Patent Publication Number: US-9835988-B2

Title: Electro-photography image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Priority Patent Application JP 2015-178631 filed on Sep. 10, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The invention relates to an image forming apparatus that uses an electro-photography method to form an image. 
     There is proposed an image forming apparatus that includes a displacement controller of a transferring member or transfer roller, as disclosed in Japanese Unexamined Patent Application Publication No. 2015-25920, for example. The displacement controller of the transfer roller moves an endless image holding body (a transferred member) that holds an image on a surface thereof and a transfer roller that transfers the image to continuous sheet, in a direction in which the image holding body and the transfer roller are brought into contact with each other and separated away from each other relatively. 
     SUMMARY 
     In an image forming apparatus, it is desirable that a correction operation for formation of a developer image on a transferred member, such as print density correction and color deviation correction be performable even in a state in which continuous paper is located between the transferred member and a transfer roller. 
     It is desirable to provide an image forming apparatus that makes it possible to form an image with better quality. 
     An image forming apparatus according to an illustrative embodiment of the invention includes: an image forming section that forms a developer image; a transferred member conveyed in a first direction and onto which the developer image is to be transferred; a transfer roller that faces the transferred member, and makes a transition between a biasing state in which the transferred member is biased by the transfer roller and a separated state in which the transfer roller is separated away from the transferred member; and a separator that separates, in the separated state, a medium away from the transferred member, in which the medium is held between the transferred member and the transfer roller in the biasing state. 
     An image forming apparatus according to an illustrative embodiment of the invention includes: an image forming section that forms a developer image; a transferred member conveyed in a first direction and onto which the developer image is to be transferred; a transfer roller that faces the transferred member, and makes a transition between a biasing state in which the transferred member is biased by the transfer roller and a separated state in which the transfer roller is separated away from the transferred member; a support that supports the transfer roller; and a separator that separates, in the separated state, a medium away from the transferred member, in which the medium is held between the transferred member and the transfer roller in the biasing state. The separator includes a driver, a cam, and a biasing member. The cam pivots, by driving force transmitted from the driver, in one of a first pivoting direction and a second pivoting direction that is opposite to the first pivoting direction. The biasing member biases, by the pivot of the cam in the second pivoting direction, the medium in a direction in which the medium is separated away from the transferred member. The support brings the transfer roller close to the transferred member by the pivot of the cam in the first pivoting direction, or separates the transfer roller away from the transferred member by the pivot of the cam in the second pivoting direction. The separator starts to separate the medium away from the transferred member after the transfer roller starts making a transition from the biasing state to the separated state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating, upon printing operation, an overall configuration example of an image forming apparatus according to a first embodiment of the invention. 
         FIG. 2  is a side view of a configuration example of a secondary transfer roller unit illustrated in  FIG. 1 , as viewed from the upstream side thereof. 
         FIG. 3  is an outline perspective view of a drive transmission mechanism for pivot operation of an eccentric cam illustrated in  FIG. 1 . 
         FIG. 4  is a schematic diagram illustrating, upon standby, an overall configuration example of the image forming apparatus illustrated in  FIG. 1 . 
         FIG. 5  is a flowchart for describing operation of the image forming apparatus illustrated in  FIG. 1 . 
         FIG. 6  is another schematic diagram illustrating, upon standby, the overall configuration example of the image forming apparatus illustrated in  FIG. 1 . 
         FIG. 7  is a schematic diagram illustrating an overall configuration example of an image forming apparatus according to a modification of the first embodiment of the invention. 
         FIG. 8A  is a schematic diagram illustrating, upon printing operation, a configuration example of a key part of an image forming apparatus according to a second embodiment of the invention. 
         FIG. 8B  is a schematic diagram illustrating, upon standby, a configuration example of the key part of the image forming apparatus illustrated in  FIG. 8A . 
         FIG. 9  is a perspective view of a secondary transfer roller unit and a retaining member in the image forming apparatus illustrated in  FIG. 8A . 
         FIG. 10  is a perspective view of a part of the secondary transfer roller unit and the retaining member in the image forming apparatus illustrated in  FIG. 8A . 
         FIG. 11  is an exploded perspective view of a part of the secondary transfer roller unit and the retaining member in the image forming apparatus illustrated in  FIG. 8A . 
         FIG. 12  is a perspective view of the retaining member in the image forming apparatus illustrated in  FIG. 8A . 
         FIG. 13A  is a schematic diagram illustrating, upon printing operation, an overall configuration example of an image forming apparatus according to a modification of the second embodiment of the invention. 
         FIG. 13B  is a schematic diagram illustrating, upon standby, the overall configuration example of the image forming apparatus illustrated in  FIG. 13A . 
     
    
    
     DETAILED DESCRIPTION 
     In the following, some example embodiments of the invention are described in detail with reference to the accompanying drawings. Note that the following description is directed to illustrative examples of the invention and not to be construed as limiting to the invention. Also, factors such as arrangement, dimensions, and a dimensional ratio of elements illustrated in each drawing are illustrative only and not to be construed as limiting to the invention. The description is given in the following order. 
     1. First Embodiment 
     An image forming apparatus having a configuration in which a support of a transfer roller and a retaining member of a medium are integrated. 
     2. Modification of First Embodiment 
     An image forming apparatus in which a retaining member of a medium is provided downstream of a secondary transferring section. 
     3. Second Embodiment 
     An image forming apparatus having a configuration in which a support of a transfer roller and a retaining member of a medium are formed separately from each other. 
     4. Modification of Second Embodiment 
     An image forming apparatus in which a retaining member of a medium is provided in an intermediate transferring unit. 
     5. Other Modifications 
     [1. First Embodiment] 
     [Outline Configuration] 
       FIG. 1  is a schematic diagram illustrating, upon printing operation, an overall configuration example of an image forming apparatus according to a first embodiment of the invention. An image forming unit may be an electro-photographic printer that forms an image (for example, a color image) on a medium (also referred to as paper, a recording medium, a print medium, or a transferred medium) M. 
