Patent Publication Number: US-7583926-B2

Title: Image recording apparatus

Description:
CROSS REFERENCE 
   This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2005-244156 filed in Japan on Aug. 25, 2005, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The invention relates to an image recording apparatus for recording an image on a sheet while transporting the sheet from a sheet feeding section to a sheet output section. 
   A duplex image recording apparatus is a type of image recording apparatus, which is used for recoding an image on both sides of a sheet. 
   JP 2003-104613A discloses a duplex image recording apparatus provided with a re-transport path and a reversing transport path. The re-transport path connects a first portion of a main transport path (which leads from a sheet feeding section to a sheet output section through an image recording section) positioned between the image recording section and the sheet output section, to a second portion of the main transport path positioned between the sheet feeding section and the image recording section. The reversing transport path, which branches out from a portion of the re-transport path, is used for transporting a sheet in forward and backward directions therein. 
   After a sheet has an image recorded on a first side, a leading end and a tail end of the sheet are reversed in the reversing transport path. Thus, the sheet is transported to the image recording section, with a second side facing the image recording section. 
   There is another type of image recording apparatus having the functions of performing face-up output process and face-down output process. In the face-up output process, a sheet is output to a sheet output section with an image-recorded side facing upward, and in the face-down output process, a sheet is output with an image-recorded side facing downward. 
   In a copying operation where an image of original document is to be copied on a sheet of paper, an operator is around the apparatus and, thus, can check the copied sheet if the sheet is output face-up to the sheet output section. When an image is to be recorded on a sheet according to image data received through a network from a terminal device, an operator is not around the apparatus. Thus, a sheet can be output face-down so that an image recorded thereon may not be readily seen by others. In this type of image recording apparatus, a sheet is turned upside down by reversing a leading end and a tail end of a sheet in a portion of a main transport path positioned between an image recording section and the sheet output section. A sheet is selectively reversed upside down after passing through the image recording section, so that the sheet is selectively output to the sheet output section with an image-recorded side facing upward or downward. 
   In order to incorporate the function of reversing a sheet into duplex image recording apparatus, an additional sheet transport path is required that leads from a reversing transport path to a sheet output section. Also, a plurality of bifurcations are required to be provided in the main transport path, the re-transport path, and the reversing transport path. However, the additional transport path may cause the apparatus to be upsized and therefore to take a longer time to transport a sheet therein. Also, a sheet jam is more likely to occur in the bifurcations. Furthermore, random arrangements of the bifurcations complicate a process of removing a jammed sheet. 
   A feature of the invention is to provide an image recording apparatus with the functions of duplex image recording and reverse sheet output, that includes a main transport path, a re-transport path, a reversing transport path, and a plurality of bifurcations, positioned in optimum arrangements that prevent the apparatus from being upsized, a sheet transport time from taking long, and a process of removing a jammed sheet from being complicated. 
   SUMMARY OF THE INVENTION 
   An image recording apparatus includes first to fifth transport paths. The first transport path transports a sheet from a sheet feeding section to a sheet output section through a first confluence, an image recording section, a first bifurcation, and a second confluence in that order. The second transport path transports a sheet from the first bifurcation down to a switchback section through a second bifurcation and a third bifurcation in that order. The third transport path transports a sheet from the third bifurcation to the first confluence through a third confluence, and vice versa. The third transport path is positioned between the switchback section and a portion of the first transport path located in the image recording section. The fourth transport path transports a sheet from the second bifurcation to the third confluence, and vice versa. The fifth transport path transports a sheet from the second bifurcation to the second confluence. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic front cross-sectional view illustrating a configuration of an image recording apparatus according to an embodiment of the invention; 
       FIG. 2  is a diagram illustrating a configuration of a sheet transport path provided in the apparatus; 
       FIG. 3  is a diagram illustrating a configuration of each of first, second, and third bifurcations of the sheet transport path; 
       FIG. 4  is a block diagram illustrating a configuration of a control section provided in the apparatus; 
       FIG. 5  is a schematic diagram illustrating a first route for a sheet to follow in a face-down transport operation; 
       FIG. 6  is a schematic diagram illustrating a second route for a sheet to follow in a face-down transport operation; and 
       FIG. 7  is a schematic diagram illustrating a route for a sheet to follow in a reverse transport operation; 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Image recording apparatus according to preferred embodiments of the invention will be described below with reference to the accompanying drawings. 
