Patent Publication Number: US-8977187-B2

Title: Post-processing device and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon, and claims the benefit of priority from the corresponding Japanese Patent Application No. 2012-042791, filed on Feb. 29, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a post-processing device that performs post-processing on a recording medium with an image formed thereon and to an image forming apparatus having the post-processing device. 
     Image forming apparatuses are known that include a main body of the image forming apparatus and a post-processing device. The main body forms an image on a recording medium (paper). The post-processing device performs post-processing such as, punching, stapling, and center-folding, on paper supplied from the main body. Specifically, the post-processing device includes a punching unit that performs punching, a stapling unit that performs stapling, and a center-folding unit that performs center-folding. The punching unit is closest to a port through which paper is supplied from the main body, and the stapling unit and center-folding unit are located downstream of the punching unit in the direction of transporting paper. In the post-processing device, paper passing through the punching unit is supplied to the stapling unit and center-folding unit. 
     Some of the post-processing devices include only one paper transport path. In one such post-processing device, even when punching is not performed, paper passes through the punching unit before being supplied to the stapling unit and center-folding unit. If the punching unit fails, the transport path for use in supplying paper to the stapling unit and center-folding unit may be blocked by the punching blade of the punching unit. To address this situation, if the punching unit in the post-processing device including only one paper transport path fails, all of the functions of the post-processing device are typically deactivated. 
     Unfortunately, deactivating all of the functions of the above-described post-processing device causes an inconvenience because the user cannot use the stapling unit and center-folding unit until, for example, a repairer fixes the punching unit. 
     SUMMARY 
     A post-processing device according to an embodiment of the present disclosure includes a post-processing recording-medium transporting unit, a punching unit, a stapling unit, a first sensor, a second sensor, a determining unit, and a transport controller. The post-processing recording-medium transporting unit feeds a recording medium. The punching unit creates a hole in the recording medium. The stapling unit is located downstream of the punching unit in a transporting direction of the recording medium. The first sensor is used for detecting the recording medium fed by the post-processing recording-medium transporting unit and is located upstream of the punching unit in the transporting direction of the recording medium. The second sensor is used for detecting the recording medium fed by the post-processing recording-medium transporting unit and is located downstream of the punching unit in the transporting direction of the recording medium and upstream of the stapling unit in the transporting direction of the recording medium. The determining unit determines whether the punching unit fails. The transport controller controls the post-processing recording-medium transporting unit such that, when the determining unit determines that the punching unit fails, the recording medium is supplied to the punching unit and, if passage of the recording medium through an arrangement position of the second sensor is detected within a predetermined first time period after detection of passage of the recording medium through an arrangement position of the first sensor, the recording medium is allowed to be supplied to the stapling unit. 
     An image forming apparatus according to another embodiment of the present disclosure includes a main device for forming an image on a recording medium and a post-processing device for performing post-processing on the recording medium. The post-processing device includes a post-processing recording-medium transporting unit, a punching unit, a stapling unit, a first sensor, a second sensor, a determining unit, and a transport controller. The post-processing recording-medium transporting unit feeds the recording medium. The punching unit creates a hole in the recording medium. The stapling unit is located downstream of the punching unit in a transporting direction of the recording medium. The first sensor is used for detecting the recording medium fed by the post-processing recording-medium transporting unit and is located upstream of the punching unit in the transporting direction of the recording medium. The second sensor is used for detecting the recording medium fed by the post-processing recording-medium transporting unit and is located downstream of the punching unit in the transporting direction of the recording medium and upstream of the stapling unit in the transporting direction of the recording medium. The determining unit determines whether the punching unit fails. The transport controller controls the post-processing recording-medium transporting unit such that, when the determining unit determines that the punching unit fails, the recording medium is supplied to the punching unit and, if passage of the recording medium through an arrangement position of the second sensor is detected within a predetermined first time period after detection of passage of the recording medium through an arrangement position of the first sensor, the recording medium is allowed to be supplied to the stapling unit. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a configuration of a copier according to an embodiment of an image forming apparatus; 
         FIG. 2  is a block diagram that illustrates a functional configuration of the copier; and 
         FIG. 3  is a flowchart for describing an operation of the copier when paper is sent to a punching unit. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a post-processing device and image forming apparatus of the present disclosure is described below with reference to the drawings. First, a general configuration of a copier  1  as the image forming apparatus is described.  FIG. 1  illustrates the configuration of the copier  1  according to an embodiment of the image forming apparatus. 
