Abstract:
A sheet conveying device includes: a conveying unit; a nonvolatile memory; and a controller. The conveying unit is configured to convey a sheet along a conveying path. The controller is configured to control the conveying unit to convey the sheet, store position data in the nonvolatile memory during conveyance of the sheet, determine whether or not the sheet conveying device is started, and drive the conveying unit for an amount determined by the position data if the sheet conveying device is started. The conveying path is divided into a plurality of segments. The position data identifies a segment in which the sheet stays. The more downstream the segment identified by the position data is in the conveying path, the smaller the amount determined by the position data is.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2012-191593 filed Aug. 31, 2012. The entire content of the priority applications is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a sheet conveying device and an image processing device, and particularly to a technique used by the sheet conveying device and the image processing device to convey sheets along its conveying path. 
     BACKGROUND 
     One method used in conventional image-processing devices to ensure that a sheet present on the conveying path is properly discharged in such situations is to always rotate the conveying rollers a fixed amount when the operating state of the device stored in the nonvolatile memory indicates that the device was in the process of executing a reading operation. However, a device having this construction does not know the last position of the sheet before the power was interrupted. Therefore, the device must rotate the conveying rollers the maximum distance required to discharge a sheet from the conveying path when the sheet is positioned near the entrance to the conveying path in order to reliably discharge a sheet positioned anywhere along the conveying path. Consequently, when the sheet is positioned closer to the exit of the conveying path, for example, the conveying rollers will continue to be rotated unnecessarily after the sheet has been discharged. 
     SUMMARY 
     In view of the foregoing, it is an object of the present invention to provide a technique for minimizing wasteful driving by the conveying unit of a sheet conveying device and an image processing device when discharging a sheet from the conveying path at startup as an improvement over devices configured to drive the conveying unit the maximum distance needed to discharge a sheet positioned anywhere along the conveying path. 
     In order to attain the above and other objects, the present invention provides a sheet conveying device comprising: a conveying unit; a nonvolatile memory; and a controller. The conveying unit is configured to convey a sheet along a conveying path. The controller is configured to: control the conveying unit to convey the sheet; store position data in the nonvolatile memory during conveyance of the sheet; determine whether or not the sheet conveying device is started; and drive the conveying unit for an amount determined by the position data if the sheet conveying device is started. The position data is related to a conveyed position of the sheet along the conveying path. The conveying path is divided into a plurality of segments. The position data identifies a segment in which the sheet stays. The more downstream the segment identified by the position data is in the conveying path, the smaller the amount determined by the position data is. 
     According to another aspect, the present invention provides a sheet conveying device comprising: a conveying unit; a nonvolatile memory; and a controller. The conveying unit is configured to convey a sheet along a conveying path. The controller is configured to: control the conveying unit to convey the sheet; store position data in the nonvolatile memory during conveyance of the sheet; and drive the conveying unit to convey the sheet a conveying distance based on the position data when the conveyance of the sheet is resumed. The position data is related to a conveyed position of the sheet along the conveying path. 
     According to still another aspect, the present invention provides an image processing device comprising: a conveying unit; an image processing unit; a nonvolatile memory; and a controller. The conveying unit is configured to convey a sheet along a conveying path. The image processing unit is configured to perform image processing for the sheet at a process position. The controller is configured to: control both the conveying unit to convey the sheet and the image processing unit to perform the image processing for the sheet that is conveyed by the conveying unit; store position data in the nonvolatile memory during conveyance of the sheet; and drive the conveying unit to convey the sheet a conveying distance determined based on the position data when the conveyance of the sheet is resumed. The position data is indicative of where the sheet has been conveyed to in the conveying path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating an appearance of a multifunction peripheral according to one embodiment; 
         FIG. 2  is a cross-sectional view illustrating a configuration of a portion of a cover and a device body; 
         FIG. 3  is a block diagram showing an electrical structure of the multifunction peripheral; 
         FIG. 4  is a flowchart illustrating steps in a read control process; 
         FIG. 5  is an explanatory diagram showing a sheet-conveying process in a conveying path; and 
         FIG. 6  is a flowchart illustrating steps in a startup process. 
