Abstract:
An image reading apparatus includes an original carriage for carrying an original; a reading element for reading an original image with relative movement therebetween, the reading element having a configuration elongated in a direction crossing with a direction of the movement; a supporting member for supporting the image reading unit; moving means for driving the supporting member to impart the relative movement; a first positioning portion for determining a position, in the longitudinal direction, of the reading element relative to the supporting member; and a second positioning portion for determining a position of the reading element in the moving direction, the second positioning portion supporting the reading element while permitting movement thereof in the longitudinal direction relative to the supporting member.

Description:
FIELD OF THE INVENTION AND RELATED ART  
         [0001]    The present invention relates to an image reading apparatus employed in a copying machine, a facsimileing machine, a printer, or the like apparatus.  
           [0002]    It has been known that some of plain copying machines, copying machines having the copying function as well as facsimileing function, image scanners equipped with an automatic document feeder (ADF), and the like, are equipped with an image reading apparatus. As for an image reading apparatus employed by such an image forming apparatus as those described above, an image reading apparatus that is capable of scanning an original in two different methods has been proposed: method in which an original is stationarily placed on an original placement glass platen and is scanned by moving an optical reading system, and method in which an original is moved by an automatic document feeder (ADF) or the like and the moving original is scanned by a stationarily placed optical reading system.  
           [0003]    Referring to FIG. 10, such an image reading apparatus is provided with a contact type image sensor  1  (CIS), that is, an image reading means, which is disposed under the glass  2  of the image reading portion. In operation, an original D 1  is stationarily placed on the glass  2 , and is read by moving the CIS 1  in the secondary scanning direction, or an original D 2  is slid on the second glass  2   a  so that as the original D 2  is slid, it is read by the stationarily placed CIS 1 .  
           [0004]    At this time, a conventional contact type image sensor will be described regarding its structure. Referring to FIG. 11, a contact type image sensor comprises an LED  3  as a light source, and a light guiding member  4  for guiding light from the LED  3  to an original. The LED  3  is fixed to one of the lengthwise ends of the light guiding member  4  (in the case of the example in FIG. 11, one LED is attached to the front end). The light emitted from the LED  3  advances through the light guiding member  4 , while repeatedly reflected by the interface between the light guiding member  4  and the ambience, and is projected from across the entire lengthwise range of the light guiding member  11 .  
           [0005]    Referring to FIG. 11(B), the light projected from the light guiding member  4  illuminates the stationary original on the glass  2 , being reflected thereby. The reflected light is focused upon a primary photodetector array  6 , for example, a CCD or the like, through a Cellfoc lens array  5 . These structural members of the image sensor are disposed within a frame  7 .  
           [0006]    Another example of a conventional contact type image sensor has been known to comprise a pair of LED arrays, as a light source, which are made up of a plurality of aligned LEDs. The pair of LED arrays are disposed in a manner to sandwich the Cellfoc lens array.  
           [0007]    The above described prior arts, however, suffer from the following problems.  
           [0008]    Referring to FIG. 12, the frame  7  which contains the structural members of the image sensor is provided with a round positioning hole  7   a  and an elongated positioning hole  7   b . The CIS 1  is properly positioned relative to a supporting member  8  (carriage) by fitting the pair of bosses  8   a  of the carriage  8  in the these round and elongated positioning holes  7   a  and  7   b.    
           [0009]    For cost and weight reduction, the carriage  8  is formed of resinous material. Therefore, there is a possibility that the lengthwise end portions of the carriage  8  will sag as indicated with an arrow mark in FIG. 12(B), that is, the vertical direction perpendicular to the primary scanning direction.  
           [0010]    If the lengthwise end portions of the carriage  8  sag, the bosses  8   a  tilt relative to the horizontal direction; the axial line of each boss  8   a  tilts relative to the horizontal direction.  
           [0011]    If an attempt is made to attach the frame  7  to the carriage  8  when the carriage  8  is in the state described above, the round and elongated holes  7   a  and  7   b  fail to align with the pair of bosses  8   a  of the carriage  8 . Forcing the bosses  8   a  into the holes  7   a  or  7   b  possibly results in the damages to the bosses  8   a.    