     As illustrated in  FIG. 1 , the copier  1 , according to an embodiment, includes a copier main body  2  as a main device that forms a toner image on paper T as a recording medium and a post-processing device  100  that performs punching, stapling, and center-folding as post-processing on the paper T with the toner image formed thereon. The post-processing device  100  is adjacent to the paper discharge side of the copier main body  2 . 
     The copier main body  2  includes a document transporting unit  10 , a document reading unit  20 , a paper transporting unit  30  as a recording-medium transporting unit, an image forming unit  40 , a transfer unit  50 , and a fixing unit  60 . 
     The document transporting unit  10  is an automatic document feeder (ADF) and includes a document plate  11 , a first feed roller  12 , a guide  13 , a pair of timing rollers  14 , and a document discharging unit  15 . The first feed roller  12  sequentially supplies documents G on the document plate  11  one at a time to the pair of timing rollers  14 . The pair of timing rollers  14  feeds the document G or stops feeding the document G to match the timing of supplying the document G to the location where an image of the document G is to be read by the document reading unit  20  (the location where the guide  13  is disposed) with the timing of reading the image of the document G by the document reading unit  20 . The guide  13  guides the fed document G to a first reading surface  21   a  described below. The document discharging unit  15  discharges the document G, whose image has been read by the document reading unit  20  (that has passed through the guide  13 ), outside the copier main body  2 . The document discharging unit  15  includes a document collecting unit  16  located outside the copier main body  2  as viewed from the document discharging unit  15 . The documents G discharged from the document discharging unit  15  are stacked and collected on the document collecting unit  16 . 
     The document reading unit  20  includes the first reading surface  21   a  and a second reading surface  22   a . The first reading surface  21   a  is located along the upper surface of a first contact glass  21  facing the guide  13  and is a surface for reading the image of the document G. The second reading surface  22   a  is adjacent to the right side of the first reading surface  21   a  and located over most of the portions on the right side of the first reading surface  21   a . The second reading surface  22   a  is used in reading an image of a document G without the use of the document transporting unit  10 . The second reading surface  22   a  is located in the upper surface of a second contact glass  22  and is a surface for reading the image of the document G. 
     The document reading unit  20  includes an illuminating unit  23 , a first mirror  24 , a second mirror  25 , a third mirror  26 , an imaging lens  27 , and an imaging unit  28  inside the copier main body  2 . Each of the illuminating unit  23  and first mirror  24  moves along the sub-scanning direction X. The second mirror  25  and third mirror  26  are located to the left of the illuminating unit  23  and the first mirror  24  in  FIG. 1 . Each of the second mirror  25  and third mirror  26  moves along the sub-scanning direction X while the optical path length, being the distance from the first reading surface  21   a  or second reading surface  22   a  to the imaging unit  28  through the first mirror  24 , second mirror  25 , third mirror  26 , and imaging lens  27 , is maintained constant. 
     The illuminating unit  23  is a light source for emitting light to the document G. The first mirror  24 , second mirror  25 , and third mirror  26  are mirrors for guiding light reflected from the document G to the imaging lens  27  while the optical path length is maintained constant. The imaging lens  27  focuses light from the third mirror  26  on the imaging unit  28 . The imaging unit  28  is an imaging element for obtaining image data based on a focused light image by converting incident light into an electrical signal. An example of the imaging unit  28  can be an image sensor, such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). 
