Abstract:
An image forming apparatus for suppressing deviations in the application position of light emitted from an optical box, thus preventing an image from being deteriorated, has an image bearing body, a light source, a deflecting device for deflecting a light emitted from the light source, a lens for imaging a light deflected in this manner onto the image bearing body, and an optical box for containing at least the light source, the deflecting device, and the lens, wherein the optical box is provided plurally and the plurality of optical boxes are stacked to be integrated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus having a plurality of scanning type optical devices used in a copy machine, a printer, a facsimile, etc. 
     2. Related Background Art 
     Conventionally, in a scanning type optical device used in a laser beam printer (LBP), a digital copy machine, etc., light flux emitted from a light source means is light-modulated on the basis of an image signal and is periodically deflected by a deflector comprising, e.g., a rotary polygon mirror and then converged in a spot by a scanning type optical element (image forming element) having an fθ characteristic onto a surface of a recording medium (photosensitive drum) having a photosensitivity, which surface is scanned optically to record the image. 
     FIG. 9 is a schematic diagram for showing an important part of the above-mentioned type of a conventional scanning type optical device. 
     In the scanning type optical device shown in FIG. 9, divergent light flux emitted from a light source means  91  is transformed by a collimator lens  92  into roughly parallel light flux, which is in turn limited in light quantity by a diaphragm  93  and then injected to a cylinder lens (cylindrical lens)  94  having a predetermined refracting power only in the sub-scanning direction. The roughly parallel light flux thus injected to the cylinder lens  94  is emitted as in a main scanning cross section, to be converged in a subscanning cross section and formed as an approximate line image on a reflecting surface  95   a  of a deflector  95  comprising a rotary polygon mirror. 
     Thus, the light deflected by (reflected from) the surface  95   a  of the deflector  95  passes through a scanning type optical element (fθ lens) having an fθ characteristic and is guided onto a photosensitive drum surface  98 , which surface is then scanned optically in a direction of an arrow B when the deflector  95  is turned in a direction of an arrow A. In this way, an image is recorded on the photosensitive drum surface  98 , which is a recording medium. 
     Recently, there has been proposed a color image forming apparatus having a plurality of (e.g., four) scanning type optical devices (see Japanese Patent Application Laid-Open Nos. 6-183056 and 10-186254). 
     A conventional color image forming apparatus, however, uses many folding mirrors and has a plurality of (e.g., four) scanning type optical devices independently screwed to a side plate of the main body thereof, so that when those optical devices are specifically fixed to that main body, their light application positions are deviated in different directions, thereby giving rise to misregistration in color, and thus causing image quality deterioration. 
     Furthermore, since they are solidly fixed in this manner, their light application positions are deviated in different directions by environmental fluctuations, i.e., high/low temperatures, distorted mounting (where the color image forming apparatus is mounted on a distorted surface), which also gives rise to misregistration in color. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an image forming apparatus for suppressing deviations in the application position of light emitted from an optical box, thus preventing an image from being deteriorated. 
     It is another object of the present invention to provide an image forming apparatus comprising an image bearing body, a light source, a polarizing means for polarizing light emitted from the light source, a lens for imaging light polarized by the polarizing means onto the image bearing body, and an optical box for containing at least the light source, the polarizing means, and the lens, wherein the optical box is provided plurally and the plurality of optical boxes to be integrated. 
     Further objects of the present invention will become apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a state where scanning type optical devices of a color image forming apparatus related to the present invention are stacked in a plurality of stages; 
     FIG. 2 is a plan view showing the scanning type optical device of the color image forming apparatus related to the present invention; 
     FIG. 3 is a perspective view showing an optical box of the scanning type optical device; 
     FIG. 4 is another perspective view showing the optical box of the scanning type optical device; 
     FIG. 5 is further another perspective view showing the optical box of the scanning type optical device; 
     FIG. 6 is still further another perspective view showing the optical box of the scanning type optical device; 
     FIG. 7 is a perspective view showing a method of fixing the scanning type optical device to the color image forming apparatus; 
     FIG. 8 is another perspective view showing the method for fixing the scanning type optical device to the color image forming apparatus; and 
     FIG. 9 is a plan view showing an important part of a conventional scanning type optical device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following will describe some embodiments of the present invention with reference to the drawings attached hereto. 
     FIG. 1 is a cross-sectional view showing a state where scanning type optical devices of a color image forming apparatus related to the present invention are stacked in a plurality of stages, FIG. 2 is a plan view showing the scanning type optical device, and FIG. 3 is a perspective view showing an optical box. 