     FIG. 1  is a schematic front cross-sectional view illustrating a configuration of an image recording apparatus according to an embodiment of the invention, such as an apparatus  100 . The apparatus  100  includes an image reading unit  200 , an image forming unit  300 , and a sheet feeding unit  400 . 
   The unit  200  has an automatic document feeder (ADF)  201 , a first document platen  202 , a second document platen  203 , a first mirror base  204 , a second mirror base  205 , a lens  206 , and a charge coupled device (CCD)  207 . 
   The ADF  201  feeds an original document, sheet by sheet, from a document tray  211  through the second document platen  203  to a first output tray  212 . The ADF  201  is mounted so as to be pivotable about a rear-end pivot between an open position and a closed position. In the closed position, the ADF  201  covers the platen  202 . The ADF  201  is pivoted upward to the open position to expose the platen  202 , so that a user can place an original document manually on the platen  202 . Each of the platens  202  and  203  includes a hard glass plate. 
   The bases  204  and  205  are provided below the platens  202  and  203  so as to be movable horizontally. The base  205  moves half as fast as the base  204 . On the base  204 , a light source and a first mirror are mounted. On the base  205 , a second mirror and a third mirror are mounted. 
   In reading an image of original document that is being transported by the ADF  201 , the base  204  is held still below the platen  203 . While passing on the platen  203 , an original document is irradiated with light from the light source. The reflected light is in turn reflected from the first mirror to the base  205 . 
   In reading an image of original document placed on the platen  202 , the bases  204  and  205  are moved horizontally below the platen  202 . An original document placed on the platen  202  is irradiated with light from the light source. The reflected light is in turn reflected from the first mirror to the base  205 . 
   Regardless of whether an original document is fed by the ADF  201  or placed on the platen  202 , thus, the reflected light from the original document is in turn reflected from the second and third mirrors, and then strikes the CCD  207  through the lens  206 . 
   The CCD  207  outputs electric signals according to an amount of the reflected light from the original document. The electric signals are input to the image forming unit  300  as image data. 
   The unit  300  is provided with an image recording section  30 . The section  30  includes a photoreceptor drum  31 , a charging device  32 , an exposure device  33 , a developing device  34 , a transfer belt  35 , a cleaner  36 , and a fusing device  37 . 
   The drum  31 , which has an outer photoreceptive surface, is rotatable in a direction indicated by an arrow. The charging device  32  applies, to the surface of the drum  31 , such a voltage as to allow the surface to have a uniform electric potential. The device  32  may be either a noncontact charger, or a contact charger of roller or brush type. 
   The exposure device  33  irradiates the surface of the drum  31  with light modulated according to image data, so that an electrostatic latent image is formed on the surface. The device  33  has a polygon mirror through which to scan the drum  31  axially with a laser light modulated according to image data. Alternatively, an exposure device provided with an array of light emitting elements such as ELs or LEDs may be used as the device  33 . 
   The developing device  34  supplies toner to the surface of the drum  31  and develops the electrostatic latent image into a toner image. 
   Under the drum  31 , the transfer belt  35  is looped over a plurality of rollers. The belt  35  has a resistance of 1×10 9  Ω·cm to 1×10 13  Ω·cm. Inside the loop of the belt  35 , a transfer roller  35 A is provided so as to be pressed against the drum  31  through the belt  35 . A predetermined amount of transfer voltage is applied to the roller  35 A, so that a toner image is transferred from the drum  31  to a sheet that passes between the belt  35  and the drum  31 . 
