Patent Publication Number: US-10764454-B1

Title: Image reading apparatus and image forming system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-109478 filed Jun. 12, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to image reading apparatuses and image forming systems. 
     (ii) Related Art 
     A known image reading apparatus in the related art reads image information of a document having an image formed thereon so as to function as, for example, a photocopier, a facsimile apparatus, or a computer-input scanner. In an image reading apparatus of this type, light is radiated from a light source disposed on a document transport path, and reflected light from the document is received by an image sensor, so that the image on the document is read. 
     Japanese Unexamined Patent Application Publication No. 2018-133697 discloses an image reading apparatus in which, when transporting of a document is to be stopped, a read image of a previous document is invalidated if the trailing edge of the previous document has not passed a rear-surface reading position, and validates the read image of the previous document if the trailing edge of the previous document has passed the rear-surface reading position. 
     There is an image reading apparatus that has a document feeder having a function for transporting documents one-by-one from a document bundle and reading each document by using a reader. In this document feeder, for example, a driving roller and a driving motor are used as a transport unit that transports each document. Sometimes, the transport unit used is of a clutchless type in which the driving roller and the driving motor are actuated in synchronization with each other without using a clutch. However, in such a clutchless transport unit, it is not possible to transport a preceding document bundle and a subsequent document bundle separately. If the subsequent document bundle is placed before the reading process performed on the preceding document bundle is completed, a document in the subsequent document bundle may sometimes be pulled into the apparatus. This may result in an improper reading process performed on the document in the subsequent document bundle. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to an image reading apparatus that may properly read a document even if the document is a document in a subsequent document bundle pulled into the apparatus. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided an image reading apparatus including a transport unit, a reader, a detector, and a controller. The transport unit transports a document. The reader reads the transported document. The detector detects whether or not a document bundle prior to being transported is present. While a document in a first document bundle corresponding to a first job is being transported, if the detector detects that a document in a second document bundle corresponding to a second job as a subsequent job is loaded, the controller changes pre-feeding operation for preliminarily pulling a document in the second document bundle into the image reading apparatus in accordance with a pull-in position of the document in the image reading apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates a hardware configuration example of an image forming apparatus; 
         FIG. 2  illustrates a configuration example of an image reader that reads a document image in accordance with this exemplary embodiment; 
         FIG. 3  illustrates a state where a document in a second document bundle is pulled into a document feeder; 
         FIG. 4  illustrates first control performed on the document feeder by a controller; 
         FIG. 5  illustrates the position of a document when another document is output onto an output load section; 
         FIGS. 6A and 6B  illustrate second control performed on the document feeder by the controller; 
         FIGS. 7A and 7B , together with  FIG. 6B , illustrate the second control performed in this exemplary embodiment; 
         FIGS. 8A and 8B , together with  FIG. 6B , illustrate the second control performed in this exemplary embodiment; 
         FIG. 9  is a block diagram illustrating a functional configuration example of the controller according to this exemplary embodiment; and 
         FIG. 10  is a flowchart illustrating the operation of the document feeder. 
     
    
    
     DETAILED DESCRIPTION 
     Overall Configuration of Image Forming Apparatus  10   
       FIG. 1  illustrates a hardware configuration example of an image forming apparatus  10 . 
     The image forming apparatus  10  is an example of an image forming system that forms an image onto a recording medium, such as a sheet, and outputs the recording medium as a printed medium. In addition to a printing function, the image forming apparatus  10  has other image processing functions, such as a scanning function and a facsimile function. 
     As shown in  FIG. 1 , the image forming apparatus  10  includes a central processing unit (CPU)  11 , a random access memory (RAM)  12 , a read-only memory (ROM)  13 , a storage unit  14 , an operation panel  15 , an image reader  16 , an image forming unit  17 , and a communication interface (I/F)  18 . These units exchange data with each other via a bus B. 
     The CPU  11  loads various types of programs stored in, for example, the ROM  13  into the RAM  12  and executes the programs, so as to realize various functions to be described later. 
     The RAM  12  is a memory used as a work memory of the CPU  11 . 
     The ROM  13  is a memory that stores, for example, the various types of programs to be executed by the CPU  11 . 
     The storage unit  14  stores, for example, image data (image information) read by the image reader  16  and image data to be used in image formation in the image forming unit  17 . The storage unit  14  is, for example, a magnetic disk device, such as a hard disk drive (HDD), or a solid state drive (SSD). 
     The operation panel  15  displays various types of information and receives an operation input by a user. The operation panel  15  is, for example, a touchscreen. 
