Patent Publication Number: US-8989651-B2

Title: Image formation device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2011-204718 filed on Sep. 20, 2011. The entire subject matter of the application is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     Aspects of the present invention relate to an image formation device capable of printing images on both sides of a printing sheet. 
     2. Conventional Art 
     An example of conventional image formation device capable of printing images on both sides of a printing sheet is configures such that two independent sheet feed paths are provided from a fixing unit to a sheet discharge exit. 
     SUMMARY 
     According to the above-described image formation device, since the sheet feed paths from the fixing unit to the discharge exit are completely independent, if a sheet jam occurs, a problem as indicated below may occur. 
     In the above-described image formation device, it is necessary to judge the sheet feed path in which the sheet jam has occurred, and then notify a user the occurrence of the jam and the path in which the jam has occurred. 
     If the notification is not made, the user needs to visually check both sheet feed paths. Therefore, if the notification is not made, workability in removing the jammed sheet is lowered. 
     If the two sheet feed paths are arranged in a two-tiered state (e.g., arranged on further side and near side) and the jam has occurred in the further side path, the near side path is exposed to outside, and thereafter, the further side path is exposed to outside to remove the jammed sheet. 
     Therefore, according to the conventional image formation device, a structure for allowing the two sheet feed paths to be exposed to outside is relatively complicated. Further, the workability in removing the jammed sheet is considerably lowered. 
     Aspects of the invention is advantageous in that an improved image formation device is provided, with which device, the jammed sheet can be removed easily. 
     According to aspects of the invention, there is provided an image formation device configured to form images on a front surface and back surface of a sheet, provided with a developing unit configured to transfer a developer image on the sheet, a fixing unit provided on a downstream side of the developing unit and configured to fixed the developer image on the sheet, a discharge tray configured to receive the sheet discharged from a discharge exit, a guide portion configuring at least a part of a first feed path and a second feed path extending from the fixing unit to the discharge exit, a reversibly rotatable roller configured to reverse a feeding direction of the sheet fed from the fixing unit to the discharge exit so that the sheet is reversely fed toward an entrance of the of the developing unit. In this configuration, the first path and the second path are converged to form a converged feed path on the discharge exit side, the reversibly rotatable roller is provided in the converged feed path, and a converged feed path guide portion, which is a part of the guide portion, is displaceable to a position to expose the converged feed path to outside. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is a cross sectional view schematically showing a structure of an image formation device according to a first embodiment of the invention. 
         FIG. 2  schematically shows a state where a rear cover of the image formation device is opened. 
         FIG. 3  shows a state where a intermediate feed roller contacts a sheet. 
         FIG. 4  is a perspective view of the intermediate feed roller and a pressure roller. 
         FIG. 5  shows a position of a switching flapper when a sheet is fed to a first feed path. 
         FIG. 6  shows a position of the switching flapper when the sheet is fed to a second feed path. 
         FIG. 7  shows a position of the switching flapper when the sheet is fed to a re-feed path. 
         FIG. 8  is a block diagram showing a control system of the image formation device according to the first embodiment. 
         FIG. 9  schematically shows a main part of an image formation device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, exemplary embodiments according to aspects of the invention will be described. 
     Aspects of the present invention provide a laser printer capable of forming image on front/back sides of a sheet. 
     First Embodiment 
     An image formation device  1  is provided with an image formation unit  2 , a sheet feeding unit  10 , a re-feed unit  20  and the like, as shown in  FIG. 1 . The image formation unit  2 , the sheet feed unit  10  and the re-feed unit  20  are assembled on a main body of the image formation device  2 . It is noted that a term “main body” means a portion of the image formation device, which is not normally disassembled or removed when the image formation device is in use. For example, the main body includes a hosing of the image formation device  1 , and a frame to which various components are secured. 
     The image formation unit  2  is an image developing unit that forms a developed image on the sheet. The sheet feed unit  10  feeds the sheets placed on a sheet feed tray  11  toward the image formation unit  2 . The re-feed unit  20  feeds the sheet discharged from the image formation unit  2  to an entrance side of the image formation unit  2  again 
     The image formation unit  2  is an electrophotographic image formation device which includes one or more process cartridges  3 , one or more exposure unit  4 , and a fixing unit  5 . Specifically, according to the first embodiment, the image formation unit  2  has a color developing units, and therefore the image formation device  2  includes a plurality of process cartridges  3  respectively corresponding to a plurality of colors of developers (i.e., black, yellow, magenta and cyan). 