   The cleaner  36  removes residual toner that remains on the drum  31  after a toner image is transferred from the drum  31  to a sheet. 
   The fusing device  37  has a heat roller  37 A and a pressure roller  37 B. The roller  37 A is heated, by an internal heater, to a sufficient temperature to melt toner. The roller  37 B is pressed against the roller  37 A at a predetermined pressure. The device  37  heats and pressurizes a sheet passing between the rollers  37 A and  37 B, thereby firmly fixing a toner image to the sheet. After passing through the device  37 , a sheet is output to a second output tray  38  mounted on a side surface of the apparatus  100 . The tray  38  corresponds to the sheet output section of the invention. 
   The sheet feeding unit  400  corresponds to the sheet feeding section of the invention. The unit  400  has sheet cassettes  401 ,  402 ,  403 , and  404 , and a manual sheet feeding tray  405 . Each of the cassettes  401  to  404  holds a plurality of sheets of the same size. The tray  405  is provided for holding sheets of sizes and types that are used infrequently. 
   The unit  400  feeds sheets, one by one, from any one of the cassettes  401  to  404  and the tray  405 . A sheet fed by the unit  400  is transported to the image recording section  30  along a sheet transport path  1  to be described below. 
     FIG. 2  is a diagram illustrating a configuration of the sheet transport path  1 . The path  1  is provided inside the image forming unit  300 . The path  1  includes a first path  11 , a second path  12 , a third path  13 , a fourth path  14 , and a fifth path  15 . 
   The first path  11  leads from the unit  400  to the tray  38 , through a first confluence  21 , the section  30 , a first bifurcation  24 , and a second confluence  22  in that order. Arranged along the path  11  are transport rollers  61 ,  62 , and  63 , a registration roller  51 , and an output roller  52 . The transport rollers  61  to  63 , the registration roller  51 , and the output roller  52  are driven by a first motor (not shown). 
   A portion of the path  11  located in the section  30  is in an approximately horizontal position. In the first portion, the belt  35  is arranged for stable transfer of toner image from the drum  31  to a sheet and for stable transport of a sheet with an pre-fusion toner image electrostatically attracted thereto. 
   The first bifurcation  24  is located between the section  30  and the tray  38 . The second path  12  leads from the bifurcation  24  to a switchback section  12 A, through a second bifurcation  25  and a third bifurcation  26  in that order. The section  12 A is located below and parallel to the portion of the path  11  located in the section  30 . The section  12 A transports a sheet in forward and backward directions therein. Along the path  12 , there are provided a reversing roller  53  and a transport roller  58 . The roller  53  is selectively driven in a frontward direction or a backward direction through a first clutch (not shown) by a second motor (also not shown). The roller  58  is driven by the first motor (not shown). 
   The third path  13  leads from the third bifurcation  26  to the first confluence  21  through a third confluence  23 . The path  13  is located between the section  12 A and the portion of the path  11  located in the section  30 . Along the path  13 , transport rollers  54 ,  55 ,  56 , and  57  are arranged. The rollers  54  to  57  are selectively driven in a frontward direction or a backward direction through a second clutch (not shown) by a third motor (also not shown). 
   The fourth path  14  leads from the bifurcation  25  to the confluence  23 . The fifth path  15  leads from the bifurcation  25  to the confluence  22 . 
   The reversing rollers  54 ,  55 ,  56 , and  57  are approximately evenly spaced along the path  13 . Thus, the path  13  needs a relatively large space thereabove and thereunder. In contrast, the single reversing roller  53  is provided around a mouth of the switchback section  12 A. Thus, the section  12 A does not need a large space thereabove and thereunder. 
   Accordingly, the sheet transport path  1  can be rendered compact by arranging the portion of the path  11  located in the section  30 , the section  12 A, and the path  13  in three layers, in that order from top to bottom. 
