Abstract:
An original reading unit has first and second arrays of sensor assemblies extending in a main scanning direction for performing readings of an original document. Each of the sensor assemblies includes a sensor holder that undergoes pivotal movement about a single rotation center as a fulcrum along a wall of a unit base to bring the sensor holder to a predetermined position whereat the sensor holder can be fixed to the units base wall. A line sensor is mounted relative to the sensor holder so as not to be shifted in the main scanning direction or in a sub-scanning direction, and to undergo movement in an approaching or a separating direction so as to be brought into contact with or separated from, respectively, the unit base wall and an original support plate attached to the unit base. A focus setup unit moves the line sensor in the approaching or separating direction and positions the line sensor at a location whereat focus can be adjusted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an original reading unit that employs line sensors to read image information from an original document (hereinafter “original”), an image scanner that includes the original reading unit and externally outputs the image information obtained by the original reading unit, and an image forming apparatus, such as a copier or a facsimile machine, that includes the original reading unit and that copies the image information obtained by the original reading unit. 
     2. Related Background Art 
     For a copier, an original reading apparatus is well known wherein multiple line sensors are arranged in a zigzag pattern to extend a first array and a second array in the main scanning direction, and an original that is first read by the line sensors of the first array, is then sequentially read by the line sensors of the second array, which is shifted, relative to the first array, in the sub-scanning direction (see, for example, Japanese Unexamined Patent Publication No. Sho 60-31357 (page 1, right column, last line to page 2, upper left column, line 12; page 2, lower left column, line 16 to page 3, upper right column, last line; and  FIGS. 1(   a ) and  1 ( b ))). 
     According to the configuration wherein the first array and the second array are shifted relative to each other in the sub-scanning direction, the individual line sensors in these arrays must be arranged in parallel, and the focal distances of the line sensors must be the same. In order to arrange the line sensors in parallel, the positions of the line sensors should be adjusted in the main scanning direction (X direction) and in the sub-scanning direction (Y direction), relative to a base, such as a substrate, on which the line sensors are to be mounted. Further, in order to control the focusing, the positions of the line sensors should also be adjusted in the direction (the Z direction) in which the line sensors are brought into contact with or are separated from the face of the original. 
     However, the arrangement wherein the adjustment of the parallel arrangement of the line sensors is enabled and the arrangement wherein the adjustment of the focusing of the line sensors is enabled are not described in Japanese Unexamined Patent Publication No. Sho 60-31357 described above. 
     Commonly, for the adjustments in the X, Y and Z directions, multiple adjustment screws are employed to individually move the line sensors, while accurate jigs must be employed to position them. During this adjustment operation, however, a procedure is required for repetitively moving the longitudinal positions of the ends of each line sensor both in the X and in the Y directions, and after the adjustments in the X and the Y directions have been completed, the longitudinal positions of the ends of each line sensor must be adjusted. As described above, since for such adjustments many procedures must be performed, a great deal of labor is required, and there is a demand for an improvement in this process. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to provide an original reading unit that can provide improved efficiency for the adjustment of the individual line sensors, and an image forming apparatus and an image scanner that employ the original reading unit. 
     According to one aspect of the present invention, an original reading unit, as a prerequisite, comprises: 
     a unit base; 
     a transparent original support plate attached to the unit base; and 
     multiple sensor assemblies arranged, in a zigzag pattern, to form on the unit base a first array, extended in a main scanning direction, for performing the first reading of an original, and a second array, also extended in the main scanning direction, for reading the original following the first array. 
     In order to achieve the above described objective, each of the sensor assemblies includes: 
     a sensor holder, which, as a fulcrum, can be pivoted at a single rotation center, along a wall of the unit base, to a predetermined position and fixed to the wall; 
     a line sensor, which is held, relative to the sensor, so as not to be shifted in the main scanning direction or in the sub-scanning direction and which is movable, in an approaching or a separating direction, so as to be brought into contact with and separated from the wall and the original support plate; and 
     a focus setup unit, which moves the line sensor in the approaching or separating direction and which positions the line sensor at a location whereat focus can be adjusted. 
