Patent Publication Number: US-2011069976-A1

Title: Image forming apparatus, recording medium transportation apparatus, recording medium transportation method and computer readable medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC §119 from Japanese Patent Application No. 2009-217729 filed Sep. 18, 2009. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image forming apparatus, a recording medium transportation apparatus, a recording medium transportation method and a computer readable medium storing a program. 
     2. Related Art 
     In general, in image forming apparatuses such as copy machines, printers and the like, a recording medium on which image forming processing has been performed is immediately outputted to an outside of the apparatus, and is supplied to a user. 
     SUMMARY 
     According to an aspect of the present invention, there is provided an image forming apparatus including: an image forming unit that forms an image on a recording medium; a recording medium transportation unit that transports, along a transportation route, the recording medium on which the image has been formed by the image forming unit, and that interrupts transportation operation for the recording medium in a state where one part of the recording medium is discharged from the transportation route and the other part of the recording medium is held in the transportation route; a detection unit that detects pull out operation by a user for the recording medium containing the other part held in the transportation route by the interruption of the transportation operation by the recording medium transportation unit; and a controller that controls the recording medium transportation unit so that the transportation operation having been interrupted is restarted, upon the detection of the pull out operation by the user by the detection unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  shows a configuration of an image forming apparatus to which the first exemplary embodiment is applied; 
         FIG. 2  is a view showing the configuration of the sheet transportation mechanism according to the first exemplary embodiment; 
         FIGS. 3A and 3B  are views for explaining the configuration of the sheet discharge mechanism part; 
         FIGS. 4-1  and  4 - 2  are flowcharts showing an example of the contents of the sheet transportation control for the sheet transportation mechanism, performed by the main controller; 
         FIG. 5  is a view showing the position of the sheet at the time point when the main controller restarts the operation of the sheet transportation mechanism; 
         FIG. 6  is a block diagram showing an internal configuration of the main controller; and 
         FIG. 7  is a view showing the configuration of the sheet transportation mechanism according to the second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. 
     First Exemplary Embodiment 
     Description of Entire Configuration of Image Forming Apparatus 
       FIG. 1  shows a configuration of an image forming apparatus  1  to which the first exemplary embodiment is applied. The image forming apparatus  1  shown in  FIG. 1  is a color printer employing an electrophotographic method, and includes an image forming mechanism  1 A that forms a color image on a recording medium (sheet) P on the basis of image data, and a sheet transportation mechanism  1 B that transports the sheet P on which the color image has been formed by the image forming mechanism  1 A to the outside. 
     The image forming apparatus  1  according to the first exemplary embodiment is different from one installed in a place such as a general office or the like where users are limited to a specific kind of people. It is assumed that the image forming apparatus  1  is installed, for example, at an aisle or along a wall in a public facility such as a station, an airport or the like where a large number of unspecified users access. Thus, the image forming apparatus  1  according to the first exemplary embodiment employs a mechanism for reducing an occurrence of breakdown caused by a user action, an occurrence that the sheet P on which the image has been formed is left as garbage, and the like, as will be described below. 
     &lt;Description of Configuration of Image Forming Mechanism&gt; 
     The image forming mechanism  1 A includes an image forming part  20 , serving as an example of an image forming unit, which forms a color image on the sheet P, a main controller  60 , serving as an example of a controller, which performs operation control of the entire image forming apparatus  1  (the image forming mechanism  1 A and the sheet transportation mechanism  1 B) and information processing such as image processing and the like, and an operation display panel  62  that is arranged on a front side of the image forming apparatus  1  (a side located on the right side of  FIG. 1 ), that receives an operation input by a user and that displays various kinds of information for the user. Further, the image forming mechanism  1 A includes a communication part  63  that is connected to, for example, a database (not shown in the figure) or the like installed in the outside, through a communication line, and that sends and receives information to and from the database or the like, and an external storage  64  in which processing programs and various kinds of information such as image information and the like are stored. 
     The image forming part  20  of the image forming mechanism  1 A includes four image formation units  10 Y,  10 M,  10 C and  10 K (hereinafter, referred to as “image formation units  10 ”) which form a yellow (Y) toner image, a magenta (M) toner image, a cyan (C) toner image, and a black (K) toner image, respectively. These image formation units  10  are arranged in parallel at certain intervals in an up-and-down direction (substantially vertical direction), and each include a photoconductive drum  11  as an image carrier, a charging device  12  that charges a surface of the photoconductive drum  11 , a developing device  13  that develops an electrostatic latent image formed on the photoconductive drum  11  with each color toner, and a cleaning unit  14  that cleans the surface of the photoconductive drum  11  after transfer. 
