Patent Publication Number: US-11655114-B2

Title: Sheet conveying device and image forming apparatus incorporating the sheet conveying device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-111589, filed on Jun. 14, 2019, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a sheet conveying device and an image forming apparatus incorporating the sheet conveying device. 
     Discussion of the Background Art 
     Various types of sheet conveying devices are known to convey a sheet in one sheet conveyance passage out of a plurality of sheet conveyance passages. 
     SUMMARY 
     At least one aspect of this disclosure provides a sheet conveying device including a first sheet conveyance passage, a second sheet conveyance passage, a pair of sheet conveying rollers, and a movable member. The second sheet conveyance passage is different from the first sheet conveyance passage. The pair of sheet conveying rollers includes two rollers configured to hold a sheet passing the first sheet conveyance passage. The movable member is configured to convey the sheet passing the second sheet conveyance passage. The two rollers are configured to be separated from each other along with movement of the movable member. 
     Further, at least one aspect of this disclosure provides an image forming apparatus including an image forming device configured to form an image on a sheet, and the above-described sheet conveying device configured to convey the sheet from the image forming device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       An exemplary embodiment of this disclosure will be described in detail based on the following figured, wherein: 
         FIG.  1    is a schematic diagram illustrating an image forming apparatus according to an embodiment of this disclosure; 
         FIG.  2    is an enlarged view illustrating an image forming mechanism including a photoconductor and image forming units disposed around the photoconductor included in the image forming apparatus of  FIG.  1   ; 
         FIG.  3    is a perspective view illustrating a main configuration of a sheet conveying device including a regular sheet feeder to feed a recording sheet from a sheet tray and a bypass sheet feeder to feed a recording sheet from a bypass sheet tray in the image forming apparatus; 
         FIG.  4    is a perspective view illustrating a configuration of a drive mechanism in the sheet conveying device for driving the regular sheet feeder and the bypass sheet feeder; 
         FIG.  5    is a diagram for explaining a sheet conveyance passage in the regular sheet feeder and a sheet conveyance passage in the bypass sheet feeder; 
         FIG.  6    is a flowchart of a control operation of sheet conveyance from the regular sheet feeder; 
         FIG.  7    is an external perspective view illustrating a state in which the bypass sheet tray is removed from the bypass sheet feeder; 
         FIG.  8    is a perspective view illustrating a main part of the bypass sheet feeder; 
         FIG.  9    is a flowchart of a control operation of sheet conveyance from the bypass sheet feeder; 
         FIG.  10    is a perspective view illustrating a state in which a bypass bottom plate is separated from the bypass sheet feed roller; 
         FIG.  11    is a perspective view illustrating a configuration of a separation unit that separates the two rollers of a pair of relay rollers from each other; 
         FIG.  12    is a perspective view illustrating the main configuration of the separation unit; 
         FIG.  13    is a perspective view illustrating a support frame of the bypass sheet feeder to which a relay driven roller of the pair of relay rollers is attached; 
         FIG.  14 A  is a diagram for explaining a state in which the two rollers of the pair of relay rollers come to contact with each other; 
         FIG.  14 B  is a diagram for explaining a state in which the two rollers of the pair of relay rollers separate from each other; 
         FIG.  15    is a flowchart of a process flow of operations for an irregular stop of the image forming apparatus according to an embodiment of this disclosure; and 
         FIG.  16    is a flowchart of a process flow of operations for finishing the irregular stop of the image forming apparatus according to an embodiment of this disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     It will be understood that if an element or layer is referred to as being “on,” “against,” “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly. 
     The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Now, a description is given of an electrophotographic printer that functions as an electrophotographic image forming apparatus for forming images by electrophotography. 
     At first, a description is given of a basic configuration of an image forming apparatus  1000  according to an embodiment of this disclosure, with reference to  FIG.  1   . 
       FIG.  1    is a schematic diagram illustrating the image forming apparatus  1000  according to an embodiment of this disclosure. 
     In  FIG.  1   , the image forming apparatus  1000  according to the present embodiment of this disclosure includes a housing  50 , a photoconductor  1 , and a sheet tray  100 . The photoconductor  1  functions as an image bearer or a latent image bearer. The sheet tray  20  functions as a sheet container that is detachably attachable to the housing  50 . The sheet tray  100  contains a plurality of recording sheets S as a sheet bundle that includes a recording sheet S. 
     As a sheet feed roller  41  is driven to rotate, the recording sheet S is fed from the sheet tray  100 . When a plurality of recording sheets S is fed from the sheet tray  100 , an uppermost recording sheet S alone is separated from the other recording sheets S in a sheet separation nip region formed between the sheet feed roller  41  and a sheet separation pad  48 , and is continuously conveyed toward downstream in a sheet conveyance direction in which the recording sheet S is conveyed. Then, the recording sheet S (i.e., the uppermost recording sheet S) reaches a regular sheet conveyance passage R 1  that functions as a first sheet conveyance passage. Thereafter, the recording sheet S is gripped (held) in a sheet conveyance nip region formed by a pair of relay rollers  42  that functions as a pair of upper conveyance rollers, so that the recording sheet S is conveyed from upstream toward downstream in the sheet conveyance direction in the regular sheet conveyance passage R 1 . Note that the pair of conveyance rollers may be a pair of conveyance bodies, at least one of which is a belt. 
     The downstream end of the regular sheet conveyance passage R 1  communicates with a common sheet conveyance passage R 3 . A pair of registration rollers  43  is provided in the common sheet conveyance passage R 3 . A registration sensor  49  that detects the recording sheet S is provided in the common sheet conveyance passage R 3 , being disposed upstream from the pair of registration rollers  43  in the sheet conveyance direction. When the recording sheet S reaches the pair of registration rollers  43 , the recording sheet S is stopped temporality in a state in which the leading end of the recording sheet S is in contact with the registration nip region of the pair of registration rollers  43  that is stopped. While the leading end of the recording sheet S contacts the pair of registration rollers  43 , skew of the recording sheet S is corrected. The registration sensor  49  is also used for an initial operation and a confirmation operation to check whether there is a remaining recording sheet S when canceling an abnormal stop of the image forming apparatus  1000 . 
     The pair of registration rollers  43  starts rotating in synchrony with conveyance of the recording sheet S at a timing at which the recording sheet S contacts the surface of the photoconductor  1  to receive a toner image on the surface of the photoconductor  1  in the sheet transfer nip region. Then, the recording sheet S is conveyed toward the sheet transfer nip region. At this time, the pair of relay rollers  42  starts rotating simultaneously with the start of rotation of the pair of relay rollers  42 , so as to start conveyance of the recording sheet S that has been temporarily stopped. 
     The image forming apparatus  1000  includes a bypass sheet feeder  30  in the housing  50 . The bypass sheet feeder  30  includes a bypass sheet tray  31 , a bypass sheet feed roller  32 , a sheet separation pad  33 , a bypass bottom plate  34 , and a bypass bottom plate cam  35 . A detailed description of the bypass sheet feeder  30  is given below. The recording sheet S placed on the bypass sheet tray  31  of the bypass sheet feeder  30  is fed from the bypass sheet tray  31  along with rotation of the bypass sheet feed roller  32  that functions as a sheet feed roller to feed the recording sheet S, to a bypass sheet conveyance passage R 2  that functions as a second sheet conveyance passage. The downstream end of the bypass sheet conveyance passage R 2  meets with the regular sheet conveyance passage R 1 , eventually being merged to the common sheet conveyance passage R 3 . The recording sheet S fed out by the bypass sheet feed roller  32  passes the sheet separation nip region formed by contact of the bypass sheet feed roller  32  and the sheet separation pad  33  in the bypass sheet conveyance passage R 2 . Then, the recording sheet S is conveyed to the common sheet conveyance passage R 3  to be conveyed to the pair of registration rollers  43 . Thereafter, similar to the recording sheet S fed from the sheet tray  100 , the recording sheet S fed from the bypass sheet tray  31  passes the pair of registration rollers  43  to be conveyed to the transfer nip region. 
       FIG.  2    is an enlarged view illustrating an image forming mechanism including the photoconductor  1  and the image forming units disposed around the photoconductor  1  included in the image forming apparatus  1000 . 