     The paper transporting unit  30  includes a second feed roller  31 , a third feed roller  32 , a pair of registration rollers  33 , a switching unit  39 , a first paper discharging unit  34 , and a second paper discharging unit  38 . The second feed roller  31  supplies paper T as a recording medium stored in a paper cassette  36  to the transfer unit  50 . The third feed roller  32  supplies paper T on a bypass tray  37  to the transfer unit  50 . The pair of registration rollers  33  feeds the paper T, or stops feeding the paper T, to match the timing of supplying the paper T to the transfer unit  50  with the timing when a toner image formed on an intermediate transfer belt  48  described below reaches the transfer unit  50 . The pair of registration rollers  33  also corrects a skew occurring in feeding the paper T. The switching unit  39  switches the transporting direction of the paper T so as to feed the paper T ejected from the fixing unit  60  to either one of the first paper discharging unit  34  and the second paper discharging unit  38 . The first paper discharging unit  34  and the second paper discharging unit  38  discharge the paper T with the toner image fixed thereon outside the copier main body  2 . A discharged-paper collecting unit  35  is located outside the copier main body  2  as viewed from the first paper discharging unit  34 . The sheets of paper T discharged from the first paper discharging unit  34  are stacked and collected on the discharged-paper collecting unit  35 . 
     The image forming unit  40  is used for forming a toner image and includes photosensitive drums  41 , charging units  42 , laser scanner units  43 , developing units  44 , cleaning units  45 , toner cartridges  46 , primary transfer rollers  47 , the intermediate transfer belt  48 , and an opposite roller  49 . 
     The photosensitive drums  41  ( 41   a ,  41   b ,  41   c , and  41   d ) function as photosensitive members or image bearing members to form toner images of black, cyan, magenta, and yellow, respectively. The charging units  42 , laser scanner units  43 , developing units  44 , and cleaning units  45  are arranged around the corresponding photosensitive drums  41   a ,  41   b ,  41   c , and  41   d  in this order from upstream to downstream along the rotation direction of the photosensitive drums  41 . Each of the charging units  42  charges the surface of the corresponding photosensitive drum  41 . Each of the laser scanner units  43  is spaced away from the surface of the corresponding photosensitive drum  41  and scans and exposes the surface of the photosensitive drum  41  based on the image data relating to the document G read by the document reading unit  20 . This removes electrical charges from the exposed portion and forms an electrostatic latent image on the surface of the photosensitive drum  41 . Each of the developing units  44  causes toner to attach to the electrostatic latent image on the surface of the corresponding photosensitive drum  41  and forms a toner image. Each of the cleaning units  45  removes toner and other substances remaining on the surface of the corresponding photosensitive drum  41  after the electrical charges are eliminated from the surface of the photosensitive drum  41  by a neutralization device (not illustrated). 
     Each of the toner cartridges  46  accommodates toner of the corresponding color to be supplied to the corresponding developing unit  44 . The toner cartridge  46  and the developing unit  44  are connected to each other with a toner supply channel (not illustrated). 
     The primary transfer rollers  47  ( 47   a ,  47   b ,  47   c , and  47   d ) are located on opposite sides of the photosensitive drums  41   a ,  41   b ,  41   c , and  41   d , respectively, with respect to the intermediate transfer belt  48 . The intermediate transfer belt  48  is a belt that passes through the image forming unit  40  and the transfer unit  50 . A part of the intermediate transfer belt  48  is inserted between the photosensitive drums  41   a ,  41   b ,  41   c , and  41   d . and the primary transfer rollers  47   a ,  47   b ,  47   c ,  47   d , respectively, and the toner images formed on the photosensitive drums  41   a ,  41   b ,  41   c , and  41   d  are primarily-transferred to the intermediate transfer belt  48 . The opposite roller  49  is located inside the intermediate transfer belt  48 , which has an annular shape, and functions as a driving roller for moving the intermediate transfer belt  48  in the direction indicated by the arrow A in  FIG. 1 . 
     The transfer unit  50  includes a secondary transfer roller  51 . The secondary transfer roller  51  is opposite to the opposite roller  49  with respect to the intermediate transfer belt  48 . The secondary transfer roller  51  sandwiches a part of the intermediate transfer belt  48  with the opposite roller  49 . In addition, the secondary transfer roller  51  secondarily-transfers the toner image primarily-transferred on the intermediate transfer belt  48  to the paper T. 
     The fixing unit  60  includes a heat rotating member  61  and a pressure rotating member  62 . The heat rotating member  61  and pressure rotating member  62  sandwich the paper T with the toner image secondarily-transferred thereon and fix the toner onto the paper T by fusing and pressing the toner. 