     Further, the image forming part  20  includes a laser exposure device  15  which exposes the photoconductive drums  11  arranged in the respective image formation units  10  on the basis of the respective color image datasets, and a sheet transportation belt  30  that transports the sheet P while being in contact with the photoconductive drums  11  of the image formation units  10 . The sheet transportation belt  30  is formed by a film-shaped endless belt that electrostatically attracts the sheet P. In addition, the sheet transportation belt  30  is stretched and held by a drive roll  32  and an idle roll  33  and cyclically moves. Further, the sheet transportation belt  30  transports the sheet P between the sheet transportation belt  30  and the photoconductive drums  11  from the lower side toward the upper side in approximately the vertical direction (arrow direction in  FIG. 1 ). 
     Furthermore, the image forming part  20  includes transfer rolls  31  which are located inside the sheet transportation belt  30  and at positions facing the corresponding photoconductive drums  11 . The transfer rolls  31  sequentially transfer the respective color toner images formed by the image formation units  10 , on the sheet P to be transported while being held by the sheet transportation belt  30 . 
     Still furthermore, the image forming part  20  includes a fixing device  40  on a downstream side of the sheet transportation belt  30  in the sheet transportation direction. Here, the fixing device  40  performs fixing processing for an unfixed toner image on the sheet P with heat and pressure. Moreover, the image forming part  20  includes a sheet output roll  54  on a downstream side of the fixing device  40  in the sheet transportation direction. Here, the sheet output roll  54  sends the sheet P subjected to the fixing processing by the fixing device  40  to the sheet transportation mechanism  1 B. 
     In addition, the image forming part  20  includes a sheet container  50  that contains sheets P, a pick-up roll  51  that feeds the sheet P contained in this sheet container  50 , a transportation roll  52  that transports the sheet P fed by the pick-up roll  51 , and a resist roll  53  that sends the sheet P to the sheet transportation belt  30  in accordance with the image forming operation. Here, the sheet container  50 , the pick-up roll  51 , the transportation roll  52  and the resist roll  53  are located on an upstream side of the sheet transportation belt  30  in the sheet transportation direction. 
     &lt;Description of Operation of Image Forming Mechanism&gt; 
     When the image forming mechanism  1 A according to the first exemplary embodiment receives an operation input by a user through the operation display panel  62 , the main controller  60  analyses contents of the instruction inputted by the user. Then, the main controller  60  transmits a transmission request on information corresponding to the contents of the instruction by the user to, for example, the database (not shown in the figure) installed in the outside, through the communication part  63 . Upon receiving, from the database to the communication part  63 , the information for which the transmission request has been made, the main controller  60  performs processing such as image processing or the like for the received information, and generates respective color image datasets. Then, the main controller  60  outputs the respective color image datasets thus generated, to the laser exposure device  15 . By this operation, the laser exposure device  15  exposes the photoconductive drums  11  of the image formation units  10  on the basis of the respective color image datasets, and thereby respective color toner images of Y, M, C and K are formed in the image formation units  10 . 
     When the respective color toner images are started to be formed in the image formation units  10 , the sheet P is picked up from the sheet container  50 . Then, the sheet P is transported to the resist roll  53  by the transportation roll  52 , and is supplied to the sheet transportation belt  30  by the resist roll  53  in accordance with the timing when the toner images are formed. The sheet transportation belt  30  holds and transports the sheet P. During this operation, the respective color toner images are sequentially transferred onto the sheet P, by using transfer electric fields formed by the transfer rolls  31 . 
     The sheet P on which the color toner images have been electrostatically transferred is separated from the sheet transportation belt  30  at a downstream position of the image formation unit  10 K, and is transported to the fixing device  40 . When the sheet P is transported to the fixing device  40 , the unfixed toner image on the sheet P is fixed on the sheet P. Thereafter, the sheet P on which the color toner images have been fixed is sent to the sheet transportation mechanism  1 B from the sheet output roll  54 . 
     &lt;Description of Configuration of Sheet Transportation Mechanism&gt; 
     The sheet transportation mechanism  1 B includes a sheet transportation route  71  that receives the sheet P sent from the sheet output roll  54  of the image forming mechanism  1 A at a receiving port  70  and that guides the sheet P to an output port  78  arranged on the front side of the image forming apparatus  1  (the side located on the right side of  FIG. 1 ), transportation rolls  72  and  73  that transport the sheet P in the sheet transportation route  71 , and a first sheet passage detection part  74  serving as an example of a detection unit (second detection unit) and a second sheet passage detection part  77  serving as an example of a detection unit (first detection unit), which detect the passage of the sheet P and are arranged at positions set in advance on the sheet transportation route  71 , respectively. Further, the sheet transportation mechanism  1 B includes a sheet discharge mechanism part  76 , serving as a recording medium transportation unit, which transports the sheet P sent by the transportation rolls  72  and  73  and discharges the sheet P being in the stopped state in the sheet transportation route  71  from the output port  78 . 