     As illustrated in  FIG. 1 , the image forming apparatus may include, for example, a medium feeding section  1 , a medium conveying section  2 , an image forming section  3 , and a fixing section  4  in order from upstream to downstream. The image forming apparatus further includes a controller  11  that controls entire operation of the image forming apparatus, including an operation of each of the medium feeding section  1 , the medium conveying section  2 , the image forming section  3 , and the fixing section  4 . The medium M that is fed from the medium feeding section  1  may be conveyed in order of the medium conveying section  2 , the image forming section  3 , and the fixing section  4 . Note that, in a direction (an arrow F) in which the medium M travels, a position close to the medium feeding section  1  that is a feed source of the medium M as viewed from any position is referred to herein as upstream, and a position far from the medium feeding section  1  is referred to herein as downstream. Further, a direction that is orthogonal to the traveling direction (the arrow F) of the medium M (a direction perpendicular to the paper surface of  FIG. 1 ) is referred to herein as a lateral direction. The image forming section  3  corresponds to a specific but non-limiting example of an “image forming section” in one embodiment of the invention. 
     The medium feeding section  1  rotatably holds a roll (a wound structure) MR with a shaft J 1  as a rotation axis, and feeds the medium M toward the downstream medium conveying section  2  upon printing operation. The roll MR may be the wound medium M on which image formation is to be performed. A feed position at which the medium M is fed out from the roll MR is defined as P 1 . 
     The medium conveying section  2  includes a roller pair  21  and a roller pair  22  that are disposed in order from upstream to downstream. The roller pair  21  includes a roller  21 A and a roller  21 B that face each other at a position P 2 . The roller pair  22  includes a roller  22 A and a roller  22 B that face each other at a position P 3 . The medium M that has been fed out from the roll MR passes through the position P 2  and the position P 3  in order. The feed position P 1  of the medium M, the position P 2 , and the position P 3  may be preferably arranged in a straight line in order to suppress load to be applied to the medium M. 
     The image forming section  3  includes an image forming unit  5 , an intermediate transfer unit  6 , a secondary transfer roller unit  7 , a sensor group  8 , a cleaning unit  9 , and a waste toner collecting container  10 . 
     The image forming unit  5  includes developing devices  51  ( 51 A to  51 E) that are disposed above the intermediate transfer unit  6 , and each develop a toner (a developer) of corresponding color to form a toner image (a developer image). The image forming unit  5  forms toner images of the respective colors in an electrophotography method on a transferred surface  61 S of an intermediate transfer belt  61  (described later) of the intermediate transfer unit  6 . Each of the developing devices  51  may include, for example, a toner feeding section  52 , a photosensitive drum  53 , and an exposure section  54 . 
     The intermediate transfer unit  6  may include, for example, the intermediate transfer belt  61 , a drive roller  62 , a tension roller  63 , a secondary transfer backup roller  64 , a primary transfer roller  65 , a reverse bending roller  66 , support rollers  67 A and  67 B, and idle rollers  68  and  69 . The intermediate transfer belt  61  may be an endless elastic belt that is made of, for example, a resin material such as a polyimide resin, and corresponds to a specific but non-limiting example of a “transferred member” in one embodiment of the invention. The intermediate transfer belt  61  may be stretched by and stretched around the drive roller  62 , the tension roller  63 , the secondary transfer backup roller  64 , the primary transfer roller  65 , the reverse bending roller  66 , the support rollers  67 A and  67 B, the idle rollers  68  and  69 , and other members. The intermediate transfer belt  61  may be stretched to allow the transferred surface  61 S, on which the toner image is to be transferred by means of a primary transfer, to face outside, for example. The drive roller  62  may be a member that is rotatably driven by a drive motor, thereby causing the intermediate transfer belt  61  to rotate in a predetermined conveying direction  6 F. The tension roller  63  may be a driven roller that follows the rotation of the intermediate transfer belt  61 , and applies tensile force to the intermediate transfer belt  61  by means of biasing force applied from a biasing member such as a coil spring. The secondary transfer backup roller  64  may be disposed to face a secondary transfer roller  71  (described later) at a position P 4 , and hold, together with the secondary transfer roller  71 , the intermediate transfer belt  61  and the medium M to thereby form a secondary transferring section upon printing operation. The secondary transfer backup roller  64  and the secondary transfer roller  71  perform, to the medium M, a secondary transfer of the toner image that has been transferred by means of the primary transfer to a surface of the intermediate transfer belt  61 . The primary transfer roller  65  may be disposed to hold, together with the photosensitive drum  53  of each developing device  51 , the intermediate transfer belt  61  to thereby form a primary transferring section. The primary transfer roller  65  applies a predetermined voltage when performing, to the surface of the intermediate transfer belt  61 , the primary transfer of the toner image that has been formed by corresponding developing device  51 . The reverse bending roller  66  bends the intermediate transfer belt  61  to secure space in which the fixing section  4  is disposed. The support roller  67 A may be disposed to face the reverse bending roller  66  and hold, together with the reverse bending roller  66 , the intermediate transfer belt  61 . The support roller  67 B may be disposed to face the cleaning unit  9 , and hold, together with a blade  91  (described later) of the cleaning unit  9 , the intermediate transfer belt  61 . The support roller  67 B stabilizes a nip between the intermediate transfer belt  61  and the blade  91 . Each of these support rollers  67 A and  67 B may be a driven roller that follows the rotation of the intermediate transfer belt  61 , and maintains stable traveling of the intermediate transfer belt  61 . The idle roller  68  may be disposed between the tension roller  63  and the primary transfer roller  65  that faces the photosensitive drum  53  of the developing device  51  located on the most downstream side. The idle roller  68  maintains the intermediate transfer belt  61  to be horizontal which has just passed through the primary transferring section. The idle roller  69  may be disposed to face the sensor group  8  with the intermediate transfer belt  61  in between, and maintains a fixed distance between the sensor group  8  and the intermediate transfer belt  61 . 
     The secondary transfer roller unit  7  includes: the secondary transfer roller  71 ; a support  72  that rotatably supports the secondary transfer roller  71 ; shaft members  73  to  75  that extend in the lateral direction; and an eccentric cam  76  that is fixed to both ends of the shaft member  75 . The secondary transfer roller  71  corresponds to a specific but non-limiting example of a “transfer roller” in one embodiment of the invention. A detailed configuration of the secondary transfer roller unit  7  is described later. 
