Abstract:
An optical element including a plurality of reference members formed on a first side surface, and a method and apparatus for fixedly joining the optical element with the first side surface facing down. The method includes providing a surface including a specific position where the optical element is placed, applying an adhesive agent to a predetermined spot within the specific position in which the optical element is placed, placing the optical element therein, causing the optical element to have convex warpage, and curing the adhesive agent. The apparatus includes mechanisms configured to apply an adhesive agent to a predetermined spot within a specific position of a surface on where the optical element is placed, and to place the optical element therein, and first and second light sources configured to cause the optical element to have convex warpage, and to cure the adhesive agent, respectively.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical element, and a method and apparatus for fixedly joining the optical element, and more particularly to an optical element, and a method and apparatus for fixedly joining the optical element capable of reducing deformation of the optical element arranged in a layer structure.  
         [0003]     2. Discussion of the Background  
         [0004]     In an image forming apparatus using an electrostatic copying method such as a digital copier and a laser printer, a laser beam emitted from a laser light source is polarized by a light deflecting unit to irradiate a previously uniformly charged photoconductor so that an electrostatic latent image is formed on the photoconductor. The electrostatic latent image is developed with toner into a toner image, and the toner image is transferred onto a sheet so that an image is output.  
         [0005]     In a case a color image is formed, the image forming apparatus using the electrostatic copying method is configured and controlled as described below. A plurality of photoconductors arranged in a row in a conveyance direction of a sheet are exposed to laser light to form respective latent images on the respective photoconductors. The electrostatic latent images are then developed into toner images in respective colors (yellow, magenta, cyan, and black) corresponding to the photoconductors. The toner images are transferred onto a sheet so that the toner images are overlaid one after another to finally form a color image. The configuration and control have achieved image forming using a plurality of colors, an increase in image forming speed, and improvement in image quality.  
         [0006]     The image forming apparatus having the above configuration and control uses a plurality of optical elements when performing optical scanning to form an electrostatic latent image. Since a large space is required to accommodate the plurality of optical elements, an optical scanning apparatus for performing the optical scanning needs to be enlarged, and the whole image forming apparatus needs to be enlarged, accordingly.  
         [0007]     Against the above background, space saving efforts have been made by arranging optical elements such as imaging lenses provided for respective colors into a layer structure.  
         [0008]     A background art for arranging the optical elements in a layer structure uses a lens holder for integrally structuring two imaging lenses in a layered arrangement in a sub-scanning direction.  
         [0009]     A background method of holding optical elements places a plurality of elongated optical elements one on another with opposite ends supported. One of the optical elements includes a protrusion arranged at a center in a longitudinal direction of the optical element, and the other optical element includes a receiving concavity arranged in a position opposing the protrusion. When the optical elements are placed, the optical elements are positioned by engaging the protrusion with the receiving concavity.  
       SUMMARY OF THE INVENTION  
       [0010]     This patent specification describes an optical element including a plurality of reference members formed in a cylinder-like shape with a flat top on a first side surface perpendicular to a light incident surface, and a method and apparatus for fixedly joining the optical element. The method includes providing a surface including a specific position on which the optical element is placed, applying an adhesive agent to a predetermined spot within the specific position of the surface on which the optical element is placed, placing the optical element with the first side surface facing down into the specific position of the surface, causing the optical element placed in the specific position to have convex warpage relative to the surface, and curing the adhesive agent. The apparatus includes mechanisms configured to apply an adhesive agent to a predetermined spot within a specific position of a surface on which the optical element is placed, and place the optical element with the first side surface facing down into the specific position of the surface, and first and second light sources configured to cause the optical element placed in the specific position to have convex warpage relative to the surface, and to cure the adhesive agent, respectively. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a schematic illustration of an optical element according to an embodiment of the present invention, viewed from a first lens surface;  
         [0013]      FIG. 2  is another schematic illustration of the optical element in  FIG. 1  viewed from a second lens surface;  
         [0014]      FIGS. 3A, 3B , and  3 C are schematic illustrations for explaining a method of fixedly joining the optical element according to the embodiment of the present invention;  
         [0015]      FIG. 4  is a flowchart of steps included in the method of fixedly joining the optical element;  
         [0016]      FIG. 5  is a schematic illustration for explaining spot light positions of UV rays emitted from light sources for a forced deformation of the optical element;  
         [0017]      FIG. 6  is a graphical representation of shifts in amounts of the deformation of the optical element;  
         [0018]      FIG. 7  is a schematic diagram of a general configuration of an apparatus for fixedly joining the optical element;  
         [0019]      FIG. 8  is a top view of an optical scanning apparatus having the optical element fixedly joined according to the embodiment of the present invention;  
         [0020]      FIG. 9  is a side view of the optical scanning apparatus shown in  FIG. 8 ;  
         [0021]      FIG. 10  is a top view of another optical scanning apparatus having the optical element fixedly joined according to the embodiment of the present invention;  
         [0022]      FIG. 11  is a side view of the optical scanning apparatus shown in  FIG. 10 ; and  
         [0023]      FIG. 12  is a schematic illustration of a general configuration of an image forming apparatus including the optical scanning apparatus according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.  
