-transmitting mechanism according to a first exemplary embodiment of the present disclosure is applied.  FIG. 2  illustrates an imaging device included in the image forming apparatus. 
     Outline of Image Forming Apparatus 
     An image forming apparatus  1  according to the first exemplary embodiment is configured as, for example, a color printer. As illustrated in  FIG. 1 , the image forming apparatus  1  includes a plurality of imaging devices  10  that form toner images developed with toners contained in developers, an intermediate transfer device  20  as an exemplary intermediate transfer component that carries the toner images formed by the imaging devices  10  and transports the toner images to a second-transfer position where the toner images are eventually second-transferred to a recording sheet  5  as an exemplary recording medium, a sheet feeding device  30  that stores predetermined recording sheets  5  and feeds each of the recording sheets  5  to be supplied to the second-transfer position in the intermediate transfer device  20 , a fixing device  40  that fixes the toner images on the recording sheet  5  obtained through second transfer performed by the intermediate transfer device  20 , and so forth. The image forming apparatus  1  further includes an apparatus body  1   a . The apparatus body  1   a  includes supporting members, an exterior covering, and so forth. The broken lines in  FIG. 1  represent transport paths along which the recording sheet  5  is transported in the apparatus body  1   a.    
     The imaging devices  10  include four imaging devices  10 Y,  10 M,  10 C, and  10 K that exclusively form toner images in four respective colors of yellow (Y), magenta (M), cyan (C), and black (K). The four imaging devices  10  (Y, M, C, and K) are arranged in an inclined line in a space provided inside the apparatus body  1   a.    
     The four imaging devices  10  are categorized into color imaging devices  10  (Y, M, and C) for yellow (Y), magenta (M), and cyan (C); and a black (K) imaging device  10 K. The black imaging device  10 K is provided at the downstreammost position in a rotating direction B of an intermediate transfer belt  21  included in the intermediate transfer device  20 . The image forming apparatus  1  has the following imaging modes: a full-color mode in which the color imaging devices  10  (Y, M, and C) and the black (K) imaging device  10 K are both activated to form a full-color image, and a monochrome mode in which only the black (K) imaging device  10 K is activated to form a monochrome image. 
     Referring to  FIG. 2 , the imaging devices  10  (Y, M, C, and K) each include a rotatable photoconductor drum  11  as an exemplary image carrier. The photoconductor drum  11  is surrounded by the following devices as exemplary toner-image-forming components: a charging device  12  that charges the peripheral surface (an image carrying surface) of the photoconductor drum  11  on which an image is to be formed to a predetermined potential, an exposure device  13  that applies light generated from image information (a signal) to the charged peripheral surface of the photoconductor drum  11  and thus produces a potential difference to form an electrostatic latent image (for each of the colors), a developing device  14  (Y, M, C, or K) that develops the electrostatic latent image into a toner image with the toner contained in the developer and having a corresponding one of the colors (Y, M, C, and K), a first-transfer device  15  (Y, M, C, or K) as an exemplary first-transfer component that transfers the toner image to the intermediate transfer device  20 , a drum cleaning device  16  (Y, M, C, or K) that removes residual matter, such as toner particles, from the image carrying surface of the photoconductor drum  11  having undergone first transfer, and other relevant devices. 
     The photoconductor drum  11  is obtained by providing a photoconductive layer (photosensitive layer), serving as an image carrying surface, made of a photosensitive material over a cylindrical or columnar base member that is to be grounded. The photoconductor drum  11  is supported in such a manner as to be rotatable in a direction indicated by arrow A when receiving power transmitted from a driving device (not illustrated). 
     The charging device  12  is a contact-type charging roller positioned in contact with the photoconductor drum  11 . The charging device  12  is supplied with a charging voltage. If the developing device  14  employs a reversal development scheme, the charging voltage to be supplied is a voltage or current of a polarity that is the same as the polarity to which the toner to be supplied from the developing device  14  is charged. The charging device  12  may alternatively be a noncontact device such as a scorotron positioned apart from the surface of the photoconductor drum  11 . 
     The exposure device  13  performs polarization scanning in the axial direction of the photoconductor drums  11  with respective laser beams LB-Y, LB-M, LB-C, and LB-K generated from the image information. The exposure device  13  may be a light-emitting-diode (LED) printhead including a plurality of LEDs as light-emitting devices arrayed along the axes of the photoconductor drums  11  to form electrostatic latent images by applying light generated from the image information to the photoconductor drums  11 . Employing an LED printhead as the exposure device  13  greatly reduces the size of the exposure device  13 . 
     As illustrated in  FIG. 2 , the developing devices  14  (Y, M, C, and K) each include a housing  140  having an opening and a developer storage chamber and in which the following are housed: a developing roller  141  that carries and transports the developer to a development area facing the photoconductor drum  11 , two stir-transporting members  142  and  143  such as screw augers that transport the developer while stirring the developer and deliver the developer over the developing roller  141 , a layer-thickness-regulating member  144  that regulates the amount of developer (the thickness of the developer layer) to be carried by the developing roller  141 , and so forth. The developing device  14  is supplied with a developing voltage from a power supply device (not illustrated). The developing voltage is applied to a point between the developing roller  141  and the photoconductor drum  11 . The developing roller  141  and the stir-transporting members  142  and  143  each receive power transmitted from a driving device (not illustrated) and thus rotate in a predetermined direction. The developers having the four respective colors (Y, M, C, and K) are each a two-component developer containing a nonmagnetic toner and a magnetic carrier 
     The first-transfer devices  15  (Y, M, C, and K) are each a contact-type transfer device including a first-transfer roller that rotates by being in contact with the periphery of the photoconductor drum  11  with the intermediate transfer belt  21  interposed therebetween and are each supplied with a first-transfer voltage. The first-transfer voltage is a direct-current voltage supplied from a power supply device (not illustrated) and having polarity opposite to the polarity to which the toner is charged. 
     The drum cleaning devices  16  each include a body  160  as a casing a part of which is open, a cleaning plate  161  pressed with a predetermined pressure against the peripheral surface of the photoconductor drum  11  having undergone first transfer in such a manner as to remove residual matter such as toner particles, a delivering member  162  such as a screw auger that collects the matter such as the toner particles removed by the cleaning plate  161  and delivers the matter to a collecting system (not illustrated), and so forth. The cleaning plate  161  is a plate-shaped member (such as a blade) made of rubber or the like. 
     Referring to  FIG. 1 , the intermediate transfer device  20  is positioned above the imaging devices  10  (Y, M, C, and K). Referring to  FIG. 2 , the intermediate transfer device  20  includes the intermediate transfer belt  21  that rotates in the direction indicated by arrow B while passing through first-transfer positions defined between the photoconductor drums  11  and the respective first-transfer devices  15  (first-transfer rollers), a plurality of belt supporting rollers  22  to  25  that rotatably support the intermediate transfer belt  21  from the inner side of the intermediate transfer belt  21  in such a manner as to retain the intermediate transfer belt  21  in a desired state, a second-transfer device  26  as an exemplary second-transfer component provided at a position on the outer peripheral side (the side on which the image is to be carried) of the intermediate transfer belt  21  supported by the belt supporting roller  25 , the second-transfer device  26  second-transferring the toner images on the intermediate transfer belt  21  to a recording sheet  5 , and a belt cleaning device  27  that removes residual matter such as toner particles and paper lint from the outer peripheral surface of the intermediate transfer belt  21  at a position past the second-transfer device  26 . The second-transfer device  26  is provided on the apparatus body  1   a.    