     In the color image forming apparatus relating to the present invention, as shown in FIG. 1, four scanning type optical devices  40   a ,  40   b ,  40   c , and  40   d  are vertically stacked in a plurality of stages and respectively comprise optical boxes  36   a ,  36   b ,  36   c , and  36   d , which respectively include laser units  30   a ,  30   b ,  30   c , and  30   d  for producing a roughly parallel light of a light flux emitted from light source semiconductor lasers  100   a ,  100   b ,  100   c , and  100   d , respectively, cylindrical lenses  31   a ,  31   b ,  31   c , and  31   d  shown in FIG. 2 for forming as an image a light flux on the reflection surface of rotary polygon mirrors  33   a ,  33   b ,  33   c , and  33   d , respectively, deflector means  32   a ,  32   b ,  32   c , and  32   d  for deflecting light flux  50   a ,  50   b ,  50   c , and  50   d , respectively for scanning, beam detecting sensors  38   a ,  38   b ,  38   c , and  38   d  shown in FIG. 2 for sampling a write-out synchronization signal, image-forming lenses  34   a ,  34   b ,  34   c , and  34   d  for forming as an image the thus-deflected light flux on image bearing bodies  37   a ,  37   b ,  37   c , and  37   d , respectively, and lenses  35   a ,  35   b ,  35   c , and  35   d.    
     In this embodiment, as shown in FIG. 3, at the upper part of the optical boxes  36   c  and  36   d  are provided with protrusions  41   c  and  41   d , respectively and, at the lower part of them are formed pores  42   c  and  42   d , respectively. The protrusion  41   d  and the pores  42   c  and  42   d  are provided on both sides of the optical box like the protrusion  41   c.    
     Thus, the protrusion  41   d  of the underlying optical box  36   d  is fitted into the pore  42   c  of the overlying optical box  36   c , thereby to align these two optical boxes  36   c  and  36   d . Then, elastic member springs  39   a  and  39   b  are pushed from both sides into lateral ribs  43   c   2  and  43   d   1 , which are expanded engaging portions for engagement with other optical boxes, of the optical boxes  36   c  and  36   d , respectively, thereby to fasten these two optical boxes with each other. 
     The four scanning type optical devices  40   a ,  40   b ,  40   c , and  40   d  can be fastened to one another by almost the same operations as above in such a configuration employed above that the optical boxes  36   a  through  36   d  are fastened to each other by use of the springs  39   a  and  39   b , thereby to fasten those four optical boxes without deformations, unlike in the case of a conventional embodiment, thus avoiding fluctuations in the position of applying light flux  50   a  through  50   d  emitted from the scanning type optical devices  40   a  through  40   d  onto the image bearing bodies  37   a  through  37   d , respectively. Moreover, even with environmental fluctuations such as high or low temperatures and skewed mounting, no residual stress is generated on the optical boxes  36   a  through  36   d , so that such optical devices as the laser units  30   a  through  30   d , the cylindrical lenses  31   a  through  31   d , the deflectors  32   a  through  32   d , and the image forming lenses  34   a  through  34   d  and  35   a  through  35   d  have no deformation or shift, with the result that the optical boxes  36   a  through  36   d  are not deformed or shifted, and so fluctuations in the light application positions do not occur. 
     Furthermore, those optical boxes can be fastened with each other by adhering them at the gap between the protrusion and the pore in place of using the spring. In addition, they can be fastened with each other by welding them at their respective protrusions. 
     Furthermore, as shown in FIG. 4, the lateral ribs  43   c   1 ,  43   c   2 ,  43   d   1 , and  43   d   2 , at which the optical boxes  36   c  and  36   d  are fixed with each other, may be provided with notches  44   c  and  44   d , respectively, to fasten the optical boxes  36   c  and  36   d  by sandwiching the ribs  44   c    1  and  44   c   2  present between the notches of the lateral ribs  43   c   2  and  43   d   1  superposed one on the other using the springs  39   a  and  39   b  from both sides, thus avoiding deformations in the portions where such optical devices are mounted as the laser units  30   c  and  30   d , the cylindrical lenses  31   c  and  31   d , the deflectors  32   c  and  32   d , and the image forming lenses  34   c ,  34   d ,  35   c , and  35   d , thereby to suppress fluctuations in the light application positions of the scanning type optical devices  40   c  and  40   d . Accordingly, the optical boxes  36   a  through  36   d  can be fastened with each other by almost the same fastening method as above to thereby suppress fluctuations in the light application positions of the scanning type optical devices  40   a  through  40   d.    
     In this case, if an inclination distance between the scanning type optical devices  40   d  and  40   c  when the scanning type optical device  40   c  is mounted to the scanning type optical device  40   d  is within an allowable range (a few tens of micrometers (μm) approximately), the scanning type optical devices  40   c  and  40   d  may be fastened to each other according to the above-mentioned method. 
     If, however, the light illumination is inclined such that the resultant misregistration in color goes out of the allowable range when the scanning type optical devices  40   a  through  40   d  are simply stacked one on another, the inclination can be adjusted according to the following procedure to then properly the scanning type optical devices  40   a  through  40   d  one another. 
     By fixing, in FIG. 5, one side of the lateral rib  43   c   2  provided to the optical box  36   c  as measuring the light application positions (light flux  50   c   1  and  50   c   2 ) of the scanning type optical device  40   c  with respect to the light application positions (light flux  50   d   1  and  50   d   2 ) of the scanning type optical device  40   d  to then adjust the light application positions by moving the other side of the lateral rib  43   c   2  vertically in a C—C′ direction in order to stop the optical box  36   c  at a predetermined position, an adhesive agent can be then poured into a gap between the protrusion  42   c  and the pore  42   d , thereby to fix the optical boxes  36   c  and  36   d  to each other. 