     The image reader  16  is an example of an image reading apparatus that reads an image recorded on a document. The image reader  16  is, for example, a scanner and may be of a charge-coupled device (CCD) type that uses a lens to reduce reflected light of light radiated onto a document from a light source and uses a CCD to receive the reflected light, or may be of a contact image sensor (CIS) type that uses a CIS to receive reflected light of light sequentially radiated onto a document from a light-emitting-diode (LED) light source. A detailed description of the image reader  16  will be provided later. 
     The image forming unit  17  forms the image read by the image reader  16  onto a recording medium. The image forming unit  17  is, for example, a printer and may be of an electrophotographic type that forms an image by transferring toner adhered to a photoconductor onto a recording medium, such as a sheet, or may be of an inkjet type that forms an image by ejecting ink onto a recording medium. 
     The communication I/F  18  exchanges various types of information with other devices via a network. 
     In this exemplary embodiment, the CPU  11 , the RAM  12 , the ROM  13 , and the storage unit  14  constitute a system controller  400  that controls the entire image forming apparatus  10 . 
     Operation of Image Forming Apparatus  10   
     A user may use such an image forming apparatus  10  to, for example, copy a document. Specifically, based on image data of a document read by the image reader  16 , the image forming unit  17  may copy the document by forming the image onto a recording medium. Moreover, the user may transmit a print job to the image forming apparatus  10  from an external device (not shown), such as a personal computer (PC), via a network (not shown), such as a local area network (LAN) connected to the image forming apparatus  10 , and the communication I/F  18 , so that printing may be performed. Specifically, based on image data contained in the print job, the image forming unit  17  may perform printing by forming the image onto a recording medium. Furthermore, the user may perform a facsimile transmission-reception process. Specifically, the image data of the document read by the image reader  16  may be transmitted via the network and the communication I/F  18 . Alternatively, the user may perform a document scanning process. Specifically, the image data of the document read by the image reader  16  may be saved in the storage unit  14  or may be saved in an external device via the network and the communication I/F  18 . 
     Image Reader  16   
       FIG. 2  illustrates a configuration example of the image reader  16  that reads a document image in accordance with this exemplary embodiment. The image reader  16  is capable of reading an image of a secured document as well as an image of a transported document. This image reader  16  includes a reader  150  that generates image data by reading a document image and a document feeder  110  that separates documents one-by-one from a bundle of stacked documents and sequentially transports each document to the reader  150 . The image reader  16  also includes a controller  100  that controls the entire image reader  16  and a signal processor  200  that processes read image data. Although the following components do not strictly constitute the image reader  16 , an image processor  300  that performs image processing on an output from the signal processor  200 , the aforementioned system controller  400  that controls the entire system including the image reader  16 , and the aforementioned image forming unit  17  that forms an image onto a recording medium, such as a sheet, are also illustrated in  FIG. 2 . 
     The document feeder  110  includes a document load section  111  on which a document bundle constituted of multiple documents is loaded, and also includes an output load section  112  that is provided below the document load section  111  and on which documents having undergone reading are loaded. The document feeder  110  also includes a transport roller  113  that fetches and transports a document from the document load section  111 . Furthermore, a separating mechanism  114  that uses a feed roller and a retardation roller to separate the documents one-by-one is provided downstream of the transport roller  113  in the document transport direction. A first transport path  131  along which a document is transported is provided with a registration roller  116  and an output roller  119  in that order from the upstream side in the document transport direction. Moreover, the document feeder  110  includes a document sensor  121  that detects a document, and also includes a scan sensor  122 . 
     The registration roller  116  feeds a document while performing a registration (displacement) adjustment process relative to the reader  150 , to be described later. A second transport path  132  for guiding a document to the output load section  112  is provided downstream of the reader  150  in the document transport direction. The second transport path  132  is provided with the output roller  119 . The transport roller  113 , the separating mechanism  114 , the registration roller  116 , and the output roller  119  function as a transport unit that transports a document. 
     The transport roller  113 , the separating mechanism  114 , the registration roller  116 , and the output roller  119  are driven in conjunction with one another when a power source, such as a driving motor (not shown), is actuated. Specifically, the document feeder  110  according to this exemplary embodiment is a so-called clutchless device in which the transport roller  113 , the separating mechanism  114 , the registration roller  116 , and the output roller  119  all rotate when the power source is actuated and all stop when the power source is stopped. In other words, it is not possible to selectively rotate any of the above components and selectively stop any of the above components when the power source is actuated. 