     The intermediate transfer belt  21  is an endless belt made of, for example, synthetic resin such as polyimide resin or polyamide resin in which a resistance regulator or the like such as carbon black is dispersed. The belt supporting roller  22  serves as a driving roller that is rotated by a driving device (not illustrated) as to be described below. The belt supporting roller  23  serves as a surface defining roller that defines the image forming surface of the intermediate transfer belt  21 . The belt supporting roller  24  serves as a tension applying roller that applies a tension to the intermediate transfer belt  21 . The belt supporting roller  25  serves as a backup roller for second transfer. The belt supporting roller  22  also serves as a counter roller that faces a cleaning plate  271  of the belt cleaning device  27 . In the first exemplary embodiment, the belt supporting roller  22  is referred to as driving roller, the belt supporting roller  23  is referred to as surface defining roller, the belt supporting roller  24  is referred to as tension applying roller, and the belt supporting roller  25  is referred to as backup roller. 
     In the monochrome mode, the surface defining roller  23  is moved to a retracted position where the first-transfer rollers  15  (Y, M, and C) for the colors of yellow (Y), magenta (M), and cyan (C) and the intermediate transfer belt  21  are spaced apart from the color photoconductor drums  11  (Y, M, and C). 
     The second-transfer device  26  is a contact-type transfer device including a second-transfer roller that rotates by being in contact with the outer peripheral surface of the intermediate transfer belt  21  at the second-transfer position where the intermediate transfer belt  21  is supported by the backup roller  25  of the intermediate transfer device  20 . The second-transfer device  26  is supplied with a second-transfer voltage. The second-transfer device  26  or the backup roller  25  of the intermediate transfer device  20  is supplied with a direct-current second-transfer voltage from a power supply device (not illustrated). The second-transfer voltage has polarity opposite to or the same as the polarity to which the toners are charged. 
     As illustrated in  FIG. 2 , the belt cleaning device  27  includes a body  270  as a casing a part of which is open, the cleaning plate  271  as an exemplary contact member that is pressed with a predetermined pressure against the peripheral surface of the intermediate transfer belt  21  having undergone second transfer in such a manner as to remove residual matter such as toner particles, a delivering member  272  such as a screw auger that collects the matter such as toner particles removed by the cleaning plate  271  and delivers the matter to a collecting system (not illustrated), and so forth. The cleaning plate  271  is a plate-shaped member (such as a blade) made of rubber or the like. 
     Referring to  FIG. 1 , the fixing device  40  includes a housing (not illustrated) having an introduction port and a discharge port for the recording sheet  5  and that houses the following: a heat-applying rotating member  41  in the form of a roller or a belt that rotates in a direction indicated by the arrow and is heated by a heating component such that the surface thereof is kept at a predetermined temperature, and a pressure-applying rotating member  42  in the form of a roller or a belt that is in contact with the heat-applying rotating member  41  with a predetermined pressure over an area extending substantially in the axial direction of the heat-applying rotating member  41  and rotates by following the heat-applying rotating member  41 , and so forth. In the fixing device  40 , the contact area where the heat-applying rotating member  41  and the pressure-applying rotating member  42  are in contact with each other corresponds to a fixing part where a predetermined fixing process (heating and pressing) is to be performed. 
     The sheet feeding device  30  is positioned below the imaging devices  10  (Y, M, C, and K). The sheet feeding device  30  includes a single sheet storage  31  (or a plurality of sheet storages  31 ) that stores a stack of recording sheets  5  of a predetermined size, kind, or the like; and a delivering device  32  that delivers the recording sheets  5  one by one from the sheet storage  31 . The sheet storage  31  is attached to the apparatus body  1   a  in such a manner as to be, for example, drawable from the front face (the left side face in  FIG. 1 ) of the apparatus body  1   a  toward which the user of the apparatus body  1   a  faces when operating the apparatus body  1   a.    
     The recording sheet  5  is any of the following, for example: thin papers such as plain paper and tracing paper intended for electrophotographic copiers, printers, and the like; over-head-projector (OHP) sheets; and the like. The surface smoothness of the fixed image is improved with the surface smoothness of the recording sheet  5 . In this respect, for example, the following may also be employed: coated paper obtained by coating plain paper with resin or the like; thick paper, such as paper for printing art, with a relatively heavy basis weight; and the like. 
     A sheet feeding path  34  extends between the sheet feeding device  30  and the second-transfer device  26 . The sheet feeding path  34  is provided with a single or plurality of pairs of sheet transporting rollers  33  and transporting guides (not illustrated) with which the recording sheet  5  fed from the sheet feeding device  30  is transported to the second-transfer position. The pair of sheet transporting rollers  33  provided immediately before the second-transfer position in the sheet feeding path  34  serves as, for example, a pair of rollers (registration rollers) that adjusts the timing of transporting the recording sheet  5 . A sheet transport path  35  extends between the second-transfer device  26  and the fixing device  40 . The recording sheet  5  having undergone second transfer and exited from the second-transfer device  26  is transported along the sheet transport path  35  to the fixing device  40 . A sheet output path  38  provided with a pair of sheet output rollers  37  extends near a sheet output port provided in the apparatus body  1   a . The recording sheet  5  having undergone fixing and exited from the fixing device  40  is outputted to a sheet output portion  36  provided at the top of the apparatus body  1   a.    
     To improve the ease of handling of the recording sheet  5  outputted to the sheet output portion  36 , the sheet output portion  36  is inclined such that, in the direction of output of the recording sheet  5 , the downstream end thereof is positioned higher than the upstream end thereof. The intermediate transfer device  20  is inclined along the inclined array of the imaging devices  10  (Y, M, C, and K) in a space provided in the apparatus body  1   a . Specifically, the intermediate transfer device  20  is inclined such that the side thereof nearer to the yellow (Y) imaging device  10 Y is positioned higher than the side thereof nearer to the black (K) imaging device  10 K. The sheet output portion  36  is spaced apart by a predetermined distance from a sheet running area defined above the intermediate transfer belt  21  of the intermediate transfer device  20 . 
     The sheet output portion  36  also serves as an upper covering that is opened and closed when the intermediate transfer device  20  is attached to or detached from the apparatus body  1   a . The sheet output portion  36  is rotatable on a pivot  36   a  defined at the upstream end thereof in the direction of output of the recording sheet  5 . When the intermediate transfer device  20  is attached to or detached from the apparatus body  1   a , the sheet output portion  36  is opened by being rotated upward on the pivot  36   a  as represented by the two-dot chain line in  FIG. 1 . Normally, the sheet output portion  36  also serving as the upper covering is kept closed by a locking mechanism (not illustrated). The sheet output portion  36  is opened by unlocking the locking mechanism when, for example, the intermediate transfer device  20  is attached to or detached from the apparatus body  1   a.    