           [0012]    There is also a possibility that even after the bosses  8   a  of the carriage  8  are fitted into the round and elongated holes  7   a  or  7   b , without forcing, the lengthwise end portions of the carriage  8  formed of resinous material will sag due to the warping of the carriage  8  caused by the temperature fluctuation (which occurs because the frame  7  contains a light source). It the lengthwise end portions of the carriage  8  sag due to the warping of the carriage  8 , it is possible that the bosses  8   a  will be pressed against the wall of the round hole  7   a  or elongated hole  7   b , being damaged by the reactive force applied thereto by the wall of the round hole  7   a  or elongated holes  7   b , since the configuration and positioning of the round and elongated holes  7   a  and  7   b  afford the bosses  8   a  virtually no latitude in terms of their movements.  
           [0013]    Further, it is possible that as the lengthwise end portions of the carriage  8  sag due to the warping of the carriage  8 , the positional relationship between the round positioning hole  7   a  and corresponding boss  8   a  changes, which results in the change in the moving range of the CIS 1 . The change in the moving range of the CIS 1  results in the reduction in the geometrical accuracy with which an image is formed. In other words, there is a possibility that the level of geometrical accuracy at which an image is formed will be lowered by the warping of the carriage  8 .  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention was made to solve the above described problems of the prior arts. Thus, the primary object of the present invention is to minimize the effects of the deformation of a reading member and the supporting member thereof, which occur they thermally expand, so that it becomes to possible to provide an image reading apparatus, the accuracy of which is not adversely affected by temperature.  
           [0015]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a phantom view of the image forming apparatus in the first embodiment of the present invention, as seen from the front side of the apparatus.  
         [0017]    [0017]FIG. 2 is a perspective view of the image forming apparatus in the first embodiment of the present invention.  
         [0018]    [0018]FIG. 3 is an enlarged phantom view of the image reading portion of the image forming apparatus in the first embodiment of the present invention.  
         [0019]    [0019]FIG. 4 is a drawing for showing the internal structure of the image reading portion of the image forming apparatus in the first embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is a perspective view of the image sensor unit in the first embodiment of the present invention, and shows the structure thereof.  
         [0021]    [0021]FIG. 6 is a sectional view of the image sensor unit in the first embodiment of the present invention, and shows the structure thereof.  
         [0022]    [0022]FIG. 7 is a drawing for showing the structural members of the image sensor unit in the first embodiment of the present invention: FIG. 7(A) is a plan view as seen from above, and FIG. 7(B) is a schematic drawing for showing how the frame and carriage are joined.  
         [0023]    [0023]FIG. 8 is a schematic perspective drawing of the image sensor unit in the first embodiment of the present invention, for showing the structural members thereof, and the state of the image sensor unit after the joining of the frame and carriage.  
         [0024]    [0024]FIG. 9 is a schematic perspective drawing of the image sensor unit in the second embodiment of the present invention, for showing the structural members thereof, and the state of the image sensor unit after the joining of the frame and carriage.  
         [0025]    [0025]FIG. 10 is a schematic drawing of a typical conventional image reading apparatus for an image forming apparatus, for showing the internal structure thereof.  
         [0026]    [0026]FIG. 11 is a schematic drawing for showing the structure of a typical conventional image sensor unit.  
         [0027]    [0027]FIG. 12 is a schematic drawing for showing the structure of another typical conventional image sensor unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the appended drawings.  
         [0029]    (Embodiment 1)  
         [0030]    Referring to FIGS.  1 - 8 , the image forming apparatus in the first embodiment of the present invention will be described. In this embodiment, the present invention was applied to a copying machine, or an example of an image forming apparatus. FIG. 1 is a phantom view of the copying machine in accordance with the present invention, as seen from the front side of the machine, and FIG. 2 is a perspective view of the copying machine in accordance with the present invention. FIG. 3 is an enlarged phantom view of the image reading portion of the copying machine.  
         [0031]    First, the general structure of the copying machine will be described.  