     The first sheet passage detection part  74  and the second sheet passage detection part  77  are each configured of an actuator swinging by contact with the sheet P and a light detection part that detects the swing of the actuator through shielding or transmission of light by a light shielded part provided in the actuator. By this configuration, the first sheet passage detection part  74  and the second sheet passage detection part  77  each detect that the top end S and the back end T of the sheet P pass therethrough, through a change from the transmission of the light to the shielding of the light and a change from the shielding of the light to the transmission of the light, by use of the light detection part. 
     The first sheet passage detection part  74  is arranged on a downstream side of the transportation roll  73 , and on an upstream side of the sheet discharge mechanism part  76  in the sheet transportation direction on the sheet transportation route  71 . The second sheet passage detection part  77  is arranged on the downstream side of the sheet discharge mechanism part  76  and on an upstream side of the output port  78  in the sheet transportation direction. 
     &lt;Description of Operation of Sheet Transportation Mechanism&gt; 
     When receiving the sheet P on which the image has been formed in the image forming mechanism  1 A, the sheet transportation mechanism  1 B according to the first exemplary embodiment transports the sheet P toward the output port  78  by use of the transportation rolls  72  and  73  and the sheet discharge mechanism part  76 . Then, when the sheet P arrives at a position where the top end S thereof is discharged from the output port  78  of the sheet transportation mechanism  1 B by a predetermined length, the transportation rolls  72  and  73  and the sheet discharge mechanism part  76  are stopped once, and the sheet transportation operation is interrupted. Thereafter, if the sheet P in a stopped state, which has one part discharged from the sheet transportation route  71  (the output port  78 ) and the other part held in the sheet transportation route  71 , is pulled out by a user, this pull out operation is detected by the first sheet passage detection part  74  serving as an example of the detection unit that detects the pull out operation for the sheet P (recording medium) by the user. Thereby, the sheet discharge mechanism part  76  restarts the transportation operation for the sheet P. After that, the second sheet passage detection part  77  detects that the back end T of the sheet P is discharged from the output port  78 , and thereby the sheet discharge mechanism part  76  finishes the sheet transportation operation. 
     &lt;Description of Interruption Processing for Sheet Transportation Operation in Sheet Transportation Mechanism&gt; 
     As mentioned above, it is assumed that the image forming apparatus  1  according to the first exemplary embodiment is used by unspecified users. Accordingly, the sheet transportation mechanism  1 B outputs the sheet P on which the image has been formed, after the user is ready to receive the sheet P so that the user may receive the sheet P more securely, instead of outputting the sheet P to the outside immediately. Thus, the sheet transportation mechanism  1 B stops the sheet P (interrupts the output operation) once at a position so that the top end S of the sheet P is discharged from the output port  78  of the sheet transportation mechanism  1 B by the predetermined length. Then, the sheet transportation mechanism  1 B discharges the entire sheet P to the outside after confirming that the user intends to pull out the sheet P being in a state where only the one part thereof on the top end S side is outputted from the output port  78  and indicates his/her intention to receive the sheet P on which the image has been formed. Thereby, for example, in a case where the user&#39;s hands are full of bags or the like and the user is unable to immediately receive the sheet P, the sheet P is held in the sheet transportation mechanism  1 B, and the sheet transportation mechanism  1 B waits until the user is ready to receive the sheet P. Accordingly, an occurrence that the sheet P on which the image has been formed is dropped onto, for example, a floor and the sheet P ends up in garbage or the like is reduced. 
     In a case where the sheet P is stopped once in the sheet transportation mechanism  1 B, the main controller  60  of the image forming mechanism  1 A measures time from the time point when the top end S of the sheet P passes through the second sheet passage detection part  77 . Then, the main controller  60  calculates the moving amount of the sheet P from the measured time and the sheet transportation speed set by the transportation rolls  72  and  73  and the sheet discharge mechanism part  76 . Further, the main controller  60  recognizes the time point when the top end S of the sheet P is discharged from the output port  78  by the predetermined length, on the basis of the calculated moving amount of the sheet P, and stops the driving of the transportation rolls  72  and  73  and the sheet discharge mechanism part  76  at this time point. 
     Note that, as “the predetermined length from the output port  78 ,” the length of the sheet P easily to be taken by a user is referred to. For example, the length of approximately 5 cm to 15 cm from the output port  78  (the length in the sheet P) is set. 
     &lt;Description of Sheet Pull-Out Mechanism&gt; 
     Next, a description will be given of a mechanism for enabling the user to pull out the sheet P being in the stopped state in the sheet transportation route  71 , in the sheet transportation mechanism  1 B. 
