Patent Publication Number: US-8988741-B2

Title: Image scanning device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of prior U.S. application Ser. No. 13/417,395, filed Mar. 12, 2012, which claims priority from Japanese Patent Application No. 2011-218078, filed on Sep. 30, 2011, the entire disclosures of each which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image scanning device. 
     2. Description of Related Art 
     A known image scanning device comprises an automatic document feeder (hereinafter referred to as ADF), and the ADF comprises a path switching unit configured to selectively move between a first position for guiding a document along a first conveying path and a second position for guiding a document along a second conveying path. 
     In such an image scanning device, if a driving source (e.g., a motor) is provided exclusively for driving the path switching unit to change its position, a wire harness and the like is required for controlling the driving source. Thus, the manufacturing cost may increase because the number of parts and the assembly man-hour increase. The device size may increase because of an extra space required for the driving source and the wire harness. An extra cost may be required to prevent electrical noise which may be generated more as driving sources and wire harnesses increase in number. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for an image scanning device comprising a path switching unit configured to selectively move a first position for guiding a document along a first conveying path and a second position for guiding a document along a second conveying path, while a driving source exclusively for the path switching unit is eliminated. 
     According to an embodiment of the invention, an image scanning device comprises a scanning unit configured to scan, at a scanning position, an image of a document, a first discharge portion, a second discharge portion, a conveying unit configured to selectively convey the document along a first conveying path from the scanning position to the first discharge portion, and along a second conveying path from the scanning position to the second discharge portion, a driving unit configured to generate a driving force for driving the conveying unit, and a path switching unit configured to receive the driving force generated by the driving unit such that the path switching unit moves between a first position for guiding the document toward the first discharge portion, and a second position for guiding the document toward the second discharge portion. 
     Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention, the needs satisfied thereby, and the features and technical advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1A  is a perspective view of a multi-function device in a first open/closed state, according to an embodiment of the invention. 
         FIG. 1B  is a perspective view of the multi-function device in a second open/closed state. 
         FIG. 2A  is a perspective view of the multi-function device in a third open/closed state. 
         FIG. 2B  is a perspective view of the multi-function device in a fourth open/closed state. 
         FIG. 3A  is a perspective view of a document conveying unit in which a top cover thereof is open. 
         FIG. 3B  is a perspective view of the document conveying unit comprising a document sensor. 
         FIG. 4A  is a vertical cross-sectional view of the multi-function device comprising a scanning unit and the document conveying unit, as viewed from the front when a cover member is closed. 
         FIG. 4B  is a vertical cross-sectional view off the multi-function device comprising the scanning unit and the document conveying unit, as viewed from the front when the cover member is open. 
         FIG. 5A  is a perspective view of a path switching member and a link member when the cover member is closed. 
         FIG. 5B  is a perspective view of the path switching member and the link member when the cover member is open. 
         FIG. 6  is a perspective view of a drive transmitting mechanism disposed in the vicinity of a rear left end of the document conveying unit. 
         FIG. 7  is a plan view showing a position of a gear mechanism for opening/closing the cover member and a position of a 4-joint link for opening/closing the cover member. 
         FIG. 8  is a schematic view showing a general structure of the four-joint link for opening/closing the cover member. 
         FIGS. 9A-9E  are schematic diagrams showing, in a step-by-step manner, motions of the four-joint link for opening/closing the cover member. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the invention and their features and technical advantages may be understood by referring to  FIGS. 1-9 , like numerals being used for like corresponding parts in the various drawings. 
     An image scanning device according to an embodiment of the invention may be a multi-function device having a scanning function and other functions, e.g., printing, copying, and facsimile transmitting/receiving functions. In the following description, the directions “top”, “bottom”, “left”, “right”, “front”, and “rear” are used to clarify the positional relationship of various parts of the multi-function device. 
     As shown in  FIGS. 1A ,  1 B,  2 A, and  2 B, a multi-function device  1  comprises a main unit  2 , a scanning unit  3  mounted on the main unit  2 , and a document conveying unit  4  mounted on the scanning unit  3 . 
     The main unit  2  comprises therein an image forming unit, a control unit, and a power supply unit. The control unit of the main unit  2  controls various mechanisms of the main unit  2 , the scanning unit  3 , and the document conveying unit  4   
     The scanning unit  3  is configured to pivot relative to the main unit  2  about an axis located in the vicinity of rear ends of the main unit  2  and the scanning unit  3  and extending in a left-right direction. The scanning unit  3  pivots between a closed position (shown in  FIG. 1A ) and an open position (shown in  FIG. 2B ). 