     Each process cartridge  3  contains a photoconductive drum  3 A on which the developer is adhered to develop an image, and a charger  3 B which uniformly charges a circumferential surface of the photoconductive drum  3 A. as the charged photoconductive drum  3 A is exposed to light beam emitted by the exposure unit  4 , an electrostatic latent image is formed on the circumferential surface of the photoconductive drum  3 . Thereafter, when charged developer is supplied to the photoconductive drum  3 A, the developer remains at a portion corresponding to the latent image (i.e., a developed image is formed on the circumferential surface of the photoconductive drum  3 ). 
     The transfer belt  7  feeds the sheet supplied from the sheet feed tray  11  toward the photoconductive drums  3 A. At portions facing the photoconductive drum  11 , a plurality of transfer rollers  8  are provided with the transfer belt  7  located between the plurality of transfer rollers and the plurality of photoconductive drums  11 . According to the first embodiment, with the process cartridges  3  and transfer rollers  8 , the developer on the photoconductive drums  3 A is transferred on the sheet. 
     The sheet picked up from the sheet feed tray  11  and fed toward the image formation unit  2 , firstly fed to a pair of register rollers  6 . The register rollers  6  correct the orientation of the sheet, and feeds the sheet further so that the sheet enters the image formation unit  2  at a predetermined timing. 
     The fixing unit  5  includes a heat roller  5 A which contacts the sheet and applies heat to the sheet, and a pressure roller  5 B which urges the sheet toward the heat roller  5 A. The fixing unit  5  applies heat, with the heat roller  5 A, to fix the developer (i.e., the developed image) which has been transferred onto the sheet. 
     The pressure roller  5 B is biased toward the heat roller  5 A with an elastic member such as spring (not shown). A nip pressure P 1  at a nip between the heat roller  5 A and the pressure roller  5 B (which will also be referred to as a fixing unit side nip pressure P 1 ) is generated by the elastic force of the elastic member. 
     On an upper surface of the main body (i.e., the image formation device  1 ), a discharge tray  1 B is formed. The sheet discharged from the sheet discharge exit  1 A is placed on the discharge tray  1 B. At the sheet discharge exit  1 A, a sheet discharge roller  9 A is provided. The sheet discharge roller  9 A contacts the sheet discharged from the fixing unit  5 , and rotates as the sheet moves thereby applying a sheet feeding force to the sheet. The discharge roller  9 A is secured to the main body. 
     When a simplex printing is performed (i.e., an image is printed only a front surface of the sheet), the sheet discharge roller  9 A discharge the sheet which is discharged from the fixing unit  5  to the discharge tray  1 B. If a duplex printing is performed (i.e., images are printed on the front and back sides of the sheet), the discharge roller  9 A functions as an reverse-feed roller that reverses the feeding direction of the sheet which has been fed from the fixing unit  5  to the discharge exit  1 A, and feeds the sheet toward an entrance of the developing unit  5 . 
     The pressure roller  9 B is biases toward the discharge roller  9 A, similarly to the pressure roller  5 B, with an elastic member (not shown). A nip pressure P 2  at the nip between the discharge roller  9 A and the pressure roller  9 B is generated by the elastic force of the elastic member. 
     Incidentally, it is noted that the term “front surface” of the sheet is intended to indicate one of the two surfaces of the sheet, and the term “back surface” of the sheet is intended to indicate the other surface (i.e., the surface opposite to the “front surface”). The terms “front surface” and “back surface” are not intended to indicate specific surfaces of the sheet. 
     The sheet feed path is diverged to a first path L 1  and a second path L 2  on the discharge side of the fixing unit. The first path L 1  and the second path L 2  are converged to a converged feed path L 12  in front of the discharge exit  1 A. The discharge roller  9 A is arranged on the discharge exit  1 A side of the converged feed path L 12 . 
     The second path L 2  communicates with a re-feed path L 3  which extends to the entrance of the image formation unit  2 , and is located on an outer side with respect to the first path L 1 , that is, on a rear side with respect to the first path L 1 . 
