Patent Publication Number: US-9904226-B2

Title: Optical apparatus and image forming apparatus including the optical apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Pat. application Ser. No. 14/962,091 filed Dec. 8, 2015, which claims the benefit of Japanese Patent Application No. 2014-250410, filed Dec. 10, 2014, the disclosures of each of which are hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an optical apparatus that receives light reflected from a target portion when the target portion is irradiated with the light and also relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, which includes the optical apparatus. 
     Description of the Related Art 
     In general, an image forming apparatus is sensitive to an operating environment and various conditions (e.g., the number of sheets to be printed) because the density of each color is variable and the tint of a formed image is variable too. A color image forming apparatus is configured to overlap a plurality of color images to form a composite color image. Therefore, positional deviation tends to occur in respective color images. For example, when the color image forming apparatus includes four-color (e.g., yellow, magenta, cyan, and black) photosensitive drums, the relative position between two of four-color images is variable. 
     There is a conventional method for correcting the positional deviation of each color or each color density. More specifically, the conventional method includes causing a light-receiving member of an optical apparatus to detect the amount of light reflected from a patch (i.e., a reference pattern) formed on an intermediate transfer member, a photosensitive member, or a sheet. The method includes calculating a positional deviation between respective colors and a density variation of each color based on a detection result representing the amount of received light. The method includes controlling various image forming conditions based on the calculation result in such a way as to appropriately adjust the positional deviation between respective colors and the density of each color. 
     As discussed in Japanese Patent Application Laid-Open No. 2013-191835, there is a conventionally known configuration capable of improving the detection accuracy of an optical apparatus (e.g., an optical sensor) that is used in the above-mentioned patch detection. 
     The optical apparatus discussed in Japanese Patent Application Laid-Open No. 2013-191835 includes a light-emitting member and a light-receiving member mounted on a substrate and covered with a housing that serves as a light-shielding member. However, according to such a conventional arrangement, the detection accuracy may deteriorate due to stray light. Therefore, the present invention intends to prevent the detection accuracy from being deteriorated by the stray light. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, an optical apparatus includes a light-emitting member, a light-receiving member, a substrate including a plate-like substrate layer and a plate-like conductive layer, on which the light-emitting member and the light-receiving member are mounted, and a light-shielding member disposed between the light-receiving member and the light-emitting member and inserted in a through-hole of the substrate provided between the light-receiving member and the light-emitting member. The light-receiving member is configured to receive reflected light from a portion to be irradiated with the light emitted from the light-emitting member. The conductive layer is excellent in light-shielding property compared to the substrate layer. The conductive layer is exposed to an inner cylindrical surface of the through-hole. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration illustrating an image forming apparatus. 
         FIG. 2  is a schematic cross-sectional view illustrating an optical sensor unit. 
         FIG. 3  is a cross-sectional view of a substrate in a state where there is not any through-hole formed therein. 
         FIG. 4  is a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the substrate, which illustrates a formation of through-holes. 
         FIG. 5  is a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the optical sensor unit. 
         FIG. 6  is a cross-sectional view of a substrate in a state where there is not any through-hole formed therein. 
         FIG. 7  illustrates a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the substrate, which illustrates a formation of through-holes. 
         FIG. 8  illustrates a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the optical sensor unit. 