         [0032]    Referring to FIGS. 1, 2, and  3 , a referential code  101  designates the main assembly of the copying machine, and a referential code  102  designates the holding/pressing plate of an ADF (automatic document feeder). The ADF separates one by one the plurality of originals D in the form of a sheet stored in layers therein, and conveys each sheet of original D. A referential code  103  designates an image reading portion, as an image reading apparatus, which reads the surface of the original in the form of a sheet, or the surface of a given page of the original in the form of a book, on the original placement glass platen of the image reading portion, and a referential code  104  designates the main assembly of a recording apparatus which employs an electrophotographic printing method which employs an LED array. A referential code  105  designates a control panel comprising a display, a set of input keys, and the like. A referential code  106  designates an original feeding tray, and a referential code  107  designates an original placement glass platen. A referential code  108  designates a reading member, which is a contact type image sensor unit, that is, a scanning unit, and a referential code  109  designates an original placement glass platen used to read the original by moving the original, that is, without moving the image reading portion.  
         [0033]    Designated by a referential code  110  is an LED head unit, and designated by a referential code  111  is an image forming portion. Designated by a referential code  112  is a sheet feeding cassette. Designated by a referential code  113  is a sheet delivery portion, which is in the top portion of the recording apparatus main assembly  104 , and into which a plurality of the sheets p of recording medium can be discharged in a manner to be placed in layers. A referential code  114  designates a cartridge cover. A referential code  115  designates the sheet separating portion of an ADF. A referential code  116  designates an original discharge path. A referential code  117  designates an original recovery tray. A referential code  118  designates a plate for holding down a plurality of bound originals in order to read one of them. A referential code  119  designates the joint between the image reading portion  103  and recording apparatus main assembly  104 , and a referential code  120  designates the control portion of the copying machine, and a referential code  121  is an original conveyance path. A referential code  122  designates a cover for exposing the path through which a recording medium is conveyed in order to form an image on both surfaces of the recording medium, and a referential code  123  is a recording medium conveyance direction switching portion. A referential code  124  designates a recording medium registering portion, and a referential code  125  designates a sheet feeding portion, which is disposed within the recording apparatus main assembly  104  and is capable of handling a plurality of recording medium sheets different in size.  
         [0034]    First, a method for reading a certain page of an original in the form of a book will be described.  
         [0035]    The holding/pressing plate  102  of the ADF is rotationally attached to the image reading portion  103  by a pair of its hinge portions  102   a , which are located on the left and right sides, one for one, of the rear end of the apparatus (left side is unshown). The holding/pressing plate  102  can be rotated away from the image forming apparatus main assembly  104 , or rotated back onto the image forming apparatus main assembly  104 , by grasping the front side of the holding/pressing plate  102  (direction indicated by a double-headed arrow mark in FIG. 2). The hinge portion  102   a  is provided with a combination of a damper, a cam, a spring, and the like, so that the holding/pressing plate  102  of the ADF can be held at a predetermined angle (for example, 70 deg.) to allow an original to be set on the original placement glass platen  107 .  
         [0036]    The image sensor unit  108  is a unit for reading an original to obtain the data for forming an image identical to the original. More specifically, the light from the LED as a light source is guided by a light guiding member formed of resinous material or the like, and is projected onto the surface of the original from which image formation data is obtained. Then, the light reflected by the original is focused by a Cellfoc lens (commercial name) as a focusing means onto a primary sensor element array as a photoelectric transducing means; in other words, the image forming data are obtained from the original.  
         [0037]    Referring to FIG. 4, the image sensor unit  108  is movable in the left and right directions of the apparatus, following the guiding shaft  103   c . It can be moved to any point within its movable range by a combination of a driving pulley  103   b  and an unshown motor. The image sensor unit  108  is supported by the guiding shaft  103   c , with the interposition of a boxy carriage  103   a , being kept under the upward pressure generated by a spring  103   e . Disposed between the image sensor unit  108  and original placement glass platen  107  are a pair of spacers  108   a . The image sensor unit  108  is structured so that in order for the image sensor unit  108  to read the image of an original placed on the predetermined range, that is, the range from the reading starting position  107   a  to the reading ending position  107   b , of the original placement glass platen  107 , the image sensor unit  108  is movable at a constant speed across the above described predetermined range.  
         [0038]    A jump step  109   b  (sheet deflecting step) protrudes upward above the original placement glass platen  107 , and its bottom surface is covered with a white sheet  109   c  so that when the image sensor unit  108  is below the jump step  109   b , the image sensor unit  108  is rectified in terms of shading. When reading an original by moving the image sensor unit  108 , each time an original is scanned by the image sensor unit  108 , the image sensor unit  108  is rectified in terms of shading as it is moved below the jump step  109   b , past the jump step  109   b . This setup is effective to reduce the effects of the fluctuation of the output of the light source of the image sensor unit  108 , which occurs with the elapse of time.  
