Patent Publication Number: US-11644764-B2

Title: Image forming apparatus

Description:
BACKGROUND 
     Field 
     The present disclosure relates to an image forming apparatus including an exposure head. 
     DESCRIPTION OF THE RELATED ART 
     There is an image forming apparatus, such as a printer or a copying machine, that uses an exposure head including a plurality of light-emitting elements for exposing the surface of a photosensitive member to light. The exposure head may use light-emitting diodes (LEDs), organic electro-luminescence (EL) devices, or the like as the light-emitting elements. United States Patent Application Publication No. 2015/346628 discusses an exposure head that includes a holder that is made of resin and holds a substrate on which light-emitting elements are arranged and a lens array for collecting light emitted from the light-emitting elements on a photosensitive member. 
     To achieve a further increase in image quality of the image forming apparatus, it is desirable to reduce the intensity of noise emitted from a wiring pattern formed on the substrate. To achieve this, it is effective to ground a ground wire for the wiring pattern formed on the substrate. However, since the substrate is held by the holder made of resin, the ground wire formed on the substrate cannot be grounded via the holder. 
     SUMMARY 
     Accordingly, the present disclosure is directed to providing a configuration for grounding a ground wire for a wiring pattern formed on a substrate with a simple configuration. 
     According to an aspect of the present disclosure, an image forming apparatus includes a photosensitive member that is rotatable, a substrate including a plurality of light-emitting elements arrayed in a rotational axis direction of the photosensitive member and configured to emit light to which a surface of the photosensitive member is exposed, a driver integrated circuit (IC) configured to drive the plurality of light-emitting elements, and a wiring pattern including a supply line configured to supply power to the driver IC and a ground wire configured to ground the driver IC, a lens array configured to collect the light emitted from the plurality of light-emitting elements on the photosensitive member, a holder configured to hold the substrate and the lens array, wherein the holder is grounded and made of metal, and a conductive member provided on the holder and configured to electrically connect the holder and the ground wire. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A and  1 B  are schematic sectional views each illustrating an image forming apparatus. 
         FIGS.  2 A and  2 B  are perspective views each illustrating a structure in the vicinity of drum units and developing units. 
         FIG.  3    is a schematic perspective view of an exposure unit. 
         FIGS.  4 A ,  4 B 1 ,  4 B 2 ,  4 C 1 , and  4 C 2  each illustrate a configuration of a substrate and a lens array. 
         FIG.  5    illustrates a configuration of a back surface of the substrate. 
         FIGS.  6 A,  6 B, and  6 C  each illustrate a conductive member. 
         FIGS.  7 A and  7 B  each illustrate a movement mechanism. 
         FIGS.  8 A and  8 B  each illustrate a link mechanism. 
         FIGS.  9 A and  9 B  each illustrate a mechanism for rotating a first link member and a second link member. 
         FIG.  10    is a perspective view illustrating a grounding mechanism. 
         FIGS.  11 A and  11 B  each illustrate a plate spring for grounding a holding member via a pin. 
         FIG.  12    is a view illustrating a conductive member according to another exemplary embodiment. 
         FIG.  13    is a view illustrating a conductive member according to still another exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments for carrying out the present disclosure will be described below with reference to the drawings. The scope of the disclosure is not limited only to the dimensions, materials, shapes, relative arrangements, and the like of components described in the following exemplary embodiments, unless otherwise specified. 
     (Image Forming Apparatus) 
     A schematic configuration of an image forming apparatus  1  will now be described.  FIG.  1 A  is a schematic sectional view of the image forming apparatus  1 . The image forming apparatus  1  illustrated in  FIG.  1 A  is a color printer (single function printer (SFP)) including no scanning device, but instead may be a copying machine including a scanning device. In exemplary embodiments of the present disclosure, not only a color image forming apparatus including a plurality of photosensitive drums  103  as illustrated in  FIG.  1 A , but also a color image forming apparatus including a single photosensitive drum  103 , or an image forming apparatus that forms a monochrome image may be used. 
     The image forming apparatus  1  illustrated in  FIG.  1 A  includes four image forming units  102 Y,  102 M,  102 C, and  102 K (hereinafter collectively referred to simply as an image forming unit  102 ). The image forming units  102 Y,  102 M,  102 C, and  102 K form toner images of yellow, magenta, cyan, and black, respectively. The image forming units  102 Y,  102 M,  102 C, and  102 K include photosensitive drums  103 Y,  103 M,  103 C, and  103 K (hereinafter collectively referred to simply as a photosensitive drum  103 ), respectively. The image forming units  102 Y,  102 M,  102 C, and  102 K also include chargers  104 Y,  104 M,  104 C, and  104 K (hereinafter collectively referred to simply as a charger  104 ) that charge the photosensitive drums  103 Y,  103 M,  103 C, and  103 K, respectively. The image forming units  102 Y,  102 M,  102 C, and  102 K also include light-emitting diode (LED) exposure units  520 Y,  520 M,  520 C, and  520 K (hereinafter collectively referred to simply as an exposure unit  520 ), respectively. The LED exposure units  520 Y,  520 M,  520 C, and  520 K are exposure light sources that emit light to expose surfaces of the photosensitive drums  103 Y,  103 M,  103 C, and  103 K, respectively. The image forming units  102 Y,  102 M,  102 C, and  102 K also include developing units  106 Y,  106 M,  106 C, and  106 K (hereinafter collectively referred to simply as a developing device  106 ), respectively. The developing device  106  is a developing unit that develops, with toner, an electrostatic latent image formed on the photosensitive drum  103  into a toner image, so that toner images of respective colors is developed on the respective photosensitive drums  103 . Characters Y, M, C, and K added to each reference numeral represent yellow, magenta, cyan, and black colors of toner, respectively. 