     The following will describe a method for once fixing the scanning type optical devices  40   a  through  40   d  to their respective members with respect to FIG.  6 . 
     A storage member  60 , which is a positioning means, for the scanning type optical devices  40   a  through  40   d  is provided with inner ribs  61   a   1 ,  61   a   2 ,  61   b   1 ,  61   b   2 ,  61   c   1 ,  61   c   2 ,  61   d   1 , and  61   d   2 , so that when the scanning type optical device  40   d  is to be mounted for example, it is put on the inner ribs  61   d   1  and  61   d   2  to thereby sandwich, in a depth direction, a pair of the lateral rib  43   d   2  and the inner rib  61   d   2  and another pair of the lateral rib  43   d   4  and the inner rib  61   d   1  of the optical box  36   d  by using the springs  39   a  and  39   b  as shown in FIG. 3 or  4 . Likewise, they are sandwiched by the springs  39   a  and  39   b  on the opposite side. 
     Likewise, the four scanning type optical devices  40   a  through  40   d  are mounted and fixed to the storage member  60 . 
     In this case, the storage member  60  has one reference pore  72   a  (the other reference pore is formed on the opposite side) formed therein, so that by inserting into and fixing to this reference pore  72   a  one reference pin  71   a  (the other reference pin is provided on the opposite side) protruding from the color image forming apparatus  70 , thereby to determine the position of the storage member  60 , thus fixing it to the color image forming apparatus  70  by a screw  73 . By providing such a storage member  60 , the four scanning type optical devices  40   a  through  40   d  can be replaced simultaneously, thus facilitating maintenance. Moreover, even if the color image forming apparatus  70  is mounted on an inclined surface, only outer ribs  76   a  and  76   b  of the storage member  60  are deformed, thus leaving the light application positions of the scanning type optical devices  40   a  through  40   d  unchanged. 
     The following will describe a method for stacking the scanning type optical devices  40   a  through  40   d  as they are one on another and then fixing them to the color image forming apparatus with reference to FIG.  7 . 
     The optical box  36   d  of the scanning type optical device  40   d  set at the lowest stage is mounted with one engaging fixture rib  79   a  and the other at the front and rear parts thereof in the light emission direction, the fixture rib  79   a  of which has one reference pore  77   a  formed therein, with the other formed on the opposite side of the optical box. 
     Thus, the scanning type optical devices  40   a  through  40   d  are stacked one on another according to almost the same method as described above with reference to FIGS. 3,  4 , or  5 . Then, the reference pore  77   a  formed in the fixture rib  79   a  is fitted to the reference pin  71   a  (the other reference pin is provided on the light emitting side) provided as protruded on the color image forming apparatus  70 , thereby to determine the positions of the scanning type optical devices  40   a  through  40   d , thus fixing the scanning type optical devices  40   a  through  40   d  to the color image forming apparatus  70  using a screw  75 . Thus, the scanning type optical devices  40   a  through  40   d  can be fixed to the color image forming apparatus  70  to thereby prevent the optical boxes  36   a  through  36   d  from being deformed, thus avoiding the fluctuations in the light application positions of the scanning type optical devices  40   a  through  40   d.    
     Next, the following will describe a method for fixing the scanning type optical devices  40   a  through  40   d  using a screw, on the basis of FIG.  8 . 
     Likewise in the above-mentioned example, the scanning type optical devices  40   a  through  40   d  are aligned and positioned through the reference pore  77   a  and the reference pin  71   a  and then fixed to the color image forming apparatus  70  by sandwiching this apparatus  70  and one pair of the ribs  80   a  and  80   b  (the other pair is provided on the opposite side) by one pair of fixture springs  81   a  and  81   b  (the other pair is provided on the opposite side). Accordingly, likewise in the above example, the optical boxes  36   a  through  36   d  are not deformed, to permit the scanning type optical devices  40   a  through  40   d  to be fixed as unchanged in light application position. In this case, the scanning type optical devices  40   a  through  40   d  can be fixed to the color image forming apparatus also by means of adhesion or welding to obtain the same effects. 
     In this embodiment in particular, in a case where the folded mirror is not arranged in the scanning type optical devices  40   a  through  40   d , there are less factors present for causing fluctuations in the light application position even with a slight deformation in the optical boxes  36   a  through  36   d , thereby to reduce those fluctuation in the light application position greatly, thus enabling obtaining a color image forming apparatus capable of high-accuracy printing. 
     Furthermore, in this embodiment, the interval (pitch) between the image bearing bodies  37   a  through  37   d  is the same as that between the scanning type optical devices  40   a  through  40   d , so that the color image forming apparatus can be made with the minimum required number of components and very inexpensively. 
     Therefore, by the present invention, a plurality of optical boxes is put in a stack and integrated to thereby constitute scanning optical devices, so that these scanning type optical devices can be prevented from, when they are mounted to a color image forming apparatus, being deformed to be shifted in their light application positions in different directions, and thus image quality deterioration due to misregistration in color is avoided, and a high quality color image is obtained in a stable manner. 
     While there have been described what are at present considered to be preferred embodiments of the present invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the present invention.