     
    
    
     DETAILED DESCRIPTION 
     A sheet-conveying device and an image-processing device according to embodiment of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     Next, a preferred embodiment of the present invention will be described with reference to  FIGS. 1 through 6 . In the preferred embodiment, a multifunction peripheral  1  serves as the image-processing device of the present invention that includes the sheet-conveying device of the present invention. The multifunction peripheral  1  according to the preferred embodiment can implement a scan mode, as well as a copy mode and a print mode, for example. In the following description, the lower right side of the multifunction peripheral  1  in  FIG. 1  will be referred to as the front side (“F” in the drawings), the lower left side as the left side (“L” in the drawings), and the top as the upper side (“U” in the drawings). 
     Mechanical Structure of the Multifunction Peripheral 
     As shown in  FIG. 1 , the multifunction peripheral  1  includes a cover  2 , and a device body  3 . Support members (not shown) are provided on the top surface of the device body  3  at the rear edge thereof. Through the support members, the rear edge of the cover  2  is connected to the device body  3  so as to be capable of pivotally move about an axis oriented in the left-right direction. This configuration allows the cover  2  to be displaced between a closed position for covering the top surface of the device body  3 , and an open position (shown in  FIG. 1 ) for revealing the top surface of the device body  3 . 
     In  FIG. 2 , the portion of the multifunction peripheral  1  above the dotted line D represents the cover  2 . The cover  2  includes a feed tray  11 , a front sensor  12 , a discharge tray  13 , an automatic-document feeder (ADF)  14 , an ADF pressing plate  15 , and a flatbed pressing plate  16 . 
     The feed tray  11  supports a plurality of sheets M of originals (see  FIG. 5 ) to be scanned. The sheets M may be sheets of paper, plastic transparencies, and the like. The front sensor  12  is disposed at a detection position R 0  on the downstream side (left side in  FIG. 2 ) of the feed tray  11  for detecting the presence of sheets M in the feed tray  11 , and transmits these detection results to a control unit  27  described later. The discharge tray  13  is disposed above the feed tray  11  and receives sheets M that are discharged from the cover  2  after an image-reading operation. A conveying path R is formed inside the cover  2 . The conveying path R is U-shaped and serves to convey the sheets M from the feed tray  11  to the discharge tray  13  while inverting and reversing directions of the conveyed sheets M. A discharge position R 2  is the furthest downstream point along the conveying path R. 
     When a plurality of sheets M is loaded in the feed tray  11 , the ADF  14  conveys the sheets M continuously along the conveying path R one sheet at a time and sequentially discharges the sheets onto the discharge tray  13 . The ADF  14  includes a feeding roller  14 A, a separating roller  14 B, a separating pad  14 C, a plurality of conveying rollers  14 D, a plurality of follow rollers  14 E contacting respective conveying rollers  14 D with pressure so as to follow the rotation of the conveying rollers  14 D, and a plurality of guide members  14 F for guiding the conveyed sheets M. 
     The feeding roller  14 A, separating roller  14 B, and conveying rollers  14 D are driven to rotate by a stepping motor  14 G described later. If a plurality of sheets M is loaded in the feed tray  11 , the feeding roller  14 A conveys the sheets M toward the conveying path R, and the separating roller  14 B and separating pad  14 C separate and convey the sheets M one sheet at a time onto the conveying path R. The conveying rollers  14 D convey the individually separated sheets M along the conveying path R and discharge the same onto the discharge tray  13 . The ADF  14  in the preferred embodiment has what is referred to as a one-way clutch and performs a continuous conveying operation from the moment a conveyance start command is received from a control unit  27  described later until a conveyance halt command is received. When a plurality of sheets M is loaded in the feed tray  11 , the ADF  14  executes this continuous conveying operation to separate and convey the sheets M one sheet at a time along the conveying path R, with a gap formed between consecutively fed sheets, and to sequentially discharge the sheets onto the discharge tray  13 . 
