Abstract:
An image reading apparatus comprises an original placement portion on which an original is to be placed, optical unit for optically scanning the original on the original placement portion while moving relative to the original placement portion and a guide member that guides movement of the optical unit. The optical unit includes a sliding member having a screw portion that slides in contact with the guide member and a screw hole portion to which the sliding member is mounted. The screw portion of the sliding member is plastically deformable and screwed into the screw hole portion while being plastically deformed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image reading apparatus for reading an original image, and particularly relates to an image reading apparatus that can read image while a reading optical member is moved relative to a fixedly placed original. 
     2. Description of Related Art 
     Conventionally, a structure as shown in  FIG. 4  has been widely used as an image reading apparatus for use in a copying machine or an image scanner or the like. 
     As shown in  FIG. 4 , a conventional image reading apparatus is provided with a platen glass  102  on which an original  101  to be read is to be placed, a white plate  103  used for shading compensation and a pressure plate  104  for pressing the original  101 . 
     A lens unit  105  is provided for reduction-imaging reflection light from the original  101  that is illuminated with light, onto a CCD linear image sensor  106 . 
     A first mirror unit  110  is composed of an original illumination lamp  111  in the form of a xenon lamp, a first reflection mirror  112  and an inverter  113  for turning the original illumination lamp  111  on. A second mirror unit  120  is composed of a second reflection mirror  121  and a third reflection mirror  122 . 
     With the above-described structure, the original  101  placed on the platen glass  102  is read while the first mirror unit  110  and the second mirror unit  120  are moved in a scanning manner in the sub-scanning direction (that is, in the right direction in  FIG. 4 ) by a stepping motor  107 . 
     A reader  130  is provided with an adjusting mechanism for adjusting various factors of a read image, such as geometrical characteristics, the magnification or the resolution. Optical adjustment is to be performed by operating this image adjusting mechanism. 
     As such an image adjusting mechanism, there has been used an adjusting mechanism that adjusts the positions of the second reflection mirror  121  and the third reflection mirror  122  in the second mirror unit  120  along the direction indicated by arrow a in  FIG. 4 . This type of mechanism is disclosed in Japanese Patent Application Laid-Open No. 2001-222075. 
     In the following, this adjusting mechanism will be described with reference to  FIGS. 5 and 6 . Each of  FIGS. 5 and 6  includes a plan view, front view, a left side view and a right side view. 
     Referring to  FIG. 5 , a second mirror frame  201  is a frame for supporting the second reflection mirror  121  and the third reflection mirror  122 . The second mirror frame  201  has sliders  204  and  205  and sliders  206  and  207  provided at positions to be in slidable contact with a front optical rail  251  and a rear optical rail  252  respectively. The front optical rail  251  and the rear optical rail  252  constitute a scanning plane of the second mirror unit  120   a.    
     The sliders  204  and  205  on one side are fixedly supported on a front slider frame  202 . The sliders  206  and  207  on the other side are fixedly supported on a rear slider frame  203 . 
     The front slider frame  202  is fixed by a screw  208  so that the position of the front slider frame  202  can be adjusted along the direction indicated by arrow b relative to the second mirror frame  201 . A screw  209  is provided in the same manner. 
     In the above-described structure, the position of the front slider frame  202  relative to the second mirror frame  201  is adjusted based on geometrical characteristics of the image in order to adjust the inclination of the second reflection mirror  121  and the third reflection mirror  122  with respect to the thrust direction. 
     The rear slider frame  203  is supported and fixed on the second mirror frame  201 . The rear slider frame  203  is constructed in such a way that its rotational position about a shaft  210  provided on the second mirror frame can be adjusted. 
     The position of the rear slider frame  203  relative to the second mirror frame  201  is adjusted in order to enhance the coplanarity of the sliders  204 ,  205 ,  206  and  207 . 
     As shown in  FIG. 6 , a structure in which a second mirror frame  301  is secured to a front side plate  302  and a rear side plate  303  by means of screws or the like may also be adopted. 