     According to this invention, the unit base is defined as a member to which the original support plate is attached and on which multiple sensor assemblies are arranged to form a zigzag pattern. The original support plate is a transparent plate that the copy face of an original contacts. For this, a glass plate is appropriate but a transparent synthetic resin plate, such as an acrylic board, can also be employed. According to this invention, a single rotation center, around which the sensor holder is pivoted, is located at the center, so that the parallel positioning of the line sensors can be adjusted. The position of the rotation center relative to the sensor holder is arbitrary, and the rotation center can, for example, be provided in the longitudinal center portion of the sensor holder. The rotation center can also be formed by employing an axle, projecting outward from one wall of the unit base or one side of the sensor assemblies, and a bearing, such as a hole or a notch, that is formed in the other side and engages the axle. Further, the axle may be integrally formed with the wall of the unit base or the sensor assembly, or may be a separate part. In addition, according to this invention, the main scanning direction is the direction in which scanning is performed by the line sensors, the sub-scanning direction is the direction in which the original is fed, and the approaching or separating direction is that in which the line sensors are brought into contact with or separated from the wall and the original support plate, and is perpendicular to the main scanning direction and the sub-scanning direction. Furthermore, the predetermined position is a position such that the sensor holder, which holds the line sensors, is rotated to adjust the positioning of the line sensors and so locate them that they are parallel. Further, in this invention, although screws may be employed as positioning means, urging members are more preferable, and springs, for example, or more appropriately, coil springs are employed. 
     According to the invention, the line sensors are held by the sensor holders so that they do not move in the main scanning direction or the sub-scanning direction, and the sensor holder is rotated, as a fulcrum, at the single rotation center and is fixed in a predetermined location. In this manner, the positions of the line sensors can be adjusted simultaneously, both in the main scanning direction and in the sub-scanning direction. In this case, a procedure for delicately adjusting the two longitudinal ends of each line sensor is not required. In addition, by using the focus setup unit, the line sensors can be moved in the approaching or separating direction to adjust the focuses. 
     According to another preferred aspect of the original reading unit of the invention, a first urging member that pushes a line sensor from one longitudinal end in the main scanning direction and a second urging member that pushes the line sensor in the sub-scanning direction are employed to hold the line sensor, relative to the sensor holder, so that it can not to be moved in the main scanning direction and the sub-scanning direction. For this aspect, a leaf spring, a coil spring, a porous flexible sponge member or a non-porous rubber member can be employed for the first and the second urging members. According to this aspect, regardless of the dimensional tolerances of parts such as the line sensors and the sensor holder, the line sensors can be held by the urging forces of the first and the second urging members, so as not to be moved relative to the sensor holder in the main scanning direction and the sub-scanning direction. This is preferable because then, the adjustment procedure for holding the line sensors is not especially required. 
     According to another preferred aspect of the original reading unit of the invention, at least part of the rotation center is located in a projection area for the line sensors, relative to the wall. This aspect is preferable because the range of an angle whereat the sensor holder is rotated can be reduced, making it possible to adjust the positions of the line sensors in both the main scanning direction and the sub-scanning direction. 
     According to an additional preferred aspect of the original reading unit, the rotation center is located immediately under, or in the vicinity of, a light-receiving device, the first that is read among an array of light-receiving devices for the line sensors. This aspect is preferable because the range of an angle whereat the sensor holder is rotated can be reduced, making it possible to adjust the positions of the line sensors in both the main scanning direction and the sub-scanning direction. 
     According to a further aspect of the original reading unit of the invention, the focus setup unit includes: 
     pressing members, for moving the line sensors toward the original support plate; and 
     spacers, which are sandwiched between the line sensors and the original plate support to define focal distances for the line sensors. According to this aspect, with the spacer sandwiched between the line sensors and the original support plate, the line sensors are moved and pressed toward the original support plate by the pressing member, so that the focal distances of the line sensors can be defined by the spacer and their focuses can be adjusted. 
     According to one more aspect of the original reading unit of the invention, an urging member is employed as the pressing member. A leaf spring, a coil spring, a porous flexible sponge member or a non-porous flexible rubber member can be employed as the urging member. This aspect is preferable because the positions of the line sensors, in the direction of the thickness of the original support plate, can be automatically designated by the urging force exerted by the urging member, without requiring the employment of a procedure for delicately adjusting the two longitudinal ends of each line sensor. 
     According to yet another aspect of the original reading unit of the invention, a first support member that includes a guide portion, for guiding the line sensors that move in the approaching or separating direction, and for regulating the movement of the line sensors in the sub-scanning direction, and a stopper portion, for regulating the movement of the line sensors in the main scanning direction, is attached to one longitudinal end of the sensor holder; a second support member, which includes a guide portion for guiding the line sensors that move in the approaching or separating direction and for regulating the movement of the line sensors in the sub-scanning direction, is attached to the other longitudinal end of the sensor holder; fitting portions, which are slidably fitted into the guide portions of the first and second support members, and an engagement portion, which abuts upon the stopper portion, are formed for the line sensors; first urging members are attached to the first support portion to apply an urging force, in the main scanning direction, to the line sensors, thereby causing the engagement portion to abut upon the stopper portion, and second urging members are sandwiched between the sensor holder and the line sensors to apply an urging force, in the sub-scanning direction, to the line sensors; and pressing members, which are formed of the first and second urging members, are sandwiched between the first and second support members and the line sensors; the spacers, which define the focal distances of the line sensors, are sandwiched between the line sensors and the original support plates. 