     The ADF pressing plate  15  is an opposing member that is provided on the bottom surface of the cover  2  via a spring  17 . The spring  17  urges the ADF pressing plate  15  toward an ADF glass  21 A described later when the cover  2  is in the closed position. Hereinafter, the point at which the ADF pressing plate  15  opposes the ADF glass  21 A will be called a read position R 1 . The flatbed pressing plate  16  is also provided on the bottom surface of the cover  2 . The flatbed pressing plate  16  covers substantially an entire flatbed glass  21 B described later when the cover  2  is in its closed state. 
     As shown in  FIG. 1 , the device body  3  has an overall box-like shape that is elongated in the left-right direction. A platen glass  21  is disposed in the top surface of the device body  3 . A partitioning member  22  is provided on the top surface of the platen glass  21  at a position toward the left side thereof. The partitioning member  22  divides the platen glass  21  into two parts. Hereinafter, the left part of the platen glass  21  will be called an ADF glass  21 A, and the right part will be called a flatbed glass  21 B. A white reference plate  22 A is also provided on the bottom surface of the partitioning member  22  (see  FIG. 2 ). The white reference plate  22 A is a white-colored member with a substantially uniform reflectance. Portions of the bottom surface of the partitioning member  22  adjacent to the white reference plate  22 A are black. 
     The device body  3  is also provided with a power switch  23  (see  FIG. 3 ), an operating unit  24 , a display unit  25 , and the like. The user operates the power switch  23  to turn the power to the multifunction peripheral  1  on and off. When the power is on, electricity is supplied from an external power supply, for example, to various components in the cover  2  and device body  3 . 
     As shown in  FIG. 2 , an image-reading unit  26  is provided inside the device body  3 . The image-reading unit  26  is provided with a reading device  26 A, and a device-moving mechanism  26 B (see  FIG. 3 ). The reading device  26 A has a contact image sensor (CIS). Specifically, the reading device  26 A includes a light source configured of red, green, and blue light-emitting elements (such as light-emitting diodes), for example; an image sensor having a plurality of light-receiving elements arranged linearly in the front-rear direction (a main scanning direction); an optical system for focusing light reflected off a sheet onto the light-receiving elements of the image sensor; and a carriage for supporting these components. Note that the reading device  26 A may be configured of a charge-coupled drive (CCD) image sensor, for example, and is not limited to a CIS. 
     The device-moving mechanism  26 B is configured to move the reading device  26 A in a left-right direction (a sub-scanning direction) beneath the ADF glass  21 A, partitioning member  22 , and flatbed glass  21 B. Hereinafter, the position at which the reading device  26 A opposes the ADF glass  21 A will be called an ADF position X 1 , the position at which the reading device  26 A opposes the partitioning member  22  will be called a home position X 0 , and the position at which the reading device  26 A opposes the flatbed glass  21 B will be called a flatbed position X 2 . The device body  3  also includes a control unit  27 , a nonvolatile memory  28 , and a printing unit  29  described later (see  FIG. 3 ). 
     Electrical Structure of the Multifunction Peripheral 
     As shown in  FIG. 3 , the multifunction peripheral  1  includes the power switch  23  and control unit  27 . The control unit  27  is connected to and capable of performing data communications with the front sensor  12 , ADF  14 , image-reading unit  26 , operating unit  24 , display unit  25 , nonvolatile memory  28 , and printing unit  29 . 
     The control unit  27  has a central processing unit (CPU)  27 A, a ROM  27 B, a RAM  27 C, an image-processing unit  27 D, and a timing signal generation unit  27 E. The ROM  27 B stores programs for implementing a read control process and a startup process described later, and programs for executing various other operations on the multifunction peripheral  1 . The CPU  27 A executes the programs read from the ROM  27 B to control various components of the multifunction peripheral  1 . The programs described above may also be stored on another type of nonvolatile memory, such as a CD-ROM, hard disk drive, or flash memory (registered trademark), instead of the ROM  27 B and RAM  27 C. 