     The sensor group  8  may include, for example, a color deviation sensor and a density sensor. The color deviation sensor detects relative positional deviation, namely, color deviation in the conveying direction  6 F of the toner images of the respective colors that have been formed by the developing devices  51  and then transferred by means of the primary transfer to the transferred surface  61 S of the intermediate transfer belt  61 . The color deviation sensor may include, for example, a light emitting diode that applies light to the transferred surface  61 S of the intermediate transfer belt  61 , and a light receiver that receives light reflected by the transferred surface  61 S, such as a phototransistor and a photodiode. Also, the density sensor detects density of each of the toner images that are formed by the respective developing devices  51 , and may be disposed to face the transferred surface  61 S of the intermediate transfer belt  61 . 
     The cleaning unit  9  includes the blade  91 , a waste toner container  92 , and a film  93 . The blade  91  scrapes remaining toners that remain on the transferred surface  61 S of the intermediate transfer belt  61 . The waste toner container  92  contains the remaining toners that have been scraped by the blade  91  once, and has a conveying device such as a conveying spiral that conveys the waste toner to the waste toner collecting container  10 . The film  93  prevents the waste toners that have been scraped once by the blade  91 , from being thrown up. 
     The waste toner collecting container  10  may be a member that is disposed inside a space surrounded by the intermediate transfer belt  61 , for example, and contains the waste toner that remains on the surface of the intermediate transfer belt  61  after the secondary transfer. 
     The fixing section  4  may be disposed downstream of the secondary transferring section in which the secondary transfer backup roller  64  and the secondary transfer roller  71  face each other. The fixing section  4  applies heat and pressure to the toner images that have been transferred to the medium M conveyed from the secondary transferring section, and allows the toner images to melt, thereby fixing the melted toner images on the medium M. The fixing section  4  includes paired rollers  41  and  42 , a heat source  43 , and a heat source  44 . The paired rollers  41  and  42  may be brought into press contact with each other at a predetermined pressure at a position P 5 . The heat source  43  may be installed in the roller  41  and heat the roller  41 . The heat source  44  may be installed in the roller  42  and heat the roller  42 . The heat sources  43  and  44  may be, for example, halogen lamps. The paired rollers  41  and  42  may be operable to perform an approaching operation in which the paired rollers  41  and  42  come close to and come into contact with each other, and a separating operation in which the paired rollers  41  and  42  move in a direction in which they are separated from each other. The fixing section  4  conveys the medium M to the downstream side while holding the medium M between the roller  41  and the roller  42  and applying heat and pressure to the medium M. Note that the separating operation that causes the paired rollers  41  and  42  to be separated away from each other may be carried out, for example, in a case where malfunction occurs in traveling of the medium M, in a case where a correction operation such as print density correction and color deviation correction is performed, upon standby in which the printing operation is not performed, or in any other occasion. In this case, the position P 3  of the roller pair  22 , the position P 4  of the secondary transferring section, and the position P 5  of the fixing section  4  may be desirably arranged in a straight line. This prevents traveling of the medium M from becoming unstable depending on a kind of the medium M, and makes it easier to ensure formation of favorable toner images. 
     [Detailed Configuration of Secondary Transfer Roller Unit  7 ] 
     The detailed configuration of the secondary transfer roller unit  7  is described with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  is a side view of the configuration of the secondary transfer roller unit  7  as viewed from the upstream side thereof.  FIG. 3  is an outline perspective view of a drive transmission mechanism for pivot operation of the eccentric cam  76 . 
     The secondary transfer roller  71  holds, together with the secondary transfer backup roller  64 , the intermediate transfer belt  61  and the medium M to thereby form the secondary transferring section. The secondary transfer roller  71  rotates along with traveling of the intermediate transfer belt  61  and the medium M, and causes positional difference between the secondary transfer roller  71  and the secondary transfer backup roller  64 , thereby performing, to the medium M, the secondary transfer of the toner images that have been transferred by means of the primary transfer to the transferred surface  61 S. 
     The support  72  rotatably supports both ends of the secondary transfer roller  71 . The support  72  corresponds to a specific but non-limiting example of a “support” in one embodiment of the invention. The support  72  may be fixed to the rod-shaped shaft member  73  that extends in the lateral direction along the secondary transfer roller  71 , and pivot within a range illustrated by an arrow Y 72  ( FIG. 1 ) with the shaft member  73  as a supporting point. The shaft member  74  penetrates through the support  72  in the lateral direction, and may be fixed to the support  72  to allow both ends thereof to protrude from the support  72 . A peripheral surface of the shaft member  74  comes into contact with a peripheral surface  76 S of the eccentric cam  76 , and slides on the peripheral surface  76 S of the eccentric cam  76  along with the pivot of the eccentric cam  76 . Two eccentric cams  76  may be preferably provided such that respective eccentric cams  76  come into contact with both ends of the shaft member  74  ( FIG. 2 ). The eccentric cam  76  may be fixed to the shaft member  75 , and may be pivotable within a range illustrated by an arrow Y 76  ( FIG. 1 ) around the shaft member  75 . 