   Also, the bifurcations  24 ,  25 , and  26 , where a sheet jam is relatively more likely to occur, are arranged along a portion of the path  12 , in that order from top to bottom. Thus, the bifurcations  24  to  26  are exposed to the outside by opening a side surface of the apparatus  100  that is parallel to a direction in which a sheet is transported on the sheet transport path  1 , i.e., a front surface of the apparatus  100 . This facilitates removal of a jammed sheet. 
     FIG. 3  is a schematic diagram illustrating a configuration of each of the first bifurcation  24 , the second bifurcation  25 , and the third bifurcation  26 , of the sheet transport path  1 . A guide  41  is provided at the bifurcation  24 . The guide  41  is pivoted between two respective positions indicated by a solid line and a chain double-dashed line by a first solenoid (not shown), to guide a sheet forwarded by the roller  63  from the bifurcation  24  into either one of the paths  11  and  12 . 
   Guides  42  and  43  are provided at the bifurcation  25 . With no external force acting thereon, the guide  42  is located in a position, indicated by a solid line, to guide a sheet into the path  15  as the sheet is transported upward on the path  12  or the path  14 . The guide  42  prevents a sheet from being guided into the path  12  as the sheet is transported upward from the path  12  or the path  13 . 
   The guide  43  is pivoted between two respective positions indicated by a solid line and a chain double-dashed line by activating and deactivating a second solenoid (not shown), to allow, in the bifurcation  25 , passage of a sheet from the path  14  to the path  15  or from the path  12  to the path  15 . 
   The guide  42  is pivoted to a position indicated by a chain double-dashed line, by contact with a sheet that is transported downward from the bifurcation  24  along the path  12 . 
   A guide  44  is provided at the bifurcation  26 . The guide  44  is urged to a position indicated by a solid line by an elastic member. The elastic member exerts such an elastic force on the guide  44  as to allow the guide  44  to be pivoted to a position indicated by a chain double-dashed line by contact with a sheet that is transported to the portion  12 A through the paths  11  and  12 . When in contact with a leading end of a sheet transported downward along the path  12 , the guide  44  allows downward passage of the sheet from the bifurcation  26  into the path  12 . Otherwise, the guide  44  allows passage of a sheet from the section  12 A to the path  13 . 
     FIG. 4  is a block diagram illustrating a configuration of a control section  70  provided in the apparatus  100 . The control section  70  has a CPU  71  provided with a ROM  72  and a RAM  73 . To the CPU  71  connected are motor drivers  74 ,  75 , and  76 , solenoid drivers  77  and  78 , clutch drivers  80  and  81 , and a sensor section  82 . 
   The section  82  has a plurality of sensors arranged in the sheet transport path  1 . Each of the sensors detects presence of a sheet at different locations in the path  1  and inputs a detection signal to the CPU  71 . 
   According to the signal input by the section  82 , the CPU  71  executes a program prewritten in the ROM  72  and outputs a driving signal to each of the motor drivers  74 ,  75 , and  76 , the solenoid drivers  77  and  78 , and the clutch drivers  80  and  81 . 
   To the drivers  74 ,  75 , and  76  connected are a first motor  83 , a second motor  84 , and a third motor  85 , respectively. The drivers  74 ,  75 , and  76  drive the motors  83 ,  84 , and  85 , respectively, according to a driving signal from the CPU  71 . 
   To the drivers  77  and  78  connected are a first solenoid  86  and a second solenoid  87 , respectively. The drivers  77  and  78  activate the solenoids  86  and  87 , respectively, according to a driving signal from the CPU  71 . 
   In a deactivated state, the solenoid  86  puts the guide  41  in the position indicated by the solid line as shown in  FIG. 3 . In an activated state, the solenoid  86  puts the guide  41  in the position indicated by the chain double-dashed line. More specifically, the guide  41  guides a sheet from the bifurcation  24  into the path  11 , where the output roller  52  is provided, with the solenoid  86  in the deactivated state. Meanwhile, the guide  41  guides a sheet from the bifurcation  24  into the path  12 , with the solenoid  86  in the activated state. 