     The post-processing device  100  includes a post-processing paper transporting unit  110  as a post-processing recording-medium transporting unit, a punching unit  120 , a stapling unit  130 , and a center-folding unit  140 . The stapling unit  130  and center-folding unit  140  are located downstream of the punching unit  120  in the transporting direction of the paper T. That is, the paper T having passed through the punching unit  120  is supplied to the stapling unit  130  and center-folding unit  140 . 
     The post-processing paper transporting unit  110  feeds the paper T by a driving roller (not illustrated) driven by a post-processing control unit  150  described below. Specifically, the post-processing paper transporting unit  110  includes an introducing unit  111 , a branch guide  112 , and a first discharging unit  113 . The introducing unit  111  introduces the paper T discharged from the second paper discharging unit  38  of the copier main body  2  into the post-processing device  100  and feeds the paper T toward the punching unit  120 . The branch guide  112  switches the transporting direction of the paper T discharged from the punching unit  120  to either the first discharging unit  113  or the stapling unit  130 . The first discharging unit  113  discharges, from the post-processing device  100 , the paper T discharged from the punching unit  120  and the paper T discharged from the stapling unit  130 . A main tray  114  is located outside the post-processing device  100  downstream in the transporting direction of the paper T as viewed from the first discharging unit  113 . The sheets of paper T discharged from the first discharging unit  113  are stacked and collected on the main tray  114 . 
     The punching unit  120  performs punching to create a hole in the paper T for use in binding the paper T. The punching unit  120  includes a punching blade  121  movable in a vertical direction with respect to the paper T. The punching unit  120  creates a punching hole in the paper T by moving the punching blade  121  in the vertical direction and causing the punching blade  121  to penetrate the paper T when the fed paper T stops under the punching blade  121 . The punching unit  120  includes a motor  122  (see  FIG. 2 ) for moving the punching blade  121  up and down and a driving sensor  123  (see  FIG. 2 ) for detecting whether the motor  122  is driven. 
     The stapling unit  130  performs stapling thereby binding and securing the paper T with a staple. The stapling unit  130  includes a paper receiving table  131 , a receiving and stopping unit  132 , a stapling processing unit  133 , and a pair of transport rollers  134 . The paper receiving table  131  temporarily retains a plurality of sheets of the paper T introduced from the punching unit  120  by switching made by the branch guide  112 . The receiving and stopping unit  132  receives the bottom of the paper T and holds the paper T introduced into the paper receiving table  131 . The stapling processing unit  133  moves to an adjacent area of the end or the center of the paper T retained on the paper receiving table  131  and performs stapling on the adjacent area of the end or the center of the paper T. The pair of transport rollers  134  feeds the bundle of paper T in which the central area of the paper T is stapled (saddle stitched) from the paper receiving table  131  to the center-folding unit  140 . 
     The center-folding unit  140  performs center-folding, thereby folding the bundle of saddle-stitched paper T in two at the central area thereof. The center-folding unit  140  includes a center-folding receiving table  141 , a pressing unit  142 , a pair of center-folding rollers  143 , and a second discharging unit  144 . The bundle of paper T saddle-stitched by the stapling unit  130  is placed on the center-folding receiving table  141 . The pressing unit  142  is movable in a direction perpendicular to the bundle of paper T placed on the center-folding receiving table  141 . The pressing unit  142  presses the central area (the portion where stapling has been performed) of the bundle of paper T between the pair of center-folding rollers  143 , which are opposite to the pressing unit  142  with respect to the bundle of paper T, by moving toward the bundle of paper T. The pair of center-folding rollers  143  folds the bundle of paper T pressed by the pressing unit  142  in the form of a booklet and feeds the folded bundle of paper T to the second discharging unit  144 . The second discharging unit  144  discharges the folded bundle of paper T from the post-processing device  100 . A discharge tray  145  is located outside the post-processing device  100  downstream in the transporting direction of the paper T as viewed from the second discharging unit  144 . The bundle of paper T discharged from the second discharging unit  144  are collected on the discharge tray  145 . 