         [0039]    The original pressing plate  118  is formed of laminar material comprising white sheet, sponge plate, and the like. It prevents an original on the original placement glass platen  107  from lifting or floating in the air. The left and right edges  118   a  and  118   b  of the original pressing plate  118  correspond to the reading starting position  107   a  and reading ending position  107   b , of the reading range of the image sensor unit  108  when reading the original by moving the image sensor unit  108 .  
         [0040]    Next, the method for reading an original by moving the original will be described.  
         [0041]    The sheet separating portion  115  of the ADF comprises: a pickup roller  115   a  vertically movable by an unshown actuator; a separation roller  115   b ; a retardation roller  115   a  which is placed in contact with the separation roller  115   b , and is rotated in the opposite direction with respect to the rotational direction of the separation roller  115   b ; and the like.  
         [0042]    First, the original D in the form of a sheet is placed in the original feeding tray  106  so that the image to be copied faces upward. Then, the pickup roller  115   a  is pressed downward so that the original D is pushed out of the original feeding tray  106  and is fed between the separation roller  115   b  and retardation roller  115   c . If two or more originals are pushed out of the original feeding tray  106  at the same time, they are separated one by one by the separation roller  115   b  kept pressed upon the retardation roller  115   c . Then, each original is conveyed, by a reading/conveying roller  121   c  upon which separating/conveying rollers  121   a  and  121   b  are kept pressed by unshown springs, through a U-turn path, being guided by an original guide  121   d.    
         [0043]    Then, the original D is conveyed onto the glass platen  109  for reading an original by moving the original, and is conveyed further, being kept flatly pressed upon the glass platen  109  by the original pressing plate  121   e  kept under the pressure from an unshown spring. When reading an original by moving the original, the image sensor unit  108  is held at the reading point  109   a  of the glass platen  109 , and as the original D is moved past the reading point  109   a , the image formation data of the image bearing surface of the original D is read by the image sensor unit  108 .  
         [0044]    As the original D is conveyed past the reading point  109   a , it is deflected toward the original holding/pressing plate  102  of the ADF by the jump step  109   b , and then, is conveyed further by the reading/conveying roller  121   c  upon which the reading/conveying roller  121   f  is kept pressed by a spring.  
         [0045]    Then, the original D is discharged into an original recovery tray  117   c  by a discharge roller  117   b  kept pressed against the discharge roller  117   a  by a spring. On the upstream side of the discharge roller  117   b , a reading completion stamp  121   g  is disposed to make it possible to stamp a reading completion mark on the original D.  
         [0046]    The original feeding tray  106  is attached to the original holding/pressing plate  102  of the ADF, being rendered immovable relative to the original holding/pressing plate  102 . The original feeding tray  106  is fitted with a slider  106   a , which is slidable in the direction (widthwise direction of original D) perpendicular to the direction in which original D is conveyed. A plurality of the originals D in the form of a sheet, placed in layers in the original feeding tray  106 , can be vertically aligned by this slider  106   a , at their lengthwise edges. The original feeding tray  106  is also provided with an original length sensor  106   b , which is on the upwardly facing surface of the actual tray portion of the original feeding tray  106  so that the length of the original D placed in the tray portion can be detected. Further, the sheet separating portion  115  of the ADF is provided with a plurality of original width sensors  115   d , which are distributed in the widthwise direction of the original D, so that the width, as well as presence or absence, of the original D can be detected. The size and orientation of the original D can be detected by the combined outputs of the original width sensors  115   d  and original length sensor  106   b.    
         [0047]    The original conveyance path  121  is provided with an original conveyance sensor  121   h  and an original edge sensor  121   i . The original conveyance sensor  121   h  detects whether or not the original D has been released from the separating portion  115  of the ADF, and whether or not the trailing edge of the original D has passed. The original edge sensor  121   i  detects the passages of the leading and trailing edges of the original D, and its outputs are used to control the reading timing.  
         [0048]    As described above, the structure of the image sensor unit  108  in accordance with the present invention is such that in order to read the image of an original, light is projected onto the original so that the light reflected by the original is focused upon a sensor through an focusing optical system.  