     When the scanning unit  3  is in the open position, a first opening  2 A defined at the top of the main unit  2  is open to allow maintenance work of the various parts, e.g., the image forming unit, the control unit, and the power supply unit. When the scanning unit  3  is in the closed position, the first opening  2 A is closed. 
     The document conveying unit  4  is configured to pivot relative to the scanning unit  3  about an axis located near rear ends of the scanning unit  3  and the document conveying unit  4  and extending in the left-right direction. The document conveying unit  4  pivots between a closed position (shown in  FIG. 1A ) and an open position (shown in  FIG. 2A ). 
     When the document conveying unit  4  is in the open position, a document holding surface (a transparent portion  25  for a stationary document) is exposed. The document conveying unit  4  located in the open position functions as a cover that covers the document holding surface. 
     A cover member  5  is attached to a left end of the document conveying unit  4 . The cover member  5  is configured to pivot relative to the document conveying unit  4  about an axis located in the vicinity of a left end of the document conveying unit and a lower end of the cover member  5 . The cover member  5  pivots between a closed position (shown in  FIG. 1A ) and an open position (shown in  FIG. 1B ). 
     When the cover member  5  is in the open position, a second opening  4 A is exposed. When the cover member  5  is in the closed position, the second opening  4 A is covered. As will be described below, when a document is conveyed along a second conveying path, the second opening  4 A is used as a discharge port through which the document is discharged. In other words, the cover member  5  is configured to move between an extended position (shown in  FIG. 4B ) for receiving the document discharged through the second opening  4 A and a retracted position (shown in  FIG. 4A ) which is retracted from the extended position. 
     An operation panel  7  is disposed at a front top of the main unit  2  so as to be operated by a user. A discharge port  8  is formed below the operation panel  7  such that a recording medium having an image printed thereon is discharged through the discharge port  8 . A cassette  9  configured to store blank recording media is mounted below the discharge port  8 . 
     As shown in  FIGS. 1A and 1B , an openable top cover  11  is disposed at the top of the document conveying unit  4 . As shown in  FIG. 3A , the top cover  11  is configured to pivot relative to the document conveying unit  4  about an axis located in the vicinity of a right end of the top cover  11  and extending in a front-rear direction. The top cover  11  pivots between a closed position (shown in  FIG. 1A ) and an open position (shown in  FIG. 3A ). 
     The top cover  11  extends substantially horizontally when the top cover  11  is in the closed position and extends obliquely right upward when the top cover  11  is in the open position. When the top cover  11  moves to the open position, a document tray  12  is exposed at the top of the document conveying unit  4 . 
     Document guides  13  are disposed on the document tray  12 . The document guides  13  are configured to slide along the front-rear direction such that when one of the documents guides  13  slides in one direction, the other slides in an opposite direction. By operating only one of the document guides  13 , the document guides  13  slide close to or away from each other thereby change a distance between the document guides  13 . 
     A partition plate  14  is disposed at a top end of each document guide  13 . Documents to be fed are set below the partition plates  15 . As will be described below, when documents are conveyed along a first conveying path, the documents are discharged on the partition plates  15 . 
     As shown in  FIG. 3B , the document tray  12  comprises document sensors  17 ,  18 . The document sensor  17  is a contact-type sensor and turns on/off by being pushed down by a document set in the document tray  12 . The document sensor  17  is disposed at such a position that a document larger than a predetermined size (e.g., a postcard size), when set in the document tray  12 , pushes down the document sensor  17 . Thus, when a document (e.g., a postcard or a business card) smaller than or equal to the predetermined size is set in the document tray  12 , the document sensor  17  is not pushed down and thereby detects whether the set document is smaller than or equal to the predetermined size. The document sensor  18 , which is the same type as the document sensor  17 , is disposed at such a position that a document either larger or smaller than the predetermined size, when set in the document tray  12 , pushes down the document sensor  18 . 
     As shown in  FIGS. 4A and 4B , the scanning unit  3  comprises a first image sensor  21 , and the document conveying unit  4  comprises a second image sensor  22 . In this embodiment, each of the first image sensor  21  and the second image sensor  22  is a contact image sensor. 