     According to this aspect, the first and the second urging members are employed to hold the line sensors, so that they do not move, relative to the sensor holder, either in the main scanning direction or in the sub-scanning direction. When the sensor holder is pivoted, as a fulcrum, at the single rotation center and is fixed in the predetermined position, the positions of the line sensors can be adjusted in the main scanning direction and the sub-scanning direction. In this case, the procedure for delicately adjusting the two longitudinal ends of each line sensor need not be repeatedly performed. Furthermore, by using the pressing members, formed of the urging members and the spacer, the focuses of the line sensors can be automatically adjusted by moving the line sensors in the approaching or separating direction. Also, in this case, the procedure for delicately adjusting the two longitudinal ends of each line sensor need not be performed repeatedly. 
     In addition, in order to achieve the above described objective, an image forming apparatus according to the present invention comprises an original reader that includes an original reading unit according to one of the above described aspects. Therefore, according to this invention, an image forming apparatus can be provided that includes an original reading unit, which can increase the efficiency with which line sensor adjustments are performed. 
     Also, to achieve the above described objective, an image scanner according to the invention comprises an original reader that includes an original reading unit according to one of the above described aspects. Therefore, according to this invention, an image scanner can be provided that includes an original reading unit, which can increase the efficiency with which line sensor adjustments are performed. 
     According to the present invention, when the individual sensor assemblies are rotated, as a fulcrum, around the rotation center, the positions of the sensor assemblies can be adjusted relative to the main scanning direction and the sub-scanning direction of the line sensors, the focuses of which are set by the focus setup unit. Therefore, an original reading unit can be provided that can increase the efficiency with which line sensor adjustments are performed. 
     According to the present invention, an image forming apparatus can be provided wherein the original reader includes an original reading unit, which can increase the efficiency with which the adjustment of the line sensors is performed. 
     Further, according to the present invention, an image scanner can be provided wherein the original reader includes an original reading unit, which can also increase the efficiency with which the adjustment of the line sensors is performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic plan view of the concept of an original reading unit according to one embodiment of the present invention; 
         FIG. 1B  is a schematic cross-sectional view of the concept of the original reading unit in  FIG. 1A ; 
         FIG. 2  is a schematic side view of a copier comprising an original reader that includes the original reading unit according to the embodiment of the invention; 
         FIG. 3  is a partially cutaway plan view of the original reading unit according to the embodiment; 
         FIG. 4  is an exploded perspective view of the original reading unit in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of the original reading unit taken along line F 5 -F 5  in  FIG. 3 ; 
         FIG. 6  is a diagram showing the holding mechanism of the sensor holder relative to the unit base in the original reading unit in  FIG. 3 ; 
         FIG. 7  is a bottom view of the unit base of the original reading unit in  FIG. 3 ; 
         FIG. 8  is a perspective view of a sensor assembly provided for the original reading unit; 
         FIG. 9  is an exploded perspective view of the sensor assembly in  FIG. 8 ; 
         FIG. 10  is a plan view of the sensor assembly in  FIG. 8 ; 
         FIG. 11  is a bottom view of the sensor assembly in  FIG. 8 ; 
         FIG. 12  is a diagram showing the sensor assembly viewed in the direction indicated by an arrow F 12  in  FIG. 10 ; 
         FIG. 13  is a right side view of the sensor assembly in  FIG. 8 ; 
         FIG. 14  is a left side view of the sensor assembly in  FIG. 8 ; 
         FIG. 15  is a perspective view of an adjustment apparatus for the original reading unit in  FIG. 3 ; 
         FIG. 16  is a perspective view of the state wherein the original reading unit in  FIG. 3  is set into the adjustment apparatus in  FIG. 15 ; 
         FIG. 17  is a schematic plan view of an adjustment jig prepared for use by the adjustment apparatus in  FIG. 15 ; 
         FIG. 18  is a side view of the distal end of the adjustment pin of the adjustment jig in  FIG. 17 ; and 
         FIG. 19  is a schematic side view of an image scanner comprising an original reader that includes the original reading unit according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention will now be described while referring to the accompanying drawings. 
     In  FIG. 2 , an image forming apparatus  1  is, for example, an electrographic copier, and comprises: a base  2  having multiple wheels  2   a ; a paper supply section  3  mounted on the base  2 ; an image forming section  4  installed on the paper supply section  3 ; and an original reading section  5  installed on the image forming section  4 . 