       FIG. 2  is a view showing the configuration of the sheet transportation mechanism  1 B according to the first exemplary embodiment. As shown in  FIG. 2 , in the sheet transportation mechanism  1 B according to the first exemplary embodiment, transportation length L 1  from the transportation roll  73  to the output roll  78  in the sheet transportation route  71  is set so that the user may pull out any size of the sheet P. In other words, the transportation length L 1  is set so that the back end T of a sheet Pmax having maximum length usable in the image forming mechanism  1 A is located on the downstream side of the transportation roll  73  in the transportation direction when the sheet Pmax is stopped in a state where the top end S of the sheet Pmax is discharged from the output port  78  by a predetermined length s 1 . 
     By this setting, in a case where the sheet P is in the stopped state, the sheet P is held only by the sheet discharge mechanism part  76  regardless of the size of the sheet P usable in the image forming mechanism  1 A, and is not held by the transportation rolls  72  and  73 . 
     The first sheet passage detection part  74  is arranged so as to detect that the user pulls out the sheet P regardless of the size of the sheet P. Specifically, the first sheet passage detection part  74  is arranged so as to be located on the downstream side of a back end T of a sheet Pmin having minimum length usable in the image forming mechanism  1 A in the transportation direction when the sheet Pmin is stopped in a state where a top end S of the sheet Pmin is discharged from the output port  78  by the predetermined length s 1 . Thus, in a case where the sheet P with any size is pulled out by the user, passage of the back end T of the sheet P through the first sheet passage detection part  74  is detected. 
     Next,  FIGS. 3A and 3B  are views for explaining the configuration of the sheet discharge mechanism part  76 . Here,  FIG. 3A  is a plan view showing the entire configuration of the sheet discharge mechanism part  76 , and  FIG. 3B  is a cross-sectional view of  FIG. 3A  taken along a line IIIB-IIIB. 
     First, as shown in  FIG. 3A , the sheet discharge mechanism part  76  includes plural discharge rolls  90  and  100  fixed to rotation axes  92  and  102 , respectively. Here, the plural discharge rolls  90  and  100  discharges the sheet P toward the output port  78  (also see  FIG. 2 , and the rotation axis  102  is not shown in  FIG. 3A  or  3 B since the rotation axis  102  is hidden by the rotation axis  92 ). Both of these rotation axes  92  and  102  are rotatably supported by the housing of the main body of the sheet transportation mechanism  1 B. Here, the discharge rolls  90  serves as an example of a transportation member. 
     On one end side of the rotation axis  92 , a drive transmission gear  91  is fixed. The drive transmission gear  91  is connected to a gear  94  fixed to a rotation axis  96  arranged in parallel to the rotation axis  92 , so as to be engaged with the gear  94 . To the rotation axis  96 , a gear  95  is also fixed. The gear  95  is connected to a gear  97  fixed to a rotation axis  98  to which the rotation drive force is transmitted from the drive motor (not shown in the figure), so as to be engaged with the gear  97 . Therefore, in the sheet discharge mechanism part  76 , the rotation drive force from the drive motor is transmitted by using a route from the rotation axis  98  to the discharge rolls  90  via the gear  97 , the gear  95 , the rotation axis  96 , the gear  94 , the drive transmission gear  91 , and the rotation axis  92 . In this configuration, the drive force is not directly applied on the discharge rolls  100 , and thus the discharge rolls  100  are driven by the discharge rolls  90  to rotate. 
     As mentioned above, in a case where the drive motor operates, the rotation drive force of the drive motor rotates the discharge rolls  90 , and the sheet P is transported toward the output port  78  by the discharge rolls  90  driven to be rotated and the discharge rolls  100  driven by the discharge rolls  90 . 
     As shown in  FIG. 3B , a one-way clutch  93 , serving as an example of a force transmission restricting member, is arranged between the drive transmission gear  91  and the rotation axis  92 . Here, the one-way clutch  93  is coaxial with the rotation axis  92 . The one-way clutch  93  transmits, to the rotation axis  92 , the rotation torque received by the drive transmission gear  91  from the gear  94 . On the other hand, the one-way clutch  93  does not transmit the rotation torque from the rotation axis  92  in the same rotational direction to the drive transmission gear  91 . Thereby, even if the driving of the drive motor is stopped and the high rotation torque is applied on the drive transmission gear  91  due to the connection and engagement between the drive transmission gear  91  and the gear  94 , the rotation axis  92  (specifically, the discharge rolls  90  and  100 ) rotates in a low load condition by an effect of the one-way clutch  93  in a case where the user intends to pull out the sheet P. Thus, the user may pull out the sheet P with relatively small force. 
     &lt;Description of the Sheet Sending Operation&gt; 
     A description will be given of sending operation for the sheet P performed by the sheet transportation mechanism  1 B in a case where the user starts to pull out the sheet P being in the stopped state in the sheet transportation route  71 . 
     Upon the start of pulling out the sheet P being in the stopped state in the sheet transportation route  71  by the user and the detection of the passage of the back end T of the sheet P by the first sheet passage detection part  74 , the sheet discharge mechanism part  76  restarts the rotation of the discharge rolls  90  and  100  to send the sheet P toward the output port  78 . 