     The image forming apparatus  1  illustrated in  FIG.  1 A  is an image forming apparatus that adopts what is called a lower surface exposure method for exposing the surface of the photosensitive drum  103  to light from below. The following description is provided on the premise that the image forming apparatus  1  adopts the lower surface exposure method. However, the image forming apparatus  1  may adopt an upper surface exposure method for exposing the surface of the photosensitive drum  103  to light from above, as with an image forming apparatus  2  illustrated in  FIG.  1 B . In  FIG.  1 B , portions that represent the same components as those in  FIG.  1 A  are denoted by the same reference symbols. 
     The image forming apparatus  1  also includes an intermediate transfer belt  107  and primary transfer rollers  108  ( 108 Y,  108 M,  108 C, and  108 K). Toner images formed on the photosensitive drums  103  are transferred to the intermediate transfer belt  107 . The primary transfer rollers  108  ( 108 Y,  108 M,  108 C, and  108 K) sequentially transfer the toner images formed on the photosensitive drums  103  to the intermediate transfer belt  107 . The image forming apparatus  1  also includes a secondary transfer roller  109  and a fixing unit  100 . The secondary transfer roller  109  is a transfer unit that transfers the toner images formed on the intermediate transfer belt  107  to recording paper P that is conveyed from a sheet feeding unit  101 . The fixing unit  100  fixes the secondarily transferred images to the recording paper P. 
     (Image Forming Process) 
     The exposure unit  520 Y exposes the surface of the photosensitive drum  103 Y, which has been charged by the charger  104 Y, to light. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum  103 Y. Next, the developing device  106 Y develops the electrostatic latent image formed on the surface of the photosensitive drum  103 Y with yellow toner. The yellow toner image developed on the surface of the photosensitive drum  103 Y is transferred to the intermediate transfer belt  107  by the primary transfer roller  108 Y. Magenta, cyan, and black toner images are transferred to the intermediate transfer belt  107  through a similar image forming process. 
     The toner images of the respective colors transferred to the intermediate transfer belt  107  are conveyed to a secondary transfer portion T 2  by the intermediate transfer belt  107 . A transfer bias for transferring the toner images to the recording paper P is applied to the secondary transfer roller  109  disposed on the secondary transfer portion T 2 . The toner images conveyed to the secondary transfer portion T 2  are transferred to the recording paper P which has been conveyed from the sheet feeding unit  101  by the transfer bias of the secondary transfer roller  109 . The recording paper P to which the toner images are transferred is conveyed to the fixing unit  100 . The fixing unit  100  fixes the toner images to the recording paper P with heat and pressure. The recording paper P on which the fixation process has been performed by the fixing unit  100  is discharged to a sheet discharge portion  111 . 
     (Drum Units and Developing Units) 
     Drum units  518 Y,  518 M,  518 C, and  518 K (hereinafter collectively referred to simply as a drum unit  518 ) including the photosensitive drums  103  are attached to the image forming apparatus  1 . In the present exemplary embodiment, the drum unit  518  is also referred to as a photosensitive member unit. The drum unit  518  is a cartridge that is replaced by an operator, such as a user or maintenance engineer. The drum unit  518  rotatably supports the photosensitive drum  103 . In this case, the drum unit  518  also functions as a drum support member that rotatably supports the photosensitive drum  103 . In the present exemplary embodiment, a drum unit including the drum support member is referred to as the drum unit  518 . Specifically, the photosensitive drum  103  is rotatably supported by a frame member of the drum unit  518 . The drum unit  518  need not necessarily include the charger  104  and a cleaning device. 
     Developing units  641 Y,  641 M,  641 C, and  641 K (hereinafter collectively referred to simply as a developing unit  641 ), which are provided separately from the drum units  518 , are attached to the image forming apparatus  1  according to the present exemplary embodiment. The developing unit  641  according to the present exemplary embodiment is a cartridge having a configuration in which the developing device  106  illustrated in  FIG.  1 A  and a toner storage portion are integrated. The developing device  106  includes a developing sleeve (not illustrated) that carries developer. The developing unit  641  is provided with a plurality of gears for rotating a screw to mix toner and carrier. For example, when the gears have degraded with time, the operator detaches the developing unit  641  from an apparatus body of the image forming apparatus  1  and replaces the developing unit  641 . The drum unit  518  and the developing unit  641  according to the present exemplary embodiment may be a process cartridge having a configuration in which the drum unit  518  and the developing unit  641  described above are integrated. 
       FIG.  2 A  is a perspective view schematically illustrating a structure in the vicinity of the drum units  518  ( 518 Y,  518 M,  518 C, and  518 K) and the developing units  641 ( 641 Y,  641 M,  641 C, and  641 K) included in the image forming apparatus  1 .  FIG.  2 B  illustrates a state where the drum units  518  are inserted into the image forming apparatus  1  from the outside of the apparatus body. 
     As illustrated in  FIG.  2 A , the image forming apparatus  1  includes a front side plate  642  that is formed of a metal sheet, and a back side plate  643  that is also formed of a metal sheet. The front side plate  642  is a side wall provided on the front side of the image forming apparatus  1 . The front side plate  642  constitutes part of a housing of the apparatus body on the front side of the apparatus body of the image forming apparatus  1 . The back side plate  643  is a side wall provided on the back side of the image forming apparatus  1 . The back side plate  643  constitutes part of the housing of the apparatus body on the back side of the apparatus body of the image forming apparatus  1 . As illustrated in  FIG.  2 A , the front side plate  642  and the back side plate  643  are arranged to be facing each other, and a metal sheet (not illustrated) serving as a beam is bridged over the front side plate  642  and the back side plate  643 . The front side plate  642 , the back side plate  643 , and the beam (not illustrated) constitute part of a frame member of the image forming apparatus  1 . The term front surface side or front side of the image forming apparatus  1  or the components thereof according to the present exemplary embodiment refers to a side where the drum unit  518  is inserted into or removed from the apparatus body. 