     The paper supply section  3  includes multiple paper trays  3   a  wherein paper supply rollers  6  are provided. As each paper supply roller  6  is rotated, paper sheets stored in the corresponding paper tray  3   a  are fed one by one to the image forming section  4 , as indicated by a chain double-dashed arrow A in  FIG. 2 , and the sheet is passed through the image forming section  4  and is discharged to the front of the copier  1 . A path indicated by an arrow B in  FIG. 2  represents the path along which a sheet manually supplied from the front of the copier  1  is conveyed. The manually fed sheet reaches the middle of the convey path extending from the paper tray  3   a , and is thereafter passed through the image forming section  4 . 
     The image forming section  4  includes an image forming unit  4   a  through which the sheet is passed. The image forming unit  4   a  records an image on the sheet based on digital data, for the image of the original, that is output by the image reading section  5 . 
     In the image reading section  5 , an original reading unit  8  is attached to an original table  7 , and an original table cover  9  is also attached thereto that can be closed to cover the top face of the original reading unit  8 . As indicated by an arrow C in  FIG. 2 , an original containing an image is supplied to the original reading section  5  from the front of the copier  1 , is passed between the original reading unit  8  and the original table cover  9 , and is discharged to the rear of the copier  1 . The original reading unit  8  photoelectrically reads the original image, and outputs the image as digital data to the image forming unit  4   a.    
     As shown in  FIGS. 1A ,  1 B and  3  to  5 , the original reading unit  8 , which serves as a close-contact image sensor, includes: a unit base  11 , an original support plate  25  and multiple sensor assemblies  31 , e.g., five sensor assemblies  31 . 
     As shown in  FIG. 4 , the unit base  11  is formed of a main base member  12  composed, for example, of an aluminum alloy die material, and a pair of base end members  13  formed of sheet metal. The main base member  12  is shaped like a thin, elongated groove, wherein side walls  12   b  and  12   c  are bent upright on both sides of a wall  12   a , the bottom wall, and wherein the inner side surfaces are flat. The pair of base end members  13  are attached to the main base member  12 , closing the openings at the two longitudinal ends, by using self-tapping screws that are fitted into the main base member  12 . Support plate fitting portions  13   a  are formed on the upper side faces of the base end members  13 . 
     As shown in  FIGS. 4 and 7 , three sets, for example, of paired bearing holes  15  and pin through holes  16  are formed, in the wall  12   a  near the side wall  12   b . The bearing hole  15  and the pin through hole  16  in each of the sets are arranged at a predetermined distance L in the longitudinal direction of the unit base  11 . A line connecting one set of one bearing hole  15  and one pin through hole  16  is extended in the longitudinal direction of the unit base  11 , and the two other sets are positioned along an extension of the line. Similarly, two sets, for example, of paired bearing holes  15  and pin through holes  16  are formed in the wall  12   a  near the other side wall  12   c . The bearing hole  15  and the pin through hole  16  in each of the two sets are also arranged at the predetermined distance L in the longitudinal direction of the unit base  11 . A line connecting one set of one bearing hole  15  and one pin through hole  16  is extended in the longitudinal direction of the unit base  12 , and the other set is positioned along an extension of the line. 
     Further, in  FIG. 7 , the leftmost pin through hole  16  located near the side wall  12   c  is substantially at the same position, in the longitudinal direction of the unit base  11 , as the leftmost bearing hole  15  near the side wall  12   b.  Also, in  FIG. 7 , the leftmost bearing hole  15  located near the side wall  12   c  is substantially at the same position, in the longitudinal direction of the unit base  11 , as the middle pin through hole  16  located near the side wall  12   b.  Similarly, in  FIG. 7 , the rightmost pin hole  16  located near the side wall  12   c  is substantially at the same position, in the longitudinal direction of the unit base  11 , as the middle bearing hole  15  located near the side wall  12   b . Furthermore, in  FIG. 7 , the rightmost bearing hole  15  located near the side wall  12   c  is substantially at the same position, in the longitudinal direction of the unit base  11 , as the rightmost pin through hole  16  located near the side wall  12   b . That is, the five sets of bearing holes  15  and pin through holes  16  are arranged so that they form a zigzag pattern. 
     Multiple clearance holes  17 , for providing clearance for screws, and multiple fastening holes are formed in the wall  12   a . In  FIG. 4 , screws are to be used to secure a substrate support frame  19  to the reverse surface of the wall  12   a , and to secure a print circuit board  20  to the substrate support frame  19 . Mounted on the print circuit board  20  are various electronic parts (not shown) that constitute reading circuits for reading digital image data from the image reading section  8 , and other circuits for appropriately processing the digital image data and outputting the results to the image forming unit  4   a.    