     The document sensor  121  is provided between the transport roller  113  and the separating mechanism  114  in the document feeder  110 . In other words, the document sensor  121  is disposed at the entrance of the first transport path  131 . Accordingly, the document sensor  121  functions as a detector that detects whether or not there is a document bundle prior to being transported. 
     The scan sensor  122  is provided in front of a document reading position of the reader  150  in the document feeder  110 . Thus, when a document is transported along the first transport path  131  by the transport roller  113 , the separating mechanism  114 , and the registration roller  116 , the scan sensor  122  detects that the document has reached the reader  150 . Accordingly, the scan sensor  122  functions as a sensor that detects a document transported to the position of the reader  150 . 
     The reader  150  supports the aforementioned document feeder  110  in an openable-closable manner and also supports this document feeder  110  by using a device frame  160 . Moreover, the reader  150  reads an image of a document transported by the document feeder  110 . The reader  150  includes the device frame  160  that constitutes a housing, a first platen glass member  152 A on which a document is placed and through which light radiated onto the document from a light emitter (not shown) and light reflected from the document are transmitted, and a second platen glass member  152 B having a light opening used for reading a document transported by the document feeder  110 . The second platen glass member  152 B is formed of, for example, a transparent glass plate having a long plate-like structure. 
     The light emitter has a light-emitting-element array having multiple light emitting elements (such as light-emitting diodes (LEDs)) arranged in a first scanning direction FS, and radiates light onto a document. Moreover, the light emitter has a light-receiving-element array (such as a CCD image sensor) that receives light reflected from the document. 
     In this exemplary embodiment, the light-receiving-element array includes three arrays of CCDs corresponding to red (R), green (G), and blue (B) colors and is capable of measuring an image recorded on a document based on RGB colors. In other words, the light-receiving-element array is a three-line-color CCD array. The light received by the light-receiving-element array undergoes photoelectric conversion to become an electric charge, and this electric charge is detected and becomes image data as an electric signal. Because the light-receiving-element array includes the three-color CCDs corresponding to the red (R), green (G), and blue (B) colors, an R signal, a G signal, and a B signal as image data respectively corresponding to the three colors are generated. 
     The reader  150  further includes a reading unit  170  disposed within the device frame  160 , a guide shaft  181  that guides the reading unit  170  within the device frame  160  in a second scanning direction SS and in a direction opposite thereto, a driving motor  182  that moves the reading unit  170  along the guide shaft  181 , and a white reference plate  190  that performs white color proofing. The reader  150  also includes a cable unit  183  having a first end attached to the device frame  160  and a second end attached to the reading unit  170 . The cable unit  183  exchanges electric power and signals with the reading unit  170 . In this exemplary embodiment, the guide shaft  181  and the driving motor  182  may be regarded as a moving unit that moves the light emitter (not shown) in the second scanning direction SS. In this case, the moving unit guides the light emitter by using the guide shaft  181  functioning as a guide member, so as to move the light emitter along the first platen glass member  152 A. 
     The reading unit  170  is normally positioned at a reference position P 1  below the second platen glass member  152 B. When a document from which an image is to be read is placed in a stationary state on the first platen glass member  152 A, the reading unit  170  moves in the second scanning direction SS in accordance with a document reading process to reach a terminal position P 2  at the downstream-most side in the second scanning direction SS, and subsequently returns to the reference position P 1 . When a document transported by the document feeder  110  is to be read, the reading unit  170  reads the document while remaining stationary at the reference position P 1 . 
     In the following description, the direction extending from the front side toward the rear side of each drawing will be referred to as “first scanning direction FS”. 
     Control of Document Feeder  110   
     When a document reading process is to be performed by using the document feeder  110 , the user places a first document bundle corresponding to a first job for the document reading process on the document load section  111 . Then, the document feeder  110  sequentially pulls the documents in the first document bundle into the document feeder  110  so that images are read therefrom. However, the user may sometimes place a second document bundle corresponding to a second job as a subsequent job on the document load section  111  before all the documents in the first document bundle are output onto the output load section  112 . In this case, if the document load section  111  has a clutch mechanism, the transport roller  113  and the separating mechanism  114  are stopped while the documents are transported by the registration roller  116  and the output roller  119 , so that the documents in the second document bundle may be prevented from being pulled into the document feeder  110 . In contrast, since the document feeder  110  according to this exemplary embodiment is a clutchless device, as mentioned above, it is not possible to stop the transport roller  113  and the separating mechanism  114 , thus causing the documents in the second document bundle to be pulled into the document feeder  110 . 