     A part of the re-feed path L 3 , below the sheet feed tray  11 , is defined by re-feed unit  20 , and a part of the re-feed path L 3  on the upstream side, in the sheet feed direction, of the re-feed unit  20  is defined as a space between the rear cover  30  and the main body of the image formation device  1 . 
     The rear cover  30  is rotatable, with respect to the main body, about the lower end portion thereof as shown in  FIG. 2 , between an opened position for exposing the sheet feed paths from the fixing unit  5  to the sheet discharge exit  1 A (see  FIG. 2 ) and a closed position (see  FIG. 1 ). On an inner surface of the rear cover  30 , that is on a fixing device  5  side surface of the rear cover  30 , a first guide portion  31  is formed. The first guide portion  31  is a portion protruding inwardly and serves as a rear cover side guiding surface of the sheet feed path. 
     The first guide portion  31  includes a second path guide portion  31 A, re-feed path guide portion  31 B, and converged feed path guide portion  31 C. It is noted that, according to the first embodiment, the first guide portion  31  (i.e., the guide portions  31 A- 31 C) is formed of resin by integral molding with the rear cover  30 . 
     The second path guide portion  31 A is a ribbed wall, which is provided with linearly extending protrusions, configuring a rear cover side guide portion of the second feed path L 2 . The re-feed path guide portion  31 B is a ribbed wall, which is provided with linearly extending protrusions, configuring a rear cover side guide portion of the re-feed path L 3 . The converged feed path guide portion  31 C is a ribbed wall, which is provided with linearly extending protrusions, configuring a rear cover side guide portion of the converged feed path L 12 . 
     If the rear cover  30  is opened to expose the rear side of the image formation device  1 , as shown in  FIG. 2 , the second path guide portion  31 A, the re-feed path guide portion  31 B and the converged feed path guide portion  31 C are shifted rearward together with the rear cover  30 . Therefore, when the rear cover  30  is opened, the rear side portions of the second feed path L 2 , the converged feed path L 12  and the re-feed path L 3  are exposed to outside. 
     The main body is formed with a second guide portion  32 , which configures main body side guiding portions for the converging feed path L 12 , the re-feed path L 3  and the first feed path L 1 . Similarly to the first guide portion  31 , the second guide portion  32  includes a first path guide portion  32 A, a re-feed path guide portion  32 B and a converged feed path guide portion  32 C. 
     The first path guide portion  32 A is a ribbed wall, which is provided with linearly extending protrusions, configuring the main body side guide portion. The converge path guide portion  31 C is a ribbed wall, which is provided with linearly extending protrusions, configuring a main body side guide portion for the converged feed path L 12 . 
     On the rear cover  30 , a partition wall  33  is provided. The partition wall  33  is a rectangular plate-like member which is configured to extend in the width direction and partition the first feed path L 1  and the second feed path L 2 . The partition  33  is attached to the rear cover  30  at positions which are shifted from the first and second feed paths L 1  and L 2 . It is noted that the term “width direction” means a direction perpendicular to both the sheet feed direction and a thickness direction of the sheet. 
     On the fixing unit  5  side surface of the partition wall  33 , at least one intermediate feed roller  40 , which applies a feeding force to the sheet fed along the first feed path L 1  or the second feed path L 2 , is provided. According to the first embodiment, the intermediate feed roller  40  is arranged between the first feed path L 1  and the second feed path L 2 , as shown in  FIG. 1 , so that with a single roller, the feeding force is applied to the sheet fed along the first feed path L 1 , and to the sheet fed along the second feed path L 2 . 
     Due to the above arrangement of the intermediate feed roller  40 , pressure rollers  41  and  42  which are configured to urge the sheet to the intermediate feed roller  40  are provided on both sides of the intermediate feed roller  40 , sandwiching the intermediate feed roller  40  therebetween. Specifically, the pressure roller  41  is a roller which urges the sheet fed along the first feed path L 1  to the intermediate feed roller  40 , while the pressure roller  42  is a roller which urges the sheet fed along the second feed path L 2  to the intermediate feed roller  40 . 