     The original support plate  25  is formed of a flat, transparent plate, such as a transparent glass plate. The two longitudinal ends of the original support plate  25  are fitted into the paired support plate fitting portions  13   a , provided for the base end members  13 , to close the upper opening of the main base member  12 , and are fixed in place by attachment members  26  shown in  FIGS. 3 to 5 . Pressing portions overlap the upper face at the longitudinal ends of the original support plate  25 , and fixing portions, bent downward from the pressing portions, overlap the external faces of the base end members  13 . The final attachment of the original support plate  25  to the main base member  12  is accomplished by using screws to fasten the fixing portions to the base end members  13 . The inner side surface of the thus secured original support plate  25  is parallel to the inner side surface of the wall  12   a  of the main base member  12 . 
     As shown in  FIGS. 1A ,  3  and  4 , for example, five sensor assemblies  31  are employed, and as shown in  FIGS. 8 to 14 , each includes a sensor holder  32 , a line sensor  51 , a focus setup unit  64 , a first leaf spring  61 , as a first urging member, and a second leaf spring  62 , as a second urging member. 
     As shown in  FIG. 9 , the sensor holder  32  includes a main holder member  33 , a first support member  41  and a second support member  46 . 
     The main holder member  33  is made, for example, of sheet metal, and includes a rectangular base piece  33   a  and a spring sheet piece  33   b  that is obtained by bending one side edge of the base piece  33   a  upward. As shown in  FIG. 11 , a shaft insertion portion  34  that is, for example, a U-shaped notched groove is formed in one longitudinal end of the base piece  33   a . This shaft insertion portion  34  may also be a hole. An elongated adjustment hole  35  is formed in the other longitudinal end of the base piece  33   a , and the line of apsis of the adjustment hole  35  is extended in the longitudinal direction of the base piece  33   a . A distance M, between the center of the adjustment hole  35  and the center of the shaft insertion portion  34 , is set equal to the predetermined distance L described above. Further, multiple fastening holes  36  are formed in the base piece  33   a.    
     The first support member  41  is, for example, a synthetic resin member fixed, using a screw (not shown), to the upper face of one longitudinal end of the base piece  33   a  in which the shaft insertion portion  34  is formed. As shown in  FIGS. 9 and 13 , the first support member  41  has a guide portion  43  and a stopper portion  44  that are positioned along the spring sheet piece  33   b.    
     The guide portion  43  guides the line sensor  51  in the direction in which it approaches the wall  12   a  and the original support plate  25 , or is separated therefrom, and also regulates the movements of the line sensor  51  in the sub-scanning direction. Therefore, the guide portion  43  is, for example, a vertically extended hole. It should be noted that the guide portion may be a groove having the same shape as the vertically elongated hole. When a fitting portion, which will be described later, is a vertically elongated hole, or a groove having the same shape as such an elongated hole, the guide portion  43  may be a shaft projected in the longitudinal direction of the base piece  33   a . The stopper portion  44  is an upward protrusion, as shown in  FIGS. 8 and 9 . 
     A pivot  45  is integrally formed and projects downward from the reverse surface of the first support member  41 . As shown in  FIGS. 11 to 14 , the pivot  45  has a tapered shape and includes multiple slots, so that it can be flexibly compressed in the direction of the diameter. The pivot  45  is passed through the shaft insertion portion  34  and tightly inserted into a bearing hole  15  of the unit base  11 , and serves as the single rotation center relative to the sensor assembly  31 . As shown in  FIG. 10 , the pivot  45  is located immediately under, or in the vicinity of, the light receiving device that is the first read in a light receiving device array for the line sensor  51 , which will be described later, while at least part of the pivot  45  is positioned in an area for projection to the wall  12   a.    
     The second support member  46  is, for example, a synthetic resin member, and is fixed, by a screw (not shown), to the upper face of the other longitudinal end of the base piece  33   a  at a position between the adjustment hole  35  and the fastening hole  36 , but nearer the adjustment hole  35 . As shown in  FIG. 8 , the second support member  46  has a guide portion  48  located along the spring sheet piece  33   b.    
     The guide portion  48  guides the line sensor  51  in the direction in which the line sensor  51  approaches the wall  12   a  and the original support plate  25  or is separated from them, and, regulates the movement of the line sensor  51  in the sub-scanning direction. The guide portion  48  has the same structure as the guide portion  43  of the first support member  41 , i.e., is a vertically elongated hole. The guide portion  48  may also be a groove having the same shape as such an elongated hole. When a fitting portion, which will be described later, is a vertically elongated hole, or a groove having the same shape as such an elongated hole, the guide portion  48  may be a shaft projected in the longitudinal direction of the base piece  33   a.    
     As shown in  FIG. 5 , the line sensor  51  is structured by uniformly exposing a sensor element  51   b  to the upper face of a sensor insulator  51   a  made of a synthetic resin. An input/output terminal (not shown), for example, is provided for the reverse face of the sensor insulator  51   a.  The sensor element  51   b  includes an array of multiple photo-electric conversion devices (not shown) arranged in the main scanning direction. 