       FIG. 3  illustrates a state where a document in the second document bundle is pulled into the document feeder  110 . 
     A document G 1  shown in  FIG. 3  is the last document in the first document bundle corresponding to the first job.  FIG. 3  illustrates a state where the document G 1  is being read by the reader  150  and a document G 2  as the first document in the second document bundle corresponding to the second job is being pulled into the document feeder  110 . In this example, the document G 2  is pulled in to the position of the scan sensor  122  in the first transport path  131 . 
     When the second job commences in this state, the document G 2  may undergo an improper reading process due to a displaced reading position, or may become jammed. Furthermore, because the document G 1  corresponding to the first job is located within the document feeder  110 , the document G 1  may also become jammed. In this case, the user has to place the document bundle corresponding to the first job on the document load section  111  again so that the reading process is performed again. In other words, regardless of the fact that the last document G 1  of the documents in the document bundle corresponding to the first job has been transported, the reading process has to be performed again from the beginning, resulting in a large load on the user. 
     In this exemplary embodiment, the controller  100  performs first control and second control, to be described below, on the document feeder  110 , so as to suppress this problem. 
     First Control 
       FIG. 4  illustrates first control performed on the document feeder  110  by the controller  100 . 
     In this exemplary embodiment, while the document G 1  in the first document bundle corresponding to the first job is being transported, if the document sensor  121  detects that the document G 2  in the second document bundle corresponding to the second job as a subsequent job is loaded, the controller  100  actuates the transport unit until all the documents G 1  in the first document bundle are output. 
     Specifically, as shown in  FIG. 4 , even in a case where the document G 2  corresponding to the second job as a subsequent job is pulled in, the transport roller  113 , the separating mechanism  114 , the registration roller  116 , and the output roller  119  constituting the transport unit are actuated without stopping until the document G 1  corresponding to the first job as a preceding job is output onto the output load section  112 . 
     In fact, since the document G 1  is the last document in the first document bundle, the first document bundle is no longer detected after the document G 1  passes through the document sensor  121 . Specifically, the document sensor  121  detects that a state where there is a document bundle has changed to a state where there is no document bundle, and the detection signal changes from ON to OFF. However, when the user places the second document bundle on the document load section  111 , the document sensor  121  detects the second document bundle. Specifically, the document sensor  121  detects again that there is a document bundle, and the detection signal changes from OFF to ON. In other words, if the document G 1  is being transported when the detection signal changes from ON to OFF and then changes again to ON, the document G 2  is pulled into the document feeder  110 . 
     The determination of whether or not the document G 1  is being transported may be performed by the scan sensor  122  based on the time from when the trailing edge of the document G 1  is detected. In other words, when the document G 1  is read by the reader  150 , the transport speed of the document G 1  is constant. Moreover, the distance from the scan sensor  122  to the output load section  112  is fixed. Thus, the determination may be performed based on a time T 1  from when the trailing edge of the document G 1  is detected. In detail, it may be determined that the document G 1  is being transported if the predetermined time T 1  has not elapsed from when the trailing edge of the document G 1  is detected. In contrast, if the predetermined time T 1  has elapsed, it may be determined that the document G 1  has been output onto the output load section  112 . The trailing edge of the document G 1  may be detected based on whether the detection signal of the scan sensor  122  changes from ON to OFF when the trailing edge of the document G 1  passes therethrough. 
     Then, the controller  100  performs the first control to temporarily stop the transporting of documents in a state where the document G 1  is output onto the output load section  112 . In fact, the document transport unit is stopped at the point where the predetermined time T 1  has elapsed from when the trailing edge of the document G 1  is detected by the scan sensor  122 . Subsequently, the controller  100  performs second control, to be described below, in accordance with the position of the document G 2  when the second job commences. 
     Second Control 
     In this exemplary embodiment, when all the documents G 1  in the first document bundle are output, the controller  100  changes the operation of the transport unit performed on the second job in accordance with the position of the document G 2  pulled into the document feeder  110  from the second document bundle. 
     This will be described below in detail. 
     First, the position of the document G 2  when all the documents G 1  are output will be described. 
       FIG. 5  illustrates the position of the document G 2  when the document G 1  is output onto the output load section  112 . 