         FIG. 9  is a cross-sectional view illustrating a comparative example of the optical sensor unit. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     [Image Forming Apparatus] 
     A first exemplary embodiment will be described in detail below.  FIG. 1  is a schematic cross-sectional view illustrating a configuration of a color laser printer, which is an image forming apparatus according to the present invention. The image forming apparatus according to the present invention includes four-color image forming units to form a composite color image by overlapping four-color images. For example, the combination of four colors is yellow (Y), magenta (M), and cyan (C) of chromatic color developers and black (Bk) of an achromatic color developer. A color laser printer  101  is an image forming apparatus that can receive image data  103  from a host computer  102 . The color laser printer  101  includes a print image generation unit  104  that can develop image data into desired video signal format data to generate an image forming video signal  105 . An image forming control unit  106  includes a central processing unit  109  (hereinafter, simply referred to as CPU  109 ) that is operable as a control unit. The video signal generated by the print image generation unit  104  can be transmitted to the image forming control unit  106  from the print image generation unit  104 . The image forming control unit  106  drives a plurality of laser diodes  111  provided in a scanner unit  110  according to the video signal. Each laser diode  111  serves as a laser emitting element. The scanner unit  110  is operable as an exposure unit. Respective photosensitive drums  115   y ,  115   m ,  115   c , and  115   k  (hereinafter, collectively referred to as “photosensitive drum  115 ”) are irradiated with laser beams  112   y ,  112   m ,  112   c , and  112   k  (hereinafter, collectively referred to as “laser beam  112 ”) emitted from respective laser diodes and traveling via a polygon mirror  107 , lenses  113   y ,  113   m ,  113   c , and  113   k  (hereinafter, collectively referred to as “lens  113 ”), mirrors  114   y ,  114   m ,  114   c , and  114   k  (hereinafter, collectively referred to as “mirror  114 ”). Respective charging units  116   y ,  116   m ,  116   c , and  116   k  (hereinafter, collectively referred to as “charging unit  116 ”) can charge the corresponding photosensitive drums  115  to have a desired electric charge amount. When the surface of each photosensitive drum  115  is irradiated with the laser beam  112 , an electrostatic latent image can be formed at an irradiated portion where the electric potential decreases. To visualize the electrostatic latent image formed on the photosensitive drum  115  irradiated with the laser beam, respective developing units  117   y ,  117   m ,  117   c , and  117   k  (hereinafter, collectively referred to as “developing unit  117 ”) can form a toner image reflecting the electrostatic latent image on the photosensitive drum  115 . Respective primary transfer members  118   y ,  118   m ,  118   c , and  118   k  (hereinafter, collectively referred to as “primary transfer member  118 ”) can primarily transfer the toner images formed on respective photosensitive drums onto an endless belt (hereinafter, referred to as “intermediate transfer belt”)  119 . In this respect, each primary transfer member  118  serves as a transfer unit to which a transfer voltage is applied. In the primary transfer operation, a yellow image is initially transferred onto the intermediate transfer belt  119 . Then, magenta, cyan, and black images are sequentially transferred onto the intermediate transfer belt  119 , in such a way as to form a composite color image. In this case, the intermediate transfer belt  119  carries a four-color toner image. The intermediate transfer belt  119  is rotatably engaged with a tension roller  127  and a driving roller  126 . The driving roller  126  can control the conveyance of the intermediate transfer belt  119 . A paper feeding roller  122  is located adjacently to a cassette  120 . The paper feeding roller  122  conveys each recording paper  121  from the cassette  120  toward a secondary transfer portion  123  in such a way as to be synchronized with the image primarily transferred on the intermediate transfer belt  119 . The color laser printer  101  performs a secondary transfer operation at the secondary transfer portion  123  so that the image can be transferred to the recording paper  121 . In this case, an appropriate bias voltage is applied to a secondary transfer roller to increase transfer efficiency. A fixing device  124  performs a thermal fixing operation by applying heat and pressure to the recording paper on which the image has been secondarily transferred. A stable color image can be fixed on the recording paper. Then, the recording paper can be discharged via a discharge portion. An optical sensor unit  125  is operable as a detection unit and is supported by the tension roller  127 . The optical sensor unit  125  is an optical sensor capable of detecting a positional deviation correction pattern and a density correction pattern that are used to detect a positional deviation amount and a density variation of each color image transferred on the intermediate transfer belt  119 . At desired timing, the optical sensor unit  125  detects the position of the correction pattern of each color formed on the intermediate transfer belt  119  and a difference from a target density. Then, the optical sensor unit  125  outputs the detection result to the CPU  109  (i.e., the control unit). The CPU  109  saves the detection result in a random access memory  180  (hereinafter, simply referred to as RAM  180 ), which is a storage unit. The saved detection result can be fed back to the image forming control unit  106 . The image forming control unit  106  can correct the positional deviation of each color toner image in a main scanning direction and a sub scanning direction. Further, the image forming control unit  106  can correct the density of each color. 