     To be more specific, a cleaning blade  2 , a toner collection screw  3 , a charging roller  4 , a charging roller cleaning roller  5 , a scraper  6 , a latent image writing device  7 , a developing device  8 , and a transfer roller  10  are provided as the image forming units around the drum-shaped photoconductor  1  which is rotated clockwise in  FIG.  2   . The photoconductor  1  and the image forming units integrally function as an image forming device. The charging roller  4  includes a conductive rubber roller and forms a charging nip region by rotating while contacting the photoconductor  1 . The charging roller  4  is applied with a charging bias that is output from a power source for the charging roller  4 . As a result, the surface of the photoconductor  1  is uniformly charged by the charging bias generated between the surface of the photoconductor  1  and the surface of the charging roller  4  in the charging nip region. 
     The latent image writing device  7  includes an LED (light-emitting diode) array and performs light scanning with LED light over the surface of the photoconductor  1  that has been uniformly charged. As the latent image writing device  7  emits laser light beams onto the charged surface of the photoconductor  1 , the electric potential of the irradiated (exposed) region of the charged surface of the photoconductor  1  attenuate, so that an electrostatic latent image is formed on the surface of the photoconductor  1 . 
     As the photoconductor  1  rotates, the electrostatic latent image passes through a development region that formed between the surface of the photoconductor  1  and the developing device  8  when the photoconductor  1  is brought to face the developing device  8 . The developing device  8  includes a developer circulation conveyance portion and a developing portion. The developer circulation conveyance portion includes developer that contains non-magnetic toner and magnetic carriers. The developer circulation conveyance portion includes a first screw  8   b  for conveying the developer to be supplied to a developing roller  8   a , a second screw  8   c  for conveying the developer in an independent space positioned beneath the first screw  8   b . The developer circulation conveyance portion further includes an inclined screw  8   d  for receiving the developer from the second screw  8   c  and supplying the developer to the first screw  8   b . The developing roller  8   a , the first screw  8   b , and the second screw  8   c  are placed at attitudes parallel with each other. By contrast, the inclined screw  8   d  is placed at an attitude inclined with respect to the developing roller  8   a , the first screw  8   b , and the second screw  8   c.    
     As the first screw  8   b  rotates, the first screw  8   b  conveys the developer from a far side toward a near side in a direction perpendicular to the drawing sheet of  FIG.  2   . At this time, the first screw  8   b  supplies a portion of the developer to the developing roller  8   a  that is disposed opposite to the first screw  8   b . The developer having been conveyed by the first screw  8   b  to the vicinity of a far end portion of the first screw  8   b  in the direction perpendicular to the drawing sheet of  FIG.  2    is dropped onto the second screw  8   c.    
     While receiving used developer from the developing roller  8   a , the second screw  8   c  conveys the received developer from the far side toward the near side in the direction perpendicular to the drawing sheet of  FIG.  2   , along with rotation of the second screw  8   c . The developer conveyed by the second screw  8   c  to the vicinity of a near end portion of the second screw  8   c  in the direction perpendicular to the drawing sheet of  FIG.  2    is supplied to the inclined screw  8   d . Further, along with rotation of the inclined screw  8   d , the developer is conveyed from the far side toward the near side in the direction perpendicular to the drawing sheet of  FIG.  2   . Thereafter, the developer is supplied to the first screw  8   b  in the vicinity of the far end portion of the first screw  8   b  in the direction perpendicular to the drawing sheet of  FIG.  2   . 
     The developing roller  8   a  includes a developing sleeve and a magnet roller. The developing sleeve is a tubular-shaped rotatable non-magnetic member. The magnet roller is fixed to the developing sleeve in such a way as not to rotate together with the developing sleeve. Part of the developer that is conveyed by the first screw  8   b  is scooped up by the surface of the developing sleeve due to magnetic force generated by the magnet roller. The developer, which is carried onto the surface of the developing sleeve, is conveyed along with rotation of the developing sleeve and passes through an opposing position at which the developing sleeve and a doctor blade are disposed facing each other. According to this structure, the thickness of a layer of the developer on the surface of the developing sleeve is regulated while the developer is rotated together with rotation of the surface of the development sleeve. Thereafter, the developing roller  8   a  moves (rotates) while sliding on the surface of the photoconductor  1  in a development region in which the developing roller  8   a  is brought to face the photoconductor  1 . 
     A development bias having the same polarity as the toner and as a uniformly charged electric potential (a background electric potential) on the surface of the photoconductor  1  is applied to the developing sleeve. The absolute value of this development bias is greater than the absolute value of the electric potential of the latent image and is smaller than the absolute value of the background electric potential on the background surface of the photoconductor  1 . Therefore, in the development region, a development potential acts between the electrostatic latent image formed on the photoconductor  1  and the developing sleeve of the developing device  8  in such a way as to electrostatically move the toner from the developing sleeve to the electrostatic latent image on the surface of the photoconductor  1 . By contrast, a background potential acts between the background surface of the photoconductor  1  and the development sleeve of the developing device  8  to electrostatically move the toner from the photoconductor  1  to the developing sleeve. This action of the background potential causes the toner to selectively adhere to the electrostatic latent image formed on the surface of the photoconductor  1 , so that the electrostatic latent image is developed in the development region. 
     The developer that has passed through the development region enters an opposite region in which the developing sleeve faces the second screw  8   c  as the developing sleeve rotates. In the opposite region, a repulsive magnetic field is formed by two magnetic poles having polarities different from each other out of multiple magnetic poles included in the magnet roller. The developer that has entered the opposite region is separated from the surface of the developing sleeve due to the effect of the repulsive magnetic field and is collected by the second screw  8   c.    
     The developer that is conveyed by the inclined screw  8   d  contains the developer that has been collected from the developing roller  8   a , and this collected developer is contributed to development in the development region, so that the toner concentration is lowered. The developing device  8  includes a toner concentration sensor that detects the toner concentration of the developer to be conveyed by the inclined screw  8   d . Based on detection results obtained by the toner concentration sensor, a controller  51  that functions as circuitry outputs a replenishment operation signal for replenishing the toner to the developer that is conveyed by the inclined screw  8   d , as required. 
     A toner cartridge  9  is disposed above the developing device  8 . The toner cartridge  9  contains toner and agitates the toner with agitators  9   b  fixed to a rotary shaft  9   a . Further, a toner replenishment member  9   c  is driven to rotate according to the replenishment operation signal output from the controller  51 . With this operation, an amount of the toner corresponding to a rotation amount of the toner replenishment member  9   c  is replenished to the inclined screw  8   d  of the developing device  8 . 
     The toner image formed on the surface of the photoconductor  1  as a result of the development by the developing device  8  enters the transfer nip region where the photoconductor  1  and the transfer roller  10  contact each other along with rotation of the photoconductor  1 . An electric bias having the opposite polarity to the latent image electric potential of the photoconductor  1  is applied to the transfer roller  10 . Accordingly, a transfer bias is formed within the transfer nip region. 
     As described above, the pair of registration rollers  43  conveys the recording sheet S toward the transfer nip region in synchrony with a timing at which the toner image formed on the photoconductor  1  is overlaid onto the sheet S in the transfer nip region. Due to the transfer bias and the nip pressure, as the recording sheet S is brought to closely contact with the toner image formed on the photoconductor  1  at the transfer nip region, the toner image is transferred onto the recording sheet S. 
     Residual toner that is not transferred onto the recording sheet S remains on the surface of the photoconductor  1  after having passed through the transfer nip region. After being scraped off from the surface of the photoconductor  1  by the cleaning blade  2  that is in contact with the photoconductor  1 , the residual toner is conveyed by the toner collection screw  3 , toward a waste toner bottle. 
     The surface of the photoconductor  1  that is cleaned by the cleaning blade  2  is electrically discharged by an electric discharging device. Thereafter, the surface of the photoconductor  1  is uniformly charged again by the charging roller  4 . Foreign materials such as toner additive agents and the toner that has not been removed by the cleaning blade  2  remain on the charging roller  4  that is in contact with the surface of the photoconductor  1 . These foreign materials are shifted to the charging roller cleaning roller  5  that is in contact with the charging roller  4 , and then are scraped off from the surface of the charging roller cleaning roller  5  by the scraper  6  that is in contact with the charging roller cleaning roller  5 . The foreign materials scraped off from the surface of the charging roller cleaning roller  5  falls onto the toner collection screw  3 . 