     As shown in  FIG. 9 , fitting portions  52  and  53  are respectively provided at one longitudinal end and the other longitudinal end of the sensor insulator  51   a . The fitting portions  52  and  53  are shaft portions that are extended, for example, in the longitudinal direction of the sensor insulator  51   a  and are projected in the same direction. Further, at one longitudinal end of the sensor insulator  51   a , an engagement portion  54   a  is located in the vicinity of the fitting portion  52 . The engagement portion  54  is, for example, a recessed portion. When the stopper portion  44  is a recessed portion for engaging the engagement portion  54 , the engagement portion  54  need only be formed as a raised portion. The stopper portion  44  and the engagement portion  54  are fitted together with a small engagement gap. 
     When the line sensor  51  having the above described structure is to be assembled with the unit base  11 , the pair of fitting portions  52  and  53  are individually fitted into the guide portions  43  and  48  of the first and second support members  41  and  46  of the unit base  11 , and the engagement portion  54  engages the stopper portion  44  of the unit base  11 . 
     The line sensor  51  is held so it can not move in the X direction and the Y direction in  FIGS. 1A and 10 , i.e., in the main scanning direction and in the sub-scanning direction. To hold the line sensor  51 , a first leaf spring  61  and a second leaf spring  62  are employed. 
     Specifically, the first leaf spring  61  is secured to the first support member  41  by the above described screw (not shown) used to secure the first support member  41 . The U-shaped portion of the first leaf spring  61  is flexibly pressed against one longitudinal end face of the line sensor  51 , and the elastic force exerted by the first leaf spring  61  urges the line sensor  51  toward the other longitudinal end, i.e., in the main scanning direction. Therefore, one of the inner faces of the groove in the engagement portion  54  abuts upon the stopper portion  44 , and movement of the line sensor  51  in the main scanning direction is prevented. 
     The second leaf spring  62  is fixed by a rivet, for example, to the longitudinal center of the spring sheet piece  33   b , and is sandwiched and compressed between the spring sheet piece  33   b  and the line sensor  51 . The line sensor  51  is urged in the sub-scanning direction by the elastic force exerted by both arm portions of the second leaf spring  62 . Therefore, when the guide portions  43  and  48  are fitted into the engage portions  52  and  53 , the guide portions  43  and  48  abut upon the inner faces of the fitting portions  52  and  53 , and movement of the two ends of the line sensor  51  in the sub-scanning direction is restricted. As a result, movement of the line sensor  51  in the sub-scanning direction is prevented. 
     As described above, the line sensor  51  is held so that it can not move, relative to the unit base  11 , either in the X direction or in the Y direction. Since this is achieved simply by employing the urging force applied to the line sensor  51  by the first leaf spring  61  and the second leaf spring  62 , a special adjustment process for removing rattling due to dimensional tolerances is not required. 
     As shown in  FIGS. 5 and 12  to  14 , the focus setup unit  64  includes urging members, such as coil springs  65 , which are pressing members, and spacers  66 . 
     The coil springs  65  are used to move the line sensor  51  toward the original support plate  25 , and are sandwiched and compressed between the unit base  11  and the reverse surface of the line sensor  51 . A plurality of coil springs  65  are provided for uniformly pushing the line sensor  51 , and these are located at positions where they can at least urge the two longitudinal ends of the line sensor  51  in the direction of the original support plate  25  (direction Z in  FIG. 1B ). In order to position the coil springs  65 , as shown in  FIG. 9 , a spring sheet  41   a , having a concave shape, is formed in the first support member  41 , and a spring sheet  46   a , also having a concave shape, is formed in the second support member  46 . 
     The spacers  66  are formed of a hard resin, for example, and are sandwiched between the line sensor  51  and the original support plate  25  to delimit the focal depth of the light receiving device at a position extremely near the upper face of the original support plate  25 . Therefore, a plurality of the spacers  66  are attached to the upper face of the line sensor  51 . Specifically, protrusions (not shown) formed on the spacers  66  are inserted into portions separated from the sensor element  51   b  of the sensor insulator  51   a , e.g., into holes  51   c  (see  FIGS. 8 and 9 ) that are formed in the upper faces of the two longitudinal ends of the sensor insulator  51   a . In this case, the spacers  66  are attached to the upper face of the line sensor  51  at the two longitudinal ends. 
     Further, as shown in  FIG. 6 , a screw  71 , a disc spring  72  and a washer  73  are employed in order to maintain the sensor assembly  31  at an adjusted position relative to the unit base  11 . The screw  71  is used to connect the sensor holder  32  to the unit base  11 , through the fastening hole  18 , and the force used to fasten the screw  71  can be reduced to adjust the position of the sensor assembly  31 . During such an adjustment, the disk spring  72  presses the sensor holder  32  against the unit base  11  through the application of an appropriate frictional force. By varying the strength of this friction force, the position of the sensor assembly  31  can be adjusted. The washer  73  is formed, for example, of an extremely smooth synthetic resin, and is provided in order that the sensor assembly  31  can be easily moved and its position adjusted. 