     A switching gate (not illustrated) that switches the sheet transport path is provided between the fixing device  40  and the pair of sheet output rollers  37 . The direction of rotation of the pair of sheet output rollers  37  is switchable between a normal direction (outputting direction) and a reverse direction. To form images on both sides of the recording sheet  5 , after the trailing end of the recording sheet  5  having an image on one side thereof goes past the switching gate, the direction of rotation of the pair of sheet output rollers  37  is switched from the normal direction (outputting direction) to the reverse direction. Then, the switching gate switches the transport path, and the recording sheet  5  transported in the reverse direction by the pair of sheet output rollers  37  is transported into a duplex transport path  44  extending substantially vertically along the rear face of the apparatus body  1   a . The duplex transport path  44  is provided with pairs of sheet transporting rollers (not illustrated), transport guides (not illustrated), and so forth with which the recording sheet  5  having been turned over is transported to the pair of sheet transporting rollers  33 . 
     Referring to  FIG. 1 , toner cartridges  145  (Y, M, C, and K) as developer containers each extend in a direction orthogonal to the plane of the page and store the developer containing at least the toner to be supplied to a corresponding one of the developing devices  14  (Y, M, C, and K). 
     A control device  100  illustrated in  FIG. 1  generally controls the operation of the image forming apparatus  1 . The control device  100  includes a central processing unit (CPU); a read only memory (ROM); a random access memory (RAM); buses connecting the CPU, the ROM, and the like to one another; a communication interface; and so forth. 
     The apparatus body  1   a  illustrated in  FIG. 1  has a manual feed tray  110  openably provided on the front face thereof. One of recording sheets  5  stacked on the manual feed tray  110  opened to extend substantially horizontally is separated from the others and is delivered by a delivering device  111 . The recording sheet  5  is then transported by pairs of sheet transporting rollers  112  and  113  to the pair of sheet transporting rollers  33 . 
     Operation of Image Forming Apparatus 
     A basic image forming operation performed by the image forming apparatus  1  will now be described. 
     Herein, an operation in the full-color mode will be described in which a full-color image as a combination of toner images in the four respective colors (Y, M, C, and K) is formed by using the four imaging devices  10  (Y, M, C, and K). 
     When the image forming apparatus  1  receives command information requesting an operation of forming (printing) a full-color image from a device such as a user interface or a printer driver (not illustrated), the four imaging devices  10  (Y, M, C, and K), the intermediate transfer device  20 , the second-transfer device  26 , the fixing device  40 , and other relevant devices are activated. 
     In the imaging devices  10  (Y, M, C, and K), as illustrated in  FIGS. 1 and 2 , the photoconductor drums  11  first rotate in the direction indicated by arrow A, and the charging devices  12  charge the surfaces of the photoconductor drums  11  to a predetermined potential of predetermined polarity (in the first exemplary embodiment, negative polarity). Subsequently, the exposure device  13  applies the laser beams LB-Y, LB-M, LB-C, and LB-K to the charged surfaces of the photoconductor drums  11 . The laser beams LB-Y, LB-M, LB-C, and LB-K are generated from an image signal obtained through the conversion of image information inputted to the image forming apparatus  1  into pieces of information on the respective color components (Y, M, C, and K). Thus, electrostatic latent images for the respective color components are formed with a predetermined potential difference produced on the surfaces of the photoconductor drums  11 . 
     Subsequently, in the imaging devices  10  (Y, M, C, and K), the toners having the respective colors (Y, M, C, and K) and charged to the predetermined polarity (negative polarity) are supplied from the developing rollers  141  to the electrostatic latent images for the respective color components on the photoconductor drums  11 . The electrostatic latent images electrostatically attract the toners and are thus developed. In this developing process, the electrostatic latent images for the respective color components on the respective photoconductor drums  11  are visualized with the toners having the respective colors into toner images having the four respective colors (Y, M, C, and K). 
     Subsequently, the toner images in the respective colors on the photoconductor drums  11  of the imaging devices  10  (Y, M, C, and K) are transported to the respective first-transfer positions. Then, the first-transfer devices  15  (Y, M, C, and K) first-transfer the toner images in the respective colors to the intermediate transfer belt  21  of the intermediate transfer device  20  such that the toner images are superposed one on top of another, the intermediate transfer belt  21  being rotating in the direction indicated by arrow B. 
     In the imaging devices  10  (Y, M, C, and K) having undergone first transfer, the drum cleaning devices  16  clean the surfaces of the photoconductor drums  11  by scraping off residual matter adhered to the photoconductor drums  11 . Thus, the imaging devices  10  (Y, M, C, and K) are ready for the next imaging operation. 
     Subsequently, in the intermediate transfer device  20 , the intermediate transfer belt  21  carrying the toner images first-transferred thereto rotates and transports the toner images to the second-transfer position. Meanwhile, in the sheet feeding device  30 , a predetermined recording sheet  5  is fed into the sheet feeding path  34  synchronously with the imaging operation. In the sheet feeding path  34 , the pair of sheet transporting rollers  33  as the pair of registration rollers supplies the recording sheet  5  to the second-transfer position synchronously with the timing of transfer. 
     At the second-transfer position, the second-transfer device  26  second-transfers the set of toner images on the intermediate transfer belt  21  to the recording sheet  5 . In the intermediate transfer device  20  having undergone second transfer, the belt cleaning device  27  removes residual matter such as toner particles from the surface of the intermediate transfer belt  21  having undergone second transfer. 
     Subsequently, the recording sheet  5  now having the set of toner images second-transferred thereto is released from the intermediate transfer belt  21  and is then transported along the sheet transport path  35  to the fixing device  40 . In the fixing device  40 , the recording sheet  5  having undergone second transfer is made to pass through the contact area defined between the heat-applying rotating member  41  and the pressure-applying rotating member  42  that are rotating. Thus, the predetermined fixing process (heating and pressing) is performed on the set of unfixed toner images, whereby the set of toner images are fixed to the recording sheet  5 . Lastly, if the image forming operation is required for only one side of the recording sheet  5 , the recording sheet  5  having undergone fixing is outputted by the pair of sheet output rollers  37  to the sheet output portion  36  at the top of the apparatus body  1   a.    
     Through the above process, a recording sheet  5  having a full-color image as a combination of toner images in the four respective colors is outputted. 
     If only the black (K) imaging device  10 K is activated, a recording sheet  5  having a monochrome image is outputted. 
     Intermediate Transfer Unit 
     Referring to  FIG. 3 , the intermediate transfer device  20  according to the first exemplary embodiment is regarded as an intermediate transfer unit  200 , which is an exemplary attaching object. The intermediate transfer unit  200  is an assembly of various members forming the intermediate transfer device  20  and is independently attachable to and detachable from the apparatus body  1   a  of the image forming apparatus  1 . 
     As illustrated in  FIGS. 2 and 3 , the intermediate transfer unit  200  includes left and right side frames  201  and  202 , by which the driving roller  22 , the surface defining roller  23 , the tension applying roller  24 , and the backup roller  25  are rotatably supported. The left and right side frames  201  and  202  are each a plate-like or frame-like member having a long triangular side-view shape, which is substantially similar to the locus of rotation of the intermediate transfer belt  21 . The left and right side frames  201  and  202  are provided with a plurality of guide pins  203 ,  204 , and others. When the intermediate transfer unit  200  is attached to or detached from the apparatus body  1   a , the guide pins  203 ,  204 , and others position and guide the intermediate transfer unit  200  with reference to guide grooves (not illustrated) provided in the apparatus body  1   a . The left and right side frames  201  and  202  are integrated with the belt cleaning device  27 . 