     The front side plate  642  is provided with an opening for inserting or removing the drum unit  518  and the developing unit  641  into or from the apparatus body on the front side of the image forming apparatus  1 . The drum unit  518  and the developing unit  641  are each mounted at a predetermined position in the apparatus body of the image forming apparatus  1  through the opening. The image forming apparatus  1  also includes covers  558 Y,  558 M,  558 C, and  558 K (hereinafter also collectively referred to simply as a cover  558 ) that cover the front side of the respective drum units  518  and the respective developing units  641 . One end of the cover  558  is fixed to the apparatus body of the image forming apparatus  1  with a hinge. The hinge enables the cover  558  to pivot relative to the apparatus body of the image forming apparatus  1 . The operator opens the cover  558 , takes out the drum unit  518  or the developing unit  641  from the apparatus body, and then inserts a new drum unit  518  or a new developing unit  641  and closes the cover  558 , to thereby complete a replacement operation. 
     As illustrated in  FIGS.  2 A and  2 B , a side where the front side plate  642  is located is hereinafter defined as the front side (or the front surface side) of the apparatus body, and a side where the back side plate  643  is located is hereinafter defined as the back side (or the back surface side) of the apparatus body. With respect to the photosensitive drum  103 K on which the electrostatic latent image for the black toner image is formed, a side where the photosensitive drum  103 Y on which the electrostatic latent image for the yellow toner image is formed is disposed is defined as the right side. With respect to the photosensitive drum  103 Y on which the electrostatic latent image for the yellow toner image is formed, a side where the photosensitive drum  103 K on which the electrostatic latent image for the black toner image is formed is disposed is defined as the left side. A direction that is perpendicular to the front-back direction and left-right direction defined herein and that is a vertically upward direction is defined as an up direction, and a direction that is perpendicular to the front-back direction and left-right direction defined herein and that is a vertically downward direction is defined as a down direction. The front direction, the back direction, the right direction, the left direction, the up direction, and the down direction, which are defined above, are illustrated in  FIG.  2 B . The term rotational axis direction of the photosensitive drum  103  used herein refers to a direction that coincides with the front-back direction illustrated in  FIG.  2 B . The term longitudinal direction of an optical printhead  105  also refers to the direction that coincides with the front-back direction illustrated in  FIG.  2 B . In other words, the rotational axis direction of the photosensitive drum  103  and the longitudinal direction of the optical printhead  105  coincide with each other. 
     (Exposure Unit) 
     Next, the exposure unit  520  including the optical printhead  105  will be described. The optical printhead  105  has a longitudinal shape extending in the rotational axis direction of the photosensitive drum  103 . The optical printhead  105  includes a holding member  505 , a lens array  506 , and a substrate  502 . The lens array  506  and the substrate  502  are held by the holding member  505 . In the present exemplary embodiment, the holding member  505  is a member that is made of metal and is formed by bending a plate material obtained by performing a plating process on a galvanized steel plate or cold-rolled steel plate. The use of a metal plate material makes it possible to achieve strength by performing a bending process, while reducing costs. However, the configuration of the holding member  505  is not limited to the configuration obtained by performing the bending process on the metal plate material. The holding member  505  can also be, for example, what is called a die-cast product. The die-cast product refers to a product manufactured by die-casting, i.e., cooling and solidifying molten metal injected into a mold (cavity). In a case where the die-casting is adopted as the manufacturing method, a product having a complex shape can be manufactured depending on a shape of the mold serving as a basis for the product&#39;s shape. Meanwhile, since fabrication of the mold is costly, there is a disadvantage in that there is no cost advantage when there is no need to manufacture a large amount of identical products. In the present exemplary embodiment, the holding member  505  may be manufactured by bending a metal sheet or may be manufactured by die-casting. The use of the holding member  505  which is made of metal for the optical printhead  105  makes it possible to increase the strength of the optical printhead  105 . The holding member  505  which is made of metal has higher thermal conductivity than that of a holding member made of resin. Accordingly, the possibility that the holding member  505  may be deformed can be reduced even when the temperature of each electronic component mounted on the substrate  502  increases and the temperature in the space near the substrate increases. 
     An example of the exposure method to be used for an electrophotographic image forming apparatus is a laser beam scanning exposure method. In this method, the surface of the photosensitive drum  103  is scanned with an irradiation beam which is emitted from a semiconductor laser, is reflected by a rotating polygon mirror or the like, and goes through an f-O lens or the like. The optical printhead  105  described in the present exemplary embodiment is used in an LED exposure method for exposing the surface of the photosensitive drum  103  using light-emitting elements such as LEDs arrayed in the rotational axis direction of the photosensitive drum  103 , and is not used in the above-described laser beam scanning exposure method. 
     The exposure unit  520  described in the present exemplary embodiment is provided on the lower side in the vertical direction relative to the rotational axis of the photosensitive drum  103 . The substrate (not illustrated) included in the holding member  505  is provided with LEDs as the light-emitting elements, and the light-emitting elements emit light to which the surface of the photosensitive drum  103  is exposed from below. However, the exposure unit  520  may be provided on the upper side in the vertical direction relative to the rotational axis of the photosensitive drum  103 , and the surface of the photosensitive drum  103  may be exposed to light from above (see  FIG.  1 B ). 
       FIG.  3    is a schematic perspective view of the exposure unit  520  included in the image forming apparatus  1  according to the present exemplary embodiment. 
     As illustrated in  FIG.  3   , the exposure unit  520  includes the optical printhead  105 , a support member  526 , a first link mechanism  530 , and a second link mechanism  540 . The holding member  505  is provided with a contact pin  514  and a contact pin  515 . The contact pin  514  and the contact pin  515  are straight pins made of metal. For example, the contact pin  515  is provided on the holding member  505  on one side (back side) of the lens array  506  in the rotational axis direction of the photosensitive drum  103 , and projects from both sides of the holding member  505  in an optical axis direction of the lens array  506 . The contact pin  514  has a configuration similar to that of the contact pin  515 . When the contact pin  514  and the contact pin  515  are brought into contact with the drum unit  518 , a gap is formed between the photosensitive drum  103  and a light-emitting surface of the lens array  506 . Thus, the position of the optical printhead  105  with respect to the photosensitive drum  103  is determined. 