     The shaft member  74  slides on the peripheral surface  76 S of the eccentric cam  76  along with such pivot of the eccentric cam  76 , which changes attitude of the support  72 . For example, upon the printing operation illustrated in  FIG. 1 , a part that is located relatively far from the shaft member  75 , of the peripheral surface  76 S of the eccentric cam  76  may come into contact with the shaft member  74 , and the support  72  may accordingly be pushed up to a relatively high position. This state corresponds to a specific but non-limiting example of a “biasing state” in one embodiment of the invention, in which the secondary transfer roller  71  supported by the support  72  biases the intermediate transfer belt  61  toward the secondary transfer backup roller  64 . In contrast, for example, upon standby illustrated in  FIG. 4 , the eccentric cam  76  may be moved to a position that is rotated rightward by, for example, 90 degrees from the position of  FIG. 1 . Thus, a part that is located relatively close to the shaft member  75 , of the peripheral surface  76 S of the eccentric cam  76  may come into contact with the shaft member  74 , and the support  72  may accordingly be dropped down to a low position relatively. This state corresponds to a specific but non-limiting example of a “separated state” in one embodiment of the invention, in which the secondary transfer roller  71  supported by the support  72  is separated away from the intermediate transfer belt  61 . Note that, in this example, the support  72  falls freely by own weight due to change in the pivot position of the eccentric cam  76  that is supported by the support  72 . Alternatively, a biasing member such as a spring may be used to actively push the support  72  downward. Such a change in attitude change of the support  72  allows the secondary transfer roller  71  supported by the support  72  to perform the approaching operation in which the secondary transfer roller  71  approaches toward the intermediate transfer belt  61  and the separating operation in which the secondary transfer roller  71  is separated away from the intermediate transfer belt  61 . In other words, the secondary transfer roller  71  may be operable to make a transition between the biasing state and the separated state. The separating operation that causes the secondary transfer roller  71  to be separated away from the intermediate transfer belt  61  may be carried out, for example, in the case where malfunction occurs in traveling of the medium M, in the case where a correction operation such as print density correction and color deviation correction is performed, upon standby in which the printing operation is not performed, or in any other occasion. 
     As illustrated in  FIG. 3 , the secondary transfer roller unit  7  further includes a motor  77  serving as a driving source that generates driving force, and gears  78 A to  78 E that transmit the driving force to the shaft member  75 . The motor  77  corresponds to a specific but non-limiting example of a “driver” in one embodiment of the invention. The motor  77  may be provided with a shaft  77 J, and the driving force may be transmitted to the gear  78 A through rotation of the shaft  77 J. The gear  78 A engages with the gear  78 B, the gear  78 B engages with the gear  78 C, the gear  78 C engages with the gear  78 D, the gear  78 D engages with the gear  78 E, and the gear  78 E may be fixed to an end of the shaft member  75 . Thus, when the motor  77  is driven and the shaft  77 J rotates, the gears  78 A to  78 E and the shaft member  75  rotate in conjunction with one another, and the eccentric cam  76  accordingly pivots around the shaft member  75 . The pivoting of the eccentric cam  76  by means of the driving force of the motor  77  causes the eccentric cam  76  itself to bias the support  72  and bring the secondary transfer roller  71  close to the intermediate transfer belt  61 . At this time, adjusting a rotation amount of the motor  77  makes it possible to appropriately change the pivot position of the eccentric cam  76 , namely, attitude of the support  72 . 
     The support  72  further includes a retaining member  79  at an upper part thereof. The retaining member  79  corresponds to a specific but non-limiting example of a “biasing member” in one embodiment of the invention. Further, a combination of the retaining member  79  and the motor  77  corresponds to a specific but non-limiting example of a “separator” in one embodiment of the invention. The retaining member  79  forms an opening  72 K together with the support  72 . Upon the printing operation illustrated in  FIG. 1 , the retaining member  79  may be located between the second roller pair  22  and the secondary transferring section, and the medium M traveling toward the secondary transferring section passes through the opening  72 K. At this time, it is preferable that the retaining member  79  be prevented from coming into contact with the medium M (be separated away from the medium M). In contrast, upon standby illustrated in  FIG. 4 , since the retaining member  79  is also moved downward together with the support  72 , the retaining member  79  may be in contact with an upper surface MS of the medium M at the upstream side of the secondary transferring section, and push down the medium M. In other words, the retaining member  79  that is fixed to the support  72  biases the medium M in a direction away from the intermediate transfer belt  61 . Therefore, a separating operation in which the medium M is separated and the separating operation of the secondary transfer roller  71  may be carried out in conjunction with each other by means of the movement of the retaining member  79  and the support  72 , namely, by means of the change in attitude of the support  72 , thereby causing both the secondary transfer roller  71  and the medium M to be separated away from the intermediate transfer belt  61 . It is to be noted that, in the biasing state, the secondary transfer roller  71  is in contact with the intermediate transfer belt  61  with the medium M in between whereas the retaining member  79  is separated away from the medium M. In the biasing state, the secondary transfer roller  71  may be separated away from the intermediate transfer belt  61  at timing different from timing at which the medium M may be separated away from the intermediate transfer belt  61 . In detail, at the time immediately after the support  72  starts to change its attitude (to move downward in  FIG. 4 ), the holding state of the medium M by the secondary transfer roller  71  and the intermediate transfer belt  61  may be released but the biasing operation of the retaining member  79  with respect to the medium M has not been started. This is due to a gap provided between the retaining member  79  and the medium M, and a predetermined time is thus necessary for the retaining member  79  to come close to and come into contact with the medium M. In other words, when the retaining member  79  is to be separated from the medium M in the biasing state, the retaining member  79  starts to separate the medium M away from the intermediate transfer belt  61  after the secondary transfer roller  71  starts making a transition from the biasing state to the separated state. 
     [Workings and Effects] 
     [Basic Operation] 
     In the image forming apparatus, the toner images may be transferred to the medium M in the following manner. An operation of the image forming apparatus according to the first embodiment is described below with reference to  FIG. 5 .  FIG. 5  is a flowchart for describing the operation of the image forming apparatus according to the first embodiment. 
     First, a main power supply is turned on to put the image forming apparatus into the standby state (step S 1 ). In the image forming apparatus at this time, the support  72  may be located on lower part, and the secondary transfer roller  71  may be separated away from the intermediate transfer belt  61  as illustrated by way of example in  FIG. 6 . Further, the roller  41  and the roller  42  of the fixing section  4  may be separated away from each other.  FIG. 6  is a diagram illustrating, upon standby before the medium M is inserted, an overall configuration example of the image forming apparatus according to the first embodiment. 
     Next, a determination is made as to whether to perform density correction and color deviation correction of the toner images (step S 2 ). 