         [0025]     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIGS. 1 and 2 , an optical element  115  is described.  
         [0026]     As shown in  FIGS. 1 and 2 , the optical element  115  includes a first lens surface  31   a,  a second lens surface  31   b,  transfer surfaces  32   a  and  32   b,  bosses  33 , flanges  34 , mounting reference surfaces  35 , outer ribs  36 , reference ribs  37 , and an incompletely transferred surface  38 .  
         [0027]     The optical element  115  is formed of a plastic material in an elongated shape having the first lens surface  31   a  and the second lens surface  31   b.  The second lens surface  31   b  is curved so that the optical element  115  has a thicker portion at a center in a longitudinal direction thereof.  
         [0028]     The transfer surfaces  32   a  and  32   b  include flat surfaces arranged at opposite sides extended between the first and second lens surfaces  31   a  and  31   b  so as to be in parallel to each other in a beam transmission direction. The transfer surface  32   a  is provided with three bosses  33  each having a cylindrically protruding shape and a flat top. One of the bosses  33  is formed at a center in a longitudinal direction of the transfer surface  32   a.  The other two of the bosses  33  are formed at respective sides in the longitudinal direction of the transfer surface  32   a.  The bosses  33  are thereby triangularly positioned and can evenly support a weight of the optical element  115 . The transfer surface  32   b  includes the incompletely transferred surface  38  having a concave shape in a longitudinal direction thereof, i.e. has a troffer-like-round shape.  
         [0029]     The optical element  115  includes the flanges  34  at opposite sides in the longitudinal direction thereof. The mounting reference surfaces  35  are flat surfaces for serving as references upon mounting and are formed on undersides of the flanges  34 . The outer ribs  36  are formed on opposite sides in a transversal direction and on opposite sides in a longitudinal direction of the second lens surface  31   b.  Further, reference ribs  37  protruding higher than the outer ribs  36  are formed on the both sides in the longitudinal direction of the second lens surface  31   b  to improve accuracy in positioning in the longitudinal direction of the optical element  115 .  
         [0030]     The optical element  115  of the embodiment is formed according to a combination of a background method of injection separation molding and a background method of air-induced sink molding. Specifically, after a resin in a cavity is caused to generate pressure to transfer a transfer surface by the method of injection separation molding, local contraction for releasing is caused against a shape of the captivity to form a recess shape of an incompletely transferred portion. Then, a difference in pressure or air pressure is generated between a mirror surface region corresponding to a mirror surface of a molding material and a vent hole region corresponding to a vent hole to generate sinkage in the vent hole region so that an optical element having a highly accurate lens surface is molded without any distortion inside thereof.  
         [0031]     A method of fixedly joining the optical element  115  to a selected one of a housing of an optical scanning apparatus and another optical element according to the embodiment of the present invention is described below referring to  FIGS. 3A, 3B ,  3 C, and  4 .  FIGS. 3A, 3B , and  3 C are schematic illustrations for explaining the method of fixedly joining the optical element  115 .  FIG. 4  is a flowchart of steps included in the method of fixedly joining the optical element  115 .  
         [0032]     As illustrated in  FIGS. 3A, 3B , and  3 C, a light source unit  160  includes a light source  161  for curing an adhesive agent  140 , and light sources  162  for forced deforming the optical element  115 . The optical element  115  is fixedly joined to a surface of a selected one of a housing  111  of an optical scanning apparatus or another optical element  115   a  by using the adhesive agent  140 .  