     Specifically, after the main controller  60  serving as an example of a controller and arranged in the image forming mechanism  1 A interrupts the sheet transportation operation in the sheet transportation mechanism  1 B, the main controller  60  drives the drive motor (not shown in the figure) that drives the discharge rolls  90  of the sheet discharge mechanism part  76  to rotate, again, in response to the detection of the passage of the back end T of the sheet P by the first sheet passage detection part  74 . Then, upon the detection of the passage of the back end T of the sheet P by the second sheet passage detection part  77 , the main controller  60  stops the drive motor after the passage of the time which is calculated from the sheet transportation speed set by the sheet discharge mechanism part  76  and the transportation length L 2  (see  FIG. 2 ) from the position of the second sheet passage detection part  77  to the output port  78  and which is required for the back end T of the sheet P to pass through the output port  78 . Note that, in a case where the sheet P is continuously discharged after the above operation, the driving of the driving motor is continued. 
     In this case, the sheet transportation speed set by the sheet discharge mechanism part  76  may be set so as to be different from the sheet transportation speed (process speed) in the image forming mechanism  1 A and the sheet transportation mechanism  1 B at the time of image formation by the image forming mechanism  1 A. 
     For example, in the image forming apparatus  1  in which the process speed of the image forming mechanism  1 A is set to be high (such as the speed exceeding 300 mm/sec, for example), if the sheet P is discharged at the sheet transportation speed that is the same as the process speed of the image forming mechanism  1 A, the sending speed for the sheet P is too fast, and thus it is difficult for the user to receive the sheet P. On the other hand, in the image forming apparatus  1  in which the process speed of the image forming mechanism  1 A is set to be low (such as the speed not greater than 50 mm/sec, for example), if the sheet P is discharged at the sheet transportation speed that is the same as the process speed of the image forming mechanism  1 A, the sending speed for the sheet P is too slow, and thus the user in a hurry may pull out the sheet P, in some cases. 
     In order that the user may easily receive the sheet P at the time when the sheet P is discharged from the output port  78  of the sheet transportation mechanism  1 B, the sheet transportation speed set by the sheet discharge mechanism part  76  may be set so as to be different from the process speed of the image forming mechanism  1 A. 
     On the other hand, in a case where the original process speed of the image forming mechanism  1 A has the value (for example, 150 to 200 mm/sec) at which the user easily receives the sheet P discharged from the output port  78 , the sheet transportation speed by the sheet discharge mechanism part  76  may be set to be the same as the process speed of the image forming mechanism  1 A. 
     As mentioned above, in the image forming apparatus  1  according to the first exemplary embodiment, the sheet P in which the image has been formed by the image forming mechanism  1 A is held once in the sheet transportation mechanism  1 B. Then, the user starts to pull out the sheet P held in the sheet transportation mechanism  1 B in order to indicate his/her intention to receive the sheet P. In response, the sheet transportation mechanism  1 B restarts the transportation of the sheet P by using the sheet discharge mechanism part  76 . Thereby, the sheet P is discharged from the image forming apparatus  1  at the time point when the user is ready to receive the sheet P. Thus, the occurrence that the user fails to receive the sheet P is reduced. Accordingly, the image forming apparatus  1 , which is installed at an aisle or along a wall in a public facility or the like such as a station, an airport or the like where a large number of unspecified people access, and which has a main purpose of printing map information, shop information or the like that has been requested by a user, reduces inconvenience, such as a situation that the user fails to receive the sheet P on which the various kinds of information has been printed and the sheet P is dropped onto the floor and left and then the sheet P ends up in garbage. 
     In addition, after the user starts to pull out the sheet P, since the sheet P is discharged by the sheet transportation mechanism  1 B, the sheet P is smoothly sent. Meanwhile, if the pull out operation of the entire sheet P is performed only by the user, the sheet P may be obliquely pulled out, in some cases. In this case, the sheet P may be torn. Further, since the part of the torn sheet P may remain in the sheet transportation route  71 , transportation failure or jamming of the following sheet P may occur. In addition, although the one-way clutch  93  is provided, the sheet P is necessary to be pulled out while the sheet discharge mechanism part  76  is rotated. Thus, the user receives the load therefrom, although the volume of the load is not so large. Thereby, the pull out operation by the user may be unstable in some cases. To avoid this, after the user starts to pull out the sheet P, influence of the user&#39;s operation is eliminated by causing the sheet transportation mechanism  1 B to transport the sheet P. Accordingly, the sheet P may be smoothly sent. 
     Alternatively, in the image forming apparatus  1  according to the first exemplary embodiment, in a case where one image is formed on multiple sheets P for multiple pages, the sheet P for the first page may be held once in the sheet transportation mechanism  1 B. Then, upon the start of pulling out operation for the sheet P for the first page held in the sheet transportation mechanism  1 B by the user, the sheets P for all of the pages on which the one image is formed may be discharged from the sheet discharge mechanism part  76 . Thereby, the multiple sheets P on which the one image has been formed are discharged in a short period of time. 