     In  FIG.  1   , the recording sheet S, which has passed through the transfer nip region formed by the photoconductor  1  and the transfer roller  10  contacting each other, is conveyed to a fixing device  44 . The fixing device  44  includes a fixing roller  44   a  and a pressure roller  44   b . The fixing roller  44   a  includes a heat generating source such as a halogen lamp. The pressure roller  44   b  is pressed against the fixing roller  44   a . The fixing roller  44   a  and the pressure roller  44   b  contact each other to form a fixing nip region. The toner image is fixed to the surface of the recording sheet S that is held in the fixing nip region due to application of heat and pressure. Thereafter, the recording sheet S that has passed through the fixing device  44  passes through a sheet ejection passage R 4 . Then, the recording sheet S is held in a sheet ejection nip region formed by a pair of sheet ejection rollers  46 . 
     The image forming apparatus  1000  switches printing modes between a single-side printing mode for performing single-side printing and a duplex printing mode for performing duplex printing. In the single-side printing mode, the image forming apparatus  1000  produces an image on one side of the recording sheet S. By contrast, the image forming apparatus  1000  prints respective images on both sides of the recording sheet S in the duplex printing mode. In the single-side printing mode or in the duplex printing mode in which images are formed on both sides of the recording sheet S, the pair of sheet ejection rollers  46  continues rotating in a forward direction and a reverse direction alternately, so that the recording sheet S in the sheet ejection passage R 4  is ejected out of the image forming apparatus  1000 . After passing through the fixing device  44 , the recording sheet S is stacked on a sheet stacker provided on the top face of the housing  50  of the image forming apparatus  1000 . 
     By contrast, in the duplex printing mode when an image is formed on one side of the recording sheet S, the pair of sheet ejection rollers  46  is rotated in the reverse direction at the timing at which the trailing end of the recording sheet S enters the sheet ejection nip region of the pair of sheet ejection rollers  46 . At this time, a switching claw  47  disposed near the downstream end of the sheet ejection passage R 4  moves to block (close) the sheet ejection passage R 4  and open an entrance of a reverse conveyance passage R 5  at the same time. As the recording sheet S starts reversing by the reverse rotation of the pair of sheet ejection rollers  46 , the recording sheet S is conveyed to the reverse sheet conveyance passage R 5 . The downstream end of the reverse sheet conveyance passage R 5  meets the common sheet conveyance passage R 3  on the upstream side from the pair of registration rollers  43  in the sheet conveyance direction. After being conveyed in the reverse sheet conveyance passage R 5 , the recording sheet S is conveyed to the pair of registration rollers  43  in the common sheet conveyance passage R 3  again. Then, after a toner image has been formed on the other side of the recording sheet S in the transfer nip region, the recording sheet S passes through the fixing device  44 , the sheet ejection passage R 4 , and the pair of sheet ejection rollers  46  and is then ejected to the outside of the housing  50  of the image forming apparatus  1000 . 
     Next, a description is given of the configuration and operations of a sheet conveying device that conveys the recording sheet S. 
       FIG.  3    is a perspective view illustrating the main configuration of a sheet conveying device  200  including a regular sheet feeder  110  to feed a recording sheet S from the sheet tray  100  a bypass sheet feeder  30  to feed a recording sheet S from the bypass sheet tray  31  in the image forming apparatus  1000 . 
       FIG.  4    is a perspective view illustrating a configuration of a drive mechanism in the sheet conveying device  200  for driving the regular sheet feeder  110  and the bypass sheet feeder  30 . 
     As illustrated in  FIGS.  3  and  4   , the drive mechanism of the regular sheet feeder  110  and the bypass sheet feeder  30  has a configuration in which a single main motor  61  applies driving force to be transmitted (distributed) to the sheet feed roller  41 , the pair of relay rollers  42 , the bypass sheet feed roller  32 , and the bypass bottom plate cam  35 . To be more specific, the driving force output from a motor shaft  61   a  of the main motor  61  that functions as a drive source is transmitted, via various idler gears, to a sheet feed roller shaft  62  mounted on the sheet feed roller  41 , a relay roller shaft  63  mounted on the pair of relay rollers  42 , a bypass sheet feed roller shaft  64  mounted on the bypass sheet feed roller  32 , and a bypass bottom plate cam shaft  65  mounted on the bypass bottom plate cam  35 . In other words, the sheet feed roller shaft  62 , the relay roller shaft  63 , the bypass sheet feed roller shaft  64 , and the bypass bottom plate cam shaft  65  receive the driving force from the motor shaft  61   a  of the main motor  61 . 
     The sheet feed roller shaft  62 , the relay roller shaft  63 , the bypass sheet feed roller shaft  64 , and the bypass bottom plate cam shaft  65  includes respective clutches, which are a regular sheet feed clutch  62   a , a relay clutch  63   a , a bypass sheet feed clutch  64   a , and a bypass sheet bottom plate cam clutch  65   a  to turn on and off transmission of the driving force. When the regular sheet feed clutch  62   a , the relay clutch  63   a , the bypass sheet feed clutch  64   a , and the bypass sheet bottom plate cam clutch  65   a  are turned on (energized), the driving force is transmitted to rotate the sheet feed roller shaft  62 , the relay roller shaft  63 , the bypass sheet feed roller shaft  64 , and the bypass bottom plate cam shaft  65 , respectively. On the other hand, when the regular sheet feed clutch  62   a , the relay clutch  63   a , the bypass sheet feed clutch  64   a , and the bypass sheet bottom plate cam clutch  65   a  are turned off, the driving force is not transmitted (transmission of the driving force is blocked), and therefore the sheet feed roller shaft  62 , the relay roller shaft  63 , the bypass sheet feed roller shaft  64 , and the bypass bottom plate cam shaft  65  are not rotated. Note that the driving force of the main motor  61  is also transmitted to the pair of registration rollers  43  via a registration clutch for the pair of registration rollers  43 . In the present embodiment, the controller  51  controls turning on and off of each clutch (i.e., the regular sheet feed clutch  62   a , the relay clutch  63   a , the bypass sheet feed clutch  64   a , and the bypass sheet bottom plate cam clutch  65   a ) using the driving force of the main motor  61 , so as to perform conveyance of the recording sheet S. In other words, the controller  51  controls conveyance of the recording sheet S. 
       FIG.  5    is a diagram for explaining a sheet conveyance passage in the regular sheet feeder  110  and a sheet conveyance passage in the bypass sheet feeder  30 .  FIG.  6    is a flowchart of a control operation of sheet conveyance from the regular sheet feeder  110 . 
     First, a description is given of conveyance of the recording sheet S from the regular sheet feeder  110 , with reference to the flowchart of  FIG.  6   . 
     The regular sheet feeder  110  includes a regular sheet feeder bottom plate  101  that is biased upward toward the sheet feed roller  41 . Since the regular sheet feeder bottom plate  101  is biased as described above, the sheet feed roller  41  is in contact with an uppermost recording sheet S of the plurality of recording sheets S loaded in a form of a sheet bundle on the regular sheet feeder bottom plate  101 . When starting conveyance of the recording sheet S from the regular sheet feeder  110 , the controller  51  confirms whether the initial operation is completed (step S 1 ). When the initial operation is not completed (NO in step S 1 ), the controller  51  starts the initial operation (step S 2 ). 
     When the initial operation is completed (YES in step S 1 ), the controller  51  turns on the main motor  61  (step S 3 ), and then turns on the regular sheet feed clutch  62   a  and the relay clutch  63   a  (step S 4 ). Consequently, as the sheet feed roller  41  rotates, the uppermost recording sheet S in the sheet tray  100  is fed toward the sheet separation pad  48 . At this time, even if the second and subsequent recording sheets S are fed together with the uppermost recording sheet S, frictional force generated by friction with the sheet separation pad  48  prevents from further conveyance of the second and subsequent recording sheets S, and therefore the uppermost recording sheet S alone passes the sheet separation pad  48 . Note that, while the recording sheet S is fed (conveyed) from the regular sheet feeder  110 , no recording sheet S is conveyed from the bypass sheet feeder  30 . Therefore, the bypass sheet feed clutch  64   a  and the bypass sheet bottom plate cam clutch  65   a  are remained in an OFF state. 