         [0033]     When the optical element  115  is fixedly joined to the selected one of the housing  111  of the optical scanning apparatus or the optical element  115   a,  at first, the adhesive agent (i.e. UV curing adhesive)  140  is applied to a plurality of spots on the selected one of the housing  111  or the optical element  115   a  (step S 101 ). Next, a mounting position of the optical element  115  is determined based on the reference surfaces  35  and the reference ribs  37  shown in  FIGS. 1 and 2  (step S 102 ). Then, irradiation of the optical element  115  with ultraviolet (UV) rays emitted from the light sources  162  for forced deforming the optical element  115  as shown in  FIG. 3A  is started so that the optical element  115  has convex warpage as shown in  FIG. 3B  (step S 103 ) relative to the surface of the selected one of the housing  111  or the optical element  115   a.  After the irradiation is started, a judgment is made on whether a predetermined amount of time has been elapsed (step S 104 ). When it is judged that the predetermined amount of time has been elapsed (Yes in step S 104 ), irradiation of the optical element  115  with an ultraviolet (UV) ray emitted from the light source  161  for curing the adhesive agent  140  as shown in  FIG. 3C  is started (step S 105 ). When it is judged that the predetermined amount of time has not been elapsed (No in step S 104 ), the irradiation of the optical element  115  with the ultraviolet (UV) rays emitted from the light sources  162  for forced deforming the optical element  115  is continued. Finally, the irradiation of the optical element  115  with the UV rays emitted from the light sources  161  and  162  is stopped (step S 106 ).  
         [0034]     In step S 104 , although the judgment is made on whether the predetermined amount of time has been elapsed in the embodiment, the judgment instead may be made on whether a predetermined amount of deformation of the convex warpage has occurred in the optical element  115 .  
         [0035]     Further, although the irradiation of the optical element  115  with the UV rays emitted from the light sources  161  and  162  is stopped in step S 106  in the embodiment, the irradiation of the optical element  115  with the UV rays emitted from the light sources  162  may be stopped in step S 106  instead, and the irradiation of the optical element  115  with the UV ray emitted from the light source  161  may be stopped at a later step (not shown).  
         [0036]     In the embodiment of the present invention, since the optical element  115  includes the three bosses (reference protrusions) each having the cylindrical shape and the flat top, the optical element  115  can have a selected one of convex warpage and concave warpage.  
         [0037]      FIG. 5  is a schematic illustration for explaining spot positions of the UV rays emitted from the light sources  162  for forced deformation of the optical element  115  when the optical element  115  is fixedly joined to the another optical element  115   a,  i.e. when the surface on which the optical element is placed is a surface of another optical element  115   a.  The optical element  115  includes the first lens surface  31   a,  the second lends surface  31   b,  and areas  1620 . The other optical element  115   a  includes a first lens surface  131   a,  a second lens surface  131   b,  and areas  1610  to which the adhesive agent  140  is applied. The areas  1610  are irradiated with the UV ray for curing the adhesive agent  140 . The areas  1620  are irradiated with the UV rays for forced deforming the optical element  115 . The areas  1620  are adjacent to an area where most significant warpage occurs by an action of curing and contraction of the adhesive agent  140 , and are located in areas where the irradiation does not affect the adhesive agent  140 . Specifically, as shown in  FIG. 5 , the two areas  1620  are adjacent to one of the three areas  1610  which is located in the middle of the first lens surface  131   a  in a longitudinal direction thereof so that the convex warpage of the optical element  115  can be stably caused.  
         [0038]     The amount of deformation having convex warpage can be controlled by changing the strength of the irradiation with the UV rays from the light sources  162  for forced deformation of the optical element  115  as a difference in temperatures of a top surface and an undersurface of the optical element  115  can be adjusted by the change. Further, a desired amount of warpage can be achieved by adjusting the timing and durations of the irradiation of the optical element  115  with the UV rays from the light sources  161  and  162 .  
         [0039]     Further, the fixed-joining of the optical element  115  can be finished in a short time by intensively irradiating the optical element  115  with the same levels of UV rays from the light sources  162  for forced deformation since the convex warpage can be achieved in a short time.  