     Also, in the image forming apparatus  1  according to the first exemplary embodiment, in a case where one image is formed on multiple sheets P for multiple pages, a piece of the one image is formed on the sheet P for the first page, and then the sheet P for the first page may be held once in the sheet transportation mechanism  1 B. By the time the user starts to pull out the sheet P for the first page held in the sheet transportation mechanism  1 B, the image formation for the subsequent pages is interrupted. Thereafter, upon the start of the pull out operation by the user for the sheet P for the first page held in the sheet transportation mechanism  1 B, the image formation for the other pages may be performed, and the sheets P for the other pages may be discharged from the sheet discharge mechanism part  76 . On the other hand, in a case where the user does not pull out the sheet P for the first page, the image formation for the following pages may be terminated. By this configuration, wasted image formation is suppressed. In addition, occurrence of paper jam due to the jamming of the sheet P in the sheet transportation route  71  is also suppressed. 
     Moreover, the image forming apparatus  1  according to the first exemplary embodiment has a setting in which the image is formed on the upper side (user&#39;s side) of the sheet P being in the state where only a part thereof on the top end S side is outputted from the output port  78 . Thus, the user easily determines whether the user should pull out the sheet P or not. 
     &lt;Description of Contents of Sheet Transportation Control by Main Controller&gt; 
     Next, a description will be given of the contents of the sheet transportation control in the sheet transportation mechanism  1 B, performed by the main controller  60 . 
       FIGS. 4-1  and  4 - 2  are flowcharts showing an example of the contents of the sheet transportation control for the sheet transportation mechanism  1 B, performed by the main controller  60 . 
     First, as shown in  FIG. 4-1 , the main controller  60  causes the sheet P on which the color image has been formed after completion of the image forming processing therefor in the image forming mechanism  1 A, to enter the sheet transportation mechanism  1 B from the image forming mechanism  1 A (Step  101 ). Thereby, the main controller  60  operates the transportation rolls  72  and  73  and the sheet discharge mechanism part  76 , and causes the sheet P to be transported toward the output port  78  (Step  102 ). 
     Thereafter, the main controller  60  waits for the second sheet passage detection part  77  as an example of the first detection unit to detect the top end S of the sheet P (No in Step  103 ). If the top end S of the sheet P is detected by the second sheet passage detection part  77  (Yes in Step  103 ), the main controller  60  acquires the detection information from the second sheet passage detection part  77 , and thereby causing a timer (not shown in the figure) to start to measure time (Step  104 ). Then, at the time point when the timer measures the time t 1  which is calculated from an additional value (L 2 +s 1 ) and the sheet transportation speed set by the sheet transportation mechanism  1 B, and which is required for the top end S of the sheet P to arrive at the position of the length s 1  in the sheet P outputted from the output port  78  (Yes in Step  105 ), the operation of the transportation rolls  72  and  73  and the sheet discharge mechanism part  76  is stopped (Step  106 ). Here, L 2  indicates transportation length from the position of the second sheet passage detection part  77  to the output port  78 , while s 1  indicates the predetermined length in the sheet P. Further, measuring time by the timer is stopped (Step  107 ). Note that, the position of the sheet P at the time point when the main controller  60  stops the operation of the transportation rolls  72  and  73  and the sheet discharge mechanism part  76  has been already shown in the above-described  FIG. 2 . 
     Meanwhile, before the timer measures the time t 1  (No in Step  105 ), the operation of the transportation rolls  72  and  73  and the sheet discharge mechanism part  76  is continued, and also measuring time by the timer is continued. 
     After that, the main controller  60  waits for the first sheet passage detection part  74  as an example of the second detection unit to detect the passage of the back end T of the sheet P through the pull out operation by the user for the sheet P (No in Step  108 ). If the first sheet passage detection part  74  detects the passage of the back end T of the sheet P (Yes in Step  108 ), the main controller  60  acquires detection information from the first sheet passage detection part  74 , and thereby restarting the operation of the sheet discharge mechanism part  76  (Step  109 ). Here,  FIG. 5  is a view showing the position of the sheet P at the time point when the main controller  60  restarts the operation of the sheet discharge mechanism part  76 . 
     The flow proceeds to  FIG. 4-2 . After restarting the operation of the sheet discharge mechanism part  76 , the main controller  60  waits for the second sheet passage detection part  77  to detect the back end T of the sheet P (No in Step  110 ). If the back end T of the sheet P is detected by the second sheet passage detection part  77  (Yes in Step  110 ), measuring time by the timer (not shown in the figure) is started (Step  111 ). Then, at the time point after the predetermined time passes since the timer has measured the time t 2  which is calculated from the transportation length L 2  (see  FIG. 2 ) from the position of the second sheet passage detection part  77  to the output port  78  and the sheet transportation speed set by the sheet discharge mechanism part  76  and which is required for the back end T of the sheet P to pass through the output port  78  (Yes in Step  112 ), the operation of the sheet discharge mechanism part  76  is stopped (Step  113 ). Further, measuring time by the timer is also stopped (Step  114 ). Then, the main controller  60  finishes the sheet transportation control. 