         [0049]    [0049]FIG. 5 shows the concrete structure of the image sensor unit  108  in this embodiment. The image sensor unit  108  comprises: a pair of LEDs  10 , that is, light emitting elements as a light source; a pair of light guiding members  11  for guiding the light emitted by the LEDs  10 , to an original; a Cellfoc lens array  12  as a focusing optical system; and a sensor  13  as a light receiving element. The pair of the light guiding member  11  are disposed in a manner to sandwich the Cellfoc lens array  12 . The sensor  13  is located directly below the Cellfoc lens array  12 . The structural members of the image sensor are disposed, as light source unit components, within a frame  14  (boxy shell).  
         [0050]    The LED  10  is fixed to one of the lengthwise ends of each light guiding member  11 . In the case of the image sensor unit  108  shown in the drawing, two LEDs  10  are fixed to the pair of the light guiding members  11 ; one LED  10  is fixed to one of the lengthwise ends of one of the light guiding members  11 , and the other LED  10  is fixed to the opposite lengthwise end of the other light guiding member  11 . In other words, the two light guiding members  11  and two LEDs  10  are symmetrical disposed with respect to an axial line C in the drawing.  
         [0051]    The light emitted from each LED  10  advances through the light guiding member  11 , and is projected from across the entire length of the light guiding member  11  while being repeatedly reflected by the interface between the light guiding member  11  and the ambience. Referring to FIG. 6, the light projected from the light guiding member  11  illuminates the original in the form of a book on the original placement glass platen  107 , being reflected thereby. The reflected light is focused upon the sensor  13 , through Cellfoc lens array  12 .  
         [0052]    At this time, the characteristic features of the structure of the image reading apparatus in accordance with the present invention will be described. FIG. 7(A) is a schematic plan view of the frame  14  as seen from above, and FIG. 7(B) is a schematic drawing for showing how the frame  14  of the reading member and the supporting member  103   d  (carriage) are joined. FIG. 8 is a schematic drawing for showing the frame  14  and carriage  103   d  after the joining of the frame and carriage.  
         [0053]    The frame  14  in which the structural members of the image sensor unit  108  is provided with a pair of elongated holes  15  and  16 , which are located in the lengthwise end portions of the frame  14 . The holes  15  and  16  are the portions for properly positioning the frame  14  relative to the carriage  103   d  in terms of the secondary scanning direction. The frame  14  is also provided with a positioning portion  17  for properly positioning the frame  14  relative to the carriage  103   d  in terms of the primary scanning direction. The positioning portion  17  is located approximately between the elongated holes  15  and  16 .  
         [0054]    The carriage  103   d  is provided with a pair of bosses  18  and  19 , which are located on the lengthwise end portions of the carriage  103   d . The carriage  103   d  is also provided with a boss  20 , which is located approximately at the center of the carriage  103   d . The configurations of the elongated holes  15  and  16  and positioning portion  17  are such that after the engagement of the bosses  18 ,  19 , and  20  with the corresponding elongated holes  15  and  16 , and the positioning portion  17 , the frame  14  is prevented, by the bosses  18  and  19 , from moving in the secondary scanning direction (short axis direction), while being afforded some degree of latitude in terms of the movement in the primary scanning direction (lengthwise direction), and is prevented, by the boss  20 , from moving in the primary scanning direction (lengthwise direction), while being afforded some degree of latitude in terms of the movement in the secondary scanning direction (short axis direction). In other words, the frame  14  is held to the carriage  103   d , being allowed to move (frame  14  is kept under the upward pressure from a spring  103   e ) only vertically, being guided by the bosses  18 ,  19 , and  20 .  
         [0055]    With the provision of the above described structural arrangement, even if the carriage  103   d , which is formed of resinous material for weight and cost reduction, sags at the lengthwise ends, and the sagging causes the bosses  18  and  19  located on the lengthwise (primary scanning direction) ends of the carriage  103   d  to tilt in the lengthwise direction of the carriage  103   d , the elongated holes  15  and  16 , in which the bosses  18  and  19  fit one for one, afford the bosses  18  and  19  a certain degree of latitude in terms of their movement in the lengthwise direction of the carriage  103   d ; in other words, the elongated holes  15  and  16  allow the bosses  18  and  19  to tilt a certain angle in the lengthwise direction of the carriage  103   d . Therefore, the bosses  18  and  19  are not damaged by the sagging of the lengthwise end portions of the carriage  103   d  which occurs due to the warping of the carriage  103   d.    