     The contact pin  514  and the contact pin  515  are fixed to the holding member  505 , which is made of metal, by welding. Thus, in the present exemplary embodiment, the contact pin  514  and the contact pin  515  are integrated with the holding member  505 . The method for fixing the contact pin  514  and the contact pin  515  to the holding member  505  is not limited to welding, but instead may be fixation with an adhesive. The contact pin  514  and the contact pin  515  may be threaded and screwed into the holding member  505  to be fastened to the holding member  505 . 
     The first link mechanism  530  includes a link member  535  and a link member  536 . The second link mechanism  540  includes a link member  537  and a link member  538 . As described in detail below, the link member  535  is attached to the back side relative to the center of the holding member  505  in the rotational axis direction of the photosensitive drum  103 , and the link member  537  is attached to the front side relative to the center of the holding member  505  in the rotational axis direction of the photosensitive drum  103 . 
     A slide member (slider)  525  to be described below slides in the front-back direction along with an opening and closing operation of the cover  558  provided on the front side of the image forming apparatus  1 . The link members  535  to  538  rotate along with the slide movement of the slide member  525 , thereby enabling the optical printhead  105  to move in the up-down direction. 
     In the present exemplary embodiment, the optical printhead  105  is provided on the lower side in the vertical direction relative to the photosensitive drum  103 . Specifically, in the image forming apparatus  1  according to the present exemplary embodiment, the surface of the photosensitive drum  103  is exposed to light emitted by the optical printhead  105  from below in the vertical direction. 
     As illustrated in  FIG.  3   , the exposure unit  520  includes the support member  526 . The support member  526  supports the optical printhead  105  via the first link mechanism  530  and the second link mechanism  540 . Specifically, the link member  535  of the first link mechanism  530  supports the holding member  505 , and the link member  537  of the second link mechanism  540  supports the holding member  505 . 
     In this manner, the link member  535  and the link member  537  support the holding member  505  directly or indirectly. Since the link member  535  and the link member  537  are made of resin, the holding member  505  is not grounded, or is in an electrically floating state. 
     The support member  526  is formed by bending a metal sheet into a U-shape. The support member  526  is a longitudinal member extending in the rotational axis direction of the photosensitive drum  103 . One end (front side) of the support member  526  in the longitudinal direction of the support member  526  is fixed to the front side plate  642 , and the other end (back side) of the support member  526  in the longitudinal direction of the support member  526  is fixed to the back side plate  643 . Thus, the position of the support member  526  is fixed with respect to the photosensitive drum  103  on the side opposite to the side where the photosensitive drum  103  is disposed with respect to the holding member  505  in the optical axis direction of the lens array  506 . The support member  526  is grounded via one or both of the front side plate  642  and the back side plate  643 . 
     The support member  526  includes the slide member  525  that is movable in the longitudinal direction of the support member  526 . The link members  535  to  538  rotate along with the movement of the slide member  525  relative to the support member  526 , thereby enabling the optical printhead  105  to move relative to the support member  526 . 
     (Configurations of Substrate and Lens Array) 
     Next, the substrate  502  and the lens array  506  will be described with reference to  FIGS.  4 A ,  4 B 1 ,  4 B 2 ,  4 C 1 , and  4 C 2 . First, the substrate  502  will be described.  FIG.  4 A  is a schematic perspective view of the substrate  502 . FIG.  4 B 1  illustrates an array of a plurality of LEDs  503  provided on the substrate  502 , and FIG.  4 B 2  illustrates an enlarged view of FIG.  4 B 1 . 
     LED chips  639  are mounted on the substrate  502 . As illustrated in  FIG.  4 A , the LED chips  639  are provided on one surface of the substrate  502 , and a connector  504  is provided on the back surface of the substrate  502 . The substrate  502  is provided with a wiring pattern for supplying a signal to each of the LED chips  639 . To the connector  504 , one end of a flexible flat cable (FFC) (not illustrated) is connected. The main body of the image forming apparatus  1  is provided with a substrate that is different from the substrate  502 . This substrate is provided with a central processing unit (CPU) for controlling a light-emitting timing of each of the LEDs  503 . The other end of the FFC is connected to a connector mounted on the substrate provided on the image forming apparatus  1 . The FFC transmits a drive signal for driving each of the LEDs  503  to the substrate  502  from the substrate provided on the image forming apparatus  1 . 
     The LED chips  639  mounted on the substrate  502  will be described in more detail. As illustrated in FIGS.  4 B 1  and  4 B 2 , a plurality of (29) LED chips  639 - 1  to  639 - 29  each including the plurality of LEDs  503  arranged thereon is arrayed on one surface of the substrate  502 . 
     On each of the LED chips  639 - 1  to  639 - 29 , 516 LEDs  503  (light-emitting elements) are arrayed in a row in the longitudinal direction of the LED chips  639 . A center-to-center distance k 2  between the adjacent LEDs  503  in the longitudinal direction of the LED chips  639  corresponds to the resolution of the image forming apparatus  1 . The image forming apparatus  1  according to the present exemplary embodiment has a resolution of 1200 dpi. Accordingly, the array of the LEDs  503  is formed such that the center-to-center distance k 2  between the adjacent LEDs  503  is 21.16 μm in the longitudinal direction of the LED chips  639 - 1  to  639 - 29 . Therefore, the optical printhead  105  according to the present exemplary embodiment has an exposure range of about 316 mm A photosensitive layer of the photosensitive drum  103  is formed to have a width greater than or equal to 316 mm Since the length of a long side of an A4-size recording sheet and the length of a short side of an A3-size recording sheet are 297 mm, the optical printhead  105  according to the present exemplary embodiment has the exposure range capable of forming images on an A4-size recording sheet and an A3-size recording sheet. 