     In this structure, the second reflection mirror  121  and the third reflection mirror  122  are supported on the second mirror frame  301 . The second mirror frame  301  has sliders  304  and  305  and sliders  306  and  307  provided at positions to be in slidable contact with a front optical rail  351  and a rear optical rail  352  respectively. The front optical rail  351  and the rear optical rail  352  constitute a scanning plane of the second mirror unit  120   b.    
     Details of the sliders  304  and  305  will be described with reference to  FIGS. 7A and 7B .  FIG. 7B  is an enlarged partial view showing a part of  FIG. 7A . 
     As shown in  FIG. 7A , the slider  304  is provided with a sliding portion  304   a  for sliding in contact with the front optical rail  351  and a screw portion  304   b  provided perpendicularly to the optical rail surface. 
     The slider  305  has the same structure as the slider  304 , namely, the slider  305  is provided with a sliding portion  305   a  for sliding in contact with the rear optical rail  352  and a screw portion  305   b  provided perpendicularly to the optical surface. 
       FIG. 7B  is an enlarged view showing the screw portion  304   b  or  305   b . As shown in  FIG. 7B , screw hole portions  301   a  for engaging with the aforementioned screw portions  304   b  and  305   b  are formed on the second mirror frame  301 . 
     Furthermore, as shown in  FIG. 7B , a recessed portion  304   c  or  305   c  for engagement with an adjusting tool  361  is provided on each of the sliders  304  and  305 . With this structure, the sliders  304  and  305  are rotated in the direction parallel to the surface of the front optical rail  351  and the surface of the rear optical rail  352  respectively by means of the adjusting tool  361  engaging with the recessed portions  304   c  and  305   c , so that the positions of the sliders  304  and  305  in the direction indicated by arrow b in  FIG. 7A  can be adjusted relative to the second mirror frame  301 . 
     The positions of the sliders  304  and  305  are adjusted based on geometrical characteristics of the image in order to adjust the inclination of the second reflection mirror  121  and the third reflection mirror  122  with respect to the thrust direction. In addition, they are adjusted in order to enhance the coplanarity of the sliders  304  to  307 . 
     The sliders  304  and  305  that have been adjusted in their positions are fixed to the second mirror frame  301  by adhesive  371  so that the position of the sliders  304  and  305  will not be changed by scanning operation of the second mirror unit  120   b.    
     However, the above-described prior art mechanism for adjusting the inclination of the second mirror  121  and the third mirror  122  and for adjusting the coplanarity of the sliders suffers from the following problems. 
     As shown in  FIG. 5 , it is necessary for that prior art that the second mirror frame  201  for supporting the second reflection mirror  121  and the third reflection mirror  122 , the front slider frame  202  and the rear slider frame  202  for supporting the sliders  204  to  207  be constituted as separate members This results in an increase in the number of parts, which causes an increase in cost. 
     Furthermore, it is necessary for the structure to allow driver access for adjusting the inclination and the coplanarity in the direction toward the side surface of the second mirror unit  120 . However, an frame (not shown) of the image reading apparatus is generally present at a position near the side of the second mirror unit  120   a , and therefore, the operationality is very low. 
     On the other hand, the prior art shown in  FIG. 6  does not suffer from the above-described problem. However, another problem arises in connection with the prior art shown in  FIG. 6 , that is, looseness of the sliders  304  and  305  on the second mirror frame  301  generated by the scanning operation of the second mirror unit  120   b.    
     Recently, with an increase in the speed of the mirror unit, a materials having high sliding ability such as a polyolefin is used as the material of the sliders  304  to  307 . Therefore, the adhesion force of the adhesive is made worse to a considerable degree, and the sliders  304  and  305  are easy to be loosened. 
     Such looseness of the sliders  304  and  305  causes inclination of the second reflection mirror  121  and the third reflection mirror  122 , which, in turn, causes deterioration of geometric characteristics of read images. 