     Referring to  FIG. 1 , when the intermediate transfer unit  200  is set at a predetermined operating position defined in the apparatus body  1   a  of the image forming apparatus  1 , a driving force is allowed to be transmitted from the apparatus body  1   a  to the intermediate transfer unit  200 . Furthermore, the first-transfer devices  15  (Y, M, C, and K) are allowed to be energized. 
     Configuration of Driving-Force-Transmitting Mechanism 
     Referring to  FIG. 4 , the apparatus body  1   a  of the image forming apparatus  1  includes a driving-force-transmitting mechanism  50  at a position corresponding to one axial end of the driving roller  22  of the intermediate transfer unit  200 . When the intermediate transfer unit  200  is attached to or detached from the apparatus body  1   a , the driving-force-transmitting mechanism  50  enables or disables the transmission of the driving force to the driving roller  22  of the intermediate transfer unit  200 . Note that part of the driving-force-transmitting mechanism  50  is included in the intermediate transfer unit  200 . 
     Referring to  FIG. 5 , the driving-force-transmitting mechanism  50  includes an intermediate-transfer-member driving gear  51  as an exemplary driving-force-transmitting component (driving gear) provided on the apparatus body  1   a  and that rotates the driving roller  22  of the intermediate transfer unit  200 , and an intermediate-transfer-member master coupling  52  as another exemplary driving-force-transmitting component provided on the apparatus body  1   a  and that is movable in an axial direction C of the intermediate-transfer-member driving gear  51 . 
     Referring to  FIG. 4 , a right frame  120  of the apparatus body  1   a  has a pair of guide portions  121  and  122  on the inner surface thereof. The guide portions  121  and  122  each have a rectangular sectional shape and extend in directions EF in which the intermediate transfer unit  200  is attached and detached (hereinafter referred to as the attaching and detaching directions EF of the intermediate transfer unit  200 ). The guide portions  121  and  122  extend parallel to each other with the intermediate-transfer-member master coupling  52  of the driving-force-transmitting mechanism  50  positioned therebetween in the vertical direction. Herein, the direction in which the intermediate transfer unit  200  is attached is denoted by E, and the direction in which the intermediate transfer unit  200  is detached is denoted by F. 
     The right frame  120  of the apparatus body  1   a  further has protecting portions  123  and  124  on the inner surface thereof. The protecting portions  123  and  124  each have a substantially cubic shape and are provided on both sides of the intermediate-transfer-member master coupling  52  in the attaching and detaching directions EF in such a manner as to protect the intermediate-transfer-member master coupling  52 . The inner surfaces of the protecting portions  123  and  124  are curved in conformity with the outline of the intermediate-transfer-member master coupling  52 . Note that  FIG. 4  illustrates only part of the right frame  120  of the apparatus body  1   a , as a matter of convenience. 
     Referring to  FIG. 5 , the intermediate-transfer-member driving gear  51  is an integral body including a cylindrical shaft portion  511  projecting from the center of one side thereof. The intermediate-transfer-member master coupling  52  is fitted to the shaft portion  511  in such a manner as to be movable in the axial direction C on the one side of the intermediate-transfer-member driving gear  51 . The intermediate-transfer-member master coupling  52  is an integral body including a cylindrical first gear portion  521  having involute spur gear teeth on the outer periphery thereof, and a cylindrical second gear portion  522  provided at the distal end of the first gear portion  521  and having a smaller outside diameter than the first gear portion  521 , the second gear portion  522  having involute spur gear teeth on the outer periphery thereof. The second gear portion  522  includes a tapered part  522   a  at the distal end thereof. The intermediate-transfer-member master coupling  52  further includes a contact portion  523  as an exemplary sliding member having an annular shape with a predetermined outside diameter in such a manner as to project radially outward from a position between the first gear portion  521  and the second gear portion  522 . The contact portion  523  may be either integrally included in or separately fixed to the intermediate-transfer-member master coupling  52 . The contact portion  523  (hereinafter also referred to as “sliding portion  523 ”) includes a tapered part  523   a  at the outer peripheral end thereof. The tapered part  523   a  is inclined such that the outside diameter increases toward the intermediate-transfer-member driving gear  51  in the thickness wise direction thereof. 
     Referring to  FIG. 6 , the intermediate-transfer-member driving gear  51  is rotatably supported at the shaft portion  511  thereof by a bearing portion  125  included in the right frame  120  of the apparatus body  1   a . The intermediate-transfer-member driving gear  51  receives a rotational driving force transmitted thereto through a single or plurality of transmission gears from a driving motor as a drive source (not illustrated) provided in the apparatus body  1   a.    
     Referring to  FIG. 5 , the shaft portion  511  of the intermediate-transfer-member driving gear  51  includes a first internal gear portion  512  forming an involute spur gear that is in mesh with the first gear portion  521  of the intermediate-transfer-member master coupling  52 . In a state where the rotational driving force is transmitted to the intermediate-transfer-member master coupling  52  with the first gear portion  521  being in mesh with the first internal gear portion  512  of the intermediate-transfer-member driving gear  51 , the intermediate-transfer-member master coupling  52  is movable in the axial direction C. Referring to  FIG. 6 , the second gear portion  522  of the intermediate-transfer-member master coupling  52  is allowed to come into mesh with (be coupled to) and to be spaced apart from an intermediate-transfer-member slave coupling  53  as an exemplary driving-force-transmitting component provided on the intermediate transfer unit  200 . The intermediate-transfer-member slave coupling  53  is provided at one end, in the axial direction C, of the driving roller  22  of the intermediate transfer unit  200 . 
     The intermediate-transfer-member slave coupling  53  includes a coupling body  531  and a third gear portion  533 . The coupling body  531  has a cylindrical shape with a relatively large outside diameter and is fixed to a rotating shaft  22   a  of the driving roller  22 . The third gear portion  533  extends outward in the axial direction C from a partition  532  provided in the coupling body  531 . The third gear portion  533  has a cylindrical shape with a relatively small outside diameter. The third gear portion  533  includes a second internal gear portion  533   a  forming an involute spur gear provided on the inner periphery thereof. The third gear portion  533  includes a tapered part  533   b  at the distal end thereof. The tapered part  533   b  is inclined inward. 
     The intermediate-transfer-member master coupling  52  and the intermediate-transfer-member slave coupling  53  are not limited to the one including the first and second gear portions  521  and  522  forming involute gears and the one including the third gear portion  533  forming an involute gear. The intermediate transfer belt  21  that is rotated by the driving roller  22  to which the rotational driving force is transmitted through the intermediate-transfer-member master coupling  52  and the intermediate-transfer-member slave coupling  53  is a member that directly affects image quality. Therefore, the rotation accuracy of the intermediate-transfer-member master coupling  52  and the intermediate-transfer-member slave coupling  53  may be as high as possible with less variation in speed and the like. The intermediate-transfer-member master coupling  52  including the first and second gear portions  521  and  522  forming involute gears and the intermediate-transfer-member slave coupling  53  including the third gear portion  533  forming an involute gear are capable of transmitting the rotational driving force to the driving roller  22  with relatively high rotation accuracy. 