         [0040]      FIG. 6  is a graphical representation of shifts in amounts of deformation of the optical element  115 . In  FIG. 6 , an x-axis represents an amount of time elapsed after the fixed-joining of the optical element  115  is started while a y-axis represents an amount of lens deformation of the optical element  115 . A period F represents a period of time over which the optical element  115  is deformed to have convex warpage by being irradiated with the UV rays emitted from the light sources  162  for forced deformation. As shown in  FIG. 6 , because the optical element  115  is fixedly joined to the selected one of the housing  111  or the optical element  115   a  after the optical element  115  has achieved the convex warpage in the period F, concave warpage due to curing and contraction of the adhesive agent  140  can be reduced. Therefore, the amount of deformation before and after the fixed-joining of the optical element  115  can be reduced. As a result, the optical element  115  has less deformation and mounting posture, thereby maintaining a good optical property.  
         [0041]     Although the optical element  115  is forcibly deformed by using heat radiated by the irradiation with the UV rays emitted from the light sources  162  in the embodiment of the present invention, the optical element  115  may be physically deformed by using a pressurizing member instead.  
         [0042]     Although UV light sources for emitting UV rays are used as the light source  161  for curing the adhesive agent  140  and the light sources  162  for forced deformation of the optical element  115  in the embodiment, the light sources are not limited to UV light sources. Further, a heat source is not limited to light, and a heating element capable of locally applying heat may be used.  
         [0043]     The optical element  115  is preferably formed of a plastic material so that the convex warpage can be achieved in a short time (several seconds), and the fixed-joining of the optical element  115  can be finished in a short time.  
         [0044]      FIG. 7  is a schematic diagram of a general configuration of an apparatus for fixedly joining the optical element  115  to the selected one of the housing  111  or the optical element  115   a  according to the embodiment of the present invention. As shown in  FIG. 7 , an apparatus  1  for fixedly joining includes an irradiation controller  2  and the light source unit  160 . The light source unit  160  includes the light source  161  for curing the adhesive agent  140  and the light sources  162  for forced deforming the optical element  115 . The irradiation controller  2  controls the irradiation of the optical element  115  with the UV rays from the light sources  161  and  162 . By using the apparatus  1  having the configuration shown in  FIG. 7 , the fixed-joining of the optical element  115  according to the embodiment can be performed with high accuracy in a short time.  
         [0045]     Next, a general configuration of the optical scanning apparatus having the optical element  115  fixedly joined according to the embodiment of the present invention is described below referring to  FIGS. 8 and 9 .  FIG. 8  is a top view of an optical scanning apparatus  10 .  FIG. 9  is a side view of the optical scanning apparatus  10 . As shown in  FIGS. 8 and 9 , the optical scanning apparatus  10  includes a laser light source  12 , a cylindrical lens  13 , a polygon scanner unit  14 , a reflex mirror  16 , a polygon mirror  17 , photoconductors  20 , reflecting mirrors  21 , the housing  111 , and the optical element  115 .  
         [0046]     The housing  111  serves as a platform of the optical scanning apparatus  10 , and is formed of a resin material. The laser light source  12  includes a selected one of a single semiconductor and a plurality of semiconductors, and emits laser light to irradiate the photoconductors  20  disposed outside the optical scanning apparatus  10  to form electrostatic latent images thereon. The cylindrical lens  13  formats the laser light emitted from the laser light source  12 . The polygon scanner unit  14  is a polariscope to polarize the formatted laser light at a constant angular velocity. The optical element  115  is, for example, an imaging lens such as an fθ lens to perform an imaging and a constant velocity scanning with the laser light polarized by the polygon scanner unit  14 . The reflex mirror  16  reflects the laser light to be guided to the photoconductors  20  disposed outside the optical scanning apparatus  10 .  
         [0047]     In the optical scanning apparatus  10  according to the embodiment, the laser light emitted from the laser light source  12  is gathered into the polygon scanner unit  14 . The laser light is polarized by the polygon mirror  17  provided in the polygon scanner unit  14  into a main scanning direction at the constant angular velocity. The polarized laser light is impinged on the photoconductors  20  via the optical elements  115  overlaid in the same position, the reflex mirrors  16 , the reflecting mirrors  21 , and so forth, to write images thereon.  