     Thereafter, the recording sheet S that is fed from the sheet tray  100  is conveyed along the regular sheet conveyance passage R 1  in  FIG.  5   . At this time, a relay drive roller  42   a  that is one of the pair of relay rollers  42  is driven to rotate by the driving force of the main motor  61 . Further, a relay driven roller  42   b  that is the other of the pair of relay rollers  42  has a roller shaft  66  that is received by a bearing  37   a . As illustrated in  FIG.  5   , the relay driven roller  42   b  is biased by a biasing force of a pressure spring  37   b  at the bearing  37   a , so that the relay driven roller  42   b  is in contact with the relay drive roller  42   a  due to the biasing force of the pressure spring  37   b . Accordingly, the relay driven roller  42   b  is rotated along with rotation of the relay drive roller  42   a . The recording sheet S conveyed through the regular sheet conveyance passage R 1  is conveyed in a state in which the recording sheet S is sandwiched (held) in a relay nip region by the relay drive roller  42   a  and the relay driven roller  42   b.    
     When the leading end of the recording sheet S reaches the registration sensor  49 , the controller  51  determines whether the registration sensor  49  has turned on (step S 5 ). When the registration sensor  49  has turned on (YES in step S 5 ), the controller  51  turns off the regular sheet feed clutch  62   a  and the relay clutch  63   a  after a given time has elapsed (before the leading end of the recording sheet S reaches the pair of registration rollers  43 ) (step S 6 ). The given time is, for example, 100 ms from the turning on of the registration sensor  49 . After step S 6 , conveyance of the recording sheet S is temporarily stopped. Accordingly, the leading end of the recording sheet S contacts the registration nip region of the pair of registration rollers  43  that has been stopped, so that skew of the recording sheet S is corrected. 
     Then, the controller  51  turns on the relay clutch  63   a  and the registration clutch at a timing at which the recording sheet S is overlaid on the toner image formed on the surface of the photoconductor  1  in the transfer nip region (step S 7 ). The timing is, for example, 200 ms after the controller  51  has turned off the regular sheet feed clutch  62   a  and the relay clutch  63   a . Accordingly, the controller  51  starts the pair of registration rollers  43  and the pair of relay rollers  42  to rotate to convey the recording sheet S toward the transfer nip region. At this time, since the regular sheet feed clutch  62   a  remains off, the sheet feed roller  41  is not rotated. Even in a state in which the trailing end of the recording sheet S is sandwiched (held) between the sheet feed roller  41  and the sheet separation pad  48 , the sheet feed roller  41  is rotated along with movement of the recording sheet S conveyed by the conveyance force of the pair of registration rollers  43  and the conveyance force of the pair of relay rollers  42 . Therefore, conveyance of the recording sheet S is not hindered. Then, the controller  51  determines whether the registration sensor  49  is turned off (step S 8 ). When the trailing end of the recording sheet S reaches the registration sensor  49  and the registration sensor  49  is turned off (YES in step S 8 ), the controller  51  turns off the relay clutch  63   a  (step S 9 ) to stop rotation of the pair of relay rollers  42 . 
     Next, a description is given of conveyance of the recording sheet S from the bypass sheet feeder  30 , with reference to  FIGS.  7  to  9   . 
       FIG.  7    is an external perspective view illustrating a state in which the bypass sheet tray  31  is removed from the bypass sheet feeder  30 . 
       FIG.  8    is a perspective view illustrating the main configuration of the bypass sheet feeder  30 . 
       FIG.  9    is a flowchart of a control operation of sheet conveyance from the bypass sheet feeder  30 . 
     The bypass bottom plate  34  is biased by a bottom plate spring  36  toward the bypass sheet feed roller  32  that is disposed facing the bypass bottom plate  34 . Further, as illustrated in  FIG.  8   , a bottom plate guide  34   a  is provided on the bypass bottom plate  34 , at a portion facing the bypass bottom plate cam  35 . As the bypass bottom plate cam shaft  65  rotates, the bypass bottom plate cam  35  contacts the bottom plate guide  34   a  to press down the bottom plate guide  34   a  (see  FIG.  10   ). By so doing, the bypass bottom plate  34  lowers against the biasing force of the bottom plate spring  36  to separate from the bypass sheet feed roller  32 . 
     When starting conveyance of the recording sheet S from the bypass sheet feeder  30 , the controller  51  confirms whether the initial operation is completed (step S 11 ). When the initial operation is not completed (NO in step S 11 ), the controller  51  starts the initial operation (step S 12 ). When the initial operation is completed (YES in step S 11 ), the controller  51  turns on the main motor  61  (step S 13 ), and then turns on the bypass sheet bottom plate cam clutch  65   a  (step S 14 ). As the bypass bottom plate cam shaft  65  rotates, the bypass bottom plate cam  35  changes states from a state in which the bypass bottom plate cam  35  is in contact with the bottom plate guide  34   a  (in other words, a state in which the bypass bottom plate  34  is separated from the bypass sheet feed roller  32 ) (see  FIG.  10   ) to a state in which the bypass bottom plate cam  35  is not in contact with the bottom plate guide  34   a  (see  FIGS.  5  and  8   ). 
     To be more specific, the bypass sheet feeder  30  includes a projecting plate  35   a  that is integrally formed with the bypass bottom plate cam  35  and a press-down lever  65   d  that presses down a cam detection feeler  65   b . As the bypass bottom plate cam shaft  65  rotates, the projecting plate  35   a  rotates from a position at which the projecting plate  35   a  contacts the press-down lever  65   d  to press down the cam detection feeler  65   b  (see  FIG.  10   ) to a position at which the projecting plate  35   a  is separated from the press-down lever  65   d . Accordingly, the cam detection feeler  65   b  is lifted due to a given biasing force to be detected by a feeler sensor  65   c . The controller  51  determines whether the feeler sensor  65   c  is turned on (step S 15 ). When the feeler sensor  65   c  is turned on (YES in S 15 ), the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 16 ). Accordingly, the bypass bottom plate cam shaft  65  stops rotating in the state in which the bypass bottom plate cam  35  is separated from the bottom plate guide  34   a . Therefore, the bypass bottom plate  34  is biased by the biasing force of the bottom plate spring  36  toward the bypass sheet feed roller  32 . As a result, the bypass sheet feed roller  32  is in contact with the uppermost recording sheet S of the plurality of recording sheets S loaded in a form of a sheet bundle on the bypass sheet tray  31  and the bypass bottom plate  34 . The bypass sheet tray  31  and the bypass bottom plate  34  are coupled to each other, each of which functioning as a sheet loader. 
     Subsequently, the controller  51  turns on the bypass sheet feed clutch  64   a  (step S 17 ). Consequently, as the bypass sheet feed roller  32  rotates, the uppermost recording sheet S on the bypass bottom plate  34  is fed toward the sheet separation pad  33 . At this time, even if the second and subsequent recording sheets S are fed together with the uppermost recording sheet S, the conveyance of the second and subsequent recording sheets S is hindered by the frictional force with the sheet separation pad  33 , and the uppermost recording sheet S alone passes the sheet separation pad  33 . 
     Note that, while the recording sheet S is fed (conveyed) from the bypass sheet feeder  30 , no recording sheet S is conveyed from the regular sheet feeder  110 . Therefore, the regular sheet feed clutch  62   a  and the relay clutch  63   a  are remained in an OFF state. 
     Thereafter, the recording sheet S that is fed from the bypass sheet tray  31  is conveyed along the bypass sheet conveyance passage R 2  in  FIG.  5   . When the leading end of the recording sheet S reaches the registration sensor  49 , the controller  51  determines whether the registration sensor  49  has turned on (step S 18 ). When the registration sensor  49  has turned on (YES in step S 18 ), the controller  51  turns off the bypass sheet feed clutch  64   a  after a given time has elapsed (before the leading end of the recording sheet S reaches the pair of registration rollers  43 ) (step S 19 ). The given time is, for example, 100 ms from the turning on of the registration sensor  49 . After step S 19 , conveyance of the recording sheet S is temporarily stopped. Accordingly, the leading end of the recording sheet S contacts the registration nip region of the pair of registration rollers  43  that has been stopped, so that skew of the recording sheet S is corrected. 
     Then, the controller  51  turns on the registration clutch at a timing at which the recording sheet S is overlaid on the toner image formed on the surface of the photoconductor  1  in the transfer nip region (step S 20 ). Accordingly, the controller  51  starts the pair of registration rollers  43  to rotate to convey the recording sheet S toward the transfer nip region. At this time, the bypass sheet feed clutch  64   a  remains in the OFF state, and therefore the bypass sheet feed roller  32  does not rotate. In a state in which the trailing end of the recording sheet S is still sandwiched (held) between the sheet feed roller  32  and each of the sheet separation pad  33  and the bypass bottom plate  34 , the sheet conveyance load is significantly great (heavy). Therefore, it is likely that the recording sheet S is not conveyed properly by the sheet conveyance force of the pair of registration rollers  43  alone. 