     On the other hand, until the predetermined time passes after the timer measures the time t 2  (No in Step  112 ), the operation of the sheet discharge mechanism part  76  is continued, and measuring time by the timer is also continued. 
     &lt;Description of Internal Configuration of Main Controller&gt; 
     Next,  FIG. 6  is a block diagram showing an internal configuration of the main controller  60 . As shown in  FIG. 6 , the main controller  60  includes a CPU  601 , a RAM  602 , a ROM  603 , a non-volatile memory (NVM)  604 , and an interface (I/F)  605 . The CPU  601  performs a digital arithmetic processing in accordance with a predetermined processing program for the execution of the sheet transportation control in the sheet transportation mechanism  1 B. The RAM  602  is used as a working memory of the CPU  601 . The ROM  603  stores various setting values to be used in the processing by the CPU  601 . The NVM  604  is a battery-backed rewritable flash memory or the like capable of storing data even when power supply is lost. The I/F  605  controls an input and an output of a signal to and from respective functional units such as the motor driver (not shown in the figure) controlling the drive motor arranged in the sheet transportation mechanism  1 B, the operation display panel  62 , the communication part  63 , the external storage  64  and the like arranged in the image forming mechanism  1 A. 
     The CPU  601  loads the processing program from the external storage  64  into the main memory (RAM  602 ), and then implements respective functions in the main controller  60 . 
     Note that, another mode of providing the processing program is to provide the processing program stored in advance in the ROM  603  and then load the processing program into the RAM  602 . Still another way, if the rewritable ROM  603  such as an electrically erasable and programmable ROM (EEPROM) is included, is to install only the program into the ROM  603  after setting of the CPU  601 , and then load the program into the RAM  602 . Still another way is to transmit the program to the main controller  60  via a network such as the Internet, install the program into the ROM  603  of the main controller  60 , and then load the program into the RAM  602 . Even still another way is to load the program from an external recording medium such as a DVD-ROM or a flash memory into the RAM  602 . 
     [Second Exemplary Embodiment] 
     In the first exemplary embodiment, the description has been given of the configuration in which the sheet transportation speed of the sheet discharge mechanism part  76  discharging the sheet P held once in the sheet transportation mechanism  1 B from the output port  78  is set at the predetermined speed. In the second exemplary embodiment, a description will be given of the configuration in which the sheet transportation speed of the sheet discharge mechanism part  76  is set in accordance with the speed at the time when the user pulls out the sheet P. Note that, the same components as those in the first exemplary embodiment are denoted by the same reference numerals, and the detailed description thereof will be omitted. 
     &lt;Description of Configuration of Sheet Transportation Mechanism&gt; 
     The sheet transportation mechanism  1 B according to the second exemplary embodiment includes a speed measurement unit that measures the pull out speed (moving speed) at the time when the user pulls out the sheet P held in the sheet transportation mechanism  1 B, and a speed setting unit that sets the sheet transportation speed at the sheet discharge mechanism part  76  in accordance with the moving speed measured by the speed measurement unit, in addition to the configuration of the first exemplary embodiment. 
       FIG. 7  is a view showing the configuration of the sheet transportation mechanism  1 B according to the second exemplary embodiment. As shown in  FIG. 7 , the sheet transportation mechanism  1 B according to the second exemplary embodiment includes a third sheet passage detection part  75 , serving as an example of a speed measurement unit, which detects the passage of the sheet P, and which is located on the downstream side of the first sheet passage detection part  74  in the sheet transportation direction by a transportation length L 3 . The main controller  60  arranged in the image forming mechanism  1 A (see  FIG. 1 ) measures a time t 3  for the third sheet passage detection part  75  to detect the passage of the back end T of the sheet P after the passage of the back end T of the sheet P is detected by the first sheet passage detection part  74  through the pull out operation by the user for the sheet P. Accordingly, the main controller  60  calculates the pull out speed at the time when the user pulls out the sheet P held in the sheet transportation mechanism  1 B from the transportation length L 3  from the position of the first sheet passage detection part  74  to the position of the third sheet passage detection part  75  and the time t 3  for the back end T of the sheet P to pass through the third sheet passage detection part  75  after the back end T of the sheet P passes through the first sheet passage detection part  74 . 
     The main controller  60 , serving also as the speed setting unit, controls the motor driver (not shown in the figure) controlling the drive motor (not shown in the figure) driving the sheet discharge mechanism part  76  so that the sheet transportation speed at the sheet discharge mechanism part  76  is set as the calculated pull out speed of the user. 