     The pressure rollers  41  and  42  are urged toward the intermediate feed roller  40 , similarly to the pressure roller  5 B, with elastic members such as a spring (not shown). Nip pressure P 3  (hereinafter, referred to as an intermediate feed roller side nip pressure) at a nip between each of the pressure rollers  41  and  42 , and the intermediate feed roller  40  is generated by the elastic forces of the elastic members. 
     It is noted that the nip pressure (i.e., the intermediate feed roller side nip pressure P 3 ) between the intermediate feed roller  40  and the pressure roller  41  is the same as that between the intermediate feed roller  40  and the pressure roller  42 . 
     Further, elastic forces of the elastic members are set so that the reverse roller side nip pressure P 2  is smaller than the intermediate feed roller side nip pressure P 3  and the intermediate feed roller side nip pressure P 3  is smaller than the fixing unit side nip pressure P 1  (i.e., P 2 &lt;P 3 &lt;P 1 ). 
     The pair of feed rollers  5 C provided at the exit portion of the fixing device  5  are for changing the feeding direction of the sheet discharged from the fixing unit  5  to an upward direction. Therefore, the nip pressure of the pair of feed rollers  5 C is set to be smaller than the reverse roller side nip pressure P 2 . 
     The intermediate feed roller  50  and the pressure roller  42  are rotatably secured to the rear cover  30  as shown in  FIG. 2 . The intermediate feed roller  40  receives a driving force from a motor (not shown in  FIG. 2 ) which is provided to the main body. 
     At an axial end of the intermediate feed roller  40 , a driven gear, which receives a rotating force from the main body and rotates, is provided. While, in the main body, provided is a driving gear, which engages with the driven gear described above and receives the rotation force from the motor, to transmits the rotation force to the driven gear, when the rear cover  30  is closed. Since such a configuration is well-known, the driving gear and the driven gear are not shown in  FIG. 2  for brevity. 
     When the rear cover  30  is opened, the engagement of the driving gear with the driven gear is released. Therefore, when the rear cover  30  is opened, transmission of the rotating force from the motor to the intermediate feed roller  40  is cut. Thus, the image formation device  1  according to the first embodiment has a function of connecting/disconnecting transmission of driving force to the intermediate feed roller  40  in association with closing/opening of the rear cover. 
     The intermediate feed roller  40  is configured to have a sufficient width (i.e., axial length) so that the intermediate feed roller  40  contacts the entire width of the sheet having a maximum size (width) which can be fed along the second path L 2  (see  FIG. 3 ). Corresponding to this configuration, the pressure roller  42  also has a sufficient width (i.e., axial length) so that the pressure roller  42  contacts the entire width of the sheet having a maximum size (width) which can be fed along the second path L 2  (see  FIG. 4 ). 
     Incidentally, on the exit side of the fixing unit  5 , a switching flapper  50  which is configured to switch the path of the sheet discharged from the fixing unit  5  between the first path L 1  and the second path L 2  as shown in  FIG. 1 . Specifically, the switching flapper  50  is rotatably located between a first position shown in  FIG. 5  and a second position shown in  FIG. 6 . 
     When the switching flapper  50  is located at the first position (see  FIG. 5 ), the sheet discharged from the fixing unit  5  is prevented from entering the second path L 2 . When the switching flapper  50  is located at the second position (see  FIG. 6 ), the sheet discharged from the fixing unit  5  is allowed to enter the second path L 2 . 
     When the duplex printing is performed, and a sheet, of which an image is formed only on the front surface, is discharged from the fixing unit  5 , the switching flapper  50  is located to the second position. Therefore, such a sheet is directed to the second path L 2 . 
     When a sheet of which images are formed on both the front and back side, or a sheet of which an image is to be formed only on the front surface, is discharged from the fixing device  5 , the switching flapper  50  is located at the first position. Therefore, in this case, the discharged sheet is directed to the first path L 1 . 
     When the sheet of which an image is to be formed on the back side has been directed to the second path L 2  after discharged from the fixing unit  5 , and the trailing end of the sheet has passed the switching flapper  50 , the switching flapper  50  is switched to be located at the first position as shown in  FIG. 7 . 