     As illustrated in  FIG. 6 , the intermediate-transfer-member master coupling  52  is urged in a direction of projection thereof by a coil spring  54  as an exemplary urging component provided between the internal end face of the shaft portion  511  of the intermediate-transfer-member driving gear  51  and the internal end face of the first gear portion  521 . The amount of projection of the intermediate-transfer-member master coupling  52  in the axial direction C of the intermediate-transfer-member driving gear  51  is limited by a fixed shaft  55  fixed to the shaft portion  511  of the intermediate-transfer-member driving gear  51 . Note that  FIG. 6  illustrates a state where the amount of projection of the intermediate-transfer-member master coupling  52  is maximum. 
     The first gear portion  521  of the intermediate-transfer-member master coupling  52  projecting by the maximum amount is in mesh with the first internal gear portion  512  of the intermediate-transfer-member driving gear  51  by a predetermined meshing length L 1  in the axial direction C. Likewise, the second gear portion  522  of the intermediate-transfer-member master coupling  52  projecting by the maximum amount is in mesh with the second internal gear portion  533   a  of the intermediate-transfer-member slave coupling  53  by a predetermined meshing length L 2  in the axial direction C. Considering the effective transmission of the driving force from the intermediate-transfer-member driving gear  51  to the intermediate-transfer-member slave coupling  53 , the meshing lengths L 1  and L 2  may each be a certain length or greater. However, if the meshing lengths L 1  and L 2  are too long, the detaching of the intermediate transfer unit  200  from the apparatus body  1   a  of the image forming apparatus  1  may be hindered. 
     According to the first exemplary embodiment, as to be described below, the driving-force-transmitting mechanism  50  is configured to assuredly and accurately transmit the rotational driving force from the intermediate-transfer-member driving gear  51  to the intermediate-transfer-member slave coupling  53  and to avoid or prevent the hindrance to the detaching of the intermediate transfer unit  200  from the apparatus body  1   a  of the image forming apparatus  1 . 
     Referring to  FIG. 7 , the intermediate transfer unit  200  is provided with the intermediate-transfer-member slave coupling  53  as the driving-force-transmitting component provided on the intermediate transfer unit  200  so as to rotate the driving roller  22 . The intermediate-transfer-member slave coupling  53  is provided at one axial end of the driving roller  22 , as described above, and projects laterally from the right side frame  202 . The intermediate-transfer-member slave coupling  53  is one of the elements of the driving-force-transmitting mechanism  50 . The rotational driving force of the intermediate-transfer-member slave coupling  53  is also transmitted to the delivering member  272  (see  FIG. 2 ) of the belt cleaning device  27  through transmission gears  205  and  206  illustrated in  FIG. 7 . Needless to say, the delivering member  272  of the belt cleaning device  27  may be rotated by another drive source. 
     Referring to  FIG. 6 , when the intermediate-transfer-member master coupling  52  moves to project outward (toward the intermediate transfer unit  200 ) in the axial direction C, the third gear portion  533  of the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200  comes into mesh with the second gear portion  522  of the intermediate-transfer-member master coupling  52 , whereby the transmission of the rotational driving force is enabled. The gear portions such as the first gear portion  521  of the intermediate-transfer-member master coupling  52  and the first internal gear portion  512  of the intermediate-transfer-member driving gear  51  are involute gears, between which backlash of a predetermined degree is provided. Therefore, when the second internal gear portion  533   a  of the intermediate-transfer-member slave coupling  53  and the second gear portion  522  of the intermediate-transfer-member master coupling  52  come into mesh with each other, the second gear portion  522  and the first gear portion  521  of the intermediate-transfer-member master coupling  52  are slightly tilted in the axial direction C with respect to the first internal gear portion  512  of the intermediate-transfer-member driving gear  51 . Hence, with the aid of the tapered parts  522   a  and  533   b , the meshing is achieved smoothly. 
     The driving-force-transmitting mechanism  50  according to the first exemplary embodiment includes a plurality of operating components. When the intermediate transfer unit  200  is attached to or detached from the apparatus body  1   a  of the image forming apparatus  1 , the operating components operate sequentially with delays in such a manner as to move the intermediate-transfer-member master coupling  52  as an exemplary driving-force-transmitting component in the axial direction C intersecting the attaching and detaching directions EF of the intermediate transfer unit  200 . Consequently, the transmission of the driving force from the apparatus body  1   a  to the intermediate transfer unit  200  is enabled or disabled. 
     Specifically, referring to  FIGS. 3 and 8 , the driving-force-transmitting mechanism  50  according to the first exemplary embodiment includes a grip member  56  as an exemplary first operating component (a first operating member) that is movable in the attaching and detaching directions EF of the intermediate transfer unit  200 . The first grip member  56  is provided at the downstream end of the intermediate transfer unit  200  in the detaching direction F (the upstream end in the attaching direction E). 
     The attaching and detaching directions EF of the intermediate transfer unit  200  literally refer to the directions in which the intermediate transfer unit  200  is attached to and detached from the apparatus body  1   a  of the image forming apparatus  1 . Note that the attaching and detaching directions EF of the intermediate transfer unit  200  are not defined to be at a certain angle with respect to the apparatus body  1   a  of the image forming apparatus  1  and are directions in which the intermediate transfer unit  200  moves when attached to or detached from the apparatus body  1   a  of the image forming apparatus  1 . In the state where the transmission of the driving force is disabled by the driving-force-transmitting mechanism  50 , the attaching and detaching directions EF each vary within a certain range (angle) in the vertical direction. 
     The grip member  56  is provided on the right side frame  202  of the intermediate transfer unit  200  with the aid of a supporting member (not illustrated) in such a manner as to be movable in the attaching and detaching directions EF. Referring to  FIGS. 8 and 9 , the grip member  56  is a flat plate-like member having a substantially rectangular side-view shape with one lengthwise end thereof being semicircular. The grip member  56  includes a grip portion  562  at the one lengthwise end thereof. The grip portion  562  has a short cylindrical shape with an opening  561  into which an operator who is attaching or detaching the intermediate transfer unit  200  inserts his/her finger to grip the grip member  56 . Referring to  FIG. 3 , the left side frame  201  of the intermediate transfer unit  200  is provided with a left grip portion  207  fixed at a position corresponding to the grip member  56 . Note that the left grip portion  207  only provides a grip and has a different function from the grip member  56 . 