     When it is determined that these correction operations are necessary (YES in step S 2 ), the density correction and the color deviation correction of the toner images are performed (step S 3 ). At this time, the controller  11  activates the developing devices  51 A to  51 E and the intermediate transfer belt  61 , and a correction toner image may be formed on the transferred surface  61 S of the intermediate transfer belt  61 . Further, the sensor group  8  detects the correction toner image, and the controller  11  performs the density correction and the color deviation correction of the toner images, on the basis of the detected data. 
     When a determination is made that the correction operations are unnecessary (NO in step S 2 ), a printing job may be transmitted from an external apparatus or any other apparatus to the controller  11  (step S 4 ). 
     When receiving the printing job, the controller  11  activates the motor  77 , and allows the eccentric cam  76  to pivot to thereby push up the support  72 , causing the secondary transfer roller  71  to nip the intermediate transfer belt  61 . Further, the controller  11  brings the roller  41  and the roller  42  close to each other, thereby causing them to nip each other (step S 5 ). 
     Thereafter, the controller  11  activates the developing devices  51 A to  51 E, the intermediate transfer belt  61 , and the fixing section  4  (step S 6 ). As a result, the toner image may be formed on (transferred by means of the primary transfer to) the transferred surface  61 S of the intermediate transfer belt  61  through the electrophotography process. 
     Further, the medium M may be fed out from the roll MR, and the medium conveying section  2  may be activated to feed the medium M to the secondary transferring section. As a result, the toner image on the transferred surface  61 S may be transferred (transferred by means of the secondary transfer) to the medium M, and the toner image may be then fixed to the medium M by the fixing section  4  (step S 7 ). 
     Then, a determination is made as to whether a situation in which the medium M is not properly conveyed, namely, so-called paper jam has occurred in the printing operation (step S 8 ). When it is determined that a paper jam has occurred (YES in step S 8 ), the controller  11  stops the developing devices  51 A to  51 E, the intermediate transfer belt  61 , and the fixing section  4  (step S 12 ). Further, the controller  11  activates the motor  77 , and causes the eccentric cam  76  to pivot to thereby move the support  72  downward, separating the secondary transfer roller  71  and the medium M from the intermediate transfer belt  61  and separating the roller  41  and the roller  42  from each other (step S 13 ). Thereafter, the process returns to step S 5  after the jammed medium M is removed (step S 14 ). 
     In contrast, when it is determined that a paper jam has not occurred in the printing operation (NO in step S 8 ), the controller  11  stops the developing devices  51 A to  51 E, the intermediate transfer belt  61 , the fixing section  4 , and the medium conveying section  2  (step S 9 ). Then, the controller  11  separates the roller  41  and the roller  42  away from each other. Further, the controller  11  activates the motor  77 , and causes the eccentric cam  76  to pivot to thereby move the support  72  downward, separating the secondary transfer roller  71  and the medium M from the intermediate transfer belt  61  (step S 10 ). Thereafter, when the printing operation is to be further performed repeatedly (YES in step S 11 ), the process returns to step S 2 . If it is determined again that the density correction or any other correction is necessary at this time, the correction operation may be performed again (step S 3 ). In this case, even when the medium M is continuous paper and the medium M remains in the image forming section  3 , the correction operation is free from any influence caused by the remaining of the medium M in the image forming section  3 , owing to the separation of the medium M away from the intermediate transfer belt  61  by the retaining member  79 . 
     When the printing operation is not to be performed any more in step S 10  (NO in step S 11 ), the main power supply may be turned off and the series of operations may be completed (end). 
     [Effects] 
     In the image forming apparatus according to the first embodiment, the medium M is separated away from the intermediate transfer belt  61  by the retaining member  79  that is driven by the motor  77 , during the operation stop (in standby). Thus, it is possible to perform a correction operation for formation of the developer image on the intermediate transfer belt  61 , such as print density correction and the color deviation correction, even when the medium M is located between the intermediate transfer belt  61  and the secondary transfer roller  71 . Japanese Unexamined Patent Application Publication No. 2015-25920 mentioned above involves a risk in which the medium may come into contact with an image holding body. In contrast, the present embodiment allows the intermediate transfer belt  61  and the medium M to be separated away from each other with higher possibility, preventing the medium M from being stained by the correction operation. In addition, since the retaining member  79  comes into contact with the upper surface MS of the medium M at the upstream of the secondary transferring section, and pushes down the medium M, it is possible to prevent the toner from being attached to the retaining member  79 . If the retaining member  79  is located downstream of the secondary transferring section, the toner of the intermediate transfer belt  61  may possibly be attached to the retaining member  79 . 
     Further, in a case where a so-called paper jam has occurred upon the printing operation, it is possible to ensure that the medium M is separated away from the intermediate transfer belt  61  when drawing out and removing the medium M that remains in the image forming apparatus. This prevents unnecessary interference, friction, and the like between the intermediate transfer belt  61  and the medium M from occurring, making it possible to prevent, for example, generation of any trace on a surface of the intermediate transfer belt  61 , and thereby preventing quality of the printed image from being impaired. Further, the roller pair  22 , the secondary transferring section, and the fixing section  4  may be arranged in a straight line (so-called straight path is formed). This makes it possible to handle various print media such as special paper. 
     Further, the driving force derived from the single motor  77  may be used to perform the separating operation that causes the secondary transfer roller  71  to be separated away from the intermediate transfer belt  61  and the separating operation that causes the medium M to be separated away from the intermediate transfer belt  61  in conjunction with each other. This achieves a simplified control operation and a simplified configuration. Further, the support  72  that supports the secondary transfer roller  71  may be integrated with the retaining member  79  that retains the medium M, which achieves a simplifier configuration. 
     Further, the biasing operation performed on the medium M by the retaining member  79  may be carried out after the holding state of the medium M by the secondary transferring section is released. This makes it possible to reduce a load applied to, for example, the intermediate transfer belt  61  and the medium M. As a result, for example, it is possible to avoid a decrease in quality of printed image. 
     The image forming apparatus according to one embodiment of the invention therefore makes it possible to form an image with better quality. 
     [2. Modification of First Embodiment] 
       FIG. 7  is a schematic diagram illustrating an overall configuration example of an image forming apparatus according to a modification of the first embodiment of the invention. The present modification has a configuration the same as that of the image forming apparatus according to the above-described first embodiment, except that the retaining member  79  is provided downstream of the secondary transferring section in which the secondary transfer backup roller  64  and the secondary transfer roller  71  face each other. 
