Abstract:
An image forming apparatus capable of controlling movement of a transparent member suitably depending on various situations by including a transparent member, a feeding unit that feeds an original document to the transparent member, a reading unit that reads an image of the document fed on the transparent member via the transparent member, a moving unit that reciprocates the transparent member in a prescribed direction, and a controller that moves the transparent member forward in one direction from a home position while one document passes through a reading position, and stops the transparent member and then moves the transparent member backward to the home position when an interruption event of reading the document occurs.

Description:
[0001]     This application is based on Japanese Patent Application No. 2004-298062 filed in Japan on Oct. 12, 2004, the entire content of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus and an image reading apparatus. In particular, the present invention relates to an image forming apparatus and an image reading apparatus for reading a document using so-called sheet-through scanning.  
         [0004]     2. Description of Related Art  
         [0005]     In recent years, in view of convenience for users, many models of image forming apparatuses (e.g., photocopiers) which adopt sheet-through scanning in addition to movable optical scanning are introduced into the market. In the movable optical scanning, a document is placed on a platen glass, and the stationary document is read by moving an optical system under the document. In the sheet-through scanning, a document is moved to pass through a reading position on a platen glass using an automatic document feeder (ADF), and the document is read by a stationary optical system under the platen glass.  
         [0006]     In the image forming apparatus, the movable optical scanning and the sheet-through scanning are selectively used depending on the application. For example, the movable optical scanning is used for copying a document such as a book which is not suitably read using the ADF. The sheet-through scanning is used for copying a document comprising a plurality of sheets which can be fed one by one automatically.  
         [0007]     When dust is attached to the platen glass, in both of the scanning methods, the dust is read together with document into an image. In the case of reading by the movable optical scanning, the dust is simply reproduced as a black point corresponding to the size of the dust. However, in the case of reading by the sheet-through scanning, the dust is reproduced as a black stripe extending from one end to the other end of the document image. The black stripe is hardly negligible.  
         [0008]     In an attempt to address the problem, image reading apparatuses for reducing the occurrence of the black stripe in the presence of dust attached to the upper surface of the platen glass have been developed.  
         [0009]     In an image forming apparatus disclosed in Japanese laid-open patent publication No. 2001-272829, at the time of reading the document (at the time of feeding the document by the ADF), the platen glass is moved in an secondary scanning direction (in a feeding direction of the document). According to the disclosure, even if dust is attached to the platen glass, the dust does not stay at the document reading position. As a result, even though it depends on the movement of the platen glass, the read dust is reproduced as a short line, for example. It is possible to at least avoid the situation in which the read dust is reproduced as a black stripe extending from one end to the other end of the document image, or it is possible to reduce the occurrence of reproducing such a black stripe.  
         [0010]     In the apparatus having the above structure, since the platen glass is a movable member, it is necessary to suitably control the movement of the platen glass. Japanese laid-open patent publication No. 2001-272829 discloses basic operation of the platen glass. Specifically, during the operation sequence from the start of reading the document to the end of the reading, a reciprocal movement is made by moving the platen glass by a predetermined distance and moving the platen glass back to the home position. However, Japanese laid-open patent publication No. 2001-272829 does not disclose any movement control of the platen glass, e.g., when a jam of the document occurs in the ADF.  
         [0011]     In view of the above, an object of the present invention is to provide an image forming apparatus and an image reading apparatus which makes it possible to suitably control movement of a platen glass depending on various situations.  
       OBJECT AND SUMMARY  
       [0012]     An object of the present invention is to provide an image forming apparatus and an image reading apparatus which solves the above problems, and which achieves improvement in suitably controlling movement of a platen glass depending on various situations.  
         [0013]     The object is achieved by providing an image forming apparatus and an image reading apparatus having the following structure.  
         [0014]     An image forming apparatus including: a transparent member, a feeding unit that feeds an original document to the transparent member, a reading unit that reads an image of the document fed on the transparent member via the transparent member, a moving unit that reciprocates the transparent member in a prescribed direction, and a controller that moves the transparent member forward in one direction from a home position while one document passes through a reading position, and stops the transparent member and then moves the transparent member backward to the home position when an interruption event of reading the document occurs.  
         [0015]     Further, the interruption event is a feeding failure of the document in said feeding unit.  
         [0016]     Further the image forming apparatus including a receiving unit that receives a reading interruption instruction from a user, wherein said interruption event is the reading interruption instruction from said receiving unit.  