     In this case, the main controller  60  may prepare, as the sheet transportation speed at the sheet discharge mechanism part  76 , plural sheet transportation speeds in advance, and select one of them which is the closest to the calculated pull out speed of the user. In a case where the calculated pull out speed of the user is faster than the plural sheet transportation speeds prepared in advance, the fastest one among the plural sheet transportation speeds prepared in advance may be selected. On the other hand, in a case where the calculated pull out speed of the user is lower than the plural sheet transportation speeds prepared in advance, the lowest one among the plural sheet transportation speeds prepared in advance may be selected. 
     The main controller  60  may set both of the upper limit and lower limit of the sheet transportation speed for the sheet transportation speed at the sheet discharge mechanism part  76  in advance. In a case where the calculated pull out speed of the user is faster than the upper limit of the sheet transportation speed set in advance, the main controller  60  may select the upper limit of the sheet transportation speed. On the other hand, in a case where the calculated pull out speed of the user is lower than the lower limit of the sheet transportation speed set in advance, the main controller  60  may select the lower limit of the sheet transportation speed that has been set in advance. 
     In such a case, alternatively, by recognizing the tendency of the pull out speed of the user, any one of the upper limit and the lower limit of the sheet transportation speed may be set. 
     By this setting, the sheet discharge mechanism part  76  discharges the sheet P at the sheet transportation speed according to the pull out speed at the time when the user pulls out the sheet P. Thus, the sheet P is discharged at the speed according to the receiving capacity of the user in response to the pull out operation by the user at the speed for easily receiving the sheet P. Thus, it facilitates the reception of the sheet P by the user. In addition, by setting at least any one of the upper limit and lower limit of the sheet transportation speed at the sheet discharge mechanism part  76 , an occurrence that the user drops the sheet P onto the floor because of the excessively high sheet transportation speed, an occurrence that the user pulls out the sheet P because of the excessively low sheet transportation speed or the like is reduced. 
     As the speed measurement unit, instead of the configuration using the first sheet passage detection part  74  and the third sheet passage detection part  75  as shown in the second exemplary embodiment, the configuration using the first sheet passage detection part  74 , a mechanism that detects the rotation of the sheet discharge mechanism part  76 , and size information on the sheet P used in the image formation may be employed. 
     Specifically, the main controller  60  recognizes the length of the sheet P in the transportation direction from the size information on the sheet P in advance, and calculates the transportation length between the back end T of the sheet P being in the stopped state in the sheet transportation route  71  and the position of the first sheet passage detection part  74 . Upon the detection of the rotation of the sheet discharge mechanism part  76 , measuring time by the timer is started, and the time for the back end T of the sheet P to pass through the first sheet passage detection part  74  is measured. Accordingly, the pull out speed at the time when the user pulls out the sheet P is calculated by use of the transportation length between the back end T of the sheet P and the position of the first sheet passage detection part  74 , and the time for the back end T of the sheet P to pass through the first sheet passage detection part  74 . 
     As another speed measurement unit, a mechanism configured by, for example, an encoder detecting the rotation speed of the sheet discharge mechanism  76  may be employed. 
     As described above, the image forming apparatus  1  according to the second exemplary embodiment, the sheet P on which the image has been formed in the image forming mechanism  1 A is held once in the sheet transportation mechanism  1 B. Then, upon the start of pulling out the sheet P held in the sheet transportation mechanism  1 B by the user, the sheet transportation mechanism  1 B restarts to discharge the sheet P. Thereby, the sheet P is discharged from the image forming apparatus  1  at the time point when the user is ready to receive the sheet P. Thus, an occurrence that the user fails to receive the sheet P is reduced. By this configuration, the image forming apparatus  1 , which is installed in a public facility such as a station, an airport or the like where a large number of people access, and which has a main purpose for printing map information, shop information or the like that has been requested by the user, reduces inconvenience that the user fails to receive the sheet P on which the various kinds of information has been printed and the sheet P is dropped onto the floor and left, and then the sheet P ends up in garbage. 
     In addition, at the time when the user starts to pull out the sheet P, the sheet P may be discharged at the sheet transportation speed according to the pull out speed at the time when the user pulls out the sheet P. It facilitates the reception of the sheet P by the user. 
     Note that, in the first and second exemplary embodiments, the description has been given of the image forming apparatus  1  including the image forming mechanism  1 A transporting the sheet P from the lower side toward the upper side in the substantially vertical direction (an arrow direction in  FIG. 1 ). However, the present invention is applicable to, for example, an image forming apparatus including the image forming mechanism transporting the sheet P in the substantially horizontal direction, and an image forming apparatus including the image forming mechanism transporting the sheet P from the lower side to the upper side in the oblique direction. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.