     In order to address this inconvenience, the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  (step S 21 ) to rotate the bypass bottom plate cam shaft  65 . Along with the rotation of the bypass bottom plate cam shaft  65 , the bypass bottom plate cam  35  changes states from the state in which the bypass bottom plate cam  35  is not in contact with the bottom plate guide  34   a  (in other words, a state in which the bypass bottom plate  34  is biased to the bypass sheet feed roller  32 ) to the state in which the bypass bottom plate cam  35  is in contact with the bottom plate guide  34   a  (in other words, the state in which the bypass bottom plate  34  is separated from the bypass sheet feed roller  32 ). To be more specific, the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  and, after a given time (for example, after 200 ms), turns off the bypass sheet bottom plate cam clutch  65   a  (step S 22 ). Accordingly, the bypass bottom plate cam shaft  65  stops rotating in the state in which the bypass bottom plate cam  35  is in contact with the bottom plate guide  34   a . Therefore, the bypass bottom plate  34  is separated from the bypass sheet feed roller  32 . As a result, the trailing end of the recording sheet S is not sandwiched (held) between the bypass sheet feed roller  32  and the bypass bottom plate  34 , and therefore the sheet conveyance load is reduced. Accordingly, the recording sheet S is conveyed properly by the sheet conveyance force of the pair of registration rollers  43  alone. 
     As illustrated in  FIG.  7   , the bypass sheet feeder  30  in the present embodiment has a unit structure in which the relay driven roller  42   b , which is one of the pair of relay rollers  42 , is supported integrally with the bypass sheet feeding mechanism. This unit structure including the relay driven roller  42   b  and the bypass sheet feeding mechanism is screwed and fixed to the housing  50  of the image forming apparatus  1000 . 
     Here, when a device error (problem) to suspend conveyance of the recording sheet S, such as a paper jam error, occurs to the image forming apparatus  1000 , the recording sheet S remaining in the image forming apparatus  1000  needs to be removed. In order to facilitate the work of removing the recording sheet S, a user opens the possible areas in which the recording sheet S is sandwiched (such as the sheet conveyance nip region of the pair of relay rollers  42  and the nip region of the bypass sheet feed roller  32  and the bypass bottom plate  34 ) and removes the sheet tray  100  from the image forming apparatus  1000  in a sheet conveyance direction or in a direction intersecting the sheet conveyance direction, so that the recording sheet S remaining in the image forming apparatus  1000  is removed downward easily. Therefore, in the image forming apparatus  1000  of the present embodiment, when a failure such as a paper jam has occurred to the image forming apparatus  1000  while the recording sheet S is being fed from the sheet tray  100  in the image forming apparatus  1000 , the rollers (i.e., the relay drive roller  42   a  and the relay driven roller  42   b ) of the pair of relay rollers  42  are separated from each other to remove the recording sheet S. 
     As a configuration in which the rollers of the pair of relay rollers  42  can be separated from each other, known image forming apparatuses employ a configuration in which the relay driven roller  42   b  is supported on the door openably and closably attached to the housing  50  of the image forming apparatus  1000 . However, in this configuration, the door to separate the pair of relay rollers  42  is needed, as well as a user operation to open the door and close the door after removing the recording sheet S. Then, normally when a failure such as a paper jam has occurred to the image forming apparatus  1000 , in addition to this user operation to open and close the door, another user operation is also needed to open the transfer nip region. Therefore, in the configuration in which the user operation to open and close the door for separating the rollers of the pair of relay rollers  42  and removing the recording sheet S remaining in the image forming apparatus  1000 , more user operations are forced to be performed, which degrades convenience of the user when removing the recording sheet S. 
     For example, a known sheet conveying device includes three sheet trays having respective sheet conveyance passages. The known sheet conveying device can convey a sheet in each of the three sheet trays via the sheet conveyance passage of the selected sheet tray, to a transfer drum. The known sheet conveying device further includes a pair of intermediate conveyance rollers (a pair of sheet conveying rollers) on the sheet conveyance passage corresponding to a selected one of the three sheet trays. The pair of intermediate conveyance rollers grips a sheet fed from the selected one of the three sheet trays. In the known sheet conveying device, each sheet fed out from the other two sheet trays is not gripped by the pair of intermediate conveyance rollers. The pair of intermediate conveyance rollers has two rollers. One roller of the pair of intermediate conveyance rollers is supported on a door. At occurrence of a paper jam, opening the door separates the one roller from the other roller of the pair of intermediate conveyance rollers, so that a user can remove the jammed sheet easily. 
     However, the known sheet conveying device does not perform convenient operations with the configuration in which the one roller of the pair of intermediate conveyance rollers is separated from the other roller of the pair of intermediate conveyance rollers. 
     In order to address the degradation of user convenience, when a failure such as a paper jam occurs in the image forming apparatus  1000 , a moving unit to move a movable member such as the bypass bottom plate  34  that moves when the recording sheet S is conveyed in the bypass sheet feeder  30 , so as to separate the rollers of the pair of relay rollers  42  along with movement of the movable member. 
     In the present embodiment, the rollers of the pair of relay rollers  42  are separated in the regular sheet conveyance passage R 1  along with movement of a movable member that is used for conveying the recording sheet S in the bypass sheet conveyance passage R 2 . In the present embodiment, when the recording sheet S is conveyed using the regular sheet conveyance passage R 1 , the recording sheet S is not conveyed in the bypass sheet conveyance passage R 2  simultaneously. Therefore, in a case in which a failure such as a paper jam occurs while the recording sheet S is conveyed in the regular sheet conveyance passage R 1 , when the rollers of the pair of relay rollers  42  are separated from each other, movement of the movable member used to conveying the recording sheet S in the bypass sheet conveyance passage R 2  does not hinder conveyance of the recording sheet S or removal of the recording sheet S remaining in the image forming apparatus  1000 . 
     In the present embodiment, a sheet feeder for bypass sheet feeding such as the bypass sheet feeder  30  causes the recording sheet S on the bypass bottom plate  34  to contact the bypass sheet feed roller  32 , thereby feeding the recording sheet S. Therefore, in the present embodiment, the bypass bottom plate  34  functions as a movable member. Along with movement of the bypass bottom plate  34 , the rollers of the pair of relay rollers  42  are separated from each other. 
     Specifically, the moving unit that causes the bypass bottom plate  34  to move rotates the bypass bottom plate cam shaft  65  by the driving force of the main motor  61 , as described above. Then, when the bypass bottom plate cam shaft  65  is located at a rotational position at which the bypass bottom plate cam  35  presses down the bottom plate guide  34   a  against the biasing force of the bottom plate spring  36 , the bypass bottom plate  34  is lowered (moved downward) to separate from the bypass sheet feed roller  32 . On the other hand, when the bypass bottom plate cam shaft  65  is located at the rotational position at which the bypass bottom plate cam  35  separates from the bottom plate guide  34   a , the bypass bottom plate  34  is lifted (moved upward) by the biasing force of the bottom plate spring  36  to contact the bypass sheet feed roller  32 . As a slide lever  38  that functions as a roller support supporting the relay driven roller  42   b , which is one roller of the pair of relay rollers  42 , to move along with rotation of the bypass bottom plate cam shaft  65 , the separation unit of the present embodiment separates or contacts the rollers of the pair of relay rollers  42 . A detailed description of the separation unit is given below. 
       FIG.  11    is a perspective view illustrating a configuration of the separation unit that separates the rollers of the pair of relay rollers  42  from each other. 
       FIG.  12    is a perspective view illustrating the main configuration of the separation unit. 
       FIG.  13    is a perspective view illustrating a support frame of the bypass sheet feeder  30  to which the relay driven roller  42   b  of the pair of relay rollers  42  is attached. Note that  FIG.  13    illustrates the support frame without the relay driven roller  42   b , for convenience. 
       FIG.  14 A  is a diagram for explaining a state in which the rollers of the pair of relay rollers  42  come to contact with each other.  FIG.  14 B  is a diagram for explaining a state in which the rollers of the pair of relay rollers  42  separate from each other. 