     Referring to  FIGS. 8 and 9 , the grip member  56  has an oblong insertion path  563  defined by a substantially U-shaped line in side view at the other lengthwise end thereof opposite the opening  561 . The second gear portion  522  of the intermediate-transfer-member master coupling  52  is to be inserted into the insertion path  563  and to move therein in the attaching and detaching directions EF. Furthermore, the grip member  56  includes first sloping portions  564  as exemplary first slopes at the other lengthwise end thereof. The first sloping portions  564  are provided on two respective sides of the insertion path  563  and are spaced apart from each other by a predetermined distance along the front surface of the grip member  56  in a direction intersecting the attaching and detaching directions EF. The predetermined distance is set to a value enough for the insertion of the second gear portion  522  of the intermediate-transfer-member master coupling  52 . Each of the first sloping portions  564  starts to project from a position on the front surface (the surface facing the inner surface of the apparatus body  1   a ) of the grip member  56  that is at a predetermined distance from the other lengthwise end, extends at a predetermined angle toward the inner surface of the apparatus body  1   a  up to a summit  564   a  at the other lengthwise end of the grip member  56 , and descends from a position past the summit  564   a  in such a manner as to form a vertical surface intersecting the front surface of the grip member  56 , thereby forming a substantially right-triangular shape in plan view. The summits  564   a  of the first sloping portions  564  are at a predetermined height H (see  FIG. 6 ) from the back surface (the surface facing the intermediate transfer unit  200 ) of the grip member  56 . The first sloping portions  564  are connected to each other with a connecting portion  567  provided at the other lengthwise end of the grip member  56  and being thinner than the grip member  56 . 
     The grip member  56  further includes rectangular guiding portions  565  at the other lengthwise end thereof. The guiding portions  565  guide the grip member  56  to move in the attaching and detaching directions EF relative to the right frame  120  of the apparatus body  1   a . The guiding portions  565  each project outward from the respective first sloping portions  564  in a direction intersecting the attaching and detaching directions EF. As illustrated in  FIG. 9 , the guiding portions  565  come into contact with the pair of guide portions  121  and  122 , respectively, provided on the inner surface of the right frame  120  of the apparatus body  1   a , whereby the grip member  56  is slidable in the attaching and detaching directions EF. The first sloping portions  564  are guided at the outer surfaces thereof by the inner surfaces of the pair of guide portions  121  and  122 , respectively, thereby being assuredly movable in the attaching and detaching directions EF. 
     The driving-force-transmitting mechanism  50  according to the first exemplary embodiment further includes an operating member  57  as an exemplary second operating component (a second operating member). The operating member  57  is moved with a delay from the grip member  56  such that the intermediate transfer unit  200  is detached from the apparatus body  1   a . The operating member  57  is provided for keeping a state where the transmission of the rotational driving force is disabled over a period from before the intermediate transfer unit  200  starts to be detached from the apparatus body  1   a  until the detaching is complete. 
     Referring to  FIG. 3 , the operating member  57  is fixed to the right side frame  202  of the intermediate transfer unit  200  with a fixing component (not illustrated) or is integrated with the right side frame  202 . 
     Referring to  FIGS. 8 and 9 , the operating member  57  is placed on the back surface (the surface facing the intermediate transfer unit  200 ) of the grip member  56  in such a manner as to be slidable in the attaching and detaching directions EF. The operating member  57  is a flat plate-like member having a substantially rectangular oblong front-view shape with a predetermined thickness. The operating member  57  has a circular insertion hole  571  at one lengthwise end thereof. The one lengthwise end of the operating member  57  has a semicircular outline similar to the insertion hole  571 . Referring to  FIG. 6 , the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200  is inserted into the insertion hole  571  of the operating member  57 . The intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200  may be fixed in the insertion hole  571  of the operating member  57 . 
     Referring to  FIG. 8 , the operating member  57  includes second sloping portions  572  as exemplary second slopes at the other lengthwise end thereof. The second sloping portions  572  are provided on two respective outer sides of the front surface of the operating member  57  in a direction intersecting the attaching and detaching directions EF. The direction of slope of the second sloping portions  572  is opposite to the direction of slope of the first sloping portions  564  of the grip member  56 . That is, the first sloping portions  564  of the grip member  56  are each inclined in the attaching direction E such that the upstream side thereof is lower than the downstream side thereof. In contrast, the second sloping portions  572  of the operating member  57  are each inclined in the attaching direction E such that the upstream side thereof is higher than the downstream side thereof. 
     Each of the second sloping portions  572  starts to project from a position on the front surface (the surface facing the inner surface of the apparatus body  1   a ) of the operating member  57  that is at the other lengthwise end, extends at a predetermined angle toward the inner surface of the apparatus body  1   a  up to a summit  572   a  at a position spaced apart from the other lengthwise end of the operating member  57 , and descends from a position past the summit  572   a  in such a manner as to form a vertical surface, thereby forming a substantially right-triangular shape in plan view. The summits  572   a  of the second sloping portions  572  are at a predetermined height H (see  FIG. 6 ) from the front surface (the surface facing the inner surface of the apparatus body  1   a ) of the operating member  57 . As described above, the operating member  57  is placed on the back surface of the grip member  56 . Therefore, as illustrated in  FIG. 6 , the summits  564   a  of the first sloping portions  564  of the grip member  56  and the summits  572   a  of the second sloping portions  572  of the operating member  57  are at the same position defined by the respective heights H. Referring to  FIG. 8 , the operating member  57  has a notch  573  at the other lengthwise end thereof. The notch  573  is provided between the second sloping portions  572  and thus separates the tips of the second sloping portions  572  from each other. The second sloping portions  572  are spaced apart from each other by a predetermined distance along the front surface of the operating member  57  in a direction intersecting the attaching and detaching directions EF. The predetermined distance is equal to the distance between the first sloping portions  564  and is set to a value enough for the insertion of the second gear portion  522  of the intermediate-transfer-member master coupling  52 . 
       FIG. 10  is a perspective view of the grip member  56  and the operating member  57 , as with  FIG. 9 , in a state where the intermediate transfer unit  200  has been attached to the apparatus body  1   a  of the image forming apparatus  1 . 
       FIG. 10  illustrates the grip member  56  moved to a rearmost position thereof in the attaching direction E of the intermediate transfer unit  200 . In this state, the vertical surfaces of the first sloping portions  564  of the grip member  56  are in contact with the vertical surfaces of the second sloping portions  572  of the operating member  57 , respectively. 
     Referring to  FIG. 9 , the operating member  57  has grooves  574  extending in the lengthwise direction thereof. The grip member  56  is held in the grooves  574  in such a manner as to be movable in the attaching and detaching directions EF. Specifically, projections  566  provided on the back surface of the grip member  56  are slidably fitted in the respective grooves  574  of the operating member  57 . 
     Referring to  FIGS. 8 and 9 , when the intermediate transfer unit  200  is attached to or detached from the apparatus body  1   a  of the image forming apparatus  1 , particularly when the intermediate transfer unit  200  is detached from the apparatus body  1   a  of the image forming apparatus  1 , the operator grips the grip portion  562  of the grip member  56  with his/her finger inserted into the opening  561  and pulls out the grip member  56  in the detaching direction F. 
     Thus, only the grip member  56  is moved in the detaching direction F with the projections  566  thereof moving along the grooves  574  of the operating member  57 . When the projections  566  of the grip member  56  come into contact with the lengthwise ends of the respective grooves  574  of the operating member  57 , the operating member  57  starts to move in the detaching direction F with a delay as a period for the projections  566  of the grip member  56  to move in the detaching direction F along the grooves  574  of the operating member  57 . 