     The first image sensor  21  is driven by a motor (not shown) to reciprocate inside the scanning unit  3  in the left-right direction (sub-scanning direction). The second image sensor  22  is fixed to a frame inside the document conveying unit  4 . 
     The scanning unit  3  comprises a transparent portion  25  for a stationary document and a first transparent portion  27  for a moving document that are disposed above a reciprocating path of the first image sensor  21 . The document conveying unit  4  comprises a second transparent portion  28  disposed below the second image sensor  22 . 
     The transparent portion  25  and the first transparent portion  27  define a top surface of the scanning unit  3  and are formed by a single glass plate in this embodiment. The second transparent portion  28  is formed by a separate glass plate from the single glass plate having the transparent portion  25  and the first transparent portion  27 . 
     The transparent portion  25  and the first transparent portion  27  may be formed by separate glass plates. The transparent portion  25 , the first transparent portion  27 , and the second transparent portion  28  may be made of other materials than glass as long as the material is transparent and allows the first image sensor  21  and the second image sensor  22  to scan a document therethrough. 
     The document conveying unit  4  comprises a first document retainer  31  disposed above the first transparent portion  27 . The scanning unit  3  comprises a second document retainer  32  disposed below the second transparent portion  28 . 
     The first document retainer  31  is urged downward by a compressed spring (not shown) so as to slightly press an upper surface of the first transparent portion  27 . The second retainer  32  is urged upward by a compressed spring (not shown) so as to slightly press a lower surface of the second transparent portion  28 . 
     The document conveying unit  4  comprises rollers, e.g., a feed roller  41 , a separation roller  42 , a registration roller  43 , and a U-turn roller  44 , and guide members disposed between these rollers and having guide surfaces for guiding a document in a predetermined direction. As one of the guide members, a movable path switching member  45  is disposed leftward of the U-turn roller  44 . 
     The path switching member  45  is configured to pivot relative to the document conveying unit  4  about an axis located at a lower end of the path switching member  45  and extending in the front-rear direction. The path switching member  45  pivots between a first position shown in  FIG. 4A  and a second position shown in a second position shown in  FIG. 4B . 
     A link member  46  is disposed between the path switching member  45  and the cover member  5 . The link member  46  is pivotably coupled, at a right end thereof, to the path switching member  45  and is pivotably coupled, at a left end thereof, to the cover member  5 . Each of the cover member  5  and the path switching member  45  is configured to pivot, at a lower end thereof, relative to the document conveying unit  4 . A four-joint link is formed in the document conveying unit  4  by the cover member  5 , the path switching member  45 , and the link member  46 . 
     Because of this four-joint link, the path switching member  45  moves to the second position as the cover member  5  is opened, and moves to the first position as the cover member  5  is closed. As will be described in detail below, in this embodiment, the cover member  5  comprises a motor-driven mechanism for opening/closing the cover member  5 , and the path switching member  45  moves as the cover member  5  is opened/closed by the motor-driven mechanism. 
     As shown in  FIGS. 5A and 5B , each of the path switching member  45  and the link member  46  has an upper surface which serves as a guide surface for guiding a document. The guide surface is formed by ribs to reduce friction between the path switching member  45  and the document. The path switching member  45  and the link member  46  have a width in the front-rear direction that is slightly smaller than that of the cover member  5  and is suitable for conveying documents smaller than or equal to a postcard. 
     As shown in  FIGS. 4A and 4B , a motor  48  is disposed behind the link member  46 , and a drive transmitting mechanism  50  shown in  FIG. 6  is disposed behind the motor  48  and in the vicinity of a rear left end of the document conveying unit  4 . The drive transmitting mechanism  50  comprises a motor gear  51  which is driven by the motor  48  to rotate, and a planet gear  53  which is driven by a driving force transmitted from the motor gear  51 . The planet gear  53  is attached to a support member  55  which oscillates between two positions which will be described below.  FIG. 6  shows at the same time the planet gear  53  moved to one of the two positions and moved to the other of the two positions. The drive transmitting mechanism  50  is an example of a drive transmitting unit. 
     When the motor gear  51  is driven by the motor  48  to rotate in a first direction, e.g., in a forward direction, the planet gear  53  and the support member  55  move to a lower position such that the planet gear  53  engages an ADF drive gear  57 . In this state, the motor gear  51  rotating in the forward direction drives a document conveying mechanism (e.g., the feed roller  41 , the separation roller  42 , the registration roller  43 , and the U-turn roller  44 ). 