     First, when all the documents G 1  are output, it is conceivable that the document G 2  is located at a position (I) shown in  FIG. 5 . The position (I) shown in  FIG. 5  is a positional range along the first transport path  131  from the document load section  111  to the document sensor  121 . At this position, the document G 2  is not pulled into the document feeder  110 . In this case, for example, the document bundle corresponding to the second job is not yet placed on the document load section  111  when all the documents G 1  are output, and the document bundle is placed on the document load section  111  after all the documents G 1  are output. The document G 2  in this case is not pulled into the document feeder  110 , and the document G 2  is located at the position (I) shown in  FIG. 5 . 
     Subsequently, when all the documents G 1  are output, it is conceivable that the document G 2  is located at a position (II) shown in  FIG. 5 . The position (II) shown in  FIG. 5  is a positional range along the first transport path  131  from the document sensor  121  to a point between the document sensor  121  and the scan sensor  122 . Such a case occurs when, for example, the user places the second document bundle on the document load section  111  immediately before all the documents G 1  are output. In this case, the document G 2  is pulled into the document feeder  110  but is not pulled therein by a large amount. 
     Furthermore, when all the documents G 1  are output, it is conceivable that the document G 2  is located at a position (III) shown in  FIG. 5 . The position (III) shown in  FIG. 5  is a positional range along the first transport path  131  from the terminal end of the position (II) to the scan sensor  122 . Such a case occurs when, for example, the user places the second document bundle on the document load section  111  shortly after the document G 1  is pulled into the document feeder  110 . In this case, the document G 2  is pulled into the document feeder  110  by a large amount. 
     When all the documents G 1  are output, it is conceivable that the document G 2  is located at a position (IV) shown in  FIG. 5 . The position (IV) shown in  FIG. 5  is a positional range along the first transport path  131  from the scan sensor  122  to the output load section  112 . Such a case occurs when, for example, the user places the second document bundle on the document load section  111  immediately after the document G 1  is pulled into the document feeder  110 . In this case, the document G 2  is pulled into the document feeder  110  by a large amount and has passed the position of the scan sensor  122 . 
     The position (II) in  FIG. 5  is where the document G 2  pulled into the document feeder  110  and transported toward the reader  150  may be accelerated to a predetermined speed by the transport unit before reaching the reading position of the reader  150 . In this case, the reader  150  is capable of performing the reading process. In other words, the position (II) shown in  FIG. 5  is where the second job is executable. In contrast, the position (III) shown in  FIG. 5  is where the document G 2  pulled into the document feeder  110  is not capable of being increased to the predetermined speed by the transport unit before reaching the reading position of the reader  150 . In other words, the position (III) shown in  FIG. 5  is where it is not possible to continue with the second job since the reading process is not properly executable. Likewise, the position (IV) shown in  FIG. 5  is also where it is not possible to continue with the second job since the reading process is not properly executable by the reader  150 . 
     The determination of which of the positions (I) to (IV) the document G 2  is located at may be performed by using the document sensor  121  and the scan sensor  122 . 
     Specifically, if the document sensor  121  is not detecting a document bundle when the document G 1  is output, it may be determined that the document G 2  is located at the position (I). If the document sensor  121  is detecting a document bundle, it may be determined that the document G 2  is located at any of the positions (II) to (IV). 
     In this case, if the scan sensor  122  is detecting the document G 2 , it may be determined that the document G 2  is located at the position (IV). 
     If the scan sensor  122  is not detecting the document G 2 , the document G 2  is located at either the position (II) or the position (III). Then, when the scan sensor  122  detects the document G 2  within a predetermined time T 2  after the second job commences, it may be determined that the document G 2  is located at the position (III). When the scan sensor  122  detects the document G 2  beyond the predetermined time T 2 , it may be determined that the document G 2  is located at the position (II). In other words, because the position (III) is closer to the scan sensor  122  and the position (II) is farther from the scan sensor  122 , there is a difference in the time it takes for the document G 2  to reach the scan sensor  122 . The controller  100  utilizes this time difference to determine whether the document G 2  is located at the position (II) or the position (III). 
       FIGS. 6A and 6B  illustrate the second control performed on the document feeder  110  by the controller  100 . 
       FIG. 6A  illustrates the contents of control performed in the related art when the document G 2  is located at the positions (I) to (IV).  FIG. 6B  illustrates the contents of the second control performed in this exemplary embodiment. 
     As shown in  FIG. 6A , in the related art, pre-feeding is performed at the positions (I) to (III). Pre-feeding involves preliminarily pulling a document into the document feeder  110 . In actuality, the document is pulled in to a position immediately before the boundary between the position (II) and the position (III) along the first transport path  131 . Accordingly, the transport distance of the document is reduced and the read rate is improved, as compared with a case where the document is pulled in from the document load section  111  without undergoing pre-feeding. After the pre-feeding, the reader  150  reads the document, and the transport unit subsequently has to transport the document to output the document onto the output load section  112 . This may be referred to as “feeding” hereinafter. 