     The functional configuration of the copier  1  is described below with reference to  FIG. 2 .  FIG. 2  is a block diagram that illustrates the functional configuration of the copier  1 . 
     The copier main body  2  includes the above-described components (document transporting unit  10 , document reading unit  20 , paper transporting unit  30 , image forming unit  40 , transfer unit  50 , and fixing unit  60 ). The paper transporting unit  30 , image forming unit  40 , transfer unit  50 , and fixing unit  60  form an engine section  3 . The components described using  FIG. 1  are not described here. The copier main body  2  further includes an operating unit  70 , a storage unit  80 , and a main control unit  90 , in addition to the above-described functional configuration. 
     The operating unit  70  can include a numeric keypad (not illustrated), a touch panel (not illustrated), a start key (not illustrated), and other elements. The numeric keypad is used for entering a numeric character, such as the number of copies. A plurality of keys assigned to various functions (for example, the function of setting a scale in printing, the function of laying out multiple pages in a single sheet of paper T (e.g., 2 in 1 printing), and the function of executing punching, stapling, or center-folding) and other settings can be displayed on the touch panel. A key displayed on the touch panel is used for causing the copier  1  to carry out at least one of various functions. The start key is operated to execute printing. When a key in the operating unit  70  is operated, the operating unit  70  supplies the main control unit  90  with a signal indicating that the key has been operated. 
     The storage unit  80  can include a hard disk, a semiconductor memory, or other media. The storage unit  80  stores image data based on the document G read by the document reading unit  20 . The storage unit  80  can store a control program used in the copier  1 , data used in this control program, and other data. 
     The main control unit  90  can control the document transporting unit  10 , document reading unit  20 , engine section  3 , operating unit  70 , post-processing control unit  150 , and other units. 
     The post-processing device  100  includes the above-described components (post-processing paper transporting unit  110 , punching unit  120 , stapling unit  130 , and center-folding unit  140 ). The components described with reference to  FIG. 1  are not described herein. The post-processing device  100  further includes a first sensor  160 , a second sensor  170 , and the post-processing control unit  150 , in addition to the above-described components. 
     The first sensor  160  is located upstream of the punching unit  120  in the transporting direction of the paper T (see  FIG. 1 ). The first sensor  160  is a sensor for detecting the paper T fed by the post-processing paper transporting unit  110 . To detect the paper T, one example of the first sensor  160  can include an actuator (not illustrated) with which the paper T fed by the post-processing paper transporting unit  110  comes into contact and a photointerrupter (not illustrated) for detecting if light is blocked by the actuator with which the paper T comes into contact. 
     The second sensor  170  is located downstream of the punching unit  120  in the transporting direction of the paper T and upstream of the stapling unit  130  and center-folding unit  140  in the transporting direction of the paper T (see  FIG. 1 ). The second sensor  170  is a sensor for detecting the paper T fed by the post-processing paper transporting unit  110 . To detect the paper T, one example of the second sensor  170  can include an actuator (not illustrated) with which the paper T fed by the post-processing paper transporting unit  110  comes into contact and a photointerrupter (not illustrated) for detecting if light is blocked by the actuator with which the paper T comes into contact. 
     The post-processing control unit  150  controls the post-processing paper transporting unit  110 , punching unit  120 , stapling unit  130 , and center-folding unit  140 . 
     The post-processing control unit  150  includes a determining unit  151 , a transport controller  152 , and a unit controller  153 . 
     The determining unit  151  determines whether the punching unit  120  has failed. The determining unit  151  determines that the punching unit  120  has failed, for example, if the post-processing control unit  150  controls the motor  122  to move the punching blade  121  upward or downward, but the driving sensor  123  does not detect driving of the motor  122 . 
     If the determining unit  151  determines that the punching unit  120  has failed, the transport controller  152  controls the post-processing paper transporting unit  110  such that it supplies the paper T to the punching unit  120 . The transport controller  152  communicates with the main control unit  90  and causes the paper transporting unit  30  to feed the paper T stored in the paper cassette  36  to the post-processing paper transporting unit  110  through the main control unit  90 . If the punching unit  120  fails, the post-processing device  100  (copier  1 ) is unable to identify the location where the punching blade  121  stops. If upward or downward movement of the punching blade  121  stops in progress, the punching blade  121  may block a transport path  115  for the paper T. Thus the transport controller  152  supplies the paper T to the faulty punching unit  120  to check whether the punching blade  121  has blocked the transport path  115  for the paper T. 