   It is to be noted that either of the respective positions indicated by the solid line and the chain double-dashed line as in  FIG. 3  can be arbitrarily selected as an initial position of the guide  41  in the deactivated state. Thus, the guide  41  can be placed in an appropriate position for face-up or face-down sheet output, depending on which of the face-up or face-down sheet output a user more often uses. 
   In a deactivated state, the solenoid  87  puts the guide  43  in the position indicated by the solid line as shown in  FIG. 3 . In an activated state, the solenoid  87  puts the guide  43  in the position indicated by the chain double-dashed line. More specifically, the guide  43  guides a sheet from the bifurcation  25  into the path  13 , and from the path  14  into the path  15 , with the solenoid  86  in the deactivated state, whereas the guide  43  guides a sheet from the bifurcation  25  into the path  12 , and from the path  12  into the path  15 , with the solenoid  87  in the activated state. 
   To the clutch drivers  80  and  81  connected are a first clutch  89  and a second clutch  90 , respectively. The drivers  80  and  81  activate the clutches  89  and  90 , respectively, according to a driving signal from the CPU  71 . 
   In a deactivated state, the clutch  89  directly transmits rotation of the second motor  84  to the reversing roller  53 . In an activated state, the clutch  89  transmits, to the roller  53 , rotation in an opposite direction to a rotational direction of the motor  84 . More specifically, the roller  53  is rotated in a forward direction to guide a sheet into the switchback section  12 A, with the clutch  89  deactivated. Meanwhile, the roller  53  is rotated in a reverse direction to guide a sheet from the section  12 A to the bifurcation  26 , with the clutch  89  activated. 
   In a deactivated state, the clutch  90  directly transmits rotation of the third motor  85  to the reversing rollers  55 ,  56 , and  57 . In an activated state, the clutch  90  transmits, the rollers  55  to  57 , rotation in an opposite direction to a rotational direction of the motor  84 . More specifically, the rollers  55  to  57  are rotated in a forward direction to guide a sheet from the bifurcation  25  into the path  13 , with the clutch  90  deactivated. Meanwhile, the rollers  55  to  57  are rotated in a reverse direction to guide a sheet from the path  13  to the bifurcation  25 , with the clutch  90  activated. 
   The apparatus  100  selectively performs a face-up transport operation, a face-down transport operation, and a reversing transport operation. In the face-up transport operation, a sheet with an image recorded on a single side is output to the tray  38 , with the image-carrying side facing upward. In the face-down transport operation, a sheet with an image recorded on a single side is output face-down to the tray  38 , with the image-carrying side facing downward. The reversing transport operation is performed when an image is to be recorded on both sides of a sheet. 
   The CPU  71  outputs a driving signal to each of the motor drivers  74  to  76 , the solenoid drivers  77  and  78 , and the clutch drivers  80  and  81 , to activate the first motor  83 , the second motor  84 , the third motor  85 , the first solenoid  86 , the second solenoid  87 , the first clutch  89 , and the second clutch  90 , so that a sheet is transported through an appropriate route for either one of the face-up, face-down, and reversing transport operations. 
   In a situation such as when an operator is to copy an original document on paper, the operator is near the apparatus  100  and ready to check the copied paper. In such a situation, the face-up transport operation is performed. 
   In the face-up transport operation, the CPU  71  drives the motor  83  through the driver  74 . A sheet fed from the sheet feeding unit  400  is transported along the path  11  by rotation of each of the transport rollers  61  to  63 , the registration roller  51 , and the output roller  52 . During passage of the sheet through the image recording section  30 , a toner image is transferred and fused on an upper side of the sheet. The sheet is output to the tray  38  with the image-carrying side facing upward. 
   The CPU  71  starts to transmit rotation of the motor  83  to the roller  51 , through a clutch (not shown in the figure), at such a timing that a leading end of the sheet meets a leading end of the toner image formed on the drum  31  in a contact area between the roller  35 A and the drum  31 . 