     One may consider to adhere the sliders  304  and  305  with an adhesive having a strong adhesion force. However, in the case that such an adhesive is used, adjustment of the height of the sliders  304  and  305  becomes impossible in the market, in spite that such adjustment is necessary for correcting geometrical characteristics of the image. Consequently, it is very difficult to adopt adhesion of the sliders  304  and  305  using an adhesive having a strong adhesion force. 
     In addition, in the sliders  304  and  305  and the second mirror frame  301  according to the prior art shown in  FIG. 6 , there is play in the mount portion of the sliders  304  and  305  to the second mirror frame  301  due to small play or backlash generated between the aforementioned screw portions  304   b  and  305   b  and the screw hole portions  301   a , even when the adhesion force of the adhesive  371  to the sliders  304  and  305  is strong. 
     Due to the play in the mount portion of the sliders  304  and  305  to the second mirror frame  301 , vibration will be generated upon the scanning operation of the second mirror unit  120   b . As a result, for example, displacement in the image position upon reading a monochrome image or misregistration of colors in the case of a color scanner can be caused. 
     As per the above, in image reading apparatus such as scanners, positional displacement of images or misregistration of colors are generated due to looseness of slider members for performing position adjustment or play in the mount portion of the slider members, so that there arise problems concerning reliability and stability of the image reading apparatus. Therefore, it is desired to prevent the looseness in slider members such as the sliders  304  and  305  and play in the mount portion of the slider members. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image reading apparatus in which play and looseness of a slider of a moving optical member are eliminated. 
     Another object of the present invention is to provided an image reading apparatus in which the position of a moving optical member in the height direction can be easily adjusted. 
     Still another object of the present invention is to provide an image reading apparatus comprising: 
     an original placement portion on which an original is to be placed; 
     optical means for optically scanning the original on the original placement portion while moving relative to the original placement portion; and 
     a guide member that guides movement of the optical means; 
     wherein the optical means includes a sliding member having a screw portion that slides in contact with the guide member and a screw hole portion to which the sliding member is mounted, the screw portion of the sliding member being plastically deformable and screwed into the screw hole portion while being plastically deformed. 
     Other objects and features of the present invention will become apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view schematically showing an image reading apparatus using slider portions according to an embodiment of the present invention. 
         FIG. 2A  is a cross sectional view showing a slider portion to be used in the image reading apparatus according to the embodiment of the present invention. 
         FIG. 2B  is a cross sectional view showing the slider portion to be used in the image reading apparatus according to the embodiment of the present invention. 
         FIG. 2C  is a side view showing the slider portion to be used in the image reading apparatus according to the embodiment of the present invention. 
         FIG. 3  is an enlarged cross sectional view showing another slider portion to be used in the image reading apparatus according to the embodiment of the present invention. 
         FIG. 4  schematically shows an image reading apparatus. 
         FIG. 5  includes a front view, a plan view, a right side view and left side view showing an example of a slider of an image reading apparatus. 
         FIG. 6  includes a front view, a plan view, a right side view and left side view showing an example of a slider of an image reading apparatus. 
         FIG. 7A  is a side view illustrating a problem concerning a slider portion used in an image forming apparatus. 
         FIG. 7B  is an enlarged cross sectional view for illustrating the problem concerning the slider portion used in an image reading apparatus. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, an embodiment of the present invention will be described with reference to the accompanying drawings. 
     In the drawings, the same parts are designated with the same reference signs and redundant description thereof will be omitted. 
     (Image Reading Apparatus) 
     First, an image reading apparatus according to an embodiment of the present invention will be described.  FIG. 1  is a cross sectional view schematically showing the image reading apparatus. 
     As shown in  FIG. 1 , the image reading apparatus according to this embodiment is provided with a platen glass  2  serving as original placement means on which an original  1  to be read is to be placed, a white plate  3  used for shading compensation and a pressure plate  4  for pressing the original  1 . In the interior of the image reading apparatus according to the embodiment, there is provided a lens unit  5 , a CCD linear image sensor  6 , a stepping motor  7 , a first mirror unit  8  serving as first scanning means and a second mirror unit  9  serving as second scanning means. 