     The discharge roller  9 A reversely rotates to feed the sheet in the reversed direction, the sheet passes through the second path L 2  and is directed to the re-feed path L 3  (see  FIG. 1 ). Then, the sheet is directed to the image formation unit  2  by the re-feed unit  20 , an image is formed on the back surface, and the sheet bearing images on both sides is discharged from the fixing unit  5 . Then, the sheet is fed through the first path L 1  and the converged feed path L 12 , and discharged, by the feed roller  9 A, and placed on the discharge tray  1 B. 
     The re-feed unit  20  feed the sheet fed through the re-feed path L 3  to a portion which is on the upstream side of the register roller  6  and on the downstream side of a separating mechanism  13  within a sheet feed path from the sheet feed unit  10  to the image formation unit  2 . 
     It is noted that the sheet feed unit  10  includes a pick-up roller  12  which contacts the uppermost sheet of one or more sheets stacked on the sheet feed tray  11  and feeds the same toward the image formation unit  2 , and the separating mechanism  13  provided with a separation pad  13 A and a separation roller  13 B. 
     Incidentally, the separating mechanism  13  is configured as follows. The pick-up roller  12  may feed a few sheets at a time. The separation pad  13 A contacts the sheet on one side to apply a resistance force thereto, while the separation roller  13 B applies a feeding force to the sheet on the other side. With this configuration, a plurality of sheets fed by the pick-up roller  12  is separated and fed one by one to the image formation unit  2 . 
     Movement of the switching flapper  50  and switching of forward/reverse rotation of the discharge roller  9 A is controlled by a control unit  60  (see  FIG. 8 ). The controller  60  is a well-known microcomputer which is typically provided with a CPU (central processing unit), a ROM (read only memory) and a RAM (random access memory). The control unit  60  (i.e., the CPU thereof) controls the operation of the switching flapper  50  and the discharge roller  9 A in accordance with programs stored in a non-volatile storage such as a ROM. 
     It is noted that, according to the embodiment, when the discharge roller  9 A forwardly rotates, the sheet is fed toward the discharge tray  1 B, while when the discharge roller  9 A reversely rotates, the sheet is fed to the entrance of the image formation unit  2  (i.e., fed toward the re-feed path L 3 ). 
     The position of the switching flapper  50  is switched by an actuator  61 . According to the embodiment, an electromagnetic actuator such as an electromagnetic solenoid is used as the actuator  61  of the switching flapper  50 . 
     The forward/reverse rotation of the discharge roller  9 A is switched by switching a driving force transmission path from the motor to the discharge roller  9 A. Switching of the driving force transmission path is performed with use of an actuator  62  for switching the rotation direction of the discharge roller  9 A. As the actuator  62 , an electromagnetic actuator such as an electromagnetic solenoid. 
     Operational timings for controlling the actuator  61  to switch the position of the switching flapper  50 , and the actuator  62  to switch the rotation directions of the discharge roller  6 A are determined based on a elapsed time with respect to a time at which the leading and or trailing end of the sheet is detected by a sheet sensor  63 . 
     Incidentally, according to the embodiment, the sheet sensor  63  is arranged in the feed path from the heat roller  5 A to the feed roller  5 C. Then, the sheet sensor  63  transmits a detection signal to the control unit  60 . 
     Next, the control unit  60  changes the rotation direction of the discharge roller  9 A from the forward rotation to the reverse rotation before the trailing end of the sheet fed to the discharge exit  1 A through the second path L 2  reaches the converged feed path L 12 , that is, after the leading end of the sheet has reached the discharge roller  9 A and the trailing end of the sheet is in the second path L 2 . 
     According to the embodiment, the converging guide unit  31 C, which is a part of the first guide member  31  and constitutes the converged feed path L 12 , can be displaced to a position where the converged feed path L 12  is exposed to outside (see  FIG. 2 ). 
     With the above configuration, regardless whether the sheet jam has occurred in the first path L 1  or in the second path L 2 , simply by opening the converging guide unit  31 C to expose the converged feed path L 12  to outside, the jammed sheet can be removed easily. Therefore, according to the embodiment, the operability of the image formation device  1  can be improved, while the workability in removing the jammed sheet can be improved. 
     According to the embodiment, as shown in  FIG. 2 , the second path L 2  communicates with the re-feed path L 3  which extends to the entrance side of the image formation unit  2 . 