         [0017]     Further, the feeding unit feeds the document from a plurality of sheets of document stack one by one at intervals and said controller moves the transparent member backward to the home position in a time period from the time when a rear end of one document passes the reading position until the time when feeding of the next document is started.  
         [0018]     Further, the feeding unit feeds the document from a plurality of sheets of document stack one by one at intervals and said controller stops the transparent member and moves the transparent member backward for returning the transparent member to the home position before the rear end of one document does not fully pass the reading position.  
         [0019]     Further the image forming apparatus including an image forming unit that reproduces a read image by printing the read image on a recording sheet, wherein said interruption event is a feeding failure of the recording sheet in the image forming unit.  
         [0020]     Further the feeding unit is attached to the image forming apparatus body such that the feeding unit can be opened and closed, and reading of the document is performed when the feeding unit is closed with respect to the image forming apparatus body; and said interruption event is opening of the feeding unit with respect to the image forming apparatus.  
         [0021]     Further the controller prohibits movement of the transparent member when the feeding unit is opened. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:  
         [0023]      FIG. 1  is a view schematically showing structure of a digital color photocopier  10  according to an embodiment of the present invention;  
         [0024]      FIG. 2  is a perspective view schematically showing structure of a drive mechanism for a glass unit of the photocopier  10 ;  
         [0025]      FIG. 3  is a view showing a operation panel of the photocopier  10 ;  
         [0026]      FIG. 4  is a block diagram showing control unit of the photocopier  10 ;  
         [0027]      FIG. 5  is a block diagram showing an image reader section  12  of the photocopier  10 ;  
         [0028]      FIGS. 6   b  and  6   b  are flowcharts showing an example of basic processing in the image reader section  12 ;  
         [0029]      FIG. 7  is a flowchart showing an example of trouble processing in the image reader section  12 ;  
         [0030]      FIG. 8  is a flowchart showing an example of trouble processing in the image reader section  12 ; and  
         [0031]      FIG. 9  is a flowchart showing an example of trouble processing in the image reader section  12 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described in conjunction with a digital color photocopier as an example.  
         [0033]      FIG. 1  is a view schematically showing the overall structure of the digital color photocopier (hereinafter simply referred to as the “photocopier”)  10 .  
         [0034]     The photocopier  10  is roughly divided into an image reader section  12  for reading a document image and a printer section  14  for reproducing the read image by printing the read image on a recording sheet.  
         [0035]     The image reader section  12  is capable of reading the document image using both of sheet-through scanning as one method in a stationary optical system and mirror moving scanning as one method in a movable optical system.  
         [0036]     In the sheet-through scanning, the document image is read by moving the document while the optical system is fixed in a stationary condition. In the mirror moving method, the document image is read by moving a mirror for guiding a reflection light from a document surface to a CCD sensor with respect to the document while the document is fixed, and the optical path length from a document reading position to the CCD sensor is always maintained at a certain length.  
         [0037]     The image reader section  12  includes an automatic document feeder (ADF)  16  for carrying out the sheet-through scanning.  
         [0038]     The automatic document feeder  16  separates a stack of document sheets set in a paper feed tray  18  one by one, feeds the document to pass through an upper surface (document reading position) of a sheet-through platen glass  20 , and discharges the document to a document catch tray  22 .  
         [0039]     The uppermost sheet in the stack of document sheets set in the paper feed tray  18  is separated from the stack of document sheets by a pickup roller  24  and a feed roller  26 . The document is fed to a resist roller  30  through a first intermediate roller  28 . Further, a document resist sensor  29  for detecting a front end and a rear end of the document is provided between the first intermediate roller  28  and the resist roller  30 .  
         [0040]     After inclination (skew) of the document is corrected by the first intermediate roller  28  and the resist roller  30 , the document is fed to the sheet-through platen glass  20  by the resist roller  30 . After the document passes through the sheet-through platen glass  20 , the document is fed to a discharge roller  36  by a second intermediate roller  32  and a third intermediate roller  34 . The document is discharged to the document catch tray  22  by the discharge roller  36 . These rollers use a document motor M 1  as a power source, and rotations of the rollers are controlled using a power transmitting mechanism and a power interruption mechanism.  
         [0041]     A document detection sensor  19  (not shown in  FIG. 1 , see  FIG. 5 ) as a photoelectric sensor comprising a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode is provided in the paper feed tray  18 . A detection light emitted from the light-emitting element is reflected on the document placed on the paper feed tray  18 , and the reflection light is received by the light-receiving element to detect the presence of the document.  