     The configuration according to the present modification may be employed in a case where it is difficult to dispose the retaining member  79  between the roller pair  22  and the secondary transferring section due to restrictions on the configuration. For example, the configuration may be employed when a distance between the roller pair  22  and the secondary transferring section is narrow. 
     [3. Second Embodiment] 
     [Outline Configuration] 
       FIG. 8A  is a schematic diagram illustrating, upon the printing operation, a configuration example of a key part of an image forming apparatus according to a second embodiment of the invention.  FIG. 8B  is a schematic diagram illustrating, upon standby, a configuration example of the key part of the image forming apparatus according to the second embodiment of the invention. The image forming apparatus has a configuration substantially similar to that of the image forming apparatus according to the first embodiment, except that a secondary transfer roller unit  7 A is provided in place of the secondary transfer roller unit  7 , and a retaining member  12  (See  FIG. 12 ) that retains the medium M is provided separately from the secondary transfer roller unit  7 A. In the following, a description is mainly given on the retaining member  12  and any component around the retaining member  12 , and other components are denoted with reference numerals similar to those of the first embodiment and the description thereof is omitted where appropriate. Note that, in  FIG. 8A  and  FIG. 8B , only key components are illustrated and other components are not illustrated. 
     As illustrated in  FIG. 8A  and  FIG. 8B , the intermediate transfer unit  6  of the image forming apparatus further includes a support roller  67 C that is provided near the upstream side of the secondary transfer backup roller  64 . The support roller  67 C stretches the intermediate transfer belt  61 . Providing the support roller  67 C makes it possible to bring the intermediate transfer belt  61  between the secondary transfer backup roller  64  and the support roller  67 C, closer to the medium M that is conveyed through the roller pair  22  and the secondary transferring section. More specifically, providing the support roller  67 C allows the intermediate transfer belt  61  to so travel as to be substantially parallel even more to the medium M that is about to go into the secondary transferring section. Hence, it is possible to expect an improvement in print quality of the toner image that is transferred to the medium M. 
     [Detailed Configuration of Secondary Transfer Roller Unit  7 A and Retaining Member  12 ] 
     The configurations of the secondary transfer roller unit  7 A and the retaining member  12  are described in more detail with reference to  FIG. 9  to  FIG. 12  in addition to  FIG. 8A  and  FIG. 8B .  FIG. 9  is a perspective view of the secondary transfer roller unit  7 A and the retaining member  12 .  FIG. 10  is a perspective view of a part of the secondary transfer roller unit  7 A and the retaining member  12 .  FIG. 11  is an exploded perspective view of a part of the secondary transfer roller unit  7 A.  FIG. 12  is a perspective view of the retaining member  12 . 
     The secondary transfer roller unit  7 A has a configuration substantially similar to that of the secondary transfer roller unit  7  according to the above-described first embodiment, except that the secondary transfer roller unit  7 A includes a support  72 A that rotatably supports the secondary transfer roller  71 , shaft members  73 A to  75 A and  75 B, and an eccentric cam  76 A. The driving force of the motor  77  may be transmitted to the shaft member  75 A through the gears  78 A to  78 E (see  FIG. 10 ). 
     Also, two eccentric cams  76 A may be so provided as to sandwich the support  72 A in the lateral direction. The two eccentric cams  76 A may be coupled to each other through the two shaft members  75 A and  75 B that extend in the lateral direction. The support  72 A may be so held by a frame  81  that is fixed to the image forming apparatus main body, as to be pivotable with the shaft member  73 A as a supporting point. Each of the eccentric cams  76 A may be so held by a frame  82  that is fixed to the image forming apparatus main body, as to be pivotable around the shaft member  75 A. Therefore, when the shaft member  74 A slides on a peripheral surface  76 AS of the eccentric cam  76 A, the support  72 A may pivot around the shaft member  73 A, for example, within a range of an arrow Y 72 A, thereby moving in the vertical direction. This allows the secondary transfer roller  71  to make a transition between the biasing state and the separated state. Note that  FIG. 8A  illustrates the biasing state in which the secondary transfer roller  71  biases the intermediate transfer belt  61  toward the secondary transfer backup roller  64 , and  FIG. 8B  illustrates the separated state in which the secondary transfer roller  71  is separated away from the intermediate transfer belt  61 . 
     The retaining member  12  includes a retaining part  121 , a supporting part  122 , and a cam receiving part  123  (for example, see  FIG. 12 ). The retaining part  121  extends in the lateral direction, and comes into contact with the medium M upon the separating operation of the medium M. The retaining part  121  may have a substantially V-shaped cross section orthogonal to the lateral direction, for example ( FIG. 1 ). The supporting part  122  supports the retaining part  121  from below, and forms an opening  12 K through which the medium M passes, together with the retaining part  121 . The cam receiving part  123  may be a protrusion that is installed upright on the supporting part  122  and extends in the lateral direction. The cam receiving part  123  comes into contact with the shaft member  75 B that is fixed to the eccentric cam  76 A, to receive downward biasing force, when the medium M is to be separated away from the intermediate transfer belt  61 . In contrast, upon the printing operation illustrated in  FIG. 8A , the cam receiving part  123  may be separated away from the shaft member  75 B. The retaining member  12  may be held by, for example, the frame  82  to be movable in the vertical direction. Further, a biasing member  13  such as a plate spring and a coil spring may be provided below the supporting part  122 . The retaining member  12  may be biased upward by biasing force of the biasing member  13 . Therefore, upon the printing operation illustrated in  FIG. 8A , the cam receiving part  123  does not receive the biasing force from the shaft member  75 B. The retaining part  121  accordingly receives only the biasing force of the biasing member  13  through the cam receiving part  123  and the supporting part  122 , thereby maintaining the separated state from the medium M. Therefore, in the biasing state, the secondary transfer roller  71  may be separated away from the intermediate transfer belt  61  at timing different from timing at which the medium M may be separated away from the intermediate transfer belt  61 . In detail, at the time immediately after the support  72 A starts to change its attitude (to move from the state in  FIG. 8A  to the state in  FIG. 8B ), the holding state of the medium M by the secondary transfer roller  71  and the intermediate transfer belt  61  may be released but the biasing operation of the retaining part  121  with respect to the medium M has not been started. This is due to a gap provided between the retaining part  121  and the medium M, and a predetermined time is thus necessary for the retaining part  121  to come close to and come into contact with the medium M. In other words, when the retaining part  121  is to be separated from the medium M in the biasing state, the retaining part  121  starts to separate the medium M away from the intermediate transfer belt  61  after the secondary transfer roller  71  starts making a transition from the biasing state to the separated state. 