     That is, if passage of the leading end of the paper T through an arrangement position of the second sensor  170  is detected based on the signal from the second sensor  170  within a first time period after detection of passage of the leading end of the paper T through an arrangement position of the first sensor  160  based on the signal from the first sensor  160 , the transport controller  152  controls the post-processing paper transporting unit  110  such that the paper T is allowed to be supplied to the stapling unit  130  and center-folding unit  140 . When passage of the leading end of the paper T through the arrangement position of the second sensor  170  is detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the transport controller  152  determines that the punching blade  121  has not blocked the transport path  115  for the paper T. In this situation, the transport controller  152  is able to supply the paper T to the stapling unit  130  and center-folding unit  140 . Accordingly, when a user selects stapling or center-folding by operating the above-described touch panel, the transport controller  152  controls the post-processing paper transporting unit  110  such that the paper T is fed to the stapling unit  130  or center-folding unit  140 . 
     In this situation, the paper T sent to the punching unit  120  to check whether the punching blade  121  has blocked the transport path  115  for the paper T is discharged from the first discharge unit  113  to the main tray  114 . 
     On the other hand, if passage of the leading end of the paper T sent to the punching unit  120  through the arrangement position of the second sensor  170  is not detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the transport controller  152  controls the post-processing paper transporting unit  110  such that the paper T is not allowed to be fed. If passage of the leading end of the paper T through the arrangement position of the second sensor  170  is not detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the transport controller  152  determines that the punching blade  121  has blocked the transport path  115  for the paper T. In this situation, the transport controller  152  is unable to supply the paper T to the stapling unit  130  and center-folding unit  140 . Accordingly, the transport controller  152  does not allow the post-processing paper transporting unit  110  to feed the paper T. 
     In this situation, the paper T sent to the punching unit  120  to check whether the punching blade  121  has blocked the transport path  115  for the paper T is stuck in the punching unit  120  (a jam occurs). However, because a gap is present between the post-processing device  100  and the main body of the copier  1  (not illustrated in  FIG. 1 ), the stuck paper T escapes to the gap. Accordingly, the copier  1  can minimize damage caused by the occurrence of the jam. The paper T stuck in the punching unit  120  is easily removable by the user, for example, laterally moving the post-processing device  100 . 
     The first time period described above is less than a second time period described below. The second time period is the time period for use in determining that a jam has occurred in the punching unit  120  when the determining unit  151  determines that the punching unit  120  has not failed (normal jam detection time period). 
     That is, when the punching unit  120  does not fail, if passage of the leading end of the paper T through the arrangement position of the second sensor  170  is not detected even when the second time period has elapsed since detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the transport controller  152  determines that a jam has occurred in the punching unit  120 . In contrast, when the punching unit  120  fails, the transport controller  152  determines that a jam has occurred in the punching unit  120  based on the first time period, which is less than the second time period (normal jam detection time period). One example of the first time period is half the second time period. 
     When determining that a jam has occurred, the transport controller  152  stops the feeding the paper T operation performed by the post-processing paper transporting unit  110 . The transport controller  152  communicates with the main control unit  90  and stops the feeding the paper T operation performed by the sheet transporting unit  30  through the main control unit  90 . Accordingly, the copier  1  can minimize damage caused by stuck paper when a jam occurs in the punching unit  120 . 
     When the determining unit  151  determines that the punching unit  120  has failed, if passage of the leading end of the paper T sent to the punching unit  120  through the arrangement position of the second sensor  170  is detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the unit controller  153  makes the stapling unit  130  and center-folding unit  140  operable. That is, when the punching unit  120  fails and the punching blade  121  does not block the transport path  115  for the paper T, the unit controller  153  makes the stapling unit  130  and center-folding unit  140  operable. Specifically, the unit controller  153  supplies the main control unit  90  with first information for making the stapling unit  130  and center-folding unit  140  operable. The main control unit  90  makes the key assigned to stapling and the key assigned to center-folding displayed on the above-described touch panel selectable based on the first information. The main control unit  90  makes the key assigned to punching unselectable based on the first information. 