     As shown in  FIG. 6A , if the document G 2  is located at the position (I), the document G 2  undergoes pre-feeding so that the position thereof after the pre-feeding becomes the position (II). In this case, when the document G 1  is output, the document G 2  is sometimes not pulled into the document feeder  110 , so that the reading process is properly completed. In other words, the second job is properly executable. 
     If the document G 2  is located at the position (II), the document G 2  undergoes pre-feeding so that the position thereof after the pre-feeding becomes the position (III) or (IV). In this case, if the pre-fed document G 2  is located at the position (III), the reading position is displaced such that the reading process is not properly performed. If the pre-fed document G 2  is located at the position (IV), the document G 2  is detected by the scan sensor  122  and is determined as being jammed when the second job commences. 
     Furthermore, if the document G 2  is located at the position (III), the document G 2  undergoes pre-feeding so that the position thereof after the pre-feeding becomes the position (IV). In this case, the document G 2  is detected by the scan sensor  122  and is determined as being jammed when the second job commences. 
     If the document G 2  is located at the position (IV), the document G 2  is detected by the scan sensor  122  and is determined as being jammed when the first job ends. In this case, since the document jam is confirmed when the first job ends, the pre-feeding for the second job is not performed. 
     In contrast, in this exemplary embodiment, the control shown in  FIG. 6B  is performed. In this exemplary embodiment, depending on which of the positions (I) to (IV) the document G 2  is located at, the controller  100  performs the second control to be described below in addition to the first control described with reference to  FIG. 4 . 
       FIGS. 7A and 7B  and  FIGS. 8A and 8B , together with  FIG. 6B , illustrate the second control performed in this exemplary embodiment. 
     In a case where the document G 2  is located at the position (I) (i.e., the case in  FIG. 7A ), the document G 2  undergoes pre-feeding so that the position thereof after the pre-feeding becomes the position immediately in front of the boundary between the position (II) and the position (III). In this case, the pre-feeding is performed over a fixed length. In other words, as a result of the pre-feeding, the document G 2  moves by a predetermined distance from the position where the document G 2  is placed to the position immediately in front of the boundary between the position (II) and the position (III). In this case, the document G 2  is sometimes not pulled into the document feeder  110 , so that the reading process is properly completed. 
     In a case where the document G 2  is located at the position (II) (i.e., the case in  FIG. 7B ), the document G 2  undergoes pre-feeding so that the position thereof after the pre-feeding becomes the position immediately in front of the boundary between the position (II) and the position (III). In this case, the pre-feeding is performed over a variable length. In other words, in accordance with the pre-feeding, the document G 2  moves by the distance from the pull-in position to the position immediately in front of the boundary between the position (II) and the position (III). In this case, the distance by which the document G 2  moves changes in accordance with the pull-in position of the document G 2 . In other words, this is different from the case in  FIG. 6A . The pre-feeding distance by which the pre-feeding is performed is shorter than the fixed length mentioned above. As mentioned above, at the position (II), the document G 2  may be accelerated to a predetermined speed by the transport unit before reaching the reading position of the reader  150 , and may be read by the reader  150 . In other words, when a document pulled into the document feeder  110  is located where the document may reach the predetermined speed before being transported to the reader  150 , the controller  100  continues with the second job. If the document G 2  is located at the position (II), the controller  100  performs pre-feeding over a variable length and controls the transport unit to transport the document. Accordingly, unlike in the related art, the second job is properly executable. 
     In a case where the document G 2  is located at the position (III) (i.e., the case in  FIG. 8A ), pre-feeding is not performed. In other words, this is different from the case in  FIG. 6A . In this case, since the document G 2  does not undergo pre-feeding, the position thereof remains unchanged at the position (III). The document G 2  in this case is determined as being jammed when the first job ends. In other words, when a document is located where the document is not able to reach a predetermined speed before being transported to the reader  150 , the controller  100  discontinues the second job. Then, the controller  100  issues a warning indicating that there is a document jam when the first job ends. In detail, a notification is provided to the user by displaying a message on the operation panel  15  indicating that a document jam has occurred. Such a notification indicating the occurrence of a document jam may alternatively be provided to the user by outputting a warning sound or outputting an audio guidance message. 