     FIG. 5  is a schematic diagram illustrating a first route for a sheet to follow in the face-down transport operation. In this case, the guide  44  is pivoted from the position indicated by the solid line to the position indicated by the chain double-dashed line as in  FIG. 3 , by a third solenoid (not shown). Also, the transport roller  58  serves as a reversing roller. To the roller  58 , the clutch  89  transmits rotation of the second motor  84 . Thus, the roller  58  is rotated in a similar manner to the roller  53 . 
   In a situation such as when an image is to be printed on paper according to image data sent from an external device by an operator, the operator is not around the apparatus  100  and therefore not ready to check the printed paper. In such a situation, the face-down transport operation is performed. The face-down transport operation is also performed when images on consecutive pages of an original document are to be recorded on sheets of paper, for the purpose of eliminating the need for collating the recorded sheets. 
   In the face-down transport operation, the CPU  71  drives the motor  83  through the driver  74  to transport, to the section  30 , a sheet fed from the unit  400 . The CPU  71  activates the first solenoid  86  and the second solenoid  87  through the solenoid drivers  77  and  78  before a leading end of the sheet reaches the first bifurcation  24 . Thus, the guides  41  and  43  are put in the respective positions indicated by the chain double-dashed lines as in  FIG. 3 , so that the sheet is guided from the bifurcation  24  into the path  12  after passing through the section  30 . 
   The CPU  71  drives the second motor  84  through the motor driver  75  by the time the leading end of the sheet passes through the second bifurcation  25 . At the time, the first clutch  89  is not activated. Thus, the reversing roller  53  and the transport roller  58  are rotated in the forward directions. 
   The sheet is transported downward along the path  12  toward the switchback section  12 A. It is to be noted that the guides  42  and  44  are pivoted to the respective positions indicated by the chain double-dashed lines by contact with the leading end of the sheet as the sheet is transported downward through the bifurcation  25 , thereby allowing passage of the sheet through the path  12 . 
   As the sheet is transported downward through the third bifurcation  26 , a tail end of the sheet becomes nipped by the reversing roller  53 . It is when the CPU  71  activates the clutch  89  through the clutch driver  80 . Thus, the rollers  53  and  58  are rotated in the reverse directions. The CPU  71  also activates the second solenoid  87  and the third solenoid in order to pivot the guides  43  and  44  to the respective positions indicated by the chain double-dashed lines as in  FIG. 3 . 
   With the tail end leading, the sheet is transported upward from the section  12 A along the path  12 , and is guided into the path  15  at the bifurcation  25 . Then, the sheet is guided into the path  11  at the second confluence  22 , and is output to the tray  38 , with the image-carrying side facing downward, by the roller  52 . 
     FIG. 6  is a schematic diagram illustrating a second route for a sheet to follow in the face-down transport operation. The CPU  71  drives the motor  83  through the driver  74  to transport, to the section  30 , a sheet fed from the unit  400 . The CPU  71  activates the first solenoid  86  through the solenoid driver  77  before a leading end of the sheet reaches the bifurcation  24 . Thus, the guide  41  is put in the position indicated by the chain double-dashed line as in  FIG. 3 , so that the sheet is guided from the bifurcation  24  into the path  12  after passing through the section  30 . It is to be noted that the guide  42  is pivoted to the position indicated by the chain double-dashed line by contact with the leading end of the sheet as the sheet is transported downward through the bifurcation  25 , thereby allowing passage of the sheet through the path  12 . 
   At the time, the second solenoid  87  is not activated. Thus, the guide  43  is put in the position indicated by the solid line as in  FIG. 3 , so that the sheet is guided from the path  12  into the path  14  at the bifurcation  25 . 