     The lens unit  5  is provided for reduction-imaging reflection light from the original  1  that is illuminated with light, onto the CCD linear image sensor  6 . 
     The first mirror unit  8  is composed of an original illumination lamp  11  in the form of a xenon lamp, a first reflection mirror  12  serving as a first reflection system and an inverter  13  for turning the original illumination lamp  11  on. The second mirror unit  9  is composed of a second reflection mirror  14  serving as a second reflection system and a third reflection mirror  15  serving as a third reflection system. 
     With the above-described structure, the original  1  placed on the platen glass  2  is read while the first mirror unit  8  and the second mirror unit  9  are moved in a scanning manner in the sub-scanning direction (that is, in the right direction in  FIG. 1 ) by a stepping motor  7 . 
     A reader  30  is provided with an adjusting mechanism for adjusting various factors of a read image, such as geometrical characteristics, the magnification or the resolution. Optical adjustment is to be performed by operating this image adjusting mechanism. 
     (Structure of Slider Member) 
     Slider members used in the image reading apparatus according to the embodiment that has the above-described structure will be described in the following.  FIGS. 2A ,  2 B,  2 C and  3  show a slider member according to this embodiment. In addition, the description will be made with additional reference to  FIGS. 6 and 7  as the need arises. In those drawings, description of portions in the structure that are the same as those in the prior art will be omitted. 
       FIG. 2A  shows a screw portion  304   b  or  305   b  of the slider  304  or  305 .  FIG. 2B  is a cross sectional view in the axial direction of the screw portion  304   b  or  305   b  of the slider  304  or  305 .  FIG. 2B  is a cross sectional view taken on the plane orthogonal to the axial direction. 
     As shown in  FIG. 2B , on the root portion of the thread of the screw portion (i.e. the threaded portion)  304   b  ( 305   b ) of the slider  304  ( 305 ), there is provided four projected portions  304   d  ( 305   d ) along the circumference. Each of the projected portions  304   d  ( 305   d ) has a convex shape extending from the root of the screw thread up to the major diameter of the screw. Each of the projected portion  304   d  ( 305   d ) has tapered portions  305   e  and  305   f  in the circumferential direction. 
     The projected portions  304   d  ( 305   d ) are provided in the range along the axial direction of the screw portion  304   b  ( 305   b ) indicated by double-sided arrow X. In other words, the projected portions  304   d  ( 305   d ) are provided in the area other than the tip end area of the screw portions  304   b  ( 305   b ), and they are not provided in the tip end area of the screw portion  304   b  ( 305   b ) indicated by arrow Y above arrow X. 
     When the slider  304  ( 305 ) is screwed into the second mirror frame  301  shown in  FIG. 6 , the projected portions  304   d  ( 305   d ) of the slider  304  ( 305 ) are threaded into the screw hole portion  301   a  of the second mirror frame while being plastically deformed. 
     In this way, the slider  304  ( 305 ) is screwed into the screw hole portion  301   a  of the second mirror frame  301  with the projected portions  304   d  ( 305   d ) being in plastically deformed states. With this feature, the loosening torque of the slider  304  ( 305 ) in relation to the second mirror frame  301  is increased. Consequently, loosening of the sliders  304  and  305  from the second mirror frame  301  due to the scanning operation of the second mirror unit  120   b  can be avoided. 
     The projected portions  304   d  ( 305   d ) of the slider  304  ( 305 ) are not provided in the tip end area (i.e. the area along the axial direction indicated by arrow Y) of the screw portion  304   b  ( 305   b ). Consequently, it is easy to commence screwing of the sliders  304  and  305  into the second mirror frame  301 . 
     In addition, the projected portions  304   d  ( 305   d ) are plastically deformed by the screw hole portion  301   a  of the second mirror frame  301  while guided by the tapered portions  305   e  and  305   f  of the projected portions  304   d  ( 305   d ). Therefore, an increase in the screw torque is small, so that it is possible to prevent problems that might occur upon assembling, such as increase in the screw torque or sticking of the sliders  304  and  305  to the second mirror frame as a result of bending of the sliders  304  and  305  from occurring. 