     When the motor gear  51  is driven by the motor  48  to rotate in a second direction, e.g., in a reverse direction, the planet gear  53  and the support member  55  move to an upper position such that the planet gear  53  engages a drive transmitting gear  59  for transmitting a driving force to open/close the cover member  5 . In this state, the motor gear  51  rotating in the reverse direction drives the drive transmitting gear  59 . 
     As shown in  FIG. 7 , the drive transmitting gear  59  is a part of a gear mechanism  61  for opening/closing the cover member  5 , and a motion of the drive transmitting gear  59  is transmitted, via the gear mechanism  61 , to a four-joint link  63  for opening/closing the cover member  5 . 
     As shown in  FIG. 8 , the four-joint link  63  is a drive transmitting mechanism comprising a first link element  63 A and a second link element  63 B, and configured to convert a unidirectional rotating motion of the first link element  63 A to a reciprocating motion of the cover member  5 . In this four-joint link  63 , the first link element  63 A is rotatably coupled to a frame of the document conveying unit  4  and is driven, by a driving force transmitted via the gear mechanism  61 , to rotate in a direction shown by an arrow in  FIG. 8 . The second link element  63 B is pivotably coupled, at one end thereof, to the first link element  63 A and is pivotably coupled, at the other end thereof, to the cover member  5 . The second link element  63 B follows the rotation of the first link element  63 A and moves to an initial position (shown by a solid line in  FIG. 8 ) and an operating position (shown by a two-dot-one-dash line in  FIG. 8 ). As the second link element  63 B moves, the cover member  5  pivots and reciprocates between a closed position (shown by a solid line in  FIG. 8 ) and an open position (shown by a two-dot-one-dash line in  FIG. 8 ). 
     The above-described motion of the four-joint link  63  will be described further in detail referring to  FIGS. 9A to 9E . The first link element  63 A is rotatably coupled at a joint P 1  to the frame (not shown) of the document conveying unit  4  and is pivotably coupled at a joint P 2  to the second link element  63 B. 
     The joint P 1  is a rotation center of the first link element  63 A. When the first link element  63 A is driven to rotate, the joint P 2 , which is distant from the joint P 1  by a predetermined distance, moves to such positions as to draw a circular locus around the joint P. 
     The second link element  63 B is pivotably coupled at the joint P 2  to the first link element  63 A and is pivotably coupled at the joint P 3  to the cover member  5 . When the joint P 2  moves as the first link element  63 A rotates, the second link element  63 B transmits the motion of the joint P 2  to the cover member  5  and moves the cover member  5  to such a position that the predetermined distance is maintained between the joint P 2  and the joint P 3 . 
     The cover member  5  is pivotably coupled at a joint P 3  to the second link element  63 B and is pivotably coupled at a joint P 4  to the frame (not shown) of the document conveying unit  4 . The joint P 4  is a pivoting center of the cover member  5 , and the joint P 3 , which is distant from the joint P 4  by a predetermined distance, moves to such positions as to draw an arcuate locus around the joint P 4 . 
     The first link element  63 A and the second link element  63 B overlap in  FIG. 9A  and are aligned in a line in  FIG. 9C . Although, in  FIGS. 8 and 9A  to  9 D, the first link element  63 A and the second link element  63 B are shown as linear, these link elements may not be linear. 
     The first link element  63 A and the second link elements  63 B are initially located in initial positions shown in  FIG. 9A  (shown by a solid line in  FIG. 8 ). At this time, the cover member  5  is in the closed position shown in  FIG. 9A  (shown by a solid line in  FIG. 8 ). In this state, when the driving force is transmitted by the gear mechanism  61  to the first link element  63 A, the first link element  63 A is driven to rotate in a direction shown by an arrow A 1  in  FIG. 9B . 
     When the first link element  63 A is driven to rotate in the direction shown by the arrow A 1 , the joint P 2  tries to move in a direction toward the joint P 3 . However, because the predetermined distance is maintained between the joint P 2  and the joint P 3  by the second link element  63 B, the joint P 3  moves as the joint P 2  moves. Because the joint P 3  moves about the joint P 4 , the cover member  5  pivots about the joint P 4  in a direction shown by an arrow B 1  in  FIG. 9B . 