     [Operation] 
     Upon the printing operation, the medium M may be held, together with the intermediate transfer belt  61 , between the secondary transfer backup roller  64  and the secondary transfer roller  71  in the secondary transferring section, and the retaining member  12  may be retracted to a position separated from the medium M ( FIG. 8A ), as with the image forming apparatus according to the foregoing first embodiment. As illustrated by way of example in  FIG. 8A , the eccentric cam  76 A pivots leftward within a range of an arrow Y 76 A. Further, the part that is located relatively far from the shaft member  75 A, of the peripheral surface  76 AS of the eccentric cam  76 A may come into contact with the shaft member  74 A, and the support  72 A may be pushed up to a high position relatively. This puts the secondary transfer roller  71  into the biasing state, and the medium M may be accordingly nipped by the secondary transferring section. At this time, since the shaft member  75 B is separated away from the cam receiving part  123 , the retaining member  12  may be pushed upward by the biasing force of the biasing member  13 , and may be retracted to the position separated from the medium M. Thus, it is possible to prevent an occurrence of a situation where the retaining member  12  damages the conveyed medium M or the retaining member  12  inhibits conveying of the medium M. 
     Upon the standby, the medium M may be retracted to a position separated from the intermediate transfer belt  61  by the retaining member  12 , and the secondary transfer roller  71  may also be retracted to a position separated from the intermediate transfer belt  61 . At this time, the medium M may be separated also from the secondary transfer roller  71 . More specifically, as illustrated by way of example in  FIG. 8B , the eccentric cam  76 A may make a transition to a position that is rotated rightward within the range (for example, 90 degrees) of the arrow Y 76 A from the position in  FIG. 8A . This brings a part that is located relatively close to the shaft member  75 A, of the peripheral surface  76 AS of the eccentric cam  76 A into contact with the shaft member  74 A, thereby putting the support  72 A into the separated state in which the support  72 A is dropped down to a low position relatively. Further, the shaft member  75 B comes into contact with the cam receiving part  123  to bias the cam receiving part  123  downward. As a result, the retaining part  121  also moves downward to bias the medium M downward, and the medium M may be separated away from the intermediate transfer belt  61  accordingly. 
     The series of operations described above may be controlled by the controller  11 , as with the above-described first embodiment. Note that the pivot position of the eccentric cam  76 A may be detected by a position sensor  14  ( FIG. 9 ) such as an optical sensor. 
     The foregoing second embodiment also makes it possible to achieve effects similar to those of the above-described first embodiment. Since the support  72 A that supports the secondary transfer roller  71  and the retaining member  12  that retains the medium M are provided separately from each other, flexibility in design relating to arrangement of the support  72 A and the retaining member  12  is increased as compared with the first embodiment in which the support and the retaining member are integrated. Further, the retaining member  12  may be forcibly brought into contact with the medium M by the eccentric cam  76 A by means of the driving force derived from the motor  77 . Therefore, it is possible to ensure that the medium M is separated away from the intermediate transfer belt  61  even when the medium M is large in thickness or high in hardness. Further, providing the support  72 A and the retaining member  12  separately from each other makes it possible to individually set the retracted positions upon the standby of the secondary transfer roller  71  and the medium M. This makes it possible to ensure that the contact between the secondary transfer roller  71  and the medium M is prevented. Further, a load applied to the secondary transfer roller  71  is reduced, and allowing for expectation for longer life of the secondary transfer roller  71 . Moreover, the intermediate transfer belt  61  is separated away from the medium M during the operation stop (upon the standby), allowing for detachment of the intermediate transfer unit  6 . This facilitates a replacement operation of the intermediate transfer unit  6  attributable to the deterioration of the intermediate transfer belt  61  or any other component. 
     Further, the biasing operation performed on the medium M by the retaining part  121  may be carried out after the holding state of the medium M by the secondary transferring section is released. This makes it possible to reduce a load applied to, for example, the intermediate transfer belt  61  and the medium M. As a result, for example, it is possible to avoid a decrease in quality of printed image. 
     [4. Modification of Second Embodiment] 
       FIG. 13A  and  FIG. 13B  each schematically illustrate a configuration example of a key part of an image forming apparatus according to a modification of the second embodiment of the invention. The present modification has a configuration the same as that of the image for apparatus according to the above-described second embodiment, except that a retaining member  15  fixed to the intermediate transfer unit  6  is provided in place of the retaining member  12 . 
     The retaining member  15  may be so fixed to a main body of the intermediate transfer unit  6  as to be rotatable around a shaft  15 J. The retaining member  15  has a retaining part  15 A at a front end thereof. The retaining part  15 A may be retracted to a position separated from the medium M upon the printing operation ( FIG. 13A ), and the retaining part  15 A biases the medium M downward (in a direction in which the medium M is separated away from the intermediate transfer belt  61 ) upon the standby ( FIG. 13B ). More specifically, a coil spring  16  serving as a biasing member may be provided at a location that is in the vicinity of an end, of the retaining member  15 , on the opposite side of the retaining part  15 A. Upon the standby illustrated in  FIG. 13B , the retaining member  15  may be pulled by biasing force of the coil spring  16  in a direction of an arrow Y 16 B, which causes the retaining part  15 A to bias the medium M downward. In contrast, upon the printing operation illustrated in  FIG. 13A , driving force derived from the motor or any other component may be transmitted to the retaining member  15  through the shaft  15 J, which causes the retaining member  15  to rotate around the shaft  15 J in a direction of an arrow Y 16 A that is a direction against the biasing force of the coil spring  16  (in a direction in which the coil spring  16  is extended). As a result, the retaining part  15 A is retracted to a position separated from the medium M. 