         [0042]     The document passing through the sheet-through platen glass  20  is radiated by a white LED array  40  fixed under the sheet-through platen glass  20 . The white LED array  40  is shown as an example of a white light source of a scanner  38 . The optical path of the reflection light from the document surface is changed by a first mirror  42 , a second mirror  44 , and a third mirror  46  to form an image on a contraction three line CCD sensor  50  (hereinafter simply referred to as the “CCD sensor  50 ”) by a condenser lens  48 .  
         [0043]     At the time of reading the document, the sheet-through platen glass  20  moves in a feeding direction of the document (i.e., in an secondary scanning direction). Next, an example of a mechanism for achieving the movement will be described with reference to  FIG. 2 . In  FIG. 2 , an arrow Y indicates the secondary scanning direction, and an arrow X indicates a main scanning direction perpendicular to the secondary scanning direction.  
         [0044]     As shown in  FIG. 2 , the sheet-through platen glass  20  is made of a plate shaped glass elongated in the main scanning direction. The plate shaped glass is shown as an example of a light-transmissive member. The light-transmissive member is not limited to the glass. The light-transmissive member may be made of light-transmissive plastic. The sheet-through platen glass  20  is held in a glass holder  52 . The glass holder  52  and the sheet-through platen glass  20  fitted in the glass holder  52  forms a glass unit  53 . Opposite ends of the glass holder  52  in the main scanning direction are held by a pair of glass holder guides  54 ,  56  such that the glass holder  52  is slidable in the secondary scanning direction. The glass holder  52  includes a pair of racks  58 ,  60  protruding in the secondary scanning direction. The racks  58 ,  60  are in mesh with a pair of pinions  64 ,  66  attached to a shaft  62 . A spur gear  68  is attached to one end of the shaft  62 , and the spur gear  68  is in mesh with a spur gear  69 . A pulley  70  is formed integrally on one surface of the spur gear  69 . A belt  72  is stretched between the pulley  70  and an output shaft  71  of a platen glass motor M 3 .  
         [0045]     In the mechanism having the above structure, when the motor M 3  is rotated in a direction indicated by an arrow D (forward rotation), the driving force of the motor M 3  is transmitted to the belt  72 , the pulley  70 , the spur gear  69 , the spur gear  68 , the shaft  62 , the pinions  64 ,  66 , and the racks  58 ,  60 , successively. Thus, the glass holder  52  and the sheet-through platen glass  20  move in the secondary scanning direction indicated by an arrow F. Further, when the motor M 3  is rotated in a direction opposite to the direction indicated by the arrow D (reverse rotation), the glass unit  53  (sheet-through platen glass  20 ) moves in the secondary scanning direction indicated by an arrow B. The movement of the glass unit  53  (sheet-through platen glass  20 ) in the direction indicated by the arrow F is referred to as the forward movement, and the movement of the glass unit  53  (sheet-through platen glass  20 ) indicated by the arrow B is referred to as the backward movement.  
         [0046]      FIG. 2  shows a condition in which the glass unit  53  (sheet-through platen glass  20 ) has fully moved to a position in the direction indicated by the arrow B (fully moved toward a paper guide  51 ). This position is referred to as the home position.  
         [0047]     The document is fed in the secondary scanning direction indicated by the arrow B to pass through the upper surface of the sheet-through platen glass  20 . At this time, part of the document corresponding to the reading position indicated by an alternate long and short dash line is radiated by the white LED array  40 , and the reflection light from the part of the document is detected by a CCD sensor  50 .  
         [0048]     The sheet-through platen glass  20  moves from the home position in the direction indicated by the arrow F while one sheet of document is read (while one sheet of document passes through the reading position). That is, the sheet-through platen glass  20  moves in the secondary scanning direction relative to the document reading position. Thus, even if foreign material such as dust is attached to the sheet-through platen glass  20 , it is possible to prevent the foreign material from staying at the document reading position. Consequently, it is possible to prevent formation of a black stripe extending from one end to the other end of the reproduced image (one end to the other end in the secondary scanning direction) on the recording sheet.  
         [0049]     A home sensor  21  detects whether the sheet-through platen glass  20  is at the home position or not. For example, the home sensor  21  is a gap type photo sensor capable of detecting a condition in which part of an end of the glass holder  52  on the side of the paper guide  51  enters a gap of the gap type photo sensor (condition in which the sheet-through platen glass  20  is at the home position) and a condition in which the end of the glass holder  52  on the side of the paper guide  51  does not enter the gap of the gap type photo sensor (condition in which the sheet-through platen glass  20  is not at the home position).  