     On the other hand, when the determining unit  151  determines that the punching unit  120  has failed, if passage of the leading end of the paper T sent to the punching unit  120  through the arrangement position of the second sensor  170  is not detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160 , the unit controller  153  makes the punching unit  120 , the stapling unit  130 , and center-folding unit  140  inoperable. That is, when the punching unit  120  fails and the punching blade  121  blocks the transport path  115  for the paper T, the unit controller  153  makes the punching unit  120 , the stapling unit  130 , and center-folding unit  140  inoperable. Specifically, the unit controller  153  supplies the main control unit  90  with second information for making the punching unit  120 , the stapling unit  130 , and center-folding unit  140  inoperable. The main control unit  90  makes the key assigned to punching, the key assigned to stapling, and the key assigned to center-folding displayed on the above-described touch panel unselectable based on the second information. 
     An operation of the copier  1  when the punching unit  120  fails is described below with reference to  FIG. 3 .  FIG. 3  is a flowchart for describing an operation of the copier  1  when paper T is sent to the punching unit  120 . 
     In step ST 1 , the determining unit  151  determines whether the punching unit  120  has failed based on the detection using the driving sensor  123 . If the punching unit  120  has not failed (No), determination in step ST 1  is conducted again. If the punching unit  120  has failed (Yes), processing proceeds to step ST 2 . 
     In step ST 2 , the transport controller  152  determines whether the paper T is to be sent to the punching unit  120  (a passage check is to be conducted) based on the selection by a user. 
     That is, when the punching unit  120  fails, the main control unit  90  displays a button for conducting a passage check on the above-described touch panel to determine whether the punching blade  121  has blocked the transport path  115  for the paper T (that is, to determine whether the punching blade  121  interferes with transportation of the paper T). If the transport controller  152  determines that the conduct of a passage check is selected by a user operating the touch panel (Yes), processing proceeds to step ST 3 . If the transport controller  152  determines that the conduct of a passage check is not selected by a user (No), processing is completed. 
     In step ST 3 , the transport controller  152  controls the post-processing paper transporting unit  110  such that paper T is allowed to be sent to the punching unit  120 . The transport controller  152  communicates with the main control unit  90  and causes the paper transporting unit  30  to feed the paper T in the paper cassette  36  to the post-processing paper transporting unit  110  through the main control unit  90 . 
     In step ST 4 , the transport controller  152  determines whether passage of the leading end of the paper T through the arrangement position of the second sensor  170  has been detected within the first time period after detection of passage of the leading end of the paper T through the first sensor  160 . If the passage of the leading end of the paper T through the arrangement position of the second sensor  170  has been detected within the first time period (Yes), processing proceeds to step ST 5 . If the passage of the leading end of the paper T through the arrangement position of the second sensor  170  has not been detected within the first time period (No), processing proceeds to step ST 7 . 
     In step ST 5 , the transport controller  152  allows the paper T to be supplied to the stapling unit  130  and center-folding unit  140  and processing proceeds to step ST 6 . 
     In step ST 6 , the unit controller  153  makes the stapling unit  130  and center-folding unit  140  operable and makes the punching unit  120  inoperable. 
     If “No” is determined in step ST 4 , the transport controller  152  does not allow the post-processing paper transporting unit  110  to feed the paper T in step ST 7  and processing proceeds to step ST 8 . 
     In step ST 8 , the unit controller  153  makes the punching unit  120 , stapling unit  130 , and center-folding unit  140  inoperable. 
     After step ST 6  and step ST 8 , when the paper T is sent to the punching unit  120 , processing performed by the copier  1  is completed. 
     As described above, the copier  1  (post-processing device  100 ) according to an embodiment can offer the advantageous effects described below. 