     In the above-described sliders  304  and  305  and the second mirror frame  301 , play in the mount portion between the aforementioned screw portion  304   b  ( 305   b ) and the screw hole portion  301   a  is absorbed by the plastic deformation of the projected portions  304   d  ( 305   d ). Consequently, play in the mount portion can be eliminated, and vibration of the second mirror unit  120   b  during the scanning operation can be prevented from occurring. 
     In this embodiment, the plastic deformation of the projected portions  304   d  ( 305   d ) of the slider  304  ( 305 ) is intended to increase the loosening torque of the slider  304  ( 305 ) from the second mirror frame  301 . 
     However, a similar effect can be attained by designing the shape of the thread of the screw portion  304   b  ( 305   b ) of the slider  304  ( 305 ) as an expanded shape as compared to the shape of the internal thread of the screw hole portion  301   a  of the second mirror frame  301  so that they will overlap (interfere) with each other. 
     As per the above, in the image reading apparatus according to the embodiment of the present invention, the slider  304  ( 305 ) is screwed into the screw hole portion  301   a  of the second mirror frame  301  with the projected portions  304   d  ( 305   d ) being in plastically deformed states. With this feature, the loosening torque of the slider  304  ( 305 ) in relation to the second mirror frame  301  is increased. Consequently, loosening of the sliders  304  and  305  from the second mirror frame  301  due to the scanning operation of the second mirror unit  120   b  can be avoided. 
     Consequently, inclination of the second reflection mirror  121  and the third reflection mirror  122  caused by loosening of the sliders  304  and  305  can be prevented from occurring, and therefore, deterioration of geometrical characteristics of read images can be avoided. 
     In addition, in the sliders  304  and  305  and the second mirror frame  301  of the image reading apparatus according to this embodiment, play in the mount portion of the screw portions  304   b  and  305   b  to the screw hole portions  301   a  can be suppressed by virtue of plastic deformation of the projected portions  304   d  and  305   d.    
     Consequently, it is possible to prevent vibration of the second mirror unit  120   b  upon the scanning operation, and therefore it is possible to avoid deteriorations of so-called read image characteristics such as positional displacement of images and misregistration of colors in the case that multiple colors are read. 
     While one embodiment of the present invention has been described in the foregoing, the present invention is not limited to the above-described embodiment but various modification can be made based on the technical concept of the present invention. 
     For example, the materials and the structures of the image reading apparatus that have been described in connection with the embodiment are mere examples, and therefore different materials and structures of the image reading apparatus may be adopted in accordance with requirements. 
     For example, while the above description of the embodiment has been directed to the sliders of the second mirror unit  120   b , the structure same as the structure of this embodiment may be applied to the sliders of the first mirror unit  110  serving as the first scanning means. In this case also, the same advantageous effects can be attained. 
     Furthermore, while in the above-described embodiment, the overlapping screw portions  304  and  305  have the shape shown in  FIGS. 2 and 3 , the overlapping screw portions  304   b  and  305   b  of the sliders  304  and  305  having other shapes than those shown in  FIGS. 2 and 3  can attain the same advantageous effects so long as the screw portions  304   b  and  305   b  of the sliders  304  and  305  overlap with the screw hole portions  301  of the second mirror frame  301 . 
     As per the above, according to the image reading apparatus according to the present invention, it is possible to avoid loosening and play in mounting of sliders that can be adjusted in their positions while allowing easy adjustment of inclination and easy adjustment of coplanarity. Consequently, it is possible to avoid deterioration of geometrical characteristics or deterioration of image characteristics of read images such as positional displacement of images or misregistration of colors in the case of color images. 
     While an embodiment of the present invention has been described in the foregoing, it will be understood that the present invention is not restricted to specific features of the embodiment, but various modification can be made without departing from the scope and spirit of the present invention.