     The image-processing unit  27 D is a hardware circuit dedicated to image processing and executes shading compensation, gamma correction, and other image processes on scan data that has undergone analog-to-digital conversion. The timing signal generation unit  27 E generates a clock signal and outputs this signal to a motor drive circuit  14 H described next. 
     The ADF  14  includes a stepping motor  14 G and the motor drive circuit  14 H for driving the rollers  14 A,  14 B, and  14 D mentioned above to rotate. The stepping motor  14 G has a construction well known in the art that includes a rotor (not shown) fixed to a rotational shaft, and a stator (not shown) mounted around the outside of the rotor. The motor drive circuit  14 H functions to drive the stepping motor  14 G. By applying an electric current in sequential pulses corresponding to an excitation phase to a coil wound about the stator, the motor drive circuit  14 H can accurately rotate the rotor in units of fixed angles. The excitation phase serves to indicate how the motor drive circuit  14 H is to supply electric current to the coil of the stepping motor  14 G. Thus, the rotated position of the stepping motor  14 G (the rotor position) is determined by this excitation phase. 
     The timing signal generation unit  27 E of the control unit  27  inputs a clock signal into the motor drive circuit  14 H. The motor drive circuit  14 H updates the signal indicating the excitation phase for each pulse of the clock signal and supplies current to the coil based on this signal for rotating the stepping motor  14 G one step (prescribed angle) at a time. 
     The image-reading unit  26  can execute an ADF reading operation and a flatbed reading operation. In the ADF reading operation, the reading device  26 A remains stationary at the ADF position X 1  while performing an operation to read an image from a sheet M conveyed by the ADF  14 . In the flatbed reading operation, the image-reading unit  26  performs an operation to read an image from a sheet M placed stationary on the flatbed glass  21 B while the device-moving mechanism  26 B moves the reading device  26 A along the flatbed glass  21 B. The RAM  27 C stores scan data for an image read by the reading device  26 A. More specifically, the image-reading unit  26  produces scan data for rows of pixels based on the scanned image; an A/D conversion unit (not shown) converts this analog data to a digital form; and the image-reading unit  26  stores the resulting data in the RAM  27 C. The image-reading unit  26  serves as a position data producing unit that generates position data described later. 
     The operating unit  24  includes a plurality of buttons that enable the user to perform various input operations, such as an operation for specifying one of the functional modes described above. The display unit  25  has a liquid crystal display, LED lamps, and the like for displaying various option screens and the operating status of the device, for example. The nonvolatile memory  28  is configured of EEPROM, for example, and is used for storing position data and reference data described later. The printing unit  29  prints an image based on image data, such as the scan data, on a printing sheet (not shown) according to an electrophotographic or inkjet method, for example. 
     Read Control Process 
     If the user performs an operation on the operating unit  24  for specifying implementation of the scan mode, for example, the control unit  27  executes the read control process shown in  FIG. 4  only after determining that a sheet M of originals is present in the feed tray  11  based on detection results received from the front sensor  12 . In the read control process, the control unit  27  begins conveying a sheet M from the feed tray  11 , while executing the ADF reading operation as the sheet M is conveyed. The control unit  27  also performs a process to continuously store in the nonvolatile memory  28  position data related to the conveyed position of the sheet M along the conveying path R. 
     Prior to executing the read control process, the CPU  27 A of the control unit  27  controls the device-moving mechanism  26 B to move the reading device  26 A to the home position X 0 . Specifically, the CPU  27 A begins moving the reading device  26 A and determines that the reading device  26 A has arrived at the home position X 0  when the image read by the reading device  26 A changes from a white image representing the white reference plate  22 A to a black image representing a part of the partitioning member  22  adjacent to the white reference plate  22 A. Upon determining that the reading device  26 A has arrived at the home position X 0 , the control unit  27  halts the device-moving mechanism  26 B. 