     In a case where the document G 2  is located at the position (IV) (i.e., the case in  FIG. 8B ), the document G 2  is detected by the scan sensor  122  and is determined as being jammed when the first job ends. In other words, when a document is pulled in to a position where it is detected by the scan sensor  122 , the controller  100  discontinues the second job. Then, the controller  100  issues a warning indicating that there is a document jam when the first job ends. In this case, the document G 2  is detected by the scan sensor  122  at the point when the first job ends. 
     Accordingly, in the second control, if the document sensor  121  detects that the second document bundle corresponding to the second job as a subsequent job is loaded while the document G 1  in the first document bundle corresponding to the first job is being transported, the pre-feeding operation for preliminarily pulling the document G 2  into the reader  150  is changed in accordance with the position at which the document G 2  in the second document bundle is pulled into the reader  150 . 
     In detail, if the document G 2  pulled into the reader  150  is located where the document G 2  is able to reach the predetermined speed (i.e., if the document G 2  is located at the position (II)) when all the documents G 1  in the first document bundle are output in accordance with the first control, the controller  100  performs pre-feeding and continues with the second job. In this case, the controller  100  performs the pre-feeding over a shorter distance than in the normal operation (i.e., when the document G 2  is located at the position (I)). As a result, the reading process may be properly performed for the second job. 
     If the document G 2  is located where the document G 2  is not able to reach the predetermined speed when all the documents G 1  in the first document bundle are output (i.e., if the document G 2  is located at the position (III)), the controller  100  does not perform pre-feeding and discontinues the second job. 
     Furthermore, if the document G 2  is pulled in to a position where it is detected by the scan sensor  122  when all the documents G 1  in the first document bundle are output (i.e., if the document G 2  is located at the position (IV)), the controller  100  does not perform pre-feeding and discontinues the second job. 
     The matter described above may be regarded that the controller  100  changes the pre-feeding distance in accordance with the position of the document G 2  pulled into the reader  150  when all the documents G 1  in the first document bundle are output in accordance with the first control. 
     In detail, the controller  100  performs pre-feeding over a normal distance when the document G 2  in the second document bundle is not pulled into the reader  150  (i.e., when the document G 2  is located at the position (I)), and reduces the pre-feeding distance in accordance with the pull-in distance when the document G 2  in the second document bundle is pulled into the reader  150  (i.e., when the document G 2  is located at the position (II), (III), or (IV)). In this case, if the pull-in distance is greater than or equal to a predetermined distance (i.e., if the document G 2  is located at the position (III) or (IV)), the controller  100  sets the pre-feeding distance to zero. In other words, pre-feeding is not performed. 
     Functional Configuration of Controller  100   
     Next, the functional configuration of the controller  100  according to this exemplary embodiment will be described. 
       FIG. 9  is a block diagram illustrating a functional configuration example of the controller  100  according to this exemplary embodiment. 
     In  FIG. 9 , some of the various functions of the controller  100  that are related to this exemplary embodiment are selectively illustrated. 
     As shown in  FIG. 9 , the controller  100  includes a detection-signal acquiring unit  101  that acquires a detection signal, a time measuring unit  102  that performs a time measuring process, a transport controller  103  that controls a transport unit H, and a storage unit  104  that stores predetermined contents. 
     The detection-signal acquiring unit  101  acquires detection signals acquired by the document sensor  121  and the scan sensor  122 . Based on the detection signal from the document sensor  121 , the controller  100  may ascertain whether or not there is a document on the document load section  111 . Based on the detection signal from the scan sensor  122 , the controller  100  may ascertain the position of a document passing through the scan sensor  122 . 
     The time measuring unit  102  performs a time measuring process based on the detection signals acquired from the document sensor  121  and the scan sensor  122 . Based on the time measured by the time measuring unit  102 , the controller  100  may ascertain which of the positions (I) to (IV) the document G 2  is located at along the first transport path  131 , as mentioned above. 
     The transport controller  103  controls the power source, such as a driving motor, for actuating the transport roller  113 , the separating mechanism  114 , the registration roller  116 , and the output roller  119  constituting the transport unit H. Accordingly, the transport controller  103  changes the operation modes of these components to perform the first control and the second control described above. 
     The storage unit  104  stores, for example, the time used for determining whether the document G 1  has been output or the time used for determining which of the positions (I) to (IV) the document G 2  is located at along the first transport path  131 . In other words, for example, the storage unit  104  stores the time T 1  and the time T 2  described above. 
     Operation of Document Feeder  110   
     Next, the operation of the document feeder  110  including the operation of the controller  100  will be described. 