     As illustrated in  FIG.  13   , the bearing  37   a  that receives the roller shaft  66  of the pair of relay rollers  42  is attached to a slide slot  37   c  formed in the support frame of the bypass sheet feeder  30 , so that the relay driven roller  42   b  is supported to be slidable in a direction in which the relay driven roller  42   b  separates from the relay drive roller  42   a . The roller shaft  66  of the pair of relay rollers  42  is supported by the slide lever  38  on the outside of each bearing  37   a  in the axial direction. In other words, the roller shaft  66  of the relay driven roller  42   b  of the pair of relay rollers  42  is supported by the slide lever  38  in the axial direction. As described above, the bearing  37   a  of the relay driven roller  42   b  is biased by the pressure spring  37   b  in a direction in which the relay driven roller  42   b  contacts the relay drive roller  42   a  (that is, a direction indicated by arrow in  FIG.  14 A ). Therefore, the slide lever  38  supporting the roller shaft  66  of the rollers of the pair of relay rollers  42  receives the biasing force in the same direction as the bearing  37   a.    
     The slide lever  38  has a slide hole  38   a  that functions as an opening through which the bypass bottom plate cam shaft  65  is inserted, at an end opposite the end supporting the roller shaft  66  of the pair of relay rollers  42 . On the other hand, as illustrated in  FIG.  12   , the bypass bottom plate cam shaft  65  has a pressing portion  65   e  configured to face the slide hole  38   a  of the slide lever  38 , so that the pressing portion  65   e  of the bypass bottom plate cam shaft  65  presses against an inner wall (that functions as a pressing target portion) of the slide hole  38   a  of the slide lever  38 . The pressing portion  65   e  rotates along with rotation of the bypass bottom plate cam shaft  65 . 
     When the rotational position of the bypass bottom plate cam shaft  65  is located at a position to lower the bypass bottom plate  34  (that is, a position at which the bypass bottom plate  34  separates from the bypass sheet feed roller  32 ), the pressing portion  65   e  on the bypass bottom plate cam shaft  65  is located at a non-pressing position, as illustrated in  FIG.  14 A . At this time, the slide lever  38  is movable in a direction in which the relay driven roller  42   b  contacts the relay drive roller  42   a  (that is, the direction indicated by arrow in  FIG.  14 A ) due to a gap between the slide hole  38   a  of the slide lever  38  and the bypass bottom plate cam shaft  65 . Therefore, the relay driven roller  42   b  contacts the relay drive roller  42   a  due to the biasing force of the pressure spring  37   b , thereby conveying the recording sheet S in the image forming apparatus  1000 . Note that, since the bypass bottom plate  34  is separated from the bypass sheet feed roller  32 , the recording sheet P is not conveyed from the bypass sheet feeder  30 , conveyance of the recording sheet S in the image forming apparatus  1000  does not hinder conveyance of the recording sheet S from the bypass sheet feeder  30 . 
     By contrast, when the rotational position of the bypass bottom plate cam shaft  65  is located at a position to lift the bypass bottom plate  34  (that is, a position at which the bypass bottom plate  34  contacts the bypass sheet feed roller  32 ), the pressing portion  65   e  on the bypass bottom plate cam shaft  65  is located at a pressing position, as illustrated in  FIG.  14 B . At this time, while the slide lever  38  is biased by the biasing force of the pressure spring  37   b , the pressing portion  65   e  presses the inner wall of the slide hole  38   a  against the biasing force of the pressure spring  37   b , so that the slide lever  38  is moved in a direction in which the relay driven roller  42   b  separates from the relay drive roller  42   a  (that is, the direction indicated by arrow in  FIG.  14 B ). As a result, the relay driven roller  42   b  is separated from the relay drive roller  42   a , thereby facilitating removal of the recording sheet S remaining in the image forming apparatus  1000  when conveying the recording sheet S in the image forming apparatus  1000 . Note that, although the bypass bottom plate  34  is in contact with the bypass sheet feed roller  32 , any jammed recording sheet S is not conveyed in the bypass sheet conveyance passage when the failure such as a paper jam occurs in the image forming apparatus  1000 . Therefore, contact of the bypass bottom plate  34  with the bypass sheet feed roller  32  does not hinder removal of the recording sheet S remaining in the image forming apparatus  1000  due to the paper jam occurred while the recording sheet S is conveyed in the image forming apparatus  1000 . 
     According to the present embodiment, the rollers of the pair of relay rollers  42  are separated in the regular sheet conveyance passage R 1  along with movement of the bypass bottom plate  34  that functions as a movable member used for conveying the recording sheet S in the bypass sheet conveyance passage R 2 . Accordingly, a simple configuration that does not include a dedicated moving unit that separates the rollers of the pair of relay rollers  42  from each other achieves a highly convenient structure without a user operation to separate the rollers of the pair of relay rollers  42 . 
     Next, a description is given of a process flow of operations for an irregular stop in the image forming apparatus  1000 . 
       FIG.  15    is a flowchart of a process flow of operations for an irregular stop of the image forming apparatus  1000  according to an embodiment of this disclosure. 
     In the image forming apparatus  1000 , when a device error (problem) to suspend conveyance of the recording sheet S, such as a device malfunction including a paper jam, is detected (step S 31 ), the controller  51  first turns off the regular sheet feed clutch  62   a , the relay clutch  63   a , and the bypass sheet feed clutch  64   a  to perform irregular stop (step S 32 ). Then, the controller  51  determines, from control data, whether the recording sheet S is being conveyed by the bypass sheet feeder  30  (step S 33 ). 
     When the recording sheet S is being conveyed by the bypass sheet feeder  30  (YES in step S 33 ), it is likely in the present embodiment that the recording sheet S is being sandwiched (held) between the bypass sheet feed roller  32  and the bypass bottom plate  34 . Therefore, the bypass sheet feed roller  32  and the bypass bottom plate  34  are separated from each other. In the present embodiment, when the bypass bottom plate cam shaft  65  rotates by 200 ms in the state in which the bypass bottom plate  34  is lifted and the feeler sensor  65   c  is turned on, the state changes to the state in which the bypass bottom plate  34  is lowered to separate from the bypass sheet feed roller  32 . Note that, at this time, the rollers of the pair of relay rollers  42  are in contact with each other. 
     In the present embodiment, as described above, while the recording sheet S is being conveyed by the bypass sheet feeder  30 , the bypass bottom plate  34  may be in contact with the bypass sheet feed roller  32  or be separated from the bypass sheet feed roller  32 . Therefore, the controller  51  determines whether the feeler sensor  65   c  is turned on (step S 34 ). When the feeler sensor  65   c  is turned on (YES in step S 34 ), the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  (step S 36 ) to rotate the bypass bottom plate cam shaft  65 . Then, after 200 ms has elapsed, the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 37 ) to stop rotation of the bypass bottom plate cam shaft  65 . Thereafter, the controller  51  turns off the main motor  61  (step S 41 ), and then stops the image forming apparatus  1000  (step S 42 ), so that a user can remove the jammed recording sheet(s) S from in the image forming apparatus  1000 . 
     On the other hand, when the feeler sensor  65   c  is turned off (NO in step S 34 ), the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 35 ) to rotate the bypass bottom plate cam shaft  65 . Then, the procedure returns to step S 34 . When the feeler sensor  65   c  is turned on (YES in step S 34 ), the controller  51  continues to turn on the bypass sheet bottom plate cam clutch  65   a  (step S 36 ) to continuously rotate the bypass bottom plate cam shaft  65 . Then, after 200 ms has elapsed, the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 37 ) to stop rotation of the bypass bottom plate cam shaft  65 . Thereafter, the controller  51  turns off the main motor  61  (step S 41 ), and then stops the image forming apparatus  1000  (step S 42 ), so that the user can remove the jammed recording sheet(s) S from in the image forming apparatus  1000 . 
     With the above-described control, when a device error (problem) to suspend conveyance of the recording sheet S occurs when conveying the recording sheet S by the bypass sheet feeder  30 , the bypass bottom plate  34  is separated from the bypass sheet feed roller  32 . This control facilitates removal of the recording sheet S remaining in the bypass sheet conveyance passage R 2  (in other words, the recording sheet S sandwiched between the bypass sheet feed roller  32  and the bypass bottom plate  34 ). 