     When the first link element  63 A is driven to rotate further in a direction shown by an arrow A 2  in  FIG. 9C , the joint P 2  still tries to move in a direction toward the joint P 3 . However, as described above, the joint P 3  moves about the joint P 4  as the joint P 2  moves. Thus, the cover member  5  pivots further about the joint P 4  in a direction shown by an arrow B 2  in  FIG. 9C  to the open position shown in  FIG. 9C  (shown by a two-dot-one-dash line in  FIG. 8 ). 
     After that, when the first link element  63 A is driven to rotate in a direction shown by an arrow A 3  in  FIG. 9D , the joint P 2  tries to move in a direction away from the joint P 3 . However, as described above, because the predetermined distance is maintained between the joint P 2  and the joint P 3  by the second link element  63 B, the joint P 3  moves as the joint P 2  moves. The joint P 3  moves about the joint P 4 . Thus, the cover member  5  pivots about the joint P 4  in a direction shown by an arrow B 3  in  FIG. 9D . 
     When the first link element  63 A is driven to rotate further in a direction shown by an arrow A 4  in  FIG. 9C , the joint P 2  still tries to move in a direction away from the joint P 3 . However, as described above, the joint P 3  moves about the joint P 4  as the joint P 2  moves. Thus, the cover member  5  pivots further about the joint P 4  in a direction shown by an arrow B 4  in  FIG. 9E  and returns to the closed position shown in  FIG. 9E  (shown by a solid line in  FIG. 8 ). 
     In short, when the first link element  63 A rotates once in the directions shown by the arrows A 1  to A 4  in  FIGS. 9A to 9E , the first link element  63 A and the second link element  63 B move step by step as shown in  FIGS. 9A to 9E  from the initial positions to the operating positions and return to the initial positions. In this case, the cover member  5  opens and closes while following the motions of the first link element  63 A and the second link element  63 B. 
     When the motor gear  51  is driven to rotate in the reverse direction, the gear mechanism  61  for opening/closing the cover member  5  transmits the rotation of the motor gear  51  to the first link element  63 A while reducing the number of rotations of the motor gear  51  at a predetermined reduction rate. For example, a sensor for detecting the initial position (shown in  FIG. 9A ) of the first link element  63 A, which corresponds to the closed position of the cover member  5 , may be provided, and the motor gear  51  may be controlled to rotate a predetermined angle such that the first link element  63 A rotates from the initial position (shown in  FIG. 9A ) to the operation position (shown in  FIG. 9C ) which corresponds to the open position of the cover member  5 . By this control, the cover member  5  may be stopped at the open position. 
     As described above, in addition to the four-joint link  63 , another four-joint member is formed by the cover member  5 , the path switching member  45 , and the link member  46 . Thus, when the four-joint link  63  opens/closes the cover member  5 , the path switching member  45  and the link member  46  moves in response to the opening/closing of the cover member  5 . 
     When the motor gear  51  is controlled to rotate by a predetermine angle, the cover member  5 , the path switching member  45 , and the link member  46  move in response to each other. The cover member  5  moves to the closed position when the path switching member  45  moves to the first position to partially define the first conveying path (as shown in  FIG. 4A ), and moves to the open position when the path switching member  45  moves to the second position to partially define the second conveying path (as shown in  FIG. 4B ). 
     The multi-function device  1  having the above-described structure is configured to scan an image on a document while conveying the document by the document conveying unit  4 . In order for the multi-function device  1  to scan a document, a document to be fed is set in the document tray  12 . Specifically, the distance between the document guides  13  are adjusted by sliding the document guides  13  in the front-rear direction according to the size of the document. Then, the document is set between the document guides  13 . 
     In this embodiment, when the document is relatively large (larger than a postcard size) is set in the document tray  12 , the document pushes the document sensor  17 . When the document (e.g. a postcard or a business card) which is relatively small (smaller than or equal to a postcard size) is set in the document tray  12 , the document does not push the document sensor  17 . In this way, the document sensor  17  detects whether or not the size of the document in a width direction is greater than a predetermined threshold value. The width direction is perpendicular to a conveying direction of the document and a thickness direction of the document. 
     When the document sensor  17  detects that the size of the document in the width direction is greater than the predetermined threshold value, the cover member  5 , the path switching member  45 , and the link member  46  remain in the initial positions, and the first conveying path (shown by a two-dot-one-dash line in  FIG. 4A ) is defined in the document conveying unit  4 . 