   The CPU  71  drives the third solenoid  85  through the motor driver  76  by the time the leading end of the sheet passes through the bifurcation  25 . At the time, the clutch  89  is not activated. Thus, the reversing rollers  54 ,  55 ,  56 , and  57  are rotated in the forward directions, so that the sheet is guided from the path  14  into the path  13 . 
   With a tail end of the sheet nipped by the roller  54 , the CPU  71  activates the second clutch  90  through the clutch driver  81 . Thus, the reversing rollers  54 ,  55 ,  56 , and  57  are rotated in the reverse directions. With the tail end leading, the sheet is transported, upward from the path  13 , along the path  14  and is guided into the path  15  at the bifurcation  25 . Then, the sheet is guided into the path  11  at the second confluence  22 , and is output to the tray  38 , with the image-carrying side facing downward, by the roller  52 . 
   In this case, the path  13  is used to reverse the leading and tail ends of a sheet. The path  13  is located above the section  12 A, and therefore nearer to the path  11  than the section  12 A. After leading and tail ends of a sheet are reversed in the path  13 , the sheet is output to the tray  38 . This allows a shorter sheet transport route, and therefore a shorter image recording process time in the face-down transport operation, compared to a case in which the section  12 A is used. 
     FIG. 7  is a schematic diagram illustrating a route for a sheet to follow in the reverse transport operation. The reverse transport operation is performed when an image is to be recorded on both sides of a sheet. In the reverse transport operation, an image is recorded on a first side of the sheet in the section  30 ; the sheet is reversed and returned to the section  30  where an image is recorded on a second side of the sheet; and then, the sheet is output to the tray  38 . 
   In the reverse transport operation, the CPU  71  drives the motor  83  through the driver  74  to transport, to the section  30 , a sheet fed from the unit  400 . The CPU  71  activates the first solenoid  86  and the second solenoid  87  through the solenoid drivers  77  and  78  before a leading end of the sheet reaches the bifurcation  24 . Thus, the guides  41 ,  43 , and  44  are put in the respective positions indicated by the chain double-dashed lines as in  FIG. 3 , so that the sheet is guided from the bifurcation  24  into the path  12  after an image is formed on a first side o the sheet in the section  30 . 
   The CPU  71  drives the second motor  84  through the motor driver  75  by the time the leading end of the sheet passes through the bifurcation  25 . At the time, the first clutch  89  is not activated. Thus, the reversing roller  53  and the transport roller  58  are rotated in the forward directions. 
   Consequently, the sheet is transported along the path  12  toward the switchback section  12 A. It is to be noted that the guide  42  is pivoted to the position indicated by the chain double-dashed line by contact with the leading end of the sheet as the sheet is transported downward through the bifurcation  25 , thereby allowing passage of the sheet through the path  12 . 
   As the sheet is transported downward through the bifurcation  26 , a tail end of the sheet becomes nipped by the reversing roller  53 . It is when the CPU  71  activates the clutch  89  through the clutch driver  80  and, at the same time, deactivates the solenoid  87 . Further, the CPU  71  drives the motor  85  through the driver  76 . At the time, the clutch  90  is not activated. Thus, the roller  53  is rotated in the reverse direction, and the rollers  54 ,  55 ,  56 , and  57  are rotated in the forward directions. At the bifurcation  26 , at the time, the guide  44  is in the position indicated by the solid line as in  FIG. 3 . 
   With the tail end leading, the sheet is transported, upward from the section  12 A, along the path  12  and is guided into the path  13  at the bifurcation  26 . Next, the sheet is transported along the path  13  toward the first confluence  21 . Then, the sheet is guided into the path  11  at the confluence  21 , and is transported along the path  11  to the section  30  with a second side facing the drum  31 . 
   By the time the leading end of the sheet with the second side facing upward passes through the section  30 , the CPU  71  deactivates the solenoid  86 . Thus, the guide  41  is put in the position indicated by the solid line as in  FIG. 3 . After an image is recorded on the second side in the section  30 , the sheet is transported through the bifurcation  24  and output to the tray  38  by the roller  52 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.