     Further, when the recording sheet S is being conveyed by the regular sheet feeder  110  (not by the bypass sheet feeder  30 ) (NO in step S 33 ), it is likely in the present embodiment that the recording sheet S is being sandwiched (held) between the rollers of the pair of relay rollers  42 . Therefore, the rollers of the pair of relay rollers  42  are separated from each other. In the present embodiment, when the feeler sensor  65   c  is turned on (in an ON state), the bypass bottom plate  34  is lifted to contact the bypass sheet feed roller  32  and, at the same time, the rollers of the pair of relay rollers  42  are separated from each other. 
     In the present embodiment, as described above, the rollers of the pair of relay rollers  42  are constantly in contact with each other while the recording sheet S is being conveyed by the regular sheet feeder  110  in the image forming apparatus  1000 . Therefore, the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  without determining whether the feeler sensor  65   c  is turned on (step S 38 ) to rotate the bypass bottom plate cam shaft  65 . Then, the controller  51  determines whether the feeler sensor  65   c  is turned on (step S 39 ). When the feeler sensor  65   c  is turned on (YES in step S 39 ), the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 40 ) to stop rotation of the bypass bottom plate cam shaft  65 . Thereafter, the controller  51  turns off the main motor  61  (step S 41 ), and then stops the image forming apparatus  1000  (step S 42 ), so that the user can remove the jammed recording sheet(s) S from in the image forming apparatus  1000 . 
     With the above-described control, when the device error (problem) to suspend conveyance of the recording sheet S occurs when conveying the recording sheet S by the regular sheet feeder  110 , the rollers of the pair of relay rollers  42  are separated from each other. This control facilitates removal of the recording sheet S remaining in the regular sheet conveyance passage R 1  (in other words, the recording sheet S sandwiched between the rollers of the pair of relay rollers  42 ). Moreover, a user operation to continuously separate the rollers of the pair of relay rollers  42  from each other is avoided, which is highly convenient. In addition, the configuration of the present embodiment achieves separation of the rollers of the pair of relay rollers  42  along with movement of the bypass bottom plate  34  functioning as a movable member used for conveying the recording sheet S in the bypass sheet conveyance passage R 2  without employing a dedicated moving unit to perform the above-described operation. Therefore, a simple configuration that does not include such a dedicated moving unit that separates the rollers of the pair of relay rollers  42  from each other achieves a highly convenient structure without a user operation to separate the rollers of the pair of relay rollers  42 . 
     Next, a description is given of a process flow of operations for finishing the irregular stop in the image forming apparatus  1000 . 
       FIG.  16    is a flowchart of a process flow of operations for finishing the irregular stop of the image forming apparatus  1000  according to an embodiment of this disclosure. 
     When an irregular stop of the image forming apparatus  1000  occurs and removal of the recording sheet S is completed, the controller  51  finishes (cancels) the irregular stop of the image forming apparatus  1000  (step S 51 ), and firstly determines whether the registration sensor  49  is turned off (step S 52 ). When a device error (problem) to suspend conveyance of the recording sheet S occurs to the image forming apparatus  1000 , the recording sheet S that has been under sheet conveyance is located at an opposing position to face the registration sensor  49 . Therefore, when the registration sensor  49  is turned off (YES in step S 52 ), the controller  51  determines that the recording sheet S remaining in the image forming apparatus  1000  at the irregular stop is removed, and then starts an initial operation to resume the print job (step S 54 ). On the other hand, when the registration sensor  49  is turned on (NO in step S 52 ), the controller  51  causes the state of the image forming apparatus  1000  to return to (or continue) the irregular stop (step S 53 ). Consequently, the controller  51  informs a user to encourage the user to remove the recording sheet S from the image forming apparatus  1000 . 
     When the initial operation is started in step S 54 , the controller  51  first turns on the main motor  61  (step S 55 ). Then, the controller  51  determines whether the feeler sensor  65   c  is turned on (step S 56 ). When the feeler sensor  65   c  is turned on (YES in step S 56 ), the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  (step S 58 ) to rotate the bypass bottom plate cam shaft  65 . Then, after 200 ms has elapsed, the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 59 ) to stop rotation of the bypass bottom plate cam shaft  65 . Then, the controller  51  turns off the main motor  61  (step S 60 ) to complete the initial operation (step S 61 ) to end the control flow in the flowchart of  FIG.  16   . 
     On the other hand, when the feeler sensor  65   c  is turned off (NO in step S 56 ), the controller  51  turns on the bypass sheet bottom plate cam clutch  65   a  (step S 57 ) to rotate the bypass bottom plate cam shaft  65 . Then, the procedure returns to step S 56 . When the feeler sensor  65   c  is turned on (YES in step S 56 ), the controller  51  continues to turn on the bypass sheet bottom plate cam clutch  65   a  (step S 58 ) to continuously rotate the bypass bottom plate cam shaft  65 . Then, after 200 ms has elapsed, the controller  51  turns off the bypass sheet bottom plate cam clutch  65   a  (step S 59 ) to stop rotation of the bypass bottom plate cam shaft  65 . Then, the controller  51  turns off the main motor  61  (step S 60 ), so that the initial operation is completed (step S 61 ) to end the control flow in the flowchart of  FIG.  16   . 
     As described above, in the configuration of the present embodiment, when removing the recording sheet S remaining in the regular sheet conveyance passage R 1 , the rollers of the pair of relay rollers  42  that is used for conveying the recording sheet S in the regular sheet conveyance passage R 1  are separated along with movement of the bypass bottom plate  34  functioning as a movable member that is used for conveying the recording sheet S in the bypass sheet conveyance passage R 2 . However, a configuration of the sheet conveying device is not limited to this configuration. For example, in a case in which the bypass sheet feeder  30  employs a sheet feeder having a configuration in which the bypass sheet feed roller  32  is lowered (moved downward) to press (contact) the bypass sheet feed roller  32  to a recording sheet on the bypass sheet tray  31  to feed the recording sheet, the bypass sheet feed roller  32  may be a movable member to separate the rollers of the pair of relay rollers  42  along with movement of the bypass sheet feed roller  32 . Further, for example, the rollers of the pair of relay rollers  42  may be separated from each other along with movement of a movable member that is used in a sheet conveyance passage other than the bypass sheet conveyance passage R 2  (for example, the reverse sheet conveyance passage R 5 ). 
     Further, in the present embodiment, a description of the separation unit to separate the rollers of the pair of relay rollers  42  used in the regular sheet conveyance passage R 1  has been made but any other separation unit may be applied. For example, a separation unit to separate rollers of other pair of conveyance rollers (for example, the pair of sheet ejection rollers  46 ) may be employed. In addition, the pair of relay rollers  42  of the present embodiment in which the rollers are separated from each other is a pair of sheet conveying rollers including a drive roller and a driven roller. However, the configuration of the pair of sheet conveying rollers applied to the present embodiment is not limited to the above-described pair of relay rollers  42 . For example, the pair of sheet conveying rollers may include two drive rollers or two driven rollers. 
     Further, in the present embodiment according to this disclosure, the image forming apparatus  1000  is described as an example of a printer. However, the image forming apparatus  1000  may be a copier including an image reading device or a copier having a function of a facsimile machine. Further, this disclosure is applicable to image forming apparatuses adapted to form images through other schemes, such as known ink jet schemes, known toner projection schemes, or the like as well as to image forming apparatuses adapted to form images through electrophotographic schemes. Further, as long as a sheet conveying device is provided, this disclosure is not limited to an image forming apparatus but is also applicable to an image reading device provided with an automatic document feeder (ADF). 
     The configurations according to the above-descried embodiments are not limited thereto. This disclosure achieves the following aspects effectively. 
     Aspect 1. 
     In Aspect 1, a sheet conveying device (for example, the sheet conveying device  200 ) includes a first sheet conveyance passage (for example, the regular sheet conveyance passage R 1 ), a second sheet conveyance passage (for example, the bypass sheet conveyance passage R 2 ) different from the first sheet conveyance passage, a pair of sheet conveying rollers (for example, the pair of relay rollers  42 ), and a movable member (for example, the bypass bottom plate  34 , the bypass sheet feed roller  32 ). The pair of sheet conveying rollers includes two rollers (for example, the relay drive roller  42   a  and the relay driven roller  42   b ) configured to hold a sheet (for example, the recording sheet S) passing the first sheet conveyance passage. The movable member is configured to convey the sheet passing the second sheet conveyance passage. The two rollers are configured to be separated from each other along with movement of the movable member. 