     In S 1  of  FIG. 4 , the CPU  27 A of the control unit  27  controls the device-moving mechanism  26 B to move the reading device  26 A from the home position X 0  to the ADF position X 1 . In S 2  the CPU  27 A controls the reading device  26 A to read an image from the opposing surface of the ADF pressing plate  15  and acquires the resulting scan data. Here, it is preferable that the opposing surface of the ADF pressing plate  15  has a color such as gray that is distinguishable from the color of the sheets of originals or has an image that is distinguishable from images on the sheets. In S 3  the CPU  27 A stores the scan data acquired in S 2  in the nonvolatile memory  28  as reference data. 
     After the reference data has been stored in the nonvolatile memory  28 , in S 4  the CPU  27 A begins driving the ADF  14 , whereby a sheet M is conveyed onto the conveying path R, as illustrated in  FIG. 5 . At this time, the leading edge of the sheet M is positioned between the detection position R 0  and read position R 1 , as is represented by sheet M 1  in  FIG. 5 . Hence, in S 5  the CPU  27 A stores an upstream position flag F 1  in the nonvolatile memory  28  as the current position data, where the upstream position flag F 1  indicates that the sheet M is in a position upstream of the read position R 1 . 
     After the upstream position flag F 1  is stored in the nonvolatile memory  28 , in S 6  at least one of the CPU  27 A and image-processing unit  27 D initiates a reading operation for detecting the sheet (hereinafter referred to as a sheet detection reading operation). The sheet detection reading operation is a process for detecting whether the sheet M is present at the read position R 1  based on scan data received from the reading device  26 A. That is, if a sheet M is not present at the read position R 1 , then the reading device  26 A will read the opposing surface of the ADF pressing plate  15 . In this case, the scan data received from the reading device  26 A will match the reference data. However, if a sheet M is present at the read position R 1 , the reading device  26 A reads the sheet M rather the opposing surface of the ADF pressing plate  15  and, hence, the scan data received from the reading device  26 A will not match the reference data. 
     In S 7  the control unit  27  sequentially acquires scan data from the reading device  26 A and determines whether this scan data matches the reference data. In this case, the control unit  27  determines that the scan data matches the reference data when one of the image color, pixel value, and color difference in an image based on the scan data matches that in the image based on the reference data, for example. Further, the term “match” in this case is not limited to cases in which the images based on both the scan data and reference data match each other completely, but also includes cases in which the images essentially match, i.e., are within a prescribed range of each other. 
     When the determination results in S 7  change from indicating that the scan data matches the reference data to indicating the scan data does not match the reference data (S 7 : NO), then the leading edge of the sheet M has arrived at the read position R 1 . Accordingly, in S 8  the control unit  27  stores a read position flag F 2  in the nonvolatile memory  28  as the current position data, where the read position flag F 2  indicates that the sheet M is present at the read position R 1 , as is represented by sheet M 2  in  FIG. 5 . 
     In S 9  at least one of the CPU  27 A and image-processing unit  27 D begins a sheet image-reading operation triggered by the timing at which the scan data no longer matches the reference data. The sheet image-reading operation is an operation for reading an image from the sheet M based on scan data received from the reading device  26 A and storing the scan data for the image in the RAM  27 C, for example. Subsequently, in S 10  the control unit  27  determines based on the sheet detection reading operation whether the determination results have changed from indicating the scan data does not match the reference data to indicating the scan data matches the reference data. When the determination results change in this way (S 10 : YES), in S 11  the control unit  27  ends the sheet image-reading operation. In S 12  the CPU  27 A determines whether a sheet M is present in the feed tray  11  based on detection results received from the front sensor  12 . 
     If the control unit  27  determines that a sheet M is present in the feed tray  11  (S 12 : YES), the control unit  27  returns to S 5  and stores the upstream position flag F 1  in the nonvolatile memory  28  as the current position data indicating that the sheet M is positioned between the detection position R 0  and read position R 1 . However, if the control unit  27  determines that a sheet M is not present in the feed tray  11  (S 12 : NO), then the sheet image-reading operation has been performed on all sheets M of originals that were loaded in the feed tray  11 . Accordingly, in S 13  the control unit  27  stores a downstream position flag F 3  in the nonvolatile memory  28  as the current position data, whereby the downstream position flag F 3  indicates that the sheet M is positioned downstream of the read position R 1 , as is represented by sheet M 3  in  FIG. 5 . 