         [0050]     Referring back to  FIG. 1 , in addition to the sheet-through platen glass  20 , a manual platen glass  74  is provided at a position facing the automatic document feeder  16 . The document is manually placed on the manual platen glass  74 .  
         [0051]     When the document image is read using the sheet-through scanning method as described above, the scanner  38  moves to a position indicated by a broken line under the sheet-through platen glass  20 , and the document fed by the automatic document feeder  16  is radiated at this position to read the document image.  
         [0052]     When the document image is read by manually placing the document on the manual platen glass  74  (when the document image is read using the mirror moving scanning), the automatic document feeder  16  is opened upwardly, and the document is set on the manual platen glass  74 . The automatic document feeder  16  is attached to the photocopier  10  positioned under the automatic document feeder  16  as a whole such that the automatic document feeder  16  can be opened and closed. An open/close detection switch  37  (not shown in  FIG. 1 , see  FIG. 5 ) is attached to the photocopier  10 . The open/close detection switch  37  is pressed by part of the automatic document feeder  16 . That is, when the automatic document feeder  16  is closed, the open/close detection switch  37  is pressed by the part of the automatic document feeder  16 , and placed in the ON state. When the automatic document feeder  16  is opened, the open/close detection switch  37  is placed in the OFF state. Therefore, it is possible to detect whether the automatic document feeder  16  is open or closed.  
         [0053]     When the mirror moving scanning is used, the scanner  38  moves in the direction indicated by the arrow A in  FIG. 1 . At this time, the second mirror  44  and the third mirror  46  move in pairs. The moving direction of the second mirror  44  and the third mirror  46  is same as the moving direction of the scanner  38 , and the moving speed of the second mirror  44  and the third mirror  46  is half of the moving speed of the scanner  38 . Thus, the distance (optical path length) between the document surface and a condenser lens  48  is always maintained at a certain length, and the reflection light from the document forms an image on a light-receiving surface of the CCD sensor  50 . The scanner  38 , the second mirror  44 , and the third mirror  46  use a scan motor M 2  as a power source, and are driven through an unillustrated power transmitting mechanism for movement.  
         [0054]     The CCD sensor  50  performs photoelectric conversion of the reflection light from the document into an image signal. The image signal is A/D converted by an image processing unit  148  (see  FIG. 5 ) as described later into multiple value digital data. The digital data (hereinafter referred to as the “image data”) is subjected to processes such as shading correction, density conversion, and edge reinforcement, and then, stored in an image memory  144  ( FIG. 4 ) as described later.  
         [0055]     The image data in the image memory  144  is read by a CPU  138  of a main control unit  136  (see  FIG. 4 ) as described later, and inputted to a laser control unit  76  of the printer section  14 . The laser control unit  76  generates a laser diode drive signal based on the image data, and causes light emission from the laser diode  78 . The laser light emitted from the laser diode  78  is deflected by a polygon mirror  80 , and passes through an fθ lens  82 . Then, the optical path of the laser light is deflected by return mirrors  84 ,  86 , and the surface (photosensitive surface) of a photosensitive drum  88  rotating in the direction indicated by an arrow C is exposed to the light (scanned).  
         [0056]     An eraser lamp  90 , an electrostatic charger  92 , toner developers  94  to  100 , and a transfer charger  102  are provided around the photosensitive drum  88 . The toner developers  94  to  100  are provided separately for respective colors of cyan, magenta, yellow, and black. Before the photosensitive drum  88  is exposed to the light (scanned), charges on the photosensitive drum  88  are removed by radiation by the eraser lamp  90 , and then, the electrostatic charger  92  uniformly charges the photosensitive drum  88 . When the uniformly charged photosensitive surface is exposed to the light, an electrostatic latent image is formed, and the electrostatic latent image is developed to a toner image by any of the toner developers.  
         [0057]     A recording sheet having a predetermined size is fed from any one of paper feed cassettes  104  to  108 , and the fed recording sheet is wound (stuck) around a transfer drum  112  rotating in the direction indicated by an arrow E by operation of an electrostatic suction charger  110 . Then, the recording sheet is fed to a transfer position facing the transfer charger  102 . The transfer charger  102  operates to transfer the toner image on the photosensitive drum  88  to the recording sheet.  
         [0058]     The above light exposure process and the transfer process are repeated separately for the respective colors of cyan, magenta, yellow, and black to one recording sheet to reproduce a color image formed by overlapping toner images of the respective colors.  