     In Aspect 1, the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage are separated from each other in synchrony with movement of the movable member used for sheet conveyance in the second sheet conveyance passage. The sheet conveying device according to Aspect 1 has the configuration to convey the sheet in a selected sheet conveyance passage among a plurality of sheet conveyance passages including the first sheet conveyance passage and the second sheet conveyance passage. Therefore, when the sheet is conveyed in the selected sheet conveyance passage, the plurality of sheet conveyance passages other than the selected sheet conveyance passage are not used as an active sheet conveyance passage. Accordingly, when separating the two rollers of the pair of sheet conveying rollers in response to occurrence of paper jam while the sheet is conveyed in the first sheet conveyance passage, even if the movable member that is used for conveying the sheet in the second sheet conveyance passage is moved, conveyance of the sheet in the first sheet conveyance passage or paper jam handling (for example, removal of the sheet remaining in an image forming apparatus) is not hindered. 
     According to Aspect 1, since the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage are separated from each other in response to movement of the movable member used for conveying the sheet in the second sheet conveyance passage, the present embodiment achieves a simple configuration without a dedicated moving unit that separates the two rollers of the pair of sheet conveying rollers from each other. Accordingly, Aspect 1 easily achieves a simple configuration that does not include a dedicated moving unit achieves a highly convenient structure without a user operation to separate the two rollers of the pair of sheet conveying rollers. 
     Aspect 2. 
     In Aspect 2, the sheet conveying device (for example, the sheet conveying device  200 ) according to Aspect 1 further includes a tray (for example, the bypass tray  31 ) on which the sheet (for example, the recording sheet S) is loaded. The movable member (for example, the bypass bottom plate  34 , the bypass sheet feed roller  32 ) is configured to move to convey the sheet on the tray to the second sheet conveyance passage (for example, the bypass sheet conveyance passage R 2 ). 
     According to this configuration, the two rollers (for example, the relay drive roller  42   a  and the relay driven roller  42   b ) of the pair of sheet conveying rollers (for example, the pair of relay rollers  42 ) are separated from each other in the first sheet conveyance passage (for example, the regular sheet conveyance passage R 1 ) along with movement of the movable member (for example, the bypass bottom plate  34 , the bypass sheet feed roller  32 ) to convey the sheet to the second sheet conveyance passage. 
     Aspect 3. 
     In Aspect 3, the sheet conveying device (for example, the sheet conveying device  200 ) according to Aspect 2 further includes a sheet feed roller (for example, the bypass sheet feed roller  32 ) configured to convey the sheet (for example, the recording sheet S). The movable member (for example, the bypass bottom plate  34 ) includes a bottom plate. The bottom plate is configured to move upward toward the sheet feed roller. The sheet feed roller is configured to convey the sheet with the bottom plate being in contact with the sheet feed roller. 
     In Aspect 3, when the tray (for example, the bypass sheet tray  31 ) is lifted to bring the sheet on the tray to be pressed against the sheet feed roller, the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage (for example, the regular sheet conveyance passage R 1 ) separate from each other. No sheet remains in the second sheet conveyance passage (for example, the bypass sheet conveyance passage R 2 ) when a remaining sheet is removed from the first sheet conveyance passage. Therefore, when the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage are separated to remove the remaining sheet from the first sheet conveyance passage, even if the sheet on the tray on the side of the second sheet conveyance passage is pressed against the sheet feed roller, conveyance of the sheet or paper jam handling (for example, removal of the sheet remaining in an image forming apparatus) is not hindered. 
     Aspect 4. 
     In Aspect 4, the sheet conveying device (for example, the sheet conveying device  200 ) according to Aspect 2 further includes a sheet feed roller (for example, the bypass sheet feed roller  32 ) configured to convey the sheet (for example, the recording sheet S). The sheet feed roller is configured to move downward toward the sheet to convey the sheet in contact with the sheet feed roller. 
     In Aspect 4, when the sheet feed roller is lowered to bring the sheet on the tray (for example, the bypass sheet tray  31 ) to be pressed against the sheet feed roller, the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage (for example, the regular sheet conveyance passage R 1 ) separate from each other. No sheet remains in the second sheet conveyance passage (for example, the bypass sheet conveyance passage R 2 ) when a remaining sheet is removed from the first sheet conveyance passage. Therefore, when the two rollers (for example, the relay drive roller  42   a  and the relay driven roller  42   b ) of the pair of sheet conveying rollers (for example, the pair of relay rollers  42 ) in the first sheet conveyance passage are separated to remove the remaining sheet from the first sheet conveyance passage, even if the sheet feed roller on the side of the second sheet conveyance passage is pressed against the sheet on the tray, conveyance of the sheet or paper jam handling (for example, removal of the sheet remaining in an image forming apparatus) is not hindered. 
     Aspect 5. 
     In Aspect 5, the sheet conveying device (for example, the sheet conveying device  200 ) according to Aspect 1 further includes a rotary shaft (for example, the bypass bottom plate cam shaft  65 ) and a roller support (for example, the slide lever  38 ). The roller support is configured to support one of the two rollers (the relay driven roller  42   b ) of the pair of sheet conveying rollers (for example, the pair of relay rollers  42 ). The rotary shaft is configured to rotate to move the movable member (for example, the bypass bottom plate  34 , the bypass sheet feed roller  32 ). As the roller support rotates along with movement of the movable member, the two rollers are separated from each other. 
     Accordingly, Aspect 5 easily achieves a simple configuration to separate the two rollers of the pair of sheet conveying rollers in the first sheet conveyance passage in synchrony with movement of the movable member used for sheet conveyance in the second sheet conveyance passage. 
     Aspect 6. 
     In Aspect 6 according to Aspect 5, the rotary shaft (for example, the bypass bottom plate cam shaft  65 ) has a pressing portion (for example, the pressing portion  65   e ) configured to face an opening (for example, the slide hole  38   a ) of the roller support (for example, the slide lever  38 ). The rotary shaft is configured to press the pressing portion of the rotary shaft against a pressing target portion (for example, the inner wall of the slide hole  38   a ) of the roller support in a direction in which the two rollers (for example, the relay drive roller  42   a  and the relay driven roller  42   b ) of the pair of sheet conveying rollers (for example, the pair of relay rollers  42 ) separates from each other. 
     Accordingly, Aspect 6 easily achieves a simple configuration to move the roller support along with rotation of the rotary shaft. 
     Aspect 7. 
     In Aspect 7 according to any one of Aspects 1 to 6, the second sheet conveyance passage is a bypass sheet conveyance passage (for example, the bypass sheet conveyance passage R 2 ). 
     Accordingly, movement of the movable member (for example, the bypass bottom plate  34 , the bypass sheet feed roller  32 ) in the bypass sheet conveyance passage is used to separate the two rollers (for example, the relay drive roller  42   a  and the relay driven roller  42   b ) of the pair of sheet conveying rollers (for example, the pair of relay rollers  42 ) in an image forming apparatus (for example, the image forming apparatus  1000 ) to remove the sheet (for example, the recording sheet S) remaining in the image forming apparatus. 
     Aspect 8. 
     In Aspect 8 according to any one of Aspects 1 to 7, wherein the movable member (for example, the bypass bottom plate  34 ) is configured to move when a device error (paper jam) occurs to the sheet (for example, the recording sheet S) passing the first sheet conveyance passage (for example, the regular sheet conveyance passage R 1 ). 
     According to this configuration, the sheet conveying device having a highly convenient configuration is achieved easily for handling a device error such as paper jam when occurred to the sheet passing the first sheet conveyance passage. 
     Aspect 9. 
     In Aspect 9, an image forming apparatus (for example, the image forming apparatus  1000 ) includes an image forming device (for example, the photoconductor  1  and the image forming units)) configured to form an image on a sheet (for example, the recording sheet S), and the sheet conveying device (for example, the sheet conveying device  200 ) according to any one of Aspects 1 to 8, configured to convey the sheet to the image forming device. 
     According to this configuration, the image forming apparatus having a highly convenient configuration is achieved easily for separating the two rollers of the pair of sheet conveying rollers. 
     The effects described in the embodiments of this disclosure are listed as most preferable effects derived from this disclosure, and therefore are not intended to limit to the embodiments of this disclosure. 
     The embodiments described above are presented as an example to implement this disclosure. The embodiments described above are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, or changes can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of the invention, and are included in the scope of the invention recited in the claims and its equivalent. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.