     Further, the second path guide unit  31 A, the re-feed path guide unit  31 B and the converging guide unit  31 C are secured to the rear cover  30  which is rotatable with respect to the main body. Therefore, according to the embodiment, by opening the rear cover  30 , the jammed sheet can be removed easily. 
     Furthermore, according to the embodiment, the intermediate feed roller  40  is secured to the rear cover  30 , while the discharge roller  9 A is secured to the main body. The reverse roller side nip pressure P 2  is set to be smaller than the intermediate feed roller side nip pressure P 3 . 
     With the above configuration, when the rear cover  30  is opened, the sheet is released from the discharge roller  9 A, therefore, the jammed sheet can be removed easily. Specifically, since the discharge roller  9 A is secured to the main body, if the sheet is jammed with being nipped at a position of the intermediate feed roller  40  and a position of the discharge roller  9 A, it is necessary to open the rear cover  30  with pulling the sheet. 
     In such a situation, if the reverse roller side nip pressure P 2  is relatively large, the sheet is strongly held by the main body, and a relatively large force is required to open the rear cover  30 . Therefore, in such a configuration (i.e., the nip pressure P 2  is relatively large), the workability in removing the jammed sheet is lowered. 
     In contrast, according to the embodiment, since the reverse roller side nip pressure P 2  is smaller than the intermediate feed roller side nip pressure P 3 , the sheet is released from the nipped condition as the rear cover is being opened and can be released from the main body. Therefore, according to the embodiment, the jammed sheet can be removed easily. 
     Further, the intermediate feed roller side nip pressure P 3  is set to be smaller than the fixing unit side nip pressure P 1 . With this configuration, the sheet is released from the intermediate feed roller  40  when the rear cover is opened, and the jammed sheet can be removed easily. Specifically, since the fixing unit  5  is provided to the main body, if the sheet is jammed with being nipped at a position of the intermediate feed roller  40  and at a position of the fixing unit  5 , it is necessary to open the rear cover with pulling the sheet. 
     Further, in order to ensure that the developer is fixed on the sheet, the fixing unit side nip pressure P 1  is generally set to have a relatively large pressure. Therefore, if the intermediate feed roller side nip pressure P 3  is also set to be large, the sheet is strongly caught by the main body as well as by the rear cover  30 . Then, a large force is required to open the rear cover  30 , which lowers the workability in removing the jammed sheet. 
     In contrast, according to the embodiment, the intermediate feed roller side nip pressure P 3  is set to be smaller than the fixing unit side nip pressure P 1 . Therefore, when the rear cover  30  is being opened, the sheet is released from the nip by the intermediate feed roller  40  and only the rear cover  30  is moved away from the main body. Therefore, the jammed sheet can be removed easily. 
     Incidentally, it may be possible that the fixing unit side nip pressure P 1  is set to be smaller than the intermediate feed roller side nip pressure P 3  so that the jammed sheet can be removed easily. However, if the fixing unit side nip pressure P 1  is reduced, the developer may not be reliably fixed on the sheet. Thus, such a solution is not appropriate. 
     Further, according to the embodiment, the intermediate feed roller  40  receives the driving force from the main body. Therefore, if the rear cover  30  is opened, transmission of the driving force from the motor (main body) to the intermediate feed roller  40  is cut. Accordingly, when the rear cover  30  is opened, resistance force applied to a pulling force to remove the sheet nipped by the intermediate feed roller  40  (i.e., the rotational resistance of the intermediate feed roller  40 ) is weakened. Accordingly, the jammed sheet can be removed easily. 
     According to the embodiment, as shown in  FIG. 3 , the intermediate feed roller  40  contacts the sheet at an entire width range. Thus, according to the embodiment, it is ensured that the sheet discharged from the fixing unit can be cooled with the intermediate feed roller  40 . Thus, according to the embodiment, the intermediate feed roller  40  can also be used as a cooling roller. Incidentally, the intermediate feed roller  40  contacts the sheet at an entire width range, and a sheet jam may occur on an immediate upstream side or an immediate downstream side of the intermediate feed roller  40 . According to the embodiment, however, the jammed sheet can be removed easily, and thus, the operability of the image formation unit will not be lowered. 
     Since it is ensured that the sheet discharged from the fixing unit  5  is cooled by the intermediate feed roller  40 , the developer image transferred on the sheet can be fixed, which can be done quicker. 