     Triggered by the determination in S 10  that the scan data matches the reference data, in S 14  the CPU  27 A begins driving the ADF  14  to rotate exactly a discharge distance. Once the ADF  14  has been driven the discharge distance (S 14 : YES), in S 15  the CPU  27 A halts the ADF  14  and in S 16  the control unit  27  ends the sheet detection reading operation. The discharge distance is at least equivalent to the distance from the read position R 1  to the discharge position R 2 . The CPU  27 A determines that the ADF  14  has been driven to rotate the discharge distance by counting the elapsed time from the determination timing in S 10  or the number of steps by which the motor drive circuit  1411  drives the stepping motor  14 G from the same point, for example. When the count value reaches a value corresponding to the discharge distance, the CPU  27 A halts the ADF  14 . 
     In S 17  the CPU  27 A stores a discharge position flag F 4  in the nonvolatile memory  28  as the current position data, whereby the discharge position flag F 4  indicates that the sheet M is present at the discharge position R 2 , as is represented by sheet M 4  in  FIG. 5 . Note that the control unit  27  may execute the process in S 17  prior to the processes in S 15  or S 16 . In S 18  the CPU  27 A controls the device-moving mechanism  26 B to return the reading device  26 A from the ADF position X 1  to the home position X 0 , and the control unit  27  ends the current read control process. 
     Startup Process 
     The control unit  27  executes the startup process shown in  FIG. 6  when the user switches the power switch  23  off and then back on or when the user restarts the multifunction peripheral  1  while the power switch  23  is in an on state, for example. When the control unit  27  determines that the multifunction peripheral  1  has been started, the control unit  27  performs the startup process for driving the ADF  14  a conveying distance sufficient for discharging the current sheet M in the conveying path R based on the position data. In the startup process, the more downstream the conveyed position of the sheet M is in the conveying path, the shorter the conveying distance of the driving of the ADF  14  is. Here, the control unit  27  determines that the multifunction peripheral  1  has been started up when electricity begins to be supplied to the CPU  27 A, for example. 
     In S 21  of  FIG. 6 , the CPU  27 A reads the current position data from the nonvolatile memory  28 . In steps S 22 , S 23 , and S 24 , the control unit  27  determines whether the current position data corresponds to one of the flags F 1  through F 4  described earlier. In this way, the control unit  27  can identify the current position of the sheet M on the conveying path R. 
     (1) When the Current Position Data is the Upstream Position Flag F 1   
     The current position data is the upstream position flag F 1  when the user switches off the power switch  23 , for example, while the sheet M is positioned upstream of the read position R 1 , as represented by the sheet M 1  in  FIG. 5 . When the control unit  27  determines that the current position data is the upstream position flag F 1  (S 22 : YES), in S 25  the CPU  27 A controls the device-moving mechanism  26 B to move the reading device  26 A temporarily to the home position X 0  and then back to the ADF position X 1 . 
     In S 26  the CPU  27 A controls the reading device  26 A to read an image from the opposing surface of the ADF pressing plate  15  in order to acquire scan data, and in S 27  stores this scan data in the nonvolatile memory  28  as the reference data. By updating the reference data to scan data received prior to the sheet M reaching the read position in this way, the control unit  27  minimizes any decline in precision for determining whether scan data matches the reference data that could occur if the reference data were not updated, due to such factors as ambient conditions and changes in reading properties of the reading device  26 A over time. 
     Once the reference data has been stored in the nonvolatile memory  28 , in S 28  the CPU  27 A begins driving the ADF  14 , thereby resuming conveyance of the sheet M positioned upstream of the read position R 1 . In S 29  the control unit  27  begins the sheet detection reading operation and in S 30  determines whether the scan data no longer matches the reference data. When the determination results change from indicating the scan data matches the reference data to indicating the scan data does not match the reference data (S 30 : NO), the control unit  27  performs the same determination to detect when the scan data again matches the reference data. When the scan data subsequently matches the reference data (S 31 : YES), in S 32  the control unit  27  determines whether another sheet M is present in the feed tray  11  based on detection results received from the front sensor  12 . 