     The LED chips  639 - 1  to  639 - 29  are alternately arranged in two rows in the rotational axis direction of the photosensitive drum  103 . Specifically, as illustrated in FIG.  4 B 1 , the odd-numbered LED chips  639 - 1 ,  639 - 3 , . . . , and  639 - 29  counted from the left side are mounted in one row in the longitudinal direction of the substrate  502 . The even-numbered LED chips  639 - 2 ,  639 - 4 , . . . , and  639 - 28  counted from the left side are mounted in one row in the longitudinal direction of the substrate  502 . By arranging the LED chips  639  in this manner, as illustrated in FIG.  4 B 2 , a center-to-center distance k 1  between an LED  503  disposed on one end of one of the adjacent different LED chips  639  and an LED  503  disposed on the other end of the other of the adjacent different LED chips  639  can be made equal to the center-to-center distance k 2  between the adjacent LEDs  503  on a single LED chip  639  in the longitudinal direction of the LED chip  639 . 
     In the present exemplary embodiment, each light-emitting element is a semiconductor LED, but instead may be, for example, an organic light-emitting diode (OLED). The OLED is also referred to as an organic electro-luminescence (EL) and is a current-driven light-emitting element. For example, OLEDs are arranged on a line in a main scanning direction (rotational axis direction of the photosensitive drum  103 ) on a substrate of a thin film transistor (TFT) and are electrically connected in parallel by a power supply line that is also provided in the main scanning direction. 
     Next, the lens array  506  will be described. FIG.  4 C 1  is a schematic view of the lens array  506  as viewed from the photosensitive drum  103 . FIG.  4 C 2  is a schematic perspective view of the lens array  506 . The lens array  506  functions to collect light emitted from the LEDs  503  on the surface of the photosensitive drum  103 . As illustrated in FIG.  4 C 1 , a plurality of lenses of the lens array  506  is arranged in two rows in the array direction of the plurality of LEDs  503 . The lenses are alternately arranged such that one of the lenses in one of the rows of lenses is disposed to contact both of adjacent lenses in the array direction of the other of the rows of lenses. Each of the lenses is a cylindrical rod lens made of glass. Each of the lenses includes an incidence surface on which light emitted from each of the LEDs  503  is incident, and an emitting surface from which light incident from the incidence surface is emitted. The material of each lens is not limited to glass, but instead may be plastic. The shape of each lens is not limited to a cylindrical shape, but instead may be, for example, a polygonal column such as a hexagonal column. 
     A dashed line Z illustrated in FIG.  4 C 2  indicates a lens optical axis. The above-described movement mechanism enables the optical printhead  105  to move in a direction that is substantially in the lens optical axis indicated by the dashed line Z. The term lens optical axis used herein refers to a line that connects a focal point of a certain lens selected from among the plurality of lenses constituting the lens array  506  and the center of the light-emitting surface of the lens. To be exact, the optical axis of each lens may slightly vary from lens to lens. Even if an angle formed between the optical axis of a certain lens and the optical axis of another lens is not 0 degrees, the angle may be only a small angle. When the term lens optical axis is used, such a slight difference is not taken into consideration, and it is assumed that the term lens optical axis indicates the optical axis of any one of the plurality of lenses constituting the lens array  506 . In addition, it is assumed that the direction of the optical axis of one lens coincides with the direction of the optical axis of another lens. 
     Next, a wiring pattern  552  formed on the substrate  502  will be described.  FIG.  5    illustrates the back surface of the substrate  502 . The LED chips  639  including the LEDs  503  are mounted on the front surface of the substrate  502 , and electronic components such as one or more driver integrated circuits (ICs)  551   a  and  551   b  for driving the LEDs  503  are mounted on the back surface of the substrate  502 . In other words, the back surface of the substrate  502  refers to a surface of the substrate  502  that is opposite to the surface on which the light-emitting elements are mounted. 
     The term wiring pattern  552  used herein refers to a plurality of electric wires formed on the substrate  502 . Typical examples of the electric wires include an electric wire  552   a  (power line) for driving the driver IC  551   a  ( 551   b ), and a ground wire  552   b  having a reference potential. The ground wire  552   b  also functions as an electric wire for grounding the driver ICs  551   a  and  551   b . While the electric wire  552   a  is described as being a power line, the electric wire  552   a  may also be a signal line for transmitting a control signal to drive each of the LEDs  503 . 
     The connector  504  is mounted in the vicinity of the center of the back surface of the substrate  502 . An FFC  510  is attached to the connector  504 . The FFC  510  is a cable formed of a plurality of electric wires. 
     Examples of the electric wires include an electric wire for transmitting a control signal (drive signal) to control the light-emitting timing of each of the LEDs  503 , a supply line (also referred to as a power line) for supplying power, and a ground wire for grounding the wiring pattern  552 . 
     The back surface of the substrate  502  is also provided with ground pads  550   a  and  550   b  each having the same potential as that of the ground wire  552   b . A conductive member  701  to be described below contacts the ground pad  550   a  ( 550   b ) and the holding member  505 , thereby electrically connecting the ground pad  550   a  ( 550   b ) and the holding member  505 . 
     (Conductive Member) 
       FIG.  6 A  is a sectional view of the optical printhead  105  taken along a section perpendicular to the longitudinal direction of the optical printhead  105 . As illustrated in  FIG.  6 A , the substrate  502  and the lens array  506  are held by the holding member  505  such that the substrate  502  and the lens array  506  face each other. 
     As seen from the sectional views of the image forming apparatus  1  illustrated in  FIGS.  1 A and  1 B , the charger  104  is disposed in the vicinity of the optical printhead  105 . A high voltage is applied to a charging roller included in the charger  104 , and an intense electric field is formed in the vicinity of the charging roller. Accordingly, the optical printhead  105  is also located in the intense electric field, and thus the holding member  505  is gradually charged. In this case, if there is a difference between the potential of the holding member  505  and the potential of the wiring pattern  552  of the substrate  502 , an electric current may be discharged from the holding member  505  and the wiring pattern  552 . Even when the holding member  505  is grounded, the holding member  505  cannot be fully grounded in some cases due to a contact failure between components constituting a ground path. Thus, it is difficult to completely eliminate the difference between the potential of the holding member  505  and the potential of the wiring pattern  552  of the substrate  502 . Therefore, it is desirable to provide a configuration for making the difference between the potential of the holding member  505  and the potential of the wiring pattern  552  of the substrate  502  as close to zero as possible. 