         [0059]     After the toner images of the four colors are transferred on the recording sheet, the suction force applied to the recording sheet toward the transfer drum  112  is eliminated by a separation removal charger  114 . After the toner image is fixed by a fixing device  116 , the recording sheet is discharged to a tray  118 .  
         [0060]     When a black-and-white image is reproduced (when monochrome copying operation is carried out), the processing sequence of the light disposure process to the transfer process is performed only for the black color.  
         [0061]     Each of the image reader section  12  and the printer section  14  has a dedicated CPU (see  FIG. 4 ) which achieves the above processing sequence of copying operation.  
         [0062]     The photocopier  10  includes a operation panel  120  as shown in  FIG. 3  at an appropriate position on its upper surface so that the user can manipulate the operation panel  120  easily.  
         [0063]     As shown in  FIG. 3 , the operation panel  120  includes a liquid crystal touch panel  122 , and various keys. Copying conditions for the current copy setting, copy modes, keys for selecting a copy condition or a copy mode, and a message such as “no paper” or “paper jam” are displayed on the liquid crystal touch panel  122 . A numeric keypad  124  is used for setting the number of copies. A clear key  126  is used for resetting the number of copies to “1”. A color copy start key (hereinafter referred to as the “color key”)  128  is used for starting color copying operation (operation of reading an image of the document in the color mode, and printing the image in the color mode). A monochrome copy start key (hereinafter referred to as the “monochrome key”)  130  is used for starting monochrome copying operation (operation of reading an image of the document in the monochrome mode, and printing the image in the monochrome mode). Both of the color key  128  and the monochrome key  130  are made of light-transmissive material. A blue lamp (not shown) is provided inside, and just below each of the keys.  
         [0064]     A stop key  132  is used to stop feeding of the document by the automatic document feeder  16  (stop reading of the document) or stop copying operation. A panel reset key  134  is used for resetting all of copying conditions such as copy density and copy magnification, and setting modes to standard values.  
         [0065]     The operation panel  120  also has a dedicated CPU (see  FIG. 4 ). The CPU controls display of the liquid crystal touch panel  122 , and detects pressing of any of the keys.  
         [0066]      FIG. 4  is a view schematically showing a main control unit  136  of the photocopier  10 .  
         [0067]     As shown in  FIG. 4 , the main control unit  136  includes a CPU  138  as a central component, and further includes a ROM  140 , a RAM  142 , and an image memory  144  connected to the CPU  138 . Further, the CPU  138  is connected to the CPUs of the above described image reader section  12 , the printer section  14 , and the operation panel  120 .  
         [0068]     The ROM  140  stores control programs carried out by the respective CPUs.  
         [0069]     The RAM  142  stores copy conditions such as the copy number and the copy density, and copy modes which are set through the operation panel  120 .  
         [0070]     As described above, the image memory  144  temporarily stores the image data outputted from the image reader section  12 .  
         [0071]     The CPU  138  systematically controls the operation panel  120 , the image reader section  12 , and the printer section  14  for achieving the smooth copying operation.  
         [0072]      FIG. 5  is a block diagram schematically showing structure of the image reader section  12 .  
         [0073]     As shown in  FIG. 5 , the image reader section  12  includes the above-described CCD sensor  50 , the white LED array  40 , the document motor M 1 , the scan motor M 2 , the platen glass motor M 3 , the document detection sensor  19 , the document resist sensor  29 , the home sensor  21 , and the open/close detection switch  37 . Further, the image reader section  12  includes a CPU  146 , an image processing unit  148 , a motor control unit  150 , and an LED drive unit  152 .  
         [0074]     The CPU  146  receives instructions from the main control unit  136  (see  FIG. 4 ), and systematically controls the image processing unit  148 , the motor control unit  150 , the LED drive unit  152  for achieving the smooth reading operation.  
         [0075]     Next, control operations performed by the CPU  146  of the image reader section  12  will be described.  
         [0000]     (Basic Processing)  
         [0076]      FIG. 6  is a flowchart mainly showing operations in the control for feeding the document by the automatic document feeder  16  and operations in the control for moving the sheet-through platen glass  20 , of the control operations performed by the CPU  146  of the image reader section  12 .  
         [0077]     When the document detection sensor  19  detects that the document is set on the paper feed tray  18  (YES in step S 2 ), referring to the detection result of the home sensor  21 , whether the glass unit  53  (sheet-through platen glass  20 ) is at the home position or not is judged (step S 4 ).  