     Note that when the control unit  27  determines in S 30  that the scan data no longer matches the reference data, the control unit  27  may store the read position flag F 2  in the nonvolatile memory  28  as the current position data. Further, when the control unit  27  determines in S 31  that the scan data once again matches the reference data, the control unit  27  may store the downstream position flag F 3  in the nonvolatile memory  28  as the current position data. In this way, data indicating the current position of the sheet M is regularly updated in the nonvolatile memory  28  during the startup process. 
     If the control unit  27  determines that a sheet M is present in the feed tray  11  (S 32 : YES), the control unit  27  returns to S 30  to track the next sheet M positioned between the detection position R 0  and read position R 1 . However, if the control unit  27  determines that another sheet M is not present in the feed tray  11  (S 32 : NO), in S 33  the control unit  27  drives the ADF  14  to rotate exactly the discharge distance and subsequently halts the ADF  14 , as described in S 14  and S 15  of  FIG. 4 , and then ends the current sheet detection reading operation in S 34 , thereby ending the current startup process. 
     (2) When the Current Position Data is the Read Position Flag F 2   
     The current position data is the read position flag F 2  when the user switches off the power switch  23 , for example, while the sheet M is present at the read position R 1 , as is represented by the sheet M 2  in  FIG. 5 . Therefore, when the control unit  27  determines that the current position data is the read position flag F 2  (S 22 : NO, S 23 : YES), in S 35  the CPU  27 A controls the device-moving mechanism  26 B to temporarily move the reading device  26 A to the home position X 0  and to subsequently move the reading device  26 A to the ADF position X 1 . 
     Since the sheet M is present at the read position R 1  in this case, the reading device  26 A is unable to read an image from the opposing surface of the ADF pressing plate  15 . Therefore, in S 36  the control unit  27  reads the reference data that was previously stored in the nonvolatile memory  28  in S 3  of the read control process. In this way, the control unit  27  minimizes any decline in precision for determining whether scan data matches the reference data that could occur due to such factors as ambient conditions and changes in reading properties of the reading device  26 A over time, even when the sheet M is present at the read position R 1 . 
     In S 37  the control unit  27  begins driving the ADF  14 , thereby resuming conveyance of the sheet M present at the read position R 1 . In S 38  the control unit  27  begins the sheet detection reading operation using the reference data read in S 36  and advances to S 31  described above. Thus, whether the sheet M is present at the read position R 1  or at a position upstream of the read position R 1 , the control unit  27  can halt the ADF  14  after driving the ADF  14  the discharge distance from the point that the scan data received from the reading device  26 A changes from not matching the reference data to matching the reference data. Accordingly, if the sheet M is present at the read position R 1  or on the upstream side of the read position R 1  when the multifunction peripheral  1  is started up, the control unit  27  can reduce the amount that the ADF  14  is driven more the closer the position of the sheet M to the read position R 1 . 
     (3) When the Current Position Data is the Downstream Position Flag F 3   
     The current position data is the downstream position flag F 3  when the user switches off the power switch  23 , for example, while the sheet M is positioned downstream of the read position R 1 , as is represented by the sheet M 3  in  FIG. 5 . In this case, it is not necessary to execute the sheet detection reading operation (S 29  and S 38 ). Therefore, when the control unit  27  determines that the current position data is the downstream position flag F 3  (S 22 : NO, S 23 : NO, and S 24 : YES), in S 39  the control unit  27  drives the ADF  14  the discharge distance and subsequently halts the ADF  14 , without controlling movement of the reading device  26 A (S 25  and S 35 ). Subsequently, the control unit  27  ends the current startup process. This method eliminates the unnecessary operation of moving the reading device  26 A when it is not necessary to perform the sheet detection reading operation. 