     The term “delay” used herein refers to a period of time elapsed from when the grip member  56  starts to move in the detaching direction F until when the operating member  57  starts to move. 
     The operating member  57  is fixed to the right side frame  202  of the intermediate transfer unit  200 . Therefore, when the operating member  57  starts to move in the detaching direction F, both the operating member  57  and the intermediate transfer unit  200  move in the detaching direction F. 
     The above “delay” has a technical meaning particularly when the intermediate transfer unit  200  is detached from the apparatus body  1   a  of the image forming apparatus  1 . 
     Specifically, at the beginning of the operation of detaching the intermediate transfer unit  200  from the apparatus body  1   a  of the image forming apparatus  1 , the intermediate-transfer-member master coupling  52  and the intermediate-transfer-member slave coupling  53  of the driving-force-transmitting mechanism  50  are in mesh with each other. 
     If the grip member  56  and the operating member  57  are integrated with each other, referring to  FIG. 6  for convenience of description, the grip member  56  and the operating member  57  start to move simultaneously, not sequentially with a delay. Accordingly, the first sloping portions  564  of the grip member  56  push down the sliding portion  523  of the intermediate-transfer-member master coupling  52 . Therefore, the second gear portion  522  of the intermediate-transfer-member master coupling  52  moves away from the intermediate-transfer-member slave coupling  53 . 
     In the case where the grip member  56  and the operating member  57  are integrated with each other and there is no delay between the movements of the grip member  56  and the operating member  57 , the above process proceeds as follows. The intermediate-transfer-member slave coupling  53  fitted in the insertion hole  571  of the operating member  57  integrated with the grip member  56  moves in the detaching direction F. With the movement of the intermediate-transfer-member slave coupling  53  in the detaching direction F, the second gear portion  522  of the intermediate-transfer-member master coupling  52  moves away from the intermediate-transfer-member slave coupling  53  while receiving a pushing force in the detaching direction F exerted by the intermediate-transfer-member slave coupling  53 . 
     That is, if the grip member  56  and the operating member  57  are integrated with each other, the intermediate-transfer-member master coupling  52  moves away from the intermediate-transfer-member slave coupling  53  while being pushed in the detaching direction F by the intermediate-transfer-member slave coupling  53 . Such a situation leads to a technical problem that the smooth decoupling of the intermediate-transfer-member master coupling  52  may be hindered. 
     The problem of hindrance to the smooth decoupling of the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  from the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200  is pronounced particularly if, as described above, the meshing lengths L 1  and L 2  between the intermediate-transfer-member master coupling  52  and the intermediate-transfer-member slave coupling  53  are set to relatively large values so as to assuredly transmit the rotational driving force from the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  to the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 . 
     Hence, the driving-force-transmitting mechanism  50  according to the first exemplary embodiment employs the grip member  56  and the operating member  57  that are separate from each other as described above. Moreover, the grip member  56  and the operating member  57  are configured to move sequentially with a delay at the time of attaching or detaching the intermediate transfer unit  200 . 
     To detach the intermediate transfer unit  200  from the apparatus body  1   a  of the image forming apparatus  1 , the grip member  56  first causes the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  to move away from the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the rotational driving force is disabled. 
     At the beginning of the operation of detaching the intermediate transfer unit  200  from the apparatus body  1   a , the operating member  57  keeps the state where the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  is spaced apart from the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the rotational driving force is disabled. Then, the operating member  57  starts to move in the detaching direction F with a delay from the grip member  56 . Thus, the intermediate transfer unit  200  is detached from the apparatus body  1   a , and the operating member  57  restores the state where the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  is made to project to enable the transmission of the rotational driving force. 
     On the other hand, at the beginning of the operation of attaching the intermediate transfer unit  200  to the apparatus body  1   a , the second sloping portions  572  of the operating member  57  cause the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  to move away from the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the rotational driving force is disabled. 
     Then, at the end of the operation of attaching the intermediate transfer unit  200  to the apparatus body  1   a , the first sloping portions  564  of the grip member  56  move the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  to come into mesh with the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the rotational driving force is enabled. 
     In the operation of causing the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  to come into mesh with the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200  in attaching the intermediate transfer unit  200 , referring to  FIG. 6 , the driving-force-transmitting mechanism  50  operates such that the force of pushing down the sliding portion  523  of the intermediate-transfer-member master coupling  52  by the first sloping portions  564  of the grip member  56  is removed. Therefore, even if the grip member  56  and the operating member  57  move simultaneously, no problem arises. 
     Operation of Driving-Force-Transmitting Mechanism 
     In the image forming apparatus  1  illustrated in  FIG. 1  to which the driving-force-transmitting mechanism  50  according to the first exemplary embodiment is applied, an operation of attaching or detaching the intermediate transfer unit  200  to or from the apparatus body  1   a  of the image forming apparatus  1  is performed in situations such as when the maintenance of the intermediate transfer unit  200  is to be performed or when the intermediate transfer unit  200  is replaced with a new one. 
     To detach the intermediate transfer unit  200  from the apparatus body  1   a  of the image forming apparatus  1 , the sheet output portion  36  also serving as the upper covering provided at the top of the apparatus body  1   a  is opened. To open the sheet output portion  36 , the sheet output portion  36  is rotated clockwise on the pivot  36   a  defined at the upstream end thereof in the direction of output of the recording sheet  5 , by moving the downstream end thereof in the direction of output of the recording sheet  5 . 
     Referring to  FIG. 1 , when the sheet output portion  36  is opened, the end of the intermediate transfer unit  200  where the driving roller  22  is provided is exposed to the outside. 
     Referring to  FIG. 3 , the operator pulls only the grip member  56  by inserting his/her fingers into the opening  561  of the grip member  56  and into the grip member  207  at the downstream end of the intermediate transfer unit  200  in the detaching direction F. 
     When the operator pulls only the grip member  56 , referring now to  FIGS. 11 and 12 , the first sloping portions  564  of the grip member  56  push down the sliding portion  523  of the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a , and the second gear portion  522  of the intermediate-transfer-member master coupling  52  moves away from the third gear portion  533  of the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the driving force is disabled. 
     Subsequently, the operator further pulls the grip member  56  in the detaching direction F. Then, the projections  566  of the grip member  56  come into contact with the ends of the respective grooves  574  of the operating member  57 , whereby the operating member  57  is pulled in the detaching direction F. Since the operating member  57  is fixed to the intermediate transfer unit  200 , the intermediate transfer unit  200  is also pulled in the detaching direction F. 
     Referring to  FIGS. 11 and 12 , the operation of pulling the operating member  57  together with the intermediate transfer unit  200  in the detaching direction F disables the second sloping portions  572  of the operating member  57  from pushing down the sliding portion  523  of the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a , whereby the second gear portion  522  of the intermediate-transfer-member master coupling  52  moves in the direction of projection thereof. 
     On the other hand, when the intermediate transfer unit  200  is attached to the apparatus body  1   a  of the image forming apparatus  1 , the operator keeps holding the intermediate transfer unit  200  during the process of setting the intermediate transfer unit  200  into the apparatus body  1   a.    