     That is, when the determining unit  151  determines that the punching unit  120  has failed, the copier  1  (post-processing device  100 ) according to an embodiment controls the post-processing paper transporting unit  110  such that it supplies the paper T to the punching unit  120 . In addition, when determining that passage of the leading end of the paper T through the arrangement position of the second sensor  170  has been detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160  (when the punching unit  120  does not block the transport path  115  for the paper T), the copier  1  controls the post-processing paper transporting unit  110  such that the paper T is allowed to be supplied to the stapling unit  130  and center-folding unit  140 . In contrast, when determining passage of the leading end of the paper T through the arrangement position of the second sensor  170  is not detected within the first time period after detection of passage of the leading end of the paper T through the arrangement position of the first sensor  160  (when the punching unit  120  blocks the transport path  115  for the paper T), the copier  1  controls the post-processing paper transporting unit  110  such that the paper T is not allowed to be fed. 
     In this way, the copier  1  (post-processing device  100 ) can identify the failure state of the punching blade  121 . The copier  1  (post-processing device  100 ) can identify the faulty state of the punching unit  120  without having to add a function. The copier  1  (post-processing device  100 ) can make the stapling unit  130  and center-folding unit  140  usable, depending on the faulty state of the punching unit  120 . 
     When the punching unit  120  fails, but the punching blade  121  does not block the transport path  115  for the paper T, the copier  1  (post-processing device  100 ) makes the punching unit  120  inoperable and makes the stapling unit  130  and center-folding unit  140  operable. In contrast, when the punching blade  121  blocks the transport path  115  for the paper T, the copier  1  (post-processing device  100 ) makes the punching unit  120 , stapling unit  130 , and center-folding unit  140  inoperable. Accordingly, when the punching blade  121  does not block the transport path  115  for the paper T, the copier  1  (post-processing device  100 ) can enable the usable functions. 
     The first time period is less than the second time period. The second time period is the time period for use in determining that a jam of the paper T occurs in the punching unit  120  when the determining unit  151  determines that the punching unit  120  has not failed. Accordingly, the copier  1  (post-processing device  100 ) can minimize damage caused by the paper T when a jam of the paper T occurs in the punching unit  120 . 
     The present disclosure is not limited to the above-described embodiment and can be carried out in various forms. 
     The present disclosure is not limited to the configuration in which the post-processing control unit  150  includes the determining unit  151 , transport controller  152 , and unit controller  153  described in the above-described embodiment. That is, at least one of the determining unit  151 , transport controller  152 , and unit controller  153  may be included in the main control unit  90 . The center-folding unit  140  included in the post-processing device  100  in an embodiment is optional. In an embodiment, the transport controller  152  detects passage of the leading end (first end) of the paper T, the leading end being one end thereof, through the arrangement position of each of the first sensor  160  and second sensor  170 . Alternatively, the transport controller  152  may detect passage of the trailing end (second end) of the paper T, the trailing end being the other end thereof, through the arrangement position of each of the first sensor  160  and second sensor  170 . Alternatively, the transport controller  152  may detect passage of the leading end of the paper T through the arrangement position of the first sensor  160  and then detect passage of the trailing end of the paper T through the arrangement position of the second sensor  170 . 
     The copier  1  in an embodiment is a color copier. The copier  1  is not limited to this configuration. The copier  1  may be a black-and-white copier. 
     The copier  1  in an embodiment is one in which a toner image is transferred to the paper T through the intermediate transfer belt  48  (indirect transfer type). The copier  1  is not limited to this configuration. The copier  1  may be one in which a toner image on the photosensitive drum is directly transferred to the paper (direct transfer type). 
     The copier  1  in an embodiment has a configuration in which printing is performed on a single side of the paper T. The copier  1  is not limited to this configuration. The copier  1  may have a configuration in which printing is performed on both sides of the paper. 
     The image forming apparatus in the present disclosure is not limited to the above-described copier  1 . That is, the image forming apparatus in the present disclosure may be a multifunctional peripheral having the copying function, printing function, and scanning function. Alternatively, it may be a facsimile machine or printer. 
     The recording medium on which a toner image is fixed by the image forming apparatus in the present disclosure is not limited to the paper T. For example, the recording medium may be a film sheet, such as an overhead projector (OHP) transparency sheet. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.