     When the document sensor  17  detects that the size of the document in the width direction is not greater than the predetermined threshold value, the motor gear  51  is driven to rotate in the reverse direction, and the cover member  5  moves to the open position. The path switching member  45  and the link member  46  move while following the motion of the cover member  5 , and the second conveying path (shown by a two-dot-one-dash line in  FIG. 4B ) is defined in the document conveying unit  4 . 
     Subsequently, a scanning command is input to the multi-function device  1  through the operation panel  7  or remotely from a personal computer (not shown). At this time, either a single-side scanning mode or a double-side scanning mode is selectively designated. Upon receipt of the scanning command, the multi-function device  1  executes initialization of each device and then drives the motor gear  51  in the forward direction to activate the rollers of the document conveying unit  4 . At this time, the feed roller  41  feeds documents from an upstream side in a conveying direction, and the separation roller  42  separates and conveys the documents one by one toward a downstream side in the conveying direction. 
     A leading edge of the separated document abuts against the registration roller  43  such that the leading edge of the document is registered and skew of the document is corrected. The document is fed toward the downstream side in the conveying direction and passes between the first transparent portion  27  and the first document retainer  31 . When the double-side scanning mode is designated or when the single-side scanning mode by the first image sensor  21  is designated, the first image sensor  21  scans an image of the document that reaches a position facing the first image sensor  21 . 
     Specifically, the first image sensor  21  scans, at a scanning position, an image of a front side of the document by repeatedly scanning a plurality of pixels arranged on the document in a main scanning direction parallel to the front-rear direction of the multifunction device while the document moves in a sub-scanning direction parallel to the conveying direction. 
     The document having passed between the first transparent member  27  and the first document retainer  31  passes between the second transparent portion  28  and the second document retainer  32 . When the double-side scanning mode is designated or when the single-side scanning mode by the second image sensor  22  is designated, the second image sensor  22  scans an image of the document that reaches a position facing the second image sensor  22 . 
     Specifically, the second image sensor  22  scans, at a scanning position, an image of a back side of the document by repeatedly scanning a plurality of pixels arranged on the document in the main scanning direction while the document moves in the sub-scanning direction. 
     The document having passed between the second transparent portion  28  and the second document retainer  32  reaches the U-turn roller  44  and is conveyed leftward from a lower end of the U-turn roller  44 . After the document is scanned at the scanning position by the first image sensor  21  or the second image sensor  22 , the U-turn roller  44  conveys the document along the first conveying path to a first discharge portion, e.g., the upper side of the partition plates  15 , or along the second conveying path to a second discharge portion, e.g., the second opening  4 A. 
     When the first conveying path is selected (as shown in  FIG. 4A ) as the document conveying path, the path switching member  45  serves as a partition wall that defines a space on each of the right and left sides of the path switching member  45 . In this state, a concave right surface of the path switching member  45  is located along an outer circumferential surface of the U-turn roller  44  and serves as a guide surface that guides upward a leading edge of the document conveyed leftward from the lower end of the U-turn roller  44 . 
     The document is conveyed along the first conveying path while being guided upward along the guide surface and making a U-turn along the U-turn roller  44 . The document conveyed along the first conveying path is discharged onto the top of the document conveying unit  4 , i.e., the upper sides of the partition plates  15 . 
     When the second conveying path is selected (as shown in  FIG. 4B ) as the document conveying path, the path switching member  45  pivots leftward about a lower end thereof such that the right and left spaces of the path switching member  45  communicate with each other. In this state, a leading edge of the document conveyed leftward from the lower end of the U-turn roller  44  passes over an upper end of the path switching member  45 . The width of the communicating spaces in the front-rear direction may be set such that the document having a predetermined size (e.g., a postcard size) passes along the second conveying path. 
     Consequently, the document is conveyed toward the link member  46  along the second conveying path. Then, the document is discharged from the second opening  4 A formed at a left end of the document conveying unit  4  and is supported from left and below by the cover member  5  that serves as a discharge tray. A trailing edge side of the discharged document is supported by the link member  46 . As shown in  FIG. 8 , a document sensor  19  is disposed in the vicinity of the link member  46 . The document sensor  19 , which is a contact-type sensor, projects beyond an upper surface of the link member  46  through a hole formed in the link member  46  when the cover member  5  is in the open position. The document sensor  19  is pushed down by the document discharged along the link member  46  onto the cover member  5 . 