         [0078]     If the glass unit  53  is not at the home position (NO in step S 4 ), reverse rotation of the platen gas motor M 3  is started such that the glass unit  53  moves backward (step S 6 ). When the home sensor  21  detects that the glass unit  53  reaches the home position (YES in step S 8 ), the paten glass motor M 3  is stopped, and the glass unit  53  is stopped at the home position (step S 10 ). If the home sensor  21  does not detect that the glass unit  53  has reached the home position even if predetermined time has passed since the start of reverse rotation of the platen glass motor M 3  (NO in step S 8 ), it is likely that, for example, the power transmitting mechanism from the platen glass motor M 3  to the pinions  64 ,  66  is malfunctioning. Therefore, a trouble display instruction is sent to the main control unit  136  (step S 12 ), and the process is finished. The predetermined time is the time sufficient for moving the glass unit  53  from a position, which is considered as the remotest from the home position, to the home position. When the main control unit  136  receives the trouble display instruction, the main control unit  136  controls the operation panel  120  to display (indicate) the occurrence of the trouble.  
         [0079]     If it is confirmed that the glass unit  53  is at the home position in step S 4 , or if the glass unit  53  is brought back to the home position by the processes in steps S 6  to S 10 , an instruction is given to the main control unit  136  to turn on a blue light of the start key (step S 14 ). When the main control unit  136  receives the instruction, the main control unit  136  turns on the blue light of the start key in the operation panel  120 . Therefore, the user can recognize that reading of the document is ready.  
         [0080]     When the operation panel  120  detects that the start key is pressed, and the notification indicating the pressing of the start key is performed through the main control unit  136  (YES in step S 16 ), feeding of the uppermost sheet of the document set in the paper feed tray  18  is started by controlling the document motor M 1  or the like (step S 18 ).  
         [0081]     When a front end of the fed document is detected by the document resist sensor  29  (YES in step S 20 ), the CPU  146  resets, and then, starts an internal timer (not shown) (YES in step S 22 ).  
         [0082]     When the internal timer counts predetermined time T 1  (YES in step S 24 ), the white LED array  40  is turned on to start light exposure of the document (step S 26 ). The predetermined time T 1  herein means the time required for moving the front end of the document from a detection position of the document resist sensor  29  to, e.g., a position between the intermediate roller  30  and the document reading position.  
         [0083]     When the internal timer counts predetermined time T 2  (YES in step S 28 ), forward rotation of the platen glass motor M 3  is started such that the glass unit  53  moves forward (step S 30 ). The predetermined time T 2  herein means the time required for moving the front end of the document from the detection position of the document resist sensor  29  to, e.g., the document reading position.  
         [0084]     Then, when a rear end of the fed document is detected by the document resist sensor  29  (YES in step S 32 ), the CPU  146  resets, and then, starts the internal timer (step S 34 ).  
         [0085]     When the internal timer counts predetermined time T 3  (YES in step S 36 ), the platen glass motor M 3  is stopped to stop the movement of the glass unit  53  (step S 38 ). Then, reverse rotation of the platen glass motor M 3  is started such that the glass unit  53  moves backward (step S 40 ). The predetermined time T 4  herein means the time required for moving the rear end of the document from the detection position of the document resist sensor  29  to, e.g., the document reading position.  
         [0086]     When the internal timer counts predetermined time T 4  (YES in step S 42 ), the white LED array  40  is turned off to stop light exposure of the document (step S 44 ). The predetermined time T 4  herein means the time required for moving the rear end of the document from the detection position of the document resist sensor  29  to, e.g., a position between the document reading position and the second intermediate roller  32 .  
         [0087]     When the home sensor  21  detects that the glass unit  53  moving backward reaches the home position (YES in step S 46 ), the platen glass motor M 3  is stopped to stop the glass unit  53  at the home position (step S 48 ).  
         [0088]     Next, referring to the detection result of the document detection sensor  19 , it is determined whether there is any sheet of document remaining on the paper feed tray  18  (step S 50 ). If any sheet of document is remaining on the paper feed tray  18  (YES in step S 50 ), the processes from step S 18  are repeated. If no sheet of document is remaining on the paper feed tray  18  (NO in step S 50 ), the processing sequence is finished.  