     In recent years, there has been a demand for a further increase in speed of the image forming apparatus  1 . Along with the recent demand, there has been an increasing demand for the higher transmission accuracy of a signal for driving light-emitting elements. One of main factors for deterioration in signal transmission accuracy is noise emitted from the wiring pattern  552  of the substrate  502 . The noise emitted from the wiring pattern  552  may have an effect on a signal transmitted through another part in the wiring pattern  552 . To reduce the intensity of the noise emitted from the wiring pattern  552 , it is desirable to fully ground the ground wire for the wiring pattern  552 . In general, the ground wire for the wiring pattern  552  is grounded via the ground wire for the FFC  510 . However, since the ground wire for the FFC  510  is extremely thin, it cannot be said that the ground wire for the wiring pattern  552  is fully grounded. 
     Accordingly, in the optical printhead  105  according to the present exemplary embodiment, the ground wire  552   b  for the wiring pattern  552  of the substrate  502  and the holding member  505  are electrically connected to thereby ground the wiring pattern  552  of the substrate  502 . 
     As illustrated in  FIG.  6 A , the holding member  505  includes a fixed portion  505   a  that is provided with an opening  708  into which the lens array  506  is inserted, and a pair of wall portions  505   b  extending from both ends of the fixed portion  505   a  in a direction perpendicular to the rotational axis direction of the photosensitive drum  103 . In the present exemplary embodiment, the holding member  505  is formed by bending a metal sheet. The holding member  505  is bent at both end portions of the fixed portion  505   a  so that the pair of wall portions  505   b  projects toward the side opposite to the side where the photosensitive drum  103  is disposed. 
     In this case, the pair of wall portions  505   b  is each provided with an opening  703 . Protrusions formed on the conductive member  701  to be described below are fitted into respective openings  703 . The conductive member  701  is a conductive component and electrically connects the holding member  505  with the ground wire  552   b  for the wiring pattern  552  formed on the substrate  502 . The configuration makes the potential of the holding member  505  equal to the potential of the ground wire  552   b  for the wiring pattern  552 . 
       FIG.  6 B  is a bottom view of the holding member  505 , and  FIG.  6 C  is a view illustrating a method for attaching the conductive member  701  to the holding member  505 . 
     As seen from  FIG.  6 B , the conductive member  701  is a metal component formed in a U-shape, and plate-like portions corresponding to both leg portions of the conductive member  701  are elastically deformable. As illustrated in  FIG.  6 C , when the conductive member  701  is inserted from below the holding member  505 , the portions corresponding to the both leg portions of the conductive member  701  are fitted to the holding member  505  while being deformed inside. 
     (Movement Mechanism) 
     Next, a mechanism that enables the optical printhead  105  to move along with the slide movement of the slide member  525  will be described with reference to  FIGS.  7 A and  7 B .  FIGS.  7 A and  7 B  illustrate the exposure unit  520  as viewed from the left side. For ease of description, the support member  526  is not illustrated.  FIG.  7 A  illustrates a state where the optical printhead  105  is located at an exposure position (first position) corresponding to a position where the photosensitive drum  103  is exposed to light.  FIG.  7 B  illustrates a state where the optical printhead  105  is located at a retracted position (second position) farther from the photosensitive drum  103  than the exposure position. In the present exemplary embodiment, a distance between the photosensitive drum  103  and the light-emitting surface of the lens array  506  when the optical printhead  105  is located at the exposure position is about 3 mm. 
     As illustrated in  FIGS.  7 A and  7 B , the link member  535  is rotatably connected to one end of the slide member  525  in the longitudinal direction of the slide member  525 , and the link member  537  is rotatably connected to the other end of the slide member  525  in the longitudinal direction of the slide member  525 . 
     The slide member  525  slides to the back side from the front side when the cover  558  (not illustrated) is rotated to an open state from a closed state. When the slide member  525  slides from the front side to the back side, the link member  535  and the link member  537  rotate counterclockwise in  FIGS.  7 A and  7 B . The link member  535  and the link member  536  are rotatably connected to each other. The link member  537  and the link member  538  are also rotatably connected to each other. 
     One end of the link member  536  is rotatably connected to the support member  526  (not illustrated). Accordingly, the link member  536  also rotates about the support member  526  along with the rotation of the link member  535 . One end of the link member  538  is rotatably connected to the support member  526  (not illustrated). Accordingly, the link member  538  also rotates about the support member  526  along with the rotation of the link member  537 . When the slide member  525  moves to the back side from the front side, the link member  536  and the link member  538  rotate clockwise about the support member  526 . In this case, the other end of the link member  535  is rotatably connected to the holding member  505 , and the other end of the link member  537  is rotatably connected to the holding member  505 . 
     Accordingly, the link member  535  and the link member  537  rotate counterclockwise when the slide member  525  slide to the back side from the front side, so that the other end of the link member  535  and the other end of the link member  537  move in a direction away from the photosensitive drum  103 . Thus, the optical printhead  105  moves to the retracted position from the exposure position. 
     Next, a procedure where the optical printhead  105  moves from the state illustrated in  FIG.  7 B  to the state illustrated in  FIG.  7 A , i.e., from the retracted position to the exposure position, along with the slide movement of the slide member  525  will be described. 
     The slide member  525  moves to the front side from the back side along with the rotation of the cover  558  (not illustrated) to the closed state from the open state. When the slide member  525  slides to the front side from the back side, the link member  535  and the link member  537  rotate clockwise in  FIGS.  7 A and  7 B . At the same time, the link member  536  and the link member  538  rotate counterclockwise. When the link member  535  and the link member  537  rotate clockwise along with the slide movement of the slide member  525  from the back side to the front side, the other end of the link member  535  and the other end of the link member  537  move in a direction approaching the photosensitive drum  103 . Thus, the optical printhead  105  moves to the exposure position from the retracted position. In the present exemplary embodiment, the movement direction of the optical printhead  105  that moves to the retracted position and to the exposure position substantially coincides with the optical axis direction of the lens array  506 . 