         [0048]     A configuration of the optical scanning apparatus  10  is not limited to the configuration described above referring to  FIGS. 8 and 9 . Another configuration of the optical scanning apparatus having the optical element  115  fixedly joined according to the embodiment of the present invention is described below referring to  FIGS. 10 and 11 .  
         [0049]      FIG. 10  is a top view of an optical scanning apparatus  10   a  having a configuration for color image forming using a plurality of toner images in respective colors.  FIG. 11  is a side view of the optical scanning apparatus  10   a  shown in  FIG. 10 .  
         [0050]     As shown in  FIGS. 10 and 11 , the optical scanning apparatus  10   a  includes a plurality of laser light sources  12   a,    12   b,    12   c,  and  12   d,  a plurality of cylindrical lens  13   a,    13   b,    13   c,  and  13   d,  and a plurality of photoconductors  20   a,    20   b,    20   c,  and  20   d.  The optical scanning apparatus  10   a  further includes the polygon scanner unit  14 , the reflex mirrors  16 , the polygon mirror  17 , the reflecting mirrors  21 , the housing  111 , and the optical elements  115 , corresponding to those shown in  FIGS. 8 and 9 .  
         [0051]     The plurality of laser sources  12   a  to  12   d  emit laser light to form electrostatic latent images for respective colors on corresponding ones of the plurality of photoconductors  20   a  to  20   d.  The cylindrical lenses  13   a  to  13   d  are provided for the laser light sources  12   a  to  12   d,  respectively. The laser light emitted from the laser sources  12   a  to  12   d  is polarized by the polygon scanner unit  14 . The polarized laser light is impinged on the photoconductors  20   a  to  20   d  via the overlaid optical elements  115  arranged at positions opposed to the polygon scanner unit  14  so as to correspond to respective laser light sources  12   a  to  12   d,  the reflex mirrors  16 , the reflecting mirrors  21 , and so forth, to write images thereon.  
         [0052]     Next, an image forming apparatus including the optical scanning apparatus having the optical element fixedly joined according to the embodiment of the present invention is described below referring to  FIG. 12 .  FIG. 12  is a schematic illustration of a general configuration of an image forming apparatus  80  including the optical scanning apparatus  10  according to the present invention. As shown in  FIG. 12 , the image forming apparatus  80  includes the optical scanning apparatus  10 , an exposure glass  81 , a reading device  82 , a development unit  84 , a photoconductor  85 , a fixing unit  86 , sheet discharging rollers  87 , a sheet discharging tray  88 , a sheet feeding tray  89 , and sheet feeding rollers  90 .  
         [0053]     The reading device  82  reads image data from an original placed on the exposure glass  81 , and sends an image signal representing the read image data to the optical scanning apparatus  10 . The optical scanning apparatus  10  emits laser light for writing according to the image signal to irradiate the photoconductor  85  therewith so that an electrostatic latent image is formed on the photoconductor  85 . The development unit  84  develops the electrostatic latent image formed on the photoconductor  85  into a toner image. The toner image is transferred onto a sheet conveyed from the sheet feeding tray  89  by the sheet feeding rollers  90 . The fixing unit  86  applies heat to the sheet to fix the transferred toner image on the sheet. The sheet having the fixed toner image is discharged into the sheet discharging tray  88  via the sheet discharging rollers  87 .  
         [0054]     The image forming apparatus  80  may include the optical scanning apparatus  10   a  instead of the optical scanning apparatus  10  with another configuration corresponding to the optical scanning apparatus  10   a.    
         [0055]     Since the image forming apparatus includes the optical element  115  which has a small amount of deformation because the optical element  115  has been fixedly joined by the method of fixedly joining according to the embodiment of the present invention, the image forming apparatus  80  can perform excellent optical scanning by maintaining a good optical property. As a result, the image forming apparatus  80  is capable of forming an image having intended image quality.  
         [0056]     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.  
         [0057]     This patent specification is based on a Japanese patent application, No. JP2005-034806 filed on Feb. 10, 2005 in the Japan Patent Office, the entire contents of which are hereby incorporated by reference herein.