         [0089]     In the basic processing as described above, while one sheet of document is read (while one sheet of document passes through the document reading position), the sheet-through platen glass  20  continuously moves in one direction, i.e., in the secondary scanning direction. Therefore, even if foreign material such as dust is attached to the sheet-through platen glass  20 , it is possible to prevent the foreign material from staying at the document reading position. Consequently, a black stripe produced on the recording sheet due to reading of the foreign material does not extend from one end to the other end of the document. That is, in comparison with the case in which the sheet-through platen glass  20  is fixed, it is possible to reduce the occurrence of the black stripe.  
         [0090]     Further, though the sheet-through platen glass may reciprocate back and forth several times while one sheet of the document is read, such reciprocal movement is not preferable for the following reason. In the reciprocal movement, the sheet-through platen glass changes the direction of movement while reading one sheet of document (forward movement to backward movement, or backward movement to forward movement). At the time of changing the direction, the speed of the movement becomes zero. When the direction is changed (when the movement speed becomes zero), if the foreign material attached on the sheet-through plate glass is at the document reading position, the foreign material stays at the document reading position for a long time in comparison with the case in which the sheet-through platen glass is continuously moving (the case in which the speed does not become zero). As a result, one black stripe formed on the recording sheet is long in comparison with the case in which the sheet-platen glass is continuously moving.  
         [0091]     Next, trouble processing will be described. The trouble processing is performed interrupting the basic processing when an interruption event occurs for some reasons, and it is not possible to continue the document reading.  
         [0000]     (First Trouble Processing)  
         [0092]     In the following description, the interruption event of reading the document occurs when the user presses the stop key  132 , or when a trouble such as a failure of feeding the document (so called document jam) occurs in the automatic document feeder (ADF)  16 .  
         [0093]      FIG. 7  is a flowchart showing processes in this case.  
         [0094]     When the stop key  132  is pressed (YES in step S 52 ) or when a trouble such as a document jam in the automatic document feeder (ADF)  16  is detected (YES in step S 54 ), the document feeding process and the light exposure process (steps S 18  to S 50  in  FIGS. 6   a  and  6   b ) are stopped (step S 55 ) and the platen glass motor M 3  is stopped to stop the movement of the glass unit  53  (step S 56 ). Further, reverse rotation of the platen glass motor M 3  is started such that the glass unit  53  moves backward (step S 58 ). When the home sensor  21  detects that the glass unit  53  moving backward reaches the home position (YES in step S 60 ), the platen glass motor M 3  is stopped, and the glass unit  53  is stopped at the home position (step S 62 ) to finish the series of processes in the first trouble processing. The pressing of the stop key  132  is detected in the operation panel  120 . The detection result is notified to the CPU  146  of the image reader section  12  through the main control unit  136 . The detection of the document jam in the automatic document feeder is well known, and description thereof will be omitted.  
         [0095]     In the above processing, when the stop key  132  is pressed, or a trouble occurs in the automatic document feeder  16 , the movement of the glass unit  53  is immediately stopped, and the glass unit  53  moves back to the home position. Therefore, when the next document is read, since the glass unit  53  is already waiting at the home position, it is possible to start reading of the document smoothly. That is, if only the glass unit is stopped when a trouble occurs in the automatic document feeder, it is necessary to move the glass unit back to the home position at the time of reading the next document. Therefore, for moving the glass unit back to the home position, the start of reading the document is delayed. The embodiment of the present invention can avoid such situation.  
         [0000]     (Second Trouble Processing)  
         [0096]     In the second trouble processing, the interruption events of reading the document include opening of the automatic document feeder (ADF).  16  in addition to the pressing of the stop key  132  by the user in the first trouble processing and the document feeding failure in the automatic document feeder (ADF)  16 .  
         [0097]      FIG. 8  is a flowchart showing processes in this case.  
         [0098]     When the stop key  132  is pressed (YES in step S 64 ), when a trouble such as a document jam in the automatic document feeder (ADF)  16  is detected (YES in step S 66 ), or when opening of the automatic document feeder (ADF)  16  is detected by the open/close detection switch  37  (YES in step S 68 ), the document feeding process and the light exposure process (steps S 18  to S 50  in  FIGS. 6   a  and  6   b ) are stopped (step S 69 ) and the platen glass motor M 3  is stopped to stop the movement of the glass unit  53  (step S 70 ).  
         [0099]     When it is confirmed that the automatic document feeder (ADF)  16  is closed referring to the detection result of the open/close detection switch  37  (NO in step S 72 ), reverse rotation of the platen glass motor M 3  is started such that the glass unit  53  moves backward (step S 74 ). When the home sensor  21  detects that the glass unit  53  moving backward reaches the home position (YES in step S 76 ), the platen glass motor M 3  is stopped, and the glass unit  53  is-stopped at the home position (step S 78 ) to finish the series of processes in the second trouble processing.  