     In an original reading unit  8  having this arrangement, the following procedure is followed when arranging, at a predetermined distance in the sub-scanning direction, a first array and a second array of the sensor assemblies  31  between the original support plate  25  and the wall  12   a  of the unit base  11 . The pivots  45  projecting downward from the lower faces of the sensor holders  32  are inserted and pressed down into the bearing holes  15  of the wall  12   a , thereby attaching the sensor assemblies  31  so they can be rotated at the rotation centers comprising the bearing holes  15  and the pivots  45 . Since once the pivots  45  have been inserted, elastic force causes them to expand in the direction of the diameter of the bearing holes  15 , there are no gaps between the pivots  45  and the bearing holes  15 . Further, since the line sensors  51  can be moved vertically and are urged upward by the coil springs  65 , they are positioned so that the spacers  66  contact the reverse surface of the original support plate  25 . Therefore, the appropriate focal distances for the line sensors  51  are set automatically, without any special process being required. At the same time, in response to the urging force exerted by the coil springs  65 , the sensor holders  32  are pressed down and contact the upper face of the wall  12   a  of the unit base  11 . In this temporary assembly state, the positions of the individual sensor assemblies  31 , which are arranged in a zigzag pattern, are adjusted so they are parallel. During this adjustment process, the sensor assemblies  31  are rotated, as fulcrums, at their rotation centers. In this case, however, since there is no need to perform a troublesome process during which the positions of the two longitudinal ends of each sensor assembly  31  are alternately and repeatedly adjusted in the X direction and the Y direction, the parallel adjustment process is easily performed. In addition, since as described above, adjusting the focal distance is not necessary, the efficiency with which the work is performed is increased. During the above described adjustment operation, with the screws  71  loosened in advance, the sensor holders  32  of the sensor assemblies  31  are slid to the wall  12   a  of the unit base  11 . And at the same time, the spacers  66  are slid across the original support plate  25  and the sensor assemblies  31  are rotated at their rotation centers and aligned so they are parallel. Then, when the screws  71  are again tightened, the parallel positioning of the sensor assemblies  31  can be maintained. 
     An adjustment apparatus that performs the parallel adjustment process is shown in  FIGS. 15 to 18 . 
     As shown in  FIGS. 15 and 16 , for the adjustment apparatus  81 , a pair of left and right set blocks  83  are located on the upper face of an adjustment base  82 , and adjustment jigs  84 , consonant in number with the arrays of sensor assemblies  31 , are positioned between the set blocks  83 . 
     The original reading unit  8 , which is detachably mounted on the pair of set blocks  83 , can be moved forward and backward along movable rails (not shown) provided for the set blocks  83 . In order to shift the movable rails, rail drive mechanisms  85  are provided on the upper face at the left and right ends of the adjustment base  82 . Each of the rail drive mechanisms  85  includes a knob  85   a  and a lever  85   b  that rotates while following a shaft that is moved forward or retracted by rotating the knob  85   a.  Through the function provided by the lever  85   b , which is fitted to the movable rail, the movement of the shaft is amplified and the movable rail is shifted forward or backward. 
     An interlocking mechanism  86  of a belt transmission type, for example, is provided for the adjustment base  82  to synchronize the movement of the pair of rail drive mechanisms  85 . Since the movable rails of the set blocks  83  are synchronously moved forward or backward, the original reading unit  8  mounted at the paired set blocks  83  can be moved, in parallel, forward or backward. 
     The individual adjustment jigs  84  each include: a micro head  87 , which is manually operated, a head holder  88 , which holds the micro head  87  on the adjustment base  82 , an adjustment lever  89  and a spring  90 , which permits the adjustment lever  89  to follow the micro head  87 . The adjustment lever  89  is rotatable at a support shaft  91  that supports one longitudinal end, and includes an upward adjustment pin  92  that is near the support shaft  91 . As shown in  FIG. 17 , the micro heads  87  push the free ends of the adjustment levers  89  on the side opposite the support shafts  91 . With this arrangement, since the travel distance for the adjustment pins  92  can be obtained in accordance with a ratio of the distance between the support shafts  91  and the micro heads  87  (the distance from the fulcrum to the point of force) and the distance between the support shafts  91  and the adjustment pins  92  (the distance from the fulcrum to the point of application), delicate adjustments of the rotation of the sensor assemblies  31  can be accurately and easily performed. 
     As shown in  FIG. 18 , upper ends  92   a  of the adjustment pins  92  are tapered. Thus, when the upper ends  92   a  are inserted upward into the adjustment holes  35 , gaps due to dimensional tolerance do not occur between the upper ends  92   a  and the adjustment holes  35 . 