         [0056]    Further, the positioning portion  17  for positioning the frame  14  relative to the carriage  103   d  in terms of the primary scanning direction is prevented from moving in the primary scanning direction (lengthwise direction), by the boss  20  located approximately at the center of the carriage  103   d  in terms of the lengthwise direction. Therefore, the amount by which the frame  14 , or the image sensor unit  108 , is displaced in terms of the primary scanning direction (lengthwise direction) by the sagging of the lengthwise end portions of the carriage  103   d  caused by the warping of the carriage  103   d , can be minimized to improve the level of geometric accuracy at which an image is formed. In other words, the present invention makes it possible to prevent the vertical warping of the carriage  103   d  from reducing the level of quality at which an image is formed.  
         [0057]    Further, the frame  14  is prevented, by the elongated holes  15  and  16  and the bosses  18  and  19 , from moving in the secondary scanning direction, while being afforded some degree of latitude in terms of the movement in the primary scanning direction (lengthwise direction), and is prevented, by the positioning portion  17  and the boss  20 , from moving in the primary scanning direction (lengthwise direction), while being afforded some degree of latitude in terms of the movement in the secondary scanning direction. Also, the frame  14  is kept pressed upward upon the glass surface by the spring  103   e . Therefore, even if the carriage  103   d  warps in the vertical direction, the frame  14 , or the image sensor unit  108  is not displaced in the primary (lengthwise) or secondary scanning direction. Therefore, the level of quality at which an image is formed does not reduce. In other words, the present invention can improve the level of geometric accuracy at which an image is formed.  
         [0058]    (Embodiment 2)  
         [0059]    [0059]FIG. 9 shows the second embodiment of the present invention. In the drawing, the structural members similar to those in the first embodiment are given the same referential codes as those in the first embodiment, and their descriptions will not be given here.  
         [0060]    In the above described first embodiment of the present invention, the boss  20  for preventing, in cooperation with the positioning portion  17 , the frame  14  from moving in the primary scanning direction (lengthwise direction), while affording some latitude in terms of the movement in the secondary scanning direction, was located approximately at the center of the carriage  103   d  in terms of the lengthwise direction. In comparison, in this second embodiment, a bearing member  40  which allows the carriage  30  to smoothly move following the guiding shaft  103   c  is provided with a boss  41 , which prevents, in cooperation with the positioning portion  17 , the frame  14  from moving in the primary scanning direction (lengthwise direction) while affording some latitude in terms of the movement in the secondary direction.  
         [0061]    To describe the characteristic features of the structure of the image sensor unit in this embodiment, the frame  14  which contains the structural members of the image sensor is provided with two elongated holes  15  and  16  as portions for fixing the position of the frame  14  relative to the carriage  30  in terms of the secondary scanning direction, and a a positioning portion  17  for fixing the position of the frame  14  relative to the carriage  30  in terms of the primary scanning direction. The elongated holes  15  and  16  are located at the lengthwise end portions of the frame  14 , one for one, and the positioning portion  17  is located between the elongated holes  15  and  16  in terms of the lengthwise direction of the frame  14 .  
         [0062]    The carriage  30  is provided with a pair of bosses  31  and  32 , which are located on the lengthwise end portions of the carriage  30 . The bearing member  40  is provided with a boss  41 , which is located approximately at the center of the carriage  30  in terms of the lengthwise direction. The configurations of the elongated holes  15  and  16  and positioning portion  17  are such that after the engagement of the bosses  31 ,  32 , and  41  with the corresponding elongated holes  15  and  16 , and the positioning portion  17 , the frame  14  is prevented, by the bosses  31  and  32 , from moving in the secondary scanning direction (short axis direction), while being afforded some degree of latitude in terms of the movement in the primary scanning direction (lengthwise direction), and is prevented, by the boss  41 , from moving in the primary scanning direction (lengthwise direction), while being afforded some degree of latitude in terms of the movement in the secondary scanning direction (short axis direction). In other words, the frame  14  is held to the carriage  30 , being allowed to move (frame  14  is kept under the upward pressure from a spring  103   e ) only vertically, being guided by the bosses  31 ,  32 , and  41 .  