     [Optical Sensor Unit] 
     Next, the optical sensor unit  125 , which is operable as an optical apparatus, will be described in detail below.  FIG. 2  is a schematic cross-sectional view illustrating the optical sensor unit  125 . A light-emitting member  202  is an LED infrared light-emitting element. Hereinafter, the light-emitting member  202  is referred to as “light-emitting element  202 .” Two light-receiving members  204  and  205  are phototransistor infrared light-receiving elements. The light-receiving member  205  can receive diffuse-reflected light of the light-emitting element  202 . The light-receiving member  204  can receive mirror surface reflected light (regular reflected light). Hereinafter, the light-receiving members  204  and  205  are referred to as light-receiving elements  204  and  205 , respectively. A substrate  201  has a surface on which the light-emitting element  202 , respective light-receiving elements  204  and  205 , and electronic circuit components (not illustrated) are mounted. Each of the light-emitting element  202  and the respective light-receiving elements  204  and  205  is a bare chip element, which is mounted on the substrate  201  in such a manner that a central axis thereof extends in a direction substantially perpendicular to the surface of the substrate  201 . 
     A through-hole  207  is provided between the light-emitting element  202  and light-receiving element  204 . Another through-hole  207  is provided between the light-emitting element  202  and the light-receiving element  205 . Each through-hole  207  extends from the front surface to the back surface of the substrate  201  in a direction perpendicular to the surface of the substrate  201 . A resin-made housing member  206  (hereinafter, referred to as “housing  206 ”) has a portion that covers the light-emitting element  202  and a diaphragm aperture through which the light emitted from the light-emitting element  202  can pass, a portion that covers the light-receiving element  204 , a diaphragm aperture through which light can enter the light-receiving element  204 , a portion that covers the light-receiving element  205 , and a diaphragm aperture through which light can enter the light-receiving element  205 . When the light-emitting element  202  emits light, a beam travels through the diaphragm aperture of the housing  206  formed at the region that covers the light-emitting element  202 . In this case, the surface of the intermediate transfer belt  119  can be irradiated with the beam that inclines by an angle of 13° relative to a direction perpendicular to the surface of the intermediate transfer belt  119 . On the other hand, the light-receiving element  204  can receive light reflected from the surface of the intermediate transfer belt  119  by an angle of 13° relative to the direction perpendicular to the surface of the intermediate transfer belt  119  and passing through the diaphragm aperture of the housing  206  formed at the region that covers the light-receiving element  204 . Similarly, the light-receiving element  205  can receive light reflected from the surface of the intermediate transfer belt  119  by an angle of 60° relative to the direction perpendicular to the surface of the intermediate transfer belt  119  and passing through the diaphragm aperture of the housing  206  formed at the region that covers the light-receiving element  205 . The housing  206  includes two wall portions  206   a  and  206   b  inserted in corresponding through-holes  207 . One wall portion  206   a  is disposed between the light-emitting element  202  and the light-receiving element  204 . The other wall portion  206   b  is disposed between the light-emitting element  202  and the light-receiving element  205 . 
     A sensor stay (stay member)  209  is a positioning member that supports the optical sensor unit  125  to the tension roller  127  at a position where a predetermined distance can be kept between the optical sensor unit  125  and the intermediate transfer belt  119 . The sensor stay  209  is a plate-like metal member. A spacer member (hereinafter, simply referred to as “spacer”)  208  is disposed between the substrate  201  and the sensor stay  209  in such a way as to prevent any interference with electronic components (not illustrated) provided on the substrate  201 . The spacer  208  is opposed to the back surface of the substrate  201 , while the light-emitting element  202  and the light-receiving elements  204  and  205  are mounted on the front surface of the substrate  201 . The spacer  208  is a resin-made member, which has a black surface that faces the back surface of the substrate  201 . The black surface can absorb the light from the light-emitting element  202 . Further, the surface of the spacer  208  is a matt finished surface capable of diffusing and reflecting stray light having not been absorbed. The spacer  208  includes boss portions by which the substrate  201 , the housing  206 , and the sensor stay  209  are positioned with each other in a predetermined relationship. The above-mentioned members are united tightly by means of screws (not illustrated), as the optical sensor unit  125 , and are brought into contact with and attached to a bearing portion of the tension roller  127 . A toner pattern  203 , which is carried by the intermediate transfer belt  119 , is a portion to be irradiated with light. When infrared light is emitted from the light-emitting element  202 , the light-receiving element  204  receives mirror surface reflected light from the surface of the intermediate transfer belt  119  and the positional deviation and density variation detecting toner pattern  203  transferred onto the intermediate transfer belt  119 . The light-receiving element  205  receives diffuse-reflected light. Therefore, it is feasible to detect a positional deviation amount of the positional deviation and density variation detecting toner pattern  203  and a density variation amount from a desired density. 