     A cover  93  is fitted to the adjustment base  82 . The cover  93  is pivotable between a closed position, whereat the original reading unit  8  mounted on the adjustment base  82  is covered, and the open position shown in  FIGS. 15 and 16 . Two parallel reference lines  94  and  95  are extended across the inner face of the cover  93 . These reference lines  94  and  95  are also parallel to the main scanning direction, and are made, for example, of a black line material. 
     When the original reading unit  8  is mounted on the adjustment base  82 , the adjustment pins  92  are passed through corresponding pin through holes  16  in the unit base  11  and are inserted into adjustment holes  35  in the sensor holders  32 . At this time, as shown in  FIG. 17 , the support shafts  91  of the adjustment levers  89  are located farther from the pivots  45  that serve as the rotation centers of the sensor assemblies  31 , while the adjustment holes  35  and the adjustment pins  92  are located near the free ends of the sensor assemblies  31 . 
     Under these conditions, the cover  93  is closed, and at first, for example, the sensor assemblies of the first array in the front are adjusted so that they are parallel to the reference line  94 , which is also positioned in the front. During this adjustment process, electric power is supplied to the line sensors  51  which read the reference line  94 , and the obtained data are displayed on a cathode-ray oscilloscope (not shown). Then, the micro heads  87  are operated to rotate the sensor assemblies  31  along the unit base  11 . Through the rotation of the sensor assemblies  31 , the position of the unit base  11  is simultaneously adjusted in the X direction and in the Y direction. During the adjustment, an operator monitors the cathode-ray oscilloscope, and halts the micro heads  87  when an appropriate display is obtained. 
     Thereafter, the operator operates the rail drive mechanisms  85  to move the original reading unit  8  in the direction in which the original is fed, i.e., in the sub-scanning direction (forward or backward in  FIGS. 15 and 16 ). Then, in the above described manner, the sensor assemblies  31  of the second array in the rear are adjusted so that they are parallel to the reference line  95 , which is also positioned in the rear. Since the reference line  95  is employed for the adjustment, only a short travel distance is required of the original reading unit  8 , and efficiency is also increased. When it is desired that this operation be ignored, only one common reference line need be employed, instead of using both reference lines  94  and  95 . 
     After the above described adjustment process has been is completed, the cover  93  is opened. And while the original reading unit  8  is still mounted on the set blocks  83 , the sensor assemblies  31 , which have been adjusted so that they are parallel, are secured by fastening the multiple screws  71  at the adjusted positions. As a result, the sensor assemblies  31  are secured to the unit base  11 . 
     In the above described performance of the parallel adjustment process, the pivots  45 , each of which functions as a single rotation center for the sensor assembly  31 , are at least partially located in the area for projection to the wall  12   a , and are provided immediately under or in the vicinity of the light receiving elements (also called first dots) that are first read from among the light receiving element array that will be described later of the line sensors  51 . Therefore, the range of the rotation angle of each sensor assembly  31  can be greatly reduced, and changes in positioning can be easily identified, visually, by using an oscilloscope. Thus, the efficiency with which adjustments are performed can be increased. 
     In addition, in the above described performance of the parallel adjustment process, the distance between the two reference lines  94  and  95  is known, and the distance the rail drive mechanisms  85  move the original reading unit  8  in the sub-scanning direction can be readily identified by viewing an oscilloscope. Therefore, the distance in the sub-scanning direction between the individual sensor assemblies  31  that are adjusted so that they are parallel can be obtained. The data for the distance between the sensor assemblies  31  (a shift in the sub-scanning direction) is stored in the memory in advance. After the adjustment has been completed, and while the original reading unit  8  attached to the original base  7  of the original reading section  5  is being employed to read data from the sensor assemblies  31 , the data reading timing is electrically controlled by using the data stored in the memory. As a result, the shift in the sub-scanning direction can be eliminated, and the data read from the line sensors  51  can be continued as lines. 
     Through this processing, a copier  1  according to this embodiment can scan an original passed through the image reading section  5  and obtain image data having a maximum effective width of, for example, nine hundred and several tens of millimeters. The obtained image data are transmitted as digital data to the image forming section  4 , and the image forming section  4  performs image forming on a sheet supplied from the paper supply section  3 . 
       FIG. 19  is a diagram showing another embodiment of the present invention. In this embodiment, the original reading section  5  of the copier  1  in  FIG. 2  is provided as an image scanner  100 . Since the arrangement of the image scanner  100  is the same as the original reading section  5  described above, the same reference numerals are employed for the corresponding components, and no further explanation will be given. The image scanner  100  obtains the same effects those obtained by the above described embodiment, and can also achieve the objective of the present invention.