     The configuration according to the present modification may be employed in a case where there are restrictions on the configuration. For example, the configuration may be employed when sufficient space is not secured around the secondary transfer roller unit  7 A. 
     [5. Other Modifications] 
     Although the invention has been described with some example embodiments and modifications thereof, the invention is not limited to the example embodiments and the modifications, and may be variously modified. 
     For example, a description has been given in the above-described example embodiments and modifications of the image forming apparatus that fouls a color image. The invention, however, is not limited thereto. Alternatively, the image forming apparatus may transfer only a toner image of a black color to thereby form a monochrome image. 
     For example, the support  72  is moved downward by own weight in the above-described first embodiment. Alternatively, for example, the support  72  may be forcibly moved downward by a biasing member such as a coil spring. Further alternatively, the support  72  may be forcibly moved upward by a biasing member such as a coil spring, and the support  72  may be forcibly moved downward by the eccentric cam  76 . 
     A description has been given in the above-described example embodiments and modifications of the image forming apparatus that has a printing function, as a specific but non-limiting example of an “image forming apparatus” in one embodiment of the invention. The image forming apparatus, however, is not limited thereto. Any embodiment of the invention is applicable to an image forming unit that functions as a multifunctional peripheral having a function such as a scanner function, a facsimile function, and an image displaying function, in addition to the printing function. 
     Furthermore, the invention encompasses any possible combination of some or all of the various embodiments and the modifications described herein and incorporated herein. 
     It is possible to achieve at least the following configurations from the above-described example embodiments of the invention. 
     (1) An image forming apparatus, including: 
     an image forming section that forms a developer image; 
     a transferred member conveyed in a first direction and onto which the developer image is to be transferred; 
     a transfer roller that faces the transferred member, and makes a transition between a biasing state in which the transferred member is biased by the transfer roller and a separated state in which the transfer roller is separated away from the transferred member; and 
     a separator starts to separate a medium away from the transferred member after the transfer roller starts making a transition from the biasing state to the separated state, the medium being held between the transferred member and the transfer roller in the biasing state. 
     (2) The image forming apparatus according to (1), wherein the separator includes: 
     a driver; and 
     a biasing member that biases the medium in a direction in which the medium is separated away from the transferred member, by one of driving force transmitted from the driver and free fall of the biasing member. 
     (3) The image forming apparatus according to (2), wherein the biasing member is separated away from the medium in the biasing state. 
     (4) The image forming apparatus according to (2), wherein the transfer roller performs an approaching operation in which the transfer roller comes close to the transferred member and a separating operation in which the transfer roller is separated away from the transferred member.
 
(5) The image forming apparatus according to (4), wherein the separating operation of the transfer roller and a separating operation in which the medium is separated away from the transferred member are performed in conjunction with each other.
 
(6) The image forming apparatus according to (5), further including a support that supports the transfer roller, wherein
 
     the biasing member is fixed to the support, and 
     both the transfer roller and the medium are separated away from the transferred member by a movement of the support. 
     (7) The image foiniing apparatus (2), wherein a separating operation in which the transfer roller is separated away from the transferred member and a separating operation in which the medium is separated away from the transferred member are performed by the driving force transmitted from the driver.
 
(8) The image forming apparatus according to (2), further including:
 
     a support that supports the transfer roller; and 
     a cam that receives the driving force transmitted from the driver and comes into contact with the support, wherein 
     the cam pivots in a first pivoting direction by the driving force transmitted from the driver, and thereby biases the support and brings the transfer roller close to the transferred member. 
     (9) The image forming apparatus according to (8), wherein the cam 
     pivots in the first pivoting direction and thereby separates the biasing member away from the medium, and 
     pivots in a second pivoting direction that is opposite to the first pivoting direction, and thereby moves the biasing member and separates the medium away from the transferred member. 
     (10) The image forming apparatus (2), wherein the biasing member is disposed at a position upstream of a transferring section in which the transfer roller and the transferred member face each other, and comes into contact with the medium at the position upstream of the transferring section.
 
(11) The image forming apparatus according to (1), further including:
 
     a first roller pair disposed upstream of a transferring section in which the transfer roller and the transferred member face each other; and 
     a second roller pair disposed downstream of the transferring section, wherein 
     the first roller pair, the transferring section, and the second roller pair are arranged in a straight line. 
     (12) An image forming apparatus, including: 
     an image forming section that forms a developer image; 
     a transferred member conveyed in a first direction and onto which the developer image is to be transferred; 
     a transfer roller that faces the transferred member, and makes a transition between a biasing state in which the transferred member is biased by the transfer roller and a separated state in which the transfer roller is separated away from the transferred member; 
     a support that supports the transfer roller; and 
     a separator that starts to separate a medium away from the transferred member after the transfer roller starts making a transition from the biasing state to the separated state, the medium being held between the transferred member and the transfer roller in the biasing state, wherein 
     the separator includes a driver, a cam, and a biasing member,
         the cam pivoting, by driving force transmitted from the driver, in one of a first pivoting direction and a second pivoting direction that is opposite to the first pivoting direction, and   the biasing member biasing, by the pivot of the cam in the second pivoting direction, the medium in a direction in which the medium is separated away from the transferred member, and       

     the support brings the transfer roller close to the transferred member by the pivot of the cam in the first pivoting direction, or separates the transfer roller away from the transferred member by the pivot of the cam in the second pivoting direction, 
     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. It should be appreciated that variations may be made in the described embodiments by persons skilled in the art without departing from the scope of the invention as defined by the following claims. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in this specification or during the prosecution of the application, and the examples are to be construed as non-exclusive. For example, in this disclosure, the term “preferably”, “preferred” or the like is non-exclusive and means “preferably”, but not limited to. The use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art. The term “about” or “approximately” as used herein can allow for a degree of variability in a value or range. Moreover, no element or component in this disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.