       FIG. 3  is a cross-sectional view of the substrate  201  in a state where the through-hole  207  is not yet formed. The substrate  201  is composed of a substrate layer  301 , two copper foil layers  302 , and two solder resist layers  303 . The substrate layer  301  is a glass epoxy resin-made member. Each copper foil layer  302  is a thin copper-made layer. One copper foil layer  302  is formed on the front surface of the substrate layer  301 . The other copper foil layer  302  is formed on the back surface of the substrate layer  301 . The copper foil layer  302  is excellent in light-shielding property compared to the substrate layer  301 . As illustrated in  FIG. 3 , the copper foil layer  302  covers a region corresponding to the through-hole  207 . The substrate layer  301 , the copper foil layers  302 , and the solder resist layers  303  are laminated layers that cooperatively constitute a plate-like configuration of the substrate  201 . 
       FIG. 4  is a set of a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the substrate  201 , which illustrates a formation of the through-holes  207 . The cross-sectional view illustrates a cross section taken along a dotted line X 1  shown in the upper surface view. A drill  401  is a rotating tool that enables a user to perform a cutting work to open each through-hole  207  in the substrate  201 . in the substrate  201 , a place where the through-hole  207  can be opened with the drill  401  is a portion where the copper foil layer  302  is provided. Each through-hole  207  extends across the solder resist layers  303 , the copper foil layers  302 , and the substrate layer  301  vertically from the front surface to the back surface of the substrate  201 . A through-hole via  403  extends from the front surface to the back surface of the substrate  201 . The through-hole via  403  includes an inner cylindrical surface on which the copper foil layer  302  is formed. The copper foil layer  302  provided on the front surface of the substrate  201  and the copper foil layer  302  provided on the back surface are conductive layers electrically connected to each other and having the same potential (ground). A signal line (a circuit pattern)  405  is formed on the surface of the substrate  201  and is electrically connected to the light-emitting element  202 , the light-receiving elements  204  and  205 , the electronic circuit components (not illustrated), and the CPU  109  illustrated in  FIG. 1 . 
       FIG. 5  illustrates a cross-sectional view (an upper part of the drawing) of the optical sensor unit  125  in a state where the light-emitting element  202  and the light-receiving elements  204  and  205  are mounted on the substrate  201  that includes the through-hole  207  formed therein and the housing  206  is attached to the substrate  201 .  FIG. 5  further illustrates an upper surface view (a lower part of the drawing) of the optical sensor unit  125  in a state where the housing  206  is not yet installed. The upper surface view of  FIG. 5  illustrates an appearance of the optical sensor unit  125  seen from a direction perpendicular to the extending direction of the plate-like substrate  201  (i.e., an axial direction of the through-hole  207  perpendicular to the surface). The cross-sectional view of  FIG. 5  illustrates a cross section taken along a dotted line X 1  shown in the upper surface view. The light-emitting element  202  and the light-receiving elements  204  and  205  are mounted on the substrate  201  by reflowing. The housing  206  is attached to the substrate  201  via the through-holes  207 . The substrate  201  and the sensor stay  209  are mutually positioned with the boss portions of the spacer  208 . Then, these members are united tightly by means of screws (not illustrated). A region where the copper foil layer  302  is provided covers the mounting positions of the light-emitting element  202  and the light-receiving elements  204  and  205  and each region A surrounding the through-hole  207 . The copper foil layer  302  extends along an inner cylindrical surface of the through-hole  207 . A cross section of the copper foil layer  302  is exposed to the inner cylindrical surface of the through-hole  207 . 
     As indicated by a path P, the light emitted from the light-emitting element  202  is reflected by the copper foil layer  302  in the region A. In other words, the copper foil layer  302  prevents the emitted light from entering the substrate layer  301 . Because unnecessary light is prevented from entering the substrate layer  301 , the light emitted from the light-emitting unit can be prevented from becoming disturbance light that travels in the substrate and reaching the light-receiving elements  204  and  205 . Further, as indicated by a path R, disturbance light having entered via a clearance between the substrate  201  and the spacer  208  is reflected by the copper foil layer  302  in the region A. In other words, the copper foil layer  302  prevents the disturbance light from entering the light-receiving elements  204  and  205 . Further, as indicated by a path Q, light leaking from a clearance between the through-hole  207  and a light-shielding member  206  to the back surface of the substrate  201  is absorbed or diffuse-reflected by the front surface of the spacer  208 . In other words, the spacer  208  can suppress the leaking light from reaching the light-receiving elements  204  and  205 . 