     When the operator moves the intermediate transfer unit  200  into the apparatus body  1   a  in the attaching direction E, the second sloping portions  572  of the operating member  57  fixed to the intermediate transfer unit  200  push down the sliding portion  523  of the intermediate-transfer-member master coupling  52 , whereby the second gear portion  522  of the intermediate-transfer-member master coupling  52  moves away from the third gear portion  533  of the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 . 
     In this state, the first sloping portions  564  of the grip member  56  may be in contact with the second sloping portions  572  of the operating member  57  as illustrated in  FIG. 10 . Alternatively, the first sloping portions  564  may be spaced apart from the second sloping portions  572  of the operating member  57  as illustrated in  FIG. 12 . 
     While the operation of attaching the intermediate transfer unit  200  to the apparatus body  1   a  is performed, the operator keeps gripping the grip member  56  and the grip member  207  illustrated in  FIG. 3 . Therefore, the first sloping portions  564  of the grip member  56  are normally in contact with the second sloping portions  572  of the operating member  57 . 
     Subsequently, the operator pushes the intermediate transfer unit  200  to the operating position defined in the apparatus body  1   a , whereby the movement of pushing down the sliding portion  523  of the intermediate-transfer-member master coupling  52  by using the first sloping portions  564  of the grip member  56  is disabled. Consequently, as illustrated in  FIG. 6 , the intermediate-transfer-member master coupling  52  provided on the apparatus body  1   a  moves in the direction of projection thereof, and the second gear portion  522  of the intermediate-transfer-member master coupling  52  comes into mesh with the third gear portion  533  of the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the driving-force-transmitting mechanism  50  falls into the state where the transmission of the rotational driving force is enabled. 
     Thus, in the image forming apparatus  1  to which the driving-force-transmitting mechanism  50  according to the first exemplary embodiment is applied, when the intermediate transfer unit  200  is attached to or detached from the apparatus body  1   a , particularly when the intermediate transfer unit  20  is detached from the apparatus body  1   a , the grip member  56  is moved in the detaching direction F of the intermediate transfer unit  200 . 
     When the grip member  56  is moved in the detaching direction F of the intermediate transfer unit  200  to detach the intermediate transfer unit  200  from the apparatus body  1   a , the first sloping portions  564  of the grip member  56  push down the sliding portion  523  of the intermediate-transfer-member master coupling  52  in such a manner as to move the second gear portion  522  of the intermediate-transfer-member master coupling  52  away from the third gear portion  533  of the intermediate-transfer-member slave coupling  53  provided on the intermediate transfer unit  200 , whereby the transmission of the driving force is disabled. 
     Subsequently, when the intermediate transfer unit  200  is further moved in the detaching direction F from the apparatus body  1   a , the intermediate transfer unit  200  is detached from the apparatus body  1   a  while the operating member  57  moving with a delay from the grip member  56  keeps disabling the driving-force-transmitting mechanism  50  from transmitting the driving force. 
     Consequently, in the driving-force-transmitting mechanism  50  according to the first exemplary embodiment, the intermediate-transfer-member master coupling  52  moves away from the intermediate-transfer-member slave coupling  53  without being pushed by the intermediate-transfer-member slave coupling  53  in the detaching direction F. 
     Second Exemplary Embodiment 
       FIG. 13  illustrates an outline of an image forming apparatus to which a driving-force-transmitting mechanism according to a second exemplary embodiment of the present disclosure is applied. Elements that are the same as those of the image forming apparatus according to the first exemplary embodiment are denoted by corresponding ones of the reference numerals used in the first exemplary embodiment, and redundant description of those elements is omitted. 
     The image forming apparatus to which the driving-force-transmitting mechanism according to the second exemplary embodiment is applied includes an apparatus body, an image forming unit detachably provided on the apparatus body and to be driven by receiving a driving force transmitted from the apparatus body, and the driving-force-transmitting mechanism, which transmits the driving force to the image forming unit from a drive source provided in the apparatus body. 
     Specifically, referring to  FIG. 13 , an image forming apparatus  1  to which the driving-force-transmitting mechanism according to the second exemplary embodiment is applied is a monochrome printer including only a monochrome (black) imaging device  10 . 
     The image forming apparatus  1  includes the monochrome (black) imaging device  10  that forms an image by using a photoconductor drum  11  and toner-image-forming components provided therearound. Referring to  FIG. 14 , the imaging device  10  is an integral body provided as an image forming unit  300  that includes the photoconductor drum  11 , a charging device  12 , an exposure device  13 , a developing device  14 , a drum cleaning device  16 , and a toner cartridge  145 . The image forming unit  300  is independently attachable to and detachable from an apparatus body  1   a  of the image forming apparatus  1 . 
     Referring to  FIG. 13 , the image forming unit  300  is attached to or detached from the apparatus body  1   a  with a covering  1   b  provided on the front face (on the left side face in  FIG. 13 ) of the apparatus body  1   a  being open. 
     As illustrated in  FIG. 14 , the image forming unit  300  includes a unit body  301 , on a side face of which a photoconductor slave coupling  303  that transmits a rotational driving force from the apparatus body  1   a  is provided to rotate the photoconductor drum  11 . The photoconductor slave coupling  303  corresponds to the intermediate-transfer-member slave coupling  53  according to the first exemplary embodiment. 
     The image forming unit  300  is further provided with a grip member  56  and an operating member  57  to be gripped by the operator with his/her fingers hooked thereon when the image forming unit  300  is attached to or detached from the apparatus body  1   a  of the image forming apparatus  1 . The grip member  56  and the operating member  57  are provided at the upstream end of the image forming unit  300  in the attaching direction E, i.e., the end nearer to the covering  1   b . The grip member  56  projects from the upstream end, in the attaching direction E, of the image forming unit  300  so that the operator is allowed to grip the grip member  56  when attaching or detaching the image forming unit  300 . The grip member  56  and the operating member  57  have the same configurations as those described in the first exemplary embodiment. 
     In the image forming apparatus  1  to which the driving-force-transmitting mechanism according to the second exemplary embodiment is applied, the grip member  56  and the operating member  57  operate in the same manner as in the first exemplary embodiment when the image forming unit  300  is attached or detached. 
     Hence, in the image forming apparatus  1  to which the driving-force-transmitting mechanism according to the second exemplary embodiment is applied, a photoconductor master coupling (not illustrated) moves away from the photoconductor slave coupling  303  without receiving the pushing force in the detaching direction F exerted by the photoconductor slave coupling  303 . 
     The other elements and functions thereof are the same as those described in the first exemplary embodiment, and description of those elements is omitted. 
     While the first exemplary embodiment concerns a case where the intermediate transfer unit  200  is attached or detached from the side thereof where the driving roller  22  is provided, the side from which the intermediate transfer unit  200  is attached or detached is not limited thereto, of course. The intermediate transfer unit  200  may be attached or detached from the side thereof where the backup roller  25  is provided. 
     In that case, the rear face, inclusive of the second-transfer roller  26 , of the apparatus body  1   a  of the image forming apparatus  1  is to be opened and closed. Furthermore, the grip member  56  and the operating member  57  are provided at a position corresponding to the second-transfer roller  26 , and the operation of attaching or detaching the intermediate transfer unit  200  is performed on the rear side of the apparatus body  1   a  of the image forming apparatus  1 . 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.