     (4) When the Current Position Data is the Discharge Position Flag F 4   
     The current position data is the discharge position flag F 4  when the user switches off the power switch  23 , for example, after the sheet M has been discharged onto the discharge tray  13 , as is represented by the sheet M 4  in  FIG. 5 . When the control unit  27  determines that the current position data is the discharge position flag F 4  (S 22 : NO, S 23 : NO, and S 24 : NO), the control unit  27  simply ends the current startup process without performing operations to control movement of the reading device  26 A (S 25  and S 35 ) and to control driving of the ADF  14  (S 28  and S 37 ). This method eliminates the unnecessary operations of driving the ADF  14  and the like when the sheet M has already been discharged onto the discharge tray  13 . 
     Effects of the Embodiment 
     In the preferred embodiment described above, position data representing the current position of the sheet M on the conveying path R is regularly stored in the nonvolatile memory  28  as the sheet M is conveyed. When the control unit  27  determines that the multifunction peripheral  1  has been started up, the control unit  27  determines the current position of the sheet M based on the stored position data, and drives the ADF  14  to convey the sheet M a distance that is shorter the further downstream the position of the sheet M on the conveying path R. This method reduces the amount that the ADF  14  is unnecessarily driven in comparison to a device that always drives the ADF  14  the maximum distance from the detection position R 0  to the discharge position R 2  when the multifunction peripheral  1  is started up. 
     Further, the control unit  27  detects the current position of the sheet M by determining whether scan data outputted from the reading device  26 A matches the reference data as the sheet M is being conveyed (S 7  and S 10  in  FIG. 4 ) and stores position data indicating the current position of the sheet M in the nonvolatile memory  28  each time the position is detected. In this way, the control unit  27  can store position data in the nonvolatile memory  28  indicating the current position of the sheet M based on scan data outputted from the reading device  26 A. 
     The sheet-conveying device of the present invention is not limited to the multifunction peripheral  1  in the embodiment, but may be a device that conveys sheets other than sheets M of originals, such as a printing device that conveys printing sheets or a currency-conveying device that conveys currency. The sheet-conveying device may also be a device not provided with an image-reading unit  26  or similar image-processing device. 
     The image-processing device of the present invention is not limited to the multifunction peripheral  1 , but may be a standalone scanner having only a scanning function, a printer having only a printing function, a facsimile machine, a copy machine, and the like. 
     The conveying path in the sheet-conveying device of the present invention is not limited to the shape of the conveying path R described in the embodiment, but may be configured of only straight sections without a U-shaped section. 
     The image-processing unit of the image-processing device according to the invention is not limited to the image-reading unit  26 , but may be a printing unit for performing printing operations on sheets, or another processing unit for performing processes such as stapling sheets together. 
     In the preferred embodiment, the control unit  27  is configured of the CPU  27 A and hardware circuits such as the image-processing unit  27 D for implementing the read control process and the startup process. However, the control unit  27  may implement the read control process and the like with only one or a plurality of CPUs or with only a hardware circuit, such as an application-specific integrated circuit (ASIC). Further, the image-processing unit  27 D may be used to implement the position storing process, position detecting process, reference data storing process, and the like described above. 
     The control unit  27  may also execute the reference data storing process (S 2  and S 3 ) in between the step to start driving of the ADF  14  (S 4 ) and the step to start reading of the sheet (S 6 ), or after the step to stop reading of the sheet (S 11 ). However, by executing the reference data storing process prior to the step to start driving of the ADF  14 , as described in the embodiment, the control unit  27  can reliably store reference data and can perform the determinations in S 7 , S 10 , and the like using the latest reference data. 
     The position storing process may also be performed without using scan data from the reading device  26 A. For example, the multifunction peripheral  1  may be provided with a sensor (such as the rear sensor  30  shown in  FIGS. 2 and 3 ) for detecting the sheet M being conveyed along the conveying path R, and the control unit  27  may detect the current position of the sheet M on the conveying path R based on these detection results. Alternatively, the control unit  27  may regularly store the elapsed time from the moment that the sheet M was initially conveyed or the number of steps by which the motor drive circuit  14 H drives the stepping motor  14 G from the same point in nonvolatile memory as the position data. 
     While the invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.