     When the holding member  505  of the optical printhead  105  gradually moves to the exposure position from the retracted position along with the slide movement of the slide member  525 , the contact pin  514  provided at one end of the holding member  505  in the longitudinal direction of the holding member  505  and the contact pin  515  provided at the other end of the holding member  505  contact the drum unit  518 . In other words, when the optical printhead  105  is located at the exposure position, the contact pin  514  and the contact pin  515  contact the frame of the drum unit  518 . The term frame used herein refers to a part of the frame member of the drum unit  518 . In the manner as described above, the position of the holding member  505  with respect to the drum unit  518 , i.e., the position of the optical printhead  105 , is determined. 
     When the position of the holding member  505  with respect to the drum unit  518  is determined as described above, the distance between the light-emitting surface of the lens array  506  and the photosensitive drum  103  is also determined, and thus the movement of the optical printhead  105  to the exposure position is completed. 
     The configurations of the first link mechanism  530  and the second link mechanism  540  will be described in more detail with reference to  FIGS.  8 A and  8 B  and  FIGS.  9 A and  9 B .  FIG.  8 A  is a schematic perspective view of the front side of the support member  526  as viewed from the left side.  FIG.  8 B  is a schematic perspective view of the front side of the support member  526  as viewed from the right side. The first link mechanism  530  provided on the front side of the support member  526  will be described below. The configuration of the second link mechanism  540  is substantially the same as the configuration of the first link mechanism  530 , and thus the description thereof is omitted. 
     As illustrated in  FIGS.  8 A and  8 B , the support member  526  includes a support shaft  531  and an E-shaped retaining ring  533 . A right side wall surface and a left side wall surface of the support member  526  processed into a U-shape are respectively provided with holes into which the support shaft  531  is inserted. In a state where the support shaft  531  is inserted into the holes, the support shaft  531  is fixed to the support member  526  with the E-shaped retaining ring  533 . 
     The slide member  525  is a plate-shaped member made of metal. As illustrated in  FIG.  8 A , the slide member  525  is provided with a long hole  691  extending in the front-back direction. The support shaft  531  is inserted into the long hole  691 . In the present exemplary embodiment, the support shaft  531  is loosely fitted into the long hole  691  with a gap of about 0.1 to 0.5 mm in the vertical direction. The diameter of the long hole  691  in the longitudinal direction is about 350 mm. The configuration enables the slide member  525  to slide in the front-back direction by about 350 mm with respect to the support member  526 . 
     An assist member  539  is attached to one end of the slide member  525  (front side of the slide member  525 ) in the longitudinal direction of the slide member  525 . The assist member  539  is provided with an accommodation space  562 . The accommodation space  562  accommodates a protrusion formed on the cover  558 . When the cover  558  rotates, the protrusion that moves with the rotating cover  558  is brought into contact with a side wall on the front side or a side wall on the back side of the accommodation space  562 . The protrusion pushes the side wall on the front side of the accommodation space  562 , thereby enabling the slide member  525  to move to the front side. In contrast, the protrusion pushes the side wall on the back side of the accommodation space  562 , thereby enabling the slide member  525  to move to the back side. With this configuration, the slide member  525  moves in the front-back direction along with the rotation of the cover  558 . 
     The first link mechanism  530  includes the link member  535  and the link member  536 . The link member  535  and the link member  536  are longitudinal resin plate materials. In the longitudinal direction of the link member  535 , a protrusion  655  is formed at one end (upper side in  FIG.  8 A ) of the link member  535 . In contrast, in the longitudinal direction of the link member  535 , a tube portion  610  is formed at the other end (lower side in  FIG.  8 A ) of the link member  535 . The protrusion  655  is fitted into an opening formed on the front side of the holding member  505 . This configuration enables the link member  536  to rotate about the protrusion  655  with respect to the holding member  505 . The tube portion  610  is a hollow cylinder. As illustrated in  FIGS.  8 A and  8 B , a protrusion projecting from the slide member  525  is fitted into the tube portion  610 . This configuration enables the link member  536  to rotate also with respect to the slide member  525 . 
     One end (upper side in  FIG.  8 B ) of the link member  536  in the longitudinal direction is rotatably attached to the link member  535 . In other words, the link member  535  and the link member  536  are rotatably connected to each other. In contrast, the other end (lower side in  FIG.  8 B ) of the link member  536  in the longitudinal direction of the link member  536  is rotatably attached to the support member  526 . Specifically, a lower side wall surface of the link member  536  and a left side wall surface of the support member  526  are provided with holes, respectively, and an insertion pin  532  is inserted into the holes. With this configuration, the link member  536  is rotatably fixed to the support member  526 . 
       FIGS.  9 A and  9 B  each illustrate a state where the link member  535  and the link member  536  included in the first link mechanism  530  rotate. As described above, the tube portion  610  formed on the link member  535  is fitted to a protrusion  534  formed on the support member  526 . Accordingly, when the slide member  525  slides from the front side to the back side, the link member  535  rotates about the protrusion  534  clockwise in  FIGS.  9 A and  9 B . Since the link member  535  and the link member  536  are rotatably connected to each other, the link member  536  rotates counterclockwise with respect to the slide member  525  along with the clockwise rotation of the link member  535 . In this case, the link member  536  rotates about the insertion pin  532  with respect to the support member  526 . When the link member  535  rotates while being rotatably supported by the link member  536 , the protrusion  655  of the link member  535  moves to the lower side. 