         [0100]     When the automatic document feeder (ADF)  16  is opened (YES in step S 72 ) while the glass unit  53  is moving backward (step S 74 ), the movement (backward movement) of the glass unit  53  is stopped (step S 70 ).  
         [0101]     In the above processing, when the automatic document feeder (ADF)  16  is opened, the movement of the glass unit  53  is prohibited (steps S 72 , S 70 ). The movement of the glass unit  53  is permitted only when the automatic document feeder (ADF)  16  is closed.  
         [0102]     For example, assuming that the sheet-through platen glass  20  is moved while it is exposed, if an unexpected object contacts the sheet-through platen glass  20 , the sheet-through platen glass  20  may be damaged. The embodiment of the present invention can avoid such situation.  
         [0000]     (Third Trouble Processing)  
         [0103]     In the first trouble processing and the second trouble processing, the interruption events of reading the document occur in the image reading section  12 . In the third trouble processing, the interruption events occur in the printer section  14 .  
         [0104]     Possible troubles (interruption events) in the printer section  14  include a failure of feeding the recording sheet (so called recording sheet jam).  
         [0105]      FIG. 9  is a flowchart showing processes in this case.  
         [0106]     Even if a trouble such as a recording sheet jam occurs in the printer section  14  (YES in step S 80 ), the document feeding process and the light exposure process (steps S 18  to S 50  in  FIG. 6 ) are continued (step S 82 ) since the trouble does not affect reading of the document. Detection of the recording sheet jam is well known, and description thereof will be omitted.  
         [0107]     In this case, since no image is formed on the recording sheet, the image data is accumulated in the image memory  144 . Therefore, when there is no remaining space in the memory (YES in step S 84 ), after the document feeding process and the light exposure process (steps S 18  to S 50  in  FIGS. 6   a  and  6   b ) are stopped (step S 85 ), processes in steps S 86  to S 92  are performed. The processes in steps S 86  to S 92  are identical to the above-described processes in steps S 56  to S 62  (see  FIG. 7 ), and thus, description thereof will be omitted. When there is no remaining memory space in the image memory  144 , this information is notified from the main control unit  136  to the CPU  146  of the image reader section  12 .  
         [0108]     In the above example, when a trouble occurs in the printer section  14  (YES in step S 80 ), the routine proceeds to the processes from step S 85  in consideration of the remaining space in the image memory  144 . However, the present invention is not limited in this respect. The routine may proceed to the process in step S 85  regardless of the remaining space in the image memory  144  (that is, steps S 82 , S 84  in the flowchart of  FIG. 9  may be omitted).  
         [0109]     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included with in the scope of the present invention as defined by the appended claims unless they depart therefrom.  
         [0110]     (1) In the basic processing shown in  FIG. 6 , at the time when the rear end of the document reaches the document reading position (YES in step S 36 ), the glass unit  53  is stopped to move the glass unit  53  backward. However, the timing is not limited to this time. For example, the glass unit  53  may be stopped before the rear end of the document fully passes the document reading position. Specifically, the glass unit  53  may be stopped when a position away from the rear end of the document internally in the secondary scanning direction (document feeding direction) by 4 mm passes the document reading position. It is likely that the area away from the end of the document by the distance of this extent is a blank area, and no image is read from this area. Therefore, even if the above-described long black stripe is reproduced on the recording sheet when the direction of the movement of the sheet-through platen glass  20  is changed, it is likely that the black stripe does not overlap on the intended document image, and the undesirable affect of the black stripe is considered to be small. In the meanwhile, since the backward movement of the glass unit  53  can be started before the rear end of the document passes through document reading position, it is possible to rapidly move the glass unit  53  back to the home position. As a result, reading of the next document can be started sooner. When a plurality of document sheets are read successively, the total time from the start to the end of reading the document can be reduced. It is a matter of course that the timing can be changed by adjustment of the predetermined time T 3 .  
         [0111]     (2) In the above-described embodiment, the direction of the forward movement of the glass unit  53  is opposite to the feeding direction of the document. Conversely, the direction of the forward movement of the glass unit  53  may be the same as the feeding direction of the document.  
         [0112]     (3) Only one of the first trouble processing, the second trouble processing, and the third trouble processing may be carried out. Alternatively, the first trouble processing and the third trouble processing may be carried out at the same time or the second trouble processing and the third trouble processing may be carried out at the same time.