       FIG. 10  is a flowchart illustrating the operation of the document feeder  110 . 
     First, in step S 101 , the transport controller  103  pre-feeds a document. In this case, the transport controller  103  changes the pre-feeding distance of the document G 2  in accordance with the pull-in amount of the document. This corresponds to a case where a document is located at the position (I) or (II) described above and where pre-feeding is performed. 
     Then, the transport controller  103  commences feeding of the document G 2  in step S 102 , and the reader  150  performs a reading (scanning) process in step S 103 . 
     In step S 104 , the detection-signal acquiring unit  101  determines whether or not a document is detected by the document sensor  121 . In other words, the detection-signal acquiring unit  101  determines whether or not there is any document still remaining on the document load section  111 . 
     If the result indicates that a document is detected (Yes in step S 104 ), the process returns to step S 101  to transport the subsequent document. 
     In contrast, if no document is detected (No in step S 104 ), it is clear that the document corresponding to this job is the last document. Therefore, the transport controller  103  determines to end this job in step S 105 . 
     In step S 106 , the transport controller  103  resets the pull-in amount of the subsequent document to zero. 
     Then, in step S 107 , the transport controller  103  determines whether or not the last document corresponding to this job has been output onto the output load section  112 . The determination of whether or not the document has been output onto the output load section  112  may be performed based on the time from when the trailing edge of the document is detected, as described above. Specifically, if the predetermined time T 1  has not elapsed from when the trailing edge of the document is detected, it may be determined that the document is being transported. In contrast, if the predetermined time T 1  has elapsed, it may be determined that the document has been output onto the output load section  112 . This time is measured by the time measuring unit  102  and is acquired by the transport controller  103 . 
     If the result indicates that the last document corresponding to this job has not been output onto the output load section  112  (No in step S 107 ), the detection-signal acquiring unit  101  determines whether or not a document is detected by the document sensor  121 . In other words, in step S 108 , the detection-signal acquiring unit  101  determines whether or not a new document bundle has been placed on the document load section  111 . 
     If a document is not detected and a new document bundle has not been placed (No in step S 108 ), the process returns to step S 107 . 
     In contrast, if a document is detected and a new document bundle has been placed (Yes in step S 108 ), the time measuring unit  102  starts to measure the pull-in amount of a subsequent document in step S 109 . The process then returns to step S 107 . 
     In contrast, if the last document has been output onto the output load section  112  (Yes in step S 107 ), the time measuring unit  102  ends the measurement of the pull-in amount of the subsequent document in step S 110 . 
     Then, the transport controller  103  determines whether or not the measured pull-in amount is greater than or equal to a predetermined threshold value in step S 111 . 
     If the result indicates that the measured pull-in amount is greater than or equal to the predetermined threshold value (Yes in step S 111 ), the transport controller  103  determines that a document jam has occurred and issues a warning in step S 112 . This corresponds to a case where a document is located at the position (III) or (IV) described above. 
     In contrast, if the measured pull-in amount is not greater than or equal to the predetermined threshold value (No in step S 111 ), the transport controller  103  performs the above-described control from step S 101  and onward on a new document bundle. This corresponds to a case where a document is located at the position (I) or (II) described above. 
     As described above in detail, in this exemplary embodiment, the first control involves actuating the transport unit until all documents in the first document bundle corresponding to the first job are output if the document sensor  121  detects that the document G 2  in the second document bundle corresponding to the second job as a subsequent job is loaded while the document G 1  in the first document bundle is being transported. Accordingly, even if the document G 2  in the document bundle corresponding to the second job as a subsequent job is pulled into the document feeder  110 , at least the document G 1  in the document bundle corresponding to the first job as a preceding job may be properly read. As a result, at least the reading process for the first job may be properly completed. Therefore, at least the document corresponding to the first job as a preceding job does not have to be re-read, thereby reducing the load on the user. 
     Furthermore, in the second control according to this exemplary embodiment, the controller  100  changes the operation of the transport unit performed on the second job in accordance with the position of the document G 2  pulled into the document feeder  110  from the second document bundle when all the documents G 1  in the first document bundle are output. Specifically, the operation of the transport unit is changed depending on which of the positions (I) to (IV) the document G 2  is located at. In this case, if the document G 2  is located at the position (III) or (IV), it is determined that a document jam has occurred. If the document G 2  is located at the position (II), the pre-feeding distance may be changed so that displacement of the reading position for the document G 2  may be suppressed. As a result, the reading process may be properly performed not only for the first job but also for the second job. 
     The foregoing description of the exemplary embodiment of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.