     [Comparative Example] 
       FIG. 9  is a cross-sectional view illustrating a comparative example of the optical sensor. A substrate  500  illustrated in  FIG. 9  has front and back surfaces on which electronic components can be mounted. The substrate  500  is composed of a substrate layer  501 , copper foil layers  502 , and solder resist layer  503 . The substrate layer  501  is a glass epoxy resin-made member. A light-emitting unit  202  and two light-receiving units  204  and  205  are fixed on the substrate  500  by surface mounting. Two through-holes  507  extend from the front surface to the back surface of the substrate  500 . A light-shielding member  206  covers the light-emitting unit  202  and respective light-receiving units  204  and  205 . A sensor stay  209  holds the substrate  500  and is attached to a detection target object. 
     The substrate  500  of the comparative optical sensor does not include the copper foil layer  502  in each region A adjacent to the corresponding through-hole  507 . Further, as indicated by a region B, there is a clearance between the through-hole  507  and the light-shielding member  206 . Therefore, as indicated by a path P, the light of the light-emitting unit  202  enters the substrate  500  via the through-hole  507  and a surrounding portion thereof where the copper foil layer  502  is not present. The sensor stay  209  reflects the light having entered the substrate  500 . The reflected light can reach the light-receiving element. This is one reason why the output of the optical sensor changes undesirably. Further, as indicated by a path R, disturbance light having entered the substrate layer  501  travels and reaches the sensor stay  209 . As indicated by a path Q, leaking light from a clearance between the through-hole  507  and the light-shielding member  206  also reaches the sensor stay  209 . The sensor stay  209  reflects the disturbance light and leaking light. The reflected light can reach the light-receiving element. This is another reason why the output of the optical sensor changes undesirably. If the sensor output changes due to the disturbance light and the leaking light as mentioned above, the dynamic range of the optical sensor decreases undesirably. The dynamic range is a ratio of maximum output value to minimum output value of a target object to be detected. The detection accuracy of the optical sensor deteriorates according to the reduction of the dynamic range. 
     The present exemplary embodiment is different from the above-mentioned comparative example in the following features. The copper foil layer  502  is present in the region covering not only the mounting portions of the light-emitting element  202  and the light-receiving elements  204  and  205  but also the position substantially identical to the outer diameter of the through-hole  507 . Therefore, it is feasible to prevent the stray light from entering the light-receiving elements  204  and  205  and suppress the detection accuracy of the optical sensor from deteriorating. 
     As mentioned above, according to the present exemplary embodiment, it is feasible to prevent the disturbance light having travelled in the substrate layer  301  from entering the light-receiving elements  204  and  205 . Further, it is feasible to prevent the light leaking via the clearance between the light-shielding member  206  and the through-hole  207  from entering the light-receiving elements  204  and  205 . Therefore, the optical sensor unit  125  can secure an adequate dynamic range (i.e., the ratio of maximum output value to minimum output value) in the detection of the positional deviation and density variation detecting toner patch (i.e., the reference pattern)  203 . When the dynamic range is maintained adequately without causing undesirable reduction, the optical sensor unit  125  can accurately detect the positional deviation and density variation detecting toner patch (i.e., the reference pattern)  203 . More specifically, the present exemplary embodiment brings an effect of suppressing the detection accuracy of the optical sensor unit  125  from deteriorating due to the stray light. 
     A second exemplary embodiment will be described in detail below. As mentioned above, the method according to the first exemplary embodiment includes forming the through-holes  207  in the glass epoxy resin-made substrate  301  having front and back surfaces on which electronic components can be mounted with the drill  401 . The second exemplary embodiment is different from the first exemplary embodiment in that the substrate  201  includes a paper phenol resin-made substrate layer  701  having only one surface on which electronic components can be mounted, as illustrated in  FIG. 6 . Further, the method according to the second exemplary embodiment includes performing a presswork to form the through-holes  207  with a die  801  in such a way as to extend across the substrate  201 , as described in detail below with reference to  FIG. 7 . The remaining components are assigned the reference numerals already described in the first exemplary embodiment when these components are similar to those described in the first exemplary embodiment. Therefore, redundant description thereof will be avoided. 