     In the meantime, when the duplex printing is performed, it is necessary to the developer images on both sides of the sheet. Therefore, when an image has been transferred on the front surface, it is preferable to cool the sheet so that the transferred developer is fixed on the sheet earlier. To enhance the cooling function, according to the embodiment, the pressure roller  42  for the second path L 2  is also configured to contact the sheet at the entire with of the sheet. 
     According to the embodiment, the rotation of the discharge roller  9 A is changed from the forward rotation to the reverse rotation before the trailing end, in the sheet feed direction, of the sheet fed toward the discharge exit  1 A reaches the converged feed path L 12 . 
     With this configuration, it is ensured that the sheet can be re-fed toward the entrance of the image formation unit  2  without providing a switching flapper or the like to guide the sheet of which the feeding direction is reversed in the converged feed path L 12 . 
     The trailing end of the sheet becomes the leading end of the sheet after the feeding direction is reversed. Therefore, if the feeding direction is changed after the trailing end of the sheet has reached the converged feed path L 12 , it is impossible to feed the sheet to the entrance of the image formation unit unless the switching flapper or the like is provided to the converged feed path L 12 . 
     According to the embodiment, the intermediate feed roller  40  is arranged between the first path L 1  and the second path L 2 , and is exposed to both the first path L 1  and the second path L 2 . 
     With the above configuration, only with a single roller (i.e., the intermediate feed roller  40 ), the feeding force can be applied to the sheet fed along the first path L 1  and the second path L 2 . 
     According to the embodiment, when the sheet of which images have been formed on both surfaces is discharged from the fixing unit  5 , the sheet is fed to pass through the first path L 1  and the converged feed path L 12 , and discharged by the feed roller  9 A onto the discharge tray  1 B. 
     With this configuration, it is ensured that formation of images on the sheets can be continuously without providing a relatively large interval between the sheets. Therefore, reduction of the number of sheets on which images are formed per unit time can be suppressed. That is, the duplex printing can be performed at a relatively high speed. 
     Second Embodiment 
     In the above-described first embodiment, a single intermediate feed roller  40  is provided between the first path L 1  and the second path L 2 . According to the second embodiment shown in  FIG. 9 , an intermediate feed roller  40 A for the first path L 1  and another intermediate feed roller  40 B for the second path L 2  are provided. 
     According to the second embodiment, a circumferential speed of the intermediate feed roller  40 B is set to be faster than that of the intermediate feed roller  40 A, thereby increasing the re-feeding speed of the sheet toward the image formation unit  2 . 
     In the above-described embodiments, the converged feed path guide portion  31 C is formed integrally with the rear cover  30 . However, the invention needs not be limited to such a configuration, and can be modified in various ways. For example, the converged feed path guide portion  31 C may be provided as a member separate from the rear cover  30 , and is configured to rotatable or removable with respect to the main body. 
     Further, in the above-described embodiments, the second path guide portion  31 A, the re-feed path guide portion  31 B and the converged feed path guide portion  31 C are all provided to the rear cover  30 . However, the invention needs not be limited to such a configuration, and can be modified without departing the scope of the invention. 
     Further, in the above-described embodiments, there is a case where a length of the sheet feed path from the fixing unit  5  to the discharge exit  1 A is longer than the length of the sheet. Therefore, the intermediate feed roller  40  is provided. It is noted that the invention needs not be limited to such a configuration, and can be modified in various ways. For example, if the length of the sheet feed path is sufficiently short, the intermediate feed roller  40  may be omitted. 
     Further, in the above-described embodiments, the intermediate feed roller  40  is provided to the rear cover  30  and receives the driving force from the main body. The invention needs not be limited to such a configuration, and can be modified. For example, the intermediate feed roller  40  may be secured to the main body. 
     Further, in the above-described embodiments, the feeding direction of the sheet is reversed before the trailing end of the sheet fed toward the discharge exit  1 A reaches the converged feed path L 12 . The invention needs not be limited to such a configuration and can be modified. For example, if a feeding direction changing mechanism such as a switching flapper is provided on the discharge exit side with respect to the partition wall  33 , it is possible to reverse the feeding direction of the sheet after the trailing end of the sheet fed toward the discharging exit  1 A has reached the converged feed path L 12 .