     Herein, where L 1  is a distance between the rotational center axis of the link member  535  with respect to the slide member  525  and the center axis of connection between the link member  535  and the link member  536 , L 2  is a distance between the rotational center axis of the link member  536  with respect to the support member  526  and the center axis of connection between the link member  535  and the link member  536 , and L 3  is a distance between the rotational center axis of the link member  535  with respect to the holding member  505  and the center axis of connection between the link member  535  and the link member  536 , the distances L 1 , L 2 , and L 3  are equal to each other. In general, such a link mechanism is referred to as a Scott-Russell mechanism. When the distances L 1  to L 3  are equal to each other, the movement direction of the protrusion  655  along with the slide movement of the slide member  525  coincides with the vertical direction. Specifically, the protrusion  655  moves along a dashed line A illustrated in  FIG.  9 B . This configuration enables the holding member  505  to move in the vertical direction along with the slide movement of the slide member  525 . 
     (Grounding Mechanism) 
     As described above, since the holding member  505  is made of metal, the holding member  505  can be charged due to the effect of an electric field formed by the charger  104 . Since the holding member  505  is a longitudinal member, the holding member  505  behaves like an antenna when the holding member  505  acquires an electric charge. When the holding member  505  behaves like an antenna, noise may be superimposed on a signal to be transmitted through the wiring pattern  552  of the substrate  502 , which may cause a defective image. For this reason, it is desirable to ground the holding member  505 . 
       FIG.  10    is a diagram illustrating a grounding mechanism according to the present exemplary embodiment. The support member  526  made of metal is supported by the front side plate  642  provided on the front side of the image forming apparatus  1  and by the back side plate  643  provided on the back side of the image forming apparatus  1 . Accordingly, the support member  526  is grounded through one or both of the front side plate  642  and the back side plate  643 . 
     A plate spring  711  that is made of metal is attached to the back side of the support member  526  with a screw  710 . As illustrated in  FIG.  10   , a leading end of the plate spring  711  contacts the contact pin  515 . The plate spring  711  is elastically deformed. The contact pin  515  is pressed in the rotational axis direction of the photosensitive drum  103  by a restoring force of the plate spring  711 . Specifically, the plate spring  711  presses the contact pin  515  in a direction from the front side to the back side of the image forming apparatus  1 . Since the plate spring  711  is constantly pressed against the contact pin  515  by an elastic force, the holding member  505  can be reliably grounded via the contact pin  515 . In the present exemplary embodiment, the plate spring  711  is used as a member via which the holding member  505  is grounded, but instead a wire spring or the like can be used as such a member. Instead of using a plate spring or a wire spring, the contact pin  515  and the support member  526  may be directly connected with a conductor wire to obtain an effect that the holding member  505  is grounded. However, since the optical printhead  105  according to the present exemplary embodiment moves to the exposure position and to the retracted position, if the contact pin  515  and the support member  526  are connected with a conductor wire, the conductor wire can be deformed when the optical printhead  105  is located at the retracted position. If the deformed conductor wire is caught on, for example, the link member  535  ( 536 ), the conductor wire can be damaged. Accordingly, it may be desirable to separately perform a process for routing the conductor wire. Therefore, it is desirable to use the plate spring  711 , as in the present exemplary embodiment, to obtain the effect that the holding member  505  is grounded. 
       FIG.  11 A  illustrates a positional relationship between the contact pin  515  and the plate spring  711  when the holding member  505  is located at the exposure position.  FIG.  11 B  illustrates a positional relationship between the contact pin  515  and the plate spring  711  when the holding member  505  is located at the retracted position. To simplify the illustration in  FIGS.  11 A and  11 B , the holding member  505  is not illustrated. As seen from  FIGS.  11 A and  11 B , even when the contact pin  515  moves together with the holding member  505  that moves to the exposure position and to the retracted position, the plate spring  711  is constantly in contact with the contact pin  515 . In other words, the contact pin  515  moves together with the holding member  505  while being in contact with the plate spring  711 . Accordingly, the holding member  505  is constantly grounded via the contact pin  515 . 
     The shape of the conductive member  701  and the portion where the conductive member  701  is attached according to another exemplary embodiment will be described. 
       FIG.  12    illustrates an example where a conductive member  704  is used in place of the conductive member  701 . As illustrated in  FIG.  12   , portions corresponding to both leg portions of the conductive member  704  are each bent at a middle portion thereof. Each of the pair of wall portions  505   b  of the holding member  505  is provided with a dent  705  in place of the opening  703 . The bent portion of each of the portions corresponding to the both leg portions of the conductive member  704  is fitted into the dent  705 . Thus, the conductive member  704  is fixed to the holding member  505 . 
       FIG.  13    illustrates an example where the conductive member  701  is attached to the substrate  502  such that the conductive member  701  is brought into contact with the surface of the substrate  502 . In this case, before the substrate  502  is attached to the holding member  505 , the conductive member  701  is first fixed to the inside of the holding member  505  by bonding or the like. After that, the substrate  502  is inserted into the holding member  505  from below, and then the substrate  502  is fixed to the holding member  505  in a state where the substrate  502  is pressed against the conductive member  701 . It is desirable to form the ground pads  550   a  and  550   b  of the substrate  502  on the surface of the substrate  502 . The use of the configuration according to the present exemplary embodiment makes it possible to effectively use a space formed between the substrate  502  and the fixed portion  505   a  of the holding member  505 . Consequently, the size of the optical printhead  105  in the vertical direction can be reduced. 
     As described above, according to the configuration of the present exemplary embodiment, the potential of the ground wire  552   b  for the wiring pattern  552  of the substrate  502  can be made equal to the potential of the holding member  505  with a simple configuration. Further, since the holding member  505  is grounded, the ground wire  552   b  for the wiring pattern  552  of the substrate  502  can be reliably grounded. Consequently, the intensity of noise emitted from the substrate  502  can be reduced. 
     The ground wire  552   b  for the wiring pattern  552  of the substrate  502  can be grounded with a simple configuration. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure 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. 
     This application claims the benefit of Japanese Patent Application No. 2021-089703, filed May 28, 2021, which is hereby incorporated by reference herein in its entirety.