       FIG. 6  is a cross-sectional view of the substrate  201  in a state where the through-holes  207  are not yet formed. The substrate  201  is composed of the substrate layer  701 , the copper foil layer  302 , and the solder resist layer  303 . The substrate layer  701  is the paper phenol resin-made member. The copper foil layer  302  is provided on only one surface of the substrate layer  701 . The copper foil layer  302  is excellent in light-shielding property compared to the substrate layer  701 . The copper foil layer  302  covers a region corresponding to the through-hole  207 . 
       FIG. 7  is a set of a cross-sectional view (an upper part of the drawing) and an upper surface view (a lower part of the drawing) of the substrate  201 , which illustrates a formation of the through-holes  207 . The cross-sectional view illustrates a cross section of the substrate  201  taken along a dotted line  803 . The die  801  is a machining tool that is usable in a presswork to open the through-holes  207  in the substrate  201 . Each through-hole  207  extends vertically across the solder resist layer  303 , the copper foil layer  302 , and the substrate layer  301  vertically from the front surface to the back surface of the substrate  201 . The portion where the through-holes  207  are provided is a region where the copper foil layer  302  is present. Therefore, the copper foil layer  302  can be disposed in such a way as to cover the position substantially identical to the outer diameter of the through-hole  207 . A signal line  405  is formed on the surface of the substrate  201  and is electrically connected to the light-emitting element  202 , the light-receiving elements  204  and  205 , the electronic circuit components (not illustrated), and the CPU  109  illustrated in  FIG. 1 . 
       FIG. 8  is a set of a cross-sectional view (an upper part of the drawing) and an upper surface view (lower part of the drawing) of the optical sensor unit  125  in a state where the light-emitting element  202  and the light-receiving elements  204  and  205  are mounted on the substrate  201  that includes the through-holes  207  formed therein and the housing  206  is attached to the substrate  201 . The configuration illustrated in  FIG. 8  is different from the configuration illustrated in  FIG. 5  in that the copper foil layer  302  and the solder resist layer  303  are provided on only one surface of the substrate  201  and in the method for forming the through-holes  207 . The region where the copper foil layer  302  is provided covers the mounting positions of the light-emitting element  202  and the light-receiving elements  204  and  205  and each region A surrounding the through-hole  207 . The copper foil layer  302  extends along an inner cylindrical surface of the through-hole  207 . As indicated by a path P, the light emitted from the light-emitting element  202  is reflected by the copper foil layer  302  in the region A. In other words, the copper foil layer  302  prevents the emitted light from entering the substrate layer  701 . Because unnecessary light is prevented from entering the substrate layer  701 , the light emitted from the light-emitting unit can be prevented from becoming disturbance light that travels in the substrate and reaching the light-receiving elements  204  and  205 . 
     Further, as indicated by a path Q, light leaking from a clearance between the through-hole  207  and the light-shielding member  206  to the back surface of the substrate  201  is absorbed by the front surface of the spacer  208 . 
     As mentioned above, according to the present exemplary embodiment, it is feasible to prevent the disturbance light having travelled in the substrate layer  701  from entering the light-receiving elements  204  and  205 . Further, it is feasible to prevent the light leaking via the clearance between the light-shielding member  206  and the through-hole  207  from entering the light-receiving elements  204  and  205 . Therefore, the optical sensor unit  125  can secure an adequate dynamic range (i.e., ratio of maximum output value to minimum output value) in the detection of the positional deviation and density variation detecting toner patch (i.e., the reference pattern)  203 . When the dynamic range is maintained adequately without causing undesirable reduction, the optical sensor unit  125  can accurately detect the positional deviation and density variation detecting toner patch (i.e., the reference pattern)  203  that is formed on the surface of an image bearing member (such as the intermediate transfer member  119  or the photosensitive drum  115 ). More specifically, the present exemplary embodiment brings an effect of suppressing the detection accuracy of the optical sensor unit  125  from deteriorating due to the stray light. 
     According to the present invention, it is feasible to suppress the detection accuracy from deteriorating due to the stray light. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.