     After the document is conveyed along the second conveying path, when the document sensor  18  detects that no document to be conveyed is in the document tray  12  and when the document sensor  19  detects that no document is left on the cover member  5 , the motor gear  51  is driven to rotate in the reverse direction thereby to return the cover member  5  to the closed position. The path switching member  45  and the link member  46  are actuated to follow the motion of the cover member  5 . Consequently, the first conveying path (shown by a two-dot-one-dash line in  FIG. 4A ) is defined again in the document conveying unit  4 . Each of the document sensors  18  and  19  is an example of a document detecting unit. 
     Further, the multi-function device  1  is configured to scan a stationary document placed on the transparent portion  25 . In this case, the document conveying unit  4  is opened and a document is placed on a document holding surface, e.g., the transparent portion  25 . In this state, a scanning command is input to the multi-function device  1  through the operation panel  7  or remotely from the personal computer. 
     When a scanning command is input to the multi-function device  1 , the multi-function device  1  executes initialization of each device and then the first image sensor  2  scans an image of the document. Specifically, the first image sensor  1  scans an image of the document placed on the transparent portion  25  by repeatedly scan a plurality of pixels arranged on the document in the main scanning direction while moving in the sub-scanning direction. 
     As described above, in the multi-function device  1 , the path switching member  45  is actuated based on a type of document (whether or not the document is larger than a postcard) detected by the document sensor  17 , and moves between the first position for guiding the document along the first conveying path and the second position for guiding the document along the second conveying path. The path switching member  45  is an example of a path switching unit. The document sensor  17  is an example of a document type obtaining unit, and the document conveying unit  4  is an example of a conveying unit. 
     Thus, the conveying path suitable for the type of document can be used selectively. The first conveying path is used for a type of document which is suitable for being bent, and the second conveying path is used for a type of document which is not suitable for being bent. 
     In order to operate the path switching member  45 , the driving force for driving the path switching member  45  is transmitted from the motor  48  via the motor gear  45 . The motor  48  serves also as a driving unit for driving the document conveying mechanism (e.g., the feed roller  41 , the separation roller  42 , the registration roller  43 , and the U-turn roller  44 ). 
     Thus, there is no need to provide driving units separately for the path switching member  45  and the document conveying mechanism. As compared to the case where separate driving units are provided, the total number of driving units can be reduced, and the device size is reduced by saving the space for the driving units. Further, the manufacturing cost can be reduced because the parts cost and the assembly man-hour can be reduced in correspondence to the reduced driving units. 
     Further, in the above-described multi-function device  1 , the document sensor  17  detects a size of the document in a width direction when the document is placed on the document tray  12 , and the path switching member  45  is actuated based on the detected size which corresponds to a predetermined type of document. Thus, the path switching member  45  is actuated readily without complicated operations. 
     Although, in the above-described embodiment, the cover member  5 , the path switching member  45 , and the link member  46  move in response to each other, the cover member  5  may be configured to move independently. The cover member  5  may be manually operated to open/close, or may be motor-driven separately from the motion of the path switching member  45 . 
     In this case, the path switching member  45  may be configured not to move in response to the motion of the cover member  5 , and a mechanism configured to transmit the driving force directly to the path switching member  45  or the link member  46  may be required instead of the gear mechanism  61  for opening/closing the cover member  5 . 
     Although, in the above-described embodiment, whether to move the path switching member  45  is determined based on the document size detected by the document sensor  17 , the path switching member  45  may be configured to move irrespective of the document size. The path switching member  45  may be configured to move based on input from the operation panel  7  of, for example, a document type. 
     In the above-described embodiment, the motor gear  51  is driven to rotate in the reverse direction to return the cover member  5  to the closed position when the document sensor  18  detects no document in the document tray  12  and when the document sensor  19  detects no document on the cover member  5  after the document is conveyed along the second conveying path. Consequently, the path switching member  45  and the link member  46  move in response to the motion of the cover member  5  such that the first conveying path is defined again in the document conveying unit  4 . However, the cover member  5  may be configured to move in an opposite manner. The cover member may return to the open position. Specifically, after the document is conveyed along the first conveying path, the cover member  5  may return to the open position such that the second conveying path is defined again in the document conveying unit  4 . 
     Although, in the above-described embodiment, the image scanning device is configured to be a multi-function device, the image scanning device is not limited to a multi-function device. 
     While the invention has been described in connection with embodiments of the invention, it will be understood by those skilled in the art that variations and modifications of the embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered merely as exemplary of the invention, with the true scope of the invention being defined by the following claims.