         [0063]    With the provision of the above described structural arrangement, even if the carriage  30 , which is formed of resinous material for weight and cost reduction, sags at the lengthwise ends, and the sagging causes the bosses  31  and  32  located on the lengthwise (primary scanning direction) ends of the carriage  30  to tilt in the lengthwise direction of the carriage  30 , the elongated holes  15  and  16 , in which the bosses  31  and  32  fit one for one, afford the bosses  31  and  32  a certain degree of latitude in terms of their movement in the lengthwise direction of the carriage  30 ; in other words, the elongated holes  15  and  16  allow the bosses  31  and  32  to tilt a certain angle in the lengthwise direction of the carriage  30 . Therefore, the bosses  31  and  32  are not damaged by the sagging of the lengthwise end portions of the carriage  30  which occurs due to the warping of the carriage  30 .  
         [0064]    Further, in this embodiment, the positioning portion  17  for positioning the frame  14  relative to the carriage  30  in terms of the primary scanning direction is prevented from moving in the primary scanning direction (lengthwise direction), by the boss  41  provided on the bearing member  40 . Therefore, the number of the positioning related components interposed between the guiding shaft  103   c  and the frame  14  in this embodiment is smaller than that in the first embodiment, improving the level of accuracy at which the position of the frame  14 , in other words, the image sensor unit  108 , relative to the carriage  30  in terms of the primary scanning direction (lengthwise direction) is fixed.  
         [0065]    Further, the boss  41  is located approximately at the center of the carriage  30  in terms of the lengthwise direction. Therefore, the amount by which the frame  14 , in other words, the image sensor unit  108 , is displaced in terms of the primary scanning direction (lengthwise direction) by the sagging of the lengthwise end portions of the carriage  30  caused by the vertical warping of the carriage  30 , is minimized, which in turn minimizes the decrease in the geometric accuracy at which an image is formed. In other words, the present invention can prevent the vertical warping of the carriage  30  from reducing the level of quality at which an image is formed.  
         [0066]    Further, the frame  14  is prevented, by the elongated holes  15  and  16  and the bosses  31  and  32 , from moving in the secondary scanning direction, while being afforded some degree of latitude in terms of the movement in the primary scanning direction (lengthwise direction), and is prevented, by the positioning portion  17  and the boss  41 , from moving in the primary scanning direction (lengthwise direction), while being afforded some degree of latitude in terms of the movement in the secondary scanning direction. Also, the frame  14  is kept pressed upward upon the glass surface by the spring  103   e . Therefore, even if the carriage  30  warps in the vertical direction, the frame  14 , in other words, the image sensor unit  108 , is not displaced in the primary (lengthwise) or secondary scanning direction. Therefore, the level of quality at which an image is formed does not reduce. In other words, the provision of the above described structural arrangement can provide a higher level of geometric accuracy at which an image is formed; it can prevent the vertical warping of the carriage  30  from reducing the level of quality at which an image is formed.  
         [0067]    To sum up, the problems caused by the vertical warping of the carriage  103   d  or  30  can be prevented by the provision of the following structural arrangement: the frame  14  is provided with two elongated holes for regulating the position of the frame  14  relative to the carriage  103   d  or  30  in terms of the secondary scanning direction while affording the frame  14  some degree of latitude in its movement in the primary scanning direction, and a positioning portion for regulating the position of the frame  14  relative to the carriage  103   d  or  30  in terms of the primary scanning direction while affording the frame  14  some degree of latitude in terms of its movement in the secondary scanning direction; and the positioning portion is located between the two elongated hole in terms of the lengthwise direction of the carriage  14 .  
         [0068]    In the above described embodiments, the structural members of the image sensor were contained in the frame  14 . However, the present invention for preventing the problems traceable to the vertical warping of the carriage caused by the temperature fluctuation caused by the heat from a light source is applicable to any image sensor unit, the frame of which comprises: a light source; a linear illuminating means which extends in the primary scanning direction to linearly illuminate an original; and the like.  
         [0069]    Also in the above described embodiments, the frame was provided with the holes, and the carriage was provided with bosses. However, the bosses and holes may be provided on the frame and carriage sides, respectively.  
         [0070]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes, regarding the measurements, materials, configurations, positional relationship, and the like, of the structural members, as may come within the purposes of the improvements or the scope of the following claims.